Silicon Composite Anode Materials for Lithium Ion Batteries Based on ...
Silicon Composite Silicon Composite Anode Materials for Lithium Ion Batteries Based on Carbon Cryogels and Carbon Paper p Anode Materials for Lithium Ion Batteries Based on Carbon Cryogels y g and Carbon Paper p Dr. James Woodworth, NASA Postdoctoral Program D Dr. J James W d Woodworth, th NASA Postdoctoral P td t l Program P Dr Richard Baldwin NASA Postdoctoral Program Dr. Richard Baldwin NASA Postdoctoral Program Mentor g Mentor Electrochemistry Electrochemistry Branch, NASA Glenn Research Center l h i Branch h NASA Glenn l Research h Center William William Bennett, Electrochemistry Branch, NASA Glenn Research Center a Bennett e ett, Electrochemistry ect oc e st y Branch a c , NASA S G Glenn e Research esea c Ce Center te
•
Central to the development of advanced lithium ion batteries is the C l h d l f d d li hi i b i i h development of advanced anode materials (figures 1 and2) development of advanced anode materials (figures 1 and2). C Current technologies are centered around graphitic anode materials h l i d d hi i d i l which have a theoretical capacity of 372 mAh/g One of the new which have a theoretical capacity of 372 mAh/g. One of the new materials being investigated is silicon which has a theoretical i l b i i i d i ili hi h h h i l capacity of 4200 mAh/g However, pure silicon suffers from a capacity of 4200 mAh/g. However pure silicon suffers from a
450 450 400
Cell 1
350
Cell 2 Cell 2
300
Cell 3 Cell 3 250
150 0
5
10
15
20
Ene erg gy de ens sitty (W Wh/litterr)
25
600
UHE Si UHE-Si
500
Carbon Anodes Carbon Anodes
400
Li-sulfur Li sulfur
300 200 100 0 200 300 Specific energy (Wh/kg)
Figure 1 Estimates for cell specific energy and energy density Figure 1. Estimates for cell specific energy and energy density
100
-0.05 0 05 1
400
(a) -0.1 01
0.5
5
10
15
50
20
100
Si Only Si Only Spe eciffic Caapaacitty ((m mAh h/gg)
1200 1000 800 600 400 200 0
C‐Si Nanofoam‐RT‐B f C Si Nanofaom 50 C‐Si Nanofaom‐50
1000
10
15
20
12 1.2
0 04 0.04
1
0.02
0.8
0
06 0.6
-0.02 0 02
04 0.4
(a)
(a)
-0.04 0 04
02 0.2
-0 0.06 06
0
-0.08 0
50
-0 0005 -0.0005
15 1.5
-0.001 0 001
1
(a)
-0.0015 0 00 5
(c)
-0.002 0 002 -0.0025 0
0
5
10
‐200
15
20
Cycle Number y
Figure 10 g The contribution of silicon to the specific capacity as a function of cycle The contribution of silicon to the specific capacity as a function of cycle number for carbon‐silicon (C‐Si) nanofoam anode material (RT)=cured at b f b ili (C Si) f d t i l (RT) d t oC, (Ni Tab) = sample with a nickel tab room temperature (50)=cured at 50 p ( ) ,( ) p attached without a copper foil current collector attached without a copper foil current collector
500
Nanofoam
500
500
Graphite Graphite With Cu With Cu
350
170
Li+
Si+PAN
500
Si+graphite+PAN g p
400 300 200 0
5
Si With Cu With Cu
1000
312
Table 1 Table 1
Theoretical specific capacities at the active Th ti l ifi iti t th ti material and electrode levels (Cu=copper material and electrode levels (Cu copper current current collector)
10
15
Cycle Number Cycle Number
Figure 16 Figure 16 Specific capacity as a function of cycle number for carbon silicon Specific capacity as a function of cycle number for carbon‐silicon nanofoam anode material (PAN=coated with polyaniline doped with LiPF6) with LiPF 2000 1800 1600
Si+graphite g p Si Si+PAN Si Si+graphite+PAN hi PAN
1400 1200 1000 800 400 200 0
5
dq q/d dv 1
1.5
Volts vs Li Volts vs. Li
Figure 20 Figure 20 dQ/dV analysis of the first two cycle of the silicon dQ/dV analysis of the first two cycle of the silicon‐ carbon‐nanofoam anode coated with polyaniline b f d d h l l doped with LiPF6 (a) de doped with LiPF (a) de‐lithiation lithiation of silicon of silicon12 (b) (b) lithiation of silicon12 (c) SEI formation lithiation of silicon (c) SEI formation
‐50 ‐40 ‐30 30 ‐20 20 ‐10 10 0 0
50
100
Z'
150
200
250
• Th The addition of graphite to the silicon containing carbon nanofaom dditi f hit t th ili t i i b f d dramatically increases capacity ti ll i it • The addition of a coating composed of polyaniline The addition of a coating composed of polyaniline and LiPF and LiPF6 to the silicon only carbon nanofoam to the silicon only carbon nanofoam resulted in a dramatic resulted in a dramatic i increase in capacity i it • The polyaniline The polyaniline coating appears to have a detrimental effect on the performance of the nanofoam coating appears to have a detrimental effect on the performance of the nanofoam that contains graphite that contains graphite • The nanofaom The nanofaom containing graphite has a lower impedance than the nanofoam containing graphite has a lower impedance than the nanofoam which does not contain graphite (figure 22) which does not contain graphite (figure 22) • Samples coated with polyaniline/LiPF Samples coated with polyaniline/LiPF6 show drastically lower impedances than those without the coating .(figure 22) 6 show drastically lower impedances than those without the coating .(figure 22) • The presence of graphite in combination with the polyaniline The presence of graphite in combination with the polyaniline coating resulted in a higher impedance than that of a coated coating resulted in a higher impedance than that of a coated sample not containing graphite.(figure 22) sample not containing graphite.(figure 22) • The features associated with the lithiation The features associated with the lithiation and de‐lithiation and de lithiation of silicon of silicon 12 are more pronounced in the samples that contain are more pronounced in the samples that contain graphite or have a polyaniline/LiPF6 6 coating (figures 18,20,21 than those that do not (figure 19) graphite or have a polyaniline/LiPF coating (figures 18,20,21 than those that do not (figure 19) • The implementation of the slow formation cycle and low current constant current step resulted in the lithiation The implementation of the slow formation cycle and low current constant current step resulted in the lithiation of the silicon of the silicon within the first cycle and the subsequent improvement in first cycle capacities. This can be observed in the dQ/dV analysis of within the first cycle and the subsequent improvement in first cycle capacities. This can be observed in the dQ/dV analysis of the nanofoams which shows pronounced formation of features associated with the lithiation the nanofoams which shows pronounced formation of features associated with the lithiation and de‐lithiation and de lithiation of silicon of silicon12 within the first two cycles (figures 18‐21) y ( g ) • dQ/dV analysis shows that features associated with the formation of an SEI layer appeared only in the first cycle around 1V analysis shows that features associated with the formation of an SEI layer appeared only in the first cycle around 1V ((feature (c) in figures (18‐21). ( ) g ( ) • First cycle irreversible capacity losses of 100% of the maximum capacity First cycle irreversible capacity losses of 100% of the maximum capacity • Coulombic efficiency of approximately 96% y pp y
10
15
• Carbon‐silicon composite anode materials have been successfully formed from nano‐Si containing resorcinol‐formaldehyde b l p d l h b f lly f df g lf ld hyd gel precursors These materials are in the form of microspheres or monolithic nanofoams Both materials have gel precursors. These materials are in the form of microspheres or monolithic nanofoams. Both materials have d demonstrated the d h ability to function as anodes and utilize the capacity of the silicon present in the material. bili y f i d d ili h p i y f h ili p i h i l
Cycle Number Cycle Number
(a)
(b)
Cycle 1 Cycle 1 Cycle 2 Cycle 2
• Th The addition of graphite or a polyaniline/LiPF ddi i f hi l ili /LiPF6 coating dramatically improves capacity, which can be correlated with an i d i ll i i hi h b l d ih improvement in the utilization of the silicon and decreases impedance improvement in the utilization of the silicon, and decreases impedance • The The implementation of the slow formation cycle and low current constant current step resulted in the lithiation implementation of the slow formation cycle and low current constant current step resulted in the lithiation of the silicon of the silicon within the first cycle and the subsequent improvement in first cycle capacities. i hi h fi l d h b i i fi l ii • SSeveral of these materials meet and/or exceed the ETDP threshold value of 600 mAh/g and would likely compare favorably, l f th t i l t d/ d th ETDP th h ld l f 600 Ah/ d ld lik l f bl with regard to specific capacity at the electrode level to conventional coated anode materials with regard to specific capacity at the electrode level to conventional coated anode materials
• Though Though the carbon nanofoam the carbon nanofoam anodes are in an early stage of development and do not yet possess all of the desired anodes are in an early stage of development and do not yet possess all of the desired performance characteristics, the recent advances in specific capacity of the materials demonstrate significant p f h i i , h d i p ifi p iy f h i l d ig ifi potential for future development This is particularly the case since these materials do not require a current collector potential for future development. This is particularly the case since these materials do not require a current collector, which represents approximately 8% of a cell’s mass, and therefore would p pp y , offer additional overall mass savings at the cell g level level.
((a))
0 0.5
1
1.5
Figure 18 Figure 18 dQ/dV dQ/dV analysis of the first two cycles of the l i f th fi t t l f th silicon‐carbon‐graphite nanofoam anode. (a) de‐ g p ( ) lithiation of silicon12 , (b) lithiation of silicon lithiation of silicon (b) lithiation of silicon12 , (c) (c) SEI f SEI formation ti
(C) (C) ((a))
1 Li+
cycle 1 cycle 2 y cycle 3 cycle 3 cycle 12 cycle 12
(b) (a)
Intercalation of Li+ Ions Into Carbon Matrix and S f Surface Si
Figure 13 Figure 13 dQ/dV analysis of carrbon silicon microsphere cell 1 dQ/dV analysis of carrbon‐silicon microsphere cell 1 ( ) d (d) d li hi i (a) and (d) de‐lithiation of silicon f ili 12 (b) and (c) (b) d ( ) lithiation of silicon12 (e) SEI formation lithiation of silicon (e) SEI formation
0 0.5
Conclusions
600
Ion Diffusion Pathways
Silicon
Volts vs Li Volts vs. Li
0
Si+Graphite+PAN Si+PAN
Recent Results Recent Results for The Silicon l for f The h Silicon‐Carbon ili Carbon Nanofoam b Nanofoam f
Si
600
((a)) (b)
Pre-Formation
Ions
Figure 14 Fi 14 Speculative mechanism explaining the increase in p p g specific capacity with continued cycling specific capacity with continued cycling
0
•This research was supported by an appointment to the NASA Postdoctoral Program at NASA Glenn Research Center •This research was supported by an appointment to the NASA Postdoctoral Program at NASA Glenn Research Center administered by Oak Ridge Associated Universities through a contract with NASA funded by the Exploration Technology y g g y p gy Development Program Energy Storage Project Development Program, Energy Storage Project •NASA Glenn Research Center Electrochemistry Branch with special thanks to: y p •Eunice Wong (ASRC) •Eunice Wong (ASRC) •Concha Reid (NASA GRC) ( ) •Tom Miller (NASA GRC) •Tom Miller (NASA GRC) •Dave Yendriga (Sierra Lobo) d g ( b ) •Marjorie Moats (SGT) •Marjorie Moats (SGT) •Michelle Manzo (Electrochemistry Branch Chief NASA GRC) h ll ( l h y h h f )
R f References 1. 1 2. 3 3. 4. 4 5. 6 6. 7. 8 8. 9.
(b)
Carbon 08 0.8
dQ Q//dV V
Si+graphite
700
Establishment of Diffusion Pathways y into Carbon Matrix Matrix and Surface Si
06 0.6
Si+Graphite Si
‐60
800
Establishment of Diffusion Pathways Through Carbon Matrix to Si
(e)
04 0.4
1.5
Figure 22 Figure 22 Nyquist plot for carbon‐silicon nanofoam anodes yq p
Volts vs. Li
((b))
02 0.2
0.5 Volts vs. Li Volts vs Li1
A k Acknowledgements l dg t
(c)
0
0
( ) (c)
Figure 15 g Voltage and Current vs Test Time for cycles 1 and 2 of the Voltage and Current vs. Test Time for cycles 1 and 2 of the carbon silicon graphite nanofoam anode (a) slow first insertion (b) low carbon‐silicon‐graphite nanofoam anode. (a) slow first insertion, (b) low current(c/100) constant current step to a cutoff voltage of 10 mV, (c) p g shoulders indicative of de‐lithiation shoulders indicative of de lithiation of silicon of silicon
Full Intercalation of Li+ Ions Into Carbon Matrix and Si
mAh/g mAh/g Active Material Electrode Active Material
(b)
‐70
1000
(c)
(a)
Electrode
(b)
(a)
TestTime(h) ( )
Figure 12 g Voltage and Voltage and C Current vs. Test t T t Time for cycles 4‐ y 5 of carbon‐silicon 5 of carbon silicon microsphere cell 1. i h ll 1 ((a) shoulders ) indicative of de‐ indicative of de lithi ti lithiation of silicon f ili
cycle 1 l cycle 2 cycle 2 cycle 3 l cycle 5 cycle 5 cycle 6 l 6 cycle 8 cycle 8 cycle 9 l 9
(d)
(a)
cycle 1 l 1 cycle 2 y
0
0
200
0.5
((b))
600 400
(a)
Vo oltag ge((V)) vs. v Lii
2
100
Test Time(h) Test_Time(h)
(b)
0.08 0 06 0.06
800
25
• Integrity and Spherical morphology are g y d ph l ph l gy maintained after cycling (figures 3‐4) d f y l g ((f g ) Indicating that the material is capable of buffering the large volume Indicating that the material is capable of buffering the large volume changes of the silicon h g f h ili • Exhibits unusual increase in capacity with cycling (figure 5) Exhibits unusual increase in capacity with cycling (figure 5) – Low capacity (150‐200 mAh/g) for first several cycles L i (150 200 Ah/ ) f fi l l – Capacity suddenly and drastically increases Capacity suddenly and drastically increases • Demonstrated ability to utilize the silicon (figure 6) D d bili ili h ili (fi 6) • Low capacity fade Low capacity fade • First cycle irreversible capacity loss of 50% of the maximum capacity Fi l i ibl i l f 50% f h i i • Coulombic efficiency of approximately 96% (desired values exceed 99%) efficiency of approximately 96% (desired values exceed 99%)
200
14 1.4
0 5
150
Voltage(V) g ( ) Current(mA)
1.6
C‐Si Nanofoam‐RT‐Ni Tab 1200
2.5
Figure 17 Figure 17 The contribution of silicon to the specific capacity as a function of cycle number for carbon‐silicon cycle number for carbon silicon nanofoam anode material (PAN nanofoam anode material (PAN= coated with polyaniline doped with LiPF6) coated with polyaniline doped with LiPF
T t Ti (h) Test_Time(h)
C‐Si Nanofoam‐RT‐A C‐Si Nanofoam‐RT‐A
1400
3
0 0005 0.0005
Figure 11 Figure 11 Voltage and Current vs. g Test Time for cycles 1‐ Test Time for cycles 1 3 of carbon silicon 3 of carbon‐silicon microsphere cell 1 (a) p ( ) extended taper charge extended taper charge observed prior to large observed prior to large increase in specific p capacity of anode capacity of anode.
-0 15 -0.15 0
Bulk Capacity p y
SSpe eciificc Caapaaciityy (m mA Ah//g)
1.5
0
Figure 9 Figure 9 Specific capacity as a function of cycle number for carbon silicon (C Si) Specific capacity as a function of cycle number for carbon‐silicon (C‐Si) nanofoam anode material (RT)=cured at room temperature (50)=cured at ( ) ( ) 50oC, (Ni Tab) C, (Ni Tab) = sample with a nickel tab attached without a copper foil sample with a nickel tab attached without a copper foil current collector current collector
SOA
100
150
0
Si Contribution Si Contribution
0 05 0.05 0
Cycle Number Cycle Number
Figure 5 Figure 5 Specific capacity as a function of cycling for cells Specific capacity as a function of cycling for cells containing carbon‐silicon microsphere anode material
1600
Voltage(V) Current(mA)
2
Results for The Silicon‐Carbon Microspheres Results for The Silicon‐Carbon Microspheres
HE
0
200
Cycle Number y
Figure 6 Figure 6 S ifi Specific capacity as a function of cycle number for cell 2 in it f ti f l b f ll 2 i fig. 4 showing capacities for the bulk material, the Si g g p , contribution and the capacity based on Si being the only contribution and the capacity based on Si being the only active material ti t i l
UHE-Li
250
30
Cycle Number Cycle Number
700
300
01 0.1
2.5
C‐Si Nanofoam‐ RT‐Ni RT Ni Tab Tab C Si Nanofoam C‐Si Nanofoam‐ RT B RT‐B C‐Si Nanofaom‐50
0
0
800
350
3
50
C/5
C/10
1400
The objective of this research project is to develop a silicon‐carbon The objective of this research project is to develop a silicon carbon composite anode material with a threshold specific capacity of 600 p p p y mAh/g and a goal of 1000 mAh/g as outlined by the Exploration mAh/g and a goal of 1000 mAh/g as outlined by the Exploration and Technology Development Program Energy Storage Project. It gy p g gy g j should be noted that the specific energy requirements are should be noted that the specific energy requirements are expressed for a traditional coated electrode that utilizes a copper p pp current collector current collector.
C‐Si Nanofoam‐ RT‐A RT A Carbon Nanofaom Carbon Nanofaom
400
200
to cells with traditional coated anode materials (figure 2, table 1). ll h d l d d l (f bl )
Objj ti Objective
Figure 8 Figure 8 Free standing Free standing carbon‐silicon nanofoam anode nanofoam anode
Figure 7 Figure 7 Scanning electron micrograph of carbon g g p nanofoam containing nano‐ silicon as nanofoam containing nano silicon as synthesized
0 001 0.001
A ly i f Cy li g Ch Analysis of Cycling Characteristics t i ti
Volta V age e(V V) vs s. Li L
Two materials , carbon microspheres ( figures 3‐4) and carbon , p ( g ) nanofoam (figures 7 8) produced from nano phase silicon nanofoam (figures 7‐8), produced from nano‐phase silicon impregnated RF gel precursors have been synthesized and p g g p y investigated In the first approach the silicon containing RF gel is investigated. In the first approach the silicon containing RF gel is 1 2 9 In the second formed into microspheres (carbon microspheres). p ( p ) 1,2,9 approach carbon paper is impregnated with the silicon containing approach, carbon paper is impregnated with the silicon containing 349 RF gel to create a free standing electrode (carbon nanofoam), g g ( ), 3,4,9 which if successful would eliminate the need for a current which, if successful, would eliminate the need for a current collector. The elimination of the current collector would result in the reduction of mass and an increase in the specific energy compared the reduction of mass and an increase in the specific energy compared
Figure 4 Fi 4 Scanning electron micrograph of g g p cast electrode composed of cast electrode composed of carbon microspheres containing b i h t i i nano‐silicon after cycling y g
SSpe eciffic Caapaacitty (m mAh h/gg)
One approach to ameliorating the expansion issues associated with One approach to ameliorating the expansion issues associated with silicon is to form a silicon carbon composite One such composite silicon is to form a silicon‐carbon composite. One such composite material is formed via the dispersion of silicon in a resorcinol‐ material is formed via the dispersion of silicon in a resorcinol formaldehyde (RF) gel followed by pyrolysis The premise behind formaldehyde (RF) gel followed by pyrolysis. The premise behind the RF gel silicon composite is that the gel will form a flexible, the RF gel silicon composite is that the gel will form a flexible, porous carbon matrix capable of absorbing the large volume porous, carbon matrix capable of absorbing the large volume expansion of the silicon upon lithiation thereby maintaining expansion of the silicon upon lithiation thereby maintaining electrical contact between particles and the current collector The electrical contact between particles and the current collector . The carbon matrix will also prevent direct electrolyte contact with the ca bo at a so p e e t d ect e ect o yte co tact t t e 1 2 9 Unlike a variety of other approaches, which use silicon 1,2,9 silicon. Unlike a variety of other approaches which use complicated expensive techniques such as chemical vapor p p q p deposition this technique makes use of traditional cost effective deposition, this technique makes use of traditional cost –effective laboratory techniques. y q
Figure 3 Fi 3 Scanning electron micrograph g g p of cast electrode composed of of cast electrode composed of carbon microspheres containing b i h t i i nano‐silicon before cycling y g
Sp peccific C Cap paccityy (mA Ah/g))
400% lattice volume expansion upon insertion of the lithium l l p p f h l h ions resulting in large irreversible capacity loss cracking of the ions, resulting in large irreversible capacity loss, cracking of the material, and eventual failure of the anode ate a , a d e e tua a u e o t e a ode10..
Current(A) Voltage(V)
0.0015
0
• Both Both the microspheres and the nanofoam the microspheres and the nanofoam anode materials showed low initial anode materials showed low initial capacity followed by a sudden and drastic increase in capacity after several capacity followed by a sudden and drastic increase in capacity after several cycles cycles. • The increase in capacity occurred after the cell had undergone an extended The increase in capacity occurred after the cell had undergone an extended t taper charge in which the cell was held at a low voltage (about 10‐15mv) vs. Li h i hi h th ll h ld t l lt ( b t 10 15 ) Li for an extended period of time (figure11 a) for an extended period of time (figure11 a). • After the extended taper charge and during cycles with improved capacity a f h d d p h g dd g y l h p d p y shoulder indicative of de litiation of silicon, appeared in the voltage vs. time shoulder, indicative of de‐litiation of silicon appeared in the voltage vs time discharge (de‐lithiation) discharge (de lithiation) curve (figure12a) curve (figure12a)12 • dQ/dV analysis revealed that the increase in capacity analysis revealed that the increase in capacity correlates with the correlates with the formation of highly lithiated amorphous silicon phases. formation of highly lithiated amorphous silicon phases 12 • Microsphere cell 1 dQ/dV Mi h ll 1 dQ/dV curves for cycles 1‐3 are dominated by characteristics f l 13 d i t db h t i ti associated with the intercalation of carbon by lithium After cycle 4 in which the associated with the intercalation of carbon by lithium. After cycle 4 in which the cell undergoes an extended taper charge at low voltage (figure 11a) the silicon ll d g d d p h g l l g ((f g ) h l de lithiation peak at 0.4 V becomes more pronounced with each successive de‐lithiation peak at 0 4 V becomes more pronounced with each successive cycle (figure13) and features associated with the lithiation cyc e ( gu e 3) a d eatu es assoc ated t t e t at o o of amorphous silicon a o p ous s co appear (figure13b c) 12 appear (figure13b,c). • Speculative mechanism to explain the unusual cycling characteristics (figure 14) Speculative mechanism to explain the unusual cycling characteristics (figure 14) – During the first few cycles, the lithium is only able to access the carbon D i th fi t f l th lithi i l bl t th b which surrounds the silicon and perhaps the small percentage of silicon which surrounds the silicon and perhaps the small percentage of silicon l located close to the surface d l h f – Carbon becomes fully lithiated Carbon becomes fully lithiated which, in turn, allows for the lithiation which in turn allows for the lithiation of of silicon surrounded by the carbon y – Diffusion pathways are established which allow for more efficient lithiation Diffusion pathways are established which allow for more efficient lithiation and de‐lithiation and de lithiation of the silicon of the silicon
Figure 21 dQ/dV analysis of silicon dQ/dV analysis of silicon‐ carbon‐graphite nanofoam b hi f anode coated with polyaniline doped with LiPF6. polyaniline doped with LiPF ( ) d li hi i (a) de‐lithiation of silicon f ili 12 , (b) lithiation of silicon12 , (c) SEI formation SEI formation
Z Z"
Cells were formed at a rate of C/10 for three cycles Cells were formed at a rate of C/10 for three cycles Cycling was performed at C/10 charge and discharge for 12‐15 cycles Cycling was performed at C/10 charge and discharge for 12‐15 cycles f ll followed by 5 cycles with a charge rate of C/10 and a discharge rate of db 5 l ith h t f C/10 d di h t f C/5 / Cells were cycled at room temperature Cells were cycled at room temperature
35 3.5
dQ Q/d dV
• •
Electrolyte: 1M LiPF Electrolyte: 1M LiPF6 1:1:1 ethylene carbonate, diethyl carbonate and 1:1:1 ethylene carbonate diethyl carbonate and di dimethyl h l carbonate b
0 002 0.002
dq q/d dv
•
Carbon microspheres were slurried Carbon microspheres were slurried with NaCMC with NaCMC and cast with 0.005 and cast with 0 005” film film onto copper foil t f il Half cells were constructed in the form of coin cells using metallic lithium g as the counter electrode as the counter electrode
•
cycle 1 cycle 1 cycle 2 l 2 cycle 5 l
(c)
Currrent(A A)
Cell Construction and Electrochemical Cycling Ce Co st uct o a d ect oc e ca Cyc g •
The National Aeronautics and Space Administration (NASA) has The National Aeronautics and Space Administration (NASA) has embarked upon a number of near and far term missions which p require advanced energy storage systems These energy storage require advanced energy storage systems. These energy storage systems must be safe, human rated, have high specific energies y , , g p g (Wh/kg) high energy densities (Wh/l) high reliability long cycle life (Wh/kg), high energy densities (Wh/l), high reliability, long cycle life, l p low power fade over the life of the battery and the ability to f d h lf f h b y d h bl y perform in a variety of unique environments The Exploration perform in a variety of unique environments. The Exploration Technology Development Program (ETDP) via the Energy Storage h l gy l p g ( ) h gy g Project supported the development of advanced lithium ion (Li‐ion) Project supported the development of advanced lithium ion (Li‐ion) cells which possess many of the required attributes. ll hi h p y f h q i d ib
Resorcinol formaldehyde gels containing 50 nm silicon were formed Resorcinol‐formaldehyde gels containing 50 nm silicon were formed Pyrolyzed at 1000 at 1000o in argon in argon
•
Sp peccific C Cap paccityy (m mA Ah//g))
• •
•
(a)
• Add Add graphite to resorcinol formaldehyde gel to improve graphite to resorcinol formaldehyde gel to improve conductivity • Coat the anode with a conductive binder composed of Coat the anode with a conductive binder composed of 11 polyaniline p y doped with LiPF p 6 6 • Improve initial capacity and promote faster lithiation Improve initial capacity and promote faster lithiation of the silicon of the silicon by developing a new formation/cycling procedure in which the y p g / y gp cell is formed very slowly and the taper charge is replace with a cell is formed very slowly and the taper charge is replace with a low current constant current step p • Use only spot welded nickel tabs and no copper current collector Use only spot welded nickel tabs and no copper current collector
Materials were shown to intercalate and de‐intercalate lithium El t d id tifi d C Si Electrodes identified as C‐Si nanofoam f RT A d RT B h RT‐A and RT‐B showed improving di i performance with cycling with final capacities of approximately 400 mAh/g and performance with cycling with final capacities of approximately 400 mAh/g and 275 mAh/g respectively /g p y at the electrode level Material has the ability to function as an anode and utilize the capacity of the Material has the ability to function as an anode and utilize the capacity of the silicon (figure 10) silicon (figure 10) Electrode with the spot welded nickel tab performed comparably with electrodes l d h h p ld d k l b p f d p bly h l d which utilized a copper foil current collector (figures 9 and 10) which utilized a copper foil current collector (figures 9 and 10) – Current collectors may not be necessary when using this material Current collectors may not be necessary when using this material – Significant reduction in electrode mass Si ifi d i i l d The absence of the current collector significantly reduces the mass of the The absence of the current collector significantly reduces the mass of the electrode thereby increasing specific energy at the electrode level electrode thereby increasing specific energy at the electrode level when when compared p d to traditional coated anode materials (figure 2, table 1) di i l d d i l ((fig 2 bl 1))
• •
SSpe eciificc Caapacityy (m mA Ah//g)
1279 SSynthesis y h i 1,2,7,9
•
I t d ti Introduction
Significance • Composed of 100% active material (carbon and silicon) C d f 100% ti t i l( b d ili ) • Free standing electrode that does not require the use of a copper current collector a copper current collector – Could significantly reduce cell mass C ld i ifi tl d ll – Effective specific capacity on the electrode Effective specific capacity on the electrode level would be higher than for traditional level would be higher than for traditional coated electrodes (table 1) t d l t d (t bl 1) Synthesis1,2,7,9 • Free standing carbon nanofoam Free standing carbon nanofoam anode was produced anode was produced f from carbon paper impregnated with resorcinol‐ b p p i p g d ih i l formaldehyde gel containing 50 nm silicon particles formaldehyde gel containing 50 nm silicon particles • Pyrolyzed at 1000 at 1000o C in argon C in argon Cell Construction and Electrochemical Cycling ll d l h l y l g • Anodes were constructed via two methods Anodes were constructed via two methods – Nanofoam material was placed on copper foil material was placed on copper foil current collectors the same size as the anode material (used only for preliminary tests) material (used only for preliminary tests) – A nickel tab is spot‐welded onto the corner of A i k lt bi t ld d t th f the nanofoam material (used on most tests) ( ) • Half cells were constructed in the form of pouch cells Half cells were constructed in the form of pouch cells using metallic lithium as the counter electrode i t lli lithi th t l t d • Electrolyte: 1M LiPF y y , y 6 1:1:1 ethylene carbonate, diethyl 6 carbonate and dimethyl carbonate carbonate and dimethyl • Cells were formed at a rate of approximately C/5 for 5 C ll f d t t f i t l C/5 f 5 cycles then cycled at C/20 for the remaining cycles cyc es t e cyc ed at C/ 0 o t e e a g cyc es reported • Cycled at room temperature C l d t t t
App Approach 1: Carbon Gel Microsphere Anodes h 1 C b G l Mi ph A d
N App New Approaches for Silicon‐Carbon Nanofoam h f Sili C b N f
dQ//dV d V
carbon microspheres and nanofoams produced from nano‐phase carbon microspheres and nanofoams produced from nano phase silicon impregnated RF gel precursors have been synthesized and p g g p y investigated Carbon microspheres are produced by forming the investigated. Carbon microspheres are produced by forming the silicon‐containing RF gel into microspheres whereas carbon nano‐ l g g l ph h b foams are produced by impregnating carbon fiber paper with the foams are produced by impregnating carbon fiber paper with the 149 silicon containing RF gel to create a free standing electrode. l g g l f d g l d 1‐4,9 Both materials have demonstrated their ability to function as Both materials have demonstrated their ability to function as anodes and utilize the silicon present in the material. Stable d d ili h ili p i h i l S bl reversible capacities above 400 mAh/g for the bulk material and reversible capacities above 400 mAh/g for the bulk material and above 1000 mAh/g of Si have been observed. b 1000 Ah/ f Si h b b d
cathode anode electrolyte separator t aluminum foil copper foil f il
Cu C urrren nt(mA A)
Estimates for component weight p g A variety of materials are under investigation for use as anode y g fraction in 30 Ah cell Mass of the anode fraction in 30 Ah cell. Mass of the anode materials in lithium ion batteries of which the most promising are materials in lithium‐ion batteries, of which, the most promising are coating represents approximately 24% i i l 24% of f 10 10 those containing silicon. g One such material is a composite formed p total mass Mass of the copper foil total mass. Mass of the copper foil via the dispersion of silicon in a resorcinol formaldehyde (RF) gel via the dispersion of silicon in a resorcinol‐formaldehyde (RF) gel c rrent collector represents current collector represents followed by pyrolysis. Two silicon‐carbon composite materials, y py y p , approximately 8% of mass. pp y
Glenn Research Center Glenn Research Center
Initial Results for The Silicon‐Carbon Nanofoam Initial Results for The Silicon‐Carbon Nanofoam
App Approach 2 : Carbon Nanofoam h2 C b N f A d Anodes
V lta Vol age e(V V) vs s. Li L
Figure 2 Figure 2
Abstract
Curre C entt(m mA A)
Glenn Research Center Glenn Research Center
05 0.5
1
15 1.5
Volts vs. Li
Figure 19 Fi 19 dQ/dV analysis of the silicon‐carbon anode. (a) Q/ y ( ) de‐lithiation of silicon12 , (b) lithiation of silicon de‐lithiation of silicon (b) lithiation of silicon12, ( ) SEI f (c) SEI formation ti
Wang, K.; He, X.; Wang, L.; Ren, J.; Jiang, C.; Chunrong, W. Solid State Ionics Wang K ; He X ; Wang L ; Ren J ; Jiang C ; Chunrong W Solid State Ionics 2007, 178, 115‐118. 2007 178 115 118 Hasegawa, T.; Mukai, S. R.; Shirato, Y.; Tamon, H. Carbon g , ; , ; , ; , 2004, 42, 2573‐2579. , , Long J W ; Bourg M E ; Wallace J M ; Fischer A E ; Lytle J C ; Pettigrew K A ; Barrow A J ; Dysart J L ; Rolinson D R Long, J. W.; Bourg, M. E.; Wallace, J. M.; Fischer, A. E.; Lytle, J. C.; Pettigrew, K. A.; Barrow, A. J.; Dysart, J. L.; Rolinson, D. R. In 215 Electrochemical Society Meeting San Francisco CA, 2009. y g , Long J W 2009 pp Personal Communication Long, J. W., 2009, pp Personal Communication. Al‐Muhtaseb, Ritter. Advanced Materials 2003, 15, 101‐114 , , , Yamamoto Endo Ohmori , Nakaiwa. Carbon Yamamoto, Endo, Ohmori Nakaiwa Carbon 2005, 43, 1231‐1238. 2005 43 1231 1238 Yamamoto, Sugimoto, Suzuki, Mukai, Tamon , g , , , Carbon 2002, 40, 1345‐1351. , , Hasegawa T ; Mukai S R ; Shirato Y ; Tamon H Carbon 2004, 42, 2573‐2579. Hasegawa, T.; Mukai, S. R.; Shirato, Y.; Tamon, H. Carbon 2004 42 2573 2579 Wang, G. X.; Ahn, J. H.; Yao, J.; Bewlay, S.; Liu, H. K. Electrochemistry Communications g, ; , ; , ; y, ; , y 2004, 6, 689‐692. , ,
10. Kasavajjula, U.; Wang, C.; Appleby, J. A. Journal of Power Sources 10 Kasavajjula U ; Wang C ; Appleby J A Journal of Power Sources 2007, 163, 1003‐1039. 2007 163 1003 1039 11.Liu, Y.; Matsumura, T.; Imanishi, N.; Hirano, A.; Ichiwaka, T.; Takeda, Y. Electrochemical and Solid State Letters , ; , ; , ; , ; , ; , 2005, 8, , , A599 A602 A599‐A602. 12.Obrovac, M.N.; Krause, L.J. Journal of The Electrochemical Society 2007, 154, A103 12.Obrovac, M.N.; Krause, L.J. Journal of The Electrochemical Society 2007, 154, A103‐A108 A108
Point of Contact: Dr. James Woodworth : [email protected] Point of Contact: Dr. James Woodworth : [email protected]
•
Central to the development of advanced lithium ion batteries is the C l h d l f d d li hi i b i i h development of advanced anode materials (figures 1 and2) development of advanced anode materials (figures 1 and2). C Current technologies are centered around graphitic anode materials h l i d d hi i d i l which have a theoretical capacity of 372 mAh/g One of the new which have a theoretical capacity of 372 mAh/g. One of the new materials being investigated is silicon which has a theoretical i l b i i i d i ili hi h h h i l capacity of 4200 mAh/g However, pure silicon suffers from a capacity of 4200 mAh/g. However pure silicon suffers from a
450 450 400
Cell 1
350
Cell 2 Cell 2
300
Cell 3 Cell 3 250
150 0
5
10
15
20
Ene erg gy de ens sitty (W Wh/litterr)
25
600
UHE Si UHE-Si
500
Carbon Anodes Carbon Anodes
400
Li-sulfur Li sulfur
300 200 100 0 200 300 Specific energy (Wh/kg)
Figure 1 Estimates for cell specific energy and energy density Figure 1. Estimates for cell specific energy and energy density
100
-0.05 0 05 1
400
(a) -0.1 01
0.5
5
10
15
50
20
100
Si Only Si Only Spe eciffic Caapaacitty ((m mAh h/gg)
1200 1000 800 600 400 200 0
C‐Si Nanofoam‐RT‐B f C Si Nanofaom 50 C‐Si Nanofaom‐50
1000
10
15
20
12 1.2
0 04 0.04
1
0.02
0.8
0
06 0.6
-0.02 0 02
04 0.4
(a)
(a)
-0.04 0 04
02 0.2
-0 0.06 06
0
-0.08 0
50
-0 0005 -0.0005
15 1.5
-0.001 0 001
1
(a)
-0.0015 0 00 5
(c)
-0.002 0 002 -0.0025 0
0
5
10
‐200
15
20
Cycle Number y
Figure 10 g The contribution of silicon to the specific capacity as a function of cycle The contribution of silicon to the specific capacity as a function of cycle number for carbon‐silicon (C‐Si) nanofoam anode material (RT)=cured at b f b ili (C Si) f d t i l (RT) d t oC, (Ni Tab) = sample with a nickel tab room temperature (50)=cured at 50 p ( ) ,( ) p attached without a copper foil current collector attached without a copper foil current collector
500
Nanofoam
500
500
Graphite Graphite With Cu With Cu
350
170
Li+
Si+PAN
500
Si+graphite+PAN g p
400 300 200 0
5
Si With Cu With Cu
1000
312
Table 1 Table 1
Theoretical specific capacities at the active Th ti l ifi iti t th ti material and electrode levels (Cu=copper material and electrode levels (Cu copper current current collector)
10
15
Cycle Number Cycle Number
Figure 16 Figure 16 Specific capacity as a function of cycle number for carbon silicon Specific capacity as a function of cycle number for carbon‐silicon nanofoam anode material (PAN=coated with polyaniline doped with LiPF6) with LiPF 2000 1800 1600
Si+graphite g p Si Si+PAN Si Si+graphite+PAN hi PAN
1400 1200 1000 800 400 200 0
5
dq q/d dv 1
1.5
Volts vs Li Volts vs. Li
Figure 20 Figure 20 dQ/dV analysis of the first two cycle of the silicon dQ/dV analysis of the first two cycle of the silicon‐ carbon‐nanofoam anode coated with polyaniline b f d d h l l doped with LiPF6 (a) de doped with LiPF (a) de‐lithiation lithiation of silicon of silicon12 (b) (b) lithiation of silicon12 (c) SEI formation lithiation of silicon (c) SEI formation
‐50 ‐40 ‐30 30 ‐20 20 ‐10 10 0 0
50
100
Z'
150
200
250
• Th The addition of graphite to the silicon containing carbon nanofaom dditi f hit t th ili t i i b f d dramatically increases capacity ti ll i it • The addition of a coating composed of polyaniline The addition of a coating composed of polyaniline and LiPF and LiPF6 to the silicon only carbon nanofoam to the silicon only carbon nanofoam resulted in a dramatic resulted in a dramatic i increase in capacity i it • The polyaniline The polyaniline coating appears to have a detrimental effect on the performance of the nanofoam coating appears to have a detrimental effect on the performance of the nanofoam that contains graphite that contains graphite • The nanofaom The nanofaom containing graphite has a lower impedance than the nanofoam containing graphite has a lower impedance than the nanofoam which does not contain graphite (figure 22) which does not contain graphite (figure 22) • Samples coated with polyaniline/LiPF Samples coated with polyaniline/LiPF6 show drastically lower impedances than those without the coating .(figure 22) 6 show drastically lower impedances than those without the coating .(figure 22) • The presence of graphite in combination with the polyaniline The presence of graphite in combination with the polyaniline coating resulted in a higher impedance than that of a coated coating resulted in a higher impedance than that of a coated sample not containing graphite.(figure 22) sample not containing graphite.(figure 22) • The features associated with the lithiation The features associated with the lithiation and de‐lithiation and de lithiation of silicon of silicon 12 are more pronounced in the samples that contain are more pronounced in the samples that contain graphite or have a polyaniline/LiPF6 6 coating (figures 18,20,21 than those that do not (figure 19) graphite or have a polyaniline/LiPF coating (figures 18,20,21 than those that do not (figure 19) • The implementation of the slow formation cycle and low current constant current step resulted in the lithiation The implementation of the slow formation cycle and low current constant current step resulted in the lithiation of the silicon of the silicon within the first cycle and the subsequent improvement in first cycle capacities. This can be observed in the dQ/dV analysis of within the first cycle and the subsequent improvement in first cycle capacities. This can be observed in the dQ/dV analysis of the nanofoams which shows pronounced formation of features associated with the lithiation the nanofoams which shows pronounced formation of features associated with the lithiation and de‐lithiation and de lithiation of silicon of silicon12 within the first two cycles (figures 18‐21) y ( g ) • dQ/dV analysis shows that features associated with the formation of an SEI layer appeared only in the first cycle around 1V analysis shows that features associated with the formation of an SEI layer appeared only in the first cycle around 1V ((feature (c) in figures (18‐21). ( ) g ( ) • First cycle irreversible capacity losses of 100% of the maximum capacity First cycle irreversible capacity losses of 100% of the maximum capacity • Coulombic efficiency of approximately 96% y pp y
10
15
• Carbon‐silicon composite anode materials have been successfully formed from nano‐Si containing resorcinol‐formaldehyde b l p d l h b f lly f df g lf ld hyd gel precursors These materials are in the form of microspheres or monolithic nanofoams Both materials have gel precursors. These materials are in the form of microspheres or monolithic nanofoams. Both materials have d demonstrated the d h ability to function as anodes and utilize the capacity of the silicon present in the material. bili y f i d d ili h p i y f h ili p i h i l
Cycle Number Cycle Number
(a)
(b)
Cycle 1 Cycle 1 Cycle 2 Cycle 2
• Th The addition of graphite or a polyaniline/LiPF ddi i f hi l ili /LiPF6 coating dramatically improves capacity, which can be correlated with an i d i ll i i hi h b l d ih improvement in the utilization of the silicon and decreases impedance improvement in the utilization of the silicon, and decreases impedance • The The implementation of the slow formation cycle and low current constant current step resulted in the lithiation implementation of the slow formation cycle and low current constant current step resulted in the lithiation of the silicon of the silicon within the first cycle and the subsequent improvement in first cycle capacities. i hi h fi l d h b i i fi l ii • SSeveral of these materials meet and/or exceed the ETDP threshold value of 600 mAh/g and would likely compare favorably, l f th t i l t d/ d th ETDP th h ld l f 600 Ah/ d ld lik l f bl with regard to specific capacity at the electrode level to conventional coated anode materials with regard to specific capacity at the electrode level to conventional coated anode materials
• Though Though the carbon nanofoam the carbon nanofoam anodes are in an early stage of development and do not yet possess all of the desired anodes are in an early stage of development and do not yet possess all of the desired performance characteristics, the recent advances in specific capacity of the materials demonstrate significant p f h i i , h d i p ifi p iy f h i l d ig ifi potential for future development This is particularly the case since these materials do not require a current collector potential for future development. This is particularly the case since these materials do not require a current collector, which represents approximately 8% of a cell’s mass, and therefore would p pp y , offer additional overall mass savings at the cell g level level.
((a))
0 0.5
1
1.5
Figure 18 Figure 18 dQ/dV dQ/dV analysis of the first two cycles of the l i f th fi t t l f th silicon‐carbon‐graphite nanofoam anode. (a) de‐ g p ( ) lithiation of silicon12 , (b) lithiation of silicon lithiation of silicon (b) lithiation of silicon12 , (c) (c) SEI f SEI formation ti
(C) (C) ((a))
1 Li+
cycle 1 cycle 2 y cycle 3 cycle 3 cycle 12 cycle 12
(b) (a)
Intercalation of Li+ Ions Into Carbon Matrix and S f Surface Si
Figure 13 Figure 13 dQ/dV analysis of carrbon silicon microsphere cell 1 dQ/dV analysis of carrbon‐silicon microsphere cell 1 ( ) d (d) d li hi i (a) and (d) de‐lithiation of silicon f ili 12 (b) and (c) (b) d ( ) lithiation of silicon12 (e) SEI formation lithiation of silicon (e) SEI formation
0 0.5
Conclusions
600
Ion Diffusion Pathways
Silicon
Volts vs Li Volts vs. Li
0
Si+Graphite+PAN Si+PAN
Recent Results Recent Results for The Silicon l for f The h Silicon‐Carbon ili Carbon Nanofoam b Nanofoam f
Si
600
((a)) (b)
Pre-Formation
Ions
Figure 14 Fi 14 Speculative mechanism explaining the increase in p p g specific capacity with continued cycling specific capacity with continued cycling
0
•This research was supported by an appointment to the NASA Postdoctoral Program at NASA Glenn Research Center •This research was supported by an appointment to the NASA Postdoctoral Program at NASA Glenn Research Center administered by Oak Ridge Associated Universities through a contract with NASA funded by the Exploration Technology y g g y p gy Development Program Energy Storage Project Development Program, Energy Storage Project •NASA Glenn Research Center Electrochemistry Branch with special thanks to: y p •Eunice Wong (ASRC) •Eunice Wong (ASRC) •Concha Reid (NASA GRC) ( ) •Tom Miller (NASA GRC) •Tom Miller (NASA GRC) •Dave Yendriga (Sierra Lobo) d g ( b ) •Marjorie Moats (SGT) •Marjorie Moats (SGT) •Michelle Manzo (Electrochemistry Branch Chief NASA GRC) h ll ( l h y h h f )
R f References 1. 1 2. 3 3. 4. 4 5. 6 6. 7. 8 8. 9.
(b)
Carbon 08 0.8
dQ Q//dV V
Si+graphite
700
Establishment of Diffusion Pathways y into Carbon Matrix Matrix and Surface Si
06 0.6
Si+Graphite Si
‐60
800
Establishment of Diffusion Pathways Through Carbon Matrix to Si
(e)
04 0.4
1.5
Figure 22 Figure 22 Nyquist plot for carbon‐silicon nanofoam anodes yq p
Volts vs. Li
((b))
02 0.2
0.5 Volts vs. Li Volts vs Li1
A k Acknowledgements l dg t
(c)
0
0
( ) (c)
Figure 15 g Voltage and Current vs Test Time for cycles 1 and 2 of the Voltage and Current vs. Test Time for cycles 1 and 2 of the carbon silicon graphite nanofoam anode (a) slow first insertion (b) low carbon‐silicon‐graphite nanofoam anode. (a) slow first insertion, (b) low current(c/100) constant current step to a cutoff voltage of 10 mV, (c) p g shoulders indicative of de‐lithiation shoulders indicative of de lithiation of silicon of silicon
Full Intercalation of Li+ Ions Into Carbon Matrix and Si
mAh/g mAh/g Active Material Electrode Active Material
(b)
‐70
1000
(c)
(a)
Electrode
(b)
(a)
TestTime(h) ( )
Figure 12 g Voltage and Voltage and C Current vs. Test t T t Time for cycles 4‐ y 5 of carbon‐silicon 5 of carbon silicon microsphere cell 1. i h ll 1 ((a) shoulders ) indicative of de‐ indicative of de lithi ti lithiation of silicon f ili
cycle 1 l cycle 2 cycle 2 cycle 3 l cycle 5 cycle 5 cycle 6 l 6 cycle 8 cycle 8 cycle 9 l 9
(d)
(a)
cycle 1 l 1 cycle 2 y
0
0
200
0.5
((b))
600 400
(a)
Vo oltag ge((V)) vs. v Lii
2
100
Test Time(h) Test_Time(h)
(b)
0.08 0 06 0.06
800
25
• Integrity and Spherical morphology are g y d ph l ph l gy maintained after cycling (figures 3‐4) d f y l g ((f g ) Indicating that the material is capable of buffering the large volume Indicating that the material is capable of buffering the large volume changes of the silicon h g f h ili • Exhibits unusual increase in capacity with cycling (figure 5) Exhibits unusual increase in capacity with cycling (figure 5) – Low capacity (150‐200 mAh/g) for first several cycles L i (150 200 Ah/ ) f fi l l – Capacity suddenly and drastically increases Capacity suddenly and drastically increases • Demonstrated ability to utilize the silicon (figure 6) D d bili ili h ili (fi 6) • Low capacity fade Low capacity fade • First cycle irreversible capacity loss of 50% of the maximum capacity Fi l i ibl i l f 50% f h i i • Coulombic efficiency of approximately 96% (desired values exceed 99%) efficiency of approximately 96% (desired values exceed 99%)
200
14 1.4
0 5
150
Voltage(V) g ( ) Current(mA)
1.6
C‐Si Nanofoam‐RT‐Ni Tab 1200
2.5
Figure 17 Figure 17 The contribution of silicon to the specific capacity as a function of cycle number for carbon‐silicon cycle number for carbon silicon nanofoam anode material (PAN nanofoam anode material (PAN= coated with polyaniline doped with LiPF6) coated with polyaniline doped with LiPF
T t Ti (h) Test_Time(h)
C‐Si Nanofoam‐RT‐A C‐Si Nanofoam‐RT‐A
1400
3
0 0005 0.0005
Figure 11 Figure 11 Voltage and Current vs. g Test Time for cycles 1‐ Test Time for cycles 1 3 of carbon silicon 3 of carbon‐silicon microsphere cell 1 (a) p ( ) extended taper charge extended taper charge observed prior to large observed prior to large increase in specific p capacity of anode capacity of anode.
-0 15 -0.15 0
Bulk Capacity p y
SSpe eciificc Caapaaciityy (m mA Ah//g)
1.5
0
Figure 9 Figure 9 Specific capacity as a function of cycle number for carbon silicon (C Si) Specific capacity as a function of cycle number for carbon‐silicon (C‐Si) nanofoam anode material (RT)=cured at room temperature (50)=cured at ( ) ( ) 50oC, (Ni Tab) C, (Ni Tab) = sample with a nickel tab attached without a copper foil sample with a nickel tab attached without a copper foil current collector current collector
SOA
100
150
0
Si Contribution Si Contribution
0 05 0.05 0
Cycle Number Cycle Number
Figure 5 Figure 5 Specific capacity as a function of cycling for cells Specific capacity as a function of cycling for cells containing carbon‐silicon microsphere anode material
1600
Voltage(V) Current(mA)
2
Results for The Silicon‐Carbon Microspheres Results for The Silicon‐Carbon Microspheres
HE
0
200
Cycle Number y
Figure 6 Figure 6 S ifi Specific capacity as a function of cycle number for cell 2 in it f ti f l b f ll 2 i fig. 4 showing capacities for the bulk material, the Si g g p , contribution and the capacity based on Si being the only contribution and the capacity based on Si being the only active material ti t i l
UHE-Li
250
30
Cycle Number Cycle Number
700
300
01 0.1
2.5
C‐Si Nanofoam‐ RT‐Ni RT Ni Tab Tab C Si Nanofoam C‐Si Nanofoam‐ RT B RT‐B C‐Si Nanofaom‐50
0
0
800
350
3
50
C/5
C/10
1400
The objective of this research project is to develop a silicon‐carbon The objective of this research project is to develop a silicon carbon composite anode material with a threshold specific capacity of 600 p p p y mAh/g and a goal of 1000 mAh/g as outlined by the Exploration mAh/g and a goal of 1000 mAh/g as outlined by the Exploration and Technology Development Program Energy Storage Project. It gy p g gy g j should be noted that the specific energy requirements are should be noted that the specific energy requirements are expressed for a traditional coated electrode that utilizes a copper p pp current collector current collector.
C‐Si Nanofoam‐ RT‐A RT A Carbon Nanofaom Carbon Nanofaom
400
200
to cells with traditional coated anode materials (figure 2, table 1). ll h d l d d l (f bl )
Objj ti Objective
Figure 8 Figure 8 Free standing Free standing carbon‐silicon nanofoam anode nanofoam anode
Figure 7 Figure 7 Scanning electron micrograph of carbon g g p nanofoam containing nano‐ silicon as nanofoam containing nano silicon as synthesized
0 001 0.001
A ly i f Cy li g Ch Analysis of Cycling Characteristics t i ti
Volta V age e(V V) vs s. Li L
Two materials , carbon microspheres ( figures 3‐4) and carbon , p ( g ) nanofoam (figures 7 8) produced from nano phase silicon nanofoam (figures 7‐8), produced from nano‐phase silicon impregnated RF gel precursors have been synthesized and p g g p y investigated In the first approach the silicon containing RF gel is investigated. In the first approach the silicon containing RF gel is 1 2 9 In the second formed into microspheres (carbon microspheres). p ( p ) 1,2,9 approach carbon paper is impregnated with the silicon containing approach, carbon paper is impregnated with the silicon containing 349 RF gel to create a free standing electrode (carbon nanofoam), g g ( ), 3,4,9 which if successful would eliminate the need for a current which, if successful, would eliminate the need for a current collector. The elimination of the current collector would result in the reduction of mass and an increase in the specific energy compared the reduction of mass and an increase in the specific energy compared
Figure 4 Fi 4 Scanning electron micrograph of g g p cast electrode composed of cast electrode composed of carbon microspheres containing b i h t i i nano‐silicon after cycling y g
SSpe eciffic Caapaacitty (m mAh h/gg)
One approach to ameliorating the expansion issues associated with One approach to ameliorating the expansion issues associated with silicon is to form a silicon carbon composite One such composite silicon is to form a silicon‐carbon composite. One such composite material is formed via the dispersion of silicon in a resorcinol‐ material is formed via the dispersion of silicon in a resorcinol formaldehyde (RF) gel followed by pyrolysis The premise behind formaldehyde (RF) gel followed by pyrolysis. The premise behind the RF gel silicon composite is that the gel will form a flexible, the RF gel silicon composite is that the gel will form a flexible, porous carbon matrix capable of absorbing the large volume porous, carbon matrix capable of absorbing the large volume expansion of the silicon upon lithiation thereby maintaining expansion of the silicon upon lithiation thereby maintaining electrical contact between particles and the current collector The electrical contact between particles and the current collector . The carbon matrix will also prevent direct electrolyte contact with the ca bo at a so p e e t d ect e ect o yte co tact t t e 1 2 9 Unlike a variety of other approaches, which use silicon 1,2,9 silicon. Unlike a variety of other approaches which use complicated expensive techniques such as chemical vapor p p q p deposition this technique makes use of traditional cost effective deposition, this technique makes use of traditional cost –effective laboratory techniques. y q
Figure 3 Fi 3 Scanning electron micrograph g g p of cast electrode composed of of cast electrode composed of carbon microspheres containing b i h t i i nano‐silicon before cycling y g
Sp peccific C Cap paccityy (mA Ah/g))
400% lattice volume expansion upon insertion of the lithium l l p p f h l h ions resulting in large irreversible capacity loss cracking of the ions, resulting in large irreversible capacity loss, cracking of the material, and eventual failure of the anode ate a , a d e e tua a u e o t e a ode10..
Current(A) Voltage(V)
0.0015
0
• Both Both the microspheres and the nanofoam the microspheres and the nanofoam anode materials showed low initial anode materials showed low initial capacity followed by a sudden and drastic increase in capacity after several capacity followed by a sudden and drastic increase in capacity after several cycles cycles. • The increase in capacity occurred after the cell had undergone an extended The increase in capacity occurred after the cell had undergone an extended t taper charge in which the cell was held at a low voltage (about 10‐15mv) vs. Li h i hi h th ll h ld t l lt ( b t 10 15 ) Li for an extended period of time (figure11 a) for an extended period of time (figure11 a). • After the extended taper charge and during cycles with improved capacity a f h d d p h g dd g y l h p d p y shoulder indicative of de litiation of silicon, appeared in the voltage vs. time shoulder, indicative of de‐litiation of silicon appeared in the voltage vs time discharge (de‐lithiation) discharge (de lithiation) curve (figure12a) curve (figure12a)12 • dQ/dV analysis revealed that the increase in capacity analysis revealed that the increase in capacity correlates with the correlates with the formation of highly lithiated amorphous silicon phases. formation of highly lithiated amorphous silicon phases 12 • Microsphere cell 1 dQ/dV Mi h ll 1 dQ/dV curves for cycles 1‐3 are dominated by characteristics f l 13 d i t db h t i ti associated with the intercalation of carbon by lithium After cycle 4 in which the associated with the intercalation of carbon by lithium. After cycle 4 in which the cell undergoes an extended taper charge at low voltage (figure 11a) the silicon ll d g d d p h g l l g ((f g ) h l de lithiation peak at 0.4 V becomes more pronounced with each successive de‐lithiation peak at 0 4 V becomes more pronounced with each successive cycle (figure13) and features associated with the lithiation cyc e ( gu e 3) a d eatu es assoc ated t t e t at o o of amorphous silicon a o p ous s co appear (figure13b c) 12 appear (figure13b,c). • Speculative mechanism to explain the unusual cycling characteristics (figure 14) Speculative mechanism to explain the unusual cycling characteristics (figure 14) – During the first few cycles, the lithium is only able to access the carbon D i th fi t f l th lithi i l bl t th b which surrounds the silicon and perhaps the small percentage of silicon which surrounds the silicon and perhaps the small percentage of silicon l located close to the surface d l h f – Carbon becomes fully lithiated Carbon becomes fully lithiated which, in turn, allows for the lithiation which in turn allows for the lithiation of of silicon surrounded by the carbon y – Diffusion pathways are established which allow for more efficient lithiation Diffusion pathways are established which allow for more efficient lithiation and de‐lithiation and de lithiation of the silicon of the silicon
Figure 21 dQ/dV analysis of silicon dQ/dV analysis of silicon‐ carbon‐graphite nanofoam b hi f anode coated with polyaniline doped with LiPF6. polyaniline doped with LiPF ( ) d li hi i (a) de‐lithiation of silicon f ili 12 , (b) lithiation of silicon12 , (c) SEI formation SEI formation
Z Z"
Cells were formed at a rate of C/10 for three cycles Cells were formed at a rate of C/10 for three cycles Cycling was performed at C/10 charge and discharge for 12‐15 cycles Cycling was performed at C/10 charge and discharge for 12‐15 cycles f ll followed by 5 cycles with a charge rate of C/10 and a discharge rate of db 5 l ith h t f C/10 d di h t f C/5 / Cells were cycled at room temperature Cells were cycled at room temperature
35 3.5
dQ Q/d dV
• •
Electrolyte: 1M LiPF Electrolyte: 1M LiPF6 1:1:1 ethylene carbonate, diethyl carbonate and 1:1:1 ethylene carbonate diethyl carbonate and di dimethyl h l carbonate b
0 002 0.002
dq q/d dv
•
Carbon microspheres were slurried Carbon microspheres were slurried with NaCMC with NaCMC and cast with 0.005 and cast with 0 005” film film onto copper foil t f il Half cells were constructed in the form of coin cells using metallic lithium g as the counter electrode as the counter electrode
•
cycle 1 cycle 1 cycle 2 l 2 cycle 5 l
(c)
Currrent(A A)
Cell Construction and Electrochemical Cycling Ce Co st uct o a d ect oc e ca Cyc g •
The National Aeronautics and Space Administration (NASA) has The National Aeronautics and Space Administration (NASA) has embarked upon a number of near and far term missions which p require advanced energy storage systems These energy storage require advanced energy storage systems. These energy storage systems must be safe, human rated, have high specific energies y , , g p g (Wh/kg) high energy densities (Wh/l) high reliability long cycle life (Wh/kg), high energy densities (Wh/l), high reliability, long cycle life, l p low power fade over the life of the battery and the ability to f d h lf f h b y d h bl y perform in a variety of unique environments The Exploration perform in a variety of unique environments. The Exploration Technology Development Program (ETDP) via the Energy Storage h l gy l p g ( ) h gy g Project supported the development of advanced lithium ion (Li‐ion) Project supported the development of advanced lithium ion (Li‐ion) cells which possess many of the required attributes. ll hi h p y f h q i d ib
Resorcinol formaldehyde gels containing 50 nm silicon were formed Resorcinol‐formaldehyde gels containing 50 nm silicon were formed Pyrolyzed at 1000 at 1000o in argon in argon
•
Sp peccific C Cap paccityy (m mA Ah//g))
• •
•
(a)
• Add Add graphite to resorcinol formaldehyde gel to improve graphite to resorcinol formaldehyde gel to improve conductivity • Coat the anode with a conductive binder composed of Coat the anode with a conductive binder composed of 11 polyaniline p y doped with LiPF p 6 6 • Improve initial capacity and promote faster lithiation Improve initial capacity and promote faster lithiation of the silicon of the silicon by developing a new formation/cycling procedure in which the y p g / y gp cell is formed very slowly and the taper charge is replace with a cell is formed very slowly and the taper charge is replace with a low current constant current step p • Use only spot welded nickel tabs and no copper current collector Use only spot welded nickel tabs and no copper current collector
Materials were shown to intercalate and de‐intercalate lithium El t d id tifi d C Si Electrodes identified as C‐Si nanofoam f RT A d RT B h RT‐A and RT‐B showed improving di i performance with cycling with final capacities of approximately 400 mAh/g and performance with cycling with final capacities of approximately 400 mAh/g and 275 mAh/g respectively /g p y at the electrode level Material has the ability to function as an anode and utilize the capacity of the Material has the ability to function as an anode and utilize the capacity of the silicon (figure 10) silicon (figure 10) Electrode with the spot welded nickel tab performed comparably with electrodes l d h h p ld d k l b p f d p bly h l d which utilized a copper foil current collector (figures 9 and 10) which utilized a copper foil current collector (figures 9 and 10) – Current collectors may not be necessary when using this material Current collectors may not be necessary when using this material – Significant reduction in electrode mass Si ifi d i i l d The absence of the current collector significantly reduces the mass of the The absence of the current collector significantly reduces the mass of the electrode thereby increasing specific energy at the electrode level electrode thereby increasing specific energy at the electrode level when when compared p d to traditional coated anode materials (figure 2, table 1) di i l d d i l ((fig 2 bl 1))
• •
SSpe eciificc Caapacityy (m mA Ah//g)
1279 SSynthesis y h i 1,2,7,9
•
I t d ti Introduction
Significance • Composed of 100% active material (carbon and silicon) C d f 100% ti t i l( b d ili ) • Free standing electrode that does not require the use of a copper current collector a copper current collector – Could significantly reduce cell mass C ld i ifi tl d ll – Effective specific capacity on the electrode Effective specific capacity on the electrode level would be higher than for traditional level would be higher than for traditional coated electrodes (table 1) t d l t d (t bl 1) Synthesis1,2,7,9 • Free standing carbon nanofoam Free standing carbon nanofoam anode was produced anode was produced f from carbon paper impregnated with resorcinol‐ b p p i p g d ih i l formaldehyde gel containing 50 nm silicon particles formaldehyde gel containing 50 nm silicon particles • Pyrolyzed at 1000 at 1000o C in argon C in argon Cell Construction and Electrochemical Cycling ll d l h l y l g • Anodes were constructed via two methods Anodes were constructed via two methods – Nanofoam material was placed on copper foil material was placed on copper foil current collectors the same size as the anode material (used only for preliminary tests) material (used only for preliminary tests) – A nickel tab is spot‐welded onto the corner of A i k lt bi t ld d t th f the nanofoam material (used on most tests) ( ) • Half cells were constructed in the form of pouch cells Half cells were constructed in the form of pouch cells using metallic lithium as the counter electrode i t lli lithi th t l t d • Electrolyte: 1M LiPF y y , y 6 1:1:1 ethylene carbonate, diethyl 6 carbonate and dimethyl carbonate carbonate and dimethyl • Cells were formed at a rate of approximately C/5 for 5 C ll f d t t f i t l C/5 f 5 cycles then cycled at C/20 for the remaining cycles cyc es t e cyc ed at C/ 0 o t e e a g cyc es reported • Cycled at room temperature C l d t t t
App Approach 1: Carbon Gel Microsphere Anodes h 1 C b G l Mi ph A d
N App New Approaches for Silicon‐Carbon Nanofoam h f Sili C b N f
dQ//dV d V
carbon microspheres and nanofoams produced from nano‐phase carbon microspheres and nanofoams produced from nano phase silicon impregnated RF gel precursors have been synthesized and p g g p y investigated Carbon microspheres are produced by forming the investigated. Carbon microspheres are produced by forming the silicon‐containing RF gel into microspheres whereas carbon nano‐ l g g l ph h b foams are produced by impregnating carbon fiber paper with the foams are produced by impregnating carbon fiber paper with the 149 silicon containing RF gel to create a free standing electrode. l g g l f d g l d 1‐4,9 Both materials have demonstrated their ability to function as Both materials have demonstrated their ability to function as anodes and utilize the silicon present in the material. Stable d d ili h ili p i h i l S bl reversible capacities above 400 mAh/g for the bulk material and reversible capacities above 400 mAh/g for the bulk material and above 1000 mAh/g of Si have been observed. b 1000 Ah/ f Si h b b d
cathode anode electrolyte separator t aluminum foil copper foil f il
Cu C urrren nt(mA A)
Estimates for component weight p g A variety of materials are under investigation for use as anode y g fraction in 30 Ah cell Mass of the anode fraction in 30 Ah cell. Mass of the anode materials in lithium ion batteries of which the most promising are materials in lithium‐ion batteries, of which, the most promising are coating represents approximately 24% i i l 24% of f 10 10 those containing silicon. g One such material is a composite formed p total mass Mass of the copper foil total mass. Mass of the copper foil via the dispersion of silicon in a resorcinol formaldehyde (RF) gel via the dispersion of silicon in a resorcinol‐formaldehyde (RF) gel c rrent collector represents current collector represents followed by pyrolysis. Two silicon‐carbon composite materials, y py y p , approximately 8% of mass. pp y
Glenn Research Center Glenn Research Center
Initial Results for The Silicon‐Carbon Nanofoam Initial Results for The Silicon‐Carbon Nanofoam
App Approach 2 : Carbon Nanofoam h2 C b N f A d Anodes
V lta Vol age e(V V) vs s. Li L
Figure 2 Figure 2
Abstract
Curre C entt(m mA A)
Glenn Research Center Glenn Research Center
05 0.5
1
15 1.5
Volts vs. Li
Figure 19 Fi 19 dQ/dV analysis of the silicon‐carbon anode. (a) Q/ y ( ) de‐lithiation of silicon12 , (b) lithiation of silicon de‐lithiation of silicon (b) lithiation of silicon12, ( ) SEI f (c) SEI formation ti
Wang, K.; He, X.; Wang, L.; Ren, J.; Jiang, C.; Chunrong, W. Solid State Ionics Wang K ; He X ; Wang L ; Ren J ; Jiang C ; Chunrong W Solid State Ionics 2007, 178, 115‐118. 2007 178 115 118 Hasegawa, T.; Mukai, S. R.; Shirato, Y.; Tamon, H. Carbon g , ; , ; , ; , 2004, 42, 2573‐2579. , , Long J W ; Bourg M E ; Wallace J M ; Fischer A E ; Lytle J C ; Pettigrew K A ; Barrow A J ; Dysart J L ; Rolinson D R Long, J. W.; Bourg, M. E.; Wallace, J. M.; Fischer, A. E.; Lytle, J. C.; Pettigrew, K. A.; Barrow, A. J.; Dysart, J. L.; Rolinson, D. R. In 215 Electrochemical Society Meeting San Francisco CA, 2009. y g , Long J W 2009 pp Personal Communication Long, J. W., 2009, pp Personal Communication. Al‐Muhtaseb, Ritter. Advanced Materials 2003, 15, 101‐114 , , , Yamamoto Endo Ohmori , Nakaiwa. Carbon Yamamoto, Endo, Ohmori Nakaiwa Carbon 2005, 43, 1231‐1238. 2005 43 1231 1238 Yamamoto, Sugimoto, Suzuki, Mukai, Tamon , g , , , Carbon 2002, 40, 1345‐1351. , , Hasegawa T ; Mukai S R ; Shirato Y ; Tamon H Carbon 2004, 42, 2573‐2579. Hasegawa, T.; Mukai, S. R.; Shirato, Y.; Tamon, H. Carbon 2004 42 2573 2579 Wang, G. X.; Ahn, J. H.; Yao, J.; Bewlay, S.; Liu, H. K. Electrochemistry Communications g, ; , ; , ; y, ; , y 2004, 6, 689‐692. , ,
10. Kasavajjula, U.; Wang, C.; Appleby, J. A. Journal of Power Sources 10 Kasavajjula U ; Wang C ; Appleby J A Journal of Power Sources 2007, 163, 1003‐1039. 2007 163 1003 1039 11.Liu, Y.; Matsumura, T.; Imanishi, N.; Hirano, A.; Ichiwaka, T.; Takeda, Y. Electrochemical and Solid State Letters , ; , ; , ; , ; , ; , 2005, 8, , , A599 A602 A599‐A602. 12.Obrovac, M.N.; Krause, L.J. Journal of The Electrochemical Society 2007, 154, A103 12.Obrovac, M.N.; Krause, L.J. Journal of The Electrochemical Society 2007, 154, A103‐A108 A108
Point of Contact: Dr. James Woodworth : [email protected] Point of Contact: Dr. James Woodworth : [email protected]
