Supporting Information
Comparative Study of Ni-rich Layered Cathodes for Rechargeable
Lithium
Batteries:
Li[Ni0.85Co0.11Al0.04]O2
and
Li[Ni0.84Co0.06Mn0.09Al0.01]O2 with Two-Step, Full Concentration Gradients Byung-Beom Lim†⊥, Seung-Taek Myung‡⊥, Chong S. Yoon*,∥, Yang-Kook Sun*,† †
Department of Energy Engineering and ∥Department of Materials Science and Engineering,
Hanyang University, Seoul, 04763, South Korea ‡
Department of Nanotechnology and Advanced Materials Engineering, Sejong University, Seoul
05006, South Korea Corresponding Author Yang-Kook Sun *E-mail:
[email protected] Chong S. Yoon *E-mail:
[email protected] 1
Experimental Material synthesis: To synthesize the TSFCG-Al Li[Ni0.84Co0.06Mn0.09Al0.01]O2 layered oxide cathode material, an NiSO4·6H2O solution in tank 1 was used as the starting material for the co-precipitation process. Then, an Ni-less aqueous solution consisting of NiSO4·6H2O and CoSO4·7H2O (molar ratio of Ni:Co= 90:10) in tank 2 was slowly pumped into tank 1. Simultaneously, the homogeneously mixed solution in tank 1 was fed into a batch reactor (40 L) that was filled with certain amounts of deionized water, an NH4OH solution (aq.), and an NaOH solution (aq.) in a replenished N2 atmosphere. At the same time, a 4.0 mol L-1 NaOH solution (aq.) (molar ratio of sodium hydroxide to transition metal = 2.0) and an NH4OH chelating agent solution (aq.) (molar ratio of ammonium hydroxide to transition metal = 1.0) were pumped separately into the reactor. During the early stages of the process, Ni(OH)2 (the center composition) was co-precipitated first. Nickel-cobalt-manganese hydroxides with different compositions were then gradually coated onto the formed Ni(OH)2 particles, resulting in a designed composition of Ni, Co, and Mn toward the outer surface of the particles. In order to synthesize the TSFCG hydroxide precursor with the second concentration gradient layer, an aqueous solution in tank 3 with an Ni-poor concentration consisting of NiSO4·6H2O, CoSO4·7H2O, and MnSO4·5H2O (molar ratio of Ni:Co:Mn = 67:6:27) was slowly pumped into the mixed solution in tank 1. The precursor powders were obtained by filtering, washing, and drying in a vacuum oven at 110 oC overnight. The obtained TSFCG [Ni0.85Co0.05Mn0.10](OH)2 was mixed with LiOH·H2O and Al(OH)3·xH2O (Li/(Ni + Co + Mn + Al) = 1.01 and Al/(Ni + Co + Mn + Al) = 0.01 in a molar ratio), and the mixture was calcined at 750 oC for 15 h in oxygen. To synthesize Li[Ni0.85Co0.11Al0.04]O2, an aqueous solution consisting of NiSO4·6H2O and CoSO4·7H2O (molar ratio of Ni:Co = 88:12) with a concentration of 2.0 mol L-1 was fed into
2
a batch reactor (40 L) that was filled with certain amounts of deionized water, a NH4OH solution (aq.), and an NaOH solution (aq.) in a replenished N2 atmosphere. At the same time, a 4.0 mol L1
NaOH solution (aq.) (molar ratio of sodium hydroxide to transition metal = 2.0) and an NH4OH
chelating agent solution (aq.) (molar ratio of ammonium hydroxide to transition metal = 1.0) were pumped separately into the reactor. The pH, temperature, and stirring speed of the mixture in the reactor were carefully controlled. The precursor powders were obtained by washing, filtering, and drying. The synthesized [Ni0.88Co0.12](OH)2 hydroxide precursor, obtained via the co-precipitation process, was mixed with LiOH·H2O.Al(OH)3·xH2O (Li/(Ni + Co + Al) = 1.01 and Al/(Ni + Co + Al) = 0.04 in a molar ratio) and calcined at 750 oC for 10 h in oxygen. Material characterization: The chemical compositions of the powders were analyzed via inductively coupled plasma spectrometry (ICP-MS, NexION 300). The chemical composition of the prepared powders was determined using inductively coupled plasma (ICP, OPIMA 8300, Perklin Elmer). Powder X-ray diffraction (XRD) (Rigaku, Rint-2000) using Cu Kα radiation was employed to identify the crystalline phases of the prepared powders. XRD data were obtained between 10 and 80o 2θ with a step size of 0.03o, and the collected XRD data were analyzed by the Rietveld refinement program Fullprof.1 To obtain the localized composition, cross-sections of the TSFCG-Al particles were prepared by focused-ion beam (FIB) and examined with a JEOL, Model JEM 2100F instrument. Line scans of the polished surfaces were analyzed with an electron probe micro-analyzer (EPMA, JXA-8500f, JEOL); beam size: 1µm, accelerating voltage: 15 kV, current: 10 nA, standard used: pure metal (100%). The morphologies of the prepared powders were observed using scanning electron microscopy (SEM, JSM-6340F, JEOL).
3
Electrochemical evaluation: To fabricate the cathode material, the working electrode consists of 85 wt. % of the prepared powders, 7.5 wt. % of carbon, and 7.5 wt. % of poly(vinylidene fluoride) (PVDF) binder. The obtained slurry was coated onto Al foil and rollpressed. The coated electrodes were dried overnight at 120 oC in a vacuum prior to use. The electrolyte solution was 1.2 M LiPF6 in ethylene carbonate-ethyl methyl carbonate (EC:EMC = 3:7 by volume with 2 wt. % of a vinylene carbonate (VC), which decreases the surface impedance of cathode materials2 PANAX ETEC Co.). Electrochemical testing was performed in a 2032 coin-type cell adopting Li metal as the anode. The cells were typically cycled in the constant current mode at a rate of 0.5 C within the voltage range of 2.7 – 4.3 V versus Li+/Li (where 1 C = 200 mA g-1). AC impedance measurements were performed with an impedance analyzer (Bio-Logic, VMP3) over the frequency range of 1 MHz to 10 mHz with an amplitude of 10 mVrms. Thermal properties of delithiated state: For the differential scanning calorimetry (DSC) analysis, 2032 coin-type cells were charged to 4.3 V and opened in an Ar-filled dry room. After the remaining electrolyte was carefully removed from the surface of the electrode, the cathode materials were recovered from the current collector. A stainless steel sealed pan with a goldplated copper seal was used to collect 3 – 5 mg samples. Measurements were performed using a DSC 200 PC (Netzsch, Germany) at a temperature scan rate of 1 °C min-1.
4
16 14
80
10
D10 : 7.02 D50 : 10.09 D90 : 13.97
8
40
6 4
20
2 0 0.1
1
Diameter / um
10
0
14
d
12
80 60
10
D10 : 6.89 D50 : 10.10 D90 : 14.33
8 6
40
4 20 0 0.1
H istogram
60
12
C um ulative values / %
c
100
H istogram
C um ulative values / %
100
2 1
10
0
Diameter / um
Figure SI 1. Low magnification SEM images of (a) Li[Ni0.85Co0.11Al0.04]O2 NCA and (b) Li[Ni0.84Co0.06Mn0.09Al0.01]O2 TSFCG-Al and the resulting particle size distribution of (c) NCA and (d) TSFCG-Al.
5
[NCA] BET Surface Area : 0.491 m2/g Adsorption Desorption
1.5 1.0 0.5 0.0 -0.5
0.0
0.2
0.4
0.6
0.8
Relative Pressure / P/P0
1.0
-1
2.0
a
Volume Adsorbed / cc g
Volume Adsorbed / cc g
-1
2.0
[TSFCG-Al] BET Surface Area : 0.336 m2/g
1.5
b
Adsorption Desorption
1.0 0.5 0.0 -0.5
0.0
0.2
0.4
0.6
0.8
Relative Pressure / P/P0
1.0 1
Figure SI 2. BET surface area measurement plots for (a) Li[Ni0.85Co0.11Al0.04]O2 NCA and (b) Li[Ni0.84Co0.06Mn0.09Al0.01]O2 TSFCG-Al.
6
Figure SI3. SEM images of as prepared electrode of (a) Li[Ni0.85Co0.11Al0.04]O2 NCA and (b) Li[Ni0.84Co0.06Mn0.09Al0.01]O2 TSFCG-Al, and cycled electrode after 100 cycles at 4.5 V of (c) Li[Ni0.85Co0.11Al0.04]O2 NCA and (d) Li[Ni0.84Co0.06Mn0.09Al0.01]O2 TSFCG-Al.
7
- Im(Z) / Ohm
0 12
10.0 mHz
25
0 0
311 mHz 25 450 mHz 50 735 mHz Re(Z) / Ohm
127 Hz 127 Hz 144 Hz 50 144 Hz 0
25
0
4
8
Re(Z) / Ohm
4
c
0 12
10.0 mHz
200
0
12 10.0 mHz 4.64 Hz
25
50
75
Al TSFCG 4.5 V
300
Re(Z) / Ohm
e
2.22 Hz
0
4
8
8
4
0 12
Re(Z) / Ohm
63.1 mHz
100
63.1 mHz
d 49.4 mHz 10.0 mHz
71.4 mHz
0 0
300
1 cycle 30 cycles 50 cycles 100 cycles
12
99.9 Hz 99.9 Hz 99.9 Hz 200 113 Hz
30.2 mHz 71.4 mHz 63.0 mHz 49.4 mHz 100
4
b
Re(Z) / Ohm
100
0 0
8
5.25 Hz 5.94 Hz
0 0
75
- Im(Z) / Ohm
113 Hz 113 Hz 200 99.9 Hz 113 Hz
8
149 mHz
12
8
4
Re(Z) / Ohm
NCA 4.5 V
300
- Im(Z) / Ohm
8
Re(Z) / Ohm
12
- Im(Z) / Ohm
4
- Im(Z) / Ohm
0
a
- Im(Z) / Ohm
- Im(Z) / Ohm
8
69.2 Hz 78.1 Hz 4 88.6 Hz 50 99.9 Hz
Al TSFCG 4.3 V
75
12
- Im(Z) / Ohm
NCA 4.3 V
75
100
200
300
Re(Z) / Ohm
Figure SI4. Electrochemical impedance spectra (Nyquist plots) of (a) Li[Ni0.85Co0.11Al0.04]O2 NCA and (b) Li[Ni0.84Co0.06Mn0.09Al0.01]O2 TSFCG-Al in the voltage ranges of 2.7-4.3 V and (c) Li[Ni0.85Co0.11Al0.04]O2 NCA and (d) Li[Ni0.84Co0.06Mn0.09Al0.01]O2 TSFCG-Al in the voltage ranges of 2.7-4.5V as function of the number of cycles at a current of 100 mA g-1 (0.5 C rate); (e) Equivalent circuit used for fitting.
8
a Intensity / A.U.
Observed Calculated Difference Bragg peak
10
20
30
40
50
60
70
80
Cu Kα 2θ / degree
b
90 100 110 10
20
Observed Calculated Difference Bragg peak
30
40
50
60
70
80
90 100 110
Cu Kα 2θ / degree
Figure SI5. Rietveld refinement results of XRD patterns of (a) Li[Ni0.85Co0.11Al0.04]O2 NCA and (b) Li[Ni0.84Co0.06Mn0.09Al0.01]O2 TSFCG-Al electrodes after 100 cycles with an upper cutoff voltage of 4.5 V.
9
5 o
-1
Heat flow / W g
TSFCG-Al NCA
204.3 C 4 o
215.2 C 3 2 1 0 100
150
200
250
Temperature /
300
350
o
C
Figure SI6. Differential scanning calorimetry (DSC) results of Li[Ni0.85Co0.11Al0.04]O2 NCA and Li[Ni0.84Co0.06Mn0.09Al0.01]O2 TSFCG-Al charged to 4.3 V.
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Table S1. Fitted Rsf and Rct of Li[Ni0.85Co0.11Al0.04]O2 NCA and Li[Ni0.84Co0.06Mn0.09Al0.01]O2 TSFCG-Al electrodes upon charging after various cycles. TSFCG-Al 4.3 V Cycle number
NCA
4.5 V
Rsf / Ω Rct / Ω Rsf / Ω Rct / Ω
4.3 V
4.5 V
Rsf / Ω Rct / Ω Rsf / Ω Rct / Ω
1 cycle
5.6
2.9
4.6
69.0
5.5
9.2
6.1
101.8
30 cycles
6.2
3.1
5.5
75.8
5.8
15.2
6.8
144.4
50 cycles
6.9
3.5
6.1
85.9
6.7
20.8
7.5
175.0
100 cycles
7.0
5.8
6.7
105.7
7.2
39.1
7.4
233.4
11
Table
S2.
Rietveld
refinement
results
of
XRD
data
for
extensively-cycled
Li[Ni0.85Co0.11Al0.04]O2 NCA and Li[Ni0.84Co0.06Mn0.09Al0.01]O2 TSFCG-Al (after 100 cycles).
Ni2+ in Li site / %
a/Å
c/Å
Rwp / %
NCA to 4.3 V
5.5
2.8650(1)
14.2231(4)
10.4
NCA to 4.5 V
6.8
2.8646(1)
14.2459(1)
12.9
TSFCG-Al to 4.3 V
3.4
2.8749(2)
14.2185(2)
14.1
TSFCG-Al to 4.5 V
4.1
2.8754(2)
14.2246(2)
14.2
12
REFERENCE (1)
T Roisnel, J. Rodriguez-Carjaval, Fullprof Manual, Institut Laue- Langevin, Grenoble,
France, 2002. (2) Aurbach, D.; Gamolsky, K.; Markovksy, B.; Gofer, Y.; Schmidt, M.; Heider, U. On the use of vinylene carbonate (VC) as an additive to electrolyte solutions for Li-ion batteries Electrochim. Acta 2002, 47, 1423-1439
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