Reduced Grain Boundary Resistance by Surface Modification ...
Reduced Grain Boundary Resistance by Surface Modification Hirotoshi Yamada,* Daisuke Tsunoe, Shota Shiraishi, Gakuho Isomichi Graduate School of Engineering, and Faculty of Engineering, Nagasaki University 1-14, Bunkyo-machi, Nagasaki 8528521, Japan E-mail: [email protected]
Supporting Information S1. Nanosized Effect on Grain-Boundary Resistance. Commercial Li2SiO3 (LSO) powder of 1−10 µm in diameter (Kishida Chemical Co. Ltd.) was pulverized by a planetary ball mill (300 rpm, 36 h) to obtain a nanosized Li2SiO3. Total conductivity of micro- and nanosized LSO was obtained from ac. impedance (1 MHz – 10 mHz) in Ar flow. For the impedance measurement, specimens were pressed into pellets without sintering. Gold electrodes were deposited by dc. sputtering. As shown in Fig. S1, the total conductivity was higher for nanosized LSO than micro-sized LSO, indicating smaller grain-boundary resistance for nanosized LSO.
Conductivity (S cm-1)
10-6
nano LSO (50 nm)
10-7 LSO (1~10 µm)
1.65
1.70
1.75 1000 / T (K-1)
1.80
Figure S1. Arrhenius plots of total conductivity of as-pressed Li2SiO3 particles and nanosized Li2SiO3 particles.
S2. Thermal Properties of Li2SiO3 Gel and Structure of Li2SiO3 Dependent on Heat Treatment Temperature Li2SiO3 sol was prepared from mixed solution of LiOEt and Si(OEt)4 in ethanol with an atomic ratio of Li to Si of 2. The sol was stirred overnight in a N2 filled grove bag to conduct slow hydrolysis. Then, white gel was obtained, which was analyzed by TG-DTA (Fig. S2) and XRD (Fig. S3). Details are explained in the main text. 5
0
Release of H2O
0
Release of CO2
-10
-5
DTA (µV)
-10 -20 -15 0
200
400
o
600
800
Temp ( C)
Figure S2. TG-DTA curves of Li2SiO3 gel.
Li2 CO3
Intensity (Arb. unit)
TG (wt%)
Crystallization
o
800 C o
500 C o
300 C as-dried Li2 SiO 3 (#29-0828)
20
40 60 2θ (deg. (CuKα))
80
Figure S3. XRD profiles of Li2SiO3 gel and Li2SiO3 heated at 300, 500, 800oC.
S3. 27Al MAS-NMR. 27
Al MAS-NMR spectra of bare LATP and LATP@LSO were recorded at room temperature
using Varian NMR System 500PS equipped with a 11.7 T superconducting magnet. Specimens were put in a 3.2-mm rotor and spun at 20 kHz. Spectra were referenced to 0.1 M Al(NO3)3 aqueous solution at 0 ppm. Details are explained in the main text.
Abundance (Arb. unit)
-14.6 ppm
-17.1 ppm
13.9 ppm
60 40 20 0 -20 -40 Chemical shift (ppm vs. 27Al(NO3)3 aq.)
Figure S4. 27Al MAS-NMR of bare LATP.
S4. Brick-Layer Model for Core-Shell Solid Electrolytes. The core-shell structured solid electrolytes of LATP@LSO were analyzed with a brick-layer model, shown in Fig. S4. Each particle is shown as a cube with a length of D, and surface layer (shell) with a thickness of a is formed. There are two pathways: penetrating inner particles (path A) and along surface layers (path B). Impedance for the path A and B in Fig. S4 are given by ZA =
Nx a 1 1 1 + 2 × 2 N y N z σ shell (D − 2a ) σ core D − 2a
ZB =
Nx NyNz
1 D 2 2 σ shell D − (D − 2a )
respectively. Here, σcore and σshell are ionic conductivity in core of particles and surface layer, respectively. As path A and B are connected in parallel, total impedance, Ztotal, satisfies 1 Z total
=
N y N z (D − 2a )2 σ shellσ core 1 1 4a ( D − a ) + = + ZA ZB N x (D − 2a )σ shell + 2aσ core D
=
DN y N z (1 − 2ξ )2 σ shellσ core + 4ξ (1 − ξ )σ shell N x (1 − 2ξ )σ shell + 2ξσ core
where ξ = a/D. On the other hand, 1/Ztotal is given using total conductivity, σtotal, as follows: 1 Z total
= σ total
L y Lz Lx
= σ total
DN y N z Nx
Lx=NxD
Lz=NzD
Ly=NyD D
Shell
Path B
a
Core
Path A
a a
D
D
Figure S5. Schematic structure of core-shell solid electrolytes by a brick-layer model. D, L, N: particle size, length of solid electrolyte, and number of particle along each axis (x, y, z), respectively. a: thickness of surface layer.
By comparing two equations, we obtaine
σ total =
(1 − 2ξ )2 σ shellσ core + 4ξ (1 − ξ )σ shell (1 − 2ξ )σ shell + 2ξσ core
Supporting Information S1. Nanosized Effect on Grain-Boundary Resistance. Commercial Li2SiO3 (LSO) powder of 1−10 µm in diameter (Kishida Chemical Co. Ltd.) was pulverized by a planetary ball mill (300 rpm, 36 h) to obtain a nanosized Li2SiO3. Total conductivity of micro- and nanosized LSO was obtained from ac. impedance (1 MHz – 10 mHz) in Ar flow. For the impedance measurement, specimens were pressed into pellets without sintering. Gold electrodes were deposited by dc. sputtering. As shown in Fig. S1, the total conductivity was higher for nanosized LSO than micro-sized LSO, indicating smaller grain-boundary resistance for nanosized LSO.
Conductivity (S cm-1)
10-6
nano LSO (50 nm)
10-7 LSO (1~10 µm)
1.65
1.70
1.75 1000 / T (K-1)
1.80
Figure S1. Arrhenius plots of total conductivity of as-pressed Li2SiO3 particles and nanosized Li2SiO3 particles.
S2. Thermal Properties of Li2SiO3 Gel and Structure of Li2SiO3 Dependent on Heat Treatment Temperature Li2SiO3 sol was prepared from mixed solution of LiOEt and Si(OEt)4 in ethanol with an atomic ratio of Li to Si of 2. The sol was stirred overnight in a N2 filled grove bag to conduct slow hydrolysis. Then, white gel was obtained, which was analyzed by TG-DTA (Fig. S2) and XRD (Fig. S3). Details are explained in the main text. 5
0
Release of H2O
0
Release of CO2
-10
-5
DTA (µV)
-10 -20 -15 0
200
400
o
600
800
Temp ( C)
Figure S2. TG-DTA curves of Li2SiO3 gel.
Li2 CO3
Intensity (Arb. unit)
TG (wt%)
Crystallization
o
800 C o
500 C o
300 C as-dried Li2 SiO 3 (#29-0828)
20
40 60 2θ (deg. (CuKα))
80
Figure S3. XRD profiles of Li2SiO3 gel and Li2SiO3 heated at 300, 500, 800oC.
S3. 27Al MAS-NMR. 27
Al MAS-NMR spectra of bare LATP and LATP@LSO were recorded at room temperature
using Varian NMR System 500PS equipped with a 11.7 T superconducting magnet. Specimens were put in a 3.2-mm rotor and spun at 20 kHz. Spectra were referenced to 0.1 M Al(NO3)3 aqueous solution at 0 ppm. Details are explained in the main text.
Abundance (Arb. unit)
-14.6 ppm
-17.1 ppm
13.9 ppm
60 40 20 0 -20 -40 Chemical shift (ppm vs. 27Al(NO3)3 aq.)
Figure S4. 27Al MAS-NMR of bare LATP.
S4. Brick-Layer Model for Core-Shell Solid Electrolytes. The core-shell structured solid electrolytes of LATP@LSO were analyzed with a brick-layer model, shown in Fig. S4. Each particle is shown as a cube with a length of D, and surface layer (shell) with a thickness of a is formed. There are two pathways: penetrating inner particles (path A) and along surface layers (path B). Impedance for the path A and B in Fig. S4 are given by ZA =
Nx a 1 1 1 + 2 × 2 N y N z σ shell (D − 2a ) σ core D − 2a
ZB =
Nx NyNz
1 D 2 2 σ shell D − (D − 2a )
respectively. Here, σcore and σshell are ionic conductivity in core of particles and surface layer, respectively. As path A and B are connected in parallel, total impedance, Ztotal, satisfies 1 Z total
=
N y N z (D − 2a )2 σ shellσ core 1 1 4a ( D − a ) + = + ZA ZB N x (D − 2a )σ shell + 2aσ core D
=
DN y N z (1 − 2ξ )2 σ shellσ core + 4ξ (1 − ξ )σ shell N x (1 − 2ξ )σ shell + 2ξσ core
where ξ = a/D. On the other hand, 1/Ztotal is given using total conductivity, σtotal, as follows: 1 Z total
= σ total
L y Lz Lx
= σ total
DN y N z Nx
Lx=NxD
Lz=NzD
Ly=NyD D
Shell
Path B
a
Core
Path A
a a
D
D
Figure S5. Schematic structure of core-shell solid electrolytes by a brick-layer model. D, L, N: particle size, length of solid electrolyte, and number of particle along each axis (x, y, z), respectively. a: thickness of surface layer.
By comparing two equations, we obtaine
σ total =
(1 − 2ξ )2 σ shellσ core + 4ξ (1 − ξ )σ shell (1 − 2ξ )σ shell + 2ξσ core
