3-D Imaging of separator pore structure and Li + diffusion behavior

Transcription

1 3-D Imaging of separator pore structure and Li + diffusion behavior Dr. Akira Yoshino Yoshino Laboratory Asahi Kasei Corp. yoshino.ab@om.asahi-kasei.co.jp

2 Outline 1. Background 2. Method to measure diffusion rate of Li + within separator by PFG-NMR 3. Direct observation of 3-D pore structure by FIB SEM 4. Summary 2

3 Outline 1. Background 2. Method to measure diffusion rate of Li + within separator by PFG-NMR 3. Direct observation of 3-D pore structure by FIB SEM 4. Summary 3

4 Three kinds of separators used for LIB SEM photo images of separators 5μm 5μm 5μm One component dry process Two components wet process Three components wet process 4

5 Important roles of separators Electronic insulation and Ionic conduction Shut down effect Impedance of separator /Ω cm 2 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 1.E+00 1.E Temperature / 5

6 Outline 1. Background 2. Method to measure diffusion rate of Li + within separator by PFG-NMR 3. Direct observation of 3-D pore structure by FIB SEM 4. Summary 6

7 Principle of pulsed field gradient NMR (PFG-NMR) Conventional NMR: Excitation by electromagnetic pulse detection PFG-NMR: Excitation by electromagnetic pulse labeling of position by pulsed field gradient diffusion time detection Intensity After certain time Migration from labeled position by self-diffusion Static magnetic field Position T3 T4 T5 T2 T1 T0 7

8 Principle of PFG-NMR Diffusion coefficient by PFG-NMR: D in the following formula ln(e/e 0 ) = -D (γ 2 δ 2 g 2 (Δ-δ/3)) E: Peak intensity at each measurement E 0 : Peak intensity without PFG γ: Gyromagnetic ratio of nuclear spin δ: PFG exposure time g: PFG intensity Δ: Diffusion time ln(e/e0) Li F H(EC) H(MEC) Li + : m 2 /s TFSI - : m 2 /s EC: m 2 /s MEC: m 2 /s Li 輸率 transport :0.46no: E E E E E E+10 γ 2 δ 2 g 2 ( -δ/3) Slope of diffusion plot D Calculation of diffusion coefficient in direction of static magnetic field (vertical direction of test tube) 8

9 New method to measure ion diffusion coefficient within separator Electrolyte 1M LiTFSI / EC-MEC (1:2 vol.%) Sample preparation Separator is impregnated with electrolyte, inserted in test tubes in three directions (X, Y, and Z axes) as shown at right Y X Y X axis X X X Y Y Y axis Z axis X axis Y axis PFG-NMR measurement conditions Apparatus: ECA400 (JEOL) Probe: GR probe (max. magnetic field gradient strength =13 T/m) Δ: 50 ms, δ: 0.3 ms ( 1 H, 19 F), 0.5 ms ( 7 Li), temp: 30 Z 方向 X 方向 Y 方向 Species detected Cation: 7 Li Anion: 19 F (CF 3 SO 2 ) 2 N - EC: 1 H MEC: 1 H CH 3 OCOC 2 H 5 Yoshino, A. et. al., The 51st Battery Symposium in Japan (2010), Nagoya, Japan 9

10 Ion diffusion coefficients within separator X axis Y axis Z axis ln(e/e0) -0.5 ln(e/e0) ln(e/e0) E+10 2E+10 3E+10 4E+10 5E+10 6E+10 7E γ 2 δ 2 g 2 ( -δ/3) Li+ TFSI- EC MEC E+10 2E+10 3E+10 4E+10 5E+10 6E+10 7E+10 γ 2 δ 2 g 2 ( -δ/3) Li+ TFSI- EC MEC Li+ TFSI- EC MEC Bulk electrolyte solution Separator Li + diffusion coefficient (m 2 s -1 ) Z Relative comparison X axis Y axis Z axis E+10 2E+10 3E+10 4E+10 5E+10 6E+10 7E+10 γ 2 δ 2 g 2 ( -δ/3) Y Anisotropy Li + の拡散係数の異方性 of Li + diffusion coefficients X 10

11 7 Li + diffusion coefficients within various separators A B C D E F D X D Y D Z Z A B C D E F To clarify this anisotropy, tried to take 3D photo images of pore of separators by FIB SEM Y Anisotropy of Li + diffusion coefficients X 11

12 Outline 1. Background 2. Method to measure diffusion rate of Li + within separator by PFG-NMR 3. Direct observation of 3-D pore structure by FIB SEM 4. Summary 12

13 FIB-SEM measurements of separators Take SEM photo Sputter 10 nm Ga + FIB Take SEM photo e - SEM Sputter 10 nm Repeat 200 times 13

14 2D and 3D SEM photo images of separator C 2D SEM photo images of separator C (200 photo images) 3D SEM photo image of separator C 14

15 3D FIB-SEM images of pore of separator C X axis Bulk electrolyte solution Separator Li + diffusion coefficient (m 2 s -1 ) Relative comparison X axis Y axis Z axis Y axis Z axis Z A B C D E F Y Anisotropy of Li + diffusion coefficients X 15

16 Animation of 3D pore structure of separator C X axis 0.84 Y axis 0.34 Z axis

17 Outline 1. Background 2. Method to measure diffusion rate of Li + within separator by PFG-NMR 3. Direct observation of 3-D pore structure by FIB SEM 4. Summary 17

18 Summary Ionic conductivity of separators is the most important performance It became possible to measure diffusion rate of Li + within separators taken in X, Y, and Z axes by PFG-NMR There was a high correlation between diffusion coefficients (D X, D Y, D Z ) and the 3D pore structures of separator measured by FIB SEM This is a useful finding for separators and electrode design 18