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1 2017 X /28

2 XAFS Li 2 X img. 3. 2/28

3 IEA/ ETP Energy Technology Perspectives 2012 HV PHV 3/28

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5 HV PHV EV FCV W/ Wh/ 5/28

6 x + xe - + CoO 2 Li x CoO 2 Li x C C + x + xe - 6/28

7 LIB 7/28

8 Li Li SOC100% Li SOC0% SOC State of charge Li / Li Li 8/28

9 Li SEM Ee 100um Ei Ei Ee Ee Ei Ee Ei 5 15um Li 1um XAFS 9/28

10 LiCoO 2 LCO 12.5um PVdF Li 1M LiPF6 EC/EMC 100um30um LCO Li 10/28

11 2 5C 4.5V DMC XAFS SPring-8 BL37XU 0.8um1.3um KB SDD IC 11/28

12 XAFS LCO Normalized Intensity / a.u. Co-K XANES Li x X=1 Li x X= Energy / ev Li XAFS Normalized Intensity / a.u. Lix X=1 Lix X= Energy / ev 7715eV Li Li LCO SPring-8 BL14B2 12/28

13 Co-X 100um 20um 25um X 13/28

14 XAFS Co-X Al Normalized Intensity / a.u. Co-K XANES Li Li Energy / ev Li Normalized Intensity / a.u Energy / ev 14/28

15 Li Co-X / um Li Li = Li x CoO 2 / x X=1 X=0.7 X=0.4 Al Li 15/28

16 Cross-section Li-ion distribution in LCO LCO Al current collector surface inside 20 m Distance from Al current collector ( m) Li-ion distribution Li X Li X CoO 2 ( X ) surface inside Fig. 6: SEM image of cross-section sample Fig. 7: Li-ion distribution Key Findings An electrode was measured from the surface to inside by u-xafs method. Li-ion conc. was estimated from the valence state of Co by XANES edge energy. Li-ion are extracted preferentially from the electrode surface. (The delithiation does not proceed at the inside of the electrode.) 16/28

17 Distribution of Li-salt conc. in electrolyte charge Li Li conc. + + Li high + Li+ conc. low Al current collector cathode separator anode Cu current collector discharge Fig. 8: Distribution of Li-salt concentration in electrolyte Main Logic The Li-ion distribution in the electrode causes Li-salt distribution in the electrolyte in the electrode and separator. During Charging (a) Positive Electrode Li-salt conc. increases due to Li-ion extraction from LCO. Li-salt conc. is higher at the electrode surface. (because Li-ion extraction preferentially proceeds at the surface) (b) Negative electrode Li-salt conc. decreases due to the insertion of Li-ion into the electrode. Li-salt conc. is expected to be lower at the electrode surface. conc. low Li Li + + Li conc. Li high /28

18 in-situ X-ray imaging method Incident X-rays Sample 2D detector X-ray tomography of cross-section of the cell discharge Cathode No X-ray transmission Separator & Anode Transmission strength depend on Li-ion conc. Fig. 9: in-situ X-ray imaging method The purpose is to visualize distribution of Li-salt conc. in an electrolyte We measured the Li-salt distribution of the separator and negative electrode. (Positive electrode is too heavy for the X-ray transmission.) It is hypothesized that absorption by P and F in Li-salt (LiPF 6 ) causes uneven distribution of the levels of the X-ray transmission intensity in the electrolyte. Thus, the X-ray tomography reflects the concentration variation of Li-salt in the electrolyte. 18/28

19 in-situ X-ray imaging model cell fastening plate < Front view > < Side view > cell case X-ray transmission window (Al laminated sheet) fastening plate X-rays electrode terminal viton rubber 45mm electrodes 5mm The cell was attached to a fastening plate and was cut to 5 mm in thickness. The cell was fixed to the imaging mode cell and the electrolyte was injected to the cell under an Ar-gas atmosphere. 19/28

20 in-situ X-ray imaging model cell fastening plate fastening plate mounted to a model cell parts for sealing model cell ( upstream side ) model cell ( downstream side ) 20/28

21 Charge Discharge Profiles 4 Voltage / V Time / s Fig. 11: Charge discharge profile at 1C CC rate The cell showed desirable functionality. The cell functioned normally in the imaging model cell. The model cell functioned stably for approximately three days. 21/28

22 in-situ X-ray imaging setups ( TOYOTA BL ) 2D detector (CMOS) incident X-rays (10 20 kev) attenuator transparent detector (IC) cell X-ray size 1 mm 1 mm Detection method 2D detector (CMOS) Space resolution 1 m Time resolution500 ms in-situ imaging measurements at BL33XU:TOYOTA BL (SPring-8, JAPAN) 22/28

23 X-ray transmission image X-ray transmission image of cross-section electrodes Al current collector cathode separator 100um anode Cu current collector Our hypothesis was verified; The electrodes, separator, and their interfaces are clearly recognized. The image of the positive electrode became dark because X-rays did not penetrate though it. 23/28

24 Experimental data analysis method (a) X-ray image before discharge (c) Intensity (before the discharge) - Intensity (after discharge) (b)-(a) Al current collector cathode separator (b) X-ray image after 15 s CC discharge anode high low Cu current collector <transmission intensity> low <Li-salt conc. in electrolyte> high The degree of X-ray transmission intensity of various conditions was obtained by subtracting the intensity degree of the initial state from that after 15 seconds. The larger intensity (light color) means low Li-salt concentration. The lower intensity (dark color) means high Li-salt concentration. 24/28

25 Relative X-ray transmission / a.u. Li-salt concentration distribution 5C Al current collector Relative X-ray transmission profile during 5C CC discharging and charging discharge charge before dischrg. 15s after dischrg. 30s after dischrg. cathode separator Cross-section of cell Li-salt conc. : low Li-salt conc. : high anode Cu current collector Al current collector before charge 15s after charge 30s after charge cathode separator Cross-section of cell Li-salt conc. : low Li-salt conc. : high The charging process showed the opposite results to the discharging process. anode Cu current collector The ionic resistance in the composite electrode is the primary factor to generate the Li-salt distribution in the negative electrode; Because the (de)lithiation reaction preferentially proceed from the surface, more Li-salts exist at the surface. The different levels of Li-salt conc. between the positive and negative electrode create the uneven distribution of Li-salt in the separator. 25/28

26 Relative X-ray transmission / a.u. Li-salt concentration distribution 1C Relative X-ray transmission profile during 1C CC discharging and charging discharge charge before dischrg. Li-salt conc. : low 15s after dischrg. 30s after dischrg. Li-salt conc. : high before charge Li-salt conc. : low 15s after charge 30s after charge Li-salt conc. : high Al current collector cathode separator anode Cross-section of cell Cu current collector Al current collector cathode separator anode Cross-section of cell Cu current collector The Li-salt concentration distribution is lower in 1C CC charge/discharge than in 5C CC. At lower C rates, the Li-salt distribution is well released during the charge/discharge process. 26/28

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