IBA Meeting, BARCELONA IN LIB FOR EV (HEV) Masaki YOSHIO ; Saga Univ. Yamagata Univ. Hideya YOSHITAKE : Yamagata Univ.

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1 2013/03/ IBA Meeting, BARCELONA SAFETY ISSUE OF GRAPITE ANODE IN LIB FOR EV (HEV) Masaki YOSHIO ; Saga Univ. Yamagata Univ. Hideya YOSHITAKE : Yamagata Univ. yoshio@cc.saga-u.ac.jp

2 Fire from PC ( etc.) Fire from battery Com.,(2007)

3 Iron impurity was found at the counter side positive electrode by EDS analysis 58 cm X X 62 cm Data from UBE Chem. Co.

4 cathode Al substrate Analysis by EDS Element Wt% At% CK OK FK FeL AlK Matrix Correction ZAF Data from UBE Chem. Co.

5 One of important mechanism getting accident for graphite based LIB

6 Sometime separator cannot stop Li dendrite growth Volta age / V Separator choice Improve separator quality Capacity / mah.g -1 -ve First charge curves of cell contain Natural Graphite (NG) First charge curves of cell contain Natural Graphite (NG) with a charge/discharge at ma/cell after charging to 5 mv then CCCV for 10 hours in 1.0 M LiPF6 EC/DEC 1/2 (v/v) solution at -10 C.

7 Charge/Discharge Curves of Graphite/Li Cells at room, Room Temperature Low Temperature(-5 o C) RoomTemperature Low Temperature(-5 o C) 0.5 Vo oltage / V Voltage / V ltage / V Vo V oltage / V Capacity / mahg Capacity / mahg Capacity / mahg -1 Capacity / mahg -1 MCMB6-28 (NG) Natural Graphite

8 The properties of used graphites NG KS-6 MCMB 6-28 MCF MAGC S.A. (m 2 /g) d 002 (nm) Graphitization( ation( %) Tentatively 3R (%) Shape Flake Plate-like Sphere fiber Mass Company China Timcal Osaka gas Petoca Definition of graphite: Definition of graphite: Franklins definition Crystallity(%)= (3.440-d 002 ) / Franklin, Acta Cryst., 4, 235(1951) Hitachi Kasei

9 The relationship between graphitization and a difference of capacity from room to low temperature 160 -C (m mah/g) m low C room 140 MAGC NG 120 MCF MCMB Capacity is proportional to graphitization 40 KS Graphitization(%) The graphite with high graphitization have a large difference of capacity between room and low temperature, while graphite with lower graphitization sh ows a lower difference in capacity.

10 The Ex-situ XRD results of graphite electrodes obtained at Inten nsity (cps s) st stage( (LiC 6 ) 2nd stage e(lic 12 ) (002) Li + Cu MCF MCMB6-28 KS-6 MAGC NG 0 graphite sheet (degree) All graphite shows is clearly showed at 2θ=51 0. mixture of LiC st 6 (1 stage) and LiC 12 (2 nd stage). Moreover, the lithium peak.

11 The relationship between amount of Li deposition and 3R phase in graphites Ti collector 4000 KS-6 NG Peak Inte ensity of Li MFC MCMB MAGC R phase(%) Higher rhombohedral phase showed higher intensity of lithium peak i n XRD.

12 Graphite is mixtures of AB(2H) and ABC stacking (3R). Main Gr for LIB contain less 3R structure LiC6 2H C LiC6 Li 3R To reduce Li deposition, Gr with less 3R phase is desirable

13 M.Yoshio etal, J.Electorochem.Soc., 147 (2000)1245 CVD method Quartz tube Flow meter furnace sample Toluene gas Toluene N 2 gas

14 CVD Coating Toluene gas is not only covered the outside of particles, but also penetrating into the pores in the particles. Then toluene gas is carbonized. This is big differences from using carbon precursor such as corks.

15 Effects of CVD coating PC/DMC=1/1.86 in volume, 0.1 mv/s, room temp. NG-18(18% coating) (NG) Natural graphite 1. Intercalation kinetic; improved 2. Reduce Li deposition 3. PC:available; Low temp. performance 4. Negligible reaction of electrolyte with Gr.

16 Electrochemical properties of NG-10/Li-metal at -5 Test condition: (cut-off voltage) 5 ~ 2500 mv, (current) 0.015mA/g, -5. (electrolyte) 1M LiPF 6 -EC/DMC(Vol. 1:2) / V Voltage 3.0 NG %carbon coated NG NG 10%carbon coated NG Capacity / mahg -1 Capacity / mahg -1

17 Problem of Graphite:Li deposition at low temp Room Temperature Low Temperature(-5 o C) 0.5 Balck means Li deposition Volta age / V Vo oltage / V Capacity / mahg Capacity / mahg -1 NG

18 View of Graphite Electrodes Charged to 5 mv and Kept for 10 hrs at 27, -5 and -10 C 27 CC - 5 CC - 10 CC LiC 6 : Golden/Yellow LiC 12 : Brown Graphite: Black

19 Ex-situ XRD Result of NG Charged to 5mV and Kept for 10 hrs at 27, -5and-10 C(TiC Current Collector) Inten nsity/ arb. un nits LiC 6 LiC 6 LiC 12 Graphit e 27 C No No No -5 C No - 10 C LiC 12 Graphite 27 Li C -5 C - 10 C Metal Li / degree

20 Effects of 3% Carbon Coating on NG(-10 ) C 12 Li GR-3 -- GR-0 Intens sity/ arb. units C 6 Li Graphite NG-3 NG / degree ee NG-0 NG-3 Lithium intercalation (formation of C 6 Li) into GR-3 is significantly higher than that of GR-0 However, Lithium deposition can also be observed on NG-3

21 Effects of 10% Carbon Coating on NG(-10 ) C 12 Li GR-10 GR-0 Intensity y/ arb. un nits C 6 Li Graphite NG-10 Li NG-0 NG-10 NG / degree The less conductive surface of NG-10 prevent the formation of Li-metal on the NG-10, while enhancing Li intercalation at -10 C

22 Effects of 15% Carbon Coating on NG(-10 ) C 6 Li GR-15 GR-0 nits Intensit ty/ arb. u C 12 Li Graphite NG-15 Li NG-0 NG-15 NG / degree NG-15 prevent the formation of Li-metal on the NG-15, because of fless conductive film, while enhancing Li intercalation at - 10 C

23 Intensities of Li Peaks of Graphite Anodes Charged to 5mV for 10 hrs (-10 ; Ti Current Collector) 4000 Peak In tensity of Lithium Coating Amount Formation of LiC 6 proportional to amount of carbon coating This would be due to modified surface treatment of graphite

24 Charge/Discharge Curves of NG with Pulse Current (5-7C-rate) at -5 Short circuit cathode Li deposi tion Li + Graphite Li +

25 Pulse charge/discharge (5C-rate) curves of NG-0 and NG-26 at Cell Volt tage / V Cell Volta age / V Capacity / mah.g -1 Capacity / mah.g -1 NG-0 NG-26

26 Conclusion 1.Since graphite anode is often used because of high energy density, but it is risky choice. 2. Battery design should be carefull. 3. One of choice would be use CVD-carbon coating to avoid safety problem. 4. The reason has been mentioned.

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