to enable Lithium metal electrodes IBA2013, Barcelona, Spain

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1 Fluorine free ionic liquid electrolytes to enable Lithium metal electrodes IBA2013, Barcelona, Spain A. S. Best, Martin (Hyun Gook) YOON, G. H. Lane, Y. Shekibi, P. C. Howlett, M. Forsyth & D. R. MacFarlane ENERGY TECHNOLOGY

2 Ionic Liquid Electrolyte vs. Conventional Organic Liquid id Electrolyte l t Ionic liquids are molten salts existing in the liquid phase at or around room temperature. Conventional Organic Liquids Ionic Liquids High conductivity Low viscosity High vapor pressure Low flash point Non volatile Non flammable Wide electrochemical window Designable unlimited combinations of organic ions Still relatively low conductivity and high viscosity Pros. Cons. High temp. applications High volt. applications Cons. Ohno, H., Importance and Possibility of Ionic Liquids. In Electrochemical Aspects of Ionic Liquids, Hiroyuki, O., Ed. 2005; A. S. Best, et al. Ch. 10 in Electrochemical properties p and applications of ionic liquids, eds. Angel A. J. Torriero and Muhammad J.A. Shiddiky, Nova Publishers 2011 pgs Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 2

3 Way back in 2004 C 4 mpyr TFSI mol kg 1 LiTFSI Li(s) Li + + e W.E. Pt C.E. Li R.E. Li 100 mvs C Li + + e Li(s) σ = ~1 x Scm S.cm 11 P. C. Howlett, et al., ESSL, 7 (5) 2004 A97 & PCT/AU2004/ Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 3

4 Improved Li behaviour in 2008 C 3 mpyr FSI mol kg 1 LiFSI W.E. Pt C.E. Pt 50 mvs 1 25 C F S N S F O O O O Li(s) Li + + e Li + + e Li(s) J. Saint et al., JES, 2008,155, A172 A. I. Bhatt et al., JES A66 A. S. Best, et al, JES, A903, H. Yoon, et al, JES, submitted 2013 & PCT/AU2008/ / Li Li + reversibility AND FAST CHARGE! Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 4

5 High LiFSI Salt Concentrations C 3 mpyr FSI mol kg 1 LiFSI (1:1 C 3 mpyr : Li) 5C 4C 3C 2C 1C 1.5C 0.5C 0.1C 01C 0.1C Voltag ge (V) C 4C 3C 0.5C 1.5C 1C 2C 01C 0.1C 0.1C H. Yoon, et al, J. Electrochem. Soc., 2013 submitted Capacity (mah.g -1 ) LiCoO 2 90 wt% (C8G, Nippon Chemical Industrial) + Carbon Black 5 wt% (Shawinigan) + PVdF 5 wt%, 4.5 mg.cm 2 Lithium electrochemistry and cyclic behaviour of DCA Martin Yoon Page 5

6 It s the Economy stupid (apologies B. Clinton) Ionic Liquids are expensive*. Small orders of ionic liquids on the kg scale can cost close to US$2000 Fluorination of the anion contributes tib t hugely to the cost Purification and moisture How do we change this? (In part by) Avoiding Fluorination! C 4 mpyr D. R. MacFarlane, et al, Chem. Commun., 2001, DCA Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 6

7 Electrochemistry of Neat ILs * Measured at an ambient temperature in a Arglovebox, 20mV/sec, 0.009cm Pt disc WE, Pt wire CE, 10mmol/kg AgTf in P 14 NTf 2 RE C 4 mpyr DCA C 4 mpyr TCM C 4 mpyr TCB C 4 mpyr NTF 2 E. W. of neat ILs : C 4 mpyrtcm (~ LiFePO 4 ) < (LiCoO 2 )< C 4 mpyrdca < C 4 mpyrntf 2 H. Yoon, et al., Energy & Environmental Science, Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 7

8 Li Salt Solubility in Different Nitrile Moieties Dicyanamide (DCA or N(CN) 2- ) Max ~0.7 7mol kg 1 with LiDCA N-butyl-N-methylpyrrolidinium (C + 4 mpyr ) No dissolution with LiDCA, LiTFSI,LiBF LiBF 4, Tricyanomethanide (TCM or C(CN) 3 - ) Tetracyanoborate (TCB or B(CN) 4 - ) LiPF 6 over ~1.5 mol kg 1 with LiDCA We ll focus on DCA from here Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 8

9 Conductivity of Electrolytes C 05mol 4 mpyr DCA kg 1 LiX T (K) m -1 ) Co onductivity (ms.c [C 4 mpyr][dca] [C 4 mpyr][dca] + LiDCA [C 4 mpyr][dca] + LiTFSI [C 4 mpyr][dca] + LiFSI [C 4 mpyr][dca] + LiBF 4 H. Yoon, et al., manuscript in preparation, / T (1000 / K) Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 9

10 Viscosity (m mpa.s) C mpyr DCA mol kg 1 LiX Neat C 4 mpyr DCA LiDCA + C 4 mpyr DCA LiTFSI + C 4 mpyr DCA LiFSI + C 4 mpyr DCA LiBF 4 + C 4 mpyr DCA C 3 mpyr TFSI 3 C 3 mpyr FSI T ( o C) H. Yoon, et al., manuscript in preparation, J. Saint et al., JES, 2008,155, A172 Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 10

11 NMR Diffusion C mpyr DCA mol kg 1 LiX 7 Li NMR diffusion data 13 C NMR Diffusion (DCA) P. Bayley T/K T/K fficient / m 2 s - Diffusion Coef [C 4 mpyr][dca] + LiDCA [C 4 mpyr][dca] + LiTFSA [C mpyr][dca] + LiFSI 4 [C 4 mpyr][dca] + LiBF Diffusion Coef fficient / m 2 s [C 4 mpyr][dca] [C 4 mpyr][dca] + LiDCA [C 4 mpyr][dca] + LiTFSA [C 4 mpyr][dca] + LiFSI [C 4 mpyr][dca] + LiBF /T / K /T / K -1 H. Yoon, et al., manuscript in preparation, We ll focus on DCA from here Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 11

12 Lithium but no cycling.) I (ma cm -2, Arb E (V vs. Li Li + ) ppm of H 2 O E (V vs. Ag Ag + ) + H. Yoon, et al., Energy & Environmental Science, Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 12

13 Moisture effect of Li cycling in C 4 mpyrdca * Measured at an ambient temperature in a Ar glovebox, 20mV/sec, 0.009cm 2 Pt disc WE, Pt wire CE, 10mmol/kg AgTf in P 14 NTf 2 RE (ma cm -2 ) I (ma cm -2 ) I ppm of H 2 O ppm of H 2 O I (ma A cm -2 ) I (ma cm -2 ) ppm of H 2 O ppm of H 2 O E (V vs. Ag Ag + ) E (V vs. Ag Ag + ) H. Yoon, et al., Energy & Environmental Science, Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 13

14 Moisture effect of Li cycling in C 4 mpyrdca * Measured at an ambient temperature t in a Arglovebox, 20mV/sec, 0.009cm Pt disc WE, Pt wire CE, 10mmol/kg AgTf in P 14 NTf 2 RE I (ma cm -2 ) deposition stripping H 2 O contents (ppm) Under 100 ppm of H 2 O, Li does not cycle in DCA. H. Yoon, et al., Energy & Environmental Science, Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 14

15 Symmetrical cells with different moisture Li symmetrical cell : 0.1mA/cm 2, 16min charge / discharge at 50 o C E (V) ppm of H 2 O Time (min) E (V) ppm of H 2 O Time (min.) E (V) 0.00 E (V) ppm of H 2 O Time (min.) 226 ppmof H 2O in the electrolyte shows the most stable over potential. H. Yoon, et al., Energy & Environmental Science, ppm of H 2 O Time (min.) Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 15

16 Kinetic or Electrochemical? Li symmetrical cell : 0.1mA/cm 2, 16min charge / discharge at 50 o C cycles 10 cycles 30 cycles 50 cycles (V) E h waiting 1 h 24 h waiting 226 ppm of H2O Time (min.) 226 ppm of H 2 O in the electrolyte shows the most stable over potential. H. Yoon, et al., Energy & Environmental Science, Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 16

17 SEM 226ppm cycled symmetrical cell Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 17

18 In situ 7 Li NMR Cathode Material or Lithium metal Copper wire mesh Plastic Bag Pristine Cycled Copper (or Aluminum) wire mesh Separator (soaked with electrolyte) Lithium metal Chemical Shift / ppm in-situ RC N. M. Trease C. Grey Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 18

19 EIS Symmetrical Cells C 4 mpyr DCA mol kg 1 LiDCA Li symmetrical cell stored at 50 o C Li symmetrical cell cycled at 50 o C Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 19

20 Equivalent circuit Evenly distributed SEI was assumed. Evenly distributed SEI equivalent circuit C_DL CPE_SEI Rs R_CT W R_SEI Solution P + DCA- 14 P + DCA - 14 Li + DCA - e - e SEI - e - C_DL, R_CT P + 14 P + 14 P + Li + Li + Li + 14 Li + e - e - e - e - e - e - e - e - e - C_DL, R_CT Li metal Li + e - Rs SEI Lewandowski, et al., J. Power Sources 2009, 194 (1), Lane, et al., Electrochim. Acta 2010, 55 (28), Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 20

21 Fitting results C mpyr DCA mol kg 1 LiX R_CT / (ohm) R SEI / (ohm) Cycled 10 Stored Time (hrs) 5 Cycled Stored Time (hrs) Fitting error (z plot) varies from 4% to 28% Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 21

22 How does the SEI form? 200ppm H 2 O G. Lane, et al., Ph.D. Thesis, Monash University 2011 Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 22

23 LiFePO 4 cells with moisture 3.8 LiFePO 4 (HP,Phostech ) 75 wt% : Shawinigan Black 15 wt% : PVdF 10 wt%, Loading : 2.48mg/cm 2 /Solupor 5P09B / Li disc. / 0.5 mol/kg LiDCA in P 14 DCA Test Condition : 0.026mA/cm 2 CC to 3.8V, 0.026mA/cm 2 CC to 3.0V, 50 o C th 10th E (V) st Capacity (mah g -1 ) Cap pacity (mah g -1 ) ppm of H 2 O, charging ppm of H 2 O, discharging ppm of H 2 O, charging 226ppm of H 2 O, discharging Cycle number C 4 mpyr DCA showed over 130 mah g 1 of discharge capacity retaining over 94% of its initial discharge capacity after 20 cycles in Li LiFePO 4 cells. H. Yoon, et al., Energy & Environmental Science, Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 23

24 Solid State Electrolyte C 1 mpyr DCA mol kg 1 C (mah.g -1 ) Capacity Charge capacity Discharge capacity Cycle number H. Yoon, et al., Energy & Environmental Science, Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 24

25 Summary 1. The electrochemical window of the cyano based ILs show that DCA has the greater cathodic stability than other nitrile moieties. However, these windows are still inferior to NTf 2 based ILs. 2. The presence of water in a C 4 mpyrdca IL improves the SEI cathodic stability suchthatrelatively efficient lithium reductionandoxidation oxidation becomespossible The use of additives can further stabilise the electrode electrolyte interface ppm to 200 ppm of H 2 O shows the best cycling ability in a Li Li symmetrical cell and a Li LiFePO 4 cell. 4. Solid (plastic crystal) electrolytes show extremely good cycling behaviour against LFP Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 25

26 Acknowledgements This research is funded by the Australian Research Council (ARC) andcsiro snationalresearch Research Flagship Energy Transformed Thanks to: Energy Storage Group, CSIRO Energy Technology Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 26

27 Thank You CSIRO Energy Technology Dr. Adam Best Senior Research Scientist t e Adam.Best@csiro.au w ENERGY TECHNOLOGY

28 SEM 97ppm cycled symmetrical cell Lithium electrochemistry and cyclic behaviour of DCA Martin Yoon Page 28

29 SEM 443ppm cycled symmetric cell Lithium electrochemistry and cyclic behaviour of DCA Martin Yoon Page 29