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
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 299 324 Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 2
Way back in 2004 C 4 mpyr TFSI + 0.5 mol kg 1 LiTFSI Li(s) Li + + e W.E. Pt C.E. Li R.E. Li 100 mvs 11 50 C Li + + e Li(s) σ = ~1 x 10 33 Scm S.cm 11 P. C. Howlett, et al., ESSL, 7 (5) 2004 A97 & PCT/AU2004/000263 Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 3
Improved Li behaviour in 2008 C 3 mpyr FSI + 0.5 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 157 2010 A66 A. S. Best, et al, JES, 157 2010 A903, H. Yoon, et al, JES, submitted 2013 & PCT/AU2008/000950 / Li Li + reversibility AND FAST CHARGE! Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 4
High LiFSI Salt Concentrations 4.2 4.0 C 3 mpyr FSI + 3.2 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) 38 3.8 3.6 3.4 5C 4C 3C 0.5C 1.5C 1C 2C 01C 0.1C 0.1C 3.2 3.0 2.8 0 20 40 60 80 100 120 140 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
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, 1430. DCA Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 6
Electrochemistry of Neat ILs * Measured at an ambient temperature in a Arglovebox, 20mV/sec, 0.009cm 0009 2 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, 6 2013 979 986. Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 7
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
Conductivity of Electrolytes C 05mol 4 mpyr DCA + 0.5 kg 1 LiX T (K) 400 380 360 340 320 300 280 260 240 m -1 ) Co onductivity (ms.c 10 1 0.1 [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, 2013. 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 1000 / T (1000 / K) Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 9
Viscosity (m mpa.s) 120 100 80 60 40 C 05 1 4 mpyr DCA + 0.5 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 20 20 30 40 50 60 T ( o C) H. Yoon, et al., manuscript in preparation, 2013. J. Saint et al., JES, 2008,155, A172 Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 10
NMR Diffusion C 05 1 4 mpyr DCA + 0.5 mol kg 1 LiX 7 Li NMR diffusion data 13 C NMR Diffusion (DCA) P. Bayley T/K T/K 330 320 310 300 330 320 310 300-1 fficient / m 2 s - Diffusion Coef [C 4 mpyr][dca] + LiDCA [C 4 mpyr][dca] + LiTFSA 10-10 [C mpyr][dca] + LiFSI 4 [C 4 mpyr][dca] + LiBF 4 10-11 1 Diffusion Coef fficient / m 2 s - 10-10 11 [C 4 mpyr][dca] [C 4 mpyr][dca] + LiDCA [C 4 mpyr][dca] + LiTFSA 10-11 [C 4 mpyr][dca] + LiFSI [C 4 mpyr][dca] + LiBF 4 3.0 3.1 3.2 3.3 3.4 3.0 3.1 3.2 3.3 3.4 1000/T / K -1 1000/T / K -1 H. Yoon, et al., manuscript in preparation, 2013. We ll focus on DCA from here Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 11
Lithium but no cycling.) I (ma cm -2, Arb 4 3 2 1 0-1 -2-3 -4 E (V vs. Li Li + ) -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 36 ppm of H 2 O -4.5-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.5 E (V vs. Ag Ag + ) + H. Yoon, et al., Energy & Environmental Science, 6 2013 979 986. Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 12
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 4 4 3 3 2 2 (ma cm -2 ) I 1 0-1 -2 (ma cm -2 ) I 1 0-1 -2-3 -4 97 ppm of H 2 O -3-4 233 ppm of H 2 O 4 4 3 3 2 2 I (ma A cm -2 ) 1 0-1 -2 I (ma cm -2 ) 1 0-1 -2-3 -4 311 ppm of H 2 O -3-4 630 ppm of H 2 O -4.5-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.5 E (V vs. Ag Ag + ) -4.5-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.5 E (V vs. Ag Ag + ) H. Yoon, et al., Energy & Environmental Science, 6 2013 979 986. Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 13
Moisture effect of Li cycling in C 4 mpyrdca * Measured at an ambient temperature t in a Arglovebox, 20mV/sec, 0.009cm 0009 2 Pt disc WE, Pt wire CE, 10mmol/kg AgTf in P 14 NTf 2 RE 2 1 0 I (ma cm -2 ) -1-2 -3-4 -5-6 deposition stripping 0 100 200 300 400 500 600 700 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, 6 2013 979 986. Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 14
Symmetrical cells with different moisture Li symmetrical cell : 0.1mA/cm 2, 16min charge / discharge at 50 o C E (V) 5 4 3 2 1 0-1 -2-3 -4-5 36 ppm of H 2 O 0 600 1200 1800 2400 3000 3600 Time (min) E (V) 0.06 0.04 0.02 0.00-0.02-0.04 004-0.06 006 0.06 006 0.06 226 ppm of H 2 O 0 600 1200 1800 2400 3000 3600 Time (min.) 0.04 0.04 0.02 0.02 E (V) 0.00 E (V) 0.00-0.02-0.02-0.04-0.06 291 ppm of H 2 O 0 600 1200 1800 2400 3000 3600 Time (min.) 226 ppmof H 2O in the electrolyte shows the most stable over potential. H. Yoon, et al., Energy & Environmental Science, 6 2013 979 986. -0.04-0.06 443 ppm of H 2 O 0 600 1200 1800 2400 3000 3600 Time (min.) Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 15
Kinetic or Electrochemical? Li symmetrical cell : 0.1mA/cm 2, 16min charge / discharge at 50 o C 0.06 0.04 10 cycles 10 cycles 30 cycles 50 cycles 002 0.02 (V) E 0.00-0.02-0.04-0.06 15 h waiting 1 h 24 h waiting 226 ppm of H2O 0 1200 2400 3600 4800 6000 Time (min.) 226 ppm of H 2 O in the electrolyte shows the most stable over potential. H. Yoon, et al., Energy & Environmental Science, 6 2013 979 986. Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 16
SEM 226ppm cycled symmetrical cell Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 17
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 300 250 200 150 100 50 0-50 Chemical Shift / ppm in-situ RC N. M. Trease C. Grey Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 18
EIS Symmetrical Cells C 4 mpyr DCA + 0.5 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
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), 502 507. Lane, et al., Electrochim. Acta 2010, 55 (28), 8947 8952. Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 20
Fitting results C 05 1 4 mpyr DCA + 0.5 mol kg 1 LiX R_CT / (ohm) 80 70 60 50 40 30 20 R SEI / (ohm) 35 30 25 20 15 10 Cycled 10 Stored 0 0 20 40 60 80 100 Time (hrs) 5 Cycled Stored 0 0 20 40 60 80 100 Time (hrs) Fitting error (z plot) varies from 4% to 28% Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 21
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
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 3.6 20th 10th E (V) 3.4 32 3.2 1st 3.0 0 20 40 60 80 100 120 140 Capacity (mah g -1 ) Cap pacity (mah g -1 ) 140 120 100 80 60 443ppm of H 2 O, charging 40 443ppm of H 2 O, discharging 20 226ppm of H 2 O, charging 226ppm of H 2 O, discharging 0 0 5 10 15 20 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, 6 2013 979 986. Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 23
Solid State Electrolyte C 1 mpyr DCA + 0.5 mol kg 1 LiDCA @80 C (mah.g -1 ) Capacity 200 180 160 140 120 100 80 60 40 20 0 Charge capacity Discharge capacity 0 50 100 150 200 Cycle number H. Yoon, et al., Energy & Environmental Science, 6 2013 979 986. Fluorine Free Electrolytes IBA2013 Barcelona A. S. Best Page 24
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 3. 100 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
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
Thank You CSIRO Energy Technology Dr. Adam Best Senior Research Scientist t +61 3 9545 8660 e Adam.Best@csiro.au w www.csiro.au ENERGY TECHNOLOGY
SEM 97ppm cycled symmetrical cell Lithium electrochemistry and cyclic behaviour of DCA Martin Yoon Page 28
SEM 443ppm cycled symmetric cell Lithium electrochemistry and cyclic behaviour of DCA Martin Yoon Page 29