Advanced Diagnostics for Testing the Impact of Electrolyte Additives on Li-Ion Batteries

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Bruno Curtis
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Advanced Diagnostics for Testing the Impact of Electrolyte Additives on Li-Ion Batteries Chris Burns, Nupur Sinha and Jeff Dahn Dalhousie University, Halifax, Canada Kevin Eberman, Ang Xiao and Bill

1 Advanced Diagnostics for Testing the Impact of Electrolyte Additives on Li-Ion Batteries Chris Burns, Nupur Sinha and Jeff Dahn Dalhousie University, Halifax, Canada Kevin Eberman, Ang Xiao and Bill Lamanna 3M Co., St. Paul, MN Gaurav Jain, Collette vanelzen and Erik Scott Medtronic Energy and Component Center, Brooklyn Center, MN Brian Way and Adil Kassam E-One Moli Energy Canada Ltd., Maple Ridge, Canada 1

2 Outline How do we study additives with High Precision Coulometry? How can we tell if additives are beneficial in only a few weeks of testing? What happens when using electrolyte additives in Li-ion cells that show gradual fade? What happens when using electrolyte additives in Li-ion cells that show no initial fade until the show catastrophic failure. 100 Norma alized Q D a 1 2 b Cycle

3 What is High Precision Coulometry? The cycle life of Li-ion cells is not infinity because small fractions of cell components are consumed during each cycle. The amount of these components consumed can be measured using the coulombic efficiency (CE): CE = Q d /Q c = [Charge out]/[charge in] If CE = , the Li-ion cell will last forever! It is of utmost importance to be able to measure the coulombic efficiency accurately, but traditional battery charger systems cannot. 10,000 cycles needs at least 99.99% CE e.g = Therefore need to measure CE to at least 1 part in 10 4 to be useful for automotive and grid energy cells. 3

4 Parameter Requirements for accurate CE measurements Associated Error Desired Error in Q For C/10 rate measurements For C rate measurements ΔI ΔQ = ΔI t < 0.01% ΔI < 0.01% ΔI < 0.01% ΔV ΔQ = dq/dv ΔV < 0.01% ΔV < V ΔV < V Δt ΔQ = I Δt < 0.01% Δt < 3.6 s Δt < 0.36 s ΔT ΔQ = dv/dt dq/dv ΔT < 0.01% ΔT < 1 K ΔT < 1 K Keithley 220/6220 can deliver current with < 0.01% error when calibrated Keithley 2000 measure voltage with an accuracy of 10 μv Voltage measurements can be made every ~3 seconds but software interpolation reduces timing error at switch point to < 1 second The thermostats built in the lab are consistent to ± 0.5ºC max (and stable to ± 0.1ºC) Factors that impact ability to precisely and accurately measure coulombic efficiency. These factors are current accuracy ( I), precision of voltage measurements ( V), time between voltage measurements ( t) and cell temperature ( T) all which lead to error in capacity ( Q). For these calculations dq/dv is taken as the full cell capacity in 1 V and dv/dt is assumed to be 100 μv/k. J. Electrochem. Soc., 157, A196-A202 (2010). 4

5 The High Precision Charger (HPC) A Cell V V Precision resistor to measure current flow Measure the current as a function of time and integrate to get capacity. 1 Q I ( t )* dt V ( t ) * dt R 5

6 How does the precision/accuracy of our charger before and after the upgrade compare to commercial chargers? a Worse 1000 b Worse Preci sion (ppm m) Better Accu racy (ppm m) Better 0 UHPC HPC Series UHPC HPC Series 4000 HPC uses Keithley 220 current sources but does not have resistors in-line to monitor current. U(Ultra)HPC uses the same equipment as HPC but also in-line resistors to monitor current and improve accuracy and precision in measurements. J. Electrochem. Soc., 160, A521-A527 (2013). 6

7 High Voltage LiCoO 2 Low Voltage LiCoO 2 NMC 40 C C/ a b c 2 wt% VC d e f Volta age (V) wt% VC g h i Control Capacity (%) J. Electrochem. Soc., 159, A85-A90 (2012). 7

8 40 C C/20 nd. Cap. (%) Ch. E High Voltage LiCoO 2 Low Voltage LiCoO 2 NMC a b c d e f Disc charge Capa acity (%) Cou ulombic Efficienc cy g h i Cycle Control Control Pair 1 wt% VC 1 wt% VC Pair 2 wt% VC 2 wt% VC Pair J. Electrochem. Soc., 159, A85-A90 (2012). 8

9 CE High Voltage LiCoO 2 Control 1% VC 2% VC 2% VC and 0.5% DS 0.5% DS 40 C C/ Cycle nal Cap pacity Fractio C/10, 55 o C High Voltage LiCoO Control 1 wt% VC 2 wt% VC 2 wt% VC and 0.5% DS 0.5% DS Cycle Short term CE measurements on LiCoO 2/graphite wound cells at 40 o C. Using High Precision Charger. Long term cycling measurements continued after CE on the same LiCoO 2 /graphite wound cells These are at 55 o C due to charger availability. These use an old Maccor charger. 9

10 F ade (%/c cycle) Ranked on CIE/hour Ranked on Ch. Slippage Control VC VC Control (%/cycle e) Ch. Slippage (1 -CE)/(Ho ours per cycle) E-005 4E-005 Control VC LiCoO 2 /graphite Control VC Dis. Slipp page (%/c cycle) Ranked on CIE/hour Ranked on Dis. Slippage 10

11 Sometimes Li-ion cells show catastrophic capacity loss. This is very bad. e - e - ive Posit Electrolyte + Electrolyte ive Negat Electrolyte oxidation products build up on negative and eventually shut it down. Higher voltage means more oxidation. CE measurements should capture this. Disch harge Cap pacity (m mah) NMC/graphite 4.25 V 4.35 V 4.45 V Cycle

12 2.16 Capa acity (A Ah) VC + VEC FEC VEC + FEC VC + PS VC + VEC + FEC + PS VC + VEC + FEC VC Cycles Experiment in collaboration with established Li-ion ion cell maker. NMC/graphite power cells with a design selected to show catastrophic failure. Can you tell which will fail first?? 12

13 NMC/graphite power cells were manufactured and formed before sending to Dalhousie for HPC and storage studies. After the HPC testing, the cells were returned to the manufacturer for the long term cycling. These are 2A discharges with a 2A CCCV charge until the cells reached 1.6Ah which was considered failure. All testing is at 30 o C. ). End.. (mah Ch Cap C E0.996 Ca apacity (Ah) HPC Cycles mah/cycle mah/cycle mah/cycle mah/cycle At Dalhousie on HPC At Manufacturer on standard cyclers Control VC FEC VC + FEC Moli Cycles

14 If the reason these cells show catastrophic fade is because electrolyte oxidation products migrate to the negative where they are reduced and eventually shut down the negative electrode, What happens when you have a highly compacted negative e electrode? ect 14

15 Cathode Q Electrolyte Electrolyte + n Graphite 15

16 Cathode Q Electrolyte Electrolyte + n Reduced products from oxidized electrolyte Graphite 16

17 Cathode Q Electrolyte Electrolyte + n Reduced products from oxidized electrolyte Graphite 17

18 Cathode Q Electrolyte Electrolyte + n Pores become filled by Reduced products from oxidized electrolyte Graphite 18

19 Cathode Q n Lithium begins plating Pores become filled by Reduced products from oxidized electrolyte Graphite 19

20 What happens when you have a more porous negative electrode? 20

21 Cathode Q Electrolyte Electrolyte + n Graphite 21

22 Cathode Q Electrolyte Electrolyte + n Reduced products from oxidized electrolyte Graphite 22

23 Cathode Q Electrolyte Electrolyte + n Pores remain open for Li + transport Reduced products from oxidized electrolyte Graphite 23

24 Cathode Q Electrolyte (1-CE) * (Cycles) Electrolyte = Constant t + n So plot: cycles vs 1/(1-CE) Pores become filled by Reduced products from oxidized electrolyte Graphite 24

25 600 VC + VEC + FEC + PS VEC + FEC + PS Cy ycles to 1.6Ah Control PS FEC VC + VEC + FEC VC + FEC + PS VC + FEC VC + VC VC + VEC VC + PS VC VEC + FEC VEC Spectacular agreement with the model predictions! /(1 - Coulombic Efficiency) 25

26 2000 5UA 1.6A Ah UE 3UF Cycles to UB 2UD 3UA 3UD 2UE 2UA VC + VEC + FEC + PS 4UA 3UC VEC + FEC + PS VC VEC + FEC VC + FEC + PS VC VC + + FEC VC 2UB VC VC + VEC + PS VEC + FEC FEC VEC Control PS /(1 - Coulombic Efficiency) 26

27 Cycles to 1.6 Ah Coul lombic Effic ciency a b Each additive is used at 1.5 wt% In these cells, the electrolyte additives appear to have an additive impact, the more the better! Combining electrolyte additives in general gives longer cycle life as well as better coulombic efficiency. Can there be a single electrolyte additive that is better than a composition of multiple electrolyte additives? Number of Additives 27

28 Conclusions High precision coulometry allows for good predictions of long term cycling performance for Li-ion i cells, even those which h show NO capacity loss in early cycles. Electrolyte additives are key in improving the lifetime and performance of Li-ion ion cells. High precision coulometry is an excellent tool for screening additives for long term cycling performance. The use of additives in cells is very complicated and depends highly on the cell construction (electrode material and properties, electrolyte, operating voltage, etc). Coupling techniques such as storage, impedance and post-mortem analysis with high precision coulometry will lead to a better understanding of the role of an electrolyte additive within a cell and help understand mechanisms and not just see the impact of using an additive. 28

29 Funding from:

30 NSERC (DREAMS), IRM and 3M Canada for funding 30

HIGH PRECISION COULOMETRY AS A TECHNIQUE FOR EVALUATING THE PERFORMANCE AND LIFETIME OF LI-ION BATTERIES. John Christopher Burns

HIGH PRECISION COULOMETRY AS A TECHNIQUE FOR EVALUATING THE PERFORMANCE AND LIFETIME OF LI-ION BATTERIES by John Christopher Burns Submitted in partial fulfillment of the requirements for the degree of