Novel Electrolytes Enabling High Efficiency Cycling of Rechargeable - PowerPoint PPT Presentation

Novel Electrolytes Enabling High Efficiency Cycling of Rechargeable Li Metal Batteries Ji-Guang Zhang Pacific Northwest National Laboratory, Richland, WA The 10 th Symposium on Energy Storage beyond Li-Ions IBM Research - Almaden June 27, 2017

Outline 1. Dendrite Free Li Deposition Using Salt Additives 2. High Rate Li Deposition with High Coulombic Efficiency (CE) 3. Accurate Determination of CE 4. Long Term Cycling of High Voltage Li Metal Batteries 5. Summary 2

Challenges on Li Metal Anode Two main barriers : 1. Dendrite growth; 2. Low Coulombic efficiency - + Short circuit Cathode Anode Safety hazards Consequences Dendrite “Dead Li” Short cycle High surface High surface area . Life Consuming Li Low energy Low CE density & electrolyte LiCoO 2 Li metal Sulfur Oxygen (a) Li metal (b) The typical morphology (c) Main problems related batteries of Li dendrite with dendrite and low (Chianelli,1976) Coulombic efficiency. Wu Xu, Jiulin Wang, Fei Ding, Xilin Chen, Eduard Nasybulin, Yaohui Ji-Guang Zhang, Energy Environ. Sci . , 2014, 7 (2), 513 – 537. Zhang and 3

1. Dendrite Free Li Deposition Using Salt Additives Nernst Equation: − 𝑺𝑼 𝒜𝑮 𝒎𝒐 𝜷 𝑺𝒇𝒆 ∅ 𝑭 𝑺𝒇𝒆 = 𝑭 𝑺𝒇𝒆 𝜷 𝑷𝒚 Li + Cs + Rb + Stand reduction -3.040 V -3.026 V -2.980 V potential (1M) Effective reduction potential - -3.103 V -3.06 V at 0.05M* Effective reduction potential - -3.144 V -3.098 V at 0.01M*  An cation may have an E Red lower than those of Li + . Fei Ding, Wu Xu, Gordon L. Graff, Jian Zhang, Maria Sushko, Xilin Chen, Yuyan Shao, Mark H. Engelhard, Zimin Nie, Jie Xiao, Xingjiang Liu, Peter V. Sushko, Jun Liu, and Ji-Guang Zhang , J. Am. Chem. Soc., 2013, 135 (11), pp 4450 – 4456, 4

Effect of CsPF 6 Additive on The Morphology of Li Deposition a b c 20 µm 20 µm 20 µm d e 20 µm 20 µm • Control electrolyte: 1 M LiPF 6 in PC. • CsPF 6 concentration in the electrolyte: ( a ) 0 M, ( b ) 0.001 M, ( c ) 0.005 M, ( d ) 0.01 M, and ( e ) 0.05 M. Cs + additive can effectively suppress Li dendrite growth.  5

Dendrite Free Li Deposition with Salt Additive 1 M LiPF 6 in PC 1 M LiPF 6 in PC+ 0.05 M CsPF 6 Surface 1  m Cross section 1  m  Dendritic surface  Smooth surface  Random growth  Highly ordered growth 6 Zhang et al, Nano Lett. , 2014, 14 (12), pp 6889 – 6896

2. High Rate Stable Li Deposition using High Concentration LiFSI-DME Electrolyte  Li deposited in 4M LiFSI-DME Electrolyte exhibits a nodule structure with much smaller surface area as compared to those deposited in carbonate based electrolyte. 7 J. Qian, W.A. Henderson, W. Xu, P. Bhattacharya, M. Engelhard, O. Borodin & J.G. Zhang Nature Communications, 2015, DOI: 10.1038/ncomms7362. 7

Effects of Current Density on the Cycling Stability 4M LiFSI in DME 4M LiFSI in DME  The average Coulombic efficiency 4M LiFSI in DME of the cycling is >99% (0.2 mA cm - 2 ), >98% (2.0 and 4.0 mA cm -2 ) and >97% (8.0 and 10.0 mA cm -2 ).  CE is stable up to1000 cycles. J. Qian, W.A. Henderson, W. Xu, P. Bhattacharya, M. Engelhard, O. Borodin & J.G. Zhang 8 Nature Communications, 2015, DOI: 10.1038/ncomms7362.

Long Term Cycling Stability of Li|Li cells Using Electrolyte E1  Current density: 10 mA/cm 2 .  Stable cycling for more than 6,000 cycles.  No short, no increase in impedance or cell voltage. J. Qian, W.A. Henderson, W. Xu, P. Bhattacharya, M. Engelhard, O. Borodin & J.G. Zhang 9 Nature Communications, 2015, DOI: 10.1038/ncomms7362.

3. Accurate Determination of CE  Different Li CEs were reported even for the same system.  There is an urgent need to identify an general methodology to measure CE for Li metal anode. 10

Factors Affecting Measurement of Li CE  Substrate selection  Substrate treatment approaches  Accuracy of the instrument  Cell design  Measurement protocols 11

Method 1: Li|Cu cells – Full stripping for Each Cycle Electrolyte: 4M LiFSI in DME 𝑅 𝑇 𝐷𝐹 = Single Cycle CE: 𝑅 𝑄 𝑅𝑇 𝑅𝑄 𝐷𝐹 𝑏𝑤𝑕 = Average CE: 𝑜 Current Density = 0.4 mA/cm 2 Q P = 0.5 mAh/cm 2  Average CE = 98.8% for 100 cycles 12

Method 2: Li|Cu cells – Partial Stripping 𝐷𝐹 𝑏𝑤𝑕 = 𝑜𝑅 𝑑 +𝑅 𝑇 𝑜𝑅 𝑑 +𝑅 𝑈 Alternative Equation when voltage exceeds upper limit in N cycles : 𝑅 𝑈 𝐷𝐹 𝑏𝑤𝑕 = 1 − 𝑂𝑅 𝑑 + 𝑅 𝑈 Current Density = 0.4 mA/cm 2 Q T = 4 mAh/cm 2 Q C = 0.5 mAh/cm 2  Average CE = 99.2% for 100 cycles 13

Proposed Universal Approach- Method 3: Combination of Conditioning Cycle and Partial Stripping 𝑜𝑅 𝑑 +𝑅 𝑇 𝐷𝐹 𝑏𝑤𝑕 = 𝑜𝑅 𝑑 +𝑅 𝑈  Conditioning cycle not included in calculation of CE Current Density = 0.4 mA/cm 2 Q T = 4 mAh/cm 2 Q C = 0.5 mAh/cm 2  Eliminate the uncertainty related to substrate material and treatment conditions  Average CE = 99.4% for 100 cycles 14

Effect of Li Deposition Rate in Carbonate Electrolytes Li||NCA cells using 1M LiPF 6 EC:EMC (4:6 wt.) electrolyte Li deposition~ charge process Cross-sectional SEM images of the Li anodes obtained from the cells after 100 cycles at a) 0.2C charge/1C discharge, b) 0.5C charge/discharge, c) 1C charge/discharge, and d) 2C charge/discharge.  CE and cycle life of Li/NCA cell can be improved by slow charge (Li deposition). Lv & Xiao et al., Adv. Energy Mater . 2015 , 5 , 1400993 15

Effect of Li Stripping Rate in Carbonate Electrolytes Li||NMC cells using 1M LiPF 6 /EC-DMC (1:2 in volume) electrolytes Li stripping ~ Discharge process  CE and cycle life of Li/NMC cell can be improved by fast discharge (Li stripping).  Fast discharging formes a transient highly concentrated Li + ion solution in the vicinity of Li surface and reduce the interaction between fresh Li metal and electrolyte. Zheng & Xu et al., Adv. Energy Mater. 2016, 1502151. 16

Effect of Charge/Discharge Protocol on CE of Li Cycling in Ether Based Electrolyte b a Electrolyte: 4M LiFSI-DME Cu||LiFePO 4 a. CE of Cu||Li cells. b. Charge/discharge voltage profiles of Cu||LiFePO 4 cells. c. Discharge capacity and CE of anode-free Cu||LiFePO 4 cells. c  The CE of Li cycling can be increased to 99.8% with the combination of high concentration electrolyte (4M LiFSI/DME) and low rate Li deposition/high rate Li stripping protocols. High  Anode-free Cu||LiFePO 4 cell can retain 54% capacity after 100 cycles. 17 Qian et al, Adv. Funct. Mater. 2016 ,DOI:10.1002/adfm.201602353

4. Long Term Cycling of High Voltage Li Metal Batteries Electrochemical behaviour of Li||NMC cells 200 200 -2 -2 -1 ) 0.175 mA cm -1 ) 0.175 mA cm 2.0 2.0 -2 ) -2 ) Specific capacity (mAh g Specific capacity (mAh g -2 -2 Areal capacity (mAh cm Areal capacity (mAh cm 1.75 mA cm 1.75 mA cm 150 150 1.5 1.5 100 100 1.0 1.0 Dual-salt + 0.05 M LiPF 6 Dual-salt ( LiTFSI + LiBOB ) Dual-salt ( LiTFSI + LiBOB ) 50 50 0.5 0.5 E-control ( 1M LiPF 6 ) E-control ( 1M LiPF 6 ) 0 0.0 0 0.0 0 0 100 100 200 200 300 300 400 400 500 500 Cycle number Cycle number Dual-salt ( LiTFSI + LiBOB ) Dual-salt + 0.05 M LiPF 6 E-control ( 1M LiPF 6 ) st st 1 1 st 4.5 4.5 4.5 1 th th 5 5 th + ) 5 th th 25 25 Voltage (V vs. Li/Li th 25 th th 50 50 th 4.0 4.0 50 4.0 th th 100 100 th 100 th th 150 150 th 150 th th 200 200 th 3.5 3.5 200 3.5 th th 250 250 th th cycle 250 500 th th 300 300 th 300 th th 350 350 th cycle th 3.0 450 3.0 350 3.0 th th 400 400 th 400 th th 450 450 th th cycle 450 100 th th 500 500 th 2.5 2.5 500 2.5 0 50 100 150 200 0 50 100 150 200 0 50 100 150 200 -1 ) -1 ) Specific capacity (mAh g Specific capacity (mAh g -1 ) Specific capacity (mAh g  LiTFSI-LiBOB dual salt electrolyte with LiPF 6 additive shows better stability with Li metal. Zheng, M. H. Engelhard, D. Mei, S. Jiao, B. J. Polzin, J.-G. Zhang, and W. Xu, 18 18 Nature Energy , 2017, 2 , 17012.

Effects of testing temperature and charge current density -2 ) 60 o C 2.0 1.75 mA cm -2 Areal capacity (mAh cm 1.5 Dual-salt + 0.05 M LiPF 6 1.0 Dual-salt (LiTFSI + LiBOB) E-control (1M LiPF 6 ) 0.5 0.0 0 100 200 300 400 Cycle number 3.0 120 -2 ) 30 o C Coulombic efficiency (%) Areal capacity (mAh cm 2.5 100 Charge: 0.58 mA cm -2 , discharge: 1.75 mA cm -2 2.0 80 1.5 60 Electrolyte: Dual-salt + 0.05 M LiPF 6 1.0 40 Efficiency 0.5 20 Capacity 0 0.0 0 0 200 200 400 400 600 600 800 800 Cycle number  LiPF 6 additive (optimum 0.05M) improves the cycling performances at high temperature and low charge current. Zheng, M. H. Engelhard, D. Mei, S. Jiao, B. J. Polzin, J.-G. Zhang, and W. Xu, 19 Nature Energy , 2017, 2 , 17012.