Investigating and inhibiting cathode-side gas generation for practical low-temperature and fast Li-ion batteries

Weakly solvating electrolytes attract increased interest in low-temperature lithium-ion batteries since they can overcome the kinetic limitations of lithium-ion desolvation. However, the high content of weakly-coordinating/free solvents poses a threat to the oxidative stability of weakly solvating electrolytes. Herein, we investigate the oxidation and gas-producing behaviour of weakly solvating electrolytes with typical low-melting-point solvents inside low-temperature pouch cells. Excluding the influence of the anode, the results show that the continuous gassing from the oxidation of solvents in weakly solvating electrolytes on the cathode significantly affects the lithium-ion chemistry, leading to low-temperature cells with a fast capacity decay. Constructing a stable cathode electrolyte interphase, such as adding lithium difluoro(oxalato)borate into weakly solvating electrolytes, could suppress oxidation-induced gas production and therefore enable the 3.5 Ah cylindrical cell with nearly two years of stable operation (2100 cycles with 81.1% retention) at −20 °C. These findings highlight the importance of a trade-off that balances the lithium-ion kinetics and oxidative stability in weakly solvating electrolytes when the low-temperature issue of lithium-ion batteries is overcome. Weakly solvating electrolytes can overcome the kinetic limitations of lithium-ion desolvation at low temperatures, but their high content of weakly coordinating/free solvents threatens oxidative stability. Here, the authors introduce lithium difluoro(oxalato)borate to construct a stable cathode electrolyte interphase, suppressing oxidation-induced gas production and enabling a 3.5 Ah cylindrical cell to achieve stable operation for nearly two years at −20 °C.