Rational design of electrolytes operating at low temperatures: Does the co-solvent with a lower melting point correspond to better performance?

XH Deng and S Zhang and C Chen and QH Lan and GZ Yang and TT Feng and HP Zhou and HY Wang and ZQ Xu and MQ Wu, ELECTROCHIMICA ACTA, 415, 140268 (2022).

DOI: 10.1016/j.electacta.2022.140268

To achieve desirable performance of lithium-ion batteries at low temperatures, using co-solvents with low melting points, especially carboxylic esters, is an efficient strategy and thus, there is a general question: does the co-solvent with a lower melting point correspond to the composite electrolytes with better performance? Herein, we chose two constitutional isomers with 22 ?C of difference in melting point, ethyl propionate and propyl acetate, as the co-solvent in the formula of two low-temperature electrolytes for comparison. At low tempera-tures, the Li||LiNi0.8Co0.1Mn0.1O2 coin cells and graphite||LiNi0.8Co0.1Mn0.1O2 pouch cells using the two elec-trolytes show close capacity retention, suggesting that the co-solvent with a lower melting point does not necessarily result in better low-temperature performance. Molecular dynamics simulations indicate that the similar solvation structure of contact ion pair for the two electrolytes is mainly responsible for their similar low-temperature performance. Furthermore, the Li||LiNi0.8Co0.1Mn0.1O2 and graphite||LiNi0.8Co0.1Mn0.1O2 cells with the two electrolytes at ambient temperature show capacity retention of 84.1%, 84.3% after 200 cycles and 88.2%, 89.6% after 360 cycles, respectively, demonstrating the reliability of the electrolytes. The results of this study provide general guidance for the development of low-temperature electrolyte regarding the choice of co-solvents.

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