Cyclable Micron‐Sized Silicon‐Based Lithium‐Ion Batteries at −40 °C Enabled by Temperature‐Dependent Solvation Regulation

Micron-sized silicon (µSi) anodes hold great promise for high-energy lithium-ion batteries (LIBs). However, the rechargeable cyclability of µSi anodes at sub-zero Celsius, especially below -20 °C remains challenging, caused by the severe volume change and cracking of solid electrolyte interphase (SEI) during cycling. Here, the low-temperature cyclability of µSi-based LIBs is realized by using an electrolyte featured with temperature-adaptive ion-dipole interactions. The synergistic effect of the methyl group as a weak electron donor and the electronegative fluorine atoms endows methyl difluoroacetate (MDFA) with a weak binding affinity for Li⁺. Moreover, the affinity between Li⁺ and the oxygen atoms in both MDFA and fluoroethylene carbonate (FEC) decreases at lower temperatures, accompanied by a temperature-responsive enhancement of Li⁺-anion coordination. Thus, the MDFA/FEC electrolyte exhibits an extraordinary contact ion pairs-dominated solvation structure at subzero temperatures, which facilitates Li⁺ desolvation and the formation of a thin, robust inorganic-rich SEI. As expected, µSi anodes show a record-breaking capacity of 786 mAh g^-1 after 100 cycles at -40 °C under 0.1 A g^-1, and µSi-based full cells display impressive rechargeability at -40 °C. This work paves the way for extending the applications of µSi anodes to extreme cold conditions.