Electrolyte Chemistry Modulation Toward High‐Performance and Ultralow‐Temperature Silicon Anode

Abstract The high‐capacity silicon (Si) anode usually suffers from rapid capacity decay and low Coulombic efficiency in carbonate electrolytes resulting from large volume expansion and unstable solid electrolyte interphase (SEI). In addition, the sluggish electrode kinetics in routine electrolytes at subzero temperatures severely hampers the operational capabilities of Si‐based batteries. Herein, a rational electrolyte design strategy is reported to tune the solvation chemistry and interfacial behavior of the electrolyte for high‐performance Si anode. The interfacial stability and electrochemical reaction kinetics can be enhanced simultaneously at both room temperature and ultralow temperature by combining two kinds of ether‐based solvents (cyclopentylmethyl ether and tetrahydrofuran), which enables high cation conductivity, low Li‐ion desolvation barrier, and formation of a robust LiF‐elastic polymer SEI. Consequently, the optimized electrolyte extends the cyclability of the Si anode, maintaining more than 80% capacity retention over 200 cycles at −20 and −35 °C. Even at −40 °C, the Si electrode still delivers a high reversible capacity of 2157.0 mAh g ⁻¹ , showing the highest capacity retention of 68.5% up to date relative to its room‐temperature capacity. Moreover, the assembled full cells Si||LiFePO ₄ and Si||LiNi _0.8 Co _0.1 Mn _0.1 O ₂ demonstrate excellent electrochemical performance with no capacity degradation over 180 and 120 cycles, respectively, at −20 °C.