Asymmetric Solvents Regulated Crystallization‐Limited Electrolytes for All‐Climate Lithium Metal Batteries

Abstract

Electrolytes that can keep liquid state are one of the most important physical metrics to ensure the ions transfer with stable operation of rechargeable lithium‐based batteries at a wide temperature window. It is generally accepted that strong polar solvents with high melting points favor the safe operation of batteries above room temperatures but are susceptible to crystallization at low temperatures (≤−40 °C). Here, a crystallization limitation strategy was proposed to handle this issue. We demonstrate that, although the high melting points of ethylene sulfite (ES, −17 °C) and fluoroethylene carbonate (FEC, ≈23 °C), their mixtures can avoid crystallization at low temperatures, which can be attributed to low intermolecular interactions and altered molecular motion dynamics. A suitable ES/FEC ratio (10 % FEC) can balance the bulk and interface transport of ions, enabling LiNi0.8Mn0.1Co0.1O2||lithium (NCM811||Li) full cells to deliver excellent temperature resilience and cycling stability over a wide temperature range from −50 °C to +70 °C. More than 66 % of the capacity retention was achieved at −50 °C compared to room temperature. The NCM811||Li pouch cells exhibit high cycling stability under realistic conditions (electrolyte weight to cathode capacity ratio (E/C)≤3.5 g Ah−1, negative to positive electrode capacity ratio (N/P)≤1.09) at different temperatures.

Silicon Composite Anode Degradation during Freeze–Thaw Temperature-Swings

“…Electrolyte freezing dynamics are complicated and involve phase transformation behavior of the electrolyte and active. 23 There are several potential mechanisms that can cause chemo-mechanical stress generation in the electrode during electrolyte freezing. The formation of salt crystals during freezing is believed to exert a crystallization pressure in the porous media.…”

“…Salt crystallizes during the freezing step and then dissolves during thawing. Electrolyte freezing dynamics are complicated and involve phase transformation behavior of the electrolyte and active . There are several potential mechanisms that can cause chemo-mechanical stress generation in the electrode during electrolyte freezing.…”