Prolonging Storage Shelf‐Life of Lithium Metal Batteries with Phase‐Change Electrolyte

ABSTRACT Long‐term electrochemical energy storage devices of lithium battery demand electrolytes that simultaneously ensure operational functionality and suppress self‐discharge during idle periods. In this work, a binary phase‐change electrolyte (B‐PCE) integrating dimethyl dodecanedioate (DDCA) and fluoroethylene carbonate (FEC) is proposed. The B‐PCE exhibits temperature‐adaptive functionality through an 18.65°C phase transition, prolonging storage properties and enhancing operational performance. The B‐PCE achieves unprecedented over 2000‐fold ionic conductivity modulation, maintaining 0.23 mS cm −1 at 25°C for efficient operation, while collapsing to 8.8 × 10 −5 mS cm −1 at 0°C to block parasitic reactions. This drastic change is accompanied by a transformation in solvation structures from solvent‐separated ion pairs to contact ion pairs and aggregates, which significantly elevates charge transfer resistance. Furthermore, it has been confirmed that the FEC‐derived LiF‐rich SEI formation on lithium metal anodes is effective in suppressing interfacial side reactions. In lithium metal batteries (LiFePO 4 ‖Li) full cells, B‐PCE delivers an ultralow daily self‐discharge rate of 0.02% after stabilization at 0°C with a projected 5.9‐year long‐shelf‐life, surpassing conventional electrolytes by 11.3‐fold. Concurrently, it exhibits exceptional cycling stability with lithium metal anodes, maintaining 82% capacity retention after 200 cycles at 1 C and high‐rate capability of 117.5 mAh g −1 at 5 C.