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

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 (LiFePO₄‖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.