Constructing PVDF-Based Polymer Electrolyte for Lithium Metal Batteries by Polymer-Induced Phase Structure Adjustment Strategy

The phase separation between solvents and polymers during the processing leads to the porous structure of PVDF electrolyte, resulting in uneven distribution of ion channels, accelerating the growth of lithium dendrites. Moreover, the various crystal structures of PVDF hinder the migration of Li⁺, setting obstacles for the improvement of ion conductivity. Here, an amorphous polymer system (BPE) with excellent lithium salt affinity is introduced into the PVDF electrolyte as a bridge to eliminate phase separation structures. The porous structure of PVDF electrolyte is densified by utilizing the amorphous properties of BPE and its affinity for PVDF and lithium salt, thus homogenizing the distribution of ion channels. Furthermore, BPE inhibited the crystallization of PVDF, improving the Li⁺ conductivity of the polymer electrolyte. The obtained polymer electrolyte system (BPLE) has high ionic conductivity (1.6 × 10⁻³ S cm⁻¹) and Li⁺ transference number (0.66) at room temperature. The LiFePO₄||Li cell assembled with BPLE-1 achieved an initial capacity of 149 mAh g⁻¹ and a capacity retention rate of 98% (1C, 500 cycles, RT). At a current density of 2C, the LiFePO₄||Li battery achieved a specific capacity of 142 mAh g⁻¹ and the capacity retention rate exceeds 84% after 800 cycles.