Polycaprolactone-poly(vinylidene fluoride) blended composite polymer electrolyte with enhanced high power performance and interfacial stability for all-solid-state Li metal batteries

Polycaprolactone (PCL) based composite polymer electrolytes (CPEs) is a promising candidate applied in all-solid-state Li metal batteries (LMBs). However, vexing issues such as poor power performances and unstable interface layers are frequently observed. To address these issues, poly(vinylidene fluoride) (PVDF) with high dissociation of Li salts and good compatibility against Li metal are introduced into PCL to prepare blended CPEs. The PCL-PVDF blended CPEs obtain a high ionic conductivity of 1.38 × 10-4 S·cm−1 and a high lithium ion transference number of 0.89 at 60 °C, owing to the high dissociation coming from the PVDF. Particularly, the Li//P5-CPEs-40 %//Li symmetrical battery can work steadily over 800 h at a high current density of 0.25 mA·cm−2. Furthermore, the LiFePO4//P5-CPEs-40 %//Li batteries exhibit high capacity retention of 84.9 % for 500cycles at 3.0 C. The excellent cycling stability for the LMBs is considered to be originated from the LiF containg SEI layer that formed during cycling. This study provides new perspectives to develop new CPEs with high power performances and stable interface for LMBs.