In-situ polymerisation of fluorene to achieve theoretical capacity in LiFePO4 cells

Abstract

This study aims to enhance the electrochemical properties of solid-state lithium-ion batteries by modifying the cathode material, LiFePO4 (LFP), via fluorene addition and in-situ polymerisation. The first modification process involves creating a shell structure (the film thickness of 10 nm) around each LFP particle and establishing a net-like structure to connect the particles before the in-situ polymerisation. Then, electrochemical in-situ polymerisation during battery cycling with a low current and obtaining the composite cathode of lithium iron phosphate (LFP) and polyfluorene. The results demonstrate that adding 20 wt.% fluorene significantly reduces the transfer resistance and enhances the rate performance with the capacity retention of 95.2 % (from 0.1C to 2C and return to 0.2C) of the solid-state batteries. Additionally, the modified LFP cathode demonstrates excellent long-term cycling performance and exhibits capacity (167.2 mAh/g in 0.2 C) close to the theoretical limit, and Coulombic efficiency remains at 99.2 %.