Across Interfacial Li⁺ Conduction Accelerated by a Single-Ion Conducting Polymer in Ceramic-Rich Composite...

Composite electrolytes have been accepted as the most promising species for solid-state batteries, exhibiting the synergistic advantages of solid polymer electrolytes (SPEs) and solid ceramic electrolytes (SCEs). Unfortunately, the interrupted Li⁺ conduction across the SPE and SCE interface hinders the ionic conductivity improvement of composite electrolytes. In our study on a ceramic-rich composite electrolyte (CRCE) membrane composed of borate polyanion-based lithiated poly(vinyl formal) (LiPVFM) and Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) particles, it is found that the strong interaction between the polyanions in LiPVFM and LATP particles results in a uniform distribution of ceramic particles at a high proportion of 50 wt % and good robustness of the electrolyte membrane with a Young's modulus of 9.20 GPa. More importantly, ab initio molecular dynamics simulation and experimental results demonstrate that Li⁺ conduction across the SPE and SCE interface is induced by the polyanion-based polymer due to its high lithium-ion transference number and similar Li⁺ diffusion coefficient with the SCE. Therefore, the unblocked Li⁺ conduction among ceramic particles dominates in the CRCE membrane with a high ionic conductivity of 6.60 × 10^-4 S cm^-1 at 25 °C, a lithium-ion transference number of 0.84, and a wide electrochemical stable window of 5.0 V (vs Li/Li⁺). Consequently, the high nickel ternary cathode LiNi_0.8Mn_0.1Co_0.1O₂-based batteries with CRCE deliver a high-rate capability of 135.08 mAh g^-1 at 1.0 C and a prolonged cycle life of 100 cycles at 0.2 C between 3.0 and 4.3 V. The polyanion-induced Li⁺ conduction across the interface sheds new light on solving composite electrolyte problems for solid-state batteries.