Enabling High‐Voltage Polymer‐Based Solid‐State Batteries Through Reinforcements with LiAlO2 Fillers

Polymer-ceramic solid composite electrolytes with passive LiAlO₂ fillers show remarkable improvements in Li-ion conductivity in polycarbonates as compared to both non-conductive Al₂O₃ and conductive Li₇La₃Zr₂O₁₂ counterparts. The exceptionally high transference numbers contribute to reversible and stable electrochemistry with Li-metal electrodes and to compatibility with LiNi_0.33Mn_0.33Co_0.33O₂ cathodes.

Abstract

Poor ionic conductivity, low Li⁺ transference number, and limited electrochemical stability plague all-solid-state Li-metal batteries based on solid polymer electrolytes (SPEs). One strategy to overcome these hurdles is the insertion of ceramic fillers to generate composite polymer electrolytes (CPEs). These are based either on active (ion-conductive) fillers like Li₇La₃Zr₂O₁₂ or passive (non-conductive) fillers like Al₂O_3. In this work, the effect of passive Li-containing fillers is showcased, exemplified by a CPE platform of poly(trimethylene carbonate) (PTMC:LiTFSI) with LiAlO₂ particles. The inclusion of such fillers shows a strikingly positive effect. The ionic conductivity is greatly improved by one order of magnitude at 20 wt% of LiAlO₂ compared to the pristine PTMC SPE. Moreover, the Li⁺ transference number is significantly boosted and reaches values close to unity (T ₊ = 0.97 at 20 wt% of LiAlO₂), effectively rendering the material a single-ion conductor. The CPEs show outstanding cycling stability vs Li-metal, and electrochemical stability of up to 5 V vs Li⁺/Li. When implemented in a solid-state battery cell with LiNi_0.33Mn_0.33Co_0.33O₂ (NMC111) and Li-metal, a stable cycling performance for over 100 cycles is observed. This demonstrates the potential of using microsized and cost-effective LiAlO₂ fillers in CPEs for applications in all-solid-state Li-metal batteries.