In-situ photo-polymerized elastomeric composite electrolytes containing Li6.4La3Zr1.4Ta0.6O12 particles for stable operation in lithium metal batteries

Composite polymer electrolytes (CPEs), produced by incorporating inorganic nanoparticles (NPs) into polymer matrices, have gained significant attention as promising candidates for solid-state lithium metal batteries (LMBs). However, the aggregation of dense inorganic fillers results in nonuniform CPEs, thereby impeding LMB performance. Here, we fabricated in-situ photo-polymerized CPEs by incorporating different weight ratios (0–20 wt%) of Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) into a polymer electrolyte system composed of poly(butyl acrylate)-based elastomer and succinonitrile-based plastic crystal phases. The rapid photo-polymerization process (~5 min) enabled homogeneous dispersion of LLZTO within the CPE matrix at 10 wt% LLZTO (L10), resulting in the high ionic conductivity (1.02 mS cm⁻¹ at 25°C) and mechanical elasticity (elongation at break ≈ 1250%) compared to those of CPE without LLZTO (L0). As a result, the L10-based LMB with a LiNi_0.8Co_0.1Mn_0.1O₂ cathode exhibited a high capacity of 166.7 mAh g⁻¹ after 200 cycles at 0.5C, significantly higher than those of L0 (74.0 mAh g⁻¹) and L20 (104.8 mAh g⁻¹). In comparison, in-situ thermal polymerized CPE with 10 wt% LLZTO NPs showed aggregation of NPs due to slow polymerization kinetics (~2 h), resulting in inferior LMB cycling performance compared to the L10. This work highlights the importance of in-situ photo-polymerized CPEs with homogenous dispersion of inorganic NPs to achieve high ionic conductivity and mechanical robustness suitable for the stable operation of LMBs.