Multi-dimensional optimization of polymer-involved Li+ solvation enabling stable polymer plastic crystal electrolyte for long-cycle lithium metal batteries

Succinonitrile (SN)-based polymer plastic crystal electrolytes (PPCEs) are regarded as promising candidates for lithium metal batteries but suffer from serious side reactions with Li metal. Herein, we propose a multi-dimensional optimization strategy to alleviate the side reactions between SN and Li metal, and develop a highly stable poly-vinylethylene carbonate-based PPCE (PPCE-VEC). Moreover, we identify the intrinsic factors of multi-dimensional polymer structures on the electrolyte stability by three typical classes of polyesters. The PPCE-VEC constructed by in situ polymerization exhibits much better stability than poly-vinylene carbonate-based PPCE (PPCE-VCA) and poly-trifluoroethyl acrylate-based PPCE (PPCE-TFA), which is verified by its fewer SN-decomposition species in X-ray photoelectron spectroscopy (XPS) and outstanding full cell performance. The PPCE-VEC-enabled LiNi_0.6Co_0.2Mn_0.2O₂ full cell achieve 73.7 % capacity retention after 1400 cycles, which outperforms PPCE-VCA- and PPCE-TFA-enabled full cells (61.9 % and 46.9 %). Spectral analysis and theoretical calculation reveal that the high solvation ability of the carbonyl site, flexible polymer chain, and homogeneous electrolyte phase of PPCE-VEC are favorable to maximizing competition coordination with Li⁺ to weaken the Li⁺–SN binding and shape an anion-rich solvation structure. This optimized polymer-involved Li⁺ solvation enhances SN stability and facilitates the formation of B/F enriched solid-electrolyte interphase (SEI), thus significantly improving PPCE stability.