Bromide-driven reorganization of lithium solvation shells enables dynamically decoupled ion transport and interfacial stability in semi-solid polymer electrolytes for lithium metal batteries

The performance of polymer electrolytes in lithium metal batteries (LMBs) is often hindered by strong Li+-ligand coordination, which leads to tightly bound solvation shells and restricts ion transport by coupling it to polymer segmental motion. In this study, a low-content ionic plasticizer additive 1-butyl-3-dimethylimidazolium bromide (BMImBr) was introduced into the PVDF-HFP/LiTFSI/DMF matrix to modulate the Li+ solvation environment. Unlike conventional dual-salt systems, the introduced Br− anions dynamically compete for Li+ coordination, disrupting the rigid Li+-TFSI−/DMF solvation shell and constructing a “statistically labile and diffuse ionic cloud” characterized by reduced coordination numbers, weakened binding energies, and a more diffuse electrostatic potential landscape. This restructured solvation environment facilitates partially decoupled Li+ transport, as evidenced by dielectric spectroscopy and molecular dynamics simulations. Furthermore, the in situ formation of a LiBr-rich solid electrolyte interphase (SEI) effectively stabilizes the Li-metal interface and significantly reduces interfacial resistance. As a result, the optimized polymer electrolyte delivers outstanding electrochemical performance, achieving a high ionic conductivity of 0.8 × 10−4 S/cm, ultra-stable symmetric cell cycling over 500 h, and superior capacity retention exceeding 94 % after 150 cycles at 0.5 C. This study elucidates a dynamic ion transport mechanism driven by competitive anion coordination and provides a viable strategy for simultaneously addressing the conductivity-stability trade-off in solid-state lithium metal batteries.

锂金属电池（LMBs）中聚合物电解质的性能常受限于强锂离子-配体配位作用，该作用会形成紧密结合的溶剂化壳层，并通过将离子传输与聚合物链段运动耦合，限制了离子传输效率。本研究将低含量离子增塑剂添加剂1-丁基-3-二甲基咪唑溴盐（BMImBr）引入PVDF-HFP/LiTFSI/DMF基体中，以调控锂离子溶剂化环境。与传统双盐体系不同，引入的溴阴离子会动态竞争锂离子配位位点，破坏刚性的锂离子-TFSI⁻/DMF溶剂化壳层，构建出具有低配位数、弱结合能以及更弥散静电势分布特征的“统计上不稳定且弥散的离子云”。这种重构后的溶剂化环境可实现部分解耦的锂离子传输，该结论已通过介电光谱与分子动力学模拟得到验证。此外，原位生成的富溴化锂固体电解质界面（SEI）可有效稳定锂金属界面，并显著降低界面阻抗。最终，优化后的聚合物电解质展现出优异的电化学性能：离子电导率可达0.8×10⁻⁴ S/cm，对称电池可实现超500小时的稳定循环，在0.5C倍率下经过150次循环后容量保持率超过94%。本研究阐明了由竞争性阴离子配位驱动的动态离子传输机制，为同时解决固态锂金属电池中的电导率-稳定性权衡问题提供了可行策略。