Synergetic modulation of bulk ion conduction and interface chemistry in polymer-based all-solid-state lithium metal batteries

Solid polymer electrolytes (SPEs) are considered one of the most promising materials for all-solid-state lithium metal batteries (ASSLMBs) due to their facile processability. However, developing SPEs with both high ionic conductivity and interfacial stability remains a challenge. Here, a donor–acceptor (D-A) like solid plasticizer, tris(pentafluorophenyl)borane (TPFPB), containing electron-rich F atoms and electron-deficient B sites, was introduced to regulate the ion transport behavior and interfacial chemistry of polyethylene oxide (PEO)-based SPEs. Owing to the multiple ion–dipole interactions (F‧‧‧Li⁺‧‧‧TFSI⁻ and B‧‧‧TFSI⁻‧‧‧Li⁺) between the TPFPB molecule and Li salts, a multimodal electrolyte environment featuring more free Li⁺ and trapped TFSI⁻ anions was generated, which cooperates with the reduced crystallinity of PEO, significantly facilitating the rapid migration of Li⁺. More importantly, TPFPB tends to be preferentially reduced to form a stable inorganic-rich solid electrolyte interphase on the Li-metal anode, ensuring uniform Li plating/stripping behavior. Thus, the TPFPB-modulated SPEs system achieves a high Li⁺ conductivity of 0.74 mS cm⁻¹ and effectively suppresses dendrite growth, which enables a long-cycle dendrite-free Li/Li symmetric cell for over 5000 h, and remarkable electrochemical performance has been further validated in operational ASSLMBs. The findings in this work would inspire efforts to develop high-performance SPEs for all-solid-state alkali-metal batteries.