Synergistic dual-phase network in rigid-flexible PU/LAGP composite electrolytes for fast-ion-conducting solid-state lithium batteries

Introduction The practical implementation of all-solid-state lithium batteries (ASSLBs) is severely hindered by the trade-off between ionic conductivity and mechanical robustness. Additionally, “ion-trapping” effects give rise to sluggish interfacial lithium-ion transport, further restricting battery performance. Developing composite solid electrolytes that simultaneously resolve these two bottlenecks remains a critical challenge. Methods A rigid-flexible composite electrolyte (denoted PLAP) was fabricated, which combines prelithiated polyurethane (PU) polymer matrix with Li 1.5 Al 0.5 Ge 0.5 P 3 O 12 (LAGP) inorganic fillers. A soft-hard segmented molecular structure was tailored for the electrolyte matrix. Spectroscopic characterizations and theoretical computations were employed to analyse interfacial lithium-ion binding energy before and after terminal-group prelithiation (−OH → −OLi). For benchmark comparison, the non-prelithiated −OH-terminated PU/LAGP electrolyte from our previous work with identical composition and test conditions was adopted. Electrochemical measurements including tensile test, ionic-conductivity evaluation, symmetric-cell cycling and LiFePO 4 |PLAP|Li full-cell galvanostatic cycling were carried out to assess mechanical property and electrochemical performance. Results The as-prepared PLAP composite electrolyte delivers a tensile strength of 5.47 MPa and an elongation of 192.4 %, benefiting from its custom soft-hard segmented architecture. Terminal-group prelithiation reduces the interfacial Li + binding energy from 1.01 eV to 0.55 eV, which releases trapped lithium ions. The PLAP electrolyte achieves a high room-temperature ionic conductivity of 3.8 × 10 -4 S/cm. Li||Li symmetric cells realise stable cycling over 750 h under an ultra-high current density of 10 mA cm -2 . The LiFePO 4 |PLAP|Li full cells exhibit outstanding cycling durability, retaining 95.7 %, 91 % and 87.8 % of initial capacity after 2000 cycles at 0.2 C, 2 C and 5 C, respectively. Discussion The terminal-group prelithiation strategy effectively mitigates ion-trapping by lowering interfacial Li + binding energy, which improves ion-transport behaviour while preserving favourable mechanical performance originating from the rigid-flexible segmented structure. This work demonstrates a feasible material-design route toward long-lifespan and fast-charging liquid-free all-solid-state lithium-metal batteries.