One-step preparation of poly(ionic liquid)-based flexible electrolytes by in-situ polymerization for dendrite-free lithium ion batteries

[Display omitted] •A novel PIL-based quasi solid electrolyte was prepared via one-step in situ polymerization.•The PIL-QSE offers outstanding flexibility, favorable thermal stability and good electrochemical stability.•The PIL-QSE can suppress dendrite formation leading to good battery performance.•The PIL-QSE shows a good application prospect in the fields of flexible devices. Solid-state battery (SSB) has a new application prospect in the fields of safe energy storage, but the solid electrolyte usually fails to maintain excellent ionic conductivity, good mechanical properties and close interfacial contact with the electrode materials simultaneously. A newly-designed poly(ionic liquid)-based quasi solid electrolyte (PIL-QSE) is prepared via one-step in-situ cross-linked polymerizing 1-vinyl-3-dodecylimidazolium bis(trifluoromethanesulfonyl) imide (VDIM-TFSI), which is filled in poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) porous membrane prepared via phase inversion. The leakage-free PIL-QSE containing a compact cross-linked network structure exhibits optimal performances with outstanding flexibility, favorable thermal stability and improved electrochemical performances including a high room-temperature ionic conductivity of 0.70 mS cm−1, a superior electrochemical window up to 5.0 V as well as a high lithium ion transference of 0.52. Furthermore, the PIL-QSE can suppress dendrite formation leading to a good battery performance. The LiFePO4|PIL-QSE|Li cells can maintain a discharge capacity 140.7 mAh g−1 at 0.05 C with 99.8% coulomb efficiency after 200 cycles and 125.9 mAh g−1 at 0.1 C with 98.9% capacity contention after 100 cycles at 25 °C. Because of the flexibility of PIL-QSE, the pouch-type battery based on PIL-QSE cannot only light the red LED lamp in a normal state, but also in a bended/cut state. Both of the excellent performance and easy fabrication of PIL-QSE make it potentially as one of the most promising electrolyte materials for SSPB.