Double-layer asymmetric interfacial modification of polyacrylonitrile/poly(vinylidene fluoride-co-hexafluoropropylene) for stable cycling of all-solid-state lithium metal batteries

The Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) solid electrolyte is widely investigated owing to good chemical stability, remarkable ionic conductivity and low cost. However, the high interfacial impedance and terrible side reaction with electrode limits the application of LATP in lithium metal batteries. To address this issue, the poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) and polyacrylonitrile (PAN) layers were introduced to both sides of LATP to prepare PVDF-HFP@LATP-Bi₂O₃@PAN (H-LB-P) for meeting the interfacial requirements between different electrodes and LATP. The PAN modified layer with Li⁺ conductivity and adhesion achieved to tight connection and perfect interfacial contact between LATP and cathode. Meanwhile, the PVDF-HFP layer effectively isolates the side reaction between lithium metal anode (Li) and LATP. Moreover, the X-ray photoelectron spectroscopy (XPS) indicates that PVDF-HFP reacts with Li-metal to form a stable LiF interfacial layer. As a result, the Li||H–B–H||Li cell exhibits stable cycling over 300 h at 0.1 mA cm⁻². The Li||H-LB-P||LiFePO₄ battery delivers the favorable initial discharge capacity of 153.06 mAh g⁻¹ and retention rate (82 %) after 100 cycles at 0.1C for 25 °C. This work provides a viable design for application of oxide electrolyte in lithium metal batteries.