Enhanced Li+ transport and uniform deposition in composite solid-state polymer electrolytes based on a dual lithium salt system with 3D ion pathways

To enhance the stability and safety of solid-state lithium metal batteries under high voltage and high energy density conditions, a flexible inorganic–organic hybrid solid-state electrolyte based on polyacrylic acid–boric acid–anhydrous lithium hydroxide–lithium oxalate salt (LiPAAOB) and holey graphene oxide (HGO) was designed and fabricated. By optimizing the doping ratio of HGO, the LiPAAOB&HGO composite electrolyte exhibited optimal electrochemical performance. This composite electrolyte achieved an ionic conductivity as high as 1.5 × 10 −3  S cm −1 at room temperature, significantly exceeding that of the unmodified PVDF-based solid electrolyte (4.6 × 10 −4  S cm −1 ); its activation energy was 0.14 eV, demonstrating excellent lithium-ion mobility. An electrochemical stability window of 4.3 V with good redox reversibility was gained; the lithium-ion transference number (t Li + ) reached 0.77, markedly higher than that of conventional Poly (vinylidene fluoride) (PVDF)-based electrolytes. Linear sweep voltammetry (LSV) further confirmed that the electrochemical stability window of the electrolyte could be extended up to 5.2 V, meeting the requirements for high-voltage cathode materials. Regarding battery performance, the Li | LiPAAOB&HGO SPE | Li symmetric cell achieved stable cycling for over 2900 h under testing conditions of 0.2 mA cm −2 , verifying its excellent interfacial stability and dendrite suppression ability; the Li | LiPAAOB&HGO SPE | LiFePO₄ full cell retained 71.5 % capacity after 900 cycles at 1C rate, with an average coulombic efficiency as high as 99.8 %.