Immobilization of Anions on Polymer Matrices for Gel Electrolytes with High Conductivity and Stability in Lithium Ion Batteries

This study reports on a high ionic-conductivity gel polymer electrolyte (GPE), which is supported by a TiO₂ nanoparticle-decorated polymer framework comprising poly(acrylonitrile-co-vinyl acetate) blended with poly(methyl methacrylate), i.e., PAVM:TiO₂. High conductivity GPE-PAVM:TiO₂ is achieved by causing the PAVM:TiO₂ polymer framework to swell in 1 M LiPF₆ in carbonate solvent. Raman analysis results demonstrate that the poly(acrylonitrile) (PAN) segments and TiO₂ nanoparticles strongly adsorb PF₆^- anions, thereby generating 3D percolative space-charge pathways surrounding the polymer framework for Li⁺-ion transport. The ionic conductivity of GPE-PAVM:TiO₂ is nearly 1 order of magnitude higher than that of commercial separator-supported liquid electrolyte (SLE). GPE-PAVM:TiO₂ has a high Li⁺ transference number (0.7), indicating that most of the PF₆^- anions are stationary, which suppresses PF₆^- decomposition and substantially enlarges the voltage that can be applied to GPE-PAVM:TiO₂ (to 6.5 V vs Li/Li⁺). Immobilization of PF₆^- anions also leads to the formation of stable solid-electrolyte interface (SEI) layers in a full-cell graphite|electrolyte|LiFePO₄ battery, which exhibits low SEI and overall resistances. The graphite|electrolyte|LiFePO₄ battery delivers high capacity of 84 mAh g^-1 even at 20 C and presents 90% and 71% capacity retention after 100 and 1000 charge-discharge cycles, respectively. This study demonstrates a GPE architecture comprising 3D space charge pathways for Li⁺ ions and suppresses anion decomposition to improve the stability and lifespan of the resulting LIBs.