High Li⁺ transference gel interface between solid-oxide electrolyte and cathode for quasi-solid lithium-ion batteries

Solid-oxide electrolytes (SEs) are an alternative to using conventional organic liquid electrolytes for lithium ion batteries (LIBs) and offer solutions to the challenges associated with safety and energy density. However, SE-based LIBs suffer from high interfacial resistance between the electrolyte and electrodes. In this study, we develop a gelled poly(acrylonitrile-co-methyl acrylate) (P(AN-co-MA)) framework to facilitate Li⁺ transfer across the interface between an SE pellet of garnet-type Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO) and a LiFePO₄ cathode. The gelled polymeric framework exhibits high ionic conductivity and a large Li⁺ transference number (tLi⁺) of 0.67 that results from the synergy between the nitrile and acrylate functionalities and minimizes the formation of ion-solvent clusters and mobility of PF₆^- anions. The large tLi⁺ characteristic is advantageous for forming a junction with SEs featuring a unity tLi⁺ and suppressing polarization caused by PF₆^- accumulation. When coupled with the LLZTO pellet, the gel polymer electrolyte may exhibit collimated Li⁺ transport that suppresses Li-dendrite formation. The resulting LiLLZTOLiFePO₄ battery demonstrates outstanding capacity (e.g., 154 mA h g^-1 at 0.1 mA cm^-2 and 25 °C), high rate retention, and excellent cycling stability. The present study demonstrates that the gelled P(AN-co-MA) framework acts an ideal interface between the SE and cathode for fabricating quasi-solid LIBs.