Building continuous Li-ion transport channels from cathode to anode in solid-state lithium-metal batteries

Abstract

High ionic resistance at the electrolyte/electrode interfaces is considered one of the main challenges in developing solid-state lithium-metal batteries. Herein, homogeneous and continuous Li⁺ transport channels are constructed from the cathode to the anode to reduce the solid–solid interface resistance. This strategy involves the surface modification of polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) and Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO), which are the key components in the solid-state electrolyte, by chemically grafting zwitterionic sulfonate betaine (SB) to endow the ionic conductivity and improve the solid–solid interface compatibility. Therefore, a series of composite solid-state electrolytes were prepared by optimizing the contents of the polymer matrix (SB-PVDF-HFP), ceramic powder (SB-LLZTO), and lithium salt. The designed composite solid-state electrolyte was used as the electrolyte film and the ion-conductive binder phase in the cathode. The assembled Li/LiFPO₄ cell delivered a reversible capacity of 146.6 mA h g⁻¹ at 1.0 C, higher than the cell without surface modifications. Furthermore, the results of molecular dynamics simulation showed that higher diffusion coefficient (D) of Li⁺ with the modified components could promote the creation of fast Li⁺ transport channels in the bulk electrolyte and at the interface, facilitating the electrochemical performance of the solid-state battery.