# Lewis Acid‐Base Effects on Molecular Structure and Charge Density in Solid Polymer Electrolytes for Solid‐State Batteries

## TL;DR

This paper explores how different lithium salts affect the properties of solid polymer electrolytes used in batteries, finding that a mix of two salts improves performance.

## Contribution

The study introduces a binary lithium salt formulation that optimizes ionic conductivity, mechanical strength, and electrochemical stability in solid polymer electrolytes.

## Key findings

- A binary lithium salt mixture improves ionic conductivity to 4.93 × 10−4 S/cm at 20°C.
- The binary formulation increases mechanical strength to 127 MPa.
- The salt mixture provides a broad electrochemical stability window.

## Abstract

Solid polymer electrolytes (SPEs) are critical for advancing the safety and performance of solid‐state batteries (SSBs). However, challenges such as low ionic conductivity, limited mechanical strength, and narrow electrochemical stability windows hinder their widespread adoption. This study investigates the role of lithium salt formulation, specifically lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and a binary mixture of the two, on the molecular structure and charge density of poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP)‐based SPEs. Through comprehensive characterization, we demonstrate that the choice of lithium salt profoundly affects the crystallinity, dehydrofluorination degree, and ionic conductivity of SPEs. Notably, the binary salt mixture provides a balanced improvement in ionic conductivity (4.93 × 10−4 S/cm at 20°C) and mechanical strength (127 MPa), alongside a broad electrochemical stability window. These findings suggest that strategic lithium salt formulation can significantly enhance the overall performance of SPEs, paving the way for their effective use in next‐generation SSBs.

Solid polymer electrolytes incorporating LiFSI, LiTFSI, and their binary mixture are investigated to reveal how salt polarity and Lewis basicity regulate dehydrofluorination, crystallinity, and charge density in PVDF‐HFP. The binary‐salt formulation achieves a balanced improvement in ionic conductivity, mechanical robustness, and electrochemical stability, offering a rational strategy to design high‐performance solid polymer electrolytes for solid‐state batteries.