Artificial Solid-Electrolyte Interphase with PVDF-ZnF2 Double-Layer Structures Enhancing Electrochemical Performance of Sodium Metal Batteries

Abstract

Sodium metal batteries (SMBs) have attracted significant attention due to their high theoretical capacity and abundant resources. However, commercialization for this cell is challenged by the high reactivity of sodium metal, leading to detrimental side reactions with electrolytes, dendritic growth, and severe volume changes over charging/discharging cycles. These issues shorten the cycle life, reduce efficiency, and increase the risk of internal short circuits and thermal runaway. A stable solid electrolyte interphase (SEI) is key to addressing these challenges by preventing dendrite growth, homogenizing sodium ion transport, and maintaining chemical stability. This study investigates an artificial SEI(ASEI) composed of polyvinylidene fluoride (PVDF) and ZnF₂, which forms a durable organic-inorganic double-layer structure. The outer organic PVDF layer enhances mechanical strength, while the inner inorganic ZnF₂ layer improves sodium ion flux, preventing dendritic growth. The ASEI significantly extends cell life and enhance electrochemical performances. The NVP||50 μL −4 wt.%+100 μL −8 wt.% PVDF-ZnF₂/Na cell demonstrates stable cycling for over 3000 cycles. This novel ASEI design offers promising potential for improving the energy storage properties and safety of sodium metal batteries.