Enabling highly stable lithium metal batteries by using dual-function additive catalyzed in-built quasi-solid-state polymer electrolytes

Abstract

Lithium metal batteries (LMBs) with high theoretical capacity are a promising candidate of high-energy density rechargeable batteries. However, the practical applications of LMBs were challenged by uncontrolled dendrite growth and the leakage of liquid electrolytes. In this paper, a new kind of quasi-solid polymer electrolyte (QSPE) was designed, which was achieved by in situ polymerizing of 1,3-dioxolane (DOL) with the aid of a multifunctional Mg(OTf)₂ additive. Mg(OTf)₂ was demonstrated to be not only an efficient catalyst for the polymerization of DOL, but also an effective additive to induce uniform deposition of Li, and the interfacial stability and ionic conductivity were further improved by introducing fluoroethylene carbonate (FEC). As a result, the Mg–PDOL–FEC electrolyte showed a high room-temperature ionic conductivity of 0.5 × 10⁻³ S cm⁻¹, an electrochemical window of 4.3 V, and a large Li⁺ transference number of 0.61. Sequentially, the Li–Li symmetric cells based on the Mg–PDOL–FEC electrolyte show no evident polarization enlargement after 1600 h cycling under a current density of 0.5 mA cm⁻², and both Li|Mg–PDOL–FEC|LiFePO₄ and high-voltage Li|Mg–PDOL–FEC|LiCoO₂-CIE cells exhibit excellent electrochemical performance at room temperature. This work provides an accessible approach to the large-scale application of LMBs with improved safety and prolonged lifetime.