Recent Progress on Polymer Solid Electrolytes for Lithium Metal Batteries

Abstract

Lithium metal is considered an ideal negative electrode material for its highest theoretical specific capacity and lowest redox potential. However, traditional lithium metal batteries have faced thorny challenges, primarily due to the growth of lithium dendrites and utilization of leaky, flammable organic liquid electrolyte, which would lead to battery failure and potential safety hazards. Replacing liquid electrolyte with solid-state electrolyte comes out to be a promising solution to the issues above. Recently, polymer solid electrolytes have garnered significant attention for their lightweight, safety, designable structure and excellent mechanical properties, which could restrain the uncontrollable growing of lithium dendrites. However, the high crystallinity and the resultant low ion conductivity at room temperature have impeded their widespread commercialization. Significant efforts have been directed towards the development of polymer solid electrolytes with superior performance. Herein, the recent development of polymer solid electrolyte is reviewed and summarized, including polyether polymers, polycarbonate polymers, fluorinated polymers, poly(ionic liquid) polymers, and single ion conductive polymers. Each of these polymer solid electrolytes offers unique advantages and challenges. The respective properties of different polymer electrolytes and the influence on the electrochemical performance are compared and discussed in detail. This article also focuses on the progress in structural designs and the innovation in synthesis process for different polymer matrixes in order to improve the ion conductivity at room temperature. For structural designs, grafting kinds of polar groups to the matrix structure, or designing various types of chain structures can reduce crystallinity, and thus enhance the ion transport. In addition to the conventional solution-casting method and phase inversion technique, electrospinning method, UV coating and other in-situ processes are utilized in the preparation of polymer solid electrolytes. Finally, in this paper, the existing fundamental research challenges and practical application issues associated with polymer solid electrolytes are thoroughly discussed. It is our sincere hope that this review will offer insights and references for the design, synthesis, and development of novel polymer solid electrolytes, which holds significant promise for electrochemical performance enhancement and safe operation of all-solid-state lithium metal batteries.