Mechanism, strategies, and characterizations of Li plating in solid state batteries

Abstract

Commercial lithium-ion batteries have inherent safety problems due to the usage of non-aqueous electrolyte as the electrolytes. The development of solid state lithium metal batteries is expected to solve these problems while achieving higher energy density. However, the problem of lithium plating still exists. This article reviews the deposition behavior of lithium metal anodes in solid-state batteries, and provides suggestions for high-energy-density and high-safety solid-state lithium batteries. This paper systematically summarizes the mechanism of Li deposition in polymers and inorganic solid state electrolytes, and discusses the strategies of controlling lithium deposition and preventing lithium dendrites and the characterization of Li metal anodes. In solid-state batteries, poor solid-solid contact between the electrolyte and the anode, defects, grain boundaries, cracks, pores, enhanced electric and ionic fields near the tip, and high electronic conductivity of the solid state electrolyte can all lead to lithium deposition, which may evolve into lithium dendrites. There are several strategies to control lithium deposition: 1). Use functional materials and structure design to induce uniform deposition of lithium, such as improving the solid state electrolyte/anode interfacial contact, using lithiophilic coatings or sites, and designing three-dimensional structure electrodes and solid state electrolytes. 2). Suppress the generation of lithium dendrites, such as limiting the free movement of anions in solid state electrolytes (especially polymer solid electrolytes), to reduce local space charge which induces lithium dendrites. In addition, optimizing the solid electrolyte synthesis process to reduce lithium dendrites caused by defects is also an important method. 3). Strategies for dendrites already formed are essential for safety concern. The dendritic deposition is one of the intrinsic properties of lithium. Thus, there is no guarantee that there will be no lithium dendrites, especially at high current density. Once lithium dendrites are formed, countermeasures are required. For example, improving the mechanical strength of solid state electrolytes, and using self-healing materials, structures, and cycling conditions are proposed to avoid safety hazards caused by lithium dendrites piercing. This article focuses on the control of lithium deposition. Suppressing lithium dendrites only solves a little problem of the application of lithium metal anodes. In the future, in order to use lithium metal as a negative electrode in practical all-solid-state batteries, many challenges need to be overcome, such as irreversible side reactions between lithium and other materials, safety and volume change of composite lithium anodes. In addition, in order to allow the laboratory's research results to be quickly transformed into applications, it is also necessary to establish battery design, assembly, and test standards that are in agreement with practical requirements. In short, all-solid-state lithium batteries still have a long way to go, but they have great potential for safe, high-performance, and low-cost energy storage systems in the future.