Li5.5PS4.5Cl1.5-Based All-Solid-State Battery with a Silver Nanoparticle-Modified Graphite Anode for Improved Resistance to Overcharging and Increased Energy Density

All-solid-state lithium batteries (ASSLBs) are attracting tremendous attention due to their improved safety and higher energy density. However, the use of a metallic lithium anode poses a major challenge due to its low stability and processability. Instead, the graphite anode exhibits high reversibility for the insertion/deinsertion of lithium ions, giving ASSLBs excellent cyclic stability but a lower energy density. To increase the energy density of ASSLBs with the graphite anode, it is necessary to lower the negative/positive (N/P) capacity ratio and to increase the charging voltage. These strategies bring new challenges to lithium metal plating and dendrite growth. Here, a nano-Ag-modified graphite composite electrode (Ag@Gr) is developed to overcome these shortcomings for Li_5.5PS_4.5Cl_1.5-based ASSLBs. The Ag@Gr composite exhibits a strong ability to inhibit lithium metal plating and fast lithium-ion transport kinetics. Ag nanoparticles can accommodate excess Li, and the as-obtained Li-Ag alloy enhances the kinetics of the composite electrode. The ASSLB with the Li(Ni_0.8Co_0.1Mn_0.1)O₂ cathode and Ag@Gr anode achieves an energy density of 349 W h kg^-1. The full cell using Ag@Gr with an N/P ratio of 0.6 also highlights the rate performance. This work provides a simple and effective method to regulate the charge transport kinetics of graphite anodes and improve the cyclic performance and energy density of ASSLBs.