Dendrite-Free Li5.5PS4.5Cl1.5-Based All-Solid-State Lithium Battery Enabled by Grain Boundary Electronic Insulation Strategy through In Situ Polymer Encapsulation

Sulfide-based all-solid-state lithium batteries (ASSLBs) have attracted unprecedented attention in the past decade due to their excellent safety performance and high energy storage density. However, the sulfide solid-state electrolytes (SSEs) as the core component of ASSLBs have a certain stiffness, which inevitably leads to the formation of pores and cracks during the production process. In addition, although sulfide SSEs have high ionic conductivity, the electrolytes are unstable to lithium metal and have non-negligible electronic conductivity, which severely limits their practical applications. Herein, a grain boundary electronic insulation strategy through in situ polymer encapsulation is proposed for this purpose. A polymer layer with insulating properties is applied to the surface of the Li_5.5PS_4.5Cl_1.5 (LPSC) electrolyte particles by simple ball milling. In this way, we can not only achieve a dense electrolyte pellet but also improve the stability of the Li metal anode and reduce the electronic conductivity of LPSC. This strategy of electronic isolation of the grain boundaries enables stable deposition/stripping of the modified electrolyte for more than 2000 h at a current density of 0.5 mA cm^-1 in a symmetrical Li/Li cell. With this strategy, a full cell with Li(Ni_0.8Co_0.1Mn_0.1)O₂ (NCM811) as the cathode shows high performance including high specific capacity, improved high-rate capability, and long-term stability. Therefore, this study presents a new strategy to achieve high-performance sulfide SSEs.