Accelerated Short Circuiting in Anode-Free Solid-State Batteries Driven by Local Lithium Depletion

Anode-free solid-state batteries (SSBs), which have no anode active material, can exhibit extremely high energy density (approximate to 1500 Wh L-1). However, there is a lack of understanding of the lithium plating/stripping mechanisms at initially lithium-free solid-state electrolyte (SSE) interfaces because excess lithium metal is often used. Here, it is demonstrated that commercially relevant quantities of lithium (>5 mAh cm(-2)) can be reliably plated at moderate current densities (1 mA cm(-2)) using the sulfide SSE Li6PS5Cl. Investigations of lithium plating/stripping mechanisms, in conjunction with cryo-focused ion beam (FIB) imaging, synchrotron tomography, and phase-field modeling, reveal that the cycling stability of these cells is fundamentally limited by the nonuniform presence of lithium during stripping. Local lithium depletion causes isolated lithium regions toward the end of stripping, decreasing electrochemically active area and resulting in high local current densities and void formation. This accelerates subsequent filament growth and short circuiting compared to lithium-excess cells. Despite this degradation mode, it is shown that anode-free cells exhibit comparable Coulombic efficiency to lithium-excess cells, and improved resistance to short circuiting is achieved by avoiding local lithium depletion through retention of thicker lithium at the interface. These new insights provide a foundation for engineering future high-energy anode-free SSBs.

Automated summary

Anode-free solid-state batteries demonstrate high energy density, and commercially relevant quantities of lithium can be plated reliably at moderate current densities using a sulfide solid-state electrolyte. The cycling stability of these batteries is limited by the nonuniform presence of lithium during stripping, leading to high local current densities and void formation. However, thicker lithium at the interface can improve resistance to short circuiting.