Ion/electron conductive layer with double-layer-like structure for dendrite-free solid-state lithium metal batteries

Solid-state lithium metal batteries (SSLMBs) promise high energy density and operational safety by using high-capacity Li metal anodes (LMAs) and nonflammable solid-state electrolytes (SSEs). However, the SSE/Li interface issues including high interface resistance, Li dendrite growth and volume changes seriously hinder the practical applications of SSLMBs. Herein, we employ a facile strategy to construct a high-performance composite lithium anode with ion/electron conductive network by introducing a fluoride ZnF2 into molten Li. Taking the typical SSE of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) as an example, the Li−ZnF2/LLZTO interface with a double-layer-like structure composed of LiF (close to LLZTO) and LiZn alloy (close to bulk Li) realizes intimate interface contact, stable electron/ion transport channels, uniform Li deposition, and Li dendrite growth suppression. The symmetric cells show a low interface resistance of 11.3 Ω cm2, a high critical current density of 1.3 mA cm−2, and superior cycling performance of 2000 h at 0.1 mA cm−2 or 1350 h at 0.4 mA cm−2 (25 °C). The SSLMBs paired with LiFePO4 and LiNi0.5Co0.2Mn0.3O2 show outstanding electrochemical performance. The key principles for the design of Li−MFx (M = Zn, Co, C, Al, etc.) anodes to form a double-layer-like conductive interface are proposed based on the control experiments. This work lays the foundation for development of high performance composite lithium anodes and practical application of high-energy-density SSLMBs.