The replacement of conventional liquid electrolytes with solid electrolytes has the potential to safely enable energy-dense Li-metal anodes. Because of the challenges surrounding solid-solid interfaces, it is crucial to better understand the Li-metal-solid-electrolyte interface. This work utilizes stack pressure to correlate mechanics with the electrochemical behavior of Li-electrolyte cells during galvanostatic cycling. Symmetric cells are constructed using Li 7-La 3 Zr 2 O 12 and tested using AC and DC techniques under dynamic stack pressure conditions. It is demonstrated that significant polarization occurs during galvanostatic cycling at a current-dependent ''critical stack pressure.'' Using reference electrodes, this effect is isolated to the Li stripping electrode. This suggests that at low pressures, the Li stripping rate exceeds the rate at which mechanical deformation replenishes the interface, inducing the formation of voids and ultimately increasing resistance. This analysis not only motivates the need for further understanding of the Li-metal-solid-electrolyte interface but also provides guidelines for the future design of all-solid-state batteries.

Compliant battery design strategy for wearable power sources with high degree of flexibility and stretchability.

The coupling of solid-state electrolytes with a Li-metal anode and state-of-the-art (SOA) cathode materials is a promising path to develop inherently safe batteries with high energy density (>1000 Wh L−1). However, integrating metallic Li with solid-electrolytes using scalable processes is not only challenging, but also adds extraneous volume since SOA cathodes are fully lithiated. Here we show the potential for “Li-free” battery manufacturing using the Li7La3Zr2O12 (LLZO) electrolyte. We demonstrate that Li-metal anodes >20 μm can be electroplated onto a current collector in situ without LLZO degradation and we propose a model to relate electrochemical and nucleation behavior. A full cell consisting of in situ formed Li, LLZO, and NCA is demonstrated, which exhibits stable cycling over 50 cycles with high Coulombic efficiencies. These findings demonstrate the viability of “Li-free” configurations using LLZO which may guide the design and manufacturing of high energy density solid-state batteries.

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All‐solid‐state batteries with an alkali metal anode have the potential to achieve high energy density. However, the onset of dendrite formation limits the maximum plating current density across the solid electrolyte and prevents fast charging. It is shown that the maximum plating current density is related to the interfacial resistance between the solid electrolyte and the metal anode. Due to their high ionic conductivity, low electronic conductivity, and stability against sodium metal, Na‐β″‐alumina ceramics are excellent candidates as electrolytes for room‐temperature all‐solid‐state batteries. Here, it is demonstrated that a heat treatment of Na‐β″‐alumina ceramics in argon atmosphere enables an interfacial resistance <10 Ω cm2 and current densities up to 12 mA cm−2 at room temperature. The current density obtained for Na‐β″‐alumina is ten times higher than that measured on a garnet‐type Li7La3Zr2O12 electrolyte under equivalent conditions. X‐ray photoelectron spectroscopy shows that eliminating hydroxyl groups and carbon contaminations at the interface between Na‐β″‐alumina and sodium metal is key to reach such values. By comparing the temperature‐dependent stripping/plating behavior of Na‐β″‐alumina and Li7La3Zr2O12, the role of the alkali metal in governing interface kinetics is discussed. This study provides new insights into dendrite formation and paves the way for fast‐charging all‐solid‐state batteries.