Unraveling the Highly Reversible Lithiation/Delithiation of Aluminum in Inorganic All-Solid-State Lithium Batteries

The all-solid-state lithium battery (ASSLB) is widely regarded as one of the most promising battery systems for the future owing to its high energy density and enhanced safety. However, the spontaneous reaction between the lithium metal and solid-state electrolytes (SSEs) results in the formation of lithium dendrites, which impedes further progress in the use of lithium metal anodes in ASSLBs. Li-In-based anodes have been widely used to address Li anode/SSE interfacial challenges; however, their synthesis and cell fabrication compromise the applicability of ASSLBs. Herein, we explore aluminum as an anode in ASSLBs by dry mixing and investigate its compatibility with two typical types of SSEs: halide-based Li₃InCl₆ and sulfide-based Li_5.4PS_4.4Cl_1.6, which show distinguished electrochemical behaviors. In halide-based ASSLBs, the continuous decomposition and reduction of Li₃InCl₆ cause the accumulation of indium metal at the interface between the Li₃InCl₆ SSE and the aluminum anode, which blocks Li-ion transport, causing cell impedance increase and rapid cell failure. By sharp contrast, a redox-active interphase is formed between the sulfide SSE and aluminum anode during the electrochemical lithiation/delithiation process. The interphase consisting of highly reversible redox intermediates addresses the limiting factor of the poor reversibility of Li-Al alloying, which accounts for the conventionally low Coulombic efficiency of Al anodes. This work aims to develop Al anodes for ASSLBs and sheds light on the significance of redox-active interphase in enabling highly reversible anodes in ASSLBs.