Prelithiated Ga₂O₃/C Nanocomposites as Self-Healing Host Materials for Stable Lithium Metal Anodes in Solid-State Batteries

To achieve safe and high energy density rechargeable batteries, it is essential to adopt lithium metal anodes (LMAs) in solid-state batteries (SSBs). Because, lithium metal has excellent electrochemical properties including both high theoretical capacity (3860 mAh/g) and exceptionally negative potential (-3.04 V vs. NHE), which provides for increasing energy density by reducing total space and/or weight of SSBs. However, Li dendrites or filaments growth caused by unstable interfacial reactions and contact between Li metal and solid electrolytes during electrochemical cycling are obstacles hindering solid-state Li-metal batteries.<br/>In the aspect of anodes engineering, rational design of 3D host materials decorated with lithiophilic sites is one of reasonable approach to suppress the growth of Li dendrites or filaments by effectively regulating Li deposition. Among the various lithiophilic materials, gallium (Ga) has been considered as a self-healing anode material due to its low melting point (29.8 °C). This unique property can facilitate form a conformal electrode-electrolyte interface in SSBs. However, its fluidic feature at close to room temperature, makes it difficult to realize nanostructured design.<br/>In this study, Ga₂O₃/C nanocomposites were simply synthesized via microwave-induced hydrothermal reaction for 20 min and subsequent carbonization. The nanocomposites exhibited that Ga₂O₃ nanodots with diameter of ~ 10 nm are densely embedded in thin carbon matrix. To evaluate stable Li plating ability of Ga₂O₃/C nanocomposites, coulombic efficiency (CE) was obtained in liquid electrolytes after specific prelithiation process. The composite electrodes presented low initial Li nucleation overpotential of 20.0 mV, and initial high CE was stably maintained over 200 cycles under the conditions of 1.0 mAh/cm² at 1.0 mA/cm². It could be confirmed by in-situ XRD analysis that the excellent performances of Ga₂O₃/C electrodes are attributed to prelithiation process resulting in lithiophilic Ga phase in electrodes. The effects of Ga phase on stable interface contact between electrode-solid electrolyte during electrochemical cycling were evaluated by controlling cell measurement temperature (above and below Ga melting point) at solid-state half-cell assembled by using PEO-based solid electrolytes. Furthermore, cell performances of carbon matrix without Ga₂O₃ were also compared at same temperature to identify the effects of cell operating temperature on PEO-based solid electrolytes in LMAs.