Chain-Transported Hypercoordinated Chloroaluminate Electrolyte for Solid-State Aluminum-Ion Batteries

Aluminum-ion batteries (AIBs) have garnered significant attention due to their high safety and environmental compatibility. However, their practical development has been hindered by conventional liquid electrolytes, which suffer from a narrow electrochemical stability window and interfacial instability. Here, we develop a hypercoordinated chloroaluminate electrolyte (HCCAE) for low-cost and long-life solid-state AIBs, featuring a chain-assisted ion transport mechanism. Different from traditional ionic liquid electrolytes (ILs) that rely on AlCl₄^– and Al₂Cl₇^– for ion conduction, the HCCAE forms a network where chloride ions from minimal 1-ethyl-3-methylimidazolium chloride (EMIC) migrate through a hypercoordinated AlCl₃-rich framework, enabling a continuous, fast and stable solid-state conduction pathway [AlCl₃–(AlCl₃)_n–AlCl₃–AlCl₄^–]. The electrolyte exhibits ionic conductivity of 0.89 mS cm^–1, an electrochemical window of >2.6 V, and electrolyte–electrode stability with Al plating/stripping over 900 h. The full battery demonstrates excellent cycling performance over 2000 cycles with high Coulombic efficiency. This work provides insights into ion transport mechanisms in aluminum-based solid electrolytes, which helps to achieve low-cost, high-safety, and long-life AIBs.