Anion manipulation for breaking through 3.0 V of aluminium–graphite batteries

Aluminium-graphite batteries offer low cost and intrinsic high safety. However, the voltage window mostly remains limited because conventional chloroaluminate ionic-liquid electrolytes with Lewis-acidic Al2Cl7−([AlCl3–AlCl4]−) anions are intrinsically moisture-sensitive and unstable beyond 2.5 V. To extend the voltage window, a polytetrafluoroethylene/AlF3 framework‑confined, fluorine-rich chloroaluminate ionic-liquid composite quasi-solid-state electrolyte cosolvated with 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether is designed for constructing stable aluminium-graphite batteries with a cut-off voltage of 3.0 V. With the presence of AlF3, the Al2Cl7− is regulated through AlF3-associated chloroaluminate interactions, which reduces its activity and suppresses its electrochemical decomposition in the range of 2.5–3.0 V. Meanwhile, the fluorinated ether coordinates with the AlCl3 units in Al2Cl7− and promotes the formation of a fluorine-rich artificial interface on the graphite, essentially improving the electrochemical stability via alleviating electrochemical decomposition of AlCl4− up to 3.0 V. Furthermore, ion transport channels could be well maintained during large mechanical deformation induced by anion-intercalation/deintercalation of graphite interlayer. Therefore, the Al|electrolyte|graphite cells deliver discharge capacity beyond 137 mAh g−1 up to 3.0 V (specific current: 5.0 A g−1) (compared to 64 mAh g−1, charged up to 2.5 V at 5.0 A g−1) along with stable cycles beyond 35,000, demonstrating long-term high-voltage operation in rechargeable aluminium–graphite batteries. Aluminium–graphite batteries are limited by electrolyte decomposition above 2.5 V. Here, authors regulate chloroaluminate anions with a fluorine-rich, framework-confined quasi-solid-state electrolyte, enabling stable 3.0 V operation for Al | |Graphite cells.