Fast-charging aluminium-chalcogen batteries resistant to dendritic shorting

Although batteries fitted with a metal negative electrode are attractive for their higher energy density and lower complexity, the latter making them more easily recyclable, the threat of cell shorting by dendrites has stalled deployment of the technology^1,2. Here we disclose a bidirectional, rapidly charging aluminium-chalcogen battery operating with a molten-salt electrolyte composed of NaCl-KCl-AlCl₃. Formulated with high levels of AlCl₃, these chloroaluminate melts contain catenated Al_nCl_3n+1^- species, for example, Al₂Cl₇^-, Al₃Cl₁₀^- and Al₄Cl₁₃^-, which with their Al-Cl-Al linkages confer facile Al³⁺ desolvation kinetics resulting in high faradaic exchange currents, to form the foundation for high-rate charging of the battery. This chemistry is distinguished from other aluminium batteries in the choice of a positive elemental-chalcogen electrode as opposed to various low-capacity compound formulations^3-6, and in the choice of a molten-salt electrolyte as opposed to room-temperature ionic liquids that induce high polarization^7-12. We show that the multi-step conversion pathway between aluminium and chalcogen allows rapid charging at up to 200C, and the battery endures hundreds of cycles at very high charging rates without aluminium dendrite formation. Importantly for scalability, the cell-level cost of the aluminium-sulfur battery is projected to be less than one-sixth that of current lithium-ion technologies. Composed of earth-abundant elements that can be ethically sourced and operated at moderately elevated temperatures just above the boiling point of water, this chemistry has all the requisites of a low-cost, rechargeable, fire-resistant, recyclable battery.