Highly Reversible Chevrel Phase Mo6Se8 Cathode with Low Voltage Hysteresis for Rechargeable Aluminum Batteries

Rechargeable aluminum (Al) batteries have attracted considerable interest as potential large-scale energy storage technologies due to the abundance, high theoretical capacity, and high safety of Al. We report here a highly reversible Al-Mo6Se8 prototype cell with low discharge-charge hysteresis (approximately 50 mV under 30 mA g-1 at 50 °C), ultra-flat discharge plateau, and exceptional cycle stability: the reversible capacity retaining at a steady 77 mA h g-1 after more than 1800 cycles. The Al intercalation-extraction mechanism is probed with ex situ and operando XRD techniques, revealing the reversible intercalation reaction from Mo6Se8 to Al4/3Mo6Se8. The stable electrochemical performance and unambiguous intercalation mechanism of the Al-Mo6Se8 system provide an alternative for beyond-lithium battery technologies.