A 3-V high-voltage and long-life magnesium-potassium hybrid ion battery

Magnesium-ion batteries are promising candidates for the next-generation energy storage systems. However, their development is restricted by the shortage of advanced insertion-type positive electrodes. Hybrid-ion batteries, which combine the facile alkali metal ions extraction/insertion of the cathode with the low-cost and high-safety magnesium metal anode, can harness the individual benefits of both electrodes and achieve satisfactory electrochemical performance. We present a high-performance magnesium-potassium hybrid ion battery utilizing a magnesium-potassium hybrid ion electrolyte, a magnesium metal anode, and a Prussian blue analogue cathode. The battery exhibits a discharge voltage of up to 3.0 V and delivers a reversible specific capacity of 120 mAh/g, resulting in an impressive energy density of 360 Wh/kg (based on the cathode mass only). Moreover, the battery demonstrates exceptional cycling stability, maintaining a capacity retention rate of 96% after 500 charge–discharge cycles at a current density of 50 mA/g. The reaction mechanism and energy storage mechanism of the hybrid ion battery were studied using various electrochemical testing methods and X-ray diffraction analysis. This work may provide new ideas and inspire the effort for the advancement of superior magnesium hybrid ion batteries.