Spinel Li 4 Mn 5 O 12 as 2.0 V Insertion Materials for Mg‐Based Hybrid Ion Batteries

With the increasing demand for electrical energy storage, a new Mg−Li hybrid battery with Mg anode is regarded as a promising candidate because of low cost, high volumetric capacity, and dendrite‐free nature of the Mg anode. Nevertheless, the characteristics of low operation voltage and low energy density for Mg−Li hybrid batteries hinders their widespread application, owing to limited reversible cathodes. To overcome these issues, a highly reversible fast Li + insertion cathode with high voltage is an effective strategy to realize high‐energy‐density Mg−Li hybrid batteries. Herein, we develop the 2 V high‐voltage spinel Li 4 Mn 5 O 12 cathode material with unique nano‐/microspheres, using a novel low‐temperature method, offering a short Li‐diffusion path and sufficient transport channels for electrolyte penetration into the electrode. For the first time, we demonstrate the feasibility of the spinel Li 4 Mn 5 O 12 nano‐/microspheres with hierarchical architecture as a cathode for 2 V hybrid Mg−Li batteries. It exhibits a reversible specific capacity of 155 mAh g −1 and a long discharge voltage platform exceeding 2.0 V (vs. Mg / Mg 2+ ) coupled with high energy density of 326 Wh kg −1 at a current density of 0.1 C (1 C=163 mA g −1 ). Our results pave the way of constructing new hybrid Mg−Li batteries with high voltage and high energy density.