A medium-entropy transition metal oxide cathode for high-capacity lithium metal batteries.

The limited capacity of the positive electrode active material in non-aqueous rechargeable lithium-based batteries acts as a stumbling block for developing high-energy storage devices. Although lithium transition metal oxides are high-capacity electrochemical active materials, the structural instability at high cell voltages (e.g., >4.3 V) detrimentally affects the battery performance. Here, to circumvent this issue, we propose a LiNiMnO (0 < x < 4) material capable of forming a medium-entropy state spinel phase with partial cation disordering after initial delithiation. Via physicochemical measurements and theoretical calculations, we demonstrate the structural disorder in delithiated LiNiMnO, the direct shuttling of Li ions from octahedral sites to the spinel structure and the charge-compensation Mn/Mn cationic redox mechanism after the initial delithiation. When tested in a coin cell configuration in combination with a Li metal anode and a LiPF-based non-aqueous electrolyte, the LiNiMnO-based positive electrode enables a discharge capacity of 314.1 mA h g at 100 mA g with an average cell discharge voltage of about 3.2 V at 25 ± 5 °C, which results in a calculated initial specific energy of 999.3 Wh kg (based on mass of positive electrode's active material).