Diphosphorus Center Derived from Polyoxometalate for High-Energy Lithium Storage of MXene Nanosheets

Two-dimensional titanium carbide (Ti3C2Tx) is a promising lithium storage anode material owing to high conductivity and larger redox sites. However, Ti3C2Tx exhibits lower specific capacitance in an organic system due to the passivation effect of surface terminals and also suffers from restacking issues with long-term cycles. Herein, the material composed of a molybdenum–phosphorus compound and Ti3C2Tx nanosheets is reported through thermal decomposition of polyoxometalate. The derived molybdenum phosphide provides greater free space to afford the volume change and facilitate lithium-ion transport. The unique diphosphorus centers are favorable to improving lithium storage capacity and electrochemical reaction. In addition, molybdenum oxide with abundant oxygen vacancies not only accelerates the electronic and ionic conductivity but also provides more active sites. The optimized 0.1PMA@Ti3C2Tx composite delivers a superior specific capacity of over 500 mAh g–1 at 30 mA g–1 and maintains the specific capacity of 155.6 mAh g–1 at 750 mA g–1 after 400 cycles. The lithium-ion capacitor based on the 0.1PMA@Ti3C2Tx anode material presents a wonderful energy density of 153.95 Wh kg–1 at a higher power density of 4696.8 W kg–1. This work provides a strategy for high-capacity lithium storage of MXene materials and opens up an idea for the application of polyoxometalates in lithium storage.