A high performance vanadium oxide@molybdenophosphate composite for 2.2 V aqueous symmetric supercapacitors

Aqueous energy storage devices hold great promise for smart electric grids and electric vehicles due to their high ionic conductivity, high safety and low cost, but are often limited by electrode materials with rather low voltage window and sluggish mass transport kinetics through thicker electrode materials. Herein, we design a vanadium oxide@molybdenophosphate composite on oxygen-functionalized carbon substrate with wide potential range of -1.2 to 1.0 V vs. SCE and highly enhanced electron/ion delivery kinetics. The oxygen-functionalized 3D carbon scaffold can bind strongly with VOx through V-O-C bonding, leading to fast electron transport within electrodes and effective suppresses structural pulverization of oxides. The molybdenophosphate coating layer improves not only the electronic structure and electrical conductivity of VOx but also the charge storage performance of the composite. Due to those effective interactions, the vanadium oxide@molybdenophosphate composite exhibits an outstanding capacitance of 3,954 mF cm-2 and good rate capability. Realistically, the assembled symmetric supercapacitor device can operate stably with a voltage window of 2.2 V and delivers extraordinary energy density of 7.56 mWh cm-3, which is superior to most advanced supercapacitors. Arbitrary series connection also practices the feasibility of the device as a stand-by power supply for 3C products such as tablets. This innovative synergistic strategy opens up new opportunities for aqueous energy storage.