Two-dimensional MXene has become popular in the energy world because of its fast energy storage capability. But unstable voltage output limits applications. A research team developed battery-like electrochemical Nb2CTx MXene electrodes with stable voltage output and high energy density using a high-voltage scanning strategy.
MXene is a large family of two-dimensional nanomaterials and has been the research focus of 2D materials in the energy storage field in the past decade. Because of excellent electronic conductivity and large surface area, MXene features fast surficial redox and demonstrates high-rate energy storage.
But the biggest challenge of MXene energy storage is that all reported MXene electrodes lack a distinct discharge voltage plateau, which means they discharge with a rapidly descending output voltage. This shortcoming deteriorates Mxene’s energy density and the stable energy output at desired high voltage regions, leading to limited energy density, usually less than 100 Wh kg-1.
To overcome the problem of unstable energy output, the research team developed battery-type Nb 2CTx MXene electrodes. The team revealed completely different electrochemical properties of the Nb 2CTx MXene electrode by regulating the voltage windows from 2.0 V to 2.4 V. Under high-voltage scanning up to 2.4 V, the Nb2CTx MXene electrode showed typical battery-type features different from the one under low voltage and other previously reported MXene systems.
The team discovered that the Nb2CTx/ Zn battery could exhibit superior rate capability, durable cyclic performance, and high energy density under high-voltage scanning. More importantly, they succeeded in equipping MXene with a flat and stable discharge plateau of 1.55 V to boost energy densities. A high-level energy density among all aqueous Mxene electrodes of 146.7 Wh kg-1 with 63 percent contribution from the plateau region was also obtained.
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