γ-Mo₂N Nanobelts with Controlled Grain and Mesopore Sizes as High-Performance Anodes for Lithium-Ion Capacitors

A lithium-ion capacitor (LIC) is a device with the dual characteristics of lithium-ion batteries (LIBs) and supercapacitors (SCs), but there is a serious dynamic imbalance between the positive and negative materials. Here, in the research work, γ-Mo2N nanobelts with different grain sizes and mesopore sizes have been prepared to study deeply the electrode dynamics. The results reveal that the reduction of the grain size and mesopore size will lead to a sharp increase in capacitance contribution, excellent rate performance, and structural stability. This is attributed to that the reduction of the grain/mesopore size will promote the oxidation–reduction reaction of the electrode material. Considering this advantage, a high-performance LIC is constructed with a γ-Mo2N-700 anode and a hierarchical porous activated carbon (AC) cathode. This device can achieve the highest energy density of 93.81 Wh kg–1 and a power density of 7513.68 W kg–1, and the excellent specific capacity of up to 87.16% is maintained after 1000 cycles. This work mainly introduces the two parameters of grain size and mesopore size to explore the structure–activity relationship that affects the performance of LIC anode materials, which provides an analysis method for the difference in lithium storage performance.