As a promising anode material in supercapacitors, vanadium nitride has been widely concerned due to its ultra‐high theoretical specific capacitance. However, its routine test capacitance value is still far from the theoretical value and its energy storage mechanism is controversial. In order to solve these two key problems, here we prepare interplanar spacing expanded vanadium nitride materials with different impurity atoms intercalation from two anionic precursors of vanadium‐based metal organic frameworks with different functional groups. The obtained vanadium nitride reaches a higher specific capacitance; and further, through ex situ X‐Ray diffraction and in situ Raman, the charge storage of vanadium nitride is contributed by two processes: the first benefit is from the K⁺ de/intercalation in the interplanar spacing, and the other one is derived from the redox reaction with OH⁻ by adsorption on surface. Furthermore, both of the first principle calculation and extended experiments support this idea. We believe that such detailed research on the energy storage mechanism can provide a clear idea for the application of metal nitrides in supercapacitors and other energy storage devices.

Tunnel-structured Na_0.44MnO₂ (NMO) has been extensively studied as a potential cathode for sodium-ion batteries (SIBs) due to its favorable cycling endurance, cost-effectiveness, environmental benignity, and notable air-moisture stability. However, limitations, such as sluggish ion diffusion kinetics, an insufficient Na⁺ storage capacity, and an unsatisfactory Jahn–Teller effect, impede its widespread application. To address these problems, this study proposes a co-doping strategy that involves the simultaneous introduction of a cation and an anion. The optimized cathode Na_0.44Mn_0.99Ni_0.01O_1.985F_0.015 demonstrates remarkable rate capabilities with average discharge capacities of 136.2, 133.0, 129.6, 124.0, 115.9, and 95.8 mAh g⁻¹ under current rates ranging from 0.1 to 5 C. Furthermore, it also exhibits exceptional long-term cyclability, retaining 86.5% and 89.4% capacity retention at 1 and 5 C after 200 and 400 cycles, respectively, accompanied by nearly 100% Coulombic efficiency. A comprehensive structural characterization and experimental analysis reveal that the synergistic incorporation of Ni and F can effectively adjust the lattice parameters and alleviate the Jahn–Teller distortion of the NMO cathode, thereby resulting in enhanced structural integrity, rapid ion transfer dynamics, and excellent sodium storage performance. Consequently, this investigation establishes a significant approach for optimizing tunnel-phase Mn-based cathodes through the synergistic effect of cation and anion co-doping, which promotes the practical implementation of advanced SIBs.

Tunnel-type Na_0.44MnO₂ is extensively regarded as an appealing cathode for sodium-ion batteries due to its cost-effectiveness and excellent cycling performance. However, low theoretical capacity, resulting from insufficient Na⁺ storage sites, hinders its practical application. Herein, the strategy of constructing a tunnel-phase-dominated layered/tunnel biphasic compound was proposed via trace W-substitution and the co-precipitation method. Experimental analysis reveals that W-introduction can effectively redistribute electronic configuration, induce tunnel-to-layered structure evolution, accelerate Na⁺ (de)intercalation kinetics, and enhance structural stability. The optimized layered/tunnel Na_0.44Mn_0.99W_0.01O₂ cathode integrates the superiorities of the layered and tunnel structures, delivering a high capacity of 153.1 mAh g⁻¹ at 0.1 C and outstanding cycle life, with 71% capacity retention over 600 cycles at 5 C. Significantly, the full cell assembled with the Na_0.44Mn_0.99W_0.01O₂ cathode and a commercial hard carbon anode exhibits a competitive energy density of 183.2 Wh kg⁻¹, along with a remarkable capacity retention of 75.5% over 200 cycles at 1 C. This work not only highlights the superior sodium storage performance of biphasic composites owing to the synergistic effects between layered and tunnel structures, but also unveils new possibilities for constructing high-performance hybrid cathodes that predominantly consist of the tunnel phase using a suitable design strategy.