Manipulating the reversible redox chemistry of transition metal dichalcogenides for energy storage often faces great challenges as it is difficult to regulate the discharged products directly. Herein we report that tensile-strained MoSe2 (TS-MoSe2) can act as a host to transfer its strain to corresponding discharged product Mo, thus contributing to the regulation of Gibbs free energy change (ΔG) and enabling a reversible sodium storage mechanism. The inherited strain results in lattice distortion of Mo, which adjusts the d-band center upshifted closer to the Fermi level to enhance the adsorbability of Na2Se, thereby leading to a decreased ΔG of the redox chemistry between Mo/Na2Se and MoSe2. Ex situ and in situ experiments revealed that, unlike the unstrained MoSe2, TS-MoSe2 shows a highly reversible sodium storage, along with an evidently improved reaction kinetics. This work sheds light on the study on electrochemical energy storage mechanism of other electrode materials.

Improving Na‐ion diffusion kinetics is an effective strategy to boost the sodium storage performance of electrode materials for sodium ion batteries (SIBs). Herein, an oxygen vacancy engineering is reported to evidently enhance Na‐ion diffusion kinetics of Na3V2(PO4)3 and accordingly boost sodium storage performance. Na3V2(PO4)3/C with different molar contents of Cu doping (0%, 2.5%, 4%, 5%, and 6%) are synthesized using a simple sol–gel method followed by an annealing treatment. The experimental results show that Cu2+ successfully replaces the V3+ sites of Na3V2(PO4)3 and that does not change its phase composition. The introduction of Cu2+ not only results in the formation of V4+ to maintain charge balance, leading to a shorter VO bond, but also promotes the generation of oxygen vacancies and accordingly facilitates Na‐ion diffusion kinetics. As expected, the optimal sample displays a stable capacity of 111.4 mA h g−1 with capacity retention of 90.4% over 300 cycles at 1 C and a high rate capacity of 83.8 mA h g−1 at 20 C. The studies demonstrate that the Cu doping is favorable for the electrochemical enhancement of Na3V2(PO4)3, which provides a promising prospect for Na3V2(PO4)3 as a cathode for SIBs.

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