Strain-regulated Gibbs free energy enables reversible redox chemistry of chalcogenides for sodium ion batteries.

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 MoSe 2 (TS-MoSe 2 ) 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 Na 2 Se, thereby leading to a decreased ΔG of the redox chemistry between Mo/Na 2 Se and MoSe 2 . Ex situ and in situ experiments revealed that, unlike the unstrained MoSe 2 , TS-MoSe 2 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.