Effect of homojunction structure in boosting sodium-ion storage: The case of MoO2

High-efficiency sodium-ion batteries (SIBs) are in great demand for energy storage applications, which are dominated by the Na' storage performance of electrode materials. Here, a one-pot solvothermal method is developed to construct amorphous/crystalline MoO2 (a/c-MoO2) homojunction for boosting Na' storage. Theoretical simulations signify that electrons redistribute at the homogenous interface of a/c-MoO2, resulting in an inbuilt driving force to easily adsorb charge carriers and promote the electron/ion transfer ability. Relying on its crystallographic superiorities, the a/c-MoO2 homojunction with high Na adsorbability (-1.61 eV) and low Na diffusion energy barrier (0.519 eV) achieves higher capacity (307 mA h g-1 at 0.1 A/g), better rate capability and cycling stability than either a-MoO2 or c-MoO2 counterpart. Combining in-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) techniques, the 'adsorption-insertion-conversion' mechanism is well established for Na' storage of MoO2. Our work opens new opportunities to optimize electrode materials via crystallographic engineering for efficient Na' storage, and helps to better understand the effects of homojunction structure in enhanced electrochemical performance. (c) 2022 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

Researchers developed a one-pot solvothermal method to construct an amorphous/crystalline MoO2 (a/c-MoO2) homojunction for high-efficiency sodium-ion batteries. Theoretical simulations showed that electrons redistributing at the homogeneous interface of a/c-MoO2 facilitated charge carrier adsorption and electron/ion transfer. The a/c-MoO2 homojunction exhibited superior Na adsorbability (-1.61 eV) and low Na diffusion energy barrier (0.519 eV), leading to higher capacity, rate capability, and cycling stability compared to a-MoO2 or c-MoO2. Mechanistic studies using in-situ XRD and ex-situ XPS techniques revealed the 'adsorption-insertion-conversion' mechanism for Na' storage of MoO2. This work provides new opportunities for optimizing electrode materials through crystallographic engineering and enhances understanding of the effects of homojunction structure on electrochemical performance.