Modulating vacancies concentration ratio of cationic and anionic in WO3 for driving high performance magnesium ions storage

Vacancy engineering is an efficient strategy for optimizing the electrochemical performance of electrodes for energy storage devices. However, it is still a challenge for modulating the concentration ratio of cationic vacancies and anionic vacancies in the electrode via a simple method for enhancing the electrochemical performance. Herein, cationic (W) vacancies and anionic (O) vacancies are constructed in WO3 simultaneously, and the concentration ratio of W and O vacancies is modulated by adding various content of glucose to regulate the W vacancies concentration via at a fixed O vacancies concentration. The characterization and DFT results confirm that moderate concentration ratio of W and O vacancies would not only expose more active sites, enhance the electronic conductivity and electrostatic potential, but also inhibit the vacancies gathering to maintain structural stability. In addition, the O□O bonding induced via moderate content of W vacancies owns rich-anionic environment to adsorb more Mg2+ as well as reduces electrostatic repulsive-force between Mg2+ and cationic lattice to facilitate Mg2+ diffusion. Therefore, the moderate concentration ratio of W and O vacancies make VW-O/WO3–1.0 cathode achieve high specific capacity of about 100 mAh g−1 at 50 mA g−1, excellent rate capacity of 37.7 mAh g−1 at 500 mA g−1 and ultralong cycling life about 1500 cycles. These findings raise the possibility for designing advanced electrodes through vacancy species and controllable concentration engineering.