Defect regulated spinel Mn3O4 obtained by glycerol–assisted method for high–energy–density aqueous zinc–ion batteries

Abstract

Rechargeable aqueous zinc–ion batteries (RAZIBs) show great potential as a competitive candidate for reliable energy storage by virtue of cost–effectiveness, high safety, and environmental friendliness. However, unsatisfactory cycle stability of cathode material impedes the development of high–performance RAZIBs. This study reveals a strategic polyol–mediated process by using glycerol as the solvent for solvothermal reaction. After heat treatment in air, Mn–deficient Mn3O4 spinel (D–Mn3O4) can be obtained with rich Mn valence states (Mn2+/Mn3+/Mn4+), expanded crystal structure, high surface area, and good electrolyte compatability. Compared to well–crystallized Mn3O4, the presence of manganese vacancies in D–Mn3O4 enables lower charge–transfer resistance (86.0 vs 196.5 Ω), reduced activation energy for ion insertion (30.9 vs 50.4 kJ mol−1), and boosted solid–state ion diffusivity (9.45 × 10−12 vs 4.61 × 10−14 cm2 s−1). Therefore, D–Mn3O4 exhibits promising electrochemical performance with high capacity (284 mAh g−1), high specific energy (388.5 Wh kg−1) and stable cycle retention (87% after 200 cyclesat 0.3 A g−1). On the contrary, the well–crystallized Mn3O4 sample suffers from severe capacity fading with only 48% capacity retention. Moreover, the specific energies obtained after 200 cycles are 336.1 and 166.0 Wh kg−1 for D–Mn3O4 and Mn3O4, respectively. The drastic differences between the electrochemical performance of D–Mn3O4 and Mn3O4 manifest that the existing manganese vacancies in Mn3O4 spinel structure enhance energy storage capability.