Oxygen Defects in β-MnO2 Enabling High-Performance Rechargeable Aqueous Zinc/Manganese Dioxide Battery

Abstract

Rechargeable aqueous Zn/manganese dioxide (Zn/MnO 2 ) batteries are attractive energy storage technology owing to their merits of low cost, high safety, and environmental friendliness. However, the b-MnO 2 cathode is still plagued by the sluggish ion insertion kinetics due to the relatively narrow tunneled pathway. Furthermore, the energy storage mechanism is under debate as well. Here, b-MnO 2 cathode with enhanced ion insertion kinetics is introduced by the efficient oxygen defect engineering strategy. Density functional theory computations show that the b-MnO 2 host structure is more likely for H + insertion rather than Zn 2+ , and the introduction of oxygen defects will facilitate the insertion of H + into b-MnO 2 . This theoretical conjecture is confirmed by the capacity of 302 mA h g À1 and capacity retention of 94% after 300 cycles in the assembled aqueous Zn/ b-MnO 2 cell. These results highlight the potentials of defect engineering as a strategy of improving the electrochemical performance of b-MnO 2 in aqueous rechargeable batteries.

Defect Engineering in Manganese‐Based Oxides for Aqueous Rechargeable Zinc‐Ion Batteries: A Review

“…[ 65 ] In addition to our report, the effect of oxygen vacancy on β‐MnO 2 was investigated recently by Han et al using DFT calculations and experimental results. [ 66 ] The kinetics of Zn 2+ and H + co‐insertion into β‐MnO 2 with/without oxygen vacancy were proved to be distinct. The energy needed for H + was ≈1.63 eV lower than that of Zn 2+ when to react with the neighboring O atoms and to insert into the perfect β‐MnO 2 .…”

“…Reproduced with permission. [ 66 ] Copyright 2019, Elsevier. c) Energy profiles of Zn diffusion within ZnMn 2 O 4 and Oxygen‐extracted ZnMn 2 O 4 .…”

“…[ 65 ] Similarly, Han and co‐workers introduced oxygen vacancy into β‐MnO 2 involved with a series of calcination and reduction process using NaBH 4 . [ 66 ] Zhang and co‐workers successfully introduced oxygen vacancy into ZnMn 2 O 4 via the extraction of oxygen anions from ZnMn 2 O 4 through heating treatment in the presence of a reducing atmosphere (H 2 ) at 200 °C. [ 67 ] Fang et al obtained an oxygen‐deficient K 0.8 Mn 8 O 16 using an annealing treatment method at 800 °C.…”

“…Han et al demonstrated that the oxygen vacancies in β‐MnO 2 not only increased the ion absorption sites but also opened up extra channels for ion insertion to achieve higher reaction activity and capacity. [ 66 ] They then applied oxygen‐deficient β‐MnO 2 for ZIBs application and found that the conversion reaction between H + and MnO 2 is the way to storage energy. As shown in Figure 9c, the [MnO 6 ] polyhedron walls were opened up by oxygen vacancy, which created extra channels for the ions insertion into β‐MnO 2 .…”

“…Reproduced with permission. [ 66 ] Copyright 2019, Elsevier. d) Mechanism of Zn 2+ insertion/extraction in Mn‐deficient MnO and comparison of the Ragone plot with other reported cathodes for aqueous ZIBs.…”