Storage mechanisms and improved strategies for manganese-based aqueous zinc-ion batteries

Layered porous Mn0.18V2O5@C with manganese and carbon provided by a metal-organic framework precursor as a cathode material for aqueous zinc-ion batteries

At present, vanadium-based cathodes for aqueous zinc-ion batteries (AZIBs) are limited by their slow reaction kinetics, poor electrical conductivity, and low capacity retention. To overcome these problems, here, we design a layered porous Mn0.18V2O5@C as the cathode material for AZIBs using a manganese-containing metal-organic framework as a template through a simple solvothermal method. Such an electrode delivers an excellent specific capacity (380 mA h g-1 at 0.1 A g-1) accompanied by superior cycling stability (about 85% capacity retention for 2000 cycles at 6 A g-1). The excellent electrochemical performance of Mn0.18V2O5@C is ascribed to the improved interface activity including smooth zinc ion transport, abundant ion reaction active sites and accelerated charge transfer resulting from the coordination of the porous structure, doped conductive carbon, and the stable channel structure derived from the pillar effect of doping manganese ions, preventing a premature collapse of the electrode structure. It is also revealed by structural evolution analysis that the residual zinc ions also combine with the original Mn0.18V2O5 to form a ZnxMnyV2O5 phase, which serves as an additional structural pillar and in the meantime, also participates in the following cycles. These favorable electrochemical results suggest that Mn0.18V2O5@C is a suitable cathode material for AZIBs.

Regulating the kinetics of zinc-ion migration in spinel ZnMn2O4 through iron doping boosted aqueous zinc-ion storage performance

Spinel ZnMn₂O₄ with a three-dimensional channel structure is one of the important cathode materials for aqueous zinc ions batteries (AZIBs). However, like other manganese-based materials, spinel ZnMn₂O₄ also has problems such as poor conductivity, slow reaction kinetics and structural instability under long cycles. Herein, ZnMn₂O₄ mesoporous hollow microspheres with metal ion doping were prepared by a simple spray pyrolysis method and applied to the cathode of aqueous zinc ion battery. Cation doping not only introduces defects, changes the electronic structure of the material, improves its conductivity, structural stability, and reaction kinetics, but also weakens the dissolution of Mn²⁺. The optimized 0.1 % Fe-doped ZnMn₂O₄ (0.1% Fe-ZnMn₂O₄) has a capacity of 186.8 mAh g^-1 after 250 charge-discharge cycles at 0.5 A g^-1 and the discharge specific capacity reaches 121.5 mAh g^-1 after 1200 long cycles at 1.0 A g^-1. The theoretical calculation results show that doping causes the change of electronic state structure, accelerates the electron transfer rate, and improves the electrochemical performance and stability of the material.

Boosting the capacity and stability of a MoO3 cathode via valence regulation and polypyrrole coating for a rechargeable Zn ion battery

Molybdenum trioxide (MoO₃) is emerging as a hugely competitive cathode material for aqueous zinc ion batteries (ZIBs) for its high theoretical capacity and electrochemical activity. Nevertheless, owing to its undesirable electronic transport capability and poor structural stability, the practical capacity and cycling performance of MoO₃ are yet unsatisfactory, which greatly blocks its commercial use. In this work, we report an effective approach to first synthesise nanosized MoO_3-x materials to provide more active specific surface areas, while improving the capacity and cycle life of MoO₃ by introducing low valence Mo and coated polypyrrole (PPy). MoO₃ nanoparticles with low-valence-state Mo and PPy coating (denoted as MoO_3-x@PPy) are synthesized via a solvothermal method and subsequent electrodeposition process. The as-prepared MoO_3-x@PPy cathode delivers a high reversible capacity of 212.4 mA h g^-1 at 1 A g^-1 with good cycling life (more than 75% capacity retention after 500 cycles). In contrast, the original commercial MoO₃ sample only obtains a capacity of 99.3 mA h g^-1 at 1 A g^-1, and a cycling stability of 10% capacity retention over 500 cycles. Additionally, the fabricated Zn//MoO_3-x@PPy battery obtains a maximum energy density of 233.6 W h kg^-1 and a power density of 11.2 kW kg^-1. Our results provide an efficient and practical approach to enhance commercial MoO₃ materials as high-performance cathodes for AZIBs.