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

Construction of high-performance aqueous zinc-ion batteries by guest pre-intercalation MnO2-based cathodes

In recent years, aqueous zinc ion batteries (AZIBs) with the benefits of high safety, low cost, high capacity and environmental protection, have broad development prospects in the area of massive energy storage. Among them, MnO2 materials are seen to be the most prospective cathode materials because of their low manufacturing costs, high operating voltage, and multi-valence state. Nevertheless, issues with low intrinsic conductivity, quick structural collapse and poor stability of MnO2 cathode materials during the charge/discharge process severely impede the development of AZIBs. Numerous investigations have demonstrated that the guest pre-intercalation MnO2 cathode structures can effectively alleviate the above problems and improve their electrochemical performance. Thus, this review summarizes the research progress of the guest pre-intercalation strategy applied to different Mn-based oxide cathode materials, focusing on α-MnO2, β-MnO2, ε-MnO2, δ-MnO2, and γ-MnO2. Meanwhile, the mechanism of performance improvement and electronic structure alteration of guest pre-intercalation in MnO2 cathode materials with different crystal structures are analyzed in detail. Finally, the challenges faced by this strategy and its development are summarized, and the future development direction of Mn-based cathode materials for high-performance AZIBs is prospected. The review describes the guest pre-intercalation strategy that promotes the commercialization and practical application of AZIBs, providing strong support for the development of renewable energy storage.

Cobalt ion doping and morphology tailoring enable superior zinc-ion storage in sodium vanadate nanoflowers

Layered sodium vanadium materials have aroused increasing interest owing to their open layered structures and high theoretical capacity. Nevertheless, the strong electrostatic interactions between vanadium oxide layers and intercalated Zn2+ and the weak electronic conductivity severely limit their further development. Here, we design a series of cobalt ion-doped sodium vanadium electrode materials with nanoflower-like morphologies. Due to the open interlayer space and improved electron transfer enabled by cobalt ion preintercalation and sufficient contact area between the electrode and electrolyte provided by the three-dimensional (3D) flower-like morphology, the cobalt ion-doped sodium vanadate (CNVO-2) cathode exhibits excellent electrochemical performance, including an exceptional specific capacity (411 mA h g-1 at 0.5 A g-1) and ultrahigh structural stability (90.4 % capacity retention after 3000 cycles at 10 A g-1), outperforming many advanced ZIBs cathode materials. In addition, through various ex situ characterization techniques, an ionic exchange and multiple ion cointercalation mechanism is first revealed in sodium vanadate cathode material.

Engineering improved strategies for spinel cathodes in high-performing zinc-ion batteries

The development of high-performing cathode materials for aqueous zinc-ion batteries (ZIBs) is highly important for the future large-scale energy storage. Owing to the distinctive framework structure, diversity of valences, and high electrochemical activity, spinel materials have been widely investigated and used for aqueous ZIBs. However, the stubborn issues of low electrical conductivity and sluggish kinetics plague their smooth applications in aqueous ZIBs, which stimulates the development of effective strategies to address these issues. This review highlights the recent advances of spinel-based cathode materials that include the configuration of aqueous ZIBs and corresponding reaction mechanisms. Subsequently, the classifications of spinel materials and their properties are also discussed. Then, the review mainly summarizes the effective strategies for elevating their electrochemical performance, including their morphology and structure design, defect engineering, heteroatom doping, and coupling with a conductive support. In the final section, several sound prospects in this fervent field are also proposed for future research and applications.

Inside-out regulation of MnO toward fast reaction kinetics in aqueous zinc ion batteries

An "inside-out regulation" strategy is proposed to improve the Zn2+ storage of MnO by Ni doping into the lattice and graphene wrapping outside the nanoparticles. The as-prepared Ni-MnO@rGO exhibits 112 mA h g-1 at 2.0 A g-1 over 800 cycles, due to the improved transport of electrons and ions from the synergistical function of intrinsic doping and external graphene encapsulation.