Cobalt Ion-Stabilized VO2 for Aqueous Ammonium Ion Hybrid Supercapacitors.

Aqueous ammonium ion hybrid supercapacitor (A-HSC) is an efficient energy storage device based on nonmetallic ion carriers (NH4+), which combines advantages such as low cost, safety, and sustainability. However, unstable electrode structures are prone to structural collapse in aqueous electrolytes, leading to fast capacitance decay, especially in host materials represented by vanadium-based oxidation. Here, the Co2+ preintercalation strategy is used to stabilize the VO2 tunnel structure and improve the electrochemical stability of the fast NH4+ storage process. In addition, the understanding of the NH4+ storage mechanism has been deepened through ex situ structural characterization and electrochemical analysis. The results indicate that Co2+ preintercalation effectively enhances the conductivity and structural stability of VO2, and inhibits the dissolution of V in aqueous electrolytes. In addition, the charge storage mechanisms of NH4+ intercalation/deintercalation and the reversible formation/fracture of hydrogen bonds were revealed.

Surface Adsorption and Proton Chemistry of Ultra-Stabilized Aqueous Zinc-Manganese Dioxide Batteries.

Aqueous rechargeable Zinc (Zn) batteries incorporating MnO2 cathodes possess favorable sustainability properties and are being considered for low-cost, high-safety energy storage. However, unstable electrode structures and unclear charge storage mechanisms limit their development. Here, advanced transmission electron microscopy, electrochemical analysis, and theoretical calculations are utilized to study the working mechanisms of a Zn/MnO2 battery with a Co2+ -stabilized, tunnel-structured α-MnO2 cathode (Cox MnO2 ). It is shown that Co2+ can be pre-intercalated into α-MnO2 and occupy the (2 × 2) tunnel structure, which improves the structural stability of MnO2 , facilitates the proton diffusion and Zn2+ adsorption on the MnO2 surface upon battery cycling. It is further revealed that for the MnO2 cathode, the charge storage reaction proceeds mainly by proton intercalation with the formation of α-Hy Cox MnO2 , and that the anode design (with or without Zn metal) affects the surface adsorption of by-product Zn4 SO4 (OH)6 ·nH2 O on MnO2 surface. This work advances the fundamental understanding of rechargeable Zn batteries and also sheds light on efficient electrode modifications toward performance enhancement.