Structural Design And Performance Optimization Of Cathode Materials For Aqueous Zinc Batteries

Zinc with large theoretical specific capacity(820 mAh g-1)and suitable redox potential(-0.763V vs.SHE)has been used to fabricate a variety of battery systems,including zinc-air battery and zinc-ion battery.Both batteries require efficient cathode materials or electrocatalysts to achieve the high battery performance via reversible charging/discharging process.In order to improve the energy density,rate performance and cycle stability of zinc batteries,research works about the design of cathode materials,performance optimization and mechanism investigation are summarized in this thesis:(1)In view of the high overpotentials of oxygen reduction and evolution reaction reactions for zinc-air battery as well as the high price and single catalytic activity of noble-metal-based electrocatalysts,the in-situ growth of manganese oxide(MnOx)on flexible carbon cloth via a simple chemical bath deposition method has been combined with the thermal treatment to regulate the structure and composition of MnOx for high-performance Zn-air battery.The redox reaction between carbon fiber and MnOx during the thermal treatment led to the gradual transition of manganese to low valence,along with the partial phase transformation from birnessite-type MnO2 into hausmannite Mn3O4 with more defect sites,thus improving the electrocatalytic performance.When coupled with a Zn anode,the solid-state battery showed a high open circuit voltage of 1.47 V,superior round-trip efficiency(62.4%after 120 cycles),long cycling life(45 h over an operating voltage of 1.2 V),and high capacity(728 mA h g-1),which are superior to those of battery using Pt/C and RuO2 electrocatalysts.Furthermore,the battery also demonstrated excellent mechanical flexibility and cycling stability without obvious performance degradation.(2)In consideration of low specific capacity and sluggish kinetics for poor rate-performance of vanadium oxides,the polyaniline molecules have been in-situ intercalated into the layers of vanadium oxide,aimed to enlarge the lattice spacing for enhancing the performance of aqueous zinc-ion battery.Typically,with enlarged lattice spacing,the polyaniline intercalated V2O5(PANI-V2O5)coupled with a Zn electrode in an aqueous electrolyte exhibited a large specific capacity of 372 mAh g-1 and good cycling stability.More importantly,the in-situ XRD results revealed that the intercalation of PANI allowed the accumulation of additional Zn2+ions without obvious phase transformation,and the conjugated polymeric chains of PANI molecules enabled the structure flexibility in the confined space for releasing the stress for the enhanced battery performance.Additionally,the in-situ infrared spectroscopy elucidated that the reversible doping process of the PANI molecules also made multiple ions involved in the charge storage process via the synergic effect for the improved performance.Uncovering the mechanism firstly is of importance in providing basic principles to rational design lamellar-type electrode materials via the combination of unique organic and inorganic features high performance aqueous zinc ion battery.