Modified Preparation And Properties Of Manganese Oxide Cathode Material For Aqueous Rechargeable Zinc-ion Batteries

Manganese dioxide（MnO₂）has the advantages of polymorphism,high operating voltage and environmental friendliness,and as a cathode material widely used in aqueous rechargeable zinc ion batteries（ARZIBs）.Its layered crystal form is an ordered structure composed of[MnO₆]octahedral co-sides along the base plane,and the two-dimensional frame can usually accommodate various cations,thereby enriching the electrochemical activity of manganese dioxide on various reactions.However,slow electrochemical kinetics and poor cycle stability are main problems to obstruct its practical application.In this paper,a strategy of ion pre-intercalation into layered manganese dioxide was employed to enhance the electrochemical performance of cathode materials in ARZIBs.A simple one-step hydrothermal method was adopted in our fabrication procedure and alkali metal ions are inserted into the layers of manganese oxides.By fabricating coin cell,the electrochemical properties and reaction kinetics of as-prepared materials were systematically explored.Based on our studies,it was found the electrochemical reaction mechanism of manganese modified manganese dioxide cathode materials in the process of charge and discharge was mainly improved due to the alkali metal ion pre-intercalation,and at the same time improving the electrochemical performance of manganese-based ARZIBs cathode materials with different properties and their optimization.The main research contents are as follows:（1）Potassium pre-intercalated layered manganese dioxide（KMO）with layer spacing of7.2?was prepared by one-step hydrothermal method,and the electrochemical performance of the assembled battery was evaluated in the large anion electrolyte of Zn（CF₃SO₃）₂solution added with manganese ion additives.KMO cathode materials can provide high capacity and good rate capability.The capacity of the KMO cathode at current density of 0.1 A g^-1is 252m Ah g^-1.Long cycling test at current density of 2.0 A g^-1shows that the KMO cathode can maintain more than 84.3%of its capacity after 4000 cycles.The reaction kinetics and reaction mechanism of KMO cathode in were discussed,and the mechanism of gradual insertion behavior of H⁺/Zn²⁺ions was confirmed by cyclic voltammetry test and constant current discharge/charge test.The Galvanostatic Intermittent Titration Technique（GITT）results show that the diffusion coefficient of H⁺insertion is greater than that of Zn²⁺ions.With these characterizations,it can be demonstrated that potassium pre-intercalation enhances the electrochemical performance ofδ-MnO₂.（2）The Na MO cathode material with sodium ion pre-intercalation was successfully synthesized by the one-step hydrothermal method.The assembled Zn//Na MO aqueous rechargeable zinc-ion battery can reach 254 m Ah g^-1at an outstanding current density of 0.1 A g^-1,and can reach 103.7%after 100 cycles.At the same time,the Na MO cathode exhibited excellent long-term cycle stability of up to 2000 cycles at 2.0 A g^-1,and the capacity retention rate was 76.7%.Experimental tests and data analysis show that the dissolution and solvation effects of manganese atoms during the cycling process can be inhibited by sodium ion pre-intercalation,high electronic conductivity and enhanced intercalation/deintercalation ability of hydrogen/divalent zinc ions can be enhanced,and long-term cycle stability can be improved.In addition,the combined effect of the charge storage mechanism of hydrogen ion intercalation and the pseudocapacitance mechanism of divalent zinc ion intercalation was eluted by various ex situ tests.This provides a reasonable approach for the design of cathode materials for high-performance manganese-based aqueous rechargeable zinc-ion batteries.Therefore,the metal ion pre-intercalation method of layered metal oxides provides a practical method for the preparation of high-performance zinc-ion battery electrode materials and other ion storage systems.