Preparation And Electrochemical Performance Test Of Reversible Aqueous Zinc/Manganese Battery

The zinc-manganese battery is a type of battery that uses manganese dioxide as a positive electrode and metal zinc as a negative electrode.Zinc can lose two electrons in the electrochemical reaction and has a higher power density and energy density than lithium,which can only lose one electron.Manganese dioxide having a plurality of variable valence ion storage properties stronger than the higher capacity,abundant reserves,inexpensive,environmentally friendly.However,the poor conductivity and poor reversibility of manganese dioxide,zinc electrode corrosion,hydrogen evolution and other issues,resulting in short cycle life of zinc-manganese battery,low discharge depth,resulting in its application has been limited.In the third chapter,the?-MnO₂ crystals were prepared at room temperature using a simple,efficient,energy-saving and environmentally friendly solution coprecipitation method.As a positive electrode material,a zinc electrode prepared from zinc powder is used as a negative electrode and assembled into a button battery.By changing the ionic species and concentration of the electrolyte,the mass ratio of the active material and the volume ratio of the electrolyte,and the preparation method of the pole piece,the discharge mechanism and optimal assembly process of reversible aqueous zinc/manganese battery batteries were studied.The study found that water-based zinc-manganese secondary batteries meet the proton-electron discharge mechanism,and the discharge process consists of two stages:firstly,H⁺concentration increases with the increase of Mn²⁺concentration,H⁺participates in the first stage discharge reaction,and Mn²⁺concentration influences the first stage discharge.With the increase of Mn²⁺concentration,the voltage of the reduction peak is higher and the reaction is more likely to occur;secondly,Zn²⁺participates in the second stage discharge reaction,and the discharge specific capacity also increases with the increase of Zn²⁺concentration in the second stage.The study also found that a certain concentration of Mn²⁺can inhibit the dissolution of manganese dioxide.As the electrolyte volume increases,the discharge specific capacity also increases.However,when the volume of the electrolyte is too large,dissolution of manganese dioxide is intensified and the specific discharge capacity is reduced.The electrochemical properties of manganese dioxide with different morpHology and microstructure were studied.Manganese sulfate and potassium permanganate were used as raw materials to prepare granular amorpHous?-MnO₂ by solution coprecipitation method,amorpHous?-MnO₂ coexisting with nanorods and nanoparticles by low temperature solid state method,and nanorod?-MnO₂ crystals with good crystallization by hydro-thermal method.It has been found that nanocrystalline?-MnO₂ crystals with good crystallinity prepared by hydrothermal method have high specific discharge capacities and exhibit excellent performance under conditions of large currents and alternating currents of large and small currents.The discharge capacity drop in the early period of the cycle should be caused by the partial dissolution of manganese dioxide in the electrolyte and the decrease in the mass of the active material.The subsequent increase in the discharge specific capacity should be the reaction of Mn²⁺in the electrolyte to produce a manganese dioxide at the positive electrode.As the mass of the active material increases,the specific discharge capacity drops first and then rises.In order to improve the conductivity of manganese dioxide and improve the poor cycling performance of manganese dioxide due to collapse of the tunnel structure,a certain amount of K⁺is introduced into its crystal lattice.The KOH solution was added during the preparation and the K⁺doping amount was controlled by adjusting the pH.The radius of K⁺is closest to O^2-.When O^2-reacts,K⁺continues to support the manganese dioxide lattice.It was found that the polarization of K⁺doped MnO₂ was smaller than that of undoped samples.With the increase of K⁺doping,the MnO₂ particle density exhibited close-loose-close.The specific discharge capacity decreases first and then increases.Under constant current of 1 C,after 600 cycles,the specific discharge capacity of sample K10 is still 87 mAh·g^-1,and the capacity retention rate is63.5%,and the cycle performance is greatly improved.