Preparation And Performance Optimization Of A Novel Aqueous Lithuim-rich Manganese-based Battery

In organic lithium-ion batteries,lithium-rich manganese-based cathode material has become a research hotspot in recent years because its specific capacity is far higher than the current commonly used lithium cobalt oxide material.To seek an environment-friendly energy system has become the focus of research as for the existence of organic lithium-ion battery electrolyte toxic,flammable and other deficiencies in recent years and continuous improvement of environmental awareness.Making it the most promising alternative to organic lithium-ion batteries because of its aqueous electrolyte solution,no hidden danger of combustion and explosion,high conductivity and low production cost.In this paper,cathode materials were synthesized by the high-temperature solid-state.Electrode material phase analysis were tested by X-ray diffraction and scanning electron microscopy and battery electrochemical performance were tested by cyclic voltammetry,AC impedance and constant current charge and discharge.The following conclusions can be drawn through these experiments,（1）The lithium-rich manganese-based Li2MnO3 had the best electrochemical performance in mixed aqueous solution electrolyte of 1mol/L lithium sulfate+0.5mol/L zinc sulfate+0.2mol/L manganese sulfate.The first discharge capacity was 66.9mAh/g,coulomb efficiency was 49%and it could be stable for a long time in the vicinity of 250mAh/g.But rate performance test was poor.（2）Analysis of the electrolyte on the battery performance.The electrochemical performance of Li₂MnO₃ and Li₂Mn_1-xNi_xO₃ cathode materials in electrolytes of lithium sulfate,lithium sulfate zinc sulfate aqueous solution and lithium sulfate zinc sulfate manganese sulfate aqueous solution showed that adding zinc ion and Manganese ions can effectively improve the performance of the battery.（3）The electrochemical performance of Li₂Mn_1-xNi_xO₃（x=0.25,0.5 and 0.75）was obviously improved in the three electrolytes,which was a positive electrode material doped with metallic nickel.Incorporation of metallic nickel could effectively improve the performance of the battery.The first discharge capacity of the three electrode materials was respectively 314.3mAh/g,297.7mAh/g and 159.3mAh/g with 1mol/L lithium sulfate+0.5mol/L zinc sulfate+0.2mol/L manganese sulfate as the electrolyte at 0.5C.In the rate test,x=0.5 had better performance.（4）Li₂Mn_1-yCo_yO₃（y=0.1,0.5,and 0.9）had a better corrosion resistance in the mixed aqueous solution of 1 mol/L lithium sulfate+0.5 mol/L zinc sulfate+0.2 mol/L manganese sulfate in low-current density（0.5C）test,the first discharge capacitiese were respectively376.7mAh/g,291.2mAh/g and 333.1mAh/g.（5）Comparing the magnification performance of Li₂MnO₃,Li₂Mn_0.5Ni_0.5O₃ and Li₂Mn_0.5Co_0.5O₃,Li₂Mn_0.5Co_0.5O₃ had the best properties at lower magnification（especially at 0.5C magnification）.The best discharge performance（about 350mAh/g）was much higher than that of Li₂MnO₃ and Li₂Mn_0.5Ni_0.5O₃.At high current density（above 1.5C）,the discharge capacity of Li₂Mn_0.5Ni_0.5O₃ was higher than that of the other two materials.At 6C rate,Li₂Mn_0.5Ni_0.5O₃ had about 125mAh/g,Li₂Mn_0.5Co_0.5O₃ had a discharge capacity of about 90mAh/g,Li₂MnO₃ had only 25mAh/g.Incorporating metal elements,not only can effectively improve the discharge capacity of the electrode material,but also can effectively improve the rate performance.（6）The cathode materials was tested by the software Jade 6.5.The cahode materials was in agreement with Li₂MnO₃（JCPDS No.73-0152）before the reaction and was in agreement with MnO₂（JCPDS No.39-0375）after the reaction.The reason why the structure of the cathode materials changed was correspond to possible reactions.From the results,it could be concluded that the incorporation of metallic nickel or cobalt ions could avoid the“step-wise”decay of the discharge specific capacity of the Li₂MnO₃.during charge and discharge,mainly due to the nickel ion/cobalt ion.Substituting part of the manganese ion position increases the stability of the Li₂MnO₃ structure and effectively increased the discharge specific capacity of the battery.The comparison between nickel-doped and cobalt-doped materials showed that nickel-doped materials were more suitable for high-rate batteries,and cobalt-doped materials were more suitable for high-capacity batteries,both of which had corresponding advantages.Adding zinc ions and manganese ions to the electrolyte could effectively improve the overall performance of the battery,comparing the three electrolytes and related literature reports,co-deintercalation of lithium ions and zinc ions,zinc ions（II）and manganese ions（II）.The synergistic effect of the reaction and the redox reaction of manganese ions provide capacity for the entire battery charge-discharge reaction.Therefore,in the electrolytes containing lithium ions,zinc ions and manganese ions,the battery has the best performance.