Study On Doping MnO₂ Cathode Material By Ion Exchange And Its Zinc Storage Mechanism

With the extensive research on energy storage system,lithium electricity stands out for its high energy density and long cycle life,and soon enters the commercial field of application.However,lithium resources are relatively rare in our country,which leads to its cost being very high.Meanwhile,the electrolyte for organic electrolyte has great risks of safety.Therefore,other alternative energy storage batteries have gradually come into the attention of people,among which zinc ion batteries also get more and more attention due to its advantages of rich resources,low cost and high safety of water electrolyte.However,the insertion/removal of zinc ion battery cathode material during the actual charging/discharging process will lead to material volume expansion and structural collapse,thus reducing the energy density of the battery.Among them,although mangan-based cathode materials have various morphologies and crystal phases,which can provide moderate voltage window,but also have good specific capacity,and have very high application potential,it is accompanied by disproportionation reaction in the charging and discharging process,which will lead to the dissolution of manganese in the cathode materials,seriously affecting its cyclic stability.It seriously hinders the further development of manganese-based zinc ion batteries.In order to solve the problem of poor stability of zinc ion batteries caused by dissolving manganese based materials due to disproportionation reaction,a simple technology to improve the stability of positive electrode materials,namely ion exchange doping modification,was proposed in this paper.The lattice stability of manganese dioxide was improved by doping and modifying the cathode material of manganese dioxide for zinc ion batteries and adding transition metal ions into it.The influence of microstructure on the performance of manganese dioxide was investigated,and the conductivity,stability and battery life of zinc ion batteries were improved.The energy storage mechanism of doping modification to improve the stability was studied.The main research contents are as follows:1.Prepared different Mn O₂precursor powders by one step hydrothermal method,and the Mn O₂precursor was modified by Ni ion doping by ion exchange method.The influence of precursor,dopant（type and concentration）and ion exchange environment（temperature and time）on the ion exchange process was investigated by the control variable method,and nickel dopedα-phase manganese dioxide（Ni-Mn O₂）was finally obtained.Through a series of electrochemical tests,it is found that doping Mn O₂by ion exchange method can effectively improve the conductivity and cycling stability of Mn O₂.The dopant is 0.15 mol/L Ni（NO₃）₂,which can improve the modification effect to the greatest extent.The activation process can be completed quickly at the current density of 0.2 A g^-1,and the capacity of 206 m Ah g^-1can be maintained stably.In the stability test of 1 A g^-1,the capacity retention rate remained at96.3%after 2800 cycles,while the unmodified Mn O₂decreased to 19.6%after 130 cycles,which effectively proved the effectiveness of the ion exchange process.2.The energy storage mechanism of Mn O₂modified by transition metal cobalt ion was investigated.Mn O₂precursor was prepared by one-step hydrothermal method,and then Co ion doped modification was carried out by ion exchange.Co doping can increase the specific capacity of Mn O₂and improve the stability of the cathode material to a certain extent.Also,by controlling variables,the enhancement effect of cobalt salt type and cobalt salt concentration on Mn O₂was studied.When 0.15 mol/L Co SO₄was used as the dopant,the hydrothermal temperature was 190℃and the hydrothermal time was 48 h,the best modification effect could be obtained.At 0.1 A g^-1current density,the specific capacity of Co-Mn O₂can reach 233 m Ah g^-1.In the cycle test of 1 A g^-1,it also showed obvious stability improvement.After 1400 cycles,there is still more than 100 m Ah g-1 specific capacity.The feasibility of ion exchange modification ofα-Mn O₂by cobalt element was proved by experiments.3.The effect of nanotube-likeδ-Mn O₂morphology on the properties of Mn O₂was analyzed by growing nanotube-likeδ-Mn O₂on a polycarbonate template.It was found that the nanotube-like morphology can improve the cyclic stability of Mn O₂to a certain extent.In order to further improve its performance,Ni ion exchange was performed on the nanotube-likeδ-Mn O₂.It is found that the ion exchange method can effectively improve the stability and specific capacity of the anode material.Under the circulating condition of 1 A g^-1current density,the capacity retention rate is more than 95%after 1700 cycles.Compared with theδ-Mn O₂without ion exchange,the stability has been greatly improved.The combination of ion exchange and morphology control is feasible.In conclusion,the ion exchange method is an effective strategy to improve the properties of positive electrode materials for Mangan-based zinc ion batteries.The doping modification of Mn O₂by ion exchange can greatly improve the cyclic stability of Mn O₂.The relevant research in this paper provides a new idea for the performance optimization of manganese based cathode materials for zinc ion batteries,and lays a certain experimental and theoretical foundation for the commercial application of Zn-MnO₂ batteries.