Performance Regulation Of Novel Manganese-Based Cathode Material And Electrochemical Properties Of Ion Pre-Interlacation Manganese Dioxide And Their Application In Aqueous Zinc Ion Batteries

Energy and environmental protection are two hot topics in the 21st century.Developing high-performance and green energy storage equipment are the inevitable choice to solve the energy and environmental problems.Commercial secondary batteries have their own advantages and disadvantages.Compared with traditional lithium-ion battery batteries,aqueous zinc ion batteries（AZIBs）have the advantages of safety,environmentally friendly,simple assembly,sufficient raw materials and low price.However,there are few available AZIBs cathode materials,so it is imperative for further research and development of new cathode materials.Manganese-based cathode materials are the focus of exploration at present,which has the characteristics of low price,various crystal forms and structures,high theoretical capacity and high voltage plateau.In this work,we investigated the electrochemical properties of new manganese-based cathode materials in AZIBs,modified the existing manganese-based cathode materials with different preparation methods in order to solve the problems such as poor inherent conductivity,low ionic conductivity and structure unstable in the cycle process.The specific content and findings of the study are as follows:（1）Nanorodsγ-MnOOH and its compositeγ-MnOOH@r GO were synthesized by one-step hydrothermal method,and the nanorods were firstly applied in AZIBs.Though a series of characterization methods to analyze the basic properties ofγ-MnOOH nanorods,and investigate the effect of r GO on the electrochemical properties ofγ-MnOOHAt the current density of 0.1 A g^-1,the reversible specific capacity of MnOOH is125.9 m Ah g^-1 after 250 cycles with 131%capacity retention,and the Coulomb efficiency is over 99%.MnOOH@r GO(268 m Ah g^-1)has a higher specific capacity than MnOOH(202 m Ah g^-1).The pseudo-capacitance analysis shows that the reaction ofγ-MnOOH is mainly controlled by the ion diffusion process.（2）Mn C₂O₄,Mn C₂O₄·2H₂O and Mn C₂O₄·3H₂O were prepared by hydrothermal method,ultrasonic-assisted method,and liquid-phase precipitation method respectively,using Mn（CH₃COO）₂·4H₂O as manganese source and H₂C₂O₄·4H₂O as carbon source.Compared with the electrochemical properties of manganese oxalate with different moisture content in AZIBs were compared,tested their pseudo-capacitance efficiency was carried out a series of characterizations.The results show that the electrochemical performance of Mn C₂O₄·2H₂O is the best.The discharge specific capacity of Mn C₂O₄·2H₂O is 197.8 m Ah g^-1 at 100 m A g^-1,and that of Mn C₂O₄·2H₂O remains 179.2 m Ah g^-1 after 200 cycles,and the capacity retention is 90.6%,it has good electrochemical performance.（3）The pure phaseδ-MnO₂、Cu_0.06MnO₂·1.7H₂O and Bi_0.09MnO₂·1.5H₂O were prepared by one-step hydrothermal method using KMnO₄ as manganese source,citric acid as reductant,Cu SO₄·5H₂O and Bi（NO₃）₃·5H₂O as pre-intercalation metal ion source.Three kinds of materials were applied in AZIBs to study the effect of metal ion pre-intercalation on the electrochemical properties ofδ-MnO₂.The results show that the three materials are 3D nanoflower structures composed of nanosheets with very large specific surface area,which can make the cathode fully contact with the electrolyte to increase the reactive sites and increase the specific capacity of the battery.The pre-intercalation metal ions and water molecules as the pillar of the layered structure can improve the cycle stability ofδ-MnO₂.The synergistic effect of 3D nanoflower structure and metal ion pre-intercalation makes Cu_0.06MnO₂·1.7H₂O and Bi_0.09MnO₂·1.5H₂O Materials exhibit excellent electrochemical properties.Copper ions which exist in Cu_0.06MnO₂·1.7H₂O will redox during the recycling process,the reaction process can properly store zinc and improve the electrical conductivity ofδ-MnO₂,thus,increaseing diffusion rate of Zn²⁺and the specific capacity of the cell.The reversible capacity of Cu_0.06MnO₂·1.7H₂O was much higher than that ofδ-MnO₂(190 m Ah g^-1 at 0.5 A g^-1).At the same time,Bi_0.09MnO₂·1.5H₂O exhibited excellent cyclic stability,and the capacity maintained 114.5 m Ah g^-1 even after 1100charge-discharge cycles at the current density of 1 A g^-1.The capacity retention rate of Bi_0.09MnO₂·1.5H₂O was 98.6%,which was much higher than that ofδ-MnO₂（53.8%）.The pseudo-capacitance analysis shows that diffusion control has an important influence on the the capacitive properties of the three materials,ex-situ characterization indicated that the energy storage process was accompanied by Zn²⁺intercalation/desorption mechanism and deposition/dissolution mechanism.