Synthesis And Doping Modification Of ZnMn₂O₄ Cathode Material For Aqueous Zinc-based Battery

Aqueous zinc ion batteries（AZIBs）are expected to be successfully applied in new foldable and wearable energy storage devices in the future due to their high safety,low cost,high energy density and high power density.As a key part of battery composition,cathode materials have attracted the research of many scholars.Among the cathode materials for AZIBs,manganese-based oxides have become the main electrode materials studied due to their low cost,environmental friendliness,and high theoretical specific capacity.The spinel-structured ZnMn₂O₄ has a high theoretical capacity of 224 m Ah g^-1,consisting of Zn-O tetrahedra and Mn-O octahedra,Zn²⁺can migrate in its three-dimensional framework,and this mixed metal oxide will make it the synergistic effect of each component is enhanced,which is beneficial to the electrochemical performance.However,ZnMn₂O₄ still has disadvantages such as poor electrical conductivity,slow ion diffusion and manganese dissolution,all of which need to be resolved.In this paper,in view of the above problems of ZnMn₂O₄ material,doping modification is carried out,and its electrochemical performance and energy storage mechanism as AZIBs cathode material are also studied.The specific research content of the paper is as follows:（1）The electrochemical performance of ZnMn₂O₄ with cationic K,Fe double doping as a cathode material for aqueous zinc-ion batteries was studied.The precursors were prepared by spray drying,and then calcined in air to obtain K,Fe-ZnMn₂O₄（K,Fe-ZMO）multilayer nested hollow nano-microspheres,which exhibited various advantages.1.The oxygen vacancies formed by the double doping of K and Fe can improve the conductivity of the material and the diffusion rate of Zn²⁺.2.The double doping of K and Fe reduces the formation energy of the material,making the material more stable and able to slow down the dissolution of manganese.3.Double doping of K and Fe promotes electron rearrangement and improves conductivity.The above advantages improve the electrochemical performance of the electrode material,K,Fe-ZMO shows a high specific capacity of 221.2 m A h g^-1(0.1 A g^-1)after 50 cycles,which is higher than that of pure ZnMn₂O₄(137.3 m A h g^-1).The capacity retention of K,Fe-ZMO(≈88.1%500 cycles,1.0 A g^-1)is also better than that of the ZnMn₂O₄ cathode material(≈27.5%370 cycles,1.0 A g^-1).The cationic doping modification strategy proposed in this work provides an example for the practical application of manganese-based materials in AZIBs.（2）The electrochemical performance of ZnMn₂O₄ complexed with CNTs as a cathode material for aqueous zinc-ion batteries through anionic S doping.The precursor was obtained by co-precipitation method,and then ZnMn₂O₄material was obtained by calcined in air.The ZnMn₂O₄ and CNT were composited by freeze-drying method,and finally ZnMn₂O₄/CNT（ZMO/CNT）was sulfurized to obtain S-ZnMn₂O₄/CNT（S-ZMO/CNT）.In the vulcanization process,not only the purpose of S-doped ZnMn₂O₄ is achieved,but also S-doped carbon nanotubes are obtained,realizing multiple optimization of materials.The S-doped S-ZMO/CNTs possess a large number of oxygen defects,which enhance the electrical conductivity of the material and facilitate the diffusion of Zn²⁺.Meanwhile,the metal-sulfur bond formed by S doping is beneficial to the intercalation/extraction of Zn²⁺.In addition,the defect degree of S-doped carbon nanotubes increases,which improves the loading of transition metal ions on the surface of carbon materials.Therefore,S-ZMO/CNT exhibits excellent electrochemical performance,with a reversible specific capacity of120.1 m A h g^-1 after 100 cycles at a current density of 500 m A g^-1,even at a higher current density(1500 m A g^-1)can also maintain a high reversible capacity of 65.8 m A h g^-1 for 400 cycles,and the capacity retention rate is as high as 93.7%,which is better than that of materials without sulfur doping.This work studies the effect of anion doping strategies on ZnMn₂O₄ materials,combined with the previous work on cation doping to explain the different effects of different types of doping on materials.