Study On Modification And Its Zinc-ion Batteries Performance Of MnO₂ Electrode

The energy shortage caused by the rapid development of society has become an increasingly prominent social problem.With the development,renewable energy,such as solar energy and wind energy,has been widely applied in people' life.The research of efficient and safe energy storage systems is gradually becoming a hotspot.However,lithium-ion batteries,which are already commercially available on a large scale,have high cost and safety issues.Aqueous zinc-ion batteries are considered to be one of the most promising energy storage devices to replace lithium-ion batteries.Among its cathode materials,manganese-based materials are widely concerned because of their low cost,non-toxicity,and environmental friendliness.However,there are still many problems,such as the poor intrinsic electrical conductivity of manganese-based oxides,the continuous dissolution of manganese ions in aqueous electrolyte,the volume expansion even the collapse of structures of manganese oxides caused by zinc ions during deintercalation,and etc,when manganese-based material is used as electrod.The application of manganese-based materials in aqueous zinc-ion batteries is still limited.To this end,the researchers conducted extensive research and put forward a series of strategies,including compounding with other conductive materials,constructing multi-dimensional nanostructures,introducing defects,adjusting layer spacing,and optimizing electrolytes.Compounding with the conductive material can improve the conductivity and stability of the manganese-based oxide elelctrod,thereby improving the electrochemical performance of the aqueous zinc-ion batteries.However,the conductive materials such as carbon nanotubes,graphene,and carbon fiber are relatively expensive,which will greatly increase the cost of aqueous zinc-ion batteries by combining these materials with manganese oxide to make electrodes.Acetylene carbon black is a very low-cost carbon material with excellent conductivity.Compounding it with MnO2 to improve the conductivity of the MnO2 electrode can reduce battery costs.In addition,introducing defects into the manganese-based oxide structure can improve the utilization rate of active sites on the surface of the material,thereby achieving higher zinc ion adsorption/desorption.At present,the application of ion-doped manganese oxide materials is mostly concentrated on the supercapacitors and lithium-ion batteries,and there are few reports on the application of aqueous zinc-ion batteries.The adjustable electronic structure of transition metal element often leads to excellent performance when it compounds with the MnO2 material and applied to the aqueous zinc-ion batteries.In this paper,the carbon material composite and metal ion doping treatment of MnO2 nanomaterials were carried out,respectively,and the improvement of the performance of these two methods on the aqueous zinc-ion batteries of MnO2 nanomaterials was investigated.The main contents are as follows:(1)Preparation of acid-treated acetylene carbon black(a-C)and MnO2 composite materials and study of aqueous zinc-ion batteries performance:Using hydrothermal method,MnO2/a-C composite nanomaterials with different carbon contents were successfully prepared by adding a-C to the precursor solution and controlling the content of added carbon materials.SEM,XRD,Raman,and electrochemical testing were used to characterize the morphologies,structure and electrochemical performance.The effect of a-C content on the performance of MnO2 based aqueous zinc-ion batteries was explored.The results show that the composition of of a-C with MnO2 can improve the conductivity of MnO2 electrod and the cycle performance of aqueous zinc-ion batteries.Among them,MnO2/a-C composite nanomaterials prepared with 12 mg a-C acheived optimal performance of aqueous zinc-ion batteries,with an initial specific capacity of 178 mAh/g at a current density of 1 A/g,a capacity retention rate of 66.8%after 1200 cycles,which was significantly improved compared with pure MnO2 sample.(2)Preparation of transition metal element doped MnO2 composite material and performance study of aqueous zinc-ion batteries:Using hydrothermal method and adding transition metal elements such as Cu,Fe,Co,Ni to the precursor solution,MnO2 nanowire materials doped with different elements are obtained,respectively.SEM,TEM,XRD,Raman,XPS,and electrochemical testing were used to characterize the material and study its electrochemical performance.The effect of different element doping on the performance of MnO2 based aqueous zinc-ion batteries was explored.The results showed that Cu element doping achieved obvious improvement effect.The doping improved the deintercalation process of zinc ions,and effectively improved the conductivity and ion storage performance of the electrode material.Study on the doping content of Cu element showsed that 0.13 mmol Cu element doped MnO2 material exhibited the best performance,with an initial specific capacity of 191 mAh/g at a current density of 1 A/g.Under the current density of 3 A/g,the capacity retention rate reached 61.5%after 1600 cycles,which was greatly improved compared with the pure MnO2 sample,and the rate performance is also excellent.