Preparation And Study Of Manganese Based Cathode Materials For Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries are considered as one of the most potential energy storage devices to solve the problem of large-scale power grid energy storage.Compared with lithium-ion batteries,zinc reserves are larger and the price is obviously lower,which makes the production cost of aqueous zinc-ion batteries lower.In addition,the simple production conditions of aqueous zinc-ion batteries greatly reduce the production cost.At the same time,aqueous zinc ion batteries also feature non-toxic,environment-friendly and safe characteristics.The cathode materials developed at present cannot meet the commercial needs of aqueous zinc ion batteries.Manganese based compounds are regarded as one of the most advanced and widely used cathode materials for aqueous zinc ion batteries.Manganese resources are aboundant on the earn,and manganese has multivalent states(Mn²⁺,Mn³⁺,Mn⁴⁺,Mn⁷⁺),which makes manganese based compounds show diversity in atomic structure.It also features the advantages of a high working voltage,an environment-friendly characteristic,low toxicity and a low cost.Therefore,it is of great significance to develop new manganese based cathode materials.In this thesis,MnMoO₄material was synthesized by a high-temperature solid-state method.The effects of calcination conditions on the physicochemical properties and electrochemical performance of MnMoO₄material were investigated;MnCO₃material was prepared by a hydrothermal method,and its physical characterization,electrochemical properties and energy storage mechanism were investigated;K_0.5Mn₂O₄·5H₂O was synthesized by a hydrothermal method.The effects of hydrothermal conditions on the physicochemical properties and electrochemical performance of K_0.5Mn₂O₄·5H₂O were investigated.The main research contents are as follows:（1）MnMoO₄material was synthesized by a high-temperature solid-state method.The effects of calcination conditions on the physicochemical properties and electrochemical performance of MnMoO₄material were investigated.Based on the physical characterization and electrochemical properties,the best experimental condition was when the sample was calcined at 500℃for 3 hours.The MnMoO₄material synthesized under this condition features high purity,regular rod structures and smooth surfaces.It exihibits better electrochemical performance.Under the current density of 0.1 A g^-1and calcination at 500℃for 3 h,the first discharge specific capacity of the synthesized MnMoO₄sample is 119 mAh g^-1,and the maximum discharge specific capacity is 278 mAh g^-1;The rate performance and cycle life are the best.（2）MnCO₃was synthesized by a hydrothermal reaction.The effects of hydrothermal conditions on the physicochemical properties and electrochemical performance of MnCO₃were investigated.The energy storage mechanism of MnCO₃material in aqueous zinc ion batteries was also explored.Based on the physical characterization and electrochemical performance,the best experimental condition was when a hydrothermal treatment was conducted at 180℃for 12 hours.Under this condition,the synthesized MnCO₃material features high purity,regular cubic structures,uniform particle sizes and smooth surfaces.It exihibits better electrochemical performance.At a current density of 0.1 A g^-1,the first discharge specific capacity of the synthesized MnCO₃sample is 144.49 mAh g^-1at a hydrothermal temperature of 180℃and a reaction time of 12 h;The rate performance and cycle life are the best;The analysis of energy storage mechanism shows that The energy storage mechanism of MnCO₃electrode in zinc ion battery may be the co insertion mechanism of H⁺and Zn²⁺.（3）K_0.5Mn₂O₄·5H₂O was synthesized by a hydrothermal reaction.The effects of hydrothermal conditions on the physicochemical properties and electrochemical performance of K_0.5Mn₂O₄·5H₂O were investigated.Based on the physical characterization and electrochemical performance,it is concluded that the best experimental condition is when a hydrothermal treatment was conducted at 120℃for12 h.The K_0.5Mn₂O₄·5H₂O sample synthesized under this condition features high purity and the morphology is micron flower balls composed of nano sheets.It exihibits better electrochemical performance.The first discharge specific capacity of K_0.5Mn₂O₄·5H₂O sample synthesized at a current density of 0.1 A g^-1at a hydrothermal temperature of 120℃and a reaction time of 12 h is 399.01 mAh g^-1;The rate performance and cycle life are the best.