Preparation Of Spinel Aluminum-Manganese Oxide Cathode Materials And Their Aluminum Storage Properties

Interest in aqueous energy storage batteries is surging in the pursuit of safer electrochemical energy storage solutions.The low energy density of today’s commercial aqueous batteries cannot meet the needs of the rapidly growing transportation and grid storage sectors,but this will change with the development of new batteries and their materials.Aluminum ion batteries have received increasingly close attention in recent years due to the high volumetric specific energy and mass specific capacity of the metallic aluminum cathode,and the advantages of abundant aluminum resources,low price,and high safety.However,the strong electrostatic interaction between aluminum ions and the cathode material,resulting in the inability to remove all aluminum ions from the material and the low diffusion rate of aluminum ions,leads to the destruction of the material structure and the reduction of the capacity,which eventually leads to the short cycle life of aluminum ion batteries,so it is urgent to develop cathode materials with high capacity and high cycle stability.In this thesis,we aim to develop cathode materials with excellent performance for aqueous aluminum ion batteries.We synthesized aluminum-manganese oxides with spinel structure by in situ electrochemical transformation and spray drying,and investigated the structure,aluminum storage performance and its storage mechanism in detail using material structure characterization and electrochemical testing techniques,and explored the feasibility of application in aqueous aluminum ion batteries.The main findings of this paper are as follows:（1）Al_2/3Li_1/3Mn₂O₄ cathode material was prepared by in situ electrochemical conversion and spray drying methods,respectively,and the cathode material exhibited high aluminum ion mobility,excellent cycling and multiplication performance.At a current density of 1A g^-1,the Al_2/3Li_1/3Mn₂O₄ cathode material has a first discharge capacity of138m Ah g^-1,and after 1000 charge/discharge cycles,the cathode material can still provide a capacity of 93.1m Ah g^-1.The assembled Al//Al_2/3Li_1/3Mn₂O₄ full cell can provide an operating voltage of 1.3V,and its energy density is as high as 183Wh kg^-1.The storage mechanism of aluminum ions in the Al_2/3Li_1/3Mn₂O₄ cathode material was investigated using non-in situ XRD,XPS and TEM characterization techniques and calculations based on the first nature principle of density flooding theory,and the results showed that the reversible deembedding reaction of Al³⁺ions was:Al_2/3Li_1/3Mn₂O₄-x Al³⁺-3xe^-（?）Al_2/3-xLi_1/3Mn ₂O₄.（2）In order to obtain cathode materials with higher capacity and excellent cycling performance,the spinel structured Al_xMn_3-xO₄（x=0.5,1,1.5,2）cathode materials were prepared by spray drying method in this paper,and the intrinsic connection between material components and aluminum storage performance was investigated in detail.It was found that the Al₂MnO₄ cathode material exhibited the highest specific capacity(384m Ah g^-1)at a current density of 1A g^-1,while the Al Mn₂O₄ cathode material showed the optimal cycle stability（89.2%,5000 cycles）.The constructed aluminum ion battery Al//Al Mn₂O₄ can provide a high capacity of 381m Ah g^-1 at 300m A g^-1（based on the mass of the active material）,and the capacity remains essentially unchanged after 100 cycles.The aluminum storage mechanism of the Al_xMn_3-xO₄（x=0.5,1,1.5,2）cathode material was confirmed using in-situ XRD and non-in situ XPS,TEM and ICP characterization techniques as:Al_xMn _3-xO₄-y Al³⁺-3ye^-（?）Al_x-yMn_3-xO₄.（3）In this paper,λ-MnO₂and Mn₃O₄ were finally prepared by acid leaching and solid phase methods,respectively,and used as cathode materials for aqueous aluminum ion batteries.It was found that Al³⁺was embedded in the lattice ofλ-MnO₂ and Mn₃O₄during the first five charge-discharge processes,gradually forming Al Mn₂O₄ and Al_0.94Mn₂O₄,respectively,and aluminum ions underwent reversible exfoliation and embedding reactions in Al Mn₂O₄ and Al_0.94Mn₂O₄during the subsequent charge-discharge processes.The two cathode materials provided specific capacities of 591 and 613m Ah g^-1 at a current density of1A g^-1,respectively,and no significant decrease in specific capacity was observed after 1000charge/discharge cycles.The aluminum ion batteries Al//λ-MnO₂ and Al//Mn₃O₄demonstrated average operating voltages of 1.55 V and 1.40 V,respectively,with capacities as high as 614m Ah g^-1 and 488m Ah g^-1,respectively,based on the mass of the cathode materials.The joint application of material structural characterization means and electrochemical testing techniques demonstrated that the aluminum ion storage mechanism of the cathode materials is as follows:firstly,Al³⁺is embedded into the lattice ofλ-MnO₂and Mn₃O₄ and undergoes irreversible phase transformation,gradually forming Al Mn₂O₄and Al_0.94Mn₂O₄,respectively.subsequently,Al³⁺undergoes reversible de-embedding in Al Mn₂O₄ and Al_0.94Mn₂O₄.