Preparation Of High Performance Cathode Material And Energy Storage Mechanism Study On Aluminum Storage

The rapid consumption of fossil fuels,coupled with the serious threat posed by global warming,has driven the development of rechargeable battery technology.Lithium-ion batteries（LIBs）,as the mainstream energy storage devices,are widely used in various fields due to their high energy and power density.However,due to the scarcity of lithium resources,safety hazards and high costs,it is still challenging to apply LIBs on a large scale to meet the growing demand,so new energy storage systems with advantages such as low cost and high safety need to be developed.In recent years,aluminum ion batteries（AIBs）have attracted much attention from researchers.They use inexpensive aluminum metal as the negative electrode,which reduces the cost of the battery and can increase the high theoretical capacity through three-electron transfer.The electrolyte is a non-flammable ionic liquid,which also greatly enhances its safety,and is therefore considered to be a very promising new energy storage device for application.However,the cathode materials for AIBs are still facing some problems,such as low capacity,low operating voltage and poor cycling stability,which have seriously hindered the development of AIBs.Therefore,there is an urgent need to find cathode materials with excellent electrochemical performance for rechargeable AIBs.To solve the above problems,graphene oxide coated tin-cobalt alloy（Co₃Sn₂@GO）,carbon coated three-dimensional porous sponge structure of nickel selenide（3D Ni Se₂@C）and Fe₂（Mo O₄）₃（P-FMO）assembled from porous thin cross-sheet were designed in this paper.Finally,a variety of experimental characterization methods combined with theoretical calculations were used to investigate the mechanism of aluminum storage.Among them,3D Ni Se₂@C and P-FMO showed excellent electrochemical performance,which has the potential of commercialization and is worthy of further study and optimization.The main studies are as follows:（1）Co₃Sn₂ nanospheres were synthesized by the solvothermal method and coated with surface graphene oxide.Subsequently,a novel"bimetallic activated central alloy reaction"aluminum storage mechanism was revealed through experimental characterization and theoretical calculations.The mechanism is that during the discharge process,Al³⁺forms Al_xSn and Al_yCo alloys with Co and Sn in Co₃Sn₂,respectively.This new bimetallic activation center alloying mechanism is different from that occurring in other alkali metal ion batteries（e.g.,LIBs）.In LIBs,Co is electrochemically inert,and its precipitation during discharge acts as a buffer for volume expansion and does not return to the alloyed state during charging.In addition,the theoretical capacity of the alloy material based on the proposed bimetallic activation center alloying mechanism is extremely high,which provides guidance for the future design of new high-performance cathode materials for AIBs.（2）For the first time,Ni Se₂ material with a three-dimensional porous sponge structure was designed by solvent thermal and solid-phase selenization methods and surface carbon coating was performed.The highest discharge plateau was found to be as high as 1.8 V after battery assembly tests,which exceeded the operating voltage of most reported cathode materials for AIBs.Electrochemical tests revealed excellent cycling and multiplicity performance,with a discharge specific capacity of 510 m Ah g^-1 at current density of 1 A g^-1 and capacity of 100 m Ah g^-1 even when the current density was increased to 5A g^-1.The cycling stability was tested at a current density of 1 A g^-1,and the capacity remained at 164m Ah g^-1 after 250 stable cycles,demonstrating the cycling performance was excellent.Finally,the energy storage mechanism was revealed,and the experimental characterization by XPS,TEM,and XRD combined with theoretical calculations demonstrated the existence of a double-ion（Al Cl₄^-and Cl^-）insertion/exclusion mechanism in the system,which is the first report of Cl^-embedding as a carrier.（3）This porous structure increases the specific surface area of P-FMO,which is conducive to the full penetration of electrolyte,thus providing more electrochemical active sites and improving the electrochemical performance.After assembling the cell for testing,it was found that its highest discharge plateau reached 1.9 V with excellent multiplicative performance.Its long cycle stability was tested at a current density of 1 A g^-1 and found to be stable for 2000 cycles with 78.8%capacity retention,which also demonstrates the structural stability of this material of P-FMO.The open three-dimensional framework structure of P-FMO provides space for the rapid embedding/removal of aluminum ions,thus achieving the excellent multiplicity performance and structural stability.and structural stability.Further theoretical simulations of the diffusion of aluminum ions on P-FMO reveal that the diffusion barrier is very small,which is the reason for the superior electrochemical performance of P-FMO aluminum cells.