Exploration And Performance Study Of Cobalt Sulfide Used As Cathode For Rechargeable Aluminum-ion Batteries

Rechargeable aluminum-ion batteries?RAB?have the advantages of high theoretical specific capacity(2980 Ah kg^-1),high safety,low cost and abundant aluminum resources?the content of aluminum in the earth's crust is 8%?.It is an ideal candidate of the new generation of large-scale grid energy storage devices.At present,the development of RAB is still in its infancy.The development of suitable new cathode materials with high capacity and long-term stability is the key to improving the electrochemical performance and practical application of RAB.To this end,this work synthesized three kinds of cobalt sulfide materials,and then prepared two composite materials of cobalt sulfide and carbon nanotubes?CNT?in different ways,and studied their electrochemical performance in aluminum-ion batteries.Firstly,CoS₂,Co₉S₈ and CoS cobalt sulfide materials were synthesized by a simple one-step hydrothermal or solvothermal method.XRD and SEM of these products showed that they were of high purity,good crystallization,complete particles and diversified morphology.When the three cobalt sulfide materials are used as the cathode of the aluminum-ion battery,they all exhibit good electrochemical performance.Moreover,as the number of cycles increases,the performance of the discharge specific capacity and the discharge voltage platform tend to increase gradually.Among them,the initial discharge specific capacity of CoS₂ material is 17mAh g^-11 at a density of 200 mA g^-11 and increases to 89 mAh g^-11 at the 300th cycle;Co₉S₈ material can continuously cycle about 600 cycles while maintaining a specific discharge capacity of 60 mAh g^-11 or more(200 mA g^-1);CoS material has up to a specific capacity of¹10 mAh g^-11 at a current density of 300 mA g^-1.Electrochemical analysis shows that the cathode material undergoes the reduction process of aluminum ion intercalation and the oxidation process of aluminum ion deintercalation,and the reversibility is good.The solid phase diffusion process of the active ions inside the cathode material is a control step that limits the reaction kinetics of the electrode.Secondly,in this thesis,CoS₂/CNT and CoS₂@CNT materials with independent self-supporting structure were prepared by mechanical compounding and in-situ growth methods,and their electrochemical performance in aluminum ion batteries was tested.The results show that CoS₂@CNT has excellent rate performance and discharge cycle performance.At a current density of 200 mA g^-1,the discharge voltage platform is 0.9 V.After 150 cycles,the discharge specific capacity reaches160 mAh g^-1,which is higher than CoS₂/CNT and twice the CoS₂ material under the same conditions.At a current density of 300 mA g^-1,CoS₂@CNT exhibits a discharge specific capacity of 200 mAh g^-1.Electrochemical AC impedance tests show that the CoS₂@CNT composite prepared by in-situ growth method has smaller battery internal resistance and higher conductivity than mechanical composite method.The good bonding force between the carbon nanotubes and the active material and the better electron conductivity of the carbon nanotubes give the composite a superior electrochemical performance.In short,cobalt sulfide material is a cathode material for RAB with great potential for development and application.The in-situ composite of carbon nanotubes and cobalt sulfide can greatly improve the electrochemical performance of cobalt sulfide.CoS₂@CNT composites with excellent rate performance and cycle performance have shown good application prospects in the practical application of RAB.