Study On Energy Storage Mechanism And Electrochemical Expansion Behavior Of Stannous Sulfide Materials With Extended Cyclic Stability

The development of anode materials with high capacity is a key factor for the large-scale commercial application of lithium/sodium-ion batteries.Stannous sulfide（Sn S）material is regarded as one of the most promising new anode materials due to its high theoretical specific capacity,low cost and abundant reserves.Nevertheless,the poor conductivity and the huge volume change during ion deintercalation severely limit its further commercial application.In this paper,the structure of the Sn S@C composite material was regulated and optimized through the nanoconfinement engineering to obtain a general anode material for lithium/sodium-ion batteries with high performance.The relationship between the microstructure and electrochemical performance of the composite material was explored.The in-situ characterization and finite element simulation provided insight into the reaction mechanism,volume expansion and kinetic behavior of Sn S electrode materials during energy storage.The specific work is as followed:Firstly,hollow Sn S@C nanospheres（Sn S@C）were constructed using S nanospheres as templates combined with a carbon coating strategy.Through in-situ XRD,real-time observation of electrode thickness and finite element analysis,the energy storage mechanism and electrochemical expansion behavior were studied.The results showed that the energy storage mechanism of the composite material includes transformation reaction（Sn S+2M⁺+2e^-→Sn+M₂S,M is Li or Na）and alloying reaction（Sn+M⁺+e^-→M_xSn）which leads to more dramatic volume expansion.In lithium-ion batteries,when the carbon layer thickness was 43 nm,the carbon layer reduced the interfacial tensile stress during lithium deintercalation and effectively limited the expanded Sn S to the reserved space,thus reducing the electrode expansion.The capacity was 618.7 m Ah g^-1,capacity retention could reach 100%after 800 cycles at the current density of 1 A g^-1,showing excellent electrochemical performance.And for sodium-ion batteries,since the radius of sodium ions is larger than that of lithium ions,the thickness of carbon layer could only be increased to 72nm to effectively limit the expansion.The capacity was 314.9 m Ah g^-1,capacity retention could reach 98.6%after 800th cycle at 5 A g^-1.On this basis,Sn S@C@r GO composites with 3D conductive network were prepared by distributing hollow Sn S@C nanospheres on ultrathin graphene sheets by electrostatic self-assembly method.The introduction of graphene accelerated the electron and ion transport,restricted the agglomeration of Sn S@C nanospheres and showed rapid transport kinetics and super structural stability.Sn S@C@r GO electrode as the anode of lithium-ion battery,after cycling 1000 times at 2 A g^-1,the reversible specific capacity was still 619.2m Ah g^-1,showing excellent cycle stability with low capacity decay of 0.081%per cycle.The rate performance of Sn S@C@r GO electrode was also excellent,showing a stable change at different current densities.Especially at high current densities of 5 and 10 A g^-1,the reversible specific capacity was 557.2 and 441.7 m Ah g^-1,respectively.As the anode of sodium-ion batteries,the discharge specific capacity was 573.5 m Ah g^-1after 500 cycles at 1 A g^-1.At high current densities of 5 and 10 A g^-1,the reversible specific capacity was357.9 and 309.2 m Ah g^-1,respectively.