Preparation And Lithium Storage Performance Of Sn-Co-(Sb)/rGo Anode Materials For Lithium-Ion Batteries

With a theoretical capacity of 994 m Ah·g^-1,metallic tin is currently one of the most promising anode materials to replace graphite for the commercialization of lithium-ion batteries.However,the poor cycling performance of tin-based anode materials has limited their commercial application.Most of the currently studied modification pathways are alloying,nanosizing,and compounding of tin-based anode materials to improve the electrochemical performance of tin-based anode materials.Reduced graphene oxide（rGO）as a substrate material exhibits high flexibility and high conductivity.Alloying elements can reduce the internal stresses generated by volume expansion and contraction during lithium-ion de-embedding to reduce the cycling stability of the battery,thus improving the electrode performance.Therefore,in this thesis,graphene oxide（GO）is used as the composite carrier,and Sn-Co/rGO and Sn-Co-Sb/rGO anode materials are prepared by the chemical reduction method followed by sintering to study the influence of the atomic ratios of Co and Sb and sintering temperature on the structure and lithium storage performance of tin-based alloys.The main contents and results of this study are as follows.According to the Sn-Co phase diagram,Sn-Co/rGO composites with atomic ratios of Sn:Co=2:1,Sn:Co=1:1,and Sn:Co=2:3 were prepared,and the results showed that the negative electrode materials consisted of Co Sn₂,Co Sn,Co₃Sn₂,and reduced graphene oxide（rGO）,in which the particle size of the Sn-Co alloy was between 5～50 nm.The first reversible capacity of the Sn-Co/rGO composite showed a trend of increasing and then decreasing with the increase of the sintering temperature.When the stoichiometric ratio was Sn:Co=2:1 and the sintering temperature was 500°C,the prepared Sn-Co/rGO material had good electrochemical properties with a first reversible capacity of 811 m Ah·g^-1.The capacity after 100 cycles is 536 m Ah·g^-1,and the capacity retention rate is 66.1%,which shows that the alloying of Co element can improve the cycle performance of Sn-based materials to some extent.To further enhance the cycling performance of the electrode materials,Sn-Co-Sb/rGO anode materials were prepared by adding Sb elements to Sn-Co/rGO.And it was found that the Sn-Co-Sb/rGO negative electrode material consisted of alloy phases such as Sn,Sb Sn,Co₆Sn Sb,and reduced graphene oxide,and the Sn-Co-Sb alloy particles were spherical in the range of10～50 nm and attached to graphene.When the atomic ratio of Sn-Co-Sb/rGO composite is Sn:Co:Sb=2:1:1,the first discharge capacity is 793 m Ah·g^-1.After 100 cycles,the capacity is645 m Ah·g^-1and the capacity retention rate is 81.3%,which indicates that the addition of appropriate amount of Sb can improve the cycle performance of Sn-based anode materials.