Preparation And Lithium Storage Properties Of Tin-Based Composite Anode Materials

Among the negative electrode materials for lithium-ion batteries,tin-based materials have received much attention due to their high specific capacity.However,the practical application of tin-based materials is limited by significant volume expansion,fast capacity decay,and poor rate performance.To alleviate these problems,various structural tin-based composite materials were synthesized by designing different compounding methods.The results are as follows:（1）Nitrogen-doped graphene oxide（GO）-supported Sn nanoparticles was successfully prepared by a liquid-phase reduction method,avoiding the agglomeration of low-melting point tin particles during pyrolysis.The tin particles anchored on the surface of GO played an important role in balancing stress throughout the whole composite during charge/discharge;the reduction of ethylenediamine caused plenty of wrinkles on the reduced GO（r GO）,which could relieve the stress caused by the volume expansion of tin nanoparticles during cycling.The obtained material exhibited a reversible capacity of 1739 m Ah g^-1 after 300 cycles at a current density of 500 m A g^-1.（2）Ultrafine Sn nanoparticles-embedded amorphous carbon was synthesized and then loaded onto r GO by a chemical precipitation-carbonization process using 1,10-phenanthroline as chelating agent and Sn Cl₂·2H₂O as tin source.In this process,the metal complex coating on the surface of r GO was pyrolyzed and ultrafine Sn nanoparticles were formed and embedded in nitrogen-doped carbon skeleton with a three-dimensional structure,alleviating the stress caused by the volume expansion of Sn during cycling.Nitrogen doping in carbon could increase active sites,and enhance the interaction between the anchored sites and metal ions,reduce charge transfer resistance and ion diffusion barriers,promote lithium ion diffusion,and improve the wetting properties of the electrode.Some lithium ions were adsorbed on the surface of the carbon matrix or combined with nitrogen atoms.This is beneficial for capacitive charge storage.The reversible capacity of the obtained sample after 300 cycles at a current density of 500 m A g^-1 was 805 m Ah g^-1.（3）Using 3-aminophenol-formaldehyde resin spheres as a template,yolk-shell Sn O₂/C submicron spheres were successfully synthesized by a simple molten salt diffusion-oxygen etching method.Compared with the previous preparation method of yolk-shell structures using Si O₂ as templates and HF as etching agent,this strategy was more environmentally friendly,convenient,and time-saving,and did not require any additional liquid oxidants or solvents.The yolk-shell structure provided sufficient space for the volume change of Sn O₂,and the carbon matrix inside the shell could optimize the electrochemical performance of the yolk-shell structure during the cycle.N-doping in the carbon matrix changes the electronic cloud structure,thus improving the electrical conductivity of the carbon matrix.When the mass ratio of APF resin spheres to Sn Cl₂·2H₂O is 1:4,the prepared sample had the best rate capability and cycle performance,and could still maintain 771 m Ah g^-1 after 500 cycles at a current density of 2A g^-1.