Study On Synthesis Of Tin-based Anodes Materials And Their Electrochemical Performance For Lithium/Sodium-ion Batteries

Alloy-based electrode has become a research hotspot due to the high specific capacity(Sn:847 mAh g^-1;SnO₂:1378 mAh g^-1;Sn Se₂:756 mAh g^-1),simple preparation process and environment-friendly.However,the huge volume change of the Sn-based anode materials?420%sodium insertion and 259%lithium insertion?causes repeated volumetric change of the electrode material during charging and discharging,leading to the pulverization and even fall off from the current collector,thus the reversible capacity decay rapidly.This is the common phenomenon for all the alloy anodes.At present,there are mainly three ways to solve the above problems of the alloy electrode materials:preparation nanomaterials,controlling special structural and preparation of composite materials.The essence of these methods is improving the structural stability and electrochemical reaction kinetics of the electrodes to obtain high reversible capacity,good structural stability and rate property.In this paper,the Sn,SnO₂ and Sn Se_x are studied regarding to their problems respectively.The main innovations including:?1?The PVP assisted room-temperature liquid reduction method was used to successfully obtain the hollow-sphere structure that was assembled by 5 nm Sn nanoparticles.It was found that the Sn nanoparticles with hollow structure presented good structural stability and was able to withstand the stress caused by the volume change?364%?,showing a higher reversible capacity than the solid structure.?2?Sn O₂/super P composites were prepared by using super P as carbon matrix,and the SnO₂ nanoparticles with diameter of 2⁵ nm anchored on the super P surface.The composite electrode showed more excellent sodium storage performance than pure SnO₂.The study found that super P could relieve the volume change of Sn O₂ in Na⁺de-intercalation process,making SnO₂/super P composite material had good structural stability.In addition,super P has good conductivity,which acts as the charge transport channel to promote the electrochemical reaction of SnO₂.?3?The core-shell structure of SnO₂/C,Sn/Sn O₂/C and Sn/C composites with Sn and SnO₂ nanoparticles uniformly dispersed in carbon microspheres were obtained by hydrothermal method and carbonized pyrolysis.Comparing the sodium storage performance of the three electrodes,it is found that the Sn/SnO₂/C ternary composite electrode demonstrated higher first coulombic efficiency and reversible capacity in comparison with the Sn O₂/C and Sn/C composites.The high reversibility of ternary composite electrode could be attributed to the synergistic effect between Sn,SnO₂ and C ternary phases.?4?SnO₂@CNTs composite with Sn-O-C bond and Sn-C bond content controllable was successfully prepared.When used as lithium storage materilals the SnO₂@CNTs composite electrode with more Sn-C bonds has a reversible conversion reaction.Controlling the content of Sn-C bonds in the SnO₂@CNTs composite,found that the high content of Sn-C bonds could achieve an in-situ pulverized structure during charge-discharge process.The structure can improve the electrochemical reaction kinetics of SnO₂.Furthermore,C@Sn O₂@CNTs composite electrodes were obtained by coating carbon on the outer layer of SnO₂@CNTs composites and the C@SnO₂@CNTs composite showed good cycling stability.?5?The structure controllable Sn Se_x nanocrystals and their composites with carbon were prepared by solvothermal method.The relationship between phase,structure and electrochemical properties was also explored.Results show that the electrochemical performance of SnSe with irregular nanoparticle structure is better than that of the SnSe₂ nanosheet.The SnSe/r-GO composite synthesized by using graphene oxide?GO?as carbon matrix shows different lithium-stored mechanism with pure SnSe electrode.The electrochemical reaction process of SnSe/r-GO electrode maintains a surface-controlled pseudocapacitive effect,while the SnSe electrode are diffusion controlled process.