Ionic Liquid-Assisted Preparation Of Tin Oxide-Carbon Composite Material For Anode Of Lithium Ion Batteries

At present,the anode materials of commercial lithium ion batteries?LIBs?are mainly carbon-based materials,which have some disadvantages,such as large capacity loss at initial cycle and low cycle life.SnO₂ has become one of the most promising candidates for commercial anode materials due to its high theoretical capacity of 1494 mA h g^-1 and low voltage of about0.6 V?vs Li⁺/Li?.However,there is still a problem,rapid capacity fade in the lithiation,which is due to the limited conductivity,poor ion transport kinetics and large volume change of SnO2.Typically,there are two strategies to solve these problems:1.Design and construct nanostructured SnO2 to prevent huge volume expansion by reducing internal stress,such as nanospheres,nanowires and hollow structure;2.Introduce carbon materials as a stable framework for coating,volume strain resistance and excellent conductivity.Meanwhile,these two strategies are used to improve the structure stability,electron/ion transport of SnO₂-based anode to a great extent.However,there are still many challenges to obtain the ideal combination of tin oxide and carbon materials,including the aggregation of SnO₂ nanoparticles,poor interfacial compatibility and hydrophobicity of carbon materials.The poor interface efficiency and weak interaction leads to the undesirable nanostructure of SnO₂-C composite.Therefore,the effective interface modification between SnO2 and carbon becomes crucial to construct an ideal nanostructure and achieve the excellent electrochemical performance of SnO₂-based anodes in LIBs.Due to its special structure,ionic liquids can play the role of polymerization and modification in the preparation of composites as solvents.Therefore,tin oxide-carbon composites with ideal interface can be prepared by ionic liquid.In this paper,the two carbon materials,graphene oxide and carbon nanotubes,were modified by ionic liquid?IL,1-allyl-3-methylimidazole chloride salt?to study the effect of ionic liquid.Finally,carbon nanotubes were selected as the carbon base compounded with tin oxide.The nanostructures of tin oxide nanoparticles uniformly and firmly grafted on carbon nanotubes were successfully constructed.The composite is called SnO₂@IL-CNTs.1.Graphene and carbon nanotubes were modified by ionic liquid and then characterized.On the one hand,ionic liquids can make?-?or/and cation-?interaction with carbon materials through the?-conjugated bond of carbon ring,which can firmly bind with carbon;in addition,ionic liquid can disperse carbon materials to a certain extent to inhibit agglomeration.At the same time,the surface of carbon nanotubes modified by ionic liquid introduces more defect sites,which is convenient for metal oxide recombination and Li⁺intercalation and deintercalation.Therefore,the carbon nanotubes is adopted as the carbon substrate.2.SnO₂@IL-CNTs are prepared by the sol-gel method.IL can interact with metal oxide particles and carbon materials and modify the interface of the two,thereby greatly promoting the electron/ion transport in SnO₂ and preventing SnO₂ continuous volume change during lithiation.When used as a negative electrode of LIB,SnO2@IL-CNTs exhibit high reversible specific capacity and rate performance,as well as excellent cycle stability.At the same time,as the charging and discharging process progresses,more Li⁺is accumulated at the electrode interface with the cycle increasing,so the specific capacity of the battery shows a reverse growth.