Preparation And Electrochemical Properties Of Tin Dioxide Composite Anode Materials For Lithium-ion Batteries

Li-ion batteries have been rapidly developed and widely used in recent decades due to their high energy density,long cycle life,and low self-discharge.In addition,LIBs continue to improve as the demand for energy-efficient energy-driven vehicles continues to increase.Researchers have conducted extensive research on anode materials,a key component of lithium-ion batteries.The physicochemical properties of anode materials significantly affect the electrochemical performance of LIBs.Therefore,research on high-energy-density,safe and durable anode(anode)materials in lithium-ion batteries is increasingly in-depth.In the beginning,graphite,as a traditional negative(anode)material,has the advantages of good economy,good electrical conductivity and long cycle life.However,the low capacity(372 m Ahg^-1)and low conversion rate restrict the development of conventional graphite.Metal oxides such as Fe₂O₃,Ti O₂,and SnO₂ are suitable anode materials for Li-ion batteries because of their relative safety,high energy density,and high theoretical capacity.Among these metal oxides,SnO₂-based materials have the advantages of high specific capacity(1494 m Ahg^-1),large storage capacity,and low pollution,and have become an alternative anode material for lithium-ion batteries.But when used as anode in LIBs,SnO₂ undergoes a significant volume change during charge-discharge cycling,leading to the formation of electrode powders that destroy the solid electrolyte phase(SEI),resulting in rapid capacity decay and poor rate.These defects restrict its practical application.Therefore,people have proposed a SnO₂ combined with carbon,graphite,graphene and other substances combined with various transition metals and their different oxides on the periodic table of elements to design a composite nanostructured ternary material as a negative electrode material for lithium ion batteries.(anode),this nanomaterial can significantly improve the electrochemical performance of lithium-ion batteries.Through the above analysis,this thesis mainly studies three different composite nano-anode materials:(1)Hydrothermal method and planetary ball milling are commonly used methods for material synthesis.In this study,a novel ternary SnO₂-Nb-C nanocomposite was synthesized by these two methods,which was intercalated by nano SnO₂ and a small amount of niobium(Nb).composed of flaky carbon.As a negative electrode(anode)material,the SnO₂-Nb-C composite has Nb in different valence states,so the n-type element is doped uniformly.This improves the electron conductivity of the electrode and suppresses the expansion of SnO₂.Thus,the electrochemical performance of the electrode is improved.At 0.2 A g^-1,the capacity after 100 cycles is 956 m Ahg^-1,and the rate capacity is 1130.2 m Ahg^-1.At 1.0 Ag^-1,the specific discharge capacity after 500 cycles is 1077.0 m Ahg^-1.According to the characterization results,SnO₂-Nb-C nanocomposites can be used as potential anode materials for Li-ion batteries.(2)In this study,a SnO₂-NbC-C ternary core-shell structure was re-synthesized by continuation of the method in(1).In this special structure,SnO₂ particles are uniformly dispersed on the hard NbC core,and the obtained SnO₂-NbC hybrid is uniformly wrapped by ultrathin carbon-carbon.It is worth noting that NbC nanomaterials can prevent the expansion of SnO₂ nanoparticles and also prevent Sn agglomeration,which can improve the electrical conduction between particles.The SnO₂-NbC-C nanocomposite has a capacity of over 1055m Ahg^-1 after 100 cycles at 200m Ag^-1 and a rate capacity of over 1130 m Ahg^-1,while the long-term cycling capacity is 700 cycles at 1000m Ag^-1 It reaches 1193.5 m Ahg^-1 under the condition of.This result indicates that the SnO₂-NbC-C ternary nanocomposite has excellent electrochemical performance and surface synthesis performance,and is a promising anode material for Li-ion batteries.(3)The SnO₂-Mo-C composite anode for Li-ion batteries was prepared by simple hydrothermal synthesis and dry ball milling.In this hybridization,nano-sized SnO₂-Mo nanoparticles are encapsulated in flake graphite.Mo additive can prevent Sn aggregation and accelerate the reversible conversion reaction(Sn/Li₂O hybrid conversion to SnO₂).SnO₂-Mo-C shows 70%higher first Coulombic efficiency,1338.3 m Ahg^-1 higher reversible specific capacity after 300 charge-discharge cycles at 0.2 Ag^-1,superior rated capacity of 715.08 m Ahg^-1 and long-term cycle stability with a capacity of 571.9 m Ahg^-1(1000 times of charge and discharge).SnO₂-Mo-C composite has excellent properties and simple synthesis process,and is a promising anode material for lithium-ion batteries.