Study On Preparation And Lithium Storage Performance Of Tin-Based Carbon Nanofiber Composite Materials

Metals and metal compounds are currently popular materials in the research of lithium-ion battery anodes,but poor conductivity and large volume expansion in the process of n intercalating/de-intercalating lithium-ion limit their commercial applications.Good design of the material’s structure and the combination of carbon materials with good conductivity and stability to form composites can effectively solve these problems.This thesis focuses on the research in order to solve the poor cycle and rate performance of tin and tin-based metals and compounds as lithium-ion battery anode materials.Electrospinning technology combined with thermal annealing is used to fabricate three kinds of one-dimensional composites with high-performance of electrochemical properties by combing high-capacity tin and tin-based metal compounds with nitrogen-doped carbon fibers.Their structures and lithium-ion storage performance have been systematically investigated.The main contents are shown below.（1）The small-sized ZnSn（OH）₆ precursor is synthesized by a co-precipitation method,and then carbon fiber-wrapped Zn₂ SnO_x is obtained by electrospinning and subsequent annealing.The anode materials consistof Zn₂ SnO_x with high capacity and carbon fiber with high conductivity and stability.The lithium-ion battery shows excellent cycle stability and rate performance with the capacity of 949 m Ah/g after 150 cycles at 0.1 A/g,645 m Ah/g after 800cycles at 1 A/g,even 331 m Ah/g at a high current density of 5 A/g.（2）The SnO₂/ SnSe₂@CNF heterostructured anode is fabricated with SnO₂/ SnSe₂nanoparticles embedded in nitrogen-doped carbon fibers by electrospinning and subsequent thermal reduction selenide process.The capacity of the optimized was maintained at 675 m Ah/g after 800 cycles at 1A/g.The stable heterogeneous crystal plane formed by SnO₂ and SnSe₂can regulate the electronic structure of the original materials,not only promoting the storage of lithium ions but also improving the mechanical stability of the material.The nitrogen-doped carbon in the outer layer acts as a high-speed channel for electron transmission,which enhances the conductivity of the composite and limits the volume expansion of the internal active material.The cycle stability and rate performance of the composite are improved.（3）The novel anode（SbSn@CNF）with SbSn alloy nanoparticles embedded in carbon fibers are prepared by electrospinning and subsequent thermal reduction.Compared with Sn@CNF,SbSn@CNF exhibits the better electrochemical performance with 641.81 m Ah/g after 1000 cycles at 1 A/g.Owing to the different potentials induced by the alloying reaction of Sb and Sn,one phase is intercalated by lithium ions,and the other acts as an inert phase to relieve the volume expansion,which can improve the stability of the anode material.In addition,The influence of alloy composition on lithium storage performance is investigated by changing the ratio of stannous salt and antimony salt.The material with a feeding ratio of 1:1 shows the best electrochemical performance.