Preparation And Electrochemical Properties Of Tin-Based And Silicon-Based Anode Materials For Lithium-Ion Batteries

With the increasing demand for new energy storage,lithium-ion batteries（LIBs）have attracted much attention due to their high energy density,no memory effect,safety and long cycle life.This dissertation mainly studies the anode materials of LIBs.At present,graphite is the most commonly used anode material in commerce.Its cycle is stable,but its theoretical specific capacity is only 372 mAh g^-1,which is difficult to meet the requirement of high performance LIBs.Tin-based and silicon-based materials are expected to become the next generation of lithium-ion（Li-ion）battery anode materials instead of graphite due to their large reserves,low cost and high theoretical specific capacity.However,the cyclic performance of tin-based and silicon-based anode materials still suffer from the low conductivity and the volume effect during charging and discharging.In order to overcome these problems,this work focus on amorphous carbon composited with tin-based and silicon-based materials by different methods,constructing porous structure materials to alleviate the volume stress.The main research work is as follows:（1）tin tetrachloride pentahydrate is chosen as tin source,GO and C₆H₁₂O₆ as carbon source,the composite of SnO₂ dispersed into amorphous carbon has been synthesized by hydrolysis and carbonization in large scale.The composite structure and morphology of the products are characterized,and the electrochemical properties of the product are analyzed by electrochemical tests.SnO₂ nanoparticles are homogeneously dispersed in the matrix of amorphous carbon.After 100 cycles,the discharge capacity of the composite is 542 mAh g^-1.Amorphous carbon can effectively suppress the volume change of SnO₂ particles during charging/discharging,improve the conductivity of the composites,and obtain better cyclic stability,and lead to an improved electrochemical properties.（2）Crystalline Si nanoparticles have been synthesized on a large-scale via a low temperature molten salt method.The crystal morphologies and electrochemical properties of the sample after HCl and HF leaching are studied in detail.The electrochemical properties and cycle stability of the as-produced silicon sample are collected as anode electrode for LIBs.A proper amount of SiO₂ with paragenesis of Si sample is helpful for the cyclic stability because it can buffer the volumetric effect of Si during lithiation/delithiation.The HF acid leach removes the impurity of SiO₂ but the as-produced sample presents lower electrochemical properties.Si sample with minor SiO₂ can deliver capacity of 1503.8 mAh g^-1 after 50 cycles at a higher current density of 1 A g^-1 and the columbic efficiency near 100%.However,Si sample after HF acid leaching only delivers a discharge capacity of 389.2 mAh g^-1 at 1 A g^-1 after50 cycles.（3）In order to improve the conductivity of Si powder,one step synthesis of silicon/reduced graphene oxide/carbon nanotubes composites by low temperature molten salt method.The Si/rGO/CNT/C electrode was prepared and circulated for 300cycles at a current density of 0.1 A g^-1.There is still a reversible specific capacity of335.7 mAh g^-1,the specific capacity retention rate is 46.5%,and the coulombic efficiency is close to 100%.（4）Preparation of rGO/CNT/SiO₂ precursor by hydrothermal reduction using hydrazine hydrate as reducing agent.The core-shell-like rGO/CNT/Si/C electrodes were prepared by reducing diatomite by low temperature molten salt method.The specific discharge capacity of 393.8 mAh g^-1 can still be maintained after 100 cycles at different rates,and the specific capacity retention rate is 53.5%.