Synthesis Of Carbon Coated Tin-based Compounds And The Studies For Their Lithium Storage Properties

Lithium-ion batteries（LIBs）are the most widely used energy storage devices.Currently,graphite,the common commercial anode material,has not been able to meet the development of lithium-ion batteries.Therefore,it is urgent to find new alternative materials.Among various anode materials,tin-based materials were considered as candidates for next generation of anode materials due to their high theoretical specific capacity,abundant reverse and environment-friendly.However,certain defects of tin-based materials limit its practical application.First,tin-base materials suffer volume expansion during charging and discharging,which causes the active materials pulverization and fall off.Second,the internal conductive of certain tin-based materials（SnO_x,SnS_x,SnSe_x,Sn_xP_y,etc）are poor.The carbon composites are aboundant and good electric conductive,which was commonly combined with other anode materials to enhance conductive and restrict volume expansion.In order to overcome those defects in tin-based materials,this paper reported reasonable methods to improve and optimize the tin-based materials by combining with carbon composites,and studied the electrochemical performance as anode materials for lithium-ion batteries.The main research contents are as follows:First of all,N-doped carbon coated amorphous SnS（a-SnS@N-C）was synthesized by facile precipitation-annealing method.Firstly,carbon has good electrical conductivity,and the nitrogen doping further improves its charge transmission capability.Secondly,the carbon also restrains the volume expansion and ensures the stability of the material during cycle.Furthermore,the carbon layer also has separation effect,avoiding the agglomeration of SnS particles and ensuring the size at nanoscale.The nanoscale SnS is facilitating rapid ion diffusion,ensuring the excellent electrochemical performance of a-SnS@N-C.Specifically,a-SnS@N-C has good rate capability and cycle performance as LIBs anode.It exhibted reversible capacity of578.8 mAh g^-1 after 200 cycles at 1 A g^-1,while the capacity of a-SnS is only 30.7 mAh g^-1 after 120 cycles at same current density.Second,the precursor was prepared by precipitation-annealing and then selenized to obtain N-doped carbon coated SnSe₂（SnSe₂@N-C）.SnSe₂ particles with nano size are well distribution,which facilitated to extraction of Li⁺and improved the reversiblility of conversion during delithiation.The ion diffusion test further proves that SnSe₂@N-C has higher ion diffusion coefficient.N-doped carbon enhances electric conductive of materials and restrict and buffer volume expansion,which further improve cycle performance.SnSe₂@N-C reveals 491.9 mAh g^-11 after 100 cycles at 100mA g^-1,while Bulk SnSe₂ only has 150.8 mAh g^-11 at same condition.Even at 500 mA g^-1,SnSe₂@N-C still exhibits 403.7 mAh g^-1 after 300 cycles.Meanwhile,it displays excellent rate performance.Finally,TiO₂ was introduced to construct（Sn₄P₃+TiO₂）@C with special morphology on the basis of Sn₄P₃@C.Its special spherical structure can provide enough space to adapt to volume change of Sn₄P₃,and external carbon layer also facilitates to improve the electrical conductivity of material.The addition of TiO₂ avoids the agglomeration of Sn₄P₃ and improves ion diffusion performance,thus（Sn₄P₃+TiO₂）@C has better lithium storage performance than Sn₄P₃@C,which is reflected in（Sn₄P₃+TiO₂）@C has better rate performance and cycle performance.It reveals reversible capacity of 455.54mAh g^-1 at 100 mA g^-1 after 100 cycles.