Synthesis Of Tin-based Composites For Anodes In Lithium-ion Batteries

Lithium-ion batteries are considered to be the most valuable commercial energy storage systems due to the advantages of high energy density,long cycle life,no memory effect,and environmental friendliness.It has been widely used in various portable applications.In recent years,the rapid development of the new energy automobile industry has put forward higher requirements for the performance of lithium-ion batteries.As we all know,the key factor of a lithium-ion battery which affect the electrochemical performance is a lithium storage material.So in order to improve the electrochemical performance of the lithium-ion battery,people need to find a suitable electrode material to make the battery have a sufficiently high lithium intercalation capacity and a good lithium deintercalability,to ensure the high voltage,large capacity and long cycle life of the battery.Among many lithium-ion battery anode materials,tin based materials' high lithium storage capacity(theoretical specific capacity:994 mAh g-1)has attracted great interest.At present,researchers focus on tin-based materials,such as tin oxides,tin composite oxides,and tin salts.Tin oxide(SnO2)is an attractive lithium-ion battery anode material due to its high theoretical specific capacity of 782 mAh g-1 and a relatively low charge-discharge voltage platform of 0.6 V SnO2 has been widely studied for practical use.As an ?-? layered material,tin diselenide(SnSe2)highlights its application prospects as a lithium ion battery anode material due to its abundant natural storage and low toxicity.As a layered material,SnSe2 has a large interlayer distance,which makes it easier for lithium ions to be inserted and extracted.SnSe2 can provide higher theoretical specific capacity(813 mAh g-1).Based on the above research background,this paper focuses on the preparation and electrochemical performance of tin-based composites(specifically for SnO2 based and SnSe2 based composites):?SnO2 nanoparticles were prepared by using one-step hydrothermal method.Furthermore,crystalline SnO2@amorphous TiO2 core-shell nanostructures were prepared by atomic layer deposition technology.The electrochemical properties of SnO2@TiO2 composites as anode materials for lithium ion batteries were also studied.?Various kinds of SnSe2 based composite materials were prepared by using a one-step hydrothermal method,including copper modification,combining SnSe2 with various carbon materials(carbon nanotubes and graphene)to prepare composite materials to improve the electrochemical performance TTT of SnSe2 as an electrode for lithium ion battery.The main research contents of this paper are as follows:(1)SnO2 nanomaterials were synthesized by a simple one-step hydrothermal method.Spherical SnO2 nanoparticles are composed of many smaller nanoparticles,and there are a large number of interstitial structures among these SnO2 nanoparticles.Considering the obvious volume expansion phenomenon of pure SnO2 nanoparticles during the charge and discharge process,this study uses reasonable structural design method to reduce the volume expansion of the SnO2 nanoparticles during the charge and discharge process of lithium ion batteries.The prepared SnO2 nanoparticles were subjected to atomic layer deposition to prepare SnO2@TiO2 core-shell nanostructures.The SnO2 core is a crystal with a diameter of about 20 nm,the TiO2 shell structure is amorphous and the shell thickness is about 3 nm.The prepared crystalline SnO2@amorphous TiO2 core-shell nanomaterials show excellent electrochemical performance.At the current density of 80 mA g-1,the reversible capacity of the SnO2@TiO2 electrode is 1259 mAh g-1,and it still maintains at 703 mAh g-1 after 50 cycles.At a high current density of 400 mA g-1,the reversible capacity of the SnO2@TiO2 electrode can still reach to 412 mAh g-1.The excellent cycle stability and rate performance are mainly due to the isotropic stress provided by the amorphous structure of the TiO2 shell,which can significantly reduce the volume expansion of SnO2 during the cycling process.(2)Various kinds of SnSe2 based composite materials were prepared by using a one-step hydrothermal method,including Cu-modified SnSe2 composite materials,SnSe2/CNTs hybrid and SnSe2/graphene hybrid.The copper element added has excellent electronic conductivity as well as electrochemical catalytic function.The carbon materials(carbon nanotubes and graphene)can build the chemically bond with the SnSe2 nanosheets,which can prevent the tin atoms generated during the lithiation process which greatly buffer the electrode volume change.Therefore,the above-mentioned three kinds of SnSe2 based composite materials have better electrochemical performance as lithium-ion battery anode materials compared with pure SnSe2 electrodes.For example,for SnSe2/graphene composites,the specific capacity reaches to 490.9 mAh g-1 at a current rate of 0.1 C,and it can still level at 126.7 mAh g-1 even at a high current rate of 1 C.After 1500 cycles at 0.5 C,the capacity retention rate was 59.3%.However,for pure SnSe2 electrodes,even after only 100 cycles at a lower current density of 0.1 C,the capacity retention rate is only 30.5%.The excellent electrochemical performance of SnSe2/carbon material hybrid can naturally be attributed to the synergistic effect of SnSe2 and carbon materials...