Mechanism Of C/TiO₂ Interfacial Interaction,Structural Evolution And Application In Si-based Lithium Ion Batteries

Si-based anode is considered as a very promising lithium ion battery anode material with a theoretical specific capacity as high as 3579 m Ah g^-1.However,it has very serious volume evolusion effect and low electronic conductivity,which make it difficult to be used in lithium ion batteries.An effective solution strategy is to use C and TiO₂as the composite matrix of Si nanoparticles and fabricate core-shell-shell（Si@C@TiO₂）structure through chemical synthesis.However,a common problem still exists as that the uniformity of the product and the cycle stability is poor.There are plenty of C/TiO₂interfaces in Si@C@TiO₂nanocomposites and they should have a very important influence on the electrochemical properties.Therefore,a key element to solve the problem of Si@C@TiO₂nanocomposites is to study clearly the C/TiO₂interface problems in its structure,which will be the main focus of the present study.The research contents of this thesis mainly include:1.C,anatase-TiO₂and C@anatase-TiO₂with similar particle size and morphology were prepared by chemical synthesis method,and their structure characterization and electrochemical properties were tested.The experimental results showed that:The C/TiO₂interface provides additional lithium storage sites and stores lithium ions through pseudocapacitance,which makes C@anatase-TiO₂have a higher charge/discharge capacity than the theoretical specific capacity.The C/TiO₂interface promotes the diffusion of lithium ions in C@anatase-TiO₂and makes it have good rate performance.In addition,the C/TiO₂interface on lithium ion storage and transport does not affect the cyclic stability of C@anatase-TiO₂.2.C,anatase/rutile-TiO₂,C@anatase-TiO₂and C@anatase/rutile-TiO₂with similar particle size and morphology were prepared by chemical synthesis method,and their structural and electrochemical properties were characterized.The experimental results showed that,by appropriately prolonging the heat treatment time of C@anatase-TiO₂nanocomposites,the C/TiO₂interface can be increased and the grain size of TiO₂can be reduced meanwhile.These two factors jointly promote the transport of lithium ions and electrons,and so that enhances the rate performance.In addition,the increased C/TiO₂interface provides more lithium storage sites,which can further improve the specific capacity of the battery.3.Three Si@C@TiO₂nanocomposites with different thickness of coated TiO₂and different interface structure of C/TiO₂were prepared by chemical synthesis method,and their structural and electrochemical properties were measured.It showed that:TiO₂has a relatively weak structure constraint effect as a coating material when the thickness is 8 nm,and a better effect when the thickness is 25 nm.However,when the TiO₂layer becomes thicker,due to its poor conductivity,lithium ions and electrons are difficult to diffuse into the inner part of the structure,resulting in inadequate utilization of core Si material.However,our experimental results show that,by appropriately prolonging the heat treatment time,new aboundant C/TiO₂interface can be created in Si@C@TiO₂nanocomposites,which can effectively improve the overall electrical conductivity and hence make the Si@C@TiO₂nanocomposites maintain good structural stability and high specific capacity.