Electrochemical Properties Of TiO₂-based Composite Film Anode Materials

At present,lithium-ion batteries are widely used,which effectively promotes the transformation and upgrading of the energy field.In terms of the selection of battery anode materials,Si material is also an optional anode material with high theoretical specific capacity(3572 m Ah g^-1 Li₁₅Si₄).In the Si@C@TiO₂ structure,C@TiO₂ may form a composite structure rather than a double shell structure during heat treatment,which is rarely discussed in general literature reports.We studied it in the form of TiO₂/C multilayer,and found that C could migrate along the grain boundary of TiO₂ to form part of TiO₂（C）composite structure during heat treatment,and C at the grain boundary also prevented the growth of TiO₂ particles.Here,we will further prepare TiO₂（C or Si）composite films by co-sputtering,and study the structural evolution and electrochemical performance of composite films.1.The TiO₂（C）composite film structure was designed based on the phase separation caused by the formation and diffusion of C to TiO₂ in the TiO₂/C multilayer film,and the interface doping between C and TiO₂ formed the composite structure.The results of this research show that the electrode material with TiO₂（C）composite ratio of 2:1 has higher specific electrode capacity and better electrochemical performance.The film electrode was further heat treated to form anatase TiO₂（C）film electrode,and the ionic diffusion coefficient of 2:1 anatase TiO₂（C）film electrode was also the highest.This is because the heterogeneous interface in the sample plays a role in promoting the transport of lithium ions.The channels formed at the interface can shorten the transport distance of ions,thus improving the transport efficiency of ions and promoting the diffusion coefficient of lithium ions.In addition,C is doped at the grain boundary position of anatase TiO₂,resulting in inconsistent crystal grain size and forming an interface titanium that can effectively store charge.The main lithium storage mechanism in anatase TiO₂（C）composite film electrode is a hybrid lithium storage mechanism combining diffusion-controlled electrochemical reaction and capacitance-controlled pseudocapacitance characteristics.This is also the reason for the high specific capacity of 2:1 anatase TiO₂（C）thin film electrode.2.In order to further study the influence of electrochemical performance of TiO₂,a uniform Si composite experiment was designed for TiO₂.By preparing TiO₂（Si）composite thin film electrode and conducting heat treatment on it,The Kirkendall effect between Si and TiO₂ was utilized to precipitate Si particles under heat treatment.The influence of Si content in TiO₂（Si）composite thin film electrode on electrochemical performance of thin film electrode was further studied.The specific conclusions are as follows:After heat treatment,more Si particles precipitate on the surface of the thin film electrode.The holes left by these precipitated Si particles provide a large buffer space for the volume expansion of the remaining active material Si,and also provide a channel for the release and embedding of lithium ions,which promotes the ion transport efficiency.The ionic diffusion coefficient and electrochemical performance of TiO₂（Si）composite electrode 2:1 are excellent.