Study On Electrochemical Behavior Of TiO₂/Si-Ge Alloy Composite Anode Material

As the key energy storage equipment in the 21st century,the use of high specific capacity anode materials is the main strategy to improve the energy density of lithium-ion batteries before there is no big breakthrough in the capacity of its cathode materials.Si is the single material with the strongest Li⁺storage capacity,but its low electronic and ionic conductivity greatly affects the electrochemical performance.Ge and Si belong to the same family of elements.Although the lithium storage capacity of Ge is weaker than that of Si,the electronic and ionic conductivity of Ge is two orders of magnitude higher than that of Si.In the early stage,our group used Si/TiO₂ multilayers to study the interface behavior of Si/TiO₂ in detail.It was found that the interface improved the overall electrochemical performance of the anode electrode material and promoted the diffusion kinetics of ions.In this paper,we take Ge as the research object to study the interfacial electrochemical behavior of TiO₂/Ge and TiO₂/(Si-Ge).1?The effects of amorphous TiO₂ on the structure and electrochemical properties of Ge-based materials in multilayer structure were discussed;The heterogeneous interface of TiO₂/Ge composite was macroscopically enlarged by TiO₂/Ge multilayer film,and the heterogeneous interface effect of TiO₂/Ge was discussed.The results show that:(1)amorphous TiO₂ as substrate can effectively alleviate the volume change of Ge material and improve the cycle stability of anode material;(2)there are a mass of lithium storage sites at the TiO₂/Ge heterogeneous interface.The interface lithium storage mode is the electrochemical behavior of the battery,which improves the specific capacity of the anode electrode material;(3)a local lithium-ion concentration gradient is formed at the TiO₂/Ge heterogeneous interface,which further promotes the transport kinetics of lithium ions.2?Compared with amorphous TiO₂,anatase TiO₂ has better thermal and mechanical properties.Therefore,TiO₂/Ge multilayer composite anode electrode materials were heat treated to make the TiO₂ phase change from amorphous to anatase and explore their electrochemical properties.The results show that:(1)Anatase TiO₂can better stabilize the electrode structure than amorphous TiO₂,improve the specific capacity retention and structural stability of anode materials;Anatase-TiO₂ can be widely used in the buffer matrix of group IV elements with large volume changes;(2)heat treatment realizes the diffusion of Ge from the inside of the film to the surface of the film;(3)sample c-TG-15:5 is the best TiO₂/Ge thickness ratio.The sample has the maximum specific capacity(650 m Ah/g)and excellent rate performance.3?Si has extremely high specific capacity and Ge has excellent diffusion kinetics.The preparation of TiO₂/(Si-Ge)alloy multilayer composite can meet the requirements of higher energy density and higher power density.At the same times,the partial substitution of Si for Ge can reduce the cost of anode electrode.The results show that:(1)when the ratio of Si:Ge is 1:1,sample TSG-50%has the best electrochemical performance,because under this ratio,the maximum local stress field is generated in the Si-Ge alloy,which limits the dislocation movement and stabilizes the electrode structure;(2)similarly,there are a large number of lithium storage sites at the heterogeneous interface of TiO₂/(Si-Ge),which improves the specific capacity of the sample;(3)Ge improve the conductivity of the electrode sheet;(4)amorphous TiO₂alleviates the volume change of Si-Ge alloy to a certain extent and stabilizes the electrode structure.