Comparative Study On The Electrochemical Properties Of Si-Coated By C And TiO₂ And The Doping Of The Coating

The solution to the problem of Si anode in lithium-ion batteries has been more clear.That is,it is solved by coating the nano-scale Si particles and then constructing the volume expansion space,and then dividing and covering the graded composite structure with the reinforcement layer.In the composite structure,carbon is a commonly used coating buffer layer,and TiO₂ is often used for structural restraint.Although this structural design can greatly improve the electrochemical performance of Si,the influence of the coating layer and the multilayer coating structure on the electrochemical performance of Si is not very clear,and the surface modification research of the multilayer coating structure is relatively rare.In this paper,through the comparative study of the three coating structures including Si@C,Si@TiO₂ and Si@C@TiO₂,the effect of different coating layers on the electrochemical response process of Si is explored,At the same time,given that the structure of TiO₂ is easy to adjust and the defected TiO₂ has better electrochemical performance,by treating Si@C@TiO₂ in H₂ and NH₃ atmospheres respectively to obtain a coating structure containing different defected TiO₂,explore different defects in TiO₂ influence on the electrochemical performance of Si@C@TiO₂,The modification of the carbon coating is mainly done by doping with N,however,the C layer in the Si@C@TiO₂ structure is difficult to be effectively doped and the high temperature environment required for doping is likely to cause structural changes of TiO₂.C material with high N content was obtained by pyrolyzing melamine-formaldehyde?MF?foam resin by low temperature method,which was prepared for the later N-doping of C coating layer.1.Based on the cladding structure,compares the electrochemical behavior of the above three cladding structures systemly.Its purpose is to study the influence of different coating materials on the electrochemical response process of Si and the influence of the interface existing in the coating structure on the electrochemical lithium storage method.The experimental results show that Si@C,Si@TiO₂ and Si@C@TiO₂have different delithium potentials and lithium storage methods,indicating that the Si/cladding material interface will affect the delithiation potential of Si,C/TiO₂interface has obvious pseudo-capacitance characteristics.2.The defect state in Si@C@TiO₂ affects the electrochemical lithium storage method of Si,the Si@C@TiO₂ samples and the Si@C@TiO₂–Ov samples have obvious pseudo-capacitor lithium storage methods.The Si@C@TiO₂–N samples showed obvious Si@C-like delithiation potential,and the specific capacity and Initial Coulomb efficiency were significantly higher than the former two.3.Compared with other samples,MF-600 has higher nitrogen content and fully degraded structure,when used as a negative electrode,it has the highest lithium ion diffusion coefficient(1.8×10^-13cm²/s),the highest specific capacity(stable specific capacity exceeds 600mAh·g^-1),and the lithium storage methods are electrochemical lithium storage and pseudocapacitor lithium storage.