Preparation And Electrochemical Properties Of Si-based Composites Si/TiO₂and Si/TiO₂/C For Lithium Ion Batteries

Silicon has been recognized as an alternative anode material for lithium ion batteries （LIBs） and hasdrawn much attention since it was firstly put forward, since its theoretical specific capacity of4200mAhg^-1is ten times higher than that of traditional graphite (372mAh g^-1). Besides, silicon has low insertionpotential （below0.5V versus Li/Li⁺） and has high relative abundance （26.3%） in the Earth’s crust.However, its large volume change （300%） during repeated charge-discharge in cycling and the resultingshort cycle life still hinders its widespread implementation.In order to overcome the rapid capacity decay of silicon, many silicon-based anode materials have beenstudied by scientists and engineers all over the world, in particularly nano-scaled silicon and silicon-basedcomposites. The enhanced cyclability of nano-scaled silicon can be mainly attributed to the alleviatedabsolute volume change. Silicon-based composites such as Si-graphite, Si-graphitization carbon, Si-othercarbon composites, Si-Ag, Si-TiN and Si-N have demonstrated improved cycling stability compared withtheir pristine silicon counterparts, which have been mainly ascribed to the buffering effect of inactivematrix in the electrode during repeated charge-discharge. Nevertheless, there still exists obvious distanceaway from the practical requirements despite of substantial progress in improving the cycling performanceof silicon.As a class of promising candidate, nano-transition metal oxides have been widely studied since theywere firstly proposed. Among many transition metal oxides, TiO₂has attracted much attention for its manyadvantages such as low price, non-toxic, and pollution-free natures. Particularly, nano TiO₂has littlestructure change in repeated charge-discharge, and demonstrates low polarization, good reversibility andsafety performances. However, the theoretical specific capacity of TiO₂is only335mAh g^-1, close to thatof the most commercialized anode material of graphite carbon, which can not meet the fast development inpower sources.Previous researchers have tried to combine the merits of Si and TiO₂, and observed improvedelectrochemical performances. Zeng et al. prepared mesoporous Si/TiO₂film on Cu sheet by sol-gelmethod, wherein the mesoporous TiO₂successfully suppressed the volume change of Si nanoparticles. However, the preparation of composite film on current collector by sol-gel method is hard for practicalapplication. Kim et al. coated Si particles with porous TiO₂through a sol-gel process, while the dischargecapacity quickly attenuated to400mAh g-1after only20cycles.In the present study, Si/TiO₂composite was synthesized by a simple hydrothermal method. Comparedwith its pristine Si powder, the demonstrates much improved reversibility, which could be attributed to thebuffering effect of TiO₂coating layer on the huge volume change of silicon.Although the cycle stability of Si can be improved by the recombination action of Si and TiO₂, thereversible capacity of Si can not fully exert since of the poor conductivity of Si and TiO₂. Therefore, thecarbon material have good conductivity was introduce in the process of preparation Si/TiO₂composite. Onthe one hand, carbon material can make the electrical conductivity of the composite well improved thus thereversible capacity of Si can fully exert; On the other hand, carbon material can also have the bufferingeffect on the huge volume change of silicon.In this paper, the Si/TiO₂composite was prepared by hydrothermal method, the Si/TiO₂/C compositewas prepared by sol gel method, physical properties and electrochemical performance were test, mainlyfinished the following several aspects.1．Si/TiO₂composite was synthesized by a simple hydrothermal method. The physical properties ofSi/TiO₂composite were characterized by using X-ray diffraction （XRD），laser Raman spectroscopy，scanning electron microscope （SEM） and inductively coupled plasma （ICP）. The electrochemicalperformance of Si/TiO₂composite is studied, the experimental results show that compared with pure TiO₂,Si/TiO₂composite has a big increase in capacity, at the same time compared with the pure Si, has the goodcycle stability.2．Si/TiO₂/C composite was synthesized by sol gel method. The physical properties of Si/TiO₂/Ccomposite were characterized by using X-ray diffraction （XRD），laser Raman spectroscopy and scanningelectron microscope （SEM）. The electrochemical performance of Si/TiO₂/C composite is studied,experimental results show that compared with pure TiO₂, Si/TiO₂/C composite has a big increase incapacity, at the same time compared with the pure Si, has the good cycle stability.