Synthesis And Lithium Storage Performance Of SiO_x And SiOC Based Anode Materials

With the rapid development of society,commercial lithium-ion batteries are difficult to meet people's demand for high energy density energy storage equipment.Although the graphite anode materials have stable performance,their energy density has already approached the theoretical value.Silicon anode materials are considered to be the most promising anode materials due to their extremely high theoretical capacity,abundant raw materials,and simple synthesis process.Silicon anode has poor conductivity and severe volume expansion,which makes it difficult to apply directly.The modified silicon-based anode materials have excellent reversible capacity and have less volume expansion than pure silicon.At present,SiO_x materials,a silicon-based anode,have entered into commercially production stage,and its preparation technology is relatively mature.Moreover,new silicon-based anode materials of SiOC which consist of silicon,oxygen,and carbon elements not only have high reversible capacity,but also have good electrical conductivity and mechanical stability.However,the volume expansion of SiO_x anode materials during the cycles leads to the capacity fading.In addition,SiOC materials have large first-cycle irreversible capacity,and inferior cycling performance and poor rate performance at large current densities.In this paper,commercial SiO_x/C composites are modified by adjusting the amount of carbon black,and the effect of the amount of carbon black on the cycling performance of the material is studied to obtain electrode materials with long service life.In addition,in order to find anode materials with high capacity,small volume expansion,and good cycling stability,the synthesis method and lithium storage mechanism of the new silicon-based anode materials of SiOC are also studied in this paper.The SiOC materials with uniform element distribution were prepared by the bio-template method and supercritical technology,and the influence of calcination temperature on the microphase composition of the SiOC material was investigated.The main conclusions are as follows:?1?Using commercial SiO_x/C as the raw material,a high-load and high-density electrode was prepared by a blade coating method.The result found that when the carbon black content exceeds 1.6%,the film formation capability of the electrode is poor,and the adhesion between SiO_x/C and the current collector decreases.In the first130 cycles,the reversible capacity of the sample with 1.2%carbon black is 491.6 m A h g^-1,which is the highest.When the content of carbon black is 1.4%,the reversible capacity of the sample is 443.9 m A h g^-1 at the current density of 0.1 A g^-1.After 300cycles,the capacity of sample with 1.4%carbon black is 408.4 m A h g^-1,and the retention rate of capacity is as high as 92%,indicating excellent cycle stability and long service life.?2?Using rose pollen as a bio-template and carbon source,supercritical carbon dioxide fluid was used to dissolve ethyl orthosilicate to controllably prepare porous SiOC microellipsoids.It is found that the calcination temperature has a great influence on the electrochemical performance of pollen-derived SiOC materials.When the calcination temperature is 600 ^oC,the SiOC materials has the highest reversible capacity of 415.1 m A h g^-1.The result of XPS spectrum indicates that the calcination temperature actually affects the composition of SiO_xC_4-x.When calcined at 600 ^oC,the ratio of SiO₂C₂ and SiO₃C which related to high reversible capacity and structural stability,contained in SiOC is the highest.