| With the rapid development of new energy vehicles,portable electronic products and communication equipment,traditional lithium-ion batteries(LIBS)have been unable to meet people's extensive needs.Therefore,the development and research of lithium-ion batteries with good environmental compatibility,high energy density and excellent rate performance has become a research hotspot.Silicon has become the most promising material due to its large theoretical capacity(4200 m Ah g-1),low discharge current and low cost.However,it will have serious volume changes(more than 300%)during the cycle.In order to improve this problem,a lot of efforts have been made,such as designing porous silicon materials,constructing suitable structures and preparing nano-silicon matrix composites.Among them,the preparation of silicon matrix composite electrode material is considered to be the most commercially feasible method,but the current research has the problems that magnesium thermal reduction will destroy the material morphology and the performance of lithium-ion battery is poor.This study through the low cost and simple operation step of the silicon/carbon composite electrode materials with different morphology,morphology after heat magnesium reduction intact and make it effective enhance battery performance,and further lead Ti O2 barrier for optimizing the performance of the composite electrode materials,this thesis mainly study specific content is as follows:(1)Preparation of Si O2/C and Si O2/C@C composite electrode materials with different morphologies and study on the performance of lithium batteries.In order to improve the inherent low conductivity of silica,Si O2/C composites with different morphologies were prepared by one-step method using cetyltrimethylammonium bromide(CTAB)as a template.The effects of different proportions of ethyl orthosilicate and glucose on the morphology of composite electrode materials were investigated.The results show that the morphology of the composite electrode material changes from bowl shape to lamellar shape with the change of Si O2/carbon ratio,indicating that carbon plays a supporting role in the composite material.At the same time,the performance of a series of composite electrode materials with different morphology was studied.The Si O2:C=1:4 composite electrode material can reach 320.6m Ah g-1 after 150 cycles.In addition,the capacity of Si O2/C@C composite electrode material with secondary carbon inclusion also shows an increasing trend.The experimental results show that the unique structure of the Si O2 ball wrapped in the carbon bowl not only enhances the conductivity of Si O2,but also has a higher initial coulomb efficiency and better structural stability,which also provides a new idea for simpler preparation of Si O2/C composite electrode materials.(2)Preparation of Si/C composite electrode materials with different morphologies by magnesium thermal reduction method and the performance of lithium-ion batteries.In order to further improve the specific capacity of lithium-ion batteries and restrain the expansion of silicon volume,magnesium powder and Si O2/C composite materials were used as raw materials,and sodium chloride(Na Cl)was used as the heat-removing agent to conduct magnesium thermal reduction in the presence of argon and hydrogen mixture.The results of XRD and SEM tests show that the morphology of Si/C composites is perfectly maintained due to its unique bowl and layered structure.When used as anode material for lithium-ion batteries,Si:C=1:4 electrode material still maintains a discharge specific capacity of 550.2 m Ah g-1 after 100 cycles,and its initial coulombic efficiency reaches 78%,which also maintains a good capacity retention rate even at high current density.The experimental results show that the step of Si O2/C composite materials have closer bonding force,and the structure of the carbon bowl strong support to make it not only appearance intact after magnesium thermal reduction,and limit the silicon in the process of lithium battery cycle the huge expansion of the volume,in order to improve this Si/C composite electrode materials circulation performance provides a new technical route to support.(3)Preparation of layered porous Si@Ti O2@C electrode material and study on the performance of lithium batteries.In order to further inhibit the expansion of silicon volume,this chapter synthesized the Hierarchical porous Si@Ti O2@C composite electrode material by magnesium thermal reduction HHSS@Ti O2@C composite material,and successfully prepared the Si@Ti O2@C composite electrode material with the best performance of lithium-ion battery by adjusting the amount of Ti O2.The morphology damage of HHSS@Ti O2@C composite electrode material during magnesium thermal reduction is avoided because Si O2 has the dual protection of Ti O2isolation and outer carbon.The performance of lithium-ion battery was tested on Si@Ti O2@C composite electrode material.It was found that the Si@Ti O2@C composite electrode material still maintained the discharge specific capacity of 627.6m Ah g-1 after 100 cycles,and the initial coulombic efficiency reached 80%.At the current density of 1C,it still has a specific discharge capacity of 354.4 m Ah g-1.The excellent cycling stability and high speed can be attributed to the dual inhibition of volume expansion of silicon by Ti O2 and carbon,which provides a theoretical basis and technical reference for the preparation of special structure Si-based anode materials by thermal reduction of magnesium. |
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