Study On Improving The Properties Of Silicon-based Anode Material With Nano Carbon Conductive Agent

Lithium ion batteries are widely used in many fields due to their high energy density,long cycle life and environmental friendliness.The cathode material of traditional commercial lithium ion battery is graphite,but the theoretical capacity density of graphite is only 372mAh·g^-1,and the theoretical capacity of silicon anode material can reach 4200 mAh·g^-1,so silicon has received more and more attention.However,as the cathode material of the next generation lithium ion battery,the silicon-based anode material still has its own disadvantages of low conductivity and volume expansion.In order to overcome these two shortcomings,the electrochemical properties of silicon-based anode were improved by combining nano carbon conductive agent with silicon-based material.The single nano carbon and the multiple nano carbon conductive agent compound micron oxidized silica anode were studied.Firstly,CNTs,Li435?a new type of conductive carbon with particle size of 20-30nm?and SuperP were compounded with micron silica oxide.Then CNTs,Li435 and graphene were compounded with micron silica in a mixture of multiple conductive agents in different proportions to make a battery and test its performance.Considering that the conductive agent is light in texture,easy to be agglomerated and difficult to be dispersed in pulping process,the homogenization process of preparing a single conductive agent composite silicon-based negative electrode slurry was explored.The results showed that:compounded with single conductive agent CNTs,the impedance of the battery is the lowest,only 1130?·cm.So CNTs is the most suitable compound conductive agent with silicon material;During the preparation of electrode paste,slurry speed 3000 r/min,homogenate 40 min is the best slurry process and the impedance of the battery is the lowest,only 1000?·cm.CNTs with Li435 with different proportion of combination for binary compound silicon-based anode conductive agent,CNTs+Li435?6%+4%?impedance is minimum,only 220?·cm,so the ratio of components is the best binary components;Add 1%of graphene to the CNTs and binary after Li435 composite conductive agent,the different combination of ternary composite conductive agent,and then respectively with micron composite for silicon and silicon oxide cathode,CNTs+Li435+graphene?3%+7%+1%?ternary composite impedance is minimum,only 104?·cm,so the component is the best ratio of ternary composite.However,it is difficult to improve the cycling performance of the silicon-based anode through simple mechanical mixing,so it is necessary to optimize the silicon-based anode material from the perspective of material synthesis.The composite anode of nano carbon conductive agent and nano silicon was studied.Nanosilicon was synthesized on the composite nanometer carbon conductive framework of Li435 and CNTs.Using tetraethyl silicate?TEOS?as the silicon source,SiO₂ was first synthesized on the nano carbon conductive agent,and then?Li435-CNTs?@Si composite was prepared by magnesium thermal reduction,and its physical and electrochemical properties were characterized.The results show that the composite material is single phase Si and C,and the crystal structure is complete and the purity is high.The?Li435-CNTs?@Si composite material was made into batteries and tested at the current density of 0.1A·g^-1 within the voltage range of 0.01-1.5V.The results showed that the initial capacity was 1320/2530 mAh·g^-1.After150 cycles,the capacity retention rate was 54.9%.At A high current density of 4.0 A·g^-1,the capacity is 700 mAh·g^-1.The composite negative electrode of nano carbon and amorphous carbon conductive agent with nano silicon was studied.By using the characteristics of honey's softness and viscosity,nano-silicon and carbon nanotubes were firmly combined,and the amorphous carbon formed after the honey was carbonized at high temperature was embedded in the conductive network of CNTs.The physical and electrochemical properties of the synthesized material were characterized.The results showed that the crystal structure of silicon in the synthesized material was complete,and the carbon generated by pyrolysis was amorphous.The nanosilicate silicon was completely wrapped by amorphous carbon,and the exposed silicon could not be detected after 200 cycles.The synthetic material showed good multiplier performance and cycling stability.At the current density of 0.1A·g^-1,the initial capacity was 953/1416 mAh·g^-1.After200 cycles,the capacity retention rate was as high as 70%.At the large current density of4.0A·g^-1,there was still A reversible capacity of 398 mAh·g^-1.Assemble the full battery with high nickel positive electrode and test it in the voltage range of 3.0-4.3 V.The capacity is up to200 mAh·g^-1,the coulomb efficiency is 100%,the capacity retention rate of 140 cycles is up to91.7%,and the power discharge ratio capacity is still 125 mAh·g^-1 under the large current of 5.0 C.