Multi-phased Composite Preparation And Cycling Perfromance Of Silicon-based Anode Materials

The development of electric vehicles and unmanned aerial vehicles has greatly promoted the prosperity of the lithium-ion battery industry,especially the power battery industry.However,it has also put forward higher requirements for the energy density of the battery.Limited by its theoretical specific capacity,traditional commercial graphite anodes can no longer meet the demand of people.Therefore,silicon-based anode materials including Si or Si O with advantages of high theoretical specific capacity,environmental friendliness,rich resources,and moderate lithium insertion potential are catching people's attention and becoming the main choice for the next generation of commercial anodes.However,at the same time,the volume expansion problem and the intrinsic conductivity still largely limit the practical application of silicon-based anode materials.Therefore,aim to industrial applications,this paper has optimized the material system of the silicon-based anode and improved its cycle stability through silicon-graphite composite by simple ball milling.This paper first introduced Sn-Co alloy into SiO material by ball milling to obtain Si O-Sn-Co composite material.The characteristic of the material system and process design is that Sn-Co alloys were formed and refined during milling with the help of brittle and hard Si O particles acting as grinding aid,and eventually embedded or closely attached to the surface of the Si O particles in the form of nanoparticles.Through the electrochemical performance test and electrochemical behavior analysis of the Si O-Sn-Co composite electrode,it is found that the introduction of Sn-Co alloy into Si O can effectively improve the reversibility and dynamic performance of the composite material.This also enables it to achieve a more comprehensive improvement in electrochemical performance compared with Si O anode.The initial coulombic efficiency(ICE)has been increased from 55%to more than 70%,and a high reversible capacity of more than 1000 m A h/g can still be achieved,and the capacity retention after 100 cycles is over 78%.In order to further optimize the cycle stability of SiO-Sn-Co composites,we designed a new silicon/graphite composite structure.By adopting the three-layer coating method of Graphite|Si O-Sn-Co|Graphite,an effective hybrid anode was prepared.After electrochemical performance test,the anode with sandwich structure provided a stable conductive matrix for Si O-Sn-Co particles while maintaining the excellent reversibility of graphite,and finally achieved improved long-cycle performance.The Si O-Sn-Co/G composite electrode exhibited higher ICE than 77%at a current density of 50 m A/g,and a reversible capacity of about 650m A h/g.At a current density of 800 m A/g,the capacity retention can still reach more than 70%after 400 cycles.Eventually it has achieved a significant improvement in the cycle stability of the Si O-Sn-Co composite.The SiSnCo/G composite anode material was prepared by a two-step ball milling.The Si Sn Co/G-1 anode obtained by ball milling in the first step achieved a high ICE of 84%.After the second step of ball milling to composite with graphite,the stability has been further improved.In the end,the Si Sn Co/G-2 anode can achieve an ICE of 74%,a high reversible capacity of 1015 m A h/g,and a high-capacity retention of more than 80%after 300cycles.Further to explore the application value,we chose the Si Sn Co/G-1 negative electrodes with high ICE and relatively stability within 100 cycles and commercial Li Fe PO₄ cathodes to assemble as full cells.The electrochemical performance and the changes of electrochemical behavior during cycling of Si Sn Co/G-1||Li Fe PO₄ full cells were explored,and corresponding adjustments have been made to achieve enhanced performance of full cells.The final Si Sn Co/G-1||Li Fe PO₄ fulls cells achieved a specific capacity of about 600 m A h/g based on anode and a capacity retention rate of 99.5%after 50cycles in a voltage window of 2.4-3.4 V,showing a good application potential.