Preparation And Electrochemical Performance Of Silicon/Carbon Anode Materials For Lithium-ion Batteries

At present,there is an increasing demand for battery energy density,and there is an urgent need to develop anode materials with higher specific capacity than commonly used graphite anodes(360 mAh g-1).Silicon-based anodes have become one of the most promising new-generation lithium-ion battery anode materials due to their high theoretical capacity(?4000 mAh g-1)and feasible working voltage.However,the huge change in volume during lithium extraction is the main challenge of silicon-based negative electrodes,which will lead to particle crushing,repeated formation of SEI films and poor Coulomb efficiency.The strategy of silicon-carbon composite materials has been proved to be effective for improving the electrochemical performance of silicon,which makes the silicon-carbon composite materials very promising for the practical application of lithium ions.However,at present,some silicon carbon composite materials have higher structure preparation costs and complicated processes.Therefore,looking for low-cost raw materials and developing simple and easy nano silicon and silicon carbon composite preparation processes,the preparation has higher mass specific capacity and more The silicon-based negative electrode material with good cycle stability is very practical to promote the large-scale application of the silicon-based negative electrode material at an early date.In this paper,starting from nano-silicon,the silicon-carbon composite material prepared by simple ball milling and spray drying process has a high first-time Coulomb efficiency and capacity retention rate,and has good commercial prospects.The main research contents of this article are as follows:1.Nano-silicon@carbon/graphite composite materials were prepared by using commercially purchased nano-silicon as a silicon source,mixed with graphite and organic additives through high-energy ball milling,combined with spray drying technology;in order to further improve the cycle performance of the material,we added Conductive agents super p and GD have prepared Si/C composite anode materials Si/C-GD/G with excellent electrochemical performance.The tap density is 0.71 g cm-3,the initial reversible specific capacity is 840.3 mAh g-1,the first Coulomb efficiency is 85.1%,and the capacity for 100 cycles at a current density of 0.2A g-1 is 774.1 mAh g-1,The capacity retention rate was 92.1%.As a binder,the bitumen improves the force of graphite and silicon particles.At the same time,the carbon coating and carbon network formed by the carbonization of the bitumen improve the conductivity of the material.At the same time,the conductive additives super p and GD and vapor deposited carbon are added.On the one hand,the layer avoids the direct contact between silicon and electrolyte and reduces the occurrence of side reactions.On the other hand,it can be used as a buffer matrix to absorb the stress caused by the volume expansion of silicon during charge and discharge,and improve the cycle stability of the composite material.2.Using cheap silicon aluminum alloy as the silicon source,micron silicon was prepared by ball milling and acid etching,and nanometer silicon was obtained by sand milling nanometer,which realized the cheap alloy raw materials to high value-added energy storage materials.Conversion,and then combined with graphite and organic carbon source by ball milling and spray drying to prepare a silicon carbon composite material Si@C/G@C,which improves the electrochemical performance of the material.The asphalt coating amount and the way of adding asphalt were optimized,and the optimal silicon-carbon composite material was selected.When the asphalt coating amount was 15%,and the asphalt was added twice during the spray drying process,its first coulombic efficiency was 75.1%.The initial reversible specific capacity is 503.3 mAh g-1,its 100-week capacity retention rate is as high as 98.6%,and the composite material tap density is 0.74 g cm-3.The problem of low first-coulomb efficiency and capacity retention rate of nano-silicon materials after sanding was solved by adjusting the amount and method of addition in the asphalt coating process.The carbon coating formed by pitch carbonization and the graphitic carbon network are more stable,and the formation of this multi-stage buffer structure can greatly improve the electrochemical performance of the material.