Research On Lithium Storage Properties Of Nanometer Silicon Particles Prepared By Pulse Discharge And High-energy Ball Milling

At present,the research of the new generation of high-energy lithium-ion batteries has entered the heat phase.Silicon material is expected to replace graphite as a new type of negative electrode material for lithium-ion batteries because of its theoretical specific capacity(4200 mAh·g^-1),low deintercalation potential,abundant reserves and no environmental pollution.However,due to the low conductivity of intrinsic silicon and the dramatic volumetric effect during charge/discharge cycles,the particles are mechanically broken,the conductive network is destroyed,and the solid electrolyte interface membrane is undergoing constant destruction-reconstruction process,the electrolyte components will continue to consume.In order to solve the above bottleneck problem,this paper improves the conductivity of silicon by doping trace elements.We used lightly doped P-type crystalline silicon,heavily doped P-type crystalline silicon and heavily doped N-type crystalline silicon as raw materials.The micro/nano silicon particles were prepared by pulse discharge and high energy ball milling.To explore the lithium storage properties of silicon particles with different sizes and the effects of doping element concentration and doping element type on the lithium storage properties were also investigated.Therefore,the work of this thesis combines special processing and lithium-ion battery in two fields,with obvious interdisciplinary characteristics,the research contents of this paper mainly include the following two aspects:1.Build the pulse discharge system and study on lithium storage properties of micron/submicron silicon particles doped with trace elements by pulsed discharge method.The pulse discharge method was used to prepare micron/submicron silicon particles with heavily doped P-type crystalline silicon and heavily doped N-type crystalline silicon as raw materials and copper tube as tool electrode.The prepared micron/submicron silicon particles were characterized and their electrochemical performance was analyzed.The lithium storage properties were improved by modification.The results showed that the electrochemical performance of micron/submicron silicon particles doped with trace elements has been greatly improved,and the electrochemical performance of N-type silicon is slightly better than that of P-type silicon.However,due to the huge volumetric effect of silicon particles,the long-term electrochemical performance of the active material is still relatively poor.At the same time,the effect of adding Cu as electrode material on the electrochemical performance of the active material was compared.The results show that adding copper particles by pulsed discharge method is not good for the electrochemical performance of silicon;2.Build the high energy ball milling system and study on lithium storage properties of nano-silicon particles doped with trace elements by high energy ball milling.In order to further reduce the volume effect of the material and study the effect of the lithium storage properties of the silicon material after further refinement of the particle size to nano-scale,as well as the influence of the nano-silicon particles with different doping types and doping concentrations on the lithium storage performance,we build the high energy ball milling system and use lightly doped P-type micron/submicron silicon,heavily doped P-type micron/submicron silicon and heavily doped P-type micron/sub-micron silicon as raw materials,by high-energy ball milling method to further refine the material particles to 100nm under the same conditions.The three kinds of nano-silicon particles were characterized and their electrochemical performance was analyzed.The lithium storage properties were further improved through modification.The results show that,after nanocrystallization,due to the decrease of the absolute volume change during charging and discharging,the diffusion distance of lithium ions is reduced and the electrochemical reaction rate is increased,so that the electrochemical performance of the material is better than that of micron/submicron silicon particles.And the electrochemical performance of heavily doped P-type silicon is better than that of lightly doped P-type silicon and heavily doped N-type silicon is better than that of heavily doped P-type silicon.