Study On Development And Electrochemical Properties Of Silicon-Carbon/Graphite Composite Anode Material System For Lithium-ion Batteries

Since the 21st century,people’s requirements for environment and energy have been increasing day by day,and lithium-ion batteries have attracted much attention in the energy market because of their excellent energy storage capacity.Silicon-based materials have a very high theoretical specific capacity(4200 m Ah·g^-1),but their industrialization process is trapped by the volume expansion effect of the material itself when de-embedding lithium,and the resulting continuous rupture and recombination of the SEI film.Silicon-carbon composites have a higher capacity while improving the volume effect of silicon-based materials,so they are considered to be the most promising lithium-ion anode materials.In this thesis,commercial silicon-carbon materials and graphite are used as the main materials,and the silicon-carbon/graphite composite materials are prepared by mechanical mixing.The electrochemical properties of electrolyte types,different conductive agent additives and different binder systems on the electrochemical properties of the material were systematically studied to determine the suitable full battery production process.（1）Using three commercial silicon-carbon materials as raw materials,three commercial silicon-carbon materials were mechanically mixed with graphite to obtain micron-grade silicon-carbon/graphite（Si/G）composites,and the electrochemical properties of soft-clad full batteries and button cells were studied.The results show that the physicochemical properties of the silicon carbon material of BTR are excellent,the D50 is 14.53 um,the vibration density is 0.95 g/cm³,the specific surface area is 1.62 m²/g,the slurry stability is good,and the rebound rate of the pole plate after roll pressing is stable at 5.58%after 72 h.In terms of material electrochemical properties,BTR silicon carbon materials show the best electrochemical properties:the first effect of the button battery is 91.3%,the first discharge specific capacity is 460.6 m Ah/g,the soft pack full battery has the first effect of 81.90%,after 250 cycles,the capacity retention rate is 99.90%.（2）Using the selected BTR silicon carbon material as raw material,the adaptability of the three electrolytes of TC-8B,TC-8C and TC-G5A to the battery process was studied.The results show that the TC-8C electrolyte is more suitable for the material,and the electrochemical properties of the button battery have a first effect of 91.76%,and the capacity retention rate after ten cycles is 95.62%;Among the electrochemical properties of the soft-packed full battery,the first effect is 81.40%,after 550 cycles,the capacity retention rate is 96.66%,and the mixed power pulse discharge test is excellent,and the discharge DC resistance is 19.73 mΩafter discharging to 10%capacity.（3）Using the selected BTR silicon carbon material as raw material,the effects of single conductive agent and composite conductive agent on the electrochemical properties of batteries under different binder systems were studied.The results show that whether it is a CMC+SBR binder system or a CMC+PAA binder system,the composite conductive agent is more conducive to the improvement of battery performance.In the case of using a composite conductive agent as a conductive additive,the first discharge specific capacity,first effect and capacity retention rate of the CMC+PAA binder system are higher than those of the CMC+SBR binder system.In the system with CMC+PAA as the binder and SP+CNT+graphene as the conductive agent,the first effect of the button battery is 94.79%,the capacity retention rate after ten cycles is 90.46%,the first effect of the soft pack full battery is80.19%,and the capacity retention rate after 200 cycles is 88.48%.