Study On The Preparation Of Silicon-based/ Graphite Anode Materials And Their Application In Pouch Lithium-Ion Battery

The development of lithium-ion batteries with higher energy density is an important direction for advanced batteries.As one of the key materials for lithium-ion batteries,graphite material is the most commonly used commercial anode material for lithium-ion batteries.However,the graphite anode material with a low theoretical specific capacity(372 m Ah/g),which does not meet the needs of the next generation of high energy density lithium-ion batteries.Silicon-based anode materials have the potential to be used as anode materials for high-energy-density lithium-ion batteries due to the high specific capacity and low voltage platforms during the charge-discharge process.However,silicon-based anode materials have not been used on a large scale due to the poor conductivity,serious volume effects,and rapid capacity decay.Therefore,combining silicon-based materials with carbon-based materials can achieve complementary advantages and form a negative electrode material with long cycle life,high stability,and stable structure.In this work,a composite anode material with high specific capacity and excellent electrochemical performance is obtained by mixing silicon-based materials with graphite materials.Meanwhile,to modify the issues of poor conductivity of silicon-based materials and low dispersion of conductive agents,we improved the dispersion of active materials by adding different conductive agents and building a conductive network to reduce electrode polarization.Finally,we apply the optimized silicon-based/graphite anode material and conductive agent to the pouch lithium-ion battery.The main work is as follows:(1)Study on the influence of silicon/graphite mixing ratio for the electrochemical properties of anode materials.Silicon-based/graphite composites with a Silicon mass ratio of 5 wt%,10 wt%,15 wt%,and20 wt% were selected as anode materials for lithium-ion batteries to investigate the electrochemical performance.The experimental results show that the mixing process does not damage the crystal structure of silicon-based materials and graphite materials.When the addition ratio of silicon-based materials is 5 wt%,the materials acquire the best electrochemical performance.The specific discharge capacity is 369.3 m Ah/g after 200 cycles at 0.5C,which is higher than other samples with a silicon content ratio.(2)The influence of different conductive agents on the electrochemical properties of 5 wt%silicon/graphite anode materialsSuper-P(SP),KBO(KBO),CNT,and GO were selected as conductive agents and applied to an anode material with 5 wt% silicon in(1).The electrochemical test showed that KBO had the best electrochemical performance,and the discharge specific capacity reached 407.1 m Ah/g after 200 cycles at the rate of 0.5C,and the discharge specific capacity was 157.2 m Ah/g at the rate of 5C,and the capacity retention rate was 37.4%,which was better than other experimental groups.(3)Study on the performance of silicon/graphite anode lithium-ion with a pouch lithium-ion battery.Using the nickel-cobalt-manganese layered oxide as the positive electrode and the silicon-based/graphite composite material as the negative electrode,and the SP0,SP5,KBO5,CNT/GO5,and KBO/CNT/GO5 pouch lithium-ion battery was made with the model of 524482.The design capacity of the pouch lithium-ion batteries is 2Ah,and the actual capacity has reached the design value.The first efficiency of the CNT/GO5 sample is 75.5%,and the capacity retention rate after 350 cycles is 73.9%.The overall performance is better than in other experimental groups.The disassembly analysis of pouch lithium-ion batteries shows that the silicon-containing composite negative pole piece remains intact after the cycle.The winding expansion rate,the semi-electric expansion rate,and the full electric expansion rate are 18%,36%,and 48%,respectively,which are lower than the other group.The results of safety tests(extrusion,puncture,short circuit and overcharge)show that the silicon/graphite anode material can improve the safety performance of pouch lithium-ion battery.