Preparation Of Silicon-based Composite Anodes And Their Application In Lithium-ion Batteries

Lithium-ion batteries are bound to play an important role in the achievement of the"dual carbon"target as an excellent energy storage device.In recent years,the requirements for the comprehensive performance of batteries are increasing with the wide application and vigorous developments of lithium-ion batteries.Thus,there is an urgent requirement to develop new lithium-ion batteries with higher energy density,higher power density,safety and longer cycle life.The anode is one of the main components in lithium-ion batteries.The performance of lithium-ion batteries can be effectively promoted by improving the electrochemical performance of the anode.The potential application of silicon in the new-generation lithium-ion batteries is immeasurable because of its extremely high lithium storage capacity,abundant resources and environmental protection.However,silicon exhibits a significant volume expansion during the electrochemical lithiation process,which severely hinders its practical application.Therefore,the weight ratio of silicon and the corresponding electrode capacity of the current industrialized silicon-carbon anode are low,and the production cost is higher than that of the traditional anode.In order to improve the electrochemical performance of silicon composites,while increasing the energy density of lithium-ion batteries and reducing the production cost as much as possible.It is necessary to carry out a thorough research on the silicon composite materials,the preparation method of material synthesis,the ratio of active material component,and the electrode preparation process.In this paper,the author attempted to improve the electrochemical performance of silicon-based anodes by optimizing the ratio of active materials and the electrode preparation process,preparation of silicon-based composite materials,and further investigated the application of the as-prepared silicon-based anode materials in lithium-ion batteries.The main contents and results of the paper are as follows:1.Porous carbon coated silicon nanoparticles were prepared and mixed with commercial graphite as anode materials for research.Controlling the specific capacity of the prepared Si@PC/G anode and reduce the utilization of expensive active material are achieved by regulating the weight ratio of porous carbon coated silicon nanoparticles to commercial graphite.The optimized Si@PC/G anode exhibits a good cycling performance with an initial Coulombic efficiency of 82.1%.After 250 cycles at a current density of 1000 m A g^-1,the discharge specific capacity of the anode is 970.59m Ah g^-1.The full cell assembled with Si@PC/G anode and Li Ni_0.8Mn_0.1Co_0.1O₂ cathode shows an excellent cycle stability with a high stack cell energy density.2.Binder-free silicon nanoparticle anode with a silicon carbon"concrete"structure was prepared.The silicon carbon"concrete"effectively combines the active material in the electrode as well as the active material and the current collector,reducing the proportion of inactive volume in the electrode.The as-prepared Si@C/G anode exhibits a good cycling performance with an initial Coulombic efficiency of 83.4%.After 250cycles at a current density of 2000 m A g^-1,the discharge specific capacity of the electrode is 983 m Ah g^-1.The full cell assembled with Si@C/G anode and Li Co O₂cathode shows a good cycle stability.The battery energy density calculated by the stack cell model is 940.2 Wh L^-1,which is much higher than the volume energy density of the traditional graphite//Li Co O₂ system.3.Silicon-based reduced graphene oxide foam obtained by gentle synthesis with the assistance of ascorbic acid while using the commercial micron-scale silicon particles and the ball mill technology.The obtained reduced graphene oxide layer is flat and distribute uniformly in silicon-based reduced graphene oxide foam which has a low oxygen content according to the experiment results.The three-dimensional conductive network provided by prepared silicon-based reduced graphene oxide foam has a fast charge transport character.At the same time,the uniformly distributed and flat graphene layers can effectively buffer the volume expansion of silicon in the cycles while stabilizing the SEI film.The initial Coulombic efficiency of the anode optimized the experimental conditions is 83.3%.After the 300 cycles at a current density of 1000 m A g^-1,the specific capacity of the anode is 738 m Ah g^-1.The full cell assembled with pre-lithiated anode and Li Ni_0.8MN_0.1Co_0.1O₂ cathode is also exhibit a good cycle stability with a high stack cell energy density of 846.3 Wh L^-1.4.Carbon coated porous silicon microparticle was obtained using Si-Al alloy raw materials and sol-gel methods.The abundant pores in the silicon microparticles can accommodate the expanded volume during the lithium intercalation reaction,and the coated carbon effectively stabilizes the SEI film while improving the conductivity of the active material,which enables the prepared silicon-based composites to exhibit a good electrochemical performance.The prepared representative anode exhibited a capacity retention rate of 97.5%after 150 cycles at a current density of 1000 m A g^-1with the discharge specific capacity of 845 m Ah g^-1.The full cell assembled with the Li Ni_0.8MN_0.1Co_0.1O₂ cathode exhibits a good cycle stability and a high volume energy density under the stack cell model,indicating the excellent electrochemical performance can be obtained through the use of inexpensive raw materials and certain modifications.