Construction Of Anode Materials For Lithium Ion And Zinc Secondary Batteries Based On Carbon Matrix And Their Performances

As an efficient and recyclable energy conversion and storage method,the utilization of high-performance secondary batteries has become an important technical path to comprehensively alleviate energy,resource and environmental problems.Lithium-ion and zinc secondary batteries are two major battery systems that have attracted much attention in secondary batteries.The former is the most common energy storage technology on the market,and is widely used in various electronic products,portable devices and even electric vehicles.The latter with the merits of environmental friendliness,low cost,safety and non-toxicity is a new type of green secondary battery that has developed rapidly in recent years.However,at present,the low theoretical specific capacity of the commercial graphite anodes of lithium-ion batteries cannot meet the demand for high energy density of large-scale devices.Although the silicon anode has a high theoretical specific capacity,the poor conductivity and volume expansion hinder its application in lithium-ion batteries.Problems such as the growth of dendrites in the zinc anode restrict the industrialization of zinc secondary batteries.Carbon materials are widely used in secondary batteries due to their high electrical conductivity,low cost,light weight,and easy functionality.In this thesis,based on carbon materials,high-capacity silicon/carbon anode for lithium-ion batteries and a long-life anode for zinc secondary battery are constructed.First,the structural uniformity of the silicon/graphite composites was improved by the electrostatic adsorption method.On this basis,a new type of silicon/carbon anode material for lithium-ion batteries with high specific capacity and long cycle stability was prepared by introducing silica components and ingeniously designing the structure of the composite materials.Secondly,taking advantage of the large specific surface area and abundant pore structure of expanded graphite,silicon@chemical expanded graphite/carbon（Si@CEG/C）anode materials with excellent rate and cycle performance for lithium-ion batteries were prepared.Finally,a three-dimensional porous zinc anode host material was constructed using expanded graphite as a raw material,thereby improving the cycle life of zinc secondary batteries.The details are as follows:Carbon-coated silicon@mesocarbon microsphere composites（Si@O-MCMB/C）with a cladding structure were successfully prepared by electrostatic adsorption method,in which the O-MCMB core and amorphous carbon shell can not only effectively improve the conductivity but also limit the volume change of silicon.In addition,compared with the liquid mixing method,electrostatic adsorption method can achieve uniform coating of silicon on the surface of O-MCMB,thereby improving the electrochemical performance of the material.The prepared Si@O-MCMB/C anode exhibits a reversible capacity of 458 mAh g^-1 with a capacity retention of 86.5%after500 cycles at a current density of 0.3 A g^-1.SiO₂ as an active additive was introduced to further improve the capacity of Si@O-MCMB/C composites.Two different composites,Si@O-MCMB sequentially embedded in SiO₂ and carbon layers（Si@O-MCMB/SiO₂ layer/C）and encapsulated in a carbon conformally coated tiny SiO₂ nanoparticle matrix（Si@O-MCMB/SiO₂NPs/C）,were well-designed.Both of these exhibit a longer cycle life than the Si@O-MCMB/C due to the unique double protective sheath of inert components（Li₂O and Li₄SiO₄）and carbon.Specifically,the Si@O-MCMB/SiO₂ NPs/C show a reversible specific capacity of 607 mAh g^-1 at a current density of 0.5 A g^-1 and a capacity retention of 92%after 800 cycles.The remarkable performances benefit from the three-dimensional porous network structure constructed by an amorphous carbon matrix shell and a graphite core,which well disperse and support Si and SiO₂,thus improving their electrochemical activity,alleviating the volume change and promoting the Li-ion diffusion.Intercalated Si@CEG/C composites were prepared by electrostatic adsorption with chemical expanded graphite（CEG）as the matrix.Benefiting from the conductive network architecture composed of porous CEG and amorphous carbon,the prepared Si@CEG/C composite exhibits a high initial reversible capacity of 1232.4 mAh g^-1 at 0.5 A g^-1 and outstanding cyclic retention of 87%after 200 cycles.In addition,the Si@CEG/C electrode also exhibits good rate performance and cycling stability at high current density.Three-dimensional porous graphene nanosheet/carbon nanotube foam with well-dispersed silver nanoparticles（Ag-GNs/CNT）was prepared as host material for zinc anode via freeze-drying and in-situ reduction methods.The unique 3D porous architecture can accommodate volume change of zinc metal during repeated plating and stripping,while the Ag nanoparticles as zincophilic can guide the uniform nucleation of zinc,thereby improving the storage capacity of zinc in the carbon skeleton.The Ag-GNs/CNT electrode shows a high average coulombic efficiency of 99.13%over 400cycles at a current density of 5 mA cm^-2 with a limited capacity of 2 mAh cm^-2.Meanwhile,the aqueous full battery based on Zn@Ag-GNs/CNT anode and manganese dioxide cathode exhibits a reversible capacity of 159.2 mAh g^-1 with a capacity retention of 77.3%after 800 cycles at a current density of 1 A g^-1.In addition,the flexible quasi-solid-state battery with Zn@Ag-GNs/CNT anode also exhibits good electrochemical stability(70% capacity retention after 3000 cycles at a current density of 2 A g^-1)and excellent mechanical properties.