Research On Preparation And Electrochemical Performance Of Carbon-based Electrode Materials For Rechargeable Batteries

Lithium-ion batteries(LIBs)have been widely employed as energy sources of portable electronic devices and electric vehicles.With the development of green and sustainable energies,longer cycle life,higher energy density and lower cost are desirable.The theoretical capacity of silicon anode materials(4200 m Ah/g)are more than 10 times that of commercial graphite anode(372 m Ah/g).The theoretical specific capacity of sulfur cathode materials(1675 m Ah/g)are nearly six times greater than the theoretical capacity of current ternary cathode materials(280 m Ah/g).They are viewed as the most promising electrode materials for the next generation high energy densty batteries.However,the large volume changes during charge-discharge processes,low electronic conductivity,and"shuttle effect"caused by the soluble polysulfide intermediates,significantly hinder their practical applications.In addition,the resouce of lithium is limited and its distribution is not even on the earth crust,which make the cost of LIBs increase year by year.Therefore,an alternative battery technology that uses abundant and low-cost materials is desired to replace LIBs.Sodium is much more abundant than lithium and has similar physical and chemical properties to those of lithium,and so sodium-ion battery(SIBs)have been considered as a promising alternative to LIBs.But the performance of SIBs is still far away the requirement for practical applications mainly due to the more severe volume-change-related problems and lower kinetics caused by the larger Na ions than Li ions.New compatible materials and battery systems are need to be developed.Carbon materials have the characteristics of excellent mechanical and electrical properties,strong designability,abundant raw materials and simple preparation methods,providing an opportunity to solve the above problems.In this study,a variety of carbon-based electrode materials were prepared,including carbon/silicon anode and carbon/sulfur cathode for LIBs,and carbon anode materials for SIBs by design the composition,structure,morphology and surface chemistry of carbon material.Exellent electrochemical performance was realized by optimizing the matching of electrolyte and electrode material.The results are as follows:(1)Carbon-based silicon composite nanosheets as anode materials with freestanding structure were prepared by the method of bidirectional freezing and ice template.The resilient and conductive carbon matrix can not only alleviate the volume expansion but also serve as electronic pathway.The gaps between the nanosheets can also buffer the volume changes and provide ionic transportation pathways.As the anode of LIBs,excellent cycling stability and a high reversible specific capacity up to 1017.9 m Ah/g were demonstrated.More importantly,a high areal reversible capacity of 6.0 m Ah/cm~2 with a high areal mass-loading of 5.5mg/cm~2can still be obtained without capacity attenuation after 50 cycles.(2)Porous carbon materials based on carbon nanotubes or graphene were prepared through self-assembly and template method.The issues of lithium polysulfide intermediates dissolving in lithium-sulfur battery and poor electronic conductivity of sulfur electrodes,which lead to fast capacity fading have been solved successfully.Carbon nanotubes or graphene can improve the electronic conductivity of materials,and the rich pores structure can increase the mass-loading of sulfur with about 70%,respectively.The"shuttle effect"in lithium-sulfur battery is effectively reduced by physical limitation and chemical adsorption of heteroatoms of ogygen and nitrogen.The reversible specific capacities with 1412.1 m Ah/g and 1502.3 m Ah/g were obtained respectively.The specific capacity of 619.9 m Ah/g and 638.2 m Ah/g can be maintained respectively after 500 cycles,and the corresponding capacity retention rate is as high as 90.0%and 97.2%,showing an excellent cycling stability.(3)Three-dimensional and freestanding graphite foam as anode materials were prepared by CVD method.The three-dimensional network structure serves as a continue electric conductive pathway and the large amount of channel architectures ensure a high ionic conductivity.As the anodes of SIBs,a long cycle life of 4000cycles at a current density of 1.0 A/g was achieved with a high capacity retention of83%.A superior rate performance was delivered with a capacity retention of 52.9%when the current density was increased from 0.02 A/g to 10.0 A/g.(4)Nitrogen-doped hard carbon as anode materials were prepared by direct carbonization with biomass-derived chitosan as precursor.With the high ionic conductivity of ether-based electrolytes,excellent cycling stability,rate performance and ultra-high areal mass loading were obtained.After 2000 cycles,the capacity is still as high as 196.3 m Ah/g,and the retention rate is 90%.Even if the current density is up to 10.0 A/g,the specific capacity can still maintain 139.5m Ah/g.When the areal mass loading was as high as 17 mg/cm~2,the areal reversible capacity up to 4.3m Ah/cm~2 was reached with the stable cycling.The results provide a technical reference for the practical application of SIBs.