| At present,the development of new energy vehicles,the large screen and diversified functions of digital terminal products have put forward new requirements for the matched energy storage system.In the upgrading of energy storage battery,lithium ion battery has been applied in a large number of energy storage projects due to its advantages of high voltage resistance,no memory effect,no pollution,environmental protection,high safety performance,low self-discharge rate,high specific capacity and strong cyclic performance.However,the current battery material system is obviously unable to meet the practical needs of lithium batteries,so it is urgent to develop new high energy and high performance materials.At present,silicon-based materials have become the most preferred choice for lithium batteries to improve the anode.Silicon anode material has the advantages of good safety,abundant resources,low discharge platform and more lithium-ion storage than carbon.However,due to the serious volume expansion and contraction of silicon anode in the process of embedded lithium removal,the material structure is destroyed and mechanical crushing is caused,which leads to the poor cycling performance of the electrode.The carbonaceous anode materials have good cyclic stability because of its small volume change during charging and discharging,and it is a mixed conductor of ions and electrons.In addition,silicon and carbon have similar chemical properties,and they can be closely combined.Therefore,the synthesis of silicon and carbon composites is an effective method to improve the electrochemical performance of silicon-based anode.In the silicon carbon composite system,the silicon particles are used as active substances to provide lithium storage capacity.Carbon can not only buffer the volume change of silicon anode in the process of charging and discharging,but also improve the conductivity of silicon-based materials and avoid the agglomeration of silicon particles in the charging and discharging process.Therefore,the silicon and carbon composites combine the advantages of showing high specific capacity and long cycle life,and are expected to replace graphite as the anode materials of the new generation of lithium ion batteries.In this paper,the composites of silicon and carbon are studied in the following aspects:?1?Silicon nanoparticles were coated by silica generated by tetraethyl orthosilicate hydrolysis.Then get a layer of polyvinylpyrrolidone on the surface.Micron-sized particles were assembled by spray drying and then pyrolysis at high temperature.Finally,silicon-carbon composite anode material with micro-nano structured porous granadilla-like structure was obtained by using hydrofluoric acid etching.The obtained composite maintained the specific capacity of 933.62 mAh g-11 after 100cycles at 100 mA g-1.When the current density is increased to 1000 mA g-1,the battery has remarkable cyclic stability,maintaining the specific capacity of 610.38mAh g-11 after 3000 cycles.?2?The waste silicon were grinded with a high-velocity universal ball crusher and washed with nitric acid solution to obtain pure silicon microparticles,then the silicon microparticles were coated silica by hydrolysis of tetraethyl orthosilicate,and the carbon nanotubes were grown by acetylene deposition.Finally,the urchin-like carbon nanotubes coated silicon microparticles anode materiasl with excellent conductivity were obtained.The specific capacity of 920.1 mAh g-11 can be maintained after 100cycles at 100 m A g-1.At the current density of 1000 mA g-1,it can still maintain the higher specific capacity of 606.2 mAh g-11 after 1000 cycles. |
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