Design And Lithium Storage Performance Of Micro-Nanostructured Silicon Based Anode Materials

Lithium-ion batteries are considered to be one of the next-generation high-efficiency energy storage devices,because they have the advantages of long cycle life,large specific capacity,good safety,and low environmental pollution.However,the current capacity increase of lithium ion battery anode materials has reached a theoretical bottleneck,they still can not meet the needs of large-capacity electricity terminals such as electric vehicles?EV?,hybrid electric vehicles?HEV?.Silicon can form a lithium alloy with lithium with a high theoretical capacity(3579mAh g^-1),which is close to 10 times that of commercial graphite anode materials.However,the large volume expansion effect of silicon during charging and discharging and its lower conductivity as a semiconductor limit its practical application.In this dissertation,a series of micro-nano-silicon composites are prepared from commercial nano-silicon materials by solvothermal method and ethylenediamine assisted method,and the microstructure and electrochemical properties of the materials are explored by a variety of characterization methods.The innovative results obtained in this paper are as follows:?1?Si/CNT@MnSiO₃ composites are prepared by a simple solvothermal reaction.Due to the amorphous MnSiO₃ coating and the introduction of CNT,the composites have good cycle performance and rate performance.There is also a specific capacity of 708.3 mAh g^-1 after 400 weeks of circulation at a current density of 1 A g^-1.Thanks to the blocking effect of MnSiO₃,the contact resistance between Si and CNT is reduced,and the composite material has a capacity up to 573.8 mA g^-1 at a current density of 4 A g^-1.?2?Si@MnSiO₃ clusters material is successfully prepared by solvothermal method,and submicron secondary clusters silicon-carbon composite material?abbreviated as nano-Si SC,the same below?is further obtained by carbon coating and hydrofluoric acid etching.The introduction of the void layer and the introduction of the conductive carbon network improve the stability and electrical conductivity of the material.The nano-Si SC composite material has good cycle performance and rate performance.The specific capacity of the composite after 250 charge-discharge cycles at a current density of 1 A g^-1 reaches 701.6 mAh g^-1,which is relative to the capacity retention rate of 82.3%?using the second week discharge capacity as a control?.?3?Silica-coated nano-silicon clusters are prepared by ethylenediamine-assisted St?ber method.Afterwards carbon-coated and hydrofluoric acid etching are performed to obtain nano-Si SC composites.The method has mild reaction conditions.At the same time the surface of the obtained nano-silicon clusters material is relatively smooth and the specific surface area is effectively reduced and the first Coulomb efficiency of the material is effectively improved.When Si:TEOS=1:8,the composites exhibit good cycle performance.There is still a specific capacity of837.9 mAh g^-1 after 300 charge-discharge cycles at a current density of 1 A g^-1.