Investigate Of Silicon-based Anode Materials’ Doping Modification And Electrospinning For Lithium-ion Batteries

Lithium-ion batteries have been garnering a lot of interests as a crucial energy storage and conversion device for the use of renewable energy sources and as a major part of new energy vehicles.As the market for high energy density lithium-ion batteries continues to expand,the actual specific capacity of the graphite negative pole of contemporary com-mercial lithium-ion batteries（340 mAh/g～365 mAh/g）is close to its theoretical specific capacity（372 mAh/g）.Due to its high specific capacity of 4200 mAh/g,environmental friendliness,low cost,and low operating potential（0.4 V vs.Li/Li⁺）,silicon-based anode materials stand out among other anode materials.However,the alloying/dealloying reac-tion between silicon and lithium ion has a large volume change rate（300%～400%）that seriously damages the structure of the silicon-based anode material,causing the active material Si to lose enough electrical contact with the fluid collector,and leading to material pulverization and SEI film instability consuming too much lithium ion.Moreover,mono-crystalline silicon’s weak intrinsic conductivity as a semiconductor material severely re-stricts its potential for commercialisation.Due to this,the technique used in this research to enhance the silicon negative electrode of lithium ion batteries uses doping modification and silicon-carbon composite.The following are the primary research findings:（1）To address the issue of weak conductivity,monocrystalline silicon（an intrinsic semiconductor）is converted into an impurity semiconductor using the impurity doping method.Thermal diffusion is used to introduce the impurity element into the monocrystal silicon crystal cell,and impurity compensation is used to convert the monocrystal silicon into an N-type impurity semiconductor.The findings demonstrate that after several cycles,P,B-doped Si’s electrode structure and surface morphology sustain only minor degradation.The initial discharge capacity in the first cycle was 3263 mAh/g with a current density of0.84 A/g.In addition,the EIS test findings reveal that P,B-doped Si has 19.6Ωcharge-transfer impedance and 61.6Ωlithium-ion diffusion impedance after 100 cycles,which demonstrates that the doped modified silicon has superior conductivity.（2）Silicon-carbon recombination technique is the more efficient approach to handle the volume change of silicon materials throughout the charge and discharge cycle.Si@PCNFs was created via electrospinning and carbonization using silicon as the negative active ingredient,polyacrylonitrile（PAN）as the carbon source,and NH₄Cl as the pore-making agent.The volume change of silicon material throughout the charge-discharge cy-cle is considerably inhibited by the material’s unique mesoporous carbon fibre three-di-mensional conductive network structure.After 50 cycles at the current density of 0.84 A/g,SEM revealed that the electrode surface morphology was still excellent and no structural damage had occurred.In the magnification performance test,the reversible capacity re-covery rate of Si@PCNFs was still 85.6%when the current density decreased from 4.2A/g to 0.42 A/g.In the subsequent long cycle test,the material similarly had a slower capacity degradation rate,continuing to have a specific capacity of 754.1 mAh/g after 100cycles.（3）In view of sodium alginate（SA）as a conventional silicon anode binder,its car-boxyl group has the characteristic of enhancing the contact force between silicon particles and between them and the collector fluid.Thus,we employed polyvinyl alcohol（PVA）co-blended with SA as the spinning precursor fluid and created Si@SA/PVA material by elec-trostatic spinning-carbonation method in order to enable SA and silicon particles to be joined by electrostatic spinning in the form of fibre encapsulation.After 50 cycles at a current density of 0.84 A/g,SEM revealed that the electrode surface was been mildly pul-verised and that the electrode structure had not been seriously harmed.When the current density changed from 4.2 A/g to 0.42 A/g during the multiplicity test,the material still had63.6%reversible capacity recovery.Moreover,Si@SA/PVA had a low capacity degrada-tion rate in a long cycle test at a current density of 0.84 A/g,and its initial discharge specific capacity reached 2034.6 mAh/g in the first cycle.