Structural Design And Lithium Storage Performance Of Nickel Sulfide/carbon Negative Electrode Material

In recent years,pertinent national industrial policies have emphasized the development of new energy and new materials sectors,particularly lithium-ion batteries（LIBs）,which are essential components of new energy vehicles.Graphite is commonly employed as the anode material for LIBs,but its comparatively low potential capacity of372 mA h g^-1 makes meeting society’s future energy storage and usage requirements challenging.Because of its superior electrical conductivity,plentiful redox reactions,huge environmental affinity,high theoretical capacity(590 mAh g^-1)and low manufacturing cost,transition metal nickel sulfide（Ni S）has proved to have considerable uses in catalysis,electronics,and energy storage.Nevertheless,a variety of challenges have been faced in subsequent applications,such as intrinsic poor conductivity,structural instability owing to extreme volume fluctuations,or delayed diffusion kinetics,all of which result in restricted specific capacity and inadequate cycle life.The following is the core research of this thesis in answer to the difficulties described above:（1）The effects of temperature on the morphology,disordering,graphitization,and structural stability of hollow tubular structured biomass carbon（HBC）were explored using physical tests such as XRD,SEM,Raman,and BET.Second,we utilized a solvothermal reaction coupled with a post-annealing process to create Ni S/C by encapsulating glucose on Ni S₂@Ni₃S₄ nanoflowers.Moreover,we successfully synthesized HBC-Ni S/C high-performance lithium-ion battery anode materials by anchoring/encapsulating Ni S/C on HBC during the solvothermal reaction and post-annealing phases to demonstrate that the roles of HBC and Ni S/C composite display complementing impacts.The HBC-Ni S/C electrode had superior cycling properties,achieving 652 mAh g^-1 in 100 cycles at 0.2 A g^-1.The excellent results of the above HBC-Ni S/C physical or chemical tests are attributed to the introduction of HBC,which has a hollow tubular structure and high specific surface area and can be loaded with more Ni S/C nanoflowers,as well as further alleviate the bulk effect generated during Ni S electrochemistry;HBC itself,as a carbon material,can also further improve the battery overall conductivity.（2）The Yolk shell structure Ni S/C（YS Ni S/C）was obtained by hard template technique,post-annealing strategy and chemical etching.Initially,SEM,TEM,and Raman characterization were used to confirm the effective creation of the yolk shell structure.Second,to demonstrate the superiority of the yolk shell structure,the internal structure and electrochemical data discrepancies between YS Ni S/C and Core-shell Ni S/C were examined,and it was concluded that their structural design gives several advantages to the electrodes.The carbon shell layer not only supports effective electron transfer and enhances total material conductivity,but it also prevents direct exposure of Ni S to the electrolyte,decreasing sulfur component loss and Ni S agglomeration.Most crucially,the space between the"Yolk"and"Shell"substantially reduces the volume change of Ni S throughout the electrochemical process while preserving its microstructural integrity.After 300 cycles at 0.2 A g^-1,the aforementioned enhancements resulted in a cycle data of up to 640 mAh g^-1.Furthermore,in light of the more severe electrode polarization,unstable SEI film,and large decay of subsequent cycling performance in the first few cycles of Chapter 3,this chapter investigates the electrochemical performance of three different electrolytes in order to further improve the reversible capacity of Ni S.Finally,the YS Ni S/C electrode with LB007 electrolyte produced good electrochemical results,with 500 cycles at 0.5 A g^-1 and a reversible capacity of 541 mAh g^-1,which was higher than the other two electrolytes(390mAh g^-1,400 mAh g^-1).At a multiplicative performance of 3 A g^-1,the reversible capacity of 389 mAh g^-1 far exceeds that of the other two electrolytes(257 mAh g^-1,84 mAh g^-1)and comparison experiment(84 mAh g^-1).