Study On Plasma Modification Of Electrode Materials For Lithium Batteries

Although the lithium secondary batteries have been a promising solution to the energy crisis and environmental pollution,there are still some problems in the current lithium-ion batteries and lithium metal batteries,especially the electrochemical performance of the anode materials（rate performance,cycling efficiency,safety）,which may hinder the practical application of the lithium secondary batteries.Considering the intrinsic problems of electrode materials for lithium secondary batteries and the advancement of plasma technology,plasma technology is conducted in this study to modify the surface of Li₄Ti₅O₁₂,C₃N₄and nickel foam.Meanwhile,the intrinsic effective mechanism has also been investigated to clarify the relationship between defects,components,structure,morphology,and their electrochemical performance.The research contents are shown as follows:（1）Effective mechanism of oxygen vacancies on the lithium storage performance of Li₄Ti₅O₁₂.The Li₄Ti₅O₁₂nanosheets have been synthesized by hydrothermal method and the H₂/N₂plasma atmosphere was used to introduce oxygen vacancies.XPS and EPR measurement verify that the modified Li₄Ti₅O₁₂possessed more oxygen vacancies after the plasma treatment.The modified Li₄Ti₅O₁₂can deliver a capacity of173.4 m Ah g^-1after 100 cycles and 133.1 m Ah g^-1after 500 cycles at 1C(about0.175A g^-1)and 20 C(3.5 A g^-1)respectively.According to the further electrochemical measurement,the oxygen introduced by plasma treatment mainly can improve the ionic diffusion coefficient with almost no effect on the bulk lithium storage capacity.（2）Effect of nitrogen vacancies in C₃N₄on the lithium storage performance.In this part,H₂atmosphere was used to modify the C₃N₄precursor.XPS and EPR measurements indicated that the nitrogen content decreased,and a large amount of nitrogen vacancies appeared.Meanwhile,O atoms were successfully introduced into the nitrogen vacancies site.DFT calculation results verify the remarkable effect of the nitrogen vacancies to decrease the band gap and increase the lithium adsorption energy.The existence of O atom can reduce the structure energy and stabilize the structure enriched with vacancies.The modified C₃N₄can even still possess 232.8m Ah g^-1after 5000 cycles under 1 A g^-1.（3）Lithiophilic matellic nitrides to inhibit the lithium dendrites.After the plasma treatment,a lay of compact Ni₃N formed on the surface of nickel foam.Moreover,when contacted with the deposited lithium,the Ni₃N transformed to Li₃N.The formed nitrides layer can significantly improve the lithiophilic ability.Thus,the composite electrode exhibited low voltage hysteresis of 13,18 and 39 m V at 1,2 and 5 m A cm^-2respectively for over 400 cycles.In addition,the fabricated full-cell paired with Li Fe PO₄cathode displayed a superior performance.Density functional theory（DFT）calculation was conducted to verify that Ni₃N and the in-situ formed Li₃N all possessed good lithiophilic ability.