Interface Regulation And Electrochemical Performance Improvement Of Graphite And Lithium Cobalt Oxide By Electrolyte Additive

With the vigorous development of science and technology,energy has become the economic lifeblood of one country.The development of energy storage technology which is as one of its key technologies is urgent,so lithium-ion batteries（LIBs）as the core of energy storage technology have received widespread attention.Although LIBs have been industrialized on a large scale,there are still some problems that need to be solved urgently,such as the short cycling life of LIBs and poor magnification performance.In order to solve the above problems,this paper proposes an electrolyte additive strategy to improve battery performance.In this thesis,the improvement and mechanism of three additives of heptafluorobutyric anhydride,bis（trifluoroacetamide）and potassium perfluorinated sulfonate on graphite and lithium cobalt oxide（Li Co O₂）electrodes were stduied.The three additives all contain fluorine,which can increase the Li F content in the solid electrolyte interphase（SEI）films during the decomposition process of the electrolyte,effectively inhibit the decomposition reaction of the electrolyte in the electrode,maintain the structural stability of graphite,and inhibit the Li precipitation.The selected additives all promote the formation of SEI films on the graphite surface and stabilize their structure,improving their electrochemical properties.For graphite anode,the three additives are to improve the electrochemical properties of Li||graphite batteries by increasing the amount of Li F in the SEI film.For Li Co O₂cathode,only bis（trifluoroacetamide）increased the Li F content in the positive electrolyte interphase（CEI）film while the heptafluorobutyric anhydride and potassium perfluorinated sulfonate additives improved the CEI films mainly by increasing the content of Li₂CO₃in CEI film.The above results show that whether the CEI film plays a protective role in Li Co O₂is determined by a variety of factors.From the perspective of performance improvement,heptabournic anhydride has a better effect on the graphite anode,and the Li||graphite cell after 150 cycles still maintains a high discharge specific capacity of 351.5 m Ah g^-1,and the capacity retention rate is as high as 99.1%.For Li Co O₂,Li||Li Co O₂cell with potassium perfluorinated sulfonate still maintains a discharge capacity of 124.3 m Ah g^-1,and the capacity retention rate is 91.9%.For graphite||Li Co O₂full cell,potassium perfluorinated sulfonate showed obvious advantages,and the discharge specific capacity after 75 cycles was 88.7 m Ah g^-1,and effectively suppressed the negative impact of the increase in positive electrode load.