Investigation Of Graphite Material With High Lithium Storage Properties Derived From Graphitic Carbon Nitride

Lithium-ion batteries play a crucial role in electrochemical storage devices due to their high power and energy density and portability,especially in electronic devices and electric vehicles.However,the commercialized graphite anodes are increasingly unable to meet the requirements of the market,and it is urgent to develop anode material with better cycle performance and higher capacity density for lithium-ion batteries.Recently,graphitic carbon nitride（g-C₃N₄）is expected to be a potential anode material due to its similar layered structure to graphite and excellent chemical stability.In this paper,g-C₃N₄ is used as precursor and different catalysts are investigated for catalytic graphitization,and the structure and morphology are thoroughly analyzed by various characterization methods,which are studied as anode material for lithium-ion batteries.The main research results are as follows:（1）g-C₃N₄ is synthesized by different precursors,in which melamine delivers the highest yield of 54.3%.Graphite materials with adjustable levels of nitrogen doping（Fe CN）are synthesized at different temperatures using g-C₃N₄ as precursor and Fe as catalyst.The results show that g-C₃N₄ converts to graphite materials after catalytic treatment with Fe.The nitrogen doping level decreases from 15.17%to 3.46%and the relative content of pyridinic N,pyrrolic N and graphitic N in the material can be easily adjusted.The electrical conductivity of Fe CN is significantly improved compared to g-C₃N₄.As anode of lithium-ion batteries,Fe CN shows superior initial charge capacity(525.8 m Ah·g^-1 at 0.05 A·g^-1)and promising rate performance(181.7 m Ah·g^-1 at 5.0A·g^-1)as well as excellent cycling stability(98.7%capacity retention after 500 cycles at 0.5 A·g^-1).The effects of different amounts of Fe on the structural and electrochemical performance are investigated and find that the increased amount of catalyst leads to higher graphitization degree of samples.When the mass ratio of reduced Fe to g-C₃N₄ is 0.5,the samples have the best electrochemical performance.（2）The first coulombic efficiency of Fe CN anode is improved by pre-lithiation technology,and the first coulombic efficiency of Fe CN anode can achieve ideal results by controlling the reaction time between the anode and lithium metal.When the pre-lithiation time is 20 min,the first coulombic efficiency increases from 62.2%to 91.3%,showing that the pre-lithiation can improve the initial coulombic efficiency of Fe CN anode.（3）A new graphite anode（Ni-g-C₃N₄）is synthesized at 850℃using g-C₃N₄ as the precursor and Ni as the catalyst.Researches show that the Ni plays an important role of denitrification during the sintering process,which reduces the nitrogen content of g-C₃N₄ from 62.1%to 1.2%,thus enhancing its electrical conductivity and significantly improving its rate performance and cycling performance.During the charge/discharge process,Ni-g-C₃N₄ anode exhibits the typical low-voltage plateau of graphite anode,and the transformation process of graphite intercalation compounds are revealed in the electrochemical in-situ XRD analysis.Its capacity retention reaches99.3%after 600 cycles at a current density of 0.5 A·g^-1,showing well structural stability.The structural evolution of Ni-g-C₃N₄ from g-C₃N₄ to graphite is analyzed by TG-MS and high-temperature XRD,which reveales the catalytic graphitization mechanism of Ni.