Synthesis And Electrochemical Performance Of The New Si/C Anode Composites With Metal Ions As Ligands

Lithium-ion batteries(LIBs)have the advantages of high energy density,long cycle life,low self-discharge rate,and environmental friendliness,so it is widely used in portable electronic equipment,electric vehicles and large energy storage systems.However,the current commercial LIBs anode material is mainly graphite,and its theoretical specific capacity is only 372 mAh g-1,which is far from meeting the future market demand for high energy density.Therefore,the development of new anode materials with high energy density to replace graphite is of great significance for the further development of LIBs.Silicon(Si)is expected to replace graphite as the next-generation anode material of lithium-ion batteries due to its extremely high theoretical capacity(approximately 4200 mAh g-1),suitable electrode potential(＜0.5V,vs.Li/Li+)and abundant reserves.However,Si also has obvious disadvantages as a negative electrode material:on the one hand,Si will have a huge volume change(>300%)in the process of lithiation/delithiation,resulting in the continuous formation of an unstable solid electrolyte interface layer(SEI)on the surface and a huge irreversible capacity loss,and the particles will violently break away from the current collector and lose electrical contact after many cycles;on the other hand,the low electrical conductivity of Si is not conducive to the rapid progress of the lithiation/delithiation process.These greatly hinder the practical application of silicon-based anode materials.For the above problems,researchers have tried various methods,finding the silicon-carbon composite can effectively relieve the volume expansion of silicon,improving the conductivity of the overall material and increasing the cycle life of LIBs.However,pure carbon coating cannot maintain the long-term cycling stability of LlBs at high current density,therefore.the optimal nanostructure and architecture of the Si/C are also critical for the integrity of the electrode and the rapid transfer of lithium ions and electrons across the electrode/electrolyte interface and within the active material.In this paper.the innovative and rational design of Si/C nanostructures using metal ions as ligands has be realized,and the layered flower-like structure of a stable substrate with highly conductivity and the spherical structure of a conductive network with high Coulomb efficiency have been successfully prepared,and we further explore the reaction mechanism of high coordination binding for different metal ions.The specific research contents are as follows:1.Preparation and electrochemical performance of three-dimensional layered Si@NiO@Ni/C compositesIn the system of designing L-lysine reaction system,the layered Ni(OH)2 was grown in situ on the surface of Si nanoparticles,and the layered Si@NiO@Ni/C(700-PDA)of a stable substrate with highly conductivity was successfully prepared.In addition,the reaction mechanism of the combination of Si nanoparticles and Ni2+ ions in the L-lysine reaction system was also explored,and compare the electrochemical performances of Si@NiO,Si@NiO@Ni/C(700-glucose)and Si@NiO@Ni/C(700-PDA)electrodes were compared.As a result,the initial charge/discharge capacity of the Si@NiO@Ni/C(700-PDA)electrode reached as high as 1758.9/1045.3 mAh g-1 with an initial Coulombic efficiency(ICE)of 59.4%,and showed a high capacity of 1265.5 mAh g-1 after 300 cycles at 0.5 A g-1 and the excellent rate capability(982.2,876.1,766.6,645.8,572 mAh g-1 at 0.2,0.5,1,2,3 A g-1,respectively),indicating Si@NiO@Ni/C(700-PDA)electrode has the most excellent electrochemical performance.2.Preparation and electrochemical performance of sphericalSi/carbon gel@void@C composites The L-lysine reaction system was improved(with citrate added)to enhance the complexation of Fe3+ ionic ligands,and a conductive network spherical Si/carbon gel@void@C structure with carbon material as the skeleton was successfully prepared.The improved reaction system was discussed,and the necessity of L-lysine was further demonstrated.In addition,the electrochemical performances of Si/carbon gel@Fe3O4@C and Si/carbon gel@void@C electrodes were compared.As a result,the initial charge/discharge capacity of the Si/carbon gel@void@C electrode reached as high as 1828.8/1508.3 mAh g-1 with a high initial coulombic efficiency(ICE)of 82.47%,and showed a high capacity of 1201.3 mAh g-1 after 300 cycles at 0.5 A g-1 and the excellent rate capability(947.1,850.2,785.7,576.7,407.5 mAh g-1 at 0.2,0.5,1,2,3 A g-1,respectively),its overall electrochemical performance is better than Si/carbon gel@Fe3O4@C.