Construction Of ZIF-8-basedcarbon-modified Anode Frombinary Compounds And Lithium-ionstorage Performance Research

With the rise of the concept of carbon peak and carbon neutralization in recent years,mankind urgently needs to find a clean,green and sustainable renewable energy.Lithium-ion batteries have attracted extensive attention due to their high specific capacity,high energy density and low production cost.Currently,graphite anode is used in most commercial lithium-ion batteries,which cannot meet the increasing energy demand due to its limited capacity(372 m A h g^-1).Therefore,the development of new high capacity anode materials has become the focus of researchers.Binary compound anode materials have many advantages,such as high theoretical specific capacity,controllable morphology and multiple complementary components,but their intrinsic conductivity is low,and there are different degrees of volume expansion in the charging and discharging process,resulting in the decline of battery cycle performance.Based on this,in this paper,binary compounds with different morphologies were used as precursors for ZIF-8 controllable coating.Zif-8derived carbon coated high specific capacity anode materials are prepared through subsequent heat treatment,and their electrochemical properties are studied.The details as follows:（1）The amorphous binary oxide Co₂SiO₄is designed and synthesized as the precursor.The surface of the precursor is modified by Poly dimethyl diallyl ammonium chloride（PDDA）/Sodiu M polystyrene sulfonate（PSS）,and the proportion of zinc nitrate and precursor is regulated to carry out ZIF-8 controlled coating on the precursor,and its coating quantity is optimized.The amorphous Co₂SiO₄@C composites are prepared by subsequent high temperature heat treatment.The amorphous structure with isotropic characteristics and potential defects can effectively shorten the diffusion path and accelerate the diffusion rate of Li⁺,and the introduction of nitrogen-doped carbon improves the conductivity of the composite.Meanwhile,Co₂SiO₄nanoparticles are highly dispersed in the conductive carbon network with high conductive connectivity,which effectively buffered the volume expansion during the charging and discharging process and improved the cycle stability.The reversible specific capacity of the Co₂SiO₄@C composite after 400 cycles at a current density of 0.2 A g^-1can reach 1133 m A h g^-1,showing good cycle stability and high reversible specific capacity.（2）Spherical binary carbonate Zn_0.33Mn_0.67CO₃with micro nano structure is used as precursor.After surface modification by PDDA/PSS,the ratio of zinc nitrate and precursor are adjusted to control the liquid phase ZIF-8 coating of precursor,and the coating amount is optimized.Subsequently,the porous spherical Mn O_x@C composite with micro/nano structure was prepared by high temperature heat treatment.In the pyrolysis process,the release of CO₂gas and the reduction and evaporation of Zn lead to the formation of abundant pore structures from inside to outside in the whole composite microspheres.Electrochemical tests showed that after 250 cycles of the negative electrode material at a current density of 0.2 A g^-1,it showed a reversible specific capacity as high as 1457 m A h g^-1.In addition,using the same binary carbonate Zn_0.33Mn_0.67CO₃as precursor,ZIF-8coating is carried out by solid phase method,and porous S-Mn O_x@C composites with micro/nano structure are prepared by subsequent high temperature pyrolysis.Electrochemical test results show that the reversible specific capacity of 1461 m A h g^-1is obtained at 0.2 A g^-1for 200 cycles.（3）Mn₂SiO₄binary oxide with hollow spherical structure is used as the precursor,ZIF-8 controlled coating is carried out on the precursor by liquid phase method and the coating amount is optimized.The Mn₂SiO₄@C composite with hollow spherical structure is prepared by subsequent high temperature heat treatment.The hollow spherical structure can not only effectively buffer the volume expansion of active components in the charging and discharging process,but also provide more active sites for electrochemical reaction with its large specific surface area.After ZIF-8 derivative carbon coating,the conductivity and cyclic stability of the material are further improved.The effect of the structure size of manganese silicate precursor and the amount of ZIF-8 coating on the electrochemical performance of the assembled battery I s studied.The reversible specific capacity of the Mn₂SiO₄@C composite synthesized from the 270 nm manganese silicate system after 300cycles at a current density of 0.2 A g^-1can reach 1343 m A h g^-1,and also shows good magnification and high ion diffusion rate(1.14×10^-10cm²s^-1).The Mn₂SiO₄@C composite synthesized by the 90 nm manganese silicate system can reach an ultra-high reversible specific capacity of 1502 m A h g^-1after 50 cycles at a current density of 0.2 A g^-1.