Study Of Preparation And Electrochemical Performance Of Silicon-based Anode Materials With Core-shell Structure

Silicon oxide has many advantages such as high capacity,low cost and abundant natural resources,making it as one of the promising new-generation anode material.However,silicon oxide has low conductivity and serious volume expansion during charge/discharge cycles.The shortcomings heavily restrict its commercial application in lithium ion battery.The Graphene/SiO_x/PPY composites,ZIF-8/SiO_x/ZIF-8 composites and Nifoam/SiO_x/Graphene composites were designed and prepared in the presented paper.Their microstructures and electrochemical performances were also detailedly studied to elaborate the potential improvement mechanisms.1.The core-shell structure of Graphene/SiO_x/PPY composites was prepared by silicone hydrolytic deposition of Graphene template,low-temperature aluminum reduction and in situ polymerization.The Graphene/SiO_x/PPY composite with a C/Si molar ratio of 1:5 showed good electrochemical performance.Its charge/discharge capacity was up to be 2068/2130 m Ah g^-1 after 100 charge/discharge cycles at a current density of 0.1 C,respectively.Its charge/discharge capacity were greater than575/569 m Ah·g^-1 at a current density of 1 C.The results of microstructure and electrochemical properties showed that the synergic effect of graphene and PPY improved the conductivity of SiO_x and effectively reduced the volume expansion of SiO_x during charge/discharge cycles.2.The core-shell structure of ZIF-8/SiO_x/ZIF-8 composite was prepared by silicone hydrolysis deposition of ZIF-8 template,low-temperature magnesium reduction and hydrothermal method.Microstructure characterizations such as XRD,XPS,SEM and TEM showed that ZIF-8 regulates the particle size of SiO_x,and ZIF-8with the three-dimensional network structure provided a buffer space,which supported the volume changes of SiO_x during charge/discharge cycle and prevented the loss of capacity caused by SiO_x breaking away from the anode surface.The ZIF-8/SiO_x/ZIF-8 composite had charge/discharege capacity of 966/986 m Ah g^-1 in the 200^th charge/discharge cycle at a current density of 0.1 C,and its efficiency was up to 99%,which was higher than SiO_x and ZIF-8/SiO_x composite.In addition,the ZIF-8/SiO_x/ZIF-8 composite remained the core-shell structure after carbonization at600°C,which effectively improved the conductivity of SiO_x.The ZIF-8/SiO_x/ZIF-8composite after carbonization had charge/discharge capacity of 926/938 m Ah g^-1 in the 200^th charge/discharge cycle at a current density of 0.1 C,and showed excellent C-rate performance.3.Nifoam/SiO_x/Graphene composite was prepared by silicone hydrolytic deposition of nickel foam,low-temperature aluminum reduction and graphene coating.When Ni/Si molar ratio was 5:1,Nifoam/SiO_x/Graphene composite showed good performance and had discharge capacity of 1868 m Ah g^-1 in the 5^th at a current density of 0.1 C.The charge/discharge capacity in the 100^th charge/discharge cycle was 1529/1519 m Ah g^-1 at a current density of 0.1 C,respectively.The nickel foam with three-dimensional network structure of provided a buffer space for SiO_x volume expansion and increased the conductivity of SiO_x.The graphene coating prevented SiO_x from breaking away from the electrode surface.The synergic effect of graphene and Nifoam improved the electrochemical performance of SiO_x.