Preparation Of Silicon-based Anode Materials And Its Application In Sulfur-lithium Ion Battery

Lithium-sulfur battery is considered to be one of the most promising high-energy-density electrochemical energy storage system owing to its high theoretical energy density of about 2600 Wh kg^-1.However,the use of elemental lithium as anode in lithium-sulfur battery remains the biggest barrier to its practical application due to safety concerns arising from the formation of lithium dendrites during cycling.In this thesis,the silicon-based anode materials with high specific capacity and good cycle stability were firstly prepared.Then the sulfur-lithium ion battery with good cycling performance was constructed by employing sulfur-based cathode and silicon-based anode to replace metal lithium.The new battery system possesses the advantages of both high safety and high energy density.The detailed experiments and results are given as follows.?1?The pore-containing silicon/nitrogen-rich carbon materials have been successfully fabricated by using the waste contact mass of organosilane industry as the pore-containing silicon source and gelatin as the nitrogen-rich carbon precursor.The pore structure within the pore-containing silicon particles can absorb its large volume expansions and the nitrogen-rich carbon matrix can accommodate the volume change as well as improve the electronic conductivity.It exhibits good electrochemical performance with a reversible capacity of 748 m A h g^-1 after 100 cycles at a current density of 100 mA g^-1.?2?Through the adoption of biosilica from the rice husks as the silica precursor,we synthesized porous silicon anode materials and study the impact mechanism of the thermal effect on the porous silicon material preparation via magnesiothermic reduction comprehensively and thoroughly.It shows that the ramp rate during magnesiothermic reduction has a big effect on the structure and electrochemical properties of the porous silicon materials.With higher ramp rates,the structure of the obtained porous silicon materials has been changed and the corresponding specific surface areas decrease dramatically compared with that of the starting material SiO₂ template.The structure change of the porous silicon materials is attributed to the heat accumulation during the magnesiothermic reduction with higher ramp rates,which can lead to the formation of the byproduct Mg₂SiO₄ and the agglomerative composite particles of Si and MgO with larger size.The heat accumulation can cause the fusion of the byproduct Mg₂SiO₄ and the disappearance of the small pores.After acid washing of large-sized MgO with HCl, macropores remain.What's more,the Mg₂SiO₄ can further reduce the purity of the Si products.With the much lower ramp rate,the situation mentioned above can be avoided.Then the final porous silicon product has high purity and the porous structure of the originated SiO₂-JRH can be well maintained.It exhibits excellent cycling performance and rate performance with a reversible capacity of 1311 mA h g^-1 after 100 cycles at a current density of 200 mA g^-1 and 1177 mA h g^-1 at 4 A g^-1.Moreover,the organic carbon reserved will have a serious impact on the structure of the porous silicon materials,as the organic carbon distributes quite inhomogenously and its content is very hard to control.Therefore,reserving the organic carbon in the porous silicon materials will lower its electrochemical performance.?3?The Si/porous C composite has been successfully fabricated by simply adhering the Si nanoparticles to the nitrogen-rich porous carbon framework prepared by using gelatin as the nitrogen-rich carbon precursor and nano-CaCO₃ particles as the template.The nitrogen-rich porous C matrix with high specific surface area and large porosity cannot only provide sufficient space to buffer the volume change of Si nanoparticles during the charging/discharging process but also can ensure the rapid Li⁺ion transport and improve the electrochemical reaction kinetics.It exhibits a reversible capacity of 1103 mA h g^-1 after100 cycles at a current density of 100 mA g^-1 and 766 mA h g^-1 at 2 A g^-1,showing good cycling performance and rate performance.?4?The core-shell structured SiO_x/C composite was prepared by coating the SiO_x particles,which were synthesized by a thermal evaporation method,with the 10-13 nm thick carbon coating layer pyrolysed from polydopamine.The uniform nitrogen-doped carbon coating layer cannot only improve the conductivity of the SiO_x particles but also act as a mechanical buffer layer to accommodate the volume changes of the SiO_x component during the lithiation/delithiation process.Meanwhile,the core-shell structured SiO_x/C composite allows for the growth of a relatively stable SEI on the surface of the N-doped carbon shell during cycling,thus ensuring the higher coulombic efficiency and better cycle stability.The as-prepared core-shell structured SiO_x/nitrogen-doped carbon composite exhibits excellent electrochemical performance.It delivers a reversible capacity of 1514mA h g^-1 after 100 cycles at a current density of 100 mA g^-1 and 933 mA h g^-1 at 2 A g^-1.?5?The sulfur-lithium ion battery was constructed by employing sulfurized polyacrylonitrile cathode,SiO_x/C anode and carbonic ester electrolyte.Three different ways of introducing lithium into sulfur-lithium ion battery system were comprehensively studied.Finally by using the chemically prelithiated SiO_x/C anode,sulfur-lithium ion battery with stable cycling performance was successfully constructed.It delivered a reversible specific capacity of 623 m A h g^-1 after 76 cycles at 100 mA g^-1 with an average working voltage of1.6 V and the estimated energy density of the full cell was about 512 Wh kg^-1,showing excellent electrochemical performance.