Synthesis And Performances Of SiO_x-Based Composites As Anode Materials For Lithium Ion Batteries

Lithium ion batteries（LIBs）have been applied in various fields（i.g.new energy vehicles and portable electronic equipments）due to their inherent advantages such as safety,environmental benignity,high energy density,long cycle and non-menory effect.However,traditional graphite anode materials can not meet the ever increasing demand for high performance storage capacity anymore.Up to now,Si-based materials especially the silicon oxides Si O_x with the obvious advantages of higher specific capacity and the relatively samaller volume change was an attractive candidate to replace the carbon anodes,but it still face the dilemma to adapt to commercial production due to its low donductivity,low cyclic stability,high-tech requirements and cost.Herein,this article introduces the facile,ultralow-cost and top-down routes to convert biomass bamboo-based materials with rich content of Si element（bamboo charcoal,bamboo leaves and bamboo shoot hulls）into 3D hierarchical porous silicon oxides/carbon（Si O_x/C）composites.The preparation process of the optimized Si O_x/C composites mainly includes the activated carbonization with different catalytic method according to their unique biomass characteristics and the mild aluminothermic reduction procedure.The in situ construction of the hierarchical composites directly utilizes the original biomass materials without adding any extra silicon and carbon sources.Also,using aluminum powder to reduce the precursor can largely retain the hierarchical structure of the biomass,and simultaneously generate partial low valence silicon oxides instead of pure Si.Furthermore,we also propose a novel core-shell Si O@Ti O₂ nanocomposite which is composed of amorphous Ti O₂-coated Si O nanoparticles preparing from the simple ball milling and a facile sol-gel hydrothermal process in low temperature.These materials combine the advantages of high specific capacity and good cyclic stability with the electrochemical activity.The BC-based Si O_x/C composites were synthesized via the carbon activation,regulation of silicon content and the aluminothermic reduction.With the suitable content of reducing agent,the optimized Si O_x/C composite with rich hierarchical pores（i.e.interconnected micropores and mesopores）shows a high specific surface area.When used as the lithium-ion battery anode material,the optimal Si O_x/C composite achieves impressive reversible capacity of 1100 m A h g^-1 at 200 m A g^-1 after 300 cycles as well as prominent cyclic stability under high rates(700 m A h g^-1 after 200 cycles at 1 A g^-1).Besides,the Si O_x/C anode demonstrates high capacity retentions and superior cyclic stability in full cells(156 m Ah g^-1 after 50 cycles).Raw bamboo leaves were activated and carbonized in a low temperature hydrothermal system due to their high content of Si and the uneven distribution.The final Si O_x/C materials were producted via the similar following reduction.Accoring to the physical characterization of the materials,the carbon layer of raw leaves was reshaped with abundant micropores on the surface and the Si O_x was coated evenly by this modified carbon.When applied for andoes of lithium ion batteries,the Si O_x/C composities display a high discharge capacity of 1017 m A h g^-1 at 200 m A g^-1 after 350 cycles with perfect cycling stability.Even at the high rate of 1000 m A g^-1 the sample can maintain reversible capacity of 429 m A h g^-1 after 500 cycles.In order to explore best variable of activated carbonization for precursors,we used Cu Cl₂ as the catalyst to prepare hierarchical porous Si O_x/C and carbon materials from bamboo shoot hulls and analyzed the principle of catalytic process.Upon the catalysis of the metal chloride,the macromolecular organics in the biomass matrix endured degradation and dissolution to create the activated carbon framework,which contributed to the hierarchical porous structure of Si O₂/C with additional nano-channels and ultra improved specific surface area of 2311 m² g^-1.When using for anode materials of lithium ion batteries,the optimal Si O_x/C shows reversible capacity of 1281 m A h g^-1 at 200 m A g^-1 after 400cycles.Even at the high rates of 3 A g^-1,the material still exhibits excellent discharge capacities of 469 m A h g^-1 after long 1000 cycles,respectively.When applying in full cells,it achieves perfect electrochemical properties as well(142 m Ah g^-1 after 100 cycles).The carbon material also displays the outstanding electromical performances when used in LIBs:It show the 600 m Ah g^-1（300 cycles）at 200 m A g^-1 and 305 m Ah g^-1（1000 cycles）at 3000m A g^-1,respectively,and it delivers 212 F g^-1 when acts as the electrode in supercapacitorLow cost and tailorable core-shell Si O@Ti O₂ nanocomposites were synthesized via simple ball milling and sol-gel hydrothermal process in low temperature.When used as anode material for lithium-ion batteries,the optimal nanocomposite delivers a high initial coulombic efficiency of 79.4%,along with a stable reversible capacity of 901 m A h g^-1after 200 cycles at 200 m A g^-1 and impressive high-rate capacity of 272 m A h g^-1 at 3 A g^-1.The excellent electrochemical performance of the nanocomposite is contributed by the synergetic core-shell structure,in which the amorphous Ti O₂ shell can not only act as protective/elastic buffer layer to accommodate the volume change of the Si O nanoparticles upon cycling,but also largely favor the Li⁺diffusion in the nanocomposite toward highly reversible lithium storage.