Synthesis And Electrochemical Characterization Of Silicon/Carbon Composite Anode For Lithium-ion Batteries

Silicon(Si) becomes the most promising anode material because of its high theoretical capacity up to 4200 mAh / g. However, more than 300%volume variation of expansion and contraction for Si anode occurs during cycling, resulting in anode pulverization, and loss of electrical contact with current collector and finally rapid capacity decay. Moreover, the cycle life of silicon is limited due to the unstable solid-electrolyte interphase(SEI) on the surface. When the silicon expands and contracts, the SEI layer deforms and breaks. The formation of new SEI on the freshly exposed silicon surface causes the cell to have poor cycling stability, with the accumulated SEI eventually blocking lithium ions transport.It is well known that pulverization and capacity fade can be significantly prevented by adopting Si nanoparticles(NPs).But this tends to causing serious aggregation of NPs, and a stable SEI film is not formed effectively.Based on these existing problems, we adopt a spin-steaming method to promote condensation reaction between hydroxyl groups of Si NPs and carboxy groups of citric acid. In this way, Si NPs coated with carbon films are prepared. The capacity retention of the composites is 91% after 20 cycles.Based on spray-drying, surface coating and heat treatment technologies, we designed and prepared hierarchical Si NPs/porous carbon framework @carbon shell(Si/po-C@C) composite derived from precursors of Si/PVA@PAN spherical secondary microparticles, where Si NPs homogeneously were embedded in the porous carbon framework in core section, and the core section composed of Si NPs and carbon framework was encapsulated in the carbon shell outside. The porous core structure provides a supporting frame to insulate Si NPs and enough space to buffer expansion of Si. Meanwhile, the external carbon shell helps to form stable SEI by blocking electrolyte. Therefore, the electrochemical performance of Si/C composite is improved. The coulombic efficiency of Si/po-C@C electrode is up to 76% for the first cycle. To 50 th cycle at a rate of 0.1C, the capacity retention is more than 99% with a reversible capacity of 1000 mAh/g. This synthesis is simple in process, low in cost, easy in industrialization.