Preparation And Properties Of Silicon/carbon Composites As Anode Matirials For Lithium-ion Batteries

Silicon has attracted great attention as anode material for lithium-ionbatteries because of its highest theoretical specific capacity. However,silicon undergoes a huge volume change during lithium-ion insertion andextraction, resulting in mechanical instability of the electrode and finallyrapid capacity fading. The key issue of silicon anode research is to restrictthe volume change, keep electrode stable in lithiation. In this work, severalkinds of Si/C composites were prepared to enhance the cyclingperformance of silicon.Silicon anodes with different weight ratio of silicon, PVDF andacetylene black were fabricated and tested. CV curves indicate thatidentical electrochemical reactions proceed in different Si anodes. Anodewith less silicon content shows better cycling performance ingalvanostatical charge/discharge tests. Electrochemical properties of the Sianodes can be improved by an annealing process after which each Si anodeshows a smaller electric resistance and a higher capacity retention. Theimprovement of cycling performance can be attributed to the enhancement of the electrode structure stability by densification of materials andenhanced adhesion after annealing.Si/SC composites were prepared by a hydrothermal and then acarbonization process from nano-silicon and sucrose. Si/SC composite withlower silicon percentage shows higher capacity retention after50cycles.The introduction of GNS can enhance the cycling performance of Si/SC bya certain extent. After the annealing process, the electrochemical propertiesof Si/SC anodes are improved conspicuously.Nano-Si/RC composites were prepared by pyrolysis of the mixture ofnano-Si and phenolic resin. The composites shows a better cyclingperformance than row silicon. The introduction of GNS or CNTs canreduce the resistance of the composites, but makes little difference on itscycling performance.Micro-Si/RC and micro-Si/G/RC composites were prepared byball-milling and carbonization from micro-Si, phenolic resin and naturalgraphite. Galvanostatical charge/discharge tests indicate that theintroduction of graphite can effectively improve the electrochemicalproperties of Si/RC composite. Micro-Si/G/RC anode with annealingshows a higher capacity retention than that without annealing, but capacityfading problem can not be totally solved by the annealing process.