Carbon-Coated Silicon Material: an Ideal Anode Material for Lithium Batteries

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Problems Facing Silicon Carbon Material System

Silicon possesses an ultra-high theoretical capacity for lithium insertion, approximately tenfold that of carbon material. Silicon also offers the benefits of a similar charging and discharging system to graphite as well as low prices and plentiful sources. Silicon will, however, produce volume changes of >400% during deintercalation, which can result in the material being pulverized, the loss of electrical connection with the current collector and conductive agents, and a rapid capacity degradation. The SEI membrane on the silicon surface is also a major factor in limiting its cycle life.
The lithium ions diffuse into the silicon particle, reducing the lithium insertion capability of the active materials. Selecting nano-scale silicon particle can also reduce material powdering. This will improve capacity. Nanoparticles, however, are easily agglomerated, and they have little effect on the thickening SEI films. The silicon anode technology is focused on two key problems: “volume growth” and “conductivity”, which are both present during the charge-discharge process. As far as anodes are concerned, the carbon materials used in silicon anodes to form conductive and buffer layer are crucial.

The nanometerization process can enhance the performance of silicon material. To reduce the cost of manufacturing nano-silicon material and to stabilize the SEI film on the surface of silicon materials, a variety of materials with good intrinsic conductivity are used to combine with silicon. Carbon materials can be used to improve the conductivity on silicon-based anodes and also stabilize the SEI films.

Neither silicon nor carbon can satisfy the demands of modern electronics for energy density or cycle life. The fact that silicon is a member of the same chemical group as carbon, and has similar properties to both, makes it easy to combine them. The composite material of silicon-carbon can be used to complement both the benefits and shortcomings of each material. It also allows for a material with a much higher gram and cycle capacity.

Moreover, the reduction of particle size in the electrode material has the aim of increasing the ionic rather than electronic conductivity. As the particle size is reduced, the diffusion path of lithium ions is also shortened. This allows the lithium ion to quickly participate in electrochemical reactions, during charge and discharge. For the enhancement of electronic conductivity there are two methods. One involves coatings of conductive material and the second is doping. This is done by producing mixed valences states to improve the intrinsic conductivity.

Carbon-Coated Silicone Material

Scientists developed a plan for using carbon to wrap silicone as a negative electrolyte material in lithium batteries. They did this by synthesizing the electrochemical characteristics of silicon and carbon. In experiments, scientists found that silicon coated with carbon can boost the material’s performance. Preparation methods for this material include hydrothermal method CVD, and coating carbon precursors to silicon particles. The array of nanowires were prepared by metal catalytically etching the silicon plate. They then coated the surface with carbon using carbon aerogel and Pyrolysis. The initial discharge capacity of this nanocomposite was 3,344mAh/g. After 40 cycles, the capacity was 1,326mAh/g. The material’s excellent electrochemical performance is due to its good electronic conductivity, contact between silicon and carbon materials, and effective inhibition of volume expansion by the silicon materials.

The Development Prospects

Carbon-coated Silicon material combines high conductivity, stability and silicon’s advantages with high capacity. It is an ideal material for lithium batteries anodes.

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