Problems Facing Silicon Carbon Material System

Silicon possesses an ultra-high theoretical capacity for lithium insertion, about tenfold that of carbon material. It has many advantages, including a low price, abundant sources, and a platform charging and discharging similar to graphite. Silicon will, however, produce volume changes of >400% during deintercalation, resulting in the pulverization and destruction of the material. It will also lose electrical contact with both the current collectors and the conductive agents, causing rapid capacity degradation. The SEI membrane on the silicon surface is also a major factor in limiting its cycle life.
In the process, lithium is released, with the expansion of silicon, the SEI films on the surface of the silicon are constantly deformed and cracking, and a new SEI will form on the exposed surface of the silicon. This causes the SEI to accumulate and thicken which greatly reduces The diffusion into silicon particles of lithium ions, which in turn, reduces lithium insertion capability of the material. 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 mainly focused on solving two key problems: “volume expansion”, and “conductivity”, in the charge and discharge processes. 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 a 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.

No single silicon or carbon material can, however, meet both the energy density and the cycle life requirements for modern electronic devices. The fact that carbon is a member of the same chemical group as silicon, and has similar properties to both, makes it easy to recombine them. The composite 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.

The reduction of particle size in the electrode material has the additional purpose 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. To improve electronic conductivity there are two methods. The first is to coat conductive material and the second is to dope, for example by producing mixed states.

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 carbon and silica. 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 a result of 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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