Why is the silicon carbon material the most potential lithium battery cathode?

Silicon is found so far lithium ion batteries cathode materials that has highest specific storage (4200 mAh/g). It is one of the most promising anode materials, but as silicon lithium battery, there are some negative application bottlenecks. The first question is that silicon can appear in the reaction volume expansion. The theoretical calculation and experiment can prove that embedded lithium and dis-embedded lithium can cause volume change. The volume change is 320%. No matter what kind of material is made, in micro level, the silicon atomic scale or nanometer scale, its expansion is 300%. The material design must consider the large volume change. High volume capacity materials will lead in the local produce mechanics issues. A series of basic researches prove that it can crack and form a serious damage.

Silicon volume expansion will lead to a series of results

1. The particle pulverizing, cycle performance is poor

2. The active substances in contact with the conductive agent binder is poor

The second problem is that at the SEI film on the surface of the silicon is relatively thick and uneven, the influence of temperature and additives is very big, can affect the lithium ion battery in the specific energy.

Because the electrical conductivity of graphite surface especially good, SEI is relatively uniform, its composition is not the same as silicon anode. In order to research this problem, the Chinese academy of sciences related scientists made a model material, nanometer made silicon micromachining by column. To observe the growth of this material in the process of charging and discharging of SEI, we found that with the increase of cycling times, SEI gradually turned silicon column fill in the gap in the middle, after the cover will also continue to grow about 4.5 microns, the silicon surface without any treatment, SEI can grow very thick. That means it is porous, solvent can always expose to dip into the silicon surface, so that in all the battery is no good in design. How to solve this problem, the Chinese academy of sciences related to scientist made some attempt to do carbon coated on silicon, in order to compare, we only do the part of graphene on silicon coated, free up elsewhere. Finally see coating and coating of the SEI film growth, carbon coated SEI is significantly reduced, there are many without coated SEI film.

From the perspective of a long-term basic research, (1) through the nano silica powder; (2) silicon carbon coated; Such technology can effectively solve the problems in silicon application of lithium battery cathode. Nano silicon carbide or oxide and silicon carbon, silicon, strive to do the following:

Silicon particle size: < 20 nm is as small as possible (theory)

Uniformity: the standard deviation is less than 5 nm

: purity > 99.95%

Appearance: spherical rate 100%

In addition, the surface of the complete coating is very important to prevent the silicon and the electrolyte contact, produce thick SEI film consumption. The micro structure of the design is very important also, want to maintain electrical contact in the process of circulation, ion channels, the expansion of the volume.

Carbon coated mechanism is: Si the volume expansion of assume jointly by graphite and amorphous coating layer, avoid negative electrode materials of lithium process in the embedded pulverization due to the huge volume change and stress. The effect of carbon coating is:

(1) the constraint and buffer volume expansion of active sites

(2) prevent the reunion of activity of the nanoparticles

(3) to prevent the electrolyte penetration to the center, keep a stable interface and SEI

(4) silicon contribution ratio capacity, carbon material contribution to the high electrical conductivity

Silicon carbon negative has a very broad market space

Anode materials technology is relatively mature, and its concentration is high, transfer capacity from Japan to China. Currently anode materials are given priority to with carbon material, low cost of lithium batteries, basic comprehensive realization industrialization in China. From the area, China and Japan is the world's major production and marketing, power battery enterprise purchase the cathode mainly comes from Japan.

In recent years, with the continuous improvement of production and technology of China, China is the main origin of raw material for anode materials, lithium electricity industry transfer to China, increasing market share. Silicon carbon anode materials is the future of lithium battery cathode material is the most potential applications, how big is the market capacity of silicon carbon anode materials, now this also explains why there are so many companies and research units layout silicon carbon anode materials.

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