Has your battery been "lithium doped with silicon"?

            In recent years, the "concept of playing" in the automobile industry is very powerful. For example, the recent "silicon doped lithium". This concept was put forward by Zhiji at its first press conference on January 13. According to Zhiji automobile, with this technology, the energy density of single battery can be 300wh / kg, and the range of electric vehicle can be 1000km.

           In addition, on January 8, GuoXuan high tech made its debut of 210wh / kg LiFePO4 battery products. Technically, it adopted the key "high-capacity silicon anode materials and advanced pre lithium technology."

         On January 9, Weilai automobile released a 150kwh "solid-state battery". It is said that the product adopts "inorganic pre lithium silicon carbon anode technology" and combines with ultra-high nickel cathode to make the energy density of the battery reach 360wh / kg. What's more, this battery

After the release of Zhiji, GAC group disclosed on January 18 that the models equipped with silicon negative battery technology have entered the real vehicle test stage as planned, and the products are planned to go on the market this year. For a while, there was a lot of excitement about batteries.

In fact, the concept of "silicon doping and lithium supplement" is a combination of silicon doping and lithium supplement. Silicon doping in negative electrode is to improve energy density, while lithium supplement is to improve first effect and cycle life. The futures concept of the combination of these two technologies is not a subversive innovation like "solid state battery", but an optimization technology like CTP. So, what are the benefits of this integration technology? And how is this technology achieved?

       We know that in order to improve the energy density of the battery, the specific capacity of the positive and negative materials of the battery (refers to the amount of electricity that can be released by a unit mass or volume of the battery or active material) needs to be improved. At present, the cathode material is usually high nickel, such as ncm811 battery, and the negative electrode is graphite.
        Now, the moment of silicon based negative electrode replacing graphite negative electrode is coming. Moreover, with Tesla's successful application of silicon carbon negative electrode on mass production model 3, this demonstration function also ushered in a wider market for silicon based anode.

         The reason why silicon is chosen as negative electrode is based on the theoretical gram capacity of silicon based negative electrode material is 4200mah/g, which is more than 10 times higher than that of graphite negative electrode. This is the advantage of silicon based negative electrodes. At present, there are two kinds of silicon based negative materials.

         One is silicon carbon negative electrode, that is, nano silicon and graphite mixed use, theoretical gram capacity is more than 3000mah/g, but the actual amount is just over 2000mah/g; the other is silicon oxide negative electrode, silicon oxide mixed graphite as the negative electrode, the approximate gram capacity is 1400-1800mah/g.

         In application, domestic 3C products generally use silicon carbon negative electrode more. In the aspect of power cell, there are many negative silicon oxygen electrodes.

In fact, the research and development of silicon materials for the application of lithium battery negative electrodes started in the 1990s, and it was not until 2013 and 2014 that the industrialization of silicon carbon negative and silicon oxygen negative electrodes was realized respectively. Panasonic was used in 2017 to supply Tesla with a large number of power batteries.
         In addition, the silicon-based anode of Samsung and LG Chemical is mainly used in the field of consumer batteries. Silicon based anode material lithium battery of GS Tangqian, Japan, is used in Mitsubishi automobile. The two have also formed a joint venture. On the whole, the industrialization of silicon-based anode is still very short.

         However, the biggest disadvantage of silicon-based materials is the high expansion rate. The charge discharge expansion of silicon anode is about 320%, while that of ordinary graphite is only about 10%. Under normal working conditions, the extremely high elasticity of expansion and contraction occurs frequently, the cycle life of the battery will be reduced, and the microstructure will collapse. In other words, although the capacity is increased, the cycle life is shortened, which is not worth the loss.

         In addition, the application of silicon-based anode is not only difficult, but also few enterprises are able to mass produce. According to the research of high tech lithium battery, at present, only Bertrand can supply large quantities of products in China and enter Panasonic's supply chain to indirectly supply Tesla. At present, the production capacity is about 3000 tons.

In addition, there are xiangfenghua, Sibao technology, Shanshan Co., Ltd., Zhongke electric and other enterprises in China, which have built pilot lines of silicon anode materials, but most of them are still in the early stage of technical verification, and have not yet been mass produced. From this point of view, graphite anode material will still be the mainstream in the future.

         In terms of demand, according to the statistical analysis of GGII, the current market demand mainly focuses on two types of silicon-based anode materials with capacity of 420mah / g and 450mah / g, and the application market of silicon-based anode with higher capacity is not mature. After all, the preparation process of silicon-based anode is complex, there is no standardized process, and the technical barrier is high (the difficulty mainly lies in the preparation process of silicon nano materials and silicon carbon composite materials).

         In addition, a small output means a high unit price. According to the data of Guosheng securities, the lowest price of silicon-based negative electrode is more than 100000 yuan. However, the birth and application of new technologies also means the opening of new markets. This is the expectation of lithium battery industry chain enterprises.

         In terms of materials, according to industry insiders, the energy density of silicon-based negative battery can be increased by 5 ~ 10% after using nano silicon. According to the average annual increase of lithium battery energy density in the industry is about 2%, the increase of 5% energy density is very difficult.

         In terms of "silicon doping", patent competition is also in progress. For example, Huawei recently announced a patent for the invention of "silicon carbon composite and its preparation method and lithium-ion battery". It is said that the capacity retention rate of the battery with silicon carbon composite material provided by the patent is 80% after 500 cycles. Of course, more domestic enterprises are catching up.