Silicon-based negative again! Where is the difference between Xiaomi Quick charging "cool techs" and Tesla and Weilai?

On Friday (26th), Xiaomi Mobile announced that Xiaomi 11Ultra will launch a super fast charged silicon negative battery. Xiaomi said that Xiaomi took the lead in applying the battery technology of new energy vehicles to mobile phones, adding nanoscale silicon through negative electrodes, bringing 10 times the theoretical gram capacity of graphite.

Since last year, big consumer electronics companies, represented by Apple, have made a big foray into the car-building field. Among them, although Xiaomi has only recently been officially announced to build cars, it has received no less attention than its competitors. On the day of the release of the silicon-oxygen negative battery, rumors of Xiaomi's joint car construction with Great Wall caused its share price to fluctuate sharply.

It should be pointed out that although the new energy vehicle charging technology is only applied to mobile phones, to some extent, Xiaomi has shown its "muscle", proving that it has long been in reserve in the core area of electric vehicle technology-lithium batteries.

What is the difference between silicon-based negative electrode recycling technology core silicon and carbon-silicon?

According to the introduction of Xiaomi, the innovation of the fast charging technology is that the negative electrode increases the nanometer silicon material and greatly increases the theoretical gram capacity, which is also one of the important directions of technological innovation in the lithium battery industry in recent years. For investors, silicon-based negative electrodes are no stranger.

On the eve of Tesla's Battery Day last year, Tesla's silicon nanowire battery negative material, which was spoiled on the official website, was once considered the biggest stunt of Battery Day; in January this year, Lai and GAC released the "150kwh solid-state battery package" and "graphene battery", whose technology core is also based on silicon-based negative electrodes.

The data show that at present, the commercial anode materials are mainly graphite carbon anode materials, and their theoretical specific capacity is only 372mAh / g, which seriously limits the further development of power lithium batteries. The silicon-based negative electrode is the material system with the highest theoretical performance, and the theoretical specific capacity is 4200mAhbing, which is 11 times that of graphite.

It is worth noting that, from the name of Xiaomi fast charging technology-- "silicon negative electrode", although it is also a silicon-based negative electrode in essence, it and the "carbon-silicon negative electrode" mainly used in the new technologies of Tesla, Lulai and Guangzhou Automobile, in fact, it represents the two development paths of silicon-based negative electrodes.

According to the report of New era Securities analyst Kai Ming on June 16, 2020, there are many preparation methods of silicon-based anode materials, and the preparation process is more complex than that of graphite, and the products have not yet reached standardization. At present, carbon-coated silicon oxide and nano-silicon carbon are the two most commercialized silicon-based anode materials, and the comparison of their advantages and disadvantages is shown in the figure.

From the commercial point of view, the better carbon-coated siliceous carbon products with graphite to 450-500m Ah/g capacity can be recycled 1000-2000 cycles in the steel shell core and 500-1000 cycles in the soft package core.

For nano-silicon-carbon, the current commercial flexible-package batteries and square aluminum shell batteries are still very sensitive to expansion, so that nano-silicon-carbon materials are still difficult to use in this kind of batteries. At present, the main application field of nano-silicon-carbon materials is still in cylindrical steel shell batteries, represented by 18650 and 21700 models.

Dr. Xie Zhengwei of the Chengdu Institute of Organic Chemistry of the Chinese Academy of Sciences said in an interview with industry media in March last year that the cycle life of carbon-silicon negative electrode is still relatively low, so it is generally used in 3C batteries. The silicon-oxygen negative electrode is mainly used in power batteries. At present, Bertre, Shanshan and Tesla all use silicon-oxygen negative electrode.

Compared with the two, Xie Zhengwei believes that both routes have a very promising future, in which the silicon-oxygen negative electrode has a high specific capacity, and the performance of the battery is relatively moderate, but after the cycle life of the carbon-silicon negative electrode can reach 1000 laps, coupled with the strong efficiency of the first charge and discharge, it will also be very promising.

The key to the breakthrough of the performance of silicon-based negative electrode battery has been mass produced and supplied by the domestic leader.

Judging from the development momentum of the entire silicon-based anode industry, the above report of New era Securities pointed out that in recent years, with the growth of the demand for high energy density anode materials in the downstream power battery industry, silicon-based anode materials will grow rapidly in the future.

According to forecasts, the demand for silicon-based anode materials will reach 22000 tons by 2022, with an annual compound growth rate of 80 per cent from 2019 to 2022. At present, the price of stable mass production silicon-based negative electrode is between 10-120000 yuan / ton, and the price is calculated according to the annual decline of 5%. By 2022, the market space of silicon-based negative electrode materials is expected to exceed 2 billion.

China International Capital Corporation analyst Li Xuan reported on September 8, 2020 that the silicon-based negative electrode is one of the important materials to improve the performance of power batteries, but its core technical difficulty lies in controlling the structural damage caused by the expansion of silicon materials. as well as the shortcomings of high technical barriers, high cost of nano-silicon, low degree of industrialization and so on.

It should be pointed out that the development of silicon-carbon anode materials in China is still in the initial stage, the practical application is still relatively small, and the overall output of the market is relatively small. According to statistics, in 2019, the shipment of silicon-based (including silicon-carbon and silicon-oxygen) anode materials is only 3700 tons, and the permeability in the anode materials is about 1.4%.

At the corporate level, according to research, there are no more than 3 domestic enterprises capable of mass production. Among them, only Beitri can supply in large quantities, and has entered Panasonic's supply chain, indirectly supplying Tesla.

Other domestic manufacturers are in the stage of research and development or small batch production: Shanshan shares silicon-carbon negative electrode products achieve small-scale mass production, with a production capacity of about 4000 tons / year at the end of 2017; Zhengtuo Energy achieved mass production in 2017 with a production capacity of 4000 tons / year; Snow 2017 silicon-carbon anode materials to achieve small-scale supply.

According to the analysis of the above report of China International Capital Corporation, the silicon-based negative electrode is the key material to improve the energy density of power batteries, and the application in the field of electric vehicles is expected to improve steadily in the future.