What is the best anode for a battery? Silicon-carbon anode seems become a trend
Tesla’s demand on silicon-carbon anode
According to related sources, Tesla currently has the need to switch the silicon oxide anode to silicon-carbon anode. The main reason is that the batteries using silicon oxide anode materials, in addition to a better C-rate performance, do not have satisfactory battery life.
In addition, according to BTR research and development personnel revealed that there is now a anode plant to do pure silicon doped carbon trend. This operation is quite magical.
Generally, car companies in China do not use silicon oxide material, mainly because most working conditions of electric vehicles only need 0.5C, and silicon oxide can do 5C, which is redundant. Therefore, it seems to be a trend to choose silicon-carbon anode with both better C-rate performance and energy density.
The early Tesla was also the adopter of silicon-carbon anode (in 2015, Tesla adopted silicon-carbon anode, which improved the electric vehicle’s endurance by 6%), because the first effect of the silicon-carbon anode and the ternary material can match, and the cylinder is the best silicon-carbon anode packaging, after all, the steel structure can hoop expansion.
Tesla’s battery evolution has gone through three phases:
Both Stage 1 and Stage 2 use 18650 batteries, but the difference is that Stage 1 uses graphite, while Stage 2 adds silicon material, which can be regarded as the “silicon-carbon anode” containing a very small amount of silicon. At Stage3, the ratio of silicon was increased again.
At a recent tech conference, Tesla also confirmed that next year it will deliver the first cars equipped with the new 4680 battery, which is likely to use Hitachi’s silicon-carbon anode material.
Tesla plans to supply early 4680 batteries for its first cars at a pilot plant in Fremont, and will soon need battery partners and material suppliers, as well as new manufacturing facilities in Berlin and Texas to support larger volumes of the 4680. It should be said that the silicon-carbon anode will have a wave of development led by Tesla’s demand.
The “rejuvenation” of silicon-carbon anode
With the increasing demand for energy density, silicon-carbon anode material has become a kind of high energy density anode material. The theoretical capacity of silicon is 4200mAh/g.
The silicon-carbon anode can be traced back to the 1970s, and in 2002, after the research of Yoshio et al., it gradually became a technological highlight, and now there are many manufacturers of silicon-carbon anode material products on the market.
For BTR, the four materials of 450mAh/g, 500mAh/g, 550mAh/g and 600mAh/g have been quite mature and recognized by customers. Of course, they also have a 1000mAh/g experimental version.
In addition, Amprius, ZICen, Shanshan, Kaijin, Xiangfenghua, Shangtai, Star City, Xinmao, Zhengtuo, National technology, Del Future, Silicon treasure are doing silicon-carbon anode materials. However, there are not many real supporting customers, with an annual production capacity of several thousand tons and limited capacity.
How much silicon doped, that’s an industry secret. However, it is generally believed that the silicon content of 1000mAh/g silicon-carbon anode material will reach 42x+3.72(100-x)=1000 according to the theory of conversion.
The silicon content will be as high as 16.4. The amount of silicon in a real product would be higher than that, but with current technology, 10% is the limit, and 20% would affect the performance of the battery.
Silicon material has the disadvantage of falling off from the anode collector due to its natural expansion, which will lead to the large attenuation of the battery capacity of silicon anode material. So there is an upper limit to the amount of silicon in the silicon-carbon anode material.
Stanford University first invented a kind of encapsulating Silicon Microparticles in a graphene shell, and the gram capacity of the silicon-carbon anode material using this method can reach 3,300 mAh/g. Much higher than the current graphite negative gram capacity. It’s like an egg, you take silicon and you wrap it around carbon, and the yolk is silicon, and the white is carbon, and the shell is steel.
In theory, the design of the structure also helps solve the problem of expansion, such as BYD’s blade batteries. Therefore, the continuous improvement of battery technology has solved the problem of material defects to a certain extent.
The main driving forces of silicon-based anode materials
The main driving forces of silicon-based anode materials are as follows:
1) After nearly 10 years of research and development, China’s silicon-based anode technology continues to mature, and product stability is gradually verified by downstream lithium-ion battery manufacturers among them, GOTION mainly adopt silicon oxide anode, CATL and Lishen mainly adopt silicon-carbon anode.
2) New energy vehicles, mobile phones, tablets and other terminal products have an increasingly strong demand for high energy density, long range and high capacity of batteries, and accelerate the introduction of high gram capacity anode materials.
High capacity cathode materials (such as high nickel ternary) gradually batch, to a certain extent drive the application of high capacity silicon based materials.
The characteristics of China’s silicon-based anode market
At present, China’s silicon-based anode market presents the following characteristics:
1) High market concentration, no more than 5 mass production enterprises, more than 20 r&d and pilot enterprises. There are three main types of silicon anode enterprises, one is the existing graphite anode enterprises, such as Beitrui, Ningbo Shanshan, Zichen, etc.;
Second, the founding team of scientific research institutions, such as Tianmu, Leader, etc. The third is battery enterprises or silicon nano manufacturing enterprises that cross into the field, such as GOTION High-tech.
2) Currently, there are fewer silicon anode models in stable mass production, mainly 420mAh/g, 450mAh/g and 680mAh/g, and silicon anode with higher capacity cannot be mass-produced.
3) The application of silicon based anode is still relatively limited, currently mainly used in cylindrical digital, a small amount of pouch digital and cylindrical power.
4) The price is still high, and much higher than graphite anode.
Future development of silicon-carbon anode”
Combined with market anxiety due to graphitization of anode materials, we can see some clues:
Silicon-carbon anode has application scenarios
It is mainly used in high-end vehicles and is the main driving force for the development of silicon-carbon anode. 2022 is a key year.
Silicon-carbon anode can effectively improve battery energy density, increase vehicle range, and the right amount of silicon can also give consideration to the C-rate performance.
But the price is higher than graphite electrode (graphite price is about 30,000 to 90,000 yuan/ton, and silicon-carbon anode price is 100,000 to 400,000 yuan/ton), so it is mainly used in high-end models. In recent years, with the intensification of competition in the high-end market, vehicles equipped with silicon carbon anode battery also began to appear in a cluster.
Tesla has always used cylindrical batteries, which have a better restraining effect on the volume expansion of the silicon-carbon anode. Starting from Model S and Model X a few years ago, Tesla has doped silicon materials into the graphite anode, but the silicon composition was very small at that time.
In the stage of Model 3, the ratio of silicon in the 21700 battery used by Tesla has been improved again, and its energy density has increased by about 20% compared with the previous generation of 18650 battery, reaching 300Wh/kg. The current range of Model 3 is about 500~ 600km. In the future, with the launch of a large number of 1000km models in China, Tesla will also have corresponding models.
GAC Aian announced its anode cell technology since the research of silicon sponge (ternary in nickel + silicon carbon anode high voltage), the technology including “nano silicon technology” “self-healing adhesive technology” “gradient composite coating technology”, etc., make the inside of the battery anode piece like a sponge soft elastic silicon, silicon in the expansion and contraction in the process of charging and discharging are limited and buffer, not broken.
It also acts like a sponge to absorb water, allowing the silicon anode to take advantage of its large capacity and store more energy. The technology can reduce the volume and weight of lithium-ion battery cells by 20 percent and 14 percent.
The technology can also prolong the battery life and improve the reliability of lithium ion battery. AION LX of GAC Aian equipped with sponge silicon anode battery technology can achieve a range of more than 1000km.
NIO announced in January 2021 that the 150kWh battery pack is expected to be delivered in 2022. The cathode uses nano-coated ultra-high nickel material, and the anode uses pre-lithium silicon carbon. Meanwhile, the semi-solid electrolyte is used, and the energy density of the single cell can reach 350Wh/kg. Nio ET7 will carry this battery.
In January 2021, IM Motor also released its first model — IM L7, which is a highly equipped version of 118kWh battery. It adopts the technology of “Silicon-doped and Prelithiation” cooperated with CATL, which can achieve 300Wh/kg energy density of monomone and increase the range of NEDC to 1000km. And it has 200 thousand kilometers of zero attenuation and “never spontaneous combustion” characteristics.
Silicon carbon technology accelerates breakthroughs
From the terminal response, under the pressure of increasing energy density of power battery, the introduction of improved new materials is imminent. After the previous “reverse attack” of lithium iron phosphate, high nickel ternary inflection point has come, the industrialization of silicon-carbon anode also began to put on the agenda.
However, the China’s production technology of silicon carbon materials is not mature, and the technology of supporting materials needs to be improved. At present, Chinese enterprises can really realize the monthly shipments of silicon-carbon anode in the hundred tons are not much.
From the technology of battery enterprises, the best pack of silicon-carbon anode is cylindrical, but the pouch is also ok. EVE can claim to solve the problem of pouch, but how to press and hoop this material is a technical problem. Therefore, the graphite anode still has a certain development space.
In fact, silicon-carbon anode material as a new generation of high capacity anode material, its battery material system has also been upgraded accordingly. At present, the high nickel ternary cathode material (NCA/NCM), high pressure ternary electrolyte and silicon based adhesive are still in the stage of rapid development.
Under the policy and market demand to promote, will further prompt the rapid development of new energy power battery, silicon carbon materials as high ratio, high energy type of new material is the material of choice for industrialization, the future development of high energy density of power battery will further promote the technical progress of high energy density batteries in China.
It is expected that under the background of the rapid development of power battery, the development of silicon-carbon anode from 0 to 1, and the sales volume of silicon based anode material for lithium battery will increase significantly in the next two years.