With the new energy vehicles in the practical application of the mileage requirements continue to improve, the current material system has been unable to meet the real needs, research and development of new high-energy high-performance materials imminent. At present, silicon-based materials have become the battery manufacturers and lithium materials to improve the anode of the highest choice. The status quo is the development of most of the material business have started on the silicon carbon composite materials to do the research and production of negative materials, at present only Bettree and Shanghai Shanshan has entered the pilot production stage, most of the material business is still in research and development.
Silicon carbon anode industry for the time
China's first large negative material manufacturers have been on the silicon anode material layout, Shenzhen Beitui and Jiangxi purple Chen has been the first to introduce a variety of silicon carbon anode material products, Shanghai Shanshan is in the process of industrialization of silicon anode material, Star City graphite has a new type of silicon anode material as a future product development direction. In addition, the battery business, BYD, CATL, Guoxuan, power of God, universal, micro-macro and so on to the silicon anode system development and trial production.
From the current production of silicon carbon anode material performance point of view, compared to graphite anode material, the biggest advantage is the increase in capacity. The specific capacity of the silicon-carbon anode material is generally higher than the theoretical specific capacity of the graphite anode material. The specific capacity of the Beitre's S1000 type silicon-carbon anode material is as high as 1050 mAh / g, although the theoretical specific capacity of silicon is 4200 mAh / g There is still a big gap, but it is already artificial graphite anode material than the capacity of 3 times the performance has greatly improved. In addition, the first efficiency of silicon anode material can reach more than 90%, to meet the application requirements, the other indicators are no less than graphite anode material.
What is the advantage of silicon negative
The theoretical energy density of graphite is 372 mAh / g, and the theoretical energy density of silicon anode is 10 times higher than that of 4200mAh / g, and it is also environment-friendly and rich in reserves. By adding silicon to graphite material, Is one of the industry recognized the direction of Japan and South Korea and other large manufacturers are doing silicon carbon negative battery commercial, including BYD, force God, BAK, universal and other domestic battery manufacturers are also tracking, but so far Have not seen the mass production of the product. Tesla used Panasonic 18650 battery The traditional graphite anode material added 10% of the silicon, the energy density of at least 550mAh / g or more, Tesla used Panasonic 18650 battery in the traditional graphite anode material added 10% of the silicon, the energy density of at least 550mAh / g or more.
Application of Silicon Material in Lithium Battery
Silicon material in the application of lithium-ion battery, mainly related to two aspects, one in the anode material by adding nano-silicon, the formation of silicon carbon anode, the second is in the electrolyte by adding organosilicon compounds to improve the nature of the electrolyte.
(A) nano-silicon: an important member of lithium anode material
Nano-silicon, refers to the diameter of less than 5 nm crystalline silicon particles, is an important non-metallic amorphous material, often by the sol-gel method and other methods. Nano-silica powder with high purity, small particle size, uniform distribution, specific surface area, high surface activity, loose density and low characteristics, and non-toxic, tasteless. Nano-silicon applications in a wide range of: ① and graphite material composition of silicon-carbon composite materials, as the lithium-ion battery anode material, a substantial increase in the capacity of lithium-ion battery, which is our focus; ② used in the manufacture of high temperature coating and refractory Materials; ③ mixed with diamond under high pressure to form silicon carbide - diamond composite materials, used as cutting tools; ④ can react with organic matter, as organic silicon polymer materials; ⑤ metal silicon through the preparation of polysilicon; ⑥ semiconductor microelectronics packaging Material; ⑦ metal surface treatment.
(2) Silicone: Functional additive for lithium electrolyte
Silicone, is a kind of synthetic, the structure of silicon atoms and oxygen atoms as the main chain of a polymer. Since the silicon-oxygen structure of the main chain has a strong chemical bond, the molecules of the silicone polymer are much more stable to the heat and oxygen than the organic polymers. Silicone unique structure, so that both the performance of inorganic materials and organic materials, with a low surface tension, viscosity coefficient is small, high compressibility, high gas permeability and other basic properties, and has high and low temperature resistance, electrical insulation, Stability, weatherability, flame retardant, hydrophobic, corrosion-resistant, non-toxic and tasteless and physiological inertia, and is widely used in aerospace, electrical and electronic, construction, transportation, chemical, textile, food, light industry, medical and other industries , Which is mainly used in silicone sealing, bonding, lubrication, coating, surface activity, stripping, defoaming, foam suppression, waterproof, moisture, inert filling.
Although the mechanical properties of organic silicon at room temperature and other materials are not very different, but its high temperature and low temperature physical and mechanical properties of excellence, the temperature at -60 to +250 ℃ multiple alternating and its performance is not affected, So the silicone polymer can be used in this temperature area for a long time, some silicone polymers can even be as low as -100 ℃ normal use.
Disadvantages of Silicon Negative Materials
The shortcomings of silicon anode materials are also obvious, there are two major shortcomings: ① silicon embedded in the process of lithium ion embedded in the process, will cause Si volume expansion of 100% to 300%, in the material to produce a greater internal stress, the material structure The silicon material on the copper foil on the surface, while the silicon surface of the SEI film continue to repeat the formation of - rupture - to form a common reduction of the electrode conductivity and cycle stability; ② silicon for the semiconductor, conductive much worse than the graphite, resulting in The irreversibility of lithium ion disassembly is further large, further reducing its first Coulomb efficiency. Therefore, it is necessary to solve the problem that the volume expansion and the initial charge / discharge efficiency of the silicon during the charging and discharging process are low.