How to match the positive electrode/electrolyte/binder of the silicon-carbon negative electrode of lithium battery?

Since the second half of 2017, a small amount of lithium batteries using silicon-carbon negative electrodes have been pushed to the high-end digital market and power battery companies are also in the process of research and development. The fastest is at the pilot level. In 2018, the amount of silicon-carbon composite materials will reach 2000-3000 tons, which is about double the year-on-year.

In order to achieve the goal of achieving a power density of 300Wh/kg for power batteries in 2020, it is impossible to achieve the use of conventional graphite. The use of silicon-carbon materials is an inevitable way out. It is precisely because of the urgent need to rapidly increase the energy density of power batteries that the era of silicon-carbon anodes is coming.

Recently, high-tech lithium-ion batteries have learned from mass-produced silicon-carbon battery companies and related supporting materials companies. Starting from the second half of 2017, lithium batteries with silicon-carbon anodes have been pushed to the high-end digital market, and power battery companies are also working hard to develop them. The fastest is at the pilot level. In 2018, the amount of silicon-carbon composite materials will reach 2000-3000 tons, which is about double the year-on-year.

"The company's silicon-carbon batteries are mainly used for high-end digital." A battery company executive revealed that although the cost of silicon-carbon anodes is high, the price for terminal products is also high. Silicon carbon batteries are not used for power for the time being, not because the development and production are particularly difficult, but the power battery needs a long service life and the verification time is not enough.

It is worth mentioning that there is a view in the industry that battery companies will first use silicon-carbon anodes for digital lithium batteries, and then they will be able to promote them to the field of power batteries. At present, cylindrical, square, and soft-package batteries are all tested with silicon-carbon anodes. Relatively speaking, the 18650 structure is more suitable for silicon-carbon anodes, which is relatively more.

In general, silicon-carbon power batteries are an inevitable trend in the development of the industry, and the production time is getting closer and closer, about one year or so, and slow for two years or so. At present, the mainstream anode material enterprises are stepping up their expansion of silicon carbon material production capacity, and the related materials (positive materials NCM811/NCA, electrolyte adhesive) research and development and production are also becoming mature.

Anode material companies are expanding the production capacity of silicon-carbon materials, and the development and production of related supporting materials are also maturing.

Power battery companies seize the silicon carbon air outlet negative enterprise response to expansion

In fact, the silicon carbon anode has already been applied to the field of power batteries. When the Tesla Model3 was released in April 2016, it was pointed out that the Model 3 uses a Panasonic battery, and the anode material is 10% silicon-based material added to the artificial graphite. Above 550mAh/g, the energy density can reach 300Wh/kg.

In addition to Panasonic's initial realization of the industrialization of silicon-carbon power batteries, domestic power battery companies BYD, Ningde era, Tianjin Lishen, Wanxiang A123, Guoxuan Hi-Tech, Weihong Power, etc. have launched research and development of silicon-carbon anode system produce.

According to the news of October 2016, the “New Generation Lithium Ion Power Battery Industrialization Technology Development” project jointly initiated by the Ningde era and the Institute of Physics of the Chinese Academy of Sciences was launched by the Provincial Science and Technology Department, and the research and development of high-nickel ternary materials was used as the positive electrode. The lithium-ion battery with the silicon-carbon composite as the negative electrode can greatly increase the specific energy of the lithium-ion battery from the current 150-180Wh/kg to more than 300Wh/kg, effectively improving the international competitiveness of the power battery industry in China.

It is understood that the above projects will be industrialized and applied in 2020, the high-energy power battery developed at that time will double the mileage of electric vehicles to 450-500 kilometers.

In the first half of 2017, the news showed that Tianjin Lishen took the lead in the national project “High Specific Energy Density Lithium Ion Power Battery Development and Industrialization Technology Research” to develop a power battery cell with an energy density of 260Wh/kg, charging and discharging at 350 times. After the cycle, the capacity retention rate reached 83.28%; at the same time, power battery samples with energy density of 280Wh/kg and 300Wh/kg were developed. Among them, the silicon-carbon composite anode material is applied.

Also in the first half of 2017, Guoxuan Hi-Tech took the lead in the special project "Routine-energy-powered lithium-ion battery research and development and integration application" progress shows that in this project, the use of high-nickel cathode material matching silicon-based anode material to achieve monomer The energy density of the battery is up to 281Wh/kg, and the capacity of the battery is kept at room temperature for 350 times at a capacity of 1C. The lithium-ion positive electrode material is matched with the silicon-based anode material to achieve an energy density of 302Wh/kg, 0.5C times and a room temperature cycle. The capacity of 195 times was maintained at 80%.

Whether it is current R&D and pilot production, or upcoming batch applications, downstream power battery companies have a clear need for silicon-carbon anode materials. Under this trend, mainstream anode materials companies responded positively, and while expanding the research and development strength of silicon-carbon anode materials, they have expanded the production capacity of silicon-carbon anode materials.

High-tech lithium battery has learned that Zhengtuo Energy has effectively improved the cycle performance of silicon-carbon materials through the use of nano-structured, carbon-coated and secondary granulation technologies, and solved the uneven coating and led to silicon materials and electrolysis, the deterioration of electrical properties and the expansion of the pole pieces caused by the reaction of the HF component in the liquid with silicon. The silicon carbon negative electrode has the advantages of high gram capacity (400 mAh/g-650 mAh/g) and good cycle performance. The first discharge capacity of the product is ≥420 mAh/g; the coulombic efficiency is ≥91%, and the capacity retention rate after 1000 cycles of 0.5C is ≥80. %.

According to the person in charge of Zhengtuo Energy, the company's annual production of 3,000 tons of silicon-carbon anode material project has been mass-produced in August 2017. In the previous period, it mainly promoted 420mAh/g and 450mAh/g models, and is currently in the sample test and small bulk supply phase. At the same time, the company is still further researching ultra-high-capacity silicon-carbon anodes of 500mAh/g and 650mAh/g to make technical reserves for the subsequent capacity improvement.

In terms of Shanshan shares, in April 2017, it said that the company's silicon-carbon negative electrode already has a monthly tonnage shipment scale, and it is expected to complete a production scale of 4,000 tons/year in 2017. In July, the company said in an investigation of investment institutions that the company's silicon-carbon negative electrode has begun to gradually increase its volume, which is priced according to energy density and measured at Wh cost.

Yantailai announced in April 2017 that it plans to invest 5 billion yuan to build diaphragm and anode materials in Xiangyang, Jiangsu Province. In this project, it will cooperate with the Institute of Physics of the Chinese Academy of Sciences to produce new silicon-carbon composite anode materials. According to the information of China Merchants Securities, Guoxuan Hi-Tech has invested in a 5,000-ton/year silicon-carbon anode material project, which is expected to be put into production in 2018.

The positive electrode / electrolyte and adhesive companies cooperate with R & D innovation products mass production

According to industry analysis, it is not difficult to make a silicon-carbon composite anode material, but it is very difficult to mass-produce composite materials with excellent electrochemical performance. The problem of restricting the large-scale application of silicon-carbon anodes is mainly concentrated in three aspects: first, the electrode expansion ratio of silicon-carbon composites is high; second, the cycle and coulombic efficiency of silicon-carbon anode materials still need to be further improved; .

If we do not consider the cost issue for the time being, we only need to solve the problem of poor expansion and cycle of silicon-carbon anodes from the technical point of view. In addition to the joint efforts of the anode materials companies and battery companies, we need to include cathode materials, electrolytes and binders, the “package” of recipes and process solutions within.

In terms of cathode materials, silicon-carbon anodes are mainly matched with cathode materials NCM811 and NCA, while the domestic cathode material industry is transitioning from NCM523 to NCM622. NCM811 has many technical problems to overcome due to the high technical barriers.

However, under the urgent situation of the industry, the positive electrode materials companies including Shanshan Energy, Dangsheng Technology and Ningbo Jinhe have accelerated the R&D process. Among them, Ningbo Jinhe and Shanshan Energy took the lead in mass production (for details, please see the high-tech lithium battery previously reported "helping power battery" to reduce the cost of "high-nickel three yuan 811 latest development").

In terms of electrolyte, most of the current silicon-carbon electrolytes use high-content FEC to stabilize the SEI of the silicon-carbon anode to improve the cycle performance of the silicon-carbon anode, but high-content FEC is easily replaced by high-nickel or high-voltage NMC anodes, catalytic decomposition, thereby degrading the high temperature storage performance and high temperature cycle performance of the battery.

In this regard, Xinzhoubang independently developed a new positive film forming additive LDY196, which can significantly inhibit the oxidative decomposition of the electrolyte on the high nickel positive electrode and the high voltage NMC positive electrode, thereby effectively improving the high content of FEC electrolyte at high nickel or high voltage, insufficient high temperature and insufficient circulation under NMC batteries.

A series of electrolyte products have been developed through the new positive film forming additive LDY196, negative film forming additive VC, FEC, lithium salt type low-impedance additive, etc., which are used in the high-nickel positive/silicon-carbon negative power battery system. It can meet the requirements of 1000 cycles and can obtain excellent high temperature performance and low temperature performance.

This series of products is widely used in high energy density NCM811, NCA, high voltage ternary positive with silicon carbon negative power battery, has been widely used in high-end customers at home and abroad.

According to public information, the R&D personnel of Zhuhai Saiwei Electronic Materials Co., Ltd. found that the silicon anode has better electrochemical performance in the mixed electrolyte than in the single electrolyte through actual cooperation with the customer. Lithium hexafluorophosphate (LiPF6) was mixed with a certain amount of lithium bis(oxalate) borate (LiBOB), and vinylene carbonate (VC) was added. The addition of LiBOB and VC produced a good synergistic effect on the formation of a thick SEI layer. In addition, the addition of a novel lithium salt such as lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) to the electrolyte can also improve the cycle performance of the silicon carbon battery.

In terms of the adhesive, from the working principle, when silicon is used as the negative electrode, lithium ions are extracted from the positive electrode material during charging, and when embedded in the internal crystal lattice of the silicon crystal, expansion (up to 300%) is caused to form a silicon-lithium alloy; Lithium ions are separated from the crystal lattice and form a large gap. It is important to develop a suitable adhesive to maintain the integrity of the electrode structure.

High-tech lithium batteries have learned that the adhesives for silicon-carbon materials are stronger than those of general products, including the ability to bond with silicon carbon and the cohesion of the product itself. When the silicon expands, the adhesive can pull it; when pulled, the adhesive cannot be deformed and can be restored to the original state to ensure the performance and life of the battery. In addition, the binder needs to be compatible with the electrolyte so that the electrolyte does not affect the cohesive force of the binder.

It is worth mentioning that, because each company's “silicon” is different, the proportion of addition is different, and the requirements for adhesives will be different. Therefore, it is necessary for the adhesive company to meet the above requirements and be targeted. Make adjustments.

Li Rengui, general manager of Chengdu Zhongkelaifang Energy Technology Co., Ltd. revealed that the company has long been applying the adhesive for silicon-carbon negative electrode as a project, combining the constructive opinions put forward by customers and the research and development of its own adhesive for many years. Experience, has developed the corresponding products, and has been mass-produced and shipped.

The page contains the contents of the machine translation.