Low temperature research in winter-exploration of low temperature resistance of power batteries

　　Introduction: Low temperature is an obstacle to the promotion of electric vehicles in China's great north and alpine regions. It is also a problem for power battery companies. Overcoming the low temperature resistance of power batteries has always been one of the key directions of the industry's efforts.

　　Introduction: Low temperature is an obstacle to the promotion of electric vehicles in China's great north and alpine regions. It is also a problem for power battery companies. Overcoming the low temperature resistance of power batteries has always been one of the key directions of the industry's efforts.

　　In winter, people who laugh at "frozen dogs" wrapped their coats tightly, trying their best to keep the temperature swayed by the wind. And the most embarrassing thing is that when you want to drive your car like the ancients, the electric car "strikes"! In winter, the desire of power batteries for warmth is no less than people's thoughts of warming around the stove in the ice and snow.

　　Low temperature is an obstacle to the promotion of electric vehicles in China's Great North, alpine regions and other places. It is also a heart disease of power battery companies. Overcoming the low temperature resistance of power batteries has always been one of the key directions of the industry's efforts.

　　Watch the impact of low temperature on power battery

　　Why do many power batteries fail in winter? In the low temperature environment, what is happening inside it?

　　Take the most used lithium iron phosphate battery in electric buses as an example. This battery has high safety and a long cell life, but its low temperature performance is slightly worse than that of other technical systems. Low temperature has an impact on the positive and negative electrodes, electrolyte and binder of lithium iron phosphate. For example, the lithium iron phosphate positive electrode itself has relatively poor electronic conductivity and is prone to polarization in low temperature environments, thereby reducing battery capacity; affected by low temperature, the speed of graphite lithium insertion is reduced, and metal lithium is likely to precipitate on the surface of the negative electrode. If it is left for insufficient time after charging When put into use, the metal lithium cannot be fully embedded in the graphite again. Part of the metal lithium continues to exist on the surface of the negative electrode, which is very likely to form lithium dendrites, which affects battery safety; in a low temperature environment, the electrolyte viscosity will increase, and the lithium ion migration resistance will also be affected. Increasing accordingly; in addition, in the production process of lithium iron phosphate, the adhesive is also a very critical factor, and low temperature will also have a greater impact on the performance of the adhesive.

　　Another problem caused by the low temperature, reflected to the user end is the prolonged charging time. When charging at low temperature, the battery is prone to release lithium, so before charging, the battery is generally heated slowly, and then the battery temperature rises to the normal temperature before charging.

　　Overcome the problem of low temperature resistance in multiple dimensions

　　To solve the low-temperature resistance of the battery, it usually starts from the three aspects of battery materials, battery cell design and PACK manufacturing to improve the low-temperature charge and discharge performance and cycle life of lithium-ion batteries. Miao Lixiao, general manager of the R&D department of Thornton New Energy, introduced the low temperature resistance solution of power batteries to Battery China.com.

　　At present, the common positive electrode materials for automobile power batteries are mainly ternary and lithium iron phosphate. The primary particles of the material can be nano-sized by nanotechnology by reducing the particle size, thereby shortening the migration path of lithium ions; lithium iron phosphate can pass Doped with La (La is the element symbol of lanthanum), Mg, increase the C axis, change the layer spacing, and increase the lithium ion transmission channel; the surface of the ternary NCM is coated with LBO-S fast ion conductor (also called super ion conductor, Sometimes called solid electrolyte, it is different from the most basic feature of general ionic conductor, that is, it has an ionic conductivity comparable to that of liquid electrolyte within a certain temperature range, in order to reduce the formation of SEI, so that the transmission of lithium ions can be directly Pass in and out of the material body through fast ion conductors.

　　For negative electrode materials, the existing graphite negative electrode materials can increase the graphite layer spacing through coating, surface oxidation, doping or coating with other elements, and accelerate the desolvation speed of lithium ions on the negative electrode surface, thereby improving the insertion of lithium ions into the graphite negative electrode. speed. Miao Lixiao said that the development of new anode materials such as lithium alloys and tin-based anodes can greatly improve the low-temperature performance of lithium-ion batteries.

　　The electrolyte is mainly divided into three parts: lithium salt, solvent and additives. Miao Lixiao introduced that with regard to lithium salt, borate can be added to help form a stable SEI film on the surface of the material and facilitate the diffusion of lithium ions. Regarding the solvent, a reasonable ratio can be configured to improve the electrolyte solvent. With regard to additives, the addition of different additives can also improve the low temperature performance of the battery in different ways. It is understood that Thornton New Energy has a dedicated team that focuses on the research and development of electrolyte formulations to solve the low temperature resistance problem of power batteries. At present, the ternary lithium battery developed by Thornton New Energy has greatly improved its low-temperature resistance. The battery cell can be discharged at minus 20°C, which can meet the operating needs of electric vehicles in cold environments.

　　In addition, the power battery of Penghui Energy can be used in the environment of -20~60℃, and does not require heating and cooling systems. Shandong Weineng is a high-tech enterprise specializing in the research and development and production of low-temperature lithium iron phosphate batteries for military use. The low-temperature performance of lithium iron phosphate batteries developed and produced in cooperation with the Institute of Chemistry has achieved a major breakthrough, and can release rated capacity at a low temperature of -40°C. 90% of the total.

　　The promotion of new energy vehicles at low temperature is a challenge and an opportunity

　　As a kind of lithium battery, the low temperature resistance of lithium titanate battery is relatively excellent. The lithium titanate anode material with spinel structure has a lithium insertion potential of about 1.5V, does not form lithium dendrites, and the volumetric strain is less than 1% during charge and discharge. The nanometerized lithium titanate battery can be charged and discharged with high current, which realizes low-temperature fast charging while ensuring the durability and safety of the battery.

　　The latest news from Battery China.com. On November 28, 2017, in this freezing season, the pure electric buses produced by Yinlong New Energy were officially put into operation in the northern city of Tianjin, which once again demonstrated Yinlong New Energy’s lithium titanate Excellent low temperature resistance of the battery. Yinlong New Energy, which focuses on lithium titanate batteries, has products with normal charge and discharge capabilities in the temperature range of -50 to 60°C. The company’s buses have been used in more than 40 countries across the country, such as Harbin, Tianjin, Shijiazhuang, Yinchuan, Baoding, and Handan. Commercial operations in these cities have achieved good low-temperature resistance. With its excellent low temperature resistance, lithium titanate battery has become a pioneer in the promotion of new energy vehicles in cold regions in China. Yinlong New Energy is a spark for lithium titanate batteries to expand into the wider market.

　　On July 31, 2017, at the launching ceremony of electric bus operation in Yanqing District, Beijing, 50 pure electric buses equipped with Weihong power fast charging battery system were delivered to Beijing Public Transport Group and put into operation. The 50 pure electric buses delivered this time are equipped with fast-charging batteries produced by Weihong Power, with high energy density and longer cruising range. So far, Weihong Power has supplied more than 1,000 various types of bus models in the Beijing market. On September 19, 2017, 70 12-meter gas-electric hybrid buses equipped with Weihong MpCO lithium batteries were officially launched in Baotou, Inner Mongolia. The lowest temperature in this area is below -30℃, and the highest temperature can reach 39℃. Baotou chooses the Weihong fast charge battery system, which takes into account the excellent environmental adaptability of the Weihong fast charge battery. Weihong Power's expansion of the bus market in cold regions is in full swing, and it is also a typical representative of the industry in exploring low-temperature resistant technology for power batteries.

　　Solving the problem of low temperature resistance still needs technology drive

　　There are many solutions to the low temperature problem of power batteries. For example, in the so-called "all-climate battery", a heating plate is added between the positive and negative plates, and the circuit is controlled by a switch to heat the battery. The efficiency of this internal heating is much higher than that of external heating, and the energy consumption is lower. All-weather batteries have greatly improved in terms of endurance, charging time and service life.

　　Solve the low temperature resistance problem of power batteries from the micro level. For example, to overcome the low temperature resistance problem from the battery materials, we still need to rely on technology to seize the root cause of the battery's fear of low temperature and prescribe the right medicine. This solution will be more thorough.

　　At present, many ternary lithium batteries also have low temperature resistance characteristics, and lithium titanate batteries are the best in low temperature resistance. The low temperature bottleneck existing in the promotion of electric vehicles will gradually be solved.