Low temperatures exploration of power batteries in winter

Introduction: low temperature is an obstacle to the promotion of electric vehicles in the north and cold regions of China, and it is also a problem for power battery enterprises. It has been one of the key efforts in the industry to overcome the problem of low temperature resistance of power batteries.

In winter, people who call themselves "frozen dogs" wrap up their coats, trying to keep a trace of the wintry heat. And the most embarrassing thing is that when you want to drive your car like the ancients, the electric car "strike"! In the winter, power batteries crave warmth as much as people want to heat a furnace in the snow.

Low temperature is an obstacle to the promotion of electric vehicles in the north and cold regions of China, and it is a sore point of power battery enterprises. It has been one of the key efforts in the industry to overcome the problem of low temperature resistance of power batteries.

Microscopically, the influence of low temperature on power battery

Why do many power batteries fail in the winter? At low temperatures, what's going on inside?

Take the lithium iron phosphate battery, the most widely used battery in electric buses, as an example. This kind of battery has high safety and long service life, but its low-temperature performance is slightly worse than that of batteries in other technical systems. Low temperature has an effect on the anode and cathode, electrolyte and adhesive of lithium iron phosphate. For example, the positive electrode of lithium iron phosphate itself has poor electrical conductivity, and is prone to generate polarization at low temperature, thus reducing the battery capacity. Due to the influence of low temperature, the speed of lithium inlaid graphite decreases and lithium metal is easy to precipitate out on the surface of the negative electrode. If lithium metal is put into use due to insufficient shelf-life after charging, lithium metal cannot be embedded into the graphite again. Some lithium metal exists on the surface of the negative electrode, which is likely to form lithium dendrite and affect the battery safety. At low temperature, the viscosity of electrolyte will increase, and the migration impedance of lithium ion will also increase. In addition, in the production process of lithium iron phosphate, the adhesive is also a very key factor, low temperature on the adhesive performance will also have a greater impact.

Another problem caused by low temperature is the extension of charging time. Low temperature charging, the battery is easy to lithium, so before charging, generally to slowly heat the battery, such as the battery temperature increased to the normal temperature before charging.

Multi - dimensional solution to low temperature problem

To solve the problem of low temperature resistance of batteries, we usually start from the three aspects of battery materials, cell design and PACK manufacturing to improve the low-temperature charging and discharging performance and cycle life of lithium ion batteries. Miao lixiao, general manager of sun ton new energy research and development department, introduced the low-temperature resistance solution of power battery to battery China.

At present, the common anode materials of automobile power batteries are ternary and lithium iron phosphate, which can shorten the migration path of lithium ions by reducing particle size and nano-technology. lithium iron phosphate can be doped with La (the element symbol of lanthanum) and Mg to increase the c-axis, change the layer spacing and increase the lithium ion transmission channel. Sliding surface coated in three Yuan LBO - S fast ion conductor (also known as super ionic conductor, sometimes also called solid electrolyte, it is different from general basic characteristics of ionic conductors, which in a certain temperature range can have compared to liquid electrolyte of ionic conductivity), in order to reduce the formation of SEI, lithium ion transmission can be directly through the fast ion conductor in and out of the material ontology.

For anode materials, existing graphite anode materials can increase the spacing between graphite layers by coating, surface oxidation, doping or coating other elements, so as to accelerate the dissolvation speed of lithium ions on the surface of the anode and improve the speed of lithium ions embedded in the graphite anode. Miao said that the development of lithium alloy, tin - based anode and other new anode materials, can greatly improve the low temperature performance of lithium ion batteries.

Electrolyte is mainly divided into lithium salts, solvents and additives in three parts. As for lithium, borate can be added to form a stable SEI film on the surface of the material and to facilitate the diffusion of lithium ions. Regarding the solvents, a reasonable proportion can be configured to improve the low temperature performance of the electrolyte solvents; As for additives, by adding different additives, the low temperature performance of the battery has different improvement. It is understood that Thornton new energy has a special team, focusing on the development of electrolyte formula, to solve the problem of low temperature resistance of power batteries. At present, Thornton ternary lithium battery research and development of new energy, low temperature resistance performance has improved greatly, batteries can be 20 ℃ below zero to devolve electricity environment, can meet the demand of the electric car run in a cold environment.

In addition, great energy power battery can be - 20 ~ 60 ℃ environment, and do not need heating and cooling systems. Shandong power is one specialized is engaged in military low temperature lithium iron phosphate battery research and development, production of high-tech enterprises, with the Chinese academy of sciences (htma cooperative research and development, the production of lithium iron phosphate batteries achieve breakthrough performance under low temperature and at low temperatures to 40 ℃ to emit more than 90% of the rated capacity.

The promotion of new energy vehicles is not only a challenge but also an opportunity

As one kind of lithium battery, lithium titanate battery has excellent low temperature resistance. The lithium titanate anode material of spinel structure has a lithium potential of about 1.5v, and no lithium dendrites are formed. The volume strain is less than 1% in the process of charging and discharging. Nano-sized lithium titanate battery can be charged and discharged at large current, which can realize quick charging at low temperature and guarantee the durability and safety of the battery at the same time.

On November 28, 2017, in this cold and freezing season, the pure electric bus produced by Yinlong new energy was officially put into operation in the northern city of Tianjin, which once again demonstrated the excellent low-temperature resistance performance of Yinlong new energy lithium titanate battery. Main new energy of lithium titanate battery of silver, its products have in - 50 ~ 60 ℃ temperature range of the normal charge and discharge capacity, the company production of bus has been in Harbin, Yinchuan, Tianjin, Shijiazhuang, Baoding, Handan and so on more than 40 cities across the country implements the commercialized operation, low temperature resistant effect is good. Lithium titanate battery, with its excellent low temperature resistance, has become a pioneer in promoting new energy vehicles in cold areas of China. Yinlong new energy is the spark for lithium titanate battery to go to a wider market.

On July 31, 2017, at the launch ceremony of electric buses in Yanqing district, Beijing, 50 pure electric buses equipped with micro-macro power quick rechargeable battery system were delivered to Beijing bus group and put into operation. The 50 pure electric buses delivered this time are equipped with fast rechargeable batteries produced by micro macro power, featuring high energy density and longer range. At this point, micro macro power has been in the Beijing market supporting more than a thousand of various bus models. On sept 19, 2017, 70 12-meter gas-electric hybrid buses equipped with micro-macro MpCO lithium batteries were officially launched in Baotou, Inner Mongolia. The region's lowest temperature below 30 ℃, the highest temperature can reach 39 ℃, Baotou choose micro macro quick charge battery system, it is considering micro macro quick charge battery good environmental adaptability. Micro macro power to cold areas of the bus market in full swing, it is also the industry to explore the power battery low temperature technology a typical representative.

Solving the problem of low temperature resistance still needs technical drive

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

From the micro level to solve the problem of low temperature resistance of power batteries, such as from the battery materials to overcome the problem of low temperature resistance, still need to rely on technology drive, seize the battery "afraid" of low temperature, the remedy to the case, so as to solve more thoroughly.

At present, many ternary lithium batteries also have the characteristics of low temperature resistance, lithium titanate battery is the leader in low temperature resistance performance, low temperature bottleneck existing in the promotion of electric vehicles will be gradually solved.

The page contains the contents of the machine translation.