Lithium batteries break through in cold temperatures or are no longer afraid of cell phones turning off in winter.

The cold weather, the original energy full of lithium batteries, the capacity of a discount, lithium batteries seem to be in hibernation state, this new energy vehicles and digital products users brought a lot of trouble. The topic of this article today is the impact of low temperature on lithium batteries and the development of research and development in the industry.

Is lithium battery most afraid is low temperature?

In tests conducted by the American Automobile Association, an electric car has a range of 105 miles (169 kilometers) at 75 degrees Fahrenheit. At 20 degrees Fahrenheit (about 7 °C), it will drop to 43 miles (about 69 kilometers)-a drop of up to 60 %. Batteries are somewhat similar to humans. When the climate turns cold, they are less active. Lead batteries, lithium cells, and fuel cells are all affected by low temperatures, but to varying degrees.

Take the lithium iron phosphate battery, which is the most used on electric buses, as an example. The battery has high safety and long life, but the low temperature performance is slightly worse than that of other technical systems. The low temperature affects both the positive and negative electrodes of lithium iron phosphate, the electrolyte and the binder. For example, the lithium iron phosphate positive electrode itself has relatively poor electronic conductivity, and is prone to polarization in a low temperature environment, thereby reducing battery capacity; due to low temperature, the graphite lithium insertion rate is lowered, and it is easy to precipitate metallic lithium on the surface of the negative electrode, and if the charging time is insufficient When it is put into use, the metal lithium cannot be completely embedded in the graphite, and some metal lithium continues to exist on the surface of the negative electrode, which is likely to form lithium dendrites, which affects the safety of the battery. At low temperatures, the viscosity of the electrolyte increases, and the lithium ion migration resistance also follows. In addition, in the production process of lithium iron phosphate, the adhesive is also a very critical factor, and the low temperature also has a great influence on the performance of the adhesive.

The same is a lithium battery, lithium titanate battery is superior in low temperature resistance. The lithium titanate negative electrode material of the spinel structure has a lithium insertion potential of about 1.5 V, and does not form lithium dendrites, and the volume strain is less than 1% during charge and discharge. The nano-sized lithium titanate battery can be charged and discharged at a high current, and achieves low-temperature fast charging while ensuring durability and safety of the battery. For example, Yinlong New Energy, which specializes in lithium titanate batteries, has a normal charge and discharge capacity of -50-60 °C.

Although lithium-ion batteries with negative graphite can be discharged at -40 °C, it is difficult to achieve conventional current charging at -20 °C and lower temperatures. This is also an area that the industry is actively exploring.

Exploration of lithium battery with low temperature resistance in industry

The research and research institutions in the industry have focused on improving the process of the existing positive and negative electrode materials and creating conditions for the battery to work at low temperatures by increasing the local ambient temperature of the battery.

The current battery material will affect the low temperature characteristics of the battery in the direction of nanotechnology, the diameter of the material, the electrical resistance, and the length of the AB plane axis. Wotema prepared lithium iron phosphate material by three processes, and used different processes to Nano and cover it. The results showed that the increase of AB axis length increased the lithium ion migration channel, which was conducive to improving the doubling performance of the battery; From the material produced by the three processes, the bulk impedance and ion transport impedance of granule graphite with large layer spacing are relatively small; In terms of electrolytes, Wotema used low-temperature additives on the basis of fixed solvent systems and lithium salts to increase the discharge capacity from 85 % to 90 %. It is understood that as early as the end of 2016, Wotema has achieved -20, -30, -40 °C environment, 0.5 C charging constant current ratio of 62.9 %, -20 °C to achieve 94 % discharge. At present, Wotema's cryogenic batteries have been widely promoted in Inner Mongolia, Northeast China and other regions.

On August 31, the Beijing Institute of Technology and other scientific research teams announced the successful development of all-climate battery products. Technicians use the principle of wire electrification to generate heat. Nickel foil is installed on the core, and nickel foil is energized to generate heat, raising the internal temperature of the battery. After reaching a certain temperature, the foil will be automatically disconnected to ensure the safety of the battery. It is understood that in the experimental environment of -30 °C, batteries using this technology can quickly heat up to 0 °C or more in 30 seconds, discharge power is increased by more than 6 times, and charging power is increased by more than 10 times. The team said that the technology does not change the original structure of the battery, and the conversion cost is extremely low, suitable for lead-acid batteries, lithium batteries and other types of batteries. The all-weather electric vehicle using the technology will be released by the end of December 2017, according to Battery China. It is expected to complete the development of a total of 11 product prototypes for four models by 2020 and start demonstration operations.

According to media reports, at the 2017 "Creative China" Xinjiang Innovation and Entrepreneurship Competition, which ended on September 20, the "All-Climate Lithium Battery" developed by Dr. Wang Lei of the Xinjiang Institute of Physics and Chemistry of the Chinese Academy of Sciences won the first prize of the Creative Group. This lithium battery can work stably in an environment of -40 °C ~ 60 °C. At present, the team has completed the product testing work under various high and low temperature conditions and is about to enter the commercial product production stage.

On September 19, 2017, 70 12-meter gas-electric hybrid buses equipped with micro-macro MpCO lithium batteries were officially launched in Baotou, Inner Mongolia. The minimum temperature in the area is below -30 °C, and the maximum temperature is up to 39 °C. The micro-macro fast recharging battery system is used in the head of the package, which takes into account the excellent environmental adaptability of the micro-macro fast recharging battery.

Shandong WeiNeng is a high-tech enterprise specializing in the research and development and production of military low-temperature iron phosphate lithium batteries. It has achieved major breakthroughs in the low-temperature performance of lithium iron phosphate batteries developed and produced in cooperation with the Institute of Chemistry of the Chinese Academy of Sciences. It can release rated capacity at a low temperature of -40 °C. More than 90 %.

In addition, Penghui Energy's power cell can be used in an environment of -20 ~ 60 °C without heating and cooling systems. Thornton New Energy has greatly improved the low-temperature performance of Sanyuan, and the core can be discharged normally at -20 °C, which can meet the needs of many vehicle companies.

Why does charging require more temperature than discharging?

Careful readers may find that many companies 'battery products can achieve normal discharge at low temperatures, but at the same temperature, it is difficult to achieve normal charging or even unable to charge. Why?

According to industry insiders, when Li + is embedded in graphite materials, it is first necessary to solvent. This process will consume a certain amount of energy and prevent Li + from diffusing into graphite; On the contrary, when Li + is removed from graphite material into solution, there will be a solvation process, and solvation does not consume energy, and Li + can quickly remove graphite. Therefore, the charging and receiving ability of graphite material is obviously inferior to that of discharge.

There is a certain risk of battery charging in a low temperature environment. Because with the decrease of temperature, the kinetic characteristics of the negative electrode of graphite have improved. During the charging process, the electrochemical polarization of the negative electrode has been significantly intensified. The efflux of metallic lithium easily forms lithium dendrites, penetrates the diaphragm and leads to a short circuit of the positive and negative poles.

Therefore, industry insiders recommend that lithium-ion batteries be avoided at low temperatures. When the battery must be charged at a low temperature, it is necessary to select a small current(ie, slow charge) to charge the lithium-ion battery as much as possible, and after charging, the lithium-ion battery is fully shelved to ensure that the negatively precipitated metallic lithium can react with graphite., Re-embedding into the graphite negative electrode.

Of course, lithium titanate batteries have the advantage of materials. It can still be quickly filled at low temperatures. This kind of willfulness makes other material batteries difficult to learn.

The page contains the contents of the machine translation.