What is the low temperature performance of the ternary lithium-ion battery that breaks through the cold weather? !
It’s cold, and the original full-bodied lithium battery has a discount on its capacity. The lithium battery seems to have entered a hibernation state, which brings a lot of trouble to new energy vehicles and digital product users. The topic of interest in this article today is the impact of low temperature on lithium batteries and the progress of research and development in the industry.
Is the ternary lithium-ion battery most afraid of low temperature?
In an American Automobile Association test, an electric car will have a cruising range of 105 miles (about 169 kilometers) at 75 degrees Fahrenheit (about 24 degrees Celsius), and will fall when it is 20 degrees Fahrenheit (about 7 degrees Celsius). To 43 miles (about 69 kilometers) - a drop of up to 60%. The battery has some similarities with people. After the climate turns cold, it is not so active. Lead batteries, lithium batteries and fuel cells are all affected by low temperature, but only to varying degrees.
Taking the lithium iron phosphate battery, which is the most used in 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 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 iron phosphate lithium ion battery is superior in low temperature resistance. The lithium titanate negative electrode material with a 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 large current, achieving 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 graphite as the negative electrode can be discharged at -40 ° C, it is difficult to achieve conventional current charging at -20 ° C and lower, which is an area that the industry is actively exploring.
The industry's exploration of low temperature resistant lithium batteries
Industry companies and research institutes have explored and tackled the low-temperature performance of batteries, focusing on the improvement of existing positive and negative 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 terms of nanometerization, particle size, electrical resistance, and axial length of the AB plane. Waterma prepares lithium iron phosphate material through three processes, and nanometerizes and coats it by different processes. The results show that the increase of AB plane length makes the lithium ion migration channel larger, which is beneficial to increase the battery's magnification. Performance; from the materials produced by the three processes, the granular graphite with large interlayer spacing has relatively small bulk impedance and ion mobility resistance; in terms of electrolyte, Watmar uses low-temperature additives based on fixed solvent systems and lithium salts. The discharge capacity increased from 85% to 90%. It is understood that as early as the end of 2016, Watmar has achieved an environment of -20, -30, -40 ° C, 0.5C charge constant current ratio of 62.9%, discharge at -20 ° C 94%. At present, Waterma's low-temperature battery has been widely promoted in Inner Mongolia, the three northeastern provinces and other regions.
On August 31, a research team such as Beijing Institute of Technology announced the successful development of a full-climate battery product. The technician uses the principle of electric heating of the wire to install a nickel foil on the battery core, and the nickel foil is energized to generate heat, so that the internal temperature of the battery rises. After reaching a certain temperature, the foil will be automatically disconnected to ensure battery safety. It is understood that in the experimental environment of -30 ° C, the battery using this technology can quickly heat up to 0 ° C in 30 seconds, the discharge power is increased by more than 6 times, and the charging power is increased by more than 10 times. The team's relevant personnel said that the technology does not change the original structure of the battery, and the transformation cost is extremely low, suitable for various types of batteries such as lead-acid batteries and lithium batteries. According to Battery China.com, the full-climate electric vehicle adopting this technology will be released at the end of December 2017. It is expected that the development of 11 models of four models will be completed in 2020 and demonstration operation will begin.
According to media reports, at the “Creator China” Xinjiang Innovation and Entrepreneurship Competition in September 20th, the “Full Climate Lithium Battery” led by Dr. Wang Lei of the Xinjiang Institute of Physics and Chemistry of the Chinese Academy of Sciences won the first prize of the maker group. The lithium battery can work stably in the environment of -40 ° C ~ 60 ° C. At present, the team has completed product testing under various high and low temperature conditions, and will enter the production stage of commercial products.
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 lowest temperature in the region is below -30 °C, the highest temperature can reach 39 °C, and Baotou uses micro-macro fast charging battery system, which is considering the excellent environmental adaptability of micro-macro fast charging battery.
In addition, Penghui Energy's power battery can be used in -20~60 °C environment without heating and cooling system. The low temperature resistance of Thornton New Energy has been greatly improved, and the battery can be discharged normally in the environment of -20 °C, which can meet the needs of many vehicle manufacturers.
Why does charging require more temperature than discharge?
Careful readers may find that many companies' battery products can achieve normal discharge at low temperatures, but at the same temperature, it is more difficult to achieve normal charging, or even unable to charge, why?
According to industry insiders, when Li+ is embedded in graphite material, it must first be desolvated. This process consumes a certain amount of energy, which hinders the diffusion of Li+ into the graphite. On the contrary, Li+ will have a solvation when it comes out of the graphite material and enters the solution. Process, while solvation does not consume energy, Li+ can quickly extract graphite. Therefore, the charge acceptance of the graphite material is significantly inferior to the discharge acceptance capability.
Battery charging has a certain risk in low temperature environments. Because the kinetics of the graphite anode deteriorates with the decrease of temperature, the electrochemical polarization of the anode is obviously intensified during the charging process, and the precipitated metal lithium easily forms lithium dendrites, which break through the separator and cause short circuit between the positive and negative electrodes. .
Therefore, people in the industry suggest that lithium-ion batteries should 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 manganese oxide lithium ion battery, and fully charge the lithium ion battery after charging, thereby ensuring that the lithium metal precipitated by the negative electrode can Reacts with graphite and reinsertes into the graphite negative electrode.
Of course, lithium titanate battery has the material advantage, it can still achieve fast charge at low temperature, this wayward, other materials battery is difficult to learn.