It's hard to imagine our daily life without lithium-ion batteries. They dominate the market for small batteries for portable electronic devices and are commonly used in electric cars. At the same time, lithium-ion batteries have some serious problems, including: potential fire hazards and performance degradation at low temperatures; And waste battery disposal has a considerable impact on the environment. Chemists have been exploring the use of REDOX active nitro-based polymers as electrochemical storage materials, according to Oleg Levine, a professor in the Department of electrochemistry at St. Petersburg University and leader of a Russian research team. These polymers are characterized by high energy density, and the polymer batteries charge and discharge quickly due to the kinetics of rapid REDOX. But when implemented into products, one of the challenges is insufficient electrical conductivity, which prevents charge collection, even with highly conductive additives such as carbon.
To find a way around this problem, researchers at St. Petersburg University synthesized a polymer based on a nickel-selenium complex (NiSalen). The molecule of this metallic polymer acts as a molecular wire to which the energy-intensive nitrosyl pituitary gland is attached. The material's molecular structure enables it to achieve high capacitance performance over a wide temperature range. 'We came up with the concept for this material in 2016. At that time, we began to develop a foundation project "Electrode Materials for Lithium-ion batteries based on organometallic polymers". The project was funded by the Russian Science Foundation. In studying the charge transport mechanism of this class of compounds, we found two key directions of development. First, such compounds could be used as a protective layer over the battery's main cable, which would otherwise be made from conventional lithium-ion battery materials. Second, they can be used as active ingredients in electrochemical energy storage materials, "explains Oleg Levin.
The polymer took more than three years to develop. In the first year, the scientists tested the concept of the new material: they combined components to mimic a conductive backbone and a nitrooxy-containing pituitary gland with REDOX activity. It is important to ensure that all parts of the structure complement and reinforce each other. The next stage is chemical synthesis of compounds. This was the most challenging part of the project. That's because some ingredients are so sensitive that even the slightest mistake by scientists can cause a sample to degrade. Of the several polymer samples obtained, only one is sufficiently stable and efficient. The main chain of the new compound is formed by a complex of nickel with the ligand Salen (the name Salen is derived from a combination of salicylaldehyde and ethylenediamine (EN)). A stable free radical capable of rapid oxidation and reduction (charge and discharge) is linked to the backbone by covalent bonds. 'Batteries made using our polymers can be recharged in a matter of seconds -- about 10 times faster than conventional lithium-ion batteries. This has been proved by a series of experiments. At the moment, however, its capacity is still behind - 30-40% less than lithium-ion batteries. "We are working on improving this indicator while maintaining the charge and discharge rate," Levin said. The cathode of the new cell has been made and used as the positive electrode of the chemical current source. Now we need the negative electrode, in fact, it doesn't have to be made from scratch, you can choose from existing electrodes. Together they will form a system that, in some areas, may soon replace lithium-ion batteries. 'The new battery is capable of working at low temperatures, making it a good choice where quick recharging is in high demand. It is safe to use and does not contain any material that could pose a combustion hazard, unlike cobalt-based batteries commonly used today. It also contains far fewer metals that could be harmful to the environment. "We have a small amount of nickel in our polymer, but much less than in lithium-ion batteries," Levin said.