Possible battery materials for electrochemical energy storage, redox-active nitroxyl-containing polymers are characterised by a high energy density and fast charging and discharging speed due to fast redox kinetics. However, one challenge towards the implementation of such a technology is the insufficient electrical conductivity, which impedes the charge collection even with highly conductive additives, such as carbon.
Looking to overcome this problem, researchers from St Petersburg University synthesised a polymer based on the nickel-salen complex (NiSalen). The molecules of this metallopolymer act as a molecular wire to which energy-intensive nitroxyl pendants are attached. The molecular architecture of the material enables high capacitance performance to be achieved over a wide temperature range.
'We came up with the concept of this material in 2016. At that time, we began to develop a fundamental project "Electrode materials for lithium-ion batteries based on organometallic polymers". It was supported by a grant from the Russian Science Foundation. When studying the charge transport mechanism in this class of compounds, we discovered that there are two keys directions of development. Firstly, these compounds can be used as a protective layer to cover the main conductor cable of the battery, which would be otherwise made of traditional lithium-ion battery materials. And secondly, they can be used as an active component of electrochemical energy storage materials,' explains Oleg Levin, Professor in the Department of Electrochemistry at St Petersburg University and head of the research team.
The polymer took over three years to develop. In the first year, the scientists tested the concept of the new material— they combined individual components to simulate the electrically conducting backbone and redox-active nitroxyl-containing pendants. It was essential to make certain that all parts of the structure worked in conjunction and reinforced each other. The next stage was the chemical synthesis of the compound. It was the most challenging part of the project. This is because some of the components are extremely sensitive and even