From Saint Petersburg University
April 6, 2021 -- Researchers at St Petersburg
University have developed a new type of battery that can charge ten times
faster than a lithium-ion battery. Moreover, it is safer in terms of potential
fire hazards and has a lower environmental impact. The results of the
research project, supported by the Russian Science Foundation, have been
published in the journal Batteries & Supercaps.
It is difficult to imagine our
daily life without lithium-ion batteries. They dominate the small format
battery market for portable electronic devices, and are also commonly used in electric
vehicles. At the same time, lithium-ion batteries have a number of serious
issues, including: a potential fire hazard and performance loss at cold
temperatures; as well as a considerable environmental impact of spent battery
disposal.
According to the leader of the team
of researchers, Professor in the Department of Electrochemistry at St Petersburg
University Oleg Levin, the chemists have been exploring redox-active
nitroxyl-containing polymers as materials for electrochemical energy storage.
These polymers are characterised by a high energy density and fast charging and
discharging speed due to fast redox kinetics. One challenge towards the
implementation of such a technology is the insufficient electrical
conductivity. This impedes the charge collection even with highly conductive
additives, such as carbon.
Looking for solutions to overcome this
problem, the 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.
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 the slightest error of a
scientist may cause degradation of the samples.
Of the several polymer specimens
obtained, only one was found to be sufficiently stable and efficient. The main
chain of the new compound is formed by complexes of nickel with salen
ligands. A stable free radical, capable of rapid oxidation and reduction
(charge and discharge), has been linked to the main chain via covalent
bonds.
‘A battery manufactured using our polymer will charge in seconds —
about ten times faster than a traditional lithium-ion battery. This has
already been demonstrated through a series of experiments. However, at this
stage, it is still lagging behind in terms of capacity — 30 to 40% lower than
in l0ithium-ion batteries. We are currently working to improve this
indicator while maintaining the charge-discharge rate,’ says Oleg Levin.
The cathode for the new battery has been
fabricated — a positive electrode for use in chemical current sources. Now
we need the negative electrode — the anode. In fact, it does not have to be
created from scratch — it can be selected from the existing ones. Paired
together they will form a system that, in some areas, may soon supersede
lithium-ion batteries.
‘The new battery is capable
of operating at low temperatures and will be an excellent option where
fast charging is crucial. It is safe to use — there is nothing that may
pose a combustion hazard, unlike the cobalt-based batteries that are widespread
today. It also contains
significantly less metals that can cause environmental harm. Nickel is present
in our polymer in a small amount, but there is much less of it than
in lithium-ion batteries,’ says Oleg Levin.
At present, the researchers are filing a
patent application for their invention. St Petersburg University will
become the copyright holder. The project
was supported by a grant from the Russian Science Foundation, No 16-13-00038.
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