Lithium breakthrough: Poms discover why nickel cathodes in batteries degrade and how to fix it
Brit scientists have made a ‘significant breakthrough’ in understanding – and overcoming – the challenges associated with the loss of oxygen in nickel-rich cathode materials which form the guts of your standard lithium-ion batteries.
It’s these nickel friendly materials that wrap around the er, lithium intestines and which scientists at the Unis of Cambridge and of Birmingham believe have the potential to achieve both high voltages and capacities if their use in practical applications were not hindered by structural instabilities and loss of oxygen.
Currently 39% of Li-ion batteries contain nickel. This is expected to rise to around 58% by 2025, according to the Nickel Peak Body, which I think is just called: Nickel.
They say nickel in the battery provides higher energy density and storage at lower cost.
Their study revealed that ‘oxygen hole’ formation – where an oxygen ion loses an electron – plays a crucial role in the degradation of LiNiO2 cathodes accelerating the release of oxygen which can then further degrade the cathode material.
Using the Poms’ “state-of-the-art” computational techniques on UK regional supercomputers, the researchers examined the behaviour of LiNiO2 cathodes as they get charged. The researchers found that during charging, the oxygen in the material undergoes changes while the nickel charge remains essentially unchanged.
Here’s co-author Professor Andrew J. Morris, from the University of Birmingham:
“We found that the charge of the nickel ions remains around +2, regardless of whether it’s in its charged or discharged form. At the same time the charge of the oxygen varies from -1.5 to about -1.
“This is unusual, the conventional model assumes that the oxygen remains at -2 throughout charging, but these changes show that the oxygen is not very stable, and we have found a pathway for it to leave the nickel-rich cathode.”
The researchers compared their calculations with experimental data and found that their results aligned well with what was observed.
They proposed a mechanism for how oxygen is lost during this process, involving the combination of oxygen radicals to form a peroxide ion, which is then converted into oxygen gas, leaving vacancies in the material.
This process apparently releases energy and forms singlet oxygen, a highly reactive form of oxygen.
Gone for good, it seems, are the days when the most crucial use of nickel was for making long-lasting 50 cent pieces.
Nickel’s also handy for plating stuff to make it cooler (ok, and harder) as well as for making lots of wires. It gets used in gas turbines and rocket engines a fair bit – as it has the capability to resist corrosion even at high temperatures. Also handy – nickel for whipping up a variety of alloys which can find their way into your armour plated Tesla, as well as some nails, or pipes.
I’ve seen dimes worth more than nickel.
That’ll change. According to something I read a year or so back, some 50kg of nickel goes into each Tesla battery.
Topline author Dr Annalena Genreith-Schriever from the University of Cambridge says:
“Potentially, by adding dopants that reduce oxygen redox, while promoting transition-metal redox particularly at the surface, mitigating the generation of singlet oxygen, we can enhance the stability and longevity of these type of lithium-ion batteries, paving the way for more efficient and reliable energy storage systems.”
In plain speak, that means that the boffins think they have figured out a way to mitigate if not outright prevent the degradation of nickel cathodes, potentially increasing their overall performance and lifespan.
This is likely to be welcome given that lithium-ion batteries are widely used for various applications because of their high energy density and rechargeability.
Researchers from the Universities of Birmingham, Cambridge, Warwick as well as The Faraday Institution, Didcot, published their findings on Wednesday 19 July in Joule Magazine.