Rechargeable batteries are an essential part of modern life and play a major role in decarbonisation. Now, 2 studies provide important new insights in the search for ways improve them.
In one study in the journal Advanced Energy Materials, chemical engineers in Korea explain a previously overlooked mechanism through which lithium-ion batteries degrade.
They say their finding could provide solutions for preserving cathodes and may play a crucial role in developing batteries with long lifecycles.
Another team of chemists in the US have found a way to peer into battery interfaces – the areas where the electrode and electrolyte meet. The imaging technique, described in a Nature Nanotechnology paper, will allow them to see the intricate structure and chemical reactions of the interfaces to better design them.
Extending the lifespans of lithium-ion batteries
Lithium-ion batteries are used extensively in electronics, electric vehicles and energy storage stations.
Some lithium-ion battery cathodes are made of mixed metal oxides of lithium, nickel, manganese and cobalt (NMC). Increasing the nickel content while minimising cobalt can reduce the costs of manufacturing, however this tends to shorten the overall cycle life of the battery.
In the Advanced Energy Materials paper, researchers showed that when a lithium-ion battery is used for extended periods without recharging, a phenomenon known as the “quasi-conversion reaction” occurs on the positive electrode (cathode) surface, accelerating battery degradation.
This reaction was more severe in nickel cathodes and when the batteries were used until they almost ran out.
But experiments on high-nickel cathodes revealed a simple solution. By optimising battery usage and avoiding full discharge, they could maintain 73.4% of a batteries’ capacity after 300 cycles.
Image01 850
When high nickel pouch-type cells were cycled more than 250 times at 1.9 V (where the quasi-conversion reaction occurs) and 3.15 V (where it does not), capacity retention improved significantly solely by adjusting the discharge cutoff voltage. Credit: POSTECH
“The impact of discharge – the actual process of using a battery – has been largely overlooked until now,” says Professor Jihyun Hong of Pohang University of Science and Technology (POSTECH), Republic of Korea, who led the research.
“This research presents an important direction for the developing longer-lasting batteries.”
Spying on battery interfaces
The second study focused on batteries using “multiphase polymer electrolytes.”
Battery electrolytes carry charged ions back and forth between the cathode and anode to charge and discharge a battery. They can be liquid, solid, gel-like, or multiphase, which shift from rigid to flexible depending on the conditions.
Multiphase electrolytes have the potential to store more energy, and be safer and cheaper, than conventional batteries.
Research teams from Virginia Tech in the US are working to build lithium and sodium batteries based on this formulation but, according to Jungki Min, a chemistry graduate student at Virginia Tech and the study’s first author, “there are major, longstanding challenges at the interfaces.”
“We are always trying to gain better control over these buried surfaces.”
Now, the teams have shown that “tender energy X-rays”, which have energies midway between higher energy “hard X-rays” and lower energy “soft X-rays”, can be used to study them.
The new Nature Nanotechnology study revealed the source of their problems: part of the architectural support system degraded as the battery cycled, leading to eventual failure.
“We now have a good mechanistic picture to guide us for a better design of interfaces and interphases in solid polymer batteries,” adds Professor Feng Lin of Virginia Tech, who co-led the research.
Subscribe to energise from cosmos
Are you interested in the energy industry and the technology and scientific developments that power it? Then our free email newsletter Energise is for you. Click here to become a subscriber.