̽��ֱ�� of Cambridge - Alice Merryweather

Watching lithium in real time could improve performance of EV battery materials

sc604 — Fri, 14 Oct 2022 13:46:50 +0000

̽��ֱ��team, led by the ̽��ֱ�� of Cambridge, tracked the movement of lithium ions inside a promising new battery material in real time.

It had been assumed that the mechanism by which lithium ions are stored in battery materials is uniform across the individual active particles. However, the Cambridge-led team found that during the charge-discharge cycle, lithium storage is anything but uniform.

When the battery is near the end of its discharge cycle, the surfaces of the active particles become saturated by lithium while their cores are lithium deficient. This results in the loss of reusable lithium and a reduced capacity.

̽��ֱ��research, funded by the Faraday Institution, could help improve existing battery materials and could accelerate the development of next-generation batteries. ̽��ֱ��results are published in Joule.

Electrical vehicles (EVs) are vital in the transition to a zero-carbon economy. Most electric vehicles on the road today are powered by lithium-ion batteries, due in part to their high energy density.

However, as EV use becomes more widespread, the push for longer ranges and faster charging times means that current battery materials need to be improved, and new materials need to be identified.

Some of the most promising of these materials are state-of-the-art positive electrode materials known as layered lithium nickel-rich oxides, which are widely used in premium EVs. However, their working mechanisms, particularly lithium-ion transport under practical operating conditions, and how this is linked to their electrochemical performance, are not fully understood, so we cannot yet obtain maximum performance from these materials.

By tracking how light interacts with active particles during battery operation under a microscope, the researchers observed distinct differences in lithium storage during the charge-discharge cycle in nickel-rich manganese cobalt oxide (NMC).

“This is the first time that this non-uniformity in lithium storage has been directly observed in individual particles,” said co-first author Alice Merryweather, from Cambridge’s Yusuf Hamied Department of Chemistry. “Real time techniques like ours are essential to capture this while the battery is cycling.”

Combining the experimental observations with computer modelling, the researchers found that the non-uniformity originates from drastic changes to the rate of lithium-ion diffusion in NMC during the charge-discharge cycle. Specifically, lithium ions diffuse slowly in fully lithiated NMC particles, but the diffusion is significantly enhanced once some lithium ions are extracted from these particles.

“Our model provides insights into the range over which lithium-ion diffusion in NMC varies during the early stages of charging,” said co-first author Dr Shrinidhi Pandurangi from Cambridge’s Department of Engineering. “Our model predicted lithium distributions accurately and captured the degree of heterogeneity observed in experiments. These predictions are key to understanding other battery degradation mechanisms such as particle fracture.”

Importantly, the lithium heterogeneity seen at the end of discharge establishes one reason why nickel-rich cathode materials typically lose around ten percent of their capacity after the first charge-discharge cycle.

“This is significant, considering one industrial standard that is used to determine whether a battery should be retired or not is when it has lost 20 percent of its capacity,” said co-first author Dr Chao Xu, from ShanghaiTech ̽��ֱ��, who completed the research while based at Cambridge.

̽��ֱ��researchers are now seeking new approaches to increase the practical energy density and lifetime of these promising battery materials.

̽��ֱ��research was supported in part by the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI). Alice Merryweather is jointly supervised by Professor Dame Clare Grey and Dr Akshay Rao, who are both co-authors on the current paper.

Reference:
Chao Xu et al. ‘Operando visualization of kinetically induced lithium heterogeneities in single-particle layered Ni-rich cathodes.’ Joule (2022). DOI: 10.1016/j.joule.2022.09.008

For more information on energy-related research in Cambridge, please visit Energy IRC, which brings together Cambridge’s research knowledge and expertise, in collaboration with global partners, to create solutions for a sustainable and resilient energy landscape for generations to come.

Researchers have found that the irregular movement of lithium ions in next-generation battery materials could be reducing their capacity and hindering their performance.

Andrew Roberts via Unsplash

Electric car charging

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Low-cost imaging technique shows how smartphone batteries could charge in minutes

sc604 — Wed, 23 Jun 2021 15:00:00 +0000

Using the low-cost technique, the researchers identified the speed-limiting processes which, if addressed, could enable the batteries in most smartphones and laptops to charge in as little as five minutes.

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge, say their technique will not only help improve existing battery materials, but could accelerate the development of next-generation batteries, one of the biggest technological hurdles to be overcome in the transition to a fossil fuel-free world. ̽��ֱ��results are reported in the journal Nature.

While lithium-ion batteries have undeniable advantages, such as relatively high energy densities and long lifetimes in comparison with other batteries and means of energy storage, they can also overheat or even explode, and are relatively expensive to produce. Additionally, their energy density is nowhere near that of petrol. So far, this makes them unsuitable for widespread use in two major clean technologies: electric cars and grid-scale storage for solar power.

“A better battery is one that can store a lot more energy or one that can charge much faster – ideally both,” said co-author Dr Christoph Schnedermann, from Cambridge’s Cavendish Laboratory. “But to make better batteries out of new materials, and to improve the batteries we’re already using, we need to understand what’s going on inside them.”

To improve lithium-ion batteries and help them charge faster, researchers need to follow and understand the processes occurring in functioning materials under realistic conditions in real time. Currently, this requires sophisticated synchrotron X-ray or electron microscopy techniques, which are time-consuming and expensive.

“To really study what’s happening inside a battery, you essentially have to get the microscope to do two things at once: it needs to observe batteries charging and discharging over a period of several hours, but at the same time it needs to capture very fast processes happening inside the battery,” said first author Alice Merryweather, a PhD student at Cambridge’s Cavendish Laboratory.

̽��ֱ��Cambridge team developed an optical microscopy technique called interferometric scattering microscopy to observe these processes at work. Using this technique, they were able to observe individual particles of lithium cobalt oxide (often referred to as LCO) charging and discharging by measuring the amount of scattered light.

They were able to see the LCO going through a series of phase transitions in the charge-discharge cycle. ̽��ֱ��phase boundaries within the LCO particles move and change as lithium ions go in and out. ̽��ֱ��researchers found that the mechanism of the moving boundary is different depending on whether the battery is charging or discharging.

“We found that there are different speed limits for lithium-ion batteries, depending on whether it’s charging or discharging,” said Dr Akshay Rao from the Cavendish Laboratory, who led the research. “When charging, the speed depends on how fast the lithium ions can pass through the particles of active material. When discharging, the speed depends on how fast the ions are inserted at the edges. If we can control these two mechanisms, it would enable lithium-ion batteries to charge much faster.”

“Given that lithium-ion batteries have been in use for decades, you’d think we know everything there is to know about them, but that’s not the case,” said Schnedermann. “This technique lets us see just how fast it might be able to go through a charge-discharge cycle. What we’re really looking forward to is using the technique to study next-generation battery materials – we can use what we learned about LCO to develop new materials.”

“ ̽��ֱ��technique is a quite general way of looking at ion dynamics in solid-state materials, so you can use it on almost any type of battery material,” said Professor Clare Grey, from Cambridge’s Yusuf Hamied Department of Chemistry, who co-led the research.

̽��ֱ��high throughput nature of the methodology allows many particles to be sampled across the entire electrode and, moving forward, will enable further exploration of what happens when batteries fail and how to prevent it.

“This lab-based technique we’ve developed offers a huge change in technology speed so that we can keep up with the fast-moving inner workings of a battery,” said Schnedermann. “ ̽��ֱ��fact that we can actually see these phase boundaries changing in real time was really surprising. This technique could be an important piece of the puzzle in the development of next-generation batteries.”

Reference:
Alice J. Merryweather et al. ‘Operando optical tracking of single-particle ion dynamics in batteries.’ Nature (2021). DOI: 10.1038/s41586-021-03584-2

Researchers have developed a simple lab-based technique that allows them to look inside lithium-ion batteries and follow lithium ions moving in real time as the batteries charge and discharge, something which has not been possible until now.

This technique could be an important piece of the puzzle in the development of next-generation batteries

Christoph Schnedermann

Image by Alexandra_Koch from Pixabay

Batteries charging

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