̽��ֱ�� of Cambridge - lithium-ion battery

Cambridge researchers awarded ERC funding to support commercial potential of their work

sc604 — Wed, 02 Aug 2023 16:05:46 +0000

Professor Cecilia Mascolo from the Department of Computer Science and Technology will use the funding to further her work on developing mobile devices – like commercially-available earbuds – that can accurately pick up wearers’ body sounds and monitor them for health purposes.

̽��ֱ��ERC Proof of Concept grants – worth €150,000 – help researchers bridge the gap between the discoveries stemming from their frontier research and the practical application of the findings, including the early phases of their commercialisation.

Researchers use this type of funding to verify the practical viability of scientific concepts, explore business opportunities or prepare patent applications.

Mascolo’s existing ERC-funded Project EAR was the first to demonstrate that the existing microphones in earbuds can be used to pick up wearers’ levels of activity and heart rate and to trace it accurately even when the wearer is exercising vigorously.

She now wants to build on this work by enhancing the robustness of these in-ear microphones and further improve their performance in monitoring human activity and physiology in 'real life' conditions, including by developing new algorithms to help the devices analyse the data they are collecting.

“There are currently no solutions on the market that use audio devices to detect body function signals like this and they could play an extremely valuable role in health monitoring,” said Mascolo. “Because the devices’ hardware, computing needs and energy consumption are inexpensive, they could put body function monitoring into the hands of the world's population accurately and affordably.”

Professor Manish Chhowalla from the Department of Materials Science and Metallurgy was awarded a Proof of Concept Grant to demonstrate large-scale and high-performance lithium-sulfur batteries.

“Our breakthrough in lithium-sulphur batteries demonstrates a future beyond lithium-ion batteries; moving away from the reliance on critical raw materials and enabling the electrification of fundamentally new applications such as aviation,” said Dr Ismail Sami, Research Fellow in Chhowalla’s group. “This Proof of Concept will help us take the essential commercial and technical steps in bringing our innovation to market.”

̽��ֱ�� of Cambridge researchers have been awarded Proof of Concept grants from the European Research Council (ERC), to help them explore the commercial or societal potential of their research. ̽��ֱ��funding is part of the EU's research and innovation programme, Horizon Europe.

̽��ֱ�� of Cambridge

Left: Cecilia Mascolo, Right: Ismail Sami

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Oxygen ‘holes’ could hold the key to higher performing EV batteries

sc604 — Wed, 19 Jul 2023 14:59:04 +0000

Nickel is already used in lithium-ion batteries, but increasing the proportion of nickel could significantly improve battery energy density, making them especially suitable for electric vehicles and grid-scale storage. However, practical applications for these materials have been limited by structural instability and the tendency to lose oxygen atoms, which cause battery degradation and failure.

̽��ֱ��researchers, led by the ̽��ֱ�� of Cambridge and the ̽��ֱ�� of Birmingham, found that ‘oxygen hole’ formation – where an oxygen ion loses an electron – plays a crucial role in the degradation of nickel-rich battery materials. These oxygen holes accelerate the release of oxygen that can further degrade the battery’s cathode, one of its two electrodes. Their results are reported in the journal Joule.

Using a set of computational techniques on UK regional supercomputers, the researchers examined the behaviour of nickel-rich cathodes as they charged. They found that during charging, the oxygen in the material undergoes changes while the nickel charge remains essentially unchanged.

“We found that the charge of the nickel ions remains around +2, regardless of whether it’s in its charged or discharged form,” said Professor Andrew J Morris, from the ̽��ֱ�� of Birmingham, who co-led the research. “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.”

̽��ֱ��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 releases energy and forms singlet oxygen, a highly reactive form of oxygen.

“Potentially, by adding compounds that shift the electrochemical reactions from oxygen more to the transition metals, especially at the surface of the battery materials, we can prevent the formation of singlet oxygen,” said first author Dr Annalena Genreith-Schriever from the Yusuf Hamied Department of Chemistry. “This will enhance the stability and longevity of these lithium-ion batteries, paving the way for more efficient and reliable energy storage systems.”

Lithium-ion batteries are widely used for various applications because of their high energy density and rechargeability, but challenges associated with the stability of cathode materials have hindered their overall performance and lifespan.

̽��ֱ��research was supported in part by the Faraday Institution, the UK’s flagship battery research programme.

Reference:
Annalena R Genreith-Schriever et al. ‘Oxygen Hole Formation Controls Stability in LiNiO2 Cathodes: DFT Studies of Oxygen Loss and Singlet Oxygen Formation in Li-Ion Batteries.’ Joule (2023). DOI: 10.1016/j.joule.2023.06.017

Adapted from a ̽��ֱ�� of Birmingham media release.

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.

Scientists have made a breakthrough in understanding and overcoming the challenges associated with nickel-rich materials used in lithium-ion batteries.

This will enhance the stability and longevity of these lithium-ion batteries, paving the way for more efficient and reliable energy storage systems

Annalena Genreith-Schriever

Cavan images via Getty Images

View of woman's hand plugging in charging lead to her electric car

Yes

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

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

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Machine learning algorithm predicts how to get the most out of electric vehicle batteries

sc604 — Tue, 23 Aug 2022 09:01:34 +0000

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge, say their algorithm could help drivers, manufacturers and businesses get the most out of the batteries that power electric vehicles by suggesting routes and driving patterns that minimise battery degradation and charging times.

̽��ֱ��team developed a non-invasive way to probe batteries and get a holistic view of battery health. These results were then fed into a machine learning algorithm that can predict how different driving patterns will affect the future health of the battery.

If developed commercially, the algorithm could be used to recommend routes that get drivers from point to point in the shortest time without degrading the battery, for example, or recommend the fastest way to charge the battery without causing it to degrade. ̽��ֱ��results are reported in the journal Nature Communications.

̽��ֱ��health of a battery, whether it’s in a smartphone or a car, is far more complex than a single number on a screen. “Battery health, like human health, is a multi-dimensional thing, and it can degrade in lots of different ways,” said first author Penelope Jones, from Cambridge’s Cavendish Laboratory. “Most methods of monitoring battery health assume that a battery is always used in the same way. But that’s not how we use batteries in real life. If I’m streaming a TV show on my phone, it’s going to run down the battery a whole lot faster than if I’m using it for messaging. It’s the same with electric cars – how you drive will affect how the battery degrades.”

“Most of us will replace our phones well before the battery degrades to the point that it’s unusable, but for cars, the batteries need to last for five, ten years or more,” said Dr Alpha Lee, who led the research. “Battery capacity can change drastically over that time, so we wanted to come up with a better way of checking battery health.”

̽��ֱ��researchers developed a non-invasive probe that sends high-dimensional electrical pulses into a battery and measures the response, providing a series of ‘biomarkers’ of battery health. This method is gentle on the battery and doesn’t cause it to degrade any further.

̽��ֱ��electrical signals from the battery were converted into a description of the battery’s state, which was fed into a machine learning algorithm. ̽��ֱ��algorithm was able to predict how the battery would respond in the next charge-discharge cycle, depending on how quickly the battery was charged and how fast the car would be going the next time it was on the road. Tests with 88 commercial batteries showed that the algorithm did not require any information about previous usage of the battery to make an accurate prediction.

̽��ֱ��experiment focused on lithium cobalt oxide (LCO) cells, which are widely used in rechargeable batteries, but the method is generalisable across the different types of battery chemistries used in electric vehicles today.

“This method could unlock value in so many parts of the supply chain, whether you’re a manufacturer, an end user, or a recycler, because it allows us to capture the health of the battery beyond a single number, and because it’s predictive,” said Lee. “It could reduce the time it takes to develop new types of batteries, because we’ll be able to predict how they will degrade under different operating conditions.”

̽��ֱ��researchers say that in addition to manufacturers and drivers, their method could be useful for businesses that operate large fleets of electric vehicles, such as logistics companies. “ ̽��ֱ��framework we’ve developed could help companies optimise how they use their vehicles to improve the overall battery life of the fleet,” said Lee. “There’s so much potential with a framework like this.”

“It’s been such an exciting framework to build because it could solve so many of the challenges in the battery field today,” said Jones. “It’s a great time to be involved in the field of battery research, which is so important in helping address climate change by transitioning away from fossil fuels.”

̽��ֱ��researchers are now working with battery manufacturers to accelerate the development of safer, longer-lasting next-generation batteries. They are also exploring how their framework could be used to develop optimal fast charging protocols to reduce electric vehicle charging times without causing degradation.

̽��ֱ��research was supported by the Winton Programme for the Physics of Sustainability, the Ernest Oppenheimer Fund, ̽��ֱ��Alan Turing Institute and the Royal Society.

Reference:
Penelope K Jones, Ulrich Stimming & Alpha A Lee. ‘Impedance-based forecasting of lithium-ion battery performance amid uneven usage.’ Nature Communications (2022). DOI: 10.1038/s41467-022-32422-w

Researchers have developed a machine learning algorithm that could help reduce charging times and prolong battery life in electric vehicles by predicting how different driving patterns affect battery performance, improving safety and reliability.

This method could unlock value in so many parts of the supply chain, whether you’re a manufacturer, an end user, or a recycler, because it allows us to capture the health of the battery beyond a single number

Alpha Lee

Monty Rakusen via Getty Images

People charging their electric cars at charging station in York

Yes

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

Yes

Professor Clare Grey awarded €1 million Körber Prize

sc604 — Tue, 22 Jun 2021 04:23:39 +0000

Grey pioneered the optimisation of batteries with the help of NMR (nuclear magnetic resonance) spectroscopy – similar to MRI technology – a method that allows non-invasive insights into the inner workings of batteries.

Her NMR studies have helped to significantly increase the performance of lithium-ion batteries, which power mobile phones, laptops and electric cars. She has been instrumental in the development of next-generation batteries and cost-effective, durable storage systems for renewable energy. She sees her fundamental research as an important contribution to achieving net-zero emissions by 2050.

“There have been significant advances in lithium-ion batteries since they were commercialised in the 1990s,” said Grey. “Their energy density has tripled and prices have fallen by 90 percent.”

Grey’s research has made key contributions to these developments. She is a pioneer in the study of solids with the help of NMR spectroscopy, which she has developed and applied to allow researchers to observe the electrochemical processes at work during charging and discharging of batteries.

Clare Grey, 56, studied chemistry at the ̽��ֱ�� of Oxford. At the age of 22, she published her first scientific article in the journal Nature. After completing her doctoral studies in 1991, she went to Radboud ̽��ֱ�� in Nijmegen, the Netherlands, and has also worked as a visiting scientist at the US chemical company Dupont.

In 1994, she joined the State ̽��ֱ�� of New York at Stony Brook as an assistant professor, and she became a full professor in 2001. In 2009, she became Geoffrey Moorhouse Gibson Professor at the ̽��ֱ�� of Cambridge’s Yusuf Hamied Department of Chemistry. She is a Fellow of Pembroke College, and has been a Fellow of the Royal Society since 2011.

At the time Grey was still a student, most chemist and physicists used X-rays to determine the internal structure of solids. Grey was one of the first in her field to use solid state NMR instead: during her time in the USA, she met researchers from the Duracell company who inspired her to use the technology to study materials in batteries.

“Previously, the usual investigations with X-rays only provided an average picture,” Grey said. “With the help of NMR, I was able to detect the local structural details in these often-disordered materials.”

Initially, she examined individual materials by opening the batteries at a certain stage of their charging and discharging cycle. ̽��ֱ��aim was to find out which chemical processes cause the batteries to age and how their lifespan and capacity could be increased. Later, she improved the NMR technology so that she could use it to examine batteries during operation without destroying them, which helped speed up the studies enormously.

Now, in addition to her work improving lithium-ion batteries, Grey is developing a range of different next-generation batteries, including lithium-air batteries (which use oxidation of lithium and reduction of oxygen to induce a current), sodium, magnesium and redox flow batteries.

Her NMR studies allow her to follow the processes at work inside these batteries in real time and help determine the processes that cause batteries to degrade. She is working on further optimising the NMR method to design even more powerful, faster-charging and more environmentally friendly batteries.

In 2019, Grey co-founded a company, Nyobolt, for ultra-fast charging batteries. Another company supplies the NMR measurement technology she designed to laboratories around the world.

To achieve climate goals and transition away from fossil fuels, Grey believes it is vital that “basic research into new battery technologies is already in full swing today – tomorrow will be too late.”

̽��ֱ��Körber European Science Prize 2021 will be presented to Professor Clare Grey on 10 September 2021 in the Great Festival Hall of Hamburg City Hall. Since 1985, the Körber Foundation has honoured a breakthrough in the physical or life sciences in Europe with the Körber Prize. It is awarded for excellent and innovative research approaches with high application potential. To date, six Körber Prize winners have been awarded the Nobel Prize.

̽��ֱ��Körber European Science Prize 2021, worth one million euros, is to be awarded to ̽��ֱ�� of Cambridge chemist Professor Clare Grey, one of the UK’s leading battery researchers.

Gabriella Bocchetti

Professor Clare Grey

Yes

New insights into lithium-ion battery failure mechanism

sc604 — Mon, 24 Aug 2020 14:59:00 +0000

̽��ֱ��researchers, from the Universities of Cambridge and Liverpool, and the Diamond Light Source, have identified one of the reasons why state-of-the-art ‘nickel-rich’ battery materials become fatigued, and can no longer be fully charged after prolonged use.

Their results, reported in the journal Nature Materials, open the door to the development of new strategies to improve battery lifespans.

As part of efforts to combat climate change, many countries have announced ambitious plans to replace petrol or diesel vehicles with electric vehicles (EVs) by 2050 or earlier.

̽��ֱ��lithium-ion batteries used by EVs are likely to dominate the EV market for the foreseeable future, and nickel-rich lithium transition-metal oxides are the state-of-the-art choice for the positive electrode, or cathode, in these batteries.

Currently, most EV batteries contain significant amounts of cobalt in their cathode materials. However, cobalt can cause severe environmental damage, so researchers have been looking to replace it with nickel, which also offers higher practical capacities than cobalt. However, nickel-rich materials degrade much faster than existing technology and require additional study to be commercially viable for applications such as EVs.

“Unlike consumable electronics which typically have lifetimes of only a few years, vehicles are expected to last much longer and therefore it is essential to increase the lifetime of an EV battery,” said Dr Chao Xu from Cambridge’s Department of Chemistry, and the first author of the article. “That’s why a comprehensive, in-depth understanding of how they work and why they fail over a long time is crucial to improving their performance.”

To monitor the changes of the battery materials in real time over several months of battery testing, the researchers used laser technology to design a new coin cell, also known as button cell. “This design offers a new possibility of studying degradation mechanisms over a long period of cycling for many battery chemistries,” said Xu. During the study, the researchers found that a proportion of the cathode material becomes fatigued after repetitive charging and discharging of the cell, and the amount of the fatigued material increases as the cycling continues.

Xu and his colleagues dived deep into the structure of the material at the atomic scale to seek answers as to why such fatigue process occurs. “In order to fully function, battery materials need to expand and shrink as the lithium ions move in and out,” said Xu. “However, after prolonged use, we found that the atoms at the surface of the material had rearranged to form new structures that are no longer able to store energy.”

What’s worse is that these areas of reconstructed surface apparently act as stakes that pin the rest of the material in place and prevent it from the contraction which is required to reach the fully charged state. As a result, the lithium remains stuck in the lattice and this fatigued material can hold less charge.

With this knowledge, the researchers are now seeking effective countermeasures, such as protective coatings and functional electrolyte additives, to mitigate this degradation process and extend the lifetime of such batteries.

̽��ֱ��research, led by Professor Clare P Grey from the Chemistry Department at Cambridge, has been supported by the Faraday Institution Degradation Project.

Reference:
Chao Xu et al. ‘Bulk fatigue induced by surface reconstruction in layered Ni-rich cathodes for Li-ion batteries.’ Nature Materials (2020). DOI: 10.1038/s41563-020-0767-8

Researchers have identified a potential new degradation mechanism for electric vehicle batteries – a key step to designing effective methods to improve battery lifespan.

Yes

New class of materials could be used to make batteries that charge faster

sc604 — Wed, 25 Jul 2018 17:03:59 +0000

Although these materials, known as niobium tungsten oxides, do not result in higher energy densities when used under typical cycling rates, they come into their own for fast charging applications. Additionally, their physical structure and chemical behaviour give researchers a valuable insight into how a safe, super-fast charging battery could be constructed, and suggest that the solution to next-generation batteries may come from unconventional materials. ̽��ֱ��results are reported in the journal Nature.

Many of the technologies we use every day have been getting smaller, faster and cheaper each year – with the notable exception of batteries. Apart from the possibility of a smartphone which could be fully charged in minutes, the challenges associated with making a better battery are holding back the widespread adoption of two major clean technologies: electric cars and grid-scale storage for solar power.

“We’re always looking for materials with high-rate battery performance, which would result in a much faster charge and could also deliver high power output,” said Dr Kent Griffith, a postdoctoral researcher in Cambridge’s Department of Chemistry and the paper’s first author.

In their simplest form, batteries are made of three components: a positive electrode, a negative electrode and an electrolyte. When a battery is charging, lithium ions are extracted from the positive electrode and move through the crystal structure and electrolyte to the negative electrode, where they are stored. ̽��ֱ��faster this process occurs, the faster the battery can be charged.

In the search for new electrode materials, researchers normally try to make the particles smaller. “ ̽��ֱ��idea is that if you make the distance the lithium ions have to travel shorter, it should give you higher rate performance,” said Griffith. “But it’s difficult to make a practical battery with nanoparticles: you get a lot more unwanted chemical reactions with the electrolyte, so the battery doesn’t last as long, plus it’s expensive to make.”

“Nanoparticles can be tricky to make, which is why we’re searching for materials that inherently have the properties we’re looking for even when they are used as comparatively large micron-sized particles. This means that you don’t have to go through a complicated process to make them, which keeps costs low,” said Professor Clare Grey, also from the Department of Chemistry and the paper’s senior author. “Nanoparticles are also challenging to work with on a practical level, as they tend to be quite ‘fluffy’, so it’s difficult to pack them tightly together, which is key for a battery’s volumetric energy density.”

̽��ֱ��niobium tungsten oxides used in the current work have a rigid, open structure that does not trap the inserted lithium, and have larger particle sizes than many other electrode materials. Griffith speculates that the reason these materials have not received attention previously is related to their complex atomic arrangements. However, he suggests that the structural complexity and mixed-metal composition are the very reasons the materials exhibit unique transport properties.

“Many battery materials are based on the same two or three crystal structures, but these niobium tungsten oxides are fundamentally different,” said Griffith. ̽��ֱ��oxides are held open by ‘pillars’ of oxygen, which enables lithium ions to move through them in three dimensions. “ ̽��ֱ��oxygen pillars, or shear planes, make these materials more rigid than other battery compounds, so that, plus their open structures means that more lithium ions can move through them, and far more quickly.”

Using a technique called pulsed field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy, which is not readily applied to battery electrode materials, the researchers measured the movement of lithium ions through the oxides, and found that they moved at rates several orders of magnitude higher than typical electrode materials.

Most negative electrodes in current lithium-ion batteries are made of graphite, which has a high energy density, but when charged at high rates, tends to form spindly lithium metal fibres known as dendrites, which can create a short-circuit and cause the batteries to catch fire and possibly explode.

“In high-rate applications, safety is a bigger concern than under any other operating circumstances,” said Grey. “These materials, and potentially others like them, would definitely be worth looking at for fast–charging applications where you need a safer alternative to graphite.”

In addition to their high lithium transport rates, the niobium tungsten oxides are also simple to make. “A lot of the nanoparticle structures take multiple steps to synthesise, and you only end up with a tiny amount of material, so scalability is a real issue,” said Griffith. “But these oxides are so easy to make, and don’t require additional chemicals or solvents.”

Although the oxides have excellent lithium transport rates, they do lead to a lower cell voltage than some electrode materials. However, the operating voltage is beneficial for safety and the high lithium transport rates mean that when cycling fast, the practical (usable) energy density of these materials remains high.

While the oxides may only be suited for certain applications, Grey says that the important thing is to keep looking for new chemistries and new materials. “Fields stagnate if you don’t keep looking for new compounds,” she says. “These interesting materials give us a good insight into how we might design higher rate electrode materials.”

̽��ֱ��research was funded in part by the European Union, the Science and Technology Facilities Council, and the Engineering and Physical Sciences Research Council.

Reference:
Kent J. Griffith et al. ‘Niobium tungsten oxides for high-rate lithium-ion energy storage.’ Nature (2018). DOI: 10.1038/s41586-018-0347-0

Researchers have identified a group of materials that could be used to make even higher power batteries. ̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge, used materials with a complex crystalline structure and found that lithium ions move through them at rates that far exceed those of typical electrode materials, which equates to a much faster-charging battery.

Fields stagnate if you don’t keep looking for new compounds.

Clare Grey

Ella Maru Studio

Impression of rapidly flowing ionic diffusion within a niobium tungsten oxide

Yes