• OXECO and WMG at the University of Warwick will conduct a 15-month research programme into lithium-ion battery coatings
• Research is expected to advance next generation active materials and coating foils used to create electrodes
• The partnership aims to improve lithium-ion battery performance, longevity, and manufacturing

OXECO, a spin-out of the University of Oxford, has partnered with WMG at the University of Warwick, for a 15-month collaboration on lithium-ion battery technology. The partnership aims to advance the lithium-ion battery industry by leveraging WMG’s research on battery cell development and optimisation, alongside OXECO’s unique technology platform.

The research programme aims to enhance the performance, longevity, and ease of manufacturing of lithium-ion batteries by focusing on the preparation of active materials and coating foils used to create electrodes.

The programme is expected to yield transformative results in the improvement of current lithium-ion batteries and be a significant step towards the development of more efficient, reliable, and sustainable energy storage solutions.

This partnership will further OXECO’s aim to leverage innovative surface chemistry to accelerate our net-zero future. Jon-Paul Griffiths, founder and Chief Technology Officer at OXECO, commented that: “This is a remarkable opportunity to help steer the progress of battery technology - a crucial industry for the realisation of a sustainable energy economy. WMG has exceptional proficiency and credibility in battery research, coupled with the ability to manufacture from bench to pilot scale.

"This marks the initial phase of our efforts towards the integration of ONTO™ chemistry into lithium-ion batteries, and we are also delving into other domains of our chemistry for diverse applications in batteries, such as separator membranes. Our team is dedicated to forging a path towards cutting-edge technological advancements that will shape the future of energy storage solutions.”

WMG has an international reputation for working successfully with industry, with a history of partnering with pioneering entities, including Lotus, Aston Martin, JLR, BAE Systems, IBM, and Plug and Play, as well as the latest technology innovators.

Dr Mark Copley, Chief Engineer in WMG's Electrochemical Materials and Manufacturing team, concluded: “We are excited to be partnering with OXECO. This collaboration will draw on the University’s extensive expertise in battery technologies and OXECO’s chemistry to improve battery performance and longevity and help the global transition to sustainable power solutions through innovative research and training.”

About OXECO

OXECO is a chemistry technology company that designs, develops, and manufactures thin coatings and materials for the transport and clean technology sectors. The company’s core innovative technology controls the way that surfaces behave using cutting-edge carbene chemistry. This technology was born in the University of Oxford’s Department of Chemistry and developed over more than two decades.

www.oxeco.co.uk

New research has shown that understanding how oxygen participates in energy storage is critical for developing higher energy density batteries, in a new paper published by experts at WMG, at the University of Warwick.

Using advanced X-ray techniques, researchers at WMG, together with the Faraday Institution's FutureCat consortium, have obtained new insights into the oxygen redox activity in conventional ni-rich cathodes, which will help to deliver improved electric vehicle performance.

Range anxiety is a key concern of many potential EV buyers, but range is steadily improving as battery technology and research evolves. The Faraday Institution’s Next Generation Lithium-Ion Cathode Materials project, FutureCat, aims to develop understanding of existing and newly discovered cathode chemistries to deliver improved EV performance, whilst considering sustainability.

Professor Louis Piper, from WMG at the University of Warwick, who led the research explained: “Transitioning to electrification requires integrating advanced materials science into battery processing to develop cheaper, safer, faster and better batteries, which is the focus of our research.”

The battery field is moving to increasing nickel contents in cathodes to meet the Government’s stringent EV 2030+ targets. These roadmaps assume successful strategies in material development to allow cathodes like W-LNO to operate at high voltages without degrading. This work provides the platform towards realising that goal by better understand the redox mechanisms (i.e., the reactions that enable charging/discharging the battery) at high voltage operation.

The study employed advanced x-ray characterisation techniques at the Diamond Light Source in Oxford and at WMG. The team at WMG utilised novel in-house x-ray absorption spectroscopy which enabled researchers to look at the electrode redox process of the battery cathodes after careful disassembly. Researchers were surprised to find that the oxidised oxygen species had the same characteristics as another group of Li-ion battery cathodes, Li-excess transition metal oxides. Reconciling how the same oxidised oxygen environment exists in both conventional and Li-excess cathodes is critical for unlocking how to develop the next generation of cathodes.

Professor Piper adds: “This work highlights how large-scale collaborative fundamental studies are needed even for supposedly ‘known’ systems.”

WMG will be continuing with further studies in this field, supported by the Faraday Institution, for the benefit of cathode battery manufacturers.

A link to the published article can be found here:

https://journals.aps.org/prxenergy/pdf/10.1103/PRXEnergy.2.013005

Researchers at WMG at the University of Warwick, are part of a unique four-way partnership, with Addionics, technology innovation catalyst CPI and James Durrans Group, which will position the UK as a technology hub for global battery development.

Project Constellation is an extension of Project STELLAR which focused on improving battery power and cycle life. Project Constellation takes the research to the next level addressing improvements to battery performance, which will in turn lower development and production costs.

The team at WMG will use its expertise in pilot scale electrode production, cell manufacturing and electrochemical testing to support and de-risk rapid technology screening and accelerate the route to market.

Farid Tariq Ph.D, CTO and Co-founder of Addionics, explains:" Constellation builds on the success of Stellar taking it beyond basic tests and towards industrially relevant scales. We are excited because it provides a strong integration piece of our technology with world leaders in coating and fabrication, and active material fabrication (WMG, CPI, James Durrans) that can show how our very smartly designed and structured current collectors can fit into a viable battery ecosystem and provide benefits from our technology. This is readily transferable knowledge and will push the creation of new methods to overcome modern limitations of batteries and fabrication."

Mark Copley, Chief Engineer in WMG at the University of Warwick’s Electrochemical Materials and Manufacturing team said: “WMG is delighted to be a partner in the CONSTELLATION consortium. Utilising our experience in scaling up new technologies, from lab to pilot line, we feel that we will be able to further the development of Addionics’ current collector technology whilst coupling in Durrans’ graphite and formulation developments, as derived by CPI.

“The project goals fit very well with the ideals of WMG, which is to work collaboratively with industry to deliver high-quality, applied, research and development. We look forward to the results that will be generated through this funded collaborative effort.

Project Constellation is a two year project, funded by the UK Government’s Faraday Institution’s Faraday Battery Challenge Round 5 Innovation.

About the partners

Addionics

Addionics is a next-generation battery technology company revolutionizing battery performance through its chemistry-agnostic Smart 3D Electrode architecture. The company’s scalable, cost-effective manufacturing process combined with its AI-based optimization software significantly improves the performance of any kind of chemistry, achieving batteries with higher energy density, faster charging, and longer lifetime, at low cost. With the mission to accelerate an electrified economy and decarbonized future, Addionics is unlocking the full potential and accelerating the electrification revolution through its drop-in solutions.

CPI

We take great ideas and inventions, and we make them a reality. Born in the North East of England in 2004, CPI is an independent deep tech innovation organisation and a founding member of the High Value Manufacturing Catapult. 

We're a team of intelligent people using advances in science and technology to solve the biggest global challenges in healthcare and sustainability. Through our incredible people and innovation infrastructure, we collaborate with our partners in industry, academia, government, and the investment community to accelerate the development and commercialisation of innovative products.   

Our work ranges from health technologies, advanced drug delivery systems, and medicines manufacturing innovations for multiple modalities including small molecules, biologics, and nucleic acids; to developing sustainable materials for energy storage and packaging, as well as novel food, feed, and nutraceuticals, that are all underpinned by digital technology. We turn the entrepreneurial spirit and radical thinking of our people and partners into incredible impact that makes our world a better place. 

Let’s innovate together: uk-cpi.comLink opens in a new window 

Connect with us: LinkedIn TwitterLink opens in a new window InstagramLink opens in a new window FacebookLink opens in a new window 

James Durrans Group

Long established family owned manufacturing company (1863) based in Penistone near Sheffield but with manufacturing sites across the globe. We provide pro-active solutions to our customer needs. Experts in carbon processing and technology and the manufacture of heat resistant coatings and graphitic dispersions.

www.durransgroup.com

WMG Associate Professor Dr Mel Loveridge, and Principal Engineer Martin Dowson, have authored a special Faraday Insight entitled “Why Batteries Fail and How to Improve Them: Understanding Degradation to Advance Lithium-Ion Battery Performance,” a key consideration as we transition to a fully electric future.

It is part of a collection, of pieces from leading UK battery experts, published by the Faraday Institution. The Faraday Insights are evidence-based assessments of the market, economics, commercial potential, and capabilities for energy storage technologies. The insights are concise briefings that aim to help bridge knowledge gaps across industry, academia, and government.

The briefing addresses key requirements in lifetime, performance and safety needed for LIBs to continue to lead electrification in multiple sectors, and explains why, to achieve this researchers need to better understand – and find ways to mitigate – the many causes of battery degradation.

Read the Insight here: www.faraday.ac.uk/get/insight-10/

Read more about WMG’s Electrochemical Engineering research here: Electrochemical Materials (warwick.ac.uk)

• By 2030 only EV’s will be in production, meaning manufacturers are racing to create a high-energy battery that’s affordable and charges efficiently, but conventional battery cathodes cannot reach the targets of 500Wh/Kg
• Lithium-excess cathodes offer the ability to reach 500Wh/Kg but unlocking their full capacity means understanding how they can store charge at high voltages
• A new X-ray study lead by WMG, University of Warwick has resolved how the metals and oxygen facilitate the charge storage at high voltages

High energy storage batteries for EVs need high capacity battery cathodes. New lithium-excess magnesium-rich cathodes are expected to replace existing nickel-rich cathodes but understanding how the magnesium and oxygen accommodate charge storage at high voltages is critical for their successful adaption. Research led by WMG, University of Warwick in collaboration with U.S. researchers employed a range of X-ray studies to determine that the oxygen ions are facilitating the charge storage rather than the magnesium ions.

Electric vehicles will one day dominate UK roads and are critical for eliminating CO2 emissions, but a major issue car manufacturers face is how to make an affordable long-lasting energy-dense battery that can be charged quickly and efficiently. There is therefore a race to make EV batteries with an energy storage target of 500 Wh/Kg, but these targets are not possible without changing to new cathode materials.

Although progress has continued over the last 10 years to push the performance of state-of-the-art nickel-rich cathodes for EV, the material is unable to provide the energy density needed. To increase the capacity more lithium needs to be used, which means going beyond the ability of nickel to store electron charge.

Lithium-excess magnesium-rich cathodes offer sufficient energy density but to reach ultimately reach energy storage targets of 500Wh/Kg we need to understand how the electron charge is stored in the material. Simply put, is the electron charge stored on the magnesium or oxygen sites.

In the paper, ‘Whither Mn Oxidation in Mn-Rich Alkali-Excess Cathodes?’, published in the Journal ACS Energy Letters today the 17th of February, researchers from WMG, University of Warwick have overcome a significant milestone in understanding of charge storage in lithium-excess magnesium-rich cathodes.

Li-excess compounds that involve conventional and non-conventional redox, conventional refers to metal ions changing their electron density. Reversibly changing the electron density on the oxygen (or oxygen redox) without it forming O2 gas is unconventional redox. Various computational models exist in the literature describing different mechanisms involving both, but careful x-ray studies performed while the battery is cycling (operando) are ultimately required to validate these models.

Researchers between the UK and US, led by WMG at the University of Warwick, performed operando x-ray studies to precisely quantify magnesium and oxygen species at high voltages. They demonstrated how x-ray beams could irreversibly drive highly oxidized magnesium (Mn7+) to trapped O2 gas irreversibly in other materials.

However, by performing careful operando x-ray studies that circumvented beam damage and observe only trace amounts of Mn7+ forming upon charging in Li-excess cathodes during battery cycling.

Professor Louis Piper, from WMG, University of Warwick explains:
“We have ultimately resolved that oxygen rather than metal redox is driving the higher capacity, which means we can now design better strategies to improve cycling and performance for this class of materials.”

ENDS

17 FEBRUARY 2021

NOTES TO EDITORS

High-res images available at:

https://warwick.ac.uk/services/communications/medialibrary/images/february_2021/operando_x-ray_louis_piper.jpg
Caption: Photo of the operando x-ray studies being performed at a Synchrotron facility.
Credit: WMG, University of Warwick

Paper available to view at: https://pubs.acs.org/doi/10.1021/acsenergylett.0c02418

For further information please contact:

Alice Scott
Media Relations Manager – Science
University of Warwick
Tel: +44 (0) 7920 531 221
E-mail: alice.j.scott@warwick.ac.uk

As the inevitable growth of transport electrification continues, the types of batteries that will be used in such vehicles, their charging parameters, infrastructure and timeframes are key considerations that will speed up the transition to electrification.

In the paper, ‘Determining the Limits and Effects of High-Rate Cycling on Lithium Iron Phosphate Cylindrical Cells’ published in and on the cover of the Journal Batteries, researchers from WMG, University of Warwick investigated the impacts on battery cell ageing from high current operation using commercial cells.

They used two tests to establish the maximum current limits before cell failure and applied this maximum current until cell failure. Testing was performed to determine how far cycling parameters could progress beyond the manufacturer’s recommendations.

During testing, current fluxes were increased up to 100 C cycling conditions. Charge and discharge current capabilities were possible at magnitudes of 1.38 and 4.4 times, respectively, more than that specified by the manufacturers’ claims. This increased current was applied for 500 charge-discharge.

However, the application of these currents resulted in a rapid decrease in capacity in the first 60 cycles as well as an increase in resistance. Furthermore, the application of such currents resulted in the increase of cell temperature, during both charge and discharge with natural convection during the rest step cooling the cell. Batteries operate in an optimum temperature range, and any deviations outside this can cause components and chemicals to start decomposing inside them.

They also identified deformation of the “jelly roll” (coiled electrodes and separator) with formation of lithium plating from testing and ageing. These deformations emanate from the centre of the cell in an axial direction towards the outside of the cell, suggesting the core of the cell was the hottest.

Lead Engineer, Justin Holloway, from WMG, University of Warwick comments:

“The testing showed there is a window for operating batteries above manufacturer stated current limits, however, whilst maintaining manufacturer stated voltage limits. We need to ensure that batteries operate in as the safest manner possible, and for an appropriate practical lifetime, which is why the manufacturers have these limits.

“We also identified thermal fatigue as the driving mechanism for jelly roll deformation. With each cycle of charge and discharge, the cell experienced thermal stresses causing deformation of its components. These deformations grew progressively with cycle number, while the jelly roll was constrained mechanically by the rigid outer can and centre pin.

“If convection cooling could be applied to the centre of the cell where the cell was the hottest, these deformations could be mitigated and controlled, allowing the cell to maintain capacity and resistance criteria for longer.”

The researchers would like to thank all involved in this work, including WMG’s High Value Manufacturing Catapult and The Faraday Institution. WMG’s Battery Forensic Group, led by Dr Mel Loveridge is keen to engage with industry and academia alike to grow advances in understanding new materials, battery performance and degradation modes.

ENDS

14 DECEMBER 2020

NOTES TO EDITORS

High-res images available at:
https://warwick.ac.uk/services/communications/medialibrary/images/december_2020/justin_holloway.jpg
Caption: Justin Holloway, from WMG, University of Warwick
Credit: WMG, University of Warwick

Paper available to view at: https://www.mdpi.com/2313-0105/6/4/57/pdf

For further information please contact:

Alice Scott
Media Relations Manager – Science
University of Warwick
Tel: +44 (0) 7920 531 221
E-mail: alice.j.scott@warwick.ac.uk

It is common knowledge in battery manufacturing that many cathode materials are moisture sensitive. However, as the popularity of high nickel-based battery components increases, researchers from WMG, University of Warwick have found that the drier the conditions that these cathodes are stored and processed in, then significant improvement in performance of the battery is gained.

High-Ni (Nickel) batteries are becoming increasingly popular worldwide, with more automotive companies investigating the use of high-Ni batteries for electric vehicles. However, high-Ni cathode materials are prone to reactivity and instability is exposed to humidity, therefore how they are stored in order to offer the best performance is crucial.

In the paper, ‘The effects of Ambient Storage Conditions on the Structural and Electrochemical Properties of NMC-811 Cathodes for Li-ion batteries,’ published in the journal Electrochimica Acta, researchers from WMG, University of Warwick propose the best way to store high-nickel cathodes in order to mitigate premature degradation.

Researchers exposed NMC-811 (high-Ni cathode material) to different temperatures and humidities, then measured the material’s performance and degradation in a battery over a 28 day period, analysing them using a combination of physical, chemical and electrochemical testing. This included high-resolution microscopy to identify the morphological and chemical changes that occurred at the micron and sub-micron scale during the batteries charging and discharging.

The storage conditions included vacuum oven-dried, as exposed (to humidity) and a control measure. Researchers looked for surface impurities, which include carbonates and H₂O, and found there were three processes that can be responsible for impurities, including:

1. Residual impurities emanating from unreacted precursors during synthesis

2. Higher equilibrium coverage of surface carbonates/hydroxides (present to stabilise the surface of Ni-rich materials after the synthesis process)

3. Impurities formed during ambient storage time

They found that in all conditions, (oven dried and as-exposed) showed inferior first discharged specific capacity and cycling performance, compared to the control. However the as-exposed measure showed that after 28 days of ambient moisture exposure the H2O and CO2 react with the Li+ ions in the battery cell, resulting in the formation of lithium carbonate and hydroxide species.

The formation of carbonates and oxides on the surface of NMC-811 contribute to the loss of the electrochemical performance during ageing of the materials, due to the inferior ionic and electronic conductivity, as well as the electrical isolation of the active particles. This means that they can no longer reversibly store lithium ions to convey “charge”. SEM analysis confirmed the inter-granular porosity and micro-cracks on these aggregate particles, following the 28 days of ambient exposure.

They can therefore conclude that the driest conditions, at dew points of around -45 ^oC, are the best for storing AND processing the materials, in order to then produce the best battery performance. Humidity conditions and exposure at junctions along the manufacturing process will cause the materials and components to experience; this results in shorter battery lifespan.

Dr Mel Loveridge from WMG at the University of Warwick comments:

“Whilst moisture is well known to be problematic here, we set about to determine the optimal storage conditions that are required to mitigate unwanted, premature degradation in battery performance. Such measures are critical to improve processing capability, and ultimately maintain performance levels. This is also of relevance to other Ni-rich systems e.g. NCA materials.”

Professor Louis Piper from WMG at the University of Warwick adds:
“Considerable global research effort will continue to focus on these materials, including how to protect their surfaces to eliminate risks of parasitic reactions prior to incorporation into electrodes. In the UK, leading research by the Faraday Institution has a project consortium entirely devoted to unravelling the degradation mechanisms of such industry-relevant materials.”

ENDS

18 NOVEMBER 2020

NOTES TO EDITORS

High-res images available at:
https://warwick.ac.uk/services/communications/medialibrary/images/october_2020/the_effects_of_ambient_air_storage_on_the_surface_stability_of_nmc-811.jpg

(1) Caption: The effects of ambient air storage on the surface of NMC-811

Credit: WMG, University of Warwick

 https://warwick.ac.uk/services/communications/medialibrary/images/october_2020/post-mortem_nmc811_particle.jpg
(2) Caption: a-b) Post-mortem NMC811 particle, with no prior exposure to moist air, analysed by FIB-SIMS, targeting Lithium detection. c-d) Post-mortem NMC811 particle, after 28 days exposure to moist air, analysed by FIB-SIMS, targeting Lithium detection.
Credit: WMG, University of Warwick

https://warwick.ac.uk/services/communications/medialibrary/images/october_2020/schematic.jpg
(3) Caption: Schematic illustration of particle breakdown during charge-discharge of a battery
Credit: WMG, University of Warwick

Paper available to view at: https://www.sciencedirect.com/science/article/pii/S0013468620317515?via%3Dihub

• Lithium (Li)-ion batteries (LIBs) are the electrochemical energy storage systems of choice for a wide variety of applications, however other types of emerging battery technologies are currently on the path to share their dominant position.
• Among them Sodium (Na)-ion batteries (NIBs) have great potential to represent the next generation low cost and environmentally friendly energy storage solution. The diverse key performance indicators required by different applications and the market diversification is the driving force pushing the Na-ion technology closer to the market.
• A team of scientists including WMG at the University of Warwick combined their knowledge and expertise to assess the current status of the Na-ion technology from materials to cell development, offering a realistic comparison of the key performance indicators for NBs and LIBs.

LIBs play a primary role in the transition to a low carbon economy. However, as the market rapidly expands, the environmental and social challenges associated with the mass production of LIBs is triggering large attention toward the search for alternative energy storage solutions based on materials that can be sourced in a sustainable and responsible way. In this scenario, NIBs represent an alternative low cost, sustainable and more environmentally friendly energy storage technology.

In the paper ‘Challenges of today for Na-based batteries of the future: from materials to cell metrics,' published on the 18^th of September 2020 in the Journal of Power Sources, a large team of Na-ion technology expert scientists, led by WMG, at the University of Warwick (UK) analyse the prospect of NIBs taking a spot in the energy storage market. The paper also includes researchers from: Helmholtz Institute Ulm (Germany), College de France (France), Humboldt University Berlin (Germany), Institute for Energy technology (Norway), Université de Picardie Jules Verne (France), University of Bordeaux (France) and CIC energiGUNE (Spain).

Na- based batteries offer a combination of attractive properties. They are low cost, use sustainable precursors and have secure raw material supplies. In addition, they are considered as a drop-in technology which could benefit from the already existing Li-ion batteries manufacturing facilities.

As Li-based systems, Na-based batteries come in different forms, such as Na-ion, Na-all-solid-state-batteries, NaO₂ and Na/S. While the last ones are seen as disruptive future technologies, the Na-ion technology represent an attractive technology almost ready to challenge the Li-ion batteries in specific applications.

Performance metrics are of utmost importance for the SIB technology to ensure a competitive cost per Wh and find a place in the market. In this work, the most promising electrode materials and electrolyte systems have been reviewed and performance metrics from the academic literature have been used to extrapolate full sodium ion cells performance indicators.

Authors indicate that with the ongoing development, the present best materials available for Na-ion cells should allow approaching the energy density of the present generation of Li-ion commercial cells. One of the most important application field for the developed sodium-ion battery prototypes is certainly stationary energy storage systems, where cost and cycle life represent two fundamental parameters. “In this field sodium-ion batteries have the potential to dominate the future market representing the most promising system to fill the gap between energy production and utilization by securing energy supply. However high-power applications in the electrified automotive field are a potential niche field application for NIBs” says Dr Ivana Hasa, Assistant Professor at WMG.

Further technological improvements are needed to increase the performance especially in terms of energy density. Extremely encouraging results have been achieved for the Na-ion technology in a very short time when compared to the Li-ion technology. Technological improvement will be achieved by cell component fabrication/assembly optimization, as occurred in the last thirty years for the LIB technology.

Dr Ivana Hasa, from WMG, University of Warwick comments:

“From an applied research point of view, the future research efforts should be devoted on fundamental research, materials discovery and understanding of the thermodynamic and kinetic processes governing the chemistry of these systems. In addition, the investigation of upscaled Na-ion batteries is of primary importance to obtain realistic data to benchmark the progress of the technology as well as the adoption of a common reporting methodology in the scientific community enabling a fair comparison among performance results.”

Researchers in WMG and the Department of Physics at the University of Warwick have found that asymmetric stresses within electrodes used in certain wearable electronic devices provides an important clue as to how to improve the durability and lifespan of these batteries.

Batteries for medical applications and wearable devices continue to evolve in size and shape, with miniaturisation of Li-ion technologies becoming increasingly popular. However, as the size of the battery shrinks, the fabrication process for composite electrodes and the use of liquid electrolyte is becoming a processing challenge for microfabrication using conventional approaches.

Lithium cobalt oxide LiCoO₂ (LCO) has remained a common choice of cathode for these small formats due to its high voltage platform and energy density. However, following the initial reported performance benefits of LCO, it is known that LCO cells have large impedance issues due to the growth of high surface layer resistance and charge transfer resistance. This can affect how efficiently the battery charges and discharges. There are also ethical and health considerations around the use of the element cobalt. The increasing impedance was thought to be attributable to the growth of a surface layer on both the anode (solid electrolyte interface, SEI) and cathode (cathode electrolyte interface, CEI) due to the reaction between the electrodes and the electrolyte.

However, in the paper “Ageing analysis and asymmetric stress considerations for small format cylindrical cells for wearable electronic devices” published recently in the Journal of Power Sources, the University of Warwick’s WMG and Physics department researchers disassembled these cells. They have found that and the condition of the cathode and anode varied greatly after 500 cycles, as a function of which side of the current collector it was on.

The inward facing cathode (under compression) when rolled into a jelly-roll, develops significant signs of coating delamination from the aluminium foil. On the outward facing cathode side (under tension), however, only a partial delamination was evident and the coating was transferred unto the separator. By contrast, severe delamination was observed on both sides of the anode coating. The inward facing anode side (under compression) showed almost no coating still adherent to the copper foil, compared to the outward facing anode side (under tension). Likewise, the delaminated coating had become adhered to the separator during operation.

Dr Mel Loveridge from WMG, University of Warwick comments:

“It is interesting to note that, for both the cathode and the anode, the delamination is more severe on the electrode coating side that would have been subjected to compression stress, rather than tensile strain. This can be further explained by considering the asymmetric forces in place on either side of double side coated electrodes.”

The research team also carried out electrochemical testing, X-ray photoelectron spectroscopy (XPS), X-ray computed tomography (XCT) and scanning electron microscopy SEM), to reveal the battery’s structural features and changes. They found that it maintains 82% cell capacity after 500 continuous charging and discharging, after which it shows severe delamination due to high bending stress exerted on the cell components. However this seemingly has minimum impact on the electrochemical performance if the coating is sufficiently compressed in the jelly roll with a good electrical contact. After ageing, the surface layers continue to grow, with more LiF found on the cathode and anode.

Their research opens up exciting areas in battery manufacturing to address winding issues for cylindrical cells (especially miniaturised formats). For example, highlighting the need to understand whether there is merit in varying the coating properties on each side of double-sided coating for wound cylindrical cells, in order to improve the mechanical resilience of coatings that have asymmetric stresses exerted on them.

ENDS

25 AUGUST 2020

NOTES TO EDITORS:

Paper available to view: https://www.sciencedirect.com/science/article/abs/pii/S0378775320309307?via%3Dihub

High-res images available at:

https://warwick.ac.uk/services/communications/medialibrary/images/july_2020/wearable_image.jpg
Caption: An image demonstrating the stresses to anodes and cathodes after cycles.
Credit: WMG, University of Warwick

https://warwick.ac.uk/services/communications/medialibrary/images/july_2020/mel_l.jpg
Caption: A diagram of how tensile strain leads to the film cracking
Credit: WMG, University of Warwick

The full research team on the paper were:

Ageing analysis and asymmetric stress considerations for small format cylindrical cells for wearable electronic devices C.C. Tan, Marc Walker, Guillaume Remy, Nadia Kourra, Faduma Maddar, Shaun Dixon, Mark Williams and Mel Loveridge.

For further information please contact:

Alice Scott
Media Relations Manager – Science
University of Warwick
Tel: +44 (0) 7920 531 221
E-mail: alice.j.scott@warwick.ac.uk

Researchers at WMG at the University of Warwick have found that use of inductive charging, whilst highly convenient, risks depleting the life of mobile phones using typical LIBs (Lithium-ion batteries)

Consumers and manufacturers have ramped up their interest in this convenient charging technology, abandoning fiddling with plugs and cables in a favour of just setting the phone directly on a charging base.

Standardisation of charging stations, and inclusion of inductive charging coils in many new smartphones has led to rapidly increasing adoption of the technology. In 2017, 15 automobile models announced the inclusion of consoles within vehicles for inductively charging consumer electronic devices, such as smartphones – and at a much larger scale, many are considering it for charging electric vehicle batteries.

Inductive charging enables a power source to transmit energy across an air gap, without the use of connecting wire but one of the main issues with this mode of charging is the amount of unwanted and potentially damaging heat that can be generated. There are several sources of heat generation associated with any inductive charging system – in both the charger and the device being charged. This additional heating is made worse by the fact that the device and the charging base are in close physical contact, any heat generated in one device may be transferred to the other by simple thermal conduction and convection.

In a smartphone, the power receiving coil is close to the back cover of the phone (which is usually electrically non-conductive) and packaging constraints necessitate placement of the phone’s battery and power electronics in close proximity, with limited opportunities to dissipate heat generated in the phone, or shield the phone from heat generated by the charger. It has been well-documented that batteries age more quickly when stored at elevated temperatures and that exposure to higher temperatures can thus significantly influence the state-of-health (SoH) of batteries over their useful lifetime.

The rule of thumb (or more technically the Arrhenuis equation) is that for most chemical reactions, the reaction rate doubles with each 10 °C rise in temperature. In a battery, the reactions which can occur include the accelerated growth rate of passivating films (a thin inert coating making the surface underneath unreactive) on the cell’s electrodes. This occurs by way of cell redox reactions, which irreversibly increase the internal resistance of the cell, ultimately resulting in performance degradation and failure. A lithium ion battery dwelling above 30 °C is typically considered to be at elevated temperature exposing the battery to risk of a shortened useful life.

Guidelines issued by battery manufacturers also specify that the upper operational temperature range of their products should not surpass the 50−60 °C range to avoid gas generation and catastrophic failure.

These facts led WMG researchers to carry out experiments comparing the temperature rises in normal battery charging by wire with inductive charging. However the WMG were even more interested in inductive charging when the consumer misaligns the phone on the charging base. To compensate for poor alignment of the phone and the charger, inductive charging systems typically increase the transmitter power and/or adjust their operating frequency, which incurs further efficiency losses and increases heat generation.

This misalignment can be a very common occurrence as the actual position of the receiving antenna in the phone is not always intuitive or obvious to the consumer using the phone. The WMG research team therefore also tested phone charging with deliberate misalignment of transmitter and receiver coils.

All three charging methods (wire, aligned inductive and misaligned inductive) were tested with simultaneous charging and thermal imaging over time to generate temperature maps to help quantify the heating effects. The results of those experiments have been published in the journal ACS Energy Letters in an article entitled “Temperature Considerations for Charging Li-Ion Batteries: Inductive versus Mains Charging Modes for Portable Electronic Devices.”

The graphics with this press release illustrates three modes of charging, based on (a) AC mains charging (cable charging) and inductive charging when coils are (b) aligned and (c) misaligned. Panels i and ii show a realistic view of the charging modes with a snapshot of the thermal maps of the phone after 50 min of charging. Regardless of the mode of charging, the right edge of the phone showed a higher rate of increase in temperature than other areas of the phone and remained higher throughout the charging process. A CT scan of the phone showed that this hotspot is where the motherboard is located In the case of the phone charged with conventional mains power, the maximum average temperature reached within 3 hours of charging did not exceed 27 °C.

In contrast this for the phone charged by aligned inductive charging, the temperature peaked at 30.5 °C but gradually reduced for the latter half of the charging period. This is similar to the maximum average temperature observed during misaligned inductive charging.

In the case of misaligned inductive charging, the peak temperature was of similar magnitude (30.5 °C) but this temperature was reached sooner and persisted for much longer at this level (125 minutes versus 55 minutes for properly aligned charging).

Also noteworthy was the fact that the maximum input power to the charging base was greater in the test where the phone was misaligned (11W) than the well-aligned phone (9.5 W). This is due to the charging system increasing the transmitter power under misalignment in order to maintain target input power to the device. The maximum average temperature of the charging base while charging under misalignment reached 35.3 °C, two degrees higher than the temperature detected when the phone was aligned, which achieved 33 °C. This is symptomatic of deterioration in system efficiency, with additional heat generation attributable to power electronics losses and eddy currents.

The researchers do note that future approaches to inductive charging design can diminish these transfer losses, and thus reduce heating, by using ultrathin coils, higher frequencies, and optimized drive electronics to provide chargers and receivers that are compact and more efficient and can be integrated into mobile devices or batteries with minimal change.

In conclusion, the research team found that inductive charging, whilst convenient, will likely lead to a reduction in the life of the mobile phone battery. For many users, this degradation may be an acceptable price for the convenience of charging, but for those wishing to eke out the longest life from their phone, cable charging is still recommended.

ENDS

26 JUNE 2019

NOTES FOR EDITORS

While one specific model of mobile phone was used to conduct the tests the issues raised obviously apply to all phones or portable devices now or in the future that seek to use inductive charging.

High-res image available at: https://warwick.ac.uk/services/communications/medialibrary/images/june2019/iphone_charging_mode_2.jpg 

Credit: WMG, University of Warwick

Paper available to view at: https://pubs.acs.org/doi/10.1021/acsenergylett.9b00663

List of Authors (all WMG) include:

Melanie. J. Loveridge

Chaou C. Tan

Faduma M. Maddar

Guillame Remy

Mike Abbott

Shaun Dixon

Richard McMahon

Ollie Curnick

Mark Ellis

Mike Lain

Anup Barai

Mark Amor-Segan

Rohit Bhagat

Dave Greenwood