Predicting battery life is a key goal for EV manufacturers, but with so many variables it’s not easy. Here, two of the partners in the innovative REDTOP project tell us about the secrets it revealed
REDTOP (real-time electrical digital twin operating platform) is a collaboration between Silver Power Systems (SPS), Imperial College, the London Electric Vehicle Company (LEVC) and JSCA (the R&D division of the Watt Electric Vehicle Company) in a real-world EV trial.
Holding 20 patents, SPS founder and CTO Pete Bishop has worked across various sectors, from EVs and UAVs to telecoms. He’s an advisor to the UK Cabinet Office as well as sitting on the Faraday Institution Battery Modelling Expert Panel.
Programme manager Liam Mifsud joined the company in 2018, the year it was founded. He has over 25 years’ experience within the telecommunications and renewable energy sectors. He’s responsible for program operations, overseeing the company’s development of battery management and telematics systems. They met while at PowerOasis, also founded by Bishop. Here they take turns to answer, Bishop first:
What EXACTLY Was REDTOP FOR?
Until recently, predicting battery lifespan has been difficult. While digital models of EV batteries have been created, they have lacked accurate real-world data to back them up. What’s more, not all batteries are born equal, and not all batteries are treated equally throughout their life, whether that’s degrading at different rates, or being subject to different drivers and charging routines. This further underlines the need for real-world data to be combined with machine learning-based predictive technology.
Over a nine-month period, our REDTOP automotive research programme has sought to bring about a step change in battery understanding by creating the world’s most advanced battery digital twin – a highly sophisticated virtual model that’s linked to a real battery.
Part-funded by The Advanced Propulsion Centre UK (APC), the project allowed us to join forces on a real-world EV trial.
Since January 2021, 50 LEVC TX electric taxis and two new EV sports cars from the Watt EV Company have collectively travelled over 645,000km as part of the programme. Each vehicle was fitted with one of our data-collecting IoT devices, which communicated with EV-OPS, our cloud-based software.
What Do You Mean, Not All Batteries Are Born Equal?
Firstly, they are the product of manufacturing processes and due to inherent variability in raw materials specifications, not all batteries are exactly identical. This means that they may test equal at the beginning of their life but may degrade in different ways due to material impurities or manufacturing inconsistencies.
Secondly, the way the battery is operated is a function of the algorithms used in the battery management system and powertrain control units. Then, after first use, batteries degrade based on multiple criteria such as temperature, storage, charge, etc, so two cars of similar age with a similar battery type can have very different performances. That is why we believe that the use of collected battery data and predictive modelling is the only way to accurately tell the state of the health of the battery.
Looking forward, based on recent trajectory and increased battery knowledge we can expect batteries to have higher capacities, increased capabilities for faster charging and also provide a longer lifetime. We can also expect advances in the battery management systems to enhance a battery’s self-management and reporting capability.
What Are The Limits Of Current Models?
Batteries are complex electrochemical devices whose performance is dependent on how they are operated. Rates of charge and discharge, temperature and the state of charge at which they are stored, as well as age, all affect their performance to varying degrees. Thus the limitation of simple representative models – however accurate they are in representing the electrical and physical aspects of a battery – is that they cannot model the effects of the highly variable operating environment of the EV battery.
Combining accurate physics-based battery models with data derived from batteries in use – the digital twin – offers the opportunity to address this challenge. A digital twin can act as a repository for the data collected over a battery’s life (more accurately representing its current state), and be used to predict future performance through its ability to model the effects of battery cycles.
Advances in sensor, software and cloud technologies have enabled a variety of digital twin models of products and services to be cost-effectively developed. These are widely used in industries such as manufacturing, building management and engineering to reduce production and lifetime operating costs.
Besides applications in battery management, the digital twin approach offers benefits primarily at the battery and vehicle design stages, where modelling and simulation, based on collected data from real vehicles, can be used to optimise battery designs and reduce new product development time.
Battery and vehicle designers can model how a battery will perform under typical operating conditions and driver behaviours, and optimise designs accordingly without having to resort to time-consuming field tests. This offers the opportunity to reduce design costs and time to market with new products.
What Happens To Batteries Over Time?
Lithium ion batteries in EVs are made up of many cells in series and parallel combinations. These can be relatively small cells, such as the ubiquitous 18650 used in laptops and many consumer products, or much larger prismatic cells, typically the size of a telephone directory. There could be 96 of the latter in series to make up a 400V battery. Batteries are often subdivided into lower voltage modules, each with their own battery management system.
Lithium ions migrate through the electrolyte to the negative electrode when the battery is charging up, and when discharging they move back across the electrolyte to the anode. Electrons move in the external circuit in the opposite direction to the ions.
The process is fully reversible but, over time, a number of different degradation effects reduce the capacity of the battery. Some of the active lithium inventory is lost, while its internal resistance also increases as the solid electrolyte interface between the electrodes and the electrolyte typically increases in thickness.
During both charge and discharge the internal resistance of the battery causes heat generation within the cells. Excessive heat is detrimental to the electrochemistry of the cell, so the battery therefore requires an active cooling system to maintain the overall, optimum pack temperature. Crucially, this will minimise any differences in temperature across the pack because any imbalance can lead to more rapid degradation.
What About Other Materials?
Lithium ion battery development has been, and will continue to be, an iterative process. We don’t see any great revolutionary change coming, just a continued steady improvement in power and energy densities as manufacturers develop and work with new anode and cathode materials, as well as optimising cell construction.
Solid-state batteries offer potential for improvement in both energy and power density, and also – significantly – cell safety due to the removal of the commonly used flammable liquid electrolyte. Solid-state cells have been successfully demonstrated on a small scale but it remains a challenge to scale up their construction to larger-format cells.
Enormous amounts of funding are being applied to battery research and development internationally, with other battery chemistries being considered such as lithium silicon, lithium sulphur, lithium metal, sodium ion and zinc air batteries. However, it remains to be seen if these can offer improved electrical performance combined with longevity, while being cost effectively manufactured commercially at scale.
How Did You Gather The Data?
There are three principal components of the Silver Power Systems set-up: the in-car controller, the transmission channel and algorithms used, and the back-end server infrastructure to receive, store and present the data for analysis.
The SPS eLite controller, installed in the vehicle, captures data from an interface with the vehicle’s internal system, either by direct connection to the vehicle CANbus or via the OBD2 port, GPS data and onboard accelerometer data, and any discrete sensor inputs. The data-transmission interval can be set by the user, from 1 second to 1 day, but is typically set to 5 minutes.
Data is transmitted via an onboard modem to a cloud server using AES256-based encryption for data in transit. The transmission algorithm includes robust handshaking to ensure reliable delivery, while the eLite controller has onboard storage so that if the IoT link is unavailable, data is stored for later transmission.
We use multi-network IoT SIMs for data transmission, ensuring that the best possible network coverage is achieved. The system also includes a return channel which allows configuration changes and software updates to be performed over-the-air (OTA). It would also allow commands to be sent to the vehicle or the battery management system, although this is not enabled for any of the systems running today. In the future, it could be used to set new charging algorithms or battery usage limits, to enhance performance based on the battery’s state of health.
The cloud infrastructure to receive, store and analyse the data is an Amazon Web Services (AWS) infrastructure, which offers security, reliability and flexibility to scale as data volumes grow. From the AWS servers, SPS offers browser-based viewing of the operational data (status of the car and battery in real-time) and online analytics of historic data via a Microsoft Power BI reporting engine. As well as insights on battery status and usage, the analysis reports allow correlation with other captured data such as charging points, types of chargers used, driver behaviour, operation in and outside of low emission zones and so on.
While the data is currently analysed retrospectively, the capability exists to integrate with future connected autonomous vehicle (CAV) systems.
What Are The Benefits For Oems And Owners?
OEMs that make EVs could benefit from this by getting rich data for R&D. Our embedded device also enables them to offer customer battery data services once the vehicle is sold.
When fleets buy new EVs, we believe they don’t currently have enough insight around the present health and future degradation of the batteries. We want to change that because the battery is the most expensive component in an EV and its state of health is directly linked to the fleet’s value.
There are two key groups that could benefit. Firstly, operators, like utility companies or parcel distributors, may be interested in having a complete picture of battery usage/health across the fleet and the ability to geofence/prove zero emission status in urban areas. Secondly, owners, like Arval or ALD – these companies own the vehicle and the battery and are concerned with the residual value (RV) of the vehicle. They could install our unit in their brand-new vehicles and get the battery ledger data throughout the life of the vehicle. This more accurately informs them of the value of the vehicle and the capability of its battery for future users.
For private owners, the technology can offer a total picture of battery activity for their EVs. This can be used to identify problems with batteries (whether performance or charging capability) in the short term and, in the long term, build up a complete picture of battery health. Just like with fleet owners, the data is also useful for individual vehicle owners looking to sell their EVs. If the vehicle has been driven, charged and generally looked after responsibly, this will be evident in the health of the battery and the battery ledger – leading to a fairer sale price.
What’s Your Advice For OTHERS In This Area?
As batteries become ubiquitous across many ground transportation methods – from passenger vehicles to commercial vehicles and beyond – we can expect greater industry and consumer focus on the environmental impact, raw material sourcing, production processes and also their second-life after they are no longer usable in the EV.
The IEA estimated last year that 100-120 GWh of electric vehicle battery capacity will be retired by 2030, a volume roughly equivalent to current global annual battery production. The battery design industry therefore needs to look beyond the pure performance targets of reducing weight, increasing range and cycle life, but also to the wider impact on environment and society. These considerations are much more efficiently addressed at the design stage.
Can Sustainability Be Improved?
Battery recycling is clearly a huge challenge for the industry as we start to see large numbers of end-of-life batteries coming from vehicles. There is a lot of potential for batteries, or cells from batteries, to have a second-life in less demanding applications, but the work to characterise the cells and the batteries is currently very labour intensive. This can result in very significant costs, making second-life batteries uncompetitive cost-wise against first-life ones.
We will need to see dramatic improvements in the ability to quickly and cheaply analyse cells and modules coming out of vehicles to assess the suitability of their components for second-life applications. One way that we are helping is to use our EV-OPS platform to record a ledger of the battery’s operation during its first-life application in the vehicle, which enables rapid assessment of the battery’s condition and suitability for second-life applications without further testing being needed.
Another important consideration is the safety of lithium ion cells once they start to degrade significantly – this is an area of some research at the moment. Cells that are not suitable for second-life applications will need to be reprocessed to extract the materials from them for reuse in the manufacturing of new cells. This will require the establishing of large automated facilities to process the expected volumes of material and create a circular economy.
Do Hybrids Differ?
Batteries in hybrids are scaled-down versions of those in pure electric vehicles. If we discount the interim light hybrid solutions (which typically use low-voltage batteries) and consider those vehicles that perhaps would be considered as true hybrids or range extenders, then the electric powertrain in a hybrid vehicle is similar to a pure EV. However, the battery capacity is smaller as it is only used when the vehicle is travelling slowly or to supplement the performance of the engine for acceleration. One of the big advantages of hybrid vehicles is the ability to capture energy that would otherwise be lost during braking and it is this, combined with the ability to operate the engine at its most efficient point, which gives the overall fuel savings and emissions reductions.
The batteries in fuel cell vehicles are very similar to those used in hybrid vehicles. The fuel cell provides the source of electrical energy to drive the vehicle, while the battery acts as a buffer to provide higher power output for acceleration and energy capture for regenerative braking. As in the case of a hybrid, the battery capacity is much smaller than in a pure electric vehicle but the technology and construction is very similar.
What Does This Mean For Other Sectors?
Silver Power Systems has been closely involved in the development of two electric aircraft already. They were both solar powered and designed to fly in the stratosphere for long durations.
We designed the battery control systems, the powertrain control and the associated ground station.
The batteries are the single greatest limiting factor on the aircraft’s performance, in terms of their energy density directly impacting the airframe design and payload capability, as well as their cycle life impacting the overall mission length.
Even with the considerable improvements in lithium ion batteries over the last few years, their energy density remains a long way behind hydrocarbon fuels – and probably always will do. For this reason we see electric aircraft being limited to short-range inner-city type services rather than long haul.
Another challenge this will present is the impact on turnaround times on the ground while aircraft are being recharged, and the provision of the necessary high-power electricity supplies to achieve this.
Hybridisation of battery systems with conventional engines can offer benefits in overall aircraft efficiency where the batteries are used to avoid running aircraft engines for ancillary power on the ground and to assist high power requirements, for example during take-off.
As battery technologies continue to improve, we expect to see more electric aircraft developments including in the vertical take-off and landing (VTOL) transport niche, as well as conventional fixed-wing aircraft.
How Will The UK Reach Net Zero By 2050?
The challenges to widespread electric vehicle take-up talked about in the industry over the past few years have included lack of charging infrastructure, affordability of vehicles and the resulting slow adoption rates by private users and fleet owners.
Data from Zapmap shows that between the end of 2016 and 2020 there was an increase of 220% in the number of public chargers, and this figure continues to rise in line with previous growth this year.
As long as major OEMs continue to produce EVs, the amount and distribution of chargers will continue to grow, alleviating EV owners’ range anxiety.
The UK government recently said that it will invest £620 million in grants for electric vehicles and street charging points, which is a further step forward: it will make EVs more affordable and public charging more convenient, two hurdles that consumers need to overcome before EV adoption becomes mainstream.
From a battery point of view, we think in future the focus will shift to real performance of EV batteries compared with manufacturers’ predictions, and the lifetime environmental impact of batteries. This will become an important hurdle to overcome on the journey to electrification of vehicle transport, supporting the achievement of Net Zero targets.
It will be critical for the industry to publish real, accurate statistics on actual battery performance, and to have the data available to manage end-of-EV-life batteries into a second-life or recycling.