A second life for electric vehicle (EV) batteries

At the ICT Spring Conference held in Meriden earlier this year, I gave a presentation on the re-use and recycling opportunities for electric vehicle batteries. While it was not directly related to printed circuit boards, the implications and challenges of producing high performance control and monitoring circuitry that can be built into the expensive and complex battery assemblies are clear; batteries must perform reliably and optimally in harsh environments for many years. This article builds on one aspect of my Meriden presentation and it covers the possibility of using end of first life electric vehicle batteries in secondary applications before they are recycled.

Section through a Nissan Leaf showing the Lithium-ion battery pack (Source: Tennen-Gas - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8249799)

The transition to electric transport is being driven by the need to address important issues such as global warming. Consequently, it is vital that the maximum benefits of battery propulsion are utilised and they include optimising activities such as charging and discharging throughout the whole life cycle of the batteries used in electric vehicles. From a sustainability perspective, one key contribution can be made by extracting as much use as possible from an EV battery before it reaches the end of its life and is recycled to make new batteries. This makes even more sense when the numbers of batteries becoming available is taken into account. It has been predicted that, by as soon as 2025, there will be around 3.4 million of these batteries available globally and that by 2040, approximately 560 million electric vehicles will be in existence.

For a typical electric vehicle, the battery life may be up to ten years, yet there could be several more years of further use potential in secondary applications. Thus, when the performance of an EV battery has dropped to the point where it is no longer suitable for use in a vehicle, it should not mean that it is automatically consigned to recycling/materials recovery. Although it will have reduced performance, it is also possible to identify less-demanding uses, where the lower capacity is not a significant issue. Extending their lifetimes makes batteries more sustainable and goes some way to adopting an enhanced circular economy approach; it reduces demand for new batteries, thereby reducing the negative impacts of battery production. Indeed, the idea of encouraging the secondary use of ex-EV batteries is so important that the subject has been taken up by the European Commission. The EC has reached an innovation agreement with several European manufacturers to adopt the objective of promoting the reuse of lithium-ion batteries before they are subsequently recycled.

An important specific example of one of these uses for second life batteries is in energy storage and supply balancing at the domestic level. Additionally, second life batteries are now being used for energy storage directly linked to the enhanced charge management of electric vehicles in an attempt to reduce demand at peak times, thus preventing potential overloads on electricity supply grids. There are already a number of products commercially available for energy storage, including ‘Offgen’ from Aceleron, ‘PowerWall 2’ from Tesla and the ‘Powervault 3’ from Powervault.

An Aceleron Offgen all-in-one energy storage solution suitable for residential or commercial use (courtesy Aceleron Ltd)

The ‘Offgen’ and ‘Powervault 3’ battery storage units are both designed and assembled in the UK and are specifically aimed at the storage of solar or off-peak electricity in residential and commercial buildings. The company Powervault found that, by using lithium-ion batteries recovered from Renault EVs instead of new ones, it was possible to reduce the cost of one of its smart battery units by 25%. The Powervault 3 is available as the greener Powervault 3 eco version, which uses recovered and tested second life batteries. Outside the UK, there have been numerous other examples of recovered batteries being reused to store electricity. For example, a second-life energy storage system was developed by a team at the University of California’s Davis Green Technology Laboratory. Approximately fifteen ex-Nissan Leaf battery packs were assembled in a shipping container to give a unit with a 300 kWh capacity. This was used as a power source to reduce the peak energy demand and carbon footprint of a winery, brewery and food processing complex. By finding secondary uses like this, it is also possible to reduce overall energy costs, thus providing benefits to both consumers and electricity providers through renewable energy integration and regulation of energy management.

However, it should be noted that only some energy storage products use second life lithium-ion batteries, as manufacturers often prefer to use brand new cells. Using second life batteries is potentially a way of offering a product at a reduced price compared to the same model using new batteries, but there may also be potential longer-term reliability issues and thus shorter warranties. Tesla prefers to directly recycle its batteries to make new ones and does not use ex-EV batteries in its PowerWall products. The reasoning is that an EV battery will reach end of first life after around 8 to 10 years. By this time, Tesla suggest that both the battery capacity and pricing will not be comparable with the latest technology, i.e. it will be more cost effective to use new batteries.

Although there will undoubtedly be a growing demand for battery-based energy storage systems, there are still some questions about the overall benefits of using second life ex-EV batteries, as highlighted by Tesla. In order to be able to reuse EV batteries in second life applications, it is necessary to have detailed information about the condition of each battery and this requires a level of testing that adds to the costs. If such information could be recorded via, for example, the original battery management system and by using more modular battery management approaches in the new units, this might become less of an issue. There are also broader concerns about the overall cost-benefit of using battery-based storage at the consumer/domestic level. The situation is rather complex, as it depends on a number of variables including the cost of power from conventional suppliers via an electricity grid. Using renewables such as solar and battery storage can be significantly more expensive, so it is probably likely to be more of a benefit to off-grid users, or those living in remoter areas, at least initially.

While there is clearly a need for more energy storage capacity, especially as the shift to renewable energy expands, and as the development of more intermittent sources of energy accelerates, the area is relatively new and will need considerable support until it is better established. Second life batteries could provide a lower cost option compared to new batteries. It was, therefore, disappointing to see that, according to the European Association for Storage of Energy (EASE), Europe’s energy storage growth activity was reduced during 2019 due to a slowdown in large-scale storage schemes for energy from renewable sources. The downturn was particularly related to projects that connected directly to energy grids, and which were designed to store renewable energy when solar and wind generation was less available. At the time of writing, there was another negative factor in the form of the Covid-19 pandemic. Depending on its duration and overall impact on the global economy, it seems likely that it will further reduce the implementation of government policies aimed at supporting energy from renewable sources and thus result in fewer battery installations, at least in the short term.

Nevertheless, although the situation is rapidly evolving, it is clear that there are circular economy and sustainability benefits to keeping former EV batteries in use for as long as possible. There are various less-demanding applications that can utilise ex-vehicle batteries for a number of additional years after first use and before they need to be recycled. However, as with the whole story around the EV-battery lifecycle, the situation is complex; there are even those who are testing and reusing EV batteries in vehicular applications, i.e. for lower cost replacement batteries to keep older electric vehicles on the road. It will be interesting to see how the opportunity develops over the next twenty years as battery production, use and the need for recycling increase dramatically.

Example of part of a lithium-ion EV battery back and control ancillaries (© HSSMI)

While the potential to reuse EV batteries is important from an environmental and sustainability perspective, it might be less immediately clear what relevance this has to the electronics and printed circuit board industries. However, if one considers the construction of an electric vehicle battery, it soon becomes obvious that there are several critical key electronic assemblies such as the battery management system, which acts rather like a brain, controlling and optimising the performance of the battery under widely varying operating and recharging conditions. If batteries are to be used for periods of fifteen years or more, it is essential that their electronics have high reliability. A car’s battery management system must be able to reliably and efficiently control these high-voltage battery packs, carefully balancing the voltages of individual cells, or groups of cells, while also monitoring their performance. There is also a need for control and monitoring electronics for individual groups of cells within the battery pack. This is typically achieved with what are known as block monitoring boards.  Groups of cells need to be monitored and kept in balance with each other. These boards are able to monitor the voltage and temperature, both of individual blocks of cells and the inter-block interconnection temperatures. The block monitoring boards also provide an additional safety feature in terms of identifying problems before they can become serious.

Overall, these sophisticated electronics assemblies must be able to operate reliably and accurately under what are considered harsh conditions, including exposure to mechanical shocks and vibrations and over a range of temperatures. All this has to be achieved with circuitry and electronics that has to be fitted into a very limited space, close to the batteries and where there is likely to be a good deal of thermal cycling. The electronics, therefore, need to have high reliability over what is likely to be an extended service life. The provision of these high reliability components will thus be the key to optimised battery performance and battery longevity. How this is achieved is beyond the scope of this article, but it could be covered in more detail in a future one. For now, the key message is that there is a real opportunity to extend the operational lifetimes of electric vehicle batteries well beyond the point where they are no longer suitable for use in the cars themselves. By using them in secondary energy storage applications it is possible to maximise their utility before they are consigned to recycling, thereby reducing their environmental impacts and enabling the EV battery industry to be more sustainable. Secondary use of EV batteries in energy storage could play a major role in helping to shape the future of our electricity generation, distribution and use.

 Written by Martin Goosey, Envaqua Research Ltd.