By ATN
Author: Dr Christian Korte, Head of Software and Engineering, Breathe Battery Technologies
Even with the rollout of ultra-fast charging stations, current electric vehicle charging software is not designed to maximise the benefits. The adoption of model-based control enables vehicle manufacturers to charge faster without compromising battery durability or safety, helping to overcome one of the main barriers to ownership
There is no doubt that electric vehicles (EVs) are essential for a cleaner, more sustainable future, and the International Energy Agency forecasts that they will cut the world’s daily oil consumption by almost 6 million barrels by the end of this decade1. But even in pioneering e-mobility states such as California, EVs accounted for only 22% of new registrations so far this year, and just 8% in the US as a whole2.
The cost of EVs is often cited as a reason why consumers are hesitant to make the switch. Lack of confidence in public charging infrastructure is another. Billions of dollars are being invested to massively increase the number of chargers worldwide, and this is clearly essential to winning over EV sceptics, but delivering a good charging experience is something else altogether.
The definition of ‘good’ will be as varied as consumers’ views on what constitutes a ‘good’ EV, but it’s a safe bet that nobody wants to spend any longer plugged in to a charge point that they really have to. This is borne-out by a McKinsey study that found that 42% of people rated charging speed as their most important consideration when selecting a public charge point, ranking ahead of cost, reliability, and availability3.
Since many navigation systems enable the driver to search for charge points based on power, it’s easy to find one that matches their vehicle’s rating. But given that many charge points show the charging power that’s actually being delivered throughout the session, they can be confused, annoyed even, if this doesn’t match the maximum figure quoted in the brochure. However, very few read the small print about how this can be affected by the age of the vehicle, the condition of the battery, or the ambient temperature – and so they are often left disappointed at their charging experience.
Even under ideal real-world conditions the battery won’t charge at its maximum rate for long, regardless of whether that’s 100kW, 200kW or 350kW. Consumers often believe there must be a fault, but in fact this is deliberate: the stepped charging profile within the battery management system (BMS) is trying to balance power against battery safety and durability. Like most engineering problems, the solution is a very complex trade-off, and, understandably, vehicle manufacturers (OEMs) tend to be conservative. At Breathe, it’s a challenge we’ve been studying for years and believe that we can push the charging process closer to the technical limits without compromising these key attributes.
Typically, the software within the BMS uses look-up tables that map three key parameters to control the charging process: battery temperature, state of charge and state of health – an approach analogous to the time-proven method employed for combustion engine ECUs. It can take many months and years of development and testing across different battery sample stages to create those look-up tables, but the end result simply doesn’t push the cells as far as they can go. This is to prevent unwanted processes taking place during fast charging that will degrade them over time.
Chief among these is lithium plating, which results in lithium building up on the anode as a result of the high currents seen during fast charging. Symptoms include increased internal resistance, which increases charge times, reduces discharge rates – resulting in lower vehicle performance because motors can’t deliver maximum power, and reduces energy storage capacity, resulting in less range. Eventually, the formation of lithium dendrites can damage the separator and result in short circuits and even thermal runaway.
Look-up tables are simple, robust, and widely-used, but they’re not intelligent and can’t always adapt the charging process – either to suit the conditions the first time the vehicle is plugged in, or as the battery ages through useage and time. So not only do they not maximise the use of the energy stored in the cells, but their fixed values can’t track the gradual decline in state-of-health, resulting in accelerated ageing – a paradoxical result. This is not only inherently wasteful – the battery represents as much as 40% of an EV’s total cost4 – it is, quite literally, unsustainable.
We want to deliver the best possible charging experience throughout the EV’s life while at the same time maximising the value of the materials within each cell, both from a cost- and resource perspective. So we developed a software solution that has a patented physics-based model at its core: it uses the same inputs as the look-up tables, but the similarities end there because running in real-time and leveraging closed-loop control allows us to accurately estimate the cells’ electrochemical state.
This level of understanding enables us to narrow the gap between actual performance and the technical limit without initiating lithium plating, even in very cold weather. Just as importantly, we can deliver this advantage from the production line through to end-of-life because the model continuously adapts the charging process as the battery ages, delivering not only a better charging experience for the customer, but also a more robust battery pack and reduced warranty costs for the OEM. Moreover, the model can be parametrized to suit each OEM’s requirements in as little as six weeks, contributing to reduced development timescales and cost, and faster time-to-market – this is becoming critical in an increasingly competitive global EV market.
With the advent of the software-defined vehicle, it will become essential for EVs to offer truly software-defined batteries. Only in this way will the charging experience meet ever-more demanding expectations and help overcome the barriers to widespread EV adoption – charging speed being chief among them. Given that a consumer typically spends just two minutes filling up at the gas pump5, OEMs need to do everything possible to narrow the gap when EVs are plugged in to the charge point: replacing look-up tables with our physics-based models will help them do that.
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1 https://www.iea.org/energy-system/transport/electric-vehicles
2 https://www.cncda.org/wp-content/uploads/Cal-Covering-3Q-24.pdf
4 https://global.honda/en/sustainability/integratedreport/business-strategy/
5 https://www.api.org/oil-and-natural-gas/consumer-information/consumer-resources/staying-safe-pump
