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Full article published in Vol 13 of E-mobility Technology International.
Article by Dr. Kai-Philipp Kairies, CEO, ACCURE Battery Intelligence
Batteries are at the heart of our energy and mobility future. But with the ever-increasing numbers of deployed battery packs around the world, we also see more incidents of failing systems – from burning electric scooters in apartment buildings in New York City to a series of electric bus fires in Paris and London. So, what are our options to prevent critical failures and make batteries—and clean energy—as safe as possible?
The financial risks associated with faulty electric vehicle (EV) batteries can be derived from two major recalls that happened after a series of battery fires in 2020 and 2021. In both cases, batteries from LG went into thermal runaway during orafter charging:
Hyundai first tried to fix the battery issue with a software update for the battery management system. When an updated Kona EV caught fire in January 2021, Hyundai issued a general recall of all its 76,000 Kona electric vehicles and 6,000 IONIQ models and electric buses that use battery cells made by LG Chem. The recall ended up costing Hyundai US$900 million.
General Motors (GM) tried two iterations of software updates but was unable to prevent more battery fires, among others in Virginia and Vermont, U.S. After that, GM told customers to park their EVs outside and not charge them unattended, before finally issuing a formal recall a week later. The recall became the most expensive recall ever on a per-vehicle basis and eventually led LG to compensate GM over US$1.9 billion.
So, what are the options to make batteries safer and to reduce financial risk? Generally speaking, there are three main areas:
1. Production quality
2. System design
3. Battery analytics
To operate safely, batteries need to be produced with the utmost care and precision, from processing active materials to manufacturing the cells to assembling the pack. Any production defect can lead to unexpected (and sometimes critical) behavior years later.
The only solution to control manufacturing defects is rigorous quality management from incoming goods control to end of line testing. But there are two major challenges: for one,most mid-stream companies in the EV space have neither the full information about, nor the ability to impact the quality of the cells and packs they buy. On the contrary, in today’s market, the sheer ability to buy batteries from a supplier weighs heavier than any quality management (QM) certification. On top of that, even the most rigorous quality management will never catch 100% of the failures.
Battery systems are equipped with several layers of protection meant to keep the battery in its intended window of operation, shield it from external harm, and minimize the impact of asingle-cell failure.
Passive safety components: From sturdy packaging to withstand crashes to hermetic sealing against water inflow, these passive safety components are last resorts to minimize the damage from critical situations that are already happening. They generally cannot prevent safety incidents.
Battery management system (BMS): BMSs are the brain of every Lithium-ion battery (LIB) system. They make sure a cell is not over or undercharged and they bring basic state estimation functionalities with them, including state of charge (SOC) and state of health (SOH). However, BMSs also have noticeable shortcomings: they only see the cells within the corresponding battery pack, have little to no access to historic data or data from other battery systems, and they have limited computing power.
The limitation of BMS safety algorithms was highly visible in the attempts of Hyundai and GM to solve their safety problems with a firmware update (in other words a BMS software update). While it’s possible to locally scan the sensor data for anomalies, such as rapidly changing impedances or sudden voltage drops, as precursors for thermal events, the lack of baseline data and ongoing comparisons to similar systems strongly limits the value of such analyses.
A proven strategy to prevent critical failures and improve battery safety is the use of cloud-based analytics. By detecting critical faults at an early stage using more sophisticated and modern analytical methods than available in any battery management system, automobile manufacturers and electric car owners can act before any damage is done. Diagnostics based on existing field data streams can be applied to any LIB system without the need for any product modification.
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There are many ways cloud-based analytics canreveal safety-critical battery behavior long before the battery management system does. In fact, there are at least 20 safety indicators a robust battery analytics solution should track daily. They are based on electrical, thermal and mechanistic models empowered by machine learning.
The algorithms mirror electrochemical relationships and processes, revealing insights about the internal states of the battery. For example, the figure below shows ananalysis of the loss of lithium inventory, a process closely linked to lithium plating. The yellow dotted line indicates a warning period recognized by ACCURE’s Safety Manager battery analytics solution. The redline denotes a severe state.
Lithium plating, where metallic lithium gathers on the outside of the anode, has been a major headache in the LIB world for decades. It mainly occurs when a battery is charged with high current rates at low temperatures, but can also happen under “normal” operating conditions. Not only does it quickly degrade a battery’s capacity, it can also become a safety threat by forming metallic dendrites and triggering side reactions such as gassing. It manifests itself in a decrease of the lithium inventory which is no longer available for the main reaction. Cloud-based safety algorithms, among other things, must closely track the loss of active lithium to accurately predict safety critical events.
In this way and by quantifying other safety indicators, ACCURE’s Safety Manager has already prevented more than 50 fires.
There are many hurdles we need to overcome for electric vehicles to become substantially safer. Cloud-based battery analytics ensures that public opinion about EV safety does not become one more hurdle to overcome. Instead, the benefits of cloud-based software analyzing operational battery data extend beyond an additional safety layer and into reducing business risk and supply chain costs, accelerating innovation, and increasing the sustainability of batteries. There’s a lot more to come out of this exciting field!
Read the full article published in Vol. 13 of E-mobility Technology International on pages 64 - 68.