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Charging Forward: How Calorimetry Drives EV Battery Innovation

Electric vehicle plugged in to charge.
Credit: iStock
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The recent surge in the use of electric vehicles (EVs), led by the introduction of global environmental policies to phase out fossil fuel-powered vehicles, is driving innovation in battery technology, with a demand for larger batteries, that last longer, with faster charging time, whilst remaining safe to use. However, this increase in battery-powered devices has led to frequent dangerous incidents involving EVs as the market challenges for better performance. For example, in September 2023, a fire at Sydney Airport destroyed five cars, with investigation results pointing to a car lithium-ion battery (LIB), while in July of the same year, a ship transporting over 3,000 cars caught fire off the coast of the Netherlands as a result of another LIB fire. But what is it about LIBs that makes them so susceptible to such incidents?

The danger of thermal runaways

During EV usage, the energy contained in a battery is released through exothermic chemical reactions, which release large volumes of heat energy. Batteries are designed in such a way that this heat can be mitigated, avoiding an excessive increase in temperature. However, if the precautions put in place to minimize heat dissipation are insufficient, core temperature will increase, leading to uncontrollable acceleration of chemical reactions in the LIB: a thermal runaway.

These can include decomposition reactions, in which chemicals inside the battery, such as the electrolyte in some LIBs, break down into smaller molecules. The result of this decomposition can include flammable hydrocarbon gases, the build-up of which can lead to deformation of the battery structure.

The cathode of LIBs is normally a metal oxide, which, under high-temperature conditions, can also undergo decomposition reactions, forming oxygen. It is the combination of this oxygen with the flammable gases that can result in potentially hazardous incidents. Once batteries enter a thermal runaway, it is virtually impossible to stop it, and the only solution is to try to minimize the spread of fire and resulting damage as much as possible.

Testing to inform battery research

Understanding the range of conditions where a battery can operate most efficiently is paramount in keeping manufacturers, transporters and users safe. Calorimetry has long been established as a powerful tool for gaining insight into thermal behavior, and supports manufacturers to make informed decisions surrounding thermal management.

Figure 1: Defining the key zones of battery operation, based on electrical and thermal behavior. Expansion of the optimum and safe zones during design and development phases (as indicated by the blue and yellow arrows) produces versatile batteries. Credit: H.E.L Group

Isothermal calorimetry is characterized by the use of constant temperatures. This testing enables developers to determine the range of temperatures at which the battery can operate safely and optimal conditions for usage. Isothermal calorimetry can help determine the number of charge/discharge cycles a battery can go through and the amount of energy that it can be supplied in order to achieve faster, but still safe, charging times.

In order to learn about the consequences of device failure, destructive testing must be incorporated into the development process. In adiabatic calorimetry, heat produced by the battery is confined within the calorimeter, preventing any exchange between the device and surroundings; any heat released from the test being performed remains inside the testing kit, deliberately inducing a thermal runaway and allowing users to characterize the process. To trigger this process, the battery can be exposed to several stressors, e.g., mechanical (impact, punctures), electrical (overcharging, exceeding maximum current, external short-circuits), and thermal (external heating). The calorimeter then measures the thermal behavior of the battery, recording the energy released, providing researchers with a comprehensive picture of battery thermal behavior.

Figure 2: Root causes of battery failure, along with testing protocols to detect failures. Credit: H.E.L Group.

A need for novel battery testing technologies

In a world where vehicle electrification is becoming ever more prevalent, there is increasing pressure to develop larger, more efficient and safer batteries. However, the larger the battery, the bigger the risk of significant damage should thermal runaway events occur, and it is therefore fundamental that rigorous testing is undertaken during battery research and development.

Batteries will play a crucial role in the future of EVs: improved capabilities in current LIBs, larger capacities using extra cells, new structures (such as solid state-state batteries), or completely new chemistries (such as sodium-based or lithium-sulfur-based) offer new and exciting possibilities. Each new opportunity comes with its own associated risks, and testing technologies must improve and evolve accordingly to meet this demand.


About the author:

Mario Toubes-Rodrigo holds a PhD in environmental microbiology from Manchester Metropolitan University. Currently serving as the global applications leader at H.E.L, he combines scientific expertise with leadership. Mario's passion for science extends to effective communication, bridging the gap between complex concepts and broader audiences.