Thermal Management: How to Maximise Battery Performance without Compromising on Safety
The popularity of hybrid vehicles is set to continue, with the latest forecasts predicting a CAGR (Compound Annual Growth Rate) of 7.1% until 2032 [1]. The main driver behind this growth is the impressive efficiencies hybrids can achieve. By combining an electric motor with an internal combustion engine, the motor delivers power at low torque, where the engine is least efficient, while the engine delivers power at high torque, where it is most efficient. This allows hybrids to save 23 to 49% of fuel compared to conventional combustion vehicles [2].
However, the rapid acceleration and braking events of racecars and high-performance vehicles demands extreme discharge and charge events from the battery, inducing high currents, and drastically increasing battery temperatures. Keeping batteries cool not only prevents catastrophic failures such as thermal runaway, but also minimises degradation, ensuring batteries sustain high performance throughout their life.
In this article, we will uncover Ricardo’s latest innovations in battery cooling and how these advanced battery modules can boost performance for both road and race vehicles.
Traditional battery cooling techniques
Typically, high performance batteries in motorsport are liquid cooled using single phase coolants via two approaches:
- Immersion cooling – where a dielectric coolant floods the battery pack
- Cold plates – a water/glycol coolant flows through a metallic heat sink attached to the base of cells
Once the coolant has extracted the heat from the battery, it flows through a radiator and rejects heat to the ambient air before circulating through the battery again.
‘Immersion cooling is effective because the dielectric fluid is in direct contact with the individual cells and so dissipates heat from the entire surface area of the cells,’ explains Dr Temoc Rodriguez, Global Technical Expert - Electronics at Ricardo. ‘The downside is that filling the battery with dense dielectric fluid increases weight, which makes it undesirable for racecars.’
‘Cold plates on the other hand are a more lightweight solution but present a thermal barrier between the coolant and the cells, increasing thermal resistance, even with extremely thin walls,’ continues Rodriguez. ‘So, we decided to develop alternative solutions for both methods that offer improved cooling capability. Our latest designs achieve precise thermal control, maintaining cell temperatures within 10degC at discharge rates as high as 30oC.’
Ricardo's immersion-cooled battery module
Instead of fully immersing the entire battery module in dielectric coolant, Ricardo has taken a more novel approach and designed three horizontal volumes that cool the top, body and bottom of the cells. This reduces the amount of fluid within the battery, minimising mass, whilst still cooling the cells effectively.
‘Cylindrical cells are essentially constructed from layers of cathode, electrolyte and anode films that are rolled into a cylinder, inserted into a can and terminated at the top and bottom,’ explains Rodriguez. ‘Heat transfers axially along the cell, so cooling the top and bottom electrodes is the most effective way to extract heat.’
‘However, this is quite a small surface area, so we have also integrated a third volume around the body of the cells,’ adds Rodriguez. ‘Although less heat flows radially from the middle of the cells due to the thermal resistance of the various layers, the larger surface area means there is still reasonable heat transfer. So that’s why we’ve implemented three volumes.’
Furthermore, this system has also been engineered to prevent thermal runaway from propagating throughout the module. This is achieved through clever cell design where any heat, gasses and particles from a thermal runaway event are vented through the electrodes of the cells, and therefore immediately mix with dielectric fluid in the upper and lower volumes. The high pressures generated from thermal runaway force this mixture through a pressure relief valve where it is then ejected into a safety container.
Ricardo’s water/glycol channel-cooled battery module
The high discharge and charge rates of modern racecar batteries makes it extremely difficult to maintain cell temperatures within their operating window using cold plates alone. The coolant is far from the body of the cells and the required insulation layers induce thermal resistance, restricting heat transfer. A much more effective strategy is to bring the cooling fluid closer to the cells, which is the design objective of Ricardo’s water/glycol channel-cooled battery module.
‘We use cooling membranes which weave between the rows of cells and extend along the length of the cells,’ reveals Rodriguez. ‘These membranes are essentially pouches that inflate with the pressure of the water/glycol coolant and conform around the shape of the cells. They consist of a 50 micrometre layer of aluminium encased in a 10 micrometre layer of polypropylene plastic on either side for electrical insulation.’
‘Although these layers form a thermal barrier, they are so thin, and the coolant is much closer to the cells, that the resulting thermal gradient is minimal,’ continues Rodriguez. ‘Also, because the cells are so tightly packed, around 1.5mm from each other, the total amount of fluid is much less than in immersion cooling, saving weight. This approach also means teams can stick with their current water/glycol coolants and avoid introducing a new coolant which then comes with additional pumps, heat exchangers and plumbing, adding both weight and cost.’
A flexible design philosophy
Both the immersion-cooled and water/glycol channel cooled battery modules are designed for cylindrical cells. Therefore, as cell chemistry improves, new cells can be easily fitted to deliver a higher power module, provided the heat rejection does not exceed the module’s original design limits.
‘We have also developed the modules to be flexible to suit a variety of vehicle platforms,’ highlights Rodriguez. ‘The immersion-cooled modules are four cells in parallel and twelve in series. While the water/glycol channel modules are seven cells in parallel and fourteen in series.’
‘Each vehicle platform is slightly different, and obviously it depends on the peak power and energy requirements,’ concludes Rodriguez. ‘But the modules are effectively miniature building blocks that can be configured in series or parallel, allowing customers to build a battery pack that suits their specific vehicle platform.’
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References
[1] 2025. Hybrid Vehicle Market Size, Share & Industry Analysis [Online]. Fortune Business Insights.
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