Batteries & Fuel Cells
Cool runnings E
lectrification has transformed the automotive landscape in less than a decade. Today’s electric vehicles rely overwhelmingly on lithium- ion chemistry – an energy-dense, mature and commercially viable solution. Emerging alternatives such as sodium-ion and solid-state batteries promise meaningful gains in cost, safety and energy density, but these technologies remain longer-term prospects for high-performance applications.
Could improved cooling enable more power to be yielded from the current generation of batteries? We have proven it can. Our work in developing bespoke battery solutions for motorsport and high-performance hypercars demonstrates how more power can be extracted for longer through taking immersion cooling to the next level.
Immersive possibilities
For high-performance road cars, hypercars and motorsport-derived platforms, the challenge is not simply energy density – it is sustained power density. Delivering repeatable, high- current charge and discharge whilst staying within safe limits is the defining constraint. At RML Group, we have focused on extracting significantly greater performance from existing lithium-ion technology. Through advanced immersion cooling and system- level optimisation, we can access the upper and lower extremes of charge and discharge performance from the same underlying cell chemistry.
The gains have come not from chemistry alone, but from thermodynamics, fluid science and intelligent control.
In high-performance EV applications, batteries are routinely asked to deliver extreme discharge rates. Whilst a typical passenger car BEV battery pack may operate around 0.5 to 1C (1C is equivalent of depleting the battery in one hour), a hypercar HEV pack that we produce is regularly called upon to deliver 100C – 100 times the relative power. The more current drawn from a battery, the more heat it generates (heat is proportional to the square of current).
And it’s not just ultra high-performance vehicles that require high power. The desire
32 April 2026
for ever-faster charging times demands mass- market passenger car batteries to be similarly power-capable.
Heat is the enemy
Excessive temperature accelerates degradation, leading to increased resistance and reduced capacity, and in extreme cases can compromise safety margins. Furthermore, the problem is not just peak temperature, but thermal gradients within the pack. Uneven heat distribution leads to cell imbalance, reducing the overall usable performance envelope. Thermal management, therefore, becomes the key enabler of power density. Conventional EV battery packs typically use indirect cooling – cells are mounted to ‘cold plates’, through which a fluid (typically ethylene glycol based) flows. These systems are effective for mainstream applications, but struggle with the heat flux associated with sustained high discharge in performance environments.
Immersion cooling takes a fundamentally different approach. Instead of cooling
Components in Electronics
Denis Gorman, head of powertrain development at RML Group, explains how immersion cooling and intelligent control can unlock the hidden potential in battery performance
Denis Gorman, RML Group’s head of powertrain, with one of their bespoke batteries that harness the potential of immersion cooling.
indirectly, cells are submerged directly in a dielectric fluid. This allows heat to be removed uniformly from the entire cell surface, dramatically improving heat transfer coefficients and eliminating localised hotspots.
Our research and testing have shown that the choice of dielectric fluid is central to a system’s effectiveness. Thermal conductivity, viscosity, density, specific heat capacity, dielectric strength and chemical compatibility all influence overall performance. We also discovered wide variations in the performance of different fluids on the market. During the development phase of a new battery pack for a US-based performance car brand, we conducted extensive comparative testing across multiple candidate fluids. Rather than accepting supplier data at face value, we ranked fluids based on real- world heat rejection performance, flow characteristics and long-term stability under repeated thermal cycling.
In one case, we worked directly with a supplier to modify their fluid formulation to improve heat transfer properties, electrostatic properties and stability.
Fluid management and thermal modelling
Once the correct dielectric fluid is selected, managing its behaviour across the pack becomes the next challenge. High performance packs are complex systems, often requiring immersion-cooling of hundreds or even thousands of individual cells, and it takes only one cell to be the limiting factor. Achieving uniform cooling requires precise control of flow rates, pressures and distribution pathways. Too little flow risks hotspots; too much increases parasitic losses and pumping energy requirements.
To optimise the system, we deploy advanced Computational Fluid Dynamics (CFD) and Conjugate Heat Transfer (CHT) analyses. These tools allow us to model fluid velocity and pressure differentials,
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