Is Immersion Cooling the Future? French Firm Unveils 500 kWh EV Battery

A French battery manufacturer, WATTALPS, has recently announced its development of electric vehicle (EV) batteries utilising immersion cooling technology. These batteries, boasting specifications ranging from 48V to 800V and capacities from 10 to 500 kWh or more, are designed for demanding commercial EV applications and incorporate native IP67 and IP69K designs. But what exactly is immersion cooling, and why is it generating so much buzz in the EV world?

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Decoding Immersion Cooling Technology

Immersion cooling involves submerging battery cells and other heating elements, like busbars and electrodes, directly in a dielectric fluid. This fluid is electrically isolating, non-flammable, non-toxic, and biodegradable. This method offers significantly better thermal performance—up to 20 times higher—than traditional cold plate technologies.

How It Works

The concept is straightforward: by immersing the battery module in a dielectric fluid, direct contact between the heat source and the cooling medium is achieved. Heat is then uniformly absorbed and transferred to a dissipation system, typically a heat exchanger, maintaining the cells within their optimal temperature range.

During charging and discharging, the total thermal energy generated within a battery cell can be expressed by the following thermodynamic equation:

$$Q=I^2{R}_i+IT\frac{dOcv}{dT}$$

Where:

• $Q$ is the heat generation rate (W).
• $I$ is the operating current (A).
• $R_i$ is the internal DC resistance of the cell ($\Omega$).
• $T$ is the absolute temperature of the cell (K).
• $\frac{dOcv}{dT}$ is the entropy coefficient or temperature coefficient of the open-circuit voltage (V/K).

As fast-charging rates increase, the current ($I$) rises quadratically in the Joule heating term ($I^2{R}_i$), leading to extreme heat generation. Direct immersion cooling removes this heat directly at the source, preventing localised hotspot formation across the cell surface.

Single-Phase vs. Two-Phase Immersion Cooling

There are two primary configurations for immersion cooling systems:

• Single-phase immersion cooling: The fluid remains in liquid form throughout the cycle and is circulated in a closed loop via a pump.
• Two-phase immersion cooling: The fluid undergoes a phase change, evaporating as it absorbs heat from the cells and then condensing back to liquid via a condenser, providing even higher thermal performance.

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The Benefits of Immersion Cooling for EV Batteries

Immersion cooling offers several key advantages for EV batteries, outlined in the table below:

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WATTALPS' Innovative Approach

WATTALPS' immersion-cooled batteries stand out due to several key features:

• Passive and Active Safety: The batteries incorporate technology that prevents the spread of cell thermal runaway, along with an active safety system managed by the proprietary battery management system (BMS).
• Robust Design: They feature a native IP67 and IP69K design, making them highly resistant to dust, high-pressure water jets, shock, and vibrations.
• Harsh Condition Performance: They maintain peak performance in temperatures ranging from -20 °C to +50 °C.
• Compact Form Factor: WATTALPS states its rectangular block-shaped modules have the smallest form factor on the market, enabling compact battery packs with quick integration.
• Customisable Solutions: WATTALPS' BMS and batteries are certified to the IEC 62619 and ISO 26262 (up to ASIL C) safety standards, and the company works with customers to design bespoke battery packs.

WATTALPS and LFP (Lithium Iron Phosphate) Chemistry

While many high-performance immersion systems historically relied on NMC (Nickel Manganese Cobalt) chemistries due to their superior gravimetric energy density, the combination of WATTALPS' technology with LFP (Lithium Iron Phosphate) chemistry is garnering significant interest for heavy-duty industrial and commercial fleets.

LFP cells are inherently safer and more cost-effective than NMC alternatives, but they suffer from two major limitations: reduced performance at low temperatures and high internal resistance during rapid charge-discharge cycles. By using an immersion cooling medium, WATTALPS can resolve these LFP pain points:

• Active Thermal Heating: In sub-zero conditions, the fluid is used to actively warm the LFP cells uniformly, eliminating the slow-charging issues commonly associated with cold LFP packs.
• Hotspot Prevention: During high-rate discharging or heavy-duty regenerative braking, the immersion fluid absorbs high heat spikes ($I^2{R}_i$ losses), preventing localised degradation and allowing LFP cells to safely operate at high C-rates.
• Maximising Cycle Life: LFP chemistry naturally supports 3,000 to 6,000 cycles. By keeping temperature deltas between cells under 2 °C via immersion cooling, WATTALPS ensures that the pack achieves its maximum theoretical lifespan.

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Challenges and Future Outlook

Despite its numerous benefits, immersion cooling faces some challenges:

• Fluid Cost: The cost of specialised dielectric fluids can be a significant upfront factor.
• System Complexity: Implementing immersion cooling systems can add complexity to battery pack design, requiring robust seal integrity to prevent leaks.
• Component Compatibility: The long-term effects of dielectric fluids on battery plastics, sealants, and adhesive components need careful verification.

However, the future of immersion cooling for lithium batteries looks highly promising. Market forecasts predict significant growth in the use of immersion cooling in energy storage systems, with some estimates suggesting an annual growth rate of over 22% through 2030. As the EV market continues to expand, the demand for more efficient, safer, and longer-lasting batteries will likely drive further adoption of immersion cooling technology.

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Immersion Cooling: Not Just for EVs

While currently making waves in the EV sector, immersion cooling isn't limited to just automotive applications. Its superior thermal management capabilities make it suitable for:

• Energy Storage Systems (ESS): Improving the safety, thermal stability, and lifespan of batteries used in grid-scale energy storage.
• Data Centres: Originally developed for cooling high-performance computing systems, immersion cooling is finding increased use in data centres to manage the intense heat generated by modern AI processors.
• Marine Applications: Providing efficient cooling and thermal isolation for batteries used in electric boats, tugs, and other marine vessels.
• Industrial Applications: Cooling heavy-duty batteries used in construction machinery, mining equipment, and agricultural vehicles where dust and vibrations prevent standard air or liquid cold plate cooling.

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Conclusion

WATTALPS' development of a modular, up to 500 kWh EV battery utilising immersion cooling tech represents a significant step forward in battery technology. By combining advanced dielectric fluid pathways with chemistry-agnostic compatibility—including both high-energy NMC and long-life LFP options—immersion cooling offers a compelling solution to the challenges of thermal management in industrial EV batteries. As the heavy transport and off-highway sectors transition to electric drivetrains, innovations like immersion cooling will play an essential role in driving widespread adoption.