Liquid Immersion Cooling for Battery Packs

Direct liquid cooling, also known as immersion cooling, is an advanced thermal management method where battery cells are submerged directly into a dielectric coolant to dissipate heat efficiently. Unlike indirect cooling methods that use cold plates or tubing, immersion cooling eliminates thermal resistance between the battery and the cooling medium, enabling superior heat transfer performance and uniform temperature distribution. With higher energy density and fast-charging demands in modern EVs and energy storage systems, traditional air and indirect liquid cooling methods struggle to keep up with thermal runaway risks and non-uniform heat dissipation. (Roe et al., Immersion Cooling for Lithium-Ion Batteries – A Review, 2022).

The key benefits of Immersion cooling are well known which are:

• Enhances thermal uniformity (Temperature Gradient within a battery) – reducing cell-to-cell temperature variations.
• Improves cooling efficiency – high heat transfer coefficient of liquid coolant.
• Minimizes thermal runaway risk – direct contact with coolant prevents overheating.
• Supports fast charging – by maintaining optimal temperature during high-current charging.

Pascal Correia, Director of Technology & Product Engineering at TotalEnergies Lubrifiants added: “We are very proud of the trust the car manufacturers have placed in us for this innovative project. Our work has demonstrated the immense potential of immersion cooling with the fluids developed by our Research & Development teams. The fact that we have succeeded in grafting our system onto a production vehicle demonstrates its potential on a large scale.”

1. Types of Immersion Cooling Fluids

The success of immersion cooling depends on the choice of dielectric fluid, which must be non-conductive, chemically stable, and thermally efficient. 

1.1. Based on type of fluids

The success of immersion cooling depends on the choice of dielectric fluid, which must be non-conductive, chemically stable, and thermally efficient. The two primary categories of immersion cooling fluids are:

A. Mineral Oils and Synthetic Hydrocarbons

• Examples: 3M Fluorinert, Shell Diala oils, Castrol ON e-thermal fluid., Total Energies Cell Shield.
• Pros:
  • High thermal stability and oxidation resistance.
  • Chemically inert and non-corrosive to battery materials.
  • Widely used in energy storage systems (ESS) and EV applications.
• Cons:
  • Relatively high viscosity, leading to increased pumping power.
  • Some fluorinated oils (e.g., Fluorinert) can be expensive.

B. Dielectric Esters and Organic Fluids

• Examples: Midel 7131, Shell aquired MIVOLT DFK and DF7.
• Pros:
  • Lower viscosity, improving coolant circulation efficiency.
  • Biodegradable and environmentally friendly options available.
  • Good fire suppression properties.
• Cons:
  • Some esters may absorb moisture, reducing long-term stability.
  • Requires compatibility testing with battery materials.

1.2. Based on phase

A. Single-Phase Cooling Fluids

These fluids remain in a liquid state throughout operation, relying on convection for heat removal.

• Examples: Hydrocarbon oils, esters, silicone oils.
• Advantages: Simple system design, lower cost compared to two-phase cooling.
• Limitations: Lower heat transfer compared to two-phase systems.

B. Two-Phase Cooling Fluids

• Examples: Hydrofluoroethers (HFE), Novec 7000.
• Advantages: Higher cooling efficiency due to latent heat absorption.
• Limitations: Requires additional condensation systems to cycle the coolant back into liquid form. (Roe et al., 2022)

2 Cooling Configurations for Immersion Cooling

A. Passive Immersion Cooling

• Mechanism: Heat is dissipated through natural convection to the surrounding coolant, which then transfers heat to an external radiator.
• Applications: Used in stationary battery energy storage systems (BESS) where weight is not a constraint.
• Pros:
  • No need for complex pump systems, reducing energy consumption.
  • Simple and reliable for moderate power densities.
• Cons:
  • Limited cooling performance for high-power battery systems.

(Roth, “Natural Convection Cooling in Immersion-Based Thermal Management Systems,” 2019)

B. Active Immersion Cooling

• Mechanism: Coolant is actively pumped through a heat exchanger to remove excess heat.
• Applications: Used in high-performance EVs, and fast-charging battery packs.
• Pros:
  • Superior heat dissipation even under high thermal loads.
  • Supports fast charging and high-discharge applications.
• Cons:
  • Requires pumps, radiators, and plumbing, increasing system complexity.
  • Potential coolant leakage if not properly sealed.

3 Challenges and Limitations of Liquid immersion cooling

Liquid immersion cooling offers clear thermal performance advantages, but like any thermal management strategy, it brings its own set of design and engineering trade-offs. However, many of the so-called limitations are now being actively addressed through smart design innovations and material advances.

1. Coolant Compatibility

One of the most critical considerations is ensuring that the dielectric fluid is chemically compatible with all materials it contacts—cell cases, seals, busbars, insulators, and connectors.

• Elastomers used in sealing, for example, may degrade or swell in some fluids, compromising the enclosure integrity over time.
• Metals like copper or aluminum require careful selection of coolant to avoid corrosion or material migration.
• Adhesives, conformal coatings, and even label inks must be tested for long-term chemical stability.

This isn’t a show-stopper, but it does demand early-stage validation and thorough long-duration testing. The design team can’t treat coolant selection as a last-minute decision—it’s foundational.

2. Weight & Packaging

Immersion cooling does introduce more fluid volume compared to cold plate or indirect systems, but the net weight gain is often overstated.

• Traditional systems require heavy cooling plates, thermal interface materials, clamping hardware, and plumbing—components that immersion systems can eliminate or significantly reduce.
• Also, new design approaches like controlled immersion—as used by companies like XLEX Batteries—target only critical thermal zones, reducing fluid volume by 90–95%. Instead of full submersion, a shallow pool or localized immersion offers much of the thermal benefit with minimal added weight.

So while packaging does change, it’s not necessarily heavier—just different. The trade-offs are real but increasingly manageable with smart mechanical layouts.

3. Cost Factors

Yes, high-performance dielectric fluids cost more than water-glycol or passive air systems—but that’s not the whole picture.

• The upfront fluid cost is higher, but these fluids are highly stable and do not degrade easily. In fact, most modern dielectric coolants outlast the battery pack’s service life, so there’s no recurring fluid replacement cost in most applications.
• Additionally, immersion cooling reduces the need for complex manifolds, cold plates, or heat spreaders, which brings down manufacturing complexity and part count.
• For high-performance applications like racing EVs, defense, or aerospace—where thermal margins are tight—the improved reliability and power throughput often justify the investment.

In short, cost is a consideration, but not necessarily a deal-breaker—especially when you take system-level simplification and pack longevity into account.

4. Leakage Risk

Ensuring the battery enclosure is leak-proof remains a valid concern. A failure here could reduce thermal performance and raise safety or serviceability issues. That said, this is more of a manufacturing quality and sealing design challenge than a fundamental flaw of immersion systems.

• Solutions like welded aluminum enclosures, redundant sealing gaskets, and pressure testing protocols are already in widespread use in the EV industry and can be adapted to immersion packs.
• For controlled immersion designs, leakage risk is inherently reduced, as the total fluid volume is low and usually isolated to specific compartments.

A well-designed system with robust validation shouldn’t suffer from chronic leakage issues—and in fact, some designs are already achieving IP68 or higher ratings even under immersion conditions.

4. Industry Adoption & Case Studies

Liquid immersion cooling has moved well beyond R&D labs—it’s now being applied in real-world systems by companies prioritizing thermal stability, safety, and performance. Both single-phase and two-phase immersion approaches are being explored, with different OEMs opting for various dielectric fluids based on their system needs.

Here’s a closer look at how leading companies are implementing immersion cooling:

Kreisel Electric

Kreisel has been a consistent advocate of immersion-cooled battery design. Their systems use Shell’s MIVOLT dielectric fluids, which offer a balance of high thermal conductivity and electrical insulation. Shell’s fluid chemistry enables safe submersion without compromising long-term material compatibility, and Kreisel integrates this into modular packs targeted at both stationary and mobile use cases.

Xing Mobility

This Taiwanese firm was one of the earliest adopters of 3M Novec-based immersion cooling. Their “IMMERSIO” modular battery system places each cell in direct contact with the fluid, achieving rapid heat dissipation. They’ve shown high thermal homogeneity even under extreme duty cycles, making this a serious contender for motorsport and industrial EVs.

Rimac Automobili

Rimac’s high-performance battery systems for hypercars use Solvay’s Galden fluids—a family of perfluoropolyether-based (PFPE) dielectric coolants. These fluids offer exceptional thermal stability and ultra-low volatility, which is critical at the high heat loads seen in Rimac’s extreme performance applications. It’s a premium solution—but so is the hardware it supports.

CARRAR

CARRAR has gone a step further with two-phase liquid immersion cooling. In this approach, the fluid boils at a controlled temperature, carrying away large amounts of heat through phase change. This provides even higher thermal efficiency than single-phase systems, although it demands tighter control of pressure and enclosure integrity. Their system targets the e-mobility and autonomous vehicle sectors where thermal spikes are common.

XLEX Batteries

XLEX is applying a controlled immersion approach, using MIVOLT & Total Energies fluid, but only submerging critical thermal zones (typically 5–10% of the cell area). This minimizes fluid volume while retaining thermal performance. It’s a practical, weight-conscious compromise aimed at EVs and energy storage systems, where every gram matters.

Kautex

Kautex Textron, traditionally known for fuel systems, is now working with two-phase immersion cooling for battery applications. Their approach combines packaging experience with advanced thermal control, leveraging phase change benefits in a compact format. It signals how legacy automotive suppliers are adapting quickly to the battery space.

E-Mersive Technologies

E-Mersive focuses on single-phase immersion cooling, targeting light EV and aerospace segments. Their systems prioritize reliability and manufacturability, with integrated monitoring for fluid quality and thermal performance. The use of single-phase fluids allows for simpler pressure control and a more predictable thermal envelope.

Ricardo

Ricardo has publicly demonstrated its immersion-cooled battery pack using Shell’s dielectric fluid. The design emphasizes modularity and serviceability, while offering consistent cell-to-cell thermal uniformity. Their work is aimed at niche automotive and motorsport applications, where compact thermal management is critical.

TotalEnergies

Renault Mégane E-Tech: TotalEnergies Lubrifiants recently integrated their Cell‑Shield dielectric fluid into a production Mégane E-Tech, reducing charge time and increasing range by 6%, all with minimal vehicle redesign. They have previously experimented on Volvo and are also working with 2 wheeler Battery packs in collaboration with multiple OEMs.

5. Key Takeaways

Immersion cooling offers superior thermal management compared to traditional methods like cold plates or air cooling. By directly surrounding the cells with dielectric fluid, it achieves faster heat dissipation, tighter thermal uniformity, and improved safety—especially during thermal events.

Coolant selection is critical. Dielectric fluids must be chemically stable, non-reactive with pack materials, and thermally efficient—without compromising cost or environmental safety. Compatibility testing for seals, adhesives, and conductors is non-negotiable.

Application context matters.

• For high-performance EVs and motorsports, active immersion cooling—with pumps or forced circulation—is needed to handle rapid charge/discharge cycles and thermal spikes.
• For stationary systems (like grid storage), passive immersion may suffice, offering reliability with lower mechanical complexity.

Key challenges remain, including:

• Cost: Dielectric fluids and sealed pack designs can add upfront expense.
• Material Compatibility: Long-term stability of all wetted materials must be verified.
• Environmental Safety: There is growing scrutiny around PFAS-based fluids (like some 3M Novec and Galden variants) due to their persistence in the environment, pushing the industry toward more eco-conscious alternatives.
• System Integration: Immersion cooling requires rethinking pack architecture, fluid handling, and serviceability.

The technology is advancing rapidly, with real-world trials by OEMs (Renault, Volvo, Kreisel, Rimac, etc.) and growing adoption across sectors. As fluid chemistry, packaging techniques, and regulatory clarity improve, immersion cooling is becoming a serious contender—not just for niche use cases but for mainstream EV and energy storage platforms.

See also: Dielectric Immersion Cooling, Battery Thermal Management: Heat Generation, Cooling & TIM