How does battery cooling work?
Battery cooling works by actively removing heat from battery cells to keep them within a safe and efficient operating temperature range. Heat is generated during charging and discharging through a process called Joule heating, and without a thermal management system in place, that heat accumulates and degrades both performance and safety. The sections below address the most important questions about how battery cooling systems work, why they matter, and what distinguishes industrial battery thermal management from standard HVAC approaches.
Why do batteries generate heat in the first place?
Batteries generate heat because electrical current passing through internal resistance converts some of that energy into thermal energy rather than useful work. This is Joule heating: the higher the current draw or charge rate, and the higher the internal resistance of the cells, the more heat is produced. In mobile and heavy-duty applications, where high power demands are common, heat generation is substantial and continuous.
In lithium-ion battery packs, heat generation is not uniform. Cells in the center of a pack have less surface area exposed to ambient air and tend to run hotter than cells at the edges. Chemical reactions inside the cells also produce heat as a byproduct, particularly at high states of charge or discharge. Over time, as cells age and internal resistance increases, heat generation intensifies even under the same operating conditions. This is why thermal management is not just a safety measure at commissioning but a requirement throughout the battery’s operational life.
What happens to a battery if it overheats?
If a battery overheats, it enters a sequence of degradation and failure modes that range from accelerated capacity loss to complete thermal runaway. At moderately elevated temperatures, lithium-ion cells degrade faster, losing usable capacity and cycle life significantly sooner than they would under controlled thermal conditions. Above certain thresholds, the degradation becomes irreversible within a single event.
At extreme temperatures, thermal runaway can occur: an uncontrolled, self-sustaining exothermic reaction where heat generation outpaces the system’s ability to dissipate it. Thermal runaway can spread from cell to cell across an entire pack, resulting in fire, structural damage, and, in mobile or enclosed environments, serious safety hazards. In industrial and defense applications, where battery systems are integrated into vehicles, machinery, or shelters, the consequences of thermal runaway extend well beyond the battery itself. This is precisely why battery heat management in demanding operating environments requires engineered systems, not passive ventilation.
What are the main types of battery cooling systems?
The main types of battery cooling systems are air cooling, liquid cooling, and phase-change material cooling. In industrial and mobile applications, liquid cooling is the dominant choice because it offers significantly higher heat transfer capacity, more precise temperature control, and a more compact form factor than air-based systems.
- Air cooling: Uses forced or natural airflow to remove heat from battery surfaces. Simple and low-cost, but limited in heat transfer capacity and ineffective in high-power or thermally demanding applications.
- Liquid cooling: Circulates a coolant fluid through channels, cold plates, or jackets in direct or indirect contact with battery cells. Offers high thermal performance and precise temperature uniformity across the pack.
- Phase-change material (PCM) cooling: Uses materials that absorb heat as they change state from solid to liquid. Effective for managing peak thermal loads but typically used as a supplementary method rather than a standalone system.
- Refrigerant-based cooling: Integrates the battery cooling circuit directly into a refrigeration cycle, allowing active temperature control even in high-ambient environments. Common in electrified heavy machinery where ambient temperatures vary widely.
The right approach depends on the application’s power density, ambient temperature range, available space, and reliability requirements. In electrified mobile machinery and defense platforms, liquid cooling and refrigerant-based systems are typically the only viable options.
How does liquid cooling keep battery packs at the right temperature?
Liquid cooling keeps battery packs at the right temperature by circulating a coolant fluid through a network of channels or cold plates that are in thermal contact with the battery cells. The coolant absorbs heat from the cells, carries it away from the pack, and transfers it to a heat exchanger where it is dissipated to the ambient environment or to another cooling circuit. A pump, thermostat, and control logic regulate flow rate and temperature continuously.
In a typical battery cooling system for mobile machinery, the coolant circuit is integrated with the machine’s broader thermal management architecture. The same system that cools the battery may also manage heat from power electronics, electric motors, or hydraulic components. Cold plates are designed to maximize contact surface area with the cells while maintaining the compact form factor required in mobile installations. The control system adjusts cooling intensity based on real-time cell temperature readings, ensuring the pack stays within its target operating window regardless of load or ambient conditions.
Heating is equally important in cold climates. A well-engineered battery thermal management system includes heating capability to bring battery cells up to the minimum operating temperature before high-power operation, preventing capacity loss and mechanical stress on the cells during cold starts. This is particularly relevant in Nordic and Arctic operating environments.
What is the ideal operating temperature range for lithium-ion batteries?
The ideal operating temperature range for lithium-ion batteries is generally between 15°C and 35°C for optimal performance and longevity. Outside this window, both capacity and cycle life degrade. Below 0°C, lithium plating during charging becomes a risk, and available power drops noticeably. Above 45°C, accelerated chemical degradation begins to reduce the battery’s usable life.
In practice, the acceptable operating range is wider than the optimal range, and manufacturers specify both. Many lithium-ion chemistries can discharge down to minus 20°C and charge up to 45°C, but sustained operation at the extremes shortens service life. For industrial and mobile applications where batteries are expected to perform reliably over years of operation in variable environments, maintaining the pack within the tighter optimal window is the engineering objective, not just staying within the broader limits.
This is why EV battery cooling and heating systems in demanding applications are active, closed-loop systems rather than passive designs. The target temperature range must be maintained regardless of whether the machine is operating in a Finnish winter at minus 30°C or a mining environment at elevated ambient temperatures.
How is battery thermal management different from standard HVAC cooling?
Battery thermal management is fundamentally different from standard HVAC cooling in its precision requirements, integration complexity, and the consequences of failure. Standard HVAC cooling manages the temperature of an air volume within a defined space, with tolerances measured in degrees across a room or cabin. Battery thermal management must control the temperature of individual cells within a tightly packed electrochemical system, with temperature uniformity across the pack being as important as the average temperature level.
In a battery thermal management system, the cooling circuit is in direct thermal contact with the energy storage cells. The system must respond to rapidly changing heat loads driven by current demand, manage both heating and cooling in the same circuit, and maintain cell-to-cell temperature uniformity to prevent uneven degradation. It also operates under the space, weight, and vibration constraints of a mobile platform, which places demands on component selection, mounting, and sealing that are far more stringent than a fixed HVAC installation.
Standard HVAC systems are designed around human comfort and equipment protection in defined enclosures. A battery thermal management system is engineered around the electrochemical behavior of specific cell types, the power profile of the application, and the operating environment of the machine. The two disciplines overlap in refrigeration technology and fluid handling, but the engineering requirements, control logic, and failure mode analysis are distinct domains.
At Lumikko, battery thermal management systems are developed as fully integrated, application-specific solutions for electrified mobile machinery and heavy equipment. Each system is engineered around the customer’s specific cell chemistry, operating cycle, temperature range, and platform constraints, and manufactured in-house at our factory in Seinäjoki, Finland. Reference customers include Sandvik, for whom Lumikko has developed battery cooling and heating solutions for electrified mining machines operating in demanding underground environments.
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