Battery Thermal Management: Key Solutions for Heat Control and Performance

What is Battery Thermal Management?

A precision-engineered battery thermal management system (BTMS) regulates battery temperature to minimize thermal stress and maintain optimal performance. Lithium-ion batteries work between 15-35°C. Deviations may increase side reactions or resistance for capacity loss or thermal runaway. 

Because of the better heat conductivity of liquids, contemporary systems like liquid cooling might disperse heat greater than air. Moreover, dielectric immersion cooling and phase-change materials are helping high-energy-density cells avoid hotspots and provide consistent heat dissipation for supercharging.

Why is Battery Thermal Management Essential?

• Performance: Temperature stability affects electrochemical reaction rates within battery cells. At high temperatures, increased ionic mobility may boost initial performance but accelerate side reactions to cut efficiency. Conversely, low temperatures slow diffusion to impair charge/discharge rates. A battery thermal management system stabilizes cell temperatures for uniform redox activity and lower internal resistance fluctuations. It adjusts energy output and sustains stabilized charging efficiency across cycles.

• Safety: Thermal runaway happens when the battery exothermic processes create more heat than they can dissipate. Elevated temperatures degrade the solid-electrolyte interface (SEI), triggering cascading reactions, electrolyte decomposition, and gas evolution. A battery thermal management system dissipates heat to avert hotspots. It prevents SEI breakdown and moderates thermal propagation to safeguard against catastrophic failures.

• Longevity: Thermal gradients within a cell cause uneven electrode aging, dendrite formation, and capacity fade. High temperatures expedite electrolyte breakdown. Low temperatures promote lithium plating on the anode. A narrow temperature range using a battery thermal management system decreases mechanical stresses and chemical imbalances. By minimizing structural and chemical degradation, a well-regulated BTMS extends battery cycle life.

Key Battery Thermal Management Solutions

Air Cooling Systems

Air cooling uses forced or natural convection with fans or airflow channels to dissipate heat from battery packs. Researchers have developed honeycomb structures and multi-inlet/outlet configurations for better cooling efficiency by up to 74%. Yet, they struggle with uniform temperature control in high-density battery packs for more hotspots and lower performance. For example, the X-type air-cooled system decreases temperature differences by 62.9%. Nevertheless, its scalability is a challenge for high-power electric vehicle applications.

Liquid Cooling Systems

Liquid cooling circulates coolants around battery cells, including water-glycol mixtures, for heat transfer. Unlike air systems, liquid cooling attains higher thermal uniformity. E.g., optimized cold plates decrease temperature differences to less than 2 K. Despite their efficiency in keeping temperatures below 40 °C under heavy loads, liquid cooling systems are complex and need sealing to avert leaks. Tesla's liquid-cooled battery packs showcase better thermal performance but at a higher cost and upkeep demand than more straightforward air-cooled solutions.

Phase-Change Materials (PCM)

PCM is integrated into BTMS to absorb heat via latent heat during phase transitions.. Such a passive method stabilizes battery temperatures during rapid charging/discharging cycles within ideal ranges. For example, a honeycomb PCM design boosts thermal efficiency and lowers volume by 3.48%. Nonetheless, PCMs might demand supplementary cooling systems once melted, which limits standalone effectiveness. PCM-liquid hybrid systems address this. They realize up to a 7.94% reduction in peak battery temperatures.

Heat Pipes

As a passive solution, heat pipes transfer heat from battery cells to external cooling systems through phase change and capillary action. They dissipate localized heat and decrease maximum cell temperatures by more than 10%. For instance, cylindrical heat pipes in cooling channels augment thermal uniformity and reliability in high-performance applications. Yet, the challenge is to assure pipe material selection to manage long-term thermal and mechanical stresses.

Thermal Pads and Insulation

Thermal pads in battery thermal management systems fill micro-gaps between cells and cooling plates for heat transfer efficiency. High-conductivity thermal pads reduce interfacial resistance, ensuring consistent heat dissipation. Also, insulation materials, including aerogel, protect adjacent components from thermal runaway with temperature barriers. Such materials and active cooling promote battery life and safety in small designs.

Battery Thermal Management in Electric Vehicles (EVs)

Managing battery temperature in EVs is tricky due to high energy demands, environmental fluctuations, and the narrow range of temperature for lithium-ion cells. Excess heat during high-speed driving or charging comes from joule heating and electrochemical reactions. Meanwhile, localized hotspots might be above 50°C and risk thermal runaway. 

Battery thermal management systems (BTMS) employ precise techniques to regulate temperature and enhance efficiency. As mentioned, they may include liquid cooling, which uses ethylene glycol-water mixtures in microchannel plates to decrease thermal resistance by 30%. Another option is PCM, which stabilizes temperature surges and absorbs latent heat during melting. Heat pipes enable passive heat transfer with thermal resistances under 0.1°C/W. It gives uniformity under rapid acceleration or charging currents. So, it raises EV reliability and decreases thermal imbalance-related efficiency losses.

Challenges in Battery Thermal Management

• Power Density: Heat generation becomes more concentrated within limited cell volumes as power density rises. It amplifies thermal gradients across the separator and electrodes. Consequently, localized hotspots can trigger uneven degradation, lithium plating, or thermal runaway. In-plane cooling via continuous-tab designs or embedding high-thermal-conductivity materials within cells can soften these effects. Yet, balancing these solutions with minimum weight and volume increases is still a challenge.

• Environmental Conditions: Grave climates demand flexibility from the battery thermal management system. At low temperatures, electrolyte viscosity increases, which decreases ionic mobility and accelerates lithium plating during charging. Conversely, high temperatures prompt rapid electrolyte decomposition and SEI layer growth for premature capacity loss. Asymmetric temperature modulations have proven effective, including preheating batteries before use and cooling them postoperatively. Still, these systems must account for parasitic energy use, which limits EV range and efficiency.

• Cost and Complexity: Liquid cooling systems provide high thermal conductivity and temperature control. Notwithstanding, they increase cost, assembly complexity, and upkeep demands in high-voltage packs. Immersion cooling with dielectric fluids shows promise. But it needs validation of fluid stability and effects on energy density. Meanwhile, air-based systems are simpler but fail to meet performance benchmarks for high-energy-density packs. Passive heat-tolerant battery designs could lower reliance on external systems. They help decrease costs without sacrificing safety.

Innovations in Battery Thermal Management

AI-powered BTMS optimization leverages neural networks to predict heat flow patterns and implement real-time adjustments, reducing energy consumption. In high-power applications, graphene-infused PCMs increase thermal conductivity by up to 472% (compared to pure paraffin wax) to assure fast heat dissipation. Modular solutions simplify manufacture and can guarantee temperature homogeneity with scalable cooling plates for EV battery packs from 50 to 200 kWh. Such improvements boost heat management efficiency, life, and safety.

For more information about battery thermal management systems, contact us.