Core Technologies of Electric Vehicle Battery Thermal Management Systems (BTMS)

The battery thermal management system (BTMS) is a critical component ensuring the safety, performance, and longevity of electric vehicles. It directly determines the vehicle’s performance under extreme temperature conditions and the durability of the battery system.

As lithium battery engineers, we recognize that the BTMS is one of the core technologies in electric vehicles. It is not merely a simple cooling system but a multifunctional integrated system designed to ensure battery safety, enhance performance, and extend lifespan.

Lithium-ion batteries are highly temperature-sensitive, with an optimal operating range of 20°C to 35°C. Below 15°C, the rate of internal chemical reactions significantly decreases, leading to a sharp drop in capacity and power output. Above 60°C, thermal runaway may occur, potentially causing severe safety incidents.

I. The Importance of Thermal Management: Temperature’s Impact on Battery Performance

High-temperature environments pose the most direct threat to lithium batteries. When temperatures exceed 60°C, battery capacity degradation accelerates, internal resistance increases, and in extreme cases, thermal runaway may occur, leading to fire or explosion.

Low-temperature environments present equally significant issues. Excessively low temperatures slow down internal chemical reaction rates, causing a sharp decline in capacity and power output, making charging difficult, and potentially triggering lithium plating that damages battery structure.

Temperature inconsistency poses another critical challenge. Significant temperature variations between individual cells or modules within a battery pack lead to uneven performance and accelerate overall pack aging. Ideally, the maximum temperature difference within a battery pack should be controlled at ≤3°C.

II. Working Principle of Lithium Battery Liquid Thermal Management System: Precise Temperature Regulation

The lithium battery liquid thermal management system utilizes circulating coolant as a thermal medium to provide cooling or heating functions for the battery.

Cooling Mechanism

Heat Absorption: Driven by an electric pump, the coolant flows through the liquid cooling plates within the battery pack (directly contacting the battery modules), absorbing heat generated by the battery.

Heat Dissipation: The heated coolant is pumped to the front-end radiator (air-cooled) or exchanges heat with the vehicle’s air conditioning refrigeration system (via a chiller heat exchanger), dissipating the heat into the external air.

Circulation Cycle: The cooled coolant flows back to the battery pack, initiating the next cycle to achieve continuous thermal management.

Heating Mechanism

When battery temperatures drop too low, the system employs PTC heaters (Positive Temperature Coefficient thermistors) to warm the coolant. The warmed coolant flows through the liquid cooling plate, providing uniform heating to the batteries.

Advanced systems further utilize waste heat generated by the electric drive system. Through plate heat exchangers, residual heat is recovered for battery heating, significantly enhancing energy efficiency.

III. Key System Components: A Precision Thermal Management Ecosystem

A typical liquid thermal management system comprises multiple precision components working in concert:

Liquid cooling plate: The core heat exchange component in direct contact with battery modules, typically made of aluminum with precision internal flow channel design. Its design must balance heat dissipation capacity, reliability, and lightweight construction.

Coolant: Requires high thermal conductivity, electrical insulation (to prevent short circuits), low viscosity, a wide operating temperature range, and excellent material compatibility. Ethylene glycol-water mixtures are commonly used, though pure organic alcohols and other dielectric fluids are also employed.

Electric Pump: Provides the driving force for coolant circulation. Its speed is often adjustable to enable demand-based supply and reduce energy consumption.

Heat Exchange System: Includes a chiller (connecting the coolant circuit and air conditioning refrigeration circuit), radiator (dissipating heat through airflow), and plate heat exchanger (facilitating heat exchange between different circuits, such as enabling waste heat recovery).

PTC Heater: A device that rapidly and precisely heats the coolant when heating is required.

Control System: Temperature sensors continuously monitor battery and coolant temperatures. The Battery Management System (BMS) or thermal management controller acts as the system’s central brain. Based on temperature signals and vehicle status, it employs intelligent algorithms to regulate the operational state of actuators including pumps, PTC heaters, valves, and air conditioning compressors.

IV. Intelligent Control Strategies: Algorithm-Driven Energy Efficiency Optimization

Simple on/off switching control no longer meets modern BTMS requirements. Advanced control strategies are critical to system performance and energy efficiency.

Model-Based Predictive Control: The system predicts future battery temperature rise trends based on battery thermal models, ambient temperature, vehicle operating conditions, and other data. It proactively intervenes in thermal management to achieve smoother, more efficient temperature control.

Dynamic Programming Algorithms: Thermal management tasks are decomposed into multiple phases. By solving for the optimal solution in each sub-phase, the strategy achieves the best balance between overall system energy consumption and cooling/heating effectiveness. This helps minimize the thermal management system’s own energy consumption while ensuring battery safety, thereby enhancing vehicle range.

Delayed Cooling Strategy: Research indicates that moderately delaying cooling intervention—rather than initiating continuous cooling immediately upon reaching the battery temperature threshold—significantly reduces system power consumption (experiments show up to approximately 20% reduction) while having minimal impact on the final battery temperature.

Multi-Objective Optimization: Utilizing tools such as Response Surface Methodology (RSM) and genetic algorithms, multiple parameters—including coolant flow rate, inlet temperature, and cooling intervention timing—are synergistically optimized to simultaneously pursue objectives like “lowest possible maximum battery temperature” and “minimum system power consumption.”

V. Technical Advantages and Challenges: Balancing Performance and Complexity

Liquid thermal management systems offer significant advantages but also face certain challenges:

Core Advantages

High heat transfer efficiency: Liquids possess high specific heat capacity, strong thermal conductivity, and rapid heat dissipation, enabling effective management of high-heat scenarios like fast charging.

Excellent temperature uniformity: Effectively reduces temperature differentials within the battery pack, extending overall pack lifespan.

Compact Structure: Easily integrated within battery packs, enabling high energy density.

Environmental Adaptability: Capable of both cooling and heating, suitable for a wide temperature range.

Challenges

System Complexity: Multiple components (pumps, valves, tubing, etc.) result in relatively higher costs and greater design/layout challenges.

Potential Leakage Risks: Coolant leaks may cause insulation failure, short circuits, and other safety hazards, demanding extremely high sealing reliability.

Weight and Energy Consumption: Pumps, PTCs, and additional coolant increase weight and energy usage, necessitating optimized control to minimize impact.

Low-Temperature Protection: In extreme cold, systems must not only heat the battery but also prevent coolant freezing.

VI. Future Development Trends: Integration and Intelligent Innovation

Highly Integrated Systems: Deeply coupling battery thermal management, motor and controller thermal management, and passenger cabin air conditioning systems to form a unified vehicle thermal management system. For example, utilizing heat pump air conditioning systems to efficiently transfer heat between different components, significantly improving energy efficiency.

Precision and Intelligence: Deploying additional sensors combined with AI algorithms enables more accurate temperature prediction and fault diagnosis, resulting in smarter and more efficient control strategies.

New Materials and Media Applications: Exploring more environmentally friendly coolants with superior thermal conductivity. Materials and manufacturing processes for components like liquid cooling plates are also undergoing continuous optimization.

Active Safety and Thermal Runaway Prevention: Thermal management systems are being tasked with active safety responsibilities. Through real-time monitoring and thermal runaway alerts, the system can proactively activate maximum cooling or employ isolation designs upon detecting anomalies, striving to suppress the spread of thermal runaway.

Immersion Cooling Technology: Solutions like Shell’s EV-Plus thermal management fluid utilize immersion cooling, allowing the coolant to permeate every micro-space within battery modules. This achieves more thorough contact between battery cells and the cooling medium, significantly boosting thermal conductivity efficiency. Test data indicates that a 34kWh battery pack using this technology can complete a 10% to 80% charge within ten minutes.

Battery thermal management systems based on liquid cooling and heating efficiently transfer heat through coolant and utilize intelligent control algorithms for precise regulation. They represent the mainstream and highly effective technical solution for ensuring the safety, optimal performance, and extended lifespan of electric vehicle power batteries.

Although the system is relatively complex and faces cost pressures, its superior thermal control capabilities and potential make it crucial for addressing future demands for higher energy density batteries and faster charging. As technology continues to evolve, more integrated, intelligent, and efficient thermal management systems will become a key driver for the further advancement of electric vehicles.