In electric vehicles (EVs), the Thermal Management System (TMS) plays a vital role in the performance, safety, and longevity of key components.
Unlike vehicles equipped with internal combustion engines, the heat generated in electric cars originates from sources such as the battery pack, electric motor, and power electronics.
To precisely control this heat, coolant (thermal fluid) is used throughout the system.

Composition and Properties of EV Coolant

The coolant used in electric vehicles typically consists of a mixture of deionized water and ethylene glycol (EG) or propylene glycol (PG).

Main characteristics of this mixture include:

• Freezing point reduction to approximately –37 °C at a 50/50 ratio
• Boiling point increase up to around 107 °C
• Effective heat transfer over a wide temperature range
• High electrical resistance to prevent short circuits in case of leakage
• Contains additives such as corrosion inhibitors, anti-foam agents, and chemical stabilizers

Components of Electric Vehicles That Use Coolant

1. Battery Cooling System

This is the most critical area where coolant is used in electric vehicles.

• Lithium-ion batteries generate heat during both charging and discharging cycles.

• Excessive heat can reduce battery life, lower performance, or even pose fire risks.

• Coolant circulates through channels between the battery cells or underneath the battery pack to transfer heat.

• In some vehicles, the coolant flows through cooling plates that make indirect contact with the cells.

2. Electric Motor Cooling

Electric motors also generate significant heat during operation—especially under high loads.

• Coolant flows around the stator and, in some designs, even through the shaft or rotor.
• Precise temperature control improves motor efficiency and reduces power losses.

3. Inverter & Power Electronics Cooling

The inverter converts the DC current from the battery into AC current for the motor.

• Power transistors (such as IGBTs or SiC MOSFETs) produce heat during switching.
• Coolant removes this heat through cooling plates attached to these components.

4. On-board Charger Cooling

During high-voltage or fast charging, the on-board charger also generates considerable heat.

• A shared or dedicated coolant circuit helps maintain its optimal temperature.

5. HVAC Integration

In many electric vehicles, the battery cooling system and cabin climate system are integrated.

• In winter, the coolant’s waste heat is used to warm the cabin via a heat pump.
• In summer, the air conditioning system may lower the coolant temperature to cool the battery.

Types of Coolants Used in Electric Passenger Vehicles

Updated on 18th October, 2025