Types of Battery thermal management Systems

Battery thermal management (BTMS) systems are of several types. BTMS with evolution of EV battery technology becomes a critical system. Earlier battery systems were just reliant on passive cooling. Now with increased size (kWh capacity), Voltage (V), Ampere (amps) in proportion to increased range requirements make the battery thermal management system a key part of the EV Auxiliary power systems. Another parameter is Temperature. Temperature has big effect on performance and workings of battery or battery pack.

In the article above from Nigel Taylor you can see in detail importance of Temperature and thus why battery thermal management system.

Types of battery thermal management systems.

different types of battery thermal management system

Battery thermal management systems are primarily split into three types:

  1. Active Cooling
  2. Passive Cooling
  3. Hybrid

Active Cooling

Active Cooling is split into three types:

  1. Force Air Cooling
  2. Liquid cooling
  3. Thermoelectric cooling

Force Air cooling

The cell or cells are held in an enclosure, air is forced through the battery pack and cools the cells. This approach can use waste cabin air that will have been filtered and cooled.Power consumption wise it consumes only power of the fan motor and thus is very light on the overall auxiliary system power consumption and thus the range. As opposed to passive air cooling which depends on external air flow speed rate this method is better as the speed rate of Air flow is controlled by a fan. Thus the rate of heat transfer between the batteries and air can be controlled by speed of fan. The heat transfer is done by forced air convection.

There can be also forced air convection between air to liquid cooling through Heat Exchanger.

Toyota Prius

We have a great article on benchmarking Toyota Prius battery pack.

Lexus UX300e battery

Lexus UX 300e also uses Air Cooling. We have another benchmarking article to go in details on the website. Link

Outside of Toyota family, Volkswagen eGolf is another OEM vehicle model which also will use Forced Air cooling. Initially VW went with liquid cooling but then changed the decision to Air Cooling.

Liquid Cooling

Liquid Cooling method involves moving a heat transfer capable liquid like a coolant over the batteries to transfer heat in or out of the batteries. Heat Transfer capability of the coolant depends on the properties of the coolant like viscosity, density, thermal conductivity and also the flow rate of the coolant. Coolants are typically a variant of ethylene glycol.

The Heat Transfer can be done Liquid to Liquid/Air through Heat exchanger/Chiller or with Cold/Hot coolant. This will depend if the EV has heat pump or not. There can be additional PTC heaters helping with the heating cycle. The Schematics is just for informational purposes. Below the schematics there are many actual OEM examples. The coolant and flows are complex depending on various modes.

Tesla Model 3 Liquid cooling System

Source: Munro and Jalopnik

Source: Conflux

My Favourite video from YouTube is below. It’s long 1 hour by Profession John Kelly but it explains very nicely and clearly Tesla Heat Pump system.

Porsche Taycan

Hyundai and Kia

Thermoelectric cooling

Thermoelectric cooling is based on Peltier effect. There are no moving parts, no vibration, its small and the operation of cooling can be controlled by controlling the current. I have done a schematic below but feel free to read in detail in the article done by Tycrorun. What is Thermoelectric Cooling?

Passive Cooling

Passive cooling can be through natural air convection where the air moves through the battery pack due to change in density. In this case there is no power consumption as there is no Pumps, Fans, Compressors involved in this system. This is the most simplest form of cooling system but in today’s world this system is not at all efficient as it only works in certain conditions and is extremely dependant on outside air temperature.

Passive cooling can be further divided into Two Types:

Passive cooling by Phase Change Material (PCM)

A solid to liquid phase change material is packaged next to the cells. This temperature at which the material changes phase is normally set around 50 to 70°C so that it can essentially add thermal inertia to overheating cells.

phase change material cooling

Passive cooling by Heat Pipe

Please go to this link to read in detail about Heat Pipes as it’s slightly more complex than other systems.

Tycorun: what is Heat Pipe based battery cooling system?

To make a simplistic explanation I have drawn a schematic below. Heat Pipe has two ends. One side is the Evaporative End where the Heat is absorbed by the liquid medium through absorbent wick to turn into vapour. On the other side is the Condensing end where the vapour gives away the heat to turn into liquid medium again.

The Liquid medium moves from condensing end to the evaporative end and the vapour the other way.

Hybrid Systems

Hybrid systems will be a combination of above systems. Below are the different combinations

  1. Heat Pipe + Air or Liquid Cooling
  2. PCM + Air or Liquid Cooling
  3. PCM + Heat Pipe
  4. Liquid + Air cooling
  5. Others plus thermoelectric cooling

1 thought on “Types of Battery thermal management Systems”

  1. This is a really detailed breakdown of battery thermal management systems! I never knew there were so many different types. Especially the different active cooling methods like forced air vs. liquid cooling seem very interesting. Thanks for sharing this informative post!

Leave a Comment