Thermal Management with Phase Change Material

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Heat is a lithium-ion battery’s greatest enemy.  Batteries generate heat as a natural byproduct when they discharge electricity, and they are often placed in hot environments or in direct sunlight.  Regardless of the source of the heat or the specific battery chemistry, when lithium-ion batteries get too hot, three bad things can happen: cycle life decreases, battery performance decreases, and the risk of a battery fire or explosion increases.

In large applications, such as automobiles and large stationary arrays, air conditioning or liquid cooling systems are often used to prevent overheating.  These active thermal management solutions are bulky, heavy, expensive, and require a portion of the energy stored in the battery to operate.  In smaller applications, like bicycles, scooters, mobile and portable systems, there is typically no thermal management system employed.  In both cases there is clearly a need for a better approach to thermal management.

Using technology developed and patented at the Illinois Institute of Technology, AllCell has found a solution to the thermal management challenge that is simple, lightweight, low cost, and passive.  AllCell uses a phase change material (PCM) – typically wax - combined with graphite to manufacture a composite material that has no moving parts and requires no energy to operate, yet provides effective protection against heat.  When integrated into a lithium-ion battery pack, AllCell’s PCM composite:

How It Works

The lithium-ion cells in the battery pack are placed in direct contact with our composite PCM.  As the pack heats up, the graphite acts as a thermal conductor and spreads the heat evenly throughout the pack, avoiding hot spots and ensuring temperature uniformity.  Once the temperature reaches the melting point of the PCM, all additional thermal energy is absorbed by the melting process rather than continuing to raise the temperature.  In this way the melting point of the PCM sets a temperature ceiling that cannot be exceeded until all of the PCM is melted (see graph below).  Even though the PCM is “melting” the composite material itself remains solid even at extremely high temperatures and nothing leaks out.  By selecting different raw materials and designing with each product’s lithium-ion chemistry and duty cycle in mind, AllCell can control the maximum temperature in each pack to ensure optimal performance and extended cycle life. 

PCM Graph v2

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