Thermal Ground Plane Technology for Battery Thermal Management 

ISSUE ADDRESSED

Currently, Li-ion batteries are the main type of battery used in electric vehicles due to their high specific energy density and cycle stability. However, electrochemical reactions in the battery generate heat and the resulting temperature rise has significant impacts on battery performance, safety and life. Although the tolerable operating temperature range is -10oC to 50oC, the recommended temperature range is between 20oC and 45oC. Additionally, if the battery temperature reaches 80oC to 90oC, an uncontrolled exothermic reaction is triggered, which can lead to thermal runaway and the battery may catch fire. So, although a vehicle's operating temperature is typically between -45oC to 55oC, the more limited operating range of the battery clearly demonstrates the need for an effective battery thermal management system.

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TECHNOLOGY

Our cooling technology is based on thermal ground planes (TGPs), also known as 2D heat pipes. TGPs transport heat by liquid-vapor phase change and wick in a sealed cavity and act as thermally conductive devices that are lightweight, compact and high performance. They are installed between battery cells to keep the cells within the required temperature range and reject heat to the surrounding environment. Their slim profile and flexible form factors allow access to areas of the battery pack that are typically not cooled by current thermal management solutions. To meet the size, cost and weight requirements of electric vehicles, the traditional manufacturing methods used for copper heat pipes and vapor chambers are not adequate. So we invented a new approach to make low-cost, high-performance TGPs.

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ADVANTAGES

The advantages of thermal ground planes (TGP) are:

• They provide a 75% cost reduction compared to existing copper PMTs through the use of inexpensive hardware.

• They are 70% lighter than copper systems, contributing to a lighter battery pack, which is essential for applications such as electric aircraft.

• Uniformity in battery cell temperature results in an estimated 25-30% increase in battery life, with cell cell non-uniformity being a significant cause of battery degradation.

• The flexible shape and low thermal resistance allow efficient transport of heat from the battery cell to the outer casing of the case. This seals the battery packs hermetically, which is essential in the event of a thermal runaway.

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APPLICATIONS

The global electric vehicle (EV) market will grow from $75.7 billion in 2017 to approximately $127.7 billion in 2022, with a compound annual growth rate (CAGR) of 11% over this period (BCC research, 2018). Specific types of vehicles that use Li-ion batteries include:

• Passenger vehicles (sedans, microcars, SUVs, crossover SUVs, pickup trucks, sports cars).

• Low-speed vehicles (golf carts, neighborhood electric vehicle, personal mobility devices, POD).

• Scooters (two-wheelers, motorcycles, some three-wheelers).

• Bus

• Commercial/industrial vehicles (handling equipment, load carriers, forklifts, trucks).

A battery pack is composed of several battery modules which are composed of several cells, as well as safety components, electrical interconnections, thermal management and battery management systems (BMS) which are all contained in a hard case. The annual market value of battery pack components (including cells, battery management system (BMS), thermal management, safety components, electrical interconnects, and enclosure) will reach $87.3 billion. by 2023, compared to 20 billion in 2017 with a compound annual growth rate (CAGR) of 27.6% (Yole Développement, 2018). In this same report, an evaluation of the costs of a battery pack shows that the thermal management share represents 10% of the cost of a battery pack and that it will remain close to this fraction throughout this period with current technologies, reaching $7.2 billion by 2023.

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INTELLECTUAL PROPERTY STATUS

TECHNOLOGY MATURITY

• TRL 4 – Validation of prototypes in the laboratory.

INTELLECTUAL PROPERTY

• US patent pending.

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WHAT WE ARE LOOKING FOR

• Development partner(s)

• Looking for investments

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PROOF OF CONCEPT

• Thermal Ground Planes (TGPs) transport heat by liquid-vapor phase change in a sealed cavity and act as lightweight, compact, high thermal performance devices for battery thermal management in electric vehicles (Figure 1.a ).

• They are installed between the battery cells to keep them at a low and uniform temperature to efficiently extract heat from the battery module (Figure 1.b). They look like thin plates with a flexible form factor that can be adapted to the battery pack. The plates, however, are hollow and consist of closed chambers lined with a wick structure, partially filled with a liquid such as water or acetone. The liquid that evaporates in the TGP from the heat produced by the cells travels along the TGP to the cold end where it condenses to then release the heat through an external heat sink connected to the cold side of the TGP. This process occurs with negligible temperature difference, as demonstrated by heat pipes operating on this principle with thermal conductivities more than >20 times higher than equivalent aluminum or copper plates. Cell temperatures are thus kept uniform and heat is efficiently conducted to the outer surface of the battery module to facilitate rejection by air or liquid cooling.

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Project Director: François Nadeau