Navy

Improved heat dissipation in rechargeable battery cells

Applicable to small batteries used in hand tools and electronics or large batteries used in electric vehicles

Energy Electronics

Dr. Jason Ostanek, working for the U.S. Navy, has invented heat-dissipating design improvements for rechargeable battery cells. The patented technology is available via license agreement to companies that would make, use, or sell it.

Li-ion cells are typically manufactured in either a prismatic or cylindrical shape, also known as a “jelly-roll,” and are commonly available on the commercial market for laptops and power tools to electric vehicles.

The spiral-wound design characterizes most cylindrical rechargeable batteries, such as lithium-ion (Li-ion) batteries, nickel-cadmium (NiCd) batteries, and nickel-metal hydride (NiMH) batteries.

A major drawback of conventional cylindrical cell architecture is the difficulty for heat removal from the very center of the cell, due to the spiral windings internal to the cell. Conventional prismatic cells also tend to be deficient in shedding heat across (e.g., normal to) the adjacent layers, even those cells that are rather flat, e.g., similar to the shape of a notepad.

Generally speaking, cell operation at cold temperatures results in reduced performance, and cell operation at high temperatures results in a reduced lifetime. In addition, cell operation at high temperatures poses a risk of cell failure (fire or explosion) that is potentially dangerous to anyone near the battery.

In order to ensure safe and reliable operation, a cell should be maintained at reasonable temperatures (e.g., at room temperature), and the temperature gradient within the cell itself should be kept to a minimum.

Traditionally, cylindrically wound battery cells have a central axial component that is solid or hollow and that extends partially or completely along the length of the cell. Such approaches to improving heat conduction characteristics of a cell seek to remove heat at the axial core of the cell using an axially-extended heat conductor.

For instance, heat can be conducted by a device extending longitudinally-axially through a hollow core region of a cylindrical cell, or by a coolant medium that is passed through a pipe extending longitudinally-axially through a hollow core region of a cylindrical cell. While configurations of this nature may improve the ability of a cell (such as a cylindrical cell) to shed heat from the centermost regions, thermal conduction in the “out-of-plane” direction is usually a significant limiting factor.

The Navy’s design enhancement is applicable to practically any cell shape (cylindrical, prismatic,) and practically any cell chemistry (lithium-ion, lead-acid, etc.).

It uses at least one high heat-conductivity plate (e.g., metal plate) that extends in the out-of-plane direction to the inside periphery within the cell casing.

Each thermally conductive plate is oriented in the out-of-plane direction so that its entire perimeter is at least substantially contiguous with the interior wall of the battery’s casing.

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