Active, dynamic, and reversible shape memory alloy film thermo-mechanical safety switches

A battery system for a lithium-ion battery (LIB) cell, the battery system comprising:

• a first electrical interface;
• a safety switch connected to the first electrical interface, the safety switch including:
• a shape memory alloy element configured to reversibly transition between an unactuated configuration and an actuated configuration in response to a change in temperature of the LIB cell, wherein the shape memory alloy element transitions to the actuated configuration in response to reaching an activation temperature, and wherein the shape memory alloy element returns to the unactuated configuration in response to cooling below a threshold temperature;
• a first electrically conductive layer positioned adjacent to and uniformly covering substantially all of a first surface of the shape memory alloy element;
• and
• a second electrically conductive layer positioned adjacent to and uniformly covering substantially all of a second surface of the shape memory alloy element;
• and
• a second electrical interface connected to the safety switch, wherein the connection between the first electrical interface, the safety switch, and the second electrical interface enables electrical current to flow through the LIB cell;
• wherein when the shape memory alloy element is in the unactuated configuration, the safety switch directly engages the first electrical interface and the second electrical interface and enables electrical current to flow through the LIB cell;
• wherein when the shape memory alloy element is in the actuated configuration, the safety switch disconnects from at least one of the first electrical interface and the second electrical interface and disables electrical current from flowing through the LIB cell;
• and
• wherein the shape memory alloy element comprises a crystalline shape memory alloy layer and an amorphous shape memory alloy layer, the amorphous shape memory alloy layer configured to reduce stress associated with a reversible phase change of the crystalline shape memory alloy layer.