Pressure-relief mechanism to improve safety in lithium-polymer battery cells

A battery pack comprising one or more battery cells coupled together and enclosed in a hard case, wherein each of the one or more battery cells includes:

• a jelly roll comprising layers which are wound together, including a cathode with a first active coating, a separator, and an anode with a second active coating;
• a pouch, which encloses the jelly roll, wherein the pouch is flexible;
• a first conductive tab coupled to the cathode;
• and
• a second conductive tab coupled to the anode;
• wherein the first and second conductive tabs extend through seals in the pouch to provide terminals for the battery cell;
• and
• wherein the pouch includes a weakness which yields when internal pressure in the pouch exceeds a threshold to create a hole which releases the internal pressure, the weakness including a wave pattern of tiny holes that extends from a first end to a second end of a predetermined portion of a seal for the pouch, the predetermined portion located on at least one side of the pouch through which the conductive tabs do not extend.

A method for assembling a battery cell, comprising:

• obtaining a jelly roll comprising layers which are wound together, including a cathode with a first active coating, a separator, and an anode with a second active coating, wherein the jelly roll includes a first conductive tab coupled to the cathode and a second conductive tab coupled to the anode;
• obtaining a pouch to accommodate the jelly roll, wherein the pouch is flexible;
• sealing the jelly roll in the pouch, wherein the pouch is sealed so that the first and second conductive tabs extend through seals in the pouch to provide terminals for the battery cell;
• and
• creating a weakness in the pouch, the weakness including a wave pattern of tiny holes that extends from a first end to a second end of a predetermined portion of a seal for the pouch, the predetermined portion located on at least one side of the pouch through which the conductive tabs do not extend, and the weaknesses configured to yield when internal pressure in the pouch exceeds a threshold to create a hole which releases the internal pressure.