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

Abstract

The disclosed embodiments relate to a battery cell which includes a weakness for relieving pressure. This battery cell includes a jelly roll comprising layers which are wound together, including a cathode with an active coating, a separator and an anode with an active coating. The jelly roll also includes a first conductive tab coupled to the cathode and a second conductive tab coupled to the anode. The jelly roll is enclosed in a flexible pouch, wherein the first and second conductive tabs extend through seals in the pouch to provide terminals for the battery cell. This pouch includes a weakness which yields when internal pressure in the pouch exceeds a threshold to create a hole which releases the internal pressure.

1 . A battery cell with a weakness for relieving pressure, comprising:
 a jelly roll comprising layers which are wound together, including a cathode with an active coating, a separator, and an anode with an 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.   
     
     
         2 . The battery cell of  claim 1 , wherein the pouch includes multiple weaknesses at different locations on the pouch. 
     
     
         3 . The battery cell of  claim 1 , wherein the weakness includes one of:
 a V-shaped notch cut into a seal for the pouch;   a half-circle cut into a seal for the pouch;   a corner of the pouch which is cut;   a pattern of tiny holes formed in a seal for the pouch; and   a thinned region of the pouch material.   
     
     
         4 . The battery cell of  claim 1 , wherein the weakness is located on one of:
 a side seal for the pouch;   a terrace seal for the pouch;   a corner of the pouch;   a fold in the pouch material; and   a location on a surface of the pouch which is not part of a seal.   
     
     
         5 . The battery cell of  claim 1 , wherein the pouch is comprised of:
 a layer of aluminum; and   a layer of polypropylene.   
     
     
         6 . The battery cell of  claim 1 , wherein the battery cell is one of:
 a lithium-polymer battery cell; and   a silver-zinc battery cell.   
     
     
         7 . 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 an active coating, a separator, and an anode with an 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.   
     
     
         8 . The battery pack of  claim 7 , wherein the one or more battery cells are coupled together:
 in series;   in parallel; or   in series and parallel.   
     
     
         9 . The battery pack of  claim 7 , wherein each pouch includes multiple weaknesses at different locations on the pouch. 
     
     
         10 . The battery pack of  claim 7 , wherein the weakness includes one of:
 a V-shaped notch cut into a seal for the pouch;   a half-circle cut into a seal for the pouch;   a corner of the pouch which is cut;   a pattern of tiny holes formed in a seal for the pouch; and   a thinned region of the pouch material.   
     
     
         11 . The battery pack of  claim 7 , wherein the weakness is located on one of:
 a side seal for the pouch;   a terrace seal for the pouch;   a corner of the pouch;   a fold in the pouch material; and   a location on a surface of the pouch which is not part of a seal.   
     
     
         12 . The battery pack of  claim 7 , wherein the pouch is comprised of:
 a layer of aluminum; and   a layer of polypropylene,   
     
     
         13 . The battery pack of  claim 7 , wherein each battery cell is one of:
 a lithium-polymer battery cell; and   a silver-zinc battery cell.   
     
     
         14 . A portable computing device, comprising:
 a processor;   a memory; and   a battery pack, which includes one or more battery cells coupled together;   wherein each of the one or more battery cells includes:
 a jelly roll comprising layers which are wound together, including a cathode with an active coating, a separator, and an anode with an 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. 
   
     
     
         15 . The portable computing device of  claim 14 , wherein the portable device includes one of:
 a laptop or notebook computer system;   a personal digital assistant; and   a cellular telephone.   
     
     
         16 . A method for assembling a battery cell, comprising:
 obtaining a jelly roll comprising layers which are wound together, including a cathode with an active coating, a separator, and an anode with an 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; and   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;   wherein the pouch includes or is configured to include one or more weaknesses, which yield when internal pressure in the pouch exceeds a threshold to create a hole which releases the internal pressure.   
     
     
         17 . The method of  claim 16 , wherein the weakness in the pouch is created:
 prior to sealing the jelly roll in the pouch; or   after sealing the jelly roll in the pouch.   
     
     
         18 . The method of  claim 16 , wherein creating the weakness in the pouch involves creating multiple weaknesses at different locations on the pouch. 
     
     
         19 . The method of  claim 16 , wherein the weakness includes one of:
 a V-shaped notch cut into a seal for the pouch;   a half-circle cut into a seal for the pouch;   a corner of the pouch which is cut;   a pattern of tiny holes formed in a seal for the pouch; and   a thinned region of the pouch material.   
     
     
         20 . The method of  claim 16 , wherein the weakness is located on one of:
 a side seal for the pouch;   a terrace seal for the pouch;   a corner of the pouch;   a fold in the pouch material; and   a location on a surface of the pouch which is not part of a seal.   
     
     
         21 . The method of  claim 16 , wherein the pouch is comprised of:
 a layer of aluminum; and   a layer of polypropylene,   
     
     
         22 . The method of  claim 16 , wherein the battery cell is one of:
 a lithium-polymer battery cell; and   a silver-zinc battery cell.