Composite heat spreader and battery module incorporating the same

Abstract

A composite heat spreader includes a first flexible graphite layer, a second flexible graphite layer, and a gas evolving layer positioned between the first flexible graphite layer and the second flexible graphite layer. The gas evolving layer is temperature sensitive and when a threshold temperature is reached, the thermal conductivity of the gas evolving layer is reduced by at least factor of five.

What is claimed: 
     
       1. A composite heat spreader comprising:
 a first flexible graphite layer; 
 a second flexible graphite layer; 
 a gas evolving layer positioned between said first flexible graphite layer and said second flexible graphite layer wherein the composite heat spreader has a predetermined thru-thickness thermal conductivity; and 
 wherein when a threshold temperature is reached, the thermal conductivity of said gas evolving layer is reduced by at least factor of five thereby reducing the predetermined thru-thickness thermal conductivity of the composite heat spreader, said threshold temperature is below about 150 degrees C. 
 
     
     
       2. The composite heat spreader according to  claim 1  wherein said first and said second flexible graphite layer comprises a sheet of a compressed mass of exfoliated natural graphite particles. 
     
     
       3. The composite beat heat spreader according to  claim 1  wherein said first and said second flexible graphite layer comprises a sheet of graphitized polyimide. 
     
     
       4. The composite heat spreader according to  claim 1  wherein said first and said second flexible graphite layer have an in-plane thermal conductivity of from between about 250 W/mK and about 700 W/mK. 
     
     
       5. The composite heat spreader according to  claim 1  wherein said first and said second flexible graphite layer have an in-plane thermal conductivity greater than at least about 400 W/mK. 
     
     
       6. The composite heat spreader according to  claim 1  wherein said gas evolving layer comprises a hydrocarbon polymer. 
     
     
       7. The composite heat spreader according to  claim 1  wherein said threshold temperature is at least about 95 degrees C. 
     
     
       8. The composite heat spreader according to  claim 1  wherein after said threshold temperature is reached, the average thickness of said gas evolving layer increases by at least about 10 percent. 
     
     
       9. The composite heat spreader according to  claim 1  wherein after said threshold temperature is reached, the average thickness of said gas evolving layer increases by at least about 50 percent. 
     
     
       10. The composite heat spreader according to  claim 1  further comprising a containment shell. 
     
     
       11. The composite beat heat spreader according to  claim 10  wherein said containment shell encapsulates said first flexible graphite layer, said second flexible graphite layer and said gas evolving layer. 
     
     
       12. A battery pack comprising:
 a plurality of battery cells arranged in a stacked configuration, said battery cells each including opposed major surfaces; 
 at least one composite heat spreader positioned between two adjacent battery cells and contacting a major surface of each said adjacent battery cells; 
 said composite heat spreader comprising a first flexible graphite layer, a second flexible graphite layer, a gas evolving layer positioned between said first flexible graphite layer and said second flexible graphite layer wherein the composite heat spreader has a predetermined thru-thickness thermal conductivity, and wherein when a threshold temperature is reached, the thermal conductivity of said gas evolving layer is reduced by at least a factor of five thereby reducing the predetermined thru-thickness thermal conductivity of the composite heat spreader, said threshold temperature is below about 150 degrees C. 
 
     
     
       13. The battery pack according to  claim 12  wherein said first and said second flexible graphite layer comprises either a sheet of a compressed mass of exfoliated natural graphite particles or a sheet of graphitized polyimide. 
     
     
       14. The battery pack according to  claim 12  wherein said first and said second flexible graphite layer have an in-plane thermal conductivity of at least about 250 W/mK. 
     
     
       15. The battery pack according to  claim 12  wherein said gas evolving layer comprises a hydrocarbon polymer. 
     
     
       16. The battery pack according to  claim 12  wherein said threshold temperature is at least about 95 degrees C. 
     
     
       17. The battery pack according to  claim 12  wherein after said threshold temperature is reached, the average thickness of said gas evolving layer increases by at least about 10 percent. 
     
     
       18. The battery pack according to  claim 12  each said battery cell is electrically connected to an electrical system and wherein after said threshold temperature is reached at least one battery is electrically disconnected from said electrical, electrical system. 
     
     
       19. The battery pack according to  claim 12  further comprising a containment shell that encapsulates said first flexible graphite layer, said second flexible graphite layer and said gas evolving layer. 
     
     
       20. A composite heat spreader comprising:
 a first flexible graphite layer;   a second flexible graphite layer;   a gas evolving layer including an expandable graphite, said gas evolving layer positioned between said first flexible graphite layer and said second flexible graphite layer wherein the composite heat spreader has a predetermined thru-thickness thermal conductivity; and   wherein when a threshold temperature is reached, the thermal conductivity of said gas evolving layer is reduced by at least factor of five thereby reducing the predetermined thru-thickness thermal conductivity of the composite heat spreader, said threshold temperature is at or above about 150 degrees C.    
     
     
       21. The composite heat spreader according to claim 20 wherein said first and said second flexible graphite layer comprises a sheet of a compressed mass of exfoliated natural graphite particles.  
     
     
       22. The composite heat spreader according to claim 20 wherein said first and said second flexible graphite layer comprises a sheet of graphitized polyimide.  
     
     
       23. The composite heat spreader according to claim 20 wherein after said threshold temperature is reached, the average thickness of said gas evolving layer increases by at least about 10 percent.  
     
     
       24. The composite heat spreader according to claim 20 wherein after said threshold temperature is reached, the average thickness of said gas evolving layer increases by at least about 50 percent.  
     
     
       25. A battery pack comprising: a plurality of battery cells arranged in a stacked configuration, said battery cells each including opposed major surfaces;
 at least one composite heat spreader positioned between two adjacent battery cells and contacting a major surface of each said adjacent battery cells;   said composite heat spreader comprising a first flexible graphite layer, a second flexible graphite layer, a gas evolving layer including an expandable graphite, said gas evolving layer positioned between said first flexible graphite layer and said second flexible graphite layer wherein the composite heat spreader has a predetermined thru-thickness thermal conductivity, and   wherein when a threshold temperature is reached, the thermal conductivity of said gas evolving layer is reduced by at least a factor of five thereby reducing the predetermined thru-thickness thermal conductivity of the composite heat spreader, said threshold temperature is at or above about 150 degrees C.    
     
     
       26. The battery pack according to claim 25 wherein said first and said second flexible graphite layer comprises either a sheet of a compressed mass of exfoliated natural graphite particles or a sheet of graphitized polyimide.  
     
     
       27. The battery pack according to claim 25 wherein after said threshold temperature is reached, the average thickness of said gas evolving layer increases by at least about 10 percent.  
     
     
       28. The battery pack according to claim 25 each said battery cell is electrically connected to an electrical system and wherein after said threshold temperature is reached at least one battery is electrically disconnected from said electrical system.