Nonaqueous electrochemical cell with improved energy density

Abstract

This invention relates to a nonaqueous cell comprising a lithium metallic foil anode and a cathode coating comprising iron disulfide as the active material wherein the coating is applied to at least one surface of a metallic substrate that functions as the cathode current collector. In particular, the cell of the within invention has improved performance on high rate discharge and is achieved, surprisingly, with an anode underbalance. The cell of the within invention has an anode to cathode input that is less than or equal to 1.0. We have discovered, unexpectedly, that the energy density for the cell both volumetrically and gravimetrically can be improved by approximately 20 to 25% while only increasing the volume of the cathode coating solids by approximately 10% through a unique and novel cathode coating formulation used in conjunction with a lithium foil anode.

1. An electrochemical cell comprising a nonaqueous electrolyte, an anode and a cathode assembly, the electrolyte comprising a solvent, the cathode assembly comprising a metallic cathode current collector having two major surfaces and a cathode coating disposed on at least one of the two major surfaces, the coating comprising iron disulfide, and the anode comprising metallic lithium, wherein the interfacial anode to cathode input ratio is less than or equal to 1.0. 
     
     
       2. The cell of  claim 1 , wherein the metallic lithium is alloyed with aluminum. 
     
     
       3. The cell of  claim 2 , wherein the metallic lithium comprises less than 1.0 percent by weight of aluminum. 
     
     
       4. The cell of  claim 3 , wherein the metallic lithium comprises between 0.1 and 0.9 percent by weight aluminum. 
     
     
       5. The cell of  claim 4 , wherein the metallic lithium comprises 0.5 percent by weight of aluminum. 
     
     
       6. The cell of  claim 1 , wherein the cathode coating further comprises a void volume of less than 43 percent. 
     
     
       7. The cell of  claim 6 , wherein the void volume is from 36 percent to 42 percent. 
     
     
       8. The cell of  claim 7 , wherein the cathode coating further comprises synthetic graphite. 
     
     
       9. The cell of  claim 8 , wherein the synthetic graphite is highly crystalline synthetic graphite. 
     
     
       10. The cell of  claim 9 , wherein the highly crystalline synthetic graphite has a mean particle size of 3.0 to 11.0 microns, a BET surface area of 3.0 to 11.0 m 2 /gm and an n-dibutyl phthalate oil absorption ratio of 160 to 200 percent. 
     
     
       11. The cell of  claim 7 , wherein the cathode coating further comprises acetylene black. 
     
     
       12. The cell of  claim 7 , wherein the cathode coating further comprises a micronized polytetrafluoroethylene powder. 
     
     
       13. The cell of  claim 12 , wherein the cathode coating further comprises a styrene-ethylene-butylene-styrene block copolymer. 
     
     
       14. The cell of  claim 13 , wherein the cathode coating further comprises fumed silica. 
     
     
       15. An electrochemical cell comprising a nonaqueous electrolyte, an anode and a cathode assembly, the cathode assembly comprising a metallic cathode current collector having two major surfaces and a cathode coating disposed on at least one of the two major surfaces, the cathode coating comprising iron disulfide, fumed silica, acetylene black and synthetic graphite, and the anode comprising metallic lithium. 
     
     
       16. The cell of  claim 15 , wherein the synthetic graphite and the acetylene black together comprise between 7.0 and 11.0 volume percent of the total solids content of the cathode coating. 
     
     
       17. The cell of  claim 16 , wherein the synthetic graphite and the acetylene black together comprise between 10.0 and 10.5 volume percent of the total solids content of the cathode coating. 
     
     
       18. The cell of  claim 17 , wherein the solids volume percent of the synthetic graphite is at least twice the solids volume percent of the acetylene black. 
     
     
       19. The cell of  claim 15 , wherein the synthetic graphite has a mean particle size of 3.0 to 11.0 microns, a BET surface area of 3.0 to 11.0 m 2 /gm and an n-dibutyl phthalate oil absorption ratio of 160 to 200 percent. 
     
     
       20. The cell of  claim 15 , wherein the cathode coating further comprises a micronized polytetrafluoroethylene powder. 
     
     
       21. The cell of  claim 20 , wherein the cathode coating further comprises a styrene-ethylene-butylene-styrene block copolymer. 
     
     
       22. The cell of  claim 15 , wherein the metallic lithium is alloyed with aluminum. 
     
     
       23. The cell of  claim 18 , wherein the cathode coating further comprises micronized polytetrafluoroethylene, and a styrene-ethylene-butylene-styrene block copolymer, and the synthetic graphite comprises highly crystalline synthetic graphite. 
     
     
       24. The cell of  claim 23 , wherein the cathode components are present in the following solids weight percents: iron disulfide 90.0 to 94.0 percent; acetylene black 1.0 to 3.0 percent; synthetic graphite 3.0 to 6.0 percent; polytetrafluoroethylene 0.2 to 0.6 percent; silica 0.2 to 0.6 percent; SEBS block copolymer 1.5 to 3.0 percent. 
     
     
       25. The cell of  claim 2 , wherein the cathode coating has a void volume of less than  43  percent. 
     
     
       26. The cell of  claim 1 , wherein the anode to cathode input ratio is less than or equal to  0 . 95 . 
     
     
       27. The cell of  claim 1 , wherein the cathode coating further comprises a conductive carbon material. 
     
     
       28. The cell of  claim 27 , wherein the conductive carbon material is synthetic graphite. 
     
     
       29. The cell of  claim 28 , wherein the synthetic graphite is highly crystalline synthetic graphite. 
     
     
       30. The cell of  claim 27 , wherein the conductive carbon material is acetylene black. 
     
     
       31. The cell of  claim 1 , wherein the cathode coating further comprises a rheological modifier. 
     
     
       32. The cell of  claim 31 , wherein the rheological modifier comprises a silanol group. 
     
     
       33. An electrochemical cell comprising:
   a nonaqueous electrolyte comprising at least one solvent;        a jellyroll electrode assembly having an anode and a cathode assembly wound together;        wherein the cathode assembly comprises a metallic cathode current collector with two major surfaces and a cathode coating comprising iron disulfide disposed on at least one of said two major surfaces; and        wherein the anode comprises metallic lithium; and        wherein an interfacial anode to cathode input ratio for the jellyroll electrode assembly is less than  1 . 0 .     
     
     
       34. The electrochemical cell according to  claim 33 , wherein the anode to cathode input ratio is less than or equal to  0 . 95 . 
     
     
       35. The electrochemical cell according to  claim 33 , wherein the metallic lithium is alloyed with aluminum. 
     
     
       36. The electrochemical cell according to  claim 35 , wherein the anode to cathode input ratio is less than or equal to  0 . 95 . 
     
     
       37. The electrochemical cell according to  claim 35 , wherein the anode comprises between about  0 . 1  and  2 . 0  percent by weight of aluminum. 
     
     
       38. The electrochemical cell according to  claim 33 , wherein the jellyroll electrode assembly also has an outer wrap comprising polypropylene. 
     
     
       39. The electrochemical cell according to  claim 33 , wherein the cathode coating has a void volume of less than  43  percent. 
     
     
       40. The electrochemical cell according to  claim 33 , wherein the cathode coating further comprises a conductive carbon material. 
     
     
       41. The cell of  claim 40 , wherein the conductive carbon material is highly crystalline synthetic graphite. 
     
     
       42. The cell of  claim 40 , wherein the conductive carbon material is acetylene black. 
     
     
       43. The cell of  claim 33 , wherein the cathode coating further comprises a rheological modifier. 
     
     
       44. The cell of  claim 43 , wherein the rheological modifier comprises a silanol group. 
     
     
       45. The cell of  claim 33 , wherein the jellyroll electrode assembly has a diameter of at least about  0 . 525  inches. 
     
     
       46. The cell of  claim 33 , wherein the jellyroll electrode assembly further comprises an anode tab. 
     
     
       47. The cell of  claim 46 , wherein the anode tab is bent over the jellyroll electrode assembly. 
     
     
       48. The cell of  claim 1 , wherein the interfacial anode to cathode input ratio=anode capacity per linear inch/cathode capacity per linear inch; wherein the anode capacity per linear inch=( foil thickness )×( interfacial electrode width )×( density of lithium foil at  20 ° C. )×( lithium energy density,  3861 . 7  mAh/g ) ; and wherein the cathode capacity per linear inch= ( final cathode coating thickness )×( interfacial electrode width )×( cathode dry mix density )×( final cathode packing percentage )×( dry weight percent FeS   2 )×( percent purity FeS   2 )×(FeS 2    energy density,  893 . 58  mAh/g ). 
     
     
       49. The cell according to  claim 48 , wherein the metallic lithium is alloyed with aluminum. 
     
     
       50. The cell according to  claim 48 , wherein the metallic lithium comprises less than  1 . 0  percent by weight of aluminum. 
     
     
       51. The cell according to  claim 50 , wherein the metallic lithium comprises between  0 . 1  and  2 . 0  percent by weight of aluminum. 
     
     
       52. The cell according to  claim 51 , wherein the metallic lithium comprises about  0 . 5  percent by weight of aluminum. 
     
     
       53. The cell according to  claim 48 , wherein the cathode coating further comprises a void volume of less than  43  percent. 
     
     
       54. The cell according to  claim 56 , wherein the void volume is from  36  percent to  42  percent. 
     
     
       55. The cell according to  claim 48 , wherein the cathode coating further comprises synthetic graphite. 
     
     
       56. The cell according to  claim 55 , wherein the synthetic graphite has a mean particle size of  3 . 0  to  11 . 0  Pm, a BET surface area of  3 . 0  to  11 . 0  m 2   /g, and a DBP of  160  to  200  percent.   
     
     
       57. The cell according to  claim 48 , wherein the cathode coating further comprises acetylene black. 
     
     
       58. The cell according to  claim 48 , wherein the cathode coating further comprises a micronized polytetrafluoroethylene powder. 
     
     
       59. The cell according to  claim 48 , wherein the cathode coating further comprises a styrene- ethylene - butylenestyrene block copolymer.   
     
     
       60. The cell according to  claim 48 , wherein the cathode coating further comprises fumed silica. 
     
     
       61. The cell according to  claim 48 , wherein the cathode coating further comprises a total of between  7 . 0  and  11 . 0  percent synthetic graphite and acetylene black, based on the total solids content of the cathode coating. 
     
     
       62. The cell according to  claim 48 , wherein the synthetic graphite and the acetylene black together comprise between  10 . 0  and  10 . 5  volume percent of the total solids content of the cathode coating. 
     
     
       63. The cell according to  claim 48 , wherein the solids volume percent of the synthetic graphite is at least twice the solids volume percent of the acetylene black. 
     
     
       64. The cell according to  claim 48 , wherein the electrolyte comprises an organic solvent. 
     
     
       65. The cell according to  claim 48 , wherein the cathode assembly and the anode are wound together into a jellyroll electrode assembly.