Battery of lithium-ion type with a cathode of varying porosity, and a corresponding method
A thin layer lithium-ion type battery comprising, on a substrate ( 20, 30 ), a cathode current collector layer ( 22, 36 ) and an active portion constituted by a stack of a cathode layer ( 23, 35 ) made of material suitable for inserting lithium ions, an electrolyte layer ( 24, 34 ), and an anode layer ( 25, 33 ), wherein the cathode layer presents, across its thickness, porosity that varies between its interface with the cathode current collector layer and its interface with the electrolyte layer, the variation in the porosity being non-zero so as to improve cohesion at both interfaces.
1. A thin layer lithium-ion type battery comprising, on a substrate ( 20 , 30 ), a cathode current collector layer ( 22 , 36 ) and an active portion constituted by a stack of a cathode layer ( 23 , 35 ) made of material suitable for inserting lithium ions, a solid electrolyte layer ( 24 , 34 ), and an anode layer ( 25 , 33 ), wherein the cathode layer presents, across its thickness, porosity that varies between its interface with the cathode current collector layer and its interface with the electrolyte layer, the variation in the porosity being non-zero so as to improve cohesion at both interfaces, wherein the porosity of the cathode layer ( 23 , 35 ) is greater at an interface between the cathode layer ( 23 , 35 ) and the cathode current collector layer ( 22 , 36 ) than at an interface between the cathode layer ( 23 , 35 ) and the electrolyte layer ( 24 , 34 ).
2. A battery according to claim 1 , wherein the porosity of the cathode layer lies in the range 0 to 70%.
3. A battery according to claim 1 , wherein the variation in the porosity is discontinuous.
4. A battery according to claim 1 , wherein the variation in the porosity is continuous.
5. A battery according to claim 1 , wherein the cathode current collector layer ( 22 , 36 ) is made of titanium, the cathode layer ( 23 , 35 ) is made of TiOS associated with lithium ions, and the electrolyte layer ( 24 , 34 ) is made of LiPON.
6. A method of making a thin layer lithium-ion type battery comprising, on a substrate ( 20 , 30 ), a cathode current collector layer ( 22 , 36 ) and an active portion constituted by a stack of a cathode layer ( 23 , 35 ) made of material suitable for inserting lithium ions, a solid electrolyte layer ( 24 , 34 ), and an anode layer ( 25 , 33 ), wherein the cathode layer ( 23 , 35 ) is obtained by depositing a material on the cathode current collector layer ( 22 ) or on the electrolyte layer ( 34 ), at least one parameter of the deposition technique used being modified between the beginning and the end of deposition operations so that the cathode layer presents, across its thickness, porosity that varies between its interface with the cathode current collector layer and its interface with the electrolyte layer, the variation in the porosity being non-zero, wherein the porosity of the cathode layer ( 23 , 35 ) is greater at an interface between the cathode layer ( 23 , 35 ) and the cathode current collector layer ( 22 , 36 ) than at an interface between the cathode layer ( 23 , 35 ) and the electrolyte layer ( 24 , 34 ).
7. A method according to claim 6 , wherein the technique used is a physical vapor deposition technique, said at least one parameter being selected from the temperature of the substrate and the deposition rate.
8. A method according to claim 6 , wherein said at least one parameter is modified at least once during the deposition operations.
9. A method according to claim 6 , wherein said at least one parameter is modified continuously during the deposition operations.
10. A battery according to claim 2 , wherein the porosity of the cathode layer lies in the range 0 to 50%.