Positive electrode for secondary battery, secondary battery, and method for fabricating positive electrode for secondary battery
A positive electrode for a secondary battery which enables both good battery characteristics and electrode strength at a predetermined level, a secondary battery, and a method for fabricating the positive electrode for a secondary battery are provided. The positive electrode for a secondary battery includes a current collector and an active material layer over the current collector. The active material layer includes an active material, graphene, and a binder. A carbon layer is on a surface of the active material. The proportion of the graphene in the active material layer is greater than or equal to 0.1 wt % and less than or equal to 1.0 wt %.
1. A positive electrode for a secondary battery comprising:
a current collector; and
an active material layer over the current collector,
wherein the active material layer comprises an active material, graphene, and a binder,
wherein a carbon layer is in contact with a surface of the active material,
wherein a proportion of the graphene in the active material layer is greater than or equal to 0.1 wt % and less than or equal to 1.0 wt %, and
wherein a maximum value of discharge capacity (mAh/g) of the positive electrode is more than or equal to 140 mAh/g at a discharging rate of 1 C.
2. The positive electrode for a secondary battery according to claim 1 , wherein the active material comprises lithium iron phosphate.
3. The positive electrode for a secondary battery according to claim 1 ,
wherein a thickness of the carbon layer is greater than or equal to 1 nm and less than or equal to 50 nm.
4. The positive electrode for a secondary battery according to claim 1 , wherein the carbon layer has an amorphous structure.
5. The positive electrode for a secondary battery according to claim 1 ,
wherein a discharge curve of the positive electrode at a lower limit voltage or more has a plateau in 60 % or more of a measuring range, and
wherein the lower limit voltage is 2 V.
6. A secondary battery comprising the positive electrode for a secondary battery according to claim 1 .
7. An electronic device comprising the secondary battery according to claim 6 .
8. A positive electrode for a secondary battery comprising:
a current collector; and
an active material layer over the current collector,
wherein the active material layer comprises an active material, graphene, and a binder,
wherein a carbon layer is in contact with a surface of the active material,
wherein a proportion of the graphene in the active material layer is greater than or equal to 0.1 wt % and less than or equal to 1.0 wt %,
wherein a maximum value of discharge capacity (mAh/g) of the positive electrode is more than or equal to 140 mAh/g at a discharging rate of 1 C, and
wherein the current collector and the active material layer are not separated from each other in a winding test using a cylinder with a diameter of 6 mm.
9. The positive electrode for a secondary battery according to claim 8 , wherein the active material comprises lithium iron phosphate.
10. The positive electrode for a secondary battery according to claim 8 , wherein a thickness of the carbon layer is greater than or equal to 1 nm and less than or equal to 50 nm.
11. The positive electrode for a secondary battery according to claim 8 , wherein the carbon layer has an amorphous structure.
12. The positive electrode for a secondary battery according to claim 8 , wherein a maximum value of discharge capacity (mAh/g) of the positive electrode is more than or equal to 140 mAh/g at a discharging rate of 1 C.
13. The positive electrode for a secondary battery according to claim 8 ,
wherein a discharge curve of the positive electrode at a lower limit voltage or more has a plateau in 60% or more of a measuring range, and
wherein the lower limit voltage is 2 V.
14. A secondary battery comprising the positive electrode for a secondary battery according to claim 8 .
15. An electronic device comprising the secondary battery according to claim 14 .
16. A method for manufacturing a positive electrode for a secondary battery, comprising the steps of:
coating a surface of an active material with a carbon layer;
mixing the active material coated with the carbon layer, graphene oxide, and a binder to form a mixture so that a proportion of the graphene oxide in the mixture is greater than or equal to 0.2 wt % and less than or equal to 1.0 wt %;
providing the mixture over a current collector; and
reducing the graphene oxide to form an active material layer containing graphene,
wherein a maximum value of discharge capacity (mAh/g) of the positive electrode is more than or equal to 140 mAh/g at a discharging rate of 1 C.
17. The method for manufacturing a positive electrode for a secondary battery according to claim 16 , wherein the active material comprises lithium iron phosphate.
18. The method for manufacturing a positive electrode for a secondary battery according to claim 16 , wherein a thickness of the carbon layer is greater than or equal to 1 nm and less than or equal to 50 nm.