Lithium ion secondary battery
In order to provide a lithium ion secondary battery having both high energy density and an excellent charge-rate characteristic, there is provided a lithium ion secondary battery including a positive electrode containing a positive electrode active material made of a lithium composite oxide, and nano-carbon having a Li ion diffusion path as an additive, and an electrolyte solution containing 0.5 mol/l or more of Li[(FSO 2 ) 2 N] as an electrolyte, LiPO 2 F 2 as an additive, and a ternary-system of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), as solvents.
1. A lithium ion secondary battery comprising:
a positive electrode comprising a positive electrode active material made of a lithium composite oxide, and nano-carbon having a Li ion diffusion path as an additive, and
an electrolyte solution comprising 0.5 mol/1 or more of Li[(FSO 2 ) 2 N] as an electrolyte, LiPO2F2 as an additive, and a ternary-system of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), as solvents;
wherein the nano-carbon comprises porous graphene and satisfies the following conditions:
(1) The porous graphene has 1 to 200 graphene layers,
(2) The sizes of pores in a graphene basal plane range from 70 nm to 200 nm,
(3) The number of pores in each graphene basal plane is 10 to 500 per μm 2 ,
(4) Oxygen content is 0.8 mass % or less,
(5) In Raman spectroscopy, the peak intensity-ratio I D /I G , which is the ratio of the peak in G band present within the range of 1596 to 1570 cm −1 to the peak in D band near 1360 cm −1 , is 0.6 to 1.35, and
(6) Pore volumes fall within the range of 1.35 to 3 cm 3 /g.
2. The lithium ion secondary battery according to claim 1 , wherein the nano-carbon coats a surface of the positive electrode active material in the positive electrode.
3. The lithium ion secondary battery according to claim 1 , wherein the electrolyte contains Li[(FSO 2 ) 2 N] and other electrolyte, and the molar ratio of Li[(FSO 2 ) 2 N] to the other electrolyte is 1 or more.
4. The lithium ion secondary battery according to claim 3 , wherein the other electrolyte is LiPF 6 .
5. The lithium ion secondary battery according to claim 3 , wherein a total concentration of the electrolytes in the electrolyte solution is 0.6 to 2 mol/L.
6. The lithium ion secondary battery according to claim 1 , wherein the LiPO 2 F 2 is contained in an amount of 0.005 to 7 mass % in the electrolyte solution.
7. The lithium ion secondary battery according to claim 1 , wherein the ternary-system of solvents are contained in a volume ratio represented by the following expression (1):
EC/DMC/EMC= x:y: 1− x−y (1)
wherein x is 0.15 to 0.5; y is 0.2 to 0.6; and x+y<1.
8. The lithium ion secondary battery according to claim 1 , wherein the lithium composite oxide is a material having a layered structure.
9. The lithium ion secondary battery according to claim 8 , wherein the material having a layered structure is a lithium-cobalt-nickel-manganese composite oxide.