Lithium-sulfur secondary battery
A lithium-sulfur secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte solution are provided. The positive electrode has an SC factor value of 0.45 or more. The electrolyte solution includes a solvent and a lithium salt, and the solvent includes a first solvent having a DV 2 factor value of 1.7 or less, and a second solvent which is a fluorinated ether-based solvent.
1. A lithium-sulfur secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte solution, wherein the positive electrode has an SC factor value of 0.45 or more represented by Equation 1 below:
SC
factor
=
∝
×
L
P
[
Equation
1
]
wherein P is the porosity (%) of the positive electrode active material layer in the positive electrode, L is the mass of sulfur (mg/cm 2 ) per unit area of the positive electrode active material layer in the positive electrode, and α is 10 (constant),
wherein the electrolyte solution comprises a first solvent, a second solvent, and a lithium salt,
wherein the first solvent is selected from the group consisting of propionitrile, dimethylacetamide, dimethylformamide, triethylamine, 1-iodopropane, and or combinations thereof, and
wherein the second solvent is a fluorinated ether-based solvent.
2. The lithium-sulfur secondary battery according to claim 1 , wherein the electrolyte solution comprises a solvent and a lithium salt, and the solvent includes a first solvent having a DV 2 factor value of 1.75 or less represented by Equation 2 below, and
the lithium-sulfur secondary battery has an NS factor value of 3.5 or less represented by Equation 3 below:
DV
2
factor
=
γ
×
μ
DV
[
Equation
2
]
wherein DV is the dipole moment per unit volume (debye (D)·mol/L), μ is the viscosity of the solvent (cP, 25° C.), and γ is 100 (constant),
NS
factor
=
DV
2
factor
SC
factor
[
Equation
3
]
wherein SC factor is equal to the value defined by Equation 1 above, and DV 2 factor is equal to the value defined by Equation 2 above.
3. The lithium-sulfur secondary battery according to claim 1 , wherein the lithium-sulfur secondary battery has an ED factor value of 850 or more represented by Equation 4 below:
ED
factor
=
V
×
SC
factor
×
C
D
[
Equation
4
]
wherein V is the nominal discharging voltage (V) for Li/Li + , D is the density of electrolyte solution (g/cm 3 ), C is the discharging capacity (mAh/g) at the time of discharging at 0.1 C rate, and SC factor is equal to the value defined by Equation 1 above.
4. The lithium-sulfur secondary battery according to claim 1 , wherein the second solvent is selected from the group consisting of 1H, 1H,2′H,3H-decafluorodipropyl ether, difluoromethyl 2,2,2-trifluoroethyl ether, 1,2,2,2-tetrafluoroethyl trifluoromethyl ether, 1,1,2,3,3,3-hexafluoropropyl difluoromethyl ether, pentafluoroethyl 2,2,2-trifluoroethyl ether, 1H, 1H,2′H-perfluorodipropyl ether, and combinations thereof.
5. The lithium-sulfur secondary battery according to claim 1 , wherein the solvent contains the first solvent in an amount of 1% by weight to 50% by weight.
6. The lithium-sulfur secondary battery according to claim 1 , wherein the solvent contains the second solvent in an amount of 50% by weight to 99% by weight.
7. The lithium-sulfur secondary battery according to claim 1 , wherein the solvent comprises the first solvent and the second solvent in a weight ratio of 3:7 to 1:9.