Positive electrode active material containing thermally expanded-reduced graphene oxide with a montmorillonite additive, and a lithium-sulfur secondary battery thereof
Disclosed is a positive electrode for a lithium secondary battery and a lithium secondary battery including the same. More particularly, disclosed is a positive electrode for a lithium secondary battery including a sulfur-carbon composite including thermally expanded-reduced graphene oxide as a positive electrode active material and montmorillonite as an additive. The positive electrode for the lithium secondary battery not only has excellent electrochemical reactivity, but also improves the problem due to leaching of lithium polysulfide, thereby improving capacity and lifetime characteristics of the lithium secondary battery.
1 . A positive electrode for a lithium secondary battery comprising:
a positive electrode active material; and
an additive,
wherein the positive electrode active material comprises a sulfur-carbon composite comprising thermally expanded-reduced graphene oxide and sulfur, and the additive comprises montmorillonite modified by cation exchange,
wherein the modified montmorillonite is montmorillonite wherein a cation thereof is substituted with at least one ion selected from hydrogen ions, lithium ions, potassium ions, rubidium ions, cesium ions, iron ions, manganese ions and nickel ions,
wherein in the sulfur-carbon composite, the sulfur is present on an inner surface and an outer surface of the thermally expanded-reduced graphene oxide,
wherein the thermally expanded-reduced graphene oxide has a specific surface area of 700 to 1200 m 2 /g,
wherein the thermally expanded-reduced graphene oxide has a pore volume of 3 to 7 cm 3 /g, and
wherein the additive is present in an amount of 1 to 10% by weight based on a total amount of 100% by weight of the positive electrode active material layer.
2 . The positive electrode for the lithium secondary battery according to claim 1 , wherein the thermally expanded-reduced graphene oxide has an electrical conductivity of 20 to 200 S/cm.
3 . The positive electrode for the lithium secondary battery according to claim 1 , wherein the sulfur comprises at least one selected from the group consisting of inorganic sulfur, Li 2 S n (n≥1), a disulfide compound, an organic sulfur compound, and a carbon-sulfur polymer ((C 2 S x ) n : x=2.5 to 50, n≥2).
4 . The positive electrode for the lithium secondary battery according to claim 1 , wherein the montmorillonite comprises at least one selected from the group consisting of sodium montmorillonite, calcium montmorillonite, and magnesium montmorillonite.
5 . A lithium secondary battery comprising the positive electrode for the lithium secondary battery according to claim 1 ; a negative electrode; and an electrolyte.
6 . The lithium secondary battery according to claim 5 , wherein the positive electrode has a loading amount of sulfur of 2 to 15 mg/cm 2 .