Positive electrode active material for lithium secondary battery, method for producing same, and lithium secondary battery comprising same
A positive electrode active material having a core/shell structure, which includes a sulfur-carbon composite containing thermally expanded-reduced graphene oxide, a carbon material as a core, and carbon nanotubes as a shell. A method for preparing a positive electrode active material having a core/shell structure for a lithium secondary battery, including the steps of thermally expanding graphene oxide by heat treatment at a temperature in a range of 300° C. to 500° C. to prepare a thermally-expanded graphene oxide. Then, reducing the thermally-expanded graphene oxide by heat treatment at a temperature in a range of 700° C. to 1200° C. to prepare a thermally expanded-reduced graphene oxide. Next, mixing the thermally expanded-reduced graphene oxide and sulfur to prepare a sulfur-carbon composite. Last, mixing the sulfur-carbon composite and carbon nanotubes to form carbon nanotubes on a surface of the sulfur-carbon composite.
1 . A positive electrode active material having a core/shell structure for a lithium secondary battery, comprising:
a core comprising a sulfur-carbon composite; and
a shell comprising carbon nanotubes on a surface of the core,
wherein the sulfur-carbon composite comprises thermally expanded-reduced graphene oxide,
wherein sulfur is present on at least a part of a surface of the thermally expanded-reduced graphene oxide and inside of the thermally expanded-reduced graphene oxide, and
wherein the thermally expanded-reduced graphene oxide has a crumbled paper structure,
wherein a specific surface area of the thermally expanded-reduced graphene oxide is 700 m 2 /g to 1200 m 2 /g,
wherein a pore volume of the thermally expanded-reduced graphene oxide is 4 cm 3 /g to 7 cm 3 /g, and
wherein the thermally expanded-reduced graphene oxide does not have a stacked structure.
2 . The positive electrode active material having the core/shell structure for the lithium secondary battery according to claim 1 , wherein the carbon nanotube is present in an amount of 0.5 parts by weight to 2 parts by weight relative to 100 parts by weight of the sulfur-carbon composite.
3 . The positive electrode active material having the core/shell structure for the lithium secondary battery according to claim 1 , wherein the shell comprising the carbon nanotubes comprises pores having a size of 2 nm to 200 nm.
4 . The positive electrode active material having the core/shell structure for the lithium secondary battery according to claim 1 , wherein the thermally expanded-reduced graphene oxide and sulfur are mixed in a weight ratio of 1:1 to 1:9.
5 . The positive electrode active material having the core/shell structure for the lithium secondary battery according to claim 1 , wherein the positive electrode active material for the lithium secondary battery is suitable for use as a positive electrode active material for a lithium-sulfur battery.
6 . A method for preparing a positive electrode active material having a core/shell structure for a lithium secondary battery according to claim 1 , comprising the steps of:
(a) thermally expanding graphene oxide by heat treatment at a temperature in a range of 300° C. to 500° C. to prepare a thermally-expanded graphene oxide;
(b) reducing the thermally-expanded graphene oxide by heat treatment at a temperature in a range of 700° C. to 1200° C. to prepare a thermally expanded-reduced graphene oxide;
(c) mixing the thermally expanded-reduced graphene oxide and sulfur to prepare a sulfur-carbon composite; and
(d) mixing the sulfur-carbon composite and carbon nanotubes to form carbon nanotubes on a surface of the sulfur-carbon composite.
7 . The method for preparing the positive electrode active material having the core/shell structure for the lithium secondary battery according to claim 6 , wherein the thermal expansion in step (a) is performed for 5 minutes to 30 minutes.
8 . The method for preparing the positive electrode active material having the core/shell structure for the lithium secondary battery according to claim 6 , wherein the reduction in step (b) is performed for 1 hours to 5 hours.
9 . The method for preparing the positive electrode active material having the core/shell structure for the lithium secondary battery according to claim 6 , wherein the carbon nanotubes in step (d) are mixed in an amount of 0.5 parts by weight to 2 parts by weight relative to 100 parts by weight of the sulfur-carbon composite.
10 . A lithium secondary battery, comprising:
a positive electrode;
a negative electrode;
a separator interposed between the positive electrode and the negative electrode; and
an electrolyte solution,
wherein the positive electrode comprises the positive electrode active material of claim 1 .
11 . The lithium secondary battery according to claim 10 , wherein a loading amount of sulfur in the positive electrode is 2 mg/cm 2 to 15 mg/cm 2 .
12 . The lithium secondary battery according to claim 10 , wherein the lithium secondary battery is a lithium-sulfur battery.