Graphene-doped lithium iron phosphate active material and method for preparing the same
A method for preparing a positive electrode active material is provided. The method for preparing a positive electrode active material may comprise the steps of: preparing a lithium precursor, an iron precursor, a phosphorus precursor, and abase solvent; mixing the base solvent and the lithium precursor to prepare a first source, mixing the base solvent and the iron precursor to prepare a second source, and mixing the base solvent and the phosphorus precursor to prepare a third source; and mixing the first source, the second source, the third source, and a chelating agent and allowing a reaction to occur in the mixture by a heat treatment method to prepare a positive electrode active material comprising a compound of lithium, iron, phosphorus, and oxygen.
1 . A method for preparing a functional positive electrode active material, the method comprising:
providing a first stock solution in which a base positive electrode active material including a compound of lithium, iron, phosphorus, and oxygen is dispersed in a first solvent;
providing a second stock solution in which graphene powder is dispersed in a second solvent; and
preparing the functional positive electrode active material in which the graphene powder is doped into the base positive electrode active material by mixing and heat-treating the first stock solution and the second stock solution,
wherein the functional positive electrode active material has a first crystallinity in a first state before a charging and discharging process of a lithium secondary battery that includes the functional positive electrode active material,
wherein the functional positive electrode active material has a second crystallinity in a second state after the charging and discharging process,
wherein the second crystallinity is higher than the first crystallinity as a result of performing the charging and discharging process,
wherein the functional positive electrode active material has a disorder/defect band (“D band”) and a graphitic band (“G band”),
wherein a ratio (I D /I G ) value of intensity of the D band to intensity of the G band is greater than 1.98 and less than 3.26 when measuring a Raman spectrum,
wherein the functional positive electrode active material has a graphene powder content greater than 1 at % and less than 3 at %, and
wherein the functional positive electrode active material has a capacity value greater than a theoretical capacity value of 170 mAh g −1 for lithium iron phosphate.
2 . The method of claim 1 , wherein the first solvent and the second solvent are a same solvent.
3 . The method of claim 2 , wherein the first solvent and the second solvent comprises N-methyl-2-pyrrolidone (NMP).
4 . The method of claim 1 , wherein providing the second stock solution comprises:
preparing a graphene colloid having the graphene powder by mixing the graphene powder with an oxidizing agent and heat-treating a mixture of the graphene powder and the oxidizing agent;
obtaining the graphene powder from the graphene colloid; and
dispersing the graphene powder in the second solvent.
5 . The method of claim 4 , wherein the oxidizing agent is hydrogen peroxide.