Method for producing anode for lithium secondary battery and anode composition, and lithium secondary battery
View Patent ↗The invention relates to an anode for lithium secondary battery comprising vapor grown carbon fiber uniformly dispersed without forming an agglomerate of 10 μm or larger in an anode active material using natural graphite or artificial graphite, which anode is excellent in long cycle life and large current characteristics. Composition used for production for the anode can be produced, for example, by mixing a thickening agent solution containing an anode active material, a thickening agent aqueous solution and styrene butadiene rubber as binder with a composition containing carbon fiber dispersed in a thickening agent with a predetermined viscosity or by mixing an anode active material with vapor grown carbon fiber in dry state and then adding polyvinylidene difluoride thereto.
1. An anode for lithium secondary battery comprising anode active material which can occlude (i.e., absorb and store) and discharge lithium, electroconductive carbon material and binder, wherein the anode active material is a graphite material which uses natural graphite or artificial graphite having d(002), a planar spacing between (002) faces, of from 0.335 to 0.337 nm in the graphite structure as measured by powder X-ray diffraction method, wherein the electroconductive carbon material is vapor grown carbon fiber which has an average fiber diameter of 1 to 200 nm with a structure having a hollow space inside each fiber and has a structure where graphene sheets are laminated vertically against the length direction of the fiber and d(002), a planar spacing between (002) faces is from 0.336 to 0.345 nm in the graphite structure as measured by powder X-ray diffraction method, and wherein the vapor grown carbon fiber is contained at an amount of 0.1 to 10 mass % based on the total mass of the anode without forming an agglomerate of 10 μm or larger.
2. The anode for lithium secondary battery according to claim 1 , wherein the average aspect ratio of the vapor grown carbon fiber is within a range of 20 to 2000.
3. The anode for lithium secondary battery according to claim 1 , wherein the vapor grown carbon fiber has branched portions.
4. A lithium secondary battery, comprising the anode for lithium secondary battery as claimed in claim 1 .
5. The lithium secondary battery as claimed in claim 4 , comprising a nonaqueous electrolyte solution and/or a nonaqueous polymer electrolyte containing at least one nonaqueous solvent selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methylethyl carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone and vinylene carbonate.