Composite negative electrode active material and non-aqueous electrolyte secondary battery
Disclosed is a composite negative electrode active material including a graphitizable carbon material containing a layered structure formed of stacked carbon layers partially having a three-dimensional regularity, and a low crystalline carbon material. A negative electrode including the composite negative electrode active material is used to produce a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery thus produced has a high energy density and demonstrates a high output/input performance for a long period of time in various environments of high to low temperatures.
1. A composite negative electrode active material comprising:
a graphitizable carbon material (A) containing a layered structure formed of stacked carbon layers partially having a three-dimensional regularity; and
a carbon material (B), wherein:
a ratio I(101)/I(100) of the graphitizable carbon material (A) satisfies 0.5<1(101)/I(100)<1.0,
the carbon material (B) is capable of absorbing and desorbing lithium via an interlayer intercalation reaction, and a ratio I(101)/I(100) of the carbon material (B) is not less than 0 and lower than the ratio I(101)/I(100) of the graphitizable carbon material (A),
the ratio I(101)/I(100) is a ratio of a peak intensity (101) attributed to a (101) plane at 2θ=about 44° to a peak intensity I(100) attributed to a (100) plane at 2θ=about 42° in a wide-angle X-ray diffraction pattern measured with CuKα radiation, and
a surface of the graphitizable carbon material (A) is coated with the carbon material (B), or at least part of the graphitizable carbon material (A) and at least part of the carbon material (B) are fused together.
2. The composite negative electrode active material in accordance with claim 1 , wherein the graphitizable carbon material (A) is coated with the carbon material (B) by coating the surface of the graphitizable carbon material (A) with a precursor of the carbon material (B) and then carbonizing the precursor.
3. The composite negative electrode active material in accordance with claim 2 , wherein the precursor of the carbon material (B) is carbonized by heating the precursor at 600 to 1500° C.
4. The composite negative electrode active material in accordance with claim 2 , wherein the precursor of the carbon material (B) is cokes.
5. The composite negative electrode active material in accordance with claim 1 , wherein the graphitizable carbon material (A) is obtained by heating a graphitizable carbon material (C) serving as a starting material.
6. The composite negative electrode active material in accordance with claim 5 , wherein the graphitizable carbon material (C) is cokes and is heated at a temperature of 1800° C. to 2200° C.
7. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing the composite negative electrode active material of claim 1 , a separator, and a non-aqueous electrolyte.