Negative electrode for lithium ion secondary battery and lithium ion secondary battery

1. A negative electrode for a lithium ion secondary battery, comprising a current collector and a negative electrode active material layer on the current collector,

wherein the negative electrode active material layer comprises:

a first composite particle comprising a first graphite core particle and a first non-graphite-based carbon material coating a surface thereof; and

a second composite particle comprising a second graphite core particle and a second non-graphite-based carbon material coating a surface thereof, and wherein

an average particle diameter d A (D 50 ) of the first composite particles is 5 to 30 μm;

an average particle diameter d B (D 50 ) of the second composite particles is 2 to 25 μm, and is smaller than the average particle diameter d A of the first composite particles;

a mixing ratio of the first composite particle A and the second composite particle B is 50:50 to 95:5 in mass ratio (A:B); and

a density of the negative electrode active material layer is 1.4 to 1.7 g/cm 3 , and

wherein, provided that D10, D50 and D95 represent particle diameters at a cumulation of 10%, 50% and 95% from the fine particle size side in a cumulative particle size distribution, respectively,

a ratio D50/D10 of D50 and D10 of the first composite particles is 1.5 or lower;

a ratio D95/D10 of D95 and D10 of the first composite particles is 1.7 or higher;

a ratio D50/D10 of D50 and D10 of the second composite particles is 1.3 or lower; and

a ratio D95/D10 of D95 and D10 of the second composite particles is lower than 1.7.

2. The negative electrode according to claim 1 , wherein a mass proportion R B of the second non-graphite-based carbon material in the second composite particle is 5 to 30% by mass, and is higher than a mass proportion R A of the first non-graphite-based carbon material in the first composite particle.

3. The negative electrode according to claim 2 , wherein the mass proportion R A of the first non-graphite-based carbon material in the first composite particle is 0.1 to 10% by mass.

4. The negative electrode according to claim 2 , wherein the mass proportion R A of the first non-graphite-based carbon material in the first composite particle is 0.1 to 5% by mass.

5. The negative electrode according to claim 1 , wherein a linear load B necessary in order to provide a compression density of the second composite particles of 1.55 g/cm 3 is higher than a linear load A necessary in order to provide a compression density of the first composite particles of 1.55 g/cm 3 .

6. The negative electrode according to claim 1 , wherein the first graphite core particle and the second graphite core particle each comprise a natural graphite.

7. The negative electrode according to claim 1 , wherein the first non-graphite-based carbon material and the second non-graphite-based carbon material each comprise an amorphous carbon.

8. The negative electrode according to claim 1 , wherein a particle diameter ratio d B /d A is 0.6 or higher and lower than 1.

9. The negative electrode according to claim 1 , wherein the first composite particle and the second composite particle each have a circularity of 0.7 or higher.

10. The negative electrode according to claim 1 , wherein

a BET specific surface area of the first composite particle is 3.7 m 2 /g or smaller; and

a BET specific surface area of the second composite particle is 6 m 2 /g or smaller.

11. The negative electrode according to claim 1 , wherein the BET specific surface area of the first composite particle is 0.9 m 2 /g or larger.

12. The negative electrode according to claim 1 , wherein the BET specific surface area of the second composite particle is 3.4 m 2 /g or larger.

13. The negative electrode according to claim 1 , wherein a coating amount (after drying) per one surface of the current collector of the active material layer is 9 mg/cm′ or larger.

14. The negative electrode according to claim 1 , wherein a particle diameter ratio d B /d A is 0.6 or higher and lower than 1, and

a mass proportion R B of the second non-graphite-based carbon material in the second composite particle is 7 to 30% by mass, and is higher than a mass proportion R A of the first non-graphite-based carbon material in the first composite particle.

15. The negative electrode according to claim 14 , wherein the mass proportion R B of the second non-graphite-based carbon material in the second composite particle is 10 to 30% by mass, and is higher than the mass proportion R A of the first non-graphite-based carbon material in the first composite particle.

16. The negative electrode according to claim 14 , wherein the mass proportion R B of the second non-graphite-based carbon material in the second composite particle is 7 to 20% by mass, and is higher than the mass proportion R A of the first non-graphite-based carbon material in the first composite particle.

17. The negative electrode according to claim 14 , wherein the first graphite core particle and the second graphite core particle are each globulized particle.

18. A lithium ion secondary battery, comprising a negative electrode according to claim 1 , a positive electrode capable of occluding and releasing lithium ions, and a nonaqueous electrolyte solution.