Negative electrode material for lithium ion secondary battery, method of manufacturing negative electrode material for lithium ion secondary battery, negative electrode material slurry for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery
A negative electrode material for a lithium ion secondary battery, including composite particles, each of the composite particles including: a spherical graphite particle; and flat graphite particles that are gathered or bound together such that the flat graphite particles have non-parallel orientation planes, wherein the composite particles satisfy the following (1) and (2): (1) a pore volume in a range of a pore diameter of from 0.10 to 8.00 μm obtained by the mercury intrusion method is from 0.20 to 1.00 mL/g; and (2) in a log differential pore volume distribution obtained by the mercury intrusion method, at least two peaks appear in a range of a pore diameter of from 0.10 to 8.00 the two peaks including a first peak P1 and a second peak P2 at a higher diameter than the first peak P1.
1. A negative electrode material for a lithium ion secondary battery, the negative electrode material comprising composite particles, each of the composite particles comprising: a spherical graphite particle; and flat graphite particles that are gathered or bound together such that the flat graphite particles have non-parallel orientation planes, wherein the composite particles satisfy the following conditions (1) and (2):
(1) a pore volume in a range of a pore diameter of from 0.10 to 8.00 μm obtained by a mercury intrusion method is from 0.20 to 1.00 mL/g; and
(2) in a log differential pore volume distribution obtained by the mercury intrusion method, wherein a peak is defined as a point at which a slope the log differential pore volume distribution changes from a positive value to a negative value, at least two peaks appear in a range of a pore diameter of from 0.10 to 8.00 μm, the at least two peaks including a first peak P1 and a second peak P2 at a higher diameter than the first peak P1, wherein:
a pore diameter corresponding to a maximum log differential pore volume of the first peak P1 is from 0.10 to less than 4.00 μm, and
a pore diameter corresponding to a maximum log differential pore volume of the second peak P2 is from 4.50 to 7.00 μm.
2. The negative electrode material for a lithium ion secondary battery according to claim 1 , wherein a ratio of peak intensities of the first peak and the second peak (P1/P2) is less than 4.0.
3. The negative electrode material for a lithium ion secondary battery according to claim 1 , wherein an R-value of the composite particles as measured by Raman spectroscopy is from 0.03 to 0.10.
4. The negative electrode material for a lithium ion secondary battery according to claim 1 , wherein the composite particles have a specific surface area as measured by the BET method from 1.5 to 6.0 m 2 /g.
5. The negative electrode material for a lithium ion secondary battery according to claim 1 , wherein a saturated tap density of the composite particles is from 0.60 to 0.90 g/cm 3 .
6. The negative electrode material for a lithium ion secondary battery according to claim 1 , wherein the spherical graphite particles have a circularity of 0.80 or higher.
7. The negative electrode material for a lithium ion secondary battery according to claim 1 , further comprising spherical natural graphite particles that are not a portion of the composite particles, wherein a content of the spherical natural graphite particles that are not a portion of the composite particles with respect to a total amount of the composite particles and the spherical natural graphite particles that are not a portion of the composite particles is 30% by mass or more.
8. A method of manufacturing the negative electrode material for a lithium ion secondary battery according claim 1 , the method comprising preparing the composite particles by a method comprising:
obtaining a mixture comprising a graphitizable aggregate, a graphitizable binder, a graphitization catalyst, and a spherical graphite particle; and
calcining the mixture.
9. The method of manufacturing the negative electrode material for a lithium ion secondary battery according to claim 8 , wherein the method of preparing the composite particles further comprises, between obtaining the mixture and calcining the mixture, at least one selected from the group consisting of molding the mixture and heat-treating the mixture.
10. A negative electrode material slurry for a lithium ion secondary battery, the slurry comprising:
the negative electrode material for a lithium ion secondary battery according to claim 1 ;
an organic binder; and
a solvent.
11. A negative electrode for a lithium ion secondary battery, the negative electrode comprising:
a current collector; and
a negative electrode material layer comprising the negative electrode material for a lithium ion secondary battery according to claim 1 , that is formed on the current collector.
12. A lithium ion secondary battery, comprising:
a positive electrode;
an electrolyte; and
the negative electrode for a lithium ion secondary battery according to claim 11 .