Negative electrode material 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, comprising graphite particles and a low-crystalline carbon layer that covers at least a portion of a surface of the graphite particles, and satisfying at least one of the following A) having two or more peaks in a R-value histogram obtained by a mapping Raman measurement; B) having a variance of 2.0 or more of a maximum peak in a R-value histogram obtained by a mapping Raman measurement; or C) having two or more carbon phases with a different degree of crystallinity.
1 . A negative electrode material for a lithium ion secondary battery, the negative electrode material comprising graphite particles and a low-crystalline carbon layer that covers at least a portion of a surface of the graphite particles, and satisfying at least one of the following conditions (1) and (2);
(1) the negative electrode material has a variance of 2.0 or more of a maximum peak in an R-value histogram obtained by a mapping Raman measurement, and
(2) the low-crystalline carbon layer has two or more carbon phases with a different degree of crystallinity from each other.
2 . The negative electrode material for a lithium ion secondary battery according to claim 1 , wherein the negative electrode material has a variance of 2.0 or more of a maximum peak in an R-value histogram obtained by a mapping Raman measurement.
3 . The negative electrode material for a lithium ion secondary battery according to claim 1 , wherein the low-crystalline carbon layer has two or more carbon phases with a different degree of crystallinity from each other.
4 . The negative electrode material for a lithium ion secondary battery according to claim 1 , having an average degree of circularity of from 0.8 to 1.0.
5 . A negative electrode for a lithium ion secondary battery, the negative electrode comprising:
a current collector, and
a negative electrode composition layer comprising the negative electrode material for a lithium ion secondary battery according to claim 1 , which is disposed at a surface of the current collector.
6 . A lithium ion secondary battery, comprising the negative electrode for a lithium ion secondary battery according to claim 5 .
7 . The negative electrode material for a lithium ion secondary battery according to claim 2 , having an average degree of circularity of from 0.8 to 1.0.
8 . A negative electrode for a lithium ion secondary battery, the negative electrode comprising:
a current collector, and
a negative electrode composition layer comprising the negative electrode material for a lithium ion secondary battery according to claim 2 , which is disposed at a surface of the current collector.
9 . A lithium ion secondary battery, comprising the negative electrode for a lithium ion secondary battery according to claim 8 .
10 . The negative electrode material for a lithium ion secondary battery according to claim 3 , having an average degree of circularity of from 0.8 to 1.0.
11 . A negative electrode for a lithium ion secondary battery, the negative electrode comprising:
a current collector, and
a negative electrode composition layer comprising the negative electrode material for a lithium ion secondary battery according to claim 3 , which is disposed at a surface of the current collector.
12 . A lithium ion secondary battery, comprising the negative electrode for a lithium ion secondary battery according to claim 11 .
13 . The negative electrode material for a lithium ion secondary battery according to claim 1 , wherein the low-crystalline carbon layer comprises a carbon material having an interlayer distance in carbon network planes (d002) measured by wide angle X-ray diffraction of 0.340 nm or more.
14 . The negative electrode material for a lithium ion secondary battery according to claim 1 , wherein the low-crystalline carbon layer has a thickness of from 0.5 nm to 500 nm.
15 . A method for producing the negative electrode material for a lithium ion secondary battery according to claim 1 , the method comprising:
subjecting a mixture containing graphite particles and two or more kinds of precursors for the low-crystalline carbon layer to a thermal treatment, thereby covering at least a portion of a surface of the graphite particles with the low-crystalline carbon layer.
16 . The method according to claim 15 , wherein the precursors comprise pitch and an organic polymer compound.
17 . A method for producing the negative electrode material for a lithium ion secondary battery according to claim 1 , the method comprising:
subjecting a mixture containing graphite particles and a precursor for the low crystalline carbon layer to a thermal treatment,
adding a different kind of precursor for the low crystalline carbon layer to the mixture, and
subjecting the mixture to a further thermal treatment, thereby covering at least a portion of a surface of the graphite particles with the low-crystalline carbon layer.
18 . The method according to claim 17 , wherein the precursors comprise pitch and an organic polymer compound.