Active material, electrode, secondary battery, battery pack, electric vehicle, electric power storage system, electric power tool, and electronic apparatus
A secondary battery includes: a cathode; an anode including an active material; and an electrolytic solution, wherein the active material includes a central section and a covering section provided on a surface of the central section, the central section includes silicon (Si) as a constituent element, the covering section includes carbon (C) and hydrogen (H) as constituent elements, and one or more of positive ions represented by CxHy (x and y satisfy 2≦x≦6 and 3≦y≦9) are detected by positive ion analysis of the covering section with the use of time-of-flight secondary ion mass spectrometry.
1. A secondary battery comprising:
a cathode;
an anode including an active material; and
an electrolytic solution, wherein
the active material includes a central section and a covering section provided on a surface of the central section,
the central section includes silicon (Si) as a constituent element,
the covering section includes carbon (C) and hydrogen (H) as constituent elements, and
one or more of positive ions represented by CxHy wherein x and y satisfy 2≦x≦6 and 3≦y≦9, are detected by positive ion analysis of the covering section with the use of time-of-flight secondary ion mass spectrometry.
2. The secondary battery according to claim 1 , wherein a ratio D1/D2 between a sum D1 of detected intensities of positive ions represented by C2H3, C2H5, and C3H5 and a detected intensity D2 of C is equal to or larger than about 1.25, or is equal to or larger than about 50, wherein D1 is the sum of detected intensities of positive ions represented by C2H3, C2H5, and C3H5, and wherein D2 is the detected intensity of carbon.
3. The secondary battery according to claim 1 , wherein a ratio D1/D3 between a sum D1 of detected intensities of positive ions represented by C2H3, C2H5, and C3H5 and a sum D3 of detected intensities of positive ions represented by CHz (z satisfies 0≦z≦3) is larger than about 1, wherein D1 is the sum of detected intensities of positive ions represented by C2H3, C2H5, and C3H5, and wherein D3 is the sum of detected intensity of positive ions represented by CHz wherein z satisfies 0≦z≦3.
4. The secondary battery according to claim 1 , wherein
an average thickness of the covering section is equal to or less than about 500 nanometers, and
an average coverage ratio of the covering section with respect to the central section is equal to or larger than about 30 percent.
5. The secondary battery according to claim 1 , wherein a surface of the covering section has a concavo-convex structure attributable to one or more of the positive ions represented by the CxHy, wherein x and y satisfy 2≦x≦6 and 3≦y≦9.
6. The secondary battery according to claim 1 , wherein the central section includes oxygen (O) as a constituent element.
7. The secondary battery according to claim 6 , wherein
the central section includes silicon oxide represented by SiOw (w satisfies 0.3≦w≦1.9), and
on the surface of the central section, an atomic ratio (Si/O) of silicon with respect to oxygen is equal to or less than about 75 atomic percent, or is from about 30 atomic percent to about 70 atomic percent both inclusive.
8. The secondary battery according to claim 1 , wherein a median diameter (D50) of the central section is from about 0.1 micrometers to about 20 micrometers both inclusive.
9. The secondary battery according to claim 1 , wherein the central section includes one or more of iron (Fe), aluminum (Al), calcium (Ca), manganese (Mn), chromium (Cr), magnesium (Mg), and nickel (Ni) as constituent elements.
10. The secondary battery according to claim 1 , wherein
in the central section, crystal regions (crystal grains) are scattered in noncrystalline regions,
average area occupancy of crystal grains attributable to a (111) plane and a (220) plane of silicon is equal to or less than about 35 percent, and
an average grain diameter of the crystal grains is equal to or less than about 30 nanometers.
11. The secondary battery according to claim 1 , wherein
in the central section in an uncharged state, part or all silicon is alloyed with lithium (Li), and
the central section includes lithium silicate.
12. The secondary battery according to claim 1 , wherein
the anode includes an active material layer on a current collector,
the active material layer includes the active material,
the current collector includes copper (Cu), carbon (C), and sulfur (S) as constituent elements, and
a sum of contents of carbon and sulfur in the current collector is equal to or less than about 100 parts per million.
13. The secondary battery according to claim 1 , wherein the secondary battery is a lithium ion secondary battery.
14. An electrode comprising an active material, wherein
the active material includes a central section and a covering section provided on a surface of the central section,
the central section includes silicon (Si) as a constituent element,
the covering section includes carbon (C) and hydrogen (H) as constituent elements, and
one or more of positive ions represented by CxHy wherein x and y satisfy 2≦x≦6 and 3≦y≦9, are detected by positive ion analysis of the covering section with the use of time-of-flight secondary ion mass spectrometry.