Negative-electrode active material, and method for production of negative-electrode active material
A negative-electrode active material characterized by containing a silicon oxide represented by a general formula SiO x (0<x<2) and a silicate compound represented by a composition formula M a Si b O c -m(OH)-n(H 2 0), and a method for the production of a negative-electrode active material which includes a mixing step of mixing a silicon oxide that is represented by a general formula SiO y (0<y<2) and a metal oxide, and a heat treatment step of performing a heat treatment on the mixture that is obtained in the mixing step in a non-oxidizing atmosphere and in which the negative absolute value of the standard Gibbs energy of the oxidation reaction of the metal oxide at the heating temperature in the heat treatment step is smaller than the negative absolute value of the standard Gibbs energy of the oxidation reaction of Si at the heating temperature in the heat treatment step.
1. A negative-electrode active material, comprising:
a silicon oxide that is represented by a general formula SiO x (0<x<2), and
a silicate compound that is represented by M a Si b O c .m(OH).n(H 2 O),
wherein a, b, c, m and n are respectively in the ranges of 0<a≦7, 0<b≦8, 0<c≦22, 0≦m≦4 and 0≦n≦10, M contains at least one of Group 3 to 12 transition metal elements in the long-form periodic table.
2. The negative-electrode active material according to claim 1 , wherein x in the general formula SiO x is in a range of 0.8≦x≦1.2.
3. The negative-electrode active material according to claim 1 , wherein at least one silicate compound phase that contains the silicate compound is present at least in a silicon oxide phase that contains the silicon oxide.
4. The negative-electrode active material according to claim 3 , wherein the silicate compound phase has a mean diameter of 10 to 2000 nm.
5. The negative-electrode active material according to claim 1 , wherein a silicate compound phase that contains the silicate compound is present at least on surfaces of silicon oxide particles that contain the silicon oxide.
6. The negative-electrode active material according to claim 5 , wherein the silicate compound phase that is present on the surfaces of the silicon oxide particles has a thickness of 10 to 2000 nm.
7. A production method for the negative-electrode active material that is the negative-electrode active material according to claim 1 , comprising:
a mixing step of mixing a silicon oxide that is represented by a general formula SiO y (0<y<2) and a metal oxide to obtain a mixture, and
a heat treatment step of performing a heat treatment on the mixture in a non-oxidizing atmosphere,
wherein a negative absolute value of the standard Gibbs energy of the oxidation reaction of the metal oxide at a heating temperature in the heat treatment step is smaller than the negative absolute value of the standard Gibbs energy of the oxidation reaction of Si at the heating temperature in the heat treatment step.
8. The production method according to claim 7 , wherein y in the general formula SiO y is in a range of 0.8≦y≦1.2.
9. The production method according to claim 7 , wherein the heat treatment is carried out at a temperature of 600° C. to 1000° C. in an inert atmosphere in the heat treatment step.
10. The production method according to claim 7 , wherein the heat treatment is carried out at a temperature of 700° C. to 900° C. in the heat treatment step.
11. The production method according to claim 7 , wherein 0.001 to 0.2 mol of the metal oxide is added per mol of the silicon oxide in the mixing step.
12. The production method according to claim 7 , wherein the metal oxide has an average particle size which is equal to or smaller than that of the silicon oxide in the mixing step.
13. The production method according to claim 7 , wherein the metal oxide is deposited on a surface of the silicon oxide in the mixing step.
14. The production method according to claim 7 , wherein the silicon oxide and the metal oxide are mixed by a mechanochemical process in the mixing step.
15. The production method according to claim 14 , wherein the mechanochemical process is carried out in a ball mill.
16. The negative-electrode active material according to claim 1 , wherein M contains, in addition to the transition metal element, at least one of Group 1 alkali metal elements and Group 2 alkaline-earth metal elements.
17. A negative-electrode active material, comprising:
a silicon oxide that is represented by a general formula SiO x 0≦x≦2, and
a silicate compound that is represented by M a Si b O c .m(OH).n(H 2 O),
wherein a, b, c, m and n are respectively in ranged of 0<a≦7, 0<b≦8, 0<c≦22, 0≦m≦4 and 0≦n≦10, M contains at least one of Group 3 to 12 transition metal elements in the long-form periodic, and Si is partially substituted by at least one of Al and B.
18. The negative-electrode active material according to claim 17 , wherein M contains, in addition to the transition metal element, at least one of Group 1 alkali elements and Group 2 alkaline-earth metal elements.