Negative electrode active material, mixed negative electrode active material, negative electrode for nonaqueous electrolyte secondary battery, lithium ion secondary battery, production method of negative electrode active material, and production method of lithium ion secondary battery
A negative electrode active material comprising: particles of negative electrode active material, wherein the particles of negative electrode active material contain particles of silicon compound containing a silicon compound (SiO x :0.5≤x≤1.6), and wherein the particles of silicon compound have, as chemical shift values obtained from a 29 Si-MAS-NMR spectrum, an intensity A of a peak derived from amorphous silicon obtained in −40 to −60 ppm, an intensity B of a peak derived from silicon dioxide obtained in the vicinity of −110 ppm, and an intensity C of a peak derived from Si obtained in the vicinity of −83 ppm, which satisfy the following formula 1 and formula 2. B≤1.5×A (1) B<C (2)
1. A negative electrode active material before being assembled into a battery, comprising:
particles of the negative electrode active material,
wherein the particles of the negative electrode active material contain particles of a silicon compound containing a silicon compound SiO x :0.5≤x≤1.6,
wherein the particles of the negative electrode active material contain Li 2 SiO 3 ,
wherein the particles of the silicon compound have, as chemical shift values obtained from a 29 Si-MAS-NMR spectrum, an intensity A of a peak derived from amorphous silicon obtained in a vicinity of −40 to −60 ppm, an intensity B of a peak derived from silicon dioxide obtained in a vicinity of −110 ppm, and an intensity C of a peak derived from Si obtained in a vicinity of −83 ppm, which satisfy the following formula 1 and formula 2:
B≤1.5×A (1)
B<C (2)
wherein the particles of the silicon compound have a half value width (2θ) of a diffraction peak derived from a Si(111) crystal plane obtained by X-ray diffractometry of 1.2° or more and a crystallite size corresponding to the Si(111) crystal plane of 7.5 nm or less, and
wherein the Li 2 SiO 3 contained in the particles of the negative electrode active material is formed by Li insertion of a redox method.
2. The negative electrode active material according to claim 1 , wherein a test cell formed of a negative electrode containing a mixture of the negative electrode active material and a carbon-based active material and a counter electrode lithium is prepared, in the test cell, charge/discharge formed of charge during which a current is flowed so as to insert lithium into the negative electrode active material and discharge during which the current is flowed so as to detach lithium from the negative electrode active material is carried out 30 times, and when a graph showing a relationship between a differential value dQ/dV obtained by differentiating a discharge capacity Q by a potential V of the negative electrode based on the counter electrode lithium and the potential V is depicted in each charge/discharge, the potential V of the negative electrode during discharges on or after X times (1≤X≤30) has a peak in the range of from 0.40 V to 0.55 V.
3. The negative electrode active material according to claim 1 , wherein the particles of the negative electrode active material have a median diameter of 1.0 μm or more and 15 μm or less.
4. The negative electrode active material according to claim 1 , wherein a carbon material is on a superficial layer of the negative electrode active material.
5. The negative electrode active material according to claim 4 , wherein an average thickness of the carbon material is 10 nm or more and 5000 nm or less.
6. A mixed negative electrode active material comprises the negative electrode active material according to claim 1 and a carbon-based active material.
7. A negative electrode for nonaqueous electrolyte secondary batteries comprising:
the mixed negative electrode active material according to claim 6 ,
wherein a ratio of a mass of the negative electrode active material relative to a total mass of the negative electrode active material and the carbon-based active material is 6% by mass or more.
8. A negative electrode for nonaqueous electrolyte secondary batteries comprising:
a negative electrode active material layer formed with the mixed negative electrode active material according to claim 7 ; and
a negative electrode current collector,
wherein the negative electrode active material layer is formed on the negative electrode current collector; and
the negative electrode current collector includes carbon and sulfur, and each of contents thereof is 70 mass ppm or less.
9. A lithium ion secondary battery comprising:
a negative electrode containing the negative electrode active material according to claim 1 .
10. A method of producing a negative electrode active material according to claim 1 , the method comprising:
preparing particles of negative electrode active material containing particles of silicon compound containing a silicon compound (SiO x : 0.5≤x≤1.6); and
selecting, from the particles of negative electrode active material, particles of negative electrode active material in which, as chemical shift values obtained from a 29 Si-MAS-NMR spectrum, an intensity A of a peak derived from amorphous silicon obtained in a vicinity of −40 to −60 ppm, an intensity B of a peak derived from silicon dioxide obtained in a vicinity of −110 ppm, and an intensity C of a peak derived from Si obtained in a vicinity of −83 ppm, which satisfy the following formula 1 and formula 2;
B≤1.5×A (1)
B<C (2)
wherein producing the negative electrode active material with the selected particles of negative electrode active material.
11. A production method of a lithium ion secondary battery, comprising:
preparing a negative electrode using the negative electrode active material produced according to the production method of the negative electrode active material according to claim 10 ; and
producing a lithium ion secondary battery with the prepared negative electrode.