WO2015064633A1 - Negative electrode active material and manufacturing method therefor, and negative electrode using negative electrode active material, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

Provided is a negative electrode active material characterized by a composition that includes silicon and an element (M) that can form a compound with silicon, and that first precipitates out a compound of silicon and the element (M) when the composition of silicon and the element (M) is cooled from a molten state, and then precipitates out pure silicon or solid-solution silicon when cooled further. The negative electrode active material is characterized, electrochemically, by a first phase having Li occlusion properties being dispersed in a second phase having Li conductivity properties, and the first phase further including a third phase with weaker Li occlusion properties than the first phase.

Description

NEGATIVE ELECTRODE ACTIVE MATERIAL, PROCESS FOR PRODUCING THE SAME, NEGATIVE ELECTRODE AND NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY USING THE SAME

The present invention is used for a negative electrode for a non-aqueous electrolyte secondary battery, specifically, a negative electrode active material that provides a lithium ion secondary battery having a particularly high capacity, excellent cycle characteristics, and capacity retention rate, and its It relates to manufacturing methods.

So far, non-aqueous electrolyte secondary batteries using various carbon-based materials such as natural graphite, artificial graphite, amorphous carbon, and mesophase carbon as a negative electrode active material have been put into practical use. However, graphite has a low theoretical capacity of 372 mAh / g, and there is a limit to further increasing the capacity.

On the other hand, negative electrodes for non-aqueous electrolyte secondary batteries using metals and alloys having a large theoretical capacity as lithium compounds, particularly silicon and alloys thereof as negative electrode active materials, have been developed with the aim of increasing the capacity. For example, Si has a theoretical capacity exceeding 4000 mAh / g.
When Si is applied as the negative electrode material, a high capacity can be obtained. However, the cycle characteristics are not sufficient due to a large volume change accompanying the insertion / desorption of Li, generation of cracks and progress of pulverization, or side reaction with the electrolytic solution. Therefore, there is a problem that the lifetime is extremely short as compared with a negative electrode made of a conventional carbon-based active material.

Since silicon has a large expansion and contraction associated with the alloying / dealloying reaction with lithium, it is necessary to make silicon-containing particles small in order to prevent cracks. By rapidly cooling the molten silicon, a fine silicon phase can be obtained. However, when silicon melt is cooled by the usual rapid cooling method to precipitate silicon crystals, the silicon crystals become several hundred μm in size, and silicon particles with a sufficiently small particle size cannot be obtained. It was. There is a limit to increasing the cooling rate of the molten silicon, and there is a limit to miniaturizing the silicon phase by increasing the cooling rate. Therefore, a method for forming a fine silicon phase by a conventional rapid cooling method is required.

In addition, when lithium ions are charged and discharged in a state where the silicon and the electrolytic solution are in contact with each other, a side reaction between the lithium ions and the electrolytic solution causes a SEI on the surface of the silicon.
A film called (Solid Electrolyte interface, solid electrolyte interface) is formed. Generation of SEI is an irreversible reaction, and lithium ions that have generated SEI during charging cannot contribute to discharging.

Silicon expands and contracts with the alloying / dealloying reaction with lithium. In order to prevent the occurrence of cracks and pulverization, it is necessary to make the silicon-containing particles small. However, when the particle size of the particles containing silicon is reduced, the surface area per unit weight is increased, the amount of SEI generated on the surface is increased, and the Coulomb efficiency is lowered.

In addition, since silicon is greatly expanded and contracted, SEI generated during charging is separated from the silicon contracted during discharging. Therefore, every time the battery is charged, SEI is generated on the surface of the silicon, and a large amount of SEI remains on the surface of the negative electrode, resulting in an increase in the thickness of the electrode and an increase in internal resistance. .

Generation of SEI due to repeated charge / discharge will be described with reference to FIG. FIG. 22A shows the silicon particle 100 before charging and discharging. As shown in FIG. 22B, when the silicon particles 100 in the electrolytic solution are charged, the silicon particles 100 expand and the first SEI 101 is formed on the surface thereof. In addition, cracks 103 are generated in the silicon particles 100 during expansion. As shown in FIG. 22C, when discharging is performed, the silicon particles 100 contract, and a part of the first SEI 101 is separated from the surface of the silicon particles 100. As shown in FIG. 22D, when the second charge is performed, the silicon particles 100 expand again, and the second SEI 105 is formed on the surface thereof. In addition, a crack 107 other than the crack 103 is generated in the silicon particle 100 during expansion. As shown in FIG. 22E, when discharging is performed, the silicon particles 100 contract, and a part of the second SEI 105 is separated from the surface of the silicon particles 100. As a result, the peeled first SEI 101 and second SEI 105 remain around the silicon particles 100, which increases the thickness of the electrode and increases the electrical resistance of the negative electrode. Further, since the electrolyte solution is excessively consumed with charging / discharging, the electrolyte solution is consumed violently, leading to liquid drainage and reducing the battery life.

Therefore, a negative electrode active material is disclosed that does not use silicon particles as a negative electrode active material as it is, but includes an intermetallic compound of silicon and metal and a metal matrix containing Cu and Al (see Patent Document 1).

Patent Document 2 discloses an invention in which a composite alloy in which a Si phase precipitates in a network form at a grain boundary of a fine Si alloy phase is used as a negative electrode material for a lithium ion battery. As a result, even if the Si phase expands and contracts during charge and discharge, pulverization and disconnection of the conductive network are suppressed, and cycle characteristics are improved.
Patent Document 3 discloses an invention of a negative electrode active material for a lithium secondary battery including a Si phase and a phase containing Si, Al, and Fe at a ratio of 3: 3: 2 atomic%. As a result, the Si content reversibly reacting with lithium is increased, and the initial discharge capacity and cycle characteristics are improved.

JP 2008-235276 A JP 2013-105655 A JP 2013-161786 A

However, the invention described in Patent Document 1 has a problem that the silicon phase is not sufficiently fine and pulverization is likely to occur. According to the Hall Petch rule, the silicon phase and the size of the crystallite are smaller and are more difficult to be pulverized because the fracture resistance is improved. In addition, since a Cu alloy that is easily oxidized is used, there is a problem that CuO is generated and initial efficiency is poor.
In the invention according to Patent Document 2, as constituent elements, Si, Al, M1 (M1 is one or more metal elements selected from transition metals excluding Groups 4 and 5 of the periodic table), M2 (M2 is one or more metal elements selected from Group 4 and Group 5 of the Periodic Table), and a Si—Al—M1-M2 alloy phase constituting fine crystal grains; And an alloy material having a Si phase that precipitates at the grain boundaries of the crystal grains and exhibits a network structure. In Patent Document 2, since the phase is two phases, the size of the phase is larger than when three or more phases are generated, and the cracks generated are caused by volume expansion and contraction due to charge and discharge. , And pulverization tends to progress. For this reason, the cycle characteristics are likely to deteriorate.
The invention according to Patent Document 3 includes a phase (Si ₃ Al ₃ Fe ₂ phase) containing Si, Al, and Fe at a ratio of 3: 3: 2 atomic%, and the Si ₃ Al ₃ Fe ₂ phase is Fe. Therefore, even if a step of quenching the mother alloy is included, the precipitation temperature is high and the size of the Si phase tends to be large. As a result, cracks tend to progress with charge / discharge, and the cycle characteristics are not sufficient.

Applicant has a negative electrode for non-aqueous electrolyte secondary batteries that is excellent in cycle characteristics by suppressing the pulverization of the active material by suppressing the progress of cracks due to the volume expansion and contraction of Si accompanying repeated charge and discharge. An object is to provide an active material and a battery.

That is, the present invention
(1) includes silicon and an element M capable of forming a compound with silicon,
When the composition of silicon and the element M is cooled from a molten state, the compound of silicon and the element M is precipitated first, and when further cooled, pure silicon or a silicon solid solution is deposited. Active material.
(2) including silicon and an element M capable of forming a compound with silicon,
When the composition of silicon and the element M is cooled from the molten state at a rate of 1000 K / s or more, the compound of silicon and the element M is deposited first, and when further cooled, pure silicon or a silicon solid solution is deposited. A negative electrode active material characterized by being.
(3) The element M is at least one element selected from the group consisting of V, Nb, Ta, Mo, W, Ti, Zr, and Cr. (1) or (2) The negative electrode active material as described.
(4) The negative electrode active material according to any one of (1) to (3), wherein the composition of silicon and the element M is in a hypereutectic region.
(5) The negative electrode active material has a silicon phase composed of pure silicon or a silicon solid solution, and a silicide phase composed of a compound of silicon and the element M,
The negative electrode active material according to any one of (1) to (4), wherein the silicon phase is 20 wt% or more in the negative electrode active material.
(6) In any one of (1) to (5), a phase having an outer diameter or width of 10 to 300 nm occupies 50% by volume or more of the silicon phase among the silicon phases. The negative electrode active material as described.
(7) Further, the negative electrode active material is an element D different from the element M (Al, Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, La, Ce, Nd, At least one element selected from the group consisting of Dy, Sm, Pr, Y, Zr, Nb, Mo, Hf, Ta, W, Re, Os, Ir, Ru, Rh, and Ba)
The negative electrode active material according to any one of (1) to (6), wherein the negative electrode active material comprises a compound of silicon and the element D.
(8) The first phase having Li storage properties is dispersed in the second phase having Li conductivity electrochemically,
The negative electrode active material, wherein the first phase further includes a third phase that is less Li-occluding than the first phase.
(9) The area ratio of the first phase to the second phase is 10 to 90%, and further, the third phase is contained in an amount of 1 to 40 atomic% with respect to the negative electrode active material material. The negative electrode active material as described in 8).
(10) The negative electrode active material according to (8) or (9), wherein the first phase is pure silicon or a silicon solid solution, and the average thickness of the cross-sectional layers is 20 to 2000 nm.
(11) The negative electrode active material according to any one of (8) to (10), wherein the second phase is silicide and the average thickness of the cross-sectional layers is 20 to 2000 nm.
(12) Any one of (8) to (11), wherein the second phase contains Si and Al, and further contains at least one element selected from the element D according to claim 6. The negative electrode active material according to 1.
(13) The second phase contains Si and Al, and further contains at least one element selected from Fe, Co, Mn, La, Ce, Nd, Pr, Sm, and Dy. The negative electrode active material according to any one of (8) to (12).
(14) The negative electrode active material according to any one of (8) to (13), wherein the second phase includes a fourth phase that is less Li-occluding than the first phase.
(15) The negative electrode active material for a nonaqueous electrolyte secondary battery according to (14), wherein the fourth phase is contained in an amount of 1 to 50 atomic% with respect to the negative electrode active material.
(16) The negative electrode active material according to any one of (8) to (15), wherein the average value of the thickness of the cross-sectional layer of the third phase is 1 to 100 nm.
(17) the third _{phase, VSi 2, TaSi 2, MoSi} 2, NbSi 2, WSi 2, TiSi 2, ZrSi 2, CrSi , characterized in that it comprises at least one compound selected from ₂ (8 ) To (16).
(18) the third _phase, the negative active material according to any one of VSi _2, TaSi 2, characterized in that it comprises at least one compound selected from _{NbSi 2 (8) ~ (17} ).
(19) The third phase or the fourth phase contains at least one compound selected from SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZnO, CaO, and MgO. The negative electrode active material according to any one of (18).
(20) A region in which the volume of particles constituting the third phase occupies 10% or more of the total volume of the first phase and the third phase is present (8) to The negative electrode active material according to any one of (19).
(21) A negative electrode for a non-aqueous electrolyte secondary battery having an active material layer on a current collector,
The active material layer includes silicon and an element M capable of forming a compound with silicon, and when the composition of silicon and the element M is cooled from a molten state, the compound of silicon and the element M is first precipitated. A negative electrode for a non-aqueous electrolyte secondary battery, comprising: a negative electrode active material characterized in that pure silicon or a silicon solid solution precipitates when further cooled; and a binder.
(22) a positive electrode capable of inserting and extracting lithium ions;
A negative electrode having an active material layer on a current collector;
Having a separator disposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte secondary battery in which the positive electrode, the negative electrode, and the separator are provided in an electrolyte having lithium ion conductivity,
The active material layer of the negative electrode includes silicon and an element M capable of forming a compound with silicon, and when the composition of silicon and the element M is cooled from a molten state, the compound of silicon and the element M is first A non-aqueous electrolyte secondary battery comprising: a negative electrode active material characterized by having a composition in which pure silicon or a silicon solid solution is deposited when cooled and further cooled; and a binder .
(23) including silicon and an element M capable of forming a compound with silicon, and when the composition of silicon and the element M is cooled from a molten state, the compound of silicon and the element M is first precipitated and further cooled. Then, the manufacturing method of the negative electrode active material characterized by cooling the molten metal which is a composition in which pure silicon or a silicon solid solution precipitates at a rate of 1000 K / s or more.
(24) The method for producing a negative electrode active material according to (23), wherein the molten metal is cooled by a single roll method, a twin roll method, a melt spinning method, a gas atomizing method, or a water atomizing method.
(25) A negative electrode for a nonaqueous electrolyte secondary battery comprising the negative electrode active material for a nonaqueous electrolyte secondary battery according to any one of (8) to (20).
(26) A non-aqueous electrolyte secondary battery comprising the negative electrode for a non-aqueous electrolyte secondary battery according to (25).
(27) Element group D excluding Si, Al, Al (Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, La, Ce, Nd, Dy, Sm, Pr, Y, At least one element selected from Zr, Nb, Mo, Hf, Ta, W, Re, Os, Ir, Ru, Rh, and Ba), element group M (V, Ta, Mo, Nb, W, Ti, After melting an alloy containing at least one element selected from Zr and Cr), it is rapidly cooled (1000K /) by any of the single roll method, twin roll method, melt spinning method, gas atomizing method, and water atomizing method. The negative electrode active for a nonaqueous electrolyte secondary battery according to any one of (8) to (19), characterized by solidifying and precipitating the second phase at a temperature of 1000 ° C. or lower Manufacturing method of material.
However, an element selected from the element group M and the element group D is not the same element.
(28)
The non-water according to (27), wherein the element of element group D excluding Al is at least one element selected from Fe, Co, Mn, La, Ce, Nd, Pr, Sm, and Dy A method for producing a negative electrode active material for an electrolyte secondary battery.

According to the present invention, the first phase contributing to the discharge capacity is ensured, and the expansion of cracks caused by the volume expansion / contraction of the first phase due to repeated charging / discharging is suppressed, thereby achieving high capacity and cycle characteristics. In this way, a negative electrode active material for a non-aqueous electrolyte secondary battery that is excellent in performance can be obtained.

The schematic diagram of the cross section of the negative electrode active material 1 which concerns on embodiment of this invention. (A)-(d) The schematic diagram which shows the manufacturing process of the negative electrode active material 1 which concerns on embodiment of this invention. (A)-(b) The schematic diagram which shows the modification of the manufacturing process of the negative electrode active material 1 which concerns on embodiment of this invention. The schematic diagram of the gas atomizer 21 which concerns on embodiment of this invention. The schematic diagram of the single roll quenching apparatus 41 which concerns on embodiment of this invention. The schematic diagram of the twin roll quenching apparatus 51 which concerns on embodiment of this invention. The schematic diagram of the melt spinning apparatus 61 which concerns on embodiment of this invention. The schematic diagram of the cross section of the nonaqueous electrolyte secondary battery 71 which concerns on embodiment of this invention. Binary phase diagram of vanadium and silicon. Niobium and silicon binary phase diagram. Binary phase diagram of tantalum and silicon. Binary phase diagram of molybdenum and silicon. Binary system phase diagram of tungsten and silicon. Binary system phase diagram of titanium and silicon. Binary phase diagram of zirconium and silicon. Binary phase diagram of chromium and silicon. 2 is a scanning electron micrograph of a cross section of the negative electrode active material according to Example 1. FIG. XRD analysis result of negative electrode active material according to Example 1 2 is a scanning electron micrograph of a cross section of a negative electrode active material according to Comparative Example 1. XRD analysis result of negative electrode active material according to Comparative Example 1 The scanning electron micrograph of the cross section of the negative electrode active material after 1 cycle concerning the comparative example 1. (A)-(e) The figure explaining SEI formed in the circumference | surroundings of the conventional silicon particle 100. FIG. Schematic diagram of negative electrode active material according to the present invention BF-STEM (Bright-Field Scanning Transmission Electron Microscope, Bright Field Scanning Transmission Electron Microscope Image) of Si—Fe—Al—V Alloy According to Example 11 XRD (X-ray diffraction, X-ray diffraction) analysis result of Si—Fe—Al—V alloy according to Example 11 EDS (Energy Dispersive X-ray Spectrometer, Energy Dispersive X-ray Spectroscopy) mapping according to Example 11

(Negative electrode active material 1)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The negative electrode active material 1 which concerns on embodiment of this invention is demonstrated. FIG. 1 is a schematic cross-sectional view of the negative electrode active material 1. The negative electrode active material 1 contains silicon and an element M capable of forming a compound with silicon. The composition of silicon and element M is a composition in which a compound of silicon and element M first precipitates when cooled from a molten state, and pure silicon or a solid solution thereof (hereinafter referred to as a silicon phase) precipitates when further cooled. . With such a composition, as will be described later, since the compound of silicon and element M is already deposited at the time of deposition of the silicon phase, the silicon phase crystal does not grow greatly and remains fine. Kept.

In particular, the element M is preferably at least one element selected from the group consisting of V, Nb, Ta, Mo, W, Ti, Zr, and Cr. This is because these elements have a composition containing a large amount of silicon and are in a hypereutectic region where silicide having an MSi ₂ composition is first deposited.

The composition of silicon and the element M is preferably in the hypereutectic region. In the hypereutectic region, since the ratio of the element M is larger than the composition at the eutectic point of silicon and the element M, the silicide of the MSi ₂ composition composed of silicon and the element M is formed during cooling from the molten state. This is because it precipitates before the silicon phase.

The negative electrode active material 1 has a silicon phase 3 made of pure silicon or a solid solution thereof, and a first silicide phase 5 made of a compound of silicon and element M, and the silicon phase 3 is 20 wt% in the negative electrode active material 1. The above is preferable. The condition that the negative electrode active material 1 expresses a capacity of about 670 mAh / g, which is judged to have a larger discharge capacity than the graphite electrode or the SiO electrode, is when the silicon phase is 20 wt% or more. Since silicon phase 3 participates in the charge / discharge reaction with lithium ions, if the amount of silicon phase 3 is too small, there is no significant difference from the charge / discharge capacity of the conventional graphite-based negative electrode active material, and the advantage of using silicon Because it will be lost. Moreover, as long as the silicon phase 3 is included in a large amount as long as charge / discharge characteristics such as cycle characteristics are maintained, there is no problem.

Further, the silicon phase 3 is embedded in the first silicide phase 5. Therefore, the conductivity of the negative electrode active material 1 is increased by the highly conductive silicide compared to silicon, and further, the expansion / contraction of the silicon phase 3 can be suppressed. In addition, since a small amount of silicide can occlude / release lithium, the silicon phase 3 embedded in the first silicide phase 5 occludes / Can be released.

Among the plurality of silicon phases 3 included in the negative electrode active material 1, when the volume of the silicon phase 3 having an outer diameter or width of 10 to 300 nm is combined, it is preferable to occupy 50% by volume or more of the silicon phase 3. If the silicon phase 3 is too large, the probability of cracks occurring in the silicon phase 3 due to stress during charging / discharging increases due to Hall Petch's law. Therefore, it is preferable that the ratio of the small silicon phase in which cracks hardly occur to the entire silicon phase 3 is half or more.

Here, the outer diameter or width of the silicon phase 3 means the outer diameter when the silicon phase 3 has a particle shape, and the thickness when the silicon phase 3 has a two-dimensional lamellar structure. When the silicon phase 3 has a one-dimensional rod-like structure, it means the diameter of the cross section. That is, it is preferable that at least one-dimensional length of the silicon phase 3 is in the range of 10 to 300 nm.
The outer shape and width of the silicon phase 3 in the negative electrode active material 1 can be obtained by observing the cross section of the negative electrode active material 1 with an electron microscope. Further, the volume ratio of the silicon phase 3 of a predetermined size in the negative electrode active material 1 is obtained by comparing the area of the silicon phase 3 of the predetermined size exposed on the cross section with the area of the cross section of the entire negative electrode active material 1. Can do.

(Addition of element D)
Further, the negative electrode active material is an element D different from the element M (Cu, Al, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, Y, Zr, Nb, Mo, Ru, Rh, Ba, lanthanoid element, at least one element selected from the group consisting of Hf, Ta, W, Re, Os and Ir), and the negative electrode active material has a compound of silicon and element D Is preferred. First, in the case of a ternary system of silicon, element M, and element D, the melting point is lowered and a molten metal can be produced at a low temperature, so that the silicon phase tends to be fine. Further, in addition to the compound of silicon and element M, the compound of silicon and element D or the compound of ternary silicide of silicon, element M and element D is formed in the negative electrode active material 1, so that silicon Phase 3 is more easily covered by the first silicide phase 5. Since the silicon phase 3 is covered by the first silicide phase 5 made of the element M or the compound of the element D and silicon, the negative electrode active material 1 becomes more conductive and can relax the volume expansion of the silicon phase 3. As will be described later, the silicide phase covering the silicon phase 3 may include a plurality of phases including the second silicide phase 7 in addition to the first silicide phase 5.

(Method for producing negative electrode active material)
A manufacturing process of the negative electrode active material 1 according to the embodiment of the present invention will be described with reference to FIG. As shown in FIG. 2A, the molten metal 11 is formed by mixing silicon and the element M and heating to high temperature. In the embodiment, the kind of the element M and the composition of the silicon and the element M such that the silicide phase is precipitated before the silicon phase are employed. As shown in FIG. 2B, when the molten metal 11 is cooled, the silicide primary crystal 13 is formed from the molten metal 11 because the types and concentrations of silicon and element M in the molten metal 11 are within a predetermined range. When the cooling is further advanced, as shown in FIG. 2C, silicon 15 which is a crystal of silicon starts to be deposited. However, the excessive growth of the silicon 15 is inhibited by the surrounding first silicide 17 formed by the growth of the silicide primary crystal 13, so that a fine silicon phase 3 is obtained as shown in FIG. . The silicon phase 3 is buried in the first silicide phase 5 on which the first silicide 17 is grown.

Further, by adding an element D different from the element M, a ternary silicide composed of silicon, the element M, and the element D may be formed in addition to the binary silicide of the silicon and the element D. . FIG. 3A shows a case where the element D is further added to the molten metal 11. As the cooling proceeds from the state of FIG. 2C, binary silicide of silicon and element D or silicon and element. The second silicide 19 made of ternary silicide composed of M and the element D starts to precipitate. However, excessive growth of the silicon 15 is inhibited by the surrounding first silicide 17 or the second silicide 19, so that a fine silicon phase 3 is obtained as shown in FIG. The second silicide phase 7 in FIG. 3B includes a binary silicide of silicon and element D, or a ternary silicide composed of silicon, element M, and element D, and a plurality of different composition ratios. It may be a seed silicide.

A specific method for producing the negative electrode active material 1 will be described. Silicon may be a solid solution containing B (boron) or Ru (ruthenium). First, a molten metal containing silicon and an element M capable of forming silicon and a compound is prepared. The composition of silicon and element M in the molten metal is such that when cooling from the molten state, the compound of silicon and element M is precipitated first, and when further cooled, the silicon phase is precipitated. Element D may be further added to the molten metal. When this molten metal is cooled at a rate of 1000 K / s or higher, silicide precipitation and subsequent silicon phase precipitation occur, and the negative electrode active material 1 is formed. Since relatively rapid cooling of 1000 K / s or more is performed, the fine silicon phase 3, the first silicide phase 5, and the second silicide phase 7 can be obtained. The negative electrode active material 1 is preferably formed by a gas atomization method or a water atomization method. Alternatively, after the molten metal is cooled by any one of a single roll method, a twin roll method, and a melt spinning method, the obtained flake-shaped, ribbon-shaped, plate-shaped or thread-shaped alloy is pulverized and classified to obtain the negative electrode active material 1. It may be formed.

(Gas atomization method and water atomization method)
A gas atomizing apparatus 21 shown in FIG. 4 is an apparatus that forms the negative electrode active material 1 by a gas atomizing method. The molten metal 11 formed by melting silicon and the element M in the crucible 23 is dropped from the nozzle 25, and at the same time, the gas jet flow 31 from the gas injector 29 to which the ejection gas 27 such as inert gas or air is supplied. The molten metal 11 is pulverized and solidified as droplets to form the powdered negative electrode active material 1. Element D may be further added to the molten metal 11. The negative electrode active material 1 can be continuously classified into a desired particle size through a cyclone or a filter connected to the gas atomizer 21. When water is supplied instead of the jet gas 27 and high-pressure water is sprayed instead of the gas jet stream 31, the water atomization method is performed.

(Single roll method)
A single roll quenching apparatus 41 shown in FIG. 5 is an apparatus used for manufacturing a ribbon-like or flake-like alloy 47 by a single roll method. The single roll quenching device 41 injects the molten metal 11 containing silicon and the element M in the crucible 43 toward the single roll 45 that rotates at high speed, and rapidly cools the molten metal 11, so that Thus, a ribbon-like or flake-like alloy 47 including the silicide phase 5 can be obtained. Element D may be further added to the molten metal 11. The single roll quenching device 41 can control the quenching speed by setting the injection amount of the molten metal 11 and the rotation speed of the single roll 45, and can control the silicon phase 3, the first silicide phase 5, and the second silicide phase. The size of 7 can be controlled. Moreover, the negative electrode active material 1 having a desired primary particle diameter can be obtained by pulverizing and classifying the obtained ribbon-like or flake-like alloy 47 as necessary. In the single roll method, when the molten metal 11 is injected from the crucible 43, the single roll 45 instantaneously cools, so that the rapid cooling rate is faster than the gas atomization method, and the finer silicon phase 3 and the first silicide phase 5 And the 2nd silicide phase 7 can be obtained.

(Two-roll method)
A twin roll quenching apparatus 51 shown in FIG. 6 is an apparatus used for manufacturing a ribbon-like or plate-like alloy 59 by a twin roll method. The twin roll quenching device 51 can obtain a ribbon-like or plate-like alloy 59 by sandwiching the molten metal 11 containing silicon and the element M in the crucible 53 with a pair of casting rolls 55. Element D may be further added to the molten metal 11. Furthermore, a quenching device 57 that blows water, air, or the like to the ribbon-like or plate-like alloy 59 may be provided at the outlet of the casting roll 55. Also in the twin roll method, when the molten metal 11 is injected from the crucible 53, it is cooled instantaneously by the pair of casting rolls 55, so that the fine silicon phase 3, the first silicide phase 5 and the second silicide phase 7 are obtained. Can do.

(Melt spinning method)
A melt spinning apparatus 61 shown in FIG. 7 is an apparatus used for manufacturing a yarn-like or ribbon-like alloy 70 by a melt spinning method. The melt spinning apparatus 61 can rapidly cool the molten metal 11 in the crucible 63 with a large amount of cooling liquid 67 in the container 65 and obtain the yarn-like or ribbon-like alloy 70 while being guided by the guide roll 69. . Also in the melt spinning method, since the molten metal 11 can be rapidly cooled, the fine silicon phase 3, the first silicide phase 5, and the second silicide phase 7 can be obtained.

(Element M)
As described above, the element M is preferably at least one element selected from the group consisting of V, Nb, Ta, Mo, W, Ti, Zr, and Cr.

FIG. 9 is a binary phase diagram of vanadium and silicon. In the hypereutectic region of vanadium and silicon, Si / (Si + V) is 52 wt% to 95 wt% (67 atomic% to 97 atomic%). If the composition is in the hypereutectic region of vanadium and silicon, when the molten metal in the high temperature state is cooled, first, silicide such as VSi ₂ is deposited, and then when pure metal is deposited at 1400 ° C. Therefore, the crystal growth of pure silicon can be prevented.
(In the figure, the hypereutectic region is α and the eutectic point is β. The same applies to the following figures.)

FIG. 10 is a binary system phase diagram of niobium and silicon. In the hypereutectic region of niobium and silicon, Si / (Si + Nb) is 38 wt% to 93.7 wt% (67 atomic% to 98 atomic%).

FIG. 11 is a binary phase diagram of tantalum and silicon. In the hypereutectic region of tantalum and silicon, Si / (Si + Ta) is 24 wt% to 94 wt% (67 atomic% to 99 atomic%).

FIG. 12 is a binary phase diagram of molybdenum and silicon. In the hypereutectic region of molybdenum and silicon, Si / (Si + Mo) is 37 wt% to 94.4 wt% (67 atomic% to 98 atomic%).

FIG. 13 is a binary phase diagram of tungsten and silicon. In the hypereutectic region of tungsten and silicon, Si / (Si + W) is 23 wt% to 94 wt% (67 atomic% to 99 atomic%).

FIG. 14 is a binary phase diagram of titanium and silicon. In the hypereutectic region of titanium and silicon, Si / (Si + Ti) is 52 wt% to 73 wt% (65 atomic% to 82 atomic%).

FIG. 15 is a binary phase diagram of zirconium and silicon. In the hypereutectic region of zirconium and silicon, Si / (Si + Zr) is 38 wt% to 80 wt% (67 atomic% to 93 atomic%).

FIG. 16 is a binary phase diagram of chromium and silicon. In the hypereutectic region of chromium and silicon, Si / (Si + Cr) is 52 wt% to 81 wt% (67 atomic% to 86 atomic%).

(About the first phase)
The first phase is preferably a material that is electrochemically Li-occlusion and has a large discharge capacity. Specifically, Si or a solid solution of Si can be used.
As will be described later, the main feature of the present invention is that the first phase is dispersed in the second phase, and further, the first phase further includes a third phase that is less Li occluding than the first phase. It is a technical feature.
Note that the silicon phase 3 in FIG. 1 corresponds to the first phase of the present invention.
The cross-sectional layer thickness of the first phase is preferably 20 to 2000 nm. If it is 20 nm or more, it is easy to produce stably, and if it is 2000 nm or less, the degree of volume expansion / contraction associated with charge / discharge is small, and cracks are unlikely to occur.
The shape of each phase can take various forms such as dots, spots, meshes and stripes. Therefore, the thickness of the phase section was measured, and the range of values corresponding to 50% by volume or more of each phase was defined as the thickness of the section layer.

(About the second phase)
The second phase requires Li conductivity electrochemically. Having Li conductivity means that it has electrochemically a small amount of Li storage and Li can reversibly pass through the second phase. The movement of Li may be Li ion conductivity or Li alloying reaction. Therefore, it is possible to make Li reach the first phase scattered in the island shape of the sea-island structure inside the second phase. In other words, if the second phase is an electrochemically Li-inactive metal such as Cu or Ni, Li cannot reach the first phase such as Si scattered in islands, so charging / discharging And no discharge capacity is generated.
Note that the first silicide phase 5 in FIG. 1 corresponds to the second phase of the present invention.
Specific examples of the second phase include silicide.
The thickness of the cross-sectional layer of the second phase is preferably 20 to 2000 nm. If it is 20 nm or more, it is easy to produce stably as in the first phase, and if it is 2000 nm or less, it is easy to secure a predetermined amount of the first phase, and this is preferable in that it is easy to secure a high discharge capacity. As described above, the first phase is dispersed in the second phase.

A preferable content ratio of the first phase in the second phase is 10 to 90%, further 20 to 80%, and further 30 to 30% as an area ratio by analysis of an SEM (Scanning Electron Microscope) image. 70% is preferred.
Further, the second phase includes Si and Al, and further includes Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, La, Ce, Nd, Dy, Sm, Pr, It is preferable to contain at least one element selected from Y, Zr, Nb, Mo, Hf, Ta, W, Re, Os, Ir, Ru, Rh, and Ba. Here, Ni is preferable from the viewpoint of improving conductivity, although the composition of crystallites to be generated varies and coarse crystallites are likely to be mixed.
Furthermore, Fe, Co, and Mn are easy to refine the silicon phase and the silicide phase, and La, Ce, Nd, Pr, Sm, and Dy are easy to produce a low melting point silicide and the silicon phase and the silicide phase are easily refined. And more preferable.

(About the third phase)
One of the technical features of the present invention is that the first phase includes a third phase that is less Li-occluding than the first phase.

FIG. 23 is a schematic diagram of a negative electrode active material in the present invention. The upper part of FIG. 23 shows that the first phase is dispersed in the second phase. When the second phase is the sea, the first phase forms an island structure and exists. The middle part of FIG. 23 is an enlarged view of a part of the upper part, a boundary part between the first phase and the second phase. The lower part of FIG. 23 is an observation obtained by enlarging the magnification of the first phase in the middle part.

By forming a fine structure like the third phase inside the first phase, the extension of cracks caused by the volume expansion / contraction of the first phase during charge / discharge can be caused by dislocation of the first phase. This can be suppressed by the third phase that makes the sliding surface intermittent.
The average value of the cross-sectional layers of the third phase is preferably 1 to 100 nm, and more preferably 2 to 40 nm or less. If the thickness is 1 nm or more, the crack extension deterrence is large, and if it is 100 nm or less, a stable first phase can be secured, so that a high discharge capacity is easily secured.
The third _{phase, VSi 2, TaSi 2, MoSi} 2, NbSi 2, WSi 2, TiSi 2, ZrSi 2, CrSi 2 _{or, SiO 2, TiO 2, Al} 2 O 3, ZnO, CaO, from MgO At least one selected compound may be included as the third phase.
The third phase is preferably contained in an amount of 1 to 40 atomic%. More preferably, the content is 3 to 30 atomic%. If it is 3 atomic% or more, the effect of suppressing the progress of cracks in the first phase is high, and if it is 30 atomic% or less, a sufficient amount of the first phase is secured and a high discharge capacity is secured. .

(About the fourth phase)
The second phase may include a fourth phase that is less Li-occluding than the first phase. Here, the phase precipitated at the boundary between the second phase and the first phase is also determined as the fourth phase included in the second phase.
Further, the fourth phase may be a dot-like, spot-like or streaky shape of about 5 to 150 nm, or a substantially spherical shape of about 30 to 150 nm. The fourth component of the phase, Al and the same _VSi 2 and the third _{phase, TaSi 2, MoSi 2, NbSi} 2, WSi 2, TiSi 2, ZrSi 2 _{and, SiO 2, TiO 2, Al} 2 O 3, It may contain at least one compound selected from ZnO, CaO, and MgO. In particular, Al is preferable because it can suppress the coarsening of the phase. The second phase includes the fourth phase having different mechanical characteristics, thereby mitigating the influence of the stress generated due to the volume expansion / contraction of the first phase accompanying charge / discharge, and contributing to the cycle characteristics. Is estimated.

The fourth phase is preferably contained in an amount of 1 to 50 atomic%. More preferably, the content is 2 to 30 atomic%. If the fourth phase is 2 atomic% or more, cracks due to volume expansion / contraction associated with charge / discharge of the first phase hardly propagate to the second phase, and the effect of suppressing crack extension of the second phase is high. . Moreover, when the fourth phase is 30 atomic% or less, a sufficient amount of the first phase is secured, and a high discharge capacity is secured.

When Al is used as an input element, if the input amount of Al is 26 atomic% or more, the second phase is sufficiently generated, and excess Al is precipitated as a metallic Al phase. For example, in the case of the Si—Fe—Al—V system, FeAl ₃ Si ₂ is generated as the second phase. However, if the amount of Al input is less than 26 atomic%, the Fe element becomes excessive, which is 300% higher than FeAl ₃ Si _2. FeSi ₂ is likely to be precipitated at a high temperature of not lower than ° C. As a result, the phase including the first phase made of Si phase is coarsened, and it is difficult to ensure a high capacity retention rate. That is, it becomes easy to ensure a high capacity maintenance rate by having a predetermined amount of elements.

(Main production method of negative electrode active material according to another embodiment of the present invention)
First, a molten metal containing Si, Al, and an element group M capable of forming a compound with Si is prepared. An element group D is further added to the molten metal. When this molten metal is cooled at a rate of 1000 K / s or more, precipitation of the third phase (DSi ₂ ) and subsequent precipitation of the first phase (Si phase) occur depending on the composition, and further the low melting point first Two phases (for example, FeAl ₃ Si ₂ when M is Fe) are precipitated.

The negative electrode active material is obtained by cooling the molten metal by any one of a single roll method, a twin roll method, a melt spinning method, a gas atomizing method, and a water atomizing method. The negative electrode active material may be formed by pulverizing and classifying a flaky alloy. Si may be a Si solid solution containing B, P, or the like.

The element group D used for the molten metal is Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, La, Ce, Nd, Dy, Sm, Pr, Y, Zr, Nb, Mo, At least one element selected from Hf, Ta, W, Re, Os, Ir, Ru, Rh, and Ba, and the element group M is V, Ta, Mo, Nb, W, Ti, Zr, Cr (however, The element selected from the element group M and the element group D is preferably not the same element).
Furthermore, since the compounds of SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZnO, CaO, and MgO have high melting points of 1650 ° C., 1640 ° C., 2054 ° C., 1975 ° C., 2613 ° C., and 2852 ° C., respectively, It is not necessary to dissolve at the same time in the stage of dissolving the raw materials constituting the phase and the second phase. The SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZnO, CaO, and MgO compounds use primary particles of 2 to 200 nm and are handled as a granulated material of 10 to 200 μm in order to improve handling properties. The compound of SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZnO, CaO, and MgO may be added to the molten metal in a granulated state, and the primary particles may be uniformly dispersed in the molten metal and mixed with the elements in the molten metal. .

The composition ratio of each element (element group) is preferably 44 to 71 atomic% for Si, 26 to 45 atomic% for Al, 2 to 12 atomic% for Element Group D, and 1 to 10 atomic% for Element Group M. .
When Si is 44 atomic% or more, the discharge capacity can be sufficiently secured, and when it is 71 atomic% or less, the crystal is prevented from becoming coarse and the capacity maintenance ratio can be maintained.
When Al is 26 atomic% or more, the crystal phase size can be adjusted appropriately, and the capacity retention rate can be maintained. When it is 45 atomic% or less, the amount of Si added can be secured, and the discharge can be ensured. This is preferable in that capacity can be secured.
When the element group D is 2 atom% or more and 12 atom% or less, it is preferable in that the addition amount of Si, which is usually the maximum amount, can be adjusted, and the balance between the capacity retention rate and the discharge capacity can be maintained.
When a certain amount of the element group M exists, a hypereutectic region defined from a binary phase diagram of Si and the individual elements D can be secured. As a result, the deposition of silicide starts at a temperature higher than that of Si. This is preferable in that silicide (DSi ₂ ) serving as a main component of the phase can be suitably formed.

(Configuration of negative electrode for non-aqueous electrolyte secondary battery)
The negative electrode for nonaqueous electrolyte secondary batteries has an active material layer on one or both sides of the current collector. The active material layer is formed by applying a slurry containing the negative electrode active material 1 and a binder.

The current collector is a foil made of at least one metal selected from the group consisting of copper, nickel, and stainless steel. Each may be used alone or may be an alloy of each. The thickness is preferably 4 μm to 35 μm, more preferably 6 μm to 18 μm.

The binder is made of polyimide (PI), polybenzimidazole (PBI), polyamideimide, polyamide, styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), polyacrylic acid One or more selected.

The binder is added to the slurry in a state dissolved in a solvent or dispersed as an emulsion. After the slurry application, the binder binds the negative electrode active material 1 onto the current collector.

Also, a conductive aid may be added to the active material layer. By adding a conductive additive, the conductivity of the active material layer of the negative electrode is improved and charging / discharging is facilitated. The conductive assistant is a powder made of at least one conductive material selected from the group consisting of carbon, copper, tin, zinc, nickel, silver and the like. A single powder of carbon, copper, tin, zinc, nickel, or silver may be used, or a powder of each alloy may be used. Various shapes such as a spherical shape, a dendritic shape, a bead shape, an indeterminate shape, a scale shape, and a linear shape can be used for the conductive auxiliary agent. For example, in the case of carbon, general carbon black such as furnace black, acetylene black, scaly graphite, carbon nanotube, carbon nanohorn, fullerene, or graphene sheet can be used.

(Method for producing negative electrode for nonaqueous electrolyte secondary battery)
First, a slurry raw material is put into a mixer and kneaded to form a slurry. The slurry raw material is the negative electrode active material 1, the conductive auxiliary agent, the binder, the thickener, the solvent, and the like according to the embodiment of the present invention.

The solid content in the slurry contains 25 to 95% by weight of the negative electrode active material, 0 to 70% by weight of the conductive aid, 1 to 30% by weight of the binder, and 0 to 25% by weight of the thickener. Preferably, the negative electrode active material is 50 to 90% by mass in solid content. The ratio is 5 to 30% by mass of the conductive additive and 5 to 25% by mass of the binder. When there are too few binders, adhesiveness will fall and it will be difficult to maintain the shape of a granulated body and an electrode. Moreover, when there are too many binders, electroconductivity will fall and charging / discharging will become difficult.

As the mixer, a general kneader used for slurry preparation can be used, and a device called a kneader, a stirrer, a disperser, a mixer, or the like that can prepare a slurry may be used. N-methyl-2-pyrrolidone can be used as a solvent.

Next, for example, using a coater, slurry is applied to one side of the current collector. As the coater, a general coating apparatus capable of applying the slurry to the current collector can be used. Examples of the coater include a roll coater, a doctor blade coater, a comma coater, and a die coater.

調製 Apply the prepared slurry uniformly to the current collector, then dry at about 50 to 150 ° C and pass through a roll press to adjust the thickness. Then, when using polyimide as the binder 67, the negative electrode 61 for a nonaqueous electrolyte secondary battery is obtained by firing at 150 ° C. to 350 ° C. as necessary. The active material layer 65 may be formed on both surfaces of the current collector 63 as necessary.

(Preparation of non-aqueous electrolyte secondary battery)
As the negative electrode used for the nonaqueous electrolyte secondary battery, the negative electrode for a nonaqueous electrolyte secondary battery according to an embodiment of the present invention is used.

(Preparation of positive electrode for nonaqueous electrolyte secondary battery)
As a positive electrode for a non-aqueous electrolyte secondary battery, a composition of a positive electrode active material obtained by mixing a positive electrode active material, a conductive additive, a binder and a solvent is directly applied on a metal current collector such as an aluminum foil. Apply and dry to produce the positive electrode.

Any positive electrode active material can be used as long as it is generally used. For example, LiCoO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3. Compounds such as O ₂ and LiFePO ₄ .

For example, carbon black is used as the conductive assistant, polyvinylidene fluoride (PVdF), a water-soluble acrylic binder is used as the binder, and N-methyl-2-pyrrolidone (NMP) is used as the solvent. Use water, etc. At this time, the contents of the positive electrode active material, the conductive additive, the binder, and the solvent are the levels that are normally used in the non-aqueous electrolyte secondary battery.

As the separator, any separator can be used as long as it has a function of insulating electronic conduction between the positive electrode and the negative electrode and is normally used in a nonaqueous electrolyte secondary battery. For example, a microporous polyolefin film, a porous aramid resin film, a porous ceramic, a nonwoven fabric, etc. can be used.

Organic electrolyte (non-aqueous electrolyte), inorganic solid electrolyte, polymer solid electrolyte, etc. can be used for the electrolyte and electrolyte in non-aqueous electrolyte secondary batteries, Li polymer batteries, and the like.
Specific examples of the organic electrolyte solvent include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate; diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol di Ethers such as butyl ether and diethylene glycol dimethyl ether; aprotic such as benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethylchlorobenzene, nitrobenzene Solvent, or two or more of these solvents Mixed solvent of thereof.

The electrolyte of the organic electrolyte includes LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAlO ₄ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) A mixture of one or more electrolytes made of a lithium salt such as ₂ can be used.

Also, a solid lithium ion conductor can be used in place of the organic electrolyte. For example, a solid polymer electrolyte in which the lithium salt is mixed with a polymer made of polyethylene oxide, polypropylene oxide, polyethyleneimine, or the like, or a polymer gel electrolyte in which a polymer material is impregnated with an electrolytic solution and processed into a gel shape can be used.

Further, lithium nitride, lithium halide, lithium oxyacid salt, Li ₄ SiO ₄ , Li ₄ SiO ₄ —LiI—LiOH, Li ₃ PO ₄ —Li ₄ SiO ₄ , Li ₂ SiS ₃ , Li ₃ PO ₄ —Li An inorganic material such as ₂ S—SiS _{2 or} a phosphorus sulfide compound may be used as the inorganic solid electrolyte.

(Assembling of non-aqueous electrolyte secondary battery)
A battery element is formed by disposing a separator between the positive electrode and the negative electrode as described above. After winding or stacking such battery elements into a cylindrical battery case or a rectangular battery case, an electrolytic solution is injected to obtain a nonaqueous electrolyte secondary battery.

FIG. 8 shows an example (cross-sectional view) of the nonaqueous electrolyte secondary battery of the present invention. The non-aqueous electrolyte secondary battery 71 includes a positive electrode 73 and a negative electrode 75 that are stacked in the order of separator-positive electrode-separator-negative electrode via a separator 77, and wound so that the positive electrode 73 is on the inner side. Configure and insert it into the battery can 79. The positive electrode 73 is connected to the positive electrode terminal 83 via the positive electrode lead 81, and the negative electrode 75 is connected to the battery can 79 via the negative electrode lead 85, and the chemical energy generated inside the nonaqueous electrolyte secondary battery 71 is externally used as electric energy. To be able to take out. Next, after filling the battery can 79 with the electrolyte 87 so as to cover the electrode plate group, the upper end (opening portion) of the battery can 79 is composed of a circular lid plate and a positive electrode terminal 83 on the upper portion thereof, and a safety valve mechanism is provided therein. The non-aqueous electrolyte secondary battery 71 of the present invention can be manufactured by attaching the sealing body 89 containing the internal structure via an annular insulating gasket.

(Effect of the nonaqueous electrolyte secondary battery according to the embodiment of the present invention)
In the nonaqueous electrolyte secondary battery using the negative electrode active material 1 according to the embodiment of the present invention, the silicon phase 3 contained in the negative electrode active material 1 is made of silicon having a higher unit volume and unit capacity than carbon. Therefore, the capacity is larger than that of the conventional nonaqueous electrolyte secondary battery.

Further, in the negative electrode active material 1 according to the embodiment of the present invention, since the fine silicon phase 3 is embedded in the first silicide phase 5 or the second silicide phase 7, silicon fine powder generation due to charge / discharge is prevented. It is suppressed and the cycle characteristics are improved. Further, silicon and the electrolytic solution are not in direct contact, and it is possible to prevent SEI from being excessively formed on the surface of the silicon phase 3 due to a side reaction between the electrolytic solution and lithium. Therefore, since the negative electrode using the negative electrode active material 1 has high Coulomb efficiency, the nonaqueous electrolyte secondary battery according to the embodiment of the present invention has a long life.

Hereinafter, the present invention will be specifically described using examples and comparative examples.
[Example 1]
(Preparation of negative electrode active material)
A granular raw material of silicon, vanadium, iron, and aluminum is mixed so that the weight ratio is Si: V: Fe: Al = 62: 7: 12: 19, and a vacuum arc melting apparatus (NEV- manufactured by Nisshin Giken Co., Ltd.) A master alloy was prepared by AD03). Thereafter, the alloy pulverized to a size of about 5 mm is put into a crucible in a liquid rapid solidification apparatus (NEV-A1 manufactured by Nisshin Giken Co., Ltd.), heated to 1650 ° C. with a high-frequency coil, and then melted. A flaky negative electrode active material was obtained by quenching using a copper single roll of the single roll quenching apparatus shown in FIG. Vanadium corresponds to the element M. Vanadium and silicon form VSi ₂ to form a first silicide, and iron, silicon, and aluminum form FeAl ₃ Si ₂ to form a second silicide. In the composition of Example 1, since aluminum is excessively added, a metallic aluminum phase that does not form silicide is generated.
The flaky negative electrode active material obtained by rapid solidification with a single roll was pulverized by a planetary ball mill, and a powdered negative electrode active material was obtained through a sieve having an opening of 20 μm.

(Preparation of negative electrode for non-aqueous electrolyte secondary battery)
(I) Preparation of Negative Electrode Slurry 70 parts by mass of the negative electrode active material and the amount of carbon nanotubes in the carbon nanotube dispersion were charged into a mixer at a ratio of 18 parts by mass. Furthermore, polybenzimidazole using N-methylpyrrolidone as a solvent as a binder was mixed at a ratio of 12 parts by mass in terms of solid content to prepare a slurry.
(Ii) Production of negative electrode Using the doctor blade of the automatic coating apparatus, the prepared slurry was 15 μm thick on a 10 μm thick electrolytic copper foil for current collector (Furukawa Electric Co., Ltd., NC-WS). After coating at 100 ° C. and drying at 100 ° C., after passing through a thickness adjustment step by press, a heat treatment step at 330 ° C. for 2 hours was performed to produce a negative electrode for a non-aqueous electrolyte secondary battery.

(Evaluation of cycle characteristics)
A negative electrode for a non-aqueous electrolyte secondary battery, an electrolytic solution obtained by adding vinylene carbonate to a mixed solution of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate containing 1.3 mol / L LiPF ₆ , and lithium using a metal Li foil counter electrode An ion secondary battery was constructed and the charge / discharge characteristics were examined.
First, in a 25 ° C. environment, charging was performed under constant current and constant voltage conditions until the current value was 0.1 C and the voltage value was 0.02 V (vs. Li / Li ⁺ ), and the current value was reduced to 0.05 C. Stopped charging. Next, discharging was performed under the condition of a current value of 0.1 C until the voltage became 1.5 V (vs. Li ^/ Li ⁺ ). 1C is a current value that can be fully charged in one hour. Both charging and discharging were performed in a 25 ° C. environment. Next, the above charge / discharge was repeated up to 50 cycles at a charge / discharge rate of 0.2C. The evaluation of the characteristics was performed based on the initial discharge capacity and the capacity maintenance ratio indicating the discharge capacity after 50 cycles with respect to the initial discharge capacity as a percentage.

[Comparative Example 1]
(Preparation of negative electrode active material)
After mixing silicon powder, iron powder and aluminum powder in a weight ratio such that Si: Fe: Al = 68: 12: 20, the dried mixed powder was heated to 1500 ° C. in a crucible and dissolved. The molten metal was quenched using the single roll quenching device of FIG. 5 to obtain a negative electrode active material.
The other steps were the same as in Example 1.

(Evaluation of composition of negative electrode active material)
As shown in FIGS. 17 and 19, secondary electron images of the cross sections of the negative electrode active materials according to Example 1 and Comparative Example 1 were observed with a scanning electron microscope. As shown in FIG. 17, in the cross section of the negative electrode active material according to Example 1, it can be seen that the silicon phase 91 that looks black and has an outer diameter or width of about 10 to 300 nm is embedded in the silicide phase 93 that looks white. . The proportion of the silicon phase 91 having an outer diameter or width of about 10 to 300 nm in the entire alloy was 50% by volume or more when the cross section was observed. Further, XRD analysis was performed as shown in FIG. 18 to identify the crystal phase. As a result, a silicon phase, a first silicide phase of vanadium silicide VSi _2, a second silicide phase made of ternary silicide (FeAl ₃ Si ₂ ), and an aluminum phase were confirmed. The Si phase of this active material was about 43 wt%. As a result of the electrode evaluation, an initial discharge capacity of 1480 mAh / g was shown. The capacity retention after 50 cycles was 86%, indicating excellent cycle characteristics.

Furthermore, according to the quantification of the silicon phase by XRD analysis, the discharge capacity was almost proportional to the weight ratio of the Si phase, and the capacity of aluminum or silicide was negligibly small.

On the other hand, as shown in FIG. 19, in the cross section of the negative electrode active material according to Comparative Example 1, a silicon phase 91 that looks black and has an outer diameter or a width of 400 nm or more is continuously formed. It was found that the silicon phase was large. The ratio of the silicon phase having an outer diameter or width of about 10 to 300 nm to the entire silicon phase was less than 50% by volume. Further, XRD analysis was performed as shown in FIG. 20 to identify the crystal phase. As a result, a silicon phase, a silicide phase composed of ternary silicide (FeAl ₃ Si ₂ ), and an aluminum phase were confirmed. The Si phase of the active material of Comparative Example 1 was about 60 wt%, and the electrode evaluation showed a sufficient capacity of an initial discharge capacity of 1530 mAh / g. However, the capacity maintenance rate after 50 cycles of Comparative Example 1 was 78%. Thus, it was found that the cycle characteristics were inferior to those of Example 1. FIG. 21 is a scanning electron micrograph of the cross section of the negative electrode active material after the first charge / discharge (one cycle) of the electrode using the active material of Comparative Example 1. The dark portion 91 in FIG. 21 is the silicon phase, and the relatively bright portion 93 is the silicide (FeAl ₃ Si ₂ ) phase. Cracks are observed starting from a silicon phase having a size of about 400 nm or more. This is because the continuous silicon phase having an outer diameter or width of 400 nm or more is charged and discharged, so that fine powder is generated and a part of the active material is dropped from the electrode, or the new surface of silicon generated by the crack is subjected to an electrolyte solution. It is considered that SEI generated by the side reaction was generated and the capacity retention rate was lowered.

Next, another embodiment of the present invention will be specifically described using examples.

[Example 11]
(Preparation of negative electrode active material)
Silicon, vanadium, iron, and aluminum ingots are mixed at an atomic ratio of Si: V: Fe: Al = 66: 3: 4: 27, and a vacuum arc melting apparatus (NEV-AD03 manufactured by Nisshin Giken Co., Ltd.) A mother alloy was prepared. Thereafter, the alloy pulverized to a particle size of about 5 mm is put into a crucible in a liquid rapid solidification apparatus (NEV-A1 manufactured by Nisshin Giken Co., Ltd.), heated to 1650 ° C. with a high-frequency coil, and then melted. Was cooled rapidly to a temperature (1000 ° C. or lower) at which a second phase having Li conductivity was electrochemically deposited using a copper single roll of a single roll quenching apparatus to obtain a flaky negative electrode active material. In this embodiment, vanadium corresponds to the element D. Vanadium and silicon make VSi ₂ corresponding to the third phase, and iron, silicon and aluminum make FeAl ₃ Si ₂ corresponding to the second phase. In the composition of Example 1, since a large amount of aluminum is added, a metallic aluminum phase is generated as the fourth phase. The flaky negative electrode active material obtained by rapid solidification with a single roll was pulverized by a planetary ball mill, and a powdered negative electrode active material was obtained through a sieve having an opening of 20 μm. The composition ratio of the negative electrode active material was confirmed by emission spectroscopic analysis such as ICP (Inductively Coupled Plasma).

(Preparation of negative electrode for non-aqueous electrolyte secondary battery)
(I) Preparation of Negative Electrode Slurry 70 parts by mass of the negative electrode active material and the amount of carbon nanotubes in the carbon nanotube dispersion were charged into a mixer at a ratio of 18 parts by mass. Further, a polybenzimidazole containing N-methylpyrrolidone as a solvent as a binder was mixed at a ratio of 12 parts by mass in terms of solid content to prepare a slurry.
(Ii) Production of negative electrode Using the doctor blade of the automatic coating apparatus, the prepared slurry was 15 μm thick on a 10 μm thick electrolytic copper foil for current collector (Furukawa Electric Co., Ltd., NC-WS). After coating at 100 ° C. and drying at 100 ° C., after passing through a thickness adjustment step by press, a heat treatment step at 330 ° C. for 2 hours was performed to produce a negative electrode for a non-aqueous electrolyte secondary battery.

(Evaluation of cycle characteristics)
A negative electrode for a non-aqueous electrolyte secondary battery, an electrolytic solution obtained by adding vinylene carbonate to a mixed solution of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate containing 1.3 mol / L LiPF ₆ , and lithium using a metal Li foil counter electrode An ion secondary battery was constructed and the charge / discharge characteristics were examined.
First, in a 25 ° C. environment, charging was performed under constant current and constant voltage conditions until the current value was 0.1 C and the voltage value was 0.02 V (vs. Li / Li ⁺ ), and the current value was reduced to 0.05 C. Stopped charging. Next, discharging was performed under the condition of a current value of 0.1 C until the voltage became 1.5 V (vs. Li ^/ Li ⁺ ). 1C is a current value that can be fully charged in one hour. Both charging and discharging were performed in a 25 ° C. environment. Next, the above charge / discharge was repeated up to 100 cycles at a charge / discharge rate of 0.2C. The evaluation of the characteristics was performed using the initial discharge capacity (mAh / g) and the percentage of the discharge capacity after 100 cycles with respect to the initial discharge capacity as the capacity maintenance rate.

[Examples 12 to 19]
As shown in Table 1, the same production method and evaluation method as in Example 1 were adopted except that the composition / composition ratio was changed.

[Comparative Example 11]
(Preparation of negative electrode active material)
After mixing silicon powder, iron powder, and aluminum powder in an atomic ratio of Si: Fe: Al = 67: 7: 26, the dried mixed powder was heated to 1500 ° C. in a crucible and dissolved. The molten metal was quenched with a single roll quenching device to obtain a negative electrode active material. The other steps were the same as in Example 11.

[Comparative Example 12]
As shown in Table 1, the same production method and evaluation method as those in Comparative Example 1 were used except that the composition / composition ratio was changed. The mixed powder was dissolved in the range of 1500 to 2000 ° C.

(Evaluation of composition of negative electrode active material)
As shown in FIG. 24, a BF-STEM image of the cross section of the negative electrode active material was observed.
Furthermore, XRD analysis was performed as shown in FIG. 25 to identify the crystal phase. As a result, the silicon phase (white portion in FIG. 24, first phase), the second phase (black portion in FIG. 24) made of ternary silicide (FeAl ₃ Si ₂ ), and the _third phase made of vanadium silicide VSi ₂ . Phase (gray portion in FIG. 24), an aluminum phase was confirmed. As shown in FIG. 26, the element distribution was measured by EDS. The round structure in the _second phase (FeAl ₃ Si ₂ ) is the fourth phase (mainly VSi ₂ ).

From this result, the positional relationship of the crystal phase and the inclusion relationship of the sea-island structure were confirmed, and the composition of the product was calculated together with the XRD analysis result. The results are shown in Table 1.

(State of the third phase)
Table 1 shows the particle diameter or thickness of the third phase, and the area ratio / volume ratio of the third phase in the first phase and the third phase. The thickness of the third phase was calculated from the analysis of the SEM or TEM image, and the range of values corresponding to 50% by volume or more of each phase was defined as the thickness of the cross-sectional layer. The area ratio was calculated with image analysis software ("A Image-kun" manufactured by Asahi Kasei Engineering).
The volume ratio can be calculated using image analysis processing software by performing a three-dimensional construction using Cut and See from the image information. The method according to Cut and See is a method of repeatedly observing a cross-sectional SEM image or a TEM image after cutting a sample with an ion beam or the like every predetermined thickness of about 10 nm. The third phase may be observed almost uniformly in the form of dots in the first phase, or may be observed as uneven spots, meshes or streaks, and within a certain three-dimensional volume. The volume ratio was calculated by calculating using image analysis software.

In addition, the area ratio evaluation criteria of the 3rd phase in Table 1 are as follows.
◎: Area ratio 20% or more ○: Area ratio 10% or more, less than 20% △: Although the presence of the third phase can be confirmed, the area ratio is less than 10%-: The third phase cannot be confirmed. The volume ratio evaluation criteria are as follows.
○: Volume ratio of 10% or more △: The presence of the third phase can be confirmed, but the volume ratio is less than 10%-: The third phase cannot be confirmed

(Performance evaluation of secondary battery using negative electrode active material)
Table 1 shows the results of evaluation performed by the method described in the preparation of the negative electrode for secondary battery and the evaluation of the cycle characteristics.
The evaluation criteria for the capacity retention rate after 100 cycles in Table 1 are as follows.
◎: Capacity maintenance rate 72% or more ○: Capacity maintenance rate 68% or more and less than 72% △: Capacity maintenance rate 64% or more and less than 68% ×: Capacity maintenance rate Less than 64% Evaluation of cycle characteristics takes practicality into consideration Thus, the capacity maintenance rate in 100 cycles was determined to be 64% or more.
In addition, the capacity maintenance rate in 50 cycles satisfied 72% or more (◎) in all Examples.

For Examples 11-19, it can be seen _{that VSi 2,} TaSi _2, NbSi 2 is a third phase to the first phase is generated. Phases were identified by XRD analysis, cross-sectional SEM observation, EPMA, and STEM-EDS in combination. Hereinafter, the measurement method will be described more specifically. ICP analysis for quantification of raw material composition, XRD analysis for product composition, SEM and SEM-EDX for product shape and size of first phase and second phase, product shape for third phase and fourth phase The size was measured by TEM and STEM-EDX, and the whole product was mapped by EPMA.

The size of the third phase (thickness of the cross-sectional layer) in Examples 11 to 19 was 1 to 100 nm from the observation result of the BF-STEM image. It is considered that the presence of the third phase can suppress the extension of cracks generated by the volume expansion of Si accompanying charge / discharge, and as a result, the capacity retention rate at a high capacity can be secured. Incidentally, as seen in viewing the example of FIG. _26, a portion of VSi _2, TaSi _2, NbSi ₂ may be distributed in the fourth phase.

On the other hand, in Comparative Example 11 and Comparative Example 12, the amount of the Si phase as the first phase is ensured to be equal to or slightly higher than that of Example 16, and the initial discharge capacity several times higher than that of graphite is ensured. Further, in Comparative Example 11 and Comparative Example 12, the second phase is secured in an amount substantially equal to that in Example 16, and the capacity retention rate after 50 cycles is ensured to be 64% or more. Since generation cannot be confirmed, it can be seen that the capacity retention rate after 100 cycles cannot secure 64%, which is a criterion for practicality.

In Examples 11 and 12, the input amount of the M group element was large as 3 at% to 10 at%, and the third phase was precipitated at 9 at% to 30 at%. Moreover, precipitation of metal Al contained in the fourth phase was also confirmed.
In Examples 13 to 15, the input amount of the M group element is smaller than those in Examples 11 and 12, and the precipitation amount of the third phase is also smaller than those in Examples 11 and 12. Moreover, precipitation of metal Al contained in the fourth phase was also confirmed. In Examples 11 to 15, the presence of the first to fourth phases was confirmed, and in particular, Example 11 in which the third phase was present as much as 9 at% had a high discharge capacity and good capacity retention rate. In Examples 12, 14, and 15, the first phase having a large volume expansion / contraction due to charge / discharge is suppressed to 22 at%, and a sufficiently high discharge capacity is ensured as compared with graphite, and the capacity maintenance ratio is high. It is good. Since the discharge capacity of the thirteenth embodiment is nearly three times that of the twelfth, fourteenth, and fifteenth embodiments, the capacity maintenance ratio is slightly low, but the capacity maintenance ratio itself is maintained at 68% or more.

In Example 16, the third phase was confirmed by the addition of the M group element, but the amount of Al element input was 20 at%, and no precipitation of the metallic Al phase was confirmed. Therefore, the proportion of coarse phases was higher than in Examples 1 to 5, and the capacity retention ratio was in the range of 64% to 68%.
In Example 17, the input amount of the M group element is about the same as in Examples 3 to 5, but Ta and Nb have a hypereutectic region on the small amount side from V. A predetermined amount of phase is secured. As the M group element decreased, the discharge capacity of the first phase was increased, and the capacity retention rate could be secured at a capacity higher than V.
Examples 18 to 19 show the lower limit values of the Si element and the M group element, and by selecting the composition range of the hypereutectic region, a high capacity retention ratio and discharge capacity could be secured.

The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea disclosed in the present application, and these are naturally within the technical scope of the present invention. Understood.

DESCRIPTION OF SYMBOLS 1 ......... Negative electrode active material 3 ......... Silicon phase 5 ......... 1st silicide phase 7 ......... 2nd silicide phase 11 ......... Molten metal 13 ......... Silicide primary crystal 15 ......... Silicon 17 ... ...... First silicide 19 ......... Second silicide 21 ......... Gas atomizing device 23 ......... Crucible 25 ......... Nozzle 27 ......... Gas 29> ... Gas injector 31 ......... Gas jet flow 41 ......... Single roll quenching device 43 ......... Crucible 45 ......... Single roll 47 ......... Alloy 51 ... …… Double roll quenching device 53 ... …… Crucible 55 ... …… Casting roll 57 ......... Quenching device 59 ... …… Alloy 61 ... Melt spinning device 63 ... Crucible 65 ... Container 67 ... Coolant 69 ... Guide roll 70 ... Alloy 71 ... Nonaqueous electrolyte secondary battery 73 ... …… Positive electrode 75 ……… Negative 77 ... …… Separator 79 ... …… Battery can 81 ……… Positive lead 83 ……… Positive terminal 85 ……… Negative lead 87 ……… Electrolyte 89 ……… Seal 91 ……… Silicon phase 93 ……… Silicide (FeAl ₃ Si ₂ )
100 ......... Silicon particle 101 ......... First SEI
103 ……… Crack 105 ……… Second SEI
107 ......... Crack 111 ... ... First phase 112 ... ... Second phase 113 ... ... Third phase 114 ... ... First phase 115 ... ... Second phase 116 ... ... First Phase 3 117 ......... First phase 118 ......... Second phase 120 ......... Negative electrode active material

Claims (28)

1. Including silicon and element M capable of forming a compound with silicon,
   When the composition of silicon and the element M is cooled from a molten state, the compound of silicon and the element M is precipitated first, and when further cooled, pure silicon or a silicon solid solution is deposited. Active material.
2. Including silicon and element M capable of forming a compound with silicon,
   When the composition of silicon and the element M is cooled from the molten state at a rate of 1000 K / s or more, the compound of silicon and the element M is deposited first, and when further cooled, pure silicon or a silicon solid solution is deposited. A negative electrode active material characterized by being.
3. 3. The negative electrode active material according to claim 1, wherein the element M is at least one element selected from the group consisting of V, Nb, Ta, Mo, W, Ti, Zr, and Cr. .
4. The negative electrode active material according to any one of claims 1 to 3, wherein the composition of silicon and the element M is in a hypereutectic region.
5. The negative electrode active material has a silicon phase made of pure silicon or a silicon solid solution, and a silicide phase made of a compound of silicon and the element M,
   The negative electrode active material according to any one of claims 1 to 4, wherein the silicon phase is 20 wt% or more of the negative electrode active material.
6. 6. The negative electrode according to claim 1, wherein a phase having an outer diameter or width of 10 to 300 nm occupies 50 volume% or more of the silicon phase among the silicon phases. Active material.
7. Furthermore, the negative electrode active material is an element D different from the element M (Al, Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, La, Ce, Nd, Dy, Sm. And at least one element selected from the group consisting of Pr, Y, Zr, Nb, Mo, Hf, Ta, W, Re, Os, Ir, Ru, Rh, and Ba),
   The negative electrode active material according to any one of claims 1 to 6, wherein the negative electrode active material includes a compound of silicon and the element D.
8. The first phase having Li storage properties is dispersed in the second phase having Li conductivity electrochemically,
   The negative electrode active material, wherein the first phase further includes a third phase that is less Li-occluding than the first phase.
9. 9. The area ratio of the first phase to the second phase is 10 to 90%, and further includes the third phase in an amount of 1 to 40 atomic% with respect to the negative electrode active material. Negative electrode active material.
10. 10. The negative electrode active material according to claim 8, wherein the first phase is pure silicon or a silicon solid solution, and the average thickness of the cross-sectional layers is 20 to 2000 nm.
11. 11. The negative electrode active material according to claim 8, wherein the second phase is silicide and the average thickness of the cross-sectional layers is 20 to 2000 nm.
12. The second phase includes Si and Al, and further includes at least one element selected from the element D according to claim 6. Negative electrode active material.
13. The second phase contains Si and Al, and further contains at least one element selected from Fe, Co, Mn, La, Ce, Nd, Pr, Sm, and Dy. The negative electrode active material according to any one of 8 to 12.
14. The negative electrode active material according to any one of claims 8 to 13, wherein the second phase includes a fourth phase that is less Li-occluding than the first phase.
15. 15. The negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 14, wherein the fourth phase contains 1 to 50 atomic% with respect to the negative electrode active material.
16. The negative electrode active material according to any one of claims 8 to 15, wherein the average thickness of the cross-sectional layer of the third phase is 1 to 100 nm.
17. The third _{phase, VSi 2, TaSi 2, MoSi} 2, NbSi 2, WSi 2, TiSi 2, ZrSi 2, claims 8 to 16, characterized in that it comprises at least one compound selected from the CrSi ₂ The negative electrode active material according to any one of the above.
18. The third _phase, the negative active material according to any one of claims 8 to 17, characterized in that it comprises at least one compound selected from _{VSi 2, TaSi 2, NbSi 2} .
19. The third phase or the fourth phase contains at least one compound selected from SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZnO, CaO, and MgO. The negative electrode active material according to claim 1.
20. The region in which the volume of particles constituting the third phase occupies 10% or more of the total volume of the first phase and the third phase is present. The negative electrode active material according to claim 1.
21. A negative electrode for a non-aqueous electrolyte secondary battery having an active material layer on a current collector,
    The active material layer includes silicon and an element M capable of forming a compound with silicon, and when the composition of silicon and the element M is cooled from a molten state, the compound of silicon and the element M is first precipitated. A negative electrode for a non-aqueous electrolyte secondary battery, comprising: a negative electrode active material characterized in that pure silicon or a silicon solid solution precipitates when further cooled; and a binder.
22. A positive electrode capable of inserting and extracting lithium ions;
    A negative electrode having an active material layer on a current collector;
    Having a separator disposed between the positive electrode and the negative electrode;
    A non-aqueous electrolyte secondary battery in which the positive electrode, the negative electrode, and the separator are provided in an electrolyte having lithium ion conductivity,
    The active material layer of the negative electrode includes silicon and an element M capable of forming a compound with silicon, and when the composition of silicon and the element M is cooled from a molten state, the compound of silicon and the element M is first A non-aqueous electrolyte secondary battery comprising: a negative electrode active material characterized by having a composition in which pure silicon or a silicon solid solution is deposited when cooled and further cooled; and a binder .
23. Silicon and an element M capable of forming a compound with silicon, and the composition of silicon and the element M first precipitates when the compound of silicon and the element M is cooled from a molten state, and when further cooled, pure silicon Or the manufacturing method of the negative electrode active material characterized by cooling the molten metal which is a composition in which a silicon solid solution precipitates at a speed | rate of 1000 K / s or more.
24. The method for producing a negative electrode active material according to claim 23, wherein the molten metal is cooled by a single roll method, a twin roll method, a melt spinning method, a gas atomizing method, or a water atomizing method.
25. A negative electrode for a nonaqueous electrolyte secondary battery, comprising the negative electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 8 to 20.
26. A nonaqueous electrolyte secondary battery comprising the negative electrode for a nonaqueous electrolyte secondary battery according to claim 25.
27. Element group D excluding Si, Al, Al (Cu, Fe, Co, Ni, Ca, Sc, Ti, V, Cr, Mn, Sr, La, Ce, Nd, Dy, Sm, Pr, Y, Zr, Nb , Mo, Hf, Ta, W, Re, Os, Ir, Ru, Rh, and Ba), element group M (V, Ta, Mo, Nb, W, Ti, Zr, Cr) After melting an alloy containing at least one element selected from the group consisting of a single roll method, a twin roll method, a melt spinning method, a gas atomizing method, and a water atomizing method (1000 K / second or more) 20. The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 8, wherein the second phase is solidified and the second phase is precipitated at a temperature of 1000 ° C. or lower.
    However, an element selected from the element group M and the element group D is not the same element.
28. 28. The non-water according to claim 27, wherein an element of element group D excluding Al is at least one element selected from Fe, Co, Mn, La, Ce, Nd, Pr, Sm, and Dy. A method for producing a negative electrode active material for an electrolyte secondary battery.

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