JP6331463B2 - Negative electrode active material - Google Patents

Description

  The present invention relates to an electrode active material, and more particularly to a negative electrode active material.

  In recent years, with the spread of small electronic devices such as home video cameras, notebook computers, and smartphones, it has become a technical issue to increase the capacity and life of batteries.

  As hybrid vehicles, plug-in hybrid vehicles, and electric vehicles become more widespread, downsizing of batteries is also a technical issue.

  At present, graphite-based negative electrode active material is used for lithium ion batteries. However, the graphite-based negative electrode active material has the above-described technical problems.

  Therefore, an alloy-based negative electrode active material having a higher capacity than a graphite-based negative electrode active material has attracted attention. As an alloy-based negative electrode active material, a silicon (Si) -based negative electrode active material and a tin (Sn) -based negative electrode active material are known. Various studies have been made on the above alloy-based negative electrode active material materials for practical use of a more compact and long-life lithium ion battery.

  However, the volume of the alloy-based negative electrode active material material repeats large expansion and contraction during charge and discharge. Therefore, the capacity of the alloy-based negative electrode active material is likely to deteriorate. For example, the volume expansion / contraction rate of graphite accompanying charging is about 12%. On the other hand, the volume expansion / contraction rate of Si alone or Sn accompanying charging is about 400%. For this reason, when the negative electrode plate of Sn alone is repeatedly charged and discharged, remarkable expansion and contraction occur, and the negative electrode mixture applied to the current collector of the negative electrode plate cracks. As a result, the capacity of the negative electrode plate rapidly decreases. This is mainly due to the fact that part of the active material is liberated due to volume expansion and contraction, and the negative electrode plate loses electronic conductivity.

  US Patent Application Publication No. 2008/0233479 (Patent Document 1) proposes a solution to the above-described problem of the alloy-based negative electrode active material. Specifically, the negative electrode material of Patent Document 1 includes a Ti—Ni superelastic alloy and Si particles formed in the superelastic alloy. Patent Document 1 describes that a large change in expansion and contraction of silicon particles caused by insertion and extraction of lithium ions can be suppressed by a superelastic alloy.

US Patent Application Publication No. 2008/0233479

  However, it is doubtful whether the charge / discharge cycle characteristics of the secondary battery are sufficiently improved by the method disclosed in Patent Document 1. In the first place, it seems extremely difficult to actually manufacture the negative electrode active material proposed in Patent Document 1.

  The objective of this invention is providing the negative electrode active material which can improve the discharge capacity per volume, charging / discharging cycling characteristics, the mixture density at the time of using for an electrode plate, and the electrical contact between particle | grains.

  The negative electrode active material of this embodiment contains a large-diameter powder having a first average particle size and a small-diameter powder having a second average particle size different from the first average particle size. The ratio of the first and second average particle diameters is first particle diameter: second particle diameter = 1.2: 1 to 20: 1. The ratio of the content (mass) of the large diameter powder and the small diameter powder is large diameter powder: small diameter powder = 25: 1 to 1: 3. The large diameter powder and the small diameter powder contain an alloy phase. The alloy phase undergoes thermoelastic non-diffusion when releasing metal ions or occludes metal ions.

  The negative electrode active material of the present embodiment can improve discharge capacity per volume, charge / discharge cycle characteristics, mixture density when used for an electrode plate, and electrical contact between particles.

FIG. 1 is a perspective view of the DO ₃ structure. FIG. 2A is a schematic diagram of the DO ₃ structure of the parent phase of the alloy phase of the present embodiment. FIG. 2B is a schematic diagram of the 2H structure of the γ1 ′ phase, which is one type of martensite phase. FIG. 2C is a schematic view of a crystal plane for explaining the thermoelastic non-diffusion transformation from the DO ₃ structure to the 2H structure. FIG. 2D is a schematic view of another crystal plane different from FIG. 2C. FIG. 2E is a schematic view of another crystal plane different from FIGS. 2C and 2D. FIG. 3 is a diagram showing an X-ray diffraction profile before and after charging / discharging of the alloy phase of Example 1 of the present invention and a simulation result by the Rietveld method.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  The negative electrode active material according to the present embodiment contains a large-diameter powder and a small-diameter powder that are two types of alloy powders having different average particle diameters. The ratio of the average particle diameter of the large diameter powder and the small diameter powder is large diameter powder: small diameter powder = 1.2: 1 to 20: 1. The ratio of the content (mass) of the large diameter powder and the small diameter powder is large diameter powder: small diameter powder = 25: 1 to 1: 3. Large diameter powders and small diameter powders contain an alloy phase. The alloy phase undergoes thermoelastic non-diffusive transformation when releasing metal ions or occluding metal ions.

  The “negative electrode active material” referred to in the present specification is preferably a negative electrode active material for a non-aqueous electrolyte secondary battery. The “thermoelastic non-diffusion transformation” referred to in this specification is a so-called thermoelastic martensitic transformation. “Metal ions” are, for example, lithium ions, magnesium ions, sodium ions, and the like. A preferred metal ion is lithium ion.

  The large diameter powder and the small diameter powder may contain a phase other than the above alloy phase. Other phases are, for example, a silicon (Si) phase, a tin (Sn) phase, an alloy phase other than the above alloy phase (an alloy phase that does not undergo thermoelastic non-diffusion transformation), and the like.

  Preferably, the alloy phase is a main component (main phase) of the large diameter powder and the small diameter powder. The “main component” means a component that occupies 50% or more volume. The alloy phase may contain impurities as long as the gist of the present invention is not impaired. However, it is preferable to have as few impurities as possible.

  The negative electrode formed using the negative electrode active material of this embodiment has a higher volume discharge capacity (discharge capacity per volume) than a negative electrode made of graphite when used in a non-aqueous electrolyte secondary battery. Furthermore, the non-aqueous electrolyte secondary battery using the negative electrode containing the negative electrode active material of the present embodiment has a higher capacity retention rate than when a conventional alloy negative electrode is used. Therefore, there is a high possibility that this negative electrode active material can sufficiently improve the charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery.

  The high capacity retention ratio is considered to be because the strain due to expansion and contraction that occurs during charging and discharging is alleviated by the thermoelastic non-diffusion transformation. Furthermore, the negative electrode active material of the present embodiment is excellent in packing density when used for a negative electrode. Therefore, the mixture density of the negative electrode plate is improved. As a result, the electrical contact between the negative electrode active material particles is excellent.

  The alloy phase contained in the large diameter powder and the small diameter powder may be any of the following four types 1 to 4. Hereinafter, the large diameter powder and the small diameter powder are also referred to as a specific powder.

  The type 1 alloy phase undergoes thermoelastic non-diffusion transformation when occluding metal ions and reverse transformation when releasing metal ions. In this case, the alloy phase is a parent phase in a normal state.

  The type 2 alloy phase undergoes reverse transformation when occluding metal ions, and undergoes thermoelastic non-diffusion transformation when releasing metal ions. In this case, the alloy phase is normally a martensite phase.

  The type 3 alloy phase undergoes supplemental deformation (slip deformation or twin deformation) when occluding metal ions, and returns to the original martensite phase when metal ions are released. In this case, the alloy phase is normally a martensite phase.

  The type 4 alloy phase changes from the martensite phase to another martensite phase when the metal ions are occluded, and returns to the original martensite phase when the metal ions are released. In this case, the alloy phase is normally a martensite phase.

In the case of the type 1 alloy phase, the crystal structure of the alloy phase after thermoelastic non-diffusion transformation is preferably any of 2H, 3R, 6R, 9R, 18R, M2H, M3R, M6R, M9R, and M18R in Ramsdell notation. The crystal structure of the alloy phase after reverse transformation is DO ₃ in Strukturbericht notation. More preferably, the crystal structure of the alloy phase after the thermoelastic type non-diffusion transformation is 2H, and the crystal structure of the alloy phase after the reverse transformation is DO ₃ .

In the case of the type 1 alloy phase, the alloy phase preferably contains Cu and Sn, contains the 2H structure after the thermoelastic non-diffusion transformation, and contains the DO ₃ structure after the reverse transformation.

  The alloy phase contains one or more selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B and C, and Sn, with the balance being Cu and Impurities may be used.

The alloy phase is further selected from the group consisting of a δ phase having an F-Cell structure, a ε phase having a 2H structure, a η ′ phase having a monoclinic crystal, and a phase having a DO ₃ structure, including site defects. It may contain seeds or more.

These δ phase, ε phase, η ′ phase including site defects, and a phase having a DO ₃ structure all form a storage site and a diffusion site for metal ions (such as Li ions) in the alloy phase. Therefore, the volume discharge capacity and cycle characteristics of the negative electrode active material are further improved.

In the negative electrode active material, the volume expansion rate or volume contraction rate of the unit cell before and after the phase transformation of the alloy phase is preferably 20% or less, and more preferably 10% or less. The volume expansion rate of the unit cell is defined by the following formula (1), and the volume contraction rate of the unit cell is defined by the following formula (2).
(Volume expansion rate of unit cell) = [(Volume of unit cell at the time of occlusion of metal ion) − (Volume of unit cell at the time of metal ion release)] / (Volume of unit cell at the time of metal ion release) × 100・ (1)
(Volume shrinkage of unit cell) = [(Volume of unit cell at the time of occlusion of metal ion) − (Volume of unit cell at the time of metal ion release)] / (Volume of unit cell at the time of occlusion of metal ion) × 100 (2)
The volume of the unit cell at the time of release corresponding to the crystal lattice range of the unit cell at the time of occlusion is substituted for “volume of the unit cell at the time of metal ion release” in the expressions (1) and (2).

  The negative electrode active material described above can be used as an active material constituting an electrode, particularly an electrode (negative electrode) of a non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery is, for example, a lithium ion secondary battery.

  Hereinafter, the negative electrode active material according to the present embodiment will be described in detail.

<Negative electrode active material>
The negative electrode active material according to the embodiment of the present invention contains a large-diameter powder and a small-diameter powder that are two types of alloy powders having different average particle diameters. The ratio of the average particle diameter of the large diameter powder and the small diameter powder is large diameter powder: small diameter powder = 1.2: 1 to 20: 1. The ratio of the content (mass) of the large diameter powder and the small diameter powder in the mixed powder is large diameter powder: small diameter powder = 25: 1 to 1: 3. Large diameter powders and small diameter powders contain an alloy phase. As described above, this alloy phase undergoes thermoelastic non-diffusion when releasing metal ions typified by Li ions or occlusion of metal ions. The thermoelastic non-diffusion transformation is also called a thermoelastic martensitic transformation. Hereinafter, in this specification, the thermoelastic martensitic transformation is simply referred to as “M transformation”, and the martensitic phase is simply referred to as “M phase”. The alloy phase that undergoes M transformation when occluding or releasing metal ions is also referred to as a “specific alloy phase”.

(I) About Alloy Phase The specific alloy phase contained in the specific powder (large diameter powder and small diameter powder) is mainly composed of at least one of the M phase and the parent phase. The specific alloy phase repeatedly occludes and releases metal ions during charge and discharge. And according to occlusion and discharge | release of a metal ion, a specific alloy phase carries out M transformation, reverse transformation, supplementary deformation, etc. These transformation behaviors alleviate the strain caused by the expansion and contraction of the alloy phase during the insertion and release of metal ions.

  The specific alloy phase may be any of the above types 1 to 4. Preferably, the specific alloy phase is type 1. That is, the specific alloy phase preferably undergoes M transformation when occluding metal ions and reverse transformation when releasing metal ions.

The crystal structure of the specific alloy phase is not particularly limited. When the alloy phase is type 1 and the crystal structure of the specific alloy phase after reverse transformation (that is, the parent phase) is β ₁ phase (DO ₃ structure), the specific alloy phase after the M transformation (that is, M phase) Crystal structures include, for example, β ₁ ′ phase (monoclinic M18R ₁ structure or orthorhombic 18R ₁ structure), γ ₁ ′ phase (monoclinic M2H structure or orthorhombic 2H structure). , Β ₁ ″ phase (monoclinic M18R ₂ structure or orthorhombic 18R ₂ structure), α ₁ ′ phase (monoclinic M6R structure or orthorhombic 6R structure), etc. .

When the crystal structure of the parent phase of the specific alloy phase is β ₂ phase (B2 structure), the crystal structure of the M phase of the specific alloy phase is, for example, β ₂ 'phase (monoclinic M9R structure or orthorhombic crystal) 9R structure), γ ₂ ′ phase (monoclinic M2H structure or orthorhombic 2H structure), α ₂ ′ phase (monoclinic M3R structure or orthorhombic 3R structure). .

  When the parent phase of the alloy phase is a face-centered cubic lattice, the crystal structure of the M phase of the alloy phase is, for example, a face-centered square lattice or a body-centered square lattice.

The symbols such as 2H, 3R, 6R, 9R, 18R, M2H, M3R, M6R, M9R, and M18R are used as a representation method of the crystal structure of the stacked structure according to the Ramsdell classification. The symbols H and R mean that the symmetry in the direction perpendicular to the laminated surface is hexagonal symmetry and rhombohedral symmetry, respectively. When M is not added to the head, it means that the crystal structure is orthorhombic. When M is added at the beginning, it means that the crystal structure is monoclinic. Even the same classification symbol may be distinguished depending on the order of stacking. For example, the two kinds of M phases, β ₁ ′ phase and β ₁ ″ phase, are different from each other in terms of the laminated structure, and are distinguished by being expressed as 18R ₁ , 18R ₂ , M18R ₁ , M18R _2, etc., respectively. There is a case.

  In general, the M transformation and reverse transformation in the normal shape memory effect and pseudoelastic effect are often accompanied by volume shrinkage or volume expansion. When the negative electrode active material according to this embodiment electrochemically releases or occludes metal ions (for example, lithium ions), the crystal structure changes in accordance with the phenomenon of volume shrinkage or volume expansion in the respective transformation directions. It is thought that there are many cases to do.

  In the negative electrode active material according to the present embodiment, in the specific alloy phase, when the M transformation or reverse transformation occurs along with the occlusion and release of metal ions, other than the crystal structure that appears in the normal shape memory effect or pseudoelastic effect The crystal structure of

  When the specific alloy phase is type 3, the specific alloy phase undergoes slip deformation or twin deformation as the metal ions are occluded or released. In slip deformation, since dislocations are introduced as lattice defects, reversible deformation is difficult. Therefore, when the specific alloy phase is type 3, it is desirable that twin deformation mainly occurs.

[Chemical composition of specific alloy phase]
The chemical composition of the specific alloy phase is not particularly limited as long as the crystal structure at the M transformation and reverse transformation contains the crystal structure.
The alloy phase contained in the large diameter powder and the alloy phase contained in the small diameter powder may be the same or different.

  When the specific alloy phase is Type 1, the chemical composition of the specific alloy phase includes, for example, Cu (copper) and Sn (tin).

When the specific alloy phase is Type 1, preferably the crystal structure of the specific alloy phase after reverse transformation by discharge of metal ions is a DO ₃ structure, and the crystal structure of the specific alloy phase after M transformation by occlusion of metal ions Is a 2H structure.

Preferably, the chemical composition of the specific alloy phase contains Sn, with the balance being Cu and impurities. More preferably, the chemical composition contains 10 to 20 at% or 21 to 27 at% of Sn, the balance is made of Cu and impurities, contains a 2H structure after M transformation, and contains a DO ₃ structure after reverse transformation. . Further preferable Sn content is 13 to 16 at%, 18.5 to 20 at%, or 21 to 27 at%.

  The chemical composition of the specific alloy phase contains at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B, and C, and Sn, with the balance May be Cu and impurities.

  Preferably, the chemical composition of the specific alloy phase in this case is Sn: 10 to 35 at%, Ti: 9.0 at% or less, V: 49.0 at% or less, Cr: 49.0 at% or less, Mn: 9. 0 at% or less, Fe: 49.0 at% or less, Co: 49.0 at% or less, Ni: 9.0 at% or less, Zn: 29.0 at% or less, Al: 49.0 at% or less, Si: 49.0 at% Hereinafter, B: 5.0 at% or less and C: one or more selected from the group consisting of 5.0 at% or less are contained, and the balance consists of Cu and impurities. Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B and C are optional elements.

  The upper limit with preferable Ti content is 9.0 at% as above-mentioned. A more preferable upper limit of the Ti content is 6.0 at%, and more preferably 5.0 at%. The minimum with preferable Ti content is 0.1 at%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

  The upper limit with preferable V content is 49.0 at% as above-mentioned. The upper limit with more preferable V content is 30.0 at%, More preferably, it is 15.0 at%, More preferably, it is 10.0 at%. The minimum with preferable V content is 0.1 at%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

  The upper limit with preferable Cr content is 49.0 at% as above-mentioned. A more preferable upper limit of the Cr content is 30.0 at%, more preferably 15.0 at%, and further preferably 10.0 at%. The minimum with preferable Cr content is 0.1 at%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

  The upper limit with preferable Mn content is 9.0 at% as above-mentioned. The upper limit with more preferable Mn content is 6.0 at%, More preferably, it is 5.0 at%. The minimum with preferable Mn content is 0.1 at%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

  The upper limit with preferable Fe content is 49.0 at% as above-mentioned. A more preferable upper limit of the Fe content is 30.0 at%, more preferably 15.0 at%, and further preferably 10.0 at%. The minimum with preferable Fe content is 0.1 at%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

  The upper limit with preferable Co content is 49.0 at% as above-mentioned. A more preferable upper limit of the Co content is 30.0 at%, more preferably 15.0 at%, and further preferably 10.0 at%. The minimum with preferable Co content is 0.1 at%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

  The upper limit with preferable Ni content is 9.0 at% as above-mentioned. The upper limit with more preferable Ni content is 5.0 at%, More preferably, it is 2.0 at%. The minimum with preferable Ni content is 0.1 at%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

  The upper limit with preferable Zn content is 29.0 at% as above-mentioned. The upper limit of the Zn content is more preferably 27.0 at%, more preferably 25.0 at%. The minimum with preferable Zn content is 0.1 at%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

  The upper limit with preferable Al content is 49.0 at% as above-mentioned. A more preferable upper limit of the Al content is 30.0 at%, more preferably 15.0 at%, and further preferably 10.0 at%. The minimum with preferable Al content is 0.1%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

  The upper limit with preferable Si content is 49.0 at% as above-mentioned. A more preferable upper limit of the Si content is 30.0 at%, more preferably 15.0 at%, and further preferably 10.0 at%. The minimum with preferable Si content is 0.1 at%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

  The upper limit with preferable B content is 5.0 at%. The minimum with preferable B content is 0.01 at%, More preferably, it is 0.1 at%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

  The upper limit with preferable C content is 5.0 at%. The minimum with preferable C content is 0.01 at%, More preferably, it is 0.1 at%, More preferably, it is 0.5 at%, More preferably, it is 1.0 at%.

Preferably, the specific alloy phase further includes a δ phase having an F-Cell structure containing site defects, an ε phase having a 2H structure containing site defects, a monoclinic η ′ phase containing site defects, and a site defect. 1 or more types selected from the group consisting of phases having a DO ₃ structure. Hereinafter, these δ phase, ε phase, η ′ phase, and phase having a DO ₃ structure containing site defects are also referred to as “site defect phases”. Here, “site deficiency” means that the occupation ratio is less than 1 at a specific atomic site in the crystal structure.

These site defect phases include a plurality of site defects in the crystal structure. These site defects function as storage sites or diffusion sites for metal ions (Li ions or the like). Therefore, if the specific powder contains an alloy phase that has a 2H structure after M transformation and a DO ₃ structure after reverse transformation, and at least one of the site-deficient phases, the volume discharge capacity and cycle characteristics of the negative electrode active material Is further improved.

  The chemical composition of the specific alloy phase may further contain a Group 2 element and / or a rare earth element (REM) as an optional element for the purpose of increasing the discharge capacity. The Group 2 element is, for example, magnesium (Mg), calcium (Ca) or the like. REM is, for example, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), or the like.

The specific powder (large diameter powder and small diameter powder) may be composed of the specific alloy phase, or may contain the specific alloy phase and another active material phase active in metal ion. Another active material phase is, for example, a tin (Sn) phase, a silicon (Si) phase, an aluminum (Al) phase, a Co—Sn alloy phase, a Cu ₆ Sn ₅ compound phase (η ′ phase or η phase), or the like. .

[Volume expansion and shrinkage of specific alloy phase]
In the case where the specific alloy phase undergoes M transformation or reverse transformation as the metal ions are occluded and released, the preferred volume expansion / contraction rate of the unit cell of the specific alloy phase is 20% or less. In this case, it is possible to sufficiently relieve strain due to volume changes associated with insertion and extraction of metal ions. A more preferable volume expansion / contraction rate of the unit cell of the specific alloy phase is 10% or less, and more preferably 5% or less.

  The volume expansion / contraction rate of the specific alloy phase can be measured by in situ X-ray diffraction during charge / discharge. Specifically, in a glove box in a pure argon gas atmosphere where moisture is controlled to a dew point of −80 ° C. or lower, a special charge / discharge cell equipped with a beryllium window that transmits X-rays, An electrode plate including a small-diameter powder, a separator, a counter electrode lithium, and an electrolytic solution are mounted and sealed. And this charging / discharging cell is mounted | worn with an X-ray-diffraction apparatus. After mounting, an X-ray diffraction profile of the specific alloy phase in the initial charge state and the initial discharge state in the charge / discharge process is obtained. The lattice constant of the specific alloy phase is obtained from this X-ray diffraction profile. The volume change rate can be calculated from this lattice constant in consideration of the crystal lattice correspondence of the specific alloy phase.

  When the shape of the X-ray diffraction profile changes due to the half-value width or the like during the charge / discharge cycle process, the analysis is performed after repeating charge / discharge about 5 to 20 times as necessary. And the average value of the volume change rate is calculated | required from several reliable X-ray diffraction profile.

[Method for analyzing crystal structure of alloy phase contained in negative electrode active material]
(1) The crystal structure of the phase (including the alloy phase) contained in the large diameter powder and the small diameter powder in the negative electrode active material is based on the X-ray diffraction profile obtained using an X-ray diffractometer. It can be analyzed by the method. Specifically, the crystal structure is analyzed by the following method.

  For the negative electrode active material before being used for the negative electrode, X-ray diffraction measurement was performed on the negative electrode active material for each of the large-diameter powder and the small-diameter powder before mixing. Obtain measured data. Based on the obtained X-ray diffraction profile (actual measurement data), the composition of the phase in the powder is analyzed by the Rietveld method. For analysis by the lead belt method, either “RIETAN2000” (program name) or “RIETAN-FP” (program name), which is general-purpose analysis software, is used.

  (2) The crystal structure of the negative electrode active material in the negative electrode before charging in the battery is also specified by the same method as in (1). Specifically, in a state before charging, the battery is disassembled in a glove box in an argon atmosphere, and the negative electrode is taken out from the battery. The taken-out negative electrode is wrapped in mylar foil. Thereafter, the periphery of the mylar foil is sealed with a thermocompression bonding machine. The negative electrode sealed with Mylar foil is taken out of the glove box.

  Subsequently, the negative electrode is attached to a non-reflective sample plate (a plate cut out so that the specific crystal plane of the silicon single crystal is parallel to the measurement plane) with a hair spray to prepare a measurement sample. The measurement sample is set in an X-ray diffractometer, the X-ray diffraction measurement of the measurement sample is performed, and an X-ray diffraction profile is obtained. Based on the obtained X-ray diffraction profile, the crystal structure of the negative electrode active material in the negative electrode is specified by the Rietveld method.

  (3) The crystal structure of the negative electrode active material in the negative electrode after one or more times of charge and after one or more times of discharge is also specified by the same method as (2).

  Specifically, the battery is fully charged in a charge / discharge test apparatus. The fully charged battery is disassembled in the glove box, and a measurement sample is prepared by the same method as in (2). A measurement sample is set in an X-ray diffractometer and X-ray diffraction measurement is performed.

  In addition, the battery is completely discharged, the fully discharged battery is disassembled in the glove box, a measurement sample is prepared by the same method as in (2), and X-ray diffraction measurement is performed.

[Particle size ratio and mixing ratio of large diameter powder and small diameter powder]
In the negative electrode active material according to the embodiment of the present invention, the large diameter powder and the small diameter powder satisfy the following relationship.
The ratio of the average particle diameter of the large diameter powder and the small diameter powder is large diameter powder: small diameter powder = 1.2: 1 to 20: 1.
The ratio of the content (mass) of the large diameter powder and the small diameter powder in the mixed powder is large diameter powder: small diameter powder = 25: 1 to 1: 3.

  In the present invention, the particle size means a particle size measured in the direction in which the particle size becomes maximum, and the average particle size is a particle size at which the volume accumulation is 50%. The average particle diameter can be determined by, for example, a laser diffraction particle size distribution measuring apparatus (for example, Nikkiso Microtrac FRA).

  By making the ratio of the average particle size in the range of large powder: small powder = 1.2: 1 to 20: 1, the capacity retention rate of the active material is remarkable when an electrode using an organic binder is produced. improves. When the average particle diameter of the small diameter powder is smaller than 1/20 of the average particle diameter of the large diameter powder or larger than 1 / 1.2, the capacity retention rate of the active material is not improved so much. For example, if the average particle size of the small-diameter powder is too small, the gap is still large even if the small-diameter powder fills the gaps between the particles of the large-diameter powder. Therefore, although the packing density is improved, the electrical contact is not improved. As a result, the capacity retention rate of the active material is not improved so much and the specific surface area increases. Therefore, the coulombic efficiency in the first cycle is lowered. On the contrary, when the average particle diameter of the small diameter powder is too large, the arrangement of the particles of the large diameter powder is disturbed. Therefore, the packing density is reduced. Furthermore, the contact between the particles of the large-diameter powder is also deteriorated, and the capacity retention rate of the active material cannot be improved. The average particle size ratio is preferably large diameter powder: small diameter powder = 2: 1 to 10: 1, more preferably large diameter powder: small diameter powder = 3: 1 to 5: 1.

  The average particle diameter of the large diameter powder is not particularly limited. However, the actual thickness of the electrode is about 150 μm. Therefore, from a practical viewpoint, the average particle size of the large-diameter powder is preferably 20 to 170 μm, more preferably 30 to 90 μm. If the average particle size of the large-diameter powder is too small, the average particle size of the smaller small-diameter powder becomes too small and the specific surface area becomes too large. Therefore, the first cycle coulomb efficiency is lowered.

  The mixing ratio of these two kinds of specific powders is set to the range of mass ratio of large diameter powder: small diameter powder = 25: 1 to 1: 3. As a result, the capacity retention rate of the active material at the electrode of the organic binder is significantly improved. If the content of the small-diameter powder is less than 1/25 of the content of the large-diameter powder, there are too few small-diameter powders that enter the gaps between the particles of the large-diameter powder, and the effect of improving the utilization rate cannot be sufficiently obtained. When the content of the small-diameter powder is more than 1/3 of the content of the large-diameter powder, the small-diameter powder is more than the amount necessary to fill the gaps between the particles of the large-diameter powder. Therefore, the arrangement of the large-diameter powder particles is disturbed, and the packing density is lowered. Furthermore, since the small-diameter powder having a large specific surface area increases, the corrosion resistance is deteriorated, and the charge / discharge repeated life is reduced. This mixing ratio is preferably in the range of mass ratio of large diameter powder: small diameter powder = 5: 1 to 1.5: 1.

  Thus, in the negative electrode active material of this embodiment using two kinds of large and small specific powders (large diameter powder and small diameter powder), the appropriate average particle diameter ratio and mixing ratio for improving electrode characteristics are the packing density. Is a range that is considerably wider than the average particle size ratio and the mixing ratio. This is because even if there is a little more or less large-diameter powder than required for the maximum packing density, it will be in an incompletely packed state, so contact with a high contact surface pressure locally at some contact points. It is considered that good electrical contact is realized at this contact point.

  In other words, under the mixing conditions where the maximum packing density is obtained, the small-diameter powder is neatly stored in the gap between the large-diameter powders, so that the number of contact points is large and the pressure applied to each contact point is substantially equal. Therefore, good electrical contact can be obtained. On the other hand, when the average particle size ratio or the mixing ratio slightly deviates from the condition for obtaining the maximum packing density, the number of contact points between the powders decreases, but a strong pressure is applied at some contact points. Therefore, electrical contact at such a contact point is good. As a result, the electrical conductivity of the entire electrode is improved as in the case of the maximum packing density, and improved electrode characteristics can be obtained in a wider range than the mixing conditions that achieve the maximum packing density.

  It is preferable to use spherical powder as the large-diameter powder. When the large-diameter powder is irregular, the packing density is lowered. Therefore, the discharge capacity cannot be made sufficiently high and the specific surface area increases. As a result, a decrease in capacity maintenance ratio due to corrosion resistance deterioration is increased.

  The small-diameter powder filled in the gap between the large-diameter powders may be either spherical powder or amorphous powder. When the small-diameter powder is an amorphous powder, the packing density is slightly reduced as compared with the case where a spherical powder is used, but the electrode characteristics are rather improved. This is because the pulverized amorphous powder particles have many flat surfaces, so that the powder contact area is larger than the spherical powder composed of curved surfaces, and is superior to the spherical powder in terms of the effect of improving the utilization rate. . That is, when an amorphous small-diameter powder is used, the capacity retention rate is improved although the filling property is unknown. Therefore, the characteristic as an electrode can be improved similarly to the case where the small-diameter powder with higher packing density is a spherical powder.

<Method for producing negative electrode active material>
A method for producing a negative electrode active material made of a mixture containing a large-diameter powder and a small-diameter powder containing the specific alloy phase will be described.

  The negative electrode active material of this embodiment can be obtained by producing a large-diameter powder and a small-diameter powder by the methods described below and mixing them at a predetermined mixing ratio.

  A molten raw material for powder containing a specific alloy phase is produced. For example, a molten metal having the above-described chemical composition is manufactured. The molten metal is manufactured by melting a material by a normal melting method such as arc melting or resistance heating melting. Next, an ingot (bulk alloy) is manufactured by the ingot-making method using the molten metal.

  Or preferably, a thin cast piece or particle | grains are manufactured by rapidly solidifying the said molten metal. This method is called a rapid solidification method. Examples of the rapid solidification method include a strip casting method, a melt spin method, a gas atomization method, a molten metal spinning method, a water atomization method, and an oil atomization method.

  Bulk alloys (ingots) obtained by melting are (1) cut, (2) roughly crushed with a hammer mill, etc. (3) mechanically with a ball mill, attritor, disc mill, jet mill, pin mill, etc. Finely pulverized to adjust the required average particle size. When the bulk alloy has ductility and normal pulverization is difficult, the bulk alloy may be cut and pulverized with a grinder disk in which diamond abrasive grains are embedded. In these pulverization processes, when an M phase is generated by stress induction, the generation ratio is adjusted as necessary by appropriately combining alloy design, heat treatment, pulverization conditions, and the like. When the powder by the atomization method can be used in a melted state or after being subjected to heat treatment, a pulverization step may not be particularly required. In addition, when obtaining a melted material by the strip casting method, if the fracture is difficult due to its ductility, the melted material is adjusted to a predetermined size by mechanical cutting such as shearing. In such a case, the melted material may be heat-treated at a necessary stage to adjust the ratio of the M phase or the parent phase.

  In the case where the composition ratio of the specific alloy phase is adjusted by heat treatment, the material may be rapidly cooled after being maintained at a predetermined temperature and time in an inert atmosphere as necessary. At this time, the cooling rate may be adjusted by selecting a quenching medium such as water, salt water, oil, or liquid nitrogen according to the size of the material and setting the quenching medium to a predetermined temperature. Moreover, liquid nitrogen subzero treatment may be performed immediately after this quenching. By this liquid nitrogen subzero treatment, the composition ratio of the specific alloy phase can be adjusted, and the martensitic transformation temperature can be adjusted.

<Method for producing negative electrode>
The negative electrode using the negative electrode active material according to the embodiment of the present invention can be manufactured by a method well known to those skilled in the art.

  For example, polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), etc., for the specific powder of the negative electrode active material according to the embodiment of the present invention. A binder is mixed, and a carbon material powder such as natural graphite, artificial graphite, and acetylene black is mixed to impart sufficient conductivity to the negative electrode. To this, a solvent such as N-methylpyrrolidone (NMP), dimethylformamide (DMF) or water is added to dissolve the binder, and if necessary, the mixture is sufficiently stirred using a homogenizer and glass beads to form a slurry. This slurry is applied to an active material support such as rolled copper foil or electrodeposited copper foil and dried. Thereafter, the dried product is pressed. The negative electrode plate is manufactured through the above steps.

  The binder to be mixed is preferably about 5 to 10% by mass from the viewpoint of mechanical strength of the negative electrode and battery characteristics. The support is not limited to copper foil. The support may be, for example, a thin foil of another metal such as stainless steel or nickel, a net-like sheet punching plate, a mesh knitted with a metal wire, or the like.

<Battery manufacturing method>
The nonaqueous electrolyte secondary battery according to the present embodiment includes the above-described negative electrode, positive electrode, separator, and electrolytic solution or electrolyte. The shape of the battery may be a cylindrical shape, a square shape, a coin shape, a sheet shape, or the like. The battery of this embodiment may be a battery using a solid electrolyte such as a polymer battery.

The positive electrode of the battery of this embodiment preferably contains a transition metal compound containing a metal ion as an active material. More preferably, the positive electrode contains a lithium (Li) -containing transition metal compound as an active material. The Li-containing transition metal compound is, for example, LiM ₁ -xM′xO ₂ or LiM ₂ yM′O ₄ . Here, in the formula, 0 ≦ x, y ≦ 1, M and M ′ are barium (Ba), cobalt (Co), nickel (Ni), manganese (Mn), chromium (Cr), titanium (Ti), respectively. , Vanadium (V), iron (Fe), zinc (Zn), aluminum (Al), indium (In), tin (Sn), scandium (Sc), and yttrium (Y).

  However, the battery of this embodiment includes a transition metal chalcogenide; vanadium oxide and its lithium (Li) compound; niobium oxide and its lithium compound; a conjugated polymer using an organic conductive material; a sheprel phase compound; Other positive electrode materials such as activated carbon fiber may be used.

The battery electrolyte of the present embodiment is generally a non-aqueous electrolyte obtained by dissolving a lithium salt as a supporting electrolyte in an organic solvent. Examples of the lithium salt include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiB (C ₆ H ₅ ), LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₂ SO ₂ ) ₂ , LiCl, LiBr, LiI or the like. These may be used alone or in combination. The organic solvent is preferably a carbonic acid ester such as propylene carbonate, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate. However, various other organic solvents including carboxylic acid esters and ethers can also be used. These organic solvents may be used alone or in combination.

  The separator is installed between the positive electrode and the negative electrode. The separator serves as an insulator. Further, the separator greatly contributes to the retention of the electrolyte. The battery of this embodiment may be provided with a known separator. The separator is, for example, a polyolefin material such as polypropylene, polyethylene, a mixed cloth of both, or a porous body such as a glass filter.

  Hereinafter, the negative electrode active material, the negative electrode, and the battery of the present embodiment will be described in more detail using examples. Note that the negative electrode active material, the negative electrode, and the battery of the present embodiment are not limited to the following examples.

  The powdery negative electrode active material, negative electrode and coin battery of Invention Example 1 to Invention Example 10 and Comparative Example 1 to Comparative Example 4 shown in Table 1 were produced by the following method. And the change of the crystal structure by charging / discharging of a negative electrode active material material was confirmed. Furthermore, the tap density of the negative electrode active material (filling density index), the mixture density on the negative electrode plate, the discharge capacity of the battery (discharge capacity per volume), the initial coulomb efficiency, and the cycle characteristics (capacity retention rate) )investigated.

[Invention Example 1]
[Manufacture of negative electrode active material]
A large-diameter powder and a small-diameter powder were prepared as follows, and these powders were mixed at a content ratio shown in Table 1. This mixture was used as the negative electrode active material of Example 1 of the present invention.

(Large diameter powder and small diameter powder)
In a melting crucible made of alumina in an argon gas atmosphere, a mixture of a plurality of materials (elements) is used so that the final chemical composition of the negative electrode active material is the chemical composition described in the column “Chemical composition” in Table 1. And melted at high frequency to produce a molten metal.

  The molten metal was rapidly solidified by bringing it into contact with a copper water-cooled roll rotating at a peripheral speed of 300 m / min to obtain a flaky slab (strip casting (SC) method). The obtained slab was pulverized with a pulverizer (name: shaker mill, manufactured by Willy A. Bachofen, TC2 type), and then combined with a sieve of 106 μm, 75 μm, 63 μm, 45 μm, 32 μm, 20 μm, and a classifier (name : Low tap, manufactured by Yoshida Seisakusho) and classified by sieving. Through the above-described steps, a large-diameter powder and a small-diameter powder having an average particle diameter shown in Table 1 were obtained. The chemical compositions of the large diameter powder and the small diameter powder were as described in the column “Chemical Composition” in Table 1.

(Negative electrode active material)
The produced large diameter powder and small diameter powder were mixed at a content ratio (mass ratio) shown in Table 1 to obtain a negative electrode active material.

[Manufacture of negative electrode]
The above-mentioned powdered negative electrode active material, acetylene black (AB) as a conductive additive, styrene butadiene rubber (SBR) (double dilution) as a binder, and carboxymethyl cellulose (CMC) as a thickener Were mixed at a mass ratio of 75: 15: 10: 5 (the amount was 1 g: 0.2 g: 0.134 g: 0.067 g). Then, using a kneader, distilled water was added to the mixture so that the slurry concentration was 27.2% to produce a negative electrode mixture slurry. Since the styrene butadiene rubber used was diluted twice with water, 0.134 g of styrene butadiene rubber was blended for weighing.

The produced negative electrode mixture slurry was applied onto a metal foil using an applicator (150 μm). The metal foil coated with the slurry was dried at 100 ° C. for 20 minutes. The dried metal foil had a coating film made of a negative electrode active material on the surface. The metal foil having a coating film was punched to produce a disk-shaped metal foil having a diameter of 13 mm. The metal foil after punching was pressed with a press pressure of 500 kgf / cm ² to produce a plate-like negative electrode. In the negative electrode used for evaluation / measurement of the negative electrode active material other than the specific crystal structure, the metal foil was a copper foil.
In the negative electrode used for specifying the crystal structure, the metal foil was a nickel foil.

[Manufacture of batteries]
A manufactured negative electrode, an EC-DMC-EMC-VC-FEC as an electrolytic solution, a polyolefin separator (φ17 mm) as a separator, and a plate-like metal Li (φ19 × 1 mmt) as a positive electrode material were prepared. A 2016-type coin battery was manufactured using the prepared negative electrode, electrolytic solution, separator, and positive electrode. The coin battery was assembled in a glove box in an argon atmosphere.

[Identification of crystal structure]
Large diameter powder and small diameter powder before use for negative electrode, large diameter powder and small diameter powder of negative electrode active material in negative electrode before first charge, and negative electrode active material in negative electrode after charge / discharge 1 to 20 times The crystal structures of the large diameter powder and the small diameter powder were identified by the following method. X-ray diffraction measurement was performed on the target negative electrode active material to obtain actual measurement data. And based on the measured data obtained, the crystal structure contained in the target negative electrode active material was specified by the Rietveld method. More specifically, the crystal structure was specified by the following method.

(1) Crystal structure analysis of large-diameter powder and small-diameter powder before used for negative electrode X-ray diffraction measurement for mixed powder (negative-electrode active material) of large-diameter powder and small-diameter powder before used for negative electrode The measurement data of the X-ray diffraction profile was obtained.

  Specifically, an X-ray diffraction profile of a mixed powder of a large-diameter powder and a small-diameter powder of the negative electrode active material was obtained using Rigaku product name SmartLab (rotor target maximum output 9 KW; 45 kV-200 mA).

  Based on the obtained X-ray diffraction profile (measured data: (e) in FIG. 3), the crystal structure of the alloy phase in the mixed powder of the large diameter powder and the small diameter powder was analyzed by the Rietveld method.

The DO ₃ regular structure is a regular structure as shown in FIG. 2A. In the Cu—Sn-based alloy, in FIG. 2A, Cu is mainly present at the black circle atomic sites, and Sn is mainly present at the white circle atomic sites. Each site may be replaced by the addition of the third element. Such a crystal structure is based on the No. of International Table (Volume-A) in the classification of the space group. 225 (Fm-3m) is known. Table 2 shows the lattice constants and atomic coordinates of the crystal structure of this space group number.

Therefore, using the structural model of this space group number as the initial structural model of Rietveld analysis, the calculated value of the diffraction profile of the β ₁ phase (DO ₃ structure) of this chemical composition (hereinafter referred to as the computational profile) is obtained by Rietveld analysis. It was. Rietan-FP (program name) was used for Rietveld analysis.

Furthermore, a calculation profile of the crystal structure of the γ ₁ 'phase was also obtained. The crystal structure of γ ₁ ′ is a 2H structure in the notation of the Ramsdel symbol, and the space group is No. of International Table (Volume-A). 59-2 (Pmmn). No. Table 3 shows the lattice constant and atomic coordinates of 59-2 (Pmmn).

Using the crystal structure of the space group number in Table 3 as an initial structure model for Rietveld analysis, a calculation profile was obtained using RIETRAN-FP. (D) in FIG. 3 is a calculation profile of the DO ₃ structure, and (c) is a calculation profile of the 2H structure.

As a result of the analysis, the mixed powder of the large-diameter powder and the small-diameter powder of Inventive Example 1 has a γ ₁ ′ phase (2H structure) that is one of the M phases and a β ₁ phase (DO ₃ structure) that is the parent phase. ) And another phase corresponding to diffraction lines near 44 degrees of (e) in FIG.

(2) Crystal structure analysis of the negative electrode active material in the negative electrode The crystal structure of the mixed powder of the large diameter powder and the small diameter powder of the negative electrode active material in the negative electrode before charging was also identified by the same method as in (1). The actually measured X diffraction profile was measured by the following method.

  In the state before charging, the above-described coin battery was disassembled in a glove box in an argon atmosphere, and the plate-like negative electrode applied to the nickel foil was taken out from the coin battery. The extracted negative electrode was wrapped in mylar foil (manufactured by DuPont). Thereafter, the periphery of the mylar foil was sealed with a thermocompression bonding machine. The negative electrode sealed with mylar foil was taken out of the glove box.

  Subsequently, the negative electrode was attached to a non-reflective sample plate made of Rigaku (a plate cut out so that the specific crystal plane of the silicon single crystal was parallel to the measurement surface) with a hair spray to prepare a measurement sample.

  The measurement sample was set in the X-ray diffractometer described in (4) described later, and the X-ray diffraction measurement of the measurement sample was performed under the measurement conditions described in (4) described later.

(3) Analysis of crystal structure of negative electrode active material in negative electrode after charge and discharge Large powder and small diameter of negative electrode active material in negative electrode after 1 to 20 charges and after 1 to 20 discharges The crystal structure of the mixed powder was also specified by the same method as (1). The actually measured X diffraction profile was measured by the following method.

  The above coin battery was fully charged in a charge / discharge test apparatus. The fully charged coin battery was disassembled in the glove box, and a measurement sample was prepared in the same manner as (2). A measurement sample was set in the X-ray diffractometer described later in (4), and the X-ray diffraction measurement of the measurement sample was performed under the measurement conditions described in (4) below.

  Further, the above coin battery was completely discharged. The fully discharged coin cell was disassembled in the glove box, and a measurement sample was prepared in the same manner as (3). This measurement sample was set in the X-ray diffractometer described later in (4), and the X-ray diffraction measurement of the measurement sample was performed under the measurement conditions described later in (4).

  X-ray diffraction measurement was performed on the negative electrode after repeated charging and discharging with a coin battery by the same method.

(4) X-ray diffractometer and measurement conditions-Apparatus: Rigaku SmartLab
・ X-ray tube: Cu-Kα ray ・ X-ray output: 45 kV, 200 mA
- incident-monochromator: Johansson element (Cu-Kα ₂ line and Cu-Kβ line cut)
-Optical system: Concentration method-Incident parallel slit: 5.0 degree
-Incident slit: 1/2 degree
・ Long limit slit: 10.0mm
-Light receiving slit 1: 8.0 mm
・ Reception slit 2: 13.0mm
-Light receiving parallel slit: 5.0 degree
Goniometer: SmartLab goniometer X-ray source-mirror distance: 90.0 mm
-Distance between X-ray source and selected slit: 114.0 mm
-Distance between X-ray source and sample: 300.0 mm
・ Distance between sample and light receiving slit 1: 187.0 mm
・ Distance between sample and receiving slit 2: 300.0 mm
-Distance between light receiving slit 1 and light receiving slit 2: 113.0 mm
Sample-detector distance: 331.0 mm
・ Detector: D / Tex Ultra
Measurement range: 10-120 degree or 10-90 degree
-Data collection angle interval: 0.02 degree
・ Scanning method: Continuous ・ Scanning speed: 2 degrees / min. Or, 2.5 degrees / min.

(5) Analysis result of X-ray diffraction measurement data The X-ray diffraction data obtained in (1) and (3) are shown in FIG. (E) in FIG. 3 is an X-ray diffraction profile of the powder of the negative electrode active material obtained in (1). (F) is an X-ray diffraction profile of the negative electrode active material after the first charge, and (g) is an X-ray diffraction profile after the first discharge. (A) in FIG. 3 is an X-ray diffraction measurement profile obtained by performing similar X-ray diffraction on a Mylar foil alone. (B) in FIG. 3 is an X-ray diffraction profile of Ni calculated to identify the diffraction lines of the Ni foil used for the current collector. (C) in FIG. 3 is a calculation profile of the 2H structure in the chemical composition of this example, and (d) in FIG. 3 is a calculation profile of the DO ₃ structure in the chemical composition of this example.

(5-1)
From the X-ray diffraction data obtained in (1), (2) and (3), it was confirmed that a large chemical reaction did not proceed between the negative electrode active material and the electrolytic solution.

(5-2)
The X-ray diffraction profiles of the “negative electrode active material after charging” (FIG. 3E) and the “negative electrode active material after discharging” (FIG. 3F) were compared, respectively. As a result, the diffraction line repeatedly and reversibly changed at a position where the diffraction angle 2θ is around 43.3 ° (position due to the M phase (γ ₁ 'phase)) (hereinafter referred to as the strongest diffraction line of the M phase). . That is, a structural change was shown.

(5-3)
Therefore, the crystal structures of the “negative electrode active material after charging” and the “negative electrode active material after discharge” were specified using the Rietveld method.

For example, in the negative electrode active material, in the matrix DO ₃ structure shown in FIGS. 1 and 2A, the crystal plane A shown in FIG. 2D and the crystal plane B shown in FIG. 2C are alternately stacked. When a phase transformation occurs between the DO ₃ structure and the γ ₁ ′ phase, which is a kind of M phase, the crystal plane B is regularly shuffled by shear stress as shown in FIGS. 2A and 2B. It shifts to the position of plane B ′. In this case, phase transformation (M transformation) occurs without diffusion of the host lattice. In the 2H structure after the M transformation, the crystal plane A shown in FIG. 2D and the crystal plane B ′ shown in FIG. 2E are alternately stacked.

Therefore, the measured data of the X-ray diffraction profile of the negative electrode active material after charging and discharging, and the calculation profile of the β ₁ phase (DO ₃ structure) (FIG. 3D: at the 2θ angle position of a typical diffraction line) ● (black circle) is marked) and γ ₁ 'phase (2H structure) calculation profile (Fig. 3 (c): ■ (black square) is marked at the 2θ angle position of typical diffraction lines) Then, it was determined whether the crystal structure of the negative electrode active material in the negative electrode of this example was accompanied by M transformation or not (that is, accompanied by diffusion of the host lattice during charge / discharge).

Referring to FIG. 3 (f), in the X-ray diffraction profile, the intensity of the strongest diffraction line of the M phase near 43.3 ° increased by the first charge, and the intensity decreased by the subsequent discharge. This diffraction line can be judged from the calculation profile of RIEtan-FP to be derived from the formation of the M phase (γ ₁ ′) by the M transformation as described below.

Specifically, as shown in (f), in the 2H structure, in the X-ray diffraction profile after the first charge, the 2H of FIG. 3C including the strongest diffraction line of M phase of 43.3 ° is included. The peak intensity at the 2θ angular position (marked with ■ (black square)) corresponding to the structure increased. On the other hand, some of the peak intensities marked with ● (black circles) corresponding to the DO ₃ structure decreased. On the other hand, in the X-ray diffraction profile after the first discharge, some intensities of diffraction lines corresponding to the 2H structure marked with ■ (black square) are reduced, and diffraction corresponding to the DO ₃ structure marked with ● (black circle) The line intensity increased. In particular, the intensity peak near 43.3 ° did not appear in X-ray profiles (simulation results) of other crystal structures other than 2H. Regarding the X-ray diffraction lines of the structural members that appear during measurement other than the active material, (a) and (b) in FIG. 3 show the measured diffraction profile of Mylar foil and the calculated profile of nickel of the current collector, respectively. The 2θ angle positions of the main diffraction lines are marked with ◇ and Δ, respectively. In the measured profiles of (f) and (g) in FIG. 3, diffraction lines derived from these members appear, and therefore ◇ (white rhombus) mark and Δ (white triangle) mark are shown at corresponding positions.

From the above, the negative electrode of the present example contained an alloy phase that transformed into M by charging to become an M phase (2H structure) and became a parent phase (DO ₃ structure) by discharging. That is, the negative electrode of this example contained an alloy phase that undergoes M transformation when occlusion of lithium ions, which are metal ions, and reverse transformation when lithium ions are released.

  In the negative electrode of this example, the M transformation was repeated during charging and the reverse transformation was repeated during discharging.

[Tap density]
The tap density of the negative electrode active material, which is a mixture of a large diameter powder and a small diameter powder, was measured using a powder tester (registered trademark) manufactured by Hosokawa Micron Corporation under the following conditions. A cylindrical tap cell having an inner diameter of 2 cm and an inner volume of 50 cm ³ was filled with a negative electrode active material, and then a tap with a stroke length of 5 mm was performed 500 times, and the density was determined from the volume and mass after tapping. . The tap density obtained by measuring in this way was as shown in Table 1.

[Negative electrode mix density]
The density of the mixture layer (mixture density) was determined for the plate-like negative electrode having a diameter of 13 mm obtained in [Manufacture of negative electrode]. Specifically, using a flat dial gauge with a diameter of 2 mm, the thickness of the negative electrode plate is measured, the thickness of the negative electrode mixture layer obtained by subtracting the thickness of the copper foil, and the mass measurement value of the applied negative electrode active material mixture From this, the mixture density was calculated. The thickness was measured at the center and four places around the negative electrode plate having a diameter of 13 mm, and the average value of these five places was used for calculating the mixture density.

[Evaluation of charge / discharge performance of coin battery]
Next, the initial Coulomb efficiency, the discharge capacity, and the capacity retention rate of the battery of Invention Example 1 were evaluated.

Current value of 0.1mA until the voltage difference 0.005V against counter electrode (the current value of 0.075mA / cm ²⁾ or coin cell at a current of 1.0 mA (current of 0.75 mA / cm ²⁾ Was subjected to constant current doping (equivalent to insertion of lithium ions into an electrode and charging of a lithium ion secondary battery). Thereafter, while maintaining 0.005 V, doping was continued with respect to the counter electrode at a constant voltage until 7.5 μA / cm ² , and the doping capacity was measured.

Next, it is dedoped until the potential difference becomes 1.2 V at a current value of 0.1 mA (current value of 0.075 mA / cm ² ) or a current value of 1.0 mA (current value of 0.75 mA / cm ² ). (Equivalent to detachment of lithium ions from the electrode and discharge of the lithium ion secondary battery) was performed, and the dedoping capacity was measured.

The doping capacity and the dedoping capacity correspond to a charging capacity and a discharging capacity when this electrode is used as a negative electrode of a lithium ion secondary battery. Therefore, the measured doping capacity was defined as the charge capacity, and the measured dedoping capacity was defined as the discharge capacity.
Using the values of the obtained discharge capacity and charge capacity, the Coulomb efficiency at the first cycle was determined by the following formula.
Coulomb efficiency (%) = (discharge capacity (mAh) / charge capacity (mAh)) × 100

  Charging / discharging was repeated 20 times under the same conditions as described above. The capacity retention rate (%) was obtained by dividing the “discharge capacity at the time of dedoping at the 20th cycle” by the “discharge capacity at the time of dedoping at the 1st cycle” and multiplying by 100.

  In the coin battery of Inventive Example 1, the initial Coulomb efficiency, the initial discharge capacity, the discharge capacity at the 20th cycle, and the capacity retention rate were as shown in Table 1.

[Invention Examples 2-3 and Comparative Examples 1-2]
In Inventive Examples 2-3 and Comparative Examples 1-2, the negative electrode active was performed in the same manner as in Inventive Example 1, except that the ratio of the average particle size of the large diameter powder and the small diameter powder was changed to the ratio shown in Table 1. Material material, negative electrode and coin battery were manufactured.

  In the same manner as Example 1 of the present invention, the crystal structure was specified, and the tap density, the mixture density of the negative electrode plate, and various charge / discharge performance evaluations of the coin battery were performed.

  The specific result of the crystal structure was the same as that of Inventive Example 1. That is, it was confirmed that the alloy phases of Invention Examples 2-3 and Comparative Examples 1-2 have a crystal structure that undergoes M transformation when occlusion of lithium ions and reverse transformation when lithium ions are released.

  Table 1 shows the results of the tap density, the mixture density of the negative electrode plate, and various charge / discharge performance evaluations of the coin battery.

[Invention Examples 4-6, Comparative Examples 3-4]
In Inventive Examples 4-6 and Comparative Examples 3-4, the negative electrode active material was obtained in the same manner as in Inventive Example 1, except that the ratio of the content of the large diameter powder and the small diameter powder was changed to the ratio shown in Table 1. Materials, negative electrode and coin cell were manufactured.

  In the same manner as Example 1 of the present invention, the crystal structure was specified, and the tap density, the mixture density of the negative electrode plate, and various charge / discharge performance evaluations of the coin battery were performed.

  The specific result of the crystal structure was the same as the example of the present invention. That is, it was confirmed that the alloy phases of Invention Examples 4 to 6 and Comparative Examples 3 to 4 have a crystal structure that undergoes M transformation when occlusion of lithium ions and reverse transformation when lithium ions are released.

  Table 1 shows the results of the tap density, the mixture density of the negative electrode plate, and various charge / discharge performance evaluations of the coin battery.

[Invention Examples 7 and 8]
[Manufacture of negative electrode active material]
Large diameter powder and small diameter powder were prepared by the following method, and these powders were mixed at a content ratio shown in Table 1 to obtain a negative electrode active material. In the same manner as in Invention Example 1, a negative electrode and a coin battery were produced.

(Large diameter powder and small diameter powder)
A mixture of a plurality of materials (elements) is dissolved in an argon gas atmosphere by arc melting so that the final chemical composition of the negative electrode active material is the chemical composition described in the column “Chemical composition” in Table 1. An ingot was manufactured. This was homogenized and heat-treated at 600 ° C. for 24 hours in an argon atmosphere, and then crushed to a size of about 5 mm was sealed in a transparent quartz sealed tube in a vacuum state, followed by solution treatment at 630 ° C. for 24 hours. Immediately after application, it was quenched into ice-cold water. At this time, the quartz tube was broken to ensure sufficient cooling. Thereafter, it was immediately put into liquid nitrogen, subjected to sub-zero treatment, held for 2 hours, and then a granular sample was collected. The obtained granular sample was pulverized using a small vibration rod mill (manufactured by Yoshida Seisakusho, model 1045). Thereafter, sieving and classification were carried out in the same manner as shown in Example 1 of the present invention to obtain a large-diameter powder and a small-diameter powder having an average particle diameter shown in Table 1.

  In the same manner as Example 1 of the present invention, the crystal structure was specified, and the tap density, the mixture density of the negative electrode plate, and various charge / discharge performance evaluations of the coin battery were performed.

  The specific result of the crystal structure was the same as that of Inventive Example 1. That is, it was confirmed that the alloy phases of Invention Examples 7 to 8 have a crystal structure that undergoes M transformation when occluding lithium ions and reverse transformation when releasing lithium ions.

  Table 1 shows the results of the tap density, the mixture density of the negative electrode plate, and various charge / discharge performance evaluations of the coin battery.

[Invention Examples 9 and 10]
In Invention Examples 9 to 10, the final alloy phase chemical composition of the large diameter powder and the small diameter powder, the ratio of the average particle diameter of the large diameter powder and the small diameter powder, and the content ratio of the large diameter powder and the small diameter powder, A negative electrode active material, a negative electrode, and a coin battery were manufactured in the same manner as in Example 1 of the invention except that the materials were changed to those shown in Table 1.

According to the identification of the crystal structure, the alloy phase changed as follows with charge and discharge. M phase (2H structure) before the first charge, M phase (2H structure) after the first charge, and mother phase (DO ₃ structure) after the first discharge. Thus, a mother phase (DO ₃ structure) was obtained by discharge. That is, it was confirmed that the negative electrode of the example of the present invention has an alloy phase that undergoes M transformation when occlusion of lithium ions, which are metal ions, and reverse transformation when lithium ions are released.

  Table 1 shows the oxygen concentration in the negative electrode active material and the results of various charge / discharge performance evaluations of the coin battery.

  The embodiment of the present invention has been described above. However, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately changing the above-described embodiment without departing from the spirit thereof.

Claims (6)

A large diameter powder having a first average particle size;
Containing a small diameter powder having a second average particle size different from the first average particle size,
The ratio of the first and second average particle sizes is: first particle size: second particle size = 1.2: 1-20: 1
The ratio of the content (mass) of the large diameter powder and the small diameter powder is large diameter powder: small diameter powder = 25: 1 to 1: 3,
The large diameter powder and the small diameter powder contain an alloy phase,
The alloy phase contains Cu and Sn,
The alloy phase contains a crystal structure which is DO ₃ in Strukturbericht notation,
The alloy phase, and thermoelastic diffusionless transformation when occluding lithium ions, and the reverse transformation when releasing the lithium ions,
The alloy phase after the thermoelastic non-diffusion transformation contains a crystal structure of 2H in Ramsdel notation,
It said alloy phase after the reverse transformation contains a crystalline structure which is DO ₃ in Strukturbericht notation, the negative electrode active material material. The negative electrode active material according to claim 1 ,
The alloy phase contains 10 to 20 at% or 21 to 27 at% of Sn, and the balance is a negative electrode active material made of Cu and impurities. The negative electrode active material according to claim 1 , further comprising:
The alloy phase contains at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B, and C instead of a part of Cu. Negative electrode active material. The negative electrode active material according to claim 3 ,
The alloy phase is
Sn: 10 to 35 at%,
Ti: 9.0 at% or less, V: 49.0 at% or less, Cr: 49.0 at% or less, Mn: 9.0 at% or less, Fe: 49.0 at% or less, Co: 49.0 at% or less, Ni: 9.0 at% or less, Zn: 29.0 at% or less, Al: 49.0 at% or less, Si: 49.0 at% or less, B: 5.0 at% or less, and C: 5.0 at% or less Containing one or more selected from
The balance is a negative electrode active material made of Cu and impurities. The negative electrode containing the negative electrode active material of any one of Claims 1-4 . A battery comprising the negative electrode according to claim 5 .