WO2016059793A1

WO2016059793A1 - Negative electrode active material, negative electrode, cell, and method for manufacturing negative electrode active material

Info

Publication number: WO2016059793A1
Application number: PCT/JP2015/005192
Authority: WO
Inventors: 永田　辰夫; 禰宜　教之
Original assignee: 新日鐵住金株式会社
Priority date: 2014-10-17
Filing date: 2015-10-14
Publication date: 2016-04-21
Also published as: JPWO2016059793A1

Abstract

　Provided is a negative electrode active material having excellent charge/discharge capacity and cycle characteristics. The negative electrode active material of the present embodiment contains a plurality of charge/discharge phases, a constraint phase, and a plurality of ceramic particles. The plurality of charge/discharge phases comprise one or more elements selected from the group consisting of Si, Sn, and Zn. The constraint phase is a solid solution or intermetallic compound comprising one or more elements selected from the group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements, and Group 14 elements (but excluding C and the element(s) of the charge/discharge phases), and the element(s) contained in the charge/discharge phases; the charge/discharge phases are dispersed therein. The ceramic particles are dispersed within the charge/discharge phases, have average particle diameters of 0.01-0.1 μm, and are contained at a level of 1-10% in mass%. In X-ray diffraction using the CuKα line, the half width of the peak of the constraint phase is 0.35-0.65°.

Description

Negative electrode active material, negative electrode, battery, and method for producing negative electrode active material

The present invention relates to a negative electrode active material, a negative electrode, a battery, and a negative electrode active material.

In recent years, small electronic devices such as home video cameras, notebook computers, and smartphones have become widespread. With the widespread use of these small electronic devices, higher battery capacity and higher cycle characteristics are required.

For secondary batteries represented by lithium ion batteries, graphite-based negative electrode active material is used. However, a graphite-based negative electrode active material has limitations in increasing capacity and cycle characteristics.

Therefore, an alloy-based negative electrode active material having a higher capacity than a graphite-based negative electrode active material has attracted attention. As the alloy-based negative electrode active material, silicon (Si) -based negative electrode active material, tin (Sn) -based negative electrode active material, and zinc (Zn) -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 alloy-based negative electrode active material material repeats large expansion and contraction during charging and discharging. Therefore, the capacity of the alloy-based negative electrode active material is likely to deteriorate. 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 cracks and cracks occur in the negative electrode plate containing the negative electrode active material. In this case, the capacity of the negative electrode is significantly reduced. This is because part of the negative electrode active material is liberated by volume expansion and contraction, and the negative electrode plate loses electronic conductivity.

Japanese Patent Application Laid-Open No. 2001-243946 (Patent Document 1) discloses a non-aqueous electrolyte secondary battery capable of suppressing capacity deterioration. This battery includes a negative electrode including a negative electrode material made of composite particles in which the whole or part of the periphery of a core particle made of solid phase A is coated with solid phase B. The solid phase A contains at least one of silicon, tin, and zinc as a constituent element. The solid phase B is selected from the group consisting of silicon, tin, and zinc, which are constituent elements of the solid phase A, and the group 2 element, transition element, group 12 element, group 13 element, and group 14 element of the periodic table. A solid solution or an intermetallic compound with at least one element (except for the constituent element of solid phase A and carbon). The composite particles contain ceramics.

In Patent Document 1, the solid phase A gives a high capacity. Solid phase B suppresses expansion associated with charging of solid phase A. Therefore, collapse of the solid phase A is suppressed and cycle characteristics are improved. Furthermore, since the ceramic suppresses the propagation of cracks, the cycle characteristics are improved.

JP 2001-243946 A

However, even when the negative electrode active material disclosed in Patent Document 1 is used, the cycle characteristics may be low.

An object of the present invention is to provide a negative electrode active material having excellent charge / discharge capacity and cycle characteristics.

The negative electrode active material according to this embodiment includes a plurality of charge / discharge phases, a constrained phase, and a plurality of ceramic particles. The plurality of charge / discharge phases are composed of one or more selected from the group consisting of Si, Sn and Zn, and have an average crystal grain size of 10 to 100 nm. The constrained phase is one or more elements selected from the group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements, and Group 14 elements (however, charge-discharge phase elements and C And a solid solution or an intermetallic compound composed of elements contained in the charge / discharge phase, in which the charge / discharge phase is dispersed. The ceramic particles are dispersed at least in the charge / discharge phase, have an average particle diameter of 0.01 to 0.1 μm, and are contained in an amount of 1 to 10% by mass. In X-ray diffraction using CuKα rays, the half-value width of the peak of the constrained phase is 0.35 to 0.65 °.

The negative electrode active material according to this embodiment is excellent in charge / discharge capacity and cycle characteristics.

FIG. 1 is a diagram showing the relationship between the heat treatment temperature and the half-value width of the constrained phase, which is an index of the amount of strain.

In the negative electrode active material of this embodiment, the charge / discharge phase absorbs and releases metal ions typified by lithium (Li). That is, the charge / discharge phase increases the capacity. Furthermore, a restraint phase suppresses the volume change (expansion and shrinkage | contraction) of the charging / discharging phase accompanying charging. By the way, when the restraint phase has a large amount of strain, the amount of strain further increases by suppressing the volume change (expansion and contraction) of the charge / discharge phase. In this case, a part of the restraint phase is detached early or collapses. As a result, the cycle characteristics of the negative electrode active material are deteriorated.

In this embodiment, the amount of strain in the constrained phase is reduced in advance by performing heat treatment described below. As a result, the diffraction peak half-value width of the constrained phase, which is an index of the strain amount, can be lowered to 0.65 ° or less. Since the strain in the constrained phase is small, the cycle characteristics are enhanced.

By the way, in order to improve cycle characteristics, it is preferable that the crystal grains of the charge / discharge phase are fine. If the crystal grains are fine, the strength of the charge / discharge phase is increased. In this case, even if charging / discharging is repeated and the charging / discharging phase repeats expansion and contraction, it is possible to suppress part of the charging / discharging phase from being separated or collapsed.

However, when heat treatment is performed to reduce the strain amount of the constrained phase, the crystal grains in the charge / discharge phase are likely to be coarsened. Therefore, in this embodiment, fine ceramic particles are dispersed at least in the charge / discharge phase. Thereby, even if it is a case where heat processing is performed, the coarsening of a crystal grain is suppressed by ceramic particles. As a result, the average grain size of the crystal grains in the charge / discharge phase is suppressed to 10 to 100 nm, and fine crystal grains can be maintained. Therefore, cycle characteristics are improved.

Ceramic particles are particles mainly composed of ceramics. “Main component” means that the volume fraction of ceramics in the particles is 50% or more. The ceramic particles are, for example, oxide-based ceramics, non-oxide-based ceramics, or a mixture thereof. Examples of the oxide-based ceramic include Al ₂ O ₃ , MgO, ZrO ₂ , Y ₂ O ₃ , TiO ₂ , La ₂ O ₃ , and CeO ₂ . Non-oxide ceramics are, for example, CrN, TiN, TaN, AlN, BN, Si ₃ N ₄ , NbN, ZrB, TaB ₂ , MoB ₂ , WC, VC, TiC, SiC, HfC, and the like.

Preferably, the ceramic particles are one or more selected from the group consisting of Al ₂ O ₃ , MgO, ZrO ₂ , Y ₂ O ₃ , TiO ₂ , La ₂ O ₃ and CeO ₂ . These ceramic particles are thermodynamically stable at a temperature of 700 ° C. or lower. Therefore, these ceramic particles hardly react chemically with the charge / discharge phase alloy and the constrained phase alloy.

For example, the charge / discharge phase of the negative electrode active material is made of Si, and the constraining phase is made of one or more metal silicides. The metal silicide may contain Ni and / or Ti.

The manufacturing method of the negative electrode active material of the present embodiment includes a preparation process, a mechanical grinding process (hereinafter referred to as MG process) process, and a heat treatment process. In the preparation step, the charge / discharge phase is composed of one or more selected from the group consisting of Si, Sn and Zn, and is composed of a Group 2 element, a transition element, a Group 12 element, a Group 13 element and a Group 14 element. A raw material containing one or more elements selected from the group (excluding charge-discharge phase elements and C) and a charge-discharge phase element solid solution or a constrained phase that is an intermetallic compound prepare. In the MG treatment step, the raw material and ceramic particles having an average particle diameter of 0.01 to 0.1 μm are mixed, and then mechanical grinding treatment is performed. As a result, a negative electrode active material containing a charge / discharge phase, a constrained phase, and 1 to 10% by mass of ceramic particles is produced. In the heat treatment step, the negative electrode active material is heat treated at 400 to 700 ° C.

By the above manufacturing method, the half-value width of the peak of the constrained phase becomes 0.65 ° or less in the X-ray diffraction by CuKα ray, and the amount of strain is reduced. Furthermore, in the charge / discharge phase, the average crystal grain size can be suppressed to 100 nm or less even when the above heat treatment is performed with ceramic particles. Therefore, the cycle characteristics (capacity maintenance ratio) of the manufactured negative electrode active material are increased.

Hereinafter, the negative electrode active material of this embodiment and the manufacturing method thereof will be described in detail.

[Negative electrode active material]
The negative electrode active material of this embodiment can reversibly absorb and release metal ions typified by Li. The negative electrode active material contains a charge / discharge phase, a constrained phase, and ceramic particles.

[Charge / discharge phase]
The charge / discharge phase is composed of one or more selected from the group consisting of silicon (Si), tin (Sn), and zinc (Zn). These elements absorb and release metal ions. That is, the charge / discharge phase increases the charge / discharge capacity of the negative electrode active material.

The average crystal grain size of the charge / discharge phase crystal grains is 10 to 100 nm. In this embodiment, the charge / discharge phase crystal grains are fine. If the average crystal grain size is 100 nm or less, the diffusion distance of metal ions in the charge / discharge phase is short, and stress concentration associated with absorption and release of metal ions is reduced. In this case, even if the charge / discharge phase repeatedly expands and contracts with charge / discharge, the charge / discharge phase is prevented from being partially detached or collapsed. A preferable upper limit of the average crystal grain size is 80 nm, and more preferably 50 nm.

The average crystal grain size of the charge / discharge phase crystal grains is measured by the following method. A sample for microstructural observation is prepared from the negative electrode active material. The produced sample is observed with a transmission electron microscope (TEM) to generate a photographic image. Using the photographic image, the average crystal grain size of the charge / discharge phase crystal grains is determined.

[Restricted Phase]
The plurality of charge / discharge phases described above are dispersed in the constraining phase. In other words, the constraining phase surrounds the charge / discharge phase. As described above, the charge / discharge phase repeats expansion and contraction. The constraining phase surrounds and constrains the charge / discharge phase, and suppresses volume changes (expansion and contraction) of the charge / discharge phase. Therefore, it is suppressed that a part of charging / discharging phase leaves | separates or collapses by the rapid volume change of a charging / discharging layer. As a result, the cycle characteristics of the negative electrode active material are enhanced.

The constrained phase is one or more elements selected from the group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements and Group 14 elements in the periodic table (however, the charge / discharge phase) And a solid solution or an intermetallic compound consisting of elements contained in the charge / discharge phase. When the charge / discharge phase is a Si phase made of Si, the constraining phase is, for example, a metal silicide phase. The metal silicide phase contains, for example, Si, Ti, and Ni.

In X-ray diffraction using CuKα rays, the half-value width of the diffraction peak of the constrained phase is 0.35 to 0.65 °.

The restraint phase suppresses the volume change (expansion and contraction) of the charge / discharge phase. At this time, the restraint phase receives an external force from the charge / discharge phase. For this reason, strain is accumulated in the constraining phase with charge and discharge.

If the amount of strain is large in the constrained phase before charging / discharging, the strain is further added along with charging / discharging. As a result, a part of the restraint phase is disengaged or collapses. In this case, the cycle characteristics (capacity maintenance ratio) of the negative electrode active material are lowered. Therefore, in the constrained phase before charging / discharging, it is preferable that the amount of strain is small.

The half width of the diffraction peak of the constrained phase is an index of the amount of strain in the constrained phase. The smaller the half width, the smaller the amount of strain in the constrained phase. If the half width exceeds 0.65 °, the amount of strain in the constrained phase is too large. In this case, the cycle characteristics of the negative electrode active material are low.

If the half width of the constrained phase is 0.65 ° or less, the amount of strain in the constrained phase is sufficiently small. Therefore, the negative electrode active material has excellent cycle characteristics. The upper limit with preferable half value width is 0.50 degree, More preferably, it is 0.35 degree.

When considering only the restraint phase, the lower limit of the full width at half maximum is not particularly limited. The strain amount of the constrained phase is adjusted by a heat treatment described later. If the heat treatment temperature is raised, the half width can be lowered. However, if the heat treatment temperature is too high, the charge and discharge phase crystal grains become coarse. In this case, as described above, the cycle characteristics deteriorate. The lower limit of the half width within the range in which the average crystal grains of the charge / discharge phase can be maintained at 10 to 100 nm is 0.35 °. Accordingly, the half width of the constrained phase is 0.35 to 0.65 °.

¡The full width at half maximum of the restraint phase is measured by the following method. X-ray diffraction is performed on the constrained phase of the negative electrode active material. In X-ray diffraction, CuKα rays (wavelength is 1.5418 mm) are used under the conditions of 30 kV and 100 mA. Based on the peak top method, the diffraction angle at the height at which the half height of the diffraction peak height is obtained is measured as the half width. Further, the half width derived from the X-ray diffractometer is measured using a single crystal of LaB6 (lanthanum hexaboride) (an ideal single crystal having no half width). Correction is performed by subtracting the measured half-value width inherent to the apparatus from the measured half-value width. The corrected value is defined as the half width of the diffraction peak of the constrained phase.

[Ceramic particles]
The plurality of ceramic particles are dispersed in the negative electrode active material. That is, the ceramic particles are dispersed in the charge / discharge phase and the constraining phase. The average particle size of the ceramic particles is 0.01 to 0.1 μm and is fine. Hereinafter, ceramic particles having an average particle diameter of 0.01 to 0.1 μm are also referred to as “fine ceramic particles”. The fine ceramic particles have the following action.

The fine ceramic particles in the charge / discharge phase keep the average crystal grain size of the charge / discharge phase crystal grains fine. As described above, in this embodiment, the amount of strain in the constrained phase is reduced by performing heat treatment. However, if heat treatment is performed, the crystal grains in the charge / discharge phase tend to be coarse. In this embodiment, the fine ceramic particles dispersed in the charge / discharge phase suppress the coarsening of crystal grains in the charge / discharge phase due to heat treatment. Therefore, the average crystal grain size of the charge / discharge phase is maintained at 10 to 100 nm.

If the average particle size of the ceramic particles exceeds 0.1 μm, the ceramic particles are too large. In this case, it is difficult to suppress the coarsening of the crystal grains of the charge / discharge phase, and the average crystal grain size of the crystal grains may exceed 100 nm. Therefore, the upper limit of the average particle size of the ceramic particles is 0.1 μm. A preferable upper limit of the average particle size of the ceramic particles is 0.06 μm. The lower limit of the average particle size of the ceramic particles is not particularly limited. However, considering the production cost, the lower limit of the average particle size of the ceramic particles is 0.01 μm.

The average particle size of the ceramic particles is measured by the following method. Measurement is performed using a laser diffraction / scattering type particle size distribution measuring apparatus (Microtrack FRA manufactured by Nikkiso Co., Ltd.). This measurement is performed after loosening the powder by ultrasonic waves using water as a dispersion solvent. At the time of data analysis, the refractive index of each substance provided by the measuring device manufacturer is input to obtain the particle size distribution.

The content of ceramic particles in the negative electrode active material is 1 to 10% by mass. If the ceramic particle content is too low, the crystal grains of the charge / discharge phase after the heat treatment become coarse. On the other hand, ceramic particles do not contribute to the charge / discharge capacity. Therefore, if the content of ceramic particles is too high, the charge / discharge capacity decreases. When the content of the ceramic particles is 1 to 10%, a high charge / discharge capacity can be obtained while maintaining fine grains of the charge / discharge phase. A preferable lower limit of the content of the ceramic particles is 2%. A preferable upper limit of the content of ceramic particles is 6%.

The negative electrode active material may contain impurities in addition to the charge / discharge phase, the constrained phase, and the ceramic particles. The negative electrode active material may further contain other phases or particles.

[Production method]
An example of the manufacturing method of the negative electrode active material of this embodiment is demonstrated. The method for producing a negative electrode active material includes a preparation step, an MG treatment step, and a heat treatment step.

[Preparation process]
In the preparation step, a raw material containing a charge / discharge phase and a constraining phase is prepared. First, one or more elements selected from the group consisting of Si, Sn and Zn, and a group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements and Group 14 elements are selected. The raw material containing the 1 or more types of element (however, the element and C of a charge / discharge phase are remove | excluded) is prepared. At this time, the blending of these elements is adjusted so that a charge / discharge phase and a constrained phase are formed. For example, when producing a negative electrode active material containing a Si phase as a charge / discharge phase and a metal silicide phase as a constraining phase, the composition of these elements is adjusted using Si, Ni, Ti, etc. as raw materials. .

* Prepare the molten metal by melting the prepared raw materials. The dissolution method is not particularly limited. Examples of the melting method include arc melting, high-frequency heating melting, resistance heating melting, and the like.

Next, the molten metal is cooled to produce an ingot or slab. The cooling method is not particularly limited. The cooling method is, for example, a strip casting method (SC method). In the strip casting method, molten metal is poured onto a rotating water-cooled roll, and the molten metal is rapidly solidified. In this case, a flaky cast piece is produced. The ingot may be manufactured by casting a molten metal in a mold.

* The raw material is manufactured by crushing the manufactured material (ingot or slab). For example, the raw material is cut or pulverized using a hammer mill or the like to obtain a coarse powder of 100 μm or less. Further, the coarse powder is pulverized using a ball mill, an attritor, a disk mill, a jet mill, a pin mill, or the like to adjust the size (particle size) of the raw material (powder particles). The average particle diameter of the raw material is not particularly limited. The average particle size of the raw material is, for example, 25 to 30 μm.

Preferably, the pulverization process is performed in an inert gas atmosphere or a dry atmosphere. This is to prevent oxidation of the raw material.

[MG treatment process]
The raw material and fine ceramic particles are mixed to produce a mixed powder. MG treatment is performed on the mixed powder. In the MG processing, for example, a ball mill is used. In the MG treatment, graphite, stearic acid, or PVP (polyvinylpyrrolidone) may be added to the mixed powder. In this case, it can suppress that the negative electrode active material (powder particle) produced | generated by MG process adheres to the inner wall of a ball mill. By the MG treatment, a negative electrode active material including a charge / discharge phase having fine crystal grains is manufactured. The average particle diameter of the negative electrode active material is, for example, 5 to 200 μm.

[Heat treatment process]
As described above, the negative electrode active material includes a charge / discharge phase having fine crystal grains, a constrained phase, and ceramic particles. However, many strains are introduced into the constrained phase by the MG treatment. Therefore, heat treatment is performed on the negative electrode active material to reduce the strain amount of the constrained phase.

The heat treatment temperature is 400 to 700 ° C. FIG. 1 is a diagram showing the relationship between the heat treatment temperature and the half width. FIG. 1 was obtained by the following method. A negative electrode active material including a constrained phase (metal silicide phase), a charge / discharge phase (Si phase) and ceramic particles shown in Table 1 described later was produced. At this time, the heat treatment temperature was changed. The heat treatment time was 4 hours. The half width of the manufactured negative electrode active material was measured, and FIG. 1 was created.

In FIG. 1, “◇” marks include a metal silicide phase composed of TiSi ₂ and Ni ₄ Ti ₄ Si ₇ as a constraining phase, a Si phase as a charge / discharge phase, and Al ₂ O ₃ as ceramic particles. It is a result of the contained negative electrode active material. The “□” mark indicates a negative electrode active material containing a metal silicide phase composed of Ni ₄ Ti ₄ Si ₇ as a constraining phase, a Si phase as a charge / discharge phase, and Al ₂ O ₃ as ceramic particles. It is a result.

Referring to FIG. 1, the higher the heat treatment temperature, the smaller the half width, and the amount of strain decreases. When the heat treatment temperature is 400 ° C. to 700 ° C., the half width is 0.65 ° or less, and the amount of strain is sufficiently reduced.

If the heat treatment temperature is too high, the strain amount of the constrained phase is reduced, but the crystal grains of the charge / discharge phase become coarse. However, in the negative electrode active material of this embodiment, the inclusion of 1 to 10% by mass of fine ceramic particles suppresses the coarsening of crystal grains in the charge / discharge phase during the heat treatment. When the heat treatment temperature is 700 ° C. or lower, the average crystal grain size of the charge / discharge phase can be suppressed to 100 nm or lower.

The preferable upper limit of the heat treatment temperature is 600 ° C. A preferred lower limit of the heat treatment temperature is 400 ° C.

A preferable heat treatment time is 3.0 hours to 12 hours. A more preferable lower limit of the heat treatment time is 4.0 hours. A more preferable upper limit of the heat treatment time is 8 hours.

The negative electrode active material is manufactured by the above manufacturing process.
[Production method of negative electrode]
An example of the negative electrode manufacturing method according to the present embodiment is as follows. A negative electrode mixture is prepared by mixing a binder with the negative electrode active material powder described above. The binder is, for example, a water-insoluble resin such as polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE), etc., and is insoluble in the solvent used for the non-aqueous electrolyte of the battery. And water-soluble resins such as carboxymethyl cellulose (CMC) and vinyl alcohol (PVA), and styrene butadiene rubber (SBR).

In the case of imparting sufficient conductivity to the negative electrode, conductive powder for increasing conductivity is mixed with the negative electrode mixture. The conductive powder is, for example, a carbon material such as natural graphite, artificial graphite or acetylene black, or a metal such as Ni. A preferred conductive powder is a carbon material. The carbon material can occlude Li ions. Therefore, the carbon material increases not only the conductivity but also the capacity of the negative electrode. The carbon material is further excellent in liquid retention. A preferred carbon material is acetylene black.

A solvent such as water is added to the negative electrode mixture, and if necessary, the mixture is sufficiently stirred using a homogenizer and glass beads to produce a negative electrode mixture 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 as necessary. A negative electrode is manufactured by the above process.

[battery]
The battery of this embodiment is a nonaqueous electrolyte secondary battery. The battery includes the above-described negative electrode. A battery is provided with the negative electrode of this embodiment, a positive electrode, a separator, and electrolyte solution or electrolyte, for example.

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 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).

The battery of this embodiment includes a transition metal chalcogenide; a vanadium oxide and its lithium (Li) compound; a niobium oxide and its lithium compound; a conjugated polymer using an organic conductive material; a sheprel phase compound; Other positive electrodes such as fibers may be used.

The electrolytic solution is generally a non-aqueous electrolytic solution in which a lithium salt as a supporting electrolyte is dissolved 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 and 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.

A laminate in which a separator and a metal Li thin plate are sequentially laminated on a negative electrode is manufactured. The laminate is placed in a case and pressed with a caulking machine to manufacture a battery.

Batteries containing negative electrode active material of test numbers 1 to 18 shown in Table 1 were prepared by the following method, and battery characteristics (initial charge capacity, initial discharge capacity, capacity maintenance rate after 50 cycles) were investigated.

[Manufacture of negative electrode active material]
[Manufacture of raw materials]
In test numbers 1 to 14, primary powders were produced by the following method. Pure raw materials of Ni, Ti and Si were stored in a melting crucible made of aluminum titanate. The mass ratio of Ni, Ti and Si was 12.0: 18.0: 70.0.

After making the inside of the melting crucible an argon (Ar) atmosphere, the raw material in the melting crucible was heated to 1500 ° C. by high frequency induction heating to produce a molten metal. The produced molten metal was brought into contact with a copper water-cooled roll rotating at a peripheral speed of 90 m / min and rapidly solidified to produce a flaky slab (SC method). The cooling rate in the SC method was 500 to 2000 ° C./second. The produced slab was pulverized and classified with a 63 μm sieve to produce a raw material having an average particle size of 25 to 30 μm.

In test numbers 15 to 18, the mass ratio of Ni, Ti and Si in the raw material stored in the melting crucible was 22.2: 18.0: 59.8. In other manufacturing processes, raw materials were prepared in the same manner as in test numbers 1 to 14.

[Manufacture of negative electrode active material]
For each test number, a mixture was prepared by mixing raw materials and alumina (Al ₂ O ₃ ) powder. The average particle diameter of the alumina powder of each test number was 0.06 μm. The mixture was put into a planetary ball mill (manufactured by Kurimoto Steel Co., Ltd., trade name: BX384E) and subjected to MG treatment to produce a negative electrode active material (powder).

Specifically, the mixture was put into a mill pot of a planetary ball mill. The material of the mill pot was SUS304, the inner diameter was 100 mm, and the depth was 67 mm. In addition, a plurality of balls were thrown into the mill pot. The material of the ball was SUS304, and the ball diameter was 4 mm. Furthermore, in order to prevent the negative electrode active material from adhering to the ball and the inner wall of the mill pot, graphite was introduced into the mill pot. The mass ratio of the charged mixture, balls and graphite was mixture: graphite: ball = 35 g: 5 g: 600 g.

In the MG treatment, the inside of the glove box was made a nitrogen atmosphere (less than 1% oxygen). Further, the MG treatment was carried out for 10 hours with the rotational speed of the mill pot set to 500 rpm. After the MG treatment, the negative electrode active material was taken out in a glove box in a nitrogen atmosphere (less than 1% oxygen) and sieved (63 μm).

[Heat treatment]
The manufactured negative electrode active material was subjected to heat treatment at the temperature and time shown in Table 1.

[Measurement method of average grain size of crystal grains in charge / discharge phase after heat treatment]
Using a FIB (focused ion beam) apparatus, a foil piece having a thickness of 200 nm or less was produced from the negative electrode active material after heat treatment by accelerated gallium (Ga) ions. A bright-field image of the foil piece was photographed using a transmission microscope, and the charge / discharge phase was observed. The observed charge / discharge phase grains had a round shape with an aspect ratio of less than 1.5. The vertical and horizontal lengths of the charge / discharge phase crystal grains observed on the photographic image were measured, the average value was taken as the crystal grain size of the charge / discharge phase, and the target phase of n = 6 was observed. The crystal grain size was calculated.

[Manufacture of negative electrode]
5 parts by mass of styrene butadiene rubber (SBR) (binder), 5 parts by mass of carboxymethyl cellulose (CMC) (binder), and 15 parts by mass of acetylene black with respect to 75 parts by mass of the produced negative electrode active material (powder) Powder (conductive powder) was mixed to prepare a mixture. Further, distilled water was added to the mixture and kneaded to prepare a negative electrode mixture slurry.

The negative electrode mixture slurry was thinly applied onto an electrolytic copper foil having a thickness of 30 μm using a doctor blade (150 μm) and dried to form a coating film. This coating film was punched out using a punch having a diameter of 13 mm to produce a negative electrode. The coating amount of the negative electrode mixture slurry on the copper foil was 2 to 3 mg / cm ² .

[Manufacture of coin-type batteries]
A coin-type battery (2016 type) using Li metal as a counter electrode (positive electrode) was manufactured. Specifically, a separator having a diameter of 19 mm was disposed on the negative electrode. Furthermore, a metal Li plate having a diameter of 15 mm was disposed on the separator to form a laminate. The laminate was placed in the case. The outer periphery of the case containing the laminate was pressed with a dedicated caulking machine to produce a coin-type battery (2016 type). 1 of ethylene carbonate and ethyl methyl carbonate: 3 mixed solvent of LiPF ₆ supporting electrolyte is obtained by dissolving LiPF ₆ as a 1 mol / L solution was used as an electrolyte. The electrolytic solution contained 8% by mass of fluoroethylene carbonate as an additive.

[Evaluation test]
[Initial charge capacity, initial discharge capacity, initial charge / discharge efficiency]
In the manufactured battery, dope with constant current until the potential difference becomes 5 mV with respect to the counter electrode (positive electrode) at a current value of 0.15 mA (equivalent to insertion of lithium ions into the negative electrode, charging of the lithium ion secondary battery). went. Thereafter, doping was continued at a constant voltage while maintaining 5 mV until the current value reached 10 μA. After a 30-minute rest period, de-doping (corresponding to detachment of lithium ions from the electrode and discharging of the lithium ion secondary battery) was performed at a constant current of 0.15 mA until the potential difference became 1.2V. After the above initial cycle, the measured dope amount was defined as the initial charge capacity (mAh / cc), and the measured dedope capacity was defined as the initial discharge capacity (mAh / cc). The ratio of initial discharge capacity to initial charge capacity (= initial discharge capacity / initial charge capacity) (%) was defined as initial charge / discharge efficiency (%).

[Capacity maintenance rate after 50 cycles]
Charging / discharging of the 2nd cycle or more was implemented as follows. Doping was performed at a constant current until the potential difference became 5 mV with respect to the counter electrode at a current value of 0.15 mA. Further, while maintaining 5 mV, doping was continued at a constant voltage until the current value reached 10 μA. After a 30-minute pause after the doping was completed, undoping was performed at a constant current of 0.15 mA until the potential difference became 1.2V. The ratio of the discharge capacity after 50 cycles to the initial discharge capacity (= discharge capacity after 50 cycles / initial discharge capacity) was defined as the capacity retention rate (%).

[Test results]
Referring to Table 1, the negative electrode active material of test numbers 2 to 6, 12, 13, 16, and 17 was within the scope of the present invention. Therefore, the initial charge capacity and the initial discharge capacity were high. Specifically, the initial charge capacity exceeded 1600 mAh / cc, and the initial discharge capacity exceeded 1400 mAh / cc. Furthermore, the capacity retention rate was 80% or more.

On the other hand, in the test number 1, fine ceramic particles (Al ₂ O ₃ ) were not contained. Therefore, the average crystal grain size of the Si phase exceeded 100 nm. As a result, the capacity retention rate was low.

In test number 7, the content of fine ceramic particles in the negative electrode active material was too high. Therefore, the initial charge capacity and the initial discharge capacity were low. The proportion of fine ceramic particles that do not contribute to the charge / discharge capacity in the Si phase is considered to be too high.

In Test Nos. 8 to 11 and 15, no heat treatment was performed on the negative electrode active material. Therefore, the half width of the metal silicide phase was too high. Therefore, the capacity retention rate was low and less than 80%.

In test numbers 14 and 18, the heat treatment temperature for the negative electrode active material was too high. Therefore, the average crystal grain size of the Si phase exceeded 100 nm. As a result, the capacity retention rate was low and less than 80%. This is probably because part of the Si phase was detached during the cycle test because the Si phase was coarse.

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

A plurality of charge and discharge phases comprising at least one selected from the group consisting of Si, Sn and Zn and having an average crystal grain size of 10 to 100 nm;
One or more elements selected from the group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements and Group 14 elements (however, the charge-discharge element and C are excluded) And a solid solution or an intermetallic compound composed of an element contained in the charge / discharge phase, and a constrained phase in which the charge / discharge phase is dispersed,
A plurality of ceramic particles dispersed in the charge / discharge phase, having an average particle diameter of 0.01 to 0.1 μm, and 1 to 10% by mass;
A negative electrode active material in which the half-value width of the peak of the constrained phase is 0.35 to 0.65 ° in X-ray diffraction by CuKα rays.
The negative electrode active material according to claim 1,
The ceramic particles are one or more selected from the group consisting of Al 2 O 3 , MgO, ZrO 2 , Y 2 O 3 , TiO 2 , La 2 O 3 and CeO 2. .
The negative electrode active material according to claim 1 or 2, wherein
The charge / discharge phase is made of Si,
The constrained phase is a negative electrode active material made of one or more metal silicides.
The negative electrode active material according to claim 3,
The metal silicide is a negative electrode active material containing Ni and / or Ti.
A negative electrode comprising the negative electrode active material according to any one of claims 1 to 4.
The negative electrode according to claim 5 is included. battery.
A charge / discharge phase consisting of one or more selected from the group consisting of Si, Sn and Zn, and a group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements and Group 14 elements. A raw material containing at least one element (excluding the charge / discharge phase element and C) and a solid phase or a constrained phase that is an intermetallic compound composed of the charge / discharge phase element. Process,
The raw material and ceramic particles having an average particle size of 0.01 to 0.1 μm are mixed, and then subjected to a mechanical grinding treatment, and the charge / discharge phase, the constrained phase, and 1% by mass. Producing a negative electrode active material containing 10% of the ceramic particles;
And a step of performing a heat treatment at 400 to 700 ° C. on the negative electrode active material.