JP2016081768A - Electrode active material, electrode and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel electrode active material.SOLUTION: An electrode active material according to an embodiment of the present invention comprises an alloy having a crystal structure of SrAuGa type. The alloy is e.g. Ln[X][Y], where Ln represents at least one kind of lanthanoid of elements of atomic numbers 57-71 in the periodic table; [X] represents at least one kind selected from a group consisting of Cu, Ni, Pd, Pt, Ag, Au, Ti, V, Cr, Mn, Fe and Co; and [Y] represents at least one kind selected from a group consisting of Al, Si, Ga, Ge, In, Sn and Zn.SELECTED DRAWING: Figure 1

Description

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

  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.

  A secondary electrode represented by a lithium ion battery uses a graphite-based electrode active material. However, the graphite-based electrode active material has limitations in increasing capacity and cycle characteristics.

  Therefore, research on electrode active material materials mainly composed of other compositions different from graphite-based electrode active material materials has been advanced.

The negative electrode material for a nonaqueous electrolyte battery proposed in Japanese Patent Application Laid-Open No. 2005-93416 (Patent Document 1) has a chemical composition represented by R _a Sn _b M _c T _d X _e A _f , and R-Sn -Includes crystalline alloys whose main phase is M phase. Of the chemical composition, R is at least one element selected from rare earth elements. M is at least one element selected from the group consisting of Co, Ni, Fe, Cu, Mn, V, and Cr. T is at least one element selected from the group consisting of Ti, Zr, Hf, Nb, Ta, Mo, and W. X is at least one element selected from the group consisting of Si, Al, Sb and In. A is at least one element selected from the group consisting of Mg, Ca, Sr and Ba. a to f are a + b + c + d + e + f = 100 atomic%, 0 <a ≦ 40, 45 ≦ b ≦ 70, 0 <c ≦ 30, 0 ≦ d ≦ 10, 0 ≦ e ≦ 20, 0 ≦ f ≦ 30, respectively. .

The non-aqueous electrolyte secondary battery proposed in Japanese Patent Application Laid-Open No. 2005-310739 (Patent Document 2) includes a container, a non-aqueous electrolyte, a positive electrode that absorbs and releases Li, and a La ₃ Co ₂ Sn ₇ type crystal structure. And a negative electrode including an alloy having

JP 2005-93416 A JP-A-2005-310739

  However, even the electrode active material disclosed in Patent Document 1 and Patent Document 2 may have low discharge capacity and cycle characteristics.

  An object of the present invention is to provide a novel electrode active material.

The electrode active material according to the present embodiment contains an alloy having a SrAu ₂ Ga ₅ type crystal structure.

  The electrode active material according to the present embodiment can function as an electrode.

FIG. 1 is a diagram showing the relationship between the number of cycles and the discharge capacity obtained by a charge / discharge test using a battery including an electrode active material of an example.

The electrode active material according to the present embodiment contains an alloy having a SrAu ₂ Ga ₅ type crystal structure.

An alloy having a SrAu ₂ Ga ₅ type crystal structure can absorb and release metal ions typified by Li. Therefore, an alloy having a SrAu ₂ Ga ₅ type crystal structure can function as an electrode active material.

The alloy is, for example, Ln [X] ₂ [Y] ₅ . Here, Ln is a lanthanoid and is one or more elements of atomic numbers 57 to 71 in the periodic table. [X] is at least one selected from the group consisting of Cu, Ni, Pd, Pt, Ag, and Au. [Y] is one or more selected from the group consisting of Al, Si, Ga, Ge, In, Sn, and Zn.

The alloy is, for example, LaCu ₂ (Al, Si) ₅ .

  Preferably, the electrode active material is a powder having an average particle size (d50) of 100 μm or less.

  When the average particle diameter is 100 μm or less, the active material material particles easily absorb and release Li. As a result, the absorption and release rates of Li are increased.

  The electrode according to the present embodiment includes the above-described electrode active material. The battery according to the present embodiment includes the above-described electrode.

  Hereinafter, the electrode active material of this embodiment will be described in detail.

[Electrode active material]
The electrode active material of the present embodiment contains an alloy having a SrAu ₂ Ga ₅ type crystal structure. Hereinafter, an alloy having a SrAu ₂ Ga ₅ type crystal structure is referred to as a “specific alloy”.

Table 1 shows lattice constants and atomic coordinates of the crystal structure of the SrAu ₂ Ga ₅ type crystal structure.

As shown in Table 1, the SrAu ₂ Ga ₅ type crystal structure has a space in which a metal ion typified by Li can easily enter. Therefore, even if a specific alloy absorbs and releases metal ions, its crystal structure is not easily destroyed. That is, even when the electrode active material containing the specific alloy is reversibly repeatedly charged and discharged, the specific alloy tends to maintain the initial crystal structure. As a result, the electrode active material containing the specific alloy is excellent in cycle characteristics.

The specific alloy is, for example, Ln [X] ₂ [Y] ₅ . Here, Ln is a lanthanoid. Lanthanoid is a general term for a group consisting of atomic numbers 57 to 71 in the periodic table. Ln in the chemical composition is lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium ( One or more elements selected from the group consisting of Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu) is there.

  [X] is at least one selected from the group consisting of Cu, Ni, Pd, Pt, Ag, Au, Ti, V, Cr, Mn, Fe, and Co.

  [Y] is one or more selected from the group consisting of Al, Si, Ga, Ge, In, Sn, and Zn. These elements are easy to occlude Li. Therefore, the discharge capacity of the electrode active material containing the specific alloy can be increased.

An example of the specific alloy is LaCu ₂ (Al, Si) ₅ , for example.

[Average particle size of electrode active material]
Preferably, the electrode active material is a powder having an average particle size (d50) of 100 μm or less. In this case, the smaller the average particle size, the easier it is to occlude and release Li. Accordingly, the absorption and release rates of Li are increased.

  The average particle diameter (d50) can be measured using a laser diffraction / scattering particle diameter distribution measuring apparatus. For example, the electrode active material powder is sonicated and dispersed together with a dispersion solvent such as water. Measurement is carried out by putting dispersed powder of electrode active material into a laser diffraction / scattering particle size distribution measuring device. By inputting the refractive index of the alloy, the particle size distribution can be calculated. In this specification, the average particle diameter (d50) refers to the median diameter (d50) based on the volume calculated from the particle diameter distribution.

  The electrode active material may contain other materials different from the specific alloy. The electrode active material is made of a specific alloy, and the balance may be impurities.

[Method for producing electrode active material]
An example of a method for producing the electrode active material containing the specific alloy phase will be described.

An alloy melt having a SrAu ₂ Ga ₅ type crystal structure is manufactured and made into an ingot. For example, a raw material is prepared so that it may become the above-mentioned chemical composition Ln [X] ₂ [Y] ₅ . The raw material is melted to form a molten metal by a normal melting method such as arc melting or resistance heating melting, and the molten metal is cooled to an ingot.

  When button arc melting is used, for example, an ingot is manufactured by the following method. The above-mentioned raw material is stored in a water-cooled copper mold. Arc melting is performed using a non-consumable electrode (for example, a W electrode) in an argon atmosphere to produce an ingot.

  Next, the ingot is powdered. Specifically, the ingot is cut or pulverized using a hammer mill or the like to make the ingot into 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 powder.

  The coarse powder is pulverized in a groove box in an inert gas atmosphere or a dry atmosphere. In this case, oxidation of the alloy can be suppressed. The preferable oxygen content in the groove box is 0.4% or less.

  When using a ball mill, the coarse powder may be mixed with stearic acid or PVP (polyvinylpyrrolidone) and pulverized. In this case, it can suppress that powder adheres to the inner wall of a ball mill.

  The electrode active material of this embodiment can be manufactured by the above process.

[Electrode manufacturing method]
An example of the electrode manufacturing method according to the present embodiment is as follows. An electrode mixture is prepared by mixing a binder with the above-described electrode active material powder. 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).

  When providing sufficient electroconductivity to an electrode, the electroconductive powder for improving electroconductivity is mixed with an 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, when a carbon material is used, it is possible to suppress a decrease in the capacity of the electrode due to mixing of conductive powder. The carbon material is further excellent in liquid retention. Preferred carbon materials are graphite and acetylene black. The electrode mixture is applied to an active material support such as rolled copper foil or electrodeposited copper foil and dried. Thereafter, the dried product is pressed to produce an electrode.

[battery]
The battery of this embodiment is a nonaqueous electrolyte secondary battery. The battery includes the electrode described above. A battery is provided with the electrode of this embodiment, the counter electrode of this embodiment, 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.

When the electrode of this embodiment is a negative electrode, the positive electrode serving as a counter 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 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.

[Production of electrode active material of inventive example]
An ingot containing La, Cu, Al, and Si and the balance being impurities was manufactured by button arc melting. The produced ingot was pulverized to produce a coarse powder of 100 μm or less. The mixture which mix | blended PVP with coarse powder was manufactured. The mixture was pulverized using a ball mill (trade name BX384E, manufactured by Kurimoto Steel Co., Ltd.) to produce an electrode active material (negative electrode active material) made of a specific alloy. At the time of pulverization by a ball mill, coarse powder: PVP: ball = 39.2: 0.8: 600 grams. The grinding time by the ball mill was 12 hours. The inside of the ball mill container was a nitrogen atmosphere.

The chemical composition of the specific alloy is LaCu ₂ (Al, Si) ₅ , 34.4% La, 31.5% Cu, 16.7% Al, and 17.4% Si in mass%. Containing.

[Production of Negative Electrode of Invention Example]
5 parts by mass of styrene butadiene rubber (SBR), 5 parts by mass of carboxymethylcellulose (CMC), and 15 parts by mass of acetylene black powder with respect to 75 parts by mass of the above-mentioned powdered electrode active material (negative electrode active material) To prepare a mixture. Furthermore, the mixture was mixed with distilled water and kneaded to prepare a slurry.

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

[Manufacture of Battery of Inventive Example]
A coin type battery (2016 type) using the manufactured negative electrode was manufactured. The positive electrode was Li metal. Specifically, a laminate in which a separator having a diameter of 19 mm was disposed on the negative electrode and a disk-shaped metal Li having a diameter of 15 mm was disposed on the separator was produced. The laminate was stored in a case, and the outer periphery of the case was pressed with a special caulking machine. A coin-type battery was manufactured through the above steps.

The electrolytic solution was a solution in which LiPF ₆ as a supporting electrolyte was dissolved in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a ratio of 1: 3 so as to be 1 mol / liter, and 8% by mass of fluoroethylene. Carbonate.

[Identification of crystal structure of specific alloy]
X-ray diffraction measurement was performed on the powder of the specific alloy to obtain actual measurement data of the X-ray diffraction profile. Specifically, the Rigaku product name RINT1000 (rotor target maximum output 18 kW; 60 kV-300 mA, or tube target maximum output 3 kW; 50 kV-60 mA) was used to obtain an X-ray diffraction profile of a specific alloy. .

Based on the obtained X-ray diffraction profile, the crystal structure of the specific alloy was analyzed by the Rietveld method. As a result, the crystal structure of the specific alloy was SrAu ₂ Ga ₅ type.

[Measurement of average particle size of electrode active material]
The average particle size (d50) of the electrode active material was measured using a laser diffraction / scattering particle size distribution measuring device (Microtrack FRA manufactured by Nikkiso Co., Ltd.). Water was used as a dispersion solvent, and the measurement was made after loosening the powder by ultrasonic waves. At the time of data analysis, the particle size distribution was calculated with the refractive index of the alloy as 1.74. As a result of the measurement, the average particle diameter of the electrode active material was 12 μm.

[Charge / discharge test at the first cycle]
In the coin-type battery, first, constant current doping (equivalent to insertion of lithium ions into the negative electrode and charging of the lithium ion secondary battery) is performed until the potential difference becomes 5 mV with respect to the counter electrode at a current value of 0.15 mA. It was. Further, while maintaining 5 mV, doping was continued at a constant voltage until the current value reached 10 μA. After 30 minutes from the end of the dope, de-doping (corresponding to detachment of lithium ions from the negative electrode and discharge of the lithium ion secondary battery) at a constant current of 0.15 mA until the potential difference becomes 1.2 V is performed. It was. After the above initial cycle, the discharge capacity (mAh / cc) was determined. Specifically, the measured dedoping capacity was taken as the discharge capacity.

[Charge / discharge test after 2nd cycle]
Charging / discharging of the 2nd cycle or more was implemented as follows. Doping was performed at a current value of 0.75 mA until the potential difference became 5 mV with respect to the counter electrode. Further, while maintaining 5 mV, doping was continued at a constant voltage until the current value reached 10 μA. After 30 minutes from the end of the dope, undoping was performed at a constant current of 0.75 mA until the potential difference became 1.2V. Each time the above cycle was performed, the discharge capacity (mAh / cc) was determined.

[Test results]
FIG. 1 is a diagram showing the relationship between the number of cycles and the discharge capacity obtained by the charge / discharge test. “●” in FIG. 1 represents the discharge capacity (mAh / cc) in the battery of the above-described example of the present invention. “■” is a discharge capacity (mAh / cc) obtained by conducting the above charge / discharge test using a button-type battery (comparative example) using a graphite negative electrode and the other structure being the same as the example of the present invention. is there.

  With reference to FIG. 1, the discharge capacity of the battery of the present invention was higher than the discharge capacity of the battery of the comparative example, and was 1400 mAh / cc or more. Further, in this example, the discharge capacity was maintained even after 40 cycles, and excellent cycle characteristics were exhibited.

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)

An electrode active material containing an alloy having a crystal structure of SrAu ₂ Ga ₅ type. The electrode active material according to claim 1,
The electrode is an electrode active material, wherein the alloy is Ln [X] ₂ [Y] ₅ .
Here, Ln is a lanthanoid and is one or more elements of atomic numbers 57 to 71 in the periodic table. [X] is at least one selected from the group consisting of Cu, Ni, Pd, Pt, Ag, Au, Ti, V, Cr, Mn, Fe, and Co. [Y] is one or more selected from the group consisting of Al, Si, Ga, Ge, In, Sn, and Zn. The electrode active material according to claim 2,
The alloy is LaCu ₂ (Al, Si) ₅ , an electrode active material. The electrode active material according to any one of claims 1 to 3,
An electrode active material that is a powder having an average particle size (D50) of 100 μm or less.   The electrode containing the electrode active material of any one of Claims 1-4.   A battery comprising the electrode according to claim 5.

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