JP2013247022A - Electrode material, method for producing the same, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having a large discharge capacity per unit volume.SOLUTION: An electrode material comprising a sintered compact containing a first crystal which is a lithium composite oxide having a layered rock-salt type crystal structure and containing at least two of Co, Mn, and Ni, and a second crystal which is a lithium cobaltate is used as a cathode 1 of the secondary battery. In an X-ray diffraction pattern of the sintered compact, the ratio of the intensity of an X-ray diffraction peak indicating a (003) plane of the second crystal to the intensity of an X-ray diffraction peak indicating a (003) plane of the first crystal is 0.05-0.1.

Description

  The present invention relates to an electrode material for a secondary battery using a nonaqueous electrolyte, a method for producing the same, and a secondary battery using the electrode material.

  In recent years, secondary batteries using non-aqueous electrolytes have expanded their use not only to mobile phones and notebook PCs, but also to batteries for electric vehicles, household batteries, and storage batteries for power generation facilities.

  Secondary batteries generally use a non-aqueous electrolyte solution impregnated in a porous membrane called a separator as an electrolyte. In recent years, electrolyte leakage and corrosion prevention, and electrolyte injection. Secondary batteries using solid electrolytes have also been proposed from the viewpoint of simplifying the liquid process and the like and simplifying the battery structure. As secondary batteries having excellent charge / discharge characteristics, lithium ion secondary batteries using lithium ions for charging / discharging the battery are known.

As a positive electrode material used for such a secondary battery, for example, a sintered body electrode mainly including LiCoO ₂ as a positive electrode active material has been proposed (see Patent Document 1).

Further, containing LiCoO ₂ as a main phase as a positive electrode active material, which porosity was placed lithium ion conductive material in the gap portion of the sintered body of 15 to 25 vol% has been proposed (Patent Documents 2 reference)

Japanese Patent No. 3427570 JP 2010-080426 A

  However, even when the positive electrode material described in Patent Document 1 or Patent Document 2 is used for a secondary battery, there is a problem that the discharge capacity cannot be sufficiently increased.

  The present invention has been made in view of the above problems, and an object thereof is to provide a secondary battery having a large discharge capacity per unit volume.

  The electrode material of the present invention has a layered rock salt type crystal structure, and includes a first crystal that is a lithium composite oxide containing at least two of Co, Mn, and Ni, and a second crystal that is lithium cobalt oxide, In the X-ray diffraction pattern of the sintered body, the intensity of the X-ray diffraction peak indicating the (003) plane of the second crystal is the (003) plane of the first crystal. The intensity of the X-ray diffraction peak shown is 0.05 to 0.1.

  In addition, the secondary battery of the present invention is characterized by having a positive electrode made of the electrode material, a non-aqueous electrolyte, and a negative electrode.

Furthermore, the manufacturing method of the electrode material of the present invention includes a first powder of 70 to 95% by mass which is a lithium composite oxide having a layered rock salt type crystal structure and containing at least two of Co, Mn and Ni. And 5 to 30% by mass of the second powder of lithium cobaltate,
It is characterized by firing at a maximum temperature of 0 ° C. or higher.

  According to the present invention, it is possible to provide a secondary battery having a large discharge capacity per unit volume.

It is sectional drawing which shows the electric power generation element of the secondary battery which is one Embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described.

  The electrode material of the present embodiment has a layered rock salt type crystal structure, and a first crystal that is a lithium composite oxide containing at least two of Co, Mn, and Ni, and a second crystal that is lithium cobalt oxide And a sintered body containing

  A lithium composite oxide having a layered rock salt type crystal structure and containing at least two of Co, Mn and Ni has a high charge / discharge voltage and a large charge / discharge capacity. It is an active material suitable for densification. Therefore, when such a material is used for the positive electrode of a secondary battery, for example, a high discharge capacity of 150 to 180 mAh / g can be obtained.

A material having such a high capacity is used as the first crystal, and cobalt acid that has a relatively high electron conductivity and is inferior in capacity to the material used for the first crystal, but itself functions as a positive electrode active material. By using lithium (LiCoO ₂ ) as the second crystal and a sintered body in which at least some of the crystal particles are bound to each other, an electrode material having a high capacity density can be obtained.

  In the present embodiment, the abundance ratio of the first crystal and the second crystal in the sintered body is expressed by an X-ray indicating the (003) plane of the second crystal in the X-ray diffraction pattern of the sintered body. By setting the intensity of the diffraction peak to a ratio of 0.05 to 0.1 with respect to the intensity of the X-ray diffraction peak indicating the (003) plane of the first crystal, the first crystal becomes the active material. It is possible to obtain a dense electrode material having a high capacity density without deteriorating the inherent capacity.

  The crystals contained in the sintered body may be identified from a diffraction pattern obtained by X-ray diffraction, and the ratio of X-ray diffraction peaks may be calculated from the intensity ratio of the identified diffraction peaks.

As a lithium composite oxide having a layered rock salt type crystal structure and containing at least two of Co, Mn and Ni, LiNi _1/2 Mn ₁ which is a solid solution of three components of LiCoO ₂ , LiNiO ₂ and LiMnO _{2 / 2} O ₂ , LiMn _1/3 Co _1/3 Ni _1/3 O ₂ , LiNi _0.8 Co _0.2 O _2, etc., and Li (Li _1/3 Mn _2/3 ) O ₂ , LiNi One example is a solid solution of three components, _1/2 Mn _1/2 O ₂ and LiCoO ₂ , represented by Li (Li, Mn, Co, Ni) O ₂ . In particular, LiMn _1/3 Co _1/3 Ni _1/3 O ₂ is preferable because it is relatively easy to synthesize and is thermally stable.

In the present embodiment, the sintered body may contain impurity elements such as Na, Mg, Fe, Al, and Zr that may be mixed during the manufacturing process. In addition to the first crystal and the second crystal, a crystal such as LiNiO _{2 or} LiMnO ₂ may be contained. In this embodiment, these impurity elements and crystals may be contained in the sintered body as long as the first crystal does not impair the capacity originally possessed as the active material. What is necessary is just to confirm the element contained in a sintered compact by elemental analysis, such as a fluorescent X ray analysis and ICP emission spectral analysis, for example.

  In addition, when considering the characteristics of a secondary battery using a non-aqueous electrolyte, energy density is one of the very important performance factors. It is preferable that the ratio to the weight is high. For this purpose, the porosity of the sintered body is preferably 20% or less, more preferably 15% or less. This is because, by setting the porosity to 20% or less, the proportion of space in the sintered body is reduced, the energy density is increased, the binding area between crystal particles as active materials is increased, and lithium ion conduction is increased. This is because the degree can be increased. The porosity of the sintered body may be calculated by, for example, the Archimedes method or an image analysis of a cross-sectional photograph of the sintered body.

  Next, the manufacturing method of the electrode material of this embodiment is demonstrated. First, as a raw material, a first powder which is a lithium composite oxide having a layered rock salt type crystal structure and containing at least two kinds of Co, Mn and Ni, and a second powder which is lithium cobalt oxide Prepare mixed powder. The mixing ratio of the mixed powder is 70 to 95% by mass for the first powder and 5 to 30% by mass for the second powder. By making the ratio of the second powder 5% by mass or more, it is possible to improve the sinterability of the first powder, which is difficult to be densified by itself, and the ratio of the first powder is 70% by mass or more. By doing so, it is possible to obtain a dense sintered body having a layered rock salt type crystal structure and without losing the capacity originally possessed by the lithium composite oxide containing at least two of Co, Mn and Ni as an active material it can.

The mixing powder preferably has the following D ₅₀ 0.6 .mu.m in the particle size distribution measurement by diffraction scattering method. Thereby, the sinterability can be further improved, the bulk density of the electrode can be increased, the porosity can be reduced, and the energy density can be improved. As a method for adjusting the particle size, any of known pulverization / disintegration means such as a ball mill, a vibration mill, a planetary mill, and a wet jet mill may be used. Further, D ₅₀ of the mixed powder after the first powder and the second powder were mixed predetermined amounts may be ground so as to 0.6μm or less, the first powder and was adjusted to a predetermined particle size A predetermined amount of the second powder may be mixed. In addition, when adjusting the particle size of the first powder and the second powder individually, it is preferable to make the particle size of the second powder smaller than the particle size of the first powder. Tissue formation is facilitated.

  To the prepared mixed powder, a binder and a dispersant are added together with a solvent and mixed to prepare a slurry. The binder is not particularly limited as long as it is a polymer that can be used for molding. For example, polyacrylic acid, carboxymethyl cellulose, polyvinylidene fluoride, polyvinyl alcohol, diacetyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, polyvinyl pyrrolidone, Examples thereof include one or a mixture of two or more such as butyral. Of these, a butyral binder is preferable because it has high strength and can reduce the amount of addition, and a high-density sintered body can be obtained. The binder amount is preferably 10% by volume or less with respect to the active material.

  A green sheet is formed from the prepared slurry by a known forming method such as a doctor blade method or a press method. If necessary, the formed green sheet may be cut into a desired shape.

  Then, the produced green sheet is fired at a maximum temperature of 900 ° C. or higher, further 1000 ° C. or higher, so that the first crystal derived from the first powder and the second crystal derived from the second powder A sintered body containing the above can be obtained, and such a sintered body can be a dense electrode material having a high capacity density.

In the sintered body thus obtained, for example, the first crystal exists as crystal particles having an average particle diameter of 0.1 to 5 μm, and the second crystal has an average particle diameter of, for example, 0.01 to 3 μm.
Exist as crystal grains. In addition, the second crystal may exist as a grain boundary phase of the first crystal between the grains of the first crystal or at a triple point. In this case, the second crystal is located between the grains of the first crystal. It is more preferable that it is thin, for example, in the form of a network, because even if it is a small amount, it is easy to ensure electron conduction between the particles of the first crystal.

  Hereinafter, the structure of the secondary battery using the electrode material of this embodiment as a positive electrode will be described with reference to FIG.

  The secondary battery of this embodiment has a power generation element 4 in which a positive electrode 1 is disposed on one surface of a nonaqueous electrolyte layer 2 and a negative electrode 3 is disposed on the other surface. A positive electrode side current collecting layer 5P and a negative electrode side current collecting layer 5N are provided on the surfaces of the positive electrode 1 and the negative electrode 3 opposite to the nonaqueous electrolyte layer 2, respectively, and a power generation element 4 and an external circuit (not shown). ) Are electrically connected to a positive electrode terminal (not shown) and a negative electrode terminal (not shown), and contact resistance between the positive electrode 1 and the negative electrode 3 is reduced.

  The above-described electrode material is used for the positive electrode 1. That is, a sintered body having a layered rock salt type crystal structure and including a first crystal that is a lithium composite oxide containing at least two of Co, Mn, and Ni, and a second crystal that is lithium cobaltate In the X-ray diffraction pattern of the sintered body, the intensity of the X-ray diffraction peak indicating the (003) plane of the second crystal is the intensity of the X-ray diffraction peak indicating the (003) plane of the first crystal. On the other hand, the electrode material which is 0.05-0.1 is used.

  Thus, by using as the positive electrode 1 a sintered body that is substantially composed only of an active material and in which at least a part of crystal particles of the active material are bound, a conductive auxiliary agent or a binding material that does not directly contribute to capacity. In addition, a decrease in capacity density due to a solid electrolyte or the like can be suppressed, a bonding area between the active materials can be greatly increased, and the original electronic conductivity and ionic conductivity of the active material can be effectively utilized.

Moreover, it has a high-capacity layered rock-salt crystal structure, and a lithium composite oxide containing at least two of Co, Mn and Ni is used as the first crystal, which has high electron conductivity and functions as an active material itself. Lithium cobalt oxide (LiCoO ₂ ) to be used as the second crystal has a layered rock salt type crystal structure and impairs the capacity originally possessed by the lithium composite oxide containing at least two of Co, Mn and Ni Therefore, the positive electrode 1 can be made dense and has a high capacity density, and a secondary battery having high capacity, high energy density, and excellent output characteristics can be obtained.

  Examples of the active material used for the negative electrode 3 include carbonaceous materials such as graphite, hard carbon, and glassy carbon, metal silicon and its alloys, silicon-containing materials such as a compound containing silicon, oxygen, and nitrogen, metal lithium, oxidation Examples thereof include titanium, niobium oxide, and lithium titanium composite oxide. In particular, the lithium titanium composite oxide can reduce the volume change of the negative electrode 3 during charging and discharging even when used as a sintered body having a relative density of 85% or more, and further 90% or more, and has good cycle characteristics. A secondary battery can be obtained.

Metal silicon and its alloys, compounds containing silicon, oxygen and nitrogen, and the like are preferable from the viewpoint of obtaining a high capacity. Such a silicon-containing material may be used as a coating film or a sintered body containing the particles and carbon. In addition, although the particle | grains containing silicon change at the time of charging / discharging, even when using as a sintered compact, the stress which generate | occur | produced by the volume change exists in a sintered compact by making a porosity into the range of 10 to 60%. Can be absorbed by pores. A sintered body containing a silicon-containing material is prepared by mixing a raw material powder of a silicon-containing material with a carbonaceous material precursor that is carbonized by heat treatment to form a carbonaceous material, and molding and drying it into a desired shape. It is obtained by performing a heat treatment in an atmosphere. As the carbonaceous material precursor, thermosetting resins such as phenol resin, epoxy resin, polyester resin, furan resin, urea resin, melamine resin, alkyd resin, xylene resin, naphthalene, acenaphthylene, phenanthrene, anthracene, triphenylene, pyrene, Examples thereof include organic materials such as pitch mainly composed of condensed polycyclic hydrocarbon compounds such as perylene, pentaphen, and pentacene, derivatives thereof, or mixtures thereof. The carbonaceous material precursor that is carbonized by heat treatment to become a carbonaceous material may further contain particles of carbonaceous material such as graphite and hard carbon described above. In order to form pores, a resin material that disappears during heat treatment and becomes pores may be added as a pore-forming agent.

  The thicknesses of the positive electrode 1 and the negative electrode 3 are preferably 20 μm to 200 μm, respectively. Thereby, the absolute amount of the active material necessary for obtaining the battery capacity can be secured, and a secondary battery having good charge / discharge characteristics can be obtained.

  As the non-aqueous electrolyte, any of an organic electrolyte, a polymer solid electrolyte, an inorganic solid electrolyte, an ionic liquid, and the like can be used.

  When using an organic electrolytic solution, a non-aqueous electrolyte layer 2 in which a separator is impregnated with an organic electrolytic solution is disposed between the positive electrode 1 and the negative electrode 3. The separator is required to pass ions and prevent a short circuit between the positive and negative electrodes. Specifically, a polyolefin fibrous nonwoven fabric, a polyolefin microporous film, a glass filter, a ceramic porous material, or the like can be used. Here, examples of the polyolefin include polyethylene and polypropylene, and a separator generally used for a secondary battery such as a lithium ion battery is applicable.

The organic electrolyte is composed of an organic solvent and an electrolyte salt, and an additive for the purpose of forming a film on the electrode surface, preventing overcharge, imparting flame retardancy, or the like may be added as necessary. As the organic solvent, those having a high dielectric constant, low viscosity and low vapor pressure are suitably used. Examples of such materials include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane, Examples thereof include a solvent in which one or two or more selected from 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, methylethyl carbonate, dimethyl carbonate, and diethyl carbonate are mixed. Examples of the electrolyte salt include lithium salts such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiN (C ₂ F ₅ SO ₂ ) ₂ .

  In addition, a polymer solid electrolyte or an inorganic solid electrolyte may be used as the electrolyte. In that case, a layer made of the polymer solid electrolyte or the inorganic solid electrolyte may be disposed as the non-aqueous electrolyte layer 2.

  By using a solid electrolyte, the thickness of the non-aqueous electrolyte layer 2 can be reduced to, for example, 10 μm or less, further 3 μm or less, and more active materials can be packed compared to a secondary battery having the same volume. As the capacity increases, the energy density can be improved as a result. However, the non-aqueous electrolyte layer 2 needs to have a necessary minimum thickness so as not to cause a dielectric breakdown or a short due to a pinhole in order to prevent a short circuit.

  A material having corrosion resistance that does not cause a reaction such as dissolution at the potential of the positive electrode 1 may be used as the material of the positive electrode side current collecting layer 5P. As such a material, for example, a metal material or alloy containing aluminum, tantalum, niobium, titanium, gold, platinum, or the like, or a carbonaceous material such as graphite, hard carbon, or glassy carbon can be used. Among these, aluminum, gold, and platinum are preferable because they are excellent in corrosion resistance and easily available. Aluminum is particularly preferable because it is passivated by forming an oxide film on the surface and excellent in corrosion resistance even at a high potential.

  As the material of the negative electrode side current collecting layer 5N, a material that does not cause a side reaction such as alloying with Li at the potential of the negative electrode 3 may be used. As such a material, for example, a metal material or alloy including copper, nickel, brass, zinc, aluminum, stainless steel, tungsten, gold, platinum or the like, or a carbonaceous material such as graphite, hard carbon, or glassy carbon is used. Can do. In particular, it is preferable to use copper or nickel from the viewpoint of high conductivity and relatively low cost.

  In addition, the positive electrode side current collecting layer 5P and the negative electrode side current collecting layer 5N are conductive using a metal foil made of these metal materials, or an oxide material such as a metal material, a carbonaceous material, ITO glass, or tin oxide as a filler. Ink may be applied to the electrode surface and dried. Moreover, what vapor-deposited metals, such as platinum, aluminum, and titanium, on the electrode surface may be used.

  Such a power generation element 4 is applied to a battery case made of a metal such as aluminum, titanium, stainless steel, zinc, iron, nickel, a laminated film made of aluminum foil and resin, a plastic case or a ceramic case provided with terminal electrodes, and the like. By storing, a secondary battery can be formed.

  The secondary battery of the present embodiment has been described above, but the present invention is not limited to the present embodiment, and can be applied to various modifications without departing from the present invention. For example, although FIG. 1 shows only one set of power generation elements 4, a plurality of power generation elements 4 may be stacked or a power generation element 4 having sheet-like electrodes may be wound. I do not care.

First, LiMn _1/3 Co _1/3 Ni _1/3 O ₂ is used as the first powder, LiCoO ₂ is used as the second powder, and the mixed powder mixed at the ratio shown in Table 1 is mixed with isopropyl alcohol (IPA). As the solvent, the mixed powder and the solvent were mixed at a mass ratio of 1: 2, and pulverized using beads made of zirconia having a diameter of 3.0 mm. The pulverization conditions were set so that D ₅₀ in the particle size distribution measurement by the diffraction scattering method of the mixed powder was 0.6 μm or less. To the obtained mixed powder, 5% by mass of a butyral binder and 4% by mass of a dispersant were added to 100% by mass of the mixed powder, and a slurry was prepared using 50% by mass of toluene as a solvent.

The sufficiently stirred slurry was molded using a coater and dried to prepare a green sheet having a thickness of 100 μm. Further, the green sheet is cut into a circular shape, fired under the condition that the temperature is raised to 5 ° C / min up to the maximum temperature shown in Table 1 and held at the maximum temperature for 10 hours, and the diameter is 1
A disk-shaped sintered body having a thickness of 5 mm and a thickness of 70 μm was produced.

The porosity of the produced sintered body was measured by Archimedes method. Further, the crystal phase contained in the sintered body is identified from the diffraction pattern obtained from the X-ray diffraction (XRD) measurement of the sintered body, and LiMn _1/3 Co _1/3 Ni _{1 /} Is / If was calculated with the intensity of the peak indicating the (003) plane of ₃ O ₂ as If and the intensity of the peak indicating the (003) plane of LiCoO ₂ being the second crystal as Is. Table 1 shows the porosity and peak intensity ratio Is / If of the sintered body.

  Next, a Pt metal layer was formed as a current collecting layer on one surface of the produced sintered body by sputtering. A graphite plate was used as the negative electrode, and a Cu metal layer was formed as a current collecting layer on one surface by sputtering. At that time, in order to prevent the metal component from wrapping around the side surface of the sintered body, a mask having an opening with a diameter of 14 mm was placed on the surface of the sintered body and the graphite plate and sputtered.

The produced sintered body is used as the positive electrode, the graphite plate as the negative electrode, and the positive electrode and the negative electrode surface on which the current collector layer is not formed are arranged so as to face each other through the porous film containing the electrolytic solution. Was made. As an electrolytic solution, lithium hexafluorophosphate LiPF _{6 was} added to an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7.
Was dissolved at 1 mol / L.

These power generation elements were set in a coin-type battery evaluation cell, an electrolyte was filled in the case, and a charge / discharge test was performed under the following conditions to confirm battery characteristics.
Charging / discharging voltage range: upper limit 4.6V, lower limit 2.75V
Charge / discharge rate: 0.2C (5-hour rate)
Measurement temperature: 30 ° C

Table 1 shows the initial discharge capacity as a result of the charge / discharge test. The discharge capacity was calculated as follows.
Discharge capacity: discharge time x current value / positive electrode volume

Sample No. The electrode materials 2 to 4 include LiMn _1/3 Co _1/3 Ni _1/3 O ₂ as the first crystal, LiCoO ₂ as the second crystal, and Is / If is 0.05 to 0.1. Since the sintered body was in the range, the discharge capacity when used as the positive electrode of the secondary battery exhibited excellent characteristics of 650 mAh / cm ³ or more. On the other hand, Sample No. In Nos. 1 and 5, the X-ray diffraction peak due to the second crystal could not be confirmed, or the first crystal was not included, and only a discharge capacity of 450 mAh / cm ³ or less was obtained.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode 2 ... Non-aqueous electrolyte layer 3 ... Negative electrode 4 ... Electric power generation element 5P ... Positive electrode side current collection layer 5N ... Negative electrode side current collection layer

Claims (6)

It has a layered rock salt type crystal structure, and comprises a sintered body containing a first crystal that is a lithium composite oxide containing at least two of Co, Mn, and Ni, and a second crystal that is lithium cobaltate. ,
In the X-ray diffraction pattern of the sintered body, the intensity of the X-ray diffraction peak indicating the (003) plane of the second crystal is equal to the intensity of the X-ray diffraction peak indicating the (003) plane of the first crystal. On the other hand, the electrode material is 0.05 to 0.1. The electrode material according to claim 1, wherein the first crystal is LiMn _1/3 Co _1/3 Ni _1/3 O ₂ .   The electrode material according to claim 1 or 2, wherein a porosity of the sintered body is 20% or less.   A secondary battery comprising a positive electrode made of the electrode material according to claim 1, a nonaqueous electrolyte, and a negative electrode.   First powder 70 to 95% by mass which is a lithium composite oxide having a layered rock salt type crystal structure and containing at least two kinds of Co, Mn and Ni, and second powder 5 which is lithium cobaltate 30. A method for producing an electrode material comprising mixing 30% by mass and firing at a maximum temperature of 900 ° C. or higher. The first powder and the second powder, method for producing the electrode material according to claim 5, characterized in that in the particle size distribution measurement by diffraction scattering method, has the following D ₅₀ 0.6 .mu.m .

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