JP5239153B2 - Electrode material composite method, electrode and lithium ion battery - Google Patents

Description

  The present invention relates to an electrode material composite method, an electrode, and a lithium ion battery.

  In recent years, secondary batteries have been developed as batteries for use in portable electronic devices and hybrid vehicles. As typical secondary batteries currently used, for example, lead storage batteries, alkaline storage batteries, lithium ion batteries, and the like are known. In particular, lithium-ion batteries can be reduced in size, weight, and capacity, and because of their excellent characteristics of high output and high energy density, various studies have been conducted to further improve performance. ing.

  A lithium ion battery is configured as a positive electrode having an active material capable of reversibly inserting and removing lithium ions, a negative electrode, and a non-aqueous electrolyte. The positive electrode of a lithium ion battery is composed of an electrode material containing a positive electrode active material, a conductive additive and a binder, and the positive electrode can be formed by applying this electrode material to the surface of a metal foil called a current collector. it can.

Examples of the material constituting the positive electrode active material include metal oxides, metal sulfides, and polymers. Specifically, for example, a lithium-free compound such as titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), niobium selenide (NbSe ₂ ), vanadium oxide (V ₂ O ₅ ), or LiMO ₂ (M = Co, Ni, Mn, Fe, etc.) and lithium composite oxides such as LiMn ₂ O ₄ are known.

Among such positive electrode active materials for lithium ion batteries, lithium cobaltate (LiCoO ₂ ), in particular, can constitute a battery having a high energy density and a high voltage. Widely used. However, since Co is a rare resource that is biased on the earth's crust and has a low output, there are problems in that procurement costs are high and stable supply is difficult. Therefore, a positive electrode active material using Ni or Mn as a material for the positive electrode active material replacing the Co compound, which is abundant and widespread on the earth's crust, so that procurement costs are low and stable supply is possible. Positive electrodes using lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ) or the like as a positive electrode active material are being put into practical use.

However, although a positive electrode using LiNiO ₂ as a positive electrode active material has a large theoretical capacity and a high discharge potential, the crystal structure of LiNiO ₂ is destroyed by repeating the charge / discharge cycle. As a result, there are problems such as a decrease in discharge capacity and deterioration in thermal stability. On the other hand, LiMn ₂ O ₄ has a positive spinel structure and has a space group Fd3m. Therefore, LiMn ₂ O ₄ has a high potential of 4V class with respect to the lithium electrode, is easily synthesized, and has a high battery capacity. Since it has excellent characteristics, it has attracted attention as a very promising positive electrode active material and has been put into practical use.

Thus, LiMn ₂ O ₄ is an excellent material as a positive electrode active material, but on the other hand, capacity degradation during high-temperature storage is large, Mn is dissolved in the electrolyte, and stability and charge / discharge cycle characteristics are improved. The problem of not being enough was left. Moreover, the subject that charging / discharging cycling characteristics deteriorates by the yarn teller distortion of Mn3 ⁺ is pointed out.

Therefore, a lithium ion battery using a transition metal having an olivine structure, for example, a phosphoric acid compound of Fe, Mn, Co, and Ni as a positive electrode active material has been proposed. In particular, Fe, which is a resource-rich and inexpensive metal, is used. A lithium ion battery using LiFePO ₄ as a positive electrode active material has been proposed. This LiFePO ₄ exhibits a potential of about 3.4 V with respect to metallic lithium and is considered to be used as a chargeable / dischargeable positive electrode material. However, on the other hand, the lithium ion battery using this LiFePO ₄ as a positive electrode active material has a low current density that can be applied during charging and discharging, and its high output is difficult to put into practical use.

  Conventionally, since a lithium ion battery has a low electronic conductivity and ionic conductivity of a positive electrode active material, a conductive additive has been added to the electrode active material for the purpose of improving the electronic conductivity of the electrode active material. It is done. In the process of adding a conductive additive to the electrode active material, a mixer such as a dry ball mill or a stirring blade type mixer has been used for mixing the electrode active material and the conductive additive. Since the auxiliary agent is not sufficiently dispersed and the conductivity of the electrode active material is insufficiently improved, there is a problem in that the capacity is reduced during high-speed charge / discharge of the battery.

In the conventional method of mixing an electrode active material and a conductive additive, Li _x Fe _y Me _1-y PO ₄ (where Me is Cu, Ce, Mn, Co, Ni, Cr, Mo, Nb, Mg, Ca). , Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y and at least one selected from rare earth elements, 0 <X <2, 0 <y <1) In general, the mixing of the electrode active material and the conductive assistant (hereinafter referred to as “compositing”) is performed by carbonizing the raw material when synthesizing the material, or by combining with the conductive assistant without using a solvent. It was.

  However, it is difficult to control the state of the conductive auxiliary agent by the method of carbonizing the raw material during material synthesis. Moreover, in the method of compounding with a conductive additive without using a solvent, uniform compounding at the nanoscale cannot be performed, and a sufficient effect cannot be obtained. For example, there is a method of performing a milling process using a dry ball mill (see Non-Patent Document 1, Patent Document 1, and Patent Document 2). It is difficult to perform mixing and compounding.

In particular, in the carbon composite method described in Patent Document 1, carbon composite is performed using a thermal decomposition method. However, in order to prevent decomposition of LiFePO ₄ , firing conditions and temperature conditions are limited, and excellent electrical conductivity is achieved. It was difficult to get sex. In addition, carbonization by pyrolysis is difficult to obtain high output characteristics due to an increase in resistance because the entire surface of LiFePO ₄ particles is coated with carbon.

In order to solve such a problem, the present inventors have proposed a method for producing an electrode-forming slurry for a lithium ion battery using a sand mill (Patent Document 3). In this invention, when the electrode active material, the conductive additive, the binder and the solvent are stirred together with the medium to form a slurry, the number of media is 3500 or more in 1 ml of the slurry.
N. Ravet, JB Goodenough, S. Besner, M. Simoneau, P, Hovington, M. Armand, 196th ECS, Honolulu, Hawaii, October 17-22 (1999). JP 2002-75364 A JP 2001-15111 A JP 2006-309958 A

  However, in the production method proposed by the present inventors, PVdF, which is a binding agent, inhibits dispersion, so the polymer chain of PVdF is cut and the binding force and adhesive force are reduced, or the dispersibility of beads is reduced. Problems remain such as it is difficult to produce an electrode-forming slurry having a high solid content concentration, and since the binder is added, the solvent cannot be evaporated to form a powder. Due to such problems, uniform composite of electrode materials is insufficient, and an electrode material with further improved conductivity has been desired.

  The present invention relates to an electrode material composite method capable of obtaining a uniform electrode material having excellent conductivity by mixing and pulverizing an electrode active material, a conductive additive, and a solvent by a wet method, and the composite It is an object to provide an electrode and a lithium ion battery using an electrode material obtained by the conversion method.

In order to solve the above-described problems, the present invention provides the following electrode material composite method, electrode, and lithium ion battery.
That is, the composite method of the electrode material of the present invention is Li _x Fe _y Me _1-y PO ₄ (where Me is Cu, Ce, Mn, Co, Ni, Cr, Mo, Nb, Mg, Ca, Sr, Electrode activity represented by at least one selected from Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y and rare earth elements, 0 <X <2, 0 <y <1) Mixing and pulverizing a substance, a conductive additive, and a solvent having a Hansen solubility parameter having a δ value of less than 12.5 and a boiling point of 150 ° C. or less by a wet method, and then removing the solvent It is characterized by.

The electrode active material preferably has an average particle size of 0.03 μm or more and 10 μm or less, and the conductive auxiliary agent preferably has an average particle size of 0.001 μm or more and 0.1 μm or less.
The conductive assistant includes a carbon-based conductive material, and the content of the conductive assistant is preferably 30 parts by weight or less with respect to 100 parts by weight of the electrode active material.

In addition, the electrode of the present invention is characterized by using an electrode material manufactured by the above-described composite method of electrode materials.
Furthermore, the lithium ion battery of the present invention is characterized in that the electrode is provided as a positive electrode.

According to the composite method of the electrode material of the present invention, the electrode active material represented by Li _x Fe _y Me _1-y PO ₄ , the conductive auxiliary agent, and the solvent are mixed and pulverized by a wet method, and then, Since the solvent is removed, it is possible to realize an electrode material suitable for a lithium ion battery and a lithium ion battery that can realize charging and discharging with a large current density.

In addition, according to the electrode material of the present invention, the electrode active material and the conductive additive are uniformly combined in a solvent. Therefore, by using this electrode material for forming an electrode, excellent conductivity can be obtained. It becomes possible to obtain the electrode which has.
Furthermore, according to the lithium ion battery of the present invention, since the electrode in which the electrode active material and the conductive additive are uniformly combined is used as the positive electrode, the discharge capacity is improved even when the discharge current is increased. A high-performance lithium ion battery that can be maintained can be realized.

  Hereinafter, the best mode of the electrode material composite method, electrode, and lithium ion battery according to the present invention will be described. The present embodiment is specifically described for better understanding of the gist of the invention, and does not limit the invention unless otherwise specified.

That is, the present invention
Li _x Fe _y Me _1-y PO ₄ (where Me is Cu, Ce, Mn, Co, Ni, Cr, Mo, Nb, Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In , Si, Ge, Sc, Y, and at least one selected from rare earth elements, an electrode active material represented by 0 <X <2, 0 <y <1), a conductive additive, and a solvent. By mixing and pulverizing, and then removing the solvent.

As the electrode active material used in the present invention, the above-described Li _x Fe _y Me _1-y PO ₄ (where Me is Cu, Ce, Mn, Co, Ni, Cr, Mo, Nb, Mg, Ca, Sr, Ba) , Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y and at least one selected from rare earth elements, having a composition represented by 0 <X <2, 0 <y <1) A substance produced by a method such as a solid phase method, a liquid phase method, or a gas phase method is used. Although there is no restriction | limiting in particular in the shape and magnitude | size of an electrode active material, The particle size of an electrode active material is 0.03 micrometer or more and 10 micrometers or less are preferable.

  When the particle size of the electrode active material is less than 0.03 μm, the difference in particle size with respect to the conductive auxiliary agent becomes small. Therefore, it is combined in a solvent using balls or beads, which are media used in pulverization and mixing by the wet method described later. It becomes difficult to uniformly combine by processing. On the other hand, when the particle size of the electrode active material exceeds 10 μm, it becomes difficult to charge and discharge with a large current density even if the electrode active material and the conductive additive are uniformly combined. Here, the particle size is an average particle size measured by an image analysis method using a transmission electron microscope, a reflection electron microscope, an optical microscope, or the like, and more specifically, one particle size. It is the size represented by the average value of the minimum and maximum parts of the particles.

  The conductive auxiliary agent is used to increase the output of the lithium ion battery, and a carbon-based conductive auxiliary agent is preferably used. Examples of the carbon-based conductive auxiliary agent include acetylene black, carbon black, and ketjen. Examples thereof include black, natural graphite, and artificial graphite. Although there is no restriction | limiting in particular in the shape and magnitude | size of a conductive support agent, It is preferable that the particle size of a conductive support agent is 0.001 micrometer or more and 0.1 micrometer or less.

  The conductive auxiliary agent is preferably contained in a proportion of 30 parts by weight or less with respect to 100 parts by weight of the electrode active material. Here, the reason why the ratio of the conductive assistant is 30 parts by weight or less is that when the conductive assistant exceeds 30 parts by weight, the ratio of the electrode active material decreases and the capacity of the lithium ion battery decreases. .

  In order to reduce the particle size of the conductive additive, for example, a dispersion improver comprising an amino group-containing organic acid, an amino group-containing organic acid salt, an imino group-containing organic acid, an imino group-containing organic acid salt, or the like is added. Also good.

As a solvent, the value of δ in Hansen's solubility parameter is preferably less than 12.5, more preferably less than 12. Here, the Hansen solubility parameter is expressed in a three-dimensional space by dividing the solubility parameter introduced by Hildebrand into three components: a dispersion term δd, a polar term δp, and a hydrogen bond term δh. It can be calculated by the following formula 1.
δ ² = δd ² + δp ² + δh ² ... (Formula 1)
The dispersion term δd represents a nonpolar interaction, the polar term δp represents a force between phase poles, and the hydrogen bond term δh represents a hydrogen bond force. In addition, Hansen's solubility parameter δ of 12.5 or more can be preferably used as a complexing solvent by using a dispersion improving agent such as a surfactant.

  Moreover, in order to evaporate a solvent after completion | finish of composite_complex, it is preferable that the boiling point of the solvent to be used is 150 degrees C or less. Specific examples of the solvent include hexane, benzene, xylene, toluene, butanol, propanol, isopropanol, pentanol, methyl acetate, ethyl acetate, butyl acetate, acetone, acetonitrile, and methyl ethyl ketone. The mixing ratio of such a solvent and the powder composed of the electrode active material and the conductive auxiliary agent is set so that the solid content concentration of the slurry is between 20% by weight and 70% by weight from the dispersed state of the slurry. Is preferred.

  In the present invention, a solvent having a Hansen solubility parameter δ of less than 12.5 is used to uniformly combine the electrode active material and the conductive additive. This is because when a solvent having a Hansen solubility parameter δ exceeding 12.5 is used, mixing of the electrode active material and the conductive additive is poor, making it difficult to form a composite. Further, the boiling point of the solvent is preferably 150 ° C. or lower, but when the boiling point of the solvent exceeds 150 ° C., it is difficult to remove the solvent. On the other hand, with respect to a solvent having a Hansen solubility parameter δ of 12.5 or more, for example, a solvent such as water or ethanol, a dispersion improver such as a surfactant is contained, so that the electrode active material and the conductive auxiliary agent The mixed state is good and can be uniformly compounded.

  For this combination, a medium agitation type dispersion apparatus that performs mixing and grinding by a wet method is used. In this medium agitating type dispersion apparatus, the electrode active material, the conductive auxiliary agent, the solvent, and the balls and beads that serve as the media for the composite are put into a container, and then operated for a predetermined time, whereby the electrode active material is dispersed. The material and the conductive additive are mixed and pulverized. When the medium particles collide with each other, the electrode active material and the conductive auxiliary agent are trapped between the medium particles, and are mixed and dispersed by receiving impact, shearing action due to collision, These electrode active materials and conductive additives are uniformly combined.

  Examples of the medium stirring type dispersing device include a sand mill, a paint shaker, an attritor, a planetary ball mill, a vibrating ball mill, and a rolling ball mill. Preferred examples of the media include glass beads, alumina beads, zirconia beads, zircon beads, titania beads and the like. The diameter of the medium particles is preferably about 10 μm or more and 10 mm or less, although it depends on the type of the medium stirring type dispersion apparatus to be used.

  If the solvent is removed by evaporation from the composite mixture in this manner, a uniformly composite electrode material can be obtained. Then, the obtained electrode material is further mixed with a binder or a solvent to prepare a paste. The obtained paste can be used as a positive electrode of a lithium ion battery by applying it to a current collector, for example, an aluminum (Al) foil, and performing drying, pressure bonding, and the like. As the binder, organic binders such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC) and the like. Are preferably used.

An enlarged schematic view of the electrode of the present invention is shown in FIG. 1 (a), and an enlarged schematic view of a conventional electrode is shown in FIG. 1 (b). In the conventional electrode 20, conductive auxiliary agent particles 22 such as carbon black aggregate and adhere to electrode active material particles 21 such as LiFePO _4, and are formed on the current collector 23 as a non-uniformly composited electrode material. Has been. On the other hand, in the electrode 10 of the present invention, the conductive auxiliary agent particles 12 are uniformly dispersed without being agglomerated with respect to the electrode active material particles 11, and are formed on the current collector 13 as a uniformly composited electrode material. Yes.
According to the electrode 10 of the present invention, the electrode active material particles 11 and the conductive auxiliary agent particles 12 are uniformly combined. Therefore, when used as a positive electrode of a lithium ion battery, the current density is excellent due to excellent conductivity. Therefore, it is possible to realize a lithium ion battery that is high and capable of high output.

EXAMPLES Hereinafter, although this invention is demonstrated concretely by Examples 1-3, Reference Examples 4, 5, and Comparative Examples 1-4, this invention is not limited by these Examples.

Example 1
14.25 g of LiFePO ₄ (manufactured by Sumitomo Osaka Cement), 0.75 g of carbon black (manufactured by Degussa) with an average primary particle diameter of 11 nm, 50 g of alumina balls with a diameter of 5 mm, and 22.5 g of toluene as a solvent, After ball milling for 12 hours, the solvent was evaporated to obtain an electrode material.
(Example 2)
It was produced in the same manner as in Example 1 using acetone as a solvent.
(Example 3)
It was prepared in the same manner as in Example 1 using acetonitrile as the solvent.
( Reference Example 4)
It was produced in the same manner as in Example 1 using 22.5 g of ethanol to which 37.5 mg of Adekathioace (manufactured by ADEKA) was added as a surfactant.
( Reference Example 5)
It was produced in the same manner as in Example 1 using 22.5 g of water to which 37.5 mg of Adekathioace (manufactured by ADEKA Corporation) was added as a surfactant.
(Comparative Example 1)
14.25 g of LiFePO ₄ and 0.75 g of carbon black were mixed to obtain an electrode material.
(Comparative Example 2)
14.25 g of LiFePO ₄ , 0.75 g of carbon black, and 50 g of alumina balls having a diameter of 5 mm were mixed and ball milled for 12 hours in a dry manner to obtain an electrode material.
(Comparative Example 3)
It was prepared in the same manner as in Example 1 using ethanol as the solvent.
(Comparative Example 4)
It was prepared in the same manner as in Example 1 using water as the solvent.

“Production of lithium-ion batteries”
The positive electrode active material slurry obtained in Example 1 was applied onto an aluminum (Al) foil having a thickness of 30 μm, then vacuum-dried using a vacuum dryer, and then pressure-bonded to form a positive electrode (positive electrode ). Subsequently, the lithium ion battery of Example 1 was produced using the 2016 coin type cell made from stainless steel (SUS) in dry Ar atmosphere.
Metal Li was used for the negative electrode, a porous polypropylene film was used for the separator, and a 1 mol / L LiPF6 solution was used for the electrolyte solution. As a solvent for this LiPF6 solution, a solvent having a ratio of ethylene carbonate to diethyl carbonate of 1: 1 was used.

In Example 2, 3, Reference Example 4, using 5 and Comparative Examples 1 to 4 each of the electrode material, in the same manner as the lithium ion battery of Example 1, Example 2, 3, Reference Example 4, 5 And each lithium ion battery of Comparative Examples 1-4 was produced.

And the discharge capacity when the discharge rate of each lithium ion battery was set to 0.1C, 1C, 2C, 3C, 5C and 8C was measured. The measurement results of Examples 1 to 3, Reference Examples 4 and 5, and Comparative Examples 1 to 4 are shown in Table 1 and FIG.

According to the measurement results shown in Table 1 and FIG. 2, in Comparative Examples 1 to 4, the discharge capacity decreases significantly as the discharge rate increases. In Examples 1 to 3 , even though the discharge rate increases. The decrease in discharge capacity is gradual, and the use of an electrode formed by the electrode material composite method of the present invention can realize a lithium ion battery with high current density and high output. confirmed.

For example, in this embodiment, metal Li is used for the negative electrode in order to reflect the behavior of the electrode material itself in the data. However, a negative electrode material such as a carbon material, a Li alloy, or Li ₄ Ti ₅ O ₁₂ may be used. . A solid electrolyte may be used instead of the electrolytic solution and the separator.

It is an expansion schematic diagram which shows the present invention and the conventional electrode notionally. It is a graph which shows the verification result of this invention.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 10 Electrode, 11 Electrode active material particle, 12 Conductive auxiliary agent particle, 13 Current collector, 20 Electrode, 21 Electrode active material particle, 22 Conductive auxiliary agent particle, 23 Current collector.

Claims (5)

Li _x Fe _y Me _1-y PO ₄ (where Me is Cu, Ce, Mn, Co, Ni, Cr, Mo, Nb, Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In , Si, Ge, Sc, Y and at least one selected from rare earth elements, an electrode active material represented by 0 <X <2, 0 <y <1), a conductive auxiliary agent, and a Hansen solubility parameter A composite method of electrode materials, characterized in that a solvent having a value of δ of less than 12.5 and a boiling point of 150 ° C. or less is mixed and pulverized by a wet method, and then the solvent is removed.   The electrode active material has an average particle diameter of 0.03 μm or more and 10 μm or less, and the conductive auxiliary agent has an average particle diameter of 0.001 μm or more and 0.1 μm or less. A composite method of the electrode material described.   The conductive assistant includes a carbon-based conductive material, and the content of the conductive assistant is 30 parts by weight or less with respect to 100 parts by weight of the electrode active material. The electrode material composite method. An electrode comprising the electrode material produced by the electrode material composite method according to any one of claims 1 to 3 . A lithium ion battery comprising the electrode according to claim 4 as a positive electrode.

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