JP6552788B2 - Electrode and lithium ion secondary battery using the same - Google Patents

Description

  The present invention relates to an electrode and a lithium ion secondary battery using the electrode.

Conventionally, LiCoO ₂ or LiN as a positive electrode material (positive electrode active material) of a lithium ion secondary battery
Li-based layered compounds such as i _1/3 Mn _1/3 Co _1/3 O ₂ and spinel compounds such as LiMn ₂ O ₄ have been used. In recent years, polyanionic compounds represented by LiFePO ₄ have attracted attention. It is known that polyanionic compounds have high thermal stability at high temperatures and high safety.

  In a polyanionic compound, electrons are strongly attracted to the tetrahedral skeleton of the crystal lattice, and metal atoms in the crystal lattice are isolated. Therefore, the electron conductivity of the polyanionic compound is lower than that of other common positive electrode active materials. Thus, in a lithium ion secondary battery using a polyanionic compound having a low electron conductivity as a positive electrode active material, a sufficient capacity relative to the theoretical capacity cannot be obtained, or a Li-based layered compound is used as a positive electrode active material. Compared with the case, there was a problem that the rate characteristic was lowered.

  Patent Document 1 discloses that lithium vanadium vanadium compounds, which are polyanionic compounds, improve rate characteristics by making the particle diameter smaller than conventional active material particles. However, by reducing the particle size, the specific surface area per unit weight of the active material also becomes relatively large, making it difficult to form an electrode. That is, when such an active material having a large specific surface area is used, the amount of adsorption of the resin component on the active material also increases compared to the conventional active material, and the viscosity of the coating liquid containing the active material increases. It is because it In addition, since the amount of resin adsorption is large, the binding property between the current collector and the active material is also reduced. Therefore, it is necessary to increase the ratio of the resin to improve the binding property with the current collector, but it is extremely difficult to densify the active material layer because the ratio of the active material decreases. The

    As an attempt to increase the density of the electrode, Patent Document 2 discloses a technique of monodispersing at the level of primary particles by performing roll press at the time of electrode formation using secondary particles that are easily crushed, Particularly in the case of an active material having a small particle diameter, monodispersion at the level of primary particles by roll pressing leads to a decrease in capacity due to a decrease in dispersibility of the conductive additive, and the rate characteristics also deteriorate.

JP 2004-303527 A JP 2004-192846 A

The present invention has been made in view of the above problems, and has as its object to provide a high-density electrode, to improve the capacity per volume, and to provide a lithium ion secondary battery with high rate characteristics.

In order to achieve the above object, in the electrode according to the present invention, a binder including a Li-M-P complex oxide, a conductive auxiliary agent, and a first resin is different from the first resin An active material layer dispersed in the second resin,
Furthermore, the first resin contains an acidic binder, and the second resin is made of polytetrafluoroethylene, styrene butadiene rubber, carboxymethyl cellulose, polyethylene, polypropylene, polyvinylidene fluoride, polyamide, polyamideimide, carboxymethyl cellulose salt, It contains at least one resin selected from the group. However, M includes one or more selected from the group of Fe, Mn, Co, Ni and VO.

According to the electrode, the Li-M-P composite oxide and the conductive additive are monodispersed by forming a binder composed of the Li-M-P composite oxide, the conductive additive and the first resin. Since higher density can be achieved than in the distribution state, and a path through which the electrolytic solution penetrates can be appropriately maintained, it is assumed that the battery has a high capacity and the rate characteristics are also good.

Moreover, according to the electrode which concerns, by using an acidic binder, stable and favorable electroconductivity can be maintained.

The acidic binder is at least one selected from the group consisting of polyacrylic acid, carboxymethylcellulose, a mixture of polyacrylic acid and polyacrylate, a mixture of polyacrylic acid and carboxymethylcellulose salt, and a mixture of carboxymethylcellulose and carboxymethylcellulose salt. It is preferable to contain a resin.

Moreover, it is preferable that the said acidic binder is 0.001 or more and 3 weight% or less with respect to the total weight of Li-MP composite oxide and a conductive support agent. Such a configuration is preferable because high conductivity can be obtained as an electrode.

The Li-M-P complex oxide preferably has an average primary particle diameter of LiVOPO ₄ of 30 to 300 nm.

According to this configuration, it is possible to expect not only excellent capacity and rate characteristics but also cycle characteristics as compared to those of coarse particle diameter.

  In the lithium ion secondary battery according to the present invention, the positive electrode, the separator, and the negative electrode are laminated in this order, the separator is impregnated with the electrolyte, and the positive electrode is Li-MP composite as described above. It is preferable to have an active material layer in which a binder including an oxide, a conductive support agent, and a first resin is dispersed in a second resin different from the first resin. By using such an electrode, a lithium ion secondary battery having high capacity and excellent rate characteristics can be obtained.

According to the electrode of the present invention, a high-density electrode can be obtained, a capacity per volume can be improved, and a lithium ion secondary battery with high rate characteristics can be provided.

It is a schematic cross section of a lithium ion secondary battery provided with the positive electrode active material layer containing the active material formed from the precursor which concerns on this embodiment. It is a scanning electron microscope (SEM) image of the electrode cross section concerning this embodiment. It is the image which binarized the scanning electron microscope (SEM) image of the electrode cross section which concerns on this embodiment. It is a scanning electron microscope (SEM) image of the binder which concerns on this embodiment.

The electrode according to the present embodiment is an active material in which a binder containing a Li-M-P composite oxide, a conductive additive and a first resin is dispersed in a second resin different from the first resin. It is an electrode provided with what applied the substance layer on the electrical power collector. The first resin contains an acidic binder, and the second resin is polytetrafluoroethylene, styrene butadiene rubber, carboxymethylcellulose, polyethylene, polypropylene, polyvinylidene fluoride, polyamide, polyamideimide, carboxymethylcellulose salt, And at least one resin selected from the group consisting of However, M includes one or more selected from the group of Fe, Mn, Co, Ni and VO.

Such an electrode can obtain a high-density active material layer with a good filling property by using a densely packed spherical and elliptical spherical particle binder as shown in FIG. 4.
The electrode has a cross-sectional structure as shown in FIG. That is, it has a structure in which the binder and the binder are provided with the second resin and the conductive aid, and the binder is also provided with the first resin and the conductive additive. The path consisting of the second resin and the conductive aid promotes the diffusion of the electrolytic solution and serves to fill the periphery of the binder with the electrolytic solution, and the path consisting of the first resin and the conductive aid constitutes the second electrolysis It becomes a diffusion path of the liquid, and lithium ions can be favorably moved in and out of the active material, and it is presumed that good rate characteristics are thereby exhibited.

(Li-MP complex oxide)
The Li-MP composite oxide is an oxide composed of lithium, phosphorus, and a metal designated M. Specifically, phosphate is preferable because it forms a chemically stable skeleton structure.

More specifically, the oxidation is represented by the general formula Li _a MPO ₄ (wherein a is 1 or 2 and M includes one or more selected from the group consisting of Fe, Mn, Co, Ni and VO). The thing is a stable structure and is preferable.
More specifically, oxides shown in the group of LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ , LiNiPO ₄ , LiVOPO ₄ and Li ₃ V ₂ (PO ₄ ) ₃ are more preferable.

  As an average primary particle diameter of such Li-M-P complex oxide, 30-300 nm is preferable.

In particular, LiVOPO ₄ having an average primary particle size of 30 to 300 nm is preferable. Excellent rate characteristics can be obtained by using such a material and having a particle diameter.

Here, when the particles have a particle diameter of 300 nm or more, the diffusion distance of lithium ions in the particles becomes long, so the conductivity may be low, and when the particle diameter is 30 nm or less, an electrolytic solution having a good capacity is obtained. It may react excessively and cycle characteristics may deteriorate.
The average primary particle diameter is more preferably in the range of 30 to 200 nm. According to such a configuration, the diffusion distance of lithium ions in the particles is further shortened, so the conductivity is improved.

  In addition, measurement of an average primary particle diameter can be measured by the existing method, and can be measured from the image obtained with a scanning electron microscope (SEM) and a transmission electron microscope (TEM).

(Conduction agent)
The conductive auxiliary agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black And conductive materials such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold etc.) powder, metal fiber, conductive ceramic material and the like. These conductive assistants may be used alone or a mixture thereof may be used.

  In particular, as a conductive additive, ketjen black is preferable from the viewpoint of electron conductivity. The addition amount of the conductive assistant is preferably 0.1% by weight to 50% by weight, and more preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode active material layer or the negative electrode active material layer.

(Current collector)
Iron, copper, stainless steel, nickel and aluminum can be used as the current collector of the electrode. Moreover, a sheet, a foam, a mesh, a porous body, an expanded lattice etc. can be used as the shape. Further, the current collector can be used with a hole formed in an arbitrary shape.

(First resin)
The first resin contains an acidic binder. The acidic binder is one or more resins selected from the group consisting of polyacrylic acid, carboxymethylcellulose, a mixture of polyacrylic acid and polyacrylate, a mixture of polyacrylic acid and carboxymethylcellulose salt, and a mixture of carboxymethylcellulose and carboxymethylcellulose salt. It is preferable to contain
The pH of the acidic binder is 2.5 to 6.5. The pH was evaluated by dispersing 0.5% by weight of an acidic binder in pure water and using a pH meter.

  The first resin is particularly preferably polyacrylic acid. According to this, it is preferable because the binding property is good and the electrode having good conductivity can be stably maintained.

  In particular, in LiVOPO4, since the pH is acidic, it is considered that the polyacrylic acid can be stably maintained even in an acidic environment.

  Further, the first resin and the above-described resins may be mixed and used. In particular, a combination of polyacrylic acid and polyacrylate, or a combination of polyacrylic acid and carboxymethylcellulose salt is preferable because an electrode having good conductivity can be obtained.

The acidic binder is preferably 0.001 wt% or more and 3 wt% or less with respect to the total weight of the Li-MP composite oxide and the conductive additive. Moreover, what is 0.001 to 0.5 weight% is more preferable. According to this, since the binding property is good and the coating amount by the resin is small, a binder having good conductivity can be produced.

According to this configuration, when it is less than 0.001% by weight, the binding property of the first resin tends to be reduced. On the other hand, when it is more than 3% by weight, the first resin may cover the Li-M-P complex oxide and the conductive additive thickly, and the rate characteristics may be deteriorated.

(Bound body)
A scanning electron microscope (SEM) image of the binder according to the present embodiment is shown in FIG. As shown in the SEM image, the active material, the Li-M-P complex oxide and the conductive auxiliary agent are in the form of granulated particles which are combined and bound at a high density.

The average particle size of such a binder is preferably 1 to 50 μm. According to this, when the average particle diameter is in the range of 1 to 50 μm, a flat active material layer can be coated on the current collector. An average particle size of 1 to 20 μm is more preferable because it can be applied with good filling properties.

  The particle size of the binder can be measured from an image obtained with a laser diffraction particle size distribution measuring device or a scanning electron microscope (SEM).

(Second resin)
The second resin contains at least one resin selected from the group consisting of polytetrafluoroethylene, styrene butadiene rubber, carboxymethyl cellulose, polyethylene, polypropylene, polyvinylidene fluoride, polyamide, polyamideimide, and carboxymethyl cellulose salt. Is preferred.

(electrode)
A layer (active material layer) in which the above-described binder is dispersed in the second resin is formed on the current collector to complete an electrode as a positive electrode.

(Lithium ion secondary battery)
Next, the configuration of the lithium ion secondary battery will be described with reference to FIG.

As shown in FIG. 1, the lithium ion secondary battery 100 according to this embodiment is disposed adjacent to each other between the plate-like negative electrode 20 and the plate-like positive electrode 10 facing each other, and between the negative electrode 20 and the positive electrode 10. A plate-shaped separator 18, an electrolyte containing lithium ions, a case 50 for containing these in a sealed state, and one end electrically connected to the negative electrode 20 and the other And a positive electrode lead 62 having one end electrically connected to the positive electrode 10 and the other end protruding outside the case.

  The negative electrode 20 has a negative electrode current collector 22 and a negative electrode active material layer 24 formed on the negative electrode current collector 22. The positive electrode 10 includes a positive electrode current collector 12 and a positive electrode active material layer 14 formed on the positive electrode current collector 12. The separator 18 is located between the negative electrode active material layer 24 and the positive electrode active material layer 14.

  In addition, the shape of a lithium ion secondary battery is not limited to what is shown in FIG. For example, the shape of the lithium ion secondary battery may be square, oval, coin, button, sheet or the like.

  The positive electrode active material layer 14 contains, as a positive electrode active material, a binder composed of the above-described Li-MP composite oxide, the first resin, and a conductive additive.

  On the other hand, the negative electrode active material layer 24 similarly contains a negative electrode active material and a resin to be a binder.

  In addition, the positive electrode active material layer 14 and the negative electrode active material layer 24 may further contain a thickener, a filler, and the like.

(Anode active material)
Any negative electrode active material may be selected as long as it can precipitate or occlude lithium ions. For example, titanium-based materials such as lithium titanate having a spinel-type crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy materials such as Si, Sb, and Sn-based materials lithium metal, lithium alloy (Lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), silicon oxide Other than the above, alloys capable of absorbing and desorbing lithium, carbon materials (eg, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) and the like can be mentioned.

(Electrolytes)
As the electrolyte, those generally proposed for use in lithium batteries and the like can be used. The nonaqueous solvent used for the electrolyte includes cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate and diethyl carbonate Chain carbonates such as ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate, methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, Ethers such as 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Etc. can be mentioned alone or a mixture of two or more thereof, but it is not limited thereto.

Furthermore, a crystalline or amorphous inorganic solid electrolyte can be used as the solid electrolyte. The inorganic solid electrolyte _{crystalline, LiI, Li 3 N, Li} 1 + x M x Ti 2-x (PO 4) 3 (M = Al, Sc, Y, La), Li 0.5-3x R 0.5 + x A thio-LISICON represented by TiO ₃ (R = La, Pr, Nd, Sm), or Li _4-x Ge _1-x P _x S ₄ can be used. The amorphous inorganic solid _{electrolyte, LiI-Li 2 O-B} 2 O 5 _system, Li ₂ O-SiO 2 _{system, LiI-Li 2 S-B} 2 S 3 _{type, LiI-Li 2 S-SiS} 2 System, Li ₂ S—SiS ₂ —Li ₃ PO ₄ system, or the like can be used.

Examples of the electrolyte salt used for the electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO. ₄ , inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K), such as KSCN, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO _{2 ) 2, LiN (CF 3 SO} 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3, (CH 3) 4 NBF 4, (CH 3 _{) 4 NBr, (C 2 H} 5) 4 NClO 4, (C 2 H 5) 4 NI, (C 3 H 7) 4 NBr, (n-C 4 H 9 _{4 NClO 4, (n-C} 4 H 9) 4 NI, (C 2 H 5) 4 N-maleate, (C 2 H 5) 4 N-benzoate, (C 2 H 5) 4 N-phtalate, stearyl sulfonate And organic ion salts such as lithium octylate, lithium octylsulfonate and lithium dodecylbenzene sulfonate. These ionic compounds can be used alone or in admixture of two or more.

  Moreover, you may use normal temperature molten salt or an ionic liquid for electrolyte.

  The concentration of the electrolyte salt in the electrolyte is preferably 0.1 mol / l to 5 mol / l, and more preferably 0.5 mol / l to 2.5 mol / l. Thereby, a lithium ion secondary battery having high battery characteristics can be obtained.

(Separator)
As the separator, it is preferable to use, alone or in combination, a porous film, a non-woven fabric or the like exhibiting excellent air permeability performance. Examples of the constituent materials include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, and fluorine. Vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer Polymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene- Hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the lithium ion secondary battery separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

  Further, as a lithium ion secondary battery separator, for example, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte may be used. Use of a nonaqueous electrolyte in a gel state has an effect of preventing leakage.

(Lead)
The leads 60 and 62 are made of a conductive material such as aluminum.

(Case)
The case 50 seals the laminated body 30 and the electrolytic solution therein. The case 50 is not particularly limited as long as it can prevent leakage of the electrolytic solution to the outside, intrusion of moisture and the like from the outside into the lithium ion secondary battery 100, and the like. For example, as the case 50, as shown in FIG. 1, a metal laminate film in which both sides of a metal foil are coated with a polymer film can be used. For example, aluminum foil can be used as the metal foil, and a film such as polypropylene can be used as the polymer film. For example, a high melting point polymer such as polyethylene terephthalate (PET) or polyamide is preferable as the material of the outer polymer film, and polyethylene (PE), polypropylene (PP) or the like is preferable as the material of the inner polymer film. preferable.

  As mentioned above, although this embodiment was described, the electrode of this embodiment can be used also as an electrode of electrochemical elements other than a lithium ion secondary battery. As such an electrochemical element, other than lithium ion secondary batteries such as metal lithium secondary batteries (using the electrode containing the active material obtained by the present invention as a positive electrode and using metallic lithium as a negative electrode) Examples include secondary batteries and electrochemical capacitors such as lithium capacitors. These electrochemical elements can be used for power sources such as self-propelled micromachines and IC cards, and distributed power sources arranged on or in a printed circuit board.

(Production method of binder)
Next, an example of the manufacturing method of the electrode of this embodiment and a lithium ion secondary battery is shown. The binder is a powder obtained by mixing in advance a Li-M-P complex oxide and a conductive auxiliary, and charged into pure water or an organic solvent dissolved or dispersed in pure water or an organic solvent, and this Li-M-P complex oxidation It is obtained by drying the slurry solution which consists of a thing, a conductive support agent, the 1st resin, a pure water, or an organic solvent.
As a drying method, a spray dryer method is preferable.

Also, the binder may be prepared by spraying pure water or an organic solvent dissolved or dispersed with an organic solvent to the powder in which the Li-M-P complex oxide and the conductive additive are previously mixed in a dry state. can get. As such a granulation method by spraying, a fluidized bed method or a rolling granulation method is preferable. In addition, you may produce with the general granulation method other than having shown above. Furthermore, a step of drying pure water or an organic solvent may be added to the binder.

(Method of manufacturing electrode)
Thereafter, the obtained binder and the second resin were appropriately selected from organic solvents such as N-methylpyrrolidone, toluene and pure water as a solvent not dissolving the first resin, and these were mixed. Thereafter, the obtained mixed solution is applied onto a current collector, pressure-bonded, and heat-treated at a temperature of about 50 ° C. to about 250 ° C. for about 2 hours to produce an electrode.

  In addition, about the application | coating method on a collector, it applies to arbitrary thickness and arbitrary shapes using means, such as roller coating, such as an applicator roll, screen coating, a doctor blade system, spin coating, and a bar coater, for example. However, it is not limited to these.

(Method of manufacturing lithium ion secondary battery)
The electrode, which is the positive electrode produced in this manner, and the negative electrode produced by the same method are enclosed in a case 50 together with a separator and an electrolytic solution so as to form a lithium ion secondary battery as shown in FIG. Do.

  The preferred embodiments of the active material, the electrode, and the lithium ion secondary battery of the present invention have been described in detail above, but the present invention is not limited to the above embodiments.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
Bonding body preparation process
Mixing the LiVOPO ₄ powder and Ketjen black, by spraying the acidic binder using a fluidized bed, to prepare a binder body. The acidic binder used as the binder (first resin) was prepared by dissolving polyacrylic acid in pure water. Compressed air was used for the airflow in the fluidized bed, and the temperature of the airflow was 80 ° C. The binder was added 0.05 wt% relative to the amount of the sum of the LiVOPO ₄ powder and conductive auxiliary agent. It was 3 when the pH of the aqueous solution which melt | dissolved PAA in the pure water was measured. The produced binder was the SEM image shown in FIG.
The average primary particle size of LiVOPO ₄ powder was confirmed to be 180nm with a transmission electron microscope (TEM) images. 20 or more the average particle diameter is an average primary particle diameter of LiVOPO ₄ powder.

<Coating process>
A slurry obtained by dispersing the binder, a binder (second resin) polyvinylidene fluoride (PVDF), and acetylene black in N-methyl-2-pyrrolidone (NMP) as a solvent. Prepared. The slurry was prepared so that the weight ratio of the combination of the binder and ketjen black in the slurry and the combination of the first resin and PVDF was 92: 8. The slurry was applied onto an aluminum foil as a current collector, dried, and rolled at 1 ton / cm to obtain an electrode (positive electrode) on which the active material layer of Example 1 was formed.

  The rolled electrode was punched to 3 × 5 cm and the weight was evaluated. The thickness of the electrode was examined at 15 points using a micrometer, and the average value was taken as the thickness of the electrode. The electrode density was calculated from the shape, thickness and weight. Similarly, ten samples were prepared, and the average value was taken as the electrode density. Moreover, it confirmed that the produced electrode had a cross-sectional structure as shown in FIG. Further, the SEM image shown in FIG. 2 was binarized and shown as FIG. 3 and it was confirmed by rolling that the granulated body did not completely collapse and existed as spherical and elliptical spheres.

Next, the obtained electrode and Li foil as the counter electrode were laminated with a separator made of a polyethylene microporous membrane interposed therebetween, to obtain a laminate (element body). The laminate was placed in an aluminum laminate pack, and a 1 M LiPF ₆ solution as an electrolyte solution was injected into the aluminum laminate pack, followed by vacuum sealing to prepare a cell for evaluation.

  The evaluation cell was evaluated with a charge / discharge test apparatus. The value obtained by normalizing the 1 C discharge capacity with the 0.1 C discharge capacity is shown in Table 1 as a rate characteristic.

(Example 2)
A binder of Example 2 was prepared in the same manner as in Example 1 except that the binder was a mixture of polyacrylic acid (80% by weight) and carboxymethylcellulose (20% by weight) in the binder preparation step. did.

(Example 3)
The binder of Example 3 in the same manner as in Example 1 except that the binder was a mixture of polyacrylic acid (80% by weight) and sodium polyacrylate (20% by weight) in the binder preparation step. Was produced.

(Example 4)
The binder of Example 4 was prepared in the same manner as in Example 1 except that the binder was a mixture of polyacrylic acid (80% by weight) and sodium carboxymethylcellulose (20% by weight) in the binder preparation step. Made.

(Example 5)
A binder of Example 5 was produced in the same manner as in Example 1 except that 0.01 wt% of the binder was added in the binder preparation step.

(Example 6)
A binder of Example 6 was prepared in the same manner as in Example 1 except that 0.5 wt% of the binder was added in the binder preparation step.

(Example 7)
A binder of Example 7 was prepared in the same manner as in Example 1 except that 1% by weight of the binder was added in the binder preparation step. By increasing the amount of the binder, the strength of the binder is improved as compared with Example 1, and the binder is less likely to be broken by rolling.

(Example 8)
A binder of Example 8 was prepared in the same manner as in Example 1 except that 0.005% by weight of a binder was added in the binder preparation step.

(Example 9)
A binder was prepared in the same manner as in Example 1 except that 0.001 wt% of the binder was added in the binder preparation step.

(Example 10)
A binder of Example 9 was prepared in the same manner as in Example 1 except that 3% by weight of the binder was added in the binder preparation step. By increasing the amount of the binder, the strength of the binder is improved as compared with Example 1, and the binder is less likely to be broken by rolling.

(Comparative example 1)
In the binder preparation step, the binder of Comparative Example 1 was prepared in the same manner as in Example 1 except that the binder was a mixture of sodium carboxymethylcellulose (80 wt%) and styrene butadiene rubber (20 wt%). Made. The rate characteristics were lower than in Example 1.

The electrode densities of the samples produced in Examples 2 to 10 and Comparative Example 1 and the values obtained by standardizing the discharge capacity of 1 C with a discharge capacity of 0.1 C in the same manner as Example 1 are shown in Table 1.
The rate characteristics were good at 80% or more, and the electrode density was good at 2.35 g / cc or more.
[Table 1]

10: positive electrode, 20: negative electrode, 12: positive electrode current collector, 14: positive electrode active material layer, 18: separator, 22: negative electrode current collector, 24: negative electrode Active material layer, 30: power generation element, 50: case, 60, 62: lead, 100: lithium ion secondary battery, A: binder

Claims (5)

It has an active material layer in which a binder containing a Li-MP composite oxide, a conductive additive, and a first resin is dispersed in a second resin different from the first resin. Yes,
The first resin contains an acidic binder,
The second resin contains at least one resin selected from the group consisting of polytetrafluoroethylene, styrene butadiene rubber, carboxymethyl cellulose, polyethylene, polypropylene, polyvinylidene fluoride, polyamide, polyamideimide, and carboxymethyl cellulose salt. The electrode characterized by the above (However, M contains 1 or more types selected from the group of Fe, Mn, Co, Ni, and VO.). The acidic binder is a resin selected from the group consisting of polyacrylic acid, carboxymethylcellulose, a mixture of polyacrylic acid and polyacrylate, a mixture of polyacrylic acid and carboxymethylcellulose salt, and a mixture of carboxymethylcellulose and carboxymethylcellulose salt. The electrode according to claim 1, comprising at least one kind of resin. The said acidic binder is 0.001 or more and 3 weight% or less with respect to the weight of the sum total of Li-M-P complex oxide and a conductive support agent, The electrode of Claim 1 or 2 characterized by the above-mentioned. . The Li-M-P composite oxide electrode according to any one of claims 1 to 3 having an average primary particle size is characterized by comprising a LiVOPO ₄ of 30 to 300 nm.   A positive electrode, a separator, and a negative electrode are laminated in this order, the separator is impregnated with an electrolyte, and the positive electrode is an electrode according to any one of claims 1 to 4. Lithium ion secondary battery.