JP6943564B2 - Positive electrode for lithium ion secondary battery and its manufacturing method, and lithium ion secondary battery - Google Patents

Description

The present invention relates to a positive electrode for a lithium ion secondary battery, a method for manufacturing the same, and a lithium ion secondary battery.

In recent years, lithium ion secondary batteries have come to be widely used in various applications, and recently, from the viewpoint of reducing the environmental load and the like, they have been widely used in applications such as EV and HEV. In such applications as EVs and HEVs, further increase in capacity of lithium ion secondary batteries is required for the purpose of extending the cruising distance.

As a means for improving the performance such as increasing the capacity, for example, in Patent Document 1, a lithium transition metal composite oxide such as _{LiNi 0.35} Co _0.35 Mn _0.3 O _{2 is used for the positive electrode.} A non-aqueous electrolyte _{secondary battery in which LiPF 2} O ₂ is added to the non-aqueous electrolyte is disclosed. In the secondary battery of Patent Document 1, it is preferable that the binder is made of PVdF-CTFE and an _{inorganic filler layer made of Al 2} O ₃ , BaTiO _3, or the like is formed on at least one of the separators. _{Further, by adding LiPF 2} O ₂ to the non-aqueous electrolyte, it is possible to mainly improve the discharge characteristics at low temperature.

Further, Patent Document 2 describes for a positive electrode of a lithium ion secondary battery based on a compound having a polyanionic skeleton in which the content of a CNT type conductive additive is as low as 1 to 2.5%. Composite materials are disclosed. By using this composite material, it is said that a lithium ion secondary battery can be provided with a large capacity and excellent charge / discharge cycle characteristics at a high current density.

Here, a lithium transition metal composite oxide containing nickel (Ni) as a main component (hereinafter, also referred to as "high nickel-based composite oxide") is a positive electrode active material that realizes a relatively high potential and a high capacity. It has received a lot of attention in recent years. Therefore, various positive electrode active materials using high nickel-based composite oxides have been proposed.

By increasing the density of the thick film of the electrode active material layer, it is possible to reduce the parts that do not contribute to the battery capacity, such as the current collector and the separator, so that the capacity can be further increased.

Japanese Unexamined Patent Publication No. 2012-177496 Japanese Unexamined Patent Publication No. 2012-500288

However, if the positive electrode active material layer using the high nickel-based composite oxide as the positive electrode active material as described above is simply thickened without changing the composition, the electron conductivity in the vicinity of the electrode surface may be lacking or Ion conductivity inside the electrode is lacking. Therefore, there are problems that the charge / discharge capacity at a high rate is lacking and the charge / discharge cycle characteristics are also deteriorated.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to increase the charge / discharge capacity at a high rate even when the positive electrode active material layer is thickened. It is an object of the present invention to provide a new and improved positive electrode for a lithium ion secondary battery, a method for manufacturing the same, and a lithium ion secondary battery capable of minimizing a decrease and improving charge / discharge cycle characteristics.

In order to solve the above problems, according to a certain viewpoint of the present invention, lithium (Li) and nickel (Ni) are contained as constituent elements, and nickel atoms are contained in the total number of all metal atoms other than lithium. For a lithium ion secondary battery, which contains a lithium transition metal composite oxide contained in a proportion of 70 atomic% or more as a positive electrode active material, and further contains a binder, a conductive auxiliary agent, and a liquid P-CTFE. A positive electrode is provided.

From this point of view, a liquid (low molecular weight) polychlorotrifluoroethylene (P-CTFE) in a positive electrode containing a lithium transition metal composite oxide (high nickel-based composite oxide) containing nickel as a main component as a positive electrode active material. ) Is contained, so even when the positive electrode active material layer is thickened to a high density, the decrease in charge / discharge capacity at high rates of the lithium ion secondary battery provided with this positive electrode is minimized, and the charge / discharge cycle The characteristics can be improved.

Here, the lithium transition metal composite oxide may be one represented by the following general formula (1).

_{Li a Ni x Co y M z} O 2 ··· (1)

In formula (1), M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), gallium (Mg), titanium (Ti), zirconium (Zr), niobium. Consists of (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lantern (La) and cerium (Ce). One or more metal elements selected from the group. Further, in the formula (1), a, x, y, and z are 0.20 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, 0.00 <y ≦ 0.20, 0.00. It is a value within the range of ≦ z ≦ 0.10. And x + y + z = 1.

From this point of view, the positive electrode for a lithium ion secondary battery minimizes a decrease in charge / discharge capacity at a high rate of the lithium ion secondary battery provided with this positive electrode even when the positive electrode active material layer is thickened and densely formed. , The charge / discharge cycle characteristics can be improved.

Further, the average molecular weight of P-CTFE may be 450 or more and 1000 or less.

From this point of view, the positive electrode for a lithium ion secondary battery minimizes a decrease in charge / discharge capacity at a high rate of the lithium ion secondary battery provided with the positive electrode even when the positive electrode active material layer is thickened and densely formed. The effect and the effect of improving the charge / discharge cycle characteristics can be further enhanced.

Further, the content of P-CTFE may be 0.2% by mass or more and 1.0% by mass or less based on the total mass of the positive electrode before contact with the electrolytic solution.

From this point of view, the positive electrode for a lithium ion secondary battery minimizes a decrease in charge / discharge capacity at a high rate of the lithium ion secondary battery provided with the positive electrode even when the positive electrode active material layer is thickened and densely formed. The effect and the effect of improving the charge / discharge cycle characteristics can be further enhanced.

According to another aspect of the present invention, lithium (Li) and nickel (Ni) are contained as constituent elements, and nickel atoms are contained in a ratio of 70 atomic% or more with respect to the total number of all metal atoms other than lithium. A step of preparing a positive electrode slurry containing a lithium transition metal composite oxide containing the mixture as a positive electrode active material and further containing a binder, a conductive auxiliary agent and a liquid P-CTFE, and coating and drying the positive electrode slurry on a current collector. Provided is a method for manufacturing a positive electrode for a lithium ion secondary battery, which comprises a step of forming a positive electrode active material layer.

From this point of view, a liquid (low molecular weight) polychlorotrifluoroethylene (P-) in a positive electrode slurry containing a lithium transition metal composite oxide (high nickel-based composite oxide) containing nickel as a main component as a positive electrode active material. Since CTFE) is added, even when the positive electrode active material layer is thickened and densely formed, the charge / discharge capacity at a high rate of the lithium ion secondary battery provided with the positive electrode manufactured using this manufacturing method. It is possible to minimize the decrease in charge and discharge cycle characteristics and improve the charge / discharge cycle characteristics.

Here, the lithium transition metal composite oxide may be one represented by the following general formula (1).

_{Li a Ni x Co y M z} O 2 ··· (1)

In formula (1), M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), gallium (Mg), titanium (Ti), zirconium (Zr), niobium. Consists of (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lantern (La) and cerium (Ce). One or more metal elements selected from the group. Further, in the formula (1), a, x, y, and z are 0.20 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, 0.00 <y ≦ 0.20, 0.00. It is a value within the range of ≦ z ≦ 0.10. And x + y + z = 1.

From this point of view, the method for manufacturing a positive electrode for a lithium ion secondary battery is a high rate of a lithium ion secondary battery provided with a positive electrode manufactured by this manufacturing method even when the positive electrode active material layer is thickened and densely formed. It is possible to minimize the decrease in charge / discharge capacity and improve the charge / discharge cycle characteristics.

Further, the average molecular weight of P-CTFE may be 450 or more and 1000 or less.

From this point of view, the method for manufacturing a positive electrode for a lithium ion secondary battery is a high rate of a lithium ion secondary battery provided with a positive electrode manufactured by this manufacturing method even when the positive electrode active material layer is thickened and densely formed. The effect of minimizing the decrease in charge / discharge capacity and the effect of improving the charge / discharge cycle characteristics can be further enhanced.

Further, P-CTFE may be added in an amount of 0.2% by mass or more and 1.0% by mass or less with respect to the total mass of the solid content of the positive electrode slurry.

From this point of view, the method for manufacturing a positive electrode for a lithium ion secondary battery is a high rate of a lithium ion secondary battery provided with a positive electrode manufactured by this manufacturing method even when the positive electrode active material layer is thickened and densely formed. The effect of minimizing the decrease in charge / discharge capacity and the effect of improving the charge / discharge cycle characteristics can be further enhanced.

According to another aspect of the present invention, the above-mentioned positive electrode for a lithium ion secondary battery, a negative electrode, and a separator layer provided between the positive electrode and the negative electrode and containing a separator and an electrolytic solution are provided. Lithium ion secondary batteries are provided.

Since the lithium ion secondary battery from this point of view includes the positive electrode for the lithium ion secondary battery described above, even when the positive electrode active material layer is thickened, the decrease in charge / discharge capacity at a high rate is minimized. It is possible to improve the charge / discharge cycle characteristics.

Here, P-CTFE may be present in at least one of the positive electrode for the lithium ion secondary battery and the electrolytic solution.

In the lithium ion secondary battery from this viewpoint, when the positive electrode for the lithium ion secondary battery comes into contact with the electrolytic solution, P-CTFE existing in the binder of the positive electrode is eluted and dispersed in the electrolytic solution. Therefore, the electrolyte retention property of the portion (poros) where the P-CTFE is removed from the binder is enhanced, and the ionic conductivity is improved.

As described above, according to the present invention, a liquid (low molecular weight) polychlorotrifluoroethylene (P-CTFE) is contained in a positive electrode containing a lithium transition metal composite oxide containing nickel as a main component as a positive electrode active material. By doing so, even when the positive electrode active material layer is thickened and densely formed, it is possible to minimize the decrease in charge / discharge capacity at a high rate and improve the charge / discharge cycle characteristics.

It is explanatory drawing which shows the schematic structure of the lithium ion secondary battery which concerns on embodiment of this invention. It is a graph which shows the Core-Cole plot of Examples 2, 3 and Comparative Example 1.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

<Structure of lithium-ion secondary battery>
Hereinafter, a specific configuration of the lithium ion secondary battery 10 according to the above-described embodiment of the present invention will be described with reference to FIG. FIG. 1 is an explanatory diagram illustrating a configuration of a lithium ion secondary battery according to an embodiment of the present invention.

As shown in FIG. 1, the lithium ion secondary battery 10 includes a positive electrode 20, a negative electrode 30, and a separator layer 40. The form of the lithium ion secondary battery 10 is not particularly limited. For example, the lithium ion secondary battery 10 may be any of a cylindrical shape, a square shape, a laminate type, a button type, and the like.

(Positive electrode)
The positive electrode 20 includes a current collector 21 and a positive electrode active material layer 22. The current collector 21 is made of a conductive material such as aluminum.

The positive electrode active material layer 22 contains at least a positive electrode active material, a conductive auxiliary agent, a binder, and liquid polychlorotrifluoroethylene (P-CTFE).

The positive electrode active material according to the present embodiment is a lithium transition metal composite oxide containing lithium (Li) and nickel (Ni) as constituent elements and Ni as a main constituent element. As described above, the high nickel-based composite oxide used as the positive electrode active material in the present embodiment is a positive electrode active material that realizes a relatively high potential and a high capacity. Specifically, the positive electrode active material according to the present embodiment is a high nickel-based composite containing nickel atoms at a ratio of 70 atomic% or more with respect to (the total number of atoms) of all metal atoms other than lithium in the positive electrode active material. It is an oxide. The composition of the positive electrode active material is represented by, for example, the following general formula (1).

_{Li a Ni x Co y M z} O 2 ··· (1)

In formula (1), M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), gallium (Mg), titanium (Ti), zirconium (Zr), niobium. Consists of (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lantern (La) and cerium (Ce). One or more metal elements selected from the group.

Further, in the formula (1), a, x, y, and z are 0.20 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, 0.00 <y ≦ 0.20, 0.00. It is a value within the range of ≦ z ≦ 0.10. And x + y + z = 1.

The content of the positive electrode active material in the positive electrode active material layer 22 is not particularly limited, and may be any content as long as it is applied to the positive electrode active material layer of the conventional lithium ion secondary battery.

Examples of the conductive auxiliary agent include carbon black such as ketjen black and acetylene black, natural graphite, and artificial graphite. The conductive auxiliary agent is not particularly limited as long as it is for increasing the conductivity of the positive electrode. The content of the conductive auxiliary agent is not particularly limited, and may be any content as long as it is applied to the positive electrode active material layer of the lithium ion secondary battery.

Binders include, for example, polyvinylidene fluoride difluoride, ethylene propylene diene ternary copolymer (ethylene-propylene-diene polymer), styrene butadiene rubber (styrene-butadiene rubber rubber), and acrylic nitrile rubber. Fluoro rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose and the like. The binder is not particularly limited as long as it can bind the positive electrode active material and the conductive auxiliary agent on the current collector 21. The binder content is not particularly limited, and may be any content as long as it is applied to the positive electrode active material layer of the lithium ion secondary battery.

The liquid P-CTFE contained in the positive electrode active material layer 22 is a polymer or oligomer represented by the following structural formula (2) and having a low molecular weight.

According to the investigation by the present inventors, a conductive auxiliary agent is obtained by adding a liquid (low molecular weight) P-CTFE to a positive electrode slurry containing a high nickel-based composite oxide as a positive electrode active material as described above. The reduction in conductivity can be minimized by adding the minimum amount of conductive auxiliary agent even in the electrode (positive electrode 20 in this embodiment) having improved dispersibility and thick film density. It has been found that the decrease in charge / discharge capacity at high rates can be minimized. Further, in the lithium ion secondary battery 10, when the positive electrode 20 comes into contact with the electrolytic solution described later, P-CTFE existing in the binder is eluted and dispersed in the electrolytic solution. Therefore, it is presumed that the electrolyte retention property of the portion (poros) where P-CTFE is removed from the binder is enhanced, and the ionic conductivity is improved. As a result, it was found that the charge / discharge cycle characteristics of the lithium ion secondary battery were improved.

In Patent Document 1, the liquid P-CTFE in the present embodiment is not used, only the PVDF-CTFE copolymer is used as the binder. The positive electrode active material used in Patent Document 1 is LiNi _0.35 Co _0.35 Mn _0.3 O _2, etc., which is different from the high nickel-based composite oxide used in the present embodiment. Further, in Patent Document 2, it is described that a PVDF-CTFE copolymer is used as a binder as in Patent Document 1, but it is described that a liquid P-CTFE as in the present embodiment is separately added. It has not been. In Patent Document 2, as a positive electrode active material, a compound having a different LiM y _{(XO z) n} type polyanionic skeleton to the present embodiment is used.

In particular, in order to more effectively exhibit the effect of minimizing the decrease in charge / discharge capacity at the high rate, the average molecular weight of liquid (low molecular weight) P-CTFE is 450 or more, preferably 500 or more, 1000. The following is preferable. If the average molecular weight of P-CTFE is larger than 1000, there is a concern that the fluidity at room temperature will be significantly lacking. The average molecular weight of P-CTFE is more preferably 650 or more, and even more preferably 850 or more. The average molecular weight in this embodiment is a weight average molecular weight, which is a value measured by a mass spectrometer.

Further, in order to more effectively exhibit the effect of minimizing the decrease in charge / discharge capacity at the high rate, the positive electrode 20 before the content of the liquid (low molecular weight) P-CTFE comes into contact with the electrolytic solution is 20. It is preferable that it is 0.2% by mass or more and 1.0% by mass or less based on the total mass of. If the content of P-CTFE is more than 1.0% by mass, there is a concern that the discharge capacity of the lithium ion secondary battery 10 will decrease.

As described above, the average molecular weight of the liquid (low molecular weight) P-CTFE is 450 or more, preferably 500 or more and 1000 or less, and the liquid (low molecular weight) P-CTFE is 0.2% by mass or more and 1 By containing 0.0% by mass or less, even when the positive electrode active material layer 22 is thickened and densely formed, the charge / discharge efficiency is rather improved without reducing the battery capacity of the lithium ion secondary battery 10. be able to. As shown in Examples described later, when the average molecular weight of P-CTFE is 500 or more and less than 700, P-CTFE is 0.5% by mass or more in order to improve the load characteristics (capacity retention rate, etc.). It is preferable to include it.

Here, P-CTFE may be present in either the positive electrode 20 or the electrolytic solution, that is, it may be present in at least one of the positive electrode 20 and the electrolytic solution, but the above-mentioned performance ( In order to exhibit the performance of minimizing the decrease in charge / discharge capacity at a high rate), it is necessary that P-CTFE is first present in the electrode slurry of the positive electrode 20.

The positive electrode active material layer 22 is, for example, a slurry in which a positive electrode active material, a conductive auxiliary agent, and a binder are dispersed in a suitable organic solvent (for example, N-methyl-2-pyrrolidone). ) Is coated on the current collector 21, dried and rolled.

(Negative electrode)
The negative electrode 30 includes a current collector 31 and a negative electrode active material layer 32. The current collector 31 is made of, for example, copper, nickel, or the like.

The negative electrode active material layer 32 may be any material as long as it is used as the negative electrode active material layer of the lithium ion secondary battery. For example, the negative electrode active material layer 32 contains a negative electrode active material and may further contain a binder. The negative electrode active material is, for example, graphite active material (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), silicon (Si) or tin (Sn), or an oxide thereof. Mixtures of fine particles and graphite active material, fine particles of silicon or tin, alloys based on silicon or tin, titanium oxide (TiO _x ) compounds such as _{Li 4} Ti ₅ O _{12 and the like can be used.} .. The oxide of silicon is represented by SiO _x (0 ≦ x ≦ 2). In addition to these, as the negative electrode active material, for example, metallic lithium or the like can be used.

Further, as the binder, the same binder as that constituting the positive electrode active material layer 22 can be used. The mass ratio of the negative electrode active material to the binder is not particularly limited, and the mass ratio adopted in the conventional lithium ion secondary battery can be applied in the present invention.

(Separator layer)
The separator layer 40 is provided between the positive electrode 20 and the negative electrode 30, and includes a separator and an electrolytic solution.

The separator according to the embodiment of the present invention is not particularly limited. Any separator body according to an embodiment of the present invention can be used as long as it is used as a separator for a lithium ion secondary battery. For example, as the separator, it is preferable to use a porous membrane, a non-woven fabric, or the like exhibiting excellent high-rate discharge performance alone or in combination. Examples of the material constituting the separator include a polyolefin-based resin typified by polyethylene (polymer), polypropylene (polymer), polyethylene terephthalate, polybutylene terephthalate, and the like. Polyester-based resin, polyvinylidene difluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, fluoride. (Tetrafluoroothylene) polymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, fluoride. Vinylidene-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropolymer copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer , Vinylidene fluoride-ethylene-tetrafluoroethylene copolymer and the like can be used. The porosity of the separator is not particularly limited, and the porosity of the separator of the lithium ion secondary battery can be arbitrarily applied.

Further, the separator may have a coating layer containing an inorganic filler. Specifically, the coating layer may contain at least one of _{Mg (OH) 2 and} Al ₂ O _{3 as an inorganic filler.} According to this configuration, the coating layer containing the inorganic filler prevents the positive electrode and the separator from coming into direct contact with each other, so that the electrolytic solution generated on the surface of the positive electrode during high-temperature storage is prevented from being oxidized and decomposed, and the electrolytic solution is decomposed and generated. It is possible to suppress the generation of gas, which is a substance.

Here, the coating layer containing the inorganic filler may be formed on both sides of the separator, or may be formed only on one side of the separator on the positive electrode side. If the coating layer containing the inorganic filler is formed at least on the positive electrode side, direct contact between the positive electrode and the electrolytic solution can be prevented.

Further, the present invention is not limited to the above examples. For example, the coating layer containing the inorganic filler may be formed on the positive electrode instead of on the separator. In such a case, the coating layer containing the inorganic filler can be formed on both sides of the positive electrode to prevent direct contact between the positive electrode and the separator. Needless to say, the coating layer containing the inorganic filler may be formed on both the positive electrode and the separator.

As the electrolytic solution, the same non-aqueous electrolytic solution conventionally used for a lithium secondary battery can be used without particular limitation. Here, the electrolytic solution has a composition in which an electrolyte salt is contained in a non-aqueous solvent. Examples of the non-aqueous solvent include propylene carbonate (propylene carbonate), ethylene carbonate (etherylene carbonate), butylene carbonate (butyrene carbonate), chloroethylene carbonate (chloroethylene carbonate), vinylene carbonate (vinylene carbonate), and the like. ) Classes; cyclic esters such as γ-butyrolactone and γ-valerolactone; chains of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like. Carbonates; Chain esters such as methyl formate, methyl acetate, methyl butyrate; tetrahydrofuran (tetrahydran) or derivatives thereof; 1,3-dioxane (1,3-dioxane) ), 1,4-Dioxane (1,4-dioxane), 1,2-dimethoxyethane (1,2-dimethoxyester), 1,4-dibutoxyethan (1,4-dibutoxyethane), methyldiglyclyme. Ethers such as ester; nitriles such as acetonitrile and benzonitrile, dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sulfone and the like. Alternatively, derivatives thereof and the like can be used alone or in combination of two or more thereof, but the present invention is not limited thereto.

Examples of the electrolyte salt 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. , KSCN and other inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K), 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, lithium stearyl sulphate, octyl sulfonic acid Organic ion salts such as lithium (lithium octyl sulphate) and lithium dodecylbenzene sulphonate can be used. These ionic compounds can be used alone or in combination of two or more. The concentration of the electrolyte salt may be the same as that of the non-aqueous electrolyte solution used in the conventional lithium secondary battery, and is not particularly limited. In the present invention, an electrolytic solution containing an appropriate lithium compound (electrolyte salt) at a concentration of about 0.5 to 2.0 mol / L can be used.

<Manufacturing method of lithium ion secondary battery>
(Manufacturing method of positive electrode active material)
First, a method for producing the positive electrode active material according to the present embodiment will be described. The method for producing the positive electrode active material is not particularly limited, and for example, a coprecipitation method can be used. Hereinafter, a method for producing a positive electrode active material using such a coprecipitation method will be described with an example.

First, by dissolving nickel sulfate hexahydrate _{(NiSO 4 · 6H 2 O)} , cobalt pentahydrate sulfate _{(CoSO 4 · 5H 2 O)} , and a compound containing a metal element M in deionized water, mixed aqueous solution To manufacture. Here, the total mass of the compound containing nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and the metal element M may be, for example, about 20% by mass with respect to the total mass of the mixed aqueous solution. Further, the compound containing nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and metal element M is mixed so that the molar ratio of each element of Ni, Co, and M becomes a desired value. .. The molar ratio of each element is determined according to the composition of the lithium transition metal composite oxide to be produced. For example, when Li _1.03 Ni _0.8 Co _0.15 Al _0.05 O ₂ is produced. The molar ratio of each element, Ni: Co: Al, is 80:15: 5.

The metal element M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), and niobium (Nb). ), Molybdenum (Mo), Tungsten (W), Copper (Cu), Zinc (Zn), Gallium (Ga), Indium (In), Tin (Sn), Lantern (La), Cerium (Ce). One or more metal elements to be selected. The compound containing the metal element M is, for example, various salts such as sulfates and nitrates of the metal element M, oxides, and hydroxides.

Further, a predetermined amount (for example, 500 ml) of ion-exchanged water is charged into the reaction layer, and the temperature of the ion-exchanged water is maintained at 50 ° C. Hereinafter, the aqueous solution in the reaction layer is referred to as a reaction layer aqueous solution. Next, the dissolved oxygen is removed by bubbling the ion-exchanged water with an inert gas (gas) such as nitrogen.

Then, the ion-exchanged water in the reaction layer is stirred, and the above-mentioned mixed aqueous solution is added dropwise to the ion-exchanged water while maintaining the temperature of the ion-exchanged water at 50 ° C. _{Further, an excess amount of a saturated aqueous solution of NaCO 3} is added dropwise to the ion-exchanged water with respect to the mixed aqueous solutions of Ni, Co and M. During the dropping, the pH of the aqueous reaction layer solution is maintained at 11.5 and the temperature is maintained at 50 ° C. The dropping rate of the mixed aqueous solution and the saturated aqueous solution of NaCO ₃ is not particularly limited, but if it is too fast, a uniform precursor (co-precipitated hydroxide salt) may not be obtained. For example, the dropping speed may be about 3 ml / min. The mixed aqueous solution and the saturated aqueous solution of NaCO ₃ are added dropwise over a predetermined time, for example, about 10 hours. As a result, the hydroxide salt of each metal element is co-precipitated.

Subsequently, solid-liquid separation (for example, suction filtration) is performed, the co-precipitated hydroxide salt is taken out from the reaction layer aqueous solution, and the taken-out co-precipitated hydroxide salt is washed with ion-exchanged water. In addition, the co-precipitated hydroxide salt is vacuum dried. The temperature at this time may be, for example, about 100 ° C., and the drying time may be, for example, about 10 hours.

Next, the dried co-precipitated hydroxide salt is pulverized in a mortar for several minutes to obtain a dry powder. Then, the dry powder and lithium hydroxide (LiOH) are mixed to produce a mixed powder. Here, the molar ratio of Li and Ni + Co + M (= Me) is determined according to the composition of the lithium nickel composite oxide. For example, when Li _1.03 Ni _0.8 Co _0.15 Al _0.05 O ₂ is produced, the molar ratio of Li to Me, Li: Me, is 1.03: 1.00.

Further, this mixed powder is fired. Since the nickel atoms in the mixed powder are easily reduced, the above firing is preferably performed in an oxidizing atmosphere. The oxidative atmosphere is, for example, an oxygen atmosphere. Further, the firing time and firing temperature may be arbitrarily adjusted. The firing temperature may be, for example, about 750 to 850 ° C., and the firing time may be, for example, about 6 hours. The positive electrode active material is produced by the above steps.

(Manufacturing method of lithium ion secondary battery)
Subsequently, an example of a method for manufacturing the lithium ion secondary battery 10 will be described. The manufacturing method described below is merely an example, and it goes without saying that the lithium ion secondary battery 10 can be manufactured by another method.

The positive electrode 20 is manufactured as follows. First, a binder solution is prepared by dissolving the binder in an organic solvent (for example, N-methyl-2-pyrrolidone: NMP). Next, the conductive auxiliary agent and the liquid P-CTFE are added to the binder solution, and the mixture is kneaded and mixed. Then, the positive electrode active material is further added, and the mixture is kneaded and mixed. Finally, a solvent such as NMP is added to adjust the viscosity to form a positive electrode slurry. Next, the positive electrode slurry is formed (for example, coated) on the current collector 21 and dried to form the positive electrode active material layer 22. The coating method is not particularly limited, but for example, a knife coater method, a gravure coater method, or the like may be used. Each of the following coating steps is also performed by the same method. Further, the positive electrode active material layer 22 is compressed to a desired thickness by a compressor. As a result, the positive electrode 20 is manufactured. Here, the thickness of the positive electrode active material layer 22 is not particularly limited as long as it is the thickness of the positive electrode active material layer of the lithium ion secondary battery.

The step of applying the positive electrode slurry to the current collector is performed in a dry environment with a dew point temperature of −40 ° C. or lower. When water or the like adheres to the positive electrode active material, gas may be generated by the reaction of water or the like with _{LiOH and Li 2} CO _{3 or the like on the surface of the positive electrode active material during high temperature storage.} Therefore, it is more preferable that the step of applying the positive electrode slurry to the current collector is performed in a dry environment where the water content is extremely low and the dew point temperature is −40 ° C. or lower.

The negative electrode 30 is obtained by first mixing a negative electrode active material, carboxymethyl cellulose (CMC) and a conductive auxiliary agent in a desired ratio, adding a predetermined amount of ion-exchanged water, and kneading and mixing them. Then, ion-exchanged water is further added to adjust the viscosity, and a styrene-butadiene rubber (SBR) binder is added to form a negative electrode slurry. Next, the negative electrode slurry is formed (for example, coated) on the current collector 31 and dried to form the negative electrode active material layer 32. Further, the negative electrode active material layer 32 is compressed to a desired thickness by a compressor. As a result, the negative electrode 30 is manufactured. Here, the thickness of the negative electrode active material layer 32 is not particularly limited as long as it is the thickness of the negative electrode active material layer of the lithium ion secondary battery. When metallic lithium is used as the negative electrode active material layer 32, the metallic lithium foil may be laminated on the current collector 31.

Subsequently, the electrode structure is manufactured by sandwiching the separator between the positive electrode 20 and the negative electrode 30. Next, the electrode structure is processed into a desired shape (for example, cylindrical shape, square shape, laminated shape, button shape, etc.) and inserted into the container of the desired shape. Further, by injecting an electrolytic solution having a desired composition into the container, each pore in the separator is impregnated with the electrolytic solution. As a result, the lithium ion secondary battery 10 is manufactured.

Hereinafter, examples according to the present embodiment will be described.

(Example 1)
(Preparation of positive electrode active material)
Nickel sulfate hexahydrate _{(NiSO 4 · 6H 2 O)} , dissolved cobalt pentahydrate sulfate _{(CoSO 4 · 5H 2 O)} , and aluminum nitrate (Al _{(NO 3) 3)} in deionized water, mixed An aqueous solution was produced. Here, the total mass of nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and aluminum nitrate was set to 20% by mass with respect to the total mass of the mixed aqueous solution. The mixing ratio of nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and aluminum nitrate is such that the molar ratio of each element of Ni, Co, and Al is Ni: Co: Al = 80: 15: 5. It was set to be.

Further, a predetermined amount (for example, 500 ml) of ion-exchanged water was added to the reaction layer, and the temperature of the ion-exchanged water was maintained at 50 ° C. Next, dissolved oxygen was removed by bubbling ion-exchanged water with nitrogen gas.

Then, the ion-exchanged water in the reaction layer was stirred, and the above-mentioned mixed aqueous solution was added dropwise to the ion-exchanged water while maintaining the temperature of the ion-exchanged water at 50 ° C. _{Further, an excess amount of a saturated aqueous solution of NaCO 3} was added dropwise to the ion-exchanged water with respect to the mixed aqueous solutions of Ni, Co and Al. During the dropping, the pH of the aqueous reaction layer solution was maintained at 11.5 and the temperature was maintained at 50 ° C. The dropping rate of the mixed aqueous solution and the saturated aqueous solution of NaCO ₃ was about 3 ml / min. The stirring speed was 4 to 5 m / s at the peripheral speed. The mixed aqueous solution and the saturated aqueous solution of NaCO ₃ were added dropwise in about 10 hours. As a result, the hydroxide salt of each metal element co-precipitated.

Subsequently, suction filtration was performed to remove the co-precipitated hydroxide salt from the aqueous reaction layer solution, and the co-precipitated hydroxide salt taken out was washed with ion-exchanged water. In addition, the co-precipitated hydroxide salt was vacuum dried. The temperature at this time was 100 ° C., and the drying time was 10 hours.

Next, the dried co-precipitated hydroxide salt was pulverized in a mortar for several minutes to obtain a dry powder. Then, a mixed powder was produced by mixing the dry powder and lithium hydroxide (LiOH). Here, the molar ratio Li: Me of Li and Ni + Co + Al (= Me) was set to 1.03: 1.00.

Further, this mixed powder was calcined in an oxidizing atmosphere. The firing temperature was 750 to 850 ° C., and the firing time was 6 hours. A positive electrode active material was produced by the above steps. The composition of the positive electrode active material is shown by Li _1.03 Ni _0.8 Co _0.15 Al _0.05 O ₂ .

(Creation of coin full cell)
A coin full cell was produced by the following processing. A binder solution was prepared by dissolving polyvinylidene fluoride in N-methyl-2-pyrrolidone (NMP). Next, acetylene black and P-CTFE (average molecular weight 900) were added to the binder solution, and the mixture was kneaded and mixed. Then, a positive electrode active material having an average particle size of 7 μm was further added, and the mixture was kneaded and mixed. Finally, a predetermined amount of NMP was added to adjust the viscosity to form a positive electrode slurry. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed so as to have a mass ratio of 96: 2: 2. Further, P-CTFE was added so as to be 0.25% by mass with respect to the total mass of the solid content (polyvinylidene fluoride, positive electrode active material and acetylene black) of the positive electrode slurry. The obtained positive electrode slurry was applied onto an aluminum foil serving as a current collector 21 in a dry environment with a dew point temperature of −40 ° C. or lower, and dried to form a positive electrode active material layer 22. Then, the positive electrode 20 was produced by rolling so that the adhesion amount of the positive electrode active material layer 22 was 20 mg / cm ² and the volume density was 3.7 g / cm ^3. It can be said that the adhesion amount and volume density of the positive electrode active material layer 22 in Example 1 are thick film density.

The negative electrode 30 was produced by applying a negative electrode slurry in which graphite was dispersed in ion-exchanged water on a copper foil which is a current collector 31 and drying the negative electrode 30. Then, as a separator, a coating layer containing an inorganic filler (as a coating layer, Mg (OH) ₂ / polyvinylidene fluoride = 70/30 with a mass ratio of Mg (OH) ₂ dispersed in polyvinylidene fluoride). A 12 μm-thick porous polypropylene film having (1) was prepared, and an electrode structure was manufactured by arranging a separator between the positive electrode 20 and the negative electrode 30. Next, the electrode structure was processed to the size of a coin full cell and stored in a coin full cell container.

Then, an electrolytic solution was produced by dissolving lithium hexafluorophosphate at a concentration of 1.3 mol / L in a non-aqueous solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 3: 7. Then, the electrolytic solution was injected into the coin full cell and the separator was impregnated with the electrolytic solution to prepare the coin full cell according to Example 1.

(Example 2)
The same treatment as in Example 1 was carried out except that the average molecular weight of P-CTFE was 500 and the addition amount was 0.50% by mass.

(Example 3)
The same treatment as in Example 1 was carried out except that the amount of P-CTFE added was 0.50% by mass.

(Example 4)
The same treatment as in Example 1 was carried out except that the amount of P-CTFE added was 1.00% by mass.

(Example 5)
The same treatment as in Example 1 was carried out except that the average particle size of the positive electrode active material was 13 μm.

(Example 6)
The same treatment as in Example 5 was carried out except that the amount of P-CTFE added was 0.50% by mass.

(Example 7)
The same treatment as in Example 1 was carried out except that the average molecular weight of P-CTFE was set to 500.

(Example 8)
The same treatment as in Example 1 was carried out except that the amount of P-CTFE added was 1.25% by mass.

(Example 9)
The same treatment as in Example 2 was carried out except that the amount of P-CTFE added was 1.50% by mass.

(Comparative Example 1)
The same treatment as in Example 1 was carried out except that a full cell was prepared without using P-CTFE.

(Comparative Example 2)
The same treatment as in Example 1 was carried out except that the waxy P-CTFE (average molecular weight 1100) was used.

(Comparative Example 3)
The same treatment as in Example 5 was carried out except that the positive electrode active material was prepared by the following steps and the ^{coil full cell was prepared with the volume density of the positive electrode active material layer being 4.0 g / cm 3.} First, cobalt sulfate pentahydrate _{(CoSO 4 · 5H 2 O)} , aluminum nitrate nonahydrate _{(Al (NO 3) 3 ·} 9H 2 O) and magnesium nitrate hexahydrate (Mg _{(NO 3) 2} · 6H ₂ O) was dissolved in ion-exchanged water to produce a mixed aqueous solution. Here, the total mass of cobalt sulfate pentahydrate, aluminum nitrate hexahydrate and magnesium nitrate hexahydrate was set to 20% by mass with respect to the total mass of the mixed aqueous solution. The mixing ratio of cobalt sulfate pentahydrate, aluminum nitrate hexahydrate and magnesium nitrate hexahydrate is such that the molar ratio of each element of Co, Al and Mg is Co: Al: Mg = 98: 1: 1. It was set to 1.

Further, a predetermined amount (for example, 500 ml) of ion-exchanged water was added to the reaction layer, and the temperature of the ion-exchanged water was maintained at 50 ° C. Next, dissolved oxygen was removed by bubbling ion-exchanged water with nitrogen gas.

Then, the ion-exchanged water in the reaction layer was stirred, and the above-mentioned mixed aqueous solution was added dropwise to the ion-exchanged water while maintaining the temperature of the ion-exchanged water at 50 ° C. _{Further, an excess amount of a saturated aqueous solution of NaCO 3} was added dropwise to the ion-exchanged water with respect to the mixed aqueous solutions of Co, Al and Mg. During the dropping, the pH of the aqueous reaction layer solution was maintained at 11.5 and the temperature was maintained at 50 ° C. The dropping rate of the mixed aqueous solution and the saturated aqueous solution of NaCO ₃ was about 3 ml / min. The stirring speed was 4 to 5 m / s at the peripheral speed. The mixed aqueous solution and the saturated aqueous solution of NaCO ₃ were added dropwise in about 10 hours. As a result, the hydroxide salt of each metal element co-precipitated.

Subsequently, suction filtration was performed to remove the co-precipitated hydroxide salt from the aqueous reaction layer solution, and the co-precipitated hydroxide salt taken out was washed with ion-exchanged water. In addition, the co-precipitated hydroxide salt was vacuum dried. The temperature at this time was 100 ° C., and the drying time was 10 hours.

Next, the dried co-precipitated hydroxide salt was pulverized in a mortar for several minutes to obtain a dry powder. Then, a mixed powder was produced by mixing the dry powder and lithium hydroxide (LiOH). Here, the molar ratio Li: Me of Li and Co + Al + Mg (= Me) was set to 1.0: 1.0.

Further, this mixed powder was fired in an air atmosphere. The firing temperature was 950 to 1050 ° C., and the firing time was 6 hours. A positive electrode active material was produced by the above steps. The composition of the positive electrode active material is shown by _{LiCo 0.98} Al _0.01 Mg _0.01 O _2.

(Comparative Example 4)
The same treatment as in Example 6 was carried out except that the positive electrode active material and the coin full cell were prepared by the same step as in Comparative Example 3.

(Evaluation method)
The following discharge rate test and charge / discharge cycle test were performed on the coin full cells of Examples 1 to 9 and Comparative Examples 1 to 4 produced as described above.

(Discharge rate test)
Full cells were charged and discharged at the charge / discharge rate (rate) and cut off voltage (unit: V) shown in Table 1 below. The temperature during charging and discharging was room temperature (25 ° C.). CC-CV means constant current and constant voltage, and CC means constant current. Then, the discharge capacity of the second cycle is measured, and this value is used as the initial capacity, and the load characteristic (load characteristic) is the capacity retention rate of the discharge capacity of the fifth cycle (0.5C) with respect to the discharge capacity of the second cycle (0.2C). Discharge rate) was evaluated.

(Charge / discharge cycle test)
Full cells were charged and discharged at the charge / discharge rate (rate) and cut off voltage (unit: V) shown in Table 2 below. The temperature during charging and discharging was room temperature (25 ° C.). CC-CV means constant current and constant voltage, and CC means constant current. Then, the discharge capacity of the third cycle was measured, this value was set as the initial capacity, the discharge capacity of the 101st cycle was measured, and this value was set as the capacity of the 100th cycle. The charge / discharge cycle characteristics were evaluated by the capacity retention rate of the discharge capacity at the 101st cycle (1.0C) with respect to the discharge capacity at the 3rd cycle (1.0C).

(Evaluation results)
The evaluation results of Examples 1 to 9 and Comparative Examples 1 to 4 are summarized in Table 3. Further, the Core-Cole plots of Examples 2 and 3 and Comparative Example 1 are shown in FIG. The horizontal axis of FIG. 2 shows the real part of impedance, and the vertical axis shows the imaginary part of impedance.

In Table 3, "discharge capacity" indicates the discharge capacity of the first cycle (0.1C), and "initial efficiency" is the first cycle (0.1C) with respect to the charge capacity of the first cycle (0.1C). The ratio of the discharge capacity of is shown.

As is clear from Table 3, regarding the discharge capacity and the initial efficiency, an example using a _{high nickel-based composite oxide (Li 1.03} Ni _0.8 Co _0.15 Al _0.05 O _{2) as the positive electrode active material.} 1-9 and Comparative Examples 1 and 2 were almost the same. When a positive electrode active material having a slightly large average particle size of 13 μm was used, the discharge capacity and initial efficiency were slightly lower than those of the others. Further, Comparative Examples 3 and 4 using a nickel-free composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ) as the positive electrode active material are shown in Examples 1 to 9 and Comparative Examples 1 to 2. Although the discharge capacity was low, the initial efficiency was high.

Further, regarding the load characteristics and the charge / discharge cycle characteristics, Examples 1 to 9 have a load efficiency equal to or higher than that of Comparative Example 1 to which P-CTFE is not added (that is, charge / discharge capacity at a high rate). The decrease in charge / discharge cycle was minimized), and the charge / discharge cycle characteristics were equivalent or improved as compared with Comparative Example 1. In particular, when P-CTFE having an average molecular weight of 900 or more was added in an amount of 0.50% by mass or more and 1.0% by mass or less, the effect of improving the load characteristics was very high. On the other hand, in Example 7 in which 0.25% by mass of P-CTFE having an average molecular weight of 500 was added,
The load characteristics were lower than those of Examples 1 to 6. Therefore, when the average molecular weight of P-CTFE is 500 or more and less than 700, it is preferable to contain 0.5% by mass or more of P-CTFE in order to enhance the load characteristics (capacity retention rate, etc.). Further, in Examples 8 and 9 in which the amount of P-CTFE added was more than 1.00% by mass, the discharge capacity and the initial efficiency tended to be slightly low, and the charge / discharge cycle characteristics also tended to be slightly low. The reason why the cycle characteristics are a little low is that as the amount of P-CTFE added increases, the binding force of the binder decreases. The effect of this decrease in binding force is not so great in the initial load characteristics, but it is presumed that the cycle characteristics are reduced due to the lack of conductivity between the particles due to the decrease in binding force after the high temperature cycle.

Further, in Comparative Example 2 using the wax-like P-CTFE, the load characteristics and the charge / discharge cycle characteristics were the same as those in Comparative Example 1, and the charge / discharge cycle characteristics were lower than those in Examples 1 to 7. Further, Comparative Examples 3 and 4 using a nickel-free composite oxide as the positive electrode active material were lower in both load characteristics and charge / discharge cycle characteristics than in Comparative Example 1.

Further, as shown in FIG. 2, the resistance components on the high frequency side of Examples 2 and 3 were lower than those of Comparative Example 1. From this, it was presumed that the addition of liquid P-CTFE to the positive electrode slurry reduced the resistance component on the high frequency side and improved the dispersibility of the conductive auxiliary agent.

As Reference Example 1, the positive electrode 20 was produced by rolling the positive electrode active material layer 22 so that the amount of adhesion was 10 mg / cm ² and the volume density was 3.3 g / cm ^3. The positive electrode active material used in the positive electrode 20 of Reference Example 1 and the evaluation results are as follows. The evaluation method is the same as in the above-mentioned Examples and Comparative Examples.

As shown in Table 4, since the electrodes are thin, the discharge capacity, initial efficiency, load characteristics and cycle characteristics are good. Here, as can be seen by comparing Reference Example 1, Comparative Example 1 and Examples 1 to 4, the positive electrode 20 using the high nickel-based composite oxide as the positive electrode active material as shown in Reference Example 1 has a thick film density. As shown in Comparative Example 1, the load characteristics and the cycle characteristics are deteriorated. However, as shown in Examples 1 to 4, by adding P-CTFE into the positive electrode 20, the decrease in load characteristics can be minimized, and the cycle characteristics should be equal to or higher than that in the case where the positive electrode 20 is a thin film. You can see that you can do it.

As described above, the lithium ion secondary battery 10 using the positive electrode 20 according to the present embodiment uses a high nickel-based composite oxide as the positive electrode active material and adds liquid P-CTFE to the positive electrode slurry. It has been proved that even when the positive electrode active material layer is thickened to a high density, the decrease in charge / discharge capacity at a high rate can be minimized and the charge / discharge cycle characteristics can be improved.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

10 Lithium-ion secondary battery 20 Positive electrode 21 Current collector 22 Positive electrode active material layer 30 Negative electrode 31 Current collector 32 Negative electrode active material layer 40 Separator layer

Claims (8)

Positive activity is a lithium transition metal composite oxide containing lithium (Li) and nickel (Ni) as constituent elements and containing nickel atoms in a proportion of 70 atomic% or more with respect to the total number of all metal atoms other than lithium. It is contained as a substance, and further contains a binder, a conductive auxiliary agent, and a liquid P-CTFE .
The lithium ion secondary battery is characterized in that the content of P-CTFE is 0.2% by mass or more and 1.0% by mass or less based on the total mass of the positive electrode before contact with the electrolytic solution. For positive electrode. The positive electrode for a lithium ion secondary battery according to claim 1, wherein the lithium transition metal composite oxide is represented by the following general formula (1).
_{Li a Ni x Co y M z} O 2 ··· (1)
(In the above formula (1), M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr). , Niob (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lantern (La) and cerium (Ce). It is one kind or two or more kinds of metal elements selected from the group consisting of. In the above formula (1), a, x, y, z are 0.20 ≦ a ≦ 1.20, 0.70. It is a value within the range of ≤x <1.00, 0.00 <y≤0.20, 0.00≤z≤0.10, and x + y + z = 1). The positive electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the average molecular weight of P-CTFE is 450 or more and 1000 or less. Positive activity is a lithium transition metal composite oxide containing lithium (Li) and nickel (Ni) as constituent elements and containing nickel atoms in a proportion of 70 atomic% or more with respect to the total number of all metal atoms other than lithium. A step of preparing a positive electrode slurry which is contained as a substance and further contains a binder, a conductive auxiliary agent, and a liquid P-CTFE.
A step of forming a positive electrode active material layer by applying and drying the positive electrode slurry to a current collector, and
Only including,
A method for producing a positive electrode for a lithium ion secondary battery, which comprises adding 0.2% by mass or more and 1.0% by mass or less of the P-CTFE with respect to the total mass of the solid content of the positive electrode slurry. The method for producing a positive electrode for a lithium ion secondary battery according to claim 4 , wherein the lithium transition metal composite oxide is represented by the following general formula (1).
_{Li a Ni x Co y M z} O 2 ··· (1)
(In the above formula (1), M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr). , Niob (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lantern (La) and cerium (Ce). It is one kind or two or more kinds of metal elements selected from the group consisting of. In the above formula (1), a, x, y, z are 0.20 ≦ a ≦ 1.20, 0.70. It is a value within the range of ≤x <1.00, 0.00 <y≤0.20, 0.00≤z≤0.10, and x + y + z = 1). The method for producing a positive electrode for a lithium ion secondary battery according to claim 4 or 5 , wherein the average molecular weight of P-CTFE is 450 or more and 1000 or less. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 3,
With the negative electrode
A separator layer provided between the positive electrode and the negative electrode and containing a separator and an electrolytic solution,
A lithium-ion secondary battery characterized by being equipped with. The lithium ion secondary battery according to claim 7 , wherein the P-CTFE is present in at least one of the positive electrode for the lithium ion secondary battery and the electrolytic solution.

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