JP2016149357A - Positive electrode active material for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a lithium ion secondary battery enabling higher cycle characteristics, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery.SOLUTION: The positive electrode active material for a lithium ion secondary battery contains compound particles represented by a general formula (1) below, and a coating part so formed as to coat part of the compound particles. The coating part is a composite layer having a hydroxide compound and a hydrophobic compound. LiMPO...(1) (M represents at least one kind selected from a group consisting of Fe, Mn, Co, Ni, and VO)SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

Currently, lithium transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are used as positive electrode active materials of lithium ion secondary batteries as those capable of constituting a 4V class secondary battery, In particular, LiCoO ₂ is the mainstream of current positive electrode active materials because it is easy to synthesize and relatively easy to handle.

  However, since cobalt is a small resource, cost is high, and crystal stability during charging is low, so there are problems with cycle characteristics, and it can cope with future mass production and enlargement for electric vehicles etc. Difficult to do.

Therefore, as a material to replace LiCoO ₂ , polyanionic positive electrode active materials typified by lithium iron phosphate and lithium manganese phosphate using iron and manganese, which have high thermal stability and are rich in resources, are attracting attention.

  However, a lithium ion secondary battery using a polyanionic positive electrode active material has a problem that cycle characteristics deteriorate, and various developments have been made for improvement. In Patent Document 1 (Japanese Patent Laid-Open No. 2011-71074), the surface of a transition metal compound containing lithium is coated with a conductive polymer to prevent elution of metal from the positive electrode active material to the non-aqueous electrolyte and to improve cycle characteristics. Has been made.

JP 2011-71074 A

  However, the cycle characteristics of the lithium ion secondary battery using the polyanionic positive electrode active material shown in the above technique are still insufficient, and further improvement of the characteristics is required.

  The present invention has been made to solve the above conventional problems, and provides a positive electrode active material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery having excellent cycle characteristics. With the goal.

In order to solve the above-described problem, a positive electrode active material for a lithium ion secondary battery according to the present invention includes a compound particle represented by the following general formula (1) and a coating formed to cover at least a part of the compound particle. And the covering portion is a composite layer having a hydroxide compound and a hydrophobic compound.
LiMPO ₄ ... General formula (1)
(M represents at least one selected from the group consisting of Fe, Mn, Co, Ni and VO.)

  It is considered that transition metal ions are unlikely to pass through the composite layer because there are many hydrogen bonds and hydrophobic bonds in the composite layer structure composed of a hydroxide compound and a hydrophobic compound, and the structure has a strong binding force. Furthermore, it is considered that the redox reaction at the interface between the hydrophobic compound and the nonaqueous electrolyte is prevented. By these effects, elution of transition metal ions into the non-aqueous electrolyte is suppressed, and high cycle characteristics can be obtained.

  In the positive electrode active material for a lithium ion secondary battery according to the present invention, it is preferable that at least a part of the surface layer portion of the composite layer is a hydrophobic compound.

  It is thought that the penetration | invasion of the water | moisture content to a compound particle can be prevented because at least one part of the surface layer part of a composite layer is a hydrophobic compound. Thereby, the contact between the compound particles and the water is prevented, and it is considered that the generation of hydrofluoric acid due to the reaction between the water content and the non-aqueous electrolyte due to the deterioration of the compound particles due to the water content. Due to these effects, higher cycle characteristics can be obtained.

  In the positive electrode active material for a lithium ion secondary battery according to the present invention, the ratio X of the hydrophobic compound to the total of the hydroxide compound and the hydrophobic compound in the composite layer is preferably 5% by mass ≦ X ≦ 25% by mass. .

  As a result, the ratio of the hydroxide compound to the hydrophobic compound becomes good, so that in addition to the effect of preventing the transition metal ions from eluting into the non-aqueous electrolyte, the positive electrode active material is prevented from deteriorating due to moisture and the generation of hydrofluoric acid is prevented. It is considered that the effect can be obtained more efficiently, and higher cycle characteristics can be obtained.

In the positive electrode active material for a lithium ion secondary battery according to the present invention, the hydroxide compound is further Fe (OH) ₂ or Fe (OH) ₃ or FeO (OH), Co (OH) ₂ or Co (OH) ₃ , It is preferable to include at least one of NiOH, Ni (OH) ₂ or NiO (OH).

Since the ionization tendency of Fe, Co, and Ni is close to that of hydrogen, it is considered that generation of hydrogen gas is suppressed by preventing reduction of H ⁺ generated by ionization of moisture in the atmosphere. Furthermore, it is considered that transition metal element defects on the surface of the positive electrode active material due to repeated charge and discharge are compensated by these elements, and higher cycle characteristics can be obtained.

  In the positive electrode active material for a lithium ion secondary battery according to the present invention, it is preferable that the hydrophobic compound further includes at least one of a paraffinic hydrocarbon compound and a naphthene hydrocarbon compound.

  Since many carbon-hydrogen bonding groups of these hydrocarbon compounds increase the hydrogen bonds in the composite layer, it is considered that stronger bonding force is generated and it becomes more difficult for transition metal ions to pass through the composite layer. That is, the effect of suppressing the elution of transition metal ions into the non-aqueous electrolyte is enhanced, and higher cycle characteristics can be obtained.

  In the positive electrode active material for a lithium ion secondary battery according to the present invention, the composite layer preferably further contains a lithium compound.

  Thereby, it is considered that lithium in the lithium compound can diffuse in the composite layer as an ionic conductor, the lithium ion conductivity in the composite layer is improved, and higher cycle characteristics can be obtained.

  It is preferable that the positive electrode for lithium ion secondary batteries which concerns on this invention contains the positive electrode active material mentioned above.

  Thereby, the positive electrode for lithium ion secondary batteries which can achieve a higher cycle characteristic can be obtained.

  The lithium ion secondary battery according to the present invention preferably further comprises the positive electrode described above, a negative electrode having a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte.

  A lithium ion secondary battery capable of achieving higher cycle characteristics is provided by including the above-described positive electrode, a negative electrode having a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. Can

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material for lithium ion secondary batteries excellent in cycling characteristics, the positive electrode for lithium ion secondary batteries, and a lithium ion secondary battery can be provided.

It is a schematic cross section of the lithium ion secondary battery according to the present embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

<Lithium ion secondary battery>
The lithium ion secondary battery according to this embodiment will be briefly described with reference to FIG.

  The lithium ion secondary battery 100 mainly includes a stacked body 40, a case 50 that accommodates the stacked body 40 in a sealed state, and a pair of leads 60 and 62 connected to the stacked body 40.

  The laminated body 40 is configured such that the positive electrode 20 and the negative electrode 30 are opposed to each other with the separator 10 interposed therebetween, and is accommodated in the case 50 in a state in which a nonaqueous electrolytic solution (not shown) is immersed.

The positive electrode 20 is a product in which a positive electrode active material layer 24 is provided on a positive electrode current collector 22. As the positive electrode current collector 22, for example, an aluminum foil or the like can be used.

The negative electrode 30 is a product in which a negative electrode active material layer 34 is provided on a negative electrode current collector 32. A copper foil or the like can be used as the negative electrode current collector 32 of the negative electrode 30.

The positive electrode active material layer 24 and the negative electrode active material layer 34 are in contact with both sides of the separator 10.

  The case 50 seals the laminated body 40 and the nonaqueous electrolyte therein. The case 50 is not particularly limited as long as it can prevent leakage of the nonaqueous electrolyte to the outside and entry of moisture and the like into the lithium ion secondary battery 100 from the outside. For example, a metal laminate film is used. it can.

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

  The separator 10 is made of a single layer of a film made of polyethylene, polypropylene or polyolefin, a stretched film of a laminate or a mixture of the above resins, or at least one constituent material selected from the group consisting of cellulose, polyester and polypropylene. A fiber nonwoven fabric can be used.

  Leads 60 and 62 are connected to the ends of the positive electrode current collector 22 and the negative electrode current collector 32, respectively, and the end portions of the leads 60 and 62 extend to the outside of the case 50.

<Positive electrode active material layer>
The positive electrode active material layer 24 contains at least the positive electrode active material according to the present embodiment and a conductive additive. The positive electrode active material layer 24 may include a binder that binds the positive electrode active material and the conductive additive.

  Examples of the conductive assistant include carbon materials such as carbon blacks, metal powders such as copper, nickel, stainless steel, and iron, mixtures of carbon materials and metal powders, and conductive oxides such as ITO.

  The binder is not particularly limited as long as the positive electrode active material and the conductive additive can be bound to the positive electrode current collector 12, and a known binder can be used. Examples thereof include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and vinylidene fluoride-hexafluoropropylene copolymer.

  The ratio of the positive electrode active material, the conductive additive, and the binder in the positive electrode active material layer 24 is not particularly limited, but the electrode density tends to decrease when the ratio of the positive electrode active material is small, and the ratio of the positive electrode active material is 80% by mass or more. Is preferred.

<Positive electrode active material>
The positive electrode active material according to the present embodiment includes a compound particle represented by the following general formula (1) and a covering portion formed so as to cover at least a part of the compound particle.
LiMPO ₄ ... General formula (1)
(M represents at least one selected from the group consisting of Fe, Mn, Co, Ni and VO.)

<Compound particles>
The compound particles forming the positive electrode active material according to the present embodiment are represented by the general formula (1) and contain a transition metal element that represents at least one selected from the group consisting of Fe, Mn, Co, Ni, and V. . When lithium ions are inserted into and extracted from the positive electrode active material by charge and discharge, the transition metal element becomes a transition metal ion by an oxidation-reduction reaction, whereby the charge neutrality in the positive electrode active material is maintained.

The compound particles according to the present embodiment preferably include at least LiVOPO ₄ and LiFePO ₄ .

As LiVOPO ₄ which is the compound particle according to the present embodiment, those having an existing crystal structure such as triclinic crystal, orthorhombic crystal and tetragonal crystal can be used, and among these, the crystal structure is orthorhombic. It is preferable to use LiVOPO ₄ which is a crystal.

  The compound particles according to the present embodiment may be composed of the above-mentioned one kind, or a plurality of kinds may be mixed.

  The particle size of the compound particles according to this embodiment is preferably 0.01 μm to 1.4 μm.

<Coating part>
The covering portion is a composite layer having a hydroxide compound and a hydrophobic compound. In the hydroxylated compound, it is considered that oxygen-hydrogen bonding groups are hydrogen-bonded to generate a strong bonding force between molecules. Furthermore, it is considered that the hydrophobic compound is separated from the non-aqueous electrolyte that is a polar molecule because a hydrophobic bond due to van der Waals attraction occurs between the molecules, and the hydrophobic compound molecules aggregate. As a result, the composite layer structure has a strong binding force due to the synergistic effect of hydrogen bonds and hydrophobic bonds, and transition metal ions in the positive electrode active material are unlikely to pass through the composite layer, so the transition metal toward the non-aqueous electrolyte side It is thought that the movement of ions is hindered. That is, the elution of transition metal ions into the nonaqueous electrolyte is suppressed. Further, at the interface between the hydrophobic compound and the non-aqueous electrolyte, it is considered that electron transfer is unlikely to occur because they are not mixed with each other due to the difference in polarity between them. Thereby, since the oxidation-reduction reaction at the interface is prevented, the elution of transition metal ions into the non-aqueous electrolyte is suppressed. Due to these effects, high cycle characteristics can be obtained.

  Moreover, it is preferable that the mass of a coating | coated part is 1 mass%-5 mass% with respect to the total amount of a positive electrode active material. Within this range, since the total amount of compound particles in the positive electrode active material can be secured, the effect of suppressing the elution of transition metal ions into the non-aqueous electrolyte without reducing the capacity and by the coating portion And the effect which prevents the electron transfer in the interface with a nonaqueous electrolyte can be acquired efficiently, and a high cycle characteristic can be acquired.

  More preferably, it is the range of 1.5 mass%-2.5 mass%. When it is within this range, the above-described effects can be obtained more efficiently.

  It is preferable that the average particle diameter of the hydroxide compound and the hydrophobic compound constituting the coating portion is smaller than the average particle diameter of the compound particles. Thereby, the hydroxide compound and the hydrophobic compound are likely to adhere to the surface of the compound particles.

  Or it is preferable that the thickness of a coating | coated part is 1 nm-100 nm. Within this range, the above-described effect of the covering portion can be obtained efficiently without increasing the resistance component of the covering portion, so that high cycle characteristics can be obtained.

  More preferably, it is the range of 5 nm-50 nm. When it is within this range, the above-described effects can be obtained more efficiently.

<Form of composite layer>
The composite layer is composed of a hydroxide compound and a hydrophobic compound, and is formed so as to cover at least a part of the compound particles, and even if an island structure is formed on the surface of the compound particles or the entire surface of the compound particles is covered. Good. Further, both compounds may be in a mixed state, or the surface of the hydroxyl compound may be covered with hydrophobicity, or the surface of the hydrophobic compound may be covered with hydroxide compound, but the form of the composite layer is This is not the case.

  Among these forms, the surface coverage of the compound particles by the composite layer is preferably 1% or more, and more preferably 3% to 80%. Within this range, an increase in the resistance of the composite layer can be avoided, and the exchange of lithium ions by the compound particles proceeds smoothly, and the composite layer suppresses the elution of transition metal ions to the non-aqueous electrolyte and the non-aqueous electrolyte. The effect of preventing electron migration at the interface with the electrolyte can be obtained more efficiently.

  Furthermore, it is preferable that at least a part of the surface layer portion of the composite layer is a hydrophobic compound. The occupation ratio of the surface portion of the composite layer by the hydrophobic compound is preferably 5% or more, and more preferably 10% or more. Thereby, it is thought that the penetration | invasion to the compound particle | grains of the water | moisture content in air | atmosphere can be prevented. Therefore, it is considered that the contact between the compound particles and the water is prevented, and the deterioration of the compound particles due to the water content and the generation of hydrofluoric acid due to the reaction between the water content and the nonaqueous electrolyte are suppressed. Due to these effects, higher cycle characteristics can be obtained.

  The occupation ratio of the surface part of the composite layer by the hydrophobic compound can be analyzed by morphological observation using SEM or the like. The occupation ratio is defined as the ratio of the hydrophobic compound in the surface layer of the composite layer covering the compound particles in the cross section of the positive electrode on which the positive electrode active material layer using the positive electrode active material is formed or in the cross section of the positive electrode active material. The average value for any 50 positive electrode active materials or positive electrode active materials in the positive electrode cross section is defined as the occupation ratio of the surface layer portion of the composite layer by the hydrophobic compound.

  In the composite layer, the ratio X of the hydrophobic compound to the total of the hydroxide compound and the hydrophobic compound is preferably 5% by mass ≦ X ≦ 25% by mass. Thereby, since the ratio of the hydroxylated compound and the hydrophobic compound becomes good, hydrogen bonds and hydrophobic bonds are present in the composite layer in an optimal ratio. This prevents the transition metal ions from leaching into the non-aqueous electrolyte due to the strong bonding force in the composite layer, prevents the infiltration of moisture in the atmosphere by the hydrophobic compound on the surface layer, and degrades the positive electrode active material due to moisture intrusion. It is considered that the effect of preventing and the effect of preventing the generation of hydrofluoric acid due to the reaction with the nonaqueous electrolyte can be obtained more efficiently, and higher cycle characteristics can be obtained.

<Hydroxy compound>
Hydroxide compounds include, for example, alkali metal elements such as Li, Na, and K, alkaline earth metal elements such as Mg, Ca, and Sr, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Y , Hydroxides containing transition metal elements such as Zr, Nb, Mo, Tc, Ru, Ru, Rh, Pd, Ag, and Cd, and other metal elements such as Al, Ga, In, and Sn, and oxyhydroxides. Can be mentioned. For example, LiOH, NaOH, KOH, Mg (OH) ₂ , Ca (OH) ₂ , Sr (OH) ₂ , Sc (OH) ₃ , Ti (OH) ₄ , V (OH) ₂ , Cr (OH) ₂ , Cr (OH) ₃ , Mn (OH) ₂ , Fe (OH) ₂ , Fe (OH) ₃ , Co (OH) ₂ , Co (OH) ₃ , NiOH, Ni (OH) ₂ , CuOH, Cu (OH) ₂ , Zn (OH) ₂ , Y (OH) ₃ , ZrO (OH) ₂ , Nb (OH) ₅ , Mo, Tc (OH) ₄ , RuOH, Rh (OH) ₃ , Pb (OH) ₂ , AgOH, Cd (OH) ₂ , Ai (OH) ₃ , Ga (OH) ₃ , In, Sn (OH) ₂ , TiO (OH) ₂ , MnO (OH), FeO (OH), CoOOH, NiO (OH) , GaO (OH).

Among these, the hydroxide compound is Fe (OH) ₂ or Fe (OH) ₃ or FeO (OH), Co (OH) ₂ or Co (OH) ₃ , NiOH or Ni (OH) ₂ or NiO (OH). More preferably, at least one of them is included.

When the case 50 is not sufficiently sealed, water (H ₂ O) in the atmosphere enters the lithium ion secondary battery 100 from the outside, or an aqueous solvent is used in the positive electrode manufacturing process described later. In the case where water (H ₂ O) of the aqueous solvent remains because the drying process is insufficient, it is considered that water (H ₂ O) is ionized in the vicinity of the positive electrode active material and H ⁺ is generated. In this case, since the ionization tendency of Fe, Co, and Ni is close to that of hydrogen in the above-mentioned hydroxylated compound, it is considered that the generation of hydrogen gas can be suppressed because its own oxidation and reduction of H ⁺ are difficult to occur. . Furthermore, in the oxidation state at the time of charge, unstable transition of the surface of the positive electrode active material due to the presence of the same or similar elements as the transition metal element forming the positive electrode active material, Fe, Co and Ni in the hydroxide compound It is considered that the metal elements are stabilized, and even if these elements are lost due to repeated charge and discharge, the lost parts can be replaced by Fe, Co, and Ni in the hydroxide compound. Thereby, higher cycle characteristics can be obtained.

<Hydrophobic compound>
The hydrophobic compound is a compound having a low affinity for water, and examples thereof include a compound having a hydrocarbon group in the molecule, a compound having silicone, and a fluoroalkyl chain. Silicone is a compound having, as a main skeleton, a siloxane bond represented by the general formula R ₃ SiO— (R ₂ SiO) _n —SiR ₃ . Of these, silicone oils exhibiting oil-like properties with a linear structure of n = 2000 or less are preferred.

  Of the above, compounds having a hydrocarbon group in the molecule are preferred. As such a compound, a paraffinic hydrocarbon compound having a chain molecular structure, an olefinic hydrocarbon compound, an acetylene hydrocarbon compound, a cycloparaffin having a cyclic molecular structure, and a naphthene hydrocarbon compound are more preferable. More preferably, at least one of paraffinic hydrocarbon compounds and naphthenic hydrocarbon compounds is included.

  Since paraffinic hydrocarbon compounds have many carbon-hydrogen bonding groups, it is considered that they form hydrogen bonds with oxygen-hydrogen bonding groups of the hydroxide compound. Thereby, since the hydrogen bond in a composite layer increases, it is thought that it becomes a structure which has stronger bond strength. Similarly, a naphthene-based hydrocarbon compound is also a saturated hydrocarbon structure having a cyclic molecular structure in the molecule, and thus is considered to have a structure having a stronger bonding force. Thereby, it becomes more difficult for the transition metal ions in the positive electrode active material to pass through the composite layer, and the effect of preventing movement to the non-aqueous electrolyte side is considered to be enhanced. That is, the effect of suppressing the elution of transition metal ions into the non-aqueous electrolyte is enhanced, and higher cycle characteristics can be obtained.

  Although it does not specifically limit as a paraffinic hydrocarbon compound, It is a normal paraffin and isoparaffin with 17 or more carbon atoms. Examples include heptadecane, octadecane, nonadecane, eicosan, heikosan, pentacosan, tricontane, tetracontane. Examples of naphthenic hydrocarbon compounds include cyclopentane and cyclohexane, but are not limited thereto.

<A more preferable state of the composite layer of the positive electrode active material>
The composite layer preferably contains a lithium compound. The structure of the composite layer containing a lithium compound is considered as follows. By adding a lithium compound, a part of hydrogen bonds or a part of hydrophobic bonds is replaced with a coordinate bond between a lithium compound and a hydroxide compound or a coordinate bond between a lithium compound and a hydrophobic compound. Thereby, the conduction path of lithium ions in the composite layer is diversified, the lithium ion conductivity is improved, and higher cycle characteristics can be obtained. Furthermore, it is also conceivable that the lithium compound in a coordinated state is ionized by the unshared electrons of the oxygen atom of the hydroxide compound, and the composite layer enters a state containing lithium ions. In such a case, since lithium ion conductivity improves more, it is more preferable.

  The inclusion of the lithium compound can be confirmed by EPMA analysis, STEM analysis, Raman spectroscopic analysis, and FT-IR analysis. In the FT-IR analysis, when a lithium compound is contained, it is possible to confirm a change in intensity of a peak due to a hydrogen bond and a peak due to a hydrophobic bond, and further, a lithium compound and a hydroxide compound, or a lithium compound and a hydrophobic compound. The peak shift considered to be caused by the coordinate bond with the functional compound can be confirmed.

<Lithium compound>
Although it does not specifically limit as a supply source of a lithium compound, Lithium compounds, such as lithium metal, an organic lithium compound, lithium hydride, lithium aluminum hydride, lithium hydroxide, lithium stearate, lithium laurate, lithium ricinoleate, are mentioned. It is done. Of these, lithium hydroxide and lithium stearate are more preferable.

  The method for supplying the lithium compound is not particularly limited. For example, a solution in which the above lithium compound is dispersed in a powder state or an organic solvent is added to and mixed with a slurry containing a hydroxide compound and a hydrophobic compound. Thus, the lithium compound can be contained in the composite layer.

  The lithium compound has a mass in the range of 0.01% by mass to 2% by mass, preferably 0.05% by mass to 1.5% by mass, based on the total amount of the composite layer composed of the hydroxide compound and the hydrophobic compound. is there. Within this range, the lithium compound does not act as a resistance component, so the resistance in the composite layer does not increase, the lithium ion conduction path is effectively formed, and the lithium ion conductivity in the composite layer is improved. Higher cycle characteristics can be obtained.

<Method for producing positive electrode>
The positive electrode 20 is applied to a surface of the positive electrode current collector 22 by applying a known method, for example, a positive electrode active material, a conductive additive, and a binder added to an organic solvent or an aqueous solvent according to the type of the positive electrode current collector 22. Can be manufactured.

  Examples of the organic solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and toluene.

  The aqueous solvent may be water or a mixed solution with an organic solvent (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water.

<Method for producing positive electrode active material>
The positive electrode active material of this embodiment is a production step for producing compound particles represented by the general formula (1) LiMPO ₄ (M represents at least one selected from the group consisting of Fe, Mn, Co, Ni and VO). The positive electrode active material is manufactured by a method including a coating step of coating with a composite layer having a hydroxide compound and a hydrophobic compound so that at least a part of the compound particles is covered.

  The production step can be produced by various production methods such as known solid phase synthesis, hydrothermal synthesis, carbothermal reduction method, coprecipitation method, sol-gel process, and the like, and is not limited to a specific method.

  If the composite layer can be uniformly coated on the surface of the compound particles to be coated, a known surface coating method such as sputtering, CVD (Chemical Vapor Deposition), dip coating, etc. It can be manufactured by a general-purpose coating method such as a simple dipping method. The simplest of these coating methods is simply by adding compound particles to the coating solution to produce a mixture (mixing step), removing the solvent (solvent removing step), and drying by drying. Although it is a law, it is not limited to a specific method.

<Negative electrode active material layer>
As the negative electrode active material layer 34, a material containing a negative electrode active material, a conductive additive, and a binder can be used.

  A conductive support agent is not specifically limited, A carbon material, a metal powder, etc. can be used.

  As the binder, a fluororesin such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) or the like can be used.

<Negative electrode active material>
The negative electrode active material of the present invention is an amorphous material mainly composed of carbon materials such as graphite and non-graphitizable carbon, metals that can be combined with lithium such as Al, Si, and Sn, and oxides such as SiO ₂ and SnO _2. Particles containing high quality compounds, lithium titanate (Li ₄ Ti ₅ O ₁₂ ) and the like.

<Method for producing negative electrode>
The manufacturing method of the negative electrode 30 may be applied to the negative electrode current collector 32 by adjusting the slurry in the same manner as the manufacturing method of the positive electrode 20.

<Nonaqueous electrolyte>
The nonaqueous electrolyte sealed in the case 50 is not particularly limited. For example, in this embodiment, a nonaqueous electrolyte containing a lithium salt in an organic solvent can be used. Examples of the lithium _salt, LiPF _6, LiClO 4, salts of LiBF ₄ or the like can be used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together.

  Preferable examples of the organic solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate. These may be used alone or in combination of two or more at any ratio.

  The positive electrode active material of this embodiment can also be used as an electrode material for electrochemical elements other than lithium ion secondary batteries. As such an electrochemical element, two types of batteries other than lithium ion secondary batteries such as a metal lithium secondary battery (one using the positive electrode active material of the present embodiment as the positive electrode and using metal lithium as the negative electrode) are used. Examples thereof include secondary batteries and electrochemical capacitors such as lithium capacitors.

  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
<Production of evaluation cell>
V ₂ O ₅ , LiOH.H ₂ O and H ₃ PO ₄ were weighed so as to have a molar ratio of about 1: 2: 2, poured into distilled water, and stirred with a magnetic stirrer for 1 hour. Hydrazine monohydrate (NH ₂ NH ₂ .H ₂ O) was added dropwise little by little with vigorous stirring, and the mixture was further stirred for 1 hour, and then the mixture was transferred to a glass container for autoclave. The container was sealed, heated with stirring at 160 ° C. for 8 hours, and the obtained paste was dried in an oven at 100 ° C. for 12 hours. The obtained paste dried product was pulverized for 10 minutes using a mortar and then baked in a box furnace at 600 ° C. for 4 hours in the air to obtain the compound particles of Example 1.

The compound particles thus obtained were confirmed to be LiVOPO ₄ having an orthorhombic crystal structure from the results of powder X-ray diffraction.

Next, Ca (OH) ₂ and silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KF-99) were dispersed in ethanol as a solvent to prepare a slurry. To this slurry, the previously synthesized LiVOPO ₄ was added to a slurry of Ca (OH) ₂ and silicone oil while stirring. The mass ratio of the compound particles and the composite layer in the positive electrode active material was adjusted to be 96: 4. Furthermore, the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 97.5: 2.5. Then, it was further dried at 120 ° C. for 2 hours to obtain a positive electrode active material in which the surface of the LiVOPO ₄ powder was coated with a composite layer made of Ca (OH) ₂ and silicone oil.

  When the occupation ratio of the surface portion of the composite layer by the hydrophobic compound of the obtained positive electrode active material was analyzed by SEM, it was 3.7%.

  The positive electrode active material and acetylene black were weighed at a mass ratio of 80:10, and pulverized for 10 minutes with a planetary ball mill. The rotation speed of the planetary ball mill was set to 530 rpm.

  A mixture of the obtained positive electrode active material and acetylene black and polyvinylidene fluoride as a binder (PVDF, KF7305 manufactured by Kureha Chemical Co., Ltd.) was mixed in N-methyl-2-pyrrolidone (NMP) as a solvent. A slurry was prepared by dispersing. The mass ratio of the mixture and PVDF in the slurry was adjusted to 90:10. This slurry was applied onto an aluminum foil as a current collector, dried, and then rolled to produce a positive electrode on which a positive electrode active material layer was formed.

  Next, artificial graphite (FSN manufactured by BTR) and N methylpyrrolidone (NMP) 5 wt% solution of polyvinylidene fluoride (PVdF) as a negative electrode were mixed so that the ratio of artificial graphite: polyvinylidene fluoride = 93: 7 was obtained. A slurry paint was prepared. The negative electrode was produced by apply | coating a coating material to the copper foil which is a collector, and drying and rolling.

A positive electrode and a negative electrode were laminated with a separator made of a polyethylene microporous film interposed therebetween to obtain a laminate. This laminate was placed in an aluminum laminate pack. As the non-aqueous electrolyte, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7, and LiPF ₆ was dissolved as a supporting salt to a concentration of 1 mol / L.

  After injecting the non-aqueous electrolyte into the aluminum laminate pack containing the laminate, it was vacuum-sealed to produce an evaluation cell of Example 1.

<Measurement of battery characteristics>
The evaluation cell of Example 1 was charged at a constant current constant voltage method up to 4.3 V at a current value of 1.9 mA / g corresponding to 0.1 C at 25 ° C., and then 1.9 mA / g corresponding to 0.1 C. The battery was discharged by a constant current method until the current value reached 2.8V. When three evaluation cells of Example 1 were prepared and the average value thereof was taken, the discharge capacity was 137 mAh / g (initial discharge capacity). A cycle test was repeated for 100 cycles of this charge / discharge cycle. Assuming that the initial discharge capacity of the evaluation cell of Example 1 is 100%, the discharge capacity after 100 cycles was 90.7%. Hereinafter, the ratio of the discharge capacity after 100 cycles when the initial discharge capacity is 100% is referred to as cycle characteristics. A high cycle characteristic indicates that the battery is excellent in charge / discharge cycle durability.

(Example 2)
The raw materials Li ₂ CO ₃ , FeCl ₂ and (NH ₄ ) H ₂ PO ₄ were mixed at a ratio of 1: 2: 2 to obtain a mixture, and then baked at 750 ° C. for 8 hours in a reducing atmosphere. LiFePO ₄ which is a compounded particle was obtained. Thus the LiFePO ₄ obtained a mass ratio of the composite layer 96: was prepared as a 4. Furthermore, tetrafluoroethylene was used as the hydrophobic compound, and the mass ratio of Ca (OH) ₂ and tetrafluoroethylene in the slurry to be the composite layer was adjusted to 98.7: 1.3. The surface of the LiFePO ₄ powder was coated with a composite layer composed of Ca (OH) ₂ and tetrafluoroethylene, and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface layer portion by the hydrophobic compound of the obtained positive electrode active material was 2.3%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 3)
Li ₂ CO _{3 as} a raw material, Mn (No ₃ ) ₂ and (NH ₄ ) H ₂ PO ₄ were mixed at a ratio of 2: 1: 1 to obtain a mixture, and then 750 ° C. in a reducing atmosphere. and calcined for 8 hours to obtain the LiMnPO ₄ is a compound particle particles. Thus the LiMnPO ₄ obtained a mass ratio of the composite layer 96: was prepared as a 4. Furthermore, tetrafluoroethylene was used as a hydrophobic compound, and the mass ratio of Ca (OH) ₂ and tetrafluoroethylene in the slurry to be a composite layer was adjusted to 96.8: 3.2. The surface of the LiMnPO ₄ powder was coated with a composite layer composed of Ca (OH) ₂ and tetrafluoroethylene, and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the surface portion of the composite layer with the hydrophobic compound of the obtained positive electrode active material was 5.2%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

Example 4
Li ₂ CO ₃ which is a raw material, (CH ₃ COO) ₂ Co, and (NH ₄ ) H ₂ PO ₄ are mixed to obtain a mixture, and then calcined in a reducing atmosphere at 750 ° C. for 8 hours, and then compounded Particles LiCoPO ₄ were obtained. Thus the LiCoPO ₄ obtained a mass ratio of the composite layer 96: was prepared as a 4. Furthermore, using silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KF-99) as the hydrophobic compound, the mass ratio of Ca (OH) ₂ and silicone oil in the slurry that becomes the composite layer is 94.4. : 5.6. The surface of the LiCoPO ₄ powder was coated with a composite layer composed of Ca (OH) ₂ and silicone oil, and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface layer portion by the hydrophobic compound of the obtained positive electrode active material was 8.4%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 5)
The mass ratio of LiMnPO ₄ obtained in the same manner as in Example 3 to the composite layer was adjusted to 96: 4. Furthermore, silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KF-99) is used as the hydrophobic compound, and the mass ratio of Ca (OH) ₂ and silicone oil in the slurry that becomes the composite layer is 89.4. To 10.6. The surface of the LiCoPO ₄ powder was coated with a composite layer composed of Ca (OH) ₂ and silicone oil, and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface layer portion by the hydrophobic compound of the obtained positive electrode active material was 11.3%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 6)
The mass ratio of LiCoPO ₄ obtained in the same manner as in Example 4 to the composite layer was adjusted to 96: 4. Furthermore, tetrafluoroethylene was used as a hydrophobic compound, and the mass ratio of Ca (OH) ₂ and tetrafluoroethylene in the slurry to be a composite layer was adjusted to 84.8: 15.2. The occupation ratio of the surface layer portion of the composite layer by the hydrophobic compound was 7.1%. Thus, the surface of the LiCoPO ₄ powder was coated with a composite layer composed of Ca (OH) ₂ and tetrafluoroethylene, and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material. Otherwise, the evaluation cell was produced and the battery characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

  The occupation ratio of the composite layer surface portion by the hydrophobic compound of the obtained positive electrode active material was 7.1%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 7)
The mass ratio of LiFePO ₄ obtained in the same manner as in Example 2 to the composite layer was adjusted to 95: 5. Furthermore, using Co (OH) ₂ as the hydroxide compound and nonadecane as the hydrophobic compound, the mass ratio of Co (OH) ₂ and nonadecane in the slurry to be the composite layer was adjusted to 77.0: 23.0. . The surface of the LiFePO ₄ powder was coated with a composite layer composed of Co (OH) ₂ and nonadecane, and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface layer portion by the hydrophobic compound of the obtained positive electrode active material was 10.5%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 8)
The mass ratio of LiMnPO ₄ obtained in the same manner as in Examples 3 and 5 and the composite layer was adjusted to 96: 4. Further, Fe (OH) ₂ as a hydroxide compound and eicosane as a hydrophobic compound were used, and the mass ratio of Fe (OH) ₂ and eicosane in the slurry to be a composite layer was adjusted to 92.3: 7.7. . The surface of the LiMnPO ₄ powder was coated with a composite layer composed of Fe (OH) ₂ and eicosane and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface layer portion by the hydrophobic compound of the obtained positive electrode active material was 6.3%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

Example 9
The mass ratio of LiCoPO ₄ obtained in the same manner as in Examples 4 and 6 and the composite layer was adjusted to 97: 3. Furthermore, FeO (OH) was used as the hydroxide compound, and henicosane was used as the hydrophobic compound, and the mass ratio of FeO (OH) and henicosane in the slurry to be the composite layer was adjusted to 88.2: 11.8. The surface of the LiCoPO ₄ powder was coated with a composite layer composed of FeO (OH) and heicosan and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface portion by the hydrophobic compound of the obtained positive electrode active material was 8.2%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 10)
The mass ratio of LiCoPO ₄ obtained in the same manner as in Example 9 to the composite layer was adjusted to 98: 2. Furthermore, NiO (OH) was used as the hydroxide compound and pentacosane was used as the hydrophobic compound, and the mass ratio of NiO (OH) and pentacosane in the slurry to be the composite layer was adjusted to 81.8: 18.2. The surface of the LiCoPO ₄ powder was coated with a composite layer composed of NiO (OH) and pentacosane, and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface layer portion by the hydrophobic compound of the obtained positive electrode active material was 10.5%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 11)
The mass ratio of LiVOPO ₄ obtained in the same manner as in Example 1 to the composite layer was adjusted to 99: 1. Furthermore, using Co (OH) ₃ as the hydroxide compound and tricontan as the hydrophobic compound, the mass ratio of Co (OH) ₃ and tricontan in the slurry to be the composite layer was adjusted to 75.3: 24.7. . The surface of the LiVOPO ₄ powder was coated with a composite layer composed of Co (OH) ₃ and tricontane, and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the surface portion of the composite layer with the hydrophobic compound of the obtained positive electrode active material was 12.5%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 12)
The mass ratio of LiVOPO ₄ obtained in the same manner as in Examples 1 and 11 and the composite layer was adjusted to 95: 5. Furthermore, Fe (OH) ₃ was used as the hydroxide compound and cyclohexane was used as the hydrophobic compound, and the mass ratio of Fe (OH) ₃ and cyclohexane in the slurry to be the composite layer was adjusted to 83.0: 17.0. . The surface of the LiVOPO ₄ powder was coated with a composite layer composed of Fe (OH) ₃ and cyclohexane, and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface layer portion by the hydrophobic compound of the obtained positive electrode active material was 13.5%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 13)
The mass ratio of LiFePO ₄ obtained in the same manner as in Examples 2 and 7 and the composite layer was adjusted to 96: 4. Furthermore, Co (OH) ₃ was used as the hydroxide compound and pentacosane was used as the hydrophobic compound, and the mass ratio of Co (OH) ₃ and pentacosane in the slurry to be the composite layer was adjusted to 93.8: 6.2. . The surface of the LiFePO ₄ powder was coated with a composite layer composed of Co (OH) ₃ and pentacosane, and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface layer portion by the hydrophobic compound of the obtained positive electrode active material was 7.8%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 14)
The mass ratio of LiMnPO ₄ obtained in the same manner as in Examples 3, 5 and 8 and the composite layer was adjusted to 97: 3. Furthermore, using Ni (OH) ₂ as the hydroxide compound and tricontan as the hydrophobic compound, the mass ratio of Ni (OH) ₂ and tricontan in the slurry to be the composite layer was adjusted to 89.7: 10.3. . The surface of the LiMnPO ₄ powder was coated with a composite layer composed of Ni (OH) ₂ and tricontane and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface layer portion by the hydrophobic compound of the obtained positive electrode active material was 10.3%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 15)
The mass ratio of LiCoPO ₄ obtained in the same manner as in Examples 4, 6, 9 and 10 and the composite layer was adjusted to 98: 2. Furthermore, using FeO (OH) as the hydroxide compound and tetracontane as the hydrophobic compound, the mass ratio of FeO (OH) to tetracontane in the slurry to be the composite layer was adjusted to 79.9: 20.1. . The surface of the LiCoPO ₄ powder was coated with a composite layer composed of FeO (OH) and tetracontane and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface portion by the hydrophobic compound of the obtained positive electrode active material was 15.2%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 16)
The mass ratio of the LiMnPO ₄ was obtained in the same manner as in Example 3, 5, 8 and 14 and the composite layer 99: was prepared to be 1. Further, using NiO (OH) as the hydroxide compound and cyclopentane as the hydrophobic compound, the mass ratio of NiO (OH) and cyclopentane in the slurry to be the composite layer was adjusted to 76.0: 24.0. . The surface of the LiMnPO ₄ powder was coated with a composite layer composed of NiO (OH) and cyclopentane, and further dried at 120 ° C. for 2 hours to obtain a positive electrode active material.

  The occupation ratio of the composite layer surface portion by the hydrophobic compound of the obtained positive electrode active material was 15.3%.

  A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the obtained positive electrode active material was used. The results are shown in Table 1.

(Example 17)
The evaluation cell was prepared in the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 95.0: 5.0. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 18)
The evaluation cell was prepared in the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 76.0: 24.0. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 19)
The evaluation cell was prepared in the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 74.0: 26.0. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 20)
In the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 70.0: 30.0, Battery characteristics were evaluated. The results are shown in Table 1.

(Example 21)
The evaluation cell was prepared in the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 47.3: 52.7. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 22)
The evaluation cell was prepared in the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 37.7: 62.3. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 23)
The evaluation cell was prepared in the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 31.2: 68.8. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 24)
The evaluation cell was prepared in the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 15.1: 84.9. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 25)
The evaluation cell was prepared in the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 6.2: 93.8. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 26)
The evaluation cell was prepared in the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 0.8: 99.2. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 27)
The evaluation cell was prepared in the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 0.2: 99.8. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 28)
The evaluation cell was prepared in the same manner as in Example 1 except that the mass ratio of Ca (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 0.1: 99.9. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 29)
Except that Fe (OH) ₂ was used as a hydroxide compound and the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be a composite layer was adjusted to 94.8: 5.2. The evaluation cell was produced and the battery characteristics were evaluated in the same manner as in Example 17. The results are shown in Table 1.

(Example 30)
The evaluation cell was prepared in the same manner as in Example 29 except that the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 84.7: 15.3. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 31)
The evaluation cell was prepared in the same manner as in Example 29 except that the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 75.5: 24.5. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 32)
The evaluation cell was prepared in the same manner as in Example 29 except that the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 73.8: 26.2. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 33)
The evaluation cell was prepared in the same manner as in Example 29 except that the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 65.2: 34.8. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 34)
The evaluation cell was prepared in the same manner as in Example 29, except that the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 47.3: 52.7. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 35)
The evaluation cell was prepared in the same manner as in Example 29 except that the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 31.2: 68.8. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 36)
The evaluation cell was prepared in the same manner as in Example 29, except that the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 14.7: 85.3. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 37)
The evaluation cell was prepared in the same manner as in Example 29 except that the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 6.2: 66.3. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 38)
The evaluation cell was prepared in the same manner as in Example 29 except that the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 0.8: 99.2. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 39)
The evaluation cell was prepared in the same manner as in Example 29 except that the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 0.2: 99.8. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 40)
The evaluation cell was prepared in the same manner as in Example 29 except that the mass ratio of Fe (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 0.1: 99.9. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 41)
Using LiFePO ₄ as the compounded particles and Ni (OH) ₂ as the hydroxide compound, the mass ratio of Ni (OH) ₂ and silicone oil in the slurry to be the composite layer is 94.9: 5.1. A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 40 except that it was prepared. The results are shown in Table 1.

(Example 42)
The evaluation cell was prepared in the same manner as in Example 41 except that the mass ratio of Ni (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 75.2: 24.8. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 43)
The evaluation cell was prepared in the same manner as in Example 41 except that the mass ratio of Ni (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 73.6: 26.4. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 44)
The evaluation cell was prepared in the same manner as in Example 41 except that the mass ratio of Ni (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 57.4: 42.6. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 45)
The evaluation cell was prepared in the same manner as in Example 41 except that the mass ratio of Ni (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 45.7: 54.3. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 46)
The evaluation cell was prepared in the same manner as in Example 41 except that the mass ratio of Ni (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 28.5: 71.5. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 47)
The evaluation cell was prepared in the same manner as in Example 41 except that the mass ratio of Ni (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 14.7: 85.3. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 48)
The evaluation cell was prepared in the same manner as in Example 41 except that the mass ratio of Ni (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 6.2: 93.8. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 49)
The evaluation cell was prepared in the same manner as in Example 41 except that the mass ratio of Ni (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 0.8: 99.2. Battery characteristics were evaluated. The results are shown in Table 1.

(Example 50)
The evaluation cell was prepared in the same manner as in Example 41 except that the mass ratio of Ni (OH) ₂ and silicone oil in the slurry to be the composite layer was adjusted to 0.2: 99.8. Battery characteristics were evaluated. The results are shown in Table 1.

(Comparative Example 1)
An evaluation cell was prepared and battery characteristics were evaluated in the same manner as in Example 1 except that only Ca (OH) ₂ was coated. The results are shown in Table 1.

(Comparative Example 2)
Without coating, LiFePO ₄ was synthesized in the same manner as in Example 2, and an evaluation cell was produced and battery characteristics were evaluated. The results are shown in Table 1.

  From the results of Examples 1 to 50, it was confirmed that by covering with a composite layer having a hydroxide compound and a hydrophobic compound, a high discharge capacity was exhibited even after repeating charge and discharge 100 times as cycle characteristics. It was confirmed that 83% or more of the discharge capacity was secured.

  Furthermore, it was confirmed that higher cycle characteristics were obtained when the ratio X of the hydrophobic compound to the total of the hydroxylated compound and the hydrophobic compound was 5% by mass ≦ X ≦ 25% by mass.

  Furthermore, it confirmed that a higher cycling characteristic was acquired because a composite layer contains a lithium compound.

  On the other hand, Comparative Examples 1 and 2 did not reach the characteristics of this example.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

  By using the positive electrode active material for a lithium ion secondary battery of the present invention, higher cycle characteristics can be obtained. Therefore, the present invention is a useful technique in the field of secondary batteries.

DESCRIPTION OF SYMBOLS 10 ... Negative electrode, 12 ... Negative electrode collector, 14 ... Negative electrode active material layer, 30 ... Power generation element, 18 ... Separator, 20 ... Positive electrode, 22 ... Positive electrode current collector Body, 24 ... positive electrode active material layer, 50 ... exterior body, 60, 62 ... lead, 100 ... lithium ion secondary battery

Claims (8)

Including compound particles represented by the following general formula (1) and a coating part formed so as to cover at least a part of the compound particles;
The positive electrode active material for a lithium ion secondary battery, wherein the covering portion is a composite layer having a hydroxide compound and a hydrophobic compound.
LiMPO ₄ ... General formula (1)
(M represents at least one selected from the group consisting of Fe, Mn, Co, Ni and VO)   The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein at least a part of a surface layer portion of the composite layer is the hydrophobic compound.   3. The lithium ion according to claim 1, wherein the composite layer has a ratio X of the hydrophobic compound to a total of the hydroxylated compound and the hydrophobic compound of 5 mass% ≦ X ≦ 25 mass%. Positive electrode active material for secondary battery. The hydroxide compound is Fe (OH) ₂ or Fe (OH) ₃ or FeO (OH), Co (OH) ₂ or Co (OH) ₃ , NiOH or Ni (OH) ₂ or NiO (OH). The positive electrode active material for a lithium ion secondary battery according to claim 1, comprising at least one kind.   5. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the hydrophobic compound includes at least one of a paraffinic hydrocarbon compound and a naphthene hydrocarbon compound.   The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the composite layer contains a lithium compound.   A positive electrode for a lithium ion secondary battery, comprising the positive electrode active material according to claim 1. A lithium ion secondary battery comprising: the positive electrode according to claim 7; a negative electrode having a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte. .

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