JP6784013B2 - Positive electrode active material for non-aqueous electrolyte secondary batteries and its manufacturing method - Google Patents

Description

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same.

In recent years, hybrid electric vehicles (HEVs), electric vehicles (EVs), and fuel cell vehicles have been manufactured and sold from the viewpoints of the environment and fuel efficiency, and new developments are continuing. In these so-called electric vehicles, it is indispensable to utilize a power supply device capable of charging and discharging. As this power supply device, a secondary battery such as a lithium ion battery or a nickel hydrogen battery, an electric double layer capacitor, or the like is used. In particular, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are considered to be suitable for electric vehicles due to their high energy density and high durability against repeated charging and discharging, and various developments are being enthusiastically promoted. ..

Non-aqueous electrolyte secondary batteries intended for application to electric vehicles are required to have high output and high capacity. As the positive electrode active material used for the positive electrode of such a non-aqueous electrolyte secondary battery, a solid solution positive electrode active material containing a transition metal such as lithium and manganese is known as a high-capacity type positive electrode active material.

In such a solid solution positive electrode active material, it is known that transition metals (for example, Ni, Mn) in the positive electrode active material are eluted into the electrolytic solution while the battery is repeatedly charged and discharged. When the transition metal is eluted, the crystal structure of the positive electrode active material is changed and sufficient lithium ions cannot be occluded, which may cause a problem that the capacity of the battery is reduced.

In order to prevent the elution of the transition metal, in Patent Document 1, the composition formula: xLiMO ₂ · (1-x) Li ₂ M'O ₃ (where 0 <x <1, M is V, Mn, Fe, Co. Alternatively, a positive electrode active material represented by (Ni, M'is Mn, Ti, Zr, Ru, Re or Pt) has been proposed. Further, in the examples of the document, it is described that the positive electrode active material having the above composition is produced by using the molten salt method and the coprecipitation method.

U.S. Patent Application Publication No. 2004/0081888

However, even with the technique described in Patent Document 1, the elution of the transition metal from the positive electrode active material is not sufficiently prevented, and the desired cycle characteristics cannot be achieved.

Therefore, an object of the present invention is to provide a positive electrode active material capable of exhibiting sufficient cycle characteristics while ensuring a high discharge capacity in a non-aqueous electrolyte secondary battery.

As a result of diligent research by the present inventor, it has been found that the above-mentioned problems can be solved by a positive electrode active material having the following constitution and a production method, and the present invention has been completed.

That is, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has the following composition formula:
[Li _1.5 ] [Li _{0.5 (1-x)} Mn _1-x M _1.5x ] O ₃
(In the formula, x satisfies 0.1 ≦ x ≦ 0.8, and M is represented by Ni _α Co _β Mn _γ . At this time, 0 ≦ α ≦ 0.5, 0 ≦ _β ≦ 0.5, 0 ≤γ≤1 and α + β + γ = 1)
It is characterized by having a composition represented by and having a layered structure from the inside of the particles constituting the active material to the outermost surface.

Further, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is characterized by including the following steps:
Conditions for a precursor containing a Li compound, an Mn compound, a Ni compound, and a raw material containing a Co compound, if necessary, at a heating rate of 50 to 100 ° C./hour, a firing temperature of 600 to 850 ° C., and a firing time of 6 to 12 hours. Step of obtaining a processed product by heat treatment with (1st firing step);
A step of obtaining a fired product by firing the processed product under the conditions of a heating rate of 200 to 400 ° C./hour, a firing temperature of 900 to 1100 ° C., and a firing time of 1 to 75 minutes (second firing step).

According to the positive electrode active material according to the present invention, the crystal growth of the surface layer is promoted, so that both high discharge capacity and cycle durability can be realized. Further, according to the production method according to the present invention, it is possible to suppress the growth of the crystallinity of the active material and suppress the decrease in crystallinity of the surface layer of the active material particles so that the crystal structure is equal to or higher than that of the internal crystal structure. .. As a result, both high discharge capacity and cycle durability can be realized.

It is sectional drawing schematically showing the outline of the laminated type flat non-bipolar lithium ion secondary battery which is a typical embodiment of the electric device which concerns on this invention. It is a perspective view which represented the appearance of the laminated flat lithium ion secondary battery which is a typical embodiment of the electric device which concerns on this invention. It is a graph which illustrated the relationship between the discharge capacity and the cycle durability based on the result of an Example. 6 is a photograph showing a TEM image of the positive electrode active material obtained in Example 2 and Comparative Example 1 and an electron diffraction image obtained by an electron beam nanobeam.

Hereinafter, embodiments of the present invention will be described. In this specification, "positive electrode active material for non-aqueous electrolyte secondary battery" is simply "positive electrode active material", "positive electrode for non-aqueous electrolyte secondary battery" is simply "positive electrode", and "non-aqueous electrolyte secondary". The "secondary battery" is also simply referred to as a "secondary battery" or a "battery".

One embodiment of the present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. In the production method, a precursor containing a Li compound, an Mn compound, a Ni compound, and a raw material containing a Co compound, if necessary, is heated at a heating rate of 50 to 100 ° C./hour, a firing temperature of 600 to 850 ° C. The first firing step of heat-treating the processed product under the conditions of ~ 12 hours, and the conditions of the temperature rising rate of 200 to 400 ° C./hour, the firing temperature of 900 to 1100 ° C., and the firing time of 1 to 75 minutes. It includes a second firing step of firing to obtain a fired product.

Hereinafter, an embodiment of a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following forms. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

Hereinafter, the basic configuration of the non-aqueous electrolyte secondary battery according to the present embodiment to which the positive electrode active material for the non-aqueous electrolyte secondary battery according to the present invention of the present invention can be applied will be described with reference to the drawings. In the present embodiment, a lithium ion secondary battery will be described as an example of the non-aqueous electrolyte secondary battery according to the present embodiment.

First, a positive electrode for a lithium ion secondary battery, which is a typical embodiment of a positive electrode containing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention, and a lithium ion secondary using the positive electrode. In a battery, the voltage of the cell (single battery layer) is large, and high energy density and high output density can be achieved. Therefore, the lithium ion secondary battery using the positive electrode active material for the lithium ion secondary battery according to the present embodiment is excellent as a drive power source for a vehicle or an auxiliary power source. As a result, it can be suitably used as a lithium ion secondary battery for driving a vehicle. In addition to this, it is fully applicable to lithium ion secondary batteries for mobile devices such as mobile phones.

That is, the lithium ion secondary battery that is the target of the present embodiment may be one that uses the positive electrode active material for the lithium ion secondary battery of the present embodiment described below, and other constituent requirements are , Should not be particularly restricted.

For example, when the lithium ion secondary battery is distinguished by its form and structure, it can be applied to any conventionally known form and structure such as a laminated (flat) battery and a wound (cylindrical) battery. It is a thing. By adopting a laminated (flat type) battery structure, long-term reliability can be ensured by a simple thermocompression bonding and other sealing technology, which is advantageous in terms of cost and workability.

Further, when viewed in terms of the electrical connection form (electrode structure) in the lithium ion secondary battery, it can be applied to both non-bipolar type (internal parallel connection type) batteries and bipolar type (internal series connection type) batteries. It is a thing.

When distinguished by the type of electrolyte layer in the lithium ion secondary battery, a solution electrolyte type battery using a solution electrolyte such as a non-aqueous electrolyte solution for the electrolyte layer, a polymer battery using a polymer electrolyte for the electrolyte layer, etc. It can be applied to any conventionally known type of electrolyte layer. The polymer battery is further divided into a gel electrolyte type battery using a polymer gel electrolyte (also simply referred to as a gel electrolyte) and a solid polymer (all solid) type battery using a polymer solid electrolyte (also simply referred to as a polymer electrolyte). Be done.

Therefore, in the following description, a non-bipolar type (internal parallel connection type) lithium ion secondary battery using the positive electrode active material for the lithium ion secondary battery of the present embodiment will be described very briefly with reference to the drawings. However, the technical scope of the lithium ion secondary battery of the present embodiment should not be limited to these.

<Overall structure of battery>
FIG. 1 schematically illustrates the overall structure of a flat (laminated) lithium-ion secondary battery (hereinafter, also simply referred to as “laminated battery”), which is a typical embodiment of the electric device of the present invention. It is the sectional drawing which showed.

As shown in FIG. 1, the laminated battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminated sheet 29 which is an exterior body. .. Here, in the power generation element 21, the positive electrode active material layers 15 are arranged on both sides of the positive electrode current collector 12, the electrolyte layer 17, and the negative electrode active material layers 13 are arranged on both sides of the negative electrode current collector 11. It has a structure in which a negative electrode is laminated. Specifically, one positive electrode active material layer 15 and a negative electrode active material layer 13 adjacent thereto are opposed to each other via an electrolyte layer 17, and a negative electrode, an electrolyte layer, and a positive electrode are laminated in this order. ..

As a result, the adjacent positive electrode, electrolyte layer, and negative electrode form one cell cell layer 19. Therefore, it can be said that the laminated battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are laminated and electrically connected in parallel. The positive electrode current collectors in the outermost layers located in both outermost layers of the power generation element 21 have the positive electrode active material layer 15 arranged on only one side, but active material layers may be provided on both sides. .. That is, instead of using a current collector dedicated to the outermost layer in which the active material layer is provided on only one side, a current collector having active material layers on both sides may be used as it is as the current collector in the outermost layer. Further, by reversing the arrangement of the positive electrode and the negative electrode as in FIG. 1, the negative electrode current collector of the outermost layer is located on both outermost layers of the power generation element 21, and one side of the negative electrode current collector of the outermost layer or The negative electrode active material layer may be arranged on both sides.

The positive electrode current collector 12 and the negative electrode current collector 11 are attached with a positive electrode current collector plate 27 and a negative electrode current collector plate 25 that are electrically connected to each electrode (positive electrode and negative electrode), and are sandwiched between the ends of the laminate sheet 29. It has a structure that is led out to the outside of the laminated sheet 29. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode via positive electrode leads and negative electrode leads (not shown), respectively, as necessary. It may be attached by resistance welding or the like.

Hereinafter, the members constituting the battery of the present embodiment will be described in detail.

(Positive electrode active material for lithium-ion batteries)
In the present embodiment, the main active material (positive electrode material) of the positive electrode (positive electrode active material layer) is obtained by a predetermined production method. That is, according to one embodiment of the present invention, a precursor containing a raw material containing a Li compound, an Mn compound, a Ni compound, and, if necessary, a Co compound, is heated at a heating rate of 50 to 100 ° C./hour and a firing temperature of 600 to 600. The first firing step of heat-treating the processed product under the conditions of 850 ° C. and firing time of 6 to 12 hours to obtain a processed product, and the temperature rising rate of 200 to 400 ° C./hour, firing temperature of 900 to 1100 ° C., firing time of 1 Provided is a method for producing a positive electrode active material, which comprises a second firing step of calcining under the condition of ~ 75 minutes to obtain a calcined product. By using such a production method, it is possible to suppress the growth of the crystallite diameter and suppress the decrease in crystallinity of the surface layer of the active material particles so that the crystal structure is equal to or higher than that of the internal crystal structure. As a result, both high discharge capacity and cycle durability of the lithium ion secondary battery can be realized. Hereinafter, the technical scope of the present invention will be described in detail in the order of steps including any step, but the technical scope of the present invention should be determined based on the description of the claims.

First, as a starting material, a predetermined amount of a raw material containing a compound of a metal element constituting a positive electrode active material, that is, a Li compound, an Mn compound, a Ni compound, and, if necessary, a Co compound is weighed to prepare a mixture thereof. .. The types of these compounds are not particularly limited, and examples thereof include sulfates, nitrates, carbonates, acetates, oxalates, oxides, hydroxides, and halides.

Specifically, as the Li compound, Li ₂ CO ₃ , LiOH, LiNO ₃ , CH ₃ COOLi, Li ₂ O and the like can be used, and LiOH or Li ₂ CO ₃ is preferably used. One of these Li compounds may be used alone, or two or more thereof may be used in combination. Moreover, these Li compounds may be used in the form of a hydrate.

As the Mn compound, manganese oxides such as Mn ₂ O ₃ , Mn O ₂ , and Mn ₃ O ₄ , MnSO ₄ , MnCO ₃ , Mn (NO ₃ ) ₂ , (CH ₃ COO) ₂ Mn, and the like can be used. Preferably (CH ₃ COO) ₂ Mn or MnO ₂ is used. One of these Mn compounds may be used alone, or two or more thereof may be used in combination. Moreover, these Mn compounds may be used in the form of a hydrate.

As the Ni _{compound, NiSO 4, Ni (OH)} 2, NiO, NiCO 3 · 2Ni (OH) 2, Ni (NO 3) 2, it can be used (CH 3 _COO) 2 Ni or the like, preferably (CH ₃ COO) _{2 Use} Ni or NiSO ₄ . One of these Ni compounds may be used alone, or two or more thereof may be used in combination. Moreover, these Ni compounds may be used in the form of a hydrate.

Examples of Co compounds include CoSO ₄ , Co (OH) ₂ , CoO, Co ₂ O ₃ , Co ₃ O ₄ , (CH ₃ COO) ₂ Co, CoCl ₂ , Co (NO ₃ ) ₂ , C ₂ O ₄ Co, etc. Can be used, preferably (CH ₃ COO) ₂ Co or CoSO ₄ . One of these Co compounds may be used alone, or two or more thereof may be used in combination. Moreover, these Co compounds may be used in the form of a hydrate.

In addition to Li, Mn, Ni, and Co if necessary, when other elements are contained, compounds of the elements (for example, sulfates, nitrates, carbonates, acetates, oxalates, oxidations). Substances, hydroxides, halides, etc.) may be added to the compounds of the above elements and mixed together.

All of these raw materials may be in powder form. From the viewpoint of enhancing the uniformity of mixing and the reactivity at the time of firing, the particle size of the raw material is usually preferably 0.01 to 200 μm in terms of average particle size.

The raw materials may be mixed by the method used for mixing ordinary powders, and either dry mixing or wet mixing can be selected. As the device used for mixing, a known means such as a ball mill, a V blender, a mortar, a mixer, and a kneading device can be selected. The mixing time and mixing temperature are not particularly limited, but are usually 1 minute or more at room temperature (23 ° C.) or higher. Insufficient mixing may reduce the performance (capacity characteristics, cycleability) of the finally obtained positive electrode active material. Therefore, it is necessary to sufficiently mix the raw materials until they are in a uniform state at the particle level. preferable. The blending amount of the raw material may be determined according to the composition of the positive electrode material to be produced. The atmosphere at which the raw materials are mixed is not particularly limited and may be carried out in an inert atmosphere or in the air, but it is preferable to carry out in the air in consideration of the production cost.

(1) Temporary firing step It is preferable to temporarily fire the mixture obtained subsequently before the main firing. However, the temporary firing step is not an essential step, and the mixture of the raw materials of the positive electrode active material obtained above may be used as it is for the main firing. By performing the calcination, segregation of the positive electrode active material can be prevented and a uniform mixed state can be obtained. The tentative firing temperature is preferably between 350 and 700 ° C. If the temperature is 350 ° C. or higher, the reaction proceeds, and if the temperature is 700 ° C. or lower, firing proceeds and pulverization becomes difficult. The tentative firing time is not particularly limited, but is usually about 4 to 10 hours. The atmosphere of the tentative firing is not particularly limited as long as it contains oxygen, but it is preferable to perform the calcining in the atmosphere in consideration of the manufacturing cost.

Then, the pre-baked raw material is pulverized again using a ball mill, a V-blender, a mortar, a mixer, a kneading device, or the like to obtain a mixture of raw material powders. The degree of pulverization is not particularly limited, but it is preferable to pulverize so that the average particle size is 0.01 to 200 μm.

(2) First firing step In this step, the mixture of the raw materials obtained above or the mixture of the raw material powders after the preliminary firing (these mixture is also referred to as "precursor" in the present specification) is heat-treated (baked). To obtain the processed product. Here, in the first firing step, the rate of temperature rise, the firing temperature, and the firing time during the heat treatment (calcination) are set to values within a predetermined range. Specifically, the heating rate is 50 to 100 ° C./hour, preferably 75 to 100 ° C./hour, and more preferably 80 to 100 ° C./hour. The firing temperature is 600 to 850 ° C, preferably 700 to 825 ° C, and more preferably 750 to 800 ° C. Further, the firing time is 6 to 12 hours, preferably 8 to 12 hours, and more preferably 10 to 12 hours. The "firing time" means the time from reaching a predetermined temperature to the end of the heat treatment. Here, if the firing conditions in the first firing step deviate from the above-mentioned predetermined range, the effects of the present invention (high discharge capacity and high cycle durability improvement in the solid solution positive electrode active material) cannot be sufficiently obtained. The atmosphere of the first firing step is not particularly limited as long as it contains oxygen, but it is preferable to carry out the first firing step in the atmosphere in consideration of the manufacturing cost.

(3) Second firing step Subsequently, the processed product obtained in the first firing step is heat-treated (baked) at a higher temperature for a short time to obtain a fired product. Here, also in the second firing step, the rate of temperature rise, the firing temperature, and the firing time during the heat treatment (calcination) are set to values within a predetermined range. Specifically, the heating rate is 200 to 400 ° C./hour, preferably 300 to 400 ° C./hour, and more preferably 350 to 400 ° C./hour. The firing temperature is 900 to 1100 ° C, preferably 850 to 1000 ° C, and more preferably 900 to 950 ° C. Further, the firing time is 1 to 75 minutes, preferably 3 to 45 minutes, and more preferably 5 to 30 minutes. Here, if the production of the active material is completed only in the first firing step without performing the second firing step, the layered structure in the surface layer of the active material is disturbed and a rock salt type structure is generated. As a result, it is considered that sufficient cycle durability cannot be realized. Further, even if the second firing step is performed, if the firing conditions in the second firing step are out of the above-mentioned predetermined range, the effect of the present invention (high discharge capacity and high cycle durability in the solid solution positive electrode active material) is improved. ) Is not sufficiently obtained. In particular, if the rate of temperature rise is too low, a sufficient discharge capacity cannot be secured even if the firing time is controlled to be short or long, and the advantage of using the solid solution positive electrode active material cannot be enjoyed. On the other hand, when the second firing step is carried out so as to satisfy the above-mentioned conditions, the formation of rock salt type structure and the disorder of the layered structure on the surface layer of the active material are suppressed by promoting the crystal growth of the surface layer. As a result, it is possible to improve the cycle durability while maintaining a high discharge capacity. The atmosphere of the second firing step is not particularly limited as long as it contains oxygen, but it is preferable to carry out the second firing step in the atmosphere in consideration of the manufacturing cost.

According to the above-mentioned production method, the following composition formula:
[Li _1.5 ] [Li _{0.5 (1-x)} Mn _1-x M _1.5x ] O ₃
(In the formula, x satisfies 0.1 ≦ x ≦ 0.8, and M is represented by Ni _α Co _β Mn _γ . At this time, 0 ≦ α ≦ 0.5, 0 ≦ _β ≦ 0.5, 0 ≤γ≤1 and α + β + γ = 1)
A positive electrode active material for a non-aqueous electrolyte secondary battery having a composition represented by, and having a layered structure from the inside to the outermost surface of particles constituting the active material. The substance is obtained. According to the present invention, the positive electrode active material is also provided as a novel and inventive step invention. In addition, in this specification, a "layered structure" means a layered structure in which a lithium layer-oxygen layer-transition metal layer is laminated. Here, in the positive electrode active material, it is preferable that the crystal structure of the outermost layer of the particles constituting the active material (for example, a position at a depth of 10 nm from the surface of the particles) does not include a rock salt type structure. The positive electrode active material according to the preferred embodiment has, for example, nanobeam electrons having a crystal structure at a position 10 nm deep and a 50 nm depth position from the surface of the particles, as described with reference to FIG. 4 in Examples described later. It can also be expressed that the diffraction patterns at both positions show similar patterns when analyzed by linear diffraction.

The lithium ion secondary battery of the present embodiment described above with reference to FIG. 1 is characterized by a positive electrode. Hereinafter, the main components of the battery including the positive electrode will be described.

<Active material layer>
The active material layer 13 or 15 contains an active material and, if necessary, further contains other additives.

[Positive electrode active material layer]
The positive electrode active material layer 15 contains a positive electrode active material.

(Positive electrode active material)
The lithium ion secondary battery according to the present embodiment is characterized in that the positive electrode active material layer 15 contains the above-mentioned positive electrode active material. Here, as described above, the positive electrode active material has a predetermined composition formula [Li _1.5 ] [Li _{0.5 (1-x)} Mn _1-x M _1.5x ] O ₃ (in the formula, x). Satisfies 0.1 ≦ x ≦ 0.8, and M is represented by Ni _α Co _β Mn _γ , in which case 0 ≦ α ≦ 0.5, 0 ≦ _β ≦ 0.5, and 0 ≦ γ ≦ 1. Yes, and it is represented by α + β + γ = 1).

In the composition formula representing the composite oxide, x in the formula is 0.1 to 0.8 as described above. If x exceeds 0.8, a discharge capacity of 200 mAh / g or more cannot be obtained, and a sufficient capacity advantage cannot be exhibited as compared with a known layered positive electrode active material. Further, when x is less than 0.1, the composition becomes close to Li ₂ MnO ₃ , and charging / discharging may not be possible.

For M in the composition formula represented by Ni _α Co _β Mn _γ , α is 0 to 0.5, β is 0 to 0.5, γ is 0 to 1, and α + β + γ is 1.

Regarding the values of x, α, β, and γ in the composition formula of the above composite oxide, 0.3 ≦ x ≦ 0.7, 0.125 ≦ α ≦ 0.25, 0 ≦ β ≦ 0.25, and 0, respectively. It is preferably in the range of ≦ γ ≦ 0.25.

The solid solution represented by the above composition formula can be identified by using X-ray diffraction (XRD), Raman spectroscopy, and inductively coupled plasma (ICP) elemental analysis. Further, whether or not the particles constituting the positive electrode active material have a layered structure from the inside to the outermost surface can be determined by using an electron beam nanobeam as described in the column of Examples described later. It can be determined based on whether or not the disorder of the layered structure is observed in the electron diffraction image.

From the viewpoint of improving the low Li diffusing ability in the solid, the smaller the crystallite diameter of the positive electrode active material is, the more preferable. Here, the "crystallite" means the maximum group that can be regarded as a single crystal, and can be measured by a method of refining the structural parameters of the crystal from the diffraction intensity obtained by powder X-ray diffraction measurement or the like. The specific value of the crystallite diameter of the positive electrode active material according to the present embodiment is not particularly limited, but is preferably 600 nm or less, more preferably 350 nm or less, and further preferably 300 nm or less. The lower limit of the crystallite diameter is not particularly limited, but is usually 20 nm or more. Here, in the present specification, the value of the crystallite diameter of the positive electrode active material shall be the value measured by the method described in the column of Examples described later.

The lithium ion secondary battery according to the present embodiment has a positive electrode active material layer 15. The lithium ion secondary battery according to the present embodiment has a positive electrode active material layer 15 containing a positive electrode active material produced by the above-mentioned production method. Although it is characterized in that, other positive electrode active materials may be contained in the positive electrode active material layer 15. However, in the lithium ion secondary battery according to the present embodiment, the positive electrode active material layer 15 contains the positive electrode active material produced by the above-mentioned manufacturing method as the main component (as a ratio of the positive electrode active material to the total amount of the positive electrode active material). It is preferably contained in an amount of 50% by mass or more), more preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass. Examples of other positive electrode active materials include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni-Mn-Co) O _2, and a part of these transition metals substituted with other elements. Such as lithium-transition metal composite oxide, lithium-transition metal phosphate compound, lithium-transition metal sulfate compound and the like. In some cases, two or more kinds of positive electrode active materials may be used in combination.

The average particle size of the positive electrode active material contained in the positive electrode active material layer 15 is not particularly limited, but is preferably 1 to 30 μm, more preferably 5 to 20 μm from the viewpoint of increasing the output. In the present specification, the "particle size" is on the contour line of the active material particle (observation surface) observed by using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It means the maximum distance among the distances between any two points. Further, in the present specification, the value of "average particle size" is a value of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of the particle size shall be adopted. The particle size and average particle size of other constituents can be defined in the same way.

The positive electrode active material layer 15 may include a binder.

(Binder)
The binder is added for the purpose of binding the active materials to each other or the active material and the current collector to maintain the electrode structure. The binder used for the positive electrode active material layer is not particularly limited, and examples thereof include the following materials. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamideimide, cellulose, carboxymethyl cellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene / butadiene Rubber (SBR), isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and its hydrogen additive, styrene / isoprene / styrene block copolymer and Thermoplastic polymers such as the hydrogenated products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether co-weight. Fluororesin such as coalescence (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), etc. Vinylidene Fluoride-Hexafluoropropylene Fluororesin (VDF-HFP Fluororesin), Vinylidene Fluoride-Hexafluoropropylene-Tetrafluoroethylene Fluororesin (VDF-HFP-TFE Fluororesin), Vinylidene Fluoride-Pentafluoro Propylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene Examples thereof include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers) and epoxy resins. Of these, polyvinylidene fluoride, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, polyamide, and polyamideimide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, are stable in both positive electrode potential and negative electrode potential, and can be used in the active material layer. These binders may be used alone or in combination of two.

The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it can bind the active material, but is preferably 0.5 to 15% by mass with respect to the active material layer. It is more preferably 1 to 10% by mass.

The positive electrode (positive electrode active material layer) can be coated by any of a kneading method, a sputtering method, a vapor deposition method, a CVD method, a PVD method, an ion plating method, and a thermal spraying method, in addition to a normal slurry coating method. Can be formed.

[Negative electrode active material layer]
The negative electrode active material layer 13 contains a negative electrode active material.

(Negative electrode active material)
Negative negative active materials include natural graphite, artificial graphite, carbon black, activated charcoal, carbon fiber, coke, soft carbon, carbon such as hard carbon, pure metals such as Si and Sn, and alloys such as Si—Sn—Ti alloy. With active materials, metal oxides such as TiO, Ti ₂ O ₃ , TiO ₂ , or SiO ₂ , SiO, SnO ₂ , lithium and transition metals such as Li _4/3 Ti _5/3 O ₄ or Li ₇ MnN Examples thereof include composite oxides, Li-Pb-based alloys, Li-Al-based alloys, and Li.

Subsequently, the negative electrode active material layer 13 includes a binder.

(Binder)
The binder is added for the purpose of binding the active materials to each other or the active material and the current collector to maintain the electrode structure. The type of binder used for the negative electrode active material layer is also not particularly limited, and the above-mentioned binder can be similarly used as the binder used for the positive electrode active material layer. Therefore, detailed description thereof will be omitted here.

The amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it can bind the active material, but is preferably 0.5 to 0.5 to the negative electrode active material layer. It is 20% by mass, more preferably 1 to 15% by mass.

(Requirements common to positive electrode and negative electrode active material layers 15 and 13)
The requirements common to the positive electrode and negative electrode active material layers 15 and 13 will be described below.

The positive electrode active material layer 15 and the negative electrode active material layer 13 contain a conductive auxiliary agent, an electrolyte salt (lithium salt), an ionic conductive polymer, and the like, if necessary. In particular, the negative electrode active material layer 13 also essentially contains a conductive auxiliary agent.

Conductive Auxiliary Agent Conductive auxiliary agent refers to an additive compounded to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive auxiliary agent include carbon black such as acetylene black, and carbon materials such as graphite and vapor-grown carbon fiber. When the active material layer contains a conductive auxiliary agent, an electronic network inside the active material layer is effectively formed, which can contribute to the improvement of the output characteristics of the battery.

The content of the conductive auxiliary agent mixed in the active material layer is in the range of 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, based on the total amount of the active material layer. The content of the conductive additive mixed in the active material layer is in the range of 15% by mass or less, more preferably 10% by mass or less, still more preferably 7% by mass or less, based on the total amount of the active material layer. is there. The electron conductivity of the active material itself is low, and the electrode resistance can be reduced by the amount of the conductive auxiliary agent. By defining the compounding ratio (content) of the conductive auxiliary agent in the active material layer within the above range, the following effects are exhibited. To. That is, the electron conductivity can be sufficiently ensured without hindering the electrode reaction, the decrease in energy density due to the decrease in electrode density can be suppressed, and the energy density can be improved by improving the electrode density. ..

Further, a conductive binder having both the functions of the conductive auxiliary agent and the binder may be used in place of the conductive auxiliary agent and the binder, or may be used in combination with one or both of the conductive auxiliary agent and the binder. .. As the conductive binder, a commercially available TAB-2 (manufactured by Hosen Co., Ltd.) can be used.

Electrolyte salt (lithium salt)
Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

Ionic Conductive Polymers Examples of ionic conductive polymers include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

The compounding ratio of the components contained in the positive electrode active material layer and the negative electrode active material layer is not particularly limited. The compounding ratio can be adjusted by appropriately referring to known knowledge about the non-aqueous solvent secondary battery.

The thickness of each active material layer (active material layer on one side of the current collector) is also not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. As an example, the thickness of each active material layer is usually about 1 to 500 μm, preferably about 2 to 100 μm, in consideration of the purpose of use of the battery (emphasis on output, emphasis on energy, etc.) and ionic conductivity.

<Current collector>
The current collectors 11 and 12 are made of a conductive material. The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires high energy density, a current collector having a large area is used.

There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

The shape of the current collector is also not particularly limited. In the laminated battery 10 shown in FIG. 1, in addition to the current collecting foil, a mesh shape (expanded grid or the like) or the like can be used.

When a thin film alloy is directly formed on the negative electrode current collector 12 by a sputtering method or the like for the negative electrode active material, it is desirable to use a current collector foil.

There are no particular restrictions on the materials that make up the current collector. For example, a metal or a resin obtained by adding a conductive filler to a conductive polymer material or a non-conductive polymer material can be adopted.

Specific examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Further, it may be a foil in which the metal surface is coated with aluminum. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoints of electron conductivity, battery operating potential, adhesion of the negative electrode active material by sputtering to the current collector, and the like.

Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

Examples of the non-conductive polymer material include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), and polyimide. (PI), Polyethyleneimide (PAI), Polyethylene (PA), Polytetrafluoroethylene (PTFE), Styrene-butadiene rubber (SBR), Polyacrylonitrile (PAN), Polymethylacrylate (PMA), Polymethylmethacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), polystyrene (PS) and the like. Such non-conductive polymer materials can have excellent potential resistance or solvent resistance.

A conductive filler may be added to the above-mentioned conductive polymer material or non-conductive polymer material, if necessary. In particular, when the resin used as the base material of the current collector is composed of only a non-conductive polymer, a conductive filler is inevitably indispensable in order to impart conductivity to the resin.

The conductive filler can be used without particular limitation as long as it is a conductive substance. For example, a material having excellent conductivity, potential resistance, or lithium ion blocking property includes metals and conductive carbon. The metal is not particularly limited, but is at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or a metal thereof. It is preferable to contain an alloy or a metal oxide containing. Further, the conductive carbon is not particularly limited. Preferably, it contains at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene.

The amount of the conductive filler added is not particularly limited as long as it can impart sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

<Electrolyte layer>
As the electrolyte constituting the electrolyte layer 17, a liquid electrolyte or a polymer electrolyte can be used.

The liquid electrolyte has a form in which a lithium salt (electrolyte salt) is dissolved in an organic solvent. Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and the like. Examples thereof include carbonates such as methylpropyl carbonate (MPC).

As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF 3 SO 3 , etc. A compound that can be added to the active material layer of the electrode can be adopted.

On the other hand, polymer electrolytes are classified into gel electrolytes containing an electrolytic solution and intrinsic polymer electrolytes not containing an electrolytic solution.

The gel electrolyte has a structure in which the above liquid electrolyte (electrolyte solution) is injected into a matrix polymer made of an ionic conductive polymer. By using a gel polymer electrolyte as the electrolyte, the fluidity of the electrolyte is lost, and it is easy to block the ionic conduction between the layers, which is excellent.

Examples of the ionic conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. An electrolyte salt such as a lithium salt can be well dissolved in such a polyalkylene oxide-based polymer.

The ratio of the liquid electrolyte (electrolyte solution) in the gel electrolyte is not particularly limited, but is preferably about several mass% to 98 mass% from the viewpoint of ionic conductivity and the like. In this embodiment, it is particularly effective for a gel electrolyte having a large amount of electrolyte and having a proportion of the electrolyte of 70% by mass or more.

When the electrolyte layer is composed of a liquid electrolyte, a gel electrolyte, or an intrinsic polymer electrolyte, a separator may be used for the electrolyte layer. Specific forms of the separator (including non-woven fabric) include, for example, a microporous membrane made of polyolefin such as polyethylene or polypropylene, a porous flat plate, and a non-woven fabric.

The true polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the above-mentioned matrix polymer, and does not contain an organic solvent as a plasticizer. Therefore, when the electrolyte layer is composed of the intrinsic polymer electrolyte, there is no concern about liquid leakage from the battery, and the reliability of the battery can be improved.

Matrix polymers of gel electrolytes and true polymer electrolytes can exhibit excellent mechanical strength by forming crosslinked structures. In order to form a crosslinked structure, a suitable polymerization initiator is used, and a polymerizable polymer for forming a polymer electrolyte (for example, PEO or PPO) is subjected to thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. It may be polymerized.

<Current collector plate and lead>
A current collector may be used for the purpose of extracting current to the outside of the battery. The current collector plate is electrically connected to the current collector and the reed, and is taken out of the laminated sheet which is the battery exterior material.

The material constituting the current collector plate is not particularly limited, and a known highly conductive material conventionally used as a current collector plate for a lithium ion secondary battery can be used. As the constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable, and more preferably aluminum, from the viewpoint of light weight, corrosion resistance, and high conductivity. Copper or the like is preferable. The same material may be used for the positive electrode current collector plate and the negative electrode current collector plate, or different materials may be used.

The positive electrode terminal lead and the negative electrode terminal lead are also used as necessary. As the material of the positive electrode terminal lead and the negative electrode terminal lead, the terminal lead used in a known lithium ion secondary battery can be used. The portion taken out from the battery exterior material 29 has heat-resistant insulation so as not to come into contact with peripheral devices or wiring and cause an electric leakage to affect the product (for example, automobile parts, especially electronic devices). It is preferable to cover with a heat-shrinkable tube or the like.

<Battery exterior material>
As the battery exterior material 29, a known metal can case can be used, or a bag-shaped case using a laminated film containing aluminum that can cover the power generation element can be used. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but the laminate film is not limited thereto. A laminated film is desirable from the viewpoint of high output and excellent cooling performance, and can be suitably used for batteries for large equipment for EVs and HEVs.

The above-mentioned lithium ion secondary battery can be manufactured by a conventionally known manufacturing method.

<Appearance configuration of lithium-ion secondary battery>
FIG. 2 is a perspective view showing the appearance of a laminated flat lithium ion secondary battery.

As shown in FIG. 2, the laminated flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode current collector plate 59 and a negative electrode collector for extracting electric power from both sides thereof. The electric plate 58 is pulled out. The power generation element 57 is wrapped by the battery exterior material 52 of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element 57 pulls out the positive electrode current collector plate 59 and the negative electrode current collector plate 58 to the outside. It is sealed in a closed state. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery (stacked battery) 10 shown in FIG. The power generation element 57 is formed by stacking a plurality of single battery layers (single cells) 19 composed of a positive electrode (positive electrode active material layer) 13, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 15.

The lithium ion secondary battery is not limited to a laminated flat battery (laminated cell). Winding lithium-ion batteries include those with a cylindrical shape (coin cell) and those with a prismatic shape (square cell), and those that are shaped like a rectangular flat shape by deforming such a cylindrical shape. Further, the cell may be a cylindrical cell, and the like is not particularly limited. The cylindrical or prismatic shape is not particularly limited, for example, a laminated film may be used for the exterior material, or a conventional cylindrical can (metal can) may be used. Preferably, the power generation element is exteriorized with an aluminum laminate film. By this form, weight reduction can be achieved.

Further, the removal of the positive electrode current collector plate 59 and the negative electrode current collector plate 58 shown in FIG. 2 is not particularly limited. The positive electrode current collector plate 59 and the negative electrode current collector plate 58 may be pulled out from the same side, or the positive electrode current collector plate 59 and the negative electrode current collector plate 58 may be divided into a plurality of each and taken out from each side. It is not limited to what is shown in FIG. 2, such as good. Further, in the winding type lithium ion battery, the terminal may be formed by using, for example, a cylindrical can (metal can) instead of the current collector plate.

As described above, the positive electrode and the lithium ion secondary battery made of the positive electrode active material for the lithium ion secondary battery of the present embodiment are large in electric vehicles, hybrid electric vehicles, fuel cell vehicles, hybrid fuel cell vehicles, and the like. It can be suitably used as a capacitive power source. That is, it can be suitably used for a vehicle driving power source or an auxiliary power source that requires a high volume energy density and a high volume output density.

Hereinafter, the present invention will be specifically described through Examples, but the present invention is not limited to the following Examples.

[Example 1]
< _{Preparation of} positive electrode active material 10 (Li _1.5 [Ni _0.281 Co _0.281 Mn _0.688 [Li _0.25 ]] O ₃ )>
(Preparation of precursor)
As a starting material, a hydroxide of Li and acetates of Ni, Co, and Mn were prepared. Of these starting materials, each acetate of Ni, Co, and Mn was mixed in a predetermined amount using a mortar and a pestle as the first step of synthesis. Then, the precursor was obtained by firing at 500 ° C. for 5 hours in an air atmosphere.

(First firing step)
A predetermined amount of Li hydroxide was added to the precursor and mixed, and the first firing step was carried out in an air atmosphere. Specifically, first, the temperature was raised to 750 ° C. at a heating rate of 50 ° C./hour. Then, the first firing step was performed by holding at 750 ° C. for 12 hours.

(Second firing step)
Following the first firing step, the second firing step was carried out in an air atmosphere. Specifically, first, the temperature was raised to 900 ° C. at a heating rate of 400 ° C./hour. Then, the second firing step was performed by holding at 900 ° C. for 7.5 minutes. As a result, the positive electrode active material 10 (Li _1.5 [Ni _0.281 Co _0.281 Mn _0.688 [Li _0.25 ]] O ₃ (in the composition formula (1), x = 0.5, α = 0.1875, β = 0.1875, γ = 0.625, α + β + γ = 1.0) were obtained.

With respect to the obtained positive electrode active material, the average particle size (D1) of the primary particles, the average particle size (D2) of the secondary particles, and the crystallite size were measured. For the measurement of D1 and D2, a cross section of the obtained positive electrode active material is cut out using a FIB (focused ion beam; Focused Ion Beam), and an image of the cross section is taken using a scanning ion microscope (SIM). Measured by For D1, 200 or more primary particles are extracted and calculated as the average value of their diameters in the major axis direction, and for D2, 50 or more secondary particles are extracted and their diameters in the major axis direction are calculated. It was calculated as the average value of. Further, the crystallite diameter was measured by the Rietveld method in which the crystallite diameter was calculated from the diffraction peak intensity obtained by the powder X-ray diffraction measurement. At this time, for the powder X-ray diffraction measurement for calculating the crystallite diameter, an X-ray diffractometer (manufactured by Rigaku) using Cu-Kα rays was used, and the analysis was performed by adopting the Fundamental Parameter. Analysis was performed using the analysis software Topas Version 3 using the X-ray diffraction pattern obtained from the diffraction angle 2θ = 15 to 120 °. The results are shown in Table 4 below.

<Preparation of positive electrode C11>
(Preparation of slurry for positive electrode)
A positive electrode slurry having the following composition was prepared.
_Positive electrode active material 10: Li _1.5 [Ni _0.281 Co _0.281 Mn _0.688 [Li _0.25 ]] O ₃ 90 parts by mass Conductive aid 1: Phosphorus graphite 1.0 parts by mass Conductive aid Agent 2: Acetylene Black 4.0 parts by mass Binder: Polyvinylidene fluoride (PVDF) 5.0 parts by mass Solvent: N-methylpyrrolidone (NMP) 74.0 parts by mass.

First, a binder solution was prepared by dissolving 5.0 parts by mass of PVDF in 50.0 parts by mass of NMP. Next, 55.0 parts by mass of the binder solution was added to a mixed powder of scaly graphite and acetylene black (5.0 parts by mass in total) and 90 parts by mass of the positive electrode active material 10 (powder), and a planetary mixer (Primix Corporation) was added. Kneaded with Hibismix 2P-03). Then, 24.0 parts by mass of NMP was added to the kneaded product to prepare a slurry for a positive electrode (solid content concentration: 57.5% by mass).

(Application and drying of positive electrode slurry)
The positive electrode slurry was applied to one side of a 20 μm-thick aluminum foil current collector with a bar coater. Subsequently, the current collector coated with this positive electrode slurry is dried on a hot plate (120 ° C. to 130 ° C., drying time 10 minutes), and the amount of NMP remaining on the coating film of the positive electrode slurry is 0.02. A sheet-shaped electrode was obtained with a mass% or less.

(Electrode press)
The sheet-shaped electrode obtained above was compression-molded by applying a roller press and cut to prepare a positive electrode C1. The mass of the active material layer on one side was about 3.5 mg / cm ² , the thickness was about 50 μm, and the density was 2.70 g / cm ³ .

(Drying of electrodes)
Next, the positive electrode C1 was dried in a vacuum drying oven. Specifically, first, the positive electrode C1 was installed inside the drying furnace, and then the pressure was reduced (100 mmHg (1.33 × 10 ⁴ Pa)) at room temperature (25 ° C.) to remove the air in the drying furnace. Subsequently, while flowing nitrogen gas (100 cm ³ / min), the temperature was raised to 120 ° C. at 10 ° C./min, the pressure was reduced again at 120 ° C., and the nitrogen in the furnace was kept exhausted for 12 hours, and then at room temperature. The temperature dropped to. In this way, the positive electrode C11 was obtained.

<Making coin cells>
A 2032 type coin cell was produced by the following method.

That is, after the positive electrode C11 produced above was punched to φ15 mm, it was dried again at 100 ° C. for 2 hours in a vacuum dryer before producing the battery. On the other hand, metal Li (φ16 mm, thickness 100 μm) was used for the negative electrode. Further, the separator and the coin cell member described later were dried in advance in a glove box having an argon gas atmosphere at room temperature for 24 hours or more before use.

As the non-aqueous electrolyte solution, 150 μL of 1M LiPF ₆ EC: DEC (1: 2 (volume ratio)) (where EC is ethylene carbonate and DEC is diethyl carbonate) was used.

The procedure for producing a coin cell is as follows. In a glove box with an argon gas atmosphere, the positive and negative electrodes are opposed to each other between the positive electrode C11 and the negative electrode (metal Li) via two polypropylene porous films having a thickness of 20 μm, and are stacked on the bottom of the coin cell. I matched it. Next, a gasket was attached to maintain the insulation between the positive and negative electrodes, an electrolytic solution was injected using a syringe, springs and spacers were laminated, and the upper part of the coin cell was overlapped and crimped to obtain a battery.

[Example 2]
A slurry for a positive electrode, a positive electrode, and a coin cell were produced by the same method as in Example 1 described above, except that the firing conditions in the second firing step were changed as follows.

(Baking conditions in the second firing step)
Temperature rise rate: 200 ° C / hour Baking temperature: 900 ° C
Baking time: 15 minutes [Example 3]
A slurry for a positive electrode, a positive electrode, and a coin cell were produced by the same method as in Example 1 described above, except that the firing conditions in the second firing step were changed as follows.

(Baking conditions in the second firing step)
Temperature rise rate: 200 ° C / hour Baking temperature: 900 ° C
Baking time: 45 minutes [Example 4]
A slurry for a positive electrode, a positive electrode, and a coin cell were produced by the same method as in Example 1 described above, except that the firing conditions in the second firing step were changed as follows.

(Baking conditions in the second firing step)
Temperature rise rate: 200 ° C / hour Baking temperature: 900 ° C
Baking time: 75 minutes [Comparative Example 1]
A slurry for a positive electrode, a positive electrode, and a coin cell were produced by the same method as in Example 1 described above except that the second firing step was not performed.

[Comparative Example 2]
A positive electrode slurry, a positive electrode, and a coin cell were produced by the same method as in Example 1 described above, except that the firing conditions in the first firing step and the second firing step were changed as follows.

(Baking conditions in the first firing step)
Temperature rise rate: 100 ° C / hour Baking temperature: 600 ° C
Baking time: 12 hours (firing conditions in the second firing step)
Temperature rise rate: 100 ° C / hour Baking temperature: 900 ° C
Baking time: 540 minutes [Comparative Example 3]
A slurry for a positive electrode, a positive electrode, and a coin cell were produced by the same method as in Comparative Example 2 described above, except that the second firing step was not performed.

[Comparative Example 4]
A slurry for a positive electrode, a positive electrode, and a coin cell were produced by the same method as in Comparative Example 2 described above, except that the firing conditions in the second firing step were changed as follows.

(Baking conditions in the second firing step)
Temperature rise rate: 100 ° C / hour Baking temperature: 900 ° C
Baking time: 15 minutes <Evaluation of battery characteristics>
The coin cell produced above was set in the evaluation cell mounting jig, and the positive electrode lead and the negative electrode lead were attached to each tab end of the battery, and the following test was performed.

(Activation treatment)
Charging is performed at a 0.1 C rate until the maximum voltage reaches 4.8 V, and then discharging is performed by a constant current discharge method that discharges at a 0.1 C rate until the minimum voltage of the battery reaches 2.0 V. , This activation treatment was carried out at room temperature (Table 1).

(Initial characteristic evaluation)
After charging at a 0.1 C rate until the maximum voltage reached 4.6 V, a constant current charge / discharge cycle of discharging at a 0.1 C rate was performed 5 times at room temperature by a constant current discharge method (Table 2). The results are shown in Table 4 below.

(Cycle durability evaluation)
The battery was evaluated by charging it at a 1.0 C rate until the maximum voltage reached 4.6 V, and then performing 100 constant current charge / discharge cycles at a 1.0 C rate to discharge the battery to 2.0 V at room temperature (Table). 3). The results are shown in Table 4 below.

Based on the results shown in Table 4, FIG. 3 shows a diagram showing the relationship between the discharge capacity and the cycle durability. From these results, rather than the performance trend consisting of Comparative Example 1 and Comparative Example 2, each example has realized both high initial capacity and high cycle durability by performing the two-step heat treatment prescribed in the present application. You can see that.

The analysis result showing the factor of this improvement is shown in FIG. FIG. 4 is a photograph showing a TEM image of the positive electrode active material obtained in Example 2 and Comparative Example 1 and an electron diffraction image obtained by using an electron beam nanobeam. The electron diffraction image shown by 1 in both figures shows information on the surface layer of about 10 nm. Further, the electron diffraction image shown in 3 of both figures shows information of about 50 nm from the surface layer. No change was observed in the electron diffraction image at a position of about 50 nm from the surface layer of both samples, and a diffraction pattern due to a beautiful layered structure was confirmed. On the other hand, when the diffraction patterns at a position of about 10 nm from the surface layer were compared, it was found that the diffraction pattern was disturbed in the positive electrode active material of Comparative Example 1 and contained a rock salt type structure from the analysis results. On the other hand, in the positive electrode active material of Example 2, it was confirmed that the diffraction pattern was not disturbed and the layered structure was maintained from the inside of the active material particles to the outermost surface. Table 4 shows the results of the same analysis for other Examples and Comparative Examples (“○” in “Surface structure state” indicates that the layered structure is maintained from the inside to the outermost surface of the active material particles. It means that no rock salt type structure was observed in the outermost layer, and "x" means that a rock salt type structure was observed in the outermost layer).

From this result, the crystallinity of the surface layer is improved by adding the two-step firing treatment specified in the present application, and the side reaction with the electrolytic solution and the deterioration reaction such as metal elution that occur in the surface layer are suppressed, which leads to the improvement of the battery performance. It was thought that it was. From the above, it was confirmed that high capacity and high cycle durability can be achieved at the same time by improving the crystal state of the surface layer while suppressing the crystal growth by the two-step heat treatment prescribed in the present application.

10,50 Lithium-ion secondary battery (stacked battery),
11 Negative electrode current collector,
12 Positive electrode current collector,
13 Negative electrode active material layer,
15 Positive electrode active material layer,
17 Electrolyte layer,
19 Single battery layer,
21,57 Power generation elements,
25, 58 Negative current collector plate,
27, 59 Positive current collector plate,
29, 52 Battery exterior material (laminated film).

Claims (7)

The following composition formula:
[Li _1.5 ] [Li _{0.5 (1-x)} Mn _1-x M _1.5x ] O ₃
(In the formula, x satisfies 0.1 ≦ x ≦ 0.8, and M is represented by Ni _α Co _β Mn _γ . At this time, 0 ≦ α ≦ 0.5, 0 ≦ _β ≦ 0.5, 0 ≤γ≤1 and α + β + γ = 1)
A positive electrode active material for a non-aqueous electrolyte secondary battery having a composition represented by.
The crystallite diameter is 272 to 600 nm, and
A positive electrode active material for a non-aqueous electrolyte secondary battery having a layered structure from the inside of the particles constituting the active material to the outermost surface. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the crystallite diameter is 272 to 350 nm. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the crystallite diameter of the positive electrode active material is 300 nm or less. A positive electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material according to any one of claims 1 to 3. A non-aqueous electrolyte secondary battery comprising the positive electrode according to claim 4. A precursor containing a Li compound, an Mn compound, a Ni compound, and a raw material containing a Co compound, if necessary, under the conditions of a heating rate of 50 to 100 ° C./hour, a firing temperature of 600 to 850 ° C., and a firing time of 6 to 12 hours. In the first firing step of obtaining a processed product by heat treatment with
A second firing step of obtaining a fired product by firing the processed product under the conditions of a heating rate of 200 to 400 ° C./hour, a firing temperature of 900 to 1100 ° C., and a firing time of 7.5 to 75 minutes.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, including. A method for producing a non-aqueous electrolyte secondary battery, which comprises a step of producing a non-aqueous electrolyte secondary battery using the positive electrode active material after producing the positive electrode active material by the production method according to claim 6.