JP2016081626A - Cathode active material for nonaqueous secondary battery, manufacturing method thereof, cathode for nonaqueous secondary battery, nonaqueous secondary battery and on-vehicle nonaqueous secondary battery module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode active material for nonaqueous secondary battery capable of obtaining high capacity at an atmospheric temperature by suppressing cycle deterioration, a nonaqueous secondary battery and on-vehicle nonaqueous secondary battery module.SOLUTION: The cathode active material for nonaqueous secondary battery comprises an internal part 1, an intermediate part 2 which is provided on a surface of the internal part, and a surface part 3 which is provided on a surface of the intermediate part. The surface part 3, the intermediate part 2 and the internal part have different compositions, contain Ni and Mn, comprise a layered structure and include particles for which an atomic concentration Cs of Ni in the surface part 3, an atomic concentration Cm of Ni in the intermediate part 2 and an atomic concentration Cc of Ni in the internal part satisfy the relation of Cs<Cm<Cc and a concentration gradient Gs of the atomic concentration of Ni in the surface part 3 and a concentration gradient Gm of the atomic concentration of Ni in the intermediate part 2 satisfy the relation of Gs<Gm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material for a non-aqueous secondary battery, a method for producing the same, a positive electrode for a non-aqueous secondary battery, a non-aqueous secondary battery, and an on-vehicle non-aqueous secondary battery module.

  One type of non-aqueous secondary battery in which a non-aqueous electrolyte mediates electrical conduction between electrodes is a lithium ion secondary battery. A lithium ion secondary battery is a secondary battery in which lithium ions are responsible for electrical conduction between electrodes in charge and discharge reactions. Compared to other secondary batteries such as nickel-hydrogen storage batteries and nickel-cadmium storage batteries, the energy density Is high and the memory effect is small. Therefore, from small power sources such as portable electronic devices and household electric devices, stationary power sources such as power storage devices, uninterruptible power supply devices, power leveling devices, drive power sources for ships, railways, hybrid vehicles, electric vehicles, etc. Applications are expanding to medium and large power supplies, and further improvements in battery performance are required. For example, in in-vehicle applications such as hybrid vehicles and electric vehicles, high energy density is required to realize a long cruising range.

In response to such demands, LiMO ₂ (M represents an element such as Ni, Co, Mn, etc.) positive electrode active material having an α-NaFeO ₂ type layered structure has a high charge / discharge capacity, and thus has been intensively developed. ing. On the other hand, the layered positive electrode active material is characterized in that charge / discharge cycle characteristics deteriorate (hereinafter referred to as cycle deterioration). Therefore, a technique has been proposed for improving the charge / discharge cycle characteristics (hereinafter referred to as cycle characteristics) of the layered positive electrode active material by changing the element concentration ratio between the vicinity of the surface of the positive electrode active material and the inside.

  For example, Patent Document 1 discloses composite particles in which cycle deterioration at a high potential is suppressed, each of the composite particles including a layered lithium metal oxide having an O3 crystal structure, And a core layer containing 30 to 85 mole percent of the composite particles with respect to the total moles of atoms of the composite particles, and a shell layer having an O3 crystal structure surrounding the core, and a layered lithium metal oxide having an oxygen deficiency Composite particles comprising a shell layer comprising an article are disclosed.

  Patent Document 2 includes an internal bulk portion in which cycle deterioration is suppressed and an external bulk portion surrounding the internal bulk portion, and a metal composition is formed on the active material surface from a boundary surface between the external bulk portion and the internal bulk portion. Is present in a continuous concentration gradient. A positive electrode active material for a lithium battery is disclosed.

Special table 2014-505992 gazette Special table 2009-525578

As disclosed in Patent Document 1, the shell layer of the positive electrode active material has oxygen vacancies so that a high potential (4.5 V (vs. Li ^/ Li ⁺ ) at the battery voltage, 4.6 V at the positive electrode single electrode ( Although the cycle deterioration in the case of using up to vs. Li ^/ Li ⁺ ) is suppressed, the low potential (battery voltage is 4.3 V (vs. Li ^/ Li ⁺ ) or less, the positive electrode single electrode is 4.4 V (vs. Li / Li ⁺ ) or less) is not taken into consideration.Also, a high capacity is obtained at 50 ° C., but there is a problem that the capacity is low at room temperature. According to the technology, it is considered that cycle deterioration can be suppressed, but it is necessary to increase the ratio of the external bulk portion, and the capacity may be insufficient.

Therefore, even when the battery is used at a low potential (battery voltage of 4.3 V (vs. Li ^/ Li ⁺ ) or less, and positive electrode single electrode of 4.4 V (vs. Li ^/ Li ⁺ ) or less), cycle deterioration is suppressed. There is a demand for non-aqueous secondary batteries capable of obtaining a high capacity even at room temperature. It is an object of the present invention to provide a positive electrode active material for a non-aqueous secondary battery that has a high capacity even at room temperature, in which the cycle deterioration is suppressed both in the use up to a high potential and in the use up to a low potential. The object is to provide a positive electrode for a secondary battery, a non-aqueous secondary battery, and a non-aqueous secondary battery module for vehicle use.

  In order to solve the above problems, a positive electrode active material for a non-aqueous secondary battery of the present invention includes an inside, an intermediate portion provided on the inner surface, and a surface portion provided on the surface of the intermediate portion, The surface part, the intermediate part, and the inside are different in composition, contain Ni and Mn, and have a layered structure. The surface part Ni atomic concentration Cs, the intermediate Ni atomic concentration Cm, and the internal Ni atomic concentration Cc is Cs <Cm <Cc, and the particles include particles having a concentration gradient Gs of Ni atomic concentration in the surface portion and a concentration gradient Gm of Ni atomic concentration in the middle portion satisfying Gs <Gm. The particles may be primary particles, secondary particles obtained by agglomerating these primary particles, or all or part of the primary particles in the vicinity of the surface of the secondary particles may be the particles.

  In order to achieve the above object, the method for producing a positive electrode active material for a non-aqueous secondary battery according to the present invention includes mixing a transition metal compound and a Li compound, and pre-baking a mixture of the transition metal compound and the Li compound. The main calcined body thus obtained is calcined to produce the precursor 1 containing Li, Ni and Mn, the transition metal compound and the Li compound are mixed, and the mixture of the transition metal compound and the Li compound is mixed. The process of baking and manufacturing the precursor 2 which is finer than the precursor 1 and whose atomic concentration of Ni is lower than the precursor 1 is mixed, and the precursor 1 and the precursor 2 are mixed. And a step of heat-treating the mixture.

  Moreover, the positive electrode for nonaqueous secondary batteries of this invention is characterized by including the said positive electrode active material for nonaqueous secondary batteries.

  Moreover, the non-aqueous secondary battery of this invention is provided with the said positive electrode for non-aqueous secondary batteries.

  Moreover, the vehicle-mounted non-aqueous secondary battery module of this invention is provided with the said non-aqueous secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, cycle deterioration is suppressed and the positive electrode active material for nonaqueous secondary batteries which is high capacity, its manufacturing method, the positive electrode for nonaqueous secondary batteries, a nonaqueous secondary battery, and a vehicle-mounted nonaqueous secondary battery A battery module can be provided.

  Problems, configurations, and effects other than those described above will become apparent from the following description of embodiments.

It is a cross-sectional schematic diagram of the positive electrode active material primary particle for non-aqueous secondary batteries. It is a cross-sectional schematic diagram of the positive electrode active material primary particle for non-aqueous secondary batteries. It is a cross-sectional schematic diagram of the positive electrode active material secondary particle for non-aqueous secondary batteries. It is a cross-sectional schematic diagram of the positive electrode active material secondary particle for non-aqueous secondary batteries. It is a cross-sectional schematic diagram of a non-aqueous secondary battery. It is a cross-sectional transmission electron micrograph of the positive electrode active material for non-aqueous secondary batteries. 4 is a diagram showing a TEM-EDX measurement result of a positive electrode active material for a non-aqueous secondary battery according to Example 1. FIG. It is a figure which shows the TEM-EDX measurement result of the positive electrode active material for non-aqueous secondary batteries which concerns on Example 2. FIG. It is a figure which shows the TEM-EDX measurement result of the positive electrode active material for non-aqueous secondary batteries which concerns on Example 3. FIG.

  Hereinafter, a positive electrode active material for a non-aqueous secondary battery, a manufacturing method thereof, a positive electrode for a non-aqueous secondary battery, a non-aqueous secondary battery, and an in-vehicle non-aqueous secondary battery module according to an embodiment of the present invention will be described in detail. To do.

1. Positive electrode active material primary particles The positive electrode active material primary particles include an inside, an intermediate portion provided on the surface of the inside, and a surface portion provided on the surface of the intermediate portion. The surface portion, the intermediate portion, and the inside have different compositions, and are made of a compound containing Ni and Mn and having a layered structure. The atomic concentration Cs of Ni in the surface portion, the atomic concentration Cm of Ni in the intermediate portion, and the atomic concentration Cc of Ni in the interior are Cs <Cm <Cc. The concentration gradient Gs of the atomic concentration of Ni in the surface portion and the concentration gradient Gm of the atomic concentration of Ni in the intermediate portion are Gs <Gm.

  The layered structure means that the crystal structure is a layered structure. The crystal structure can be confirmed by, for example, transmission electron microscope-energy dispersive X-ray detector (TEM-EDX).

  1 and 2 show schematic cross-sectional views of the positive electrode active material primary particles. As shown in FIG. 1 and FIG. 2, the positive electrode active material primary particles are particles including an inner portion 1, an intermediate portion 2 provided on the inner surface, and a surface portion 3 provided on the surface of the intermediate portion. As shown in FIG. 1, the intermediate part 2 may be provided on all the surfaces of the inner part 1, and the surface part 3 may be provided on all the surfaces of the intermediate part 2, or as shown in FIG. The intermediate part 2 and the surface part 3 may be provided in a part of the surface of 1. That is, there may be a portion where the inside is exposed on the surface of the primary particle of the positive electrode active material, or there may be a portion where the surface portion is in contact with the inside.

  The surface part, the intermediate part, and the inside of the positive electrode active material primary particles are defined as follows. For particles randomly selected by observation with TEM-EDX, etc., TEM-EDX line analysis and point analysis every few nm to 10 nm are performed. When there is a concentration gradient in which the atomic concentration decreases, the surface portion is from the outermost surface of the particle to a portion where the concentration gradient in which the atomic concentration of Ni decreases disappears, and the inside is from the center of the particle to the center of the particle and Ni. The difference in atomic concentration is up to a site within 2 mol%, and the intermediate part is a part between the surface part and the inside. In addition, when there is no concentration gradient in which the Ni atomic concentration decreases at a distance within 200 nm from the surface of the particle toward the center, the surface portion has a difference in atomic concentration between the outermost surface and the Ni from the outermost surface of the particle. The portion is within 2 mol%, the inside is from the center of the particle to the portion where the difference in atomic concentration between the center of the particle and Ni is within 2 mol%, and the intermediate portion is the portion between the surface portion and the inside It is. Here, the case where there is a concentration gradient in which the atomic concentration of Ni decreases means that there is a portion where the concentration gradient in which the atomic concentration of Ni decreases is greater than 0.2 mol% / nm. Further, the absence of the concentration gradient in which the Ni atomic concentration decreases means that the concentration gradient in which the Ni atomic concentration decreases is 0 mol% / nm to 0.2 mol% / nm.

  In the positive electrode active material primary particles, the atomic concentration Cs of Ni in the surface portion, the atomic concentration Cm of Ni in the intermediate portion, and the atomic concentration Cc of Ni in the interior are Cs <Cm <Cc. As a result, the primary particles of the positive electrode active material can have a high capacity in the interior where the atomic concentration of Ni is high, and the cycle deterioration can be suppressed at the surface portion where the atomic concentration of Ni is low. The atomic concentration of Ni is the concentration of Ni atoms in transition metal atoms.

  The atomic concentration Cs of Ni in the surface portion is, for example, 5 mol% to 90 mol%. The atomic concentration Cm of Ni in the intermediate part is, for example, 5 mol% to 90 mol%. The atomic concentration Cc of Ni inside is, for example, 60 mol% to 95 mol%.

  In the primary particles of the positive electrode active material, the concentration gradient Gs of the atomic concentration of Ni in the surface portion and the concentration gradient Gm of the atomic concentration of Ni in the intermediate portion are Gs <Gm. An intermediate layer with a larger Ni atom concentration gradient than the surface part is interposed at the interface between the inside and the surface part, thereby suppressing the difference in the atomic structure between the surface part and the inside, smoothing the movement of Li ions, and maintaining a high capacity. can do. The concentration gradient of the atomic concentration of Ni is the change (mol%) of the atomic concentration of Ni with respect to the change (nm) in the thickness direction of the particles.

  The concentration gradient Gs of the atomic concentration of Ni in the surface portion may be a gradient in which the atomic concentration of Ni continuously increases from the particle surface side to the center side in the surface portion, or may be a gradient that continuously decreases. Gs may be 0. Gs is, for example, 0 mol% / nm or more and less than 0.2 mol% / nm. The concentration gradient Gm of the atomic concentration of Ni in the intermediate part is Gm> 0. In the intermediate portion, the atomic concentration of Ni continuously changes from the surface portion side to the inner side or from the inner side to the surface portion side. Gm is preferably a gradient in which the atomic concentration of Ni continuously increases from the particle surface side toward the center side. Gm is, for example, greater than 0 mol% / nm and not greater than 0.2 mol% / nm. The concentration gradient of the atomic concentration of Ni inside is not particularly limited, but is usually Gs and Gm or less.

  The ratio (Gm / Gs) of the concentration gradient Gm of the atomic concentration of Ni in the intermediate portion to the concentration gradient Gs of the atomic concentration of Ni in the surface portion is preferably 2 or more, and Gm / Gs is further 4 or more. preferable. When Gm / Gs is 2 or more, the thickness of the intermediate portion can be reduced, the proportion of the high capacity inside can be increased, and the capacity can be increased.

  The concentration gradient Gs of the atomic concentration of Ni in the surface portion and the concentration gradient Gm of the atomic concentration of Ni in the intermediate portion are measured by TEM-EDX line analysis or several nm Point analysis is performed every 10 nm, and the concentration gradient of the atomic concentration of Ni in the surface portion and the intermediate portion is measured and determined.

  The primary particles of the positive electrode active material preferably have an atomic concentration Cs (Mn) of Mn in the surface portion, an atomic concentration Cm (Mn) of Mn in the intermediate portion, and an atomic concentration Cc (Mn) of Mn in the inner portion Cs (Mn)> Cm (Mn)> Cc (Mn). Thereby, the life of the positive electrode active material primary particles can be extended. The atomic concentration of Mn is the concentration of Mn atom in the transition metal atom.

  The primary particles of the positive electrode active material preferably have a concentration gradient Gs (Mn) of atomic concentration of Mn in the surface portion and a concentration gradient Gm (Mn) of atomic concentration of Mn in the intermediate portion such that Gs (Mn) <Gm (Mn) It is. The concentration gradient Gm of the atomic concentration of Mn in the intermediate part is preferably a gradient in which the atomic concentration of Mn decreases from the surface side to the center side of the particle. The concentration gradient of Mn atomic concentration can be measured in the same manner as the concentration gradient of Ni atomic concentration.

The compositional formula of the surface part, the intermediate part, and the inside of the positive electrode active material primary particles is preferably Li _{1 + X} Ni _A Mn _B Co _C M _D O _2-Y [wherein X is −0.1 ≦ X ≦ 0. .3, Y is a number that satisfies −0.1 ≦ Y ≦ 0.1, A is a number that satisfies 0.2 ≦ A ≦ 0.95, and B is 0 < B ≦ 0.95, C is a number satisfying 0 ≦ C ≦ 0.6, and M is at least one selected from the group consisting of Mg, Al, Ti, Mo and Nb. It is an element, and D is a number satisfying 0 ≦ D ≦ 0.1, and A + B + C + D = 1. Thereby, the positive electrode active material primary particles have a high capacity, and cycle deterioration can be suppressed.

  The composition of the surface part, intermediate part, and internal part of the positive electrode active material primary particles should be measured by TEM-EDX, Transmission Electron Microscopy-Electron Energy Loss Spectroscopy (TEM-EELS), etc. Can do.

  It is preferable that the inside has a higher capacity when A is 0.6 ≦ A ≦ 0.9 in the composition formula. Moreover, it is preferable that B is 0.05 <= B <= 0.3 in the said compositional formula inside. When B is 0.05 or more, cycle deterioration can be further suppressed, and when B is 0.3 or less, the capacity becomes higher. The inside is preferably such that C is 0.05 ≦ C ≦ 0.2 in the composition formula. When C is 0.05 or more, cation mixing can be suppressed and the capacity becomes higher, and when C is 0.2 or less, the amount of expensive Co is not excessive and the cost is low.

  The surface portion is preferably such that X is 0 <X ≦ 0.3 in the composition formula. When X is 0 <X ≦ 0.3, that is, the Li is excessive, cycle deterioration at a high potential can be further suppressed. By the way, if the Li concentration is high, cycle deterioration at a high potential can be suppressed, but the rate characteristics deteriorate. Therefore, it is preferable that the atomic concentration of Li in the surface portion of the positive electrode active material is higher than the atomic concentration of Li inside. The atomic concentration of Li is the concentration of Li atoms in all atoms. Suppresses cycle deterioration at a high potential at the surface portion where the atomic concentration of Li is high, maintains rate characteristics inside the low atomic concentration of Li, and suppresses cycle deterioration at a high potential while maintaining rate characteristics. it can.

  The molar ratio of Ni and Mn in the surface part, intermediate part and internal part of the positive electrode active material primary particles can be selected according to the required characteristics. The molar ratio of Ni and Mn on the surface is, for example, Ni: Mn = 7: 20 to 20: 1, preferably Ni: Mn = 20: 20 to 20: 2. The molar ratio of Ni and Mn inside is, for example, Ni: Mn = 20: 8 to 20: 1, preferably Ni: Mn = 20: 7 to 20: 2.

  The thickness of the surface portion of the positive electrode active material primary particles is preferably 20 nm or more and 200 nm or less. When the thickness of the surface portion is 20 nm or more, the cycle deterioration is sufficiently suppressed, and when the thickness of the surface portion is 200 nm or less, the internal ratio that bears a high capacity is sufficient, so that the capacity becomes high.

  The thickness of the intermediate part of the positive electrode active material primary particles is preferably 10 nm or more and 100 nm or less. If the thickness of the surface portion is 10 nm or more, the movement of Li is smooth, and if the thickness of the intermediate portion is 100 nm or less, the ratio of the internal capacity that bears a high capacity is sufficient, resulting in a high capacity.

  The median diameter of the positive electrode active material primary particles is preferably 50 nm or more and 2000 nm or less. When the median diameter of the primary particles of the positive electrode active material is less than 50 nm, the specific surface area increases, that is, the contact area with the liquid solution increases and cycle deterioration increases. On the other hand, if the median diameter of the primary particles of the positive electrode active material is larger than 2000 nm, the diffusion distance of Li ions becomes long and the resistance becomes low.

  The thickness of the surface portion and the intermediate portion can be determined by, for example, performing TEM-EDX line analysis or point analysis every several nm to 50 nm on particles randomly selected by observation with a transmission electron microscope. The thickness of the part is measured and determined. The median diameter of the primary particles of the positive electrode active material can be measured using, for example, a laser diffraction / scattering particle size distribution measuring apparatus.

  The formation rate, which is the ratio of the surface portion and the intermediate portion formed on the surface inside the primary particles of the positive electrode active material, is preferably 80% or more because cycle deterioration can be suppressed.

  The formation rate of the positive electrode active material can be measured, for example, as follows. The atomic concentration of Ni at a distance of 10 nm from the surface is measured from 4 points in the vertical and horizontal directions on the surface of the randomly selected positive electrode active material primary particles toward the center by TEM-EDX, and is higher than the atomic concentration of Ni at the center. The number of places is divided by the number of places to be measured, and a value obtained by multiplying by 100 is taken as the formation rate.

  Even if a part of the positive electrode active material primary particles has a surface particle portion and a middle particle portion formed on the surface, the formed particle ratio is preferably 50% or more because cycle deterioration can be suppressed.

  The formed particle ratio can be measured, for example, as follows. The atomic concentration of the primary particles of the positive electrode active material selected at random and the atomic concentration of Ni at a distance of 10 nm from the surface from four points in the vertical and horizontal directions of the surface are measured by TEM-EDX. The number of particles higher than the central atomic concentration of Ni at any one of the atomic concentrations of Ni at a distance of 10 nm from the center is divided by the number of measured particles, and a value obtained by multiplying by 100 is defined as the formed particle ratio.

2. Method for producing positive electrode active material primary particles The positive electrode active material primary particles are prepared by mixing a transition metal compound and a Li compound, pre-baking a mixture of the transition metal compound and the Li compound, and main baking the obtained pre-fired body. The precursor 1 containing Li, Ni, and Mn is manufactured (step 1), the transition metal compound and the Li compound are mixed, the mixture of the transition metal compound and the Li compound is baked, and the precursor 1 A step (step 2) for producing a precursor 2 that is finer and has a lower atomic concentration of Ni than the precursor 1, a mixture of the precursor 1 and the precursor 2, and a heat treatment of the mixture of the precursor 1 and the precursor 2 It can manufacture by the method including the process to perform (process 3). The obtained positive electrode active material primary particles have a three-layer structure of an inner part, an intermediate part, and a surface part.

  In step 1, the precursor 1 which mainly becomes an inside is manufactured. The precursor 1 is a particle having a layered structure containing Li, Ni, and Mn. In the precursor 1, the atomic concentration of Ni in the transition metal atom is preferably 50 mol% or more. Thereby, the inside of the positive electrode active material primary particle obtained can be made into a high capacity | capacitance.

  Examples of transition metals other than Ni and Mn contained in the precursor 1 include Co, Mg, Al, Ti, Mo, Nb, and the like, and Co is preferable from the viewpoint of capacity and resistance. The precursor 1 can also contain two or more of these transition metals.

  The precursor 1 is preferably a material constituting the inside of the positive electrode active material primary particles.

The precursor 1 is preferably a composition formula Li _{1 + X} Ni _A Mn _B Co _C M _D O _2-Y [wherein X is a number satisfying −0.1 ≦ X ≦ 0.3, and Y is -0.1 ≦ Y ≦ 0.1, A is a number satisfying 0.2 ≦ A ≦ 0.95, B is a number satisfying 0 <B ≦ 0.95, C is a number that satisfies 0 ≦ C ≦ 0.6, M is at least one element selected from the group consisting of Mg, Al, Ti, Mo, and Nb, and D is 0 ≦ D ≦ It is a number satisfying 0.1, and A + B + C + D = 1].

  More preferably, in the precursor, the precursor 1 is more preferably 0.6 ≦ A ≦ 0.9 and B is 0.05 ≦ B ≦ 0. 3 and C is 0.05 ≦ C ≦ 0.2.

  As the Li compound, for example, lithium acetate, lithium nitrate, lithium carbonate, lithium hydroxide, lithium chloride, lithium sulfate and the like can be used. As the Ni compound, for example, nickel acetate, nickel nitrate, nickel carbonate, nickel sulfate, nickel hydroxide, nickel oxide and the like can be used. As the Mn compound, for example, manganese acetate, manganese nitrate, manganese carbonate, manganese sulfate, manganese oxide, manganese hydroxide and the like can be used. When Co, Mg, Al, Ti, Mo, and Nb are contained, these acetates, nitrates, carbonates, sulfates, hydroxides, oxides, and the like can be used.

  In step 1, first, raw material Li compound, Ni compound, Mn compound and optionally other transition metal compounds are weighed at a ratio of a predetermined elemental composition, and pulverized and mixed to prepare raw material powder.

  For pulverization and mixing, any of dry pulverization and wet pulverization can be used. As the pulverizing means, for example, a pulverizer such as a ball mill, a bead mill, a planetary ball mill, an attritor, or a jet mill can be used.

  Next, the prepared raw material powder is fired to obtain the precursor 1. The raw material powder is fired by calcining it under an inert gas atmosphere or an oxidizing gas atmosphere by thermally decomposing the raw material compound, appropriately pulverizing and classifying it, and then firing the obtained temporary fired body. Tie. The heating temperature in temporary baking is, for example, about 300 to 700 ° C., and the heating temperature in main baking is, for example, 700 to 1100 ° C.

  The obtained precursor 1 may be used after being pulverized into primary particles, or may be used as secondary particles.

  In step 2, a precursor 2 that mainly becomes a surface portion is manufactured. The precursor 2 is fine particles having a smaller median system than the precursor 1. The precursor 2 has a lower atomic concentration of Ni than the precursor 1. In the precursor 2, the molar ratio of Li to the total molar ratio of transition metals is preferably larger than 1. By being a Li-excess composition, cycle deterioration at a high potential can be further suppressed.

  The precursor 2 is not particularly limited as long as it can constitute the surface portion of the positive electrode active material. Preferably, the precursor 2 is a particle containing Li and Mn, or a particle containing Li, Mn and Ni. is there. As will be described later, since the components of the precursor 1 and the precursor 2 are interdiffused by heat-treating the mixture of the precursor 1 and the precursor 2 in the step 3, the precursor 2 to be used and the obtained positive electrode active material It differs from the composition of the surface part.

The precursor 2 is preferably a composition formula Li _{1 + X} Ni _A Mn _B Co _C M _D O _2-Y [wherein, X is a number satisfying −0.1 ≦ X ≦ 0.3, and Y is -0.1 ≦ Y ≦ 0.1, A is a number satisfying 0.2 ≦ A ≦ 0.95, B is a number satisfying 0 <B ≦ 0.95, C is a number that satisfies 0 ≦ C ≦ 0.6, M is at least one element selected from the group consisting of Mg, Al, Ti, Mo, and Nb, and D is 0 ≦ D ≦ It is a number satisfying 0.1, and A + B + C + D = 1].
In the precursor 2, more preferably, X is 0 <X ≦ 0.3 in the composition formula.

In addition to the above, the precursor 2 contains, for example, Li and Mn but does not contain Ni. Li _{1 + X} Mn _1-X O _{2 + Y} (−0.1 ≦ X ≦ 0.4, −0 0.1 ≦ Y ≦ 0.1), and Li ₂ MnO ₃ (Li _1.33 Mn _0.67 O ₂₎ is preferably used.
The obtained precursor 2 is preferably used after being crushed or ground.

  In step 3, precursor 1 and precursor 2 are mixed, and the mixture of precursor 1 and precursor 2 is heat-treated. By mixing the precursor 1 and the precursor 2, a mixture in which the particles of the precursor 2 are adhered to the surface of the particles of the precursor 1 is obtained. When this mixture is heat-treated, the components of the precursor 1 and the precursor 2 are interdiffused, so that the composition of the surface portion of the particles after the heat treatment approaches the composition of the precursor 1 from the composition of the precursors 2, and the particles after the heat treatment Has a three-layer structure having an inner portion, an intermediate portion, and a surface portion. As described above, the atomic concentration of Ni continuously changes in the intermediate portion.

  The median diameter D50A of the precursor 1 and the median diameter D50B of the precursor 2 are preferably 2 ≦ D50A / D50B ≦ 100. It is preferable that D50A / D50B is 2 or more because the thickness of the surface portion becomes appropriate. Moreover, since the precursor 2 does not become small too much that D50A / D50B is 100 or less, it can manufacture easily.

  Mixing of the precursor 1 and the precursor 2 may be performed by supporting the precursor 2 on the surface of the precursor 1. Mixing or loading can be performed using a mixer such as a levester, a Henschel mixer, a ball mill, a bead mill, a planetary ball mill, an attritor, a surface reforming device, or a compounding device.

  The weight ratio of the precursor 1 and the precursor 2 is not particularly limited, and is, for example, precursor 1: precursor 2 = 100: 1 to 100: 20, from the viewpoint of capacity, resistance, and reaction suppression with the electrolytic solution. , Preferably 100: 1 to 100: 10

  The heat treatment is performed by mixing the precursor 1 and the precursor 2 or heating the raw material powder having the precursor 2 supported on the surface of the precursor 1.

  The heat treatment is not particularly limited as long as the obtained particles have a three-layer structure, and heat treatment conditions can be selected according to the precursor 1 and the precursor 2 to be used. The heat treatment can be performed in an inert gas atmosphere or an oxidizing gas atmosphere, but is preferably performed in an oxidizing gas atmosphere. This is because oxygen vacancies can be prevented even when the atomic concentration of Ni is high. Regarding the heat treatment, in order to keep the diffusion distance of the component from the precursor 1 to the precursor 2 within a certain distance, the heating temperature is preferably a temperature not higher than 50 degrees higher than the main firing temperature in the production of the precursor 1. When heat treatment is performed at a temperature higher than this temperature, component diffusion proceeds too much, and the composition of the surface portion approaches the internal composition. In addition, the heating temperature in the heat treatment is preferably a temperature that is 200 ° C. or lower than the main firing temperature in the production of the precursor 1 from the viewpoint of the formation rate and the formed particle ratio, and the main firing temperature in the production of the precursor 1 More preferably, the heat treatment is performed at a temperature of 100 ° C. or lower. The heating temperature is, for example, about 300 to 1100 ° C. The heating time in the heat treatment can be appropriately selected according to the precursor 1, the precursor 2 to be used, and the heating temperature in the heat treatment, but is preferably a time shorter than the main firing time in the production of the precursor 1. When the heat treatment is performed for a longer time, the component diffusion proceeds too much, and the composition of the surface portion approaches the internal composition. The heat treatment time is, for example, 30 minutes to 6 hours.

  The positive electrode active material for a non-aqueous secondary battery manufactured as described above is used as a material for a positive electrode for a non-aqueous secondary battery.

3. Positive electrode active material secondary particles The positive electrode active material can be secondary particles in which primary particles are aggregated. By using secondary particles as the positive electrode active material, the energy density of the positive electrode can be improved. Secondary particles are distinguished from primary particles having no grain boundaries in the particles by the presence of grain boundaries in the particles.

  The positive electrode active material composed of secondary particles may be such that all primary particles in the secondary particles may be the positive electrode active material, or some primary particles in the secondary particles may be the positive electrode active material. Good. Of the primary particles in the secondary particles, all or part of the primary particles in the vicinity of the surface (outside) of the secondary particles are preferably the positive electrode active material. This is because cycle deterioration can be suppressed by arranging the positive electrode active material in the vicinity of the surface of the secondary particles in contact with the electrolytic solution. In this case, primary particles having a high Ni atomic concentration are preferably used in the central part of the secondary particles. For example, primary particles composed only of the positive electrode active material primary particles are used. Thereby, it can be set as a high capacity | capacitance positive electrode active material.

  Of the primary particles in the secondary particles, when a part of the primary particles in the vicinity of the surface of the secondary particles is the positive electrode active material, the primary particles have an intermediate portion and a surface portion on the entire inner surface. It may be provided, or it may be provided with a surface portion and an intermediate portion on a part of its inner surface. 3 and 4 are schematic cross-sectional views of such secondary particles. In FIG. 3, the positive electrode active material secondary particles 4 are a part of the primary particles in the vicinity of the surface of the positive electrode active material primary particles including the inner part 1, the intermediate part 2, and the surface part 3. These parts and the central part of the secondary particles are primary particles composed only of the inside 1. In FIG. 4, the positive electrode active material secondary particle 4 includes a part of primary particles in the vicinity of the surface, and a positive electrode active material primary provided with an intermediate portion 2 and a surface portion 3 on the surface of the inner particle 1 on the secondary particle surface side. The other parts and the central part in the vicinity of the surface are primary particles composed of only the interior 1.

  In the secondary particles, the primary particles in the secondary particles may be aggregated by a physical force, but the primary particles in the secondary particles are preferably sintered. Since the primary particles in the secondary particles are sintered, the strength of the secondary particles is increased, the cutting force applied during the production of the positive electrode is increased, and the production of the positive electrode is facilitated.

  The median diameter of the primary particles in the secondary particles is, for example, about 50 nm to 2000 nm, like the positive electrode active material primary particles. The median diameter of the secondary particles depends on the median diameter of the primary particles, but is preferably 1 μm to 30 μm. When the surface portion and the intermediate portion are provided only on the primary particles arranged in the vicinity of the surface of the secondary particles, the primary particles arranged at a distance of 5% to 30% of the median diameter of the secondary particles from the secondary particle surface. It is preferable that a surface portion and an intermediate portion are provided on the surface.

4). Method for Producing Positive Electrode Active Material Secondary Particles The method for producing the secondary particles will be described. The secondary particles can be produced, for example, by agglomerating and bonding the primary particles obtained by the above production method into secondary particles. In this method, secondary particles in which all primary particles in the secondary particles are the positive electrode active material are obtained.

  The primary particles can be converted into secondary particles by, for example, heat-treating a slurry of primary particles after spray drying. The slurry in which the precursor 1 and the precursor 2 are mixed may be spray-dried and then heat-treated to form secondary particles simultaneously with the heat treatment of the precursor 1 and the precursor 2.

  The secondary particles can also be produced by preparing secondary particles in which the precursor 1 is aggregated, mixing the secondary particles and the precursor 2, and then performing a heat treatment. In this method, among the primary particles in the secondary particles, secondary particles in which all or part of the primary particles near the surface of the secondary particles are the positive electrode active material are obtained. The secondary particles in which the precursor 1 is aggregated may be produced by sintering the primary particles of the precursor 1, or the secondary particles obtained during the production of the precursor 1 may be used as they are.

5. Positive electrode for non-aqueous secondary battery The positive electrode for non-aqueous secondary battery is mainly coated with a positive electrode mixture layer containing a positive electrode active material, a conductive material and a binder for a non-aqueous secondary battery, and a positive electrode mixture layer. A positive electrode current collector. The positive electrode may contain other positive electrode active materials in addition to the positive electrode active material. As another positive electrode active material to be contained, for example, Li ₂ MnO ₃ —LiM ₂ O ₂ (M ₂ represents an element such as Co, Ni, Mn and the like), a solid solution positive electrode active material, such as LiM ₃ O ₂ And a polyanion-based positive electrode active material represented by LiM4A _p O _q , and the like. In the above formula, M3 and M4 are at least one element selected from the group consisting of Mn, Ni, Co, and Fe, and A is bonded to oxygen to form PO ₄ , SiO ₄ , BO _3. And p and q are numbers satisfying 1 ≦ p ≦ 2 and 3 ≦ q ≦ 7, respectively. Part of the elements M3 and M4 may be substituted with elements such as Ti, Zr, Al, Mg, Cr, V, Nb, Ta, W, and Mo.

  As the conductive material, a conductive material used in a general lithium ion secondary battery can be used. Specific examples include carbon particles such as graphite powder, acetylene black, furnace black, thermal black, and channel black, carbon fibers, and the like.

  What is necessary is just to use the quantity used as a conductive material, for example about 1 to 10 weight% with respect to the weight of the whole positive electrode compound material.

  As the binder, a binder used in a general lithium ion secondary battery can be used. Specific examples include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyhexafluoropropylene, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylonitrile, and modified polyacrylonitrile.

  What is necessary is just to use the quantity used as a binder, for example about 1 to 10 weight% with respect to the weight of the whole positive electrode compound material.

  As the positive electrode current collector, foil made of aluminum or aluminum alloy, expanded metal, punching metal, or the like can be used. For example, the foil may have a thickness of about 8 μm to 30 μm.

  The positive electrode for nonaqueous secondary batteries can be manufactured according to the manufacturing method of a general positive electrode.

  An example of the manufacturing method of the positive electrode for non-aqueous secondary batteries includes a positive electrode mixture preparation step, a positive electrode mixture coating step, and a molding step.

  In the positive electrode mixture preparation step, a positive electrode active material, a conductive material, and a binder are mixed in a solvent to prepare a slurry-like positive electrode mixture. At least the positive electrode active material is used and stirred and homogenized together with the conductive material in a solvent in which the binder is dissolved.

  Solvents are N-methylpyrrolidone, water, N, N-dimethylformamide, N, N-dimethylacetamide, methanol, ethanol, propanol, isopropanol, ethylene glycol, diethylene glycol, glycerin, dimethyl sulfoxide, depending on the type of binder. , Tetrahydrofuran and the like.

  Examples of the stirring means for mixing the materials include a planetary mixer, a disper mixer, and a rotation / revolution mixer.

  In the positive electrode mixture coating step, the prepared slurry-like positive electrode mixture is applied onto the positive electrode current collector, and then the solvent is dried by heat treatment to form the positive electrode mixture layer.

  Examples of the coating means for applying the positive electrode mixture include a bar coater, a doctor blade, and a roll transfer machine.

  In the molding step, the dried positive electrode mixture layer is pressure-molded using a roll press or the like, and cut with a positive electrode current collector as necessary to obtain a positive electrode for a non-aqueous secondary battery having a desired shape. . The thickness of the positive electrode mixture layer formed on the positive electrode current collector may be, for example, about 15 μm to 300 μm.

6). Non-aqueous secondary battery The positive electrode for a non-aqueous secondary battery is used as a material for a non-aqueous secondary battery.
The non-aqueous secondary battery mainly includes a positive electrode for a non-aqueous secondary battery, a negative electrode for a non-aqueous secondary battery, a separator, and a non-aqueous electrolyte, and these are cylindrical, rectangular, button, and laminate sheets. It is set as the structure accommodated in exterior bodies of shapes, such as a type | mold.

  FIG. 5 is a schematic cross-sectional view showing an example of a non-aqueous secondary battery. FIG. 5 illustrates a cylindrical non-aqueous secondary battery. The non-aqueous secondary battery 5 includes a positive electrode 6 having a positive electrode mixture coated on both surfaces of a positive electrode current collector, and a negative electrode current collector. The electrode group which consists of the negative electrode 7 by which the negative electrode compound material was coated on both surfaces of this, and the separator 8 interposed between the positive electrode 6 and the negative electrode 7 is provided. The positive electrode 6 and the negative electrode 7 are wound through a separator 8 and accommodated in a cylindrical battery can 9. The positive electrode 6 is electrically connected to the sealing lid 12 via the positive electrode lead piece 10, and the negative electrode 7 is electrically connected to the battery can 9 via the negative electrode lead piece 11, and the positive electrode lead piece 10 and the negative electrode 7. An insulating plate 14 made of an epoxy resin or the like is disposed between the negative electrode lead piece 11 and the positive electrode 6 to be electrically insulated. Each lead piece is a current drawing member made of the same material as each current collector, and is joined to each current collector by spot welding or ultrasonic welding.

  The battery can 9 has a structure in which a nonaqueous electrolyte is injected into the battery can 9 and then sealed with a sealing material 13 such as rubber, and the top is sealed with a sealing lid 12.

  As the negative electrode for a non-aqueous secondary battery, a negative electrode active material and a negative electrode current collector used in a general lithium ion secondary battery can be used.

  As the negative electrode active material, for example, one or more of a carbon material, a metal material, a metal oxide material, and the like can be used. Examples of the carbon material include graphites such as natural graphite and artificial graphite, carbides such as coke and pitch, amorphous carbon, and carbon fibers. Examples of the metal material include lithium, silicon, tin, aluminum, indium, gallium, magnesium, and alloys thereof, and examples of the metal oxide material include metal oxides including tin, silicon, lithium, and titanium.

  As the negative electrode for a non-aqueous secondary battery, a material selected from the same group as the binder and the conductive material used in the positive electrode for a non-aqueous secondary battery may be used as necessary. What is necessary is just to use the quantity used as a binder about 5 weight% with respect to the weight of the whole negative electrode compound material, for example.

  As the negative electrode current collector, copper or nickel foil, expanded metal, punching metal, or the like can be used. For example, the foil may have a thickness of about 5 μm to 20 μm.

  A negative electrode for a non-aqueous secondary battery is coated with a negative electrode mixture obtained by mixing a negative electrode active material and a binder on a negative electrode current collector and pressure-molded, as with a positive electrode for a non-aqueous secondary battery. It is manufactured by cutting according to. The thickness of the negative electrode mixture layer formed on the negative electrode current collector may be, for example, about 20 μm to 150 μm.

  As the separator, a polyolefin resin such as polyethylene, polypropylene, and a polyethylene-polypropylene copolymer, a microporous film such as a polyamide resin and an aramid resin, a nonwoven fabric, and the like can be used.

Non-aqueous electrolytes include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) _2. A solution in which a lithium salt such as LiN (CF ₃ SO ₂ ) ₂ or LiC (CF ₃ SO ₂ ) ₃ is dissolved in a non-aqueous solvent can be used. The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.7M or more and 1.5M or less.

  As the non-aqueous solvent, diethyl carbonate, dimethyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl acetate, dimethoxyethane and the like can be used. In addition, various additives should be added to the non-aqueous electrolyte for the purpose of suppressing oxidative decomposition and reductive decomposition of the electrolytic solution, preventing precipitation of metal elements, improving ion conductivity, and improving flame retardancy. Can do. Examples of such additives include 1,3-propane sultone and 1,4-butane sultone that suppress decomposition of the electrolytic solution, insoluble polyadipic anhydride that improves the storage stability of the electrolytic solution, and hexahydrophthalic anhydride. Examples include acids and the like, and fluorine-substituted alkylborons that improve flame retardancy.

7). Secondary battery module The non-aqueous secondary battery includes, for example, small power sources such as portable electronic devices and household electrical devices, stationary power sources such as uninterruptible power sources and power leveling devices, ships, railways, hybrid vehicles, electric It can be used as a drive power source for automobiles and the like.

  The in-vehicle non-aqueous secondary battery module is a secondary battery module suitable as an in-vehicle drive power source for hybrid vehicles, electric vehicles, etc., and mainly includes the non-aqueous secondary battery, a controller, a fuse, And a balance circuit. In a non-aqueous secondary battery module for in-vehicle use, a plurality of non-aqueous secondary batteries are connected in series to form a battery group in order to secure a desired output, and these battery groups are combined in parallel to form a casing. A stored and high capacity battery module is formed.

  The fuse has a protection function against overcurrent, and the balance circuit has a function of leveling the voltage between the electrodes. The controller has a function to monitor the voltage, current, and temperature between the electrodes of the non-aqueous secondary battery, and a function to prevent overcharge and overdischarge in the range of the set charge / discharge end potential by the protection circuit. ing. The controller is connected to signal input / output means for communicating with the outside, and the signal input / output means inputs, for example, a control signal from an ECU provided in the vehicle and outputs battery monitoring information to the ECU. Has the function to perform. As a configuration of the secondary battery module, in addition to these, a capacity monitoring function, a leveling function, a cooling function, and the like of each secondary battery may be further provided.

  In-vehicle non-aqueous secondary battery modules, in particular, include non-aqueous secondary batteries in which cycle deterioration is suppressed, so that, for example, in an electric vehicle or a hybrid vehicle, a stable output even over time It is useful in that it can be obtained.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated concretely, the technical scope of this invention is not limited to this.

Synthesis of Precursor 1 First, a precursor 1 having a high atomic concentration of Ni mainly inside was produced.
Lithium carbonate, nickel carbonate, cobalt carbonate, and manganese carbonate as raw materials are weighed so that Li: Ni: Co: Mn is 1.03: 0.80: 0.10: 0.10 in molar concentration ratio, These were wet pulverized and mixed to prepare a raw material powder. The obtained raw material powder was dried by a nozzle type spray drying apparatus, then charged into a high-purity alumina container, and pre-baked at 650 ° C. for 12 hours under an oxygen stream. The obtained pre-fired body was air-cooled and pulverized so as not to pulverize the secondary particles, and then charged again into a high-purity alumina container and subjected to main calcination at 850 ° C. for 8 hours in an oxygen stream. . And the obtained sintered body was air-cooled and classified.

When the elemental analysis of the particle | grains of the obtained precursor 1 was conducted, Li: Ni: Co: Mn was 1.00: 0.80: 0.10: 0.10. Therefore, the elemental composition is estimated to be Li _1.0 Ni _0.8 Co _0.1 Mn _0.1 O ₂ .

  Next, the crystal structure of the precursor 1 was analyzed. As a result of measurement using an X-ray diffractometer (RINT III manufactured by Rigaku Corporation) using CuKα rays, a peak of a layered structure belonging to R3-m could be confirmed.

  Moreover, as a result of measuring the particle size distribution with a laser diffraction / scattering particle size distribution measuring apparatus (LA-920, manufactured by Horiba, Ltd.), the median diameter (D50) was 11 μm.

Synthesis of Precursor 2A Next, a precursor 2A having a low atomic concentration of Ni mainly serving as a surface portion and a high atomic concentration of Li was manufactured.
Lithium carbonate, nickel carbonate and manganese carbonate as raw materials are weighed so that Li: Ni: Mn is a molar concentration ratio of 1.20: 0.2: 0.6, and these are wet-ground and mixed. Raw material powder was prepared. After drying the obtained raw material powder, it was put into a high-purity alumina container and heat-treated at 700 ° C. for 12 hours in the atmosphere. And the obtained temporary baking body was air-cooled and grind | pulverized.

When elemental analysis of the particles of the obtained precursor 2A was performed, Li: Ni: Mn was 1.16: 0.2: 0.6. Therefore, the elemental composition is estimated to be Li _1.16 Ni _0.2 Mn _0.6 O ₂ .

  Moreover, as a result of measuring the particle size distribution with a laser diffraction / scattering type particle size distribution measuring apparatus (LA-920 manufactured by Horiba, Ltd.), the median diameter (D50) was 0.17 μm.

Synthesis of Precursor 2B Next, a precursor 2B having a high atomic concentration of Li, which does not mainly include Ni as a surface portion, was manufactured.
Raw material lithium carbonate and manganese carbonate were weighed so that Li: Mn was 2.02: 1.0 in terms of molar concentration ratio, and these were wet pulverized and mixed to prepare raw material powder. After drying the obtained raw material powder, it was put into a high-purity alumina container and heat-treated at 700 ° C. for 12 hours in the atmosphere. And the obtained temporary baking body was air-cooled and grind | pulverized.

When elemental analysis of the particles of the obtained precursor 2B was performed, Li: Mn was 2.00: 1.0. Therefore, the elemental composition is estimated to be Li ₂ MnO ₃ .

  Moreover, as a result of measuring the particle size distribution with a laser diffraction / scattering type particle size distribution measuring apparatus (LA-920 manufactured by Horiba Ltd.), the median diameter (D50) was 0.18 μm.

Example 1
Manufacture of the non-aqueous secondary battery positive electrode active material was performed in the following procedure. 100 parts by weight of precursor 1 and 5 parts by weight of precursor 2A were mixed using a mortar. The obtained mixed powder was put into a high-purity alumina container and heat-treated at 800 ° C. for 1 hour in an oxygen atmosphere.

As a result of measuring the particle size distribution of the produced positive electrode active material of Example 1 with a laser diffraction / scattering particle size distribution measuring device (LA-920, manufactured by Horiba, Ltd.), the median diameter (D50) was 9 μm. When elemental analysis was performed, it was Li: Ni: Mn: Co = 1.02: 0.77: 0.13: 0.10. Therefore, the composition of the positive electrode active material of Example 1 is estimated to be Li _1.02 Ni _0.77 Mn _0.13 Co _0.10 O ₂ . Further, the TEM-EDX measurement was performed on the positive electrode active material of Example 1. The surface and internal electron diffraction patterns were measured by TEM, and a pattern of a layered structure belonging to R3-m was confirmed. The primary particle 1 was subjected to point analysis in a line shape and the surface portion was measured. The measured locations are shown in FIG. 6 and the measurement results are shown in FIG.

  The primary particle 1 has an Ni atomic concentration (Cs) of 71 mol%, an Ni atomic concentration gradient (Gs) of 0.028 mol% / nm, and an Mn atomic concentration (Cs (Mn)) of 21 mol%. , The atomic concentration gradient of Mn (Gs (Mn)) is 0.028 mol% / nm, the surface portion is 50 nm thick, the atomic concentration of Ni (Cm) is 75 mol%, and the atomic concentration gradient of Ni ( Gm) is 0.18 mol% / nm, the atomic concentration of Mn (Cm (Mn)) is 15 mol%, the gradient of atomic concentration of Mn (Gm (Mn)) is 0.22 mol% / nm, The intermediate portion of 50 nm, the atomic concentration (Cc) of Ni is 80 mol%, the gradient of atomic concentration of Ni is 0.012 mol% / nm, the atomic concentration of Mn is 10 mol%, and the gradient of atomic concentration of Mn Is 0.022 mol% / And internal m, it was confirmed that is formed.

  Moreover, also about the surface part of the other primary particles 2-4, the TEM-EDX of the surface part and center part was measured similarly to the primary particle 1. The measurement results are shown in Table 1. In the primary particles 2 and 4, the concentration of Ni atoms in the center is low, and it is considered that the Ni particles are completely dissolved up to the center and have a substantially uniform composition. The formation rate of the positive electrode active material of Example 1 was 88%, and the formation particle rate was 50%.

(Example 2)
Manufacture of the non-aqueous secondary battery positive electrode active material was performed in the following procedure. 100 parts by weight of the precursor 1 and 2.5 parts by weight of the precursor 2A were mixed using a composite apparatus. The obtained mixed powder was put into a high-purity alumina container and heat-treated at 800 ° C. for 1 hour in an oxygen atmosphere.

The produced positive electrode active material of Example 2 was measured for particle size distribution with a laser diffraction / scattering particle size distribution analyzer (LA-920, manufactured by Horiba, Ltd.). As a result, the median diameter (D50) was 10 μm. When elemental analysis was performed, it was Li: Ni: Mn: Co = 1.02: 0.79: 0.11: 0.10. Therefore, the composition of the positive electrode active material of Example 2 is estimated to be Li _1.02 Ni _0.79 Mn _0.11 Co _0.10 O ₂ . The formation rate was 86% and the formation particle rate was 70%. Moreover, the surface part and the internal electron diffraction pattern were measured by TEM, and the pattern of the layered structure which all belonged to R3-m has been confirmed.

  Table 2 shows the TEM-EDX measurement results for the primary particles 5 to 14 of the positive electrode active material of Example 2. The precursor 1 and the precursor 2A diffused to each other by firing, and the atomic concentration of Ni in the surface portion was 61.6 mol% or more.

  In addition, FIG. 8 shows the results of line point analysis of the primary particles 8 measured in the same manner as the primary particles 1. The primary particle 8 has an Ni atomic concentration (Cs) of 72 mol%, an Ni atomic concentration gradient (Gs) of 0.12 mol% / nm, and an Mn atomic concentration (Cs (Mn)) of 19 mol%. , The atomic concentration gradient of Mn (Gs (Mn)) is 0.132 mol% / nm, the surface portion is 100 nm thick, the atomic concentration of Ni (Cm) is 73 mol%, and the atomic concentration gradient of Ni ( Gm) is 0.80 mol% / nm, the atomic concentration of Mn (Cm (Mn)) is 18 mol%, the gradient of atomic concentration of Mn (Gm (Mn)) is 0.9 mol% / nm, 20 nm intermediate portion, Ni atomic concentration (Cc) is 79 mol%, Ni atomic concentration gradient is 0.0086 mol% / nm, Mn atomic concentration is 10 mol%, Mn atomic concentration gradient Is 0.006 mol% / It was confirmed that the internal m are formed.

(Example 3)
Manufacture of the non-aqueous secondary battery positive electrode active material was performed in the following procedure. 100 parts by weight of the precursor 1 and 5 parts by weight of the precursor 2B were mixed using a mortar. The obtained mixed powder was put into a high-purity alumina container and heat-treated at 800 ° C. for 1 hour in an oxygen atmosphere.

The particle size distribution of the positive electrode active material of Example 3 was measured with a laser diffraction / scattering particle size distribution analyzer (LA-920, manufactured by Horiba Ltd.), and as a result, the median diameter (D50) was 9 μm. When elemental analysis was performed, it was Li: Ni: Mn: Co = 1.05: 0.76: 0.14: 0.10. Therefore, the composition of the positive electrode active material of Example 1 is estimated to be Li _1.05 Ni _0.76 Mn _0.14 Co _0.10 O ₂ . The formation rate was 88% and the formation particle rate was 66%. Moreover, the surface part and the internal electron diffraction pattern were measured by TEM, and the pattern of the layered structure which all belonged to R3-m has been confirmed.

  Table 3 shows the TEM-EDX measurement results for the positive electrode active material primary particles 15 to 17 of Example 3. Further, FIG. 9 shows the results of line point analysis of the primary particles 17 measured in the same manner as the primary particles 1. The primary particles 17 have an Ni atomic concentration (Cs) of 75 mol%, an Ni atomic concentration gradient (Gs) of 0.0095 mol% / nm, and an Mn atomic concentration (Cs (Mn)) of 17 mol%. , The Mn atomic concentration gradient (Gs (Mn)) is 0.149 mol% / nm, the surface portion is 115 nm thick, the Ni atomic concentration (Cm) is 78 mol%, and the Ni atomic concentration gradient (Gm ) Is 0.30 mol% / nm, the Mn atomic concentration (Cm (Mn)) is 13 mol%, the Mn atomic concentration gradient (Gm (Mn)) is 0.4 mol% / nm, and the thickness is 15 nm. The intermediate concentration of Ni, the atomic concentration (Cc) of Ni is 81 mol%, the atomic concentration gradient of Ni is 0.028 mol% / nm, the atomic concentration of Mn is 10 mol%, and the atomic concentration gradient of Mn is 0 .018 mol% / It was confirmed that the internal m are formed.

(Comparative Example 1)
The composition of the surface portion and the inside is different, both the surface portion and the inside contain Ni and Mn, and has a layered structure. The intermediate concentration Cs of Ni in the surface portion and the atomic concentration Cc of Ni in the interior are Cs <Cc A positive electrode active material having no part was synthesized. Specifically, 100 parts by weight of Precursor 1 and 2.5 parts by weight of Precursor 2A are mixed using a compounding apparatus and compared without performing heat treatment for mutual diffusion of Precursors 1 and 2A. The positive electrode active material of Example 1 was used.

(Comparative Example 2)
A positive electrode active material having a single composition, that is, only the inside was used. Specifically, for comparison with Examples and Comparative Example 1, Precursor 1 was used as the positive electrode active material of Comparative Example 2.

  Using the positive electrode active materials for non-aqueous secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2, non-aqueous secondary batteries were produced by the following procedures. First, 90 parts by weight of a positive electrode active material, 6 parts by weight of a conductive material, and 4 parts by weight of a binder were mixed with N-methylpyrrolidone as a solvent and homogenized to prepare a slurry-like positive electrode mixture. As the conductive material, acetylene black “DENKA BLACK (registered trademark)” (manufactured by Denki Kagaku Kogyo Co., Ltd.) was used. In addition, polyvinylidene fluoride was used as the binder. Subsequently, the prepared positive electrode mixture was applied to a foil-like aluminum positive electrode current collector having a thickness of 15 μm, dried at 120 ° C., and then pressed twice at 60 MPa to form an electrode plate. Then, the electrode plate was punched into a disk shape having a diameter of 15 mm to obtain a positive electrode for a non-aqueous secondary battery.

The non-aqueous secondary battery was manufactured using the manufactured non-aqueous secondary battery positive electrode and the non-aqueous secondary battery negative electrode made of metallic lithium. As the non-aqueous electrolyte, a solution in which LiPF ₆ was dissolved to a concentration of 1.0 mol / L in a solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 2 was used.

  Next, the following charge / discharge tests were performed on the manufactured non-aqueous secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2, and the discharge capacity was measured. The charge / discharge test was conducted at an environmental temperature of 25 ° C.

  Charging / discharging at a constant current equivalent to 0.2C up to an upper limit voltage of 4.3V and resting for 30 minutes and then discharging to a lower limit voltage of 3.3V at a constant current equivalent to 0.2C and resting for 30 minutes Two cycles were initialized. The discharge capacity was the value at the first cycle. After that, constant current and constant voltage charging with a current equivalent to 1C is performed up to an upper limit voltage of 4.4V, and resting for 5 minutes, then discharging to a lower limit voltage of 3.3V with a constant current equivalent to 1C and charging and discharging for 5 minutes is performed for 50 cycles. It was. The discharge capacity at the 50th cycle of constant current discharge equivalent to 1C was divided by the discharge capacity at the first cycle of constant current discharge equivalent to 1C, and a value multiplied by 100 was taken as the capacity retention rate. The results are shown in Table 4 below.

  Next, the manufactured non-aqueous secondary batteries of Example 1 and Comparative Example 2 were subjected to the following charge / discharge test, and the discharge capacity was measured. The charge / discharge test was conducted at an environmental temperature of 25 ° C.

  Charge and discharge with constant current and constant voltage charge up to an upper limit voltage of 4.6 V at a current equivalent to 0.2 C and resting for 30 minutes, then discharging to a lower limit voltage of 3.3 V with a constant current equivalent to 0.2 C and resting for 30 minutes Two cycles were initialized. After that, constant current and constant voltage charging with a current equivalent to 1 C is performed up to an upper limit voltage of 4.6 V, and resting for 5 minutes, then discharging to a lower limit voltage of 3.3 V with a constant current equivalent to 1 C and charging and discharging for 5 minutes are performed for 50 cycles. It was. The discharge capacity at the 50th cycle of constant current discharge equivalent to 1C was divided by the discharge capacity at the first cycle of constant current discharge equivalent to 1C, and a value multiplied by 100 was taken as the capacity maintenance rate at 4.6V. The results are shown in Table 4 below.

  As shown in Table 4, in the non-aqueous secondary batteries of Examples 1 to 3, the composition of the surface portion and the interior are different for the capacity retention rate, both the surface portion and the inside contain Ni and Mn, Compared to Comparative Example 1, which has a layered structure, the atomic concentration Cs of Ni in the surface portion, and the atomic concentration Cc of the internal Ni is Cs <Cc, compared with Comparative Example 2 in which there is almost no difference in composition between the surface portion and the inside. did. Further, in the secondary batteries of Examples 1 to 3, the discharge capacity is as high as 179 Ah / kg or more. The capacity retention rate at 4.6 V was also improved compared to Comparative Example 2 where there was almost no difference in composition between the surface portion and the inside.

Therefore, the positive electrode active material of the present invention has a high capacity and a high potential (battery voltage of 4.5 V (vs. Li ^/ Li ⁺ ), positive electrode single electrode of 4.6 V (vs. Li ^/ Li ⁺ )). Cycle deterioration in the case of use is also in the case of using up to a low potential (battery voltage of 4.3 V (vs. Li ^/ Li ⁺ ) or less, positive electrode single electrode of 4.4 V (vs. Li ^/ Li ⁺ ) or less). It was confirmed that cycle deterioration can also be suppressed.

DESCRIPTION OF SYMBOLS 1 Inner 2 Middle part 3 Surface part 4 Positive electrode active material secondary particle 5 Non-aqueous secondary battery 6 Positive electrode for non-aqueous secondary battery 7 Negative electrode 8 for non-aqueous secondary battery Separator 9 Battery can 10 Positive electrode lead piece 11 Negative electrode lead piece 12 Sealing lid 13 Sealing material 14 Insulating plate 15 Cathode active material primary particle 16 Measurement location of TEM-EDX point analysis

Claims (16)

An inner portion, an intermediate portion provided on the inner surface, and a surface portion provided on the surface of the intermediate portion;
The surface part, the intermediate part, and the inside are different in composition, contain Ni and Mn, and have a layered structure,
The atomic concentration Cs of Ni in the surface portion, the atomic concentration Cm of Ni in the middle portion, and the atomic concentration Cc of Ni in the interior are Cs <Cm <Cc,
A positive electrode active material for a non-aqueous secondary battery, comprising particles having a concentration gradient Gs of Ni concentration in a surface portion and a concentration gradient Gm of Ni concentration in a middle portion of Gs <Gm. Surface portion and the intermediate portion and the interior of the composition formula _{Li 1 + X Ni A Mn B} Co C M D O 2-Y [ wherein, X is a number satisfying the -0.1 ≦ X ≦ 0.3, Y is , −0.1 ≦ Y ≦ 0.1, A is a number that satisfies 0.2 ≦ A ≦ 0.95, and B is a number that satisfies 0 <B ≦ 0.95. , C is a number satisfying 0 ≦ C ≦ 0.6, M is at least one element selected from the group consisting of Mg, Al, Ti, Mo and Nb, and D is 0 ≦ D 2 is a number satisfying ≦ 0.1, and A + B + C + D = 1]. The positive electrode active material for a non-aqueous secondary battery according to claim 1. The compositional formula of the surface portion is Li _{1 + X} Ni _A Mn _B Co _C M _D O _2-Y [wherein X is a number satisfying 0 <X ≦ 0.3, and Y is −0.1 ≦ Y ≦ 0.1, A is a number that satisfies 0.2 ≦ A ≦ 0.95, B is a number that satisfies 0 <B ≦ 0.95, and C is 0 ≦ C ≦ 0.95. 0.6 is a number satisfying 0.6, M is at least one element selected from the group consisting of Mg, Al, Ti, Mo and Nb, and D is a number satisfying 0 ≦ D ≦ 0.1. The positive electrode active material for a non-aqueous secondary battery according to claim 1, wherein A + B + C + D = 1.   The positive electrode active material for a non-aqueous secondary battery according to any one of claims 1 to 3, wherein the atomic concentration of Li in the surface portion is higher than the atomic concentration of internal Li.   The thickness of a surface part is 20 nm or more and 200 nm or less, The positive electrode active material for non-aqueous secondary batteries of any one of Claims 1-4 characterized by the above-mentioned.   The thickness of the intermediate part is 10 nm or more and 100 nm or less, The positive electrode active material for a non-aqueous secondary battery according to any one of claims 1 to 5. A non-aqueous system comprising secondary particles in which primary particles are aggregated, wherein all or part of primary particles in the vicinity of the surface of the secondary particles are particles according to any one of claims 1 to 6. Positive electrode active material for secondary battery. The transition metal compound and the Li compound are mixed, the mixture of the transition metal compound and the Li compound is temporarily fired, and the obtained temporary fired body is fired to produce the precursor 1 containing Li, Ni, and Mn. Process,
A step of mixing a transition metal compound and a Li compound, and firing a mixture of the transition metal compound and the Li compound to produce a precursor 2 that is finer than the precursor 1 and lower in atomic concentration of Ni than the precursor 1 When,
A positive electrode active material for a non-aqueous secondary battery comprising particles having a three-layer structure, comprising: a step of mixing the precursor 1 and the precursor 2 and heat-treating the mixture of the precursor 1 and the precursor 2 Manufacturing method.   The method for producing a positive electrode active material for a non-aqueous secondary battery according to claim 8, wherein the atomic concentration of Ni in the precursor 1 is 50 mol% or more.   The method for producing a positive electrode active material for a non-aqueous secondary battery according to claim 8 or 9, wherein the molar ratio of Li to the total molar ratio of the transition metals of the precursor 2 is greater than 1.   11. The non-aqueous secondary battery according to claim 8, wherein a median diameter D50A of the precursor 1 and a median diameter D50B of the precursor 2 satisfy 2 ≦ D50A / D50B ≦ 100. For producing a positive electrode active material for use.   The heating temperature in the heat treatment of the mixture of the precursor 1 and the precursor 2 is a temperature not higher than 50 degrees higher than the main firing temperature in the step of manufacturing the precursor 1. The manufacturing method of the positive electrode active material for non-aqueous secondary batteries of Claim 1.   The nonaqueous secondary battery according to any one of claims 8 to 12, wherein the heating time in the heat treatment of the mixture of the precursor 1 and the precursor 2 is equal to or shorter than the main firing time of the precursor 1. For producing a positive electrode active material for use.   A positive electrode for a non-aqueous secondary battery, comprising the positive electrode active material for a non-aqueous secondary battery according to claim 1.   A non-aqueous secondary battery comprising the positive electrode for a non-aqueous secondary battery according to claim 14.   An in-vehicle non-aqueous secondary battery module comprising the non-aqueous secondary battery according to claim 15.

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