JP7222188B2 - Positive electrode active material for lithium ion secondary battery and manufacturing method thereof, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

The present invention relates to a positive electrode active material for lithium ion secondary batteries, a method for producing the same, a positive electrode for lithium ion secondary batteries, and a lithium ion secondary battery.

In recent years, with the spread of portable electronic devices such as smart phones, tablet terminals, and laptop computers, there is a strong demand for the development of small, lightweight secondary batteries with high energy density. In addition, there is a strong demand for the development of secondary batteries with excellent output characteristics and charge/discharge cycle characteristics as batteries for electric vehicles such as hybrid cars.

As a secondary battery that satisfies such requirements, there is a lithium ion secondary battery. This lithium-ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of desorbing and intercalating lithium is used as an active material for the negative electrode and the positive electrode. As the electrolyte, a non-aqueous electrolytic solution obtained by dissolving a lithium salt, which is a supporting salt, in an organic solvent, or a non-aqueous electrolyte such as a nonflammable solid electrolyte having ion conductivity is used.

Such lithium ion secondary batteries are currently being actively researched and developed. Since the ion secondary battery can obtain a high voltage of the 4V class, it is being put to practical use as a battery having a high energy density.

Lithium-transition metal-containing composite oxides mainly proposed so far include lithium-cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, and lithium-nickel composite oxide using nickel, which is cheaper than cobalt ( LiNiO ₂ ), lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), and the like.

Among the positive electrode active materials described above, lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), which has excellent thermal stability and high capacity, has been attracting attention in recent years. Lithium-nickel-cobalt-manganese composite oxides are layered compounds like lithium-cobalt composite oxides and lithium-nickel composite oxides. Included in the ratio of 1.

On the other hand, for the purpose of obtaining a positive electrode having high performance (high cycle characteristics, high capacity, high output) as a lithium ion secondary battery, lithium and Various techniques have been proposed to combine composite oxides containing niobium.

For example, in Patent Document 1, a positive electrode active material for a non-aqueous electrolyte secondary battery made of a lithium-nickel-manganese composite oxide composed of secondary particles in which a plurality of primary particles are aggregated, wherein the lithium-nickel-manganese composite oxide is represented by the general formula (1): Li _d Ni _{1-ab-c Mna} M _b Nb _c O _2+γ (in the general formula (1), M is Co, W, Mo, V, Mg, Ca, At least one element selected from Al, Ti, Cr, Zr and Ta, 0.05≦a≦0.60, 0≦b≦0.60, 0.0003≦c≦0.03, 0 .95 ≤ d ≤ 1.20 and 0 ≤ γ ≤ 0.5), and at least part of the niobium in the lithium-nickel-manganese composite oxide is solid-dissolved in the primary particles. Active materials for electrolyte secondary batteries have been proposed. It is also described that the positive electrode active material may contain a compound containing lithium and niobium on at least part of the surface of the primary particles. According to Patent Literature 1, the lithium niobium compound formed on the surfaces of the primary particles reduces the positive electrode resistance of the obtained secondary battery and improves the output characteristics.

For example, in Patent Document 2, a second composite oxide composed of a composite oxide of Li and Al or Nb is formed on the surface of a first composite oxide containing Li, Ni, Co, Mn, and W. A positive electrode active material for a lithium ion battery in which an oxide is present has been proposed, and a first composite oxide containing Li, Ni, Co, Mn and W is coated on the particle surface with a composite of Li and Al or Nb. It has been shown that the presence of the second composite oxide composed of oxides results in excellent battery properties.

WO2018/043669 JP 2017-084674 A

However, as shown in Patent Documents 1 and 2, if the composite oxide containing lithium and niobium is present only on the surface of the composite oxide containing Li, Ni, Co, and Mn, the output characteristics of the secondary battery not enough to improve

In view of the above problems, an object of the present invention is to provide a positive electrode whose positive electrode resistance (reaction resistance) is greatly reduced and which can have higher output characteristics when used as a positive electrode active material for a lithium ion secondary battery. An object of the present invention is to provide an active material and a method for producing the same.

In order to solve the above problems, the inventors have made intensive studies and found that the presence of a specific amount of first particles having lithium ion conductivity on the surface of the lithium metal composite oxide significantly increases the positive electrode resistance. The present invention was completed by discovering that it can be reduced to .

According to the first aspect of the present invention, the positive electrode includes a first lithium metal composite oxide composed of secondary particles in which a plurality of primary particles are aggregated, and first particles having lithium ion conductivity . The active material, the positive electrode active material, contains lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and element M, and the material amount (molar) ratio of these elements is Li: Ni: Co: Mn: M = d1: (1-abc): a: b: c (provided that 0.05 ≤ a ≤ 0.60, 0.05 ≤ b ≤ 0.60, 0≦c≦0.60, 0.40≦a+b+c, 0.95≦d1≦1.5, M is W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta at least one element selected from), the first particles contain lithium, oxygen, and elements other than lithium and oxygen, and the number of elements other than lithium and oxygen in the first particles The amount is 0.01% by mass or more and 4% by mass or less with respect to the entire positive electrode active material, and at least a part of the first particles is present bonded to the surface of the first lithium metal composite oxide Provided is a positive electrode active material for a lithium ion secondary battery.

Moreover, it is preferable that at least part of the first particles exist separately from the first lithium metal composite oxide. Also, the first particles preferably contain at least one selected from the group consisting of lithium niobium composite oxides, lithium tungsten composite oxides, lithium phosphorus composite oxides, and lithium silicon composite oxides. Also, the first particles preferably contain at least one of LiNbO ₃ and Li ₃ NbO ₄ . At least part of the first particles preferably have a longest diameter of 0.5 μm or more.

According to the second aspect of the present invention, the positive electrode includes a first lithium metal composite oxide composed of secondary particles in which a plurality of primary particles are aggregated, and first particles having lithium ion conductivity . A method for producing an active material, comprising: mixing a second lithium metal composite oxide with second particles capable of forming the first particles by reacting with lithium; and heat-treating the obtained mixture at a temperature of 400° C. or more and 900° C. or less, wherein the second lithium metal composite oxide is lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn ), and the element M, and the material amount (molar) ratio of these elements is Li: Ni: Co: Mn: M = d2: (1-a-b-c): a: b: c (however, , 0.05≤a≤0.60, 0.05≤b≤0.60, 0≤c≤0.60, 0.40≤a+b+c, 0.95≤d2≤1.5, M is W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and at least one element selected from Ta), and the first particles are composed of lithium, oxygen, lithium and oxygen The second particles contain the elements other than lithium and oxygen, and the amount of the elements other than lithium and oxygen in the mixture is 0.01% by mass with respect to the entire positive electrode active material There is provided a method for producing a positive electrode active material for a lithium ion secondary battery, wherein the content is 4% by mass or less, and at least part of the first particles are bonded to the surface of the first lithium metal composite oxide. .

Also, the second particles preferably contain at least one element selected from the group consisting of niobium, tungsten, phosphorus, and silicon. Also, the second particles preferably contain niobic acid. Also, the second lithium metal composite oxide is formed by firing a compound containing nickel, cobalt, and manganese obtained by crystallization and a lithium compound at a temperature of 700° C. or more and 1000° C. or less. is preferred.

According to a third aspect of the present invention, a positive electrode for a lithium ion secondary battery comprising a first lithium metal composite oxide and first particles having lithium ion conductivity , wherein the first The lithium metal composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and an element M, and the material amount (molar) ratio of these elements is Li:Ni: Co:Mn:M=d3:(1-abc):a:b:c (where 0.05≤a≤0.60, 0.05≤b≤0.60, 0≤c≤ 0.60, 0.40≦a+b+c, 0.95≦d3≦1.5, M is selected from W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta at least one element), the first particles contain lithium, oxygen, and an element other than lithium and oxygen, and a portion of the first particles is the first lithium-metal composite oxide Provided is a positive electrode for a lithium ion secondary battery, which exists in combination with the surface of an object, and where a part of the first particles exists separately from the first lithium metal composite oxide.

Also, the first particles preferably contain at least one of LiNbO ₃ and Li ₃ NbO ₄ .

According to a fourth aspect of the present invention, there is provided a lithium ion secondary battery comprising a positive electrode containing the above positive electrode active material, a negative electrode, and an electrolyte.

Since the positive electrode active material of the present invention contains the lithium metal composite oxide and the first particles having lithium ion conductivity, the positive electrode resistance of the resulting lithium ion secondary battery can be significantly reduced. Therefore, the lithium ion secondary battery using the positive electrode active material of the present invention for the positive electrode can further improve the output characteristics. In addition, the method for producing a positive electrode active material of the present invention can easily produce the above positive electrode active material with high productivity.

FIG. 1A is a diagram showing an example of a positive electrode active material according to this embodiment, and FIG. 1B is a diagram showing an example of the structure of a lithium metal composite oxide. FIG. 2 is a diagram showing an example of a method for producing a positive electrode active material according to this embodiment. FIG. 3 is a diagram showing an example of a method for producing a positive electrode active material according to this embodiment. FIG. 4 is a schematic cross-sectional view of a coin-type battery used for battery evaluation. FIG. 5 is a schematic explanatory diagram of an example of impedance evaluation measurement and an equivalent circuit used for analysis. FIG. 6 is a graph showing the relationship between the positive electrode resistance of the positive electrode active materials obtained in Examples and Comparative Examples and the amount of niobium. 7 is a diagram showing a backscattered electron image (COMPO image) by SEM of the positive electrode active material obtained in Example 1. FIG. FIG. 8 is a SEM backscattered electron image (COMPO image) of the positive electrode active material obtained in Comparative Example 4. As shown in FIG.

Hereinafter, a positive electrode active material for lithium ion secondary batteries, a method for producing the same, a positive electrode mixture paste for lithium ion secondary batteries, and a lithium ion secondary battery according to the present embodiment will be described with reference to the drawings. In addition, in the drawings, in order to make each configuration easy to understand, some parts are emphasized or some parts are simplified, and the actual structure, shape, scale, etc. may differ.

1. 1. Positive Electrode Active Material for Lithium Ion Secondary Battery FIG. 1A is a schematic diagram showing an example of a positive electrode active material for a lithium ion secondary battery according to the present embodiment. As shown in FIG. 1A, the positive electrode active material 100 according to this embodiment includes a first lithium metal composite oxide 10 and first particles 20 having lithium ion conductivity.

(1) Composition of positive electrode active material (whole) The positive electrode active material 100 contains lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and element M, and the amount of these elements The (molar) ratio is Li:Ni:Co:Mn:M=d1:(1-abc):a:b:c (where 0.05≦a≦0.60, 0.05≦ b≦0.60, 0≦c≦0.60, 0.40≦a+b+c, 0.95≦d1≦1.5, M is W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr , La, and Ta). As will be described later, the positive electrode active material 100 also contains niobium derived from the first particles 20 .

Nickel (Ni) is an element that contributes to increasing the potential and capacity of secondary batteries. In the above molar ratio, the value of (1-abc) indicating the Ni content is 0.05 or more and 0.6 or less, preferably 0.3 or more and 0.6 or less, more preferably 0.3 0.4 or less. If the value of (1-ab) is less than 0.05, the effect of improving the battery capacity of the secondary battery obtained by containing Ni cannot be sufficiently obtained.

Cobalt (Co) is an element that contributes to the improvement of charge-discharge cycle characteristics. In the above molar ratio, the value of a indicating the Co content is 0.05 or more and 0.6 or less, preferably 0.05 or more and 0.4 or less, more preferably 0.1 or more and 0.4 or less. If the value of a is less than 0.05, the effect of improving charge-discharge cycle characteristics obtained by containing Co cannot be sufficiently obtained.

In the above molar ratio, the value of b, which indicates the content of Mn, is 0.05 or more and 0.6 or less, preferably 0.05 or more and 0.4 or less, more preferably 0.1 or more and 0.4 or less. If the value of b is less than 0.05, the effect of improving charge-discharge cycle characteristics obtained by containing Mn cannot be sufficiently obtained.

M representing an additional element is at least one element selected from W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta. In the above molar ratio, the value of c, which indicates the content of M, is 0 ≤ c ≤ 0.60. Among them, when c is greater than 0, thermal stability, output characteristics, cycle characteristics, etc. can be improved. can.

In the above molar ratio, d1 indicating the content of lithium is preferably 0.95 or more and 1.5 or less, more preferably 1.0 or more and 1.10 or less. If the molar ratio (d1) of lithium is less than 0.95, other elements may occupy the sites that should be occupied by lithium in the crystal of the lithium metal composite oxide, resulting in a decrease in charge/discharge capacity. On the other hand, when the molar ratio of lithium exceeds 1.5, a surplus lithium compound that does not contribute to charging and discharging is present together with the lithium-nickel composite oxide, resulting in an increase in battery resistance and a decrease in charge-discharge capacity. sometimes

In addition, the positive electrode active material 100 has a composition excluding niobium, which is represented by the general formula (1): Li _d1 Ni _1-ab-c Co _a Mn _b M _c O _2+α (wherein M is at least one element selected from W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta, 0.05≦a≦0.60, 0.05≦b ≤0.60, 0≤c≤0.60, 0.40≤a+b+c, 0.95≤d1≤1.5, 0≤α≤0.5). In addition, in the general formula (1), the preferable range of each element can be the same range as the molar ratio described above.

(2) First Lithium-Metal Composite Oxide FIG. 1B is a schematic diagram showing an example of the first lithium-metal composite oxide 10 . The first lithium metal composite oxide 10 is composed of secondary particles 2 formed by aggregation of a plurality of primary particles 1 . The shape of the secondary particles 2 is not particularly limited, and may have, for example, a solid structure, a hollow structure, a porous structure, or the like. Here, the solid structure refers to a structure in which the secondary particles 2 are entirely composed of agglomerates of a plurality of primary particles 1, and the hollow structure refers to the presence of one or more spaces inside the secondary particles 2. A structure that Moreover, the porous structure refers to a structure in which a large number of voids are present inside the secondary particles 2 . Note that the first lithium metal composite oxide 10 may contain not only the secondary particles 2 but also a small number of individual primary particles 1 .

The size of the first lithium metal composite oxide 10 is not particularly limited, but the volume average particle diameter MV is preferably about 1 μm or more and 30 μm or less, more preferably 3 μm or more and 10 μm or less. The volume-average particle diameter MV can be obtained, for example, from a volume integrated value measured with a laser beam diffraction/scattering particle size distribution meter.

(3) First Particles The first particles 20 are not particularly limited as long as they have lithium ion conductivity and contain lithium, oxygen, and an element other than lithium and oxygen. Elements other than lithium and oxygen are not particularly limited, and may be, for example, at least one element selected from the group consisting of Nb, W, P, and Si. In addition, the first particles may be of one type, or may be of a plurality of types.

The first particles 20 preferably contain, for example, at least one selected from the group consisting of lithium-niobium composite oxide, lithium-tungsten composite oxide, lithium-phosphorus composite oxide, and lithium-silicon composite oxide. For example, as the first particles 20, lithium niobium _composite oxides such _{as Li3NbO4 and LiNbO3 ;} lithium tungsten composite oxides such as _Li2WO4 , _{Li2W2O7 and} Li4WO5 _; Lithium phosphorus composite oxides such as ₃ PO ₄ , lithium silicon composite oxides such as Li ₄ SiO ₄ and the like. Among these, from the viewpoint of increasing lithium ion conductivity, it is more preferable to contain at least one of LiNbO ₃ and Li ₃ NbO ₄ , and it is even more preferable to consist of LiNbO ₃ . If the first particles 20 contain LiNbO ₃ , they can have higher lithium ion conductivity.

The composition of the compound of the first particles 20 and the type of compound can be evaluated and identified by analysis by ICP emission spectrometry and X-ray diffraction (XRD), which will be described later. Note that the first particles 20 may contain an amorphous phase. The amorphous phase is excellent in lithium ion conductivity and may further improve battery characteristics.

The amount of elements other than lithium and oxygen in the first particles 20 is 0.01% by mass or more and 4% by mass or less, preferably 0.01% by mass or more and 4% by mass or less, relative to the entire positive electrode active material 100. More preferably 0.05% by mass or more and 3.5% by mass or less. When the amounts of elements other than lithium and oxygen are within the above range, the reaction resistance (positive electrode resistance) of the secondary battery can be reduced and the output characteristics can be improved.

Further, when the first particles 20 are lithium-niobium composite oxide, the amount of niobium in the lithium-niobium composite oxide is, for example, 0.5% by mass or more and 2.5% by mass with respect to the entire positive electrode active material. It may be below. When the amount of niobium is within the above range, the positive electrode resistance (reaction resistance) of the secondary battery can be further reduced, and the output characteristics can be further improved.

In the positive electrode active material 100, at least part of the first particles 20 are present in a state of bonding (or adhering) to the surface of the first lithium metal composite oxide 10 (see 20a in FIG. 1(A)). . The first particles 20 may be present bonded to at least a part of the surface of the first lithium metal composite oxide 10, and may cover the entire surface, and the first lithium metal composite oxide It may be attached to a portion of the surface of 10. The first particles 20 can be bonded (adhered) to the surface of the first lithium metal composite oxide 10 by heat treatment (step S20), which will be described later.

Moreover, in the positive electrode active material 100, at least part of the first particles 20 is preferably separated from the first lithium metal composite oxide 10 (see 20b in FIG. 1A). When the positive electrode of the secondary battery is formed due to the presence of the first particles 20a that exist in combination with the first lithium metal composite oxide 10 and the first particles 20b that exist separately, It is presumed that a lithium ion conductive path is formed between the particles of the first lithium metal composite oxide 10 and the ion conductivity between the particles of the first lithium metal composite oxide 10 is improved.

The first particles 20b present separately from the first lithium metal composite oxide 10 contain the same element as the first particles 20a present bonded to the surface of the first lithium metal composite oxide 10. It is preferable that they contain, and more preferably that they have the same composition.

The size of the first particles 20 is not particularly limited, but at least some of the first particles 20 preferably have a longest diameter of 0.5 μm or more, and may be 1 μm or more. Also, the average particle size of the first particles 20 may be 0.5 μm or more. When the first particles 20 are amorphous or the like, the average particle size may be the average longest diameter when observing the plurality of first particles 20 with a scanning electron microscope (SEM).

2. Method for Producing Positive Electrode Active Material FIG. 2 is a diagram showing an example of a method for producing a positive electrode active material according to the present embodiment. A method for producing a positive electrode active material includes mixing a second lithium metal composite oxide and second particles capable of forming first particles by reacting with lithium (step S10); and heat-treating the resulting mixture (step S20). By this method for manufacturing a positive electrode active material, the above-described positive electrode active material 100 can be easily manufactured with high productivity.

Further, as shown in FIG. 3, the second lithium metal composite oxide is obtained by crystallization to obtain a compound containing nickel, cobalt, and manganese (hereinafter also simply referred to as "nickel compound") (step S1 ), mixing the resulting nickel compound and lithium compound (step S2), and firing the resulting mixture (step S3). When a nickel compound obtained by crystallization is used as a precursor of a positive electrode active material, a positive electrode active material having a more uniform composition can be obtained. In addition, the said nickel compound contains the form of one or both of a hydroxide and an oxide. An example of the method for manufacturing the positive electrode active material according to this embodiment will be described below.

[Crystallization step (Step S1)]
The compound containing nickel (precursor of the positive electrode active material) can be obtained by a known production method, but is preferably obtained by crystallization. It is more preferable to separate into one step. By separating the crystallization into the above two steps, a nickel compound having a more uniform particle size and a narrow particle size distribution can be obtained. Since the form of the nickel compound (precursor of the positive electrode active material) is inherited by the form of the second lithium metal composite oxide after firing, the finally obtained positive electrode active material must also have a uniform particle size. It is possible to improve battery characteristics such as cycle characteristics. As an example of the crystallization process, the case where the crystallization process is separated into a nucleation stage and a grain growth stage will be described below.

(Nucleation step)
First, a compound containing nickel, cobalt, manganese, and optionally the element M is dissolved in water at a predetermined ratio to prepare an aqueous raw material solution. In addition, an alkaline aqueous solution and an aqueous solution containing an ammonium ion donor are supplied and mixed in a reaction tank, and the pH value measured at a liquid temperature of 25 ° C. is 12.0 or more and 14.0 or less, and the ammonium ion concentration is 3 g. /L or more and 25 g/L or less of the pre-reaction aqueous solution is prepared. The pH value of the pre-reaction aqueous solution can be measured with a pH meter, and the ammonium ion concentration can be measured with an ion meter.

Next, while stirring the pre-reaction aqueous solution, the raw material aqueous solution is supplied. As a result, an aqueous solution for nucleation, which is a reaction aqueous solution in the nucleation step, is formed in the reaction tank. Since the pH value of the aqueous solution for nucleation is within the range described above, nucleation takes place preferentially with little growth of nuclei in the nucleation step. In the nucleation step, the pH value and the concentration of ammonium ions in the aqueous solution for nucleation change with nucleation. The pH is controlled to be in the range of 12.0 to 14.0 on a °C basis and the concentration of ammonium ions is maintained in the range of 3 g/L to 25 g/L.

(Particle growth step)
After the nucleation step is completed, the pH value of the nucleation aqueous solution in the reaction tank is adjusted to 10.5 or more and 12.0 or less based on the liquid temperature of 25° C., and the particle growth aqueous solution, which is the reaction aqueous solution in the particle growth step, is adjusted. Form. The pH value can also be adjusted by stopping the supply of the alkaline aqueous solution, but in order to obtain a nickel compound with a narrow particle size distribution, it is necessary to temporarily stop the supply of all the aqueous solution and adjust the pH value. is preferred. Specifically, after stopping the supply of all the aqueous solution, it is preferable to adjust the pH value by supplying the same inorganic acid as the acid that constitutes the metal compound as a raw material to the aqueous solution for nucleation.

Next, while stirring the particle growth aqueous solution, the raw material aqueous solution is supplied. At this time, since the pH value of the aqueous solution for particle growth is within the range described above, almost no new nuclei are generated, nuclei (particles) grow, and nickel compound particles having a predetermined particle size are formed. . Also in the particle growth process, the pH value and ammonium ion concentration of the aqueous solution for particle growth change as the particles grow. Therefore, the alkaline aqueous solution and the ammonia aqueous solution are supplied at appropriate times to maintain the pH value and the ammonium ion concentration within the above ranges. It is necessary to

The reaction atmosphere in the nucleation step and the particle growth step is appropriately adjusted according to the required structure of the secondary particles 2 . For example, throughout the nucleation step and the particle growth step, the reaction atmosphere is a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less, and when the nickel compound is calcined, a solid-structure lithium-transition metal composite oxide can be obtained. you get something.

On the other hand, when the reaction atmosphere in the early stages of the nucleation step and the grain growth step is set to an oxidizing atmosphere with an oxygen concentration exceeding 5% by volume, and the reaction atmosphere is switched from the oxidizing atmosphere to the non-oxidizing atmosphere in the grain growth step, The resulting nickel compound is composed of a low-density core composed of fine primary particles and a high-density outer shell composed of plate-like primary particles larger than the fine primary particles. By firing such a nickel compound, the first lithium metal composite oxide 10 having a hollow structure is obtained.

Further, the reaction atmosphere in the nucleation step is set to a non-oxidizing atmosphere, and in the grain growth step, after switching to an oxidizing atmosphere, the reaction atmosphere is controlled to switch back to a non-oxidizing atmosphere once or several times. , a nickel compound having a laminated structure in which low-density layers and high-density layers are alternately laminated can be obtained. By firing such a nickel compound, the first lithium metal composite oxide 10 having a porous structure in which a plurality of voids are dispersed inside the particles is obtained.

The nickel composite hydroxide (nickel compound) obtained after the crystallization (step S1) may be oxidized and roasted to convert at least part of the hydroxide into a nickel composite oxide, or all of the hydroxide may be nickel composite oxide. It may be a substance (nickel compound).

[Mixing step before firing (step S2)]
Next, the obtained nickel compound and lithium compound are mixed (step S2). The type of lithium compound to be mixed before firing is not particularly limited, but lithium carbonate, lithium hydroxide, lithium nitrate, and the like can be preferably used. Among these, lithium carbonate or lithium hydroxide is preferably used, and lithium carbonate is more preferably used, in consideration of ease of handling and stability of quality.

In the mixing step (step S2), the sum (Me) of the number of metal atoms other than lithium in the mixture obtained by mixing, transition metals such as nickel, cobalt, manganese, and other elements M, and lithium The ratio (Li/Me) to the number of atoms (Li) is 0.95 or more and 1.5 or less, preferably 1.0 or more and 1.5 or less, more preferably 1.0 or more and 1.35 or less, still more preferably A nickel compound and a lithium compound are mixed so that the ratio is 1.0 or more and 1.2 or less. That is, since Li/Me does not change before and after the firing step (step S3) described later, Li/Me in the mixing step (step S2) is the desired positive electrode active material 100 (or the second lithium composite oxidation A nickel compound and a lithium compound are mixed so as to obtain the Li/Me of item 1).

It is preferable that the nickel compound and the lithium compound are sufficiently mixed to the extent that fine powder is not generated. Insufficient mixing may cause variations in Li/Me among individual particles, making it impossible to obtain sufficient battery characteristics. In addition, a general mixer can be used for mixing. For example, shaker mixers, Loedige mixers, Julia mixers, V-blenders, etc. can be used.

[Baking step (step S3)]
The resulting mixture is then fired to obtain a second lithium metal composite oxide (step S3). The furnace used in the firing step is not particularly limited as long as it can be heated in the air or in an oxygen stream. Similarly, from the viewpoint of maintaining a uniform atmosphere in the furnace, it is preferable to use a batch-type or continuous-type electric furnace that does not generate gas.

The firing temperature in the firing step (step S3) is preferably 700° C. or higher and 1000° C. or lower, and more preferably 750° C. or higher and 950° C. or lower. If the firing temperature is lower than 700° C., the obtained second lithium metal composite oxide may have insufficient crystallinity. On the other hand, if the firing temperature exceeds 1000° C., intense sintering occurs between the particles of the second lithium metal composite oxide, causing abnormal grain growth and increasing the proportion of irregularly shaped coarse particles.

The retention time at the firing temperature in the firing step (step S3) is preferably 1 hour or more and 10 hours or less, more preferably 2 hours or more and 6 hours or less. If the holding time at the firing temperature in the firing step (step S3) is less than 1 hour, the obtained second lithium metal composite oxide may have insufficient crystallinity.

The atmosphere during firing is preferably an oxidizing atmosphere, more preferably an atmosphere with an oxygen concentration of 18% by volume or more and 100% by volume or less, and a mixed atmosphere of oxygen having the above oxygen concentration and an inert gas. is particularly preferred. That is, it is preferable to carry out the calcination in the atmosphere or in an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the lithium composite oxide may be insufficient.

Aggregation or mild sintering may occur in the secondary particles constituting the obtained second lithium composite oxide. In such a case, it is preferable to pulverize the aggregates or sintered bodies of the secondary particles. Thereby, the average particle size and particle size distribution of the obtained second lithium composite oxide can be adjusted to a suitable range.

Crushing means applying mechanical energy to agglomerates consisting of a plurality of secondary particles generated by sintering necking between secondary particles during firing, without almost destroying the secondary particles themselves. It means the operation of separating and loosening aggregates.

A known means such as a pin mill or a hammer mill can be used for crushing. At this time, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles.

The second lithium metal composite oxide obtained after the firing step (step S3) contains lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and element M, and these elements is Li:Ni:Co:Mn:M=d2:(1-abc):a:b:c (where 0.05≦a≦0.60, 0 .05≤b≤0.60, 0≤c≤0.60, 0.40≤a+b+c, 0.95≤d2≤1.5, M is W, Mo, V, Mg, Ca, Al, Ti, at least one element selected from Cr, Zr, La, and Ta). A preferred range of the molar ratio of each element is the same as that of the first lithium metal composite oxide described above. As will be described later, in the heat treatment step (step S20), part of the lithium in the second lithium metal composite oxide may react with the second particles. Therefore, the molar ratio (d2) of lithium in the second lithium metal composite oxide is higher than the molar ratio (d3) of lithium in the finally obtained first lithium metal composite oxide in the second particles. You may prepare so that it may increase as much as it reacts with.

[Mixing step (step S10)]
Next, the second lithium metal composite oxide and second particles capable of reacting with lithium to form first particles 20 are mixed (step S10). The second lithium metal composite oxide may be obtained by a method other than the method of steps S1 to S3 described above.

The second particles contain elements similar to the elements other than lithium and oxygen contained in the target first particles 20 . For example, the second particles preferably contain at least one element selected from the group consisting of niobium, tungsten, phosphorus, and silicon, and are more preferably compounds containing niobium (niobium compounds). The second particles may or may not contain lithium, but it is preferable that the second particles do not contain lithium. When the second particles do not contain lithium, they can efficiently react with excess lithium or the like in the second lithium metal composite oxide in the heat treatment step (step S20) described later. In this specification, the term "not containing lithium" means substantially not containing lithium. For example, it may contain a trace amount of lithium as an impurity. It may contain 0.1% by mass or less of lithium.

As the niobium compound, known compounds containing niobium can be used, such as niobic acid, niobium oxide, niobium nitrate, niobium pentachloride, and niobium nitrate. Among these, niobic acid, niobium oxide, or a mixture thereof is preferable from the viewpoint of easy availability and avoiding contamination of impurities in the first lithium metal composite oxide, and niobic acid (Nb ₂ O ₅ ·nH ₂ O) is more preferred. Note that if impurities are mixed in the first lithium metal composite oxide, the thermal stability, battery capacity, and cycle characteristics of the obtained secondary battery may deteriorate.

The amount of the second particles mixed is such that the amount of the elements other than lithium and oxygen in the mixture is 0.01% by mass or more and 4% by mass or less, preferably 0.01% by mass, based on the entire positive electrode active material 100 to be obtained. % or more and 4 mass % or less, more preferably 0.05 mass % or more and 3.5 mass % or less.

Also, the second particles are preferably mixed in the form of particles (solid phase). The average particle diameter of the second particles is preferably 0.01 μm or more and 10 μm or less, more preferably 0.03 μm or more and 3.0 μm or less, and still more preferably 0.05 μm or more and 1.5 μm or less. When the average particle size is within the above range, the reactivity with the second lithium metal composite oxide is improved. Also, the average particle size of the second particles may be, for example, 0.1 μm or more, or may be 0.5 μm or more.

If the average particle size of the second particles is less than 0.01 μm, a problem may arise in that handling of the powder becomes very difficult. On the other hand, if the average particle size is larger than 10 μm, the elements (eg, Nb) other than lithium and oxygen contained in the second particles are not uniformly distributed in the positive electrode active material 100, and the battery characteristics are not improved. There is The average particle size of the second particles is the volume average particle size MV, which can be obtained, for example, from the volume integrated value measured by a laser beam diffraction scattering type particle size distribution meter.

The second particles may be pulverized in advance using various pulverizers such as a ball mill, a planetary ball mill, a jet mill/nano jet mill, a bead mill, and a pin mill so as to have a particle size within the above range. Moreover, the niobium compound may be classified by a dry classifier or sieving, if necessary. For example, sieving can be performed to obtain particles close to 0.01 μm.

It is preferable that the second lithium metal composite oxide and the second particles are sufficiently mixed to the extent that fine powder is not generated. Insufficient mixing causes variations in reactivity between the lithium derived from the second lithium metal composite oxide and the second particles among the individual particles, making it impossible to obtain sufficient battery characteristics. Sometimes. In addition, a general mixer can be used for mixing. For example, shaker mixers, Loedige mixers, Julia mixers, V-blenders, etc. can be used.

In addition to the second lithium metal composite oxide and the second particles, a lithium compound may be further mixed. The second particles can react with lithium (excess lithium or lithium in the crystal) in the second lithium metal composite oxide in a heat treatment step (step S20) described later. Lithium in the crystals of the lithium metal composite oxide may be excessively extracted, resulting in deterioration of battery characteristics. In the mixing step (step S10), when a lithium compound is further mixed, the lithium compound becomes a lithium source that reacts with the second particles, and excessively extracts lithium from the crystals of the second lithium metal composite oxide. can be suppressed. Although the lithium compound is not particularly limited, for example, the lithium compound described in the mixing step (step S2) before firing can be used.

[Heat Treatment Step (Step S20)]
Next, the mixture obtained by mixing is heat-treated at a temperature of 400° C. or more and 900° C. or less (step S20). By the heat treatment (step S20), the second lithium metal composite oxide or lithium derived from an arbitrarily mixed lithium compound reacts with the second particles to form the first particles 20. can be done.

The heat treatment temperature is 400° C. or higher and 900° C. or lower, preferably 500° C. or higher and 800° C. or lower, more preferably 550° C. or higher and 700° C. or lower. When the heat treatment temperature is within the above range, the lithium reacts with the second particles, and the first particles 20 can be easily and uniformly formed in the positive electrode active material.

The furnace used for the heat treatment is not particularly limited as long as it can heat in the air or in an oxygen stream. Similarly, from the viewpoint of maintaining a uniform atmosphere in the furnace, it is preferable to use a batch-type or continuous-type electric furnace that does not generate gas.

The holding time at the above heat treatment temperature is preferably 1 hour or more and 10 hours or less, and preferably 2 hours or more and 6 hours or less. If the holding time at the heat treatment temperature in this step is less than 1 hour, the obtained lithium composite oxide may have insufficient crystallinity.

The atmosphere during the heat treatment (step S20) is preferably an oxidizing atmosphere, more preferably an atmosphere with an oxygen concentration of 18% by volume to 100% by volume, and a mixed atmosphere of oxygen and an inert gas having the above oxygen concentration. is particularly preferred. That is, calcination is preferably carried out in the atmosphere or in an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the lithium composite oxide may deteriorate.

3. Positive Electrode The positive electrode according to the present embodiment includes a first lithium metal composite oxide 10 and first particles 20 having lithium ion conductivity , and can be suitably used for a lithium ion secondary battery.

The first lithium metal composite oxide 10 includes, for example, lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and element M, and the material amount (molar) ratio of these elements However, Li:Ni:Co:Mn:M=d3:(1-abc):a:b:c (where 0.05≤a≤0.60, 0.05≤b≤0. 60, 0≤c≤0.60, 0.40≤a+b+c, 0.95≤d3≤1.5, M is W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and , Ta). A preferred range of the molar ratio of each element is the same as that of the first lithium metal composite oxide described above. As described above, in the heat treatment step (step S20), part of lithium in the second lithium metal composite oxide may react with the second particles. Therefore, the molar ratio (d3) of lithium in the finally obtained first lithium metal composite oxide is higher than the molar ratio (d2) of lithium in the first lithium metal composite oxide of the second particles. may be reduced by the amount reacted with.

Moreover, the preferred composition and characteristics of the first lithium metal composite oxide 10 and the first particles 20 are the same as those described in the item of the positive electrode active material above.

In the positive electrode according to the present embodiment, some of the first particles 20 are present bonded to the surface of the first lithium metal composite oxide 10, and some of the first particles 20 are present in the first It is preferable to exist separately from the lithium metal composite oxide 10 of . In the positive electrode, the distribution of the first particles 20 as described above is presumed to form suitable lithium ion conduction paths between the particles of the first lithium metal composite oxide 10 .

The method for manufacturing the positive electrode is not particularly limited. manufactured as

First, the positive electrode active material 100, a conductive material, and a binder are mixed, and if necessary, activated carbon and a solvent for viscosity adjustment are added, and the mixture is kneaded to prepare a positive electrode mixture paste. . At that time, the mixing ratio of each component in the positive electrode mixture paste can be appropriately adjusted according to the intended performance of the secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass or more and 95 parts by mass or less, and the content of the conductive material is 1 part by mass or more and 20 parts by mass or less. and the content of the binder may be 1 part by mass or more and 20 parts by mass or less.

The conductive material is not particularly limited, and for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black can be used.

The binder plays a role of binding the active material particles, and is not particularly limited. system resin, polyacrylic acid, etc. can be used.

If necessary, the positive electrode active material, the conductive material, and the activated carbon may be dispersed, and a solvent that dissolves the binder may be added to the positive electrode mixture. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, activated carbon may be added to the positive electrode mixture in order to increase the electric double layer capacity.

The obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil and dried to scatter the solvent. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. Thus, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size depending on the intended battery, and used for manufacturing the battery. The method for producing the positive electrode is not limited to the method described above, and other methods may be used.

4. Lithium Ion Secondary Battery A lithium ion secondary battery (hereinafter also referred to as a “secondary battery”) according to the present embodiment includes a positive electrode containing the positive electrode active material described above, a negative electrode, and an electrolyte. A lithium ion secondary battery can be composed of the same components as conventionally known lithium ion secondary batteries, and includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. Also, the secondary battery may be, for example, an all-solid secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte. Each component other than the positive electrode will be described below.

Note that the embodiments described below are merely examples, and the lithium ion secondary battery according to the present embodiment can be variously modified based on the knowledge of those skilled in the art based on the embodiments described herein. , can be implemented in modified form. Moreover, the lithium-ion secondary battery according to the present embodiment is not particularly limited in its application.

(negative electrode)
For the negative electrode, metal lithium, lithium alloy, etc. may be used. The material may be applied to the surface of a metal foil current collector such as copper, dried, and optionally compressed to increase electrode density.

As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon substances such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the binder for the negative electrode in the same manner as the binder for the positive electrode. Solvents can be used. In addition to the organic binder such as PVDF described above, a water-based binder such as styrene-butanediene rubber may be used as the binder. Carboxymethyl cellulose (CMC) may be used as a viscosity modifier for the water-based binder. For example, with a water-based binder containing styrene-butadiene latex as a main additive and CMC as a viscosity modifier, the binding strength can be enhanced with a small amount.

(separator)
Between the positive electrode and the negative electrode, a separator is interposed and arranged as necessary. The separator separates the positive electrode from the negative electrode and holds the electrolyte, and may be a thin film of polyethylene, polypropylene, or the like, having a large number of minute pores.

(Non-aqueous electrolyte)
A non-aqueous electrolyte can be used as the non-aqueous electrolyte. The non-aqueous electrolytic solution may be, for example, one obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Further, as the non-aqueous electrolytic solution, an ionic liquid in which a lithium salt is dissolved may be used. The ionic liquid refers to a salt composed of cations and anions other than lithium ions and exhibiting a liquid state even at room temperature.

Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate; One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or two or more may be mixed. can be used as

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ , composite salts thereof, and the like can be used. Furthermore, the non-aqueous electrolytic solution may contain radical scavengers, surfactants, flame retardants, and the like.

Moreover, when the lithium ion secondary battery is an all-solid secondary battery, a solid electrolyte may be used as the non-aqueous electrolyte. Solid electrolytes have the property of withstanding high voltages. Solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

As the inorganic solid electrolyte, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or the like is used.

The oxide-based solid electrolyte is not particularly limited, and can be used as long as it contains oxygen (O) and has lithium ion conductivity and electronic insulation. Examples of oxide-based solid electrolytes include lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO ₄ -Li _{3 PO4} , _Li4SiO4 - _Li3VO4 , _{Li2O - B2O3 - P2O5} , _{Li2O - SiO2 , Li2O} - _{B2O3 -} ZnO, Li1 _{+X AlXTi 2-X} (PO ₄ ) ₃ (0≦X≦1), Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ (0≦X≦1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2/ 3-X} TiO ₃ (0≦X≦2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ and the like.

The sulfide-based solid electrolyte is not particularly limited, and any solid electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Li ₂ SP ₂ S ₅ , LiI—Li ₂ S—B ₂ S ₃ , Li ₃ PO ₄ —Li ₂ S—Si ₂ S, Li ₃ PO ₄ —Li ₂ S—SiS ₂ , LiPO ₄ —Li ₂ S—SiS, LiI—Li ₂ S—P ₂ O ₅ , LiI—Li ₃ PO ₄ —P ₂ S ₅ and the like.

Inorganic solid electrolytes other than those described above may be used, such as Li ₃ N, LiI, Li ₃ N--LiI--LiOH, and the like.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ion conductivity . For example, polyethylene oxide, polypropylene oxide, copolymers thereof, and the like can be used. Moreover, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may also be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

(Battery shape and configuration)
The lithium ion secondary battery according to the present embodiment, which is composed of the positive electrode, the negative electrode, the separator, the non-aqueous electrolyte solution, the positive electrode, the negative electrode, and the solid electrolyte described above, has a cylindrical shape, a laminated shape, and the like. Various shapes are possible.

When a non-aqueous electrolytic solution is used as the non-aqueous electrolyte, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, and the obtained electrode body is impregnated with the non-aqueous electrolytic solution. A lead for current collection is used to connect between the connected positive electrode terminal and between the negative electrode current collector and the negative electrode terminal connected to the outside, and the battery case is sealed to complete the lithium ion secondary battery. .

EXAMPLES Next, the positive electrode active material according to one embodiment of the present invention will be described in detail with reference to examples. However, the present invention is not limited to these examples. The analysis method of the metal contained in the positive electrode active material and the various evaluation methods of the positive electrode active material in Examples and Comparative Examples are as follows.

[composition]
After dissolving the positive electrode active material in acid, it was measured with an ICP emission spectrometer (ICPS-8100 manufactured by Shimadzu Corporation).

[Compound species identification]
The positive electrode active material was evaluated by a powder X-ray diffractometer (X'Pert, PROMRD manufactured by Spectris).

[Evaluation of battery characteristics of positive electrode active material]
A 2032-type coin battery CBA (hereinafter also referred to as “coin battery CBA”) having the structure shown in FIG. 6 was used. The method for producing the 2032-type coin battery CBA is as follows.

First, positive electrode active material: 52.5 mg, acetylene black: 15 mg, and PTEE: 7.5 mg were mixed and press molded at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm, and then placed in a vacuum dryer at 120 ° C. The positive electrode PE was produced by drying for 12 hours at .

Next, using this positive electrode PE, a 2032 type coin battery CBA was produced in an Ar atmosphere glove box with a controlled dew point of -80°C. Lithium metal with a diameter of 17 mm and a thickness of 1 mm was used for the negative electrode NE of this 2032-type coin battery CBA, and the electrolytic solution was composed of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 M LiClO ₄ as the supporting electrolyte. An equal mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. A polyethylene porous film having a film thickness of 25 μm was used as the separator SE. The 2032-type coin battery CBA has a gasket GA and is assembled into a coin-shaped battery with a positive electrode can PC and a negative electrode can NC.

The coin battery CBA was left for about 24 hours after it was produced, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density for the positive electrode was set to 0.1 mA/cm ² and the cutoff voltage was set to 4.3 V. After 1 hour of rest, the battery was discharged until the cutoff voltage reached 3.0V. After that, the coin-type battery CBA was charged to a potential corresponding to SOC 20%, and measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) to obtain the Nyquist plot shown in FIG. be done. Since this Nyquist plot is expressed as the sum of characteristic curves showing the solution resistance, the negative electrode resistance and its capacity, and the positive electrode resistance and its capacity, a fitting calculation is performed using an equivalent circuit based on this Nyquist plot, and the positive electrode resistance (reaction resistance) was calculated.

(Example 1)
(A) Crystallization step [Nucleation step]
First, water was put into the reaction vessel and the temperature inside the vessel was set to 40° C. while stirring. At this time, nitrogen gas was passed through the reaction tank for about 30 minutes to make the reaction atmosphere a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less. Subsequently, an appropriate amount of 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water were supplied into the reaction tank, and the pH value was adjusted to 12.4 and the ammonium ion concentration was adjusted to 10 g/L. An aqueous solution was formed.

At the same time, nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in water so that the molar ratio of the respective metal elements was Ni:Mn:Co=38:30:32 to prepare a 2 mol/L raw material aqueous solution.

Next, by supplying this raw material aqueous reaction solution to the pre-reaction aqueous solution at a constant rate, an aqueous solution for the nucleation step was formed, and nucleation was performed. At this time, a 25% by mass aqueous sodium hydroxide solution and a 25% by mass aqueous ammonia solution were supplied at appropriate times to maintain the pH value and the ammonium ion concentration of the aqueous solution for nucleation within the ranges described above.

[Particle growth step]
After the nucleation was completed, the supply of all the aqueous solution was temporarily stopped, and sulfuric acid was added to adjust the pH value to 11.2, thereby forming an aqueous solution for particle growth. After confirming that the pH value reached a predetermined value, the raw material aqueous solution was supplied to grow the nuclei (particles) generated in the nucleation step. Thereafter, the obtained product was washed with water, filtered and dried to obtain particles of powdery nickel composite hydroxide (nickel compound).

In the grain growth process, a 25% by mass sodium hydroxide aqueous solution and a 25% by mass aqueous ammonia solution were supplied at appropriate times throughout the process to maintain the pH value and the ammonium ion concentration of the aqueous solution for particle growth within the ranges described above. .

(B) Mixing and sintering process The nickel compound obtained as described above is mixed with a shaker-mixer device (manufactured by Willie & Bacchofen (WAB)) so that the molar ratio of Li/(Ni + Co + Mn) is 1.10. , TURBULA Type T2C) to obtain a lithium mixture.

This lithium mixture is held at a temperature of 900° C. to 950° C. for 4 hours in an air flow (oxygen concentration: 21% by volume) using an electric furnace (manufactured by Toyo Seisakusho, electric muffle furnace) to obtain lithium metal. A composite oxide powder was synthesized.

Agglomeration or mild sintering occurred in the lithium metal composite oxide thus obtained. Therefore, this lithium metal composite oxide was pulverized using a continuous mill (manufactured by IKA, MF10 basic).

(C) Mixing step of second particles (niobium compound) The obtained lithium metal composite oxide powder and niobic acid powder (D50 particle size: 1.0 μm) are mixed, and an electric furnace (manufactured by Toyo Seisakusho, electric A positive electrode active material was produced by holding at a temperature of 650° C. for 3 hours in an air stream (oxygen concentration: 21% by volume) using a muffle furnace.

(D) Evaluation of positive electrode active material [composition]
Analysis using an ICP emission spectrometer revealed that the positive electrode active material had a molar ratio of the metal elements Li:Ni:Mn:Co=1.10:0.38:0.30:0.32. It was found to contain 2.0 wt% of Nb.
[Crystal structure]
The obtained positive electrode active material was evaluated by powder X-ray diffraction. As a result, a peak derived from the layered rock salt type of LiNi _0.38 Mn _0.30 Co _0.32 O ₂ and a peak derived from LiNbO ₃ were confirmed. Table 1 shows the evaluation results of the obtained positive electrode active material.
[Shape observation]
When the obtained positive electrode active material was confirmed by observing a backscattered electron image (COMPO image) by SEM, as shown in FIG. High-intensity particles were observed in the state of In the backscattered electron image, the _higher the atomic number of the element, the higher the brightness contrast observed. 1 particles 20a, 20b).

(Example 2)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1, except that niobic acid was mixed so that the amount of the niobium compound added was 0.70 wt %. Table 1 shows the evaluation results of the obtained positive electrode active material. In addition, as a result of observation of a backscattered electron image (COMPO image) by SEM, it was confirmed that, in the same manner as in Example 1, high-brightness particles were observed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide. It is believed that LiNbO ₃ (first particles) are present as in Example 1.

(Example 3)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1, except that niobic acid was mixed so that the amount of the niobium compound added was 0.30 wt %. Table 1 shows the evaluation results of the obtained positive electrode active material. In addition, as a result of observation of a backscattered electron image (COMPO image) by SEM, it was confirmed that, in the same manner as in Example 1, high-brightness particles were observed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide. It is believed that LiNbO ₃ (first particles) are present as in Example 1.

(Comparative example 1)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1, except that the sintering step was performed and the niobium compound was not mixed and heat treated. Table 1 shows the evaluation results of the obtained positive electrode active material.

(Comparative Example 4)
The composite hydroxide (nickel compound) obtained in the crystallization step of Example 1 was weighed so that the molar ratio of Li/(Ni+Co+Mn) was 1.10, and niobic acid powder (D50 particle size: 1 .0 μm) was weighed and mixed using a shaker mixer (TURBULA Type T2C manufactured by Willie & Bacchofen (WAB)) to obtain a lithium mixture.

This lithium mixture is held at a temperature of 900° C. to 950° C. for 4 hours in an air flow (oxygen concentration: 21% by volume) using an electric furnace (manufactured by Toyo Seisakusho, electric muffle furnace) to activate the positive electrode. material was synthesized.

Aggregation or mild sintering occurred in the positive electrode active material thus obtained. Therefore, this positive electrode active material was pulverized using a continuous mill (manufactured by IKA, MF10 Basic). The obtained positive electrode active material was evaluated in the same manner as in Example 1. Table 1 shows the evaluation results of the obtained positive electrode active material. Moreover, when it was confirmed by observation of a backscattered electron image (COMPO image) by SEM, as shown in FIG. 8, no particles with high brightness were observed.

(Comparative Example 3)
In the (A) crystallization step of Example 1, the raw material aqueous solution had a molar ratio of Ni:Co:Mn = 1:1:1, 2 mol/L, and (C) the addition of the niobium compound, Nb Lithium hydroxide powder was mixed together so that the amount was 5.0 wt% and further so that the molar ratio of Li:Nb to the amount of Nb added was 1:1. In the same manner as in Example 1, a positive electrode active material was produced and evaluated. Table 2 shows the evaluation results of the obtained positive electrode active material.
(Example 4)
A positive electrode active material was produced and evaluated in the same manner as in Comparative Example 3, except that Nb was added so that the Nb amount was 1.0 wt %. Table 2 shows the evaluation results of the obtained positive electrode active material.
(Comparative example 2)
Positive electrode in the same manner as in Comparative Example 1 except that in the crystallization step (A) of Comparative Example 1, the raw material aqueous solution had a molar ratio of the metal elements Ni:Co:Mn=1:1:1, 2 mol/L. An active material was produced and evaluated. Table 2 shows the evaluation results of the obtained positive electrode active material.

[Evaluation results]
FIG. 6 shows a graph plotting the reaction resistance of the examples and comparative examples shown in Tables 1 and 2 against the amount of niobium.

As shown in the graph of FIG. 6, the examples in which a specific amount of the niobium compound was added had the effect of reducing the reaction resistance and improving the output characteristics of the secondary battery. In addition, as in Comparative Example 4, in the positive electrode active material in which the niobium compound was mixed before firing, high-brightness particles (first particles) having a definite particle shape were not observed, and the reaction rate was lower than that in Examples. resistance was high. In Comparative Example 4, niobium is presumed to exist mainly inside the secondary particles. From this, the niobium compound particles (first particles) having lithium ion conductivity are present in the form of distinct particles on the surface of the lithium metal composite oxide, thereby reducing the reaction resistance. it is conceivable that.

DESCRIPTION OF SYMBOLS 100... Positive electrode active material 10... First lithium metal composite oxide 1... Primary particles 2... Secondary particles 20... First particles 20a... First particles (present on the surface of the first lithium metal composite oxide)
20b... First particles (existing separately from the first lithium metal composite oxide)
CBA... Coin type battery PE... Positive electrode NE... Negative electrode GA... Gasket PE... Positive electrode NE... Negative electrode SE... Separator

Claims (9)

A positive electrode active material comprising a first lithium metal composite oxide composed of secondary particles in which a plurality of primary particles are aggregated, and first particles having lithium ion conductivity,
The positive electrode active material contains lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and an element M, and the material amount (molar) ratio of these elements is Li:Ni:Co : Mn: M = d1: (1-a-b-c): a: b: c (where 0.05 ≤ a ≤ 0.60, 0.05 ≤ b ≤ 0.60, 0 ≤ c ≤ 0 .60, 0.40≦a+b+c, 0.95≦d1≦1.5, M is at least selected from W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta 1 element),
The first particles contain at least one selected from the group consisting of lithium niobium composite oxides, lithium tungsten composite oxides, and lithium silicon composite oxides,
The amount of elements other than lithium and oxygen in the first particles is 0.01% by mass or more and 4% by mass or less with respect to the entire positive electrode active material,
at least part of the first particles are present bound to the surface of the first lithium metal composite oxide;
At least part of the first particles have a longest diameter of 0.5 μm or more,
Positive electrode active material for lithium ion secondary batteries. 2. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein at least part of said first particles are separated from said first lithium metal composite oxide. The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2 _, wherein said first particles contain at least one of _LiNbO3 and _Li3NbO4 . A method for producing a positive electrode active material containing a first lithium metal composite oxide composed of secondary particles in which a plurality of primary particles are aggregated and first particles having lithium ion conductivity,
mixing a second lithium metal composite oxide with second particles capable of reacting with lithium to form the first particles;
heat-treating the mixture obtained by the mixing at a temperature of 400° C. or more and 900° C. or less;
The second lithium metal composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and element M, and the material amount (molar) ratio of these elements is Li: Ni: Co: Mn: M = d2: (1-a-b-c): a: b: c (provided that 0.05 ≤ a ≤ 0.60, 0.05 ≤ b ≤ 0.60, 0≦c≦0.60, 0.95≦d2≦1.5, M is at least one selected from W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta species element),
The first particles contain at least one selected from the group consisting of lithium niobium composite oxides, lithium tungsten composite oxides, and lithium silicon composite oxides,
The second particles contain at least one element selected from the group consisting of niobium, tungsten, and silicon ,
The amount of the element other than lithium and oxygen in the mixture is 0.01% by mass or more and 4% by mass or less with respect to the entire positive electrode active material,
At least part of the first particles are present bound to the surface of the first lithium metal composite oxide,
At least part of the first particles have a longest diameter of 0.5 μm or more,
A method for producing a positive electrode active material for a lithium ion secondary battery. 5. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 4 , wherein said second particles contain niobic acid. The second lithium metal composite oxide is formed by firing a compound containing nickel, cobalt, and manganese obtained by crystallization and a lithium compound at a temperature of 700 ° C. or higher and 1000 ° C. or lower. A method for producing the positive electrode active material for a lithium ion secondary battery according to claim 4 or 5 . A positive electrode for a lithium ion secondary battery comprising a first lithium metal composite oxide and first particles having lithium ion conductivity,
The first lithium metal composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and an element M, and the material amount (molar) ratio of these elements is Li: Ni: Co: Mn: M = d3: (1-a-b-c): a: b: c (provided that 0.05 ≤ a ≤ 0.60, 0.05 ≤ b ≤ 0.60, 0≦c≦0.60, 0.40≦a+b+c, 0.95≦d3≦1.5, M is W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta at least one element selected from),
The first particles contain at least one selected from the group consisting of lithium niobium composite oxides, lithium tungsten composite oxides, and lithium silicon composite oxides,
Some of the first particles are present in combination with the surface of the first lithium metal composite oxide, and some of the first particles are present with the first lithium metal composite oxide exists separately,
At least part of the first particles have a longest diameter of 0.5 μm or more,
Positive electrode for lithium-ion secondary batteries. 8. The positive electrode for _a lithium ion secondary battery according to claim 7 , wherein said first particles contain at least one of _LiNbO3 and _Li3NbO4 . A lithium ion secondary battery comprising a positive electrode containing the positive electrode active material according to any one of claims 1 to 3 , a negative electrode, and an electrolyte.

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