JP7143593B2 - Method for producing positive electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries.

In recent years, with the spread of small information terminals such as smart phones and tablet PCs, there is a strong demand for the development of small and lightweight lithium ion secondary batteries with high energy density. There is also a strong demand for the development of high-output secondary batteries suitable for use in electric vehicles including hybrid vehicles.

Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are available as secondary batteries that meet such demands. A lithium-ion secondary battery is composed of a negative electrode, a positive electrode, a separator, an electrolytic solution, and the like, and the active material of the negative electrode and the positive electrode is a material that can desorb and insert lithium during charging and discharging.

Lithium ion secondary batteries are currently being actively researched and developed. Among them, lithium ion secondary batteries using a lithium metal composite oxide with a layered structure or a spinel structure as a positive electrode active material have a 4V Since a high-class voltage can be obtained, it is being put to practical use as a battery with high energy density.

As positive electrode active materials mainly proposed so far, lithium cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel which is cheaper than cobalt, Furthermore, lithium nickel cobalt manganese composite oxides (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ etc.), which are excellent in safety using inexpensive manganese, spinel lithium manganese composite oxides (LiMn ₂ O ₄ ) and the like.

By the way, the positive electrode of a non-aqueous electrolyte secondary battery is prepared by mixing a positive electrode active material, a binder such as polyvinylidene fluoride (PVDF), and a solvent such as N-methyl-2-pyrrolidone (NMP), for example. It is formed by making an agent paste and applying it to a current collector such as aluminum foil. At this time, if lithium is liberated from the positive electrode active material in the positive electrode mixture paste, it may react with moisture contained in the binder or the like to generate lithium hydroxide. The generated lithium hydroxide raises the pH of the positive electrode mixture, causing a polymerization reaction of the binder and the solvent, which may cause gelation of the positive electrode mixture paste. Gelation of the positive electrode material mixture paste causes poor operability and deterioration of yield. This tendency becomes more pronounced when the positive electrode active material contains more lithium than the stoichiometric ratio and has a higher proportion of nickel.

Several attempts have been made to suppress the gelation of the positive electrode mixture paste. For example, Patent Literature 1 proposes a positive electrode composition for a non-aqueous electrolyte secondary battery containing a positive electrode active material made of a lithium transition metal composite oxide and additive particles made of acidic oxide particles. In this positive electrode composition, the lithium hydroxide generated by reacting with the moisture contained in the binder preferentially reacts with the acidic oxide, suppressing the reaction between the generated lithium hydroxide and the binder, resulting in a positive electrode mixture paste. It is said that it suppresses gelation. In addition, the acidic oxide plays a role as a conductive material in the positive electrode, lowers the resistance of the entire positive electrode, and contributes to improving the output characteristics of the battery.

In addition, Patent Document 2 describes a method for manufacturing a lithium ion secondary battery, in which a lithium transition metal oxide containing LiOH outside the composition is prepared as a positive electrode active material; LiOH contained per 1 g of the positive electrode active material Grasping the molar amount P; preparing 0.05 mol or more of tungsten oxide in terms of tungsten atoms per 1 mol of LiOH with respect to the molar amount P of LiOH; kneading with an organic solvent together with a material and a binder to prepare a positive electrode mixture paste; According to this method, it is said that there is not only an effect of suppressing thickening of the positive electrode mixture paste, but also an effect of suppressing low-temperature reaction resistance in the secondary battery.

On the other hand, several attempts have been made to obtain lithium ion secondary batteries with excellent output characteristics and charge/discharge cycle characteristics. For example, when the positive electrode active material has a small particle size and a narrow particle size distribution, a lithium ion secondary battery with excellent output characteristics and charge/discharge cycle characteristics can be obtained. This is because particles with a small particle size have a large specific surface area, and when used as a positive electrode active material, not only can a sufficient reaction area with the electrolyte be secured, but also the positive electrode can be formed thin, and lithium ions This is because the movement distance between the positive electrode and the negative electrode can be shortened, so that the positive electrode resistance can be reduced. In addition, since the particle size distribution is narrow, that is, the particles have a uniform particle size, the voltage applied to each particle in the electrode can be uniformed, so the decrease in battery capacity due to the selective deterioration of the fine particles can be suppressed. because it is possible.

For example, in Patent Documents 3 to 5, particles of a transition metal composite hydroxide, which is a precursor of a positive electrode active material, are divided into two stages: a nucleation step in which nucleation is mainly performed and a particle growth step in which particles are mainly grown. A method of preparation is disclosed with a distinctly separated crystallization reaction. In these methods, the pH value of the reaction aqueous solution is controlled in the range of 12.0 to 14.0 in the nucleation process and in the range of 10.5 to 12.0 in the particle growth process, based on the liquid temperature of 25 ° C. is doing. In addition, the reaction atmosphere is set to an oxidizing atmosphere at the beginning of the nucleation step and the grain growth step, and is switched to a non-oxidizing atmosphere at a predetermined timing.

The particles of the transition metal composite hydroxide obtained by such a method have a small particle size and a narrow particle size distribution, and consist of a low-density central portion composed of fine primary particles and plate-like or needle-like primary particles. It consists of a high-density outer shell. When such transition metal composite hydroxide particles are mixed with a lithium compound and fired, the low-density central portion shrinks significantly, forming a space inside. Moreover, the particle properties of the transition metal composite hydroxide particles are inherited by the positive electrode active material. Specifically, the positive electrode active material obtained by the techniques described in these documents has an average particle diameter in the range of 2 μm to 8 μm or 2 μm to 15 μm, which is an index showing the spread of the particle size distribution [(d90-d10 )/average particle size] is 0.60 or less and has a hollow structure.

Therefore, secondary batteries using these positive electrode active materials are said to be capable of improving capacity characteristics, output characteristics, and charge/discharge cycle characteristics. However, there is a demand for further improvements in output characteristics and charge/discharge cycle characteristics.

It has also been reported that adding a compound containing tungsten to the positive electrode active material improves output characteristics and charge/discharge cycle characteristics. For example, in Patent Document 6, an alkaline solution in which a tungsten compound is dissolved is added to a lithium metal composite oxide powder, mixed, and then heat-treated to form fine particles containing W and Li into a lithium metal composite oxide powder. or the surface of the primary particles of the powder, a method for producing a positive electrode active material has been proposed. According to Patent Document 6, it is reported that output characteristics are improved by forming fine particles containing W and Li on the surfaces of primary particles of lithium metal composite oxide powder.

JP 2012-28313 A JP 2013-84395 A JP 2012-246199 A JP 2013-147416 A WO2012/131881 JP 2012-079464 A

However, it is desired to suppress gelation of the positive electrode material mixture paste and improve battery characteristics by an easier and simpler method.

As proposed in Patent Documents 3 to 5, increasing the reaction area with the electrolytic solution in order to improve output characteristics and charge/discharge cycle characteristics causes a new problem that gelation of the positive electrode mixture paste is promoted. Dots may occur. In addition, further improvements are required for output characteristics and charge/discharge cycle characteristics. Further, in the proposal of Patent Document 5, although output characteristics are studied, suppression of gelation of the positive electrode mixture paste is not studied at all. Therefore, in the above proposals, although gelation suppression of the positive electrode material mixture paste has been studied, it cannot be said that the problem has been sufficiently solved.

Moreover, in the proposal of Patent Document 6, a water washing process, an addition process, and a drying process are required, which increases the number of manufacturing processes, resulting in an increase in manufacturing costs.

In view of the above-mentioned problems, the present invention provides a positive electrode active material for non-aqueous electrolyte secondary batteries that can achieve both suppression of gelation of positive electrode mixture paste and high battery characteristics when used in secondary batteries. The object is to provide a simple and highly productive manufacturing method.

According to a first aspect of the present invention, mixing a lithium metal composite oxide with nickel tungstate, wherein the lithium metal composite oxide is lithium (Li), nickel (Ni), cobalt (Co ), and optionally a metal element M1, and the atomic ratio of each metal element is Li:Ni:Co:M1=s:(1-xy):x:y (however, 1.00 ≤s≤1.30, 0.10≤x≤0.35, 0≤y≤0.35, metal element M1 is at least one selected from Mn, W, V, Mg, Mo, Nb, Ti and Al There is provided a method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries, which is represented by the species element).

Moreover, it is preferable that the method for producing the positive electrode active material described above includes mixing the lithium metal composite oxide, the nickel tungstate, and water. Further, the powder mixture obtained by mixing the lithium metal composite oxide and nickel tungstate is mixed by spraying water so that the droplets have an average particle size of 100 μm or less in a mist state. It is preferable to have and drying the mixture obtained by mixing. Further, it is preferable that lithium ions contained in the lithium metal composite oxide react with at least part of the nickel tungstate in the presence of water to form lithium tungstate. Moreover, the mixture preferably contains 0.1% by mass or more of water with respect to the entire lithium metal composite oxide. Moreover, the mixture preferably contains 0.2% by mass or more and 1.0% by mass or less of tungsten with respect to the entire lithium metal composite oxide.

In addition, lithium tungstate exists on the surface of the lithium metal composite oxide after drying, and the particle size of 0.5 μm or more present on the surface of the particle, which is obtained from observation of the surface of the particle using a scanning electron microscope. The area ratio of lithium tungstate is preferably 5% or less with respect to the area of the entire viewing surface.

Moreover, the lithium metal composite oxide after drying preferably has a specific surface area of 0.5 cm ² /g or more and 2 m ² /g or less. Moreover, the dried lithium metal composite oxide preferably has a Karl Fischer moisture content at 300° C. of 0.05% by mass or more and 0.2% by mass or less. Moreover, the lithium metal composite oxide after drying preferably has a volume average particle diameter MV of 4 μm or more and 6 μm or less.

Further, the lithium metal composite oxide containing tungsten, nickel tungstate, and water are mixed, and the lithium metal composite oxide containing tungsten is 0.1% by mass with respect to the entire lithium metal composite oxide. More than 1.0% by mass or less is preferably included. Moreover, nickel tungstate preferably contains 0.1% by mass or more and 0.5% by mass or less of tungsten with respect to the entire lithium metal composite oxide. In addition, lithium tungstate exists on the particle surface of the lithium metal composite oxide after drying, and the amount of tungsten present on the particle surface is 0.1% by mass or more and 1.0% by mass or less with respect to the entire positive electrode active material. and the amount of tungsten present inside the particles of the lithium metal composite oxide after drying is preferably 0.1% by mass or more and 1.0% by mass or less with respect to the entire positive electrode active material. Moreover, it is preferable that the amount of tungsten present on the particle surface of the lithium metal composite oxide after drying is 0.1 times or more and 1 time or less as much as the amount of tungsten contained inside the particles.

According to the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery that can achieve both suppression of gelation of a positive electrode mixture paste and high battery characteristics when used in a secondary battery can be easily and It can be manufactured with high productivity. Moreover, the production method of the present invention is easy and suitable for production on an industrial scale, and its industrial value is extremely high.

FIG. 1 is a diagram showing an example of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment. FIG. 2 is a diagram showing an example of a method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries according to the embodiment. FIG. 3 is a diagram showing an example of a method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries according to the embodiment. FIG. 4 is a diagram showing an example of a method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries according to the embodiment. FIGS. 5A and 5B are diagrams showing examples of positive electrode active materials according to embodiments. FIG. 6 is a schematic cross-sectional view of a coin-type battery used for battery evaluation. FIG. 7 is a schematic explanatory diagram of an example of impedance evaluation measurement and an equivalent circuit used for analysis.

Hereinafter, embodiments of the present invention 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. Hereinafter, a method for manufacturing a positive electrode active material for non-aqueous electrolyte secondary batteries and a positive electrode active material for secondary batteries according to embodiments will be described with reference to the drawings.

1. Manufacturing method of positive electrode active material for non-aqueous electrolyte secondary battery FIGS. It is a figure which shows an example of the manufacturing method (it may be abbreviate|abbreviated as a "manufacturing method" hereafter.). 5A and 5B are schematic diagrams showing an example of the positive electrode active material 10 (for example, positive electrode active materials 10A and 10B) obtained by the manufacturing method according to this embodiment. The following description is an example of the method for manufacturing the positive electrode active material 10, and the method for manufacturing the positive electrode active material 10 is not limited to the method described below.

In the first embodiment, as will be described later, the lithium metal composite oxide (base material) may or may not contain tungsten, but in the following first embodiment, the lithium metal composite oxide The case where the (base material) does not contain tungsten (obtained positive electrode active material 10A, see FIG. 5A) will be mainly described, and the case where the titanium metal composite oxide (base material) contains tungsten (obtained The positive electrode active material 10B (see FIG. 5B) will be described in the second embodiment.

(1) First Embodiment [Mixing Step (Step S1)]
FIG. 1 is a diagram showing an example of a method for manufacturing the positive electrode active material 10 according to the first embodiment. The manufacturing method of the first embodiment includes, as shown in FIG. 1, mixing lithium metal composite oxide and nickel tungstate (step S1).

In the positive electrode active material 10 obtained by the manufacturing method of the present embodiment, nickel tungstate may be present on the surface of the lithium metal composite oxide. Nickel tungstate contained in the positive electrode active material 10 reacts with lithium hydroxide derived from the lithium composite oxide eluted in the moisture contained in the positive electrode mixture paste when the positive electrode is produced, and forms a gel of the positive electrode mixture paste. can be expected to suppress

Moreover, in the mixing in step S1, it is preferable to mix the lithium metal composite oxide and the nickel tungstate in the presence of water. The presence of water allows lithium ions (lithium) contained in the lithium metal composite oxide to react with at least a portion of nickel tungstate to form (generate) lithium tungstate 3 . The formed lithium tungstate 3 can suppress gelation of the positive electrode mixture paste.

FIG. 2 is a diagram showing a preferred example of a method for manufacturing the positive electrode active material 10 according to the first embodiment. As for mixing of step S1, as shown in FIG. 2, it is preferable to mix a lithium metal composite oxide, nickel tungstate, and water. In the presence of water, it is believed that lithium tungstate 3 and lithium nickelate are formed by the reaction of lithium ions liberated from the lithium metal composite oxide with nickel tungstate.

Although the details are unknown, the formation of lithium tungstate 3 suppresses gelation of the positive electrode mixture paste, maintains the battery capacity when a secondary battery is formed, has high output characteristics, and has excellent performance. It is considered that both the charge-discharge cycle characteristics can be achieved. Lithium nickelate is also considered to contribute to the charge-discharge reaction in secondary batteries in the same manner as lithium metal composite oxides. In addition, the presence of lithium nickelate on the surface of the lithium metal composite oxide improves the affinity of the interface between the particle surface of the lithium metal composite oxide and the particle surface of the lithium tungstate 3, resulting in higher battery characteristics. I can expect it. Each raw material used in the mixing step (step S1) will be described below.

[Lithium metal composite oxide]
The lithium metal composite oxide (base material) used as a raw material contains lithium (Li), nickel (Ni), cobalt (Co), and optionally a metal element M1, and the atomic ratio of each metal element is Li: Ni: Co: M1 = s: (1-xy): x: y (where 1.00 ≤ s ≤ 1.30, 0.10 ≤ x ≤ 0.35, 0 ≤ y ≤ 0 .35, and the metal element M1 is represented by at least one element selected from Mn, W, V, Mg, Mo, Nb, Ti and Al). In addition, the lithium metal composite oxide can be mainly composed of secondary particles formed by aggregation of a plurality of primary particles, but in addition to the secondary particles, it may contain a small amount of single primary particles. good.

In the above atomic number ratio, z, which indicates the content of lithium, exceeds 1. When z exceeds 1, that is, when the lithium metal composite oxide contains lithium in excess, in the presence of water, part of the lithium (lithium ions) released from the lithium metal composite oxide is , can readily react with nickel tungstate to form lithium tungstate 3 .

Further, the lithium metal composite oxide (base material) has the general formula (1): Li _s Ni _1-xy-z Co _x Mn _y M1 _z O _2+α (where 0.05≦x≦0.35, 0≤y≤0.35, 0≤z≤0.10, 1.00<s<1.30, 0≤α≤0.2, M is V, Mg, Mo, Nb, Ti, W and Al at least one metal element selected from). In the above formula (1), α is a coefficient that changes according to the valence of the metal element other than lithium contained in the lithium metal composite oxide and the atomic ratio of lithium to the metal element other than lithium.

The lithium metal composite oxide (base material) can optionally contain the metal element M1, and may contain tungsten (W) in the lithium metal composite oxide (base material). The case where the lithium metal composite oxide (base material) contains tungsten (for example, see FIG. 5B) will be described in detail in a second embodiment described later.

Although the specific surface area of the lithium metal composite oxide (base material) is not particularly limited, it is preferably, for example, 0.5 m ² /g or more and 2 m ² /g or less. When the specific surface area is within the above range, the contact area with the electrolyte solution is in an appropriate range, and the positive electrode active material 10 having a good balance between battery characteristics such as battery capacity and mechanical strength can be obtained. If the specific surface area is less than 0.5 m ² /g, the battery capacity of the obtained positive electrode active material 10 may be insufficient in applications where high capacity is desired. On the other hand, if it exceeds 2 m ² /g, the mechanical strength of the resulting positive electrode active material 10 may be insufficient due to the porous particle structure, which may cause stability problems during electrode production and use as an electrode. There is

Although the moisture content of the lithium metal composite oxide (base material) is not particularly limited, it is preferably, for example, 0.05% by mass or more and 0.2% by mass or less with respect to the entire lithium metal composite oxide. If the moisture content exceeds 0.2% by mass, it may absorb gas components containing carbon and sulfur in the atmosphere to form a lithium compound on the surface of the lithium metal composite oxide. The above moisture content is a value measured with a Karl Fischer moisture meter under the condition of a vaporization temperature of 300°C.

The particle structure of the lithium metal composite oxide (base material) is not particularly limited, and the secondary particles may have a hollow structure with a hollow inside. Moreover, the lithium metal composite oxide may have a solid structure, or may have a void structure having voids inside the secondary particles. In addition, since the powder characteristics and particle structure of the lithium metal composite oxide are inherited to the positive electrode active material 10 obtained after the mixing step (step S1), the powder characteristics and particle structure of the lithium metal composite oxide are It can be selected according to the positive electrode active material 10 to be obtained.

The method for producing the lithium metal composite oxide (base material) is not particularly limited as long as it has the above composition, and known methods can be used. As a method for producing a lithium metal composite oxide, for example, an aqueous solution containing Ni, Co, and optionally a metal element M1 is used to perform neutralization crystallization to obtain a nickel composite hydroxide, and then the nickel composite hydroxide is obtained. may be mixed with a compound containing lithium (lithium compound) as a precursor and fired. Further, the nickel composite hydroxide obtained after crystallization may be heat-treated to convert at least a part thereof into a nickel composite oxide, and then mixed with a lithium compound. When a lithium metal composite oxide is produced using a precursor obtained by crystallization, it is possible to obtain a lithium metal composite oxide having more uniform composition, physical properties, etc. among particles.

[Nickel tungstate]
Nickel tungstate is not particularly limited, and known nickel tungstate can be used. Note that nickel tungstate is also referred to as nickel tungsten oxide. Nickel tungstate is represented, for example, by _NiWO4 . Also, the average particle diameter of nickel tungstate is preferably 1 μm or less. Although the lower limit of the average particle size of nickel tungstate is not particularly limited, it is, for example, 0.05 μm or more.

For example, when a lithium metal composite oxide (base material) containing no tungsten, nickel tungstate, and water are mixed, the mixed amount of nickel tungstate is the amount of tungsten (W) in nickel tungstate, and the amount of lithium For example, it is 0.05% by mass or more and 2.0% by mass or less with respect to the entire metal composite oxide, and more preferably 0.1% by mass or more and 1.0% by mass or less from the viewpoint of improving battery characteristics. more preferably 0.1% by mass or more and 0.5% by mass or less.

As a compound to be mixed with the lithium metal composite oxide, a compound below nickel tungstate may be mixed, for example, nickel tungstate and tungsten oxide may be mixed. The average particle size of both is preferably 1 μm or less, and the lower limit of the average particle size is not particularly limited, but is, for example, 0.05 μm or more.

When both nickel tungstate and tungsten oxide are contained, the total amount of tungsten (W) contained in both of them is, for example, 0.1% by mass or more with respect to the entire lithium metal composite oxide. It is 2.0 mass % or less, preferably 0.1 mass % or more and 1.0 mass % or less, and more preferably 0.1 mass % or more and 0.5 mass % or less. When the mixed amount is within the above range, it is possible to obtain the positive electrode active material 10 having a high positive electrode resistance reduction effect while maintaining a high battery capacity.

In addition, the mixture obtained in the mixing step (step S1) may contain, for example, 0.05% by mass or more and 2.0% by mass or less of tungsten with respect to the entire lithium metal composite oxide, and 0.1% by mass % or more and 1.0 mass %, more preferably 0.5 mass % or more and 1.0 mass % or less. When the mixture contains tungsten within the above range, gelation of the positive electrode mixture paste can be suppressed.

[water]
As for water, it is preferable to use pure water. As described above, the water in the mixture contains unreacted lithium compounds present in the lithium metal composite oxide and lithium present in the crystals (hereinafter collectively referred to as "surplus lithium"). As it melts, it can melt the mixed nickel tungstate.

As long as the amount of water contained in the mixture can dissolve at least part of the nickel tungstate in the mixture, a certain effect can be obtained. From the viewpoint of achieving both of the above, it is preferable that the amount is enough to dissolve the nickel tungstate in the mixture. The amount of water contained in the mixture is, for example, 0.1% by mass or more, preferably 0.5% by mass or more and 40% by mass or less, and more preferably, relative to the lithium metal composite oxide (base material). is 1% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 10% by mass or less.

When the amount of water contained in the mixture is sufficient, the nickel tungstate is sufficiently penetrated to the surface of the primary particles existing inside the particles of the lithium metal composite oxide (base material), and the lithium metal composite oxide Nickel tungstate can be uniformly dispersed even between particles of the material (base material), and output characteristics and cycle characteristics can be further improved.

The amount of water contained in the mixture can be appropriately adjusted within the above range depending on the amount of mixture of the lithium metal composite oxide (base material) used, the particle structure, etc., and the amount of water contained in the mixture is such that the resulting mixture does not become a paste. A range of mixing is preferred. For example, when a lithium composite oxide (base material) having a porosity of 10% or more is used, the amount of water contained in the mixture is, for example, 10% by mass or more with respect to the lithium metal composite oxide (base material). % by mass.

[Mixing method]
The method of mixing the lithium metal composite oxide (base material), nickel tungstate, and water is not particularly limited. and may be mixed by a known mixing device.

FIG. 3 shows an example of a method that can be suitably used in the method for manufacturing the positive electrode active material 10 according to this embodiment. As shown in FIG. 3, the mixing step (step S1) includes a step of mixing lithium metal composite oxide (base material) and nickel tungstate (step S11, first mixing step), It is preferable to include a step of spraying water to the mixture of and mixing (step S12, second mixing step). Each mixing step will be described below.

(First mixing step: step S11)
First, a lithium metal composite oxide (base material) and nickel tungstate are mixed (step S11). By dry-mixing these powders, nickel tungstate can be more uniformly dispersed in the lithium metal composite oxide (base material).

The amount of nickel tungstate mixed is such that tungsten (W) in nickel tungstate is contained in an amount of 0.1% by mass or more and 0.5% by mass or less with respect to the lithium metal composite oxide (base material). preferable. If the mixed amount of tungsten in the nickel tungstate is less than 0.1% by mass, the surplus lithium liberated on the surface of the lithium metal composite oxide (base material) cannot be sufficiently neutralized. Suppression of gelation may not be sufficient, and sufficient output characteristics may not be obtained. On the other hand, when the mixed amount of tungsten in the nickel tungstate exceeds 0.5% by mass, the particle size of the lithium tungstate 3 crystallized on the surface of the lithium metal composite oxide 4 after drying (step S2) is Particles having a size of 0.5 μm or more increase, and sufficient battery capacity may not be obtained.

[Second Mixing Step: Step S12]
Next, the obtained powdery mixture is mixed by spraying water (step S12). As a result, the reaction between surplus lithium such as lithium hydroxide liberated on the surface of the lithium metal composite oxide (base material) and nickel tungstate can proceed more uniformly in the presence of water.

The amount (total amount) of water to be sprayed is preferably 1% by mass or more and 10% by mass or less with respect to the entire lithium metal composite oxide (base material). If the amount of water to be sprayed is less than 1% by mass, the above-described effects due to the addition of water may be poorly expressed and nickel tungstate may remain. On the other hand, when the amount of water to be sprayed exceeds 10% by mass, the amount of lithium eluted from the lithium metal composite oxide (base material) into water ( amount of surplus lithium) becomes excessive, the lithium content in the obtained positive electrode active material 10 decreases, and the effect of reducing the resistance may not be sufficient. In addition, when the amount of water to be sprayed exceeds 10% by mass, the moisture content in the lithium metal composite oxide (positive electrode active material 10) after drying is reduced, so a long drying time is required, and productivity is reduced. I have something to do.

The water droplets to be sprayed are preferably in a mist state with an average particle diameter of 100 μm or less. When water in a mist state is added, the reaction between surplus lithium and nickel tungstate in the vicinity of the surface of the lithium metal composite oxide can be promoted more uniformly, and the surface of the lithium metal composite oxide after drying is formed. The particle size of the lithium tungstate 3 can be set within a suitable range. On the other hand, when the average particle diameter of the pure water to be sprayed is larger than 100 μm, the positive electrode active material 10 to which moisture is directly supplied by spraying and the positive electrode active material 10 to which moisture is supplied by stirring after spraying are mixed. The amount of elution varies, which may cause heterogeneity in the reaction.

[Drying step (step S2)]
When water is added and mixed in the mixing step (step S1), it is preferable to dry the obtained mixture (step S2) as shown in FIGS. In the mixing step (step S1) and the drying step (step S2), excess lithium in the lithium metal composite oxide (base material) reacts efficiently with nickel tungstate to form lithium tungstate. The lithium metal composite oxide obtained after drying has lithium tungstate 3 formed near the particle surface.

The drying temperature is not particularly limited as long as the moisture content is sufficiently reduced. For example, 500° C. or less is preferable. If the drying temperature exceeds 500° C., lithium is further liberated from the inside of the lithium metal composite oxide powder, and sufficient slurry stability of the positive electrode mixture paste cannot be obtained. Although the lower limit of the drying temperature is not particularly limited, it is, for example, 100° C. or higher. Moreover, the pressure during drying is desirably 1 atm or less. If the pressure is higher than 1 atm, there is a possibility that the moisture content may not sufficiently decrease. The drying time is not particularly limited as long as the moisture content is sufficiently reduced. For example, it is about 5 hours or more and 24 hours or less.

The lithium metal composite oxide after drying may be used as it is as the positive electrode active material 10, or may be used as the positive electrode active material 10 after further performing other steps such as a crushing step for adjusting the particle size distribution. may be used.

[Positive electrode active material for non-aqueous electrolyte secondary battery]
The positive electrode active material for non-aqueous electrolyte secondary batteries (positive electrode active material 10) obtained by the production method of the first embodiment is, for example, as shown in FIG. It contains at least secondary particles 2) and lithium tungstate 3. Each characteristic of the positive electrode active material 10 will be described below.

[Composition (entire positive electrode active material)]
In the positive electrode active material 10, the atomic ratio of lithium (Li), nickel (Ni), cobalt (Co), and the element M is Li:Ni:Co:M=z:(1-xy):x : y (where 1.00 < z < 1.30, 0.10 ≤ x ≤ 0.35, 0 ≤ y ≤ 0.35, M is from Mn, V, Mg, Mo, Nb, Ti and Al at least one selected element).

The positive electrode active material 10 has a composition excluding tungsten, such as general formula (3): Li _z Ni _1-xy Co _x M _y O ₂ (where 0.10≦x≦0.35, 0≦ y≦0.35, 1.00<z<1.30, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al). In addition, the positive electrode active material 10 has a hexagonal layered crystal structure.

[lithium tungstate]
The lithium tungstate 3 exists on the surface of the secondary particles 2 of the lithium metal composite oxide after drying. The presence of lithium tungstate 3 can be confirmed by powder X-ray diffraction or the like.

The area ratio of the lithium tungstate 3 having a particle size of 0.5 μm or more present on the surface of the secondary particle 2, which is obtained from observation of the surface of the secondary particle 2 using a scanning electron microscope (SEM), is the entire observation area. , preferably 5% or less, more preferably 1% or less. When the area ratio of the lithium tungstate 3 having a particle size of 0.5 μm or more is within the above range, the positive electrode resistance can be further reduced while suppressing a decrease in battery capacity in the secondary battery. On the other hand, when the area ratio of the lithium tungstate 3 having a particle size of 0.5 μm or more existing on the surface of the secondary particles 2 exceeds 5%, the resistance of lithium ions passing through the lithium tungstate 3 increases, so the reaction Resistance may increase.

The area ratio of the lithium tungstate 3 is determined, for example, by observing the surface of the secondary particles 2 with an SEM, and by image analysis or the like, the area of the entire surface of the secondary particles 2 on the observation surface is determined as particles having a particle size of 0.5 μm or more. It can be calculated by dividing by the area occupied by the lithium tungstate 3 having the diameter. The area of the entire surface of secondary particles 2 includes the portion covered with lithium tungstate 3 .

Specifically, the area ratio of the lithium tungstate 3 is determined by observing the surface of a plurality of secondary particles 2, for example, among the secondary particles 2 in the field of view, particles close to the volume average particle diameter (MV). 50 particles are randomly selected, and for these 50 particles, the area occupied by the entire particle surface and the area occupied by lithium tungstate 3 having a particle size of 0.5 μm or more are obtained, and the area of the entire observation surface is obtained. to the area ratio (%) occupied by the lithium tungstate 3 having a particle size of 0.5 μm or more.

Lithium tungstate 3 may exist not only on the surface of secondary particles 2 but also inside secondary particles 2 . Moreover, the lithium tungstate 3 may exist on the surfaces of the primary particles 1 existing inside and on the surfaces of the secondary particles 2 , and may exist on the grain boundaries between the primary particles 1 .

The positive electrode active material 10 preferably does not substantially contain nickel tungstate used as a raw material. Here, "substantially free of nickel tungstate" means that nickel tungstate cannot be detected by a method such as powder X-ray diffraction. When nickel tungstate is detected in the positive electrode active material 10, it indicates that tungsten oxide or nickel tungstate used as raw materials remains, and the positive electrode resistance may not be sufficiently reduced.

[Tungsten content]
The amount of tungsten present on the surface of the positive electrode active material 10 is, for example, 0.05% by mass or more and 2.0% by mass or less with respect to the entire positive electrode active material 10, and from the viewpoint of improving battery characteristics, more preferably It is preferably 0.1% by mass or more and 1.0% by mass or less, more preferably 0.1% by mass or more and 0.5% by mass or less. When the amount of tungsten present on the surface of the positive electrode active material 10 is within the above range, the lithium tungstate 3 present inside the secondary particles 2 and the lithium tungstate 3 formed on the surface of the secondary particles 2 are favorable. It is believed that a conductive path for Li ions can be formed, and the initial charge/discharge capacity, positive electrode resistance, and cycle characteristics can be further improved in the secondary battery.

[Moisture percentage]
The positive electrode active material 10 preferably has a Karl Fischer moisture content at 300° C. of 0.05% or more and 0.2% or less. If the moisture content exceeds 0.2%, the compatibility with the solvent contained in the positive electrode mixture paste may be hindered, and the film formed by coating and drying may become uneven.

The volume average particle size MV of the positive electrode active material 10 is preferably 3 μm or more and 15 μm or less, more preferably 4 μm or more and 6 μm or less. When the volume average particle diameter MV is in the above range, the specific surface area is large, and when used in the positive electrode, not only can a sufficient reaction area with the electrolytic solution be secured, but the positive electrode can be formed thin, and lithium ions It is possible to shorten the moving distance between the positive electrode and the negative electrode. The volume average particle diameter MV is a value measured by a laser diffraction scattering method.

In addition, the positive electrode active material 10 is obtained by dispersing 5 g of the positive electrode active material 10 in 100 ml of pure water and measuring the supernatant liquid after standing for 10 minutes. Also referred to as "value") is preferably 11 or more and 11.9 or less. 5 g of the positive electrode active material 10 was dispersed in 100 ml of pure water, and the pH of the supernatant was measured after standing for 10 minutes. The degree of lithium elution can be evaluated. When the pH of the positive electrode active material 10 is controlled within a specific range, it is possible to improve battery characteristics and suppress gelation of the paste.

(2) Second Embodiment A second embodiment will be described below. The production method according to the present embodiment differs from the production method according to the first embodiment in that the lithium metal composite oxide (base material) contains tungsten as an essential element. In addition, in the present embodiment, the same reference numerals are assigned to the same configurations as in the above-described first embodiment, and the description thereof is appropriately omitted or simplified. In addition, among the matters described in the embodiments of the present specification, configurations applicable to the present embodiment are also applied to the present embodiment as appropriate. The present embodiment will be described below with reference to FIGS. 4 and 5B.

[Mixing step (step S1a)]
The method for producing the positive electrode active material 10B according to the second embodiment includes mixing a lithium metal composite oxide containing tungsten, nickel tungstate, and water (step S1a), and and drying (step S2a). The manufacturing method of the positive electrode active material 10B according to this embodiment differs from the first embodiment in that a lithium metal composite oxide containing tungsten is used as the base material.

FIG. 5B is a schematic diagram showing an example of the positive electrode active material 10B obtained by the manufacturing method according to this embodiment. As shown in FIG. 5B, when a lithium metal composite oxide (base material) containing tungsten is used, the inside of the secondary particles 2 of the lithium metal composite oxide after drying and the particle surface are more Lithium tungstate 3, 3a can be uniformly present.

The positive electrode active material 10B obtained by the production method according to the present embodiment (for example, FIG. 5B) is obtained by using a lithium metal composite oxide containing tungsten only inside the secondary particles as a positive electrode active material. Or, as shown in FIG. 5A, compared to the positive electrode active material when using a lithium metal composite oxide (base material) that does not contain tungsten, the initial charge and discharge capacity, positive electrode resistance, and A secondary battery with improved cycle characteristics can be obtained. In addition, a secondary battery using the positive electrode active material 10B obtained by the manufacturing method according to the present embodiment can have battery characteristics equivalent to those of the conventional positive electrode active material even if the amount of tungsten used is less than that of the conventional positive electrode active material. , is also superior from a cost point of view.

Although the details of the above reason are unknown, the lithium metal composite oxide (base material) containing tungsten forms lithium tungstate 3a on the surface and at least a part of the inside as shown in FIG. 5(B). it seems to do. Then, in steps S1a and S2a described above, the lithium in the lithium metal composite oxide (base material) reacts with nickel tungstate to form, for example, tungsten on the surface of the lithium metal composite oxide 4 after drying. A lithium oxide 3 is formed. Since the lithium tungstates 3 and 3a are present in the interior and the entire surface of the lithium metal composite oxide 4 after drying, lithium tungstates 3 and 3a are present between the electrolytic solution and the interior of the positive electrode active material 10B in the secondary battery. It is considered that a conductive path for Li ions is formed, and lithium ions can be easily taken in and out.

Hereinafter, each raw material used in the mixing step (step S1) will be described with respect to points different from those of the first embodiment.
[Lithium metal composite oxide]
The lithium metal composite oxide (base material) used as a raw material includes lithium (Li), nickel (Ni), cobalt (Co), and element M, Li:Ni:Co:M1=z:(1-x -y): x: y (where 1.00 < z < 1.30, 0.10 ≤ x ≤ 0.35, 0 ≤ y ≤ 0.35, M1 is Mn, V, Mg, Mo, Nb , Ti and Al) and tungsten in an amount of 0.1% by mass or more with respect to the entire first lithium metal composite oxide1. Contains 0% by mass or less.

Further, the composition of the lithium metal composite oxide (base material) containing tungsten is, for example, the general formula (2): Li _z Ni _1-x-y Co _x M _y W _a O ₂ (1.00<z<1 .30, 0.10≦x≦0.35, 0≦y≦0.35, 0.0005≦a≦0.005, M is selected from Mn, V, Mg, Mo, Nb, Ti and Al at least one element). A small amount of tungsten (W) may be solid-dissolved in the primary particles forming the base material.

In the lithium metal composite oxide (base material) containing tungsten, tungsten (W) is 0.1% by mass or more and 1.0% by mass or less, preferably 0.5% by mass, with respect to the entire lithium metal composite oxide. 1.0% by mass or less. When the lithium metal composite oxide (base material) contains tungsten in the above range, the amount of nickel tungstate used for mixing (step S1a) can be reduced, and furthermore, the amount of tungsten in the entire positive electrode active material 10B can be reduced. Even so, it is possible to obtain the positive electrode active material 10B having a high positive electrode resistance reduction effect while maintaining a high battery capacity.

The location of tungsten in the tungsten-containing lithium metal composite oxide (base material) is not particularly limited. Tungsten may be present in a solid solution in the crystal of the lithium metal composite oxide (base material), and the surface of the secondary particles of the lithium metal composite oxide (base material) and the surface of the primary particles arranged inside Alternatively, it may exist as a tungsten compound at the grain boundaries between these primary grains. Moreover, a part of tungsten may be solid-dissolved and the other part may exist as a compound containing tungsten. As the compound containing tungsten, lithium tungstate 3a is preferable. The type of compound containing tungsten can be confirmed by powder X-diffraction or the like.

The tungsten-containing lithium metal composite oxide (base material) is not particularly limited as long as it has the above composition, and can be obtained by a known production method. An example of a method for producing a tungsten-containing lithium metal composite oxide (base material) is shown in (i) to (iii) below.

(i) Using an aqueous solution containing Ni, Co, W, and optionally the element M, neutralization crystallization is performed to prepare a transition metal composite hydroxide, which is then used as a precursor containing lithium It is mixed with a compound and fired to obtain a lithium metal composite oxide (base material).
(ii) After preparing a transition metal composite hydroxide containing Ni and Co excluding W, and optionally containing the element M, the transition metal composite hydroxide, a compound containing W, and a compound containing Li are mixed. and fired to obtain a lithium metal composite oxide (base material).
(iii) At least part of the surface of the lithium metal composite oxide having the above composition excluding W is coated with a compound containing W to obtain a lithium metal composite oxide (base material).

Among these, from the viewpoint of uniformity of tungsten distribution, the production methods (i) and (ii) are preferred, and the production method (i) is more preferred to produce a lithium metal composite oxide (base material). be able to. In addition, W added in the production method (i) has tungsten uniformly distributed in the transition metal composite hydroxide, so when synthesized into a lithium metal composite oxide, tungsten is on the surface of the secondary particles and It is possible to more uniformly coat the surfaces of the primary particles present inside. In addition, in the production method of the present embodiment, a lithium metal composite oxide (base material) obtained by any of the above production methods and production methods other than the above can be used.

When the surface of the tungsten-containing lithium metal composite oxide (base material) is observed with a scanning electron microscope (SEM), it is preferred that no tungsten-containing compound having a particle size of 0.5 μm or more is observed. When a compound containing tungsten with a particle size of 0.5 μm or more is not observed on the surface, a sufficiently fine compound containing tungsten is present on the surface and inside the lithium metal composite oxide (base material) and contains tungsten, which will be described later. Together with the compound, it is possible to obtain the effect of further improving the battery capacity and reducing the resistance. The particle diameter of the tungsten-containing compound can be reduced to 0.5 μm or less by using the production methods (i) and (ii) above.

In addition, in the lithium metal composite oxide (base material) containing tungsten, the amount of tungsten (W) present inside is preferably 0.1% by mass or more with respect to the entire lithium metal composite oxide (base material). It is 1.0% by mass or less, more preferably 0.5% by mass or more and 1.0% by mass or less. Here, the amount of tungsten present inside means that the amount of tungsten present on the surface of the lithium metal composite oxide (base material) is removed by dispersing the lithium metal composite oxide (base material) in water. It refers to the amount of tungsten remaining without being eluted into water when the compound contained in it is removed. When the amount of tungsten present inside the lithium metal composite oxide (base material) is within the above range, in the resulting positive electrode active material 10B, the lithium tungstate 3a present inside the secondary particles 2 and the subsequent process (step The lithium tungstate 3 formed on the surface of the secondary particles 2 in S1a and S2a) can form a good lithium ion conduction path, and the initial charge/discharge capacity, positive electrode resistance, and cycle characteristics are further improved. Let

The amount of tungsten present inside the lithium metal composite oxide (base material) can be measured by the following method. First, the amount of tungsten (W _T ) in the entire lithium metal composite oxide (base material) is measured by ICP emission spectrometry (ICP method). Next, put 5.0 g of lithium metal composite oxide (base material) in a beaker together with 100 ml of pure water, stir and disperse with a magnetic stirrer, continue stirring for 30 minutes, and after standing for 10 minutes, remove the supernatant. It is separated by filtration, and the amount of tungsten (W) eluted in the supernatant is measured by the ICP method. The amount of tungsten eluted in this supernatant is defined as the amount of tungsten present on the surface of the lithium metal composite oxide (base material) (W _s ), and from the following formula, present inside the lithium metal composite oxide (base material) Calculate the amount of tungsten (W _I ) to be used.
Formula: W _I = W _T - W _S

[Nickel tungstate]
Nickel tungstate can be of the same type as in the first embodiment. The mixed amount of nickel tungstate is preferably 0.1% by mass or more and 0.5% by mass or less with respect to the entire lithium metal composite oxide in terms of the amount of tungsten (W) in the nickel tungstate. When the mixed amount of nickel tungstate is within the above range, it is possible to obtain the positive electrode active material 10B having a high positive electrode resistance reduction effect while maintaining a high battery capacity. Further, in the present embodiment, the mixed amount of nickel tungstate is increased so that the amount of tungsten contained in the nickel tungstate is 0.1% by mass or more and 0.2% by mass or less with respect to the entire lithium metal composite oxide. Even when it is reduced, the above effects can be sufficiently obtained.

In addition, when tungsten oxide is mixed together, the mixed amount of tungsten oxide and nickel tungstate is such that the total amount of tungsten contained in both is 0.1% by mass or more with respect to the entire lithium metal composite oxide. .5% by mass or less. When the mixed amount is within the above range, it is possible to obtain the positive electrode active material 10B having a high positive electrode resistance reduction effect while maintaining a high battery capacity. Further, in the production method of the present embodiment, the amount of tungsten in the mixture of tungsten oxide and nickel tungstate is 0.1% by mass or more and 0.2% by mass or less with respect to the entire lithium metal composite oxide. Even when the mixing amount is reduced, the above effects can be sufficiently obtained.

[water]
As for water, it is preferable to use pure water. As described above, the water in the mixture contains unreacted lithium compounds present in the lithium metal composite oxide and lithium present in the crystals (hereinafter collectively referred to as "surplus lithium"). As it melts, it can melt the mixed nickel tungstate. Other conditions such as water content can be the same as in the first embodiment.

[Mixing method]
The method of mixing the lithium metal composite oxide (base material), nickel tungstate, and water is not particularly limited. and may be mixed by a known mixing device. A suitable method for mixing the tungsten-containing lithium metal composite oxide (base material), nickel tungstate, and water can be the same method as in the first embodiment.

[Drying step (step S2a)]
Next, as shown in FIG. 4, the mixture obtained by mixing the lithium metal composite oxide (base material), nickel tungstate, and water is dried (step S2a). Incidentally, the drying conditions can be the same conditions as in the first embodiment.

[Positive electrode active material for non-aqueous electrolyte secondary battery]
The positive electrode active material 10B obtained by the manufacturing method of the second embodiment includes, for example, a dried lithium metal composite oxide 4 (secondary particles 2) and lithium tungstate 3, as shown in FIG. including at least Hereinafter, each characteristic of the positive electrode active material 10B will be described with reference to FIG. 5(B).

Lithium metal composite oxide 4 after drying includes both lithium tungstate 3a derived from tungsten contained in the lithium metal composite oxide (base material) and lithium tungstate 3a formed in steps S1a and S2a described above. have

The positive electrode active material 10B contains, for example, 0.2% by mass or more and 1.2% by mass or less, preferably 0.2% by mass or more and 1% by mass or less of tungsten with respect to the entire positive electrode active material.

The amount of tungsten present on the surface of the lithium metal composite oxide after drying is preferably 0.1% by mass or more and 1.0% by mass or less, more preferably 0.1% by mass or more, with respect to the entire positive electrode active material 10B. It is 0.5% by mass or less. When the amount of tungsten present on the surface of the lithium metal composite oxide after drying is within the above range, a compound containing tungsten present inside the secondary particles 2 (e.g., lithium tungstate 3a) and the secondary particles 2 on the surface The formed lithium tungstate 3 can form a good lithium ion conduction path, and it is thought that the initial charge/discharge capacity, positive electrode resistance, and cycle characteristics can be further improved in the secondary battery. be done.

In addition, the amount of tungsten present inside the particles of the lithium metal composite oxide after drying is preferably 0.1% by mass or more and 1.0% by mass or less, more preferably 0.5% by mass, relative to the entire positive electrode active material. % or more and 1.0 mass % or less. Since the lithium tungstate 3 is mainly present near the surface of the lithium metal composite oxide after drying, the amount of tungsten present inside the particles of the lithium metal composite oxide after drying is the lithium metal composite oxide (base material ) may be approximately the same amount as the amount of tungsten inside. Moreover, the amount of tungsten present on the surface of the positive electrode active material 10B is preferably 0.1 to 1 time the amount of tungsten contained inside the positive electrode active material 10B.

The amount of tungsten present on the surface and inside the lithium metal composite oxide after drying is the amount of tungsten present on the surface and inside the lithium metal composite oxide (base material) containing tungsten described above, W _S and W _I. It can be measured in a similar way.

The properties of the positive electrode active material 10B obtained by the production method of the present embodiment can be the same as the properties of the positive electrode active material 10 obtained by the first embodiment except for the above. In addition, regarding the area ratio of lithium tungstate 3 having a particle size of 0.5 μm or more present on the surface of the secondary particle 2, which is obtained from the observation of the surface of the secondary particle 2 using the scanning electron microscope (SEM) described above. is the area ratio including the lithium tungstate 3a contained in the lithium metal composite oxide (base material) and the lithium tungstate 3 formed in steps S1a and S2a described above.

2. Non-Aqueous Electrolyte Secondary Battery The positive electrode active material 10 obtained by the manufacturing method of the present embodiment described above can be suitably used for the positive electrode of a non-aqueous electrolyte secondary battery (hereinafter also referred to as “secondary battery”). . A secondary battery includes, for example, a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. A secondary battery may also include, for example, a positive electrode, a negative electrode, and a solid electrolyte. Also, the secondary battery may be composed of components similar to those of a general non-aqueous electrolyte secondary battery.

A secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator will be described below. It should be noted that the embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery of the present invention can be modified, It can be implemented in a modified form. Moreover, the non-aqueous electrolyte secondary battery of the present embodiment is not particularly limited in its application.

(a) Positive Electrode Using the positive electrode active material 10 described above, for example, a positive electrode of a non-aqueous electrolyte secondary battery can be produced as follows.

First, a powdery positive electrode active material 10, 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. .

The mixing ratio of each in the positive electrode mixture paste is also an important factor that determines the performance of the non-aqueous electrolyte secondary battery. When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material 10 is 60 to 95 parts by mass, similar to the positive electrode of a general non-aqueous electrolyte secondary battery. It is desirable that the content of the material is 1 to 20 parts by mass and the content of the binder is 1 to 20 parts by mass.

The obtained positive electrode material 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 according to the intended battery, and used for manufacturing the battery. However, the method for producing the positive electrode is not limited to the illustrated one, and other methods may be used.

In manufacturing the positive electrode, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black materials such as acetylene black and ketjen black can be used as the conductive agent.

The binder plays a role of binding the active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, and polyacrylic. An acid or the like can be used.

If necessary, the positive electrode active material 10, the conductive material, and the activated carbon are dispersed, and a solvent that dissolves the binder is 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 can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(b) Negative electrode For the negative electrode, a negative electrode mixture made by mixing a binder with a negative electrode active material such as metallic lithium or a lithium alloy, or a negative electrode active material capable of intercalating and deintercalating lithium ions, and adding an appropriate solvent to form a paste is added. is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as needed.

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, as the negative electrode binder, similar to the positive electrode, fluorine-containing resin such as PVDF can be used. Organic solvents can be used.

(c) Separator A separator is interposed between the positive electrode and the negative electrode. 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.

(d) Non-Aqueous Electrolyte The non-aqueous electrolyte is prepared by dissolving a lithium salt as a supporting salt in an organic solvent.

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, and the like, or a mixture of two or more thereof is used. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ and the like, and composite salts thereof can be used.

Furthermore, the non-aqueous electrolytic solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(e) Shape and Configuration of Secondary Battery The shape of the secondary battery can be various, such as cylindrical and laminated. Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolytic solution, and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal connected to the outside are connected using a current collecting lead or the like, and sealed in the battery case to complete the non-aqueous electrolyte secondary battery. .

(f) Characteristics A non-aqueous electrolyte secondary battery using the positive electrode active material 10 obtained by the manufacturing method according to the present embodiment has high capacity and high output. A non-aqueous electrolyte secondary battery using the positive electrode active material 10 according to the present invention obtained in a particularly more preferable form has a high initial discharge capacity of 150 mAh/g or more and a low A positive electrode resistance is obtained.

In addition, the positive electrode resistance can be measured by, for example, the following method. When the frequency dependence of the battery reaction is measured by the AC impedance method, which is commonly used as an electrochemical evaluation method, the Nyquist diagram based on the solution resistance, the negative electrode resistance and the negative electrode capacity, and the positive electrode resistance and the positive electrode capacity is shown in FIG. is obtained as

The battery reaction at the electrodes consists of a resistance component associated with charge transfer and a capacity component due to the electric double layer. Expressing these in an electric circuit results in a parallel circuit of resistance and capacity. It is represented by an equivalent circuit in which circuits are connected in series. Using this equivalent circuit, a fitting calculation can be performed on the measured Nyquist diagram, and each resistance component and capacitance component can be estimated. The positive electrode resistance is equal to the diameter of the semicircle on the low frequency side of the resulting Nyquist diagram. Therefore, the resistance of the positive electrode can be estimated by performing AC impedance measurement on the positive electrode to be manufactured and performing fitting calculation with an equivalent circuit to the obtained Nyquist diagram.

EXAMPLES The present invention will be specifically described below using Examples, but the present invention is not limited to these Examples.

[Measurement of W amount]
The amount of tungsten existing on the surface and inside of the positive electrode active material was measured by the following method. First, the amount of tungsten (W _T ) in the entire positive electrode active material was measured by ICP emission spectrometry (ICP method). Next, put 5.0 g of the positive electrode active material together with 100 ml of pure water in a beaker, stir and disperse with a magnetic stirrer, stir for 30 minutes, and then leave to stand for 10 minutes. The amount of eluted tungsten (W) was measured by the ICP method. The amount of tungsten eluted into the supernatant was defined as the amount of tungsten present on the surface of the positive electrode active material (W _s ), and the amount of tungsten present inside the positive electrode active material (W _I ) was calculated from the following formula.
Formula: W _I = W _T - W _S

[Area ratio of lithium tungstate of 0.5 μm or more]
The area ratio of lithium tungstate is determined by observing the surface of a plurality of secondary particles with an SEM, and among the secondary particles in the field of view, particles having a particle diameter of 80% or more and 120% or less of the volume average particle diameter (MV). Randomly select 50 pieces, and for these 50 particles, determine the area of the entire particle surface and the area occupied by lithium tungstate with a particle size of 0.5 μm or more. , the area ratio (%) occupied by lithium tungstate having a particle size of 0.5 μm or more was calculated. As a result of powder X-ray diffraction, only lithium tungstate was detected as a compound containing tungsten, so all the compounds present on the surface of the secondary particles were assumed to be lithium tungstate, and the area ratio was calculated.

[Evaluation of stability of positive electrode mixture paste]
25.0 g of the positive electrode active material, 1.5 g of conductive carbon powder, 2.9 g of polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (NMP) are mixed by a planetary kneader to form a positive electrode mixture. got a paste. The amount of N-methyl-2-pyrrolidone (NMP) added was adjusted so that the viscosity was 1.5 to 2.5 Pa·s according to the viscosity measurement method using a vibration viscometer specified in JIS Z 8803:2011. The resulting paste was stored for 76 hours and visually evaluated for gelation. If the viscosity of the paste remained the same as immediately after mixing and fluidity was maintained, it was determined that gelation had not occurred. Gelation was judged to have occurred when the paste solidified and lost fluidity, or when the viscosity increased and the paste was not biased even when the container was tilted. The case where gelation did not occur was indicated by ◯, and the case where gelation occurred was indicated by x.

[Production of secondary battery and evaluation of battery performance]
Regarding the secondary battery having a positive electrode using the positive electrode active material obtained in Examples and Comparative Examples, the performance (initial discharge capacity, positive electrode resistance, discharge capacity retention rate after repeating 500 charge-discharge cycles at 60 ° C. ) was measured.

(Manufacturing of batteries)
A 2032 type coin battery CBA (hereinafter referred to as coin battery CBA) shown in FIG. 6 was used for evaluation of the positive electrode active material.

As shown in FIG. 5, the coin-type battery CBA is composed of a case CA and an electrode EL accommodated in the case CA.

The case CA has a hollow cathode can PC with one end open, and an anode can NC arranged in the opening of the cathode can PC. When the anode can NC is arranged in the opening of the cathode can PC, , a space for accommodating the electrode EL is formed between the negative electrode can NC and the positive electrode can PC.

The electrode EL is composed of a positive electrode PE, a separator SE, and a negative electrode NE, which are stacked in this order, with the positive electrode PE in contact with the inner surface of the positive electrode can PC and the negative electrode NE with the inner surface of the negative electrode can NC. are accommodated in the case CA.

The case CA is provided with a gasket GA, and the gasket GA fixes relative movement between the positive electrode can PC and the negative electrode can NC so as to maintain a non-contact state. The gasket GA also has the function of sealing the gap between the positive electrode can PC and the negative electrode can NC to airtightly and liquidtightly isolate the inside of the case CA from the outside.

The coin-type battery CBA shown in FIG. 6 was manufactured as follows.

First, 52.5 mg of a positive electrode active material for a non-aqueous electrolyte secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press molded at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm. , a positive electrode PE was produced. The produced positive electrode PE was dried in a vacuum dryer at 120° C. for 12 hours.

Using this positive electrode PE, negative electrode NE, separator SE, and electrolytic solution, the above-described coin-type battery CBA was produced in an Ar atmosphere glove box in which the dew point was controlled at -80°C.

As the negative electrode NE, a negative electrode sheet in which graphite powder having an average particle size of about 20 μm and polyvinylidene fluoride, which was punched into a disk shape of 14 mm in diameter, and polyvinylidene fluoride were coated on a copper foil was used.

A polyethylene porous film having a film thickness of 25 μm was used as the separator SE. As the electrolytic solution, an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1M LiClO ₄ as the supporting electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.) was used.

The initial discharge capacity, the positive electrode resistance, and the discharge capacity retention rate after repeating 500 charge-discharge cycles at 60° C., which indicate the performance of the manufactured coin-type battery CBA, were evaluated as follows.

For the initial discharge capacity, the coin-type battery CBA was left for about 24 hours after production, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density for the positive electrode was 0.1 mA / cm ² and the cutoff voltage was 4. The battery was charged to 3 V, rested for 1 hour, and then discharged to a cut-off voltage of 3.0 V. The capacity was taken as the initial discharge capacity.

The positive electrode resistance was measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) after charging the coin-type battery CBA at a charging potential of 4.1 V. The Nyquist resistance shown in FIG. A plot is obtained. 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 was calculated.

The discharge capacity retention rate after 500 cycles is the difference between the discharge capacity and the initial discharge capacity after repeating 500 cycles of charging to 4.3 V and discharging to 3.0 V at a temperature of 60 ° C. and a charge / discharge rate of 0.2 C. It was obtained by calculating the ratio.

In this example, each sample of special grade reagent manufactured by Wako Pure Chemical Industries, Ltd. was used for the production of the composite hydroxide and the production of the positive electrode active material and the secondary battery.

[Example 1]
(Production of first lithium metal composite oxide)
Using a known crystallization method, a lithium metal composite oxide represented by Li _1.20 Ni _0.35 Co _0.35 Mo _0.30 O ₂ (W: 0 wt%, specific surface area 1.2 cm ² /g ) (base material) was obtained. Specifically, using a metal salt solution containing Ni, Co, and Mn and a sodium tungstate solution as raw materials, NaOH as a neutralizing agent, and ammonia as a complexing agent, Ni and Co , Mn-containing transition metal composite hydroxides were synthesized. After lithium hydroxide was mixed with the resulting transition metal composite hydroxide, the mixture was calcined to obtain the lithium metal composite oxide (base material). The moisture content of the base material (Karl Fischer moisture content at 300° C.) was 0.07% by mass with respect to the entire base material.

(Mixing process)
Nickel tungstate (reagent manufactured by Wako Pure Chemical Industries, Ltd., nickel tungsten oxide) is added to the lithium metal composite oxide (base material) in an amount such that the amount of tungsten is 0.9% by mass with respect to the entire lithium metal composite oxide. , After mixing, water is sprayed in a mist state with an average particle size of 100 μm or less to 2% by mass with respect to the entire first lithium metal composite oxide, and further mixed, and then dried at 150 ° C. for 12 hours. A positive electrode active material was obtained by Table 1 shows the properties of the obtained dried lithium metal composite oxide (positive electrode active material). Moreover, the volume average particle size (MV) of the positive electrode active material was 5.2 μm.

[Example 2]
Using a known crystallization method, a lithium metal composite oxide represented by Li _1.20 Ni _0.35 Co _0.35 Mn _0.30 W _0.0037 (W: 0.07 mass%, specific surface area 1 .2 cm ² /g) (base material). Specifically, using a metal salt solution containing Ni, Co, and Mn and a sodium tungstate solution as raw materials, NaOH as a neutralizing agent, and ammonia as a complexing agent, Ni and Co , Mn and W were synthesized. After lithium hydroxide was mixed with the resulting transition metal composite hydroxide, the mixture was calcined to obtain the lithium metal composite oxide (base material).
(Mixing process)
Nickel tungstate (reagent manufactured by Wako Pure Chemical Industries, Ltd., nickel tungsten oxide) is added to the lithium metal composite oxide (base material) in an amount such that the amount of tungsten is 0.05% by mass with respect to the entire lithium metal composite oxide. After mixing, 2% by mass of water is sprayed with respect to the entire lithium metal composite oxide in a mist state with an average particle size of 100 μm or less, and further mixed, and then dried at 150 ° C. for 12 hours. got the substance. Table 1 shows the properties of the obtained dried lithium metal composite oxide (positive electrode active material). Moreover, the volume average particle diameter (MV) of the positive electrode active material was 5.2 μm.

[Battery evaluation]
Battery characteristics of a coin-type battery CBA having a positive electrode produced using the obtained second lithium metal composite oxide were evaluated. Table 1 shows the evaluation results.

[Example 3]
A positive electrode active material for a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 2, except that the amount of nickel tungstate added was such that the amount of tungsten was 0.1% by mass with respect to the entire lithium metal composite oxide. The battery characteristics were evaluated, and the results are shown in Table 1.

[Example 4]
A positive electrode active material for a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 2, except that the amount of nickel tungstate added was such that the amount of tungsten was 0.2% by mass with respect to the entire lithium metal composite oxide. The battery characteristics were evaluated, and the results are shown in Table 1.

[Example 5]
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and battery characteristics were evaluated in the same manner as in Example 4, except that the amount of sprayed pure water was 1% by mass.

[Example 6]
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and the battery characteristics were evaluated in the same manner as in Example 4, except that the amount of sprayed pure water was 5% by mass.

[Example 7]
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and the battery characteristics were evaluated in the same manner as in Example 4, except that the amount of sprayed pure water was 10% by mass.

[Example 8]
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and battery characteristics were evaluated in the same manner as in Example 4, except that the amount of sprayed pure water was changed to 20% by mass.

[Example 9]
A positive electrode active material for a nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 2, except that the amount of nickel tungstate added was such that the amount of tungsten was 0.7% by mass with respect to the entire lithium metal composite oxide. The battery characteristics were evaluated, and the results are shown in Table 1.

[Example 10]
A positive electrode active material for a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 2, except that the amount of nickel tungstate added was such that the amount of tungsten was 1.0% by mass with respect to the entire lithium metal composite oxide. The battery characteristics were evaluated, and the results are shown in Table 1.

[Example 11]
Non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the amount of nickel tungstate added was such that the amount of tungsten was 0.2% by mass with respect to the entire lithium metal composite oxide, and pure water was not added. A positive electrode active material for the next battery was obtained and the battery characteristics were evaluated. Table 1 shows the results.

[Example 12]
In the same manner as in Example 1, except that the amount of nickel tungstate added was such that the amount of tungsten was 0.5% by mass with respect to the entire lithium metal composite oxide, and the amount of pure water sprayed was 2% by mass. A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and the battery characteristics were evaluated. Table 1 shows the results.

[Comparative Example 1]
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and battery characteristics were evaluated in the same manner as in Example 2, except that nickel tungstate was not added and pure water was not sprayed. .

[Comparative Example 2]
Lithium metal composite oxide (base material), lithium metal composite oxide represented by Li _1.20 Ni _0.35 Co _0.35 Mo _0.30 W _0.0048 O ₂ (W: 0.9 mass% containing) was used and nickel tungstate was not added, in the same manner as in Example 2 to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery and evaluate battery characteristics. shown.

[Comparative Example 3]
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and battery characteristics were evaluated in the same manner as in Example 1, except that nickel tungstate was added and pure water was not sprayed. .

[Evaluation results]
It is shown that the positive electrode active materials obtained in the examples are suppressed in gelation and exhibit initial charge/discharge capacity, positive electrode resistance, and charge/discharge cycle characteristics comparable to or higher than those of comparative examples containing no tungsten. was done. In particular, in Examples 2 to 10 in which the lithium metal composite oxide (base material) contained tungsten, the initial charge/discharge capacity, positive electrode resistance, and charge/discharge cycle characteristics were good. It was confirmed by XRD that tungsten oxide was not detected in the positive electrode active materials obtained in Examples, and only lithium tungstate was detected.

In Example 1, in which the area ratio of lithium tungstate having a size of 0.5 μm or more, which is present on the surface of the positive electrode active material, exceeds 5%, the amount of tungsten in the positive electrode active material is the same, but the area ratio is 5%. As compared with Example 4 below, the positive electrode resistance was slightly lowered.

On the other hand, in the positive electrode active materials obtained in Comparative Examples 1 to 3 in which nickel tungstate was not added, gelation of the positive electrode mixture paste was observed.

Further, when comparing the positive electrode active materials obtained in Example 4 and Comparative Example 2 in which the amount of water added was the same, the amount of tungsten in the positive electrode active material was the same, but the positive electrode active material obtained in Example showed higher initial discharge capacity and positive electrode resistance than the positive electrode active material obtained in the comparative example. Therefore, it was shown that the positive electrode active material obtained by using the production method of the present embodiment can have higher battery characteristics with a small amount of tungsten used.

It should be noted that the technical scope of the present invention is not limited to the aspects described in the above embodiments and the like. One or more of the requirements described in the above embodiments and the like may be omitted. Also, the requirements described in the above-described embodiments and the like can be combined as appropriate.

Reference Signs List 1 Primary particles 2 Secondary particles 3 Lithium tungstate 3a Lithium tungstate (derived from base material)
4 Lithium metal composite oxide after drying 10, 10A, 10B Positive electrode active material CBA Coin type battery CA Case PE Positive electrode NE Negative electrode GA Gasket PE Positive electrode NE Negative electrode SE …… Separator

Claims (15)

mixing a lithium metal composite oxide and nickel tungstate;
The lithium metal composite oxide includes lithium (Li), nickel (Ni), cobalt (Co), and optionally metal elements M1, and the atomic ratio of the respective metal elements is Li:Ni:Co: M1 = s: (1-xy): x: y (where 1.00 ≤ s ≤ 1.30, 0.10 ≤ x ≤ 0.35, 0 ≤ y ≤ 0.35, metal element M1 is , at least one element selected from Mn, W, V, Mg, Mo, Nb, Ti and Al),
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, comprising mixing the lithium metal composite oxide, the nickel tungstate, and water. spraying and mixing the water into the powder mixture obtained by mixing the lithium metal composite oxide and the nickel tungstate so that the water droplets have an average particle size of 100 μm or less; The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, comprising: The method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 2 or 3, comprising drying the mixture obtained by said mixing. Lithium ions contained in the lithium metal composite oxide react with at least a portion of the nickel tungstate in the presence of water to form lithium tungstate. 5. The method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of 4. The non-aqueous electrolyte secondary according to any one of claims 1 to 5, wherein the mixture obtained by mixing contains 0.1% by mass or more of water with respect to the entire lithium metal composite oxide. A method for producing a positive electrode active material for a battery. 7. The mixture according to any one of claims 1 to 6, wherein the mixture obtained by the mixing contains 0.2% by mass or more and 1.0% by mass or less of tungsten with respect to the entire lithium metal composite oxide. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. Lithium tungstate is present on the particle surface of the lithium metal composite oxide after drying,
The area ratio of lithium tungstate with a particle size of 0.5 μm or more present on the surface of the particle, which is obtained from observation of the surface of the particle using a scanning electron microscope, is 5 with respect to the area of the entire observation surface. % or less, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, wherein the lithium metal composite oxide after drying has a specific surface area of 0.5 ^cm2 /g or more and 2 ^m2 /g or less. The cathode active material for a non-aqueous electrolyte secondary battery according to claim 4, wherein the dried lithium metal composite oxide has a Karl Fischer moisture content of 0.05% by mass or more and 0.2% by mass or less at 300°C. manufacturing method. 5. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, wherein the lithium metal composite oxide after drying has a volume average particle diameter MV of 4 μm or more and 6 μm or less. mixing a lithium metal composite oxide containing tungsten, nickel tungstate, and water; and drying the mixture obtained by the mixing, wherein the lithium metal composite oxide containing tungsten is Production of a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 11, which contains 0.1% by mass or more and 1.0% by mass or less with respect to the total lithium metal composite oxide. Method. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 12, wherein the nickel tungstate contains 0.1% by mass or more and 0.5% by mass or less of tungsten with respect to the entire lithium metal composite oxide. Production method. Lithium tungstate is present on the particle surface of the lithium metal composite oxide after drying,
The amount of tungsten present on the particle surface is 0.1% by mass or more and 1.0% by mass or less with respect to the entire positive electrode active material, and present inside the particles of the lithium metal composite oxide after drying. Manufacture of the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 12 or 13, wherein the amount of tungsten is 0.1% by mass or more and 1.0% by mass or less with respect to the entire positive electrode active material. Method. Any one of claims 12 to 14, wherein the amount of tungsten present on the surface of the lithium metal composite oxide particles after drying is 0.1 to 1 time the amount of tungsten contained inside the particles. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of items.

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