JP2020181647A - Method for manufacturing positive electrode active material for lithium ion secondary battery, positive electrode active material for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

To provide a method for manufacturing a positive electrode active material for a lithium ion secondary battery, which hardly worsens the cycle characteristic.SOLUTION: Disclosed are a positive electrode active material 100 for a lithium ion secondary battery and a method for manufacturing the same. The method comprises the steps of: mixing a first lithium metal composite oxide including secondary particles 2 resulting from agglomeration of primary particles 1, a tungsten oxide A1, and water to obtain a mixture; and drying the mixture to obtain a second lithium metal composite oxide 20. In the method, the first lithium metal composite oxide contains tungsten of 0.1-1.0 mass% to a total mass of the first lithium metal composite oxide. The mixture contains tungsten in the tungsten oxide A1 in a range of 0.1-0.5 mass% to a total mass of the first lithium metal composite oxide.SELECTED DRAWING: Figure 4

Description

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

In recent years, with the spread of portable electronic devices such as mobile phones and notebook personal computers, the development of a compact and lightweight lithium ion secondary battery having a high energy density is strongly desired. There is also a strong demand for the development of high-power secondary batteries suitable for electric vehicle applications including hybrid vehicles.

As a secondary battery satisfying such a demand, there is a lithium ion secondary battery such as a lithium ion secondary battery. The 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 capable of desorbing and inserting lithium.

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

The positive electrode active materials that have been mainly proposed so far include lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, and lithium nickel composite oxide (LiNiO ₂ ), which uses nickel, which is cheaper than cobalt. Lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and spinel-based lithium manganese composite oxide (LiMn ₂ O ₄ ), which are excellent in safety by using cheaper manganese. ) And so on.

By the way, when the positive electrode active material has a small particle size and a narrow particle size distribution, a lithium ion secondary battery having excellent output characteristics and charge / discharge cycle characteristics can be obtained. This is because particles having 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 an electrolytic solution be secured, but also the positive electrode is made thin and lithium ions are formed. This is because the moving distance between the positive electrode and the negative electrode can be shortened, so that the positive electrode resistance can be reduced. Further, since the particles having a narrow particle size distribution, that is, particles having a uniform particle size, can make the voltage applied to each particle uniform in the electrode, the decrease in battery capacity due to the selective deterioration of the fine particles is suppressed. Because it is possible.

For example, Patent Documents 1 to 3 clearly describe transition metal composite hydroxide particles that are precursors of a positive electrode active material in two stages, a nucleation step in which nucleation is mainly performed and a particle growth step in which particle growth is mainly carried out. A method for producing the particles by the crystallization reaction separated into the above is disclosed. 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 step and in the range of 10.5 to 12.0 in the particle growth step based on the liquid temperature of 25 ° C. doing. Further, the reaction atmosphere is changed to an oxidizing atmosphere at the initial stage of the nucleation step and the particle growth step, and is switched to a non-oxidizing atmosphere at a predetermined timing.

The transition metal composite hydroxide particles obtained by such a method have a small particle size, a narrow particle size distribution, a low density center composed of fine primary particles, and a high height composed of plate-shaped or needle-shaped primary particles. It is composed of a density outer shell. When a lithium compound is mixed with such transition metal composite hydroxide particles and fired, the low-density central portion contracts significantly, and a space portion is formed 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 size in the range of 2 μm to 8 μm or 2 μm to 15 μm, and 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, it is said that a secondary battery using these positive electrode active materials can improve the capacity characteristics, output characteristics, and charge / discharge cycle characteristics. However, further improvement in output characteristics and charge / discharge cycle characteristics is required.

It is known that it is effective to contain lithium in excess of the stoichiometric composition with respect to metal elements such as nickel, cobalt and manganese in order to further improve the charge / discharge cycle characteristics. Further, it has been reported that the output characteristics and the charge / discharge cycle characteristics are improved by adding a compound containing tungsten to the positive electrode active material.

For example, Patent Document 4 proposes a positive electrode composition obtained by mixing an acidic oxide such as tungsten oxide with a positive electrode active material. According to this positive electrode composition, lithium hydroxide produced by the reaction of lithium liberated from the positive electrode active material and the water contained in the binder reacts preferentially with the acidic oxide to produce hydroxide. It is said that the reaction between lithium and the binder is suppressed to suppress the gelation of the positive electrode slurry. Further, it is said that the acid oxide acts as a conductive agent in the positive electrode regardless of whether or not it reacts with lithium hydroxide, lowers the resistance of the entire positive electrode, and as a result contributes to the improvement of the output characteristics of the battery.

Further, in Patent Document 5, a positive electrode active material, a conductive material, a binder such as polyvinylidene fluoride (PVDF), and an organic solvent such as N-methyl-2-pyrrolidone (NMP) are mixed. A method of mixing a predetermined amount of tungsten oxide particles when preparing the positive electrode paste has been proposed. According to this method, it is said that not only the effect of suppressing the thickening of the positive electrode paste but also the effect of suppressing the low temperature reaction resistance in the secondary battery is obtained.

Further, in Patent Document 6, a lithium metal composite oxide powder is obtained by adding an alkaline solution in which a tungsten compound is dissolved to the lithium metal composite oxide powder, mixing the mixture, and then heat-treating the fine particles containing W and Li. A method for producing a positive electrode active material, which is formed on the surface of the powder or the surface of the primary particles of the powder, has been proposed. According to Patent Document 6, it is reported that the output characteristics are improved by forming fine particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide powder.

Japanese Unexamined Patent Publication No. 2012-246199 Japanese Unexamined Patent Publication No. 2013-147416 International Publication 2012/131881 Japanese Patent No. 5382061 Japanese Unexamined Patent Publication No. 2013-08435 Japanese Unexamined Patent Publication No. 2012-079464

For the further spread of electric vehicles, it is necessary to further increase the capacity and cost of lithium-ion secondary batteries. Therefore, it is considered to reduce the amount of cobalt contained in the positive electrode active material and increase the amount of nickel. Has been done.

However, with such a measure, nickel oxide is likely to be formed on the surface of the positive electrode active material, and the structure of the positive electrode active material may become unstable. In particular, the formation of nickel oxide can not only increase the resistance of the positive electrode active material, but also cause a non-uniform lithium desorption reaction. Further, if the desorption reaction of lithium occurs locally in the positive electrode active material, there may be a problem that the cycle characteristics of the secondary battery are deteriorated.

The present invention has been made in view of such a background, and in the present invention, even when the amount of nickel with respect to cobalt is relatively increased, the cycle characteristics are unlikely to deteriorate for a lithium ion secondary battery. An object of the present invention is to provide a method for producing a positive electrode active material. Another object of the present invention is to provide a positive electrode active material for a lithium ion secondary battery in which cycle characteristics are unlikely to deteriorate, and further to provide a lithium ion secondary battery containing such a positive electrode active material.

In the present invention
To obtain a mixture by mixing first lithium metal composite oxide containing secondary particles composed of agglomerated primary particles, tungsten oxide, and water.
Drying the mixture to obtain a second lithium metal composite oxide
Have,
The first lithium metal composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), and element M as Li: Ni: Co: M = z: (1-xy) :. x: y (where 0.97 <z <1.30, 0≤x≤0.10, 0≤y≤0.10, 0≤x + y≤0.10, M is Mn, V, Mg, Mo. , Nb, Ti, and at least one element selected from Al), and contains tungsten in an amount of 0.1% by mass or more based on the total amount of the first lithium metal composite oxide. Contains 1.0% by mass or less
The mixture is used for producing a positive electrode active material for a lithium ion secondary battery, which contains 0.1% by mass or more and 0.5% by mass or less of tungsten in the tungsten oxide with respect to the entire first lithium metal composite oxide. A method is provided.

Here, in the production method of the present invention, the second lithium metal composite oxide contains lithium tungstate, and 0.2% by mass or more of tungsten is added to the whole of the second lithium metal composite oxide. It may contain 0.0% by mass or less.

Further, the water may be mixed in an amount of 1% by mass or more and 10% by mass or less with respect to the entire first lithium metal composite oxide.

Further, after mixing the first lithium metal composite oxide and the tungsten oxide, the water may be sprayed and mixed so that the average particle size of the droplets is 100 μm or less.

Further, the first lithium metal composite oxide may have a specific surface area of 0.5 cm ² / g or more and 2 m ² / g or less.

Further, the first lithium metal composite oxide may have a Karl Fischer moisture content of 0.05% by mass or more and 0.2% by mass or less at 300 ° C.

Further, the second lithium metal composite oxide contains secondary particles formed by aggregating a plurality of primary particles and lithium tungstate.
The area ratio of lithium tungstate having a particle size of 0.5 μm or more present on the surface of the secondary particles, which is obtained from the observation of the surface of the secondary particles using a scanning electron microscope, is the area of the entire observation surface. It may be 5% or less.

Further, the area ratio of lithium tungstate having a particle size of 0.5 μm or more existing on the surface may be 1% or less.

Further, the second lithium metal composite oxide may have a volume average particle size MV of 4 μm or more and 6 μm or less.

Further, in the present invention,
A positive electrode active material for lithium-ion secondary batteries
It contains secondary particles formed by aggregating a plurality of primary particles and lithium tungstate.
The atomic number ratio of lithium (Li), nickel (Ni), cobalt (Co), element M, and tungsten (W) is Li: Ni: Co: M: W = z: (1-xy): x. : Y: a (where 0.97 <z <1.30, 0 ≦ x ≦ 0.10, 0 ≦ y ≦ 0.10, 0 ≦ x + y ≦ 0.10, 0.0005 ≦ a ≦ 0.005 , M is represented by at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al).
The amount of tungsten present on the surface of the positive electrode active material 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 positive electrode active material. Provides a positive electrode active material that is 0.1% by mass or more and 1.0% by mass or less with respect to the entire positive electrode active material.

Here, the amount of tungsten present on the surface of the positive electrode active material may be 0.1 times or more and 1 time or less with respect to the amount of tungsten contained inside the positive electrode active material.

Further, the area ratio of lithium tungstate having a particle size of 0.5 μm or more present on the surface of the secondary particles, which is obtained from the observation of the surface of the secondary particles using a scanning electron microscope, is determined with respect to the entire observation surface. It may be 5% or less.

Further, the positive electrode active material may contain tungsten in an amount of 0.2% by mass or more and 1% by mass or less with respect to the entire positive electrode active material.

Further, the positive electrode active material may have a Karl Fischer moisture content of 0.05% or more and 0.2% or less at 300 ° C.

Further, the positive electrode active material may have a volume average particle size MV of 4 μm or more and 6 μm or less. ..

Further, the present invention provides a lithium ion secondary battery including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a positive electrode active material having the above-mentioned characteristics.

INDUSTRIAL APPLICABILITY The present invention can provide a method for producing a positive electrode active material for a lithium ion secondary battery, in which the cycle characteristics are unlikely to deteriorate even when the amount of nickel relative to cobalt is relatively increased. Further, in the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery in which deterioration of cycle characteristics is unlikely to occur, and further, a lithium ion secondary battery containing such a positive electrode active material. The production method of the present invention is easy and suitable for production on an industrial scale, and its industrial value is extremely large.

FIG. 1 is a diagram showing an example of a method for producing a positive electrode active material for a lithium ion 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 a lithium ion secondary battery according to an embodiment. FIG. 3 is a diagram showing an example of the first and second lithium metal composite oxides according to the embodiment. FIG. 4 is a diagram showing an example of the positive electrode active material according to the embodiment. FIG. 5 is a schematic explanatory view of a measurement example of impedance evaluation and an equivalent circuit used for analysis. FIG. 6 is a schematic cross-sectional view of the coin-type battery used for battery evaluation.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Further, in the drawings, in order to make each configuration easy to understand, a part is emphasized or a part is simplified, and the actual structure or shape, scale, etc. may be different. Hereinafter, a method for producing a positive electrode active material for a lithium ion secondary battery, a positive electrode active material for a lithium ion secondary battery, and a positive electrode active material for a secondary battery will be described with reference to the drawings.

(1) Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Battery FIGS. 1 and 2 show the positive electrode active material for lithium ion secondary battery (hereinafter, also referred to as “positive electrode active material 100”) according to the present embodiment. It is a figure which shows an example of the manufacturing method. Further, FIGS. 3 and 4 are schematic views showing an example of the first lithium metal composite oxide 10 and the second lithium metal composite oxide 20 according to the present embodiment, respectively.

As shown in FIG. 1, the method for producing the positive electrode active material 100 according to the present embodiment is to obtain a mixture by mixing the first lithium metal composite oxide 10 containing tungsten, tungsten oxide, and pure water. (Step S1) and drying the mixture to obtain a second lithium metal composite oxide 20 (step S2). The second lithium metal composite oxide 20 may be used as it is as the positive electrode active material 100, or after further performing other steps such as a crushing step for adjusting the particle size distribution, the positive electrode active material 100 May be used as.

The second lithium metal composite oxide 20 (for example, FIG. 4) obtained by the production method according to the present embodiment contains the conventional lithium metal composite oxide 10 containing W (for example, FIG. 3) alone. A secondary battery with improved cycle characteristics as compared with the case where it is used as a positive electrode active material or when a lithium metal composite oxide containing no W is used as a raw material instead of the first lithium metal composite oxide 10. Can be obtained. Further, the secondary battery using the second lithium metal composite oxide 20 (positive electrode active material 100) has the same battery characteristics even if the amount of tungsten used is smaller than that of the conventional positive electrode active material as described above. It can have and is excellent from the viewpoint of cost.

Although the details of the above reason are unknown, as shown in FIG. 3, the first lithium metal composite oxide 10 containing W forms a compound A1 containing tungsten on at least a part of the surface and the inside thereof. It is thought that there is. Then, in steps S1 and S2 described above, lithium in the first lithium metal composite oxide 10 reacts with tungsten oxide, and as shown in FIG. 4, the second lithium metal composite oxide 20 A compound A2 containing tungsten such as lithium tungstate is formed on the surface. Then, the electrolytic solution and the positive electrode active material 100 in the secondary battery due to the presence of the compounds A1 and A2 containing tungsten inside and on the entire surface of the positive electrode active material 100 (second lithium metal composite oxide 20). It is considered that a conduction path for Li ions is formed between the inside and the inside of the lithium ion, which facilitates the movement of lithium ions in and out.

Further, in the production method of the present invention, a compound containing tungsten is formed on the surfaces of the primary particles and the secondary particles of the lithium metal composite oxide. The presence of this low-resistance tungsten-containing compound significantly suppresses an increase in the resistance of the positive electrode active material even when the amount of nickel contained in the lithium metal composite oxide is relatively high with respect to the amount of cobalt. Can be done.

Further, as a result, the desorption of lithium ions becomes relatively uniform in the entire positive electrode active material, and the deterioration of the cycle characteristics of the positive electrode active material can be significantly suppressed.

Hereinafter, the method for producing the positive electrode active material of the present invention will be described in detail with reference to FIGS. 1 to 4.
[Mixing step: Step S1]
First, as shown in FIG. 1, the first lithium metal composite oxide 10, tungsten oxide, and water are mixed to obtain a mixture (step S1). Hereinafter, each material used in this step will be described with reference to FIGS. 3 and 4 as appropriate.

(First Lithium Metal Composite Oxide)
The first lithium metal composite oxide 10 contains secondary particles 2 formed by aggregating a plurality of primary particles 1, and also contains lithium (Li), nickel (Ni), cobalt (Co), and tungsten (W). ), And optionally the element M.

In the first lithium metal composite oxide 10, lithium (Li), nickel (Ni), cobalt (Co), and the element M are Li: Ni: Co: M = z :( 1-xy) :. x: y (where 0.97 <z <1.30, 0≤x≤0.10, 0≤y≤0.10, 0≤x + y≤0.10, M is Mn, V, Mg, Mo. , Nb, Ti and Al) are included in the atomic number ratio represented by (at least one element).

The first lithium metal composite oxide 10 contains an excess of lithium (z exceeds 1 in the above ratio), so that the lithium metal composite oxide 10 is liberated from the first lithium metal composite oxide 10 as described later. A part of it can be neutralized with tungsten oxide in the presence of water to easily form lithium tungstate.

The first lithium-containing metal composite oxide 10 overall composition is, for example, the general formula _{(1): 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 at least one selected from Mn, V, Mg, Mo, Nb, Ti and Al. It can be represented by a species element).

In the first lithium metal composite oxide 10, tungsten (W) is 0.1% by mass or more and 1.0% by mass or less, preferably 0.5% by mass, based on the entire first lithium metal composite oxide 10. % Or more and 1.0% by mass or less are included. When the first lithium metal composite oxide 10 contains tungsten in the above range, the amount of tangten oxide used for mixing (step S1) can be reduced, and the amount of tungsten in the entire positive electrode active material 100 can be reduced. However, it is possible to obtain a positive electrode active material having a high positive electrode resistance reducing effect while maintaining a high battery capacity.

In the first lithium metal composite oxide 10, the site where tungsten is present is not particularly limited. Tungsten may be present as a solid solution in the crystal of the first lithium metal composite oxide 10, and as shown in FIG. 3, the surface of the secondary particles 2 and the surface of the primary particles 1 arranged inside , Tungsten-containing compound A1 may be present at the grain boundaries between these primary particles 1. Further, a part of tungsten may be dissolved as a solid solution, and a part of the other part may be present as compound A1 containing tungsten. Examples of the compound A1 containing tungsten include lithium tungstate and the like. The type of compound A1 containing tungsten can be confirmed by powder X diffraction or the like.

The first lithium metal composite oxide 10 is not particularly limited as long as it has the above composition, and can be obtained by a known production method. An example of the method for producing the first lithium metal composite oxide 10 is shown in (i) to (iii) below.
(I) Using an aqueous solution containing Ni, Co, W, and optionally element M, neutralization crystallization is performed to prepare a transition metal composite hydroxide, which is used as a precursor and contains lithium. It is mixed with a compound and fired to obtain the first lithium metal composite oxide 10.
(Ii) After preparing a transition metal composite hydroxide containing Ni, Co excluding W and optionally element M, the transition metal composite hydroxide, a compound containing W, and a compound containing Li are mixed. Then, it is fired to obtain the first lithium metal composite oxide 10.
(Iii) At least a 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 the first lithium metal composite oxide 10.

Among these, from the viewpoint of uniformity of W distribution, the first lithium metal composite oxide 10 is produced preferably by the production methods of (i) and (ii), more preferably by the production method of (i). be able to. Further, since W added in the production method (i) is uniformly distributed in the transition metal composite hydroxide, W is generated on the surface of the secondary particles 2 when synthesized into the lithium metal composite oxide. And it is possible to coat the surface of the primary particles existing inside more uniformly.

In the production method of the present embodiment, the first lithium metal composite oxide 10 obtained by either the above production method or a production method other than the above can be used.

Further, when the surface of the first lithium metal composite oxide 10 is observed with a scanning electron microscope (SEM), it is preferable that compound A1 containing tungsten having a particle size of 0.5 μm or more is not observed. When compound A1 containing tungsten having a particle size of 0.5 μm or more is not observed on the surface, compound A1 containing sufficiently fine tungsten is present on the surface and inside of the first lithium metal composite oxide 10, and is described later. In combination with the compound A2 containing the above, the effect of further improving the battery capacity and reducing the resistance can be obtained. The particle size of the compound A1 containing tungsten can be set to 0.5 μm or less by using the above-mentioned production methods (i) and (ii).

Further, the amount of tungsten (W) present in the first lithium metal composite oxide 10 is preferably 0.1% by mass or more and 1.0 with respect to the entire first lithium metal composite oxide 10. It is mass% or less, more preferably 0.5 mass% or more and 1.0 mass% or less. Here, the amount of tungsten (W) existing inside means that the first lithium metal composite oxide 10 is dispersed in water in the tungsten (W) contained in the first lithium metal composite oxide 10. It refers to the amount of tungsten (W) remaining on the surface of the compound A1 containing tungsten without being eluted with water. When the amount of tungsten (W) existing inside the first lithium metal composite oxide 10 is in the above range, in the obtained positive electrode active material 100, the compound A1 containing tungsten existing inside the secondary particles 2 (for example, Lithium tungstate) and the tungsten-containing compound A2 (eg, lithium tungstate) formed on the surface of the secondary particles 2 in subsequent steps (steps S1 and S2) form a good conduction path for Li ions. The initial charge / discharge capacity, positive electrode resistance, and cycle characteristics can be further improved.

The amount of tungsten present inside the first lithium metal composite oxide 10 can be measured by the following method. First, the amount of tungsten (WT) in the entire first lithium metal composite oxide 10 is measured by ICP emission spectroscopic analysis (ICP method). Next, 5.0 g of the first lithium metal composite oxide 10 was placed in a beaker together with 100 ml of pure water, stirred and dispersed with a magnetic stirrer, stirred for 30 minutes, allowed to stand for 10 minutes, and then the supernatant was added. The amount of tungsten (W) eluted in the supernatant is measured by the ICP method. The supernatant amount of tungsten eluted, amount of tungsten present on the surface of the first lithium metal composite oxide 10 and (W _S), from the following formula, present within the first lithium metal composite oxide 10 tungsten amount of the _{(W I)} is calculated.

_Formula: W _{I =} W T -W _S

The first lithium metal composite oxide 10 is composed of, for example, as shown in FIG. 3, secondary particles 2 composed of lithium (Li), nickel (Ni), cobalt (Co), and optionally element M. The base metal and the compound A1 containing tungsten are contained.

Base material constituting the first lithium metal composite oxide 10, for example, the general formula _{(2): Li z Ni 1} -x-y Co x M y O 2 + α ( although, 0.97 <z <1.30 , 0 ≦ x ≦ 0.10, 0 ≦ y ≦ 0.10, 0 ≦ x + y ≦ 0.10, −0.2 ≦ α ≦ 0.2, M is Mn, V, Mg, Mo, Nb, Ti And at least one element selected from Al), and has a hexagonal layered crystal structure. A small amount of tungsten (W) may be dissolved in the primary particles constituting the base material.

The specific surface area of the first lithium metal composite oxide 10 is not particularly limited, but is preferably 0.5 m ² / g or more and 2 m ² / g or less. When the specific surface area is in the above range, the contact area with the electrolyte is in an appropriate range, and a positive electrode active material having a good balance between battery characteristics such as battery capacity and mechanical strength can be obtained. When the specific surface area is less than 0.5 m ² / g, the battery capacity of the obtained positive electrode active material 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 obtained positive electrode active material may be insufficient due to the porosity of the particle structure, which may cause a problem in stability during electrode manufacturing or use as an electrode. is there.

When the first lithium metal composite oxide 10 is mixed (step S1), the Karl Fischer moisture content at 300 ° C. is 0.05% by mass or more with respect to the entire first lithium metal composite oxide 10. It is preferably 2% by mass or less. When the water content exceeds 0.2% by mass, a gas component containing carbon and sulfur in the atmosphere may be absorbed to form a lithium compound on the surface of the first lithium metal composite oxide 10. The moisture content is a measured value when measured with a Karl Fischer moisture meter under the condition of a vaporization temperature of 300 ° C.

The particle structure of the first lithium metal composite oxide 10 is not particularly limited, and for example, as shown in FIG. 3, a hollow structure having a hollow portion 3 inside the secondary particles 2 may be provided. .. Further, the first lithium metal composite oxide 10 may have a solid structure, or may have a void structure having voids inside the secondary particles 2.

The first lithium metal composite oxide 10 can be mainly composed of secondary particles 2 formed by aggregating a plurality of primary particles 1, but in addition to the secondary particles 2, a small amount It may contain a single primary particle 1.

(Tungsten trioxide)
The tungsten oxide is not particularly limited, and known tungsten oxide can be used. Tungsten oxide can be represented, for example, by the chemical formula WO _n (2 ≦ n ≦ 3, n is a positive real number). The average particle size of tungsten oxide is preferably 1 μm or less. The lower limit of the average particle size of tungsten oxide is not particularly limited, but is, for example, 0.05 μm or more.

The mixed amount of tungsten oxide is an amount in which tungsten in tungsten oxide is contained in an amount of 0.1% by mass or more and 0.5% by mass or less with respect to the entire first lithium metal composite oxide 10. When the mixing amount of tungsten oxide is in the above range, a positive electrode active material having a high positive electrode resistance reducing effect can be obtained while maintaining a high battery capacity. Further, in the production method of the present embodiment, the amount of tungsten (W) in tungsten oxide is 0.1% by mass or more and 0.2% by mass or less with respect to the entire first lithium metal composite oxide 10. Even when the mixing amount of tungsten oxide is reduced, the above effect can be sufficiently obtained.

(water)
It is preferable to use pure water as the water. As will be described later, the water in the mixture includes an unreacted lithium compound present in the first lithium metal composite oxide 10 and excess lithium present in the crystal (hereinafter, these are collectively referred to as “surplus lithium”. ”) Is dissolved, and the mixed tungsten oxide can be dissolved.

The amount of water to be mixed is not particularly limited as long as it can sufficiently dissolve tungsten oxide in the mixture, but is, for example, 0.5% by mass or more and 40 with respect to the first lithium metal composite oxide 10. It can be mass% or less, preferably 1% by mass or more and 30% by mass or less, and more preferably 1% by mass or more and 10% by mass or less. When the amount of water to be mixed is a sufficient amount, the tungsten oxide is sufficiently permeated to the surface of the primary particles 1 inside the secondary particles 2, and the tungsten oxide is uniform even among the first lithium metal composite oxides 10. The output characteristics and cycle characteristics can be further improved. The amount of water to be mixed can be appropriately adjusted within the above range depending on the mixing amount of the first lithium metal composite oxide 10 to be used, the particle structure, and the like, and the mixture is mixed within a range that does not form a paste. Is preferable.

(Mixing method)
The method for mixing the first lithium metal composite oxide 10, tungsten oxide, and water is not particularly limited, and these may be added at the same time and mixed by a known mixing device, or added separately. Then, it may be mixed by a known mixing device.

FIG. 2 shows an example of a method that can be suitably used in the method for producing a positive electrode active material according to the present embodiment. As shown in FIG. 2, in the step of mixing the first lithium metal composite oxide, tungsten oxide, and water (step S1), the first lithium metal composite oxide and tungsten oxide are mixed. It is preferable to include the mixing step of 1 (step S11) and the second mixing step (step S12) of spraying and mixing the obtained mixture with water. Hereinafter, each mixing step will be described.

[First mixing step: step S11]
First, the first lithium metal composite oxide 10 and tungsten oxide are mixed (step S11). By dry-mixing these powders with each other, tungsten oxide can be more uniformly dispersed in the first lithium metal composite oxide 10.

The mixing amount of tungsten oxide is preferably an amount in which tungsten (W) in tungsten oxide is contained in an amount of 0.1% by mass or more and 0.5% by mass or less with respect to the first lithium metal composite oxide 10. When the mixing amount of tungsten oxide is less than 0.1% by mass, excess lithium such as lithium hydroxide liberated on the surface of the first lithium metal composite oxide 10 cannot be neutralized, so that the slurry is sufficiently stable. Sex and output may not be obtained. On the other hand, when the mixed amount of tungsten oxide exceeds 0.5% by mass, the particle size of lithium tungstate crystallized on the surface of the second lithium metal composite oxide 20 in the subsequent step (step S2). The number of particles having a size of 0.5 μm or more increases, and a sufficient battery capacity may not be obtained.

[Second mixing step: step S12]
Then, water is sprayed and mixed with the obtained mixture of the first lithium metal composite oxide and tungsten oxide (step S12). As a result, in the presence of water, the neutralization reaction between the excess lithium such as lithium hydroxide liberated on the surface of the first lithium metal composite oxide 10 and tungsten oxide can proceed more uniformly.

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 first lithium metal composite oxide 10. When the amount of water to be sprayed is less than 1% by mass, the above-mentioned effects due to the addition of water are poorly exhibited, and tungsten oxide may remain. On the other hand, when the amount of water to be sprayed exceeds 10% by mass, the third lithium metal composite oxide (base material) elutes into water from water spraying (step S12) to drying (step S2). The amount of Li (the amount of excess lithium) may be excessive, the Li content in the obtained positive electrode active material may decrease, and the effect of reducing resistance may not be sufficient. Further, when the amount of water to be sprayed exceeds 10% by mass, the water content in the second lithium metal composite oxide 20 (positive electrode active material) is lowered, so that a long drying time is required and the productivity is lowered. I have something to do.

The water particles to be sprayed are preferably in a mist state with an average particle size of 100 μm or less. When atomized water is added, the neutralization reaction between excess lithium and tungsten oxide can proceed more uniformly in the vicinity of the surface of the first lithium metal composite oxide 10, and the second lithium metal composite oxide can proceed more uniformly. The particle size of the tungsten-containing compound A2 formed on the surface of 20 can be set in a suitable range. On the other hand, when the average particle size of the pure water to be sprayed is larger than 100 μm, the amount of Li eluted between the positive electrode active material to which water is directly supplied by spraying and the positive electrode active material to which water is supplied by stirring after spraying. May cause non-uniformity in the reaction.

[Drying step: Step S2]
Then, as shown in FIGS. 1 and 2, the mixture obtained by mixing the first lithium metal composite oxide 10, tungsten oxide, and water was dried to dry the second lithium metal composite oxide. 20 is obtained (step S2). The second lithium metal composite oxide 20 is lithium tungstate (compound A2 containing tungsten) formed by reacting tungsten oxide with excess lithium in the first lithium metal composite oxide 10 in the presence of water. )including.

(Drying conditions)
The drying temperature is not particularly limited, and the moisture content may be sufficiently reduced, but for example, 500 ° C. or lower is preferable. When the drying temperature exceeds 500 ° C., lithium is further liberated from the inside of the lithium metal composite oxide powder, so that sufficient slurry stability cannot be obtained. The lower limit of the drying temperature is not particularly limited, but is, for example, 100 ° C. or higher. Further, the pressure at the time of drying is preferably 1 atm or less. If it is higher than 1 atm, the water content may not drop sufficiently. The drying time is not particularly limited, and the moisture content may be sufficiently reduced, but is, for example, about 5 hours or more and 24 hours or less.

(Second lithium metal composite oxide)
FIG. 4 is a schematic view showing an example of the second lithium metal composite oxide 20 (positive electrode active material 100) obtained in the drying step (step S2). The second lithium metal composite oxide 20 contains compound A2 containing tungsten in the vicinity of its surface. Compound A2 containing tungsten contains lithium tungstate. Lithium tungstate is formed by the reaction of lithium in the first lithium metal composite oxide 10 with tungsten oxide in the presence of water. Lithium tungstate is formed on the surface of the secondary particles 2 and at least a part of the surface of the primary particles 1 arranged inside.

Further, the second lithium metal composite oxide 20 is a compound A1 containing tungsten derived from tungsten contained in the first lithium metal composite oxide 10 and lithium tungstate formed by the above-mentioned steps S1 and S2. It may have both the compound A2) containing tungsten.

The entire second lithium metal composite oxide 20 (including compounds A1 and A2 containing tungsten) contains tungsten, for example, 0.2% by mass or more and 1.2% by mass with respect to the entire second lithium metal composite oxide. % Or less, preferably 0.2% by mass or more and 1% by mass or less.

The amount of tungsten present on the surface of the second lithium metal composite oxide 20 is preferably 0.1% by mass or more and 1.0% by mass or less, more preferably, with respect to the entire second lithium metal composite oxide 20. It is 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 second lithium metal composite oxide 20 is within the above range, the tungsten-containing compound A1 (for example, lithium tungstate) existing inside the secondary particle 2 and the surface of the secondary particle 2 It is considered that the lithium tungstate formed in the above can form a good conduction path for Li ions, and the initial charge / discharge capacity, positive electrode resistance, and cycle characteristics can be further improved in the secondary battery. Be done.

The amount of tungsten present inside the second lithium metal composite oxide 20 is preferably 0.1% by mass or more and 1.0% by mass or less, more preferably, with respect to the entire second lithium metal composite oxide 20. Is 0.5% by mass or more and 1.0% by mass or less. Since the compound A2 containing tungsten is mainly formed near the surface of the second lithium metal composite oxide 20, the amount of tungsten present inside the second lithium metal composite oxide 20 is the amount of the first lithium metal. The amount may be substantially the same as the amount of tungsten inside the composite oxide 10.

Incidentally, amount of tungsten present on the surface and inside of the second lithium-containing metal composite oxide 20, a tungsten weight W _S existing surface and in the interior of the first lithium metal composite oxide 10 described _above, similar to the W _I It can be measured by the method.

It is preferable that the second lithium metal composite oxide 20 does not have residual tungsten oxide used as a raw material. If tungsten oxide remains, the positive electrode resistance may not be sufficiently reduced in the secondary battery. The presence or absence of residual tungsten oxide can be confirmed by a qualitative method such as powder X-ray diffraction.

(2) Positive Electrode Active Material for Lithium Ion Secondary Battery The positive electrode active material for lithium ion secondary battery (hereinafter, also referred to as “positive electrode active material”) according to the present embodiment can be easily manufactured by the above-mentioned manufacturing method. be able to. For example, as shown in FIG. 4, the positive electrode active material 100 contains at least secondary particles 2 formed by aggregating a plurality of primary particles 1 and lithium tungstate (compounds A1 and A2 containing tungsten). Hereinafter, each configuration will be described.

[composition]
In the positive electrode active material 100, the atomic number ratios of lithium (Li), nickel (Ni), cobalt (Co), and element M are Li: Ni: Co: M = z: (1-xy): x. : Y (where 0.97 <z <1.30, 0≤x≤0.10, 0≤y≤0.10, 0≤x + y≤0.10, M is Mn, V, Mg, Mo, It is represented by at least one element selected from Nb, Ti and Al).

The positive electrode active material 100, a composition excluding tungsten, for example, the general formula _{(3): Li z Ni 1} -x-y Co x M y O 2 + α ( although, 0.97 <z <1.30,0 ≦ x≤0.10, 0≤y≤0.10, 0≤x + y≤0.10, -0.2≤α≤0.2, M is from Mn, V, Mg, Mo, Nb, Ti and Al. It is represented by at least one element selected). Further, the primary particles 1 and the secondary particles 2 constituting the positive electrode active material 100 have a hexagonal layered crystal structure.

The positive electrode active material 100 may contain a small amount of tungsten (W) inside the primary particles 1. When tungsten is contained inside the primary particle 1, for example, tungsten may be dissolved in the crystallites constituting the primary particle 1, and exists as a tungsten compound at the grain boundary between the crystallites constituting the primary particle 1. You may.

[Lithium tungstate]
At least a portion of lithium tungstate is present on the surface of the secondary particles 2. The positive electrode active material 100 obtained by the above-mentioned production method is the first in the presence of lithium tungstenate (compound A1 containing tungsten) derived from the tungsten compound contained in the first lithium metal composite oxide 10 and water. Lithium sulfonate (compound A2 containing tungsten) formed by the reaction of Li compound eluted from the lithium metal composite oxide 10 of the above and tungsten oxide is contained.

The area ratio of lithium tungstate having a particle size of 0.5 μm or more present on the surface of the secondary particles 2 determined from the observation of the surface of the secondary particles 2 using a scanning electron microscope (SEM) is the entire observation area. On the other hand, it is preferably 5% or less, and more preferably 1% or less. When the area ratio of lithium tungstate having a particle size of 0.5 μm or more is within the above range, the positive electrode resistance can be further reduced in the secondary battery while suppressing the decrease in battery capacity. On the other hand, when the area ratio of lithium tungstate 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 increases, so that the cycle characteristics are deteriorated. May decrease.

The area ratio of lithium tungstate is such that the surface of the secondary particles 2 is observed by SEM, and the area of the entire surface of the secondary particles 2 on the observation surface is measured by image analysis or the like to obtain a particle size of 0.5 μm or more. It can be calculated by dividing by the area occupied by lithium tungstate having. The area of the entire surface of the secondary particles 2 includes a portion covered with lithium tungstate.

Specifically, the area ratio of lithium tungstate is such that the surfaces of a plurality of secondary particles 2 are observed, and for example, among the secondary particles 2 in the visual field, 50 particles having a particle size close to the volume average particle size (MV) are selected. Randomly selected, the area occupied by the entire particle surface and the area occupied by lithium tungstenate having a particle size of 0.5 μm or more were obtained for these 50 particles, and the area occupied by the entire observation surface was determined. It can be obtained by calculating the area ratio (%) occupied by lithium tungstate having a particle size of 0.5 μm or more.

It is preferable that the positive electrode active material 100 does not substantially contain tungsten oxide. Here, "substantially free of tungsten oxide" means that tungsten oxide cannot be detected by a qualitative method such as powder X-ray diffraction. When tungsten oxide is detected in the positive electrode active material 100, it indicates that the tungsten oxide used as a raw material 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 100 is preferably 0.1% by mass or more and 1.0% by mass or less, and more preferably 0.1% by mass or more and 0.5% by mass with respect to the entire positive electrode active material 100. % Or less is preferable. When the amount of tungsten present on the surface of the positive electrode active material 100 is within the above range, the compound A1 containing tungsten (for example, lithium tungstate) existing inside the secondary particles 2 and the tungsten formed on the surface of the secondary particles 2 It is considered that lithium acid can form a good conduction path for Li ions, and the initial charge / discharge capacity, positive electrode resistance, and cycle characteristics can be further improved in the secondary battery.

The amount of tungsten present inside the positive electrode active material 100 is preferably 0.1% by mass or more and 1.0% by mass or less, and more preferably 0.3% by mass or more and 1.0% by mass with respect to the entire positive electrode active material 100. % Or less. Since lithium tungstate (compound A2 containing tungsten) is mainly formed near the surface of the positive electrode active material 100, the amount of tungsten present inside the positive electrode active material 100 is inside the first lithium metal composite oxide 10. The amount may be substantially the same as the amount of tungsten in. Further, the amount of tungsten present on the surface of the positive electrode active material is preferably 0.1 times or more and 1 time or less with respect to the amount of tungsten contained inside the positive electrode active material.

Incidentally, amount of tungsten present on the surface and inside of the positive electrode active material 100 is tungsten weight W _S existing surface and in the interior of the first lithium metal composite oxide 10 described _above, it is measured by the same method as W _I Can be done.

Further, the content of tungsten in the entire positive electrode active material 100 is, for example, 0.2% by mass or more and 1.2% by mass or less, and 0.2% by mass or more and 1% by mass or less with respect to the entire positive electrode active material. Is preferable. By setting the tungsten content in the above range, the positive electrode resistance can be reduced while maintaining a high battery capacity.

The present form of tungsten in the positive electrode active material 100 is not particularly limited, and as described above, it may exist as lithium tungstate and is solid-solved in the crystals constituting the primary particles 1 or the secondary particles 2. May exist.

Further, lithium tungstate may be present not only on the surface of the secondary particles 2 but also inside the secondary particles 2. Further, lithium tungstate may be present on the surface of the secondary particles 2 and the surface of the primary particles 1 existing inside, or may be present at the grain boundaries between the primary particles 1.

The positive electrode active material 100 preferably has a Karl Fischer moisture content of 0.05% or more and 0.2% or less at 300 ° C. If the water content exceeds 0.2%, the compatibility with the solvent contained in the positive electrode mixture paste may be hindered, and the film formation by coating and drying may become inhomogeneous.

The positive electrode active material 100 has a volume average particle size MV of preferably 3 μm or more and 15 μm or less, and more preferably 4 μm or more and 6 μm or less. When the volume average particle size MV is in the above range, the specific surface area is large, and when used for the positive electrode, not only a sufficient reaction area with the electrolytic solution can be secured, but also the positive electrode is made thin and lithium ions are formed. The moving distance between the positive electrode and the negative electrode can be shortened. The volume average particle size MV is a value measured by the laser light diffraction / scattering method.

Further, the positive electrode active material 100 has a pH at 25 ° C. when 5 g of the positive electrode active material is dispersed in 100 ml of pure water and allowed to stand for 10 minutes, and then the supernatant is measured (hereinafter, simply “pH value of the positive electrode active material”). Also referred to as) is preferably 11 or more and 11.9 or less. By dispersing 5 g of the positive electrode active material 100 in 100 ml of pure water and measuring the pH of the supernatant after allowing it to stand for 10 minutes, a surplus in the paste when a paste was prepared using the positive electrode active material 100. The degree of lithium elution can be evaluated. When the pH of the positive electrode active material 100 is controlled within a specific range, the battery characteristics can be improved and the gelation of the paste can be suppressed.

[Lithium-ion secondary battery]
The lithium ion secondary battery of the present embodiment (hereinafter, also referred to as “secondary battery”) can have a positive electrode containing the above-mentioned positive electrode active material.

Hereinafter, one configuration example of the secondary battery of the present embodiment will be described for each component. The secondary battery of the present embodiment includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte, and is composed of the same components as a general lithium ion secondary battery. The embodiment described below is merely an example, and the lithium ion secondary battery of the present embodiment is implemented in a form in which various changes and improvements are made based on the knowledge of those skilled in the art, including the following embodiment. can do. Moreover, the use of the secondary battery is not particularly limited.

(Positive electrode)
The positive electrode of the secondary battery of the present embodiment may contain the above-mentioned positive electrode active material.

An example of a method for manufacturing a positive electrode will be described below. First, the above-mentioned positive electrode active material (powder), conductive material and binder (binder) are mixed to form a positive electrode mixture, and if necessary, activated carbon or a solvent for viscosity adjustment or the like is added. This can be kneaded to prepare a positive electrode mixture paste.

Since the mixing ratio of each material in the positive electrode mixture is a factor that determines the performance of the lithium ion secondary battery, it can be adjusted according to the application. The mixing ratio of the materials can be the same as that of the positive electrode of a known lithium ion secondary battery. For example, when the total mass of the solid content of the positive electrode mixture excluding the solvent is 100% by mass, the positive electrode active material is used. The conductive material can be contained in a proportion of 60% by mass or more and 95% by mass or less, the conductive material in an amount of 1% by mass or more and 20% by mass or less, and the binder in an amount of 1% by mass or more and 20% by mass or less.

The obtained positive electrode mixture paste is applied to the surface of a current collector made of aluminum foil, for example, and dried to disperse the solvent to prepare a sheet-shaped positive electrode. If necessary, pressurization can be performed by a roll press or the like in order to increase the electrode density. The sheet-shaped positive electrode thus obtained can be cut into an appropriate size according to the target battery and used for manufacturing the battery.

As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black and Ketjen black (registered trademark), and the like can be used.

As a binder, it plays a role of binding active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylenepropylene diene rubber, styrene butadiene, cellulose-based One or more kinds selected from resin, polyacrylic acid and the like can be used.

If necessary, a positive electrode active material, a conductive material, or the like can be dispersed, and a solvent that dissolves the binder can be added to the positive electrode mixture. Specifically, as the solvent, 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.

The method for producing the positive electrode is not limited to the above-described example, and other methods may be used. For example, it can be produced by press-molding a positive electrode mixture and then drying it in a vacuum atmosphere.

(Negative electrode)
As the negative electrode, metallic lithium, a lithium alloy, or the like can be used. For the negative electrode, a binder is mixed with a negative electrode active material that can occlude and desorb lithium ions, and a paste-like negative electrode mixture is added to a suitable solvent on the surface of a metal leaf current collector such as copper. It may be coated, dried, and if necessary, compressed to increase the electrode density.

As the negative electrode active material, for example, a calcined organic compound such as natural graphite, artificial graphite and phenol resin, and a powdered carbon substance such as coke can be used. In this case, a fluororesin such as PVDF can be used as the negative electrode binder as in the case of the positive electrode, and an organic such as N-methyl-2-pyrrolidone can be used as the solvent for dispersing these active substances and the binder. A solvent can be used.

(Separator)
A separator can be sandwiched between the positive electrode and the negative electrode, if necessary. As the separator, a positive electrode and a negative electrode are separated to retain an electrolyte, and a known one can be used. For example, a thin film such as polyethylene or polypropylene, which has a large number of fine pores, may be used. it can.

(Non-aqueous electrolyte)
As the non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used.

As the non-aqueous electrolytic solution, for example, a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent can be used. Further, as the non-aqueous electrolyte solution, one in which a lithium salt is dissolved in an ionic liquid may be used. The ionic liquid is a salt that is composed of cations and anions other than lithium ions and is liquid even at room temperature.

Examples of the organic solvent 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, and tetrahydrofuran and 2-methyltetrahydrofuran. And ether compounds such as dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesulton, phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or two or more thereof may be mixed. It can also be used.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and a composite salt thereof can be used. Further, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant and the like.

Moreover, you may use a solid electrolyte as a non-aqueous electrolyte. The solid electrolyte has a property of being able to withstand a high voltage. Examples of the solid electrolyte include an inorganic solid electrolyte and an organic solid electrolyte.

Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.

The oxide-based solid electrolyte is not particularly limited, and for example, an oxide-based solid electrolyte containing oxygen (O) and having lithium ion conductivity and electron insulating property can be preferably used. Examples of the oxide-based solid electrolyte include lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _X , LiBO ₂ N _X , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO _4- Li ₃ PO ₄ , Li ₄ SiO _4- Li ₃ VO ₄ , Li ₂ O-B ₂ O _3- P ₂ O ₅ , Li ₂ O-SiO ₂ , Li ₂ O-B ₂ O _3- ZnO, Li _{1 + X} Al _X Ti _2-X (PO ₄ ) ₃ (0 ≦ X ≦ 1), Li _{1 + X} Al _X Ge _2-X (PO ₄ ) ₃ (0 ≦ X ≦ 1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2 / 3-X} TiO ₃ (0 ≤ X ≤ 2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 One or more types selected from P _0.4 O _{4 and the} like can be used.

The sulfide-based solid electrolyte is not particularly limited, and for example, one containing sulfur (S) and having lithium ion conductivity and electron insulating property can be preferably used. Examples of the sulfide-based solid electrolyte include Li ₂ S-P ₂ S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ S-P ₂ S ₅ , LiI-Li _{2. S-B 2 S 3, Li} 3 PO 4 -Li 2 S-Si 2 S, Li 3 PO 4 -Li 2 S-SiS 2, LiPO 4 -Li 2 S-SiS, LiI-Li 2 S-P 2 O One or more types selected from ₅ , LiI-Li ₃ PO _4- P ₂ S _{5 and the} like can be used.

As the inorganic solid electrolyte, an electrolyte other than the above may be used, and for example, Li ₃ N, LiI, Li ₃ N-LiI-LiOH or the like may be used.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity, and for example, polyethylene oxide, polypropylene oxide, copolymers thereof and the like can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt).

(Shape and configuration of secondary battery)
The lithium ion secondary battery of the present embodiment described as described above can have various shapes such as a cylindrical shape and a laminated shape. Regardless of which shape is adopted, if the secondary battery of the present embodiment uses a non-aqueous electrolyte solution as the non-aqueous electrolyte, the positive electrode and the negative electrode are laminated via a separator to form an electrode body. The obtained electrode body is impregnated with a non-aqueous electrolyte solution, and a lead for collecting current is provided between the positive electrode current collector and the positive electrode terminal communicating with the outside, and between the negative electrode current collector and the negative electrode terminal communicating with the outside. It can be connected using such as, and the structure can be sealed in the battery case.

As described above, the secondary battery of the present embodiment is not limited to the form in which the non-aqueous electrolyte solution is used as the non-aqueous electrolyte. For example, the secondary battery using a solid non-aqueous electrolyte, that is, all. It can also be a solid-state battery. In the case of an all-solid-state battery, the configurations other than the positive electrode active material can be changed as needed.

The secondary battery of the present embodiment can suppress the generation of gas and is excellent in storage stability. Therefore, it can be particularly preferably used for a battery that is easily affected by gas generation, such as a laminated battery. Further, since the secondary battery of the present embodiment can stabilize the battery characteristics by suppressing the generation of gas, it can be suitably used for batteries other than the laminated type.

The secondary battery of the present embodiment can be used for various purposes, but since it can be a high-capacity, high-output secondary battery, for example, a small portable electronic device (notebook) that always requires a high capacity. It is suitable as a power source for (type personal computers, mobile phone terminals, etc.), and is also suitable as a power source for electric vehicles that require high output.

Further, since the secondary battery of the present embodiment can be miniaturized and has a high output, it is suitable as a power source for an electric vehicle whose mounting space is restricted. The secondary battery of the present embodiment can be used not only as a power source for an electric vehicle driven by purely electric energy, but also as a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine. it can.

(Characteristic)
The lithium ion secondary battery using the positive electrode active material of the present embodiment has a high capacity and a high output.

The lithium ion secondary battery using the positive electrode active material according to the present invention obtained in a particularly preferable form has a high initial discharge capacity of 150 mAh / g or more and a low positive electrode resistance when used for the positive electrode of a 2032 type coin battery, for example. Is obtained.

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 general AC impedance method as an electrochemical evaluation method, the Nyquist diagram based on the solution resistance, the negative electrode resistance and the negative electrode capacitance, and the positive electrode resistance and the positive electrode capacitance is shown in FIG. Obtained like this.

The battery reaction at the electrode consists of a resistance component due to charge transfer and a capacitance component due to the electric double layer. When these are represented by an electric circuit, it becomes a parallel circuit of resistance and capacitance, and the battery as a whole is a solution resistance, a negative electrode, and a positive electrode in parallel. It is represented by an equivalent circuit in which the circuits are connected in series. Fitting calculation can be performed on the Nyquist diagram measured using this equivalent circuit, and each resistance component and capacitance component can be estimated. The positive electrode resistance is equal to the diameter of the resulting semicircle on the low frequency side of the Nyquist diagram.

From the above, the positive electrode resistance can be estimated by measuring the AC impedance of the manufactured positive electrode and calculating the fitting of the obtained Nyquist diagram with an equivalent circuit.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. As described below, a battery was manufactured using the positive electrode active material prepared in each Example and Comparative Example, and the evaluation was carried out. First, a battery manufacturing method and an evaluation method will be described.

(Battery manufacturing and evaluation)
A 2032 type coin-type battery 10 (hereinafter referred to as a coin-type battery) shown in FIG. 6 was used for the evaluation of the positive electrode active material.

As shown in FIG. 6, the coin-type battery 10 is composed of a case 11 and an electrode 12 housed in the case 11.

The case 11 has a positive electrode can 11a that is hollow and has one end opened, and a negative electrode can 11b that is arranged in the opening of the positive electrode can 11a. When the negative electrode can 11b is arranged in the opening of the positive electrode can 11a, , A space for accommodating the electrode 12 is formed between the negative electrode can 11b and the positive electrode can 11a.

The electrode 12 is composed of a positive electrode 12a, a separator 12c, and a negative electrode 12b, and is laminated so as to be arranged in this order. The positive electrode 12a contacts the inner surface of the positive electrode can 11a via a current collector 13, and the negative electrode 12b collects. It is housed in the case 11 so as to come into contact with the inner surface of the negative electrode can 11b via the electric body 13. A current collector 13 is also arranged between the positive electrode 12a and the separator 12c.

The case 11 is provided with a gasket 11c, and the gasket 11c fixes the relative movement of the case 11 so as to maintain a non-contact state between the positive electrode can 11a and the negative electrode can 11b. Further, the gasket 11c also has a function of sealing the gap between the positive electrode can 11a and the negative electrode can 11b to seal the inside and the outside of the case 11 in an airtight and liquidtight manner.

The coin-type battery 10 shown in FIG. 6 above was manufactured as follows.

First, 52.5 mg of the positive electrode active material for a lithium ion secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) prepared in the following Examples and Comparative Examples were mixed, and the diameter was 11 mm at a pressure of 100 MPa. , Press-molded to a thickness of 100 μm to prepare a positive electrode 12a. The prepared positive electrode 12a was dried in a vacuum dryer at 120 ° C. for 12 hours.

Using the positive electrode 12a, the negative electrode 12b, the separator 12c, and the electrolytic solution, the above-mentioned coin-type battery 10 was produced in a glove box having an Ar atmosphere with a dew point controlled at −80 ° C.

For the negative electrode 12b, a graphite powder having an average particle diameter of about 20 μm punched into a disk shape having a diameter of 14 mm and a negative electrode sheet coated with polyvinylidene fluoride on a copper foil were used.

A polyethylene porous membrane having a film thickness of 25 μm was used for the separator 12c. As the electrolytic solution, an equal amount mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO ₄ as a supporting electrolyte (manufactured by Tomiyama Pure Chemical Industries, Ltd.) was used.

The initial discharge capacity and cycle characteristics indicating the performance of the manufactured coin-type battery 10 were evaluated as follows.

The initial discharge capacity is set to 0.1 mA / cm ² for the positive electrode after the open circuit voltage OCV (Open Circuit Voltage) is stabilized by leaving the coin-type battery 10 for about 24 hours after being manufactured, and the cutoff voltage 4 The initial discharge capacity was defined as the capacity when the battery was charged to 3 V, paused for 1 hour, and then discharged to a cutoff voltage of 3.0 V.

In addition, the cycle characteristics of the obtained coin-type battery were evaluated as a battery evaluation. The cycle characteristics were evaluated by measuring the capacity retention rate after 200 cycles of charging and discharging. Specifically, the produced coin-type battery is charged to a cutoff voltage of 4.3 V in a constant temperature bath held at 25 ° C. with a current density of 0.3 mA / cm ² , and cut after a one-hour rest. After conditioning to repeat the cycle of discharging to an off voltage of 3.0 V for 5 cycles, the current density is set to 2.0 mA / cm ² and the cut-off voltage is charged to 4.3 V in a constant temperature bath maintained at 60 ° C. After a one-hour rest, the cycle of discharging to a cutoff voltage of 3.0 V was repeated for 200 cycles, and the discharge capacity of each cycle was measured for evaluation.

Then, only the lithium metal composite oxide has a capacity retention rate that is the ratio obtained by dividing the discharge capacity obtained in the first cycle after conditioning of the coin-type battery by the discharge capacity obtained in the cycle 200 cycles after conditioning. When it was higher than the case evaluated in, it was judged that the cycle characteristics were excellent.

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

Hereinafter, each condition of Examples and Comparative Examples will be described.

[Example 1]
(Manufacturing of the first lithium metal composite oxide)
Using a known crystallization method, the first lithium metal composite oxide represented by Li _1.20 Ni _0.91 Co _0.05 Al _0.04 W _0.0037 O ₂ (W: 0.7 wt%) , Specific surface area 1.2 cm ² / g) was obtained. Specifically, Ni, Co by a continuous crystallization method 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. , Al and W-containing transition metal composite hydroxides were synthesized. Lithium hydroxide was mixed with the obtained transition metal composite hydroxide and then calcined to obtain the first lithium metal composite oxide.

(Mixing process)
To the first lithium metal composite oxide, tungsten oxide (manufactured by Nippon Inorganic Chemical Industry Co., Ltd.) having an amount of tungsten oxide of 0.2% by mass based on the total amount of the first lithium metal composite oxide was added and mixed. After that, water was sprayed at 2% by mass on the entire first lithium metal composite oxide in a mist state having an average particle size of 100 μm or less, further mixed, and then dried at 150 ° C. for 12 hours. Lithium metal composite oxide was obtained. Table 1 shows the characteristics of the obtained second lithium metal composite oxide (positive electrode active material). The volume average particle size (MV) of the positive electrode active material was 11.6 μm.
[Battery evaluation]
The battery characteristics of the coin-type battery 1 having a positive electrode formed by using the obtained positive electrode material were evaluated.

The initial discharge capacity in Example 1 was 213.0 mAh / g, the discharge capacity after 200 cycles was 171.5 mAh / g, and the capacity retention rate before and after the cycle was 80.5%.
Hereinafter, with respect to Examples 2 to 9 and Comparative Examples 1 to 5, only the conditions changed from Example 1 are shown. Table 1 shows the evaluation values of the initial discharge capacity and the cycle characteristics of Examples 1 to 9 and Comparative Examples 1 to 5.
[Example 2]
The positive electrode active material for the lithium ion secondary battery was prepared in the same manner as in Example 1 except that the amount of tungsten oxide added was 0.1 wt% of the total amount of the first lithium metal composite oxide. At the same time, the battery characteristics were evaluated, and the results are shown in Table 1.
[Example 3]
The positive electrode active material for the lithium ion secondary battery was prepared in the same manner as in Example 1 except that the amount of tungsten oxide added was 0.4 wt% with respect to the total amount of the first lithium metal composite oxide. At the same time, the battery characteristics were evaluated, and the results are shown in Table 1.
[Example 4]
Table 1 shows the results obtained by obtaining a positive electrode active material for a lithium ion secondary battery and evaluating the battery characteristics in the same manner as in Example 3 except that the amount of pure water sprayed was 1 wt%.
[Example 5]
Table 1 shows the results obtained by obtaining a positive electrode active material for a lithium ion secondary battery and evaluating the battery characteristics in the same manner as in Example 3 except that the amount of pure water sprayed was 10 wt%.
[Example 6]
Table 1 shows the results obtained by obtaining a positive electrode active material for a lithium ion secondary battery and evaluating the battery characteristics in the same manner as in Example 1 except that the amount of pure water sprayed was 0.5 wt%.
[Example 7]
The positive electrode active material for a lithium ion secondary battery was obtained and the battery characteristics were evaluated in the same manner as in Example 3 except that the amount of pure water sprayed was 20 wt%, and the results are shown in Table 1.
[Example 8]
The amount of tungsten oxide added is set so that the amount of tungsten is 0.5 wt% with respect to the first lithium metal composite oxide powder, and the first lithium metal composite remains in a liquid state without atomizing water. A positive electrode active material for a lithium ion secondary battery was obtained and the battery characteristics were evaluated in the same manner as in Example 1 except that 2% by mass was added to the entire oxide, and the results are shown in Table 1.
[Example 9]
The positive electrode active material for a lithium ion secondary battery is the same as in Example 8 except that 0.5% by mass is added to the entire first lithium metal composite oxide in a liquid state without atomizing water. The battery characteristics were evaluated and the results are shown in Table 1.
[Comparative Example 1]
Table 1 shows the results obtained by obtaining a positive electrode active material for a lithium ion secondary battery and evaluating the battery characteristics in the same manner as in Example 1 except that tungsten oxide was added and pure water was not sprayed.
[Comparative Example 2]
The positive electrode active material for the lithium ion secondary battery was prepared in the same manner as in Example 1 except that the amount of tungsten oxide added was 0.05 wt% with respect to the first lithium metal composite oxide powder. At the same time, the battery characteristics were evaluated, and the results are shown in Table 1.
[Comparative Example 3]
The positive electrode active material for the lithium ion secondary battery was prepared in the same manner as in Example 1 except that the amount of tungsten oxide added was 0.7 wt% with respect to the first lithium metal composite oxide powder. At the same time, the battery characteristics were evaluated, and the results are shown in Table 1.
[Comparative Example 4]
The first lithium metal composite oxide is a lithium metal composite oxide represented by Li _1.20 Ni _0.91 Co _0.05 Al _0.04 W _0.0037 O ₂ (W: 0.9 wt% content). In the same manner as in Example 1 except that the above was used and tungsten oxide was not added, a positive electrode active material for a lithium ion secondary battery was obtained and the battery characteristics were evaluated, and the results are shown in Table 1.
[Comparative Example 5]
The first lithium metal composite oxide does not contain W, and a lithium metal composite oxide represented by Li _1.20 Ni _0.91 Co _0.05 Al _0.04 O ₂ is used, and the amount of tungsten oxide added is adjusted. The same as in Example 1 except that the amount of tungsten is 0.9 wt% (0.32 mol% with respect to the total number of moles of Ni, Co, and M) with respect to the first lithium metal composite oxide powder. Then, a positive electrode active material for a lithium ion secondary battery was obtained and the battery characteristics were evaluated, and the results are shown in Table 1.

実施例１、６及び比較例４、５で得られた正極活物質は、正極活物質全体に含まれるタングステン量が同一であるが、実施例で得られた正極活物質の方が、比較例で得られた正極活物質よりも、より高い初期放電容量と、２００サイクル後の放電容量維持率を示した。よって、本実施形態の製造方法を用いて得られる正極活物質は、少ないタングステン使用量で、より高い電池特性を有することができる。

The positive electrode active materials obtained in Examples 1 and 6 and Comparative Examples 4 and 5 have the same amount of tungsten contained in the entire positive electrode active material, but the positive electrode active material obtained in Examples is in Comparative Example. It showed a higher initial discharge capacity and a discharge capacity retention rate after 200 cycles than the positive electrode active material obtained in. Therefore, 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.

Further, in Example 9 in which the area ratio of lithium tungstate having a thickness of 0.5 μm or more 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%. Compared with the following Example 1, the discharge capacity retention rate after 200 cycles was lowered.

In the positive electrode active materials obtained in Examples 1 to 5 in which the amount of water added was in the range of 1% by mass to 10% by mass, Comparative Examples 1 and 4 in which tungsten oxide was not added and Comparative Example 2 in which the amount of tungsten oxide added was small. Compared with the obtained positive electrode active material, the discharge capacity retention rate after 200 cycles was improved.

In Comparative Example 3 in which the amount of tungsten oxide added was large, the area ratio in which lithium tungstate having a particle size of 0.5 μm or more was present exceeded 5%, and the initial discharge capacity and the discharge capacity retention rate after 200 cycles were lowered.
The technical scope of the present invention is not limited to the embodiments described in the above-described embodiments. One or more of the requirements described in the above embodiments and the like may be omitted. In addition, the requirements described in the above-described embodiments can be combined as appropriate. In addition, to the extent permitted by law, the contents of Japanese Patent Application No. 2017-087509 and all documents cited in this specification shall be incorporated as part of the description of the main text.

1 ... Primary particles 2 ... Secondary particles 3 ... Hollow portion 10 ... First lithium metal composite oxide 20 ... Second lithium metal composite oxide 100 ... Positive electrode active materials A1, A2 ... Compounds containing tungsten CBA ... Coin Molded battery CA …… Case PE …… Positive electrode NE …… Negative electrode GA …… Gasket PE …… Positive electrode NE …… Negative electrode SE …… Separator

Claims (16)

To obtain a mixture by mixing first lithium metal composite oxide containing secondary particles composed of agglomerated primary particles, tungsten oxide, and water.
Drying the mixture to obtain a second lithium metal composite oxide
Have,
The first lithium metal composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), and element M as Li: Ni: Co: M = z: (1-xy) :. x: y (where 0.97 <z <1.30, 0≤x≤0.10, 0≤y≤0.10, 0≤x + y≤0.10, M is Mn, V, Mg, Mo. , Nb, Ti, and at least one element selected from Al), and contains tungsten in an amount of 0.1% by mass or more based on the total amount of the first lithium metal composite oxide. Contains 1.0% by mass or less
The mixture is used for producing a positive electrode active material for a lithium ion secondary battery, which contains 0.1% by mass or more and 0.5% by mass or less of tungsten in the tungsten oxide with respect to the entire first lithium metal composite oxide. Method. Claim 1 that the second lithium metal composite oxide contains lithium tungstate and contains 0.2% by mass or more and 1.0% by mass or less of tungsten with respect to the entire second lithium metal composite oxide. The manufacturing method described in. The production method according to claim 1 or 2, wherein the water is mixed in an amount of 1% by mass or more and 10% by mass or less with respect to the entire first lithium metal composite oxide. The first lithium metal composite oxide and the tungsten oxide are mixed, and then the water is sprayed and mixed so that the average particle size of the droplets is 100 μm or less. The manufacturing method according to any one of the above. The production method according to any one of claims 1 to 4, wherein the first lithium metal composite oxide has a specific surface area of 0.5 cm ² / g or more and 2 m ² / g or less. The production method according to any one of claims 1 to 5, wherein the first 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. The second lithium metal composite oxide contains secondary particles formed by aggregating a plurality of primary particles and lithium tungstate.
The area ratio of lithium tungstate having a particle size of 0.5 μm or more present on the surface of the secondary particles, which is obtained from the observation of the surface of the secondary particles using a scanning electron microscope, is the area of the entire observation surface. The production method according to any one of claims 1 to 6, wherein the content is 5% or less. The production method according to claim 7, wherein the area ratio of lithium tungstate having a particle size of 0.5 μm or more existing on the surface is 1% or less. The production method according to any one of claims 1 to 8, wherein the second lithium metal composite oxide has a volume average particle size MV of 4 μm or more and 6 μm or less. A positive electrode active material for lithium-ion secondary batteries
It contains secondary particles formed by aggregating a plurality of primary particles and lithium tungstate.
The atomic number ratio of lithium (Li), nickel (Ni), cobalt (Co), element M, and tungsten (W) is Li: Ni: Co: M: W = z: (1-xy): x. : Y: a (where 0.97 <z <1.30, 0 ≦ x ≦ 0.10, 0 ≦ y ≦ 0.10, 0 ≦ x + y ≦ 0.10, 0.0005 ≦ a ≦ 0.005 , M is represented by at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al).
The amount of tungsten present on the surface of the positive electrode active material 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 positive electrode active material. Is a positive electrode active material that is 0.1% by mass or more and 1.0% by mass or less with respect to the entire positive electrode active material. The positive electrode active material according to claim 10, wherein the amount of tungsten present on the surface of the positive electrode active material is 0.1 times or more and 1 time or less with respect to the amount of tungsten contained inside the positive electrode active material. The area ratio of lithium tungstate having a particle size of 0.5 μm or more present on the surface of the secondary particles, which is determined from the observation of the surface of the secondary particles using a scanning electron microscope, is relative to the entire observation surface. The positive electrode active material according to claim 10 or 11, which is 5% or less. The positive electrode active material according to any one of claims 10 to 12, which contains 0.2% by mass or more and 1% by mass or less of tungsten with respect to the entire positive electrode active material. The positive electrode active material according to any one of claims 10 to 13, wherein the Karl Fischer moisture content at 300 ° C. is 0.05% or more and 0.2% or less. The positive electrode active material according to any one of claims 10 to 14, wherein the volume average particle diameter MV is 4 μm or more and 6 μm or less. A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing the positive electrode active material according to any one of claims 10 to 15.

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