JP2018186065A - Positive electrode active material for nonaqueous electrolyte secondary battery, method for manufacturing the same, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a positive electrode active material for a nonaqueous electrolyte secondary battery, which enables the achievement of an excellent battery capacity, output characteristics, and charge/discharge cycle characteristics when used for a positive electrode of a secondary battery; and a method for manufacturing the same.SOLUTION: A positive electrode active material 100 for a nonaqueous electrolyte secondary battery and a method for manufacturing the same are herein disclosed. The method comprises the steps of: mixing a first lithium metal composite oxide including secondary particles 2 each constructed by agglomeration of a plurality of primary particles 1, a tungsten oxide A1 and water into a mixture; and drying the mixture to obtain a second lithium metal composite oxide 20. The first lithium metal composite oxide includes 0.1-1.0 mass% of tungsten to a total mass of the first lithium metal composite oxide. The mixture includes 0.1-0.5 mass% of tungsten in the tungsten oxide A1 to the total mass of the first lithium metal composite oxide.SELECTED DRAWING: Figure 4

Description

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

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

  As a secondary battery satisfying such a demand, there is a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. A lithium ion secondary battery includes a negative electrode, a positive electrode, a separator, an electrolytic solution, and the like, and a material capable of desorbing and inserting lithium is used as an active material for the negative electrode and the positive electrode.

  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. As a battery having a high energy density is being put into practical use, a high voltage can be obtained.

As positive electrode active materials mainly proposed so far, lithium cobalt composite oxide (LiCoO ₂ ) that is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel that is cheaper than cobalt, Furthermore, 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 ) excellent in safety using inexpensive manganese. ) And the like.

  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 excellent in 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 ensure a sufficient reaction area with the electrolyte, 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. 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 made uniform, thereby suppressing the decrease in battery capacity due to the selective deterioration of the fine particles. Because it is possible.

  For example, in Patent Documents 1 to 3, the transition metal composite hydroxide particles that are the precursors of the positive electrode active material are clarified in two stages, a nucleation process that mainly performs nucleation and a particle growth process that mainly performs particle growth. A method for producing by a crystallization reaction separated into two is disclosed. In these methods, the pH value of the aqueous reaction solution is controlled within the range of 12.0 to 14.0 in the nucleation step and within the range of 10.5 to 12.0 in the particle growth step, based on a liquid temperature of 25 ° C. doing. The reaction atmosphere is 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.

  By such a method, the obtained transition metal composite hydroxide particles have a small particle size, a narrow particle size distribution, and a low density center portion composed of fine primary particles and a high density composed of plate-like or needle-like primary particles. Consists of a density outer shell. When such a transition metal composite hydroxide particle is mixed with a lithium compound and baked, the low density center portion is greatly shrunk, and a space portion is formed inside. In addition, 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, and is an index indicating the spread of the particle size distribution [(d90-d10 ) / Average particle size] is 0.60 or less and has a hollow structure.

  For this reason, in a secondary battery using these positive electrode active materials, it is said that capacity characteristics, output characteristics, and charge / discharge cycle characteristics can be improved. However, further improvements in output characteristics and charge / discharge cycle characteristics are required.

  In order to further improve the charge / discharge cycle characteristics, 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. It has also been reported that the output characteristics and 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, the lithium hydroxide generated by the reaction between lithium released from the positive electrode active material and the moisture contained in the binder reacts preferentially with the acidic oxide, thereby generating the generated hydroxide. It is said that the reaction between lithium and the binder is suppressed, and gelation of the positive electrode slurry is suppressed. Furthermore, it is said that the acidic oxide plays a role as a conductive agent in the positive electrode regardless of whether it reacts with lithium hydroxide, lowers the resistance of the entire positive electrode, and contributes to the improvement of the output characteristics of the battery.

  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, not only the thickening suppression effect of the positive electrode paste but also the low temperature reaction resistance suppression effect in the secondary battery is supposed.

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

JP 2012-246199 A JP 2013-147416 A International Publication No. 2012/131818 Japanese Patent No. 5382061 JP2013-084395A JP 2012-077944 A

  However, in the proposals in Patent Documents 4 and 5, the separator may be damaged due to the acidic oxide particles remaining in the positive electrode. In addition, the proposal of Patent Document 6 requires a water washing process, an addition process, and a drying process, which increases the manufacturing process, resulting in an increase in manufacturing cost.

  As described above, in the methods described in Patent Documents 4 to 6, battery characteristics, in particular, output characteristics and charge / discharge cycle characteristics cannot be sufficiently improved by a small number of steps, and output characteristics and charge / discharge. Further improvement in cycle characteristics has been demanded.

  In view of the above problems, the present invention provides a positive electrode active material capable of simultaneously improving battery characteristics when a secondary battery is configured, in particular, output characteristics and charge / discharge cycle characteristics, and a method for manufacturing the same. The purpose is to do. Moreover, an object of this invention is to provide the secondary battery using such a positive electrode active material.

  According to the first aspect of the present invention, a mixture is obtained by mixing the first lithium metal composite oxide containing secondary particles formed by aggregation of a plurality of primary particles, tungsten oxide, and water. And drying the mixture to obtain a second lithium metal composite oxide, wherein the first lithium metal composite oxide comprises 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, and M is an atomic ratio represented by Mn, V, Mg, Mo, Nb, Ti, and Al. 0.1 mass% or more and 1.0 mass% or less with respect to the whole lithium metal composite oxide, The compound includes 0.1% by mass or more and 0.5% by mass or less of tungsten in tungsten oxide with respect to the entire first lithium metal composite oxide, and a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery Is provided.

Moreover, it is preferable that 2nd lithium metal complex oxide contains lithium tungstate and contains 0.2 mass% or more and 1.0 mass% or less of tungsten with respect to the whole 2nd lithium metal complex oxide. Moreover, it is preferable to mix water in 1 mass% or more and 10 mass% or less with respect to the whole 1st lithium composite hydroxide. Moreover, it is preferable that after mixing the first lithium composite hydroxide and tungsten oxide, water is sprayed and mixed so that the average particle diameter of the droplets is in a mist state of 100 μm or less. The first lithium metal composite oxide preferably has a specific surface area of 0.5 cm ² / g or more and 2 m ² / g or less. The first 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.

  The second lithium metal composite oxide contains secondary particles composed of a plurality of primary particles aggregated, and lithium tungstate, and observation of the surface of the secondary particles using a scanning electron microscope It is preferable that the required area ratio of lithium tungstate having a particle diameter of 0.5 μm or more present on the surface of the secondary particles is 5% or less with respect to the area of the entire observation surface. Further, the area ratio of lithium tungstate having a particle size of 0.5 μm or more present on the surface is preferably 1% or less. The second lithium metal composite oxide preferably has a volume average particle size MV of 4 μm or more and 6 μm or less.

  According to the second aspect of the present invention, the atomic ratio of lithium (Li), nickel (Ni), cobalt (Co), and element M is Li: Ni: Co: M = z: (1-x -Y): x: y (where 1.00 <z <1.30, 0.10 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, M is Mn, V, Mg, Mo, Nb) , At least one element selected from Ti and Al), a secondary particle formed by agglomerating a plurality of primary particles, and lithium tungstate, and a positive electrode active material 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, and the amount of tungsten present inside the positive electrode active material is The nonaqueous electrolyte secondary battery is 0.1% by mass to 1.0% by mass with respect to The positive electrode active material is provided.

  In the positive electrode active material for a non-aqueous electrolyte secondary battery, 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 in the positive electrode active material. It is preferable. 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 observation of the surface of the secondary particles using a scanning electron microscope, It is preferable that it is 5% or less. Moreover, it is preferable that 0.2 mass% or more and 1 mass% or less of tungsten are included with respect to the whole positive electrode active material. Further, the Karl Fischer moisture content at 300 ° C. is preferably 0.05% or more and 0.2% or less. The volume average particle size MV is preferably 4 μm or more and 6 μm or less.

  According to the 3rd aspect of this invention, the non-aqueous electrolyte secondary battery provided with the positive electrode containing said positive electrode active material, a negative electrode, a separator, and a non-aqueous electrolyte is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material for nonaqueous electrolyte secondary batteries which can obtain the battery capacity, output characteristics, and charging / discharging cycling characteristics which were excellent when used for the positive electrode of a secondary battery can be provided. . Moreover, the manufacturing method is easy and suitable for production on an industrial scale, and its industrial value is extremely large.

Drawing 1 is a figure showing an example of the manufacturing method of the cathode active material for nonaqueous system electrolyte rechargeable batteries concerning an embodiment. FIG. 2 is a diagram illustrating an example of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the embodiment. FIG. 3 is a diagram illustrating an example of the first and second lithium metal composite oxides according to the embodiment. FIG. 4 is a diagram illustrating an example of the positive electrode active material according to the embodiment. FIG. 5 is a schematic cross-sectional view of a coin-type battery used for battery evaluation. FIG. 6 is a schematic explanatory diagram of an impedance evaluation measurement example and an equivalent circuit used for analysis.

  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 of the structure is emphasized or a part of the structure is simplified, and an actual structure, shape, scale, or the like may be different. Hereinafter, a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, a positive electrode active material for a non-aqueous electrolyte secondary battery, and a positive electrode active material for a secondary battery according to an embodiment will be described with reference to the drawings.

(1) Method for Producing Positive Electrode Active Material for Nonaqueous Electrolyte Secondary Battery FIGS. 1 and 2 are also referred to as a positive electrode active material for nonaqueous electrolyte secondary batteries according to the present embodiment (hereinafter referred to as “positive electrode active material 100”). It is a figure which shows an example of the manufacturing method of). 3 and 4 are schematic views showing examples 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 manufacturing the positive electrode active material 100 according to this embodiment obtains 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 the second lithium metal composite oxide 20 (Step S2). The second lithium metal composite oxide 20 may be used as the positive electrode active material 100 as it is, or after further performing other steps such as a crushing step for adjusting the particle size distribution, the positive electrode active material 100. It may be used as

  The second lithium metal composite oxide 20 (for example, FIG. 4) obtained by the manufacturing method according to the present embodiment is the same as the conventional first lithium metal composite oxide 10 (for example, FIG. 3) containing W. When used as a positive electrode active material or when a lithium metal composite oxide not containing W is used as a raw material instead of the first lithium metal composite oxide 10, more initial charge / discharge capacity, positive electrode resistance A secondary battery with improved cycle characteristics can be obtained. In addition, 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. From the viewpoint of cost.

  Although the details of the above reason are unclear, the first lithium metal composite oxide 10 containing W is formed by forming compound A1 containing tungsten on at least a part of the surface and the inside as shown in FIG. It is thought that there is. And by said step S1 and step S2, lithium in the 1st lithium metal complex oxide 10 and tungsten oxide react, and as shown in FIG. On the surface, for example, a compound A2 containing tungsten such as lithium tungstate is formed. In addition, the presence of the compounds A1 and A2 containing tungsten in the inside and on the entire surface of the positive electrode active material 100 (second lithium metal composite oxide 20) allows the electrolytic solution and the positive electrode active material 100 to be used in the secondary battery. It is considered that a Li ion conduction path is formed between the inside and the inside of the metal, making it easy to take in and out lithium ions.

Hereinafter, the manufacturing method of the positive electrode active material of this invention is demonstrated in detail with reference to FIGS.
[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 includes secondary particles 2 formed by agglomerating a plurality of primary particles 1, and includes lithium (Li), nickel (Ni), cobalt (Co), 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 1.00 <z <1.30, 0.10 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, M is Mn, V, Mg, Mo, Nb, Ti and Al At least one element selected from the group consisting of:

  The first lithium metal composite oxide 10 contains excessive lithium (in the above ratio, z is greater than 1), so that the lithium liberated from the first lithium metal composite oxide 10 will be described later. Some can neutralize 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 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 with respect to the entire first lithium metal composite oxide 10. % To 1.0% by mass. When the first lithium metal composite oxide 10 contains tungsten in the above range, the amount of tungsten oxide used for mixing (step S1) can be reduced, and further, the amount of tungsten in the entire positive electrode active material 100 can be reduced. In addition, it is possible to obtain a positive electrode active material having a high positive electrode resistance reduction effect while maintaining a high battery capacity.

  In the first lithium metal composite oxide 10, the location of tungsten 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 the The compound A1 containing tungsten may be present at the grain boundary between these primary particles 1. Alternatively, a part of tungsten may be dissolved, and the other part may exist as compound A1 containing tungsten. Examples of the compound A1 containing tungsten include lithium tungstate. In addition, the kind of compound A1 containing tungsten can be confirmed by powder X diffraction etc.

  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 manufacturing method of the first lithium metal composite oxide 10 is shown in the following (i) to (iii).

(I) Neutral crystallization is performed using an aqueous solution containing Ni, Co, W, and optionally the element M to produce a transition metal composite hydroxide, which is then used as a precursor and contains lithium. The first lithium metal composite oxide 10 is obtained by mixing with a compound and baking.
(Ii) After producing a transition metal composite hydroxide containing Ni, Co, and optionally element M except W, a transition metal composite hydroxide, a compound containing W, and a compound containing Li are mixed. And firing 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 preferably manufactured by the manufacturing methods (i) and (ii), more preferably by the manufacturing method (i). be able to. In addition, W added by the production method (i) is uniformly distributed in the transition metal composite hydroxide, so that when synthesized into the lithium metal composite oxide, W is the surface of the secondary particle 2. In addition, it is possible to more uniformly coat the surface of the primary particles existing inside.

  In addition, in the manufacturing method of this embodiment, even if it is the 1st lithium metal complex oxide 10 obtained by either said manufacturing method or manufacturing methods other than the above, it can be used.

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

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

The amount of tungsten present in the first lithium metal composite oxide 10 can be measured by the following method. First, the amount of tungsten (W _T ) 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 with 100 ml of pure water, stirred and dispersed with a magnetic stirrer, and stirred for 30 minutes. After standing for 10 minutes, the supernatant was removed. After filtration, the amount of tungsten (W) eluted in the supernatant is measured by the ICP method. The amount of tungsten eluted in the supernatant is defined as the amount of tungsten (W _s ) present on the surface of the first lithium metal composite oxide 10, and is present inside the first lithium metal composite oxide 10 from the following formula. The amount of tungsten (W _I ) to be calculated is calculated.
Formula: W _I = W _T −W _S

  For example, as shown in FIG. 3, the first lithium metal composite oxide 10 is composed of secondary particles 2 made of lithium (Li), nickel (Ni), cobalt (Co), and optionally an element M. And a compound A1 containing tungsten.

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 ( however, 0.10 ≦ x ≦ 0.35 , 0 ≦ y ≦ 0.35, 1.00 <z <1.30, where M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), hexagonal It has a crystallized 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 solution 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 a high capacity is desired. On the other hand, when it exceeds 2 m ² / g, the mechanical strength of the obtained positive electrode active material is insufficient due to the porous structure of the particle structure, which may cause a problem in stability during electrode production 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 and 0.0. It is preferable that it is 2 mass% or less. When the moisture content exceeds 0.2 mass%, a gas component containing carbon and sulfur in the atmosphere may be absorbed to generate a lithium compound on the surface of the first lithium metal composite oxide 10. The moisture content is a value measured with a Karl Fischer moisture meter under a vaporization temperature of 300 ° C.

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

  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 of A single primary particle 1 may be included.

(Tungsten oxide)
The tungsten oxide is not particularly limited, and a known tungsten oxide can be used. Tungsten oxide can be represented, for example, by the chemical formula WO _n (2 ≦ n ≦ 3, where n is a positive real number). The average particle size of tungsten oxide is preferably 1 μm or less. Although the minimum of the average particle diameter of tungsten oxide is not specifically limited, For example, it is 0.05 micrometer 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 mass% or more and 0.5 mass% or less with respect to the entire first lithium metal composite oxide 10. When the mixing amount of tungsten oxide is within the above range, a positive electrode active material having a high positive electrode resistance reduction effect can be obtained while maintaining a high battery capacity. Moreover, in the manufacturing method of this embodiment, the quantity in which tungsten (W) in tungsten oxide is contained by 0.1 mass% or more and 0.2 mass% or less with respect to the first lithium metal composite oxide 10 as a whole. 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 water. As will be described later, the water in the mixture includes unreacted lithium compounds present in the first lithium metal composite oxide 10 and excess lithium present in the crystals (hereinafter these are collectively referred to as “excess lithium”). ") And the mixed tungsten oxide can be dissolved.

  The amount of water to be mixed is not particularly limited as long as tungsten oxide in the mixture can be sufficiently dissolved. For example, the amount of water to be mixed is 0.5% by mass or more and 40% by mass with respect to the first lithium metal composite oxide 10. It can be set to 1 mass% or less, preferably 1 mass% or more and 30 mass% or less, more preferably 1 mass% or more and 10 mass% or less. When the amount of water to be mixed is sufficient, the tungsten oxide is sufficiently infiltrated to the surface of the primary particles 1 inside the secondary particles 2 and the tungsten oxide is evenly distributed between 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 and particle structure of the first lithium metal composite oxide 10 to be used, and is mixed within a range where the mixture does not become a paste. It is preferable.

(Mixing method)
The method of mixing the first lithium metal composite oxide 10, tungsten oxide, and water is not particularly limited, and these may be added simultaneously and mixed with a known mixing device, or added separately. And you may mix with a well-known mixing apparatus.

  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, the step of mixing the first lithium metal composite oxide, tungsten oxide, and water (step S1) involves mixing the first lithium metal composite oxide and tungsten oxide. It is preferable to provide the 1st mixing process (step S11) and the 2nd mixing process (step S12) which sprays and mixes water to the obtained mixture. 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, tungsten oxide can be more uniformly dispersed in the first lithium metal composite oxide 10.

  The amount of tungsten oxide mixed is preferably such that tungsten (W) in the tungsten oxide is contained in an amount of 0.1 mass% to 0.5 mass% with respect to the first lithium metal composite oxide 10. When the mixed amount of tungsten oxide is less than 0.1% by mass, surplus lithium such as lithium hydroxide liberated on the surface of the first lithium metal composite oxide 10 cannot be neutralized, so that sufficient slurry stability is achieved. 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 the lithium tungstate crystallized on the surface of the second lithium metal composite oxide 20 in the subsequent step (step S2). May increase the number of particles having a particle size of 0.5 μm or more, and a sufficient battery capacity may not be obtained.

[Second mixing step: Step S12]
Next, water is sprayed and mixed into the obtained mixture of the first lithium metal composite oxide and tungsten oxide (step S12). Thereby, in the presence of water, the neutralization reaction between surplus lithium such as lithium hydroxide liberated on the surface of the first lithium metal composite oxide 10 and tungsten oxide can be more uniformly advanced.

  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-described effects due to the addition of water are poor 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) is eluted from the water spray (step S12) to the drying (step S2). The amount of Li (excess lithium amount) becomes excessive, the Li content in the obtained positive electrode active material is reduced, and the resistance reduction effect may not be sufficient. Further, when the amount of water to be sprayed exceeds 10% by mass, the moisture content in the second lithium metal composite oxide 20 (positive electrode active material) is lowered, so that a lot of necessary drying time is required and productivity is lowered. There are things to do.

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

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

(Drying conditions)
The drying temperature is not particularly limited, and it is sufficient that the moisture content is sufficiently reduced. For example, 500 ° C. or less 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. In addition, the minimum of drying temperature is although it does not specifically limit, For example, it is 100 degreeC or more. The drying pressure is preferably 1 atm or less. If it is higher than 1 atm, the moisture content may not be lowered sufficiently. The drying time is not particularly limited as long as the moisture content is sufficiently reduced. For example, the drying time is about 5 hours to 24 hours.

(Second lithium metal composite oxide)
FIG. 4 is a schematic diagram 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 includes a compound A2 containing tungsten in the vicinity of the surface thereof. 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. The lithium tungstate is formed on at least a part of the surface of the secondary particle 2 and the surface of the primary particle 1 disposed inside.

  The second lithium metal composite oxide 20 is composed of a compound A1 containing tungsten derived from tungsten contained in the first lithium metal composite oxide 10 and the lithium tungstate formed by the above-described steps S1 and S2 ( You may have both with the compound A2) containing tungsten.

  The second lithium metal composite oxide 20 as a whole (including compounds A1 and A2 containing tungsten) contains, for example, 0.2 mass% or more and 1.2 mass% of tungsten 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 preferable that it is 0.1 mass% or more and 0.5 mass% or less. When the amount of tungsten existing on the surface of the second lithium metal composite oxide 20 is in the above range, the compound A1 containing tungsten existing inside the secondary particles 2 (for example, lithium tungstate) and the surface of the secondary particles 2 It is considered that the lithium tungstate formed on the surface can form a good Li ion conduction path, and in the secondary battery, the initial charge / discharge capacity, the positive electrode resistance, and the cycle characteristics can be further improved. It is done.

  Further, the amount of tungsten present in the second lithium metal composite oxide 20 is preferably 0.1% by mass or more and 1.0% by mass or less, more preferably, based on the entire second lithium metal composite oxide 20. Is 0.5 mass% or more and 1.0 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 may be substantially the same as the amount of tungsten in the composite oxide 10.

In addition, the amount of tungsten existing on the surface and inside of the second lithium metal composite oxide 20 is the same as the amount of tungsten W _S and W _I existing on the surface and inside of the first lithium metal composite oxide 10 described above. Can be measured by the method.

  The second lithium metal composite oxide 20 preferably has no residual tungsten oxide used as a raw material. When tungsten oxide remains, the positive electrode resistance may not be sufficiently reduced in the secondary battery. The presence or absence of tungsten oxide can be confirmed by a qualitative method such as powder X-ray diffraction.

(2) Positive electrode active material for non-aqueous electrolyte secondary battery The positive electrode active material for non-aqueous electrolyte secondary battery according to the present embodiment (hereinafter also referred to as “positive electrode active material”) is easily produced by the above-described manufacturing method. Can be manufactured. For example, as shown in FIG. 4, the positive electrode active material 100 includes at least secondary particles 2 formed by aggregating a plurality of primary particles 1 and lithium tungstate (compounds A1 and A2 containing tungsten). Each configuration will be described below.

[composition]
In the positive electrode active material 100, the atomic ratio of lithium (Li), nickel (Ni), cobalt (Co), and element M is Li: Ni: Co: M = z: (1-xy): x. : Y (however, 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).

As the composition positive electrode active material 100, except for tungsten, for example, the general formula _{(3): Li z Ni 1} -x-y Co x M y O 2 ( however, 0.10 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35, 1.00 <z <1.30, and M represents at least one element selected from Mn, V, Mg, Mo, Nb, Ti, and Al). 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 in the primary particles 1, for example, tungsten may be dissolved in the crystallites constituting the primary particles 1, and exist as tungsten compounds at the grain boundaries between the crystallites constituting the primary particles 1. May be.

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

  The area ratio of lithium tungstate having a particle size of 0.5 μm or more present on the surface of the secondary particle 2 obtained from observation of the surface of the secondary particle 2 using a scanning electron microscope (SEM) is the entire observation area. On the other hand, it is preferably 5% or less, more preferably 1% or less. When the area ratio of lithium tungstate having a particle size of 0.5 μm or more is in 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 lithium tungstate having a particle size of 0.5 μm or more present on the surface of the secondary particle 2 exceeds 5%, the resistance of lithium ions passing through the lithium tungstate increases, so that the reaction resistance May increase.

  The area ratio of lithium tungstate is determined by, for example, observing the surface of the secondary particle 2 with an SEM, and analyzing the area of the entire surface of the secondary particle 2 on the observation surface by image analysis or the like. It can be calculated by dividing by the area occupied by the lithium tungstate having In addition, the area of the whole surface of the secondary particle 2 contains the part coat | covered with lithium tungstate.

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

  The positive electrode active material 100 preferably does not substantially contain tungsten oxide. Here, substantially not containing 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 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, 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) present in the secondary particles 2 and tungsten formed on the surfaces of the secondary particles 2 Lithium acid can form a good Li ion conduction path, and it is considered that in the secondary battery, the initial charge / discharge capacity, the positive electrode resistance, and the cycle characteristics can be further improved.

  The amount of tungsten present in the positive electrode active material 100 is preferably 0.1% by mass or more and 1.0% by mass or less, 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 in the vicinity of the surface of the positive electrode active material 100, the amount of tungsten present in the positive electrode active material 100 is the amount of the first lithium metal composite oxide 10 inside. The amount of tungsten may be almost the same. Moreover, it is preferable that the amount of tungsten present on the surface of the positive electrode active material is 0.1 to 1 times the amount of tungsten contained in the positive electrode active material.

In addition, the amount of tungsten existing on the surface and inside of the positive electrode active material 100 is measured by the same method as the amount of tungsten W _S and W _I existing on the surface and inside of the first lithium metal composite oxide 10 described above. Can do.

  Further, the entire positive electrode active material 100 has a tungsten content of, 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. It is preferable that By setting the tungsten content within the above range, the positive electrode resistance can be reduced while maintaining a high battery capacity.

  The presence form of tungsten in the positive electrode active material 100 is not particularly limited, and may be present as lithium tungstate as described above, and is dissolved in the crystallites constituting the primary particles 1 or the secondary particles 2. May exist.

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

  The positive electrode active material 100 preferably has a Karl Fischer moisture content at 300 ° C. of 0.05% or more and 0.2% or less. When the moisture content exceeds 0.2%, the familiarity with the solvent contained in the positive electrode mixture paste is 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 can a sufficient reaction area with the electrolytic solution be ensured, but 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 a laser light diffraction scattering method.

  The positive electrode active material 100 was prepared by dispersing 5 g of the positive electrode active material in 100 ml of pure water and measuring the supernatant after standing for 10 minutes at 25 ° C. (hereinafter simply referred to as “pH value of the positive electrode active material”). Is also preferably 11 or more and 11.9 or less. 5 g of the positive electrode active material 100 is dispersed in 100 ml of pure water, and the pH of the supernatant after standing for 10 minutes is measured, whereby the excess in the paste when the paste is produced 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, battery characteristics can be improved and gelation of the paste can be suppressed.

(3) Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery (hereinafter also referred to as “secondary battery”) of this embodiment includes, for example, a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. In addition, the secondary battery may include, for example, a positive electrode, a negative electrode, and a solid electrolyte. Further, the secondary battery may be composed of the same components as those of a general non-aqueous electrolyte secondary battery.

  Hereinafter, a secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator will be described. The embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery of the present invention can be variously modified based on the knowledge of those skilled in the art based on the embodiment described in the present specification. It can be implemented in an improved form. Further, the use of the nonaqueous electrolyte secondary battery of the present embodiment is not particularly limited.

(A) Positive electrode Using the positive electrode active material described above, for example, a positive electrode of a nonaqueous electrolyte secondary battery can be produced as follows.

  First, a powdered positive electrode active material, a conductive material, and a binder are mixed, and, if necessary, a target solvent such as activated carbon and viscosity adjustment is added and kneaded to prepare a positive electrode mixture paste.

  Each mixing ratio in the positive electrode mixture paste is also an important factor for determining 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 is 60 to 95 parts by mass in the same manner as the positive electrode of a general non-aqueous electrolyte secondary battery, and the conductive material It is desirable to set the content of 1 to 20 parts by mass and the content of the binder to 1 to 20 parts by mass.

  The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, an aluminum foil and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size or the like according to the target battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the illustrated one, and other methods may be used.

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

  The binder plays a role of anchoring the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene rubber, styrene butadiene, cellulosic resin, polyacrylic. An acid or the like can be used.

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

(B) Negative electrode A negative electrode mixture in which a negative electrode active material capable of occluding and desorbing lithium ions is mixed with a binder and an appropriate solvent is added to the negative electrode. Is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as necessary.

  As the negative electrode active material, for example, natural graphite, artificial graphite, a fired organic compound such as phenol resin, or a powdery carbon material such as coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as PVDF can be used as in the case of the positive electrode, and as a solvent for dispersing these active materials and the binder, N-methyl-2-pyrrolidone or the like 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 and the negative electrode and retains the electrolyte, and a thin film such as polyethylene or polypropylene and a film having many minute holes can be used.

(D) Non-aqueous electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.

  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, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. are used alone or in admixture of two or more. be able to.

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

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

(E) Battery shape and configuration The shape of the non-aqueous electrolyte secondary battery of the present invention composed of the positive electrode, negative electrode, separator and non-aqueous electrolyte described above can be various, such as a cylindrical type and a laminated type. Can be.

  In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte 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 communicating with the outside are connected using a current collecting lead or the like and sealed in a battery case to complete a non-aqueous electrolyte secondary battery. .

(F) Characteristics The nonaqueous electrolyte secondary battery using the positive electrode active material of the present embodiment has a high capacity and a high output.
The non-aqueous electrolyte secondary battery using the positive electrode active material according to the present invention obtained in a particularly preferred form is, for example, a high initial discharge capacity of 150 mAh / g or more and a low positive electrode when used for the positive electrode of a 2032 type coin battery. Resistance is obtained.

  In addition, the measuring method of positive electrode resistance can be performed by the following method, for example. When the frequency dependence of the battery reaction is measured by a 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 capacity, and the positive electrode resistance and the positive electrode capacity is shown in FIG. Is obtained as follows.

  The battery reaction at the electrode consists of a resistance component accompanying the charge transfer and a capacity component due to the electric double layer. When these are expressed as an electric circuit, it becomes a parallel circuit of resistance and capacity. It is represented by an equivalent circuit in which circuits are connected in series. Fitting calculation is 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 semicircle on the low frequency side of the obtained Nyquist diagram.

  From the above, the positive electrode resistance can be estimated by performing AC impedance measurement on the manufactured positive electrode and performing fitting calculation on the obtained Nyquist diagram with an equivalent circuit.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[Measurement of W amount]
The amount of tungsten present 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 spectroscopic analysis (ICP method). Next, 5.0 g of the positive electrode active material is placed in a beaker together with 100 ml of pure water, stirred and dispersed with a magnetic stirrer, stirred for 30 minutes, and the supernatant obtained after standing for 10 minutes is separated by filtration. The amount of tungsten (W) eluted was measured by the ICP method. The amount of tungsten eluted in the supernatant was defined as the amount of tungsten (W _s ) present on the surface of the positive electrode active material, and the amount of tungsten (W _I ) present inside the positive electrode active material 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 a particle having a particle diameter of 80% or more and 120% or less of the volume average particle diameter (MV) among the secondary particles in the field of view by observing the surface of a plurality of secondary particles. Are randomly selected, and the area of the entire particle surface and the area occupied by lithium tungstate having a particle size of 0.5 μm or more are obtained for these 50 particles, and the total area of the particle surface is determined. 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. Therefore, the area ratio of all compounds present on the surface of the secondary particles was calculated as lithium tungstate.

[Production of secondary batteries and evaluation of battery performance]
About the secondary battery which has a positive electrode using the positive electrode active material obtained by the Example and the comparative example, its performance (initial discharge capacity, positive electrode resistance, discharge capacity maintenance ratio after repeating the charge / discharge cycle 500 times at 60 ° C. ) Was measured.

(Manufacture of batteries)
For the evaluation of the positive electrode active material, a 2032 type coin battery CBA (hereinafter referred to as a coin type battery CBA) shown in FIG. 5 was used.

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

  The case CA has a positive electrode can PC that is hollow and open at one end, and a negative electrode can NC that is disposed in the opening of the positive electrode can PC, and the negative electrode can NC is disposed in the opening of the positive electrode 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, and is stacked so as to be arranged in this order. The positive electrode PE is in contact with the inner surface of the positive electrode can PC, and the negative electrode NE is in contact with the inner surface of the negative electrode can NC. Thus, it is accommodated in the case CA.

  The case CA includes a gasket GA, and relative movement is fixed by the gasket GA so that the positive electrode can PC and the negative electrode can NC are kept in a non-contact state. Further, the gasket GA also has a function of sealing the gap between the positive electrode can PC and the negative electrode can NC so as to block the inside and outside of the case CA in an airtight and liquidtight manner.

  The coin-type battery CBA shown in FIG. 5 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) are mixed, and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. A positive electrode PE was prepared. The produced positive electrode PE was dried at 120 ° C. for 12 hours in a vacuum dryer.

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

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

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

  The initial discharge capacity, the positive electrode resistance, and the discharge capacity maintenance rate after repeating the charge / discharge cycle 500 times at 60 ° C. showing the performance of the manufactured coin-type battery CBA were evaluated as follows.

The initial discharge capacity is left for about 24 hours after the coin-type battery CBA is manufactured. After the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 0.1 mA / cm ² and the cut-off voltage 4 The capacity when the battery was charged to 3 V, discharged after a pause of 1 hour to a cutoff voltage of 3.0 V was defined as the initial discharge capacity.

  In addition, the positive electrode resistance was measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (1255B manufactured by Solartron) after charging a coin-type battery CBA at a charging potential of 4.1 V. A plot is obtained. Since this Nyquist plot is represented as the sum of the solution resistance, the negative electrode resistance and its capacity, and the characteristic curve indicating the positive electrode resistance and its capacity, the fitting calculation was performed using an equivalent circuit based on this Nyquist plot, and the positive resistance The value of was calculated.

  The discharge capacity maintenance rate after 500 cycles is the discharge capacity and initial discharge capacity after 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. The ratio was calculated.

  Note that, in this example, Wako Pure Chemical Industries, Ltd. reagent grade samples were used for the production of composite hydroxide, the production of the positive electrode active material, and the secondary battery.

[Example 1]
(Production of the first lithium metal composite oxide)
By using a known crystallization method, a first lithium metal composite oxide represented by Li _1.20 Ni _0.35 Co _0.35 Mn _0.30 W _0.0037 O ₂ (W: 0.07 wt%) Specific surface area 1.2 cm ² / g). Specifically, as raw materials, a metal salt solution and a sodium tungstate solution containing Ni, Co, and Mn, respectively, NaOH as a neutralizing agent, ammonia as a complexing agent, and Ni, Co by continuous crystallization. , Mn and W-containing transition metal composite hydroxides were synthesized. Lithium hydroxide was mixed with the obtained transition metal composite hydroxide and then fired to obtain the first lithium metal composite oxide.

(Mixing process)
To the first lithium metal composite oxide, tungsten oxide (made by Nippon Inorganic Chemical Industry Co., Ltd.) was added in an amount such that the amount of tungsten was 0.2% by mass relative to the entire first lithium metal composite oxide, and mixed. Thereafter, water is sprayed at 2% by mass with respect to the entire first 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. Lithium metal composite oxide was obtained. Table 1 shows the characteristics of the obtained second 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]
The battery characteristics of a coin-type battery CBA having a positive electrode produced using the obtained second lithium metal composite oxide were evaluated. The evaluation results are shown in Table 1.

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

[Example 3]
A positive electrode active material for a non-aqueous electrolyte secondary battery in the same manner as in Example 1 except that the amount of tungsten oxide added was such that the tungsten amount was 0.4 wt% with respect to the entire first lithium metal composite oxide. The pH and battery characteristics were evaluated and the results are shown in Table 1.

[Example 4]
A positive electrode active material for a nonaqueous electrolyte secondary battery was obtained and the pH and battery characteristics were evaluated in the same manner as in Example 3 except that the amount of pure water sprayed was 1 wt%. Table 1 shows the results.

[Example 5]
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and the pH and battery characteristics were evaluated in the same manner as in Example 3 except that the amount of pure water sprayed was 10 wt%. Table 1 shows the results.

[Example 6]
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and the pH and battery characteristics were evaluated in the same manner as in Example 1 except that the amount of pure water sprayed was 0.5 wt%. Show.

[Example 7]
A positive electrode active material for a nonaqueous electrolyte secondary battery was obtained and the pH and battery characteristics were evaluated in the same manner as in Example 3 except that the amount of pure water sprayed was 20 wt%. Table 1 shows the results.

[Example 8]
The amount of tungsten oxide added is such that the tungsten amount is 0.5 wt% with respect to the first lithium metal composite oxide powder, and the first lithium metal composite is left in a liquid state without being in a mist state. A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and the pH and battery characteristics were evaluated in the same manner as in Example 1 except that 2% by mass of the oxide was added. The results are shown in Table 1. .

[Example 9]
The positive electrode active for a non-aqueous electrolyte secondary battery was carried out in the same manner as in Example 8 except that 0.5% by mass of water was added to the entire first lithium metal composite oxide while the water remained in a mist state. The materials were obtained and the pH and battery characteristics were evaluated. The results are shown in Table 1.

[Comparative Example 1]
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and the pH and battery characteristics were evaluated in the same manner as in Example 1 except that tungsten oxide was not added and pure water was not sprayed. Show.
[Comparative Example 2]
Cathode active material for non-aqueous electrolyte secondary battery in the same manner as in Example 1 except that the amount of tungsten oxide added was changed to an amount such that the tungsten amount was 0.05 wt% with respect to the first lithium metal composite oxide powder. The pH and battery characteristics were evaluated and the results are shown in Table 1.
[Comparative Example 3]
Cathode active material for non-aqueous electrolyte secondary battery in the same manner as in Example 1 except that the amount of tungsten oxide added was changed to an amount such that the amount of tungsten was 2.0 wt% with respect to the first lithium metal composite oxide powder. The pH and battery characteristics were evaluated and the results are shown in Table 1.
[Comparative Example 4]
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 wt% contained) in the first lithium metal composite oxide In the same manner as in Example 1 except that tungsten oxide was not added, a positive electrode active material for a non-aqueous electrolyte secondary battery was obtained, and the pH and battery characteristics were evaluated. The results are shown in Table 1. Show.
[Comparative Example 5]
A lithium metal composite oxide represented by Li _1.20 Ni _0.35 Co _0.35 Mo _0.30 O ₂ that does not contain W in the first lithium metal composite oxide is used. Except that the amount of tungsten was 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, the same as in Example 1. Thus, a positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and the pH and battery characteristics were evaluated. The results are shown in Table 1.

[Evaluation results]
The positive electrode active material obtained in the examples had good initial charge / discharge capacity, positive electrode resistance, and charge / discharge cycle characteristics. XRD confirmed that tungsten oxide was not detected and only lithium tungstate was detected in the positive electrode active material obtained in the example.

  The positive electrode active materials obtained in Examples 1 and 6 and Comparative Examples 4 and 5 have the same amount of tungsten in the positive electrode active material, but the positive electrode active materials obtained in the Examples are the comparative examples. It showed higher initial discharge capacity and positive electrode resistance than the positive electrode active material obtained in (1). Therefore, the positive electrode active material obtained using the manufacturing method of the present embodiment can have higher battery characteristics with a small amount of tungsten used.

  In Example 9 where the area ratio of lithium tungstate of 0.5 μm or more existing 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 to Example 1 below, the positive electrode resistance was slightly reduced.

  In the positive electrode active materials obtained in Examples 1 to 5 in which the amount of water added is in the range of 1 to 10% by mass, Comparative Examples 1 and 4 in which no tungsten oxide is added and Comparative Example 2 in which the added amount of tungsten oxide is small. Compared with the obtained positive electrode active material, the positive electrode resistance was further reduced.

  In Comparative Example 3 in which the amount of tungsten oxide added was large, the positive electrode resistance was reduced to some extent, but the area ratio where lithium tungstate having a particle diameter of 0.5 μm or more was present exceeded 5%, and the initial discharge capacity was reduced.

  The technical scope of the present invention is not limited to the aspects 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 and the like can be combined as appropriate. In addition, as far as permitted by law, Japanese Patent Application No. 2017-087509, which is a Japanese patent application, and the contents of all the references cited in this specification are incorporated as part of the description of the text.

DESCRIPTION OF SYMBOLS 1 ... Primary particle 2 ... Secondary particle 3 ... Hollow part 10 ... 1st lithium metal complex oxide 20 ... 2nd lithium metal complex oxide 100 ... Positive electrode active material A1, A2 ... Compound CBA containing tungsten ... Coin Type battery CA ... case PE ... positive electrode NE ... negative electrode GA ... gasket PE ... positive electrode NE ... negative electrode SE ... separator

Claims (16)

Mixing a first lithium metal composite oxide containing secondary particles constituted by aggregation of a plurality of primary particles, tungsten oxide, and water;
Drying the mixture to obtain a second lithium metal composite oxide,
The first lithium metal composite oxide includes lithium (Li), nickel (Ni), cobalt (Co), and element M, 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 Mn, V, Mg, Mo, Nb, Ti and Al And at least one element selected from the group consisting of 0.1% by mass and 1.0% by mass with respect to the entire first lithium metal composite oxide. Including
The mixture 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 for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.   The second lithium metal composite oxide contains lithium tungstate, and contains 0.2 mass% or more and 1.0 mass% or less of tungsten with respect to the entire second lithium metal composite oxide. The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries as described in any one of.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, 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 composite hydroxide. Manufacturing method.   After mixing said 1st lithium compound hydroxide and said tungsten oxide, the said water is sprayed and mixed so that it may become a fog state whose average particle diameter of a droplet is 100 micrometers or less. The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries as described in any one of these. 5. The positive electrode for a nonaqueous electrolyte secondary battery according to claim 1, 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. A method for producing an active material.   The non-aqueous electrolyte according to any one of claims 1 to 5, wherein the first lithium metal composite oxide has a Karl Fischer moisture content at 300 ° C of 0.05% by mass or more and 0.2% by mass or less. A method for producing a positive electrode active material for a secondary battery. The second lithium metal composite oxide includes secondary particles formed by aggregation of a plurality of primary particles, and lithium tungstate,
The area ratio of lithium tungstate having a particle diameter of 0.5 μm or more present on the surface of the secondary particle, which is obtained from observation of the surface of the secondary particle using a scanning electron microscope, is the area of the entire observation surface. On the other hand, the manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries as described in any one of Claims 1-6 which is 5% or less.   The production of a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein an area ratio of lithium tungstate having a particle size of 0.5 µm or more present on the surface is 1% or less. Method.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery 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. . The atomic ratio of lithium (Li), nickel (Ni), cobalt (Co), and element M is Li: Ni: Co: M = z: (1-xy): x: y (however, 1 0.00 <z <1.30, 0.10 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, M is at least one selected from Mn, V, Mg, Mo, Nb, Ti and Al Element), a positive electrode active material represented by
Secondary particles formed by aggregation of a plurality of primary particles, and lithium tungstate, the amount of tungsten present on the surface of the positive electrode active material is 0.1% by mass or more based on the total amount of the positive electrode active material 1.0 mass% or less, and the amount of tungsten present inside the positive electrode active material is 0.1 mass% or more and 1.0 mass% or less with respect to the entire positive electrode active material.
Positive electrode active material for non-aqueous electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to claim 10, wherein the amount of tungsten present on the surface of the positive electrode active material is 0.1 to 1 time the amount of tungsten contained in the positive electrode active material. 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 particle, which is obtained from observation of the surface of the secondary particle using a scanning electron microscope, is based on the entire observation surface. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10 or 11, which is 5% or less.   The positive electrode active material for non-aqueous electrolyte secondary batteries according to any one of claims 10 to 12, comprising tungsten in an amount of 0.2% by mass to 1% by mass with respect to the entire positive electrode active material.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 10 to 13, wherein a Karl Fischer moisture content at 300 ° C is 0.05% or more and 0.2% or less.   The positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 10 to 14, wherein the volume average particle size MV is 4 µm or more and 6 µm or less. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing the positive electrode active material according to claim 10.

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