JP2022130698A - 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 a high output and high durability as to a secondary battery.

SOLUTION: A positive electrode active material for a nonaqueous electrolyte secondary battery comprises: lithium metal composite oxide powder including at least one of primary particles and secondary particles formed as a result of agglomeration of primary particles; and a coating layer formed on the surface of the lithium metal composite oxide powder. The positive electrode active material includes Li, Ni, Co and Al, and the proportion of the respective metal atoms is represented by: Li:Ni:Co:Al=z:(1-x-y):x:y (where x, y and z satisfy 0.01≤x≤0.15, 0<y≤0.05 and 0.97≤z≤1.20). The coating layer comprises a compound including tantalum and lithium.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

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

In recent years, with the spread of mobile electronic devices such as mobile phones and laptop computers, there is a strong demand for the development of small, lightweight non-aqueous electrolyte secondary batteries with high energy density. There is also a strong demand for the development of a high-output secondary battery as a battery for such applications. As a secondary battery that satisfies such requirements, there is a lithium ion secondary battery.

In this lithium ion secondary battery, a material from which lithium can be desorbed and intercalated is used as the active material of the negative electrode and the positive electrode. Such lithium ion secondary batteries are currently being actively researched and developed. can obtain a voltage as high as 4 V, and is being put to practical use as a battery with a high energy density.

Positive electrode active materials that have been proposed so far include lithium-cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, lithium-nickel composite oxide (LiNiO ₂ ), which uses nickel, which is cheaper than cobalt, and lithium. A nickel-cobalt-manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and the like are included.

In order to use the lithium metal composite oxide as a positive electrode active material for secondary batteries that require high output such as for automobiles, it is required to improve the positive electrode active material to obtain a higher output than the current state. For example, in the case of a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte, interfacial resistance of the positive electrode occurs between the electrolyte and the positive electrode active material. When the interface resistance (positive electrode resistance) of this positive electrode is high, the voltage applied to the load side becomes relatively low, and high output cannot be obtained.

So far, several techniques have been reported for improving battery characteristics by coating the surface of a lithium metal composite oxide (positive electrode active material) with a metal oxide.

For example, in Non-Patent Document 1, a pulsed laser deposition method is used to form a film of Li ₂ WO ₄ , which is a lithium metal oxide having properties as an ionic conductor, on lithium cobalt composite oxide (LLiCoO ₂ ). This improves the diffusion of lithium at the cathode/electrolyte interface, lowers the interfacial resistance, and by creating an amorphous state, the lithium diffusion path works effectively, promoting the resistance reduction effect and improving the output characteristics. has been reported.

In addition, in Non-Patent Document 2, output characteristics are improved by coating lithium-cobalt composite oxide (LiCoO ₂ ) with BaTiO ₃ , which is a metal oxide having dielectric properties, using a sol-gel method. reported to do. It is believed that this is because the intercalation and deintercalation of lithium at the interface between the dielectric and the active material is promoted by the polarization effect of the dielectric.

Further, in Patent Document 1, Li _1.3 Al _0.3 Ti, which is a lithium ion conductive member, is added to positive electrode active material powder (LiNi _0.5 Mn _1.5 O ₄ ) using a nanoparticle compounding device. _1.7 A cathode active material powder coated with (PO ₄ ) ₃ and Li ₃ PO ₄ has been proposed. According to Patent Literature 1, it is stated that the positive electrode active material powder improves cycle characteristics in lithium ion secondary batteries, but improvement of output characteristics is not studied.

JP 2016-51566 A

J. Power Sources 305 (2016) 46. APPLIED PHYSICS LETTERS 105 (2014) 143904. J. Appl. Phys. 49 (1978) 4808. "Remarkable Dielectric Ceramic Materials", T.I.C. Co., Ltd. (2003).

However, although Non-Patent Documents 1 and 2 and Patent Document 1 describe a positive electrode active material having a coating layer made of a specific metal oxide, the coating layer having a compound containing tantalum and lithium is described. is not described at all. Further, improvement of the output characteristics of the lithium-ion secondary battery described in Patent Document 1 has not been studied.

Furthermore, none of the above prior art documents mentions any specific effect when using lithium nickel cobalt aluminum composite oxide (LiNi _x Co _y Al _z O ₂ ) as the lithium metal composite oxide powder. not

In view of such problems, the present invention provides a positive electrode active material for a non-aqueous electrolyte secondary battery that can provide a non-aqueous electrolyte secondary battery having high output and high durability when used for a positive electrode, and a method for producing the same. intended to provide

According to the first aspect of the present invention, a lithium metal composite oxide powder comprising at least one of primary particles and secondary particles formed by aggregation of a plurality of primary particles, and on the surface of the lithium metal composite oxide powder A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the lithium metal composite oxide powder contains Li, Ni, Co and Al, and the atomic ratio of each metal is Li : Ni: Co: Al = z: (1-x-y): x: y (where 0.01 ≤ x ≤ 0.15, 0 < y ≤ 0.05, 0.97 ≤ z ≤ 1.20 is satisfied.), and the coating layer contains a compound containing tantalum and lithium.

Further, the amount of tantalum contained in the coating layer is 0.1 atomic % or more and 2.0 atomic % with respect to the total number of atoms of Ni, Co and Al contained in the positive electrode active material for non-aqueous electrolyte secondary batteries. The following are preferable. Also, the compound containing tantalum and lithium preferably contains at least one of LiTaO ₃ and Li ₃ TaO ₄₄ .

According to a second aspect of the present invention, spraying an alkoxide solution containing tantalum alkoxide and at least one of lithium alkoxide and lithium onto the lithium metal composite oxide powder being stirred; heat-treating the subsequent lithium metal composite oxide powder to form a coating layer containing a compound containing niobium and lithium on the surface of the lithium metal composite oxide powder; The oxide powder contains Li, Ni, Co, and Al, and the atomic ratio of each metal is Li:Ni:Co:Al=z:(1-xy):x:y (however, 0.01 ≦x≦0.15, 0<y≦0.05, and 0.97≦z≦1.20). .

Further, the alkoxide solution is preferably sprayed in an amount of 2 parts by mass or more and 91 parts by mass or less with respect to 100 parts by mass of the lithium metal composite oxide powder. Further, the heat treatment is preferably performed at a temperature of 300° C. to 400° C. for 1 hour or longer. Further, the amount of tantalum contained in the alkoxide solution is 0.1 atomic % or more and 2.0 atomic % or less with respect to the total number of atoms of nickel, cobalt and aluminum contained in the lithium metal composite oxide powder. is preferred. The compound containing tantalum and lithium preferably contains lithium tantalate composed of at least one of LiTaO ₃ and Li ₃ TaO ₄ .

According to a third aspect of the present invention, a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolytic solution, wherein the positive electrode comprises the positive electrode active material for a non-aqueous electrolyte secondary battery provided.

According to the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, when used for a positive electrode, a non-aqueous electrolyte secondary battery with high output and high durability can be obtained. Moreover, according to the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, the positive electrode active material can be produced simply and with high productivity.

FIG. 1 is a schematic diagram showing an example of a positive electrode active material for a non-aqueous electrolyte secondary battery according to this embodiment. FIG. 2 is a diagram showing an example of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to this embodiment. FIG. 3 is a schematic explanatory diagram of a coin-type secondary battery used in Examples. FIG. 4 is a schematic diagram showing an example of impedance spectrum measurement results. FIG. 5 is an explanatory diagram of an equivalent circuit used for analysis.

Hereinafter, a positive electrode active material for non-aqueous electrolyte secondary batteries, a method for producing the same, and a non-aqueous electrolyte secondary battery according to one embodiment of the present invention will be described with reference to the drawings. In addition, the present invention is not limited to the following description. Moreover, in the drawings, in order to describe the embodiments, part or all of the parts are schematically shown, and parts are expressed by changing the scale as appropriate, such as by enlarging or emphasizing part of the parts.

1. 1. Positive Electrode Active Material FIG. 1 is a schematic diagram showing an example of a positive electrode active material for a non-aqueous electrolyte secondary battery (hereinafter also referred to as "positive electrode active material") of the present embodiment. The positive electrode active material PA, as shown in FIG. and a coating layer 20 formed on the surface of the oxide powder 10 .

The present inventors have extensively studied the powder characteristics of the positive electrode active material and the effect on the positive electrode resistance of the secondary battery. The lithium ion conductivity and dielectric properties of the coating layer 20 improve lithium ion conductivity in the positive electrode (electrode) and lithium insertion/extraction at the interface between the coating layer 20 and the lithium metal composite oxide powder 10. It has been found that it is possible to significantly reduce the positive electrode resistance of the obtained secondary battery, improve the output characteristics, and improve the durability of the secondary battery. Each component included in the positive electrode active material PA will be described below.

(1) Coating Layer The coating layer 20 contains a compound containing tantalum and lithium, and may be formed from a compound containing tantalum and lithium. The compound containing tantalum and lithium is preferably a lithium ion conductor containing dielectric.

Normally, when the surface of the lithium metal composite oxide powder 10 is completely covered with a different compound, the movement (intercalation) of lithium ions is greatly restricted, and as a result, the lithium metal composite oxide powder 10 has The advantage of high capacity is lost. In addition, dissolving a different element in the lithium composite oxide powder 10 tends to cause a decrease in capacity.

On the other hand, a compound containing tantalum and lithium has a high lithium ion conductivity and has the effect of promoting the movement of lithium ions, so the surface of the lithium metal composite oxide powder 10 is coated with a compound containing niobium and lithium. By doing so, it is possible to promote intercalation on the surface of the positive electrode active material PA.

(Compound containing tantalum and lithium)
The compound containing tantalum and lithium preferably contains lithium tantalate, more preferably at least one of LiTaO ₃ and Li ₃ TaO ₄ , and still more preferably LiTaO ₃ . The compound containing tantalum and lithium may also consist of lithium tantalate. Note that the compound containing tantalum and lithium can be confirmed by powder X-ray diffraction (XRD) or the like.

Lithium tantalate has been reported to have properties as an ionic conductor and to exhibit good dielectric properties (see Non-Patent Documents 3 and 4). That is, lithium tantalate has not only properties as a lithium ion conductor but also properties as a dielectric. It is believed that lithium intercalation/deintercalation at the interface with the layer 20 is promoted, and the output characteristics of the secondary battery using the positive electrode active material PA are greatly improved.

(Content of tantalum)
The content of tantalum contained in coating layer 20 is preferably 0.1 atomic % or more and 2.0 atomic % or less with respect to the total number of atoms of nickel, cobalt and aluminum in positive electrode active material PA. When the tantalum content is within the above range, both high output characteristics and durability can be achieved. On the other hand, if the tantalum content is less than 0.1 atomic percent, the effect of improving output characteristics may not be sufficiently obtained. On the other hand, if the amount of tantalum exceeds 2.0 atomic %, the amount of lithium tantalate becomes too large, and the lithium ion conduction between the lithium metal composite oxide and the electrolyte is inhibited, and the battery performance may deteriorate. .

The tantalum content is preferably 0.1 atomic % or more and 2.0 atomic % or less, and 0.5 atomic % or more and 1.7 atomic % or more, from the viewpoint of achieving both output characteristics and durability at a higher level. Atom % or less is more preferable, and 0.8 atomic % or more and 1.3 atomic % or less is even more preferable.

If the coating layer 20 covers the surface of the lithium composite oxide powder 10 unevenly, lithium ions may move unevenly among the particles of the lithium metal composite oxide powder 10 . In such a case, a load is applied to the specific lithium metal composite oxide particles, which may lead to deterioration of cycle characteristics and increase in reaction resistance. Therefore, it is preferable that the coating layer 20 is uniformly coated on the surface of the lithium composite oxide powder 10 . By using the manufacturing method of this embodiment, which will be described later, the surface of the lithium composite oxide powder 10 can be uniformly coated with the coating layer 20 .

(2) Lithium metal composite oxide powder (particle shape)
As shown in FIG. 1, the lithium metal composite oxide powder 10 consists of at least one of primary particles 1 and secondary particles 2 formed by agglomeration of a plurality of primary particles 1 . Such a particle shape increases the contact area with the electrolytic solution, which is advantageous for improving the output characteristics. The lithium metal composite oxide powder 10 may be composed of only the secondary particles 2, may be composed of only the single primary particles 1, or may be composed of both the secondary particles 2 and the single primary particles 1. good too. Moreover, the lithium metal composite oxide powder 10 contains secondary particles 2 as a main component and may contain a small amount of independent primary particles 1 .

(Specific surface area of lithium metal composite oxide powder)
The lithium metal composite oxide powder 10 preferably has a specific surface area of 0.3 m ² /g or more and 2 m ² /g or less. When the specific surface area is within the above range, the contact with the electrolytic solution can be enhanced to improve output characteristics and battery capacity, and thermal stability can be ensured. On the other hand, when the specific surface area is less than 0.3 m ² /g, sufficient contact with the electrolytic solution cannot be obtained, and output characteristics and battery capacity may decrease. Moreover, when the specific surface area exceeds 2 m ² /g, the decomposition of the electrolytic solution may be accelerated and the thermal stability may be lowered.

(compositional formula)
The lithium metal composite oxide powder 10 can have a layered crystal structure, for example, general formula (1): Li _z Ni _1-x-y-t Co _x Al _y M _t O _2+α (where M is , Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W, and 0.01≦x≦0.15, 0 < y ≤ 0.05, 0 ≤ t ≤ 0.1, 0.97 ≤ z ≤ 1.20, -0.1 ≤ α ≤ 0.1), and general formula (2): Li _z Ni _1-xy Co _x Al _y O ₂ (where 0.01≦x≦0.15, 0<y≦0.05, and 0.97≦z≦1.20 are satisfied). preferably.

(Other characteristics)
The positive electrode active material PA has improved output characteristics by having a coating layer 20 containing lithium tantalate or the like on the surface of the lithium metal composite oxide powder 10. Main powder characteristics of the positive electrode active material PA inherits the characteristics of the lithium metal composite oxide powder 10 used as the base material. The powder characteristics such as the particle size and tap density of the lithium metal composite oxide powder 10 can be within the range of commonly used positive electrode active materials, and are appropriately selected according to the required battery characteristics and the like. be able to. Moreover, the lithium metal composite oxide powder 10 can be obtained by a known method, and can be one that satisfies the above composition and powder characteristics.

(3) Positive Electrode Active Material As described above, the positive electrode active material PA is formed on the surface of the lithium metal composite oxide powder 10 composed of at least one of the primary particles 1 and the secondary particles 2 and the lithium metal composite oxide powder 10. and a covering layer 20 which is applied.

The positive electrode active material PA contains Li, Ni, Co, and Al, and the atomic ratio of these metals is Li:Ni:Co:Al=z:(1-xy):x:y (where 0. satisfies 01≦x≦0.15, 0<y≦0.05, and 0.97≦z≦1.20).

Since the positive electrode active material PA has the above atomic ratio, a secondary battery using this positive electrode active material PA can obtain a high charge/discharge capacity. Furthermore, as described later, the surface of the lithium metal composite oxide powder 10 has a coating layer 20 containing a compound containing tantalum and lithium, so that the positive electrode active material PA can be used in a secondary battery using it. In addition to having a high charge-discharge capacity, it is possible to improve output characteristics and suppress a decrease in capacity retention rate due to charge-discharge cycles. The content of each metal element in the positive electrode active material PA can be measured by ICP emission spectrometry. Further, the atomic ratio of each metal element can be set within the above range by appropriately selecting the composition of the lithium metal composite oxide used as the raw material (base material).

(lithium)
In the above atomic ratio, z indicating the content of lithium (Li) is 0.97 or more and 1.20 or less. In addition, z is the ratio (Li/Me ). When the Li/Me ratio is less than 0.97, the reaction resistance of the positive electrode in the secondary battery using the positive electrode active material PA increases, resulting in a low output of the secondary battery. On the other hand, when Li/Me exceeds 1.20, the discharge capacity of the positive electrode active material decreases and the reaction resistance of the positive electrode also increases. Moreover, from the viewpoint of obtaining a larger discharge capacity, Li/Me is preferably 1.10 or less.

(cobalt)
In the above atomic ratio, x indicating the content of cobalt (Co) is 0.01 or more and 0.15 or less. When the Co content is within the above range, the battery characteristics such as cycle characteristics and output characteristics of the secondary battery using the positive electrode active material PA can be improved, and the battery capacity can be further improved. On the other hand, when x exceeds 0.15, the amount of Ni that contributes to the Redox reaction decreases, resulting in a decrease in battery capacity. Moreover, when x is less than 0.01, sufficient cycle characteristics and thermal stability cannot be obtained.

(aluminum)
In the above atomic ratio, y, which indicates the content of aluminum (Al), is more than 0 and 0.05 or less. When the content of Al is within the above range, it is possible to improve battery characteristics such as cycle characteristics and output characteristics of a secondary battery using the positive electrode active material PA. On the other hand, if y exceeds 0.05, the amount of Ni that contributes to the Redox reaction decreases, resulting in a decrease in battery capacity.

(nickel)
In the above atomic ratio, (1-xy) indicating the content of nickel (Ni) is 0.8 or more and less than 0.99. When (1-xy) is within the above range, a secondary battery using the positive electrode active material PA can have a high battery capacity.

(other metal elements)
The metal elements in the lithium metal composite oxide powder 10 can consist of lithium, nickel, cobalt and aluminum, but may also contain metal elements (M) other than these. As other metal elements (M), for example, M is one or more selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W element. When another metal element (M) is included, the atomic ratio of the metal element (M) is 0 or more and 0 with respect to the sum (Me) of the number of atoms of nickel (Ni), cobalt (Co) and aluminum (Al). 0.05 or less.

(Specific surface area of positive electrode active material)
The main powder properties of the positive electrode active material PA inherit the properties of the lithium metal composite oxide powder 20 used as the base material. Therefore, the specific surface area of the positive electrode active material PA is preferably in the same range as the specific surface area of the ^lithium metal composite oxide powder ¹⁰ described above. Preferably.

Note that part of the effects obtained by forming the coating layer 20 formed from a compound containing tantalum and lithium is not only the positive electrode active material PA containing the lithium metal composite oxide 10 according to the present embodiment, It can also be applied to positive electrode active materials for commonly used lithium secondary batteries. However, in the positive electrode active material PA of the present embodiment, by combining the lithium metal composite oxide 10 having a specific atomic ratio and the coating layer 20, battery capacity, output characteristics and durability are improved at a higher level. It is compatible.

2. Method for manufacturing positive electrode active material for non-aqueous electrolyte secondary battery FIG. 2 shows a method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment (hereinafter, also referred to as "method for manufacturing positive electrode active material"). It is a figure which shows an example. By using the method for producing a positive electrode active material according to the present embodiment, the positive electrode active material PA in which the coating layer 20 is uniformly coated on the surface of the lithium metal composite oxide powder 10 can be produced easily and with high productivity. can be obtained with

As shown in FIG. 2, the method for producing a positive electrode active material includes spraying an alkoxide solution containing tantalum alkoxide and at least one of lithium alkoxide and lithium onto a stirred lithium metal composite oxide powder. (step S10) and heat-treating (step S20). Each step will be described below.

(Step S10)
First, an alkoxide solution containing tantalum alkoxide and at least one of lithium alkoxide and lithium is sprayed onto the stirred lithium metal composite oxide powder (step S10).

A general stirrer can be used for stirring the lithium metal composite oxide powder. The metal composite oxide powder should be sufficiently stirred.

As the lithium metal composite oxide powder, a powder having properties similar to those of the lithium metal composite oxide powder 10 described above can be used.

The alkoxide solution can be obtained by mixing tantalum alkoxide and at least one of lithium alkoxide and lithium. The alkoxide solution can be prepared by adding, for example, tantalum alkoxide and at least one of lithium alkoxide and lithium to an organic solvent.

Examples of tantalum alkoxides include tantalum (V) methoxide [Ta(OCH ₃ ) ₅ ], tantalum (V) ethoxide [Ta(OC ₂ H ₅ ) ₅ ], tantalum (V) isopropoxide [Ta(OC ₃ H ₇ ) ₅ ], tantalum (V)-n-butoxide [Ta(OC ₄ H ₉ ) ₅ ], tetraethoxyacetylacetonatotantalum (V) [Ta(OC ₂ H ₅ ) ₄ (C ₅ H ₇ O ₂ ) ] and the like, and among these, tantalum (V) ethoxide is preferred.

Examples of at least one of lithium alkoxide and lithium include lithium ethoxide, lithium methoxide, propoxylithium, and lithium. Among these, lithium ethoxide and lithium are preferred, and lithium is more preferred.

The organic solvent is not particularly limited as long as it can dissolve the above compounds. For example, an alcohol can be used, and a lower alcohol having 4 or less carbon atoms is preferably used. Lower alcohols include ethanol, 2-propanol and 1-butanol, with ethanol and 2-propanol being preferred. Moreover, when alcohol is used as an organic solvent, dehydrated alcohol is preferable.

The alkoxide solution is sprayed in a mist state onto the stirred lithium metal composite oxide powder. The alkoxide solution is sprayed in an amount of preferably 2 parts by mass or more and 91 parts by mass or less, more preferably 16 parts by mass or more and 49 parts by mass or less with respect to 100 parts by mass of the lithium metal composite oxide powder.

(Heat treatment: step 20)
Next, the lithium metal composite oxide powder sprayed with the alkoxide solution is heat-treated (step S20). In a state in which an alkoxide solution containing tantalum and lithium is only sprayed onto the lithium metal composite oxide powder, carbon tends to remain on the surface of the lithium metal composite oxide powder, which can be a factor in increasing the interfacial resistance of the positive electrode. Therefore, heat treatment is performed to thermally decompose the metal alkoxide in the alkoxide solution.

The temperature of the heat treatment can be, for example, in the range of 250° C. or higher and 450° C. or lower, preferably 300° C. or higher and 400° C. or lower, and more preferably 350° C. or higher and 400° C. or lower. When the heat treatment temperature is within the above range, it is possible to obtain a positive electrode active material in which the interfacial resistance of the positive electrode is reduced and which is excellent in durability when used in a secondary battery.

The heat treatment time can be, for example, 0.5 hours or longer, preferably 1 hour or longer. Although the upper limit of the heating time is not particularly limited, it is, for example, 12 hours or less.

2. Non-Aqueous Electrolyte Secondary Battery A non-aqueous electrolyte secondary battery (hereinafter also referred to as a "secondary battery") according to the present embodiment includes a positive electrode, a negative electrode, and a non-aqueous electrolytic solution. Also, the secondary battery can be composed of the same components as those of a general non-aqueous electrolyte secondary battery. Each configuration of the secondary battery according to the present embodiment will be described below.

It should be noted that the embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery of the present invention can be modified, It can be implemented in a modified form. Moreover, the use of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited.

(positive electrode)
The positive electrode contains the positive electrode active material PA according to the present embodiment described above. A positive electrode can be produced, for example, as follows.

First, the positive electrode active material PA, a conductive material, and a binder are mixed, and if necessary, activated carbon and a solvent for viscosity adjustment are added, and the mixture is kneaded to prepare a positive electrode mixture paste. do.

The mixing ratio of each material in the positive electrode mixture paste is not particularly limited, and can be appropriately adjusted according to the required performance of the secondary battery. The mixture ratio of the materials can be in the same range as the positive electrode of a known non-aqueous electrolyte secondary battery. The content of the active material PA is 60 parts by mass or more and 95 parts by mass or less, the content of the conductive material is 1 part by mass or more and 20 parts by mass or less, and the content of the binder is 1 part by mass or more and 20 parts by mass or less. can.

The obtained positive electrode mixture paste can be applied, for example, to the surface of a current collector made of aluminum foil, dried, and the solvent can be dispersed to prepare a sheet-like positive electrode. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density.

The produced sheet-like positive electrode can be cut into an appropriate size according to the intended battery, and used for production of the battery. However, the method for producing the positive electrode is not limited to the above examples, and other methods may be used.

Examples of conductive agents that can be used include graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black.

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

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

(negative electrode)
Metallic lithium, a lithium alloy, or the like can be used for the negative electrode. In addition, the negative electrode is prepared by mixing a negative electrode active material capable of intercalating and deintercalating lithium ions with a binder, adding an appropriate solvent to make a paste, and applying the negative electrode mixture on the surface of a metal foil current collector such as copper. , dried, and optionally compressed to increase electrode density.

As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon substances such as coke can be used.

Similar to the positive electrode, a fluorine-containing resin such as PVDF can be used as the negative electrode binder, and an organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing the active material and the binder. can be used.

(separator)
A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode from the negative electrode and holds the electrolyte, and may be a thin film containing a resin such as polyethylene or polypropylene and having a large number of fine pores.

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

Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, and dipropyl carbonate; One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, and the like, or a mixture of two or more thereof is used. be able to.

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

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

(Shape and configuration of non-aqueous electrolyte secondary battery)
The shape of the non-aqueous electrolyte secondary battery of the present invention, which is composed of the positive electrode, negative electrode, separator, and non-aqueous electrolytic solution described above, can be cylindrical, laminated, and the like.

Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolytic solution, and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal connected to the outside are connected using a current collecting lead or the like, and sealed in the battery case to complete the non-aqueous electrolyte secondary battery. .

(Characteristic)
Since the non-aqueous electrolyte secondary battery using the positive electrode active material PA according to the present embodiment has low positive electrode resistance and high discharge capacity retention rate, it can have high output characteristics and high durability. For example, the positive electrode resistance of a coin secondary battery CBA having a positive electrode using the positive electrode active material PA obtained in a preferred embodiment is 1 , a low positive electrode resistance of preferably 0.96 or less, more preferably 0.95 or less, and even more preferably 0.90 or less can be obtained. Further, for example, in a coin secondary battery CBA having a positive electrode using a positive electrode active material PA obtained in a preferred form, the discharge capacity retention rate after 100 cycles is preferably more than 80%, more preferably 84%. A high discharge capacity retention rate of more than 90% is obtained, more preferably more than 90%.

The positive electrode (interface) resistance can be measured by the following method. First, the 2032-type coin-type secondary battery CBA as shown in FIG. obtain a good impedance spectrum. In the obtained impedance spectrum, two semicircles are observed in the high frequency region and the intermediate frequency region, and a straight line is observed in the low frequency region. was analyzed. In FIG. 4, Rs is the bulk resistance, R1 is the cathode film resistance, Rct is the electrolyte/cathode interfacial resistance (Li ^{2 +} transfer resistance at the interface), and W is the Warburg component.

The positive electrode interfacial resistance was confirmed for a non-aqueous electrolyte secondary battery having a positive electrode using the positive electrode active material obtained by the present invention.

EXAMPLES The present invention will be specifically described below using Examples, but the present invention is not limited to these Examples. A method for evaluating the obtained positive electrode active material will be described below.

(Manufacturing and evaluation of evaluation batteries)
A coin-type secondary battery CBA for evaluation (see FIG. 3) was produced by the following method, and the positive electrode interfacial resistance was measured and a charge-discharge cycle test was performed.

(Production of coin-type secondary battery CBA)
52.5 mg of the positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa to prepare a positive electrode (evaluation electrode) PE. did. Next, the produced positive electrode PE was dried in a vacuum dryer at 120° C. for 12 hours. Using the dried positive electrode (evaluation electrode) PE, negative electrode NE, separator SE, and electrolytic solution, the coin-type secondary battery CBA as shown in FIG. Made in a glove box.

For the negative electrode NE, a negative electrode sheet in which graphite powder with an average particle size of about 20 μm and polyvinylidene fluoride, which are punched into a disk shape with a diameter of ₁₄ mm, and polyvinylidene fluoride are coated on a copper foil is used. A mixture of equal amounts of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Ube Industries, Ltd.) was used. A polyethylene porous film having a film thickness of 25 μm was used as the separator SE. The coin-shaped secondary battery CBA has a gasket GA and a wave washer WW, and is assembled into a coin-shaped battery with a positive electrode can PC and a negative electrode can NC.

(positive electrode resistance)
The manufactured coin-type secondary battery CBA was charged at a charging potential of 4.0 V and measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B). Impedance spectra were obtained.

In the obtained impedance spectrum, two semicircles are observed in the high frequency region and the intermediate frequency region, and a straight line is observed in the low frequency region. was analyzed. 4 and 5, Rs is the bulk resistance, R1 is the cathode film resistance, Rct is the electrolyte/cathode interfacial resistance (li+ migration resistance at the interface), W is the Warburg component, and CPE1 and CPE2 are the constant phase elements.

(Charge-discharge cycle test)
In the charge-discharge cycle test, charging and discharging were repeated 100 cycles in a voltage range of 3.0 to 4.2 V under an environment of 60°C.

(Example 1)
As a base material, it is represented by Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ obtained by a known technique in which an oxide containing nickel as a main component and lithium hydroxide are mixed and fired. A lithium metal composite oxide powder was used. The specific surface area of the base material was 0.3 m ² /g. The composition of the lithium metal composite oxide powder was evaluated by the ICP method.

An alkoxide solution was prepared by dissolving 2.0 g of Li and 126 g of Ta(OC ₂ H ₅ ) ₅ in 859 g of absolute ethanol. 1.5 kg of the above lithium metal composite oxide powder was subjected to surface treatment by spraying the prepared alkoxide solution onto the surface of the positive electrode active material powder while sufficiently stirring it using a tumbling fluidizer. After that, heat treatment was performed at 400° C. for 1 hour in an oxygen atmosphere to obtain a positive electrode active material.

The composition and the content of Ta in the obtained positive electrode active material were analyzed by the ICP method, and it was confirmed that the composition was 2.0 atomic % with respect to the total number of atoms of nickel, cobalt and aluminum. . When the form of the compound containing Ta coated on the surface of the positive electrode active material was analyzed by XRD, it was confirmed that LiTaO ₃ was formed. Moreover, the battery characteristics were evaluated using the obtained positive electrode active material. Table 1 shows the composition and evaluation results of the positive electrode active material.

(Example 2)
The lithium metal composite oxide powder used as the base material was sprayed with an alkoxide solution prepared by dissolving 1.5 g of Li and 95 g of Ta(OC ₂ H ₅ ) ₅ in 638 g of absolute ethanol. A positive electrode active material was obtained under the same conditions as in Example 1. A coin-type battery CBA was produced using the obtained positive electrode active material, and the battery was evaluated. The content of Ta in the positive electrode active material was 1.5 atomic %, and the form of Ta was _LiTaO3 . Table 1 shows the composition and evaluation results of the positive electrode active material.

(Example 3)
The lithium metal composite oxide powder as the base material was sprayed with an alkoxide solution prepared by dissolving 1.0 g of Li and 63 g of Ta(OC ₂ H ₅ ) ₅ in 418 g of absolute ethanol. A positive electrode active material was obtained under the same conditions as in Example 1. A coin-type battery CBA was produced using the obtained positive electrode active material, and the battery was evaluated. The content of Ta in the positive electrode active material was 1.0 atomic %, and the form of Ta was _LiTaO3 . Table 1 shows the composition and evaluation results of the positive electrode active material.

(Example 4)
The lithium metal composite oxide powder as the base material was sprayed with an alkoxide solution prepared by dissolving 0.5 g of Li and 31.5 g of Ta(OC ₂ H ₅ ) ₅ in 202 g of absolute ethanol. , a positive electrode active material was obtained under the same conditions as in Example 1. A coin-type battery CBA was produced using the obtained positive electrode active material, and the battery was evaluated. The content of Ta in the positive electrode active material was 0.5 atomic %, and the form of Ta was _LiTaO3 . Table 1 shows the composition and evaluation results of the positive electrode active material.

(Example 5)
The lithium metal composite oxide powder as the base material was sprayed with an alkoxide solution prepared by dissolving 0.1 g of Li and 6 g of Ta(OC ₂ H ₅ ) ₅ in 21 g of absolute ethanol. A positive electrode active material was obtained under the same conditions as in Example 1. A coin-type battery CBA was produced using the obtained positive electrode active material, and the battery was evaluated. The content of Ta in the positive electrode active material was 0.1 atomic %, and the form of Ta was _LiTaO3 . Table 1 shows the composition and evaluation results of the positive electrode active material.

(Example 6)
A coin-type battery CBA was produced using the positive electrode active material produced under the same conditions as in Example 3, except that the material was heat-treated at 350° C. for 1 hour, and the battery was evaluated. The Ta content at this time was 1.0 atomic %, and the form of Ta was _LiTaO3 .

(Example 7)
A coin-type battery was produced using the positive electrode active material for a non-aqueous electrolyte secondary battery produced in the same manner as in Example 3 except that the material was heat-treated at 300° C. for 1 hour, and the battery was evaluated. The content of Ta in the obtained positive electrode active material was 1.0 atomic %, and the form of Ta was _LiTaO3 .

(Example 8)
Except that the lithium metal composite oxide powder as the base material was sprayed with an alkoxide solution prepared by dissolving 3.0 g of Li and 63 g of Ta(OC ₂ H ₅ ) ₅ in 1299 g of absolute ethanol. A positive electrode active material was obtained under the same conditions as in Example 1. A coin-type battery CBA was produced using the obtained positive electrode active material, and the battery was evaluated. The content of Ta in the positive electrode active material was 1.0 atomic %, and the form of Ta was Li ₃ TaO ₄ . Table 1 shows the composition and evaluation results of the positive electrode active material.

(Comparative example 1)
A coin-type battery CBA was produced using the lithium metal composite oxide powder used as the base material in Example 1 as a positive electrode active material, and the battery was evaluated. Table 1 shows the composition and evaluation results of the positive electrode active material.

(evaluation)
The non-aqueous electrolyte secondary batteries using the positive electrode active materials of Examples had a lower positive electrode interface resistance and a higher discharge capacity retention rate after the cycle test than the Comparative Examples, and exhibited excellent battery characteristics. confirmed to have In particular, it was confirmed that the non-aqueous electrolyte secondary battery using the positive electrode active material of Example 3 had a significantly reduced positive electrode interfacial resistance and excellent output characteristics.

In the positive electrode active material of Comparative Example 1, the surface of the lithium metal composite oxide was not coated with lithium tantalate, and the non-aqueous electrolyte secondary battery using the positive electrode active material of Comparative Example 1 was compared with the Examples. Therefore, the positive electrode interfacial resistance was high, and the capacity retention rate after the 100-cycle test was low.

From the above results, the non-aqueous electrolyte secondary batteries using the positive electrode active materials of Examples have low positive electrode interfacial resistance, good durability, and excellent battery characteristics. It becomes easy to respond to output and high durability.

A secondary battery using the positive electrode active material of the present invention can be suitably used as a power source for small portable electronic devices (notebook personal computers, mobile phone terminals, etc.) that are always required to have a high capacity. It can also be suitably used for electric vehicle batteries that require high output and high durability.

In addition, the secondary battery using the positive electrode active material of the present invention has excellent durability and can be made smaller and higher in output, so it can be used as a power source for electric vehicles that are limited in mounting space. It can be used preferably. In addition, the secondary battery using the positive electrode active material of the present invention is not only a power source for electric vehicles driven by electrical energy, but also a so-called hybrid vehicle that uses a combustion engine such as a gasoline engine or a diesel engine and a secondary battery. It can also be used as a power source for plug-in hybrid vehicles.

PA: positive electrode active material 1: primary particles 2: secondary particles 10: lithium metal composite oxide 20: coating layer PE: positive electrode (evaluation electrode)
NE... Negative electrode SE... Separator GA... Gasket WW... Wave washer PC... Positive electrode can NC... Negative electrode can CBA... Coin type secondary battery

Claims (9)

A lithium metal composite oxide powder composed of at least one of primary particles and secondary particles formed by agglomeration of a plurality of primary particles, and a coating layer formed on the surface of the lithium metal composite oxide powder. A positive electrode active material for an aqueous electrolyte secondary battery,
The positive electrode active material contains Li, Ni, Co, and Al, and the atomic ratio of the respective metals is Li:Ni:Co:Al=z:(1-xy):x:y (where 0. satisfies 01 ≤ x ≤ 0.15, 0 < y ≤ 0.05, 0.97 ≤ z ≤ 1.20),
The coating layer contains a compound containing tantalum and lithium,
Positive electrode active material for non-aqueous electrolyte secondary batteries. The amount of tantalum contained in the coating layer is 0.1 atomic % or more and 2.0 atomic % or less with respect to the total number of atoms of Ni, Co and Al contained in the positive electrode active material powder. 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to 1. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or ₂ , wherein the compound containing tantalum and lithium contains lithium tantalate composed of at least one of _LiTaO3 and _Li3TaO4 . . spraying an alkoxide solution containing tantalum alkoxide and at least one of lithium alkoxide and lithium onto the lithium metal composite oxide powder being stirred;
heat-treating the sprayed lithium metal composite oxide powder to form a coating layer containing a compound containing tantalum and lithium on the surface of the lithium metal composite oxide powder,
The lithium metal composite oxide powder contains Li, Ni, Co, and Al, and the atomic ratio of each metal is Li:Ni:Co:Al=z:(1-xy):x:y (where , 0.01 ≤ x ≤ 0.15, 0 < y ≤ 0.05, 0.97 ≤ z ≤ 1.20.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. 5. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, wherein the alkoxide solution is sprayed in an amount of 2 parts by mass or more and 91 parts by mass or less with respect to 100 parts by mass of the lithium metal composite oxide powder. . The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4 or 5, wherein the heat treatment is performed in the range of 300°C or higher and 400°C or lower for 1 hour or longer. The amount of tantalum contained in the alkoxide solution is 0.1 atomic % or more and 2.0 atomic % or less with respect to the total number of atoms of nickel, cobalt and aluminum contained in the lithium metal composite oxide powder. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 4 to 6. The non-aqueous electrolyte secondary according to any one of claims 4 to 7, wherein the compound containing tantalum and lithium contains lithium tantalate consisting of at least one of LiTaO ₃ and Li ₃ TaO ₄ A method for producing a positive electrode active material for a battery. including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery, wherein the positive electrode comprises the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3.

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