JP2010064944A - Lithium-nickel composite oxide and nonaqueous electrolyte secondary battery using the lithium-nickel composite oxide as positive electrode active material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a material to form into a positive electrode active material having high initial discharge capacity and initial charge capacity, and to provide a nonaqueous electrolyte secondary battery of high performance using the positive electrode active material. <P>SOLUTION: The lithium-nickel composite oxide is composed of a hexagonal lithium-nickel composite oxide with a layered structure and is expressed by the compositional formula of Li<SB>x</SB>Ni<SB>(1-y-z)</SB>Co<SB>y</SB>M<SB>z</SB>O<SB>2</SB>; wherein: x is 0.95 to 1.10; y is >0 to 0.20; z is >0 to 0.15; and the M element is at least one of element selected from the elemental group consisting of Al, Ti, Mn, Ga, Mg and Nb, and has a specific surface area of 0.5 to 2.0 m<SP>2</SP>/g. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lithium nickel composite oxide suitable for a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same.

In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, development of secondary batteries having high energy density, small size and light weight is strongly desired. The use of lithium ion secondary batteries as water-based electrolyte secondary batteries is highly desired.
In this lithium ion secondary battery, lithium metal, lithium alloy, metal oxide, carbon, or the like is used as the negative electrode material. These negative electrode materials are materials capable of removing and inserting Li. In addition, research and development are actively being conducted on the positive electrode material of such a lithium ion secondary battery.

In particular, a lithium ion secondary battery using a lithium metal composite oxide, particularly a lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, as a positive electrode material can obtain a high voltage of 4 V, and thus has high energy. Practical use is progressing as a battery of high density.
In the lithium ion secondary battery using this lithium cobalt composite oxide, many developments have been made so far to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained.

  However, since the lithium cobalt composite oxide uses a rare and expensive cobalt compound as a raw material, it causes an increase in the cost of the battery. Specifically, the unit price per capacity of a battery using a lithium cobalt composite oxide is about four times as high as that of a nickel-metal hydride battery already used as a secondary battery, so that the application to be applied is considerably limited. Is the actual situation. For this reason, it is expected that a positive electrode active material having a performance equal to or higher than that of the lithium cobalt composite oxide as the positive electrode active material and cheaper will be provided.

  Recently, not only small secondary batteries for portable electronic devices but also expectations for the application of lithium ion secondary batteries to large secondary batteries for power storage and electric vehicles are increasing. For this reason, reducing the cost of the active material and making it possible to manufacture a cheaper lithium ion secondary battery is expected to have a large ripple effect in a wide range of fields.

Under such circumstances, materials newly proposed as positive electrode active materials for lithium ion secondary batteries include lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese, which is cheaper than cobalt, and nickel. It may be mentioned the lithium nickel composite oxide with (LiNiO _2).

  Here, lithium manganese composite oxide is an inexpensive alternative material, and has excellent thermal stability, especially safety with respect to ignition. However, since it is only about half of the lithium cobalt composite oxide, it has a drawback that it is difficult to meet the demand for higher capacity of lithium ion secondary batteries, which is increasing year by year. Further, in the temperature range of 45 ° C. or higher, there is a drawback that self-discharge is intense and the charge / discharge life is also reduced.

  On the other hand, the lithium nickel composite oxide has almost the same theoretical capacity as the lithium cobalt composite oxide, and shows a slightly lower battery voltage than the lithium cobalt composite oxide. For this reason, decomposition | disassembly by oxidation of electrolyte solution does not become a problem, and development is performed actively from expecting higher capacity | capacitance. However, when a lithium-ion secondary battery is made using a lithium-nickel composite oxide that is purely composed of nickel without replacing nickel with other elements as the positive electrode active material, the cycle is higher than that of the lithium-cobalt composite oxide. There were also problems that the characteristics were inferior, and that battery performance was relatively easily lost during use and storage in a high temperature environment.

For this reason, various proposals have been made for improving the performance of the lithium nickel composite oxide for the purpose of solving these drawbacks.
For example, Patent Document 1 discloses Li _x Ni _a Co _b McO ₂ (where 0.8 ≦ x ≦ 1.2, 0.01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, 0 .01 ≦ c ≦ 0.3, 0.8 ≦ a + b + c ≦ 1.2, M is at least selected from Al, V, Mn, Fe, Cu and Zn
A lithium-containing composite oxide represented by one kind of element) has been proposed.

Patent Document 2 discloses Li _w Ni _x CoB _z O ₂ (where 0.05 ≦ w ≦ 1.10, 0.5 ≦ x ≦ 0.995, 0.005 ≦ z ≦ 0.2, x + y + z). = 1) Lithium-containing composite oxides have been proposed.

In Patent Document _3, at least one metal is _{Li a M b Ni c Co d} O e (M to Al, Mn, Sn, In, Fe, V, Cu, Mg, Ti, Zn, is selected from the group consisting of Mo And 0 <a <1.3, 0.02 ≦ b ≦ 0.5, 0.02 ≦ d / c + d ≦ 0.9, 1.8 <e <2.2, b + c + d = 1) has been proposed.

  These lithium composite oxides disclosed in Patent Documents 1 to 3 have been proposed in order to maintain good battery performance during storage and use in a high-temperature environment. It is a lithium-containing composite oxide that is partially substituted with elements such as boron, cobalt, and aluminum. For example, when aluminum is selected as the substitution element, it is confirmed that if the substitution amount from nickel to aluminum is increased, the decomposition reaction of the positive electrode active material is suppressed and the thermal stability is improved. Yes. It has also been confirmed that the cycle characteristics are improved by replacing a part of nickel with cobalt.

Further, Patent Document 4 discloses Li _(1-xa) A _x Ni _{(1 )} for the purpose of providing a positive electrode active material having a high capacity and excellent charge / discharge cycle and a high-performance secondary battery using the positive electrode active material. _{-y-b) B y O 2} ( where, a is either Sr strontium or Ba barium, or of Mg magnesium, Ca calcium, Sr strontium and Ba and at least two alkaline earth metal element selected from among barium B is composed of at least one transition metal element excluding Ni, wherein x and y are 0 <x ≦ 0.10, 0 <y ≦ 0.30, and a and b are −0. 10 ≦ a ≦ 0.10, −0.15 ≦ b ≦ 0.15; provided that x represents the total number of moles of a, and when a is composed of two or more alkaline earth metal elements, x is all The total number of moles of alkaline earth metal elements, y is the total number of b A positive electrode active material, wherein y is the total number of moles of all transition metal elements except Ni when b is composed of two or more transition metal elements Has been proposed.

Patent Document 5 discloses a general formula Li _x (Ni _(1-y) Co _y ) _(1-z) M _z O ₂ (0.98 ≦ x ₎ as a positive electrode active material for a lithium secondary battery having a high initial discharge capacity. ≦ 1.10, 0.05 ≦ y ≦ 0.2, 0.01 ≦ z ≦ 0.2, M = one or more of Al, Zn, Ti, and Mg) in the crystal by Rietveld analysis The specific surface area of the positive electrode active material, which is a spherical secondary particle having an average particle diameter of 5 to 15 μm, is less than 1.0 m ² / g before and after water treatment, with the Li site occupation ratio of the Li site being 98% or more. A lithium nickel composite oxide has been proposed.

  These substitution elements will definitely help solve some of the problems of lithium-nickel composite oxides, but in order to bring out the original performance of lithium-nickel composite oxides, the crystal structure is precisely controlled. It is most important to do. For example, in Patent Document 6, it is said that the Ni seat occupancy of the 3a site needs to be 1.5% to 2.9% in the crystal structure, and the Ni seat occupancy of the 3a site is actually low. It is confirmed that the lower the capacity, the higher the initial charge / discharge capacity and the lower the irreversible capacity.

  In order to synthesize a positive electrode active material having a complete crystal structure with a low Ni site occupancy rate at the 3a site, that is, a high Li site occupancy rate, generally, Li is charged to a higher stoichiometric ratio. There is a need. However, if Li is charged higher than the stoichiometric ratio, excess Li will remain unreacted after firing, and this will react with carbon dioxide in the atmosphere and change to lithium carbonate, which is then incorporated into the secondary battery as an electrode. In such a case, gas may be generated and the battery may swell. Further, the remaining unreacted lithium may cause a problem that when the positive electrode active material is made into a paste in a later electrode forming process, the paste is gelled and cannot be applied. On the other hand, when Li is charged and synthesized without making it higher than the stoichiometric ratio, the Li seat occupancy becomes insufficient and the charge / discharge characteristics deteriorate.

The positive electrode active material for a non-aqueous electrolyte secondary battery proposed in Patent Document 7 has been developed in consideration of such points, and LixNi (1-y) MyO ₂ (provided that 0.96 ≦ x ≦ 1. 09, 0 <y ≦ 0.25, and M is a lithium metal represented by Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, Ga). It is a positive electrode active material for a non-aqueous electrolyte secondary battery made of a composite oxide powder, the transition metal ions contained in the 3a site that is the Li site move to the 3b site, and the seat occupancy rate of the Li ions in the 3a site is It is a positive electrode active material for a non-aqueous electrolyte secondary battery that is increased by 0.1% to 0.6% compared to that before the water stirring treatment, and achieves a long life with good cycle characteristics.
Japanese Patent Laid-Open No. 8-213015 JP-A-8-45509 Japanese Patent Laid-Open No. 5-242891 Japanese Patent No. 3460413 JP 2004-171961 A JP-A-9-298062 JP 2007-242288 A

The positive electrode active material for a non-aqueous electrolyte secondary battery disclosed in Patent Document 7 certainly reduces the disturbance of primary particles, reduces the internal resistance of the crystal, and has a long-life non-aqueous electrolyte with good cycle characteristics. A positive electrode active material for a secondary battery can be obtained stably. However, as can be seen from Table 1 on page 14 of the specification of Patent Document 7, the initial discharge capacity of this positive electrode active material is on the order of 190 mAh / g, which can cope with the current situation where a higher initial discharge capacity is required. is not.
Therefore, the present invention has been made in view of such problems, and provides a material used for a positive electrode active material having an initial discharge capacity and an initial charge capacity higher than those of the prior art, and a high performance using the same. An object is to provide a non-aqueous electrolyte secondary battery.

The inventors have a composition formula Li _x Ni _(1-yz) Co _y M _z O ₂ (0.95 ≦ x ≦ 1.10, 0 <y ≦ 0.20, 0 <z ≦ 0.15). , M is at least one element selected from Al, Ti, Mn, Ga, Mg, and Nb), and a hexagonal lithium-nickel composite oxide having a layered structure has been investigated. The lithium-nickel composite oxide that satisfies the above condition has been found to satisfy the above-mentioned problems, and the present invention has been achieved.

That is, the first invention for solving the above problems is a hexagonal lithium nickel composite oxide having a layered structure, wherein x is 0.95 or more and 1.10 or less, y is greater than 0, 0.20 Hereinafter, Li _x Ni _{(1-y−), which is} composed of at least one element selected from the group consisting of Al, Ti, Mn, Ga, Mg, and Nb, with z greater than 0 and 0.15 or less. _z) A hexagonal lithium nickel composite oxide having a layered structure and a specific surface area of 0.5 to 2.0 m ² / g, represented by a composition formula of Co _y M _z O ₂ .

Further, the intermediate product has x of 0.95 or more and 1.10 or less, y is greater than 0, 0.20 or less, z is greater than 0 and 0.15 or less, and the M element is Al, Ti, Li of the Li main layer represented by the composition formula of Li _x Ni _(1-yz) Co _y M _z O ₂ composed of at least one element selected from the element group of Mn, Ga, Mg, and Nb The seat occupancy is 95% or more, the crystallite diameter is 73 to 200 nm, and the specific surface area is 0.2 to 1.0 m ² / g.

Further, a nickel composite oxide containing a Co element and an M element represented by a composition formula of a raw material lithium compound and Ni _(1-yz) Co _y M _z O is used as the Li element of the lithium compound and the nickel. The molar ratio in the molar sum of Ni element, Co element, and M element of the composite oxide: a mixture of [Li / Ni + Co + M] of 1.0 or more is fired. An intermediate product having a diameter of 73 to 200 nm and a specific surface area of 0.2 to 1.0 m ² / g is generated by subjecting the intermediate product to Li removal treatment. X is 0.95 or more and 1.10 or less, y Is greater than 0 and not greater than 0.20, z is greater than 0 and not greater than 0.15, and the M element is composed of at least one element selected from the group consisting of Al, Ti, Mn, Ga, Mg, and Nb. _{li x Ni (1-y-} z) C represented by a composition formula of _y M _z O _2, specific surface area of hexagonal system lithium nickel composite oxide having a layered structure is 0.5~2.0m ² / g.

  These lithium nickel composite oxides are characterized by being composed of spherical or oval spherical secondary particles in which a plurality of primary particles having an average particle size of 0.1 to 1.0 μm are assembled.

  A second invention of the present invention is a non-aqueous electrolyte secondary battery using the lithium nickel composite oxide according to any one of claims 1 to 4 as a positive electrode active material.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is represented by a composition formula: Li _x Ni _(1-yz) Co _y M _z O ₂ , 0.95 ≦ x ≦ 1.10. Hexagonal layered structure composed of at least one element selected from the group consisting of Al, Ti, Mn, Ga, Mg, and Nb, with 0 <y ≦ 0.20 and 0 <z ≦ 0.15 A lithium compound and a compositional formula: Ni _(1-yz) Co _y M _z O represented by a lithium compound and a nickel composite oxide containing M element and Li, Molar ratio in the sum of Ni element, Co element and M element: After mixing so that [Li / Ni + Co + M] becomes 1.0 or more, it is obtained by removing unreacted lithium by baking and washing with water. Specific surface area by removing unreacted lithium in the intermediate product Is 0.5 to 2.0 m ² / g, and it is easy to secure a reaction area between the positive electrode and the electrolytic solution, and a good charge / discharge capacity can be obtained.

  Further, by collecting a plurality of primary particles having an average particle size of 0.1 to 1.0 μm to form secondary particles, it is easy to secure a reaction area between the positive electrode and the electrolyte and secure a high packing density. be able to. Moreover, by setting the crystallite diameter to 73 to 200 nm, fine powder can be reduced and spherical or elliptical secondary particles having high filling properties can be obtained.

From the above, the lithium nickel composite oxide of the present invention is suitable as a positive electrode active material having a high initial discharge capacity and an initial charge capacity. Therefore, when used as a positive electrode active material of a non-aqueous electrolyte secondary battery, A secondary battery having a high coulomb efficiency of the secondary battery and a small irreversible capacity can be provided, and at the same time, gas generation in a high-temperature storage environment that causes the battery to swell can be suppressed.
The non-aqueous electrolyte secondary battery of the present invention satisfies the recent demand for higher capacity for small secondary batteries such as portable electronic devices, and is also demanded as a power source used for large secondary batteries for hybrid vehicles and electric vehicles. Safety, and has a significant industrial effect.

In order to solve the above problems, the present inventors have advanced various studies, and as a result, have obtained the following knowledge.
The stoichiometry of a compound is determined by the seat occupancy of each ion of the compound in a Rietveld analysis of X-ray diffraction (for example, RA Young, ed., “The Rietveld Method”, Oxford University Press (1992)). It can be evaluated by using as an index. In the case of a hexagonal compound, at the 3a, 3b, and 6c sites, when LiNiO ₂ has a complete stoichiometric composition, the 3a site is Li and the 3b site is Ni. In the 6c site, O shows 100% seat occupancy.

  That is, the lithium nickel composite oxide in which the Li ion seat occupancy at the 3a site is 97% or more is excellent in stoichiometry, and this Li seat occupancy is considered as an index for the active material for secondary batteries. In this case, since Li can be desorbed and inserted, the integrity of the crystal can be maintained even if Li deficiency occurs. It is thought to show gender.

  In the present invention, a part of Ni is replaced with Co for improving cycle characteristics, and M element of a metal element (M element is Al, Ti, Mn, Ga, Mg, Nb for improving thermal stability and storage characteristics). Is a lithium nickel composite oxide that can be used as a positive electrode active material of a secondary battery substituted with at least one element selected from In the case where Li ions proceed in a reversible manner, if other metal ions enter the 3a site, which is the Li diffusion path in the solid phase, the diffusion path is inhibited, which deteriorates the charge / discharge characteristics of the battery. As a result of repeated investigations on positive electrode active materials prepared by various synthesis methods, the present inventors have found that non-lithium ions at the 3a site obtained by Rietveld analysis of powder X-ray diffraction patterns. By finding a deep relationship between the mixing rate and the irreversible capacity, and using a positive electrode active material having a non-lithium ion occupancy rate of 3% or less at the 3a site, a diffusion path for Li in the solid phase is secured. In addition, the present inventors have found that the irreversible capacity can be improved.

  Such a positive electrode active material having a high Li site occupancy at the 3a site uses a nickel composite oxide containing a lithium compound, Co, and a metal element M as a raw material, and a molar ratio between the Li and the metal element (Ni + Co + M): It can be obtained by firing a mixture having [Li / Ni + Co + M] of 1.0 or more.

However, when the molar ratio: [Li / Ni + Co + M] is increased more than necessary, excess Li remains unreacted in the positive electrode active material after firing, and this reacts with carbon dioxide in the atmosphere to change to lithium carbonate. When it is incorporated in a battery as an electrode, it may cause gas generation, which may cause the battery to swell. Further, the remaining unreacted Li may cause a problem that when the positive electrode active material is made into a paste in a later electrode forming process, the paste is gelled and cannot be applied.
On the other hand, when Li is made lower than the stoichiometric ratio, the Li seat occupancy becomes insufficient, and the charge / discharge characteristics, particularly the irreversible capacity and the initial capacity are deteriorated.

Then, the residual lithium compound which causes gas generation is reduced by performing the process which removes excess Li after baking.
As a method for removing this excess Li, a method is adopted in which the fired lithium nickel composite oxide is washed with water or an aqueous solution in which lithium is dissolved, filtered, and then heated and dried in a vacuum. When this drying is performed in the air, lithium contained in the slightly remaining water is carbonated again and becomes a causative substance for gas generation. Therefore, the drying is preferably performed in a vacuum.

  Furthermore, although some metal elements move to the 3a site depending on the Li removal treatment, and the Li seat occupancy is reduced, the surface residual lithium compound is removed at the Li seat occupancy of 95% or more. Even if it is a lithium nickel composite oxide that does not inhibit the diffusion of lithium on the surface and has a lower Li seat occupancy than before, it becomes a positive electrode active material having a good charge / discharge capacity.

When the intermediate product produced after firing is washed with water or an aqueous solution in which Li is dissolved, if the specific surface area of the lithium nickel composite oxide is extremely large, the effect of removing residual lithium compounds is sufficiently obtained. Therefore, the specific surface area of the lithium nickel composite oxide before the removal treatment is desirably 0.2 to 1.0 m ² / g. On the other hand, if the specific surface area after the removal treatment is too small, the contact area with the electrolytic solution becomes small, the resistance accompanying the entry / exit of lithium ions increases, and the charge / discharge characteristics deteriorate. It is desirable that the specific surface area of the lithium nickel composite oxide produced by the removal treatment is 0.5 to 2.0 m ² / g.

The positive electrode active material is preferable from the viewpoint of the contact area with the electrolytic solution, the smaller the primary particles constituting the positive electrode active material, but if it is too fine, it becomes a fine powder and reduces the molding density of the electrode, resulting in high Charge / discharge characteristics cannot be obtained. Therefore, it is preferable that the average value of the particle diameter of a primary particle is 0.1-1.0 micrometer.
However, since the filling properties are poor if the primary particles remain, it is preferable to form a secondary particle by aggregating a plurality of these primary particles, and in order to ensure particularly high filling properties, it is preferable to form secondary particles. The shape of the particles is preferably spherical or elliptical.

Furthermore, when the powder of the positive electrode active material is formed by agglomeration of small primary particles to form secondary particles, fine gaps are formed between the primary particles inside the secondary particles by growing each primary particle to some extent. Thus, it is possible to supply the Li ions to the inside of the secondary particles through the electrolytic solution through the penetration of the electrolytic solution into the gap. As a result, the speed at which Li ions diffuse throughout the secondary particles is increased, and the irreversible capacity is reduced.
In this case, the degree of primary particle growth can be determined by the crystallite diameter calculated from the 003 peak of the X-ray diffraction pattern. If the crystallite diameter is in the range of 73 to 200 nm, the filling property and charge / discharge are determined. A positive electrode active material having both properties can be obtained.

  When a non-aqueous electrolyte secondary battery is configured using such a positive electrode active material of lithium nickel composite oxide, even a lithium nickel composite oxide having a lower Li seat occupancy than the conventional one has good charge / discharge capacity. A secondary battery is formed.

  Next, an embodiment of a non-aqueous electrolyte secondary battery, that is, a lithium ion secondary battery will be described in detail for each component. The non-aqueous electrolyte secondary battery according to the present invention is composed of the same constituent elements as a general lithium ion secondary battery, such as a positive electrode, a negative electrode, and a non-aqueous electrolyte. The embodiments described below are only examples, and the non-aqueous electrolyte of the present invention is implemented in various modified and improved forms based on the knowledge of those skilled in the art including the following embodiments. The use of the secondary battery is not particularly limited.

Hereinafter, a non-aqueous electrolyte secondary battery using the lithium nickel composite oxide of the present invention as a positive electrode active material will be described.
(1) Positive electrode active material, positive electrode The positive electrode active material used for the non-aqueous electrolyte secondary battery according to the present invention is an alkaline solution added to a mixed aqueous solution of nickel salt and cobalt salt and an aqueous solution of M element, and these are added at a constant rate. The atomic ratio of Co, Ni, and M in the reaction vessel is determined by the composition formula: Li _x Ni _(1-yz) Co _y M _z O ₂ (0.95 ≦ x ≦ 1.10. , 0 <y ≦ 0.20, 0 <z ≦ 0.15, and the M element has an atomic ratio of at least one element selected from the group consisting of Al, Ti, Mn, Ga, Mg, and Nb) Co-precipitate. Then, after reaching a steady state, a precipitate is collected, filtered and washed with water to obtain a composite hydroxide of Ni, Co and M.

Thereafter, the obtained composite hydroxide is heat-treated at a temperature of 300 ° C. or higher and lower than 800 ° C. The heat treatment temperature is more preferably 650 ° C to 800 ° C. When the heat treatment temperature is 800 ° C. or higher, the grain growth after the composite hydroxide is changed to an oxide is remarkable, the reactivity with the lithium compound is deteriorated, and the target lithium composite oxide cannot be obtained. Further, if the temperature is lower than 300 ° C., the temperature at which the hydroxide changes to an oxide is not reached, so that the diffusion of the M element is not sufficient, and at the same time, the primary particle growth does not proceed. I can't.
In order to maximize the effect of increasing the tap density by promoting the grain growth of the primary particles forming the secondary particles to reduce the specific surface area and reducing the gap between the primary particles. Done.

  The lithium nickel composite compound which is the positive electrode active material of the present invention is a mixture of lithium compound, nickel, cobalt and M element composite oxide obtained by the above method, respectively, and 650 ° C. to 800 ° C. in an oxygen stream. It can be synthesized by baking at a temperature of about 5 to 50 hours. When the temperature is lower than 650 ° C., the reaction with the lithium compound does not proceed sufficiently, and it becomes difficult to synthesize a lithium nickel composite oxide having a desired layered structure. When the temperature exceeds 800 ° C., Ni is mixed into the Li layer and Li is mixed into the Ni layer, and the layer structure is disturbed. The site occupancy rate of metal ions other than lithium at the 3a site becomes larger than 3%, and the lithium site. In this case, the mixing rate of metal ions at the 3a site is increased, the lithium ion diffusion path is obstructed, and a battery using the positive electrode is not preferable because the initial capacity and output are reduced.

  The particle size distribution D50 of the obtained positive electrode active material is 4.5 to 10.0 μm, and the tap density is preferably 1.5 g / ml or more. This is because the cathode active material becomes unsuitable as a cathode material, such as being unable to be filled.

Next, the positive electrode mixture forming the positive electrode and each material constituting the positive electrode mixture will be described.
A powdered positive electrode active material, a conductive material, and a binder are mixed, and activated carbon and a target solvent such as viscosity adjustment are added as necessary, and these are kneaded to prepare a positive electrode mixture paste.
The respective mixing ratios in the positive electrode mixture are also important factors that determine the performance of the lithium secondary battery. Therefore, when the total mass of the solid content of the positive electrode mixture excluding the solvent is 100% by mass, the content of the positive electrode active material is 60 to 95% by mass, respectively, in the same manner as the positive electrode of a general lithium secondary battery. It is desirable that the content of the material is 1 to 20% by mass and the content of the binder is 1 to 20% by mass.

  The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, aluminum foil, and dried to scatter 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 according to the intended battery and used for battery production. However, the manufacturing method of the positive electrode is not limited to the above-described examples, and may depend on other methods.

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

  As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluorine rubber, styrene butadiene, cellulose resin, polyacrylic acid, or the like can be used.

  The binder plays the role of holding the active material particles, and for example, fluorine-containing resins such as polytetrafluoroethylene, polyvinylidene fluoride, and fluororubber, and thermoplastic resins such as polypropylene and polyethylene 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. Moreover, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(2) Negative electrode active material, negative electrode For the negative electrode, metallic lithium, lithium alloy, etc., and a negative electrode active material capable of occluding and desorbing lithium ions are mixed with a binder, and an appropriate solvent is added to form a paste. The negative electrode mixture is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as necessary.

  In addition, as the negative electrode active material, for example, a fired organic compound such as natural graphite, artificial graphite, or a phenol resin, or a powdery material of a carbon material such as coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as polyvinylidene fluoride can be used as in the case of the positive electrode, and the active material and the solvent for dispersing the binder include N-methyl-2-pyrrolidone. Organic solvents can be used.

(3) 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 fine holes can be used.

(4) 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 , and their complex salts can be used, and the non-aqueous electrolyte includes a radical scavenger, A surfactant, a flame retardant, and the like may be included.

(5) Shape and configuration of battery The shape of the non-aqueous electrolyte secondary battery according to the present invention composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte described above can be various, such as a cylindrical type and a laminated type. However, in any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the electrode body is impregnated with a non-aqueous electrolyte. The positive electrode current collector and the positive electrode terminal that communicates with the outside, and the negative electrode current collector and the negative electrode terminal that communicates with the outside are connected using a current collecting lead or the like. The battery having the above structure can be sealed in a battery case to complete the battery.

Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples.
Lithium obtained from Rietveld analysis of the composition of the positive electrode active material Li _x Ni _(1-yz) Co _y MzO ₂ of each example and comparative example, specific surface area before unreacted lithium removal treatment, and X-ray diffraction pattern Table 1 shows the Li seat occupancy of the main layer, the specific surface area after the unreacted lithium removal treatment, and the Li seat occupancy of the Li main layer obtained from the Rietveld analysis of the X-ray diffraction pattern.

A 2032 type coin battery 10 as shown in FIG. 1 was prepared using the positive electrode active materials of the examples and comparative examples, and the battery was evaluated.
70% by mass of the positive electrode active material powder was mixed with 20% by mass of acetylene black and 10% by mass of PTFE. Lithium metal is used for the negative electrode 1, and the separator 2 is impregnated with an equivalent mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (made by Toyama Pharmaceutical Co., Ltd.) using 1M LiClO ₄ as a supporting salt. It was used in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C. In FIG. 1, 4 is a gasket, 5 is a negative electrode can, 6 is a positive electrode can, and 7 is a current collector.

The produced coin battery is left to stand for about 24 hours, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 0.5 mA / cm ² and charged to a cutoff voltage of 4.3 V to be initially charged. The capacity when discharging to a cut-off voltage of 3.0 V after a 1 hour rest was defined as the initial discharge capacity. Table 2 shows the initial charge / discharge capacity and irreversible capacity obtained by this method.

Example 1
LiNi _0.82 Co _0.15 Al _0.03 O _{2 in} which 15 at% of Ni is replaced with Co and 3 at% is replaced with Al so that x = 1, y = 0.15, and z = 0.03. In order to synthesize, a mixture of nickel sulfate, cobalt sulfate, and aluminum sulfate was appropriately dissolved so that the molar ratio of Ni, Co, and Al was 82: 15: 3 to prepare a raw material aqueous solution.
Next, an alkaline aqueous solution was poured into this raw material aqueous solution, and a metal composite hydroxide formed by solid solution with Ni _0.82 Co _0.15 Al _0.03 (OH) ₂ by a coprecipitation method was obtained. After filtering the resulting composite hydroxide precipitate, it is further washed with water and filtered, dried in the air atmosphere, and further heat treated at 700 ° C. for 10 hours using an electric furnace, and the molar ratio of Ni, Co, and Al is A metal composite oxide formed by solid solution at 82: 15: 3 was obtained.

After mixing this metal composite oxide and commercially available lithium hydroxide monohydrate (manufactured by FMC) so that the molar ratio [Li / Ni + Co + M] of Li and the metal element (Ni + Co + Al) is 1.00 The mixture was sufficiently mixed using a mixer (Spartan Luther manufactured by Fuji Powder Co., Ltd.), and the temperature was increased at 2 ° C / min in a stainless steel mortar and held at 450 ° C for 5 hours in an oxygen atmosphere. Subsequently, it was baked at 750 ° C. for 20 hours, and cooled to room temperature to obtain an intermediate product as a baked product. After pulverization and classification, the specific surface area of the powder was measured using the BET method.
Next, as a treatment for removing unreacted lithium, pure water having the same weight as that of the intermediate product is added and stirred at room temperature for 30 minutes to remove unreacted lithium. I got a thing. The specific surface area of the obtained lithium nickel composite oxide was measured using the BET method.

  When this intermediate product was observed by SEM, it was confirmed that the average particle diameter of the primary particles was 0.2 μm, and a plurality of these primary particles were aggregated to form spherical secondary particles. Further, analysis by X-ray diffraction using Cu Kα rays confirmed that the desired positive electrode active material had a hexagonal layered structure. From the Rietveld analysis of this powder X-ray diffraction pattern, the Li seat occupancy of the 3a site was determined.

The battery evaluation using this positive electrode active material was performed as follows. 70% by mass of the positive electrode active material powder was mixed with 20% by mass of acetylene black and 10% by mass of PTFE, and 150 mg was taken out from this to produce a pellet to obtain a positive electrode. Lithium metal is used for the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (made by Toyama Pharmaceutical Co., Ltd.) using 1M LiClO ₄ as a supporting salt is used as the electrolyte, with a dew point of −80. A 2032 type coin battery as shown in FIG. 1 was produced in a glove box in an Ar atmosphere controlled at 0 ° C.

The produced coin battery is left to stand for about 24 hours, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 0.5 mA / cm ² and charged to a cutoff voltage of 4.3 V to be initially charged. The capacity when discharging to a cut-off voltage of 3.0 V after a 1 hour rest was defined as the initial discharge capacity. Table 2 shows the initial charge / discharge capacity and irreversible capacity obtained by this method.

(Example 2)
A metal composite oxide formed by solid solution with a molar ratio of nickel, cobalt, and aluminum of 82: 15: 3 and a commercially available lithium hydroxide monohydrate are converted into a molar ratio of Li to metal (Ni + Co + Al) [Li / A positive electrode active material was produced in the same manner as in Example 1 except that Ni + Co + M] was weighed to 1.02. Table 1 shows the specific surface area measurement results by the BET method before and after the lithium removal treatment and the Li site occupancy of the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern. Table 2 shows the initial charge / discharge capacity and irreversible capacity of the positive electrode active material measured by the same method as in Example 1.

(Example 3)
A metal composite oxide formed by solid solution with a molar ratio of nickel, cobalt, and aluminum of 82: 15: 3 and a commercially available lithium hydroxide monohydrate are converted into a molar ratio of Li to metal (Ni + Co + Al) [Li / A positive electrode active material was produced in the same manner as in Example 1 except that Ni + Co + M] was weighed to 1.05. Table 1 shows the specific surface area measurement results by the BET method before and after the lithium removal treatment and the Li site occupancy of the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern. Table 2 shows the initial charge / discharge capacity and irreversible capacity of the positive electrode active material measured by the same method as in Example 1.

Example 4
A metal composite oxide formed by solid solution with a molar ratio of nickel, cobalt, and aluminum of 82: 15: 3 and a commercially available lithium hydroxide monohydrate are converted into a molar ratio of Li to metal (Ni + Co + Al) [Li / A positive electrode active material was produced in the same manner as in Example 1 except that Ni + Co + M] was 1.08. Table 1 shows the specific surface area measurement results by the BET method before and after the lithium removal treatment and the Li site occupancy of the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern. Table 2 shows the initial charge / discharge capacity and irreversible capacity of the positive electrode active material measured by the same method as in Example 1.

(Example 5)
A metal composite oxide formed by solid solution with a molar ratio of nickel, cobalt, and aluminum of 82: 15: 3 and a commercially available lithium hydroxide monohydrate are converted into a molar ratio of Li to metal (Ni + Co + Al) [Li / A positive electrode active material was produced in the same manner as in Example 1 except that Ni + Co + M] was 1.10. Table 1 shows the specific surface area measurement results by the BET method before and after the lithium removal treatment and the Li site occupancy of the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern. Table 2 shows the initial charge / discharge capacity and irreversible capacity of the positive electrode active material measured by the same method as in Example 1.

(Example 6)
A metal composite oxide formed by solid solution with a molar ratio of nickel, cobalt, and aluminum of 82: 15: 3 and a commercially available lithium hydroxide monohydrate are converted into a molar ratio of Li to metal (Ni + Co + Al) [Li / A positive electrode active material was produced in the same manner as in Example 1 except that Ni + Co + M] was 1.12. Table 1 shows the specific surface area measurement results by the BET method before and after the lithium removal treatment and the Li site occupancy of the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern. Table 2 shows the initial charge / discharge capacity and irreversible capacity of the positive electrode active material measured by the same method as in Example 1.

(Example 7)
A positive electrode active material was prepared in the same manner as in Example 3 except that titanyl sulfate was used instead of aluminum sulfate. Table 1 shows the specific surface area measurement results by the BET method before and after the lithium removal treatment and the Li site occupancy of the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern. Table 2 shows the initial charge / discharge capacity and irreversible capacity of the positive electrode active material measured by the same method as in Example 1.

(Example 8)
A positive electrode active material was produced in the same manner as in Example 3 except that manganese sulfate was used instead of aluminum sulfate. Table 1 shows the specific surface area measurement results by the BET method before and after the lithium removal treatment and the Li site occupancy of the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern. Table 2 shows the initial charge / discharge capacity and irreversible capacity of the positive electrode active material measured by the same method as in Example 1.

(Comparative Example 1)
A metal composite oxide formed by solid solution with a molar ratio of Ni, Co, and Al of 82: 15: 3 and a commercially available lithium hydroxide monohydrate are converted into a molar ratio of Li to (Ni + Co + Al) [Li / Ni + Co + M. ] Was prepared in the same manner as in Example 1 except that the mixture was mixed so as to be 0.98. Table 1 shows the specific surface area measurement results by the BET method before and after the lithium removal treatment and the Li site occupancy of the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern. Table 2 shows the initial charge / discharge capacity and irreversible capacity of the positive electrode active material measured by the same method as in Example 1.

(Comparative Example 2)
A metal composite oxide formed by solid solution with a molar ratio of Ni, Co, and Al of 82: 15: 3 and a commercially available lithium hydroxide monohydrate are converted into a molar ratio of Li to (Ni + Co + Al) [Li / Ni + Co + M. ] Was produced in the same manner as in Example 1 except that the mixture was mixed so that the ratio was 0.95. Table 1 shows the specific surface area measurement results by the BET method before and after the lithium removal treatment and the Li site occupancy of the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern. Table 2 shows the initial charge / discharge capacity and irreversible capacity of the positive electrode active material measured by the same method as in Example 1.

(Comparative Example 3)
A positive electrode active material was produced in the same manner as in Example 2 except that lithium removal treatment was not performed. Table 1 shows the specific surface area measurement results by the BET method before and after the lithium removal treatment of the obtained fired product and the Li site occupancy of the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern. Table 2 shows the initial charge / discharge capacity and irreversible capacity of the positive electrode active material measured by the same method as in Example 1.

(Comparative Example 4)
A positive electrode active material was produced in the same manner as in Example 6 except that lithium removal treatment was not performed. Table 1 shows the specific surface area measurement results by the BET method before and after the lithium removal treatment and the Li site occupancy of the 3a site obtained from the Rietveld analysis of the X-ray diffraction pattern. Table 2 shows the initial charge / discharge capacity and irreversible capacity of the positive electrode active material measured by the same method as in Example 1.

[Evaluation]
As shown in Table 1, the lithium nickel composite oxide obtained in Examples 1 to 8 shows a high discharge capacity of 180 mAh / g or more, and a new high capacity positive electrode replacing lithium cobalt composite oxide (LiCoO ₂ ). It turns out that it is a material which can be used as a material.
In particular, it is considered that one of the reasons is that the Li seat occupancy rate is higher than that of Comparative Examples 1 and 2. However, as shown in Example 1, the Li seat occupancy rate is 97% or higher. It can be seen that a high capacity of 180 mAh / g or more, which could not be obtained unless otherwise, was obtained even with a Li seat occupancy of less than 97% by performing the removal treatment of unreacted lithium. This is also clear from the fact that the discharge capacity is low, even though Comparative Examples 3 and 4 that have not been subjected to lithium removal treatment show a high Li seat occupancy of 97% or more.

  The positive electrode material according to the present invention reduces the amount of unreacted lithium, thereby suppressing the generation of gas when the battery is formed and the gelation during electrode preparation, etc., improving battery safety and stabilizing the battery preparation process. Leads to. In addition, even a lithium nickel composite oxide having a relatively low Li seat occupancy has a high discharge capacity, which reduces the synthesis conditions and leads to improved product quality stability. A battery using such a positive electrode material is suitable for use as a power source for small portable electronic devices that always require a high capacity and a power source for electric vehicles. The electric vehicle power source can be used not only for an electric vehicle driven purely by electric energy but also for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.

It is a figure which shows the coin battery used for the present Example, (a) is an external appearance perspective view, (b) is the sectional view on the aa line of Fig.1 (a).

Explanation of symbols

1 Negative electrode (lithium metal negative electrode)
2 Separator (electrolyte impregnation)
3 Positive electrode (Evaluation electrode)
4 Gasket 5 Negative electrode can 6 Positive electrode can 7 Current collector 10 Coin battery

Claims (5)

A hexagonal lithium nickel composite oxide having a layered structure,
Li _x Ni _(1-yz) Co _y M _z O ₂ is represented by a composition formula,
X in the composition formula is 0.95 or more and 1.10 or less, y is greater than 0, 0.20 or less, z is greater than 0, and 0.15 or less.
M element consists of at least one element selected from the element group of Al, Ti, Mn, Ga, Mg, Nb,
The lithium nickel composite oxide has a specific surface area of 0.5 to 2.0 m ² / g.
The intermediate product has x of 0.95 or more and 1.10 or less, y is greater than 0, 0.20 or less, z is greater than 0 and 0.15 or less, and M element is Al, Ti, Mn, Ga Li seat occupancy of the Li main layer represented by the composition formula of Li _x Ni _(1-yz) Co _y M _z O ₂ composed of at least one element selected from the element group of Mg, Mg, and Nb ^2. The lithium nickel composite oxide according to claim 1, having a crystallite diameter of 73 to 200 nm and a specific surface area of 0.2 to 1.0 m ² / g.
x is 0.95 or more and 1.10 or less, y is greater than 0, 0.20 or less, z is greater than 0 and 0.15 or less, and the M element is Al, Ti, Mn, Ga, Mg, or Nb. A specific surface area represented by a composition formula of Li _x Ni _(1-yz) Co _y M _z O ₂ composed of at least one element selected from the element group is 0.5 to 2.0 m ² / g. A hexagonal lithium nickel composite oxide having a layered structure,
The hexagonal lithium-nickel composite oxide having a layered structure is a nickel composite oxide containing a Co element and an M element represented by a composition formula of a raw material lithium compound and Ni _(1-yz) Co _y M _z O. Li main layer obtained by firing a mixture in which a molar ratio of a Li element of the lithium compound and a Ni element, a Co element and a M element of the nickel composite oxide in a molar sum: [Li / Ni + Co + M] is 1.0 or more Produced by subjecting an intermediate product having a Li seat occupancy of 95% or more, a crystallite diameter of 73 to 200 nm, and a specific surface area of 0.2 to 1.0 m ² / g to Li removal treatment Lithium nickel composite oxide.
The lithium nickel composite oxide is composed of spherical or oval spherical secondary particles in which a plurality of primary particles having an average particle diameter of 0.1 to 1.0 μm are assembled. The lithium nickel composite oxide according to any one of the above.
A non-aqueous electrolyte secondary battery comprising the lithium nickel composite oxide according to claim 1 as a positive electrode active material.

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