JP2019081703A - Lithium-containing composite oxide, positive electrode active material, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

To provide a lithium-containing composite oxide, positive electrode active material and positive electrode for lithium ion secondary battery capable of producing a lithium ion secondary battery that has a large discharge capacity and in which the reduction in discharge voltage due to repeated charge and discharge cycles is suppressed, and to provide the lithium ion secondary battery.SOLUTION: A lithium-containing composite oxide is represented by formula I: LiNiCoMnMO(M is Na, Mg, Ti, Zr, Al, W or Mo, a+b+c+d+e=2, 1.1≤a/(b+c+d+e)≤1.4, 0.2≤b/(b+c+d+e)≤0.5, 0≤c/(b+C+d+e)≤0.25, 0.3≤d/(b+c+d+e)≤0.6, 0≤e/(b+c+d+e)≤0.1), and the valence of Ni is 2.15 to 2.45.SELECTED DRAWING: None

Description

  The present invention relates to a lithium-containing composite oxide, a positive electrode active material, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

As a positive electrode active material contained in the positive electrode of a lithium ion secondary battery, a lithium-containing composite oxide, in particular, LiCoO ₂ is well known. However, in recent years, size reduction and weight reduction are required for portable electronic devices and lithium ion secondary batteries for vehicles, and the discharge capacity of lithium ion secondary batteries per unit mass of positive electrode active material (hereinafter simply referred to as discharge) Further improvement of the capacity is also required.

  As a positive electrode active material capable of further increasing the discharge capacity of a lithium ion secondary battery, a positive electrode active material having a high content of Li and Mn, that is, a so-called lithium-rich positive electrode active material attracts attention. As a lithium-rich positive electrode active material capable of obtaining a lithium ion secondary battery having a large discharge capacity, the following have been proposed.

  (1) A positive electrode active material particle powder comprising a compound having a crystal system belonging to at least space group R-3m and a crystal system belonging to space group C2 / m, wherein the compound comprises at least Li, Mn, boron, Co and And / or Ni, and the intensity (a) of the maximum diffraction peak at 2θ = 20.8 ± 1 ° of the powder X-ray diffraction diagram using Cu-Kα rays of the positive electrode active material particle powder A positive electrode active material particle powder, wherein the relative intensity ratio (a) / (b) to the intensity (b) of the maximum diffraction peak at 2θ = 18.6 ± 1 ° is 0.02 to 0.5, and the positive electrode Mn / (Ni + Co + Mn) is 0.55 or more by molar ratio, and, as for Mn content of active material particle powder, 0.001 to 3 wt% of boron is included, The positive electrode active material particle powder (patent document 1).

  (2) A positive electrode active material particle powder comprising a compound having a crystal system belonging to at least space group R-3 m and a crystal system belonging to space group C2 / m, wherein the compound comprises at least Li, Mn and element A (Si , And at least one element selected from Zr and Y) and Co and / or Ni, and 2θ of powder X-ray diffraction diagram using Cu-Kα ray of positive electrode active material particle powder The relative intensity ratio (a) / (b) of the intensity (a) of the maximum diffraction peak at 20.8 ± 1 ° to the intensity (b) of the maximum diffraction peak at 2θ = 18.6 ± 1 ° is 0.02 to The positive electrode active material particle powder is 0.2, and the Mn content of the positive electrode active material particle powder is 0.55 or more in molar ratio (Mn / (Ni + Co + Mn)), and the element A is 0.03 to 5 wt% Containing, tap density 0.8-2.4 g / A c, the positive electrode active material particles compressed density being a 2.0~3.1g / cc (Patent Document 2).

JP, 2011-096650, A JP, 2013-211239, A

However, even with the lithium-rich positive electrode active materials of (1) and (2), the discharge capacity of the lithium ion secondary battery is still insufficient. In order to further increase the energy density of lithium ion secondary batteries, further improvement of discharge capacity is required.
In addition, a lithium ion secondary battery using a lithium-rich positive electrode active material has a problem that the discharge voltage is lowered by repeating charge and discharge cycles. Since a decrease in discharge voltage of a lithium ion secondary battery leads to a decrease in energy density, it is required to suppress a decrease in discharge voltage due to repeated charge and discharge cycles.

  The present invention provides a lithium-containing composite oxide, a positive electrode active material and a lithium ion secondary battery capable of obtaining a lithium ion secondary battery in which the discharge capacity is large and the decrease in discharge voltage due to repeated charge and discharge cycles is suppressed. It is an object of the present invention to provide a lithium ion secondary battery which has a large discharge capacity and which has a reduced discharge voltage due to repeated charge and discharge cycles.

The present invention has the following aspects.
[1] It is represented by the following formula I, and the valence of Li is 1, the valence of Co is 3, the valence of Mn is 4, the valence of Na is 1, the valence of Mg is 2, the valence of Ti The valence of Ni is 4 when the valence of Zr is 4, the valence of Al is 3, the valence of W is 6, the valence of Mo is 6 and the valence of oxygen (O) is -2. Lithium-containing composite oxide, wherein is 2.15 to 2.45.
Li _a Ni _b Co _c Mn _d M _e O ₂ Formula I
However, M is one or more selected from the group consisting of Na, Mg, Ti, Zr, Al, W and Mo;
a + b + c + d + e = 2,
1.1 ≦ a / (b + c + d + e) ≦ 1.4,
0.2 ≦ b / (b + c + d + e) ≦ 0.5,
0 ≦ c / (b + c + d + e) ≦ 0.25,
0.3 ≦ d / (b + c + d + e) ≦ 0.6,
It is 0 <= e / (b + c + d + e) <= 0.1.
[2] The lithium-containing composite oxide of [1], wherein 0.05 ≦ c / (b + c + d + e) ≦ 0.25 in the formula I.
[3] The lithium-containing composite oxide of [1] or [2], wherein M in the formula I is one or more selected from the group consisting of Ti, Zr and Al.
[4] A positive electrode active material comprising the lithium-containing composite oxide of any one of the above [1] to [3].
[5] The positive electrode active material of [4], which has a coating comprising a compound containing one or more selected from the group consisting of Zr, Ti, Al and F on the surface of the lithium-containing composite oxide.
[6] The _{D 50} of the positive electrode active material is a 3 to 10 [mu] m, positive electrode active material [4] or [5].
[7] The positive electrode active material according to any one of [4] to [6], wherein the specific surface area of the positive electrode active material is 0.5 to ⁵ m ² / g.
[8] A positive electrode for a lithium ion secondary battery, comprising the positive electrode active material according to any one of the above [4] to [7], a conductive material and a binder.
[9] A lithium ion secondary battery having the positive electrode for a lithium ion secondary battery according to the above [8], a negative electrode and a non-aqueous electrolyte.

According to the lithium-containing composite oxide of the present invention, it is possible to obtain a lithium ion secondary battery which has a large discharge capacity and in which a decrease in discharge voltage due to repeated charge and discharge cycles is suppressed.
According to the positive electrode active material of the present invention, it is possible to obtain a lithium ion secondary battery having a large discharge capacity and in which a decrease in discharge voltage due to repeated charge and discharge cycles is suppressed.
According to the positive electrode for a lithium ion secondary battery of the present invention, it is possible to obtain a lithium ion secondary battery having a large discharge capacity and in which a decrease in discharge voltage due to repeated charge and discharge cycles is suppressed.
The lithium ion secondary battery of the present invention has a large discharge capacity, and the decrease in discharge voltage due to repeated charge and discharge cycles is suppressed.

The following definitions of terms apply throughout the specification and claims.
The “valence number of Ni” is selected from the group consisting of Li, Co, Mn and M (Na, Mg, Ti, Zr, Al, W and Mo in the formula I (Li _a Ni _b Co _c Mn _{d Me} O ₂ ) Fix the valence of each element selected (one or more kinds) to the most stable oxidation number, and fix the valence of oxygen (O) to -2, to satisfy the electrical neutrality condition of formula I It is the calculated valence of Ni. That is, assuming that the valence of Ni is x and the valence of M is y,
1 x a + x x b + 3 x c + 4 x d + y x e-2 x 2 = 0
Calculated from x = {2 × 2− (1 × a + 3 × c + 4 × d + y × e)} / b.
“D ₅₀ ” is a particle diameter at a point of 50% in the cumulative volume distribution curve where the total volume of the particle size distribution determined on a volume basis is 100%, that is, the volume based cumulative 50% diameter.
The “particle size distribution” is obtained from the frequency distribution and the cumulative volume distribution curve measured by a laser scattering particle size distribution measuring apparatus (for example, a laser diffraction / scattering type particle size distribution measuring apparatus etc.). The measurement is carried out by sufficiently dispersing the powder in an aqueous medium by ultrasonic treatment or the like.
"Specific surface area" is a value measured by the BET (Brunauer, Emmet, Teller) method. In the measurement of the specific surface area, nitrogen gas is used as the adsorption gas.
The notation “Li” indicates that the element is not elemental Li but the element Li unless otherwise noted. The same applies to the other elements such as Ni, Co and Mn.
Composition analysis of the lithium-containing composite oxide is performed by inductively coupled plasma analysis (hereinafter referred to as ICP). Further, the ratio of the elements of the lithium-containing composite oxide is a value in the lithium-containing composite oxide before the first charge (also referred to as activation treatment).

Lithium-containing complex oxide
The lithium-containing composite oxide of the present invention is a compound represented by the following formula I (hereinafter also referred to as composite oxide (I)).
Li _a Ni _b Co _c Mn _d M _e O ₂ Formula I
The total amount (a + b + c + d + e) of a, b, c, d and e is 2.

  a is the number of moles of Li contained in the composite oxide (I). a / (b + c + d + e) is 1.1 to 1.4, preferably 1.13 to 1.37, and more preferably 1.15 to 1.35. If a / (b + c + d + e) is in the above range, the discharge capacity of the lithium ion secondary battery having the complex oxide (I) can be increased.

  b is the number of moles of Ni contained in the composite oxide (I). b / (b + c + d + e) is 0.2 to 0.5, preferably 0.25 to 0.5, and more preferably 0.3 to 0.47. If b / (b + c + d + e) is in the above range, the discharge capacity of the lithium ion secondary battery having the complex oxide (I) can be increased, and the discharge voltage can be increased.

  c is the number of moles of Co contained in the complex oxide (I). c / (b + c + d + e) is 0-0.25, and 0.05-0.20 are preferable. If c / (b + c + d + e) is within the above range, the discharge capacity of the lithium ion secondary battery having the complex oxide (I) can be increased, and the discharge voltage can be increased. Moreover, if c / (b + c + d + e) is 0.05 or more, the direct current resistance (hereinafter also referred to as DCR) of the lithium ion secondary battery having the complex oxide (I) becomes low, and the rate characteristic becomes good. .

  d is the number of moles of Mn contained in the composite oxide (I). d / (b + c + d + e) is 0.3 to 0.6, preferably 0.35 to 0.57, and more preferably 0.4 to 0.55. If d / (b + c + d + e) is in the above range, the discharge capacity of the lithium ion secondary battery having the complex oxide (I) can be increased, and the discharge voltage can be increased.

The composite oxide (I) may contain other metal element M, if necessary. The other metal element M is one or more selected from the group consisting of Na, Mg, Ti, Zr, Al, W and Mo. The other metal element M is selected from Ti, Zr, and Ti from the viewpoints of easily increasing the discharge capacity of the lithium ion secondary battery having the complex oxide (I) and suppressing a decrease in discharge voltage due to repeated charge and discharge cycles. One or more selected from the group consisting of Al is preferable.
e is the number of moles of M contained in the complex oxide (I). e / (b + c + d + e) is 0 to 0.1, preferably 0 to 0.05, and more preferably 0 to 0.03.

The complex oxide (I) is a layered rock salt type crystal of Li (Li _1/3 Mn _2/3 ) O ₂ (lithium excess phase) having a layered rock salt type crystal structure of a space group C2 / m and a space group R-3 m. It is a solid solution with LiMeO ₂ having a structure (wherein Me is one or more elements selected from the group consisting of Ni, Co, Mn and M). It can be confirmed by X-ray diffraction measurement that the complex oxide (I) has these crystal structures.
Typically, in the X-ray diffraction measurement, a peak of the (020) plane of the space group C2 / m is observed at 2θ = 20 to 22 deg. Further, in the X-ray diffraction measurement, a peak of the (003) plane of the space group R-3 m is observed at 2θ = 18 to 20 deg.

As the complex oxide (I) has a valence of Ni of 2.15 to 2.45, the discharge capacity of the lithium ion secondary battery can be increased, and the discharge voltage is lowered by repeating the charge and discharge cycle. It is suppressed.
If the valence number of Ni is equal to or more than the lower limit value of the above range, the formation of other crystal phases such as spinel and the formation of a non-uniform solid solution can be suppressed. As a result, it is possible to suppress a decrease in discharge voltage due to repeated charge and discharge cycles. In addition, when the valence number of Ni is equal to or less than the upper limit value of the above range, the change amount of the Ni valence number does not decrease in charge and discharge of the lithium ion secondary battery. Therefore, the fall of the discharge capacity of the lithium ion secondary battery which has complex oxide (I) can be suppressed.
From the above reasons, the valence of Ni is preferably 2.15 to 2.4, and more preferably 2.15 to 2.35.

(Method of producing complex oxide (I))
Complex oxide (I) is obtained by mixing a transition metal-containing compound containing Ni and Mn as an essential component, and optionally containing Co and M, and a lithium compound, and calcining the obtained mixture.
By adjusting the feed ratio of Li, Ni, Co, Mn and M at the time of producing the complex oxide (I), the valence of Ni can be made within the above range.

As one embodiment of the method for producing the complex oxide (I), for example, a method having the following steps (a) to (b) can be mentioned.
(A) obtaining a transition metal-containing compound containing Ni and Mn as essential and optionally containing Co and M;
(B) A step of mixing the transition metal-containing compound and the lithium compound, and calcining the obtained mixture to obtain a lithium-containing composite oxide.

Process (a):
When the transition metal-containing compound contains M, the ratio of Ni, Co, Mn and M contained in the transition metal-containing compound is the same as the ratio of Ni, Co, Mn and M contained in the complex oxide (I) Is preferred.
When the transition metal-containing compound does not contain M, and the compound containing M is further mixed in step (b), the transition metal-containing compound is used based on the ratio of Ni, Co, Mn and M contained in the complex oxide (I) It is preferable to determine the ratio of Ni, Co and Mn contained in the compound.
M is the same as M contained in the complex oxide (I).

  The transition metal-containing compound may, for example, be a hydroxide or a carbonate, and is preferably a hydroxide from the viewpoint of easily suppressing a decrease in discharge capacity of the lithium ion secondary battery due to repeated charge and discharge cycles. The hydroxides also include oxyhydroxides which are partially oxidized.

The hydroxide can be prepared, for example, by the alkaline coprecipitation method.
In the alkaline coprecipitation method, a metal salt aqueous solution containing Ni and Mn as essential and optionally containing Co and M and a pH adjusting liquid containing a strong alkali are continuously supplied to the reaction tank and mixed, and the liquid mixture is mixed. It is a method of precipitating a hydroxide which contains Ni and Mn as essential and optionally contains Co and M while keeping the pH of the solution constant.

  The metal salts include nitrates, acetates, chlorides and sulfates of the respective metal elements, and sulfates are preferable from the viewpoint of relatively low material cost and excellent battery characteristics. As metal salts, sulfates of Ni, sulfates of Mn, and sulfates of Co are more preferable.

Examples of the sulfate of Ni include nickel (II) sulfate hexahydrate, nickel (II) sulfate heptahydrate, and nickel (II) ammonium sulfate hexahydrate.
Examples of the sulfate of Co include cobalt (II) sulfate heptahydrate, cobalt (II) ammonium sulfate hexahydrate and the like.
Examples of the sulfate of Mn include manganese (II) sulfate pentahydrate, manganese (II) ammonium sulfate hexahydrate and the like.

The ratio of Ni, Co, Mn and M in the metal salt aqueous solution is the same as the ratio of Ni, Co, Mn and M contained in the finally obtained composite oxide (I).
0.1-3 mol / kg is preferable and, as for the total density | concentration of the metallic element in metal salt aqueous solution, 0.5-2.5 mol / kg is more preferable. If the total concentration of the metal elements is at least the lower limit value of the above range, the productivity is excellent. If the total concentration of the metal elements is equal to or less than the upper limit value of the above range, the metal salt can be sufficiently dissolved in water.

The aqueous metal salt solution may contain an aqueous medium other than water.
As an aqueous medium other than water, methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, butanediol, glycerin and the like can be mentioned. The proportion of the aqueous medium other than water is preferably 0 to 20 parts by mass, more preferably 0 to 10 parts by mass, with respect to 100 parts by mass of water from the viewpoint of safety, environment, handleability, and cost. 1 part by mass is particularly preferred.

As the pH adjusting solution, an aqueous solution containing a strong alkali is preferable.
The strong alkali is preferably at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide.
A complexing agent (an aqueous ammonia solution or an aqueous ammonium sulfate solution) may be added to the mixed solution in order to adjust the solubility of the metal element.

The metal salt aqueous solution and the pH adjusting solution are preferably mixed while being stirred in the reaction tank.
As a stirring apparatus, a three-one motor etc. are mentioned. As a stirring blade, an anchor type, a propeller type, a paddle type, etc. are mentioned.
The reaction temperature is preferably 20 to 80 ° C., and more preferably 25 to 60 ° C. from the viewpoint of reaction promotion.

The mixing of the metal salt aqueous solution and the pH adjusting solution is preferably performed under a nitrogen atmosphere or an argon atmosphere from the viewpoint of suppressing the oxidation of the hydroxide, and particularly preferably under a nitrogen atmosphere from the viewpoint of cost .
During the mixing of the metal salt aqueous solution and the pH adjusting solution, it is preferable to maintain the pH in the reaction tank at a pH set in the range of 10 to 12 from the viewpoint of appropriately advancing the coprecipitation reaction. If the pH of the mixture is above 10, the coprecipitate is considered as a hydroxide.

  As a method of precipitating the hydroxide, a method of extracting the mixed solution in the reaction tank using a filter material (filter cloth etc.) and performing a precipitation reaction while concentrating the hydroxide (concentration method), and There are two types of methods (overflow method) in which the mixed solution is withdrawn together with the hydroxide without using a filter medium and the precipitation reaction is performed while keeping the concentration of the hydroxide low. The concentration method is preferred because the spread of the particle size distribution can be narrowed.

  The hydroxide is preferably washed to remove impurity ions. Examples of the washing method include a method in which pressure filtration and dispersion in distilled water are repeated. In the case of washing, it is preferable to repeat until the electric conductivity of the supernatant or filtrate when the hydroxide is dispersed in distilled water is 50 mS / m or less, more preferably 20 mS / m or less preferable.

After washing, the hydroxide may be dried if necessary.
60-200 degreeC is preferable and 80-130 degreeC of a drying temperature is more preferable. If the drying temperature is at least the lower limit value of the above range, the drying time can be shortened. If drying temperature is below the upper limit of the said range, advancing of the oxidation of a hydroxide can be suppressed.
The drying time may be appropriately set according to the amount of hydroxide, preferably 1 to 300 hours, and more preferably 5 to 120 hours.

3-60 m < ² > / g is preferable and, as for the specific surface area of a hydroxide, 5-50 m < ² > / g is more preferable. If the specific surface area of the hydroxide is within the above range, it is easy to control the specific surface area of the positive electrode active material within the preferable range. The specific surface area of the hydroxide is a value measured after drying the hydroxide at 120 ° C. for 15 hours.

_{D 50} of the hydroxide is preferably 3～18Myuemu, more preferably from 3 to 15 [mu] m, more preferably 3 to 10 [mu] m. Within D ₅₀ is the range of the hydroxide, easily controlled within the preferred range of D ₅₀ of the positive electrode active material.

Process (b):
The lithium-containing composite oxide is formed by mixing the transition metal-containing compound and the lithium compound and calcining the obtained mixture. The mixture may further contain a compound containing M.

The lithium compound is preferably one selected from the group consisting of lithium carbonate, lithium hydroxide and lithium nitrate. Lithium carbonate is more preferable in terms of the ease of handling in the production process.
The mixing ratio of the hydroxide to the lithium compound is such that the ratio of the molar amount of Li contained in the lithium compound to the total molar amount of Ni, Co, Mn and M contained in the hydroxide is 1.1 to 1.4 A mixing ratio of

When the transition metal-containing compound contains M, the ratio of Ni, Co, Mn and M contained in the mixture is preferably the same as the ratio of Ni, Co, Mn and M contained in the complex oxide (I) .
When the transition metal-containing compound does not contain M, and the mixture further contains a compound containing M, the ratio of Ni, Co, Mn, and M contained in the mixture after mixing the compound containing M is a complex oxide ( It is preferable to make it the same as the ratio of Ni, Co, Mn, and M contained in I).

  The compound containing M is preferably one or more selected from the group consisting of oxides, hydroxides, carbonates, nitrates, acetates, chlorides and fluorides of M. With these compounds, in the step (b), the impurities are volatilized, and the impurities are less likely to remain in the complex oxide (I).

  Examples of the method of mixing the transition metal-containing compound and the lithium compound include methods using a rocking mixer, a Nauta mixer, a spiral mixer, a cutter mill, a V mixer, and the like.

As a baking apparatus, an electric furnace, a continuous baking furnace, a rotary kiln, etc. are mentioned.
Since the transition metal-containing compound is oxidized at the time of firing, the firing is preferably performed in the air, and particularly preferably performed while supplying air.
The air supply rate is preferably 10 to 200 mL / min, and more preferably 40 to 150 mL / min, per 1 L of internal volume of the furnace.
By supplying air at the time of firing, the metal element contained in the transition metal-containing compound is sufficiently oxidized. As a result, a complex oxide (I) having high crystallinity and a crystal structure of space group C2 / m and a crystal structure of space group R-3m is obtained.

800-1100 degreeC is preferable, 850-1050 degreeC is preferable, and 890-1000 degreeC is more preferable. If the firing temperature is at least the lower limit of the above range, the discharge capacity of the lithium ion secondary battery having the complex oxide (I) can be easily increased, and the decrease in discharge voltage due to repeated charge and discharge cycles can be easily suppressed.
The firing time is preferably 4 to 40 hours, more preferably 4 to 20 hours.

  The firing may be one-step firing or may be two-step firing in which main firing is performed after temporary firing. When two-stage firing is performed, the temperature of the main firing is performed in the above-described range of the firing temperature. And 500-700 degreeC is preferable and, as for the temperature of temporary baking, 500-650 degreeC is more preferable.

(Mechanism of action)
The complex oxide (I) described above is a lithium-containing complex oxide represented by the formula I, a so-called lithium-rich positive electrode active material, and the valence of Ni is 2.15 to 2.45. As a result, a lithium ion secondary battery can be obtained in which the discharge capacity is large and the decrease in discharge voltage due to repeated charge and discharge cycles is suppressed.

<Positive electrode active material>
The positive electrode active material of the present invention (hereinafter referred to as the present positive electrode active material) may be the complex oxide (I) itself, and the surface of the complex oxide (I) is composed of Zr, Ti, Al and F. You may have a coating which consists of a compound containing 1 or more types selected from a group.
The present positive electrode active material having a coating on the surface of the complex oxide (I) is likely to increase the discharge capacity of the lithium ion secondary battery, and to easily suppress the decrease in discharge voltage due to repeated charge and discharge cycles.

Examples of the coating include compounds containing one or more selected from the group consisting of Zr, Ti, Al and F. As a compound containing 1 or more types selected from the group which consists of Zr, Ti, and Al, an oxide, a sulfate, carbonate, etc. are mentioned. Examples of the compound containing F include lithium fluoride, aluminum fluoride and zirconium fluoride.
The coating may be present on the surface of the complex oxide (I), may be present on the entire surface of the complex oxide (I), or may be present on part of the complex oxide (I).

  The total content of Zr, Ti, Al and F in the coating is preferably 0.1 to 5 mol%, preferably 0.3 to 3 mol%, with respect to the complex oxide (I) (100 mol%). More preferable.

  To form the coating, for example, a coating solution containing one or more selected from the group consisting of Zr, Ti, Al and F is sprayed onto the complex oxide (I), and the solvent of the coating solution is removed by calcination or This can be carried out by immersing the composite oxide (I) in a coating solution, solid-liquid separation by filtration, and removal of the solvent by calcination.

The positive electrode active material is preferably a secondary particle in which a plurality of primary particles are aggregated.
MotoTadashi active _{D 50} of the secondary particulate material is preferably 3～18Myuemu, more preferably from 3 to 15 [mu] m, more preferably 4 to 10 [mu] m. If D ₅₀ is in the above range, it is easy to increase the discharge capacity of the lithium ion battery.

The specific surface area of MotoTadashi active material is preferably 0.5 to 5 m ² / g, more preferably 0.5-3 m ² / g, more preferably 1~2.5m ² / g. If the specific surface area is at least the lower limit value of the above range, the discharge capacity of the lithium ion secondary battery can be easily increased. If the specific surface area is equal to or less than the upper limit value of the above range, it is easy to suppress a decrease in discharge voltage of the lithium ion secondary battery due to repeated charge and discharge cycles.

The tap density of MotoTadashi active material is preferably from 1 to 3 g / cm ^3, more preferably 1.3~2.5g / cm ^3, more preferably 1.5~2g / cm ^3. If the tap density is within the above range, the density of the positive electrode active material in the electrode can be increased, and the energy density of the positive electrode can be increased.

(Mechanism of action)
Since the present positive electrode active material described above contains the complex oxide (I), it is possible to obtain a lithium ion secondary battery having a large discharge capacity and capable of suppressing a decrease in discharge voltage due to repeated charge and discharge cycles. be able to.

<Positive electrode for lithium ion secondary battery>
The positive electrode for a lithium ion secondary battery of the present invention (hereinafter referred to as the present positive electrode) contains the present positive electrode active material. Specifically, a positive electrode active material layer containing the present positive electrode active material, a conductive material, and a binder is formed on a positive electrode current collector.

Examples of the conductive material include carbon black (acetylene black, ketjen black and the like), graphite, vapor grown carbon fiber, carbon nanotube and the like.
As the binder, fluorine resin (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyolefin (polyethylene, polypropylene, etc.), polymer or copolymer having unsaturated bond (styrene / butadiene rubber, isoprene rubber, butadiene rubber, etc.) And acrylic acid polymers or copolymers (acrylic acid copolymers, methacrylic acid copolymers, etc.) and the like.
Examples of the positive electrode current collector include aluminum foil and stainless steel foil.

The present positive electrode can be produced, for example, by the following method.
The positive electrode active material, the conductive material and the binder are dissolved or dispersed in a medium to obtain a slurry. The obtained slurry is applied to a positive electrode current collector, and the medium is removed by drying or the like to form a positive electrode active material layer. As needed, after forming a positive electrode active material layer, you may roll with a roll press etc. Thus, the present positive electrode is obtained.
Alternatively, a kneaded material is obtained by kneading the positive electrode active material, the conductive material and the binder with a medium. The obtained kneaded product is rolled to a positive electrode current collector to obtain the present positive electrode.

(Mechanism of action)
Since the present positive electrode described above contains the present positive electrode active material, it is possible to obtain a lithium ion secondary battery having a large discharge capacity and in which a decrease in discharge voltage due to repeated charge and discharge cycles is suppressed.

<Lithium ion secondary battery>
The lithium ion secondary battery (hereinafter referred to as the present battery) of the present invention has the present positive electrode. Specifically, it has the present positive electrode, a negative electrode, and a non-aqueous electrolyte.

(Negative electrode)
The negative electrode contains a negative electrode active material. Specifically, a negative electrode active material layer and, if necessary, a negative electrode active material layer containing a conductive material and a binder are formed on a negative electrode current collector.

  The negative electrode active material may be any material that can occlude and release lithium ions at a relatively low potential. As the negative electrode active material, lithium metal, lithium alloy, lithium compound, carbon material, oxide mainly composed of metal of periodic table group 14, oxide mainly composed of metal of periodic table group 15, carbon compound, silicon carbide compound And silicon oxide compounds, titanium sulfide, and boron carbide compounds.

  As a carbon material of the negative electrode active material, non-graphitizable carbon, artificial graphite, natural graphite, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, glassy carbons, organic high materials A molecular compound fired body (phenol resin, furan resin, etc. fired and carbonized at an appropriate temperature), carbon fiber, activated carbon, carbon blacks, etc. may be mentioned.

As a metal of periodic table 14 group used for a negative electrode active material, Si and Sn are mentioned, and Si is preferable.
Other negative electrode active materials include oxides such as iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titanium oxide and tin oxide, and other nitrides.

As the conductive material of the negative electrode and the binder, the same materials as those of the positive electrode can be used.
Examples of the negative electrode current collector include metal foils such as nickel foil and copper foil.

The negative electrode can be produced, for example, by the following method.
The negative electrode active material, the conductive material and the binder are dissolved or dispersed in a medium to obtain a slurry.
The medium is removed by coating the obtained slurry on a negative electrode current collector, drying, pressing or the like to obtain a negative electrode.

(Non-aqueous electrolyte)
Examples of the non-aqueous electrolyte include a non-aqueous electrolytic solution in which an electrolyte salt is dissolved in an organic solvent; an inorganic solid electrolyte; and a solid or gel polymer electrolyte in which an electrolytic salt is mixed or dissolved.

  As an organic solvent, what is well-known as an organic solvent for non-aqueous electrolytes is mentioned. Specifically, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, acetate, butyric acid Ester, propionic acid ester and the like can be mentioned. From the viewpoint of voltage stability, cyclic carbonates (such as propylene carbonate) and linear carbonates (such as dimethyl carbonate and diethyl carbonate) are preferable. An organic solvent may be used individually by 1 type, and may mix and use 2 or more types.

The inorganic solid electrolyte may be a material having lithium ion conductivity.
Examples of the inorganic solid electrolyte include lithium nitride and lithium iodide.

  Examples of the polymer used for the solid polymer electrolyte include ether-based polymer compounds (polyethylene oxide, crosslinked products thereof, etc.), polymethacrylate ester-based polymer compounds, acrylate-based polymer compounds and the like. The polymer compounds may be used alone or in combination of two or more.

As polymers used for gel-like polymer electrolytes, fluorine-based polymer compounds (polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, etc.), polyacrylonitrile, acrylonitrile copolymer, ether polymer compounds ( Polyethylene oxide, its crosslinked body, etc. are mentioned. Examples of the monomer to be copolymerized with the copolymer include polypropylene oxide, methyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate and the like.
As the polymer compound, a fluorine-based polymer compound is preferable from the viewpoint of the stability to the oxidation-reduction reaction.

The electrolyte salt may be any one as long as it is used in a lithium ion secondary battery. Examples of the electrolyte salt include LiClO ₄ , LiPF ₆ , LiBF ₄ , CH ₃ SO ₃ Li and the like.

  A separator may be interposed between the positive electrode and the negative electrode to prevent a short circuit. A porous membrane is mentioned as a separator. The non-aqueous electrolyte is used by impregnating the porous membrane. Further, a porous membrane impregnated with a non-aqueous electrolytic solution and gelled may be used as a gel electrolyte.

  Examples of the material of the battery outer package include nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, a resin material, a film material and the like.

  The shape of the lithium ion secondary battery may, for example, be a coin, a sheet (film), a fold, a winding type, a bottomed cylindrical, a button, or the like, which can be appropriately selected according to the application.

(Mechanism of action)
In the present battery described above, since the present positive electrode is provided, the discharge capacity is large, and the decrease in discharge voltage due to repeated charge and discharge cycles is suppressed.

Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto.
Examples 1 to 15 are Examples, and Examples 16 to 21 are Comparative Examples.

(Composition analysis)
The composition of the lithium-containing composite oxide (Li _a Ni _b Co _c Mn _d M _e O ₂ ) is such that the charged Li / X molar ratio (X is the total amount of Ni, Co, Mn and M) is v. The amount of Ni in the hydroxide is w (mol%), the amount of Co is x (mol%), the amount of Mn is y (mol%), and the amount of M in the compound containing M is z (mol%). Calculated from the equation. However, w + x + y + z = 100 and a + b + c + d + e = 2.
a = 2 v / (1 + v)
b = w / {50 (1 + v)}
c = x / {50 (1 + v)}
d = y / {50 (1 + v)}
e = z / {50 (1 + v)}

(Particle size)
The positive electrode active material is sufficiently dispersed in water by ultrasonic treatment, and measurement is performed using a laser diffraction / scattering particle size distribution measuring device (MT-3300EX manufactured by Nikkiso Co., Ltd.) to obtain a frequency distribution and a cumulative volume distribution curve. A volume based particle size distribution was obtained. D ₅₀ was determined from the cumulative volume distribution curve obtained.

(Tap density)
The tap density (unit: g / cm ³ ) of the positive electrode active material was calculated from the following equation. V in the following equation is the volume (unit: cm ³ ) of the sample after tapping, and the sample (positive electrode active material) is weighed in a resin container (volume: 20 cm ³ ) with a scale, and the container is tapped It is the value which attached to a corporation company company KYT-4000K, performed 700 times taps, and read the volume of the sample in a container with the scale of a container. In the following formula, m is the mass of the sample (unit: g), which is the mass of the sample added to the resinous container.
ρt = m / V

(Specific surface area)
The specific surface area of the positive electrode active material was calculated by the nitrogen adsorption BET method using a specific surface area measurement device (manufactured by Mountech Co., HM model-1208). Degassing was performed at 200 ° C. for 20 minutes.

(Production of positive electrode sheet)
Polyvinylidene fluoride solution (solvent: N) containing 12.1% by mass of positive electrode active material, acetylene black (Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd.), and polyvinylidene fluoride (manufactured by Kureha KF # 1120) The slurry was prepared by mixing with -methyl pyrrolidone) and further adding N-methyl pyrrolidone. The positive electrode active material, acetylene black and polyvinylidene fluoride had a mass ratio of 90: 5: 5.
The slurry was coated on one side using a doctor blade on an aluminum foil (E-FOIL manufactured by Toyo Aluminum Co., Ltd.) having an average thickness of 20 μm. After drying at 120 ° C., roll press rolling (0.3 t / cm) was performed twice to prepare a positive electrode.

(Manufacturing of lithium secondary battery)
A negative electrode was prepared by laminating a 1 mm thick stainless steel plate and a 500 μm thick metal lithium foil (lithium foil manufactured by Honso Chemical Co., Ltd.).
As a separator, porous polypropylene (manufactured by Polypore, Celgard (registered trademark) # 2500) having a thickness of 25 μm was prepared.
A 1 mol / dm ³ LiPF ₆ solution was prepared as a non-aqueous electrolyte. As a solvent of the non-aqueous electrolyte, a mixed solution of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1 was used.
A stainless steel simple closed cell lithium secondary battery was assembled in an argon glove box using the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte.

(Initial discharge capacity)
The lithium secondary battery was charged to 4.5 V at a load current of 20 mA per 1 g of the positive electrode active material in a constant current / constant voltage mode. Next, in a constant current mode, the battery was discharged to 2.5 V at a load current of 200 mA per 1 g of the positive electrode active material. A second charge and discharge was performed under the same conditions as the first charge and discharge except that the load current of the discharge was changed to 40 mA per 1 g of the positive electrode active material. This second discharge capacity was taken as the initial discharge capacity.

(Early DCR)
The lithium secondary battery was charged at a constant current and a constant voltage of 4.5 V after the initial charge and discharge, and was fully charged. In this fully charged state, a voltage drop value (V) after 10 seconds when discharged with a load current (I) of 20 mA, 100 mA, 200 mA, 400 mA, or 800 mA per 1 g of the positive electrode active material was measured. V at each I was plotted, and the slope of the line linearly approximated by the least square method was taken as the direct current resistance (initial DCR).

(Voltage drop)
In the constant current / constant voltage mode, after charging to 4.5 V at a load current of 200 mA per 1 g of the positive electrode active material, in the constant current mode, charging to discharge 2.5 V at a load current of 200 mA per 1 g of the positive electrode active material 50 discharge cycles were performed. The difference between the discharge voltage at the first cycle and the discharge voltage at the 50th cycle was taken as the voltage drop.

(Example 1)
The hydroxide of the composition shown in Table 1 obtained by the coprecipitation method and lithium carbonate (manufactured by SQM, MIC grade), the mole of Li and X (X is Ni, Co and Mn) It weighed and mixed so that ratio (Li / X) might become a value shown in Table 1.
The obtained mixture was baked at 890 ° C. for 8 hours in the air atmosphere while supplying air in an electric furnace to obtain a lithium-containing composite oxide, which was used as a positive electrode active material. The results are shown in Tables 1 and 2.

(Examples 2 to 8)
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the hydroxide and Li / X in Example 1 were changed to the hydroxides and Li / X shown in Table 1, and these were used as a positive electrode active material. . The results are shown in Tables 1 and 2.

(Example 9)
The hydroxide of the composition shown in Table 1 obtained by the coprecipitation method and lithium carbonate (manufactured by SQM, MIC grade) are weighed so that Li / X becomes a value shown in Table 1, and further zirconium oxide Powder (Shin Nippon Electric Co., Ltd. make, brand name: PCS) was measured and mixed so that it might become a quantity which becomes 0.5 mol% of metal content (except Li) in lithium compound oxide.
The obtained mixture was baked at 890 ° C. for 8 hours in the air atmosphere while supplying air in an electric furnace to obtain a lithium-containing composite oxide, which was used as a positive electrode active material. The results are shown in Tables 1 and 2.

(Example 10)
A lithium-containing composite oxide was obtained in the same manner as in Example 9 except that the zirconium oxide powder of Example 9 was changed to a titanium oxide powder (trade name: AMT-100, manufactured by Tayca Corporation), and this was used as a positive electrode active material. . The results are shown in Tables 1 and 2.

(Example 11)
A lithium-containing composite oxide is obtained in the same manner as in Example 9 except that the zirconium oxide powder of Example 9 is changed to an aluminum hydroxide powder (trade name: C-301, manufactured by Sumitomo Chemical Co., Ltd.), and this is used as a positive electrode active. It was a substance. The results are shown in Tables 1 and 2.

(Example 12)
A lithium-containing composite oxide was obtained in the same manner as in Example 10 except that the firing temperature was changed to 910 ° C. The Zr content of the Zr-containing aqueous solution (Nippon Light Metal Co., Ltd., trade name: Baycoat 20) having a mass ratio of 5% by mass with respect to the lithium-containing composite oxide and the lithium-containing composite oxide The lithium-containing composite oxide was sprayed and mixed in an amount of 0.5 mol% with respect to%). The obtained mixture was fired in an air atmosphere at 500 ° C. for 8 hours in an electric furnace while supplying air, to obtain a positive electrode active material. The results are shown in Tables 1 and 2.

(Example 13)
A positive electrode active material was obtained in the same manner as in Example 12 except that the Zr-containing aqueous solution of Example 12 was changed to a Ti-containing aqueous solution (manufactured by Matsumoto Fine Chemical Co., Ltd., trade name: Organix TC-315). The results are shown in Tables 1 and 2.

(Example 14)
A positive electrode active material was obtained in the same manner as in Example 12 except that the Zr-containing aqueous solution of Example 12 was changed to an Al-containing aqueous solution (Takiceram K-ML16, manufactured by Taki Chemical Co., Ltd.). The results are shown in Tables 1 and 2.

(Example 15)
A positive electrode active material was obtained in the same manner as in Example 12 except that the aqueous solution containing Zr in Example 12 was changed to an aqueous solution of ammonium fluoride. The results are shown in Tables 1 and 2.

(Examples 16 to 21)
A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that the hydroxide and Li / X in Example 1 were changed to the hydroxides and Li / X shown in Table 1, and these were used as a positive electrode active material. . The results are shown in Tables 1 and 2.

Since Examples 1 to 15 are represented by the formula I and the valence number of Ni is 2.15 to 2.45, the discharge capacity is large, and the decrease of the discharge voltage due to the repetition of charge and discharge cycles is suppressed. .
In particular, in Examples 9 to 11 in which the lithium-containing composite oxide contains another metal element M, and in Examples 12 to 15 in which the coating has on the surface of the lithium-containing composite oxide, the discharge voltage is lowered by repeating charge and discharge cycles. Was well suppressed. In Examples 7 and 8 in which the lithium-containing composite oxide did not contain Co, DCR became high.
In Examples 16 to 18, since the valence number of Ni was less than 2.15, the discharge capacity was small, and the decrease in the discharge voltage due to the repetition of charge and discharge cycles was large.
In Example 19, the discharge capacity was small because the valence of Ni exceeded 2.45.
In Examples 20 and 21, since c / (b + c + d + e) exceeds 0.25, the discharge capacity was small.

  According to the lithium-containing composite oxide of the present invention, it is possible to obtain a lithium ion secondary battery which has a large discharge capacity and in which a decrease in discharge voltage due to repeated charge and discharge cycles is suppressed.

Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto.
Examples 1 to 15 are Examples, and Examples 16 to 21 are Comparative Examples. Examples 1-2, 4-6, 9-15 are used as reference examples.

Claims (9)

It is represented by the following formula I, and the valence of Li is 1, the valence of Co is 3, the valence of Mn is 4, the valence of Na is 1, the valence of Mg is 2, the valence of Ti is 4, When the valence of Zr is 4, the valence of Al is 3, the valence of W is 6, the valence of Mo is 6 and the valence of oxygen (O) is −2, the valence of Ni is 2. Lithium containing complex oxide which is 15-2.45.
Li _a Ni _b Co _c Mn _d M _e O ₂ Formula I
However, M is one or more selected from the group consisting of Na, Mg, Ti, Zr, Al, W and Mo;
a + b + c + d + e = 2,
1.1 ≦ a / (b + c + d + e) ≦ 1.4,
0.2 ≦ b / (b + c + d + e) ≦ 0.5,
0 ≦ c / (b + c + d + e) ≦ 0.25,
0.3 ≦ d / (b + c + d + e) ≦ 0.6,
It is 0 <= e / (b + c + d + e) <= 0.1.   The lithium-containing composite oxide according to claim 1, wherein 0.05 ≦ c / (b + c + d + e) ≦ 0.25 in the formula I.   The lithium-containing composite oxide according to claim 1 or 2, wherein M in the formula I is one or more selected from the group consisting of Ti, Zr and Al.   The positive electrode active material containing lithium containing complex oxide as described in any one of Claims 1-3.   5. The positive electrode active material according to claim 4, wherein the surface of the lithium-containing composite oxide has a coating made of a compound containing one or more selected from the group consisting of Zr, Ti, Al and F. 6. The positive electrode active material according to claim 4, wherein D _{50 of the} positive electrode active material is 3 to 10 μm. The positive electrode active material according to any one of claims 4 to 6, wherein a specific surface area of the positive electrode active material is 0.5 to ⁵ m ² / g.   The positive electrode for lithium ion secondary batteries containing the positive electrode active material as described in any one of Claims 4-7, a electrically conductive material, and a binder.   A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to claim 8, a negative electrode and a non-aqueous electrolyte.