JP2017182927A - Square lithium ion battery, and method for manufacturing positive electrode active material for lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a square lithium ion battery which is arranged so that the occurrence of the expansion of the battery owing to charge and discharge can be suppressed well, and which enables the achievement of an adequate discharge capacity and good cycle characteristics; and a method for manufacturing a positive electrode active material for a lithium ion battery.SOLUTION: A square lithium ion battery comprises a positive electrode having a positive electrode active material represented by the following composition formula: Li(NiCoMnM)O(where 0.98≤a≤1.02, x+y+z+b=1, 0.5≤x≤0.9, 0.05≤y≤0.3, 0≤z≤0.3, 0≤b≤0.05, and M is at least one element selected from Mg, Al and Zr). As to the positive electrode, the value (α/y) determined by dividing a total cobalt elution amount α by y before charging the battery from 3.0 V is 4 μg or less, and the coefficient of volumetric expansion given by the formula 1 below, and calculated from a volume Vmeasured according to an Archimedes method, and a volume Vmeasured according to the Archimedes method after execution of 100 cycles of charging and discharging the battery at 90°C is 37% or less. Battery volumetric expansion coefficient (%)=100×(V-V)÷V(1).SELECTED DRAWING: None

Description

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

  Currently, there are three types of lithium-ion batteries: cylindrical, square, and laminate. Among these, prismatic lithium ion batteries have been commercialized in the form of being attached to and mounted on devices such as mobile phones and smartphones, and various types of batteries are manufactured and sold according to the size of each device.

As a positive electrode active material used for a prismatic lithium ion battery, it is particularly required to reduce residual alkali, which is the sum of Li ₂ CO ₃ and LiOH. The reason for this is that, in the case of the square type, the internal pressure rises due to residual Li ₂ CO _{3 and the} like, the battery swells and the outer shape is significantly deformed, and as a result, between the positive electrode and the terminal inside the device. This is because contact failure occurs and the battery does not function. For this reason, in the step of preparing a positive electrode active material for a prismatic battery, Li is slightly insufficient before firing (a metal other than Li / Li (hereinafter also referred to as Me) is 0.00). 95 to 1.00) to obtain an active material with little residual alkali. In this case, since Li is slightly volatilized during firing, the Li / Me in the positive electrode active material is actually about 0.94 to 0.99.

  However, when Li is insufficient, battery characteristics such as battery capacity generally deteriorate. That is, there was a trade-off relationship between reducing residual alkali and improving battery characteristics. Ideally, if Li / Me in which Li and Me react completely at 1: 1 during firing is considered while considering the amount of Li volatilized during firing, there is no impurity alkali and there is a lack of Li It should be possible to synthesize a positive electrode active material without any of the above.

  However, in reality, no matter how much the mixing is devised, there is a problem that Li-rich and Me-rich portions are partially present, and unreacted Li and unreacted Me remain, and only Li / Me is considered. Then, it was difficult to solve the above problem.

  Therefore, as described in Patent Document 1 or Patent Document 2, as a method of reducing the impurity alkali while maintaining the battery characteristics, a slightly larger amount of Li is charged, and the positive electrode active material precursor obtained by firing once In the prismatic battery, attention has been paid to a technique in which the remaining alkali is washed away with water, fired (or dried) again, and used as an active material.

JP 2012-17253 A JP 2013-26199 A

  However, when the technique described in Patent Document 1 or Patent Document 2 is actually applied, Li is desorbed from the positive electrode material particle surface by washing, and the crystal structure of the particle surface is destroyed after refiring. However, depending on the composition, there are problems such as a decrease in capacity and a deterioration in cycle characteristics.

  Accordingly, the present invention provides a method for producing a prismatic lithium ion battery and a positive electrode active material for a lithium ion battery in which the occurrence of swelling due to charging / discharging of the battery is satisfactorily suppressed and the discharge capacity and cycle characteristics are good. Let it be an issue.

  As a result of various studies to solve such a problem, the present inventor analyzed Li / Me in the positive electrode active material after washing the positive electrode active material, and determined a predetermined Li by desorption of Li. After replenishing a shortage of Li with respect to / Me by adding a lithium source, the positive electrode active material is calcined to reduce residual alkali and have a predetermined Li / Me It was found that can be produced. And it discovered that the square-shaped lithium ion battery from which discharge capacity and cycling characteristics become favorable by this is obtained.

In one aspect, the present invention completed on the basis of the above knowledge has a composition formula: Li _a (Ni _x Co _y Mn _z M _b ) O ₂
(Wherein 0.98 ≦ a ≦ 1.02, x + y + z + b = 1, 0.5 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.3, 0 ≦ z ≦ 0.3, 0 ≦ b ≦ 0.05, M is at least one element selected from Mg, Al, and Zr), and the positive electrode is charged before being charged from 3.0V. The value (α / y) obtained by dividing the total cobalt elution amount α measured under the following measurement conditions by y (α / y) is 4 μg or less, and after performing charge / discharge of 100 cycles at 90 ° C. with the volume V ₁ measured by Archimedes method This is a prismatic lithium ion battery having a volume expansion coefficient of 37% or less represented by the following formula 1 calculated using the volume V ₂ measured by the Archimedes method.
Battery volume expansion rate (%) = 100 × (V ₂ −V ₁ ) ÷ V ₁ (Formula 1)
<Measurement conditions of total cobalt elution amount α>
(1) Production of positive electrode The positive electrode for the rectangular lithium ion battery is used as a positive electrode sheet, and the positive electrode of the test coin battery is cut out from the positive electrode sheet so as to be a circle having a diameter of 16 mm.
(2) Preparation of negative electrode Circular lithium metal having a diameter of 16 mm is prepared as a negative electrode.
(3) Preparation of separator A separator having a diameter larger than 16 mm but fit in a 2032 coin battery is prepared.
(4) Preparation of test coin battery A positive electrode, a negative electrode, and a separator are impregnated with a non-aqueous electrolyte. In the non-aqueous electrolyte, LiPF ₆ was dissolved at a rate of 1 M (mol / liter) in a mixed solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 30:70. Shall. The impregnated positive electrode, negative electrode, and separator are assembled and caulked together with an outer shell and a spacer into a 2032 type coin battery.
(5) Trickle Charging The test coin battery is charged at a current of 0.66 mA up to 4.5 V in an environment of 45 ° C., and then trickle charged at 45 ° C. for 1 week.
(6) Measurement of metal elution amount The test coin battery after trickle charge is disassembled, the lithium metal of the negative electrode is taken out, and the total cobalt elution amount α per coin battery is calculated by ICP analysis. This α is divided by y separately calculated by ICP analysis.

In one embodiment, the prismatic lithium ion battery of the present invention has a residual alkali content of 0.8% by mass or less, which is the sum of Li ₂ CO ₃ and LiOH in the positive electrode active material.

In another embodiment of the prismatic lithium ion battery of the present invention, the positive electrode active material has a composition formula: Li _a (Ni _x Co _y Mn _z M _b ) O ₂
(Where, 0.98 ≦ a ≦ 1.02, x + y + z + b = 1, 0.8 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.15, 0 ≦ z ≦ 0.1, 0 ≦ b ≦ 0.05 and M are at least one element selected from Mg, Al, and Zr).

In still another aspect of the present invention, the composition formula: Li _a (Ni _x Co _y Mn _z M _b ) O ₂
(Wherein 0.98 ≦ a ≦ 1.02, x + y + z + b = 1, 0.5 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.3, 0 ≦ z ≦ 0.3, 0 ≦ b ≦ 0.05, M is at least one element selected from Mg, Al, and Zr), a step of drying the positive electrode active material after the cleaning, After drying, the metal element other than Li in the positive electrode active material is quantified by ICP, and the Li in the positive electrode active material is quantified by ion chromatography to calculate the ratio of Li / (metal element other than Li). A step of adding an insufficient amount of Li source to the positive electrode active material such that a ratio of Li / (metal element other than Li) becomes a predetermined value, and a step of firing the positive electrode active material after the addition of the Li source The manufacturing method of the positive electrode active material for lithium ion batteries provided with this.

  In one embodiment of the method for producing a positive electrode active material for a lithium ion battery of the present invention, the Li source is lithium nitrate and / or lithium hydroxide.

  In another embodiment of the method for producing a positive electrode active material for a lithium ion battery according to the present invention, the cleaning is performed with a cleaning solution having a pH of 5.5 to 7.5, a Ca concentration of 10 ppm or less, and an Mg concentration of 10 ppm or less. Use to do.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the swelling by charging / discharging of a battery is suppressed favorably, and the manufacturing method of the square-shaped lithium ion battery and positive electrode active material for lithium ion batteries with which discharge capacity and cycling characteristics become favorable is provided. it can.

(Configuration of prismatic lithium-ion battery)
The prismatic lithium ion battery of the present invention has a composition formula: Li _a (Ni _x Co _y Mn _z M _b ) O ₂
(Wherein 0.98 ≦ a ≦ 1.02, x + y + z + b = 1, 0.5 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.3, 0 ≦ z ≦ 0.3, 0 ≦ b ≦ 0.05, M is at least one element selected from Mg, Al and Zr).
The ratio of lithium to all metals in the positive electrode active material for a square lithium ion battery is 0.98 to 1.02, but if it is less than 0.98, it may be difficult to maintain a stable crystal structure, This is because if it exceeds 1.02, it may be difficult to secure a high capacity of the battery. Further, when the nickel ratio is less than 0.5, the discharge capacity is reduced.

  The metal element M, which is at least one element selected from Mg, Al, and Zr, is a trace element added to improve cycle characteristics. If the composition b of the metal element M exceeds 0.05, battery characteristics may be poor. Therefore, the composition b of the metal element M is controlled to 0 ≦ b ≦ 0.05.

The positive electrode active material for prismatic lithium ion battery of the present invention, the composition _{formula: Li a (Ni x Co y} Mn z M b) O 2
(Where, 0.98 ≦ a ≦ 1.02, x + y + z + b = 1, 0.8 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.15, 0 ≦ z ≦ 0.1, 0 ≦ b ≦ 0.05 and M are preferably represented by at least one element selected from Mg, Al and Zr).

In the positive electrode active material for a prismatic lithium ion battery of the present invention, the content of residual alkali, which is the sum of Li ₂ CO ₃ and LiOH, is preferably 0.8% by mass or less. When the content of residual alkali, which is the sum of Li ₂ CO ₃ and LiOH, is suppressed to 0.8% by mass or less, charging caused by residual alkali in the positive electrode active material, which has been a problem in prismatic batteries, etc. The side reaction in the battery accompanying discharge can be suppressed more favorably. For this reason, the swelling of a square-shaped lithium ion battery is suppressed more by using the said positive electrode active material for square-shaped lithium ion batteries. The content of residual alkali which is the sum of Li ₂ CO ₃ and LiOH is more preferably 0.6% by mass or less, still more preferably 0.4% by mass or less, still more preferably 0.2% by mass or less, and 0% More preferably, it is 1% by mass or less.

By suppressing the residual alkali content of the positive electrode active material, the residual alkali of the positive electrode active material, which has been a problem in prismatic batteries and the like, satisfactorily suppresses side reactions in the battery associated with charge / discharge, If the residual alkali is simply reduced by washing or the like, the Li at the 3a site of the positive electrode active material is insufficient, and if it is baked as it is, the battery characteristics are adversely affected. In contrast, the positive electrode for the prismatic lithium ion battery of the present invention is controlled so that the total cobalt elution amount α divided by y (α / y) is 4 μg or less. Here, the total cobalt elution amount α is measured under the following measurement conditions.
<Measurement conditions of total cobalt elution amount α>
(1) Production of positive electrode The positive electrode for the rectangular lithium ion battery is used as a positive electrode sheet, and the positive electrode of the test coin battery is cut out from the positive electrode sheet so as to be a circle having a diameter of 16 mm.
(2) Preparation of negative electrode Circular lithium metal having a diameter of 16 mm is prepared as a negative electrode.
(3) Preparation of separator A separator having a diameter larger than 16 mm but fit in a 2032 coin battery is prepared.
(4) Preparation of test coin battery A positive electrode, a negative electrode, and a separator are impregnated with a non-aqueous electrolyte. In the non-aqueous electrolyte, LiPF ₆ was dissolved at a rate of 1 M (mol / liter) in a mixed solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 30:70. Shall. The impregnated positive electrode, negative electrode, and separator are assembled and caulked together with an outer shell and a spacer into a 2032 type coin battery.
(5) Trickle Charging The test coin battery is charged at a current of 0.66 mA up to 4.5 V in an environment of 45 ° C., and then trickle charged at 45 ° C. for 1 week.
(6) Measurement of metal elution amount The test coin battery after trickle charge is disassembled, the lithium metal of the negative electrode is taken out, and the total cobalt elution amount α per coin battery is calculated by ICP analysis. This α is divided by y separately calculated by ICP analysis.

In the positive electrode active material of the positive electrode for the prismatic lithium ion battery in which the total cobalt elution amount α divided by y (α / y) is controlled to 4 μg or less, a low-valent metal such as Co ²⁺ is used. The content of is very low. In general, it is known that when Li is desorbed by washing or the like, the valence of the metal in the desorbed portion is reduced and becomes lower than the state in which Li was present at the 3a site. In general, when a positive electrode sheet containing a low-valent metal is taken out and trickle charging is performed, the low-valent metal is dissolved in the electrolytic solution and deposited on the negative electrode. That is, by measuring the amount of metal deposited on the negative electrode after charging, the Li deficiency at the 3a site in the positive electrode active material can be evaluated. For this reason, a battery is constructed using a positive electrode active material in which the total cobalt elution amount α divided by y (α / y) is extremely small. Can be obtained. The value (α / y) obtained by dividing the total cobalt elution amount α by y is more preferably 3 μg or less, and even more preferably 2 μg or less.

  The positive electrode for a prismatic lithium ion battery according to the present invention includes, for example, a positive electrode mixture prepared by mixing a positive electrode active material for a prismatic lithium ion battery having the above-described configuration, a conductive additive, and a binder from an aluminum foil or the like. It is produced by providing it on one or both sides of the current collector.

(Square type lithium ion battery)
The prismatic lithium ion battery according to the embodiment of the present invention is manufactured using the positive electrode for the prismatic lithium ion battery of the present invention. Further, prismatic lithium ion battery of the present invention, the volume V ₁ measured by the Archimedes method, calculated following equation using the volume V ₂ measured by the Archimedes method after the 100 cycles of charge and discharge at 90 ° C. The volume expansion coefficient indicated by 1 is 37% or less.
Battery volume expansion rate (%) = 100 × (V ₂ −V ₁ ) ÷ V ₁ (Formula 1)
According to such a configuration, the volume expansion coefficient due to charging and discharging is satisfactorily suppressed, so that the discharge capacity and cycle characteristics are good.

(Method for producing positive electrode active material for rectangular lithium ion battery)
The manufacturing method of the positive electrode active material for square-shaped lithium ion batteries which concerns on embodiment of this invention is demonstrated.
First, the composition formula: Li _a (Ni _x Co _y Mn _z M _b ) O ₂
(Where, 0.98 ≦ a ≦ 1.02, x + y + z + b = 1, 0.8 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.15, 0 ≦ z ≦ 0.1, 0 ≦ b ≦ 0.05, M is at least one element selected from Mg, Al, and Zr).
Although the said positive electrode active material is not specifically limited, For example, it can produce by baking 700-1000 degreeC * 3-48 hours with respect to the positive electrode active material precursor of the said composition.

Next, the positive electrode active material is cleaned using a cleaning liquid. Residual alkali can be sufficiently removed by the washing. At this time, the cleaning is preferably performed using a cleaning solution having a pH of 5.5 to 7.5, a Ca concentration of 10 ppm or less, and an Mg concentration of 10 ppm or less. If the pH of the cleaning liquid exceeds 7.5, residual alkali (Li ₂ CO ₃ or LiOH) that is an alkaline substance may not be cleaned. If the pH of the cleaning liquid is less than 5.5, the positive electrode active material is dissolved. There is a risk that. Further, when the Ca concentration in the cleaning liquid exceeds 10 ppm or the Mg concentration exceeds 10 ppm, the element remains in the positive electrode active material after cleaning, which may cause deterioration of battery characteristics.
As the cleaning liquid, water or dilute acid can be used.

  Next, the washed positive electrode active material is dried by heating at 110 to 130 ° C. for 1 to 48 hours.

  Next, after the drying, metal elements (Me) other than Li in the positive electrode active material are quantified by ICP (Inductively Coupled Plasma), and Li in the positive electrode active material is quantified by ion chromatography. Then, the Li / Me ratio is calculated, and a shortage of Li source is added to the positive electrode active material so that the Li / Me ratio becomes a predetermined value (for example, Li / Me = 0.98 to 1.02). To do. The Li source may be lithium nitrate and / or lithium hydroxide.

  Usually, when the Li source is simply mixed with the positive electrode active material precursor, the generation of the positive electrode active material and the grain growth occur at the same time. At this time, the positive electrode active material precursor and Li are slightly segregated, and residual alkali after firing. As likely to occur. On the other hand, in the present invention, as described above, an insufficient Li source with respect to appropriate Li / Me is added to the washed and dried positive electrode active material, and then fired as described later. In this way, when the cathode active material is washed and then a sufficient amount of Li source is added and baked, Li is inserted into the crystal structure of the cathode active material already present during the solid-phase reaction, so the reactivity of the solid-phase reaction is reduced. Good, residual alkali hardly remains on the surface. Therefore, it is possible to achieve both reduction of residual alkali in the resulting positive electrode active material and improvement of Li occupancy in the 3a site.

  Next, the positive electrode active material after the addition of the Li source is fired by heating at 700 to 900 ° C. for 2 to 24 hours (when the positive electrode active material before washing is produced by firing, “refire”) Be) Subsequently, if necessary, crushing and classification are performed to obtain a positive electrode active material.

  Examples for better understanding of the present invention and its advantages are provided below, but the present invention is not limited to these examples.

Example 1
First, nickel sulfate, manganese sulfate, and cobalt sulfate are dissolved in pure water at 40 ° C., the concentration of (Ni + Co + Mn) is 1.15 mol / kg, and the molar ratio of Ni: Co: Mn is 8: 1: 1. A 40 ° C. aqueous solution A was prepared. The aqueous solution A is substantially free of components other than Ni, Co, Mn, SO ₄ and H ₂ O. Separately from the aqueous solution A, NaOH was dissolved in pure water to prepare a 1.85 mol / kg NaOH aqueous solution B. In addition, a commercially available about 29 wt% ammonia aqueous solution (Kanto Chemical) was diluted with pure water to obtain a 0.1 mol% ammonia aqueous solution C. The temperature of the aqueous solutions B and C was set to 40 ° C. by heating, and nitrogen was passed through each of the separately prepared reaction tanks and aqueous solutions A, B, and C to expel the air. Then, after the aqueous solutions A and B are sent to the reaction tank by 1.5 L per minute to the reaction tank for about 10 minutes to form seed crystals, the aqueous solutions A, B and C are sent 0.8 L per minute by the tube pump. Liquid. The produced slurry was subjected to particle size distribution measurement with a laser diffraction / scattering type particle size distribution meter (Microtrac), and when the average particle diameter (D50) exceeded 15 μm, all liquid feeding was stopped. This was filtered and washed with water, and then heated in nitrogen at 400 ° C. for 3 hours to obtain a precursor.
Next, the contents of nickel, manganese, and cobalt contained in the precursor were analyzed by ICP, and the amount of LiOH.H ₂ O was determined so that Li / (Ni + Co + Mn) was 0.98 in molar ratio. The analysis of ICP was performed by a conventional method. Commercially available LiOH · H ₂ O was pulverized with a jet mill, and the determined amount was weighed. The precursor and LiOH · H ₂ O were placed in this order in a Henschel mixer vessel, and the lid was closed and mixed for 5 minutes. After taking out the mixed powder, it is heated to 500 ° C. at 10 ° C./min, heated to 760 ° C. at 5 ° C./min, held at 760 ° C. for 24 hours, cooled to 400 ° C. at 5 ° C./min, and then the furnace door Was gradually opened, cooled to room temperature and crushed to obtain a lithium composite oxide.
Next, the lithium composite oxide was washed with water at pH 5.8 for 10 minutes, filtered and dried at a temperature of 120 ° C. for 1 hour. ICP was used to quantify metal elements (Me) other than Li in the positive electrode active material, and Li in the positive electrode active material was further quantified by ion chromatography to calculate Li / Me. Li / Me was the value shown in Table 1. Insufficient Li source (LiOH) was added. Subsequently, firing (re-firing) was performed at a temperature of 760 ° C. for 12 hours to obtain a positive electrode active material.

(Example 2)
A positive electrode active material was obtained in the same manner as in Example 1 except that LiNO ₃ was added as a Li source after the lithium composite oxide was washed with water, and the pH of the cleaning liquid was 6.1.

(Example 3)
A positive electrode active material was obtained in the same manner as in Example 1 except that the Li source added after the lithium composite oxide was washed with water was Li ₂ CO ₃ and the pH of the washing liquid was 6.8.

Example 4
A positive electrode active material was obtained in the same manner as in Example 1 except that Li / Me was set to 1.00.

(Example 5)
A positive electrode active material was obtained in the same manner as in Example 4 except that the Li source added after the lithium composite oxide was washed with water was LiNO ₃ , and the pH of the washing liquid was 7.2.

(Example 6)
A positive electrode active material was obtained in the same manner as in Example 4 except that Li ₂ CO ₃ was added after the lithium composite oxide was washed with water, and the pH of the washing liquid was 6.3.

(Example 7)
A positive electrode active material was obtained in the same manner as in Example 1 except that Li / Me was 1.02 and the pH of the cleaning liquid was 5.7.

(Example 8)
A positive electrode active material was obtained in the same manner as in Example 7 except that the Li source added after washing the lithium composite oxide with water was LiNO ₃ , and the pH of the washing liquid was 7.4.

Example 9
A positive electrode active material was obtained in the same manner as in Example 7 except that the Li source added after the lithium composite oxide was washed with water was Li ₂ CO ₃ and the pH of the washing liquid was 5.5.

(Example 10)
A positive electrode active material was obtained in the same manner as in Example 4 except that the molar ratio of Ni: Co: Mn in the aqueous solution A was 90: 5: 5, the firing temperature was 740 ° C., and the pH of the cleaning solution was 6.7. .

(Example 11)
A positive electrode active material was obtained in the same manner as in Example 10, except that LiNO ₃ was added as a Li source to be added after the lithium composite oxide was washed with water, and the pH of the cleaning liquid was 6.3.

Example 12
A positive electrode active material was obtained in the same manner as in Example 10 except that the Li source added after the lithium composite oxide was washed with water was Li ₂ CO ₃ and the pH of the washing liquid was 5.7.

(Example 13)
In the same manner as in Example 4, except that the molar ratio of Ni: Co: Mn in the aqueous solution A was 5: 2: 3, the firing temperature was 880 ° C., the drying time was 48 hours, and the pH of the cleaning solution was 6.9. A positive electrode active material was obtained.

(Example 14)
A positive electrode active material was obtained in the same manner as in Example 13, except that the Li source added after washing the lithium composite oxide with water was LiNO ₃ and the pH of the cleaning liquid was 6.4.

(Example 15)
A positive electrode active material was obtained in the same manner as in Example 13 except that the Li source added after the lithium composite oxide was washed with water was Li ₂ CO ₃ , and the pH of the washing liquid was 6.2.

(Example 16)
First, nickel sulfate, magnesium sulfate, and cobalt sulfate are dissolved in pure water at 40 ° C., the concentration of (Ni + Co + Mg) is 1.15 mol / kg, and the molar ratio of Ni: Co: Mg is 80: 15: 5. A 40 ° C. aqueous solution A was prepared. The aqueous solution A is substantially free of components other than Ni, Co, Mg, SO ₄ and H ₂ O. Separately from the aqueous solution A, NaOH was dissolved in pure water to prepare a 1.85 mol / kg NaOH aqueous solution B. In addition, a commercially available about 29 wt% ammonia aqueous solution (Kanto Chemical) was diluted with pure water to obtain a 0.1 mol% ammonia aqueous solution C. The temperature of the aqueous solutions B and C was set to 40 ° C. by heating, and nitrogen was passed through each of the separately prepared reaction tanks and aqueous solutions A, B, and C to expel the air. Then, after the aqueous solutions A and B are sent to the reaction tank by 1.5 L per minute to the reaction tank for about 10 minutes to form seed crystals, the aqueous solutions A, B and C are sent 0.8 L per minute by the tube pump. Liquid. The produced slurry was subjected to particle size distribution measurement with a laser diffraction / scattering type particle size distribution meter (Microtrac), and when the average particle diameter (D50) exceeded 15 μm, all liquid feeding was stopped. This was filtered and washed with water, and then heated in nitrogen at 400 ° C. for 3 hours to obtain a precursor.
Next, the contents of nickel, magnesium, and cobalt contained in the precursor were analyzed by ICP, and the amount of LiOH.H ₂ O was determined so that the molar ratio of Li / (Ni + Co + Mg) was 1.00. The analysis of ICP was performed by a conventional method. Commercially available LiOH · H ₂ O was pulverized with a jet mill, and the determined amount was weighed. The precursor and LiOH · H ₂ O were placed in this order in a Henschel mixer vessel, and the lid was closed and mixed for 5 minutes. After taking out the mixed powder, it is heated to 500 ° C. at 10 ° C./min, heated to 760 ° C. at 5 ° C./min, held at 760 ° C. for 24 hours, cooled to 400 ° C. at 5 ° C./min, and then the furnace door Was gradually opened, cooled to room temperature and crushed to obtain a lithium composite oxide.
Next, the lithium composite oxide was washed with water at pH 7.0 for 10 minutes, filtered and dried at a temperature of 120 ° C. for 1 hour. ICP was used to quantify metal elements (Me) other than Li in the positive electrode active material, and Li in the positive electrode active material was further quantified by ion chromatography to calculate Li / Me. Li / Me was the value shown in Table 1. Insufficient Li source (LiOH) was added. Subsequently, firing (re-firing) was performed at a temperature of 760 ° C. for 12 hours to obtain a positive electrode active material.

(Example 17)
First, nickel sulfate and cobalt sulfate are dissolved in pure water at 40 ° C., and a 40 ° C. aqueous solution A having a (Ni + Co) concentration of 1.09 mol / kg and a Ni: Co molar ratio of 82:15 is prepared. did. The aqueous solution A is substantially free of components other than Ni, Co, Al, SO ₄ and H ₂ O. Separately from the aqueous solution A, NaOH and aluminum sulfate were dissolved in pure water to prepare a 1.85 mol / kg aqueous NaOH solution B containing Al. At this time, the Al concentration was adjusted so that the ratio of (Ni + Co): Al was 97: 3. In addition, a commercially available about 29 wt% ammonia aqueous solution (Kanto Chemical) was diluted with pure water to obtain a 0.1 mol% ammonia aqueous solution C. The temperature of the aqueous solutions B and C was set to 40 ° C. by heating, and nitrogen was passed through each of the separately prepared reaction tanks and aqueous solutions A, B, and C to expel the air. Then, after the aqueous solutions A and B are sent to the reaction tank by 1.5 L per minute to the reaction tank for about 10 minutes to form seed crystals, the aqueous solutions A, B and C are sent 0.8 L per minute by the tube pump. Liquid. The produced slurry was subjected to particle size distribution measurement with a laser diffraction / scattering type particle size distribution meter (Microtrac), and when the average particle diameter (D50) exceeded 15 μm, all liquid feeding was stopped. This was filtered and washed with water, and then heated in nitrogen at 400 ° C. for 3 hours to obtain a precursor.
Next, the contents of nickel, magnesium, and cobalt contained in the precursor were analyzed by ICP, and the amount of LiOH.H ₂ O was determined so that the molar ratio of Li / (Ni + Co + Al) was 1.00. The analysis of ICP was performed by a conventional method. Commercially available LiOH · H ₂ O was pulverized with a jet mill, and the determined amount was weighed. The precursor and LiOH · H ₂ O were placed in this order in a Henschel mixer vessel, and the lid was closed and mixed for 5 minutes. After taking out the mixed powder, it is heated to 500 ° C. at 10 ° C./min, heated to 760 ° C. at 5 ° C./min, held at 760 ° C. for 24 hours, cooled to 400 ° C. at 5 ° C./min, and then the furnace door Was gradually opened, cooled to room temperature and crushed to obtain a lithium composite oxide.
Next, the lithium composite oxide was washed with water at pH 6.5 for 10 minutes, filtered and dried at a temperature of 120 ° C. for 1 hour. ICP was used to quantify metal elements (Me) other than Li in the positive electrode active material, and Li in the positive electrode active material was further quantified by ion chromatography to calculate Li / Me. Li / Me was the value shown in Table 1. Insufficient Li source (LiOH) was added. Subsequently, firing (re-firing) was performed at a temperature of 760 ° C. for 12 hours to obtain a positive electrode active material.

(Example 18)
First, nickel sulfate, zirconium sulfate, and cobalt sulfate are dissolved in pure water at 40 ° C., the concentration of (Ni + Co + Zr) is 1.15 mol / kg, and the molar ratio of Ni: Co: Zr is 80: 15: 5. A 40 ° C. aqueous solution A was prepared. The aqueous solution A is substantially free of components other than Ni, Co, Zr, SO ₄ , and H ₂ O. Separately from the aqueous solution A, NaOH was dissolved in pure water to prepare a 1.85 mol / kg NaOH aqueous solution B. In addition, a commercially available about 29 wt% ammonia aqueous solution (Kanto Chemical) was diluted with pure water to obtain a 0.1 mol% ammonia aqueous solution C. The temperature of the aqueous solutions B and C was set to 40 ° C. by heating, and nitrogen was passed through each of the separately prepared reaction tanks and aqueous solutions A, B, and C to drive out air. Then, after the aqueous solutions A and B are sent to the reaction tank by 1.5 L per minute to the reaction tank for about 10 minutes to form seed crystals, the aqueous solutions A, B and C are sent 0.8 L per minute by the tube pump. Liquid. The produced slurry was subjected to particle size distribution measurement with a laser diffraction / scattering type particle size distribution meter (Microtrac), and when the average particle diameter (D50) exceeded 15 μm, all liquid feeding was stopped. This was filtered and washed with water, and then heated in nitrogen at 400 ° C. for 3 hours to obtain a precursor.
Next, the contents of nickel, zirconium and cobalt contained in the precursor were analyzed by ICP, and the amount of LiOH.H ₂ O was determined so that Li / (Ni + Co + Zr) was 1.00 in molar ratio. The analysis of ICP was performed by a conventional method. Commercially available LiOH · H ₂ O was pulverized with a jet mill, and the determined amount was weighed. The precursor and LiOH · H ₂ O were placed in this order in a Henschel mixer vessel, and the lid was closed and mixed for 5 minutes. After the mixed powder is taken out, it is heated to 500 ° C. at 10 ° C./min, heated to 750 ° C. at 5 ° C./min, kept at 750 ° C. for 24 hours, cooled to 400 ° C. at 5 ° C./min, and then the furnace door Was gradually opened, cooled to room temperature and crushed to obtain a lithium composite oxide.
Next, the lithium composite oxide was washed with water at pH 5.9 for 10 minutes, filtered and dried at a temperature of 120 ° C. for 1 hour. ICP was used to quantify metal elements (Me) other than Li in the positive electrode active material, and Li in the positive electrode active material was further quantified by ion chromatography to calculate Li / Me. Li / Me was the value shown in Table 1. Insufficient Li source (LiOH) was added. Subsequently, firing (re-firing) was performed at a temperature of 750 ° C. for 12 hours to obtain a positive electrode active material.

(Comparative Examples 1-5)
Comparative Examples 1 to 5 were produced in the same procedure as in the Examples, except that all the steps after the water washing step were not performed.

(Comparative Examples 6 to 10)
The production methods of Comparative Examples 6 to 10 were prepared in the same procedure as in the Examples, except that only the addition of the lithium source after washing was not performed.

(Evaluation)
-Composition-
The obtained positive electrode active material powder was measured for the contents of Li, Ni, Mn, Co and other metal elements by ICP and ion chromatography. From the analysis results, the composition of the product _{formula: Li a (Ni x Co y} Mn z M b) when expressed by the composition formula of O _2, obtained a, x, y, and z and b.

-Residual alkali-
After the obtained positive electrode active material powder is added to water and stirred for 10 minutes, the lithium compound present in the water is regarded as residual alkali in the positive electrode active material, and the pH is titrated with an acid. Was used to determine the mass of residual alkali (Li ₂ CO ₃ and LiOH), and the mass ratio (mass%) relative to the positive electrode active material was determined.

-Battery characteristics-
<Preparation of positive electrode>
3 kg of the positive electrode active material for each prismatic lithium ion battery produced in Examples and Comparative Examples, and PVDF # 1320 (N-methyl-2-pyrrolidone containing 12% by weight of PVDF (hereinafter, NMP (abbreviated as NMP) Solution) 1 kg, acetylene black 90 g, and an appropriate amount of NMP were stirred with a double-arm kneader to prepare a positive electrode mixture paste. This paste was applied to both surfaces of a positive electrode core material made of an aluminum foil having a thickness of 15 μm, dried and rolled to form a positive electrode active material layer, whereby a positive electrode having a total thickness of 130 μm was obtained. The positive electrode was cut into a strip having a width of 43 mm. Two of these were prepared, one for the following prismatic lithium ion battery and the other for the following test coin battery.

<Production of negative electrode>
3 kg of artificial graphite, 75 g of BM-400B (an aqueous dispersion containing 40% by weight of modified styrene butadiene rubber) manufactured by Nippon Zeon Co., Ltd., 30 g of CMC and an appropriate amount of water were stirred with a double arm kneader. A negative electrode mixture paste was prepared. This paste was applied to both sides of a negative electrode core material made of a copper foil having a thickness of 10 μm, dried and rolled to form a negative electrode active material layer, and a negative electrode having a total thickness of 140 μm was obtained. The negative electrode was cut into a 45 mm wide strip.

<Preparation of prismatic lithium ion battery>
A positive electrode and a negative electrode are wound through a separator (A089 (trade name) manufactured by Celgard Co., Ltd.) made of a polyethylene microporous film having a thickness of 20 μm between the positive electrode and the negative electrode. Groups were made up. The electrode group was accommodated in a rectangular battery can made of aluminum. The battery can has a bottom and a side wall. The upper part of the battery can is opened and its shape is substantially rectangular. The thickness of the main flat part of the side wall was 80 μm. Thereafter, an insulator for preventing a short circuit between the battery can and the positive electrode lead or the negative electrode lead was disposed on the upper part of the electrode group. Next, a rectangular sealing plate having a negative electrode terminal surrounded by an insulating gasket in the center was disposed in the opening of the battery can. The negative electrode lead was connected to the negative electrode terminal. The positive electrode lead was connected to the lower surface of the sealing plate. The end of the opening and the sealing plate were welded with a laser to seal the opening of the battery can. Thereafter, 2.5 g of nonaqueous electrolyte was injected into the battery can through the injection hole of the sealing plate. Finally, the liquid injection hole was closed with a seal by welding. Thus, a prismatic lithium secondary battery having a height of 50 mm, a width of 34 mm, an inner space thickness of about 5.2 mm, and a design capacity of 850 mAh was completed. As the non-aqueous electrolyte, a mixed solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) are mixed at a volume ratio of 30:70, a ratio of LiPF ₆ to 1 M (mol / liter). What was melt | dissolved in was used. The open circuit voltage was measured and found to be 3.0V in all cases.

<Charging / discharging conditions of prismatic lithium ion battery>
About each square-shaped lithium ion battery produced in the Example and the comparative example, it charged to the end-of-charge potential 4.2V with the charging current 850mA, Then, it discharged to the end-of-discharge potential 3.0V with the discharge current 850mA. This condition was repeated 20 cycles, and the percentage (%) of the initial discharge capacity (mAh / g) relative to the initial charge capacity (mAh / g) was determined as the charge / discharge efficiency, the discharge capacity after 20 cycles relative to the initial discharge capacity (mAh / g) ( The percentage (%) of mAh / g) was defined as the capacity retention rate after 20 cycles. In order to investigate battery swelling, the battery was charged at 90 ° C. with a charging current of 850 mA to a charge end potential of 4.2 V, and then discharged with a discharge current of 850 mA to a discharge end potential of 3.0 V. This condition was repeated 100 cycles, a change from an initial inner space thickness of 5.2 mm was measured by X-ray CT scan, and the largest value among these changes was defined as a thickness increment (mm). X-ray CT scan measurement was performed by a conventional method.

<Volume expansion coefficient of prismatic lithium ion battery>
About each square-shaped lithium ion battery produced in the Example and the comparative example, the thickness of the inner space is 5.2 mm, and the open circuit voltage is 3.0 V. The volume V ₁ was measured by Archimedes method. Next, the battery which was charged and discharged at 90 ° C. and investigated the battery swelling was similarly put in 1 L of water with the open circuit voltage kept at 3.0 V, and the volume V ₂ was measured by Archimedes method. From these values, the battery volume expansion rate (%) was determined by the following formula. When the battery volume expansion rate was 37% or less, it was determined that the swelling was well controlled.
Battery volume expansion rate (%) = 100 × (V ₂ −V ₁ ) ÷ V ₁

<Test coin cell evaluation conditions>
For each test coin battery production positive electrode produced in Examples and Comparative Examples, the positive electrode was cut into a circle so as to have a diameter of 16 mm. Furthermore, metallic lithium and a separator (A089 (trade name) manufactured by Celgard Co., Ltd.) used as the negative electrode were cut into a circle so as to have the same shape as the positive electrode. However, the separator was cut out slightly larger to fit in the 2032 coin battery. The cut out positive electrode, negative electrode, and separator were impregnated with a non-aqueous electrolyte similar to the above, and caulked together with members such as an outer shell and a spacer into a 2032 type coin battery. The 2032 coin battery thus obtained was charged at 0.66 mA up to 4.5 V under an environment of 45 ° C., and then trickle charging was performed at 45 ° C. and maintained at 4.5 V for one week. The cell after trickle charge was disassembled, and the amount of cobalt deposited on the negative electrode lithium metal was analyzed by ICP and calculated as the amount α (μg) per coin battery. This value α was divided by y in the composition formula.
Tables 1 and 2 show the test conditions and evaluation results of Examples 1 to 18 and Comparative Examples 1 to 10, respectively.

(Evaluation results)
In the batteries of Examples 1 to 18, the value (α / y) obtained by dividing the total cobalt elution amount α by y was 4 μg or less, and the volume expansion coefficient before and after charging and discharging was 37% or less. Generation | occurrence | production of the swelling by discharge was suppressed favorably, and discharge capacity and cycling characteristics were favorable.
In Comparative Examples 1 to 5, the value (α / y) obtained by dividing the total cobalt elution amount α by y exceeds 4 μg, and the volume expansion coefficient before and after charging and discharging exceeds 37%. The occurrence of was large.
In Comparative Examples 6 to 10, the value (α / y) obtained by dividing the total cobalt elution amount α by y exceeds 4 μg, and the discharge capacity or cycle characteristics are poor when compared with Examples having the same Ni composition. A square lithium-ion battery was obtained.

Claims (6)

Composition _{formula: Li a (Ni x Co y} Mn z M b) O 2
(Wherein 0.98 ≦ a ≦ 1.02, x + y + z + b = 1, 0.5 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.3, 0 ≦ z ≦ 0.3, 0 ≦ b ≦ 0.05, M is at least one element selected from Mg, Al, Zr), and a positive electrode having a positive electrode active material represented by
The positive electrode has a value (α / y) obtained by dividing the total cobalt elution amount α measured under the following measurement conditions by y before charging from 3.0 V is 4 μg or less,
The volume V ₁ measured by the Archimedes method, at 90 ° C. in 100 cycles of charge and discharge a volume expansion ratio represented by the following formula 1 calculated by using the volume V ₂ measured by the Archimedes method after 37% or less A certain prismatic lithium-ion battery.
Battery volume expansion rate (%) = 100 × (V ₂ −V ₁ ) ÷ V ₁ (Formula 1)
<Measurement conditions of total cobalt elution amount α>
(1) Production of positive electrode The positive electrode for the rectangular lithium ion battery is used as a positive electrode sheet, and the positive electrode of the test coin battery is cut out from the positive electrode sheet so as to be a circle having a diameter of 16 mm.
(2) Preparation of negative electrode Circular lithium metal having a diameter of 16 mm is prepared as a negative electrode.
(3) Preparation of separator A separator having a diameter larger than 16 mm but fit in a 2032 coin battery is prepared.
(4) Preparation of test coin battery A positive electrode, a negative electrode, and a separator are impregnated with a non-aqueous electrolyte. In the non-aqueous electrolyte, LiPF ₆ was dissolved at a rate of 1 M (mol / liter) in a mixed solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 30:70. Shall. The impregnated positive electrode, negative electrode, and separator are assembled and caulked together with an outer shell and a spacer into a 2032 type coin battery.
(5) Trickle Charging The test coin battery is charged at a current of 0.66 mA up to 4.5 V in an environment of 45 ° C., and then trickle charged at 45 ° C. for 1 week.
(6) Measurement of metal elution amount The test coin battery after trickle charge is disassembled, the lithium metal of the negative electrode is taken out, and the total cobalt elution amount α per coin battery is calculated by ICP analysis. This α is divided by y separately calculated by ICP analysis. _2. The prismatic lithium ion battery according to claim 1, wherein the content of residual alkali, which is the sum of Li ₂ CO ₃ and LiOH in the positive electrode active material, is 0.8% by mass or less. The positive electrode active material has a composition formula: Li _a (Ni _x Co _y Mn _z M _b ) O ₂
(Where, 0.98 ≦ a ≦ 1.02, x + y + z + b = 1, 0.8 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.15, 0 ≦ z ≦ 0.1, 0 ≦ b ≦ The prismatic lithium ion battery according to claim 1 or 2, wherein 0.05 and M are at least one element selected from Mg, Al, and Zr). Composition _{formula: Li a (Ni x Co y} Mn z M b) O 2
(Wherein 0.98 ≦ a ≦ 1.02, x + y + z + b = 1, 0.5 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.3, 0 ≦ z ≦ 0.3, 0 ≦ b ≦ 0.05, M is at least one element selected from Mg, Al, and Zr), and the step of cleaning the positive electrode active material represented by
Drying the positive electrode active material after washing,
After the drying, the metal element other than Li in the positive electrode active material is quantified by ICP, and the Li in the positive electrode active material is quantified by ion chromatography to determine the ratio of Li / (metal element other than Li). Calculating and adding a deficient Li source to the positive electrode active material such that the ratio of Li / (metallic element other than Li) is a predetermined value;
Firing the positive electrode active material after the addition of the Li source;
The manufacturing method of the positive electrode active material for lithium ion batteries provided with.   The method for producing a positive electrode active material for a lithium ion battery according to claim 4, wherein the Li source is lithium nitrate and / or lithium hydroxide.   The positive electrode active material for a lithium ion battery according to claim 4 or 5, wherein the cleaning is performed using a cleaning solution having a pH of 5.5 to 7.5, a Ca concentration of 10 ppm or less, and an Mg concentration of 10 ppm or less. Method.