JP2017130414A - Coated positive electrode active material for composite lithium ion battery, and lithium ion battery arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material useful as a positive electrode active material of a laminate battery.SOLUTION: A positive electrode active material for a lithium ion secondary battery comprises a lithium metal composite oxide expressed by the following formula: LiNiCoAlO(where a=0.8-1.2, b=0.7-0.95, c=0.02-0.2, d=0.005-0.1, and b+c+d=1). The lithium metal composite oxide is coated with a compound including an element M2 (where M2 is selected from an alkali metal, an alkali-earth metal, a lanthanoid element, an actinoid element, and elements of Groups III to XVII of the periodic table). The amount (weight) of aluminum eluting into high-temperature sodium hydroxide is over 10% of a total weight of aluminum included in the positive electrode active material.SELECTED DRAWING: None

Description

  The present invention relates to a positive electrode active material for a lithium ion battery and a lithium ion battery using the positive electrode active material as a positive electrode, and more particularly, to a laminate battery using the same as a positive electrode.

  Lithium ion batteries have a long history and their commercial production began in the 1990s. However, it can be said that the development of lithium-ion batteries has been developed in earnest with the spread of mobile terminals, smartphones, electric vehicles and the like since 2000. Lithium ion batteries, like other batteries, have a positive electrode, a negative electrode, an electrolyte, and an outer package as the main components. Among them, the positive electrode active material used for the positive electrode is an important material that affects the battery performance of the lithium ion battery. is there. Various lithium metal oxides have already been found as positive electrode active materials used in lithium ion batteries (Non-patent Document 1).

  So far, positive electrode active materials for high-power lithium-ion batteries have been proposed in order to achieve low cost and long-time use of portable terminals, smartphones, and electric vehicles. On the other hand, since safety and durability are also required for mobile terminals, smartphones, and electric vehicles equipped with lithium ion batteries, the positive electrode active material is required to have high heat resistance and the property of not causing deformation of the battery body. The In order to satisfy such requirements, various positive electrode active materials for lithium ion batteries have been proposed (Non-Patent Document 1).

  Among these, the NCA-based positive electrode active material has an advantage that an electrode having a high energy density can be produced. In recent years, in particular, mobile terminals and smartphones have been made thinner and smaller, and the form of the lithium ion battery itself is showing signs of change. Up to now, prismatic batteries and cylindrical batteries, which have excellent durability when loaded, have been mainstream, but thinner and lighter laminate batteries have also been put into practical use (Patent Document 1). However, since the laminated battery covers the electrode and other members with a thin and flexible film, there is a problem that it is weaker to the pressure from the inside and outside than the rectangular or cylindrical battery having a conventional metal outer casing. is there. And in a lithium ion battery, it is known that gas, such as a carbon dioxide gas, will be generated by the impurity contained in a positive electrode active material in the use process of a battery. Such swelling of the battery due to gas generation is a more serious problem in laminated batteries. Even in the case of gas generation to such an extent that battery expansion does not occur in rectangular batteries and cylindrical batteries, there is a possibility of causing expansion and destruction in laminated batteries.

  In view of this, a structure of a laminated battery has been proposed in order to reduce defects at the time of gas generation. For example, a laminated battery case is provided with a through-hole through which gas generated inside is released (Patent Document 2), and a positive electrode mixture-uncoated portion is provided on the positive electrode, thereby making it difficult to cause unevenness inside (Patent Document 3). The improvement method of arrange | positioning a gas adsorbent in a storage part (patent document 4) is proposed.

  As described above, examples of providing a special laminated structure and additional members for the laminated battery as a means of solving the problem at the time of gas generation particularly concerned with the laminated battery and improving the safety and durability of the battery have been found. It is. However, positive electrode active materials suitable for laminated batteries, particularly NCA-based positive electrode active materials, have not been sufficiently studied.

  For example, in Patent Document 5, nickel sulfate and cobalt sulfate are dissolved in a predetermined composition, a sodium hydroxide solution is added to this solution, the nickel and cobalt composite hydroxide is dried, and aluminum hydroxide is added. Lithium metal composite oxide by adding, stirring and mixing, and further mixing lithium hydroxide monohydrate with a mixture of coprecipitated hydroxide and aluminum hydroxide and firing in an oxygen atmosphere at 800 ° C. for 5 hours Have gained. However, the battery performance of the positive electrode active material obtained here was not completely satisfactory. For example, the initial charge / discharge efficiency is only 85 to 90%, which cannot be said to be a high-quality positive electrode active material that can withstand a highly efficient battery design.

JP 2011-77030 A JP 2003-168410 A JP 2004-303590 A JP2012-59489A JP 2001-266876 A “Functional Materials” September 2011 Vol. 9 pages 12-19

  The inventors of the present invention have improved the laminate battery by a different approach, that is, improvement of the positive electrode active material itself. The inventors of the present invention have the performance required for all positive electrode active materials for lithium ion batteries such as high capacity, good initial charge / discharge efficiency, and high thermal stability, and the generation of internal gas particularly required for positive electrode active materials for laminated batteries. An NCA-based positive electrode active material having the performance of being extremely suppressed was sought.

  Surprisingly, it is effective for the present inventors to quantify a specific fraction of aluminum atoms contained in the positive electrode active material as an index for identifying a positive electrode active material suitable for such a laminated battery. I found out. The “specific fraction” is a fraction extracted under a particularly high load among the aluminum atoms contained in the positive electrode active material, and specifically, the aluminum atom contained in the positive electrode active material. Among them, it is a fraction that elutes into sodium hydroxide in a molten state at high temperature.

The method of quantifying the fraction eluted in the high-temperature sodium hydroxide contained in the positive electrode active material newly found by the present inventors follows the following method (A).
Method (a): Take 12.5 g of the positive electrode active material and 20.0 g of sodium hydroxide in a nickel crucible. This crucible is placed in a muffle furnace heated to 500 ° C. 5 minutes after the sodium hydroxide is sufficiently dissolved, the crucible is removed from the muffle furnace. Immediately disperse the contents of the crucible in 250 ml of pure water and stir. By analyzing the supernatant by inductively coupled plasma optical emission spectrometry (ICP analysis), the weight of aluminum element eluted in sodium hydroxide at 500 ° C. is measured.

The present inventors have a high aluminum elution amount obtained by the above method (a), that is, a positive electrode in which the aluminum elution amount obtained by the above method (a) is more than 10% of the total aluminum weight contained in the positive electrode active material. It has been found that the active material has a well-balanced performance required for the above-described positive electrode for a lithium ion battery, particularly a positive electrode for a laminated lithium ion battery.
That is, the present invention is as follows.
(Invention 1) A lithium metal composite oxide having a composition represented by the following general formula (1):
Li _a Ni _b Co _c Al _d O ₂ (1)
(However, a = 0.8 to 1.2, b = 0.7 to 0.95, c = 0.02 to 0.2, d = 0.005 to 0.1, and b + c + d = 1. is there.)
The lithium metal composite compound further includes
Element M2 (M2 is at least one element selected from alkali metals, alkaline earth metals, lanthanoid elements, actinoid elements, and elements of Groups 3 to 17 of the periodic table). Coated with a compound,
The amount of aluminum (weight) eluted in high-temperature sodium hydroxide measured by the following method (a) exceeds 10% of the total aluminum weight contained in the lithium metal composite oxide,
[Method (a): Take 12.5 g of the positive electrode active material and 20.0 g of sodium hydroxide in a nickel crucible. This crucible is placed in a muffle furnace heated to 500 ° C. 5 minutes after the sodium hydroxide is sufficiently dissolved, the crucible is removed from the muffle furnace. Immediately disperse the contents of the crucible in 250 ml of pure water and stir. By analyzing the supernatant by inductively coupled plasma optical emission spectrometry (ICP analysis), the weight of aluminum element eluted in sodium hydroxide at 500 ° C. is measured. ]
Positive electrode active material for lithium ion secondary battery.
(Invention 2) The positive electrode active material of Invention 1, wherein the LiOH residue is 0.2% by weight or less and the Li ₂ CO ₃ residue is 0.2% by weight or less.
(Invention 3) A positive electrode for a lithium ion battery using the positive electrode active material of Invention 1 or 2.
(Invention 4) A lithium ion battery comprising the positive electrode for a lithium ion battery of Invention 3.
(Invention 5) The lithium ion battery of Invention 4, which is a laminate battery.

  In the present invention, a positive electrode active material effective as a positive electrode active material for a laminated battery is selected according to a novel index. By using the positive electrode active material thus obtained, the present inventors have succeeded in developing battery performance superior to that of the prior art. The positive electrode using the positive electrode active material selected by the above index exhibits high capacity, good initial charge / discharge efficiency, and high thermal stability, and the generation of internal gas is extremely suppressed. Therefore, the positive electrode active material of the present invention is particularly suitable for laminated battery applications.

[Positive electrode active material and its production method]
The lithium metal composite oxide constituting the positive electrode active material of the present invention has a composition represented by the following general formula (1).
Li _a Ni _b Co _c Al _d O ₂ (1)
(However, a = 0.8 to 1.2, b = 0.7 to 0.95, c = 0.02 to 0.2, d = 0.005 to 0.1, and b + c + d = 1. is there.)
The method for producing the lithium metal composite oxide used in the present invention is not limited, but in general, the lithium metal composite oxide obtained by the following methods (I) to (III) is coated with a compound containing the element M2. A manufacturing method is used.
(I) A Li compound, an Al compound, a Co compound, and a Ni compound are separately prepared and mixed, and the resulting mixture is fired in the presence of oxygen.
(II) A composite hydroxide containing both Ni and Co is produced by a coprecipitation method, and then a Li compound and an Al compound are mixed with the composite hydroxide. The resulting mixture is calcined in the presence of oxygen.
(III) A composite hydroxide containing all of Ni, Co, and Al is produced by a coprecipitation method, and then the composite hydroxide is fired in the presence of oxygen.
Among the above methods (I) to (III), the method (II) is preferable. Hereinafter, the manufacturing method of the positive electrode active material using the method (II) will be described in detail.

  (Dissolution of raw material) As a raw material, a water-soluble salt of a metal constituting the general formula (1) such as sulfate or nitrate can be used. However, the use of nitrate is not industrially preferable because of the cost of treating waste liquid containing nitrate nitrogen. For this reason, nickel and cobalt sulfates are usually used. In this case, each sulfate of nickel sulfate and cobalt sulfate is dissolved in water.

  (Precipitation) Nickel sulfate sulfate, cobalt sulfate sulfate aqueous solution, sodium hydroxide as a precipitating agent, and ammonia water as a complexing agent are mixed in a precipitation tank. A composite hydroxide composed of nickel hydroxide and cobalt hydroxide is produced as a coprecipitate in the precipitation tank. The coprecipitate is removed as a slurry. For commercial production corresponding to various varieties, it is preferable to use a precipitation tank capable of adjusting the solid concentration of the coprecipitate, generally a precipitation tank equipped with a solid-liquid separation mechanism. There is no restriction | limiting in particular as a solid-liquid separation mechanism, For example, a centrifugal separator, a filter, etc. are used. From the standpoint of production efficiency, the solid concentration of the coprecipitate slurry is preferably 300 g / L or more, more preferably 400 g / L or more, and even more preferably 500 g / L or more.

  (Filtration and washing) The resulting precipitate is filtered to remove water and separate the hydroxide cake. The hydroxide cake is washed with an aqueous sodium hydroxide solution to remove sulfate ions. Further, the hydroxide cake is washed with pure water to remove sodium hydroxide. Thus, a precursor cake made of nickel-cobalt-complex hydroxide is obtained.

  (Drying) The obtained precursor cake is dried. The drying method may be any of hot air drying under atmospheric pressure, infrared drying, vacuum drying, and the like. Vacuum drying which can be dried in a short time is preferable. The precursor powder is obtained by drying until the moisture in the precursor is about 1% by weight.

  (Powder Mixing) Lithium hydroxide powder or lithium carbonate powder and aluminum hydroxide are added to the obtained precursor powder and mixed by applying a shearing force. As a device used for mixing, a device used for mixing various powders such as a ball mill and a Henschel mixer can be used without limitation. In this way, a powder for firing is obtained.

(Firing) The obtained powder for firing is fired in the presence of oxygen. The following reaction occurs by firing. However, the following reaction formula shows the reaction when lithium hydroxide is used as the lithium raw material.
4Co (OH) ₂ + 4LiOH + O ₂ → 4LiCoO ₂ + 6H ₂ O
Al (OH) ₃ + LiOH → LiAlO ₂ + 2H ₂ O
4Ni (OH) ₂ + 4LiOH + O ₂ → 4LiNiO ₂ + 6H ₂ O
Firing is performed in the temperature range of 450 to 900 ° C. in the presence of oxygen. Firing can be performed a plurality of times. In any of the firings, the reaction is completed by holding at the maximum temperature for 2 to 30 hours. Although there is no restriction | limiting in the baking furnace used when baking, A tubular furnace, a muffle furnace, RK (rotary kiln), RHK (roller hearth kiln), etc. are preferable. A particularly preferred firing furnace is RHK. After firing, preferably, a lithium metal composite oxide obtained after firing is appropriately pulverized using various mixers, mortars, and the like to provide a step of loosening the particles. By this step, coarse particles of 50 μm or more that are harmful to electrode production are removed.

(Coating with compound containing element M2)
The lithium metal composite oxide obtained through the above steps is further coated with a compound containing the element M2. The element M2 is at least one element selected from alkali metals, alkaline earth metals, lanthanoid elements, actinoid elements, and elements of Groups 3 to 17 of the periodic table, preferably alkali metals, alkalis One or more elements selected from earth metals and elements of groups 4 to 17 of the periodic table, more preferably Na, Mg, Ca, Ba, Ti, Zr, V, Nb, Mo, W , Mn, Fe, Co, Ni, Cu, Zn, B, Al, C, Si, N, P, O, S, F, Cl, particularly preferably Na, Mg One or more elements selected from Ca, Ba, Ti, Zr, Nb, Mo, W, Mn, Fe, Co, Cu, Zn, Al, C, Si, N, P, O, S, and F is there.

  The coating method may be either a wet method or a dry method. The coating amount with the compound containing the element M2 is not limited as long as the effect of the present invention is exhibited, but is preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight with respect to the lithium metal composite oxide. More preferably, it is 1 to 4% by weight. Even when the lithium metal composite oxide subjected to the above-described methods (I) and (III) is used, the same coating method can be used after the firing step.

  After the coating treatment, heat treatment is preferably performed in order to stabilize the coating and make it suitable for use as a battery. The temperature of the heat treatment is generally 200 ° C to 800 ° C, preferably 300 ° C to 700 ° C, more preferably 400 ° C to 600 ° C. Thus, the lithium metal composite oxide constituting the positive electrode active material of the present invention is obtained.

(Amount of aluminum eluted in high-temperature sodium hydroxide (weight))
In the lithium metal composite oxide constituting the positive electrode active material of the present invention, the amount of aluminum (weight) eluted in high-temperature sodium hydroxide measured by the following method (a) More than 10% by weight, preferably more than 10% and less than 50%, more preferably more than 15% and less than 30%, particularly preferably more than 15% and less than 20%.
Method (a): Take 12.5 g of the positive electrode active material and 20.0 g of sodium hydroxide in a nickel crucible. This crucible is placed in a muffle furnace heated to 500 ° C. 5 minutes after the sodium hydroxide is sufficiently dissolved, the crucible is removed from the muffle furnace. Immediately disperse the contents of the crucible in 250 ml of pure water and stir. The supernatant is analyzed by inductively coupled plasma emission spectrometry (ICP analysis), and the weight of aluminum element contained in the supernatant is measured.

The total amount (weight) of aluminum contained in the lithium metal composite oxide used in the above method (a) can be determined by ICP analysis. Lithium using a positive electrode active material as a positive electrode active material such that the amount (weight) of aluminum eluted in sodium hydroxide determined by the above method (a) exceeds 10% of the total aluminum weight contained in the positive electrode active material For ion batteries, the initial charge / discharge efficiency is good.
It has not yet been fully clarified how the sodium hydroxide elution amount (weight) of aluminum affects the battery characteristics, but the sodium hydroxide elution amount (weight) of aluminum by the above method (a) is not positive electrode active. It is noteworthy that it reflects the uneven distribution of aluminum atoms contained in the material.

  When a lithium metal composite oxide is produced by firing a mixture of a metal composite hydroxide and a lithium compound such as lithium hydroxide, all of the aluminum atoms contained in the raw material during the firing process are contained in the lithium metal composite oxide. There is a possibility that a part of the lithium metal composite oxide particles is not taken in and distributed on the periphery or surface of the fired lithium metal composite oxide particles. It is speculated that such aluminum atoms are unevenly distributed by constituting aluminum compounds such as aluminum oxide, aluminum hydroxide, and lithium aluminate, and are not completely complexed with a lithium metal composite oxide that functions as a positive electrode active material. . Such aluminum atoms, unlike the aluminum atoms in the lithium metal composite oxide, are considered not to function completely as constituent elements of the positive electrode active material, so it has been considered that a smaller amount is preferable. . However, since aluminum compounds such as aluminum oxide, aluminum hydroxide, and lithium aluminate containing ubiquitous aluminum atoms have low solubility in water, they are often used as analytical methods for positive electrode active materials such as the Warder titration method. Cannot be quantified by the method used. For this reason, there have been few reports so far on the attempts to detect such unevenly distributed aluminum atoms associated with the positive electrode active material.

  In the present invention, the above-mentioned method (a), which is not proposed so far, that is, the positive electrode active material is dispersed and dissolved in sodium hydroxide at 500 ° C. for the first time on the particle surface portion. We succeeded in separating and quantifying the ubiquitous aluminum atom positive electrode active material. The method (a) used in the present invention is notable as a novel analysis method of the positive electrode active material.

  Surprisingly, in the present invention, contrary to conventional expectations, a positive electrode active material in which the content of unevenly distributed aluminum atoms exceeds a certain value functions as a positive electrode active material for a lithium ion battery, which is superior in terms of irreversible capacity ratio I found it to be.

  At the same time, the present invention has succeeded in providing the method (a) as a new method for selecting a positive electrode active material for a lithium ion secondary battery. The present invention makes it possible for the first time to select a positive electrode active material that can function as a positive electrode active material that has a high content of the above-mentioned ubiquitous aluminum atoms and that maintains its initial capacity even after charging and discharging. In order to achieve a good balance between the discharge capacity, initial charge / discharge efficiency, and low heat generation required for the lithium ion battery, and particularly the low gas generation characteristics required for the laminate battery, the unevenly distributed aluminum atoms of the positive electrode active material are used. The content is more than 10%, preferably more than 10% and less than 50%, more preferably more than 15% and less than 30%, particularly preferably more than 15% and less than 20% with respect to the total weight of aluminum atoms contained in the positive electrode active material. It is required to be.

Thus, the positive electrode active material of the present invention can be obtained by using the lithium metal composite oxide in which the content of the latent aluminum atoms is further limited to a certain amount. The positive electrode active material of the present invention is a novel material characterized by its composition, coating, and ubiquitous aluminum content.
[LiOH residue and Li ₂ CO ₃ residue content of positive electrode active material]
It is preferable that excess lithium is removed from the positive electrode active material used in the present invention. As a method for removing excess lithium from the positive electrode active material, a method of washing the positive electrode active material with an aqueous solvent is common. As an aqueous solvent used for washing, pure water, acidic water, alkaline water, an aqueous solution of a metal compound, or the like is used. Of these, pure water, acidic water or alkaline water is preferred. As a result of washing, it is preferable that the LiOH residue extracted with water from the positive electrode active material is 0.2 wt% or less and the Li ₂ CO ₃ residue is 0.2 wt% or less.

[Positive electrode, laminated lithium-ion battery]
The positive electrode active material of the present invention is suitable as a positive electrode material for a laminated battery. A laminated battery can be manufactured by a normal method. That is, the positive electrode active material of the present invention is mixed with a binder and a conductive additive to produce a slurry containing the positive electrode active material and the like, and this slurry is applied to a positive electrode substrate and dried to produce a positive electrode. The negative electrode is obtained by applying and drying a negative electrode agent containing a negative electrode active material composed of carbons on a negative electrode substrate. A laminated body including a positive electrode, a negative electrode, and a separator is laminated with an exterior film and filled with an electrolyte to complete a laminated battery including the positive electrode, the negative electrode, the separator, and the electrolyte.

[Example 1] A positive electrode comprising a lithium metal composite oxide having the composition represented by the formula Li _1.0 Ni _0.80 Co _0.15 Al _0.05 and the element M2 being Co in the following procedure. An active material was produced.
(Dissolution of raw materials) Nickel sulfate hexahydrate and cobalt sulfate heptahydrate were dissolved in pure water so that the concentration of nickel sulfate was 139.3 g / L and the concentration of cobalt sulfate was 10.8 g / L. A mixed solution of metal salts (hereinafter referred to as a metal salt solution) was obtained. On the other hand, a sodium hydroxide aqueous solution having a sodium hydroxide concentration of 84.0 g / L was prepared (hereinafter referred to as an alkali solution).
(Precipitation) The obtained metal salt solution, alkali solution, and 25% by weight ammonia water as a complexing agent are continuously supplied to a reactor having a capacity of 190 L provided with a filter composed of inclined multi-stage plates, The metal hydroxide coprecipitation reaction was allowed to proceed. At this time, the excess amount of sodium hydroxide and the ammonia amount were adjusted to be 2.7 g / L and 12 g / L, respectively. At the same time, by passing the slurry through the filter of the reactor, a part of the mother liquor contained in the slurry was discharged out of the system. As a result, a metal hydroxide coprecipitate was produced and precipitated, and a slurry having a solid concentration adjusted to 400 g / L was obtained.
(Filtration / Washing) After a sufficient time had elapsed from the start of the supply of the metal salt solution and the alkali mixture, the slurry was continuously extracted from the slurry extraction pipe installed inside the reaction vessel. The extracted metal hydroxide slurry was filtered and washed with water.
(Drying) The obtained metal hydroxide was vacuum-dried. Thus, a nickel-cobalt-aluminum composite hydroxide was obtained.
(Powder mixing) 3.809 kg of the above nickel-cobalt composite hydroxide, 0.147 kg of aluminum hydroxide, and 1.044 kg of lithium hydroxide were powder-mixed while applying a shearing force to obtain a mixture.
(Baking) 4 kg of this mixture was baked in two stages under oxygen flow. In the first stage baking, the temperature was raised from room temperature to 730 ° C. over 3 hours and held at 730 ° C. for 4 hours. Then, it cooled to room temperature over 4 hours. In the second stage baking, the temperature was raised from room temperature to 770 ° C. over 3 hours and held at 770 ° C. for 10 hours. Thereafter, it was cooled to room temperature over 4 hours. Thus, a lithium metal composite oxide was obtained.
(Coating with Co) 100 g of the obtained calcined product was taken, and 187.8 wt% (1.0 mol / L) of cobalt nitrate aqueous solution 67.8 g was gently dropped and stirred on the hot plate. Evaporate to dryness. Then, it baked at 700 degreeC in oxygen stream for 5 hours, and the lithium metal complex oxide coat | covered with cobalt was obtained.
(Crushing) The lithium metal composite oxide coated with cobalt was crushed with a jet mill (AFG-100) manufactured by Hosokawa Micron.
(Washing) 100 g of the crushed material was dispersed in 100 g of water. The dispersion was stirred for 3 minutes, suction filtered, dried under reduced pressure, and further dried in oxygen at 500 ° C. for 5 hours.

(Amount of aluminum eluted in high-temperature sodium hydroxide (weight))
The sodium hydroxide elution amount of aluminum contained in the obtained cobalt-coated lithium metal composite oxide was measured by the following method. 12.5 g of the obtained cobalt-coated lithium metal composite oxide and 20.0 g of sodium hydroxide were placed in a nickel crucible, and the crucible was placed in a muffle furnace heated to 500 ° C. Five minutes after the sodium hydroxide was sufficiently dissolved, the crucible was taken out of the muffle furnace, and the contents of the crucible were dispersed in 250 ml of pure water and stirred. The supernatant was analyzed by inductively coupled plasma emission spectrometry (ICP analysis). Further, the total aluminum amount (weight) contained in the obtained cobalt-coated lithium metal composite oxide was determined by ICP analysis. As a result, it was found that the aluminum element corresponding to 18.9% of the aluminum element (weight) contained in the cobalt-coated lithium metal composite oxide was eluted.
(LiOH residue, Li ₂ CO ₃ residue)
2 g of the obtained positive electrode active material is taken, added to 100 ml of pure water at 25 ° C., stirred for 3 minutes with a magnetic stirrer, and then subjected to suction filtration. The obtained filtrate was titrated with 0.1 N hydrochloric acid using an automatic titrator, and the amounts of lithium hydroxide and lithium carbonate were quantified. The results are shown in Table 1.

(Manufacture of positive electrode)
100 parts by weight of the obtained positive electrode active material, 1 part by weight of acetylene black as a conductive assistant, 5 parts by weight of graphite carbon, and 4 parts by weight of polyvinylidene fluoride as a binder were mixed together with N-methylpyrrolidone as a dispersion medium. A positive electrode mixture was obtained. This positive electrode mixture was applied to an aluminum foil as a current collector in a thickness of 50 μm and dried to produce a positive electrode.
(Manufacture of laminated batteries)
98 parts by weight of artificial graphite (MAG-D), 1 part by weight of carboxymethyl cellulose (CMC) as a binder and 1 part by weight of styrene butadiene copolymer (SBR) are mixed with water as a dispersion medium to obtain a negative electrode mixture. It was. This negative electrode mixture was applied to a copper foil as a current collector and dried to produce a negative electrode. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and vinyl carbonate (VC) in which LiPF ₆ is dissolved at a concentration of 1 mol / L, the weight ratio (EC: EMC: VC) is 50: 50: 1. To prepare an electrolytic solution. A laminate battery was manufactured by laminating and enclosing the above positive electrode, negative electrode, and electrolyte.

The performance of the obtained laminated battery was evaluated from the following viewpoints. The results are shown in Table 1.
-Initial discharge capacity and initial charge / discharge efficiency: The capacity when charging at a rate of 0.1 C between 3.0 and 4.2 V was defined as the initial charge capacity. The capacity when performing 0.1 C discharge between 4.2 V and 3.0 was defined as the initial discharge capacity. The initial charge / discharge efficiency was determined by the following formula.
Initial charge / discharge efficiency (%) = (initial discharge capacity / initial charge capacity) × 100
DSC calorific value: After charging the positive electrode active material by a method according to the method used in the evaluation of the initial electrical characteristics described above, the battery was disassembled, the positive electrode was taken out, and its differential scanning calorimetric analysis was performed. A differential scanning calorimeter manufactured by Hitachi High-Tech Science Co., Ltd. was used for measurement of the differential scanning calorific value.

  [Example 2] During the production of the positive electrode active material, the conditions of Example 1 were changed in the precipitation step. That is, the amount of the mother liquor discharged out of the system through the filter was changed to adjust the solid concentration of the slurry to 600 g / L. Other conditions were the same as in Example 1. Table 1 shows the evaluation results of the obtained positive electrode active material and laminated battery.

  [Example 3] During the production of the positive electrode active material, the conditions of Example 1 were changed in the firing step. That is, the maximum temperature setting in the roller hearth kiln was set to 730 ° C., and firing was performed in the following three consecutive steps over a total of 11 hours. First stage: The temperature was raised from room temperature to 730 ° C. over 3 hours. Second stage: held at 730 ° C. for 5 hours. Third stage: Cooled from 730 ° C. to room temperature over 3 hours. Table 1 shows the evaluation results of the obtained positive electrode active material laminated battery.

[Comparative Example 1] During the production of the positive electrode active material, the conditions of Example 1 were changed in the precipitation step. That is, the amount of mother liquor discharged out of the system through the filter was changed to adjust the solid concentration of the slurry to 200 g / L. Other conditions were the same as in Example 1. Table 1 shows the evaluation results of the obtained positive electrode active material laminated battery.
[Comparative Example 2] During the production of the positive electrode active material, the conditions of Example 1 were changed in the precipitation step. That is, the amount of the mother liquor discharged out of the system through the filter was changed to adjust the solid concentration of the slurry to 100 g / L. Other conditions were the same as in Example 1. Table 1 shows the evaluation results of the obtained positive electrode active material laminated battery.

The ratio of the amount (weight) of aluminum eluted in the high-temperature sodium hydroxide to the total weight of aluminum contained in the positive electrode active material was more than 10% in the examples, but 10% or less in the comparative examples. In the positive electrode active material of the example, LiOH residue and Li ₂ CO ₃ residue are reduced. Therefore, in the laminated battery using the positive electrode active material of the example, the gas generation amount can be suppressed to an extremely low level. Moreover, in the examples, since both the initial discharge capacity and the initial charge / discharge efficiency are high, it is expected that extremely excellent battery performance is maintained. Moreover, the calorific value of the example is low. On the other hand, in the comparative example, although the calorific value is equal to that in the example, since both the initial discharge capacity and the initial charge / discharge efficiency are low, it is expected that the battery performance rapidly decreases. As described above, the positive electrode active material of the present invention is suitable for a laminated battery that particularly dislikes gas generation, and can provide the required performance of the battery such as initial discharge capacity, initial charge / discharge efficiency, and low heat generation in a well-balanced manner.

  The positive electrode active material of the present invention is suitable for a positive electrode material for a lithium ion battery, and is particularly useful for a laminate battery. The present invention contributes to improving the performance of a laminated battery, and can further reduce the size, improve safety, and prolong the life of a battery for mobile terminals and a battery for automobiles.

Claims (5)

It consists of a lithium metal composite oxide having a composition represented by the following general formula (1),
Li _a Ni _b Co _c Al _d O ₂ (1)
(However, a = 0.8 to 1.2, b = 0.7 to 0.95, c = 0.02 to 0.2, d = 0.005 to 0.1, and b + c + d = 1. is there.)
The lithium metal composite compound further includes
Element M2 (M2 is at least one element selected from alkali metals, alkaline earth metals, lanthanoid elements, actinoid elements, and elements of Groups 3 to 17 of the periodic table). Coated with a compound,
The amount of aluminum (weight) eluted in high-temperature sodium hydroxide measured by the following method (a) exceeds 10% of the total aluminum weight contained in the lithium metal composite oxide,
[Method (a): Take 12.5 g of the positive electrode active material and 20.0 g of sodium hydroxide in a nickel crucible. This crucible is placed in a muffle furnace heated to 500 ° C. 5 minutes after the sodium hydroxide is sufficiently dissolved, the crucible is removed from the muffle furnace. Immediately disperse the contents of the crucible in 250 ml of pure water and stir. By analyzing the supernatant by inductively coupled plasma optical emission spectrometry (ICP analysis), the weight of aluminum element eluted in sodium hydroxide at 500 ° C. is measured. ]
Positive electrode active material for lithium ion secondary battery. The positive electrode active material according to claim 1, wherein the LiOH residue is 0.2% by weight or less and the Li ₂ CO ₃ residue is 0.2% by weight or less.   The positive electrode for lithium ion batteries using the positive electrode active material of Claim 1 or 2.   A lithium ion battery comprising the positive electrode for a lithium ion battery according to claim 3.   The lithium ion battery according to claim 4 which is a laminate battery.