JP2002211931A - Lithium nickel compound oxide for active material for positive electrode of lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium nickel compound oxide for an active material of a positive electrode capable of constituting a lithium secondary battery less liable to decrease of its capacity and the rise of its internal resistance even when preserved in a charged state over a long period of time. SOLUTION: The lithium nickel compound oxide is represented by the formula LiNi1-x-yCoxAlyO2 (where 0.1<=x<=0.2 and 0.05<=y<=0.1) and has a particle structure with secondary particles formed by aggregating primary particles of 1-4 μm average particle diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for storing and storing lithium.
The present invention relates to a lithium nickel composite oxide for a positive electrode active material, which can constitute a lithium secondary battery utilizing a desorption phenomenon.

[0002]

2. Description of the Related Art Lithium secondary batteries utilizing the insertion and extraction of lithium have a high energy density.
With the miniaturization of mobile phones, personal computers, and the like, they have become widespread in the field of communication devices and information-related devices. On the other hand,
Due to environmental issues and resource issues, the development of electric vehicles is urgently required in the field of automobiles, and lithium secondary batteries are being studied as power sources for electric vehicles.

[0003] Lithium secondary batteries are demanded in such a wide field, but due to their high price, they are required to have a longer life than other secondary batteries. One of the requirements for long life is that when a lithium secondary battery is stored while maintaining a high charge rate, the so-called storage characteristics such as the capacity does not decrease and the internal resistance of the battery does not increase are good. Is required. In particular,
At high temperatures, the battery reaction is activated and the capacity is greatly reduced.For example, if it is assumed that a lithium secondary battery is used for an electric vehicle power supply that may be left outdoors, a high temperature One of the important characteristics is that the storage characteristics below are good.

At present, development of a lithium secondary battery using a lithium-transition metal composite oxide containing Ni and Co as main constituent elements as a positive electrode active material is in progress. However, when the battery is stored in a state where the charge rate is maintained at a high level, the capacity of the battery is greatly reduced and the internal resistance is greatly increased, and there is a problem in the storage characteristics, particularly, the storage characteristics at high temperatures.

[0005] As an attempt to improve the storage characteristics, for example, Japanese Patent Application Laid-Open Nos. 9-17446 and 9-9232 disclose the method.
No. 9 discloses that a solvent of an electrolytic solution has a specific composition. Japanese Patent Application Laid-Open No. 9-199126 discloses improvement of a negative electrode active material. However, in the above attempts, the storage characteristics of a lithium secondary battery formed using a lithium transition metal composite oxide containing Ni and Co as main constituent elements as a positive electrode active material cannot be said to be sufficient.

[0006]

As a result of repeated studies by the present inventor, the decrease in capacity and the increase in internal resistance due to the storage of the above lithium secondary battery are caused by the fact that the positive electrode potential increases due to charging,
It has been found that one of the causes is that the lithium-transition metal composite oxide, which is a positive electrode active material, reacts with the electrolyte when the state is maintained for a long time, and the electrolyte is decomposed.
In addition, in the positive electrode, lithium is desorbed from the lithium-transition metal composite oxide by charging, and one of the causes is that the crystal structure of the lithium-transition metal composite oxide is collapsed by maintaining the state for a long time. Conceivable.

The present invention is based on the above findings and stabilizes the crystal structure of the positive electrode active material and suppresses the reaction between the positive electrode active material and the electrolyte so that the battery can be stored for a long time in a charged state. It is an object of the present invention to provide a lithium-nickel composite oxide for a positive electrode active material that can constitute a lithium secondary battery in which a decrease in capacity and a rise in internal resistance are small.

[0008]

The lithium nickel composite oxide for a positive electrode active material of a lithium secondary battery according to the present invention has a composition formula of LiNi _1-xy Co _x Al _y O ₂ (0.1 ≦ x ≦ 0.2;
0.05 ≦ y ≦ 0.1), and has a particle structure in which primary particles having an average particle diameter of 1 μm or more and 4 μm or less are aggregated to form secondary particles.

In other words, the lithium-nickel composite oxide of the present invention has Ni as its main constituent element from the viewpoint of a large theoretical capacity and is relatively inexpensive, and has a Ni site composed of two elements (Co and Al) having different roles. Has been partially replaced.

[0010] Co mainly serves to stabilize the crystal structure of the lithium nickel composite oxide. In order to sufficiently exhibit the effect of improving storage characteristics by stabilizing the crystal structure of the lithium nickel composite oxide, the substitution ratio of Co, that is, the value of x in the composition formula, is set to 0.1 ≦ x ≦ 0.2. Further, Co has the advantage of suppressing a decrease in capacity due to elemental substitution, and Li (Co, Ni) O ₂ being an all-solid solution type, which minimizes the decrease in crystallinity.

[0011] Al plays a role mainly in suppressing the decomposition reaction of the active material accompanying the release of oxygen and improving the thermal stability. In order to sufficiently exert the effect of improving the storage characteristics by improving the thermal stability of the lithium nickel composite oxide, Al
, That is, the value of y in the composition formula is 0.05
≦ y ≦ 0.1. Further, Al has the advantage of minimizing capacity loss while improving thermal stability.

Therefore, by substituting appropriate amounts of Co and Al, the lithium-nickel composite oxide of the present invention can be used even when the battery is stored in a charged state for a long time.
A stable lithium-nickel composite oxide without crystal structure collapse is obtained.

In general, a lithium nickel composite oxide is formed by aggregating primary particles, which are particles substantially close to a single crystal, into two particles.
It has a particle structure that forms secondary particles. When a lithium nickel composite oxide is used as the positive electrode active material, a paste of the positive electrode mixture obtained by mixing a conductive material and a binder with the powdery lithium nickel composite oxide is used as a current collector. A positive electrode is formed by coating or the like on the surface. Therefore, the specific surface area of the powdery lithium nickel composite oxide as the active material increases as the particle diameter of the primary particles constituting the powder particles decreases. In other words, it is considered that the smaller the particle diameter of the primary particles, the larger the surface area of the lithium nickel composite oxide involved in the reaction with the electrolytic solution, so that the decomposition reaction of the electrolytic solution is likely to proceed.

[0014] The lithium nickel composite oxide of the present invention comprises:
The primary particles constituting the secondary particles have an average particle size of 1 μm or more and 4
It is thought that since the particles have a large particle diameter of μm or less, the surface area involved in the reaction with the electrolytic solution is reduced, and as a result, the decomposition reaction of the electrolytic solution can be suppressed. That is, the lithium nickel composite oxide of the present invention has a stable crystal structure by replacing Ni sites with appropriate amounts of Co and Al and increasing the particle diameter of primary particles in the particle structure, and A lithium nickel composite oxide that has little reaction with the electrolyte is obtained.

Therefore, when the lithium nickel composite oxide of the present invention is used as a positive electrode active material, the battery capacity can be maintained even when the battery is stored in a charged state for a long time, and the battery capacity can be maintained. Since the increase in the internal resistance of the lithium secondary battery is also suppressed, a lithium secondary battery that is inexpensive and has excellent storage characteristics can be obtained.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a lithium nickel composite oxide for a positive electrode active material of a lithium secondary battery of the present invention will be described.
Explain the composition and particle structure and manufacturing method, and then
A lithium secondary battery, which is an application of the lithium nickel composite oxide of the present invention, will be described.

<Composition and particle structure of lithium nickel composite oxide> The lithium nickel composite oxide of the present invention
Compositional formula LiNi _1-xy Co _x Al _y O ₂ (0.1 ≦ x ≦ 0.
2; 0.05 ≦ y ≦ 0.1), and its crystal structure is a layered rock salt structure. In addition, the lithium nickel composite oxide of the present invention includes not only the stoichiometric composition represented by the above composition formula, but also a non-stoichiometric composition in which some elements are missing or excessive. .

The substitution ratio of Co, that is, x in the composition formula
Is 0.1 ≦ x ≦ 0.2. In the case of x <0.1, the stabilization of the crystal structure is not sufficient because the amount of substitution of Co is small. Conversely, in the case of x> 0.2, the amount of substitution of Co is large, so that Ni This is because some change occurs in the solid solution state of Co and Co, and the crystallinity of the lithium nickel composite oxide decreases. In particular, in consideration of storage characteristics at high temperatures, it is desirable that the value of x be 0.12 ≦ x ≦ 0.17.

The substitution ratio of Al, that is, the value of y in the composition formula, is set to 0.05 ≦ y ≦ 0.1. y <0.
In the case of No. 05, since the substitution amount of Al is small, the thermal stability in the crystal structure is not sufficient, and conversely, y> 0.1
This is because, in the case of (1), the discharge capacity is reduced due to a large amount of Al substitution. In particular, in consideration of storage characteristics at high temperatures, it is desirable that the value of y be 0.06 ≦ y ≦ 0.08.

[0020] The lithium nickel composite oxide of the present invention comprises:
It has a particle structure in which primary particles having an average particle size of 1 μm or more and 4 μm or less are aggregated to form secondary particles. When the primary particles have an average particle size of less than 1 μm, the surface area involved in the reaction with the electrolytic solution increases, so that the decomposition reaction of the electrolytic solution is promoted,
This is because the internal resistance of the battery increases and causes a reduction in capacity. Conversely, if the thickness exceeds 4 μm, the secondary particles also increase in size, making it difficult to produce a positive electrode coated with the active material uniformly, and the coating surface of the positive electrode mixture becomes difficult to be smooth, so that the electrode becomes difficult. This is because it may cause a short circuit. The average particle size of the secondary particles is 5 μm from the viewpoint of producing a positive electrode coated with the active material uniformly.
It is desirable that the thickness be at least 30 μm.

As a simple method for measuring the average particle size of the primary particles and the secondary particles, for example, there is a method using a scanning electron microscope (SEM) photograph of a lithium nickel composite oxide. That is, the lithium nickel composite oxide S
An EM photograph is taken, and the diameter of the primary particles and the like of the lithium nickel composite oxide in the photograph, which is regarded as the longest diameter and the shortest diameter, are measured. Then, the average value of these two values may be regarded as the particle size of the primary particles and the like, and the average thereof may be adopted as the average particle size of the primary particles and the like.

<Production method of lithium-nickel composite oxide> Although the production method of the lithium-nickel composite oxide of the present invention is not particularly limited, it can be more easily produced by the following method. . That is, the method includes a raw material mixing step of mixing the respective compounds serving as a lithium source, a nickel source, a cobalt source, and an aluminum source to obtain a mixture, and a firing step of firing the mixture in an oxygen atmosphere. . By appropriately adjusting the conditions in each step, a lithium-nickel composite oxide having a desired average primary particle size can be produced. Hereinafter, each step will be described.

(1) Raw Material Mixing Step In the raw material mixing step, a lithium compound serving as a lithium source, a nickel compound serving as a nickel source, a cobalt compound serving as a cobalt source, and an aluminum compound serving as an aluminum source are mixed. This is a step of obtaining a mixture.

As the lithium compound serving as a lithium source, lithium oxide, lithium hydroxide, lithium carbonate, lithium nitrate and the like can be used. In particular, it is desirable to use lithium hydroxide and lithium nitrate because of their relatively low melting points.

As a compound serving as a cobalt source, cobalt hydroxide, cobalt carbonate, cobalt nitrate and the like can be used. Nickel compounds serving as nickel sources include:
Nickel hydroxide, nickel carbonate, nickel nitrate and the like can be used. As an aluminum compound serving as an aluminum source, aluminum oxide, aluminum hydroxide, aluminum nitrate, or the like can be used. In particular,
It is desirable to use cobalt hydroxide and nickel hydroxide for the reason of high reactivity, and to use aluminum hydroxide and aluminum oxide for the reason that no gas is generated during firing.

It should be noted that cobalt forms a solid solution with nickel.
It is desirable to use a cobalt composite compound. In particular, when using the above cobalt hydroxide and nickel hydroxide,
As a method for easily synthesizing a nickel-cobalt composite compound, for example, an aqueous solution obtained by dissolving nickel hydroxide and cobalt hydroxide in water is dropped into a strong alkali aqueous solution, and nickel-cobalt hydroxide (hereinafter, referred to as hydroxide) is used. .)
Can be used to coprecipitate and synthesize. According to this method, it is possible to control the particle diameter of particles serving as nuclei of the lithium-nickel composite oxide, so that it is possible to easily obtain a lithium-nickel composite oxide corresponding to the particle diameter of desired primary particles. . In particular, in order to produce a lithium-nickel composite oxide having an average primary particle size of 1 μm or more and 4 μm or less, it is necessary to synthesize the hydroxide such that the average primary particle size of the hydroxide is in the range of 1 μm to 4 μm. I just need. Also, an aqueous solution in which nickel hydroxide or the like is dissolved in water,
From the viewpoint of satisfying both the reactivity and the yield, the concentration is desirably adjusted to be 0.5 to 2M.

As the strong alkaline aqueous solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, aqueous ammonia or the like can be used. Among them, it is preferable to use an aqueous solution of sodium hydroxide in consideration of economy. When using an aqueous sodium hydroxide solution, it is desirable to use a solution having a concentration of about 1 to 5M.

In order to carry out the above reaction uniformly, it is desirable to stir the aqueous solution obtained by dissolving nickel hydroxide or the like in water when dropping the solution into a strong alkaline aqueous solution. Stirring speed,
Conditions such as the pH value and the reaction temperature of the strong alkaline aqueous solution affect the particle size and the like of the hydroxide particles to be synthesized, and may be appropriately set to obtain desired particles. For example, the pH value of the strong alkaline aqueous solution is desirably adjusted so as to be substantially constant during the reaction, and the value is desirably 11 to 12. Further, the reaction temperature is desirably 20 to 40 ° C. in order to obtain an appropriate reaction rate. In addition,
Since the hydroxide is obtained as a precipitate, it may be filtered, washed, and used for mixing with another compound.

The mixing of each of the above-mentioned raw materials may be carried out by a method used for mixing ordinary powders. Specifically, for example, mixing can be performed using a ball mill, a mixer, a mortar or the like. The mixing ratio of the raw materials may be a ratio according to the composition of the lithium nickel composite oxide to be produced.

(2) Firing Step The firing step is a step of firing the mixture obtained in the raw material mixing step in an oxygen atmosphere to obtain a lithium nickel composite oxide. The firing temperature is desirably 750 ° C or more and 950 ° C or less. When the firing temperature is lower than 750 ° C,
This is because the reaction does not proceed sufficiently and the crystallinity becomes low.
Conversely, if the temperature exceeds 950 ° C., lithium gasifies and the contribution to the reaction decreases. The sintering time may be a time sufficient for completing the sintering.
It may be performed for about two hours.

<Lithium Secondary Battery> A lithium secondary battery can be constructed using the lithium nickel composite oxide of the present invention as a positive electrode active material. Hereinafter, the main configuration of the lithium secondary battery will be described. Generally, a lithium secondary battery includes a positive electrode and a negative electrode that occlude and release lithium ions, a separator that is interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte that moves lithium ions between the positive electrode and the negative electrode. Consists of Since the secondary battery of the present embodiment also follows this configuration, the following description will be made for each of these components.

As described above, the positive electrode was prepared by mixing a conductive material and a binder with a positive electrode active material capable of occluding and releasing lithium ions, and adding an appropriate solvent if necessary, to form a paste-like positive electrode mixture. The active material can be formed by applying the material on the surface of a current collector made of a metal foil such as aluminum, drying the material, and then increasing the active material density by pressing.

In this embodiment, the lithium nickel composite oxide of the present invention is used as a positive electrode active material. Note that one of the lithium-nickel composite oxides can be used as the positive electrode active material, or two or more can be used as a mixture.

The conductive material used for the positive electrode is for ensuring the electrical conductivity of the positive electrode active material layer, and may be a mixture of one or more carbon materials such as carbon black, acetylene black, and graphite. Can be used. The binder plays a role of binding the active material particles, and a fluororesin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene can be used. As a solvent for dispersing these active material, conductive material and binder, N-
An organic solvent such as methyl-2-pyrrolidone can be used.

The negative electrode is formed by sheeting metallic lithium, which is the negative electrode active material, in the same manner as that of a general battery, or by pressing the sheet-like material onto a current collector network of nickel, stainless steel, or the like. be able to. As the negative electrode active material, a lithium alloy or a lithium compound can be used instead of metal lithium.

As another form of the negative electrode, the negative electrode can be constituted by using a carbon material capable of inserting and extracting lithium ions as the negative electrode active material. Examples of the carbon material that can be used include natural graphite, spherical or fibrous artificial graphite, easily graphitizable carbon such as coke, and non-graphitizable carbon such as a phenol resin fired body. They can be used alone or in combination of two or more. In this case, the negative electrode active material can be formed by mixing a binder with the negative electrode active material, adding a suitable solvent to form a paste, and applying and drying the negative electrode mixture on the surface of a metal foil current collector such as copper. .

When the carbon material is used as the negative electrode active material, a fluorine-containing resin such as polyvinylidene fluoride or the like is used as the negative electrode binder and an organic solvent such as N-methyl-2-pyrrolidone is used as the solvent, similarly to the positive electrode. Can be.

The separator sandwiched between the positive electrode and the negative electrode separates the positive electrode from the negative electrode, holds the electrolytic solution and allows ions to pass therethrough, and uses a thin microporous membrane such as polyethylene or polypropylene. Can be.

The non-aqueous electrolyte is obtained by dissolving an electrolyte in an organic solvent. Examples of the organic solvent include aprotic organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and the like.
One kind of γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolane, methylene chloride and the like, or a mixture of two or more kinds thereof can be used. As the electrolyte to be dissolved, LiI, LiCl which generates lithium ions when dissolved are used.
O ₄ , LiAsF ₆ , LiBF ₄ , LiPF _{6 and the} like can be used.

In place of the above-described structure of the separator and the non-aqueous electrolyte, a polymer solid electrolyte using a high molecular weight polymer such as polyethylene oxide and a lithium salt such as LiClO ₄ or LiN (CF ₃ SO ₂ ) ₂ is used. It is also possible to use a gel electrolyte in which the above non-aqueous electrolyte is trapped in a solid polymer matrix such as polyacrylonitrile.

The lithium secondary battery constituted as described above can be formed in various shapes such as a coin type, a stacked type and a cylindrical type. In any case, the separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and conduction is provided between the positive electrode and the negative electrode to the positive electrode terminal and the negative electrode terminal that communicate with the outside. Can be sealed in a battery case together with the non-aqueous electrolyte to complete the battery.

<Allowance of Other Embodiments> The embodiments of the lithium-nickel composite oxide and the lithium secondary battery of the present invention described above are merely examples, and the lithium-nickel composite oxide of the present invention and the present invention The lithium secondary battery using the lithium-nickel composite oxide as the positive electrode active material can be implemented with various modifications and improvements based on the knowledge of those skilled in the art, including the above embodiment.

[0043]

EXAMPLES Based on the above embodiment, various lithium nickel composite oxides having different average particle diameters of primary particles and substitution ratios of Co and Al in the composition were produced. Then, lithium secondary batteries using these lithium-nickel composite oxides as positive electrode active materials were produced, and storage characteristics of the batteries were evaluated by performing a high-temperature storage test. This will be described below.

<Relationship Between Co and Al Substitution Ratio and Capacity and Internal Resistance Increase Rate of Battery> (a) Lithium Nickel Composite Oxide Manufactured In the lithium nickel composite oxide used as the positive electrode active material, substitution of Co and Al was performed. Various lithium nickel composite oxides having different substitution ratios of Co and Al were manufactured in order to examine the relationship between the ratio and the capacity of the battery and the increase rate of the internal resistance. Specifically, the substitution ratio of Al is set to 5 mol% (hereinafter, “%” means mol% in the substitution ratio of Al and Co), and the substitution ratios of Co are 15, 20, 30, and 40.
%, The substitution ratio of Al was 10%, and the substitution ratio of Co was 15, 20, and 30%, thereby producing a total of seven types of lithium nickel composite oxides. The average particle size of the primary particles of the lithium nickel composite oxide is 1 μm
And

LiOH.H ₂ O as a lithium source, nickel and cobalt, and Ni (OH) as an aluminum source
₂ , Co (OH) ₂ , and Al (OH) ₃ were mixed so as to have the composition of the lithium nickel composite oxide to be produced. In addition, each aqueous solution of 2M Ni (OH) ₂ and Co (OH) _{2 was} previously mixed, and this aqueous solution was dropped into an aqueous sodium hydroxide solution to precipitate and synthesize hydroxide particles. The reaction temperature was 30 ° C and the pH value during the reaction was 1
1-12. The precipitated hydroxide particles were separated by filtration, washed, and then mixed with LiOH · H ₂ O and Al (OH) ₃ .
The average primary particle size of the hydroxide was 2 μm. Then, the mixture is heated at 850 ° C. for 1 hour in an oxygen stream.
By firing for 2 hours, a lithium nickel composite oxide was obtained.

# 01, 02, 03, 04 in order from the one where the substitution ratio of Al is 5% and the substitution ratio of Co is small.
And # 05, 06, and 07 in order from the one with the Al substitution ratio of 10% and the Co substitution ratio being small. Note that # 01, # 02, # 05, and # 0
The lithium-nickel composite oxide of No. 6 corresponds to the lithium-nickel composite oxide of the present invention.

(B) Lithium secondary battery A lithium secondary battery was manufactured using each of the above seven lithium nickel composite oxides as a positive electrode active material. The positive electrode is
First, 10 parts by weight of carbon black as a conductive material and 5 parts by weight of polyvinylidene fluoride as a binder were mixed with 85 parts by weight of each lithium nickel composite oxide serving as a positive electrode active material, and an appropriate amount of N was used as a solvent. -Methyl-2-
Pyrrolidone was added to prepare a paste-like positive electrode mixture, and then this paste-like positive electrode mixture was 20 μm thick.
Was coated on both sides of an aluminum foil current collector, dried, and then compressed by a roll press to produce a sheet-shaped positive electrode mixture having a thickness of 40 μm per side. This sheet-shaped positive electrode was cut into a size of 54 mm × 450 mm for use.

As a negative electrode to be opposed, graphitized mesocarbon microbeads (graphitized MCMB) were used as an active material. First, 95 parts by weight of graphitized MCMB as a negative electrode active material, 5 parts by weight of polyvinylidene fluoride as a binder were mixed, and an appropriate amount of N-methyl-2-pyrrolidone was added as a solvent, and a paste-like negative electrode was added. A mixture was prepared, and then this paste-like negative electrode mixture was applied to both sides of a copper foil current collector having a thickness of 10 μm, dried, and then compressed by a roll press. A sheet having a thickness of 30 μm was prepared. This sheet-shaped negative electrode is 56 mm x 50
It was cut into a size of 0 mm and used.

The positive electrode and the negative electrode were wound with a polyethylene separator having a thickness of 25 μm and a width of 58 mm interposed therebetween to form a roll-shaped electrode body. Then, the electrode body was inserted into a 18650-type cylindrical battery case (outside diameter 18 mmφ, length 65 mm), a non-aqueous electrolyte was injected, and the battery case was sealed to produce a cylindrical lithium secondary battery. . As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ at a concentration of 1 M in a mixed solvent obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 was used.

The lithium secondary batteries using the lithium nickel composite oxides # 01 to # 07 as the positive electrode active material were referred to as lithium secondary batteries # 01 to # 07, respectively.

(C) Evaluation of storage characteristics of lithium secondary battery The storage characteristics of each of the lithium secondary batteries # 01 to # 07 were evaluated. First, as conditioning, at a temperature of 20 ° C., a current density of 0.2 mA / cm ²
After charging to 4.1 V at a constant current of 0.2 m, the current density was 0.2 m
Discharge was performed to 3.0 V at a constant current of A / cm ² . After the conditioning, three cycles of charge and discharge were performed at a temperature of 20 ° C. to measure the initial capacity. The charging and discharging conditions are as follows: charging is performed at a constant current of a current density of 0.1 mA / cm ^{2 up to} a charging upper limit voltage of 4.1 V, and charging is further continued at a constant voltage of 4.1 V for 2 hours.
The charge / discharge in which discharge is performed at a constant current of / cm ^{2 to} a discharge lower limit voltage of 3.0 V is defined as one cycle. The discharge capacity at the third cycle of this charge / discharge was defined as the initial capacity at 20 ° C.

Next, in order to calculate the initial internal resistance, the input / output power was measured, and the internal resistance at the time of input / output was calculated. The input / output power measurement was performed under the following conditions. First, in a state where each lithium secondary battery was charged to 50% of the initial capacity (SOC 50%), the battery was discharged at a current of 1 A for 10 seconds, and the voltage at the 10th second was measured. After being charged again to the state of SOC 50%, the battery was discharged at a current of 3 A for 10 seconds, and
The voltage at 0 seconds was measured. Further, after the battery was charged to the state of 50% SOC, the battery was discharged at a current of 5 A for 10 seconds, and the voltage at the 10th second was measured. Then, the current dependence of the voltage was determined, and the gradient of the current-voltage straight line was defined as the internal resistance at the time of output.
In addition, charging was performed in the same manner, the voltage at each 10 seconds was measured, and the internal resistance at the time of input was obtained from the gradient of the current-voltage straight line. The average value of the obtained internal resistance at the time of input and output was defined as the initial internal resistance.

Next, a storage test was performed. In the storage test, after charging was performed at a constant current of 0.2 mA / cm ² until the voltage reached 4.1 V, charging was further continued at a constant voltage of 4.1 V, and charging was performed for a total of 7 hours. As a result, each of the secondary batteries was kept in a constant temperature bath at 60 ° C. for one month after the state of the SOC was set to 100%. After storage, the internal resistance during input / output was determined in the same manner as above, and the average value was taken as the internal resistance after storage. Then, from the values of the internal resistance before and after the storage test, the internal resistance increase rate was calculated using the formula [{(internal resistance after storage / initial internal resistance) −1} × 100].

FIG. 1 shows the relationship between the initial capacity and the rate of increase in the internal resistance of the secondary batteries # 01 to # 07. From FIG. 1, it can be seen that, when the average particle size of the primary particles is the same, the initial capacity becomes smaller as the secondary battery using the lithium-nickel composite oxide having a higher Co substitution ratio becomes smaller. Furthermore, Al
It can be seen that a secondary battery using a lithium-nickel composite oxide having a larger percentage of substitution has a smaller increase in internal resistance. Therefore, a practical secondary battery capacity of 140
Considering that mAh / g or more is required, the substitution ratio of Co is 10 to 20% and the substitution ratio of Al is 5 to 1%.
Secondary battery using lithium nickel composite oxide of 0% of the present invention (# 01, # 02, # 05, and # 06)
Was confirmed to have a large capacity and a small increase in internal resistance.

<Relationship between Co and Al substitution ratios and particle diameters of primary particles and residual capacity ratio> (a) Lithium nickel composite oxide produced (1) Lithium nickel composite oxide of the first series Composition formula LiNi A lithium-nickel composite oxide having an ordered layered rock salt structure represented by _0.85 Co _0.1 Al _0.05 O ₂ , wherein the primary particles have an average particle size of 0.2 μm, 1 μm,
Four types different from 4 μm and 5 μm were produced.

In the production of the lithium-nickel composite oxides of # 01 to # 07, the mixing ratio of each compound as a raw material is such that Li, Ni, Co, and Al are mixed in a molar ratio of 1: 0.8.
Except that the ratio was 5: 0.1: 0.05, it was produced in the same manner as the lithium-nickel composite oxides of # 01 to # 07. In addition,
The average particle size of the primary particles of the hydroxide was appropriately adjusted in consideration of the particle size of the primary particles of the lithium nickel composite oxide to be produced.

This lithium nickel composite oxide is referred to as a first series lithium nickel composite oxide, and the primary particles have an average particle size of 0.2 μm, 1 μm, 4 μm, and 5 μm in this order.
11, # 12, # 13, and # 14.

(2) Lithium-nickel composite oxide of the second series This is a lithium-nickel composite oxide having an ordered layered rock salt structure represented by the composition formula LiNi _0.7 Co _0.2 Al _0.1 O ₂ , similar to the first series. Four types of primary particles having different average particle sizes were produced. In the production of the lithium-nickel composite oxides of # 01 to # 07, the mixing ratio of each compound as a raw material was such that Li, Ni, Co, and Al were mixed at a molar ratio of 1:
# 01 to #, except for changing to 0.7: 0.2: 0.1
07 lithium nickel composite oxide.

This lithium nickel composite oxide is referred to as a second series of lithium nickel composite oxide, and the average particle size of the primary particles is 0.2 μm, 1 μm, 4 μm, and 5 μm in this order.
21, # 22, # 23, and # 24.

(3) Lithium-nickel composite oxide of the third series This is a lithium-nickel composite oxide having an ordered layered rock salt structure represented by a composition formula: LiNi _0.83 Co _0.15 Al _0.02 O ₂ , wherein the average of primary particles is Four types having different particle sizes were produced. In the production of the lithium nickel composite oxides of # 01 to # 07, the mixing ratio of each compound as a raw material is represented by L
i, Ni, Co, Al in molar ratio of 1: 0.83: 0.1
Except having changed to 5: 0.02, it manufactured similarly to the lithium nickel composite oxide of # 01- # 07.

The lithium-nickel composite oxide is referred to as a third series of lithium-nickel composite oxides. The primary particles have an average particle size of 0.2 μm, 1 μm, 4 μm, and 5 μm in this order.
31, # 32, # 33, and # 34.

(4) Lithium-nickel composite oxide of the fourth series This is a lithium-nickel composite oxide having an ordered layered rock-salt structure represented by the composition formula LiNi _0.65 Co _0.15 Al _0.2 O ₂ , wherein the average of primary particles thereof is Four types having different particle sizes were produced. In the production of the lithium nickel composite oxides of # 01 to # 07, the mixing ratio of each compound as a raw material was changed to Li,
Ni, Co, Al in molar ratio of 1: 0.65: 0.15:
Except having changed to 0.2, it manufactured similarly to the lithium nickel composite oxide of # 01- # 07.

The lithium-nickel composite oxide is referred to as a fourth series of lithium-nickel composite oxides. The average primary particle diameter is 0.2 μm, 1 μm, 4 μm, and 5 μm in this order.
41, # 42, # 43, and # 44.

(5) Fifth series lithium-nickel composite oxide This is a lithium-nickel composite oxide having an ordered layered rock salt structure represented by a composition formula: LiNi _0.9 Co _0.05 Al _0.05 O ₂ , wherein the average of primary particles is Four types having different particle sizes were produced. In the production of the lithium nickel composite oxides of # 01 to # 07, the mixing ratio of each compound as a raw material was changed to Li,
Ni, Co, Al in molar ratio of 1: 0.9: 0.05:
Except having changed to 0.05, it manufactured similarly to the lithium nickel composite oxide of # 01- # 07.

This lithium nickel composite oxide is referred to as a fifth series lithium nickel composite oxide, and the average primary particle size is 0.2 μm, 1 μm, 4 μm, and 5 μm in this order.
51, # 52, # 53, and # 54.

(6) Lithium-nickel composite oxide of the sixth series This is a lithium-nickel composite oxide having an ordered layered rock salt structure represented by a composition formula: LiNi _0.7 Co _0.25 Al _0.05 O ₂ , wherein the average of primary particles is Four types having different particle sizes were produced. In the production of the lithium nickel composite oxides of # 01 to # 07, the mixing ratio of each compound as a raw material was changed to Li,
Ni, Co, Al in molar ratio of 1: 0.7: 0.25:
Except having changed to 0.05, it manufactured similarly to the lithium nickel composite oxide of # 01- # 07.

This lithium nickel composite oxide is referred to as a sixth series of lithium nickel composite oxide, and the primary particles have an average particle size of 0.2 μm, 1 μm, 4 μm, and 5 μm in this order.
61, # 62, # 63, and # 64.

Table 1 shows the compositions and the average primary particle diameters of the lithium nickel composite oxides of the first to sixth series. Note that # 12, # 13, #
The lithium nickel composite oxides Nos. 22 and # 23 correspond to the lithium nickel composite oxide of the present invention.

[0069]

[Table 1]

(B) Lithium Secondary Battery The lithium secondary batteries of the first to sixth series were used as the positive electrode active materials, respectively. Various kinds of lithium secondary batteries were produced. A lithium secondary battery using the first series lithium-nickel composite oxide (# 11 to # 14) as a positive electrode active material is referred to as a first series lithium secondary battery, and a second series lithium-nickel composite oxide ( A lithium secondary battery using # 21 to # 24) as a positive electrode active material is referred to as a second series lithium secondary battery, and a third series lithium nickel composite oxide (# 31 to # 34)
A lithium secondary battery using as a positive electrode active material is a third series of lithium secondary batteries, and a fourth series lithium secondary battery using a lithium nickel composite oxide (# 41 to # 44) as a positive electrode active material is used. The fourth series of lithium secondary batteries is the same as the fifth series of lithium nickel composite oxide (#
Lithium secondary batteries using 51 to # 54) as positive electrode active materials were used as fifth series lithium secondary batteries, and sixth series lithium nickel composite oxides (# 61 to # 64) were used as positive electrode active materials. The lithium secondary battery was designated as a sixth series lithium secondary battery.

(C) Evaluation of storage characteristics of lithium secondary batteries In order to evaluate the storage characteristics of each of the first to sixth series lithium secondary batteries, evaluation of storage characteristics of secondary batteries # 01 to # 07 was performed. Conditioning, measurement of the initial capacity, and storage test were performed in the same manner as in the above. Then, the capacity when each battery after the storage test was discharged at a temperature of 20 ° C. was measured to determine the remaining capacity, and the capacity remaining rate was determined from the formula [remaining capacity / initial capacity × 100].

For each of the secondary batteries of the first to sixth series,
FIG. 2 shows the relationship between the average particle size of the primary particles of the lithium nickel composite oxide as the positive electrode active material and the residual capacity ratio. FIG.
As is clear from the above, the secondary batteries # 12, # 13, # 22, and # 23 using the lithium nickel composite oxide of the present invention had a high remaining capacity of about 90%.
On the other hand, even in a secondary battery using a lithium nickel composite oxide having an average primary particle diameter of 1 μm or more and 4 μm or less as a positive electrode active material, the composition of the lithium nickel composite oxide is A secondary battery using a material different from the oxide composition has a remaining capacity ratio of about 50 to 70%.
And has declined.

As a composition different from the composition of the lithium nickel composite oxide of the present invention, for example, the substitution ratio of Co is 10
%, It is considered that the crystal structure is not sufficiently stabilized because the amount of substitution of Co is small. Conversely, when a lithium-nickel composite oxide having a Co substitution ratio of more than 20% was used (indicated by ■ in the figure), the crystallinity of the lithium-nickel composite oxide was reduced due to a large amount of Co substitution. it is conceivable that. The replacement ratio of Al is 5%.
When a lithium-nickel composite oxide of less than (（in the figure) is used, it is considered that the thermal stability of the crystal structure is not sufficient because the amount of Al substitution is small. Conversely, Al
It is considered that when a lithium-nickel composite oxide having a substitution ratio of more than 10% was used (indicated by ▲ in the figure), since the substitution amount of Al was large, the lattice distortion was large and the residual capacity ratio was lowered. .

Further, the average primary particle size is 0.2 μm.
When the lithium nickel composite oxide is used, the residual capacity is a low value of about 40 to 65%, although there is a difference in the composition. This is presumably because the lithium nickel composite oxide has a large specific surface area, so that the reaction with the electrolytic solution was promoted. Also, when a lithium nickel composite oxide of 5 μm is used, the capacity remaining ratio is a low value of about 35 to 55%, although there is a difference in the composition. This is presumably because, when the primary particles become too large, the secondary particles also become large, so that the lithium nickel composite oxide is not uniformly present in the positive electrode.

Therefore, the lithium-nickel composite oxide of the present invention can constitute a secondary battery having a high capacity remaining rate, that is, a large capacity can be maintained even when stored for a long time at a high charge rate. That was confirmed.

As described above, a lithium secondary battery using the lithium nickel composite oxide of the present invention as a positive electrode active material is:
It was confirmed that the lithium secondary battery had a small decrease in capacity and a small increase in internal resistance even when stored for a long time at a high charge rate.

[0077]

The crystal structure of the lithium-nickel composite oxide of the present invention is stabilized, and the reaction with the electrolytic solution is also suppressed. Is a lithium secondary battery having excellent storage characteristics, with a small decrease in capacity and a small increase in internal resistance even when stored for a long time in a charged state.

[Brief description of the drawings]

FIG. 1 shows the relationship between the initial capacity and the rate of increase in internal resistance for secondary batteries # 01 to # 07.

FIG. 2 shows the relationship between the average particle size of primary particles of lithium nickel composite oxide as a positive electrode active material and the residual capacity ratio for each of the first to sixth series secondary batteries.

Continuation of the front page (72) Inventor Yoshio Ukyo 41-41, Chuchu-ji, Yokomichi, Nagakute-cho, Aichi-gun, Aichi F-term in Toyota Central R & D Laboratories Co., Ltd. 4G048 AA04 AC06 AD04 5H029 AJ04 AK03 AL06 AL07 AL08 AL12 AM02 AM03 AM04 AM05 AM07 DJ16 HJ02 HJ05 5H050 AA09 BA16 BA17 CA08 FA17 HA02 HA05

Claims (2)

[Claims] 1. Composition formula LiNi _1-xy Co _x Al _y O
₂ (0.1 ≦ x ≦ 0.2; 0.05 ≦ y ≦ 0.1), a particle structure in which primary particles having an average particle diameter of 1 μm or more and 4 μm or less are aggregated to form secondary particles. Lithium-nickel composite oxide for lithium secondary battery positive electrode active material with 2. The secondary particles have an average particle size of not less than 5 μm and not more than 3 μm.
The lithium-nickel composite oxide for a lithium secondary battery positive electrode active material according to claim 1, having a thickness of 0 µm or less.