JP2004355986A - Positive electrode active material for lithium secondary battery, its manufacturing method and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode active material for a lithium secondary battery, with a small average particle size, to provide its manufacturing method, and to provide a lithium secondary battery with a large capacity of high efficiency discharge. <P>SOLUTION: The method for manufacturing a positive electrode active material for a lithium secondary battery, comprises a step of obtaining a solid transition metallic compound by forming a precipitate out of a solution. A carbon material is suspended in a liquid reaction area where a precipitate is produced, suppressing nuclear growth of the precipitate to allow a precipitate with fine particles of submicron order to be produced. Even when the precipitate is heat-treated as a precursor, since secondary pulverization is suppressed, a positive electrode active material of an ultra-fine particle diameter for a lithium secondary battery can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１２５】
【表２】

【０１２６】
以上の結果から明らかなように、本発明の製造方法によれば、平均粒子径を顕著に小さいものとした正極活物質とその製造方法を提供することができる。また、本発明の正極活物質を用いると、高率放電容量の大きなリチウム二次電池を提供することができる。
【０１２７】
なお、本発明は、その精神又は主要な特徴から逸脱することなく、他のいろいろな形で実施することができる。そのため、上記した実施の形態若しくは実施例はあらゆる点で単なる例示に過ぎず、限定的に解釈してはならない。本発明の範囲は、請求の範囲によって示すものであって、明細書本文にはなんら拘束されない。さらに、請求の範囲の均等範囲に属する変形や変更は、すべて本発明の範囲内のものである。
【０１２８】
【発明の効果】
以上詳述したように、本発明によれば、平均粒子径の小さなリチウム二次電池用正極活物質を提供することができる。また、平均粒子径の小さなリチウム二次電池用正極活物質の製造方法を提供することができる。また、放電容量の大きなリチウム二次電池を提供することができる。
【図面の簡単な説明】
【図１】実施例に係る電池の斜視図である。
【符号の説明】
１ 極群
２ 外装体
３Ａ 正極端子
３Ｂ 負極端子[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery.
[0002]
[Prior art]
At present, lithium secondary batteries typified by lithium ion batteries and lithium polymer batteries are used as power sources for current small-sized consumer portable terminals and mobile communication devices. Current lithium secondary batteries include α-NaFeO as a positive electrode active material.₂LiCoO which is a Li-Co composite oxide having a structure₂Is mainly used.
[0003]
Recently, since cobalt is a rare metal and its price is high, and since the advent of the ubiquitous society, a higher energy density is required for secondary batteries, LiCoO₂A high-performance positive electrode active material that can be used instead is also being studied.
[0004]
For example, α-NaFeO₂Li-Ni-based composite oxide having a structure (LiNiO₂), Li-Ni-Co-based composite oxide, Li-Mn-Ni-based composite oxide, Li-Mn-Ni-Co-based composite oxide, and the like have been proposed. Elements such as Mn and Ni are LiCoO₂Can be replaced by a solid solution with the Co element, which can be replaced by Ni, the capacity can be increased by replacing with Ni, and the thermal stability can be improved by replacing with Mn.
[0005]
In particular, LiMn having an equal composition of Mn and Ni_xNi_xCo_1-2xO₂As reported in Non-Patent Documents 1 to 3, the Li-Mn-Ni-Co-based composite oxide represented by the composition maintains a stable crystal structure even when deep Li is drawn (charged). Current characteristics of LiCoO₂4.3 V (vs. Li / Li) considered to be the limit in the system⁺) Can be operated at a higher voltage.
[0006]
By the way, generally, a method of producing a positive electrode active material by performing a heat treatment (for example, a temperature of several hundred degrees Celsius or more) on a solid transition metal compound is known. At this time, as one of the methods for producing a solid transition metal compound before heat treatment (hereinafter, also referred to as “precursor”), there is a method of producing a precipitate in a liquid reaction field.
[0007]
In particular, in the case of producing a positive electrode active material containing a plurality of transition metal elements, when a solid state transition metal compound containing a single transition metal element is physically mixed and heat-treated, elements between different transition metal elements Substitution does not proceed sufficiently, and it is difficult to produce a single positive electrode active material having high crystallinity. For example, as described in Patent Literatures 1 and 2 for a Li—Mn—Ni—Co-based composite oxide, Mn is precipitated from an aqueous solution in which a transition metal element is dissolved in a liquid reaction field by a precipitation method. By preparing a coprecipitated precursor in which Ni and Co are solid-solution-mixed extremely uniformly and heat-treating the same, a positive electrode active material having a single and high crystallinity can be prepared. . Thus, in the case of producing a positive electrode active material by performing a heat treatment on the precursor, it is effective to obtain the precursor by forming it from an aqueous solution in which a transition metal element is dissolved in a liquid reaction field, This is particularly effective when the positive electrode active material contains a plurality of types of transition metal elements.
[0008]
[Non-patent document 1]
Zhonghua Lu; Macneil, D .; D; Dahn, J .; R. Layered Li [Ni_cCo_1-2xMn_x] O₂  Cathode Materials for Lithium-Ion Batteries, Electrochem. Solid-State Lett. vol. 4, no. 12, 2001, page. A200-A203.
[0009]
[Non-patent document 2]
Koyama, Yukinori; Tanaka, Isao; Adachi, Hirohiroko; Makimura, Yoshinari; Yabuuchi, Naoki; Ohzuku, Tsutomu. Lithium Insertion Material of LiCo_1/3Ni_1/3Mn_1/3O₂  for Advanced Batteries; (I) Prediction on the Crystal and Electronic Structure. The 42nd Battery Symposium. 2001, page. 50-51.
[0010]
[Non-Patent Document 3]
Makimura, Yoshinari; Yabuchi, Naoaki; Ohzuku, Tsutomu; Koyama, Yukinori; Tanaka, Isao; Adachi, Hirohiko. Lithium Insertion Material of LiCo_1/3Ni_1/3Mn_1/3O₂  (II) Synthesis and Characterization as a Possible Alternate to LiCoO. The 42nd Battery Symposium. 2001, page. 52-53.
[0011]
[Patent Document 1]
WO 02/073718 pamphlet
[0012]
[Patent Document 2]
WO 02/086993 pamphlet
[0013]
[Problems to be solved by the invention]
However, the conventional cathode active material has a problem that the discharge capacity of the cathode active material is not always sufficient.
[0014]
One of the measures for improving the discharge capacity of the positive electrode active material is to increase the surface area of the positive electrode active material and increase the contact area between the positive electrode active material and the electrolyte. In order to increase the contact area, it is effective to reduce the particle size of the positive electrode active material.
[0015]
Α-NaFeO described in Patent Documents 1 and 2₂The case of a Li—Mn—Ni—Co-based composite oxide having a structure will be described as an example. This document describes a method in which an Mn-Ni-Co coprecipitated precursor is prepared in a liquid reaction field, and the precursor is heat-treated to prepare an active material. (Note that the “precursor” here corresponds to the “solid-state transition metal compound” described above.) However, according to the production method described in the document, particles of the coprecipitated precursor are almost 5 μm or more. And the average particle diameter (D₅₀) Could not be less than 1 μm. The active material particles obtained by heat-treating such precursor particles are also affected by the fluidity distribution of the entire substrate, so that the average particle diameter (D₅₀) Could not be less than 1 μm.
[0016]
Here, generally, in order to reduce the average particle size of the positive electrode active material, the precursor particles may be physically pulverized. However, when the precursor particles are physically pulverized, there is a high possibility that the crystal planes of the precursor particles formed will be destroyed. Therefore, when the cathode active material obtained by heat-treating the precursor particles is used for a lithium secondary battery, The charge / discharge performance is not sufficient. This is considered to be because the crystal plane of the positive electrode active material particles is broken, which promotes the crushing of the particle crystals due to the expansion and contraction of the positive electrode active material particles due to charge and discharge. Therefore, such a method of destroying the primary grain crystal plane should be avoided.
[0017]
The present invention has been made in view of the above problems, and has as its object to provide a positive electrode active material for a lithium secondary battery having a small average particle diameter. Another object of the present invention is to provide a method for producing a positive electrode active material for a lithium secondary battery having a small average particle diameter. Another object of the present invention is to provide a lithium secondary battery having a high high rate discharge capacity.
[0018]
[Means for Solving the Problems]
The technical configuration, operation and effect of the present invention are as follows. However, the mechanism of action includes estimation, and the correctness of the mechanism of action does not limit the present invention.
[0019]
The present invention provides a method for producing a positive electrode active material for a lithium secondary battery, comprising a step of forming a solid transition metal compound from an aqueous solution in which a transition metal element is dissolved, as described in claim 1. The system reaction field is a method for producing a positive electrode active material for a lithium secondary battery, wherein a carbon material coexists.
[0020]
The present inventors have proposed a positive electrode active material for a lithium secondary battery including a step of forming a solid transition metal compound from an aqueous solution in which one or more transition metal elements are dissolved in a liquid reaction field. In the production method, the liquid-based reaction field coexists with the carbon material, so that the average particle diameter of the solid transition metal compound formed in the liquid-based reaction field is extremely small. I found that I can do it.
[0021]
The cause of such an effect is not necessarily clear, but the present inventors consider as follows. A detailed examination of the production conditions described in Patent Documents 1 and 2, which are conventional techniques, reveals that a precipitation reaction that can occur rapidly by using a complexing material to uniformly precipitate Mn, Ni, and Co in the literature. Has been relaxed. As a result, the nucleus growth reaction takes precedence over the nucleus generation reaction of the precipitate (solid state transition metal compound). As a result, the nucleus growth progresses, but the solid state transition metal compound has a large particle diameter. Is thought to be generated in the liquid reaction field. As described above, the process in which the solid transition metal compound is formed in the liquid reaction field includes a nucleation reaction and a subsequent nucleus growth reaction. Here, it is inferred that the coexistence of the carbon material in the liquid reaction field suppresses the nucleus growth reaction, so that a solid transition metal compound having a small particle diameter may be obtained. In other words, the nuclei generated in the liquid-based reaction field are considered to be in an unstable state with a very large surface energy, but the generated nuclei are adsorbed on the surface by the presence of a carbon material with a very large surface area. As a result, it is speculated that the subsequent nuclear growth reaction will be suppressed.
[0022]
When the thus obtained solid transition metal compound having a small particle diameter is heat-treated together with a lithium compound such as lithium hydroxide, a lithium transition metal composite oxide having a small average particle diameter can be obtained.
[0023]
What is extremely interesting here is that the positive electrode active material particles obtained by heat-treating the transition metal compound (precursor) having a large particle diameter obtained under the conditions described in Patent Documents 1 and 2 are mostly converted into secondary particles. However, the size itself of the primary particles constituting the particles having the form of the secondary particles is, surprisingly, particularly larger than that obtained by the production method of the present invention. Is not recognized. According to the study by the present inventors on this point, when the particle diameter of the solid transition metal compound obtained in the liquid reaction field is about 10 μm or more, when the solid transition metal compound is heat-treated, One particle after heat treatment obtained from one particle of the compound has a secondary particle form in which primary particles are gathered, for example, reminiscent of a cell division of one fertilized egg. I know that. In contrast, when the small-diameter transition metal compound obtained by the method of the present invention is heat-treated, it is surprisingly surprising that one solid-state transition metal compound obtained from one particle after the heat treatment is obtained. In most cases, the particles are particles in a form in which one particle exists alone, and do not have a “secondary particle form in which primary particles are gathered”.
[0024]
Further, the manufacturing method of the present invention is characterized in that the transition metal element contains at least nickel (Ni).
[0025]
In the case where a solid-state transition metal compound is formed in a liquid-based reaction field, in the case where a complex-forming agent such as ammonia is contained in the liquid-based reaction field, nickel among the transition metal elements is particularly the above-mentioned. Nucleation processes tend to take precedence over nucleation processes. Therefore, when the transition metal element contains at least nickel (Ni) and a solid transition metal compound containing Ni is formed in a liquid-based reaction field, the present invention is particularly effective. Effectively demonstrated.
[0026]
Further, according to the production method of the present invention, as described in claim 3, the transition metal element is at least two kinds selected from the group consisting of nickel (Ni), manganese (Mn), and cobalt (Co). It is characterized by having.
[0027]
Among the positive electrode active materials containing nickel as a constituent element, a positive electrode active material containing manganese or cobalt as a constituent element is excellent in that it has high thermal stability and the like. When producing a positive electrode active material containing a plurality of types of transition metal elements, such as a Ni—Co system, as described above, a production method including a step of forming a transition metal compound in a liquid reaction field By doing so, a positive electrode active material having a uniform composition can be obtained. Therefore, by applying the present invention in this case, the effect of the present invention is particularly effective.
[0028]
In addition, the manufacturing method of the present invention is characterized in that the transition metal element includes at least nickel (Ni), manganese (Mn), and cobalt (Co).
[0029]
According to such a configuration, a solid transition metal compound having a small particle diameter can be obtained by applying the present invention in a method for producing a Ni—Mn—Co-based positive electrode active material that requires a particularly homogeneous precursor. In particular, the effect of the present invention, such as the effect of
[0030]
Further, the manufacturing method of the present invention is characterized in that, as described in claim 5, the carbon material can exist in a suspension state in the liquid-based reaction field.
[0031]
In the process of forming a solid-state transition metal compound (precursor) in the liquid-based reaction field, the carbon material coexisting in the liquid-based reaction field is brought into a suspended state, so that the carbon material is transferred to the liquid-based reaction field. Since the effect can be spread, the effect of suppressing the growth of the generated nuclei is evenly exhibited in the liquid-based reaction field, so that the above-mentioned effect is more efficiently exhibited.
[0032]
Further, according to the manufacturing method of the present invention, as described in claim 6, a method of manufacturing a positive electrode active material for a lithium secondary battery, wherein the solid state transition metal compound and the Li compound are mixed and manufactured through a heat treatment step. Wherein the carbon material is at least partially decomposed and removed by the heat treatment step.
[0033]
The solid transition metal compound (precursor) formed in the liquid reaction field is filtered and dried, and is in a state of being mixed with the carbon material. When heat treatment is performed to obtain a positive electrode active material, by selecting heat treatment conditions and the type of carbon material, the obtained positive electrode active material may include the carbon material, or may include the carbon material. It can also be absent. For example, by performing heat treatment in an atmosphere containing oxygen, at least a part of the carbon material can be decomposed and removed. By selecting the carbon material from those which are at least partially decomposed and removed by the heat treatment step, the obtained cathode active material does not contain excess carbon material, so that the cathode active material excellent in energy density It can be.
[0034]
Further, according to the manufacturing method of the present invention, as described in claim 7, a method of manufacturing a positive electrode active material for a lithium secondary battery, wherein the solid state transition metal compound and the Li compound are mixed and manufactured through a heat treatment step. The carbon material is characterized in that at least a part thereof remains by the heat treatment step.
[0035]
The carbon material is present in the fine structure between the positive electrode active material particles or in the fine structure portion in the positive electrode active material particles by selecting conditions such as a heat treatment condition in which at least a part of the carbon material remains in the heat treatment step and a type of the carbon material. Therefore, a positive electrode using such a positive electrode active material is preferable because it can have excellent electron conductivity. In addition, the solid-state transition metal compound formed by coexisting the carbon material in the solution, as well as the positive electrode active material obtained by heat-treating the same, have a secondary It has been found that the proportion of particles is very small. The reason for this is not necessarily clear, but it is speculated that it may be related to at least a part of the carbon material remaining in the heat treatment step.
[0036]
Further, according to the production method of the present invention, as described in claim 8, the solid transition metal compound has an average particle diameter (D₅₀) Is a solid transition metal compound having a particle size of less than 1.0 μm.
[0037]
According to such a configuration, the average particle diameter (D) of the solid transition metal compound formed in the liquid reaction field is₅₀) Can be less than 1.0 μm, so that it is possible to provide a positive electrode active material having a smaller average particle diameter than before.
[0038]
Further, according to the production method of the present invention, as described in claim 9, the solid transition metal compound and the Li compound are mixed, and the mixture is subjected to a heat treatment step to obtain an average particle diameter (D₅₀) For producing a positive electrode active material for a lithium secondary battery having a thickness of less than 1.0 μm.
[0039]
According to such a configuration, it is possible to provide a positive electrode active material for a lithium secondary battery having a smaller average particle diameter than in the related art.
[0040]
Here, a preferred method for measuring the average particle diameter will be described.
[0041]
As for solid transition metal compound particles formed in a liquid reaction field, it is preferable to use a method of dispersing a powder in a dispersion medium and irradiating it with light such as a laser to measure. The solid transition metal compound particles formed in the liquid-based reaction field are in a state of being mixed with the carbon material. When the particle size is sufficiently smaller than the particle size of the metal compound (for example, when acetylene black having a particle size of nm order) is used, it is possible to separate and measure the two according to the above-mentioned measuring method. Further, when the particle diameters of both particles are close to each other, it may be performed by image analysis of the result of the observation with an electric microscope. In many cases, since the carbon material has high electron conductivity, it is easy to distinguish them from the observed image.
[0042]
Next, for the particles obtained by heat-treating a solid transition metal compound formed in a liquid-based reaction field, a method in which the powder is dispersed in a dispersion medium and measured by irradiating light such as a laser is suitable. ing. At this time, a method based on image analysis may be used, but it should be noted that a method based on image analysis may lead to an incorrect result in some cases. That is, for example, as to the case where a lithium transition metal composite oxide is obtained by performing a heat treatment by mixing a solid transition metal compound and a lithium compound formed in a liquid reaction field, as described above, In the case of heat-treated transition metal compounds with large particle diameters obtained by the conventional technology, secondary particle morphologies such as primary particles gathering are often observed, but these particles are converted into primary particles even when dispersed in a dispersion medium. Never do. On the other hand, the powder obtained by heat-treating the transition metal compound having a small particle size obtained according to the present invention may have agglomeration of particles depending on storage conditions. However, according to the method of dispersing in a dispersion medium, the agglomeration is eliminated. Therefore, a correct measurement result can be obtained. Thereby, the prior art product and the product of the present invention can be distinguished. However, it is difficult to distinguish the aggregated product of the present invention from the conventional product in the form of secondary particles by the method of performing image analysis of particles existing in the air.
[0043]
Further, according to the manufacturing method of the present invention, the positive electrode active material for a lithium secondary battery is α-NaFeO.₂Having a crystal structure of the general formula: Li_aMn_bNi_cCo_dO_e(0 ≦ a ≦ 1.3, | c−b | ≦ 0.05, 0 <d <1, 1.7 ≦ e ≦ 2.3, b + c + d = 1, b ≠ 0, c ≠ 0) It is a lithium transition metal composite oxide having a composition.
[0044]
According to such a configuration, the present invention can be applied to the production of the lithium transition metal composite oxide having the above composition having particularly excellent charge / discharge cycle performance, high energy density, and excellent thermal stability. It is possible to provide a method for producing a lithium transition metal composite oxide having the above-mentioned composition having a small diameter. Therefore, a lithium secondary battery using this as a positive electrode active material has excellent high-rate discharge characteristics.
[0045]
Further, the present invention is a positive electrode active material for a lithium secondary battery manufactured by the method for manufacturing a positive electrode active material for a lithium secondary battery.
[0046]
Thereby, a positive electrode active material having a small average particle diameter can be provided.
[0047]
Further, the present invention includes, as described in claim 12, a positive electrode including the positive electrode active material for a lithium secondary battery, a negative electrode using a negative electrode material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte. Lithium secondary battery.
[0048]
Accordingly, a lithium secondary battery using a positive electrode active material having a small particle diameter is provided, so that a lithium secondary battery having excellent high-rate discharge characteristics can be provided.
[0049]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is widely applicable to any method for producing a positive electrode active material for a lithium secondary battery including a step of forming a solid transition metal compound from an aqueous solution in which a transition metal element is dissolved in a liquid reaction field. can do.
[0050]
As a method for forming a solid transition metal compound from a solution in which a transition metal element is dissolved, for example, a method utilizing a salt formation phenomenon generated by a reaction between an acid component and an alkali component may be mentioned. Specifically, for example, a method in which a solution in which a transition metal is not dissolved is dropped into a solution in which a transition metal is dissolved, or a solution in which a transition metal is not dissolved is dropped into a solution in which a transition metal is dissolved And the like. Here, the carbon material can be present in one or both of the above solutions to be mixed.
[0051]
According to the production method of the present invention, the transition metal compound formed in the liquid reaction field may be dried and used as an active material as it is, and the transition metal compound formed in the liquid reaction field is further subjected to heat treatment or the like. May be used as an active material.
[0052]
A raw material for preparing a solution in which a transition metal element is dissolved can be appropriately selected depending on a constituent element, a crystal structure, a composition, and the like of a positive electrode active material which is a target final material. For example, α-NaFeO₂When a positive electrode active material having a type crystal structure is intended, as a Ni raw material, nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, etc., and as a Mn compound, manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, etc. Examples of the Co compound include cobalt sulfate and cobalt nitrate. When the purpose is to form a solid-state transition metal compound containing two or more transition metal elements, the above materials may be appropriately mixed and used.
[0053]
In the production method of the present invention, the carbon material coexisting in the liquid reaction field is not particularly limited. Raw materials for carbon materials include wood, fruit husks, lignin, rice husks, plant matter such as bacas, beans, minerals such as coal and petroleum, pulp mill effluent, alcohol factory effluent, waste plastic, construction waste, and other waste materials. Alternatively, fibers or the like made from cellulose, acrylic, phenol, or pitch are selected, and these can be heat-treated in various atmospheres to produce a carbon material. As described above, since various kinds of materials can be used as the raw material of the carbon material used in the present invention, a wide range of physical properties of the carbon material obtained from these raw materials can be applied. The shape of the carbon material that can be used in the present invention can be selected from powder, granule, and fiber. The BET specific surface area of the carbon material that can be used in the present invention is 5 × 10⁰~ 1x10⁴cm²/ G range. By selecting the carbon material in this manner, the nuclei generated of the solid transition metal compound formed in the liquid reaction field can be sufficiently adsorbed, which is preferable. Generally, the higher the specific surface area, the lower the degree of graphitization, and the lower the specific surface area, the higher the degree of graphitization.
[0054]
When the carbon material used in the present invention is selected from those having electron conductivity, when at least a part of the carbon material is left by the heat treatment step, there is no possibility of lowering the electron conductivity of the obtained positive electrode active material. ,preferable.
[0055]
Since the carbon material according to the present application is preferably suspended in a liquid reaction field, a carbon material having a high bulk density is preferable.
[0056]
The amount of the carbon material coexisting in the liquid reaction field varies depending on physical properties such as the surface area of the carbon material, but is 0.1% by weight or more based on the weight of the solid transition metal compound formed in the liquid reaction field. This is preferable because the effect of reducing the particle diameter of the transition metal compound formed in the liquid reaction field can be sufficiently exhibited. There is no particular upper limit on the amount of the coexisting carbon material. Even if the amount is excessive, the effect of reducing the particle diameter of the transition metal compound formed in the liquid reaction field is not impaired. However, from the viewpoint of production efficiency, the content is preferably set to 10% by weight or less. When the formed solid transition metal compound is used as it is in a battery, the solid transition metal compound is obtained in a state mixed with a coexisting carbon material. It is preferable to use an inconsistent amount of carbon material.
[0057]
In addition, carbon materials that do not contain much elements other than carbon atoms are basically used as the carbon material to coexist in the liquid reaction field.However, by using a carbon material containing elements other than carbon, the lithium secondary battery can be used. Special effects can be added to performance.
[0058]
For example, using a carbon material containing B (boron) is preferable in that a lithium secondary battery having excellent characteristics such as high-rate discharge performance, storage performance, charge / discharge cycle performance, and high-temperature stability can be obtained. Further, when a carbon material containing a specific transition metal is used, when a heat treatment is performed using a transition metal compound formed in an aqueous solution as a precursor, a part of the transition metal element constituting the precursor is converted to the specific transition metal. It can be replaced by a metal. Examples of the specific transition metal element include Cr, Ni, Fe, Co, Mn, Cu, Ag, S, Ti, Si, Sn, V, Nb, Bi, Sb, Mo, and W.
[0059]
In the method for producing a positive electrode active material for a lithium secondary battery, which is obtained by mixing the solid transition metal compound and a Li compound and then performing a heat treatment step, as the Li compound, lithium hydroxide and lithium carbonate are preferably used. .
[0060]
As a negative electrode material capable of inserting and extracting lithium ions that can be used for the lithium secondary battery of the present invention, a material generally used for a lithium secondary battery can be used as it is. For example, lithium metal, lithium alloy (lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and lithium metal-containing alloys such as wood alloy), lithium composite oxide (lithium-titanium) , Silicon oxide, and carbon materials (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, and the like). Among these, graphite has an operating potential very close to that of metallic lithium, and can realize charging and discharging at a high operating voltage. When a lithium salt is used as the electrolyte salt, self-discharge can be reduced, and irreversible capacity in charge and discharge can be reduced. For example, artificial graphite and natural graphite are preferred. In particular, graphite in which the surface of the negative electrode material particles is modified with amorphous carbon or the like is preferable because gas generation during charging is small.
[0061]
The analysis results of X-ray diffraction of graphite which can be suitably used are shown below;
Lattice spacing (d₀₀₂) 0.333-0.350 nm
Crystallite size La in the a-axis direction La 20 nm or more
Crystallite size Lc in the c-axis direction 20 nm or more
True density 2.00 to 2.25 g / cm³
[0062]
It is also possible to modify the graphite by adding a metal oxide such as tin oxide and silicon oxide, phosphorus, boron, amorphous carbon and the like to graphite. Particularly, by modifying the surface of graphite by the above-described method, it is possible to suppress the decomposition of the electrolyte and to improve the battery characteristics, which is desirable. Further, lithium metal, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and a lithium metal-containing alloy such as a wood alloy may be used in combination with graphite, Graphite into which lithium has been inserted by chemical reduction can also be used as the negative electrode material.
[0063]
As the non-aqueous electrolyte constituting the lithium secondary battery, those generally used for lithium secondary batteries, such as a non-aqueous electrolyte, a gel electrolyte, and a solid electrolyte, can be used as they are. Non-aqueous solvents constituting the non-aqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate , Diethyl carbonate, ethyl methyl carbonate and other chain carbonates; methyl formate, methyl acetate, methyl butyrate and other chain esters; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2- Ethers such as dimethoxyethane, 1,4-dibutoxyethane and methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sultone or derivatives thereof And the like, or a mixture of two or more thereof, but is not limited thereto.
[0064]
As the electrolyte salt constituting the non-aqueous electrolyte, for example, LiClO₄, LiBF₄, LiAsF₆, LiPF₆, LiSCN, LiBr, LiI, Li₂SO₄, Li₂B₁₀Cl₁₀, NaClO₄, NaI, NaSCN, NaBr, KClO₄, An inorganic ion salt containing one kind of lithium (Li), sodium (Na) or potassium (K) such as KSCN, LiCF₃SO₃, LiN (CF₃SO₂)₂, LiN (C₂F₅SO₂)₂, LiN (CF₃SO₂) (C₄F₉SO₂), LiC (CF₃SO₂)₃, LiC (C₂F₅SO₂)₃, (CH₃)₄NBF₄, (CH₃)₄NBr, (C₂H₅)₄NCLO₄, (C₂H₅)₄NI, (C₃H₇)₄NBr, (n-C₄H₉)₄NCLO₄, (N−C₄H₉)₄NI, (C₂H₅)₄N-maleate, (C₂H₅)₄N-benzoate, (C₂H₅)₄Organic ion salts such as N-phtalate, lithium stearylsulfonate, lithium octylsulfonate, lithium dodecylbenzenesulfonate and the like can be mentioned, and these ionic compounds can be used alone or as a mixture of two or more. .
[0065]
Furthermore, LiBF₄And LiN (C₂F₅SO₂)₂By mixing and using a lithium salt having a perfluoroalkyl group as described above, the viscosity of the electrolyte can be further reduced, and the low-temperature characteristics can be further improved, which is more desirable.
[0066]
The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably from 0.1 mol / l to 5 mol / l, more preferably from 0.5 mol / l to 2 mol / l in order to reliably obtain a non-aqueous electrolyte battery having high battery characteristics. 0.5 mol / l.
[0067]
The use of a gel electrolyte as the non-aqueous electrolyte is preferable in that it has the effect of preventing liquid leakage, that a lightweight exterior body material can be used, and that the degree of freedom in shape is increased. As the polymer used for the gel electrolyte, for example, acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and other crosslinked, non-crosslinked, or IPN-structured polymers can be used.
[0068]
Hereinafter, in order to explain the present invention in more detail based on specific examples, α-NaFeO is used as a positive electrode active material.₂Having a crystal structure of the general formula: Li_aMn_bNi_cCo_dO_e(However, 0 ≦ a ≦ 1.3, 0.95 ≦ c / b ≦ 1.05, 0 <d <1, 1.7 ≦ e ≦ 2.3, b + c + d = 1, b ≠ 0, c ≠ 0 The case where a lithium transition metal composite oxide having the composition shown in ()) is obtained will be described as an example.
[0069]
Such a lithium transition metal composite oxide can be obtained by using a solid transition metal compound as a precursor, mixing the precursor with a Li compound, and performing a heat treatment. Here, the precursor has Mn and Ni as transition metal elements and Co as required, and β-Ni (OH)₂It is preferable to mainly include a compound having a type crystal structure.
[0070]
A preferred embodiment of the precursor and a method for producing the precursor will be described. The precursor is Ni (OH)₂It is preferable that the compound is a compound in which Mn atoms and, where necessary, Co atoms are uniformly arranged with Ni atoms at Ni sites in the type crystal structure. Here, the valence of the Mn atom constituting the precursor crystal is preferably divalent. By making the precursor crystal mainly contain divalent Mn, Li which is an impurity phase is contained in the product after the heat treatment.₂MnO₃Can be reduced. This Li₂MnO₃Is a substance which is electrochemically inactive at around 4 V and has a function of stabilizing the crystal structure of the composite oxide, but causes a reduction in capacity, and thus is contained in the composite oxide (positive electrode active material). Li₂MnO₃This is because it is preferable that the content of is not excessively increased.
[0071]
As a method for producing the precursor, an alkaline aqueous solution such as a sodium hydroxide aqueous solution as a reaction liquid is used as a liquid reaction field, and an acidic aqueous solution containing at least Ni and Mn is dropped into the liquid reaction field to form a precipitate. The "coprecipitation method" can be adopted. The precursor is obtained by drying the precipitate obtained in the “coprecipitation method”. When the “coprecipitation method” is used, it is easy to obtain a composite oxide (cathode active material) as a final product, which has high stability of the crystal structure accompanying the elimination / insertion reaction of Li, and exhibits particularly high battery performance. A positive electrode active material can be manufactured.
[0072]
When the “coprecipitation method” is adopted, it is extremely important to maintain the liquid reaction field in a reducing atmosphere in order for the precursor to mainly contain divalent Mn. This is because if the liquid reaction field is in an oxidizing atmosphere, Mn is oxidized to a higher order and the precursor is α-Ni (OH)₂This is because it has a mold structure. As a method of keeping the liquid-based reaction field in a reducing atmosphere, a reducing agent such as hydrazine is put into the liquid-based reaction field, or oxygen is removed by filling the liquid-based reaction field with an inert gas, and the liquid-based reaction field is changed to a reducing atmosphere. can do.
[0073]
In the “coprecipitation method”, it is preferable that ammonium ions be present in the reaction solution. The presence of ammonium ions is preferable because the precipitation reaction rate is reduced by passing through a metal-ammine complex formation reaction, so that the crystal orientation is good and the composition becomes uniform. As a method for causing ammonium ions to be present, ammonium sulfate, aqueous ammonia, or the like is charged into the reaction solution system. Conversely, in the absence of ammonium ions, the metal ions rapidly precipitate due to the acid-base reaction, so that the crystal orientation is disordered, the particle shape is non-uniform, and the non-uniform precipitation of the particle internal composition is generated. Or a problem that the particle distribution is widened.
[0074]
Among the reaction conditions related to the “coprecipitation method”, device factors such as the shape of the reactor and the type of the rotor, the time during which the sediment stays in the reaction tank, the reaction tank temperature, the total ion amount, and the oxidation number adjusting agent By selecting various factors such as the concentration of, the physical properties such as the particle shape, bulk density and surface area of the coprecipitated compound can be slightly controlled.
[0075]
Further, the lithium transition metal composite oxide having the above composition has Mn and Ni as transition metal elements and has β-Ni (OH)₂It may be obtained by mixing and heat-treating a precursor mainly containing a compound having a type crystal structure, a Li compound and, if necessary, a precursor made of a Co compound. In this case, the precursor composed of the Co compound is preferably an oxide or a carbonate salt. In this case, cobalt oxides include cobalt monoxide, cobalt oxyhydroxide, and cobalt trioxide, and cobalt carbonates include basic cobalt carbonate.
[0076]
In the method for producing a positive electrode active material for a lithium secondary battery, wherein the solid state transition metal compound and the Li compound are mixed and produced through a heat treatment step, the heat treatment temperature of the mixture of the precursor and the Li compound is 800 ° C. or higher. The temperature is preferably 1050 ° C. or lower, more preferably 850 ° C. to 1025 ° C. When the heat treatment temperature is lower than 800 ° C., a problem that the discharge capacity is reduced is likely to occur because of a structural factor that hinders the movement of Li. On the other hand, if the heat treatment temperature exceeds 1050 ° C., the solid phase reaction between the particles proceeds and the particle size increases compared to the precursor, and the composite oxide having the target composition because Li tends to volatilize during the heat treatment cannot be obtained. The problem that it is difficult to obtain easily occurs. Further, when the heat treatment temperature exceeds 1050 ° C., the battery performance tends to decrease due to excessive atom exchange between the 3a site occupied by Li and the 3b site occupied by Mn, Ni, and Co elements in crystal structure. Show. From the above viewpoints, by setting the heat treatment temperature to the range of 850 ° C. or more and 1025 ° C. or less, it is possible to synthesize a positive electrode active material for a lithium secondary battery that exhibits particularly high energy density and has excellent charge / discharge cycle performance. preferable. Among the above temperature ranges, particularly preferred heat treatment temperatures are currently under study, but generally, when the ratio of cobalt in the transition metal element constituting the transition metal compound is high, a relatively low temperature may be used. If the ratio of cobalt in the transition metal element constituting the transition metal compound is low, on the contrary, it seems that a relatively high temperature tends to be appropriate.
[0077]
In the method for producing a positive electrode active material for a lithium secondary battery, in which the solid transition metal compound and the Li compound are mixed and subjected to a heat treatment step, the heat treatment time is preferably 3 hours or more and 50 hours or less. By setting the heat treatment time to 50 hours or less, it is possible to reduce the risk that Li is volatilized during the heat treatment and it becomes difficult to obtain a composite oxide having a desired composition, and thus the battery performance can be improved. On the other hand, by setting the heat treatment time to 3 hours or more, the crystal can be sufficiently developed, so that the battery performance can be improved.
[0078]
The heat treatment atmosphere is preferably an atmosphere containing oxygen. In particular, in the heat treatment process, after the stage of lowering the temperature, which is the final stage of the process, an oxygen-containing atmosphere should be used because oxygen atoms tend to desorb from the crystal structure of the generated composite oxide. Is very preferred. By setting the atmosphere to include oxygen, at least a part of the carbon material coexisting with the precursor can be decomposed and removed. Further, by adjusting the heat treatment conditions, at least a part of the carbon material coexisting with the precursor can be left. The atmosphere containing oxygen includes air.
[0079]
The lithium secondary battery according to the present invention (hereinafter, also simply referred to as “battery”) has a positive electrode containing a positive electrode active material for a lithium secondary battery (hereinafter, also simply referred to as “positive electrode active material”), and has a function of inserting and extracting lithium ions. It has a negative electrode containing a possible negative electrode material and a non-aqueous electrolyte in which an electrolyte salt is contained in a non-aqueous solvent. Generally, a separator is provided between the positive electrode and the negative electrode.
[0080]
The positive electrode and the negative electrode may contain a conductive agent, a binder, a thickener, a filler, and the like as other components in addition to the main components.
[0081]
As the conductive agent, the carbon material used in the production method of the present invention may be left, and the carbon material may serve as the conductive agent. When the conductive material is separately added, the material is not limited as long as it is an electron conductive material which does not adversely affect the battery performance. Usually, natural graphite (scale graphite, flake graphite, earth graphite, etc.), artificial graphite, carbon Conductive materials such as black, acetylene black, Ketjen black, carbon whiskers, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, conductive ceramic material, etc. as one kind or a mixture thereof Can be included.
[0082]
Among these, acetylene black is preferable as the conductive agent from the viewpoints of electron conductivity and coatability. The amount of the conductive agent to be added is preferably 0.1% by weight to 50% by weight, particularly preferably 0.5% by weight to 30% by weight based on the total weight of the positive electrode or the negative electrode. In particular, it is preferable to use acetylene black after being crushed into ultrafine particles of 0.1 to 0.5 μm since the required carbon amount can be reduced. These mixing methods are physical mixing, and ideally, homogeneous mixing. Therefore, a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, and a planetary ball mill can be dry- or wet-mixed.
[0083]
Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, and polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and styrene-butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used alone or as a mixture of two or more. The addition amount of the binder is preferably 1 to 50% by weight, and particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.
[0084]
As the thickener, generally, polysaccharides such as carboxymethylcellulose and methylcellulose can be used alone or as a mixture of two or more. Further, it is desirable that a thickener having a functional group that reacts with lithium, such as a polysaccharide, be deactivated by, for example, methylation. The amount of the thickener added is preferably 0.5 to 10% by weight, particularly preferably 1 to 2% by weight, based on the total weight of the positive electrode or the negative electrode.
[0085]
Any material may be used as the filler as long as it does not adversely affect battery performance. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The amount of the filler is preferably 30% by weight or less based on the total weight of the positive electrode or the negative electrode.
[0086]
For the positive electrode and the negative electrode, the active material, the conductive agent and the binder are mixed with an organic solvent such as N-methylpyrrolidone and toluene, and the obtained mixed solution is applied on a current collector described in detail below. Then, by drying, it is suitably produced. Regarding the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as an applicator roll, screen coating, doctor blade method, spin coating, and bar coater, but is not limited thereto. It is not done.
[0087]
Any current collector may be used as long as it does not adversely affect the constructed battery. For example, as the current collector for the positive electrode, aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer, conductive glass, etc., in addition to the purpose of improving the adhesiveness, conductivity and oxidation resistance, aluminum A material obtained by treating the surface of copper, copper, or the like with carbon, nickel, titanium, silver, or the like can be used. Current collectors for negative electrodes include copper, nickel, iron, stainless steel, titanium, aluminum, calcined carbon, conductive polymers, conductive glass, Al-Cd alloy, etc., as well as adhesiveness, conductivity, and reduction resistance. For the purpose of properties, a product obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver, or the like can be used. These materials can be oxidized on the surface.
[0088]
Regarding the shape of the current collector, in addition to a foil shape, a film shape, a sheet shape, a net shape, a punched or expanded material, a lath body, a porous body, a foamed body, a formed body of a fiber group, and the like are used. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used. Among these current collectors, the positive electrode is an aluminum foil excellent in oxidation resistance, and the negative electrode is a reduction resistance, and excellent in electrical conductivity, inexpensive copper foil, nickel foil, iron foil, and It is preferable to use alloy foils containing some of them. Further, it is preferable that the foil has a rough surface roughness of 0.2 μm Ra or more, whereby the adhesion between the positive electrode active material or the negative electrode material and the current collector becomes excellent. Therefore, it is preferable to use an electrolytic foil because of having such a rough surface. In particular, an electrolytic foil subjected to a napping treatment is most preferable. Further, when the foil is coated on both sides, it is desired that the foils have the same or almost the same surface roughness.
[0089]
Non-aqueous electrolyte battery according to the present invention, the electrolyte, for example, before or after laminating the non-aqueous electrolyte battery separator and the positive electrode and the negative electrode are injected, and finally sealed with an exterior material It is preferably made. Further, in a non-aqueous electrolyte battery in which a positive electrode and a negative electrode are wound around a power generation element laminated via a non-aqueous electrolyte battery separator, the electrolyte is injected into the power generation element before and after the winding. Is preferred. As the liquid injection method, it is possible to inject liquid at normal pressure, but a vacuum impregnation method or a pressure impregnation method can also be used.
[0090]
Examples of the material of the outer package of the lithium secondary battery include nickel-plated iron, stainless steel, aluminum, and a metal-resin composite film. For example, a metal-resin composite film having a configuration in which a metal foil is sandwiched between resin films is preferable. Specific examples of the metal foil include, but are not limited to, aluminum, iron, nickel, copper, stainless steel, titanium, gold, silver, and other foils having no pinholes, and are preferably lightweight and inexpensive aluminum foil. As the resin film on the outside of the battery, a resin film having excellent piercing strength such as a polyethylene terephthalate film or a nylon film can be used, and as the resin film on the inside of the battery, a polyethylene film or a nylon film can be used. It is preferable to use a film that has a solvent resistance.
[0091]
The configuration of the lithium secondary battery is not particularly limited, and a coin battery or a button battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and a cylindrical battery having a positive electrode, a negative electrode, and a roll-shaped separator , A prismatic battery, a flat battery, and the like.
[0092]
【Example】
Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited by the following description, the test method and the positive electrode active material of the battery to be configured, the negative electrode material, the positive electrode, the negative electrode, the electrolyte , Separator, battery shape and the like are arbitrary.
[0093]
(Example 1)
2.0 L (liter) of water was put into the closed reaction tank, and 0.886 g of acetylene black was added. Further, a 32% aqueous sodium hydroxide solution was added so that the pH became 11.6. The solution was stirred at 1200 rpm using a stirrer equipped with paddle type stirring blades, and the temperature of the solution in the reaction tank was kept at 50 ° C. by an external heater. Argon gas was blown into the solution to reduce dissolved oxygen in the solution. Thus, the liquid reaction field where the carbon material coexists was adjusted.
[0094]
On the other hand, an aqueous solution in which a transition metal element as a raw material liquid was dissolved was prepared. Manganese sulfate pentahydrate aqueous solution, sulfuric acid, so that the manganese concentration becomes 0.0176 mol / L, the nickel concentration becomes 0.0176 mol / L, the cobalt concentration becomes 0.316 mol / L, and the hydrazine concentration becomes 0.0020 mol / L. It was obtained by mixing an aqueous solution of nickel hexahydrate, an aqueous solution of cobalt sulfate heptahydrate and an aqueous solution of hydrazine monohydrate.
[0095]
The raw material liquid was continuously dropped into the reaction tank at a flow rate of 2.9 mL / min while stirring the solution in the liquid reaction field. In synchronization with this, a 1.275 mol / L ammonia solution was dropped into the reaction vessel at a flow rate of 0.4 mL / min. From the start of the dropping to the completion of the reaction, a 32% aqueous sodium hydroxide solution was intermittently introduced so that the pH of the solution in the reaction tank was constant at 11.6 (± 0.05). The heater was intermittently controlled to keep the temperature of the reaction field constant at 50 ° C., and argon gas was directly blown into the liquid so that the reaction field became a reducing atmosphere. When the raw material liquid was dropped for 5 hours and 3 minutes, the dropping was terminated, and the reaction was completed for 30 minutes while maintaining the pH, temperature, and argon gas in the above-mentioned state.
[0096]
In the reaction field, a solid transition metal compound was formed in a state of being uniformly mixed with the acetylene black powder. A slurry containing the solid transition metal compound (Ni-Mn-Co coprecipitated precursor) was collected, washed with water, filtered, and the filter residue was collected, dried at 100 ° C overnight, and solidified. A mixture of the transition metal compound and acetylene black was obtained. This mixture was sieved to less than 75 μm using a sieve for the purpose of loosening. The contents of Ni, Mn and Co in the mixture were determined by elemental analysis.
[0097]
Lithium hydroxide monohydrate powder was added to the mixture at a ratio of Li / (Ni + Mn + Co) = 1.02 and mixed using a planetary kneader. This was filled in an alumina mortar and heat-treated. In the heat treatment, the temperature was raised to 1000 ° C. at 100 ° C./hr using an electric furnace under flowing dry air, kept at 1000 ° C. for 15 hours, then cooled to 200 ° C. at 100 ° C./hr, and then allowed to cool.
[0098]
The obtained powder was sieved to 75 μm using a sieve for the purpose of loosening lightly. As a result of the X-ray diffraction measurement, the powder obtained was α-NaFeO₂Mainly the type crystal structure. As a result of ICP composition analysis, LiMn_0.05Ni_0.05Co_0.90O₂The composition was confirmed. Further, it was confirmed that a trace amount of carbon ash was present.
[0099]
According to a laser diffusion type particle size distribution measurement (LA-910, manufactured by Horiba, Ltd.), the powder was found to have an average particle diameter (D₅₀) = 0.6 μm. At the same time, as a result of observation by a scanning electron microscope (SEM), it was observed that the oxide was mainly composed of primary particles of about 0.6 μm, and almost no secondary particles were observed. When the particle diameter was measured by approximating the shape of any of a plurality of primary particles to a sphere, the result almost coincided with the result of the particle size distribution.
[0100]
(Example 2)
Manganese sulfate pentahydrate (MnSO4) such that the manganese concentration becomes 0.0352 mol / L, the nickel concentration becomes 0.0352 mol / L, the cobalt concentration becomes 0.281 mol / L, and the hydrazine concentration becomes 0.0020 mol / L.₄) Aqueous solution, nickel sulfate hexahydrate aqueous solution (NiSO₄) Aqueous solution, cobalt sulfate heptahydrate (CoSO₄) Aqueous solution and hydrazine (NH₂NH₂A) A mixture of a solid transition metal compound and acetylene black was obtained in the same manner as in Example 1 except that a raw material liquid obtained by mixing an aqueous solution was used.
[0101]
Subsequently, in the same manner as in Example 1, mixed with LiOH and heat-treated, α-NaFeO₂LiMn mainly composed of a type crystal structure_0.10Ni_0.10Co_0.80O₂A composition was obtained.
[0102]
As a result of laser diffusion type particle size distribution measurement, the average particle diameter (D₅₀) = 0.8 μm, and the SEM observation result almost supported the result.
[0103]
(Example 3)
Manganese sulfate pentahydrate (MnSO4) such that the manganese concentration becomes 0.1055 mol / L, the nickel concentration becomes 0.1055 mol / L, the cobalt concentration becomes 0.1406 mol / L, and the hydrazine concentration becomes 0.0020 mol / L.₄) Aqueous solution, nickel sulfate hexahydrate aqueous solution (NiSO₄) Aqueous solution, cobalt sulfate heptahydrate (CoSO₄) Aqueous solution and hydrazine (NH₂NH₂A) A mixture of a solid transition metal compound and acetylene black was obtained in the same manner as in Example 1 except that a raw material liquid obtained by mixing an aqueous solution was used.
[0104]
Subsequently, in the same manner as in Example 1, mixed with LiOH and heat-treated, α-NaFeO₂LiMn mainly composed of a type crystal structure_0.30Ni_0.30Co_0.40O₂A composition was obtained.
[0105]
As a result of laser diffusion type particle size distribution measurement, the average particle diameter (D₅₀) = 0.8 μm, and the SEM observation result almost supported the result.
[0106]
(Example 4)
Manganese sulfate pentahydrate (MnSO4) such that the manganese concentration is 0.1723 mol / L, the nickel concentration is 0.1723 mol / L, the cobalt concentration is 0.0062 mol / L, and the hydrazine concentration is 0.0020 mol / L.₄) Aqueous solution, nickel sulfate hexahydrate aqueous solution (NiSO₄) Aqueous solution, cobalt sulfate heptahydrate (CoSO₄) Aqueous solution and hydrazine (NH₂NH₂A) A mixture of a solid transition metal compound and acetylene black was obtained in the same manner as in Example 1 except that a raw material liquid obtained by mixing an aqueous solution was used.
[0107]
Subsequently, in the same manner as in Example 1, mixed with LiOH and heat-treated, α-NaFeO₂LiMn mainly composed of a type crystal structure_0.49Ni_0.49Co_0.02O₂A composition was obtained.
[0108]
As a result of laser diffusion type particle size distribution measurement, the average particle diameter (D₅₀) = 1.0 μm, and the SEM observation result almost supported the result.
[0109]
(Comparative Example 1)
A solid transition metal compound was obtained using the same raw material liquid as in Example 2 except that acetylene black was not added to the reaction field and under the same conditions and operations.
[0110]
Subsequently, heat treatment is performed by mixing with LiOH in the same manner, and α-NaFeO₂LiMn mainly composed of a type crystal structure_0.10Ni_0.10Co_0.80O₂A composition was obtained.
[0111]
As a result of laser diffusion type particle size distribution measurement, the average particle diameter (D₅₀) = 8.0 μm. As a result of SEM observation, the morphology of the particles is clearly different from that of the above example, and as far as observed, all the particles have a form in which a plurality of primary particles are aggregated to form secondary particles. I was
[0112]
As described above, the solid transition metal compound having a small particle diameter (here, the Mn—Ni—Co coprecipitate precursor) formed in the liquid reaction field where the carbon material coexists is mixed with the Li compound. It was found that when heat treatment was performed, a positive electrode active material for a lithium secondary battery having a small average particle size (Li-Mn-Ni-Co composite oxide) was obtained.
[0113]
Next, in order to compare the performance of a lithium secondary battery using the obtained positive electrode active material, the LiMn obtained in the above Example 2 and Comparative Example 1 having the same composition was used._0.10Ni_0.10Co_0.80O₂Using the composition as a positive electrode active material, a lithium secondary battery having a designed capacity of 800 mAh shown in FIG. 1 was produced in the following procedure.
[0114]
The positive electrode active material, acetylene black and polyvinylidene fluoride (PVdF) were mixed at a weight ratio of 90: 5: 5, N-methylpyrrolidone was added as a dispersion medium, and the mixture was kneaded and dispersed to prepare a coating solution. PVdF was converted to a solid weight using a liquid in which a solid content was dissolved and dispersed. The coating solution was applied to both sides of a 20 μm-thick aluminum foil current collector, adjusted to a total thickness of 100 μm, and adjusted to 20 mg / cm 2.²A positive electrode sheet having a capacity of was prepared. The positive electrode sheet was cut into a shape having a width of 61 mm and a length of 445 mm, the positive electrode at the end of the sheet was removed, and an aluminum positive electrode terminal 3A having a thickness of 100 μm and a width of 3 mm was attached by ultrasonic welding to form a positive electrode plate.
[0115]
Using artificial graphite (particle diameter 6 μm) as a negative electrode carbon material, 2% by weight of styrene-butadiene rubber as a binder and 1% by weight of sodium salt of carboxymethylcellulose as a thickener are mixed, kneaded with purified water and applied. A liquid was obtained. The coating solution was applied to both sides of a copper foil current collector having a thickness of 10 μm, and adjusted to a total thickness of 90 μm, and then 12 mg / cm 2²A negative electrode sheet having the negative electrode carbon material was prepared. The negative electrode sheet was cut into a shape having a width of 63 mm and a length of 460 mm, the negative electrode at the end of the sheet was removed, and a nickel negative electrode terminal 3B having a thickness of 100 μm and a width of 3 mm was attached by resistance welding to form a negative electrode plate.
[0116]
The positive electrode plate and the negative electrode plate were dried under reduced pressure at 150 ° C. for 12 hours.
[0117]
A microporous membrane made of polypropylene, which was surface-modified with polyacrylate to improve electrolyte retention, was used as a separator, laminated in the order of negative electrode plate / separator / positive electrode plate, and wound into a flat shape to obtain electrode group 1.
[0118]
A metal resin composite film composed of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal adhesive polypropylene film (50 μm) is used as the outer package 2, and the open ends of the positive electrode terminal 3 </ b> A and the negative electrode terminal 3 </ b> B are exposed outside. The electrode group 1 was housed as described above, and the fusion allowance in which the inner surfaces of the metal-resin composite film faced each other was hermetically sealed except for a portion serving as a liquid injection hole.
[0119]
LiPF at a concentration of 1 mol / l in a solvent in which ethylene carbonate, propylene carbonate, diethyl carbonate and vinylene carbonate are mixed at a volume ratio of 50: 20: 30: 2.₆Was dissolved to obtain an electrolytic solution. After about 3 g of the electrolytic solution was injected from the injection hole, the injection hole portion was heat-sealed in a vacuum state to produce a flat nonaqueous electrolyte secondary battery 10 having a designed capacity of 800 mAh. At 20 ° C., constant voltage charging of 4.2 V was performed at 80 mA, and discharging was performed to 3 V at 80 mA.
[0120]
A lithium secondary battery was produced by the above procedure, a battery using the composition obtained in Example 2 was defined as a battery of the present invention, and a battery using the composition obtained in Comparative Example 1 was defined as a comparative battery.
[0121]
(Battery performance test)
A large number of the batteries of the present invention and comparative batteries were prepared, and the initial charge and discharge were performed for 10 cycles. Here, the charging conditions were a current of 0.1 ItA (10 hour rate), 4.2 V, constant current and constant voltage charging for 15 hours, and the discharging conditions were a current of 0.1 ItA (10 hour rate) and a final voltage of 3.0 V. At a constant current. The discharge capacity at the 10th cycle was defined as “initial discharge capacity (mAh)”.
[0122]
Subsequently, the high rate discharge performance was compared. After the initial 10 cycles of charge / discharge, the charging conditions were 0.2 ItA (5 hour rate), 4.2 V, 1.5 hour constant current / constant voltage charging, and the discharge conditions were current 10 ItA (0.1 hour rate), The final voltage was a constant current discharge of 2.50V. The ratio of the discharge capacity obtained at this time to the initial discharge capacity was calculated as a percentage and defined as "high-rate discharge performance (%)".
[0123]
Tables 1 and 2 summarize the above results.
[0124]
[Table 1]

[0125]
[Table 2]

[0126]
As is apparent from the above results, according to the production method of the present invention, it is possible to provide a positive electrode active material having an average particle diameter remarkably small and a production method thereof. Further, when the positive electrode active material of the present invention is used, a lithium secondary battery having a large high-rate discharge capacity can be provided.
[0127]
Note that the present invention can be embodied in various other forms without departing from the spirit or main characteristics thereof. Therefore, the above-described embodiments or examples are merely examples in all aspects and should not be construed as limiting. The scope of the present invention is defined by the claims, and is not limited by the text of the specification. Furthermore, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.
[0128]
【The invention's effect】
As described in detail above, according to the present invention, a positive electrode active material for a lithium secondary battery having a small average particle diameter can be provided. Further, a method for producing a positive electrode active material for a lithium secondary battery having a small average particle diameter can be provided. Further, a lithium secondary battery having a large discharge capacity can be provided.
[Brief description of the drawings]
FIG. 1 is a perspective view of a battery according to an embodiment.
[Explanation of symbols]
1 pole group
2 Exterior body
3A positive terminal
3B Negative terminal

Claims (12)

In a method for producing a positive electrode active material for a lithium secondary battery, comprising a step of forming a solid transition metal compound from an aqueous solution in which a transition metal element is dissolved in a liquid reaction field, the liquid reaction field is a carbon material A method for producing a positive electrode active material for a lithium secondary battery, characterized by coexisting. 2. The method according to claim 1, wherein the transition metal element includes at least nickel (Ni). The positive electrode active material for a lithium secondary battery according to claim 1, wherein the transition metal element is at least two kinds selected from the group consisting of nickel (Ni), manganese (Mn), and cobalt (Co). The method of manufacturing the substance. The method of claim 1, wherein the transition metal element includes at least nickel (Ni), manganese (Mn), and cobalt (Co). The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 4, wherein the carbon material can exist in a suspended state in the liquid reaction field. A method for producing a positive electrode active material for a lithium secondary battery, comprising mixing a solid transition metal compound and a Li compound and producing the mixture through a heat treatment step, wherein the carbon material is at least partially decomposed by the heat treatment step. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material is removed. A method for producing a positive electrode active material for a lithium secondary battery, comprising mixing the solid transition metal compound and a Li compound, and producing the mixture through a heat treatment step, wherein at least a part of the carbon material remains by the heat treatment step. The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 6, wherein: The positive electrode active material for a lithium secondary battery according to claim 1, wherein the solid transition metal compound is a solid transition metal compound having an average particle diameter (D ₅₀ ) of less than 1.0 μm. Production method. The positive electrode active material for a lithium secondary battery having an average particle diameter (D ₅₀ ) of less than 1.0 μm is produced by mixing the solid transition metal compound and a Li compound and subjecting the mixture to a heat treatment step. The method for producing a positive electrode active material for a lithium secondary battery according to any one of the above. The positive electrode active material for the lithium secondary battery has a alpha-NaFeO ₂ type crystal structure represented by the general _{formula; Li a Mn b Ni c Co} d O e ( where, 0 ≦ a ≦ 1.3, | c-b | ≦ 0.05, 0 <d <1, 1.7 ≦ e ≦ 2.3, b + c + d = 1, b ≠ 0, c ≠ 0) The method for producing a positive electrode active material for a lithium secondary battery according to claim 1. A positive electrode active material for a lithium secondary battery manufactured by the method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 1. A lithium secondary battery comprising: a positive electrode including the positive electrode active material for a lithium secondary battery according to claim 11; a negative electrode using a negative electrode material capable of inserting and extracting lithium ions; and a nonaqueous electrolyte.

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