JP5094144B2 - Positive electrode active material for lithium secondary battery and method for producing the same, positive electrode for lithium secondary battery, and lithium secondary battery - Google Patents

Description

  The present invention relates to a lithium secondary battery capable of high-power charge / discharge, a positive electrode active material that can constitute the lithium secondary battery, and a positive electrode.

  Lithium ion secondary batteries having high energy density are widely used as power sources for notebook computers and mobile phones. In recent years, lithium secondary batteries as power sources for power tools such as hybrid vehicles and electric tools have been developed, and higher output has been demanded.

Many lithium-ion secondary batteries currently have high energy density, and as a positive electrode active material, lithium cobaltate, lithium nickelate, spinel-type lithium manganate, or some of these transition metal parts with other elements. Substituted lithium complex oxides are often used. Among them, lithium cobaltate is often used in commercially available lithium ion secondary batteries, but an alternative is considered because the Co raw material is expensive. Lithium manganese cobalt nickel-based composite oxides typified by LiMn _1/3 Co _1/3 Ni _1/3 O ₂ have a good balance in terms of energy density, safety, and cost. Development of utilization as a positive electrode active material for use is underway (for example, Patent Documents 1 and 2).

  Many of the positive electrode active materials as described above are obtained by using a wet co-precipitation method (co-precipitation method) to obtain a precursor as a co-precipitate, and the co-precipitate and a lithium compound such as lithium hydroxide and lithium carbonate. It is manufactured by the method of mixing and baking. The form of the positive electrode active material obtained by such a manufacturing method is a secondary aggregate (secondary particle) obtained by agglomerating primary particles in a spherical shape, and the median diameter of the secondary particles is generally about 5 to 15 μm. With such a configuration, the packing density of the positive electrode active material in the electrode is increased to increase the capacity of the battery.

Lithium manganese cobalt nickel-based composite oxides such as LiMn _1/3 Co _1/3 Ni _1/3 O ₂ are often made into spherical secondary particles. For example, in Patent Document 3, manganese compounds and nickel compounds are used. And a cobalt compound are mixed, and the mixture is mixed with a lithium hydroxide solution to prepare a slurry. The slurry is spray-dried, and the powder formed is fired to form LiMn _1/3 Co _1/3 Ni _1/3. O ₂ is obtained. LiMn _1/3 Co _1/3 Ni _1/3 O ₂ obtained by this spray drying method also has secondary particles agglomerated in a spherical shape and is excellent in filling property at the electrode.

Japanese Patent Laid-Open No. 2002-201028 JP 2003-59490 A JP 2006-172753 A

  However, lithium secondary batteries used as power sources for power tools such as hybrid vehicles and electric tools are required to have higher output, and the above-described conventional positive electrode active materials are sufficient to meet such demands. Can not respond to. That is, for the above application, it is ideal to directly contact the individual primary particles with the conductive additive, but the shape of the secondary particles of the positive electrode active material obtained by the above production method is nearly spherical. Although the primary particles present on the surface of the secondary particles can come into contact with the conductive aid, the primary particles present inside do not come into direct contact with the conductive aid, resulting in a decrease in conductivity. Therefore, in the case of a shape close to a spherical shape, the proportion of primary particles that can be in direct contact with the conductive additive is reduced, which causes a problem in the conductivity of the secondary particles as a whole.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lithium secondary battery excellent in high output characteristics, a positive electrode for constituting the lithium secondary battery, and a positive electrode active for constituting the positive electrode. It is to provide a substance and a method for producing the same.

  The positive electrode active material for a lithium secondary battery of the present invention that has achieved the above object contains a lithium manganese cobalt nickel composite oxide represented by the following general formula (1), and is for the above lithium secondary battery. The positive electrode active material has at least secondary particles, the median diameter of the whole positive electrode active material for a lithium secondary battery is 1 to 10 μm, and the average circularity of the secondary particles is 0.05 or more and 0.00. In the X-ray diffraction by CuKα ray, the integrated intensity of the peak having the highest integrated intensity in the range of 2θ of 18 ° to 50 ° among the peaks other than the peak due to the lithium manganese cobalt nickel composite oxide. S1 and the integrated intensity of the peak appearing in the vicinity of 18.7 ° 2θ due to the lithium manganese cobalt nickel composite oxide as S2, the ratio S1 / 2 is characterized in that it is 0.145 or less.

_{Li A Mn B Co C Ni D} M E O F (1)
However, in said formula (1), M is elements other than Li, Mn, Co, Ni, and O, and 0.95 <= A <= 1.2, 0.3 <= B <0.36, 0.3. ≦ C <0.36, 0.3 ≦ D <0.36, B + C + D + E = 1, 1.8 ≦ F ≦ 2.2.

  In addition, the primary particle as used in the field of this invention is a particle which is surrounded by the surface and does not contain a boundary (grain boundary) in it, and a secondary particle is that these primary particles are aggregated in some form. It is an aggregate, and secondary particles have grain boundaries at the interface between primary particles.

  Moreover, the average circularity of the secondary particles and the median diameter of the positive electrode active material referred to in the present invention are measured by the methods described in the examples described later.

  When the average circularity referred to in the present invention is 1, it means that the positive electrode active material is a sphere (true sphere), and as the average circularity decreases, the shape of the positive electrode active material moves away from the sphere. Means.

  The first aspect of the method for producing a positive electrode active material for a lithium secondary battery according to the present invention is that, in X-ray diffraction by CuKα rays, the half widths of all peaks appearing in 2θ in the range of 20 ° to 55 ° are The raw material is pulverized and mixed with a pulverization aid until the temperature reaches 0.75 ° or more, and a first step of forming a composite containing Mn, Co, and Ni, and the composite obtained in the first step, It has the 2nd process of baking in an oxygen containing atmosphere with a compound, It is characterized by the above-mentioned.

  And the 2nd aspect of the manufacturing method of the positive electrode active material for lithium secondary batteries of this invention is a peak derived from the compound of Li in which 2 (theta) appears in the range of 20 degrees to 55 degrees in the X-ray diffraction by CuK alpha ray. The first step, in which the raw material is pulverized and mixed with the pulverization aid until the half width of all the peaks except 0.75 is 0.75 ° or more, and a composite containing Mn, Co, Ni and Li is formed, and the first step It has the 2nd process of baking the said composite obtained by above in oxygen-containing atmosphere.

  The positive electrode active material for a lithium secondary battery of the present invention can be produced by the production methods of the first aspect and the second aspect. Here, the “composite” refers to a mixture, a compound, a complex in which two or more substances are somehow complexed at the particle level, and all of them.

  Moreover, the positive electrode for lithium secondary batteries which has the positive electrode active material for lithium secondary batteries of this invention, and the lithium secondary battery which has this positive electrode for lithium secondary batteries are also contained in this invention.

  In order to improve the high output characteristics of the lithium secondary battery, the voltage value corresponding to the current value corresponding to 1C, 5C and 10C is plotted on a two-dimensional coordinate composed of current (I) versus voltage (V), Examples thereof include suppressing the obtained resistance value [(ΔV / ΔI) = DCR] to be low and suppressing an increase in DCR after repeated charge and discharge. As a result of intensive studies, the present inventors have found that the form of the positive electrode active material for a lithium secondary battery having the lithium manganese cobalt nickel composite oxide represented by the general formula (1) and having at least secondary particles is described above. It has been found that, by controlling in this way, in a lithium secondary battery using a positive electrode having such a positive electrode active material, the DCR can be kept low, and an increase in DCR after repeated charge and discharge can be suppressed. And according to the manufacturing method of this invention, it discovered that the positive electrode active material for lithium secondary batteries of this invention which has said form was able to be manufactured, and came to complete this invention.

  The battery having “high output characteristics” in the present invention is specifically a battery that can draw out a high capacity when a current having a high current density is passed, and a sufficient capacity can be obtained at a high rate of about 10 C, for example. For this purpose, it is necessary to reduce the DCR and suppress its rise.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium secondary battery excellent in the high output characteristic, the positive electrode for comprising this lithium secondary battery, the positive electrode active material for comprising this positive electrode, and its manufacturing method can be provided.

  The positive electrode active material for a lithium secondary battery of the present invention is mainly composed of a lithium manganese cobalt nickel composite oxide represented by the above general formula (1). By using a positive electrode having a positive electrode active material composed of the above lithium manganese cobalt nickel composite oxide, it is possible to improve the high output characteristics and increase the capacity of the battery.

  In the general formula (1), the amount A of Li is 0.95 ≦ A ≦ 1.2. If A is less than 0.95, subphases other than the target positive electrode active material are likely to be generated, the capacity is inferior, and the charge / discharge cycle characteristics of the battery are also deteriorated. On the other hand, when A is larger than 1.2, coarse particles are likely to be produced when fired, and the pH of the positive electrode active material powder is also increased. Therefore, a composition containing a positive electrode active material used in manufacturing a positive electrode It becomes difficult to prepare an object (paint). Moreover, in the said General formula (1), B, C, D, E, and F showing the quantity of Mn, Co, Ni, M, and O are 0.3 <= B <0.36, 0.3 <= C <. 0.36, 0.3 ≦ D <0.36, B + C + D + E = 1, 1.8 ≦ F ≦ 2.2. In B, C, and D representing the amounts of Mn, Co, and Ni, an error of about 0.33 to 10% in which Mn, Ni, and Co are approximately 1: 1: 1 in molar ratio is included in the present invention. It is. In the general formula (1), M represents an element other than Li, Mn, Co, Ni and O, and the amount E is 0 ≦ E ≦ 0.2. If E exceeds 0.2, impurities may be generated or the capacity may be reduced. As the element M, Ti, Zr, Zn or the like is preferably used.

  The positive electrode active material of the present invention has primary particles and secondary particles such as the above lithium manganese cobalt nickel composite oxide, and among these, the average circularity of the secondary particles is 0.05 or more and 0.6. It is as follows. Basically, the lower the average circularity, the better. However, secondary particles such as 0.05 or less are difficult to obtain unless the primary particles are smaller than 100 nm or the surface of the primary particles has irregularities. Such an active material has poor powder filling properties, and may have poor battery safety due to its large surface area.

  The lithium manganese cobalt nickel composite oxide produced by the conventional coprecipitation method is obtained as a spherical aggregate (secondary particle). In the positive electrode having such a lithium manganese cobalt nickel composite oxide, although the filling property of the positive electrode active material is improved, the conductive auxiliary agent used to ensure conductivity is only from the outside of the spherical aggregate. The primary particles of the lithium manganese cobalt nickel composite oxide that are in contact with each other and exist inside the spherical aggregate cannot contact the conductive assistant, and cannot provide sufficient conductivity. Therefore, in the battery using the lithium manganese cobalt nickel composite oxide that is a spherical aggregate as described above as the positive electrode active material, the DCR at the initial stage of battery manufacture becomes high. In addition, in a battery using a positive electrode active material that is a spherical aggregate, since the conductive additive can be contacted only from the outside, the electron diffusion path may be biased from the whole positive electrode. When charging / discharging is repeated in a battery using such a positive electrode, it is thought that the current flows locally and the deterioration of the positive electrode active material is accelerated. In such a battery, charging / discharging of the battery is repeated in addition to the initial DCR. The rate of increase of DCR due to increases.

  On the other hand, the positive electrode active material of the present invention contains many primary particles present alone, and the secondary particles have an average circularity of 0.6 or less, for example, a chain-like shape or It has an indefinite shape such as a complicated shape with many irregularities and a spindle shape. Therefore, in the positive electrode active material of the present invention, the primary particles can directly contact with the conductive auxiliary agent, and the secondary particles can contact with the conductive auxiliary agent not only from the outside but also from the inside. That is, the positive electrode active material of the present invention has primary particles and secondary particles, and the secondary particles have the above average circularity, so that they can come into contact with the conductive additive in the positive electrode. The number of active material primary particles (primary particles present alone and primary particles in secondary particles) can be increased, and conductivity can be imparted more uniformly over the entire positive electrode. Therefore, according to the positive electrode active material of the present invention, it is possible to suppress the DCR at the initial stage of battery manufacture, further suppress an increase in DCR after repeated charge and discharge, and to provide a battery with excellent high output characteristics. Can do.

  The positive electrode active material of the present invention has an overall median diameter of 1 μm or more, preferably 2 μm or more and 15 μm or less, preferably 10 μm or less, more preferably 7 μm or less. By using the median diameter of the whole positive electrode active material as described above, the uniformity of the dispersion of the positive electrode active material and the conductive additive in the positive electrode (positive electrode mixture layer) is increased, and the battery using the positive electrode active material It is possible to suppress an increase in the DCR after the initial manufacturing and the repeated charging and discharging.

  The average particle diameter of the primary particles constituting the positive electrode active material is preferably 0.05 μm or more, more preferably 0.2 μm or more, preferably 3 μm or less, more preferably 2 μm or less. In addition, the average particle diameter of the primary particle here is equivalent to the area of each primary particle (or primary particle constituting the selected particle if the selected particle is a secondary particle) by randomly selecting particles from the SEM image of the active material. The arithmetic average of diameters. Note that at least 100 primary particles are selected.

Moreover, the positive electrode active material of the present invention preferably has a volume resistivity of 5 × 10 ⁵ Ω · cm or less when compressed at a pressure of 39.2 MPa (400 kgf / cm ² ), and 1 × 10 ⁵ Ω. More preferably, it is cm or less, and further preferably 3 × 10 ⁴ Ω · cm or less. If the volume resistivity of the positive electrode active material is too high, there is a possibility that rate characteristics and low-temperature characteristics as a battery may be deteriorated. In addition, it is preferable that the minimum of the volume resistivity of the positive electrode active material measured on the said conditions is 1 * 10 < ² > ohm * cm, for example. Below this lower limit, the safety of the battery may be impaired.

  In the X-ray diffraction (CuKα), the positive electrode active material of the present invention has a peak other than the peak caused by the lithium manganese cobalt nickel composite oxide represented by the general formula (1) in the range of 2θ of 18 ° to 50 °. Among them, the integrated intensity S1 of the peak with the highest integrated intensity, and the integrated intensity S2 of the peak where 2θ caused by the lithium manganese cobalt nickel composite oxide represented by the general formula (1) appears at about 18.7 ° The ratio S1 / S2 is 0.145 or less. When the value of S1 / S2 exceeds this value, the capacity is lowered, and there is a possibility that the direct current resistance when the battery is made increases.

  A positive electrode active material composed of a lithium manganese cobalt nickel composite oxide represented by the above general formula (1), having the above-described form, satisfying the above S1 / S2 value, and preferably having the above volume resistivity Can be produced by the method of the present invention having the following first and second steps. Further, according to the method of the present invention, the average particle diameter of primary particles in the positive electrode active material can be controlled within the above-mentioned preferable range.

  The first step of the method of the present invention is a step of forming a composite containing at least Mn, Co, and Ni by adding a grinding aid to the raw material and grinding and mixing.

  In the first step, first, a compound containing Mn (hereinafter referred to as “manganese compound”), a compound containing Co (hereinafter referred to as “cobalt compound”), a compound containing Ni (hereinafter referred to as “nickel compound”), and A compound containing Li (in the case of obtaining a composite containing Li; hereinafter referred to as “lithium compound”) is measured at a predetermined ratio and processed by a pulverizing mixer.

  As the pulverizer, one that is subjected to strong compression and shear stress is desirable. The type is not particularly limited, but examples include “dry attritor”, “wet attritor”, “dynamic mill” manufactured by Mitsui Mining Co., Ltd .; “stirring ball mill ATR” manufactured by Hosokawa Micron Corporation; ";

  Manganese compounds, cobalt compounds, nickel compounds and lithium compounds as raw materials are oxides, hydroxides, oxyhydroxides, carbonates, basic carbonates, nitrates, chloride salts, sulfates, organic acid salts, etc., respectively However, since mineral salts generate harmful gases during firing, industrially preferred are oxides, hydroxides, oxyhydroxides, carbonates, and basic carbonates. Each of these raw materials may be used alone or in combination of two or more. Further, it is not necessary to use a manganese compound, a cobalt compound, a nickel compound, and a lithium compound separately, and a composite such as a coprecipitate containing two or more elements of a cobalt element, a manganese element, a nickel element, and a lithium element. Or a compound containing two or more elements of cobalt element, manganese element, nickel element and lithium element. In short, cobalt element, manganese element, nickel element and lithium element may be used. The necessary amount may be included. Regarding the lithium compound, it is not necessary to pulverize and mix together with the manganese compound, cobalt compound, and nickel compound, and the lithium compound may be added after pulverizing and mixing the manganese compound, cobalt compound, and nickel compound. Further, the method of adding the lithium compound is not particularly limited, and the lithium compound may be pulverized and mixed in the same manner as that applied to the manganese compound, cobalt compound, and nickel compound, or dissolved in water or an organic solvent, and manganese. You may mix with the thing which the compound, the cobalt compound, and the nickel compound grind | pulverized and mixed.

  In the first step, unlike just pulverizing and mixing, pulverizing media (balls if a ball mill is used as a pulverizing mixer, meaning pulverizing parts such as disk-shaped rings and rotors if mechanomicros) and pulverizing By applying very strong energy such as compression and shear stress to the powder on the walls of the mixing vessel and grinding media, each raw material powder becomes amorphous and promotes the mechanochemical reaction at the interface. The mixed powder is produced while generating an intermediate phase (amorphous phase). The intermediate phase that has caused a mechanochemical reaction grows as the nucleus of the lithium cobalt nickel manganese composite oxide during firing in the second step described later.

  In the first step, it is necessary to add a grinding aid in order to prevent reaggregation of the powder during grinding. Depending on the properties of the powder, the powder may re-agglomerate at the time of pulverization or adhere to the container of the pulverization mixer so that the pulverization does not proceed. By adding a grinding aid, fluidity is generated in the powder, re-aggregation and sticking can be prevented, energy during grinding can be efficiently transmitted to the powder, and a mechanochemical reaction can be promoted. Further, the pulverization may be carried out in water or an organic solvent, and the reaction may be carried out as wet pulverization. However, dry pulverization does not require drying of the pulverization obtained after pulverization, which is advantageous in terms of production cost. In the method of the present invention, one kind of this grinding aid may be used, or a plurality thereof may be used in combination. In particular, when performing the mixing and pulverization in a dry method, a premix step may be inserted before the first step in order to prevent uneven mixing due to adhesion of the raw material to the container.

  Examples of the grinding aid include water, silicon oil, acetone, fatty acids (maleic acid, oleic acid, caprylic acid, stearic acid, etc.), metal alkoxides (tetraethoxysilane, etc.), amines (triethanolamine, etc.), Glycols (ethylene glycol, propylene glycol, etc.), alcohols (methanol, ethanol, 1-butanol, etc.), fatty acid salts (sodium stearate, etc.), amine acetate, colloidal silica, carbon black, fine mineral powders (kaolin, talc, etc.) ), Cationic surfactants (such as dodecyl ammonium chloride), nonionic surfactants (such as polyoxyethylene sorbitan monolaurate), inorganic salts (such as sodium carbonate, sodium chloride, sodium silicate), water-soluble polymers (such as Carboxylate etc.), and sodium tripolyphosphate.

  The addition amount of the grinding aid is usually 0.01 parts by weight or more and 30 parts by weight or less in the dry grinding with respect to 100 parts by weight of the mixture used for grinding in the first step. It is preferable that they are 1 mass part or more and 10 mass parts or less. When a large amount of liquid grinding aid is used, so-called wet grinding is achieved. In this case, it is preferable that it is 0.01 mass part or more with respect to 100 mass parts of mixtures used for the grinding | pulverization at a 1st process, and it is preferable that it is 100000 mass parts or less with respect to 100 mass parts of mixtures. If there are too many grinding aids, it is disadvantageous in terms of cost, and if a large amount of a liquid with a too high viscosity is used, the reaction becomes difficult to proceed and causes impurities.

  The pulverization conditions in the first step vary depending on the pulverization mixer to be used, and thus cannot be generally limited, but can be determined by whether the powder obtained by pulverization and mixing forms an amorphous phase. A compound containing an element that diffuses quickly during firing, such as Li element, is not a problem, but the crystallinity is inferior after firing so that the peaks of raw materials such as Co, Mn, and Ni can be clearly confirmed by X-ray diffraction after pulverization. In the X-ray diffraction (CuKα) profile of the powder after pulverization, 2θ is 20 ° to 55 ° among the peaks of the respective raw materials due to the raw materials containing Co, Mn, and Ni. In this range, the half width of the peak with the smallest half width needs to be 0.75 ° or more. Therefore, in the first step, when the raw material does not contain a Li compound, the raw material is pulverized until the half width of all peaks appearing in the range of 2θ in the range of 20 ° to 55 ° is 0.75 ° or more. And a mixture containing Mn, Co and Ni may be formed. When the raw material contains a Li compound, the peak where 2θ appears in the range of 20 ° to 55 ° is derived from the Li compound. The raw material may be pulverized and mixed with the pulverization aid so that the peak other than the peak to have the above half width is formed to form a composite containing Mn, Co, Ni and Li. In addition, about the peak derived from the compound of Li, a half value width may be smaller than this, and of course, a half value width may be 0.75 degree or more.

  The second step of the method of the present invention is a firing step in which the powder obtained in the first step is fired in an oxygen-containing atmosphere. When the composite formed in the first step contains a necessary amount of Li, the above compound may be fired as it is, but when it does not contain Li or the content of Li is low, it is fired together with the Li compound. A composite oxide having a desired composition is obtained.

  For firing the powder, for example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln, or the like can be used. When the firing process is divided into three steps of temperature rise, maximum temperature hold, and temperature drop, the second maximum temperature hold portion is not necessarily one time, and two or more steps are included depending on the purpose. The temperature may be raised and the maximum temperature maintained, with a crushing step that means eliminating aggregation to the extent that the secondary particles are not destroyed, or a crushing step that means crushing to primary particles or even fine powder. The temperature lowering process may be repeated twice or more.

  In the temperature raising step, the temperature in the furnace is usually raised in the range of 1 to 20 ° C./min. If the heating rate is too fast, the furnace temperature cannot follow the set temperature, and if it is too slow, it is industrially disadvantageous.

  The baking temperature is preferably 400 ° C. or higher and 1200 ° C. or lower, and more preferably 600 ° C. or higher and 1000 ° C. or lower. The holding time after raising the temperature to the firing temperature is preferably 0.5 to 50 h, more preferably 4 to 20 h. If the holding time is too long, sintering between the powders proceeds and subsequent crushing becomes difficult, and if it is too short, a powder with high crystallinity cannot be obtained.

  Although the positive electrode active material of the present invention is obtained through the second step, a crushing step may be added after the second step for the purpose of loosening light agglomeration due to baking of the positive electrode active material after baking.

  The positive electrode active material of the present invention obtained by the method of the present invention can be preferably used as an active material for a positive electrode of a high power lithium secondary battery.

  The positive electrode for a lithium secondary battery of the present invention may have the positive electrode active material for a lithium secondary battery of the present invention. For example, the positive electrode for a lithium secondary battery of the present invention may be provided on one or both sides of a current collector. What has the positive mix layer containing a positive electrode active material is mentioned.

  The positive electrode mixture layer in the positive electrode is formed by layering the positive electrode mixture having at least the positive electrode active material of the present invention on the current collector. The positive electrode mixture layer preferably contains a binder and a conductive additive. By including a conductive additive and a binder in the positive electrode mixture layer, the electronic conductivity and strength of the positive electrode can be increased.

  As the conductive additive for the positive electrode, any inorganic material or organic material can be used as long as it is chemically stable in the battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black (trade name), channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fiber and metal fiber; aluminum Metal powder such as powder; carbon fluoride; zinc oxide; conductive whisker made of potassium titanate; conductive metal oxide such as titanium oxide; organic conductive material such as polyphenylene derivative; These conductive assistants may be used alone or in combination of two or more. Among these, carbon black is particularly preferable. Since carbon black has a small average particle diameter of 0.01 to 1 μm, it can be filled in the gaps between the positive electrode active material particles, and a space not originally involved in the battery capacity can be used, so without reducing the amount of the positive electrode active material particles This is because electron conductivity can be imparted.

As the binder for the positive electrode, any thermoplastic resin or thermosetting resin can be used as long as it is chemically stable in the battery. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin) , Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrif Oroechiren copolymer (ECTFE), vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene copolymer, ethylene - acrylic acid copolymer or its Na ⁺ Ionic cross-linked product, ethylene-methacrylic acid copolymer or its Na ⁺ ionic cross-linked product, ethylene-methyl acrylate copolymer or its Na ⁺ ionic cross-linked product, ethylene-methyl methacrylate copolymer or its Na ⁺ ionic cross-linked product Etc. These binders may be used alone or in combination of two or more. Among these, PVDF and PTFE are particularly preferable. This is because the binding force can be exerted in a small amount.

  For the positive electrode, for example, a positive electrode mixture obtained by appropriately adding a conductive additive or a binder to the positive electrode active material is dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) (the binder is dissolved in the solvent). It may be prepared by forming a slurry-like or paste-like composition and applying the composition to a current collector to form a band-shaped molded body (positive electrode mixture layer). However, the manufacturing method of the positive electrode is not limited to the above method, and may be manufactured by other methods. The thickness of the positive electrode mixture layer formed on the current collector is usually 20 to 100 μm.

  The material for the current collector of the positive electrode is not particularly limited as long as it is an electron conductor that is chemically stable in the constructed battery. For example, in addition to aluminum or aluminum alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of aluminum, aluminum alloy, or stainless steel can be used. . Among these, aluminum or an aluminum alloy is particularly preferable. This is because they are lightweight and have high electron conductivity. For the current collector, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like made of the above material is used. In addition, the surface of the current collector can be roughened by surface treatment. Although the thickness of a collector is not specifically limited, Usually, it is 1-500 micrometers.

  In the positive electrode mixture layer, the positive electrode active material is contained in an amount of 80% by mass to 98% by mass with respect to the total mass of the positive electrode active material, the binder, and the conductive additive, and the binder is contained in an amount of 1% by mass to 10% by mass. It is preferable to include 1% or more and 19% or less of a conductive assistant. This is because, within this range, the content of the binder that does not directly participate in the electrode reaction is small, so that the capacity of the electrode can be increased.

  As long as the lithium secondary battery of the present invention has the positive electrode (the positive electrode of the present invention) having the positive electrode active material of the present invention, there are no particular restrictions on the other configurations and structures, and conventionally known lithium secondary batteries Various configurations / structures adopted in can be applied.

  As the negative electrode, for example, a negative electrode mixture having a negative electrode active material and a binder can be formed into a layer shape (negative electrode mixture layer) on a current collector. Examples of the negative electrode active material for the negative electrode include graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, Si, and Sn such as Sn. An alloyable metal or an alloy thereof is used. Metal lithium or lithium-aluminum alloy can also be used.

As the binder for the negative electrode, various binders exemplified as the binder for the positive electrode can be used. Among them, styrene butadiene rubber, PVDF, ethylene-acrylic acid copolymer or its Na ⁺ ion crosslinked body, ethylene -A methacrylic acid copolymer or its Na ⁺ ion crosslinked product, an ethylene-methyl acrylate copolymer or its Na ⁺ ion crosslinked product, an ethylene-methyl methacrylate copolymer or its Na ⁺ ion crosslinked product are particularly preferred.

  Although it is not necessary to add a conductive support agent to the negative electrode mixture layer, it may be added. As the conductive aid for the negative electrode, various conductive aids exemplified as the conductive aid for the positive electrode can be used.

  In the negative electrode, for example, a negative electrode mixture obtained by appropriately adding a binder (and optionally a conductive auxiliary agent) to the negative electrode active material is dispersed in a solvent such as NMP (the binder is dissolved in the solvent). Or a slurry-like or paste-like composition, and the composition is applied to a current collector and formed into a strip-shaped molded body (negative electrode mixture layer). However, the manufacturing method of the negative electrode is not limited to the above method, and may be manufactured by other methods. The thickness of the negative electrode mixture layer formed on the current collector is usually 20 to 100 μm.

  The material of the current collector of the negative electrode is not particularly limited as long as it is an electron conductor that is chemically stable in the constructed battery. For example, in addition to copper or copper alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of copper, copper alloy, or stainless steel can be used. . Among these, copper or a copper alloy is particularly preferable. This is because they are not alloyed with lithium and have high electron conductivity. For the current collector of the negative electrode, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, etc. made of the above-mentioned materials, etc. Is used. In addition, the surface of the current collector can be roughened by surface treatment. Although the thickness of a collector is not specifically limited, Usually, it is 1-500 micrometers.

  As the non-aqueous electrolyte, an electrolyte salt dissolved in a solvent can be used. Examples of the solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone, 1, 2 -Dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, Sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propane sultone, etc. One aprotic organic solvent mixed solvent or a mixture of two or more can be used. In these, the mixed solvent of EC, MEC, and DEC is preferable, and it is especially preferable that this mixed solvent contains 15 volume% or more and 80 volume% or less of DEC with respect to the whole volume of a mixed solvent. This is because within this range, the stability of the solvent during high-voltage charging can be enhanced while maintaining the low-temperature characteristics and charge / discharge cycle characteristics of the battery.

As the electrolyte salt related to the non-aqueous electrolyte, a salt of a fluorine-containing compound such as lithium perchlorate, lithium organic boron, trifluoromethanesulfonate, imide salt, or the like is preferably used. Specific examples of the electrolyte salt, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F2 _{n + 1} SO ₃ (n ≧ 2), LiN (Rf ₃ OSO ₂ ) ₂ [where Rf Represents a fluoroalkyl group. These may be used alone or in combination of two or more. Among these, LiPF ₆ and LiBF ₄ are particularly preferable because of good charge / discharge characteristics. This is because these fluorine-containing organic lithium salts have a large anionic property and are easily ion-separated, so that they are easily dissolved in the solvent.

  The material and shape of the separator are not particularly limited, and those having insulating properties, high ion permeability, low electrical resistance, and high liquid retention are preferable. Usually, a separator having a thickness of 10 to 300 μm and a porosity of 30 to 80% is used. Further, the pore diameter of the separator is preferably such that the active material, the conductive auxiliary agent, the binder, and the like detached from the electrode do not pass through, for example, 0.01 to 1 μm.

  It is preferable that the separator has a shutdown function in which the separator is softened or melted according to heat generated by an internal short circuit (100 to 140 ° C.), whereby the pores of the separator are closed to cut off the current. This is because the safety of the battery can be further improved. Specifically, for example, it is preferable to use a microporous film or nonwoven fabric made of polyolefin such as polyethylene, polypropylene, or polymethylpentene as a separator because a shutdown function can be provided. Further, by using a separator having a multilayer structure constituted by laminating a plurality of microporous films and non-woven fabrics of the above materials or laminating a plurality of microporous films or non-woven fabrics, in a high temperature environment. The reliability of the battery when used can be further increased.

  As a battery case for storing these battery parts, a metal square case, a metal cylindrical case, a laminate case made of a laminate film, and the like are preferably used.

  Since the lithium secondary battery of the present invention is compatible with high output charge / discharge and has a high capacity, taking advantage of these characteristics, power supply applications for power tools such as hybrid vehicles and electric tools are being used. Therefore, it can be preferably used in applications where a conventionally known lithium secondary battery is applied.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

  The evaluation method used in this example is as follows.

<Volume resistivity of positive electrode active material>
Using a volume resistivity measuring device ("Lorestar GP powder low-efficiency measurement system MCP-PD51" manufactured by Dia Instruments Co., Ltd.), the sample weight of the positive electrode active material is 2 g, and a probe unit for powder (four-probe method, cylinder part) The volume resistivity (Ω · cm) of the powder under various pressures was measured using a diameter of 20 mm, and the value of the volume resistivity under a pressure of 39.2 MPa was determined.

<Particle size of positive electrode active material>
The median diameter and 90% integrated diameter (volume basis) of the positive electrode active material were measured as follows.
After calcination, the positive electrode active material obtained by crushing is measured using a laser diffraction / scattering particle size distribution measuring device (“LA920” manufactured by Horiba, Ltd.) as a measuring device, and a 0.1% sodium hexametaphosphate aqueous solution as a dispersion medium. The positive electrode active material was added to the dispersion medium, and after ultrasonic dispersion for 3 minutes, the particle size of the positive electrode active material in the dispersion medium was measured. The particle size distribution was calculated by volume standard, and the relative refractive index value was 1.24. The relative refractive index was set so that the particle diameter obtained by observing the particles of the positive electrode active material with a micrograph such as SEM coincided with the particle diameter obtained by laser diffraction. In the measurement in this example, the imaginary number term is not included in the relative refractive index.

<Average circularity of secondary particles of positive electrode active material>
First, the secondary particles are mounted thinly on the sample stage, and the secondary particles are not solidified in the particle image obtained by observation with a scanning electron microscope (SEM). 100 or more secondary particles were selected at random, and the circularity of each particle was determined. The circularity is obtained from the area equivalent diameter and the perimeter of the two-dimensional projection image, and the average circularity is the arithmetic average of the circularity of all the sampled secondary particles. That is, the average circularity is obtained from the following formula (2).
Average circularity = Σ [4π × area / (perimeter length) ² ] ÷ number of sampled secondary particles (2)

  In the above formula (2), “perimeter” refers to the perimeter of the sampled secondary particle image. Since it was difficult to photograph 100 or more particles in one photo, a sufficient number of images were taken until 100 or more photos could be taken. In addition, the particle | grains which exist only by the primary particle are not counted for measurement. The actual measurement was performed by obtaining the circularity (circularity 3) of the photographed image using commercially available image analysis software (“A Image-kun Ver. 2.20” manufactured by Asahi Kasei Corporation).

<Identification of crystal phase of positive electrode active material>
About the positive electrode active material, the X-ray diffraction (XRD) measurement was performed and the crystal phase was specified.

<Elemental analysis of positive electrode active material>
The element contained in the positive electrode active material was quantified by ICP (Inductively Coupled Plasma) emission analysis.

<Evaluation of initial discharge capacity of lithium secondary battery>
The initial discharge capacity means the discharge capacity at the first cycle in the charge / discharge cycle test. A lithium secondary battery (bipolar cell) for charge / discharge capacity measurement was first charged to a voltage of 4.3 V at a constant current density of 0.2 mA / cm ² at a temperature of 25 ° C. and then fixed at 4.3 V. Constant current constant voltage charging for voltage charging was performed for 8 hours. The lithium secondary battery after completion of charging was allowed to stand for 5 minutes, and then discharged to a final voltage of 2.6 V with a constant current of 0.2 mA / cm ² . The discharge capacity per gram of the positive electrode active material at this time was defined as the initial discharge capacity of the lithium secondary battery.

<Initial DC resistance (DCR) measurement>
For a lithium secondary battery (laminated cell) for measuring direct current resistance (DCR), Ohm's law is calculated from the voltage change after a current equivalent to 1C, 5C, or 10C is applied for 5 seconds after the charging depth is 50%. The DCR was determined by A DCR before a pulse cycle test described later is defined as an initial DCR.

<Pulse cycle test>
For a lithium secondary battery (laminate cell) for DCR measurement, a charge cycle of 10C for 10 seconds was performed after a charge depth of 50% was charged, and a pulse cycle test was repeated for 10 cycles. The DCR of the lithium secondary battery after 100,000 cycles was measured by the same method as the above initial DCR measurement, and the DCR increase rate (%) was obtained by the following formula.
DCR increase rate (%)
= 100 x (DCR after 100,000 cycles-initial DCR) / initial DCR

Example 1
<Preparation of positive electrode active material>
[Premix process]
Co (OH) ₂ , Ni (OH) ₂ , MnO _2, and Li ₂ CO ₃ in molar ratio (1/3) :( 1/3) :( 1 / 3): A total of 2 kg was added so as to be (1.05 / 2), and mixed at 1850 rpm for 5 minutes. The powder color was a reddish mouse color and was uniformly mixed. Hereinafter, this mixture is referred to as premix powder, and refers to the premix powder produced by the method of Example 1 unless otherwise specified.

[First step]
“Attritor MA1D” manufactured by Mitsui Mining Co., Ltd. was charged with 11.9 kg of 10 mmφ ZrO ₂ beads, 250 g of premix powder, and 3 parts by mass of propylene glycol with respect to 100 parts by mass of premix powder, and 300 rpm For 1 h to obtain a powder. The color of the resulting powder changed from a red mouse color to a dark brown color, indicating that it had reacted. An X-ray diffraction profile obtained by XRD measurement of this powder is shown in FIG. As the amorphization of the powder progressed, the half-value width of the peak with the smallest half-value width was 1.52 ° in the peak excluding the peak caused by the Li raw material in the range of 2θ between 20 ° and 55 °. .

[Second step]
In a box furnace, 200 g of the powder obtained in the first step was heated at 10 ° C./min while flowing air at 1 L / min, and baked at 1000 ° C. for 6 hours. The obtained powder was crushed to obtain a layered compound (positive electrode active material) of Li _1.04 Mn _0.33 Co _0.33 Ni _0.34 O ₂ .

  FIG. 2 shows an X-ray diffraction profile obtained by XRD measurement of the obtained positive electrode active material. As can be seen from FIG. 2, the positive electrode active material has a clear peak in the X-ray diffraction profile, All of the R-3m crystal groups could be indexed. No impurity phase was observed.

Further, in the obtained positive electrode active material, the volume resistivity when compressed at a pressure of 39.2 MPa was 2.5 × 10 ⁴ Ω · cm. The median diameter of the positive electrode active material was 3.5 μm, and the 90% cumulative diameter (hereinafter referred to as “D ₉₀ ”) was 6.3 μm. Furthermore, the average circularity of the secondary particles of the positive electrode active material was 0.55. In addition, the SEM photograph of the obtained positive electrode active material is shown in FIG.

<Preparation of lithium secondary battery for initial discharge capacity measurement>
The above positive electrode active material, PVDF as a binder, graphite and acetylene black as conductive aids are mixed at a mass ratio of 86: 3: 9: 2 to obtain a positive electrode mixture, A slurry containing a positive electrode mixture was prepared by dispersing in NMP. This slurry was applied to one side of an Al foil serving as a current collector, dried, pressed with a rolling roll, and further dried to produce an electrode. This electrode was punched out with a size of 11 mmφ to obtain a positive electrode.

Using the above positive electrode, metallic lithium foil as the counter electrode, polyethylene microporous membrane as the separator, and 1M LiPF ₆ EC / EMC solution [mixed solvent of ethylene carbonate, (EC) and ethyl methyl carbonate (EMC) as the electrolyte A lithium secondary battery (bipolar cell) for measuring initial discharge capacity was prepared using each (solution in which 1 mol / l LiPF ₆ was dissolved in volume ratio EC: EMC = 3: 7).

<Preparation of lithium secondary battery for DCR measurement>
An electrode produced using the above positive electrode active material in the same manner as the positive electrode for a lithium secondary battery for initial discharge capacity measurement was punched into a 40 mm × 72 mm rectangle to obtain a positive electrode. Further, the negative electrode was obtained by adding and kneading NMP as a dispersion solvent to a negative electrode mixture in which 90 parts by mass of low crystalline carbon as an active material and 10 parts by mass of PVDF as a binder were blended. The slurry was applied to one side of an 8 μm copper foil, dried, and pressed with a rolling roll. This was punched out to 40 mm × 70 mm and used as a negative electrode. A tab for current / voltage measurement was bonded to the positive electrode and the negative electrode by ultrasonic welding.

A separator made of a porous resin was sandwiched between the tabbed positive electrode and the negative electrode so that they were not in contact with each other, and this was stored in a bag-shaped laminate film outer package. In a dry room, an electrolyte is injected into the laminated film housing containing the laminated electrode body, the outer housing is sealed in a vacuum state, and a DCR measurement having a voltage extraction terminal (tab) and a current extraction terminal (tab) A lithium secondary battery (laminate cell) was prepared. Note that the electrolytic solution, using the same 1M LiPF ₆ EC / EMC solution as an initial discharge capacity measurement for a lithium secondary battery.

Example 2
[First step]
In a 500 mL zirconia container, 0.6 kg of 5 mmφ zirconia balls and 12.5 g of the premix powder prepared in Example 1 are added, 3 parts by mass of propylene glycol is added to 100 parts by mass of the premix powder, and Fritsch Japan Ltd. It was made to react at 200 rpm for 2 hours with a planetary ball mill “P-5 type” to obtain a powder. The color of the obtained powder changed from a red mouse color to a dark brown color, indicating that it had reacted. When the XRD of this powder was measured, the powder became amorphous and the half-value width of the peak with the smallest half-value width in the 2θ range from 20 ° to 55 °, excluding the peak due to the Li raw material. The value of was 1.61 °.

[Second step]
In a box furnace, 32 g of the powder obtained in the first step was heated at 10 ° C./min while flowing air at 1 L / min, and baked at 1000 ° C. for 6 hours. The obtained powder was crushed to obtain a layered compound (positive electrode active material) of Li _1.05 Mn _0.33 Co _0.33 Ni _0.34 O ₂ .

  When the XRD of the obtained positive electrode active material was measured, a clear peak was observed as in the X-ray diffraction profile of FIG. 2, and all of the R-3m crystal groups could be indexed. No impurity phase was observed.

Further, in the obtained positive electrode active material, the volume resistivity when compressed at a pressure of 39.2 MPa was 4.4 × 10 ⁴ Ω · cm. The median size of the positive electrode active material is 4.8 _{.mu.m, D 90} was 7.0 .mu.m. Furthermore, the average circularity of the secondary particles of the positive electrode active material was 0.60.

  A lithium secondary battery for initial discharge capacity measurement (bipolar cell) and a lithium secondary battery for DCR measurement (laminate cell) were prepared in the same manner as in Example 1 except that the positive electrode active material was used.

Example 3
A powder was obtained by performing the first step in the same manner as in Example 2 except that ethanol was added as a grinding aid to 3 parts by mass with respect to 100 parts by mass of the premix powder. The color of the obtained powder changed from a red mouse color to a dark brown color, indicating that it had reacted. When the XRD of this powder was measured, the powder became amorphous, and the peak of the half-value width of the peak with the smallest half-value width was 2θ in the range of 20 ° to 55 °, excluding the peak due to the Li raw material. The value was 0.92 °. Using this powder, the second step was carried out in the same manner as in Example 2, and further pulverized after firing to obtain a layered compound of Li _1.04 Mn _0.34 Co _0.33 Ni _0.33 O ₂ ( A positive electrode active material) was obtained.

  When the XRD of the obtained positive electrode active material was measured, a clear peak was observed as in the X-ray diffraction profile of FIG. 2, and all of the R-3m crystal groups could be indexed. No impurity phase was observed.

The obtained positive electrode active material had a volume resistivity of 6.5 × 10 ⁴ Ω · cm when compressed at a pressure of 39.2 MPa. The median size of the positive electrode active material is 3.9 _{.mu.m, D 90} was 7.5 [mu] m. Furthermore, the average circularity of the secondary particles of the positive electrode active material was 0.49.

  A lithium secondary battery for initial discharge capacity measurement (bipolar cell) and a lithium secondary battery for DCR measurement (laminate cell) were prepared in the same manner as in Example 1 except that the positive electrode active material was used.

Example 4
Except using Co (OH) ₂ , Ni (OH) ₂ , MnCO ₃ and Li ₂ CO ₃ as raw materials, a premix step and a first step were performed in the same manner as in Example 2 to obtain a powder. The color of the obtained powder changed from a red mouse color to a dark brown color, indicating that it had reacted. When the XRD of this powder was measured, the powder became amorphous, and the peak of the half-value width of the peak with the smallest half-value width was 2θ in the range of 20 ° to 55 °, excluding the peak due to the Li raw material. The value was 1.18 °. Using this powder, the second step was carried out in the same manner as in Example 2, and further pulverized after firing to form a layered compound of Li _1.03 Mn _0.33 Co _0.33 Ni _0.34 O ₂ ( A positive electrode active material) was obtained. No impurity phase was observed.

  When the XRD of the obtained positive electrode active material was measured, a clear peak was observed as in the X-ray diffraction profile of FIG. 2, and all of the R-3m crystal groups could be indexed.

Moreover, in the obtained positive electrode active material, the volume resistivity when compressed at a pressure of 39.2 MPa was 6.6 × 10 ⁴ Ω · cm. The median size of the positive electrode active material is 4.8 _{.mu.m, D 90} was 7.5 [mu] m. Furthermore, the average circularity of the secondary particles of the positive electrode active material was 0.52.

  A lithium secondary battery for initial discharge capacity measurement (bipolar cell) and a lithium secondary battery for DCR measurement (laminate cell) were prepared in the same manner as in Example 1 except that the positive electrode active material was used.

Example 5
25% by mass of ammonia water adjusted to pH 12 by adding sodium hydroxide in the reaction vessel was prepared and bubbled with nitrogen for about 30 minutes to drive out dissolved oxygen. Then, a mixed aqueous solution containing 1 mol / L each of nickel sulfate and cobalt sulfate is added dropwise at a rate of 46 mL / min, and 25% by mass of ammonia water is added dropwise at a rate of 3.3 mL / min using a metering pump. A coprecipitated hydroxide of Mn, Ni and Co was generated. At this time, the temperature of the reaction solution was maintained at 50 ° C., and a 3.2 mol / L sodium hydroxide aqueous solution was simultaneously added dropwise so that the pH of the reaction solution was maintained at about 12. Further, during the reaction, nitrogen gas was continuously bubbled at a rate of 1 L / min so that the atmosphere of the reaction solution became an inert atmosphere.

  The obtained product was washed with water, filtered, and dried to obtain a manganese cobalt nickel composite coprecipitated hydroxide containing Mn, Ni, and Co at an atomic ratio of 1: 1: 1.

A total of 2 kg of the above manganese cobalt nickel composite coprecipitated hydroxide and Li ₂ CO ₃ were measured at a molar ratio of 1: 1.05 / 2, and premix powder was produced under the same conditions as in Example 1.

A layered compound of Li _1.04 Mn _0.34 Co _0.33 Ni _0.33 O ₂ (positive electrode active) was used in the same manner as in Example 2 except that the premix powder was used as a raw material in the first step. Material). When the XRD of the powder after the first step was measured, the powder became amorphous and the peak with the smallest half-value width in the 2θ range from 20 ° to 55 °, excluding the peak due to the Li raw material. The half width value of was 1.24 °.

  When the XRD of the obtained positive electrode active material was measured, a clear peak was observed as in the X-ray diffraction profile of FIG. 2, and all of the R-3m crystal groups could be indexed. No impurity phase was observed.

Moreover, in the obtained positive electrode active material, the volume resistivity when compressed at a pressure of 39.2 MPa was 5.8 × 10 ⁴ Ω · cm. The median size of the positive electrode active material is 3.8 _{.mu.m, D 90} was 7.2 [mu] m. Furthermore, the average circularity of the secondary particles of the positive electrode active material was 0.57.

  A lithium secondary battery for initial discharge capacity measurement (bipolar cell) and a lithium secondary battery for DCR measurement (laminate cell) were prepared in the same manner as in Example 1 except that the positive electrode active material was used.

Example 6
As raw materials for the positive electrode active material, Co (OH) ₂ , Ni (OH) ₂ and MnCO ₃ were weighed so as to have a molar ratio of 1: 1: 1 and mixed uniformly. 0.6 kg of 5 mmφ zirconia balls were put into a 500 mL zirconia container, and 12.5 g of the above mixed powder was further added. 100 mL of water was added thereto, and the mixture was reacted at 200 rpm for 2 h with a planetary ball mill “P-5 type” manufactured by Fritsch Japan KK to obtain a slurry. The powder obtained by filtering and drying this slurry and LiOH.H ₂ O were put in a mortar so that Li / (Mn + Co + Ni) = 1.10 and mixed for 30 minutes. When the XRD of this powder was measured, the powder became amorphous, and the peak of the half-value width of the peak with the smallest half-value width was 2θ in the range of 20 ° to 55 °, excluding the peak due to the Li raw material. The value was 1.29 °.

The powder was fired in the second step under the same conditions as in Example 2 to obtain a layered compound (positive electrode active material) of Li _1.07 Mn _0.33 Co _0.33 Ni _0.34 O ₂ . .

  When the XRD of the obtained positive electrode active material was measured, a clear peak was observed as in the X-ray diffraction profile of FIG. 2, and all of the R-3m crystal groups could be indexed. No impurity phase was observed.

Moreover, in the obtained positive electrode active material, the volume resistivity when compressed at a pressure of 39.2 MPa was 6.6 × 10 ⁴ Ω · cm. The median size of the positive electrode active material is 5.2 _{.mu.m, D 90} was 8.8 .mu.m. Furthermore, the average circularity of the secondary particles of the positive electrode active material was 0.55.

  A lithium secondary battery for initial discharge capacity measurement (bipolar cell) and a lithium secondary battery for DCR measurement (laminate cell) were prepared in the same manner as in Example 1 except that the positive electrode active material was used.

Comparative Example 1
When the XRD of the premix powder produced under the same conditions as in Example 1 was measured, the raw material peaks were observed. And in the range of 2θ between 20 ° and 55 °, the half width of the peak with the smallest half width was 0.18 ° except the peak due to the Li raw material.

  When this premix powder was calcined in the second step under the same conditions as in Example 1 and pulverized to measure the XRD of the powder (positive electrode active material), it was represented by the above general formula (1). Sub-phases other than lithium manganese cobalt nickel composite oxide are considerably observed, and in the X-ray diffraction (CuKα), 2θ is in the range of 18 ° to 50 °, the lithium manganese cobalt nickel composite oxide represented by the above general formula (1) Among the peaks other than the peak caused by the product, the integrated intensity S1 of the peak having the largest integrated intensity and 2θ caused by the lithium manganese cobalt nickel composite oxide represented by the general formula (1) are about 18.7 °. The ratio S1 / S2 with the integrated intensity S2 of the peak appearing in FIG.

Comparative Example 2
In the first step, a powder was prepared in the same manner as in Example 1 except that propylene glycol was not added as a grinding aid. After completion of the reaction, powder adhered to the bottom and wall of the vessel container. The yield of the powder other than the fixed portion was as small as 78 g with respect to the charged amount of 250 g, and the fixed portion was close to the color of the premix powder and the reaction did not proceed. When the XRD of the powder (positive electrode active material) obtained by firing and crushing this powder in the second step under the same conditions as in Example 1 was measured, LiMn _1/3 Co _1/3 Ni _{1 / 3} O ₂ subphases are observed, and in X-ray diffraction (CuKα), 2θ is in the range of 18 ° to 50 °, and the peak attributed to the lithium manganese cobalt nickel composite oxide represented by the above general formula (1) Among the other peaks, the integrated intensity S1 of the peak having the largest integrated intensity and the integrated intensity of the peak where 2θ caused by the lithium manganese cobalt nickel composite oxide represented by the general formula (1) appears at about 18.7 ° The ratio S1 / S2 with respect to S2 was 0.168.

  A lithium secondary battery for initial discharge capacity measurement (bipolar cell) and a lithium secondary battery for DCR measurement (laminate cell) were prepared in the same manner as in Example 1 except that the positive electrode active material was used.

Comparative Example 3
Manganese cobalt nickel composite coprecipitated hydroxide was obtained under the same conditions as in Example 5. This and LiOH.H ₂ O were mixed at a ratio of Li / (Mn + Co + Ni) = 1.05 to such an extent that stirring was performed without applying a share enough to destroy the spherical secondary particles. This mixture was baked in the second step under the same conditions as in Example 1 to obtain a layered compound (positive electrode active material) having a composition of Li _1.06 Mn _0.33 Co _0.34 Ni _0.33 O ₂ .

  When the XRD of the obtained positive electrode active material was measured, a clear peak was observed as in the X-ray diffraction profile of FIG. 2, and all of the R-3m crystal groups could be indexed. Moreover, when the obtained positive electrode active material was observed by SEM, this positive electrode active material was a secondary aggregate in which primary particles were aggregated in a spherical shape.

The obtained positive electrode active material had a volume resistivity of 5.5 × 10 ⁴ Ω · cm when compressed at a pressure of 39.2 MPa. The median size of the positive electrode active material is 6.6 [mu] _{m, D 90} was 9.7Myuemu. Furthermore, the average circularity of the secondary particles of the positive electrode active material was 0.77.

  A lithium secondary battery for initial discharge capacity measurement (bipolar cell) and a lithium secondary battery for DCR measurement (laminate cell) were prepared in the same manner as in Example 1 except that the positive electrode active material was used.

  In Table 1, the manufacturing conditions of the positive electrode active material in Examples 1-6 and Comparative Examples 1-3 are shown. Table 2 shows the evaluation results of the positive electrode active materials of Examples 1 to 6 and Comparative Examples 1 to 3, and Table 3 shows the lithium secondary batteries for initial discharge capacity measurement of Examples 1 to 6 and Comparative Examples 2 to 3. And the evaluation result of the lithium secondary battery for DCR measurement is shown.

  Note that “PG” in the column of the grinding aid in Table 1 means propylene glycol.

  As is clear from Tables 2 and 3, the lithium secondary battery constructed using the positive electrode active material having an average circularity of 0.6 or less from the comparison between Example and Comparative Example 3 was subjected to the pulse cycle test. It can be seen that the rate of increase of DCR in the can be reduced.

  Moreover, in Comparative Example 1, since there is no step corresponding to the first step at the time of manufacturing the positive electrode active material, the raw materials are not sufficiently mixed, and therefore, the lithium manganese cobalt nickel composite oxide itself cannot be obtained in a single phase.

  In Comparative Example 2, since the pulverization aid is not used in the first step during the production of the positive electrode active material, the powder adheres to the container of the pulverization mixer, making it difficult to recover and the reaction does not proceed sufficiently. . Therefore, in the lithium secondary battery using this positive electrode active material, the initial discharge capacity is reduced and the initial value of DCR is increased. From this, it can be seen that the use of the grinding aid in the first step is important for uniformly producing the lithium manganese cobalt nickel composite oxide.

As described above, in the present invention, as shown in the examples, the average circularity of the secondary particles is controlled to 0.6 or less, and more preferably, the volume resistivity when compressed at a pressure of 39.2 MPa is set. By constructing a lithium secondary battery with a positive electrode active material of 5 × 10 ⁵ Ω · cm or less, the DCR was lowered and the rate of increase in DCR after repeated charge / discharge was reduced. That is, according to the present invention, a lithium manganese cobalt nickel composite oxide having substantially 1: 1: 1 manganese, cobalt, and nickel can be configured as a lithium secondary battery having higher output characteristics than conventional products. Succeeded.

  Further, the present invention is industrially very advantageous because the process is simple and the cost is low compared with conventional wet methods such as coprecipitation.

2 is a diagram showing an X-ray diffraction profile of a powder obtained by the first step of Example 1. FIG. 2 is a diagram showing an X-ray diffraction profile of a positive electrode active material of Example 1. FIG. 2 is a SEM photograph of the positive electrode active material of Example 1.

Claims (6)

A positive electrode active material for a lithium secondary battery,
The positive electrode active material for the lithium secondary battery represented by the general formula _{Li A Mn B Co C Ni D} M E O F ( although, M is Li, Mn, Co, an element other than Ni and O, 0.95 ≦ A ≦ 1.2, 0.3 ≦ B <0.36, 0.3 ≦ C <0.36, 0.3 ≦ D <0.36, B + C + D + E = 1, 1.8 ≦ F ≦ 2.2 Is comprised of lithium manganese cobalt nickel composite oxide represented by
The positive electrode active material for a lithium secondary battery has at least secondary particles,
The median diameter of the whole positive electrode active material for lithium secondary batteries is 1 to 10 μm,
The average circularity of the secondary particles is 0.05 or more and 0.6 or less,
In the X-ray diffraction by CuKα ray, among the peaks other than the peak due to the lithium manganese cobalt nickel composite oxide, the integrated intensity of the peak having the largest integrated intensity in the range of 2θ of 18 ° to 50 ° is S1, and the above The positive electrode active for a lithium secondary battery in which the ratio S1 / S2 is 0.145 or less, where S2 is an integrated intensity of a peak where 2θ caused by lithium manganese cobalt nickel composite oxide appears in the vicinity of 18.7 ° A method for producing a substance, comprising:
In the X-ray diffraction by CuKα ray, the raw material is pulverized and mixed with a pulverization aid until the half width of all peaks appearing in the range of 2θ in the range of 20 ° to 55 ° is 0.75 ° or more, Mn, Co, and A method for producing a positive electrode active material for a lithium secondary battery, comprising: a first step of forming a composite containing Ni; and a second step of firing the composite together with a compound of Li in an oxygen-containing atmosphere. . The volume resistivity when the obtained positive electrode active material for a lithium secondary battery was compressed at a pressure of 39.2 MPa was 5 × 10. ⁵ The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, which is Ω · cm or less. A positive electrode active material for a lithium secondary battery,
The positive electrode active material for the lithium secondary battery represented by the general formula _{Li A Mn B Co C Ni D} M E O F ( although, M is Li, Mn, Co, an element other than Ni and O, 0.95 ≦ A ≦ 1.2, 0.3 ≦ B <0.36, 0.3 ≦ C <0.36, 0.3 ≦ D <0.36, B + C + D + E = 1, 1.8 ≦ F ≦ 2.2 Is comprised of lithium manganese cobalt nickel composite oxide represented by
The positive electrode active material for a lithium secondary battery has at least secondary particles,
The median diameter of the whole positive electrode active material for lithium secondary batteries is 1 to 10 μm,
The average circularity of the secondary particles is 0.05 or more and 0.6 or less,
In the X-ray diffraction by CuKα ray, among the peaks other than the peak due to the lithium manganese cobalt nickel composite oxide, the integrated intensity of the peak having the largest integrated intensity in the range of 2θ of 18 ° to 50 ° is S1, and the above The positive electrode active for a lithium secondary battery in which the ratio S1 / S2 is 0.145 or less, where S2 is an integrated intensity of a peak where 2θ caused by lithium manganese cobalt nickel composite oxide appears in the vicinity of 18.7 ° A method for producing a substance, comprising:
In the X-ray diffraction using CuKα rays, the raw material is pulverized until the full width at half maximum of all peaks excluding the peak derived from the Li compound that appears in the range of 2θ of 20 ° to 55 ° is 0.75 ° or more. And a first step of forming a composite containing Mn, Co, Ni, and Li, and a second step of firing the composite in an oxygen-containing atmosphere. A method for producing a positive electrode active material. The volume resistivity when the obtained positive electrode active material for a lithium secondary battery was compressed at a pressure of 39.2 MPa was 5 × 10. ⁵ The method for producing a positive electrode active material for a lithium secondary battery according to claim 3, which is Ω · cm or less. A positive electrode for a lithium secondary battery, comprising the positive electrode active material for a lithium secondary battery obtained by the method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 4 . A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 5.

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