JP3709446B2 - Positive electrode active material for lithium secondary battery and method for producing the same - Google Patents

Description

【００５３】
実施例１のサンプルは、圧力の上昇に伴い二次粒子が解砕され、ｄ５０、ｄ９０が低下していることがわかる。また、ｄ１０は圧力が上昇してもそれほど変化していない。これは、圧力をかけても二次粒子が解砕されるだけで、解砕された一次粒子はそれ以上崩れないことを意味している。
これに対して比較例１のサンプルは、圧力が上昇しても粒度ｄ１０、ｄ５０、ｄ９０のいずれも殆ど変化していない。圧力を上げても二次粒子が解砕されず、一次粒子が凝集したままであることが分かる。
【００５４】
二次粒子が解砕されやすいということは、弱い力で二次粒子が解砕され一次粒子が分散した状態にすることができるということである。そのため、実施例１のような材料は、予め二次粒子を解砕して電極材料に使用した場合であっても、一次粒子が粉砕することなく、比表面積を比較的低く保ったまま一次粒子を単分散させることができる。
【００５５】
表２に各サンプルの電池特性の結果を示す。
【００５６】
【表２】

【００５７】
これより実施例１のサンプルは、他のサンプルと比較してサイクル特性に優れることが分かる。これの原因を調査するために、電極のＳＥＭ像を観察した。図３に実施例１の電極（０．２ｔの圧力負荷）のＳＥＭ像を、図４に比較例１の電極（０．２ｔの圧力負荷）のＳＥＭ像を示す。
【００５８】
実施例１では、二次粒子が解砕されて一次粒子のレベルで分散していることが分かる。これにより、導電材が一次粒子にまで行き届いているのが分かる。
これに対して、比較例１の電極では二次粒子が解砕されずそのまま残っており、二次粒子内部の一次粒子は導電剤と接していない。このため、電池の充放電サイクルに伴う体積膨張・収縮により二次粒子に割れが発生すると、その部分で導電性が損なわれてサイクルが劣化すると考えられる。
【図面の簡単な説明】
【図１】 実施例１で得られたサンプル（層構造化合物）のプレス試験結果を示したグラフである。
【図２】 比較例１で得られたサンプル（層構造化合物）のプレス試験結果を示したグラフである。
【図３】 実施例１で得られた電極（０．２ｔの圧力負荷）のＳＥＭ写真である。
【図４】 比較例１で得られた電極（０．２ｔの圧力負荷）のＳＥＭ写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode active material for a lithium secondary battery and a method for producing the same.
[0002]
[Prior art]
Lithium secondary batteries (lithium ion secondary batteries) are small in weight per unit of electricity and yet high in energy density, so power sources for portable electronic devices such as video cameras, laptop computers, and mobile phones, and power sources for automobiles And so on.
[0003]
In this type of lithium secondary battery, carbon or graphite capable of lithium insertion / extraction is generally used for the negative electrode, and various lithium composite oxides are used for the positive electrode.
At the time of charging, lithium atoms in the positive electrode crystal are released into the electrolyte as lithium ions. At the same time, lithium ions in the electrolytic solution enter the negative electrode crystal, and at the time of discharge, the lithium atoms in the negative electrode are in the positive electrode. Operate to return. For example, when lithium cobaltate is used as the positive electrode active material and graphite is used as the negative electrode active material, the charge / discharge reaction is performed as follows.
Positive electrode: LiCoO₂  Ｌｉ xLi⁺+ Li_1-xCoO₂+ Xe^-
Negative electrode: 6xC + xLi⁺+ Xe^-  ⇔ xC₆Li
Battery: LiCoO₂ + 6xC Ｌｉ Li_1-xCoO₂+ XC₆Li
[0004]
  The high energy density of the lithium secondary battery is mainly due to the potential of the positive electrode material, and this positive electrode active material includes LiCoO having a layered structure.₂, LiNiO₂And LiMnO₂LiMn with spinel structure₂O_FourEtc. are typically used.
In addition, lithium composite oxide (LiM_XO_Y) Has been known to improve characteristics by substituting a part of M with a different metal, for example, lithium manganese oxide (LiMn₂O_Four) By substituting a part of Mn with a dissimilar metal such as Ni, Cr, Fe, Co (LiMn)_2-xM_xO_Four(M = Ni, Cr, Fe, Co, etc.)), it is disclosed that the crystal structure is stabilized and the cycle characteristics are improved (Japanese Patent Laid-Open Nos. 4-119554, 4-160758, 4-160769). JP-A-4-16976, JP-A-4-237970, JP-A-4-282560, JP-A-4-28962, JP-A-5-28991, JP-A-7-14572, JP-A-9-213333, JP-A-9-270259, etc. ). In addition, lithium manganese oxide (LiMn₂O_Four) Is replaced with a dissimilar metal (LiCoMnO)_Four, Li₂FeMn_ThreeO₈, Li₂CuMn_ThreeO₈, Li₂CrMn_ThreeO₈, Li₂NiMn_ThreeO₈It is also reported that the device operates at a potential of 5 V class (see Masao Yoshio / Akiya Ozawa, “Lithium ion secondary battery”, January 27, 2000, Nikkan Kogyo Shimbun, p. 53, Table 3.9).
[0005]
The synthesis method of such a positive electrode active material is lithium salt powder (LiOH, LiOH,₂Co_ThreeEtc.) and transition metal oxides (MnO)₂In general, the positive electrode active material is obtained by mixing conductive powders such as carbon powder having good electrical conductivity and PVdF. In general, it is kneaded with an adhesive or the like to form a paste, which is applied to a current collector foil and then pressed to be used for a positive electrode.
[0006]
However, the positive electrode active material particles synthesized by the above method have a mixture of primary particles grown reflecting the crystal form of the active material and secondary particles formed by aggregation of the primary particles. Has a wide range from several microns to several hundred microns, and the particle shape varies and is not constant. Therefore, if it is applied as it is on the electrode, the conductive auxiliary agent does not reach the inside of the aggregated particles, causing electrical contact failure and causing capacity deterioration. In addition, when there are large secondary particles of several hundred microns, the expansion and contraction of crystals during charge and discharge increase, cracking occurs at the particle interface, and a gap is formed between the conductor and the effective area decreases. I also do.
[0007]
Thus, conventionally, attempts have been made to prevent capacity deterioration while ensuring electrical conductivity by controlling the secondary particle diameter of the positive electrode active material to be relatively small and to narrow the particle size distribution.
[0008]
For example, Patent Document 1 discloses that a powdered active material obtained by spraying and firing a solution in which an active material raw material is emulsified in a flammable liquid is subjected to heat treatment. It is disclosed to improve the charge / discharge characteristics at high current density as an aggregate.
Patent Document 2 discloses primary particle aggregates (secondary particles) having an average particle diameter of 0.1 to 15 μm formed by aggregation of primary particles having an average particle diameter of 0.01 to 5.0 μm. Patent Document 4 states that the particle size of the composite oxide of lithium and nickel is 0.1 to 3 μm and the particle size of the secondary particles is 5 to 50 μm. It has been proposed to suppress the decrease in capacity by controlling the average particle diameter and porosity of the particles within a predetermined range.
In Patent Document 5, lithium carbonate and manganese dioxide are mixed and fired at a predetermined molar ratio, pulverized to produce a raw material powder, and pure water and polyvinyl alcohol are added to this to make a slurry, which is aggregated by a disk spray. Spherical secondary particles are formed, and after firing, secondary particles having a fixed shape are obtained and used as a positive electrode active material, thereby obtaining particles having a substantially spherical lithium oxide particle shape and a fixed particle size. Proposed method.
[0009]
However, simply making the positive electrode active material finer increases the required amount of conductive material and binder and restricts the filling rate of the active material into the positive electrode plate. Proposals have been made to increase the filling ratio of the active material into the positive electrode plate by mixing larger secondary particles and smaller primary particles.
[0010]
For example, Patent Document 6 discloses that a mixture of microcrystalline particles having a fixed direction diameter of 0.1 to 2 μm in SEM observation and spherical secondary particles having a fixed direction diameter of 2 to 20 μm in SEM observation is used as the positive electrode active material. Discloses a technique for improving the filling of the active material into the battery electrode plate.
Patent Document 7 discloses that in the production of a positive electrode active material for a non-aqueous lithium secondary battery comprising a lithium manganese composite oxide having a spinel structure, a mixture of manganese oxide and a lithium salt such as lithium carbonate is granulated to produce granules. After the first baking of a mixture of a lithium salt such as manganese oxide and lithium carbonate in an air atmosphere at a temperature of 1000 ° C. or higher and 1100 ° C. or lower to grow substantially octahedral-like primary particles , Once crushing, and then performing the second baking again at a temperature of 600 ° C. ± 100 ° C., primary particles that are substantially octahedral-like aggregated, and secondary particles that are easy to break up are formed. Discloses a method for regulating the ratio of the particle size distribution and the particle size together with the electrode density.
[0011]
[Patent Document 1]
JP-A-9-320603
[Patent Document 2]
JP-A-6-325791
[Patent Document 3]
JP-A-7-183047
[Patent Document 4]
JP 10-32227 A
[Patent Document 5]
JP 2000-223118 A
[Patent Document 6]
JP-A-9-129230
[Patent Document 7]
JP 2001-155728 A
[0012]
[Problems to be solved by the invention]
By the way, when manufacturing the positive electrode, the positive electrode active material of the lithium ion secondary battery is to apply a mixture (slurry) for high density filling and then roll press to increase the bulk density of the electrode. In general, secondary particles that are not easily collapsed are concerned that the utilization factor of the positive electrode material is reduced because the conductive material does not reach the particles inside the secondary particles. In addition, during the roll press or repeated charging and discharging, the secondary particles are crushed and gaps are formed, with which the contact with the conductive material is deteriorated, the battery capacity is reduced, and the cycle characteristics are deteriorated. Is also possible.
[0013]
Further, it is known that the discharge characteristics and the like of the positive electrode active material vary greatly depending on its specific surface area. The positive electrode active material composed of particles having a large specific surface area has a large reaction area and a short ion movement distance in the active material, so that the electrode reaction is performed with high density and high efficiency, but the larger the specific surface area, the greater the specific surface area. It has been pointed out that the contact with the electrolyte increases and the capacity may be significantly reduced during storage (see the description of [0014] of JP-A-10-162830), and particularly high reliability and reproducibility are required. This is an important issue for practical batteries.
[0014]
  Therefore, the present invention consists of secondary particles with weak cohesion of primary particles, and is naturally dispersed in primary particles by appropriate crushing or in the process of electrode preparation, and the particle size after dispersion is small.Specific surface areaWith small characteristics and good mixingPositive electrode active materialIt is to be provided.
[0015]
[Means for Solving the Problems]
  The first feature of the present invention is that it is composed of a lithium composite oxide having a layered structure or a spinel structure, and each particle has an average aggregate diameter of about 10 formed by agglomerating primary particles having an average particle diameter of about 0.5 to 3 μm. The second feature is that it consists of secondary particles of ˜100 μm, and the secondary feature is that the secondary particles are easily crushed to such an extent that they are naturally crushed into primary particles in an electrode manufacturing process such as a roll press. And after secondary particle crushing, it is monodispersed in primary particles (dispersed state where most of the particles are dispersed)ShiThe specific surface area of the primary particles is about 2.0 m²/ G or less, wherein the positive electrode active material for a lithium secondary battery has a fourth characteristic (provided that the general formula Li_xCo_2-xO₂A positive electrode active material for a lithium secondary battery comprising a lithium composite oxide, wherein x is 0.945 ≦ x ≦ 1.052General formula Li _x Co _2-xyz B _y Mg _z O ₂ Represented by the formula x = 0.97 to 1.005, y = 0.01-0.04, z = Positive electrode active material for lithium secondary battery comprising lithium composite oxide of 0.01 to 0.05, general formula Li _x Co _2-xy B _y O ₂ Represented by the formula x = 0.97 to 1.005, y = Positive electrode active material for lithium secondary battery comprising lithium composite oxide of 0.01 to 0.12, general formula LiCo _0.92 Mg _0.08 O ₂ Lithium secondary battery positive electrode active material comprising a lithium composite oxide represented by _0.96 Co _0.96 B _0.05 Mg _0.03 O ₂ A positive electrode active material for a lithium secondary battery comprising a lithium composite oxide represented by the general formula LiCoO ₂ A positive electrode active material for a lithium secondary battery comprising a lithium composite oxide represented by the general formula LiCoB _0.147 O ₂ The positive electrode active material for a lithium secondary battery composed of a lithium composite oxide represented by formula (1) and a raw material powder are wet pulverized and mixed, and the mixture is primarily fired at 350 to 600 ° C, cooled to 45 ° C or lower, and wet pulverized. By mixing and forming particles having an average secondary particle diameter of 0.1 to 100 μm from the resulting slurry using a spray drying granulator, and secondary firing the particles in an oxygen stream at 600 to 1000 ° C. A positive electrode active material for a lithium secondary battery comprising the resulting lithium composite oxide, and a positive electrode active material for a lithium secondary battery comprising a lithium composite oxide obtained from aluminum hydroxide oxide as a raw materialexcept. ) Is proposed.
[0016]
  In the above-described positive electrode active material for a lithium secondary battery, the ease with which the secondary particles are crushed is determined by applying a pressure of 2 t in a test in which 1 g of powder is put in a 10.5 mmφ die and pressure is applied in a uniaxial direction. It is preferable that the value of d50 of the particle size distribution of the powder is about 70% or less before the pressure is applied, and more preferably, the d50 value of the powder when the pressure of 1 t is applied is the value before the pressure is applied. It is about 50% or less.
  In addition, after the secondary particles are crushed into primary particlesSpecific surface areaAbout 2.0cm²/ G or less, especially about 1.5 cm²/ G or less.
[0017]
According to such a positive electrode active material for a lithium secondary battery, since the cohesive force between primary particles is weak, the primary particles can be easily crushed by an appropriate pulverization or electrode preparation process, and the secondary particles can be dissolved. Since the primary particles themselves do not collapse during the crushing process, the primary particles are in a monodispersed state (dispersion in which most of the particles are dispersed) while maintaining the size and shape. Furthermore, the powder in which the primary particles are dispersed has a feature that the specific surface area is small for a small average particle diameter.
[0018]
The positive electrode active material for a lithium secondary battery can also be provided as a positive electrode active material for a lithium secondary battery that is pulverized until the value of d50 in the particle size distribution is about 70% or less before pulverization.
[0019]
If the positive electrode active material for a lithium secondary battery of the present invention is used as a battery material, the secondary particles are released and monodispersed at the primary particle level in the electrode preparation process, etc., so that the density of the electrodes can be increased, and the battery The amount of the positive electrode active material filled in can be increased. In addition, the compatibility with the conductive material is improved, the conductive material can easily reach all the primary particles, the contact area is increased, and a battery material having excellent discharge capacity and rate characteristics can be obtained. In addition, cracks due to volume changes associated with charge / discharge are less likely to occur, and cycle characteristics are also improved.
[0020]
  The positive electrode active material for a lithium secondary battery of the present invention is prepared by mixing a Li raw material powder, a transition metal raw material powder, and, if necessary, a substitution element raw material powder, adding water to form a slurry, and a wet pulverizer. , Until the average particle size is about 3 μm or less, for example, about 0.5 to 3 μm, and dried,In this case, the granule is preferably granulated to an average particle size of about 30 μm to 50 μm, and thenIt can be produced by firing at a temperature of about 850 to 1000 ° C. for about 0.5 to 30 hours.
[0021]
In the present invention, “the secondary particles are easily pulverized to such an extent that they are naturally pulverized into primary particles in the electrode preparation process” means the degree of ease of pulverizing the secondary particles. It is not always necessary to be crushed in the electrode manufacturing process. For example, a crushing step may be inserted before the electrode manufacturing step to crush into primary particles. Moreover, it is meant to include “the extent that it is naturally broken into primary particles by appropriate crushing”, which will be described later, but not to exclude this.
In addition, “monodispersed in primary particles” means that the primary particles are in a dispersed state, and the primary particle size range is about 80% by weight or more, especially about 90% by weight or more. Is preferred.
Further, in the present invention, “about” means that it is particularly permissible if the same effect is exhibited even before and after the numerical value. However, there is no intention of strictly interpreting values that do not have a contract.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described, but the scope of the present invention is not limited to this embodiment. In particular, the lithium composite oxide having a layered structure will be described here, but the same can be considered for a spinel structure.
[0023]
(Positive electrode active material: layered lithium composite oxide)
The positive electrode active material for a lithium secondary battery as an example of the present invention is composed of a lithium composite oxide having a layered structure, each particle is composed of secondary particles formed by aggregation of primary particles, and the secondary particles are average particles. Particles having an average particle diameter of about 10 to 100 μm formed by agglomeration of primary particles having a diameter of about 0.5 to 3 μm, each secondary particle is easily crushed into primary particles, and after pulverization, the primary particles are shaped and It has the feature of monodispersing while ensuring the size.
[0024]
The size of the secondary particles is preferably about 10 to 70 μm in average aggregate diameter.
The agglomerated diameter here can be measured by a laser diffraction particle size distribution measuring method using MIE scattering theory.
[0025]
The ease with which the secondary particles are crushed (in other words, the cohesive force between the primary particles) is preferably such that the secondary particles are naturally crushed into primary particles in an appropriate crushing or electrode preparation process.
Here, “the degree to which the primary particles are naturally crushed by moderate crushing” refers to the degree to which the particles are naturally broken into primary particles in the process of being crushed by a vibration mill or a roller mill.
In addition, “the degree of being naturally crushed into primary particles in the electrode preparation process” means that the primary particles are naturally dissolved in the process of pressing using a roll press (clearance 50 to 200 μm) that is usually used in the electrode preparation process. Say the degree of crushing.
Specifically, the ease with which the secondary particles are crushed is the d50 of the particle size distribution of the powder when a pressure of 2 t is applied in a test in which 1 g of powder is put in a 10.5 mmφ die and pressure is applied in a uniaxial direction. Is preferably about 70% or less, preferably 50% or less, particularly 30% or less before the pressure is applied. In the same test, it is more preferable that the value of d50 of the particle size distribution of the powder when a pressure of 1 t is applied is about 70% or less, preferably 50% before the pressure is applied.
[0026]
The specific surface area of the secondary particles is about 0.2 to 2.0 m² / G is preferably in the range of about 0.5 to 1.0 m.² / G is particularly preferable. Specific surface area is about 0.2m² When it is smaller than / g, when used as a positive electrode active material of a lithium ion secondary battery, there is a possibility that a large amount of electricity cannot be taken out rapidly. On the other hand, specific surface area is about 2.0m² When exceeding / g, the elution amount of the transition metal into the electrolyte in the lithium ion secondary battery becomes large, and the charge / discharge capacity may decrease (cycleability).
In the present invention, the specific surface area of the secondary particles can be determined by the BET single point method using an automatic surface area measuring device (for example, monosorb MS-15 manufactured by Yuasa Ionics).
[0027]
The primary particles as the particles generated by crushing the secondary particles, in other words, the primary particles as the constituent units of the secondary particles have an average particle diameter of about 0.5 to 3 μm by SEM (scanning electron micrograph) observation, In particular, the thickness is preferably about 1 to 2 μm, and the shape is preferably almost spherical or elliptical.
When the particle diameter is smaller than about 0.5 μm, the specific surface area increases, the fluidity as a powder deteriorates, the slurry viscosity increases when mixed with an organic solvent, and the tap density There is a possibility that the charging amount per volume is reduced and the charge / discharge capacity is lowered. On the other hand, when the particle diameter exceeds about 3 μm, the specific surface area becomes small, the electron conductivity may be lowered, and the load characteristics may be deteriorated.
Note that the above “substantially spherical” does not need to be “spherical”, but generally “spherical”, and “elliptical spherical” does not need to be “true elliptical”, It means that it should be generally “elliptical spherical”.
The average particle diameter of primary particles is determined by selecting 200 arbitrary primary particles (optional if it is about 200 or more) from SEM (scanning electron micrograph), and calculating the weighted average of the major diameters as the average particle diameter. be able to.
[0028]
After secondary particle crushing, it is preferable to be in a state of being monodispersed in primary particles (dispersed state in which most of the particles are dispersed). Highly reliable and reproducible characteristics such as stability against negative electrode, internal resistance, sensitivity, response speed during charge / discharge, capacitance, etc., if primary particles with a certain size range are monodispersed Can be obtained.
Here, the state in which the primary particles are monodispersed means a dispersed state in which the primary particles occupy most, and in the particle size distribution after secondary particle crushing, the particle size range of the primary particles (0.5 to 3 μm). Occupy about 80% by weight or more, preferably about 90% by weight or more, and the content of ultrafine particles of submicron order (particle diameter of 0.5 μm or less) is about 10% by weight, preferably about 5% or less. preferable.
[0029]
The specific surface area of the powder after the secondary particles are crushed is about 2.0 m.²/ G or less, especially about 1.5m²/ G or less. With this rate of increase in specific surface area, after the secondary particles are crushed, it can be evaluated that the specific surface area is small for a small average particle size.
The specific surface area of the powder after the secondary particles have been crushed can be determined by the BET single point method using an automatic surface area measuring device (for example, monosorb MS-15 manufactured by Yuasa Ionics).
[0030]
The strength of primary particles (hardness to break) is about 5 μm or less when a pressure of 1 t is applied in a test in which 1 g of powder is put in a 10.5 mmφ die and pressure is applied in a uniaxial direction. % Or less is preferable.
If it has such strength, the primary particles will not collapse in the crushing or electrode preparation process to the extent that the secondary particles are crushed, and a positive electrode having an appropriate particle size distribution and particle size will be produced. can do.
[0031]
Further, the tap density of the primary particles generated by crushing the secondary particles is about 1.8 to 2.5 g / cm.^ThreeIt is preferable that it exists in the range.
The tap density here is 10 g of powder in a 50 mL graduated cylinder, dropped 50 times vertically from a height of 50 mm onto a horizontal and flat hard rubber plate, and then the volume V (cm after tapping).^Three) At that time, 10 / V (g / cm^Three(The tap density is measured by a tap method based on JIS Z 2504).
[0032]
Since the positive electrode active material of the present invention has the above characteristics, it is crushed with a vibration mill or a roller mill as necessary, and then mixed with a conductive material, a binder, a filler, and the like and kneaded. Thus, a positive electrode can be produced by applying a mixture (paste) to a positive electrode current collector made of, for example, a stainless mesh, performing roll pressing, and then drying by heating under reduced pressure.
If necessary, the positive electrode can be produced by pressure-molding the above mixture into an appropriate shape such as a disc and heat-treating it under vacuum as necessary.
The obtained positive electrode is in a state where the primary particles as described above are monodispersed in the composition, and the primary particles are not crushed even after repeated charge and discharge, so that it is possible to prevent a decrease in battery capacity and a deterioration in cycle characteristics. .
[0033]
The conductive material used is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the lithium ion secondary battery. For example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, Examples thereof include carbon fiber, metal powder, metal fiber, and polyphenylene derivative. These may be used alone or in combination of two or more.
Examples of the binder include starch, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose polyvinyl chloride, polyvinyl pyrrolidone, tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, and ethylene-propylene-diene copolymer. (EPDM), sulfonated EPDM, styrene-butadiene rubber, polybutadiene, fluororubber, polyethylene oxide and the like.
The filler is not particularly limited as long as it is a fibrous material that does not cause a chemical change in the lithium ion secondary battery, and examples thereof include olefin polymers such as polypropylene and polyethylene, fibers such as glass and carbon, and the like. .
[0034]
The lithium secondary battery using the positive electrode obtained from the present invention includes, for example, a notebook computer, a mobile phone, a cordless phone, a video movie, a liquid crystal television, an electric shaver, a portable radio, a headphone stereo, a backup power supply, and a memory card. It can be used for electronic devices such as medical devices such as pacemakers and hearing aids. It is not limited to these.
[0035]
(Positive electrode active material: process for producing layered structure lithium composite oxide)
Next, although the manufacturing method of the positive electrode active material of this invention is demonstrated, what is demonstrated here is an example to the last of a manufacturing method, and is not limited to this manufacturing method.
[0036]
  The positive electrode active material of the present invention is prepared by mixing Li raw material powder, transition metal raw material powder, and, if necessary, substitution element raw material powder, adding water to form a slurry, and optionally adding a binder thereto , Defoaming agent, dispersing agent, etc. are added and pulverized with a wet pulverizer until the average particle size becomes about 0.5 to 3 μm and dried. It can be obtained by sintering to synthesize a layered structure lithium composite oxide.In this case, it is preferable to granulate simultaneously with drying, and as an example of the standard, it is preferable to granulate to an average particle size of about 30 μm to 50 μm.
[0037]
(Raw materials and mixing of raw materials)
As the lithium raw material, at least one of lithium (metallic lithium) and a lithium compound can be used. The lithium compound is not particularly limited as long as it contains lithium, and examples thereof include lithium acetate and lithium oxalate. Inorganic lithium salts such as organic acid lithium, lithium hydroxide, lithium carbonate, and lithium nitrate can be used. Among these, lithium carbonate (Li₂CO_Three), Lithium nitrate (Li₂NO_Three), Lithium hydroxide (LiOH) and the like are preferable. The average particle size of the lithium raw material is preferably 1 to 20 μm.
[0038]
As the transition metal, Mn, Co, or Ni can be used.
As the Mn raw material, at least one of manganese (metallic manganese) and a manganese compound can be used. As the manganese compound, MnO₂, Mn₂O_Three, Mn_ThreeO_FourAnd MnCO_ThreeIs preferably used. The average particle size of the Mn raw material is preferably 1 to 30 μm.
As the Co raw material, at least one of cobalt (metal cobalt) and a cobalt compound can be used. The cobalt compound is not particularly limited as long as it contains cobalt._ThreeO_Four, Oxides such as CoO, CoCO_Three, Co (NO_Three)₂CoCl₂Salts such as Co (OH)₂And hydroxides such as CoOOH and the like. Among these, especially Co_ThreeO_FourOr Co (OH)₂Etc. are preferable. The average particle size of the Co raw material is preferably 1 to 30 μm.
As the Ni raw material, at least one of nickel (metallic nickel) and a nickel compound can be used. The nickel compound is not particularly limited as long as it contains nickel. For example, an oxide such as NiO, NiCO, etc._Three, Ni (NO_Three)₂・ 6H₂O, NiCl₂Salts such as Ni (OH)₂And hydroxides such as NiOOH and the like. Among these, especially NiO or Ni (OH)₂Etc. are preferable. The average particle diameter of the Ni raw material is preferably 1 to 30 μm.
[0039]
Substitution elements, that is, elements that substitute part of the transition metal in the layered structure include Cr, Al, B, Mg, Si, Sc, Ti, V, Fe, Co, Ni, Cu, Zn, Ga, Y, Examples include Zr, Nb, Mo, Ru, Sn, Sb, Ce, Pr, Nd, Hf, Ta, and a mixture or solid solution composed of two or more selected from the group consisting of Ta and Pb. Mg, Ti and Fe.
Examples of the substitution element material include chromium oxide, chromium hydroxide, chromium nitrate, chromium sulfate, chromium acetate, aluminum hydroxide, aluminum nitrate, aluminum sulfate, aluminum acetate, boric acid, magnesium hydroxide, magnesium carbonate, magnesium chloride, Magnesium acetate, silicon dioxide, silicic acid, scandium oxide, titanium dioxide, titanium hydroxide, vanadium pentoxide, ammonium metavanadate, iron hydroxide, iron nitrate, iron sulfate, iron chloride, cobalt hydroxide, cobalt nitrate, cobalt sulfate, Cobalt chloride, nickel hydroxide, nickel nitrate, nickel sulfate, copper nitrate, copper sulfate, zinc nitrate, zinc sulfate, gallium oxide, yttrium oxide, yttrium nitrate, zirconium oxide, zirconyl nitrate, niobium oxide, niobium chloride, molybdenum oxide, chloride Lute Umum, tin oxide, tin chloride, antimony chloride, cerium oxide, cerium nitrate, praseodymium nitrate, neodymium chloride, hafnium chloride, tantalum chloride, lead sulfate, lead acetate, lead chloride and other oxides, hydroxides, inorganic salts, organic Mention may be made of salts.
[0040]
You may make it grind | pulverize the said Li raw material, a transition metal raw material, and a substitution element raw material before or after raw material mixing.
In addition, the mixing method in this case is not specifically limited as long as these can be mixed uniformly. For example, the raw materials may be blended simultaneously or in an appropriate order using a known mixer such as a mixer and mixed in a wet or dry manner.
[0041]
(Slurry production process)
  The above mixture is put into a wet pulverizer, mixed with water and, if necessary, a binder and a dispersant as necessary. The mixture is pulverized until the average particle size is about 3 μm or less to obtain a slurry having a uniform particle size. Make it. Moreover, it is good also to adjust the viscosity of a slurry by adding a diluent and a dispersing agent as needed.
[0042]
(Drying process)
The obtained slurry may be dried by a known drying method such as spray heat drying, hot air drying, vacuum drying, freeze drying and the like.
[0043]
(Baking process)
After drying, the obtained raw material powder is fired in a firing furnace in an air atmosphere so as to be held at a temperature of about 850 to 1000 ° C., particularly about 950 to 980 ° C. for about 0.5 to 30 hours. Synthesize oxide. Here, the firing temperature means the product temperature in the firing furnace.
When the firing temperature exceeds about 1000 ° C., the primary particles become large and the specific surface area becomes small, but monodispersion becomes difficult. On the other hand, when the temperature is lower than about 850 ° C., the primary particles become small and the specific surface area becomes large.
The firing time is preferably about 0.5 hours or more, particularly about 10 to 20 hours in order to obtain a uniform reaction.
As the baking furnace, a rotary kiln or a stationary furnace can be used.
As the firing atmosphere, an oxidizing atmosphere can be adopted in addition to an air atmosphere.
[0044]
Most of the particles of the positive electrode active material synthesized in this way have an average particle size of about 0.5 to 3 μm and an average particle size of about 1 to 3 μm. It is a secondary particle of 10 to 100 μm, and each secondary particle has many gaps and is easily crushed into primary particles, and is crushed with a vibration mill or a roller mill, or an electrode such as a roll press is produced. In the process, the primary particles are crushed, and the pulverized primary particles have a feature that their shape and size can be secured.
Therefore, when the positive electrode is manufactured, the primary particles as described above are monodispersed in the composition, and the primary particles are not crushed even after repeated charge and discharge, thereby preventing a decrease in battery capacity and deterioration in cycle characteristics. Can do.
[0045]
Next, although an Example and a comparative example are compared and demonstrated, this invention is not limited to an Example.
[0046]
Example 1
As raw materials, lithium carbonate having an average particle size of about 23 μm, electrolytic manganese dioxide having an average particle size of about 6 μm, nickel hydroxide having an average particle size of about 23 μm, cobalt hydroxide having an average particle size of about 18 μm, and molar ratio Li: Mn: Ni : Co = 1.15: 0.33: 0.33: 0.33 Weighed so that the solid content ratio was 1: 1, and further added a binder and a dispersant. It grind | pulverized until the average particle diameter became about 0.5-3.0 micrometers using the wet grinder, and this was granulated and dried using spray drying, and the raw material powder | flour with an average particle diameter of about 30-50 micrometers was obtained. . The obtained raw material powder was baked in the atmosphere at about 970 ° C. (product temperature) for about 20 hours to obtain the target layer structure compound.
[0047]
The obtained layer structure compound was mixed at a ratio of layer structure compound: conductive material: binder = 0.67: 0.22: 0.11, formed into a sheet shape using a mortar, and then punched with a 13 mmφ punch. To make a positive electrode. Then, a coin-type battery was prepared using 1M-LiPF6 / PC: DMC (1: 1) as the electrolyte and Li metal as the negative electrode, and a cycle test was performed.
[0048]
In order to obtain an index of the ease of crushing of the obtained powder, it was measured how much the secondary particles were crushed when pressure was applied.
After putting 1 g of the layer structure compound obtained above in a 10.5 mmφ die and applying a pressure of 0.2 to 3 t in a uniaxial direction, the particle size distribution of the powder was measured, and the pressure and particle size d10, d50, d90 The relationship was investigated.
[0049]
(Comparative Example 1)
Ni, Co, Mn mixed sulfuric acid aqueous solution of Ni: Co: Mn = 1: 1: 1 in a molar ratio is continuously supplied into an alkaline solution whose pH is controlled to about 11.6 by a coprecipitation method. A hydroxide was obtained. The obtained raw material was mixed with lithium carbonate so that the molar ratio (Li: Ni, Co, Mn) = 1.15: 1, and baked in the atmosphere at about 970 ° C. (product temperature) for about 20 hours. The layer structure compound was obtained. The obtained compound was evaluated by the same method as described above.
[0050]
(Comparative Example 2)
After adjusting the raw material powder in the same manner as in Example 1, baking was performed in the atmosphere at about 1100 ° C. (product temperature) for about 20 hours to obtain a layer structure compound. The obtained layer structure compound was evaluated by the same method as described above.
[0051]
(result)
Table 1, FIG. 1 and FIG. 2 show the press test results of the samples (layer structure compounds) obtained in Example 1 and Comparative Example 1.
[0052]
[Table 1]

[0053]
In the sample of Example 1, it can be seen that the secondary particles are crushed as the pressure increases, and d50 and d90 are lowered. Moreover, d10 does not change so much even if the pressure increases. This means that even if pressure is applied, only the secondary particles are crushed and the pulverized primary particles are not broken further.
On the other hand, in the sample of Comparative Example 1, none of the particle sizes d10, d50, and d90 changed substantially even when the pressure increased. It can be seen that even when the pressure is increased, the secondary particles are not crushed and the primary particles remain aggregated.
[0054]
The fact that the secondary particles are easily crushed means that the secondary particles can be crushed with a weak force and the primary particles can be dispersed. Therefore, even if the material like Example 1 is a case where secondary particles are previously crushed and used as an electrode material, the primary particles are not pulverized and the primary particles are kept relatively low. Can be monodispersed.
[0055]
Table 2 shows the results of battery characteristics of each sample.
[0056]
[Table 2]

[0057]
From this, it can be seen that the sample of Example 1 is superior in cycle characteristics compared to other samples. In order to investigate the cause of this, an SEM image of the electrode was observed. FIG. 3 shows an SEM image of the electrode of Example 1 (0.2 t pressure load), and FIG. 4 shows an SEM image of the electrode of Comparative Example 1 (0.2 t pressure load).
[0058]
In Example 1, it can be seen that the secondary particles are crushed and dispersed at the primary particle level. Thereby, it can be seen that the conductive material reaches the primary particles.
On the other hand, in the electrode of Comparative Example 1, the secondary particles remain as they are without being crushed, and the primary particles inside the secondary particles are not in contact with the conductive agent. For this reason, when cracks occur in the secondary particles due to volume expansion / contraction associated with the charge / discharge cycle of the battery, it is considered that the conductivity deteriorates at that portion and the cycle deteriorates.
[Brief description of the drawings]
1 is a graph showing the results of a press test of a sample (layer structure compound) obtained in Example 1. FIG.
2 is a graph showing the results of a press test of a sample (layer structure compound) obtained in Comparative Example 1. FIG.
3 is a SEM photograph of an electrode (0.2 t pressure load) obtained in Example 1. FIG.
4 is an SEM photograph of an electrode (0.2 t pressure load) obtained in Comparative Example 1. FIG.

Claims (3)

The first characteristic is that it is composed of a lithium composite oxide having a layered structure or a spinel structure,
The second feature is that each particle is composed of secondary particles having an average aggregate diameter of about 10 to 100 μm formed by aggregation of primary particles having an average particle diameter of about 0.5 to 3 μm.
The second feature is that the secondary particles are easily crushed to such an extent that they are naturally crushed into primary particles in the electrode manufacturing process,
After secondary particle crushing, the positive electrode active material for a lithium secondary battery is characterized in that it is monodispersed into primary particles and the primary particles have a specific surface area of about 2.0 m ² / g or less (provided that The following positive electrode active material for lithium secondary battery is excluded.
A positive electrode active material for a lithium secondary battery represented by a general formula Li _x Co _2−x O ₂ and comprising a lithium composite oxide in which the value of x in the formula is 0.945 ≦ x ≦ 1.052;
· General formula represented by _{Li x Co 2-xyz B y} Mg z O 2, wherein x = 0.97~1.005, y = 0.01~0.04, z = 0.01~0. A positive electrode active material for a lithium secondary battery comprising a lithium composite oxide of 05,
- represented by the general formula _{Li x Co 2-xy B y} O 2, a lithium secondary consists wherein x = from .97 to 1.005, a y = 0.01 to 0.12 lithium composite oxide primary Positive electrode active materials for batteries,
A positive electrode active material for a lithium secondary battery comprising a lithium composite oxide represented by the general formula LiCo _0.92 Mg _0.08 O ₂ ;
A positive electrode active material for a lithium secondary battery comprising a lithium composite oxide represented by the general formula Li _0.96 Co _0.96 B _0.05 Mg _0.03 O ₂ ;
A positive electrode active material for a lithium secondary battery comprising a lithium composite oxide represented by the general formula LiCoO ₂ ;
A positive electrode active material for a lithium secondary battery comprising a lithium composite oxide represented by the general formula LiCoB _0.147 O ₂ ;
・ The raw material powder is wet pulverized and mixed, and the mixture is subjected to primary firing at 350 to 600 ° C., cooled to 45 ° C. or lower, wet pulverized and mixed, and the resulting slurry is averaged using a spray drying granulator. A positive electrode active material for a lithium secondary battery comprising a lithium composite oxide obtained by forming particles having a particle size of 0.1 to 100 μm and subjecting the particles to secondary firing in an oxygen stream at 600 to 1000 ° C .;
A positive electrode active material for a lithium secondary battery comprising a lithium composite oxide made from aluminum hydroxide oxide. ).   In a test in which 1 g of powder is put in a 10.5 mmφ die and pressure is applied in a uniaxial direction to determine whether the secondary particles are easily crushed, the value of d50 of the particle size distribution of the powder when pressure of 2 t is applied is the pressure The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material is about 70% or less before being applied.   A positive electrode active material for a lithium secondary battery obtained by crushing the positive electrode active material for a lithium secondary battery according to claim 1 or 2 until the value of d50 of the particle size distribution is about 70% or less before crushing.

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