JP2004311427A - Positive electrode active material for lithium secondary battery and its manufacturing method and non-aqueous lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery of which increase of output and impairment of output due to inner resistance decrease is prevented and to provide a positive electrode active material to be used for this and its manufacturing method. <P>SOLUTION: In the non-aqueous lithium secondary battery using a composite oxide consisting of lithium and a transition metal as a positive electrode active material, filling property (%) of the positive electrode active material for the lithium secondary battery which is represented by (tap density/actual density)×100 is less than 55%. For the positive electrode active material, size of a crystallite measured by the Hall method is 400Å to 850Å and represented by the composition formula Li<SB>a</SB>Mn<SB>x</SB>Ni<SB>y</SB>X<SB>z</SB>O<SB>2</SB>(X: at least one of Co and A1), and is preferably a composite oxide having a layer structure for satisfying the ranges below: 1≤a≤1.2, 0.2≤x≤0.5, 0.35≤y≤0.8, 0≤z≤0.45, x+y+z=1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a positive electrode active material of a lithium secondary battery used for a small portable information terminal, a power storage power supply or an electric vehicle, and a method for manufacturing the same, and has a low internal resistance and an increased internal resistance even when repeatedly charged and discharged. The present invention relates to a method for producing a positive electrode active material capable of providing high output from a low temperature to a high temperature region, a positive electrode active material, and a lithium secondary battery equipped with the same.

2. Description of the Related Art In recent years, lithium secondary batteries have attracted attention not only for portable terminals but also for vehicles such as hybrid vehicles and electric vehicles due to their high output and light weight.
Generally, a lithium secondary battery is configured by disposing a positive electrode, a negative electrode, and a separator in a container, and filling a nonaqueous electrolyte with an organic solvent. The positive electrode material is obtained by applying a positive electrode active material to a current collector such as an aluminum foil. As the positive electrode active material, lithium as represented by lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ) having a layered rock salt structure, lithium manganate (LiMn ₂ O ₄ ) having a spinel structure, etc. A powder composed of a transition metal oxide is mainly used. For example, Patent Document 1 discloses a method for producing the same in detail. For the synthesis of these positive electrode active materials, generally, a method of mixing a lithium salt powder (LiOH, Li ₂ CO _3, etc.) and a transition metal oxide (MnO ₂ , Co ₃ O ₄ , NiO, etc.) powder and firing the mixture is widely adopted. Have been.
Since the electric conductivity of this positive electrode active material is 10 ⁻¹ to 10 ⁻⁶ S / cm ² , which is lower than that of a general conductor, the electric conductivity between the current collector such as aluminum and the positive electrode active material or between the active materials is low. A conductive auxiliary material such as carbon powder having better electric conductivity than the positive electrode active material is used so as to increase electric conductivity (for example, see Patent Document 2). Actually, carbon powder of about several to several tens% by weight is mixed with the positive electrode material, and further kneaded with a binder such as PVdF (polyvinyl fluoride), PTFE (polytetrafluoroethylene), and then paste. The positive electrode is manufactured by kneading it into a shape, applying it to a current collector foil with a thickness of about 100 μm, drying and pressing steps.

In general, the battery capacity per unit volume can be estimated by the product of the capacity per weight of the positive electrode active material (mAh / g) and the electrode density (g / cm ³ ). That is, one factor that determines the battery capacity is to increase the capacity per unit weight of the active material itself, and this largely depends on the composition of the raw material and the purification. The other is an increase in the density of the electrode, which largely depends on the filling property of the positive electrode active material relating to the shape, particle size, particle size distribution, and the like of the particles.

Conventionally, various proposals for increasing the capacity have been made. For example, in order to improve the filling property, Patent Literature 3 discloses a composite oxide particle including Li and at least one transition element selected from the group consisting of Co, Ni, Mn, and Fe. A positive electrode active material is described in which the particles have 90% or more of spherical and / or elliptical spherical particles having a D1 / D2 in the range of 1.0 to 2.0 when the longest diameter is D1 and the shortest diameter is D2.
There are also many proposals for improving the capacity by controlling the particle size and the like. For example, Patent Document 4 discloses a spinel-type lithium manganese composite oxide of ultrafine particles in which the median particle size of primary particles is 0.01 μm or more and 0.2 μm or less, and the median particle size of secondary particles is 0.2 μm or more and 100 μm or less. Is disclosed. Further, Patent Document 5 discloses a spinel-type lithium manganese having an average particle diameter of 5 to 20 μm, a BET specific surface area of 1.0 m ² · g ⁻¹ or less, and an average crystallite diameter of 1000 ° or more determined by the Hall method. A composite oxide is disclosed.

  On the other hand, as for the composition of the positive electrode active material, it is known that the spinel-type lithium manganese composite oxide is advantageous in terms of cost, but has a low capacity and a problem in durability at high temperatures. Although the improvement is advanced in Patent Document 6 and the like, it is only far from practical use. Lithium-cobalt composite oxides (LiCoO2) and lithium-nickel composite oxides (LiNiO2) with a layered rock salt structure have better capacity and durability at high temperatures than spinel type, but have problems in cost and safety. It is still difficult to put it into practical use for electric vehicles. In this regard, the Li-Mn-Ni-Co composite oxide disclosed in Patent Document 7 is notable because its capacity and cost are balanced.

JP-A-8-17471 JP-A-10-125323 JP-A-2003-17050 JP-A-2002-104827 JP 2002-226214 A JP 2001-110417 A Japanese Patent No. 3244314

  A lithium secondary battery deteriorates when repeatedly charged and discharged. This deterioration includes capacity deterioration and output deterioration. The capacity deterioration means that when charge and discharge are repeated at a constant charge and discharge current density, the amount of electricity (Ah) that can be extracted from the battery decreases. Regarding this deterioration, improvements such as examination of the composition of the raw materials have been attempted. On the other hand, output deterioration means that when a battery is repeatedly charged and discharged, the internal resistance of the battery increases, and when the battery is discharged at a large current density, the battery voltage (V) drops and the voltage (V) decreases. This is a phenomenon in which the output (W) that can be expressed by the product of the current (A) decreases. Particularly, in a hybrid vehicle using both an engine and an electric motor, rapid charging and discharging are repeatedly performed in a low to high temperature environment. Under this severe environment, the degree of the output deterioration determines the life of the battery. For these reasons, a countermeasure against this output deterioration is keenly desired.

  In view of the above, the present invention aims to increase the output by reducing the internal resistance, and to reduce the internal resistance and reduce the output deterioration with a positive electrode active material, a method for producing the same, and output characteristics using the positive electrode active material. It is an object of the present invention to provide an excellent lithium secondary battery.

As described above, it is generally considered that the higher the filling property of the positive electrode active material, the higher the capacity per unit volume is obtained, the better the electrical contact state between the active materials, and the higher the output. Therefore, various studies have been made for the purpose of improving the filling property, and Patent Document 3 and the like are also examples. However, in particular, when trying to obtain a cathode active material having a small internal resistance and a small output deterioration, it is possible to contain the electrolyte to some extent while maintaining electrical contact when the cathode active material is filled inside the battery. It is considered that a feature is necessary. From such a viewpoint, the inventor of the present application has found out that there is a filling condition of the positive electrode active material which has a small output deterioration even when repeatedly charged and discharged with high output in the filling property of the positive electrode active material, and arrived at the present invention.
That is, the present invention relates to the positive electrode active material for a non-aqueous lithium secondary battery using a lithium-containing composite oxide capable of inserting and extracting lithium ions as a positive electrode active material, wherein (tap density / true density) × 100 [%] Is a positive electrode active material for a lithium secondary battery, characterized by having a filling property of less than 55%.
Here, if the filling property is too small, the positive electrode active material is likely to be agglomerated when coated on the positive electrode, and a large amount of binder is required. Therefore, the filling rate (%) = (tap density / true density) ) Is in the range of 25% to 50%, more preferably 30% to 45%. Incidentally, the positive electrode active material of Patent Document 3 has a tap density of 2.9 g / cm ³ or more, and the true densities of these positive electrode active materials are distributed to about 4 to 5 g / cm ^3, and the true density is estimated to be 5. Then, the value of filling property (%) = (tap density / true density) × 100, which is an index of the present invention, is 58% or more. As described above, it is common sense that the filling property of the conventional positive electrode active material is 55% or more, and attention has been paid to improving the filling property exclusively.

As described above, the filling property of the positive electrode active material of the present invention is out of the range of conventional common sense values. In such a positive electrode active material, when the size of the crystallite obtained by the Hall method is within a predetermined range, even if the power is repeatedly output and charged, the increase in the internal resistance is suppressed, and the output deterioration is reduced. It is also a feature of the present invention that it has been found that a small amount is required.
That is, the positive electrode active material of the present invention is characterized in that the crystallite size measured by the Hall method from the integral width of each diffraction peak obtained from the X-ray diffraction pattern is 400 ° or more and 850 ° or less. I have.
It has been found that when the crystallite size obtained by the Hall method is smaller than 400 °, the internal resistance tends to increase, and when it exceeds 850 °, the internal resistance tends to increase. If the crystallite size determined by the Hall method is smaller than 400 °, it is presumed that the diffusion rate of Li ions in the crystal during charging / discharging decreases because the crystal structure has not yet been firmly formed. When the crystallite has a value of 850 ° or more, grain growth, that is, sintering, is also progressing, and it is considered that the element containing the electrolytic solution is deteriorated. Therefore, there is a range of crystallites in which an increase in internal resistance can be suppressed. According to the study by the present inventors, the size is desirably 400 to 850 °, and more desirably in the range of 600 to 850 °. At this time, the internal resistance can be reduced and a high output can be obtained, which is particularly suitable for vehicles and the like. In this regard, the positive electrode active material disclosed in Patent Document 5 is a fine particle, but does not focus on the crystallite size. In Patent Document 6, the size of the crystallite obtained by the Hall method is specified, but it is 1000 ° or more, which deviates from the above range. However, both Patent Documents 5 and 6 are positive electrode materials having a spinel structure, which have a problem in durability at high temperatures as described above, and do not take into consideration reduction in internal resistance.

Next, the composition of the positive electrode active material of the present invention, the composition formula _{Li a Mn x Ni y X z} O 2 is represented by (X = Co, at least one of Al), 1 ≦ a ≦ 1.2,0 ≦ x ≦ It is a composite oxide having a layered rock salt structure in the range of 0.65, 0.35 ≦ y ≦ 1, 0 ≦ z ≦ 0.65 and x + y + z = 1. This composition forms a spinel structure or a layered structure depending on the mixing ratio of Mn, Ni, and Co, the firing atmosphere, and the firing temperature. It was confirmed that the composition of the multi-component composite oxide having the layered rock salt structure as described above was effective as the positive electrode active material of the present invention. The present inventors have further studied as follows. Increasing the amount of Mn in this composition is advantageous in terms of cost, but tends to generate a spinel phase, which causes problems in capacity and durability at high temperatures. In addition, when the amount of Ni is increased, there is a problem of safety (such as overcharging, nail sticking, rupture or ignition at the time of crushing). A large content of Co is disadvantageous in cost. In addition, a composition that can be synthesized in the air is desirable for low cost. In some cases, Co may be partially replaced with Al in consideration of capacity, safety, and cost. However, when a large amount of Al is substituted, the safety is increased and the cost is advantageous, but the capacity tends to decrease. As described above, in the present invention, the following composition having only a layered rock salt structure even when fired in the air and having a balance in terms of capacity, safety, and cost is more desirable. That is, the composition formula _{Li a Mn x Ni y X z} O 2: is represented by (X least one Co or Al), 1 ≦ a ≦ 1.2,0.2 ≦ x ≦ 0.5,0.35 ≦ y ≦ 0.8,0 ≦ z It is a composite oxide having a layered rock salt structure of ≦ 0.45 and x + y + z = 1. More preferably, it is a composite oxide having a layered rock salt structure in the range of 1 ≦ a ≦ 1.2, 0.2 ≦ x ≦ 0.5, 0.35 ≦ y ≦ 0.7, 0.1 ≦ z ≦ 0.45 and x + y + z = 1.

Next, in the positive electrode active material and the method for producing the same according to the present invention, lithium salt powder (LiOH, Li ₂ CO _3, etc.), transition metal oxide (MnO ₂ , Co ₃ O ₄ , NiO, etc.) powder, water, It is important to mix and mix aluminum oxide or aluminum oxide and bake it to synthesize the positive electrode active material. In the case of a multicomponent composition used in the present invention, it is necessary to make the composition in a mixed state uniform. Otherwise, the composition will differ depending on the location, and there will be portions where the spinel phase is generated and the capacity is reduced, and the performance of the positive electrode active material will be reduced as a whole.
That is, the positive electrode active material of the present invention is obtained by dispersing at least a lithium salt and a transition metal oxide, cobalt oxide and / or aluminum hydroxide, aluminum oxide and the like in a solvent, and pulverizing the media so that the median particle diameter D50 becomes 1 μm or less. The mixed slurry is used as a raw material. As a result of the study by the present inventors, it has been found that when D50 is larger than 1 μm, a tendency to adversely affect the characteristics starts to appear.

  Next, the method for producing a positive electrode active material for a non-aqueous lithium secondary battery of the present invention comprises dispersing at least a lithium salt and a transition metal oxide, cobalt oxide and / or aluminum hydroxide, aluminum oxide, or the like in a solvent, The raw material slurry is dried, granulated and granulated to a particle diameter D50 of 1 μm or less, then granulated and then fired at a temperature of 800 ° C. to 1100 ° C. in the air, nitrogen atmosphere or oxygen atmosphere. And then crushed, and then heat-treated at a temperature of 400 ° C. to 900 ° C. in air, nitrogen atmosphere or oxygen atmosphere.

  When the raw material slurry is dried and fired, usually, there are a method of putting the slurry in a filter cloth or the like, pressing, dehydrating, drying and firing, and a method of drying and firing using a slurry dryer. When the mixed raw material dried by these methods is fired, sintering considerably progresses until the reaction is sufficiently completed, and it takes time to disintegrate in the subsequent step, and it is difficult to control the particle size distribution. If the firing temperature is lowered in order to avoid the progress of sintering, there is a concern that unreacted portions remain. For this reason, in the present invention, the raw material slurry is granulated into granules while being dried using a spray dryer or the like, and then fired. Due to this process, sintering can be performed in a short time without sintering, and crushing in a subsequent step can be completed in a short time. In addition, the particle size distribution is easy to control. As a result of the examination in the examples, the firing temperature is desirably 800 ° C to 1100 ° C. After the crushing, it is desirable to perform a heat treatment. The heat treatment stabilizes the battery characteristics. This is considered to have an effect of removing distortion generated in the positive electrode active material during crushing. The heat treatment temperature is desirably 400 ° C to 900 ° C.

  In addition, the crushing step is not preferably performed with a strong crushing force. Not only gives a strong damage to the crystal structure itself of the positive electrode active material, but also there is a possibility that the particle size during the disintegration during the disintegration is sharp and the disintegration is excessive, so that control in the process is difficult. Therefore, it is desirable to use a ball whose surface is coated with an organic material such as a resin. That is, the present invention is characterized in that the crushing is performed using a ball coated with an organic material such as a resin as a medium. The material to be coated is desirably nylon or the like. When this method is used, the disintegration does not proceed excessively, and damage to the crystal structure of the positive electrode active material can be minimized. Further, it is also preferable in that the strain can be removed in a short time by the heat treatment in the next step, and the contamination that enters from the ball at the time of crushing can be burned off in the heat treatment step because the contamination is also an organic substance.

  As described above, in the positive electrode active material for a lithium secondary battery of the present invention and the method for producing the same, at least a lithium salt and a transition metal oxide, cobalt oxide and / or aluminum hydroxide, aluminum oxide, etc. are dispersed in a solvent. The raw material slurry is dried, granulated and granulated to a median particle diameter D50 of 1 μm or less, and then granulated to a temperature of 800 ° C. to 1100 ° C. in the air, nitrogen atmosphere or oxygen atmosphere. Then, heat treatment is performed at a temperature of 400 ° C. to 900 ° C. in the air, a nitrogen atmosphere, or an oxygen atmosphere, and classification is performed to obtain a positive electrode active material. Manufacturing parameters (composition, particle size of mixed raw material slurry, firing temperature, crushing conditions, heat treatment temperature) so that the filling property and crystallite size of the positive electrode active material produced by this process fall within the scope of the present invention. Etc.).

  According to the present invention, a method for producing a positive electrode active material having high output and small output deterioration due to a reduction in internal resistance, and a positive electrode active material, and a lithium secondary battery excellent in output characteristics using the positive electrode active material, particularly suitable for vehicles A battery can be provided.

Hereinafter, embodiments of the present invention will be described based on examples. First, a method and means for measuring a parameter in the present invention will be described below.
First, a method for measuring the filling property of the positive electrode active material will be described. Approximately 200 g of the positive electrode active material vacuum-dried at 120 ° C. for about 8 hours was filled in a cylindrical sample holder by free fall, and the tapping was performed 180 times at a rate of once a second. The tap density (weight / apparent volume) was calculated from the apparent volume and weight of the positive electrode active material after tapping. For the measurement in the present invention, a powder tester manufactured by Hosokawa Micron (type: PT-D) was used. The true density of the positive electrode active material was calculated from the lattice constant and the weighed composition obtained from X-ray diffraction. When the calculation is difficult, the measurement may be performed by using a commercially available particle density measuring device by a pycnometer method. Fillability = (tap density / true density) × 100 was calculated from the tap density and true density obtained above.

Ｈａｌｌ法によると、正極活物質の回折ピ−クのθとその積分幅βには以下の関係が成り立つ。

ここでεは結晶子のサイズ、λはCuKα線の波長、ηは正極活物質の歪に相当する。Ｘ軸にsinθ、Ｙ軸にβcosθを取り、得られた正極活物質の回折ピ−クのθとその積分幅βをＸ軸とＹ軸にプロットしてゆき、最小二乗法を用いて近似直線を引く。Ｙ軸との交点から結晶子サイズεを求める。図２に測定結果の一例を示す。因みに図２の結晶子サイズは850Åを示している。このＨａｌｌ法から求まる結晶子の大きさは、実際の電子顕微鏡観察から得られる結晶子のサイズとはかならずしも一致しない場合がある。しかし、電子顕微鏡に比べ測定方法が簡便であり、本発明では正極活物質の性能と相関を見出したので、評価方法としてＸ線回折によるＨａｌｌ法を使用した。 An evaluation method for measuring the size of a crystallite will be described. In the present invention, a Rigaku X-ray diffractometer (RINT 2500) was used. The positive electrode active material was filled in a sample cell, and X-ray diffraction was measured by a reflection type diffractometer method using a monochromatic CuKα ray having a wavelength of 1.5406 ° as a radiation source. The measurement range was 10 degrees to 70 degrees in 2θ. The angle step at the time of measurement was 0.006 deg, and the scanning speed was 1 deg / min. Subtracting the diffraction intensity by K [alpha ₂ line from the obtained X-ray diffraction curves, each diffraction peak - to determine the integral breadth beta _M of click. β _M contains a component β derived from the positive electrode active material and a component βs derived from the measurement device. The integral width βs derived from the measuring device is determined in advance. The integral of the diffraction peak obtained from the high-purity X-ray standard silicon powder was used for the calculation of βs. Next, the integral width β derived from the positive electrode active material was determined using the following equation.

According to the Hall method, the following relationship is established between θ of the diffraction peak of the positive electrode active material and its integral width β.

Here, ε is the size of the crystallite, λ is the wavelength of the CuKα ray, and η is the strain of the positive electrode active material. Taking sinθ on the X-axis and βcosθ on the Y-axis, plot the θ of the diffraction peak of the obtained positive electrode active material and its integral width β on the X-axis and the Y-axis. pull. The crystallite size ε is determined from the intersection with the Y axis. FIG. 2 shows an example of the measurement result. Incidentally, the crystallite size in FIG. 2 is 850 °. The size of the crystallite obtained by the Hall method may not always match the size of the crystallite obtained from actual electron microscopic observation. However, the measurement method is simpler than the electron microscope, and the present invention has found a correlation with the performance of the positive electrode active material. Therefore, the Hall method by X-ray diffraction was used as the evaluation method.

  Next, a method for evaluating battery characteristics of the positive electrode material will be described. A positive electrode material, a conductive auxiliary material (carbon powder), and a binder (8 wt% PVdF / NMP) were kneaded in an agate bowl at a weight ratio of 85: 10: 5 to obtain a slurry-like mixture. The obtained mixture was applied with a stainless steel spatula to a thickness of about 200 μm on a current collector (Al foil) having a thickness of 20 μm. The applied mixture was pre-dried at 80 ° C. for 2 hours, cut into predetermined dimensions (width 10 mm, length approximately 50 mm), and pressed with a mold at a pressure of 1.5 t / cm 2 for 2 minutes. Finally, vacuum drying was performed at 120 ° C. for 2 hours to obtain a test positive electrode. At this time, the thickness of the applied positive electrode material is about 100 μm. The size of the applied portion is 10 mm × 10 mm.

A simple battery was prepared according to the following procedure. The positive electrode was transferred into a glove box in an Ar atmosphere maintained at a dew point of −60 ° C. or less, and was infiltrated with an electrolyte (EC: DMC = 1: 2, electrolyte 1M-LiPF ₆ ). (A polyethylene film), a 1 mm thick metal lithium counter electrode and a reference electrode each having a sufficiently reduced oxide film, stacked together, sandwiched between coin-shaped stainless steel plates, and sealed in a glass bottle with terminals to obtain a simple battery. After leaving the cell for several hours so that the cell is electrochemically equilibrated, each terminal (test electrode, counter electrode, reference electrode) is connected to a charge / discharge measuring device (TOSCAT-3100 manufactured by Toyo System) to perform measurement. Was. The current density with respect to the electrode area during charging was 0.5 mA / cm ² . When the potential of the positive electrode became 4.3 V vs. the Li reference electrode, the charging was completed, and the initial voltage when the current density at the time of discharging was changed to 0.5, 3.0, 6.0 mA / cm ² was measured. The horizontal axis indicates the discharge current density, and the vertical axis indicates the battery voltage, and the internal resistance of the battery was calculated from the slope. In the measurement of the rise rate of the internal resistance after leaving at high temperature, the battery whose measurement has been completed at room temperature is charged again, and then the battery is disassembled in the glove box and the positive electrode is taken out. Next, 7 g of the electrolytic solution is weighed and immersed in a closed container. The sealed container is left in a water bath maintained at 50 ° C. After being left for 10 days, the positive electrode was taken out in a glove box, assembled into a simple battery, and the internal resistance was measured in the same manner as described above. The value obtained by dividing the change in resistance before and after standing by the resistance before standing and multiplying by 100 was defined as the internal resistance increase rate (%).

Hereinafter, examples will be described.
(Examples 1 and 2)
The positive electrode active material of the present invention was manufactured according to the manufacturing process shown in FIG. First, powders of lithium carbonate (Li ₂ CO ₃ ), manganese dioxide (MnO ₂ ), cobalt oxide (Co ₃ O ₄ ), and nickel oxide (NiO) were used as raw materials, and the composition of the positive electrode active material was Li _1.08 Mn _0.33 Ni _It was weighed to _0.36 Co _0.31 O ₂ . For the subsequent pulverization and mixing, a medium containing zirconia (ZrO ₂ ) as a main component was used. Raw material powder, pure water, and media were charged into a ball mill pot and mixed by a wet method. The median particle diameter D50 of the raw material powder is about 10 μm in the initial stage, and a raw material slurry in which the median particle diameter D50 of the raw material powder is changed in the range of 10 to 0.5 μm (4 steps of 10, 5, 1, 0.5 μm) is prepared. . Here, the raw material slurry of Example 1 has a median particle size of 1 μm, and the raw material slurry of Example 2 has a median particle size of 0.5 μm. The time required for the median particle diameter D50 of the raw material powder to reach 0.5 μm was about 24 hours. After mixing, an appropriate amount of an aqueous solution in which PVA (polyvinyl alcohol) is dissolved is added, and the mixture is further mixed for 1 hour. Next, the slurry is removed from the pot and transferred to a storage tank. The granules are granulated by a spray dryer and dried to prepare granules having a diameter of 10 to 100 μm. Next, the granules are fired in air at 1000 ° C. for 4 hours. After calcination, pulverization is performed by a ball mill using a medium coated with resin or the like until a particle size distribution having a maximum particle size of 20 μm or less is obtained. Next, heat treatment was performed at 600 ° C. in the air for 4 hours, and the particles were classified with a vibrating screen having a mesh size of 63 μm to obtain a positive electrode active material. Using this positive electrode active material, the filling property, the internal resistance by a simple battery and the internal resistance increase rate were measured.

(Comparative Example 1)
A positive electrode active material manufactured by the same method as in Examples 1 and 2, but using a raw material slurry having a median particle diameter D50 of 10 μm in the raw material slurry stage.

(Comparative Example 2)
A positive electrode active material manufactured by the same method as in Examples 1 and 2, except that a raw material slurry having a median particle diameter D50 of 5 μm was used in the raw material slurry stage.

(Comparative Examples 3 to 6)
Raw materials were weighed to a predetermined amount so as to have the same composition as in Examples 1 and 2, and raw materials in which the median particle diameter D50 of the raw material powder was changed in the range of 10 to 0.5 μm (4 stages of 10, 5, 1, 0.5 μm) A slurry was prepared, and these were used as Comparative Examples 3 to 6. Next, these slurries were dried with a slurry drier. Then, it is baked at 1000 ° C. for 4 hours in the atmosphere. In this comparative example, as in the above example, granules were not granulated before firing, so that the mixed raw material became a cookie-like sintered body after firing. Next, crushing after firing is performed. However, sintering progresses and the sintering is hard, so that crushing cannot be performed with the media coated with the resin coat or the like of the present invention. Therefore, ball milling using a zirconia ball having a higher crushing capacity was performed. Next, heat treatment was performed at 600 ° C. in the air for 4 hours, and the particles were classified with a vibrating screen having a mesh size of 63 μm to obtain a positive electrode active material. Using this positive electrode active material, the filling property, the internal resistance, and the rate of increase in the internal resistance were measured.

(Comparative Example 7)
Raw materials were weighed in predetermined amounts so as to have the same composition as in Examples 1 and 2, and a raw material slurry having a median particle diameter D50 of the raw material powder of 0.5 μm was prepared. Next, the slurry was granulated by a spray dryer and dried to prepare granules having a diameter of 10 to 100 μm. Then, it is baked at 1000 ° C. for 4 hours in the atmosphere. Next, ball milling using a zirconia ball was performed. Thereafter, a heat treatment was performed at 600 ° C. for 4 hours in the air, and classification was carried out using a vibrating screen having a mesh size of 63 μm to obtain a positive electrode active material. Using this positive electrode active material, the filling property, the internal resistance, and the rate of increase in the internal resistance were measured.
Hereinafter, the obtained evaluation results are shown in Table 1.

  From the above results, when the particle size of the raw slurry is 1 μm or less, the internal resistance tends to decrease. This is probably because the composition uniformity has increased. In Comparative Examples 1 and 2 in which the filling property was 55% or more even in the case of the battery produced by the manufacturing process of the present invention, the internal resistance and the rate of increase of the internal resistance in the case of a battery were relatively large, satisfying the present invention. Can not. The reason that the samples prepared in Comparative Examples 3 to 6 have high filling properties is that granulation is not performed before firing, so that the positive electrode active material becomes a cookie-like hard sintered body after firing. In other words, it is considered that it is difficult to disintegrate, and even after disintegration, coarse particles that have advanced in sintering are mixed and the particle size distribution has a width. On the other hand, in the case of Comparative Example 7 in which granulation was performed and fired, and then crushed with a zirconia ball having a strong pulverizing ability, the filling property was 25%, and application on the electrode became difficult. FIG. 3 shows the relationship between the filling property and the rate of increase in internal resistance. The filling property can be controlled by adjusting the crushing time in the crushing step using the resin coat ball of the present invention, further reducing the filling property, improving the characteristics including the electrolytic solution, and improving the internal resistance. It seems possible to reduce the rate of increase. For applications requiring a high output, such as a hybrid car, the internal resistance is desirably 35Ω or less and the internal resistance rise rate is desirably 20% or less in the above-described simple cell evaluation. For this reason, the positive electrode active material of the present invention is suitable as a lithium secondary battery for vehicles.

Next, the composition of the positive electrode active material was examined. Examples and comparative examples are shown below.
(Examples 3 to 7)
The powders of lithium carbonate (Li ₂ CO ₃ ), manganese dioxide (MnO ₂ ), cobalt oxide (Co ₃ O ₄ ), nickel oxide (NiO), and aluminum hydroxide (Al (OH) ₃ ) are shown below as raw materials. It was weighed so as to fall within the composition range of the positive electrode active material of the present invention. Subsequent manufacturing methods and steps were the same as in Examples 1 and 2. However, the median particle diameter D50 of the raw slurry was 0.5 μm.

(Comparative Examples 8 to 11)
Powders of lithium carbonate (Li ₂ CO ₃ ), manganese dioxide (MnO ₂ ), cobalt oxide (Co ₃ O ₄ ), and nickel oxide (NiO) are used as raw materials outside the composition range of the positive electrode active material of the present invention shown below. Weighed so that Subsequent manufacturing methods and steps were the same as in Examples 1 and 2. However, the median particle diameter D50 of the raw slurry was 0.5 μm.
The initial capacity was evaluated using the positive electrode active materials of the above Examples and Comparative Examples. The compositions produced in Examples 3 to 7 and Comparative Examples 8 to 11 are shown in FIG. FIG. 4 shows a ternary phase diagram of Mn-Ni- (Co, Al), in which the inside of the double line is the composition range of the present invention, and the shaded portion is a more desirable composition range. In addition, ● indicates an example, and ▲ indicates a comparative example. Table 2 shows the evaluation results. The crystal structure was determined from the pattern of X-ray diffraction.

From the above results, in the composition regions of the present invention of Examples 3 to 7, only the layered rock salt structure was stably obtained. In Examples 5 and 6, part of Co was replaced with Al. However, although the capacity was slightly reduced, a stable layered rock salt structure was obtained. Al is a replacement species that can provide a cost merit because the amount of expensive Co used can be reduced as described above. In each case, the capacity is 130mAh / g or more, the internal resistance is 35Ω or less, and the resistance rise rate is 20% or less. In addition, in the regions other than the present composition region of Comparative Examples 8 to 11, a spinel structure was generated together with the layered rock salt structure. As the content of Mn is increased, the cost merit increases. However, as in Comparative Examples 10 and 11, an unknown X-ray diffraction pattern which is considered to be an unreacted portion of the raw material starts to be observed, and the capacity is extremely increased. Is declining. The formation of the spinel phase not only lowers the capacity but also lowers the internal resistance and the rate of increase in resistance as compared with the embodiment. There is also a concern about the high-temperature durability described above. In this evaluation, for an electric vehicle, the capacity is desirably 130 mAh / g or more.
A stable layered structure can be obtained even in a region where the amount of Co is large in the composition region other than the present invention, and the capacity, the internal resistance, the rate of increase in resistance, and the high-temperature durability may possibly have satisfactory performance. This is an area that cannot be put to practical use.

Next, the results of the examination of the effect of the heat treatment will be described.
(Examples 8, 9 and Comparative Examples 12 to 14)
A positive electrode active material was manufactured using the same raw materials, compositions, manufacturing methods, and steps as in Examples 1 and 2. However, the median particle diameter D50 of the raw slurry was 0.5 μm. Then, the temperature in the heat treatment step was changed. The internal resistance and the rate of increase of the internal resistance in this example and the comparative example were measured.
Table 3 shows the results.

  From the above results, it can be seen that the internal resistance and the rate of increase in internal resistance can be suppressed by performing the heat treatment. This is presumed to be because the intra-crystal strain of the positive electrode active material received in the crushing step was reduced as described above. It is presumed that when the heat treatment temperature was 1000 ° C., sintering began to progress and the grain morphology changed. In addition, in the heat treatment at 300 ° C., the internal resistance and the rate of increase in the internal resistance are presumed to be deteriorated because the intracrystalline strain could not be alleviated properly. As described above, in an application requiring a high output such as a hybrid car, in the simple cell evaluation, the internal resistance is desirably 35Ω or less, and the internal resistance rise rate is desirably 20% or less. Accordingly, it was found that the heat treatment temperature was desirably 400 to 900 ° C.

Next, the results of studies on crystallites will be described.
(Examples 10 to 13 and Comparative Examples 15 and 16)
A positive electrode active material was manufactured using the same raw materials, compositions, manufacturing methods, and steps as in Examples 1 and 2. However, the median particle diameter D50 of the raw slurry was 0.5 μm. Then, the firing temperature was changed. The crystallite size, the internal resistance, and the rate of increase of the internal resistance in this example and the comparative example were measured.
Table 4 shows the results.

  The above results show that the crystallite size can be controlled by the firing temperature. As the firing temperature increases, the diffusivity of atoms increases and the crystallite size grows, but sintering proceeds in the same manner, and the possibility of mixing of grains after crushing increases. For this reason, it is considered that the filling property of the positive electrode active material is also increased, and the characteristics including the electrolytic solution are deteriorated, and the internal resistance and the internal resistance increase rate are considered to be high values. In the case of firing at 700 ° C., a value having a crystallite size of 400 ° or less has been measured. In other words, it is highly probable that the crystal structure has not yet been firmly formed, which is presumed to have an adverse effect on the diffusion rate of Li ions during charging and discharging. FIG. 5 shows the relationship between the crystallite size and the rate of increase in internal resistance. In this evaluation, the internal resistance increase rate is desirably 20% or less. Accordingly, it was found that the crystallite size was desirably in the range of 400 to 850 °.

3 is a flowchart showing steps of a manufacturing method according to the present invention. FIG. 3 is a diagram illustrating measurement of crystallites by a Hall method. FIG. 4 is a characteristic diagram showing a relationship between a filling property and a rate of increase in internal resistance. FIG. 3 is a Mn—Ni— (Co, Al) ternary phase diagram showing the composition of the composite oxide described in Examples and Comparative Examples of the present invention. FIG. 4 is a characteristic diagram showing a relationship between a crystallite size and an internal resistance increase rate by a Hall method.

Claims (11)

In the positive electrode active material for a non-aqueous lithium secondary battery using a lithium-containing composite oxide capable of inserting and extracting lithium ions as a positive electrode active material, the filling property represented by (tap density / true density) × 100 [%] Is less than 55%. In the above-mentioned positive electrode active material, the crystallite size measured by the Hall method from the integral width of each diffraction peak obtained from the X-ray diffraction pattern is 400 ° or more and 850 ° or less. Positive electrode active material for batteries. In the positive electrode active material for a non-aqueous lithium secondary battery using a lithium-containing composite oxide capable of inserting and extracting lithium ions as a positive electrode active material, the filling property represented by (tap density / true density) × 100 [%] Is less than 55%, and the crystallite size measured by the Hall method from the integral width of each diffraction peak obtained from the X-ray diffraction pattern is 400 ° or more and 850 ° or less. Positive electrode active material for secondary batteries. The positive electrode active material, the composition formula _{Li a Mn x Ni y X z} O 2 is represented by (X = Co, at least one of Al), 1 ≦ a ≦ 1.2,0 ≦ x ≦ 0.65,0.35 ≦ y ≦ 1 The positive electrode for a lithium secondary battery according to claim 1, wherein the positive electrode is a composite oxide having a layered rock salt structure in a range of 0 ≦ z ≦ 0.65 and x + y + z = 1. Active material. The positive electrode active material, the composition formula _{Li a Mn x Ni y X z} O 2: is represented by (X Co or at least one of Al), 1 ≦ a ≦ 1.2,0.2 ≦ x ≦ 0.5,0.35 ≦ y ≦ 0.8 5. The positive electrode active material for a lithium secondary battery according to claim 4, wherein the composite oxide has a layered rock salt structure in the range of 0 ≦ z ≦ 0.45 and x + y + z = 1. At least a lithium salt and a transition metal oxide, cobalt oxide and / or aluminum hydroxide, aluminum oxide and the like used for synthesizing the positive electrode active material are dispersed in a solvent and pulverized so that the median particle diameter D50 becomes 1 μm or less. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 5, wherein the mixed slurry is used as a raw material. At least a lithium salt and a transition metal oxide, cobalt oxide and / or aluminum hydroxide, aluminum oxide, and the like are dispersed in a solvent, pulverized and mixed so that the median particle diameter D50 becomes 1 μm or less, and the raw material slurry is dried. After granulating into granules, baking is performed at a temperature of 800 ° C. to 1100 ° C. in the air, in a nitrogen atmosphere or in an oxygen atmosphere, and crushed, and then in the air, in a nitrogen atmosphere or in an oxygen atmosphere, and then crushed. A method for producing a positive electrode active material for a non-aqueous lithium secondary battery, comprising performing heat treatment at a temperature of from 900C to 900C. The positive electrode active material, the composition formula _{Li a Mn x Ni y X z} O 2 is represented by (X = Co, at least one of Al), 1 ≦ a ≦ 1.2,0 ≦ x ≦ 0.65,0.35 ≦ y ≦ 1 The positive electrode active material for a non-aqueous lithium secondary battery according to claim 7, wherein the composite oxide has a layered rock salt structure in the range of 0≤z≤0.65 and x + y + z = 1. Method. The positive electrode active material, the composition formula _{Li a Mn x Ni y X z} O 2: is represented by (X least one Co or Al), 1 ≦ a ≦ 1.2,0.2 ≦ x ≦ 0.5,0.35 ≦ y ≦ 0.8 9. The method for producing a positive electrode active material for a lithium secondary battery according to claim 8, wherein the composite oxide has a layered rock salt structure in the range of 0 ≦ z ≦ 0.45 and x + y + z = 1. The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 7 to 9, wherein the crushing uses a ball coated with an organic material as a medium. A non-aqueous lithium secondary battery comprising the positive electrode active material according to claim 1 or the method for producing a positive electrode active material according to claim 7.

Images