TWI459619B - A positive electrode active material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery - Google Patents

Description

Positive electrode active material for lithium ion battery, positive electrode for lithium ion battery, and lithium ion battery

The present invention relates to a positive electrode active material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery.

For the positive electrode active material of a lithium ion battery, a lithium-containing transition metal oxide is usually used. Specifically, it is lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc., in order to improve characteristics (high capacity, cycle characteristics, storage characteristics, internal resistance reduction, Rate characteristics) or improve security, and constantly compositing them. For lithium-ion batteries in large-scale applications such as vehicles or load leveling, they are designed to have different characteristics from those used in mobile phones or personal computers.

In order to improve the battery characteristics, various methods have been previously used. For example, Patent Document 1 discloses a method for producing a positive electrode material for a lithium secondary battery, which is characterized in that Li _x Ni _1-y M _y O _2-δ

(0.8≦x≦1.3,0<y≦0.5, M means selected from Co, Mn, Fe, Cr, V, Ti, Cu, Al, Ga, Bi, Sn, Zn, Mg, Ge, Nb, Ta, Be At least one element selected from the group consisting of B, Ca, Sc, and Zr, δ corresponds to an oxygen deficiency or an excess amount of oxygen, and the lithium nickel composite oxide represented by the composition of -0.1 < δ < 0.1) passes through a classifier. The particles having a larger particle diameter and a smaller one are separated by a balanced separation particle diameter Dh of 1 to 10 μm, and a larger particle diameter and a smaller one are added in a weight ratio of 0:100 to 100:0. Further, according to this method, a positive electrode material for a lithium secondary battery in which the balance between the ratio characteristics and the capacity can be easily produced can be easily produced.

[Patent Document 1] Japanese Patent No. 4175526

The lithium-nickel composite oxide described in Patent Document 1 is one in which the amount of oxygen in the composition formula is excessive. However, there is still room for improvement in the high-quality positive electrode active material for lithium ion batteries.

Therefore, an object of the present invention is to provide a positive electrode active material for a lithium ion battery having good battery characteristics.

As a result of intensive studies, the inventors have found that there is a close correlation between the amount of oxygen of the positive electrode active material and the characteristics of the battery. That is, it was found that when the amount of oxygen of the positive electrode active material is a certain value or more, particularly excellent battery characteristics can be obtained. Further, it has been found that the particle size distribution and the angle of repose of the powder are controlled in the positive electrode active material having a certain oxygen amount or more, whereby more excellent battery characteristics can be obtained.

The present invention based on the above findings is, in one aspect, a positive electrode active material for a lithium ion battery, which is represented by the following composition formula:

Li _x Ni _1-y M _y O _2+α

(In the above formula, M is Co as an essential component, and is selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, Al, Bi, Sn, Mg, Ca, B, and Zr. One or more kinds, 0.9≦x≦1.2, 0<y≦0.7, α>0.05), the median diameter of the particle size distribution is 1 to 20 μm, and the angle of repose is 80° or less.

In the embodiment, the positive electrode active material for a lithium ion battery of the present invention has an angle of repose of 30 to 80°.

In another embodiment, the positive electrode active material for a lithium ion battery of the present invention has an angle of repose of 50 to 80°.

In still another embodiment, the positive electrode active material for a lithium ion battery of the present invention has a median diameter of 5 to 15 μm and a repose angle of 30 to 80°.

In still another embodiment, the positive electrode active material for a lithium ion battery of the present invention is one or more selected from the group consisting of Mn and Co.

In still another embodiment of the positive electrode active material for a lithium ion battery of the present invention, in the composition formula, α > 0.15.

In still another embodiment of the positive electrode active material for a lithium ion battery of the present invention, in the composition formula, α>0.20.

In still another embodiment, the positive electrode active material for a lithium ion battery of the present invention has a specific surface area of 0.2 to 1.0 cm ² /g.

In still another embodiment, the positive electrode active material for a lithium ion battery of the present invention has a specific surface area of 0.3 to 0.7 cm ² /g.

In another aspect, the present invention provides a positive electrode for a lithium ion battery, which uses the positive electrode active material for a lithium ion battery of the present invention.

In still another aspect, the present invention is a lithium ion battery using the positive electrode for a lithium ion battery of the present invention.

According to the present invention, a positive electrode active material for a lithium ion battery having good battery characteristics can be provided.

(Composition of positive active material for lithium ion battery)

The material of the positive electrode active material for a lithium ion battery of the present invention can be widely used as a compound for a positive electrode active material for a positive electrode for a general lithium ion battery, and particularly preferably lithium cobaltate (LiCoO ₂ ) or lithium nickelate (LiNiO ₂ ). A lithium-containing transition metal oxide such as lithium manganate (LiMn ₂ O ₄ ). The positive electrode active material for a lithium ion battery of the present invention produced by using the above materials is represented by the following composition formula:

Li _x Ni _1-y M _y O _2+α

(In the above formula, M is Co as an essential component, and is selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, Al, Bi, Sn, Mg, Ca, B, and Zr. One or more kinds, 0.9≦x≦1.2, 0<y≦0.7, α>0.05).

In the positive electrode active material for a lithium ion battery, the ratio of lithium to the total metal is 0.9 to 1.2. If the ratio is less than 0.9, it is difficult to maintain a stable crystal structure, and if it exceeds 1.2, the high capacity of the battery cannot be ensured.

The oxygen of the positive electrode active material for a lithium ion battery of the present invention is expressed as O _{2+ α} (α>0.05) as described above in the composition formula, and is excessively contained. When used in a lithium ion battery, the capacity and ratio are used. Battery characteristics such as characteristics and capacity retention rate are good. Moreover, since the baking in the manufacturing process can be sufficiently performed by excessively containing oxygen, the particle shape or size is uniformized, and as a result, the particle size distribution and the angle of repose described later can be favorably controlled. Here, with respect to α, α is preferably 0.15, more preferably α>0.20.

The positive electrode active material for a lithium ion battery of the present invention is composed of a primary particle, a secondary particle formed by agglomerating primary particles, or a mixture of primary particles and secondary particles. The median diameter (central value of the average particle diameter) of the particle size distribution of the secondary particles formed by the aggregation of the primary particles or the primary particles or the mixture of the primary particles and the secondary particles is 1 to 20 μm. When the median diameter is 1 to 20 μm, the powder having unevenness is suppressed, and the active material can be uniformly applied during the production of the electrode of the lithium ion battery, and the unevenness of the electrode composition can be suppressed. Therefore, when used in a lithium ion battery, the ratio characteristics and cycle characteristics become good. The median diameter is preferably from 5 to 17 μm.

The cathode active material for a lithium ion battery of the present invention has an angle of repose of 80 or less. Here, the angle of repose refers to an inclination angle generated between a conical layer formed by dropping the powder quietly from above and a horizontal plane. The angle of repose indicates an index of the adhesion between the powder particles. The smaller the value of the angle of repose, the weaker the aggregability and the better the fluidity, that is, the property of being less entangled. By setting the angle of repose to 80° or less, unevenness can be suppressed, and the active material can be uniformly applied during the production of the electrode of the lithium ion battery, and variation in electrode composition can be suppressed. Therefore, when used in a lithium ion battery, the ratio characteristics and cycle characteristics become good. However, when the aggregability is too small, it is easy to disperse, and when the slurry of the electrode is produced, each particle is easily passivated by the adhesive. Therefore, proper entanglement or adhesion is required. From this point of view, the angle of repose is typically from 15 to 80, preferably from 30 to 80, more preferably from 50 to 80.

The positive electrode active material for a lithium ion battery of the present invention has a specific surface area of 0.2 to 1.0 cm ² /g. When the specific surface area is 0.2 to 1.0 cm ² /g, the reaction with the electrolytic solution is suppressed, and the cycle characteristics are improved. The specific surface area is preferably from 0.3 to 0.7 cm ² /g.

(Construction of a positive electrode for a lithium ion battery and a lithium ion battery using the same)

The positive electrode for a lithium ion battery according to the embodiment of the present invention has a structure in which a positive electrode mixture prepared by mixing a positive electrode active material for a lithium ion battery, a conductive auxiliary agent, and a binder, which are configured as described above, is provided, and is provided in an aluminum foil or the like. One or both sides of the collector. Moreover, the lithium ion battery according to the embodiment of the present invention includes the positive electrode for a lithium ion battery having the above configuration.

(Method for producing positive electrode active material for lithium ion battery)

Next, a method for producing a positive electrode active material for a lithium ion battery according to an embodiment of the present invention will be described in detail.

First, a metal salt solution is prepared. The metal is Ni and one or more selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Ga, Ge, Al, Bi, Sn, Mg, Ca, B, and Zr. Further, the metal salt is a sulfate, a chloride, a nitrate, an acetate or the like, and particularly preferably a nitrate. The reason for this is that even if it is mixed into the calcined raw material in the form of impurities, it can be directly calcined, so that the washing step can be omitted; the nitrate functions as an oxidizing agent and has a function of promoting oxidation of the metal in the calcining raw material. . The metal contained in the metal salt is adjusted in advance to have a desired molar ratio. Thereby, the molar ratio of each metal in the positive electrode active material is determined.

Next, lithium carbonate was suspended in pure water, and then a metal salt solution of the above metal was introduced to prepare a metal carbonate solution slurry. At this time, lithium carbonate containing fine particles is precipitated in the slurry. In the case where the lithium compound is not reacted during heat treatment such as a sulfate or a chloride of a metal salt, it is washed with a saturated lithium carbonate solution and then subjected to filtration separation. For example, in the case of a nitrate or an acetate, when a lithium compound is reacted as a lithium raw material during heat treatment, it may be directly used as a firing precursor without being washed and directly separated by filtration and dried.

Next, a powder of a lithium salt composite (precursor for a lithium ion battery positive electrode material) is obtained by drying the filtered lithium-containing carbonate.

Next, the powder of the lithium ion battery positive electrode material obtained by drying is classified using a sieve or a commercially available classifying device, and only a powder having a particle diameter of 1 to 30 μm is obtained.

Next, a firing vessel having a capacity of a specific size is prepared, and the calcination vessel is filled with a powder of a precursor for a lithium ion battery positive electrode material having a particle size of 1 to 30 μm. Next, the firing container filled with the powder of the precursor for the positive electrode material for a lithium ion battery is transferred to a baking furnace and fired. The firing is carried out by heating in an oxygen atmosphere for a specific period of time. Further, if the firing is carried out under a pressure of 101 to 202 KPa, the amount of oxygen in the composition is further increased, which is preferable.

Then, the powder is taken out from the firing container, and pulverized using a commercially available pulverizing apparatus or the like to obtain a powder of the positive electrode active material. The pulverization at this time is carried out by adjusting the appropriate pulverization strength and pulverization time so as to obtain the desired median diameter and the angle of repose.

[Examples]

The following examples are provided to better understand the present invention and its advantages, but the invention is not limited to the embodiments.

(Examples 1 to 15)

First, the amount of lithium carbonate described in Table 1 was suspended in 3.2 liters of pure water, and then 4.8 liters of the metal salt solution was charged. Here, the metal salt solution adjusts the hydrate of the nitrate of each metal, and each metal has the composition ratio shown in Table 1, and is adjusted so that the total metal mole number is 14 mol.

Further, the amount of lithium carbonate suspended is represented by Li _x Ni _1-y M _y O _2+α (a lithium ion secondary battery positive electrode material, that is, a positive electrode active material), and x is an amount of Table 1, respectively The following formula is calculated.

W(g)=73.9×14×(1+0.5X)×A

In the above formula, "A" is a value obtained by multiplying the amount of lithium of the lithium compound other than the lithium carbonate remaining in the filtered raw material from the amount of suspension in addition to the amount necessary for the precipitation reaction. "A" is 0.9 when the nitrate or acetate is reacted as a raw material of the lithium salt, and is 1.0 when the sulfate or chloride is not reacted as a raw material for the calcination.

By this treatment, lithium carbonate containing fine particles was precipitated in the solution, and the precipitate was separated by filtration using a filter press.

Then, the precipitate was dried to obtain a lithium-containing carbonate (precursor for a positive electrode material for a lithium ion battery).

Next, the lithium-containing carbonate obtained by drying is classified into a particle diameter of 1 to 30 μm through a sieve.

Next, a baking container is prepared, and a lithium-containing carbonate is filled in the baking container. Next, the baking container was placed in an oxygen atmosphere furnace under atmospheric pressure, and heated and held at the baking temperature shown in Table 1 for 10 hours, and then cooled to obtain an oxide.

Next, the obtained oxide was pulverized to a median diameter of 1 to 20 μm using a small pulverizer (hosokawamicron ACM-2EC) to obtain a powder of a lithium ion secondary battery positive electrode material.

(Embodiment 16)

In Example 16, the metal of the raw material was a composition shown in Table 1, and the metal salt was a chloride. After the lithium carbonate was precipitated, it was washed and filtered with a saturated lithium carbonate solution, and all were carried out and carried out. The same processing as in Examples 1 to 15.

(Example 17)

In Example 17, the metal of the raw material was a composition shown in Table 1, and the metal salt was a sulfate. After the lithium carbonate was precipitated, it was washed and filtered with a saturated lithium carbonate solution, and all were carried out and carried out. The same processing as in Examples 1 to 15.

(Embodiment 18)

In Example 18, the respective metals of the raw materials were the compositions shown in Table 1, and the same treatments as in Examples 1 to 15 were carried out except that the firing was carried out under the pressure of 120 KPa under atmospheric pressure.

(Comparative Examples 1 to 3)

In Comparative Example 1, each metal of the raw material was made into the composition shown in Table 1, and the classification of the precursor after drying was not performed, and the median diameter was 1 μm or less or 20 μm or more, and the final oxide was pulverized. The same processes as in Examples 1 to 15 were carried out.

(Comparative examples 4 to 7)

In Comparative Examples 4 to 7, each of the metals of the raw materials was the composition shown in Table 1, and the firing step was carried out in an air atmosphere furnace instead of the oxygen atmosphere furnace, except that the same procedure as in Comparative Example 1 was carried out. Processing.

(Evaluation)

(Evaluation of composition of positive electrode material)

The metal content in each of the positive electrode materials was measured by an inductively coupled plasma emission spectrometer (ICP-OES), and the composition ratio (mol ratio) of each metal was calculated, and it was confirmed as shown in Table 1. Further, the oxygen content was measured by the LECO method and α was calculated.

(evaluation of median particle size)

The powder of each positive electrode material was collected, and the particle size distribution median diameter was measured by a laser diffraction type particle size distribution measuring apparatus (Shimadzu Corporation SALD-3000).

(evaluation of the angle of repose)

The powder of each positive electrode material was collected, and the powder was thrown into the standard sieve according to the standard sieve vibration according to JIS Z 8801. The powder passing through the standard sieve was passed through a funnel onto a horizontal table. At this time, the standard sieve has a vibration amplitude of 2 mm, a sieve time of 4 minutes, and a funnel diameter of 8 mm.

The angle of repose was measured on a pile of powder falling on the table. The measurement of the angle of repose was performed using an angle calculation method (least flat method) of a displacement sensor based on a semiconductor laser (wavelength: 670 nm), and the minimum read decomposition ability was 0.1 degree.

(Evaluation of specific surface area)

The specific surface area measurement by the BET method was carried out. (Refer to JIS-Z-8830). For the measurement, a flow method BET single point method specific surface area measuring device MONOSORB manufactured by Yuasa-ionics Co., Ltd. was used.

(Evaluation of battery characteristics)

The positive electrode material, the conductive material and the binder are weighed in a ratio of 85:8:7, and the binder is dissolved in an organic solvent (N-methylpyrrolidone), and then the positive electrode material is mixed with the conductive material. The slurry was applied thereto, coated on an Al foil, dried, and pressed to prepare a positive electrode. Then, a 2032 coin cell for evaluation of Li as a counter electrode was prepared, and 1 M-LiPF _{6 was} dissolved in EC-DMC (1:1) as an electrolyte solution, and a discharge capacity at a current density of 0.2 C was measured. . Moreover, the ratio of the discharge capacity of the battery capacity with respect to the current density of 0.2 C at the current density 2C was calculated, and the ratio characteristic was obtained. Further, the capacity retention ratio was measured by comparing the initial discharge capacity obtained by discharging a current of 1 C at room temperature with the discharge capacity after 100 cycles.

The results of these are shown in Table 1.

Claims (11)

A positive electrode active material for a lithium ion battery, which is represented by the following composition formula: Li _x Ni _1-y M _y O _2+α (in the above formula, M is Co as an essential component, and is selected from Sc, Ti, V One or more of Cr, Mn, Fe, Cu, Zn, Ga, Ge, Al, Bi, Sn, Mg, Ca, B and Zr, 0.9≦x≦1.2, 0<y≦0.7, α>0.05) The median particle diameter of the particle size distribution is 1 to 20 μm, and the angle of repose is 80° or less. The positive electrode active material for a lithium ion battery according to the first aspect of the invention, wherein the angle of repose is 30 to 80°. The positive electrode active material for a lithium ion battery according to the second aspect of the invention, wherein the angle of repose is 50 to 80°. The positive electrode active material for a lithium ion battery according to any one of claims 1 to 3, wherein the median diameter is 5 to 17 μm. The positive electrode active material for a lithium ion battery according to any one of claims 1 to 3, wherein the M is one or more selected from the group consisting of Mn and Co. The positive electrode active material for a lithium ion battery according to any one of claims 1 to 3, wherein α>0.15 in the composition formula. The positive electrode active material for a lithium ion battery according to claim 6, wherein α>0.20 in the composition formula. The positive electrode active material for a lithium ion battery according to any one of claims 1 to 3, wherein the specific surface area is 0.2 to 1.0 cm ² /g. The positive electrode active material for a lithium ion battery according to the eighth aspect of the invention, wherein the specific surface area is 0.3 to 0.7 cm ² /g. A positive electrode for a lithium ion battery, which uses the positive electrode active material for a lithium ion battery according to any one of claims 1 to 3. A lithium ion battery using a positive electrode for a lithium ion battery of claim 10 of the patent application.