JP7014674B2 - Positive electrode active material for lithium-ion batteries, positive electrode for lithium-ion batteries, and lithium-ion batteries - Google Patents

Description

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.

A lithium-containing transition metal oxide is generally used as the positive electrode active material of a lithium ion battery. Specifically, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc. have improved characteristics (high capacity, cycle characteristics, storage characteristics, internal resistance reduction). , Rate characteristics) and these are being combined in order to improve safety. Lithium-ion batteries for large-scale applications such as in-vehicle use and road leveling are required to have characteristics different from those for conventional mobile phones and personal computers.

Regarding the improvement of the characteristics (high capacity, cycle characteristics, storage characteristics, internal resistance reduction, rate characteristics) of the positive electrode active material of the lithium ion battery and the improvement of safety, for example, various things as described in Patent Document 1. It has been known.

Japanese Unexamined Patent Publication No. 2006-004724

The residual alkali on the surface of the positive electrode material, the water contained in the positive electrode, and the hydroxyl group that reacts with the water taken in are reacted with the electrolytic solution when the battery is manufactured, so that the amount of the electrolytic solution required for the battery is insufficient. In addition, the reaction may be accompanied by gas generation, which leads to deterioration of battery characteristics. Further, when water is brought into the battery, the morphology of the particle surface may change, which may hinder the diffusion of Li during charging and discharging. Therefore, it is necessary to remove the water as much as possible.

Generally, there are two types of water adsorption, physical adsorption and chemisorption. Similarly, in the positive electrode active material of a lithium ion battery, water is adsorbed on the surface, and the water physically adsorbed by a relatively weak van der Waals force is taken into the particles by chemical bonds and chemically adsorbed. There are two types, moisture. Of these, physical adsorption in particular reacts on the surface of the positive electrode material, and if it is too much, it adversely affects the characteristics. However, conventionally, the control of the water content of the positive electrode active material has not been studied in detail to the type of adsorption, and there is still room for improvement in the means for controlling the water content of the positive electrode active material and the battery characteristics thereof. ..

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

The water content in the positive electrode material is generally measured using a Karl Fisher Moisture Meter. However, in the Karl Fischer Moisture Meter, it is not clear to which temperature range the physical adsorption occurs in order to obtain the integrated water content at the temperature. Further, the heating temperature measurement region by the Karl Fischer Moisture Meter is in the range of room temperature to 300 ° C., and it is difficult to measure in the temperature region higher than that. However, in many cases, the actual water content, particularly the water content taken into the particles of the positive electrode material and the water content reacting with the particles, cannot be removed in the temperature range of about 300 ° C. The present inventor clearly distinguishes whether the water content of the positive electrode material is physical adsorption or chemical adsorption by using the TPD-MS measurement method capable of measuring up to the high temperature measurement region, and further improves the battery characteristics. It has been found that a positive electrode active material having good battery characteristics can be obtained by controlling the generation rate of water that has an influence.

The present invention completed on the basis of the above findings has one aspect: composition formula: Li _x Ni _{1- y My} O _{2 + α.}
(In the above formula, M is one or more selected from Ti, V, Cr, Mn, Fe, Co, Cu, Al, Zn, Sn, Mg and Zr, and 0.9 ≦ x ≦ 1.2. Yes, 0 <y ≦ 0.7, −0.1 ≦ α ≦ 0.1.)
When 30 mg of the positive electrode active material was sampled and measured by TPD-MS measurement, the generation rate of water derived from _H2O in the region of 25 ° C. or higher and 260 ° C. or lower was 0.08 wtppm / sec or less. It is a positive electrode active material for a lithium ion battery in which the generation rate of water derived from _H2O in the region of more than 260 ° C. and 500 ° C. or lower is 0.32 wtppm / sec or less.

In one embodiment, the positive electrode active material for a lithium ion battery according to the present invention is H ₂ O-derived water content in a region of 25 ° C. or higher and 260 ° C. or lower when 30 mg of the positive electrode active material is sampled and measured by TPD-MS measurement. The ratio A / B of the maximum value A of the generation rate of H 2 O to the maximum value B of the generation rate of water derived from H ₂ O in the region of more than 260 ° C. and 500 ° C. or less is 1.2 or more and 2.0 or less. ..

In another embodiment, the positive electrode active material for a lithium ion battery according to the present invention has a water content of 500 ppm in a region of more than 260 ° C. and 500 ° C. or lower when 30 mg of the positive electrode active material is sampled and measured by TPD-MS measurement. It is as follows.

In still another embodiment, the positive electrode active material for a lithium ion battery according to the present invention has a water content in the region of 25 ° C. or higher and 260 ° C. or lower when 30 mg of the positive electrode active material is sampled and measured by TPD-MS measurement. It is 250 ppm or less.

In one embodiment, the positive electrode active material for a lithium ion battery according to the present invention is one or more in which M is selected from Mn and Co.

In another aspect, the present invention is a positive electrode for a lithium ion battery using the positive electrode active material for a lithium ion battery according to the present invention.

In yet another aspect, the present invention is a lithium ion battery using a positive electrode for a lithium ion battery according to the present invention.

According to the present invention, it is possible to provide a positive electrode active material for a lithium ion battery having good battery characteristics.

It is a graph of the generation rate curve of moisture in the TPD-MS measuring apparatus of Example 5. It is a graph of the generation rate curve of moisture in the TPD-MS measuring apparatus of Example 3.

(Composition of positive electrode active material for lithium-ion batteries)
As the material of the positive electrode active material for a lithium ion battery of the present invention, a compound useful as a positive electrode active material for a general positive electrode for a lithium ion battery can be widely used, and in particular, lithium cobalt oxide (LiCoO ₂ ), It is preferable to use a lithium-containing transition metal oxide such as lithium nickel oxide (LiNiO ₂ ) and lithium manganate (LiMn ₂ O ₄ ). The positive electrode active material for a lithium ion battery of the present invention produced using such a material is
Composition formula: Li _x Ni _{1- y My} O _{2 + α}
(In the above formula, M is a metal, 0.9 ≦ x ≦ 1.2, 0 <y ≦ 0.7, and −0.1 ≦ α ≦ 0.1.)
It is represented by.
Further, M is preferably one or more selected from Ti, V, Cr, Mn, Fe, Co, Cu, Al, Zn, Sn, Mg and Zr, and more preferably selected from Mn and Co. One or more.

In the positive electrode active material for a lithium ion battery of the present invention, when the positive electrode active material is measured by TPD-MS measurement, the generation rate of water derived from _H2O in the region of 25 ° C. or higher and 260 ° C. or lower is 0.08 wtppm / sec. The rate of generation of water derived from _H2O in the region of more than 260 ° C. and 500 ° C. or lower is 0.32 wtppm / sec or less. The TPD-MS (Temperature Programmed Desorption-Mass Spectrometry) measuring device is configured by directly connecting a mass spectrometer (MS) to a special heating device with a temperature controller, and heats according to a determined temperature rise program. The change in concentration of gas generated from the sample is tracked as a function of temperature or time. Since it is an online analysis, it is possible to simultaneously detect inorganic and organic components such as water with a single measurement. In addition, the organic component can be qualitatively analyzed by GC / MS analysis of the collected trap material. By TPD-MS measurement, it is possible to detect the water content at the time of temperature rise and investigate the temperature dependence. In the present invention, in the temperature rise region from 25 ° C. as the room temperature to 500 ° C. where the water will evaporate, a low temperature region (25 ° C. or higher and 260 ° C. or lower) and a high temperature region (260 ° C.) that further affects the battery characteristics. The rate of water generation is controlled at temperatures above ° C and below 500 ° C.

In the present invention, the TPD-MS measurement method capable of measuring up to the high temperature measurement region is used to clearly distinguish whether the water content of the positive electrode material is physical adsorption or chemisorption, and then further. By controlling the rate of water generation that affects the battery characteristics, a positive electrode material that exhibits good battery characteristics is realized. Specifically, physical adsorption is adsorption by a weak interaction such as van der Waals force between an adsorbed substance (here, water) and an individual. On the other hand, chemical adsorption is adsorption by a relatively strong chemical bond between an adsorbed substance (here, water) and an individual. Therefore, according to the TPD-MS measurement, it can be confirmed that the removal temperature of the physically adsorbed water and the chemically adsorbed water is separated, and the water is generated in the low temperature region in the water generation rate curve. It is observed separately as a mountain having a peak of velocity and a mountain having a peak of moisture generation rate in a high temperature region. In the present invention, when the positive electrode active material is measured by TPD-MS measurement, the generation rate of water derived from _H2O in the region of 25 ° C. or higher and 260 ° C. or lower is 0.08 wtppm / sec or less, and is over 260 ° C. and 500 ° C. The rate of generation of water derived from H ₂ O in the region below ° C is controlled to 0.32 wtppm / sec or less, which allows the amount of water that can be finally removed in the high temperature region, which further affects the battery characteristics. It can be controlled, and as a result, the battery characteristics using the positive electrode material are improved.

Further, when the positive electrode active material was measured by TPD-MS measurement, the maximum value A of the generation rate of water derived from H ₂ O in the region of 25 ° C. or higher and 260 ° C. or lower and the maximum value A in the region of more than 260 ° C. and 500 ° C. or lower. It is preferable that the ratio A / B of the generation rate of water derived from H ₂ O to the maximum value B is 1.2 or more and 2.0 or less. According to such a configuration, it is possible to control the amount of water that can be finally removed in the high temperature region that further affects the battery characteristics, and as a result, the battery characteristics using the positive electrode material become better. The ratio A / B is more preferably 1.2 or more and 1.4 or less.

Further, when the positive electrode active material is measured by TPD-MS measurement, it is preferable that the water content in the region of more than 260 ° C. and 500 ° C. or lower is 500 ppm or less. Here, the water content is the integrated water content measured by TPD-MS in the region of more than 260 ° C. and 500 ° C. or lower. According to such a configuration, it is possible to control the amount of water that can be finally removed in the high temperature region that further affects the battery characteristics, and as a result, the battery characteristics using the positive electrode material become better. The water content in the region above 260 ° C. and 500 ° C. or lower is more preferably 400 ppm or less, and even more preferably 300 ppm or less.

When the positive electrode active material is measured by TPD-MS measurement, the water content in the region of 25 ° C. or higher and 260 ° C. or lower is preferably 250 ppm or less. Here, the water content is the integrated water content measured by TPD-MS in the region of more than 260 ° C. and 500 ° C. or lower. By suppressing the water content of the positive electrode material in this way, the battery characteristics using the positive electrode material become better. The water content in the region of 25 ° C. or higher and 260 ° C. or lower is more preferably 150 ppm or less, and even more preferably 100 ppm or less.

(Positive electrode for lithium-ion battery and configuration of lithium-ion battery using it)
The positive electrode for a lithium ion battery according to the embodiment of the present invention is, for example, a positive electrode mixture prepared by mixing a positive electrode active material for a lithium ion battery having the above configuration, a conductive auxiliary agent, and a binder from an aluminum foil or the like. It has a structure provided on one side or both sides of the current collector. Further, the lithium ion battery according to the embodiment of the present invention includes a positive electrode for a lithium ion battery having such a configuration.

(Manufacturing method of positive electrode active material for lithium-ion batteries)
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 metals are Ni and Metal M. The metal M is preferably one or more selected from Ti, V, Cr, Mn, Fe, Co, Cu, Al, Zn, Sn, Mg and Zr, and more preferably selected from Mn and Co. One or more. The metal salt is a sulfate, a chloride, a nitrate, an acetate or the like, and a nitrate is particularly preferable. This is because even if it is mixed as an impurity in the firing raw material, it can be fired as it is, so that the cleaning step can be omitted, and the nitrate functions as an oxidizing agent to promote the oxidation of the metal in the firing raw material. Each metal contained in the metal salt is adjusted to have a desired molar ratio. Thereby, the molar ratio of each metal in the positive electrode active material is determined.

Next, lithium carbonate is suspended in pure water, and then a metal salt solution of the above metal is added to prepare a metal carbonate slurry. At this time, fine lithium-containing carbonates are deposited in the slurry. If the lithium compound does not react during heat treatment such as sulfate or chloride as a metal salt, it is washed with a saturated lithium carbonate solution and then filtered. When the lithium compound reacts as a lithium raw material during heat treatment, such as nitrate and acetate, it can be used as a firing precursor by filtering and drying as it is without washing.
Next, the filtered lithium-containing carbonate is dried to obtain a powder of a lithium salt composite (a precursor for a lithium ion battery positive electrode material).

Next, a firing container having a capacity of a predetermined size is prepared, and the firing container is filled with the powder of the precursor for the positive electrode material of the lithium ion battery. Next, the firing container filled with the powder of the precursor for the positive electrode material of the lithium ion battery is transferred to the firing furnace and fired. The rate of water generation and the amount of water derived from H ₂ O of the present invention can be controlled by adjusting the temperature rise rate, the holding temperature (maximum temperature), and the temperature decrease rate from the maximum temperature to 300 ° C. in the firing step. .. The temperature rise rate in the firing step is preferably 150 to 170 ° C./h, the holding temperature (maximum temperature) is 850 to 1000 ° C., and the temperature lowering rate from the maximum temperature to 300 ° C. is preferably 75 to 90 ° C./h. Firing is performed by heating and holding for a predetermined time in an oxygen atmosphere and an air atmosphere. Further, it is preferable to perform calcination under a pressure of 101 to 202 KPa because the amount of oxygen in the composition further increases. After firing, it is cooled to room temperature and then crushed to obtain a powder of a positive electrode material of a lithium ion secondary battery.

Hereinafter, examples for better understanding the present invention and its advantages are provided, but the present invention is not limited to these examples.

(Examples 1 to 10)
First, a predetermined amount of lithium carbonate was suspended in 3.2 liters of pure water, and then 4.8 liters of a metal salt solution was added. Here, the metal salt solution was adjusted so that the nitrate hydrate of each metal had the composition ratio shown in Table 1 and the total number of moles of the metal was 14 mol.
By this treatment, fine particles of lithium-containing carbonate were precipitated in the solution, and this precipitate was filtered off using a filter press.
Subsequently, the precipitate was dried to obtain a lithium-containing carbonate (precursor for a positive electrode material of a lithium ion battery).
Next, a firing container was prepared, and the firing container was filled with a lithium-containing carbonate. Next, the firing container was fired under the firing conditions shown in Table 1 (heating rate, maximum temperature × holding time, temperature decreasing rate from maximum temperature to 300 ° C.) with the firing atmosphere as the atmosphere. Subsequently, after cooling to room temperature, the powder was crushed while the dew point was controlled at 11 ° C. to obtain a powder of a positive electrode material of a lithium ion secondary battery.

(Comparative Examples 1 to 3)
As Comparative Examples 1 to 3, the same treatment as in Example 1 was carried out except that each metal of the raw material had a composition as shown in Table 1 and the firing conditions were the conditions shown in Table 1.

(evaluation)
-Evaluation of positive electrode material composition-
The metal content in each positive electrode material was measured by an inductively coupled plasma emission spectrophotometer (ICP-OES), and the composition ratio (molar ratio) of each metal was calculated. It was confirmed that the composition ratio of each metal was as shown in Table 1. The oxygen content was measured by the LECO method and α was calculated.

-Evaluation of water content-
30 mg of the positive electrode material was set in the TPD-MS measuring device manufactured by Toray Research Center Co., Ltd., and after confirming that it was in a stable state by flowing an argon carrier gas for 15 minutes, the measurement of the water generation rate was started. .. Sodium tungstate dihydrate was used as a standard substance and heated from room temperature (25 ° C.) to 500 ° C. at a heating rate of 10 ° C./min. As a result, the integrated water content in each measurement temperature range of the positive electrode material and the water generation rate derived from H ₂ O were measured.
In addition, the integrated water content in each measurement temperature range of the positive electrode material was measured using a Karl Fischer Moisture Meter manufactured by Hiranuma Sangyo.

-Evaluation of discharge capacity and capacity retention rate-
Each positive electrode active material, the conductive material, and the binder are weighed at a ratio of 85: 8: 7, and the positive electrode active material and the conductive material are mixed with the binder dissolved in an organic solvent (N-methylpyrrolidone). The mixture was made into a slurry to prepare a positive electrode mixture, which was applied onto an Al foil, dried, and then pressed to obtain a positive electrode. Subsequently, a 2032 type coin cell for evaluation with Li as the counter electrode was prepared, and 1M-LiPF ₆ was dissolved in EC-DMC (1: 1) in an electrolytic solution, and the current density was 0.2 C. The discharge capacity was measured. The capacity retention rate was calculated from the initial discharge capacity and the initial charge capacity obtained by battery measurement.
These results are shown in Tables 1 and 2.

From Table 2, in each of Examples 1 to 10, when the positive electrode active material was measured by TPD-MS measurement, the generation rate of water derived from H ₂ O in the region of 25 ° C. or higher and 260 ° C. or lower was 0.08 wtppm /. The rate of generation of water derived from _H2O in the region of more than 260 ° C. and 500 ° C. or less was 0.32 wtppm / sec or less, and the discharge capacity and capacity retention rate of the produced battery were good.
In Comparative Examples 1 to 3, when the positive electrode active material was measured by TPD-MS measurement, the rate of generation of water derived from _H2O in the region of 25 ° C. or higher and 260 ° C. or lower exceeded 0.08 wtppm / sec, and / Or, the rate of generation of water derived from _H2O in the region of more than 260 ° C. and 500 ° C. or lower was more than 0.32 wtppm / sec, and the capacity retention rate of the manufactured batteries was poor in both cases.
Graphs of the water generation rate curves in the TPD-MS measuring devices of Examples 5 and 3 are shown in FIGS. 1 and 2, respectively.

Claims (6)

Composition formula: Li _x Ni _{1- y My} O _{2 + α}
(In the above formula, M is one or more selected from Ti, V, Cr, Mn, Fe, Co, Cu, Al, Zn, Sn, Mg and Zr, and 0.9 ≦ x ≦ 1.2. Yes, 0 <y ≦ 0.7, −0.1 ≦ α ≦ 0.1.)
Represented by
When 30 mg of the positive electrode active material was sampled by TPD-MS measurement and measured at a temperature rise rate of 10 ° C./min using a TPD-MS measuring device, the water content derived from H 2 O in the region above ₂₆₀ ° C. and 500 ° C. or lower. A positive electrode active material for lithium-ion batteries whose generation rate is 0.32 wtppm / sec or less. The positive electrode active material for a lithium ion battery according to claim 1 , wherein 30 mg of the positive electrode active material is sampled and measured by TPD-MS measurement, and the water content in the region of more than 260 ° C. and 500 ° C. or lower is 500 ppm or less. The positive electrode active material for a lithium ion battery according to claim 1 or 2 , wherein when 30 mg of the positive electrode active material is sampled and measured by TPD-MS measurement, the water content in the region of 25 ° C. or higher and 260 ° C. or lower is 250 ppm or less. The positive electrode active material for a lithium ion battery according to any one of claims 1 to 3 , wherein M is one or more selected from Mn and Co. A positive electrode for a lithium ion battery using the positive electrode active material for a lithium ion battery according to any one of claims 1 to 4 . A lithium ion battery using the positive electrode for a lithium ion battery according to claim 5 .

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