JPH103916A - Manufacture of positive electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transition metal composite oxide having high homogeneity with a high yield and few number of processes at a low cost by heat-fusing the raw material of the transition metal composite oxide, then liquid phase- mixing, solidifying, and sintering it to generate the transition metal composite oxide. SOLUTION: CH3 COOLi.2H2 O and Mn(NO3 )2 .6H2 O are mixed at the mol ratio of 1:2 and heat-fused, the mixture is stirred for 1hr in the liquid phase at 70-100 deg.C, it is kept at 130-200 deg.C for 6hr to be solidified, then it is crushed to obtain a positive electrode active material precursor, for example. The precursor is temporarily baked for 5hr in the air at 230-300 deg.C, then it is baked for 20hr in the air at 650-800 deg.C to obtain positive electrode active material powder. This powder is made of LiMn2 O4 single phase of the spinel phase, and it can be confirmed as the aggregation of fine particle powder of 10-200nm. A battery excellent in the capacity characteristic and cycle characteristic can be obtained at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for producing a positive electrode active material constituting a lithium ion secondary battery or the like.

[0002]

2. Description of the Related Art In recent years, with advancement of electronic technology, electronic devices have been improved in performance, downsized, and portable, and these electronic devices have been required to have a secondary battery having a high energy density. Conventionally, as a secondary battery used in these electronic devices, a nickel-cadmium secondary battery, a lead storage battery, a lithium secondary battery and the like can be mentioned. In particular, a lithium secondary battery has a high battery voltage, a high energy density, low self-discharge, and excellent cycle characteristics.

[0003] This lithium secondary battery comprises a positive electrode and a negative electrode capable of reversibly inserting and removing lithium, a separator interposed between the two electrodes, and a non-aqueous electrolyte or solid electrolyte.

In general, as the negative electrode active material, lithium or lithium alloy capable of reversibly inserting and removing lithium ions,
Alternatively, a substance such as a conductive polymer or a layered compound (a carbon material or a metal oxide) is used.

As the positive electrode active material, TiS ₂ , MoS ₂ ,
Lithium-free compounds such as NbSe ₂ and V ₂ O ₅ , and LiM
A transition metal composite oxide already containing lithium such as O ₂ (M represents a transition metal such as Co, Ni, Mn, and Fe) is used. At present, from the viewpoint of obtaining a high energy density and a high voltage, the positive electrode of a 4V class battery is L
iCoO ₂ has been widely put to practical use.

By the way, LiCoO ₂ is an ideal cathode material in various aspects, but Co is ubiquitous and scarce as a resource on the earth, so it is expensive and difficult to supply stably. There was a problem that there was.

[0007] Accordingly, attention has been paid to a lower-cost cathode material based on Mn. At present, LiMn ₂ O ₄ having a positive spinel structure is the only cathode material of a Mn-based 4V-class battery. Had become.

In order to maximize the performance of LiMn ₂ O ₄ and achieve a high level of capacity and cycle characteristics, it is necessary to optimize the synthesis conditions, and it is known that uniform mixing is particularly important. ing.

Usually, synthesis of LiMn ₂ O ₄ is carried out by a solid phase reaction method. However, it is difficult to obtain a uniform mixture, and it is difficult to obtain a high level of capacity characteristics and cycle characteristics. In order to obtain sufficient uniformity, it is necessary to repeat mixing for a long time, or firing and crushing steps,
The process was complicated.

To solve these problems, low melting point Li
There has been reported a method of achieving uniformity by impregnating NO ₃ in a Mn source at about 260 ° C. and then firing. Also, as a way to achieve a higher level of uniformity,
A method has also been reported in which a Li source and a Mn source are dissolved in a solvent, mixed at the molecular level, and the solvent is removed before firing.

[0011]

However, in the method of impregnating LiNO ₃ having a low melting point in a Mn source at about 260 ° C. and then calcining it, a certain degree of uniformity can be obtained, but the Mn source is in a solid phase. For this reason, there is a limit to the uniformity, and processing at a relatively high temperature of 260 ° C. is required, so that the number of steps also increases.

In a method in which a Li source and a Mn source are dissolved in a solvent, mixed at a molecular level, and the solvent is skipped and then fired, extremely high uniformity is obtained, but the yield is high because a solvent is used. There is a problem that the energy is reduced, a large amount of energy is required for the process of removing the solvent, the cost for the solvent is added, or the process becomes complicated.

Accordingly, the present invention has been proposed to solve the above-mentioned problems, and it is an object of the present invention to obtain a transition metal composite oxide having high uniformity with low cost, high yield, and a small number of steps. It is an object of the present invention to provide a method for producing a positive electrode active material capable of producing a positive electrode.

[0014]

SUMMARY OF THE INVENTION According to the present invention, there is provided a method for producing a positive electrode active material, comprising: a step of melting a raw material of a transition metal composite oxide; Producing an object.

It is preferable to use a material having a melting point of 200 ° C. or less as a raw material of the transition metal composite oxide. The transition metal composite oxide to be generated is preferably a composite oxide of lithium and manganese.

According to the method for producing a positive electrode active material according to the present invention, the transition metal composite oxide is produced by hot-melting the raw material of the transition metal composite oxide and directly mixing in a liquid phase, so that the yield is high. A highly uniform positive electrode active material can be obtained with a small number of steps. Further, when the transition metal composite oxide to be generated is a composite oxide of lithium and manganese, it is possible to obtain a highly uniform cathode active material at a lower cost than in the past.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a positive electrode active material according to the present invention, a transition metal composite oxide is obtained by thermally melting a raw material of a transition metal composite oxide, mixing the resulting mixture in a liquid phase, and then solidifying and sintering. Generate.

The raw materials of the transition metal composite oxide include:
It is desirable to use one having a melting point of 200 ° C. or lower, more preferably 100 ° C. or lower. Therefore, when mixing these raw materials of the transition metal composite oxide, the mixing temperature is set to 200.
C. or lower, more preferably 100 ° C. or lower. If the mixing temperature is higher than this, it is difficult to maintain the liquid phase, and the solidification reaction tends to proceed.

According to the method for producing a positive electrode active material of the present invention, the transition metal composite oxide is produced by hot-melting the raw material of the transition metal composite oxide and directly mixing in a liquid phase. A highly uniform positive electrode active material can be obtained with a small number of steps. Therefore, according to this positive electrode active material, it is possible to provide a battery having excellent charge / discharge capacity and cycle characteristics.

In the positive electrode active material according to the present invention, the powdered positive electrode active material is finally pulverized, for example, after solidification to obtain the positive electrode active material. The precursor obtained by the solidification is uniformly and finely pulverized. Thus, a positive electrode active material powder having a very small particle size can be obtained. As a result, the ratio of the reaction surface area to the bulk of the positive electrode active material increases, and this does not change much during charging. Therefore, in a lithium ion secondary battery using this positive electrode active material, the distance over which lithium ions move in the electrolytic solution is significantly reduced, and the load characteristics of the battery are improved.

The method for producing a positive electrode active material according to the present invention is applicable to any transition metal composite oxide. For example, a lithium manganese composite oxide having a spinel structure, which had a low material cost but was difficult to obtain uniformity in the past, has a high yield and uniform properties according to the present invention. Will be formed.

The lithium manganese composite oxide having a spinel structure is LiMn ₂ O ₄ , or Li (Li _x Mn _2-x ) O in which a small amount of Li is substituted at the Mn site.
₄ is mentioned. The raw material of the lithium manganese composite oxide is not particularly limited as long as it has a low melting point, but may be CH ₃ COOLi.2H ₂ O, Mn (NO ₃ ) ₂ .6.
A mixed material of H ₂ O and the like can be mentioned.

In the production method of the present invention, an appropriate amount of a solvent such as ethanol or ethylene glycol may be added at the time of liquid phase mixing in order to perform the treatment at a lower temperature and to improve the uniformity.

In the production method of the present invention, in the process of solidifying the mixed solution, the temperature may be simply increased,
In this process, a spray drying method or the like in which the molten material is atomized by a nozzle or the like and heated may be applied. As a result, the time for solidification can be shortened, and speeding up and mass synthesis can be achieved. In this process, a solidification reaction can be promoted by introducing an airflow such as oxygen, nitrogen, or air. Further, in this step, additives and the like are added,
By forming a strong secondary aggregate, the electrode density can be improved during battery assembly.

The transition metal oxide produced as described above can be applied to any battery as a positive electrode active material. In particular, when it is applied to a lithium secondary battery or a lithium ion secondary battery, for example, Can be used in combination with the negative electrode and the electrolytic solution.

As the negative electrode, any one capable of reversibly inserting and removing lithium can be used. Pyrolytic carbons, cokes (pitch coke, needle coke,
Petroleum coke, etc.), graphites, glassy carbons, organic polymer compound fired products (calculated by firing phenolic resin, furan resin, etc. at an appropriate temperature and carbonized), carbonaceous materials such as carbon fiber and activated carbon, or In addition to lithium metal and lithium alloy (for example, lithium-aluminum alloy), polymers such as polyacetylene and polypyrrole can be used.

As the electrolytic solution, an electrolytic solution in which a lithium salt is used as an electrolyte and this is dissolved in an organic solvent is used. Here, the organic solvent is not particularly limited, for example, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, γ-butyrolactone,
Tetrahydrofuran, 2-methyltetrahydrofuran,
1,3-dioxolan, sulfolane, acetonitrile,
A single solvent or a mixed solvent of two or more such as diethyl carbonate and dipyrropyl carbonate can be used.

The electrolyte includes LiClO ₄ , LiAsF ₆ ,
LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiC
1, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li and the like can be used.

[0029]

EXAMPLES Hereinafter, a lithium secondary battery was actually manufactured using the positive electrode active material manufactured by applying the present invention, and its effect was examined. Although the present invention will be described specifically with reference to the present embodiment, the present invention is not limited to the present embodiment, and various modifications based on the technical idea of the present invention are possible.

Example 1 First, a positive electrode was produced as follows. CH ₃ COOL
i.2H ₂ O and Mn (NO ₃ ) ₂ .6H ₂ O were mixed at a molar ratio of 1: 2, melted by heat, stirred for 1 hour in a temperature range of 70 to 100 ° C. while maintaining a liquid phase, and stirred at 130 ° C. The positive electrode active material precursor was obtained by solidifying by holding in a temperature range of ~ 200 ° C for 6 hours and pulverizing. 230-300 of this precursor
After calcination in air at a temperature range of 5 ° C. for 5 hours,
The powder was calcined in the air at a temperature of 00 ° C. for 20 hours to obtain a positive electrode active material powder.

An X-ray powder diffraction experiment was performed on the positive electrode active material powder, and it was confirmed that the powder was a single phase of LiMn ₂ O _{4 as} a spinel phase. In addition, as a result of observation of the positive electrode active material with an electron microscope, it was confirmed that the positive electrode active material was an aggregate of fine particle powders of 10 to 200 nm.

Then, with respect to 80 parts by weight of the obtained positive electrode active material powder, 15 parts by weight of graphite and 5 parts by weight of a fluoropolymer binder were added and mixed with dimethylformamide (DMF). It was adjusted. DMF
After volatilization, about 60 mg of the positive electrode mixture was weighed, and about 2 cm ²
Pressure molding was performed on a disk-shaped electrode having a surface area of, and this was used as a positive electrode.

Next, metal lithium was punched out in the same disk shape as the positive electrode to obtain a negative electrode. The amount of lithium is several hundred times the maximum charging capacity of the positive electrode, and does not limit the electrochemical performance of the positive electrode.

Using the positive electrode and the negative electrode described above, a lithium secondary battery was manufactured using propylene carbonate (PC) in which LiPF ₆ was dissolved in an electrolytic solution.

Example 2 First, a positive electrode was produced as follows. CH ₃ COOL
i.2H ₂ O and Mn (NO ₃ ) ₂ .6H ₂ O were mixed at a molar ratio of 1.03: 1.97 and melted by heat.
Stir for 1 hour while maintaining the liquid phase in the temperature range of 100 ° C.
The positive electrode active material precursor was obtained by solidifying by holding in a temperature range of 30 to 200 ° C. for 6 hours and pulverizing the solid. This precursor was calcined in the air at a temperature of 230 to 300 ° C. for 5 hours, and then calcined in the air at a temperature of 650 to 800 ° C. for 20 hours to obtain a positive electrode active material powder.

When a powder X-ray diffraction experiment was performed on the positive electrode active material powder, Li (Li _0.03 M
n _1.97 ) O ₄ single phase was confirmed. In addition, as for the positive electrode active material, as a result of observation with an electron microscope, 10 to 2
It was confirmed that it was an aggregate of 00 nm fine particle powder.

A lithium secondary battery was manufactured in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 1 First, a positive electrode was produced as follows. Lithium carbonate and Mn ₂ O ₃ are mixed at a molar ratio of 1: 2, and are mixed in air at 700 to 8%.
The powder was fired at a temperature of 50 ° C. for 20 hours to obtain a positive electrode active material powder.

An X-ray powder diffraction experiment was performed on the positive electrode active material powder, and it was confirmed that the powder was a single phase of LiMn ₂ O _{4 as} a spinel phase. Further, as a result of observation of the positive electrode active material with an electron microscope, it was confirmed that the positive electrode active material was an aggregate of fine particles of 1 to 2 μm.

A lithium secondary battery was manufactured in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 2 First, a positive electrode was prepared as follows. Lithium carbonate and Mn ₂ O ₃ are mixed at a molar ratio of 1.03: 1.97, and calcined in air in a temperature range of 700 to 850 ° C. for 20 hours,
A positive electrode active material powder was obtained.

When a powder X-ray diffraction experiment was performed on the positive electrode active material powder, Li (Li _0.03 M
n _1.97 ) O ₄ single phase was confirmed. Further, as a result of electron microscopic observation of this positive electrode active material,
m was confirmed to be a collection of fine particle powders.

A lithium secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

In order to evaluate the cycle characteristics of the lithium secondary batteries (Example 1, Example 2, Comparative Example 1, and Comparative Example 2) manufactured as described above, the charge / discharge current density was set to 0.5.
The charge / discharge test was repeatedly performed within a potential range of 3 to 4.5 V while fixing to mA / cm ² . These results are shown in FIG. 1 and FIG.

As can be seen from FIG. 1 and FIG.
Has an initial capacity of 137.1.
mAh / g, in the lithium secondary battery of Example 2,
The initial capacity was as high as 131.0 mAh / g, and much better charge / discharge capacity and cycle characteristics could be obtained as compared with Comparative Examples 1 and 2 by the solid-state reaction method.

In the cycle characteristics, the first embodiment
The lithium secondary battery of Example 2 is slightly superior to the lithium secondary battery of Example 2. From this, a small amount of Li
To replace the Mn site is effective. Here, the Mn site is doped with lithium ions, but a divalent or trivalent cation other than lithium ions may be doped.

As described above, according to the manufacturing method to which the present invention is applied, a positive electrode active material having high uniformity and a small particle size can be obtained, so that a lithium secondary battery having excellent capacity characteristics and cycle characteristics is provided. be able to.

[0048]

As is apparent from the above description, the method for producing a positive electrode active material according to the present invention is characterized in that the transition metal composite oxide Thus, a positive electrode active material having high uniformity and small particle size can be obtained with a high yield and a small number of steps. In addition, when the transition metal composite oxide to be generated is a composite oxide of lithium and manganese, a positive electrode active material with high uniformity and small particle size can be obtained at lower cost than in the past.

Therefore, according to the method for producing a positive electrode active material according to the present invention, it is possible to provide a low-cost battery having excellent capacity characteristics and cycle characteristics.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between the number of cycles and a charge capacity in a lithium secondary battery manufactured using a positive electrode active material manufactured by applying the present invention.

FIG. 2 is a characteristic diagram showing a relationship between the number of cycles and a charge capacity in the lithium secondary battery.

Claims (5)

[Claims] 1. A method for producing a positive electrode active material, wherein a raw material of a transition metal composite oxide is thermally melted, mixed in a liquid phase, and then solidified and sintered to produce a transition metal composite oxide. 2. The method for producing a positive electrode active material according to claim 1, wherein a material having a melting point of 200 ° C. or less is used as a raw material of the transition metal composite oxide. 3. The method for producing a positive electrode active material according to claim 1, wherein the generated transition metal composite oxide is a composite oxide of lithium and manganese. 4. The method for producing a positive electrode active material according to claim 3, wherein the generated transition metal composite oxide has a spinel structure. 5. As a raw material of a transition metal composite oxide, CH
_{3 COOLi · 2H 2 O, Mn} (NO 3) The method for producing a positive electrode active material according to claim 3, which comprises using a ₂ · 6H ₂ O.