JPH09293506A - Manufacture of positive pole active material for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a positive pole active material for a nonaqueous electrolyte secondary battery having the specified composition, capable of increasing discharging capacity by baking in two steps a mixture of a compound obtained by replacing part of a nickel salt with a salt of Co or the like and a lithium salt in the specified condition. SOLUTION: As a nickel salt, nickel oxide or nickel hydroxide is used, and part of the nickel of the nickel salt is replaced with the salt of Co, Mn, Fe, V, Cr, Al, or Mg. A mixture of this compound and a lithium salt is baked in two steps, and a positive pole active material represented by the general formula of LiNi1- YMYO2 (M is at least one element selected from Co, Mn, Fe, V, Cr, Al, Mg, and 0<Y<=0.25) is synthesized. As the lithium salt, LiOH or LiNO3 is preferable. In the two step baking, a first step baking is conducted in an air flow at 590-690 deg.C for preferably 2-20 hours, and a second step baking is conducted in an oxygen flow at 700-850 deg.C for preferably 0.25-30 hours. Thereby, the positive active material with high characteristics is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, and more specifically, to improve the characteristics of the positive electrode active material by specifying the two-step firing temperature and the atmosphere thereof. The present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery in which the discharge capacity of the non-aqueous electrolyte secondary battery is improved.

[0002]

2. Description of the Related Art Conventionally, a lithium composite oxide has been used as a positive electrode active material for a non-aqueous electrolyte secondary battery.

However, lithium cobalt oxide (Li
CoO ₂ ) has a small discharge capacity as a battery, and there is concern about supply. Therefore, lithium nickel oxide (LiNiO
_{Although 2} ) was tried to be used as the positive electrode active material, it may be insufficiently formed or may have low crystallinity depending on the firing conditions. Further, it was extremely weak against moisture and could not withstand long-term storage in an atmosphere with a high dew point. Therefore, there is a problem that the discharge capacity of the battery is small.

[0004]

DISCLOSURE OF THE INVENTION The present invention is to solve the above problems, and aims to improve the characteristics of the positive electrode active material and improve the discharge capacity of the non-aqueous electrolyte secondary battery. It aims at providing the positive electrode active material for.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
This is achieved by specifying the temperature of the stage calcination and its atmosphere.

That is, according to the present invention, nickel oxide or nickel hydroxide is used as a nickel salt, and a part of the nickel is replaced with a salt of cobalt, manganese, iron, vanadium, chromium, aluminum or magnesium, and a lithium salt. Of the general formula LiNi _1-Y M _Y O ₂ (M = C
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery represented by at least one element selected from o, Mn, Fe, V, Cr, Al and Mg: 0 <Y ≦ 0.25),
The first stage firing was performed at 590 to 690 ° C in the air stream at the second
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery is characterized in that the second-stage firing is performed in an oxygen stream at 700 to 850 ° C., respectively.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below.

In the present invention, a mixture of a lithium salt and a compound in which nickel oxide or nickel hydroxide is used as the nickel salt, and a part of the nickel is replaced with cobalt, manganese, iron, vanadium, chromium, aluminum and magnesium salts, respectively. The general formula LiNi _1-Y M _Y O ₂ (M = Co, Mn, F
At least one element selected from e, V, Cr, Al and Mg: a lithium composite oxide represented by 0 <Y ≦ 0.25) is obtained and used as a positive electrode active material of a non-aqueous electrolyte secondary battery. .

Here, Y in the above general formula is 0.2.
It is necessary to be 5 or less, and if Y exceeds 0.25, only a discharge capacity comparable to the conventional one can be obtained. Further, lithium hydroxide and / or lithium nitrate is preferably used as the lithium salt.

In the present invention, a mixture of a nickel salt partially substituted with a substituting element and a lithium salt is fired in two steps. Here, the first-stage firing is performed in an air stream at 590-6.
90 ° C., preferably 2 to 20 hours, second stage firing in an oxygen stream at 700 to 850 ° C., preferably 0.25 to 3
Perform each at 0 hours. By changing the firing conditions in this way, a lithium composite oxide having a basic skeleton of R-3m can be formed by the first-step firing, and the crystallinity can be improved by the second-step firing. . When the firing conditions are deviated from the above, a non-aqueous electrolyte secondary battery having a high discharge capacity and excellent cycle characteristics cannot be obtained.

The same effect can be obtained even if the ratio of lithium to nickel in the present invention is stoichiometrically decreased from 5% to 10%.

FIG. 1 is a side sectional view showing an example of the non-aqueous electrolyte secondary battery (lithium secondary battery) of the present invention. In the figure, 1 is a negative electrode terminal, 2 is an insulator, 3 is a negative electrode current collector plate, 4
Is a negative electrode material, 5 is a separator, 6 is a positive electrode mixture, and 7 is a positive electrode terminal.

[0013]

EXAMPLES The present invention will be specifically described below based on Examples and the like. It should be noted that the present invention is not limited to the raw materials, the battery configuration, etc. shown below.

Examples 1 to 3 Nickel hydroxide substituted with cobalt as a nickel salt by 18 mol% and lithium hydroxide as a lithium salt were weighed and mixed so that the molar ratio of nickel and lithium was 1: 1 respectively, and mixed with air. The mixture was baked in an air stream at each temperature shown in Table 1, cooled, pulverized, and again baked in an oxygen stream at 750 ° C. to obtain a lithium composite oxide (positive electrode active material). The firing time was 10 hours each.

The discharge capacity was evaluated by making the lithium secondary battery shown in FIG. That is, as the positive electrode mixture, a mixture of 85 parts by weight of the lithium composite oxide in an amount of 10 parts by weight of acetylene black and 5 parts by weight of a fluororesin-based binder was pressure-molded with a load of 3 t to obtain a diameter. 1
A pellet having a diameter of 0.6 mm was used.

As an electrolytic solution, lithium tetrafluoroborate (Li) is mixed in a 1: 1 mixed solvent of propylene carbonate and 1,2-dimethoxyethane so as to be 1 mol / l.
A solution of BF ₄ ) was used and used by being included in the separator.

Metallic lithium was used as the negative electrode material, and it was designed to be a sufficient amount (about twice the equivalent amount) with respect to the positive electrode mixture.

Using the obtained lithium secondary battery, a charge / discharge test was conducted under the conditions of a charge / discharge current density of 1 mA / cm ² , a charge end voltage of 4.3V and a discharge end voltage of 3.0V. The results are shown in Table 1.

Comparative Examples 1 and 2 As shown in Table 1, the firing temperature of the first stage was 550.
C., 750.degree. C., the other conditions were the same as in Example 1 to obtain a positive electrode active material, a lithium secondary battery was prepared in the same manner as in Example 1, and a charge / discharge test was conducted (Comparative Examples 1 to 1).
2). The results are shown in Table 1.

Examples 4 to 6 Nickel hydroxide substituted with 18 mol% of cobalt as a nickel salt and lithium hydroxide as a lithium salt were weighed and mixed so that the molar ratio of nickel and lithium was 1: 1 respectively, and mixed with air. The mixture was fired at 650 ° C. in an air stream, cooled, pulverized, and fired again in an oxygen stream at each temperature shown in Table 1 to obtain a lithium composite oxide (positive electrode active material). The firing time was 10 hours each.

Using the positive electrode active material thus obtained, a lithium secondary battery was prepared in the same manner as in Example 1 and a charge / discharge test was conducted. The results are shown in Table 1.

Comparative Example 3 As shown in Table 1, the firing temperature of the second step was 900 ° C.
Then, a positive electrode active material was obtained under the same conditions as in Example 4, except that the lithium secondary battery was prepared in the same manner as in Example 1 and subjected to a charge / discharge test. The results are shown in Table 1.

Comparative Example 4 As shown in Table 1, the second-stage firing temperature was set to 750.
The positive electrode active material was obtained in the same manner as in Example 4, except that the atmosphere was air-flowed at 0 ° C., and a lithium secondary battery was prepared in the same manner as in Example 1 and subjected to a charge / discharge test. . The results are shown in Table 1.

Example 7 As shown in Table 1, cobalt 25 was used as a nickel salt.
A positive electrode active material was obtained in the same manner as in Example 1 except that nickel hydroxide substituted by mol% was used, and a lithium secondary battery was prepared in the same manner as in Example 1 and a charge / discharge test was conducted. The results are shown in Table 1.

Comparative Example 5 As shown in Table 1, cobalt 30 was used as a nickel salt.
A positive electrode active material was obtained in the same manner as in Example 1 except that nickel hydroxide substituted by mol% was used, and a lithium secondary battery was prepared in the same manner as in Example 1 and a charge / discharge test was conducted. The results are shown in Table 1.

[0026]

[Table 1] As is clear from Table 1, when the firing temperature of the first stage of Examples 1 to 3 is fired within a certain range, the discharge capacity is superior to that of Comparative Examples 1 and 2.

Similarly, when the second stage firing temperature of Examples 4 to 6 is performed within a fixed range and in an oxygen stream, the discharge capacities are superior to those of Comparative Examples 3 and 4. .

From the comparison between Example 7 and Comparative Example 5, it can be seen that the discharge capacity is excellent when the substitution rate is 25 mol% or less.

Example 8 The raw material mixture used in Example 1 was fired in the air stream at 650 ° C. for various firing times as the first stage firing, and the second stage firing was performed at 750 ° C. The mixture was baked in an oxygen stream for 20 hours to obtain a lithium composite oxide (positive electrode active material).

Using the positive electrode active material thus obtained, a lithium secondary battery was prepared in the same manner as in Example 1 and a charge / discharge test was conducted. The results are shown in FIG.

As is apparent from FIG. 2, it is clear that an excellent discharge capacity can be obtained when the firing time of the first stage is 2 to 20 hours.

Example 9 The raw material mixture used in Example 1 was fired in the air stream at 650 ° C. for 10 hours as the first stage firing, and then the second step was fired in the oxygen stream at 750 ° C. for a firing time. Were variously changed and fired to obtain a lithium composite oxide (positive electrode active material).

Using the positive electrode active material thus obtained, a lithium secondary battery was prepared in the same manner as in Example 1 and a charge / discharge test was conducted. The results are shown in FIG.

As is apparent from FIG. 3, it is clear that an excellent discharge capacity can be obtained in the second stage firing for 0.25 to 30 hours.

Example 10 The discharge capacity when various lithium salts are used is shown. The lithium salts used were lithium hydroxide, lithium oxide, lithium nitrate and lithium carbonate. After mixing with nickel in a stoichiometric ratio of 1: 1, the first step was calcined in an air stream at 650 ° C. The second stage firing was performed in an oxygen stream at 750 ° C. for 20 hours to obtain a lithium composite oxide (positive electrode active material).

Using the positive electrode active material thus obtained, a lithium secondary battery was prepared in the same manner as in Example 1 and a charge / discharge test was conducted. FIG. 4 shows the results.

As is apparent from FIG. 4, it was found that excellent discharge capacity was obtained when lithium hydroxide or lithium nitrate was used.

[0038]

As described above, since the characteristics of the positive electrode active material are improved by the manufacturing method of the present invention, a non-aqueous electrolyte secondary battery having a high discharge capacity and excellent cycle characteristics can be obtained. .

[Brief description of drawings]

FIG. 1 is a side sectional view showing an example of a lithium secondary battery according to the present invention.

FIG. 2 is a graph showing the relationship between the discharge capacity and the first-stage firing time.

FIG. 3 is a graph showing the relationship between discharge capacity and first stage firing time.

FIG. 4 is a graph showing the relationship between the discharge voltage and the discharge capacity of a lithium raw material.

[Explanation of symbols]

1: Negative electrode terminal, 2: Insulator, 3: Negative electrode current collector plate, 4: Negative electrode material, 5: Separator, 6: Positive electrode mixture, 7: Positive electrode terminal.

Claims (3)

[Claims] 1. Nickel oxide or nickel hydroxide is used as a nickel salt, and a part of the nickel is cobalt,
A compound of the general formula LiNi _{1 -Y} M _Y O ₂ (M = Co, Mn, which is synthesized by firing a mixture of a compound substituted with salts of manganese, iron, vanadium, chromium, aluminum and magnesium and a lithium salt in two steps Fe, V, C
At least one element selected from r, Al, and Mg: 0
<Y ≦ 0.25), which is a method for producing a positive electrode active material for an electrolyte secondary battery, wherein the first-stage firing is performed in an air stream at 590 to 690 ° C., and the second-stage firing is oxygen. 7 in the airflow
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which is performed at 00 to 850 ° C., respectively. 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the first stage firing is performed for 2 to 20 hours and the second stage firing is performed for 0.25 to 30 hours. Manufacturing method. 3. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein lithium hydroxide and / or lithium nitrate is used as the lithium salt.