JP2001319648A - Spinel manganese oxide for lithium secondary battery and lithium ion battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel doped lithium rich spinel compound [Li]8a[LixMn2-x-y-zNiy(square)z]16dO4 (0.01<x<0.15, 0.01<y<0.2, z<0.02) used as a positive electrode material for a lithium secondary battery of high energy density type. SOLUTION: In a spinel manganese oxide for the lithium secondary battery, lithium hydroxide and chemically synthesized manganese dioxide and a nickel nitrate are burned at the temperature between 400 deg.C and 570 deg.C. After an additional thermal processing, a specific surface area of the resulting spinel compound (its structural formula is represented by [Li]8a[LixMn2-x-y-zNiy(square)z]16dO4 (0.01<x<0.15, 0.01<y<0.2, z<0.02)) is 1.2 m2/g or less, and its line width at the 3/4 of the peak height of the peek (400) in the X-ray diffraction diagram that has been measured by using FeKα is within 0.16 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a lithium secondary battery using an intercalation compound such as metallic lithium or lithium carbon (lithium-graphite) as a negative electrode active material. ] _8a [Li _x Mn _2-xyz Ni _y □ _z ] _16d
O ₄ on.

[0002]

_2. Description of the Related Art In addition to LiNiO ₂ , as a positive electrode active material for a 4 volt high energy density type lithium secondary battery, L
iCoO ₂ and LiMn ₂ O ₄ can be used. LiCo
Batteries using O ₂ as a positive electrode active material are already commercially available. However, cobalt has a small amount of resources and is expensive, so it is not suitable for mass production accompanying the spread of batteries. Manganese compounds are promising cathode materials in terms of resources and prices. Manganese dioxide, which can be used as a raw material, is currently being produced in large quantities as dry cell material.

[0003] LiMn ₂ O ₄ having a spinel structure has a disadvantage that its capacity decreases with repeated cycles, and in order to improve this disadvantage, the addition of Mg, Zn, or the like (see Thackeray et al.,
Solid State Ionics, 69, 59
(1994)) and addition of Co, Ni, Cr, etc. (Okada et al.
Battery Technology, Vol. 5, (1993)), and its effectiveness has already been demonstrated. However, 50 ° C
At the time of the above-mentioned high-temperature operation, Mn dissolution in the electrolytic solution becomes remarkable, so that the capacity is greatly reduced due to the cycle, and it is difficult to maintain a sufficient cycle life of the positive electrode simply by doping the above metal.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has a feature of a lithium-rich spinel in which Li is present at a 16d site having excellent cycle characteristics and a capacity decrease due to doping is higher than that of lithium. A metal having a small amount and excellent cycle characteristics is doped into the 16d site to improve the cycle characteristics at a high temperature. The amount of vacancies (□) is made as small as 0.02 or less in order to suppress the capacity reduction caused by metal doping to the 16d site. Furthermore, consideration is given to the dissolution of Mn, which controls the cycle characteristics at high temperatures, with the aim of improving the cycle life at high temperatures by reducing the specific surface area by high crystallization, reducing the rate of elution of manganese into the electrolytic solution. It is.

[0005]

The stoichiometric LiMn ₂ O ₄ becomes a lithium-rich spinel compound having a low capacity as charging and discharging are repeated, and it is confirmed that the lithium-rich spinel gradually shows a stable capacity. It is natural that the characteristics are good, and it has been confirmed experimentally (Yoshio et al .: J. Electrochem. So
c. 143, 625 (1996)). However, L
The higher the i / Mn ratio, the lower the capacity, making it impossible to use as a positive electrode material. As described above, the doping of a different metal is also effective for improving the cycle characteristics, and the present invention aims to improve the cycle characteristics by changing the configuration of the 16d site to Li, Mn, and Ni.

The capacity of the spinel manganese-based cathode material is 16
Determined by the amount of Mn (III) at the d-site, the decrease in capacity decreases as the oxidation number of the doped metal increases to 1, 2, or 3 valences. Further, even if the number of vacancies in the spinel structure is reduced, this capacity decrease is small (Yoshio et al., Electrochemistry, 66, 335).
(1998)). In order to dope a 16d site with Ni, which is a divalent metal, to draw out a relatively large capacity and secure a high capacity, it is necessary to reduce the proportion of vacancies. In order to achieve this object, firing was performed at a relatively high temperature of 750 ° C. As an incidental result, an improvement in crystallinity and a decrease in specific surface area occur.

The manganese dissolution rate decreases as the specific surface area decreases. In addition to stabilization of the structure itself as described above, the reduction in specific surface area also contributes to suppression of a capacity decrease due to dissolution of manganese.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The vacancy amount of a Ni-doped spinel compound is determined by chemical analysis. To calculate vacancies from the results of chemical analysis, it is necessary to clarify the oxidation number of Ni. Yoshio et al. (Electrochemistry, 66, 335 (1998)) revealed that the oxidation number of Ni in the spinel compound exists divalently from the relationship between the substitution rate of Ni and the charge capacity. The value of the vacancy amount z is obtained as follows.

The total amount of Mn and Ni determined by chelate titration is defined as V ₁ mmol / g, and the Li content determined by atomic absorption spectrometry and the Ni content determined by dimethylglyoxime gravimetric analysis.
The contents are respectively V ₂ and V ₃ mmol. The content of Mn is V ₁ -V ₃ . The average oxidation number m of manganese is determined from this value and redox titration.

From the above analysis results, the total oxygen amount V ₀ can be calculated by the following equation. _{V 0 = V 2/2 +} V 3 + m (V 1 -V 3) / 2 ···· (1)

An oxide having a spinel structure is represented by the general formula of AB ₂ O ₄ , and the number of all cation occupied sites is ／ of that of oxygen. If the amount of vacancies is V ₄ mmol / g, this value can be calculated from equation (2). V ₄ = 3V ₀ / 4−V ₁ −V ₂ (2)

Spinel structural formula [Li] _8a [Li _x Mn
_2-xyz Ni _y □ _z ] The oxygen and vacancy amount in _16d O ₄ are 1:
Since the molar ratio is 4, z: 4 = V ₄ : V _{0, that} is, z = 4 × V ₄ / V ₀ (3)

By substituting the expressions (1) and (2) into the expression (3), the expression (4) is finally obtained, and the vacancy amount z is obtained by using this expression. _{z = (6V 3 + 3m (} V 1 -V 3) -8V 1 -5V 2) / (V 2 + 2V 3 + m (V 1 -V 3)) ···· (4)

Using the Ni-doped lithium-rich spinel compound produced in Example 1 and Comparative Example 1 as a positive electrode active material, the characteristics of a lithium secondary battery were examined at 50 ° C. The electrolyte is 1M LiBF ₄ -EC · DMC (volume ratio 1: 2). Spinel structural formula [Li] _8a [L obtained in Example 1
i _0.017 Mn _1.916 Ni _0.049 □ _0.008 ] _16d O ₄ The first discharge capacity of the compound represented by 16dO 4 was 120.2 mAh / g, and the capacity at the 50th cycle was 115.6 mAh / g. When the capacity retention rate at the 50th cycle (capacity at the 50th cycle / capacity at the 1st cycle) is calculated, it is 96.2%.

On the other hand, the spinel structural formula of the sample synthesized at 650 ° C. shown in the comparative example is [Li] _8a [Li _0.010 Mn _1.912 ]
Ni _0.049 □ _0.029 ] _16d O ₄ , and the first discharge capacity is 109.8 mAh / g, which is about 10% lower than the discharge capacity of the first embodiment. The capacity at the 50th cycle is 104.1
Although relatively high at mAh / g, the capacity retention was 94.8.
% Is lower than that of Example 1 by about 1.4%. That is,
It was confirmed that the sample fired at 750 ° C. was superior in both capacity and cycle characteristics. The specific surface area of the sample of Example 1 was less than half of 1.8 m ² / g of the sample of Comparative Example 1 and 0.8 m ² / g. The X-ray diffraction pattern also shows a great difference between the two.

FIG. 1 shows a first embodiment measured using FeKα.
The XRD figure of the sample of FIG. The characteristic of the sample of Example 1 is 2θ
The peak at> 60 ° splits into two peaks. This is because the peak width was reduced as the crystallinity was improved, and the diffraction peaks due to Kα1 and Kα2 having slightly different wavelengths were separated. Usually, the crystallite size is calculated from the half width of the peak, and the crystallinity is discussed. In the case of this spinel compound, a highly reliable high intensity peak exists only at a low angle of 2θ <50 ° or less. Diffraction peaks due to Kα1 and Kα2 overlap, making it difficult to accurately measure the half width of the peak. Therefore, the peak (400) located at the highest angle side is selected from the peaks having relatively high intensities,
Crystallinity was evaluated from the line width at an intensity of 3/4. This value was 0.15 ° for the sample of Example 1 and 0.22 ° for the sample of Comparative Example 1.

As described above, the configuration of the 16d site is L
i, Mn, and Ni, the vacancy amount is suppressed, the specific surface area is reduced, and the crystallinity is increased.
It has been clarified that a positive electrode active material having high cycle characteristics can be produced.

[0018]

<Example 1> Lithium hydroxide, chemically synthesized manganese dioxide, and nickel nitrate were added in an amount of 1.03: 1.95: 0.
The mixture is pulverized at a molar ratio of 05. After heating at 470 ° C. for 5 hours, it was further heated at 530 ° C. for 5 hours. After cooling, the mixture was pulverized, baked at 750 ° C. for 40 hours, and cooled to room temperature in 3 hours.

This sample was analyzed by chemical analysis to obtain [Li] _8a [L
_{i 0.017 Mn 1.926 Ni 0.049 □ 0.008} ] it was confirmed that the spinel structure expressed compound of _16d O _4. The specific surface area is 0.8 m ² / g, and as shown in FIG.
It was confirmed that the peak on the high angle side in FIG. D was split into two peaks.

The above sample 25 mg and the conductive binder 10
A film-shaped mixture was prepared using the mg, and pressed against a stainless steel mesh to obtain a positive electrode. The positive electrode was dried at 200 ° C. and used. Lithium metal for the negative electrode and LiB for the electrolyte
F ₄ -EC · DMC (volume ratio 1: 2) was used. The charge / discharge current was 0.25 mA (0.1 mA / cm ² ), and the charge / discharge voltage range was 4.5 to 3.5 V. The charge / discharge test was performed at 50 ° C. The evaluations in the following Examples and Comparative Examples were all performed under the above conditions.

Example 2 Lithium hydroxide, chemically synthesized manganese dioxide, and nickel nitrate were prepared as 1.10: 1.90:
The mixture is pulverized at a molar ratio of 0.10. After heating at 470 ° C. for 5 hours, it was further heated at 530 ° C. for 5 hours. After cooling, the mixture was pulverized, baked at 750 ° C. for 40 hours, and cooled to room temperature in 3 hours. Also in the XRD diagram of this sample, it was confirmed that the peak on the high angle side was split into two peaks. The first discharge capacity is 1
Although the capacity was reduced to 06.2 mAh / g, the capacity retention at 50 cycles was 96% or more.

Example 3 Lithium hydroxide, chemically synthesized manganese dioxide, nickel nitrate and aluminum nitrate
The mixture is pulverized at a molar ratio of 03: 1.95: 0.025: 0.025. After heating at 470 ° C. for 5 hours, it was further heated at 530 ° C. for 5 hours. After cooling, the mixture was pulverized, baked at 750 ° C. for 40 hours, and cooled to room temperature in 3 hours. XR of this sample
In FIG. D, it was confirmed that the peak on the high angle side was split into two peaks. The first discharge capacity was 123.5 mAh / g, which was higher than that of Example 1, and the capacity retention rate at 50 cycles was 9
6% or more.

Example 4 Lithium hydroxide, chemically synthesized manganese dioxide, nickel nitrate, and zinc nitrate were added in the form of 1.030:
The mixture is pulverized at a molar ratio of 1.95: 0.025: 0.025. After heating at 470 ° C. for 5 hours, it was further heated at 530 ° C. for 5 hours. After cooling, the mixture was pulverized, baked at 750 ° C. for 40 hours, and cooled to room temperature in 3 hours. The initial discharge capacity of this sample was 117 mAh / g or more, and the capacity retention at 50 cycles was 96% or more.

Example 5 Lithium hydroxide, chemically synthesized manganese dioxide, nickel nitrate, and magnesium nitrate were used in the following manner.
The mixture is pulverized at a molar ratio of 03: 1.95: 0.025: 0.025. After heating at 470 ° C. for 5 hours, it was further heated at 530 ° C. for 5 hours. After cooling, the mixture was pulverized, baked at 750 ° C. for 40 hours, and cooled to room temperature in 3 hours. The initial discharge capacity of this sample was 115 mAh / g or more, and the capacity retention at 50 cycles was 96% or more.

EXAMPLE 6 Lithium hydroxide, chemically synthesized manganese dioxide, nickel nitrate and iron oxide were added in an amount of 1.03: 1.
The mixture is pulverized at a molar ratio of 95: 0.025: 0.025. After heating at 470 ° C. for 5 hours, it was further heated at 530 ° C. for 10 hours. After cooling, the mixture was pulverized, baked at 750 ° C. for 40 hours, and cooled to room temperature in 3 hours. The initial discharge capacity of this sample was 122 mAh / g, which was larger than that of Example 1, and
The capacity retention rate after 50 cycles was 96% or more.

<Comparative Example 1> Lithium hydroxide, chemically synthesized manganese dioxide, and nickel nitrate were used in an amount of 1.03: 1.95:
The mixture is pulverized at a molar ratio of 0.05. After heating at 470 ° C. for 5 hours, it was further heated at 530 ° C. for 5 hours. After cooling, it was pulverized, baked at 650 ° C. for 20 hours, and cooled to room temperature in 3 hours. The XRD profile of this sample showed a spinel structure, and it was confirmed that the sample did not contain any impurities.
The diffraction line on the high angle side was different from that in Example 1-6, and no peak splitting was observed. This sample was analyzed by chemical analysis [L
i] _8a [Li _0.010 Mn _1.912 Ni _0.049 □ _0.029 ] _16d O ₄
It was confirmed that can be displayed with.

[0027]

As described above, according to the present invention, the highly crystalline lithium-rich spinel manganese oxide substituted with a different metal has a function as a positive electrode of a lithium secondary battery and has excellent cycle characteristics at high temperatures. Therefore, it is useful as a positive electrode active material of a lithium ion battery or a lithium secondary battery used in a high temperature environment.

[Brief description of the drawings]

FIG. 1 [Li] _8a [Li _0.017 Mn _1.926 Ni _0.049
□ _0.008 ] XRD diagram at _16d O ₄ .

Continued on the front page (72) Inventor Shunji Taniguchi 2-1-2 Watanabe-dori, Chuo-ku, Fukuoka City Inside Kyushu Electric Power Company (72) Inventor Kazuyuki 2-1-1 Watanabe-dori, Chuo-ku, Fukuoka City, Fukuoka Prefecture No. 82 F-term in Kyushu Electric Power Co., Inc. (reference)

Claims (3)

[Claims] 1. A spinel structural formula [Li] _8a [Li _x Mn
_2-xyz Ni _y □ _z ] _{16 dO 4} (where □ is an empty lattice) The value of x is 0.01 to 0.15 and the value of y is 0.01 to 0.1
A compound having a value of 0.20 and z of 0.02 or less, a specific surface area of 1.2 m ² / g or less, and a 3/4 peak of a (400) peak in an X-ray diffraction diagram measured using FeKα. A spinel-based manganese oxide for a lithium secondary battery having a line width in height of 0.16 ° or less. 2. The metal doped at the 16d site is only Ni or Ni-Fe, Ni-Zn, Ni-Al, Ni-
The spinel-based manganese oxide for a lithium secondary battery according to claim 1, which is two kinds of alloys of Mg. 3. The aforementioned [Li] _8a [Li _x Mn _2-xyz N]
i _y □ _z ] A lithium secondary battery using _{16dO 4} as a positive electrode active material and a lithium ion battery using an intercalation compound such as carbon as a negative electrode.