JP2512239B2 - Method for producing positive electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

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.

[0002]

2. Description of the Related Art Attempts to put a non-aqueous electrolyte secondary battery using lithium, an oxide or a lithium alloy capable of absorbing and releasing lithium, and an organic electrolyte as an electrolyte into a negative electrode have been actively made. It is well known that a battery is conventionally constructed by using a sulfide or oxide of a transition metal as a positive electrode active material. However, non-aqueous electrolyte secondary batteries using sulfides or oxides as these positive electrode active materials have any of the drawbacks such as low discharge voltage, small discharge capacity, short charge / discharge cycle life, high energy density, Long-life non-aqueous electrolyte secondary batteries have not been obtained.

In recent years, LiMn ₂ O ₄ and LiCoO have been used as positive electrode active materials in the development of high voltage and high energy density batteries.
_2, etc. have been noticed and various researches have been made.

[0004]

At present, there are cobalt complex oxides and manganese complex oxides as positive electrode active materials for which high energy density can be expected, and these studies have been actively conducted. Although it has a feature of high energy density, it has a problem of short charge / discharge cycle life, and has not yet been used as a practical battery.

LiMn ₂ O _{4 is} a currently promising positive electrode active material.
However, the cycle characteristics in the voltage range of 4.5 V to 3 V are poor, and the discharge capacity decreases to half in about 50 cycles. Therefore, as an improvement of this active material, Mn of LiMn ₂ O ₄
An attempt was made to replace a part of the metal with a metal such as Co, Ni, Fe, or Cr, and the cycle characteristics could be significantly improved. However, substituting Mn with another metal causes a decrease in capacity.

The present invention solves the above problems and provides a method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery, which provides a non-aqueous electrolyte secondary battery having an increased charge / discharge capacity. To aim.

[0007]

In order to solve this problem, a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is to use a manganese composite oxide Li _x Mn which is a positive electrode active material.
_{(2-y) M y O} 4 (0.85 ≦ x ≦ 1.15,0.02 ≦ y
≦ 0.5, M is Mn, Co, F in the manufacturing method of at least one metal selected from Co, Fe, Ni and Cr).
The acetylacetonate complex of the metal is used as at least one of the starting materials of e, Ni and Cr.

[0008]

With this structure, in the method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, LiMn ₂ O ₄ has a cubic crystal structure having a spinel structure, and LiMn ₂ O ₄ is converted to Li from the crystal by charging.
Is extracted, and Li enters the crystal due to discharge. charging,
When the LiMn ₂ O ₄ after repeating the discharge cycle was examined by X-ray diffraction, it was found that the crystallinity was lowered.

In order to prevent deterioration of the crystallinity of LiMn ₂ O ₄ , L
By substituting a part of Mn in iMn ₂ O ₄ with Co, Cr, Fe, and Ni, it was possible to control the lattice constant of the active material and improve the cycle characteristics. At this time, the larger the amount of the substituting element, the better the cycle characteristics, but the increase in the amount of the substituting element also decreased the charge / discharge capacity.

Therefore, when a positive electrode active material using an acetylacetonate complex of each metal of Mn, Co, Fe, Ni, and Cr was synthesized and a battery was made using this, the charge / discharge capacity was increased more than before. I understand. The reason for this is that a metal acetylacetonate complex is used and Li ₂ CO ₃ is dissolved in an organic solvent such as ethyl alcohol.
It is considered that this is because the starting material was dispersed well by mixing with other raw materials such as, and an extremely fine active material was obtained after firing.

[0011]

EXAMPLES A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an example of the present invention will be described below with reference to the drawings.

(Example 1) 10% of Mn in LiMn ₂ O ₄
When preparing an active material in which is substituted with at least one element selected from Co, Ni, Fe and Cr, Mn ₃ O ₄ is used as a starting material of Mn and selected from Co, Ni, Fe and Cr. An acetylacetonate complex of each metal was used as a starting material for at least one element.

[0013] represents the composition in _{Li x Mn (2-y)} M y O 4, M
Is the above metal element, and is a positive electrode active material with x = 1 in the range of 0.85 ≦ X ≦ 1.15 and y = 0.2 in the range of 0.02 ≦ Y ≦ 0.5.

Next, this LiMn _1.8 M _0.2 O ₄ (M = C
A method of synthesizing at least one element selected from o, Fe, Ni, and Cr) will be described.

Using Li ₂ CO ₃ and one of the acetylacetonate complexes of Co, Fe, Ni and Cr and Mn ₃ O ₄ , the number of Li atoms is 1 and the number of Mn atoms is 1.8. , M
Is weighed so that the number of atoms in the
Were mixed with each other and heated in air at 900 ° C. for 10 hours to obtain a positive electrode active material.

As conventional examples, Co, Fe, Ni,
A positive electrode active material synthesized by using an oxide of each metal in place of the acetylacetonate complex of Cr was manufactured by the above-described synthesis method.

The oxide of each metal here is Co ₃
O ₄ , Fe ₂ O ₃ , NiO and Cr ₂ O ₃ were used.

The positive electrode active material thus obtained and the conductive material
Acetylene black, which is an electric agent, and poly-4, which is a binder.
Weigh ethylene fluoride so that the weight ratio is 7: 2: 1.
Then, they were mixed to obtain a positive electrode mixture. Diameter of positive electrode mixture 0.1g
1 ton / cm for 17.5 mm ²Press molded with
And In FIG. 1, the molded positive electrode 1 is placed in the case 2.
Ku. Porous polypropylene as the separator 3 on the positive electrode 1
A pyrene film was placed. Diameter of negative electrode 4 is 17.5 m
m 0.3 mm thick lithium plate
It was pressure-bonded to the sealing plate 6 to which the sket 5 was attached. With non-aqueous electrolyte
To give 1 mol / l of lithium perchlorate
Using a ren carbonate solution, place this on the separator 3.
And on the negative electrode 4. After that, the battery was sealed.

The charge / discharge cycle characteristics of these batteries were compared. The charging / discharging cycle test in this example was performed by charging / discharging at a constant current of 0.5 mA and a voltage range of 4.3V to 3.0V.

Table 1 shows the initial discharge capacity and the capacity retention ratio of the discharge capacity at the 100th cycle with respect to the initial discharge capacity. The number of samples n was 50 for each.

The discharge capacity here is converted per 1 g of the positive electrode active material.

[0022]

[Table 1]

As shown in (Table 1), Co, Fe, Ni,
The active material using the acetylacetonate complex of Cr as the starting material has an initial discharge capacity higher than that of the active material using the oxide of each metal of Co, Fe, Ni and Cr as the starting material. There is. Further, the capacity retention rate at 100 cycles did not differ depending on the starting material.

Looking at, for example, LiMn _1.8 Co _0.2 O ₄ , when an oxide is used as a starting material for Co, the initial discharge capacity is 115 mAh / g and the capacity retention rate is 87%, whereas An active material using an acetylacetonate complex as a starting material has an initial discharge capacity of 125 m.
Ah / g and capacity retention ratio were 88%. Therefore,
The initial discharge capacity can be greatly improved while maintaining excellent cycle characteristics.

Further, it can be seen that this result has a similar tendency for Fe, Ni and Cr.

(Example 2) Next, a study was conducted in the case where the starting material of Mn of the active material was also an acetylacetonate complex. When preparing an active material in which 10% of Mn of LiMn ₂ O ₄ is replaced with at least one element selected from Co, Ni, Fe, and Cr as in Example 1, Co, Ni, and F are prepared.
An acetylacetonate complex of each metal was used as a starting material for at least one element selected from e and Cr.

[0027] represents the composition in _{Li x Mn (2-y)} M y O 4, M
Is the above metal element, and is a positive electrode active material with x = 1 in the range of 0.85 ≦ X ≦ 1.15 and y = 0.2 in the range of 0.02 ≦ Y ≦ 0.5.

Next, this LiMn _1.8 M _0.2 O ₄ (M = C
A method of synthesizing at least one element selected from o, Fe, Ni, and Cr) will be described.

Li ₂ CO ₃ and Mn, Co, Fe, Ni, C
Using an acetylacetonate complex of r, the number of Li atoms is 1
On the other hand, the number of Mn atoms was 1.8 and the number of M atoms was 0.2, and they were mixed by using ethyl alcohol.
It was heated in air at 900 ° C. for 10 hours to obtain a positive electrode active material.

As comparative examples, Co, Fe, Ni,
A positive electrode active material using an oxide of each metal in place of the acetylacetonate complex of Cr was manufactured by the above-described synthesis method.

The oxide of each metal here is Co ₃
O ₄ , Fe ₂ O ₃ , NiO and Cr ₂ O ₃ were used. In addition,
An acetylacetonate complex was used as a starting material for Mn.

The positive electrode active material thus obtained, acetylene black as a conductive agent, and polytetrafluoroethylene as a binder were weighed in a weight ratio of 7: 2: 1,
The mixture was mixed to obtain a positive electrode mixture. 0.1g of positive electrode mixture 1
It was press-molded into 7.5 mm at 1 ton / cm ² to obtain a positive electrode. In FIG. 1, the molded positive electrode 1 is placed in the case 2.
A porous polypropylene film as the separator 3 was placed on the positive electrode 1. As the negative electrode 4, a lithium plate having a diameter of 17.5 mm and a thickness of 0.3 mm was pressure-bonded to the sealing plate 6 provided with the polypropylene gasket 5. As the non-aqueous electrolyte, a propylene carbonate solution in which 1 mol / l lithium perchlorate was dissolved was used and added to the separator 3 and the negative electrode 4. Thereafter, the battery was sealed.

The charge / discharge cycle characteristics of these batteries were compared. The charging / discharging cycle test in this example was performed by charging / discharging at a constant current of 0.5 mA and a voltage range of 4.3V to 3.0V.

Table 2 shows the initial discharge capacity and the capacity retention ratio of the discharge capacity at the 100th cycle with respect to the initial discharge capacity. The number of samples n was 50 for each.

The discharge capacity here is converted per 1 g of the positive electrode active material.

[0036]

[Table 2]

As shown in (Table 2), Co, Fe, Ni,
An active material using a Cr acetylacetonate complex as a starting material has a large increase in initial discharge capacity as compared with an active material using an oxide of each metal of Co, Fe, Ni and Cr as a starting material. Also, the capacity retention rate at 100 cycles is 8
It shows 5% or more.

Further, as compared with (Table 1), it can be seen that the initial discharge capacity is increased and the excellent cycle characteristics are maintained by changing only the Mn starting material from the oxide to the acetylacetonate complex. .

In this way, Mn, Co, Fe, Ni, C
r By using one of the starting materials for each metal as an acetylacetonate complex, it is possible to obtain an active material having a large initial capacity and a small decrease in discharge capacity with the cycle.

(Example 3) Furthermore, the amount of metal substituting a part of Mn of the active material was examined when the starting material was an acetylacetonate complex.

The case where a part of Mn of LiMn ₂ O ₄ is replaced with Co will be described. When preparing the active material, Mn ₃ O ₄ was used as the Mn starting material, and an acetylacetonate complex was used as the Co starting material.

The composition of the synthesized positive electrode active material was changed to LiMn.
Expressed as _(2-y) Co _y O ₄ , y = 0.02, 0.1, 0.
There are five types: 2, 0.3, and 0.5.

The synthesis method and the battery manufacturing method were the same as in Example 1 and Example 2. Also, the test conditions of the charge / discharge cycle characteristics of the obtained battery were the same as in Example 1 and Example 2. As a comparative example, the same test was performed on an active material using an oxide as a starting material of Co. The results are shown in (Table 3).

[0044]

[Table 3]

As shown in (Table 3), the active materials using the Co acetylacetonate complex as the starting material are compared in terms of the Co substitution amounts (y values). Compared with the active materials used, the initial discharge capacities greatly increased, and the capacity retention ratio after 100 cycles showed the same value.

[0046] Further, where the _{Li x Mn (2-y)} M y O 4 (M
Is at least one element selected from Co, Fe, Ni and Cr), x = 1, y = 0.02, 0.1, 0.
The active materials of 2, 0.3 and 0.5 have been described, but as a result of further study, 0.85 ≦ x ≦ 1.15 and 0.02 ≦ y
The same effect was obtained in the range of ≦ 0.5.

Further, as a result of evaluating the conventional LiMn ₂ O ₄ , the initial discharge capacity was 127 mAh / g, and
The capacity retention rate at 00 cycles was 48%. Among the active materials of this example, for example, LiMn _1.8 Co _0.2 O ₄ (see Table 3), the initial discharge capacity was 125 mAh / g, and the capacity retention ratio after 100 cycles was 88%, so that the equivalent capacity was It can be seen that an active material having the following characteristics and excellent cycle characteristics can be obtained.

As described above, in the method for producing a positive electrode active material, by using an acetylacetonate complex of each metal as a starting material for Mn, Co, Ni, Fe and Cr,
4.0 with high capacity and stable charge / discharge cycle characteristics
A V-class non-aqueous electrolyte secondary battery can be obtained.

Although the reason why the discharge capacity greatly increases is not clear, other than Li ₂ CO ₃ or the like in the state of being dissolved in an organic solvent such as ethyl alcohol using a metal acetylacetonate complex. It is considered that this is because the starting material was well dispersed and a very fine active material was obtained after firing by mixing with the raw material.

In the above examples, the electrolyte solution was 1 mol / mol.
This is the result when a propylene carbonate solution in which 1 liter of lithium perchlorate was dissolved was used. Lithium fluoride, propylene carbonate as a solvent,
It was confirmed that the same effect can be obtained when an electrolytic solution using carbonates such as ethylene carbonate, gamma-butyrolactone, esters such as methyl acetate and dimethoxyethane, or ethers such as tetrahydrofuran is used. In the examples, the substitution metal M of Mn
However, the effect of Mn on the charge and discharge capacity by the starting material is similarly observed when using a carbonate, an oxide or a hydroxide of Co, Ni, Fe or Cr instead of the nitrate. Have confirmed that there is.

[0051]

As is apparent from the above description of the embodiments,
According to the preparation of non-aqueous electrolyte secondary battery of the present invention, a lithium or lithium alloy as a negative electrode, using a non-aqueous electrolyte containing a lithium salt, LiMn _(2-y) as a positive electrode active material M _y O
₄ (M is at least one metal selected from Co, Ni, Fe and Cr, 0.85 ≦ x ≦ 1.15, 0.02 ≦ y
The use of the acetylacetonate complex of the metal as a starting material for Mn, Co, Ni, Fe, and Cr in manufacturing a non-aqueous electrolyte secondary battery using ≦ 0.5) increases the charge / discharge capacity. Contribute to the industry and have great industrial significance.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a coin battery used in a test of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

 1 Positive Electrode 2 Case 3 Separator 4 Negative Electrode 5 Gasket 6 Sealing Plate

Front page continuation (72) Inventor Masaki Hasegawa 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

(57) [Claims] 1. A lithium negative electrode and a lithium alloy or a lithium compound of formula _{Li x Mn (2-y)} M y O 4 (M is Co, N
at least one element selected from i, Fe and Cr,
0.85 ≦ x ≦ 1.15, 0.02 ≦ y ≦ 0.5) Production of a positive electrode active material for a non-aqueous electrolyte battery having a positive electrode and a non-aqueous electrolyte solution using a positive electrode having a composite oxide as an active material A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein at least one of the starting materials of Mn, Co, Ni, Fe and Cr is an acetylacetonate complex of the metal.