JP2554370B2 - Method for manufacturing non-aqueous electrolyte secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery,
In particular, the present invention provides a method for manufacturing a non-aqueous electrolyte secondary battery, in which the Li ions are excellently taken in and out by charge and discharge and which has excellent cycle life characteristics.

<< Prior Art >> In a non-aqueous electrolyte secondary battery using Li as a negative electrode, metallic lithium, a lithium alloy, a dielectric polymer doped with lithium ions as a negative electrode active material, and further lithium ions in a crystal are used. A mixed intercalation compound is used, and an organic electrolytic solution is used as the electrolytic solution.

On the other hand, various materials have been studied for the positive electrode active material, and typical examples include MoS ₂ , TiS ₂ , MoO ₃ , V ₂ O ₅ ,
Examples include metal sulfides such as LiMn ₂ O ₄ and metal oxides, Li-Mn-based composite oxides, and Mn-Cr-based materials.

The discharge reaction of the battery using these positive electrode materials proceeds by the transfer of lithium ions in the negative electrode between the layers of these materials that are the positive electrode active material, and in the case of reverse charging, lithium ions are transferred from the layers of the material to the negative electrode. Charging and discharging can be repeated by carrying out a transition reaction.

<< Problems to be Solved by the Invention >> However, when a positive electrode material such as a conventional metal oxide, sulfide, or Li-Mn-based complex oxide is repeatedly charged and discharged as a secondary battery, the discharge capacity gradually decreases. There was a drawback.

This is because the lithium ions that have penetrated into the positive electrode active material due to the discharge gradually become less likely to come out, and less of them return to the negative electrode side due to the charging reaction.

That is, if manganese oxide is taken as an example, on the positive electrode side, it remains bound in the crystal structure of the Mn oxide, and a new stable oxide is generated, which is involved in the next discharge reaction. It is speculated that the amount of lithium ions will decrease.

Therefore, when the current material is used, the discharge capacity is reduced even when charging is performed, and the secondary battery has a poor cycle life characteristic.

The present invention has been made in view of the above problems, and an object thereof is to reduce deterioration of discharge capacity due to migration of lithium ions as seen in conventional positive electrode materials and to provide excellent cycle life characteristics. It is to provide a method for manufacturing a non-aqueous electrolyte secondary battery.

<< Means for Solving the Problem >> The present inventor studied a composition containing lithium in the positive electrode material from the beginning in order to achieve the above object, and found that a composite oxide represented by Li Mn Cr O ₄ was used. It has been found out that the cycle life characteristic is remarkably increased by using as a positive electrode.

The present invention was made based on such findings, and after mixing lithium hydroxide, MnO ₂ and CrO ₃ , heat treatment was performed at 300 to 450 ° C. in an air atmosphere to obtain Li Mn Cr O ₄
The composite oxide represented by is produced and pulverized to obtain a positive electrode for a non-aqueous electrolyte secondary battery.

Then, this composite oxide was mixed with acetylene black as a positive electrode active material and PTFE powder as a binder, molded into a disk shape, and then pressed onto a net-shaped current collector, followed by drying, and PC-in a battery case. A non-aqueous electrolyte secondary battery can be obtained by contacting a negative electrode composed of an excess amount of metallic lithium or its alloy or a dielectric polymer containing lithium in a sufficient organic non-aqueous electrolyte such as DME or LiClO _4. .

The mixing ratio of the composite oxide obtained as the positive electrode active material was Li: Mn: Cr = 1: 1: 1, and in the other combinations, the conventional LiMn ₂ O ₄ or CrMnO ₄ was used. The capacity reduction rate is about the same as the cycle number of the battery, and no effect is observed.

Therefore, at the time of production, a compound oxide having the above composition ratio can be obtained by blending a mixing ratio according to the above composition ratio, and in a secondary battery using the same, a conventional positive electrode active material is used. It is possible to obtain an improvement in cycle life characteristics as compared with the one used.

<< Operation and Effect >> By using the composite oxide having the above composition as the positive electrode active material, even after a large number of charge / discharge reactions are repeated,
It has been clarified from the measurement results in Examples described later that the lithium ions transferred to the positive electrode side due to the discharge reaction are favorably re-migrated to the negative electrode side during the charge reaction.

This also means that Cr which forms the substitutional solid solution of Mn described above.
It has a relatively stable crystal structure, and it is presumed that even if Li ions enter from the outside, they do not bond as new compounds and the decrease in the amount of transfer during charging is reduced.

Therefore, in the non-aqueous electrolyte secondary battery manufactured according to the present invention, the cycle life characteristics can be significantly improved as compared with the conventional positive electrode active material.

<< Examples >> 40% in the air atmosphere after mixing the materials having the mixing ratios of the respective raw materials constituting the positive electrode active material shown in Table 1 below.
Treatment was carried out at 0 ° C. for 72 hours, and a pulverized composite oxide was used as a positive electrode to prepare a non-aqueous electrolytic secondary battery.

This battery uses a complex oxide as the positive electrode active material.
By mixing 10 parts by weight of acetylene black and 10 parts by weight of PTFE powder as a binder, the diameter of
mm-thickness 0.5 mm disc-shaped, press-bonded to a net-shaped current collector, dried at 250 ° C for 10 hours, and placed in a battery case. PC-DME, LiClO ₄ It is obtained by contacting with a negative electrode made of an excessive amount of metallic lithium in another organic non-aqueous electrolyte.

The composite oxide was chemically analyzed and the composition ratio is shown in Table 1.

In the same manner as above, as shown in Table 2 below, conventional Li-
Batteries made of Mn-based positive electrode active material (Sample Nos. 21 to 24) and batteries made of Mn-Cr positive electrode active material (Samples No. 25 to 2)
9) created.

Next, sample No. 1 to 20 mix ratio of the secondary battery 30
As a result of measuring the degree of decrease in capacity (%) with respect to charge / discharge cycles up to the number of times, the characteristics shown in FIGS. 1 (a) to 1 (e) were obtained. Moreover, this condition was performed by repeating charging / discharging from 3.8v to 2.0v with a constant current of 1 mA.

Further, FIG. 2 (a) shows the cycle characteristics using the positive electrode active material of Sample Nos. 21 to 24 made of conventional Li-Mn oxide, and as shown in the figure, the degree of capacity decrease with the cycle is remarkable. .

Further, FIG. 2 (b) shows the cycle characteristics using the positive electrode active material of Sample No. 25 to 29 made of the conventional Mn-Cr oxide, and as shown in FIG. .

As is clear from FIGS. 1 and 2 above, the conventional compositions shown in Table 2 are significantly inferior to the compositions shown in Table 1. On the other hand, among the compositions shown in Table 1, in addition to those of the present invention shown in Sample No. 11, Sample No.
12, 19 and 20 also show excellent characteristics, but sample No. 1
No. 2 has a large amount of added lithium and little cost merit, and sample Nos. 19 and 20 have much Cr and likewise have little cost merit. Therefore, practically, it can be said that the sample No. 11 of the present invention has the optimum composition.

In addition, FIG. 3 shows the results of measuring the capacity of 50 cycles of the NO. 11 sample according to the present invention shown in Table 1 under different heating temperature conditions.

In the figure, the one heated at 400 ° C is shown as an index with 100, but it shows good characteristics between 300 ° C and 400 ° C, and the best result was obtained especially under the condition of 400 ° C. .

[Brief description of drawings]

1 (a) to 1 (e) are graphs showing cycle life characteristics of a non-aqueous electrolyte secondary battery in which a composite oxide having various compositions including an embodiment of the present invention is used as a positive electrode, FIG. 2 (a), (B) is a graph showing cycle life characteristics of a non-aqueous electrolyte secondary battery using a conventional composite oxide having various compositions as a positive electrode, and FIG. 3 shows temperature conditions and cycle capacity of heat treatment of the positive electrode of the present invention. It is a graph which shows a relationship.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masanori Nakanishi 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Kikai Co., Ltd. (72) Hidenori Nagura 5-36-11 Shinbashi, Minato-ku, Tokyo (56) References JP-A-2-65061 (JP, A) JP-A-63-210028 (JP, A)

Claims (1)

(57) [Claims] 1. A method of manufacturing a non-aqueous electrolyte secondary battery comprising a negative electrode containing Li, an organic electrolyte and a positive electrode, wherein lithium hydroxide, MnO ₂ and CrO ₃ are mixed and then in an air atmosphere. 30
A method for producing a non-aqueous electrolyte secondary battery, which comprises subjecting a composite oxide represented by Li Mn Cr O ₄ to heat treatment at 0 to 450 ° C. and pulverizing the composite oxide to obtain the positive electrode.