JP2001345094A - Method of testing active material mixture for positive electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of testing an active material mixture for positive electrode, by which presence of foreign metals in the active material mixture for positive electrode can be proved with ease and certainty. SOLUTION: A positive electrode plate 1 on which an active material mixture for positive electrode has been coated, and a negative electrode plate 2 are opposed to each other through a separator 3 and immersed in an electrolyte, and predetermined voltage is applied between the positive electrode plate 1 and the negative electrode plate 2 to forcedly deposit foreign metals such as Fe and Cu in the positive electrode active material mixture on the separator. When foreign metals are mixed into the layer of the active material mixture for the positive electrode, black spots are visually observed on the separator 3 even when the mixed amount is 1 ppm or so. The black spots are separated from the separator 3 and subjected to elementary analysis, whereby the foreign metals are identified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a positive electrode active material mixture, and more particularly, to a method for containing a positive electrode active material capable of absorbing and releasing lithium ions and a binder for binding the positive electrode active material. The present invention relates to a method for testing a positive electrode active material mixture for determining the presence or absence of a different metal in a positive electrode active material mixture.

[0002]

2. Description of the Related Art Lithium ion batteries are mainly used for portable devices such as VTR cameras, notebook computers, and mobile phones, taking advantage of the high energy density. In recent years, research and development of large-sized lithium-ion batteries for electric vehicles and power storage have been actively conducted. In particular, in the automotive industry, development of electric vehicles that use a motor as a power source and hybrid electric vehicles that use both an internal combustion engine and a motor as a power source are being promoted in order to respond to environmental issues. Some of them are already in practical use.

[0003] Large lithium ion batteries used in these electric vehicles and the like are required to have high capacity and high output, as well as safety and reliability. However, in the conventional lithium ion battery, the foreign metal ions (Fe, Cu, etc.) contained in the positive electrode active material mixture elute into the electrolytic solution, grow and precipitate on the negative electrode side by charge and discharge, and precipitate. In some cases, an internal short circuit between the positive and negative electrodes was caused.

[0004] Since these different metals, which are precipitates, cause an internal short circuit even if present in a concentration of less than 10 ppm in the positive electrode active material mixture layer, it is important to select raw materials used for the positive electrode. For this reason, conventional ICP analysis (In
Inductively-coupled plasma analysis) or the like was used to check whether a different metal was mixed in the positive electrode active material mixture.

[0005]

SUMMARY OF THE INVENTION However, the ICP
In the analysis, even if a different metal such as Fe or Cu was contained in the positive electrode active material mixture, the content was very small, so it was near the analysis limit, and it was not clear whether the different metal was mixed. . For this reason, there has been a problem that mixing of different metals has been found after the actual battery production, and the yield of battery production has been reduced. In addition, the battery is repeatedly charged and discharged with time, and the dissimilar metal is gradually deposited on the negative electrode side. Therefore, in order to ensure the reliability of the lithium ion battery, it is necessary to prevent the cause of the defect beforehand.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a method for inspecting a positive electrode active material mixture that can easily and clearly determine the presence or absence of a different metal in the positive electrode active material mixture.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a positive electrode active material containing a positive electrode active material capable of inserting and extracting lithium ions and a binder for binding the positive electrode active material. A method for testing a positive electrode active material mixture for determining the presence or absence of a dissimilar metal in a mixture, wherein the positive electrode coated with the positive electrode active material mixture and the negative electrode are opposed to each other with a separator therebetween in an electrolytic solution. And injecting a predetermined voltage between the positive electrode and the negative electrode to forcibly precipitate different metals in the positive electrode active material mixture as black spots on the separator.

In the present invention, a positive electrode coated with a positive electrode active material mixture containing a positive electrode active material capable of occluding and releasing lithium ions and a binder for binding the positive electrode active material, and a negative electrode are separated by a separator. To infiltrate into the electrolytic solution while facing each other, and apply a predetermined voltage between the positive electrode and the negative electrode. If a different metal is mixed in the positive electrode active material mixture, the different metal is forcibly precipitated as a black spot on the separator. According to the present invention, since dissimilar metals are forcibly precipitated as black spots on the separator, by visually observing the black spots on the separator, it is easy to determine whether the dissimilar metals are mixed in the positive electrode active material mixture. And it can be clearly distinguished.

In this case, if the method further includes a step of performing an elemental analysis of the deposited black spots, it is possible to identify a different metal in the positive electrode active material mixture, so that the material constituting the positive electrode active material mixture can be identified. Of these, the material having the dissimilar metal can be easily specified.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for testing a positive electrode active material mixture according to the present invention will be described with reference to the drawings.

<Preparation of Positive Electrode> Lithium manganate (LiMn ₂ O ₄ ) powder as a positive electrode active material, flaky graphite (average particle size: 20 μm) as a conductive agent, and polyvinylidene fluoride (Binylidene fluoride) as a binder PVDF) in a mass ratio of 9
The mixture was mixed at a ratio of 0: 4.5: 5.5, N-methyl-2-pyrrolidone (NMP) was added as a dispersion solvent to the mixture, and the mixture was kneaded to prepare a slurry. This slurry,
It was applied on one side of a 20 μm-thick aluminum foil (positive electrode current collector) to form a positive electrode active material mixture layer.

As shown in FIG. 1A, when the slurry was applied, an uncoated portion having a width of 30 mm was left on one of the side edges in the longitudinal direction of the aluminum foil. Then drying,
The positive electrode plate 1 having a width of 100 mm and a length of 100 mm was obtained after pressing and cutting to leave an uncoated portion of the side edge. The thickness of the positive electrode active material mixture layer (excluding the thickness of the aluminum foil) was 120 μm, and the coating amount of the positive electrode active material per one side of the aluminum foil was 344 g / m 2.
^{And 2} . A part of the 30 mm uncoated portion formed on the positive electrode plate 1 was removed to obtain a positive electrode current collecting lead piece 11 having a width of 10 mm and a length of 30 mm.

<Preparation of Negative Electrode Plate> 90 parts by mass of Carbotron P (product name: manufactured by Kureha Chemical Industry Co., Ltd.) which is amorphous carbon as an active material for a negative electrode, and 10 parts by mass of polyvinylidene fluoride as a binder Is added thereto, and N-
After adding methyl-2-pyrrolidone, the mixture was kneaded to prepare a slurry. This slurry was applied to one side of a rolled copper foil (negative electrode current collector) having a thickness of 10 μm.

As shown in FIG. 1 (B), when the slurry is applied, the width 30 is applied to one of the side edges in the longitudinal direction of the copper foil.
mm was left uncoated. Thereafter, drying, pressing and cutting were performed to obtain a negative electrode plate 2 having a width of 105 mm and a length of 105 mm. The bulk density of the negative electrode active material mixture layer is about 1.0 g / cm ³
And A part of the 30 mm wide uncoated portion formed on the negative electrode plate 2 was removed to obtain a negative electrode current collecting lead piece 21 having a width of 10 mm and a length of 30 mm.

<Electrode Assembly> As shown in FIG. 2, each of the prepared positive electrode plate 1 and negative electrode plate 2 was coated with the active material mixture,
A Teflon (registered trademark) container 4 is opposed to the separator 4 through a polyethylene separator 3 through which lithium ions can pass.
5 cc of the electrolytic solution was injected into the lower cover 42 to infiltrate the positive electrode plate 1, the negative electrode plate 2 and the separator 3 into the electrolytic solution. Thereafter, a simple cell was assembled by covering the container 4 with the upper lid 41 with an O-ring 5 made of EPDM interposed therebetween.
The upper cover 41 has an aluminum screw 6 and a copper screw 7
Are screwed respectively, and by turning these screws 6 and 7, the tip ends are respectively connected to the positive current collecting lead pieces 11 and
The negative electrode current collecting lead piece 12 was surely brought into contact.

The electrolytic solution includes ethylene carbonate (E
C) An organic electrolyte obtained by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a mole ratio of 1 mol / L in a mixed solution of dimethyl carbonate (DMC) and diethyl carbonate (DEC) at a volume ratio of 1: 1: 1 was used. .

<Voltage Application> Next, between the screws 6 and 7 of the fabricated simple cell, the battery was charged at a current of 50 mA at 4.2 V for 3 hours, discharged at a current of 50 mA to 2.5 V, and further discharged at 50 V.
After charging for 3 hours at mA and 4.2V, the battery was left for 24 hours.

<Disassembly inspection> After standing for 24 hours, the simple cell was disassembled and the presence or absence of black spots on the separator 3 was observed. If different metals such as Fe and Cu are mixed in the positive electrode active material mixture layer, the different metals are forcibly precipitated as black spots on the separator 3. Therefore, when a black spot is visually recognized on the separator 3, it is understood that a foreign metal is mixed in the positive electrode active material.

Further, the black spots are separated from the separator 3,
The dissimilar metal is specified by performing elemental analysis.

[0020]

Next, a description will be given of an example in which the presence or absence of a dissimilar metal is determined according to the above embodiment.

Example 1 In Example 1, as shown in Table 1 below, a positive electrode plate 1 coated with a positive electrode active material mixture in which Fe was mixed, and a negative electrode plate 2 were interposed with a separator 3 interposed therebetween. And assembled to form a simple cell. In this example, 1.0 ppm of Fe, which is a dissimilar metal, was intentionally mixed into the positive electrode mixture layer.

[0022]

[Table 1]

(Example 2) In Example 2, as shown in Table 1, a positive electrode plate 1 coated with a positive electrode active material mixture containing Cu and a negative electrode plate 2 were interposed with a separator 3 interposed therebetween. Assembled into a simple cell. In this example, Cu, which is a dissimilar metal, was intentionally mixed into the positive electrode mixture layer at 1.0 ppm.

Example 3 In Example 3, as shown in Table 1, a positive electrode plate 1 coated with a positive electrode active material mixture in which Cr was likely to be mixed, and a negative electrode plate 2 were separated by a separator 3
And assembled into a simple cell.

(Example 4) In Example 4, as shown in Table 1, a positive electrode plate 1 coated with a positive electrode active material mixture containing no dissimilar metal was mixed with a negative electrode plate 2 with a separator 3 interposed therebetween. And assembled to form a simple cell.

<Test> Next, the above-described voltage application and disassembly inspection were performed on each simple cell of the embodiment fabricated as described above. In this test, the voltage of each simple cell was measured after standing for 24 hours (before the dismantling inspection).

Table 2 below shows the test results.

[0028]

[Table 2]

(Evaluation) As shown in Tables 1 and 2, the simple cells of Examples 1 and 2 in which about 1 ppm of a different metal was mixed in the positive electrode active material mixture produced black spots on the separator 3, This caused a voltage drop. This black spot is caused by charging and discharging
u and Fe were deposited on the negative electrode plate 2. As a result of elemental analysis, Fe was detected in Example 1 and Cu was detected in Example 2.
Also, in the simple cell of Example 3, black spots were observed on the separator 3, and Cr was detected by elemental analysis of the black spots. However, although the ICP analysis was also performed on the positive electrode active material mixtures of Examples 1, 2, and 3, Fe, Cu, and Cr could not be clearly detected.

The simple cell of Example 4 did not cause a voltage drop after standing for 24 hours, and the separator had no black spots.
There is a certain relationship between the presence or absence of a black spot on the separator 3 and the voltage of the simple cell after 24 hours. That is, since a black point is recognized on the separator 3 in the simple cell which causes a voltage drop, the voltage drop of the simple cell can be estimated by observing the black point without performing the voltage measurement.

As described above, in this embodiment, the dissimilar metal is forcibly precipitated as black spots on the separator 3,
By visually observing the black spots on the separator 3, it is possible to easily and clearly determine whether or not a different metal is mixed in the positive electrode active material mixture. In addition, since the different metal can be specified by separating the black spot from the separator 3 and performing elemental analysis, it is possible to easily specify the positive electrode side material having the different metal.

Accordingly, the cause of the failure of the lithium ion battery can be prevented beforehand, so that the yield of the battery can be improved, and the precipitation of the dissimilar metal on the negative electrode side due to repeated charge and discharge can be prevented. So you can
The reliability of the lithium ion battery can be improved.

In this embodiment, an example is shown in which lithium manganate is used as the positive electrode active material.
It is possible to determine the presence or absence of the incorporation of a different metal in the general positive electrode active material mixture such as a cobalt composite oxide and a lithium-nickel composite oxide.

In this embodiment, an example in which amorphous carbon is used as the negative electrode active material has been described. However, carbon materials such as natural graphite, artificial graphite, and coke, and metal Li can also be used.
The shape of the particles is not particularly limited.

Further, in the present embodiment, the method of manufacturing and the size of the simple cell have been described, but the present invention is not limited to these, and various aspects can be adopted in the above-described claims. .

[0036]

As described above, according to the present invention,
Since foreign metals are forcibly precipitated as black spots on the separator, it is easy to clearly and clearly determine whether or not foreign metals are mixed in the positive electrode active material mixture by visually observing the black spots on the separator. Can be obtained.

[Brief description of the drawings]

FIG. 1 shows a positive electrode plate and a negative electrode plate manufactured according to a method for testing a positive electrode active material mixture according to an embodiment to which the present invention can be applied;
(A) is a plan view of a positive electrode plate, and (B) is a plan view of a negative electrode plate.

FIG. 2 is an external perspective view of a simple cell manufactured according to the inspection method of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode plate 3 Separator 4 Container 5 O-ring 6, 7 screw 11 Positive current collecting lead piece 21 Negative current collecting lead piece 41 Upper lid 42 Lower lid

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomohiro Iguchi 2-8-7 Nihonbashi Honcho, Chuo-ku, Tokyo Inside Shin-Kobe Electric Machinery Co., Ltd. (72) Kensuke Hironaka 2-87 Nihonbashi Honcho, Chuo-ku, Tokyo F-term in Shin-Kobe Electric Co., Ltd. (reference) 5H029 AJ14 AK03 AL06 AM03 AM05 AM07 5H050 AA19 BA05 BA17 CA08 CA09 CB07 GA28

Claims (2)

[Claims] 1. A positive electrode active material mixture comprising: a positive electrode active material mixture containing a positive electrode active material capable of occluding and releasing lithium ions and a binder for binding the positive electrode active material; A method for testing an agent, in which the positive electrode coated with the positive electrode active material mixture and the negative electrode are opposed to each other via a separator, soaked in an electrolytic solution, and a predetermined voltage is applied between the positive electrode and the negative electrode. A method for testing a positive electrode active material mixture, comprising forcibly precipitating a dissimilar metal in the positive electrode active material mixture as a black spot on the separator. 2. The method for testing a positive electrode active material mixture according to claim 1, further comprising an elemental analysis step of the deposited black spots.