JP2016050797A - Sample container for thermal analysis, and evaluation method of positive electrode active material for nonaqueous electrolyte secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sample container for thermal analysis capable of thermal analysis of a positive electrode active material for a nonaqueous electrolyte secondary battery with high accuracy and high reliability, and also to provide an evaluation method of the positive electrode active material for a nonaqueous electrolyte secondary battery using the sample container.SOLUTION: A sample container for thermal analysis of a positive electrode active material for a nonaqueous electrolyte secondary battery is used, which is characterized in being a metal quality container which is composed of a pan 3 and a lid body 2 and has a structure from which inner pressure due to gas generated in the sample container during heating in the thermal analysis is released and a structure which suppresses inflow of atmosphere gas into the sample container.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a thermal analysis sample container and a method for evaluating a positive electrode active material for a non-aqueous electrolyte secondary battery using the sample container.

In recent years, non-aqueous electrolyte secondary batteries, in particular lithium secondary batteries, have attracted attention as power sources for portable devices such as mobile phones and small computers, power storage power sources, and electric vehicle power sources.
A nonaqueous electrolyte secondary battery is generally composed of a positive electrode having a positive electrode active material as a main constituent, a negative electrode having a negative electrode active material as a main constituent, and a nonaqueous electrolyte, and the constituent materials are packaged with a metal can. There are a hard pack type and a soft pack type (laminate cell) packaged with an aluminum laminate film. As the positive electrode active material constituting the non-aqueous electrolyte secondary battery, a lithium-containing transition metal oxide typified by lithium cobaltate is used, and as the negative electrode active material, a carbonaceous material typified by graphite (graphite) is used. As an aqueous electrolyte, an electrolyte salt typified by lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a non-aqueous solvent combining a high boiling point solvent typified by ethylene carbonate and a low boiling point solvent typified by diethyl carbonate. Things are widely used.

In researching batteries, it is important to elucidate the mechanisms such as charging / discharging and heat generation of the batteries, and many studies have been conducted on analysis methods therefor. As an analysis technique, for example, there is a quantitative analysis method using a thermal analyzer such as thermogravimetry or differential scanning calorimetry. In particular, as an analysis method for elucidating the mechanism of heat generation from the positive electrode active material, a method in which a battery is disassembled, a constituent material of the positive electrode is taken out, and differential scanning calorimetry analysis is performed is useful.
In these analysis methods, the constituent material of the positive electrode is used as a sample, the temperature is increased to 300 to 400 ° C. at a temperature increase rate of 5 to 20 ° C./min in the container, and the metal oxide in the sample is sequentially phase-transduced. The weight stability of each positive electrode active material is evaluated by measuring each weight decrease in the weight measurement and measuring each calorific value in the differential scanning calorimetry.
Here, the sample container used in the thermal analyzer is usually a metallic container having an inner diameter of 5 to 7 mm and a height of 2.5 to 5 mm, and the sample is placed in this container at 10 to 30% of the container volume. Used to fill to the extent.

  Since the constituent material of the positive electrode contains an organic solvent in addition to the positive electrode active material, it is necessary to shut off the atmosphere outside the container and to seal the container in order to prevent burning of the organic solvent during temperature rise. I got it. However, when the temperature is raised in a sealed container, the various pressures generated from the measurement sample may cause the internal pressure in the container to become too high at the time of temperature rise, and the container may burst or fall over. Therefore, it has been performed to reduce the amount of gas generated by reducing the amount filled in the container.

  As a method for exhausting the gas generated in the container during thermal analysis, for example, Patent Document 1 discloses that in a thermal analysis sample container used for thermal analysis such as thermogravimetry or differential scanning calorimetry, A metallic container has been proposed which has only a hole with a diameter of 5 to 60 μm in its lid and a sealed state other than the hole. However, this sample container for thermal analysis is used for thermal analysis of a sample having a dehydration reaction temperature close to each other such as dihydrate gypsum and hemihydrate gypsum in cement powder, and the internal pressure in the container is increased. It is intended to cause a dehydration reaction in a state, and is not suitable for use as a thermal analysis of a constituent material of a positive electrode that generates a large amount of gas.

  In order to elucidate the heat generation mechanism of the positive electrode active material, it is effective to analyze the positive electrode constituent material of the battery using a sealed thermal analysis sample container. However, when the thermal analysis is performed, the constituent material of the positive electrode constituting the battery itself releases a large amount of gas, which may break the sealed sample container as described above or cause the sample container to collapse. And stable measurement was difficult. In addition, there is a problem that measurement accuracy is poor and measurement results sufficient for elucidating mechanisms such as charging / discharging and heat generation of the battery cannot be obtained.

JP-A-6-242035

  In view of the above problems, the present invention provides a thermal analysis sample container capable of thermal analysis of a highly accurate and reliable positive electrode active material for a non-aqueous electrolyte secondary battery while preventing the sample container from bursting or overturning. It aims at providing the evaluation method of the positive electrode active material for non-aqueous electrolyte secondary batteries using this sample container.

  In order to solve the above problems, the present inventor has intensively studied a thermal analysis method capable of obtaining high analysis accuracy of the positive electrode active material, and as a result, in the sample container for thermal analysis used for thermal analysis, the internal pressure due to the generated gas is reduced. By using a sample container for thermal analysis having a structure that opens and a structure that suppresses the inflow of atmospheric gas into the sample container, it is possible to fill a larger amount of sample into the sample container than before. Obtained knowledge. Furthermore, by increasing the number of samples filled in the sample container, the peak of the thermal analysis curve was clearly observed and the knowledge that the analysis accuracy was improved was obtained, and the present invention was completed.

That is, the sample container for thermal analysis of the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a sample container for thermal analysis composed of a tray and a lid, and is generated in the sample container during heating in thermal analysis. It is a metallic container having a structure for releasing internal pressure due to gas and a structure for suppressing the inflow of atmospheric gas into the sample container.
The thermal analysis sample container preferably has a structure in which the lid has one hole having a diameter of 400 to 700 μm and the tray and the lid are pressure-bonded.
The thermal analysis is preferably differential scanning calorimetry, and is preferably used for evaluating the thermal stability of the positive electrode active material for a non-aqueous electrolyte secondary battery.

The method for evaluating a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is characterized in that a thermal analysis is performed by filling a measurement sample in the thermal analysis sample container.
The thermal analysis is preferably a differential scanning calorimetry analysis.
Moreover, it is preferable to fill the sample container with the measurement sample of 50 to 90% of the internal volume of the sample container for analysis, and the measurement sample has a configuration of a positive electrode taken out by disassembling the battery after charging. A material is preferred.

  The present invention makes it possible to increase the amount of sample that can be filled in the sample container for thermal analysis while preventing the sample container from being ruptured or overturned by gas or water vapor generated from the sample, and clearly separates the peaks of the thermal analysis curve. can do. In addition, the reaction with the measurement sample can be suppressed by suppressing the inflow of the atmosphere outside the container into the sample container. Thereby, it is possible to easily perform thermal analysis of the positive electrode active material for a non-aqueous electrolyte secondary battery with high accuracy and high reliability, and the industrial value is extremely large.

It is the schematic which shows the structure of the sample container used in the Example. It is the figure which showed the exothermic curve obtained by the differential scanning calorimetry analysis in an Example.

  A sample container for thermal analysis of a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention (hereinafter simply referred to as a sample container) is a sample container for thermal analysis composed of a tray and a lid, and is being heated in thermal analysis. And a metal container having a structure for releasing the internal pressure due to the gas generated in the sample container and a structure for suppressing the inflow of atmospheric gas outside the sample container into the sample container.

  Typical quantitative analysis methods as thermal analysis include thermogravimetry (hereinafter abbreviated as TG) and differential scanning calorimetry (hereinafter abbreviated as DSC). The quantitative analysis method using these thermal analyzers is a method in which a sample container is filled with a measurement sample, the container is set in a heater of the measurement apparatus main body, and the thermal behavior of the sample is observed while the temperature is raised. This is an analysis method for evaluating characteristics.

  The sample container used for the analysis method is generally composed of aluminum or alumina. Further, the lid of the sample container is normally used in a sealed state in order to prevent the reaction between the oxygen gas in the atmosphere to which the sample container is exposed and the measurement sample. For this reason, in the analysis method, the internal pressure of the sample container is increased by the gas component generated from the measurement sample, and the sample container may be ruptured. In an open sample container, since the measurement is usually performed in an air atmosphere, the measurement peak may be obscured by the reaction between the air atmosphere, particularly oxygen gas, and the measurement sample.

  The sample container of the present invention has a structure that releases the internal pressure due to the gas generated in the sample container during heating in thermal analysis, thereby releasing the gas component generated from the measurement sample to the outside of the measurement container and rupturing the sample container. And can prevent falls. As a structure for releasing the internal pressure, it is simple and preferable to make a hole in the lid of the sample container. Although depending on the size of the sample container, in order to fill the sample container with a sufficient amount of sample to obtain a highly accurate measurement result, for example, the commonly used inner diameter is 5 to 7 mm and the height is 2 In a sample container having a size of 5 to 5 mm, it is preferable that the number of holes having a lid is one with a diameter of 400 to 700 μm, and more preferably 600 to 700 μm. Moreover, it is preferable that the lid body and the tray are bonded by pressure bonding. By pressure bonding, gas can be released only from the hole provided in the lid, and the inflow of atmospheric gas into the sample container can be sufficiently suppressed. Further, the thickness of the lid is preferably 10 to 200 μm in order to increase the drilling accuracy.

Thereby, the gas generated in the sample container during heating can be released more sufficiently, and the sample container can be further prevented from being ruptured or toppled. In addition, by setting the diameter of the hole of the lid within the above range, it is possible to suppress the inflow of the atmospheric gas into the sample container due to the release of the gas generated in the sample container.
If the diameter is less than 400 μm, the sealed state in the container becomes too high, and the internal pressure becomes too high when the temperature rises, and the container may burst. On the other hand, if the diameter exceeds 700 μm, atmospheric gas flows into the container, and the separation of the peak of the exothermic curve may become unclear.

  It is easy to make one hole in the range of the diameter of the lid, but it is also possible to make a plurality of holes. In that case, the diameter and the number may be adjusted so that the internal pressure can be released and the inflow of atmospheric gas can be suppressed.

  The material of the sample container may be a ceramic material such as alumina. However, in order to improve the measurement accuracy, the material of the sample container is a metal material having good heat conduction. The metal container is easy to make a hole in the lid and press the lid and the tray. Furthermore, it is preferable that it is aluminum excellent in heat conduction and workability.

The method for evaluating a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is characterized in that the measurement sample is filled in the sample container for thermal analysis and thermal analysis is performed. As a result, a sufficient amount of measurement sample can be filled in the sample container, and analysis can be performed with high accuracy while preventing the sample container from bursting or falling.
Examples of thermal analysis include TG and DSC. As described above, a method of performing DSC analysis is useful as an analysis method for elucidating the mechanism of heat generation from the positive electrode active material, particularly for evaluating thermal stability. Yes, it is preferable.

  The filling amount of the measurement sample into the sample container may be that gas generated from the measurement sample is released to the outside of the container, but is preferably 50 to 90% of the internal volume of the sample container. This makes it possible to fill a sample container with a sufficient amount of measurement sample to obtain high measurement accuracy, and to release the internal pressure of the generated gas and suppress the inflow of atmospheric gas. If the sample is filled to exceed 90% of the internal volume, the gas generated from the measurement sample may not be released outside the container. In particular, when the gas is released through the hole in the lid, it is likely that the hole is blocked by the measurement sample and the gas is not released. On the other hand, if a sample with less than 50% of the internal volume is filled, the measurement peak may become unclear and the measurement accuracy may be lowered.

  The measurement sample is selected according to the purpose of analysis. However, when evaluating thermal stability, it is preferable to use a constituent material of the positive electrode taken out by disassembling the battery after charging. Thereby, it becomes possible to evaluate the positive electrode active material after the charge whose thermal stability is lowered.

  Hereinafter, embodiments of the present invention will be described in detail using examples, but the present invention is not limited to the examples.

(Example)
A sample container for thermal analysis shown in FIG. 1 was prepared and subjected to DSC analysis using a differential scanning calorimeter (NETZSCH JAPAN Co., Ltd. (formerly Bruker AXS), DSC3100SA). The sample container was made of aluminum, the pan was 5 mm in diameter and 2.5 mm in height, the lid was 200 μm thick, and had one hole with a diameter of 400 μm in the center of the lid. The positive electrode constituent material taken out by disassembling the charged battery inside the sample tray was filled with 50% of the internal volume of the sample container, and the outer peripheral portion of the lid was crimped to be in close contact with the tray. The measurement atmosphere was air, the temperature was raised at 10 ° C./min, and the measurement was performed from room temperature to 400 ° C.
Furthermore, DSC analysis was performed in the same manner as in Example 1 except that the filling amount of the constituent material of the positive electrode was changed from 50 to 90% and the hole of the lid body was changed at a diameter of 400 to 700 μm. The DSC analysis results are shown in Table 1. FIG. 2 shows an example of a heat generation curve obtained in the example.

(Comparative example)
DSC analysis was performed in the same manner as in Example 1 except that the filling amount of the constituent material of the positive electrode was 40% or 100% and that the hole of the lid was 300 μm or 800 μm in diameter. The DSC analysis results are shown in Table 1. FIG. 2 shows an example of a heat generation curve obtained in the comparative example.

(Evaluation)
In the embodiment, the gas generated in the sample container is released, the inflow of the atmospheric atmosphere outside the sample container into the container can be suppressed, and a sufficient amount of the measurement sample is filled in the container. Therefore, good DSC analysis was possible. On the other hand, in the comparative example, the filling amount of the measurement sample was large and the hole of the lid was closed, or the hole of the lid was too small, so the gas generated in the sample container could not be released, and the sample container Burst. Moreover, the filling amount of the measurement sample was too small, or the hole in the lid was too large to suppress the inflow of the atmospheric atmosphere into the container, and the exothermic peak became unclear.

1 Lid hole 2 Lid 3 Saucepan

Claims (8)

  A sample container for thermal analysis comprising a saucer and a lid, wherein the internal pressure due to the gas generated in the sample container during heating in the thermal analysis is released, and the structure for suppressing the inflow of atmospheric gas into the sample container; A sample container for thermal analysis of a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that the container is a metallic container.   2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lid body has one hole having a diameter of 400 to 700 μm, and the tray and the lid body are pressure-bonded. Sample container for thermal analysis.   The thermal analysis sample container according to claim 1, wherein the thermal analysis is differential scanning calorimetry.   The thermal analysis sample container according to any one of claims 1 to 3, wherein the thermal analysis is used for evaluation of thermal stability of a positive electrode active material for a non-aqueous electrolyte secondary battery.   A method for evaluating a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the thermal analysis sample container according to claim 1 is filled with a measurement sample and subjected to thermal analysis.   The said thermal analysis is differential scanning calorimetry analysis, The evaluation method of the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 5 characterized by the above-mentioned.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5 or 6, wherein analysis is performed by filling the sample container with the measurement sample of 50 to 90% of the internal volume of the sample container. Evaluation method.   The method for evaluating a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein the measurement sample is a constituent material of a positive electrode obtained by disassembling and removing a battery after charging. .

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