JP6531488B2 - Thermal history detection method for lithium ion secondary battery - Google Patents

Description

  The present invention relates to a method of detecting the heat history of a lithium ion secondary battery, and more particularly to a method of detecting the heat history nonelectrochemically.

  Conventionally, in lithium ion secondary batteries, various non-electrochemical detection methods of abnormal temperature attainment history have been developed.

  For example, by making part of the exterior of the secondary battery transparent and filling the inside with the thermosetting resin precursor, heat is applied to change the thermosetting resin precursor from the transparent state to the opaque state. There is a technique for determining that the abnormal temperature has been reached (Patent Document 1).

  Further, there is a technology provided on the outer surface of the secondary battery with heat sensitive means that changes its color when the temperature of the battery reaches 80 ° C. or more, and the abnormal temperature rise of the battery is judged by the color change (Patent Document 2).

  In addition, there is a technology to judge that the abnormal temperature has been reached based on the color change by sticking a temperature indicator such as a thermo paint or a thermo seal that irreversibly changes color over the entire outer surface of the secondary battery (patented Literature 3).

JP, 2013-171780, A Japanese Patent Application Publication No. 2006-12825 JP 2012-174458 A

  However, as in the prior art, the temperature detection means whose transparency or color changes with temperature has low quantitativeness and shows that it has become an abnormal temperature, but can not know several times the temperature reached beyond the abnormal temperature. .

  Therefore, an object of the present invention is to provide a thermal history detection method of a lithium ion secondary battery, which can later know non-electrochemically the maximum temperature reached, which is the thermal history of the lithium ion secondary battery.

In the method of detecting the heat history of a lithium ion secondary battery of the present invention for achieving the above object, a calibration curve or a calibration formula is prepared in advance. Preparation of a calibration curve or calibration formula prepares multiple test bodies containing resin contained in a lithium ion secondary battery. Heat of different known temperatures is applied to each of a plurality of prepared specimens to give a thermal history of one degree . Each of the plurality of test pieces is subjected to two differential scanning calorimetry measurements to determine a differential profile between the first differential scanning calorimetry result and the second differential scanning calorimetry result. The correlation between the peak temperature appearing in the differential profile and the known temperature of the applied heat is taken as a calibration curve or calibration equation. And the part containing resin is taken out as a test object from a lithium ion secondary battery with an unknown heat history. Differential scanning calorimetry is performed on the subject at least twice. The differential profile of the first differential scanning calorimetry result and the second and subsequent differential scanning calorimetric measurement results is determined, and the peak temperature appearing in the differential profile is applied to a calibration curve or calibration equation to obtain the maximum reach added to the lithium ion secondary battery Estimate the temperature.

  According to the present invention, a calibration curve or a calibration equation is prepared in advance by two differential scanning calorimetry measurements using a test body containing a resin in a lithium ion secondary battery. Then, the portion containing the resin is taken out from the lithium ion secondary battery whose heat history is unknown, differential scanning calorimetry is performed at least twice, the peak temperature of the difference is obtained, and the secondary battery is applied by applying a calibration curve or equation. The highest achievable temperature of This makes it possible to detect the heat history of a wide temperature range quantitatively.

It is a perspective view showing the appearance of the flat lithium ion secondary battery as an example of a lithium ion secondary battery. It is a schematic sectional drawing which shows the internal structure of a lithium ion secondary battery. It is the graph which showed the 1st profile of the sample 2 of 130 degreeC application, and the 2nd profile. It is a difference profile of the 1st time of sample 1 of 125 ° C application, and the 2nd time. It is the differential profile of the 1st time in the sample 2 of 130 degreeC application, and the 2nd time. It is a difference profile of the 1st time in the sample 3 of 135 degreeC application, and the 2nd time. It is the difference profile of the 1st time in the sample 4 of 140 degreeC application, and the 2nd time. It is the graph which drew the approximated curve T calculated | required from the application temperature and the peak temperature of the difference profile. The first and second differential profiles of the subject sample whose thermal history is unknown.

  Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional proportions of the drawings are exaggerated for the convenience of the description, and are different from the actual proportions.

  In the following description of the embodiment, an example of a lithium ion secondary battery to which the heat history detection method according to the present invention is applied will be described first. Subsequently, a heat history detection method according to the present embodiment will be described. However, these descriptions are merely examples, and the present invention is not limited to the application to the lithium ion secondary battery described herein.

[Overall battery structure]
FIG. 1 is a perspective view showing the appearance of a flat lithium ion secondary battery as an example of a lithium ion secondary battery.

  As shown in FIG. 1, the flat lithium ion secondary battery 10 has a rectangular flat shape, and the positive electrode tab 27 and the negative electrode tab 25 for extracting electric power are drawn from both sides thereof. There is. The power generation element 21 is wrapped by the battery outer package 29 of the lithium ion secondary battery 10, and the periphery thereof is heat-sealed. The power generation element 21 is sealed with the positive electrode tab 27 and the negative electrode tab 25 drawn out.

  The removal position of the tab shown in FIG. 1 is not particularly limited. The form shown in FIG. 1 may be such that the positive electrode tab 27 and the negative electrode tab 25 may be drawn out from the same side, or the positive electrode tab 27 and the negative electrode tab 25 may be divided into a plurality and taken out from each side. It is not limited to

  FIG. 2 is a schematic cross-sectional view showing an internal configuration of the lithium ion secondary battery.

  As shown in FIG. 2, the lithium ion secondary battery 10 is a stacked battery. The lithium ion secondary battery 10 has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction proceeds is sealed inside a battery exterior material 29 which is an exterior body. Here, the power generation element 21 has a configuration in which the positive electrode 150, the separator 17, and the negative electrode 130 are stacked. The separator 17 contains a non-aqueous electrolyte (for example, a liquid electrolyte). The positive electrode 150 has a structure in which the positive electrode active material layer 15 is disposed on both sides of the positive electrode current collector 12. The negative electrode 130 has a structure in which the negative electrode active material layer 13 is disposed on both sides of the negative electrode current collector 11.

  In the laminated structure, the negative electrode 130, the separator 17 and the positive electrode 150 are laminated in this order. Thereby, the negative electrode 130, the separator 17 and the positive electrode 150 constitute one single battery layer 19. The lithium ion secondary battery 10 shown in the figure indicates that six cell layers 19 are stacked. Of course, in an actual battery, it is not limited to such a number of layers. Thus, the unit cells are electrically connected in parallel. The negative electrode 130 is configured of a negative electrode current collector 11 and a negative electrode active material layer 13. The separator 17 contains a non-aqueous electrolyte as an electrolyte. The positive electrode 150 is configured of a positive electrode current collector 12 and a positive electrode active material layer 15.

  The positive electrode current collector 12 and the negative electrode current collector 11 are attached with a positive electrode current collector plate (27) and a negative electrode current collector plate (25) respectively conducted to the respective electrodes (positive electrode 150 and negative electrode 130). Of the battery case 29 so as to be held outside the battery case 29. Portions of the positive electrode current collector plate (27) and the negative electrode current collector plate (25) which are exposed to the outside of the battery case 29 are a positive electrode tab 27 and a negative electrode tab 25. The positive electrode current collector plate (27) and the negative electrode current collector plate (25) are provided on the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode via the positive electrode lead and the negative electrode lead (not shown), respectively. It may be attached by ultrasonic welding or resistance welding.

[Positive electrode active material layer]
The positive electrode active material layer 15 contains a positive electrode active material. As a positive electrode active material, what is generally used for the lithium ion secondary battery 10 should just be used. For example, lithium-transition metal complex oxides such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni-Co-Mn) O _2, and some of these transition metals substituted by other elements, Lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds and the like can be mentioned. In some cases, two or more positive electrode active materials may be used in combination. Preferably, in view of capacity and output characteristics, a lithium-transition metal complex oxide is used as a positive electrode active material. Of course, positive electrode active materials other than those described above may be used.

  In addition, the positive electrode active material layer 15 may contain, if necessary, an additive such as a surfactant, a conductive aid, an electrolyte (a polymer matrix, an ion conductive polymer, an electrolytic solution, etc.), and a lithium salt for enhancing ion conductivity. Can be included. As these materials, those used in the well-known lithium ion secondary battery 10 can be used.

  The positive electrode active material layer 15 has a positive electrode active material and other additives bonded thereto by a binder. In the present embodiment, the heat history applied to the binder resin is detected later. Details will be described later.

  The binder used is, for example, hydrophobic. Among them, preferred binders for detecting the heat history include, for example, the following materials.

  Polyvinylidene fluoride (PVDF) (including compounds in which a hydrogen atom is substituted with another halogen element), polybutylene terephthalate, polyethylene terephthalate, tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / peroper Fluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF) And other fluorine resins. These resins may be used alone or in combination of two or more.

  Each of these resins is a halogen-containing resin such as a fluorocarbon resin, and therefore can have the same differential scanning calorimetry (DSC) profile as PVDF shown in the examples described later. Therefore, with these resins, the heat history can be detected by the heat history detection method (described in detail later) in the present embodiment. In particular, polyvinylidene fluoride (PVDF) is preferable. However, the resin material is not limited to these, as long as it is a resin material whose heat history can be determined by differential scanning calorimetry.

[Anode active material layer]
The negative electrode active material layer 13 contains a negative electrode active material. As a negative electrode active material, what is generally used for the lithium ion secondary battery 10 should just be used. For example, carbon materials such as graphite (graphite), soft carbon and hard carbon, lithium-transition metal complex oxide (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials, lithium alloy based negative electrode materials and the like can be mentioned. In some cases, two or more negative electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a carbon material or a lithium-transition metal complex oxide is used as the negative electrode active material. Of course, negative electrode active materials other than those described above may be used.

  The negative electrode active material layer 13 further contains, if necessary, an additive such as a surfactant, a conductive aid, an electrolyte (a polymer matrix, an ion conductive polymer, an electrolytic solution, etc.), and a lithium salt for enhancing the ion conductivity. Including. As these materials, those used in the well-known lithium ion secondary battery 10 can be used.

  Also in the negative electrode active material layer 13, a binder is used to bind the active material and other additives. As the binder, a resin similar to that used for the positive electrode active material layer 15 is used, and can be used for detection of heat history.

[Electrolyte layer]
The electrolyte layer in the present embodiment has a configuration in which the separator 17 is impregnated with the electrolytic solution.

(Separator 17)
The separator 17 has a function of holding an electrolyte to secure lithium ion conductivity between the positive electrode 150 and the negative electrode 130, and a function as a partition between the positive electrode 150 and the negative electrode 130.

(Electrolytes)
The electrolyte with which the separator 17 is impregnated is not particularly limited as long as it is an electrolyte used in a general lithium ion secondary battery 10. For example, if a non-aqueous electrolyte is mentioned, it has the form which the lithium salt which is a support salt melt | dissolved in the organic solvent. Examples of the organic solvent to be used include, for example, carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, etc. You may mix and use. As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF ₃ SO ₃ Compounds that can be added to the active material layer of the electrode may be employed as well.

[Current collector]
Although there is no restriction | limiting in particular in the material which comprises a collector (the negative electrode collector 11 and the positive electrode collector 12), A metal is used suitably.

  Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, copper, other alloys, and the like. In addition, combinations of these metals and plating materials can be preferably used. The current collector is also not particularly limited as long as it is used in a general lithium ion secondary battery 10.

  Moreover, the metal similar to a collector is used also for a positive electrode lead, a negative electrode lead, etc., and it does not specifically limit.

[Battery body]
As the battery exterior body 29, a laminated film containing aluminum is used. As the laminate film, for example, a laminate film having a three-layer structure in which polypropylene, aluminum and nylon (registered trademark) are laminated in this order can be used. There is no particular limitation as long as it is used in the lithium ion secondary battery 10. Moreover, you may use a well-known metal can case.

[Heat history detection method]
The heat history detection method according to the present embodiment will be described.

  The thermal history detection method of the present embodiment is to detect the highest reachable temperature applied to the resin by differential scanning calorimetry (DSC) of the resin contained in the lithium ion secondary battery 10 .

  The resin used to detect the heat history is present in the lithium ion secondary battery 10. In the present embodiment, as described above, the heat history is detected from the resin contained in the positive electrode active material layer 15 or the negative electrode active material layer 13 as a binder. Therefore, the thermal history to be detected is the thermal history of the electrode (positive electrode or negative electrode) as it is, and also the thermal history of the lithium ion secondary battery 10.

(Calibration curve or calibration formula creation)
The preparation of the calibration curve or calibration formula uses the resin contained in the lithium ion secondary battery 10. In the present embodiment, an electrode containing a resin used as a binder is used as a calibration curve or a test body for preparing a calibration formula.

  First, a test curve for preparing a calibration curve or calibration formula is prepared from an electrode containing a resin. Prepare multiple test specimens. Then, a different heat history (maximum temperature) is applied to each test body. The temperature (applied temperature) of the heat applied at this time is recorded.

  Thereafter (after the test body has cooled after heat application), DSC measurement is performed twice or more for each test body. And I take a differential profile between the first and second times. An approximate curve T showing the correlation between the applied temperature and the peak temperature appearing in this difference profile, that is, the portion where the heat flow value in the DSC measurement is the largest, is determined. The fitted curve T may, for example, actually plot the peak temperature and the applied temperature on a graph to draw the fitted curve T, or use the least squares method or other statistical methods to represent the fitted curve T and it Formulas may be determined. For specific examples of the profile and the calibration curve or calibration equation, refer to the examples described later.

  The electrode used for DSC measurement may be a positive electrode or a negative electrode. This is because both the positive electrode and the negative electrode contain a binder. However, the resin for which the calibration curve or calibration formula has been prepared needs to be used also for a lithium ion secondary battery whose thermal history is unknown.

  The positive electrode or the negative electrode contains components other than the binder, for example, in the case of the positive electrode, a positive electrode active material, other additives, a current collector, and the like. In the case of the negative electrode, a negative electrode active material, other additives, a current collector and the like are included. The components other than the binder are inorganic substances. Therefore, the position of heat absorption or heat generation in DSC measurement is hardly moved by components other than the binder. Therefore, an electrode containing a component other than the binder can be used to detect the heat history. In particular, many negative electrodes are preferable because they only have a carbon material bonded by a binder as an active material, and they have less influence on thermal history detection, which is preferable.

  For the DSC measurement, the electrode itself taken out of the lithium ion secondary battery 10 may be cut out to a size that can be measured and used as a test body, or the active material layer may be scraped off from the current collector of the electrode.

(Measurement of secondary battery with unknown heat history)
Next, from the lithium ion secondary battery 10 whose thermal history (maximum reached temperature) is unknown, the portion including the resin is taken out as a subject. Since the subject to be removed at this time is a portion containing a resin, an electrode is used. Here too, it is preferable to take out the subject from the negative electrode, but it may be a positive electrode. The electrode taken out of the lithium ion secondary battery 10 is washed away with components such as the electrolyte by washing with water and then dried.

  Then, DSC measurement is performed at least twice using the taken out subject. From the obtained two DCS measurement results, a differential profile of the first and second DSC measurement results is created. Then, the peak position (also referred to as peak temperature) of the obtained difference profile is compared with a calibration curve or calculated using a calibration equation. Thereby, the temperature of the peak position of the difference profile is determined. That is, the highest reachable temperature as the heat history of the lithium ion secondary battery 10 is found.

  As described above, in the present embodiment, if a calibration curve or a calibration formula is prepared in advance by twice performing DCS measurement using a resin used for the lithium ion secondary battery 10, two DSC measurements are similarly performed. By doing this, it is possible to know the maximum reachable temperature of the lithium ion secondary battery 10 whose thermal history is unknown.

  Here, the principle by which the thermal history applied to the resin can be determined by such DSC measurement will be described.

  (I) The measurement profile in which the thermal history (maximum temperature) is reflected appears by the first DCS measurement. Then, the resin melts in the process of raising the temperature to the melting point (or near the melting point) by the first DCS measurement, and the heat history added is canceled.

  This is because the resin (polymer) changes its microcrystalline state by the application of heat. During the first DSC measurement, the heat applied to the secondary battery changes the microcrystalline state. Then, in the first DSC, an endotherm (or heat generation) appears due to the microcrystalline state changed by the applied heat. And when the temperature is raised to the melting point (or near the melting point) of the resin, there is almost no microcrystalline state due to the influence of the heat applied so far. For this reason, the heat history applied so far is canceled. When raising the temperature in the first DSC measurement, the vicinity of the melting point may be a temperature higher than the heat history applied to the resin, and may be set, for example, as the upper limit temperature of the detection temperature.

  (Ii) By the second time DCS measurement, the original profile of the resin appears. This profile is a baseline.

  (Iii) By taking a differential profile between the first and second DCS measurements, the thermal history (maximum reached temperature) of the resin appears as a peak. That is, by subtracting the profile reflecting the heat history at the first time and the baseline profile at the second time, a portion corresponding to the highest reachable temperature appears as a peak in the heat history.

  (Iv) The temperature can be estimated by applying the peak temperature of the difference profile to a calibration curve or calibration formula prepared in advance.

  Briefly, the first and second times have different heat treatment conditions (temperature) applied to the resin, which affects the degree of crystallinity in the resin. Due to the influence, the appearance of the DSC profile also differs between the first and second times. In the present embodiment, the highest reachable temperature is detected from such a difference in the influence of heat applied to the resin.

  Thus, the heat history added to the resin disappears when the temperature is raised to the melting point or its vicinity. Therefore, the upper limit of the detectable temperature range is up to the melting point Tm of the resin. On the other hand, the lower limit is possible to the glass transition point Tg. However, the temperature that one wants to know as a thermal history is the highest reachable temperature of the secondary battery that is expected to have an abnormally high temperature. Therefore, the lower limit may be the maximum temperature as the specification of the battery. Specifically, for example, the detectable temperature is about 60 to 200 ° C., although it varies depending on the specifications of the secondary battery.

  An example using this embodiment will be described.

(Creating a calibration curve or equation)
PVDF was used as a resin. The negative electrode which used PVDF as a binder of a lithium ion secondary battery was used for the calibration curve or the test object for calibration formula creation. Three negative electrodes were punched out so that a test body might be 5 mm in diameter and 16 mg in weight. Four specimens (samples 1 to 4) were prepared.

  A different maximum temperature heat was applied to each test specimen. The temperature of applied heat (application temperature) is 125 ° C for sample 1 for 3 hours, sample 2 for 130 ° C for 3 hours, sample 3 for 135 ° C for 3 hours and sample 4 for 140 ° C. The application time is 2 hours. The heat was applied by placing each sample in a thermostatic bath adjusted to each temperature.

  The sample was taken out of the thermostat, allowed to stand at room temperature and sufficiently cooled, and then the first DSC measurement was performed.

  For DSC measurement, a differential scanning calorimeter DSC-Q1000 manufactured by TA Instruments was used. The reference material used indium.

  The temperature rise rate is 10 ° C./min and the temperature drop rate is 5 ° C./min at the time of DSC measurement. In addition, the measurement temperature range was from room temperature to 200 ° C.

  After the first DSC measurement, the second DSC measurement was performed. Measurement equipment and conditions were the same as in the first round.

  Here, the first profile and the second profile, and their differential profiles are described by taking sample 2 to which heat of 130 ° C. is applied as an example.

FIG. 3 is a graph showing the first and second profiles of sample 2 applied at 130 ° C. The horizontal axis is temperature, and the vertical axis is heat flow. Moreover, FIG. 5 is a differential profile of 1st time and 2nd time in the sample 2 of 130 degreeC application. The horizontal axis is the temperature, and the vertical axis is the difference between the first and second heat flows (the same applies to FIGS. 4, 6, 7).
As shown in FIG. 3, when the first and second profiles are compared, subtle undulations are observed in the curve of the graph in the first round compared to the second round. This first variation is caused by the heat history applied to the resin. However, just looking at the first profile does not clarify where the change is happening. Note that the large fluctuation around 170 ° C. is due to the characteristics of the resin itself and not due to the heat history (since it occurs in the same way for the first time and the second time).

  On the other hand, as shown in FIG. 5, when looking at the differential profile of sample 2 applied at 130 ° C., in addition to the overall gentle fluctuation, a peak in the valley direction is observed around 130 ° C. which is the applied temperature. This peak position is the peak of the difference between the first and second times. As described above, by taking the difference between the variation that was not clarified only by the first profile in which the heat history is reflected and the second variation which becomes the baseline, a peak appears and it becomes easy to understand.

  The position of the peak (valley) in this difference profile is taken as the peak temperature, and is correlated with the applied temperature for each sample.

  The difference profile is illustrated for the other samples. FIG. 4 shows the first and second differential profiles of sample 1 applied at 125 ° C. FIG. 6 shows the first and second differential profiles of sample 3 applied at 135 ° C. FIG. 7 shows first and second differential profiles in sample 4 applied at 140 ° C. In addition, Table 1 summarizes the applied temperature and the peak temperature of the differential profile.

  Next, an approximate curve T to be a calibration curve is determined from the correlation between the applied temperature of each sample and the peak temperature of the differential profile.

FIG. 8 is a graph depicting an approximate curve T obtained from the applied temperature and the peak temperature of the differential profile. The horizontal axis is the applied temperature, and the vertical axis is the peak temperature of the differential profile. The approximate curve T of this graph is a calibration curve. Further, the equation of the approximate curve T obtained by the minimum dichotomy method is a calibration equation represented by the following equation (1). The correlation R ² in this equation (1) is 0.999. The approximate curve T is substantially an approximate straight line.

y = 1.32x-29.9 (1)
In equation (1), y is the peak temperature of the differential profile, and x is the applied temperature. Therefore, when the equation (1) is used as a calibration equation, the equation (1) is modified as in the following equation (2), and the peak temperature of the differential profile in the secondary battery whose thermal history is unknown as described later is y. Substitute to find the value of x.

  However, in the present embodiment, the obtained temperature is rounded off to the nearest decimal point.

x = (29.9 + y) /1.32 (2)
As can be seen from this calibration curve and calibration equation (FIG. 8 and equation (1)), the correlation between the applied temperature and the peak temperature is very high. Therefore, it is understood that the use of such a calibration curve or calibration equation makes it possible to estimate the temperature in 1 ° C. units. In addition, although the calibration curve or calibration formula at four points (four samples with different applied temperatures) was prepared in the present embodiment, further increase in the number of samples makes it possible to accurately quantify at a finer temperature. .

(Measurement of secondary battery with unknown heat history)
The negative electrode was taken out as a subject from a secondary battery which is a secondary battery whose heat history is unknown and which uses PVDF as a binder. The taken-out negative electrode was washed with water and then dried to obtain an analyte sample. DSC measurement was performed twice using this subject sample. The size, weight, temperature, etc. of the sample in the DSC measurement were measured under the same conditions as in the preparation of the calibration curve or equation.

  FIG. 9 shows first and second differential profiles of an object sample whose thermal history is unknown.

  It can be seen from FIG. 9 that the peak temperature in the differential profile is about 113.degree. This peak temperature is approximately 108 ° C. when the maximum achieved temperature, which is a thermal history, is estimated using equation (2) obtained by modifying equation (1) which is the calibration curve or calibration equation of FIG.

  By preparing the calibration curve or calibration equation in this way, it is possible to know the highest attainable temperature of the lithium ion secondary battery whose thermal history is not known.

  According to the embodiments and examples described above, the following effects can be obtained.

  (1) According to the embodiment and the example, quantification of the highest temperature can be performed by performing at least two DSC measurements. Therefore, when an abnormally high temperature occurs in the lithium ion secondary battery, it becomes possible to quantitatively investigate to what degree the temperature of the battery has risen by the non-electrochemical method.

  In addition, since quantitative determination at 1 ° C. becomes possible, it becomes possible to identify a locally abnormal heat generation site inside the battery later. For example, the stacked lithium ion secondary battery 10 described in the embodiment has a structure in which a plurality of electrodes (the negative electrode 130 and the positive electrode 150) separated by the separator 17 are stacked. When an abnormally high temperature occurs in such a battery, a subject is prepared from each of the stacked electrodes, and two DSC measurements are performed on each subject. Then, the highest reachable temperature is estimated using a calibration curve or calibration formula prepared in advance. As a result, it becomes possible to know at which position inside the laminated battery the electrode which has been at a higher temperature. Since the temperature of the portion where a large amount of current flowed is the highest, it can be understood that a large amount of current flowed at that point if a local high temperature portion was found. Being able to identify such local defects is a very effective means in defect analysis.

  (2) In the embodiment and the examples, it is preferable to perform DSC measurement at the negative electrode. As described above, the substance contained in the negative electrode active material constituting the negative electrode is a stable inorganic substance such as carbon and a resin component serving as a binder. For this reason, the profile (curve of the graph) in the DSC measurement appears clearly, making it easy to determine the peak temperature.

  (3) In the embodiment and examples, the temperature range for detecting the heat history is a temperature between the glass transition point of the resin contained in the secondary battery and the melting point. This makes it possible to detect the thermal history (maximum achieved temperature) in a very wide temperature range.

  (4) In the embodiment and the example, the resin used to detect the heat history is one used as a binder in the electrode of the lithium ion secondary battery. Therefore, it is not necessary to use a secondary battery of a new configuration to apply the present invention, and the heat history can be known also in the existing lithium ion secondary battery.

  (5) In the embodiment and the examples, as described above, the resin used to detect the heat history is a fluorine resin, and a peak corresponding to the highest reached temperature of the heat history by two DCS measurements. The temperature is likely to appear and the heat history can be known.

  The embodiments and examples to which the present invention is applied have been described above, but the present invention is not limited to these embodiments and examples.

  In the above-described embodiment, the calibration curve or calibration formula is created by applying four temperatures, but more temperatures may be used to perform DSC measurement for calibration curve or calibration formula creation.

  Moreover, although the electrode of the lithium ion secondary battery was taken out and used as a test body in the said Example for preparation of a calibration curve or a calibration formula, it is not limited to this. The resin used to create the calibration curve or calibration equation may be any resin as long as it is a resin contained in a lithium ion secondary battery. For example, a single resin used as a binder may be used as a test body, or a state in which it is mixed with an active material or the like (before electrode formation) may be used as a test body. The resin (polymer) may have different peak positions in DCS measurement if the molecular weight is largely different. For this reason, when using a resin alone as a test body, it is preferable to use a resin used for a lithium ion secondary battery (for example, the same product number and specification).

  In addition, when the binder is composed of a plurality of resins, it is preferable to use a test body in which the same plurality of resins are combined also when preparing a calibration curve or calibration formula. Specifically, for example, a state in which a plurality of resins used as a binder are mixed is preferably used as a test body, and more preferably, the electrode itself is used as a test body as in the example.

  Further, in the example, two DSC measurements are performed, but the number of DSC measurements may be any number as long as it is two or more. After the second time, since a baseline of the resin appears, any measurement results may be used for comparison with the first time.

  In the embodiments and examples, the heat history is detected by DSC measurement of the resin of the binder contained in the electrode of the lithium ion secondary battery, but the present invention detects the heat history from the resin of the binder It is not limited to. Even resins other than binders can be used as long as they are resins included in a lithium ion secondary battery and, as in the embodiments and examples described above, peak temperatures appear in at least two DSC measurements. It is. For example, a dedicated resin may be provided for detecting the heat history on the inside of the lithium ion secondary battery or on the outer surface of the packaging material.

  Besides, the present invention is not limited to the embodiments and examples, and various modifications are possible, and the present invention is defined by the matters defined by the claims.

10 lithium ion rechargeable batteries,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 separators,
19 cell layers,
21 power generation elements,
130 negative electrode,
150 positive electrode.

Claims (5)

A plurality of test bodies containing a resin contained in a lithium ion secondary battery are prepared, and heat of different known temperatures is applied to the prepared plurality of test bodies to give one heat history, and the heat history is calculated The differential profile of the first differential scanning calorimetry result and the second differential scanning calorimetry result is determined by performing differential scanning calorimetry twice for each of the plurality of applied test bodies, and the peak appeared in the differential profile Preparing a calibration curve or equation in advance based on the correlation between the temperature and the known temperature of the applied heat;
The portion containing the resin is taken out from the lithium ion secondary battery whose heat history is unknown as a subject, differential scanning calorimetry is performed at least twice on the subject, and the first differential scanning calorimetry result and the second and subsequent ones Obtaining a differential profile of differential scanning calorimetry results, and applying the peak temperature appearing in the differential profile to the calibration curve or calibration equation to estimate the maximum reached temperature applied to the lithium ion secondary battery;
A heat history detection method of a lithium ion secondary battery characterized by having. Differential scanning calorimetry in the step of estimating the maximum ultimate temperature, using the negative electrode of said lithium ion secondary battery, the negative electrode and said der Rukoto those bonded by the resin of a carbon material as an active material The heat history detection method of the lithium ion secondary battery according to claim 1.   3. The heat history detection method for a lithium ion secondary battery according to claim 1, wherein the temperature range for detecting the heat history is a temperature between the glass transition point of the resin and the melting point.   The heat history detection method of a lithium ion secondary battery according to any one of claims 1 to 3, wherein the resin is a binder contained in an electrode in the lithium ion secondary battery.   The resin includes polyvinylidene fluoride (PVDF) (including a compound in which a hydrogen atom is substituted by another halogen element), polybutylene terephthalate, polyethylene terephthalate, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetra- Fluoroethylene-perfluoroalkylvinylether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyfluorination The method for detecting the heat history of a lithium ion secondary battery according to any one of claims 1 to 4, wherein the resin is at least one resin of vinyl (PVF).