Secondary battery electrode recovery determination method and secondary battery electrode recovery determination program

Abstract

The invention provides a recovery determination method of an electrode of a secondary battery, which can determine the deterioration degree of the electrode to be recovered. A secondary battery electrode recovery determination method is provided with: a step (step S1) for estimating a characteristic parameter at a determination time of a secondary battery to be determined; a step (step S2) for determining the relationship between the electrolyte diffusion coefficient and the discharge capacity; a step (step S3) for determining a threshold value (Dth) for the electrolyte solution diffusion coefficient on the basis of the relationship between the electrolyte solution diffusion coefficient and the discharge capacity; and a step (step S4) in which the threshold value Dth is compared with a threshold value Dth0 of the electrolyte diffusion coefficient before degradation, which is acquired in advance for the secondary battery to be determined or a secondary battery of the same type as the secondary battery to be determined, and the secondary battery to be determined is classified on the basis of the difference [Delta] Dth = Dth-Dth0 between the threshold value Dth and the threshold value Dth0.

Description

Technical Field

[0001] The present invention relates to a recycling determination method for a secondary battery electrode and a recycling determination program for a secondary battery electrode. Background Art

[0002] The EU is the main body of legislation regarding the recycling of secondary batteries such as lithium-ion batteries. Specifically, legislation is being developed that requires that a specified percentage or more of materials used in secondary batteries be recycled into secondary batteries.

[0003] In this specification, the term "recycling" of secondary batteries is used as a term to refer to concepts that also include any of the following: (a) dismantling secondary batteries and recovering reusable parts; (b) subjecting the parts obtained by dismantling secondary batteries to a predetermined treatment to make them reusable; and (c) recovering materials (valuable metals, etc.) from the parts that constitute the secondary batteries. The "recycling" of secondary batteries in this specification is a different concept from the "reuse" of secondary batteries (not the reuse of parts and materials but the reuse of the secondary batteries themselves). Usually, secondary batteries that are judged to be unsuitable for reuse become the subject of recycling.

[0004] Japanese Patent Publication No. 2010-34021 describes a method for recovering battery materials containing oxides from battery waste. The recovery method includes: immersing a substrate to which the battery material containing oxides is attached in a solvent that does not substantially dissolve the oxides, and peeling the battery material from the substrate; and separating the peeled battery material from the substrate. In the publication, N-methyl-2-pyrrolidone, water, dimethyl carbonate, diethyl carbonate, chloroform, etc. are described as solvents. The publication also describes calcining the recovered oxides at a temperature of 600°C or more and 1100°C or less.

[0005] Japanese Patent Gazette No. 5141970 describes a method for recovering positive electrode active material from the positive electrode of a lithium battery. The lithium battery to which the recovery method is applied has a positive electrode active material layer, which is formed by applying a material including a positive electrode active material dispersed with an aqueous solvent, a conductive material, and a binding material to the surface of a positive electrode collector. The recovery method includes: a step of immersing the positive electrode in an alkaline aqueous solution to peel off the positive electrode active material layer from the positive electrode collector; a step of adding an organic solvent to the peeled positive electrode active material layer peeled product to extract the binding material from the peeled product; and a step of separating a supernatant containing a conductive material and a sediment containing a positive electrode active material from the extracted product after the extraction step.

[0006] Japanese Patent Publication No. 2017-97997 describes a method for analyzing the characteristics of a secondary battery, which uses a model formula with characteristic values ​​of components constituting the battery as parameters to fit the voltage value of the battery represented by the model formula with measured data, thereby estimating the characteristic values ​​of the components. In this method for analyzing the characteristics, as measured data, data obtained by applying a charge and discharge pattern to a battery to be analyzed is used, and the charge and discharge pattern includes an action period consisting of either a constant current discharge period or a constant current charge period, and a rest period set following the action period.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2010-34021

[0010] Patent Document 2: Japanese Patent No. 5141970

[0011] Patent Document 3: Japanese Patent Application Publication No. 2017-97997 Summary of the invention

[0012] Problems to be solved by the invention

[0013] There are roughly three ways to recycle secondary battery electrodes.

[0014] (1) Parallel recycling: The secondary battery is disassembled, the electrode mixture is cleaned, and it is directly reused as an electrode.

[0015] (2) Wet recovery: The secondary battery is disassembled, the active material is recovered from the electrode mixture, and a regeneration process such as adding lithium is performed as needed to reuse the active material.

[0016] (3) Dry recycling: Secondary batteries are dismantled or directly burned, and the used materials are refined and recovered as metal materials.

[0017] Among the above methods, dry recovery is the most costly method. Therefore, if possible, parallel recovery and wet recovery are preferred. Whether parallel recovery and wet recovery can be performed depends on the degree of electrode degradation. Therefore, it is considered to evaluate the degree of electrode degradation separately and change the recovery method according to the degree of degradation.

[0018] An object of the present invention is to provide a method for determining the recovery of a secondary battery electrode and a program for determining the recovery of a secondary battery electrode that can determine the degree of degradation of an electrode to be recovered.

[0019] Means for solving problems

[0020] A recycling determination method for electrodes of a secondary battery according to one embodiment of the present invention determines the degree of deterioration of an electrode contained in a secondary battery as a determination object, and the recycling determination method includes the following steps: based on data obtained by measuring the secondary battery as the determination object, using a predetermined model formula, estimating characteristic parameters of the secondary battery as the determination object at the determination time, including the electrolyte diffusion coefficient of the secondary battery as the determination object at the determination time; based on the model formula and the estimated characteristic parameters, calculating the discharge capacity when the electrolyte diffusion coefficient is changed, and calculating the relationship between the electrolyte diffusion coefficient and the discharge capacity; determining a threshold value Dth of the electrolyte diffusion coefficient based on the relationship between the electrolyte diffusion coefficient and the discharge capacity; and comparing the threshold value Dth with a threshold value Dth0 of the electrolyte diffusion coefficient before deterioration obtained in advance for the secondary battery as the determination object or a secondary battery of the same type as the secondary battery as the determination object, and classifying the secondary battery as the determination object based on the difference ΔDth=Dth-Dth0 between the threshold value Dth and the threshold value Dth0.

[0021] A recovery determination program for electrodes of a secondary battery according to one embodiment of the present invention determines the degree of deterioration of an electrode contained in a secondary battery as a determination object, and causes a computer to execute the following steps: based on data obtained by measuring the secondary battery as a determination object, using a predetermined model formula, estimating characteristic parameters of the secondary battery as a determination object at the determination time, including the electrolyte diffusion coefficient of the secondary battery as a determination object at the determination time; based on the model formula and the estimated characteristic parameters, calculating the discharge capacity when the electrolyte diffusion coefficient is changed, and calculating the relationship between the electrolyte diffusion coefficient and the discharge capacity; determining a threshold value Dth of the electrolyte diffusion coefficient based on the relationship between the electrolyte diffusion coefficient and the discharge capacity; and comparing the threshold value Dth with a threshold value Dth0 of the electrolyte diffusion coefficient before deterioration obtained in advance for the secondary battery as a determination object or a secondary battery of the same type as the secondary battery as the determination object, and classifying the secondary battery as the determination object based on the difference ΔDth=Dth-Dth0 between the threshold value Dth and the threshold value Dth0.

[0022] Effects of the Invention

[0023] According to the present invention, the degree of deterioration of an electrode to be recycled can be determined. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of a secondary battery diagnosis method.

[0025] Figure 2 It is a flowchart showing an example of more specific steps of the process of estimating characteristic parameters.

[0026] Figure 3 This is a graph showing an example of the relationship between the electrolyte diffusion coefficient and the discharge capacity.

[0027] Figure 4 This is a diagram showing an example of a method for determining the threshold value Dth.

[0028] Figure 5 This is a flowchart of the recovery determination method of the secondary battery electrode according to the first embodiment of the present invention.

[0029] Figure 6 This is a flowchart of a recovery determination method for a secondary battery electrode according to a second embodiment of the present invention.

[0030] Figure 7 This is an example of a method of classifying determination target batteries according to the present embodiment.

[0031] Figure 8 This is another example of a method of classifying determination target batteries according to the present embodiment.

[0032] Fig. 9 This is a flowchart of a method for determining recovery of a secondary battery electrode according to a third embodiment of the present invention.

[0033] Fig.10 These are SEM photographs of the initial states of the positive electrodes (LCO) of Evaluation Examples 1 to 3.

[0034] Fig.11 This is a SEM photograph of the positive electrode of Evaluation Example 1 after deterioration.

[0035] Fig.12 This is a SEM photograph of the positive electrode of Evaluation Example 2 after degradation.

[0036] Fig.13 This is a SEM photograph of the positive electrode of Evaluation Example 3 after deterioration.

[0037] Fig.14 This is a SEM photograph of the initial state of the positive electrode (NCM) of Evaluation Examples 4 and 5.

[0038] Fig.15 This is a SEM photograph of the positive electrode of Evaluation Example 4 after deterioration.

[0039] Fig.16 This is a SEM photograph of the positive electrode of Evaluation Example 5 after deterioration. DETAILED DESCRIPTION

[0040] The degree of electrode degradation is mainly determined by the discharge capacity per unit weight and the discharge characteristics. Even if the discharge capacity per unit weight can be maintained, if the discharge characteristics are reduced, it is difficult to use the electrode for parallel recovery.

[0041] The inventors of the present invention have previously developed a diagnostic method for secondary batteries focusing on the electrolyte diffusion coefficient (PCT / JP2023 / 003516). In this diagnostic method, first, based on the data obtained by measuring the load characteristics of the secondary battery, the characteristic parameters (electrolyte diffusion coefficient Dn, electrolyte conductivity, etc.) of the secondary battery as the diagnostic object at the diagnostic time are estimated. Next, based on the model formula and the estimated parameters, the relationship between the electrolyte diffusion coefficient and the discharge capacity is calculated. Based on this "relationship between the electrolyte diffusion coefficient and the discharge capacity", the value (threshold) Dth of the electrolyte diffusion coefficient when the secondary battery becomes unsuitable for reuse is determined. The larger the difference ΔD=Dn-Dth between the electrolyte diffusion coefficient Dn at the diagnostic time and the threshold Dth, the higher the possibility that the secondary battery as the diagnostic object can be evaluated as being able to be used for a long time (i.e., having a long remaining life).

[0042] The inventors of the present invention focused on the threshold value Dth obtained in the process of implementing the above-mentioned diagnostic method. The threshold value Dth is a value that changes according to the rate of current. Therefore, the threshold value Dth may indirectly reflect the discharge characteristics of the electrode to be recovered.

[0043] The above diagnostic method can evaluate the remaining life by one parameter (electrolyte diffusion coefficient) by rounding off the change of characteristic parameters other than the electrolyte diffusion coefficient. Even so, it can be seen that the remaining life of the secondary battery can be evaluated with a certain degree of high accuracy.

[0044] However, in actual secondary batteries, characteristic parameters other than the electrolyte diffusion coefficient (e.g., electrolyte conductivity, etc.) also change with cycle degradation. Therefore, when the latest characteristic parameters are estimated by re-measuring the load characteristics after the diagnosis time, and the threshold value Dth is determined in the same way as above based on the latest characteristic parameters, the threshold value Dth reflecting the latest characteristic parameters may be different from the threshold value Dth determined based on the characteristic parameters at the diagnosis time.

[0045] That is, strictly speaking, the threshold value Dth obtained in the process of implementing the above-mentioned diagnosis method changes according to the timing of implementing the diagnosis. In other words, the threshold value Dth itself changes with the cycle degradation of the secondary battery.

[0046] The inventors investigated the relationship between the degradation form of the secondary battery electrode and the threshold value Dth. As a result, in a secondary battery in which the threshold value Dth changes in the direction of increasing with cycle degradation, a new relationship was found in which (i) the porosity of the electrode mixture layer is significantly reduced, thereby hindering the ion path in the electrolyte, and (ii) the structural degradation of the electrode occurs.

[0047] Here, (i) is supplemented. Generally speaking, the electrode mixture layer has a tendency to expand due to use. When there are few precipitates produced by the electrolyte reaction, the porosity increases with the cycle. However, when a large amount of precipitates are produced by the electrolyte reactant, the precipitates sometimes block the gaps and the porosity decreases.

[0048] However, in actual secondary batteries, degradation such as (i) in which the porosity decreases significantly with cycle degradation rarely occurs. Therefore, when the threshold value Dth increases with cycle degradation, it can be judged that (ii) structural degradation of the electrode has occurred in many cases.

[0049] That is, the threshold value Dth0 obtained by implementing the above-mentioned diagnostic method on the secondary battery before deterioration (for example, in the initial state) is compared with the threshold value Dth obtained by implementing the above-mentioned diagnostic method on the secondary battery after deterioration. If the difference between the two ΔDth=Dth-Dth0 is larger than the predetermined value, it can be judged that the possibility of structural degradation of the electrode is high.

[0050] Here, the "structural degradation" of the electrode refers to a state in which, for example, cracks are generated in the active material particles in the electrode, or phase changes occur due to chemical degradation, thereby reducing the ion diffusivity in the solid phase of the active material particles themselves. It is believed that electrodes with structural degradation are not only unsuitable for parallel recovery, but also unsuitable for wet recovery. The regeneration treatment in wet recovery is, for example, a process in which the active material whose lithium content has been reduced due to degradation is mixed with a lithium raw material and re-fired to restore the lithium content to the initial amount. In the case where cracks are generated by rupture of the active material itself, it is difficult to restore it by regeneration treatment.

[0051] On the other hand, if the difference ΔDth is below a predetermined value, it can be determined that structural degradation (ii) has not occurred, or even if it has occurred slightly, the porosity of the electrode mixture layer has increased due to mixture expansion, ensuring a wider ion diffusion path, and there is a high possibility that the discharge characteristics are maintained.

[0052] The present invention has been accomplished based on the above findings. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0053] [Implementation Method]

[0054] A recovery determination method for a secondary battery electrode according to an embodiment of the present invention is a method for classifying secondary batteries by determining the degree of degradation of the secondary battery electrode based on a "threshold value Dth of the electrolyte diffusion coefficient" described later. Here, first, in order to explain the "threshold value Dth of the electrolyte diffusion coefficient", a "diagnostic method for a secondary battery" using the "threshold value Dth of the electrolyte diffusion coefficient" is described.

[0055] The "secondary battery diagnosis method" described below is different from the "secondary battery electrode recovery determination method". It is mainly used to determine whether the reuse of a secondary battery is appropriate or not. More specifically, it is a method for evaluating the remaining life of a secondary battery. In addition, the applicant has also filed a patent application for the invention of this method (PCT / JP2023 / 003516).

[0056] (Diagnostic method for secondary batteries)

[0057] Figure 1 This is a flowchart of a secondary battery diagnostic method. The diagnostic method includes: a process of estimating characteristic parameters of a secondary battery (hereinafter referred to as "target battery") at the time of diagnosis (step SA1); a process of finding the relationship between the electrolyte diffusion coefficient and the discharge capacity (step SA2); a process of determining the threshold value Dth of the electrolyte diffusion coefficient (step SA3); and a process of finding the difference ΔD between the threshold value Dth and the electrolyte diffusion coefficient Dn at the time of diagnosis (step SA4). Each process is described in detail below.

[0058] [Process of estimating characteristic parameters]

[0059] Estimating characteristic parameters of the target battery at the time of diagnosis (step SA1). More specifically, based on data obtained by measuring the load characteristics of the target battery, characteristic parameters of the target battery at the time of diagnosis, including the electrolyte diffusion coefficient Dn at the time of diagnosis of the target battery, are estimated using a predetermined model.

[0060] In this process, the data obtained by measuring the load characteristics of the target battery are fitted using a predetermined model formula, thereby estimating the characteristic parameters of the target battery at the time of diagnosis. This analysis (simulation) can be performed by a computer program capable of fluid analysis, for example, it can be performed by the software Battery Design Studio manufactured by Siemens.

[0061] The model formula may be a well-known model formula in the field, for example, the model formula described in Marc Doyle et al., "Modeling of Galvanostatic Charge and Discharge of the Lithium / Polymer / Insertion Cell", J. Electrochem. Soc., vol. 140, No. 6, June (1993).

[0062] The target battery is, for example, a lithium-ion battery.

[0063] The data obtained by measuring the load characteristics of the target battery is, for example, a discharge curve obtained by measuring the target battery at multiple discharge rates. The data preferably includes a discharge curve measured at a very small discharge rate (for example, 0.02C). In addition, the data preferably includes a discharge curve measured at a discharge rate of 1C or more. The data preferably includes a discharge curve measured at a discharge rate of more than 3 levels, and more preferably includes a discharge curve measured at a discharge rate of more than 4 levels. The data obtained by measuring the load characteristics of the target battery may also be a charging curve obtained by measuring the target battery at multiple charging rates.

[0064] The characteristic parameters estimated in this process (characteristic parameters of the target battery at the time of diagnosis) include at least the electrolyte diffusion coefficient Dn at the time of diagnosis of the target battery. The characteristic parameters may also include, for example, the solid phase diffusion coefficient of the positive and negative electrode active materials, the electrolyte conductivity, etc. Other specific examples of characteristic parameters are described later.

[0065] Figure 2 This is a flowchart showing an example of more specific steps of the process of estimating characteristic parameters (step SA1). In this example, the process of estimating characteristic parameters (step SA1) includes: a process of inputting basic specifications of the target battery (step SA1-1); a process of inputting data obtained by measuring the load characteristics of the target battery (step SA1-2); a process of estimating static parameters of the target battery (step SA1-3); and a process of estimating dynamic parameters of the target battery (step SA1-4).

[0066] The basic specifications of the secondary battery to be diagnosed are input to the analysis software (step SA1 - 1 ). The input basic specifications are not limited to these, and can include the following specifications, for example.

[0067] · Electrode composition of positive and negative electrodes (constituent materials, content, particle size, etc.)

[0068] ·Thickness, density, and curvature of the positive and negative electrodes (= about 1.5 in most cases)

[0069] Material, thickness and conductivity of positive and negative electrode collector foil

[0070] ·Thickness and porosity of the diaphragm

[0071] · Electrolyte composition (constituent materials, content)

[0072] Thermal conductivity and heat capacity of the above-mentioned constituent materials (basic physical properties unique to the materials)

[0073] Electrode area

[0074] The diagnosis is basically performed in a non-destructive manner, so it is impossible to obtain accurate composition information of the electrolyte at the time of diagnosis. Therefore, general information of the secondary battery as the diagnosis object (or specification information of a new battery) is obtained and input as a parameter. When the simulation is actually implemented, certain values ​​need to be input, but the composition of the electrolyte itself will not have a significant impact on the results of the simulation. The positioning of the composition information of the electrolyte is a reference level in the diagnostic method of this embodiment.

[0075] The density of the positive and negative electrodes is also assumed to change suddenly from the initial state due to expansion, but it is impossible to determine the exact value at the time of diagnosis. Therefore, the initial value (standard value, etc.) or the value predicted based on the initial value is input. In the case of complete uncertainty, a general value can also be input. Fine-tuning can be performed in step SA1-4 as needed.

[0076] The data obtained by measuring the load characteristics of the target battery is input into the analysis software (step SA1-2). As described above, the data obtained by measuring the load characteristics of the target battery is a discharge curve obtained by measuring the target battery at multiple discharge rates. Hereinafter, the "data obtained by measuring the load characteristics of the target battery" is sometimes referred to as "actually measured data".

[0077] Based on the measured data and the model formula, the static parameters of the target battery are estimated (step SA1-3). For example, the static parameters of the target battery are adjusted to be consistent with the shape of the discharge curve measured at a very small discharge rate. The discharge curve measured at a very small discharge rate (for example, 0.02C) can be considered to be roughly consistent with the voltage curve (OCV curve) when no load is connected. The static parameters are not limited to this, and may include, for example, the following parameters:

[0078] ·Capacity per unit weight of the positive and negative electrode active materials (the discharge capacity of the battery decreases after use.)

[0079] Utilization rate of each of the positive and negative electrode active materials (not all areas are used for each other.)

[0080] · Maximum and minimum voltages of the battery’s operating range

[0081] Based on the measured data and the model formula, the dynamic parameters of the target battery are estimated (step SA1-4). For example, a simulation is performed to discharge the target battery at a current value equal to the measurement conditions of the measured data, and the results of the simulation are compared with the measured data while adjusting the dynamic parameters to make the two consistent. The simulation can be performed, for example, using the discharge curve prediction of the above-mentioned BatteryDesign Studio. The dynamic parameters are not limited to this, and can include, for example, the following parameters:

[0082] Conductivity of electrolyte

[0083] Electrolyte diffusion coefficient

[0084] Solid phase diffusion coefficient of positive and negative electrode active materials

[0085] Thermal capacity of the target battery

[0086] The ambient temperature during simulation is preferably set to be consistent with the ambient temperature when the measured data is obtained. In the case of medium-sized or larger product batteries, especially product batteries that are assumed to be used at a high rate, it is preferable to consider the effect of heat. Therefore, it is preferable to measure at least 1C and fit the measured data affected by heat. On the other hand, if the target battery is a small single cell for desktop testing, the effect of heat can be ignored.

[0087] Through the above steps, characteristic parameters at the time of diagnosis of the target battery, including the electrolyte diffusion coefficient Dn at the time of diagnosis of the target battery, can be estimated.

[0088] [Step of determining the relationship between electrolyte diffusion coefficient and discharge capacity]

[0089] Based on the model formula used in step SA1 and the characteristic parameters estimated in step SA1, the relationship between the electrolyte diffusion coefficient and the discharge capacity is obtained (step SA2). More specifically, the other characteristic parameters in the characteristic parameters estimated in step SA1 are set to be constant and only the electrolyte diffusion coefficient is changed to perform discharge simulation to obtain the discharge capacity. The discharge rate and ambient temperature during the discharge simulation are preferably set according to the reuse purpose. For example, if it is envisaged that the purpose is to be used at an average of about 1C, the discharge rate when obtaining the relationship between the electrolyte diffusion coefficient and the discharge capacity is also 1C. Since it is difficult to strictly make all environments consistent, the average value can also be used for simulation.

[0090] Figure 3 is a graph showing an example of the relationship between the electrolyte diffusion coefficient and the discharge capacity. In this example, for an electrolyte diffusion coefficient of 4.8×10 -6 4.0×10 -6 , 2.95×10 -6 , 1.85×10-6 , 1.48×10 -6 and 1.1×10 - 6 cm 2 / sec, the discharge capacity when the ambient temperature is 45°C and the discharge rate is 0.5C is calculated.

[0091] As shown in this example, generally, the smaller the electrolyte diffusion coefficient is, the smaller the discharge capacity is. In addition, the relationship between the electrolyte diffusion coefficient and the discharge capacity is not linear, and there is a tendency that the lower the electrolyte diffusion coefficient is, the greater the reduction in discharge capacity is.

[0092] [Step of determining the threshold value Dth of the electrolyte diffusion coefficient]

[0093] Based on the relationship between the electrolyte diffusion coefficient and the discharge capacity obtained in step S2, the threshold value Dth of the electrolyte diffusion coefficient is determined (step SA3). More specifically, referring to the relationship between the electrolyte diffusion coefficient and the discharge capacity obtained in step SA2, the value of the electrolyte diffusion coefficient when the target battery is no longer suitable for reuse is determined as the threshold value Dth. Under what circumstances is it judged as "unsuitable for reuse" depends on the reuse purpose of the target battery. Therefore, the criterion for judging as "unsuitable for reuse" is set according to the purpose.

[0094] For example, when the discharge capacity becomes less than a predetermined allowable value, it may be determined that the battery is not suitable for reuse. In this case, the electrolyte diffusion coefficient when the discharge capacity becomes less than a predetermined allowable value is determined as the threshold value Dth. Figure 3 In the example, when the allowable value of the discharge capacity is set to 36.02 mAh, the threshold Dth is 1.40×10 -6 cm 2 / sec.

[0095] Alternatively, when the discharge capacity starts to drop suddenly, it may be determined that the battery is not suitable for further use. In this case, the electrolyte diffusion coefficient when the discharge capacity starts to drop suddenly is determined as the threshold value Dth. For example, the electrolyte diffusion coefficient when the slope of the discharge capacity becomes greater than a predetermined value may be set as the threshold value Dth. Figure 4 As shown in FIG. 1 , the point where the tangent lines of the respective curves before and after the discharge capacity starts to drop suddenly intersect may be set as the threshold value Dth.

[0096] [Step of Calculating Difference ΔD Between Threshold Value Dth and Electrolyte Diffusion Coefficient Dn at Diagnosis Time]

[0097] The difference ΔD between the threshold value Dth determined in step SA3 and the electrolyte diffusion coefficient Dn at the time of diagnosis estimated in step SA1 is obtained (step SA4). For example, if Dn=2.22×10-6 cm 2 / sec、Dth=1.40×10 -6 cm 2 / sec, then ΔD=Dn-Dth=0.82×10 -6 cm 2 / sec.

[0098] This ΔD can be used as an indicator of the remaining life of the target battery. That is, it can be evaluated that the larger the ΔD, the higher the possibility that the target battery can be used for a long time, and the smaller the ΔD, the lower the possibility that the target battery can be used for a long time. Even if the discharge capacity at the time of diagnosis is the same, ΔD may be different. By using ΔD, the remaining life of the target battery can be evaluated more accurately compared to the previous method of evaluating the remaining life based on the size of the discharge capacity at the time of diagnosis.

[0099] (Method for determining recovery of secondary battery electrodes)

[0100] The “secondary battery diagnosis method” using the “threshold value Dth of the electrolyte diffusion coefficient” has been described above. Next, the “secondary battery electrode recovery determination method” using the “threshold value Dth of the electrolyte diffusion coefficient” will be described.

[0101] A recycling determination method for electrodes of a secondary battery according to an embodiment of the present invention is a method for determining the degree of deterioration of an electrode contained in a secondary battery as a determination object (hereinafter referred to as a "determination object battery"). The recycling determination method of this embodiment, for example, evaluates the degree of deterioration of the electrodes of the determination object battery and classifies the determination object battery into a plurality of categories (for example, "parallel recycling possible", "wet recycling possible", "unsuitable for either parallel recycling or wet recycling", etc.).

[0102] The battery to be determined is, for example, a lithium-ion battery. The electrode of the battery to be determined is not limited thereto, and may include, for example, a current collector (typically a metal foil) and an electrode mixture layer formed on the current collector. The electrode mixture layer may include, for example, an electrode active material, a conductive additive, a binder, etc. The electrode to be determined is preferably a positive electrode.

[0103] The determination target battery is not limited thereto, and may be, for example, a secondary battery whose discharge capacity decreases due to repeated charge and discharge and becomes unsuitable for reuse and is collected.

[0104] [First embodiment]

[0105] Figure 5The present invention is a flowchart of a recycling determination method for a secondary battery electrode according to a first embodiment of the present invention. The recycling determination method comprises: a process of estimating characteristic parameters of a battery at the time of determination, including an electrolyte diffusion coefficient of the battery at the time of determination, using a predetermined model formula based on data obtained by measuring the battery to be determined (step S1); a process of calculating the discharge capacity when the electrolyte diffusion coefficient is changed based on the model formula and the estimated characteristic parameters, and calculating the relationship between the electrolyte diffusion coefficient and the discharge capacity (step S2); a process of determining a threshold value Dth of the electrolyte diffusion coefficient based on the relationship between the electrolyte diffusion coefficient and the discharge capacity (step S3); and a process of comparing the threshold value Dth with a threshold value Dth0 of the electrolyte diffusion coefficient before deterioration obtained in advance for the battery to be determined or a secondary battery of the same type as the battery to be determined, and classifying the battery to be determined based on the difference ΔDth=Dth-Dth0 between the threshold value Dth and the threshold value Dth0 (step S4).

[0106] In this embodiment, first, similarly to the case of the secondary battery diagnosis method, the characteristic parameter at the time of determination is estimated based on the measured data of the determination target battery, and the threshold value Dth of the electrolyte diffusion coefficient is determined based on the characteristic parameter (steps S1 to S3). Steps S1 to S3 can be similar to the case of the secondary battery diagnosis method ( Figure 1 The threshold Dth is compared with the threshold Dth0 of the secondary battery before degradation acquired in advance, and the battery to be determined is classified based on the difference ΔDth=Dth-Dth0 between the threshold Dth and the threshold Dth0 (step S4).

[0107] The threshold value Dth0 is a threshold value of the electrolyte diffusion coefficient determined by performing the same steps as steps S1 to S3 on the determination target battery or a secondary battery of the same type as the determination target battery before deterioration. “Before deterioration” is preferably before use, that is, in a new state.

[0108] "A secondary battery of the same type as the battery to be determined" refers to a secondary battery with the same positive and negative electrode materials, shapes, electrolyte types and amounts as the battery to be determined. For example, when the battery to be determined is a product battery, "a secondary battery of the same type as the battery to be determined" refers to a secondary battery of the same model, etc. When "a secondary battery of the same type as the battery to be determined" is used to determine the threshold value Dth0, it is preferred to use multiple secondary batteries to determine the threshold value Dth0 and find the average value thereof.

[0109] When implementing steps S1 to S3, the model formula used, the conditions of the discharge simulation, and the criteria for judging "not suitable for reuse" are the same when determining the threshold value Dth and when determining the threshold value Dth0. In particular, when determining the threshold value Dth and when determining the threshold value Dth0, the magnitude of the current during the discharge simulation is made the same. For example, when the discharge rate is 1C when determining the threshold value Dth0, the magnitude of the current when determining the threshold value Dth is set to a magnitude equivalent to 1C based on the single cell capacity when determining the threshold value Dth0. The threshold value Dth and the threshold value Dth0 vary according to the magnitude of the current during use. Therefore, in step SA2 ( Figure 1 ), it is preferred to perform the discharge simulation taking into account the normal range of usage rate of the battery.

[0110] On the other hand, in the process of estimating the characteristic parameters at the time of determination, it is not necessary to update all the characteristic parameters of the battery to be determined. For example, characteristic parameters that are considered to be almost unchanged before and after degradation can also directly use the characteristic parameters estimated when the threshold value Dth0 is determined. Therefore, the data used for estimating the characteristic parameters at the time of determination can be data required for estimating the characteristic parameters to be updated, and it is not necessary to make the data of the same type as the measured data used when determining the threshold value Dth0 consistent. The data used in estimating the characteristic parameters at the time of determination can also be, for example, only a discharge curve at a single discharge rate. However, if discharge curves at multiple discharge rates can be used, it is preferred to use the discharge curve.

[0111] It is preferred that when estimating the characteristic parameters at the time of determination, only the discharge capacity, electrolyte diffusion coefficient, and electrolyte conductivity are changed based on the characteristic parameters estimated when the threshold value Dth0 is determined, and other characteristic parameters are fixed to the characteristic parameters estimated when the threshold value Dth0 is determined for fitting. When estimating the characteristic parameters at the time of determination, all characteristic parameters may be changed for fitting, but if it is performed by someone other than a skilled technician, the number of parameters increases, which may result in an inaccurate fitting.

[0112] In the present embodiment, the battery to be determined is classified based on the difference ΔDth=Dth-Dth0 between the threshold value Dth and the threshold value Dth0. For example, when the difference ΔDth is less than a predetermined boundary value, the battery to be determined is classified into the first category, and when the difference ΔDth is greater than the predetermined boundary value, the battery to be determined is classified into the second category.

[0113] It is known from experiments that when the threshold Dth changes in a direction of increasing with cycle degradation, that is, when ΔDth>0, the possibility of structural degradation of the secondary battery electrode is high. Therefore, for example, the "predetermined boundary value" can be set to 0, and the electrode of the secondary battery with ΔDth greater than 0 (classified as the second classification secondary battery) is determined to be unsuitable for either parallel recovery or wet recovery.

[0114] In ΔDth, the analytical error includes 0.01×10 -6 cm 2 Therefore, the above-mentioned “predetermined boundary value” (the boundary value for dividing the first category and the second category) is preferably from -0.01×10 -6 ~0.01×10 -6 cm 2 For example, when the "predetermined boundary value" is set to 0.01×10 -6 cm 2 / sec, if the difference ΔDth is 0.01×10 -6 cm 2 / sec or less, the battery to be determined is classified as the first category. If the difference ΔDth is greater than 0.01×10 - 6 cm 2 / sec, the battery to be determined is classified as the second category.

[0115] The classified secondary batteries may be further measured and inspected to determine the recycling method. For example, the classification in step S4 may be performed as a primary screening, and only the secondary batteries classified into the first classification or only the secondary batteries classified into the second classification may be subjected to additional measurement and inspection. Alternatively, the content of the additional measurement and inspection may be changed between the first classification and the second classification.

[0116] The above is a description of the recycling determination method of the secondary battery electrode according to the first embodiment of the present invention. According to this embodiment, the degree of deterioration of the electrode to be recycled can be determined.

[0117] [Second embodiment]

[0118] Figure 6 1 is a flowchart of a recycling determination method for a secondary battery electrode according to a second embodiment of the present invention. The recycling determination method includes the steps ( Figure 5 ), there is also a step (step S5) of classifying the batteries to be determined based on the reduction rate of the discharge capacity of the batteries to be determined (hereinafter referred to as "capacity reduction rate"). Figure 6, the step of classifying the determination target batteries based on the capacity reduction rate (step S5) is shown after the step of classifying the determination target batteries based on the difference ΔDth (step S4), but the order of step S4 and step S5 may be reversed.

[0119] The capacity reduction rate is the value obtained by subtracting the discharge capacity of the secondary battery at the time of determination from the discharge capacity of the secondary battery before use (when new) and dividing it by the discharge capacity of the secondary battery before use (when new). The discharge capacity of the secondary battery decreases due to various reasons, so even if the capacity reduction rate of the secondary battery (single cell) is high, it is not necessarily possible to say that the electrodes deteriorate to the same extent. However, even so, in the case of a high capacity reduction rate of the secondary battery, the possibility of electrode deterioration is high, and at least it can be judged as unsuitable for parallel recovery.

[0120] In the process of classifying the target batteries based on the capacity reduction rate (step S5), for example, the batteries are classified into secondary batteries with a capacity reduction rate less than a predetermined threshold and secondary batteries with a capacity reduction rate greater than a predetermined threshold. The capacity reduction rate threshold here varies depending on the purpose after recycling, etc., and can be set to 20% to 40%, for example.

[0121] Figure 7 This is an example of a method for classifying the target battery by this embodiment. In this example, classification based on the capacity reduction rate is first performed. Specifically, the battery with a capacity reduction rate above a predetermined threshold is classified as a target for wet recovery or dry recovery. For the case where the capacity reduction rate is less than the predetermined threshold, classification based on the difference ΔDth is further performed. Specifically, the battery with a difference ΔDth below a predetermined boundary value is classified as a target for parallel recovery or wet recovery, and the battery with a difference ΔDth greater than a predetermined boundary value is classified as a target for dry recovery.

[0122] Figure 8 This is another example of a method for classifying the target battery by using the present embodiment. In this example, classification based on the difference ΔDth is first performed. Specifically, the difference ΔDth greater than the predetermined boundary value is classified as a target for dry recovery. For the case where the difference ΔDth is below the predetermined boundary value, classification based on the capacity reduction rate is further performed. Specifically, the capacity reduction rate above the predetermined threshold is classified as a target for wet recovery, and the capacity reduction rate less than the predetermined threshold is classified as a target for parallel recovery or wet recovery.

[0123] Figure 7 and Figure 8 The classification method is of course also an example, and the recovery determination method of this embodiment is not limited to this. In addition, as in the case of the first embodiment, further measurements and inspections can also be performed to determine the recovery method.

[0124] [Third Embodiment]

[0125] Fig. 9 1 is a flowchart of a recycling determination method for a secondary battery electrode according to a third embodiment of the present invention. The recycling determination method includes the steps ( Figure 5 ), there is also a step (step S6) of classifying the batteries to be determined based on the difference ΔD between the threshold value Dth and the electrolyte diffusion coefficient at the time of determination. Preferably, the step (step S6) of classifying the batteries to be determined based on the difference ΔD is performed before the step (step S4) of classifying the batteries to be determined based on the difference ΔDth.

[0126] The recycling determination method of this embodiment is to Figure 1 A method of combining the diagnostic method for a secondary battery described in the description with the recovery determination method for the electrode of a secondary battery. That is, in the present embodiment, it is determined whether the determination object battery can be reused (reuse). Specifically, for example, when the difference ΔD is above a predetermined threshold, the determination object battery is classified as a secondary battery that can be reused. When the difference ΔD is less than a predetermined threshold, the determination object battery is classified as a secondary battery that is not suitable for reuse, and then a classification based on ΔDth (determination of the degree of degradation of the electrode) is performed.

[0127] Since steps S1 to S3 are common in the secondary battery diagnosis method and the secondary battery electrode recovery determination method, the cost of work and calculation can be reduced by performing them together.

[0128] In the present embodiment, the step of classifying the determination target batteries based on the capacity reduction rate described in the second embodiment may be further performed (step S5 ).

[0129] (Recycling determination program for secondary battery electrodes, etc.)

[0130] The above-mentioned recovery determination method of the electrode of the secondary battery can also be implemented as a computer program. The recovery determination program of the electrode of the secondary battery of one embodiment of the present invention enables the computer to execute the following steps: based on the data obtained by measuring the determination object battery, using a predetermined model formula, the characteristic parameters of the determination object battery at the determination time, including the electrolyte diffusion coefficient of the determination object battery, are estimated; based on the model formula and the estimated characteristic parameters, the discharge capacity when the electrolyte diffusion coefficient is changed is calculated, and the relationship between the electrolyte diffusion coefficient and the discharge capacity is calculated; based on the relationship between the electrolyte diffusion coefficient and the discharge capacity, the threshold value Dth of the electrolyte diffusion coefficient is determined; and the threshold value Dth is compared with the threshold value Dth0 of the electrolyte diffusion coefficient before deterioration obtained in advance for the determination object battery or a secondary battery of the same type as the determination object battery, and the determination object battery is classified according to the difference ΔDth=Dth-Dth0 between the threshold value Dth and the threshold value Dth0. According to this embodiment, the degree of deterioration of the electrode to be recovered can also be determined.

[0131] The above-mentioned method for determining whether to collect or recover an electrode of a secondary battery can also be realized as a computer-readable recording medium having the above-mentioned computer program recorded thereon.

[0132] The above-mentioned recovery determination method of the electrode of the secondary battery can also be implemented as a computer system. The recovery determination computer system of the electrode of the secondary battery of one embodiment of the present invention has a memory and a processor, and the processor performs the following steps according to the program of the memory: based on the data obtained by measuring the determination object battery, using a predetermined model formula, the characteristic parameters of the determination object battery at the determination time, including the electrolyte diffusion coefficient of the determination object battery, are estimated; based on the model formula and the estimated characteristic parameters, the discharge capacity when the electrolyte diffusion coefficient is changed is calculated, and the relationship between the electrolyte diffusion coefficient and the discharge capacity is calculated; based on the relationship between the electrolyte diffusion coefficient and the discharge capacity, the threshold value Dth of the electrolyte diffusion coefficient is determined; and the threshold value Dth is compared with the threshold value Dth0 of the electrolyte diffusion coefficient before deterioration obtained in advance for the determination object battery or a secondary battery of the same type as the determination object battery, and the determination object battery is classified based on the difference ΔDth=Dth-Dth0 between the threshold value Dth and the threshold value Dth0.

[0133] Example

[0134] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0135] [Manufacturing of Secondary Batteries]

[0136] A plurality of medium-sized laminated batteries with rated capacities of 13Ah, 5Ah, and 2.7Ah were produced.

[0137] [5Ah medium-sized laminated battery]

[0138] <Production of positive electrode>

[0139] LiCoO as the positive electrode active material 2 : 93 parts by mass, carbon black as a conductive aid: 3 parts by mass, and PVDF as a binder: 4 parts by mass were mixed evenly using a solvent NMP to prepare a slurry containing a positive electrode mixture. The slurry containing the positive electrode mixture was applied to both sides of a positive electrode collector consisting of an aluminum foil with a thickness of 15 μm, and after drying, it was press-formed using a roller press, and a portion of the positive electrode collector not coated with the slurry containing the positive electrode mixture was punched out in a manner that a pole ear portion was formed, thereby preparing a positive electrode.

[0140] <Production of negative electrode>

[0141] 97.5 parts by mass of graphite as a negative electrode active material, 1.5 parts by mass of carboxymethyl cellulose as a binder, and 1 part by mass of styrene-butadiene rubber were mixed, and an appropriate amount of water was added and mixed thoroughly to prepare a slurry containing a negative electrode mixture. The slurry containing the negative electrode mixture was applied to both sides of a negative electrode collector composed of a copper foil having a thickness of 10 μm, and after drying, pressure molding was performed using a roller press, and a portion of the negative electrode collector not coated with the slurry containing the negative electrode mixture was punched out in such a way that it became a pole ear portion, thereby preparing a negative electrode.

[0142] <Battery Production>

[0143] Seven sheets of the positive electrodes and eight sheets of the negative electrodes were alternately stacked via a three-layer polyolefin microporous membrane separator having a thickness of 18 μm and a polyethylene layer as an intermediate layer and two polypropylene layers as outer layers to form a stacked electrode body.

[0144] Next, the tabs of the positive electrode and the tabs of the negative electrode of the stacked electrode body were welded to each other, and the leads were connected to each other, and the LiPF 6 After being dissolved in a solution prepared by mixing ethylene carbonate, diethyl carbonate and ethyl methyl carbonate in a volume ratio of 1:1:1 at a concentration of 1 mol / L, it is further sealed in an outer casing composed of an aluminum laminate film together with a non-aqueous electrolyte prepared by dissolving vinylene carbonate in an amount of 1% by mass to produce a non-aqueous electrolyte secondary battery with a rated capacity of 5 Ah.

[0145] [2.7Ah medium-sized laminated battery]

[0146] <Production of positive electrode>

[0147] LiCoO as the positive electrode active material 2: 93 parts by mass, carbon black as a conductive aid: 3 parts by mass, and PVDF as a binder: 4 parts by mass were mixed evenly using a solvent NMP to prepare a slurry containing a positive electrode mixture. The slurry containing the positive electrode mixture was applied to both sides of a positive electrode collector consisting of an aluminum foil with a thickness of 15 μm, and after drying, it was press-formed using a roller press, and a portion of the positive electrode collector not coated with the slurry containing the positive electrode mixture was punched out in a manner that a pole ear portion was formed, thereby preparing a positive electrode.

[0148] <Production of negative electrode>

[0149] 94.5 parts by mass of graphite as a negative electrode active material, 3 parts by mass of SiO particles (D50: 5.0 μm) with carbon on the surface, 1.5 parts by mass of carboxymethyl cellulose as a binder, and 1 part by mass of styrene-butadiene rubber were mixed, and an appropriate amount of water was added and mixed thoroughly to prepare a slurry containing a negative electrode mixture. The slurry containing the negative electrode mixture was applied to both sides of a negative electrode collector composed of a copper foil with a thickness of 10 μm, and after drying, it was press-formed using a roller press, and a portion of the negative electrode collector not coated with the slurry containing the negative electrode mixture was punched out in a manner that a pole ear portion was formed, thereby preparing a negative electrode.

[0150] <Battery Production>

[0151] Seven sheets of the positive electrodes and eight sheets of the negative electrodes were alternately stacked via a three-layer polyolefin microporous membrane separator having a thickness of 18 μm and having a polyethylene layer as an intermediate layer and two polypropylene layers as outer layers to form a stacked electrode body.

[0152] Next, the tabs of the positive electrode and the tabs of the negative electrode of the stacked electrode body were welded to each other, and after connecting leads, LiPF was dissolved at a concentration of 1 mol / L in a solution of ethylene carbonate and diethyl carbonate mixed at a volume ratio of 3:7. 6 Then, the mixture was sealed in an outer casing composed of an aluminum laminate film together with a nonaqueous electrolyte solution prepared by dissolving vinylene carbonate in an amount of 1% by mass, thereby manufacturing a nonaqueous electrolyte secondary battery with a rated capacity of 36 mAh.

[0153] [13Ah medium-sized laminated battery]

[0154] Replace LiCoO 2 , using LiNi 0.5 Co 0.2 Mn 0.3 O 2 A medium-sized laminated battery with a rated capacity of 13 Ah was produced in the same manner as the 5 Ah medium-sized laminated battery except that the positive electrode active material was changed according to the target rated capacity in the areas of the positive electrode, negative electrode, and separator, the amount of electrolyte, etc.

[0155] [Production of Degraded Cells]

[0156] For a medium-sized laminated battery with a rated capacity of 5Ah, a charge and discharge cycle test was carried out under different conditions such as charge and discharge rate and ambient temperature to produce degraded cells whose discharge capacity was reduced to 4.5Ah and 3.7Ah. Similarly, a degraded cell whose discharge capacity was reduced to 2.4Ah was produced from a medium-sized laminated battery with a rated capacity of 2.7Ah, and a degraded cell whose discharge capacity was reduced to 11Ah and 12.5Ah was produced from a medium-sized laminated battery with a rated capacity of 13Ah. In addition, the "discharge capacity" after deterioration here is the discharge capacity measured at a current value of 0.2C based on the "rated capacity" of each battery (hereinafter, this capacity is referred to as the "cell capacity").

[0157] [Recycling diagnosis of secondary battery electrodes]

[0158] The load characteristics of these cells were measured before and after degradation. Specifically, discharge curves were measured at discharge rates of 0.02C, 0.2C, 0.5C, and 1C based on the initial rated capacity of each cell.

[0159] Next, the single cell before degradation was used as the target cell, and the threshold value Dth0 of the electrolyte diffusion coefficient was determined by the method described in the embodiment. The analysis (simulation) was performed using the software Battery Design Studio manufactured by Siemens. In the basic specifications, the solvent ratio and salt concentration were input with the same values ​​as those at the time of production.

[0160] After estimating the characteristic parameters of the single cell before degradation, the discharge capacity at an ambient temperature of 45°C and a discharge rate of 0.5C was calculated while changing the electrolyte diffusion coefficient based on the estimated characteristic parameters, and the relationship between the electrolyte diffusion coefficient and the discharge capacity was obtained. The point where the tangent lines of each curve before and after the discharge capacity began to drop sharply intersected was calculated as the threshold value Dth0.

[0161] Next, the threshold value Dth of the electrolyte diffusion coefficient of the degraded single cell is determined. Regarding the threshold value Dth of the electrolyte diffusion coefficient after degradation, based on the characteristic parameters estimated when determining the threshold value Dth0 of the electrolyte diffusion coefficient before degradation, only the single cell capacity, electrolyte diffusion coefficient and electrolyte conductivity are changed, and other characteristic parameters are fixed to the characteristic parameters estimated when determining the threshold value Dth0 of the electrolyte diffusion coefficient before degradation and estimated by fitting. The magnitude of the current during the discharge simulation is the same as the magnitude of the current when the threshold value Dth0 is determined. That is, it is set to a magnitude equivalent to 0.5C based on the capacity (rated capacity) of each battery before degradation.

[0162] The results are shown in Table 1. In Table 1, "LCO" (Judgment Examples 1 to 3) represents lithium cobalt oxide, "SiO·graphite" (Judgment Example 3) represents a mixture of graphite and SiO particles whose surfaces are coated with carbon, and "NCM" (Judgment Examples 4 and 5) represents lithium nickel·cobalt·manganese oxide.

[0163] [Table 1]

[0164]

[0165] In judgment examples 1, 3, and 5, the capacity reduction rate of the secondary battery (single battery) is less than 10%, so the capacity reduction rate of the electrode is also expected to be less than 10%. In addition, the difference ΔDth of the threshold value of the electrolyte diffusion coefficient before and after degradation shows a negative value, so it can be inferred that the structural degradation of the electrode has not been caused. Therefore, it can be determined that the electrodes of these secondary batteries can be recovered in parallel or by wet recovery.

[0166] On the other hand, in Judgment Example 2, the capacity reduction rate of the secondary battery (single battery) is as large as 25% or more. In this secondary battery, the discharge capacity of the electrode is also likely to be greatly reduced from the initial value. In addition, the difference ΔDth of the threshold value of the electrolyte diffusion coefficient before and after degradation shows a positive value, so it can be inferred that the possibility of structural degradation of the electrode is high. Therefore, it can be determined that the electrode of the secondary battery is not suitable for either parallel recovery or wet recovery.

[0167] In judgment example 4, the capacity reduction rate of the secondary battery (single cell) is suppressed, but the difference ΔDth of the threshold value of the electrolyte diffusion coefficient before and after degradation shows a positive value, which can be inferred that the possibility of structural degradation of the electrode is high. Therefore, it can be determined that the electrode of the secondary battery is not suitable for either parallel recovery or wet recovery.

[0168] Next, the positive electrode and negative electrode were recovered from the secondary battery of each judgment example, and the capacity reduction rate of the positive electrode, the capacity reduction rate of the negative electrode, the expansion rate of the positive electrode mixture, and the expansion rate of the negative electrode mixture were measured. In addition, a scanning electron microscope (SEM) photograph of the positive electrode of the secondary battery of each judgment example was taken to investigate whether the active material particles had cracks. The results are shown in Table 2.

[0169] [Table 2]

[0170]

[0171] Fig.10 These are SEM photographs of the initial states of the positive electrodes (LCO) of Evaluation Examples 1 to 3. Fig.11 This is a SEM photograph of the positive electrode after deterioration of Judgment Example 1. Fig.12 This is a SEM photograph of the positive electrode after deterioration of Judgment Example 2. Fig.13This is a SEM photograph of the positive electrode after deterioration of Judgment Example 3. It can be seen that in Judgment Example 1 ( Fig.11 ) and Judgment Example 3( Fig.13 ) no cracks were observed, whereas in judgment example 2 ( Fig.12 ) in which a large number of cracks are generated in each particle.

[0172] Fig.14 This is a SEM photograph of the initial state of the positive electrode (NCM) of Evaluation Examples 4 and 5. The particle structure of NCM is secondary particles composed of a sintered body of primary particles. Fig.15 This is a SEM photograph of the positive electrode after deterioration of Judgment Example 4. Fig.16 This is a SEM photograph of the positive electrode after deterioration of Judgment Example 5. Judgment Example 4 ( Fig.15 ), the sintered parts between the primary particles broke and a large number of cracks were generated. On the other hand, in Judgment Example 5 ( Fig.16 ), there are very few cracks.

[0173] As shown in Table 2 and Figures 10 to 16 As shown, it was confirmed that the determination result was well consistent with the degradation state of the electrode.

[0174] Furthermore, the single-pole discharge characteristics of the positive electrodes recovered in parallel were measured for Judgment Examples 1 and 4. As a result, in Judgment Example 1, the initial discharge was 0.5C / 96%, and the discharge was 0.5C / 92% after recovery, maintaining a high level. On the other hand, in Judgment Example 4, the initial discharge was 0.5C / 94%, and the discharge was 0.5C / 72% after recovery, which was significantly reduced.

[0175] In addition, the above percentages (0.5C / 96% and 0.5C / 94%) of the initial electrode represent the ratio of the discharge capacity at 0.5C to the discharge capacity (single cell capacity) at 0.2C before deterioration. In addition, the above percentages (0.5C / 92% and 0.5C / 72%) of the recovered electrode are obtained by taking the single cell capacity after deterioration recorded in Table 1 as the "rated capacity" of the recovered battery, and measuring the discharge capacity at the current value at 0.2C and 0.5C in the same manner as the initial electrode, and representing the ratio of the discharge capacity at 0.5C to the discharge capacity at 0.2C.

[0176] For example, in the case of judgment example 1, the initial single-pole discharge characteristic "0.5C / 96%" is the ratio of the discharge capacity measured at 0.5C (i.e., 2.5A) based on the rated capacity of 5Ah to the discharge capacity measured at 0.2C (i.e., 1A) based on the rated capacity of 5Ah. In contrast, the single-pole discharge characteristic "0.5C / 92%" of the positive electrode recovered in parallel is the ratio of the discharge capacity measured at 0.5C (i.e., 2.25A) based on the degraded single cell capacity of 4.5Ah to the discharge capacity measured at 0.2C (i.e., 0.9A) based on the degraded single cell capacity of 4.5Ah.

[0177] The reason why the presence or absence of structural degradation of the electrode can be determined by the difference ΔDth in the threshold value of the electrolyte diffusion coefficient before and after degradation is not fully elucidated, but is presumed to be as follows.

[0178] The threshold value Dth of the electrolyte diffusion coefficient may depend on the internal resistance of the secondary battery. The electrolyte conductivity obtained by this analysis not only reflects the ohmic resistance and the actual resistance of the electrolyte, but also reflects the interface resistance during the positive and negative electrode reactions. Therefore, the structural degradation of the electrode (if the active material cracks, an electrically discontinuous interface is generated, thereby causing a substantial increase in resistance) is reflected in the electrolyte conductivity. Thus, it is believed that by investigating the threshold value Dth of the electrolyte diffusion coefficient, the structural degradation of the electrode can be indirectly evaluated.

[0179] In addition, the judgment results this time mainly reflect the degree of degradation of the positive electrode. If the negative electrode also degrades, the interface resistance increases, but the increase is mostly smaller than that of the positive electrode. This is because the degradation of the negative electrode is mainly caused by the deactivation caused by the isolation of the active material and the potential shift caused by the consumption of Li in the formation of SEI. The probability of structural degradation such as the generation of cracks is lower than that of the positive electrode.

[0180] As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment only, Various changes are possible within the scope of this invention.

Claims

1. A method for determining the recovery of electrodes of a secondary battery, wherein the method determines the degree of degradation of an electrode contained in a secondary battery as a determination target, wherein: The recycling determination method comprises the following steps: estimating characteristic parameters of the secondary battery as the determination object at the determination time, including the electrolyte diffusion coefficient of the secondary battery as the determination object at the determination time, using a predetermined model formula based on data obtained by measuring the secondary battery as the determination object; Based on the model formula and the estimated characteristic parameters, the discharge capacity when the electrolyte diffusion coefficient is changed is obtained, and the relationship between the electrolyte diffusion coefficient and the discharge capacity is obtained; Determining a threshold value Dth of the electrolyte diffusion coefficient according to the relationship between the electrolyte diffusion coefficient and the discharge capacity; as well as The threshold Dth is compared with a threshold Dth0 of the electrolyte diffusion coefficient before degradation obtained in advance for the secondary battery as the judgment object or a secondary battery of the same type as the secondary battery as the judgment object, and the secondary battery as the judgment object is classified based on the difference ΔDth=Dth-Dth0 between the threshold Dth and the threshold Dth0.

2. The method for determining the recovery of a secondary battery electrode according to claim 1, characterized in that: The recycling determination method further comprises the following steps: The secondary batteries to be determined are classified based on the reduction rates of the discharge capacities of the secondary batteries to be determined.

3. The method for determining the recovery of a secondary battery electrode according to claim 1, characterized in that: The recycling determination method further comprises the following steps: The secondary battery to be determined is classified based on the difference ΔD between the threshold value Dth and the diffusion coefficient of the electrolyte at the determination time.

4. The method for determining recovery of secondary battery electrodes according to claim 1, characterized in that: The characteristic parameter of the secondary battery as the determination object at the determination time further includes the electrolyte conductivity of the secondary battery as the determination object at the determination time.

5. The method for determining recovery of secondary battery electrodes according to claim 1, characterized in that: The step of classifying the secondary battery as the determination target based on the difference ΔDth=Dth-Dth0 includes the following steps: When the difference ΔDth is less than a predetermined boundary value, the secondary battery as the determination target is classified into a first category, and when the difference ΔDth is greater than the predetermined boundary value, the secondary battery as the determination target is classified into a second category. The predetermined boundary value is from -0.01×10 -6 ~0.01×10 -6 cm 2 / sec range setting value.

6. The method for determining recovery of secondary battery electrodes according to claim 1, characterized in that: The electrode is a positive electrode.

7. The method for determining recovery of secondary battery electrodes according to claim 1, characterized in that: The secondary battery to be determined is a lithium-ion battery.

8. A recycling determination program for a secondary battery electrode, which determines the degree of degradation of an electrode included in a secondary battery as a determination target, characterized in that: Make the computer execute the following process: estimating characteristic parameters of the secondary battery as the determination object at the determination time, including the electrolyte diffusion coefficient of the secondary battery as the determination object at the determination time, using a predetermined model formula based on data obtained by measuring the secondary battery as the determination object; Based on the model formula and the estimated characteristic parameters, the discharge capacity when the electrolyte diffusion coefficient is changed is obtained, and the relationship between the electrolyte diffusion coefficient and the discharge capacity is obtained; Determining a threshold value Dth of the electrolyte diffusion coefficient according to the relationship between the electrolyte diffusion coefficient and the discharge capacity; as well as The threshold Dth is compared with a threshold Dth0 of the electrolyte diffusion coefficient before degradation obtained in advance for the secondary battery as the judgment object or a secondary battery of the same type as the secondary battery as the judgment object, and the secondary battery as the judgment object is classified based on the difference ΔDth=Dth-Dth0 between the threshold Dth and the threshold Dth0.

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