Method for measuring electrolyte permeability coefficient

Abstract

This invention provides a method for determining the electrolyte permeability coefficient, which is unaffected by the thickness of the electrode (laminated structure) and can simply and accurately determine the electrolyte permeability coefficient of the electrode (laminated structure). The method for determining the electrolyte permeability coefficient of this invention includes the following steps: Step S1, determining the pore size distribution of the electrode (laminated structure) and calculating the mode D in the pore size distribution. M Cumulative 10% particle size D in volume-based cumulative pore size distribution 10 ; and process S2, based on formula (A) to calculate the electrolyte permeability coefficient k p In the following formula, k p The electrolyte permeability coefficient [m] 2 ], k is the Cozenni constant, ε is the porosity, D M D is the mode of the fine aperture [m]. 10 The cumulative 10% pore size [m] in the volumetric cumulative fine pore size distribution. [Equation 1]

Description

Technical Field

[0001] This invention relates to a method for determining the permeability coefficient of an electrolyte. Background Technology

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, are used as power sources for vehicles such as electric vehicles (EVs), hybrid electric vehicles (HVs), and plug-in hybrid electric vehicles (PHVs). A non-aqueous electrolyte secondary battery comprises an electrode stack with multiple electrodes laminated via a separator and a non-aqueous electrolyte.

[0003] One of the required characteristics for non-aqueous electrolyte secondary batteries is high rate tolerance. One physical property related to high rate tolerance is the electrolyte permeability coefficient, which represents the ease with which a non-aqueous electrolyte penetrates the in-plane direction of the electrode (laminate). By reducing the electrolyte permeability coefficient of the electrode (laminate), and suppressing electrolyte outflow from the electrode (laminate), high rate tolerance can be improved.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2024-130393 Summary of the Invention

[0005] Previously, the electrolyte permeability coefficient was measured using an electrolyte permeability measuring device. Specifically, it was calculated based on Darcy's formula from the amount of non-aqueous electrolyte that permeated through the electrode (laminated body) when argon (Ar) gas was applied to the electrode (laminated body) under constant pressure (paragraph 0012 of Patent Document 1).

[0006] In existing measuring apparatuses, a wound body with electrodes (laminated layers) is required as a sample. The wound body is placed inside a cylindrical container, with an O-ring positioned between the wound body and the container. A non-aqueous electrolyte is supplied from above the wound body, and the volume of the non-aqueous electrolyte flowing out from below is measured. In this existing method, thick electrodes (laminated layers) cannot be wound, and cracks will form in the electrodes (laminated layers), making measurement impossible.

[0007] Preferably, even without preparing a winding body, the electrolyte permeability coefficient can be determined with high accuracy using a simple method.

[0008] The present invention was made in view of the above circumstances, and its purpose is to provide a method for measuring the electrolyte permeability coefficient, which is not affected by the thickness of the electrode (laminate) and can simply and accurately measure the electrolyte permeability coefficient of the electrode (laminate).

[0009] The method for determining the electrolyte permeability coefficient of the present invention is a method for determining the electrolyte permeability coefficient of a battery electrode or electrode stack, wherein the battery comprises an electrode stack having a plurality of electrodes stacked thereon via a separator and an electrolyte, and the method for determining the electrolyte permeability coefficient includes the following steps:

[0010] Step (S1): Determine the pore size distribution of the electrode or the electrode stack, and calculate the mode (D) of the pore size distribution. M ) and the cumulative 10% particle size in the volume-based cumulative pore size distribution (D 10 );and

[0011] In step (S2), the electrolyte permeability coefficient is calculated based on the following formula (A).

[0012] [Formula 1]

[0013]

[0014] (In the above formula, k) p The electrolyte permeability coefficient [m] 2 ], k is the Cozenni constant, ε is the porosity, D M D is the mode of the fine aperture [m]. 10 The cumulative 10% pore size [m] in the volumetric cumulative fine pore size distribution.

[0015] In the method of this invention, it is not necessary to measure the amount of non-aqueous electrolyte that has permeated through the electrode (laminated body); the electrolyte permeability coefficient (k) can be determined simply by measuring the pore size distribution of the electrode (laminated body). p The pore size distribution of the electrode (laminate) can be determined using known methods such as mercury porosimetry without the need for a winding. In the method of the present invention, since no winding is required, the thickness of the electrode (laminate) can be measured with high precision regardless of its thickness.

[0016] Invention Effects

[0017] According to the present invention, a method for determining the electrolyte permeability coefficient is provided, which is not affected by the thickness of the electrode (laminate) and can simply and accurately determine the electrolyte permeability coefficient of the electrode (laminate). Attached Figure Description

[0018] Figure 1 This is a flowchart of the method for determining the electrolyte permeability coefficient of the present invention.

[0019] Figure 2 The figure above is a schematic overall view showing a structural example of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. Figure 2 The figure below is a schematic cross-sectional view of the electrode stack.

[0020] Figure 3 It represents the pore size distribution and mode (D). M The chart shows the determination examples.

[0021] Figure 4 The graph above shows the relationship between the calculated value 1 and the measured value. Figure 4 The following figure is a graph showing the method for finding the Kozeny constant (k) that matches the calculated value 1 with the measured value.

[0022] Figure 5 The graph above shows the relationship between the calculated value 2 and the measured value. Figure 5 The following figure is a chart comparing the calculated values ​​and measured values ​​based on the method of the present invention.

[0023] Figure 6 This is a conceptual diagram of Darcy's formula. Detailed Implementation

[0024] [Methods for determining the electrolyte permeability coefficient]

[0025] This invention relates to a method for determining the electrolyte permeability coefficient of a battery electrode or electrode stack comprising an electrode stack with multiple electrodes stacked via a diaphragm and an electrolyte.

[0026] Examples of batteries include non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries.

[0027] The electrode stack is a stack consisting of one or more positive electrodes and one or more negative electrodes stacked together via a diaphragm.

[0028] In this specification, "electrode (laminated body)" is a general term for electrodes and electrode laminates.

[0029] like Figure 1 As shown in the flowchart,

[0030] The method for determining the electrolyte permeability coefficient of the present invention includes the following steps:

[0031] Step (S1): Determine the pore size distribution of the electrode (laminated body) and calculate the mode (D) of the pore size distribution. M ) and the cumulative 10% particle size in the volume-based cumulative pore size distribution (D 10 );and

[0032] In process (S2), the electrolyte permeability coefficient (k) is calculated based on the following formula (A). p ).

[0033] [Formula 2]

[0034]

[0035] (In the above formula, k) p The electrolyte permeability coefficient [m] 2 ], k is the Cozenni constant, ε is the porosity, D M D is the mode of the fine aperture [m]. 10 The cumulative 10% pore size [m] in the volumetric cumulative fine pore size distribution.

[0036] In existing methods, only Darcy's formula is used to calculate the electrolyte permeability coefficient (k). p ).

[0037] The Darcy formula is shown below. The concept of the Darcy formula is illustrated in the diagram below. Figure 6 .

[0038] [Formula 3]

[0039]

[0040] (In the above formula, u is the empty tower velocity [m / s], k p Permeability coefficient [m] 2 ], ΔP is the pressure loss [Pa], μ is the fluid viscosity [Pa·s], and L [m] is the layer height.

[0041] The inventors derived the calculation formula based on Darcy's formula and the Körzani-Kalman formula. Furthermore, in order to improve accuracy, they improved the calculation formula obtained from Darcy's formula and the Körzani-Kalman formula, and derived an improved calculation formula.

[0042] The following shows the Kozeny-Kalman formula.

[0043] [Formula 4]

[0044]

[0045] (In the above formula, u is the empty tower velocity [m / s], ΔP is the pressure loss [Pa], μ is the fluid viscosity [Pa·s], L is the tower height, k is the König constant, and S...) v Specific surface area [m 2 / m 3 ], where ε is the porosity.

[0046] The following calculation formula is derived using Darcy's formula and the Kozeny-Kalman formula.

[0047] [Formula 5]

[0048]

[0049] (In the above formula, k) p Permeability coefficient [m] 2 ], k is the Közennih constant, S vSpecific surface area [m 2 / m 3 ], where ε is the porosity.

[0050] If the cumulative 50% of the cumulative pore size (D) in the volumetric datum cumulative pore size distribution is taken as... 50 Using [m] to rewrite the above equation (3) for the apparent aperture (de), we get the following equation (4).

[0051] [Formula 6]

[0052]

[0053] (In the above formula, k) p The electrolyte permeability coefficient [m] 2 ], k is the Cozenni constant, ε is the porosity, D 50 The cumulative 50% pore size [m] in the volumetric cumulative fine pore size distribution.

[0054] It is assumed that the electrodes (layers) have a fine pore size distribution, with the fine pore size being the mode (D). M The fine pores of the electrolyte form the main pathway.

[0055] It is believed that the pores of the electrode (laminated structure) contain a number less than the mode (D). M The smaller the pore size, the less likely the electrolyte can pass through. Specifically, it is considered that the smaller the pore size, the more likely the electrolyte will pass through. M The fine pores, the pore diameter and the mode (D) M The ratio of ) is D 10 / D M The pores below have very small diameters, making it difficult for electrolyte to pass through.

[0056] Therefore, the inventors have adopted formula (4) as the apparent fine pore size (de) instead of the cumulative 50% fine pore size (D). 50 Using the mode (D) M The improved calculation formula of the present invention was constructed by adding "a term representing the obstruction of electrolyte flow by the narrow flow path".

[0057] The following shows the improved calculation formula of the present invention.

[0058] [Formula 7]

[0059]

[0060] (In the above formula, k) p The electrolyte permeability coefficient [m] 2 ], k is the Cozenni constant, ε is the porosity, D M D is the mode of the fine aperture [m]. 10The cumulative 10% pore size [m] in the volumetric cumulative fine pore size distribution.

[0061] The pore size distribution of the electrode (laminated body) can be determined by known methods such as mercury intrusion porosimetry.

[0062] There are no special restrictions on the value of the Kozeny constant (k), and the general value of "5" can be used.

[0063] If necessary, the Kozeny constant (k) that matches the measured value can be obtained to improve the accuracy of the calculated value and make it usable.

[0064] The Kozeny constant (k) that is consistent with the calculated value and the measured value can be obtained as follows.

[0065] For multiple electrode stacks, the electrolyte permeability coefficient (k) was determined using an electrolyte permeability measuring device. p ), to obtain multiple electrolyte permeability coefficients (k p The measured value of ). Plot the x-axis parameter set to εD. M 2 (1-D) 10 / D M And set the y-axis parameter to the electrolyte permeability coefficient (k). p The measured value of εD M 2 (1-D) 10 / D M ) and electrolyte permeability coefficient (k p The relationship between the measured values ​​of the data is determined by performing a linear fit on the obtained data to obtain an approximate formula, and then determining the Kozenni constant (k) based on the slope (1 / k) of the approximate formula.

[0066] As described in the section on [Technical Problem to be Solved by the Invention], in existing measuring devices, a wound body with electrodes (laminated bodies) needs to be prepared as a sample. The wound body is placed in a cylindrical container, and an O-ring is placed in the gap between the wound body and the cylindrical container. A non-aqueous electrolyte is supplied from above the wound body, and the amount of non-aqueous electrolyte flowing out from below the wound body is measured. In this existing measuring method, thick electrodes (laminated bodies) cannot be wound, and cracks will form in the electrodes (laminated bodies), making measurement impossible.

[0067] In the method of this invention, it is not necessary to measure the amount of non-aqueous electrolyte that has permeated through the electrode (laminated body); the electrolyte permeability coefficient (k) can be determined simply by measuring the pore size distribution of the electrode (laminated body). p ).

[0068] The pore size distribution of an electrode (laminated structure) can be determined using known methods such as mercury porosimetry. In the determination of pore size distribution based on methods such as mercury porosimetry, there is no need to prepare a winding body. For example, in mercury porosimetry, it is sufficient to cut a sheet-like or plate-like electrode (laminated structure) to the size required to enter the sample tube.

[0069] In the method of the present invention, since there is no need to prepare a winding body, the thickness of the electrode (layer) can be measured with high precision regardless of its thickness.

[0070] As explained above, according to the present invention, a method for determining the electrolyte permeability coefficient can be provided that is not affected by the thickness of the electrode (laminate), and can simply and accurately determine the electrolyte permeability coefficient of the electrode (laminate).

[0071] "Non-aqueous electrolyte secondary battery"

[0072] Referring to the accompanying drawings, the structure of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention will be described. Figure 2 The above figure is a schematic overall view of the non-aqueous electrolyte secondary battery of this embodiment. Figure 2 The figure below is a schematic cross-sectional view of the electrode stack.

[0073] The non-aqueous electrolyte secondary battery 1 contains an electrode stack 20 and a non-aqueous electrolyte (symbol omitted) within a battery container 11. The electrode stack 20 is a stack formed by stacking one or more positive electrodes 21 and one or more negative electrodes 23 via a separator 22. Known negative electrodes, positive electrodes, and electrolytes can be used as the negative electrode, positive electrode, and electrolyte.

[0074] Examples of non-aqueous electrolyte secondary batteries include lithium-ion secondary batteries.

[0075] The following section uses lithium-ion secondary batteries as an example to explain the main components.

[0076] (positive electrode)

[0077] There are no particular limitations on the active material used as a positive electrode; for example, LiCoO2, LiMnO2, LiMn2O4, LiNiO2, and LiNi can be cited. x Co （1-x） O2 and LiNi x Co y Mn （1-x-y） O2 and other lithium-containing composite oxides, etc. (where 0 < x < 1, 0 < y < 1).

[0078] (negative electrode)

[0079] There are no particular restrictions on the active material for the negative electrode, but it is preferred to have a lithium adsorption capacity of less than 2.0V based on Li / Li+. Examples of active materials for the negative electrode include carbon such as graphite, metallic lithium, lithium alloys, transition metal oxides / transition metal nitrides / transition metal sulfides that can be doped / de-doped with lithium ions, and combinations thereof.

[0080] (Non-aqueous electrolyte)

[0081] There are no particular limitations on the non-aqueous electrolyte, but it is preferred to be a non-aqueous electrolyte containing lithium electrolyte dissolved in a mixed solvent of high dielectric constant carbonate solvents such as propylene carbonate and ethylene carbonate and low viscosity carbonate solvents such as diethyl carbonate, methyl ethyl carbonate and dimethyl carbonate.

[0082] As a mixed solvent, a mixed solvent of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) is preferred.

[0083] Examples of lithium-containing electrolytes include LiPF6, LiBF4, LiClO4, LiAsF6, Li2SiF6, and LiiOSO2C. k F （2k+1） (k = integers from 1 to 8) and LiPF n {C k F （2k+1）} （6-n） Lithium salts and their combinations thereof (n = 1 to 5 integers, k = 1 to 8 integers).

[0084] (Diaphragm)

[0085] The membrane can be any membrane that provides electrical insulation between the positive and negative electrodes and allows lithium ions to permeate; porous polymer films are preferred. For example, porous membranes made of polyolefins such as PP (polypropylene), PE (polyethylene), and laminated PP-PE (polyethylene) membranes are preferred.

[0086] (External casing (battery container))

[0087] As an outer casing, it is possible to use known outer casings.

[0088] As for the types of secondary batteries, there are cylindrical, coin-shaped, square, and thin-film (laminated) types, and the outer casing can be selected according to the desired type.

[0089] Example

[0090] The embodiments and comparative examples involved in this invention will be described.

[0091] [Preparation of the electrode stack]

[0092] To compare calculated and measured values, several methods for determining the electrolyte permeability coefficient (k) using existing techniques were prepared. p A sheet electrode stack (stacked structure: positive electrode / separator / negative electrode) for lithium-ion secondary batteries. The following materials are used as battery materials.

[0093] Positive electrode active material: NCM (LiNi) 1 / 3 Co 1 / 3 Mn 1 / 3 O2)

[0094] Positive current collector: aluminum foil,

[0095] Negative electrode active material: carbon,

[0096] Negative current collector: copper foil,

[0097] Diaphragm: Polyethylene diaphragm

[0098] Electrolyte: A solution of LiPF6 dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) = 1 / 1 / 1 (volume ratio).

[0099] [Actual Measurement of Electrolyte Permeability Coefficient]

[0100] Regarding each electrode stack, the electrolyte permeability coefficient (k) was determined using an electrolyte permeability measuring device and existing methods. p (Measured value).

[0101] As a sample, a wound body containing an electrode laminate was prepared. This wound body was placed inside a cylindrical container, with an O-ring positioned between the wound body and the container. A non-aqueous electrolyte was supplied from above the wound body at a predetermined pressure, and the volume of non-aqueous electrolyte flowing out from below the wound body was measured. Based on this volume and Darcy's formula, the electrolyte permeability coefficient (k) was calculated. p ), as the measured value.

[0102] [Determination of pore size distribution]

[0103] The micropore size distribution of the sheet electrode stack was determined by mercury intrusion porosimetry, and the mode (D) of the micropore size distribution was calculated. M ) and the cumulative 10% particle size in the cumulative fine pore size distribution (D 10 [m] and cumulative 50% particle size (D) 50 )[m.

[0104] The pore size distribution and mode (D) M Examples of the determination of ) are shown in Figure 3 .

[0105] [Comparative Example 1]

[0106] The Kozenni constant (k) is commonly referred to as "5". Therefore, the Kozenni constant (k) is set to 5, and the cumulative 50% particle size (D) as the apparent pore size (de) is used, determined by mercury porosimetry. 50 Based on the data, the electrolyte permeability coefficient (k) is calculated using equation (4). p ), as the comparison calculation value 1. The relationship between the measured value and the comparison calculation value 1 is shown in Figure 4 The above figure shows the relationship between the measured value and the calculated value when the measured value is completely consistent with the calculated value 1. As shown in the figure, the measured value is completely inconsistent with the calculated value 1.

[0107] Therefore, the Kozeny constant (k) that is consistent with the measured value and the calculated value is obtained as follows.

[0108] Set the x-axis parameter to εD 50 2 Set the y-axis parameter to the electrolyte permeability coefficient (k). p The measured value of εD 50 2 With electrolyte permeability coefficient (k) p The relationship between the measured values ​​of ) is shown in Figure 4 The following figure shows the approximate expression obtained by fitting a straight line to these data. The approximate expression is y = 0.0334x. The slope of this approximate expression is 1 / k, therefore 1 / k = 0.0334.

[0109] Therefore, the Kozeny constant (k) was set to 28.2, and the cumulative 50% particle size (D) determined by mercury porosimetry was used as the apparent pore size (de). 50 Based on the data, the electrolyte permeability coefficient (k) is calculated using equation (4). p ), as the comparison calculated value 2. The relationship between the measured value and the comparison calculated value 2 is shown in Figure 5 The above figure shows the approximate result obtained by fitting a straight line to these data, which is y = 28.28x. The coefficient of determination (R²) obtained by a known method is 0.96, showing a good correlation between the measured values ​​and the calculated values.

[0110] [Example 1]

[0111] To further improve accuracy, in equation (4), the main diameter of the aperture, i.e., the mode (D), is used as the apparent aperture (de). M By adding a term to represent the obstruction of electrolyte flow by the narrow flow path, equation (A) was constructed.

[0112] In Comparative Example 1, by comparing with the reference Figure 4Using the same method as illustrated in the figure below, the Kozeny constant (k) was obtained, which is consistent with the measured value and the calculated value.

[0113] The plot shows the x-axis parameter set to εD. M 2 (1-D) 10 / D M And set the y-axis parameter to the electrolyte permeability coefficient (k). p The measured value of εD M 2 (1-D) 10 / D M ) and electrolyte permeability coefficient (k p The relationship between the measured values ​​of the data is determined by performing a linear fit on these data to obtain an approximate formula, and then calculating the Kozenni constant (k) based on the slope (1 / k) of the approximate formula. The result is that the Kozenni constant (k) is 23.3.

[0114] Setting the Cozeni constant (k) to 23.3, the electrolyte permeability coefficient (k) is calculated based on equation (A). p The measured values ​​are used as calculated values ​​based on the method of the present invention. A comparison between the measured values ​​and the calculated values ​​based on the method of the present invention is shown below. Figure 5 The figure below shows the approximate result obtained by fitting a straight line to these data, which is y=23.05x, with a coefficient of determination (R2) of 0.99. A high-precision correlation was obtained between the measured and calculated values.

[0115] Based on the above results, the effectiveness of the method of the present invention is demonstrated.

[0116] Symbol Explanation

[0117] 1-Non-aqueous electrolyte secondary battery, 11-Battery container, 20-Electrode stack, 21-Positive electrode, 22-Separator, 23-Negative electrode.

Claims

1. A method for determining the electrolyte permeability coefficient, which is a method for determining the electrolyte permeability coefficient of a battery electrode or electrode stack, wherein the battery comprises an electrode stack having a plurality of said electrodes stacked via a separator and an electrolyte, the method for determining the electrolyte permeability coefficient being characterized by comprising the following steps: Step S1: Measure the pore size distribution of the electrode or the electrode stack, and calculate the mode D in the pore size distribution. M Cumulative 10% particle size D in volume-based cumulative pore size distribution 10 ;and In step S2, the electrolyte permeability coefficient is calculated based on the following formula (A). [Formula 1] In the above formula, k p The electrolyte permeability coefficient [m] 2 ], k is the Cozenni constant, ε is the porosity, D M D is the mode of the fine aperture [m]. 10 The cumulative 10% pore size [m] in the volume-based cumulative fine pore size distribution.

2. The method for determining the electrolyte permeability coefficient according to claim 1, characterized in that, In step S1, the pore size distribution of the electrode or the electrode stack is determined by mercury porosimetry.

3. The method for determining the electrolyte permeability coefficient according to claim 1 or 2, characterized in that, The Kozeny constant k is 5.

4. The method for determining the electrolyte permeability coefficient according to claim 1 or 2, characterized in that, For multiple electrode stacks, the electrolyte permeability coefficient k is determined using an electrolyte permeability measuring device. p And obtain multiple electrolyte permeability coefficients k p The measured value, To plot, set the x-axis parameter to εD. M 2 (1-D) 10 / D M And set the y-axis parameter to the electrolyte permeability coefficient k. p The measured value of εD M 2 (1-D) 10 / D M ) and electrolyte permeability coefficient k p The relationship between the measured values ​​is used to obtain an approximate formula by fitting a straight line to the obtained data, and the Cozenni constant k is determined based on the slope 1 / k of the approximate formula.

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