KR102772866B1 - Method for measuring electrochemical device separator resistance - Google Patents

Abstract

The present invention relates to a method for measuring the resistance of a separator for an electrochemical device.
Specifically, one embodiment of the present invention provides a method for measuring the resistance of a separator for an electrochemical device with high reliability while spending little cost and time.

Description

{METHOD FOR MEASURING ELECTROCHEMICAL DEVICE SEPARATOR RESISTANCE}

The present invention relates to a method for measuring the resistance of a separator for an electrochemical device.

Since the resistance of the separator is one of the factors that reduces the speed and output of electrochemical devices, its measurement is very important.

In general, a method is known in which a separator whose resistance is to be measured is applied to a resistance measuring cell, and then a Nyquist plot for the coin cell is obtained using the EIS (Electrochemical impedance spectroscopy) method and the plot is interpreted.

However, there are two major problems with this method. First, since a resistance measurement cell must be manufactured using positive and/or negative active materials each time, and then the resistance must be measured after going through an aging process, it is costly and time-consuming.

In addition, there may be deviations in the measurement results depending on the type and distribution of the electrode active material, and if some of the electrode active material dissolves in the electrolyte and precipitates on the separator, this may also cause resistance, making it difficult to obtain the resistance of the separator itself.

In one embodiment of the present invention, a method for measuring the resistance of a separator for an electrochemical device with high reliability while spending little cost and time is provided.

The advantages and features of the embodiments of the present invention, and the methods for achieving them, will become clear with reference to the embodiments described in detail below. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, and these embodiments are provided only to make the disclosure of the present invention complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims.

In the following, technical and scientific terms used in the present invention have meanings commonly understood by those of ordinary skill in the art to which this invention belongs, unless otherwise defined. In addition, repeated explanations of technical configurations and operations identical to those of the prior art will be omitted.

Throughout this specification, when a part is said to be “connected” to another part, this includes not only the case where it is “directly connected,” but also the case where it is “electrically connected” with another element in between.

Throughout this specification, when it is said that an element is “on” another element, this includes not only cases where the element is in contact with the other element, but also cases where there is another element between the two elements.

Throughout this specification, whenever a part is said to “include” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

The terms “about,” “substantially,” etc., used throughout this specification are used to mean at or near the numerical value when manufacturing and material tolerances inherent in the meanings stated are provided, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure where exact or absolute values are stated to aid understanding of this specification.

The terms “step of” or “step of” as used throughout this specification do not mean “step for”.

Throughout this specification, the term “combination(s) thereof” included in the expressions in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the Makushi format, and means including one or more selected from the group consisting of said components.

Throughout this specification, references to “A and/or B” mean “A or B, or A and B.”

Method for measuring resistance of separator for electrochemical device

Generally, the separator itself is an insulator, but the concept of the resistance of the separator refers to the resistance that occurs when an electric field passes through the electrolyte in the separator while the separator is impregnated with the electrolyte, and the resistance that occurs at this time is affected by the structure of the separator. In this regard, the meaning of "resistance of the separator" used in the following specification is defined as "the resistance that occurs when an electric field passes through the electrolyte in the separator while the separator is impregnated with the electrolyte."

In one embodiment of the present invention, a method for measuring resistance of a separator for an electrochemical device is provided, including the steps of: wetting an aqueous electrolyte having a conductivity of 100 to 180 mS/cm at 20 to 30° C., into a separator for an electrochemical device as a measurement target; positioning the separator impregnated with the aqueous electrolyte between a negative electrode current collector and a positive electrode current collector, and assembling the separator into a 2032 type coin cell; and connecting an impedance analyzer to the coin cell and applying a frequency in the range of 100 kHz to 10 kHz to obtain a Nyquist plot; and measuring the resistance of the separator from the x-axis intercept value of the obtained Nyquist plot.

After measuring the resistance of the electrochemical device separator which is the above measurement target, the form of the electrochemical device actually applied is not particularly limited. For example, any one electrochemical device separator selected from the group including a lithium secondary battery, a super capacitor, a lithium-sulfur battery, a sodium ion battery, a lithium-air battery, a zinc-air battery, an aluminum-air battery, an aluminum ion battery, and a magnesium ion battery can be subjected to resistance measurement by the method of the above embodiment.

1) Measurement method without using electrode active material

The measurement method of the above-mentioned embodiment uses a negative electrode current collector and a positive electrode current collector whose surfaces are not coated with electrode active materials (bare), so that there can be no deviation in the measurement results depending on the type of electrode active material.

In addition, since it does not use electrode active materials, not only can the cost of raw materials be reduced, but resistance can be measured immediately after coin cell assembly without the need for an aging process, shortening the measurement time compared to generally known methods.

2) Frequency during EIS measurement

Meanwhile, in the above-described embodiment, the frequency range is controlled from 100 kHz to 10 kHz when measuring EIS of a coin cell assembled without using any electrode active material.

Specifically, when measuring EIS of a coin cell assembled without using the above electrode active material, a high frequency in the range of 100 kHz to 10 kHz must be applied so that resistance can be measured with high accuracy without being affected by diffusion of the electrolyte.

Specifically, a higher frequency can be applied to obtain a more accurate resistance value, but when it exceeds 100 kHz, there is a point where noise becomes significantly prominent. On the other hand, when it is less than 10 kHz, the influence of electrolyte diffusion is received, and the resistance due to electrolyte diffusion within the membrane cannot be ignored from the measured value.

However, at high frequencies of 100 kHz to 10 kHz, the signal change is too fast, so the measurable current is small. Depending on the performance of the potentiostat, it is necessary to use an electrolyte with very high conductivity to increase this current to a measurable level.

3) Composition of aqueous electrolyte and concentration of solutes

In other words, the accuracy of the measurement results according to the above implementation example may be due to the conductivity of the electrolyte.

Specifically, the separator being the measurement target is an insulator having a high resistance compared to the electrolyte impregnated therein. However, according to the law of resistance addition, if the separator being the measurement target is the same but the type of electrolyte impregnated therein is different, the difference in the measured resistance value is due to the difference in the electrolyte, and can be considered unrelated to the resistance of the separator itself being the measurement target.

In fact, in the experimental examples described below, the resistance values were measured by using the same separator as the measurement target but using different types of electrolytes. Specifically, in the comparative examples, an electrolyte with significantly lower conductivity (approximately 45 mS/cm) was used, and in the examples, an electrolyte with significantly higher conductivity (approximately 162.5 mS/cm) was used compared to the comparative examples.

The resistance value measured here can be determined by the electrolyte impregnated in the separator which is the measurement target and the movement path of the electrolyte within the separator which is the measurement target. In this regard, when using an electrolyte having a high conductivity, specifically, when using an electrolyte having a conductivity of 100 to 180 mS/cm, for example, 140 to 180 mS/cm at 20 to 30° C., it was possible to measure the resistance value of the separator which is the measurement target with higher accuracy.

More specifically, in the examples, the accuracy of the measurement results was improved by using an aqueous electrolyte containing water and lithium nitrate. Since the aqueous electrolyte uses water as a solvent, it is easy to use even in an experimental environment that does not use an organic solvent.

In particular, lithium nitrate, a solute of the above-mentioned aqueous electrolyte, has excellent solubility in water (known to be 52.2 g/100 mL at 20°C and 90 g/100 Ml at 28°C) and is a neutral solute with excellent conductivity, making it suitable as an electrolyte for EIS measurements. As mentioned above, the conductivity of a 5 M lithium nitrate aqueous solution at 25°C is measured to be 162.5 mS/cm.

The higher the molar concentration of the solute, such as lithium nitrate, in the above-mentioned aqueous electrolyte, the more advantageous it may be for improving the conductivity, but if it is too high, measurement errors may occur due to precipitation of the solute, the conductivity of the electrolyte may decrease, and the cost of manufacturing the electrolyte may increase. Accordingly, the molar concentration is preferably 3 M or more to 8 M or less, specifically 4 M or more to 7 M or less, for example 5 M or more to 6 M or less. Can be controlled.

The conductivity of the aqueous electrolyte can be controlled by controlling the molar concentration of the above solute, and can be controlled in the range of 140 to 180 mS/cm, specifically 150 to 140 to 170 mS/cm, and more specifically 145 to 165 mS/cm at 20 to 30°C.

The above lithium nitrate is only an example, and in some cases, in addition to the lithium nitrate, a neutral solute with excellent conductivity can be added as a solute of the aqueous electrolyte, for example, commercially available NaCl, HCl, LNO, LSO, LiOH, KCl, Na ₂ CO ₃ , etc., or a mixture of two or more of these can be added. However, strongly basic substances such as potassium hydroxide (KOH), strongly acidic substances such as hydrochloric acid (HCI), nitric acid (HNO ₃ ), etc., although they have higher conductivity than the lithium nitrate, their addition as solutes of the aqueous electrolyte is avoided because they cause excessively strong metal corrosion signals.

For example, the aqueous electrolyte used in the above-described embodiment includes water (H ₂ O) as a solvent, and NaNO ₃ , NaCl, HCl, LNO, LSO, LiOH, KCl, Na ₂ CO ₃ , or a mixture of two or more thereof as a solute, and the molar concentrate of the solute can be 1 M or more and 8 M or less. Specifically, the lower limit of the molar concentration of the solute can be 1 M or more, 1.5 M or more, 1.6 M or more, 1.7 M or more, 1.8 M or more, 1.9 M or more, or 2 M, and the upper limit of the molar concentration of the solute can be 8 M or less, 7 M or less, 6 M or less, or 5 M or less.

However, even when the solute includes NaNO ₃ , NaCl, HCl, LNO, LSO, LiOH, KCl, Na ₂ CO ₃ , or a mixture of two or more thereof, the case where the conductivity is reduced by the additive is avoided. For example, in Manufacturing Example 2 described below, NaNO ₃ was used as the solute, but the conductivity was reduced by the added urea, and the conductivity at 20 to 30° C. was confirmed to be only 45 mS/cm. In this way, the aqueous electrolyte of the above embodiment should first be confirmed whether the conductivity at 20 to 30° C. is 100 to 180 mS/cm, and even when the exemplified solute is used, if the conductivity is reduced by the additive, etc. and satisfies the above range, the aqueous electrolyte of the above embodiment is unsuitable.

Meanwhile, although not particularly limited, for the aqueous electrolyte of the above-mentioned embodiment, either a wetting agent and a surfactant, or both, may be added. Whether or not these substances are added may be determined depending on the characteristics of the membrane to be measured.

Specifically, compared to separators manufactured for aqueous electrolytes, separators commonly used for lithium ion batteries have strong hydrophobicity, which results in less wetting of the electrolyte in the separator, which can cause errors in resistance measurements.

In particular, among the latter membranes, in the case of membranes having low porosity or tortuosity characteristics, a considerably long aging time is required so that the electrolyte can be sufficiently impregnated into the membrane in order to reduce measurement errors. In order to reduce this aging time or omit the aging process itself, either one of a wetting agent and a surfactant, or both, may be added to the aqueous electrolyte of the above embodiment.

Of course, the above substances can be added when measuring the resistance of not only a separator for a lithium ion battery but also a separator manufactured for an aqueous electrolyte, and in this case, the impregnation rate of the aqueous electrolyte for the separator to be measured increases, which can contribute to further improving the accuracy of the measurement results.

Examples of the wetting agent include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, polyethylene glycol, or Air Product's Surfynol and Dynol series, and examples of the surfactant include nonionic surfactants, anionic, cationic, or amphoteric surfactants, and more specific types of materials may be selected within a range known in the art.

4) Resistance calculation method that pursues speed and convenience in a non-standardized system where resistance deviation exists.

Meanwhile, when measuring EIS of a coin cell assembled without using any of the above electrode active materials, the frequency range is controlled to 100 kHz to 10 kHz, and the accuracy of the measurement results is improved by using an aqueous electrolyte containing water and lithium nitrate. There may be some inevitable variation in resistance.

Specifically, resistance also exists in EIS measurement equipment of coin cells, which causes deviation in measurement results. These resistances are not a problem when measuring the large resistance of the coin cell itself, but can be a problem when measuring the resistance of the separator, which is very small compared to the resistance of the coin cell itself.

In order to pursue speed and convenience in the non-standardized system, the above series of steps are performed for each of the measurement target, 1 separator; and the measurement target, a laminate of n separators; to measure resistance, and the average resistance value per measurement target, 1 separator, can be measured.

For example, a single separator, a laminate comprising two separators, and a laminate comprising three separators are prepared, and each of them is used as a measurement target, and the resistance value can be obtained by the method of the above-described embodiment. At this time, the measured resistance value can increase as the number of separators increases. Therefore, by dividing the increase in the measured resistance value by the increase in the number of separators, which are the measurement targets, the average resistance value per separator, which is the measurement target, can be obtained.

In particular, the error rate can be further reduced by obtaining a linear plot of the Nyquist plot for each number of membranes, taking the x-axis intercept value, and then calculating the average resistance per membrane.

More specifically, for each number of separators, 2032 coin cells are manufactured using the same electrolyte, and then impedance analysis is performed on each coin cell at the same frequency within the range of 100 kHz to 10 kHz described above to obtain a polar coordinate plot (Nyquist plot) and then each x-axis intercept value can be obtained. At this time, as the number of separators increases, the x-axis intercept value, i.e., the measured resistance value, can increase.

The error rate can be further reduced by taking the x-axis intercept value as the resistance value for each number of membranes and then calculating the average resistance per membrane.

5) Other features of the above implementation example

Meanwhile, from the measurement results according to the above implementation example, it may also be possible to predict the membrane resistance when using a different electrolyte.

As mentioned above, the separator itself, which is the measurement target, is an insulator, but the concept of the resistance of the separator is that when an electric field passes through the electrolyte in the separator while the separator is impregnated with the electrolyte, resistance may be applied. Accordingly, the measured resistance of the separator may vary depending on the type of electrolyte impregnated in the separator, which is the measurement target.

Specifically, by substituting the measured membrane resistance value using the aqueous electrolyte, the conductivity of the aqueous electrolyte, and the cross-sectional area of the positive or negative electrode current collector into Equation 1 below, the expected membrane resistance value when a different electrolyte is used instead of the aqueous electrolyte can be measured, and the error range can be within ±5%, ±4%, ±3%, for example, ±2%:

[Formula 1] (r_separator)={(R_xM Electrolyte)/(k_electrolyte)}*(k_xM Electrolyte)*(area)

In the above equation 1,

r_separator is the product of the expected membrane resistance value and the cross-sectional area of the separator when a different electrolyte is used instead of the aqueous electrolyte, but the same membrane as the one measured using the aqueous electrolyte is used (Ohm*cm ² ); k_electrolyte is the conductivity of the different electrolyte;

R_xM Electrolyte is the membrane resistance value measured using the above aqueous electrolyte;

k_xM Electrolyte is the conductivity of the aqueous electrolyte; x is the molar concentration of the aqueous electrolyte;

The area is the cross-sectional area of the positive or negative electrode collector and may be equal to the cross-sectional area of the separator.

Specifically, the above equation 1 is an equation for calculating the product (Ohm*m ² ) of the expected resistance value and the area of the separator when a different electrolyte is impregnated in the separator.

By dividing the resistance value of the separator measured by the method of the above embodiment by the conductivity of the aqueous electrolyte itself of the above embodiment used for its measurement, and then multiplying it by the conductivity of the heterogeneous electrolyte and the area of the electrode current collector in the coin cell (i.e., the area through which the electric field passes), the product (Ohm*m ² ) of the expected resistance value and the area of the separator when the heterogeneous electrolyte is impregnated in the separator can be obtained.

Here, the heterogeneous electrolyte may be an aqueous electrolyte or a non-aqueous electrolyte. In the case of a non-aqueous electrolyte, it may be a lithium salt dissolved in an organic solvent known in the art.

Meanwhile, the positive electrode collector used in the resistance measurement of the above-described embodiment is not particularly limited as long as it has high conductivity and does not cause chemical change during EIS measurement of an assembled coin cell without using any electrode active material at all, and for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The current collector can also form fine unevenness on its surface to increase the adhesive strength of the positive electrode active material, and can be in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

The above negative current collector is not particularly limited as long as it is conductive and does not cause chemical change during EIS measurement of an assembled coin cell without using any electrode active material at all, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the positive current collector, the surface may be formed with fine unevenness to strengthen the bonding strength of the negative active material, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

The thickness of each of the above electrode current collectors can be appropriately selected within the range of 3 to 500 ㎛.

The step of wetting the separator with the aqueous electrolyte including water and lithium nitrate; and the step of positioning the separator impregnated with the aqueous electrolyte between the negative electrode current collector and the positive electrode current collector, and then assembling it into a 2032 type coin cell; can use an electrolyte injection method and a 2032 type coin cell assembling method generally known in the art, and therefore a detailed description thereof will be omitted.

According to the above-mentioned embodiment, by using an aqueous electrolyte having a composition with excellent conductivity without using an electrode active material and using an EIS method that applies a high range of frequencies, the overall cost is reduced and the measurement time is shortened, while the resistance of the separator can be measured with high reliability and accuracy.

Figure 1 shows the EIS resistance of Examples 1 to 3 measured according to Experimental Example 1 described below, and represented as a polar coordinate diagram (Nyquist plot).
Figure 2 shows the EIS resistance of Comparative Examples 1 to 3 measured according to Experimental Example 2 described below, and represented in a polar coordinate diagram (Nyquist plot).
Figure 3 shows the EIS resistances of Comparative Examples 4 to 8 and Example 4 measured according to Experimental Example 3 described below, and represented as a polar coordinate graph (Nyquist plot).
Figure 4 shows the EIS resistance of Comparative Examples 9 to 13 measured according to Experimental Example 4 described below, and represented as a polar coordinate graph (Nyquist plot).

The following specific examples of the invention will explain the operation and effects of the invention in more detail. However, these are presented as examples of the invention and the scope of the invention's rights is not limited in any way by these.

Manufacturing Example 1: Manufacturing of an aqueous electrolyte (a 5 M lithium nitrate solution) having a conductivity of 162.5 mS/cm at 25°C

A 5M lithium nitrate aqueous solution was prepared using distilled water ( _H2O ) as a solvent and lithium nitrate ( _LiNO3 ) as a solute, and this was used as the aqueous electrolyte of Manufacturing Example 1. The conductivity of the aqueous electrolyte of Manufacturing Example 1 was measured to be 162.5 mS/cm at 25°C.

Example 1: Manufacturing and resistance measurement of a coin cell using the aqueous electrolyte and one separator of Manufacturing Example 1

Two pieces of SUS stainless steel (Steel Use Stainless) of JIS G 4303 standard were cut into circles (thickness: 10 ㎛) with a cross-sectional area of 2.01 cm ² and used as current collectors.

The separator to be measured was placed between the two SUS current collectors and then assembled into a 2032 type coin cell according to a conventional method known in the art.

Here, the separator to be measured is a mixed material of polypropylene and polyethylene, and its cross-sectional area was cut to 2.01 cm ² , the same as that of the SUS current collector.

Thereafter, the aqueous electrolyte of Manufacturing Example 1 was poured into the coin cell, and the coin cell of Example 1 was completed.

An electrochemical impedance spectroscopy (Electrochemical impedance spectroscopy, device name: Bio-logic VMP3) was connected to the coin cell of the above Example 1, and an experiment was conducted by applying an AC signal of 10 mV in the frequency range of 100 kHz - 10 kHz using the software program ZPlot by EC-lab.

Example 2: Manufacturing and resistance measurement of coin cells using the aqueous electrolyte and two separators of Manufacturing Example 1

In Example 2, two separators identical to those in Example 1 were laminated in the thickness direction, and the resistance of the laminate was measured.

A stack of the above two separators was applied instead of the separator of Example 1, and the rest of the coin cells were manufactured according to the method of Example 1, and the resistance was measured according to the EIS method.

Example 3: Manufacturing and resistance measurement of coin cells using the aqueous electrolyte and three separators of Manufacturing Example 1

In Example 3, three separators identical to those in Example 1 were laminated in the thickness direction, and the resistance of the laminate was measured.

A stack of three of the above separators was applied instead of the separator of Example 1, and the rest were manufactured into coin cells according to the method of Example 1, and the resistance was measured according to the EIS method.

Experimental Example 1: Resistance measurement results of Examples 1 to 3

According to the EIS method, the polar coordinate diagrams (Nyquist plots) of each of Examples 1 to 3 were obtained and are shown in Fig. 1.

From each polar coordinate line (Nyquist plot) of Fig. 1, by taking the x-axis intercept value, the resistance value can be obtained for each number of separators impregnated with the electrolyte of Manufacturing Example 1 having a conductivity of 162.5 mS/cm at 25°C.

The resistance values of the separators used in the above examples 1 to 3 can be obtained. That is, the resistance values of each of the one separator of the above example 1, the two separators of the above example 2, and the three separators of the above example 3 can be obtained.

By taking the x-axis intercept value as the resistance value for each number of membranes and calculating the average resistance per membrane, it can be seen that the average resistance of one membrane impregnated with the electrolyte of Manufacturing Example 1, which has a conductivity of 162.5 mS/cm at 25°C, is 25 mOhm.

Manufacturing Example 2: Manufacturing of an aqueous electrolyte (a 5 M lithium nitrate solution with urea added) having a conductivity of 45 mS/cm at 25°C

A 5M lithium nitrate aqueous solution was prepared using distilled water ( _H2O ) as a solvent and lithium nitrate ( _LiNO3 ) as a solute, and urea was added to obtain an electrolyte of Manufacturing Example 2 having lower conductivity than that of Manufacturing Example 1.

The electrolyte conductivity of Manufacturing Example 2 was measured to be 45 mS/cm at 25 ℃.

Comparative Example 1: Manufacturing and resistance measurement of a coin cell using the electrolyte and one separator of Manufacturing Example 2

In Comparative Example 1, the electrolyte and one separator of Manufacturing Example 2 were applied and resistance was measured.

Using the same separator as in Example 1, the electrolyte of Manufacturing Example 2 was used as the electrolyte, and a coin cell was manufactured according to the method of Example 1 for the remainder, and the resistance was measured.

Comparative Example 2: Manufacturing and resistance measurement of a coin cell using the electrolyte and two separators of Manufacturing Example 2

In Comparative Example 2, the electrolyte and two separators of Manufacturing Example 2 were applied and the resistance was measured.

Two separators identical to those in Example 1 were laminated, and the laminate was applied as a separator. The electrolyte of Manufacturing Example 2 was used as an electrolyte, and a coin cell was manufactured according to the method of Example 1 for the remainder, and the resistance was measured.

Comparative Example 3: Manufacturing and resistance measurement of coin cells using the electrolyte and three separators of Manufacturing Example 2

In Comparative Example 3, the electrolyte and three separators of Manufacturing Example 2 were applied and the resistance was measured.

Three separators identical to those in Example 1 were laminated, and the laminated body was applied as a separator. The electrolyte of Manufacturing Example 3 was used as an electrolyte, and a coin cell was manufactured according to the method of Example 1 for the remainder, and the resistance was measured.

Experimental Example 2: Resistance inference results of Comparative Examples 1 to 3

As mentioned above, the separator itself, which is the measurement target, is an insulator, but the concept of the resistance of the separator is that when an electric field passes through the electrolyte in the separator while the separator is impregnated with the electrolyte, resistance may be applied. Accordingly, the measured resistance of the separator may vary depending on the type of electrolyte impregnated in the separator, which is the measurement target.

In the above Experimental Example 1, when the electrolyte of the above Manufacturing Example 1 having a conductivity of 162.5 mS/cm at 25°C was impregnated, the average resistance of one separator was measured to be 25 mOhm.

In the case of Comparative Examples 1 to 3 in which the electrolyte of Manufacturing Example 2 is impregnated into the same separator, the resistance of one separator can be inferred according to the following Equation 1:

[Formula 1] r_separator = {(R_5M LiNO ₃ /(k_electrolyte)}*(k_5M LiNO ₃ )*(area)

Specifically, in the above equation 1,

k_electrolyte is the conductivity of the electrolyte of the above-mentioned manufacturing example 2 at 25 ℃, which is 45 mS/cm,

R_5M LiNO ₃ is the resistance value of the membrane (average per membrane) in the above experimental example 1, which is 25 mOhm,

The above k_5M LiNO ₃ is the conductivity of the aqueous electrolyte of the above-mentioned manufacturing example 1 at 25 ℃, which is 162.5 mS/cm.

Since the area is 2.01 cm ² , which is the cross-sectional area of the electrode collector of the above-mentioned manufacturing example 1,

If we substitute this into Equation 1 above, the right side is = {25 mOhm/ 45 mS/cm}*162.5mS/cm* 2.01 cm ² = approximately 181.5.

Meanwhile, on the left side, r_electrode is the product of the expected membrane resistance value and area (Ohm* ^m2 ) when the electrolyte of Manufacturing Example 2 is used, and since the cross-sectional area of the separator applied in Manufacturing Example 2 is the same as the cross-sectional area of the electrode current collector of Manufacturing Example 1, this can be substituted:

(Expected membrane resistance value when using the electrolyte of the above manufacturing example 2)*2.01 cm ² = approximately 181.5 mOhm*cm ²

Therefore, the expected membrane resistance value when using the electrolyte of Manufacturing Example 2 is 90.27 mOhm.

To verify this expected value, a polar coordinate plot (Nyquist plot) was obtained for Comparative Examples 1 to 3 in the same manner as Experimental Example 1, and is shown in Figure 2.

If Fig. 2 is interpreted in the same manner as Experimental Example 1, it can be seen that the average resistance of one separator is 92 mOhm when the electrolyte of Manufacturing Example 2 having a conductivity of 45 mS/cm at 25°C is impregnated.

Such actual measurement values are within the error range (±2%) of the expected values according to Equation 1 above, proving the reliability of Equation 1.

Meanwhile, Comparative Examples 1 to 3 had resistance values measured to be greater even though they used the same membrane as Examples 1 to 3.

As mentioned above, the separator, which is the subject of measurement, is an insulator with a high resistance compared to the electrolyte impregnated in it. However, according to the law of resistance addition, if the separator, which is the subject of measurement, is the same but the type of electrolyte impregnated in it is different, the difference in the measured resistance value is due to the difference in the electrolyte, and can be considered unrelated to the resistance of the separator itself, which is the subject of measurement.

The resistance value measured here can be determined by the electrolyte impregnated in the separator, which is the measurement target, and the movement path of the electrolyte within the separator, which is the measurement target. In this regard, the higher the conductivity of the electrolyte used, the more accurately the resistance value of the separator, which is the measurement target, can be measured.

Manufacturing Example 3: Manufacturing of an aqueous electrolyte (aqueous lithium nitrate solution having a concentration of 0.1 to 0.5 M) having a conductivity of 8 to 37 mS/cm at 25°C

Electrolyte samples of Manufacturing Example 3, which had significantly lower conductivity than Manufacturing Examples 1 and 2, were obtained by using distilled water (H ₂ O) as a solvent and lithium nitrate (LiNO ₃ ) as a solute at molar concentrations of 0.1 M, 0.2 M, 0.3 M, 0.4 M, and 0.5 M. The measured conductivity values were in the range of 8 to 37 mS/cm, and the specific measured values are shown in Table 1 below.

Comparative Examples 4 to 8: Manufacturing and resistance measurement of coin cells using the electrolyte and one separator of Manufacturing Example 3

In Comparative Examples 4 to 8, each electrolyte sample and one separator of Manufacturing Example 3 were applied and resistance was measured.

One separator identical to that in Comparative Example 1 was used, each electrolyte of Manufacturing Example 3 was used as the electrolyte, and the remainder was manufactured into a coin cell according to the method of Comparative Example 1, and the resistance was measured.

Manufacturing Example 4: Manufacturing of an aqueous electrolyte (2 M lithium nitrate aqueous solution) having a conductivity of 107.4 mS/cm at 25°C

Using distilled water ( _H2O ) as a solvent and lithium nitrate ( _LiNO3 ) as a solute at a molar concentration of 2 M, an electrolyte sample having a conductivity similar to that of Manufacturing Example 1 was obtained, and the specific conductivity measurement values are shown in Table 1 below.

Example 4: Manufacturing and resistance measurement of a coin cell using the electrolyte and one separator of Manufacturing Example 4

In Example 4, the electrolyte sample and one separator of Manufacturing Example 4 were applied, and the resistance was measured.

Using the same separator as in Comparative Example 1, the electrolyte of Manufacturing Example 4 was used as the electrolyte, and a coin cell was manufactured according to the method of Comparative Example 1 for the remainder, and the resistance was measured.

Experimental Example 3: Resistance measurement results of Comparative Examples 4 to 8 and Example 4

The conductivity of each electrolyte used in Comparative Examples 4 to 8 and Example 4 and the reciprocal of the conductivity of each electrolyte are recorded in Table 1 below. In addition, using each electrolyte, the resistance was measured according to the EIS method to obtain a polar coordinate plot (Nyquist plot), and the resistance value of one separator was recorded in Table 1 below from the x-axis intercept value.

Furthermore, the reciprocal of each electrolyte conductivity recorded in Table 1 above was used as the x-axis, and the y-axis was used as the resistance value of one separator measured by the EIS, to obtain a trend of a linear plot, and the results were shown in Fig. 3.

Molar concentration of lithium nitrate in electrolyte (M) Conductivity of electrolyte
(mS/cm, @ 25 ℃) 1/(conductivity of electrolyte)
(cm/mS, @ 25 ℃) Resistance value of the separator measured by EIS
(Ohms) Comparative Example 4 0.1 8.531 0.1172 0.544 Comparative Example 5 0.2 16.52 0.0605 0.35 Comparative Example 6 0.3 23.45 0.0426 0.233 Comparative Example 7 0.4 30.48 0.0328 0.182 Comparative Example 8 0.5 36.79 0.0272 0.157 Example 4 2 107.4 0.0093 0.077

(In Table 1 above, “1/(conductivity of electrolyte)” is a value rounded to the fifth decimal place.)

According to Table 1 and Figure 3 above, the electrolyte solute is lithium nitrate, the same as in Example 1, but as its concentration decreases, the conductivity decreases, and the resistance value of one separator measured by EIS is confirmed to increase.

Through this, it can be seen that the resistance measurement value of the separator according to the above-mentioned embodiment is in a linear relationship with the reciprocal conductivity value of the electrolyte, and when the solute of the electrolyte is the same, the resistance measurement value of the separator increases as its concentration decreases.

In particular, in Comparative Examples 4 to 8 where the molar concentration of lithium nitrate in the electrolyte is less than 1 M, the measured membrane resistance value exceeds 0.150 Ohms (=150 mOhms). In contrast, in Example 4 where the molar concentration of lithium nitrate in the electrolyte is 1 M or more, specifically 2 M, the measured membrane resistance value decreased to 0.077 Ohms (=77 mOhms).

When the electrolyte conductivity (162.5 mS/cm) of Example 1 is substituted into the trend line of Fig. 3, a resistance of 27.02 mOhms is confirmed, which is almost the same as the actual measured value.

Manufacturing Example 5: Manufacturing of an aqueous electrolyte (aqueous solution containing various solutes at 0.1 M concentration) having a conductivity of 8 to 18 mS/cm at 25°C

Electrolyte samples of Manufacturing Example 5, which had significantly lower conductivity than Manufacturing Examples 1 and 2, were obtained by using distilled water (H ₂ O) as a solvent and lithium nitrate (LiNO ₃ ), lithium hydroxide (LiOH), lithium sulfate (Li ₂ SO ₄ ), lithium chloride (LiCl), and calcium nitrate (Ca(NO ₃ ) ₂ ) as solutes at a molar concentration of 0.1 M each. The measured conductivity values are in the range of 8 to 18 mS/cm, and the specific measured values are shown in Table 2 below.

Comparative Examples 9 to 13: Manufacturing and resistance measurement of coin cells using the electrolyte and one separator of Manufacturing Example 5

In Comparative Examples 9 to 13, each electrolyte sample and one separator of Manufacturing Example 5 were applied and resistance was measured.

One separator identical to that in Comparative Example 1 was used, each electrolyte of Manufacturing Example 5 was used as the electrolyte, and the remainder was manufactured into a coin cell according to the method of Comparative Example 1, and the resistance was measured.

Experimental Example 4: Resistance measurement results of comparative examples 9 to 13

The conductivity of each electrolyte used in Comparative Examples 9 to 13 and the reciprocal of the conductivity of each electrolyte are recorded in Table 2 below. In addition, using each electrolyte, the resistance was measured according to the EIS method to obtain a polar coordinate plot (Nyquist plot), and the resistance value of one separator was recorded in Table 2 below from the x-axis intercept value.

Furthermore, the reciprocal of each electrolyte conductivity recorded in Table 2 above was used as the x-axis, and the y-axis was used as the resistance value of one separator measured by the EIS, to obtain a trend of a linear plot, and the results were shown in Fig. 4.

Type of solute Conductivity of electrolyte
(mS/cm, @ 25 ℃) 1/(conductivity of electrolyte)
(cm/mS, @ 25 ℃) Resistance value of the separator measured by EIS
(Ohms) Comparative Example 9 LiNO ₃ 8.531 0.1172 0.544 Comparative Example 10 LiOH 25.14 0.0398 0.253 Comparative Example 11 Li ₂ SO ₄ 14.57 0.0686 0.368 Comparative Example 12 LiCl 10.31 0.0970 0.511 Comparative Example 13 Ca( _NO3 ) ₂ 17.6 0.0568 0.323

(In Table 2 above, “1/(conductivity of electrolyte)” is a value rounded to the fifth decimal place.)

In the above Table 2 and Fig. 4, the concentration of the solute in the electrolyte is the same as 0.1 M, but the conductivity of the electrolyte varies depending on the type of the solute, and it is confirmed that the resistance value of one separator measured by EIS increases in proportion to the reciprocal value of the conductivity of the electrolyte.

As examined in the above Experimental Example 3, it can be seen in the above Experimental Example 4 that the resistance measurement value of the separator according to the above embodiment is linearly related to the reciprocal conductivity value of the electrolyte. When the electrolyte conductivity (162.5 mS/cm) of the above Example 1 is substituted into the trend line of Fig. 4, a resistance of 24.28 mOhms is confirmed, which is almost the same as the actual measured value.

Claims (12)

A step of wetting an aqueous electrolyte having a conductivity of 100 to 180 mS/cm at 20 to 30°C in a separator for an electrochemical device to be measured;
A step of assembling a 2032 type coin cell by positioning the separator impregnated with the above aqueous electrolyte between the negative electrode current collector and the positive electrode current collector; and
A step of connecting an impedance analyzer to the coin cell and applying a frequency in the range of 100 kHz to 10 kHz to obtain a polar coordinate plot (Nyquist plot); and
A step of measuring the resistance of the membrane from the x-axis intercept value of the obtained Nyquist plot; including;
Method for measuring resistance of a separator for electrochemical devices.
In the first paragraph,
The above negative electrode current collector and the above positive electrode current collector are each bare and have no electrode active material coated on their surfaces.
Method for measuring resistance of a separator for electrochemical devices.
In the first paragraph,
The above negative electrode collector,
Containing copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or a combination thereof;
Method for measuring resistance of a separator for electrochemical devices.
In the first paragraph,
The above positive electrode collector,
Containing aluminum, stainless steel, nickel, titanium, calcined carbon, or a combination thereof;
Method for measuring resistance of a separator for electrochemical devices.
In the first paragraph,
The above aqueous electrolyte is,
The conductivity at 20 to 30 ℃ is 140 to 180 mS/cm,
Method for measuring resistance of a separator for electrochemical devices.
In the first paragraph,
The above aqueous electrolyte is,
Containing water (H ₂ O) as a solvent;
A solute comprising NaNO ₃ , NaCl, HCl, LNO, LSO, LiOH, KCl, Na ₂ CO ₃ , or a mixture of two or more of these;
Method for measuring resistance of a separator for electrochemical devices.
In Article 6,
The above aqueous electrolyte is,
The molar concentration of the above solute is 1 M or more and 8 M or less,
Method for measuring resistance of a separator for electrochemical devices.
In the first paragraph,
The above aqueous electrolyte is,
Containing a wetting agent, a surfactant, or a mixture thereof,
Method for measuring resistance of a separator for electrochemical devices.
In the first paragraph,
The voltage when applying a frequency in the range of 100 kHz to 10 kHz is 10 mV.
Method for measuring resistance of a separator for electrochemical devices.
In the first paragraph,
The resistance is measured by performing all of the above-described series of steps on each of the following: one separator as the measurement target; a stack of two separators as the measurement target; and a stack of three separators as the measurement target;
The average resistance value per separator, which is the measurement target, is measured.
Method for measuring resistance of a separator for electrochemical devices.
In the first paragraph,
By substituting the measured membrane resistance value using the above aqueous electrolyte, the conductivity of the above aqueous electrolyte, and the cross-sectional area of the positive or negative electrode current collector into the following equation 1,
This is to measure the expected membrane resistance value when a heterogeneous electrolyte is used instead of the above-mentioned aqueous electrolyte.
Method for measuring resistance of separator for electrochemical device:
[Equation 1] (r_separator)={(R_xM Electrolyte)/(k_electrolyte)}*(k_xM Electrolyte)*(area)
In the above equation 1,
r_separator is the product of the expected membrane resistance value and the cross-sectional area of the separator when a different electrolyte is used instead of the above aqueous electrolyte, except that the same membrane as the one measured using the above aqueous electrolyte is used (Ohm*cm ² ); k_electrolyte is the conductivity of the different electrolyte;
R_xM electrolyte is the membrane resistance value measured using the above aqueous electrolyte;
k_xM electrolyte is the conductivity of the aqueous electrolyte; x is the molar concentration of the aqueous electrolyte;
The area is the cross-sectional area of the positive or negative electrode collector and may be equal to the cross-sectional area of the separator.
In the first paragraph,
The separator for the electrochemical device, which is the subject of the above measurement, is
A separator for an electrochemical device selected from the group consisting of a lithium secondary battery, a super capacitor, a lithium-sulfur battery, a sodium ion battery, a lithium-air battery, a zinc-air battery, an aluminum-air battery, an aluminum ion battery, and a magnesium ion battery,
Method for measuring resistance of a separator for electrochemical devices.