KR20210012269A - Method for measuring electrochemical device separator resistance - Google Patents

Abstract

The present invention relates to a method for measuring resistance of a separator for an electrochemical device. More specifically, in one embodiment of the present invention, provided is the method for measuring resistance of a separator for an electrochemical device, which has high reliability while spending a small amount of time and money.

Description

Method for measuring resistance of separator for electrochemical device {METHOD FOR MEASURING ELECTROCHEMICAL DEVICE SEPARATOR RESISTANCE}

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

Since the resistance of the separator is one of the factors that lowers the speed and output of the electrochemical device, its measurement has a very important meaning.

In general, after applying a separator to measure resistance to a cell for measuring resistance, a Nyquist plot for the coin cell is obtained by using EIS (Electrochemical Impedance Spectroscopy). , And how to interpret the plot is known.

However, there are two main problems with this method. First of all, a cell for measuring resistance must be manufactured using a positive electrode active material and/or a negative electrode active material each time, and the resistance must be measured after an aging process, which wastes cost and time.

In addition, variations in measurement results may occur depending on the type and distribution of electrode active materials, and when some electrode active materials are dissolved in the electrolyte and precipitated in the separator, it may also cause resistance, making it difficult to obtain the resistance of the separator itself. Lose.

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

Advantages and features of the embodiments of the present invention, and a method of achieving them will become apparent with reference to the embodiments described below in detail. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in a variety of different forms. It is provided to fully inform the knowledgeable person of the scope of the invention, and the invention is only defined by the scope of the claims.

Unless otherwise defined, technical terms and scientific terms used in the present invention have the meanings commonly understood by those of ordinary skill in the art to which this invention belongs. In addition, repeated descriptions of the same technical configuration and operation as in 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 that it is “directly connected”, but also the case that it is “electrically connected” with another element interposed therebetween. do.

Throughout this specification, when a member is positioned “on” another member, this includes not only the case where a member is in contact with another member, but also the case where another member exists between the two members.

In the entire specification of the present application, when a certain part “includes” a certain constituent element, it means that other constituent elements may be further included rather than excluding other constituent elements unless otherwise indicated.

The terms "about", "substantially", etc. of the degree used throughout the present specification are used at or close to the numerical value when manufacturing and material tolerances specific to the stated meaning are presented. To assist, accurate or absolute figures are used to prevent unfair use of the stated disclosure by unscrupulous infringers.

As used throughout the specification of the present application, the term "step (to)" or "step of" does not mean "step for".

Throughout the present specification, the term “combination(s) thereof” included in the expression of the Makushi format refers to one or more mixtures or combinations selected from the group consisting of components described in the expression of the Makushi format, It means to include at least one selected from the group consisting of the above components.

In the entire specification of the present application, the description of “A and/or B” means “A or B, or A and B”.

Method of measuring resistance of separator for electrochemical device

In general, the separator itself is a non-conductor, but the concept of resistance of the separator takes resistance when an electric field passes through the electrolyte in the separator while the electrolyte is impregnated in the separator, and the resistance applied 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 "resistance applied when an electric field passes through the electrolyte in the separator in a state in which the electrolyte is impregnated in the separator".

In one embodiment of the present invention, the step of impregnating (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; Placing the separator impregnated with the aqueous electrolyte between the negative electrode current collector and the positive electrode current collector, and assembling a 2032 type coin cell; And connecting an impedance analyzer to the coin cell and applying a frequency ranging from 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 polar coordinate diagram (Nyquist plot).

After measuring the resistance of the separator for the electrochemical device to be measured, the shape of the electrochemical device that is actually applied is not particularly limited. For example, selected from the group including lithium secondary batteries, super capacitors, lithium-sulfur batteries, sodium ion batteries, lithium-air batteries, zinc-air batteries, aluminum-air batteries, aluminum ion batteries, and magnesium ion batteries. Any one separator for an electrochemical device may be measured for resistance by the method of the embodiment.

1) Measurement method without using electrode active material

In the measurement method of the embodiment, as a negative electrode current collector and a positive electrode current collector, each of which is not coated with an electrode active material on the surface, are used, there may be no deviation in the measurement result according to the type of the electrode active material.

In addition, since the electrode active material is not used, the cost of raw materials can be reduced, and resistance can be measured immediately without having to go through the aging process after assembling the coin cell, which shortens the measurement time compared to commonly known methods. I can.

2) Frequency when measuring EIS

Meanwhile, in the above embodiment, the frequency range is controlled to 100 kHz to 10 kHz when measuring the EIS of an assembled coin cell without using an electrode active material at all.

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

Specifically, the higher the frequency is applied, the more accurate resistance value can be obtained. However, if it exceeds 100 kHz, there is an excitation that will cause the noise to stand out. On the other hand, at less than 10 kHz, it is affected by diffusion of the electrolyte, and the resistance due to diffusion of the electrolyte in the separator cannot be ignored from the measured value.

However, at the high frequencies of 100 kHz to 10 kHz, the signal changes too fast, so the size of the measurable current is small, but it is necessary to use an electrolyte having a very high conductivity in order to increase this amount of current to a measurable level according to the performance of the potentiostat. .

3) Composition of aqueous electrolyte and concentration of solute

In other words, the accuracy of the measurement result according to the embodiment may be due to the conductivity of the electrolyte.

Specifically, the separation membrane to be measured is a nonconductor having a higher resistance compared to an electrolyte impregnated therein. However, according to the law of the summation of resistance, if the separation membrane to be measured 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 is irrelevant to the resistance of the membrane itself to be measured. It can be seen as one.

In fact, in the experimental examples to be described later, the same separation membrane as the object to be measured was used, but the resistance value was measured by different types of electrolyte. Specifically, in the comparative examples, an electrolyte having a remarkably low conductivity (about 45 mS/cm) was used, and in the examples, an electrolyte having a significantly higher conductivity (about 162.5 mS/cm) was used compared to the comparative examples. .

The resistance value measured here may be determined by a movement path of an electrolyte impregnated in a separation membrane as a measurement target and an electrolyte in a separation membrane as a measurement target. In this regard, when an electrolyte having a higher conductivity is used, specifically, when an electrolyte having a conductivity of 100 to 180 mS/cm at 20 to 30° C., for example, 140 to 180 mS/cm is used, the resistance value of the separator to be measured is more It could be possible to measure with high accuracy.

More specifically, in the examples, the accuracy of the measurement result was improved by using an aqueous electrolyte containing water and lithium nitrate (Lithium Nitrate). Since the aqueous electrolyte uses water as a solvent, it is easy to use even in an experimental environment where an organic solvent is not used.

In particular, lithium nitrate, the solute of the aqueous electrolyte, has excellent solubility in water (known as 52.2 g/100 mL at 20°C and 90 g/100 Ml at 28°C) , and is a neutral and highly conductive solute. It is suitable for measuring electrolyte. As mentioned above, the conductivity of the lithium nitrate aqueous solution having a concentration of 5 M at 25° C. is about to be measured as 162.5 mS/cm.

The higher the molar concentration of a solute such as lithium nitrate in the aqueous electrolyte is, the more advantageous it is to improve the conductivity, but if it is too high, a measurement error may occur due to precipitation of the solute, and the conductivity of the electrolyte decreases, and the electrolyte is produced. The cost can be high. Thus, 3 M or more to 8 M or less, specifically 4 M or more to 7 M or less, such as 5 M or more to 6 M or less Can be controlled.

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

The lithium nitrate is only an example, and in some cases, in addition to the lithium nitrate, a neutral solute having excellent conductivity may be added as a solute of the aqueous electrolyte, such as NaCl, HCl, LNO, LSO, LiOH, KCl, which are commercially available. , Na ₂ CO ₃ , and the like, or a mixture of two or more of these may be added. However, strong basic substances such as potassium hydroxide (KOH), strongly acidic substances such as hydrochloric acid (HCI), nitric acid (HNO ₃ ), etc., have a higher conductivity than lithium nitrate, but since the metal corrosion signal is too strong, the solute of the aqueous electrolyte Do not add to the above (止揚).

For example, the aqueous electrolyte used in the above embodiment includes water (H ₂ O) as a solvent, and as a solute NaNO ₃ , NaCl, HCl, LNO, LSO, LiOH, KCl, Na ₂ CO ₃ , or among these A mixture of two or more; includes, and the molar concentration of the solute may be 1 M or more to 8 M or less. Specifically, the lower limit of the molar concentration of the solute may 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 is 8 It can be M or less, 7 M or less, 6 M or less, or 5 M or less.

However, even if the solute contains NaNO ₃ , NaCl, HCl, LNO, LSO, LiOH, KCl, Na ₂ CO ₃ , or a mixture of two or more of them, the case where the conductivity is lowered by the additive is avoided. For example, in Preparation Example 2 to be described later, NaNO ₃ was used as a solute, but the conductivity was lowered by urea added thereto, and it was confirmed that the conductivity at 20 to 30° C. was only 45 mS/cm. As such, the aqueous electrolyte of the embodiment should be first checked whether the conductivity at 20 to 30 °C is 100 to 180 mS/cm, and even when the exemplified solute is used, the conductivity is lowered due to additives, etc. and satisfies the above range. It is unsuitable for the aqueous electrolyte of the above embodiment.

Meanwhile, although not particularly limited, any one or both of a wetting agent and a surfactant may be added to the aqueous electrolyte of the embodiment. Whether to add these substances can be determined according to the characteristics of the separation membrane to be measured.

Specifically, compared to a separator manufactured for an aqueous electrolyte, in the case of a separator for lithium ion batteries, which is commonly used, it is highly hydrophobic, so that less electrolyte is impregnated into the separator (wetting), which may cause errors in measuring resistance. have.

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

Of course, the above substances can be added not only when measuring the resistance of a separator manufactured for an aqueous electrolyte as well as a separator for a lithium ion battery, and in this case, the impregnation rate of the aqueous electrolyte for the separator to be measured increases, and the accuracy of the measurement result Can contribute to higher

Examples of the wetting agent include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, polyethylene glycol, or Air Product's Surfynol and Dynol series. In general, the surfactant may include a nonionic surfactant, an anion, a cationic, or an amphoteric surfactant, and a more specific type of material may be selected within a range known in the art.

4) A resistance calculation method that pursues quickness and convenience in a non-standardized system with resistance variations

On the other hand, when measuring the EIS of the coin cell assembled without using the electrode active material at all, the frequency range was controlled to 100 kHz to 10 kHz, and the measurement result was obtained by using an aqueous electrolyte containing water and lithium nitrate. Even if you increase the accuracy of There may be a variation in resistance that inevitably occurs.

Specifically, resistance exists in the coin cell's EIS measurement equipment, etc., and this becomes a factor that causes deviation of the measurement result. These resistances are not a problem in measuring the large resistance of the coin cell itself, but may be problematic in measuring the resistance of a very small separator compared to the resistance of the coin cell itself.

Accordingly, in order to pursue speed and convenience in a non-standardized system, one separation membrane as the measurement object; And it is possible to measure resistance by performing the series of steps for each of the n-layered membranes to be measured, and to measure an average resistance value per one membrane to be measured.

For example, one separator, a laminate in which two separators are stacked, and a laminate in which three separators are stacked are prepared, respectively, and each is used as a measurement object, and a resistance value may be obtained by the method of the embodiment described above. In this case, as the number of separators increases, the measured resistance value may increase. Accordingly, by dividing the increase in the measured resistance value by the increase in the number of separators to be measured, an average resistance value per one separator to be measured can be obtained.

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

More specifically, after each 2032 coin cell was manufactured using the same electrolyte for each number of separators, impedance analysis of each coin cell was performed at the same frequency within the range of 100 kHz to 10 kHz, and a Nyquist plot After finding, each x-axis intercept can be obtained. In this case, as the number of separators increases, an x-axis intercept value, that is, a measured resistance value may increase.

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

5) Other features of the above embodiment

On the other hand, from the measurement result according to the exemplary embodiment, it may be possible to predict the membrane resistance when using another electrolyte.

As mentioned above, the separation membrane itself to be measured is a non-conductor, but the concept of resistance of the separation membrane is that resistance may take place when an electric field passes through the electrolyte in the separation membrane while the electrolyte is impregnated in the separation membrane. Accordingly, depending on the type of electrolyte impregnated in the separation membrane to be measured, the measured resistance of the separation membrane may vary.

Specifically, by substituting the membrane resistance value measured using the aqueous electrolyte, the conductivity of the aqueous electrolyte, and the cross-sectional area of the positive or negative current collector in Equation 1 below, a heterogeneous electrolyte replacing the aqueous electrolyte When using, the expected membrane resistance value can be measured, and the error range may be within ± 5%, ±4%, ±3%, such as within ±2%:

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

In Equation 1 above,

The r_separator uses a separator of the same kind as the separator measured using the aqueous electrolyte, but the product of the expected separator resistance value and the cross-sectional area of the separator when using a heterogeneous electrolyte in place of the aqueous electrolyte ( Ohm*cm ² ); k_electrolyte is the conductivity of the heterogeneous electrolyte;

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

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

An area is a cross-sectional area of the positive electrode or negative electrode current collector, and may be the same as the cross-sectional area of the separator.

Specifically, Equation 1 is an equation for obtaining the product (Ohm*m ² ) of the expected resistance value and the area of the separation membrane when the separation membrane is impregnated with an electrolyte of a heterogeneous (異種).

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

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

On the other hand, the positive electrode current collector used in the resistance measurement of the embodiment is not particularly limited as long as it has high conductivity without causing a chemical change when measuring the EIS of an assembled coin cell without using an electrode active material at all. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, or the like may be used. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes when measuring the EIS of an assembled coin cell without using an electrode active material at all. 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. may be used. In addition, like the positive electrode current collector, it is possible to enhance the bonding strength of the negative electrode active material by forming fine irregularities on the surface thereof, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

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

Impregnating the separation membrane with an aqueous electrolyte including water and lithium nitrate; And placing the separator impregnated with the aqueous electrolyte between the negative electrode current collector and the positive electrode current collector, and then assembling a 2032 type coin cell; is, an electrolyte injection method generally known in the art and a 2032 type coin. Since the cell (coin cell) assembly method can be used, a detailed description thereof will be omitted.

According to the above embodiment, by using the EIS method in which an electrode active material is not used, an aqueous electrolyte having a composition having excellent conductivity is used, and a high frequency range is applied, various costs are reduced and measurement time is shortened, while a high The resistance of the separator can be measured with reliability and accuracy.

1 is a diagram showing a Nyquist plot by measuring the EIS resistance of Examples 1 to 3 according to Experimental Example 1 to be described later.
FIG. 2 is a diagram showing a Nyquist plot by measuring the EIS resistance of Comparative Examples 1 to 3 according to Experimental Example 2 to be described later.
3 is a diagram showing a Nyquist plot by measuring the EIS resistance of Comparative Examples 4 to 8 and Example 4 according to Experimental Example 3 to be described later.
4 is a diagram showing a Nyquist plot by measuring the EIS resistance of Comparative Examples 9 to 13 according to Experimental Example 4 to be described later.

Hereinafter, the action and effect of the invention will be described in more detail through specific examples of the invention. However, this is presented as an example of the invention, and the scope of the invention is not limited to any meaning.

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

Distilled water (H ₂ O) was used as a solvent, and lithium nitrate (LiNO ₃ ) was used as the solute, to prepare a 5 M aqueous lithium nitrate solution, which was used as the aqueous electrolyte of Preparation Example 1. The conductivity of the aqueous electrolyte of Preparation Example 1 at 25 °C was measured to be 162.5 mS/cm.

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

Two pieces of SUS stainless steel of JIS G 4303 standard were cut into a circle (thickness: 10 μm) having a cross-sectional area of 2.01 cm ² , respectively, and used as a current collector.

Between the two SUS current collectors, a separation membrane to be measured was placed, and then assembled into a 2032 type coin cell according to a conventional method known in the art.

Here, the separation membrane to be measured is a mixed material of polypropylene and polyethylene, and the cross-sectional area was cut into 2.01 cm ² and used in the same manner as the SUS current collector.

Thereafter, the aqueous electrolyte of Preparation Example 1 was injected into the coin cell, and the coin cell of Example 1 was completed.

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

Example 2: Preparation and resistance measurement of a coin cell using two aqueous electrolytes and separators of Preparation Example 1

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

The stacked body of the two separators was applied instead of the separator of Example 1, and a coin cell was manufactured according to the method of Example 1 for the rest, and resistance was measured according to the EIS method.

Example 3: Preparation of a coin cell using the aqueous electrolyte and three separators of Preparation Example 1 and measurement of resistance

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

The stacked body of the three separators was applied instead of the separator of Example 1, and a coin cell was manufactured according to the method of Example 1 for the rest, and resistance was measured according to the EIS method.

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

According to the EIS method, each polar coordinate diagram (Nyquist plot) of Examples 1 to 3 was obtained, and is shown in FIG. 1.

When the x-axis intercept value is taken from each of the Nyquist plots of FIG. 1, the resistance value can be obtained for each number of separators impregnated with the electrolyte of Preparation Example 1 having a conductivity of 162.5 mS/cm at 25°C. .

The resistance value of the separator used in Examples 1 to 3 can be obtained. That is, each resistance value according to one separator of Example 1, two separators of Example 2, and three separators of Example 3 may be obtained.

After taking the x-axis intercept value for each number of separators as a resistance value, and calculating the average resistance per separator, the average resistance of one separator impregnated with the electrolyte of Preparation Example 1 having a conductivity of 162.5 mS/cm at 25 °C It can be seen that it is 25 mOhm.

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

Distilled water (H ₂ O) is used as a solvent and lithium nitrate (LiNO ₃ ) is used as a solute to prepare a 5M lithium nitrate aqueous solution, but the conductivity is lower than that of Preparation Example 1 by adding urea 2 An electrolyte was obtained.

The electrolyte conductivity of Preparation Example 2 was measured at 25 °C to 45 mS/cm.

Comparative Example 1: Preparation and resistance measurement of a coin cell to which the electrolyte of Preparation Example 2 and one separator were applied

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

The same separator as in Example 1 was used, and the electrolyte of Preparation Example 2 was used as an electrolyte, and the rest were prepared according to the method of Example 1 to prepare a coin cell, and the resistance was measured.

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

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

The same two separators as in Example 1 were stacked and the laminate was applied as a separator, and the electrolyte of Preparation Example 2 was used as an electrolyte, and the rest were prepared by a coin cell according to the method of Example 1. Measured.

Comparative Example 3: Preparation and resistance measurement of a coin cell to which the electrolyte and three separators of Preparation Example 2 were applied

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

The same three separators as in Example 1 were stacked, and the laminate was applied as a separator, and the electrolyte of Preparation Example 3 was used as an electrolyte, and the rest were prepared by a coin cell according to the method of Example 1, Measured.

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

As mentioned above, the separation membrane itself to be measured is a non-conductor, but the concept of resistance of the separation membrane is that resistance may take place when an electric field passes through the electrolyte in the separation membrane while the electrolyte is impregnated in the separation membrane. Accordingly, depending on the type of electrolyte impregnated in the separation membrane to be measured, the measured resistance of the separation membrane may vary.

In Experimental Example 1, when the electrolyte of Preparation 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 Preparation Example 2 was impregnated in the same separator, the resistance of one separator can be deduced according to Equation 1:

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

Specifically, in Equation 1,

k_electrolyte is the conductivity of the electrolyte in Preparation Example 2 at 25° C., and is 45 mS/cm,

R_5M LiNO ₃ is a membrane (average per one) resistance value in Experimental Example 1, 25 mOhm,

The k_5M LiNO ₃ is the conductivity of the aqueous electrolyte in Preparation Example 1 at 25° C., and is 162.5 mS/cm,

The area is 2.01 cm ^{2 in the} cross-sectional area of the electrode current collector of Preparation Example 1,

Substituting this into Equation 1 above, the right side = {25 mOhm/ 45 mS/cm}*162.5mS/cm* 2.01 cm ² =about 181.5.

On the other hand, r_electrode on the left side is the product (Ohm*m ² ) of the membrane resistance value and the area expected when the electrolyte in Preparation Example 2 is used, and the cross-sectional area of the separator applied in Preparation Example 2 is the electrode collection of Preparation Example 1 above. It is equal to the total cross-sectional area, so you can substitute it:

(Expected membrane resistance value when using the above Preparation Example 2 electrolyte) * 2.01 cm ² = about 181.5 mOhm * cm ²

Therefore, when the electrolyte of Preparation Example 2 is used, the expected separator resistance value is 90.27 mOhm.

In order to verify this expected value, a Nyquist plot was obtained in the same manner as in Experimental Example 1 for Comparative Examples 1 to 3, and is shown in FIG. 2.

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

Such an actual measured value is within the error range (± 2%) of the expected value according to Equation 1 above, and proves the reliability of Equation 1.

On the other hand, Comparative Examples 1 to 3, despite using the same separator as in Examples 1 to 3, the resistance value was measured to be larger.

As mentioned above, the separation membrane to be measured is a non-conductor having a higher resistance than an electrolyte impregnated therein. However, according to the law of the summation of resistance, if the separation membrane to be measured 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 is irrelevant to the resistance of the membrane itself to be measured. It can be seen as one.

The resistance value measured here may be determined by a movement path of an electrolyte impregnated in a separation membrane as a measurement target and an electrolyte in a separation membrane as a measurement target. In this regard, it could be possible to measure the resistance value of the membrane to be measured with higher accuracy as the electrolyte having higher conductivity was used.

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

Distilled water (H ₂ O) was used as a solvent, and lithium nitrate (LiNO ₃ ) was used as the solute, but the molar concentration was 0.1 M, 0.2 M, 0.3 M, 0.4 M, and 0.5 M, and Preparation Examples 1 and 2 Electrolyte samples of Preparation Example 3 having a significantly lower conductivity than were obtained. Their conductivity measured values are in the range of 8 to 37 mS/cm, and specific measured values are shown in Table 1 below.

Comparative Examples 4 to 8: Preparation of a coin cell to which the electrolyte of Preparation Example 3 and one separator were applied and measurement of resistance

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

One separator identical to that of Comparative Example 1 was used, and each electrolyte of Preparation Example 3 was used as an electrolyte, and the rest were prepared coin cells according to the method of Comparative Example 1, and resistance was measured.

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

Distilled water (H ₂ O) was used as a solvent and lithium nitrate (LiNO ₃ ) was used as the solute, but the molar concentration was 2 M to obtain an electrolyte sample having a conductivity similar to that of Preparation Example 1, and specific The measured conductivity values are shown in Table 1 below.

Example 4: Preparation and resistance measurement of a coin cell to which the electrolyte of Preparation Example 4 and one separator were applied

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

One separator identical to that of Comparative Example 1 was used, and the electrolyte of Preparation Example 4 was used as an electrolyte, and the rest were manufactured according to the method of Comparative Example 1, and 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, resistance was measured according to the EIS method to obtain a Nyquist plot, and the resistance value of one separator was recorded in Table 1 below from the x-axis intercept value.

Further, the reciprocal of the conductivity of each electrolyte recorded in Table 1 is taken as the x-axis, and the y-axis is the resistance value of one separator measured by the EIS, to obtain a trend of a linear plot, and the results are shown in FIG. .

Lithium nitrate molar concentration in electrolyte (M) Electrolyte conductivity
(mS/cm, @ 25 ℃) 1/(conductivity of electrolyte)
(cm/mS, @ 25 ℃) Membrane resistance value 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 the value rounded to the 5th decimal place)

According to Tables 1 and 3, the electrolyte solute is the same lithium nitrate as in Example 1, but the conductivity decreases as the concentration decreases, and the resistance value of one separator measured by EIS increases.

Through this, the resistance measurement value of the separation membrane according to the embodiment is in a linear relationship with the reciprocal conductivity of the electrolyte, and when the solute of the electrolyte is the same, the resistance measurement value of the separation membrane increases as the concentration decreases. Can be seen.

In particular, in Comparative Examples 4 to 8 in which the molar concentration of lithium nitrate in the electrolyte is less than 1 M, the measured value of the membrane resistance exceeds 0.150 Ohms (=150 mOhms). On the other hand, in the case of Example 4, in which the molar concentration of lithium nitrate in the electrolyte was 1M or more, specifically 2M, the membrane resistance measurement value was lowered 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 measured value.

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

Distilled water (H ₂ O) is used as a solvent, and as a solute, lithium nitrate (LiNO ₃ ), lithium hydroxide (LiOH), lithium sulfate (Li ₂ SO ₄ ), lithium chloride (LiCl), and calcium nitrate (Ca(NO ₃₎ ) ₂ ) was respectively 0.1 M molar concentration, to obtain the electrolyte samples of Preparation Example 5 significantly lowered the conductivity compared to Preparation Examples 1 and 2. Their conductivity measured values are in the range of 8 to 18 mS/cm, and specific measured values are shown in Table 2 below.

Comparative Examples 9 to 13: Preparation and resistance measurement of coin cells to which the electrolyte and one separator of Preparation Example 5 were applied

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

One separator identical to that of Comparative Example 1 was used, and each electrolyte of Preparation Example 5 was used as an electrolyte, and the rest were prepared according to the method of Comparative Example 1, and 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 Nyquist plot, and the resistance value of one separator was recorded in Table 2 below from the x-axis intercept value.

Further, the reciprocal of the conductivity of each electrolyte recorded in Table 2 is taken as the x-axis, and the y-axis is the resistance value of one separator measured by the EIS, to obtain a trend in a linear plot, and the results are shown in FIG. .

Type of solute Electrolyte conductivity
(mS/cm, @ 25 ℃) 1/(conductivity of electrolyte)
(cm/mS, @ 25 ℃) Membrane resistance value 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(NO ₃ ) ₂ 17.6 0.0568 0.323

(In Table 2 above, "1/(conductivity of electrolyte)" is the value rounded to the 5th decimal place)

In Tables 2 and 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 the resistance value of one separator measured by EIS is the reciprocal of the conductivity of the electrolyte. It is found to increase proportionally.

As described in Experimental Example 3, also in Experimental Example 4, it can be seen that the resistance measurement value of the separator according to the embodiment is in a linear relationship with the reciprocal conductivity of the electrolyte. When the electrolyte conductivity (162.5 mS/cm) of Example 1 is substituted for the trend line of FIG. 4, a resistance of 24.28 mOhms is confirmed, which is almost the same as the measured value.

Claims (12)

Impregnating (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;
Placing the separator impregnated with the aqueous electrolyte between the negative electrode current collector and the positive electrode current collector, and assembling 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
Including; measuring the resistance of the separator from the x-axis intercept value of the obtained polar coordinate diagram (Nyquist plot)
A method of measuring the resistance of a separator for an electrochemical device.
The method of claim 1,
Each of the negative electrode current collector and the positive electrode current collector is not coated with an electrode active material on its surface (bare),
A method of measuring the resistance of a separator for an electrochemical device.
The method of claim 1,
The negative electrode current collector,
Copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or a combination thereof,
A method of measuring the resistance of a separator for an electrochemical device.
The method of claim 1,
The positive electrode current collector,
Aluminum, stainless steel, nickel, titanium, calcined carbon, or a combination thereof,
A method of measuring the resistance of a separator for an electrochemical device.
The method of claim 1,
The aqueous electrolyte,
The conductivity at 20 to 30 °C is 140 to 180 mS / cm,
A method of measuring the resistance of a separator for an electrochemical device.
The method of claim 1,
The aqueous electrolyte,
Including; water (H ₂ O) as a solvent,
As a solute NaNO ₃ , NaCl, HCl, LNO, LSO, LiOH, KCl, Na ₂ CO ₃ , or a mixture of two or more of them;
A method of measuring the resistance of a separator for an electrochemical device.
The method of claim 6,
The aqueous electrolyte,
The molar concentration of the solute is 1 M or more to 8 M or less,
How to measure the resistance of the separator.
The method of claim 1,
The aqueous electrolyte,
Containing a wetting agent, a surfactant, or a mixture thereof,
How to measure the resistance of the separator.
The method of claim 1,
The voltage when applying a frequency in the range of 100 kHz to 10 kHz is 0 V,
How to measure the resistance of the separator.
The method of claim 1,
1 separation membrane to be measured; And measuring the resistance by performing the series of steps for each of the n-layered separation membranes to be measured,
To measure the average resistance value per one separation membrane to be measured,
How to measure the resistance of the separator.
The method of claim 1,
The separation membrane resistance value measured using the aqueous electrolyte, the conductivity of the aqueous electrolyte, and the cross-sectional area of the positive electrode or negative electrode current collector are substituted into Equation 1 below,
To measure the expected separator resistance value when using a heterogeneous electrolyte in place of the aqueous electrolyte,
Membrane resistance measurement method:
[Equation 1] (r_separator)={(R_xM Electrolyte)/(k_electrolyte)}*(k_xM Electrolyte)*(area)
In Equation 1 above,
The r_separator uses a separator of the same kind as the separator measured using the aqueous electrolyte, but the product of the expected separator resistance value and the cross-sectional area of the separator when using a heterogeneous electrolyte in place of the aqueous electrolyte ( Ohm*cm ² ); k_electrolyte is the conductivity of the heterogeneous electrolyte;
R_xM electrolyte is a membrane resistance value measured using the aqueous electrolyte;
k_xM electrolyte is the conductivity of the aqueous electrolyte; X is the molar concentration of the aqueous electrolyte;
An area is a cross-sectional area of the positive electrode or negative electrode current collector, and may be the same as the cross-sectional area of the separator.
The method of claim 1,
The separation membrane for an electrochemical device to be measured,
Any one selected from the group including lithium secondary batteries, super capacitors, lithium-sulfur batteries, sodium ion batteries, lithium-air batteries, zinc-air batteries, aluminum-air batteries, aluminum ion batteries, and magnesium ion batteries Membrane for electrochemical devices of
How to measure the resistance of the separator.

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