CN116745939A

CN116745939A - electrode

Info

Publication number: CN116745939A
Application number: CN202280009017.6A
Authority: CN
Inventors: 李根成; 李一何; 宋寅宅; 朴镇宇; 金起焕; 李镐赞; 咸允慧
Original assignee: LG Chem Ltd
Current assignee: LG Chem Ltd
Priority date: 2021-01-29
Filing date: 2022-01-28
Publication date: 2023-09-12
Also published as: KR20220109833A

Abstract

The present application relates to an electrode including a current collector and an active material layer, which can provide an electrode capable of ensuring a high level of inter-particle adhesion and adhesion between the active material layer and the current collector with respect to the binder content in the active material layer. With this, the present application can also provide a secondary battery having a high capacity while having excellent performance and the like.

Description

Electrode

Technical Field

The present application claims the benefit of priority of korean patent application No.10-2021-0013324 filed 29 in 2021 and korean patent application No.10-2021-0013322 filed 29 in 2021, the disclosures of which are incorporated herein by reference in their entirety.

The present application relates to an electrode.

Background

The application field of energy storage technology is extended to mobile phones, video cameras, notebook computers, electric vehicles, etc.

One of the research fields of energy storage technology is secondary batteries capable of charge and discharge, and research and development for improving the capacity density and specific energy of such secondary batteries have been conducted.

An electrode (positive electrode or negative electrode) applied to a secondary battery is generally manufactured by forming an active material layer including an electrode active material and a binder on a current collector.

In order to smoothly induce electron transfer between active materials in electrodes of a secondary battery and electron transfer between a current collector and an active material layer, it is necessary to ensure adhesion between active material particles and adhesion between an active material layer and a current collector.

When the adhesion between the particles in the active material layer is insufficient, a phenomenon in which the particles fall off from the electrode may occur, wherein such a phenomenon deteriorates the stability and performance of the battery. For example, particles that fall off due to insufficient adhesion between particles from the surfaces of the negative electrode and the positive electrode may cause micro-short circuits or the like inside the battery, thereby causing deterioration in performance and fire caused by the short circuits.

When the adhesion between the active material layer and the current collector is reduced, the transfer speed of electrons between the active material layer and the current collector is reduced, which may also lead to deterioration of the speed characteristics and the cycle characteristics.

Accordingly, in order to increase the adhesion between particles in the active material layer or the adhesion between the active material layer and the current collector, attempts have been made to introduce a large amount of binder into the active material layer.

However, in this case, the proportion of the active material decreases with an increase in the proportion of the binder, so that there are problems such as deterioration in battery performance and deterioration in capacity due to an increase in electrode resistance and a decrease in conductivity.

Disclosure of Invention

Technical problem

The present application relates to an electrode. An object of the present application is to provide an electrode including a current collector and an active material layer, wherein the electrode can ensure a high level of inter-particle adhesion and adhesion between the active material layer and the current collector as compared to the binder content in the active material layer. Another object of the present application is to provide a secondary battery having excellent performance and the like while having a high capacity.

Technical proposal

Among the physical properties mentioned in the present specification, the physical properties of the measured temperature influence results are the results measured at room temperature unless otherwise specified.

The term room temperature is a natural temperature without increasing or decreasing temperature, which means, for example, any temperature in the range of 10 ℃ to 30 ℃, or a temperature of about 23 ℃ or about 25 ℃.

In this specification, unless otherwise specified, temperature is in degrees celsius (°c).

The term atmospheric pressure is a natural pressure without pressurization or depressurization, which generally refers to an atmospheric pressure at an atmospheric pressure level, and refers to an atmospheric pressure of, for example, about 740mmHg to 780mmHg or so.

In the case of measuring physical properties of which humidity affects the result, the relevant physical properties are physical properties measured under the condition of room temperature and/or normal pressure without particular control over natural humidity.

The electrode of the present application may include a current collector; and an active material layer present on one or both sides of the current collector. Fig. 1 is a cross-sectional view of an exemplary electrode, and illustrates a structure including a current collector 100 and an active material layer 200 located at one side thereof. In the electrode structure, the active material layer may also be formed in contact with the surface of the current collector, or another layer may also be present between the current collector and the active material layer.

By controlling the distribution of the binder in the active material layer, particularly the distribution of the binder in the active material layer adjacent to the current collector, the electrode of the present application can ensure high adhesion between particles in the active material layer, and can simultaneously ensure high adhesion between the active material layer and the current collector as compared with the content of the binder in the active material layer.

The active material layer contains an electrode active material and a binder, wherein the adhesion is represented by the binder. Accordingly, the method for ensuring adhesion in the prior art is to improve the wettability of the binder to the current collector by increasing the amount of the binder introduced and/or increasing the affinity between the binder and the current collector, whereby the binder is uniformly distributed over the entire area of the surface of the current collector. However, this method has a problem in that as the amount of the binder increases, the amount of active material that can be introduced decreases, so that the battery performance and capacity decrease, or the proportion of the binder that contributes to improving the actual adhesion of the binder over the entire area of the current collector surface decreases.

For example, as conceptually shown in fig. 2, the electrode active material 1001 typically present in the active material layer has a larger particle size relative to the binder 2001. In this state, for example, when the binder 2001 is uniformly distributed on the current collector 100 by a method of increasing affinity of the current collector with the binder or the like, the probability that the binder 2001 on the current collector 100 contacts the electrode active material 1001 may be reduced. That is, among the binders distributed on the current collector, the proportion of the binder that does not contribute to the improvement of the adhesion increases. As the proportion of the binder that does not contribute to the improvement of the adhesion increases, the amount of the binder introduced to implement the required adhesion increases, and thus, the amount of the electrode active material that can be introduced into the active material layer decreases. This may lead to an increase in electrode resistance, a decrease in conductivity, degradation in performance and capacity of the battery, and the like.

The inventors have identified that such problems can be solved by controlling the distribution of the binder at various locations on the surface of the current collector. Unlike the prior art, which intends to improve the adhesion by simply increasing the amount of binder and/or increasing the affinity between the binder and the surface of the current collector, etc., it has been confirmed in the electrode of the present application that the proportion of binder contributing to the improvement of the adhesion can be increased by repeatedly disposing the region where the binder is largely distributed and the region where the binder is little distributed or not distributed, and therefore, the adhesion between particles in the active material layer and the adhesion between the active material layer and the current collector can be greatly improved with respect to the content of the binder. In addition, by this, it is also possible to provide a secondary battery having excellent performance while having a high capacity or the like.

In the electrode of the present application, for example, after a standard peeling test, a waveform chart may be shown according to the occupation area ratio of the adhesive at a position along one direction on the surface of the current collector. For example, when an arbitrary point on the surface of the current collector after the standard peeling test is set as the starting point, the one direction may refer to at least one of right, left, upper, and/or lower directions from the starting point, and the waveform pattern may also appear in one or two or more directions from the starting point.

Standard peel tests were performed using 3M Scotch Magic tape cat.810 r. To perform the standard peeling test, first, the electrode was cut into a size of about 20mm in width and about 100mm in length. The Scotch Magic tape cat.810r was cut to a horizontal length of 10mm and a vertical length of 60mm. Thereafter, as shown in fig. 3, scotch Magic tape cat.810r 300 was adhered to the active material layer 200 of the electrode in a crossed state. This adhesion may be performed such that a certain portion of the Scotch logic tape cat.810r 300 protrudes. Then, the protruding portion was grasped, and the Scotch logic tape cat.810r 300 was peeled off. In this case, the peeling rate and the peeling angle are not particularly limited, but the peeling rate may be about 20 mm/sec and the peeling angle may be about 30 degrees. In addition, regarding the adhesion of the Scotch Magic tape cat.810r 300, once the tape was adhered, the tape was adhered by reciprocally pushing the surface of the tape with rollers having a weight of about 1kg and a radius and width of 50mm and 40mm, respectively.

Through the above process, when the Scotch Magic tape cat.810r 300 is peeled off, the components of the active material layer 200 are peeled off together with the Scotch Magic tape cat.810r 300. Subsequently, the above procedure was repeated using a new Scotch logic tape cat.810r 300.

The standard peeling test can be performed by performing this process until the components of the active material layer 200 are not peeled off on the Scotch Magic tape cat.810r 300, and thus are not observed.

Regarding the problem that the components of the active material layer 200 do not fall off on the Scotch Magic tape cat.810r 300, when the surface of the Scotch Magic tape peeled off from the active material layer is compared with the surface of the unused Scotch Magic tape so that the color tones of the two are substantially the same, it can be determined that the components of the active material layer do not fall off (visual observation).

Specific methods of operating a standard peel test are described in the examples.

The area-to-footprint ratio of the adhesive may be, for example, a value measured by: the region where the adhesive is present and the region where the adhesive is not present are divided with respect to an image obtained by photographing an arbitrary region of the current collector surface after the standard peeling test, and the area ratio of the region where the adhesive is present in the arbitrary region with respect to the area of the arbitrary region is calculated. In the present application, the area where the adhesive is present and the area where the adhesive is not present can be distinguished based on brightness using, for example, trainable Weka Segmentation Plug-in of Image J software (manufacturer: image J). In the present application, a specific measurement of the area ratio occupied by the adhesive may follow the method described in the following examples.

The waveform chart may refer to, for example, a chart depicted by setting an arbitrary point on the surface of a current collector sample obtained after a standard peeling test is performed on an electrode of the present application as a starting point, measuring an area ratio occupied by an adhesive from the starting point in at least one direction (e.g., right, left, up and/or down directions), and setting a distance (position) of a measurement region from the starting point as an x-axis, and setting an area ratio occupied by the adhesive as a y-axis.

In the present specification, the term waveform chart may refer to a chart showing a tendency that when a position (distance of a measurement region from a start point) is set to an x-axis and an area ratio occupied by an adhesive is set to a y-axis, the area ratio occupied by the adhesive increases, decreases, and then increases again with an increase in the value of the x-axis. That is, in the present specification, when the occupation area ratio of the adhesive shows the above-described tendency, even if the correlation chart is not necessarily in the form of an ideal waveform chart, it can be defined as a waveform chart.

In the present application, when the arithmetic average value of the area ratio occupied by the adhesive measured for each position is set to a, the term average line may be expressed as, for example, a line expressed by y=a on the drawing. The arithmetic average of the area ratios occupied by the adhesives measured for the respective positions may be expressed as, for example, a value obtained by dividing the sum of the area ratios occupied by the respective adhesives measured for the respective positions by the total number of positions.

In the present application, the term peak may denote a region having the largest area ratio occupied by the adhesive (a portion having an area ratio occupied by the adhesive larger than the average value) among regions corresponding to the upward direction of the average value. When there are two or more regions having the largest occupied area ratio of the adhesive within one wavelength unit, a region having the largest x-axis value therein is called a peak. In the present application, the term trough may denote a region having a minimum adhesive-occupied area ratio (a portion where the adhesive-occupied area ratio is smaller than the average value) among regions corresponding to the downward direction of the average value. When there are more than two regions having the smallest occupied area ratio of the adhesive within one wavelength unit, the region having the largest x-axis value therein is called a trough. In the present application, a peak and a trough cannot be present together in one wavelength unit, two or more peaks cannot be present, and two or more troughs cannot be present. That is, only one peak or only one trough may exist within one wavelength unit of the present application.

In the present application, the term wavelength unit may refer to a region from an arbitrary point where a waveform diagram and an average line intersect in one direction (left or right direction) to a nearest intersection point (see fig. 4).

In the present application, the term wavelength may denote a distance between a trough and an adjacent trough and/or a distance between a peak and an adjacent peak.

In the present specification, the fact that the occupation area ratio of the adhesive according to the position represents the waveform pattern may mean that, for example, the region having a relatively high occupation area ratio of the adhesive and the region having a relatively low proportion are repeatedly arranged according to the position of the current collector surface. Fig. 4 shows an example of a waveform diagram showing the area ratio of the adhesive occupation measured with respect to the respective positions of the electrodes of the present application. The waveform pattern of the present application may be a pattern derived from at least one direction at any point on the surface of the current collector. Here, the one direction may refer to a left, right, up and/or down direction, and all the graphs derived for the left, right, up and down directions may be represented as waveform graphs.

Since the electrode of the present application controls the distribution of the binder such that the occupation area ratio of the binder according to the position shows a waveform pattern having peaks and valleys, the effective adhesion area between the electrode active material in the active material layer and the binder can be increased when the active material layer is filled, and accordingly, the adhesion between the active material layer and the current collector or between the electrode active materials can be improved.

In the present specification, the occupied area ratio of the adhesive in the peak portion of the waveform diagram may be, for example, about 55% or more. In another example, the area ratio of the adhesive at the peak portion may be 56% or more, 57% or more, 58% or more, 59% or more, 60% or more, 61% or more, 62% or more, 63% or more, 64% or more, 65% or more, 66% or more, 67% or more, 68% or more, 69% or more, 70% or more, 71% or more, or 72% or more, or may be 90% or less, 85% or less, 80% or less, or 75% or less.

In the present specification, the area ratio occupied by the adhesive in the trough portion of the waveform diagram may be, for example, about 50% or less. In another example, the adhesive may occupy a proportion of about 49% or less, about 48% or less, or about 47% or less, or may be about 10% or more, about 15% or more, about 20% or more, about 25% or more, about 30% or more, about 35% or more, about 40% or more, or about 45% or more at the trough portion.

In the electrode of the present application, for example, a difference between a maximum value of the occupied area ratio of the binder and a minimum value of the occupied area ratio of the binder in the waveform diagram (hereinafter, described as a difference between the maximum value and the minimum value) may be 9%p or more. The term% p (percentage points) refers to the arithmetic difference between the two percentages. In another example, the difference between the maximum and minimum values may be 10% p or more, 11% p or more, 12% p or more, 13% p or more, 14% p or more, 15% p or more, 16% p or more, 17% p or more, 18% p or more, 19% p or more, 20% p or more, 21% p or more, 22% p or more, 23% p or more, 24% p or more, 25% p or 26% p or more. The upper limit of the difference between the maximum value and the minimum value is not particularly limited, but may be 60% p or less, 55% p or less, 50% p or less, 45% p or less, 40% p or less, 35% p or less, or 30% p or less.

In the present application, the wavelength of the waveform diagram may be, for example, in the range of 3mm to 25 mm. As described above, the waveform patterns of the present application may not be ideal shapes, and thus the respective wavelengths of the waveform patterns may be the same as or different from each other. In the present application, in another example, the wavelength of the waveform diagram may be 4mm or more, 5mm or more, 6mm or more, 7mm or more, 8mm or more, 9mm or more, or 10mm or more, or may be 20mm or less, 19mm or less, 18mm or less, 17mm or less, or 16mm or less.

As described above, the adhesive behavior is controlled such that the waveform pattern displayed according to the occupation area ratio of the adhesive along any direction on the surface of the current collector is different from the concept of the prior art, which intends to secure the adhesion by improving the wettability of the adhesive to the current collector. It is different from the concepts of the prior art. Although the reason why the binder exhibits the above-described behavior is not clearly elucidated in the present application, the present inventors have confirmed that by controlling the composition of a slurry to be described below and/or the surface characteristics of a current collector, etc., the behavior of the binder on the surface of the current collector can be controlled as described above, and by controlling the binder behavior as described above, it is possible to increase the contact probability between the component of the electrode active material particles, such as the active material layer, and the binder during the electrode manufacturing process, to appropriately distribute the effective adhesion region, and to achieve appropriate spreading during the rolling process. With this, the electrode of the present application can ensure a high level of inter-particle adhesion with respect to the binder content in the active material layer and adhesion between the active material and the current collector, and with this, it is possible to provide a secondary battery having excellent performance while having a high capacity or the like.

In the electrode of the present application, for example, there may be a region in which the area ratio of the binder to the current collector surface after the standard peeling test is 60% or more, which satisfies the following equation 1.

[ equation 1]

18≤A/W

In equation 1, a may be a ratio (unit:%) of the occupied area of the particulate binder, and W may be a content (wt%) of the binder in the active material layer. In equation 1, a may be in units of W may be in weight%. Thus, the unit of A/W in equation 1 may be wt ^-1 (weight) ^-1 )。

When the composition of the slurry in the electrode manufacturing process is known, the content of the binder in the active material layer may be substantially the same as the content ratio of the binder in the solid content (the portion other than the solvent) of the relevant slurry. In addition, when the composition of the slurry in the electrode manufacturing process is not known, the content of the binder may be determined by TGA (thermogravimetric analysis) analysis of the active material. For example, when an SBR (styrene-butadiene rubber) binder is used as the binder, the content of the binder can be confirmed by performing TGA analysis of the active material layer and decreasing the content of the resulting SBR binder from 370 ℃ to 440 ℃ in a temperature-mass curve obtained by increasing the temperature at a rate of 10 ℃ per minute.

In another example, the A/W in equation 1 may be 19 weight ^-1 Above, 20 weight percent ^-1 Above, 21 weight ^-1 Above, 22 weight percent ^-1 Above, 23 weight percent ^-1 Above, 24 weight ^-1 Above, 25 weight percent ^-1 Above, 26 weight ^-1 Above, 27 weight percent ^-1 Above, 28 weight percent ^-1 Above, 29 weight percent ^-1 Above, 30 weight percent ^-1 Above 31 weight percent ^-1 Above, 32 weight percent ^-1 Above, 33 weight percent ^-1 Above, 34 weight ^-1 Above 35 weight percent ^-1 Above, 36 wt ^-1 Above or 37 weight percent ^-1 The above. The upper limit of A/W is not particularly limited, but may be 80 wt ^-1 The weight of the catalyst is 75 ^-1 The following are 70 weight percent ^-1 The weight of the catalyst is 65 ^-1 Hereinafter, 60% by weight ^-1 The following are 55 weight percent ^-1 The weight of the catalyst is 50 ^-1 Below 45 weight percent ^-1 Below or 40 weight percent ^-1 The following is given.

By controlling the a/W ratio of equation 1 as described above, the present application can provide an electrode having excellent adhesion between active materials and/or between a current collector and an active material layer with respect to the binder content.

There is no particular limitation on the type of current collector used in the present application, wherein known current collectors may be used. In order to realize the binder behavior, such as the waveform diagrams described above, the surface characteristics (water contact angle, etc.) of the current collector can be controlled as described below. As the current collector, for example, a film, sheet, or foil made of one or more selected from stainless steel, aluminum, nickel, titanium, baked carbon, copper, carbon, stainless steel surface-treated with nickel, titanium, or silver, and aluminum-cadmium alloy may be used. To achieve the desired binder distribution, a current collector having the surface characteristics described below may be selected from the current collectors, or the surface characteristics may be adjusted by additional treatment.

There are no particular restrictions on the thickness, shape, etc. of the current collector, and suitable types may be selected within a known range.

The active material layer formed on the current collector may substantially contain an electrode active material and a binder.

As the binder, a known material may be used, and a known composition that contributes to the bonding of components such as an active material in the active material layer and the bonding of the active material layer to the current collector may be used. As a suitable binder, one or a combination of two or more selected from PVDF (polyvinylidene fluoride), PVA (polyvinyl alcohol), polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, SBR (styrene-butadiene rubber) and fluororubber may be used.

In order to more effectively achieve the object of the present application, it is suitable to use a particulate adhesive as the adhesive, and for example, it is suitable to use a particulate adhesive having an average particle diameter of about 50nm to 500 nm. In the present specification, the term average particle diameter may refer to a value measured for one kind of particulate binder (or particulate active material) according to the following examples, to a value measured for two or more kinds of particulate binders (or mixtures of particulate active materials) according to the following examples, or to a value calculated from a value measured for two or more kinds of particulate binders (or particulate active materials) according to the following examples, respectively taking their weight fractions into consideration. For example, when the particulate binder (or the particulate active material) having the average particle diameter D1 is present by the weight of W1, the particulate binder (or the particulate active material) having the average particle diameter D2 is present by the weight of W2, the average particle diameter D may be defined as d= (d1×w1+d2×w2)/(w1+w2). In the above-mentioned confirmation, the particle diameters D1 and D2, and the weights W1 and W2 are values of the same unit as each other, respectively. In another example, the average particle diameter of the particulate binder may be 70nm or more and 90nm or more and 110nm or more and 130nm or more and 140nm or more and may be 450nm or less and 400nm or less and 350nm or less and 300nm or less and 250nm or less and 200nm or less.

In addition, in order to achieve a desired adhesive distribution or the like, it may be advantageous to use an adhesive having a solubility parameter within the range described below as the adhesive.

In the present application, a high level of adhesion can be ensured while the active material layer contains a relatively small proportion of binder. For example, the proportion of the binder in the active material layer may be about 0.5 to 10 wt%. In another example, the ratio may be further controlled within the following range: 1 wt% or more, 1.5 wt% or more, 2 wt% or more, 2.5 wt% or more, 3 wt% or more, 3.5 wt% or more, or about 4 wt% or more, and/or 9.5 wt% or less, 9 wt% or less, 8.5 wt% or less, 8 wt% or less, 7.5 wt% or less, 7 wt% or less, 6.5 wt% or less, 6 wt% or less, 5.5 wt% or less, 5 wt% or less, 4.5 wt% or less, 4 wt% or less, 3.5 wt% or less, or about 2 wt% or less. The method of determining the proportion (content) of the binder in the active material layer is as described above.

The electrode active material contained in the active material layer may be a positive electrode active material or a negative electrode active material, and is not particularly limited with respect to a specific type. For example, as the positive electrode active material, a material containing LiCoO can be used ₂ 、LiNiO ₂ 、LiMn ₂ O ₄ 、LiCoPO ₄ 、LiFePO ₄ 、LiNiMnCoO ₂ And LiNi _1-x-y-z Co _x M1 _y M2 _z O ₂ Active materials such as (M1 and M2 are each independently any one selected from Al, ni, co, fe, mn, V, cr, ti, W, ta, mg and Mo, and x, y and z are each independently an atomic fraction of an oxide constituent element, satisfying 0.ltoreq.x < 0.5, 0.ltoreq.y < 0.5, 0.ltoreq.z < 0.5, 0 < x+y+z.ltoreq.1) and the like, and as the negative electrode active material, an active material containing a material selected from natural graphite, artificial graphite, and the like can be usedA carbon-rich material, a lithium-containing titanium composite oxide (LTO), si, sn, li, zn, mg, cd, ce, ni, or a Fe metal (Me), an alloy consisting of the metal (Me), an oxide (MeOx) of the metal (Me), and a composite of the metal (Me) and carbon.

In order to achieve an appropriate binder distribution or the like, it is appropriate to use a particulate active material as an electrode active material, and for example, it is appropriate to use an active material having an average particle diameter of about 1 μm to 100 μm. The average particle size may be measured or calculated according to the methods described above. In another example, the average particle diameter of the particulate active material may be 5 μm or more and 10 μm or more and 15 μm or may be 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 25 μm or less or about 20 μm or less.

In order to achieve proper binder distribution and the like, the particle size relationship between the particulate binder and the active material may be adjusted. For example, the ratio (D1/D2) of the average particle diameter (D1, unit nm) of the particulate electrode active material to the average particle diameter (D2, unit nm) of the particulate binder may be in the range of 10 to 1,000. In another example, the ratio (D1/D2) may be 20 or more, 30 or more, 40 or more, 50 or more, 60 or more, 70 or more, 80 or more, 90 or more, 100 or more, 110 or more, 120 or more, or 130 or about 900 or less, 800 or less, 700 or less, 600 or less, 500 or less, 400 or less, 300 or less, 200 or 150 or less.

Meanwhile, with respect to the rolled active material layer, the average particle diameter of the particulate binder and the active material mentioned in the present specification refers to the average particle diameter before rolling in the case of the rolled electrode active material layer.

In the present application, by reducing the binder content ratio in the active material layer, a relatively large amount of active material can be contained, and by this, an electrode having excellent adhesion can be provided.

For example, the active material in the active material layer may be in the range of 1000 parts by weight to 10000 parts by weight with respect to 100 parts by weight of the binder. In another example, the ratio may be 1500 parts by weight or more, 2000 parts by weight or more, 2500 parts by weight or more, 3000 parts by weight or more, 3500 parts by weight or more, 4000 parts by weight or more, or 4500 parts by weight or more, or 9500 parts by weight or less, 9000 parts by weight or less, 8500 parts by weight or less, 8000 parts by weight or less, 7500 parts by weight or less, 7000 parts by weight or less, 6500 parts by weight or less, 6000 parts by weight or less, or 5500 parts by weight or less.

The active material layer may further contain other necessary components in addition to the above-described components. For example, the active material layer may further include a conductive material. As the conductive material, for example, a known composition may be used without any particular limitation as long as it exhibits conductivity without causing chemical changes in the current collector and the electrode active material. For example, as the conductive material, one or a mixture of two or more of graphite selected from, for example, natural graphite or artificial graphite, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lampblack black or summer black (summer black), conductive fiber such as carbon fiber or metal fiber, metal powder such as aluminum powder or nickel powder, conductive whisker such as zinc oxide or potassium titanate, conductive metal oxide such as titanium oxide, polyphenylene derivative, and the like may be used.

The content of the conductive material is controlled as needed without particular limitation, but may be generally contained in an appropriate ratio in the range of 0.1 to 20 parts by weight or 0.3 to 12 parts by weight with respect to 100 parts by weight of the active material. A method of determining the content of the conductive material to an appropriate level in consideration of the cycle life of the battery and the like is known.

In addition to the above-described components, the active material layer may contain other necessary known components (for example, thickeners such as carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, or the like).

The thickness of the active material layer is not particularly limited, and may be controlled to have an appropriate thickness level in consideration of the required performance. The thickness of the active material layer may refer to, for example, the thickness of the active material layer after rolling described below. The thickness of the active material layer may be, for example, in the range of about 10 μm to 500 μm. In another example, the thickness may be about 30 μm or more, 50 μm or more, 70 μm or more, 90 μm or more, or 100 μm or more, or about 450 μm or less, 400 μm or less, 350 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, or 150 μm or less.

The active material layer may be formed to have a certain level of porosity. In the process of manufacturing an electrode, the porosity is typically controlled by rolling. The active material layer may have a porosity of about 35% or less. The porosity can be further adjusted within the following range: 33% or less, 31% or less, 29% or less, or 27% or less, and/or 5% or more, 7% or more, 9% or more, 11% or more, 13% or more, 15% or more, 17% or more, 19% or more, 21% or more, 23% or more, or 25% or more. The purpose of the application is that: controlling the rolling process to have porosity can help achieve binder distribution with wave patterns and the like. Here, the porosity, for example, the porosity of the rolled active material layer, may be calculated by comparing the ratio of the difference between the actual density of the active layer and the density after rolling, wherein such a method is known.

The above-described electrode may be manufactured in the manner described below. Typically, the electrode is manufactured by coating a slurry on a current collector, drying, and then performing a rolling process. In the present application, by controlling the composition of the slurry in the above-described process, the surface characteristics of the current collector coated with the slurry, as well as the drying condition and/or rolling condition, the desired distribution of the binder can be achieved.

Thus, the manufacturing method of the present application may include at least the step of forming a slurry layer on the current collector. In this case, the slurry may contain at least a solvent, a binder, and an electrode active material.

In the production method of the present application, as the slurry, a method of dispersing a relatively hydrophobic binder in a relatively polar solvent in a certain amount may be applied.

In the manufacturing method of the present application, a layer is formed on the current collector with such slurry. At this time, there is no particular limitation on the method of forming the slurry layer, and for example, the layer may be formed by a known coating method. The reason is not clear, but when the same slurry having the following composition is coated on the current collector, the dispersion state of the binder in the slurry, the affinity of the solvent of the slurry to the surface of the current collector, the affinity of the surface of the current collector to the binder in the slurry and/or the particle size relationship of the particulate materials in the case where they are applied, etc. are combined with each other to control the position of the binder in a desired form.

For example, the affinity of a solvent to the current collector surface affects the contact angle of the solvent on the current collector surface, wherein upon evaporation of the solvent, the contact angle may create a force in a certain direction in the slurry due to capillary action or the like. The affinity of the binder to the solvent and the amount of the binder (also, the particle diameter in the case of the particulate binder) influence the dispersion state of the binder in the slurry, and the affinity of the binder to the current collector surface influences the dispersion state of the binder in the slurry, or the distribution shape of the binder to the current collector surface, and the like.

In the present application, it has been confirmed that when a slurry of a composition to be described below has been formed on a current collector having surface characteristics to be described below, a desired arrangement of the binder is achieved by the dispersed state of the binder and the evaporation condition of the solvent, and the shearing force in the slurry generated thereby.

For example, the slurry applied to the manufacturing process may comprise a solvent. As the solvent, a solvent capable of appropriately dispersing slurry components such as an electrode active material is generally used, and examples thereof are water, methanol, ethanol, isopropanol, acetone, dimethyl sulfoxide, formamide, dimethylformamide, and the like.

In the present application, it may be desirable to use a solvent having a dipole moment of about 1.3D or more among the above solvents. In another example, the dipole moment of the solvent may be further controlled within the following ranges: about 1.35D or more, 1.4D or more, 1.45D or more, 1.5D or more, 1.55D or more, 1.6D or more, 1.65D or more, 1.7D or more, 1.75D or more, 1.8D or more, or 1.85D or more, and/or about 5D or less, 4.5D or less, 4D or less, 3.5D or less, 3D or less, 2.5D or less, 2D or less, or 1.9D or less. For each solvent, the dipole moment of the solvent is known.

As the binder contained in the slurry, an appropriate one of the above types of binders may be selected and used. In order to obtain the desired dispersion in the solvent, it may be necessary to use a solubility parameter of about 10MPa ¹¹² To 30MPa ^1/2 Left and right adhesives are used as the adhesives. In another example, the solubility parameter may be 11MPa ^1/2 Above, 12MPa ^1/2 Above, 13MMPa ^1/2 Above, 14MPa ^1/2 Above 15MPa ^1/2 Above or 16MPa ^1/2 Above, or may be 28MPa ^1/2 Below, 26MPa ^1/2 Below, 24MPa ^1/2 Below, 22MPa ^1/2 Below, 20MPa ^1/2 Below or 18MPa ^1/2 The following is given. The solubility parameters of the adhesive may be determined by literature (e.g., yanlong Luo et al, 2017, etc.). For example, among the above types of adhesives, the type having the above solubility parameter may be selected.

As the binder, a particulate binder may be used, for example, a binder exhibiting the above-described ratio (D1/D2) by using the average particle diameter (D2) of the binder and the average particle diameter (D1) of the particulate electrode active material, or a particulate binder having an average particle diameter in the above-described range.

The binder content in the slurry can be controlled in consideration of the desired dispersion state. For example, the binder may be included in the slurry such that the concentration of the binder relative to the solvent (=100×b/(b+s), where B is the weight of the binder in the slurry (g) and S is the weight of the solvent in the slurry (g)) is about 0.1% to about 10%. In another example, the concentration may be 0.5% or more, 1% or more, 1.5% or more, or 2% or more, or may be 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, or about 2.5% or less by weight.

In addition to the above components, the slurry may further contain an electrode active material. As the electrode active material, an appropriate type may be selected from the above types, and in consideration of contribution to a desired dispersion state, an electrode active material in the form of particles having an average particle diameter (D50 particle diameter) within the above range and a ratio to an average particle diameter of a binder within the above range may be used.

The proportion of the electrode active material in the slurry may be adjusted so that the proportion of the electrode active material in the active material layer may be achieved.

For example, the electrode active material in the slurry may be contained in a proportion of 1000 parts by weight to 10000 parts by weight with respect to 100 parts by weight of the binder. In another example, the ratio may be 1500 parts by weight or more and 2000 parts by weight or more and 2500 parts by weight or more and 3000 parts by weight or more and 3500 parts by weight or more and 4000 parts by weight or more and 4500 parts by weight or less and 9500 parts by weight or less and 9000 parts by weight or less and 8500 parts by weight or less and 8000 parts by weight or less and 7500 parts by weight or less and 7000 parts by weight or less and 6500 parts by weight or less and 6000 parts by weight or less and 5500 parts by weight or less and 5000 parts by weight or less and 4500 parts by weight or less and 3500 parts by weight or less and 3000 parts by weight or 2500 parts by weight or less.

In addition to the above components, the slurry may contain other components including the above conductive materials, thickeners, and the like, depending on the purpose.

Such a slurry may be applied to the surface of the current collector. In this process, there is no particular limitation on the coating method, and a known coating method, for example, a method such as spin coating, comma coating, or bar coating may be applied.

The surface characteristics of the current collector to which the slurry is applied can be controlled.

The current collector surface may have, for example, a water contact angle of 25 degrees or less. In another example, the water contact angle may be in the following range: 24 degrees or less, 23 degrees or less, 22 degrees or less, or 21 degrees or less, and/or 1 degree or more, 2 degrees or more, 3 degrees or more, 4 degrees or more, 5 degrees or more, 6 degrees or more, 7 degrees or more, 8 degrees or more, 9 degrees or more, 10 degrees or more, 11 degrees or more, 12 degrees or more, 13 degrees or more, 14 degrees or more, 15 degrees or more, 16 degrees or more, 17 degrees or more, 18 degrees or 19 degrees or more. The water contact angle can be measured in the manner described in the examples.

The collector surface may have a surface energy of, for example, 40mN/m or more. In another example, the surface energy may be 45mN/m or more, 50mN/m or more, 55mN/m or more, 60mN/m or more, 65mN/m or more, 70mN/m or more, or 75mN/m or more, or may be 200mN/m or less, 150mN/m or 100mN/m or less. The surface energy can be measured in the manner described in the examples.

The current collector surface of the present application may have, for example, a polarity energy of 30mN/m or more. In another example, the polar property may be 32mN/m or more, 34mN/m or more, 36mN/m or more, 38mN/m or more, 40mN/m or more, 42mN/m or more, 44mN/m or more, 46mN/m or more, or 48mN/m or more, or 150mN/m or less, 140mN/m or less, 130mN/m or less, 120mN/m or less, 110mN/m or less, 100mN/m or less, 90mN/m or less, 80mN/m or less, 70mN/m or 60mN/m or less.

The current collector surface of the present application may have, for example, a dispersion energy of 40mN/m or less. In another example, the dispersion energy may be 38mN/m or less, 36mN/m or less, 34mN/m or less, 32mN/m or less, 30mN/m or less, or 28mN/m or less, or may be 5mN/m or more, 10mN/m or more, 15mN/m or more, 20mN/m or more, or 25mN/m or more.

Here, the surface energy, the dispersion energy, and the polarity energy are physical quantities that can be obtained by the WORK (Owens-Wendt-Rabel-Kaelble) method based on the water contact angle and the DM contact angle.

The above electrode active material layer is applied to the surface of the current collector satisfying at least one, two or more or all of the surface characteristics, whereby an electrode having a desired binder distribution or the like can be provided.

Among the above-mentioned collectors, a collector having such surface characteristics may also be selected, and if necessary, additional treatment may be performed to control the surface characteristics of the collector.

Currently, the kind of the applied treatment is not particularly limited. Various treatments are known in the industry that are capable of controlling the surface characteristics of the current collector surface.

As a suitable treatment method, a so-called plasma method can be exemplified. As is well known, plasma is a state in which electrons and ions formed by applying energy to a gas exist, and a water contact angle, surface energy, polar properties, dispersion energy, and the like of a current collector surface can be controlled by exposure to plasma.

For example, the plasma treatment may be performed by exposing the current collector to plasma generated by applying a voltage while injecting air or oxygen together with an inert gas into the treatment space. At this time, the type of inert gas that can be applied is not particularly limited, but may be exemplified by, for example, argon, nitrogen, helium, and/or the like, and preferably may be exemplified by argon.

Air or oxygen may be injected, for example, at a flow rate of about 0.01LPM to 2 LPM. The injection flow rate may also be adjusted within the following ranges: 0.02LPM or more, 0.03LPM or more, 0.04LPM or more, 0.05LPM or more, 0.06LPM or more, 0.07LPM or more, 0.08LPM or more, or 0.09LPM or more, and/or 1.5LPM or less, 1LPM or less, 0.9LPM or less, 0.8LPM or less, 0.7LPM or less, 0.6LPM or less, 0.5LPM or less, 0.4LPM or less, 0.3LPM or 0.2LPM or less.

In addition, an inert gas, for example, argon (Ar) may be injected at a flow rate in the range of about 0.1LPM to 30 LPM. The injection flow rate may also be adjusted within the following ranges: 0.5LPM or more, 1LPM or more, 1.5LPM or more, 2LPM or more, 2.5LPM or more, 3LPM or more, 3.5LPM or more, 4LPM or more, 4.5LPM or more, 5LPM or more, or 5.5LPM or more, and/or 25LPM or less, 20LPM or less, 15LPM or less, 10LPM or less, 9LPM or less, 8LPM or 7LPM or less.

In addition, at the time of the treatment, the ratio (I/O) of the injection flow rate (I) of the inert gas to the injection flow rate (O) of oxygen or air may be controlled to be in the range of, for example, 10 to 1000. In another example, the ratio (I/O) may be 15 or more, 20 or more, 25 or more, 30 or more, 35 or more, 40 or more, 45 or more, 50 or more, 55 or more, or may be 900 or less, 800 or less, 700 or less, 600 or less, 500 or less, 400 or less, 300 or less, 200 or less, 100 or less, 90 or less, 80 or less, or 70 or less.

The injection flow rates of oxygen or air and inert gas may affect the partial pressure of the respective gases in the process space, thus determining the state of the generated plasma. In the present application, by controlling the injection flow rate at the above level, it is possible to efficiently generate plasma capable of forming the current collector to have a desired surface characteristic.

In a suitable example, only oxygen (and/or air) and inert gas may be injected into the process space during plasma processing.

The plasma treatment may be performed under power conditions in the range of, for example, 100W to 300W. In another example, the power may be 110W or more, 120W or more, 130W or more, 140W or more, 150W or more, or 160W or more, or 290W or less, 280W or less, 270W or less, 260W or less, 250W or less, 240W or less, 230W or less, 220W or less, 210W or less, 200W or less, 190W or 180W or less.

When the plasma treatment is performed in a continuous process such as a roll-to-roll process, the exposure time can be controlled by adjusting the moving speed of the current collector. For example, when the plasma treatment is performed while moving the current collector into the treatment space at a constant speed, the moving speed of the current collector may be controlled in a range of, for example, about 1 mm/sec to 100 mm/sec. In another example, the movement speed may be further adjusted within the following range: about 3 mm/s or more, about 5 mm/s or more, about 7 mm/s or more, or 9 mm/s or more, and/or 95 mm/s or less, 90 mm/s or less, 85 mm/s or less, 80 mm/s or less, 75 mm/s or less, 70 mm/s or less, 65 mm/s or less, 60 mm/s or less, 55 mm/s or less, 50 mm/s or less, 45 mm/s or less, 40 mm/s or less, 35 mm/s or less, 30 mm/s or less, 25 mm/s or less, 20 mm/s or less, 15 mm/s or less, or 13 mm/s or less.

By controlling the moving speed of the current collector within the above range, a desired exposure time can be obtained.

The exposure time (T) of the current collector to plasma can be controlled to be about 0.1 seconds to about 20 seconds or so at the time of plasma treatment. In another example, the plasma treatment time (T) may be 0.5 seconds or more, 1 second or more, 1.5 seconds or more, 2 seconds or more, 2.5 seconds or more, 3 seconds or more, 3.5 seconds or more, 4 seconds or more, 4.5 seconds or more, 5 seconds or more, or 5.5 seconds or more, or 19 seconds or less, 18 seconds or less, 17 seconds or less, 16 seconds or less, 15 seconds or less, 14 seconds or less, 13 seconds or less, 12 seconds or less, 11 seconds or less, 10 seconds or less, 9 seconds or 8 seconds or less.

In the present application, for example, according to the plasma treatment as described above, the physical properties of the current collector surface can be controlled to a desired level.

After the slurry is applied to the surface of the current collector with the surface characteristics adjusted, a drying process of the slurry may be performed. Although there is no particular limitation on the conditions under which the drying process is performed, it may be appropriate to adjust the drying temperature in a range of about 40 to 400 ℃ in consideration of the position of the desired binder, etc. In another example, the drying temperature may be about 45 ℃ or higher, about 50 ℃ or higher, about 55 ℃ or higher, about 60 ℃ or higher, about 65 ℃ or higher or about 70 ℃ or higher, or about 380 ℃ or lower, about 360 ℃ or lower, about 340 ℃ or lower, about 320 ℃ or lower, about 300 ℃ or lower, about 280 ℃ or lower, about 260 ℃ or lower, about 240 ℃ or lower, about 220 ℃ or lower, about 200 ℃ or lower, about 180 ℃ or lower, about 160 ℃ or lower, about 150 ℃ or lower, about 140 ℃ or lower, about 130 ℃ or lower, about 120 ℃ or lower, about 110 ℃ or lower, about 100 ℃ or lower, about 90 ℃ or lower or about 80 ℃ or lower.

The drying time may also be controlled in consideration of the position of the desired binder, in consideration of the dispersion state, etc., and may be adjusted, for example, in the range of about 1 minute to 30 minutes. In another example, the time may be further controlled within the following ranges: about 2 minutes or more, about 3 minutes or more, about 4 minutes or more, about 5 minutes or more, about 6 minutes or more, about 7 minutes or more, about 8 minutes or more, or about 9 minutes or more, and/or about 25 minutes or less, about 20 minutes or less, or about 15 minutes or less.

After the drying process, a rolling process may be performed. In this case, the position of the adhesive or the like may also be adjusted by rolling conditions (for example, pressure during rolling, or the like). For example, rolling may be performed such that the porosity of the rolled slurry (active material layer) falls within the above range.

As described above, the thickness of the rolled slurry (i.e., the active material layer) is within the thickness range of the active material layer.

In the manufacturing process of the electrode of the present application, necessary additional processes (e.g., a cutting process, etc.) may be performed in addition to the slurry coating, drying, and rolling.

The application also relates to an electrochemical element, such as a secondary battery, comprising such an electrode.

The electrochemical element may include an electrode as a positive electrode and/or a negative electrode. If the electrode of the present application is used as a negative electrode and/or a positive electrode, there is no particular limitation on other constructions or manufacturing methods of the electrochemical element, and known methods may be applied.

Advantageous effects

The present application relates to an electrode including a current collector and an active material layer, which can provide an electrode capable of ensuring a high level of inter-particle adhesion and adhesion between the active material layer and the current collector with respect to the binder content in the active material layer. With this, it is also possible to provide a secondary battery having a high capacity and excellent performance and the like.

Drawings

Fig. 1 is a cross-sectional view of an exemplary electrode of the present application.

FIG. 2 is a conceptual view of a state of formation of an active material layer in the prior art

Fig. 3 is a conceptual diagram of a state in which a standard peeling test is performed.

Fig. 4 is a waveform diagram showing the area ratio occupied by the adhesive measured at each position in example 1.

Fig. 5 is an image obtained by photographing the adhesive behavior in the region a (one example of the peak portion of the waveform chart) of fig. 4 (photographed after the standard peeling test).

Fig. 6 is an image obtained by photographing the adhesive behavior in the region B (one example of the trough portion in the waveform diagram) of fig. 4 (photographed after the standard peeling test).

Fig. 7 is an image obtained by photographing the active material behavior in the region a (one example of the peak portion of the waveform chart) of fig. 4 (photographed after the measurement of the adhesion force).

Fig. 8 is an image obtained by photographing the active material behavior in the region B (one example of the trough portion in the waveform diagram) of fig. 4 (photographed after the measurement of the adhesion force).

Fig. 9 is a graph showing the area ratio of the occupation of the adhesive measured for each position in comparative example 1.

Fig. 10 is an image obtained by photographing the adhesive behavior in the region C of fig. 9 (photographed after the standard peel test).

Fig. 11 is an image obtained by photographing the active material behavior in the region C of fig. 9 (photographed after measuring the adhesion force).

Fig. 12 is a graph showing the area ratio occupied by the adhesive measured at each position in comparative example 2.

Fig. 13 is an image obtained by photographing the adhesive behavior in the region D of fig. 12 (photographed after the standard peel test).

Fig. 14 is an image obtained by photographing the active material behavior in the region D of fig. 12 (photographed after measuring the adhesion force).

Fig. 15 is a graph showing the area ratio occupied by the adhesive measured for each position in comparative example 3.

Fig. 16 is an image obtained by photographing the adhesive behavior in the region E of fig. 15 (photographed after the standard peel test).

Fig. 17 is an image obtained by photographing the active material behavior in the region E of fig. 15 (photographed after measuring the adhesion force).

Fig. 18 shows an image photographing method of adhesive behavior and active material behavior.

[ description of reference numerals ]

100: current collector

200: active material layer

300: scotch Magic tape

1001: electrode active material

2001: adhesive agent

Detailed Description

Hereinafter, the present application will be described in more detail by way of examples and comparative examples, but the scope of the present application is not limited to the following examples.

1. Measuring water contact angle and surface energy

The water contact angle was measured by the chamfer method by dropping 3. Mu.l of droplets at a rate of 3. Mu.l/s using a droplet shape analyzer apparatus (manufacturer: KRUSS, trade name: DSA 100). Water and DM (diiodomethane) were dropped in the same manner, and the surface energy was calculated by the OWRK (Owens-Wendt-Rabel-Kaelble) method.

2. Determination of the average particle size (D50 particle size) of the particulate Binder and electrode active Material

The average particle size (D50 particle size) of the particulate binder and electrode active material was measured using a Marvern MASTERSIZER3000 apparatus according to ISO-13320 standard. At the time of measurement, water was used as a solvent. When a particulate binder or the like is dispersed in a solvent and irradiated with laser light, the laser light is scattered by the binder dispersed in the solvent, and the intensity and directivity values of the scattered laser light vary according to the size of the particles, so that the average diameter can be obtained by analyzing the intensity and directivity values by using Mie theory. By the above analysis, a cumulative chart of the volume-based particle size distribution was obtained by converting into diameters of spheres having the same volume as the dispersed binder, and the particle diameter (median diameter) of 50% of the cumulative chart was designated as the average particle diameter (D50 particle diameter).

Example 1.

Copper foil (Cu foil) having a thickness of 8 μm was used as a current collector, and after the surface energy and water contact angle were adjusted by the following argon (Ar) plasma treatment, it was applied to the manufacture of an electrode.

The copper foil was exposed to a plasma for 6 seconds for argon plasma treatment while being transferred at a speed of about 10 mm/sec by injecting argon (Ar) at a flow rate of 6LPMInto the chamber and oxygen (O) was injected at a flow rate of 0.1LPM ₂ ) Generated by simultaneously applying 170W of power.

After the above-described operation, the surface energy of the current collector surface was measured in the manner described in evaluation example 1 above. As a result of the measurement, the surface energy was 77.7mN/m, the polar property was 50.1mN/m and the dispersion energy was 27.6mN/m. In addition, after the above operation, the water contact angle on the surface of the collector was 20 degrees.

As the slurry, a slurry containing water, SBR (styrene-butadiene rubber) binder, thickener (CMC, carboxymethyl cellulose), and electrode active material (1) (artificial Graphite (GT), average particle diameter (D50 particle diameter): 20 μm) and electrode active material (2) (natural graphite (PAS), average particle diameter (D50 particle diameter): 15 μm) in a weight ratio of 48.5:1:0.5:45:5 (water: SBR: CMC: active material (1): active material (2)) was used.

Here, the water is a solvent having a dipole moment of about 1.84D, and the SBR binder is a solvent having a dipole moment of about 16.9MPa ^1/2 And about the solubility parameter. The solubility parameter of SBR adhesives was the value described in Yanlong Luo et al, 2017. The SBR binder is a granular binder having an average particle diameter (D50 particle diameter, median particle diameter) of about 150 nm.

Subsequently, the slurry having a thickness of about 280 μm was coated on the surface of the current collector treated with argon plasma by a gap coating method, and dried at a temperature of about 75 ℃ for about 10 minutes.

After drying, the slurry layer was rolled with a conventional electrode rolling mill to a final thickness of about 110 μm and a porosity of about 26% to form an active material layer, with a thickness of about 180 μm.

The porosity of the active material layer is a value calculated by a method of comparing the ratio of the actual density to the density after rolling. In addition, when considering the composition of the slurry, the content of SBR binder in the active material layer of the electrode was about 1.94 wt% and the content of the electrode active material was about 97 wt%.

Comparative example 1.

An electrode was manufactured in the same manner as in example 1, except that an active material layer was formed on a copper foil having a thickness of 8 μm, which was not subjected to surface treatment.

As a result of measuring the surface energy of the surface of the copper foil which was not subjected to the surface treatment in the manner described in the above evaluation example 1, the surface energy of the current collector was 71.2mN/m, the polar performance was 26.2mN/m, and the dispersion energy was 45mN/m. In addition, after the above operation, the water contact angle on the surface of the current collector was 30.1 degrees.

Comparative example 2.

An electrode was produced in the same manner as in example 1, except that ethyl TMS (ethyltrimethoxysilane) coating was performed on a copper foil having a thickness of 8 μm.

The ethyl TMS coating is performed by a method in which a coating liquid obtained by dispersing ethyl TMS in ethanol as a solvent at a concentration of about 1 wt% is coated on one side of a copper foil to a thickness of about 10 μm, and the coating is performed using a bar coater. Subsequently, the coating was formed by annealing at a temperature of about 100 ℃ for about 5 minutes, and washing with ethanol, and then drying at a temperature of about 100 ℃ for about 5 minutes.

After the above operation, the surface energy of the ethyl TMS-coated current collector surface was measured in the manner described in evaluation example 1 above. As a result of the measurement, the surface energy of the collector was 29.7mN/m, the polar property was 1.4mN/m, and the dispersion energy was 28.3mN/m. In addition, after the above operation, the water contact angle on the surface of the current collector was 95 degrees.

Comparative example 3.

An electrode was produced in the same manner as in example 1, except that the copper foil having a thickness of 8 μm was subjected to atmospheric pressure plasma treatment.

The copper foil was exposed to a plasma at a flow rate of 450LPM for 2 seconds while being transferred at a speed of about 30 mm/sec to perform an atmospheric pressure plasma treatment, the plasma being a plasma of nitrogen (N) ₂ ) Into the chamber and air was injected at a flow rate of 0.9LPM and generated by applying a voltage of 12 kV.

After the above-described operation, the surface energy of the current collector surface was measured in the manner described in evaluation example 1 above. As a result of the measurement, the surface energy of the collector was 76.8mN/m, the polar property was 44.6mN/m, and the dispersion energy was 32.2mN/m. In addition, after the above operation, the water contact angle on the surface of the collector was 14 degrees.

Test example 1 Standard Peel test

After rolling, the electrode was cut into a size of about 20mm in width and about 100mm in length to obtain a sample. Standard peel tests were performed on the samples. Standard peel tests were performed using 3M Scotch Magic tape cat.810 r.

On the active material layer of the sample, scotch Magic tape cat.810r was adhered by pushing back and forth a roll having a weight of 1kg, a radius of 50mm, and a width of 40mm once. At this time, the Scotch Magic tape was cut to have a width of about 10mm and a length of about 60mm and used, as shown in fig. 3, the Scotch Magic tape and the electrode active material layer were cross-adhered to a length of about 20mm, and the protruding portion was grasped and peeled off. At this time, the peeling rate and the peeling angle were set to a speed of about 20 mm/sec and an angle of about 30 degrees. A new Scotch tape was replaced and used each time the tape was peeled off. The above procedure was repeated until the composition of the active material layer was not present on the surface of the Scotch Magic tape. The presence or absence of the composition of the active material layer was visually observed, and when the color tone was substantially unchanged from that of the unused adhesive tape, it was determined that the composition of the active material layer was not present.

Test example 2 determination of adhesive behavior and occupied area ratio at various locations

For the surface of the current collector sample (width: about 20mm, length: about 100 mm) obtained after the standard peeling test, images of the adhesive behavior at each position were taken using an FE-SEM (field emission scanning electron microscope) device (manufacturer: HITACHI, trade name: S4800).

The image was measured in the same manner as in fig. 18. The image is measured by setting a specific point (a in fig. 18) on the sample surface as a start point. Square areas (squares indicated by blue dotted lines in fig. 18) each having a horizontal and vertical length of about 0.5mm are photographed from the start point toward the right direction so that the respective areas of the sample surface do not overlap. As a result, 40 images (magnification: 500 times) were obtained in total.

Subsequently, for each Image, measurement was performed using Image J software (manufacturer: image J) Trainable Weka Segmentation Plug-in, in which a region having a luminance of 96 or less was set as a region where an adhesive was present, and a region having a luminance of more than 96 was set as a region where an adhesive was not present.

In this method, for each image, the area of the region where the adhesive is present and the area of the region where the adhesive is not present are determined, and the area ratio occupied by the adhesive is derived by the equation of (area of the region where the adhesive is present×100)/(area of the region where the adhesive is present+area of the region where the adhesive is not present).

Thereafter, by setting the distance (position) of the measurement region from the start point as the x-axis and the area ratio occupied by the adhesive as the y-axis, a map of the area ratio occupied by the adhesive at each position is derived.

The maximum and minimum values of the area ratios occupied by the adhesives in the respective figures, and the difference between the maximum and minimum values are shown in table 1 below.

TABLE 1

As a result, it was confirmed that a graph showing the area ratio occupied by the adhesive measured for each position in example 1 was displayed as a waveform chart in fig. 4. At this time, it was confirmed that the wavelength of the waveform chart of fig. 4 was about 12mm, and the difference between the maximum value and the minimum value of the area ratio occupied by the adhesive was 26.2% p, and thus was greater than the wavelengths of comparative examples 1 to 3. Meanwhile, graphs showing the area ratios occupied by the adhesives measured for the respective positions in comparative examples 1 to 3 are shown in fig. 9, 12 and 15, respectively, whereby the wavelength cannot be confirmed.

Test example 3 measurement of adhesion

After rolling, the electrode was cut into a size of about 20mm in width and about 100mm in length to obtain a sample. For this sample, the adhesion force was measured according to a known method for measuring adhesion force of an active material layer. When the adhesion was measured, the peel angle was 90 degrees and the peel rate was about 5 mm/sec. After measurement, the peak stabilized fraction was averaged and defined as adhesion.

For the electrodes of examples and comparative examples 1 to 3, the adhesion measured by the above method is described in table 2 below.

TABLE 2

As a result of confirming the adhesion, it was confirmed that the adhesion between the active material layer and the current collector was changed due to different binder distribution or the like even though the content of SBR binder, the content of electrode active material, and the like in the active material layer were the same. In particular, in the case of example 1 showing the behavior of the adhesive as shown in fig. 4, superior adhesion was exhibited as compared with comparative examples 1 to 3.

Test example 4 confirmation of active Material behavior at various sites

For the surface of the current collector sample (width: about 20mm, length: about 100 mm) obtained after the measurement of the adhesion force, images of the adhesive behavior at each position were taken using a confocal laser spectrum microscope (manufacturer: keyenece, product name: VK-X200).

The image was measured in the same manner as in fig. 18. The image is measured by setting a specific point (a in fig. 18) on the sample surface as a start point. Square areas (squares indicated by blue dotted lines in fig. 18) each having a horizontal and vertical length of about 0.5mm are photographed from the start point toward the right direction so that the respective areas of the sample surface do not overlap. As a result, 40 images (magnification: 200 times) were obtained in total.

An active material behavior image photographed by example 1 is shown in fig. 7 (an example of a peak portion in a waveform chart) and fig. 8 (an example of a trough portion in a waveform chart). Fig. 11, 14 and 17 show examples of active material behavior images captured in comparative examples 1 to 3, respectively.

Claims

1. An electrode, comprising:

a current collector; and

an active material layer on one or both sides of the current collector,

wherein the active material layer contains an electrode active material and a binder, and

wherein the proportion of the area occupied by the adhesive, i.e. the proportion observed along one direction on the current collector, is shown in a waveform diagram after the following standard peel test:

standard peel test: the process of adhering the Scotch Magic tape cat.810r to the active material layer and then peeling the Scotch Magic tape cat.810r from the active material layer was repeated until no component of the active material layer was observed on the Scotch Magic tape cat.810 r.

2. The electrode according to claim 1, wherein a proportion of an area occupied by the adhesive is 55% or more at a peak portion of the waveform diagram.

3. The electrode according to claim 1 or 2, wherein the adhesive occupies 50% or less of the area at the trough portion of the waveform pattern.

4. An electrode according to any one of claims 1 to 3, wherein the wavelength of the waveform is from 3nm to 25mm.

5. The electrode according to any one of claims 1 to 4, wherein a difference between a maximum value of a ratio of an area occupied by the binder in the waveform diagram and a minimum value of a ratio of an area occupied by the binder in the waveform diagram is 9%p or more.

6. The electrode according to any one of claims 1 to 5, wherein after the standard peeling test, there is a region on the current collector that satisfies the following equation 1 and the binder occupies an area of 60% or more:

[ equation 1]

18≤A/W

Where A is the ratio of the area occupied by the binder in this region (unit:%) and W is the content of binder in the active material layer (wt%).

7. The electrode according to any one of claims 1 to 6, wherein the binder is a particulate binder.

8. The electrode according to any one of claims 1 to 7, wherein both the electrode active material and the binder are in particle form, and wherein the ratio (D1/D2) of the average particle diameter (D1) of the electrode active material to the average particle diameter (D2) of the binder is 10 to 1000.

9. The electrode according to any one of claims 1 to 8, wherein the binder is a particulate binder having an average particle diameter in the range of 50nm to 500 nm.

10. The electrode according to any one of claims 1 to 9, wherein the electrode active material is a particulate material having an average particle diameter in a range of 1 μm to 100 μm.

11. The electrode according to any one of claims 1 to 10, wherein a proportion of the binder in the electrode active material layer is 0.5 to 10 wt%.

12. The electrode according to any one of claims 1 to 11, wherein the content of the electrode active material is 1000 parts by weight to 10000 parts by weight with respect to 100 parts by weight of the binder.

13. A method of manufacturing an electrode as claimed in any one of claims 1 to 12, comprising:

a slurry layer is formed on the current collector,

wherein the slurry contains a solvent and has a solubility parameter of 10MPa ^1/2 To 30MPa ^1/2 The binder and the electrode active material in the range, and

wherein the current collector surface on which the slurry layer is formed has a surface energy of 40mN/m or more.

14. An electrochemical element comprising:

the electrode of any one of claims 1 to 12 as a negative electrode or a positive electrode.

15. A secondary battery, comprising: