KR20220058196A - Method for estimating adhesion strength of electrode - Google Patents

Abstract

The present invention relates to a method for predicting adhesion of an electrode for an electrode substrate comprising: a step of collecting measured value data by measuring a binder ratio in slurry when drying coated electrode slurry, a volume fraction of a solvent in the slurry, an electrode drying speed of a dried initial section, and the adhesion of the electrode; a step of deriving correlation among the adhesion of the electrode, the binder ratio, the volume fraction of the solvent, and the electrode drying speed of the dried initial section through linear regression analysis from the measured value data; and a step of predicting the adhesion of the electrode depending on the binder ratio, the volume fraction of the solvent, and the electrode drying speed of the dried initial section. The present invention can predict the adhesion of a real electrode.

Description

Electrode adhesion prediction method {METHOD FOR ESTIMATING ADHESION STRENGTH OF ELECTRODE}

The present invention relates to a method for predicting adhesion of an electrode, and more particularly, a method for predicting adhesion of an electrode using the correlation between the binder ratio during electrode drying, the volume fraction of the solvent, and the electrode drying rate and the electrode adhesion force in the initial drying section is about

Recently, rechargeable batteries capable of charging and discharging have been widely used as energy sources for wireless mobile devices. In addition, the secondary battery is attracting attention as an energy source for electric vehicles, hybrid electric vehicles, etc., which have been proposed as a way to solve air pollution of conventional gasoline vehicles and diesel vehicles using fossil fuels. Accordingly, the types of applications using secondary batteries are diversifying due to the advantages of secondary batteries, and it is expected that secondary batteries will be applied to more fields and products in the future than now.

These secondary batteries are sometimes classified into lithium ion batteries, lithium ion polymer batteries, lithium polymer batteries, etc. depending on the composition of the electrode and electrolyte. is increasing In general, secondary batteries, depending on the shape of the battery case, a cylindrical battery and a prismatic battery in which the electrode assembly is built in a cylindrical or prismatic metal can, and a pouch-type battery in which the electrode assembly is built in a pouch-type case of an aluminum laminate sheet The electrode assembly built into the battery case consists of a positive electrode, a negative electrode, and a separator structure interposed between the positive electrode and the negative electrode, and is a power generating element capable of charging and discharging. It is classified into a jelly-roll type wound with a separator interposed therebetween, and a stack type in which a plurality of positive and negative electrodes of a predetermined size are sequentially stacked with a separator interposed therebetween.

The positive electrode and the negative electrode are formed by applying a positive electrode slurry containing a positive electrode active material and a negative electrode slurry containing a negative electrode active material to a positive electrode current collector and a negative electrode current collector, respectively to form a positive electrode active material layer and a negative electrode active material layer, followed by drying and rolling them do.

1 is a simplified schematic diagram of a heat drying apparatus for drying an electrode substrate.

As shown in FIG. 1, while the current collector sheet 2a is unwound from the unwinding roller 1a and wound on the winding roller 1b, the electrode slurry is applied to the surface of the current collector sheet 2a through a coater 7 The coated electrode substrate 2 is passed through the electrode oven 4 by the roller 6 and dried by heating, and then wound around the winding roller 1b. The electrode oven (4) has one or more drying chambers (4a, 4b, 4c), each of which is configured such that the temperature is controlled by heat generated by the heater (5).

On the other hand, the bonding between the electrode part and the current collector (electrode base part) is an important factor in the quality of the electrode, and if this bonding is deteriorated, the quality deteriorates due to the separation of the electrode and the base part during battery use. The adhesion or adhesion of the electrode to the electrode substrate is greatly affected by the binder migration phenomenon during electrode drying. The electrode consists of an active material, a conductive material with a much smaller diameter, and a binder. In the case of an electrode drying system, the phenomenon experienced during the drying process is different depending on the size of the internal material. In general thin film particle coating, solvent evaporation, diffusion, and sedimentation occur simultaneously. Evaporation is a phenomenon in which particles are moved by a solvent flux, diffusion is a phenomenon that occurs due to a particle concentration gradient and Brownian motion inside the film, and finally, a phenomenon of settling simultaneously with drying due to the weight of particles, etc. occurs. Evaporation, diffusion, etc. occur in a drying system of a porous medium such as an electrode, and a binder migration phenomenon occurs in which the binder moves to the upper layer of the electrode at the same time as the solvent evaporates, which is one of the causes of lowering of adhesion.

However, conventionally, only a method of predicting electrode performance by comparing and analyzing the coverage and adhesive force of the electrode active material by the binder is known (see Patent Document 1 below). Considering the complicated mechanism during electrode drying, the amount of binder, There has been little access to specifically how evaporative flux and the like affect the adhesion of electrodes.

As described above, the adhesion of the electrode after drying the electrode varies greatly depending on how the electrode drying process is performed.

Therefore, with reference to the electrode drying mechanism, it is desired to develop a technology capable of predicting the adhesion of the electrode in consideration of variables during electrode drying, such as the influence of a binder or an evaporation flux.

Republic of Korea Patent Publication No. 10-2020-0027693

The present invention has been devised to solve the above problems, and it is possible to predict the actual electrode adhesion by understanding the correlation between the binder ratio, the volume fraction of the solvent, and the electrode drying speed and the adhesion of the electrode during drying of the electrode. An object of the present invention is to provide a method for predicting adhesion of

The electrode adhesion prediction method according to the present invention measures the binder ratio in the slurry when drying the electrode slurry coated on the current collector, the volume fraction of the solvent in the slurry, the electrode drying rate in the initial drying section, and the adhesion of the electrode. collecting measurement data; deriving a correlation between the adhesive force of the electrode, the binder ratio, the volume fraction of the solvent, and the electrode drying rate in the initial drying section through linear regression analysis from the measured value data; and predicting the adhesion of the electrode according to the binder ratio, the volume fraction of the solvent, and the electrode drying rate in the initial drying section from the correlation.

As an example, before deriving the correlation, the adhesion of the electrode and the volume of the solvent based on the relationship between the Pecle number (Pe), which is a dimensionless number, and the adhesion force of the electrode as a variable related to the movement of the binder in the drying process The method may further include deriving a relationship between the fraction and the electrode drying rate.

The Pecle number (Pe) and the adhesive force of the electrode have the relationship of Equations 1 and 2 below.

[식 1]

[Equation 1]

[식 2]

[Equation 2]

(Where L = the characteristic length, the thickness of the electrode,

Do = diffusion coefficient

= 용매의 부피 분율

= volume fraction of solvent

Vo = electrode drying speed in the initial period of drying)

As a specific example, the following Equation 3 is derived through linear regression analysis of the relationship between Equations 1 and 2, the binder ratio, the volume fraction of the solvent, and the measurement data related to the electrode drying rate in the initial drying section, the following Equation 3 is derived, 3, the adhesion of the electrode can be predicted by calculating the adhesion of the electrode according to the binder ratio, the volume fraction of the solvent, and the electrode drying rate.

[식 3]

[Equation 3]

(where TS = predicted adhesion between the electrode active material layer and the current collector,

BR = proportion of binder in the electrode slurry,

= 용매의 부피 분율,

= volume fraction of solvent,

= 전극 건초 초기 구간 건조속도,

= Drying speed in the initial section of the electrode hay,

a and b are parameters as constants)

As an example, a and b may be calculated by a least squares method.

In addition, the measurement of the adhesive force of the electrode may be performed by performing a 90° peel test.

The drying rate of the electrode in the initial drying section is the drying rate in the constant rate drying section.

In addition, preferably, the drying rate of the electrode in the initial drying section is the drying rate when 20 to 40% drying is in progress.

The electrode drying rate in the initial drying section may be the volume of the electrode dried per second, or it may be the electrode thickness reduction rate by drying (mm/sec).

In addition, as an example, measured value data may be collected by changing at least one of a hot air temperature and an air volume input during drying of the electrode to change the electrode drying speed in the initial drying section.

According to the present invention, it is possible to predict the actual adhesion of the electrode by grasping the correlation between the binder ratio, the volume fraction of the solvent, and the electrode drying rate and the adhesion of the electrode during drying of the electrode.

In addition, it is possible to determine the operating range of the electrode manufacturing process to obtain the desired actual adhesion in the determined electrode slurry properties based on the predicted adhesion value.

1 is a simplified schematic diagram of a heat drying apparatus for drying an electrode substrate.
2 is a flowchart illustrating a sequence of a method for predicting adhesion of an electrode according to an embodiment of the present invention.
3 is a flowchart illustrating a sequence of a method for predicting adhesion of an electrode according to another embodiment of the present invention.
4 is a graph showing the actual adhesive force according to the measured value data measured in the embodiment of the present invention.
5 is a graph showing the relationship between the adhesion force calculated by the equation derived from the linear regression analysis of the embodiment of the present invention and the actually measured adhesion force.

Hereinafter, the present invention will be described in detail. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined in

In the present application, terms such as "comprise" or "have" are intended to designate that a feature, number, step, operation, component, part, or a combination thereof described in the specification exists, but one or more other features It is to be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof. Also, when a part of a layer, film, region, plate, etc. is said to be “on” another part, it includes not only the case where the other part is “directly on” but also the case where there is another part in between. Conversely, when a part of a layer, film, region, plate, etc. is said to be “under” another part, it includes not only cases where it is “directly under” another part, but also cases where another part is in between. In addition, in the present application, “on” may include the case of being disposed not only on the upper part but also on the lower part.

Hereinafter, the present invention will be described in detail.

The electrode adhesion prediction method according to the present invention measures the binder ratio in the slurry when drying the electrode slurry coated on the current collector, the volume fraction of the solvent in the slurry, the electrode drying rate in the initial drying section, and the adhesion of the electrode. collecting measurement data; deriving a correlation between the adhesive force of the electrode, the binder ratio, the volume fraction of the solvent, and the electrode drying rate in the initial drying section through linear regression analysis from the measured value data; and predicting the adhesion of the electrode according to the binder ratio, the volume fraction of the solvent, and the electrode drying rate in the initial drying section from the correlation.

The present invention deviates from the one-dimensional approach of increasing the binder content that affects the adhesion of the electrode or measuring the binder ratio in the electrode slurry in order to improve or predict the electrode adhesion, the electrode drying rate and the solvent when drying the electrode slurry. This is to predict the adhesion of the electrode by considering the volume fraction. The reason that all three variables of the binder ratio, the electrode drying rate, and the volume fraction of the solvent are considered when drying the electrode is that the drying system of the electrode slurry is a porous media drying system. As described above, in such a drying system, in addition to the binder content, the effect of the evaporation flux of the solvent, that is, the electrode drying rate and the volume fraction of the solvent should be evaluated together.

Therefore, the present invention is to predict the electrode adhesion by comprehensively considering the effects of the above three variables in consideration of the mechanism of the electrode drying system as a porous medium drying system.

Hereinafter, each step of the electrode adhesion prediction method according to the present invention will be described in detail.

2 is a flowchart illustrating a sequence of a method for predicting adhesion of an electrode according to an embodiment of the present invention.

<Collection of measured value data>

First, in order to understand the correlation between the electrode adhesion force and the three variables described later, the binder ratio in the slurry when drying the electrode slurry, the volume fraction of the solvent, and the electrode drying rate in the initial drying section were measured and the measured values Collect data. Also, measure the actual adhesion of the electrode after drying.

To this end, a plurality of electrodes may be prepared and data on the binder ratio of the electrode, the volume fraction of the solvent, and the electrode drying rate in the initial drying period may be collected. Specifically, the data may be obtained by manufacturing a plurality of electrodes by varying any one or more of the binder ratio, the volume fraction of the solvent, and the electrode drying speed in the initial drying section, and measuring the actual adhesion of the electrodes. That is, when n electrodes are manufactured, n sets of measured values are stored in the data.

The electrode may be manufactured by applying an electrode slurry including an electrode active material and a solvent on a current collector to form an electrode active material layer.

The current collector may be a positive electrode current collector or a negative electrode current collector, and the electrode active material may be a positive electrode active material or a negative electrode active material. In addition, the electrode slurry may further include a conductive material and a binder in addition to the electrode active material.

In the present invention, the positive electrode current collector is generally made to have a thickness of 3 to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Carbon, nickel, titanium, silver, etc. surface-treated on the surface of the can be used. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface thereof, and various forms such as a film, sheet, foil, net, porous body, foam body, and non-woven body are possible.

In the case of a sheet for a negative electrode current collector, it is generally made to a thickness of 3 to 500 μm. Such a negative current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Carbon, nickel, titanium, a surface-treated material such as silver, aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven body, and the like.

In the present invention, the positive active material is a material capable of causing an electrochemical reaction, as a lithium transition metal oxide, containing two or more transition metals, for example, lithium cobalt oxide (LiCoO ₂ ) substituted with one or more transition metals. ), layered compounds such as lithium nickel oxide (LiNiO ₂ ); lithium manganese oxide substituted with one or more transition metals; Formula LiNi _1-y M _y O ₂ (wherein M = Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga, including at least one of the above elements, 0.01≤y≤0.7) Lithium nickel-based oxide represented by; Li _1+z Ni _1/3 Co _1/3 Mn _1/3 O ₂ , Li _1+z Ni _0.4 Mn _0.4 Co _0.2 O ₂ , etc. Li _1+z Ni _b Mn _c Co _{1-(b+c+d )} M _d O _(2-e) A _e (where -0.5≤z≤0.5, 0.1≤b≤0.8, 0.1≤c≤0.8, 0≤d≤0.2, 0≤e≤0.2, b+c+d <1, M = Al, Mg, Cr, Ti, Si or Y, and A = F, P or Cl) a lithium nickel cobalt manganese composite oxide; Formula Li _1+x M _1-y M' _y PO _4-z X _z where M = transition metal, preferably Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S, or N, and -0.5≤x≤+0.5, 0≤y≤0.5, 0≤z≤0.1 olivine-based lithium metal phosphate represented by), but is not limited thereto.

The negative electrode active material includes, for example, carbon such as non-graphitizable carbon and graphitic carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _1-x Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : metal composite oxides such as Al, B, P, Si, elements of Groups 1, 2, and 3 of the periodic table, halogen; 0<x≤1;1≤y≤3;1≤z≤8); lithium metal; lithium alloy; silicon-based alloys; tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , metal oxides such as Bi ₂ O ₅ ; conductive polymers such as polyacetylene; A Li-Co-Ni-based material or the like can be used.

The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive active material. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, poly propylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, various copolymers, and the like.

Meanwhile, such an electrode slurry may be prepared by dissolving an electrode active material, a conductive material, a binder, and the like in a solvent. The solvent is not particularly limited in its kind as long as it can disperse the electrode active material and the like, and either an aqueous solvent or a non-aqueous solvent may be used. For example, as the solvent, the solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP) ), acetone, or water, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is not particularly limited, as long as it can be adjusted so that the slurry has an appropriate viscosity in consideration of the application thickness of the slurry, production yield, workability, and the like.

At this time, the electrode may be manufactured by varying any one or more of the binder ratio in the electrode, the volume fraction of the solvent, and the electrode drying rate in the initial drying section.

The binder ratio in the electrode may be the same or different depending on the type of electrode to be manufactured.

The volume fraction of the solvent in the slurry can be defined as in Equation 4 below.

[Equation 4]

The solute refers to the solid content in the slurry, that is, the solid content such as an active material, a binder, a thickener, and a conductive material. The volume fraction of the solvent is a factor influencing the solvent evaporation flux.

The drying rate of the electrode measures the drying rate in the initial section of drying the slurry.

Electrode drying consists of a constant-rate drying section in which the drying rate is almost constant until the solvent content is reduced to some extent at the beginning of drying, and a decreasing-rate drying section in which the drying rate decreases over time as surface moisture evaporates and internal diffusion occurs after the constant-rate drying section. rough Evaporation of the solvent and movement of the evaporative flux mainly occur in the constant-rate drying section. Accordingly, the binder migration phenomenon described above also mostly occurs in the constant-rate drying section. Since a significant change in behavior due to binder movement or solvent evaporation is not captured in the drying section at the reduced rate, the drying rate measures the drying rate in the initial section of drying the slurry. Among them, by measuring the drying speed in the constant constant drying section, it is provided for predicting the adhesive force. Since the constant rate drying section is slightly different depending on the electrode type or composition, measuring the drying rate when it is dried to a certain extent may be a problem, but the drying rate at the initial stage of drying when about 20-40% drying has progressed see. Preferably, if the drying rate at 30% drying is measured, it is estimated that the drying rate most closely related to the solvent evaporation or binder migration described above can be obtained.

The drying rate of the electrode can be obtained by measuring the volume of the electrode dried per second (m3/sec) or by measuring the electrode thickness decrease (mm/sec) due to drying.

In addition, the drying speed of the electrode can be changed by adjusting the wind speed or direction of the hot air input during the electrode drying, or both. By adjusting these process parameters, several measurements of the electrode drying rate can be obtained.

The adhesion of the electrode can be measured by a so-called 90° peel test. Specifically, the 90° peel test is performed by cutting an electrode to a predetermined width and length to prepare a sample, attaching a tape to the sample, and pulling the tape at a rate of 100 mm/min and a peeling angle of 90° while pulling the tape The adhesion force of the electrode can be obtained by measuring the force (gf/20mm) until it detaches from the sample.

<Deduction of correlation between electrode adhesion and binder ratio, solvent volume fraction, and electrode drying speed>

After the data are collected, the correlation between the binder ratio, the volume fraction of the solvent, the electrode drying speed and the adhesion of the electrode is derived based on the data. Such a correlation can be derived through linear regression analysis.

For example, since there are three types of factors determining electrode adhesion, a correlation can be derived through a multiple regression model as shown in Equation 5 below.

[Equation 5]

및 Vo 는 각각 바인더 비율, 용매의 부피 분율 및 건조 초기 전극의 건조속도의 인자들을 나타낸다. 또한 a₁ 내지 a₃는 각 인자들에 대한 매개변수를 의미한다.)(In Equation 1, TS means the predicted adhesion of the electrode, BR,

and Vo represent factors of the binder ratio, the volume fraction of the solvent, and the drying rate of the electrode in the initial stage of drying, respectively. Also, a ₁ to a ₃ mean parameters for each factor.)

Also, the parameters a ₁ , a ₂ , and a ₃ may be calculated by the least squares method.

Specifically, from the data of the measured values, the adhesion of the electrode, the binder ratio, the volume fraction of the solvent, and the adhesion of the electrode according to the drying rate of the electrode at the initial stage of drying are shown in separate graphs, and the adhesion of the electrode and each factor (binder, ratio, the volume fraction of the solvent, and the drying rate of the electrode in the initial stage of drying) can be visually checked.

및 Vo 는 선형 스케일로 표현될 수 있다. 반면에 종속변수가 독립변수에 대해 선형적으로 비례하지 않는 경우 지수 스케일 또는 로그 스케일로 표현될 수 있다.At this time, if the dependent variable (electrode adhesion) has a shape that is linearly proportional to the independent variable (each factor), BR,

and Vo may be expressed on a linear scale. On the other hand, if the dependent variable is not linearly proportional to the independent variable, it can be expressed on an exponential scale or logarithmic scale.

Deriving the relational expression between the three factors and the electrode adhesion by linear regression analysis and the least squares method is statistically known, and thus detailed description is not provided herein. What is important is that, in addition to the binder ratio, it is possible to predict the adhesion of the electrode by deriving a correlation that considers the volume fraction of the solvent and the variable of the electrode drying rate in the initial drying section as well.

3 is a flowchart illustrating a procedure of a method for predicting adhesion of an electrode according to another embodiment of the present invention.

Referring to FIG. 3 , in the present embodiment, based on the relationship between the Pecle number (Pe), which is a dimensionless number, as a variable related to the movement of the binder in the drying process, and the adhesive force of the electrode before the derivation of the correlation, The method further includes deriving a relationship between the adhesive force, the volume fraction of the solvent, and the electrode drying rate.

In the present invention, the reason for introducing the concept of a dimensionless number, the Pecle number, is to more intuitively predict the adhesion of the electrode by reducing the number of variables affecting the adhesion of the electrode. That is, if the number of variables is reduced, the electrode adhesion can be obtained through a simpler linear regression analysis without performing multiple regression analysis. In this case, if only the parameter values are obtained by the least squares method, the correlation for predicting the adhesion force of the electrode can be obtained intuitively.

The Pecle number (Pe) represents the effect of convection and conduction in hydrodynamics, and is expressed by Equation 6-1 below.

[식 6-1]

[Equation 6-1]

Here, L is the characteristic length, U is the flow rate, and Dff is the effective diffusion coefficient.

As shown in the above equation, the evaporation rate increases as the convection flux increases, and it is difficult to accurately calculate the diffusion flux in the current electrode drying system. In a system in which micron particles are piled up, such as an electrode drying system, the effective diffusion coefficient is expressed as Equation 6-2 below.

[식 6-2]

[Equation 6-2]

는 용매의 부피 분율이고, τ는 굴곡도(torutuosity)이다.where Do is the diffusion coefficient,

is the volume fraction of the solvent and τ is the torutuosity.

^-0.5 로 표시되므로 식 6-2는 하기 식 6-3이 된다.In a system where the particles are spherical, τ is

Since it is expressed as ^-0.5 , Equation 6-2 becomes Equation 6-3 below.

[식 6-3]

[Equation 6-3]

By substituting Equation 6-3 into Equation 6-1, the following Equation 6-4 can be obtained.

[식 6-4]

[Equation 6-4]

In the electrode drying system, the characteristic distance L is the electrode thickness, and the flow rate U can be regarded as the electrode drying speed Vo in the initial drying section in which the evaporation flux is most active, so Equation 6-4 becomes Equation 1 below.

[식 1]

[Equation 1]

In addition, as the electrode drying rate Vo in the initial drying period increases, the adhesion of the electrode decreases. As a result, the relationship between the adhesion TS of the electrode and the Pecle number (Pe) satisfies Equation 2 below.

[식 2]

[Equation 2]

That is, in the electrode drying system, the adhesion of the electrode is inversely proportional to the Pecle number.

On the other hand, when the binder content of the slurry in the electrode increases, the adhesion of the electrode naturally increases. Therefore, the binder ratio BR in the electrode, the Pecle number, and the electrode adhesion force satisfy Equations 2-1 and 2-2 below.

[식 2-1]

[Equation 2-1]

[식 2-2]

[Equation 2-2]

Here, the diffusion coefficient Do is a constant determined depending on the electrode, and the electrode thickness L, which is the characteristic length, is also a specific value determined in the battery manufacturing process conditions. Accordingly, when the constants Do and L are excluded from Equation 2-2, the following Equation 2-3 is obtained.

[식 2-3]

[Equation 2-3]

및 전극 건조 초기 구간의 전극 건조속도 Vo의 특정 함수에 비례하는 것을 알 수 있다.From Equation 2-3, the electrode adhesion is the binder ratio BR, the volume fraction of the solvent

And it can be seen that it is proportional to a specific function of the electrode drying rate Vo in the initial period of electrode drying.

Based on the above formula, multiple sets of measured value data of the electrode adhesion force, binder ratio, solvent volume fraction, and initial electrode drying speed were substituted, and the following Equation 3 was obtained through linear regression analysis.

[식 3]

[Equation 3]

a and b are parameters and can be obtained by the least squares method as described above.

The value in parentheses of Equation 3 can be obtained by the binder ratio, the volume fraction of the solvent, and the electrode drying speed data at the initial stage of drying. do. Therefore, by deriving a correlation for calculating the electrode adhesion force based on the relationship between the Peccle number and the electrode binder ratio, the electrode adhesion force is expressed in the form of a linear function to facilitate the electrode adhesion based on the measured value data in the electrode drying system. became predictable.

Hereinafter, examples will be given to help the understanding of the present invention be described in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the following examples. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example

Graphite functioning as an anode active material, carbon black (trade name: SUPER-C65) as a conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) (trade name BM-L302) as a binder are water-based with the composition shown in Table 1 An electrode slurry was prepared by containing it in a solvent.

This slurry was coated on both sides of an aluminum foil having a thickness of 8 μm and dried to prepare a negative electrode.

electrode model active material composition ratio
(weight%) conductive material composition ratio
(weight%) CMC
(thickener) composition ratio
(weight%) bookbinder composition ratio
(weight%) Electrode 1 Synthetic Graphite
+Natural Graphite

97.1
SUPER-C65

One

BG-L01

One

BM-L302

0.9 Electrode 2 Graphite 96.6 SUPER-C65 1.0 DAICEL2200 1.2 BM-L302 1.2 Electrode 3 Natural
Graphite 94.5 SUPER-C65 1.5 DAICEL2200 2.0 BM-L302 2.0

For the electrodes prepared in this way, the electrode drying rate and the volume fraction of the solvent in the initial drying section were measured, and the actual adhesion of the electrode after drying was measured.

The drying rate of the electrode was measured by the volume of the electrode dried per second (eg, 10 ^-3 m 3 /sec) in the initial drying section.

As for the volume fraction of the solvent, the volume fraction of the solvent at the initial stage of drying was measured according to Equation 4, and the range was somewhat different depending on the electrode, but it was confirmed that it was in the range of 0.64 to 0.73 in this example.

The adhesive force of the electrode is measured by the following peel test. That is, after cutting the electrode to 10×250mm, leave about 50mm on one end of the electrode, and attach 200mm of the other end to the support using double-sided tape, and then use a roller of a predetermined weight to apply the electrode double-sided tape with a certain force. attach with Then, pull one end not attached to the tape to separate the electrode and the tape by about 10 mm, and then fix it on a universal testing machine (UTM). After fixing the opposite end to the floor and fixing the one end to a jig for a tensile test, the adhesive force (gf/20mm) of the electrode is measured by measuring the tensile strength while separating the electrode by applying a certain force.

Table 2 shows the measured values of the binder ratio BR for each of the samples of the electrodes 1, 2, and 3, the electrode drying rate Vo in the initial drying section, and the actual electrode adhesion TS.

TS(gf/20mm) v ₀ BR Electrode1 sample 1 27.98 103 0.9 sample 2 18.09 118 0.9 sample 3 13.12 122 0.9 sample 4 22.66 118 0.9 sample 5 13.64 122 0.9 Electrode2 sample 6 36.16 145 1.2 sample 7 23.39 153 1.2 Electrode3 sample 8 69.82 134 2 sample 9 55.08 131 2 sample 10 64.40 128 2 sample 11 48.40 157 2 sample 12 36.88 191 2 sample 13 26.25 198 2

Based on the measured value data of Table 2 and the value of the volume fraction of the solvent, the adhesive force TS of the actual electrode is graphed as shown in FIG. 4 .

를 지칭한다.In FIG. 4, the 'A' value of the X-axis is the right side of Equation 3 above.

refers to

That is, FIG. 4 shows the relationship with the actual measured value of the dependent variable TS using 'A' as the independent variable.

= a + b A의 형태가 된다.As shown in FIG. 4 , 'A' and the actual measured value TS are arranged with a certain tendency (proportional relationship of the linear function). If the function of TS is obtained through linear regression analysis of this graph,

= a + b A.

As a result of linear regression analysis, it was found that a was -33.71 and b was 14.64 (note that the unit of TS is 10 times or more compared to the order of 'A').

In FIG. 4, samples 1 to 5 of electrode 1 are shown as triangles. The adhesive strengths of samples 3 and 5 were very close to 13,12 and 13.64, and are shown in the graph in the form of overlapping triangles.

The a and b may be changed when the type and composition of the electrode are different. Importantly, even if the electrode or composition is changed, the adhesion of the electrode has the tendency of Equation 3 above.

From the above embodiment, it can be seen that when the drying speed of the electrode in the initial drying period is increased, the adhesion of the electrode is generally decreased. In addition, as the binder ratio increases, the adhesion of the electrode increases. In Table 2, the case where the electrode adhesion strength does not decrease even when the electrode evaporation rate is decreased in the same composition is understood to be due to the effect of the volume fraction of the solvent. In addition, the reason that the electrodes 1, 2, and 3 have different adhesive strengths in Table 2 is also due to the fact that the composition of the electrodes is different and the volume fraction of the solvent varies depending on the electrodes.

Experimental example

= -33.71 + 14.64 A( 여기서 A=

)의 상관 관계식으로 계산한 계산값을 하나의 그래프에 나타내어 도 5로 하였다.In order to find out whether the adhesive force of the real electrode can be predicted by the relationship of Equation 1 obtained by the linear regression analysis, the measured value of the real electrode and the formula

= -33.71 + 14.64 A (where A=

), the calculated value calculated by the correlation formula is shown in one graph and is shown in FIG. 5 .

As shown in FIG. 5 , the measured values TS exhibited a tendency to generally agree with respect to the straight line of the calculated values TS. The standard deviation of the difference between the calculated values and the measured values was 0.9219, indicating that the value of the actual electrode adhesion force could be easily estimated from the calculated values.

Therefore, as shown in FIG. 5 , the calculated value and the measured value of electrode adhesion showed similar values, and it was confirmed that the correlation according to the calculated value and the correlation according to the actual measured value were consistent.

Therefore, according to the present invention, the value of the actual adhesive force can be predicted by calculating the electrode adhesive force in the electrode drying process using the specific correlation. In addition, it is possible to determine the operating range of the electrode manufacturing process to obtain a desired adhesion in the specified slurry properties. For example, by changing the wind direction or wind speed of the hot air during drying and adjusting the electrode drying speed accordingly, the electrode adhesion can be adjusted.

The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Accordingly, the drawings disclosed in the present invention are for explanation rather than limiting the technical spirit of the present invention, and the scope of the technical spirit of the present invention is not limited by these drawings. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (11)

collecting measured value data by measuring the binder ratio in the slurry, the volume fraction of the solvent in the slurry, the electrode drying rate in the initial drying section, and the adhesion of the electrode when drying the electrode slurry coated on the current collector;
deriving a correlation between the adhesive force of the electrode, the binder ratio, the volume fraction of the solvent in the slurry, and the electrode drying rate in the initial drying section through linear regression analysis from the measured value data; and
The method of predicting adhesion of an electrode comprising the step of estimating the adhesion of the electrode according to the binder ratio, the volume fraction of the solvent, and the electrode drying rate in the initial drying section from the correlation.
The method of claim 1,
Before deriving the correlation, based on the relationship between the dimensionless number Pecle number (Pe) as a variable related to the movement of the binder in the drying process and the adhesion force of the electrode, the adhesion of the electrode, the volume fraction of the solvent, and the electrode drying rate Adhesion prediction method of the electrode further comprising the step of deriving a relationship of.
3. The method of claim 2,
The Pecle number (Pe) and the adhesive force of the electrode have a relationship of Equations 1 and 2 below.

[Equation 1]

[Equation 2]
(Where L = characteristic length, the thickness of the electrode,
Do = diffusion coefficient

= volume fraction of solvent in the slurry
Vo = electrode drying speed in the initial period of drying)
4. The method of claim 3,
Through the linear regression analysis of the relationship between Equations 1 and 2, the binder ratio, the volume fraction of the solvent, and the measurement data related to the electrode drying rate in the initial drying section, the following Equation 3 is derived, and the A method for predicting electrode adhesion by calculating the adhesion force of the electrode according to the binder ratio, the volume fraction of the solvent, and the electrode drying rate.

[Equation 3]
(where TS = predicted adhesion between the electrode active material layer and the current collector,
BR = proportion of binder in the electrode slurry,

= volume fraction of solvent,

= Drying speed in the initial section of the electrode hay,
a and b are parameters as constants)
5. The method of claim 4,
Wherein a and b are the method of predicting the adhesion force of the electrode calculated by the least-squares method.
The method of claim 1,
The measurement of the adhesive force of the electrode is a method of predicting the adhesive force of the electrode to measure the adhesive force of the electrode by performing a 90 ° peel test.
The method of claim 1,
The electrode drying rate in the initial drying section is a drying rate in the constant-rate drying section.
8. The method of claim 7,
The electrode drying rate in the initial drying section is a drying rate when 20 to 40% drying is in progress.
The method of claim 1,
The electrode drying rate in the initial drying section is the electrode's adhesion force prediction method, which is the volume of the electrode dried per second.
The method of claim 1,
The electrode drying rate in the initial drying section is the electrode thickness reduction rate (mm/sec) by drying.
The method of claim 1,
An electrode adhesion prediction method for collecting measured value data by adjusting at least one of a hot air temperature and an air volume input during drying of the electrode to change the electrode drying speed in the initial drying section.

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