KR20170112106A - Method for preparing lithium secondary battery - Google Patents

Abstract

The present invention provides a method of visually measuring the degree of impregnation of an electrolyte with respect to an electrode active material, and based on the results obtained by this method, an optimal amount of the electrolyte solution is set and reflected in the production process, And a manufacturing method of a lithium secondary battery capable of improving performance.

Description

METHOD FOR PREPARING LITHIUM SECONDARY BATTERY [0002]

The present invention relates to a method for producing a lithium secondary battery. Specifically, it is possible to measure the degree of impregnation of an electrolyte with respect to an electrode active material, which is a raw material, before preparation of an electrode. By setting optimal electrolyte impregnation conditions based on the measurement results, To a method of manufacturing a lithium secondary battery capable of improving the productivity and performance of the secondary battery.

In recent years, in the field of electrochemical devices, over time, consumers are demanding devices with larger amounts of energy.

In order to produce such an energy-dense device, it is necessary to increase the amount of loading of the electrode, that is, the thickness of the active material layer applied to the current collector of the electrode, while decreasing the volume and weight of other other components.

In addition, in order to prevent an increase in the volume of the device due to an increase in the thickness of the electrode, it is necessary to reduce the number of windings of the electrode assembly stack or the electrode assembly roll, Height is required.

However, when the thickness of the electrode is increased or the density is increased, various problems occur.

One of the biggest problems is the impregnation or wetting of the electrolyte due to the reduction of the porosity of the electrode due to the high density of the electrode.

Generally, the electrolytic solution is hydrophilic compared to the hydrophobic electrode active material components, and the affinity with the electrode active material component is not high. In addition, since the porosity of the electrode due to the high density of the electrodes and the movement path of the electrolyte due to the volume increase of the electrode active material layer are prolonged, penetration of the electrolyte is not easy and sufficient wetting characteristics are difficult to achieve. If the electrolyte can not sufficiently penetrate into the electrode, the mobility of the ions is slowed and the electrode reaction can not be performed smoothly, resulting in a decrease in the efficiency of the battery. Moreover, the poor impregnation of the electrolyte may cause a problem of shortening the lifetime of the battery by accelerating degradation of the electrode even though the state of other portions of the electrode is good.

Therefore, it is necessary to develop an impregnation method capable of improving the impregnation degree of the electrolytic solution in the production of the lithium secondary battery and a method capable of evaluating the impregnation degree of the electrolytic solution.

At present, a lot of studies have been made on the electrolyte impregnation method, but there is insufficient study on the impregnation degree evaluation method of electrolyte having time-saving and quantitative discrimination power without decomposing the cell (unit cell).

Korean Patent Registration No. 10-1495760

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made in view of the above problems occurring in the prior art, and an object of the present invention is to provide a method of manufacturing a lithium secondary battery which can easily measure the impregnation degree of an electrolyte with respect to an electrode active material.

In order to achieve the above object, in one embodiment of the present invention,

Compressing the electrode active material slurry to produce a cylindrical pellet (Sl);

Measuring the porosity and the median pore diameter of the cylindrical pellet (S2);

(I) a contact angle of the non-aqueous electrolyte with respect to one surface of the pellet becomes 0 DEG, and (ii) a time point when the electrolyte completely disappears from the surface of the pellet (S3) of measuring an electrolyte absorption time;

(S4) a step of immersing the end of the pellet in the electrolytic solution by 1 mm or more to measure the amount of absorption of the electrolytic solution over time;

Calculating (S5) an electrolyte impregnation degree with respect to the active material based on the measured absorption time and absorption amount of the electrolyte; And

(S6) comparing the measured porosity and average pore diameter with the calculated electrolyte impregnation degree to select an optimal electrolyte impregnation condition for each electrode active material (S6).

According to the method of the present invention, it is possible to measure the degree of impregnation of an electrolyte with respect to an electrode active material, which is a raw material, before the production of the electrode. Based on the measurement results, porosity of the electrode itself, electrolyte viscosity, Conditions and the like can be predicted and set in advance to reduce the manufacturing time and cost of the lithium secondary battery design, thereby improving the productivity and performance of the lithium secondary battery.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the invention and together with the detailed description of the preferred embodiments given below, serve to better understand the spirit and principles of the invention Therefore, the present invention should not be construed as being limited to the matters described in such drawings.
1 is a schematic view of a process for calculating the impregnation degree of an electrolyte in a method of manufacturing a lithium secondary battery according to the present invention.
2 is a graph showing a change in the contact angle of the electrolyte on the surface of the pellet according to the shape of the pellet.
FIG. 3 is a graph showing the amount of electrolyte absorption over time for the pellets of Examples 1 and 2 prepared according to the method of the present invention. FIG.
4 is a graph showing the pore size and distribution of the pellets of Examples 1 and 2 prepared according to the method of the present invention.
5 is a graph showing the amount of electrolyte absorption over time for the pellets of Examples 3 and 4 prepared according to the method of the present invention.
6 is a graph showing the amount of electrolyte absorption over time for the pellets of Examples 5 and 6 prepared according to the method of the present invention.
7 is a graph showing the pore size and distribution of the electrodes of Examples 7 and 8 prepared according to the method of the present invention.
FIG. 8 is a graph showing impregnation of an electrolyte according to Examples 7 and 8 prepared according to the method of the present invention over time. FIG.
9 is a graph showing the normal temperature lifetime characteristics of the secondary batteries of Examples 7 and 8 manufactured according to the method of the present invention.

Hereinafter, the present invention will be described in more detail.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

As used herein, the term " impregnation degree " refers to the degree to which an electrolyte penetrates into an electrode active material. As used herein, the term "impregnable "," And the like, and can be used interchangeably.

The term "secondary battery" used in the present invention means any secondary battery that performs an electrochemical reaction. Examples of the secondary battery include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery . ≪ / RTI >

Further, the term "electrode assembly " as used herein refers to only one unit cell or an assembled form in which two or more unit cells have a separator interposed therebetween.

The term "unit cell " used herein refers to a unit having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The unit cell includes a full- And a structure such as a bi-cell.

Generally, a secondary battery is manufactured by laminating positive and negative electrodes and a separator alternately with each other to manufacture an electrode assembly, inserting the electrode assembly into a can or pouch-shaped case of a predetermined size and shape, .

At this time, the finally injected electrolyte is impregnated between the positive electrode, the negative electrode and the separator by a capillary force. However, due to the nature of the material, the anodes, the cathodes and the separators are both hydrophobic substances, whereas the electrolytic solution is a hydrophilic substance, so impregnation or wetting of the electrodes and separator of the electrolyte requires a considerable amount of time and difficult processing conditions.

In order to improve the degree of impregnation of the secondary battery electrolyte, it is the most common method to carry out the aging process for a long time after the electrolyte injection process or the activation process. However, such a method has a disadvantage of lowering the productivity of the secondary battery.

In order to improve the productivity of the secondary battery, it is necessary to shorten and optimize the aging time and not to waste unnecessary time. Optimization of the aging time can be achieved by quantitatively measuring the electrolyte impregnation degree.

At present, many methods for measuring and evaluating the electrolyte impregnation degree in the production of lithium secondary batteries are not known. In addition, even if the electrolyte impregnation criterion is set for a specific type of electrode, it is not possible to measure the impregnation degree of the electrolyte solution in the electrode coalescence layer formed on the current collector, and the requirements such as the kind and content of each active material constituting the electrode And the density and porosity of the electrode due to the deviation of lamination process conditions and the like are different, it is difficult to apply a constant standard. Therefore, there is a need for a method for setting the electrolyte impregnation degree evaluation standard in consideration of each electrode configuration.

Accordingly, the present invention provides a method of evaluating the degree of impregnation of an electrolyte according to the type of electrode active material, and reflecting the measured values obtained by using the measured value in the production process of the electrochemical device, thereby improving the productivity and performance, And to provide a method that can be manufactured.

Specifically, in one embodiment of the present invention

Compressing the electrode active material slurry to produce a cylindrical pellet (Sl);

Measuring the porosity and the median pore diameter of the cylindrical pellet (S2);

(I) a contact angle of the non-aqueous electrolyte with respect to one surface of the pellet becomes 0 DEG, and (ii) a time point when the electrolyte completely disappears from the surface of the pellet (S3) of measuring an electrolyte absorption time;

(S4) a step of immersing the end of the pellet in the electrolytic solution by 1 mm or more to measure the amount of absorption of the electrolytic solution over time;

Calculating (S5) an electrolyte impregnation degree with respect to the active material based on the measured absorption time and absorption amount of the electrolyte; And

(S6) comparing the measured porosity and average pore diameter with the calculated electrolyte impregnation degree to select an optimal electrolyte impregnation condition for each electrode active material (S6).

First, in the method of manufacturing a lithium secondary battery of the present invention, the step (S1) of producing the cylindrical pellet includes the steps of charging the electrode active material slurry into a molding mold, drying, compressing, And then pelletized.

At this time, the electrode active material slurry may be prepared by mixing at least one of a negative electrode active material and a positive electrode active material with a binder.

Typical examples of the negative electrode active material include a carbonaceous material such as natural graphite or artificial graphite; Lithium-containing titanium composite oxide (LTO), metals (Me) selected from the group consisting of Si, Sn, Li, Zn, Mg, Cd, Ce, Ni and Fe; An alloy composed of the metal (Me); An oxide of said metal (Me) (MeO _x ); And a composite of the above metal (Me) and a carbonaceous material; and at least one negative electrode active material selected from the group consisting of:

In addition, examples of the cathode active material include LiCoO ₂ (LCO), LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO ₄ , LiNi _{0 . 6} Mn _{0 . 2} Co _{0 . 2} O ₂ (NMC) and _{LiNi 1 -xy- z Co x M1 y} M2 z O 2 (M1 and M2 are independently selected from Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg each other And Mo, and x, y and z are independently selected from the group consisting of 0? X <0.5, 0? Y <0.5, 0? Z <0.5 and x + y + z Lt; = 1). Specific examples thereof include LiCoO ₂ , LiFePO ₄ , LiNi _{0 . 6} Mn _{0 . 2} Co _{0 . 2} O _2, or _{LiNi 1 -xy- z Co x M1 y} M2 z O 2 (M1 and M2 are independently selected from Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo each other X, y and z are independently selected from the group consisting of 0 <x <0.5, 0 <y <0.5, 0 <z <0.5 and x + y + z≤1 .

The binder is not particularly limited as long as it is a component that assists in bonding between the active material and the conductive material and bonding to the current collector. Examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various types of polyolefins, polyolefins, polyolefins, Copolymers and the like.

The binder may be contained in an amount that does not affect pore formation of the active material during the formation of the cylindrical pellet, and may be contained in an amount of 1 to 3% by weight based on the total weight of the electrode active material slurry.

The electrode active material slurry of the present invention may further include a conductive material as the case may be.

Further, the compression process for forming the pellets may be carried out at a temperature of 20 to 50 DEG C under a pressure of 30 to 60 MPa.

The diameter of the cylindrical pellet produced by the compression may be 2 mm to 30 mm, specifically 13 mm, and the thickness may be 1 mm to 20 mm, specifically 5 mm.

If the diameter of the pellet exceeds 30 mm or the thickness exceeds 20 mm, the amount of the active material and the size of the molding mold required for manufacturing the pellet increase, resulting in an increase in manufacturing cost and cracking of the pellet.

Particularly, the cylindrical pellet means a column having a circular bottom surface. If the pellet is manufactured in a rectangular hexahedron shape instead of a cylindrical shape, cracks or cracks may occur at the corner portions, and the absorption rate of the electrolytic solution increases and data reliability may be deteriorated.

For example, as shown in Fig. 2, when the electrolytic solution is dropped on the upper surface of the cylindrical pellet (a) and the hexagonal pellet (b), the contact angle of the electrolytic solution is changed as follows. (A) In the case of cylindrical pellets, The height of the electrolytic solution is low at both edge regions, and as the time elapses, the electrolytic solution is absorbed to the entire pellet, and the contact angle of the electrolytic solution is uniformly decreased. On the other hand, in the case of (b) pellets of the hexagonal hexahedron shape, since the height of the electrolytic solution dropped on the upper surface of the pellet is not constant, it is difficult to measure the duration of impregnation or the contact angle. Therefore, it is difficult to obtain reliable data.

In the method for manufacturing a lithium secondary battery of the present invention, the porosity and average pore diameter (MPD) of the cylindrical pellet (S2) may be measured using a mercury porosimeter The method comprising the steps of: At this time, the average pore diameter (MPD) is a median value of the pores represented by the volume, and the lower the MPD value, the lower the degree of impregnation.

The porosity measurement using the mercury penetration utilizes a capillary phenomenon in which liquid penetrates into fine pores. When a non-wetting liquid such as mercury is subjected to pressure from the outside, penetration occurs. The smaller the pore size, the higher the pressure is required. The measurement results are a function of the cumulative penetration volume or volume of mercury penetrated by the pressure (or pore size).

On the other hand, the average pore diameter and the porosity (porosity) of the pellets differ depending on the kind of the electrode active material, and can be controlled by the compressive strength or the like when the pellets are formed.

Specifically, the cylindrical pellets may comprise a porosity of about 20 to 35% by volume, specifically about 28 to 32% by volume. When the porosity is less than 20% by volume, there is a disadvantage that the penetration rate of Hg is slowed. When the porosity exceeds 35% by volume, the penetration rate of Hg increases, while meaningless data can be obtained out of porosity used in actual cells There are disadvantages. The average pore diameter (MPD) represented by the area (volume) of the cylindrical pellet cylindrical shape may be 100 nm to 1000 nm, specifically 300 nm to 800 nm.

More specifically, the porosity may be about 28 to 32% by volume when the electrode active material is a cathode active material, particularly NMC. In addition, when the electrode active material is a cathode active material, particularly LCO, the porosity of the pellet may be about 18 to 22% by volume. When the electrode active material is an anode active material (graphite), the porosity of the pellets may be about 17 to 30% by volume.

In the method for manufacturing a lithium secondary battery according to the present invention, the step (S3) for measuring the time of absorption of the electrolyte may include a step of dropping the nonaqueous electrolyte solution 13 on one surface of the molded cylindrical pellet 11, (I) a time at which the contact angle of the non-aqueous electrolyte with respect to one surface of the pellet becomes 0 DEG, and (ii) a time from the surface of the pellet to the point at which the electrolyte completely disappears, thereby measuring the electrolyte absorption time (See Fig. 1).

At this time, the point of time when the contact angle of the non-aqueous electrolyte becomes 0 DEG and the point at which the electrolyte completely disappears from the surface of the pellet may be the same or different.

As described above, in the present invention, it is possible to grasp the impregnation level different from the porosity through the point of time when the contact angle of the non-aqueous electrolyte reaches 0 ° and when the electrolyte completely disappears from the surface of the pellet. That is, the electrolyte impregnation level can be predicted in advance without manufacturing the secondary battery.

Particularly, in the present invention, the time at which the electrolyte passes through the pellets and appears on the back surface can be easily confirmed or measured visually. Here, the expression "visual confirmation or measurement" is meant to include directly confirming directly with an observer's eye, or indirectly confirming a mediator between an analyte and an observer such as a lens, a camera, or a microscope.

On the other hand, the non-aqueous electrolyte is a non-aqueous electrolyte used in a conventional lithium secondary battery, and is composed of an organic solvent and a lithium salt.

The non-aqueous organic solvent is not particularly limited as long as it can minimize decomposition due to an oxidation reaction during charging and discharging of the battery and can exhibit desired properties together with additives. Examples of the non-aqueous organic solvent include carbonates and propionates And so on. These may be used alone, or two or more of them may be used in combination.

Examples of the carbonate compound in the non-aqueous organic solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinylene carbonate (VC) or a mixture of two or more thereof.

Examples of the propionate compound include ethyl propionate (EP), propyl propionate (PP), n-propyl propionate, isopropyl propionate, n-butyl propionate, And a mixture of at least two selected from the group consisting of propionate, isobutyrate, fionate, and tert-butylpropionate.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidone (NMP), propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, dimethyl carbonate Ethyl carbonate, ethylene propionate (EP), gamma-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide , Dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone , Propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate and the like can be used.

In addition, the lithium salt may be used, without limitation, those which are commonly used in a lithium secondary battery electrolyte, for the example including Li ⁺ as the cation, and the anion is F ^-, Cl ^-, Br ^-, I ^-, NO _{^{3 -, N (CN) 2}} -, BF 4 -, ClO 4 -, AlO 4 -, AlCl 4 -, PF 6 -, SbF 6 -, AsF 6 -, BF 2 C 2 O 4 -, BC 4 O 8 _{^{-, (CF 3) 2 PF}} 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 - ^{_{, C 4 F 9 SO 3 -}} , CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 ^{_{SO 2) 2 CH -, (}} SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - And (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , and specifically, examples of the lithium salt include LiPF ₆ , LiFSI, and LiBF ₄ .

The lithium salt may be contained in the non-aqueous electrolyte at a concentration of 0.8M to 2.0M, and if the concentration of the lithium salt is less than 0.8M, the battery performance may deteriorate. If the concentration is more than 2.0M, There may be problems

The electrolytic solution may be added in an amount of approximately 1 to 10 μl, approximately 10 μl, irrespective of the diameter and thickness of the pellet.

In the method for manufacturing a lithium secondary battery according to the present invention, the step (S4) of measuring the amount of absorption of the electrolytic solution includes the step of immersing the end of the pellet in the electrolyte solution for 1 mm or more and then measuring the electrolyte impregnation amount according to the electrolytic solution absorption time .

In the method for producing a lithium secondary battery according to the present invention, the step (S5) for calculating the electrolyte impregnation degree may include calculating the electrolyte impregnation degree of the electrode active material on the basis of the electrolyte absorption time and the absorption amount measured in the previous step Step &lt; / RTI &gt;

Specifically, the impregnation degree of the electrolytic solution using the electrolyte absorption time can be calculated using the Washburn equation of the following equation (1).

[Formula 1]

The degree of impregnation of the electrolytic solution using the amount of absorption of the electrolytic solution can be calculated using the Washburn equation of the following formula (2).

[Formula 2]

In addition, in the method for producing a lithium secondary battery of the present invention, the optimum porosity and average pore diameter may be compared with the calculated electrolyte impregnation degree (S5), and the optimal electrolyte impregnation condition may be selected for each electrode active material.

In addition, the method for producing a lithium secondary battery of the present invention can set an optimum amount of an electrolyte to be injected and an injection condition based on the calculated results.

That is, by referring to the calculated electrolyte impregnation degree, that is, the result of the absorption rate, it is possible to dataize or standardize the amount of the electrolytic solution to be injected and the injection conditions with respect to the kind of the electrode active material and the porosity. These data or standardized dosing values may be reflected in the adjustment of the production process of the cell either immediately or as mentioned above.

Therefore, the production time and cost of the lithium secondary battery can be reduced, and the productivity and performance of the lithium secondary battery can be improved.

Conventionally, the electrolyte impregnation degree measurement method is a method of measuring the impregnation degree of an electrolyte by forming an active material mixture layer on a current collector, preparing an electrode, conducting an electrolyte injection process, observing the surface of the electrode with a naked eye by disassembling the secondary battery, And a method of quantitating the electrolyte impregnation degree according to the magnitude of the charge and discharge capacity by carrying out a charge and discharge test.

The former method has a limitation that it is impossible to measure the shape and time of impregnation with the naked eye before disassembling the secondary battery. In addition, although the latter method can quantitatively measure the degree of impregnation of the electrolyte to a certain extent, the charging and discharging test must be separately performed, and it takes a long time to carry out the charge-discharge test.

On the other hand, in the present invention, since the pellet is produced using only the conventional electrode active material without using the current collector, and the rate at which the electrolyte passes through the pellet can be visually measured, the electrolyte impregnability evaluation Is possible.

Further, according to the present invention, since the degree of impregnation of the electrolyte solution is quantitatively measured from the starting material active material to the electrolyte solution, it is necessary to determine how long it takes for the impregnation of the electrolyte solution to saturate, It is possible to quantitatively evaluate the degree of improvement in impregnation and various measures to be performed in the aging step, and thus, the kind and / or amount of the electrolyte having excellent impregnation can be easily selected. In particular, the impregnability of the electrolyte solution can be evaluated in consideration of the material of the electrode active material and the electrode characteristics due to the deviation of the lamination process conditions. Thus, a lithium secondary battery with improved productivity and performance can be manufactured effectively.

Hereinafter, the present invention will be described in detail by way of examples with reference to the following examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

I. Pellets  Produce

Example  One.

As a cathode active material, LiNi _{0 . 6} Mn _{0 . 2} Co _{0 . 2} O ₂ (NMC) as a binder and polyvinylidene fluoride (KF 1100) as a binder at a weight ratio of 98: 2 to prepare a cathode active material slurry. The slurry was put into a cylindrical forming mold, compressed at 25 ° C under a pressure of 30 MPa And a cylindrical pellet having a diameter of 12.7 mm, a thickness of 3.52 mm, a density of 3.39 (g / cc) and a porosity of 28.9% by volume was produced.

An organic solvent was mixed with ethylene carbonate (EC), propylene carbonate (PC) and ethylene carbonate (EMC) at a ratio of 20:10:70 (vol%), and LiPF ₆ was dissolved To prepare a nonaqueous electrolytic solution.

Then, the porosity and the average pore diameter of the pellets prepared using the mercury porosimeter were measured, and the results are shown in Table 1 and FIG.

Next, 10 占 퐇 of a nonaqueous electrolyte solution was dropped onto one surface of the prepared cylindrical pellet. The absorption time from the point of time of dropping to the point of time when the contact angle was 0 占 폚 and the electrolyte completely disappeared from the surface of the pellet was measured, The results are shown in Table 1 below.

Subsequently, the tip of the pellet was immersed in the electrolyte for at least 1 mm, and then the electrolyte impregnation amount was measured according to the time of absorption of the electrolyte. The results are shown in Table 1 and FIG.

The impregnation rate of the electrolyte solution (impregnation speed) was calculated from the absorption time and the impregnation amount of the electrolyte measured using the above Equations 1 and 2, and the results are shown in Table 1 below.

Example  2.

The slurry of the cathode active material of Example 1 was charged into a cylindrical mold and compression molded at 25 ° C under a pressure of 40 MPa to obtain a slurry having a diameter of 12.7 mm, a thickness of 3.58 mm, a density of 3.40 g / cc and a porosity of 28.5% Lt; / RTI &gt; pellets were prepared.

Then, the porosity and average pore diameter of the pellets, the absorption time and the amount of absorption of the electrolyte, and the like were measured in the same manner as in Example 1, and the results are shown in the following Table 1 and FIG. 3 and FIG.

Next, the electrolyte impregnation degree was calculated from the absorption time and the electrolyte impregnation amount measured using Equations 1 and 2, and the results are shown in Table 1 below.

Example  3.

And this is, in Example 1 and by a method similar to 12.7mm diameter, thickness 3.04mm, a density 3.90 (g / cc) and a porosity but using ₂ (LCO) LiCoO as NMC instead of the positive electrode active material of Example 1 A cylindrical pellet of 22.8 vol% was prepared.

Then, the absorption time of the electrolytic solution was measured in the same manner as in Example 1. In addition, the amount of electrolyte absorption over time was measured, and the results are shown in Table 1 and FIG.

Then, the electrolyte impregnation degree was calculated from the measured absorption time and electrolyte impregnation amount, and the results are shown in Table 1 below.

Example  4.

And this, the second embodiment and the diameter 12.7mm, thickness 3.02mm, a density 3.92 (g / cc) and a porosity in a similar way but using ₂ (LCO) as LiCoO NMC instead of the positive electrode active material of Example 2 A cylindrical pellet of 22.4 vol% was prepared.

Then, the absorption time of the electrolytic solution was measured in the same manner as in Example 2. In addition, the amount of electrolyte absorption over time was measured, and the results are shown in Table 1 and FIG.

Then, the electrolyte impregnation degree was calculated from the measured absorption time and electrolyte impregnation amount, and the results are shown in Table 1 below.

Example  5.

A diameter of 12.7 mm, a thickness of 4.97 mm, a density of 1.59 (g / cc), and a porosity of 1.57 (g / cc) were obtained in the same manner as in Example 1, except that graphite (graphite) was used as a negative electrode active material in place of the positive electrode active material of Example 1. [ A cylindrical pellet of 28.4 vol% was prepared.

Then, the absorption time of the electrolytic solution was measured in the same manner as in Example 1. Further, the amount of electrolyte absorption over time was measured, and the results are shown in Table 1 and FIG. 6 below.

Then, the electrolyte impregnation degree was calculated from the measured absorption time and electrolyte impregnation amount, and the results are shown in Table 1 below.

Example  6.

A diameter of 12.7 mm, a thickness of 4.96 mm, a density of 1.59 (g / cc), and a porosity of 1.50 (g / cc) were obtained in the same manner as in Example 2 except that graphite (graphite) was used as a negative electrode active material in place of the positive electrode active material of Example 2. [ A cylindrical pellet of 28.2 vol% was prepared.

Then, the absorption time of the electrolytic solution was measured in the same manner as in Example 2. Further, the amount of electrolyte absorption over time was measured, and the results are shown in Table 1 and FIG. 6, respectively.

Then, the electrolyte impregnation degree was calculated from the measured absorption time and electrolyte impregnation amount, and the results are shown in Table 1 below.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Pel
RET Electrode active material NMC LCO Artificial graphite Diameter (mm) 12.7 Thickness (mm) 3.52 3.58 3.04 3.02 4.97 4.96 Density (g / cc) 3.39 3.40 3.90 3.92 1.59 1.59 Porosity (%) 28.9 28.5 22.8 22.4 28.4 28.2 Hg
Measure density 3.37 3.37 - - - - Porosity (%) 28.0 27.8 - - - - MPD (nm) 581.2 628.8 - - - - Contact angle is 0 ℃
Time 890 763 432 501 86 98 Electrolyte on the surface
Immersed time (sec) 1023 893 567 638 102 166 K value (volume ² )
= Solvent impregnation rate 0.0110 0.0141 0.0842 0.0777 0.1666 0.1412

Referring to Table 1, the pellets prepared in Example 1 were thinner in thickness, lower in density and higher in porosity (%) than the pellets prepared in Example 2, It can be seen that the impregnation speed of the electrolyte is slow because the pore diameter (MPD) is low (see FIGS. 3 and 4).

In addition, the results of the pellets prepared in Examples 3 and 4 were similar to those of the pellets prepared in Example 3, but the density was low and the porosity was high , And the electrolyte impregnation speed is substantially slow (see FIG. 5). It is also predicted that this is due to the fact that the actual average pore diameter (MPD) is low.

Meanwhile, the results of the pellets prepared in Examples 5 and 6 were as follows. The pellets prepared in Example 5 had a higher porosity and a higher rate of electrolyte impregnation than the pellets prepared in Example 6 (See Fig. 6).

II. Electrode Manufacturing

Example  7

(Anode manufacture)

The slurry of the cathode active material prepared in Example 1 was coated on aluminum foil to have a thickness of 100 탆 and dried and rolled to have a density of 3.42 (g / cc), a porosity (%) of 25.7% and an average pore diameter (MPD) of 130.3 nm (see Fig. 7).

The positive electrode was immersed in the nonaqueous electrolyte solution of Example 1, and the electrolyte impregnation time for the positive electrode was measured. The results are shown in FIG.

(Secondary Battery Manufacturing)

Graphite as an anode active material, an SBR binder as a binder, and carbon black as a conductive material in a ratio of 98: 1: 1 (wt%). water to prepare an anode active material slurry. The negative electrode active material slurry was coated on a negative electrode current collector (Cu thin film) having a thickness of 90 탆, dried, and rolled to produce a negative electrode.

The prepared positive electrode and negative electrode were sequentially laminated with a polyethylene porous film to prepare an electrode assembly. The electrode assembly was inserted into a battery case, and the nonaqueous electrolyte solution of Example 1 was injected and sealed to prepare a lithium secondary battery (full cell) .

The normal temperature lifetime characteristics of the pull cell were measured, and the results are shown in FIG.

Example  8

(Anode manufacture)

A density of 3.43 g / cc and a porosity of 24% were obtained in the same manner as in Example 7, except that the slurry of the cathode active material prepared in Example 2 was used in place of the slurry of the cathode active material prepared in Example 1 above. And an average pore diameter (MPD) of 138.5 nm (see Fig. 7).

The positive electrode was immersed in the nonaqueous electrolyte solution of Example 1, and the electrolyte impregnation time for the positive electrode was measured. The results are shown in FIG.

(Secondary Battery Manufacturing)

Graphite as an anode active material, an SBR binder as a binder, and carbon black as a conductive material in a ratio of 98: 1: 1 (wt%). water to prepare an anode active material slurry. The negative electrode active material slurry was coated on a negative electrode current collector (Cu thin film) having a thickness of 90 탆, dried, and rolled to produce a negative electrode.

The prepared positive electrode and negative electrode were sequentially laminated with a polyethylene porous film to prepare an electrode assembly. The electrode assembly was inserted into a battery case, and the nonaqueous electrolyte solution of Example 1 was injected and sealed to prepare a lithium secondary battery (full cell) .

The normal temperature lifetime characteristics of the pull cell were measured, and the results are shown in FIG.

7, when the electrode of Example 7 was compared with the electrode of Example 8 using the active material slurry of Example 1 having a low electrolyte impregnation rate in the active material stage as shown in Table 1, It can be seen that the electrolytic solution impregnation time is long.

That is, the results of the electrolyte impregnation obtained in the active material step and the electrolyte impregnation obtained after the electrode production are similar.

Referring to FIG. 8, the lifetime characteristics of the pull-cell battery were measured. As a result, it can be seen that the life characteristics of the rechargeable battery of Example 7 were drastically reduced after 100 cycles as compared with the rechargeable battery of Example 8. [ That is, in this case, the impregnation of the electrode is not sufficiently performed, and the possibility that problems such as capacity reduction and lithium precipitation may occur may increase. Therefore, it is a result indicating that more time is required for impregnation of the electrode.

From these results, it can be confirmed that not only the porosity and density but also the average pore diameter are important factors in the measurement of electrolyte impregnation in the case of the electrode active material. In the present invention, it is possible to predict the impregnation level of the electrolyte in the future active material stage based on the conventional electrode design and results, and it can be reflected in the porosity (density) considering the proper impregnation time . Therefore, a lithium secondary battery improved in productivity and performance can be produced.

11: Pellets
13: Non-aqueous electrolyte

Claims (15)

Compressing the electrode active material slurry to produce a cylindrical pellet (Sl);
Measuring the porosity and the median pore diameter of the cylindrical pellet (S2);
(I) a contact angle of the non-aqueous electrolyte with respect to one surface of the pellet becomes 0 DEG, and (ii) a time point when the electrolyte completely disappears from the surface of the pellet (S3) of measuring an electrolyte absorption time;
(S4) a step of immersing the end of the pellet in the electrolytic solution by 1 mm or more to measure the amount of absorption of the electrolytic solution over time;
Calculating (S5) an electrolyte impregnation degree with respect to the active material based on the measured absorption time and absorption amount of the electrolyte; And
(S6) comparing the measured porosity and average pore diameter with the calculated electrolyte impregnation degree to select an optimal electrolyte impregnation condition for each electrode active material.
The method according to claim 1,
Wherein the electrode active material slurry includes at least one of a negative electrode active material and a positive electrode active material, and a binder.
The method of claim 2,
The negative electrode active material may include a carbonaceous material; Lithium-containing titanium composite oxide (LTO), metals (Me) selected from the group consisting of Si, Sn, Li, Zn, Mg, Cd, Ce, Ni and Fe; An alloy composed of the metal (Me); An oxide of the metal (Me); And a composite of the metal (Me) and a carbonaceous material; and a mixture of at least two selected from the group consisting of a mixture of the metal (Me) and the carbonaceous material.
The method of claim 2,
The cathode active material may be LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO ₄ , LiNi _0.6 Mn _0.2 Co _0.2 O ₂ (NMC), and LiNi _{1 -xy z} Co _x M _y M2 _z O ₂ (M1 and M2 are independently selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo; x, y and z are, Wherein the atomic fraction of the elements is 0? X <0.5, 0? Y <0.5, 0? Z <0.5, x + y + z? 1 or a mixture of two or more thereof. A method of manufacturing a secondary battery.
The method according to claim 1,
Wherein the non-aqueous electrolyte comprises an organic solvent and a lithium salt.
The method according to claim 1,
Wherein the compression process for producing the cylindrical pellet is carried out at a temperature in the range of 20 캜 to 50 캜 while applying a pressure of 30 MPa to 60 MPa.
The method according to claim 1,
And the diameter of the cylindrical pellet is 2 mm to 30 mm.
The method according to claim 1,
Wherein the thickness of the cylindrical pellet is 1 mm to 20 mm.
The method according to claim 1,
Wherein the cylindrical pellet comprises a porosity of 20% by volume to 35% by volume.
The method according to claim 1,
Wherein the average pore diameter (MPD) of the cylindrical pellet is 100 nm to 1000 nm.
The method according to claim 4 or 9,
Wherein the positive electrode active material LiNi _{0. 6} Mn _{0 . 2} Co _{0 . 2} O ₂ (NMC), the porosity of the pellet is 28% by volume to 32% by volume.
The method according to claim 4 or 9,
Wherein when the positive electrode active material is LiCoO ₂ , the porosity of the pellet is 18 vol% to 22 vol%.
The method according to claim 3 or 9,
Wherein when the negative electrode active material is a carbonaceous material, the porosity of the pellet is from 17 vol% to 30 vol%.
The method according to claim 1,
Wherein the porosity and average pore diameter of the cylindrical pellet are measured using a mercury porosimetry analyzer.
The method according to claim 1,
Wherein the step of measuring the electrolyte absorption time is directly confirmed by an observer's eye or indirectly through an intermediary between an analyte and an observer.

Images