KR20190017516A - Method of fabricating an electrode - Google Patents

Abstract

A method for manufacturing an electrode of the present invention comprises the steps of: (a) manufacturing an active material linear dispersion in which first active material particles are dispersed in an organic solvent; and (b) mixing the active material linear dispersion, second active material particles, a conductive material, and a binder with the organic solvent to manufacture electrode slurry. An average particle diameter (D50) of the first active material particles is smaller than an average particle diameter of the second active material particles. Provided is an electrode having an active material layer in which an active material is uniformly dispersed, thereby providing an electrode which is excellent in energy density without increasing the rolling density and free from damage to a current collector.

Description

[0001] METHOD OF FABRICATING AN ELECTRODE [0002]

The present invention relates to a method of manufacturing an electrode including two kinds of active material particles having different average particle diameters.

As the size and weight of electronic equipment are reduced and the use of portable electronic devices is becoming common, researches on secondary batteries having high energy density as their power source have been actively conducted.

Examples of the secondary battery include a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, and a lithium secondary battery. Among them, the secondary battery exhibits a discharge voltage two times higher than that of a conventional battery using an aqueous alkaline solution In addition, studies have been made on a lithium secondary battery which has a high energy density per unit weight and can be rapidly charged.

Lithium metal oxide is used as the positive electrode active material of the lithium secondary battery, and lithium metal, lithium alloy, crystalline or amorphous carbon or carbon composite material is used as the negative electrode active material. The active material is coated on the current collector with an appropriate thickness and length, or the active material itself is coated in a film form and wrapped or laminated together with a separator as an insulator to form an electrode group. The electrode group is then placed in a can or similar container, Thereby manufacturing a secondary battery.

In the case of such a lithium secondary battery, the market needs for a high capacity are increasing, and it is very important to maximize the energy density in the electrode. In order to maximize the energy density in the electrode as described above, the rolling density of the electrode is increased. However, in order to increase the rolling density, the pressure to be applied during the electrode rolling must be increased. , There is a problem of quality deterioration due to damage to the current collectors as well as lowering of the fairness.

Therefore, it is necessary to develop the electrode without maximizing the energy density of the battery and without sacrificing fairness and quality.

The present invention provides a method of manufacturing an electrode for providing an electrode having a high energy density while preventing damage to the current collector. Specifically, a bimodal active material is applied to improve the energy density, and the uniform dispersion problem is solved to provide a high quality electrode with high energy density and at the same time no increase in rolling density, .

According to an aspect of the present invention, there is provided a method of manufacturing an active material, comprising: (a) preparing an active material ray dispersion in which first active material particles are dispersed in an organic solvent; And (b) mixing the active material ray dispersion, the second active material particles, the conductive material and the binder with an organic solvent to prepare an electrode slurry, wherein the average particle size (D50) of the first active material particles is Wherein the average particle diameter of the particles is smaller than the average particle diameter of the particles.

INDUSTRIAL APPLICABILITY The electrode manufacturing method according to the present invention provides an electrode having an active material layer in which active materials having different average particle diameters are dispersed and uniformly dispersing the active materials. Thus, even if the rolling density is not increased, the energy density of the electrode is excellent, Electrode can be provided.

Hereinafter, preferred embodiments of the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined.

Therefore, the constitutions shown in the embodiments described herein are merely the most preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention, so that various equivalents and variations Examples should be understood.

A method of manufacturing an electrode according to an embodiment of the present invention includes the steps of (a) preparing an electrode active material dispersion in which first active material particles are dispersed in an organic solvent, step; And (b) mixing the active material ray dispersion, the second active material particles, the conductive material and the binder with an organic solvent to prepare an electrode slurry, wherein the average particle size (D50) of the first active material particles is Is smaller than the average particle diameter of the particles.

In the present invention, the average particle size of the active material particles is obtained by measuring the particle size distribution using a light scattering particle size meter, and means 50% diameter (median diameter) of the particles.

The electrode manufacturing method may be a method capable of improving the energy density by uniformly dispersing two kinds of active material particles having different average particle diameters. In the case of applying two kinds of active materials having different particle sizes to each other, there is a strong tendency that active material particles having small particle diameters tend to aggregate, so that the active material particles are not uniformly dispersed Has come.

However, according to the method of manufacturing an electrode according to the present invention, even if two kinds of bimodal active materials having different particle diameters are applied, the active material particles can be uniformly dispersed as a whole and the active material particles having small particle diameters Can be distributed. Accordingly, the energy density of the electrode can be greatly improved, and the energy density can be improved without decreasing the rolling density, so that damage to the electrode collector can be minimized.

More specifically, a method of manufacturing an electrode according to an embodiment of the present invention may include the step (a) of producing an active material ray dispersion in which first active material particles are dispersed in an organic solvent.

That is, the small-diameter active material particles may be a step of dispersing the first active material particles in the organic solvent so that the small-diameter active material particles having a strong tendency to aggregate are maintained at a certain interval.

In this case, the first active material particles need to be contained in the organic solvent in a certain amount so that the inter-particle spacing can be maintained. When the first active material particles are contained in an excessive amount, the inter-particle agglomeration phenomenon may be expressed as it is and uniform dispersion may not be expected. It may be difficult to achieve the purpose of improving the energy density. In this regard, the first active material particles may preferably contain 3 to 50 parts by weight, more preferably 3 to 30 parts by weight, and most preferably 3 to 10 parts by weight, based on 100 parts by weight of the organic solvent.

In this case, when the first active material particles are linearly dispersed and the second active material particles are also subjected to linear dispersion, that is, when two kinds of active material particles having different particles are contained, there is a possibility that the dispersion- It is difficult to expect a dispersion effect.

After the active material line dispersion is prepared as described above, a step of producing an electrode slurry (step (b)) may be performed. In the step (b), an electrode slurry for forming an active material layer is prepared by introducing the active material linear dispersion, the conductive material, the binder, and the second active material particles having an average particle diameter larger than that of the first active material particles into the organic solvent Lt; / RTI >

The first active material particle and the second active material particle may have different average particle diameters, and the reference point may preferably be 10 탆. That is, the first active material particle having a small diameter may have an average particle diameter of 10 mu m or less, and the second active material particle having a large diameter may have an average particle diameter exceeding 10 mu m. More preferably, the average particle size of the first active material particles may be 0.1 to 8 占 퐉, optimally 2 to 7 占 퐉, and preferably the average particle diameter of the second active material particles is 11 to 50 占 퐉, optimally 12 to 20 占 퐉 Lt; / RTI >

However, the average particle diameter of the first active material particles and the second active material particles is not limited to the above range, and it may be preferable that the sizes of the first and second active material particles are separated on the basis of about 10 탆.

On the other hand, there may be cases where both the first active material particle and the second active material particle are smaller than 10 탆. In this case, the difference in average particle diameter between the first active material particle and the second active material particle may be 3 to 9 탆 have. It is preferable that the average particle size is differentiated in the above range in view of the small diameter active material particles being distributed as the pores of the large-diameter active material particles.

The first active material particle and the second active material particle may preferably have a volume ratio of 5:95 to 50:50, more preferably 5:95 to 40:60, or 5:95 to 30:70. The above-mentioned volume ratio range may be appropriate for improving the energy density, in which the small-diameter particles can be distributed among the large-diameter particles when the small-diameter and large-diameter active material particles are mixed. In addition, in the case of the above-mentioned volume ratio range, since the amount of the first active material particles is relatively small, the linear dispersion effect, that is, the uniform dispersion effect can be maximized.

The conductive material may be prepared by dispersing the conductive material particles in an organic solvent to prepare a conductive material linear dispersion and then introducing the conductive material linear dispersion liquid into the organic solvent together with the second active material particles, the active material line dispersion, and the binder to prepare an electrode slurry . Since the conductive material also has a small particle size, it has a strong cohesive property. Therefore, it may be preferable to first disperse the conductive material in an organic solvent and then to introduce it into the slurry forming solution.

When the active material ray dispersion is prepared and mixed at the time of preparing the electrode slurry as described above, it is expected that the active material particles having different average particle sizes can be uniformly dispersed as a whole. Further, for more uniform dispersion, the second active material particles, the conductive material (or the conductive line dispersion) and the binder are first dispersed in the organic solvent before the active material line dispersion is put into the organic solvent, and then the two dispersions are mixed The step (b) may be performed in this case, and in this case, it may further assist in increasing the dispersibility.

Such a method of manufacturing an electrode can be applied to both manufacturing of a positive electrode and manufacturing of a negative electrode, and it is preferable to apply a method of manufacturing a positive electrode.

As the organic solvent for forming the electrode (preferably, the anode), a solvent such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone or dimethylacetamide may be used. Or a mixture of two or more of them may be used. The organic solvent in the step (a) and the organic solvent in the step (b) may be the same, and the same type of organic solvent as the conductive material may be used.

The amount of the organic solvent to be used is not particularly limited in the case of preparing the electrode slurry in the case of preparing the active material line dispersion in the step (a), but the relative amount with respect to the first active material particles is not particularly limited. It is sufficient that the electrode active material, the binder and the conductive material can be dissolved and dispersed in consideration of the coating thickness and the production yield.

The first active material particle and the second active material particle may preferably contain 60 to 97% by weight, more preferably 80 to 97% by weight, based on the total weight of the electrode slurry, It may be preferable in terms of density.

When the first active material particle and the second active material particle are a cathode active material, the cathode active material may be a lithium-containing transition metal oxide For example, Li _x CoO ₂ (0.5 <x <1.3), Li _x NiO ₂ (0.5 <x <1.3), Li _x MnO ₂ (0.5 <x <1.3), Li _x Mn ₂ O _{4 (0.5 <x <1.3)} , Li x (Ni a Co b Mn c) O 2 (0.5 <x <1.3, 0 <a <1, 0 <b <1, 0 <c <1, a + b + _{c = 1), Li x Ni} 1-y Co y O 2 (0.5 <x <1.3, 0 <y <1), LixCo 1 - y Mn y O 2 (0.5 <x <1.3, 0≤y <1) _{, Li x Ni 1 -y Mn y} O 2 (0.5 <x <1.3, O≤y <1), Li x (Ni a Co b Mn c) O 4 (0.5 <x <1.3, 0 <a <2, 0 <b <2, 0 < c <2, a + b + c = 2), Li x Mn 2 - z Ni z O 4 (0.5 <x <1.3, 0 <z <2), Li x Mn 2 - _{z Co z O 4 (0.5 <} x <1.3, 0 <z <2), Li x CoPO 4 (0.5 <x <1.3) and Li _x FePO ₄ one selected from the group consisting of (0.5 <x <1.3) Or a mixture of two or more of them may be used, and xLi ₂ MO ₃ (1-x) LiMeO ₂ (M is Ni , Co or Mn and Me is at least two transition metals selected from the group consisting of Ni, Co, Mn, Cr, Fe, V, Al, Mg and Ti and 0 & A high content of active material can also be applied.

The lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also be used.

On the other hand, the conductive material may preferably contain 0.05 to 5.0% by weight based on the total weight of the electrode slurry. When the conductive material is included in the range, it is possible to provide an electrode having a conductive path and ensuring electrical conductivity.

The conductive material is not particularly limited as long as it can be used in the art. Examples of the conductive material include artificial graphite, natural graphite, carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, carbon fiber, A metal such as aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, ruthenium, platinum, iridium, Thiophene, polyacetylene, polypyrrole, or a mixture thereof may be used.

The binder may include the active material particles and the remaining amount of the conductive material in relation to the total weight of the electrode slurry. Any binder may be used as long as it is generally used in the art. Examples thereof include polyvinylidene fluoride (PVdF), polyhexafluoro (PVdF / HFP), poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, polyvinyl pyridine, alkylated polyethylene oxide, polyvinyl ether, poly Methyl methacrylate), poly (ethyl acrylate), polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, ethylene- Diene monomer (EPDM) sulfonated ethylene-propylene-diene monomer, carboxymethylcellulose (CMC), regenerated cellulose , Starch, hydroxypropylcellulose, tetrafluoroethylene, or a mixture thereof.

If necessary, a filler may be further added to the above-mentioned slurry. The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

After the step (b) is performed, the electrode slurry may be coated by a method commonly known in the art, (c) coating the electrode slurry on the electrode slurry, followed by drying and rolling, Rolling conditions may be performed by conventional methods known in the art. However, in the case of applying the electrode manufactured by the electrode manufacturing method of the present invention, there is almost no gap in the active material layer due to uniform dispersion even when the pressure for rolling is not increased, and thus energy density can be increased. And it is possible to manufacture an electrode having a sufficient energy density even at a relatively small pressure so that damage to the current collector can be prevented.

The cathode current collector is generally made to have a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and is a metal having a high conductivity and capable of easily adhering a slurry of the positive electrode active material, Any of those which are not reactive can be used. Non-limiting examples of the positive electrode current collector include foil produced by aluminum, nickel, or a combination thereof.

According to another embodiment of the present invention, it is possible to provide a lithium secondary battery having an improved energy density and at the same time, no damage to the current collector, so that the lithium secondary battery can be manufactured by using the positive and negative electrode active materials prepared by the above- A separator disposed between the positive electrode and the negative electrode, and the electrolyte described above, and the lithium secondary battery of the present invention can be manufactured according to a conventional method known in the art. For example, a porous separator may be placed between an anode and a cathode, and an electrolyte in which a lithium salt is dissolved may be added.

The above-mentioned negative electrode can also be manufactured by the above-mentioned method, and it is not excluded that the above-mentioned method is applied to manufacture of a negative electrode. However, in the case of a cathode, a carbon-based material or a silicon-based material is generally applied, and since a material having a large particle size is rarely applied, the effect obtained compared to the case where the material is applied to the anode may not be large.

Examples of the negative electrode active material include amorphous carbon or regular carbon, and specifically carbon such as non-graphitized carbon and graphite 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 complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{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, And Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The binder and the conductive material contained in the cathode may be applied in the same manner as applied to the anode.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

As the separator for insulating the electrodes from each other between the anode and the cathode, a polyolefin separator commonly used in the art or a composite separator having an organic-inorganic hybrid layer formed on an olefin based material may be used without particular limitation .

The nonaqueous electrolyte may include a nonaqueous organic solvent, a lithium salt, and an additive. The nonaqueous organic solvent may include an organic solvent that can be used as a nonaqueous electrolyte in a conventional lithium secondary battery. At this time, their content can also be appropriately changed within a generally usable range.

Specifically, the non-aqueous organic solvent may include conventional organic solvents which can be used as a non-aqueous organic solvent for a lithium secondary battery such as a cyclic carbonate solvent, a linear carbonate solvent, an ester solvent or a ketone solvent. It can be used in combination of species or more.

The cyclic carbonate solvent may be a mixed solution of one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

Examples of the linear carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), fluoroethylene carbonate (MPC) and ethyl propyl carbonate (EPC). These solvents may be used alone or in combination of two or more.

The ester solvents include alkyl acetates having 1 to 4 alkyl carbon atoms, alkyl propionates having 1 to 4 alkyl carbon atoms, alkyl butyrate having 1 to 4 alkyl carbon atoms, gamma -butyrolactone, gamma -valerolactone ,? -caprolactone,? -valerolactone, and? -caprolactone. As the ketone solvent, polymethyl vinyl ketone or the like may be used.

On the other hand, the non-aqueous organic solvent may be a mixed organic solvent in which three kinds of carbonate-based solvents are mixed, and may be more preferable when using a ternary non-aqueous organic solvent. Examples of the compound which can be used include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, vinylene carbonate, fluoroethylene carbonate, methylpropyl carbonate or ethylpropyl carbonate And a mixed solvent obtained by mixing three kinds of the carbonate compounds may be applied.

The lithium salt that can be included in the nonaqueous electrolyte may provide a predetermined lithium ion conductivity and may be applied without limitation as long as it is commonly used in an electrolyte for a lithium secondary battery. For example, as the anion of the lithium salt, ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF _{^{3 -, (CF 3) 4}} PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, F 3 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 -, At least one lithium salt selected from the group consisting of 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 ^- have.

The additive that can be included in the non-aqueous electrolyte is not particularly limited, and various substances may be contained for various purposes such as forming an SEI film on the negative electrode, protecting the SEI film, preventing side reactions between the electrolyte and the electrode, and improving lithium ion conductivity. And can be divided into a lithium type additive and a non-lithium type additive. In the case of a lithium type additive, it may be preferable that one kind of lithium salt is added. In the case of a non-lithium type additive, there is no particular limitation.

In the lithium secondary battery of the present invention, the positive electrode, the negative electrode, and the separator having the above-described structure may be contained in the pouch case, and then the non-aqueous electrolyte may be injected to form the pouch type battery. However, the present invention is not limited thereto. The outer shape of the lithium secondary battery according to the present invention is not particularly limited and a cylindrical shape or a square shape using a can can be applied, and a coin shape or the like can be applied.

Example

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to 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  One

5 kg of a positive electrode active material (Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ ) having an average particle diameter of 5 μm as the first active material particles was added to 100 kg of an organic solvent N-methylpyrrolidone to prepare a linear dispersion Respectively. Thereafter, the first active material having an average particle diameter of 5 μm and the second active material particles having an average particle diameter of 15 μm were mixed with the positive electrode active material (Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ ) was mixed with 96.5 parts by weight of a cathode active material having a weight ratio of 2: 8, 1.5 parts by weight of a conductive material and 2.0 parts by weight of a binder (polyvinylidene fluoride) to prepare a first cathode active material slurry.

Subsequently, a slurry using the first cathode active material ray dispersion liquid and a slurry using the first cathode active material that was not linearly dispersed were sequentially coated on the aluminum current collector, followed by drying and rolling to prepare a cathode.

Example  2

The first cathode active material (Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ ) having an average particle diameter of 5 μm and the second cathode active material having an average particle diameter of 15 μm were mixed in a ratio of 1: 9 A positive electrode and a secondary battery including the positive electrode were prepared in the same manner as in Example 1.

Comparative Example  One

A positive electrode was prepared in the same manner as in Example 1, except that the first active material particles were not pre-dispersed in an organic solvent but were put into an organic solvent in the form of dry particles together with the second active material particles.

Comparative Example  2

A positive electrode was prepared in the same manner as in Example 1 except that the first active material particles were linearly dispersed in an organic solvent and the second active material particles were also added.

Experimental Example  One: Rolling property  evaluation

The rolled properties of the prepared positive electrodes of Examples 1 to 2 and Comparative Examples 1 and 2 were evaluated by the following methods, and the results are shown in Table 1 below.

During rolling Line pressure

A load cell (pressure measurement) was placed under the cylinders on both sides of the rolling mill, and the pressure was measured by the load cell while the rolling roll was opened by the electrode during rolling, and the pressure was calculated and divided by the coating width.

Limit rolling thickness

The thickness at which the electrodes were rolled when the line pressure measuring equipment was rolled under the greatest force during the rolling was measured.

Evaluation items Example Comparative Example One 2 One 2 Line pressure at rolling (ton / cm) 2.905 3.162 3.402 3.394 Limit rolling thickness (㎛) 154 155 157 157

Referring to Table 1, it can be seen indirectly whether or not the active materials are uniformly dispersed in the active material layer. The results of measuring the line pressure and the critical rolling thickness at the time of rolling can be seen. 1 and 2, it is possible to realize a thickness to be targeted even at a low pressure due to a low line pressure at the time of rolling, which can be inferred from the fact that the active material layer is uniformly dispersed, The damage of the aluminum current collector can be suppressed.

It can be understood that the limiting rolling thickness is smaller in Examples 1 and 2 than in Comparative Examples 1 and 2 and this means that the rolled thickness is thinner because the active material distribution is uniform and the filling rate is excellent .

Experimental Example  2: crack Occurrence  evaluation

The positive electrodes of Examples 1 and 2 and Comparative Examples 1 and 2 were wound on a circular column having diameters of 3, 3.5, 4.0, 4.5, and 5.0 mm, respectively, and the degree of occurrence of disconnection (or cracking) , And the results are shown in Table 2 below.

Evaluation items Example Comparative Example One 2 One 2 3.0 mm X O O O 3.5 mm X X O O 4.0 mm X X O X 4.5 mm X X X X 5.0 mm X X X X

Referring to Table 2, as shown in Table 1, cracks (disconnection) occurred in the positive electrode of Comparative Example 1 at 4.0 mm or less, disconnection occurred in the cylindrical electrode of 3.5 mm in diameter at the positive electrode of Comparative Example 2 , It was confirmed that cracks (broken lines) did not occur even when winding was performed on a cylinder of 3.0 mm in Example 1 and a cylinder of 3.5 mm in diameter in Example 2 anode.

That is, the smaller the diameter of the cylinder, the greater the bending stress at the time of winding. Compared with the active material layer of the comparative examples, the bending stress at the time of winding is concentrated at a certain point of the anode It can be confirmed that cracks do not occur because there is no phenomenon, and it can be seen that the active material is uniformly dispersed by the fact that the stress is not concentrated at a specific point during bending.

Experimental Example  3: Battery performance evaluation

A lithium secondary battery was prepared using the positive electrodes prepared in Examples 1 and 2 and Comparative Examples 1 and 2, respectively.

An anode slurry was prepared by mixing an artificial graphite anode active material, a conductive material (Super-P) and a thickener (carboxymethyl cellulose) binder (styrene butadiene rubber) in a ratio of 97.5: 0.5: 1.0: 1.0, And then dried and rolled to prepare a negative electrode.

A lithium secondary battery was prepared by preparing an electrode assembly between the negative electrode prepared above and a separator of porous polyethylene between the positive electrode and the electrode assembly, placing the electrode assembly inside the case, and then injecting an electrolyte into the case. The electrolyte solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1.15 M in an organic solvent composed of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / EMC / DEC = 3/4/3) Respectively.

Charge-discharge life characteristics of the lithium secondary battery were evaluated, and the results are shown in Table 3 below.

Evaluation condition

Charging conditions: 0.5C, 4.2V, 1 / 20C cut off

Discharge condition: 1C, 2.75V cutoff

Evaluation items Example Comparative Example One 2 One 2 Efficiency after 100 cycles 98% 98% 98% 98% Efficiency after 300 cycles 95% 95% 95% 95% Efficiency after 500 cycles 93% 93% 92% 92% Efficiency after 1000 cycles 86% 86% 84% 84%

Referring to Table 3, it was found that the efficiencies of 100 cycles were not significantly changed in Examples 1 and 2 as compared with Comparative Examples 1 and 2. However, when 1000 cycles elapsed after 500 cycles, the efficiency difference was observed have.

In other words, it has been confirmed that the anode manufactured by applying the active material line dispersion can achieve a performance equal to or higher than that of the anode manufactured by the conventional method. Further, even though the performance is equal to or more than that, It can be greatly reduced and accordingly, the fairness can be improved, and as a result, the quality of the battery can be improved.

Claims (11)

(a) preparing an active material ray dispersion in which the first active material particles are dispersed in an organic solvent; And
(b) mixing the active material line dispersion, the second active material particles, the conductive material and the binder with an organic solvent to prepare an electrode slurry,
Wherein an average particle diameter (D50) of the first active material particles is smaller than an average particle diameter (D50) of the second active material particles.
The method according to claim 1,
Wherein the first active material particle has an average particle diameter of 10 mu m or less and the second active material particle has an average particle diameter of 10 mu m or more.
The method according to claim 1,
Wherein the first active material particle has an average particle diameter of 1 to 7 占 퐉 and the second active material particle has an average particle diameter of 12 to 17 占 퐉.
The method according to claim 1,
Wherein the average particle diameter of the first active material particle and the average particle diameter of the second active material particle are both 10 占 퐉 or less and the difference in average particle diameter of the two active material particles is 3 to 9 占 퐉.
The method according to claim 1,
Wherein the conductive material is added in the form of a conductive material linear dispersion by dispersing the conductive material particles in the organic solvent.
The method according to claim 1,
And (c) after the step (b), coating the electrode slurry on the electrode current collector, followed by drying and rolling.
The method according to claim 1,
Wherein the first active material particles are contained in an amount of 3 to 50 parts by weight based on 100 parts by weight of the organic solvent in the step (a).
The method according to claim 1,
Wherein the step (b) comprises adding the second active material particles, the conductive material and the binder to the organic solvent, and adding the active material ray dispersion liquid.
The method according to claim 1,
Wherein the first active material particle and the second active material particle have a volume ratio of 5:95 to 40:60.
The method according to claim 1,
Wherein the electrode is an anode.
A method of manufacturing a lithium secondary battery, comprising the method of manufacturing an electrode according to claim 1.