KR102277226B1 - Method for Preparing Electrode for a Secondary Battery - Google Patents

Abstract

The present invention provides a method for manufacturing an electrode for a secondary battery,
(i) preparing an electrode slurry including an electrode active material and a binder;
(ii) preparing a temporary electrode by coating the electrode slurry with the one surface facing downward with respect to the direction of gravity when the electrode slurry is applied to one surface of both surfaces of the current collector; and
(iii) drying the temporary electrode in a state in which the electrode slurry coated on one surface of the current collector faces downward with respect to the direction of gravity;
It relates to a method of manufacturing an electrode for a secondary battery, characterized in that it comprises a.

Description

Method for Preparing Electrode for a Secondary Battery {Method for Preparing Electrode for a Secondary Battery}

The present invention relates to a method for manufacturing an electrode for a secondary battery, and more particularly, to a method for manufacturing an electrode for a secondary battery in which the coating of the electrode slurry is made at the lower end of the current collector based on the direction of gravity and the drying process is performed in that state.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries have been commercialized and widely used.

In addition, as interest in environmental issues has increased in recent years, electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, have been developed. There is a lot of research going on. As a power source for such electric vehicles (EVs) and hybrid electric vehicles (HEVs), lithium secondary batteries with high energy density, high discharge voltage, and output stability are mainly researched and used.

This lithium secondary battery is being developed as a model that can realize high voltage and high capacity according to the needs of consumers. In order to realize high capacity, the four major elements of lithium secondary batteries in a limited space: a cathode material, anode material, and a separator , and an electrolyte solution optimization process are required.

In general, the easiest method for realizing high capacity is to prepare a high-loading electrode by placing a large amount of electrode active material on the current collector, but if a certain level of electrode adhesion is not secured, electrode coating, drying, and rolling processes When the electrode is detached, it may cause a problem in which battery performance and stability are deteriorated.

Therefore, in order to manufacture a battery with excellent battery performance and stability while implementing a high capacity, research on a method for improving electrode adhesion has been actively conducted in the art, and a method including a binder for improving electrode adhesion in an electrode is currently conducted. It is widely used.

The electrode active material, the conductive material, and the current collector constituting the electrode are solid at room temperature and have different surface properties, so it is difficult to bond easily at room temperature, but when using a polymer binder, the bonding force between the components of the electrode is increased, It is possible to suppress the detachment of the electrode during the electrode coating, drying, and rolling processes.

However, if the content of the binder is increased in order to improve electrode adhesion, the internal resistance of the electrode is increased, the electronic conductivity is lowered, and the capacity is reduced. On the other hand, when the content of the binder is small, the adhesion is reduced. Therefore, there is a problem in that the electrode is broken during the charging and discharging process, and the cycle characteristics are deteriorated.

In addition, as shown in FIG. 1, when the electrode slurry is coated and dried at a high temperature of 70° C. or higher as in the conventional electrode manufacturing method, in the drying process, due to the temperature condition of Tg or higher of the binder, it is contained in a slurry state. As the binder moves in the direction in which the solvent is volatilized (a direction away from the current collector), a significant number of the binders are present on the surface of the electrode, thereby further weakening the adhesive force between the current collector and the electrode mixture.

Therefore, there is a high need for the development of an electrode manufacturing method capable of improving overall battery performance by having sufficient electrode adhesion even with a small amount of binder while having a high theoretical capacity.

An object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

When the inventors of the present application repeat in-depth research and various experiments, the electrode slurry is coated at the bottom of the current collector, and the electrode slurry is dried while the coating surface of the electrode slurry is located at the bottom of the current collector. , confirmed that a desired effect can be achieved even with a small amount of binder because the binder moves in the direction of the current collector by the drying process and exists in a significant amount near the current collector, and thus the present invention has been completed.

Therefore, the manufacturing method of the electrode for a secondary battery according to the present invention,

(i) preparing an electrode slurry including an electrode active material and a binder;

(ii) preparing a temporary electrode by coating the electrode slurry with the one surface facing downward with respect to the direction of gravity when the electrode slurry is applied to one surface of both surfaces of the current collector; and

(iii) drying the temporary electrode in a state in which the electrode slurry coated on one surface of the current collector faces downward with respect to the direction of gravity;

It is characterized in that it includes.

In addition, after step (iii)

(iv) coating the electrode slurry on the other surface of the current collector with the electrode having the electrode slurry coating layer formed on one surface of the current collector, with the other surface of the current collector facing downward with respect to the gravitational direction; and

(v) drying the electrode in a state in which the electrode slurry coated on the other surface of the current collector faces downward with respect to the direction of gravity;

It is possible to manufacture an electrode in which the electrode mixture layer is formed on both sides of the current collector by further including.

As described above, in the method of manufacturing an electrode according to the present invention, the electrode slurry is applied from the bottom with respect to the direction of gravity, and the electrode slurry is dried while being coated on the lower surface of the current collector.

In this case, unlike the conventional method in which a relatively light binder in the solid content in the slurry rises toward the surface of the electrode during the drying process of the electrode, the current collector exists above the direction of gravity, so the binder rises toward the current collector. A significant amount of the binder is present in the vicinity of the current collector, and even a small amount has an effect of improving the adhesion between the current collector and the electrode mixture layer.

However, in this case, when the electrode slurry is applied, since the electrode slurry is applied under the current collector with respect to the direction of gravity, there may be a problem that the electrode slurry falls due to gravity, which causes difficulties in the process and waste of materials. Therefore, the electrode slurry according to the present invention needs to have a viscosity that does not fall off the current collector even by gravity for a predetermined period of time, and specifically, a Brookfield L-type viscometer at a temperature of 25° C. The viscosity after rotation for 1 minute at a furnace rotor number 64 and rotation speed 12 rpm may be 3000 to 30000 cP, specifically 5000 to 15000 cP.

Out of the above range, if the viscosity is less than 3000 cP, the electrode slurry is detached during the application process, so that normal application of the electrode slurry is impossible, and material damage to the electrode slurry occurs, which is not preferable in terms of fairness and economic feasibility, 30000 If it exceeds cP, the viscosity becomes too high, so it is difficult to apply the electrode slurry itself, and the coating surface is not uniformly formed, which is not preferable.

In addition, even if the electrode slurry according to the present invention has a predetermined viscosity within the above range, if a lot of time is taken between application and drying of the electrode slurry, the electrode slurry may have a problem that the electrode slurry falls under the influence of gravity. Preferably, the steps (ii) and (iii), and/or the steps (iv) and (v) are continuously performed.

Here, continuously performed means that all is performed in a series of processes. For example, if the drying process is performed as soon as the coating process is completed, the drying process is sequentially performed from the first coated part during the coating process. case (refer to FIG. 3), or a case in which the coating process and the drying process are performed almost simultaneously.

Specifically, the time interval between the coating start point of the electrode slurry of step (ii) and the drying start point of step (iii) and/or the coating start point of the electrode slurry of step (iv) and the drying start point of step (v) It is more effective if the execution time interval is within 20 seconds, specifically within 10 seconds.

Out of the above range, if it exceeds 20 seconds, the electrode slurry may flow down, which is not preferable.

On the other hand, the coating method is not limited, and as a known technique, a die coating method, a slide-slot die coating method, a roll coating method, an electrospinning or spraying method, or a combination thereof It may be carried out, but in detail, it may be a die coating method so that the coating can be easily performed in the downward direction based on the direction of gravity.

The drying is a process in which all of the solvent of the electrode slurry is volatilized to completely harden, and it can be performed under the same conditions as in the conventional drying process, for example, in the range of 60 to 150 degrees Celsius, for 1 hour or less, in detail In the range of 80 to 130 degrees Celsius, it may be carried out for 10 minutes or less.

In addition, the method for manufacturing an electrode according to the present invention may further include a step of rolling after the step (iii) and/or step (v), wherein the rolling is performed in which the electrode density may vary depending on the rolling strength. Bar, it may be appropriately set in consideration of this, and in detail as the method, it may be performed by a roll press method.

In the electrode for a secondary battery prepared from this process, in the electrode mixture layer obtained after drying the coated electrode slurry, as the binder moves upward in the direction opposite to the gravity direction during the electrode drying process, the binder content in the area adjacent to the current collector is collected. It may have a structure relatively more than the binder content of the portion spaced apart from the whole.

Therefore, even with a small amount of binder, the adhesive force between the current collector and the electrode mixture layer can be increased, and as a result, overall battery performance can be improved.

The current collector and the electrode active material may be determined according to the type of electrode to be manufactured, and specifically, when the electrode is a positive electrode, it may be a positive electrode current collector and a positive electrode active material, or when the electrode is a negative electrode, a negative electrode current collector and It may be an anode active material.

The positive electrode current collector is generally made to have a thickness of 3 to 500 μm. Such a 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. may be used on the surface of the surface-treated. 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, a sheet, a foil, a net, a porous body, a foam body, and a nonwoven body are possible.

The positive active material may _{include a layered compound such as lithium cobalt oxide (LiCoO 2} ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Formula Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO _{2 ;} lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O _{7 ;} Ni site-type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _2-x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, lithium manganese composite oxide represented by Ni, Cu or Zn; LiNi _x Mn _2-x O ₄ A lithium manganese composite oxide having a spinel structure; _{LiMn 2} O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; disulfide compounds; And the like Fe ₂ (MoO _{4) 3,} but is not limited to these.

The negative electrode current collector is generally made to have a thickness of 3 ~ 500 ㎛. Such a negative current collector is not particularly limited as long as it has conductivity without causing a 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, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding force 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, a sheet, a foil, a net, a porous body, a foam, and a non-woven body.

The negative active material may include, 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 , and metal oxides such as _{Bi 2} O _{5 ;} conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxide; Lithium titanium oxide etc. are mentioned.

On the other hand, the binder included in the electrode slurry is a component that assists in bonding of 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 slurry containing the electrode active material. do. However, according to the manufacturing method according to the present invention, sufficient adhesive force can be exhibited even with a small amount of binder. Specifically, the content of the binder may be 1 wt% to 5 wt% based on the total weight of the slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butyrene rubber, fluororubber, various copolymers, and the like.

In addition, the electrode slurry may further include a conductive material and/or a filler in addition to the active material and the binder.

The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the slurry including the electrode 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; A conductive material such as a polyphenylene derivative may be used.

The filler is optionally used as a component for inhibiting the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. For example, an olipine-based polymer such as polyethylene or polypropylene; A fibrous material such as glass fiber or carbon fiber is used.

The present invention also provides a lithium secondary battery including an electrode for a secondary battery manufactured according to the manufacturing method, a battery pack using the lithium secondary battery as a unit battery, and a device including the battery pack.

Specific examples of the device include, but are not limited to, small devices such as computers, mobile phones, and power tools, and power tools that are powered by an omniscient motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooter); electric golf carts; mid- to large-sized devices such as a power storage system, but is not limited thereto.

In addition, since the manufacturing method of the lithium secondary battery and the manufacturing method of the battery pack are known in the art, the description thereof will be omitted in the present invention.

As described above, in the method for manufacturing an electrode for a secondary battery according to the present invention, when the electrode slurry is applied, the electrode slurry is coated with the application surface facing down, and the electrode slurry is coated as it is, that is, of the electrode slurry. By including the process of drying with the coated surface located at the bottom of the current collector, the binder moves in the direction of the current collector by the drying process and exists in a significant amount near the current collector, so even a small amount of binder exhibits sufficient adhesion, so overall There is an effect that can improve the performance of the secondary battery.

1 is a schematic diagram of an electrode for a secondary battery manufactured according to the prior art;
2 is a flowchart illustrating a method of manufacturing an electrode for a secondary battery according to an embodiment of the present invention;
3 is a schematic diagram showing a method of manufacturing an electrode for a substantial secondary battery according to an embodiment of the present invention;
4 is a schematic diagram of an electrode manufactured by the manufacturing method according to the present invention.

Hereinafter, although described with reference to the drawings according to the embodiment of the present invention, this is for easier understanding of the present invention, and the scope of the present invention is not limited thereto.

2 is a flowchart schematically showing a method of manufacturing an electrode for a secondary battery according to an embodiment of the present invention.

Referring to FIG. 2 , the current collector 110 is prepared (step (a)). Then, the electrode slurry 120 including an active material (not shown) and a binder (not shown) is coated with one surface 111 of the current collector 110 facing downward with respect to the direction of gravity (not shown) ( process (b)).

When the application of the electrode slurry 120 is completed, the coating surface is dried in the range of 80 to 130 degrees Celsius for 10 minutes or less while the coating surface faces downward with respect to the direction of gravity to evaporate all the solvent in the electrode slurry 120 . to manufacture the electrode 100 in which the electrode mixture 130 layer is formed on the lower surface of the current collector 110 (process (c)).

The electrode 100 manufactured by this process is shown in FIG. 4 .

Referring to FIG. 4 , in the electrode mixture 130 including the active material 131 and the binder 132 formed on one surface of the current collector 110 , a significant portion of the binder 132 is located near the current collector 110 . exist.

Referring back to FIG. 2 , after the process (c), the electrode slurry 120 is applied to the other surface 112 of the current collector 110 again to form an electrode mixture 130 layer on both sides of the current collector 110 . have.

Specifically, the electrode 100 on which the electrode mixture 130 layer is formed on one surface 111 of the current collector 110, the other surface 112 of the current collector 110 on which the electrode mixture 130 layer is not formed is gravity Prepare with the direction facing downward (process (d)).

Then, by repeating the process performed in steps (b) and (c), the active material (shown in the figure) is placed on the other surface 112 with the other surface 112 of the current collector 110 facing downward with respect to the direction of gravity. Not shown) and a binder (not shown) is coated (process (e)), and when the application of the electrode slurry 120 is completed, the other surface 112 is lowered based on the direction of gravity. By forming the electrode mixture 130 layer on the other surface 112 of the current collector 110 by drying it in the range of 80 to 130 degrees Celsius for 10 minutes or less to volatilize all of the solvent in the electrode slurry 120 as it is facing toward the The electrode 200 in which the electrode mixture 130 layer is formed on both sides of the current collector 110 is manufactured (process (f)).

A method of manufacturing an electrode for a secondary battery according to an embodiment of the present invention substantially illustrating such a manufacturing method is schematically shown in FIG. 3 .

Referring to FIG. 3 , the current collector 110 is supplied in a state supported by the roller 140 , and the electrode slurry 120 is applied to one surface 111 of the current collector 110 from the lower surface of the current collector 110 . In order to sequentially apply the current collector 110, the current collector moves by the rotating roller 140 in contact with the current collector 110, and includes a coating die 150 for supplying the electrode slurry 120 to the electrode slurry ( 120 is applied to one surface 111 of the current collector 110 from the lower surface of the current collector 110 .

As described above, the current collector 110 coated with the electrode slurry 120 directly moves to the dryer 160 , and finally the electrode 100 according to the present invention is manufactured through a drying process.

In the electrode manufactured in this way, as the binder moves upward during the drying process, as shown in FIG. 4 , an electrode structure in which the binder is present in a significant portion near the current collector may be formed.

At this time, the electrode slurry 120 coated on the lower surface has a viscosity of 5000 to 15000 cP after rotation at a temperature of 25° C. with a Brookfield L-type viscometer for 1 minute at a rotor number of 64 and a rotation speed of 12 rpm, and after coating Since the starting point is continuously coated and dried within 20 seconds, there is no risk of dripping even if it is coated from the bottom.

Hereinafter, the present invention will be described with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

<Example 1>

The positive active material Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ , the conductive material Denka black and the binder polyvinylidene fluoride are mixed with NMP (Nmethyl pyrrolidone) in a weight ratio of 96:2:2 A mixed slurry was prepared.

The slurry was coated on the cross section so that the slurry was applied from the bottom in the same manner as in the processes (a) to (c) and 3 of Fig. 2 on an Al foil having a thickness of 20 μm, and dried at 120 degrees Celsius for 5 minutes to form a positive electrode. prepared.

<Comparative Example 1>

The same slurry as in Example 1 was coated on the cross section in a manner of applying the same slurry to the upper surface of an Al foil having a thickness of 20 μm, and dried at 120° C. for 5 minutes to prepare a positive electrode.

<Experimental Example 1>

The electrode plate of the positive electrode prepared in Example 1 and Comparative Example 1 was cut to a certain size and fixed to a slide glass, and then the current collector was peeled off to measure the peel strength at 180 degrees, and the results are shown in Table 1 below.

Example 1 Comparative Example 1 Adhesion (gf/10mm) 130 10

In Table 1, first, referring to Example 1 and Comparative Example 1, it can be seen that the adhesive strength of Example 1 is very high compared to Comparative Example 1.

<Experimental Example 2>

A slurry in which graphite as an anode active material, a conductive material, Denka black, and polyvinylidene fluoride, as a binder, were mixed in a weight ratio of 96:2:2 as the positive electrode of Example 1 and Comparative Example 1 A monocell was prepared using an electrolyte solution containing 1M LiPF6 in a solvent of EC:EMC=3:7, using a coating, drying, and rolling over the whole.

After charging and discharging (2.5V) the monocell for 100 cycles in 1C CC/CV mode with an upper limit voltage of 4.25V at a room temperature of 25 degrees Celsius, the capacity retention rate was measured, and the results are shown in Table 2.

Example 1 Comparative Example 1 Initial discharge capacity (mAh/g) 153.2 154.0 Capacity retention rate (100 ^th , %) 98.1 97.5

Referring to Table 2, it can be seen that the higher the adhesive force, the better the lifespan characteristics.

Those of ordinary skill in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Claims (10)

A method for manufacturing an electrode for a secondary battery, comprising:
(i) preparing an electrode slurry including an electrode active material and a binder;
(ii) preparing a temporary electrode by coating the electrode slurry with the one surface facing downward with respect to the direction of gravity when the electrode slurry is applied to one surface of both surfaces of the current collector; and
(iii) drying the electrode slurry coated on one surface of the current collector in a state in which the electrode slurry is directed downward with respect to the direction of gravity,
The steps (ii) and (iii) are performed continuously,
The electrode slurry has a viscosity of 5000 to 15000 cP after rotation at a temperature of 25° C. with a Brookfield L-type viscometer at a rotor number of 64 and a rotation speed of 12 rpm for 1 minute. The method of claim 1, wherein after step (iii)
(iv) coating the electrode slurry on the other surface of the current collector with the electrode having the electrode slurry coating layer formed on one surface of the current collector, with the other surface of the current collector facing downward with respect to the gravitational direction; and
(v) drying the electrode in a state in which the electrode slurry coated on the other surface of the current collector faces downward with respect to the direction of gravity;
A method of manufacturing an electrode for a secondary battery, comprising: The secondary according to claim 2, wherein the electrode slurry has a viscosity of 5000 to 15000 cP after rotation at a temperature of 25° C. with a Brookfield L-type viscometer at a rotor number of 64 and a rotation speed of 12 rpm for 1 minute. A method of manufacturing an electrode for a battery. The method according to claim 1 or 2, wherein the coating is performed by a die coating method, a slide-slot die coating method, a roll coating method, an electrospinning or spraying method, or a combination thereof. A method of manufacturing an electrode for a secondary battery. The method according to claim 2, wherein the steps (iv) and (v) are continuously performed. The method according to claim 1, wherein a time interval between the coating start point of the electrode slurry in step (ii) and the drying start point in step (iii) is within 10 seconds. The method according to claim 2, wherein the time interval between the coating start point of the electrode slurry in step (iv) and the drying start point in step (v) is within 10 seconds. The method of claim 1 or 2, wherein the drying is performed in a range of 80 to 130 degrees Celsius for 10 minutes or less. The method of claim 1 or 2, further comprising a step of rolling after step (iii) and/or step (v). An electrode for a secondary battery manufactured by the method according to claim 1, wherein in the electrode mixture layer obtained after drying of the coated electrode slurry, the binder content in the portion adjacent to the current collector is relatively higher than the binder content in the portion spaced from the current collector An electrode for a secondary battery, characterized in that.

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