KR20240031089A - Method for preparing electrode of secondary battery - Google Patents

Abstract

The present invention provides a method for manufacturing electrodes for secondary batteries that can effectively reduce the amount of moisture remaining in the electrode and at the same time significantly improve electrode adhesion. The method for manufacturing an electrode for a secondary battery includes manufacturing an electrode on which an electrode active material layer is formed; rolling the electrode; A step of drying the rolled electrode, wherein the drying step is such that the drying temperature in at least some sections is 170°C to 210°C, which is a temperature higher than the melting point (170°C) of the polyvinylidene fluoride (PVDF)-based binder resin. It can be done.

Description

Method for manufacturing electrodes for secondary batteries {METHOD FOR PREPARING ELECTRODE OF SECONDARY BATTERY}

The present invention relates to a method for manufacturing electrodes for secondary batteries, and specifically, to a method for manufacturing electrodes for secondary batteries that can significantly improve the adhesion between the electrode active material layer and the electrode current collector by effectively reducing the amount of moisture remaining in the electrode while minimizing the decline in binder crystallinity. It's about.

Recently, due to the rapid increase in the use of fossil fuels, the demand for the use of alternative or clean energy is increasing. As part of this, the field that has been most actively researched in recent years is the field of power generation and storage using electrochemistry.

A representative example of an electrochemical device that uses such electrochemical energy is a secondary battery, and its use area is gradually expanding. In particular, as technology development and demand for portable devices such as portable computers, portable phones, and cameras increase recently, the demand for secondary batteries with medium-high energy density, that is, high-capacity lithium secondary batteries, as an energy source is rapidly increasing. .

Among such secondary batteries, much research has been conducted to develop lithium secondary batteries that exhibit high energy density and operating potential while having a long cycle life and low self-discharge rate.

On the other hand, the lithium secondary battery has a structure in which an electrode assembly capable of charging and discharging of a positive electrode/separator/negative electrode structure is mounted on a battery case, and the electrodes of the positive electrode and negative electrode are formed by mixing a slurry of an active material and a binder resin component with a metal collector. It is manufactured by applying it to one or both sides of the entire body to form an electrode active material layer, followed by drying and rolling.

At this time, conventionally, in order to remove moisture remaining inside the electrode after rolling the active material layer, a drying process is generally performed at a low temperature at which a conventional binder resin, such as polyvinylidene fluoride (PVDF)-based binder resin, does not melt. It was. If the drying process is performed at a temperature above the melting point (170°C) of the polyvinylidene fluoride (PVDF)-based binder resin after rolling, the polyvinylidene fluoride (PVDF)-based binder resin melts and the crystallinity decreases, causing the electrode to Brittleness decreases, which causes the electrode strength to decrease and durability to decrease. On the other hand, when drying is performed at a temperature of 170°C or lower, a long drying time is required to reduce the amount of moisture remaining in the electrode to the desired level, resulting in another problem of reduced productivity.

Therefore, there is a need to develop a new electrode manufacturing method that can prevent a decrease in electrode strength during electrode manufacturing and improve adhesion by reducing the amount of moisture remaining inside the electrode to a desired level.

Korean Patent Registration No. 0670488

The present invention is intended to solve this problem, and when performing a drying process after rolling, the drying temperature of at least some sections is performed above the binder melting point (170°C) and the total drying time is performed for 5 seconds or less. The object is to provide a method for manufacturing electrodes for batteries.

According to one embodiment, the present invention includes manufacturing an electrode having an electrode active material layer formed on an electrode current collector; rolling the electrode; and drying the rolled electrode, wherein the drying step is performed so that the drying temperature in at least some sections is 170°C to 210°C.

The total drying time of the electrode rolled in the above method may be 2 to 5 seconds.

Additionally, the step of drying the rolled electrode may be performed as a roll-to-roll process.

The step of drying the rolled electrode is performed at a temperature of 130°C or higher, and specifically includes performing a first drying process at 130°C to 150°C; Carrying out a second drying process at 150°C to 170°C; And performing a third drying process at 170°C to 210°C.

According to the method of manufacturing an electrode for a secondary battery of the present invention, during the drying process after rolling, the drying temperature in some sections is performed above the binder melting point temperature (170°C), and the total drying time is performed for 5 seconds or less, thereby reducing the binder crystallinity. Since the residual amount of moisture in the electrode can be effectively reduced while minimizing it, the adhesion between the electrode active material layer and the electrode current collector can be significantly improved, thereby making it possible to implement a lithium secondary battery with improved durability.

The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention along with the contents of the above-described invention. Therefore, the present invention is limited to the matters described in such drawings. It should not be interpreted as limited.
Figure 1 is a graph showing the results of evaluating the amount of moisture remaining inside the electrode according to Experimental Example 1.
Figure 2 is a graph showing the results of electrode adhesion evaluation according to Experimental Example 2.

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

Terms (including technical and scientific terms) or words used in this specification and claims may be used with meanings that can be commonly understood by those skilled in the art in the technical field to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not interpreted ideally or excessively unless clearly specifically defined.

The terminology used herein is for describing embodiments and is not intended to limit the invention. As used herein, singular forms also include plural forms, unless specifically stated otherwise in the context. As used in the specification, “comprises” and/or “comprising” does not exclude the presence or addition of one or more other elements in addition to the mentioned elements.

In this specification, when it is said that a part includes a certain component, this does not mean that other components are excluded, but that it may further include other components, unless specifically stated to the contrary.

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

Method for manufacturing electrodes for secondary batteries

The method for manufacturing electrodes for secondary batteries of the present invention is

(S1) manufacturing an electrode with an electrode active material layer formed on an electrode current collector;

(S2) rolling the electrode; and

(S3) comprising drying the rolled electrode,

The drying step may be performed so that the drying temperature in at least some sections is 170°C to 210°C.

Conventionally, a slurry mixed with an active material and a binder resin component is applied to one or both sides of a metal current collector, the electrode on which the electrode active material layer is formed is rolled, and then the crystallinity of the binder resin, such as polyvinylidene fluoride (PVDF)-based binder resin, is changed. To prevent deterioration, a method was required to perform the drying process at a low temperature (below 170°C) where the binder resin is not melted. However, when drying is performed at a low temperature, a long drying time is required to reduce the amount of moisture remaining in the electrode to the desired level, which causes the problem of reduced productivity.

As a result of repeated research to solve this problem, the present inventors conducted a drying process such that the drying temperature in some sections of the drying process after rolling was above the melting point (170°C) of the polyvinylidene fluoride (PVDF)-based binder resin, and the total The present invention was completed by finding that by performing a drying time of 5 seconds or less, the amount of moisture remaining in the electrode can be effectively reduced while minimizing the decrease in crystallinity of the binder resin.

This will be explained in detail below.

(S1) Electrode manufacturing steps

The method for manufacturing an electrode for a secondary battery according to the present invention may include manufacturing an electrode in which an electrode active material layer is formed on an electrode current collector.

The electrode active material layer can be prepared by mixing or dispersing the electrode active material and the binder in a solvent to prepare an electrode slurry composition, then applying it on an electrode current collector and drying it.

At this time, the process of applying the electrode slurry composition to the electrode current collector can be performed by a method commonly known in the art, for example, uniformly dispersed using a doctor blade, etc., Die casting. It can be performed through methods such as comma coating and screen printing.

In addition, the drying process of the electrode slurry composition applied on the electrode current collector may be performed according to commonly known methods, for example, vacuum heat treatment in a certain temperature range, or heat treatment such as hot air injection. It can be.

Additionally, the temperature range of the drying process may be 60°C to 130°C, specifically 80°C to 130°C, and more specifically 100°C to 130°C. At this time, when the temperature satisfies the above range, the moisture content inside the electrode active material layer can be minimized, and the volatile components included in the process are sufficiently removed to prevent side reactions from occurring and battery characteristics during subsequent charging and discharging of the battery. Deterioration can be prevented. In particular, by performing the drying process at a temperature of 130°C or lower, the migration phenomenon of the electrode active material or binder constituting the electrode active material layer is suppressed and distributed evenly within the electrode active material layer, thereby increasing the resistance of the secondary battery and Deterioration of adhesion between the current collector and the electrode active material layer can be improved.

The time required for the drying process may be 5 minutes to 3 hours, specifically 5 minutes to 20 minutes, and more specifically 5 minutes to 10 minutes.

Meanwhile, the electrode manufactured by the method of the present invention may be an anode and/or a cathode, and the anode is specifically preferred.

Specifically, when the electrode manufactured by the method of the present invention is a positive electrode, the electrode active material is lithium and one or more metals such as cobalt, manganese, nickel, or aluminum capable of reversible intercalation and deintercalation of lithium. A positive electrode active material containing a lithium complex metal oxide containing can be used.

Specifically, the positive electrode active material is lithium-cobalt-based oxide (for example, LiCoO ₂ , etc.), lithium-manganese-based oxide (for example, LiMnO ₂ , LiMn ₂ O ₄ , etc.), lithium-nickel-based oxide (for example, , LiNiO _2, etc.), lithium-nickel-manganese oxides (e.g., LiNi _1-Y Mn _Y O ₂ (where 0<Y<1), LiMn _2-z Ni _z O ₄ (where 0 <Z<2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi _1-Y1 Co _Y1 O ₂ (where 0<Y1<1), etc.), lithium-manganese-cobalt-based oxides (e.g. For example, LiCo _1-Y2 Mn _Y2 O ₂ (where 0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (where 0<Z1<2), etc.), lithium-nickel-manganese-cobalt based oxide (for example, Li(Ni _p Co _q Mn _r1 )O ₂ (where 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li (Ni _p1 Co _q1 Mn _r2 )O ₄ (where 0＜p1＜2, 0＜q1＜2, 0＜r2＜2, p1+q1+r2=2), etc.), lithium-nickel-cobalt-transition Metal (M) oxide (for example, Li(Ni _p2 Co _q2 Mn _r3 M _S2 )O ₂ (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, Ti and Mo) is selected, and p2, q2, r3 and s2 are the atomic fractions of independent elements, respectively, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3+ s2 = 1)), etc., and any one or two or more of these compounds may be included.

Among these, in that the capacity characteristics and stability of the battery can be improved, the positive electrode active material is lithium-cobalt oxide, lithium-manganese-based oxide, lithium-nickel-manganese-cobalt-based oxide, and lithium-nickel-cobalt-transition metal (M ) It may include at least one selected from the group consisting of oxides.

Specifically, the positive electrode active material is a lithium-nickel-manganese-cobalt-based oxide with a nickel content of 50 atm% or more, specifically 55 atm% or more, and/or lithium-nickel with a nickel content of 50 atm% or more, specifically 55 atm% or more. -It may contain at least one selected from cobalt-transition metal (M) oxides. Specifically, the positive electrode active material may include lithium-nickel-cobalt-transition metal (M) oxide represented by the following formula (1).

[Formula 1]

Li _a Ni _x Co _y M ¹ _z M ² _w O ₂

In Formula 1,

The M ¹ may be Mn, Al, or a combination thereof, and preferably may be Mn or Mn and Al.

The M ² is at least one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca, and Sr, and preferably may be at least one selected from the group consisting of Al, Zr, Y, Mg, and Ti, More preferably, it may be Al.

The a represents the molar ratio of lithium in the lithium-nickel-cobalt-transition metal (M) oxide, and may be 0.8≤a≤1.2, specifically 0.85≤a≤1.15, or more specifically 0.9≤a≤1.05. . When the molar ratio of lithium satisfies the above range, the crystal structure of lithium-nickel-cobalt-transition metal (M) oxide can be stably formed.

The x represents the molar ratio of nickel among all metals excluding lithium in the lithium-nickel-cobalt-transition metal (M) oxide, 0.55≤x<1, specifically 0.55≤a≤0.95, more specifically 0.60≤a ≤0.95, more specifically, 0.8≤x≤0.95. When the molar ratio of nickel satisfies the above range, high energy density is exhibited, making it possible to implement high capacity.

The y represents the molar ratio of cobalt among all metals excluding lithium in the lithium-nickel-cobalt-transition metal (M) oxide, 0<y≤0.3, preferably 0.001<y<0.3, specifically 0.025≤b≤0.20. , more specifically, 0.01≤y<0.20, and even more specifically, 0.01≤y<0.15. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be achieved.

The z represents the molar ratio of the M ¹ element among all metals excluding lithium in the lithium-nickel-cobalt-transition metal (M) oxide, 0<z≤0.3, preferably 0.001<z≤0.25, more preferably It may be 0.01≤z≤0.20, more preferably 0.01≤z≤.20, and more specifically 0.01≤z≤0.15. When the molar ratio of the M ¹ element satisfies the above range, the structural stability of the positive electrode active material is excellent.

The w represents the molar ratio of the M ² element among all metals excluding lithium in the lithium-nickel-cobalt-transition metal (M) oxide, 0<w≤0.2, specifically 0<w≤0.1, preferably 0< w≤0.05.

Specifically, in order to implement a high capacity battery, the positive electrode active material is Li(Ni _0.65 Mn _0.2 Co _0.15 )O ₂ , Li(Ni _0.7 Mn _0.2 Co _0.1 )O ₂ , Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , Li(Ni _0.8 Co _0.15 Al _0.05 )O ₂ , Li(Ni _0.86 Mn _0.07 Co _0.05 Al _0.02 )O ₂ or Li(Ni _0.90 Mn _0.05 Co _0.05 )O ₂ and other lithium complex transition metal oxides. , preferably Li(Ni _0.86 Mn _0.07 Co _0.05 Al _0.02 )O ₂ containing 80 mol% or more of Ni based on the total number of moles of transition metal.

Meanwhile, the positive electrode active material according to the present invention may be applied to the surface of the lithium nickel-based oxide particle as Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca. , Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S may further include a coating layer containing one or more coating elements selected from the group consisting of. Preferably, the coating element may be Al, B, Co, or a combination thereof.

When a coating layer is present on the surface of the lithium nickel-based oxide particle, the contact between the non-aqueous electrolyte and the lithium composite transition metal oxide is suppressed by the coating layer, which has the effect of reducing transition metal elution or gas generation due to side reactions with the non-aqueous electrolyte. can be obtained.

The positive electrode active material may be included in an amount of 80% to 99% by weight, specifically 90% to 99% by weight, based on the total weight of solids in the positive electrode slurry composition. When the content of the positive electrode active material satisfies the above range, the battery capacity of the positive electrode can be improved by securing sufficient positive electrode energy density.

The binder is a component that improves adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of solids in the positive active material layer. An example of such a binder is a polyvinylidene fluoride (PVDF)-based binder resin with a melting point of 170°C or higher.

According to one embodiment of the present invention, the binder may be included in the solid content of the positive electrode slurry composition in an amount of 0.5% by weight to 3.5% by weight, specifically 0.5% by weight to 3.0% by weight, and more specifically 0.5% by weight to 1.5% by weight. .

Meanwhile, the positive electrode slurry composition can be prepared by additionally mixing or dispersing a conductive material and a dispersant in a solvent in addition to the positive electrode active material and binder, if necessary.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black. carbon black; Graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives, etc. may be used.

The conductive material may be included in the solid content of the positive electrode slurry composition in an amount of 1.5% by weight or less, specifically 0.5% by weight to 1.0% by weight, and more specifically 0.6% by weight to 1.0% by weight. When the content of the conductive material in the solid content of the positive electrode slurry composition satisfies the above range, the electrical conductivity of the positive electrode can be improved by securing the positive electrode conductive network.

The dispersant suppresses excessive aggregation of the positive electrode active material in the positive electrode slurry composition and allows the positive active material to exist effectively dispersed in the manufactured positive electrode active material layer. The dispersant may include a hydrogenated nitrile-based copolymer, and is specifically a copolymer containing a structural unit derived from an α,β-unsaturated nitrile and a structural unit derived from a hydrogenated conjugated diene, or a structural unit derived from an α,β-unsaturated nitrile, It may be a copolymer comprising a structural unit derived from a conjugated diene and a structural unit derived from a hydrogenated conjugated diene. As the α,β-unsaturated nitrile monomer, for example, acrylonitrile or methacrylonitrile may be used, and one type of these may be used alone or a mixture of two or more types may be used. As the conjugated diene monomer, for example, conjugated diene monomers having 4 to 6 carbon atoms, such as 1,3-butadiene, isoprene, or 2,3-methyl butadiene, may be used, one or two of these. Mixtures of the above may be used.

More specifically, the hydrogenated nitrile-based copolymer may be hydrogenated nitrile-based butadiene rubber (H-NBR).

The dispersant may be included in the solid content of the positive electrode slurry composition in an amount of 1.5% by weight or less, specifically 1.2% by weight or less, and more specifically 0.1% by weight to 1.0% by weight. When the content of the dispersant satisfies the above range, the positive electrode conductive network can be improved by suppressing aggregation of the conductive material in the solid content of the positive electrode slurry composition.

Meanwhile, when the electrode manufactured by the method of the present invention is a positive electrode, the electrode current collector is not particularly limited as long as it is a positive electrode current collector that has conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. can be used.

Specifically, the positive electrode current collector may have a thickness of 3 ㎛ to 500 ㎛, and fine irregularities may be formed on the surface of the positive electrode current collector to increase adhesion to the positive electrode active material layer. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

In addition, the solvent used in preparing the electrode slurry composition may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and a desirable viscosity when including the positive electrode active material and optionally a binder and a conductive material. It can be used in an amount that is . For example, the solid content concentration in the active material slurry including the positive electrode active material and, optionally, the binder and the conductive material may be 10% by weight to 90% by weight, preferably 30% by weight to 80% by weight.

(S2) Rolling the electrode

The method of manufacturing an electrode for a secondary battery according to the present invention may include performing a rolling process on the dried electrode.

The rolling process may be performed using a roll press method, but is not limited thereto. For example, the rolling process may be performed using a hot press method.

Before performing the rolling process, the porosity of the dried electrode active material layer may be 55% or less, specifically 35% to 55%, and more specifically 40% to 55%. When the porosity of the dried electrode active material layer satisfies the above range, it is preferable in that the rolling process of the dried electrode active material layer is easy.

The rolling process may be performed on the dried electrode active material layer once or multiple times, specifically 2 to 5 times, and more specifically 3 to 5 times. In this case, the rolling process may be performed until the rolling rate of the electrode active material layer exceeds a certain numerical value. For example, the rolling rate of the electrode active material layer after the rolling process may be 10% or more, specifically 10% to 17%, and more specifically 10% to 15%. When the rolling rate of the electrode active material layer after the rolling process satisfies the above range, the electrode active material is sufficiently rolled without detachment of the electrode active material layer, thereby minimizing the number of rollings in the second rolling process.

Additionally, the thickness change rate after the rolling process may be 3.5% or less, specifically, 0.1% to 3.5%, and more specifically, 0.5% to 3.5%. When the thickness of the electrode active material layer after the rolling process satisfies the above range, a high-density electrode can be manufactured while preventing detachment of the electrode active material layer. If the thickness change rate during the rolling process exceeds 3.5%, the weak strength part of the electrode active material layer (for example, a part with a thickness thinner than the average thickness or an edge part) breaks, causing the electrode active material layer to separate from the electrode current collector. It may be detached.

Additionally, after the rolling process, the porosity of the electrode active material layer may be 20% to 36%, more specifically 20% to 34%, and specifically 25% to 34%. The porosity of the electrode active material layer after the rolling process is related to the thickness of the electrode active material layer after the rolling process. Therefore, when the porosity of the electrode active material layer satisfies the above range after the rolling process, a high-density positive electrode can be manufactured while preventing detachment of the electrode active material layer.

(S3) Drying the rolled electrode

The method for manufacturing an electrode for a secondary battery according to the present invention may include drying the rolled electrode.

At this time, the drying step is performed at a temperature of 130 ℃ or higher, and the drying temperature in at least some sections is 170 ℃ to 210 ℃, which is a temperature higher than the melting point (170 ℃) of polyvinylidene fluoride (PVDF)-based binder resin. You can.

The drying process may be performed in a roll-to-roll process, but is not limited thereto.

Specifically, the step of drying the rolled electrode may be performed as a three-step drying process while sequentially raising the temperature. Specifically, drying the rolled electrode includes performing a first drying process at 130°C to 150°C; Carrying out a second drying process at 150°C to 170°C; And it may include a third drying process at 170°C to 210°C.

As such, in the method of the present invention, when performing the drying process after rolling, the drying temperature is sequentially raised from 130 ℃ to 210 ℃, and the drying temperature in some sections is 170 ℃ to 210 ℃, so that the inside of the electrode layer Heat can be applied evenly to the active material or binder, minimizing the decline in crystallinity of the polyvinylidene fluoride (PVDF)-based binder resin and effectively reducing the amount of moisture remaining in the electrode to the desired level, preventing an increase in resistance of the secondary battery. In addition, the adhesion between the current collector and the electrode active material layer can be further improved, and the effect of improving productivity can be realized.

On the other hand, when the drying process is performed while lowering the temperature from high temperature to low temperature, for example, the first process is performed at about 180°C to 170°C, which is around the melting point (170°C) of polyvinylidene fluoride (PVDF)-based binder resin. Then, when the drying process is performed while sequentially lowering the temperature to 130℃, the crystals of the partially melted polyvinylidene fluoride (PVDF)-based binder resin gradually grow irregularly, increasing the imbalance of electrode physical properties inside the electrode. And, there is a high possibility that electrode brittleness will increase due to irregularly grown crystals. Therefore, as in the present invention, the drying process is performed while sequentially increasing the temperature from 130°C, but the drying temperature of some drying processes is performed at a temperature higher than the melting point (170°C) of the polyvinylidene fluoride (PVDF)-based binder resin, Polyvinylidene fluoride (PVDF)-based binder resin can be uniformly dissolved. Therefore, even if a room temperature (rapid) cooling process is performed as a subsequent process, the overall crystal size of the binder resin is formed uniformly, making it possible to manufacture an electrode with similar physical properties overall. In particular, small crystals formed by the quenching process can improve the toughness of the electrode.

Meanwhile, the total drying time of the rolled electrode may be 5 seconds or less, specifically 2 to 5 seconds.

When the drying time satisfies the above range, the residual amount of moisture in the electrode can be effectively reduced while minimizing the decrease in crystallinity. If the drying time exceeds the above range, the physical properties (adhesion, toughness) of the electrode may change from before drying due to the decrease in crystallinity of the polyvinylidene fluoride (PVDF)-based binder, and the thickness or area of the electrode may change. there is.

This anode can be usefully used as an anode for a lithium secondary battery.

Meanwhile, the lithium secondary battery provided with the above-described positive electrode will be described as an example.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode uses the positive electrode described above. In addition, the lithium secondary battery may further include a case for storing an electrode assembly in which the positive electrode, the separator, and the negative electrode are sequentially stacked.

Next, each component of the lithium secondary battery of the present invention will be described in more detail.

The negative electrode may have a structure in which a negative electrode active material layer is formed on one or both sides of a long sheet-shaped negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material, and optionally further include a conductive material and/or binder. can do.

Specifically, the negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples of negative electrode active materials include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; Si, Si-Me alloy (where Me is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (where 0< y<2), silicon-based materials such as Si-C composites, etc.; Lithium metal thin film; Metal materials that can be alloyed with lithium, such as Sn, Al, etc.; and the like, and any one or a mixture of two or more of these may be used.

Preferably, the negative electrode active material of the present invention may include at least one of a carbon-based negative electrode active material and a silicon-based negative electrode active material.

The silicon-based negative electrode active material is Si, Si-Me alloy (where Me is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (here, 0<y<2), Si-C composite, or a combination thereof, preferably SiOy (here, 0<y<2). Since the silicon-based negative electrode active material has a high theoretical capacity, the capacity characteristics can be improved when the silicon-based negative electrode active material is included.

Meanwhile, the silicon-based negative electrode active material may be doped with M ^b metal, and in this case, the M ^b metal may be a Group 1 metal element or a Group 2 metal element, and specifically, Li, Mg, etc. Specifically, the silicon anode active material may be Si doped with M ^b metal, SiOy (where 0<y<2), Si-C composite, etc. In the case of a metal-doped silicon-based negative active material, the active material capacity is somewhat reduced due to the doping element, but it has high efficiency, so high energy density can be realized.

Additionally, the silicon-based negative active material may further include a carbon coating layer on the particle surface. At this time, the carbon coating amount may be 20% by weight or less, preferably 1 to 20% by weight, based on the total weight of the silicon-based negative electrode active material.

The conductive material is a component to further improve the conductivity of the negative electrode active material, and may be added in an amount of 1 to 20% by weight based on the total weight of solids in the negative electrode active material layer. These conductive materials are not particularly limited as long as they have conductivity without causing chemical changes in the battery, and examples include graphite such as natural graphite or artificial graphite; Carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive powders such as fluorinated carbon powder, aluminum powder, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of solids in the negative electrode active material layer. Examples of such binders include fluororesin binders containing polyvinylidene fluoride or polytetrafluoroethylene; Rubber-based binders including styrene-butadiene rubber, acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxymethylcellulose, starch, hydroxypropylcellulose, and regenerated cellulose; A polyalcohol-based binder containing polyvinyl alcohol; Polyolefin-based binders including polyethylene and polypropylene; polyimide-based binder; polyester-based binder; Silane-based binders, etc. can be mentioned.

The cathode can be manufactured according to a cathode manufacturing method known in the art. For example, the negative electrode is prepared by dissolving or dispersing the negative electrode active material and optionally the binder and the conductive material in a solvent to prepare a negative electrode active material slurry, applying it on a negative electrode current collector, rolling and drying to form a negative electrode active material layer, Alternatively, it can be manufactured by casting the negative electrode active material layer on a separate support and then peeling off the support and laminating the film obtained on the negative electrode current collector.

The negative electrode current collector generally has a thickness of 3 to 500 μm. This negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the positive electrode current collector, fine irregularities can be formed on the surface of the negative electrode current collector to strengthen the bonding power of the negative electrode active material, and can include various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics. there is.

The solvent may include water or an organic solvent such as NMP or alcohol, and may be used in an amount that provides a desirable viscosity when including the negative electrode active material and optionally a binder, a conductive material, etc. For example, the solid content concentration in the active material slurry including the negative electrode active material and, optionally, the binder and the conductive material may be 50% by weight to 75% by weight, preferably 50% by weight to 65% by weight.

The separator separates the negative electrode from the positive electrode and provides a passage for lithium ions to move. It can be used without particular restrictions as long as it is normally used as a separator in a lithium secondary battery. In particular, it has low resistance to ion movement in non-aqueous electrolytes. It is desirable that the aqueous electrolyte has excellent moisture retention capacity.

Specifically, a porous polymer film as a separator, for example, a porous polymer film made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, ethylene/methacrylate copolymer, etc. Alternatively, a laminated structure of two or more layers thereof may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., may be used. Additionally, a coated separator containing a ceramic component or polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

Electrolytes used in the present invention include various electrolytes that can be used in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes. and the type is not particularly limited.

Additionally, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), and ethylene carbonate (EC). ), carbonate-based solvents such as propylene carbonate (PC); Ester solvents such as methyl acetate and ethyl acetate; Ether-based solvents such as dibutyl ether or tetrahydrofuran; Ketone-based solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolane, etc. may be used. Among these, carbonate-based solvents are preferable, and cyclic carbonates (e.g., ethylene carbonate or propylene carbonate, etc.) with high ionic conductivity and high dielectric constant that can improve the charge/discharge performance of the battery, and low-viscosity linear carbonate-based compounds ( For example, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are more preferable.

The lithium salt can be used without particular restrictions as long as it is a compound that can provide lithium ions used in lithium secondary batteries. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0M, preferably 0.1 to 3.0M. When the concentration of lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be achieved and lithium ions can move effectively.

In addition to the electrolyte components, the electrolyte may further include additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. For example, the additives include haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and tria hexamethyl phosphate. Mead, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride, etc. Alternatively, it can be used in combination, but is not limited to this. The additive may be included in an amount of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, based on the total weight of the electrolyte.

The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, laptop computers, and digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEV).

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention.

[Example]

Example 1.

(1) Preparation of anode slurry composition

Cathode active material (Li(Ni _0.86 Mn _0.07 Co _0.05 Al _0.02 )O ₂ ), carbon nanotubes as a conductive material, polyvinylidene fluoride (PVDF) as a binder, and N-methyl-2 as a solvent in a weight ratio of 97:1:2. -A positive electrode slurry composition (solid content: 70% by weight) was prepared by adding pyrrolidone (NMP).

(2) Anode manufacturing

The positive electrode slurry composition prepared above was applied onto an aluminum thin film current collector with a thickness of 15 μm, and then dried at 130° C. for 1 minute to form a positive electrode active material layer (thickness: 218 μm).

Next, a rolling process is performed on the dried positive electrode active material layer until the thickness of the positive electrode active material layer becomes 164 ㎛, then a first drying process is performed at 130 ° C., and a second drying process is performed at 150 ° C. , the third process was performed sequentially at 170°C to manufacture the positive electrode. The total drying time was performed within 5 seconds.

Example 2.

The positive electrode slurry composition prepared in Example 1 was applied onto an aluminum thin film current collector with a thickness of 15 μm, and then dried at 130° C. for 1 minute to form a positive electrode active material layer (thickness: 218 μm).

Next, a rolling process is performed on the dried positive electrode active material layer until the thickness of the positive electrode active material layer becomes 164 ㎛, then a first drying process is performed at 150 ° C., and a second drying process is performed at 170 ° C. , the third process was performed sequentially at 190°C to manufacture the positive electrode. The total drying time was performed within 5 seconds.

Example 3.

The positive electrode slurry composition prepared in Example 1 was applied onto an aluminum thin film current collector with a thickness of 15 μm, and then dried at 130° C. for 1 minute to form a positive electrode active material layer (thickness: 218 μm).

Next, a rolling process is performed on the dried positive electrode active material layer until the thickness of the positive electrode active material layer becomes 164 ㎛, then a first drying process is performed at 150 ° C., and a second drying process is performed at 170 ° C. A positive electrode was manufactured by sequentially performing a third drying process at 210°C. The total drying time was performed within 5 seconds.

Comparative Example 1.

The positive electrode slurry composition prepared in Example 1 was applied onto an aluminum thin film current collector with a thickness of 15 μm, and then dried at 130° C. for 1 minute to form a positive electrode active material layer (thickness: 218 μm).

Subsequently, a rolling process is performed on the dried positive electrode active material layer until the thickness of the positive electrode active material layer becomes 164 ㎛, then a first drying process is performed at 110 ° C., and a second drying process is performed at 130 ° C. The steps were performed sequentially to prepare a positive electrode. The total drying time was performed within 5 seconds.

Comparative Example 2.

The positive electrode slurry composition prepared in Example 1 was applied onto an aluminum thin film current collector with a thickness of 15 μm, and then dried at 130° C. for 1 minute to form a positive electrode active material layer (thickness: 218 μm).

Next, a rolling process was performed on the dried positive electrode active material layer until the thickness of the positive electrode active material layer reached 164 ㎛, and then a drying process was performed at 130°C for 5 seconds.

[Experimental example]

Experimental Example 1. Measurement of moisture remaining in the positive electrode active material layer

The solvent (moisture) content of each of the anodes prepared in Examples 1 to 3 and the anodes prepared in Comparative Examples 1 and 2 was measured by Karl Fischer titration. Specifically, the anode prepared in Examples 1 to 3 and the anode prepared in Comparative Example 1 were each cut into small pieces of 5 cm × 5 cm in a glove box filled with argon gas. A cut anode measuring 5 cm × 5 cm was weighed in a sample vial. Afterwards, the weighed anode was measured three times repeatedly using a Karl Fischer coulometry moisture analyzer (831 KF Coulometer, Metrohm, Switzerland), and the average value was calculated. The results are shown in Figure 1 below.

Referring to Figure 1, it can be seen that the amount of moisture remaining in the positive electrodes manufactured in Examples 1 to 3 of the present invention was significantly reduced compared to the positive electrodes manufactured in Comparative Examples 1 and 2.

Experimental Example 2. Evaluation of adhesion to electrode current collector

The positive electrodes prepared in Examples 1 to 3 and the positive electrodes prepared in Comparative Examples 1 and 2 were each cut to 20 mm wide and 125 mm long and fixed on a glass slide, and then the current collector was peeled off to measure the 90° peel strength. Measurements were repeated three times, the average value was calculated, and the results are shown in Figure 2.

Looking at Figure 2, it can be seen that the adhesive strength of the positive electrodes manufactured in Examples 1 to 3 of the present invention was significantly increased compared to the positive electrodes manufactured in Comparative Examples 1 and 2.

Claims (11)

Manufacturing an electrode having an electrode active material layer formed on an electrode current collector;
rolling the electrode; and
It includes: drying the rolled electrode,
The drying step is performed so that the drying temperature in at least some sections is 170°C to 210°C.
In claim 1,
A method of manufacturing an electrode for a secondary battery, wherein the total drying time of the rolled electrode is 2 to 5 seconds.
In claim 1,
A method of manufacturing an electrode for a secondary battery, wherein the step of drying the rolled electrode is performed in a roll-to-roll process.
In claim 1,
A method of manufacturing an electrode for a secondary battery, wherein the step of drying the rolled electrode is performed at a temperature of 130° C. or higher.
In claim 1,
Drying the rolled electrode includes performing a first drying process at 130°C to 150°C; Carrying out a second drying process at 150°C to 170°C; and performing a third drying process at 170°C to 210°C. A method of manufacturing an electrode for a secondary battery, which is performed sequentially.
In claim 1,
The electrode active material layer includes an electrode active material and a binder,
A method of manufacturing an electrode for a secondary battery, wherein the electrode active material includes a positive electrode active material or a negative electrode active material.
In claim 6,
A method of manufacturing an electrode for a secondary battery, wherein the binder includes a polyvinylidene fluoride-based resin.
In claim 6,
A method of manufacturing an electrode for a secondary battery, wherein the electrode active material is a positive electrode active material.
In claim 8,
A method of manufacturing an electrode for a secondary battery, wherein the positive electrode active material includes lithium-nickel-cobalt-transition metal (M) oxide represented by the following formula (1):
[Formula 1]
Li _a Ni _x Co _y M ¹ _z M ² _w O ₂
(In Formula 1, M ¹ is Mn, Al, or a combination thereof, and M ² is at least one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca, and Sr, and 0.8≤a≤1.2, 0.55 ≤x<1, 0<y≤0.3, 0<z≤0.3, 0<w≤0.2).
In claim 9,
A method of manufacturing an electrode for a secondary battery, wherein the positive electrode active material has a Ni content of 55% or more.
In claim 1,
A method of manufacturing an electrode for a secondary battery, wherein the electrode is a positive electrode.