Electrode mixture membrane, method for manufacturing electrode mixture membrane, and lithium secondary battery including same

Abstract

The present invention relates to an electrode mixture film comprising an electrode active material, a conductive material, and a fibrillated binder, the electrode mixture film comprising: side portions positioned at respective ends of the electrode mixture film in a width direction; and a central portion disposed between the side portions, in which the crystallinity of the adhesive contained in the central portion is higher than the crystallinity of the adhesive contained in the side portions.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0138115, filed on October 16, 2023, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to an electrode mixture membrane, a method for manufacturing the electrode mixture membrane, and a dry electrode and a lithium secondary battery comprising the electrode mixture membrane. Background Technology

[0005] Secondary batteries are used in small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable gaming devices, power tools, and electric bicycles, as well as in large products requiring high power such as electric or hybrid vehicles, and in power storage devices for storing surplus generated electricity or renewable energy, and power storage devices for backup power.

[0006] Typically, a secondary battery is manufactured by applying an electrode active material slurry to a positive current collector and a negative current collector to form an electrode active material layer, followed by a drying and rolling process to produce the positive and negative electrodes. The positive and negative electrodes are then stacked on two sides of a separator to form an electrode assembly with a predetermined shape. The electrode assembly is then housed in a battery case, and an electrolyte is injected into the case and the case is sealed.

[0007] Meanwhile, during the drying process of the electrode active material, the solvent contained in the slurry evaporates, which may lead to defects such as pinholes or cracks forming on the electrode active material layer on the current collector. In addition, since the interior and exterior of the electrode active material slurry are not dried uniformly during the drying process, there is a risk of powder floating due to differences in solvent evaporation rates. That is, powder in the first dried part rises, thus forming gaps with the relatively later dried parts, leading to a decrease in electrode quality.

[0008] To address the aforementioned issues, drying equipment capable of adjusting the solvent evaporation rate is being considered to ensure uniform drying of the electrode active material slurry both inside and out. However, such drying equipment is very expensive and consumes a significant amount of money and time during operation, thus hindering manufacturing processability.

[0009] On the other hand, the solvent included in typical electrode active material slurries is N-methyl-2-pyrrolidone (NMP), which has a high boiling point. Therefore, high thermal energy and very long drying ovens are required to dry this solvent, making it very unfavorable for large-scale production. In addition, N-methyl-2-pyrrolidone (NMP) is a toxic substance, harmful to organisms, and therefore has the disadvantage of being environmentally unfriendly.

[0010] Therefore, research on dry electrodes, which manufacture electrodes without the use of solvents, has recently been actively pursued. Dry electrodes are typically manufactured by laminating a self-standing electrode mixture film onto a current collector. This electrode mixture film includes an electrode active material, a binder, a conductive material, etc. The aforementioned electrode mixture film involves the following process: first, the electrode active material, a carbon material as a conductive material, and a fiberizable binder are mixed together using a mixer or the like; then, shear force is applied to the binder through a process such as jet milling or kneading to fiberize the binder; finally, the resulting mixture is calendered into a film form to manufacture a self-standing membrane.

[0011] However, in the case of manufacturing electrode mixture films using a typical calendering method, there is a problem of uneven edges at both ends in the width direction of the electrode mixture film, resulting in uneven serrated defect portions. Serrated defect portions may accelerate the formation of cracks in the electrode mixture film, and furthermore, may cause the electrode mixture film to break, thus requiring an excessive cutting process to remove them.

[0012] Excessive cutting has several drawbacks. Firstly, the width of the electrode mixture film is significantly reduced compared to its initial width due to the width of the defective portion. Secondly, the width of the calendering rolls needs to be increased to achieve the target width of the electrode mixture film, and it is impossible to continuously manufacture electrode mixture films with a uniform width. Thirdly, the larger the portion removed by the cutting process, the greater the loss of electrode material, leading to increased electrode manufacturing costs.

[0013] Therefore, there is a need to develop an electrode mixture film in which edge defect portions at both ends in the width direction of the electrode mixture film are minimized. Summary of the Invention Technical issues

[0014] One aspect of the present invention provides an electrode mixture film and a lithium secondary battery including the electrode mixture film, wherein edge defect portions at both ends in the width direction of the electrode mixture film are minimized.

[0015] Another aspect of the present invention provides a method for manufacturing an electrode mixture film, which can minimize edge defect portions at both ends of the electrode mixture film in the width direction, reduce the amount of electrode mixture film removed during the slitting process, manufacture the widest possible electrode mixture film with only a narrow calender roll width, and recycle the removed electrode mixture film. Technical solution

[0016] [1] The present invention provides an electrode mixture membrane comprising an electrode active material, a conductive material and a fiberizable adhesive, wherein the electrode mixture membrane comprises side portions located at two ends in the width direction of the electrode mixture membrane and a central portion disposed between the side portions, and the crystallinity of the adhesive contained in the central portion is higher than that of the adhesive contained in the side portions.

[0017] [2] In [1] above, in this invention, the width of the side portion can be 0.1% to 40% of the width of the two ends of the electrode mixture film in the width direction of the electrode mixture film, respectively.

[0018] [3] In [1] or [2] above, in this invention, the crystallinity of the adhesive contained in the central portion may be 5% to 40%.

[0019] [4] In at least one of [1] to [3] above, in this invention, the crystallinity of the adhesive contained in the side portion may be less than or equal to 4.5%.

[0020] [5] In at least one of [1] to [4] above, in this invention, the electrode active material may have an average particle size (D) of 0.1 μm to 5 μm. 50 ).

[0021] [6] The present invention provides a method for manufacturing an electrode mixture film, the method comprising: (S1) obtaining each of a first electrode powder and a second electrode powder, each of the first electrode powder and the second electrode powder comprising an electrode active material, a conductive material and a fiberizable binder; and (S2) introducing the first electrode powder and the second electrode powder into a calendering roll, the calendering roll being divided into three or more sections in the width direction by a baffle, wherein the binder contained in the first electrode powder in the above (S1) has a higher crystallinity than the binder contained in the second electrode powder in the above (S1), and introducing the first electrode powder into the central portion of the roll in the above (S2), and introducing the second electrode powder into the side portions located at two ends of the central portion of the roll.

[0022] [7] In [6] above, in the present invention, in the above (S2), the calender roll can be divided into three sections in the width direction by a baffle, and the length of the side sections can be 1% to 45% of the length of the central section independently.

[0023] [8] In [6] or [7] above, in this invention, the length of the side portions can each be 2% to 30% of the length of the central portion independently.

[0024] [9] In at least one of [6] to [8] above, in this invention, the first electrode powder and the second electrode powder can each be prepared independently by a method comprising the steps of: (a) preparing a mixture composition comprising an electrode active material, a conductive material and a fiberizable binder, and (b) kneading the mixture composition at a temperature of 70°C to 200°C to prepare a mixed aggregate.

[0025]

[10] In [9] above, in this invention, the kneading above (b) can be performed at a temperature of 70°C to 200°C and a rotational speed of less than or equal to 100 rpm.

[0026]

[11] In [9] or

[10] above, in this invention, the time period for performing kneading to prepare the powder for the first electrode can be shorter than the time period for performing kneading to prepare the powder for the second electrode.

[0027]

[12] In at least one of [6] to

[11] above, in this invention, the crystallinity of the binder contained in the first electrode powder may be from 5% to 40%, and the crystallinity of the binder contained in the second electrode powder may be less than or equal to 8%.

[0028]

[13] In at least one of [6] to

[12] above, in this invention, the method may further include a step (S3) of removing side portions of the film manufactured after (S2), wherein the width of the side portions may be individually 10% or less of the width length of the electrode mixture film manufactured after (S2).

[0029]

[14] The present invention provides a lithium secondary battery comprising a dry electrode having at least one of the electrode mixture films of [1] to [5] above. Beneficial effects

[0030] The electrode mixture film according to the invention is characterized by adjusting the crystallinity of the adhesive contained in the central portion of the electrode mixture film and the crystallinity of the adhesive contained in the side portions of the electrode mixture film. Thus, while minimizing the defect rate of the side portions, the electrode mixture film can be controlled to have a constant width, and the electrode mixture film exhibits excellent tensile strength and elongation at break.

[0031] Furthermore, according to the method for manufacturing an electrode mixture film according to the present invention, the electrode mixture film has all the above-mentioned advantages, and its side portions also contain electrode active materials, so they can be recycled as electrode powder, and the side portions removed during slitting can be minimized, resulting in excellent processability. Attached Figure Description

[0032] The accompanying drawings illustrate preferred embodiments of the invention by way of example and are used to further understand the technical concept of the invention together with the detailed description of the invention given below. Therefore, the invention is explained only based on the contents of these drawings. Furthermore, the shape, size, scale, or proportion of the elements in the drawings included in this specification may be exaggerated for clearer description.

[0033] Figure 1 This is a schematic diagram of a method for manufacturing an electrode mixture film according to an embodiment of the present invention, and the electrode mixture film thus manufactured.

[0034] Figure 2 This is a schematic diagram of a method for manufacturing an electrode mixture film according to an embodiment of the present invention, and the electrode mixture film thus manufactured.

[0035] Figure 3 This is a schematic diagram of a method for manufacturing an electrode mixture film according to Comparative Example 1, and the electrode mixture film thus manufactured.

[0036] Figure 4 This is a photograph of the electrode mixture film manufactured in Example 1.

[0037] Figure 5 This is a photograph of the electrode mixture film manufactured in Example 3.

[0038] Figure 6 This is a photograph of the electrode mixture film manufactured in Comparative Example 1. Detailed Implementation

[0039] The invention will be described in more detail below.

[0040] It will be understood that, based on the inventor's concept of appropriately defining terms to best interpret the invention, the terms or words used in this specification and claims should not be construed as having the meanings defined in commonly used dictionaries, but should be construed as having meanings and concepts consistent with the technical concept of the invention.

[0041] In this invention, the machine direction (MD) refers to the length direction of the electrode mixture film, and the transverse direction (TD) refers to the width direction of the electrode mixture film.

[0042] In this invention, the average particle size D 50 This refers to the particle size corresponding to 50% volume accumulation in the particle size distribution curve. (D) 50 This can be measured using methods such as laser diffraction. Laser diffraction can typically measure particle sizes from the submicron region to a few millimeters, thus providing highly reproducible and high-resolution results.

[0043] In this invention, crystallinity (Xc) can be measured by differential scanning calorimetry (DSC). Based on the temperature (peak temperature) at the point in time during crystallization where the highest enthalpy is observed, crystallinity can be calculated using the following [Equation 1], where the enthalpy of fusion (ΔH) is actually measured by DSC. m The value divided by the enthalpy of fusion of a theoretically perfect crystal (100% crystallinity) (ΔH) m O (Equilibrium enthalpy of fusion) value, expressed as a percentage. Here, the enthalpy of fusion of a theoretically perfect crystal (ΔH) is... m O For more information, refer to the Polymer Handbook (J. Brandrup et al., 2003) or academic papers such as *Polymer*. For example, the theoretical enthalpy of fusion for perfect PTFE crystals is 85.4 J / g (Polymer Journal, Vol. 46, pp. 8872-8882, 2005). Meanwhile, typically, thermal analyses of polymers, such as DSC, can be measured and calculated according to ASTM D3418-21.

[0044] [Equation 1]

[0045]

[0046] In this specification, "mixture composition" means a mixture comprising electrode active material, conductive material, and fibrous binder, which has been physically mixed into a homogeneous dispersed phase, and may be a mixture of powder phases as a product of a mixing process (mixing procedure) according to this specification, and may be a mixture in which substantially no solvent is contained. Here, "substantially no solvent" means that when the mixture composition is obtained by mixing, no solvent or only trace amounts of solvent are introduced.

[0047] In this specification, "mixed aggregate" is the product of the kneading process (kneading process) according to this specification, in which the mixed composition is subjected to shear force, thereby causing the binder to fibrousize, so as to allow the powdered mixture to bond or connect with each other and transform into a mixed aggregate in a paste state, wherein the product is 100% solid.

[0048] In this specification, "electrode powder" may refer to a material in which a mixed aggregate is pulverized, thereby having a small particle size and being in a powder phase, and may mean an electrode material in powder form comprising electrode active materials and binders, and optionally conductive materials.

[0049] In this specification, "electrode mixture film" can refer to an electrode mixture film manufactured in the form of a self-standing single sheet using an "electrode mixture" comprising an electrode active material, a conductive material, and a binder, without the involvement of a solvent, or it can refer to an electrode mixture layer laminated onto a current collector. In this specification, the term "self-standing" means that it can maintain its independent form without relying on other components and that it can be moved or handled on its own. As described below, the electrode mixture film can be formed by pressing electrode powder. For example, the electrode mixture film can have the following shape, wherein the powder used for the electrode powder is integrated by pressing, thereby having a layered structure.

[0050] In this specification, "powder-pressed film" refers to the film from the moment electrode powder passes through the powder pressing process—in which the electrode powder first passes through the rollers in the roller-to-roll process—to the moment the sheet passes through the final roller in the process. This film can be a self-supporting sheet, but it can also be a sheet with relatively weak self-support. Here, "powder pressing" means that the electrode powder is molded into a self-supporting sheet form by passing through the rollers in the roller-to-roll process. "Powder pressing" is a process performed during the manufacture of the powder-pressed film into an electrode mixture film, which may mean the process of rolling the powder-pressed film.

[0051] In the case of typical electrode mixture films, such as [ Figure 6 As illustrated in the figure, there is an issue of uneven edges at both ends of the electrode mixture film in the width direction, resulting in uneven, serrated defect portions. These serrated defect portions may accelerate the formation of cracks in the electrode mixture film and, moreover, may cause the electrode mixture film to rupture. If such an electrode mixture film is included in a battery, not only will the electrode uniformity be poor, but the electrochemical performance of the battery will also be significantly degraded, for example, leading to an inversion of the N / P ratio between the positive and negative electrodes.

[0052] To solve the above problems, the inventors of this invention have repeatedly studied electrode mixture films with fewer defects in the side portion and excellent tensile strength and elongation at break. They discovered that when the crystallinity of the binder in the central and side portions of the electrode mixture film meets specific conditions, an electrode mixture film with fewer defects in the side portion and excellent tensile strength and elongation at break can be obtained, and thus this invention was completed.

[0053] Electrode mixture membrane

[0054] The electrode mixture membrane according to the present invention will be described below.

[0055] The electrode mixture film according to the present invention comprises an electrode active material, a conductive material and a fiberizable adhesive, wherein the electrode mixture film includes side portions located at two ends in the width direction of the electrode mixture film and a central portion disposed between the side portions, and the crystallinity of the adhesive contained in the central portion is higher than that of the adhesive contained in the side portions.

[0056] The crystallinity of the binder in the central portion of the electrode mixture film is higher than that in the side portions. Within the electrode mixture film, the crystallinity of the binder decreases less in portions with higher fibrillation and decreases less in portions with lower fibrillation.

[0057] Depending on the degree of fibrosis in the electrode mixture film, the extent of serrated defects generated in the side portion of the electrode mixture film may vary.

[0058] For example, if the electrode mixture film has a low degree of fibrosis (if the binder has a high degree of crystallinity), the electrode mixture film may contain a large amount of coarse fibers and a large amount of crystalline binder. Therefore, when applying shear force to manufacture the electrode mixture film, the force holding the particles together is relatively large, and the limit point for fracture may be high. However, if shear force exceeding the limit point is applied, fracture may occur, and the fracture may result in a wide and long fracture section, i.e., a wide and long serrated defect section, proportional to the stress applied within that time.

[0059] Conversely, if the electrode mixture film has a high degree of fibrosis (if the binder has low crystallinity), there may be a large number of fine fibers and a small amount of crystalline binder in the electrode mixture film. Therefore, when applying shear force to manufacture the electrode mixture film, the limit point for bearing fracture may not be high, so that even if fracture occurs, there may be narrow and short serrated defect sections.

[0060] Therefore, to make the serrated defect portion as narrow and short as possible, the electrode mixture film requires a high degree of fibrosis (requiring low crystallinity of the binder). However, in this case, the force holding the particles together is small, resulting in low tensile strength and elongation at break of the electrode mixture film. Electrode mixture films with low tensile strength and low elongation at break cannot withstand the large forces applied by the equipment during the film manufacturing process, and thus may suffer from overall fracture. Furthermore, if the manufacturing speed is increased to improve film productivity, even greater forces will be applied to the film, potentially further increasing the likelihood of fracture and thus worsening processability.

[0061] In this invention, in order to make the serrated defect portion as narrow and short as possible, a side portion with higher fibrillation and a central portion with lower fibrillation and a predetermined width are applied to the electrode mixture film to withstand the large forces applied during the manufacturing process.

[0062] In the electrode mixture film according to the invention, regions with higher fibrillation are located in the side portions of the electrode mixture film, thereby reducing serrated defects appearing in the side portions of the electrode mixture film. Additionally, regions with less fibrillation are located in the central portion of the electrode mixture film, resulting in excellent tensile strength and elongation at break of the electrode mixture film.

[0063] In this case, the crystallinity of the binder in the central and side portions of the electrode mixture film can be controlled by the following method: In this method, when preparing the electrode powder described later, the kneading and pulverizing conditions are appropriately adjusted, thereby adjusting the degree of fibrosis of the electrode powder so that electrode powders with different degrees of fibrosis are introduced into the central and side portions respectively.

[0064] Preferably, the crystallinity of the adhesive contained in the central portion can be 5% to 40%, more preferably 10% to 35%, or even more preferably 15% to 30%. If the above ranges are met, the electrode mixture film can exhibit excellent properties in terms of tensile strength and elongation at break, and therefore can withstand large forces applied by the equipment during the manufacturing process, thereby preventing the electrode mixture film from breaking. Furthermore, the adhesive used to bond the electrode active material breaks bonds less frequently, thereby preventing the electrode active material from separating from the electrode, thus improving capacity and resistance properties.

[0065] Preferably, the crystallinity of the binder contained in the side portion can be less than or equal to 4.5%, more preferably less than or equal to 4%, even more preferably less than or equal to 3%, even more preferably less than or equal to 2%, and even more preferably less than or equal to 1.5%. If the above range is met, the generation of serrated defect portions appearing in the side portion of the electrode mixture film can be appropriately reduced, thereby improving the electrochemical properties of the battery.

[0066] The width of the side portions located at both ends in the width direction of the electrode mixture film can be independently 0.1% to 40% of the width of the electrode mixture film at both ends in the width direction of the electrode mixture film. Preferably, the side portions can be independently 0.1% to 30%, more preferably 0.15% to 20%, and even more preferably 1% to 15% of the width of the electrode mixture film at both ends in the width direction of the electrode mixture film. If the above ranges are met, the serrated defect portions of the side portions of the electrode mixture film can be appropriately reduced, and the tensile strength and elongation at break properties of the electrode mixture film can be improved. For example, if the width of the side portions is independently smaller than a specific value of the width of the electrode mixture film at both ends in the width direction of the electrode mixture film, longer serrated defect portions are formed in the side portions of the electrode mixture film, resulting in problems with processability because the electrochemical properties of the battery are reduced, an electrode mixture film with a predetermined width is not obtained, and the width of the electrode mixture film is significantly smaller than the width of the calendering roll. If the width of each side portion is independently greater than a specific value of the width of the two ends of the electrode mixture film in the width direction of the electrode mixture film, the tensile strength and elongation at break of the electrode mixture film are low, which may lead to problems such as electrode mixture film breakage or disconnection of the adhesive used to bond the electrode active materials, thereby reducing the capacity and resistance performance of the battery.

[0067] Furthermore, according to embodiments of the present invention, the central portion and the side portions may each independently include an electrode active material, a conductive material, and a fiberizable adhesive. For example, the central portion may include an electrode active material, a conductive material, and a fiberizable adhesive, and the side portions may include an electrode active material, a conductive material, and a fiberizable adhesive. The electrode active material, the conductive material, and the fiberizable adhesive will be described later.

[0068] Meanwhile, in this invention, the porosity of the electrode mixture membrane can be 20 vol% to 50 vol%, specifically 20 vol% to 40 vol%, and more specifically 25 vol% to 35 vol%. If the above range is met, electrolyte solution impregnation is excellent, which can improve lifetime performance and output performance, and the energy density can be excellent.

[0069] The porosity can be obtained by measuring the apparent density of the electrode mixture film and using the actual density calculated based on the actual density and composition of each component using the following [Equation 1].

[0070] [Relation 1]

[0071] Porosity (%) = {1 - (apparent density / actual density)} × 100

[0072] Method for manufacturing electrode mixture films

[0073] The method for manufacturing electrode mixture films will be described below.

[0074] A method for manufacturing an electrode mixture film includes: (S1) obtaining each of a first electrode powder and a second electrode powder, each of the first electrode powder and the second electrode powder comprising an electrode active material, a conductive material, and a fiberizable binder; and (S2) introducing the first electrode powder and the second electrode powder into a calendering roll, the calendering roll being divided into three or more sections in the width direction by a baffle, wherein the crystallinity of the first electrode powder in the upper (S1) section is higher than that of the second electrode powder in the upper (S1) section, and the first electrode powder is introduced into the central portion of the upper (S2) roll, and the second electrode powder is introduced into the side portions located at both ends of the central portion of the roll.

[0075] The following sections will describe each step in more detail.

[0076] (Step (S1))

[0077] This is the step of obtaining a first electrode powder and a second electrode powder, each of which contains an electrode active material, a conductive material, and a fiberizable binder, and the crystallinity of the binder contained in the first electrode powder is higher than that of the binder contained in the second electrode powder.

[0078] The powder for the first electrode and the powder for the second electrode each independently comprise an electrode active material, a conductive material, and a fiberizable binder, without needing to have the same composition.

[0079] The binder in the powder for the first electrode has a higher crystallinity than the binder in the powder for the second electrode. Therefore, the binder in the central portion of the electrode mixture film can have a high crystallinity, while the binder in the side portions of the electrode mixture film can have a low crystallinity. This can appropriately reduce the defective portions appearing in the side portions of the electrode mixture film and improve the tensile strength and elongation at break of the electrode mixture film.

[0080] Preferably, the crystallinity of the binder contained in the first electrode powder may be 5% to 40%, specifically 10% to 35%, and more specifically 15% to 30%. If the above ranges are satisfied, the electrode mixture film may have excellent properties in terms of tensile strength and elongation at break and, thus, can withstand the large forces applied by the equipment during the manufacturing process, thereby preventing the overall fracture of the electrode mixture film. In addition, the binder is less disconnected, thereby preventing the electrode active material from detaching from the electrode.

[0081] Preferably, the crystallinity of the binder contained in the second electrode powder may be less than or equal to 8%, specifically less than or equal to 7%, more specifically less than or equal to 6%, and even more specifically less than or equal to 5%. If the above ranges are satisfied, the generation of zigzag defect portions occurring in the side portions of the electrode mixture film can be appropriately reduced, thereby improving the electrochemical properties of the battery.

[0082] The electrode active material is not particularly limited as long as it is a commonly used electrode active material, and, for example, the electrode active material may be a positive electrode active material or a negative electrode active material.

[0083] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and specifically, the positive electrode active material may include lithium metal oxides containing lithium and one or more metals such as cobalt, manganese, nickel, aluminum, etc. More specifically, the lithium metal oxide may be a lithium manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium cobalt-based oxide (e.g., LiCoO2, etc.), a lithium nickel-based oxide (e.g., LiNiO2, etc.), a lithium nickel manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), a lithium nickel cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium manganese cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), a lithium nickel manganese cobalt-based oxide (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1)O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, and p1 + q1 + r1 = 2), etc.), or lithium nickel cobalt transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are each the atomic fraction of an independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M is one or more selected from Al, Mg, and Ti, X is one or more selected from F, S, and N, and -0.5 ≤ a ≤ 0.5, 0 ≤ x ≤ 0.5, and 0 ≤ b ≤ 0.1), etc., and may include a compound of any one of them or two or more of them.

[0084] Among them, due to the fact that the capacity performance and stability of the battery can be improved, the lithium metal oxide can be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni<s 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2), etc.), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), lithium nickel manganese cobalt aluminum oxide (e.g., Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2), lithium iron phosphate (e.g., LiFePO4), etc., and a mixture of any one of them or two or more of them can be used.

[0085] The negative electrode active material may include at least one selected from lithium metal, a carbon material capable of reversibly inserting / extracting lithium ions, a metal or an alloy of a metal and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0086] As the carbon material capable of reversibly inserting / extracting lithium ions, a carbon-based negative electrode active material commonly used in lithium ion secondary batteries can be used without particular limitation, and representative examples thereof may include crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon may include graphite, such as irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon may include soft carbon (carbon fired at low temperature) or hard carbon, mesophase pitch carbide, fired coke, etc.

[0087] As the metal or the alloy of a metal and lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of the metal and lithium can be used.

[0088] As the metal composite oxide, one selected from the group consisting of PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), and Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, elements of Group 1, Group 2, and Group 3 of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8) can be used.

[0089] The material capable of doping and dedoping lithium may be Si, SiO xWhen \(0 < x\leq2\), Si - Y alloys (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but not including Si), Sn, SnO₂, Sn - Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but not including Sn), etc., or at least one of them can be mixed with SiO₂ and used. The element Y can be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0090] The transition metal oxide can be a lithium - containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0091] The average particle size (D 50 ) of the electrode active material can be from 0.1 μm to 5.0 μm, specifically from 0.2 μm to 4.0 μm, more specifically from 0.3 μm to 3.0 μm, and even more specifically from 0.4 μm to 2.5 μm. If the above range is satisfied, the average particle size of the electrode - used powder can be uniform. When manufacturing the electrode mixture film, the film can be easily formed, and the tensile strength and elongation at break can be excellent. In addition, since the crystallinity of the binder can be easily evaluated, an electrode mixture film having regions with different degrees of fibrillation can be easily manufactured.

[0092] The conductive material is a component for further improving the conductivity of the electrode active material, and the conductive material is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal - crack carbon black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; fluorocarbon powders; conductive powders such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. Specifically, in order to uniformly mix and improve the conductivity of the conductive material, it can include one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes (CNT).

[0093] There are no particular requirements for fibrillable adhesives, as long as they can be fibrillated. Fibrillation refers to the process of breaking down a polymer into smaller pieces. For example, fibrillation can be performed using mechanical shear forces, thus loosening the surface of the fibrillated polymer fibers to produce a large number of microfibrils (fibrils). Examples of fibrillable adhesives may include one or more selected from the group consisting of polytetrafluoroethylene (PTFE) and polyolefins, and may preferably include PTFE, and more preferably PTFE. Specifically, PTFE may be included in an amount of 60 wt% or more based on the total weight of the adhesive. In this case, the adhesive may also include one or more selected from polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), and polyolefin-based adhesives.

[0094] Each electrode powder can be obtained by performing the following methods, and each electrode powder does not necessarily need to be prepared by the same method.

[0095] First, the aforementioned electrode active material, conductive material, and fibrous binder are mixed to obtain a composite composition. During this process, the mixing is performed to ensure a uniform distribution of the electrode active material, conductive material, and fibrous binder. Since the electrode active material, conductive material, and binder are mixed into a powder phase, various methods can be used without limitation, as long as these methods can easily mix the electrode active material, conductive material, and binder. However, in this invention, dry electrodes are manufactured without the use of solvents. Mixing can be performed by dry mixing, and the aforementioned materials can be introduced into equipment such as a mixer or agitator to perform the mixing.

[0096] At this point, mixing can be performed in the mixer at 500 rpm to 100,000 rpm for 0.5 to 30 minutes, and specifically, at 1,000 rpm to 20,000 rpm for 2 to 15 minutes. If performed within the above range, the materials can be mixed uniformly, which can improve battery performance.

[0097] Next, a fiberization process can be performed on the mixture composition obtained from the above mixing to fiberize the fiberizable adhesive.

[0098] The fiberization process is not particularly limited, as long as it generally involves mixing, but it is preferably carried out by high-temperature low-shear kneading (kneading), and can be carried out by, for example, a kneading machine. The fiberizable binder is fiberized by the above-described kneading, thereby bonding or connecting the electrode active material and conductive material powders to each other to form a mixed aggregate with a solid content of 100%.

[0099] Kneading can be performed at a rate of 10 rpm to 100 rpm, and more specifically, at a rate of 20 rpm to 70 rpm. Furthermore, kneading can be performed for 1 minute to 120 minutes, and more specifically, for 2 minutes to 60 minutes. If these ranges are met, sufficient fibrosis can be achieved to improve battery performance.

[0100] In this case, when kneading the mixture composition to prepare the first electrode powder, the kneading time period can be shorter than when kneading the mixture composition to prepare the second electrode powder. If the above conditions are met, the mixture composition used to prepare the first electrode powder is less fibrous, such that the crystallinity of the binder contained in the first electrode powder to be prepared later may be higher than the crystallinity of the binder contained in the second electrode powder to be prepared later.

[0101] Specifically, when kneading the mixture composition to prepare a first electrode powder, kneading can be performed at a speed of 10 rpm to 100 rpm for 1 minute to 30 minutes, and when kneading the mixture composition to prepare a second electrode powder, kneading can be performed at a speed of 10 rpm to 100 rpm for 10 minutes to 60 minutes, and the time required to knead the mixture composition to prepare the first electrode powder can be shorter than the time required to mix the mixture composition to produce the second electrode powder. If the above ranges are met, the crystallinity of the binder contained in the electrode powder to be prepared later can be appropriately different.

[0102] In addition, kneading can be performed at high temperatures and pressures above atmospheric pressure, and specifically, it can be performed at pressures above atmospheric pressure.

[0103] More specifically, kneading can be performed at temperatures ranging from 50°C to 230°C, preferably from 90°C to 200°C. If kneading is performed at temperatures within this range, the fiberization and agglomeration of the kneaded adhesive can be readily achieved, and the problem of the fiberized adhesive breaking apart can be appropriately prevented.

[0104] Additionally, kneading can be performed at pressures equal to or higher than atmospheric pressure, specifically between 1 atm and 3 atm, and more specifically between 1.1 atm and 3 atm. Performing kneading within these ranges effectively prevents the fiberized adhesive from breaking apart and also prevents the density of the mixed aggregates from becoming too high.

[0105] In other words, according to the present invention, the intended effects of the present invention can be achieved when a high-temperature and low-shear kneading process is performed under conditions of high temperature and pressure equal to or higher than atmospheric pressure, instead of performing a high-shear kneading process.

[0106] Next, the mixed aggregate prepared by the above kneading step can be pulverized to obtain electrode powder.

[0107] The mixed aggregates prepared by the above kneading process can be directly subjected to calendering. However, in this case, the mixed aggregates need to be pressed under high pressure and high temperature to form a film. Therefore, there may be problems such as the film density becoming too high or the film not being uniform. Therefore, the mixed aggregates prepared as described above are pulverized to prepare electrode powders in powder phase.

[0108] The equipment used in the above-mentioned pulverization is not particularly limited, but equipment such as a mixer or a grinder may be preferred.

[0109] The pulverization can be performed at a speed of 5000 rpm to 20000 rpm for 5 seconds to 10 minutes, preferably at a speed of 8000 rpm to 1800 rpm for 10 seconds to 5 minutes. If the pulverization is performed within the above range, sufficient pulverization is achieved, thereby preparing powder of sufficient size to form a film, and a large amount of fine powder can be avoided from the mixed aggregates.

[0110] In this case, when pulverizing the mixed aggregates to prepare the powder for the first electrode, the pulverization period can be longer than when pulverizing the mixed aggregates to prepare the powder for the second electrode. If the above conditions are met, the crystallinity of the first electrode powder to be prepared later can be higher than the crystallinity of the second electrode powder to be prepared later.

[0111] Specifically, when pulverizing the mixed aggregates to prepare powder for the first electrode, pulverization can be performed at a speed of 5000 rpm to 20000 rpm for 10 seconds to 5 minutes, preferably at a speed of 8000 rpm to 18000 rpm for 30 seconds to 3 minutes. When pulverizing the mixed aggregates to prepare powder for the second electrode, pulverization can be performed at a speed of 5000 rpm to 20000 rpm for 1 second to 2 minutes, particularly at a speed of 8000 rpm to 18000 rpm for 5 seconds to 50 seconds. If the above ranges are met, the crystallinity of the binder in the central and side portions of the electrode mixture film to be manufactured can be appropriately adjusted, thereby reducing defective portions formed in the side portions and improving the tensile strength and elongation at break of the electrode mixture film.

[0112] Next, step (S2) is performed on the powder for the first electrode and the powder for the second electrode to manufacture an electrode mixture film.

[0113] (Step (S2))

[0114] Reference Figure 2 and Figure 3 The steps (S2) will be described in detail.

[0115] Step (S2) includes introducing first electrode powder and second electrode powder into a calendering roll, the calendering roll being divided into three or more sections in the width direction by a baffle, and step (S2) is the step of introducing the first electrode powder into the central portion of the roll mentioned above (S2), and introducing the second electrode powder into the side portions located at the two ends of the central portion of the roll to produce an electrode mixture film.

[0116] Electrode mixture films can be manufactured by calendering, in which the first electrode powder 11 and the second electrode powder 12 prepared in step (S1) are supplied to a calendering apparatus, and the supplied material is hot-pressed using a roll press included in the calendering apparatus. At this time, the first electrode powder 11 and the second electrode powder 12 can be supplied to the calendering rolls through separate introduction paths. For example, the introduction path of the second electrode powder 12 can be provided on both sides of the introduction path of the first electrode powder 11. Furthermore, the first electrode powder 11 introduced to the central portion and the second electrode powder 12 introduced to the side portion can be connected to each other at the boundary surface between the central and side portions during the calendering step. For this purpose, the division of the introduction paths is set to be implemented upstream of the calendering apparatus, and the materials introduced into the calendering apparatus have overlapping boundaries, such that the first electrode powder 11 and the second electrode powder 12 can be connected to each other at the boundary surface. The separation of the introduction paths can be achieved by providing a baffle upstream of the calendering rolls to separate the introduction paths.

[0117] Reference Figure 2 and Figure 3 By providing a supply member 31 including a guide baffle 33 or a dividing baffle 34 before the calender roll 32, the calender roll, which is divided into three or more sections in the width direction by the baffle, can be divided into three sections in the width direction. As in the above method, the introduction paths of the first electrode powder 11 and the second electrode powder 12 are divided into a central portion of the roll where the first electrode powder 11 is introduced and a side portion of the roll where the second electrode powder 12 is introduced, such that the side portion of the electrode mixture film to be manufactured later can have low crystallinity, and its central portion can have high crystallinity. After passing through the separated introduction paths, the first electrode powder 11 and the second electrode powder 12 can combine at the dividing boundary surface, such that at the boundary surface, the first electrode powder 11 and the second electrode powder 12 can be mixed to a certain extent. Furthermore, at the boundary surface, the electrode powders present in the central portion and the side portion respectively are subjected to shear force and thus combine to form the boundary surface, so that the central portion and the side portion do not separate from each other.

[0118] At this point, the central portion of the electrode mixture film mainly contains the first electrode powder 11, and the side portion of the electrode mixture film mainly contains the second electrode powder 12. The term "mainly" above means a content greater than 50 wt%.

[0119] The lengths of the side portions located at the two ends of the central portion of the roller can each be independently 1% to 45%, specifically 2% to 30%, and more specifically 3% to 25% of the length of the central portion of the roller. If the above ranges are met, an appropriate amount of first electrode powder 11 can be introduced into the central portion of the electrode mixture film to be manufactured later, and an appropriate amount of second electrode powder 12 can be introduced into the side portions of the electrode mixture film, thereby producing an electrode mixture film with excellent tensile strength and elongation at break, while reducing defective portions formed in the side portions.

[0120] First electrode powder 11 and second electrode powder 12 are supplied to calendering rolls and hot-pressed to prepare an electrode mixture film in sheet form. The temperature of the calendering rolls can be between 50°C and 200°C.

[0121] The calendering roller includes a pressing component, wherein two rollers are arranged facing each other, and multiple pressing components can be arranged continuously. In this case, the rotational speed ratio of the two rollers in each pressing component can be adjusted independently within the range of 1:1 to 1:10.

[0122] In addition, in order to adjust the manufactured electrode mixture film to an appropriate thickness, the electrode mixture film can be reintroduced into the rolling element and subjected to hot pressing 1 to 10 times.

[0123] At this point, the manufacturing method may further include a step (S3) of removing the edge portion of the film manufactured after (S2) above, wherein the edge portion is located at two ends in the width direction of the electrode mixture film manufactured after (S2) above, and the width of each edge portion is independently 10% or less of the width length of the electrode mixture film manufactured after (S2) above.

[0124] The width of the edge portions can be independently 10% or less, specifically 8% or less, more specifically 6% or less, and even more specifically 3% or less of the width length of the electrode mixture film manufactured after step (S2). If the above ranges are met, unlike typical processes, electrode mixture films with wider widths can be obtained from calendering rolls with limited widths, potentially resulting in superior processing performance. Furthermore, the edge portions are included in the side portions, and the length of the edge portions is the same as the length of the side portions, thus eliminating the need to remove the entire side portions.

[0125] The width of the side portion can be reduced based on the width of the edge portion.

[0126] The removed edge portion can be recycled and used as powder for the second electrode.

[0127] dry electrode

[0128] The dry electrode according to the present invention comprises the electrode mixture membrane described above. Specifically, the dry electrode may include a current collector and an electrode mixture membrane formed on the current collector. Since the electrode mixture membrane has already been described above, a detailed description thereof will be omitted, and in the following text, only the remaining components will be described in detail.

[0129] Electrodes can be manufactured by stacking electrode mixture films on one or both sides of a current collector and laminating the resulting product. Lamination can be a rolling step, thereby attaching the electrode mixture film to the current collector. Lamination can be performed by using a rolling method with laminating rollers, and in this case, the laminating rollers can be maintained at a temperature of 20°C to 200°C.

[0130] If the dry electrode is the positive electrode, the current collector can be any conductive material that does not cause a chemical change in the corresponding battery, and is not particularly limited thereto. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used as the current collector.

[0131] The thickness of the current collector can range from 8 μm to 500 μm, but is not limited to this. In addition, fine irregular structures can be formed on the surface of the current collector to improve the adhesion of the electrode mixture film.

[0132] If the dry electrode is the negative electrode, the current collector is not particularly restricted, as long as it has high conductivity and does not cause changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel, aluminum-cadmium alloys, etc., can be used.

[0133] Electrode current collectors can typically have a thickness of 3 μm to 500 μm, and when a dry electrode is used as the positive electrode, micro-irregularities can be formed on the surface of the current collector to increase the adhesion of the electrode mixture film.

[0134] The current collector may be wholly or partially coated with a conductive primer to reduce resistance and improve surface adhesion. In this document, the conductive primer may include conductive materials and adhesives, wherein the conductive materials are not limited as long as they are conductive, but may be, for example, carbon-based materials. The adhesives may include fluorine-based adhesives (including PVDF and PVDF copolymers) that are soluble in solvents, acrylic-based adhesives, and water-based adhesives.

[0135] Lithium secondary batteries

[0136] The lithium secondary battery according to the present invention will be described below.

[0137] The lithium secondary battery according to the present invention includes a dry electrode according to the present invention. Specifically, the lithium secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode and / or the negative electrode can be a dry electrode, and specifically, the lithium secondary battery can be a lithium secondary battery including a dry electrode, a negative electrode, a separator, and an electrolyte according to the present invention. If only one of the positive electrode and the negative electrode is a dry electrode according to the present invention, the other electrode can be an electrode manufactured by a typical wet manufacturing method.

[0138] The separator is used to separate the negative and positive electrodes and provide a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is a separator commonly used in lithium secondary batteries. In particular, separators with excellent electrolyte retention and low resistance to ion movement in the electrolyte are preferred. Specifically, porous polymer membranes can be used, for example, porous polymer membranes made from polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, or ethylene / methacrylate copolymers, or a stacked structure body formed of two or more layers of porous polymer membranes can be used. Alternatively, typical porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, separators including coatings with ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0139] In addition, the electrolyte used in this invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. All of these electrolytes can be used to manufacture lithium secondary batteries, but the electrolyte is not limited to these.

[0140] Specifically, electrolytes may include organic solvents and lithium salts.

[0141] As organic solvents, any organic solvent can be used without particular restriction, as long as it can serve as a medium through which the ions involved in the electrochemical reactions of the battery can move. Specifically, as organic solvents, the following can be used: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic hydrocarbon solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group, and may include double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate-based solvents are preferred, and even more preferred are mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate-based compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) that can improve the charge / discharge performance of the battery.

[0142] Any compound can be used as a lithium salt, without particular restriction, as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from F... - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N -At least one of the constituent groups, and as a lithium salt, can be used, such as LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The lithium salt can be used in a concentration range of 0.1 M to 4.0 M, preferably 0.5 M to 3.0 M, and more preferably 1.0 M to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, and therefore can exhibit excellent electrolyte performance, and lithium ions can move efficiently.

[0143] In order to improve battery life performance, suppress battery capacity reduction, and increase battery discharge capacity, the electrolyte may include one or more additives in addition to the electrolyte components mentioned above. Examples include haloalkylene carbonate compounds of difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum oxide. In this case, the additives may be included in an amount from 0.1 wt% to 10.0 wt% based on the total weight of the electrolyte.

[0144] Furthermore, the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity and output performance, and stably exhibits capacity retention rate. Therefore, the lithium secondary battery is useful in portable devices such as mobile phones, laptops and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0145] Therefore, according to another embodiment of the present invention, a battery module including a lithium secondary battery as a unit battery and a battery pack including the battery module are provided.

[0146] Battery modules or battery packs can be used as a power source for power tools, electric vehicles including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs), or for one or more medium to large-sized devices in a system for energy storage.

[0147] The embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments set forth herein.

[0148] The invention will be described in more detail below with reference to specific examples.

[0149] Preparation examples, examples and comparative examples

[0150] Preparation Example 1: Preparation of Powder for the First Electrode

[0151] 940 g of lithium iron phosphate (LFePO4, Aleees Corp., M121, D) will be used as the positive electrode active material. 50 20 g of carbon black (2.2 μm) as a conductive material and 40 g of polytetrafluoroethylene (PTFE) as a binder were introduced into a mixer (HanilCorp, SHMF-3260S) and mixed at 10,000 rpm for 10 minutes to prepare a mixture composition.

[0152] The mixture composition was introduced into a kneader (Hanil Corp.) and kneaded for 5 minutes at 25 rpm at 150°C to prepare a mixed aggregate.

[0153] The mixed aggregates were introduced into a mixer (Hanil Corp, SHMF-3260S) and pulverized at 10,000 rpm for 1 minute to prepare powder for the first electrode.

[0154] Preparation Example 2: Preparation of Powder for the Second Electrode

[0155] Except for preparing the mixed aggregate by kneading the mixture composition at 50 rpm for 20 minutes at 150°C, and introducing the mixed aggregate into a mixer and pulverizing it at 10,000 rpm for 20 seconds, the powder for the second electrode is prepared in the same manner as the powder for the first electrode.

[0156] Example 1: Manufacturing an electrode mixture film

[0157] The first electrode powder prepared in Preparation Example 1 above is introduced into the central portion of the calender roll, and the second electrode powder prepared in Preparation Example 2 above is introduced into each side portion of the side portion of the calender roll to prepare an electrode mixture film.

[0158] At this time, the diameter of the calender roll is 88 mm, the temperature is 100°C, and the roll speed ratio is 20 / 24 rpm. The width of the central portion of the calender roll is 280 mm, and the width of each side portion of the side portion of the calender roll is 10 mm.

[0159] Example 2: Manufacturing an electrode mixture film

[0160] Except that the width of the central portion of the calender roll is 240 mm and the width of each side portion of the side portion of the calender roll is 30 mm, the electrode mixture film is manufactured in the same manner as in Example 1.

[0161] Example 3: Manufacturing an electrode mixture film

[0162] Except that the width of the central portion of the calender roll is 200 mm and the width of each side portion of the side portion of the calender roll is 50 mm, the electrode mixture film is manufactured in the same manner as in Example 1.

[0163] Comparative Example 1: Manufacturing an Electrode Mixture Film

[0164] Only the first electrode of Example 1 is introduced into the calendering roll with powder to prepare an electrode mixture film.

[0165] At this time, the diameter of the calendering roll is 88 mm, the temperature is 100°C, and the roll speed ratio is 20 / 24 rpm.

[0166] Comparative Example 2: Manufacturing an Electrode Mixture Film

[0167] Only the second electrode of Example 1 is introduced into the calendering roll with powder to prepare an electrode mixture film.

[0168] At this time, the diameter of the calendering roll is 88 mm, the temperature is 100°C, and the roll speed ratio is 20 / 24 rpm.

[0169] The preparation methods of the electrode mixture films prepared in Examples 1 to 3 and Comparative Examples 1 and 2 are summarized in Table 1 below.

[0170] exist[ Figure 4 ]to[ Figure 6 The images show photographs of the electrode mixture films prepared in Examples 1 and 3, as well as Comparative Example 1.

[0171] [Table 1]

[0172] Experimental Example 1: Measuring the crystallinity of the binder in the central and side portions of an electrode powder and electrode mixture film.

[0173] Using differential scanning calorimetry (DSC), the crystallinity of each of the first electrode powder prepared in Preparation Example 1 and the second electrode powder prepared in Preparation Example 2, as well as the crystallinity of the binder in the central and side portions of the electrode mixture films manufactured in Examples 1 to 3 and Comparative Examples 1 and 2, was calculated according to [Equation 1] above.

[0174] Specifically, 15 mg of sample was introduced into a differential scanning calorimeter (DSC) manufactured by TA Corp., and heated at a rate of 10°C / min over a nitrogen atmosphere from 25°C to 370°C. The heat of fusion (Δheat of fusion) was measured according to temperature. Then, using TA Corp.'s TROIS program, the melting point (Tm) and enthalpy of fusion (ΔH) were analyzed based on the temperature at the point in time that exhibited the highest enthalpy during melting (peak temperature). m ).

[0175] The crystallinity of each sample is calculated using [Equation 1] above, where the enthalpy of fusion (ΔH) is actually measured by DSC. m The value divided by the enthalpy of fusion of a theoretically perfect crystal (100% crystallinity) (ΔH) m O The enthalpy of fusion for PTFE in its theoretical perfect crystal form is set at 85.4 J / g (Polymer Journal, Vol. 46, pp. 8872-8882, 2005).

[0176] The measurement results are shown in Tables 2 and 3 below.

[0177] [Table 2]

[0178] [Table 3]

[0179] Experimental Example 2: Measuring the width of the side defect portion and the normal portion of the electrode mixture film.

[0180] The appearance of the electrode mixture films manufactured by each of Examples 1 to 3 and Comparative Examples 1 and 2 was observed from the outside to measure the width of the defective portions formed in the side portions and the width of the normal portions. Specifically, the width of the normal portions was measured by measuring the width of the electrode mixture film between the parallel lines of the MD direction through which the deepest point of the serrated defect portion forms on one side surface and the parallel lines of the MD direction through which the deepest point of the serrated defect portion forms on the other side surface, and the width of the defective portions formed in the side portions was obtained by measuring the average length from one end of the width of the normal portion to the outermost portion of the serrated defect portion.

[0181] The measurement results are shown in Table 4 below.

[0182] [Table 4]

[0183] As can be confirmed from [Table 4] above, it can be confirmed that, unlike Comparative Example 1 which only uses powder for the first electrode, the width of the side defect portion in Examples 1 to 3 is significantly reduced.

[0184] Experimental Example 3: Measuring the tensile strength and elongation at break of an electrode mixture film

[0185] The electrode mixture films manufactured in Examples 1 to 3 and Comparative Examples 1 and 2 were cut to a size of 70 × 10 mm, and their tensile strength was measured using a tensile strength tester (UTM device manufactured by ZwickRoell Corp.) in accordance with ASTM 638. Tensile strength was measured 10 times at a tensile rate of 50 mm / min and a preload of 0.01 kg / cm, and the results were averaged and presented.

[0186] During the tensile strength measurement, the length was measured at the point of fracture, and the elongation at break was calculated by multiplying (length at fracture - length of the initial sample) / length of the initial sample by 100.

[0187] The measurement results are shown in Table 5 below.

[0188] [Table 5]

[0189] As can be confirmed from [Table 2] above, it can be confirmed that, unlike Comparative Example 2 which only uses powder for the second electrode, Examples 1 to 3 are superior in both tensile strength and elongation at break.

[0190] [Description of reference numerals or symbols in the attached figures]

[0191] 11: Powder for the first electrode

[0192] 12: Powder for the second electrode

[0193] 31: Supply Components

[0194] 32: Calendering roll

[0195] 33: Guide baffle

[0196] 34: Divider

[0197] 150: Electrode mixture film

[0198] 151: Electrode mixture film side portion

[0199] 152: Central portion of the electrode mixture film

Claims

1. An electrode mixture membrane, said electrode mixture membrane comprising an electrode active material, a conductive material, and a fiberizable binder, wherein, The electrode mixture film includes: side portions located at two ends in the width direction of the electrode mixture film; and a central portion disposed between the side portions, wherein the crystallinity of the adhesive contained in the central portion is higher than that of the adhesive contained in the side portions.

2. The electrode mixture film according to claim 1, wherein, The width of each side portion is independently 0.1% to 40% of the width of the electrode mixture film at both ends in the width direction of the electrode mixture film.

3. The electrode mixture film according to claim 1, wherein, The adhesive contained in the central portion has a crystallinity of 5% to 40%.

4. The electrode mixture film according to claim 1, wherein, The adhesive contained in the side portion has a crystallinity of less than or equal to 4.5%.

5. The electrode mixture film according to claim 1, wherein, The electrode active material has an average particle size (D) of 0.1 μm to 5.0 μm. 50 ).

6. A method for manufacturing an electrode mixture film, the method comprising: (S1) The step of obtaining each of a first electrode powder and a second electrode powder, each of the first electrode powder and the second electrode powder comprising an electrode active material, a conductive material, and a fibrous binder; and (S2) The step of introducing the first electrode powder and the second electrode powder into a calendering roll, wherein the calendering roll is divided into three or more sections in the width direction by a baffle. In this process, the binder contained in the first electrode powder in (S1) has a higher crystallinity than the binder contained in the second electrode powder in (S1), and the first electrode powder is introduced into the central portion of the roller in (S2), and the second electrode powder is introduced into the side portions located at the two ends of the central portion of the roller.

7. The method according to claim 6, wherein, The calendering roll described in (S2) above is divided into three sections in the width direction by the baffle, and the length of each of the side sections is independently 1% to 45% of the length of the central section.

8. The method according to claim 6, wherein, The length of each of the side portions is independently 2% to 30% of the length of the central portion.

9. The method according to claim 6, wherein, The first electrode powder and the second electrode powder are each prepared independently by a method comprising the following steps: (a) The step of preparing a mixture composition comprising an electrode active material, a conductive material and a fibrous binder; as well as (b) The step of kneading the mixture composition at a temperature of 70°C to 200°C to prepare a mixed aggregate.

10. The method according to claim 9, wherein, The kneading described in (b) above is performed at a temperature of 70°C to 200°C and a rotational speed of less than or equal to 100 rpm.

11. The method according to claim 9, wherein, The time period for kneading to prepare the powder for the first electrode is shorter than the time period for kneading to prepare the powder for the second electrode.

12. The method according to claim 6, wherein, The binder contained in the first electrode powder has a crystallinity of 5% to 40%, and the binder contained in the second electrode powder has a crystallinity of less than or equal to 8%.

13. The method according to claim 6, further comprising a step (S3) of removing the edge portions of the film manufactured after (S2), wherein, The edge portions are located at both ends in the width direction of the electrode mixture film manufactured after (S2), and the width of each edge portion is independently 10% or less of the width length of the electrode mixture film manufactured after (S2).

14. A lithium secondary battery comprising a dry electrode containing an electrode mixture membrane according to claim 1.

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