阅读说明：本技术 二次电池的隔板、其制造方法和包括该隔板的锂二次电池 (Separator for secondary battery, method of manufacturing the same, and lithium secondary battery including the same ) 是由 赵宰贤 金柄秀 于 2019-12-11 设计创作，主要内容包括：实施方式提供用于二次电池的隔板、其制造方法和包括该隔板的锂二次电池,隔板包括：多孔基板；和在多孔基板的至少一个表面上包括多个环图案的涂层,其中：环图案包含多个聚合物微粒；环图案以规则间隔分隔；环图案的粒径为10μm至200μm；且环图案的环的宽度(环的厚度)为0.2μm至1.5μm。(Embodiments provide a separator for a secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same, the separator including: a porous substrate; and a coating comprising a plurality of ring patterns on at least one surface of the porous substrate, wherein: the ring pattern comprises a plurality of polymer microparticles; the ring patterns are spaced at regular intervals; the particle size of the ring pattern is 10 μm to 200 μm; and the width of the ring pattern (the thickness of the ring) is 0.2 to 1.5 μm.)

1. A separator for a secondary battery comprising

A porous substrate; and

a coating layer including a plurality of ring patterns on at least one surface of the porous substrate,

wherein the ring pattern comprises a plurality of polymer microparticles,

the ring patterns are spaced apart from each other at regular intervals,

the ring pattern has a particle diameter of 10 to 200 μm, and

the width of the ring pattern (the thickness of the ring) is 0.2 to 1.5 μm.

2. The separator of claim 1, wherein the ring patterns are spaced apart from each other at intervals of 10 μm to 1000 μm.

3. The separator of claim 1, wherein the ring pattern has a particle size of 50 μm to 150 μm.

4. The separator of claim 1, wherein a width of the ring pattern (a thickness of the ring) is 0.5 μm to 1.2 μm.

5. The separator of claim 1, wherein the polymer particles comprise at least one selected from the group consisting of fluorine-based polymer particles, (meth) acrylic polymer particles, and a mixture thereof.

6. The separator of claim 1, wherein the polymer microparticles have a particle size of 100nm to 600 nm.

7. The separator of claim 5, wherein the fluorine-based polymer particles comprise at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-co-hexafluoropropylene, and polyvinylidene fluoride-co-trichloroethylene.

8. The separator of claim 5, wherein the (meth) acrylic polymer particles comprise at least one selected from the group consisting of poly (meth) acrylate, poly (butyl (meth) acrylate), poly (pentyl (meth) acrylate, poly (hexyl (meth) acrylate), and polyacrylonitrile.

9. The separator of claim 1 wherein the loading of the ring pattern is 0.5g/m²To 1.5g/m²。

10. The separator of claim 1, wherein the coating has a thickness of 0.1 μm to 5 μm.

11. The separator of claim 1, wherein the area of the ring pattern is 40% to 80% of the total area of the porous substrate, and the area occupied by the rings of the ring pattern is 5% to 30% of the total area of the porous substrate.

12. A method of manufacturing a separator for a secondary battery, comprising

Mixing at least one of fluorine-based polymer fine particles, (meth) acrylic acid polymer fine particles and a mixture thereof with water to prepare a coating composition, and

coating the coating composition on at least one surface of a porous substrate by an inkjet coating method and drying the coating composition to manufacture the separator according to any one of claims 1 to 11.

13. The method of claim 12, wherein the coating composition has a viscosity of 0.1cps to 10 cps.

14. The method of claim 12, wherein the coating composition comprises fluorine-based polymer particles and (meth) acrylic polymer particles in a weight ratio of 90:10 to 50: 50.

15. The method of claim 12, wherein the fluorine-based polymer particles comprise polymer particles having a particle size of 100nm to 300 nm.

16. The method of claim 12, wherein the (meth) acrylic polymer comprises polymer microparticles having a particle size of 250nm to 600 nm.

17. The method according to claim 12, wherein the inkjet coating method comprises jetting and coating the coating composition on a porous substrate at a temperature of 20 ℃ to 55 ℃ and a speed of 10 mm/sec to 500 mm/sec at a frequency of 1.0KHz to 10KHz with a nozzle number density of 50(dpi) to 1000(dpi) of an inkjet head.

Technical Field

To a separator for a secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same.

Background

A positive electrode and a negative electrode including a material capable of intercalating and deintercalating lithium ions are impregnated into an electrolyte, and a separator is disposed between the positive electrode and the negative electrode. Wherein the separator serves as a moving path of electrolyte ions while preventing direct contact (internal short circuit) between the positive electrode and the negative electrode.

In the case of manufacturing a lithium secondary battery, if electrodes and separators are not properly combined, positive and negative electrodes repeatedly contract and expand during the charge and discharge of the lithium battery, which may cause deformation of the shape of the battery and problems in battery performance and stability due to uneven reactions during the operation of the battery.

When the lithium secondary battery is externally short-circuited, a large current flows to generate heat, thereby increasing the battery temperature and starting thermal runaway, which may cause the operation of a safety valve or the ignition due to evaporation or heat generation of an electrolyte. In order to prevent this, a porous body including a hot-melt resin such as polyolefin is used in the separator. When the temperature inside the battery rises above a certain temperature, the separator melts to block the opening, so that a shutdown function of stopping the reaction of the battery and suppressing heat generation can be applied.

However, in the case of a large-sized secondary battery for power storage or vehicles, heat dissipation is poor, and when overheating occurs inside the secondary battery, the temperature of the secondary battery rises to 400 ℃ to 500 ℃ in a short time. If this condition continues, the separator may melt or melt crack, a short-circuit current flows due to contact between the electrodes, and an exothermic state causes thermal runaway.

Disclosure of Invention

[ problem ] to provide a method for producing a semiconductor device

Embodiments provide a separator for a secondary battery, a method of manufacturing the separator, and a lithium secondary battery including the separator according to embodiments, the separator having improved adhesion between an electrode and the separator and reduced interfacial resistance.

[ technical solution ] A

Embodiments provide a separator for a secondary battery, including: a porous substrate; and a coating layer including a plurality of ring patterns on at least one surface of the porous substrate, wherein the ring patterns include a plurality of polymer microparticles, the ring patterns are spaced apart from each other at regular intervals, a particle diameter of the ring patterns is 10 μm to 200 μm, and a width of a ring of the ring patterns (a thickness of the ring) is 0.2 μm to 1.5 μm.

The ring patterns may be spaced apart from each other at intervals of 10 μm to 1000 μm.

The particle size of the ring pattern may be 50 μm to 150 μm.

The width of the ring pattern (the thickness of the ring) may be 0.5 μm to 1.2 μm.

The polymer fine particles may include at least one selected from fluorine-based polymer fine particles, (meth) acrylic acid polymer fine particles, and a mixture thereof.

The polymer microparticles may have a particle size of 100nm to 600 nm.

The fluorine-based polymer microparticles may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-co-hexafluoropropylene, and polyvinylidene fluoride-co-trichloroethylene.

The (meth) acrylic polymer microparticles may include at least one selected from the group consisting of poly (meth) acrylate, poly (butyl (meth) acrylate), poly (pentyl (meth) acrylate, poly (hexyl (meth) acrylate), and polyacrylonitrile.

The amount of the supported ring pattern may be 0.5g/m²To 1.5g/m²。

The thickness of the coating may be 0.1 μm to 5 μm.

The area of the ring pattern may be 40% to 80% of the total area of the porous substrate, and the area occupied by the rings of the ring pattern may be 5% to 30% of the total area of the porous substrate.

In another embodiment, a method of manufacturing a separator for a secondary battery includes: mixing at least one of fluorine-based polymer microparticles, (meth) acrylic acid polymer microparticles, and a mixture thereof with water to prepare a coating composition, and coating the coating composition on at least one surface of the porous substrate by an inkjet coating method and drying the coating composition.

The viscosity of the coating composition can be from 0.1cps to 10 cps.

The coating composition may include fluorine-based polymer particles and (meth) acrylic polymer particles in a weight ratio of 90:10 to 50: 50.

The fluorine-based polymer fine particles may include polymer fine particles having a particle diameter of 100nm to 300 nm.

The (meth) acrylic polymer may include polymer fine particles having a particle size of 250nm to 600 nm.

The inkjet coating method may include ejecting and coating the coating composition on the porous substrate at a temperature of 20 ℃ to 55 ℃ and a speed of 10 mm/sec to 500 mm/sec at a frequency of 1.0KHz to 10KHz with a nozzle number density of 50(dpi) to 1000(dpi) of the inkjet head.

Another embodiment provides a lithium secondary battery including a positive electrode; a negative electrode; a separator for a secondary battery between the positive electrode and the negative electrode; and an electrolyte.

[ PROBLEMS ] the present invention

By improving the adhesion between the electrode and the separator and reducing the interface resistance, the cycle life characteristics of the battery can be improved.

Drawings

Fig. 1 is a schematic view showing a coating layer of a separator according to an embodiment.

Fig. 2 is a schematic view of a ring pattern included in a coating layer of a separator according to an embodiment.

Fig. 3 is an exploded perspective view of a lithium secondary battery according to an embodiment.

Fig. 4 and 5 are SEM photographs of the separator according to example 1, respectively measured at different magnifications.

Fig. 6 and 7 are cross-sectional SEM photographs of the separators according to examples 1 and 2, respectively.

< description of symbols >

1: ring pattern 3: ring (C)

5: coating 7: porous substrate

100: lithium secondary battery 112: negative electrode

113: partition 114: positive electrode

120: the battery case 140: sealing member

Detailed Description

Hereinafter, the present invention will be described in more detail. The embodiment described herein and the configuration shown in the drawings are only one of the most preferable embodiments of the present invention and do not represent all the technical spirit of the present invention, and there are various equivalents or exemplary variations that may substitute them at the time of the present application.

In the present specification, "(meth) acrylic acid" and "(meth) acrylate" may mean acrylic acid or methacrylic acid and acrylate or methacrylate, respectively, when no definition is otherwise provided.

In addition, in the present specification, when a definition is not otherwise provided, the particle diameter may be an average particle size of 50% by volume in a cumulative size-distribution curve (D50). The average particle size (D50) can be measured by methods well known to those of ordinary skill in the art. For example, it can be measured by a particle size analyzer, or from TEM (transmission electron microscope) or SEM (scanning electron microscope) photographs. Alternatively, data analysis is performed using a dynamic light scattering measurement device, and the number of particles is counted for each particle size range, whereby the D50 value can be easily obtained by calculation.

Embodiments provide a separator comprising a porous substrate and a coating comprising a plurality of ring patterns on at least one surface of the porous substrate.

The lithium secondary battery is generally manufactured by: a separator is interposed between the positive electrode and the negative electrode, wound, and then compressed (heated) at a predetermined temperature and pressure. Through the compression process, as the adhesion (resistance) at the interface between the positive electrode and the separator and/or at the interface between the negative electrode and the separator increases, the discharge capacity may be continuously decreased as the charge/discharge cycle of the lithium secondary battery proceeds, the high-rate charge/discharge characteristics may be decreased, and a problem in terms of battery safety may occur. In order to solve these problems, separators having a coating layer formed by coating a mixture of a plurality of binder polymers and inorganic materials on at least one surface of a porous substrate are being manufactured. However, even in this case, in order to increase the bondability between the separator and the electrode, a large amount of the binder polymer is exposed to the surface of the separator, so that a side reaction may occur between the binder polymer and the electrolyte, causing the separator to swell, and as a result, the ionic conductivity and the battery cycle life may deteriorate.

In order to solve the above problems, there is provided a separator for a secondary battery, including a coating layer of the separator, the coating layer including a plurality of ring patterns spaced apart from each other at regular intervals, wherein the ring patterns include a plurality of polymer microparticles, a particle diameter of the ring patterns is 10 μm to 200 μm, and a width of a ring of the ring patterns (a thickness of the ring) is 0.2 μm to 1.5 μm.

Hereinafter, the separator is described with reference to fig. 1 and 2.

Fig. 1 is a schematic view showing a coating layer of a separator, and fig. 2 is a schematic view of a ring pattern included in the coating layer of the separator.

Referring to fig. 1, a plurality of ring patterns included in the coating layer 5 according to an embodiment may be spaced apart from each other at regular intervals. Within the range of any separation distance (D) (e.g., average separation distance) ± 20% (e.g., ± 10%), the plurality of ring patterns separated from each other at regular intervals may have a separation distance corresponding to greater than or equal to 50%, specifically, greater than or equal to 60%, or greater than or equal to 80% of the total number of ring patterns on a 100% basis.

The plurality of ring patterns may have a separation distance (D) at regular intervals of 10 μm to 1000 μm, specifically, 10 μm or more, 20 μm or more, 30 μm or more, 40 μm or more, or 50 μm or more, and 1000 μm or less, 800 μm or less, 600 μm or less, 400 μm or less, 300 μm or less, or 270 μm or less. On the other hand, the separation distance (D) may be a distance between centers of adjacent ring patterns 1. When the separation distance (D) is within this range, the effect of adhesion between the coating and the electrode can be increased. Therefore, the swelling phenomenon of the battery, which occurs when the adhesion between the electrode and the separator is insufficient, can be effectively suppressed, and the ionic conductivity can be improved, thereby improving the cycle-life characteristics of the battery.

On the other hand, in the separator for a secondary battery according to the embodiment, the coating layer is formed in an inkjet coating method described later, and a plurality of ring patterns included in the coating layer may be regularly aligned.

Referring to fig. 2, in the plurality of ring patterns 1, a plurality of polymer microparticles are present in the ring 3, and polymer particles are substantially absent or present at a small loading of less than or equal to 50 wt% inside the ring patterns 1 except the ring 3, as compared to in the ring 3. Therefore, the pore blocking phenomenon can be minimized, compared to the case of applying a ring pattern filled with a polymer material or uniformly coating the polymer material on the entire surface of the porous substrate. Therefore, the swelling phenomenon of the separator due to a side reaction with the electrolyte solution can be improved, and the ion conductivity can be improved.

On the other hand, in order to maintain the adhesive force between the electrode and the separator, it is important to find an optimum numerical range of the particle diameter of the ring pattern 1 and the width of the ring 3 (the thickness (d) of the ring). In this regard, the ring pattern may have a particle size of 10 μm to 200 μm, for example, a particle size of 50 μm to 150 μm, or 100 μm to 150 μm. The width of the ring pattern is 0.2 μm to 1.5 μm, for example, 0.4 μm to 1.3 μm, or 0.5 μm to 1.1 μm. When the ring pattern has a particle diameter and a ring width (ring thickness) within this range, the cycle-life characteristics of the battery can be improved by improving the adhesion between the electrode and the separator and minimizing the interfacial resistance.

On the other hand, the particle diameter range of the ring pattern 1 and the thickness range of the ring pattern 3 belong to specifically 50% or more, specifically 60% or more or 80% or more of the ring pattern 1 based on 100% of the total number of the ring pattern 1.

The plurality of polymer microparticles present in the ring 3 of the ring pattern 1 may include at least one selected from fluorine-based polymer microparticles, (meth) acrylic acid polymer microparticles, and a mixture thereof, and the particle diameter of the polymer microparticles may be 100nm to 600 nm.

The fluorine-based polymer microparticles may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-co-hexafluoropropylene, and polyvinylidene fluoride-co-trichloroethylene. In addition, the fluorine-based polymer fine particles may have a particle diameter of 100nm to 300nm, for example, 100nm to 250nm, 100nm to 200nm, or 150nm to 200 nm. Therefore, the adhesion and the oxidation resistance between the separator and the electrode plate may be improved, and when the particle diameter of the fluorine-based polymer particles is within this range, the battery performance may be improved by minimizing the movement resistance of lithium ions and minimizing the thickness of the coating layer.

The (meth) acrylic polymer microparticles may include at least one selected from the group consisting of poly (meth) acrylate, poly (butyl (meth) acrylate), poly (pentyl (meth) acrylate, poly (hexyl (meth) acrylate), and polyacrylonitrile.

The (meth) acrylic polymer microparticles may have a particle size of 250nm or more, 300nm or more, or 350nm or more, and 600nm or less, 550nm or less, 500nm or less, or 450nm or less. When the particle diameter of the (meth) acrylic polymer fine particles falls within the above range, the movement resistance of lithium ions can be minimized to ensure the performance of the lithium secondary battery.

The loading of the ring pattern in the coating may be 0.5g/m²To 1.5g/m²For example 0.7g/m²To 1.3g/m²Or 1.0g/m²To 1.2g/m². When the ring pattern has a load amount within this range, the cycle-life characteristics of the battery may beBy improving the adhesion and ionic conductivity of the separator, but reducing the interfacial resistance between the electrode and the separator.

The coating layer may be formed as a thin film having a thickness (total thickness) of 0.1 μm to 5 μm, for example, 0.5 μm to 3.5 μm, 0.5 μm to 3.0 μm, 0.5 μm to 1.5 μm, or 0.5 μm to 1.2 μm.

In the coating layer, the area of the ring pattern (including the inner space of the ring pattern) may be 40% to 80%, for example, 40% to 75%, of the total area of the porous substrate. On the other hand, the area of the ring pattern indicates the sum of the area of the ring pattern and the area of the inner region of the ring pattern other than the ring.

In the coating, an area occupied by the rings of the ring pattern (excluding the inner space of the ring pattern) may be 5% to 30%, for example, 10% to 20%, of the total area of the porous substrate. In the coating layer, when the area of the ring pattern and the area occupied by the rings of the ring pattern are within the ranges, respectively, the adhesion between the separator and the electrode may be maintained at a proper level, and the interfacial resistance may be reduced, thereby improving the cycle-life characteristics of the battery.

Hereinafter, a method of manufacturing a separator according to an embodiment is described.

Another embodiment provides a method of manufacturing a separator for a secondary battery, including: mixing at least one of fluorine-based polymer particles, (meth) acrylic acid polymer particles, and a mixture thereof with water to prepare a coating composition, coating the coating composition on at least one surface of a porous substrate by an inkjet coating method, and drying the coating composition to manufacture a separator.

The fluorine-based polymer fine particles have a polymer fine particle having a particle diameter of 100nm to 300nm, for example, 100nm to 250nm, 100nm to 200nm, or 150nm to 200nm, and the (meth) acrylic polymer fine particles may include a polymer fine particle having a particle diameter of greater than or equal to 250nm, greater than or equal to 300nm, or greater than or equal to 350nm and less than or equal to 600nm, less than or equal to 550nm, or less than or equal to 500 nm.

The coating composition may include fluorine-based polymer particles and (meth) acrylic polymer particles in a weight ratio of 90:10 to 50:50, 90:10 to 55:45, 90:10 to 60:40, 90:10 to 65:35, or 90:10 to 70: 30. Within this range, the interfacial resistance between the electrode and the separator is reduced, the adhesion of the separator is improved, and therefore, the cycle life characteristics of the battery can be improved.

The coating composition can have a viscosity ranging from greater than or equal to 0.1cps, greater than or equal to 0.5cps, greater than or equal to 1cps, or greater than or equal to 2cps, and less than or equal to 50cps, less than or equal to 45cps, less than or equal to 40cps, less than or equal to 35cps, less than or equal to 30cps, less than or equal to 25cps, less than or equal to 20cps, less than or equal to 15cps, less than or equal to 10cps, or less than or equal to 7 cps. According to the embodiment of the present invention, when the viscosity of the coating composition is within the range, the loop pattern may be well formed to have a particle diameter and a loop width within the range. When the coating composition has too low or too high viscosity, it may be difficult to form a coating layer by applying an inkjet coating method, and the particle diameter and ring width of the ring pattern according to an embodiment may be difficult to achieve.

The inkjet coater used to manufacture the separator according to the embodiment is a piezo-type or a hot bubble type coater, and may be used to spray the coating composition from a nozzle. The inkjet coating method is a coating method in which voltage is applied by frequency control to push ink (coating composition).

Specifically, the inkjet coating method may jet and coat the coating composition on the porous substrate by setting the number of nozzles of the inkjet head to have a density of 50(dpi) to 1000(dpi) at 20 ℃ to 55 ℃, a frequency of 1.0KHz to 10KHz, and a coating speed of 10 mm/sec to 500 mm/sec. When the inkjet coating method has process conditions within this range, a coating layer in which ring patterns having particle diameters and ring widths (thicknesses) are spaced at regular intervals on a porous substrate can be well formed. For example, as the density of the number of nozzles increases, the particle size of the ring pattern, the ring width, and the separation distance of the ring pattern all decrease, and the number of ring patterns in the coating increases. Conversely, when the density of the number of nozzles is decreased, the opposite result is obtained.

The lithium secondary battery according to the embodiment includes a positive electrode; a negative electrode; a separator between the positive electrode and the negative electrode; and an electrolyte solution.

The separator 113 separates the positive electrode 114 and the negative electrode 112 and provides a transport channel for lithium ions. The detailed description thereof is as described above. The overall thickness of the separator may be determined by the target capacity of the battery. The thickness of the separator may be, for example, 5 μm to 30 μm.

The negative electrode 112 includes a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer includes a negative electrode active material.

The negative active material may include a material that reversibly intercalates/deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

The material reversibly intercalating/deintercalating lithium ions may be a carbon material, which is any commonly used carbon-based negative electrode active material in a lithium ion secondary battery, and examples thereof may be crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon may be graphite such as amorphous, flake-shaped, spherical-shaped, or fiber-shaped natural graphite or artificial graphite. Examples of the amorphous carbon may be soft carbon (low-temperature-fired carbon) or hard carbon, mesophase pitch carbonized products, fired coke, and the like.

The lithium metal alloy may Be an alloy of lithium with a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al or Sn.

The material capable of doping and dedoping lithium can be Si, SiO_x(0<x<2) Si-C composite, Si-Q alloy (wherein Q is selected from the group consisting of alkali metals, alkaline earth metals, group 13 to 16 elements, transition elements, rare earth elements, and combinations thereof, and is not Si), Sn, SnO₂Sn-C composite, Sn-R (where R is selected from alkali metals, alkaline earth metals, group 13 to 16 elements, transition elements, rare earth elements, and combinations thereof, and is not Sn). The elements Q and R may 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, Ti, Ge, P, Si,As, Sb, Bi, S, Se, Te, Po or combinations thereof.

The transition element oxide may include vanadium oxide, lithium vanadium oxide, and the like.

The anode active material layer further includes a binder, and may further optionally include a conductive material.

The binder improves binding properties of the anode active material particles to each other and to the current collector, and examples thereof may be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but are not limited thereto.

The conductive material improves the conductivity of the electrode, and any conductive material may be used as the conductive material unless it causes a chemical change, and examples thereof may be carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, and the like; metal-based materials such as metal powders and metal fibers of copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives and the like; or mixtures thereof.

The current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

The positive electrode 114 includes a collector and a positive active material layer formed on the collector.

The positive electrode active material may be a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). Specifically, at least one lithium metal composite oxide of lithium and a metal of cobalt, manganese, nickel, or a combination thereof may be used, and a specific example thereof may be a compound represented by one of the following chemical formulae. Li_aA_1-bR_bD₂(wherein, in the above chemical formula, a is 0.90. ltoreq. a.ltoreq.1.8 and b is 0. ltoreq. b.ltoreq.0.5); li_aE_1-bR_bO_2-cD_c(wherein, inIn the chemical formula, a is more than or equal to 0.90 and less than or equal to 1.8, b is more than or equal to 0 and less than or equal to 0.5, and c is more than or equal to 0 and less than or equal to 0.05); LiE_2-bR_bO_4-cD_c(wherein, in the chemical formula, b is more than or equal to 0 and less than or equal to 0.5, and c is more than or equal to 0 and less than or equal to 0.05); li_aNi_1-b-cCo_bR_cD_α(wherein, in the above chemical formula, a is 0.90. ltoreq. a.ltoreq.1.8, b is 0. ltoreq. b.ltoreq.0.5, c is 0. ltoreq. c.ltoreq.0.05 and 0<α≤2)；Li_aNi_1-b-cCo_bR_cO_2-αZ_α(wherein, in the above chemical formula, a is 0.90. ltoreq. a.ltoreq.1.8, b is 0. ltoreq. b.ltoreq.0.5, c is 0. ltoreq. c.ltoreq.0.05 and 0<α<2)；Li_aNi_{1-b- c}Co_bR_cO_2-αZ₂(wherein, in the above chemical formula, a is 0.90. ltoreq. a.ltoreq.1.8, b is 0. ltoreq. b.ltoreq.0.5, c is 0. ltoreq. c.ltoreq.0.05 and 0<α<2)；Li_aNi_1-b-cMn_bR_cD_α(wherein, in the above chemical formula, a is 0.90. ltoreq. a.ltoreq.1.8, b is 0. ltoreq. b.ltoreq.0.5, c is 0. ltoreq. c.ltoreq.0.05 and 0<α≤2)；Li_aNi_1-b-cMn_bR_cO_2-αZ_α(wherein, in the above chemical formula, a is 0.90. ltoreq. a.ltoreq.1.8, b is 0. ltoreq. b.ltoreq.0.5, c is 0. ltoreq. c.ltoreq.0.05 and 0<α<2)；Li_aNi_1-b-cMn_bR_cO_2-αZ₂(wherein, in the above chemical formula, a is 0.90. ltoreq. a.ltoreq.1.8, b is 0. ltoreq. b.ltoreq.0.5, c is 0. ltoreq. c.ltoreq.0.05 and 0<α<2)；Li_aNi_bE_cG_dO₂(wherein, in the chemical formula, a is more than or equal to 0.90 and less than or equal to 1.8, b is more than or equal to 0 and less than or equal to 0.9, c is more than or equal to 0 and less than or equal to 0.5, and d is more than or equal to 0.001 and less than or equal to 0.1); li_aNi_bCo_cMn_dGeO₂(wherein, in the chemical formula, a is more than or equal to 0.90 and less than or equal to 1.8, b is more than or equal to 0 and less than or equal to 0.9, c is more than or equal to 0 and less than or equal to 0.5, d is more than or equal to 0 and less than or equal to 0.5, and e is more than or equal to 0.001 and less than or equal to 0.1); li_aNiG_bO₂(wherein, in the above chemical formula, a is 0.90. ltoreq. a.ltoreq.1.8 and b is 0.001. ltoreq. b.ltoreq.0.1); li_aCoG_bO₂(wherein, in the above chemical formula, a is 0.90. ltoreq. a.ltoreq.1.8 and b is 0.001. ltoreq. b.ltoreq.0.1); li_aMnG_bO₂(wherein, in the above chemical formula, a is 0.90. ltoreq. a.ltoreq.1.8 and b is 0.001. ltoreq. b.ltoreq.0.1); li_aMn₂G_bO₄(wherein, in the above chemical formula, 0.90A is more than or equal to 1.8 and b is more than or equal to 0.001 and less than or equal to 0.1); QO₂；QS₂；LiQS₂；V₂O₅；LiV₂O₅；LiTO₂；LiNiVO₄；Li_(3-f)J₂(PO₄)₃(0≤f≤2)；Li_(3-f)Fe₂(PO₄)₃(f is more than or equal to 0 and less than or equal to 2); and LiFePO₄。

In the above formula, A is Ni, Co, Mn or a combination thereof; r is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or the combination thereof; d is O, F, S, P or a combination thereof; e is Co, Mn or a combination thereof; z is F, S, P or a combination thereof; g is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; q is Ti, Mo, Mn or a combination thereof; t is Cr, V, Fe, Sc, Y or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

The positive electrode active material may include a positive electrode active material having a coating layer, or a mixture of an active material and an active material coated with a coating layer. The coating may include the following compounds of the coating elements: an oxide or hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a hydroxycarbonate of the coating element. The compounds used for the coating may be amorphous or crystalline. The coating element included in the coating may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating process may include any conventional process as long as it does not cause any adverse effect on the properties of the positive electrode active material (e.g., inkjet coating, dipping), which is well known to those of ordinary skill in the art, and thus a detailed description thereof is omitted.

The positive electrode active material layer may also include a binder and a conductive material.

The binder improves the binding property of the positive electrode active material particles to each other and the binding property of the positive electrode active material particles to the current collector, and examples thereof may be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but are not limited thereto.

The conductive material improves the conductivity of the electrode, and any conductive material may be used as the conductive material unless it causes a chemical change, and examples thereof may be one or more of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder and metal fiber of copper, nickel, aluminum, silver, and the like, or polyphenylene derivatives, and the like.

Al may be used for the current collector, but is not limited thereto.

The negative and positive electrodes may be fabricated by the following method: comprising mixing an active material, a conductive material and a binder into an active material composition, and coating the composition on a current collector. Electrode manufacturing methods are well known and therefore are not described in detail in this specification. The electrolyte includes a nonaqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

The non-aqueous organic solvent may be selected from carbonates, esters, ethers, ketones, alcohols or aprotic solvents. The carbonate-based solvent includes dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), ethylene glycol carbonate (EC), propylene glycol carbonate (PC), butylene glycol carbonate (BC), and the like, and the ester-based solvent includes methyl acetate, ethyl acetate, n-propyl acetate, 1-dimethylethyl acetate, methyl propionate, ethyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, and the like. The ether solvent includes dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the like, and the ketone solvent includes cyclohexanone, and the like. The alcohol solvent may be ethanol, isopropyl alcohol, or the like. Aprotic solvents may include nitriles such as R — CN (where R is a C2 to C20 straight, branched, or cyclic hydrocarbon group, and R may include double bonds, aromatic rings, or ether linkages), amides such as dimethylformamide, dioxolanes such as 1, 3-dioxolane, sulfolane, and the like.

The non-aqueous organic solvent may be used alone or in combination of one or more, and in the case of mixing one or more, the mixing ratio may be appropriately adjusted according to the desired battery performance, as widely understood by those skilled in the art.

The carbonate-based solvent may include a mixture of cyclic carbonate and chain carbonate. The cyclic carbonate and the linear carbonate are mixed together in a volume ratio of about 1:1 to about 1: 9. Within this range, the performance of the electrolyte may be improved.

The non-aqueous organic electrolyte may be further prepared by mixing a carbonate-based solvent with an aromatic hydrocarbon-based solvent. The carbonate and aromatic hydrocarbon solvents may be mixed together in a volume ratio ranging from about 1:1 to about 30: 1.

The aromatic hydrocarbon organic solvent may be an aromatic hydrocarbon compound represented by chemical formula 1.

[ chemical formula 1]

In chemical formula 1, R₁To R₆Independently hydrogen, halogen, C1 to C10 alkyl, C1 to C10 haloalkyl, or combinations thereof.

The aromatic hydrocarbon-based organic solvent may include benzene, fluorobenzene, 1, 2-difluorobenzene, 1, 3-difluorobenzene, 1, 4-difluorobenzene, 1,2, 3-trifluorobenzene, 1,2, 4-trifluorobenzene, chlorobenzene, 1, 2-dichlorobenzene, 1, 3-dichlorobenzene, 1, 4-dichlorobenzene, 1,2, 3-trichlorobenzene, 1,2, 4-trichlorobenzene, iodobenzene, 1, 2-diiodobenzene, 1, 3-diiodobenzene, 1, 4-diiodobenzene, 1,2, 3-triiodobenzene, 1,2, 4-triiodobenzene, toluene, fluorotoluene, 1, 2-difluorotoluene, 1, 3-difluorotoluene, 1, 4-difluorotoluene, 1,2, 3-trifluorotoluene, 1,2, 4-trifluorotoluene, chlorotoluene, 1, 2-dichlorotoluene, 1, 3-dichlorotoluene, 1, 4-dichlorotoluene, 1,2, 3-trichlorotoluene, 1,2, 4-trichlorotoluene, iodotoluene, 1, 2-diiodotoluene, 1, 3-diiodotoluene, 1, 4-diiodotoluene, 1,2, 3-triiodotoluene, 1,2, 4-triiodotoluene, xylene, or a combination thereof.

The non-aqueous electrolyte may further include an additive of vinylene carbonate or ethylene carbonate-based compound of chemical formula 2 in order to improve the cycle life of the battery.

[ chemical formula 2]

In chemical formula 2, R₇And R₈Independently hydrogen, halo, Cyano (CN), Nitro (NO)₂) Or C1 to C5 fluoroalkyl, provided that R₇And R₈At least one of which is halo, Cyano (CN), Nitro (NO)₂) Or a C1 to C5 fluoroalkyl group.

Examples of the vinyl carbonate-based compound may be ethylene difluorocarbonate, ethylene chlorocarbonate, ethylene dichlorocarbonate, ethylene bromocarbonate, ethylene dibromocarbonate, ethylene nitrocarbonate, ethylene cyanocarbonate, ethylene fluorocarbonate, and the like. When vinylene carbonate or ethylene carbonate-based compounds are further used, the amount thereof may be appropriately adjusted so as to improve cycle life.

The lithium salt dissolved in the nonaqueous organic solvent supplies lithium ions to the battery, substantially operates the lithium secondary battery, and improves the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts include those selected from LiPF₆、LiBF₄、LiSbF₆、LiAsF₆、LiC₄F₉SO₃、LiClO₄、LiAlO₂、LiAlCl₄、LiN(C_xF_2x+1SO₂)(C_yF_2y+1SO₂) (wherein x and y are natural numbers), LiCl, LiI, LiB (C)₂O₄)₂At least one supporting salt of (lithium bis (oxalato) borate: LiBOB) or a combination thereof. The concentration of the lithium salt may be in the range of 0.1M to 2.0M. When the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion physical gel polymer battery, and a lithium ion chemical gel polymer battery according to the type of a separator and an electrolyte solution thereof. It may be classified into a cylindrical, prismatic, button-type or pouch-type according to shape, and a block-type and film-type according to size. The structure and methods of manufacture of such cells in connection with the present disclosure are well known in the art.

Fig. 3 is an exploded perspective view of a lithium secondary battery according to an embodiment. Referring to fig. 3, the lithium secondary battery 100 is a cylindrical battery including a negative electrode 112, a positive electrode 114, a separator 113 disposed between the negative electrode 112 and the positive electrode 114, an electrolyte (not shown) impregnating the negative electrode 112, the positive electrode 114, and the separator 113, a battery case 120, and a sealing member 140 sealing the battery case 120. The lithium secondary battery 100 is manufactured by: the negative electrode 112, the separator 113, and the positive electrode 114 are laminated in this order, spirally wound, and the spirally wound product is contained in the battery case 120.

Hereinafter, the preparation examples and examples are described in detail to describe the present invention in detail. However, the preparation examples and embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the preparation examples and embodiments described below. The preparation examples and examples of the present invention are provided to explain the present invention in detail to those skilled in the art.

Preparation example

Preparation example 1

Polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) (XPH-883, manufactured by Solvey, weight average molecular weight of 450,000g/mol) emulsion was mixed with distilled water to 25 wt%, and then, stirred at 25 ℃ for 30 minutes to prepare a solution including fluorine-based polymer fine particles having a particle diameter of 200 nm. The prepared solution was mixed with acrylic polymer fine particles having a particle diameter of 350nm (composition of the compound: a mixture of polystyrene, 2-ethylhexyl acrylate and butyl acrylate, BM900B, manufactured by ZEON) so that the weight ratio between the PVdF-HFP copolymer emulsion and the acrylic polymer fine particles was 90: 10. Distilled water was added thereto so that the solid content in the mixed solution was 5% by weight, and then, stirred at 25 ℃ for 30 minutes to prepare a coating composition. The coating composition has a viscosity (at 25 ℃) of 4 cps.

Preparation example 2

Polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) (weight average molecular weight: 450,000g/mol, XPH-883, manufactured by Solvey) emulsion was mixed with distilled water to 25 wt%, and then, stirred at 25 ℃ for 30 minutes to prepare a solution including fluorine-based polymer fine particles having a particle diameter of 200nm, and distilled water was added thereto to make a solid content to be 5 wt%, and then, stirred at 25 ℃ for 30 minutes to prepare a coating composition. The coating composition has a viscosity (at 25 ℃) of 2 cps.

Preparation example 3

Distilled water was added to acrylic polymer fine particles (compound: a mixture of polystyrene, 2-ethylhexyl acrylate and butyl acrylate, BM900B, manufactured by ZEON) having a particle diameter of 350nm so as to have a solid content of 5 wt%, and then, stirred at 25 ℃ for 30 minutes to prepare a coating composition. The coating composition has a viscosity (at 25 ℃) of 6 cps.

Comparative preparation example 1

An emulsion of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) (weight average molecular weight 450,000g/mol, XPH-883, manufactured by Solvey) was mixed with distilled water to 25 wt%, and then, stirred at 25 ℃ for 30 minutes to prepare a solution including fluorine-based polymer fine particles having a particle diameter of 200 nm. The prepared solution was mixed with acrylic polymer fine particles (compound: mixture of polystyrene, 2-ethylhexyl acrylate and butyl acrylate, BM900B, manufactured by ZEON) having a particle diameter of 350nm so that the weight ratio between the PVdF-HFP copolymer emulsion and the acrylic polymer fine particles was 90: 10. Distilled water was added to the mixed solution to make the solid content 20 wt%, and then, stirred at 25 ℃ for 30 minutes to prepare a coating composition. The coating composition has a viscosity (at 25 ℃) ranging from 50cps to 100 cps.

Examples

Example 1

(production of separator)

The coating composition prepared in preparation example 1 was coated on both surfaces of a porous substrate (SK 612HS, thickness: 12 μm, air permeability: 115 seconds/100 cc) to form a coating layer including a plurality of ring patterns spaced at regular intervals in an inkjet coating method. Inkjet coating was performed by using a digital coater (Techno Smart Corp.) at 25 deg.C, a frequency of 2.0KHz, and 83 mm/sec, with the number of nozzles of the inkjet head set to have a density of 360 (dpi). Subsequently, the coating layer was dried at a temperature of 80 ℃ and a wind speed of 15 m/sec for 3 minutes, to manufacture a separator having the coating layer.

(production of button cell)

A positive electrode active material, a carbon conductive agent (Denka Korea), and polyvinylidene fluoride (PVDF) were mixed at a weight ratio of 92:4:4, and then mixed with N-methylpyrrolidone (NMP) to prepare a slurry. The slurry bar was coated on a 15 μm thick aluminum current collector, dried at room temperature, dried again at 120 ℃ under vacuum, and compressed and punched to manufacture a 45 μm thick positive electrode plate.

Using the manufactured positive electrode plate, lithium metal counter electrode, separator and electrolyte prepared by the above process, a button cell was manufactured by a conventional method. By dissolving 1.5M LiPF in a mixed solvent of EC (ethylene carbonate), DEC (diethyl carbonate) and EMC (ethyl methyl carbonate) (volume ratio of 2:4:4)₆To prepare the electrolyte.

Example 2

A button cell was manufactured according to the same method as example 1, except that the coating composition of preparation example 1 was used, and the number of nozzles of the inkjet head was set to have a density of 120 dpi.

Example 3 and example 4

A separator and a button cell were respectively manufactured according to the same methods as examples 1 and 2, except that a 16 μm-thick separator (a separator formed by coating inorganic layers including inorganic particles having a total thickness of 4 μm on both surfaces of a 12 μm-thick polyethylene porous substrate) was used instead of the porous substrate.

Comparative example 1

The separator and the button cell were manufactured according to the same methods as in examples 1 and 2, respectively, except that the coating was performed in a dip coating method.

Comparative example 2

A separator and a button cell were produced according to the same method as in example 3, except that a dip coating method was used.

Comparative example 3

A separator and a button cell were manufactured according to the same method as in example 1, except that the coating composition of comparative preparation example 1 was used instead of the coating composition of preparation example 1.

Reference example 1

The coating composition of preparation example 1 was sprayed on both surfaces of a porous substrate at a liquid pressure of 0.2 bar and an air pressure of 0.5 bar in a 60% pulse to form a coating layer while the porous substrate (thickness: 12 μm, air permeability: 115 seconds/100 cc, 612HS manufactured by SK) was moved at a speed of 20 m/min. Subsequently, the coated porous substrate was dried at 80 ℃ for 0.03 hour at a wind speed of 15 m/sec to manufacture a separator having the coating layer, and a button cell was manufactured in the same manner as in example 1.

For the separators according to examples 1 to 4, comparative examples 1 to 3, and reference example 1, table 1 below shows particle diameters of the ring patterns, widths of the rings of the ring patterns (thicknesses of the rings), area ratios of the ring patterns based on the area of the porous substrate, and area ratios of the ring portions of the ring patterns based on the area of the porous substrate, loading amounts of the coating compositions, total thicknesses of the coatings, and coating methods.

(Table 1)

On the other hand, in comparative example 3, a separator including a coating layer including a ring pattern was not formed in the inkjet coating method due to the high viscosity of the coating composition.

Evaluation example 1: measuring air permeability of a separator

The separators according to examples 1 to 4, comparative examples 1 and 2, and reference example 1 were cut into sizes of 50mm × 50mm, respectively, to prepare each sample. The air permeability was obtained by measuring the time (seconds) taken for 100cc of air to completely pass through each sample, respectively, and the results are shown in table 2.

Evaluation example 2: evaluation of ion conductivity characteristics of separator

The ionic conductivity of the separators according to examples 1 to 4, comparative example 1, comparative example 2, and reference example 1 was measured by using an electrical impedance spectroscopy meter (VSP model manufactured by Bio-Logic SAS). Here, an amplitude of 1000mV was scanned at an open circuit potential and a frequency of 10000MHz to 1Hz, and the results are shown in table 2.

Evaluation example 3: evaluation of flexural Strength characteristics (adhesion) of separator

The electrode adhesion of the separators according to examples 1 to 4, comparative example 1, comparative example 2, and reference example 1 was measured. The electrode adhesion was evaluated by measuring the adhesion (bending strength) between the active materials of the substrates, and each separator was measured in a 3-point bending (Instron) method. The pouch-shaped single cells after forming were pressed at a rate of 5 mm/min by using a jig (charged state for sale (1C/36 min)) and MAX values (N, MPa) from zero point until 3mm of bending were measured, an average value of bending strength was obtained by measuring five samples and averaging three values except for the maximum value and the minimum value, the results are shown in table 2.

Evaluation example 4: measuring the film resistance of a button cell

The button cells according to examples 1 to 4, comparative example 1, comparative example 2, and reference example 1 were left at room temperature for one day, and the resistance of each separator was measured by using an impedance measurement method, respectively. The results are shown in table 2.

Evaluation example 5: evaluation of high temperature cycle life characteristics

The button cells according to examples 1 to 4, comparative example 1, comparative example 2 and reference example 1 were constant-current charged at a current rate of 0.1C up to a voltage (vs. li) of 4.3V at 45C and then cut off at a current rate of 0.05C while maintaining 4.3V in a constant voltage mode. Subsequently, the button cell was discharged to a voltage (vs. li) of 3.0V at a constant current of 0.1C rate (first period). Then, the button cell was constant-current charged at 45 ℃ to a voltage (vs. li) of 4.3V at a current rate of 1.0C, and was cut off at a current rate of 0.05C while maintaining 4.3V in a constant voltage mode. Next, the button cell was discharged at a constant current of 1.0C rate and to a voltage (vs. li) of 3.0V, which was repeated in cycles up to 500 cycles. A 10 minute pause was set for each charge/discharge cycle, of all charge and discharge cycles. Cycle life results reflecting the results of the charge and discharge experiments are shown in table 2.

(Table 2)

Referring to table 2, the separators according to examples 1 to 4 exhibited improved air permeability from 111 seconds/100 cc to 135 seconds/100 cc, compared to the comparative examples. In addition, the separators of examples 1 to 4 exhibited bending strengths in the range of 410N to 450N similar to those of comparative examples, and thus exhibited adhesion between the electrode and the separator similar to those of comparative examples, greatly improved ionic conductivity of 0.017S/mm to 0.022S/mm as compared to that of comparative examples and membrane resistance, and greatly improved membrane resistance. Therefore, the button cells according to examples 1 to 4 exhibited greatly improved high-temperature cycle life characteristics of 90% or more in 500 cycles, as compared to those of the comparative examples.

Evaluation example 6: optical microscope image measurement and Scanning Electron Microscope (SEM) image measurement of separator

SEM photographs taken of the separator of example 1 at different magnifications are shown in fig. 4 and 5.

In addition, SEM photographs showing the cross-sections of the separators according to examples 1 and 2 are provided in fig. 6 and 7.

Referring to fig. 4 and 5, the ring pattern according to the embodiment is spaced at regular intervals, and has a particle diameter of 10 to 200 μm and a width (thickness of the ring) of 0.2 to 1.5 μm, and most of the polymer microparticles are present in the ring portion of the ring pattern.

In addition, referring to fig. 6 and 7, in each of the separators of examples 1 and 2, very thin coatings each having a thickness of 1.06 μm and 661nm were formed.

Although preferred embodiments of the present invention have been described in detail hereinabove, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention as defined in the appended claims are also within the scope of the present invention.