KR102555253B1 - Composites separator for secondary battery and lithium secondary battery containing the same - Google Patents

Abstract

The present invention relates to a composite separator for a secondary battery including a porous substrate aramid porous resin layer and an inorganic particle layer and a lithium secondary battery including the same

Description

Composite separator for secondary battery and lithium secondary battery including the same

The present invention relates to a composite separator for a secondary battery and a lithium secondary battery including the same.

As the use of lithium secondary batteries expands, the demand for large-area and high-capacity tends to increase. As the capacity of secondary batteries increases, the area of electrode plates widens and many positive and negative active materials enter the same area, causing problems with battery safety.

In addition, when the battery is abnormally used, such as a charger failure or being left in a high-temperature environment, heat is generated inside the battery and the temperature rises. At this time, as the capacity of the battery increases, the amount of heat generated also increases rapidly. If a short circuit occurs between the positive electrode and the negative electrode due to contraction or melting of the separator, there is a risk of ignition or explosion due to thermal runaway. Therefore, as the capacity of a battery increases, a highly heat-resistant separator that does not shrink or melt even at a higher temperature is required.

Accordingly, various methods for imparting safety to polyolefin-based films, which are separators used in lithium secondary batteries, have been attempted.

In addition, in order to improve the battery safety of the most widely used polyolefin-based separator, a separator coated with inorganic particles on a polyolefin film is widely used. However, if a positive electrode active material with a high Ni ratio is used to increase the energy density of the battery, the energy density increases but the thermal stability of the battery becomes weak. is difficult to satisfy.

In order to solve this problem, conventionally, a coating layer made of an aramid resin is provided on a polyolefin-based film, but the technology reacts with an electrolyte solution to cause shrinkage and deformation, causing wrinkles on the surface of the battery to cause poor appearance. In addition, the aramid resin was made into a nano non-woven fabric and provided as a coating layer on a polyolefin-based film. However, in the above technology, a nonwoven fabric is electrospun on a polyolefin film, and at this time, separation between layers with the polyolefin film occurs, resulting in separation of the separator.

Various attempts have been made to solve this problem, but it still secures high heat resistance and does not cause poor penetration performance, poor appearance due to electrolyte reaction, and deterioration in life characteristics due to low electrolyte moisture when provided to secondary batteries. There is a need for a separator that does not

One aspect of the present invention is to provide a composite separator for a secondary battery having low thermal shrinkage and improved thermal stability.

In addition, one aspect of the present invention is to provide a composite separator for a secondary battery having excellent battery stability such as penetration performance.

In addition, one aspect of the present invention is to provide a composite separator for a secondary battery in which wrinkles do not occur due to reaction with an electrolyte solution, and thus, a secondary battery appearance defect does not occur.

In addition, one aspect of the present invention is to provide a lithium secondary battery including the composite separator for secondary batteries.

A composite separator for a secondary battery according to an aspect of the present invention includes a porous substrate; Aramid porous resin layer formed on one surface of the porous substrate; and an inorganic particle layer formed on the aramid porous resin layer.

A composite separator for a secondary battery according to another aspect of the present invention includes a porous substrate; Aramid porous resin layer formed on one surface of the porous substrate; and an inorganic particle layer formed on the other surface of the porous substrate.

The porosity of the aramid porous resin layer may be 10 to 60%.

The aramid porous resin layer may further include inorganic particles, and may include 10 to 30% by weight of inorganic particles and 70 to 90% by weight of aramid resin, based on the total weight.

The inorganic particle layer may include inorganic particles and a binder, and may include 70 to 99% by weight of inorganic particles and 1 to 30% by weight of a binder based on the total weight of the inorganic particle layer.

The inorganic particles of the aramid porous resin layer and the inorganic particle layer may each have an average particle diameter of 5 nm to 2 μm.

The average particle diameter of the inorganic particles of the aramid porous resin layer and the inorganic particle layer may satisfy Equation 1 below.

[Equation 1]

In Formula 1, D ₁ is the average particle diameter of the inorganic particles in the aramid porous resin layer, and D ₂ is the average particle diameter of the inorganic particles in the inorganic particle layer.

The composite separator for secondary batteries may have a gas permeability of 700 sec/100 ml or less measured according to the JIS P8117 measurement method.

The composite separator for a secondary battery may have a thermal contraction rate of 10% or less at 160°C.

A lithium secondary battery including the secondary battery composite separator according to an aspect of the present invention may be provided.

As the heat resistance of the composite separator for a secondary battery according to one aspect of the present invention is improved, ignition or rupture due to abnormal phenomena such as rapid temperature rise can be prevented.

In addition, the composite separator for secondary batteries according to one aspect of the present invention has excellent gas permeability, so that lithium ions move smoothly, and electrical characteristics such as capacity retention rate of the secondary battery can be remarkably improved.

In addition, the composite separator for secondary batteries according to one aspect of the present invention can improve battery stability such as excellent penetration performance.

In addition, the composite separator for secondary batteries according to one aspect of the present invention reacts with the electrolyte in the secondary battery and does not generate wrinkles, so the appearance of the secondary battery is excellent.

In addition, the composite separator for secondary batteries according to one aspect of the present invention may be introduced to improve performance such as thermal stability and electrical characteristics of large-sized lithium secondary batteries applied to electric vehicles.

1 is a scanning electron microscope image of the surface of an inorganic particle layer of a composite separator prepared in Example 1 of the present invention.
2 is a scanning electron microscope observation picture of the surface of the aramid porous resin layer of the composite separator prepared in Comparative Example 1 of the present invention.
3 is a photograph of the surface of a lithium-ion battery jelly roll (J/R) including a composite separator prepared in Example 1 of the present invention.
4 is a surface photograph of a lithium-ion battery jelly roll (J/R) including a composite separator prepared in Comparative Example 1 of the present invention.

Hereinafter, the present invention will be described in more detail. However, the following examples are only references for explaining the present invention in detail, but the present invention is not limited thereto, and may be implemented in various forms.

Also, unless defined otherwise, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description herein is merely to effectively describe specific embodiments and is not intended to limit the present invention.

The present invention relates to a composite separator for a secondary battery, which is excellent in heat resistance and appearance, and can improve battery stability and prevent a sharp decline in the lifespan of a secondary battery.

The present invention will be described in detail as follows.

A composite separator for a secondary battery according to an aspect of the present invention includes a porous substrate; Aramid porous resin layer formed on one surface of the porous substrate; and an inorganic particle layer formed on the aramid porous resin layer.

A composite separator for a secondary battery according to another aspect of the present invention includes a porous substrate; Aramid porous resin layer formed on one surface of the porous substrate; and an inorganic particle layer formed on the other surface of the porous substrate.

The composite separator for secondary batteries does not deform at high temperatures due to its excellent heat resistance such as low thermal contraction rate, and can prevent ignition, rupture, and reduction in life due to abnormal phenomena such as rapid temperature rise in the lithium secondary battery. In addition, it is included in the secondary battery and shrinkage due to the reaction with the electrolyte is suppressed, so that defects in appearance of wrinkles can be prevented.

In addition, penetration performance of the secondary battery is improved, and battery stability can be further improved by maintaining a short circuit between electrodes.

The aramid porous resin layer according to one aspect of the present invention may further include inorganic particles in addition to the aramid resin. At this time, the aramid resin may form a network to form pores in the aramid resin. The inorganic particles may be uniformly dispersed in the aramid resin network. Specifically, the aramid resin forms a continuous phase, and the inorganic particles are formed and distributed as a dispersed phase.

As described above, as the porous aramid resin layer in which inorganic particles are dispersed in the aramid resin is included in the composite separator, shrinkage due to reaction with the electrolyte is suppressed by being included in the secondary battery, so that the effect of preventing wrinkles from occurring on the exterior can be further enhanced. .

The aramid porous resin layer may have a porosity of 10 to 60%, preferably 30 to 60%, but is not limited thereto. When the porosity is formed as described above, the capacity retention rate of the lithium secondary battery can be further improved as lithium ions move smoothly.

The aramid resin may be any one or a mixture of two or more selected from meta-aramid resins and para-aramid resins. Preferably, it can have high heat resistance and mechanical strength, and it is more preferable to use meta-aramid to improve battery stability. The meta-aramid means an aromatic aramid in which a benzene ring is bonded to an amide group at a meta-position.

The aramid porous resin layer may include 10 to 40% by weight of inorganic particles and 60 to 90% by weight of an aramid resin based on the total weight. Preferably, 15 to 30% by weight of inorganic particles and 70 to 85% by weight of an aramid resin may be included. When included in the above range, it is possible to improve battery performance by preventing pore closure.

The inorganic particles include alumina, boehmite, aluminum hydroxide, titanium oxide, barium titanium oxide, magnesium oxide, and magnesium hydroxide. ), silica, clay, glass powder, and the like, but may be any one or two or more inorganic particles selected, but is not limited thereto. Preferably, aluminum-based oxide, which is any one or a mixture of two or more selected from high-purity alumina, boehmite, and aluminum hydroxide having a low impurity content, may be used.

The inorganic particle layer may further include a binder in addition to the inorganic particles, and may include 70 to 99% by weight of the inorganic particles and 1 to 30% by weight of the binder with respect to the total weight of the inorganic particle layer. Preferably, 80 to 99% by weight of inorganic particles and 1 to 20% by weight of a binder may be included. When included in the above range, it is possible to suppress shrinkage due to reaction with the electrolyte to prevent appearance defects such as wrinkles, and improve life capacity retention rate.

The inorganic particles included in the inorganic particle layer may be the same as or different from the inorganic particles included in the aramid porous resin layer described above.

In addition, the average particle diameter of the inorganic particles means D50, which is a particle diameter corresponding to 50% of the total volume when the particle diameters of the inorganic particles are measured and the volume is accumulated from the smallest particles.

The binder included in the inorganic particle layer is not particularly limited to increase the binding force between the inorganic particles, but is, for example, selected from acrylic polymers, styrenic polymers, vinyl alcohol polymers, vinylpyrrolidone polymers, and fluorine polymers. Any one or a mixture of two or more may be included. Specifically, the acrylic polymer may be selected from polyacrylamide, polymethacrylate, polyethylacrylate, polyacrylate, polybutylacrylate, sodium polyacrylate, acrylic acid-methacrylic acid copolymer, and the like. The styrenic polymer may be selected from polystyrene, polyalphamethylstyrene, and polybromostyrene. The vinyl alcohol-based polymer may be selected from polyvinyl alcohol, polyvinyl acetate, and polyvinyl acetate-polyvinyl alcohol copolymer. The vinylpyrrolidone polymer may be selected from polyvinylpyrrolidone and a copolymer containing vinylpyrrolidone. The fluorine-based polymer is any one or two or more selected from polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, hexafluoropropylene, polyfluoride-hexafluoropropylene, polychlorotrifluoroethylene, and the like. It may be a mixture, but is not limited thereto.

The average particle diameter of the inorganic particles of the aramid porous resin layer and the inorganic particle layer is not particularly limited, but may be 5 nm to 2 μm, preferably 10 nm to 1 μm, and more preferably 30 to 700 nm. . In the case of having the above average particle diameter, the composite separator has excellent heat resistance, and thus wrinkles caused by shrinkage can be prevented.

Preferably, the inorganic particle average particle diameter of the aramid porous resin layer and the inorganic particle layer may satisfy Equation 1 below in order to provide a secondary battery having better heat resistance and battery stability and not causing appearance defects.

[Equation 1]

In Formula 1, D ₁ is the average particle diameter of the inorganic particles in the aramid porous resin layer, and D ₂ is the average particle diameter of the inorganic particles in the inorganic particle layer. Preferably, the average particle diameter may satisfy 5 to 20.

The thickness of the aramid porous resin layer and the inorganic particle layer is not particularly limited, but may be 1 to 10 μm, respectively. In the case of having the above thickness, the ion conductivity of the separator is improved and the internal resistance of the battery is reduced during charging and discharging, thereby improving the lifespan of the secondary battery and securing battery stability.

The porous substrate can be used without limitation as long as it is a microporous film adopted in the art, and further has pores such as non-woven fabrics, paper and microporous films containing inorganic particles on the surface or internal pores of these microporous films and can be applied to batteries It is not particularly limited as long as it is a porous film.

The porous substrate may be made of any one or a mixture of two or more selected from homopolymers and copolymers derived from olefinic monomers. For specific example, it may be any one or a mixture of two or more selected from polyethylene, polypropylene, and copolymers thereof.

In addition, the porous substrate may be prepared by using the polyolefin resin alone or the polyolefin resin as a main component, and further including inorganic particles or organic particles. In addition, the porous substrate can be used in a laminated form, for example, polyolefin resin may be composed of multiple layers, and any one layer or all layers of the multilayer substrate layer may contain inorganic particles and organic particles in the polyolefin resin. Inclusion does not exclude.

The thickness of the porous substrate is not particularly limited, but may be 5 to 30 μm. As the porous substrate, a porous substrate made mainly through stretching may be employed, but is not limited thereto.

The porous substrate may have a tensile strength of 500 kgf/cm 2 or more, specifically, 500 to 1,000 kgf/cm 2 in the transverse direction (TD) and machine direction (MD, machine direction), preferably the width It can be manufactured through biaxial stretching in order to uniformly improve the strength in the TD (Transverse Direction) and MD (Machine Direction) directions. Porous substrates made through uniaxial stretching have the advantage of increasing tensile strength in the stretching direction, but shrinkage problems may occur when the temperature increases because stress to shrink in the stretching direction remains.

The composite separator for secondary batteries according to one aspect of the present invention may have a gas permeability of 700 sec/100 ml or less, preferably 650 sec/100 ml or less per unit thickness, measured according to the JIS P8117 measurement method. Specifically, it may be 10 to 700 sec/100ml, preferably 10 to 650 sec/100ml. In the case of having gas permeability as described above, since lithium ions move smoothly, electrical characteristics such as capacity retention rate of the secondary battery can be remarkably improved.

The composite separator for a secondary battery according to one aspect of the present invention may have a heat shrinkage rate of 10% or less at 160°C, preferably 5% or less at 160°C. Specifically, it may be 0.1 to 10%, preferably 0.1 to 5%. As described above, by having a low thermal contraction rate, it is possible to prevent ignition or rupture due to abnormal phenomena such as rapid temperature rise in the lithium secondary battery.

The composite separator for a secondary battery according to one aspect of the present invention may have a water content of 2,000 ppm or less. Preferably, the moisture content may be 1,200 ppm or less. Specifically, the water content may be 100 to 2,000 ppm. Preferably, the moisture content may be 100 to 1,200 ppm. As described above, the performance and lifespan of the battery can be improved by preventing decomposition of the electrolyte and generating less acid.

The above-described composite separator for a secondary battery according to the present invention may be manufactured by the following manufacturing method.

The composite separator for a secondary battery according to an aspect of the present invention includes a) applying a slurry containing an aramid resin alone or a slurry containing an aramid resin and inorganic particles on a porous substrate; and b) forming an aramid porous resin layer by drying after the applying step.

After the step b), in one aspect, c-1) forming an inorganic particle layer by applying a slurry containing inorganic particles and a binder on the aramid porous resin layer and then drying the slurry.

In another aspect, after step b), c-2) forming an inorganic particle layer by applying a slurry containing inorganic particles and a binder on the porous substrate and then drying the slurry. At this time, the porous substrate means the other surface on which the aramid porous resin layer is not formed.

The drying temperature is not particularly limited, but may be 60 to 100 °C. When the drying is performed, coating defects can be prevented by uniformly drying the coating layer without affecting the physical properties of the porous substrate.

The coating method according to one aspect of the present invention is not particularly limited to what can be manufactured by a conventional method adopted in this field, but specific examples include a bar coating method, a rod coating method, Die coating method, wire coating method, comma coating method, micro gravure/gravure method, dip coating method, spray method, ink-jet coating method, or these A mixed method and a modified method may be used.

In addition, a multi-layer coating method was used to form the aramid porous resin layer and the inorganic particle layer, and it is more preferable to increase the productivity of the process.

One aspect of the present invention provides a lithium secondary battery including the above-described composite separator for secondary batteries. The lithium secondary battery may be manufactured by including the secondary battery separator, a positive electrode, a negative electrode, and a non-aqueous electrolyte solution according to an aspect of the present invention.

As described above, the embodiments of the present invention have been described in detail, but those of ordinary skill in the art to which the present invention pertains, without departing from the spirit and scope of the present invention defined in the appended claims. It will be possible to implement the invention by modifying it in various ways. Therefore, changes in future embodiments of the present invention will not deviate from the technology of the present invention.

[Physical property measurement method]

1. Tensile strength measurement

The method for measuring the tensile strength of the porous substrate follows the ASTM D882 standard, and after measuring each in the width direction (TD, Transverse Direction) and the machine direction (MD, Machine Direction), the lower value was taken.

2. Measurement of heat shrinkage at 160 ° C

In the method for measuring the 160 ° C heat shrinkage rate of the composite separator prepared in Examples and Comparative Examples, the composite separator was cut into a square shape with a side of 10 cm to make a sample, and then the area of the sample was measured and recorded using a camera before the experiment. did Place 5 sheets of paper each above and below the sample so that the sample is located in the center, and fix the four sides of the paper with clips. The sample wrapped in paper was left in a hot air drying oven at 160 ° C. for 1 hour. After leaving the stand, the sample was taken out and the area of the separator was measured with a camera to calculate the shrinkage rate of Equation 1 below.

[Equation 1]

Shrinkage rate (%) = (Area before heating - Area after heating) × 100 / Area before heating

3. Measurement of gas permeability

The method for measuring the gas permeability of the composite membranes prepared in Examples and Comparative Examples was in accordance with the JIS P8117 standard, and the time required for 100 ml of air to pass through the area of 1 inch ² of the membrane was recorded in seconds and compared.

4. Moisture content measurement

In order to measure the water content contained in the membrane, the Karl Fischer water quantification method was used. Metrohm's 831 KFC Coulometer and 885 Compact Oven were used for measurement equipment, and the measurement conditions were a separator sample weight of 0.3 g, an oven temperature of 150 ° C, and a measurement time of 600 seconds.

5. Penetration evaluation

In order to measure the safety of the battery, each manufactured battery was fully charged to 100% SOC (charge rate), and then nail penetration was evaluated. At this time, the diameter of the nail was 3.0 mm, and the penetration speed of the nail was fixed at 80 mm/min. L1: No change, L2: Slight exotherm, L3: Leakage, L4: Smoke, L5: Ignition, L1 to L3 are judged OK, and L4 to L5 are determined as NG.

6. Life Assessment

The secondary battery manufactured with the separator of the present invention was repeatedly charged and discharged from 5% to 95% of the state of charge (SOC) using a charge/discharger. Charging was carried out under CC/CV conditions of 1C/4.14V, 2.58A cut-off, and discharging was carried out under CC conditions of 1C, 3.03V cut-off, and the capacity retention rate (%) at 2,000 cycles was measured and expressed.

7. Appearance evaluation

The secondary battery manufactured with the separator of the present invention was dismantled, and whether wrinkles were generated in the jelly roll state and whether wrinkles were generated on the exterior of the secondary battery were visually observed and confirmed, and then OK (Pass) / NG (Fail) were indicated.

8. Porosity measurement

The porosity was calculated by calculating the space within the separator. The sample was cut into a rectangle (thickness T ㎛) of A cm × B cm, the mass was measured, and the porosity was calculated through the ratio of the weight of the same volume of resin and the weight of the separator (M g). The formula is as follows.

[mathematical expression]

Porosity (%) = 100 × {1 - M × 10000 / (A × B × T × ρ)}

In the above equation, ρ (g/cm 3 ) is the density of the resin.

[Example 1]

(1) Manufacture of anode

94% by weight of LiCoO ₂ as a cathode active material, 2.5% by weight of Polyvinylidene fluoride as an adhesive, 3.5% by weight of Super-P (Imerys) as a conductive agent, and NMP (N-methyl-2 as an organic solvent) -pyrrolidone) and stirred to prepare a uniform cathode slurry. The slurry was coated on aluminum foil with a thickness of 30 μm, dried at a temperature of 120° C., and then compressed to prepare a positive electrode plate with a thickness of 150 μm.

(2) Manufacture of cathode

95% by weight of artificial graphite as an anode active material, 3% by weight of acrylic latex (BM900B, 20% by weight of solid content) having a T _g of -52 ° C as an adhesive, and 2% by weight of CMC (Carboxymethyl cellulose) as a thickener, It was added to water as a solvent and stirred to prepare a uniform negative electrode slurry. The slurry was coated on a copper foil having a thickness of 20 μm, dried at a temperature of 120° C., and then compressed to prepare a negative electrode plate having a thickness of 150 μm.

(3) Manufacture of Separation Membrane

50 parts by weight of a mixture of 20% by weight of α-alumina having an average particle diameter of 50 nm and 80% by weight of meta-aramid resin (weight average molecular weight of 50,000 g/mol) in 100 parts by weight of N-methylpyrrolidone solvent is mixed and stirred to obtain uniformity. An aramid porous resin layer slurry was prepared.

94% by weight of boehmite having an average particle diameter of 600 nm in 100 parts by weight of water, 2% by weight of polyvinyl alcohol having a melting temperature of 220 ° C and a degree of saponification of 99%, and acrylic latex having a T _g of -52 ° C (ZEON, BM900B, solid content 20% by weight) was mixed with 4% by weight of 50 parts by weight of the mixture and stirred to prepare a uniformly dispersed inorganic particle layer slurry.

As a porous substrate, a polyolefin microporous membrane product (SK Innovation, ENPASS) having a thickness of 9 μm was used, and an aramid porous resin layer slurry was coated on one side of the substrate at a speed of 10 m/min using a slot coating die, and then dried through a dryer. It was dried at 80 °C for 1 hour. An inorganic particle layer slurry was coated on the aramid porous resin layer. After evaporating water at 80 ° C. for 1 hour through a dryer, it was wound into a roll form. The thickness of the aramid porous resin layer was 7 μm, the porosity was 49%, and the thickness of the inorganic particle layer was 3 μm.

(4) Manufacture of batteries

A pouch-type battery was assembled in a stacking method using the positive electrode, the negative electrode, and the separator prepared in Example 1, and 1M of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in each assembled battery. Ethylene A lithium secondary battery was prepared by injecting an electrolyte having a carbonate (EC)/ethyl methyl carbonate (EMC)/dimethyl carbonate (DMC) = 3:5:2 (volume ratio).

[Example 2]

In Example 1, a polyolefin microporous film product (SK Innovation, ENPASS) having a thickness of 9 μm was used as the porous substrate, and an aramid porous resin layer slurry was applied to one side of the substrate at a speed of 10 m/min using a slot coating die. Coated and dried for 1 hour at 80 ℃ through a dryer. The inorganic particle layer slurry was coated on the other surface of the porous substrate on which the aramid porous resin layer was not formed. After evaporating water at 80 ° C. for 1 hour through a dryer, the same procedure was performed except that it was wound in a roll form. The thickness of the aramid porous resin layer was 7 μm, and the thickness of the inorganic particle layer was 3 μm.

[Example 3]

It was carried out in the same manner as in Example 1, except that 30% by weight of inorganic particles and 70% by weight of aramid resin were mixed in the aramid porous resin layer slurry. The porosity of the aramid porous resin layer was 51%.

[Example 4]

In the inorganic particle layer slurry, 75% by weight of inorganic particles, 21% by weight of polyvinyl alcohol, and 4% by weight of acrylic latex (ZEON, BM900B, solid content 20% by weight) having a T _g of -52 ° C. Example 1 and The same was carried out.

[Example 5]

The same procedure as in Example 1 was performed except that the thickness of the aramid porous resin layer was 5 μm and the thickness of the inorganic particle layer was 5 μm.

[Example 6]

It was carried out in the same manner as in Example 1, except that 40% by weight of inorganic particles and 60% by weight of aramid resin were mixed in the aramid porous resin layer slurry. The porosity of the aramid porous resin layer was 55%.

[Example 7]

It was carried out in the same manner as in Example 1, except that the average particle diameter of the inorganic particles of the aramid porous resin layer slurry was 5 nm.

[Example 8]

It was carried out in the same manner as in Example 1, except that the average particle diameter of the inorganic particles of the aramid porous resin layer slurry was 200 nm.

[Example 9]

It was carried out in the same manner as in Example 1, except that the inorganic particle layer slurry had an average particle diameter of 5 nm.

[Example 10]

It was carried out in the same manner as in Example 1, except that the inorganic particle layer slurry had an average particle diameter of 2 μm.

[Example 11]

The same procedure as in Example 1 was performed except that the average particle diameter of inorganic particles of the aramid porous resin layer slurry was 5 nm and the average particle diameter of inorganic particles of the inorganic particle layer slurry was 60 nm.

[Example 12]

The same procedure as in Example 1 was performed except that the average particle diameter of inorganic particles of the aramid porous resin layer slurry was 125 nm and the average particle diameter of inorganic particles of the inorganic particle layer slurry was 1.2 μm.

[Comparative Example 1]

It was carried out in the same manner as in Example 1 except that the inorganic particle layer was not formed.

[Comparative Example 2]

It was carried out in the same manner as in Example 1, except that the inorganic particle layer was not formed and the thickness of the aramid porous resin layer was 10 μm.

[Comparative Example 3]

It was carried out in the same manner as in Example 1 except that the aramid porous resin layer was not formed.

[Comparative Example 4]

It was carried out in the same manner as in Example 1 except that the aramid porous resin layer was not formed and the thickness of the inorganic particle layer was 10 μm.

[Comparative Example 5]

It was carried out in the same manner as in Example 1 except that the aramid resin was 100% by weight in the aramid porous resin layer slurry. The porosity of the aramid porous resin layer was 8%.

[Comparative Example 6]

In the inorganic particle layer slurry, 50% by weight of inorganic particles, 25% by weight of polyvinyl alcohol, and 25% by weight of acrylic latex (ZEON, BM900B, solid content 20% by weight) having a T _g of -52 ° C. Example 1 and The same was carried out.

sample name Aramid porous resin layer inorganic particle layer [Equation 1]
_D2 / _D1 Thickness (㎛) Inorganic particle weight (%) Inorganic particle diameter (nm) Thickness (㎛) Inorganic particle weight (%) inorganic particles
Diameter (nm) Example 1 7 20 50 3 94 600 12 Example 2 7 20 50 3 94 600 12 Example 3 7 30 50 3 75 600 12 Example 4 5 20 50 5 94 600 12 Example 5 3 20 50 7 94 600 12 Example 6 7 40 50 3 94 600 12 Example 7 7 20 5 3 94 600 120 Example 8 7 20 200 3 94 600 3 Example 9 7 20 50 3 94 5 0.1 Example 10 7 20 50 3 94 2000 40 Example 11 7 20 5 3 94 60 12 Example 12 7 20 125 3 94 1200 12 Comparative Example 1 7 20 50 - - - - Comparative Example 2 10 20 50 - - - - Comparative Example 3 - - - 3 94 600 - Comparative Example 4 - - - 10 94 600 - Comparative Example 5 7 0 - 3 94 600 - Comparative Example 6 7 20 50 3 50 600 12

sample name Separator properties Secondary battery evaluation Gas permeability (sec) 160°C
Heat shrinkage rate (%) Moisture content (ppm) life span
Capacity retention rate (%) Penetrate
evaluation Exterior Example 1 487 4.74 1090 88 OK OK Example 2 469 4.64 980 87 OK OK Example 3 621 4.45 1120 82 OK OK Example 4 420 4.74 920 88 OK OK Example 5 400 4.84 880 87 OK OK Example 6 693 4.45 1090 55 OK OK Example 7 452 4.77 1040 86 NG OK Example 8 660 4.75 1100 52 OK OK Example 9 690 4.72 950 62 NG OK Example 10 420 4.82 920 66 NG OK Example 11 566 4.88 1110 70 OK OK Example 12 332 4.91 980 72 OK OK Comparative Example 1 391 0.99 1080 76 OK NG Comparative Example 2 407 0.99 1100 75 OK NG Comparative Example 3 203 6.39 330 76 NG OK Comparative Example 4 212 5.42 420 77 NG OK Comparative Example 5 252 3.96 1200 73 NG OK Comparative Example 6 920 4.93 760 44 OK NG

In the case of the composite separator according to the present invention, it not only has excellent heat resistance and air permeability, but also has excellent life capacity retention rate and penetration performance as it is made of a lithium secondary battery, and it can be confirmed that there is no appearance defect such as wrinkles on its appearance.

In addition, it can be confirmed that the porous aramid resin layer of the composite separator further includes inorganic particles, thereby further improving heat resistance and life capacity retention rate and excellent battery stability.

In addition, when the inorganic particle content ratio of the aramid porous resin layer satisfies 10 to 30% by weight and the inorganic particle content ratio of the inorganic particle layer satisfies 70 to 99% by weight, not only better heat resistance and air permeability, but also life capacity retention rate and penetration It can be confirmed that the performance is excellent, and there is no appearance defect such as wrinkles on its appearance.

When the average particle diameter of the inorganic particles of the aramid porous resin layer and the inorganic particles of the inorganic particle layer satisfies the above-mentioned Equation 1, when provided as a lithium secondary battery, the life capacity retention rate and penetration performance are further improved, and wrinkles on the appearance of the secondary battery It can be confirmed that there is no appearance defect that occurs.

In the case of Comparative Examples 1 and 2, heat resistance and air permeability are excellent without including the inorganic particle layer, but when it is provided to a lithium secondary battery, it can be confirmed that wrinkles are generated in the separator by reacting with the electrolyte and contracting as shown in FIG. there was.

Therefore, the separator for a secondary battery of the present invention not only has excellent thermal stability and battery stability, but also has excellent electrical properties such as capacity retention rate, so when applied to a lithium secondary battery, it can exhibit remarkably excellent characteristics.

As described above, in the present invention, a composite separator for a secondary battery and a lithium secondary battery including the same have been described through specific details and limited examples, but this is only provided to help a more general understanding of the present invention, and the present invention It is not limited to the examples, and various modifications and variations can be made from these descriptions by those skilled in the art in the field to which the present invention belongs.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and it will be said that not only the claims to be described later, but also all modifications equivalent or equivalent to these claims belong to the scope of the present invention. .

Claims (9)

porous substrates;
Aramid porous resin layer formed on one surface of the porous substrate; and
an inorganic particle layer formed on the aramid porous resin layer or on the other surface of the porous substrate;
Including,
A composite separator for a secondary battery, wherein the average particle diameter of the inorganic particles of the aramid porous resin layer and the inorganic particle layer satisfies Equation 1 below.
[Equation 1]

In Equation 1,
D ₁ is the average particle diameter of the inorganic particles in the aramid porous resin layer, and D ₂ is the average particle diameter of the inorganic particles in the inorganic particle layer. According to claim 1,
A composite separator for a secondary battery in which the porosity of the aramid porous resin layer is 10 to 60%. According to claim 1,
The aramid porous resin layer is a composite separator for a secondary battery comprising 10 to 40% by weight of inorganic particles and 60 to 90% by weight of an aramid resin, based on the total weight. According to claim 1,
The inorganic particle layer includes inorganic particles and a binder,
A composite separator for a secondary battery comprising 70 to 99% by weight of inorganic particles and 1 to 30% by weight of a binder, based on the total weight of the inorganic particle layer. According to claim 1,
The inorganic particles of the aramid porous resin layer and the inorganic particle layer each have an average particle diameter of 5 nm to 2 μm. delete According to claim 1,
The composite separator for secondary batteries has a gas permeability of 700 sec / 100 ml or less measured according to the JIS P8117 measurement method. According to claim 1,
The composite separator for secondary batteries has a heat shrinkage rate of 10% or less at 160 ° C. A lithium secondary battery comprising the composite separator of any one of claims 1 to 5, 7 and 8.

Images