KR20200034249A - Composite separator for secondary battery and secondary battery containing the same - Google Patents

Abstract

The present invention relates to a composite separator for a secondary battery, which can suppress a change in volume of a secondary battery due to volume expansion of a negative electrode material during charge/discharge, and a secondary battery including the same. The composite separator for a secondary battery comprises: a porous substrate; and a shear thickening fluid layer formed on one surface or both sides of the porous substrate.

Description

Composite separator for secondary battery and secondary battery including the same {COMPOSITE SEPARATOR FOR SECONDARY BATTERY AND SECONDARY BATTERY CONTAINING THE SAME}

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

In recent years, as the use of secondary batteries has expanded, the demand for large area and high capacity has been increasing. Due to the high capacity of the secondary battery, the area of the electrode plate is enlarged, and a large amount of positive or negative active material enters the same area, resulting in a problem in battery safety.

In the trend of high capacity and high output of the secondary battery, there is an increasing demand for improving the characteristics of the separator for electrical safety of the secondary battery during charging and discharging.

In particular, a means for preventing physical deformation of the secondary battery due to external shock or physical deformation due to internal elasticity is particularly required.

For example, a swelling phenomenon in which a secondary battery expands and contracts due to a volume expansion of a negative electrode active material due to a reaction between a gas or a negative electrode active material and lithium ions generated during charging and discharging of the secondary battery may be repeatedly generated. You can.

Due to this, a twisting phenomenon occurs at the anode or the cathode. When the torsion occurs, a space may occur between the electrode and the separator, and the negative electrode active material may be detached from the current collector. For this reason, there is a problem that the internal resistance of the secondary battery increases and the capacity decreases. In addition, since the separator between the positive electrode and the negative electrode is melted, the positive electrode and the negative electrode are short-circuited and ignited, causing a problem that the safety of the battery cannot be guaranteed.

In order to fundamentally solve this problem, it is desirable to prevent the shrinkage and expansion of the electrode, but due to the characteristics of the secondary battery, the shrinkage and expansion of the electrode inevitably occurs, so it is difficult to implement such a solution realistically.

Therefore, there is a need for a separator capable of further improving the safety of the battery by preventing problems due to contraction and expansion of the electrode or preventing damage due to external impact.

One aspect of the present invention is to provide a composite separator for a secondary battery that can suppress the volume change of the secondary battery due to the volume expansion of the negative electrode material during charge and discharge.

In addition, an aspect of the present invention is to provide a composite separator for a secondary battery that can prevent damage due to external shock of the secondary battery.

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

The composite separator for a secondary battery according to the present invention includes a porous substrate and a shear thickening fluid layer formed on one or both surfaces of the porous substrate.

The shear thickening fluid (STF) layer according to an aspect of the present invention has non-Newtonian fluid characteristics including inorganic particles and polymers.

The shear thickening fluid layer according to an aspect of the present invention may include a shear thickening fluid comprising 5 to 50% by weight of the first inorganic particles and 50 to 95% by weight of the polymer.

The first inorganic particles according to an aspect of the present invention may be any one or two or more selected from silica, alumina, calcium carbonate and zirconia.

The first inorganic particles according to an aspect of the present invention may be porous inorganic particles.

The first inorganic particles according to an aspect of the present invention may have an average particle diameter of 1 to 100㎛.

The polymer according to an aspect of the present invention may be a polyalkylene glycol-based polymer.

The shear thickening fluid layer according to an aspect of the present invention may be formed on one surface of a porous substrate, and may form an inorganic particle layer including second inorganic particles on the other surface of the porous substrate.

The secondary battery according to the present invention includes the above-described composite separator.

When the secondary battery according to an aspect of the present invention is 100% of SOC (State of charge), the thickness change rate may satisfy Equation 1 below.

[Equation 1]

In the above formula 1,

The T ₁₀₀ is the thickness when the secondary battery is SOC 100%, and the T ₀ is the thickness when the secondary battery is SOC 0%.

The composite separator for a secondary battery according to an aspect of the present invention can further improve the battery safety by absorbing the volume expansion generated during charging and discharging of the secondary battery to suppress external expansion of the secondary battery.

In addition, the composite separator for a secondary battery according to an aspect of the present invention can reduce the internal resistance to improve the electron transfer speed between the anode and the cathode.

In addition, the secondary battery according to an aspect of the present invention, when an external shock is applied, absorbs the external shock to prevent damage due to the shock.

1 is a scanning electron microscope observation photograph of a composite separator for a secondary battery prepared in Example 1 of the present invention.
Figure 2 shows the thickness change of the secondary battery when charging and discharging the secondary battery including the composite separator for a secondary battery according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail. However, the following examples are only a reference for explaining the present invention in detail, and 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 for effectively describing a specific embodiment, and is not intended to limit the present invention.

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

The present invention will be described in detail as follows.

The composite separator for a secondary battery according to the present invention includes a porous substrate and a shear thickening fluid layer formed on one or both surfaces of the porous substrate.

The composite separator for a secondary battery absorbs shock applied from the outside of the secondary battery to prevent damage to the secondary battery and detachment between the composite separator and the electrode in the secondary battery, and further improve battery safety. In addition, the volume expansion of the secondary battery can be suppressed by absorbing the pressure generated according to the volume expansion generated during charging and discharging. In addition, it is possible to significantly improve the output of the secondary battery by reducing the internal resistance of the secondary battery to provide an excellent electron transfer speed between the positive electrode and the negative electrode.

For a specific example, according to an aspect of the present invention, the composite separator for a secondary battery may include a porous substrate and a shear thickening fluid layer formed on one surface of the porous substrate.

According to another aspect of the present invention, the composite separator for a secondary battery may include a porous substrate and a shear thickening fluid layer formed on both sides of the porous substrate.

According to an aspect of the present invention, the shear thickening fluid layer may be formed as a coating layer by coating the shear thickening fluid on a porous substrate.

According to another aspect, after the shear thickening fluid is coated on the substrate, the porous substrate may be laminated on one side or both sides.

According to another aspect of the present invention, the shear thickening fluid layer may be formed on one surface of the porous substrate, and may further form an inorganic particle layer including second inorganic particles on the other surface of the porous substrate.

The substrate for coating the shear thickening fluid for the lamination may be the same or different from the porous substrate. The substrate is not particularly limited as long as it does not affect the properties of the secondary battery by coating the shear thickening fluid, but for example, the substrate is polyolefin, polyimide, aramid, cellulose, polyacrylonitrile, polyester And it may be a non-woven fabric or a microporous membrane substrate comprising any one or two or more selected from polyamide and the like.

According to one aspect of the present invention, the shear thickening fluid layer includes first inorganic particles and a polymer, and may have non-Newtonian flow characteristics. The shear thickening fluid layer may include non-Newtonian flow characteristics in which the viscosity changes according to the shear rate by including the first inorganic particles and the polymer. Having such a flow characteristic, it is possible to protect the secondary battery against forces such as pressure applied to the secondary battery.

Specifically, when an instantaneous strong shock is applied from the outside, due to the non-Newtonian flow characteristics, excellent battery safety can be realized by absorbing an external shock and preventing ignition or rupture due to a decrease in fluidity against a shock.

In addition, as it has a non-Newtonian flow characteristic, it is possible to prevent a volume expansion and a decrease in the life of the secondary battery by absorbing the force exerted in the volume expansion generated inside the secondary battery due to charging and discharging inside the secondary battery.

Moreover, as shown in FIG. 2, as shown in Comparative Example 1, the anode 100 including the anode active material 200, the separator 300, and the cathode 500 including the anode active material 400, and an embodiment When the volume expansion of the composite membrane and the cathode 500 including the anode 100, the porous substrate 310, and the shear thickening fluid layer 320 as shown in 1 was compared.

Specifically, the composite separation membrane according to the present invention includes a shear thickening fluid layer, so that the size of the pores in the shear thickening fluid layer is reduced, so that rapid movement of lithium ions according to the close distance between the negative electrode and the positive electrode can be suppressed. In addition, the composite membrane may be penetrated by pressure, and an explosion caused by the active material of the positive electrode and the negative electrode may be prevented.

According to an aspect of the present invention, the shear thickening fluid layer is a layer having shear thickening fluid properties comprising 5 to 50% by weight of the first inorganic particles and 50 to 95% by weight of the polymer. Preferably, the shear thickening fluid may include 5 to 45% by weight of the first inorganic particles and 55 to 95% by weight of the polymer. When included in the above content, it may have a non-Newtonian flow characteristics, by absorbing the force applied from the inside or outside of the secondary battery, to prevent damage to the secondary battery, it can have more excellent battery safety. In addition, it is possible to prevent a short circuit inside the battery by implementing a low compressive strength, has excellent durability, and can smoothly move lithium ions of the prepared composite separator, thereby significantly improving electrical characteristics such as capacity retention of the secondary battery.

According to an aspect of the present invention, the first inorganic particles may include any one or two or more selected from silica, alumina, calcium carbonate and zirconia. In terms of having non-Newtonian flow characteristics and absorbing pressure, preferably, the inorganic particles may be silica.

More preferably, according to an aspect of the present invention, the first inorganic particles may be porous inorganic particles having pores. The porous inorganic particles have an active interfacial interaction at the surface, so that non-Newtonian flow characteristics are more clearly displayed, and battery safety can be further improved.

Particularly, preferably, a porous silaca can be used to better exhibit non-Newtonian flow characteristics.

According to an aspect of the present invention, the porous silica may have a specific surface area of 100 to 800 m 2 / g, preferably a specific surface area of 200 to 700 m 2 / g. When having the specific surface area as described above, the non-Newtonian flow property is strong to resist shock, and physical damage such as perforation or sinking can be prevented.

 According to one aspect of the invention, the first inorganic particles may have an average particle diameter of 1 to 100㎛. Preferably, the average particle diameter may be 6 to 50㎛. More preferably, the average particle diameter may be 6 to 30㎛. When the average particle diameter is as described above, the critical shearing speed may be improved, and the safety of the secondary battery may be secured by absorbing the force even if a strong force is applied instantaneously as well as a force applied slowly.

According to an aspect of the present invention, the polymer may be a polyalkylene glycol-based polymer. For a specific example, the polymer may include any one or two or more selected from polyethylene glycol, polypropylene glycol, polybutylene glycol, polytetramethylene glycol, and copolymers containing them as repeating units. In terms of having non-Newtonian flow characteristics and absorbing pressure, preferably, the polymer may be a polyethylene glycol-based polymer.

According to an aspect of the present invention, the polymer may have a weight average molecular weight of 100 to 100,000 g / mol. Preferably, the weight average molecular weight may be 100 to 50,000 g / mol. When the weight average molecular weight is as described above, the critical shear rate may be improved, damage to the secondary battery and detachment between the composite separator and the electrode in the secondary battery may be prevented, and battery safety may be further improved.

According to one aspect of the present invention, the porous substrate can be used without limitation as long as it is a microporous membrane adopted in the art, and further includes non-woven fabric, paper, and inorganic particles in the pores or surfaces of the microporous membrane. The porous membrane that has pores and can be applied to the battery is not particularly limited.

The porous substrate may be one or two or more mixtures selected from homopolymers and copolymers derived from olefinic monomers. Specific examples may include any one or 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 a polyolefin resin as a main component, and further comprising inorganic particles or organic particles.

In addition, the porous substrate may be used in a stacked form, for example, a polyolefin resin may be composed of multiple layers, and a substrate layer composed of multiple layers may also include inorganic particles and organic particles in polyolefin resin. Inclusion is not excluded. In addition, the porous substrate may have a form in which a particle layer containing inorganic particles or organic particles is laminated on one or both sides of a layer containing a polyolefin resin.

According to an aspect of the present invention, the thickness of the porous substrate is not particularly limited, but may be 5 to 100 μm. The porous substrate may be a porous substrate made mainly through stretching, but is not limited thereto.

According to an aspect of the present invention, the porous substrate has a tensile strength of 500 kgf / cm 2 or more, specifically 500 to 1,000 kgf / cm 2 in the transverse direction (TD) and the machine direction (MD). It may be, preferably, it can be manufactured through biaxial stretching to uniformly improve the strength of the width direction (TD, Transverse Direction) and the machine direction (MD, Machine Direction). The porous substrate made through uniaxial stretching has the advantage of increasing the tensile strength in the stretched direction, but the stress to shrink in the stretched direction remains, which may cause a problem of shrinking when the temperature increases.

According to an aspect of the present invention, the shear thickening fluid layer may be formed on one surface of the porous substrate, and may form an inorganic particle layer including second inorganic particles on the other surface of the porous substrate.

Specifically, according to an aspect of the present invention, a shear thickening fluid layer may be formed on one surface of the porous substrate, and an inorganic particle layer may be formed on the other surface of the porous substrate.

According to an aspect of the present invention, the inorganic particle layer may further include a binder in addition to the second inorganic particle, and based on the total weight of the inorganic particle layer, 70 to 99.9% by weight of the second inorganic particle and 0.1 to 30% by weight of the binder You can. Preferably, the second inorganic particles may contain 80 to 99% by weight and 1 to 20% by weight of the binder. When included in the above range, it is possible to prevent the appearance defects such as wrinkles by suppressing shrinkage due to reaction with the electrolyte, and improve the life capacity retention rate.

According to an aspect of the present invention, the second inorganic particles may be the same or different from the first inorganic particles described above. For a specific example, the second inorganic particles are alumina, boehmite, aluminum hydroxide, titanium oxide, barium titanate oxide, and magnesium oxide ), Magnesium hydroxide (Magnesium Hydroxide), silica (Silica), clay (Clay), and may include any one or more selected from glass powder (Glass powder), but is not limited thereto.

Preferably, a high-purity alumina, boehmite, and aluminum hydroxide (Aluminum Hydroxide) having a low impurity content may be included in any one or two or more mixtures of aluminum-based oxides.

In addition, the average particle diameter of the second inorganic particles means D50, which is a particle diameter corresponding to 50% of the total volume when measuring the particle diameter of each inorganic particle and accumulating the volume from small particles.

The binder contained in the inorganic particle layer is not particularly limited to increase the binding force between the second inorganic particles, for example, acrylic polymer, styrene polymer, vinyl alcohol polymer, vinyl pyrrolidone polymer and fluorine polymer, etc. It may include any one or two or more mixtures selected. Specifically, the acrylic polymer may be selected from polyacrylamide, polymethacrylate, polyethylacrylate, polyacrylate, polybutylacrylate, sodium polyacrylate, and acrylic acid-methacrylic acid copolymer. The styrene-based 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 copolymers containing vinylpyrrolidone. The fluorine-based polymer is any one or two or more selected from polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, hexafluoropropylene, polyfluoride-hexafluoro propylene, and polychlorotrifluoroethylene. It may be a mixture, but is not limited thereto.

The average particle diameter of the second inorganic particles in the inorganic particle layer is not particularly limited, but may be 5 nm to 10 μm, preferably 10 nm to 1 μm, and more preferably 30 to 700 nm. When having the average particle diameter, the composite membrane has excellent heat resistance, and thus wrinkles caused by shrinkage can be prevented.

According to an aspect of the present invention, the composite separator for a secondary battery may be manufactured by the following manufacturing method.

According to an aspect of the present invention, the composite separator for a secondary battery comprises: a) applying a slurry comprising a shear thickening fluid on one or both sides of a porous substrate; And b) drying after the applying step to form a shear thickening fluid layer.

According to another embodiment, in step a), the porous substrate may be formed by laminating a substrate on which a shear thickening fluid layer is formed on one or both surfaces. The substrate on which the shear thickening fluid layer is formed may be formed by applying a slurry containing a shear thickening fluid to one or both surfaces of the substrate and drying the substrate.

According to an aspect of the present invention, the slurry containing the shear thickening fluid may be provided as a slurry by mixing the first inorganic particles and the polymer and diluting it in a solvent. At this time, the mixing method is not particularly limited as long as it is a method that can be uniformly mixed, for example, it can be mixed using a method selected from a ball mill (Ball mill), a mixer, a jet mill or a homogenizer. have.

The slurry comprising the shear thickening fluid prepared as described above can be coated on a porous substrate or other substrate to provide a shear thickening fluid layer having excellent battery safety.

According to an aspect of the present invention, the coating method is not particularly limited to those that can be manufactured by a conventional method adopted in this field, but for example, a bar coating method, a rod coating method, etc. , Die coating method, wire coating method, comma coating method, micro gravure / gravure method, dip coating method, spray method, ink-jet coating method or A mixed method and a modified method may be used.

The secondary battery according to the present invention includes the above-described composite separator.

The composite separator for a secondary battery absorbs shock applied from the outside of the secondary battery to prevent damage to the secondary battery and detachment between the composite separator and the electrode in the secondary battery, and further improve battery safety. In addition, it is possible to suppress the volume expansion of the secondary battery by absorbing the pressure generated according to the volume expansion generated during charging and discharging of the secondary battery.

According to an aspect of the present invention, the secondary battery may be manufactured by including the composite separator for the secondary battery, the positive electrode, the negative electrode, and a non-aqueous electrolyte.

According to an aspect of the present invention, when the secondary battery is SOC 100%, the thickness change rate may satisfy Equation 1 below.

[Equation 1]

In the above formula 1,

The T ₁₀₀ is the thickness when the secondary battery is SOC 100%, and the T ₀ is the thickness when the secondary battery is SOC 0%. Preferably, Equation 1 may satisfy 0.03 or less.

In this case, the thickness refers to the total thickness of the secondary battery including the composite separator of the secondary battery, the positive electrode, the negative electrode, and the non-aqueous electrolyte.

Specifically, when the remaining capacity (State of charge, SOC) is 100% due to charging, the secondary battery combines lithium and a negative electrode active material, and at this time, the volume of the negative electrode expands to increase the thickness of the secondary battery. do. As such, as the volume expands, a twisting phenomenon may occur in the anode or the cathode. When the torsion phenomenon occurs, a space may occur between the electrode and the composite separator, and the active material may be detached from the current collector. Due to this, a problem may arise that the internal resistance of the secondary battery increases and the capacity decreases.

Accordingly, according to an aspect of the present invention, the secondary battery may have the small thickness change rate satisfying Equation 1, thereby preventing the above-described problem.

It is an effect that can be implemented by including the composite separator for a secondary battery according to the present invention can be prevented such a problem.

The description of the composite separator for a secondary battery is the same as described above, and thus is omitted.

In addition, the positive electrode, the negative electrode, the composite separator, and the non-aqueous electrolyte material of the secondary battery are not particularly limited in the present invention, and materials known in the art may be adopted according to the type of secondary battery to be employed. A specific example is as follows.

According to an aspect of the present invention, the positive electrode and the negative electrode are prepared by mixing and stirring a positive electrode active material and a negative electrode active material with a solvent, a binder, a conductive material, and a dispersing material, if necessary, and then applying the mixture to a current collector of a metal material and drying it. After that, it can be produced by pressing.

The positive electrode active material may be used as long as it is an active material commonly used for the positive electrode of a secondary battery. For example, Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and combinations thereof Lithium metal oxide particles including one or more metals selected from the group consisting of may be included.

The negative electrode active material may be used as long as it is an active material commonly used for the negative electrode of a secondary battery. The negative electrode active material of the lithium secondary battery is preferably a lithium intercalable material. In one non-limiting embodiment, the negative electrode active material is lithium (metallic lithium), bigraphitizable carbon, non-graphitizable carbon, graphite, silicon, Sn alloy, Si alloy, Sn oxide, Si oxide, Ti oxide, Ni oxide, Fe The oxide (FeO) and lithium-titanium oxide (LiTiO ₂ , Li ₄ Ti ₅ O ₁₂ ) It may be one or more materials selected from the negative electrode active material group.

As the conductive material, a conventional conductive carbon material can be used without particular limitation.

The current collector of the metal material has high conductivity and is a metal to which the mixture of the positive electrode or the negative electrode active material can be easily adhered, and any one that is not reactive in the voltage range of the battery can be used. Non-limiting examples of the positive electrode current collector include foil made of aluminum, nickel, or a combination thereof, and non-limiting examples of the negative electrode current collector are copper, gold, nickel or copper alloy, or combinations thereof. Foil or the like.

A composite separator is interposed between the positive electrode and the negative electrode. As a method of applying the composite separator to a battery, in addition to winding, which is a general method, lamination, stacking and folding of the composite separator and electrode are possible. .

The non-aqueous electrolyte solution includes an electrolyte, a lithium salt, and an organic solvent, and the lithium salt can be used without limitation, those commonly used in an electrolyte for a lithium secondary battery, and can be expressed as Li ⁺ X ⁻ .

With the lithium salt of the anion is not particularly ^{limited, F -, Cl -, Br} -, I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) _{^{2 PF 4 -, (CF 3}} ) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO _{^{3 -, (CF 3 SO 2}} ) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C - _{, (CF 3 SO 2) 3} C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N - selected from Any one or two or more can be used.

The organic solvent includes propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma- Any one or two or more mixtures selected from butyrolactone, tetrahydrofuran and the like can be used.

The non-aqueous electrolyte may be injected into an electrode structure made of a positive electrode, a negative electrode, and a composite separator interposed between the positive electrode and the negative electrode.

The external shape of the lithium secondary battery is not particularly limited, but may be selected from a cylindrical shape, a square shape, a pouch shape, or a coin shape using a can.

Since the secondary battery according to the present invention includes a composite separator for a secondary battery, it is possible to suppress the volume expansion of the secondary battery by absorbing the pressure generated according to the volume expansion generated during charging and discharging. In addition, it is possible to prevent damage to the secondary battery and detachment between the composite separator and the electrode in the secondary battery by absorbing an impact applied from the outside of the secondary battery.

Thus, by absorbing the force applied inside or outside the secondary battery, it is possible to provide a secondary battery having better battery safety.

As described above, although the embodiments of the present invention have been described in detail, a person having ordinary knowledge in the technical field to which the present invention pertains, the present invention without departing from the spirit and scope of the present invention as defined in the appended claims. The invention may be modified in various ways. Therefore, changes in the embodiments of the present invention will not be able to escape the technology of the present invention.

 [Method of measuring properties]

1. Direct current internal resistance (DC-IR)

With respect to the secondary battery, DC resistance (CD-IR) at room temperature (25 ° C) was measured by the following method.

Under a 25 ° C. environment, it was charged with a constant current of 80 A to achieve a 50% state of charge (SOC). Thereafter, pulse discharge and pulse charging were repeated for 10 seconds at 40A, 80A, 160A, and 320A, respectively, and the voltage at 10 seconds at each pulse discharge was measured, and a current-voltage characteristic plot was created. The least squares method was applied to the obtained plot, and the slope of the approximate line was set to DC resistance (DC-IR). Moreover, DC-IR was measured in the same manner even under an O ° C environment.

2. Battery safety

In order to measure the safety of the battery, each of the prepared batteries was completely charged to 100% SOC (charge rate), and then nail penetration or blunt rod penetration evaluation was performed. At this time, the diameter of the nail or blunt rod was fixed to 3.0 mm and the penetration speed to 80 mm / min. L1: No change, L2: Slight fever, L3: Leakage, L4: Smoke, L5: Ignition, L1 to L3 are OK, and L4 to L5 are judged as NG.

3. Battery thickness measurement

In order to check the excitation phenomenon between the electrode plate and the composite separator during battery charging and discharging and whether the battery is deformed, the thickness of the battery was measured using Mitsutoyo's Thickness Gauge after 500 charges and discharges, and then compared with the thickness before charging and discharging. , The increase rate of the battery thickness of the following equation 1 was measured.

[Equation 1]

In the above formula 1,

The T ₁₀₀ is the thickness when the secondary battery is SOC 100%, and the T ₀ is the thickness when the secondary battery is SOC 0%.

4.Compressive strength measurement

When both sides of the cell are fixed with a steel sheet and discharged after charging, the volume is expanded from SOC0 to SOC100. Force is generated as the physical volume expansion is suppressed by the steel sheet. At this time, the generated force was measured using a BONGSHIN load cell.

[Example 1]

(1) Preparation of a composite separation membrane

A suspension was prepared by mixing 40% by weight of porous silica (average particle diameter of 10 µm, specific surface area of 500 m 2 / g) and 60% by weight of polyethylene glycol (200 g / mol by weight average molecular weight) at 1,500 rpm with a ball mill. The suspension and methanol were mixed in a 1: 3 weight ratio to prepare a shear thickening fluid slurry. The shear thickening fluid slurry was coated to a thickness of 3 μm after drying at a rate of 10 m / min using a slot coating die on one surface of a porous substrate (ES innovation, ENPASS, thickness 9 μm). Thereafter, the composite separation membrane was prepared by drying at 60 ° C. for 25 minutes.

(2) Preparation of anode

LiCoMn111 is 94% by weight as a positive electrode 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-, an organic solvent) pyrrolidone) and stirred to prepare a uniform anode slurry. The slurry was coated on an aluminum foil having a thickness of 20 μm, dried at a temperature of 120 ° C., and pressed to prepare a positive electrode plate having a thickness of 100 μm.

(3) Preparation of cathode

95% by weight of artificial graphite as a negative electrode active material, 3% by weight of acrylic latex (ZEON, BM900B, 20% by weight of solid content) with a T _g of -52 ° C as an adhesive, and 2% by weight of CMC (Carboxymethyl cellulose) as a thickener Furnace, it was added to water as a solvent and stirred to prepare a uniform cathode slurry. The slurry was coated on a copper foil having a thickness of 15 μm, dried at a temperature of 120 ° C., and pressed to prepare a 100 μm thick negative electrode plate.

(4) Battery manufacturing

The prepared positive electrode, negative electrode, and composite separators were used to assemble a pouch-type battery in a stacking method, and ethylene carbonate (EC) / in which 1M of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in each assembled battery / A lithium secondary battery was prepared by injecting an electrolyte solution of ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) = 3: 5: 2 (volume ratio).

[Example 2]

In Example 1, the shear thickening fluid slurry was coated on both sides of the porous substrate to perform the same procedure, except that a shear thickening fluid layer was formed.

[Example 3]

A suspension was prepared by mixing 40% by weight of porous silica (average particle diameter of 10 µm, specific surface area of 500 m 2 / g) and 60% by weight of polyethylene glycol (200 g / mol by weight average molecular weight) at 1,500 rpm with a ball mill. The suspension and methanol were mixed in a 1: 3 weight ratio to prepare a shear thickening fluid slurry.

The shear thickening fluid slurry was coated on one side of a polyethylene nonwoven fabric at a rate of 10 m / min using a slot coating die. Then, drying was performed at 60 ° C. for 25 minutes to prepare a shear thickening fluid layer. The shear thickening fluid layer was laminated on one surface of a porous substrate (ES innovation, ENPASS, thickness 9 µm) to prepare a composite separator.

[Example 4]

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

In Example 1, the inorganic particle layer slurry was dried on the other surface of the porous substrate at a rate of 10 m / min using a slot coating die and then coated to a thickness of 3 μm. Subsequently, drying was performed at 60 ° C. for 25 minutes to perform the same procedure, except that an inorganic particle layer was further formed.

[Example 5]

In Example 1, except that the content of the shear thickening fluid slurry was 5% by weight of porous silica (average particle size: 10 µm, specific surface area: 500 m 2 / g) and 95% by weight of polyethylene glycol (weight average molecular weight: 200 g / mol). It carried out similarly.

[Example 6]

In Example 1, except that the content of the shear thickening fluid slurry was 60% by weight of porous silica (average particle size: 10 µm, specific surface area: 500 m 2 / g) and 40% by weight of polyethylene glycol (weight average molecular weight: 200 g / mol). It carried out similarly.

[Example 7]

In Example 1, the content of the shear thickening fluid slurry was 80% by weight of porous silica (average particle size 10 µm, specific surface area 500 m 2 / g) and 20% by weight of polyethylene glycol (weight average molecular weight 200 g / mol). It carried out similarly.

[Example 8]

In Example 1, except that the porous silica of the shear thickening fluid slurry had an average particle size of 5 μm, the same procedure was performed.

[Example 9]

It was carried out in the same manner as in Example 1, except that the porous silica of the shear thickening fluid slurry had an average particle diameter of 50 μm.

[Example 10]

In Example 1, except that the porous silica of the shear thickening fluid slurry had an average particle diameter of 10 µm and a specific surface area of 50 m 2 / g, the same procedure was performed.

[Comparative Example 1]

It was carried out in the same manner as in Example 1, except that the shear thickening fluid layer was not formed.

A secondary battery was prepared in the following manner, including the composite separators prepared in Examples 1 to 10 and Comparative Example 1, and physical properties were measured as shown in Table 1.

When the composite membrane of Example 1 was observed with a scanning electron microscope (HITACHI S-3700N) as shown in FIG. 1, it was confirmed that it had porosity.

Compressive strength
SOC0 → SOC100 DC resistance Thickness change rate
(Equation 1) Safety evaluation Nail penetration Blunt penetration Example 1 0 N → 5.0 kN 1.5mΩ 0.015 OK (L4) OK (L4) Example 2 0 N → 4.0 kN 1.3mΩ 0.013 OK (L4) OK (L4) Example 3 0 N → 5.0 kN 2.0mΩ 0.014 OK (L4) OK (L4) Example 4 0 N → 5.0 kN 1.6mΩ 0.014 OK (L4) OK (L4) Example 5 0 N → 7.0 kN 1.5mΩ 0.020 OK (L4) OK (L4) Example 6 0 N → 3.0 kN 2.2mΩ 0.028 NG (L5) NG (L5) Example 7 0 N → 3.0 kN 3.0mΩ 0.030 NG (L5) NG (L5) Example 8 0 N → 8.0 kN 1.5mΩ 0.021 OK (L4) OK (L4) Example 9 0 N → 9.0 kN 1.8 mΩ 0.033 NG (L5) NG (L5) Example 10 0 N → 8.5 kN 2.0mΩ 0.026 NG (L5) NG (L5) Comparative Example 1 0 N → 10.0 kN 1.5mΩ 0.050 NG (L5) NG (L5)

As shown in Table 1, the secondary battery including the composite separator for a secondary battery according to the present invention suppresses volume expansion during charging and discharging, so that the rate of change in thickness is remarkably low, and resistance to external shock is strong even through penetration with various nails. It could be confirmed that it has excellent battery safety. In addition, it was confirmed that by implementing a low compressive strength, excellent elasticity capable of absorbing the force generated from the outside or inside can be realized.

In addition, it was confirmed that the electron transfer speed between the positive electrode and the negative electrode can be significantly increased with a low direct current resistance compared to Comparative Example 1.

Moreover, even if a composite separation membrane is provided in various embodiments as in Examples 1 to 4, the composite separation membrane including the shear thickening fluid layer is included in the secondary battery, so that the rate of change of thickness is significantly low even for internal or external stimuli, and for penetration evaluation. , It was confirmed that it has excellent battery safety and durability.

In addition, when comparing Examples 5 to 7 and Example 1, when the first inorganic particles and the polymer content in the shear thickening fluid satisfy the first inorganic particles 5 to 45% by weight and the polymers 55 to 95% by weight, It was confirmed that the rate of change in thickness can be significantly reduced by absorbing more force.

In addition, when the Examples 8 and 9 and Example 1 were compared, when the average particle diameter of the first inorganic particles in the shear thickening fluid satisfies 6 to 30 μm, the force due to the volume expansion is absorbed more and the thickness change rate is significantly reduced. I could confirm that I could do it. In addition, it was confirmed that the battery safety is excellent by absorbing the shock even when the shock is applied from the outside.

In addition, when compared with Examples 10 and 1, when the first inorganic particles in the shear thickening fluid used porous silica having a specific surface of 100 to 800 m 2 / g, resistance to external shock was strong and physical It was confirmed that damage can be prevented. Moreover, when using porous silica that satisfies 200 to 700 m 2 / g, it was confirmed that the shock absorption effect is significantly improved, and thus the battery safety can be further improved.

In addition, as in Comparative Example 1, when the shear thickening fluid layer was not included, it was confirmed that the battery safety was remarkably deteriorated because it could not absorb not only the volume expansion occurring inside the secondary battery but also the impact applied from the outside.

As described above, in the present invention, a composite separator for a secondary battery and a secondary battery including the same have been described through specific matters and limited embodiments, but this is provided only to help a more comprehensive understanding of the present invention. It is not limited to the examples, and those skilled in the art to which the present invention pertains can make various modifications and variations from these descriptions.

Therefore, the spirit of the present invention is limited to the described embodiments, and should not be determined, and all claims that are equivalent to or equivalent to the claims, as well as the claims described below, will belong to the scope of the spirit of the present invention. .

100: positive electrode 200: positive electrode active material
300: separator 310: porous substrate 320: shear thickening fluid layer
400: negative electrode active material 500: negative electrode

Claims (10)

Porous substrate and
A composite separator for a secondary battery comprising a shear thickening fluid layer formed on one or both surfaces of the porous substrate. According to claim 1,
The shear thickening fluid layer is a composite separator for a secondary battery having non-Newtonian flow characteristics including first inorganic particles and a polymer. According to claim 2,
The shear thickening fluid layer is a composite separator for a secondary battery comprising a shear thickening fluid comprising 5 to 50% by weight of the first inorganic particles and 50 to 95% by weight of the polymer. According to claim 2,
The first inorganic particles are a composite separator for a secondary battery of any one or more selected from silica, alumina, calcium carbonate and zirconia. According to claim 2,
The first inorganic particles are composite separators for secondary batteries, which are porous inorganic particles. According to claim 2,
The first inorganic particles have a composite separator for a secondary battery having an average particle diameter of 1 to 100㎛. According to claim 2,
The polymer is a polyalkylene glycol-based polymer composite separator for secondary batteries. According to claim 1,
The shear thickening fluid layer is formed on one surface of the porous substrate,
A composite separator for a secondary battery to form an inorganic particle layer including second inorganic particles on the other surface of a porous substrate. A secondary battery comprising the composite separation membrane of any one of claims 1 to 8. The method of claim 9,
When the secondary battery is SOC 100%, the secondary battery having a thickness change rate of Equation 1 below.
[Equation 1]

In the above formula 1,
The T ₁₀₀ is the thickness when the secondary battery is SOC 100%, and the T ₀ is the thickness when the secondary battery is SOC 0%.

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