KR102601936B1 - 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 including a porous substrate and a shear thickening fluid layer formed on one or both sides of the porous substrate, and to a secondary battery including the same.

Description

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

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

Recently, as the use of secondary batteries has expanded, the demand for larger areas and higher capacities has become stronger. As the capacity of secondary batteries increases, the area of the electrode plate increases and a large amount of positive or negative active materials are placed in the same area, causing problems with battery safety.

With the trend of high capacity and high output of secondary batteries, the demand for improving the characteristics of the separator for the electrical safety of secondary batteries during charging and discharging is growing.

In particular, there is a need for a means to prevent physical deformation of the secondary battery due to external shock or physical deformation due to internal elasticity.

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

This causes twisting in the anode or cathode. When the twisting phenomenon occurs, a space may be created between the electrode and the separator, and the negative electrode active material may be separated from the current collector. Because of this, there is a problem that the internal resistance of the secondary battery increases and the capacity decreases. In addition, the separator between the anode and the cathode melts, short-circuiting the anode and the cathode, and ignites, causing a problem in which the safety of the battery cannot be guaranteed.

In order to fundamentally solve this problem, it is desirable to prevent electrode contraction and expansion, but due to the characteristics of secondary batteries, electrode contraction and expansion inevitably occur, so this solution is difficult to implement in reality.

Therefore, there is a need for a separator that can further improve the safety of the battery by preventing problems caused by shrinkage and expansion of electrodes or damage by external shock.

One aspect of the present invention seeks to provide a composite separator for a secondary battery that can suppress the volume change of the secondary battery due to volume expansion of the anode material during charging and discharging.

In addition, one aspect of the present invention seeks to provide a composite separator for secondary batteries that can prevent damage to secondary batteries from external impacts.

Additionally, one aspect of the present invention seeks to provide a secondary battery including the composite separator for secondary batteries.

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

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

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

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

The first inorganic particle according to one aspect of the present invention may be a porous inorganic particle.

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

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

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

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

When the secondary battery according to one aspect of the present invention has a state of charge (SOC) of 100%, the thickness change rate may satisfy Equation 1 below.

[Equation 1]

In equation 1 above,

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

The composite separator for secondary batteries according to one aspect of the present invention can further improve battery safety by absorbing volume expansion that occurs during charging and discharging of secondary batteries and suppressing external expansion of secondary batteries.

Additionally, the composite separator for secondary batteries according to one aspect of the present invention can improve the electron transfer rate between the anode and the cathode by reducing internal resistance.

Additionally, the secondary battery according to one aspect of the present invention can prevent damage caused by the impact by absorbing the external impact when an external impact is applied.

Figure 1 is a scanning electron microscope observation photograph of a composite separator for a secondary battery manufactured in Example 1 of the present invention.
Figure 2 illustrates the change in thickness of the secondary battery including a composite separator for secondary batteries according to an embodiment of the present invention when the secondary battery is charged and discharged.

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

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

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

The present invention will be described in detail as follows.

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

The composite separator for secondary batteries can absorb shock applied from outside the secondary battery, preventing damage to the secondary battery and separation between the composite separator and electrodes within the secondary battery, and further improving battery safety. In addition, it is possible to suppress the volume expansion of the secondary battery by absorbing the pressure generated due to the volume expansion that occurs during charging and discharging. In addition, by reducing the resistance inside the secondary battery, excellent electron transfer speed between the anode and the cathode can be provided, thereby significantly improving the output of the secondary battery.

For a specific example, according to one 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 one 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, the shear thickening fluid may be coated on the substrate and then laminated on one or both sides of the porous substrate.

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

The substrate onto which the shear thickening fluid for lamination is coated may be the same or different from the porous substrate. The substrate is not particularly limited as long as it coats the shear thickening fluid and does not affect the physical properties of the secondary battery. Specific examples include polyolefin, polyimide, aramid, cellulose, polyacrylonitrile, and polyester. and polyamide.

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 includes first inorganic particles and a polymer, and thus may have non-Newtonian flow characteristics in which viscosity changes depending on the shear rate. By having such flow characteristics, the secondary battery can be protected against forces such as pressure applied to the secondary battery.

Specifically, when a strong impact is momentarily applied from the outside, the non-Newtonian flow characteristics reduce the fluidity of the shock (shear), absorbing the external shock and realizing excellent battery safety by preventing ignition or rupture.

In addition, as it has non-Newtonian flow characteristics, the force applied from the volume expansion generated inside the secondary battery due to charging and discharging can be absorbed inside the secondary battery, thereby preventing volume expansion and reduction of the lifespan of the secondary battery.

Moreover, as shown in FIG. 2, as in Comparative Example 1, it is composed of a positive electrode 100 containing the positive electrode active material 200, a separator 300, and a negative electrode 500 containing the negative electrode active material 400, and the Example As shown in 1, the volume expansion of the composite separator including the anode 100, the porous substrate 310, and the shear thickening fluid layer 320 and the cathode 500 was compared.

Specifically, the composite separator according to the present invention includes a shear-thickening fluid layer, thereby reducing the size of the pores in the shear-thickening fluid layer, thereby suppressing rapid movement of lithium ions due to the increased distance between the cathode and the anode. In addition, it is possible to prevent explosions that occur when the composite separator is pierced by pressure and the active materials of the positive and negative electrodes meet.

According to one aspect of the present invention, the shear thickening fluid layer is a layer having shear thickening fluid properties including 5 to 50% by weight of first inorganic particles and 50 to 95% by weight of polymer. Preferably, the shear thickening fluid may contain 5 to 45% by weight of the first inorganic particle and 55 to 95% by weight of the polymer. When included in the above amount, it can have non-Newtonian flow characteristics, absorb force applied from inside or outside the secondary battery, prevent damage to the secondary battery, and have better battery safety. In addition, by implementing low compressive strength, it is possible to prevent internal short circuit of the battery, it has excellent durability, and the movement of lithium ions in the manufactured composite separator is smooth, thereby significantly improving the electrical characteristics such as capacity retention rate of the secondary battery.

According to one 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, the inorganic particles may preferably be silica.

More preferably, according to one aspect of the present invention, the first inorganic particle may be a porous inorganic particle having pores. The porous inorganic particles have active interfacial interactions on the surface, so non-Newtonian flow characteristics appear more clearly and battery safety can be further improved.

In particular, it is preferable to use porous silica because it can better exhibit non-Newtonian flow characteristics.

According to one aspect of the present invention, the porous silica may have a specific surface area of 100 to 800 m2/g, preferably 200 to 700 m2/g. When it has the above specific surface area, it has strong resistance to impact due to non-Newtonian flow characteristics and can prevent physical damage such as perforation or sinking.

According to one aspect of the present 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 shear speed can be improved, and the safety of the secondary battery can be secured by absorbing not only a slowly applied force but also a strong force that is applied momentarily.

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

According to one 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 can be improved, damage to the secondary battery and separation between the composite separator and the electrode in the secondary battery can be prevented, and battery safety can 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 present technical field, and further includes non-woven fabric, paper, and their microporous membranes containing inorganic particles in pores or surfaces, etc. There is no particular limitation as long as it is a porous film that has pores and can be applied to a battery.

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

In addition, the porous substrate may be manufactured using the polyolefin resin alone or with polyolefin resin as a main ingredient and further containing inorganic particles or organic particles.

In addition, the porous substrate can be used in a laminated form. For example, the polyolefin resin may be composed of multiple layers, and the multilayered substrate layer also has one layer or all layers that contain inorganic particles and organic particles in the polyolefin resin. Inclusion is not excluded. Additionally, the porous substrate may be in the form of a particle layer containing inorganic particles or organic particles laminated on one or both sides of a layer containing polyolefin resin.

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

According to one aspect of the present invention, the porous substrate has a tensile strength of 500 kgf/cm2 or more, specifically 500 to 1,000 kgf/cm2 in the transverse direction (TD) and machine direction (MD). It may be manufactured through biaxial stretching to uniformly improve the strength in the transverse direction (TD) and machine direction (MD). A porous substrate made through uniaxial stretching has the advantage of increasing tensile strength in the stretched direction, but the stress remaining to shrink in the stretched direction may cause shrinkage when the temperature increases.

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

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

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

According to one aspect of the present invention, the second inorganic particles may be the same as or different from the above-described first inorganic particles. For specific examples, the second inorganic particles include Alumina, Boehmite, Aluminum Hydroxide, Titanium Oxide, Barium Titanium Oxide, and Magnesium Oxide. ), magnesium hydroxide, silica, clay, glass powder, etc., but is not limited thereto.

Preferably, it may include an aluminum-based oxide selected from high-purity alumina, Boehmite, and aluminum hydroxide with low impurity content, or a mixture of two or more.

In addition, the average particle diameter of the second inorganic particles means D50, which is the particle size corresponding to 50% of the total volume when the particle diameter of each inorganic particle is measured and the volume is accumulated starting from the smallest particle.

The binder included in the inorganic particle layer is not particularly limited to increase the binding force between the second inorganic particles, but includes, for example, acrylic polymers, styrene-based polymers, vinyl alcohol-based polymers, vinylpyrrolidone-based polymers, and fluorine-based polymers. It may include any one selected or a mixture of two or more. Specifically, the acrylic polymer may be selected from polyacrylamide, polymethacrylate, polyethyl acrylate, 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-hexafluoropropylene, and polychlorotrifluoroethylene. It may be a mixture, but is not limited thereto.

The average particle diameter of the second inorganic particles of 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 it has the above average particle size, the heat resistance of the composite separator is excellent and wrinkles caused by shrinkage can be prevented.

According to one aspect of the present invention, the composite separator for secondary batteries can be manufactured by the following manufacturing method.

According to one aspect of the present invention, the composite separator for a secondary battery includes the steps of a) applying a slurry containing a shear thickening fluid to 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 aspect, in step a), a substrate having a shear thickening fluid layer formed on one or both sides of the porous substrate may be laminated. The substrate on which the shear thickening fluid layer is formed may be formed by applying a slurry containing the shear thickening fluid to one or both sides of the substrate and drying it.

According to one 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 the mixture in a solvent. At this time, the mixing method is not particularly limited as long as it can be mixed uniformly, but for example, mixing can be performed using a method selected from a ball mill, mixer, jet mill, or homogenizer. there is.

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

According to one aspect of the present invention, the application method is not particularly limited to that it can be manufactured by a conventional method adopted in this field, but specific examples include a bar coating method and 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 A mixture of these methods, a modified method, etc. may be used.

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

The composite separator for secondary batteries can absorb shock applied from outside the secondary battery, preventing damage to the secondary battery and separation between the composite separator and electrodes within the secondary battery, and further improving battery safety. In addition, it is possible to suppress the volume expansion of the secondary battery by absorbing the pressure generated due to the volume expansion that occurs during charging and discharging of the secondary battery.

According to one aspect of the present invention, a secondary battery can be manufactured including the composite separator for a secondary battery, an anode, a cathode, and a non-aqueous electrolyte.

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

[Equation 1]

In equation 1 above,

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

At this time, the thickness refers to the total thickness of the secondary battery including the composite separator, anode, cathode, and non-aqueous electrolyte of the secondary battery.

Specifically, when the secondary battery has a remaining capacity (state of charge, SOC) of 100%, lithium and the negative electrode active material are combined, and at this time, the volume of the negative electrode expands and the thickness of the secondary battery increases. do. As the volume expands like this, twisting may occur in the anode or cathode. When the twisting phenomenon occurs, a space may be created between the electrode and the composite separator, and the active material may be separated from the current collector. As a result, the internal resistance of the secondary battery may increase and the capacity may decrease.

Accordingly, according to one aspect of the present invention, the secondary battery has a small thickness change rate that satisfies Equation 1, thereby preventing the above-mentioned problems.

Such problems can be prevented by the effect that can be realized by including the composite separator for secondary batteries according to the present invention.

The description of the composite separator for secondary batteries is the same as described above and is therefore omitted.

Additionally, the materials for the anode, cathode, composite separator, and non-aqueous electrolyte of the secondary battery are not particularly limited in the present invention, and materials known in the art can be adopted depending on the type of secondary battery being adopted. Specific examples include:

According to one aspect of the present invention, the positive electrode and negative electrode are prepared by mixing and stirring the positive electrode active material and the negative electrode active material with a solvent, a binder, a conductive material, a dispersant, etc. as necessary, and then applying the mixture to a current collector of a metal material and drying it. Then, it can be manufactured by pressing.

The positive electrode active material can be any active material commonly used in the positive electrode of secondary batteries. 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. It may contain lithium metal oxide particles containing one or two or more metals selected from the group consisting of.

The negative electrode active material can be any active material commonly used in the negative electrode of secondary batteries. The negative electrode active material of a lithium secondary battery is preferably a material capable of lithium intercalation. As a non-limiting example, the negative electrode active material is lithium (metallic lithium), easily graphitizable carbon, non-graphitizable carbon, graphite, silicon, Sn alloy, Si alloy, Sn oxide, Si oxide, Ti oxide, Ni oxide, Fe. It may be one or two or more materials selected from the group of negative electrode active materials such as oxide (FeO) and lithium-titanium oxide (LiTiO ₂ , Li ₄ Ti ₅ O ₁₂ ).

As the conductive material, a typical conductive carbon material can be used without particular restrictions.

The current collector of the metal material is a metal that has high conductivity and to which the mixture of the positive or negative active materials can easily adhere, and any material can be used as long as it is not reactive in the voltage range of the battery. Non-limiting examples of positive electrode current collectors include foils made of aluminum, nickel, or a combination thereof, and non-limiting examples of negative electrode current collectors include foils made of copper, gold, nickel, or copper alloys, or combinations thereof. It may be selected from foil, etc.

A composite separator is interposed between the anode and the cathode. Methods for applying the composite separator to a battery include lamination, stacking, and folding of the composite separator and the electrode, in addition to the general winding method. .

The non-aqueous electrolyte solution includes a lithium salt as an electrolyte and an organic solvent. The lithium salt may be any type commonly used in electrolyte solutions for lithium secondary batteries without limitation, and may be expressed ^as Li ⁺

The anion of the lithium salt is not particularly limited and includes 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 ^-, etc. Any one or more than two may be used.

The organic solvents include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfuroxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma- Any one or a mixture of two or more selected from butyrolactone, tetrahydrofuran, etc. may be used.

The non-aqueous electrolyte solution can be injected into an electrode structure consisting of an anode, a cathode, and a composite separator interposed between the anode and the cathode.

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

The secondary battery according to the present invention includes a composite separator for secondary batteries, thereby absorbing pressure generated due to volume expansion that occurs during charging and discharging, thereby suppressing volume expansion of the secondary battery. In addition, it can absorb shock applied from outside the secondary battery to prevent damage to the secondary battery and separation between the composite separator and electrodes within the secondary battery.

As a result, it is possible to provide a secondary battery with superior battery safety by absorbing force applied from inside or outside the secondary battery.

As discussed above, the embodiments of the present invention have been described in detail, but those skilled in the art will understand the present invention without departing from the spirit and scope of the present invention as defined in the appended claims. The invention may be implemented by modifying it in various ways. Therefore, changes in future embodiments of the present invention will not depart from the scope of the present invention.

[Physical property measurement method]

1. Direct current internal resistance (DC-IR)

For secondary batteries, direct current resistance (CD-IR) was measured at room temperature (25°C) using the following method.

In an environment of 25°C, it was charged at a constant current of 80A to reach a 50% state of charge (SOC). After that, pulse discharge and pulse charge were repeated for 10 seconds each at 40A, 80A, 160A, and 320A, the voltage at 10 seconds of 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 taken as direct current resistance (DC-IR). Additionally, DC-IR was measured in the same manner even in an 0°C environment.

2. Battery safety

To measure the safety of the battery, each manufactured battery was fully charged to 100% SOC (rate of charge), and then nail penetration or blunt rod penetration evaluation was performed. At this time, the diameter of the nail or blunt rod was fixed at 3.0 mm, and the penetration speed was fixed at 80 mm/min. L1: no change, L2: small explosion heat, L3: leakage, L4: smoke, L5: ignition, L1 to L3 are judged as OK, and L4 to L5 are judged as NG.

3. Cell thickness measurement

In order to check the phenomenon of lifting between the electrode plate and the composite separator and deformation of the battery when charging and discharging the battery, the thickness of the battery was measured using Mitsutoyo's Thickness Gauge after charging and discharging 500 times, and then compared with the thickness before charging and discharging. , the battery thickness increase rate according to the following equation 1 was measured.

[Equation 1]

In equation 1 above,

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

4. Compressive strength measurement

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

[Example 1]

(1) Manufacturing of composite membrane

A suspension was prepared by mixing 40% by weight of porous silica (average particle diameter 10㎛, specific surface area 500 m2/g) and 60% by weight polyethylene glycol (weight average molecular weight 200g/mol) at 1,500 rpm using a ball mill. A shear thickening fluid slurry was prepared by mixing the suspension and methanol at a weight ratio of 1:3. The shear-thickening fluid slurry was coated on one side of a porous substrate (SK Innovation, ENPASS, 9㎛ thick) to a thickness of 3㎛ after drying at a speed of 10m/min using a slot coating die. Afterwards, it was dried at 60°C for 25 minutes to prepare a composite separator.

(2) Manufacturing of anode

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

(3) Manufacturing of cathode

The anode active material is 95% by weight of artificial graphite, the adhesive is 3% by weight of acrylic latex (ZEON, BM900B, solid content 20% by weight) with a T _g of -52°C, and the thickener is 2% by weight of CMC (Carboxymethyl cellulose). A uniform cathode slurry was prepared by adding water as a solvent and stirring. The slurry was coated on 15 ㎛ thick copper foil, dried at a temperature of 120°C, and then compressed to prepare a 100 ㎛ thick negative electrode plate.

(4) Manufacturing of batteries

A pouch-type battery was assembled using the above-manufactured positive electrode, negative electrode, and composite separator using a stacking method, and each assembled battery was filled with ethylene carbonate (EC)/ethylene carbonate (EC) in which 1M lithium hexafluorophosphate (LiPF ₆ ) was dissolved. A lithium secondary battery was manufactured by injecting an electrolyte solution with ethylmethyl carbonate (EMC)/dimethyl carbonate (DMC) = 3:5:2 (volume ratio).

[Example 2]

The same procedure as in Example 1 was carried out, except that a shear-thickening fluid layer was formed by coating the shear-thickening fluid slurry on both sides of the porous substrate.

[Example 3]

A suspension was prepared by mixing 40% by weight of porous silica (average particle diameter 10㎛, specific surface area 500 m2/g) and 60% by weight polyethylene glycol (weight average molecular weight 200g/mol) at 1,500 rpm using a ball mill. A shear thickening fluid slurry was prepared by mixing the suspension and methanol at a weight ratio of 1:3.

The shear thickening fluid slurry was coated on one side of the polyethylene nonwoven fabric using a slot coating die at a speed of 10 m/min. Afterwards, the shear thickening fluid layer was prepared by drying at 60°C for 25 minutes. A composite separator was manufactured by laminating the shear thickening fluid layer on one side of a porous substrate (SK Innovation, ENPASS, thickness 9㎛).

[Example 4]

In 100 parts by weight of water, 94% by weight of boehmite with an average particle diameter of 600nm, 2% by weight of polyvinyl alcohol with a melting temperature of 220℃ and a degree of saponification of 99%, and acrylic latex with a T _g of -52℃ (ZEON, BM900B, solid content) A uniformly dispersed inorganic particle layer slurry was prepared by mixing and stirring 50 parts by weight of a mixture of 4 wt% (content 20 wt%).

In Example 1, the inorganic particle layer slurry was coated on the other side of the porous substrate to a thickness of 3 μm after drying at a speed of 10 m/min using a slot coating die. Thereafter, the same procedure was performed except that drying was performed at 60° C. for 25 minutes to further form an inorganic particle layer.

[Example 5]

Except that in Example 1, the content of the shear thickening fluid slurry was 5% by weight of porous silica (average particle diameter 10㎛, specific surface area 500 m2/g) and 95% by weight of polyethylene glycol (weight average molecular weight 200g/mol). The same procedure was performed.

[Example 6]

Except that in Example 1, the content of the shear thickening fluid slurry was 60% by weight of porous silica (average particle diameter 10㎛, specific surface area 500 m2/g) and 40% by weight of polyethylene glycol (weight average molecular weight 200g/mol). The same procedure was performed.

[Example 7]

Except that in Example 1, the content of the shear thickening fluid slurry was 80% by weight of porous silica (average particle diameter 10㎛, specific surface area 500 m2/g) and 20% by weight of polyethylene glycol (weight average molecular weight 200g/mol). The same procedure was performed.

[Example 8]

In Example 1, the shear thickening fluid slurry was carried out in the same manner, except that porous silica with an average particle diameter of 5㎛ was used.

[Example 9]

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

[Example 10]

In Example 1, the shear thickening fluid slurry was carried out in the same manner, except that porous silica with an average particle diameter of 10 ㎛ and a specific surface area of 50 m2/g was used.

[Comparative Example 1]

The same procedure as in Example 1 was performed except that the shear thickening fluid layer was not formed.

Secondary batteries were manufactured in the following manner, including the composite separators prepared in Examples 1 to 10 and Comparative Example 1, and the 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 to have porosity.

compressive strength
SOC0 → SOC100 direct current resistance Thickness change rate
(Equation 1) Safety assessment nail piercing 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 1.8mΩ 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 containing the composite separator for secondary batteries according to the present invention suppresses volume expansion during charging and discharging, has a significantly low thickness change rate, and has strong resistance to external impact even when penetrated by various nails, preventing physical damage. It was confirmed that it has excellent battery safety by being able to prevent. In addition, it was confirmed that by implementing low compressive strength, excellent elasticity capable of absorbing forces generated externally or internally could be achieved.

In addition, compared to Comparative Example 1, it was confirmed that the electron transfer speed between the anode and the cathode could be significantly increased with low direct current resistance.

Moreover, even if the composite separator is provided in various forms as in Examples 1 to 4, the composite separator including the shear thickening fluid layer is included in the secondary battery, so the thickness change rate is significantly low even in response to internal or external stimulation, and it is difficult to conduct penetration evaluation. , it was confirmed that the battery had excellent safety and durability.

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

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

In addition, when comparing Example 10 and Example 1, when the first inorganic particle in the shear thickening fluid used porous silica with a specific surface of 100 to 800 m2/g, the resistance to external shock was strong and physical It was confirmed that damage could be prevented. Furthermore, it was confirmed that when porous silica satisfying 200 to 700 m2/g was used, the shock absorption effect was significantly improved, thereby further improving battery safety.

In addition, when the shear thickening fluid layer was not included as in Comparative Example 1, it was confirmed that not only the volume expansion generated inside the secondary battery but also the impact applied from the outside could not be absorbed, resulting in a significant decrease in battery safety.

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 details and limited examples. However, this is only provided to facilitate a more general understanding of the present invention, and the present invention is not intended for the implementation of the above. It is not limited to examples, and various modifications and variations can be made from these descriptions by those skilled in the art.

Accordingly, the spirit of the present invention should not be limited to the described embodiments, and the scope of the patent claims described below as well as all modifications that are equivalent or equivalent to the scope of this patent claim shall fall within 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
It includes a shear thickening fluid layer formed on one or both sides of the porous substrate,
The shear thickening fluid layer is a composite separator for a secondary battery containing 5 to 50% by weight of first inorganic particles and 50 to 95% by weight of polymer. According to clause 1,
The shear thickening fluid layer is a composite separator for a secondary battery having non-Newtonian flow characteristics. delete According to paragraph 2,
The first inorganic particle is a composite separator for a secondary battery, wherein the first inorganic particle is one or more selected from silica, alumina, calcium carbonate, and zirconia. According to clause 2,
The first inorganic particle is a composite separator for a secondary battery wherein the first inorganic particle is a porous inorganic particle. According to clause 2,
The first inorganic particle is a composite separator for a secondary battery having an average particle diameter of 1 to 100㎛. According to clause 2,
The polymer is a composite separator for secondary batteries, which is a polyalkylene glycol-based polymer. According to clause 1,
The shear thickening fluid layer is formed on one side of the porous substrate,
A composite separator for secondary batteries that forms an inorganic particle layer containing second inorganic particles on the other side of a porous substrate. A secondary battery comprising any one of the composite separators selected from claims 1, 2, and 4 to 8. According to clause 9,
The secondary battery is a secondary battery whose thickness change rate satisfies Equation 1 below when SOC is 100%.
[Equation 1]

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