KR20100058228A - Separator for secondary cell and lithium secondary cell containing thereof - Google Patents

Abstract

PURPOSE: A separator for a secondary battery and the lithium secondary battery including thereof are provided to prevent the formation of macro pores, squeezing out of a melted polymer, generation of shorts, and induction of fire and explosions. CONSTITUTION: A separator for a secondary battery comprises the following: a bulk layer including pores, containing a thermosetting resin or a thermoplastic resin with a melting point of 170~250 deg C; and a skin layer laminated on both sides of the bulk layer while including the pores and containing the thermoplastic resin with a melting point of 80~150 deg C. Either the bulk layer or the skin layer includes ceramic powder with a diameter of 0.1~1 micron. The thermosetting resin contains one or two resins selected from the group consisting of a phenol resin, a urea resin, an epoxy resin, and a polyester resin.

Description

Separators for secondary batteries and lithium secondary batteries comprising the same {Separator for secondary cell and Lithium secondary cell containing according}

The present invention is characterized in that the secondary battery separator; and laminated on one or both sides of the thermosetting resin or the bulk layer containing a thermoplastic resin having a melting point of 170 ~ 250 ℃; the skin layer containing a thermoplastic resin having a melting point of 80 ~ 150 ℃; It relates to a lithium secondary battery containing.

The separator of the battery is placed between the positive electrode and the negative electrode inside the battery, thereby suppressing electrical insulation between the two electrodes, that is, shorting between the electrodes, and serves to provide a path of charge flow through the pores inherent. Ionic conductive electrolyte is impregnated inside the pores, so that charge (ion) flows through the liquid phase.

On the other hand, the use or neglect of the battery is in a variety of risks or abuse situations, in particular, when exposed to high temperatures, overcharge or internal short circuit occurs, the battery will cause an exothermic side reaction. In such high temperature situations, one of the ideal safety mechanisms is to shut off the charge flow by shutting down the pores of the separator to further suppress temperature rise, ie thermal runaway. In other words, the above mechanism is achieved by melting and flowing near the melting point of the polymer constituting the separator to close the pores. Therefore, it is very important to design a polymer material and manufacturing process such that the pore clogging at the appropriate temperature as well as the dimensional stability of the separator. However, there is a high probability that an abnormal situation in which the safety mechanism does not operate at the high temperature may occur. For example, the pore blocking mechanism may operate up to a certain temperature, but if the temperature rises abnormally further above the melting point (T _m ) or the membrane is squeezed by the battery internal pressure, the macro-pore The formed or molten polymer may squeeze out, resulting in short circuits between electrodes, high current flow, and thermal runaway. However, when the temperature outside the battery decreases, or when the temperature of the battery itself decreases due to a pore blocking due to a safety mechanism, only the pore blocking function of the prior art may be sufficient. However, unfortunately, if the outside temperature is further increased or the air gap is not enough to block the unsafe situation, the prior art alone may not be a complete solution.

In order to solve this problem, a heat resistant separator having a higher melting point is being developed, but only the difference between the melting point (T _m ) and the melt flow rate (MFR) is inevitably shown. In other words, the problem is not fundamentally solved in that it is safe in terms of dimensional stability to a little higher temperature than a general separator and does not realize an ideal safety mechanism. For example, a general separator uses a thermoplastic polyolefin polymer having a T _m of 100 to 150 ° C. such as polyethylene or polypropylene, and a high molecular weight or ultra high molecular weight thermoplastic polyolefin having a T _m of 150 to 200 ° C. in a heat resistant separator.

Therefore, there is a demand for improvement of an existing battery separator or development of a new battery separator for developing a high efficiency secondary battery.

Accordingly, the present inventors endless efforts and studies to solve the problem of the conventional secondary battery separator, the bulk and bulk layer containing a polymer resin that can ensure the dimensional stability by maintaining the basic thickness and pore structure even at high temperature The secondary battery separator has a lower melting point than the polymer resin contained therein, and a polymer resin capable of blocking pores at an appropriate temperature is introduced into the skin layer. That is, the present invention has an object to provide a secondary battery separator with improved safety.

The secondary battery separator of the present invention for solving the above problems

A bulk layer having a pore containing a thermosetting resin or a thermoplastic resin having a melting point of 170 to 250 ° C .; a cross section or both surfaces of the skin layer having a pore containing a thermoplastic resin having a melting point of 80 to 150 ° C .; It is characterized in that.

In addition, the present invention is to provide a lithium secondary battery comprising the secondary battery separator.

As described above, the separator for secondary batteries of the present invention can prevent thermal runaway due to formation of large voids, squeeze out of molten polymer, and short circuit between electrodes. Bar, by using the secondary battery separator of the present invention, it is possible to provide a lithium secondary battery with improved safety.

The present invention described above in more detail as follows.

The secondary battery separator of the present invention

A bulk layer having a pore containing a thermosetting resin or a thermoplastic resin having a melting point of 170 to 250 ° C .; a cross section or both surfaces of the skin layer having a pore containing a thermoplastic resin having a melting point of 80 to 150 ° C .; It is characterized in that.

In addition, the secondary battery separator of the present invention

The monolayer or two kinds of layers selected from the bulk layer and the skin layer are characterized by comprising ceramic powder having a diameter of 1 μm or less, preferably 0.1 to 1 μm.

And, the secondary battery separator of the present invention

The single or two kinds of layers selected from the bulk layer and the skin layer may further include the ceramic powder and a pore former.

The secondary battery separator of the present invention has a polymer layer, that is, a skin layer, containing a thermoplastic resin coated on the surface of the bulk layer. The bulk layer and skin layer have pores, through which the charge flows. There is also a polymer electrolyte capable of charge flow along the polymer chain (conducting only the ion conductive polymer without a pore in the separator), but the separator of the present invention is limited to a polymer separator having pores in the case of using an electrolyte solution.

The present invention is intended to suppress the formation of large voids or squeeze out of melted polymer even under abnormal circumstances, resulting in a short circuit between electrodes and a high current flow. This is to prevent the worst situation that leads to thermal runaway.

Therefore, in order to achieve this, the present invention has a bulk layer that can maintain dimensional stability at a much higher temperature than a polymer membrane of the prior art and a skin layer applied by adjusting a melting point to prevent voids at an appropriate temperature. The basic configuration is used. As the pores are blocked and the charge flow is blocked by melting and flowing the skin layer polymer above the melting point of the skin layer polymer, battery heat generation is suppressed and the battery temperature can be lowered. In addition, even if the temperature rises higher than the temperature, the bulk polymer maintains dimensional stability without causing deformation, thereby preventing a dangerous situation in which a large void is formed or extruded and short-circuit between electrodes occurs. Furthermore, even if the temperature is higher than the melting point of the skin layer, the skin layer polymer that has melted and has already flowed into the voids is inhibited from flowing in the narrow space, making it difficult to escape out of the voids, so that the voids in the bulk layer are continuously blocked and the charge flow is blocked. And the safety mechanism of temperature drop is activated. In addition, since the bulk layer does not cause deformation, dimensional stability is maintained, thereby preventing unstable mechanisms in which large voids occur or the overall thickness of the secondary battery separator is severely reduced.

This invention will be described in more detail according to the components.

Bulk layer

As described above, the bulk layer of the present invention is characterized by having a pore and containing a thermosetting resin or a thermoplastic resin having a melting point of 170 to 250 ° C. Here, the porosity of the bulk layer is preferably 30 to 70%, more preferably 40 to 60%. If the porosity is less than 30%, there may be a problem that the ion conductivity is lowered, the output characteristics are lowered. If the porosity is greater than 70%, the dimensional stability is lowered, and micro-short is easily generated, and thus safety may be lowered. When the melting point of the thermoplastic resin is less than 170 ° C., it is difficult to ensure the dimensional stability of the separator, and when the melting point is higher than 250 ° C., the manufacturing process is not easy. Therefore, it is preferable to use a thermoplastic resin having a melting point within the above range. In addition, the thermoplastic resin should use a higher melting point than the thermoplastic resin used in the skin layer, the thermoplastic resin used in the bulk layer is polyvinyl chloride (PVC), polystyrene (PS), It is preferable to use one or two or more selected from polyester, polycarbonate, polyamide, polyethylene, PE, and polypropylene (PP). , Polyethylene is more preferred, and ultra high molecular weight polyethylene (UHMW PE) is more preferable.

In addition, the thermosetting resin is preferably selected from the group consisting of phenol (urea) resin, urea (urea) resin, epoxy (epoxy) resin and polyester (polyester) or two or more kinds, polyester-based porous non-woven fabric, Felt, paper, etc. are more preferable.

The thickness of the bulk layer is preferably 5 to 50 μm, preferably 10 to 30 μm, more preferably 10 to 25 μm, where the problem that mechanical strength may deteriorate if the thickness of the bulk layer is less than 5 μm. In addition, when the thickness is greater than 50 μm, the ion conductivity of the separator and the energy density of the manufactured battery may decrease, so that the thickness is within the above range.

Skin layer

The skin layer of the present invention shuts down the pores of the separator at an appropriate temperature when the battery and / or the separator is subjected to misuse, thereby blocking the flow of charge and suppressing the operation of the incomplete mechanism to raise the temperature. And prevents thermal runaway. It is also characterized by having a pore and containing a thermoplastic resin having a melting point of 80 to 150 占 폚. Here, the porosity is preferably 30 to 70%, more preferably 40 to 60%. Here, if the porosity is less than 30%, there may be a problem that the output characteristics are lowered due to poor ion conductivity, and when the porosity is greater than 70%, the dimensional stability is lowered, and micro-short is easily generated, which may lower safety. have. In addition, when the melting point of the thermoplastic resin is less than 80 ° C., void clogging may occur even in an unwanted and unnecessary situation, and when the temperature exceeds 150 ° C., the pore blocking may occur too late, thereby minimizing the effect of suppressing thermal runaway. It is preferable to use a thermoplastic resin having a melting point.

And, the thermoplastic resin of the skin layer is a melt index (MI: Melt Index or MFR: Melt Flow Rate, measured under the conditions 190 ^° C / 2.16 kg disclosed in ASTM D1238) is 500 g / _{10 minutes} to 1,000 g / _{10 minutes} and Melt index ratio (MFRR, Melt Flow Rate Ratio, measured under the conditions disclosed in ASTM D1238, MFR (190 ^o C / 21.6 kg) / MFR (190 ^o C / 2.16 kg)) is preferably used that is 20 or less, where MFR is an index that is inversely proportional to the molecular weight of the polymer, and when it is used less than 500 g / _{10 minutes,} it may take longer to close the pores or it may be difficult to completely block the pores, and when the MFR exceeds 1,000 g / _{10 minutes} , This may cause pore blockages to occur too easily, or to run away again without being fixed in the enclosed voids. And MFRR is proportional to the molecular weight distribution and inversely proportional to the uniformity or uniformity of the properties (monodispersity), the thermoplastic resin is used when the MFRR is more than 20, the uniformity of the physical properties is reduced, the pore clogging at the desired temperature It is preferable to use thermoplastic resins having MFR and MFRR within these ranges because they can cause problems of improper operation and uneven pore clogging over a fairly wide temperature range.

The thermoplastic resin of the skin layer should be excellent in affinity (adhesiveness) with the polymer resin used in the bulk layer, a paraffin wax having excellent affinity, preferably fractionated paraffin wax, more It is preferable to use HDPE based fractionated paraffin wax having a density of 0.950 to 0.980 g / cm ³ (measured by the density gradient method disclosed in ASTM D1505). However, it is not limited to this.

Such skin layer preferably has a thickness of 1 to 10 μm, preferably 1 to 5 μm, more preferably 2 to 3 μm, where the thickness of the skin layer is less than 1 μm to sufficiently prevent voids. The problem may occur, and when the thickness exceeds 10 μm, problems may occur such that the ion conductivity of the separator and the energy density of the manufactured battery may decrease.

Ceramic powder

According to the present invention, the bulk layer and the skin layer may include ceramic powder having a diameter of 1 μm or less, preferably 0.1 to 1 μm. In the present invention, the ceramic powder may have mechanical strength and electrolyte solution of the skin layer and the bulk layer. It serves to improve hygroscopicity. If the mechanical strength of the skin layer is improved, it can be expected that not only the thermal safety of the separator but also the safety will be improved even in a mechanical and electrical misuse situation. Also, a polar solvent is used as a general electrolyte of a secondary battery, and thus the thermoplastic used in the skin layer can be expected. It can be expected that the electrolyte hygroscopicity is improved by overcoming the problem of affinity with the resin. In addition, by mixing the ceramic powder in the bulk layer, the mechanical strength of the bulk layer can also be improved, and thus the short circuit suppressing ability can be further enhanced.

Such ceramic powders should have chemical and electrochemical stability, be less or less reactive with organic solvents, salts, and the like used as electrolyte, and should be used with other environmental stability, especially those having high temperature stability. In addition, in order to show uniform physical properties in the long term, it is necessary to use affinity with the resins used in the skin layer and the bulk layer, that is, those in which a bonding force is maintained.

In the present invention, the ceramic powder is silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), zinc oxide (ZnO), iron oxide (Fe ₂ O ₃ ), zirconium oxide (ZrO ₂ ) single or two or more oxides selected from bismuth oxide (Bi ₂ O ₃ ), lead oxide (PbO), titanium barium oxide (BaTiO ₃ ), lead titanium oxide (PbTiO ₃ ) and silicon oxide (CaSiO ₃ ) Alternatively, other inorganic materials such as fluoride, nitride, sulfide, and phosphate of the metal element may be used, and in view of improving mechanical strength and hygroscopicity of the electrolyte, it is preferable to use them in combination.

In addition, the ceramic powder used in the bulk layer and the skin layer may be the same or different.

When using a ceramic powder in the skin layer,

The skin layer is preferably used to include 20 to 75% by weight, preferably 20 to 60% by weight, more preferably 20 to 55% by weight of the ceramic powder with respect to the total weight of the skin layer, wherein the ceramic powder is 20 When used in an amount less than%, the effect of increasing the electrolyte absorbency of the skin layer decreases, and when used in an amount greater than 75 wt%, a problem may occur that the binding force in the skin layer and the adhesion between the skin layer and the bulk layer may be weakened. It is good.

In addition, when using a ceramic powder for a bulk layer,

The bulk layer is preferably used to contain 5 to 20% by weight of the ceramic powder, more preferably 10 to 15% by weight based on the total weight of the bulk layer, in which case, when using less than 5% by weight of the ceramic powder, Since the effect of increasing the mechanical strength of the layer is inferior, and the mechanical strength may be lowered when using more than 20% by weight, it is preferable to use within the above range.

Pore former

The pore forming agent serves to make pores of the skin layer or bulk layer better. Such pore forming agents may use low molecular weight paraffin wax or oligomer, and the like. Oils used in film formation, plasticizers such as dibutyl phthalate (DBP, dibutylphthalate), dioctylphthalate (DOP, dioctylphthalate), dioctyl adipate (DOA, dioctyladipate) and tricresylphosphate (TCP, tricresylphosphate) ) May also be used. That is, if the material can be extracted separately from the bulk and skin, and does not affect the physical properties of the bulk and skin polymer can be used as a pore-forming agent.

Referring to the manufacturing method of the secondary battery separator of the present invention described above are as follows.

Manufacturing method

Melt extrusion casting the skin layer on one or both sides of the bulk layer, the extrusion process is the same as the general film manufacturing process of the thermoplastic resin. At this time, if the thermoplastic resin of the skin layer or the thermoplastic resin of the bulk layer can be dissolved in an organic solvent or the like, a method such as comma, die, spray, gravure coating may be applied.

In order to further enhance the adhesion between the skin layer and the bulk layer or to make the final thickness even, hot or cold pressing may be performed after casting or coating. In addition, annealing may be carried out at a high temperature for stabilization of the overall structure.

Care should be taken not to block the voids in the bulk layer during casting or coating of the skin layer, and the process must be carefully controlled so that voids connected to the bulk layer voids can also be formed in the skin layer. If the bulk layer pores are blocked or no pores connected to the bulk layer pores are formed in the skin layer, they cannot function as separators under normal circumstances. When the layer selected from the skin layer and the bulk layer includes ceramic powder, the skin layer may be mixed with the ceramic powder during melt extrusion, or the ceramic powder may be mixed in the melt of the thermoplastic resin of the skin layer. Powder spraying is also possible on the surface of the skin layer immediately after layer fusion extrusion casting. In addition, hot or cold pressing may be performed after casting or coating, and annealing may be performed. Depending on the plastic polymer, methods such as comma, die, spray, and gravure coating may be applied.

A pore former may be used to make the pores of the bulk layer and the skin layer better. In some cases, the pore former may be included in both layers or may be included in only one side. In the case of using the pore-forming agent, following the procedure of extracting the pore-former after preparing the bulk layer and preparing the skin layer on the bulk layer, or by simultaneously extruding the bulk and the skin, bonding and extracting the pore-forming agent at once. Can be followed. In addition, various modifications are possible.

Hereinafter, the present invention will be described in more detail based on examples. However, the scope of the present invention is not limited thereto.

Example 1

High-density polyethylene-class paraffin wax (Temperature melted at 100 ° C, MFR 700 g / _{10 min} , MFRR 11, density 0.960 g / cm ³ ) on both sides of a bulk layer with a thickness of 25 μm and a porosity of 55% consisting of a polyester nonwoven fabric, a thermosetting resin After extrusion-casting the skin layer consisting of, and pressurized at 60 ℃ hot and annealed (annealing) at the same temperature for 2 hours to prepare a separator for a secondary battery disclosed in the table, a scanning electron microscope of the prepared secondary battery separator (scanning electron microscope) , SEM) photo is shown in Figure 1 (a). The pores of the skin layer and the skin layer formed on the bulk layer can be seen from FIG.

Example 2

A separator was prepared in the same manner as in Example 1. However, the skin layer is 45% by weight of high density polyethylene classification paraffin wax (melting point 100 ℃, MFR 700 g / _{10 minutes} , MFRR 11, density 0.960 g / cm ³ ) and 55% by weight of aluminum oxide having a particle diameter of 0.8 ~ 1 ㎛ A secondary battery separator was prepared, and a SEM photograph of the prepared secondary battery separator is shown in FIG. 1 (b). The skin layer formed on the bulk layer, the ceramic powder constituting the skin layer, and the pores can be seen from FIG.

Example 3

In the same manner as in Example 1 to prepare a separator,

After preparing a bulk layer comprising a thermoplastic resin melting point 190 ℃ (ASTM D2117), 85% by weight ultra-high molecular weight polyethylene having a molecular weight of 200,000 g / mol (solution viscosity method) and 15% by weight of aluminum oxide having a particle diameter of 0.8 ~ 1 ㎛, Secondary with a skin layer comprising 45% by weight of high density polyethylene classified paraffin wax (melting point 100 ° C., MFR 700 g / _{10 min} , MFRR 11, density 0.960 g / cm ³ ) and 55% by weight of aluminum oxide with a particle diameter of 0.8-1 μm A battery separator was prepared.

Comparative Examples 1 and 2

In order to compare with the embodiment of the present invention, the existing commercial products were selected as follows. Comparative Example 1 is a secondary battery separator composed of a thermoplastic resin having a melting point of 140 ° C. (ASTM D2117), a polypropylene having a Gurley index of 21 seconds, and a thickness of 25 μm and a porosity of 45%.

Comparative Example 2 is a separator for secondary batteries composed of a single membrane having a thickness of 25 μm and a porosity of 50% composed of a polyester nonwoven fabric which is a thermosetting resin, and is a product used as the bulk layers of Examples 1 and 2.

In addition, SEM pictures of the prepared separators for Comparative Batteries of Comparative Examples 1 and 2 are the same as those of FIGS. 2 (a) and 2 (b). From FIG. 2, the shape, voids, and the like of the bulk layer polymer can be confirmed.

Experimental Example 1

The effects of the separators for secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were measured by the following methods, and the results are shown in Table 1 below.

(1) electrolyte solution

The separator cut to a predetermined dimension was impregnated in the electrolyte solution containing lithium salt and then taken out to measure the weight increase rate of the separator.

(2) ion conductivity

The separator cut to a predetermined size was impregnated into an electrolyte solution containing lithium salt, and then bonded between two stainless steel (SUS) electrodes, and then ion conductivity was measured.

(3) shut-down

After impregnating the separator cut into a predetermined dimension in the electrolyte containing lithium salt, the electrical resistance was measured according to the temperature (Hot ER test), and the temperature at which the resistance rapidly increased was defined as the pore blocking temperature.

(4) thickness reduction and shrinkage

After leaving the separator cut to a predetermined size in a 150 ℃ oven for 10 minutes, the shrinkage was calculated by measuring the thickness change and the area change of the separator, Figure 4 (a) is the surface of Example 2 and Comparative Example 1 before the high temperature standing It is a photograph and FIG.4 (b) is a photograph of the surface after high temperature standing.

division Electrolyte solution
(%) Ion conductivity
(mS / cm) Pore blockage
(℃) Thickness reduction
(Μm) Shrinkage
(%) Example 1 59 0.45 To 110 - 4 5 Example 2 65 0.54 To 110 - 2 3 Example 3 68 0.55 To 110 -6 8 Comparative Example 1 54 0.30 To 140 -15 25 Comparative Example 2 39 0.17 - - One 5

In the separator for secondary batteries of Comparative Example 1, pore blocking occurs around 140 ° C., in which case the pore blocking is too late, and thus, there is little effect of suppressing thermal runaway.

In the case of Comparative Example 1, it can be seen that the change in thickness and shrinkage rate is very large, which causes the battery short circuit due to heat shrinkage, causing thermal runaway. On the contrary, the separators for secondary batteries of Examples 1 to 3 manufactured in accordance with the present invention do not cause thermal short circuits at high temperatures since there is no heat shrinkage.

Experimental Example 2

Electric resistance characteristic test

After impregnating the separator for secondary batteries prepared in Example 2 and Comparative Example 1 in an electrolyte solution containing lithium salt, the electrical resistance of the separator according to temperature was measured (Hot ER test), and the results are shown in FIGS. It is shown in FIG.3 (b), respectively.

The temperature at which the resistance increases rapidly means the temperature at which the pore blocking occurs. Referring to FIG. 3 (a), it can be seen that the pore blocking occurs at a suitable temperature of about 110 ° C. in the separator for the secondary battery. 3 (b), the secondary battery separator of Comparative Example 1 has a pore blockage at about 140 ° C. In this case, the pore blockage is made too late, and thus, it is confirmed that there is little effect of suppressing thermal runaway.

Production Example

Manufacture of Secondary Battery

Lithium nickel cobalt manganese composite oxide (LiNi1 / 3Co1 / 3Mn1 / 3O2) as a cathode active material, 94% by weight, carbon black 3% by weight and 3% by weight polyvinylidene fluoride as a binder N-methylpyrrolidone, a solvent, was added to the mixture and kneaded in a planetary-disper mixer for 4 hours to prepare a cathode mixture slurry. The positive electrode slurry was applied to a 20 μm thick aluminum thin film, which is a positive electrode current collector, by reverse comma coating, dried, and rolled to prepare a positive electrode.

N-methylpyrrolidone as a solvent was added to a mixture composed of 95 wt% graphite powder as a negative electrode active material and 5 wt% polyvinylidene fluoride as a binder, and kneaded for 4 hours in the same manner as the positive electrode to prepare a negative electrode mixture slurry. . The negative electrode slurry was applied to a 10 μm-thick copper thin film, which is a negative electrode current collector, in the same manner as the positive electrode, dried, and subjected to roll press to prepare a negative electrode.

The prepared positive electrode and negative electrode were cut to a predetermined dimension, and assembled by stacking the secondary battery separators prepared in Example 2 and Comparative Example 1. The laminate is placed in an aluminum pouch, which is an exterior material, and a general electrolyte solution composed of an organic solution in which ethylene carbonate (EC) and DEC (diethyl carbonate) in which LiPF ₆ lithium salt is dissolved has a volume ratio of 3: 7 is injected. And the secondary battery was prepared by sealing to carry out Preparation Example 1 and Comparative Preparation Example 1.

Experimental Example 3

Capacity maintenance rate according to the number of charge and discharge of the secondary battery Life characteristic experiment

The life characteristics of the secondary batteries prepared in Preparation Example 1 and Comparative Preparation Example 1 were tested by the following conditions and methods, and the results are shown graphically in FIG. 5.

It can be seen from FIG. 5 that the secondary battery manufactured by using the commercial separator of Comparative Example 1 and the secondary battery prepared by using the secondary battery separator of Example 2 of the present invention exhibit similar performance.

Charging Condition: CC (1.0C) / CV (4.2 V to 0.1C)

Discharge Condition: CC (1.0C) to 3.0 V

* CC: constant current, CV: constant voltage

Experimental Example 4

Overcharge safety measurement experiment

An overcharge stability measurement experiment of the secondary batteries prepared in Preparation Example 1 and Comparative Preparation Example 1 was performed, and the results are shown graphically in FIGS. 6A and 6B.

The batteries prepared in Preparation Example 1 and Comparative Preparation Example 1 were overcharged to 12 V at a current value of 1 C rate for 150 minutes, and changes in battery voltage and battery surface temperature were observed.

In the case of Preparation Example 1, no internal short circuit occurred and the maximum surface temperature of the battery was also very safe at about 90 ° C., which can be seen from the graph of FIG. This is because the flow of charge is blocked by blocking the membrane pores at an appropriate temperature, and there is no internal short circuit due to the absence of membrane heat shrinkage. On the other hand, in the case of the secondary battery of Comparative Preparation Example 1, the membrane pore blocking was too late, so that the effect of suppressing thermal runaway was insignificant, and the battery ignited with thermal runaway due to the internal short circuit due to the membrane heat shrinkage.

Overcharge condition: CC (1.0C) / CV (12 V to 150min)

It can be confirmed through Experimental Examples 1 to 4 that the secondary battery separator of the present invention has an effect of greatly improving the safety of the secondary battery.

1 (a) is a SEM photograph of the secondary battery separator prepared in Example 1, (b) is a SEM photograph of the secondary battery separator prepared in Example 2.

2 (a) is a SEM photograph of the secondary battery separator prepared in Comparative Example 1, (b) is a SEM photograph of the secondary battery separator prepared in Comparative Example 2.

3 is a graph showing the electrical resistance characteristics test results of Experimental Example 2, (a) is the experimental results of the secondary battery separator of Example 2, (b) is the experimental results of the secondary battery separator of Comparative Example 1.

Figure 4 is a photograph before and after the shrinkage experiment of Experimental Example 1, (a) is before the experiment, (b) is a photograph after the experiment.

5 is a result of the capacity maintenance rate measurement experiment according to the number of charge and discharge of the secondary battery prepared in Preparation Example 1 and Comparative Preparation Example 1 performed in Experimental Example 3.

6 is a result of the overcharge safety test of the secondary battery performed in Experimental Example 4, (a) is a manufacturing example 1, (b) is a test result for Comparative Preparation Example 1.

Claims (10)

A bulk layer having pores containing a thermosetting resin or a thermoplastic resin having a melting point of 170 to 250 ° C .; a cross-section or both sides of a bulk layer having a pore containing a thermoplastic resin having a melting point of 80 to 150 ° C .; Separation membrane for secondary batteries. The method of claim 1, Separation type or two kinds of layers selected from the bulk layer and the skin layer comprises a ceramic powder having a diameter of 0.1 ~ 1 ㎛ secondary battery separator. The method of claim 2, Separation type or two kinds of layers selected from the bulk layer and the skin layer further comprises a pore former (pore former) separator for a secondary battery. The method of claim 1, wherein the thermosetting resin Separation membrane for secondary batteries, characterized in that it comprises one or two or more resins selected from phenol resins, urea resins, epoxy resins and polyester resins. The thermoplastic resin of claim 1, wherein the thermoplastic resin having a melting point of 170 to 250 ° C. Separation membrane for secondary batteries, characterized in that the polyvinyl chloride resin, polystyrene resin, polycarbonate resin, polyamide resin, polyethylene resin and polypropylene resin selected from single or two or more kinds of resins. The separator of claim 1, wherein the thermoplastic resin having a melting point of 80 ° C. to 150 ° C. is MFR 500 g / _{10 min,} and 1,000 g / _{10 min} . The separator of claim 6, wherein the thermoplastic resin having a melting point of 80 to 150 ° C. is a high density polyethylene classified paraffin wax having a density of 0.950 to 0.980 g / cm ³ . The method of claim 1, The thickness of the bulk layer is 5 ~ 50 ㎛, the thickness of the skin layer is a secondary battery separator, characterized in that 1 ~ 10 ㎛. The method of claim 1, wherein the ceramic powder It is 0.1-1 micrometer in diameter, and it is single or 2 or more types chosen from silicon oxide, aluminum oxide, titanium oxide, zinc oxide, iron oxide, zirconium oxide, bismuth oxide, lead oxide, a titanium barium oxide, lead titanium oxide, and a silicon calcium oxide. Separator for a secondary battery characterized in that. A lithium secondary battery comprising the separator of any one of claims 1 to 9.

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