Title of Invention: Separator and Electrochemical Device Containing Same
technical field
[One]
The present invention relates to a separator that can be used in an electrochemical device such as a lithium secondary battery and an electrochemical device including the same.
[2]
This application is an application claiming priority to Korean Patent Application No. 10-2019-0070943 filed on June 14, 2019, and all contents disclosed in the specification and drawings of the application are incorporated herein by reference.
background
[3]
Recently, interest in energy storage technology is increasing. Efforts for research and development of electrochemical devices are becoming more concrete as the fields of application are expanding to cell phones, camcorders, notebook PCs, and even the energy of electric vehicles. Electrochemical devices are receiving the most attention in this aspect, and among them, the development of rechargeable batteries that can be charged and discharged is the focus of interest. and research and development of battery design.
[4]
Among the currently applied secondary batteries, lithium secondary batteries developed in the early 1990s have a higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and lead sulfate batteries that use aqueous electrolyte solutions. is in the spotlight as
[5]
Electrochemical devices such as lithium secondary batteries are produced by many companies, but their safety characteristics show different aspects. It is very important to evaluate the safety and secure the safety of these electrochemical devices. The most important consideration is that the electrochemical device must not cause injury to the user when malfunctioning, and for this purpose, the safety standards strictly regulate ignition and fuming within the electrochemical device. In terms of safety characteristics of the electrochemical device, if the electrochemical device is overheated and thermal runaway occurs or the separator penetrates, there is a high risk of causing an explosion. In particular, polyolefin-based porous polymer substrates commonly used as separators for electrochemical devices exhibit extreme heat shrinkage behavior at a temperature of 100° C. or higher due to material properties and characteristics of the manufacturing process including elongation. caused a short circuit.
[6]
In order to solve the safety problem of the electrochemical device, a separator in which a porous coating layer is formed by coating a mixture of inorganic particles and a binder polymer on at least one surface of a porous polymer substrate having a plurality of pores has been proposed.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[7]
An object to be solved in one aspect of the present invention is to provide a separator having improved physical properties of the separator by lowering resistance in a porous coating layer, and an electrochemical device including the same.
means of solving the problem
[8]
One aspect of the present invention provides a separator for an electrochemical device according to the following embodiments.
[9]
A first embodiment is
[10]
porous polymer substrate; and
[11]
Including; a porous coating layer formed on at least one surface of the porous polymer substrate,
[12]
The porous coating layer includes a binder polymer,
[13]
The binder polymer includes P (VDF-TrFE-CTFE) and PVDF-CTFE,
[14]
The β-phase content of the P (VDF-TrFE-CTFE) is 0.90 or more,
[15]
The weight ratio of P(VDF-TrFE-CTFE) to PVDF-CTFE is 35: 65 to 87: 13, and relates to a separator for an electrochemical device.
[16]
In the second embodiment, according to the first embodiment,
[17]
The weight ratio of P(VDF-TrFE-CTFE) to PVDF-CTFE is 50: 50 to 80: 20, and relates to a separator for an electrochemical device.
[18]
A third embodiment, according to any one of the preceding embodiments,
[19]
It relates to a separator for an electrochemical device, wherein the P (VDF-TrFE-CTFE) binder polymer contains 10 wt% or less of CTFE based on its weight.
[20]
A fourth embodiment, according to any one of the preceding embodiments,
[21]
The porous coating layer has a thickness of 1 to 10 μm, and relates to a separator for an electrochemical device.
[22]
A fifth embodiment, according to any one of the preceding embodiments,
[23]
The porous coating layer relates to a separator for an electrochemical device that further comprises inorganic particles.
[24]
A sixth embodiment, according to the fifth embodiment,
[25]
The weight ratio of the inorganic particles to the binder polymer is 90: 10 to 60: 40, it relates to a separator for an electrochemical device.
[26]
A seventh embodiment, according to the fifth or sixth embodiment,
[27]
The porous coating layer has a thickness of 1 to 15 μm, and relates to a separator for an electrochemical device.
[28]
An eighth embodiment, according to any one of the preceding embodiments,
[29]
The separator has a resistance of 0.8 ohm or less, and the adhesive force between the separator and the electrode is 50 gf/25 mm or more, and relates to a separator for an electrochemical device.
[30]
Another aspect of the present invention provides an electrochemical device according to the following embodiments.
[31]
The ninth embodiment is
[32]
An electrochemical device comprising a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is a separator manufactured according to any one of the first to eighth embodiments It's about the little ones.
[33]
The tenth embodiment, according to the ninth embodiment,
[34]
The electrochemical device relates to an electrochemical device that is a lithium secondary battery.
Effects of the Invention
[35]
According to an embodiment of the present invention, it is possible to provide a separator suitable for use as a separator for an electrochemical device and an electrochemical device including the same while having a lower resistance than before by using a binder polymer having predetermined physical properties.
[36]
In addition, since the surface of the porous coating layer has a high adhesive strength, it may have an adhesive strength suitable for a stacking process, and the adhesive strength between the separator and the electrode may be increased.
Brief description of the drawing
[37]
1 shows FT-IR spectra of PVDF crystal structures in separators according to Example 1, Comparative Example 6, and Comparative Example 7. FIG.
Modes for carrying out the invention
[38]
Hereinafter, the present invention will be described in detail. The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention.
[39]
[40]
Throughout this specification, when a part is "connected" with another part, this includes not only "directly connected" but also "indirectly connected" with another member interposed therebetween. . Also, the connection includes an electrochemical connection as well as a physical connection.
[41]
[42]
Throughout this specification, when a part "includes" a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated.
[43]
Also, as used herein, “comprise” and/or “comprising” refers to the specified presence of the mentioned shapes, numbers, steps, actions, members, elements, and/or groups thereof. and does not exclude the presence or addition of one or more other shapes, numbers, movements, members, elements and/or groups.
[44]
[45]
As used throughout this specification, the terms "about", "substantially", etc. are used as meanings at or close to the numerical values ​​when manufacturing and material tolerances inherent in the stated meaning are presented, and are used precisely in order to facilitate the understanding of the present application. or absolute figures are used to prevent unreasonable use of the mentioned disclosure by an unconscionable infringer.
[46]
[47]
Throughout this specification, the term "combination(s) of these" included in the surface of the Markush-type means one or more mixtures or combinations selected from the group consisting of the components described in the expression of the Markush-type, It means to include one or more selected from the group consisting of the above components.
[48]
[49]
Throughout this specification, the description of “A and/or B” means “A or B or both”.
[50]
[51]
Hereinafter, the present invention will be described in detail.
[52]
[53]
In an electrochemical device such as a lithium secondary battery, the separator typically uses a porous polymer substrate, so there is a problem in showing a thermal contraction behavior. Accordingly, a porous coating layer was introduced to lower the thermal contraction rate of the separator.
[54]
However, the binder polymer used in the porous coating layer acts as a resistance, and as a result, the properties of the binder polymer greatly affect the improvement of battery output.
[55]
The present inventors have improved the physical properties of the binder polymer by paying attention to the above points. Accordingly, an object of the present invention is to provide a separator having low resistance and improving battery output, and an electrochemical device including the same.
[56]
[57]
The polyvinylidene fluoride-based binder polymer may exist in three types of crystal structures: α-phase, β-phase, and γ-phase. Among them, β-phase has relatively high polarity because fluoro (F) atoms with high electronegativity are arranged on one side. On the other hand, α-phase and γ-phase have no or very low polarity because fluoro atoms are arranged in opposite directions.
[58]
The present inventors focused on the above characteristics of the polyvinylidene fluoride-based binder polymer, and applied it to a predetermined binder polymer in the porous coating layer. Accordingly, it is an object to provide a separator with improved output while low resistance by forming a local electric field in the porous coating layer to allow lithium cations to move rapidly within the separator, and an electrochemical device including the same.
[59]
On the other hand, the present inventors intend to provide a separator having low resistance and improved adhesion to electrodes by improving phase separation characteristics when P(VDF-TrFE-CTFE) and PVDF-CTFE as described above are used at the same time.
[60]
[61]
Accordingly, the separator according to one aspect of the present invention comprises:
[62]
porous polymer substrate; and
[63]
Including; a porous coating layer formed on at least one surface of the porous polymer substrate,
[64]
The porous coating layer includes a binder polymer,
[65]
The binder polymer includes poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene, P(VDF-TrFE-CTFE)) and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE). and
[66]
The β-phase content of the P (VDF-TrFE-CTFE) is 0.90 or more,
[67]
The weight ratio of P(VDF-TrFE-CTFE) to PVDF-CTFE is 35:65 to 87:13.
[68]
[69]
A separator according to an aspect of the present invention includes P(VDF-TrFE-CTFE) and PVDF-CTFE as a binder polymer in the porous coating layer.
[70]
The poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene, P(VDF-TrFE-CTFE)) is a terpolymer, and has a β-phase content of 0.90 or more. Since the P(VDF-TrFE-CTFE) has a β-phase content as high as 0.90 or more, it is advantageous to form a local ion channel by applying it in the porous coating layer. In addition, the P(VDF-TrFE-CTFE) can maintain a high β-phase content without a separate process such as heat treatment, stretching, and introduction of additives. Thereby, the resistance of the separator can be lowered.
[71]
However, when P(VDF-TrFE-CTFE) is used alone, there is a problem in that adhesion with the electrode is deteriorated, particularly in the case of a thin porous coating layer.
[72]
The present inventors simultaneously used P(VDF-TrFE-CTFE) and PVDF-CTFE to solve this problem.
[73]
In the porous coating layer according to an aspect of the present invention, by using P(VDF-TrFE-CTFE) and PVDF-CTFE at the same time, a thin adhesive layer can be formed on the porous coating layer by using the phase separation properties of PVDF-CTFE. This seems to be due to the characteristic of PVDF-CTFE being sensitive to moisture and solidifying rapidly. In addition, since the β-phase content in the binder polymer can be maintained high, it is possible to provide a separator having a low resistance and improved adhesion to an electrode.
[74]
In a specific embodiment of the present invention, the weight ratio of P(VDF-TrFE-CTFE) to PVDF-CTFE is 35: 65 to 87: 13, 50: 50 to 80: 20, or 50: 50 to 67: 33 can be It is possible to provide a separator having a low resistance within the above numerical range and improved adhesion to an electrode. In particular, when the content of P(VDF-TrFE-CTFE) is excessive, the β-phase content in the binder is high, thereby improving the resistance of the porous coating layer.
[75]
[76]
In a specific embodiment of the present invention, the P(VDF-TrFE-CTFE) binder polymer may contain 10% by weight or less of CTFE based on its weight.
[77]
[78]
When the porous coating layer does not include inorganic particles, the thickness of the porous coating layer is preferably 0.1 μm to 10 μm, specifically 0.5 μm to 4 μm based on single-sided coating. When the inorganic particles are not included, the thickness of the porous coating layer can be controlled to be thinner to increase the energy density of the electrochemical device.
[79]
[80]
In the separator according to an aspect of the present invention, the porous coating layer may further include inorganic particles.
[81]
The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as oxidation and/or reduction reactions do not occur in the operating voltage range of the applied electrochemical device (eg, 0-5V based on Li/Li+). In particular, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolyte can be improved by contributing to an increase in the degree of dissociation of an electrolyte salt, such as a lithium salt, in a liquid electrolyte.
[82]
For the above reasons, the inorganic particles may be inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transport ability, and mixtures thereof.
[83]
The inorganic particles having a dielectric constant of 5 or more are Al 2 O 3 , SiO 2 , ZrO 2 , AlO(OH), TiO 2 , BaTiO 3 , Pb(Zr x Ti 1-x )O 3 (PZT, where 0 < x < 1), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT, where 0 < x < 1, 0 < y < 1), (1-x)Pb(Mg 1/3 Nb 2/ 3 )O 3 -xPbTiO 3 (PMN-PT, where 0 < x < 1), hafnia (HfO 2 )), SrTiO 3 , SnO 2 , CeO 2 , MgO, NiO, CaO, ZnO and SiC may be one or a mixture of two or more selected from the group consisting of.
[84]
The inorganic particles having the lithium ion transport ability are lithium phosphate (Li 3 PO 4 ), lithium titanium phosphate (Li x Ti y (PO 4 ) 3 , 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO 4 ) 3 , 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y series glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO 3 , 0 < x < 2, 0 < y < 3), Lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x <4, 0 < y < 2), SiS 2 series glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4) and P 2 S 5 series glass (Li x P y S z , 0 < It may be one or a mixture of two or more selected from the group consisting of x < 3, 0 < y < 3, 0 < z < 7).
[85]
The average particle diameter of the inorganic particles is not particularly limited, but is preferably in the range of 0.001 to 10 μm, more preferably 1 to 700 nm, and even more preferably 20 to 500 nm.
[86]
When the porous coating layer includes inorganic particles, the thickness of the porous coating layer is 1 to 15 μm, more specifically 1.5 to 5 μm, based on the single-sided coating, and the porosity of the porous coating layer is also not particularly limited, but 35 to 85% It is preferable to be As such, in the case of the porous coating layer including the inorganic particles, there is an effect of improving heat shrinkage.
[87]
In a specific embodiment of the present invention, the weight ratio of the inorganic particles to the binder polymer may be 90: 10 to 60: 40. When the content ratio of inorganic particles to the binder polymer satisfies the above range, the problem of reducing the pore size and porosity of the porous coating layer formed due to an increase in the content of the binder polymer can be prevented, and since the content of the binder polymer is small The problem that the peeling resistance of the formed porous coating layer is weakened can also be solved.
[88]
[89]
In addition, the slurry for forming the porous coating layer may further include a binder polymer commonly used in the art as having adhesive properties in addition to the above-described polyvinylidene fluoride-based binder polymer.
[90]
The method of manufacturing a separator according to an aspect of the present invention may further include other additives as a component of the porous coating layer in addition to the inorganic particles and binder polymer described above.
[91]
[92]
The separator according to an aspect of the present invention may be manufactured according to a conventional method in the art.
[93]
For example, a polymer solution obtained by dissolving a binder polymer in a solvent may be prepared.
[94]
Thereafter, the porous coating layer can be formed by applying and drying the prepared polymer solution on the porous polymer substrate.
[95]
The separator according to an aspect of the present invention may be manufactured according to a conventional method in the art.
[96]
For example, a slurry for forming a porous coating layer can be prepared by dissolving a binder polymer in a solvent, adding inorganic particles, and then grinding and dispersing.
[97]
Thereafter, by applying and drying the prepared slurry on the porous polymer substrate, a porous coating layer may be formed.
[98]
At this time, non-limiting examples of the solvent that can be used include one compound selected from water, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, methyl ethyl ketone, and cyclohexane. Or there may be a mixture of two or more.
[99]
The method of coating the polymer solution or the slurry for forming the porous coating layer on the porous polymer substrate is not particularly limited, but it is preferable to use a slot coating method or a dip coating method. Slot coating is a method in which the slurry supplied through the slot die is applied to the entire surface of the substrate, and the thickness of the coating layer can be adjusted according to the flow rate supplied from the metering pump. In addition, dip coating is a method of coating by immersing the substrate in the tank containing the slurry. The thickness of the coating layer can be adjusted according to the concentration of the slurry and the speed at which the substrate is taken out from the slurry tank. can be post-weighed through
[100]
By drying the porous polymer substrate coated with the slurry for forming the porous coating layer in this way using a dryer such as an oven, the porous coating layer formed on at least one surface of the porous polymer substrate is formed.
[101]
In the porous coating layer, inorganic particles are charged and bound to each other by the binder polymer in a state in which they are in contact with each other, thereby forming an interstitial volume between the inorganic particles, and the interstitial volume between the inorganic particles. The interstitial volume may become an empty space to form pores.
[102]
That is, the binder polymer may attach the inorganic particles to each other so as to maintain a state in which they are bound to each other, for example, the binder polymer may connect and fix the inorganic particles. In addition, the pores of the porous coating layer are pores formed by an interstitial volume between inorganic particles becoming an empty space, which is an inorganic material that is substantially interviewed in a structure filled with inorganic particles (closely packed or densely packed). It can be a space defined by particles
[103]
[104]
The porous polymer substrate may be, specifically, a porous polymer film substrate or a porous polymer nonwoven substrate.
[105]
The porous polymer film substrate may be a porous polymer film made of polyolefin such as polyethylene or polypropylene, and the polyolefin porous polymer film substrate exhibits a shutdown function at a temperature of, for example, 80°C to 150°C.
[106]
In this case, the polyolefin porous polymer film is formed by mixing polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, polypentene, etc., such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene individually or by mixing two or more of them. can be formed with
[107]
In addition, the porous polymer film substrate may be manufactured by molding into a film shape using various polymers such as polyester in addition to polyolefin. In addition, the porous polymer film substrate may be formed in a structure in which two or more film layers are laminated, and each film layer may be formed of a polymer such as the aforementioned polyolefin or polyester alone or a polymer obtained by mixing two or more thereof. there is.
[108]
In addition, the porous polymer film substrate and the porous nonwoven substrate are polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, in addition to the polyolefin-based substrate as described above. ), polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalene and the like may be formed of polymers each alone or a mixture thereof.
[109]
The thickness of the porous polymer substrate is not particularly limited, but is specifically 1 to 100 μm, more specifically 5 to 50 μm, and the pore size and pores present in the porous polymer substrate are also not particularly limited, but 0.01 to 50, respectively. μm and preferably from 20 to 75%.
[110]
[111]
In a specific embodiment of the present invention, the separator manufactured as described above may have a resistance of 0.8 ohm or less, and an adhesive force between the separator and the electrode may be 50 gf/25 mm or more. It is suitable for use as a separator for an electrochemical device because of the low resistance in the above numerical range and high adhesion between the separator and the electrode.
[112]
[113]
An electrochemical device according to an aspect of the present invention includes a cathode, an anode, and a separator interposed between the cathode and the anode, and the separator is the separator according to the embodiment of the present invention described above.
[114]
Such an electrochemical device includes all devices that undergo an electrochemical reaction, and specific examples thereof include all kinds of primary, secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor devices. In particular, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery among the secondary batteries is preferable.
[115]
The positive electrode of the cathode and the anode to be applied together with the separator of the present invention is not particularly limited, and the electrode active material may be prepared in a form bound to the electrode current collector according to a conventional method known in the art. As a non-limiting example of the cathode active material among the electrode active materials, conventional cathode active materials that can be used in cathodes of conventional electrochemical devices can be used, and in particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a combination thereof. It is preferable to use one lithium composite oxide. As a non-limiting example of the anode active material, a conventional anode active material that can be used for the anode of a conventional electrochemical device can be used, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, A lithium adsorbent material such as graphite or other carbons is preferable. Non-limiting examples of the cathode current collector include a foil made of aluminum, nickel, or a combination thereof, and non-limiting examples of the anode current collector include copper, gold, nickel or a copper alloy or a combination thereof. foil, etc.
[116]
The electrolyte that can be used in the electrochemical device of the present invention is a salt having the same structure as A + B - , A + contains an ion consisting of an alkali metal cation such as Li + , Na + , K + or a combination thereof, and B - is PF 6 - , BF 4 - , Cl - , Br - , I - , ClO 4 - , AsF 6 - , CH 3 CO 2 - , CF 3 SO 3 -, N(CF 3 SO 2 ) 2 - , C(CF 2 SO 2 ) 3 - A salt containing an anion such as or a combination thereof is propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl Some are dissolved or dissociated in an organic solvent consisting of methyl carbonate (EMC), gamma butyrolactone (g-butyrolactone), or a mixture thereof, but is not limited thereto.
[117]
The electrolyte injection may be performed at an appropriate stage during the battery manufacturing process according to the manufacturing process and required physical properties of the final product. That is, it may be applied before assembling the battery or in the final stage of assembling the battery.
[118]
[119]
Hereinafter, examples will be given to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.
[120]
[121]
Example 1
[122]
P (VDF-TrFE-CTFE, β-phase content: 0.98) and PVDF-CTFE as a binder polymer in acetone solvent were added in a weight ratio of 50:50 and dissolved at 50° C. for about 4 hours to prepare a binder polymer solution. At this time, the ratio of the solvent and the solid content (weight after removing the solvent from the slurry) in the binder polymer solution was 19:1.
[123]
Thereafter, the binder polymer solution was dip-coated on both sides of a 9 μm-thick polyethylene porous polymer substrate (porosity: 43%, ventilation time: 110 sec, resistance 0.45 ohm) and dried at 23° C. relative humidity of 40% to form a porous coating layer The formed separator was manufactured.
[124]
[125]
Example 2
[126]
P (VDF-TrFE-CTFE, β-phase content: 0.98) and PVDF-CTFE as a binder polymer in acetone solvent were added in a weight ratio of 50:50 and dissolved at 50° C. for about 4 hours to prepare a binder polymer solution. Then , as inorganic particles, alumina (Al 2 O 3 ) (particle size: 500 nm) and boehmite (AlOOH) (particle size: 250 nm) were mixed in a 9: 1 weight ratio, and the weight ratio of the binder polymer and the inorganic particles It was added to the binder polymer solution so as to be 20:80. After adding 2 parts by weight of a dispersant based on 100 parts by weight of the total weight of the inorganic particles, the inorganic particles were crushed and dispersed using a ball mill method for a total of 12 hours to prepare a slurry for forming a porous coating layer. At this time, the ratio of the solvent and the solid content was controlled to be 4:1.
[127]
The slurry for forming the porous coating layer was dip-coated on both sides of a 9 μm-thick polyethylene porous polymer substrate (porosity: 43%, ventilation time: 110 sec, resistance 0.45 ohm) and dried at 23 ° C. relative humidity of 40% to form a porous coating layer The formed separator was prepared.
[128]
[129]
Examples 3 to 4
[130]
A separator was prepared in the same manner as in Example 2, except that the contents of P(VDF-TrFE-CTFE) and PVDF-CTFE were controlled as shown in Table 1.
[131]
[132]
Comparative Examples 1 to 8
[133]
A separator was manufactured in the same manner as in Example 2, except that the types and contents of the inorganic particles and the binder polymer were controlled as shown in Table 1.
[134]
At this time, the β-phase content of the injected PVDF-HFP was 0.47, and the β-phase content of PVDF-CTFE was 0.45.
[135]
[136]
Comparative Examples 9 to 10
[137]
A separator was prepared in the same manner as in Example 2, except that the contents of P(VDF-TrFE-CTFE) and PVDF-CTFE were controlled as shown in Table 1.
[138]
[139]
Experimental example
[140]
(1) Table 1 shows the thickness, resistance, resistance, thermal contraction rate, and lami strength of the separators according to Examples 1 to 4 and Comparative Examples 1 to 10.
[141]
[142]
[Table 1]
division Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Comparative Example 9 Comparative Example 10
P(VDF-TrFE-CTFE) + PVDF-CTFE (1:1)+Inorganic particle input X P(VDF-TrFE-CTFE) + PVDF-CTFE (1:1)+Inorganic particle input 0 P(VDF-TrFE-CTFE) + PVDF-CTFE (67 : 33) + Inorganic particle input 0 P(VDF-TrFE-CTFE) + PVDF-CTFE (80 : 20) + Inorganic particle input 0 PVDF-TrFE + inorganic particles 0 PVDF-HFP+Inorganic particle 0 PVDF-TrFE+ PVDF-CTFE (1:1)+ inorganic particles 0 PVDF-HFP+ PVDF-CTFE (1:1) + inorganic particles 0 PVDF-TrFE + inorganic particles X PVDF-HFP+Inorganic particle X PVDF-CTFE+Inorganic particle X PVDF-CTFE+Inorganic particle O P(VDF-TrFE-CTFE) + PVDF-CTFE (19:1)+Inorganic particle input 0 P(VDF-TrFE-CTFE) + PVDF-CTFE (1:4)+Inorganic particle input 0
P(VDF-TrFE-CTFE) VDF 67 67 67 67 70 - 70 - 70 - - - 67 67
TrFE 24 24 24 24 30 - 30 - 30 - - - 24 24
CTFE 9 9 9 9 0 - 0 - 0 - - - 9 9
PVDF-HFP VDF - - - - - 85 - 85 - 85 - - - -
HFP - - - - - 15 - 15 - 15 - - - -
PVDF-CTFE PVDF 80 80 80 80 - - 80 80 - - 80 80 80 80
CTFE 20 20 20 20 - - 20 20 - - 20 20 20 20
Separator thickness (um) 14.2 15.3 15.2 15.7 14.7 15.5 14.7 18.0 13.5 15.3 13.0 14.2 14.1 14.3
Loading amount (g/m 2 ) 4.7 9.3 9.2 9.4 9.2 9.5 9.4 9.2 4.7 4.5 5.0 9.5 9.3 9.5
resistance (ohm) 0.59 0.73 0.65 0.65 0.58 1.1 0.66 0.98 0.59 1.26 1.02 0.95 0.72 0.85
Lami Strength (gf/25mm) 82 76 79 71 19 23 29 34 38 49 88 39 29 33
Thermal shrinkage (MD/TD, 150 ℃, 30 minutes) 50% or more shrinkage, not measurable 22/21 26/25 30/28 23/22 47/45 18/16 22/20 50% or more shrinkage, not measurable 50% or more shrinkage, not measurable 50% or more shrinkage, not measurable 17/16 45/43 21/22
P(VDF-TrFE-CTFE) : weight ratio of PVDF-CTFE 50:50 50:50 67:33 80:20 - - 50:50 - - - - - 95: 5 20:80
[143]
[144]
1) How to measure thickness
[145]
The thickness of the separator was measured using a thickness gauge (Mitutoyo, VL-50S-B).
[146]
[147]
2) Measure the resistance of the separator
[148]
Resistance values ​​when the separators prepared in Examples 1 to 4 and Comparative Examples 1 to 10 were impregnated with an electrolyte, 1M LiPF 6 -Ethylene carbonate/ethylmethyl carbonate (weight ratio 3:7) AC at 25° C. Measured by the law.
[149]
[150]
3) How to measure heat shrinkage
[151]
The heat shrinkage rate is calculated as (initial length - length after heat shrinkage treatment for 150° C./min)/(initial length) X 100.
[152]
[153]
4) How to measure the adhesion between the electrode and the separator (Lami Strength)
[154]
In order to measure the adhesion between the electrode and the separator (Lami Strength), the anode was prepared as follows.
[155]
First, the anode is made by mixing artificial graphite, carbon black, carboxymethyl cellulose (CMC, Carboxy Methyl Cellulose), and styrene-butadiene rubber (SBR, Styrene-Butadiene Rubber) with water in a weight ratio of 96: 1: 2: 2 to form an anode slurry. prepared. The anode slurry was coated on copper foil (Cu-foil) with a capacity of 3.5 mAh/cm2 to form a thin electrode plate, dried at 135° C. for 3 hours or more, and then pressed to prepare an anode.
[156]
The prepared anode was prepared by cutting it to a size of 25mm X 100mm. The separators prepared in Examples 1 to 4 and Comparative Examples 1 to 10 were prepared by cutting them to a size of 25 mm X 100 mm. After overlapping the prepared separator and the anode, they were sandwiched between 100 μm PET film and then adhered using a flat plate press. At this time, the conditions of the flat plate press were heated and pressurized for 1 second at a pressure of 600 kgf at 70°C. The bonded separator and anode were attached to the slide glass using double-sided tape. Remove the distal end (10 mm or less from the end of the adhesive surface) of the adhesive surface of the separator and attach it in a longitudinal direction using a 25 mm X 100 mm PET film and single-sided adhesive tape. After that, the slide glass is mounted on the lower holder of the UTM instrument (LLOYD Instrument LF Plus), and the PET film attached to the separator is mounted on the upper holder of the UTM instrument. The force required to peel off the porous coating layer facing the anode was measured.
[157]
[158]
As can be seen from Table 1, Examples 1 to 4 use P(VVDF-TrFE-CTFE) and PVDF-CTFE at the same time, and control their weight ratio. In the case of Examples 1 to 4, the resistance value is maintained low, and as a result, the output of the electrochemical device including the separator may be improved. In addition, since the resistance value is maintained low and the adhesion between the electrode and the separator is high (Lami Strength), processability in manufacturing an electrochemical device can be improved, and physical properties can be improved. In the case of Example 1, it was confirmed that the inorganic particles were not added, and in this case, the thermal contraction rate was not improved. However, the resistance value is kept quite low and the thickness of the separator is kept thin, so that the energy density can be calculated high, so that it can be used for the type of electrochemical device in which the rate of thermal contraction is not strict.
[159]
On the other hand, Comparative Examples 1, 2, 5 to 8 are cases in which P(VVDF-TrFE-CTFE) and PVDF-CTFE are not used at the same time. In the case of Comparative Example 1, the Lami Strength was low and it was not suitable for use in a separator requiring a stack process, that is, adhesion with an electrode. In the case of Comparative Example 2, the Lami Strength is low and the resistance value is high, which is not suitable for use as a separator. In addition, in Comparative Examples 5 to 8, while the resistance value was high, the Lami Strength was measured to be low, so that it was not suitable for use as a separator. Next, in Comparative Examples 3 to 4, P(VVDF-TrFE-CTFE) was not used, and in Comparative Example 3, the adhesion to the electrode was poor. In the case of Comparative Example 4, the resistance value was also high and the Lami Strength was measured low, so it was not suitable for use as a separator. Comparative Examples 9 to 10 used P(VVDF-TrFE-CTFE) and PVDF-CTFE at the same time, but the content of P(VVDF-TrFE-CTFE) was too high or PVDF-CTFE was too high, so the adhesion with the electrode was poor. . Specifically, in Comparative Example 9, when the ratio of PVDF-CTFE was 5 wt% or less, it was impossible to secure adhesion in the thin film. In Comparative Example 10, the ratio of PVDF-CTFE was 80 wt%, and pores were not formed properly due to the rapid phase separation of CTFE, so adhesion was not secured and resistance was also increased.
[160]
[161]
(2) Table 2 and FIG. 1 show FT-IR spectra of PVDF crystal structures in separators according to Example 1, Comparative Example 6, and Comparative Example 7.
[162]
[Table 2]
division A(α) A(β) F(β) Avg.F(β)
Example 1 (P(VDF-TrFE-CTFE)) #One 0.038 0.000 1.01 0.99
#2 0.036 0.000 1.01
#3 0.030 0.000 1.02
Comparative Example 6 (PVDF-HFP) #One 0.028 0.066 0.65 0.65
#2 0.029 0.069 0.65
#3 0.029 0.066 0.65
Comparative Example 7 (PVDF-CTFE) #One 0.061 0.047 0.38 0.39
#2 0.055 0.047 0.40
#3 0.060 0.048 0.39
[163]
At this time, the AvgF(β) value was calculated using FT-IR spectroscopy, after measuring the sample spectrum 5 times in ATR mode (diamond crystal), and then calculating the average value of the β-phase crystal structure ratio. F(β) was calculated in the same way as in Equation 1 below.
[164]
[Equation 1]
[165]

[166]
As can be seen from Table 2, when the β-phase content of P(VVDF-TrFE-CTFE) is 0.90 or more, as can be seen from FIG. 1, in the case of Example 1, the β-phase content is also maintained high. A separator with low resistance can be provided. On the other hand, in Comparative Examples 6 and 7, the β-phase content was 0.65 and 0.39, respectively, and the resistance was maintained high.
Claims
[Claim 1]
porous polymer substrate; and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer includes a binder polymer, and the binder polymer is poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene; P(VDF-TrFE-CTFE)) and polyvinylidenefluoride-chlorotrifluoroethylene (PVDF-CTFE), wherein the β-phase content of P(VDF-TrFE-CTFE) is 0.90 or more, The weight ratio of P(VDF-TrFE-CTFE) and PVDF-CTFE is 35: 65 to 87: 13, a separator for an electrochemical device.
[Claim 2]
The separator for an electrochemical device according to claim 1, wherein the weight ratio of P(VDF-TrFE-CTFE) to PVDF-CTFE is 50:50 to 80:20.
[Claim 3]
The separator for an electrochemical device according to claim 1, wherein the P(VDF-TrFE-CTFE) binder polymer contains 10 wt% or less of CTFE based on its weight.
[Claim 4]
The separator for an electrochemical device according to claim 1, wherein the porous coating layer has a thickness of 1 to 10 μm.
[Claim 5]
The separator for an electrochemical device according to claim 1, wherein the porous coating layer further comprises inorganic particles.
[Claim 6]
The separator for an electrochemical device according to claim 5, wherein the weight ratio of the inorganic particles to the binder polymer is 90: 10 to 60: 40.
[Claim 7]
The separator for an electrochemical device according to claim 5, wherein the porous coating layer has a thickness of 1 to 15 μm.
[Claim 8]
The separator for an electrochemical device according to claim 1, wherein a resistance of the separator is 0.8 ohm or less, and an adhesive strength between the separator and the electrode is 50 gf/25mm or more.
[Claim 9]
An electrochemical device comprising a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is a separator manufactured according to any one of claims 1 to 8.
[Claim 10]
The electrochemical device according to claim 9, wherein the electrochemical device is a lithium secondary battery.