KR20170101451A - Secondary Battery Comprising Separator Having Fine Pores - Google Patents

Abstract

The present invention relates to a secondary battery in which an electrode assembly including an electrode and a membrane is sealed in a battery case with an electrolyte. The membrane includes pores having a diameter of 0.1 to 1.0 micrometer so as to prevent a short circuit due to contact between an anode and a cathode while preventing pores from being closed due to byproducts generated during a charging process.

Description

Technical Field [0001] The present invention relates to a secondary battery including a separator of fine pores,

The present invention relates to a secondary battery comprising a membrane of micropores.

In recent years, the demand for environmentally friendly alternative energy sources has become an indispensable factor for the future, as the increase in the price of energy sources due to depletion of fossil fuels and the interest in environmental pollution are amplified. Various researches on power generation technologies such as nuclear power, solar power, wind power, and tidal power have been continuing, and electric power storage devices for more efficient use of such generated energy have also been attracting much attention.

Particularly, as technology development and demand for mobile devices are increasing, the demand for batteries as energy sources is rapidly increasing, and accordingly, a lot of researches on batteries that can meet various demands have been conducted.

Typically, in terms of the shape of a battery, there is a high demand for a prismatic secondary battery and a pouch-type secondary battery which can be applied to products such as mobile phones with a small thickness, and has advantages such as high energy density, discharge voltage, There is a high demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries.

The secondary battery includes a cylindrical battery and a prismatic battery in which the electrode assembly is housed in a cylindrical or rectangular metal can according to the shape of the battery case, and a pouch type battery in which the electrode assembly is housed in a pouch-shaped case of an aluminum laminate sheet .

Also, the secondary battery is classified according to the structure of the electrode assembly having the positive electrode, the negative electrode, and the separator interposed between the positive electrode and the negative electrode. Typically, the long battery- A stacked (stacked) electrode assembly in which a plurality of positive electrodes and negative electrodes cut in a predetermined size unit are sequentially stacked with a separator interposed therebetween, the jelly-roll type (wound type) electrode assembly having a structure in which a separator is interposed; In recent years, in order to solve the problems of the jelly-roll type electrode assembly and the stack type electrode assembly, an electrode assembly having an advanced structure, which is a combination of the jelly-roll type and the stack type, A stack / folding type electrode having a structure in which unit cells stacked with a separator interposed between an anode and a cathode are sequentially wound while being placed on a separation film Developed body lip.

In particular, in recent years, a pouch-shaped battery having a structure in which a stacked or stacked / folded electrode assembly is embedded in a pouch-shaped battery case of an aluminum laminate sheet has attracted much attention due to low manufacturing cost, small weight, And its usage is gradually increasing.

In general, a separator of an electrode assembly constituting such a secondary battery uses an insulating thin film having high ion permeability and mechanical strength. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

Meanwhile, the secondary battery is configured such that the electrode assembly is sealed in the battery case together with the electrolyte, so that elution of the electrode active material component, surface reaction, or dislocation of the secondary battery, which occurs in the charging process of the secondary battery, By-products may occur due to various factors such as oxidation of the electrolyte resulting from reaching the oxidation potential.

At this time, the pore diameter of the separator constituting the electrode assembly is generally 0.1 m or less, and thus the pore can be closed due to the by-product, which reduces the battery performance and increases the resistance, Thereby causing a problem of lowering the safety of the battery.

Particularly, in recent years, such a secondary battery has been designed and manufactured so that high-speed charging can be performed under a high C-rate condition in order to effectively exhibit such a high capacity and high energy, There is a problem that it occurs more seriously.

Therefore, there is a high need for a technique capable of fundamentally solving such problems.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have succeeded in various experiments so that the separator of the secondary battery includes pores having a diameter of 0.1 micrometer to 1.0 micrometer, It is possible to prevent the pores from being closed due to the byproducts generated in the charging process of the secondary battery even though the secondary battery is charged at a high rate, , It has been found that the diameter of the separation membrane pores can be more easily controlled by manufacturing the separation membrane using a material and a manufacturing method different from those of the conventional separation membrane, and thus completed the present invention.

According to an aspect of the present invention, there is provided a secondary battery comprising:

A secondary battery in which an electrode assembly including an electrode and a separator is sealed in a battery case together with an electrolyte,

The separator may have pores having a diameter of 0.1 to 1.0 micrometer so as to prevent a short circuit due to contact between the positive electrode and the negative electrode while preventing the pore from being closed due to by- have.

Therefore, it is possible to prevent the phenomenon that the pores are closed by the byproducts generated in the charging process of the secondary battery even though the secondary battery is charged at a high speed by the separation membrane including the pores having the specific range of the diameter, Accordingly, performance degradation and safety degradation of the secondary battery can be prevented.

In this case, when the diameter of the separation membrane pores is less than 0.1 micrometers, it is impossible to prevent deterioration of the performance and safety of the secondary battery, which may be caused by the pores of the separation membrane being closed by the by- On the contrary, when the diameter of the separator pores is more than 1.0 micrometer, the diameter of the separator becomes too large, and the positive electrode and the negative electrode facing each other with the separator interposed therebetween may cause a short circuit .

More specifically, the separation membrane may have a structure including pores having a diameter of 0.5 micrometer to 1.0 micrometer, so that the above effect can be more easily exhibited.

In one specific example, the by-product may occur during the fast charging process of the secondary battery.

As described above, the secondary battery can cause by-products to be generated due to the elution of the constituent components of the electrode active material generated during the charging process, the surface reaction, or the oxidation of the electrolyte generated when the working potential of the secondary battery reaches the oxidation potential of the electrolyte And the generation of such by-products can be further intensified in the fast charging process of a secondary battery, which has become popular in recent years.

Accordingly, in the secondary battery according to the present invention, since the separation membrane includes pores having a diameter of 0.1 micrometer to 1.0 micrometer, unlike the secondary battery including the conventional separation membrane, the generation of the by- It is possible to prevent clogging of the membrane pores due to the by-products, and to effectively prevent degradation of performance and safety of the secondary battery.

Here, the fast charging may mean charging the secondary battery at a rate of 1.5 to 7.0C, and more specifically, charging the secondary battery at 2.0C or more.

If the fast charge is performed at less than 1.5 C rate, since the charge potential corresponds to the charge range for the conventional secondary battery, it does not cause a serious problem as compared with the fast charge, The effect to be exerted by having the diameter of this specific range may not be large.

On the contrary, when the fast charge is performed in a range exceeding the 7.0C rate, the charge potential is excessively high, and the electrochemical performance of the anode, the cathode, and the electrolyte constituting the secondary battery may be problematic.

In addition, 50% to 100% of the total pores formed in the separation membrane may be pores having a diameter of 0.1 to 1.0 micrometer.

More specifically, the secondary battery according to the present invention can exhibit a desired effect by having the pores of the separation membrane have a specific range of diameters.

In this case, the pores having the diameter of the specific range constitute 50% to 100% of the total pores formed in the separation membrane, so that the above effect can be maximized.

If the pores having a diameter of 0.1 micrometer to 1.0 micrometer are less than 50% of the total pores formed in the separator, the amount of the pores having a diameter of the specific range is not sufficient, It is impossible to effectively prevent the secondary battery from being shut down and deteriorating in performance and safety.

Accordingly, in the secondary battery according to the present invention, 50% to 100% of the total pores formed in the separation membrane may be pores having a diameter of 0.1 to 1.0 micrometer, and more specifically, All of the pores formed are composed of pores having a diameter of 0.1 micrometer to 1.0 micrometer, so that the above effect can be exhibited to the maximum.

On the other hand, the pores may have a regular arrangement structure or an irregular arrangement structure in the separation membrane.

That is, the arrangement of the pores is not limited, and more specifically, the pores are formed in a regular array structure in the separation membrane, thereby preventing the pores of the separation membrane from being locally closed by the by- On the contrary, the pores may have a structure in which the pores are formed in an irregular arrangement structure in the separation membrane, considering ease of membrane production.

In one specific example, the separation membrane may be a structure composed of aggregated nanofibers while forming pores.

That is, like the conventional separation membrane, the separation membrane is a structure in which the nanofibers are formed as an aggregate. In the process of forming the aggregates of the nanofibers, the pores can be formed naturally. By controlling the amount of the nanofibers, And the distribution can be more easily adjusted.

The average diameter of the nanofibers may be between 10 nanometers and 1,000 nanometers.

If the average diameter of the nanofibers is less than 10 nanometers, the average diameter of the nanofibers may be too small to increase the cost and time required to fabricate the separator. On the contrary, When the average diameter exceeds 1,000 nanometers, it may not be easy to control the diameter and distribution of the pores formed in the aggregation process of the nanofibers.

Further, the separation membrane may be a structure formed by electrospinning.

More specifically, the electrospinning is carried out by preparing a spinning solution by mixing a fiber-forming polymer in a solvent, spinning a low-viscosity spinning solution onto a charged metal plate (foil or wafer) in the form of fiber or fiber, Or solidifying the polymeric fibers to obtain polymeric fibers. Various polymeric materials can be used, and the shape of the finished fibers or fibers can be relatively easily adjusted.

Accordingly, since the separation membrane of the secondary battery according to the present invention is formed by electrospinning, a variety of polymer materials can be used as the material of the separation membrane, and the shape of the finished fiber or fiber can be more easily controlled.

On the other hand, the separation membrane may be made of an engineering plastic resin having high heat resistance.

More specifically, since the separation membrane is required to function as a lithium ion passage while insulating the positive electrode and the negative electrode, it is necessary to secure mechanical stability necessary for mass production including a predetermined gap, and in recent years, Heat is accumulated in the battery cells, and high thermal stability is required.

Unlike the conventional separator made of a polyolefin polymer, a technique of using a nonwoven fabric made of fibers or fibers using a polymer having excellent heat resistance as a separator has been developed.

Accordingly, the separation membrane of the secondary battery according to the present invention is also made of the high-temperature-resistant engineering plastic resin, so that the performance degradation and the safety deterioration of the battery cell can be prevented more effectively can do.

At this time, if the engineering plastic resin is capable of easily exhibiting the effect of preventing deterioration of performance and safety of the battery cell despite the high-speed charging of the high-capacity secondary battery and the high-energy secondary battery, And more specifically, it may be made of at least one selected from the group consisting of polyacrylonitrile, polyimide, and aramid.

Meanwhile, the separation membrane may be made of polyvinylidene fluoride resin.

More specifically, the polyvinylidene fluoride resin has excellent properties such as weather resistance, chemical resistance, heat resistance and strength.

That is, the separator according to the present invention is also made of polyvinylidene fluoride resin, so that it can be manufactured to have excellent properties such as weather resistance, chemical resistance, heat resistance and strength.

In general, the separator made of fibers or fibers of such a high heat-resistant engineering plastic resin or polyvinylidene fluoride resin is difficult to secure the mechanical properties required for the electrode assembly process due to irregular structure, and the diameter of the pores becomes relatively large, The tensile strength is lowered, the uniformity of the thickness is difficult to control, the processability is lowered, and the process becomes complicated, thereby increasing the process cost.

However, the separation membrane of the secondary battery according to the present invention may be formed by the electrospinning as described above, thereby eliminating the restriction on the material for forming the separation membrane and exhibiting excellent physical properties Heat-resistant engineering plastic resin or polyvinylidene fluoride resin can be used as the material of the separation membrane, and it is easy to control the shape of the finished fiber or fiber, and the diameter of the nanofibers and the shape of the nanofibers It is possible to more easily adjust the diameter of the pores to be formed, and accordingly, the tensile strength can be adjusted to a desired range, thereby exhibiting excellent mechanical performance.

In one specific example, the separator may be a structure having a tensile strength of 100 kgf / mm ² to 800 kgf / mm ² .

In general, when the temperature of the secondary battery rises during the operation of the secondary battery, the separator may cause heat shrinkage due to the high temperature, so that the anode and the cathode having the separator therebetween are in direct contact with each other, There is a problem that a short circuit may occur.

Here, the heat shrinkage of the separator may have a high physical property and a high correlation with the tensile strength of the separator. Specifically, when the tensile strength of the separator is low, it means that the elongation of the separator is low. As a result, the heat shrinkability of the separator is lowered and the heat shrinkage does not occur or relatively less occurs despite the temperature rise of the secondary battery, thereby securing the safety of the secondary battery.

On the contrary, when the tensile strength of the separator is high, it means that the elongation of the separator is high. Accordingly, the heat shrinkability of the separator is increased and heat shrinkage occurs at the time of temperature rise of the secondary battery, Can be lowered.

Accordingly, the separator of the secondary battery according to the present invention has a tensile strength of 100 kgf / mm ² to 800 kgf / mm ² , so that it can exhibit relatively low heat shrinkage, thereby improving safety.

More specifically, when the separator has a tensile strength of less than 100 kgf / mm < ² >, the tensile strength is too weak to cause repeated shrinkage and expansion of the positive electrode and the negative electrode occurring during charging and discharging of the secondary battery, It may be easily damaged by a stimulus such as an applied physical impact, so that the safety of the secondary battery may be deteriorated.

On the contrary, when the separator has a tensile strength exceeding 800 kgf / mm ² , the elongation and heat shrinkage due to the excessively high tensile strength may be excessively high, and the safety of the secondary battery may be deteriorated have.

The separation membrane may be bonded to the electrode.

As described above, the separator may have a specific range of pores so as to prevent the pore from being closed due to by-products generated during the charging process of the secondary battery.

Therefore, the separation membrane can exhibit a more excellent effect when the by-products are bonded to the electrode which can occur with a higher probability.

At this time, the separator may be interposed between the anode and the cathode, or may be bonded to one side of the anode or the cathode located at the outermost periphery.

The secondary battery may be a lithium secondary battery such as a lithium ion battery or a lithium ion polymer battery having advantages such as high energy density, discharge voltage, and output stability, although the secondary battery is not particularly limited in its kind .

Generally, a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

The positive electrode is prepared, for example, by coating a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, and then drying the mixture. Optionally, a filler may be further added to the mixture.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode is manufactured by applying and drying a negative electrode active material on a negative electrode collector, and if necessary, the above-described components may be selectively included.

Examples of the negative electrode active material include carbon such as non-graphitized carbon and graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The nonaqueous electrolyte solution containing a lithium salt is composed of a polar organic electrolyte and a lithium salt. As the electrolytic solution, a non-aqueous liquid electrolytic solution, an organic solid electrolyte, an inorganic solid electrolyte and the like are used.

Examples of the nonaqueous liquid electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the non-aqueous liquid electrolyte may contain, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. are added It is possible. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The present invention also provides a device including the secondary battery as a power source, wherein the device is used in a mobile phone, a tablet computer, a notebook computer, a power tool, a wearable electronic device, an electric vehicle, a hybrid electric vehicle, a plug- , And a power storage device.

Such devices or devices are well known in the art, so a detailed description thereof will be omitted herein.

As described above, the secondary battery according to the present invention is configured such that the separation membrane includes pores having a diameter of 0.1 micrometer to 1.0 micrometer, so that even though the secondary battery is charged at a high rate, It is possible to prevent degradation of the performance and safety of the secondary battery and to prevent the deterioration of the safety of the secondary battery by using a material and a manufacturing method different from those of the conventional separator, Thereby, the diameter of the separation membrane pores can be more easily controlled.

1 is an electron microscope (SEM) photograph of the separation membrane of Example 1 according to the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings according to the embodiments of the present invention, but the scope of the present invention is not limited thereto.

Preparation of Membrane

&Lt; Example 1 >

The solution was added to DMF solvent so that the concentration of polyacrylonitrile (PAN) was 10% by weight and stirred to prepare a spinning solution.

The prepared spinning solution was charged into a barrel of an electrospinning apparatus and the spinning solution was applied to the charged metal plate (collector) at a rate of 0.1 mL / min using a pump while maintaining the distance between the spinneret and the metal plate at 10 cm. Was discharged for 5 hours. At this time, a 30 kV charge was applied to the spinneret of the electrospinning device using a high voltage generator to form a fibrous thin film.

The fibrous thin film containing the solvent was placed in an oven and the solvent was removed by drying at 40 ° C for 2 hours to prepare a cured fibrous separator.

An electron microscope (SEM) photograph of the fibrous separation membrane is shown in FIG.

&Lt; Example 2 >

A separator was prepared in the same manner as in Example 1, except that polyimide (PI) was added to a DMF solvent in an amount of 10 wt% instead of polyacrylonitrile and stirred to prepare a spinning solution.

&Lt; Example 3 >

A separator was prepared in the same manner as in Example 1, except that aramid instead of polyacrylonitrile was added to the DMF solvent so that the aramid content was 10% by weight and stirred to prepare a spinning solution.

<Example 4>

Except that polyvinylidene fluoride (PVdF) was added in an amount of 10% by weight instead of polyacrylonitrile to an NMP solvent and stirred to prepare a spinning solution. The membrane was prepared in the same manner as in Example 1 .

&Lt; Comparative Example 1 &

The polyacrylonitrile resin was heated to 380 캜 and melted to prepare a polymer melt.

The polymer melt thus prepared was charged into a barrel of a spinning apparatus, and a non-charged metal plate (collector) was spin-dried at a rate of 0.1 mL / min using a pump while maintaining the distance between the spinneret and the metal plate at 10 cm. Was discharged for 5 hours to form a fibrous thin film.

The fibrous thin film was placed in an oven and the solvent was removed by drying at 40 ° C for 2 hours to prepare a cured fibrous separation membrane.

&Lt; Comparative Example 2 &

A separator was prepared in the same manner as in Comparative Example 1, except that polyimide resin was melt-spun instead of polyacrylonitrile resin.

&Lt; Comparative Example 3 &

A separator was prepared in the same manner as in Comparative Example 1, except that aramid resin was melt-spun instead of polyacrylonitrile resin.

&Lt; Comparative Example 4 &

A separator was prepared in the same manner as in Comparative Example 1, except that polyvinylidene fluoride resin was melt-spun instead of polyacrylonitrile resin.

&Lt; Comparative Example 5 &

A separator was prepared in the same manner as in Comparative Example 1, except that polyethylen (PE) resin was melt-spun at 230 ° C instead of polyacrylonitrile resin.

&Lt; Comparative Example 6 >

A polyethylene terephthalate (PET) multifilament is cut to a predetermined length to produce a bundle of polyethylene terephthalate fibers. The bundle of the short fiber bundle is put into a separating and collecting device, and then a polyethylene terephthalate The phthalate staple fibers were separated and collected.

The above-described separating and collecting group staple fibers were dispersed in water to prepare a monofilament slurry. The monofilament slurry thus prepared was laminated on a wet lamination machine, followed by papermaking, followed by drying / pressing, Fibrous membranes were prepared.

&Lt; Comparative Example 7 &

Polypropylene (PP) was formed into a thin film through a T-die attached to the discharge port side of a uniaxial screw extruder at 250 ° C, and after the crystallization was improved at a high temperature, it was uniaxially stretched to prepare a porous separator.

Measurement of pore diameter distribution

<Experimental Example 1>

The diameters of the pores formed in the membranes of Examples 1 to 4 and Comparative Examples 1 to 7 were observed using an electron microscope (SEM), and the results are shown in Table 1 below.

Material Method of forming membrane Diameter distribution of membrane pores (nm) Example 1 PAN Electric radiation 541 Example 2 PI Electric radiation 763 Example 3 Aramid Electric radiation 590 Example 4 PVdF Electric radiation 626 Comparative Example 1 PAN Melt spinning 2,564 Comparative Example 2 PI Melt spinning 2,171 Comparative Example 3 Aramid Melt spinning 2,023 Comparative Example 4 PVdF Melt spinning 1, 577 Comparative Example 5 PE Melt spinning 1,826 Comparative Example 6 PET wet-laid > 10,000 Comparative Example 7 PP Dry stretching 23

Referring to Table 1, Examples 1 to 4 formed using electrospinning have pores having diameters ranging from 100 nanometers to 1,000 nanometers, in particular, 541 nanometers to 763 nanometers In Comparative Examples 1 to 7, pores having a diameter of less than 100 nanometers are distributed, or pores having a diameter of more than 1,000 nanometers are distributed. That is, in Comparative Examples 1 to 7 formed by melt spinning, wet-laid, or dry stretching in addition to electrospinning, the shape of the nanofibers is not easily controlled, and pores having a diameter outside the desired range are distributed.

In particular, Comparative Examples 1 to 4 formed using melt spinning were not formed into a structure in which pores having a desired range of diameters were distributed, although they were made of the same material as in Examples 1 to 4 formed using electrospinning You can see the sound.

Heat shrinkage measurement

<Experimental Example 2>

The separation membrane (5 cm 2 cm) prepared in the above Examples and Comparative Examples was sandwiched between the slide glasses, and both ends were fixed with clips. The resultant was placed in an oven maintained at a set temperature of 150 ° C, held for 30 minutes, And the area shrinkage (%) was measured after cooling at room temperature. The results are shown in Table 2 below.

Material Method of forming membrane Area Shrinkage (%) Example 1 PAN Electric radiation 0 Example 2 PI Electric radiation 0 Example 3 Aramid Electric radiation 0 Example 4 PVdF Electric radiation 0 Comparative Example 1 PAN Melt spinning One Comparative Example 2 PI Melt spinning 0 Comparative Example 3 Aramid Melt spinning 0 Comparative Example 4 PVdF Melt spinning One Comparative Example 5 PE Melt spinning 2 Comparative Example 6 PET wet-laid One Comparative Example 7 PP Dry stretching 29

Referring to Table 1, Comparative Examples 5 to 7 formed by using PE, PET, and PP, respectively, as the conventional separation membrane materials were prepared in the same manner as in Examples 1 to 4, which were formed using PAN, PI, and aramid, which are high- 3 shows a high shrinkage ratio.

That is, when the internal temperature of the battery rises, as in Comparative Examples 5 to 7, the conventional separator formed of a material having a low heat resistance changes its shape to a high shrinkage ratio, so that the internal short- There is a risk of explosion.

On the other hand, in Examples 1 to 3 formed of a material having high heat resistance, it is confirmed that the heat shrinkage of the separator is relatively small, thereby improving the safety of the battery.

Manufacture of lithium secondary battery

LiCoO ₂ was used as the positive electrode active material and 2.5 wt% of LiCoO ₂ , 2.5 wt% of Super-P (conductive agent) and 2.5 wt% of PVDF (binder) were added to NMP (N-methyl-2-pyrrolidone) The mixture slurry was prepared and then coated on an aluminum current collector, dried and pressed to prepare a positive electrode.

Artificial graphite was used as an anode active material, and an anode mixture slurry was prepared by adding 95.5 wt% of artificial graphite, 2.5 wt% of Super-P (conductive agent) and 2 wt% of PVDF (binder) to NMP as a solvent, The whole phase was coated, dried and pressed to prepare a negative electrode.

The positive electrode and the negative electrode were interposed in the separator prepared in Examples and Comparative Examples, and an electrolyte solution was injected to prepare a lithium secondary battery. The electrolytic solution was prepared by dissolving LiPF ₆ electrolyte at a concentration of 1M using a mixed solvent of EC: DEC: EMC = 4: 3: 3 (volume ratio).

Life characteristics

<Experimental Example 3>

The secondary batteries manufactured using the separators according to the above-described examples and comparative examples were charged and discharged at 1.8 C for 100 cycles in the range of 3 V to 4.35 V, and the initial discharge capacity and discharge efficiency were measured. Respectively.

Material Method of forming membrane Initial discharge capacity
(mah) CV SOC reach (%) 100 cycle efficiency (%) Example 1 PAN Electric radiation 650 79 95.5 Example 2 PI Electric radiation 651 80 95.6 Example 3 Aramid Electric radiation 650 80 95.1 Example 4 PVdF Electric radiation 649 81 95.5 Comparative Example 1 PAN Melt spinning n / a n / a n / a Comparative Example 2 PI Melt spinning n / a n / a n / a Comparative Example 3 Aramid Melt spinning n / a n / a n / a Comparative Example 4 PVdF Melt spinning n / a n / a n / a Comparative Example 5 PE Melt spinning n / a n / a n / a Comparative Example 6 PET wet-laid n / a n / a n / a Comparative Example 7 PP Dry stretching 651 65 91.6

Referring to Table 2, the initial discharge capacities of Examples 1 to 4 and Comparative Example 7 were similar, but Comparative Example 7 in which pores having diameters of less than 1,000 nanometers were distributed had a higher charge capacity than that of Examples 1 to 4 The CV reaching SOC and the 100 cycle efficiency were remarkably decreased.

On the other hand, in Comparative Examples 1 to 6 in which pores with a diameter exceeding 1,000 nanometers were distributed, short-circuiting occurred due to contact between the positive electrode and the negative electrode during the activation process of the secondary battery, and due to the diameter of the excessively large pore, It is possible to confirm that the safety of the present invention is lowered.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (17)

A secondary battery in which an electrode assembly including an electrode and a separator is sealed in a battery case together with an electrolyte,
Wherein the separation membrane includes pores having a diameter of 0.1 to 1.0 micrometer so as to prevent a short circuit due to contact between the anode and the cathode while preventing the pore from being closed due to byproducts generated during the charging process Secondary battery. The secondary battery according to claim 1, wherein the by-product occurs in a fast charging process of the secondary battery. The secondary battery according to claim 2, wherein the secondary battery is charged at a rate of 1.5C to 7.0C. The secondary battery according to claim 1, wherein the separator comprises pores having a diameter of 0.5 micrometer to 1.0 micrometer. The secondary battery according to claim 1, wherein 50% to 100% of the total pores formed in the separation membrane have pores having a diameter of 0.1 to 1.0 micrometer. The secondary battery according to claim 5, wherein all of the pores formed in the separation membrane have pores having a diameter of 0.1 to 1.0 micrometer. The secondary battery according to claim 1, wherein the pores are formed in a regular arrangement or an irregular arrangement in the separator. The secondary battery according to claim 1, wherein the separator comprises nanofibers that are aggregated while forming pores. The secondary battery according to claim 8, wherein the average diameter of the nanofibers is 10 nanometers to 1,000 nanometers. The secondary battery according to claim 1, wherein the separation membrane is formed by electrospinning. The secondary battery according to claim 1, wherein the separation membrane is made of an engineering plastic resin having high heat resistance. 12. The secondary battery according to claim 11, wherein the engineering plastic resin comprises at least one selected from the group consisting of polyacrylonitrile, polyimide, and aramid. The secondary battery according to claim 1, wherein the separator is made of a polyvinylidene fluoride resin. The secondary battery according to claim 1, wherein the separation membrane has a tensile strength of 100 kgf / mm ² to 800 kgf / mm ² . The secondary battery according to claim 1, wherein the separation membrane is bonded to an electrode. The secondary battery according to claim 1, wherein the secondary battery is a lithium secondary battery. A device comprising the secondary battery according to claim 16 as a power source.

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