Method for evaluating internal short circuit of secondary battery
阅读说明：本技术 评估二次电池的内部短路的方法 (Method for evaluating internal short circuit of secondary battery ) 是由 尹瑞瑛 金炳秀 金周彬 于 2019-09-30 设计创作，主要内容包括：本发明的评估内部短路的方法将离子聚合物-金属复合物(IPMC)插入电池单体中；并且向与IPMC电连接的外部导线施加电压,以诱导借助于IPMC的弯曲变形导致的内部短路,由此评估内部短路是否发生。根据本发明的评估内部短路的方法将甚至在室温和低电压下也能够工作的IPMC插入电池中并定位,并且调节电压,由此具有如下优点：能够使短路在期望的位置、面积,在期望的时间段内发生。(The method for evaluating internal short circuit of the present invention inserts an ionic polymer-metal composite (IPMC) into a battery cell; and applying a voltage to an external wire electrically connected to the IPMC to induce an internal short circuit by means of bending deformation of the IPMC, thereby evaluating whether the internal short circuit occurs. The method of evaluating the internal short circuit according to the present invention inserts and positions IPMC capable of operating even at room temperature and low voltage into a battery, and adjusts the voltage, thereby having the following advantages: the short circuit can be caused to occur at a desired position, area, and within a desired period of time.)
1. A method for evaluating an internal short circuit of a secondary battery cell having a structure in which an electrode assembly of a cathode/separator/anode is embedded in a battery case, and an electrode tab of the electrode assembly is coupled with an electrode lead and sealed in such a manner as to protrude to the outside, the method comprising:
inserting an ionic polymer-metal composite (IPMC) into a battery cell; and
inducing an internal short circuit due to bending deformation of the ionic polymer-metal composite by applying a voltage to an external conductor electrically connected to the ionic polymer-metal composite.
2. The method according to claim 1, wherein the ionic polymer-metal composite (IPMC) is formed of metal electrodes coated on both sides of a polymer electrolyte membrane,
wherein the polymer electrolyte membrane includes one selected from the group consisting of:
sulfonated tetrafluoro-ethylenes including Nafion, Flemion, and Aciplex;
sulfonated styrenic block copolymers including sulfonated poly (styrene-co-ethylene) (SPSE);
sulfonated styrenic triblock copolymers including sulfonated poly (styrene-b-ethylene-co-butylene-b-styrene) (SSEBS);
sulfonated styrenic pentablock copolymers (SSPB);
a blend of styrene-maleimide alternating copolymer with polyvinylidene fluoride (PVDF) (PMSI/PVDF); and
blends of sulfonated poly (ether ketone) and polyvinylidene fluoride (PVDF) (SPEEK/PVDF).
3. The method of claim 2, wherein one selected from the group consisting of montmorillonite (MMT), silica, alumina, Carbon Nanotube (CNT), fullerene (C60), and graphene is mixed with Nafion.
4. The method of claim 2, wherein the metal electrode is one selected from the group consisting of platinum, gold, palladium, and silver.
5. The method of claim 1, wherein the ionic polymer-metal composite is inserted into at least one location between the separator and the electrode to induce an internal short circuit by energizing the positive and negative electrodes.
6. The method of claim 1, wherein the ionic polymer-metal composite is inserted to at least one location between the separator and the negative electrode, thereby inducing an internal short circuit by energizing a positive electrode lead and the negative electrode.
7. The method of claim 1, wherein the ionic polymer-metal composite is inserted to at least one location between the separator and the positive electrode, thereby inducing an internal short circuit by energizing a negative lead and the positive electrode.
8. The method of claim 1, wherein the occurrence of the internal short circuit is detected by detecting a voltage drop.
9. The method of claim 1, wherein the voltage is applied in a range of 0.01V to 5.00V.
10. The method of claim 9, wherein the voltage is applied in a range of 1V to 1.23V.
Technical Field
The present application claims benefits based on the priority of korean patent application No. 10-2018-.
The present invention relates to a method of evaluating an internal short circuit of a secondary battery, and more particularly, to an evaluation method of: by inserting an electroactive polymer into a battery and inducing an internal short circuit due to structural deformation thereof, it is possible to determine a short circuit of the battery under various states and environments.
Background
With the increase in energy prices due to depletion of fossil fuels and the increase in concern for environmental pollution, the need for environmentally friendly alternative energy sources has become an indispensable factor for future life. In particular, as the technical development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing.
In general, in terms of the shape of a battery, demand for a prismatic type secondary battery and a pouch type secondary battery that can be applied to products such as mobile phones having a small thickness is high. In terms of materials, there is a high demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, having high energy density, discharge voltage, and output stability.
The concern for the stability of the secondary battery is increasing. The lithium secondary battery has a problem of low safety while having excellent electrical properties. For example, the lithium secondary battery generates heat and gas due to decomposition reaction of an active material and an electrolyte, which are battery components, under abnormal operating conditions such as overcharge, overdischarge, exposure to high temperature and electrical short, and the like, and the resulting high-temperature and high-pressure conditions further promote the decomposition reaction and sometimes cause ignition or explosion.
In addition, it is very important to ensure stability even when an internal short circuit occurs in the battery, and for this purpose, it is important to correctly evaluate the stability of the secondary battery when the internal short circuit occurs. As items of Battery Stability of the Lithium Secondary Battery, details of a Battery evaluation test for evaluating heat generation behavior during internal short-circuiting are explained in UL standard for Lithium batteries (UL1642), Battery Industry Association guide (SBAG 1101-1997), Lithium Secondary Battery Stability evaluation standard guide (Lithium Secondary Battery Stability evaluation Guidelines), and the like.
Conventionally, in the internal short evaluation test, there are a nail penetration test, a pressing test, a shape memory alloy utilization test, and the like. The nail penetration test is intended to intentionally cause an internal short circuit of a secondary battery by loading the secondary battery in a test apparatus capable of measuring the temperature and voltage of the secondary battery, then penetrating the secondary battery using pointed metal nails having various diameters prepared in advance, then measuring the temperature and voltage variation of the secondary battery according to the diameter and penetration speed of the nails, and visually confirming whether the secondary battery is ignited or not. The compression test is a test for measuring a change in temperature or voltage of a battery by physically deforming the battery using a round bar, a square bar, or a flat plate to cause an internal short circuit between a positive electrode plate and a negative electrode plate. In the case of an internal short test using a shape memory alloy, when the shape memory alloy is mounted in a battery and heated above a certain temperature, the shape of the shape memory alloy is changed to physically break an insulating layer to determine whether an internal short of the battery occurs. However, in the case of the nail penetration test and the pressing test, when the internal separator is penetrated in advance, a desired reaction may not occur due to a chemical reaction in a portion where the separator is broken, and in the case of the test using the shape memory alloy, there are limitations as follows: the battery should be heated above a certain temperature or a high temperature environment should be provided.
Disclosure of Invention
Technical problem
Accordingly, the present invention is designed to solve the above-mentioned problems, and an object of the present invention is to provide an internal short circuit evaluation method as follows: the evaluation can be performed at normal temperature and atmospheric pressure by inserting and positioning an ionic polymer-metal composite (IPMC) in a monomer, the internal short circuit can be evaluated in various applied voltages and environments, and the internal short circuit can be evaluated as much as the evaluator needs in a desired position, a desired area size, a desired period of time.
Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. It will also be readily understood that the objects and advantages of the present invention may be realized by the means as set forth in the claims and combinations thereof.
Technical scheme
The present invention provides a method of evaluating an internal short circuit of a secondary battery cell having a structure in which an electrode assembly of a positive electrode/a separator/a negative electrode is embedded in a battery case, and an electrode tab of the electrode assembly is coupled with an electrode lead and sealed in such a manner as to protrude to the outside, the method being characterized in that: by inserting an ionic polymer-metal composite (IPMC) into a battery cell; and inducing an internal short circuit by bending deformation of the ionic polymer-metal composite by applying a voltage to an external conductor electrically connected to the ionic polymer-metal composite.
Herein, the ionic polymer-metal composite (IPMC) may be formed of metal electrodes coated on both sides of the polymer electrolyte membrane, and the polymer electrolyte membrane may include one selected from the group consisting of: sulfonated tetrafluoro-ethylenes including Nafion, Flemion, and Aciplex; sulfonated styrenic block copolymers including sulfonated poly (styrene-co-ethylene) (SPSE); sulfonated styrenic triblock copolymers including sulfonated poly (styrene-b-ethylene-co-butylene-b-styrene) (SSEBS); sulfonated styrenic pentablock copolymers (SSPB); a blend of styrene-maleimide alternating copolymer with polyvinylidene fluoride (PVDF) (PMSI/PVDF); and blends of sulfonated poly (ether ketone) and polyvinylidene fluoride (PVDF) (SPEEK/PVDF).
Meanwhile, one selected from the group consisting of montmorillonite (MMT), silica, alumina, Carbon Nanotube (CNT), fullerene (C60), and graphene may be mixed with Nafion.
Further, the metal electrode may be one selected from the group consisting of platinum, gold, palladium, and silver.
According to another embodiment of the present invention, an ionic polymer-metal composite may be inserted to at least one position between the separator and the electrode, thereby inducing an internal short circuit by electrifying the positive electrode and the negative electrode.
According to another embodiment of the present invention, an ionic polymer-metal composite may be inserted to at least one position between the separator and the anode to induce an internal short circuit by electrifying the cathode lead and the anode.
According to another embodiment of the present invention, the ionic polymer-metal composite may be inserted to at least one position between the separator and the positive electrode, thereby inducing an internal short circuit by electrifying the negative electrode lead and the positive electrode.
Further, in the method of evaluating the internal short circuit, the occurrence of the internal short circuit may be detected by detecting a voltage drop.
Further, the voltage is applied in a range of 0.01V to 5.00V, more preferably 1V to 1.23V.
In another aspect, the present invention provides a battery characterized in that an electrode assembly including two or more unit electrodes including a positive electrode or a negative electrode and wound in a state in which a separator is interposed between the unit electrodes is embedded in a battery case, and the ionic polymer-metal composite (IPMC) has been inserted into a battery cell. The battery monomer can be cylindrical, square or bag type battery monomer.
In the present invention, the unit electrode may be manufactured by: an electrode mixture containing an electrode active material is applied on a current collector, and then the electrode mixture is dried. The electrode mixture may further include a binder, a conductive material, a filler, etc., as necessary.
In the present invention, both a weakly magnetic and a non-magnetic metal ultra-thin body may be used as the current collector. The positive electrode current collector generally has a thickness of 3 to 500 micrometers. The positive electrode current collector is not particularly limited so long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium or stainless steel having a surface treated with carbon, nickel, titanium, silver or the like. The current collector may have fine irregularities on the surface thereof to increase the adhesion of the cathode active material, and may have various forms such as a sheet, a foil, and a mesh.
The negative electrode current collector generally has a thickness of 3 to 500 micrometers. The anode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, and the like. In addition, as with the cathode current collector, fine irregularities may be formed on the surface to improve the adhesion of the anode active material, and it may be used in various forms such as a sheet, a foil, and a mesh.
In the present invention, the positive electrode active material is a material capable of causing an electrochemical reaction, and is a lithium transition metal oxide, and contains two or more transition metals. Examples thereof include: such as lithium cobalt oxide (LiCoO) substituted with more than one transition metal2) And lithium nickel oxide (LiNiO)2) The layered compound of (1); lithium manganese oxide substituted with one or more transition metals; from the formula LiNi1-yMyO2(wherein M ═ Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn, or Ga and contains at least one of the above elements, and 0.01. ltoreq. y.ltoreq.0.7); from the formula Li1+zNibMncCo1-(b+c+d)MdO(2-e)Ae(wherein z is more than or equal to 0.5 and less than or equal to 0.5, b is more than or equal to 0.1 and less than or equal to 0.8, and b is more than or equal to 0.1 and less than or equal to 0.5c≤0.8，0≤d≤0.2，0≤e≤0.2，b+c+d<1, M ═ Al, Mg, Cr, Ti, Si or Y, and a ═ F, P or Cl), such as Li-nickel-cobalt-manganese complex oxides1+zNi1/3Co1/3Mn1/3O2、Li1+ zNi0.4Mn0.4Co0.2O2Etc.; from the formula Li1+xM1-yM'yPO4-zXz(wherein M ═ transition metal, preferably Fe, Mn, Co or Ni, M ═ Al, Mg or Ti, X ═ F, S or N, and-0.5. ltoreq. x.ltoreq.0.5, 0. ltoreq. y.ltoreq.0.5, 0. ltoreq. z.ltoreq.0.1).
Examples of the negative active material include carbon such as non-graphitizable carbon and graphitic carbon; metal complex oxides, such as LixFe2O3(0≤x≤1)、LixWO2(0≤x≤1)、SnxMe1-xMe’yOz(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, groups 1,2 and 3 of the periodic Table, halogen; 0<x is less than or equal to 1; y is more than or equal to 1 and less than or equal to 3; z is more than or equal to 1 and less than or equal to 8); a lithium alloy; a silicon alloy; a tin alloy; metal oxides, e.g. SnO, SnO2、PbO、PbO2、Pb2O3、Pb3O4、Sb2O3、Sb2O4、Sb2O5、GeO、GeO2、Bi2O3、Bi2O4And Bi2O5(ii) a Conductive polymers such as polyacetylene; and Li-Co-Ni based materials.
The conductive material is generally added in an amount of 1 to 30 wt% 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 conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite and 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 fibers and metal fibers; metal powders such as carbon fluoride, aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium carbonate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives and the like.
The binder is added in an amount of 1 to 30 wt% based on the total weight of the mixture containing the positive electrode active material as an ingredient contributing to the adhesion between the active material and the conductive material and the adhesion to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, various copolymers, and the like.
The filler is optionally used as a component for suppressing the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes in the battery. Examples of fillers include olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers.
Other ingredients such as viscosity modifiers, adhesion promoters may be further included, optionally or as a combination of two or more. The viscosity modifier is a component that adjusts the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the current collector thereof may be easy, and may be added up to 30 wt% based on the total weight of the anode mixture. Examples of such viscosity modifiers include, but are not limited to, carboxymethylcellulose, polyvinylidene fluoride, and the like. In some cases, the above-mentioned solvents may act as viscosity modifiers.
The adhesion promoter is an auxiliary component added for improving adhesion of the active material to the current collector, and may be added in an amount of less than 10% by weight with respect to the binder, and some examples thereof include oxalic acid, adipic acid, formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.
A separator is interposed between the positive electrode and the negative electrode, and an insulating thin film having high ion permeability and mechanical strength is used. The separator typically has a pore size of 0.01 to 10 microns and a thickness of 5 to 300 microns. Examples of such separators include chemically resistant and hydrophobic olefin-based polymers, such as polypropylene; a sheet or nonwoven fabric made of glass fiber, polyethylene, or the like. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.
The lithium salt-containing nonaqueous electrolytic solution is composed of an electrolyte and a lithium salt. A nonaqueous organic solvent, an organic solid electrolyte, an electrodeless solid electrolyte, or the like is used as the electrolytic solution.
Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ -butyrolactone, 1, 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1, 3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphotriester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1, 3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate, and the like.
Examples of the organic solid electrolyte include polymer electrolytes such as polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, alginate lysine (gelation lysine), polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymerization agents containing ionic dissociation groups, and the like.
Examples of the inorganic solid electrolyte include nitrides, halides and sulfates of Li, such as Li3N、LiI、Li5NI2、Li3N-LiI-LiOH、LiSiO4、LiSiO4-LiI-LiOH、Li2SiS3、Li4SiO4、Li4SiO4-LiI-LiOH and Li3PO4-Li2S-SiS2。
The lithium salt is a substance soluble in the nonaqueous electrolyte. Examples of lithium salts include LiCl, LiBr, LiI, LiClO4、LiBF4、LiB10Cl10、LiPF6、LiCF3SO3、LiCF3CO2、LiAsF6、LiSbF6、LiAlCl4、CH3SO3Li、(CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylates, lithium 4-phenylboronate, lithium imide, and the like.
For the purpose of improving charge and discharge characteristics, flame retardancy, and the like, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, N-ethylene glycol dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, and the like may be added to the electrolyte. In some cases, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be further added to impart incombustibility, or carbon dioxide gas may be further added to improve high-temperature storage characteristics, and FEC (fluoroethylene carbonate), PRS (propylene sultone), or the like may be further added.
In a preferred embodiment, a material such as LiPF may be used6、LiClO4、LiBF4And LiN (SO)2CF3)2Is added to a mixed solvent of a cyclic carbonate EC or PC as a high dielectric solvent and a linear carbonate DEC, DMC or EMC as a low viscosity solvent, thereby preparing a lithium salt-containing non-aqueous electrolyte.
Advantageous effects
In the internal short evaluation method according to the present invention, an ionic polymer-metal composite (IPMC) capable of operating even at room temperature and low voltage is inserted and positioned, and the voltage is adjusted, thereby enabling internal short evaluation of desired location, area, and time.
Drawings
Fig. 1 is a view schematically illustrating the structure of a cylindrical battery cell in which an ionic polymer-metal composite (IPMC) according to the present invention is inserted and positioned.
Fig. 2 is a view schematically showing the structure of a pouch type battery cell in which an ionomer-metal composite according to the present invention is inserted.
Fig. 3 is a diagram schematically illustrating the shape and operation principle of an ionic polymer-metal composite (IPMC) according to the present invention.
Fig. 4 is a view schematically showing a position where an ionic polymer-metal composite according to the present invention is installed between a separator and an electrode.
Fig. 5 is a schematic view illustrating an internal short circuit caused by bending deformation of the ionic polymer-metal composite of the present invention between a separator and an electrode.
Fig. 6 is a view schematically showing a position where an ionic polymer-metal composite according to the present invention is installed between a separator and a negative electrode.
Fig. 7 is a schematic view illustrating an internal short circuit caused by contact between a negative electrode and a positive electrode lead due to bending deformation of an ionic polymer-metal composite of the present invention.
Fig. 8 is a view schematically showing a position where an ionic polymer-metal composite according to the present invention is installed between a separator and a positive electrode.
Fig. 9 is a schematic view illustrating an internal short circuit caused by contact between positive and negative electrode leads due to bending deformation of the ionic polymer-metal composite of the present invention.
Detailed Description
The terms and words used in the present specification and claims should not be construed as being limited to general or dictionary meanings, and the inventor can appropriately define the concept of the term to best describe his invention. The terms or words should be interpreted as meanings and concepts consistent with the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations described in the drawings are only the most preferable embodiments of the present invention, and do not represent all of the technical ideas of the present invention. It should be understood that various equivalents and modifications may exist in place of them at the time of filing this application.
In this specification, when one part is "connected" to another part, this includes not only "direct connection" but also "electrical connection" between the parts with other elements therebetween.
Further, throughout the specification, when an element is referred to as "comprising" an element, it is understood that the element may further comprise other elements, unless specifically stated otherwise.
As used throughout this specification, the terms "about," "substantially," and the like, when used in reference to inherent manufacturing and material tolerances, are used in a sense of referring to a numerical value or a value approximating such value, and are used to prevent disclosure including precise or absolute numerical values provided to aid understanding of the present disclosure from being improperly utilized by an unscrupulous infringer.
In the present specification, the term "combination thereof" included in the expression of Markush (Markush) form means a mixture or combination of one or more selected from the group consisting of the elements described in the expression of Markush form, and it means including one or more selected from the group consisting of the above-mentioned elements.
The present invention provides a method of evaluating an internal short circuit of a secondary battery cell having a structure in which an electrode assembly of a cathode/separator/anode is embedded in a battery case, and electrode tabs of the electrode assembly are coupled with electrode leads and sealed in such a manner as to protrude to the outside, the method being characterized by inserting an ionic polymer-metal composite (IPMC) into the battery cell; and inducing an internal short circuit by bending deformation of the ionic polymer-metal composite by applying a voltage to an external conductor electrically connected to the ionic polymer-metal composite.
Conventionally, in order to evaluate the internal short circuit of the battery, a user uses a method of disassembling the battery and physically damaging a separator or the like, or installing a shape memory alloy inside the battery. However, there are problems in that: the accuracy of the experimental result is lowered due to side reactions caused by chemical reactions of the damaged portion during the process of re-assembling the physically damaged battery, and in the case of compensating for this using the shape memory alloy, there is a problem that the experimental temperature should be set high.
Therefore, the present invention uses an electroactive polymer, specifically, an ionic polymer-metal composite (IPMC), as a test material for internal short evaluation of a battery, so that it can operate at normal temperature and low voltage, and can be miniaturized for convenient operation. In addition, by adjusting the applied voltage, short circuit evaluation can be performed according to the position, area, and time desired by the user.
Generally, electroactive polymers (EAPs) are materials that mechanically deform when subjected to an electrical stimulus, and are materials that emit an electrical signal when mechanically deformed. Materials with properties similar to those of electroactive polymers are typically shape memory alloys, but have limitations due to: environmental restrictions result from deformation under conditions where heating is carried out to a temperature above a specific temperature. In contrast, electroactive polymers have a relatively high degree of deformation and are characterized by excellent toughness and rapid response.
Electroactive polymers are classified into electroactive polymers activated by an electric field and electroactive polymers activated by ion transport according to their driving methods. First, the electronic EAP is a polymer that increases or decreases in volume by coulomb force induced by an electric field. It is capable of inducing a relatively large force, has excellent mechanical properties, and reacts and works rapidly in air within seconds. In addition, the deformed state of the polymer can be maintained for a long time by the series voltage. Therefore, it is mainly applied to industrial and military robots. However, it has the following disadvantages: a relatively high driving voltage of more than several hundreds to several kilovolts is required but the degree of deformation is not large.
On the other hand, the ionic electroactive polymers can operate at higher displacements and lower voltages than the electronic electroactive polymers, and their structures are simple and advantageous for miniaturization. Therefore, applications to miniaturized robot parts and bionic artificial muscles have been studied.
Some examples of ionic electroactive polymers include ionic polymer gels, conductive polymers, ionic polymer-metal composites (IPMC), and Carbon Nanotubes (CNTs). Specifically, since the polymer forms a mesh via a crosslinking reaction, the ionic polymer gel has an elastic modulus such that the ionic polymer gel maintains its shape while properties of the swollen material are changed and deformed according to external environmental conditions such as temperature, solvent, pH, and electric field. Representative examples include polyacrylic acid, polyacrylonitrile, and the like. The Conductive Polymer (CP) is deformed mainly due to a volume change caused by movement of ions during redox, and representative examples thereof include pyrrole (PPy), Polyaniline (PANI), and polythiophene (PTh). Ionic polymer-metal composites (IPMC) are representative ionic electroactive polymers that exhibit large bending strains when low electric fields are applied. The ionic polymer-metal composite generally has a structure in which metal electrodes are positioned on both sides of a polymer electrolyte membrane. A typical example thereof is IPMC with a platinum electrode coated on a Nafion polymer membrane, and Nafion is chemically very stable and shows large deformation in both ac and dc voltages.
In the present invention, an electroactive polymer, specifically, an ionic polymer-metal composite (IPMC), is preferably used as an internal short circuit material for inducing a battery. IPMC is advantageous in terms of miniaturization, and has a feature of exhibiting large bending deformation even when a low electric field is applied.
Hereinafter, a method of evaluating an internal short circuit of a secondary battery according to an embodiment of the present invention will be described with reference to the accompanying drawings.
First, fig. 3 is a view schematically showing the shape and operation principle of an ionic polymer-metal composite (IPMC) according to the present invention.
Generally, an ionic polymer-metal composite (IPMC) is composed of a polymer electrolyte membrane (or ion exchange membrane) 320 and
In the present invention, the metal electrode is generally a noble metal deposited on the polymer electrolyte membrane by electroless plating.
In the present invention, platinum is preferably used as a material of the metal electrode.
On the other hand, as the length of the IPMC increases, the effect of bending deformation increases, whereby the damaged area of the separator also increases, so that the damaged area can be adjusted.
Specifically, referring to 300a of fig. 3, before the electric field or voltage is applied, the
300b of fig. 3 shows the bending deformation of the IPMC when a voltage is applied. Referring to this, when a positive electrode is connected and a voltage of 0.01V to 5.00V is applied in order to drive the IPMC, bending occurs in which the positively charged electrode is bent in the connection direction. The driving principle is as follows. When a voltage is applied to the IPMC, cations present therein move in the direction of the electrode of the negatively charged IPMC in the state of
In the present invention, the voltage is applied in the range of 0.01V to 5.00V, preferably 1.00V to 1.23V. When the applied voltage is less than 0.01V, there is a problem that the internal short evaluation cannot be performed because bending deformation does not occur due to sufficient voltage application, and when the voltage is higher than 5V, there is a problem that IPMC as an electroactive polymer is deformed or decomposed.
On the other hand, the total thickness of the IPMC is preferably 1 μm to 100 μm. If the thickness is less than 1 μm, there is a problem in that an internal short circuit does not occur due to an insufficient degree of damage of the separator caused by bending deformation, and if the thickness exceeds 100 μm, there is a problem in that it is not easily inserted into the battery due to a large thickness.
In the present invention, two platinum electrodes of IPMC are connected to an external conductor connected to the outside, and the internal short evaluation is performed by bending deformation caused by applying a voltage via the external conductor.
The performance of the IPMC may vary depending on factors such as the material of the polymer electrolyte membrane, the metal electrodes, the interface between the electrolyte and the electrodes, the internal solution, the applied voltage and frequency.
In the present invention, the polymer electrolyte membrane may include one selected from the group consisting of:
sulfonated tetrafluoro-ethylenes including Nafion, Flemion, and Aciplex;
sulfonated styrenic block copolymers including sulfonated poly (styrene-co-ethylene) (SPSE);
sulfonated styrenic triblock copolymers including sulfonated poly (styrene-b-ethylene-co-butylene-b-styrene) (SSEBS);
sulfonated styrenic pentablock copolymers (SSPB);
a blend of styrene-maleimide alternating copolymer with polyvinylidene fluoride (PVDF) (PMSI/PVDF); and
blends of sulfonated poly (ether ketone) and polyvinylidene fluoride (PVDF) (SPEEK/PVDF).
Most preferably, Nafion is used.
First, Nafion, Flemion, and Aciplex are sulfonated tetrafluoroethylenes, which have the following structures.
(DuPont Co.) m>1，n＝2，x＝5～13.5，y＝1
(Tokuai chemical Co., Ltd.) m is 0.3, n is 2 to 5, and x is 1.5 to 14
Nafion is most desirable because of its unique chemical structure, high ionic conductivity, and excellent thermal, chemical, and mechanical stability. Flemion and Aciplex have similar structures to Nafion.
On the other hand, when Nafion is used as the polymer electrolyte membrane, one selected from the group consisting of montmorillonite (MMT), silica, alumina, Carbon Nanotube (CNT), fullerene (C60), and graphene may be further included.
In addition, the polymer electrolyte membrane may include water or an ionic liquid. Ionic liquids are salts that exist in liquid form at room temperature and have low volatility, water-like viscosity, and high conductivity.
On the other hand, it is preferable to use one selected from the group consisting of palladium, silver, gold and platinum as the metal electrode deposited on the polymer electrolyte membrane. Most preferably, it is desirable to deposit platinum. Platinum electrodes are deposited on polymer electrolyte membranes to protect them from acids and corrosive environments.
As a method of depositing a metal electrode on a polymer electrolyte membrane, there are mechanical compression, electrochemical and chemical deposition methods. Generally, electroless plating methods are preferred.
Metal electrodes are expensive and, due to the complexity of the plating process, conductive polymers such as carbon nanotubes can also be used as electrodes instead of metal electrodes.
In the present invention, a cylindrical or pouch type battery cell may be used as the secondary battery cell in which the IPMC is mounted and positioned, but is not limited thereto.
Fig. 1 is a view schematically showing the structure of a typical cylindrical battery cell in which an ionic polymer-metal composite according to the present invention can be inserted.
Referring to fig. 1, in a cylindrical battery cell 100, a jelly-roll type (winding type) electrode assembly 110 is received in a receiving part of a cylindrical can 120, an electrolyte is injected into the receiving part such that the electrode assembly 110 is completely submerged in the cylindrical can 120, and a cap assembly 132 is mounted and coupled to an open upper end of the cylindrical can 120.
The electrode assembly 110 has a structure in which a positive electrode 113, a separator 112, and a negative electrode 111 are sequentially stacked and wound in a circular shape, and a cylindrical center pin (not shown) may be inserted into the center of the electrode assembly 110. The center pin is generally made of a metal material to impart predetermined strength, and has a hollow cylindrical structure in which a plate is bent into a circular shape. In some cases, the center pin may be removed after welding the electrode of the electrode assembly 110 to the cylindrical can 120 or the cap assembly 132.
The cap assembly 132 has the following structure: wherein at the inside of the hermetic gasket mounted on the upper inner surfaces of the curled portion and the curled portion 140 of the cylindrical can 120, the upper cap 131 and the inner pressure drop safety hole are in close contact with each other, the upper cap 131 protrudes upward and serves as a positive electrode, and a plurality of through-holes through which gas inside the can be discharged may be formed along the circumference of the protruding portion. In addition, at the center of the electrode assembly 110, a positive electrode tab protrudes from the insulating plate in the upper axial direction, thereby being electrically connected to the upper cover 131 of the cover assembly 132 to apply current. Further, the safety vent 134 is a thin film structure through which current can flow, and a central portion thereof is depressed to form a concave central portion, and 2 notches reaching a depth are formed at upper and lower bent portions of the central portion.
The insulating plate 133 is mounted on the upper surface of the electrode assembly 110 to prevent contact with the electrode leads, thereby preventing a short circuit due to the contact of the electrode assembly 110 with the electrode leads.
The cylindrical can 120 may be made of metal, preferably stainless steel. In addition, the cylindrical can 120 may include a receiving unit in which the electrode assembly 110 may be received, and the upper end portion may be open.
On the other hand, the positive electrode tab of the electrode assembly 110 protrudes from the insulating plate 133 in the upper axial direction and is coupled with the upper cap of the cap assembly by spot welding, and may be electrically connected to achieve energization. In addition, a negative electrode tab of the electrode assembly may be spot-welded to the lower inner surface of the cylindrical can and electrically connected to apply current.
Fig. 2 is a view schematically showing the structure of a pouch type battery cell in which an ionomer-metal composite according to the present invention is inserted.
The pouch type battery cell 200 includes an electrode including a positive electrode plate 211 and a negative electrode plate 212 in a state in which an electrode active material is filled in a mesh form, and an electrode assembly 210 in which separators 213 are alternately stacked, and an electrolyte interposed between the positive electrode plate 211 and the negative electrode plate 212 is impregnated in the separators 213. In this case, a positive electrode tab 260 is formed at one side of the positive electrode plate 211, a negative electrode tab (not shown) is formed at one side of the negative electrode plate 212, and the positive electrode tab 260 and the negative electrode tab are arranged side by side at a certain interval. The tabs are connected to an external circuit by being connected to a positive electrode lead 250 and a negative electrode lead (not shown), respectively. The electrode assembly 210, the positive electrode lead 250, and the negative electrode lead are sealed by a pouch 240, the pouch 240 being a battery case in which a can is formed. In addition, insulating films may be attached to upper and lower portions of the cathode lead and the anode lead to increase a degree of sealing with the pouch and ensure an electrical insulation state. The bag 240 has a form in which thermal adhesive materials are stacked on the upper and lower surfaces of the aluminum film, and the inside of the bag 240 is sealed by bonding the thermal adhesive materials to each other. In this case, for the electrical connection of the electrode assembly 210 to the outside, the sealing is performed by the pouch 240 in a state in which a part of the cathode lead 250 and the anode lead is exposed to the outside.
The battery case is generally made of an aluminum laminate sheet, provides a space for accommodating the electrode assembly, and has a pouch shape as a whole. The pouch type battery cell may be manufactured as follows: the electrode assembly is inserted into the receiving part of the battery case, the electrolyte is injected, and the outer circumferential surfaces of the upper and lower laminate sheets of the battery case, on which the upper and lower laminate sheets contact each other, are thermally welded.
Looking in more detail at the battery case of the laminate sheet structure, it is composed of an inner sealant layer for sealing, a metal layer for preventing permeation of materials, and an outer resin layer forming the outermost layer of the case. Wherein the inner sealant layers are thermally welded to each other by applying heat and pressure in a state in which the electrode assembly is embedded, and serve to provide sealability, and are mainly composed of CPP (unstretched polypropylene film). The metal layer serves to prevent air, moisture, etc. from flowing into the battery, and aluminum (Al) is mainly used. In addition, since the outer resin layer serves to protect the battery from the outside, excellent tensile strength with respect to thickness and weather resistance are required, and ONy (stretched nylon film) is often used.
Next, a method of mounting the IPMC according to the present invention in a battery will be described.
Fig. 4 is a view schematically showing that an ionic polymer-metal composite (IPMC) according to an embodiment of the present invention is installed between a separator and an electrode, that is, between the separator and a positive electrode or between the separator and a negative electrode. In the present invention, an ionic polymer-metal composite (IPMC) as an electroactive polymer is inserted at one or more positions between a separator and an electrode to induce an internal short circuit by applying current to a positive electrode and a negative electrode.
Referring to fig. 4,
Platinum electrodes on both sides of the polymer electrolyte membrane containing Nafion are preferably used as IPMC.
IPMC typically has ends that are not connected to external conductors and are typically perpendicular to the length direction. However, the IPMC may have a pointed end portion so as to easily penetrate the separator when a voltage is applied. If one side of the separator is damaged by bending of IPMC due to voltage application, an internal short circuit may occur due to contact with the electrode at the backside of the separator. This easily damages the separator, and the shape of the end of the IPMC is not particularly limited as long as it can contact the electrode at the backside of the separator.
In addition, when a voltage is applied through the external conductor, the IPMC bends toward the platinum electrode to which a positive voltage is applied. Therefore, it is preferable to apply a positive voltage to the external conductor connected to the platinum electrode in contact with the separator of IPMC. This is because, in the case where the platinum electrode to which the positive voltage is applied is not the separator side but the platinum electrode on the positive or negative electrode side, even if bending occurs, the internal short circuit desired in the present invention does not occur.
Fig. 5 is a schematic view illustrating an internal short circuit due to bending deformation of IPMC as an electroactive polymer between a separator and an electrode. Referring to fig. 5, it can be seen that an internal short circuit occurs due to bending deformation after the IPMC is mounted as shown in fig. 4.
Specifically, IPMC 514 connected to outer conductor 515 is mounted between positive electrode 511 and separator 513, and bending of IPMC 514 is generated by applying a voltage to outer conductor 515. Here, by applying a voltage to outer conductor 515 connected to the platinum electrode of IPMC 514 in contact with separator 513, IPMC 514 is bent toward separator 513, with the result that separator 513 is torn. IPMC 514 penetrates torn separator 513 and contacts negative electrode 512 across the separator. As a result, one surface of the IPMC is in contact with the positive electrode 511, and the other side is in contact with the negative electrode 512, so that current conduction occurs and an internal short circuit occurs.
According to another embodiment of the present invention, the IPMC may be installed between the separator and the negative electrode.
Fig. 6 is a view schematically showing a position where an ionic polymer-metal composite according to the present invention is installed between a separator and a negative electrode. In the present invention, a long electroactive polymer IPMC is inserted at one or more positions between the separator and the negative electrode to induce an internal short circuit by energizing the negative electrode and the positive electrode lead.
Referring to fig. 6, an IPMC 614 having a longer length is located between one surface of the negative electrode 612 and the separator 613. In the positive electrode 611, a positive electrode tab 616 is collected and welded to one surface of a positive electrode lead 650. In this case, the cathode tab 616 and the IPMC 614 do not overlap each other and do not contact each other. That is, the other end of the IPMC does not contact the positive electrode tab and the positive electrode lead.
The IPMC 614 is connected to an outer conductor 615 exposed to the outside of the battery, and when a voltage is applied to the outer conductor, bending occurs in a direction toward the platinum electrode to which a positive voltage is applied. Specifically, a positive voltage is applied to the outer conductor 615 connected to the platinum electrode of the IPMC. The bending of the IPMC is formed in the direction in which the positive voltage is applied, and the direction in which the positive voltage is applied is set to the direction of the positive electrode lead 650. When the direction of application of the positive voltage is set not to the direction of the positive electrode lead 650 but to the direction of the battery case 640, the IPMC is bent toward the battery case so that the internal short circuit desired in the present invention does not occur.
Fig. 7 is a schematic view illustrating an internal short circuit caused by contact between a negative electrode and a positive electrode lead due to bending deformation of an ionic polymer-metal composite of the present invention. Referring to fig. 7, it can be seen that an internal short circuit occurs due to bending deformation after the IPMC is mounted as shown in fig. 6.
Specifically, IPMC714 connected to outer conductor 715 is arranged between negative electrode 712 and separator 713, and bending of IPMC714 occurs by applying a voltage to outer conductor 715. The long tensile IPMC714 bends towards the positive lead 750 by applying a voltage such that positive charge flows to the outer lead 715 connected to the platinum electrode of IPMC714 towards the positive lead 750.
In the present invention, the length of the IPMC714 is long enough to be able to contact the electrode lead by bending, thereby energizing the electrode and the electrode lead.
In detail, in fig. 7, IPMC714 is in contact with positive electrode lead 750 by bending, and as a result, current conduction is achieved as negative electrode 712 and positive electrode lead 750 are in contact with each other through IPMC, which causes an internal short circuit.
According to another embodiment of the present invention, the IPMC may be installed between the separator and the positive electrode.
Fig. 8 schematically shows that the ionic polymer-metal composite according to the present invention is installed between a separator and a positive electrode. In the present invention, a long electroactive polymer IPMC is inserted at one or more positions between the separator and the positive electrode to induce an internal short circuit by electrifying the positive and negative electrode leads.
Referring to fig. 8, an
The
Fig. 9 is a schematic view illustrating an internal short circuit caused by contact between positive and negative electrode leads due to bending deformation of the ionic polymer-metal composite of the present invention. Referring to fig. 8, it can be seen that an internal short circuit occurs due to bending deformation after the IPMC is mounted as shown in fig. 8.
Specifically, IPMC914 connected to external conductor 915 is interposed between positive electrode 911 and separator 913, and IPMC914 is bent by applying a voltage to external conductor 915. The long stretched IPMC914 is bent toward the negative electrode lead 950 by applying a voltage such that positive charges flow to the external lead 915 connected to the platinum electrode of IPMC914 facing the negative electrode lead 950.
In the present invention, the length of IPMC914 is long enough to be able to contact the electrode lead by bending, thereby energizing the electrode and the electrode lead.
In detail, in fig. 9, the IPMC914 is in contact with the negative electrode lead 950 by bending, and as a result, current conduction is achieved as the positive electrode 911 and the negative electrode lead 950 are in contact with each other through the IPMC, which causes an internal short circuit.
The internal short circuit evaluation method according to the present invention includes: a step of preparing an ionic polymer-metal composite (IPMC) connected to an external conductor exposed to the outside of the battery cell; a step of installing and positioning the ionic polymer-metal complex in the monomer; a step of applying a voltage to an external conductor connected to the ionic polymer-metal composite (IPMC); and a step of evaluating the internal short circuit by measuring the voltage of the battery cell.
When a voltage is applied to the ionic polymer-metal composite of the present invention, bending deformation occurs to induce energization, thereby reducing the cell voltage. The occurrence of the internal short circuit can be specified by the difference (voltage drop width) between the voltages after the occurrence of the internal short circuit and before the occurrence of the internal short circuit. The voltage drop of the battery cell can be measured using a voltmeter, and the device capable of measuring the pressure in the battery is not particularly limited.
In the present invention, IPMC is used as the electroactive polymer, but is not limited thereto.
In the present invention, the internal short circuit can be evaluated at room temperature and normal pressure, and by controlling the IPMC using voltage, there is an advantage that the influence of the internal and external environments is not significant.
In addition, the appropriate voltage range can be adjusted depending on the electroactive polymer used.
As the length of the IPMC increases, the degree of bending increases, and thus the damaged area of the separator tends to increase, so that a desired damaged area can be adjusted. In addition, the internal short circuit occurs due to the application of a voltage corresponding to the short circuit time desired by the experimenter, resulting in an advantage of evaluation of the internal short circuit according to the desired position, area and time.
Description of the symbols
100: the battery cell 110: electrode assembly
111: negative electrode 112: separator
113: the positive electrode 120: cylindrical can
131: upper cover 132: cap assembly
133: insulating plate 134: safety hole
140: curl and bead portion 200: pouch type battery cell
210: electrode assembly 211: positive plate
212: negative electrode plate 213: separator
240: bag 250: positive electrode lead
260: positive electrode tab 270: insulating film
300. 300a, 300 b: IPMC 310: metal electrode
320: polymer electrolyte membrane 321: cation(s)
322: water molecule 400: pouch type battery cell
411: positive electrode 412: negative electrode
413: the separator 414: IPMC
415: outer conductor 440: battery case
500: battery cell 511: positive electrode
512: negative electrode 513: separator
514: IPMC 515: external conductor
600: the battery cell 611: positive electrode
612: negative electrode 613: separator
614: IPMC 615: external conductor
616: positive electrode tab 640: battery case
650: positive electrode lead
700: the battery cell 711: positive electrode
712: negative electrode 713: separator
714: IPMC 715: external conductor
716: positive electrode tab 740: battery case
750: positive electrode lead
800: battery cell 811: positive electrode
812: negative electrode 813: separator
814: IPMC 815: external conductor
816: negative electrode tab 840: battery case
850: negative electrode lead
900: the battery cell 911: positive electrode
912: negative electrode 913: separator
914: IPMC 915: external conductor
916: and (3) a negative electrode tab 940: battery case
950: negative electrode lead
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