KR20220170510A - Coin Cell Having Uniform Pressure - Google Patents

Abstract

The present invention relates to a coin cell type secondary battery having lithium metal as an anode. The coin cell according to the present invention is an electrolyte-based coin cell in which a lithium metal electrode, a counter electrode of the lithium metal electrode, a separator interposed between the lithium metal electrode and the counter electrode, and an electrolyte are internally accommodated. The coin cell includes an elastic polymer film positioned between the bottom surface of a coin cell case and an electrode positioned on the bottom surface side of the lithium metal electrode and the counter electrode.

Description

Pressure equalized coin cell {Coin Cell Having Uniform Pressure}

The present invention relates to a pressure-homogenized coin cell, and, more particularly, the pressure applied to a lithium metal electrode inside the coin cell is homogenized, thereby reducing the performance deviation of the coin cell and improving reliability, and preventing the formation of non-uniform dendrite lithium. It relates to a pressure equalized coin cell capable of suppressing.

As the electric vehicle and energy transportation industries develop, the demand for high-energy capacity batteries has steadily increased, and research on lithium secondary batteries is being actively conducted to secure higher energy density and stability. In conducting lithium secondary battery research, coin-type batteries (coin cells) have a smaller size than commercial batteries such as pouch-type batteries or cylindrical batteries, cost reduction in manufacturing equipment construction and material use, and high research accessibility through simple battery assembly. In addition, it has the advantage of securing reliability of research results due to standardized battery configuration and enabling performance prediction at commercial level.

Among next-generation lithium battery candidates, lithium/air batteries, lithium/sulfur batteries, and lithium metal batteries using lithium metal as an anode have recently been attracting attention. Lithium metal realizes a very high theoretical capacity (3860 mAh/g), which is about 10 times higher than the graphite anode (372 mAh/g) used as the anode of today's commercial lithium secondary batteries. In addition, due to its low reduction potential (-3.040V) and low density (0.544 g/cm ³ ), it is being re-examined as a very effective anode material for improving energy density. Lithium metal batteries are predicted to be capable of realizing energy densities exceeding 500 Wh/kg, and in fact, the Battery 500 consortium of Solid Energy Systems and Pacific Northwest National Laboratory in the US has demonstrated the possibility of realizing high energy densities at the level of commercial pouches. In addition, the lithium metal battery has the advantage of being advantageous for commercialization because it can utilize the existing lithium secondary battery manufacturing process.

Despite this promise, the biggest problems to be solved in the commercialization of lithium metal batteries are electrodeposition of lithium dendrites during the charging process and extreme consumption of lithium and electrolyte due to low coulombic efficiency. Recently, verification at a commercial level through the production of a pouch-type lithium metal battery suggests that these problems can be further intensified during commercialization. In particular, in order to realize a practical high energy density, it is required to improve the loading of the positive electrode active material, use thin-film lithium metal and a very small amount of electrolyte, so the consumption of lithium metal and the depletion of the electrolyte are very accelerated, and the deterioration due to the extreme volume increase in the negative electrode It may involve changes in the cell structure and threaten the safety of the cell.

Unlike lithium ion batteries, the performance of lithium metal batteries is sensitive to pressure due to the large volume change of the negative electrode and tends to depend very much on the design and structure of the battery, making it difficult to predict the characteristics of a pouch cell from the characteristics of a coin cell. It is necessary to solve the problems that occur when using lithium metal within the cell's own structure.

In addition, along with the adverse effects of lithium dendrites (dendritic phase), the amount of electrolyte, the thickness of lithium metal and Even if the anode loading amount is the same, there is a problem in that the performance variation of each coin cell is large and the reproducibility is poor.

Accordingly, there is a need for a technology capable of suppressing adverse effects caused by lithium dendrites in a coin cell type secondary battery using lithium metal as an anode, reducing a performance difference between coin cells, and increasing the reproducibility and reliability of coin cells.

Republic of Korea Patent Publication No. 2017-0127723

An object of the present invention is to provide a coin cell in which uniform pressure is applied to an electrode assembly including electrodes, and performance deviation of the coin cell and formation of non-uniform lithium dendrites due to the non-uniform pressure are suppressed.

The electrolyte-based coin cell according to the present invention is an electrolyte-based coin cell in which a lithium metal electrode, a counter electrode of the lithium metal electrode, a separator interposed between the lithium metal electrode and the counter electrode, and an electrolyte are internally accommodated, and the bottom surface and and an elastic polymer film positioned between the lithium metal electrode and an electrode positioned on a bottom side of the counter electrode.

In an electrolyte-based coin cell according to an embodiment of the present invention, the coin cell includes a first electrode that is a lithium metal electrode, a second electrode that is a counter electrode provided with an active material layer into which lithium ions are reversibly intercalated, and the first electrode A separator interposed between an electrode and a second electrode, one side of which is open, and a lower case accommodating the first electrode, the separator, the second electrode, and a liquid electrolyte; and an upper cap coupled to one open side of the lower case, one of the first electrode and the second electrode positioned on the lower case side, and a bottom surface of the coin cell case forming the lower portion of the coin cell case. It may be the bottom surface of the case.

In the electrolyte-based coin cell according to an embodiment of the present invention, a spring and a spacer positioned between the upper cap and the other one of the first electrode and the second electrode may be further included.

In the electrolyte-based coin cell according to an embodiment of the present invention, the elastic polymer film includes a metal area formed on a surface of the film, and the metal area electrically connects between the one electrode positioned on the lower case side and the lower case. can be linked to

In the electrolyte-based coin cell according to an embodiment of the present invention, the metal region may include a metal strip extending from an edge of one surface of the elastic polymer membrane through a side surface of the membrane to an edge of the other surface of the elastic polymer membrane. .

In the electrolyte-based coin cell according to an embodiment of the present invention, two or more of the metal strips may be spaced apart from each other.

In the electrolyte-based coin cell according to an embodiment of the present invention, part or all of the surface of the elastic polymer film may be plasma-treated.

In the electrolyte-based coin cell according to an embodiment of the present invention, the elastic polymer film may be a siloxane-based polymer or a fluorine-based polymer.

In the electrolyte-based coin cell according to an embodiment of the present invention, the thickness of the elastic polymer film may be 50 to 250 μm.

In the electrolyte-based coin cell according to an embodiment of the present invention, the elastic polymer film may be positioned in contact with each of the lower case and the one electrode.

In the coin cell according to the present invention, the pressure is uniformized by the elastic polymer layer located inside the coin cell, which is a secondary battery, and a uniform pressure can be applied to the electrode structure including the electrode, which is generated during the charging / discharging process of the coin cell. As the constant pressure is maintained by directly accepting the contraction/expansion due to the volume change of the electrodes, it is possible to prevent performance deviation between coin cells caused by uneven pressure, and to reduce process variables that inevitably occur during coin cell manufacturing. Reliability can be improved as a uniform pressure is formed even in the event of a change, etc., and it can be manufactured through a conventionally established process without a high degree of change in the conventional coin cell manufacturing process, and non-uniform dendrite formation caused by uneven pressure can be suppressed. There are advantages to doing so.

1 is an exploded perspective view of a coin cell according to an embodiment of the present invention.
FIG. 2 is a perspective view illustrating an elastic polymer film 400 having a metal region 410 formed thereon.
3 is a diagram illustrating a pressure distribution inside a cell of a reference coin cell manufactured in Comparative Example.
4 is a diagram showing the pressure distribution inside the cell of the coin cell manufactured in Example.

Hereinafter, the lithium metal-based coin cell of the present invention will be described in detail with reference to the accompanying drawings. The drawings introduced below are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art. Therefore, the present invention may be embodied in other forms without being limited to the drawings presented below, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. At this time, unless there is another definition in the technical terms and scientific terms used, they have meanings commonly understood by those of ordinary skill in the art to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings Descriptions of well-known functions and configurations that may be unnecessarily obscure are omitted.

Also, the singular forms used in the specification and appended claims may be intended to include the plural forms as well, unless the context dictates otherwise.

In this specification and the appended claims, terms such as first and second are used for the purpose of distinguishing one element from another, not in a limiting sense.

In this specification and the appended claims, terms such as include or have mean that features or elements described in the specification exist, and unless specifically limited, one or more other features or elements may be added. It does not preclude the possibility that it will happen.

In this specification and the appended claims, when a part of a film (layer), region, component, etc. is on or on another part, not only when it is in contact with and directly on top of another part, but also when another film ( layer), other areas, other components, etc. are interposed.

In a coin cell type lithium secondary battery using lithium metal as an anode, the coin cell assembly process involves permanent deformation of the metal exterior material (case), and this deformation of the metal exterior material is a major factor in the uneven distribution of internal pressure in the coin cell. It was confirmed that it works. In addition, since the pressure auxiliary parts such as springs and spacers provided in conventional coin cells are all made of rigid materials, they cannot accommodate such uneven internal pressure, and rather deepen the shape deformation of the metal exterior material, resulting in internal pressure unevenness. This further aggravated the problem was recognized. In addition, along with the deformation of the metal casing and the limitations of the rigid material-based pressure assisting part, the positive/cathode misalignment and the pressure assisting part misalignment also cause internal pressure nonuniformity, and this pressure nonuniformity causes coin cell performance (electrochemical characteristics) was noted. In addition, it was confirmed that when a liquid electrolyte (electrolyte solution) is used, non-uniform formation of lithium dendrites is amplified by such pressure non-uniformity and acts as a main cause of deterioration. Accordingly, the present applicant recognizes that, above all, the pressure unevenness inside the coin cell must be resolved in order to secure the reproducibility and reliability of a coin cell type lithium secondary battery based on a liquid electrolyte and adopting lithium metal as a negative electrode, and conducting various experiments for a long period of time. As a result, when a pressure equalization member capable of equalizing the pressure applied to the battery components inside the coin cell is introduced, it is confirmed that the reproducibility and reliability of the coin cell are significantly improved through this to complete the present invention. reached

Therefore, the coin cell according to the present invention is an electrolyte-based coin cell in which a lithium metal electrode, a counter electrode of the lithium metal electrode, a separator interposed between the lithium metal electrode and the counter electrode, and an electrolyte are internally accommodated, and the bottom surface of the coin cell case and an elastic polymer film positioned between a lithium metal electrode and an electrode positioned on a bottom surface side of a large electrode. Here, the elastic polymer membrane may also be referred to as a pressure equalization film.

As described above, the coin cell according to the present invention is a coin cell type lithium metal secondary battery using lithium metal as one electrode and an electrolyte based coin cell type lithium metal secondary battery using a liquid electrolyte.

The coin cell according to the present invention is equipped with an elastic polymer film inside the coin cell that equalizes uneven pressure by its own elasticity, so that the coin cell case where the largest change (deformation) occurs during the coin cell assembly process. By locating the elastic polymer membrane on the bottom side, it is possible to absorb uneven pressure caused by uneven deformation of the case, preventing uneven pressure from being applied to battery components inside the cell, and aligning electrodes or pressure inside the coin cell. Pressure unevenness caused by micro-distortions in the alignment of auxiliary parts can be resolved. In addition, as the elastic polymer film is located inside the cell, the volume change generated from the electrode during charging and discharging of the cell is also absorbed by the elastic polymer film, Since a constant and uniform pressure can be formed inside the cell regardless of substantially, the reliability of the coin cell can be greatly increased, the performance deviation between coin cells can be suppressed, and according to the process margin inevitable in the assembly process It is possible to eliminate even the pressure non-uniformity generated inside the cell caused by the fine distortion, thereby improving productivity.

In one embodiment, the coin cell includes a first electrode that is a lithium metal electrode, a second electrode that is a counter electrode provided with an active material layer into which lithium ions are reversibly intercalated, a separator interposed between the first electrode and the second electrode, a lower case having one side open and accommodating the first electrode, the separator, the second electrode, and the liquid electrolyte; And it may include an upper cap coupled to one open side of the lower case, one of the first electrode and the second electrode may be located on the lower case side, and the bottom surface of the coin cell case is the bottom of the lower case. It can be cotton.

In addition, the coin cell may further include a spring and a spacer positioned between the other one of the first electrode and the second electrode (an electrode positioned on the upper cap side) and the upper cap, and if necessary, a gasket, etc., common in conventional coin cells. Members used as may be further provided.

1 is an exploded perspective view of a coin cell according to an embodiment of the present invention.

As in the example shown in FIG. 1 , a coin cell may include a lower case 110 that is a coin cell case and an upper cap 120 . The lower case 110 and the upper cap 120 may each be made of a metal material commonly used as a case material in a conventional coin cell, and may be made of, for example, stainless steel. The lower case 110 may have an internal accommodation space formed by a side wall (first side wall) and a bottom surface, and may have a structure in which one side (top) is open, and the bottom surface may be circular. The upper cap 120 may also have a side wall (second side wall) and an upper surface, and when the upper cap 120 and the lower case 110 are assembled, they are combined while covering the lower case 110 to seal the inner accommodation space. can make it At this time, of course, the upper surface of the upper cap 120 may have a shape corresponding to the bottom surface of the lower case 110 .

An electrode assembly including the first electrode 220 , the separator 300 and the second electrode 210 and a liquid electrolyte (not shown) may be accommodated in the inner accommodation space. At this time, in FIG. 1, the first electrode 220 (corresponding to the negative electrode), which is a lithium metal electrode, is located on the side of the upper cap 120, and has an active material layer in which lithium ions are reversibly inserted and detached. The second electrode 210, which is a counter electrode, . ) The second electrode may be located on the upper surface side of.

In the inner accommodation space, the elastic polymer film 400 may be positioned between the bottom surface of the lower case 110 and the second electrode 210 . The elastic polymer film 400 absorbs and equalizes the uneven pressure formed inside the coin cell by its inherent elasticity, so that a uniform and constant pressure is applied to the battery components (electrode assembly and electrolyte) inside the coin cell.

Furthermore, when the elastic polymer film 400 is positioned between the bottom surface of the lower case 110 and the second electrode 210, the coin cell assembly (lower case) inevitably involves physical deformation of the metal case. and the upper cap), the battery assembly (including electrodes and separators) may be prevented from being physically deformed like the case by acting as a buffer against physical deformation of the case.

The second electrode 210 may include a current collector and an active material layer into which lithium ions are reversibly intercalated. The active material (cathode active material) may be any material capable of reversible desorption/intercalation of lithium ions, for example, LiMO ₂ (M is a transition metal selected from one or more than one of Co and Ni), Li _α Ni _x Co _y M _z O ₂ (1≤α≤1.2 real number, 0.2≤x≤0.9 real number, 0.01≤y≤0.5 real number, 0.01≤z≤0.5 real number, x + y + z = 1, M is Mg, Sr, At least one element selected from the group consisting of Ti, Zr, V, Nb, Ta, Mo, W, B, Al, Fe, Cr, Mn, and Ce), or Li ₄ Mn ₅ O lithium oxide of spinel structure represented by ₁₂ etc.; or a lithium phosphate-based material having an olivine structure represented by LiMPO ₄ (M is Fe, Co, Mn), or a mixture thereof, but is not limited thereto. As is known, the active material layer, if necessary, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, polyvinylpyrrolidone, polyacrylonitrile, polyvinylidene fluoride-trichlorethylene , polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethyl methacrylate, polyvinyl acetate, ethylene-co-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butylate, cellulose acetate Propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile styrene butadiene copolymer, polyimide, polyvinyl alcohol, Organic binders such as carboxymethylcellulose, starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, etc., and/or carbon black, acetylene black, Ketjen It goes without saying that a conductive material such as black, channel black, panes black, lamp black, thermal black, carbon fiber, metal fiber, carbon nanotube or graphene may be further contained.

The first electrode 220 may be a lithium metal film, and specifically, may be a collector-lithium metal multilayer film. In this case, the thickness of the lithium metal film may be appropriately adjusted to a level of several tens of micrometers to several hundreds of micrometers in consideration of the coin cell capacity.

The current collector of the first electrode 220 or the current collector of the second electrode 210 may be made of a material that has excellent conductivity and is chemically stable during charging and discharging of the battery. Specifically, the current collector may be a conductive material such as graphite, graphene, titanium, copper, platinum, aluminum, nickel, silver, gold, aluminum, or carbon nanotubes. However, from the viewpoint of strong bonding with the plasma-treated elastic polymer film described later, it is preferable that the current collector of the first electrode 220 or the second electrode 210 be a metal current collector. Examples of the metal current collector include titanium, copper, platinum, aluminum, nickel, silver, gold, and aluminum, but are not limited thereto.

As the separator, an insulating microporous film capable of electrically shorting two electrodes while conducting lithium ions is sufficient. Examples of the separator include polyethylene, polypropylene, polybutylene, polypentene, polymethylpentene, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyethersulfone, and polyphenylene. oxide, polyphenylene sulfide, polyethylene naphthalene, polyvinylidene fluoride, polyvinylidene fluoride hexafluoropropylene, polymethyl methacrylate, polystyrene, polyvinylacetate, polyacrylonitrile, polyethylene oxide and their airborne Any one or more porous films selected from composites, etc. may be mentioned, but is not limited thereto.

The modulus of elasticity of the elastic polymer membrane 400 may be in the range of 0.5 to 5 MPa, preferably in the range of 0.8 to 3 MPa. The modulus of elasticity of the elastic polymer film absorbs the pressure applied by the physical deformation of the metal material to protect the electrode assembly from deformation, and to equalize the uneven pressure caused by misalignment of internal members such as electrodes or pressure auxiliary parts. It is advantageous because it is possible to minimize the pressure drop within the cell by the elastic polymer membrane 400.

The elastic polymer film 400 may cover part or all of the bottom surface of the lower case 110, and advantageously, the elastic polymer film 400 has a shape and size corresponding to the bottom surface of the lower case 110. , The bottom surface of the lower case 110 may be completely covered by the elastic polymer film 400 . The thickness of the elastic polymer film 400 may be 50 to 250 μm. This thickness allows the elasticity inherent in the elastic polymer to be isotropically and stably expressed, and the surface of the elastic polymer film on the electrode side to be substantially flat while absorbing deformation of the case. It is a thickness that can maintain , and a thickness that can minimize the volume increase of the coin cell.

As the spherical material of the elastic polymer film 400, any polymer material that does not react chemically or electrochemically with the electrolyte, does not affect the charge/discharge reaction of the cell, and satisfies the above-mentioned modulus of elasticity is sufficient. However, the elastic polymer membrane is made of a siloxane-based polymer (siloxane-based rubber) or It may be a fluorine-based polymer (fluorine-based rubber). Examples of fluorine-based polymers include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, and tetrafluoroethylene- chlorotrifluoroethylene copolymers, ethylene-chlorotrifluoroethylene resins, or mixtures thereof or copolymers thereof, but are not necessarily limited thereto. Examples of siloxane-based polymers include polydimethylsiloxane, polydiethylsiloxane, polymethylethylsiloxane, polydimethylsiloxane-co-diethylsiloxane, polydimethylsiloxane-co-ethylmethylsiloxane, polymethylhydroxysiloxane, and polymethylpropyl. Siloxane, polymethylbutylsiloxane, polydiphenylsiloxane, polymethylphenylsiloxane, polyethylphenylsiloxane, poly(dimethylsiloxane-co-diphenylsiloxane), or mixtures thereof or copolymers thereof, etc. may be mentioned, but not necessarily limited thereto. it is not going to be

In an advantageous example, the elastomeric membrane 400 may include a metal region formed on the membrane surface. This is due to the insulating properties of the elastic polymer, and the second electrode 210 in contact with the elastic polymer film 400 can be electrically conducted with the lower case 110 through the metal region of the elastic polymer film 400 .

FIG. 2 is a perspective view illustrating an elastic polymer film 400 having a metal region 410 formed thereon. 2, the metal region 410 is a conductive region formed on the surface of the elastic polymer membrane 400, and the metal region 410 extends from the edge of one side of the elastic polymer membrane 400 to the side of the membrane. Metal strips 411 and 412 extending to the edge of the other side of the elastic polymer membrane 400 may be included. Such a metal strip shape positioned across the two opposing surfaces of the elastic polymer film 400 through the side surface (surface in the thickness direction) does not adversely affect the pressure equalization action of the elastic polymer film 400, while the elastic polymer film 400 It is advantageous because it enables stable conduction between the contacting electrode and the lower case 110 . In this case, for stable electrical connection, the metal region 410 may include a plurality of metal strips 411 and 412 spaced apart from each other. In the metal area 410 or in the non-metal area where the metal strip is not located, the elasticity of the polymer is substantially the same as each other, so that the pressure equalization action is not hindered by the metal area 410, and the battery is electrically connected by the metal strip. In order to suppress an increase in internal resistance, the length l of the metal strip may be 5t0 to 50t0, specifically 10t0 to 30t0, based on the thickness t0 of the elastic polymer film, and the width w of the metal strip is the same. It may be 1t0 to 20t0, specifically 2t0 to 10t0 based on the thickness (t0) of the elastic polymer film, but is not necessarily limited thereto. Also, unlike the example of FIG. 2 , two to five metal strips spaced apart from each other in the elastic polymer film 400 can form one metal region, and two or more metal regions are located at different positions. Of course, it can be formed. For example, two to six metal regions may be formed at different positions where an angle between the center of the elastic polymer film 400 and a virtual line extending each metal region is 180° to 60°.

In one embodiment, part or all of the surface of the elastic polymer film 400 may be plasma treated. When the surface of the elastic polymer film, particularly the siloxane-based polymer film, is treated with plasma, various polar functional groups are introduced to the surface of the film and the surface is chemically modified. / Alternatively, the binding force between the elastic polymer film 400 and the bottom surface of the lower case 110 may be increased, and particularly when binding by compression, the binding force may be greatly increased. When the binding force between the elastic polymer membrane 400 and the electrode and/or the bottom surface is strengthened, it is advantageous because the degree of pressure equalization is improved by the elastic polymer membrane 400, and furthermore, the pressure inside the coin cell by the elastic polymer membrane 400 It is advantageous because it can suppress the decrease in (compression force).

As a practical example, the electrode 210-side surface, the bottom-side surface, or both surfaces of the elastic polymer film 400 may be plasma-treated, and all or part of the treated surface (based on one surface) may be plasma-treated. It can be. When a partial area of one surface is treated with plasma, one surface of the elastic polymer film 400 may include a plasma-treated bonding area and a non-plasma-treated unbonded area. The binding area is located in the center of the elastic polymer membrane 400 and the non-binding area surrounds the binding area so that the degree of pressure uniformity can be further improved by binding (to reduce the deviation of applied pressure depending on the position). It is good that the concentric circle structure of When the radius of the elastic polymer membrane 400 is R, the radius of the binding region may be 0.2 to 0.6R, but is not necessarily limited thereto. During plasma treatment of the elastic polymer film, the plasma source may be air, oxygen, nitrogen, etc., the plasma may be corona plasma, and the plasma treatment may be performed in a range of 1 to 3 kV, but is not necessarily limited thereto.

A liquid electrolyte commonly used in a lithium metal battery is sufficient as the electrolyte solution accommodated in the internal accommodating space together with the elastic polymer membrane and the electrode assembly (first electrode, separator, and second electrode). For example, the liquid electrolyte may contain a solvent and a lithium salt (electrolyte salt). The solvent of the liquid electrolyte may be one or more non-aqueous solvents selected from carbonate-based, ester-based, ether-based, ketone-based, amine-based and phosphine-based solvents, and substantially, carbonate-based solvents, ether-based solvents or It may be a mixed solvent. At this time, an ether-based solvent or a mixed solvent of a carbonate-based solvent and an ether-based solvent is advantageous for inhibiting the formation of lithium dendrites. Representative carbonate-based solvents include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinyl Ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, dipropyl carbonate, dibutyl carbonate, ethyl methyl carbonate, 2,2,2-trifluoro ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 2,2,2-trifluoroethyl propyl carbonate, methyl isopropyl carbonate, or mixed solvents thereof. The ether-based solvent may be a non-cyclic ether-based solvent, a cyclic ether-based solvent, or a mixture thereof. Practical examples of the cyclic ether-based solvent include 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-di 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane -1,3-dioxolane, tetrahydrofuran, 2-methyl tetrahydrofuran, 2,5-dimethyl tetrahydrofuran, 2,5-dimethyl 2,5-dimethoxy tetrahydrofuran, 2-ethoxy tetrahydrofuran, 2-methoxy-1,3-dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane (2-methoxy-1,3-dioxolane), 2-ethyl-2-methyl-1,3-dioxolane (2-ethyl-2-methyl-1, 3-dioxolane), tetrahydropyran, 1,4-dioxane (1,4-dioxane), 1,2-dimethoxy benzene, 1,3-dimethoxy benzene ( 1,3-dimethoxy benzene), 1,4-dimethoxy benzene, isosorbide dimethyl ether, or a mixed solvent thereof, and the like. As an acyclic ether solvent, 1,2 -Dimethoxyethane (1,2-dimethoxyethane), 1,2-diethoxyethane (1,2-diethoxyethane), 1,2-dibutoxyethane (1,2-dibuthoxyethane), diethylene glycol dimethyl ether dimethyl ether), diethylene glycol Diethylene glycol diethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether (tetraethylene glycol diethyl ether) or a mixed solvent thereof, but the present invention is not limited by the specific solvent material of the electrolyte.

Examples of lithium salts that are electrolyte salts include LiSCN, LiBr, LiI, LiNO ₃ , LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiClO ₄ , LiC(CF ₃ SO ₂ ) ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(SFO ₂ ) ₂ , and one or more compounds selected from LiN(CF ₃ CF ₂ SO ₂ ) ₂ , , but is not limited thereto. The concentration of the electrolyte salt in the liquid electrolyte may be 0.5 to 5M level, specifically 1.5 to 4M level, but is not limited thereto.

Optionally, if necessary, the electrolyte is SEI (Solid Electrolyte Interface) such as halogen-substituted or unsubstituted cyclic carbonate-based compounds, nitrile-based compounds, phosphate-based compounds, borate-based compounds, sulfate-based compounds, sultone-based compounds, lithium salt-based compounds, etc. Of course, known additives commonly used in conventional liquid electrolytes, such as additives for film formation, may be further included.

In one embodiment, the coin cell may further include various members commonly used in coin cells, along with an electrolyte solution, an electrode assembly, and an elastic polymer membrane. For example, as in the example shown in FIG. 1 , the coin cell includes a spring 600 (wave spring) and a spacer disk 500 located between the electrode 220 located on the upper cap side and the upper cap 120. can include more. The metal spacer 500 reduces internal resistance and enables uniform transmission of pressure applied through the spring 600 . As in the example shown in FIG. 1 , the spring 600 suffices to have a shape in which bends or wrinkles are formed along the ring-shaped circumference to exert elastic force in the height direction of the coin cell. Pressure is applied to the spacer 500 by the elasticity of the spring 600, and the spacer 500 and the electrode 220 can be in close contact, and the pressure transmitted through the spacer 500 causes the two electrodes 210 and 220 to It is possible to maintain a state in which they are in close contact with each other. The spacer and the spring may be made of stainless steel similarly to the coin cell case, but are not limited thereto. In addition to the above-described spacer and spring, other components known to be used together with the electrode assembly may be further included to assemble the coin cell or improve characteristics. As an example of these other parts, as shown in FIG. 1, the gap between the side walls of the upper cap 120 and the lower case 110 is completely blocked to accommodate the battery when assembling using a crimper or the like. A gasket 700 that helps to completely seal the space may be used.

As is known, a coin cell can be specified by numerically listing the thickness and diameter when all components are assembled. For example, when the diameter is 20 mm and the thickness is 3.2 mm, it is collectively referred to as CR2032 and standardized. A coin cell according to one embodiment of the present invention may be CR2032, CR2025, or CR2016, but is not necessarily limited to these standards.

(Example)

LiNi _0.6 Mn _0.2 Co _0.2 O ₂ (NMC622) was used as the positive electrode active material, PVDF (Polyvinylidene fluoride) was used as the binder, and Super P was used as the conductive material. After preparing a slurry by mixing it with phosphorus NMP (N-methyl-2-pyrrolidone), it was uniformly coated on an Al foil (15 μm) as a current collector using a doctor blade. The coated electrode was dried at 160 °C for 12 hours, the electrode loading amount was 22.6 mg/cm ² and the capacity per area was unified to about 3.8 mAh/cm ² , and the electrode dried through a roll press to match the electrode density of 3.0 g/cm ³ was rolled. The positive electrode manufactured by rolling was vacuum dried, cut using a punch having a diameter of 12 mm, and used as an electrode (anode) for a coin cell. However, in the case of varying the anode/cathode area ratio, the size of the electrode was adjusted using dies of various sizes instead of a 12 mm diameter punching die.

To prepare an elastomeric membrane, a ^{base material of SYLGARD TM 184} (The Dow Chemical Co., Ltd, US) and a crosslinking agent were mixed in a weight ratio of 10:1. Then, it was cast on a CPP (Cast Polypropylene) film with a doctor blade and cured at 60 ° C for 2 hours to produce a PDMS (Polydimethylsiloxane) film with a thickness of 220 μm. Then, similar to FIG. 2, a metal region was formed by attaching a metal strip having a length of 5 mm and a width of 1 mm to the PDMS film. At this time, a metal region was formed on the manufactured PDMS film itself, or the metal region was formed after plasma processing the entire surface of the PMDS film.

Among ether-based electrolytes, HCE (High Concentration Electrolyte) electrolyte was used by dissolving 4.0M LiFSI (Lithium bis(fluorosulfonyl)imide, ENCHEM, Korea) in DME (1,2-Dimetoxyethane, ENCHEM, Korea), and HCE TTE (1,1,2,2,-Tetrafluoroethyl-2,2,3,3,-Tetrafluoropropyl Ether, ENCHEM, Korea) was added to the electrolyte at a concentration of 1.7 M and used as a Localized High Concentration Electrolyte (LHCE) electrolyte.

To manufacture the coin cell, a CR2032 standard coin cell kit (Hoshen Co., Ltd, Japan) was used, and aluminum foil was placed on the bottom to prevent corrosion and used for cell assembly. A lithium metal film (China Energy Lithium Co., Ltd.) was used as a negative electrode together with a positive electrode having a capacity per area of 3.8 mAh/cm ² prepared previously. The thickness of the lithium metal film was 50 μm, and the copper-coated film was punched out and used as a coin cell negative electrode. The capacity of the negative electrode was about 10 mAh/cm ² , and the ratio of capacities per unit area between the negative electrode and the positive electrode (N/P ratio) was 2.63. As a separator, a PE (Polyethylene) separator (Toray Co., Ltd, Japan) having a thickness of 20 μm was used. The electrolyte-to-capacity ratio (E/C Ratio) was determined according to the electrolyte amount at 4.0 g/Ah, which is close to commercial conditions.

(Comparative example)

A coin cell was manufactured in the same manner as in Example 1, except that the PDMS film was not used.

Electrochemical property evaluation

The performance evaluation of the fabricated coin cell was performed using a charge/discharger (WonATech's WBCS3000), and the charge/discharge evaluation was conducted in the voltage range of 2.8 to 4.3 V (vs. Li/Li ⁺ ) at 25 °C. All coin cells are initially charged and discharged twice under C/10 (1C = 3.8mA/cm ² ) rate and constant current (CC) conditions, and after going through the formation process, CC charging at C/5 rate and 4.3 V constant voltage (CV) charge, discharge rate C / 3 CC was carried out a cycle test. The end condition of CV charging was set when the charging current decreased below C/50.

Cell internal pressure analysis

To measure the size and distribution of the pressure inside the coin cell, Prescale (Fujifilm Co., Ltd. Japan) pressure sensitive paper was used. Since the range of measurable pressure differs depending on the product type, LLW (0.5-2.5 MPa), LLLW (0.2-0.6 MPa), and 4LW (0.05-0.2 MPa) were selected as suitable models for the pressure level. Then, a Matlab algorithm was implemented to quantify and visualize the pressure measured with pressure sensitive paper. The temperature and humidity conditions were set at 25° C. and 50%, respectively, and a standard pressure chart and a standard magenta color chart provided by Fujifilm were used for each pressure-sensitive paper model. The color density and pressure values of the magenta standard color chart were approximated, and additionally, the graypic value, which is the pixel value when the image was converted to black and white and saved in Matlab, and the color density were approximated. Through this, the decompression result was scanned and the pressure value of each pixel was calculated through the image converted to black and white. In addition, in order to analyze the pressure in a wide range using pressure strips of various models, 10 × 10 pixels were set as one grid, the average of the pressure values of each pixel was set as the pressure value of the grid, and the grid at the same location of each pressure strip was merged to enable visual and quantitative analysis of a wide range of pressure analysis results that could not be measured with a single pressure strip.

FIG. 3 is a diagram showing pressure distribution inside a cell of a reference coin cell manufactured in Comparative Example, and FIG. 4 is a diagram showing pressure distribution inside a cell of a coin cell manufactured in Example.

As shown in the internal pressure distribution shown in FIGS. 3 and 4, in the case of the reference coin cell (coin cell of the conventional structure) manufactured through the comparative example, uniform pressure within the cell using pressure auxiliary parts such as springs and spacers Even if the application is induced, it can be seen that there is a limit to pressure equalization, and it can be seen that a very large pressure deviation occurs due to fine alignment misalignment between parts. On the other hand, in the case of the coin cell manufactured through the embodiment, except that the elastic polymer film is additionally introduced to the bottom surface, it is manufactured through substantially the same process as the comparative example, despite the occurrence of fine alignment misalignment similar to that of the reference coin cell. It can be seen that an extremely uniform pressure is applied within the cell. Specifically, the average pressure and standard deviation of the pressure of the reference coin cell were 0.69 MPa and 0.43, and in the case of the coin cell manufactured through the example, the average pressure and standard deviation of the pressure were 0.33 MPa and 0.16, indicating that the pressure uniformity was markedly increased. In addition, in the case of the coin cell having the plasma-treated elastic polymer membrane in the example, the average pressure and the standard deviation of the pressure were 0.36 MPa and 0.14, indicating that the pressure drop inside the cell was suppressed and the pressure distribution within the cell became more uniform. can

In order to confirm the reliability and reproducibility improvement by pressure equalization, the coin cells manufactured in Examples and Comparative Examples were charged and discharged 120 times under the preceding electrochemical property evaluation conditions, and the capacity retention rate of each cell based on 120 cycles was measured. The standard deviation between dose retention rates was calculated. In the case of the coin cell(s) manufactured in Example, the standard deviation of the capacity retention rate between coin cells at 120 cycles was 1.76, and the coin cell(s) manufactured in Example showed substantially the same charge/discharge cycle characteristics. In the case of the coin cell(s) manufactured in the example, the standard deviation of the capacity retention rate between coin cells based on 120 cycles was 19.11, and the difference in electrical characteristics between coin cells was very large. % was confirmed. The very large deviation in electrochemical performance of the reference coin cell is mainly due to the non-uniform lithium dendrite formation caused by the non-uniform internal pressure distribution. It can be seen that dendrite formation is prevented and there is little variation in electrochemical performance between coin cells.

As described above, the present invention has been described by specific details and limited embodiments and drawings, but this is only provided to help a more general understanding of the present invention, the present invention is not limited to the above embodiments, and the present invention Those skilled in the art can make various modifications and variations from these descriptions.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and it will be said that not only the claims to be described later, but also all modifications equivalent or equivalent to these claims belong to the scope of the present invention. .

Claims (10)

An electrolyte-based coin cell in which a lithium metal electrode, a counter electrode of the lithium metal electrode, a separator interposed between the lithium metal electrode and the counter electrode, and an electrolyte are accommodated inside, and the bottom surface of the coin cell case and the bottom of the lithium metal electrode and the counter electrode An electrolyte-based coin cell containing an elastic polymer membrane positioned between electrodes located on the side of a surface. According to claim 2,
The coin cell
A first electrode that is a lithium metal electrode;
A second electrode that is a counter electrode provided with an active material layer into which lithium ions are reversibly intercalated and deintercalated;
A separator interposed between the first electrode and the second electrode;
a lower case having one side open and accommodating the first electrode, the separator, the second electrode, and the liquid electrolyte; and
And an upper cap coupled to the open side of the lower case,
One of the first electrode and the second electrode is positioned on the lower case side, and the bottom surface of the coin cell case is a bottom surface of the lower case coin cell. According to claim 2,
The coin cell further comprises a spring and a spacer positioned between the upper cap and the other one of the first electrode and the second electrode. According to claim 2,
The elastic polymer film includes a metal region formed on a surface of the membrane, and the metal region electrically connects the one electrode positioned at the lower case side to the lower case. According to claim 4,
wherein the metal region comprises a metal strip extending from an edge of one side of the elastomeric membrane through a side of the membrane to an edge of the other side of the elastomeric membrane. According to claim 5,
A coin cell in which two or more of the metal strips are spaced apart. According to claim 1,
A coin cell in which part or all of the surface of the elastic polymer film is plasma-treated. According to claim 1,
The elastic polymer film is a coin cell of a siloxane-based polymer or a fluorine-based polymer. According to claim 1,
The coin cell wherein the thickness of the elastic polymer membrane is 50 to 250 μm. According to claim 2,
The elastic polymer film is positioned in contact with each of the lower case and the one electrode.

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