KR102663587B1 - Bipolar lithium secondary battery - Google Patents

Abstract

The present invention relates to a bipolar lithium secondary battery, and more specifically, to a bipolar lithium secondary battery including a bipolar unit including a current collector with positive and negative electrodes formed on both sides, respectively, and a polymer film attached to the edge of the current collector. Electrolyte solutions adjacent to electrodes showing different polarities are separated and mutual movement of the separated electrolytes is prevented, thereby preventing self-discharge and generation of bypass current.

Description

Bipolar lithium secondary battery {BIPOLAR LITHIUM SECONDARY BATTERY}

The present invention relates to a bipolar lithium secondary battery including a bipolar unit in which electrode layers with different polarities are formed on both sides of a current collector.

Secondary batteries are batteries that can be charged and discharged, unlike primary batteries that cannot be recharged. Low-capacity secondary batteries are used in small, portable electronic devices such as mobile phones, laptops, or camcorders, and high-capacity secondary batteries are widely used as a power source for driving motors in hybrid vehicles.

Recently, high-capacity secondary batteries with high energy density and high output using non-aqueous electrolytes have been developed. The high-capacity secondary battery with high energy density and high output is constructed by connecting a plurality of secondary batteries in series so that it can be used to drive a motor of a device that requires high power, such as an electric vehicle.

Such secondary batteries may include general monopolar electrodes in which active materials with the same polarity are applied to both sides of a current collector, or bipolar electrodes in which active materials with different polarities are applied to both sides of a current collector.

A secondary battery using a general monopolar electrode includes a structure in which a connection part connecting electrodes is formed, but this structure causes a problem of lowering the output due to the electrical resistance of the connection part. A bipolar electrode is an electrode that can be used by stacking electrodes without such connections, and connection resistance can be minimized.

Meanwhile, it is very important to seal a bipolar secondary battery including bipolar electrodes to prevent electrolyte from leaking between the stacked bipolar electrodes, and at the same time, it is necessary to reduce the thickness of the bipolar secondary battery.

Generally, gaskets are used for sealing to prevent electrolyte leakage, but it is difficult to manufacture gaskets with a thickness of 1 mm or less. If the thickness of the gasket is too large, the empty space between the bipolar electrodes increases, resulting in a decrease in output compared to the volume. there is a problem.

In addition, when electrolyte solutions adjacent to electrodes with different polarities move and mix in the bipolar electrode, self-discharge and lateral current may occur, and there is a need to develop technology that can prevent such problems.

Japanese Patent Publication No. 2005-190713

Accordingly, the present inventors found that in a battery including a bipolar unit in which an anode and a cathode are stacked on both sides of one current collector, when a polymer film is attached to the edge of the current collector, the polymer film causes the anode and the cathode to It was confirmed that it was possible to prevent adjacent electrolytes from moving and mixing, thus preventing self-discharge and generation of right current.

Therefore, the purpose of the present invention is to provide a bipolar lithium secondary battery that prevents self-discharge and generation of right current.

In order to achieve the above object, the present invention,

house collector;

A polymer film attached to surround the edge of the current collector;

an electrode layer including an anode and a cathode respectively formed on both sides of the current collector;

first and second separators formed on the anode and cathode, respectively; and

Includes an electrolyte solution contained between the first and second separators,

A bipolar lithium secondary battery is provided in which the electrolyte solution contained between the first and second separators is separated by the polymer film.

According to the present invention, in a lithium secondary battery including a bipolar unit in which a positive electrode and a negative electrode are formed on both sides of one current collector, the electrolyte solution adjacent to the positive electrode and the negative electrode, respectively, is separated by a polymer film attached to the edge of the current collector. This prevents movement and mixing between separated electrolytes, thereby preventing self-discharge and generation of right current.

In addition, in the lithium secondary battery according to the present invention, unit cells including a positive electrode and a negative electrode are connected in series within the battery through a current collector included in the bipolar unit, thereby reducing the weight and volume of auxiliary materials. Higher energy density can be secured.

1 is a schematic diagram showing a cross section of a bipolar lithium secondary battery according to an embodiment of the present invention.
Figure 2 is a schematic diagram showing a cross section of a lithium-sulfur secondary battery according to Comparative Example 1.
Figure 3 is a schematic diagram showing a cross section of a bipolar lithium-sulfur secondary battery according to Comparative Example 2.
Figure 4 is a graph measuring the discharge capacity of the lithium-sulfur secondary batteries manufactured in Comparative Example 1 and Comparative Example 2, respectively.
Figure 5 is a graph measuring the discharge capacity of the lithium-sulfur secondary batteries manufactured in Comparative Example 1 and Example 1, respectively.
Figure 6 is a photograph showing the cross-section of the negative electrode and positive electrode respectively formed on both sides of the current collector in the bipolar lithium-sulfur secondary battery of Example 1.

Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention.

The term "bipolar unit" used herein includes an electrode layer containing active materials having different polarities on both sides of one current collector. For example, the bipolar unit includes a current collector and both sides. It may include an anode and a cathode formed respectively.

The terms “anode” and “cathode” used in this specification may refer to a positive electrode active material layer and a negative electrode active material layer, respectively. Generally, the positive electrode includes a positive electrode current collector and a positive electrode active material layer, and the negative electrode includes a negative electrode current collector and a negative electrode active material layer. However, the “positive electrode” and “negative electrode” included in the bipolar unit according to the present invention are different from the current collector. This may mean a separately formed positive electrode active material layer and negative electrode active material layer.

The term “unit cell” used herein refers to a structure including an anode, a cathode, and a separator interposed between them.

The term “bipolar lithium secondary battery” used herein refers to a lithium secondary battery including at least one “bipolar unit” as defined above.

Bipolar lithium secondary battery

The present invention relates to a bipolar lithium secondary battery including a bipolar unit in which electrode layers containing active materials having different polarities are formed on both sides of one current collector.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

1 is a schematic diagram showing a cross section of a bipolar lithium secondary battery according to an embodiment of the present invention. The cross section may be a longitudinal cross section.

Referring to FIG. 1, the bipolar lithium secondary battery 1 includes a current collector 110 and a polymer film 120 formed on the edge of the current collector 110, and electrode layers of different polarities are placed on both sides of the current collector 110. That is, the anode 320 and the cathode 210 may be formed by stacking each other. In this way, a structure in which the anode 320 and the cathode 210, which are electrode layers of different polarities, are formed on both sides of one current collector 110 can be referred to as a bipolar unit (B/U). At this time, the current collector 110 may also be referred to as a current pathway.

In addition, a second separator 230, a positive electrode 220, and a positive electrode current collector 221 may be sequentially stacked on the negative electrode 210 formed on one side of the current collector 110, which is formed as a second unit cell 200. ).

In addition, the first separator 330, the negative electrode 310, and the negative electrode current collector 311 may be sequentially stacked on the positive electrode 320 formed on the other side of the current collector 110, which is formed into a first unit cell ( 300).

The bipolar lithium secondary battery 1 may have a second unit cell 200 and a first unit cell 300 connected in series inside the battery, and specifically may be connected in series through the current collector 110. You can.

Additionally, the bipolar lithium secondary battery 1 may contain an electrolyte solution 400 injected therein.

In addition, the cross-sectional size (area) of the separators 330 and 230 may be equal to the sum of the cross-sectional sizes of the current collector 110 and the polymer film 120, and the positive electrodes 220 and 320 and the negative electrode ( 210, 310) may be larger than the cross-sectional size. When the cross-sectional size of each component included in the bipolar lithium secondary battery 1 is defined as such, the electrolyte solution 400 contained between the separators 330 and 230 can be separated by the polymer film 120. .

Accordingly, the polymer film 120 attached in a form surrounding the edge of the current collector 110 separates the electrolyte solution contained between the separators 230 and 330 into the first electrolyte solution 420 and the second electrolyte solution 410. can be distinguished. Specifically, the first electrolyte 420 may be surrounded by a polymer film 120, an anode 320, and a first separator 330, and the second electrolyte 410 may be surrounded by a polymer film 120 and a cathode ( 210) and a second separator 230. At this time, the first electrolyte 420 refers to the electrolyte in contact with the anode 320 and can also be called the anode-side electrolyte, and the second electrolyte 410 refers to the electrolyte in contact with the cathode 210 and can be referred to as the anode-side electrolyte. It can also be called electrolyte.

The first electrolyte 420 and the second electrolyte 410 are separated by the polymer film 120 to prevent mutual movement, thereby preventing self-discharge and bypass current that may occur when these electrolytes are mixed. .

In the present invention, the polymer film may serve to prevent movement and mixing of electrolyte adjacent to the positive and negative electrodes formed on both sides of the current collector in the bipolar lithium secondary battery. Specifically, when the negative electrode is a lithium negative electrode containing lithium metal, lithium ions (Li ⁺ ) dissolved from the negative electrode into the electrolyte solution can be prevented from moving from the negative electrode to the positive electrode through the electrolyte solution. In addition, when the anode is an anode containing sulfur, polysulfide dissolved from the anode into the electrolyte solution can be prevented from moving from the anode to the cathode through the electrolyte solution.

In this way, the polymer film physically separates the electrolyte on the positive electrode and the electrolyte on the negative electrode, preventing the movement of lithium ions through the electrolyte. Therefore, it is not particularly limited as long as it is insoluble in the electrolyte and does not allow the electrolyte to pass through. .

For example, the polymer film may be a single-layer film including a non-porous membrane, or a laminated film in which a non-porous membrane and a porous membrane are stacked.

The non-porous membrane may have a porosity of 30% or less, 20% or less, or 10% or less. If the porosity of the non-porous membrane is greater than 30%, lithium ions can move smoothly and bypass current may occur. Additionally, in the case of a lithium-sulfur secondary battery in which sulfur is contained in the positive electrode, lithium poly sulfide (LiPS) may be eluted from the positive electrode and then flow into the negative electrode, causing a direct reaction between the positive electrode and the negative electrode included in the bipolar unit. Additionally, the porosity of the non-porous membrane may preferably be greater than 0%.

Expressing the porosity of the non-porous membrane in another way, it can be defined as Gurley Number, which is a measure of air permeability. For example, the Gurley Number of the non-porous membrane is 1,000 [s/100cc] or more, 2,000 [s/100cc] or more, 3,000 [s/100cc] or more, 4,000 [s/100cc] or more, 5,000 [s/100cc] or more. , 6,000 [s/100cc] or more, 7,000 [s/100cc] or more, 8,000 [s/100cc] or more, 9,000 [s/100cc] or more, or 10,000 [s/100cc] or more, and the upper limit of the Gurley Number is It may be less than 15,000 [s/100cc], but is not limited thereto. The Gurley Number means that the larger the number, the more difficult it is for the substance to pass through. If the Gurley Number is less than 1,000 [s/100cc], mutual movement between electrolytes separated by the non-porous membrane is possible, and bypass current and self-discharge may occur.

Additionally, the porous membrane is not particularly limited as long as it is a porous membrane commonly used as a separator for lithium secondary batteries.

For example, the porous membrane may have a porosity of more than 30% or less than 70%, specifically, more than 30%, more than 35%, more than 40%, or more than 45%, and less than 55%, less than 60%, or less than 65%. It may be less than or equal to 70%.

In addition, the non-porous membrane and the porous membrane can be distinguished by the prescribed porosity and/or Gurley number as described above. The material of the non-porous membrane and the porous membrane may be the same or different, and may include one or more selected from the group consisting of polyolefin, cellulose, and fluororesin. The polyolefin may include one or more selected from the group consisting of polyethylene, polypropylene, polybutylene, polypentene, polyhexene, and polyoctene.

Additionally, the polymer film can be applied to all types of bipolar lithium secondary batteries. Specifically, the polymer film serves to physically prevent the movement of lithium ions dissolved in the electrolyte solution, so compared to batteries in which lithium ions are inserted into the positive electrode active material (Lithiation or Delithiation, Li ⁺ Insertion or Intercalation), lithium Self-discharge and bypass current can be prevented more efficiently in conversion type secondary batteries, where a reaction occurs when ions are dissolved into the electrolyte. An example of this conversion type secondary battery is a lithium-sulfur secondary battery.

In the present invention, the positive electrode includes a positive electrode active material; bookbinder; and a conductive material; and a positive electrode active material layer containing a conductive material.

The positive electrode active material may include sulfur. Specifically, the sulfur may be selected from the group consisting of elemental sulfur (S8), sulfur-based compounds, and sulfur-carbon complexes. Specifically, the sulfur-based compound may be Li ₂ Sn (n≥1), an organic sulfur compound, or a carbon-sulfur polymer ((C ₂ S _x ) _n : x=2.5∼50, n≥2).

In general, a battery containing sulfur in the positive electrode may be a lithium-sulfur secondary battery, and therefore, the bipolar lithium secondary battery according to the present invention may be a bipolar lithium-sulfur secondary battery.

The positive electrode active material may be included in an amount of 60 to 95% by weight based on the total weight of the positive electrode active material layer. Specifically, the content of the positive electrode active material may be 60% by weight or more, 65% by weight or more, or 70% by weight or more, and 85% by weight. % or less, 90% by weight or less, or 95% by weight or less. If the content of the positive electrode active material is less than the above range, battery performance may deteriorate, and if it exceeds the above range, the content of the conductive material or binder other than the positive electrode active material may be relatively reduced, thereby reducing characteristics such as conductivity or durability.

In addition, the binder is SBR (Styrene-Butadiene Rubber)/CMC (Carboxymethyl Cellulose), poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, cross-linked polyethylene oxide, Polyvinyl ether, poly(methyl methacrylate), polyvinylidene fluoride, copolymer of polyhexafluoropropylene and polyvinylidene fluoride, poly(ethylacrylate), polytetrafluoroethylene, polyvinyl chloride, Polyacrylonitrile, polyvinylpyridine, polystyrene, polyacrylic acid, their derivatives, blends, copolymers, etc. can be used.

In addition, the content of the binder may be 1% by weight to 20% by weight based on the total weight of the positive electrode active material layer, and specifically may be 1% by weight or more, 3% by weight or more, or 5% by weight or more, and 15% by weight or less. , may be 18% by weight or less or 20% by weight or less. If it is below the above range, the binding force between the positive electrode active materials or between the positive active material and the current collector may be greatly improved, the problem of deterioration in capacity characteristics may occur, and the interaction between the polysulfide and the specific functional group of the polymer chain used as a binder may be weakened, resulting in polysulfide may be eluted. If it exceeds the above range, battery capacity may decrease.

In addition, the conductive material is not particularly limited, but includes, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black (super-p), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and Denka black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; It may be a conductive material such as polyphenylene derivative. The conductive material may typically be included in an amount of 0.05% to 10% by weight based on the total weight of the positive electrode active material layer. Specifically, the content of the conductive material may be 0.05% by weight or more, 1% by weight or more, 3% by weight or more, or 5% by weight or more, and may be 8% by weight or less, 9% by weight or less, or 10% by weight or less.

In addition, the positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or on the surface of aluminum or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc. can be used. At this time, the positive electrode current collector can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics with fine irregularities formed on the surface to increase adhesion with the positive electrode active material.

In the present invention, the negative electrode may include lithium metal or lithium alloy.

Alternatively, the negative electrode may include a negative electrode active material, a binder, and a conductive material. The negative electrode active material includes a material that can reversibly intercalate or deintercalate lithium ions (Li ⁺ ), a material that can reversibly form a lithium-containing compound by reacting with lithium ions, lithium metal, or a lithium alloy. can be used. The material that can reversibly occlude or release lithium ions (Li ⁺ ) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The material that can react with the lithium ion (Li ⁺ ) to reversibly form a lithium-containing compound may be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy includes, for example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium ( It may be an alloy of a metal selected from the group consisting of Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

Additionally, the binder and the conductive material may be composed of materials used in the above-mentioned positive electrode.

In addition, the negative electrode current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc.

In the present invention, the separator is a physical separator that has the function of physically separating electrodes, and can be used without particular restrictions as long as it is used as a normal separator. In particular, it has low resistance to ion movement in the electrolyte solution and has excellent electrolyte moisturizing ability. desirable.

Additionally, the separator separates or insulates the positive and negative electrodes from each other and enables the transport of lithium ions between the positive and negative electrodes. This separator is porous with a porosity of 30 to 50% and may be made of a non-conductive or insulating material.

Specifically, porous polymer films, such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, can be used. and non-woven fabrics made of high melting point glass fibers, etc. can be used. Among these, a porous polymer film is preferably used.

If a polymer film is used for both the buffer layer and the separator, the electrolyte impregnation amount and ion conduction characteristics are reduced, and the effects of reducing overvoltage and improving capacity characteristics are minimal. Conversely, when all non-woven materials are used, mechanical rigidity cannot be secured, resulting in the problem of battery short circuit. However, if a film-type separator and a polymer non-woven buffer layer are used together, mechanical strength can be secured along with improved battery performance due to the adoption of the buffer layer.

According to a preferred embodiment of the present invention, an ethylene homopolymer (polyethylene) polymer film is used as a separator and a polyimide nonwoven fabric is used as a buffer layer. At this time, the polyethylene polymer film preferably has a thickness of 10 to 25 ㎛ and a porosity of 40 to 50%.

In the present invention, the electrolyte solution may be a non-aqueous electrolyte solution, and the electrolyte salt contained in the non-aqueous electrolyte solution is a lithium salt. The lithium salt may be used without limitation to those commonly used in electrolytes for lithium secondary batteries. For example, the lithium salt is LiFSI, LiPF ₆ , LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiPF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, and lithium 4-phenyl borate.

Organic solvents included in the above-mentioned non-aqueous electrolyte solution can be used without limitation those commonly used in electrolyte solutions for lithium secondary batteries, for example, ether, ester, amide, linear carbonate, cyclic carbonate, etc., individually or in combination of two or more types. Can be used by mixing. Among them, representative examples may include carbonate compounds that are cyclic carbonates, linear carbonates, or slurries thereof.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, There is a slurry selected from the group consisting of 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halogenates thereof, or two or more types thereof. Examples of these halides include, but are not limited to, fluoroethylene carbonate (FEC).

In addition, specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate. Among these, two or more types of slurries may be typically used, but are not limited thereto. In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high viscosity organic solvents and have a high dielectric constant, so they can better dissociate lithium salts in the electrolyte. These cyclic carbonates include dimethyl carbonate and diethyl carbonate. By mixing low-viscosity, low-dielectric constant linear carbonate in an appropriate ratio, an electrolyte solution with higher electrical conductivity can be made.

In addition, as the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a slurry of two or more of these may be used. , but is not limited to this.

In addition, esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, Any one or two or more slurries selected from the group consisting of σ-valerolactone and ε-caprolactone may be used, but the slurry is not limited thereto.

Injection of the non-aqueous electrolyte may be performed at an appropriate stage during the manufacturing process of the electrochemical device, depending on the manufacturing process and required physical properties of the final product. In other words, it can be applied before electrochemical device assembly or at the final stage of electrochemical device assembly.

The lithium secondary battery according to the present invention is capable of lamination (stack) and folding processes of separators and electrodes in addition to the general winding process.

Additionally, the shape of the battery case is not particularly limited, and may be of various shapes such as cylindrical, stacked, prismatic, pouch-shaped, or coin-shaped. The structures and manufacturing methods of these batteries are widely known in the field, so detailed descriptions are omitted.

In addition, the lithium secondary battery can be classified into various batteries, such as lithium-sulfur battery, lithium-air battery, lithium-oxide battery, and lithium all-solid-state battery, depending on the anode/cathode material used.

The present invention also provides a battery module including the lithium secondary battery as a unit cell.

The battery module can be used as a power source for medium to large-sized devices that require high temperature stability, long cycle characteristics, and high capacity characteristics.

Examples of the medium-to-large devices include power tools that are powered by an omni-electric motor; Electric vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc.; Electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf cart; Examples include, but are not limited to, power storage systems.

Preferred examples are presented below to aid understanding of the present invention. However, the following examples are merely illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention. It is natural that changes and modifications fall within the scope of the attached patent claims.

Example One

As a current collector, a non-porous PE film (polyethylene, 20 ㎛ thick) with a porosity of 20% was attached to the edge of Cu foil (LS wire, 20 ㎛ thick) as a polymer film.

Afterwards, an anode and a cathode were formed on the upper and lower surfaces of the current collector, respectively, in the following manner.

To form the positive electrode, the sulfur-carbon composite, conductive material, and binder were mixed at a weight ratio of 90:5:5 and then dissolved in water to prepare a positive electrode slurry with a concentration of 20% (concentration based on solid content). did. The positive electrode slurry was coated on the upper surface of the current collector using a bar coating method and then dried at 50°C for 2 hours to form a positive electrode. The dried positive electrode was rolled using a roll press to have a porosity of 65%. At this time, the sulfur-carbon composite was prepared by mixing sulfur and carbon at a weight ratio of 70:30 and heat treatment at 155°C, and the carbon was a CNT with a specific surface area of 300 ㎡/g and a particle diameter of 30 ㎛. was used. In addition, vapor grown carbon fiber (VGCF) was used as the conductive material, and polyvinylidene fluoride (PVDF) was used as the binder.

As the negative electrode, lithium foil was attached to the lower surface of the current collector. At this time, the lithium foil was attached by pressing it with a roll press.

Additionally, first and second separators were laminated on the anode and cathode. As the first and second separators, polyethylene separators with a thickness of 20 μm and a porosity of 45% were used.

Afterwards, a lithium negative electrode and Cu foil, a negative electrode current collector, were sequentially laminated on the first separator formed on the positive electrode, and the positive electrode and aluminum foil, a positive electrode current collector, were sequentially laminated on the second separator formed on the negative electrode. At this time, the anode and cathode of the same type as described above were formed in the same manner.

Afterwards, an electrolyte was injected into the case to manufacture a lithium-sulfur secondary battery. At this time, the electrolyte solution was prepared by dissolving lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) at a concentration of 3.0M in an organic solvent, and the organic solvent was propionitrile (first solvent), 1H, 1H, It is a solvent mixed with 2'H,3H-decafluorodipropyl ether (second solvent) at a weight ratio (w/w) of 3:7.

In Example 1, two unit cells including an anode, a cathode, and a separator were internally connected in series through a current collector to which the polymer film was attached.

Comparative Example 1

As shown in Figure 2, after sequentially stacking copper foil as the positive electrode 220, separator 230, negative electrode 210, and negative electrode current collector 211 on aluminum foil as the positive electrode current collector 221, The unit cell 200 was manufactured by injecting the electrolyte 400 into the case. At this time, the configuration and formation method of the positive electrode current collector, positive electrode, separator, negative electrode, and negative electrode current collector are the same as Example 1. At this time, the polymer film was not attached to the positive electrode current collector 221 and the negative electrode current collector 211.

The two unit cells were externally connected in series to manufacture a lithium-sulfur secondary battery (FIG. 2).

Comparative Example 2

A bipolar lithium-sulfur secondary battery was manufactured in the same manner as Example 1, except that the polymer film was not attached to the edge of the current collector. In Comparative Example 2, two unit cells including an anode, a cathode, and a separator were internally connected in series through the current collector (FIG. 3).

Experimental Example 1: Analysis of performance improvement effect of lithium-sulfur secondary battery

An experiment was conducted on the performance of the lithium-sulfur secondary batteries prepared in Example 1 and Comparative Examples 1 and 2, respectively. Example 1 is a bipolar lithium-sulfur secondary battery including a current collector with a polymer film attached to the edge (two unit cells are connected in series inside the battery by a current collector with a polymer film attached to the edge). , Comparative Example 1 is a lithium-sulfur secondary battery in which two unit cells are connected in series outside the battery, and Comparative Example 2 is a bipolar lithium-sulfur secondary battery including a current collector without a polymer film attached in Example 1. am.

The lithium-sulfur secondary batteries prepared in Example 1 and Comparative Examples 1 and 2, respectively, were discharged at 0.1C and the discharge capacity was measured.

Figure 4 is a graph measuring the discharge capacity for the lithium-sulfur secondary batteries prepared in Comparative Example 1 and Comparative Example 2, respectively, and Figure 5 is a graph measuring the discharge capacity for the lithium-sulfur secondary batteries prepared in Comparative Example 1 and Example 1, respectively. This is a graph measuring discharge capacity.

Referring to FIG. 4, when a bipolar lithium-sulfur secondary battery is constructed without attaching a polymer film to the edge of the current collector as in Comparative Example 2, charge/discharge compared to Comparative Example 1 in which two unit cells are externally connected in series It was confirmed that as the process continued, self-discharge occurred due to the generation of bypass current, and the discharge capacity decreased.

Referring to Figure 5, in Example 1, two unit cells are connected in series inside the battery by a current collector to which a polymer film is attached, and in Comparative Example 1, the two unit cells are connected in series outside the battery. It can be seen that the reduction in discharge capacity is lower than that.

Figure 6 is a photograph showing the cross-section of the negative electrode and positive electrode respectively formed on both sides of the current collector in the bipolar lithium-sulfur secondary battery of Example 1.

As shown in Figure 6, looking at the photo of the cross-section of the negative electrode of the bipolar lithium-sulfur secondary battery of Example 1, you can see the polymer film attached to the edge of the negative electrode and the current collector laminated on the negative electrode, and looking at the photo of the positive electrode, You can check the anode and polymer film. From this, it can be seen that the anode and cathode are separated by the polymer film attached to the edge of the current collector, and this structure can block the movement of Li ⁺ ions and polysulfide within the electrolyte when the battery is actually operated. can be seen.

Although the present invention has been described above with limited examples and drawings, the present invention is not limited thereto, and the technical idea of the present invention and the following description will be provided by those skilled in the art in the technical field to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalence of the patent claims.

1: Bipolar lithium secondary battery
B/U: Bipolar unit
110: house whole
120: polymer film
200: second unit cell
300: first unit cell
210, 310: cathode
211,311: negative electrode current collector
220, 320: anode
221: Anode current collector
230: second separator, 330: first separator
400: electrolyte
410: second electrolyte, 420: first electrolyte

Claims (9)

Current collector (110);
A polymer film 120 attached to surround the edge of the current collector 110;
An electrode layer including an anode 320 and a cathode 210 formed on both sides of the current collector 110, respectively;
First and second separators 330 and 230 formed on the anode 320 and cathode 210, respectively; and
An electrolyte solution 400 included between the first and second separators 330 and 230,
The electrolyte solution 400 contained between the first and second separators 330 and 230 is a bipolar lithium secondary battery (1) separated by the polymer film 120,
The electrolyte 400 is separated into a first electrolyte 420 and a second electrolyte 410 by the polymer film 120,
The first electrolyte solution 420 is surrounded by the polymer film 120, the anode 320, and the first separator 330,
The second electrolyte solution 410 is a bipolar lithium secondary battery (1) surrounded by the polymer film 120, the negative electrode 210, and the second separator 230. According to paragraph 1,
The polymer film 120 is a bipolar lithium secondary battery (1) including a non-porous membrane. According to paragraph 1,
The polymer film 120 is a bipolar lithium secondary battery (1), which is a laminated polymer film including a non-porous membrane and a porous membrane. According to paragraph 2 or 3,
A bipolar lithium secondary battery (1), wherein the non-porous membrane includes at least one selected from the group consisting of polyolefin, cellulose, and fluororesin. According to paragraph 2 or 3,
A bipolar lithium secondary battery (1) wherein the non-porous membrane has a porosity of 30% or less. According to paragraph 1,
A bipolar lithium secondary battery (1) in which the positive electrode 320 of the electrode layer includes at least one selected from the group consisting of elemental sulfur (S8), sulfur-based compounds, and sulfur-carbon complexes. According to paragraph 1,
A bipolar lithium secondary battery (1) in which the negative electrode 210 of the electrode layer contains lithium metal or lithium alloy. According to paragraph 1,
The electrolyte solution 400 is separated by the polymer film 120 and mutual movement is prevented, the bipolar lithium secondary battery (1). According to paragraph 1,
The electrolyte solution 400 is separated by a polymer film 120, and the electrolyte solution 400 is separated into an electrolyte solution adjacent to the anode and an electrolyte solution adjacent to the cathode,
A bipolar lithium secondary battery (1) in which mutual movement of polysulfide contained in the electrolyte solution adjacent to the positive electrode and lithium ions contained in the electrolyte solution adjacent to the negative electrode is prevented by the polymer film 120.