KR20200145333A - Lithium secondary battery structure and lithium secondary battery using the same - Google Patents

Abstract

The present invention relates to a lithium secondary battery structure and a lithium secondary battery comprising the same and, more specifically, to a lithium secondary battery structure comprising a blocking film surrounding an outer surface of an electrode assembly and to a lithium secondary battery comprising the same. The lithium secondary battery structure of the present invention has an excellent effect of inhibiting the dissolution of lithium polysulfide, thereby improving capacity and service life characteristics of a lithium-sulfur battery.

Description

Lithium secondary battery structure and lithium secondary battery including the same {LITHIUM SECONDARY BATTERY STRUCTURE AND LITHIUM SECONDARY BATTERY USING THE SAME}

The present invention relates to a lithium secondary battery structure and a lithium secondary battery including the same.

As the scope of use of lithium secondary batteries has expanded to not only portable electronic devices and communication devices, but also electric vehicles (EVs) and electric storage systems (ESSs), the high capacity of lithium secondary batteries used as power sources has been improved. The demand is increasing.

Among various lithium secondary batteries, a lithium-sulfur battery uses a sulfur-based material containing a sulfur-sulfur bond as a positive electrode active material, and lithium metal, a carbon-based material in which lithium ions are inserted/deinserted, or lithium It is a battery system that uses silicon or tin, which forms an alloy with an alloy, as an anode active material.

In lithium-sulfur batteries, sulfur, which is the main material of the positive electrode active material, has a low weight per atom, rich in resources, easy supply and demand, inexpensive, non-toxic, and has the advantage of being an environmentally friendly material.

Further, a lithium-sulfur battery is a lithium ion and the sulfur conversion (conversion) reaction at the anode ^- the theoretical discharge capacity resulting from ^{_{(S 8 + 16Li + + 16e}} → 8Li 2 S) reached 1,675 mAh / g, a lithium metal as a negative electrode ( Theoretical capacity: 3,860 mAh/g) shows a theoretical energy density of 2,600 Wh/kg. This is another battery system currently being studied (Ni-MH battery: 450 Wh/kg, Li-FeS battery: 480 Wh/kg, Li-MnO ₂ battery: 1,000 Wh/kg, Na-S battery: 800 Wh/kg) And since it has a very high value compared to the theoretical energy density of a lithium ion battery (250 Wh/kg), it is attracting attention as a secondary battery medium and high capacity, eco-friendly, and inexpensive lithium secondary battery that has been developed so far. Research is being done.

In a lithium-sulfur battery, when discharging, sulfur accepts electrons from the positive electrode and undergoes a reduction reaction, and the negative electrode undergoes an oxidation reaction in which lithium is ionized. During the discharge of such a lithium-sulfur battery, lithium polysulfide (Li ₂ S _x , x = 2 to 8) is produced in the positive electrode, which is dissolved in the electrolyte and eluted from the positive electrode, so that the reversible capacity of the positive electrode is greatly reduced. In addition, the dissolved lithium polysulfide diffuses to the negative electrode, causing various side reactions. In addition, such lithium polysulfide causes a shuttle reaction during the charging process, greatly reducing charging and discharging efficiency.

Since the elution of lithium polysulfide adversely affects the capacity and life characteristics of the battery, various techniques have been proposed to solve the lithium polysulfide problem.

For example, Korean Patent Application Publication No. 2018-0020096 discloses that by including a separator on which a catalyst layer containing a transition metal compound is formed, it is possible to improve the capacity and cycle characteristics of a battery by suppressing the shuttle reaction due to elution of lithium polysulfide. have.

In addition, Korean Patent Laid-Open No. 2017-0139761 includes a positive electrode active material layer and a protective layer containing a carbon material doped with nitrogen, and includes chitosan as a binder in the positive electrode active layer, thereby delaying the elution of lithium polysulfide. It discloses that capacity and lifespan can be improved.

In addition, Korean Patent Laid-Open No. 2016-0037084 discloses that by coating graphene on a carbon nanotube aggregate containing sulfur, it blocks the dissolution of lithium polysulfide, and increases the conductivity of the sulfur-carbon nanotube composite and the loading amount of sulfur. Disclosed that you can.

In addition, Korean Patent Application Publication No. 2018-0057339 discloses that the external diffusion of lithium polysulfide can be suppressed by sealing the outer side of the side surface of the electrode assembly with an organic molding material, thereby minimizing the reduction in capacity and life characteristics of the battery. .

These patents have improved the performance or lifespan degradation problem of the lithium-sulfur battery to some extent by introducing a material having lithium polysulfide adsorption capability into the anode or separator or completely sealing the electrode assembly to prevent the loss of sulfur, but the effect is not sufficient. Accordingly, there is a need for further development of a lithium-sulfur battery having excellent performance by solving the lithium polysulfide elution problem.

Republic of Korea Patent Publication No. 2018-0020096 (2018.02.27), Multi-layered separator for lithium sulfur battery coated with catalyst layer and lithium sulfur battery using the same Republic of Korea Patent Publication No. 2017-0139761 (2017.12.20), a positive electrode for a metal-sulfur battery having a positive electrode active material layer and a protective film containing nitrogen-doped carbon, and a method for manufacturing the same Republic of Korea Patent Publication No. 2016-0037084 (2016.04.05), sulfur-carbon nanotube composite, manufacturing method thereof, cathode active material for lithium-sulfur battery including the same, and lithium-sulfur battery including the same Republic of Korea Patent Publication No. 2018-0057339 (2018.05.30), Lithium-sulfur battery for suppressing the diffusion of lithium polysulfide and a method for manufacturing the same

Accordingly, the present inventors conducted various studies to solve the above problem, and as a result of including a lithium polysulfide impermeable barrier film on the outer surface of the electrode assembly, the lithium polysulfide elution was suppressed to improve the capacity and life of the lithium-sulfur battery. It was confirmed that the present invention was completed.

Accordingly, an object of the present invention is to provide a lithium secondary battery structure having excellent life and capacity characteristics.

In addition, another object of the present invention is to provide a lithium-sulfur battery including the lithium secondary battery structure.

In order to achieve the above object, the present invention is an electrode assembly comprising a unit cell in which at least one anode and at least one cathode are alternately stacked with a separator boundary; It provides a lithium secondary battery structure including a blocking film surrounding the outer surface of the electrode assembly and an electrolyte injected into the blocking film.

The blocking film may be impermeable to electrolyte and polysulfide.

The blocking layer may have an open electrode lead tab area.

The blocking film may include at least one selected from the group consisting of polyethylene and polypropylene.

The blocking layer may have a thickness of 1 to 50 μm.

The electrode assembly may include one or more unit cells selected from the group consisting of a mono cell, a full cell, and a bi-cell.

The electrode assembly may be a wound electrode assembly, a stack electrode assembly, a stack/folding electrode assembly, or a laminate/stack electrode assembly.

The anode is inorganic sulfur (S ₈ ), Li ₂ S _n (n≥1), a disulfide compound, an organosulfur compound and a carbon-sulfur polymer ((C ₂ S _x ) _n , x=2.5 to 50, n≥2) It may include at least one positive electrode active material selected from the group consisting of.

In addition, the present invention provides a lithium secondary battery including the lithium secondary battery structure.

In the lithium secondary battery structure according to the present invention, since lithium polysulfide is not eluted through the blocking film and remains in the vicinity of the electrode assembly, there is no loss of the positive electrode active material, and thus the capacity and capacity of a lithium secondary battery, specifically a lithium-sulfur battery, and It is possible to improve the life-reduction problem, thereby enabling high capacity and long life of the lithium-sulfur battery. In addition, since it is possible to secure a desired effect by simply introducing a blocking film without a change in a new layer or composition inside the electrode assembly, there is an advantage that it is economical and easy to apply to the manufacturing process of an existing lithium secondary battery.

1 is a cross-sectional view schematically showing the structure of a lithium secondary battery structure according to the prior art.
2 is a cross-sectional view schematically showing the structure of a lithium secondary battery structure according to an embodiment of the present invention.
3 is a view showing a three-dimensional structure of a lithium secondary battery structure according to an embodiment of the present invention.
4 is a graph showing a result of evaluating characteristics of a battery according to Experimental Example 1 of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, only this embodiment makes the disclosure of the present invention complete, and the scope of the invention to those of ordinary skill in the art It is provided to inform you.

The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

The terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present invention, terms such as'include' or'have' are intended to designate the presence of features, numbers, steps, actions, components, parts, or a combination thereof described in the specification, but one or more other features It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance.

The term “polysulfide” as used herein refers to “polysulfide ion (S _x ^2- , x = 8, 6, 4, 2))” and “lithium polysulfide (Li ₂ S _x Or LiS _x ^- x = 8, 6, 4, 2)”.

Lithium-sulfur batteries have a high theoretical discharge capacity and theoretical energy density among various secondary batteries, and sulfur used as a positive electrode active material is in the spotlight as a next-generation secondary battery due to the advantage of being inexpensive and environmentally friendly due to its abundant reserves.

Sulfur, which is used as a positive electrode active material in a lithium-sulfur battery, is converted from cyclic S ₈ to linear lithium polysulfide (Li ₂ S _x , x = 8, 6, 4, 2) by a reduction reaction, When the lithium polysulfide is completely reduced, lithium sulfide (Li ₂ S) is finally produced. Among lithium polysulfide, which is an intermediate product of the sulfur reduction reaction, lithium polysulfide (Li ₂ S _x , usually x> 4) with a high oxidation number of sulfur is a material with strong polarity and is easily dissolved in an electrolyte containing a hydrophilic organic solvent to react with the anode. There is a loss of sulfur that elutes out of the domain and no longer participates in the electrochemical reaction.

Due to the outflow of sulfur, the amount of sulfur participating in the electrochemical reaction is drastically reduced, and the lithium-sulfur battery does not realize all of the theoretical capacity and energy density in actual operation, despite the above-described advantages. In addition, there is a problem in that the deterioration of initial capacity and cycle characteristics is accelerated after a certain cycle due to a side reaction between lithium metal used as a negative electrode and lithium polysulfide.

To this end, in the prior art, a method such as introducing a material capable of suppressing the elution of lithium polysulfide into a positive electrode or separator in the form of a coating layer, changing the structure or material of the positive electrode active material, or forming a sealing structure of the electrode assembly using a sealing material has been proposed. In addition, the dissolution improvement effect of lithium polysulfide was insignificant, and the loading amount of sulfur was limited, and there were disadvantages of causing serious problems in the stability of the battery or inefficient in terms of the process.

Accordingly, the present invention provides a lithium secondary battery structure in which the elution of lithium polysulfide to the outside is suppressed by including a blocking film made of an impermeable lithium polysulfide material on the outer surface of the electrode assembly.

Specifically, FIG. 1 is a cross-sectional view schematically showing a structure of a lithium secondary battery structure 100 according to the prior art. Referring to FIG. 1, the existing lithium secondary battery structure 100 includes one unit cell including at least one positive electrode 11, at least one negative electrode 13, and at least one separator 15 interposed therebetween. The electrode assembly 10 and an electrolyte (not shown) included above are included, and at this time, the electrolyte is impregnated into the electrode assembly.

In the prior art, the lithium secondary battery structure as described above is accommodated in a predetermined battery case and sealed. In this case, as shown by arrows in FIG. 1, lithium polysulfide generated during battery operation and an electrolyte including the same easily diffuse to the outside of the structure. Accordingly, sulfur, which is a positive electrode active material, is lost, so that it no longer participates in the charging/discharging reaction of the battery, and as a result, the capacity and lifespan of the lithium secondary battery are reduced.

Accordingly, the present invention fundamentally blocks the movement of lithium polysulfide and an electrolyte containing the same to the outside of the structure by providing a lithium polysulfide impermeable blocking film surrounding the outer surface of the lithium secondary battery structure having the structure of FIG. 1. In particular, since lithium polysulfide is not eluted and remains in the vicinity of the electrode assembly, the loss of the positive electrode active material does not occur, and thus the capacity and lifetime reduction problem of a lithium secondary battery, specifically a lithium-sulfur battery, can be improved.

2 is a cross-sectional view schematically showing the structure of a lithium secondary battery structure according to an embodiment of the present invention.

2, a lithium secondary battery structure 200 according to an embodiment of the present invention is a unit in which at least one positive electrode 11 and at least one negative electrode 13 are alternately stacked with the separator 15 as a boundary. An electrode assembly 10 including a cell; It includes a blocking film 20 surrounding the outer surface of the electrode assembly 10 and an electrolyte injected into the blocking film 20.

In the present invention, the blocking film 20 serves to prevent leakage of lithium polysulfide to the outside of the electrode assembly. Therefore, the barrier layer has impermeability to the electrolyte in which the lithium polysulfide is dissolved in addition to the lithium polysulfide.

In particular, the lithium secondary battery structure according to the present invention solves the problem of reducing the reactivity of the electrode and the capacity of the battery due to the elution of lithium polysulfide and the shuttle reaction by confining lithium polysulfide around the electrode assembly through the blocking film. Thus, the capacity and life of the lithium secondary battery can be improved.

3 is a view showing a three-dimensional structure of a lithium secondary battery structure according to an embodiment of the present invention. Referring to FIG. 3, the blocking film is formed on the outer surface of the structure of the lithium secondary battery, but the electrode lead tab junction region may be open. It is preferable that the barrier layer has a minimum clearance in the direction of the junction of the electrode lead tab, and the clearance of the barrier layer in the direction of the junction of the electrode lead tab is for securing a minimum passage through which an electrolyte can be injected thereafter.

The blocking film may be a thin, easy to form, and chemically stable polymer film with an electrolyte. The blocking membrane is not particularly limited, and all separation membrane materials generally used in the art may be used. Preferably, the blocking film may be at least one selected from the group consisting of polyethylene and polypropylene.

The barrier layer may have a thickness of 1 to 50 µm, preferably 5 to 20 µm. When the thickness of the barrier layer is less than the above range, the mechanical strength is weakened and the barrier layer may be damaged during assembly of the electrode assembly.On the contrary, when the thickness of the barrier layer exceeds the above range, the energy density of the cell increases by increasing the volume and weight of the electrode assembly. It can be degraded.

In general, the electrode assembly 10 includes one or more unit cells having a basic structure of a positive electrode, a negative electrode, and a separator through which lithium ions can move while blocking electrical contact between the positive electrode and the negative electrode.

The unit cell is not particularly limited as long as at least one positive electrode and at least one negative electrode are alternately stacked across a separator to cause a battery reaction. For example, the unit cell is a mono-cell composed of one separator and one electrode, a full-cell composed of electrodes having different polarities, and the outermost electrodes having the same polarity. It may be one or more selected from the group consisting of a bi-cell consisting of. As an example, FIG. 2 is a lithium secondary battery structure according to an embodiment of the present invention, and includes an electrode assembly including a bi-cell as a unit cell.

The full cell is a unit cell having a structure of an anode/separator/cathode, and is a cell in which an anode and a cathode are respectively located on the outermost sides of both sides of the cell. These full cells include the most basic structure of an anode/separator/cathode and an anode/separator/cathode/separator/anode/separator/cathode. In order to construct a battery using such full cells, a plurality of full cells must be stacked so that the positive electrode and the negative electrode face each other with a separator interposed therebetween.

The bi-cell is a unit cell in which the same electrode is located on both outermost sides of the cell, such as a structure of an anode/separator/cathode/separator/anode and a structure of a cathode/separator/anode/separator/cathode. In order to construct a battery using such a bi-cell, a bi-cell with a positive electrode/separator/cathode/separator/anode structure (anode bi-cell) and a negative electrode/separator/anode/separator/cathode bi-cell with a separator interposed therebetween Multiple bi-cells should be stacked so that the (cathode bi-cells) face each other. In some cases, bicells with a larger number of stacks are also possible, e.g., anode/separator/cathode/separator/anode/separator/cathode/separator/anode and cathode/separator/anode/separator/cathode/separator Bi-cell of /positive/separator/cathode structure is also possible.

The number of unit cells included in the electrode assembly can be flexibly adjusted by a person skilled in the art according to the shape and required capacity of the device in which the battery is mounted. It goes without saying that an electrode assembly composed of 1 to 3 unit cells as well as an electrode assembly composed of 4 or more unit cells may be configured.

The type of the electrode assembly is not particularly limited, and may be, for example, a wound type (jelly-roll type) electrode assembly, a stack type (stack type) electrode assembly, a stack/fold type electrode assembly, or a laminate/stack type electrode assembly.

In the wound electrode assembly, after coating an electrode active material on a current collector, drying and pressing, a separator is interposed between a positive electrode and a negative electrode in a sheet shape cut to a desired width and length, and then spirally wound ( winding) is manufactured.

The stacked electrode assembly has a structure in which two or more electrodes are stacked, in which an anode and a cathode are alternately stacked in order, and a separate separator is inserted between the electrodes.

The stack/folding type electrode assembly has a structure in which bi-cells or full cells in which positive and negative electrodes of a predetermined unit are stacked with a separator interposed therebetween are folded into a long sheet-shaped separator.

In the stack/folding type electrode assembly, specifically, the bi-cell and/or full-cell are arranged to face opposite polarities after being wound and wound by a separating film, and the bi-cell has the same type of electrodes on both sides of the cell. It is composed of a stacked structure located in, for example, A-type bi-cell (anode bi-cell) and cathode/separator/a positive electrode having a structure in which the anode is located at both ends of the unit cell such as anode/separator/cathode/separator/anode. A C-type bi-cell (cathode bi-cell) has a structure in which a cathode is located at both ends of a unit cell, such as an anode/separator/cathode. When configuring the electrode assembly using only such bicells, both the A-type bi-cell and the C-type bi-cell may be included. The full cell has a stacked structure in which different types of electrodes are located on both sides of the cell, and may be, for example, a cell consisting of an anode/separator/cathode or a cell comprising an anode/separator/cathode/separator/anode.

More detailed information on the electrode assembly having the stack/folding structure is disclosed in Korean Patent Publication Nos. 2001-0082058, 2001-0082059 and 2001-0082060 of the applicant of the present invention. Incorporated by reference into the content.

The laminate/stack type electrode assembly is a structure in which the bi-cells or full cells are stacked with a separator interposed therebetween.

In the present invention, the unit cell constituting the electrode assembly may be a lithium-sulfur battery cell.

As described above, the lithium-sulfur battery cell includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and is not particularly limited as described above.

The positive electrode includes a positive electrode current collector and a positive electrode active material coated on one or both surfaces of the positive electrode current collector, and a plurality of positive electrodes having this structure may be stacked.

The positive electrode current collector supports a positive electrode active material and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, and the like may be used.

The positive electrode current collector may form fine irregularities on its surface to enhance the bonding strength with the positive electrode active material, and various forms such as films, sheets, foils, meshes, nets, porous bodies, foams, and nonwoven fabrics may be used.

The positive electrode active material may include a positive electrode active material and optionally a conductive material and a binder.

A sulfur-based compound is included as the positive electrode active material. The sulfur-based compounds are inorganic sulfur (S ₈ ), Li ₂ S _n (n≥1), disulfide compounds, organosulfur compounds and carbon-sulfur polymers ((C ₂ S _x ) _n , x=2.5 to 50, n≥ It may be one or more selected from the group consisting of 2). Preferably, inorganic sulfur (S ₈ ) may be used.

Since the sulfur-based compound alone has no electrical conductivity, it is used in combination with a conductive material. Preferably, the positive electrode active material may be a sulfur-carbon composite.

In the sulfur-carbon composite, carbon is a porous carbon material, providing a skeleton through which sulfur, which is a positive electrode active material, can be uniformly and stably fixed, and complements the electrical conductivity of sulfur so that an electrochemical reaction can proceed smoothly.

The porous carbon material may generally be prepared by carbonizing precursors of various carbon materials. The porous carbon material includes irregular pores therein, the average diameter of the pores is in the range of 1 to 200 nm, and the porosity or porosity may be in the range of 10 to 90% of the total volume of the porosity. If the average diameter of the pores is less than the above range, the pore size is only at the molecular level and impregnation of sulfur is impossible. Conversely, if the pore size exceeds the above range, the mechanical strength of the porous carbon is weakened, which is preferable to be applied to the manufacturing process of the electrode. Not.

The porous carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, tube-shaped, or bulk-shaped, and may be used without limitation as long as it is commonly used in lithium-sulfur batteries.

The porous carbon material may have a porous structure or a high specific surface area, so long as it is commonly used in the art. For example, as the porous carbon material, graphite; Graphene; Carbon blacks such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT); Carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); It may be one or more selected from the group consisting of natural graphite, artificial graphite, expanded graphite, and activated carbon, but is not limited thereto. Preferably, the porous carbon material may be a carbon nanotube.

In the present invention, the sulfur-carbon composite may contain 60 to 90 parts by weight of sulfur, preferably 65 to 85 parts by weight, more preferably 70 to 80 parts by weight, based on 100 parts by weight of the sulfur-carbon composite. . When the sulfur content is less than the above-described range, the specific surface area increases as the content of the porous carbon material in the sulfur-carbon composite is relatively increased, so that the content of the binder increases when preparing the slurry. Increasing the amount of the binder used may eventually increase the sheet resistance of the positive electrode and act as an insulator to prevent electron pass, thereby deteriorating the performance of the battery. On the contrary, when the sulfur content exceeds the above-described range, the sulfur or sulfur compounds that cannot be combined with the porous carbon material are aggregated with each other or re-elute to the surface of the porous carbon material, making it difficult to receive electrons and thus not participating in the electrochemical reaction. This may result in loss of battery capacity.

In addition to the above-described composition, the positive electrode active material may further include at least one additive selected from a transition metal element, a group IIIA element, a group IVA element, a sulfur compound of these elements, and an alloy of these elements and sulfur.

The transition metal element is Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, or Hg and the like are included, and the group IIIA element includes Al, Ga, In, and Ti, and the group IVA element may include Ge, Sn, and Pb.

The positive electrode active material may be included in an amount of 50 to 95 parts by weight, preferably 70 to 90 parts by weight, based on 100 parts by weight of the positive electrode slurry composition. When the content of the positive electrode active material is less than the above range, it is difficult to sufficiently exhibit the electrochemical reaction of the positive electrode, and on the contrary, when the content of the positive electrode active material exceeds the above range, the content of the conductive material and binder described below is relatively insufficient, and the resistance of the positive electrode increases, There is a problem that the physical properties of the anode are deteriorated.

In addition, the positive electrode may further include a conductive material, and the conductive material is a material that serves as a path through which electrons move from a current collector to the positive electrode active material by electrically connecting the electrolyte and the positive electrode active material. And any one having conductivity can be used without limitation.

For example, a carbon-based material having a porosity may be used as the conductive material, and examples of such a carbon-based material include carbon black, graphite, graphene, activated carbon, carbon fiber, etc., and metallic fibers such as metal mesh; Metallic powders such as copper, silver, nickel, and aluminum; Or an organic conductive material such as a polyphenylene derivative. The conductive materials may be used alone or in combination.

The conductive material may be included in an amount of 1 to 10 parts by weight, preferably 5 parts by weight, based on 100 parts by weight of the positive electrode slurry composition. If the content of the conductive material is less than the above range, the non-reacting portion of sulfur in the positive electrode increases, resulting in a decrease in capacity. On the contrary, if it exceeds the above range, it is preferable to determine an appropriate content within the above-described range since it adversely affects the high-efficiency discharge characteristics and charge/discharge cycle life.

In addition, the positive electrode may further include a binder, and the binder further enhances binding strength between components constituting the positive electrode and between them and a current collector, and any binder known in the art may be used.

For example, the binder may include a fluororesin binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); A rubber-based binder including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxyl methyl cellulose (CMC), starch, hydroxy propyl cellulose, and regenerated cellulose; Poly alcohol-based binder; Polyolefin-based binders including polyethylene and polypropylene; Polyimide binder; Polyester binder; And a silane-based binder; one, two or more mixtures or copolymers selected from the group consisting of may be used.

The binder may be included in an amount of 1 to 10 parts by weight, preferably about 5 parts by weight, based on 100 parts by weight of the positive electrode slurry composition. If the content of the binder is less than the above range, the physical properties of the positive electrode may be deteriorated and the positive electrode active material and the conductive material may be eliminated, and if the content of the binder exceeds the above range, the ratio of the active material and the conductive material in the positive electrode may be relatively reduced, thereby reducing the battery capacity. It is desirable to determine the appropriate content within one range.

The positive electrode can be manufactured by a conventional method known in the art. For example, after preparing a slurry by mixing and stirring a solvent, a binder, a conductive material, and a dispersant as necessary in a positive electrode active material, it is applied (coated) to a current collector of a metal material, compressed, and dried to prepare a positive electrode. have.

As the solvent, a positive electrode active material, a binder, and a conductive material may be uniformly dispersed. As such a solvent, water is most preferred as an aqueous solvent, and in this case, water may be distilled water or deionzied water. However, the present invention is not limited thereto, and if necessary, lower alcohol that can be easily mixed with water may be used. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol, butanol, and the like, and preferably, they may be used by mixing with water.

The porosity of the positive electrode prepared by the above-described composition and manufacturing method, specifically, the layer including the positive electrode active material may be 60 to 75%, preferably 60 to 70%. When the porosity of the positive electrode is less than 60%, the filling degree of the positive electrode slurry composition including the positive electrode active material, the conductive material, and the binder becomes too high, so that a sufficient electrolyte solution capable of showing ionic conduction and/or electrical conduction between the positive electrode active materials is provided. Since it cannot be maintained, the output characteristics or cycle characteristics of the battery may be deteriorated, and there is a problem that the overvoltage and discharge capacity of the battery are severely reduced. On the contrary, when the porosity of the positive electrode exceeds 75% and has an excessively high porosity, there is a problem that the physical and electrical connection with the current collector is lowered, resulting in a decrease in adhesion and difficulty in reaction, and the increased porosity is filled with an electrolyte solution. Since there is a problem that the energy density of may be lowered, it is appropriately adjusted within the above range.

The negative electrode includes a negative electrode current collector and a negative electrode active material coated on one or both surfaces of the negative electrode current collector, and a plurality of negative electrodes having this structure may be stacked.

The negative electrode current collector is as described in the positive electrode current collector.

The negative electrode is a material capable of reversibly intercalating or deintercalating lithium (Li ⁺ ) as a negative active material, a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, lithium metal or lithium It may contain an alloy.

The material capable of reversibly inserting or deintercalating lithium ions (Li ⁺ ) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. A material capable of reversibly forming a lithium-containing compound by reacting with the lithium ion (Li ⁺ ) may be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy is, for example, lithium (Li) and 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).

Preferably, the negative active material may be lithium metal, and specifically, may be in the form of a lithium metal thin film or lithium metal powder.

In addition, the negative electrode may further include additives such as a binder, a conductive material, and a thickener in addition to the negative active material described above, and is not particularly limited as long as it is a conventional one used in manufacturing the negative electrode. The binder and the conductive material are as described in the positive electrode.

In addition, the method of manufacturing the negative electrode is as described for the positive electrode.

The separator separates or insulates the positive electrode and the negative electrode from each other, and enables transport of lithium ions between the positive electrode and the negative electrode, and can be used without particular limitation as long as it is used as a separator in a general lithium-sulfur battery. It is preferable that it has low resistance to movement and has excellent electrolyte moisture content.

The separator is porous and may be made of a non-conductive or insulating material. This separator may be an independent member such as a film, or may be a coating layer added to the anode and/or the cathode.

The separator may be made of a porous substrate, and the porous substrate may be used as long as it is a porous substrate commonly used in an electrochemical device, and for example, a polyolefin-based porous membrane or a nonwoven fabric may be used, but is not particularly limited thereto. .

Examples of the polyolefin-based porous membrane include polyolefin-based polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, respectively, or a mixture of them. There is one membrane.

As the nonwoven fabric, in addition to the polyolefin nonwoven fabric, for example, polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate ), polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalate, respectively, independently Alternatively, a nonwoven fabric formed of a polymer obtained by mixing them may be mentioned. In addition, the nonwoven fabric may include a nonwoven fabric made of a high melting point glass fiber or ceramic material. In addition, the structure of the nonwoven fabric may be a sponbond nonwoven fabric composed of long fibers or a melt blown nonwoven fabric.

The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm.

The size and porosity of the pores present in the porous substrate are also not particularly limited, but may be 0.001 to 50 μm and 10 to 95%, respectively.

The electrolyte is impregnated into the electrode assembly as described above, contains lithium ions, and causes an electrochemical oxidation or reduction reaction at the anode and the cathode through this.

The electrolyte may be a non-aqueous electrolyte or a solid electrolyte that does not react with lithium metal, but is preferably a non-aqueous electrolyte and includes an electrolyte salt and an organic solvent.

The electrolyte salt contained in the non-aqueous electrolyte solution is a lithium salt. The lithium salt may be used without limitation as long as it is commonly used in an electrolyte for a lithium secondary battery. For example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, ( CF ₃ SO ₂ ) ₂ NLi, LiN(SO ₂ F) ₂ , lithium chloroborane, lithium lower aliphatic carboxylic acid, lithium 4-phenyl borate, lithium imide, and the like may be used.

The concentration of the lithium salt depends on several factors such as the exact composition of the electrolyte solvent mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and preconditioning of the battery, the working temperature and other factors known in the lithium battery field, from 0.2 to 2 M, Specifically, it may be 0.4 to 2 M, more specifically 0.4 to 1.7 M. If the concentration of the lithium salt is less than 0.2 M, the conductivity of the electrolyte may be lowered, resulting in deterioration of electrolyte performance, and if the concentration of the lithium salt exceeds 2 M, the viscosity of the electrolyte may increase, thereby reducing the mobility of lithium ions.

As organic solvents included in the non-aqueous electrolyte, those commonly used in electrolytes for lithium secondary batteries can be used without limitation, for example, ether, ester, amide, linear carbonate, cyclic carbonate, etc., alone or in combination of two or more Can be used. Among them, representatively, an ether-based compound may be included.

The ether compound may include an acyclic ether and a cyclic ether.

For example, the acyclic ether includes dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethylpropyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol Dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methylethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methylethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, At least one selected from the group consisting of tetraethylene glycol methylethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, and polyethylene glycol methylethyl ether may be used, but is not limited thereto.

For example, the cyclic ether is 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1, 3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 2-methyl-1,3 -Dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl-1, 3-dioxolane, tetrahydropyran, 1,4-dioxane, 1,2-dimethoxy benzene, 1,3-dimethoxy benzene, 1,4-dimethoxy benzene, isosorbide dimethyl ether One or more selected from the group consisting of may be used, but is not limited thereto.

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

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, or any one of them. A mixture of two or more types may be used as a representative, but is not limited thereto.

In addition, 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 , 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and any one selected from the group consisting of halides thereof, or a mixture of two or more thereof. These halides include, for example, fluoroethylene carbonate (FEC), but are not limited thereto.

The injection of the non-aqueous electrolyte may be performed at an appropriate step in the manufacturing process of the battery according to the manufacturing process and required physical properties of the final product. That is, it may be applied before assembling the lithium secondary battery structure or in the final step of assembling the lithium secondary battery to be described later.

The method of manufacturing the lithium secondary battery structure according to the present invention is not particularly limited, and a known method or various methods of modifying it may be used by a person skilled in the art.

The lithium secondary battery structure according to the embodiment of the present invention as described above improves the reactivity and capacity of the electrode by suppressing the diffusion of lithium polysulfide to the outside of the electrode assembly, and finally increases the energy density of the lithium secondary battery. do. As a result, the lithium secondary battery according to the present invention can be preferably applied as a high-density and long-life battery.

In addition, the present invention provides a lithium secondary battery including the lithium secondary battery structure.

The lithium secondary battery includes a lithium secondary battery structure according to the present invention and a battery case accommodating at least one lithium secondary battery structure.

At this time, the lithium secondary battery may be a variety of batteries such as a lithium-sulfur battery, a lithium-air battery, a lithium-oxide battery, and a lithium all-solid battery, depending on the type of the unit cell constituting the lithium secondary battery structure, specifically, the electrode assembly. have. In addition, according to the battery case to be described later, it can be classified into a cylindrical type, a square type, a coin type, a pouch type, and the like, and can be divided into a bulk type and a thin film type according to the size. The structure and manufacturing method of these batteries are well known in this field, and thus detailed descriptions are omitted.

In particular, the lithium secondary battery according to the present invention may be a lithium-sulfur battery in which the positive electrode includes a sulfur (S)-based active material.

As described above, in the lithium-sulfur battery, the amount of sulfur participating in the electrochemical reaction in the positive electrode decreases due to the elution of lithium polysulfide generated during operation, resulting in a decrease in the capacity and lifespan of the lithium-sulfur battery. However, as described in the present invention, when a blocking film surrounding the outer surface of the electrode assembly is provided, the elution of lithium polysulfide is effectively suppressed, thereby improving the capacity and life characteristics of the battery.

The lithium secondary battery structure is according to the present invention and follows the aforementioned description.

The battery case is for accommodating the lithium secondary battery structure of the present invention, and is made of a material having a predetermined flexibility in which the storage unit can be formed, and the shape is not limited, but is preferably a cylindrical, coin-shaped, rectangular or pouch This is my brother. The upper case and the lower case constituting such a battery case may be members independent of each other, or may be substantially one member having one end connected thereto. The external shape of the battery case may be manufactured by various methods, and the present invention is not limited thereto.

For example, the battery case may be a pouch type.

The pouch-type case is composed of a pair of laminate sheets having a structure in which three sides are sealed, and has the advantage of being light and easy to manufacture.

The laminate sheet may be formed of a laminated structure of an outer resin layer, an air and moisture barrier metal layer, and a heat-sealing inner resin layer.

Since the outer resin layer must have excellent resistance to the external environment, it is necessary to have a predetermined or higher tensile strength and weather resistance. In this aspect, the polymer resin of the outer coating layer may include polyethylene naphthalate (PEN), polyethylene terephthalate (PET), or stretched nylon having excellent tensile strength and weather resistance.

The outer coating layer may be made of polyethylene naphthalate (PEN) and/or a structure in which a polyethylene terephthalate (PET) layer is provided on the outer surface of the outer coating layer.

The polyethylene naphthalate (PEN) is preferable to be used as an outer coating layer because it has excellent tensile strength and weather resistance even at a thin thickness compared to polyethylene terephthalate (PET).

As the polymer resin of the inner resin layer, a polymer resin having heat adhesion (heat adhesion), low hygroscopicity in the electrolyte solution to suppress invasion of the electrolyte, and not swelling or eroding by the electrolyte may be used, More preferably, it may be made of a non-stretched polypropylene film (CPP).

For example, the laminate sheet according to the present invention has a structure in which the thickness of the outer coating layer is 5 to 40 μm, the thickness of the barrier layer is 20 to 150 μm, and the thickness of the inner sealant layer is 10 to 50 μm. I can. When the thickness of each layer of the laminate sheet is too thin, it is difficult to expect an improvement in the blocking function and strength of the material. Conversely, when the thickness of the laminate sheet is too thick, the workability decreases and the thickness of the sheet increases, which is not preferable.

The lithium secondary battery of the present invention can be manufactured by sealing and assembling the battery case in which the lithium secondary battery structure according to the present invention is embedded as described above. The manufacturing method of the lithium secondary battery can be used without limitation in a conventional method.

In addition, the present invention provides a battery module including the lithium-sulfur battery as a unit cell.

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

Examples of the medium and large-sized devices include a power tool that is powered by an omniscient motor and moves; Electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; Electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); Electric golf cart; Power storage systems, etc., but are not limited thereto.

Hereinafter, a preferred embodiment is presented to aid the understanding of the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, It is natural that such modifications and modifications fall within the appended claims.

Examples and Comparative Examples

[Example 1]

에서 30 분동안 열처리하여 황-탄소 복합체를 제조하였다.After evenly mixing 4.2 g of sulfur and 1.8 g of carbon nanotubes in the reactor, 155

Heat treatment was performed at for 30 minutes to prepare a sulfur-carbon composite.

Subsequently, 87% by weight of the prepared sulfur-carbon composite (S:C=7:3) as a positive electrode active material, 5% by weight of carbon fiber (VGCF, manufactured by Showa Denko) as a conductive material, as a binder. A positive electrode slurry composition was prepared by mixing 7% by weight of lithium polyacrylate and 1% by weight of polyvinyl alcohol.

에서 12시간 동안 건조하여 양극을 제조하였다.Then, the prepared slurry composition was applied on an aluminum current collector, and 50

Drying at for 12 hours to prepare a positive electrode.

Along with the positive electrode, a 35 μm-thick lithium metal thin film was used as the negative electrode, and 1M concentration of lithium in an organic solvent consisting of 1,3-dioxolane and dimethyl ether (DOL:DME=1:1 (volume ratio)) A mixed solution in which bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1% by weight of lithium nitrate (LiNO ₃ ) were dissolved was used.

Specifically, the prepared four positive electrodes and five negative electrodes were repeatedly stacked so as to face each other, and a polyethylene separator was placed therebetween, and then 2 ml of the prepared electrolyte was injected to prepare an electrode assembly.

A 10 μm-thick polyethylene film was wrapped around the outer side of the electrode assembly, and the seams were taped to form a barrier film to prepare a lithium-sulfur battery.

[Comparative Example 1]

A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that a blocking film was not formed.

Experimental Example 1. Evaluation of battery characteristics

Using a charge/discharge measuring device (LAND CT-2001A, Wuhan, China) for the batteries prepared in Example 1 and Comparative Example 1, discharged to 0.1 C for 1 to 3 cycles and charged to 0.1 C. , After the fourth cycle, the discharge was performed at 0.2 C, and the capacity was measured while repeating the cycle of charging to 0.2 C. The results obtained at this time are shown in FIG. 4.

As shown in FIG. 4, it can be seen that the capacity and life characteristics of the battery according to Example 1 are superior to those of Comparative Example 1.

4, in the case of the lithium-sulfur battery according to Example 1, compared with maintaining a capacity of 70% or more of the initial capacity throughout the cycle, in the case of Comparative Example 1, it can be seen that the capacity rapidly decreases after 5 cycles. have.

From these results, it can be seen that in the lithium-sulfur battery manufactured according to the present invention, the capacity retention rate is improved by suppressing the elution of lithium polysulfide by the blocking film, thereby improving the capacity and life characteristics of the lithium-sulfur battery.

100, 200: lithium secondary battery structure
10: electrode assembly
11: anode
13: cathode
15: separator
20: barrier

Claims (10)

An electrode assembly including unit cells in which at least one positive electrode and at least one negative electrode are alternately stacked with a separator boundary;
A blocking film surrounding the outer surface of the electrode assembly, and
Lithium secondary battery structure comprising an electrolyte injected into the blocking film. The method of claim 1,
The blocking membrane is impermeable to electrolyte and polysulfide, a lithium secondary battery structure. The method of claim 1,
The barrier layer is a lithium secondary battery structure in which the electrode lead tab junction region is open. The method of claim 1,
The blocking film comprises at least one selected from the group consisting of polyethylene and polypropylene, a lithium secondary battery structure. The method of claim 1,
The blocking film has a thickness of 1 to 50 μm, a lithium secondary battery structure. The method of claim 1,
The electrode assembly comprises one or more unit cells selected from the group consisting of a mono cell, a full cell, and a bi-cell, a lithium secondary battery structure. The method of claim 1,
The electrode assembly is a wound electrode assembly, a stack electrode assembly, a stack/folding electrode assembly, or a laminate/stack electrode assembly, a lithium secondary battery structure. The method of claim 1,
The anode is inorganic sulfur (S ₈ ), Li ₂ S _n (n≥1), a disulfide compound, an organosulfur compound and a carbon-sulfur polymer ((C ₂ S _x ) _n , x=2.5 to 50, n≥2) A lithium secondary battery structure comprising at least one positive electrode active material selected from the group consisting of. The lithium secondary battery structure according to claim 1 and
A lithium secondary battery comprising a battery case accommodating at least one lithium secondary battery structure. The method of claim 9,
The lithium secondary battery is a lithium-sulfur battery, a lithium secondary battery.

Images