Lithium secondary battery and manufacturing method for the same

Abstract

To provide a lithium secondary battery in a pouch cell mode in which an electrolyte solution is carried uniformly, and a manufacturing method for the lithium secondary battery.SOLUTION: A lithium secondary battery according to the present invention is manufactured by a process of injecting an electrolyte solution in an environment of pressing the battery. A small amount of electrolyte solution can be uniformly carried in a high-density electrode with low porosity, and the performance and life characteristic of the battery can be improved.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application No. 10-2021-0134880 filed on October 12, 2021.

[0002] The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery that minimizes volume expansion, a manufacturing system for a lithium secondary battery that minimizes volume expansion, and a manufacturing method for a lithium secondary battery that minimizes volume expansion.

Background Art

[0003] In this specification, although a certain document, act, or knowledge is referred to or discussed, this reference or discussion does not admit that such document, act, knowledge, or a combination of two or more of them is publicly available, publicly available, known to the public, part of common general knowledge, or constitutes prior art based on the provisions of applicable law, or is known to be related to an attempt to solve any problem related to this specification.

[0004] In recent years, the demand for portable electronic products such as laptop computers, video cameras, and mobile phones has been significantly increasing. In addition, the development of electric vehicles, energy storage batteries, robots, satellites, etc. has been increasing by leaps and bounds. Thus, research and development on high-performance secondary batteries have been actively carried out.

[0005] Unlike general primary batteries, secondary batteries can be repeatedly charged and discharged. Therefore, for example, a low-capacity secondary battery in which one battery cell is packaged in a pack form can be used in portable electronic devices such as mobile phones, notebook computers, and camcorders. Or, a high-capacity battery having a battery pack unit in which dozens of battery cells are connected to each other can be used as a power source for driving an electric motor of an electric vehicle or a hybrid electric vehicle, for example.

[0006] Currently, commercially available secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium-ion secondary batteries, etc. Among these batteries, lithium secondary batteries have attracted attention due to their relatively low self-discharge rate, low battery memory effect, and high energy density characteristics compared to nickel-based secondary batteries. In particular, among lithium-ion secondary batteries, lithium-sulfur (Li-S) secondary batteries are currently in the spotlight as next-generation batteries that can exhibit high energy density. However, the materials currently used in the manufacture of Li-S secondary batteries have relatively low density. For example, the density of the positive electrode containing sulfur in a Li-S battery is as low as about 0.3 to 0.6 g / cc. Thus, improving the performance of Li-S secondary batteries due to the low density characteristics of the positive electrode is a difficult problem.

[0007] Therefore, in order to improve the efficiency and performance of Li-S batteries, research and development on high-density electrodes for Li-S batteries have been continuously promoted. However, when increasing the density of the electrode, the porosity decreases, making it difficult to uniformly impregnate the electrolyte. In addition, volume expansion may be caused during battery operation, which may result in a decrease in the electrochemical performance of the battery and / or a decrease in battery life. For this reason, there is a strong demand for the development of Li-S batteries using high-density electrodes in which the electrolyte is uniformly impregnated while swelling is reduced or minimized.

[0008] On the other hand, the description of the background art provided in this specification is for generally presenting the context of the disclosure of the present invention. Unless otherwise indicated in this specification, the materials described in this background art are not prior art with respect to the claims of the present invention, and are not recognized as prior art or prior art proposals merely because they are included in the background art section.

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention is for solving the above-described technical problems. As a result of conducting extensive research to solve the above problems, the inventors of the present invention have found that, in the manufacturing process of a pouch cell type lithium secondary battery, when a laminate in which a positive electrode, a separator (separation membrane), and a negative electrode are sequentially laminated is inserted into a pouch, the pouch is externally pressurized to fix the thickness, and then an electrolytic solution is injected into the pouch, a small amount of the electrolytic solution can be uniformly supported on a high-density electrode, and it is confirmed that the life characteristics of the battery can be improved.

[0010] Accordingly, an object of the present invention is to provide a lithium secondary battery in a pouch cell form in which an electrolytic solution is uniformly supported and a method for manufacturing the same.

Means for Solving the Problems

[0011] It has been found that, according to the disclosure, the foregoing drawbacks can be addressed and certain advantages can be achieved. For example, the battery, method, and system of the present disclosure provide a novel approach for minimizing the swelling of a lithium secondary battery.

[0012] It should be understood that the various individual aspects and features of the present invention described herein may be combined in any one or more individual aspects or features in any number to form specific embodiments of the present invention to be specifically considered, and such combinations are also included in the scope of the present disclosure.

[0013] The present invention relates to a lithium-sulfur battery having a sulfur-based compound as a positive electrode active material.

[0014] In a first aspect of the present invention, the battery includes an electrode assembly having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, a pouch for housing the electrode assembly, and an electrolytic solution, and the lithium-sulfur battery has an expansion coefficient SF represented by the following formula (1) that is 0 or more and less than 10; [Formula (1)] SF = (T2 - T1) / (T1) × 100 (In the formula, T1 is the first thickness of the lithium-sulfur battery, and T2 is the second thickness of the lithium-sulfur battery).

[0015] The second aspect of the present invention is the lithium-sulfur battery according to the first aspect, wherein the first thickness is the thickness of the lithium-sulfur battery before injecting the electrolyte into the pouch, and the second thickness is the thickness of the lithium-sulfur battery after injecting the electrolyte into the pouch.

[0016] The third aspect of the present invention is the lithium-sulfur battery according to the first aspect or the second aspect, wherein both the first thickness and the second thickness are measured after injecting the electrolyte, and the first thickness and the second thickness are measured at arbitrary positions of the battery, respectively, and the measurement positions of the first thickness and the second thickness are different from each other.

[0017] The fourth aspect of the present invention is the lithium-sulfur battery according to any one of the first aspect to the third aspect, wherein the positive electrode contains a sulfur-carbon composite having a carbon material and sulfur as a positive electrode active material.

[0018] The fifth aspect of the present invention is the lithium-sulfur battery according to the fourth aspect, wherein the weight of sulfur is 70% or more based on the total weight of the sulfur-carbon composite.

[0019] The sixth aspect of the present invention is the lithium-sulfur battery according to any one of the first aspect to the fifth aspect, wherein the positive electrode has a density of the positive electrode active material layer of 0.5 g / cc to 4.5 g / cc.

[0020] The seventh aspect of the present invention is the lithium-sulfur battery according to any one of the first aspect to the sixth aspect, wherein the negative electrode contains lithium metal as a negative electrode active material.

[0021] The eighth aspect of the present invention is that in the lithium-sulfur battery according to any one of the first to seventh aspects, the E / S, which is the ratio of the weight of the electrolyte to the weight of the sulfur, is 2.7 or less.

[0022] The ninth aspect of the present invention is that in the lithium-sulfur battery according to any one of the first to eighth aspects, the positive electrode active material layer of the positive electrode has a porosity of 35 vol% to 75 vol%.

[0023] The tenth aspect of the present invention is that in the lithium-sulfur battery according to any one of the first to ninth aspects, the capacity of the battery is 950 mAh / g s ~1300 mAh / g s and is such.

[0024] The eleventh aspect of the present invention is an electrochemical element including the lithium-sulfur battery according to any one of the first to tenth aspects as a power source, and the electrochemical element includes an electric vehicle.

[0025] The twelfth aspect of the present invention relates to a method for manufacturing a lithium-sulfur battery. The method includes a step of laminating a positive electrode, a separator, and a negative electrode to form an electrode assembly, a step of housing the electrode assembly in a pouch, a step of applying a predetermined pressure to the pouch in which the electrode assembly is housed, a step of injecting a predetermined amount of electrolyte into the pouch while maintaining the predetermined pressure, and a step of sealing the pouch. The lithium-sulfur battery has an expansion coefficient SF according to the following formula 1 of 0 or more and less than 10: [Formula 1] SF = (T2 - T1) / (T1) × 100 (wherein, T1 is the first thickness of the lithium-sulfur battery, and T2 is the second thickness of the lithium-sulfur battery).

[0026] The thirteenth aspect of the present invention further includes a step of measuring the expansion coefficient before sealing the pouch in the method for manufacturing a lithium-sulfur battery according to the twelfth aspect.

[0027] The 14th aspect of the present invention is the method for manufacturing a lithium-sulfur battery according to the 13th aspect, wherein the step of measuring the expansion coefficient includes a step of measuring a first thickness of the lithium-sulfur battery before injecting an electrolyte into the pouch, and a step of measuring a second thickness of the lithium-sulfur battery after injecting the electrolyte into the pouch.

[0028] The 15th aspect of the present invention is the method for manufacturing a lithium-sulfur battery according to any one of the 12th to 14th aspects, further including a step of measuring the expansion coefficient after sealing the pouch.

[0029] The 16th aspect of the present invention is the method for manufacturing a lithium-sulfur battery according to the 15th aspect, wherein the step of measuring the expansion coefficient includes a step of measuring a first thickness of the battery in a first region of the lithium-sulfur battery, and a step of measuring a second thickness of the battery in a second region of the lithium-sulfur battery.

[0030] The 17th aspect of the present invention is the method for manufacturing a lithium-sulfur battery according to any one of the 12th to 16th aspects, wherein the amount of the pressure is 100 atm or less.

[0031] The 18th aspect of the present invention relates to a manufacturing system for a lithium-sulfur battery. The system includes a control device, a jig connected to the control device and having a first flat plate and a second flat plate, applying pressure between the first flat plate and the second flat plate, and the amount of the pressure being based on the expansion coefficient of the lithium-sulfur battery, and an electrolyte injection device connected to the control device and injecting an electrolyte into the pouch of the lithium-sulfur battery. The expansion coefficient SF is represented by the following formula 1: [Formula 1] SF=(T2-T1) / (T1)×100 (wherein, T1 is the first thickness of the lithium-sulfur battery, and T2 is the second thickness of the lithium-sulfur battery).

[0032] The 19th aspect of the present invention is a lithium-sulfur battery manufacturing system according to the 18th aspect, further including a control device that adjusts the amount of pressure applied to the lithium-sulfur battery based on the expansion coefficient.

Advantages of the Invention

[0033] The method for manufacturing a lithium secondary battery according to the present invention is characterized in that, in an environment where the battery is pressurized, an electrolyte injection step of injecting an electrolyte into the battery is performed. Thereby, the volume expansion of the battery due to the electrolyte can be minimized, and a small amount of electrolyte can be uniformly supported on a high-density electrode with a low porosity, improving the performance and life characteristics of the battery. Further, according to the above method, a battery having a uniform thickness and a small volume change before and after electrolyte injection can be provided. In particular, in the case of a lithium-sulfur battery, it is preferable to lower the porosity of the positive electrode active material layer in order to increase the energy density, and the electrolyte can be uniformly supported on such a low-porosity positive electrode and an electrode assembly including the same.

[0034] When the battery is a pouch type, since the volume expansion of the battery is controlled by pressurization, it is particularly effective to apply the manufacturing method of the present invention.

[0035] The following drawings attached to this specification illustrate a specific embodiment of the present invention and serve to further understand the technical idea of the present invention together with the detailed description of the invention. Therefore, the present invention should not be construed as being limited only to the matters described in such drawings. On the other hand, the shape, size, scale, or ratio of elements in the drawings incorporated in this specification may be exaggerated for the purpose of emphasizing a clearer explanation.

Brief Description of the Drawings

[0036]

Figure 1

Figure 2a

Figure 2b

Figure 3

Figure 4a

Figure 4b

Figure 5

Figure 6

Figure 7

Figure 8

MODE FOR CARRYING OUT THE INVENTION

[0037] Further aspects, features and advantages of the present disclosure will become apparent from the following detailed description.

[0038] As used herein, the singular forms of terms (in English, "a", "an" and "the") include the plural forms unless otherwise specified in the context. Further, the use of "or" includes "and / or" unless otherwise specified in the context.

[0039] As used herein, "about" is a term of approximation and includes minor variations of the quantity so stated as would be understood by one of ordinary skill in the art. Such variations include, for example, standard deviations associated with the components or amounts of components of alloys or composite materials, or other properties and with the techniques generally used for the measurement of such properties. All values characterized by the modifier "about" as set forth above also include the exact numerical values disclosed herein. Also, all ranges include an upper and lower limit.

[0040] Any composition described herein, unless otherwise indicated, consists of or consists essentially of the various components identified herein and includes compositions containing the various components identified herein.

[0041] As used herein, the recitation of a numerical range for a variable is intended to convey that the variable can be the same as any value within that range and can also be the same as any of the entire sub-ranges included by the broader range. Thus, a variable can be the same as all integer values within a numerical range including the endpoints of the range. For example, a variable described as having values from 0 to 10 can be 0, 4, 2 to 6, 2.75, 3.19 to 4.47, etc.

[0042] In this specification and the claims, unless otherwise indicated in the context, the singular forms also include the plural referents. As used herein, unless otherwise specified, the word "or" is used in the "inclusive" sense of "and / or" and not in the "exclusive" sense of "either / or".

[0043] Unless otherwise indicated, each individual feature or example herein can be combined with any other individual feature or embodiment described herein without limitation. Such combinations are specifically contemplated as being within the scope of the present disclosure, whether or not explicitly described as combinations herein.

[0044] The technical and scientific terms used in this specification have the meanings generally understood by those of ordinary skill in the art to which this specification pertains, unless otherwise defined. Various methodologies and materials known to those of skill in the art are referenced herein.

[0045] Even when used in conjunction with the detailed description of specific examples of the present disclosure, the terms can be interpreted in the broadest reasonable manner. In fact, certain terms may be emphasized below. However, any terms intended to be interpreted in a limiting manner are explicitly and specifically defined in this section of the detailed description. Of the content described in the specification, both the general description and the detailed description are merely exemplary and explanatory and do not limit the features recited in the claims.

[0046] In this specification, the terms "for example, exemplary" are used in the sense of "merely an example" rather than in the sense of "preferred" or "ideal". The term "or" is meant to be inclusive and means some or all of the recited items. The terms "have, comprise, include(s), including" or other variations thereof mean that a process, method or product comprising an element may include other elements not necessarily limited to only these elements, not explicitly listed, or not inherent to such process, method, article, or apparatus.

[0047] One aspect of the present invention relates to a lithium secondary battery that can be manufactured by inserting an electrode assembly into a housing of the lithium secondary battery. The electrode assembly may include a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. In one embodiment of the present invention, the electrode assembly may include a plurality of positive electrodes and a plurality of negative electrodes that are sequentially and repeatedly stacked. For example, a positive electrode may be provided as the first layer of the electrode assembly. Next, a separator may be stacked on top of the positive electrode, and a negative electrode may be stacked on top of the separator. Further, another separator may be provided on top of the negative electrode, or may be provided in a manner of stacking another positive electrode. Also, the electrode assembly may be of a stack type or a stack / folding type in which the electrodes and the separator are sequentially stacked, or may be of a jelly roll type. The electrode assembly thus prepared can then be inserted into the housing of the battery. For example, the housing of the battery may have a form of a metal can or a pouch containing a polymer film, but is not limited thereto.

[0048] For example, a pouch-type battery (or a pouch-type battery cell) may be formed by inserting an electrode assembly (e.g., a laminated electrode assembly or a jelly roll-type electrode assembly) into a pouch. Thereafter, an electrolytic solution can be injected into the pouch and sealed to assemble the pouch-type battery cell. The electrolytic solution injected into the pouch can flow into the pores present in the electrode assembly to fill the pores, and at the same time can fill the empty space in the housing other than the volume (apparent volume) occupied by the electrode assembly. The pores may include pores formed in one or more of the positive electrode, the negative electrode, and the separator, or may be the positive electrode. Thus, the amount of the electrolytic solution to be injected into the pouch can be determined in advance before injecting the electrolytic solution into the pouch, so as to ensure uniform impregnation and prevent overflow of excess electrolytic solution. Therefore, a change in the thickness of the pouch cell (or battery cell) detected after injecting the electrolytic solution into the pouch cell means that the electrolytic solution is unevenly distributed or unevenly impregnated in the electrode assembly, particularly the positive electrode.

[0049] As described above, in a Li-S battery, non-uniform impregnation of the electrolyte may occur due to the low porosity of one or more electrodes (e.g., a high-density positive electrode). Therefore, when the electrolyte is not uniformly impregnated in the high-density positive electrode of the Li-S battery, excess electrolyte may expand and induce battery defects, which may reduce performance and battery life.

[0050] According to one aspect of the present invention, a lithium-ion secondary battery including a high-density electrode and suppressing swelling to a minimum is provided. In one aspect, the lithium secondary battery according to the present invention has a swelling factor (SF) according to the following formula 1 of 0 or more and less than 10, 0 or more and 7 or less, or 0 or more and 5 or less.

[0051] [Formula 1] SF=(T2-T1) / (T1)×100, In Formula 1 above, T1 means the first thickness and T2 means the second thickness.

[0052] In one embodiment of the present invention, the first thickness is the thickness at any location of the battery before electrolyte injection, and the second thickness is the thickness of the battery after electrolyte injection (Embodiment A). At this time, it is preferable that the first thickness and the second thickness are measured at the same location before and after electrolyte injection. On the other hand, in one embodiment of the present invention, the SF may be a value obtained by averaging values measured at two or more locations. In one embodiment of the present invention, the SF may be measured at two or more or three or more locations. On the other hand, the second thickness may be measured before or after sealing the battery.

[0053] In one embodiment of the present invention, in Embodiment A, the battery injects the electrolyte with an external pressure applied to the battery. In this case, T2 may be measured with the pressure maintained after electrolyte injection, or may be measured with the pressure released. Since T1 is the value measured before electrolyte injection, it may have substantially the same thickness whether pressure is applied or not.

[0054] Additionally or alternatively, the first thickness may be the thickness measured at any one location of the battery, and the second thickness may be the thickness measured at any other location (Embodiment B). Hereinafter, when it is necessary to distinguish from the SF of Embodiment A, it is denoted as SF'. In the SF', the first thickness and the second thickness may be measured after the electrolyte is injected. Also, the first thickness and the second thickness may be measured before or after sealing the pouch after the electrolyte is injected. Further, in one embodiment of the present invention, the first thickness and the second thickness may be a combination showing the largest value of the SF of two values selected from a plurality of values measured at two or more arbitrary locations. With the SF', it is possible to confirm whether the thickness of the battery is uniform after the electrolyte is injected. That is, according to Embodiment B, the deviation of the thickness of the battery after the electrolyte is injected can be confirmed, and thereby, it can be confirmed whether the electrolyte flows uniformly into the electrode assembly. On the other hand, in Embodiment B, the battery is one in which the electrolyte is injected with an external pressure applied to the battery, and the first thickness and the second thickness may both be measured with the pressure applied or may be measured with the pressure released.

[0055] The lithium secondary battery according to the present invention may have an SF value according to Embodiment A of 0 or more and less than 10, 0 or more and 7 or less, or 0 or more and 5 or less.

[0056] Additionally or alternatively, the lithium secondary battery according to the present invention may have an SF value (SF') according to Embodiment B of 0 or more and 7 or less, 0 or more and 5 or less, 0 or more and 3 or less, or 0 or more and 1 or less.

[0057] In one embodiment of the present invention, the battery may satisfy at least Embodiment A or may satisfy both Embodiment A and Embodiment B.

[0058] Since the battery according to the present invention injects the electrolyte with pressure applied, the volume expansion of the battery is suppressed. Thus, when the SF value according to Embodiment A is less than 10, the SF value according to Embodiment B may be substantially 7 or less.

[0059] The SF value described below will be mainly described centering on Embodiment A. However, the description of Embodiment B is not excluded, and it goes without saying that it can also be applied to Embodiment B.

[0060] In the lithium-ion secondary battery, when the value of SF according to the formula 1 satisfies 0 or more and less than 10 (0 ≦ SF < 10), 0 or more and 7 or less (0 ≦ SF ≦ 7), or 0 or more and 5 or less (0 ≦ SF ≦ 5), it indicates that there is little or no swelling of the lithium secondary battery. Preferably, the SF is 0 or more and 5 or less. Regarding the SF of Embodiment B, the above-mentioned range can be referred to.

[0061] On the other hand, in the present invention, the thickness means the height of the battery along the direction in which battery components such as electrodes and separators are stacked with respect to the electrode assembly.

[0062] According to a specific embodiment of the present invention, a lithium-ion secondary battery that minimizes or does not cause swelling at all, for example, a lithium secondary battery that satisfies 0 ≦ SF < 10, or 0 ≦ SF ≦ 7 or 0 ≦ SF ≦ 5 can be manufactured.

[0063] Such a lithium secondary battery can be manufactured by inserting an electrode assembly (e.g., a laminated electrode assembly, a jelly roll type electrode assembly, etc.) into a battery housing. Thereafter, the housing may be placed in a jig that applies a predetermined pressure to one or more surfaces of the battery housing. For example, the housing may be a pouch used for a pouch type battery, but is not limited thereto. In one embodiment of the present invention, when the housing is a pouch, the effects of the present invention can be further exerted compared to the case where the housing is a metal can. In the case of a metal can, volume expansion can be suppressed by the rigidity of the metal. However, the pouch type exterior material has lower rigidity than a metal can and is easily deformed by an external force. Therefore, when manufacturing the battery according to the present invention using a pouch type exterior material, the effects can be maximized. However, even when a metal can is used as the housing material, it goes without saying that improved effects can be achieved by the battery manufacturing method according to the present invention depending on the metal material used and its inherent properties.

[0064] Thereafter, an electrolyte is injected into the pouch, and at this time, due to the predetermined pressure applied by the jig, the electrolyte can be uniform or uniformly impregnated in the electrode assembly, particularly in the positive electrode. For example, the Li-S battery manufactured according to the present invention may include a high-density positive electrode and an electrolyte uniformly impregnated in the high-density positive electrode. Such a Li-S battery can satisfy 0 ≦ SF < 10, preferably 0 ≦ SF ≦ 5, thereby minimizing or not causing volume expansion at all. In addition, since the high-density positive electrode of the Li-S battery according to the present invention has a structure that reduces the porosity and improves the energy density, when the range of 0 ≦ SF < 10 is satisfied after electrolyte injection, the amount of electrolyte required for driving the Li-S battery can be substantially reduced, improving battery performance and battery life.

[0065] According to one embodiment of the present invention, before injecting the electrolytic solution, any one or more positions of the battery housing are identified, and by measuring the thickness before and after injecting the electrolytic solution at each position, the change in the thickness of the lithium secondary battery can be detected or determined. When there is one measurement position, the value may be used as the thickness value, and when there are two or more measurement positions, the average value of the individual values may be used as the thickness value. Alternatively, as described above, when two or more measurement locations are identified, the average value of the SF values calculated at each location may be used as the overall SF value.

[0066] On the other hand, alternatively or additionally, after the battery is completely assembled (for example, after completion of electrolytic solution injection or after completion of electrolytic solution injection and pouch sealing of the battery cell), the change in the thickness of the battery may be detected or determined by measuring the unevenness of the surface of the lithium secondary battery (the difference between the first thickness and the second thickness may be used as the SF value).

[0067] Next, the present invention will be described in more detail with reference to the accompanying drawings. The description of the invention with reference to the drawings is given with respect to specific aspects of the present invention, and while the present invention is shown in the drawings, it is not limited to the specific aspects based on the drawings. Here, embodiments or aspects described as "exemplary" should not be construed as, for example, being more desirable or advantageous compared to other embodiments or aspects. Rather, it is intended to reflect or indicate that the embodiment is an "exemplary" embodiment. The technical subject matter of the present invention can be realized in various different forms, and thus, it must not be construed that the scope of the invention is limited by any of the exemplary embodiments described herein. The exemplary embodiments are provided for illustrative purposes only. Therefore, within the scope reasonably interpretable based on this specification, the scope of the present invention, particularly the scope of the claims, includes a broader range than what is exemplified. Above all, for example, the technical idea or the patentable subject matter of the present invention can be realized as a method, an apparatus, a component, or a system. Therefore, an embodiment can take the form of, for example, hardware, software, firmware, or any combination thereof (excluding software itself). For this reason, the following detailed description is not intended to be construed in a limiting sense.

[0068] Throughout this specification and the entire scope of the claims, the terms used may have subtle meanings proposed or implied in the context beyond the explicitly mentioned meanings. Similarly, the phrase "in one embodiment" used herein does not necessarily refer to the same embodiment, and the phrase "in other embodiments" used herein does not necessarily refer to other embodiments. For example, the claimed subject matter is intended to include the whole or part of a combination of exemplary embodiments.

[0069] The following will be described in more detail with reference to the accompanying drawings.

[0070] FIG. 1 is a schematic diagram showing an exemplary lithium secondary battery 100 according to one aspect of the present invention. The lithium secondary battery 100 may include an electrode assembly (not shown), a housing 102, a first electrode tab, and a second electrode tab 106. For example, the housing 102 may be the pouch shown in FIG. 1. However, the housing 102 may be a rectangular housing, a cylindrical housing, or the like, but is not limited thereto. The first electrode tab 104 may be a positive electrode tab, the second electrode tab 106 may be a negative electrode tab, or vice versa. The first electrode tab 104 and the second electrode tab 106 may be electrically coupled to an electrode assembly (to be shown in detail in FIG. 2B later) of the lithium secondary battery 100. In one embodiment, the first electrode tab 104 may be electrically connected to one or more positive electrodes of the electrode assembly. Also, the second electrode tab 104 may be electrically connected to one or more negative electrodes of the electrode assembly. In FIG. 2, the first electrode tab 104 and the second electrode tab 106 are shown to be disposed on both sides (opposite to each other) of the lithium secondary battery 100, but the first electrode tab 104 and the second electrode tab 106 are not limited thereto and may be disposed on any side or position of the lithium secondary battery 100, individually or together.

[0071] Figure 2a is a diagram schematically showing a state before injecting an electrolytic solution into a lithium secondary battery 200 according to one side edge of the present invention. The battery 200 may include a housing (for example, a pouch), an electrode assembly 210, and a free volume (or free space, for example, dead space) 204. The housing 102 may include an opening 202. In the manufacturing process of the battery 100 of the present invention, the electrolytic solution can be injected into the housing through the opening 202, and the electrolytic solution can flow into the inside of the electrode assembly 210 (for example, pores of the electrodes) to impregnate the electrode assembly with the electrolytic solution. Any remaining electrolytic solution can be filled or dispersed in the free space 204. The free space 204 is a space generated when a substantially sheet-shaped pouch film is deformed (for example, while being folded or bent) to accommodate an electrode assembly of a specific shape. Therefore, it is preferable that the internal space of the housing conforms (fits) to the shape of the electrode assembly so that such a free space does not occur. However, substantially, the volume of the internal space of the housing exceeds the volume (apparent volume) of the accommodated electrode assembly, and thus a free space is generated. When manufacturing the battery, it is preferable that the free space of the housing be designed to be minimized. In one embodiment of the present invention, the excess electrolytic solution remaining without being impregnated in the electrode assembly 210 can be stored in the free space 204. Thus, during the manufacture of the battery, a predetermined free space 204 actually occurs, and when injecting the electrolytic solution, the injection amount of the electrolytic solution is determined in consideration of the volume of such a free space. On the other hand, when the amount of the electrolytic solution injected into the housing 102 is substantially equivalent to the volume of the pores of the electrode assembly 210 and the volume of the free space, and the electrolytic solution is uniformly impregnated in the electrode assembly, the thickness of the battery 200 after injecting the electrolytic solution may be substantially the same as the thickness of the battery before injecting the electrolytic solution.

[0072] FIG. 2b schematically shows an exemplary electrode assembly 210 of a battery 200 (or a cell) according to one aspect of the present invention. The electrode assembly 210 may include one or more positive electrodes 212, one or more separators 214, and one or more negative electrodes 216. For example, the electrode assembly 210 may be formed by repeatedly and sequentially laminating the positive electrode 212, the separator 214, and the negative electrode 216, and laminating a final layer 218 (a positive electrode layer or a negative electrode layer according to the lamination order and the lamination direction). The number of each negative electrode, positive electrode, and separator included in the electrode assembly may be based on, for example, the desired capacity and / or function of the electrode assembly 210 for the battery 100 or 200.

[0073] According to one embodiment of the present invention, the positive electrode 212 may include at least a positive electrode current collector and a positive electrode active material layer (not shown) disposed on at least one surface or both surfaces of the positive electrode current collector.

[0074] The positive electrode current collector may include a conductive (electrically conductive) material such as an aluminum foam or a nickel foam, but is not limited thereto. The positive electrode active material layer may include, for example, a positive electrode active material, a binder, and a conductive material (conductive agent).

[0075] The content of the total positive electrode active material in the positive electrode active material layer may occupy about 70% to 95% of the total weight of the positive electrode active material layer. When the proportion of the positive electrode active material included in the positive electrode active material layer is less than the aforementioned 70% to 95% (for example, less than 60%), the capacity of the battery 100 may decrease. When the proportion of the positive electrode active material exceeds the above range (for example, exceeds 95%), overvoltage of the battery 100 may occur.

[0076] Also, in one aspect of the present invention, the positive electrode active material may include, for example, a sulfur-based positive electrode active material, and preferably, the sulfur-based positive electrode active material in the positive electrode active material may be contained at 70 wt% or more, 80 wt% or more, 90 wt% or more, or 99 wt% or more. In a specific embodiment of the present invention, the positive electrode active material may contain 90 wt% or more of the sulfur-based positive electrode active material, or may contain only the sulfur-based positive electrode active material. The sulfur-based positive electrode active material may include sulfur, sulfur element (S8), sulfur-based compounds having sulfur, etc., but is not limited thereto. For example, the sulfur-based positive electrode active material is Li2S n (n is a real number of 1 or more), an organic sulfur composite material, or a carbon-sulfur composite (C2S x ) n (x is a real number including 2.5 to 50, n is a real number of 2 or more) may be included.

[0077] On the other hand, in the present invention, the sulfur content in the sulfur-based positive electrode active material may be 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more. In a specific embodiment, the sulfur-based positive electrode active material may be a carbon-sulfur composite, and the sulfur content in 100 wt% of the carbon-sulfur composite may be 60 wt% or more, 70 wt% or more, or 80 wt% or more.

[0078] Non-limiting examples of the conductive material include carbon-based materials such as carbon black, acetylene black, or ketjen black; conductive polymers such as polyaniline, polythiophene, polyacetylene, polypyrrole; The conductive material may account for about 1 wt% to 20 wt%, 1 wt% to 10 wt%, or 1 wt% to 7 wt% of the total weight of the positive electrode active material layer. If the conductive material is less than 1% of the total weight of the positive electrode active material layer, the effect or result of improving the conductivity (electrical conductivity) by the conductive material may be negligible. On the contrary, if the conductive material exceeds about 20 wt%, the amount of the positive electrode active material becomes relatively small and the capacity of the battery 100 may decrease or reduce. On the other hand, the conductive material is different from that contained in the carbon material of the sulfur-carbon composite.

[0079] The binder is a binder material for an electrochemical element, and is not limited to a specific material as long as it can bind the constituent components in the electrode such as the electrode active material and ensure a desired adhesive force between the electrode active material layer and the current collector. Non-limiting examples thereof include acrylic binder polymers such as poly(methyl methacrylate) or poly(ethyl acrylate) containing a polyacrylic acid polymerization unit, fluorine-based binder polymers containing a vinylidene fluoride-based polymerization unit (polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polyvinylidene fluoride-co-tetrafluoroethylene, polyvinylidene fluoride-co-trifluoroethylene, polyvinylidene fluoride-co-trifluorochloroethylene, and polyvinylidene fluoride-co-ethylene, etc.), poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, (alkylated) polyethylene oxide, crosslinked polyethylene oxide, polyvinyl ether, polyvinyl pyrrolidone, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinyl pyridine, polystyrene, derivatives, blends, copolymers, etc., but are not limited thereto.

[0080] The binder may account for about 2 wt% to 10 wt% of the total weight of the positive electrode active material layer. If the content of the binder is less than 2 wt%, the effect or result of improving the adhesion between the positive electrode active material or between the positive electrode active material and the positive electrode current collector may be negligible. On the contrary, if the content of the binder exceeds 10 wt%, the amount of the positive electrode active material will be relatively reduced, and the capacity of the battery 100 may decrease or reduce.

[0081] In one embodiment of the present invention, the positive electrode 212 may be manufactured by applying and drying a composition for forming a positive electrode active material layer, which contains a positive electrode material including a positive electrode active material, a conductive material, a binder, etc., onto the upper part of the positive electrode current collector in an organic solvent. Further, if necessary, the electrode manufactured by the above-described method may be pressed to a predetermined thickness, and in that case, heat having a predetermined temperature may be applied if necessary. In one aspect, the organic solvent may be a dispersion medium of the positive electrode material and may be a solvent that easily evaporates. As the organic solvent, for example, it may contain one or more selected from methylpyrrolidone (NMP), acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol. Further, the positive electrode material may be prepared in a state where no organic solvent is added and it is dry-mixed, or in a state where a small amount of solvent is added and it is moistened. After applying such a positive electrode material onto the surface of the positive electrode current collector, the positive electrode can be manufactured by pressing.

[0082] According to one embodiment of the present invention, the negative electrode 216 includes a negative electrode active material layer containing a negative electrode active material. If necessary, the negative electrode may include a negative electrode current collector, and in this case, a negative electrode active material layer (not shown) may be disposed on at least one surface of the negative electrode current collector or the positive electrode surface.

[0083] In one embodiment, the negative electrode current collector may be selected from the group consisting of copper, aluminum, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be surface-treated with carbon, nickel, titanium, silver, etc., and as the alloy, an aluminum-cadmium alloy may be used. Further, fired carbon, surface-treated non-conductive polymers, conductive polymers, etc. can be used as precursors.

[0084] The negative electrode active material may include lithium metal, crystalline carbon, amorphous carbon, or a carbon material containing a combination of crystalline carbon and amorphous carbon, tin, tin oxide (such as SnO2), lithium titanate (LTO), titanium nitrate, silicon (Si), silicon oxide, an alloy of lithium and a metal such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, or Cd, and the like.

[0085] In one embodiment of the present invention, when lithium metal is used as the negative electrode active material, the lithium metal can form a thin film and bind to the current collector.

[0086] Additionally or alternatively, the negative electrode active material layer may include a conductive material and a binder together with the negative electrode active material. The types and contents of the conductive material and / or the binder are substantially similar to the conductive material and the binder described above in relation to the positive electrode 212 of the present invention.

[0087] According to one embodiment of the present invention, the separator 214 of the electrode assembly 210 is a battery component disposed between the positive electrode 212 and the negative electrode 216 to electrically insulate the positive electrode and the negative electrode and provide a migration path for ions. The separator can be used without limitation as long as it can be used in a lithium secondary battery. According to one embodiment of the present invention, it is preferable to use a separator having low resistance and excellent electrolyte absorption characteristics. The separator may include a porous polymer film, a non-woven fabric made of a polymer material, a glass fiber at the eutectic point, and the like. Non-limiting examples of the polymer include porous polymers made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, and the like. These polymer films may be used in a single layer or in a multilayer form by laminating a plurality of layers.

[0088] Figure 3 schematically illustrates a battery manufacturing system 300 for manufacturing a lithium secondary battery according to an aspect of the present invention. The system 300 may include a controller 302, an electrolyte dispensing unit 304, and a jig 306.

[0089] In one embodiment of the present invention, the jig may have two flat plates arranged in parallel, and by narrowing the gap between the flat plates, pressure may be evenly applied to the components (e.g., batteries) arranged between the flat plates. Also, when pressure is applied and released by the jig, the flat plates can be maintained in parallel.

[0090] In one embodiment of the present invention, a battery may be arranged between the two flat plates of the jig, and the stacking direction of the electrode assembly may be perpendicular to the direction in which the flat plates are arranged. That is, the electrode plates (positive electrode and / or negative electrode) included in the electrode assembly and the flat plates may be arranged in parallel.

[0091] In one embodiment of the present invention, the system may further include a thickness measurement unit having a thickness measurement sensor for measuring the thickness of the battery. For example, the thickness measurement unit may be included in the jig or may be connected to the jig. When a battery is inserted between the two flat plates of the jig, for example, between the upper plate which is the first flat plate and the lower plate which is the second flat plate, the thickness measurement sensor can measure the distance between the upper and lower plates of the jig and recognize it as the thickness of the battery. The system may further include an arithmetic unit (not shown), and the arithmetic unit calculates an SF value based on the battery thickness value sent from the thickness measurement sensor and sends it to the control device. On the other hand, the timing when the thickness measurement sensor measures the thickness can be controlled automatically by the control device or manually by the operator.

[0092] In one embodiment of the present invention, the thickness T1 of the battery before electrolyte injection may be the distance between the upper plate and the lower plate of the jig when the distance between the upper plate and the lower plate of the jig decreases and the first plate (upper plate) of the jig contacts the battery after the battery is placed on the second plate (lower plate) of the jig. That is, the thickness of T1 is the thickness in a state where no pressure is substantially applied to the battery. Further, the T1 may be input to the arithmetic unit after being measured using another contact-type or non-contact-type thickness measuring device other than the jig. On the other hand, the thickness T2 of the battery after electrolyte injection may be continuously measured at predetermined time intervals by the sensor while injecting the electrolyte. At this time, the SF value may be continuously measured by the arithmetic unit, and these may be sent to the control device to adjust the pressure so that the measured SF value has a value less than 10, 7 or less, 5 or less, or 3 or less.

[0093] On the other hand, after the electrolyte injection is completed, the value of the thickness T2 of the battery may be measured. In this case, it may be measured in a state where the pressure finally applied to the battery is maintained. Alternatively, the T2 may be measured in a state where the pressure applied to the battery is released. The thickness T2 of the battery after pressure release may be measured by the same method as the above-described method for measuring the thickness of T1. Alternatively, it goes without saying that the thickness of the battery can also be measured by various contact-type or non-contact-type thickness measuring equipment known in the art of thickness measurement technology in addition to the method using the jig. On the other hand, the measurement of the T1 and T2 thicknesses for confirming the SF' may be performed in a state where the pressure finally applied to the battery is maintained, or in a state where the pressure applied to the battery is released.

[0094] Further, in one embodiment, the system 300 may further include a machine or device (not shown) for manufacturing the electrode assembly 210, such as a device for mounting the electrode assembly on the housing 102.

[0095] The control device 302 may be configured to facilitate the battery manufacturing process described in this specification, such as the process shown in FIG. 5. The control device 302 may include a computer system or one or more processors of a computer system. The process or process steps executed by the computer system and the one or more processors may mean an operation. When executed by the one or more processors, the one or more processors may be configured to execute such a process by accessing instructions (e.g., software or computer-readable code) that cause the one or more processors to execute the process. The instructions (commands) may be stored in the memory of the computer system. The processor may be a central processing unit (CPU), a graphics processing unit (GPU), or another type of processing device.

[0096] In one embodiment, the control device 302 can automatically control the electrolyte dispensing unit 304 to inject a predetermined amount of electrolyte into the battery 200. Alternatively, the control device 302 and / or the electrolyte dispensing unit 304 may be operated so that an operator manually injects the electrolyte.

[0097] In one embodiment, the control device 302 may be configured to apply pressure (or force) to one or more sides of the jig 306. The pressure may be applied from the first direction 308 and / or the second direction 310. In one embodiment, the jig 306 may include one or more pressurizing devices (or mechanisms) configured to apply pressure from at least the first direction 308 and / or the second direction 310. The control device 302 may be configured to control the amount of pressure applied to the battery 200 by or from the jig 306. In one embodiment, the jig 306 may be configured to apply the same or constant pressure to each of a single surface or all surfaces. Additionally or alternatively, the jig 306 may be configured to apply different amounts of pressure to different surfaces of the battery 200, or to different regions of a single surface, or to each of multiple surfaces of the battery 200.

[0098] In one embodiment, the jig 306 may be configured to apply pressure to the battery 200 based on a predetermined battery structure (e.g., the thickness of the battery before electrolyte injection) and structural strength (e.g., the tensile strength or elastic strength of the battery). For example, based on the size, material, and shape of the jig 306, various amounts of pressure can be applied to the battery 200 without additional external force or pressure being applied to the jig 306. For example, the jig 306 may be a container, housing, etc., or alternatively or additionally, a pressurizing device (or mechanism) may be coupled to or incorporated into the jig 306 to apply one or more configurable pressures to or from the jig 306 to facilitate the application of one or more pressures. For example, the pressurizing device may include a motor, a spring, etc. In one embodiment, the control device 302 may be configured to automatically or manually adjust the amount of pressure applied or the amount of pressure applied to the battery from the jig through one or more pressurizing devices or pressurizing mechanisms. At this time, the amount of the pressure may be determined by the operation of the system 300.

[0099] As described above, in the case of the Li-S battery according to the present invention, non-uniform impregnation of the electrolyte may occur due to the low porosity of the high-density cathode. For example, when the electrolyte is injected into the housing of the battery 200 without applying pressure or force to the battery 200, strong capillary action may occur at the position where the cathode contacts the electrolyte. Therefore, excessive swelling may occur at or near the initial contact point between the cathode and the electrolyte. Such excessive expansion can prevent the electrolyte from being distributed or dispensed to other regions of the cathode of the battery 200. In this case, the cathode may include pores in which the electrolyte is not uniformly distributed or not impregnated, and for this reason, the electrochemical performance such as the life characteristics may deteriorate. FIG. 8 schematically illustrates a shape in which the thickness of the battery is non-uniformly manufactured due to volume expansion at the position of the liquid injection port when the electrolyte is injected.

[0100] Referring to FIG. 3, the battery 200 may be a Li-S battery containing sulfur as a positive electrode active material. The positive electrode active material layer 212 may have a density of 0.5 g / cc to 1.3 g / cc or 0.7 to 1.3 g / cc. The density of the positive electrode active material layer may be the apparent density, and the apparent density may be calculated by {weight (g) of the positive electrode active material layer / volume (cc) of the positive electrode active material layer}. In one embodiment of the present invention, the positive electrode 212 may have a porosity of 75 vol% or less, 70 vol% or less, or 65 vol% or less. On the other hand, the porosity of the positive electrode may be 35 vol% or more. When the porosity of the positive electrode is less than 35 vol%, problems may occur in ion transport. On the other hand, when the porosity exceeds 75 vol%, the energy density and the mechanical strength of the electrode decrease. In addition, the amount of electrolyte injection may increase. In the unlikely event that the porosity exceeds 75 vol%, when injecting the electrolyte within an appropriate E / S range as described later, the entire electrode assembly may not be impregnated with the electrolyte. On the other hand, the porosity (vol%) may be calculated by [{1 - (apparent density / true density)} × 100]. The true density may be measured from the components of the materials contained in the positive electrode active material layer and the density of each component. Alternatively, the porosity may be measured by the mercury intrusion method of ASTM D 4284-92 using an apparatus such as the autoprore IV 9500 of Micrometrics.

[0101] In one embodiment of the present invention, in the battery 200, the weight ratio of the electrolyte to sulfur (electrolyte / sulfur, E / S) may be 2.7 or less. The weight of the sulfur means the weight of sulfur contained in the positive electrode active material of the positive electrode 212, and the weight of the electrolyte means the weight of the electrolyte injected into the battery. For example, the ratio E / S may be more than 0, 1.0 or more, or 1.5 or more. On the other hand, the ratio E / S may be 2.7 or less, 2.5 or less, or 2.0 or less. That the ratio E / S is 0 (E / S = 0) can indicate a state where there is no electrolyte, for example, before the electrolyte is injected into the battery 200. On the other hand, that the ratio E / S exceeds 2.7 (e.g., E / S>2.7) can indicate that the porosity of the positive electrode 212 of the battery 200 is too high and that an excessive amount of electrolyte is present in the battery 200. This means that the density of the positive electrode does not fall within an appropriate range.

[0102] As shown in FIG. 3, the system 300 according to the present invention can manufacture a cell 200 that minimizes or does not cause volume expansion of the battery at all by a pressurization process. In one embodiment, the battery 200 may be inserted, placed, or arranged in the jig 306 before the electrolyte is injected into the battery 200. In one embodiment, the battery 100 may be a Li-S battery. The electrode assembly of the Li-S battery (e.g., electrode assembly 210) may include a high-density positive electrode 212 with a low porosity. For example, the electrode assembly 210 may be a lithium-ion battery including a high-density positive electrode having a density of 0.5 g / cc to 4.5 g / cc or 0.7 g / cc to 4.5 g / cc. In this specification, the density of the electrode means the density of the electrode active material layer. That is, in this specification, the density of the positive electrode means the density of the positive electrode active material layer.

[0103] In one embodiment of the present invention, the positive electrode density of the present invention may be 0.5 g / cc or more, 0.7 g / cc or more, 0.8 g / cc or more, or 0.9 g / cc or more. Also, the density of the positive electrode may be 4.5 g / cc or less, or 4.0 g / cc or less. If the density of the positive electrode exceeds the above range and becomes excessively high, the life and / or performance of the battery may be reduced or deteriorated. In particular, the positive electrode of the present invention contains a sulfur-based positive electrode active material as the positive electrode active material, and preferably has a density of 0.7 g / cc or more. Also, the upper limit of the density of the positive electrode may be appropriately adjusted within the above-described range.

[0104] According to the present invention, when manufacturing a battery, specifically when injecting an electrolytic solution, a pressurization step may be performed so that the electrolytic solution is uniformly impregnated into the pores of the positive electrode. The pressurization step may be performed based on one or more of a plurality of factors including the porosity and density of the positive electrode, the ratio E / S, and the shape and size of the battery.

[0105] In one embodiment of the present invention, the amount of pressure applied during the pressurization step may be controlled based on the thickness of the cell, specifically T1 and T2. While the electrolytic solution is being injected, T2 may be continuously measured by a thickness measuring device connected to the jig. Based on each measured T2, a relatively strong pressure may be applied to a battery with a large SF (a large degree of expansion) in order to reduce the expansion, and a relatively weak pressure may be applied to a battery with a small SF (a small degree of expansion). Since the liquid injection is performed in a limited space where the position is fixed by the thickness of the cell, it is possible to suppress the expansion of the electrode that occurs when the electrolytic solution is impregnated.

[0106] In one embodiment of the present invention, the amount of pressure during pressurization may be 100 atm or less. For example, the amount of pressure may be 0.1 atm to 100 atm, 1 atm to 100 atm, 3 atm to 100 atm, or 5 atm to 100 atm. As a specific example, the amount of pressure may be 100 atm or less, 70 atm or less, 50 atm or less, 30 atm or less, or 10 atm or less. When the amount of pressure is less than 0.1 atm, it may not be possible to keep the thickness of the battery constant. That is, when the pressure applied to the battery housing is insufficient, excessive expansion may occur at the position where the electrolyte first contacts the electrode assembly (or the positive electrode), and the thickness of the battery may increase. Or, when the pressure during pressurization exceeds 100 atm, excessive pressure is applied to the housing, and components of the electrode assembly such as electrodes and separators may be deformed, shrunk, or damaged. On the other hand, in one embodiment of the present invention, it is preferable that the amount of pressure is maintained in the range where T2 measured continuously during electrolyte injection is the same as or higher than T1, that is, the SF value is 0 or more.

[0107] As shown in FIG. 3, based on the desired expansion coefficient SF of the battery 200, the amount of pressure applied to the battery 200 from or by the jig 306 can be adjusted.

[0108] In one embodiment of the present invention, the expansion coefficient SF of the battery 100 and / or the battery 200 may be defined by the following [Formula 1].

[0109] [Formula 1] SF = (T2 - T1) / (T1) × 100.

[0110] In one embodiment of the present invention, in the above Formula 1, SF is the expansion coefficient, T1 means the thickness of the battery 200 before injection of the electrolyte into the housing 102, and T2 means the thickness of the battery 200 after injection of the electrolyte into the housing 102. Additionally or alternatively, T1 may be the thickness of the battery at any first location on the battery surface, and T2 may be the thickness of the battery at any second location different from T1.

[0111] Referring to FIG. 4a, FIG. 4a exemplarily shows the thickness measurement area of the battery 200. In one embodiment, the thickness T1 of the battery 200 may be measured before the electrolyte is injected into the housing. In one embodiment, the battery 200 may include area A, area B, and area C, and the thickness of the battery 200 may be measured individually or in combination at area A, area B, and / or area C. Although three areas are shown in this embodiment, the number of measurement areas may be changed. In a specific embodiment of the present invention, the thickness may be measured at one or more specific locations in each area.

[0112] FIG. 4B exemplarily shows the thickness measurement area of the battery 200. In one embodiment, the thickness T2 of the battery 200 may be measured after the electrolyte is injected into the housing. In one embodiment, the battery 200 may include area A, area B, and area C. The thickness of the battery 200 may be measured individually or in combination at area A, area B, and / or area C. Although three areas are shown in this embodiment, the number of measurement areas may be changed. In a specific embodiment of the present invention, the thickness may be measured at one or more specific locations in each area.

[0113] As shown in FIGS. 3 to 4b, the battery manufacturing system 300 according to the present invention can manufacture the battery 200 having a swelling coefficient in the range of 0 ≦ SF < 10. This SF range indicates that after the injection of the electrolytic solution into the battery, the swelling of the battery 200 is minimized or does not occur at all. As described above, when the electrolytic solution is injected into the housing of the battery 200, the electrolytic solution fills the empty space 204 in the housing. Therefore, any change in the thickness of the battery 200 after the injection of the electrolytic solution indicates that the electrolytic solution is not uniformly impregnated in the housing. Therefore, a swelling coefficient greater than 0 can indicate that the electrolytic solution does not completely fill the pores of the electrode assembly and the empty space inside the battery 200. When the SF value is 10 or more, it can be shown that there is an excessive amount of electrolytic solution that is not impregnated in the internal pores of the electrode. On the other hand, since the thickness of the battery does not substantially decrease, it is difficult for SF < 0 to occur after the injection of the electrolytic solution. When the electrolytic solution completely and uniformly impregnates the pores of the electrode and the excessive electrolytic solution (the amount of electrolytic solution exceeding the pore volume of the electrode assembly) sufficiently fills the dead space of the battery 200, the swelling coefficient is substantially SF = 0. On the other hand, when the swelling coefficient does not exceed 10, since the change in thickness is not substantially large, in the present invention, when SF shows a value of 0 or more and less than 10, it is considered that the electrolytic solution is uniformly filled in the electrode assembly. According to a specific embodiment of the present invention, the swelling coefficient of the battery 200 is 0 ≦ SF < 10, 0 ≦ SF ≦ 7, 0 ≦ SF ≦ 5, 0 ≦ SF ≦ 3, 0 ≦ SF ≦ 2, or 0 ≦ SF ≦ 1, preferably, SF is 5 or less, and most preferably, SF can be 0.

[0114] On the one hand, after injecting the electrolyte into the pouch battery to completely fill the pores of the electrode assembly with the electrolyte, the remaining electrolyte is filled into the empty space 204 in the pouch. The empty space is a space that normally exists inside the pouch and is a space into which the remaining electrolyte may flow after the pores of the electrodes are filled with the electrolyte. Therefore, considering the volume of the pores in the electrode assembly, when an amount of electrolyte corresponding to the volume is injected, in some cases, even if it does not all flow into the inside of the electrode assembly and remains outside the electrode assembly, it is filled into the empty space 204. Thus, the SF can have a value less than 10, 7 or less, 5 or less, or even less, and preferably can have a value close to 0.

[0115] Therefore, by configuring the positive electrode with a low porosity and a high density, especially by configuring the positive electrode of a lithium-sulfur battery with a high density and a low porosity, even when a small amount of electrolyte is used compared to a conventional Li-S battery, the battery can be driven or operated with improved performance.

[0116] The lithium secondary battery according to the present invention includes a high-density electrode and has a low E / S ratio, and the electrolyte can be uniformly impregnated to realize a high-capacity lithium secondary battery.

[0117] In this specification, the lithium secondary battery means that the E / S ratio has the aforementioned range and the weight of the electrolyte with respect to the weight of sulfur contained as the positive electrode active material is below a certain value.

[0118] In the present invention, the lithium secondary battery has a high density of the positive electrode and the electrolyte uniformly flows into the electrode assembly and has a uniform thickness, so it can exhibit a high capacity. In one embodiment of the present invention, the capacity of the lithium secondary battery is 950 mAh / g s ~1300 mAh / g s and can be. Specifically, the capacity of the lithium secondary battery is 950 mAh / g s or more, 1000 mAh / g s or more, or 1050 mAh / g sIt may be as described above. Further, the capacity of the secondary battery is 1300 mAh / g s or less, 1250 mAh / g s or less, or may be 1200 mAh / g s or less. The battery capacity is based on the capacity per unit weight (g) of the positive electrode active material, i.e., sulfur.

[0119] On the other hand, in the present invention, the electrolyte may contain an organic solvent and a lithium salt. Further, the electrolyte may be a liquid electrolyte.

[0120] The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. As the organic solvent, those commonly used in electrolytes for lithium secondary batteries can be used without limitation. For example, ether, ester, amide, linear carbonate, cyclic carbonate, etc. may be used alone, or two or more of them may be used in combination. Among them, ether compounds can be typically cited.

[0121] The ether compound may include acyclic ether and cyclic ether.

[0122] For example, the acyclic ether may be one or more selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dimethoxyethane, diethoxyethane, ethylene glycol ethyl methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, and polyethylene glycol methyl ethyl ether.

[0123] For example, the cyclic ether may be one or more selected from the group consisting of dioxolane, 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-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, isosorbdimethyl ether, furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, and 2,5-dimethylthiophene, but is not limited thereto.

[0124] Examples of the ester of the organic solvent include any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, and mixtures of two or more thereof, but are not limited thereto.

[0125] Specific examples of the chain carbonate compound typically include, but are not limited to, any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, or a mixture of two or more thereof.

[0126] 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, vinyl ethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of such halides include, but are not limited to, fluoroethylene carbonate (FEC).

[0127] The lithium salt is a compound capable of supplying lithium ions in the electrolyte. Such lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3CO2, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiCH3SO3, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiC4BO8, LiCl, LiBr, LiB 10 Cl 10 , LiI, or LiB(C2O4)2, etc. can be used. In the present invention, from the viewpoint of enhancing the availability of sulfur and realizing a high-capacity and high-voltage battery, it is preferable that the lithium salt contains Li-TFSI. More preferably, the lithium salt may contain LiN(CF3SO2)2 (Li-TFSI) at a content of 80 wt% or more, 90 wt% or more, or 100 wt% based on 100 wt% of the total lithium salt.

[0128] The concentration of the lithium salt ranges from 0.1 to 2.0 M, preferably from 0.5 to 1 M, more preferably from 0.5 to 0.75 M. When the concentration of the lithium salt is within the above range, the electrolytic solution can have excellent performance and lithium ion mobility because it has appropriate conductivity and viscosity. When the concentration of the lithium salt is less than the above range, it may be difficult to ensure ionic conductivity suitable for driving the battery. When it exceeds the above range, the viscosity of the electrolytic solution may increase, resulting in a decrease in the mobility of lithium ions, or the decomposition reaction of the lithium salt itself may increase, leading to a possible decrease in the performance of the battery.

[0129] In addition to the components of the electrolytic solution, the electrolytic solution may further contain additives for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc. For example, as the additives, nitrate compounds, nitrite-based compounds, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc. may be used alone or in combination. The additives may be contained in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the electrolytic solution.

[0130] In a specific embodiment of the present invention, the electrolytic solution may contain a nitric acid compound and / or a nitrous acid-based compound as an additive. The above nitric acid compound / nitrous acid-based compound has the effect of forming a stable film on the lithium metal electrode which is the negative electrode and improving the charge / discharge efficiency. Examples of such nitric acid or nitrous acid-based compounds include inorganic nitric acid or nitrous acid compounds such as lithium nitrate (LiNO3), potassium nitrate (KNO3), cesium nitrate (CsNO3), barium nitrate (Ba(NO3)2), ammonium nitrate (NH4NO3), lithium nitrite (LiNO2), potassium nitrite (KNO2), cesium nitrite (CsNO2), ammonium nitrite (NH4NO2); organic nitric acid or nitrous acid compounds such as methyl nitrate, dialkylimidazolium nitrate, guanidine nitrate, imidazolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, octyl nitrite; organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, dinitrotoluene, and one or more selected from the group consisting of combinations thereof, but are not limited thereto. In a preferred embodiment of the present invention, the additive may contain lithium nitrate.

[0131] On the other hand, FIG. 5 is a process flowchart explaining step by step an exemplary method 500 for manufacturing the lithium secondary battery of the present invention. The manufacturing of the battery can be performed by the battery manufacturing system 300 described above.

[0132] First, an electrode assembly is formed by laminating a first electrode, a separator, and a second electrode (step 502). In one embodiment, the first electrode may be a positive electrode, and the second electrode may be a negative electrode. Thereafter, the electrode assembly is inserted into a housing (step 504). In one embodiment of the present invention, the housing may be a pouch. The housing into which the electrode assembly is inserted is placed in a jig. In one embodiment of the present invention, the thickness T1 of the battery may be measured before or after being placed in the jig. Thereafter, pressure may be applied to the surface of the inserted battery (step 506). The pressure may be controlled to exhibit a desired expansion coefficient SF. In one embodiment of the present invention, the amount of pressure may be controlled to satisfy the above conditions at 100 atm or less. In one embodiment of the present invention, the expansion coefficient SF of the battery may be 0 to less than 10. Next, a predetermined amount of electrolyte is injected into the housing (step 508). On the other hand, as described above, the thickness of the battery can be measured while injecting the electrolyte, and based on this, the amount of pressure applied to the battery can be appropriately controlled. The control of the amount of pressure may be performed based on the SF value. When the injection of the electrolyte is completed, the battery is then sealed (step 510). On the other hand, the expansion coefficient of the battery may be measured before the sealing. In other embodiments, the expansion coefficient may be measured after sealing the pouch. In still other embodiments, the thickness T2 may be measured before or after releasing the pressure applied to the battery. The expansion coefficient SF is calculated based on the above formula 1. In one embodiment of the present invention, the expansion coefficient may be measured before or after pressure release of T2, and may have a value of 0 or more and less than 10, preferably 7 or less, more preferably 5 or less, and even more preferably 3 or less or less.

[0133] Also, in one embodiment of the present invention, after the pressure of the battery is released, the thicknesses T1 and T2 may be measured at any two locations, and the SF value may be calculated therefrom.

[0134] Exemplary embodiments are presented to assist in the understanding of the present invention. However, the following embodiments are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope and spirit of the present invention. Such various changes and modifications are included within the scope of the appended claims.

[0135] Example 1 (1) Manufacture of the electrode assembly A sulfur-carbon composite was prepared as the positive electrode active material. Sulfur (S) and carbon (for example, CNT) were uniformly mixed in a solid state (S:CNT = 75:25, weight ratio), and then heat-treated at 155 °C for 35 minutes to produce a sulfur-carbon composite. The positive electrode active material (sulfur-carbon composite), CNT (specific surface area 300 m 2 / g, particle size 20 μm), and SBR (styrene-butadiene rubber) were mixed at a ratio of 90:5:5 (weight ratio) using a mixer to prepare a composition for forming a positive electrode active material layer. This composition and ethanol as an organic solvent were mixed to produce a slurry for forming a positive electrode active material layer. The slurry was coated on an Al current collector, dried, and pressure-bonded to fabricate a positive electrode.

[0136] Also, a lithium metal thin film was prepared as the negative electrode. After the fabricated positive electrode and negative electrode were positioned opposite to each other, a polyethylene separator was interposed between the positive electrode and the negative electrode to manufacture an electrode assembly.

[0137] (2) Pressurization A pressurization jig with the upper plate and the lower plate arranged in parallel was prepared, and a pouch containing the electrode assembly was placed in the jig. Then, it was pressurized to about 5 atmospheres (atm) to maintain a constant thickness of the pouch cell.

[0138] (3) Electrolyte injection An electrolyte solution was prepared by adding 1 mol of LiTFSI to a mixed organic solvent of tetraethylene glycol dimethyl ether (TEGDME) / dioxolane (DOL) / dimethoxyethane (DME) (1:1:1 volume ratio). On the other hand, LiNO3 was added at a weight ratio of 1 / 10 of LiTFSI. After injecting the electrolyte solution, the pressure was reduced for about 3 seconds to maintain a vacuum state. Then, after completely injecting the electrolyte solution, the jig was removed from the pouch cell.

[0139] Comparative Example 1 A pouch cell type Li-S secondary battery was manufactured in the same manner as in Example 1, except that the pressurization steps before and after electrolyte injection were not performed.

[0140] Test Example 1 Performance experiments of the Li-S secondary batteries manufactured in Example 1 and Comparative Example 1 were conducted.

[0141] (1) Initial discharge capacity and battery life For the pouch cell type Li-S secondary battery, charge and discharge tests were performed by repeating charge and discharge at room temperature. After the first discharge at 0.1C, the same charge and discharge were repeated 2 more times, and after repeating charge and discharge 3 times at 0.2C, charge and discharge were continuously repeated at 0.3C / 0.5C. The initial discharge capacity was evaluated by obtaining the capacity-voltage graph at the first discharge, and the high-speed performance was evaluated by obtaining the capacity change graph by cycle repetition.

[0142] (2) 0.1C nominal voltage (V) The 0.1C nominal voltage was measured using a PNESOLUTION charger.

[0143] (3) Electrolyte / sulfur ratio After measuring the weight of sulfur respectively, the weight ratio was calculated.

[0144] (4) Energy density (Wh / kg) The energy density was calculated by dividing the capacity (Wh) of the pouch cell by the weight (kg) of the pouch cell.

[0145] (5) Measurement of expansion coefficient SF The expansion coefficient was calculated based on the following formula (1).

[0146] [Formula (1)] SF = (Thickness of the pouch cell after electrolyte injection - Thickness of the pouch cell before electrolyte injection) / (Thickness of the pouch cell before electrolyte injection) × 100

[0147] [Table 1]

[0148] Figure 6 is a graph 600 comparing the initial discharge capacities of Example 1 and Comparative Example 1 manufactured according to one aspect of the present invention. As can be seen from Table 1 and graph 600, it was confirmed that the battery of Example 1 is superior in initial discharge capacity characteristics compared to the battery of Comparative Example 1.

[0149] Figure 7 is a graph 700 comparing the discharge cycle characteristics of Example 1 and Comparative Example 1 manufactured according to one aspect of the present invention. As can be seen from Table 1 and graph 700, it was confirmed that the battery of Example 1 is superior in life characteristics compared to the battery of Comparative Example 1.

[0150] In addition, Example 1 exhibits an excellent 0.1C discharge nominal voltage and energy density compared to Comparative Example 1. Although the electrolyte / sulfur ratio of Example 1 and Comparative Example 1 is the same, all other physical properties of Example 1 are superior to those of Comparative Example 1, which is because the electrolyte was uniformly injected by the pressurization process. [Description of Reference Numerals]

[0151] 100 Battery 102 Housing 104 First Electrode Tab 106 Second Electrode Tab 104a Insulating Protection Tape 106a Insulating Protection Tape 200 Battery 202 Opening (Electrolyte Inlet) 210 Electrode Assembly 204 Dead Space 210 Electrode Assembly 212 Positive Electrode 214 Separator 216 Negative Electrode 218 Final Layer 300 System 304 Electrolyte Dispensing Unit 302 Controller 306 Jig 308 Second Direction 308 First Direction

Claims

1. A lithium-sulfur battery having a sulfur-based compound as a positive electrode active material, comprising an electrode assembly having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, a pouch for housing the electrode assembly, and an electrolytic solution, wherein the lithium-sulfur battery has a swelling coefficient (SF) according to the following formula 1 of 0 or more and less than 10, and the positive electrode has a density of the positive electrode active material layer of 0.5 g / cc to 4.5 g / cc, the lithium-sulfur battery: [Formula 1] SF = (T2 - T1) / (T1) × 100 (wherein, T1 is the first thickness of the lithium-sulfur battery, and T2 is the second thickness of the lithium-sulfur battery) The first thickness is the thickness of the lithium-sulfur battery before injecting the electrolytic solution into the pouch, and the second thickness is the thickness of the lithium-sulfur battery after injecting the electrolytic solution into the pouch.

2. The lithium-sulfur battery according to claim 1, wherein the positive electrode contains a sulfur-carbon composite having a carbon material and sulfur as a positive electrode active material.

3. The lithium-sulfur battery according to claim 2, wherein the weight of sulfur is 70% or more based on the total weight of the sulfur-carbon composite.

4. The lithium-sulfur battery according to claim 1, wherein the negative electrode contains lithium as a negative electrode active material.

5. The lithium-sulfur battery according to claim 2, wherein E / S, which is the ratio of the weight of the electrolytic solution to the weight of sulfur, is 2.7 or less.

6. The lithium-sulfur battery according to claim 1, wherein the positive electrode active material layer of the positive electrode has a porosity of 35 vol% to 75 vol%.

7. The capacity of the lithium-sulfur battery is 950 mAh / g ｓ to 1300 mAh / g ｓ The lithium-sulfur battery according to claim 1, which is such.

8. An electric vehicle comprising the lithium-sulfur battery according to claim 1 as a power source.

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