Lithium secondary battery with high specific capacity

Abstract

The present invention relates to a lithium-sulfur battery having high capacity and high energy density, and provides novel parameters for the characteristics of a lithium-sulfur battery having high capacity and high energy density. A lithium-sulfur battery according to one embodiment of the present invention includes a positive electrode containing a sulfur-carbon composite, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the content ratio of sulfur element (S) according to the above formula 1 (R SL ) is 15% or less.

Description

[Technical Field]

[0001] This invention relates to lithium secondary batteries, particularly lithium-sulfur batteries having a high specific capacity.

[0002] This application claims priority based on Korean Patent Application No. 10-2023-0057999 filed on 3 May 2023 and Korean Patent Application No. 10-2023-0133558 filed on 6 October 2023, and all contents disclosed in the specifications of said applications are incorporated into this application. [Background technology]

[0003] As the applications of lithium-ion batteries expand beyond portable electronic devices to include electric vehicles (EVs) and electric storage systems (ESSs), the demand for high-capacity, high-energy-density, and long-life lithium-ion batteries is increasing.

[0004] Among the various types of lithium-ion secondary batteries, lithium-sulfur batteries are battery systems that use a sulfur-based substance having a sulfur-sulfur bond as the positive electrode active material, and lithium metal, a carbon-based substance where lithium ion insertion / deinsertion occurs, or silicon or tin that form an alloy with lithium as the negative electrode active material.

[0005] Sulfur, the main material for the positive electrode active material in lithium-sulfur batteries, has several advantages: it is lightweight per atom, readily available and inexpensive due to its abundance of resources, non-toxic, and environmentally friendly.

[0006] Furthermore, lithium-sulfur batteries involve the conversion reaction (S8 + 16Li) between lithium ions and sulfur at the positive electrode. + +16e -The theoretical specific capacity (IQ) of 8Li2S reaches 1,675 mAh / g, and when lithium metal is used as the negative electrode, it exhibits a theoretical energy density of 2,600 Wh / kg. This is significantly higher than the theoretical energy densities of other battery systems currently under research (Ni-MH batteries: 450 Wh / kg, Li-FeS batteries: 480 Wh / kg, Li-MnO2 batteries: 1,000 Wh / kg, Na-S batteries: 800 Wh / kg) and lithium-ion batteries (250 Wh / kg), making it a noteworthy lithium secondary battery among those currently under development for its environmental friendliness, high capacity, and low cost.

[0007] In the positive electrode of a lithium-sulfur battery, sulfur accepts electrons during discharge, causing a reduction reaction. At this time, lithium polysulfide (Li2S) is produced at the positive electrode. x These generate (x=1~8), some of which dissolve in the electrolyte and cause side reactions within the battery, accelerating battery degradation. They also cause shuttle reactions during the charging process, significantly reducing charge and discharge efficiency. As a result, the specific capacity of lithium-sulfur batteries developed to date falls far short of the theoretical specific capacity.

[0008] Therefore, there is a need to develop lithium-sulfur batteries with a specific capacity as high as that of the theoretical specific capacity. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The present invention aims to solve the above-mentioned problems and provide a lithium-sulfur battery having a specific capacity as high as that of the theoretical specific capacity.

[0010] Furthermore, the present invention aims to provide a lithium-sulfur battery having a high energy density. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, According to one aspect of the present invention, a lithium-sulfur battery of the following embodiments is provided.

[0012] The lithium-sulfur battery according to the first embodiment is a lithium-sulfur battery including a positive electrode containing a sulfur-carbon composite, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution, where at least one of the positive electrode and the electrolytic solution contains a sulfur-based compound, and the content ratio (R SL ) of sulfur element (S) according to the following formula 1 is 15% or less. [Formula 1] R SL (%) = W SE / W SP ×100 In formula 1, W SE is the weight of sulfur element (S) among the sulfur-based compounds present in the electrolytic solution, W SP is the weight of sulfur element (S) among the sulfur-based compounds present in the positive electrode.

[0013] According to the second embodiment, in the first embodiment, W SE and W SP of the above formula 1 can each be values measured in a discharge state of 1.7V to 1.9V.

[0014] According to the third embodiment, in the first embodiment or the second embodiment, the sulfur-based compound present in the electrolytic solution may include inorganic sulfur (S8), lithium polysulfide (Li2S x , 1 ≤ x ≤ 8), or a mixture thereof.

[0015] According to the fourth embodiment, in any one of the first embodiment to the third embodiment, the sulfur-based compound present in the positive electrode may include inorganic sulfur (S8).

[0016] According to the fifth example of manifestation, in any one of the first to fourth examples of manifestation, The aforementioned W SE This may be 15% by weight or less, based on the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery.

[0017] According to the sixth example, in any one of the first to fifth examples, The aforementioned W SP This can be 65% by weight or more, based on the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery.

[0018] According to the 7th embodiment example, in any one of the 1st to 6th embodiment examples, The aforementioned W SP This can be 75.5% by weight or more, based on the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery.

[0019] According to the eighth example of implementation, in any one of the seventh examples of implementation, The aforementioned lithium-sulfur battery may satisfy the following equation 2. [Formula 2] W' SP >1.2×W' SE +56.86 In equation 2, W' SE This is the weight percentage of sulfur element (S) in the sulfur-based compounds present in the electrolyte, based on the total weight of sulfur element (S) in the sulfur-based compounds contained in the lithium-sulfur battery. W' SP This is the weight percentage of sulfur element (S) in the sulfur-based compounds present in the positive electrode, based on the total weight of sulfur element (S) in the sulfur-based compounds contained in the lithium-sulfur battery.

[0020] According to the 9th embodiment example, in any one of the 1st to 8th embodiment examples, The aforementioned lithium-sulfur battery may satisfy the following equation 3. [Formula 3] 10.667×R S / C -10.633>R SL In equation 3, R SL This is the content ratio of sulfur element (S) according to the above formula 1, R S / C This is the weight ratio of sulfur (S) to carbon (C) in the sulfur-carbon composite.

[0021] According to the 10th embodiment, in any one of the 1st to 9th embodiments, The sulfur-carbon composite may have a sulfur-to-carbon weight ratio (S / C weight ratio) of 2.5 g / g or less.

[0022] According to the 11th embodiment, in any one of the 1st to 10th embodiments, The positive electrode includes a current collector and a positive electrode active material layer containing the sulfur-carbon composite, The weight of the sulfur-carbon composite may be 80% by weight or more, based on the total weight of the positive electrode active material layer.

[0023] According to the 12th embodiment, in any one of the 1st to 11th embodiments, The weight ratio of the electrolyte to the sulfur in the sulfur-carbon composite (El / S weight ratio) may be 3.5 g / g or less.

[0024] According to the 13th embodiment example, in any one of the 1st to 12th embodiment examples, The electrolyte may include acyclic ethers, cyclic ethers, or mixtures thereof.

[0025] According to the 14th embodiment example, in any one of the 1st to 13th embodiment examples, The electrolyte comprises a mixture of the acyclic ether and the cyclic ether, and the volume ratio of the acyclic ether to the cyclic ether may be 5:95 to 95:5 (v / v).

[0026] According to the 15th example, in any one of the 1st to 14th examples, The lithium-sulfur battery may have a specific capacity of 60% or more of the theoretical specific capacity calculated from the total content of sulfur compounds contained in the lithium-sulfur battery.

[0027] According to the 16th example, in any one of the 1st to 15th examples, The aforementioned sulfur-based compounds include inorganic sulfur (S8), lithium (poly)sulfide (Li2S x It may include (1 ≤ x ≤ 8), or a mixture of two or more of these.

[0028] According to the 17th example, in any one of the 1st to 16th examples, The specific capacity of the lithium-sulfur battery may be 1,000 mAh / g or more.

[0029] According to the 18th example, in any one of the 1st to 17th examples, The energy density of the lithium-sulfur battery may be 300 Wh / kg or more.

[0030] According to the 19th embodiment example, in any one of the 1st to 18th embodiment examples, The lithium-sulfur battery may be a coin-type battery, a pouch-type battery, or a cylindrical battery.

[0031] According to another aspect of the present invention, a method is provided for evaluating the specific capacity of a lithium-sulfur battery in the following embodiment.

[0032] The method for evaluating the specific capacity of a lithium-sulfur battery according to the 20th embodiment example is: A method for evaluating the specific capacity of a lithium-sulfur battery comprising a positive electrode containing a sulfur-carbon composite, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, At least one of the positive electrode and the electrolyte contains a sulfur-based compound. The sulfur (S) content ratio (R) according to the following formula 1 SLThis includes a step of determining that a lithium-sulfur battery with a specific capacity of 15% or less is a high-specific-capacity battery. [Formula 1] R SL (%)=W SE / W SP ×100 In equation 1, W SE This is the weight of the sulfur element (S) among the sulfur-based compounds present in the electrolyte, W SP This is the weight of the sulfur element (S) among the sulfur-based compounds present at the positive electrode.

[0033] According to the 21st example, in the 20th example, The aforementioned high specific capacity battery may be a battery having a specific capacity of 1,000 mAh / g or more. [Effects of the Invention]

[0034] A lithium-sulfur battery according to one aspect of the present invention can have a high specific capacity, comparable to its theoretical specific capacity.

[0035] In particular, the lithium-sulfur battery of the present invention can have a specific capacity of 1,000 mAh / g or more.

[0036] Furthermore, a lithium-sulfur battery according to one aspect of the present invention can have a high energy density.

[0037] In particular, the lithium-sulfur battery of the present invention can have an energy density of 300 Wh / kg or more. [Modes for carrying out the invention]

[0038] The present invention will be described in more detail below.

[0039] Throughout this specification, when a part states that a certain component "includes", "has", or "comprises" a certain component, unless otherwise specified, it does not exclude other components and may further include other components.

[0040] Also, throughout this specification, terms such as "about" and "substantially" are used as meanings equal to or close to the numerical values when manufacturing and material tolerances inherent to the mentioned meanings are presented, in order to prevent unscrupulous infringers from misusing the disclosure content where exact or absolute numerical values are mentioned to assist in the understanding of this application.

[0041] Throughout this specification, the description "A and / or B" means "A, B, or all of these".

[0042] As used in this specification, the term "composite" means a substance in which two or more materials are combined to form physically and chemically different phases while exhibiting a more effective function.

[0043] The term "(poly)sulfide" used in this specification refers to the concept that includes all of "(poly)sulfide ion (S x 2- , 1 ≦ x ≦ 8)" and "lithium (poly)sulfide (Li2S x or Li2S x - , 1 ≦ x ≦ 8)".

[0044] In this specification, the term "polysulfide" refers to the concept that includes all of "polysulfide ion (S x 2- , 1 < x ≦ 8)" and "lithium polysulfide (Li2S x or Li2S x - , 1 < x ≦ 8)".

[0045] The unit "mAh / g" used in this specification sUnless otherwise specified, mAh / g(s) is used to indicate the volume per unit weight of sulfur (S) and may be used interchangeably with other expressions such as mAh / g(s) and mAh / gs.

[0046] The unit used herein is "mg" s / cm 2 Unless otherwise specified, "mg(s) / cm²" indicates the weight of sulfur (S) per unit area. 2 , mAh / g s It can be used in combination with other forms of expression, such as those mentioned above.

[0047] Lithium-sulfur batteries have a problem in that lithium polysulfide, formed by the reduction reaction of sulfur (S8) at the positive electrode during charging and discharging, dissolves from the positive electrode into the electrolyte, preventing the battery from reaching its theoretical capacity.

[0048] According to one embodiment of the present invention, a lithium-sulfur battery having high capacity, specifically high specific capacity, is provided.

[0049] A lithium-sulfur battery according to one embodiment of the present invention includes a positive electrode containing a sulfur-carbon composite, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte.

[0050] In one embodiment of the present invention, the lithium-sulfur battery may specifically include an electrode assembly comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, all of which contain the sulfur-carbon composite; an electrolyte; and a case housing the electrode assembly.

[0051] At this time, the lithium-sulfur battery has a sulfur element (S) content ratio (R) according to the following formula 1. SL ) is 15% or less.

[0052] [Formula 1] R SL (%)=W SE / W SP ×100

[0053] In equation 1, WSE is the weight of sulfur element (S) among the sulfur-based compounds present in the electrolyte, and W SP is the weight of sulfur element (S) among the sulfur-based compounds present in the positive electrode.

[0054] As described above, the lithium-sulfur battery contains inorganic sulfur (S8) as a positive electrode active material. In the lithium-sulfur battery, lithium (poly) sulfide is formed by a reduction reaction at the positive electrode during discharge. If the formed lithium (poly) sulfide is dissolved by the electrolyte and elutes from the positive electrode into the electrolyte, the amount of lithium (poly) sulfide oxidized at the positive electrode during charging of the lithium-sulfur battery decreases, which may consequently cause a reduction in the capacity of the lithium-sulfur battery.

[0055] The inventors of the present invention have found that a lithium-sulfur battery with an R SL value of 15% or less according to the above-described formula 1 exhibits a high capacity. That is, when the active material present in the electrolyte is maintained below a specific standard compared to the active material present in the positive electrode of the lithium-sulfur battery, it is advantageous for realizing a high capacity. To quantify this, the weight ratio (W SP ) of sulfur element (S) among the sulfur-based compounds present in the positive electrode to the weight ratio (W SE ) of sulfur element (S) among the sulfur-based compounds present in the electrolyte is newly defined as the R SL .

[0056] Considering such a mechanism, in this specification, substances containing sulfur element (S) derived from the positive electrode active material of the lithium-sulfur battery are collectively referred to as "sulfur-based compounds". The sulfur-based compounds may include all sulfur-containing compounds formed through, for example, a reduction reaction of inorganic sulfur (S8) or an oxidation reaction of lithium sulfide (Li2S), and more specifically, inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2S x , 1 < x ≤ 8), disulfide compounds, carbon-sulfur polymers ((C2S y )) nThe equation may include y = 2.5 to 50, n ≥ 2, or two or more of these.

[0057] In one embodiment of the present invention, for the sake of explanation, the lithium sulfide (Li2S) is referred to as lithium (poly) sulfide (Li2S x Sometimes, the lithium (poly) sulfide is included in the explanation (x=1), and in this case, the lithium (poly) sulfide is referred to as "Li2S x It can be represented by the chemical formula "1 ≤ x ≤ 8". Thus, in one embodiment of the present invention, the sulfur compound is, for example, inorganic sulfur (S8), lithium (poly)sulfide (Li2S x It may include , 1 ≤ x ≤ 8, or two or more of these.

[0058] According to one embodiment of the present invention, a novel ratio is proposed for the amount of sulfur element (S) present in the electrolyte relative to the amount of sulfur element (S) present in the positive electrode of a lithium-sulfur battery, which enables the realization of a high specific capacity.

[0059] Specifically, according to one embodiment of the present invention, the content ratio of sulfur element (S) according to the above formula 1 (R SL A lithium-sulfur battery is provided in which the sulfur content is 15% or less.

[0060] The aforementioned R SL This represents the percentage (%) of the weight of sulfur (S) in the sulfur-based compounds present in the electrolyte relative to the weight of sulfur (S) in the sulfur-based compounds present in the positive electrode of a lithium-sulfur battery. Specifically, it is expressed by R using the following formula 1. SL By controlling the ratio to 15% or less, a lithium-sulfur battery with high capacity is provided. [Formula 1] R SL (%)=W SE / W SP ×100 In equation 1, W SE This is the weight of the sulfur element (S) among the sulfur-based compounds present in the electrolyte, and W SP This is the weight of the sulfur element (S) among the sulfur-based compounds present at the positive electrode.

[0061] In one embodiment of the present invention, a lithium-sulfur battery having a high specific capacity, regardless of the charge / discharge state, the R SL This may be 15% or less. However, preferably, it is necessary to control the ratio at which lithium (poly)sulfide formed at the positive electrode during discharge of a lithium-sulfur battery dissolves in the electrolyte and disappears from the positive electrode, so the R SL This can be a lithium-sulfur battery where the discharge rate is 15% or less.

[0062] In another embodiment of the present invention, the lithium-sulfur battery having high specific capacity is R SL The percentage may be 14% or less, 13% or less, or 12% or less. SL The smaller R is, the greater the capacity of the lithium-sulfur battery, so there is no particular lower limit to it. For example, the R SL It may have values ​​of 0.5% or more, 1% or more, 3% or more, 5% or more, 7% or more, or 10% or more, within the range that satisfies the above-mentioned range. Another example is the R SL This can be 0.5% to 15%, 1% to 14%, 2% to 13%, 3% to 12%, 4% to 12.5%, or 5% to 12%, but the present invention is not limited thereto.

[0063] Below, the above R SL This section explains the measurement method.

[0064] In one embodiment of the present invention, the R SL This can be measured when the lithium-sulfur battery is discharged to 1.7V to 1.9V, for example, 1.8V.

[0065] Specifically, the aforementioned R SL This can be measured by disassembling a lithium-sulfur battery in a discharged state, for example, a lithium-sulfur battery discharged to 1.7V to 1.9V, specifically to 1.8V, and examining the ratio of the weight of sulfur (S) derived from sulfur-based compounds present in the electrolyte to the weight of sulfur (S) derived from sulfur-based compounds present in the positive electrode.

[0066] In Formula 1, the weight of sulfur element (S) present in the sulfur-based compound present in the electrolyte is denoted as "W SE ", and the weight of sulfur element (S) present in the sulfur-based compound present in the positive electrode is denoted as "W SP ".

[0067] In one embodiment of the present invention, W SE and W SP can each be measured by disassembling the lithium-sulfur battery in the discharged state of the lithium-sulfur battery, for example, discharged to 1.7V to 1.9V, specifically 1.8V, as described above.

[0068] In one embodiment of the present invention, the sulfur-based compound present in the electrolyte of the lithium-sulfur battery may be derived from elution from the positive electrode during the operation of the lithium-sulfur battery. Such sulfur-based compounds may include, for example, inorganic sulfur (S8), lithium (poly) sulfide (Li2S x , 1 ≦ x ≦ 8), or a mixture thereof. Preferably, the sulfur-based compound present in the electrolyte is a substance that can be dissolved by the electrolyte of the lithium-sulfur battery and may include lithium polysulfide (Li2S x , 1 < x ≦ 8).

[0069] In one embodiment of the present invention, the W SE may be the total weight of inorganic sulfur (S8), lithium (poly) sulfide (Li2S x , 1 ≦ x ≦ 8), or a mixture thereof present in the electrolyte. Preferably, the W SE may be the total weight of lithium polysulfide (Li2S x , 1 < x ≦ 8) present in the electrolyte. More preferably, the W SE may be the total weight of lithium polysulfide (Li2S x , 2 < x ≦ 8) present in the electrolyte, and even more preferably the total weight of lithium polysulfide (Li2S x , 3 ≦ x ≦ 4) present in the electrolyte.

[0070] The W SEThis can be measured by known methods for measuring the content of elemental sulfur (S) in sulfur-based compounds dissolved in the electrolyte of a lithium-sulfur battery, or by newly developed methods, and the measurement method is not particularly limited.

[0071] According to one embodiment of the present invention, the W SE It can be measured by the following methods:

[0072] First, the lithium-sulfur battery to be measured is disassembled to separate the positive electrode, separation membrane, and negative electrode. The separated positive electrode, separation membrane, and negative electrode are then placed in containers filled with a predetermined mass of solvent, and sulfur compounds are extracted. At this time, it is preferable to extract the sulfur compounds for at least 20 minutes, specifically 20 minutes. After extraction, they can be stored in a glove box. Therefore, the extraction solvents for the positive electrode, separation membrane, and negative electrode can be stored separately or combined, preferably separately from each other. The remaining positive electrode, separation membrane, and negative electrode are stored in a glove box. The glove box can be filled with an inert gas, such as nitrogen or argon gas.

[0073] In one embodiment of the present invention, the extraction solvent may be, for example, dimethoxyethane to which a derivatization reagent is added and vortexed, then the extract from each electrode is added and vortexed, and analyzed using HPLC. Generally, derivatized lithium (poly)sulfide (LiPS) is short-chain LiPS (Me2S 3~4 ) and / or long-chain LiPS(Me2S 5~8 It can exist as ). Data analyzed using HPLC are separated into derivatized LiPS and inorganic sulfur (S8), but quantitative analysis is performed using calibration curves for each concentration of short-chain LiPS and inorganic sulfur for which standards are available. Long-chain LiPS is quantitatively analyzed from samples obtained through preparative sampling, and the concentration of the stock solution is calculated using the dilution ratio.

[0074] At this time, a suitable extraction solvent may be used for each of the sulfur-based compounds to be extracted, or a solvent having the same composition as the non-aqueous solvent in the electrolytic solution may be used. After the extraction is completed, each solvent is obtained and analyzed to measure the amount of sulfur-based compounds present in the electrolytic solution, and by summing them up, the weight of sulfur element (S) in the electrolytic solution is calculated.

[0075] As described later, at this time, after the positive electrode is dried at room temperature for 1 hour or more, for example, 1 hour after extraction, it is scraped off from the current collector, and the weight (W SP ) of the sulfur element present in the positive electrode can be calculated through elemental analysis.

[0076] As a method for extracting sulfur-based compounds from the separated electrolytic solution, for example, liquid chromatography (LC: Liquid Chromatography) can be used, but the extraction means is not limited thereto.

[0077] In one embodiment of the present invention, the sulfur-based compounds present in the positive electrode of the lithium-sulfur battery may be substances introduced during the manufacture of the lithium-sulfur battery or formed through redox reactions during the operation of the lithium-sulfur battery. Such sulfur-based compounds may particularly include inorganic sulfur (S8), lithium (poly) sulfide (Li2S x , 1 ≦ x ≦ 8), or mixtures thereof.

[0078] Specifically, as described later, since the W SP is measured after discharging and decomposing the lithium sulfur battery, the sulfur-based compounds present in the positive electrode may include the sulfur-based compounds present in the discharged state of the lithium sulfur battery. Specifically, the sulfur-based compounds present in the positive electrode may include lithium (poly) sulfide (Li2S x [[ID=2E]]、1≦x≦8)、具体的にはリチウムスルフィド(Li2S)、リチウムポリスルフィド(Li2S x , 1 < x < 3), or mixtures thereof. More specifically, the sulfur-based compounds present in the positive electrode may include lithium sulfide (Li2S), lithium polysulfide (Li2S xmay contain 1 < x ≤ 2), or a mixture thereof. More specifically, the sulfur-based compound present in the positive electrode may contain lithium sulfide (Li2S), lithium polysulfide (Li2S2), or a mixture thereof.

[0079] In one embodiment of the present invention, the W SP may be the total weight of inorganic sulfur (S8), lithium (poly) sulfide (Li2S x where 1 ≤ x ≤ 8), or a mixture thereof, present in the positive electrode. Preferably, the W SP may be the total weight of lithium sulfide (Li2S), lithium polysulfide (Li2S x where 1 < x ≤ 2), or a mixture thereof, present in the positive electrode. More preferably, the W SP may be the total weight of lithium sulfide (Li2S), lithium polysulfide (Li2S2), or a mixture thereof, present in the positive electrode.

[0080] The W SP can be measured by a known method for measuring the content of sulfur element (S) among the sulfur-based compounds present in the positive electrode of a lithium-sulfur battery, or may be measured by a newly developed method, and the measurement method is not particularly limited.

[0081] In one embodiment of the present invention, the W SPThe content can be measured by scraping the positive electrode from the current collector after decomposition / drying and performing elemental analysis on the resulting powder. In one embodiment of the present invention, multiple electrodes may be scraped from the current collector, and the sample obtained by removing heterogeneity may be used for analysis. As an example, the sample may be analyzed using an elemental analyzer that incorporates a thermal decomposition method, and the component corresponding to inorganic sulfur (S8) can be analyzed by this analysis method. The method for analyzing the content of inorganic sulfur (S8) is not particularly limited by specific means and methods, as long as it excludes components that have formed compounds with sulfur (S) in addition to the inorganic sulfur (S8) present in the positive electrode. In this case, the method for analyzing the sulfur element (S) content is one that can analyze all components other than sulfur (S), and is based on the weight % content of elemental sulfur (S) that balances the mass with all the analyzed components.

[0082] In one embodiment of the present invention, the W SP is the aforementioned W SE As described above regarding the measurement method, the lithium-sulfur battery to be measured is disassembled to separate the positive electrode, separator membrane, and negative electrode. After extracting sulfur compounds present in the electrolyte from the separated positive electrode, the mixture is dried at room temperature for at least one hour. The powder obtained by scraping the active material layer from the current collector is then subjected to elemental analysis for measurement.

[0083] Therefore, in one embodiment, the weight of sulfur present at the positive electrode (W SP ) may be the weight of sulfur (S) that has not been extracted by the extraction solvent of the sulfur-based compound used to measure the weight of sulfur in the electrolyte, as described above. That is, the weight of sulfur (W) present at the positive electrode. SP ) may mean sulfur compounds that are not extracted in the solvent for 20 minutes or more, preferably within 20 minutes. After 1 hour or more, preferably 1 hour has elapsed, the current collector is completely scraped off from the dry positive electrode to obtain sulfur (S) that may be present in the mixture from the positive electrode, the weight of the mixture containing the obtained sulfur (S) is measured, and elemental analysis is performed to determine the weight (W) of sulfur present in the positive electrode. SP ) is determined. Therefore, in one embodiment, the weight of sulfur (W) present at the positive electrode is determined. SP ) can be based on lithium-sulfur batteries.

[0084] In other embodiments, the sulfur (S) content in the negative electrode can be measured by elemental analysis. Thus, a lithium-sulfur battery can be disassembled and the weight (W) of sulfur present in the electrolyte can be determined. SE As with the method described above for measuring sulfur, after extracting sulfur compounds that can be extracted with a solvent from the negative electrode, and after drying the negative electrode, the weight of sulfur present in the negative electrode can be measured by elemental analysis. The weight of sulfur present in the negative electrode may be about 0, preferably 0, at the time of or immediately after the manufacture of the lithium-sulfur battery.

[0085] In yet another embodiment, the sulfur (S) content in the separation membrane may be about 0, preferably 0, when measured by elemental analysis. To measure the sulfur (S) content in the separation membrane, first, the lithium-sulfur battery is disassembled, and then sulfur compounds are extracted with a solvent used to measure the weight of sulfur in the electrolyte as described above. The separation membrane is then dried, and the sulfur (S) content present in the separation membrane can be measured. In lithium-sulfur batteries, the separation membrane does not chemically react with sulfur (S), particularly sulfur compounds, especially sulfur compounds derived from the sulfur-carbon complex of the positive electrode, so sulfur (S) may not be chemically bonded. Furthermore, sulfur compounds that may be present on and / or in the pores of the separation membrane can be completely removed when extracted from the solvent by the method of measuring the sulfur element present in the electrolyte as described above.

[0086] In one embodiment of the present invention, elemental analysis may be performed using, for example, ion chromatography (IC) analysis, inductively coupled plasma emission spectroscopy (ICP-OES) analysis, elemental analysis (EA), ONH analysis, etc., but the elemental analysis method is not limited to these.

[0087] In one embodiment of the present invention, the content of sulfur compounds present in the electrolyte of the lithium-sulfur battery can be measured, for example, by the method described in Korean Patent Application No. 2021-0188588, but the present invention is not limited thereto.

[0088] In one embodiment of the present invention, the content of sulfur compounds present in the positive electrode of the lithium-sulfur battery can be measured by, for example, the method described in Korean Patent Application No. 2021-0173961, but the present invention is not limited thereto.

[0089] In one embodiment of the present invention, W measured as described above SE and W SP Using the value of R SL This can be derived.

[0090] In one embodiment of the present invention, the W SE and W SP Each is measured in units of weight, converted to the same weight, and then R is calculated in that ratio. SL This can be derived.

[0091] In one embodiment of the present invention, the W SE and W SP The range of these values ​​can vary depending on factors such as the size of the lithium-sulfur battery and the amount of sulfur loaded into the positive electrode.

[0092] However, the above W SE and W SP Each of these can be expressed in weight percent based on the total weight of sulfur element (S) from the total sulfur-based compounds contained in the lithium-sulfur battery. Alternatively, it can be expressed in weight percent based on the total weight of sulfur element (S) derived from the sulfur-based compounds introduced as positive electrode active material during the manufacture of the lithium-sulfur battery. In this specification, this is referred to as "W' SE " and "W' SP It is also called "..."

[0093] In other words, depending on the measurement method, the W' SE and W' SP The sulfur (S) content ratio (R'SL) can also be measured using the following formula 1-2. However, in formula 1-2 below, W' SE and W' SPSince the "total sulfur element (S) value of the total sulfur compounds contained in the lithium-sulfur battery," which serves as the basis for the weight % of R', the formula R' in equation 1-2 is the same. SL R according to formula 1 SL It is obvious that this will be the same value.

[0094] [Formula 1-2] R' SL (%)=W' SE / W' SP ×100

[0095] In equation 1-2, W' SE This is the weight percentage of sulfur (S) in the sulfur compounds present in the electrolyte, based on the weight of sulfur (S) in the sulfur compounds present in the lithium-sulfur battery, and W' SP This is the weight percentage of sulfur (S) in the sulfur-based compounds present in the positive electrode, based on the weight of sulfur (S) in the sulfur-based compounds present in the lithium-sulfur battery.

[0096] In one embodiment of the present invention, the sulfur element among the sulfur-based compounds present in the lithium-sulfur battery in Equation 1-2 can be measured by a method that calculates the total content of sulfur element (S) among the sulfur-based compounds introduced as positive electrode active material during the manufacturing stage of the lithium-sulfur battery.

[0097] In another embodiment of the present invention, if the content of the sulfur compound introduced as the positive electrode active material during the manufacturing stage of the lithium-sulfur battery is unknown, the lithium-sulfur battery is decomposed and inorganic sulfur (S8) and lithium (poly)sulfide (Li2S) are obtained according to the method described above. x It can be measured by measuring the content of each element (1 ≤ x ≤ 8) and calculating the total content of sulfur (S) from these measurements.

[0098] In one embodiment of the present invention, the W' SE This may be 15% by weight or less based on the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery. For example, the W' SEThe amount of sulfur (S) present in the sulfur-based compound contained in the lithium-sulfur battery may be, but is not limited to, 0.1% to 15% by weight, 1% to 15% by weight, 1% to 10% by weight, 2% to 9.5% by weight, 3% to 9.5% by weight, 5% to 9.5% by weight, or 7% to 9% by weight.

[0099] In one embodiment of the present invention, the W' SP This can be 65% by weight or more based on the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery. In another embodiment of the present invention, the W' SP This may be 75% by weight or more, or 75.5% by weight or more, based on the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery. For example, the W SP This can be 65% to 99% by weight, 70% to 98% by weight, 75% to 95% by weight, 75% to 90% by weight, 75% to 85% by weight, 75% to 80% by weight, or 75.5% to 80% by weight, based on the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery, but is not limited to these values.

[0100] In one embodiment of the present invention, the W' SE and W' SP This can satisfy equation 2 below.

[0101] [Formula 2] W' SP >1.2×W' SE +56.86

[0102] In equation 2, W' SE W' is the weight percentage of sulfur element (S) in the sulfur-based compounds present in the electrolyte, based on the total weight of sulfur element (S) in the sulfur-based compounds contained in the lithium-sulfur battery. SPThis is the weight percentage of sulfur element (S) in the sulfur-based compounds present in the positive electrode, based on the total weight of sulfur element (S) in the sulfur-based compounds contained in the lithium-sulfur battery.

[0103] In one embodiment of the present invention, when the lithium-sulfur battery satisfies Equation 2, further improvements in the specific capacity and energy density of the lithium-sulfur battery can be achieved, but the present invention is not limited thereto.

[0104] In one embodiment of the present invention, the W' SE and W' SP These are the aforementioned W SE and W SP As in the measurement method described above, the voltage can be measured using a discharged lithium-sulfur battery as a reference. For example, a lithium-sulfur battery discharged to 1.7V to 1.9V, or even 1.8V, can be disassembled and measured.

[0105] In one embodiment of the present invention, as described above, the total weight of sulfur elements (S) present in the sulfur-based compound contained in the lithium-sulfur battery may represent the weight of sulfur elements (S) contained in the positive electrode, negative electrode, electrolyte, and separation membrane of the lithium-sulfur battery.

[0106] In one embodiment of the present invention, the total weight of sulfur element (S) present in the sulfur-based compounds contained in the lithium-sulfur battery can be determined by separating the positive electrode, negative electrode, electrolyte, and separation membrane contained in the lithium-sulfur battery, extracting the sulfur-based compounds present in each of the positive electrode, negative electrode, electrolyte, and separation membrane, measuring the sulfur element content in the extracted sulfur-based compounds, and summing the measured contents.

[0107] In another embodiment of the present invention, it is preferable that the sulfur element (S) contained in the lithium-sulfur battery originates from a sulfur-based compound used as a positive electrode active material during the manufacture of the lithium-sulfur battery. This allows the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery to match the content of sulfur element (S) in the sulfur-based compound that was introduced into the positive electrode during or immediately after the manufacture of the lithium-sulfur battery.

[0108] In one embodiment of the present invention, the total weight of sulfur element (S) contained in the lithium-sulfur battery is the amount of inorganic sulfur (S8) and lithium (poly)sulfide (Li2S) present in the positive electrode, negative electrode, electrolyte, and separation membrane, respectively, contained in the lithium-sulfur battery. x It can be the sum of the sulfur (S) content contained in (1 ≤ x ≤ 8).

[0109] In one embodiment of the present invention, the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery may be the weight of sulfur element (S) calculated from the content of inorganic sulfur (S8) added as a positive electrode active material during the manufacture of the lithium-sulfur battery.

[0110] In one embodiment of the present invention, the R SL This can be measured immediately after the manufacture of the lithium-sulfur battery, but may also be measured based on a battery that has deteriorated after one or more charge-discharge cycles. R according to the above formula 1. SL For lithium-sulfur batteries with a value of 15% or less, the timing of measurement is not particularly limited, as they exhibit excellent performance in terms of specific capacity and / or energy density.

[0111] As described above, W SE and W SPThis originates from sulfur-based materials introduced as positive electrode active material during the manufacture of lithium-sulfur batteries. For example, it originates from the sulfur-carbon composite within the positive electrode. Specifically, it does not originate from sulfur-based salts introduced into the electrolyte as lithium salts or other additives during the manufacture of lithium-sulfur batteries. More specifically, according to the measurement method described above, the content of sulfur elements derived from sulfur-based materials originating from the positive electrode can be measured, rather than the content of sulfur elements derived from sulfur-based salts contained in lithium salts or other additives.

[0112] More specifically, the sulfur-based salts include, for example, CF3SO3, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)3CLi, and especially (CF3SO2)2NLi (LiTFSI), which are the sulfur-based materials mentioned above (inorganic sulfur (S8), lithium polysulfide (Li2S) x This is distinguished from other types of inequalities such as 1 ≤ x ≤ 8.

[0113] The following describes in detail each component of the lithium-sulfur battery.

[0114] <Positive electrode> In one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector.

[0115] The positive electrode current collector is not particularly limited as long as it supports the positive electrode active material, does not induce chemical changes in the battery, and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface treatments with carbon, nickel, silver, etc., and aluminum-cadmium alloys may be used.

[0116] The positive electrode current collector may have fine irregularities formed on its surface to strengthen its bonding force with the positive electrode active material, and can be used in a variety of forms such as film, sheet, foil, mesh, net, porous material, foam, or nonwoven fabric.

[0117] The positive electrode active material layer contains a positive electrode active material and may further contain a conductive material, a binder, an additive, and the like.

[0118] In one embodiment of the present invention, the positive electrode active material contains a sulfur-carbon composite.

[0119] In one embodiment of the present invention, the sulfur-carbon composite may include a porous carbon material and a sulfur-based compound supported on at least one of the pores inside the porous carbon material and the outer surface of the porous carbon material. In the case of sulfur acting as the positive electrode active material, since it has no electrical conductivity alone, it is used in combination with a conductive material such as a carbon material, and a porous carbon material can be used to support sulfur. Further, the sulfur-based compound is added as a positive electrode active material, and examples thereof include inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2S x , 1 < x ≦ 8), disulfide compounds, carbon-sulfur polymers ((C2S a y ), n y = 2.5 to 50, n ≧ 2), or may include two or more of these. Preferably, the sulfur-based compound may be inorganic sulfur (S8).

[0120] In one embodiment of the present invention, the porous carbon material is for supporting a sulfur-based compound as a positive electrode active material and improving the conductivity of the positive electrode while providing a skeleton in which the sulfur-based compound is uniformly and stably fixed, and can be used without particular limitation as long as it is a porous carbon material.

[0121] The porous carbon material can generally be produced by carbonizing various carbonaceous precursors. The porous carbon material contains irregular pores inside, and the average diameter of the pores is 1 nm to 200 nm, and the porosity can be 10% to 90% by volume of the total volume of the porous carbon material. If the average diameter of the pores is less than the above range, the pore size is only at the molecular level and sulfur cannot be impregnated, and if it exceeds the above range, the mechanical strength of the porous carbon material is weakened and it is difficult to apply it to the electrode manufacturing process.

[0122] In one embodiment of the present invention, the average diameter of the pores can be measured by a method known in the industry for measuring the pore size of porous materials, and the measurement method is not particularly limited. For example, the pore size can be measured by scanning electron microscopy (SEM), field emission electron microscopy, laser diffraction, or the BET (Brunauer-Emmett-Teller) method. For measurement using the laser diffraction method, for example, a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT3000) can be used. For measurement using the BET method, for example, an analyzer from the BELSORP series manufactured by BEL Japan can be used, but is not limited to these.

[0123] In one embodiment of the present invention, "porosity" means the ratio of the volume occupied by pores to the total volume of a structure, and is expressed in units of "%", and can be used interchangeably with terms such as void ratio and porosity. In one embodiment of the present invention, the measurement of porosity is not particularly limited and can be performed, for example, by the BET method using nitrogen gas, the mercury intrusion method (Hg porosimeter), or ASTMD2873.

[0124] The shape of the porous carbon material can be spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk-shaped, as long as it is one of those commonly used in lithium-sulfur batteries.

[0125] The porous carbon material is not particularly limited as long as it has a porous structure or a large specific surface area and is commonly used in the industry. For example, the porous carbon material may be one or more selected from the group consisting of graphite; graphene; carbon black such as Denka Black, acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, and Thermal Black; carbon nanotubes (CNTs) such as Single Walled Carbon Nanotubes (SWCNTs) and Multi Walled Carbon Nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs); graphite such as natural graphite, artificial graphite, and expanded graphite; and activated carbon. Preferably, the porous carbon material may be carbon nanotubes.

[0126] In one embodiment of the present invention, the porous carbon material may include, for example, carbon nanotubes (CNTs).

[0127] In one embodiment of the present invention, the sulfur-carbon composite may have a weight ratio of sulfur to carbon of, for example, 5 g / g or less, and more specifically, 2.5 g / g or less. For example, the sulfur-carbon composite may have a weight ratio of sulfur to carbon of 2.4 g / g. When the S / C ratio of the sulfur-carbon composite is within the above range, it is preferable in terms of securing the electron transfer capability (conductivity) and electrochemical specific surface area of ​​the sulfur-carbon composite. For example, the usable surface area of ​​the sulfur-carbon composite becomes larger, making it easier to suppress the elution of sulfur from the positive electrode. However, the present invention is not limited thereto.

[0128] In one embodiment of the present invention, the S / C ratio can be calculated from the weight (g) of sulfur and the weight (g) of carbon present in the sulfur-carbon composite. Alternatively, it can be calculated from the weight (weight%) of sulfur and the weight (weight%) of carbon, based on the total weight of the sulfur-carbon composite. Thus, the S / C ratio may be a unitless value.

[0129] In one embodiment of the present invention, the S / C weight ratio may be, for example, 0.5 to 2.5, 1.0 to 2.50, 1.5 to 2.45, 2.0 to 2.45, or 2.35 to 2.45. As an example, the S / C ratio can be calculated from the ratio of the weight of the inorganic sulfur (S8) to the weight of the porous carbon material. For example, the S / C ratio can be calculated from the weight ratio of S8 / CNT.

[0130] The method for producing the sulfur-carbon composite is not particularly limited, and methods commonly used in the industry may be used. As an example, a method may be used in which the sulfur and the porous carbon material are simply mixed and then heat-treated to form the composite.

[0131] In addition to the composition described above, the positive electrode active material may further include one or more selected from transition metal elements, group 13 elements, group 14 elements, sulfur compounds of these elements, and alloys of these elements with sulfur.

[0132] The transition metal elements include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, or Hg, the group 13 elements include Al, Ga, In, Ti, and the group 14 elements may include Ge, Sn, Pb, etc.

[0133] In one embodiment of the present invention, the S / C ratio of the sulfur-carbon composite is the R SL Based on the relationship with the values, the following equation 3 can be satisfied.

[0134] [Formula 3] 10.667×R S / C -10.633>R SL

[0135] In equation 3, R SL This is the content ratio of sulfur element (S) according to the above formula 1, and R S / C This is the weight ratio of sulfur (S) to carbon (C) in the sulfur-carbon composite.

[0136] The inventors have confirmed that when a lithium-sulfur battery satisfies the above formula 3, its specific capacity and / or energy density are greatly improved.

[0137] In one embodiment of the present invention, the sulfur-carbon composite may be present in an amount of 50% by weight or more based on the total weight of the positive electrode. Specifically, when the positive electrode includes a current collector and a positive electrode active material layer formed on the current collector, and the sulfur-carbon composite is included in the positive electrode active material layer, the sulfur-carbon composite may be present in an amount of, for example, 80% by weight or more, 90% by weight or more, or 95% by weight or more based on the total weight of the positive electrode active material layer. Specifically, the sulfur-carbon composite may be present in an amount of 80% to 100% by weight, more specifically 85% to 99% by weight, 90% to 100% by weight, 90% to 99% by weight, 95% to 98% by weight, 95% to 97% by weight, or 96% by weight based on the total weight of the positive electrode active material layer. If the content of the sulfur-carbon composite is below the above range, the relative content of auxiliary materials such as conductive materials and binders increases, and the content of the sulfur-carbon composite decreases, making it difficult to realize a battery with high capacity and high energy density. If it exceeds the above range, the content of the conductive material or binder described later becomes relatively insufficient, leading to a problem of degraded physical properties of the electrodes.

[0138] In one embodiment of the present invention, the loading amount of the positive electrode is, for example, 1.67 mg s / cm 2 Specifically, the range is 1.67 to 2.92 mg. s / cm 2 More specifically, 1.67-2.08 mg s / cm 2 This is possible. The loading amount can be calculated from the content of the active material in the positive electrode and the sulfur (S) content in the active material.

[0139] In one embodiment of the present invention, when the loading amount of the positive electrode is converted to a capacity, for example, the loading amount is 2.0 mAh / cm². 2 Specifically, the above is 2.0mAh / cm². 2 ~3.5mAh / cm 2More specifically, 2.0mAh / cm² 2 ~2.5mAh / cm 2 This is possible, but the present invention is not limited thereto.

[0140] The conductive material is a substance that electrically connects the electrolyte and the positive electrode active material, acting as a pathway for electrons to move from the current collector to the positive electrode active material. It is an electrode component that is physically distinct from the carbon contained in the sulfur-carbon composite, and can be used without limitation as long as it is conductive.

[0141] In one embodiment of the present invention, the conductive material may be carbon black such as Super P, Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, Thermal Black, and Carbon Black; carbon derivatives such as carbon nanotubes and fullerenes; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole, either alone or in combination.

[0142] In one embodiment of the present invention, the content of the conductive material may be 0 to 10% by weight, for example, 1 to 10% by weight, relative to the total weight of the positive electrode active material. If the content of the conductive material is less than the above range, electron transfer between the positive electrode active material and the current collector will not be easy, and the voltage and capacity will decrease. If it exceeds the above range, the relative ratio of the positive electrode active material will decrease, which may reduce the total energy (charge amount) of the battery. Therefore, it is preferable to determine an appropriate content within the above range.

[0143] In one embodiment of the present invention, the binder maintains the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active materials to each other, further enhancing the bonding force between them, and any binder known in the industry can be used.

[0144] For example, the binder may be one, a mixture of two or more, or a copolymer selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride polymers containing at least one repeating unit of polyvinylidene fluoride, polytetrafluoroethylene (PTFE), or a mixture of two or more of these; rubber binders containing styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; acrylic binders; cellulose binders containing carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, or regenerated cellulose; polyalcohol binders; polyolefin binders containing polyethylene or polypropylene; polyimide binders; polyester binders; silane binders; polyacrylic acid binders; and polyacrylonitrile binders. In one embodiment of the present invention, the binder may include, for example, polyacrylate (PAA).

[0145] In one embodiment of the present invention, the binder content may be 1 to 10% by weight relative to the total weight of the positive electrode active material layer. If the binder content is less than the above range, the physical properties of the positive electrode will deteriorate and the positive electrode active material and conductive material may fall off. If it exceeds the above range, the ratio of positive electrode active material to conductive material in the positive electrode will relatively decrease, which may reduce the battery capacity. Therefore, it is preferable to determine an appropriate content within the above range.

[0146] In one embodiment of the present invention, the method for manufacturing the positive electrode for the lithium secondary battery is not particularly limited, and various methods known to the ordinary art or variations thereof can be used.

[0147] As an example, the positive electrode for the lithium secondary battery may be manufactured by first producing a positive electrode slurry composition containing the above-described composition, and then applying this slurry to at least one surface of the positive electrode current collector to form the positive electrode active material layer.

[0148] The positive electrode slurry composition contains the positive electrode active material described above, and may further contain a binder, a conductive material, and a solvent.

[0149] The solvent used is one that allows for the uniform dispersion of the positive electrode active material. As such a solvent, water is most preferably an aqueous solvent, and in this case, the water may be distilled water or deionized water. However, it is not limited to these, and if necessary, a lower alcohol that is easily miscible with water may be used. Examples of such lower alcohols include methanol, ethanol, propanol, isopropanol, and butanol, and these may preferably be used in combination with water.

[0150] The solvent may be contained in a concentration sufficient for easy coating, and the specific concentration may vary depending on the coating method and apparatus.

[0151] The positive electrode slurry composition may optionally contain additional substances commonly used in the art for purposes such as improving functionality. Examples include viscosity modifiers, fluidizers, and fillers.

[0152] The method for applying the positive electrode slurry composition is not particularly limited and includes methods such as doctor blade, die casting, comma coating, and screen printing. Alternatively, the positive electrode slurry may be applied to the positive electrode current collector by pressing or lamination after being formed on a separate substrate.

[0153] After coating, a drying process may be performed to remove the solvent. This drying process is carried out at a temperature and for a time sufficient to remove the solvent, and the conditions are not particularly limited as they may vary depending on the type of solvent. Examples include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays and electron beams. The drying rate is usually adjusted to remove the solvent as quickly as possible, within a range that does not cause cracks in the positive electrode active material layer due to stress concentration or cause the positive electrode active material layer to peel off from the positive electrode current collector.

[0154] Furthermore, after drying, the density of the positive electrode active material within the positive electrode may be increased by pressing the current collector. Examples of pressing methods include die pressing and roll pressing.

[0155] The porosity of the positive electrode, specifically the positive electrode active material layer, manufactured using the composition and manufacturing method described above, may be 50% to 80% by volume, specifically 60% to 75% by volume. If the porosity of the positive electrode is less than 50% by volume, the packing of the positive electrode slurry composition, including the positive electrode active material, conductive material, and binder, becomes excessively high, making it impossible to maintain sufficient electrolyte between the positive electrode active materials for ion conduction and / or electrical conduction. This leads to a decrease in the battery's output and cycle characteristics, and serious problems of battery overvoltage and reduced discharge capacity. On the other hand, if the porosity of the positive electrode is excessively high, exceeding 80% by volume, the physical and electrical connection with the current collector weakens, reducing adhesion and making the reaction difficult. Excess pores may become filled with electrolyte, potentially reducing the battery's energy density. Therefore, the porosity should be appropriately adjusted within the above range.

[0156] <Negative electrode> The negative electrode may include a negative electrode current collector and a negative electrode active material layer coated on one or both sides of the negative electrode current collector. Alternatively, the negative electrode may be a lithium metal plate or lithium foil.

[0157] The aforementioned negative electrode current collector is for supporting the negative electrode active material layer, and is as described above for the positive electrode current collector.

[0158] The negative electrode active material layer may include, in addition to the negative electrode active material, a conductive material, a binder, etc. In this case, the conductive material and binder are as described above.

[0159] The negative electrode active material is lithium (Li + This may include materials that can be reversibly intercalated or deintercalated, materials that can react with lithium ions to reversibly form lithium-containing compounds, lithium metals, or lithium alloys.

[0160] The aforementioned lithium ion (Li + The material from which the lithium ion (Li) can be reversibly inserted or removed may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. + A substance capable of reversibly forming a lithium-containing compound by reacting with ) may be, for example, tin oxide, titanium nitride, or silicon. The lithium alloy may be, for example, an alloy of lithium (Li) with a metal selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

[0161] Preferably, the negative electrode active material may be a lithium metal, specifically in the form of a lithium metal thin film or lithium metal powder.

[0162] <Separation membrane> The separation membrane separates or insulates the positive electrode and the negative electrode and transports lithium ions between the positive electrode and the negative electrode, and may contain a porous, nonconductive or insulating material. It is not particularly limited to any material commonly used as a separation membrane in lithium secondary batteries. Such a separation membrane may be an independent component such as a film, or it may be a coating layer applied to the positive electrode and / or negative electrode.

[0163] The separation membrane is preferably one that has low resistance to ion movement of the electrolyte and excellent wettability with respect to the electrolyte.

[0164] In one embodiment of the present invention, the separation membrane may include a porous substrate, and the porous substrate is not limited to any porous substrate commonly used in secondary batteries, and porous polymer films may be used alone or in a laminated manner. For example, nonwoven fabrics or polyolefin-based porous membranes made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. may be used, but are not limited thereto.

[0165] The material of the porous substrate is not particularly limited, and any porous substrate commonly used in electrochemical elements can be used. For example, the porous substrate may include one or more selected from the group consisting of polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamide, polyacetal, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, poly(p-phenylenebenzobisoxazole) and polyarylate.

[0166] In one embodiment of the present invention, the thickness of the porous substrate is not particularly limited, but may be 1 μm to 100 μm, preferably 5 μm to 50 μm. The thickness range of the porous substrate is not limited to the range described above, but if it is thinner than the lower limit described above, the mechanical properties will deteriorate and the separation film will be easily damaged during battery use.

[0167] In one embodiment of the present invention, the average diameter and porosity of the pores present in the porous substrate are not particularly limited, but may be 0.001 μm to 50 μm and 10 volume% to 95 volume%, respectively.

[0168] In one embodiment of the present invention, the separation membrane may further include a porous coating layer formed on at least one surface of the porous substrate and containing inorganic particles and a binder.

[0169] In one embodiment of the present invention, the inorganic particles and binder contained in the porous coating layer are not particularly limited as long as they are those commonly used in the porous coating layer of a separation membrane, and the method of manufacturing them is also not particularly limited.

[0170] <Electrolyte> The electrolyte is a medium through which ions involved in the electrochemical reaction of a lithium-sulfur battery can move, and comprises a non-aqueous solvent and a lithium salt as the electrolyte.

[0171] The electrolyte is not particularly limited as long as it has a composition suitable for use in lithium secondary batteries, specifically lithium-sulfur batteries.

[0172] In one embodiment of the present invention, the non-aqueous solvent can be any type suitable for use in lithium-sulfur batteries, and may include, for example, ether solvents, esters, amides, linear carbonates, and cyclic carbonates.

[0173] In one embodiment of the present invention, the ester may be 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, or a mixture of two or more of these, but is not limited thereto.

[0174] In one embodiment of the present invention, the chain-like carbonate may typically be one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, or a mixture of two or more of these, but is not limited to these.

[0175] In one embodiment of the present invention, the cyclic carbonate is, for example, one selected from the group consisting of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more of these. These halides include, but are not limited to, fluoroethylene carbonate.

[0176] In one embodiment of the present invention, the non-aqueous solvent may include an ether-based solvent.

[0177] In one embodiment of the present invention, the ether solvent may be contained in an amount of 60% by volume or more, for example, 60% to 100% by volume, 70% to 100% by volume, 80% to 100% by volume, 85% to 100% by volume, 90% to 100% by volume, or 95% to 100% by volume, based on the total volume of the non-aqueous solvent. While it is advantageous in terms of the solubility of electrolyte components such as lithium salts if the content of the ether solvent is within the above range based on the total volume of the non-aqueous solvent, the present invention is not limited thereto.

[0178] In one embodiment of the present invention, the ether-based solvent may include an acyclic ether, a cyclic ether, or a mixture thereof.

[0179] In one embodiment of the present invention, the acyclic ether may include one or more selected from the group consisting of, for example, dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethyl methyl ether, ethyl propyl ether, ethyl tert-butyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol, diethylene glycol diethyl ether, triethylene glycol, tetraethylene glycol, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, diethylene glycol tert-butyl ethyl ether, and ethylene glycol ethyl methyl ether. Preferably, it may include one or more selected from the group consisting of dimethoxyethane, diethoxyethane, diethylene glycol, triethylene glycol, and tetraethylene glycol, and more preferably it may include dimethoxyethane.

[0180] In one embodiment of the present invention, the cyclic ether may include one or more selected from the group consisting of, for example, 2-methylfuran, 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, tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, and isosorbide dimethyl ether. Preferably, it may contain one or more selected from the group consisting of 2-methylfuran, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2,5-dimethyltetrahydrofuran, and more preferably it may contain 2-methylfuran.

[0181] In one embodiment of the present invention, the non-aqueous solvent may include, for example, dimethoxyethane (DME), ethylene glycol, propylene glycol, or a mixture of two or more of these.

[0182] In one embodiment of the present invention, the non-aqueous solvent may include a mixture of an acyclic ether and a cyclic ether.

[0183] In one embodiment of the present invention, the non-aqueous solvent may include dimethoxyethane (DME) and 2-methylfuran (2-MeF).

[0184] In one embodiment of the present invention, the volume ratio of the acyclic ether to the cyclic ether may be 5:95 to 95:5 (v / v), more specifically 95:5 to 50:50, more specifically 90:10 to 70:30, 85:15 to 75:25, or 80:20 (v / v). In the present invention, the volume ratio corresponds to the ratio of the "volume % of acyclic ether" to the "volume % of cyclic ether" in the ether-based solvent.

[0185] In one embodiment of the present invention, the non-aqueous solvent may be free of carbonate-based solvents in terms of electrolyte solubility. Alternatively, the non-aqueous solvent may contain a very small amount of carbonate-based solvent that does not affect the solubility of the lithium salt. For example, if the non-aqueous solvent contains the carbonate-based solvent, the content of the carbonate-based solvent may be 3% by weight or less, 2% by weight or less, 1% by weight or less, 0.5% by weight or less, or 0% by weight (i.e., not present at all), based on the total weight of the electrolyte for the lithium secondary battery.

[0186] In one embodiment of the present invention, the lithium salt can be used without particular limitation as long as it is suitable for use as an electrolyte in a lithium secondary battery. Examples of the lithium salt include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 It may contain LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carhonate, lithium tetraphenylborate, lithium imide, or two or more of these.

[0187] In one embodiment of the present invention, the concentration of the lithium salt can be appropriately determined considering ionic conductivity, solubility, etc., and may be, for example, 0.1M to 4M, preferably 0.25M to 2M, 0.5M to 2M, 0.5M to 1.5M, or 0.5M to 1.0M. When the concentration of the lithium salt is within the above range, it is easier to ensure ionic conductivity suitable for driving the battery, or the electrolyte has an appropriate viscosity, which is advantageous in terms of improving the mobility of lithium ions and suppressing the decomposition reaction of the lithium salt itself, but the present invention is not limited thereto.

[0188] In one embodiment of the present invention, the electrolyte may further contain a nitrogen compound in addition to the lithium salt to improve the electrical conductivity of the electrolyte and extend the lifespan of the lithium-sulfur battery. Specifically, although the effects of the nitrogen compound are not limited to these, it can, for example, suppress the reduction reaction of polysulfide that occurs during the charging and discharging process of the lithium-sulfur battery, thereby preventing irreversible depletion of polysulfide and improving the performance of the lithium-sulfur battery.

[0189] In one embodiment of the present invention, the nitrogen compound is not particularly limited as long as it forms a stable film on the lithium metal electrode, which is the negative electrode of a lithium secondary battery, specifically a lithium-sulfur battery, and has the effect of improving the charge-discharge efficiency. For example, it may be a nitrate compound, a nitrite compound, or a mixture thereof.

[0190] In one embodiment of the present invention, the nitrogen compound may be selected from the group consisting of, for example, inorganic nitric or nitrite 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), and ammonium nitrite (NH4NO2); organic nitric or nitrite compounds such as methyl nitrate, dialkylimidazolium nitrate, guanidine nitrate, imidazolium nitrate, pyridinium nitrate, ethyl nitrate, propyl nitrate, butyl nitrate, pentyl nitrate, and octyl nitrate; organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, and dinitrotoluene, and combinations thereof, and preferably may include lithium nitrate.

[0191] In one embodiment of the present invention, the nitrogen compound may be included in a content of, for example, 1% to 10% by weight, 2% to 10% by weight, or 3% to 10% by weight, specifically 3% to 8% by weight, 3% to 6% by weight, or 3% to 5% by weight, based on the total weight of the electrolyte for the lithium secondary battery, but is not limited thereto. When the nitrogen compound is included in the above-mentioned content, it is advantageous in terms of improving the electrical conductivity of the electrolyte and suppressing the reduction of polysulfide when applied to a lithium-sulfur battery, but the present invention is not limited thereto.

[0192] In one embodiment of the present invention, the lithium-sulfur battery may have a variety of energy densities depending on the ratio of the electrolyte to the positive electrode active material. However, in terms of the energy density of the lithium-sulfur battery, a smaller ratio of the electrolyte to the positive electrode active material is advantageous, and for example, the weight ratio of the electrolyte to the sulfur in the sulfur-carbon composite (El / S weight ratio) may be 3.5 g / g or less.

[0193] In one embodiment of the present invention, the lithium-sulfur battery may be manufactured such that the El / S ratio is, for example, 3 g / g or less or 2.9 g or less.

[0194] A lithium-sulfur battery with the above configuration may have a specific capacity of 60% or more, specifically 65% ​​or more, 70% or more, or 75% or more, of the theoretical specific capacity calculated from the total content of sulfur compounds contained in the lithium-sulfur battery. More specifically, the lithium-sulfur battery may have a specific capacity of 80% or more, and even 90% or more, of the theoretical specific capacity calculated from the total content of sulfur compounds contained in the lithium-sulfur battery.

[0195] In one embodiment of the present invention, the specific capacity of the lithium-sulfur battery may be, for example, 1,000 mAh / g or more. For example, the specific capacity of the lithium-sulfur battery may be 1,050 mAh / g or more, 1,080 mAh / g or more, specifically 1,000 mAh / g to 1,675 mAh / g, 1,000 mAh / g to 1,300 mAh / g, 1,050 mAh / g to 1,250 mAh / g, or 1,080 mAh / g to 1,150 mAh / g.

[0196] In one embodiment of the present invention, the energy density of the lithium-sulfur battery may be, for example, 300 Wh / kg or more. For example, the energy density of the lithium-sulfur battery may be 300 Wh / kg to 2,600 Wh / kg, 300 Wh / kg to 1,600 Wh / kg, 300 Wh / kg to 1,000 Wh / kg, 300 Wh / kg to 800 Wh / kg, 300 Wh / kg to 450 Wh / kg, or 330 Wh / kg to 400 Wh / kg.

[0197] In one embodiment of the present invention, the specific capacity and energy density of the lithium-sulfur battery can be measured by known methods for measuring the specific capacity and energy density of a lithium-sulfur battery, and are not particularly limited by the measurement method.

[0198] In one embodiment of the present invention, the specific capacity and energy density of the lithium-sulfur battery can be measured by discharging at a rate of 0.5C and charging at a rate of 0.3C at room temperature of, for example, 23°C in the range of 1.8V to 2.5V.

[0199] In one embodiment of the present invention, the lithium-sulfur battery can have various forms, for example, it can be a coin type, a pouch type or a cylindrical type, but is not limited thereto.

[0200] According to another embodiment of the present invention, a method for evaluating the specific capacity of a lithium-sulfur battery using the above formula (1) is provided.

[0201] The method includes a step of determining a lithium-sulfur battery in which the content ratio (R SL ) of sulfur element (S) according to the above formula (1) is 15% or less as a high specific capacity battery.

[0202] In one embodiment of the present invention, the high specific capacity battery can be, for example, a battery having a specific capacity of more than 1,000 mAh / g.

[0203] Hereinafter, in order to help the understanding of the present invention, preferred examples are presented. However, it is obvious to those skilled in the art that the following examples are only illustrative of the present invention, and various changes and modifications are possible within the scope of the present invention and the scope of the technical idea, and it is needless to say that such modifications and corrections belong to the scope of the claims.

[0204] [Manufacture of Lithium-Sulfur Battery] Example 1 Inorganic sulfur (S8) and carbon nanotubes (CNT) were mixed as a positive electrode active material to prepare a sulfur-carbon composite (S / C weight ratio = 2.45). 96% by weight of the prepared sulfur-carbon composite and 4% by weight of polyacrylate (PAA) as a binder were mixed to produce a positive electrode slurry composition. After applying the positive electrode slurry composition to an aluminum current collector, it was dried to produce a positive electrode. The loading amount of the produced positive electrode was 2.08 mg(s) / cm 2 (2.5 mAh / cm2 ) was used.

[0205] Lithium metal with a thickness of 60 μm was used as the negative electrode.

[0206] The positive electrode and the negative electrode were positioned to face each other, and an electrode assembly was prepared with a polyethylene separator having a thickness of 16 μm and a porosity of 46 vol% interposed therebetween.

[0207] The prepared electrode assembly was housed in a pouch-type case, and an electrolyte solution in which 0.75 M of lithium salt (LiTFSI) and 3 wt% of lithium nitrate (LiNO3) were dissolved in a solvent obtained by mixing dimethoxyethane (DME) and 2-methylfuran (2-MeF) at a volume ratio of 8:2 was injected so that the El / S ratio became 2.9 g / g, and a lithium-sulfur battery was manufactured.

[0208] Comparative Example 1 A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the S / C weight ratio was adjusted to 2.9 during the production of the sulfur-carbon composite.

[0209] Comparative Example 2 A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the S / C weight ratio was adjusted to 2.6 during the production of the sulfur-carbon composite.

[0210] [Measurement of R(SL) and Evaluation of Battery Performance] The manufactured lithium-sulfur batteries of Example 1, Comparative Example 1, and Comparative Example 2 were each charged once in the range of 1.8 V to 2.5 V at a normal temperature (23°C) and a 0.3C rate, and then discharged to 1.8 V at a 0.5C rate while measuring the battery capacity (mAh) and energy (Wh) at this time. Then, the specific capacity (mAh / g) and energy density (Wh / kg) of the battery were evaluated by dividing by the respective battery capacities, and the results are shown in Table 1 below.

[0211] Next, the lithium-sulfur battery discharged to 1.8 V was disassembled, and R was measured by the following formula 1. SL was measured.

[0212] [Formula 1] R SL (%)=W SE / W SP ×100

[0213] In equation 1, W SE This is the weight of the sulfur element (S) among the sulfur-based compounds present in the electrolyte, and W SP This is the weight of the sulfur element (S) among the sulfur-based compounds present at the positive electrode.

[0214] W SE To measure the properties of the battery, the disassembled battery was placed in an extraction solvent (DME) and extracted for 48 hours. After removing the battery from the extract, methyl trifluoromethanesulfonate (CF3SO3CH3) was added to the extract for methyl derivatization. The methyl derivatized components were analyzed and separated by liquid chromatography (LC) under the following conditions, and then fractionated according to their respective ranges.

[0215] [LC / UV analysis conditions] Column: CAPCELLPAL C18 column (inner diameter 4.6 mm, length 50 mm, particle size 3 μm, OSAKA SODA) Mobile phase: H2O / methanol mixed solvent, gradient elution method (0 min: H2O / methanol = 75 / 25 (v / v), 10 min: H2O / methanol = 0 / 100 (v / v), 20 min: H2O / methanol = 0 / 100 (v / v)) Flow rate: 0.7ml / min Column temperature: 40℃ Injection volume: 10μl Detection wavelength: 254nm

[0216] Subsequently, using standards of each concentration manufactured according to Korean Patent Application No. 2021-0188588, the peak area of ​​each methyl derivatized component that appeared in the chromatogram obtained by the above LC / UV analysis was measured, and the content of each lithium polysulfide component present in the extract was calculated, and these were then summed up to obtain W SE The value was measured.

[0217] W SP To measure W SE After extraction for measurement, the separated positive electrode was dried at room temperature, and the sulfur (S) content in the positive electrode was measured according to the method described in Korean Patent Application No. 2021-0173961. Specifically, the positive electrode active material layer was scraped off and separated, placed in a Sn capsule, and placed in an EA apparatus (Flash 2100, Thermo) and burned at 990°C to generate gas. The generated gas was separated using a GC column, and the sulfur (S) content was measured. At this time, BBOT (2,5-bis(5-tert-butyl-benzoxazole-2-yl)thiophene) was used as the standard substance for quantitative analysis.

[0218] W' was measured as described above, based on the total weight of sulfur (S) derived from the content of inorganic sulfur (S8) used in the production of the sulfur-carbon composite used in each battery. SE and W' SP The respective weight ratios are shown in Table 1 below. From this, R' is calculated using Equation 1-2. SL Calculate R' SL R according to formula 1 SL Since it is identical, Table 1 below contains R SL This was shown.

[0219] [Formula 1-2] R' SL (%)=W' SE / W' SP ×100

[0220] In equation 1-2, W' SE W' is the weight percentage of sulfur element (S) in the sulfur-based compounds present in the electrolyte, based on the weight of sulfur element (S) in the sulfur-based compounds present in the lithium-sulfur battery. SP This is the weight percentage of sulfur element (S) in the sulfur-based compounds present in the positive electrode, based on the weight of sulfur element (S) in the sulfur-based compounds present in the lithium-sulfur battery.

[0221] Also, the measured W' SE and W'SP Using this, the satisfaction of the following Equations (2) and (3) was evaluated, and T (satisfied) / F (failed) was evaluated and summarized in Table 1 below.

[0222] [Equation 2] W’ SP > 1.2×W’ SE + 56.86

[0223] [Equation 3] 10.667×R S / C - 10.633 > R SL

[0224]

Table 1

[0225] From Table 1, it was confirmed that Example 1 with an R ratio of 15% or less for the lithium-sulfur battery discharged to 1.8V had a lower S / C ratio compared to Comparative Example 1 and Comparative Example 2, showed a specific capacity of 1,000 mAh / g or more, and also had excellent energy density. However, when comparing Comparative Example 1 and Comparative Example 2, although the S / C ratio of Comparative Example 1 was higher, Comparative Example 2 had a lower specific capacity and energy density than Comparative Example 1. Therefore, it was confirmed that a lithium-sulfur battery with a high specific capacity could be identified through the R value. SL When discharged to 1.8V, since the reduction reaction of sulfur is difficult to proceed further, the state is such that the maximum capacity that the battery can exhibit is achieved, and the R value is in the lowest state. Therefore, it can be confirmed that in order to realize a lithium-sulfur battery having a high specific capacity and high energy density, R must be controlled to 15% or less. SL

[0226] When discharged to 1.8V, since the reduction reaction of sulfur is difficult to proceed further, the state is such that the maximum capacity that the battery can exhibit is achieved, and the R SL value is in the lowest state. Therefore, it can be confirmed that in order to realize a lithium-sulfur battery having a high specific capacity and high energy density, R SL must be controlled to 15% or less.

Claims

1. A lithium sulfur battery comprising a positive electrode containing a sulfur-carbon composite, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, At least one of the positive electrode and the electrolyte contains a sulfur-based compound. Formula 1 below: [Formula 1] R ＳＬ (%)=W ＳＥ / W ＳＰ ×100 The ratio of sulfur element (S) content (R ＳＬ ) is 15% or less, In equation 1, The aforementioned W ＳＥ This is the weight of the sulfur element (S) among the sulfur-based compounds present in the electrolyte, The aforementioned W ＳＰ A lithium-sulfur battery in which is the weight of the sulfur element (S) among the sulfur-based compounds present at the positive electrode.

2. In the above formula 1, W ＳＥ and W ＳＰ The lithium-sulfur battery according to claim 1, wherein the values ​​are measured in a discharge state of 1.7V to 1.9V, respectively.

3. The sulfur-based compound present in the electrolyte is inorganic sulfur (S ８ ), lithium (poly)sulfide (Li ２ S ｘ , 1 ≤ x ≤ 8), or a mixture thereof, the lithium-sulfur battery according to claim 1.

4. The sulfur-based compound present at the positive electrode is inorganic sulfur (S ８ ), lithium (poly) sulfide (Li ２ S ｘ A lithium-sulfur battery according to claim 1, comprising , 1 ≤ x ≤ 8, or a mixture thereof.

5. The aforementioned W ＳＥ The lithium-sulfur battery according to claim 1, wherein the amount is 15% by weight or less based on the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery.

6. The aforementioned W ＳＰ The lithium-sulfur battery according to claim 1, wherein is 65% by weight or more based on the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery.

7. The aforementioned W ＳＰ The lithium-sulfur battery according to claim 6, wherein the amount is 75.5% by weight or more based on the total weight of sulfur element (S) present in the sulfur-based compound contained in the lithium-sulfur battery.

8. Formula 2 below: [Formula 2] W' ＳＰ >1.2×W' ＳＥ +56.86 Satisfying the conditions, In equation 2, The aforementioned W' ＳＥ This is the weight percentage of sulfur element (S) in the sulfur-based compounds present in the electrolyte, based on the total weight of sulfur element (S) in the sulfur-based compounds contained in the lithium-sulfur battery. The aforementioned W' ＳＰ The lithium-sulfur battery according to claim 1, wherein is the weight percentage of the sulfur element (S) in the sulfur-based compound present in the positive electrode, based on the total weight of the sulfur element (S) in the sulfur-based compound contained in the lithium-sulfur battery.

9. Formula 3 below: [Equation 3] 10.667×R Ｓ／Ｃ -10.633>R ＳＬ Satisfying the conditions, In equation 3, The aforementioned R ＳＬ This is the content ratio of sulfur element (S) according to the above formula 1, The aforementioned R Ｓ／Ｃ The lithium-sulfur battery according to claim 1, wherein is the weight ratio of sulfur (S) to carbon (C) in the sulfur-carbon composite.

10. The lithium-sulfur battery according to any one of claims 1 to 9, wherein the sulfur-carbon composite has a weight ratio of sulfur to carbon of 2.5 g / g or less.

11. The positive electrode includes a current collector and a positive electrode active material layer containing the sulfur-carbon composite, The lithium-sulfur battery according to claim 1, wherein the weight of the sulfur-carbon composite is 80% by weight or more based on the total weight of the positive electrode active material layer.

12. The lithium-sulfur battery according to claim 1, wherein the weight ratio of the electrolyte to the sulfur in the sulfur-carbon composite is 3.5 g / g or less.

13. The lithium-sulfur battery according to claim 1, wherein the electrolyte comprises an acyclic ether, a cyclic ether, or a mixture thereof.

14. The electrolyte comprises a mixture of the acyclic ether and the cyclic ether, The lithium-sulfur battery according to claim 13, wherein the volume ratio of the acyclic ether to the cyclic ether is 5:95 to 95:5 (v / v).

15. The lithium-sulfur battery according to claim 1, having a specific capacity of 60% or more of the theoretical specific capacity calculated from the total content of sulfur compounds contained in the lithium-sulfur battery.

16. The sulfur-based compound is inorganic sulfur (S ８ ), lithium (poly) sulfide (Li ２ S ｘ A lithium-sulfur battery according to claim 15, comprising , 1 ≤ x ≤ 8, or a mixture of two or more of these.

17. The lithium-sulfur battery according to claim 1, wherein the specific capacity of the lithium-sulfur battery is 1,000 mAh / g or more.

18. The lithium-sulfur battery according to claim 1, wherein the energy density of the lithium-sulfur battery is 300 Wh / kg or more.

19. The lithium-sulfur battery according to claim 1, wherein the lithium-sulfur battery is a coin-type battery, a pouch-type battery, or a cylindrical battery.

20. A method for evaluating the specific capacity of a lithium-sulfur battery comprising a positive electrode containing a sulfur-carbon composite, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, At least one of the positive electrode and the electrolyte contains a sulfur-based compound. Formula 1 below: [Formula 1] R ＳＬ (%)=W ＳＥ / W ＳＰ ×100 The ratio of sulfur element (S) content (R ＳＬ This includes a step of determining that a lithium-sulfur battery with a specific capacity of 15% or less is a high-specific-capacity battery. In equation 1, The aforementioned W ＳＥ This is the weight of the sulfur element (S) among the sulfur-based compounds present in the electrolyte, The aforementioned W ＳＰ The method wherein is the weight of the sulfur element (S) among the sulfur-based compounds present at the positive electrode.

21. The method according to claim 20, wherein the high specific capacity battery is a battery having a specific capacity of 1,000 mAh / g or more.

Images