Negative electrode for lithium secondary battery and lithium secondary battery including same

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, using lithium metal as a negative electrode active material, and, specifically, to a negative electrode for a lithium-sulfur battery, having, on a lithium metal layer, a protective layer comprising ion conductive inorganic particles and a binder polymer, and thus exhibiting the effect of improving the lifespan and coulombic efficiency of the lithium secondary battery.

Description

Anode for lithium secondary battery and lithium secondary battery including same

[0001] The present invention relates to an anode for use in a lithium secondary battery. In particular, it relates to an anode usable in a lithium-sulfur battery.

[0002] This application claims priority to Patent Application No. 2023-0179123, filed with the Korean Intellectual Property Office on December 11, 2023, the disclosure of which is incorporated herein by reference.

[0003] As the scope of application of lithium secondary batteries expands beyond portable electronic devices to include electric vehicles (EVs) and electric storage systems (ESS), the demand for lithium secondary batteries with high capacity, high energy density, and long lifespan is increasing.

[0004] Among various lithium secondary batteries, the lithium-sulfur battery is a battery system that uses a sulfur-based material containing a sulfur-sulfur bond as a positive electrode active material, and lithium metal, a carbon-based material in which lithium ions can be inserted / deinserted, or silicon or tin that forms an alloy with lithium as a negative electrode active material.

[0005] Lithium-sulfur batteries are based on the conversion reaction of lithium ions and sulfur (S8+16Li) at the cathode. + +16e - → The theoretical specific capacity from 8Li2S reaches 1,675 mAh / g, and when lithium metal is used as the negative electrode, it shows a theoretical energy density of 2,600 Wh / kg. This is a very high figure compared to the theoretical energy density of other battery systems currently being studied (Ni-MH battery: 450 Wh / kg, Li-FeS battery: 480 Wh / kg, Li-MnO2 battery: 1,000 Wh / kg, Na-S battery: 800 Wh / kg) and lithium ion batteries (250 Wh / kg), and therefore, it is attracting attention as a high-capacity, eco-friendly, and low-cost lithium secondary battery among the secondary batteries being developed so far.

[0006] However, lithium-sulfur batteries have a problem in that lithium ions can be reduced to lithium metal on the surface of the solid electrolyte interface (SEI) on the anode during the charging process, forming an uneven structure on the anode surface and causing uneven resistance distribution. Consequently, repeated charging and discharging eventually causes lithium to accumulate unevenly, resulting in the appearance of structures such as some dendrites and inactive lithium.

[0007] Among these, dendrites are the main cause of separator destruction and short circuits, so research is ongoing to ensure uniform desorption of lithium ions and deposition of lithium on the negative electrode surface of lithium-sulfur batteries.

[0008] The present invention seeks to provide a cathode having a protective layer to solve the above-described problem.

[0009] Specifically, the present invention aims to provide a negative electrode having a protective layer that uniformly reduces the desorption and deposition rates of lithium ions on the negative electrode surface during charge and discharge through the protective layer and suppresses the growth of lithium ion dendrites.

[0010] Through this, the present invention aims to provide a lithium secondary battery, particularly a lithium-sulfur battery, with improved lifespan.

[0011] To achieve the above purpose,

[0012] According to one aspect of the present invention, a negative electrode for a lithium secondary battery according to the following embodiments is provided.

[0013] The cathode according to the first embodiment is

[0014] Comprising a lithium metal layer and a protective layer formed on at least a portion of one surface of the lithium metal layer,

[0015] The above protective layer comprises ion-conductive inorganic particles and a binder polymer,

[0016] Based on 100% of the thickness of the lithium metal layer, the thickness of the protective layer is 4% to 15%.

[0017] According to the second embodiment, in the first embodiment,

[0018] The average particle diameter (D) of the above ion-conducting inorganic particles 50 ) may have a size of less than 50% of the thickness of the above protective layer.

[0019] According to the third embodiment, in the first embodiment or the second embodiment,

[0020] The thickness of the above protective layer may be 0.5 ㎛ to 5 ㎛.

[0021] According to the fourth embodiment, in any one of the first to third embodiments,

[0022] The thickness of the above protective layer may be 1 ㎛ to 3.5 ㎛.

[0023] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0024] The surface of the protective layer may include one or more holes having a diameter of 2 μm or more.

[0025] According to the sixth embodiment, in any one of the first to fifth embodiments,

[0026] The protective layer may have a structure in which the surface thereof may include one or more holes having a diameter of 2 μm or more, and the surface of the lithium metal layer is exposed to the outside at a location where the holes are formed.

[0027] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0028] The surface of the protective layer may include one or more holes having a diameter of 2 μm or more, and the diameter of the holes may be 2 μm or more and 10 μm or less.

[0029] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0030] The area on which the protective layer is formed on the lithium metal layer may be 50% or more based on 100% of the area of ​​one side of the lithium metal layer on which the protective layer is formed.

[0031] According to the ninth embodiment, in any one of the first to eighth embodiments,

[0032] The above ion-conducting inorganic particles may include lithium lanthanum zirconate (LLZO), lithium aluminum titanate phosphate (LATP), lithium aluminum germanium phosphate (LAGP), lithium lanthanum titanate (LLTO), or a mixture of two or more thereof.

[0033] According to the tenth embodiment, in any one of the first to ninth embodiments,

[0034] The above binder polymer may include a polymer including a vinylidene-derived repeating unit and a hexafluoropropylene (HFP)-derived repeating unit.

[0035] According to the eleventh embodiment, in any one of the first to tenth embodiments,

[0036] The above binder polymer may include a polymer including a vinylidene-derived repeating unit and a hexafluoropropylene (HFP)-derived repeating unit, and the polymer including the vinylidene-derived repeating unit and the hexafluoropropylene (HFP)-derived repeating unit may have an HFP substitution rate of 3% to 20%.

[0037] According to the 12th embodiment, in any one of the 1st to 11th embodiments,

[0038] The mass ratio of the ion-conducting inorganic particles and the binder polymer may be 99:1 to 50:50.

[0039]

[0040] According to another aspect of the present invention, a lithium secondary battery of the following embodiments is provided.

[0041] A lithium secondary battery according to the 13th embodiment,

[0042] It may include a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, an electrolyte, and a battery case for a lithium secondary battery according to any one of the first to twelfth embodiments.

[0043] According to the 14th embodiment, in the 13th embodiment,

[0044] The above positive electrode may include a sulfur series compound containing a sulfur (S)-sulfur (S) bond as an active material.

[0045] According to the 15th embodiment, in the 13th embodiment or the 14th embodiment,

[0046] The active material of the positive electrode may include a sulfur-carbon complex in which the sulfur-based compound is supported on at least one of the outer surface and the interior of the pores of the porous carbon material.

[0047] According to the 16th embodiment, in any one of the 13th to 15th embodiments,

[0048] The active material of the positive electrode may include a sulfur-carbon complex, and the sulfur-carbon complex may include the sulfur-carbon compound in an amount of 65 wt% or more based on the total weight of the sulfur-based compound and the porous carbon material.

[0049] According to the 17th embodiment, in any one of the 13th to 16th embodiments,

[0050] The above lithium secondary battery may be a coin-type, pouch-type, or cylindrical battery.

[0051]

[0052] According to another embodiment of the present invention, a method for manufacturing a lithium secondary battery according to the following embodiments is provided.

[0053] The method for manufacturing a lithium secondary battery according to the 18th embodiment is as follows:

[0054] A step of preparing a cathode having a protective layer on at least part of its surface,

[0055] It includes a step of interposing a separator between the positive electrode and the negative electrode.

[0056] Here, the protective layer is located on the surface where the cathode and the separator face each other,

[0057] The steps for preparing the above cathode are:

[0058] Comprising forming a protective layer by applying and drying a slurry for forming a protective layer on at least a part of one surface of a lithium metal layer,

[0059] The slurry for forming the above protective layer includes ion-conductive inorganic particles and a binder polymer.

[0060] Here, the thickness of the protective layer may be 4% to 15% based on 100% of the thickness of the lithium metal layer.

[0061] According to one aspect, the negative electrode of the present invention can exhibit the effect of uniformly increasing the desorption and deposition rates of lithium ions on the negative electrode surface during charge and discharge through the protective layer and suppressing the growth of lithium ion dendrites.

[0062] Through this, by using the negative electrode of the present invention, a lithium secondary battery, particularly a lithium-sulfur battery, with improved lifespan and coulombic efficiency can be provided.

[0063] According to one aspect, the lithium secondary battery according to the present invention can achieve an effect of maintaining a capacity of 80% compared to the initial discharge capacity for 200 cycles or more, particularly for 300 cycles or more, when discharging at 1C.

[0064] Figure 1 is a SEM image obtained by observing the surface of the cathode of Example 3 in the present specification using FESEM (Jeol, IT-800 SHL) at 5 kV and 1000x magnification. The area where holes with a diameter of 2 ㎛ or more were observed is marked with a dotted line.

[0065] Figure 2 is an SEM image obtained by observing the surface of the cathode of Comparative Example 4 in this specification.

[0066] Figure 3 is an SEM image obtained by observing the surface of the cathode of Comparative Example 5 in the present specification.

[0067] Hereinafter, the present invention will be described in more detail.

[0068] The term "composite" used in this specification refers to a material in which two or more materials are combined to form physically and chemically different phases and exhibit more effective functions.

[0069] The term "(poly)sulfide" as used herein means "(poly)sulfide ion (S x 2- , 1≤x≤8)" and "lithium (poly)sulfide (Li2S x or Li2S x- It is a concept that includes all of "1≤x≤8".

[0070] The term "polysulfide" as used herein means "polysulfide ion (S x 2- , 1 <x≤8)" 및 "리튬폴리설파이드(Li2S x or Li2S x - 1 <x≤8)"를 모두 포함하는 개념이다.

[0071] Lithium secondary batteries have the characteristic that lithium ions are reduced on the surface of the negative electrode during charging and discharging, and lithium metal accumulates on the negative electrode through repeated charging and discharging.

[0072] According to one aspect of the present invention, an anode is provided that allows lithium ions to be desorbed and deposited at a uniform rate on the surface of the anode, and that suppresses the formation of dendrites of lithium ions on the surface of the anode, thereby improving the lifespan of a lithium secondary battery using the same.

[0073] A negative electrode according to one aspect of the present invention comprises a lithium metal layer and a protective layer formed on at least a portion of one surface of the lithium metal layer.

[0074] According to one aspect of the present invention, the protective layer includes ion-conductive inorganic particles and a binder polymer.

[0075] According to one aspect of the present invention, the thickness of the protective layer is 4% to 15% based on 100% of the thickness of the lithium metal layer.

[0076] In one embodiment of the present invention, the ion-conductive inorganic particles refer to inorganic particles capable of improving the ionic conductivity of the electrolyte and enhancing the mechanical strength of the negative electrode. Any ion-conductive inorganic particle known in the art to be capable of achieving these effects may be used without particular limitation.

[0077] For example, according to one embodiment of the present invention, the ion-conductive inorganic particles may include lithium lanthanum zirconium oxide (LLZO), lithium aluminum titanate phosphate (LATP), lithium aluminum germanium phosphate (LAGP), lithium lanthanum titanate (LLTO), or a mixture of two or more thereof, but the present invention is not limited thereto.

[0078] According to one embodiment of the present invention, the protective layer may include only LLZO (lithium lanthanum zirconium oxide) as the ion-conductive inorganic particles, but the present invention is not limited thereto.

[0079] According to one embodiment of the present invention, the ion-conductive inorganic particles may include a form in which at least a portion of the above-described inorganic particles is coated with or substituted with a trace amount of another metal. By coating or substituting at least a portion of the ion-conductive inorganic particles with another metal, the ion conductivity of the inorganic particles can be advantageously increased and the crystal structure can be stabilized. Specifically, the ion-conductive inorganic particles may have a structure in which at least a portion of the surface of the ion-conductive inorganic particles is coated with another metal, and / or a portion of the crystal structure of the ion-conductive inorganic particles is substituted with another metal.

[0080] Specifically, the ion-conducting inorganic particles may include LLZO, LATP, LAGP, LLTO, or particles having at least a portion of the surface of these particles coated with another metal and / or partially replaced by the other metal, or a mixture of two or more thereof.

[0081] In one embodiment of the present invention, the metal that can be coated or substituted on the surface of the ion-conductive inorganic particle may be, for example, boron (B), aluminum (Al), gallium (Ga), indium (In), calcium (Ca), zirconium (Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru), palladium (Pd), silver (Ag), tantalum (Ta), tungsten (W), iridium (Ir), platinum (Pt), gold (Au), yttrium (Y), scandium (Sc), or two or more of these metals, but the present invention is not limited thereto.

[0082] In one embodiment of the present invention, the ion conductive inorganic particles have an average particle diameter (D) of 500 nm or less, taking into account the thickness of the protective layer. 50 ) may be desirable to use only those having the ion-conducting inorganic particles. If the size of the ion-conducting inorganic particles is too large, the thickness uniformity of the protective layer may be low when forming a thin protective layer, and thus the effect of inhibiting deterioration of the negative electrode by the protective layer may be minimal, but the present invention is not limited thereto.

[0083] Specifically, the average particle diameter (D) of the ion-conducting inorganic particles 50 ) may be, for example, 5 nm to 500 nm, specifically 100 nm to 500 nm, 200 nm to 400 nm, 250 nm to 350 nm, or 250 nm to 300 nm. The ion-conductive inorganic particles may also exist in the form of secondary particles in which a plurality of primary particles are aggregated together. In the present specification, the average particle diameter (D of the ion-conductive inorganic particles 50 ) is based on the size of the primary particle.

[0084] In this specification, the above “average particle diameter Dn” means the particle diameter at the n% point of the volume cumulative distribution of particles according to particle diameter. That is, D 50Dn refers to the particle diameter at the 50% point of the volume cumulative distribution of particles according to particle diameter. The above Dn can be measured using the laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and the particle size distribution is calculated by measuring the difference in the diffraction pattern according to the particle size when the particles pass through the laser beam. By calculating the particle diameter at the point that becomes n% of the volume cumulative distribution of particles according to particle diameter in the measuring device, Dn can be measured.

[0085] According to one embodiment of the present invention, the binder polymer may be included, for example, to bind ion-conductive inorganic particles together and to bind ion-conductive inorganic particles together with a lithium metal layer, although its use is not limited thereto. Accordingly, any binder polymer known in the art may be used without limitation as long as it can achieve the above-described effects.

[0086] According to one embodiment of the present invention, in consideration of stability when used together with the ion-conducting inorganic particles, the binder polymer may include a polymer including a vinylidene-derived repeating unit and a hexafluoropropylene (HFP)-derived repeating unit.

[0087] In one embodiment of the present invention, when the binder polymer does not include a repeating unit derived from hexafluoropropylene (HFP), the stability over time of the slurry for forming a protective layer in which the binder polymer reacts with the ion-conductive inorganic particles to form a protective layer may be reduced, the dispersibility of the ion-conductive inorganic particles and / or the binder polymer in the slurry may be reduced, or the color of the protective layer may change. Accordingly, the binder polymer includes a repeating unit derived from hexafluoropropylene (HFP), and in terms of improving the adhesive strength of the binder polymer, includes a repeating unit derived from vinylidene.

[0088] Specifically, the polymer comprising the above vinylidene-derived repeating unit and hexafluoropropylene (HFP)-derived repeating unit includes a vinylidene compound and hexafluoropropylene as monomers, and is a general term for a polymer obtained by polymerizing these monomers. In this case, the polymerization of the monomers generally refers to a form such as block polymerization, alternating polymerization, or random polymerization of two or more different monomers, and the present invention is not limited thereto.

[0089] In one embodiment of the present invention, the polymer comprising the vinylidene-derived repeating unit and the hexafluoropropylene (HFP)-derived repeating unit may include, for example, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0090] In one embodiment of the present invention, in terms of adhesiveness of the binder polymer, the polymer comprising the vinylidene-derived repeating unit and the hexafluoropropylene (HFP)-derived repeating unit preferably has an HFP substitution rate of 50% or less. Specifically, the HFP substitution rate may be 1% to 50%, 3% to 30%, 3% to 20%, specifically 5% to 15%, 8% to 15%, or 8% to 10%.

[0091] In the present specification, the HFP substitution rate represents the ratio (%) of the number of hexafluoropropylene-derived repeating units based on the total number of each monomer in the binder polymer. That is, the HFP substitution rate of the polymer including the vinylidene-derived repeating units and the hexafluoropropylene-derived repeating units means the ratio of the number of hexafluoropropylene-derived repeating units based on the total number of the vinylidene-derived repeating units and the hexafluoropropylene-derived repeating units. This can be analyzed by a conventional analysis method for measuring the content of functional groups in the polymer.

[0092] In one embodiment of the present invention, the main component exhibiting the function of inhibiting degradation of the negative electrode in the protective layer is ion-conductive inorganic particles, and it is preferable that the main component of the protective layer is ion-conductive inorganic particles. For example, 50 wt% or more based on the total weight of the protective layer may be ion-conductive inorganic particles, and specifically 50 wt% to 99 wt%, 60 wt% to 99 wt%, 70 wt% to 95 wt%, 80 wt% to 95 wt%, and 85 wt% to 90 wt% may be ion-conductive inorganic particles. When the content of the ion-conductive inorganic particles is within the above-described range, it can exhibit advantageous effects in terms of inhibiting degradation of the negative electrode and improving the lifespan of a lithium secondary battery.

[0093] In another embodiment of the present invention, the ion-conductive inorganic particles and the binder polymer may be included in a mass ratio of, for example, 99:1 to 50:50 (ion-conductive inorganic particles:binder polymer). Specifically, the mass ratio may be 99:1 to 60:40, 95:5 to 70:30, 90:10 to 80:20, or 90:10 to 85:15, but the present invention is not limited thereto.

[0094] According to one aspect of the present invention, a negative electrode may be formed such that a protective layer having the above-described composition has a thickness of 4% to 15% based on 100% of the thickness of the lithium metal layer.

[0095] Even if the protective layer includes ion-conductive inorganic particles and a binder polymer, if it is too thick relative to the weight of the lithium metal layer containing the negative electrode active material, a loss in terms of battery capacity may occur, and if it is too thin, the performance exerted by the protective layer may be minimal. Therefore, the thickness of the protective layer may be limited to 4% to 15% based on 100% of the thickness of the lithium metal layer.

[0096] In one embodiment of the present invention, the thickness of the protective layer may be specifically 4% to 15%, 5% to 15%, 5% to 13%, 5% to 10.5%, or 5% to 10% based on 100% of the thickness of the lithium metal layer.

[0097] In this specification, the thickness of each of the lithium metal layer and the protective layer may be measured using a known thickness measuring device. For example, the thickness of each of the lithium metal layer and the protective layer may be measured using a U-Hite thickness measuring device from TESA. Specifically, the thickness may be measured using the commercial thickness measuring device under the conditions of 0.6 N and an accuracy of 0.01 ㎛.

[0098] The thickness ratio of the protective layer based on 100% of the thickness of the lithium metal layer can be measured by measuring the thickness of each of the lithium metal layer and the protective layer as described above, and then calculating the thickness ratio thereof. Alternatively, the thickness ratio of the lithium metal layer and the protective layer can be measured and calculated through SEM images of the cross-section of the negative electrode, etc.

[0099] In one embodiment of the present invention, the protective layer may be formed on at least a portion of one surface of the lithium metal layer. Specifically, the protective layer may be formed to cover the entirety of one surface of the lithium metal layer, or may be formed to cover a portion of one surface of the lithium metal layer such that a portion of one surface of the lithium metal layer is exposed to the outside.

[0100] At this time, the thickness of the protective layer is measured only based on the area covering the surface of the lithium metal layer, and it is preferable to measure the thickness at at least 5 points and then calculate the average value of these as the thickness of the protective layer.

[0101] In one embodiment of the present invention, the thickness of the lithium metal layer may be, for example, 20 μm or more. For example, the thickness of the lithium metal layer may be 20 μm to 100 μm, 20 μm to 80 μm, 20 μm to 70 μm, 20 μm to 60 μm, 20 μm to 55 μm, 25 μm to 55 μm, 25 μm to 50 μm, 25 μm to 45 μm, 30 μm to 45 μm, 25 μm to 40 μm, 25 μm to 35 μm, or 30 μm. When the thickness of the lithium metal layer is in the above-described range, it may exhibit advantageous effects in terms of the packing density of the battery and the energy density of the battery, but the present invention is not limited thereto.

[0102] In one embodiment of the present invention, the thickness of the protective layer may be, for example, 0.5 μm to 5 μm. For example, the thickness of the protective layer may be 0.5 μm to 4 μm, 1 μm to 3.5 μm, 1 μm to 3 μm, 1.5 μm to 3.1 μm, 1.5 μm to 3.0 μm, 1.5 μm to 2.5 μm, 1.5 μm to 2.5 μm, or 1.5 μm to 2.0 μm.

[0103] As described above, according to one embodiment of the present invention, the protective layer may be formed only on a portion of the surface of the lithium metal layer. This may be done by intentionally applying and drying the slurry for forming the protective layer only on a portion of the surface of the lithium metal layer, or by holes formed on the surface of the protective layer due to the organic relationship between the weight ratio of the ion-conductive inorganic particles and the binder polymer and the thickness of the protective layer during the formation of the protective layer. Both cases are possible.

[0104] Specifically, the surface of the protective layer may be formed with one or more holes having a size that can be observed with the naked eye or under a microscope. For example, the surface of the protective layer may include one or more holes having a diameter of 2 μm or more. For example, the diameter of the holes may be 2 μm to 10 μm.

[0105] According to one embodiment of the present invention, the negative electrode may have a structure in which the surface of the lithium metal layer under the protective layer is exposed to the outside at a location where a hole is formed on the surface of the protective layer. In this case, since the surface of the lithium metal layer is exposed to the outside through the hole, the charge / discharge efficiency of the battery using the lithium metal layer is further improved, and the coulombic efficiency of the battery can exhibit an excellent effect, but the present invention is not limited thereto.

[0106] Fig. 1 shows a SEM image of the surface of a negative electrode according to one embodiment of the present invention, observed using FESEM (Jeol, IT-800 SHL). Referring to Fig. 1, it can be seen that a large number of ion-conductive inorganic particles are distributed on the surface of the negative electrode, and at this time, several holes having a diameter of 2 ㎛ or more, which expose the surface of the lithium metal layer to the outside, are formed.

[0107] In one embodiment of the present invention, it may be preferable that the holes are observed in a number of 2 to 10 within a measurement area of ​​120 ㎛ X 90 ㎛ when observed with a SEM. For example, when the number of the holes within the measurement area is within the above-described range, it may exhibit advantageous effects in terms of suppressing the growth of lithium dendrites and improving ionic conductivity. For example, if the number of the holes within the measurement area is too large, the amount of lithium desorbed through the holes increases regardless of whether a protective layer is formed, and the rate of uneven electrodeposition around the holes increases during electrodeposition, which may cause a problem in which the growth of lithium dendrites is not controlled. Conversely, if no holes are formed within the measurement area, lithium ions move between the inorganic particles and the binder polymer, thereby reducing ionic conductivity, which may cause a problem in which the capacity of the cell is reduced.

[0108] In another embodiment of the present invention, even if the above-described number of holes is observed within the measurement region, it may be preferable that the hole diameter be formed within a range of 2 μm or more, specifically 2 μm to 10 μm. If the hole diameter is too small, the lithium desorption rate may be delayed and the ionic conductivity may be reduced, which may cause a problem in that the cell capacity may not be fully realized. In addition, if the hole diameter is too large, the shape of the lithium deposited around the hole may not be controlled, which may cause a problem in that lithium dendrites grow excessively.

[0109] According to one embodiment of the present invention, it may be preferable that the protective layer has the thickness range described above and includes 2 to 10 holes having a diameter of 2 ㎛ or more, specifically 2 ㎛ to 10 ㎛, within a measurement area of ​​120 ㎛ X 90 ㎛ on one surface of the protective layer.

[0110] In one embodiment of the present invention, in order to enhance the performance improvement effect by the protective layer including the ion conductive inorganic particles and the binder polymer, the area of ​​the lithium metal layer covered by the protective layer may be 50% or more, for example, 50% to 100%, 50% to 99%, 60% to 95%, 70% to 95%, or 80% to 90%, or 85% to 90%, based on 100% of the area of ​​one side of the lithium metal layer, but the present invention is not limited thereto.

[0111] In the present specification, the area of ​​the protective layer formed on the lithium metal layer based on 100% of the area of ​​one side of the lithium metal layer on which the protective layer is formed can be measured through an SEM image of the surface of the negative electrode, etc., as described above. For example, after obtaining an SEM image of the surface of the negative electrode, the area of ​​the area of ​​the area where the protective layer is formed can be measured by calculating the ratio of the area of ​​the area where the protective layer is formed to the total area of ​​one side of the negative electrode after image processing to distinguish the area where the lithium metal layer is exposed and the area where the protective layer is formed, but the measurement method is not limited thereto.

[0112] In one embodiment of the present invention, as described above, if the size of the ion-conductive inorganic particles is too large, the thickness uniformity of the protective layer may be low when forming a thin protective layer, and thus the effect of inhibiting deterioration of the negative electrode by the protective layer may be minimal. Considering this, in one embodiment of the present invention, in order to control the thickness uniformity and thickness of the protective layer, the average particle diameter (D) of the ion-conductive inorganic particles 50 ) may have a size of less than 50% of the thickness of the above protective layer.

[0113] For example, the average particle diameter (D) of the ion-conducting inorganic particles 50) may have an advantageous effect in terms of improving the performance of the negative electrode and the performance of the lithium secondary battery by the protective layer when the thickness of the protective layer is 1% to 50%, 1% to 30%, 1% to 20%, 5% to 20%, 1% to 10%, or 5% to 10% of the thickness of the protective layer, but the present invention is not limited thereto.

[0114] As described above, when the ion-conducting inorganic particles exist in the form of secondary particles in which a plurality of primary particles are aggregated, the average particle diameter (D) of the ion-conducting inorganic particles 50 ) is based on the size of the primary particle.

[0115] In one embodiment of the present invention, the slurry for forming the protective layer can be prepared by, for example, the following method.

[0116] As components of the above protective layer, the ion-conductive inorganic particles and the binder polymer are each as described above.

[0117] In one embodiment of the present invention, the slurry for forming the protective layer can be prepared by dispersing and mixing the ion-conductive inorganic particles and the binder polymer in an appropriate solvent. In this case, since the slurry for forming the protective layer can be directly applied and dried on a lithium metal layer to form the protective layer, it is preferable to use a non-aqueous solvent as the solvent.

[0118] In another embodiment of the present invention, the slurry for forming the protective layer can be prepared by first preparing a dispersion solution in which the ion-conductive inorganic particles are dispersed and a binder solution in which a binder polymer is dissolved, and then mixing them, in order to improve stability over time.

[0119] In one embodiment of the present invention, it may be preferable to use a non-aqueous solvent as the solvent for preparing the slurry for forming the protective layer, taking into consideration the reactivity with the lithium metal layer, the dispersibility of the inorganic particles, and the type of binder polymer as described above.

[0120] In one embodiment of the present invention, the non-aqueous solvent may be, for example, tetrahydrofuran (THF), dimethoxyethane (DME), N-methyl-2-pyrrolidone (NMP), acetone, acetonitrile, dichloromethane, dimethylformamide, dimethyl sulfoxide, ethyl acetate, or a mixture of two or more thereof, but the present invention is not limited thereto.

[0121] In one embodiment of the present invention, in order to control the thickness and uniformity of the protective layer, the solid content in the slurry for forming the protective layer may be controlled. For example, it may be preferable that the solid content in the slurry for forming the protective layer is 50 wt% or less, and for example, it may be preferable that it is 10 wt% to 40 wt%, 15 wt% to 40 wt%, 15 wt% to 30 wt%, 15 wt% to 25 wt%, or 20 wt% to 25 wt%. When the solid content in the slurry for forming the protective layer is within the above-described range, it may be advantageous in that the thickness of the protective layer is formed thinly and uniformly, and may also exhibit an advantageous effect in that holes are formed on the surface of the protective layer.

[0122] In one embodiment of the present invention, the protective layer can be formed by applying the slurry for forming the protective layer described above to one surface of the lithium metal layer and then drying it.

[0123] In one embodiment of the present invention, after applying a slurry for forming a protective layer to one surface of the lithium metal layer, a planarization process can be performed using a Meyer bar to ensure thickness uniformity.

[0124] In one embodiment of the present invention, in order to form the protective layer, a step of applying the slurry for forming the protective layer and then drying in an oven at a temperature of 40°C to 60°C, for example, 50°C, may be included, but the method for manufacturing the protective layer is not limited thereto.

[0125] In one embodiment of the present invention, the lithium metal layer may be a thin film layer composed only of lithium metal (Li).

[0126] In another embodiment of the present invention, the lithium metal layer may be a thin film layer made of lithium and a material that forms an alloy with lithium, such as silicon, tin, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, radium, aluminum, or a lithium alloy alloyed with two or more of these materials.

[0127] In one embodiment of the present invention, the negative electrode may be provided as a free-standing film including a lithium metal layer and a protective layer without a separate support.

[0128] In another embodiment of the present invention, the negative electrode may be provided in a form including a lithium metal layer and a protective layer on a support.

[0129] At this time, the support may be a polyolefin porous support used as a current collector or a separator used in a conventional lithium secondary battery electrode, but is not limited thereto.

[0130] In one embodiment of the present invention, the current collector supports the lithium metal layer, and is not particularly limited as long as it has high conductivity without causing chemical changes in the lithium secondary battery using the current collector. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0131] In one embodiment of the present invention, the current collector may be a copper foil having a thickness of, for example, 6 to 30 μm, for example, 10 μm.

[0132] In addition, the negative electrode according to one embodiment of the present invention may further include a conventional configuration that can be used for the negative electrode of a lithium secondary battery, particularly a lithium-sulfur battery, and is not particularly limited to the configuration further included as long as it does not impede the purpose of the present invention.

[0133]

[0134] According to another aspect of the present invention, a lithium secondary battery including the above-described negative electrode is provided.

[0135] In one embodiment of the present invention, the lithium secondary battery may be a lithium-sulfur battery including a sulfur series compound containing a sulfur (S)-sulfur (S) bond as a positive electrode active material, but the present invention is not limited thereto.

[0136] A lithium secondary battery according to one aspect of the present invention includes the above-described negative electrode, positive electrode, a separator interposed between the negative electrode and positive electrode, an electrolyte, and a battery case.

[0137] In one embodiment of the present invention, the positive electrode can be used without particular limitation as long as it is used in a lithium secondary battery, and when used as a lithium-sulfur secondary battery, the positive electrode includes a sulfur series compound containing a sulfur (S)-sulfur (S) bond as an active material.

[0138] In one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer applied to one or both surfaces of the positive electrode current collector.

[0139] The above-mentioned positive electrode current collector supports the positive electrode active material and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0140] The above positive electrode current collector can form fine irregularities on its surface to strengthen the bonding strength with the positive electrode active material, and can be used in various forms such as a film, sheet, foil, mesh, net, porous body, foam, and non-woven fabric.

[0141] The above positive electrode active material layer includes a positive electrode active material and may further include a conductive material, a binder, and additives.

[0142] In one embodiment of the present invention, the positive electrode active material may include a sulfur-carbon complex.

[0143] 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 outer surface and the interior of the pores of the porous carbon material. In the case of sulfur acting as the positive electrode active material, since sulfur alone does not have electrical conductivity, it is used in a composite with a conductive material such as a carbon material, and a porous carbon material may be used to support sulfur. In addition, the sulfur-based compound may include, for example, inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 1 < x ≤ 8), a disulfide compound, a carbon-sulfur polymer ((C2S) y ) n, y = 2.5 to 50, n≥2), lithium sulfide (Li2S) or two or more thereof. Preferably, the sulfur compound may be inorganic sulfur (S8).

[0144] In one embodiment of the present invention, the porous carbon material is used to support a sulfur-based compound as a positive electrode active material, and to provide a framework in which the sulfur-based compound can be uniformly and stably fixed, while improving the conductivity of the positive electrode. Any porous carbon material can be used without particular limitation in its type.

[0145] The shape of the porous carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk-shaped, and may be any shape commonly used in lithium-sulfur batteries. The porous carbon material may be any shape commonly used in the art, as long as it has a porous structure or a high specific surface area.

[0146] For example, the porous carbon material may be at least one 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 summer 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); and graphite and activated carbon such as natural graphite, artificial graphite, and expanded graphite, but is not limited thereto. Preferably, the porous carbon material may be a carbon nanotube.

[0147] In one embodiment of the present invention, the porous carbon material may include, for example, carbon nanotubes (CNTs).

[0148] In one embodiment of the present invention, the sulfur-carbon composite may contain the sulfur-based compound in an amount of 65 wt% or more, for example, 65 wt% to 90 wt%, 65 wt% to 85 wt%, 70 wt% to 80 wt%, or 70 wt% to 75 wt%, based on the total weight of the sulfur-based compound and the porous carbon material.

[0149] When the content of the sulfur series compound in the above sulfur-carbon complex is within the above-described range, it may be preferable in terms of the electron transfer area of ​​the sulfur-carbon complex and wettability with the electrolyte of the positive electrode, and for example, the available surface of the sulfur-carbon complex increases, which may be preferable in suppressing the elution of sulfur from the positive electrode, but the present invention is not limited thereto.

[0150] The method for manufacturing the above sulfur-carbon composite is not particularly limited in the present invention, and any method commonly used in the art may be used. For example, a method may be used in which the sulfur and porous carbon material are simply mixed and then heat-treated to form a composite.

[0151] In addition to the composition described above, the positive electrode active material may include at least one selected from among transition metal elements, group IIIA elements, group IVA elements, sulfur compounds of these elements, and alloys of these elements and sulfur.

[0152] The above 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, etc., the above group IIIA elements include Al, Ga, In, Ti, etc., and the above group IVA elements may include Ge, Sn, Pb, etc.

[0153] In one embodiment of the present invention, the conductive material, binder, and other components that can be used in the positive electrode active material layer can utilize conventional techniques and are not particularly limited to the present invention.

[0154] In one embodiment of the present invention, the separator separates or insulates the positive electrode and the negative electrode from each other and enables lithium ion transport between the positive electrode and the negative electrode. The separator may be made of a porous non-conductive or insulating material, and any material commonly used as a separator in a lithium secondary battery may be used without special limitation. The separator may be an independent member such as a film, or may be a coating layer added to the positive electrode and / or the negative electrode.

[0155] In one embodiment of the present invention, the electrolyte may include a non-aqueous solvent and a lithium salt as a medium through which ions involved in the electrochemical reaction of a lithium secondary battery, for example, a lithium-sulfur battery, can move.

[0156] The above electrolyte is not particularly limited as long as it has a composition that can be used in a lithium secondary battery, specifically a lithium-sulfur battery.

[0157] In one embodiment of the present invention, the lithium-sulfur battery may have various shapes, for example, a coin shape, a pouch shape, or a cylindrical shape, but is not limited thereto.

[0158] As described above, when the negative electrode according to one embodiment of the present invention is applied to a lithium secondary battery, it can exhibit an excellent effect in suppressing dendrite growth on the negative electrode surface due to the physical blocking effect against dendrite growth by the protective layer and the suppression of dendrite growth by improving ionic conductivity, and thus can exhibit an effect of improving the lifespan and coulombic efficiency of the battery.

[0159] In particular, according to one embodiment of the present invention, a lithium-sulfur battery having improved lifespan and coulombic efficiency can be provided.

[0160]

[0161] According to another embodiment of the present invention, a method for manufacturing the above-described lithium secondary battery is provided.

[0162] The method for manufacturing the above lithium secondary battery is not limited thereto, but may include, for example, a step of preparing an anode having a protective layer on at least a portion of one surface, and a step of interposing a separator between the anode and the anode. In this case, it is preferable that the protective layer of the anode be positioned on the surface where the anode and the separator face each other.

[0163] In one embodiment of the present invention, the step of preparing the negative electrode may include forming a protective layer on one surface of the lithium metal layer.

[0164] For example, in one embodiment of the present invention, the step of preparing the negative electrode may include forming a protective layer by applying and drying a slurry for forming a protective layer on at least a portion of one surface of a lithium metal layer.

[0165] In one embodiment of the present invention, the composition of the slurry for forming the protective layer is as described above.

[0166] An anode manufactured according to one embodiment of the present invention includes the lithium metal layer and a protective layer formed on at least a portion of one surface of the lithium metal layer. In addition, the protective layer includes ion-conductive inorganic particles and a binder polymer, and the thickness of the protective layer may be 4% to 15% based on 100% of the thickness of the lithium metal layer.

[0167] According to one embodiment of the present invention, manufacturing a lithium secondary battery using an anode having a protective layer formed on a lithium metal layer may include positioning the surface of the anode having the protective layer formed thereon so as to face the separator. In providing a protective layer at the interface between the anode and the separator, it is preferable that the protective layer according to one embodiment of the present invention be formed on the lithium metal layer and then brought into contact with the separator. In general, the separator of a lithium secondary battery is a porous material having a plurality of pores on its surface. At this time, when forming a protective layer including ion-conductive inorganic particles and a binder polymer on the separator according to one embodiment of the present invention, at least a portion of the pores of the separator may be closed by the binder polymer, which may cause a problem of deteriorating the performance of the separator. Alternatively, in order to prevent the closing of the pores of the separator, a limitation may arise in that the content of the binder polymer is used in a small amount or the type of the binder polymer is limited. As in one embodiment of the present invention, a negative electrode having a protective layer formed on the lithium metal layer can prevent the problem of the binder polymer being impregnated into the substrate (i.e., the lithium metal layer), so that not only can the ion-conductive inorganic particles and the binder polymer within the protective layer be uniformly distributed, but also can exhibit the advantage of the protective layer not being broken even when the volume of the negative electrode changes, but the present invention is not limited thereto.

[0168] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0169]

[0170] [Preparation of slurry for forming a protective layer]

[0171] A slurry for forming a protective layer was prepared using the following method, as shown in Table 1.

[0172] Manufacturing Example 1

[0173] As ion-conducting inorganic particles, particle size (D 50 ) was added (30 wt%) to 21 g of tetrahydrofuran (THF) (Aldrich, anhydrous tetrahydrofuran) and mixed using a zirconia ball (1 mm). Then, the mixture was stirred for 5 minutes at 80 G using an acoustic mixer (Resodyn, Lab RAM I) to prepare an LLZO dispersion.

[0174] A binder solution was prepared by adding HFP-PVDF polymer (Solvay, Solef 20808) with an HFP substitution rate of 8% as a binder polymer to a mixed solvent of tetrahydrofuran (THF) and 1,2-dimethoxyethane (DME) (1 / 1 mass ratio) at a content of 5 wt%.

[0175] The LLZO dispersion prepared above and the binder solution were mixed so that the mass ratio of LLZO and binder polymer was 9:1, and a mixed solvent of THF and DME (mass ratio of 1 / 1) was further added as a solvent, and mixed for 30 minutes to prepare a slurry for forming a protective layer with a solid content of 20 wt%.

[0176]

[0177] Manufacturing Example 2

[0178] A slurry for forming a protective layer was prepared using the same method as in Manufacturing Example 1, except that HFP-PVDF polymer (Solvay, Solef 21510) with an HFP substitution rate of 15% was used as a binder polymer (solid content 20 wt%).

[0179]

[0180] Manufacturing Example 3

[0181] A slurry for forming a protective layer was prepared in the same manner as in Manufacturing Example 1, except that a binder solution was prepared by adding HFP-PVDF polymer (Solvay, Solef 75130) with an HFP substitution rate of 5% as a binder polymer to N-methyl-2-pyrrolidone (NMP) (solid content 30 wt%).

[0182]

[0183] Manufacturing Example 4

[0184] A slurry for forming a protective layer was prepared in the same manner as in Manufacturing Example 1, except that the mass ratio of LLZO and binder polymer was mixed to be 13:100 (solid content 20 wt%).

[0185]

[0186] Comparative Manufacturing Example 1

[0187] The binder solution prepared above was prepared as a slurry for forming a protective layer without mixing it with the LLZO dispersion.

[0188]

[0189] Comparative Manufacturing Example 2

[0190] Only the LLZO dispersion prepared above was prepared as a slurry for forming a protective layer without mixing with a binder solution.

[0191]

[0192] Composition Manufacturing Example 1 Manufacturing Example 2 Manufacturing Example 3 Manufacturing Example 4 LLZO / PVDF (mass ratio) 9 / 19 / 19 / 113 / 100 Binder polymer type 8% HFP-PVDF 15% HFP-PVDF 5% HFP-PVDF 15% HFP-PVDF Solvent (mass ratio) THF / DME (1 / 1) THF / DME (1 / 1) NMPTHF / DME (1 / 1) Solid content (%) 20% 20% 30% 20% Coating liquid state Dispersibility Good Dispersibility Good Dispersibility Good Dispersibility Good

[0193] [Manufacturing of the cathode]

[0194] A single-sided lithium foil was prepared by laminating a 10 ㎛ thick copper foil and a 30 ㎛ or 45 ㎛ thick lithium foil.

[0195] Thereafter, the slurry for forming a protective layer prepared above was applied onto the lithium side of a cross-sectional lithium foil, flattened to a certain thickness using a Meyer bar, and then dried in an oven at 50°C for 5 to 60 minutes to completely dry the slurry, depending on the amount of slurry applied. Through this, an anode having a protective layer formed on the surface of the lithium metal foil was manufactured.

[0196] The characteristics of each manufactured negative electrode are summarized in Tables 2 to 4 below, and Comparative Example 1 used a single-sided lithium foil without forming a protective layer as the negative electrode.

[0197]

[0198] Measuring the thickness of the protective layer

[0199] The thickness of the protective layer was measured at five locations on the manufactured cathode using a U-Hite thickness gauge from TESA, and the average thickness was obtained. The measuring pressure of the thickness gauge was 0.6 N, and the accuracy was 0.01 ㎛.

[0200]

[0201] Surface observation of the protective layer

[0202] For the cathode prepared above, a surface image was obtained at 5 kV and 1000x magnification using Jeol's FESEM (IT-800 SHL).

[0203] The particle size, hole size, and shape of LLZO were observed in the surface image. When observing the particle size of LLZO, the particle size was measured at a magnification of 5,000 times, and when observing the hole size, the observation was made at a magnification of 1,000 times.

[0204] Fig. 1 shows an SEM image of the cathode surface of Example 3 below, Fig. 2 shows an SEM image of the cathode surface of Comparative Example 4 below, and Fig. 3 shows an SEM image of the cathode surface of Comparative Example 5 below.

[0205] Cathode Example 1 Example 2 Example 3 Example 4 Slurry for forming protective layer Preparation Example 1 Preparation Example 2 Preparation Example 2 Preparation Example 2 LLZO particle size (D 50 )300 nm300 nm300 nm300 nmProtective layer thickness1.5 ㎛2.6 ㎛3.1 ㎛3.0 ㎛Lithium foil thickness30 ㎛30 ㎛30 ㎛30 ㎛Protective layer thickness / lithium foil thickness X 1005%8.7%10.3%10%LLZO particle size / protective layer thickness X 10020%11.5%9.7%10%

[0206] Cathode Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Slurry for forming a protective layer - Manufacturing Example 2 Manufacturing Example 3 Manufacturing Example 2 LLZO particle size (D 50 )-300 nm300 nm300 nmProtective layer thickness- ㎛16 ㎛19.5 ㎛0.3 ㎛Lithium foil thickness30 ㎛45 ㎛45 ㎛30 ㎛Protective layer thickness / lithium foil thickness X 100-35.6%43.3%1%LLZO particle size / protective layer thickness X 100-1.9%1.5%100%

[0207] Cathode Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Slurry for forming a protective layer Manufacturing Example 2 Comparative Manufacturing Example 1 Comparative Manufacturing Example 2 Manufacturing Example 4 LLZO particle size (D 50 )300 nm300 nm300 nm300 nmProtective layer thickness6.2 ㎛1.0 ㎛3.0 ㎛1.0 ㎛Lithium foil thickness30 ㎛30 ㎛30 ㎛30 ㎛Protective layer thickness / Lithium foil thickness X 10020.7%3.3%10%3.3%LLZO particle size / Protective layer thickness X 1004.8%30%10%30%

[0208] [Manufacturing of Lithium Secondary Batteries]

[0209] Coin cells were manufactured using each cathode manufactured above using the following method.

[0210] First, a sulfur-carbon composite (S8 70 wt%) was prepared by mixing inorganic sulfur (S8) and carbon nanotubes (CNT) as positive electrode active materials, and 96 wt% of the prepared sulfur-carbon composite and 4 wt% of polyacrylate (PAA) as a binder were mixed to prepare a positive electrode slurry composition. The positive electrode slurry composition was applied to an aluminum current collector and then dried to obtain a positive electrode having a capacity of 3.4 mAh / cm 2 After manufacturing the positive electrode with the loading amount, it was punched to a size of 14 φ.

[0211] After the cathode prepared above was punched to a size of 15 φ as a cathode, a polyethylene separator having a thickness of 12 ㎛ and a porosity of 46 vol% punched to a size of 19 φ was interposed between the cathode and the anode.

[0212] After placing the above positive electrode / separator / cathode assembly in a coin-shaped case, 50 μl of electrolyte was injected and the lid was covered and sealed (El / S ratio = 11.1 g / g).

[0213] At this time, the electrolyte used was an electrolyte in which 0.75 M lithium salt (LiTFSI) and 2.1 wt% lithium nitrate (LiNO3) were dissolved in a solvent mixed with dimethyl ether (DME):2-methyl furan (2-MeF) in a volume ratio of 8:2.

[0214]

[0215] [Performance Evaluation of Lithium Secondary Batteries]

[0216] The lithium secondary battery manufactured as described above was aged at room temperature (25°C) for 24 hours, and then activated by repeating 0.5C discharge and 0.3C charge six times.

[0217] Afterwards, charging and discharging were repeated with 1C discharge and 0.5C charge until the capacity retention rate dropped to 80% based on the first discharge capacity, and the number of charge and discharge repetitions (cycle number) when the capacity retention rate reached 80% was evaluated as the lifespan of the battery, and the evaluation results are shown in Tables 5 and 6 below.

[0218] Performance evaluation of lithium secondary battery cathode Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 21 st Cycle discharge capacity (mAh / cm2) 754.1746.6745.8754.1764.5771.5 Lifespan (80% retention) 273238364224173150 Capacity retention rate % (100 cycles) 11010410090.710586.1

[0219] Performance Evaluation of Lithium Secondary Battery Anode Comparison Example 3 Comparison Example 4 Comparison Example 5 Comparison Example 6 Comparison Example 7 Comparison Example 81 st Cycle discharge capacity (mAh / cm2) 808.7746.6745.8764.5771.5808.7 Lifespan (80% retention) 1081118511817195 Capacity retention rate % (100 cycles) 81.485.876.386.293.079.5

[0220] Referring to the above evaluation results, it was confirmed that the batteries according to Examples 1 to 4 exhibited a lifespan of 200 cycles or more, whereas the batteries according to Comparative Examples 1 to 8 exhibited a lifespan of less than 200 cycles. Through this, it was confirmed that the lifespan of a lithium secondary battery using an anode according to an embodiment of the present invention was much superior to that of the comparative examples.

[0221] Specifically, it was confirmed that the life of the battery using the negative electrode of Comparative Example 1 without a protective layer was inferior. In addition, even when using a negative electrode equipped with a protective layer including ion conductive particles and a binder polymer, it was confirmed that the life was inferior when the thickness of the protective layer was too thick compared to the lithium metal layer, as in Comparative Examples 2, 3, and 5. In particular, referring to Fig. 3, it was observed through surface observation that the negative electrodes of Comparative Examples 2, 3, and 5 had holes having a diameter of 2 ㎛ or more formed on the surface, but the holes were formed in a form in which the surface of the lithium metal layer under the protective layer was not exposed.

[0222] In addition, even when using a negative electrode equipped with a protective layer including ion-conductive particles and a binder polymer, it was confirmed that the lifespan was actually inferior when the thickness of the protective layer was too thin compared to the lithium metal layer, as in Comparative Examples 4 and 8. Referring to Fig. 2, when observing the surface of these negative electrodes, it was observed that a protective layer was formed on the lithium metal layer, but the protective layer was formed in an island shape with an area of ​​less than 50% of the surface of the lithium metal layer. Based on this, it was inferred that the lifespan improvement effect by the protective layer was not exerted.

[0223] Furthermore, it was confirmed that the batteries using the negative electrodes of Comparative Examples 6 and 7, which did not use a binder polymer as a composition of the protective layer or did not use ion-conductive inorganic particles, also had inferior lifespans.

[0224] Through the above experiments, it was confirmed that a lithium secondary battery, particularly a lithium-sulfur battery, using a negative electrode according to one embodiment of the present invention can exhibit a significant lifespan improvement effect.

Claims

1. Lithium metal layer and Comprising a protective layer formed on at least a portion of one surface of the lithium metal layer, The above protective layer comprises ion-conductive inorganic particles and a binder polymer, A negative electrode for a lithium secondary battery, wherein the thickness of the protective layer is 4% to 15% based on a thickness of 100% of the lithium metal layer.

2. In claim 1, The average particle diameter (D) of the above ion-conducting inorganic particles 50 ) A negative electrode for a lithium secondary battery having a size of 50% or less of the thickness of the above protective layer.

3. In claim 1, A negative electrode for a lithium secondary battery, wherein the thickness of the protective layer is 0.5 ㎛ to 5 ㎛.

4. In claim 1, A negative electrode for a lithium secondary battery, wherein the thickness of the protective layer is 1 ㎛ to 3.5 ㎛.

5. In claim 1, A negative electrode for a lithium secondary battery, comprising at least one hole having a diameter of 2 ㎛ or more on the surface of the protective layer.

6. In claim 5, A negative electrode for a lithium secondary battery having a structure in which the surface of the lithium metal layer is exposed to the outside at a location where the hole is formed.

7. In claim 5, A negative electrode for a lithium secondary battery, wherein the diameter of the hole is 2 ㎛ to 10 ㎛.

8. In claim 1, A negative electrode for a lithium secondary battery, wherein the area on which the protective layer is formed on the lithium metal layer is 50% or more based on 100% of the area of ​​one side of the lithium metal layer on which the protective layer is formed.

9. In claim 1, A negative electrode for a lithium secondary battery, wherein the ion conductive inorganic particles include lithium lanthanum zirconate (LLZO), lithium aluminum titanate phosphate (LATP), lithium aluminum germanium phosphate (LAGP), lithium lanthanum titanate (LLTO), or a mixture of two or more thereof.

10. In claim 1, A negative electrode for a lithium secondary battery, wherein the binder polymer comprises a polymer including a vinylidene-derived repeating unit and a hexafluoropropylene (HFP)-derived repeating unit.

11. In claim 10, A polymer comprising the above vinylidene-derived repeating unit and hexafluoropropylene (HFP)-derived repeating unit, wherein the HFP substitution rate is 3% to 20%, and the negative electrode for a lithium secondary battery.

12. In claim 1, A negative electrode for a lithium secondary battery, wherein the mass ratio of the ion conductive inorganic particles and the binder polymer is 99:1 to 50:

50.

13. A lithium secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, an electrolyte, and a battery case according to any one of claims 1 to 12.

14. In claim 13, A lithium secondary battery, wherein the positive electrode comprises a sulfur series compound containing a sulfur (S)-sulfur (S) bond as an active material.

15. In claim 14, A lithium secondary battery, wherein the active material of the positive electrode includes a sulfur-carbon complex in which the sulfur series compound is supported on at least one of the outer surface and the interior of the pores of the porous carbon material.

16. In claim 15, A lithium secondary battery, wherein the sulfur-carbon complex comprises the sulfur series compound in an amount of 65 wt% or more based on the total weight of the sulfur series compound and the porous carbon material.

17. In claim 13, The above lithium secondary battery is a lithium secondary battery of coin type, pouch type or cylindrical type.

18. A step of preparing a cathode having a protective layer on at least a part of its surface, and Comprising a step of interposing a separator between the positive electrode and the negative electrode, The protective layer is located on the surface where the cathode and the separator face each other, The steps for preparing the above cathode are: Comprising forming a protective layer by applying and drying a slurry for forming a protective layer on at least a part of one surface of a lithium metal layer, The slurry for forming the above protective layer contains ion-conductive inorganic particles and a binder polymer, A method for manufacturing a lithium secondary battery, wherein the thickness of the protective layer is 4% to 15% based on a thickness of 100% of the lithium metal layer.

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