Positive electrode, method for producing the same, and lithium secondary battery including said positive electrode

Abstract

The present invention relates to a positive electrode and a lithium secondary battery including the positive electrode, wherein the active material layer of the positive electrode includes a positive electrode active material and a carbonate-based compound including a fluorine-containing functional group, and the peak intensity in a C1s spectrum obtained by XPS analysis satisfies a specific ratio. The positive electrode has excellent resistance characteristics, suppresses degradation, and improves life characteristics. Furthermore, a lithium secondary battery including the positive electrode has improved resistance characteristics, suppresses degradation of the positive electrode and negative electrode, prevents a sudden drop in capacity, and improves life characteristics.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0013847 filed on February 1, 2023, and all the contents disclosed in the literature of the Korean patent application are incorporated herein by reference as part of this specification.

[0002] The present invention relates to an over-lithiated cathode, a method for manufacturing a cathode including a method for over-lithiating the cathode, and a lithium secondary battery including the cathode.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative and clean energy has been increasing. As part of this, the most actively studied fields are power generation and power storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage areas are increasingly expanding. In recent years, with the increase in technology development and demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, many studies have been conducted on lithium secondary batteries with high energy density, that is, high capacity, and they have also been commercialized and widely used.

[0005] Generally, a secondary battery is composed of a cathode, an anode, an electrolyte, and a separator. The anode contains an anode active material that inserts and desorbs lithium ions emitted from the cathode, and as the anode active material, silicon-based active material particles with a large discharge capacity can be used. The silicon-based active material particles correspond to Si or SiO X (0 < X < 2), etc. The silicon-based active material particles have the advantages of a large theoretical capacity and low cost. However, the silicon-based active material particles have the disadvantage that the volume change is too large during the operation of the battery, so the battery life rapidly decreases as the battery cycle progresses.

[0006] Therefore, in order to minimize the volume change of silicon-based active material particles, there is a method of using only a portion of the total capacity of the silicon-based active material particles. To achieve this, a so-called prelithiation process is used, in which lithium ions are pre-intercalated into a negative electrode containing silicon-based active material particles. Specifically, when lithium ions are intercalated into a negative electrode by a method such as transferring lithium metal to the negative electrode, the lithium ions react with irreversible sites of the negative electrode, reducing the total capacity of the negative electrode to the level of the reversible capacity. Therefore, the amount of lithium ions intercalated during battery operation can be suitably reduced to the level required for battery operation, thereby minimizing the volume change of the silicon-based active material particles.

[0007] However, during the process of disposing lithium metal on the surface of the negative electrode and carrying out pre-lithiation, excessive heat is generated due to the alloy reaction between lithium and silicon, and the possibility of fire due to the reaction between lithium and moisture increases. Furthermore, during the process of notching and punching the negative electrode, the reaction area between lithium and the silicon-based active material increases, further increasing the possibility of fire. There is also a serious safety issue in that there is a possibility of fire due to the pre-lithiated silicon-based active material particles.

[0008] Therefore, there is a need for a new technology that can improve the battery's lifespan by inserting lithium ions into the negative electrode before the battery is driven, while also reducing the possibility of excessive heat generation and fire. Summary of the Invention [Problem to be solved by the invention]

[0009] One problem to be solved by the present invention is to provide a method for manufacturing a positive electrode that can significantly shorten the time required for the perlithiation step without causing detachment and cracking of the active material when the positive electrode is perlithiated.

[0010] Another problem to be solved by the present invention is to provide a perlithiated positive electrode that suppresses cracking of the active material during cycle operation, thereby providing excellent resistance characteristics, and that reduces the amount of lithium loss even over long periods of cycling, thereby suppressing capacity loss, through stable perlithiation and the formation of a solid electrolyte coating (SEI) on the surface of the positive electrode.

[0011] Yet another object of the present invention is to provide a lithium secondary battery that includes the overlithiated positive electrode and controls the usable region of the negative electrode, thereby realizing the inherent properties of the negative electrode active material without drawbacks, thereby improving life characteristics, and in particular, is excellent in suppressing degradation, thereby expecting a synergistic effect in improving life characteristics, and has a low resistance increase rate, thereby minimizing the problem of output reduction even when driven for a long period of time. [Means for solving the problem]

[0012] In order to solve the above-mentioned problems, in one aspect of the present invention, there is provided a cathode active material comprising: a cathode active material layer including a cathode active material and a carbonate-based compound including a fluorine-containing functional group; and a current collector on which the cathode active material layer is disposed, wherein in a C1s spectrum by XPS analysis, a peak P C1 Peak intensity I C1 However, the peak P with binding energy of 284 eV to 286 eV C2 Peak intensity I C2 A positive electrode is provided that is smaller than

[0013] In order to solve the above-mentioned problems, in another aspect of the present invention, there is provided a method for manufacturing a positive electrode, including the steps of: (S1) placing a transfer laminate including a substrate film and a lithium metal layer positioned on the substrate film on a preliminary positive electrode active material layer, and forming a positive electrode structure such that the lithium metal layer and the preliminary positive electrode active material layer are in contact with each other; and (S2) impregnating the positive electrode structure with an electrolyte containing a carbonate-based compound having a fluorine-containing functional group.

[0014] In order to solve the above problems, in yet another aspect of the present invention, there is provided a lithium secondary battery including the positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0015] In order to solve the above problems, in yet another aspect of the present invention, there is provided a lithium secondary battery including: an electrode assembly including a perlithiated positive electrode having a perlithiated positive electrode active material layer, an anode including silicon (Si) particles as an active material, and a separator interposed between the positive electrode and the anode; a battery case that houses the electrode assembly; and an electrolyte that is injected into the battery case so that the electrode assembly is impregnated, the electrolyte including a carbonate-based compound having a fluorine-containing functional group, wherein when the lithium content relative to the total weight of the positive electrode active material layer in the perlithiated positive electrode, as measured by inductively coupled plasma spectroscopy (ICP-OES), is less than 5.0 wt%, the content of the carbonate-based compound having a fluorine-containing functional group relative to the total weight of the electrode assembly and the electrolyte, as measured by inductively coupled plasma spectroscopy (ICP-OES), is 3.5 wt% or more. [Effects of the Invention]

[0016] The method for producing a positive electrode according to the present invention has the advantage that by performing overlithiation through electrolyte impregnation, it is possible to mitigate the phenomenon of desorption and cracking of the active material, thereby reducing side reactions with the electrolyte and reducing process risks that arise when prelithiating the negative electrode.

[0017] Furthermore, the positive electrode according to the present invention is perlithiated, and since it is produced by the above-described method and stably perlithiated, a solid electrolyte interlayer (SEI) is uniformly formed on the surface of the positive electrode, which prevents cracking of the active material during cycle operation, resulting in excellent resistance characteristics and a small decrease in the amount of lithium even over long-term cycles, thereby preventing a decrease in capacity.

[0018] Furthermore, by including the perlithiated positive electrode, the lithium secondary battery according to the present invention can reduce the usable area of ​​the negative electrode without lithium loss from the positive electrode by transferring lithium ions to the negative electrode during the activation process, and in some cases, can suppress volume expansion of the negative electrode and eliminate causes of battery degradation, such as reducing side reactions with the electrolyte, thereby extending the battery's lifespan. Furthermore, perlithiated battery using an electrolyte containing a fluorine-containing carbonate compound can improve the surface stability of the positive electrode, suppressing electrode degradation and thereby preventing a sudden drop in capacity. Furthermore, the low rate of increase in resistance is expected to provide the advantage of maintaining an excellent level of output power for a long period of time. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 2 is a schematic diagram showing step S1 in a method for producing a positive electrode according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing step S1 using a transfer laminate including a polymer layer in a method for producing a positive electrode according to one embodiment of the present invention. [Figure 3] FIG. 2 is a schematic diagram showing step S1a in the method for producing a positive electrode according to one embodiment of the present invention. [Figure 4] FIG. 2 is a schematic diagram showing step S1b in the method for producing a positive electrode according to one embodiment of the present invention. [Figure 5] 1 is a scanning electron microscope (SEM) image of a cross section of a positive electrode of Example 1-5 produced by a method for producing a positive electrode according to one embodiment of the present invention. [Figure 6] 1 is a scanning electron microscope (SEM) image of a cross section of the positive electrode of Comparative Example 1-2. [Figure 7] This shows the results of measuring the surface resistance depending on the change in SOC. [Figure 8] This is the measurement result of charge transfer resistance due to changes in SOC. [Figure 9]This is the measurement result of the diffusion resistance due to the change in SOC. [Figure 10] 10 shows the results of life measurement in Experimental Example 3, in which the capacity was measured as the number of cycles increased. [Figure 11] 1 shows C1s spectra obtained by XPS analysis of the surfaces of the positive electrodes of Example 2-5 and Comparative Example 2-1. [Figure 12] 1 shows F1s spectra obtained by XPS analysis of the surfaces of the positive electrodes of Example 2-5 and Comparative Example 2-1. [Figure 13] 1 shows O1s spectra obtained by XPS analysis of the surfaces of the positive electrodes of Example 2-5 and Comparative Example 2-1. DETAILED DESCRIPTION OF THE INVENTION

[0020] For better understanding of the present invention, the present invention will be described in more detail below.

[0021] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0022] The terms used in this specification are used only to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0023] As used herein, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0024] In this specification, D 50 can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 can be measured by, for example, the laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0025] positive electrode According to one embodiment of the present invention, a cathode active material layer including a cathode active material and a carbonate-based compound including a fluorine-containing functional group, and a current collector on which the cathode active material layer is disposed, are provided. In a C1s spectrum obtained by XPS analysis, a peak intensity I C1 However, the peak intensity I at binding energies of 284 eV to 286 eV C2 A positive electrode characterized by a smaller

[0026] The positive electrode is a perlithiated positive electrode and is produced by a perlithiation method described below. In particular, the positive electrode is impregnated with an electrolyte containing a carbonate-based compound having a fluorine-containing functional group. This allows the carbonate-based compound having a fluorine-containing functional group to be deposited on the surface of the positive electrode and penetrate into the internal voids. By penetrating not only the surface but also the internal voids, a coating formed from the carbonate-based compound having a fluorine-containing functional group on the inside and outside of the positive electrode not only suppresses cracking of the positive electrode active material on the surface but also significantly contributes to suppressing deterioration of the entire positive electrode during cycle operation.

[0027] In addition, the lithium inserted by perlithiation migrates to the negative electrode during battery operation, reducing the available capacity of the negative electrode. This allows the perlithiation of lithium in the positive electrode to reduce the available capacity of the negative electrode without losing lithium in the positive electrode active material, thereby suppressing excessive volume change in the silicon-based active material and improving the battery's lifespan. This also allows the full capacity of the positive electrode active material to be utilized, thereby increasing battery efficiency and maximizing energy density.

[0028] Unlike conventional pre-lithiation processes in which a lithium metal layer is placed in contact with a negative electrode, a positive electrode according to one embodiment of the present invention is characterized in that a lithium metal layer is transferred to a positive electrode and rolled, and then the lithium ions inserted into the positive electrode are transferred to the negative electrode during the battery activation process. The electrolyte impregnation overcomes the problems of active material desorption that occurs during the process of transferring lithium to the positive electrode instead of the negative electrode, and reduced process efficiency due to prolonged overlithiation.

[0029] That is, because the anode and the lithium metal layer are not in contact and lithium ions are not inserted directly into the anode from the lithium metal layer, it is possible to avoid the phenomenon of excessive heat generation due to an alloy reaction between lithium and silicon in the anode, and the possibility of fire due to a reaction between lithium and moisture can be significantly reduced. Furthermore, because lithium ions are not inserted into the anode when the anode is notched and punched (because it is not in a pre-lithiation state), the possibility of fire during the notching and punching process can also be significantly reduced.

[0030] According to one embodiment of the present invention, the positive electrode has a peak P1s having a binding energy of 288 eV to 292 eV in a C1s spectrum obtained by XPS analysis. C1 Peak intensity I C1 However, the peak P with binding energy of 284 eV to 286 eV C2 Peak intensity I C2 Preferably, the I C2 / I C1 may be 1 or less, or may be 0.9 or less, 0.8 or less, or 0.7 or less.

[0031] In the C1s spectrum obtained by XPS analysis, peaks appear due to compounds with functional groups in which carbon is involved in bonding, and peaks can appear due to various factors such as carbonate by-products (-CO3) and fluorocarbons (CF2). C1 is caused by, for example, carbonate-based by-products. The positive electrode according to one embodiment of the present invention includes a fluorine-containing carbonate-based compound in the positive electrode active material layer. A stable solid electrolyte film (SEI) can be formed on the surface through a process of impregnating the electrolyte. The formation of this film prevents the formation of by-products, and therefore, the peak P C1 can appear relatively small. Also, the peak P C2 is a peak that appears due to a general C-C bond or C-H bond, and is usually due to electrode materials such as active materials and binders. C1 For example, if there are many by-products, the peak P C1 When is strongly expressed, peak P C2 may appear relatively weakly.

[0032] On the other hand, if the process of impregnation with the electrolyte, especially the process of impregnation with an electrolyte that does not contain a fluorine-containing carbonate compound, is not carried out, a stable coating film is not formed, and as a result, the peak P C1 This means that a relatively large amount of carbonate by-products may be formed. Therefore, the positive electrode according to one embodiment of the present invention has a peak P C1 is relatively small, and the peak P C2 Furthermore, the ratio of the two peaks I C2 / I C1 When the value of the perlithiation is within the above-mentioned range, it can be said that the effect of perlithiation using electrolyte impregnation is highly realized.

[0033] In addition, in the C1s spectrum, the peak P C3 That is, the peak P C1 and P C2 Peak P as a weak peak between C3 can be detected, and the peak P C3 is caused by, for example, a CO bond or a CCF bond, and can be said to be a result of the fluorine-containing carbonate compound being contained in the positive electrode active material layer.

[0034] In addition, according to one embodiment of the present invention, the positive electrode has a peak P at a binding energy of 687 eV to 689 eV in an F1s spectrum obtained by XPS analysis. F1 Peak intensity I F1 However, the peak P with binding energy of 684 eV to 686 eV F2 Peak intensity I F2 Preferably, in the F1s spectrum by XPS analysis, the ratio of the two peaks, I F2 / I F1 is 1 or less, and may be 0.8 or less, 0.7 or less, or 0.6 or less.

[0035] In the F1s spectrum obtained by XPS analysis, peaks appear due to compounds with functional groups in which fluorine is involved in bonding, such as compounds with bonds such as CF, PF, Li-F, and SF.

[0036] Specifically, the peak P F2 is formed by a bond between a metal and fluorine, for example, a bond such as Li-F. A positive electrode according to one embodiment of the present invention includes a fluorine-containing carbonate compound in the positive electrode active material layer, and a solid electrolyte interlayer (SEI) is formed on the surface through a process of impregnating the positive electrode with an electrolyte, and lithium reacts with the fluorine-containing functional group to produce Li-F, thereby increasing the durability of the interlayer.

[0037] Also, peak P F2 is a peak that appears due to a general CF, PF, or SF bond, and is usually due to electrode materials such as active materials and binders. F2 For example, if there is a lot of Li-F and the peak P F2 When is strongly expressed, peak P F1 This means that the peak P F1 Peak intensity I F1 is the peak P F2 Peak intensity I F2 It is preferable that the ratio of the two peaks is smaller than I F2 / I F1 When satisfies the above range, it can be understood that the overlithiation of the positive electrode according to one embodiment of the present invention is normally achieved.

[0038] In addition, the positive electrode has a peak P O1 Peak intensity I O1 may be 4.00 or less, preferably 3.90 or less, 3.80 or less, or 3.75 or less.

[0039] The O1s spectrum peak appears as a single peak and can be due to bonds such as C-O, C=O, or C03. The bonds usually appear due to by-products rather than electrode materials, and the peak P O1 Peak intensity I O1 The smaller the value, the less by-products there are. O1 may be 4.00 or less, and preferably may be in the above-mentioned range. When this range is satisfied, it means that the perlithiation according to one embodiment of the present invention is sufficiently carried out, thereby forming a stable solid electrolyte coating.

[0040] According to one embodiment of the present invention, the carbonate-based compound having a fluorine-containing functional group may include, for example, one or more selected from the group consisting of fluoroethylene carbonate, methyl 2,2,2-trifluoroethyl carbonate, and 2,2,2-trifluoroethyl carbonate, preferably fluoroethylene carbonate. When the carbonate-based compound having a fluorine-containing functional group is added to an electrolyte during perlithiation of the positive electrode, a stable solid electrolyte coating can be formed on the surface of the positive electrode, and the compound can remain in the positive electrode active material layer. Furthermore, the carbonate-based compound having a fluorine-containing functional group may be included in an amount of 10 wt% or less, preferably 8 wt% or less, based on the total weight of the positive electrode active material layer. This range can be confirmed from the XPS analysis results described above, and a portion of the compound reacts with lithium during the perlithiation process, while the remainder remains in the positive electrode active material layer.

[0041] According to one embodiment of the present invention, the positive electrode includes a positive electrode active material layer and a current collector on which the positive electrode active material layer is disposed. The current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. Examples of the current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel surfaces that have been surface-treated with carbon, nickel, titanium, silver, or the like. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and the surface of the current collector may be provided with fine irregularities to enhance the adhesive strength of the positive electrode active material. The current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0042] According to an embodiment of the present invention, the positive electrode active material layer may include a positive electrode active material, a positive electrode conductive material, and a positive electrode binder. The positive electrode active material is a material capable of undergoing an electrochemical reaction and may be a lithium transition metal oxide. For example, the positive electrode active material may be a layered compound such as lithium cobalt oxide or lithium nickel oxide substituted with one or more transition metals; lithium manganese oxide substituted with one or more transition metals; Li[Ni 1-y M 1 y ]O2 (where M 1 is at least one selected from Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn, and Ga, and 0.01≦y≦0.7; Li 1+z [Ni b Mn c Co 1-(b+c+d) M 2 d ]O (2-e) A e (where M 2 is at least one selected from the group consisting of Al, Mg, Cr, Ti, Si, and Y; A is at least one selected from the group consisting of F, P, and Cl; and −0.5≦z≦0.5, 0.1≦b≦0.8, 0.1≦c≦0.8, 0≦d≦0.2, 0≦e≦0.2, b+c+d<1; Li 1+x [M 3 1-q M 4 q ]PO 4-r X r (where M 3 is at least one selected from the group consisting of Fe, Mn, Co, and Ni, and M 4 is at least one selected from the group consisting of Al, Mg, and Ti, X is at least one selected from the group consisting of F, S, and N, and -0.5≦x≦0.5, 0≦q≦0.5, 0≦r≦0.1.

[0043] Specifically, the positive electrode active material may be composed of a lithium nickel-based oxide, a lithium nickel cobalt manganese composite oxide, an olivine-based lithium metal phosphate, or a combination thereof, and these may be combined to form one layer or separate layers to form a positive electrode active material layer.

[0044] According to an embodiment of the present invention, the positive electrode active material may include a compound represented by the following Formula 1, more specifically, the compound represented by the following Formula 1:

[0045] [Chemical formula 1] Li 1+x [Ni a Co b Mn c M 1 (1-a-b-c) ]O (2-d) A d

[0046] In the above Chemical Formula 1, M 1 may be at least one selected from the group consisting of Al, Mg, Cr, Ti, Si, and Y, and specifically may be Al.

[0047] A is at least one selected from the group consisting of F, P, and Cl, and specifically may be F.

[0048] The x may satisfy the range of -0.5≦x≦0.5, specifically, -0.3≦x≦0.3.

[0049] The a may satisfy 0.6≦a<1, specifically 0.7≦a≦0.9.

[0050] The b may satisfy 0.03≦b≦0.1, specifically 0.05≦b≦0.1.

[0051] The c may satisfy 0.03≦c≦0.1, specifically 0.05≦c≦0.1.

[0052] The d may satisfy 0 ≦ d ≦ 0.1, specifically 0 ≦ d ≦ 0.05.

[0053] The a, b, and c satisfy 0 < a + b + c ≦ 1, specifically a + b + c = 1.

[0054] The compound of Chemical Formula 1 may be in the form of particles.

[0055] The compound of Chemical Formula 1 may be in the form of secondary particles in which a plurality of primary particles are bonded to each other. Specifically, the compound of Chemical Formula 1 may be in the form of secondary particles in which 10 or more primary particles are bonded to each other. Thereby, there is an effect that lithium can be uniformly inserted into and desorbed from the inside of the positive electrode active material.

[0056] The D of the compound of Chemical Formula 1 50 may be 5 μm to 15 μm, specifically 7 μm to 12 μm, and more specifically 9 μm to 10 μm. The D 50 is the D of the secondary particles 50 and may be such. When the above range is satisfied, the dispersion of the positive electrode slurry is easy and a uniform coating of the positive electrode active material layer is possible.

[0057] The positive electrode active material may be contained in the positive electrode active material layer at 90% to 99% by weight, specifically 92% to 98% by weight, and more specifically 95% to 98% by weight.

[0058] According to one embodiment of the present invention, the positive electrode active material layer may further include a positive electrode binder. The positive electrode binder serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0059] The positive electrode binder may be included in the positive electrode active material layer in an amount of 0.5 wt % to 5.0 wt %, specifically 1.0 wt % to 2.5 wt %, and more specifically 1.0 wt % to 2.0 wt %.

[0060] According to one embodiment of the present invention, the positive electrode active material layer may further include a positive electrode conductive material. The positive electrode conductive material is used to impart conductivity to the electrode and may be any material that does not cause chemical changes in the resulting battery and has electronic conductivity. Specific examples of the positive electrode conductive material include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination.

[0061] The positive electrode conductive material may be contained in the positive electrode active material layer in an amount of 0.5 wt % to 30.0 wt %, specifically 0.5 wt % to 10.0 wt %, and more specifically 1.0 wt % to 4.0 wt %.

[0062] Positive electrode manufacturing method The method for manufacturing a positive electrode according to the present invention includes the steps of: (S1) disposing a transfer laminate including a substrate film and a lithium metal layer disposed on the substrate film on a preliminary positive electrode active material layer, and forming a positive electrode structure such that the lithium metal layer and the preliminary positive electrode active material layer are in contact with each other; and (S2) impregnating the positive electrode structure with an electrolyte including a carbonate-based compound having a fluorine-containing functional group.

[0063] The positive electrode as described above can be manufactured by the manufacturing method, and the manufactured positive electrode can have peak characteristics of the C1s spectrum, F1s spectrum, and O1s spectrum by the XPS analysis. The specific details are the same as those described above, so the description is omitted.

[0064] Furthermore, according to one embodiment of the present invention, the method for manufacturing a positive electrode may further include, between step S1 and step S2, a step (S1a) of rolling the positive electrode structure, and a step (S1b) of removing the rolled substrate film from the transfer laminate.

[0065] Steps S1, S1a, S1b, and S2 will be described in order below.

[0066] According to one embodiment of the present invention, in the method for manufacturing a positive electrode, step S1 is a step of placing a transfer laminate including a substrate film and a lithium metal layer on a preliminary positive electrode active material layer to form a positive electrode structure such that the lithium metal layer and the preliminary positive electrode active material layer are in contact with each other.

[0067] 1, the transfer laminate 300 may include a substrate film 310 and a lithium metal layer 320 disposed on the substrate film 310. The substrate film 310 may be made of any material that can withstand the high temperature conditions that occur during the deposition of the lithium metal layer 320 on the substrate film 310. Specifically, the substrate film may include at least one material selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0068] According to an embodiment of the present invention, the lithium metal layer may be located on the substrate film. The lithium metal layer may serve to supply lithium ions to the spare positive electrode active material layer. The lithium metal layer may include solid-phase lithium metal, and more specifically, the lithium metal layer may be composed of solid-phase lithium metal.

[0069] According to one embodiment of the present invention, in the transfer laminate, the lithium metal layer may have a thickness of 1.0 μm to 10.0 μm, specifically 2.0 μm to 9.0 μm, and preferably 2.5 μm or more, 3.0 μm or more, 3.5 μm or more, or 4.0 μm or more, and 8.5 μm or less, 8.0 μm or less, 7.5 μm or less, or 7.0 μm or less. When the above range is satisfied, the degree of cracking of the positive electrode active material particles on the surface of the positive electrode can be reduced, thereby suppressing a decrease in the initial capacity of the battery.

[0070] According to one embodiment of the present invention, the loading amount (unit: mAh / cm) of the lithium metal layer is 2 ) is the loading amount (unit: mAh / cm 2) may be 4% to 40%, specifically 12% to 35%, more specifically 20% to 30%. When the above range is satisfied, little by-product is produced, lithium is easily inserted into the positive electrode active material, and the target lithium insertion capacity can be easily achieved.

[0071] In step S1 according to an embodiment of the present invention, referring to FIG. 1 , the preliminary positive electrode active material layer 120′ is positioned on the preliminary positive electrode current collector 110, and the transfer laminate 300 is disposed on the preliminary positive electrode active material layer 120′, so that the lithium metal layer 320 and the preliminary positive electrode active material layer are in contact with each other to form a positive electrode structure 400.

[0072] According to one embodiment of the present invention, the preliminary positive electrode active material layer in step S1 refers to a positive electrode active material layer before being perlithiated. The preliminary positive electrode active material layer may be located on a positive electrode current collector, and the positive electrode active material layer may be located on one or both sides of the positive electrode current collector.

[0073] According to an embodiment of the present invention, the transfer laminate 300 may further include a polymer layer 330. Referring to FIG. 2, the polymer layer 330 may be located between the substrate film 310 and the lithium metal layer 320. The polymer layer may facilitate the effective peeling of the lithium metal layer from the transfer laminate and the easy transfer of the lithium metal layer to the positive electrode active material layer during the manufacture of the positive electrode. That is, the polymer layer is separated from the transfer laminate together with the lithium metal layer and positioned on the positive electrode active material layer. The polymer layer may be in contact with the positive electrode active material layer, or alternatively, a lithium metal layer may be located between the polymer layer and the positive electrode active material layer.

[0074] The polymer layer may be at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate. As a result, in a secondary battery including the positive electrode, the polymer layer can be dissolved in an electrolyte contained in the secondary battery, thereby preventing an increase in battery resistance. In particular, the polymer layer may include PMMA, in which case the above-mentioned effects can be further improved.

[0075] The thickness of the polymer layer may be 0.1 μm to 10 μm, specifically 0.5 μm to 5 μm, more specifically 1 μm to 2.5 μm. When the thickness satisfies the above range, the lithium metal layer can be easily transferred to the positive electrode active material layer, and reverse transfer, in which the positive electrode active material layer is transferred to the transfer laminate, can be prevented.

[0076] According to one embodiment of the present invention, the step S1a in the method for manufacturing the positive electrode is a step of rolling the positive electrode structure.

[0077] Referring to FIG. 3 , in step S1a, the fabricated cathode structure 400 may be rolled. The rolling may be performed using a roll press. Specifically, two rolls R spaced apart by a predetermined vertical distance may apply pressure from above and below the cathode structure 400 passing through the space, and the pressure may be linear pressure. The rolling process may cause at least a portion of the lithium ions in the lithium metal layer contained in the transfer laminate to be intercalated into the preliminary cathode active material layer. During this process, the preliminary cathode active material layer may become a cathode active material layer. While FIGS. 3 and 4 show the lithium metal layer as being included in the cathode, if the entire lithium metal layer is intercalated into the preliminary cathode active material layer during the rolling process, the lithium metal layer may not necessarily be present as a separate layer.

[0078] During the rolling, the pressure applied to the cathode structure may be 10 kgf / cm to 90 kgf / cm, specifically 15 kgf / cm to 80 kgf / cm, and preferably 20 kgf / cm or more, 25 kgf / cm or more, or 30 kgf / cm or more, and may be 70 kgf / cm or less, or 60 kgf / cm or less.

[0079] When the rolling pressure is applied within the above range, the lithium metal layer can be effectively transferred, lithium can be inserted into the positive electrode at a desired level, and the positive electrode active material particles can be controlled to avoid detachment and cracking, thereby achieving the effects of improving both the lifespan and capacity characteristics.

[0080] According to one embodiment of the present invention, in the method for producing a positive electrode, step S1b is a step of removing the rolled substrate film from the transfer laminate to produce a positive electrode.

[0081] 4, in step S1b, the substrate film 310 after the rolling performed in step S1a is removed from the transfer laminate to manufacture the cathode 100. When the polymer layer 330 is positioned between the substrate film 310 and the lithium metal layer 320, the polymer layer 330 may make it easier to remove the substrate film 310.

[0082] According to one embodiment of the present invention, the method for manufacturing a positive electrode may further include step S1b' of resting (leaving) the preliminary positive electrode for 1 minute to 600 minutes, specifically 1 minute to 30 minutes. Step S1b' may be performed after step S1a. Specifically, step S1b' may be performed in at least one of "between step S1a and step S1b" and "immediately after step S1b." Step S1b' effectively releases reaction heat generated by the reaction between the lithium metal layer and the preliminary positive electrode active material layer in step S1a, thereby allowing lithium to be uniformly inserted into the positive electrode and reducing the generation of by-products.

[0083] According to one embodiment of the present invention, step S2 is a step of immersing the prepared cathode structure in an electrolyte containing a carbonate-based solvent. When lithium is transferred into the cathode by immersing the cathode structure in the electrolyte, the time required for overlithiation can be significantly shortened and cracking and detachment of active material particles can be suppressed, thereby significantly contributing to improved lifespan.

[0084] On the other hand, when prelithiation of the negative electrode is performed, regardless of the method used, there are problems in that it is difficult to prevent excessive heat generation that occurs when the negative electrode comes into contact with the lithium metal layer and ignition that occurs when the negative electrode is notched or punched. Furthermore, when prelithiation of the negative electrode is performed, the active material does not desorption and the time required for lithium transfer is not long, so the advantages of prelithiation using an electrolyte impregnation process are not realized.

[0085] However, when perlithiation (prelithiation) of a positive electrode is performed, the time required for lithium transfer is too long, resulting in very poor process efficiency. In addition, due to the desorption of active material that occurs during the transfer, perlithiation of a positive electrode is accompanied by many process difficulties. In light of these points, the present inventors have attempted to provide a method for perlithiation of a positive electrode that employs an electrolyte impregnation process.

[0086] A method for manufacturing a positive electrode according to an embodiment of the present invention can solve problems that occur during overlithiation of a positive electrode by impregnating a positive electrode structure with an electrolyte, particularly an electrolyte containing a carbonate-based compound having a fluorine-containing functional group.

[0087] When the electrolyte impregnation process is applied, the overlithiation time can be dramatically shortened, and the detachment and cracking of active material particles can be significantly alleviated, thereby improving the life of the lithium secondary battery.

[0088] Generally, examples of carbonate-based solvents that can be used include propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, and diethyl carbonate. When only a carbonate-based solvent is used as the electrolyte solvent, a white film may form on the surface of the positive electrode after perlithiation, which may result in increased resistance. Therefore, the use of a carbonate-based compound containing a fluorine-containing functional group can eliminate the cause of the increased resistance. Therefore, from the perspective of improving output, it is preferable to use a carbonate-based compound containing a fluorine-containing functional group. Since a carbonate-based compound containing a fluorine-containing functional group can also be expected to suppress deterioration of the positive electrode and negative electrode, it is preferable to use both of them.

[0089] The carbonate-based compound containing a fluorine-containing functional group may include one or more selected from the group consisting of fluoroethylene carbonate, methyl 2,2,2-trifluoroethyl carbonate, and 2,2,2-trifluoroethyl carbonate. The carbonate-based compound containing a fluorine-containing functional group may be included in an amount of 5 wt% to 40 wt% of the total weight of the electrolyte, preferably 8 wt% or more, or 10 wt% or more, or 35 wt% or less, or 30 wt% or less.

[0090] According to an embodiment of the present invention, the electrolyte may further include a lithium salt. The lithium salt is a material that is easily dissolved in the non-aqueous electrolyte. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0091] The lithium salt preferably has a concentration in the electrolyte of more than 0.1 M and not more than 1.0 M. When the lithium salt concentration is in this range, the effects of overlithiation by electrolyte impregnation can be realized, and the phenomenon of active material detachment and poor lithium transfer can be minimized or prevented. The concentration of the lithium salt may be preferably 0.2 M or more, 0.23 M or more, 0.25 M or more, or 0.3 M or more, and may be 0.95 M or less, 0.9 M or less, or 0.85 M or less.

[0092] According to an embodiment of the present invention, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, a cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, a nitrobenzene derivative, sulfur, a quinoneimine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in addition to the constituent components of the electrolyte.

[0093] The method for manufacturing a positive electrode according to an embodiment of the present invention may further include, after step S2, step S3 of washing and drying the positive electrode structure. After perlithiation of the positive electrode structure by impregnating it with an electrolyte is completed, the positive electrode structure may be washed and dried, and then assembled with a separator and a negative electrode to form an electrode assembly. An electrolyte may be injected into the electrode assembly to manufacture a lithium secondary battery. The washing and drying may be performed under conditions and by methods commonly used in this technical field.

[0094] Lithium secondary battery According to one embodiment of the present invention, there is provided a lithium secondary battery including a positive electrode manufactured by the above manufacturing method, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0095] The method for producing the positive electrode and the positive electrode have been described above, and therefore further description thereof will be omitted.

[0096] In addition, a lithium secondary battery according to another embodiment of the present invention includes an electrode assembly including a positive electrode having a perlithiated positive electrode active material layer, a negative electrode having silicon (Si) particles as an active material, and a separator interposed between the positive electrode and the negative electrode; a battery case that houses the electrode assembly; and an electrolyte that is injected into the battery case so that the electrode assembly is impregnated, and that includes a carbonate-based compound having a fluorine-containing functional group. When the lithium content relative to the total weight of the positive electrode active material layer of the perlithiated positive electrode, as measured by inductively coupled plasma spectroscopy (ICP-OES), is less than 5.0 wt%, the content of the carbonate-based compound having a fluorine-containing functional group relative to the total weight of the electrode assembly and the electrolyte, as measured by inductively coupled plasma spectroscopy (ICP-OES), is 3.5 wt% or more.

[0097] Here, the lithium content in the perlithiated positive electrode active material layer and the content of the carbonate-based compound having a fluorine-containing functional group in the electrode assembly and the electrolyte may be measured by inductively coupled plasma spectroscopy (ICP-OES).

[0098] The perlithiated positive electrode is a positive electrode that has been perlithiated by a process of impregnating the positive electrode with an electrolyte containing a carbonate-based compound having a fluorine-containing functional group, as described above, and the negative electrode is characterized in that an active material layer using silicon particles as an active material is formed, and the electrolyte contains the carbonate-based compound having a fluorine-containing functional group used during the perlithiation. By simultaneously applying these features, a lithium secondary battery can be provided in which, when the lithium content relative to the total weight of the positive electrode active material layer in the perlithiated positive electrode is less than 5.0 wt %, the carbonate-based compound having a fluorine-containing functional group in the electrolyte is 3.5 wt % or more relative to the total weight of the electrolyte.

[0099] The lithium content of less than 5.0 wt % means that repeated cycling has been going on for a long period of time, and may indicate that the lithium secondary battery has deteriorated to some extent. According to one embodiment of the present invention, even after the lithium secondary battery has deteriorated considerably, the content of the carbonate-based compound having a fluorine-containing functional group in the electrolyte is 3.5 wt % or more based on the total weight of the electrolyte.

[0100] The carbonate-based compound containing a fluorine-containing functional group may be included in the electrolyte as an additive or solvent, but most of it is lost due to side reactions during cycling, and the remaining amount may become very small after significant degradation. That is, if cycling is continued until the lithium content in the positive electrode drops below 5.0 wt %, the content may become very small. However, when a positive electrode according to one embodiment of the present invention, i.e., a perlithiated positive electrode, is used, a stable coating is formed on the surface of the positive electrode, so the amount lost due to side reactions on the surface of the positive electrode and the amount consumed for coating formation are minimal. Therefore, the compound can remain in the electrolyte for a long period of time, preventing a sudden drop in capacity.

[0101] For example, the content of the carbonate-based compound having a fluorine-containing functional group may be 3.5 wt % or more, preferably 4.0 wt % or more, 4.5 wt % or more, 5.0 wt % or more, 5.3 wt % or more, or 5.5 wt % or more, based on the total weight of the electrode assembly and the electrolyte, and may be 15.0 wt % or less, 10.0 wt % or less, or 9.0 wt % or less.

[0102] As mentioned above, the carbonate-based compound having a fluorine-containing functional group is generally used in the electrolyte in a range of about 5 wt% to 40 wt%, and the 40 wt% is the maximum content that can be contained. In other words, even if the carbonate-based compound having a fluorine-containing functional group is contained in the maximum content, it continues to be consumed during cycle operation, and after a certain point when the remaining amount is almost gone, a sudden drop in capacity may occur.

[0103] However, in a lithium secondary battery according to one embodiment of the present invention, a perlithiated positive electrode, for example, a positive electrode perlithiated using a carbonate-based compound containing a fluorine-containing functional group, is used. This allows the carbonate-based compound containing a fluorine-containing functional group to form an SEI coating on the surface and internal voids of the positive electrode in advance, allowing the compound to remain, thereby minimizing the consumption of the carbonate-based compound containing a fluorine-containing functional group from the electrolyte. This can suppress deterioration of both the positive electrode and the negative electrode, thereby preventing problems such as a sudden drop in capacity and a sudden increase in resistance.

[0104] The above range can be achieved by applying the above-mentioned combination. In this case, even if the SEI coating of the already formed positive electrode is lost, it can be compensated for by the remaining carbonate-based compound having a fluorine-containing functional group, and the effect of maintaining the life for a long period of time can be expected.

[0105] In addition, a lithium secondary battery according to another embodiment of the present invention includes an electrode assembly including a perlithiated positive electrode having a perlithiated positive electrode active material layer, an anode including silicon (Si) particles as an active material, and a separator interposed between the positive electrode and the anode; a battery case that houses the electrode assembly; and an electrolyte that is injected into the battery case so that the electrode assembly is impregnated, and that includes a carbonate-based compound having a fluorine-containing functional group. When the content of the carbonate-based compound having a fluorine-containing functional group relative to the total weight of the electrode assembly and the electrolyte, as measured by inductively coupled plasma spectroscopy (ICP-OES), is 8.0 wt% or less, the lithium content relative to the total weight of the positive electrode active material layer in the perlithiated positive electrode, as measured by inductively coupled plasma spectroscopy (ICP-OES), is 3.0 wt% or more.

[0106] Preferably, the lithium content may be 3.5 wt% or more, 4.0 wt% or more, 4.5 wt% or more, or 5.0 wt% or more.

[0107] That is, in the lithium secondary battery according to one embodiment of the present invention, even after long-term cycle driving, a large amount of lithium remains in the positive electrode, and a large amount of a carbonate compound containing a fluorine-containing functional group also remains in the electrolyte. Lithium moving between the positive electrode and the negative electrode can be abundantly present over a long period, and a carbonate compound containing a fluorine-containing functional group that prevents side reactions and deterioration is also abundant. Therefore, the lithium secondary battery is excellent in capacity retention rate and resistance increase rate, and a remarkable effect of increasing the life can be obtained.

[0108] On the other hand, the negative electrode includes a negative electrode active material layer, and the negative electrode active material layer may include a negative electrode active material. As the negative electrode active material, a silicon-based negative electrode active material, a carbon-based negative electrode active material, or a combination thereof can be applied.

[0109] The negative electrode active material may include a silicon-based negative electrode active material. The silicon-based negative electrode active material may include at least one of Si and SiO x (0 < x < 2).

[0110] The Si is silicon particles, and may be silicon particles (particles made of silicon) called so-called pure silicon (Pure Silicon). The silicon particles can effectively improve the capacity of the negative electrode. The SiO x (0 < x < 2) may be a form containing Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon-based composite particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0111] According to one embodiment of the present invention, the silicon-based negative electrode active material, particularly silicon particles (Si), has the problem of undergoing drastic volumetric changes during battery operation and resulting in very poor lifespan characteristics. However, when combined with the positive electrode of the present invention, during activation, excess lithium ions, rather than the lithium in the positive electrode active material that determines capacity, migrate from the overlithiated positive electrode to the silicon (Si) negative electrode active material and react with the silicon particles (Si) in advance to form an irreversible phase, reducing the available area. As a result, the volumetric changes during battery operation are no longer drastic, significantly improving lifespan and allowing the high capacity characteristics inherent to silicon particles to be fully exhibited.

[0112] According to an embodiment of the present invention, the negative electrode active material may further include a carbon-based negative electrode active material, which may include at least one selected from the group consisting of artificial graphite, natural graphite, and graphitized mesocarbon microbeads.

[0113] According to an embodiment of the present invention, the negative electrode active material layer may further include a negative electrode binder. The negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen atoms in these materials are substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0114] According to an embodiment of the present invention, the negative electrode active material layer may further include a negative electrode conductive material. The negative electrode conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0115] According to one embodiment of the present invention, the lithium secondary battery includes a separator. The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator commonly used in secondary batteries can be used without particular limitations. In particular, a separator with low resistance to electrolyte ion movement and excellent electrolyte moisture absorption is preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material can also be used, and it can be selectively used in a single-layer or multi-layer structure.

[0116] According to an embodiment of the present invention, the lithium secondary battery may further include an electrolyte. In this case, the electrolyte may be the same as or different from the electrolyte used in the overlithiation, and may be used independently. Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0117] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt. The non-aqueous organic solvent may include a carbonate-based compound containing a fluorine-containing functional group, and may further include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0118] In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferred because they are high-viscosity organic solvents with high dielectric constants and can easily dissociate lithium salts. Mixing such cyclic carbonates with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio can provide an electrolyte with high electrical conductivity, and is therefore preferred.

[0119] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0120] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0121] As described above, the secondary battery including the positive electrode according to the present invention stably exhibits excellent capacity and capacity retention rate, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0122] Therefore, according to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same.

[0123] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0124] Example Below, preferred embodiments are presented to help understand the present invention. However, these embodiments are merely for illustrative purposes, and it will be apparent to those skilled in the art that various modifications and alterations are possible within the scope of the scope and technical ideas of the present description. It goes without saying that such modifications and alterations fall within the scope of the appended claims.

[0125] Electrode manufacturing Example 1-1: Preparation of positive electrode A PET film (base film), a polymer layer (thickness 2.5 μm) made of PMMA disposed on the PET film, and a lithium metal layer (thickness 6.0 μm, loading amount 0.62 mAh / cm) made of solid-phase lithium metal disposed on the polymer layer. 2 ) and a transfer laminate including the same was prepared.

[0126] On the other hand, Li[Ni 0.86 Co 0.05Mn 0.08 Al 0.01 ]O2 was used. The positive electrode active material was Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 ]O2 are bonded to each other to form secondary particles, and the average particle diameter of the secondary particles is D 50 The loading capacity of the preliminary positive electrode active material layer was 9 μm. The loading capacity of the preliminary positive electrode active material layer was 4.5 mAh / cm. The loading capacity of the preliminary positive electrode active material layer was 4.5 mAh / cm. The loading capacity of the preliminary positive electrode active material layer was 4.5 mAh / cm. The loading capacity of the preliminary positive electrode active material layer was 4.5 mAh / cm. The loading capacity of the preliminary positive electrode active material layer was 9 μm ... 2 and the thickness was 140 μm.

[0127] The transfer laminate was placed on the preliminary positive electrode active material layer so that the lithium metal layer and the preliminary positive electrode active material layer were in contact with each other.

[0128] The positive electrode with the transfer laminate disposed thereon was then rolled under a pressure of 50 kgf / cm using a roll press, and the positive electrode structure was then impregnated with a 0.2 M electrolyte (solvent: fluoroethylene carbonate (FEC) and diethylene carbonate (DEC) in a weight ratio of 3:7, lithium salts: LiPF6 and LiFSI, additives: vinylene carbonate (VC), propylene carbonate (PC), and 1,3-propene sultone (PRS)). This resulted in the lithium ions of the lithium metal layer being inserted into the preliminary positive electrode active material layer, forming a positive electrode active material layer. The substrate film was then removed and left for 10 minutes to produce a positive electrode comprising a positive electrode current collector, a positive electrode active material layer, and a polymer layer.

[0129] Example 1-2: Preparation of positive electrode A positive electrode was produced in the same manner as in Example 1-1, except that the concentration of the electrolyte impregnated into the positive electrode structure was set to 0.3M.

[0130] Example 1-3: Preparation of positive electrode A positive electrode was produced in the same manner as in Example 1-1, except that the concentration of the electrolyte impregnated into the positive electrode structure was set to 0.5M.

[0131] Example 1-4: Preparation of positive electrode A positive electrode was produced in the same manner as in Example 1-1, except that the concentration of the electrolyte impregnated into the positive electrode structure was set to 0.7M.

[0132] Example 1-5: Preparation of positive electrode A positive electrode was produced in the same manner as in Example 1-1, except that the concentration of the electrolyte impregnated into the positive electrode structure was 1.0M.

[0133] Examples 1-6: Preparation of positive electrode A positive electrode was produced in the same manner as in Example 1-5, except that the thickness of the lithium metal layer was 3 μm.

[0134] Comparative Example 1-1: Production of Positive Electrode A positive electrode was produced in the same manner as in Example 1-1, except that after rolling, the positive electrode was left to stand for 24 hours without being impregnated with an electrolyte.

[0135] Comparative Example 1-2: Production of Positive Electrode A positive electrode was produced in the same manner as in Example 1-6, except that after rolling, the positive electrode was left to stand for 24 hours without being impregnated with an electrolyte.

[0136] Comparative Example 1-3: Production of negative electrode The battery consisted of a PET film (base film), a polymer layer (thickness 1 μm) made of PMMA and disposed on the PET film, and a lithium metal layer (thickness 3 μm, loading 0.6 mAh / cm) made of solid-phase lithium metal and disposed on the polymer layer. 2 ) and a transfer laminate including the same was prepared.

[0137] On the other hand, as the negative electrode active material, the average particle size D 50Silicon particles with a particle size of 5 μm were used. A negative electrode was prepared including a preliminary negative electrode active material layer containing the above negative electrode active material, carboxymethyl cellulose (CMC) as a negative electrode binder, and carbon nanotubes as a negative electrode conductive material in a weight ratio of 80:10:10. The loading capacity of the preliminary negative electrode active material layer was 10 mAh / cm. 2 and the thickness was 75 μm.

[0138] The transfer laminate was placed on the preliminary negative electrode active material layer so that the lithium metal layer and the preliminary negative electrode active material layer were in contact with each other.

[0139] Thereafter, electrolyte impregnation, washing, and drying were carried out in the same manner as in Example 1-1 to prepare a negative electrode.

[0140] Comparative Example 1-4: Production of Positive Electrode A positive electrode was produced in the same manner as in Example 1-5, except that the solvent of the electrolyte in which the positive electrode structure was impregnated was replaced with ethylene carbonate and ethyl methyl carbonate, and the lithium salt was changed from LiFSI to LiPF6.

[0141] Experimental Example 1: Perlithiation reaction and evaluation of positive electrode properties Cross sections of the positive electrodes of Examples 1-5 and Comparative Examples 1-2 were photographed (magnification: 500 times) with a scanning electron microscope (SEM, JEOL, JSM-7200F), and the images are shown in FIGS.

[0142] Looking at the cross section of the positive electrode of Example 1-5 in Figure 5, it can be seen that there are almost no cracks in the active material particles. However, looking at Figure 6, which is an image of the cross section of the positive electrode of Comparative Example 1-2, it can be seen that a large number of cracks are observed in the active material particles near the surface.

[0143] In addition, in Comparative Example 1-1, the lithium metal layer had a thickness of 6 μm, which was thicker than that of Comparative Example 1-2, but a phenomenon in which part of the lithium metal layer was detached from the electrode during the overlithiation reaction was observed in some cases.

[0144] For the perlithiation reactions of Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-3, the peak reaction temperature, the time to reach the peak temperature, and the total perlithiation reaction time were measured and are shown in Table 1 below.

[0145] [Table 1]

[0146] Referring to Table 1, it can be seen that in Examples 1-1 to 1-6, in which perlithiation was performed by electrolyte impregnation, the time required for perlithiation was significantly shorter than in cases in which electrolyte impregnation was not performed. Furthermore, when prelithiation was performed on the negative electrode by electrolyte impregnation as in Comparative Example 1-3, the temperature rose to 60°C in 10 seconds and the reaction could not proceed any further. In other words, it can be seen that the reaction occurred explosively at the negative electrode, making it impossible to apply prelithiation by this method.

[0147] Secondary battery manufacturing Example 2-1: Manufacturing of secondary battery As the negative electrode active material, the average particle size D 50 Silicon (Si) particles with a particle size of 5 μm were used. A negative electrode was prepared including a preliminary negative electrode active material layer containing the above negative electrode active material, CMC as a negative electrode binder, and carbon nanotubes as a negative electrode conductive material in a weight ratio of 80:10:10. The loading capacity of the preliminary negative electrode active material layer was 10 mAh / cm. 2 and the thickness was 75 μm.

[0148] The positive electrode of Example 1-1, the negative electrode, and a porous polyethylene separator were assembled by a winding method, and an electrolyte (solvent: fluoroethylene carbonate (FEC) and diethylene carbonate (DEC) in a weight ratio of 3:7, lithium salts: LiPF6 and LiFSI, additives: vinylene carbonate (VC), propylene carbonate (PC), and 1,3-propene sultone (PRS)) was injected into the assembled battery to prepare a spare lithium ion secondary battery.

[0149] The spare lithium ion secondary battery was charged to 4.2 V at a C-rate of 0.1 C, and then discharged to 2.5 V to perform an activation process.

[0150] Examples 2-2 to 2-6: Production of secondary batteries Lithium secondary batteries of Examples 2-2 to 2-6 were produced in the same manner as in Example 2-1, except that the positive electrodes of Examples 1-2 to 1-6 were used instead of the positive electrode of Example 1-1.

[0151] Comparative Examples 2-1, 2-2, and 2-4: Production of Secondary Batteries Lithium secondary batteries of Comparative Examples 2-1, 2-2, and 2-4 were produced in the same manner as in Example 2-1, except that the positive electrodes of Comparative Examples 1-1, 1-2, and 1-4 were used instead of the positive electrode of Example 1-1.

[0152] Experimental example 2: Evaluation of resistance characteristics The resistance of each of the lithium secondary batteries of Example 2-5, Comparative Example 2-1, and Comparative Example 2-4 was measured by the following method.

[0153] The lithium secondary battery was charged and discharged, and then fully charged and discharged. A 2.5C pulse current was applied for a specific time depending on the change in SOC, and the surface resistance (0.1 second resistance), charge transfer resistance (0.1-30 second resistance), and diffusion resistance (30 second resistance) were measured. The results are shown in Table 2 and Figures 7 to 9.

[0154] [Table 2]

[0155] 7 to 9, it can be seen that the coating formed on the surface by the electrolyte impregnation acts as a resistor, resulting in a slight increase in resistance in Example 2-5 compared to Comparative Examples 2-1 and 2-4. However, it can be seen that the degree of increase in resistance is very small compared to the time required for perlithiation, and Example 2-5, which used a fluorine-based electrolyte, was at a level almost equivalent to that of the case without electrolyte impregnation, so it can be predicted that there is substantially no performance degradation due to the increase in resistance.

[0156] Experimental Example 3: Analysis of the cathode and electrolyte after cycling The lithium secondary batteries of Examples 2-1 to 2-6 and Comparative Examples 2-1, 2-2, and 2-4 were charged and discharged at 0.1 C in the first and second cycles, and at 0.5 C from the third cycle onwards, for a total of 550 cycles. Thereafter, the lithium secondary batteries were disassembled, and surface XPS analysis and lithium content analysis of the positive electrodes, as well as component analysis of the electrolytes, were performed by the following methods.

[0157] 1) Surface XPS analysis of positive electrode: Using an X-ray photoelectron spectroscopy (XPS) (Nexsa ESCA System, Thermo Fisher Scientific (ESCA-02)), a C1s spectrum, an O1s spectrum, and an F1s spectrum were obtained under the following conditions: Al-Kα light source (1486.6 eV), accelerating voltage 1 kV / 300 W, energy resolution approximately 1.0 eV, minimum analysis area 400 microns, and sputter rate 0.13 nm / min, and the respective peak intensity values ​​are listed in Table 3 below. Here, the peak intensity values ​​are unitless values ​​derived from the measuring instrument and indicate the relative intensity of the peaks due to binding energy.

[0158] 2) Analysis of Lithium Amount (wt%) in Positive Electrode: After cycling the lithium secondary batteries of Examples 2-1 to 2-6 and Comparative Examples 2-1, 2-2, and 2-4, the batteries were disassembled, and the positive electrodes, excluding the current collectors, were powdered. 0.02 g of the positive electrode powder was added to a mixed solution of 3.0 mL of hydrochloric acid and 0.5 mL of hydrogen peroxide and heated until completely dissolved. Then, 500 μL of 1,000 mg / kg internal standard deviation (Sc) was added and diluted to 50 mL with ultrapure water to prepare a measurement sample. The measurement sample was analyzed for the proportion of wavelengths corresponding to the lithium element using inductively coupled plasma spectroscopy (ICP-OES, Perkin Elmer).

[0159] 3) Analysis of electrolyte composition (wt%): After cycling the lithium secondary batteries of Examples 2-1 to 2-6 and Comparative Examples 2-1 and 2-2, the batteries were disassembled and placed in a mixed solution of hydrochloric acid and hydrogen peroxide to thoroughly dissolve any residual compounds deposited on the electrode assembly and battery case. 3.5 mL of the solution was then sampled, 500 μL of 1,000 mg / kg internal standard deviation (Internal Standard Discharge) (Sc) was added, and the solution was diluted to 50 mL with ultrapure water to prepare a measurement sample. Subsequently, inductively coupled plasma spectroscopy (ICP-OES, Perkin Elmer) was used to analyze the compound content.

[0160] [Table 3]

[0161] 11 to 13, it can be seen that the differences between the Examples and the Comparative Examples can be clearly distinguished from the results of the C1s spectrum and the F1s spectrum. C2 is smaller than the comparative example, and I C2 I C1The smaller value indicates that the application of electrolyte impregnation using a fluorine-containing carbonate-based compound during the perlithiation of the positive electrode can actually reduce carbonate-based by-products on the surface of the positive electrode. The difference can be seen in FIG. 11, which shows the XPS results for Example 2-5 and Comparative Example 2-1.

[0162] Also, I O1 The values ​​of σ in the Examples are also smaller than those in the Comparative Examples, which ultimately confirms that less carbonate by-products are formed. This difference can also be confirmed from Figure 13, which shows the representative XPS results for Example 2-5 and Comparative Example 2-1.

[0163] Furthermore, I F2 and I F1 Also, I F2 I F1 Smaller, I F2 The fact that the values ​​for the Examples were smaller than those for the Comparative Examples indicates that when perlithiation is performed in an electrolyte containing a fluorine-containing carbonate compound, a LiF-containing coating is well formed on the surface of the positive electrode, and the electrolyte impregnation actually prevents the generation of other by-products. This can also be confirmed from Figure 12, which shows representative XPS results for Example 2-5 and Comparative Example 2-1. As can be seen, during perlithiation of the positive electrode, the lithium remaining on the surface reacts with the fluorine-containing carbonate compound to produce LiF. However, in Comparative Example 2-2, because the amount of lithium used in perlithiation was small, it completely penetrated into the positive electrode from the time the electrode assembly was assembled until it was impregnated with the electrolyte, and no lithium remained on the surface, so LiF was not detected.

[0164] Experimental Example 4: Evaluation of capacity retention rate and resistance increase rate Charge and discharge were carried out on the lithium secondary batteries of Examples 2-1 to 2-6 and Comparative Examples 2-1, 2-2, and 2-4, as well as the lithium secondary battery of Reference Example, which was produced in the same manner as in Example 2-5 except that overlithiation (lithium transfer and electrolyte impregnation) was not performed. The capacity and resistance of the secondary batteries were measured for each cycle by the following method, and the capacity retention rate and resistance increase rate were calculated as follows. The results are shown in Table 3 below and FIG. 10.

[0165] *Capacity retention rate and resistance increase rate: The first and second cycles were charged and discharged at 0.1C, and from the third cycle onwards, the rate was 0.5C. Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) 4.2V Discharge condition: CC (constant current) condition 3.27V Capacity retention rate (%) = (Nth discharge capacity / initial discharge capacity) x 100 Resistance increase rate (%) = [(Nth discharge resistance / initial discharge resistance) - 1] x 100

[0166] [Table 4]

[0167] 10, it can be seen that in the Reference Example using a positive electrode that was not perlithiated, the capacity began to decrease rapidly after 200 cycles, whereas in Examples 2-1 to 2-6 and Comparative Example 2-1, which were perlithiated, the capacity was maintained at a constant level even after subsequent cycles. Furthermore, when perlithiation was performed using a transfer laminate, as in Comparative Example 2-1, the capacity retention rate was superior to that of Example 2-6 up to approximately 300 cycles, but the capacity decreased rapidly after 500 cycles. However, it can be seen that in Examples 2-1 to 2-6, which were perlithiated by impregnation with an electrolyte containing a fluorine-containing carbonate compound, the capacity retention rate continued to be maintained at an excellent level even after 500 cycles.

[0168] Furthermore, referring to Table 3, it can be seen that there is a clear difference in the resistance increase rate between the secondary batteries of the example and the comparative example. It can be seen that the difference in resistance increase begins to be seen from the relatively early stage of the cycle, 200 cycles, and after 600 cycles, the resistance increase accelerates by more than two times. This difference can be understood as being due to the suppression of degradation in the secondary batteries of the example. [Explanation of symbols]

[0169] 110 Positive electrode current collector 120, 120' spare positive electrode active material layer 300 Transfer laminate 310 Base film 320 Lithium metal layer 330 Polymer layer 400 Positive electrode structure R Roll R.Ex. Reference example Example: Example C.Ex. Comparative example

Claims

1. a positive electrode active material layer including a positive electrode active material and a carbonate-based compound including a fluorine-containing functional group; and a current collector on which the positive electrode active material layer is disposed; In the C1s spectrum obtained by XPS analysis, the peak P Ｃ１ Peak intensity I Ｃ１ However, the peak P Ｃ２ Peak intensity I Ｃ２ smaller than the positive pole.

2. In the C1s spectrum by XPS analysis, Ｃ２ / I Ｃ１ The positive electrode according to claim 1 , wherein

3. In the F1s spectrum obtained by XPS analysis, a peak P Ｆ１ Peak intensity I Ｆ１ However, the peak P Ｆ２ Peak intensity I Ｆ２ The positive electrode of claim 1 , wherein

4. In the F1s spectrum by XPS analysis, Ｆ２ / I Ｆ１ The positive electrode according to claim 3 , wherein R is 1 or less.

5. In the O1s spectrum obtained by XPS analysis, the peak P Ｏ１ Peak intensity I Ｏ１ 2. The positive electrode according to claim 1, wherein the σ is 4.00 or less.

6. 2. The positive electrode according to claim 1, wherein the carbonate-based compound having a fluorine-containing functional group includes one or more compounds selected from the group consisting of fluoroethylene carbonate, methyl 2,2,2-trifluoroethyl carbonate, and 2,2,2-trifluoroethyl carbonate.

7. a step (S1) of forming a positive electrode structure by disposing a transfer laminate including a substrate film and a lithium metal layer disposed on the substrate film on a preliminary positive electrode active material layer so that the lithium metal layer and the preliminary positive electrode active material layer are in contact with each other; and (S2) impregnating the cathode structure with an electrolyte containing a carbonate-based compound having a fluorine-containing functional group.

8. 8. The method for producing a positive electrode according to claim 7, wherein the electrolyte further contains a lithium salt, and the lithium salt has a concentration in the electrolyte of more than 0.1 M and not more than 1.0 M.

9. The method for producing a positive electrode according to claim 7, wherein the lithium metal layer has a thickness of 1 μm to 10 μm.

10. 8. The method for manufacturing a positive electrode according to claim 7, wherein the loading amount of the lithium metal layer is 4% to 40% of the loading amount of the preliminary positive electrode active material layer.

11. Between the S1 step and the S2 step, a step (S1a) of rolling the cathode structure; The method for producing a positive electrode according to any one of claims 7 to 10, further comprising: a step (S1b) of removing the base film after the rolling from the transfer laminate.

12. 12. The method for producing a positive electrode according to claim 11, wherein the pressure applied to the positive electrode structure during the rolling is 10 kgf / cm to 90 kgf / cm.

13. A lithium secondary battery comprising: the positive electrode according to any one of claims 1 to 6; a negative electrode; and a separator interposed between the positive electrode and the negative electrode.

14. an electrode assembly including: a perlithiated positive electrode including a perlithiated positive electrode active material layer; a negative electrode including silicon (Si) particles as an active material; and a separator interposed between the positive electrode and the negative electrode; a battery case that houses the electrode assembly; an electrolyte that is injected into the battery case so as to impregnate the electrode assembly, the electrolyte including a carbonate-based compound having a fluorine-containing functional group; When the lithium content of the perlithiated positive electrode is less than 5.0 wt % relative to the total weight of the positive electrode active material layer as measured by inductively coupled plasma spectroscopy (ICP-OES), The lithium secondary battery has a content of the carbonate-based compound having a fluorine-containing functional group of 3.5 wt % or more relative to the total weight of the electrode assembly and the electrolyte, as measured by inductively coupled plasma spectroscopy (ICP-OES).

15. 15. The lithium secondary battery of claim 14, wherein the carbonate-based compound having a fluorine-containing functional group is included in an amount of 5.0 wt % to 10 wt % based on the total weight of the electrode assembly and the electrolyte.

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