Positive electrode, method of preparing same, and lithium secondary battery including positive electrode

Abstract

The present invention relates to a positive electrode and a lithium secondary battery comprising the same, in which the positive electrode is characterized in that a positive electrode active material and a carbonate compound containing a fluorine-containing functional group are included in an active material layer, the intensity of a peak appearing in a C 1s spectrum of X-ray photoelectron spectroscopy (XPS) analysis satisfies a certain ratio, and the ratio of the intensity of the peak appearing in the C 1s spectrum of X-ray photoelectron spectroscopy (XPS) analysis satisfies a certain ratio. Moreover, the positive electrode has excellent resistance characteristics and is suppressed in deterioration, so that the service life characteristics can be improved. Further, the lithium secondary battery including the positive electrode has improved resistance characteristics, in which deterioration of the positive electrode and the negative electrode can be suppressed to prevent a sharp drop in capacity, and thus life characteristics can also be improved.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority of Korean Patent Application No. 10 - 2023 - 0013847, filed on February 1, 2023, the disclosure of which is incorporated herein by reference. Technical field

[0003] The present invention relates to an over - lithiated positive electrode, a positive electrode manufacturing method including a method for over - lithiating a positive electrode, and a lithium secondary battery including the positive electrode. Background art

[0004] Due to the rapid increase in the use of fossil fuels, the demand for alternative or clean energy sources has also increased. As part of this trend, the generation and storage of electrical energy using electrochemical reactions are the most active research fields.

[0005] Currently, typical examples of electrochemical devices using electrochemical energy can be secondary batteries, and their scope of use has a tendency to expand more and more. In recent years, with the technological development and increasing demand for portable devices such as laptops, mobile phones, and cameras, the demand for secondary batteries as an energy source has increased significantly. Among them, lithium secondary batteries with high energy density (i.e., high capacity) have been widely studied and have been commercialized and widely used.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material for inserting and extracting lithium ions from the positive electrode, and silicon - based active material particles with a high discharge capacity can be used as the negative electrode active material. The silicon - based active material particles can correspond to silicon (Si) or SiO x (0 < x < 2). The silicon - based active material particles have the advantages of a large theoretical capacity and low price. However, because the silicon - based active material particles have too large a volume change during battery operation, the disadvantage is that the battery life will rapidly decrease as the battery cycles.

[0007] Therefore, in order to minimize the volume change of the silicon - based active material particles, there is a method of using only a part of the total capacity of the silicon - based active material particles. For this purpose, a so - called prelithiation process is adopted, in which lithium ions are pre - inserted into the negative electrode including the silicon - based active material particles. Specifically, if lithium ions are inserted into the negative electrode by methods such as transferring lithium metal to the negative electrode, the total capacity of the negative electrode may be reduced to the level of the reversible capacity because the lithium ions react at irreversible sites in the negative electrode. Therefore, since the amount of lithium ions inserted during battery operation can be appropriately reduced to the level required for battery operation, the volume change of the silicon - based active material particles can be minimized.

[0008] However, during the process of pre-lithiation by setting lithium metal on the negative electrode surface, due to the alloy reaction between lithium and silicon, overheating will occur, and at the same time, the possibility of lithium reacting with moisture and catching fire will also increase. In addition, during the process of grooving and punching the negative electrode, due to the increased reaction area between lithium and the silicon-based active material, the possibility of catching fire will further increase, and the pre-lithiated silicon-based active material particles also have the possibility of catching fire, presenting serious safety problems.

[0009] Therefore, a new technology is needed to suppress the possibility of excessive heat generation and fire by pre-embedding lithium ions into the negative electrode before the battery operation, while improving the battery life. Summary of the Invention

[0010] Technical Problem

[0011] One aspect of the present invention is to provide a method for preparing a positive electrode, which does not cause the peeling or cracking of the active material during over-lithiation of the positive electrode, and can significantly shorten the time required for the over-lithiation process.

[0012] Another aspect of the present invention provides an over-lithiated positive electrode, which suppresses the cracking phenomenon of the active material during the cycling operation due to stable over-lithiation and the formation of a solid electrolyte interface (SEI) film on the positive electrode surface, thus suppressing the capacity decline, having excellent resistance characteristics, and having less lithium loss even during long-term cycling.

[0013] Another aspect of the present invention provides a lithium secondary battery, in which, by controlling the available area of the negative electrode by including an over-lithiated positive electrode, the unique characteristics of the negative electrode active material can be achieved without any drawbacks, thereby improving the life characteristics. In particular, due to the excellent ability to suppress the deterioration phenomenon, a synergistic effect in improving the life characteristics can be expected, and due to the low resistance increase rate, the problem of output reduction can be minimized even during long-term operation.

[0014] Technical Solution

[0015] To solve the above problems, according to one aspect of the present invention, there is provided a positive electrode, which includes: a positive electrode active material layer containing a positive electrode active material and a carbonate compound containing a fluorine-containing functional group; and a current collector provided with the positive electrode active material layer thereon, wherein, in the C1s spectrum analyzed by X-ray photoelectron spectroscopy (XPS), the peak intensity I of the peak P at a binding energy of 288 eV to 292 eV C1 is lower than the peak intensity I of the peak P at a binding energy of 284 eV to 286 eV C1 C2 C2 .

[0016] ​​To solve the above problems, according to another aspect of the present invention, there is provided a method for preparing a positive electrode, which includes the following steps: disposing a transfer laminate including a base film and a lithium metal layer disposed on the base film 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 (S1); and immersing the positive electrode structure in an electrolyte containing a carbonate compound having a fluorine-containing functional group (S2).

[0017] To solve the above problems, according to another aspect of the present invention, there is provided a lithium secondary battery, which includes the above positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

[0018] To solve the above problems, according to another aspect of the present invention, there is provided a lithium secondary battery, which includes: an electrode assembly including a hyperlithiated positive electrode including a hyperlithiated positive electrode active material layer, a negative electrode including silicon (Si) particles as an active material, and a separator disposed between the positive electrode and the negative electrode; a battery case accommodating the electrode assembly; and an electrolyte injected into the battery case to immerse the electrode assembly, the electrolyte including a carbonate compound having a fluorine-containing functional group, wherein when the amount of lithium based on the total weight of the positive electrode active material layer of the hyperlithiated positive electrode measured by inductively coupled plasma optical emission spectrometry (ICP-OES) is less than 5.0% by weight, the amount of the carbonate compound having a fluorine-containing functional group based on the total weight of the electrode assembly and the electrolyte measured by inductively coupled plasma optical emission spectrometry (ICP-OES) is 3.5% by weight or more.

[0019] Beneficial effects

[0020] The method for preparing a positive electrode of the present invention can reduce the peeling phenomenon and cracking phenomenon of the active material caused by hyperlithiation through electrolyte impregnation, thereby reducing side reactions with the electrolyte, and has the advantage of being able to reduce the process risk brought by negative electrode prelithiation.

[0021] In addition, the positive electrode of the present invention is hyperlithiated. Since it is prepared by the above method, a solid electrolyte interface (SEI) film is uniformly formed on the surface of the positive electrode while the positive electrode is stably hyperlithiated. Therefore, it has the advantage of being able to suppress capacity degradation because the cracking phenomenon of the active material is suppressed during the cycling operation, the resistance characteristics are excellent, and the loss amount of lithium is small even during long-term cycling.

[0022] In addition, in the formation process of the lithium secondary battery of the present invention, by including an over-lithiated positive electrode, as lithium ions move to the negative electrode, without loss of lithium in the positive electrode, the available area of the negative electrode can be reduced. Thus, in some cases, volume expansion of the negative electrode can be suppressed. The battery life can be extended by eliminating the causes of battery performance degradation such as side reactions with the electrolyte. Over-lithiation can be achieved by using an electrolyte including a fluorinated carbonate compound, and the stability of the positive electrode surface can be improved to suppress electrode degradation. Therefore, the phenomenon of a sharp drop in capacity can also be prevented. In addition, starting from the advantage of a low resistance increase rate, the advantage of being able to maintain an excellent output level for a long time can be expected. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 FIG. is a schematic diagram showing step S1 in the method for preparing a positive electrode according to an embodiment of the present invention.

[0024] Figure 2 FIG. is a schematic diagram showing step S1 of using a transfer laminate including a polymer layer in the method for preparing a positive electrode according to an embodiment of the present invention.

[0025] Figure 3 FIG. is a schematic diagram showing step S1a in the method for preparing a positive electrode according to an embodiment of the present invention.

[0026] Figure 4 FIG. is a schematic diagram showing step S1b in the method for preparing a positive electrode according to an embodiment of the present invention.

[0027] Figure 5 FIG. is a scanning electron microscope (SEM) image of the cross-section of the positive electrodes of Examples 1-5 prepared by using the method for preparing a positive electrode according to an embodiment of the present invention.

[0028] Figure 6 FIG. is a scanning electron microscope (SEM) image of the cross-section of the positive electrodes of Comparative Examples 1-2.

[0029] Figure 7 FIG. is a measurement result of the change in surface resistance with the state of charge (SOC).

[0030] Figure 8 FIG. is a measurement result of the change in charge transfer resistance with SOC.

[0031] Figure 9 FIG. is a measurement result of the change in diffusion resistance with SOC.

[0032] Figure 10 FIG. is the measurement result of the life in Experimental Example 3, in which the change in the capacity cycle process was measured.

[0033] Figure 11is the C1s spectrum obtained by analyzing the surface of the positive electrodes of Examples 2-5 and Comparative Example 2-1 by X-ray photoelectron spectroscopy (XPS).

[0034] Figure 12 is the F1s spectrum obtained by analyzing the surface of the positive electrodes of Examples 2-5 and Comparative Example 2-1 by XPS.

[0035] Figure 13 is the O1s spectrum obtained by analyzing the surface of the positive electrodes of Examples 2-5 and Comparative Example 2-1 by XPS. Detailed Description

[0036] Hereinafter, the present invention will be described in more detail for a clearer understanding of the present invention.

[0037] It should be understood that the words or terms used in the specification and claims should not be construed as having the meanings defined in a common dictionary, and it should also be understood that, based on the principle that the inventor can correctly define the meanings of the words or terms to best explain the present invention, these words or terms should be construed as having meanings consistent with their meanings in the context of the relevant art and the technical idea of the present invention.

[0038] The terms used herein are for the purpose of describing specific example embodiments only and are not intended to limit the present invention. In this specification, terms in the singular form may include the plural form unless otherwise stated.

[0039] It will be further understood that when used in this specification, the terms "comprising", "including" or "having" specify the presence of the stated features, numbers, steps, elements or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, elements or combinations thereof.

[0040] D in this specification 50 can be defined as the particle size at 50% cumulative volume in the particle size distribution curve. D 50 For example, it can be measured by using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the sub-micron level to several millimeters and can obtain results with high repeatability and high resolution.

[0041] Positive Electrode

[0042] According to an embodiment of the present invention, there is provided a positive electrode, characterized in that it comprises: a positive electrode active material layer containing a positive electrode active material and a carbonate compound containing a fluorine-containing functional group; and a current collector provided with the positive electrode active material layer thereon, wherein, in the C1s spectrum analyzed by X-ray photoelectron spectroscopy (XPS), the peak intensity I at a binding energy of 288 eV to 292 eV C1 is lower than the peak intensity I at a binding energy of 284 eV to 286 eV C2。

[0043] The positive electrode is a over-lithiated positive electrode. Since it is prepared by the over-lithiation method described below, specifically, through an impregnation process in an electrolyte containing a carbonate compound with a fluorine-containing functional group, the carbonate compound with a fluorine-containing functional group can be deposited on the surface of the positive electrode and penetrate into the internal pores. Therefore, the phenomenon of cracking of the positive electrode active material on the surface can be inhibited by the film formed inside and outside the positive electrode by the carbonate compound with a fluorine-containing functional group that penetrates into the internal pores and the surface, and it can significantly contribute to inhibiting the deterioration of the entire positive electrode during the cycling operation.

[0044] In addition, the lithium embedded by over-lithiation may move to the negative electrode during the operation of the battery, which plays a role in reducing the available area of the negative electrode. Therefore, since the available range of the negative electrode capacity can be reduced without causing lithium loss in the positive electrode active material due to the over-lithiated lithium in the positive electrode, the excessive volume change of the silicon-based active material can be particularly inhibited, and the life characteristics of the battery can be improved. In addition, since the capacity of the positive electrode active material can be used throughout the range, it has the advantages of improving battery efficiency and maximizing the energy density.

[0045] The positive electrode according to an embodiment of the present invention is characterized in that the prelithiation is not carried out by usually contacting a lithium metal layer with the negative electrode, but during the formation process of the battery, the lithium metal layer is transferred to the positive electrode and rolled, and then the lithium ions embedded in the positive electrode are transferred to the negative electrode. Through electrolyte impregnation, the phenomenon of active material peeling newly occurring during the transfer of lithium to the positive electrode rather than the negative electrode, or the problem of reduced process efficiency caused by long-term over-lithiation can be overcome.

[0046] That is, since the negative electrode does not contact the lithium metal layer and the lithium ions do not directly embed into the negative electrode from the lithium metal layer, the phenomenon of overheating caused by the alloy reaction of lithium and silicon at the negative electrode can be avoided, and the possibility of fire caused by the reaction of lithium and moisture is greatly reduced. Moreover, since lithium ions do not embed into the negative electrode during grooving and punching of the negative electrode (because prelithiation has not been carried out), the possibility of fire during the grooving and punching processes can be significantly reduced.

[0047] According to an embodiment of the present invention, the positive electrode is characterized in that in the C1s spectrum of the XPS analysis, the peak P at a binding energy of 288 eV to 292 eV c1 of the peak intensity I C1 is lower than the peak P at a binding energy of 284 eV to 286 eV c2 of the peak intensity I C2 . In addition, I C2 / I C1 is preferably 1 or less, and may also be 0.9 or less, 0.8 or less, or 0.7 or less.

[0048] In the C1s spectrum of XPS analysis, peaks may appear due to compounds with functional groups involving carbon in bonding. For example, peaks may appear due to various factors such as carbonate by-products (-CO3) or fluorocarbons (CF2). Specifically, for peak P C1 , for example, it appears due to carbonate by-products. Among them, for the positive electrode of the embodiment of the present invention, although the positive electrode active material layer contains fluorinated carbonate compounds, due to the process of impregnation in the electrolyte, a stable solid electrolyte interface (SEI) film can be formed on the surface, and the formation of by-products can be prevented through the formation of this film. Therefore, peak P C1 may appear relatively small. And, peak P C2 is a peak that appears due to general C-C bonds or C-H bonds. Among them, it may usually be caused by electrode materials such as active materials and binders, and may have a relative relationship with peak P C1 . For example, in the case where peak P C1 appears strong due to a large amount of by-products, peak P C2 may appear relatively weak.

[0049] On the contrary, if the process of impregnation in the electrolyte is not carried out, especially the process of impregnation in an electrolyte that does not contain fluorinated carbonate compounds, a stable film may not be formed. Therefore, peak P C1 may be strongly detected, which means that a relatively large amount of carbonate by-products may be formed. Therefore, the positive electrode of the embodiment of the present invention is characterized in that peak P C1 can be relatively small and have a lower peak intensity than peak P C2 . In addition, the ratio I C2 / I C1 within the above range can be considered to have an excellent over-lithiation effect using electrolyte impregnation.

[0050] In addition, in the C1s spectrum, a peak P C3 can be detected at a binding energy of 286 eV to 288 eV. That is, peak P C3 can be detected as a weak peak between peak P C1 and peak P C2 . For example, it may appear due to C-O bonds or C-C-F bonds, or may be the result of the positive electrode active material layer containing fluorinated carbonate compounds.

[0051] In addition, according to the embodiment of the present invention, in the F1s spectrum of the XPS analysis of the positive electrode, the peak intensity I F1 of the peak P F1 at a binding energy of 687 eV to 689 eV can be lower than the peak intensity of the peak P F2 at a binding energy of 684 eV to 686 eV.Peak intensity I F2 . Preferably, in the F1s spectrum of XPS analysis, the ratio of the two peaks I F2 / I F1 can be 1 or less, or can be 0.8 or less, 0.7 or less, or 0.6 or less.

[0052] In the F1s spectrum of XPS analysis, peaks may appear due to compounds having functional groups in which fluorine participates in bonding. For example, since the compound contains bonds such as C-F, P-F, Li-F, and S-F, peaks may thus appear.

[0053] Specifically, for peak P F2 , its appearance is due to the bonding between a metal and fluorine. Among them, for example, it may be due to bonds such as Li-F. For the positive electrode of the embodiment of the present invention, a fluorine-containing carbonate compound is included in the positive electrode active material layer. However, due to the process of impregnation in the electrolyte, Li-F can be formed by reacting lithium with a fluorine-containing functional group, and at the same time, a solid electrolyte interface (SEI) film is formed on the surface, so that the durability of the film can be improved.

[0054] In addition, peak P F2 is a peak that appears due to general C-F, P-F, or S-F bonds. Among them, it is usually caused by electrode materials such as active materials and binders, and may be in a relative relationship with peak P F1 . For example, in the case where peak P F1 appears to be stronger due to a large amount of Li-F, peak P F2 may appear relatively weaker. Therefore, it is preferable that the peak intensity I F1 of peak P F1 is lower than the peak intensity I F2 of peak P F2 , and when the ratio I F2 / I F1 of the two peaks satisfies the above range, it can be considered that over-lithiation of the positive electrode of the embodiment of the present invention has been normally achieved.

[0055] In addition, in the O1s spectrum of XPS analysis of the positive electrode, the peak intensity I O1 of peak P O1 at a binding energy of 531 eV to 533 eV can be 4.00 or less, and preferably can be 3.90 or less, 3.80 or less, or 3.75 or less.

[0056] For the peak of the O1s spectrum, it may appear as a single peak, or may appear due to bonds such as C-O, C═O, or CO3. The bonds that usually appear may not be caused by electrode materials, but may be caused by by-products, which may mean that the peak intensity I O1 of peak PO1 The lower it is, the less the amount of by-products. Therefore, I O1 can be 4.00 or less, preferably satisfying the above range, and satisfying this range means that the over-lithiation of the embodiment of the present invention has been carried out well, thus forming a stable solid electrolyte interface film.

[0057] According to an embodiment of the present invention, the carbonate compound containing a fluorine-containing functional group may include, for example, at least one selected from the group consisting of fluoroethylene carbonate, methyl (2,2,2-trifluoroethyl) carbonate, and ethyl (2,2,2-trifluoroethyl) carbonate, and preferably fluoroethylene carbonate. During the over-lithiation of the positive electrode, when over-lithiation is carried out by adding a carbonate compound containing a fluorine-containing functional group to the electrolyte, a stable solid electrolyte interface film can be formed on the surface of the positive electrode, and this compound can remain in the positive electrode active material layer. In addition, based on the total weight of the positive electrode active material layer, the content of the carbonate compound containing a fluorine-containing functional group may be 10% by weight or less, and the preferred content may be 8% by weight or less. This range can be confirmed from the above XPS analysis results, in which part may react with lithium during over-lithiation, and the rest may remain in the positive electrode active material layer.

[0058] According to an embodiment of the present invention, the positive electrode includes a positive electrode active material layer and a current collector provided with the positive electrode active material layer thereon. The current collector is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector generally may have a thickness of 3 μm to 500 μm, and minute irregularities may be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes, such as the shapes of a film, sheet, foil, net, porous body, foam body, non-woven fabric body, etc.

[0059] 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 agent, and a positive electrode binder. The positive electrode active material is a material capable of causing an electrochemical reaction, and it may be a lithium transition metal oxide. For example, the positive electrode active material may include at least one selected from the group consisting of: layered compounds such as lithium cobalt oxide or lithium nickel oxide substituted with at least one transition metal; lithium manganese oxide substituted with at least one transition metal; lithium nickel-based oxides represented by Li[Ni 1-y M 1 y O2 (where M 1is at least one selected from cobalt (Co), manganese (Mn), aluminum (Al), copper (Cu), iron (Fe), magnesium (Mg), boron (B), chromium (Cr), zinc (Zn), and gallium (Ga), and 0.01 ≤ y ≤ 0.7); and Li 1+z [Ni b Mn c Co 1-(b+c+d) M 2 d O (2-e) A e represents a lithium nickel cobalt manganese composite oxide (wherein, M 2 is at least one selected from the group consisting of Al, Mg, Cr, Ti, silicon (Si), and yttrium (Y), A is at least one selected from the group consisting of fluorine (F), phosphorus (P), and chlorine (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, and b + c + d < 1); and Li 1+x [M 3 1-q M 4 q PO 4-r X r represents an olivine-type lithium metal phosphate (wherein, M 3 is at least one selected from the group consisting of Fe, Mn, Co, and Ni, 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, sulfur (S), and nitrogen (N), and -0.5 ≤ x ≤ 0.5, 0 ≤ q ≤ 0.5, and 0 ≤ r ≤ 0.1).

[0060] Specifically, the positive electrode active material may be composed of a lithium nickel-based oxide, a lithium nickel cobalt manganese composite oxide, an olivine-type lithium metal phosphate, or a combination thereof, and these materials may be combined to form the positive electrode active material layer as one layer or different layers.

[0061] According to an embodiment of the present invention, more specifically, the positive electrode active material may include a compound of Formula 1, and more specifically, may be a compound of Formula 1.

[0062] [Formula 1]

[0063] Li 1+x [Ni a Co b Mn c M 1 (1-a-b-c) O (2-d) A d

[0064] In Formula 1,

[0065] M 1 is at least one selected from the group consisting of Al, Mg, Cr, Ti, Si, and Y, and may specifically be Al.

[0066] A is at least one selected from the group consisting of F, P, and Cl, and may specifically be F.

[0067] x may satisfy -0.5 ≤ x ≤ 0.5, specifically, -0.3 ≤ x ≤ 0.3.

[0068] a may satisfy 0.6 ≤ a < 1, specifically, 0.7 ≤ a ≤ 0.9.

[0069] b may satisfy 0.03 ≤ b ≤ 0.1, specifically, 0.05 ≤ b ≤ 0.1.

[0070] c may satisfy 0.03 ≤ c ≤ 0.1, specifically, 0.05 ≤ c ≤ 0.1.

[0071] d may satisfy 0 ≤ d ≤ 0.1, specifically, 0 ≤ d ≤ 0.05.

[0072] a, b, and c may satisfy 0 < a + b + c ≤ 1, specifically, a + b + c = 1.

[0073] The compound of Formula 1 may be in the form of particles.

[0074] The compound of Formula 1 may be in the form of secondary particles in which a plurality of primary particles are combined with each other. Specifically, the compound of Formula 1 may be in the form of secondary particles in which 10 or more primary particles are combined with each other. Therefore, there is an effect that lithium can be uniformly inserted into and deintercalated from the positive electrode active material.

[0075] D of the compound of Formula 1 50 may be 5 μm to 15 μm, particularly 7 μm to 12 μm, more particularly 9 μm to 10 μm. D 50 may be the D of the secondary particles 50 . When the above range is satisfied, the positive electrode paste is easily dispersed, and thus the positive electrode active material layer can be uniformly coated.

[0076] The content of the positive electrode active material in the positive electrode active material layer may be 90% by weight to 99% by weight, particularly 92% by weight to 98% by weight, more particularly 95% by weight to 98% by weight.

[0077] According to an embodiment of the present invention, the positive electrode active material layer may further include a positive electrode binder. The positive electrode binder improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder may be polyvinylidene fluoride (PVDF), polyvinylidene 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, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used.

[0078] The content of the positive electrode binder in the positive electrode active material layer may be 0.5% by weight to 5.0% by weight, particularly 1.0% by weight to 2.5% by weight, and more particularly 1.0% by weight to 2.0% by weight.

[0079] According to an embodiment of the present invention, the positive electrode active material layer may further include a positive electrode conductive agent. The positive electrode conductive agent is used to provide conductivity to the electrode, and any conductive agent may be used without particular limitation as long as it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of the positive electrode conductive agent may be: graphite, such as natural graphite or artificial graphite; carbon - based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal - cracking carbon black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one of them or a mixture of two or more thereof may be used.

[0080] The content of the positive electrode conductive agent in the positive electrode active material layer may be 0.5% by weight to 30.0% by weight, particularly 0.5% by weight to 10.0% by weight, and more particularly 1.0% by weight to 4.0% by weight.

[0081] <Method for preparing the positive electrode>

[0082] The method for preparing the positive electrode of the present invention is characterized in that it includes the following steps: disposing a transfer laminate including a base film and a lithium metal layer disposed on the base film on a preliminary positive electrode active material layer to form a positive electrode structure body such that the lithium metal layer and the preliminary positive electrode active material layer are in contact with each other (S1); and immersing the positive electrode structure body in an electrolyte containing a carbonate compound having a fluorine - containing functional group (S2).

[0083] The above positive electrode can be prepared by the above preparation method, and the prepared positive electrode can have the peak characteristics of the above C1s spectrum, F 1s spectrum, and O 1s spectrum obtained by XPS analysis. Since the specific details are the same as the above, the description thereof is omitted.

[0084] In addition, according to an embodiment of the present invention, the method for preparing a positive electrode may further include the following steps between step (S1) and step (S2): roll-pressing the positive electrode structure body (S1a); and removing the base film in the roll-pressed transfer laminate (S1b).

[0085] Hereinafter, step (S1), step (S1a), step (S1b), and step (S2) will be described in sequence.

[0086] According to an embodiment of the present invention, step (S1) of the method for preparing a positive electrode is a step of disposing a transfer laminate including a base film and a lithium metal layer on a preliminary positive electrode active material layer to form a positive electrode structure body such that the lithium metal layer is in contact with the preliminary positive electrode active material layer.

[0087] Refer to Figure 1 , the transfer laminate 300 may include a base film 310 and a lithium metal layer 320 disposed on the base film 310. The use of the base film 310 is not limited as long as it is a material that can withstand the high temperature conditions during the deposition of the lithium metal layer 320 on the base film 310. Specifically, the base film may include at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), polymethyl methacrylate (PMMA), polypropylene, polyethylene, and polycarbonate.

[0088] According to an embodiment of the present invention, the lithium metal layer may be disposed on the base film. The lithium metal layer serves to supply lithium ions to the preliminary positive electrode active material layer. The lithium metal layer includes solid-phase lithium metal, and specifically, the lithium metal layer may be formed of solid-phase lithium metal.

[0089] According to an embodiment of the present invention, in the transfer laminate, the thickness of the lithium metal layer may be 1.0 μm to 10.0 μm, specifically, 2.0 μm to 9.0 μm, and preferably its thickness may be 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, since the degree of breakage of the positive electrode active material particles on the surface of the positive electrode can be reduced, a decrease in the initial capacity of the battery can be suppressed.

[0090] According to an embodiment of the present invention, the loading amount of the lithium metal layer (unit: mAh / cm 2 ) may be the loading amount of the preliminary positive electrode active material layer (unit: mAh / cm 2) ranges from 4% to 40%, specifically it can be from 12% to 35%, and more specifically it can be from 20% to 30%. When the above range is satisfied, since the formation of by-products is small and lithium can be easily embedded into the positive electrode active material, the target lithium embedding capacity can be easily achieved.

[0091] In step (S1) of the embodiment of the present invention, referring to Figure 1 , a preliminary positive electrode active material layer 120' is provided on the positive electrode current collector 110, and the transfer laminate 300 is provided on the preliminary positive electrode active material layer 120' to form a positive electrode structure body 400, such that the lithium metal layer 320 is in contact with the preliminary positive electrode active material layer.

[0092] According to an embodiment of the present invention, the preliminary positive electrode active material layer in step (S1) may refer to the positive electrode active material layer before over-lithiation. The preliminary positive electrode active material layer may be provided on the positive electrode current collector, and may be provided on one surface or both surfaces of the positive electrode current collector.

[0093] According to an embodiment of the present invention, the transfer laminate 300 may further include a polymer layer 330. Referring to Figure 2 , the polymer layer 330 may be provided between the base film 310 and the lithium metal layer 320. The polymer layer can play a role in effectively peeling the lithium metal layer from the transfer laminate during the preparation of the positive electrode and making the lithium metal layer easily transferred onto the positive electrode active material layer. That is to say, the polymer layer can be separated from the transfer laminate together with the lithium metal layer and provided on the positive electrode active material layer. The polymer layer may be in contact with the positive electrode active material layer, or the lithium metal layer may be present between the polymer layer and the positive electrode active material layer.

[0094] The polymer layer may be at least one selected from the group consisting of: polyethylene terephthalate (PET), polyimide (PI), polymethyl methacrylate (PMMA), polypropylene, polyethylene, and polycarbonate. Therefore, in a secondary battery including a positive electrode, since the polymer layer can be dissolved in the electrolyte contained in the secondary battery, an increase in battery resistance can be prevented. In particular, the polymer layer may include PMMA, and in this case, the above effect can be further improved.

[0095] The thickness of the polymer layer may be from 0.1 μm to 10 μm, especially from 0.5 μm to 5 μm, and more especially from 1 μm to 2.5 μm. When the above range is satisfied, the lithium metal layer can be easily transferred onto the positive electrode active material layer, and the reverse transfer phenomenon of the positive electrode active material layer being transferred onto the transfer laminate can be prevented.

[0096] According to an embodiment of the present invention, step (S1a) of the method for preparing a positive electrode is a step of roll-pressing the positive electrode structure body.

[0097] Referring to Figure 3 , in step (S1a), the prepared positive electrode structure 400 can be roll-pressed. The roll-pressing can be carried out by a roll-pressing method. Specifically, two rollers R spaced apart by a predetermined space in the vertical direction can apply pressure to the positive electrode structure 400 passing through this space in the vertical direction, and this pressure can be a linear pressure. Through the roll-pressing process, at least a part of the lithium ions in the lithium metal layer contained in the transfer laminate can be embedded in the as-prepared positive electrode active material layer. In this process, the as-prepared positive electrode active material layer can become the positive electrode active material layer. In Figure 3 and Figure 4 , it is shown that the lithium metal layer is contained in the positive electrode, but in the case where the entire lithium metal layer is embedded in the as-prepared positive electrode active material layer during the roll-pressing process, the lithium metal layer may not exist as a separate layer.

[0098] The pressure applied to the positive electrode structure during the roll-pressing process can be 10 kgf / cm to 90 kgf / cm, particularly 15 kgf / cm to 80 kgf / cm, and can preferably be 20 kgf / cm or more, 25 kgf / cm or more, or 30 kgf / cm or more, and 70 kgf / cm or less, or 60 kgf / cm or less.

[0099] When the roll-pressing pressure within the above range is applied, the lithium metal layer can be effectively transferred, lithium can be embedded in the positive electrode at a desired level, and the positive electrode active material particles can be controlled so that they do not break or peel off. Therefore, the effects of simultaneously satisfying life improvement and capacity characteristics can be achieved.

[0100] According to an embodiment of the present invention, step (S1b) of the positive electrode preparation method is a step of preparing a positive electrode by removing the base film from the roll-pressed transfer laminate.

[0101] Referring to Figure 4 , in step (S1b), the positive electrode 100 can be prepared by removing the base film 310 from the transfer laminate after roll-pressing in step (S1a). When the polymer layer 330 is located between the base film 310 and the lithium metal layer 320, the base film 310 may be more easily removed through the polymer layer 330.

[0102] In addition, according to an embodiment of the present invention, the method for preparing the positive electrode may further include step S1b': leaving the preliminary positive electrode standing (placing) for 1 minute to 600 minutes, specifically, leaving it standing for 1 minute to 30 minutes. Step S1b' may be executed after step S1a. Specifically, step S1b' may be executed in at least one of the steps "between step S1a and step S1b" and "immediately after step S1b". Since the heat of reaction generated by the reaction between the lithium metal layer and the preliminary positive electrode active material layer in step S1a can be effectively released through step S1b', lithium can be uniformly embedded in the positive electrode, thereby having the effect of reducing the formation of by-products.

[0103] According to an embodiment of the present invention, step S2 is a step of immersing the prepared positive electrode structure in an electrolyte containing a carbonate solvent. In the case of transferring lithium to the positive electrode by immersing the positive electrode structure in the electrolyte, since the time required for over-lithiation can be greatly shortened and the phenomenon of peeling or cracking of the active material particles can be suppressed, the lifespan can be significantly improved.

[0104] In the case of pre-lithiation on the negative electrode, regardless of which pre-lithiation method is adopted, there are problems such as the phenomenon of excessive heat generation caused by the difficulty of preventing contact between the negative electrode and the lithium metal layer and the phenomenon of ignition when grooving or punching the negative electrode. And, in the case of pre-lithiation on the negative electrode, since the phenomenon of peeling of the active material does not occur and the transfer time of lithium is not long, the advantages of pre-lithiation using the electrolyte impregnation process cannot be demonstrated.

[0105] However, the present inventors have noticed that when over-lithiating (pre-lithiating) the positive electrode, due to the too long transfer time of lithium, the process efficiency is too low, and since the phenomenon of peeling of the active material occurs during the transfer process, over-lithiation of the positive electrode is more difficult to handle than pre-lithiation of the negative electrode. Therefore, it is intended to provide a method for over-lithiating the positive electrode using the electrolyte impregnation process.

[0106] The method for preparing the positive electrode according to the embodiment of the present invention can solve the problems that occur during the over-lithiation process of the positive electrode by immersing the positive electrode structure in an electrolyte, especially an electrolyte containing a carbonate compound having a fluorine-containing functional group.

[0107] In the case of adopting the electrolyte impregnation process, since the over-lithiation time can be significantly shortened and the phenomenon of peeling or cracking of the active material particles can be greatly reduced, the lifespan of the lithium secondary battery can be improved.

[0108] Generally, as the carbonate solvent, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, or diethyl carbonate can be used, for example. When only the carbonate solvent is used as the solvent of the electrolyte, sometimes a white layer is formed on the surface of the positive electrode after over-lithiation, which leads to an increase in resistance. Therefore, by using a carbonate compound containing a fluorine-containing functional group, the cause of the above-mentioned increase in resistance can be eliminated. Therefore, from the viewpoint of improving the output, it is more preferable to use a carbonate compound containing a fluorine-containing functional group, and the effect of suppressing the deterioration of the positive electrode and the negative electrode brought by the carbonate compound containing a fluorine-containing functional group can also be expected. Therefore, it is preferable to use them together.

[0109] The carbonate compound containing a fluorine-containing functional group may include at least one selected from the group consisting of fluoroethylene carbonate, methyl (2,2,2-trifluoroethyl) carbonate, and ethyl (2,2,2-trifluoroethyl) carbonate. Based on the total weight of the electrolyte, the content of the carbonate compound containing a carbonate functional group may be 5% by weight to 40% by weight, preferably 8% by weight or more, or 10% by weight or more, and the content may also be 35% by weight or less, or 30% by weight or less.

[0110] 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 soluble in the non-aqueous electrolyte. Among them, for example, at least one selected from the group consisting of the following may be used as the anion of the lithium salt: 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 - .

[0111] Desirably, the concentration of the lithium salt in the electrolyte satisfies a range greater than 0.1 M and less than or equal to 1.0 M. When the concentration of the lithium salt is within the above range, the effects obtained by over-lithiation through electrolyte impregnation can be achieved, and the phenomena of active material peeling or poor lithium transfer can be minimized or prevented. The concentration of the lithium salt is preferably 0.2 M or more, 0.23 M or more, 0.25 M or more, or 0.3 M or more, and can be 0.95 M or less, 0.9 M or less, or 0.85 M or less.

[0112] According to an embodiment of the present invention, in addition to the above electrolyte components, the electrolyte may further contain at least one additive, for example, halogenated alkylene carbonate compounds such as ethylene difluorocarbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, diethylene glycol dimethyl ether, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0113] The method for preparing the positive electrode according to the embodiment of the present invention may further include a step (S3) of washing and drying the positive electrode structure after step (S2). When the over-lithiation of the positive electrode structure is completed by electrolyte impregnation, the positive electrode structure can be washed and dried, assembled with the separator and the negative electrode to form an electrode assembly, and an electrolyte is injected into the electrode assembly to prepare a lithium secondary battery. Washing and drying can be carried out under conventional conditions and methods known in the art.

[0114] Lithium secondary battery

[0115] The lithium secondary battery according to the embodiment of the present invention includes a lithium secondary battery, which includes a positive electrode, a negative electrode prepared by the above preparation method, and a separator disposed between the positive electrode and the negative electrode.

[0116] Since the method for preparing the positive electrode and the positive electrode have been described above, the description thereof will be omitted.

[0117] In addition, a lithium secondary battery according to another embodiment of the present invention is characterized in that it includes: an electrode assembly including a positive electrode including a hyperlithiated positive electrode active material layer, a negative electrode including silicon (Si) particles as an active material, and a separator disposed between the positive electrode and the negative electrode; a battery case accommodating the electrode assembly; and an electrolyte injected into the battery case to impregnate the electrode assembly, the electrolyte including a carbonate compound containing a fluorine-containing functional group, wherein when the amount of lithium based on the total weight of the positive electrode active material layer of the hyperlithiated positive electrode measured by inductively coupled plasma optical emission spectrometry (ICP-OES) is less than 5.0% by weight, the amount of the carbonate compound containing a fluorine-containing functional group based on the total weight of the electrode assembly and the electrolyte measured by inductively coupled plasma optical emission spectrometry (ICP-OES) is 3.5% by weight or more.

[0118] Wherein, the amount of lithium in the hyperlithiated positive electrode active material layer and the amount of the carbonate compound containing a fluorine-containing functional group in the electrode assembly and the electrolyte can be measured by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0119] As described above, the hyperlithiated positive electrode is a positive electrode that has been hyperlithiated, and the hyperlithiation includes a process of impregnating the positive electrode in an electrolyte containing a carbonate compound containing a fluorine-containing functional group, wherein it is characterized in that an active material layer including silicon particles as an active material is formed in the negative electrode, and it is characterized in that the carbonate compound containing a fluorine-containing functional group that has been used in the hyperlithiation process is included in the electrolyte. By simultaneously utilizing these characteristics, a lithium secondary battery can be provided that satisfies that when the amount of lithium based on the total weight of the positive electrode active material layer in the hyperlithiated positive electrode is less than 5.0% by weight, the amount of the carbonate compound containing a fluorine-containing functional group based on the total weight of the electrolyte in the electrolyte is 3.5% by weight or more.

[0120] The amount of lithium being less than 5.0% by weight means that repeated cycling has been carried out for a relatively long time, which may mean that the lithium secondary battery has deteriorated to a certain extent. According to an embodiment of the present invention, it is characterized in that even after the lithium secondary battery has significantly deteriorated, the amount of the carbonate compound containing a fluorine-containing functional group based on the total weight of the electrolyte in the electrolyte is still 3.5% by weight or more.

[0121] Carbonate compounds containing fluorine-containing functional groups can be included as additives or solvents for electrolytes. Among them, during the cycling operation, most of them will be lost due to side reactions. After the deterioration has developed to a considerable extent, the remaining amount may be quite small. That is, when the amount of lithium in the positive electrode decreases to less than 5.0% by weight during cycling, the remaining amount will be quite small. However, when using the positive electrode (i.e., over-lithiated positive electrode) of the embodiment of the present invention, since a stable film is formed on the surface, the loss caused by side reactions on the positive electrode surface or the amount consumed for film formation can be negligible. Therefore, it is possible to prevent a sharp drop in capacity due to long-term stay in the electrolyte.

[0122] For example, based on the total weight of the electrode assembly and the electrolyte, the amount of the carbonate compound containing a fluorine-containing functional group can be 3.5% by weight or more, and can preferably be 4.0% by weight or more, 4.5% by weight or more, 5.0% by weight or more, 5.3% by weight or more, or 5.5% by weight or more. In addition, the amount of the carbonate compound containing a fluorine-containing functional group is preferably 15.0% by weight or less, 10.0% by weight or less, or 9.0% by weight or less.

[0123] As described above, the amount of the carbonate compound containing a fluorine-containing functional group used in the electrolyte is generally in the range of about 5% to 40% by weight, and 40% by weight is the maximum amount that can be included. That is, even when including the maximum amount of the carbonate compound containing a fluorine-containing functional group, it will be continuously consumed during the cycling operation, and a sudden drop in capacity may occur after a certain point when the remaining amount has almost disappeared.

[0124] However, for the lithium secondary battery of the embodiment of the present invention, since an SEI film is formed on the surface and internal pores of the positive electrode in advance by the carbonate compound containing a fluorine-containing functional group, and by using an over-lithiated positive electrode, such as a positive electrode over-lithiated with a carbonate compound containing a fluorine-containing functional group, the compound can remain. Therefore, the amount of the carbonate compound containing a fluorine-containing functional group consumed in the electrolyte can be minimized as much as possible, thereby suppressing the deterioration of the negative electrode and the positive electrode, and preventing problems such as a sudden drop in capacity and a rapid increase in resistance.

[0125] The above range can be achieved by adopting the above combination. In this case, even if the SEI film already formed on the positive electrode is damaged, since it can be replenished by the remaining carbonate compound containing a fluorine-containing functional group, the effect of maintaining a long life can be expected.

[0126] In addition, a lithium secondary battery according to another embodiment of the present invention is characterized in that it includes: an electrode assembly including a hyper-lithiated positive electrode including a hyper-lithiated positive electrode active material layer, a negative electrode including silicon (Si) particles as an active material, and a separator disposed between the positive electrode and the negative electrode; a battery case accommodating the electrode assembly; and an electrolyte injected into the battery case to impregnate the electrode assembly, the electrolyte including a carbonate compound containing a fluorine-containing functional group, wherein when the amount of the carbonate compound containing a fluorine-containing functional group based on the total weight of the electrode assembly and the electrolyte measured by inductively coupled plasma optical emission spectrometry (ICP-OES) is 8.0% by weight or less, the amount of lithium based on the total weight of the positive electrode active material layer of the hyper-lithiated positive electrode measured by inductively coupled plasma optical emission spectrometry (ICP-OES) is 3.0% by weight or more.

[0127] Preferably, the amount of lithium can be 3.5% by weight or more, 4.0% by weight or more, 4.5% by weight or more, or 5.0% by weight or more.

[0128] That is to say, in the lithium secondary battery according to the embodiment of the present invention, after long-term cycling operation, a large amount of lithium still remains in the positive electrode, and a large amount of carbonate compounds containing fluorine-containing functional groups also remain in the electrolyte. Therefore, a large amount of lithium moving between the positive electrode and the negative electrode can exist for a long time, and a large amount of carbonate compounds containing fluorine-containing functional groups that can prevent side reactions and deterioration also exist. Therefore, due to the excellent capacity retention rate and resistance increase rate of the lithium secondary battery, the effect of increasing the lifespan can be significantly achieved.

[0129] The negative electrode includes a negative electrode active material layer, and the negative electrode active material layer may include a negative electrode active material, and a silicon-based negative electrode active material, a carbon-based negative electrode active material, or a combination thereof may be used as the negative electrode active material.

[0130] The negative electrode active material may include a silicon-based negative electrode active material. The silicon-based negative electrode active material may include Si and SiO x (0 < x < 2) at least one of them.

[0131] Si is silicon particles, and among them, it may be silicon particles (particles formed of silicon), which are called pure silicon. The silicon particles can effectively improve the capacity of the negative electrode. SiO x (0 < x < 2) may be in a form including Si and SiO2, and Si may form a phase. That is to say, x corresponds to the number ratio of oxygen (O) to Si contained in SiO x (0 < x < 2). When the silicon-based composite particles contain SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0132] According to an embodiment of the present invention, for a silicon-based anode active material, especially silicon (Si) particles, due to the drastic volume change during battery operation, there is a problem of extremely poor life characteristics. However, in the case of combination with the positive electrode of the present invention, since excessive lithium ions (lithium in the positive electrode active material that does not determine the capacity) transfer from the over-lithiated positive electrode to the silicon (Si) anode active material during activation and react with the silicon (Si) particles in advance to form an irreversible phase, reducing the available area, the volume change during battery operation is not drastic. Therefore, the life can be significantly improved, and the high-capacity characteristics inherent to the silicon-based anode active material can be fully realized.

[0133] According to an embodiment of the present invention, the anode active material may further include a carbon-based anode active material. The carbon-based anode active material may include at least one selected from the group consisting of artificial graphite, natural graphite, and graphitized mesophase carbon microspheres.

[0134] According to an embodiment of the present invention, the anode active material layer may further include an anode binder. The anode binder may include at least one selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylate, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen therein is replaced by lithium (Li), sodium (Na), or calcium (Ca), or may include various copolymers thereof.

[0135] According to an embodiment of the present invention, the anode active material layer may further include an anode conductive agent. The anode conductive agent is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery. For example, the following conductive materials can be used, such as: graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers such as carbon fiber or metal fiber; conductive tubes such as carbon nanotube; carbon fluoride powder; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whisker and potassium titanate whisker; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0136] According to an embodiment of the present invention, a lithium secondary battery includes a separator. The separator separates the negative electrode and the positive electrode and provides a path for the movement of lithium ions. Any separator can be used as the separator without particular limitation as long as it is commonly used in secondary batteries. Specifically, a separator having a high water retention capacity for the electrolyte and a low resistance to the transfer of electrolyte ions is preferred. Specifically, a porous polymer membrane can be used. For example, a porous polymer membrane prepared from polyolefin polymers (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or a laminated structure having two or more layers thereof can be used. In addition, typical porous non-woven fabrics can be used. For example, non-woven fabrics formed from high melting point glass fibers or polyethylene terephthalate fibers can be used. In addition, a coated separator including a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure can be optionally used.

[0137] 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 during over-lithiation, and the electrolytes can be used independently of each other. The electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten-type inorganic electrolyte that can be used to prepare a lithium secondary battery, but the present invention is not limited thereto.

[0138] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt. As the non-aqueous organic solvent, carbonate compounds containing fluorine-containing functional groups are included. In addition, for example, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, methyl propionate, and ethyl propionate can be used.

[0139] In particular, since cyclic carbonates (ethylene carbonate and propylene carbonate) in carbonate organic solvents can dissociate lithium salts in the electrolyte well due to their high dielectric constants as high-viscosity organic solvents, cyclic carbonates are preferably used; in addition, when cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constant (such as dimethyl carbonate and diethyl carbonate) in an appropriate ratio, an electrolyte having high conductivity can be prepared, which is more preferably used.

[0140] A lithium salt can be used as the metal salt, and the lithium salt is a material that is soluble in the non-aqueous electrolyte. Among them, for example, at least one selected from the group consisting of the following can be used as the anion of the lithium salt: 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 - .

[0141] In addition to the above electrolyte components, for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and increasing the discharge capacity of the battery, the electrolyte may further include at least one additive, for example, halogenated alkylene carbonate compounds such as vinylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, diethylene glycol dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0142] As described above, since the secondary battery including the positive electrode of the present invention stably exhibits excellent capacity and capacity retention rate, the secondary battery is suitable for portable devices such as mobile phones, laptop computers, and digital cameras, as well as electric vehicles, such as hybrid electric vehicles (HEVs).

[0143] Therefore, according to another embodiment of the present invention, there is provided a battery module including the above secondary battery as a unit cell and a battery pack including the battery module.

[0144] The battery module and the battery pack can be used as a power source for at least one medium and large-sized device selected from the following group: power tools; electric vehicles (EVs); hybrid electric vehicles; plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0145] Examples

[0146] Preferred examples will be provided below for a better understanding of the present invention. It is obvious to those skilled in the art that these examples are provided only to illustrate the present invention, and various modifications and changes can be made within the scope and technical spirit of the present invention. Such modifications and changes fall within the scope of the claims included herein.

[0147] Electrode Preparation

[0148] Example 1-1: Preparation of the Positive Electrode

[0149] A transfer laminate was prepared, which included a PET film (base film), a polymer layer (2.5 μm thick) formed of PMMA provided on the PET film, and a lithium metal layer (6.0 μm thick, loading amount of 0.62 mAh / cm 2 ) formed of solid-phase lithium metal provided on the polymer layer.

[0150] Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 O2 was used as the positive electrode active material. The positive electrode active material was in the form of secondary particles formed by combining multiple (more than 10) Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 O2 primary particles, and the average particle size D 50 of the secondary particles was 9 μm. A positive electrode was prepared, which included a preliminary positive electrode active material layer and an aluminum foil (thickness: 6 μm) as the positive electrode current collector. The preliminary positive electrode active material layer contained a positive electrode active material, PVdF as the positive electrode binder, and carbon nanotubes as the positive electrode conductive agent in a weight ratio of 98:1:1. The loading amount of the preliminary positive electrode active material layer was 4.5 mAh / cm 2 , and the thickness was 140 μm.

[0151] The transfer laminate was set on the preliminary positive electrode active material layer such that the lithium metal layer was in contact with the preliminary positive electrode active material layer.

[0152] Subsequently, after the positive electrode provided with the transfer laminate was roll-pressed at a pressure of 50 kgf / cm by the roll-pressing method, the positive electrode structure was immersed in an electrolyte with a concentration of 0.2 M (solvent: fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) with a weight ratio of 3:7, lithium salt: LiPF6 and LiFSI, additive: vinylene carbonate (VC), propylene carbonate (PC), and 1,3-propane sultone (PRS)). Thereby, the lithium ions in the lithium metal layer were embedded into the as-prepared positive electrode active material layer to form the positive electrode active material layer. After that, the base film was removed, and the roll-pressed positive electrode was allowed to stand for 10 minutes to prepare a positive electrode including a positive electrode current collector, a positive electrode active material layer, and a polymer layer.

[0153] Example 1-2: Preparation of Positive Electrode

[0154] A positive electrode was prepared in the same manner as in Example 1-1, except that the concentration of the electrolyte in which the positive electrode structure was immersed was 0.3 M.

[0155] Example 1-3: Preparation of Positive Electrode

[0156] A positive electrode was prepared in the same manner as in Example 1-1, except that the concentration of the electrolyte in which the positive electrode structure was immersed was 0.5 M.

[0157] Example 1-4: Preparation of Positive Electrode

[0158] A positive electrode was prepared in the same manner as in Example 1-1, except that the concentration of the electrolyte in which the positive electrode structure was immersed was 0.7 M.

[0159] Example 1-5: Preparation of Positive Electrode

[0160] A positive electrode was prepared in the same manner as in Example 1-1, except that the concentration of the electrolyte in which the positive electrode structure was immersed was 1.0 M.

[0161] Example 1-6: Preparation of Positive Electrode

[0162] A positive electrode was prepared in the same manner as in Example 1-5, except that the thickness of the lithium metal layer was 3 μm.

[0163] Comparative Example 1-1: Preparation of Positive Electrode

[0164] A positive electrode was prepared in the same manner as in Example 1-1, except that after roll-pressing, the positive electrode was not immersed in the electrolyte but allowed to stand for 24 hours.

[0165] Comparative Example 1-2: Preparation of Positive Electrode

[0166] A positive electrode was prepared in the same manner as in Example 1-6, except that after roll-pressing, the positive electrode was not immersed in the electrolyte but allowed to stand for 24 hours.

[0167] Comparative Examples 1-3: Preparation of the negative electrode

[0168] A transfer laminate was prepared, which included a PET film (base film), a polymer layer (1 μm thick) formed of PMMA provided on the PET film, and a lithium metal layer (3 μm thick, loading of 0.6 mAh / cm 2 ) provided on the polymer layer.

[0169] Silicon particles with an average particle size D 50 of 5 μm were used as the negative electrode active material. A negative electrode was prepared, which included a raw negative electrode active material layer. The raw negative electrode active material layer contained a negative electrode active material, carboxymethyl cellulose (CMC) as a negative electrode binder, and carbon nanotubes as a negative electrode conductive agent in a weight ratio of 80:10:10. The loading of the raw negative electrode active material layer was 10 mAh / cm 2 , and the thickness was 75 μm.

[0170] The transfer laminate was disposed on the raw negative electrode active material layer such that the lithium metal layer was in contact with the raw negative electrode active material layer.

[0171] Then, electrolyte impregnation, washing, and drying were carried out in the same manner as in Example 1-1 to prepare the negative electrode.

[0172] Comparative Examples 1-4: Preparation of the positive electrode

[0173] The positive electrode was prepared in the same manner as in Example 1-5, except that the solvent of the electrolyte impregnating the positive electrode structure was replaced with ethylene carbonate and ethyl methyl carbonate, LiFSI was excluded from the lithium salt, and LiPF6 was used as the lithium salt.

[0174] Experimental Example 1: Over-lithiation reaction and physical property evaluation of the positive electrode

[0175] Images of the cross-sections of the positive electrodes of Example 1-5 and Comparative Example 1-2 were taken at a magnification of x500 using a scanning electron microscope (SEM, JEOL Ltd., JSM-7200F), and the images are as shown in Figure 5 and Figure 6 .

[0176] Referring to Figure 5 the cross-section of the positive electrode of Example 1-5, it can be confirmed that almost no cracks appeared in the active material particles. However, referring to Figure 6 the cross-section image of the positive electrode of Comparative Example 1-2, it can be confirmed that quite a number of cracks were observed in the active material particles near the surface.

[0177] In addition, the thickness of the lithium metal layer in Comparative Example 1-1 was 6 μm, which was thicker than that in Comparative Example 1-2. During the over-lithiation reaction, the phenomenon of partial peeling of the lithium metal layer from the electrode was also observed.

[0178] For the over-lithiation reactions of Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-3, the peak temperature of the reaction, the time to reach the peak temperature, and the total over-lithiation reaction time were measured and are shown in Table 1 below.

[0179] [Table 1]

[0180]

[0181] Referring to Table 1, for Examples 1-1 to 1-6 where over-lithiation was carried out by electrolyte impregnation, it was confirmed that the time required for over-lithiation was significantly shortened compared to the case without electrolyte impregnation. In addition, since pre-lithiation by electrolyte impregnation carried out on the negative electrode as in Comparative Example 1-3 raised the temperature to 60 °C within 10 seconds, the reaction might not proceed further. That is, for the negative electrode, since the reaction occurred explosively, it was confirmed that pre-lithiation could not be applied by this method.

[0182] Preparation of secondary battery

[0183] Example 2-1: Preparation of secondary battery

[0184] Silicon (Si) particles with an average particle size D 50 of 5 μm were used as the negative electrode active material. A negative electrode was prepared, which included a primary negative electrode active material layer containing the negative electrode active material, carboxymethyl cellulose (CMC) as the negative electrode binder, and carbon nanotubes as the negative electrode conductive agent in a weight ratio of 80:10:10. The loading of the primary negative electrode active material layer was 10 mAh / cm 2 , and the thickness was 75 μm.

[0185] The positive electrode of Example 1-1, the above negative electrode, and a porous polyethylene separator were assembled by the winding method, and a primary lithium-ion secondary battery was prepared by injecting an electrolyte (solvent: fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a weight ratio of 3:7, lithium salt: LiPF6 and LiFSI, additives: vinylene carbonate (VC), propylene carbonate (PC), 1,3-propane sultone (PRS)) into the assembled battery.

[0186] The primary lithium-ion secondary battery was charged to 4.2 V at a C rate of 0.1C and then discharged to 2.5 V to carry out the formation process.

[0187] Examples 2-2 to 2-6: Preparation of secondary battery

[0188] The lithium secondary batteries of Examples 2-2 to 2-6 were prepared 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.

[0189] Comparative Examples 2-1, 2-2, and 2-4: Preparation of Secondary Batteries

[0190] The lithium secondary batteries of Comparative Examples 2-1, 2-2, and 2-4 were prepared 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.

[0191] Experimental Example 2: Evaluation of Resistance Characteristics

[0192] The resistance of each lithium secondary battery of Example 2-5 and Comparative Examples 2-1 and 2-4 was measured as follows.

[0193] After charging and discharging the lithium secondary battery, while discharging again after the lithium secondary battery was fully charged, a 2.5C pulse current was applied for a certain period of time according to the change in the state of charge (SOC) to measure the surface resistance (0.1-second resistance), charge transfer resistance (0.1 to 30-second resistance), and diffusion resistance (30-second resistance). The results are shown in Table 2 and Figures 7 to 9 as shown.

[0194] [Table 2]

[0195] Surface resistance (ohm) Charge transfer resistance (ohm) Diffusion resistance (ohm) Examples 2 - 5 0.54 0.64 1.19 Comparative Example 2 - 1 0.47 0.63 1.10 Comparative Example 2 - 4 0.56 0.71 1.25

[0196] Referring to Table 2 and Figures 7 to 9 , since the film formed by electrolyte impregnation on the surface acts as a resistance, it can be confirmed that the resistance of Example 2-5 is slightly increased compared to the resistances of Comparative Examples 2-1 and 2-4. However, it can be understood that the degree of increase in resistance is insignificant compared to the time required for over-lithiation, and since Example 2-5 using a fluorine-based electrolyte is almost at the same level as the case without electrolyte impregnation, it can be predicted that there will be no significant performance degradation due to the increase in resistance.

[0197] Experimental Example 3: Analysis of Positive Electrode and Electrolyte after Cycling

[0198] 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 0.1C in the first and second cycles, and from the third cycle, they were charged and discharged at 0.5C. After a total of 550 cycles, each lithium secondary battery was disassembled, and the surface X-ray photoelectron spectroscopy (XPS) analysis, lithium content analysis of the positive electrode, and component analysis of the electrolyte were performed according to the following methods.

[0199] 1) XPS analysis of the positive electrode surface: Using X-ray photoelectron spectroscopy (XPS) (Nexsa ESCA System, ThermoFisher Scientific (ESCA-02)), the C1s spectrum, O 1s spectrum, and F 1s spectrum were obtained under the conditions of an Al-Kα (1486.6 eV) light source, an acceleration voltage of 1 kV / 300 W, an energy resolution of approximately 1.0 eV, a minimum analysis area of 400 micro, and a sputtering rate of 0.13 nm / min. The intensity values of each peak are listed in Table 3 below. The peak intensity values here are the values obtained by the measuring instrument, without units, and are the relative intensity values of the peaks expressed according to the binding energy.

[0200] 2) Analysis of the lithium content (wt%) in the 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, each lithium secondary battery was disassembled, and the positive electrode excluding the current collector was pulverized. 0.02 g of the above positive electrode powder was added to a mixed solution of 3.0 mL of hydrochloric acid and 0.5 mL of hydrogen peroxide, heated until completely dissolved, 500 μL of an internal standard (Sc) with a concentration of 1000 mg / kg was added, and it was diluted to 50 mL with ultrapure water as the measurement sample. For the measurement sample, the wavelength ratio corresponding to the lithium element was analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES, Perkin Elimner Inc.).

[0201] 3) Analysis of the electrolyte components (wt%): After cycling and disassembling the lithium secondary batteries of Examples 2-1 to 2-6 and Comparative Examples 2-1 and 2-2, the entire disassembled lithium secondary battery was placed in a mixed solution of hydrochloric acid and hydrogen peroxide to fully dissolve the residual compounds deposited on the electrode assembly and the battery case. 3.5 mL of the above solution was collected, 500 μL of an internal standard (Sc) with a concentration of 1000 mg / kg was added, and it was diluted to 50 mL with ultrapure water as the measurement sample. Subsequently, the compound content was analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES, Perkin Elimner Inc.).

[0202] [Table 3]

[0203]

[0204] Referring to Table 3 and Figures 11 to 13 , it can be confirmed 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. For Examples 2-1 to 2-6, from the I C2 values are all lower than those of the comparative examples, and the I C2 value is lower than I C1It can be seen that during the over-lithiation of the positive electrode, by using an electrolyte impregnated with a fluorinated carbonate compound, the carbonate by-products on the surface of the positive electrode can be reduced instead. Typically, the above differences can be passed through Figure 11 be confirmed, Figure 11 shows the XPS results of Examples 2-5 and Comparative Example 2-1.

[0205] In addition, the I of the examples O1 value is also lower than the I of the comparative examples O1 value, where this can ultimately confirm that fewer carbonate products are formed, and their differences can be passed through Figure 13 to be confirmed, Figure 13 typically shows the XPS results of Examples 2-5 and Comparative Example 2-1.

[0206] In addition, for I F2 and I F1 , from I F2 is also lower than I F1 , and the fact that the I of the examples F2 value is lower than that of the comparative examples indicates that in the case of over-lithiation using an electrolyte containing a fluorinated carbonate compound, due to the impregnation of the electrolyte, a film containing LiF is well formed on the surface of the positive electrode, which instead prevents the formation of other by-products, which can be passed through Figure 12 also be confirmed, Figure 12 typically shows the XPS results of Examples 2-5 and Comparative Example 2-1. For reference, during the over-lithiation of the positive electrode, the lithium remaining on the surface reacts with the fluorinated carbonate compound to generate LiF. Among them, for Comparative Example 2-2, since the amount of lithium used for over-lithiation is small, before the electrode assembly is assembled and then impregnated with the electrolyte, no lithium completely penetrates into the positive electrode and remains on the surface, so it can be confirmed that no LiF is detected.

[0207] Experimental Example 4: Evaluation of capacity retention rate and resistance increase rate

[0208] The lithium secondary batteries of Examples 2-1 to 2-6 and Comparative Examples 2-1, 2-2, 2-4 and the lithium secondary battery of the reference example (prepared in the same manner as Example 2-5, except that over-lithiation (lithium transfer and electrolyte impregnation) was not performed) were charged and discharged to measure the capacity and resistance of each secondary battery in each cycle using the following method, and the capacity retention rate and resistance increase rate were calculated as follows, and the results are shown in Table 3 below and Figure 10 in.

[0209] * Capacity retention rate and resistance increase rate: Each secondary battery was charged and discharged at 0.1C in the first and second cycles, and charged and discharged at 0.5C from the third cycle.

[0210] Charging conditions: CC (constant current) / CV (constant voltage) (current cut-off at 5 mV / 0.005C) 4.2 V

[0211] Discharging conditions: CC (constant current) condition 3.27 V

[0212] Capacity retention rate (%) = (discharge capacity after N cycles / initial discharge capacity) × 100

[0213] Rate of increase in resistance (%) = [(resistance after N cycles / initial resistance) - 1] × 100

[0214] [Table 4]

[0215]

[0216] Referring to Table 4 and Figure 10 , for the reference examples using a non-over-lithiated positive electrode, it can be confirmed that the capacity starts to rapidly decline after 200 cycles. However, it can be confirmed that the capacities of Examples 2-1 to 2-6 and Comparative Example 2-1 with over-lithiation remain at a constant level even in subsequent cycles. Additionally, in the case of over-lithiation using a transfer laminate as in Comparative Example 2-1, a better capacity retention rate than that of Example 2-6 was exhibited until about 300 cycles. However, the capacity rapidly declined after 500 cycles. However, for Examples 2-1 to 2-6 with over-lithiation by impregnating with an electrolyte containing a fluorinated carbonate compound, it can be confirmed that the capacity retention rate still remains at an excellent level even after 500 cycles.

[0217] Furthermore, referring to Table 3, it can be confirmed that there is a significant difference in the effect of the rate of increase in resistance between the secondary batteries of the examples and those of the comparative examples. The difference in the increase in resistance starts to appear from the relatively early 200th cycle during cycling, and it can be confirmed that the increase in resistance accelerates by more than twice after 600 cycles. It can be understood that this difference appears due to the suppression of the deterioration of the secondary batteries of the examples.

[0218] [Description of reference numerals]

[0219] 110: Positive electrode current collector

[0220] 120, 120’: Initial positive electrode active material layer

[0221] 300: Transfer laminate

[0222] 310: Base film

[0223] 320: Lithium metal layer

[0224] 330: Polymer layer

[0225] 400: Positive electrode structure

[0226] R: Roller

[0227] R.Ex.: Reference Example

[0228] Ex.: Example

[0229] C.Ex.: Comparative Example

Claims

1. A positive electrode, comprising: A positive electrode active material layer, the positive electrode active material layer containing a positive electrode active material and a carbonate compound containing a fluorine-containing functional group; And A current collector, on which the positive electrode active material layer is provided, Among them, in the C1s spectrum of X-ray photoelectron spectroscopy (XPS) analysis, the peak P at a binding energy of 288 eV to 292 eV C1 The peak intensity I C1 is lower than the peak P at a binding energy of 284 eV to 286 eV C2 The peak intensity I C2 .

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

3. The positive electrode according to claim 1, wherein, In the F1s spectrum analyzed by XPS, the peak P at a binding energy of 687 eV to 689 eV F1 has a peak intensity I F1 lower than the peak intensity I F2 of the peak P at a binding energy of 684 eV to 686 eV F2 .

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

5. The positive electrode according to claim 1, wherein, In the O1S spectrum analyzed by XPS, the peak P at a binding energy of 531 eV to 533 eV O1 with a peak intensity I O1 is 4.00 or less.

6. The positive electrode according to claim 1, wherein, The carbonate compound containing a fluorine-containing functional group includes at least one selected from the group consisting of fluoroethylene carbonate, methyl (2,2,2-trifluoroethyl) carbonate, and ethyl (2,2,2-trifluoroethyl) carbonate.

7. A method for preparing a positive electrode, the method comprising the following steps: Step (S1): Dispose a transfer laminate including a base film and a lithium metal layer provided on the base film on a preliminary positive electrode active material layer to form a positive electrode structure body, such that the lithium metal layer and the preliminary positive electrode active material layer are in contact with each other; And Step (S2): Immerse the positive electrode structure body in an electrolyte containing a carbonate compound containing a fluorine-containing functional group.

8. The method according to claim 7, wherein, The electrolyte further includes a lithium salt, and the concentration of the lithium salt in the electrolyte is greater than 0.1 M and equal to or less than 1.0 M.

9. The method according to claim 7, wherein, The thickness of the lithium metal layer is 1 μm to 10 μm.

10. The method 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. The method according to claim 7, further comprising the following steps between step (S1) and step (S2): Step (S1a): Roll press the positive electrode structure body; And Step (S1b): Remove the base film in the roll-pressed transfer laminate.

12. The method according to claim 11, wherein, The pressure applied to the positive electrode structure body during the roll pressing is 10 kgf / cm to 90 kgf / cm.

13. A lithium secondary battery, comprising: The positive electrode according to claim 1; A negative electrode; And A separator provided between the positive electrode and the negative electrode.

14. A lithium secondary battery, comprising: An electrode assembly, the electrode assembly including: a hyperlithiated positive electrode containing a hyperlithiated positive electrode active material layer; a negative electrode containing silicon (Si) particles as an active material; and a separator provided between the positive electrode and the negative electrode; A battery case accommodating the electrode assembly; and An electrolyte, the electrolyte being injected into the battery case to immerse the electrode assembly and including a carbonate compound containing a fluorine-containing functional group, Wherein, when the amount of lithium based on the total weight of the positive electrode active material layer of the hyperlithiated positive electrode measured by inductively coupled plasma optical emission spectrometry (ICP-OES) is less than 5.0% by weight, The amount of the carbonate compound containing a fluorine-containing functional group based on the total weight of the electrode assembly and the electrolyte measured by inductively coupled plasma optical emission spectrometry (ICP-OES) is 3.5% by weight or more.

15. The lithium secondary battery according to claim 14, wherein, Based on the total weight of the electrode assembly and the electrolyte, the content of the carbonate compound containing a fluorine-containing functional group is 5.0% by weight to 10% by weight.

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