Lithium secondary battery, and battery module and battery pack comprising same

Abstract

The present invention relates to a lithium secondary battery, and a battery module and a battery pack comprising same, the lithium secondary battery comprising: a pre-lithiated negative electrode; and a positive electrode, wherein the lithium secondary battery satisfies a charge capacity N / P ratio (%) represented by formula 1 of 108% or more and 123% or less, thereby ensuring cycle life performance.

Description

Lithium secondary battery, battery module including the same, and battery pack

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2024-0191357 filed with the Korean Intellectual Property Office on December 19, 2024, the entire contents of which are incorporated herein.

[0002] The present invention relates to a lithium secondary battery, a battery module including the same, and a battery pack.

[0003] Due to the rapid increase in the use of fossil fuels, there is a growing demand for alternative or clean energy. As part of this effort, the fields of power generation and energy storage utilizing electrochemical reactions are the most actively researched.

[0004] Currently, a representative example of an electrochemical device utilizing such electrochemical energy is the secondary battery, and its scope of application is steadily expanding.

[0005] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly rising. Among these secondary batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used. Furthermore, active research is being conducted on methods to manufacture high-density electrodes with higher energy density per unit volume for use in such high-capacity lithium-ion batteries.

[0006] Meanwhile, lithium loss begins to occur in lithium secondary batteries from the first charge after manufacturing, and the battery degrades as lithium loss continues, albeit in small amounts, during subsequent charge-discharge cycles and high-temperature storage periods. To compensate for this lithium loss, a pre-lithiation process is applied to additionally inject lithium into the battery before operation.

[0007] The present invention aims to provide a lithium secondary battery capable of preventing lithium plating and ensuring lifespan performance, a battery module including the same, and a battery pack.

[0008] One embodiment of the present specification comprises a pre-lithiated cathode; and an anode, and

[0009] A lithium secondary battery is provided having a charge capacity N / P ratio (%) expressed by the following Equation 1 that is 108% or more and 123% or less.

[0010] [Equation 1] (A - B) / C x 100

[0011] In the above Equation 1,

[0012] A is the charging capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode. 2 ) and,

[0013] B is the pre-lithiation capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode 2 ) and,

[0014] C is the charging capacity of the above anode (mAh / cm²) 2 )am.

[0015] One embodiment of the present specification provides a battery module or battery pack comprising the aforementioned lithium secondary battery.

[0016] Another embodiment of the present specification provides a battery pack comprising the aforementioned battery module.

[0017] Finally, one embodiment of the present specification includes the step of preparing a pre-lithiated cathode; and the step of preparing an anode, and

[0018] A method for manufacturing a lithium secondary battery having a charge capacity N / P ratio (%) expressed by the following formula 1, which is 108% or more and 123% or less.

[0019] [Equation 1] (A - B) / C x 100

[0020] In the above Equation 1,

[0021] A is the charging capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode. 2 ) and,

[0022] B is the pre-lithiation capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode 2 ) and,

[0023] C is the charging capacity of the above anode (mAh / cm²) 2 )am.

[0024] According to one embodiment of the present specification, by having an appropriate N / P ratio considering the charging capacity of the negative electrode reflecting pre-lithiation, it is possible to provide a lithium secondary battery with improved lifespan performance, a battery module and a battery pack including the same, by preventing lithium plating (Li-plating) or resistance increase caused by positive / negative capacity reversal.

[0025] FIG. 1 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment of the present specification.

[0026] FIG. 2 is a flowchart illustrating a method for manufacturing a pre-lithiated cathode according to one embodiment of the present specification.

[0027] Figure 3 is a graph showing the capacity retention rate according to charging and discharging of the embodiments and comparative examples of the present specification.

[0028] Before describing the present invention, we will first define some terms.

[0029] In this specification, when a part is described as "comprising" a certain component, it means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0030] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0031] In this specification, when a part such as a layer is described as being "above" or "on" another part, this includes not only the case where it is "immediately above" another part, but also the case where there is another part in between. Conversely, when a part is described as being "immediately above" another part, it means that there is no other part in between. Furthermore, being described as being "above" or "on" a reference part means being located above or below the reference part, and does not necessarily mean being located "above" or "on" in a direction opposite to gravity.

[0032] In this specification, when it is stated that a certain member is provided on both sides of another member, it means that a certain member is provided on one side of the other member, and a certain member is provided on another side corresponding to said one side. Furthermore, this includes not only cases where a certain member is in direct contact with one side of the other member and the corresponding side, but also cases where another member exists between the two members.

[0033] In this specification, 'p to q' means a range of 'p or more and q or less'.

[0034] In this specification, terms such as “…part,” “device,” etc. refer to a unit that processes at least one function or operation.

[0035] In this specification, "Dn" refers to the particle size distribution and represents the particle size (average particle size) at the n% point of the cumulative distribution of particle numbers according to particle size. That is, D50 is the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size, and D 90 The particle size at the 90% point of the cumulative distribution of particle numbers according to particle size is D 10 is the particle size at the 10% point of the cumulative distribution of the number of particles according to particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction patterns according to particle size is measured as the particles pass through the laser beam to calculate the particle size distribution.

[0036] In one embodiment of the present specification, particle size or particle diameter may refer to the average diameter or representative diameter of each individual grain constituting the metal powder.

[0037] The singular expressions of terms used in this specification include the plural expressions unless the context clearly indicates otherwise.

[0038] Terms or words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0039] Preferred embodiments of the present invention are described in detail below. However, embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.

[0040] Lithium secondary battery

[0041] The researchers of the present invention intend to use a pre-lithiated anode to compensate for irreversible capacity loss by pre-replenishing lithium lost during the charge-discharge process, thereby improving the capacity or cycle performance of the battery. However, since the use of a pre-lithiated anode results in some lithium being pre-charged in the anode, it was recognized that it is important to define the N / P ratio (%), which is one of the key factors that must be considered during battery design, taking this into account.

[0042] Accordingly, the researchers investigated the change in performance according to the charge capacity N / P ratio (%) of a battery using a positive electrode and a pre-lithiated negative electrode, and as a result, derived an appropriate charge capacity N / P ratio (%) reflecting the pre-lithiated capacity and defined it as Equation 1 below.

[0043] A lithium secondary battery according to one embodiment of the present specification comprises a pre-lithiated negative electrode; and a positive electrode, wherein the charge capacity N / P ratio (%) expressed by Formula 1 below is 108% or more and 123% or less.

[0044] [Equation 1] (A - B) / C x 100

[0045] In the above Equation 1,

[0046] A is the charging capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode. 2 ) and,

[0047] B is the pre-lithiation capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode 2 ) and,

[0048] C is the charging capacity of the above anode (mAh / cm²) 2 )am.

[0049] In the present specification, the charging capacity N / P ratio (%) expressed by Equation 1 above refers to the charging capacity N / P ratio (%) of a lithium secondary battery that reflects the pre-lithiation capacity, and represents the charging capacity of the negative electrode that reflects pre-lithiation as a percentage of the charging capacity of the positive electrode. At this time, the charging capacity of the negative electrode that reflects pre-lithiation (A - B) is obtained by subtracting the pre-lithiation capacity (B) from the charging capacity of the pre-lithiated negative electrode (A).

[0050] According to one embodiment of the present specification, the charge capacity N / P ratio (%) expressed by Equation 1 of the lithium secondary battery may be 108% or more and 123% or less, specifically 108.5% or more and 120% or less, and more specifically 110% or more and 119.5% or less.

[0051] If the charge capacity N / P ratio (%) reflecting the pre-lithiation capacity of a lithium secondary battery containing a pre-lithiated cathode is smaller than the above range, positive and negative electrode capacity inversion may occur due to tolerances occurring during the manufacturing process. In the region where positive and negative electrode capacity inversion occurs, overcharging may occur, leading to a phenomenon where unused lithium ions on the surface of the cathode are plated onto the metal (Li-Plating). Consequently, this can lead to the formation of dendrites, which may cause a short circuit and result in rapid degradation of lifespan. If the N / P ratio (%) reflecting the pre-lithiation capacity of the lithium secondary battery exceeds the above range, the Li-Plating phenomenon does not occur, but lifespan performance deteriorates due to increased resistance, and energy density may also be inferior.

[0052] However, the present invention is characterized by compensating for irreversible capacity by including a pre-lithiated cathode, thereby improving the capacity or cycle performance of the battery, while also preventing the lithium plating phenomenon by satisfying the charge capacity N / P ratio (%) within the above range and ensuring lifespan performance.

[0053] In the present specification, the lithium secondary battery may be, for example, a battery immediately after the activation process, but may also be a battery after a certain period of time has elapsed since the time of manufacture.

[0054] A lithium secondary battery according to one embodiment of the present specification has a capacity retention rate of 94% or more after 150 charge-discharge cycles, and during the charge-discharge cycles, charging may be performed at 1C, upper limit voltage 4.35V, constant current / constant voltage mode (CC / CV mode) and cut-off current 0.05C, and discharging may be performed at 5C, lower limit voltage 2.5V, and constant current mode (CC mode).

[0055] In a lithium secondary battery according to one embodiment of the present specification, the capacity retention rate after performing 150 charge-discharge cycles according to the charge-discharge conditions may be 94% or higher, specifically 94.5% or higher, and more specifically 95% or higher. This indicates a lithium secondary battery that exhibits excellent lifespan performance by satisfying an appropriate range of charge capacity N / P ratio (%) according to one embodiment of the present specification.

[0056] A lithium secondary battery according to one embodiment of the present specification comprises a pre-lithiated negative electrode; and a positive electrode, wherein the pre-lithiated negative electrode and the positive electrode will be described later.

[0057] FIG. 1 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment of the present specification. Specifically, a pre-lithiated negative electrode (100) including a negative active material layer (20) on one side of a negative electrode current collector layer (10) can be seen, and a positive electrode (200) including a positive active material layer (40) on one side of a positive electrode current collector layer (50) can be seen, and the pre-lithiated negative electrode (100) and the positive electrode (200) are formed in a structure that is stacked with a separator (30) in between.

[0058] Pre-lithiated cathode

[0059] A lithium secondary battery according to one embodiment of the present specification includes a pre-lithiated negative electrode. In this case, the pre-lithiated negative electrode may have at least one surface of the negative electrode active material layer pre-lithiated, and a method for manufacturing the pre-lithiated negative electrode will be described later.

[0060] In one embodiment of the present specification, the charging capacity (A) (mAh / cm²) of the pre-lithiated negative electrode 2 ) is 3.5mAh / cm 2 6.0mAh / cm or higher 2 It may be less than.

[0061] In the present specification, the charge capacity (A) of the pre-lithiated cathode refers to the maximum charge capacity of the pre-lithiated cathode, and can be measured after fabricating a cathode half-cell with Li metal as the counter electrode, performing CC / CV charging (0.005C Cut) at 0.1C to 0.005V and CC discharging at 0.1C to 1.5V once.

[0062] In one embodiment of the present specification, the charging capacity (mAh / cm²) of the pre-lithiated cathode 2 ) is 3.5mAh / cm 2 6.0mAh / cm or higher 2 It may be less than, specifically 4mAh / cm 2 5.5mAh / cm or higher 2 Below, more specifically 4.2mAh / cm 2Above 4.808mAh / cm² 2 It may be less than.

[0063] The charging capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode 2 If the above range is satisfied, the energy density of the battery can be improved, and excellent fast charging performance can also be secured.

[0064] In addition, in one embodiment of the present specification, the pre-lithiation capacity (B) (mAh / cm²) of the pre-lithiated cathode 2 ) is 0.1mAh / cm 2 1.0mAh / cm or higher 2 It may be less than.

[0065] In this specification, the pre-lithiation capacity (mAh / cm²) 2 ) can be measured as the difference in charging capacity measured by preparing a half-cell of a pre-lithiated cathode and a half-cell of a pristine cathode manufactured in the same way as the pre-lithiated cathode except that pre-lithiation is not applied, and then performing CC / CV charging (0.005C Cut) at 0.1C to 0.005V.

[0066] Specifically, the above half-cells each have the above-mentioned pre-lithiated cathode or the above-mentioned pristine cathode as the working electrode, and 1.7671 cm as the counter electrode. 2 It can be manufactured by using a 100 μm thick lithium metal thin film cut into a circular shape, interposing a polyethylene separator between the working electrode and the counter electrode to manufacture an electrode assembly, then placing the electrode assembly in a coin-type case and injecting an electrolyte.

[0067] The electrolyte used in the manufacture of the above half-cell can be prepared by adding LiPF6 as a lithium salt at a concentration of 1.0 M to an organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:10:70.

[0068] In one embodiment of the present specification, the pre-lithiation capacity (mAh / cm²) of the pre-lithiated cathode 2 ) is 0.1mAh / cm 2 1.0mAh / cm or higher 2 It may be less than, specifically 0.12mAh / cm² 2 Above 0.8mAh / cm 2 Below, more specifically, 0.165mAh / cm 2 0.5mAh / cm or higher 2 It may be less than.

[0069] Pre-lithiation capacity (mAh / cm²) according to one embodiment of the present specification 2 If the above range is satisfied, a lithium secondary battery with excellent capacity and lifespan characteristics can be realized. Specifically, if the pre-lithiation capacity of the negative electrode is too small, it may be difficult to secure sufficient energy density, and if the pre-lithiation capacity of the negative electrode is too large, overcharging may occur due to the occurrence of a positive / negative NP ratio reversal phenomenon, and rapid battery degradation may occur due to the Li-Plating phenomenon.

[0070] In one embodiment of the present specification, the aforementioned pre-lithiated cathode may be pre-lithiated by transferring one surface of the cathode active material layer to a lithium metal layer, and specifically, may be pre-lithiated by transferring at least one surface of the cathode active material layer to a transfer laminate comprising a lithium metal layer and a substrate layer.

[0071] A pre-lithiated cathode according to one embodiment of the present specification is pre-lithiated by a lithium direct contact method on at least one surface of the cathode active material layer to solve the problem of irreversibility and improve Coulomb efficiency. It is characterized by having a lower degree of cell degradation during battery operation and a faster reaction rate compared to pre-lithiation by the SLMP method or electrochemical method. In particular, a dry pre-lithiation process is applied among the lithium direct contact methods, and since pre-lithiation proceeds from the moment the cathode active material layer comes into contact with the lithium metal, pre-lithiation can proceed faster than a wet pre-lithiation process.

[0072] A pre-lithiated negative electrode according to one embodiment of the present specification may be manufactured by a step of transferring a lithium metal layer and a substrate layer into a transfer laminate such that a lithium metal layer contacts at least one surface of the negative electrode active material layer.

[0073] In one embodiment of the present specification, the transfer laminate may include a lithium metal layer. The lithium metal layer is a layer containing lithium metal for pre-lithiating one surface of the electrode active material layer, and may use a commonly used Li metal foil, but is not limited thereto.

[0074] In one embodiment of the present specification, the thickness of the lithium metal layer may be 0.1 μm or more and 15 μm or less, specifically 1 μm or more and 10 μm or less, and more specifically 1 μm or more and 6 μm or less.

[0075] If the thickness of the lithium metal layer satisfies the above range, the irreversible capacity during charging and discharging of the lithium secondary battery can be sufficiently compensated.

[0076] In one embodiment of the present specification, the transfer laminate may include a substrate layer. In this case, the substrate layer is an essential component for supporting a lithium metal layer during the process of preparing the transfer laminate, and may be used without limitation as long as it has the characteristics of being able to withstand process conditions such as a high temperature during the step of depositing the lithium metal layer and preventing the problem of reverse delamination where the lithium metal layer is transferred onto the substrate layer during the process of transferring the transfer laminate.

[0077] In one embodiment of the present specification, the substrate layer may comprise one or more selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate), PMMA, polypropylene, polyethylene, and polycarbonate, specifically may comprise one or more selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), and polyethylene, and more specifically may comprise polyethylene terephthalate (PET).

[0078] In one embodiment of the present specification, the thickness of the substrate layer may be 1 μm or more and 300 μm or less, specifically 5 μm or more and 200 μm or less, and more specifically 10 μm or more and 100 μm or less.

[0079] As the thickness of the above substrate layer satisfies the above range, the transfer of the lithium metal layer to the negative electrode active material layer can occur efficiently, and it has the characteristic of preventing reverse transfer.

[0080] In one embodiment of the present specification, the transfer laminate may be manufactured by any one of the methods of depositing, rolling, and melting the lithium metal layer on one surface of the substrate layer. Specifically, in one embodiment of the present specification, the transfer laminate comprising the lithium metal layer and the substrate layer may be manufactured by any one of the methods of depositing and rolling the lithium metal layer on one surface of the substrate layer, and more specifically, may be manufactured by the method of depositing the lithium metal layer on one surface of the substrate layer.

[0081] In one embodiment of the present specification, the method for depositing the lithium metal layer on one surface of the substrate layer may be selected from Physical Vapor Deposition (PDV) and Chemical Vapor Deposition (CVD). Among the Physical Vapor Deposition methods, Thermal Evaporation may be primarily used, but is not limited thereto, and various deposition methods used in the industry may be used.

[0082] In one embodiment of the present specification, the method of rolling the lithium metal layer onto one surface of the substrate layer may involve contacting a lithium foil onto one surface of the substrate layer and then forming a lithium thin film with a thickness of 10 μm or less through a continuous rolling process.

[0083] That is, according to one embodiment of the present specification, the transfer laminate may have a lithium metal layer and a substrate layer sequentially stacked.

[0084] In one embodiment of the present specification, the transfer laminate may further include a release layer between the lithium metal layer and the substrate layer, specifically, the lithium metal layer, the release layer, and the substrate layer may be sequentially laminated. In this case, the release layer serves as a means to facilitate the removal of the substrate layer after the transfer of the transfer laminate is completed, and can prevent the lithium metal layer from being removed together with the substrate layer when the substrate layer is removed.

[0085] In one embodiment of the present specification, the release layer may be one or more selected from the group consisting of polycarbonate (PC), polydimethylsiloxane (PDMS), polymethylhydrosiloxane (PMHS), polyimide (PI), and polymethylmethacrylate (PMMA); specifically, it may be one or more selected from the group consisting of polycarbonate (PC), polydimethylsiloxane (PDMS), and polymethylmethacrylate (PMMA); more specifically, it may be polymethylmethacrylate (PMMA).

[0086] In one embodiment of the present specification, the thickness of the release layer may be 0.1 μm or more and 5 μm or less, specifically 0.2 μm or more and 3 μm or less, and more specifically 0.5 μm or more and 1 μm or less.

[0087] In one embodiment of the present specification, when the thickness of the release layer satisfies the above range, sufficient release force can be secured, and when the substrate layer is removed after the transfer of the transfer laminate is completed, the release layer may be removed together or may remain on the surface of the lithium metal layer; however, even if it remains on the surface of the lithium metal layer, it does not perform the function of blocking heat release and thus may not accelerate the formation of by-products.

[0088] In one embodiment of the present specification, the release layer may be formed by a coating method, for example, the coating method may be selected from the group consisting of dip coating, spray coating, spin coating, die coating, gravure coating, micro-gravure coating, comma coating, and roll coating, but is not limited thereto, and various coating methods that can be used in the art to form a coating layer may be used.

[0089] A pre-lithiated negative electrode according to one embodiment of the present specification may be manufactured by the steps of: contacting a transfer laminate comprising a lithium metal layer and a substrate layer such that a lithium metal layer contacts at least one surface of a negative electrode active material layer; pressing the negative electrode active material layer contacted by the transfer laminate; aging the negative electrode active material layer contacted by the transfer laminate; and removing the substrate layer from the transfer laminate.

[0090] In one embodiment of the present specification, by pressing the negative electrode active material layer in contact with the transfer laminate, pre-lithiation can proceed more actively in the negative electrode active material layer, and there is an effect of being able to form a thin thickness of the negative electrode despite high energy density.

[0091] At this time, the pressurization step may be performed through a roll pressing process after contacting the transfer laminate such that the lithium metal layer contacts at least one surface of the negative electrode active material layer. That is, in one embodiment of this specification, the step of pressurizing the negative electrode active material layer contacted by the transfer laminate is a step of causing the pre-lithiation reaction between the negative electrode active material layer and the lithium metal layer to occur actively by applying a load through a roller. Since the load is applied in a linear manner as it passes through the roller, the unit is kgf.

[0092] In one embodiment of the present specification, the pressurizing step may be to apply pressure with a load of 10 kgf or more and 600 kgf or less, specifically 100 kgf or more and 500 kgf or less, and more specifically 200 kgf or more and 500 kgf or less.

[0093] In one embodiment of the present specification, when the load in the pressurization step satisfies the above range, pre-lithiation due to transfer can proceed more actively, and simultaneously, since pre-lithiation proceeds to an appropriate range, residual lithium on the surface of the cathode can be minimized and the loss of the added lithium can be minimized. In addition, the thickness of the cathode can be formed thinly despite the high energy density.

[0094] That is, the pressurizing step according to one embodiment of the present specification may involve contacting the transfer laminate so that the lithium metal layer contacts one or both sides of the negative electrode active material layer, and then applying a load within the range and performing the transfer through a roll pressing process; the contacting step and the pressurizing step may be performed sequentially or simultaneously, but there are no limitations thereon.

[0095] For example, when the step of contacting a transfer laminate to one surface of the cathode active material layer and the step of pressing the cathode active material layer contacted by the transfer laminate are performed sequentially, the pre-lithiation reaction may begin from the moment a point of the transfer laminate is contacted at a point on one surface of the cathode active material layer, or the pre-lithiation reaction may begin from the moment a point of the transfer laminate is pressed at a point on the cathode active material layer contacted by the transfer laminate, and there may be a time difference of several seconds to several minutes between the contact step and the pressing step.

[0096] For example, when the step of contacting a transfer laminate to one surface of the cathode active material layer and the step of pressing the cathode active material layer contacted by the transfer laminate are performed simultaneously, the pressing of the point of the cathode active material layer contacted by the transfer laminate may begin at the moment the point of contact with a point of the transfer laminate on one surface of the cathode active material layer begins simultaneously with the moment the transfer laminate begins contact and pressurization begins, and in this case, the pre-lithiation reaction may begin from the moment the contact and pressurization begin, or it may begin after a few seconds to minutes.

[0097] In one embodiment of the present specification, the aging step is a step of storing while a pre-lithiation reaction occurs in which one side of the negative electrode active material layer reacts with a lithium metal layer.

[0098] In one embodiment of the present specification, the aging step may be performed before, simultaneously with, or after the end of the pressurization step, and there are no limitations thereon.

[0099] For example, the aging step may begin a few seconds to minutes before pressurization begins at a point on the negative active material layer in contact with the transfer laminate. In this case, the aging step may begin simultaneously with the step of contacting the transfer laminate, or it may begin within a few seconds to minutes from the contact step. In this case, the pre-lithiation reaction may proceed prior to the pressurization step, and the pressurization step may be a step to promote the pre-lithiation reaction.

[0100] For example, the aging process may begin at the moment when pressure is applied at a point on the negative active material layer in contact with the transfer laminate. In this case, the step of contacting the transfer laminate, the pressure application step, and the aging step may all begin simultaneously, or the pressure application and aging steps may begin within a few seconds to minutes from the contact step.

[0101] For example, the aging may begin from the moment the pressure is terminated at the last point of the negative active material layer in contact with the transfer laminate.

[0102] In one embodiment of the present specification, the aging step may be performed at any one of a temperature between 0°C and 40°C, specifically at any one of a temperature between 10°C and 30°C, and more specifically at any one of a temperature between 20°C and 28°C.

[0103] In one embodiment of the present specification, the aging step may be performed at room temperature, but is not limited to such conditions, and the pre-lithiation reaction rate can be controlled to an appropriate range by controlling the temperature range of the aging step within the said range.

[0104] In one embodiment of the present specification, the aging step may be performed until the pre-lithiation of one surface of the negative electrode active material layer is completed. At this time, whether pre-lithiation is completed can be confirmed by visually observing the color change of the electrode surface. Specifically, it can be confirmed that the surface of the negative electrode, which was silver like lithium metal immediately after lithium transfer, completely changes to the original color of the negative electrode (black) after the pre-lithiation is completed. At this time, since the substrate layer is transparent, the silver color of the lithium metal or the original color of the negative electrode can be confirmed regardless of whether the substrate layer is peeled off.

[0105] In one embodiment of the present specification, the step of removing the substrate layer from the transfer laminate is a step of preventing the release of heat generated by the pre-lithiation reaction, which is an exothermic reaction, from the substrate layer so as not to form by-products on the surface of the cathode where pre-lithiation is completed.

[0106] In one embodiment of the present specification, the step of removing the substrate layer may be performed simultaneously with the termination of the pressurization step, may be performed during the aging step, or may be performed after the pre-lithiation of one side of the negative electrode active material layer is completed, and there are no limitations thereon.

[0107] For example, the removal of the substrate layer may begin simultaneously with the termination of pressurization at a point on the negative electrode active material layer contacted by the transfer laminate. That is, the removal of the substrate layer may begin at that point the moment the point on the negative electrode active material layer contacted by the transfer laminate for pressurization passes the aforementioned roller.

[0108] For example, during the process of aging the negative active material layer in contact with the transfer laminate, the removal of the substrate layer may begin from a point on the transfer laminate. In this case, the step of removing the substrate layer may begin within a few seconds to minutes from the aging step, or the removal of the substrate layer may begin from the last moment when the aging step ends.

[0109] For example, the removal of the substrate layer may begin after the prelithiation of one side of the cathode active material layer is completed. In this case, by performing the process of contacting the transfer laminate with the cathode active material layer, applying pressure, and aging without removing the substrate layer, the chemical reaction between the cathode active material layer and the lithium metal layer can be promoted, thereby suppressing the formation of residual lithium remaining on the electrode surface.

[0110] Specifically, the step of removing the substrate layer according to one embodiment of the present specification may be performed after the pre-lithiation of one surface of the negative electrode active material layer is completed.

[0111] In one embodiment of the present specification, the pre-lithiation may begin with a pre-lithiation reaction between the negative electrode active material layer and the lithium metal layer from the time when the lithium metal layer contacts one surface of the negative electrode active material layer, may begin within a few seconds to minutes from the time when the lithium metal layer contacts, or may begin with a pre-lithiation reaction from the time when the substrate layer begins to be removed.

[0112] In one embodiment of the present specification, the pre-lithiation reaction may be terminated within a few days from the time when the lithium metal layer contacts one surface of the negative electrode active material layer, may be terminated within 24 hours, or may be terminated within minutes to seconds.

[0113] FIG. 2 is a flowchart illustrating a method for manufacturing a pre-lithiated cathode according to one embodiment of the present specification. Specifically, FIG. 2 illustrates a method for manufacturing a pre-lithiated cathode comprising the steps of: contacting a transfer laminate including a lithium metal layer and a substrate layer such that a lithium metal layer contacts one surface of a cathode active material layer (S1); pressing the cathode active material layer contacted by the transfer laminate (S2); aging the cathode active material layer contacted by the transfer laminate (S3); and removing the substrate layer from the transfer laminate (S4).

[0114] At this time, the above method for manufacturing a pre-lithiated cathode may further include a step (not shown) of providing a cathode active material layer on at least one surface of a cathode current collector layer, which may be performed prior to step S1, but there are no limitations thereon.

[0115] In another embodiment of the present specification, the method for manufacturing the lithium secondary battery comprises the steps of: preparing a pre-lithiated negative electrode; and preparing a positive electrode, wherein the charge capacity N / P ratio (%) expressed by Formula 1 below may be 108% or more and 123% or less:

[0116] [Equation 1] (A - B) / C x 100

[0117] In the above Equation 1,

[0118] A is the charging capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode. 2 ) and,

[0119] B is the pre-lithiation capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode 2 ) and,

[0120] C is the charging capacity of the above anode (mAh / cm²) 2 )am.

[0121] In a method for manufacturing a lithium secondary battery according to another embodiment of the present specification, the step of preparing the pre-lithiated negative electrode may include: contacting a transfer laminate comprising a lithium metal layer and a substrate layer such that a lithium metal layer contacts at least one surface of a negative electrode active material layer; pressing the negative electrode active material layer contacted by the transfer laminate; aging the negative electrode active material layer contacted by the transfer laminate; and removing the substrate layer from the transfer laminate, wherein the details of each step may be applied in the same manner as the details regarding the pre-lithiated negative electrode described above.

[0122] In one embodiment of the present specification, the negative active material layer may be formed by applying and drying a negative slurry on at least one surface of the negative current collector layer.

[0123] In one embodiment of the present specification, the cathode slurry may comprise a cathode active material layer composition; and a slurry solvent.

[0124] In one embodiment of the present specification, the solid content of the cathode slurry may satisfy a range of 5% or more and 40% or less, specifically 7% or more and 35% or less, and more specifically 10% or more and 30% or less.

[0125] The solid content of the above-mentioned cathode slurry may refer to the content of the cathode active material layer composition included in the above-mentioned cathode slurry, and may refer to the content of the cathode active material composition based on 100 parts by weight of the cathode slurry.

[0126] When the solid content of the above cathode slurry satisfies the above range, the viscosity is suitable when forming the cathode active material layer, thereby minimizing particle aggregation of the cathode active material layer composition and enabling the cathode active material layer to be formed efficiently.

[0127] In one embodiment of the present specification, the slurry solvent is not limited thereto as long as it can dissolve the cathode active material layer composition, and for example, the slurry solvent may be water (e.g., distilled water) or NMP.

[0128] According to one embodiment of the present specification, a negative active material layer can be formed by applying and drying the negative slurry on a negative current collector layer, and the slurry solvent in the negative slurry can be dried through the drying step.

[0129] In one embodiment of the present specification, the negative electrode active material layer composition may include a negative electrode active material described below; a negative electrode conductive material; and a negative electrode binder, and the negative electrode active material may include one or more of a carbon-based active material and a silicon-based active material.

[0130] In other words, the pre-lithiated cathode according to one embodiment of the present specification may include one or more of a carbon-based active material and a silicon-based active material as a cathode active material.

[0131] According to one embodiment of the present specification, the pre-lithiated negative electrode comprises one or more of a carbon-based active material and a silicon-based active material as a negative electrode active material, and the silicon-based active material may comprise one or more selected from the group consisting of Si, silicon oxide, Si / C, and Si alloy.

[0132] Specifically, in one embodiment of the present specification, the silicon-based active material may comprise one or more selected from the group consisting of Si and silicon oxide, and more specifically, the silicon-based active material may comprise Si.

[0133] In one embodiment of the present specification, the silicon-based active material may particularly use pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material means that, when the silicon-based active material is based on 100 parts by weight of the total as described above, pure Si particles that are not combined with other particles or elements are included in the above range.

[0134] In one embodiment of the present specification, the average particle size (D) of the silicon-based active material is, 50 The average particle size (D) can be 1 μm to 10 μm, specifically 2 μm to 8 μm, and more specifically 3 μm to 7 μm. 50 If ) is below the above lower limit range, the specific surface area of ​​the silicon-based active material increases excessively, which may cause the viscosity of the cathode slurry to rise excessively, and as a result, the dispersion of the particles constituting the cathode slurry may not be smooth. In addition, the average particle size (D) of the silicon-based active material 50 If ) is excessively small, the contact area between the cathode active material and the conductive materials by the composite composed of the conductive material and the binder within the cathode slurry decreases, thereby increasing the likelihood of the conductive network being disconnected and potentially lowering the capacity retention rate. Meanwhile, the above average particle size (D 50 If ) exceeds the upper limit range, the presence of excessively large silicon-based active materials results in an uneven surface of the negative electrode, which may cause non-uniform current density during charging and discharging. In addition, the average particle size (D) of the silicon-based active material 50 If ) is excessively large, the phase stability of the cathode slurry becomes unstable, which reduces processability and may lower the capacity retention rate of the battery.

[0135] Meanwhile, although attempts to apply silicon-based active materials are increasing due to their significantly higher capacity compared to conventionally used graphite-based active materials, their high volume expansion rate during the charging and discharging process reduces the battery's lifespan; therefore, to suppress this, the negative electrode active material according to one embodiment of the present specification may be used by mixing the silicon-based active material with the carbon-based active material.

[0136] In one embodiment of the present specification, the carbon-based active material may comprise one or more selected from the group consisting of graphite such as natural graphite or artificial graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerene, and activated carbon, and specifically, may comprise one or more selected from the group consisting of natural graphite and artificial graphite.

[0137] When the carbon-based active material is used as the negative electrode active material according to one embodiment of the present specification, reversible intercalation and extraction of lithium ions are possible, and structural and electrical properties can be maintained. Among these, the graphite-based active material can guarantee the lifespan characteristics of the battery due to its excellent reversibility. Since the discharge voltage of the graphite-based active material is low at -0.2V compared to lithium, a battery using the graphite-based active material can exhibit a high discharge voltage of 3.6V, thereby providing many advantages in terms of energy density of the lithium secondary battery.

[0138] In one embodiment of the present specification, when artificial graphite is used as the carbon-based active material, the degree of orientation during electrode rolling is relatively low, so the lithium ion inflow / outflow characteristics are good, resulting in excellent rapid charging performance of the battery, and the degree of expansion due to charging and discharging is low, so the lifespan characteristics can be excellent.

[0139] In one embodiment of this specification, when natural graphite is used as a carbon-based active material, the output and capacity of the lithium secondary battery are improved, and since the adhesive strength is excellent, a high-capacity, high-density negative electrode can be realized while reducing the amount of binder used. The natural graphite may generally be in the form of plate-like aggregates prior to processing, and the plate-like particles may be manufactured into a spherical shape with a smooth surface through post-processing, such as particle grinding and reassembly, in order to be used as an active material for electrode manufacturing.

[0140] In one embodiment of the present specification, the pre-lithiated negative electrode comprises a carbon-based active material and a silicon-based active material as negative electrode active materials, the carbon-based active material comprises one or more selected from the group consisting of natural graphite and artificial graphite, and the silicon-based active material may comprise Si.

[0141] In one embodiment of the present specification, the pre-lithiated negative electrode comprises a carbon-based active material and a silicon-based active material as negative electrode active materials, and the silicon-based active material may be included in an amount of 50 parts by weight or less with respect to 100 parts by weight of the total negative electrode active material, specifically 40 parts by weight or less, and more specifically 30 parts by weight or less.

[0142] In one embodiment of the present specification, the negative electrode active material may include the carbon-based active material and the silicon-based active material in a weight ratio of 95:5 to 50:50, specifically 90:10 to 60:40, and more specifically 85:15 to 70:30.

[0143] In one embodiment of the present specification, when the carbon-based active material is used in an amount greater than that of the silicon-based active material, a high capacity can be secured due to the high specific capacity of the silicon-based active material while minimizing the reduction in lifespan caused by battery expansion during charging and discharging.

[0144] In one embodiment of the present specification, the negative electrode active material may be included in an amount of 60 parts by weight or more and 99 parts by weight or less based on 100 parts by weight of the aforementioned negative electrode active material layer composition, specifically in an amount of 70 parts by weight or more and 98 parts by weight or less, and more specifically in an amount of 80 parts by weight or more and 97 parts by weight or less.

[0145] In one embodiment of the present specification, the cathode conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0146] Specifically, according to one embodiment of the present specification, the cathode conductive material may be a linear conductive material, and more specifically, a single-walled CNT may be used.

[0147] In one embodiment of the present invention, the content of the cathode conductive material may be 0.01 to 20 parts by weight, specifically 0.03 to 10 parts by weight, and more specifically 0.03 to 5 parts by weight, based on 100 parts by weight of the cathode active material layer composition.

[0148] In one embodiment of the present specification, the cathode binder may serve to improve adhesion between cathode active material particles and adhesion between the cathode active material particles and the cathode current collector. The above-mentioned cathode binder may include those known in the art, and non-limiting examples may include at least one selected from the group consisting of polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylamide, and materials in which hydrogens thereof are substituted with Li, Na, or Ca, etc., and may also include various copolymers thereof.

[0149] In particular, the binder according to one embodiment of the present specification serves to hold the cathode active material and the cathode conductive material to prevent distortion and structural deformation of the cathode structure during volume expansion and relaxation of the silicon-based active material. Any general cathode binder that satisfies the above role can be applied, and specifically, styrene butadiene rubber (SBR) and CMC can be used.

[0150] In one embodiment of the present invention, the content of the cathode binder may be 1 to 30 parts by weight, specifically 2 to 20 parts by weight, and more specifically 3 to 10 parts by weight, relative to 100 parts by weight of the cathode active material layer composition.

[0151] In one embodiment of the present specification, the negative current collector layer may generally have a thickness of 1 μm to 100 μm. Such a negative current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy may be used. In addition, fine irregularities may be formed on the surface to strengthen the bonding strength of the negative active material, and it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0152] <Polar>

[0153] A lithium secondary battery according to one embodiment of the present specification includes a positive electrode.

[0154] In one embodiment of the present specification, the charging capacity (C) (mAh / cm²) of the anode is given. 2 ) is 3.0mAh / cm 2 4.5mAh / cm or higher 2 It may be less than.

[0155] In the present specification, the charging capacity (C) of the anode refers to the maximum charging capacity, and can be measured after manufacturing an anode half-cell with Li metal as the counter electrode, performing CC / CV charging (0.005C Cut) to 4.4V at 0.1C and CC discharging to 3V at 0.1C once, and the method for manufacturing the anode half-cell may be the same as the method for manufacturing the pre-lithiated cathode half-cell.

[0156] In one embodiment of the present specification, the charging capacity (mAh / cm²) of the anode is given. 2 ) is 3.0mAh / cm 2 4.5mAh / cm or higher 2 It may be less than, specifically 3.5mAh / cm 2 4.0mAh / cm or higher 2Below, more specifically 3.7mAh / cm 2 Above 3.9mAh / cm 2 It may be less than or equal to the above. When the charging capacity of the anode satisfies the above range, the charging capacity N / P ratio within an appropriate range according to one embodiment of the present specification can be satisfied, thereby ensuring excellent lifespan performance.

[0157] In one embodiment of the present specification, the positive electrode may have a positive active material layer formed thereon comprising a positive active material on at least one surface of the positive electrode current collector layer, and specifically, the positive active material layer may be formed by applying and drying a positive electrode slurry containing a positive active material on at least one surface of the positive electrode current collector layer.

[0158] In one embodiment of the present specification, the anode may comprise a lithium complex transition metal compound as an anode active material, which comprises nickel (Ni) and cobalt (Co) and further comprises one or more elements selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr.

[0159] In one embodiment of the present specification, the anode may include a lithium complex transition metal compound comprising nickel (Ni), cobalt (Co), and manganese (Mn) as the anode active material.

[0160] In one embodiment of the present specification, the positive active material may be included in an amount of 60 parts by weight or more and 99 parts by weight or less based on 100 parts by weight of the positive active material layer, specifically 70 parts by weight or more and 98 parts by weight or less, and more specifically 80 parts by weight or more and 97.5 parts by weight or less.

[0161] In one embodiment of the present specification, the anode slurry comprises an anode conductive material and an anode binder, and may further comprise a thickener and a slurry solvent.

[0162] In one embodiment of the present specification, additional components such as the anode current collector layer, anode conductive material, anode binder, thickener and slurry solvent, and the method for manufacturing the anode may be used without limitation as long as they are known in the art within the scope to which the above description applies.

[0163] A lithium secondary battery according to one embodiment of the present specification may further comprise a separator provided between a positive electrode and a pre-lithiated negative electrode; and an electrolyte.

[0164] In one embodiment of the present specification, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It may be used without special limitations as long as it is typically used as a separator in a secondary battery, and it is particularly desirable that it has low resistance to the movement of ions in the electrolyte and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0165] In one embodiment of the present specification, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0166] The above-mentioned non-aqueous organic solvents include, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, fluoroethylene carbonate (FEC), butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, etc. Aprotic organic solvents can be used.

[0167] In particular, among the above carbonate-based organic solvents, ethylene carbonate and ethylmethyl carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts, so they can be used preferably. Furthermore, if low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed with these cyclic carbonates in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making it even more preferable to use.

[0168] In one embodiment of the present specification, the electrolyte may be ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 20:10:70.

[0169] The metal salt mentioned above may be a lithium salt, and the lithium salt is a substance that dissolves well in the non-aqueous electrolyte; for example, 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 - One or more selected from the group consisting of may be used, and specifically, LiPF6 may be used as the lithium salt.

[0170] In addition to the components of the above electrolyte, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0171] According to another embodiment of the present specification, a battery module or battery pack including the lithium secondary battery may be provided.

[0172] According to another embodiment of the present specification, a battery pack including the battery module can be provided.

[0173] According to another embodiment of the present specification, a battery module comprising the lithium secondary battery as a unit cell, a battery pack comprising the same, and a battery pack comprising the lithium secondary battery may be provided. Since the battery module and the battery pack include the lithium secondary battery having high capacity, high rate capability and cycle capability, they may be used as a power source for medium-to-large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0174] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the above embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the description, and that such variations and modifications fall within the scope of the appended claims.

[0175] Preparation Example

[0176] Example 1

[0177] 1. Preparation of pre-lithiated cathode

[0178] As a negative electrode active material, Si (average particle size (D 50 A cathode slurry was prepared by including 16 kg (96.33 parts by weight) of graphite in a ratio of 15:85, 0.4 kg (2.41 parts by weight) of SBR (styrene butadiene rubber) and 0.2 kg (1.2 parts by weight) of CMC (carboxymethyl cellulose) as binders, and additionally including 0.01 kg (0.06 parts by weight) of single-walled CNT as a conductive material.

[0179] The above cathode slurry is placed on a copper foil (thickness: 8 μm) with a charge capacity of 4.808 mAh / cm² per unit area. 2 A cathode active material layer was prepared by coating and drying to achieve this.

[0180] A release layer was formed by coating a solution containing polymethylmethacrylate (PMMA) on one side of a polyethylene terephthalate (PET) substrate layer, and a lithium metal layer with a thickness of 1 μm was deposited on top of it by physical vapor deposition (PVD) to manufacture a transfer laminate.

[0181] Subsequently, after contacting the transfer laminate in a dry room so that the lithium metal layer faces the upper part of the negative electrode active material layer, 4.2 kgf / cm² 2 When pressurized to the pressure, the total lithium capacity (B) is 0.165 mAh / cm² 2 A pre-lithiated cathode was manufactured.

[0182] 2. Manufacture of cathode half-cell

[0183] A cathode half-cell was manufactured to measure the charge capacity (A) and pre-lithiation capacity (B) of the pre-lithiated cathode.

[0184] Specifically, the pre-lithiated cathode prepared above is used as the working electrode, and 1.7671 cm is used as the counter electrode. 2 An electrode assembly was manufactured by using a 100 μm thick lithium metal thin film cut into a circular shape and interposing a polyethylene separator between the working electrode and the counter electrode.

[0185] In addition, an electrolyte was prepared by adding LiPF6 as a lithium salt at a concentration of 1.0 M to an organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:10:70.

[0186] The above electrode assembly was placed in a coin-type case, and the prepared electrolyte was injected to manufacture the coin-type cathode half-cell of Example 1.

[0187] - Method for measuring the charge capacity (A) of the pre-lithiated cathode: For the cathode half-cell of Example 1 prepared above, the charge capacity was measured after charging at 0.1C to 0.005V (0.005C Cut) and discharging at 0.1C to 1.5V once using an electrochemical charge / discharger.

[0188] - Method for measuring pre-lithiation capacity (B): Calculated as the difference between the charging capacity measured by charging the cathode half-cell of Example 1 prepared above to 0.005V at CC / CV (0.005C Cut) at 0.1C and the charging capacity measured by the same method for a pristine cathode half-cell prepared in the same way as the cathode half-cell of Example 1, except that pre-lithiation was not performed.

[0189] 3. Manufacture of the anode

[0190] LiNi as a positive electrode active material 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D 50 20 kg (97.3 parts by weight) of 4.6 μm), 0.25 kg (1.2 parts by weight) of carbon black as a conductive material, and 0.3 kg (1.5 parts by weight) of polyvinylidene fluoride (PVDF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming an anode slurry to prepare an anode slurry.

[0191] As an anode current collector, the above anode slurry is applied to both sides of an aluminum current collector (thickness: 15 μm) with a charge capacity (C) per unit area of ​​3.896 mAh / cm² 2 An anode (thickness: 130 μm) was prepared by coating and drying to achieve this.

[0192] 4. Manufacture of anode half-cells

[0193] An anode half-cell was manufactured to measure the charging capacity (C) of the anode.

[0194] Except for using the anode prepared above as the working electrode, an anode half-cell was prepared in the same manner as the preparation of the cathode half-cell in 2. above.

[0195] - Method for measuring positive charge capacity (C): For the positive half-cell of Example 1 prepared above, the charge capacity was measured after charging with CC / CV at 0.1C to 4.4V (0.005C Cut) and discharging with CC at 0.1C to 3V once using an electrochemical charge / discharger.

[0196] 5. Manufacturing of lithium secondary battery full cells

[0197] A full-cell lithium secondary battery was manufactured by interposing a polyethylene separator between the above-mentioned pre-lithiated cathode and the above-mentioned anode and injecting an electrolyte.

[0198] The above electrolyte is prepared by adding LiPF6 as a lithium salt at a concentration of 1.0 M to an organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:10:70.

[0199] Example 2

[0200] Except for using a lithium metal layer with a thickness of 2 μm to pre-lithiate the pre-lithiated cathode charge capacity (A), pre-lithiation capacity (B), and anode charge capacity (C) to satisfy Table 1 below, the cathode half-cell, anode half-cell, and lithium secondary battery full cell of Example 2 were manufactured in the same manner as Example 1.

[0201] Example 3

[0202] Except for using a lithium metal layer with a thickness of 3 μm to pre-lithiate the pre-lithiated cathode charge capacity (A), pre-lithiation capacity (B), and anode charge capacity (C) to satisfy Table 1 below, the cathode half-cell, anode half-cell, and lithium secondary battery full cell of Example 3 were manufactured in the same manner as Example 1.

[0203] Comparative Example 1

[0204] Except for not applying pre-lithiation to the cathode, the cathode half-cell, anode half-cell, and lithium secondary battery full cell of Comparative Example 1 were manufactured in the same manner as in Example 1.

[0205] Comparative Example 2

[0206] The cathode slurry of Example 1 has a charge capacity of 4.226 mAh / cm² per unit area. 2 A negative electrode active material layer was prepared by coating and drying to achieve the desired result, and a lithium metal layer with a thickness of 1 μm was used to pre-lithiate the negative electrode so that the pre-lithiated negative electrode's charge capacity (A), pre-lithiation capacity (B), and positive electrode charge capacity (C) satisfy the values ​​in Table 1 below. Except for this, a negative electrode half-cell, a positive electrode half-cell, and a lithium secondary battery full cell of Comparative Example 2 were prepared in the same manner as in Example 1.

[0207] Comparative Example 3

[0208] The cathode slurry of Example 1 has a charge capacity of 4.226 mAh / cm² per unit area. 2 A negative electrode active material layer was prepared by coating and drying to achieve the desired result, and a lithium metal layer with a thickness of 2 μm was used to pre-lithiate the negative electrode so that the pre-lithiated negative electrode's charge capacity (A), pre-lithiation capacity (B), and positive electrode charge capacity (C) satisfy the values ​​in Table 1 below. Except for this, a negative electrode half-cell, a positive electrode half-cell, and a lithium secondary battery full cell of Comparative Example 3 were prepared in the same manner as in Example 1.

[0209] The charging capacity (A), anode charging capacity (C), and pre-lithiation capacity (B) of the pre-lithiated cathode measured in Examples 1 to 3 and Comparative Examples 1 to 3 above are listed in Table 1 below.

[0210] In addition, since the charging capacity (A) of the pre-lithiated cathode obtained above is a capacity that includes the pre-lithiation capacity (B), the charging capacity of the cathode alone reflecting pre-lithiation was calculated (A - B) and listed in Table 1 below.

[0211] Total Lithium Capacity (B) (mAh / cm²) 2 )Positive charging capacity (C)(mAh / cm²) 2 Pre-lithiated cathode charging capacity (A) (mAh / cm²) 2 ) Pre-lithiation reflected cathode charging capacity (A - B) (mAh / cm² 2 Example 10.1653.8964.8084.643 Example 20.3303.8964.8084.478 Example 30.4953.8964.8084.313 Comparative Example 103.8964.8084.808 Comparative Example 20.1653.8964.2264.051 Comparative Example 30.3303.8964.2263.896

[0212] Experimental Example: Evaluation of Capacity Retention Rate of Lithium Secondary Battery (Full Cell)

[0213] The charging capacity (A), anode charging capacity (C), and pre-lithiation capacity (B) of the pre-lithiated cathode measured in Examples 1 to 3 and Comparative Examples 1 to 3 were substituted into Equation 1 below to calculate the charging capacity N / P ratio (%), which is shown in Table 2 below.

[0214] [Equation 1] (A - B) / C x 100

[0215] In addition, a lifespan evaluation was conducted on the lithium secondary battery full cells of Examples 1 to 3 and Comparative Examples 1 to 3. Specifically, each full cell was charged using an electrochemical charge / discharger with a charge of 1C, an upper limit voltage of 4.35V, a constant current / constant voltage mode (CC / CV mode), and a cut-off current of 0.05C, and discharged with a discharge of 5C, a lower limit voltage of 2.5V, and a constant current mode (CC mode) up to 150 cycles to measure the capacity retention rate, which is shown in Table 2 and Figure 3 below.

[0216] Capacity retention rate (%) = {(Discharge capacity at the Nth cycle) / (Discharge capacity at the 1st cycle)} x 100 %.

[0217] Pre-lithiation reflected cathode charging capacity (A - B) (mAh / cm²) 2)Positive charging capacity (C)(mAh / cm²) 2 ) Charging Capacity N / P Ratio (%) Capacity Retention Rate (%) @ 150 cycles Example 1 4.64 3.896 119.17 95.43 Example 2 4.47 8.896 114.94 96.84 Example 3 4.31 3.896 110.70 98.24 Comparative Example 1 4.80 8.896 123.41 93.63 Comparative Example 2 4.05 1.896 103.98 73.02 Comparative Example 3 3.896 3.896 100 58.98

[0218] According to Table 2 and Figure 3, in the case of the full cell of Comparative Example 1 having a value exceeding the range of the charging capacity N / P ratio (%) expressed by Equation 1, it can be seen that although the lithium plating phenomenon did not occur, the energy loss increased due to the increase in resistance and the lifespan performance was degraded.

[0219] In the case of the full cells of Comparative Examples 2 and 3 having a value below the range of the charging capacity N / P ratio (%) expressed by Equation 1 above, it can be confirmed that a rapid degradation of lifespan occurred as a result of the positive / negative capacity reversal caused by tolerances occurring during the process, and overcharging occurred in the region where the positive / negative capacity reversal occurred, causing unused lithium ions on the surface of the negative electrode to be plated onto metal (Li-Plating).

[0220] However, it can be confirmed that the full cells of Examples 1 to 3, which satisfy the range of the charging capacity N / P ratio (%) expressed by Equation 1 according to one embodiment of the present specification, do not exhibit lithium plating phenomena when compared to the full cells of Comparative Examples 1 to 3, which do not satisfy the range, and also secure appropriate resistance, resulting in excellent lifespan performance.

[0221] In conclusion, a lithium secondary battery according to one embodiment of the present specification can secure excellent lifespan performance by preventing lithium plating or resistance increase caused by positive / negative capacity reversal, by satisfying a charge capacity N / P ratio (%) expressed by Equation 1, which is defined by considering the charge capacity of the negative electrode reflecting pre-lithiation, of 108% or more and 123% or less.

[0222]

[0223] [Explanation of the symbol]

[0224] 10: Cathode current collector layer

[0225] 20: Cathode active material layer

[0226] 30: Separator

[0227] 40: Positive active material layer

[0228] 50: Positive current collector layer

[0229] 100: Pre-lithiated cathode

[0230] 200: Anode

Claims

1. A pre-lithiated cathode; and a positive electrode, comprising, A lithium secondary battery having a charge capacity N / P ratio (%) expressed by Equation 1 below of 108% or more and 123% or less: [Equation 1] (A - B) / C x 100 In the above Equation 1, A is the charge capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode. 2 ) and, B is the pre-lithiation capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode 2 ) and, C is the charging capacity of the above anode (mAh / cm²) 2 )am.

2. In Claim 1, The charging capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode 2 ) is 3.5mAh / cm 2 6.0mAh / cm or higher 2 A lithium secondary battery that is less than or equal to the following.

3. In Claim 1, Pre-lithiation capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode 2 ) is 0.1mAh / cm 2 1.0mAh / cm or higher 2 A lithium secondary battery that is less than or equal to the following.

4. In Claim 1, The above lithium secondary battery has a capacity retention rate of 94% or higher after 150 charge-discharge cycles, and A lithium secondary battery in which, when performing the above charge-discharge cycle, charging is performed at 1C, upper limit voltage 4.35V, constant current / constant voltage mode (CC / CV mode) and cut-off current 0.05C, and discharging is performed at 5C, lower limit voltage 2.5V, and constant current mode (CC mode).

5. In Claim 1, The above-mentioned pre-lithiated cathode comprises a carbon-based active material and a silicon-based active material as cathode active materials, and A lithium secondary battery comprising 50 parts by weight or less of the silicon-based active material based on 100 parts by weight of the total negative electrode active material.

6. In Claim 1, The above-mentioned pre-lithiated cathode is a lithium secondary battery in which one side of the cathode active material layer is transferred to a lithium metal layer to achieve pre-lithiation.

7. A battery module comprising a lithium secondary battery according to any one of claims 1 to 6.

8. A battery pack comprising a lithium secondary battery according to any one of claims 1 to 6.

9. A battery pack comprising a battery module according to claim 7.

10. A step of preparing a pre-lithiated cathode; and a step of preparing an anode, comprising, Method for manufacturing a lithium secondary battery having a charge capacity N / P ratio (%) expressed by the following Equation 1 that is 108% or more and 123% or less: [Equation 1] (A - B) / C x 100 In the above Equation 1, A is the charge capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode. 2 ) and, B is the pre-lithiation capacity (mAh / cm²) of the above-mentioned pre-lithiated cathode 2 ) and, C is the charging capacity of the above anode (mAh / cm²) 2 )am.

11. In Claim 10, The step of preparing the above-mentioned pre-lithiated cathode A step of contacting a transfer laminate comprising a lithium metal layer and a substrate layer such that a lithium metal layer contacts at least one surface of a negative electrode active material layer; A step of pressurizing the negative active material layer in contact with the above-mentioned transfer laminate; A step of aging the negative active material layer in contact with the above-mentioned transfer laminate; and A method for manufacturing a lithium secondary battery comprising the step of removing the substrate layer from the above-described transfer laminate.

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