Anode for lithium secondary battery, method for preparing same, and lithium secondary battery comprising same

Abstract

The present invention relates to an anode for a lithium secondary battery, a method for preparing same, and a lithium secondary battery comprising same, the anode comprising: a current collector; and a protective layer positioned on the current collector, wherein the protective layer contains magnesium nitride (Mg3N2), amorphous carbon, and a binder.

Description

Negative electrode for a lithium secondary battery, method for manufacturing the same, and lithium secondary battery including the same

[0001] The present invention relates to a negative electrode for a lithium secondary battery comprising a protective layer containing magnesium nitride (Mg3N2) and amorphous carbon, a method for manufacturing the same, and a lithium secondary battery comprising the same.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0190990, filed on December 19, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Due to the recent rapid advancements in portable electronic devices, electric vehicles, and renewable energy storage systems, the demand for batteries with high energy density and high performance is surging. While lithium-ion batteries are widely used for their high energy density and long lifespan, they face limitations such as safety concerns, the limited supply of lithium resources, and the need to improve energy density.

[0005] To address these issues, interest in alternative energy storage systems is growing, and the development of anode-less (or anode-free) batteries is receiving particular attention. Anode-less batteries can increase energy density and simplify battery design by eliminating or minimizing the negative electrode material. In this structure, lithium metal is directly plated onto the current collector during charging, reducing the amount of inert material and improving the overall energy density of the cell.

[0006] However, direct plating of lithium metal faces several challenges, including dendrite formation, low Coulomb efficiency, and safety issues. Dendrites grow as needle-shaped crystals on the surface of lithium metal and can cause internal short circuits, leading to battery performance degradation and safety problems. Therefore, technological development is required for stable plating and uniform growth of lithium metal.

[0007] Therefore, there is a need for a cathode-free electrode technology that can improve the performance and safety of batteries through stable plating of lithium metal and suppression of dendrite formation.

[0008]

[0009] The technical problem that the present invention aims to solve is to provide a negative electrode for a lithium secondary battery that has excellent charge / discharge efficiency due to improved lithium ion conductivity and excellent durability due to high bonding strength of the protective layer.

[0010] Another technical problem that the present invention aims to solve is to provide a method for manufacturing a cathode for a lithium secondary battery that can provide a cathode having the aforementioned advantages and improve the productivity of said cathode.

[0011] Another technical problem that the present invention aims to solve is to provide a lithium secondary battery with improved charge / discharge efficiency and lifespan characteristics by including a negative electrode for a lithium secondary battery having the aforementioned advantages.

[0012]

[0013] A negative electrode for a lithium secondary battery according to one embodiment of the present invention comprises a current collector; and a protective layer located on the current collector; wherein the protective layer contains magnesium nitride (Mg3N2), amorphous carbon, and a binder, and as a result of performing X-ray diffraction (XRD) analysis on the protective layer, it can satisfy the following Equation 1.

[0014] [Equation 1]

[0015] 0.5 < I(Mg3N2) / I(Carbon) < 2.0

[0016] (In Equation 1, I(Mg3N2) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 41 to 43 during XRD analysis, and I(Carbon) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 24 to 26 during XRD analysis.)

[0017] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the content of magnesium nitride (Mg3N2) may be 10% by weight or more and 80% by weight or less, based on 100% of the total weight of the protective layer.

[0018] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the bonding strength of the protective layer may be 150 to 800 mN / cm.

[0019] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the thickness of the protective layer may be 1 to 20 μm.

[0020] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, a lithium-affinity metal layer is further included between the current collector and the protective layer, and the lithium-affinity metal layer comprises at least one of Ag, Au, Sn, Al, Zn, Si, Ge, Ni, Co, Fe, Ti, Mo, and Cr, and the thickness of the lithium-affinity metal layer may be 5 to 500 nm.

[0021] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the lithium affinity metal layer contains Ag, and as a result of performing X-ray diffraction (XRD) analysis on the protective layer, the following Equation 2 can be satisfied.

[0022] [Equation 2]

[0023] 0.5 < I(Mg3N2) / I(Ag) < 2.0

[0024] (In Equation 2, I(Mg3N2) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 41 to 43 during XRD analysis, and I(Ag) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 37 to 39 during XRD analysis.)

[0025] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, when EDS analysis is performed on the surface of the negative electrode, the average diameter of the Mg clusters confirmed may be 0.1 to 15 μm.

[0026] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the magnesium nitride (Mg3N2) is a plate-shaped particle, and the average particle size of the plate-shaped particle may be 0.2 to 15 μm.

[0027] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the binder is a non-aqueous binder, and the non-aqueous binder may include at least one selected from PVDF (polyvinylidene fluoride), PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), PTFE (polytetrafluoroethylene), PAI (polyamideimide), PEO (polyethylene oxide), PANI (polyaniline), PDO (polypyrrole), and polythiophene.

[0028] A method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention comprises the steps of: preparing a current collector; and forming a protective layer by applying a coating slurry containing magnesium nitride (Mg3N2), amorphous carbon, and a binder on at least one surface of the current collector; and may satisfy the following formula 3.

[0029] [Equation 3]

[0030] 0.16<[Mg3N2] / (T+P)<0.35

[0031] (In Equation 3, [Mg3N2] represents the input amount of magnesium nitride (Mg3N2) (in weight% units) based on 100% of the total weight of magnesium nitride (Mg3N2) and amorphous carbon during the protective layer formation stage, T represents the temperature (°C) at which the coating slurry is dried after application during the protective layer formation stage, and P represents the drying time (min) after application of the coating slurry during the protective layer formation stage; the units of the calculated values ​​in Equation 3 are not considered.)

[0032] In a method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention, the amount of magnesium nitride (Mg3N2) added in the protective layer forming step may be greater than 20% by weight and less than or equal to 70% by weight, based on 100% of the total weight of magnesium nitride (Mg3N2) and amorphous carbon.

[0033] In a method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention, the drying temperature after applying the coating slurry may be 80 to 190 ℃.

[0034] In a method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention, the drying time after applying the coating slurry may be 5 minutes to 12 hours.

[0035] In a method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention, when drying after applying the coating slurry, the air atmosphere may have a moisture (H2O) content of 4 vol% or less based on 100% of the total volume of air.

[0036] A lithium secondary battery according to another embodiment of the present invention may include the aforementioned negative electrode for a lithium secondary battery.

[0037] When a lithium secondary battery according to another embodiment of the present invention undergoes at least one charge-discharge cycle, the protective layer of the negative electrode for the lithium secondary battery may additionally include Li3N and Li-NC compounds.

[0038]

[0039] A negative electrode for a lithium secondary battery according to one embodiment of the present invention forms a protective layer containing Mg3N2 and carbon components, thereby enabling the formation of a lithium-friendly Li-Mg alloy layer and a Li3N SEI layer on the electrode when charging a battery including the negative electrode. This ensures sufficient lithium ion conductivity and improves the charge-discharge efficiency of the battery. Furthermore, the formation of the SEI layer improves the bonding strength of the protective layer, thereby enhancing the durability of the negative electrode and the battery including it.

[0040] A method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention can provide a negative electrode having the aforementioned advantages, and can easily electrodeposit lithium on the negative electrode current collector even when charged under high current density conditions, thereby securing high-speed charge / discharge characteristics of the battery.

[0041] A lithium secondary battery according to another embodiment of the present invention may have improved charge / discharge efficiency, high-speed charge / discharge characteristics, and lifespan characteristics by including a negative electrode for a lithium secondary battery having the aforementioned advantages.

[0042]

[0043] Figure 1 shows the XPS analysis results for Mg 1s of the cathode after lithium electrodeposition of the comparative example.

[0044] Figure 2a shows the XPS analysis results for Mg 1s of the electrode in the non-cathode state before lithium electrodeposition in the example.

[0045] Figure 2b shows the XPS analysis results for Mg 1s of the cathode after lithium electrodeposition in the example.

[0046] Figure 3 shows the XPS analysis results for N 1s of the cathode after lithium electrodeposition of the comparative example.

[0047] Figure 4 shows the XPS analysis results for N 1s of the cathode after lithium electrodeposition in the example.

[0048] Figure 5 shows the SEM image and EDS analysis results of the cross-sectional portion of Example 3-1.

[0049] Figure 6a shows the results of the lithium electrodeposition evaluation according to the magnesium nitride content of the protective layer coating slurry.

[0050] Figure 6b shows the results of lithium electrodeposition evaluation according to the drying temperature and magnesium nitride content of the protective layer coating slurry.

[0051] Figure 6c shows the results of lithium electrodeposition evaluation according to drying time and magnesium nitride content of the protective layer coating slurry.

[0052] Figure 6d shows the results of lithium electrodeposition evaluation according to drying time and magnesium nitride content of the protective layer coating slurry.

[0053] Figure 7a shows the results of measuring the initial charge-discharge efficiency according to discharge current density for the cathodes of Example 3-1 and Comparative Example 1-1.

[0054] Figure 7b shows the measurement results of the charge-discharge efficiency of the second cycle according to the discharge current density for the cathode of Example 3-1 and Comparative Example 1-1.

[0055] Figure 7c shows the measurement results of the charge-discharge efficiency of the third cycle according to the discharge current density for the cathode of Example 3-1 and Comparative Example 1-1.

[0056] Figure 8 shows the results of evaluating the bonding strength between the current collector and the protective layer for the cathodes of the examples and comparative examples.

[0057] Figure 9 is an image showing the appearance of the remaining protective layer after measuring the peel strength of the cathode according to the example and comparative example.

[0058] Figure 10 is an SEM image showing the surface portion of the cathode of Comparative Example 1-1.

[0059] Figure 11 is an SEM image showing the surface of the electrode (non-cathode) before lithium electrodeposition in Example 1-1.

[0060] Figure 12 is an SEM image showing the surface portion of the electrode (non-cathode) before lithium electrodeposition in Example 2-1.

[0061] Figure 13 is an SEM image showing the surface of the electrode (non-cathode) before lithium electrodeposition in Example 3-1.

[0062] Figure 14 is an SEM image (20k magnification) showing the surface of the lithium electrode (non-cathode) before electrodeposition in Example 3-1.

[0063] Figure 15 is an SEM image (20k magnification) showing the surface of the electrode after lithium electrodeposition in Example 3-1.

[0064] Figure 16 shows the EDS mapping results of the electrode surface before and after lithium electrodeposition in Example 3-1.

[0065] Figure 17 shows the charge / discharge test results before and after lithium electrodeposition of Example 3-1.

[0066] Figure 18 shows the XRD analysis results for the lithium electrode (non-cathode) of Comparative Example 1-1.

[0067] Figure 19 shows the XRD analysis results for the lithium electrode (non-cathode) of Example 1-1.

[0068] Figure 20 shows the XRD analysis results for the lithium electrode (anode-free) of Example 2-1.

[0069] Figure 21 shows the XRD analysis results for the lithium electrode (non-cathode) of Example 3-1.

[0070]

[0071] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0072] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of “comprising” specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0073] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0074] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0075] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0076] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0077] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0078]

[0079] A lithium metal electrode for a lithium secondary battery according to one embodiment of the present invention will be described below.

[0080] In this specification, "lithium metal electrode" refers to an electrode in which lithium is electrodeposited to a predetermined thickness after a pre-coating layer is formed on a current collector. According to one embodiment of the present invention, it refers to an electrode in which a portion of magnesium nitride and amorphous carbon within the pre-coating layer react with the electrodeposited lithium to form a protective layer containing a Li3N component.

[0081] In this specification, "non-cathode" refers to an electrode in which lithium is not electrodeposited after a pre-coating layer is formed on a current collector.

[0082] 1. Negative electrode for lithium secondary battery

[0083] A negative electrode for a lithium secondary battery according to one embodiment of the present invention comprises a current collector; and a protective layer located on the current collector; wherein the protective layer contains magnesium nitride (Mg3N2), amorphous carbon, and a binder, and as a result of performing X-ray diffraction (XRD) analysis on the protective layer, it can satisfy the following Equation 1.

[0084] [Equation 1]

[0085] 0.5 < I(Mg3N2) / I(Carbon) < 2.0

[0086] (In Equation 1, I(Mg3N2) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 41 to 43 during XRD analysis, and I(Carbon) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 24 to 26 during XRD analysis.)

[0087] Preferably, the above formula 1 may be 0.53 < I(Mg3N2) / I(Carbon) < 1.6, 0.53 < I(Mg3N2) / I(Carbon) < 1.52, 0.534 ≤ I(Mg3N2) / I(Carbon) ≤ 1.519, and 0.534 ≤ I(Mg3N2) / I(Carbon) ≤ 0.535.

[0088] When the above Equation 1 is satisfied, the ionic conductivity and electronic conductivity of the cathode can be improved. Accordingly, this can help improve the output and charge / discharge speed of a battery to which the cathode is applied. In addition, since a uniform and robust SEI layer can be formed, appropriate mechanical strength can be imparted to the electrode, and the cycle stability and lifespan of the battery can be improved. Furthermore, mechanical stability can be maintained even with repeated charge / discharge cycles.

[0089] On the other hand, in Equation 1 above, if I(Mg3N2) / I(Carbon) is below the lower limit, it may be difficult to secure sufficient lithium-ion conductivity, which may lead to a decrease in battery output and a reduction in charge / discharge speed. There may be a problem where the electron conductivity of the electrode increases rapidly due to an excessive increase in carbon components. If electron conductivity becomes abnormally high, the risk of self-discharge or internal short circuits within the cell may increase. In addition, electrochemical imbalances may occur on the electrode surface, which may degrade the efficiency and lifespan characteristics of the battery.

[0090] In addition, in Equation 1 above, if I(Mg3N2) / I(Carbon) exceeds the upper limit, the brittleness of the protective layer increases, and cracks may occur during repeated charge-discharge cycles. As a result, the stability of the protective layer is reduced, and the deterioration of the negative electrode may be accelerated. Since the electrochemical reaction efficiency decreases due to poor electronic conductivity, it may cause a decrease in battery capacity and a shortened lifespan.

[0091] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the content of magnesium nitride (Mg3N2) may be 10% by weight or more and 80% by weight or less, based on 100% of the total weight of the protective layer.

[0092] Preferably, the content of the magnesium nitride (Mg3N2) may be 20 wt% or more and 70 wt% or less, 20 wt% or more and 60 wt% or less, and 40 wt% or more and 60 wt% or less.

[0093] More preferably, the content of the magnesium nitride (Mg3N2) may be 60 weight%.

[0094] When a protective layer is formed on the surface of the negative electrode by mixing the magnesium nitride (Mg3N2) and amorphous carbon, and the battery undergoes one or more charge-discharge cycles, a stable solid electrolyte interface (SEI) layer can be formed. Specifically, during battery charging, lithium electrodeposited on the negative electrode and the magnesium nitride contained in the protective layer can chemically react to form a lithium-friendly Li-Mg alloy and Li3N (corresponding to the SEI). Both the Li-Mg alloy and Li3N have excellent lithium ion conductivity, which facilitates the movement of lithium ions. In particular, Li3N can prevent short circuits in the battery by suppressing the growth of lithium dendrites.

[0095] In addition, the amorphous carbon included in the protective layer has structurally flexible and excellent electrical conductivity. Specifically, the amorphous carbon can suppress the excessive growth of lithium dendrites by providing a pathway for lithium ions to penetrate uniformly. Furthermore, it can have the effect of preventing excessive lithium deposition by making the current distribution on the surface of the negative electrode uniform.

[0096] Therefore, a protective layer formed by mixing magnesium nitride (Mg3N2) and amorphous carbon forms a stable SEI layer during battery charging, and because it has high mechanical strength and structural flexibility, it can effectively suppress lithium dendrites and prevent lithium loss. In addition, it has the advantage of improving the lithium ion conductivity of the negative electrode. Accordingly, if a lithium metal electrode including the above protective layer is introduced into a lithium secondary battery, electrical conductivity, charge / discharge efficiency, and lifespan characteristics are simultaneously improved, thereby making the overall electrochemical performance of the battery excellent.

[0097] When the content of the magnesium nitride (Mg3N2) satisfies the aforementioned range, the cathode has excellent lithium ion conductivity and can effectively suppress lithium dendrites, so when introduced into a lithium secondary battery, it has the advantage of improving electrical conductivity, charge / discharge efficiency, and lifespan characteristics.

[0098] On the other hand, if the content of the magnesium nitride (Mg3N2) is below the lower limit of the aforementioned range, it may be difficult to form a stable SEI layer because sufficient Li-Mg alloy and Li3N cannot be generated within the protective layer during battery charging. As a result, the lithium ion conductivity is lowered, and the growth of lithium dendrites is not effectively suppressed, which may lead to the problem of uneven lithium deposition on the negative electrode surface. This can cause safety issues such as internal short circuits or thermal runaway within the lithium secondary battery. Furthermore, as the amount of lithium consumed increases due to uneven lithium deposition, it can cause an imbalance in current distribution on the electrode surface, leading to a decrease in capacity and charge / discharge efficiency.

[0099] Furthermore, if the content of the magnesium nitride (Mg3N2) exceeds the upper limit of the aforementioned range, a protective layer may not be properly formed on the cathode, or the electrode performance may be significantly degraded due to excessive curing of the protective layer. In addition, when preparing a slurry for coating the protective layer, it is very difficult to optimize the viscosity of the slurry, and the time required for viscosity optimization becomes considerably long. Consequently, the productivity of the cathode equipped with the protective layer decreases. Moreover, even if a cathode equipped with a protective layer is manufactured, problems such as reduced electrical conductivity and lithium ion conductivity, increased mechanical brittleness, and reduced energy density may occur. Specifically, if the content of the magnesium nitride is excessive, the magnesium nitride, which has low electrical conductivity, hinders the movement of electrons, thereby increasing the resistance of the cathode and potentially reducing the electrical conductivity of the electrode. Furthermore, during the charging cycle, Li-Mg and Li3N are not properly generated, and the proportion of magnesium nitride remaining in the protective layer increases. This partially blocks the lithium ion pathway and inhibits the diffusion of lithium ions, which may lead to a decrease in the reaction rate of the electrode. Furthermore, as charge-discharge cycles are repeated, the protective layer may consume additional lithium, leading to a decrease in capacity. In addition, if the protective layer contains an excessive amount of magnesium nitride, it becomes difficult to flexibly respond to volume changes caused by repeated charge-discharge cycles, which may result in cracking or delamination of the negative electrode. Moreover, the SEI layer may be destroyed, causing a rapid decrease in the electrochemical performance and lifespan of the battery. Additionally, since the protective layer contains a large amount of metallic components, it may increase the weight and volume of the electrode, thereby reducing energy density.

[0100] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the bonding strength of the protective layer may be 150 to 800 mN / cm.

[0101] If the bonding strength of the protective layer satisfies the aforementioned range, the protective layer may not easily peel off due to mechanical impact, and the lifespan of the lithium secondary battery may be improved. In addition, the high mechanical rigidity of the protective layer allows lithium to be deposited stably and uniformly even under high current density conditions.

[0102] On the other hand, if the bonding strength of the protective layer is below the lower limit of the aforementioned range, the protective layer may easily peel off or break, making it difficult to suppress lithium dendrites and potentially causing a short circuit in the battery. Additionally, the lithium ion conductivity may not be uniform, which can degrade the electrochemical performance of the electrode and the battery.

[0103] If the bonding strength of the above protective layer exceeds the upper limit of the aforementioned range, the durability of the electrode and the battery containing it may be excellent, but excessive magnesium nitride content may instead cause damage to the electrode due to repeated charge-discharge cycles and a decrease in electrochemical performance.

[0104] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the thickness of the protective layer may be 1 to 20 μm.

[0105] Preferably, the thickness of the protective layer may be 4 to 20 μm, 4 to 7 μm, or 4 to 6 μm.

[0106] The thickness of the protective layer was calculated by observing the cross-section of the lithium metal electrode with an SEM, measuring the thickness of the protective layer at 10 points, and then calculating the average.

[0107] When the thickness of the protective layer satisfies the aforementioned range, lithium dendrites can be effectively suppressed while stably securing lithium ion conductivity, thereby improving electrochemical properties. In addition, the protective layer is maintained uniformly, ensuring the durability, sufficient mechanical strength, and thermal stability of the electrode.

[0108] On the other hand, if the thickness of the protective layer is less than the lower limit of the aforementioned range, a discontinuous or non-uniform protective layer may be formed, which can accelerate the degradation of the electrode and may lead to problems such as increased performance variation between electrodes. In addition, the inhibitory effect on lithium dendrites may be low, which may result in a risk of electrical short circuits, and the protective layer may be significantly thin, allowing cracks or pinholes to easily form due to external forces, thereby degrading the protective function.

[0109] Furthermore, if the thickness of the protective layer exceeds the upper limit of the aforementioned range, the movement path of lithium ions becomes longer, which may reduce ion conductivity and consequently decrease the output and charge / discharge efficiency of the battery. In addition, if the thickness of the protective layer becomes excessively thick, internal stress due to differences in the coefficient of thermal expansion increases, which may frequently cause cracks or delamination of the protective layer, thereby degrading the lifespan characteristics of the battery. Moreover, as thermal conductivity decreases, thermal energy tends to accumulate inside the device, which may increase the risk of overheating of the battery. If the thickness of the protective layer exceeds a predetermined range, the performance of the protective layer relative to the thickness is not actually high, and the amount of material used merely increases, which may lead to the problem of unnecessary resource waste.

[0110] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, a lithium-affinity metal layer is further included between the current collector and the protective layer, and the lithium-affinity metal layer comprises at least one of Ag, Au, Sn, Al, Zn, Si, Ge, Ni, Co, Fe, Ti, Mo, and Cr, and the thickness of the lithium-affinity metal layer may be 5 to 500 nm.

[0111] Preferably, the thickness of the lithium-affinity metal layer may be 5 to 300 nm, 10 to 200 nm, 10 to 100 nm, 20 to 100 nm, 50 to 100 nm, or 100 nm.

[0112] The thickness of the above lithium-affinity metal layer was calculated by observing the cross-section of the lithium metal electrode with an SEM, measuring the thickness of the lithium-affinity metal layer at 10 points, and then calculating the average.

[0113] When the thickness of the lithium-affinity metal layer satisfies the aforementioned range, the precipitation and exfoliation behavior of lithium during charging and discharging can be stabilized, thereby suppressing the formation of lithium dendrites and improving the safety and lifespan characteristics of the battery. Furthermore, structural stability of the electrode can be ensured by providing a buffering effect against volume changes of lithium metal due to repeated charging and discharging. In addition, high electrical conductivity can be secured, thereby improving the output characteristics of the battery.

[0114] On the other hand, if the thickness of the lithium-affinity metal layer is less than the lower limit of the aforementioned range, the precipitation of lithium is uneven, which increases the likelihood of lithium dendrite formation, and there may be problems such as difficulty in securing an electron transfer path or low stability of the electrode.

[0115] Furthermore, if the thickness of the lithium evolution metal layer exceeds the upper limit of the aforementioned range, it may impede the diffusion of lithium ions, thereby increasing the internal resistance of the electrode and reducing the charging speed and output characteristics of the battery. Additionally, excessive alloying reactions with lithium may occur, significantly increasing the volume change of the electrode and causing the lifespan of the electrode and battery to deteriorate rapidly.

[0116] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the lithium affinity metal layer contains Ag, and as a result of performing X-ray diffraction (XRD) analysis on the protective layer, the following Equation 2 can be satisfied.

[0117] [Equation 2]

[0118] 0.5 < I(Mg3N2) / I(Ag) < 2.0

[0119] (In Equation 2, I(Mg3N2) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 41 to 43 during XRD analysis, and I(Ag) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 37 to 39 during XRD analysis.)

[0120] When the above Equation 2 is satisfied, the precipitation and exfoliation behavior of lithium during charging and discharging can be stabilized to suppress the formation of lithium dendrites, thereby improving the safety and lifespan characteristics of the battery.

[0121] On the other hand, if I(Mg3N2) / I(Ag) in Equation 2 above is below the lower limit, it may be difficult to ensure sufficient lithium-ion conductivity, which may lead to a decrease in battery output and a reduction in charge / discharge speed. There may be a problem where the electron conductivity of the electrode increases rapidly due to an excessive increase in carbon components. If electron conductivity becomes abnormally high, the risk of self-discharge or internal short circuits within the cell may increase. In addition, electrochemical imbalances may occur on the electrode surface, which may degrade the efficiency and lifespan characteristics of the battery.

[0122] In addition, if I(Mg3N2) / I(Ag) in Equation 2 above exceeds the upper limit, it may impede the diffusion of lithium ions, thereby increasing the internal resistance of the electrode and reducing the charging speed and output characteristics of the battery. Furthermore, excessive alloying reactions with lithium may occur, significantly increasing the volume change of the electrode and rapidly degrading the lifespan of the electrode and battery.

[0123] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, when EDS analysis is performed on the surface of the negative electrode, the average diameter of the Mg clusters confirmed may be 0.1 to 15 μm.

[0124] Preferably, the average diameter of the Mg cluster may be 0.7 to 3 μm, 1 to 2.93 μm, or 1.17 to 1.5 μm.

[0125] More preferably, the average diameter of the Mg cluster may be 1.177 to 1.474 μm.

[0126] The average diameter of the Mg cluster above was calculated by taking the longest line segment connecting two points on the perimeter of the Mg cluster as the diameter after performing surface SEM-EDS analysis of the lithium metal electrode, and calculating the average of 20 diameter data.

[0127] When the average diameter of the above Mg cluster satisfies the aforementioned range, it can be seen that magnesium nitride is decomposed by the lithium electrodeposition process during battery charging, thereby uniformly forming a lithium-friendly alloy such as Li-Mg and a Li3N SEI layer. Accordingly, the effects of improved lithium ion conductivity and lithium dendrite suppression can be enjoyed simultaneously.

[0128] On the other hand, if the average diameter of the Mg cluster is less than the lower limit of the aforementioned range, the thickness of the protective layer may become excessively thick, and consequently, the lithium ion conductivity, structural stability, and thermal stability of the electrode may be reduced, which may result in the deterioration of the battery's output and lifespan characteristics.

[0129] In addition, if the average diameter of the Mg cluster exceeds the upper limit of the aforementioned range, it can be determined that an excessive amount of magnesium nitride that has not reacted with lithium remains in the protective layer. As a result, the thickness of the protective layer is too thin, so the protective function cannot be properly performed, and the risk of a short circuit may be high.

[0130] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the magnesium nitride (Mg3N2) is a plate-shaped particle, and the average particle size of the plate-shaped particle may be 0.2 to 15 μm.

[0131] Preferably, the average particle size of the plate-shaped particles may be 0.2 to 3 μm, 0.5 to 2 μm, or 1 to 1.5 μm.

[0132] The average particle size of the above plate-shaped particles was calculated by taking the longest line segment connecting two points on the perimeter of the plate-shaped particles as the diameter after performing surface SEM-EDS analysis of the lithium metal electrode, and calculating the average of 20 diameter data.

[0133] When the magnesium nitride is plate-shaped and the average particle size satisfies the aforementioned range, the protective layer can be formed densely and uniformly, and the formation of lithium dendrites can be effectively suppressed.

[0134] On the other hand, if the average particle size of the above plate-shaped particles is less than the lower limit of the aforementioned range, the specific surface area increases significantly, increasing the likelihood of side reactions and causing the SEI layer to become excessively thick, which may reduce the efficiency of the battery. In addition, there may be a problem where the stability of the protective layer is reduced due to aggregation between particles.

[0135] In addition, if the average particle size of the plate-shaped particles exceeds the upper limit of the aforementioned range, it may cause multiple pinholes or cracks within the protective layer, thereby easily exposing the lithium metal layer and promoting the growth of lithium dendrites. It may also degrade the lifespan of the battery.

[0136] In a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the binder is a non-aqueous binder, and the non-aqueous binder may include at least one selected from PVDF (polyvinylidene fluoride), PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), PTFE (polytetrafluoroethylene), PAI (polyamideimide), PEO (polyethylene oxide), PANI (polyaniline), PDO (polypyrrole), and polythiophene.

[0137] When the aforementioned water-based binder is applied as a component of the protective layer, the bonding strength of the protective layer can be improved.

[0138]

[0139] A method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention will be described below.

[0140] 2. Method for manufacturing a negative electrode for a lithium secondary battery

[0141] A method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention comprises the steps of: preparing a current collector; and forming a protective layer by applying a coating slurry containing magnesium nitride (Mg3N2), amorphous carbon, and a binder on at least one surface of the current collector; and may satisfy the following formula 3.

[0142] [Equation 3]

[0143] 0.16<[Mg3N2] / (T+P)<0.35

[0144] (In Equation 3, [Mg3N2] represents the input amount of magnesium nitride (Mg3N2) (in weight% units) based on 100% of the total weight of magnesium nitride (Mg3N2) and amorphous carbon during the protective layer formation stage, T represents the temperature (°C) at which the coating slurry is dried after application during the protective layer formation stage, and P represents the drying time (min) after application of the coating slurry during the protective layer formation stage; the units of the calculated values ​​in Equation 3 are not considered.)

[0145] Preferably, the above Equation 3 may be 0.17391 ≤ [Mg3N2] / (T+P) ≤ 0.34286.

[0146] By using the coating slurry containing the magnesium nitride (Mg3N2) and amorphous carbon to form a protective layer on a current collector and performing one or more charge-discharge cycles of the battery, a stable solid electrolyte interface (SEI) layer can be formed on the protective layer. Specifically, after the protective layer is formed, lithium electrodeposited on the negative electrode by charging the battery reacts chemically with the magnesium nitride contained in the protective layer to form a lithium-friendly Li-Mg alloy and Li3N (corresponding to the SEI). Both the Li-Mg alloy and Li3N have excellent lithium ion conductivity, which facilitates the movement of lithium ions. In particular, Li3N can prevent short circuits in the battery by suppressing the growth of lithium dendrites.

[0147] In addition, the amorphous carbon included in the protective layer has structurally flexible and excellent electrical conductivity. Specifically, the amorphous carbon can suppress the excessive growth of lithium dendrites by providing a pathway for lithium ions to penetrate uniformly. Furthermore, it can have the effect of preventing excessive precipitation of lithium by making the current distribution on the electrode surface uniform.

[0148] Accordingly, a protective layer formed using a coating slurry containing magnesium nitride (Mg3N2) and amorphous carbon forms a stable SEI layer, which has high mechanical strength and high structural flexibility, thereby effectively suppressing lithium dendrites and preventing lithium loss, as well as having the advantage of improving lithium ion conductivity. Accordingly, when a negative electrode containing the above protective layer is introduced into a lithium secondary battery, electrical conductivity, charge / discharge efficiency, and lifespan characteristics are simultaneously improved, resulting in excellent overall electrochemical performance.

[0149] In addition, when the above Equation 3 is satisfied, lithium can be effectively electrodeposited between the current collector of the cathode equipped with the protective layer and the lower portion of the protective layer. Specifically, the excellent ion conductivity of magnesium nitride contained in the protective layer can improve the electrodeposition of lithium, and the uniformity of lithium electrodeposition and desorption can be maintained even when charge-discharge cycles are repeated several times by ensuring sufficient lithium ion conductivity and forming a uniform current density distribution through Li3N and Li-NC compounds generated in the protective layer by lithium electrodeposition.

[0150] On the other hand, if the above Equation 3 is not satisfied, the lithium electrodeposition and desorption performance may be significantly reduced.

[0151] In a method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention, the amount of magnesium nitride (Mg3N2) added in the protective layer forming step may be greater than 20% by weight and less than or equal to 70% by weight, based on 100% of the total weight of magnesium nitride (Mg3N2) and amorphous carbon.

[0152] Preferably, the content of the magnesium nitride (Mg3N2) may be greater than 20 weight% and less than or equal to 60 weight%, or greater than or equal to 40 weight% and less than or equal to 60 weight%.

[0153] More preferably, the content of the magnesium nitride (Mg3N2) may be 60 weight%.

[0154] When the amount of magnesium nitride (Mg3N2) added satisfies the aforementioned range, the cathode has excellent lithium ion conductivity and can effectively suppress lithium dendrites, so when introduced into a lithium secondary battery, it has the advantage of improving electrical conductivity, charge / discharge efficiency, and lifespan characteristics.

[0155] On the other hand, if the input amount of magnesium nitride (Mg3N2) is less than the lower limit of the aforementioned range, it may be difficult to form a stable SEI layer because the Li-Mg alloy and Li3N are not sufficiently generated during battery charging. As a result, the lithium ion conductivity is lowered and the growth of lithium dendrites is not effectively suppressed, which may lead to the problem of uneven lithium deposition on the negative electrode surface. This can cause safety issues such as internal short circuits or thermal runaway within the lithium secondary battery. Furthermore, as the amount of lithium consumed increases due to uneven lithium deposition, it can cause an imbalance in current distribution on the electrode surface, leading to a decrease in capacity and charge / discharge efficiency.

[0156] Furthermore, if the input amount of the magnesium nitride (Mg3N2) exceeds the upper limit of the aforementioned range, problems such as reduced electrical conductivity and lithium ion conductivity of the cathode, increased mechanical brittleness, and reduced energy density may occur. Specifically, if the content of the magnesium nitride is excessive, the magnesium nitride, which has low electrical conductivity, hinders electron movement, thereby increasing the resistance of the cathode and potentially reducing the electrical conductivity of the electrode. Moreover, as the proportion of residual magnesium nitride that fails to generate Li-Mg and Li3N increases, it partially blocks lithium ion pathways, hindering lithium ion diffusion and potentially slowing down the reaction rate of the electrode. Additionally, problems may arise where capacity is reduced due to the additional consumption of lithium during repeated charge-discharge cycles. Furthermore, if the protective layer contains an excessive amount of magnesium nitride, it becomes difficult to flexibly respond to volume changes during repeated charge-discharge cycles, which may lead to cracking or delamination of the cathode. Moreover, the SEI layer may be destroyed, causing a rapid decrease in the electrochemical performance and lifespan of the battery. In addition, since the protective layer contains a large amount of metal components, there may be a problem of increasing the weight and volume of the electrode, thereby reducing energy density.

[0157] In a method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention, the drying temperature after applying the coating slurry may be 80 to 190 ℃.

[0158] Preferably, the drying temperature may be 150 to 190 ℃ or 160 to 180 ℃.

[0159] More preferably, the drying temperature may be 170 ℃.

[0160] In a method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention, the drying time after applying the coating slurry may be 5 minutes to 12 hours.

[0161] Preferably, the drying time may be 5 to 120 minutes, 5 to 60 minutes, 5 to 30 minutes, or 5 to 10 minutes.

[0162] When the above drying temperature and drying time fall within the aforementioned range, the bonding strength of the protective layer is improved, and lithium can be uniformly electrodeposited on the lower surface of the protective layer. In addition, lithium can be smoothly electrodeposited even under high current density (high-speed charging state) conditions.

[0163] On the other hand, if the above drying temperature and drying time are below the lower limit of the aforementioned range, the solvent in the slurry may not volatilize sufficiently, which may cause defects in the protective layer, and there may be problems such as lithium dendrites not being well suppressed or uneven current distribution. In addition, because the protective layer is not robust and has low bonding strength, although the lithium electrodeposition performance may be improved, problems such as easy peeling from the electrode or damage may occur, and the life characteristics of the battery may deteriorate.

[0164] Furthermore, if the drying temperature and drying time exceed the upper limit of the aforementioned range, the binder or magnesium nitride may thermally decompose to form unnecessary compounds, which may lower the bonding strength of the protective layer. Additionally, due to the rapid evaporation of the solvent caused by high-temperature drying, cracks or wrinkles may occur on the surface of the protective layer, or the thickness of the protective layer may not be uniform. Moreover, as the amorphous carbon contained within the protective layer undergoes structural deformation, a problem of reduced electronic conductivity may occur.

[0165] In a method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention, when drying after applying the coating slurry, the air atmosphere may have a moisture (H2O) content of 4 vol% or less based on 100% of the total volume of air.

[0166] Preferably, the moisture (H2O) content may be 3 vol% or less.

[0167] When the air atmosphere satisfies the aforementioned conditions during drying after application of the coating slurry, the bonding strength of the protective layer can be improved.

[0168] On the other hand, if the moisture (H2O) content in the air exceeds the aforementioned range during drying, Mg3N2 within the protective layer reacts vigorously with moisture to generate a large amount of Mg(OH)2, which makes it difficult to form lithium-friendly Li-Mg alloys and Li3N during battery charging. In other words, since it is difficult to form a robust protective layer, the durability of the electrode and battery may be significantly reduced.

[0169]

[0170] A lithium secondary battery according to another embodiment of the present invention will be described below.

[0171] 3. Lithium secondary battery

[0172] A lithium secondary battery according to another embodiment of the present invention may include the aforementioned negative electrode for a lithium secondary battery.

[0173] When a lithium secondary battery according to another embodiment of the present invention undergoes at least one charge-discharge cycle, the protective layer of the negative electrode for the lithium secondary battery may additionally include Li3N and Li-NC compounds.

[0174] A lithium secondary battery according to another embodiment of the present invention may more specifically include a positive electrode, a negative electrode positioned opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0175] The above-mentioned negative electrode is the same as the negative electrode for a lithium secondary battery described above.

[0176] In addition, the lithium secondary battery may optionally further include a battery container housing an electrode assembly of a positive electrode, a negative electrode, and a separator, and a sealing member sealing the battery container.

[0177] The above positive electrode may include a positive current collector and a positive active material layer disposed on the positive current collector, and the positive active material layer may include a positive active material.

[0178] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0179] As the above-mentioned cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithated intercalation compound) may be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used, and specific examples thereof may include compounds represented by any one of the following chemical formulas:

[0180] Li a A 1-b B b D2(wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li a E 1-b B b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE 2-b B b O 4-c D c (In the above equation, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B c D α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Co b B c O 2-α T α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Co b B c O 2-α T2(wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-cMn b B c D α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Mn b B c O 2-α T α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c O 2-α T2(wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c G d O2(wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d GeO2(wherein the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2(in the above equation, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O2(in the above equation, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a MnG b O2(in the above equation, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G bO4(wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); and LiFePO4.

[0181] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; T is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; and J may be V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0182] Of course, the compound having a coating layer on its surface or the compound having a coating layer may also be used in combination.

[0183] The above coating layer may include at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming these coating layers may be amorphous or crystalline. As coating elements included in the above coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof may be used. For the coating layer formation process, any coating method may be used as long as the compound can be coated using these elements in a way that does not adversely affect the physical properties of the cathode active material (e.g., spray coating, immersion method, etc.). Since this is a matter that is well understood by those engaged in the relevant field, a detailed explanation will be omitted.

[0184] The above positive active material layer may further include a binder and / or a conductive material together with the aforementioned positive active material.

[0185]

[0186] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the positive current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these alone or a mixture of two or more may be used, but is not limited thereto. The above binder may be included in an amount of 1 to 30 weight% based on the total weight of the positive active material layer.

[0187] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include 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 black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used, but is not limited thereto. The above conductive material may typically be included in an amount of 1 to 30 weight% relative to the total weight of the positive electrode active material layer.

[0188] The above anode can be manufactured according to a conventional anode manufacturing method.

[0189] Specifically, the anode can be manufactured by applying a composition for forming an anode active material layer, comprising an anode active material and optionally a binder, conductive material, or solvent as needed, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0190] The above solvent may be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that allows for the dissolution or dispersion of the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0191] Alternatively, the anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0192] The above separator separates the positive and negative electrodes and provides a pathway for the movement of lithium ions. It can be used without special restrictions as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and 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 fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0193] The above electrolytes may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but are not limited thereto.

[0194] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0195] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0196] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0197] In addition to the above electrolyte components, 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, haloalkylene carbonate-based compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexamethylphosphate triamide, 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. In this case, the additive may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0198]

[0199] The following describes embodiments, comparative examples, and experimental examples of the present invention. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited by the following examples. Furthermore, it is possible to implement the invention with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and such modifications may also fall within the scope of the present invention.

[0200] Example 1-1

[0201] (1) Preparation of the entire house

[0202] To manufacture the negative electrode for a lithium secondary battery according to the present invention, a nickel (Ni) / silver (Ag) current collector was prepared. Specifically, the current collector was used by electrodepositing silver, a lithium-affinity metal, onto the surface of a nickel current collector. At this time, the thickness of the nickel current collector was 10 μm, and the silver was plated to a thickness of 100 nm on each side of the current collector.

[0203] (2) Formation of a protective layer

[0204] A protective coating layer was formed on the surface of the current collector using a comma coater by slurry coating. Specifically, 1 g of magnesium nitride (Mg3N2) powder, 5 g of acetylene black as amorphous carbon, and 0.27 g of polyvinylidene fluoride (PVdF) as a binder were added to 40 g of NMP as a solvent and mixed to prepare a coating slurry. At this time, the magnesium nitride (Mg3N2) powder was added at 20 wt% based on the total weight of the magnesium nitride and amorphous carbon. Next, the prepared slurry was thinly applied to the current collector, and then aged at 190 ℃ for 12 hours under a dry gas atmosphere with a moisture content of 1 vol% or less, followed by vacuum drying for 2 hours to remove the solvent and form a protective layer with a thickness of 5 μm.

[0205] Examples 1-2 to 3-7 and Comparative Examples 1-1 to 2-1 manufactured the cathode using the same process as Example 1-1, but with the input amount of magnesium nitride and the current density D during electrodeposition according to the process conditions listed in Tables 1 to 3. C The cathode was manufactured by controlling it.

[0206]

[0207]

[0208] Evaluation Example 1 - Evaluation of Lithium Electrodeposition Type (Maximum Current Density during Electrodeposition)

[0209] After preparing an electrode in a non-cathode state with a protective layer formed according to the magnesium nitride content of the examples and comparative examples (see Table 1), lithium was electrodeposited for a certain period of time with a predetermined current density (see Table 1) as the maximum current density.

[0210] Specifically, after stacking the lithium source in the plating solution and the electrode in a non-cathode state while electrically insulated, a power supply was used to apply current to the lithium source and the current collector as the (+) and (-) electrodes, respectively. In this case, a lithium metal plate with a purity of over 99.9% and a thickness of 500 μm was used as the lithium source by pressing it onto a copper current collector (Cu Plate). The current density of the electrodeposition process was set to 0.2 mA / cm² 2 , 0.5 mA / cm 2 , 1 mA / cm 2 After electrodepositing for 10 minutes each while increasing in steps in sequence, 12 mA / cm 2 The maximum current density was set. The electrodeposition time at the maximum current density was calculated as the time required to electrodeposit a final accumulated lithium thickness of 10 μm, and was set variably according to the magnitude of the maximum current density.

[0211] For reference, the above maximum current density (mA / cm²) 2 ) refers to the limit of current density at which lithium deposited according to the above process can precipitate lithium between the protective layer and the current collector.

[0212] At this time, the plating solution was prepared by adding 40 wt% of lithium bis(fluorosulfonyl)imide and 10 wt% of lithium nitrate, which are nitrogen-based compounds, and 10 wt% of fluoroethylene carbonate, which is a fluorine-based compound, to a 1,2-dimethoxyethane solvent, based on 100 wt% of the plating solution, and adding 10 wt% of fluoroethylene carbonate, which is a fluorine-based compound, based on 100 wt% of the plating solution. After the electrodeposition was completed, the presence of electrodeposition was determined by comparing the appearance of the cathode.

[0213] Classification Process Conditions Battery Charging Parameters Mg3N2 Input Amount [Mg3N2] (Wt%) Slurry Drying Temperature (°C) Slurry Drying Time (min) Current Density D During Electrodeposition C (mA / cm 2 )Lithium Electrodeposition Result Formula 3[Mg3N2] / (T+P) Comparative Example 1-2019012012BAD0 Comparative Example 1-3201706012BAD0.08696 Example 2-2401506012GOOD0.19048 Example 2-3401706012GOOD0.17391 Comparative Example 2-1401906012BAD0.16000 Example 2-4401703012GOOD0.20000 Example 2-5401701012GOOD0.22222 Example 2-640170512GOOD0.22857 Example 3-2601506012GOOD0.28571 Example 3-3601706012GOOD0.26087 Example 3-4601906012GOOD0.24000 Example 3-5601703012GOOD0.30000 Example 3-6601701012GOOD0.33333 Example 3-760170512GOOD0.34286

[0214] Table 1 above is a table showing the lithium electrodeposition results and the calculated values ​​of Equation 3 according to the process conditions of the examples and comparative examples. Figure 6a shows the lithium electrodeposition evaluation results according to the magnesium nitride content of the protective layer coating slurry.

[0215] Figure 6b shows the results of lithium electrodeposition evaluation according to the drying temperature and magnesium nitride content of the protective layer coating slurry.

[0216] Figure 6c shows the results of lithium electrodeposition evaluation according to drying time and magnesium nitride content of the protective layer coating slurry.

[0217] Figure 6d shows the results of lithium electrodeposition evaluation according to drying time and magnesium nitride content of the protective layer coating slurry.

[0218] According to Figure 6a above, it was confirmed that lithium electrodeposition on the underside of the protective layer is easier at high current densities as the magnesium nitride content increases. In particular, for a lithium metal electrode in which the protective layer is formed solely of amorphous carbon without the addition of magnesium nitride, the maximum current density at which lithium electrodeposition is possible is 12 mA / cm². 2 On the other hand, in the case of a cathode with a protective layer formed by adding 60 wt% magnesium nitride, 24 mA / cm 2 It was confirmed that lithium electrodeposition was easy even in this case. These results mean that as the amount of magnesium nitride added increases when forming the protective layer, charging is possible even at high current densities, and it can be understood that the high-speed charge / discharge characteristics of the battery with the above-mentioned negative electrode are improved.

[0219] According to Table 1 and Figures 6a to 6d above, it was confirmed that, generally, as the amount of magnesium nitride added increases, the lithium electrodeposition results are excellent even at relatively high current densities. In addition, it was confirmed that when the drying temperature of the protective layer coating slurry is 150 to 170 ℃, the lithium electrodeposition results are generally better than when it is 190 ℃, regardless of the magnesium nitride content. It can be understood that if the slurry drying temperature exceeds a predetermined range, it may cause structural deformation of the protective layer or a decrease in lithium ion conductivity, resulting in inferior lithium electrodeposition results. Furthermore, under the same drying temperature, it was confirmed that lithium is not well electrodeposited on the underside of the protective layer as the drying time increases. Although there may be differences in the lithium electrodeposition pattern depending on the magnesium nitride content, it may be advantageous to set the drying time to approximately 5 to 60 minutes to maintain stable charge / discharge performance. Preferably, it may be advantageous to apply a drying time of approximately 5 to 30 minutes, and more preferably 5 to 10 minutes. In other words, it was confirmed that increasing the magnesium nitride content is favorable for lithium electrodeposition, while increasing the drying time or drying temperature beyond a predetermined range is unfavorable for electrodeposition. As drying time or temperature increases, the binder component within the protective layer hardens excessively, which may impede lithium ion mobility. Consequently, it can be understood that during the charging cycle, it becomes difficult for lithium ions to pass through the protective layer and electrodeposit between the current collector and the protective layer.

[0220]

[0221] Evaluation Example 2 - XPS Analysis Before and After Lithium Electrodeposition

[0222] The surface of the negative electrode for a lithium secondary battery prepared according to the examples and comparative examples was analyzed by X-ray photoelectron spectroscopy (XPS), and the results are shown in FIGS. 1 to 4. Specifically, the composition of the surface was analyzed by investigating the peak intensities corresponding to Mg 1s and N 1s on the surface of the electrode before and after lithium electrodeposition.

[0223] Figure 1 shows the XPS analysis results for Mg 1s of the cathode after lithium electrodeposition of the comparative example.

[0224] Figure 2a shows the XPS analysis results for Mg 1s of the electrode in the non-cathode state before lithium electrodeposition in the example.

[0225] Figure 2b shows the XPS analysis results for Mg 1s of the cathode after lithium electrodeposition in the example.

[0226] Figure 3 shows the XPS analysis results for N 1s of the cathode after lithium electrodeposition of the comparative example.

[0227] Figure 4 shows the XPS analysis results for N 1s of the cathode after lithium electrodeposition in the example.

[0228] According to FIGS. 1, 2a, and 2b above, since no peak for Mg 1s occurred in the cathode of Comparative Example 1-1, it was confirmed that the protective layer does not contain an Mg component. On the other hand, in the case of Example 3-1, it was confirmed that a peak occurred in the range of binding energy of 1304 to 1306 eV in the electrode in the non-cathode state before lithium electrodeposition. This indicates that Mg 2+ As a peak corresponding to this, it was confirmed that magnesium nitride (Mg3N2) was contained within the protective layer prior to lithium electrodeposition. However, when lithium was electrodeposited on the electrode with the protective layer formed thereon, it was confirmed that a peak occurred in the binding energy range of 1301.5 to 1303.5 eV. This indicates that Li x Mgy This is a peak for the Li-Mg alloy represented by, and it can be seen that after the lithium electrodeposition process (charging), the electrodeposited lithium and the Mg component in the protective layer chemically react to form a Li-Mg alloy.

[0229] According to Table 2 and Figures 3 and 4 above, in Comparative Example 1-1, which used only amorphous carbon without adding magnesium nitride during the formation of the protective layer, the Li3N peak was observed faintly, whereas in Example 3-1, which mixed magnesium nitride and amorphous carbon during the formation of the protective layer, the peak corresponding to Li3N was observed with an intensity approximately 7 times higher than that of the Comparative Example. Although Comparative Example 1-1 does not contain N components within the protective layer, since Li3N components may be partially formed by the LiNO3 components contained in the plating solution (electrolyte) during lithium electrodeposition (charging), the peak corresponding to Li3N may appear with weak intensity during XPS analysis. In Example 3-1, it can be understood that the N components contained in the magnesium nitride undergo a chemical reaction with each other during lithium electrodeposition to generate a large amount of Li3N. Furthermore, the electrodeposited Li and the N and C components within the protective layer may react with each other to form a protective layer in the form of Li-NC.

[0230] In other words, it can be seen that when a protective coating layer is formed solely of amorphous carbon, Li3N is not formed at all, or an amount sufficient to perform a protective function cannot be formed. However, it can be seen that when magnesium nitride is added during the formation of the protective layer, a significant amount of Li3N can be formed within the protective layer for protective purposes.

[0231]

[0232] Evaluation Example 3 - SEM and EDS Analysis

[0233] A protective layer was formed, and SEM image analysis and EDS analysis evaluation were performed on the lithium metal electrode sample of Example 3-1 before and after electrodeposition. During the EDS analysis, the evaluation was conducted in mapping mode to determine the distribution of each element. In addition, the analysis was performed on the upper surface of the protective layer of the lithium metal electrode and on a cross-section of the lithium metal electrode cut in the thickness direction.

[0234] Figure 5 shows the SEM image and EDS analysis results of the cross-sectional portion of Example 3-1.

[0235] Figure 10 is an SEM image showing the surface portion of the cathode of Comparative Example 1-1.

[0236] Figure 11 is an SEM image showing the surface of the electrode (non-cathode) before lithium electrodeposition in Example 1-1.

[0237] Figure 12 is an SEM image showing the surface portion of the electrode (non-cathode) before lithium electrodeposition in Example 2-1.

[0238] Figure 13 is an SEM image showing the surface of the electrode (non-cathode) before lithium electrodeposition in Example 3-1.

[0239] Figure 14 is an SEM image (20k magnification) showing the surface of the lithium electrode (non-cathode) before electrodeposition in Example 3-1.

[0240] Figure 15 is an SEM image (20k magnification) showing the surface of the electrode after lithium electrodeposition in Example 3-1.

[0241] Figure 16 shows the EDS mapping results of the electrode surface before and after lithium electrodeposition in Example 3-1.

[0242] According to Figure 5, it can be seen that a lithium-affinity metal layer (Ag) and a protective layer are formed sequentially on a nickel current collector. It can also be seen that N, Mg, and C components are distributed in high concentrations within the protective layer, and that Li-Mg, Li3N, and Li-NC are formed throughout the protective layer. Furthermore, it can be inferred that the Ag component within the lithium-affinity metal layer (Ag layer) formed between the current collector and the protective layer migrates to the protective layer after lithium electrodeposition, forming a lithium-friendly alloy.

[0243] According to Figures 10 to 13, it was confirmed that as the content of magnesium nitride in the protective layer increased, the number of plate-shaped magnesium nitride particles increased.

[0244] According to FIGS. 14 to 16, in the non-cathode state prior to lithium electrodeposition, it can be observed that a large amount of plate-shaped, large magnesium nitride particles with a particle size exceeding 1 μm exist on the surface of the protective layer. However, after lithium electrodeposition, large magnesium nitride particles are hardly observed, and a large amount of nano-sized particles with generally uniform particle sizes exist on the surface of the protective layer. This structural change can be understood as a phenomenon that occurs because the large magnesium nitride particles are decomposed by lithium during the lithium electrodeposition process to produce Li-Mg alloy, Li3N, or Li-NC components. In particular, when examining the EDS mapping results before and after lithium electrodeposition, it can be confirmed that Mg clusters, which were relatively large before electrodeposition, were converted into relatively small Mg clusters after electrodeposition. From this, it was further confirmed that the magnesium nitride component contained within the protective layer decomposes due to lithium electrodeposition to form an SEI layer.

[0245]

[0246] Evaluation Example 4 - XRD Analysis

[0247] After forming a protective layer and additionally depositing lithium between the protective layer and the current collector through an electrodeposition process, the sample was subjected to phase analysis using XRD evaluation by Rikaku. The XRD analysis was evaluated in thin film mode.

[0248] Process Conditions XRD Peak Intensity Parameter Classification Mg3N2 Input Amount [Mg3N2] (Wt%) Slurry Drying Temperature (°C) Slurry Drying Time (hr) I(Mg3N2) (2θ: 41~43) I(Carbon) (2θ: 24~26) I(Ag) (2θ: 37~39) Formula 1 I(Mg3N2) / I(Carbon) Formula 2 I(Mg3N2) / I(Ag) Comparative Example 1-10 190 120 249 9.85 215 48.82 200 Example 1-12 0 190 122 170.50 414 28.57 120 33.15 31.51 91.068 Example 2-14019012852.0911594.354961.5380.5340.886 Example 3-160190121044.3171950.5491402.1760.5350.745

[0249] Table 2 above is a table showing the calculated values ​​of Equations 1 and 2 as a result of measuring the XRD peak intensities of the examples and comparative examples. Figure 18 shows the XRD analysis results for the lithium electrode (anode-free) of Comparative Example 1-1. Figure 19 shows the XRD analysis results for the lithium electrode (anode-free) of Example 1-1.

[0250] Figure 20 shows the XRD analysis results for the lithium electrode (anode-free) of Example 2-1.

[0251] Figure 21 shows the XRD analysis results for the lithium electrode (non-cathode) of Example 3-1.

[0252] According to Table 2 and Figures 18 to 21 above, regarding the negative electrode before lithium electrodeposition, the magnesium nitride peak could not be confirmed in Comparative Example 1-1, while the magnesium nitride peak could be confirmed in the XRD analysis results of Examples 1-1, 2-1, and 3-1. In addition, it was confirmed that as the magnesium nitride content increased, I(Mg3N2) / I(Carbon) corresponding to Formula 1 in this specification and I(Mg3N2) / I(Ag) corresponding to Formula 2 increased.

[0253]

[0254] Evaluation Example 5 - Evaluation of Bonding Strength of Protective Layer

[0255] After preparing lithium metal electrodes according to the examples and comparative examples, the bonding strength between the current collector and the protective layer was measured using a peel strength tester. Specifically, a 10 mm wide polyimide tape (No. 360A, thickness: 0.08 mm, adhesion: 4.4 N / 19 mm) from Nitto was adhered to the protective layer, and the bonding strength was measured through a tensile test using a peel strength tester (AND, MCT-2150 W). At this time, the tensile speed was set to 50 mm / min, and the tensile test distance was set to within a total of 200 mm. The bonding strength was calculated as the average strength over a 100 mm section starting from the 50 mm mark of the tensile test. In addition, the appearance of the remaining protective layer was compared after the peel strength measurement.

[0256] Process Conditions Battery Charge Classification Mg3N2 Input Amount [Mg3N2] (Wt%) Slurry Drying Temperature (°C) Slurry Drying Time (hr) Current Density D During Electrodeposition C (mA / cm 2 )Lithium Electrodeposition Result Bond Strength (mN / cm) Comparative Example 1-10 190 1212 BAD 22.78 Example 1-12 0 190 1212 GOOD 157.44 Example 2-14 0 190 1212 GOOD 295.13 Example 3-16 0 190 1212 GOOD 741.10

[0257] Table 3 above shows the results of the evaluation of the bonding strength between the current collector and the protective layer for a lithium metal electrode. Figure 8 shows the results of the evaluation of the bonding strength between the current collector and the protective layer for the cathodes of the examples and comparative examples. Figure 9 is an image showing the appearance of the remaining protective layer after measuring the peel strength for the cathodes according to the examples and comparative examples.

[0258] According to Table 3 and Figure 8 above, it can be seen that as the amount of magnesium nitride added during the formation of the protective layer increases, the peel strength of the protective layer also increases. In particular, it was observed that the rate of increase in peel strength increased sharply when the amount of magnesium nitride added increased from 40 wt% to 60 wt%.

[0259] In addition, according to Figure 9 above, when the magnesium nitride input amount is 0 to 40 wt%, the loss of the protective layer is clearly confirmed after measuring the peel strength. However, when the magnesium nitride input amount is 60 wt%, it can be confirmed that the protective layer remains even after measuring the peel strength. That is, it was found that a lithium metal electrode with the best bonding strength can be manufactured when the magnesium nitride content is 60 wt%.

[0260]

[0261] Evaluation Example 6 - Analysis of Charge / Discharge Characteristics

[0262] Charge-discharge evaluations were conducted using a 500 μm lithium metal reference electrode and injecting a liquid electrolyte between the evaluation electrodes. 0.2 mA / cm² 2 , 0.5 mA / cm 2 , 1 mA / cm 2 After electrodepositing for 10 minutes at progressively increasing rates, the current was charged by electrodepositing at 1 mA / cm² for 18 minutes to achieve a final accumulated lithium thickness of 10 µm. Subsequently, the current densities during discharge were 0.1, 0.5, 1, and 2 mA / cm², respectively. 2The charge-discharge efficiency for 1 to 3 cycles was measured. The charge-discharge life was defined as ending when a short circuit occurred between the reference electrode and the evaluation electrode during the charge-discharge process or when the voltage between the two electrodes exceeded 1 V.

[0263]

[0264] Classification Initial Efficiency (%)2 nd Efficiency (%)3 rd Efficiency (%) Discharge current density (mA / cm²) 2 Comparative Example 1-1 Example 3-8 Comparative Example 1-1 Example 3-8 Comparative Example 1-1 Example 3-8 0.162.4470.8373.9476.4571.9076.980.573.4079.9083.1489.1479.4684.301.076.3680.3186.4590.7885.1689.342.071.4890.3984.9095.1984.2495.46

[0265] Table 4 above is a table showing the charge-discharge test results of the examples and comparative examples. Figure 7a shows the results of measuring the initial charge-discharge efficiency according to discharge current density for the cathodes of Example 3-1 and Comparative Example 1-1. Figure 7b shows the results of measuring the charge-discharge efficiency of the second cycle according to discharge current density for the cathodes of Example 3-1 and Comparative Example 1-1.

[0266] Figure 7c shows the measurement results of the charge-discharge efficiency of the third cycle according to the discharge current density for the cathode of Example 3-1 and Comparative Example 1-1.

[0267] Figure 17 shows the charge / discharge test results before and after lithium electrodeposition of Example 3-1.

[0268] According to Table 4, Figures 7a to 7c, and Figure 17, it was confirmed that the charge / discharge efficiency of the cathode in Example 3-1, in which a protective layer was formed by adding 60 wt% of amorphous carbon and magnesium nitride, was significantly higher than that of Comparative Example 1-1, in which a protective layer was formed solely of amorphous carbon. Furthermore, it was confirmed that the charge / discharge efficiency increased as the number of cycles increased from 1 to 3. In addition, in the case of Comparative Example 1-1, the discharge current density was 0.1 to 1 mA / cm² 2 In the region, efficiency increased with increasing current density, but at a current density of 2 mA / cm² 2 In that case, the charge / discharge efficiency actually decreased. On the other hand, in Example 3-1, the charge / discharge efficiency increased with increasing current density, confirming that the high-speed charge / discharge characteristics were also excellent.

[0269] In other words, it can be confirmed that the cathode according to the embodiment of the present invention simultaneously improves the bonding strength of the protective layer and the electrochemical performance.

[0270]

[0271] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. The entire house; and A protective layer located on the above-mentioned entire house; comprising, The above protective layer contains magnesium nitride (Mg3N2), amorphous carbon, and a binder, and As a result of performing X-ray diffraction (XRD) analysis on the above protective layer, satisfying the following Equation 1, Negative electrode for lithium secondary batteries: [Equation 1] 0.5 < I(Mg3N2) / I(Carbon) < 2.0 (In Equation 1, I(Mg3N2) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 41 to 43 during XRD analysis, and I(Carbon) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 24 to 26 during XRD analysis.) 2. In Paragraph 1, The content of the magnesium nitride (Mg3N2) is 10% by weight or more and 80% by weight or less, based on 100% of the total weight of the protective layer. Negative electrode for lithium secondary battery.

3. In Paragraph 1, The bonding strength of the above protective layer is 150 to 800 mN / cm, Negative electrode for lithium secondary battery.

4. In Paragraph 1, The thickness of the protective layer is 1 to 20 μm, Negative electrode for lithium secondary battery.

5. In Paragraph 1, The above-mentioned current collector and protective layer further include a lithium-affinity metal layer, and The above lithium-affinity metal layer comprises at least one of Ag, Au, Sn, Al, Zn, Si, Ge, Ni, Co, Fe, Ti, Mo, and Cr, and The thickness of the lithium-affinity metal layer is 5 to 500 nm, Negative electrode for lithium secondary battery.

6. In Paragraph 5, The above lithium-affinity metal layer contains Ag, and As a result of performing X-ray diffraction (XRD) analysis on the above protective layer, satisfying Equation 2 below, Negative electrode for lithium secondary batteries: [Equation 2] 0.5 < I(Mg3N2) / I(Ag) < 2.0 (In Equation 2, I(Mg3N2) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 41 to 43 during XRD analysis, and I(Ag) represents the maximum peak intensity occurring in the region where the 2theta(2θ) value is 37 to 39 during XRD analysis.) 7. In Paragraph 1, When EDS analysis is performed on the above cathode surface, the average diameter of the identified Mg clusters is 0.1 to 15 μm, Negative electrode for lithium secondary battery.

8. In Paragraph 1, The above magnesium nitride (Mg3N2) is a plate-shaped particle, and The average particle size of the above plate-shaped particles is 0.2 to 15 μm, Negative electrode for lithium secondary battery.

9. Steps for preparing the entire house; and The method comprises the step of forming a protective layer by applying a coating slurry containing magnesium nitride (Mg3N2), amorphous carbon, and a binder onto at least one surface of a current collector. Satisfying Equation 3 below, Method for manufacturing a negative electrode for a lithium secondary battery: [Equation 3] 0.16<[Mg3N2] / (T+P)<0.35 (In Equation 3, [Mg3N2] represents the input amount of magnesium nitride (Mg3N2) (in weight% units) based on 100% of the total weight of magnesium nitride (Mg3N2) and amorphous carbon during the protective layer formation stage, T represents the temperature (°C) at which the coating slurry is dried after application during the protective layer formation stage, and P represents the drying time (min) after application of the coating slurry during the protective layer formation stage; the units of the calculated values ​​in Equation 3 are not considered.) 10. In Paragraph 9, In the above protective layer formation step, the amount of magnesium nitride (Mg3N2) added is greater than 20% by weight and less than or equal to 70% by weight, based on 100% of the total weight of magnesium nitride (Mg3N2) and amorphous carbon. Method for manufacturing a negative electrode for a lithium secondary battery.

11. In Paragraph 9, After applying the above coating slurry, the drying temperature is 80 to 190 ℃, Method for manufacturing a negative electrode for a lithium secondary battery.

12. In Paragraph 9, After applying the above coating slurry, the drying time is 5 minutes to 12 hours, Method for manufacturing a negative electrode for a lithium secondary battery.

13. In Paragraph 9, When drying after applying the above coating slurry, the air atmosphere has a moisture (H2O) content of 4 vol% or less based on 100% of the total volume of air, Method for manufacturing a negative electrode for a lithium secondary battery.

14. A negative electrode for a lithium secondary battery comprising any one of claims 1 to 8, Lithium secondary battery.

15. In Paragraph 14, When the above lithium secondary battery has undergone at least one charge-discharge cycle, the protective layer of the negative electrode for the lithium secondary battery further comprises Li3N and Li-NC compounds. Lithium secondary battery.

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