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

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery comprising the same, the negative electrode comprising: a current collector; the lithium-based negative electrode active material layer is positioned on the current collector; and a protective layer on the lithium-based negative electrode active material layer, in which the protective layer comprises a gel polymer electrolyte and lithium ion conductive nanoparticles, the gel polymer electrolyte comprises lithium ions derived from a lithium salt, anions, an organic solvent, and a polymer, and the lithium ion binding energy of the anions is greater than the lithium ion binding energy of the organic solvent.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2024-0080561, filed with the Korean Intellectual Property Office on June 20, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode. Background Technology

[0004] Batteries using lithium metal anodes are attracting significant attention as next-generation lithium-ion rechargeable batteries with high capacity and energy. Representative examples include lithium metal batteries, lithium-sulfur batteries, and lithium-air batteries. Lithium metal, used as the anode, has a low density (0.54 g / cm³). 3 With its low standard reduction potential (-3.040V vs. SHE), it offers a very high theoretical capacity (3860mAh / g) and excellent gravimetric and volumetric energy densities.

[0005] However, lithium metal batteries suffer from lithium dendrite formation and low coulombic efficiency. During electrochemical cycling, lithium dendrites and dead lithium form on the lithium metal anode, leading to the loss of active material. Due to its high reactivity, lithium metal forms a passivation layer (solid electrolyte interface; SEI) on its surface by reacting with the electrolyte and residual moisture. However, the formation of lithium dendrites and inert lithium (dead lithium) increases the electrode surface area, causing the passivation layer to be repeatedly damaged and reformed. Therefore, lithium metal and electrolyte are continuously consumed, reducing coulombic efficiency and shortening battery cycle life. Furthermore, if lithium dendrites grow through the separator, internal short circuits may occur, potentially leading to safety issues such as fires or explosions. Therefore, strategies to induce uniform lithium growth and reduce electrolyte decomposition are crucial for achieving high-performance and high-safety lithium metal batteries.

[0006] To induce uniform lithium growth, conventionally designed electrolytes incorporate numerous anions that coordinate around lithium ions, forming an inorganic SEI layer through anion decomposition. This SEI layer is characterized by high mechanical strength, rapid ion conduction, and uniform composition, which induces denser lithium growth.

[0007] However, for high-energy-density lithium metal batteries, a lean electrolyte is crucial. In this case, battery life depends primarily on the electrolyte consumption factor, rather than the consumption factor of available lithium. Therefore, there is an urgent need to develop technologies to reduce electrolyte decomposition. Summary of the Invention

[0008] Therefore, one objective of the present invention is to provide a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode, which can improve the battery life characteristics by reducing electrolyte decomposition.

[0009] One embodiment of the present invention provides a negative electrode for a lithium secondary battery, the negative electrode comprising:

[0010] A current collector; a lithium-based negative electrode active material layer on the current collector; and a protective layer on the lithium-based negative electrode active material layer, wherein the protective layer comprises a gel polymer electrolyte and lithium-ion conductive nanoparticles, the gel polymer electrolyte comprising lithium ions, anions, an organic solvent, and a polymer derived from lithium salts, and the lithium-ion binding energy of the anions is greater than that of the lithium-ion binding energy of the organic solvent.

[0011] The negative electrode used in lithium secondary batteries can satisfy the following formula 1.

[0012] [Formula 1]

[0013] BE Li (Anion)-BE Li (Organic solvent) ≥0.25 (eV)

[0014] In Equation 1, BE Li (Anion) is the lithium-ion binding energy of the anion, BE Li (Organic solvent) refers to the lithium-ion binding energy of the organic solvent.

[0015] The average lithium-ion concentration of lithium-ion conductive nanoparticles can be greater than that of gel polymer electrolytes.

[0016] An interfacial region is formed between the gel polymer electrolyte and the lithium-ion conductive nanoparticles, and a lithium-ion concentration gradient may exist in the interfacial region.

[0017] The average lithium-ion concentration of lithium-ion conductive nanoparticles can be greater than 30M.

[0018] The average lithium-ion concentration of the gel polymer electrolyte can be less than 3M.

[0019] The interface region can form a space charge composed of lithium ions.

[0020] The coordination number between lithium ions and anions in the interface region can be less than 1.

[0021] The coordination number between lithium ions and organic solvents in the interface region can be less than 0.5.

[0022] In the interface region, the coordination number between lithium ions and lithium-ion conductive nanoparticles can be greater than 50% of the total coordination number of lithium ions.

[0023] The lithium salt can be LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiBF4 (lithium tetrafluoroborate), LiPF6 (lithium hexafluorophosphate), LiBOB (lithium bis(oxalate)borate) or a combination thereof.

[0024] The organic solvent can be FSA (N,N-dimethylaminosulfonyl fluoride), DME (1,2-dimethoxyethane), FEC (fluoroethylene carbonate), or a combination thereof.

[0025] The polymer is formed by cross-linking a polymer compound, and the polymer compound can be PEGDA (poly(ethylene glycol) diacrylate), PEGDMA (polyethylene glycol dimethacrylate), PEG (poly(ethylene glycol)), EGDMA (ethylene glycol dimethacrylate), PEGDE (poly(ethylene glycol) diglycidyl ether) or a combination thereof.

[0026] The molecular weight of the polymeric compound can range from 500 g / mol to 5000 g / mol.

[0027] The molecular weight of the polymer can range from 10,000 to 1,000,000.

[0028] Lithium-ion conductive nanoparticles can be oxide nanoparticles.

[0029] Lithium-ion conductive nanoparticles can be LLZO-based oxides, LSTP-based oxides, LATP-based oxides, LAGP-based oxides, LLTO-based oxides, LGPO-based oxides, or combinations thereof.

[0030] Lithium-ion conductive nanoparticles can be LLZO-based oxides represented by the following chemical formula 1.

[0031] [Chemical Formula 1]

[0032] Li a M1 b La c Zr d M2 e O f

[0033] In the above chemical formula 1, M1 is Al, M2 is Ta, Nb, W or a combination thereof, 5≤a≤7, 0≤b≤3, 2≤c≤4, 1≤d≤3, 0≤e≤2 and 10≤f≤14.

[0034] The average particle diameter D50 of lithium-ion conductive nanoparticles can range from 100 nm to 5 μm.

[0035] The weight ratio of lithium-ion conductive nanoparticles to the total weight of lithium salt and polymer (lithium-ion conductive nanoparticles: lithium salt + polymer) can be from 5:5 to 9:1.

[0036] The weight ratio of lithium salt to polymer (lithium salt: polymer) can be from 2:8 to 9:1.

[0037] The thickness of the protective layer can range from 1 μm to 20 μm.

[0038] Another embodiment of the present invention provides a lithium secondary battery comprising the above-described negative electrode for a lithium secondary battery.

[0039] According to one embodiment of the present invention, the negative electrode for a lithium secondary battery includes a protective layer located on a lithium-based negative electrode active material layer, thereby reducing electrolyte decomposition within the battery and improving the battery's lifespan characteristics.

[0040] As discussed, the methods and apparatus appropriately include the use of a controller or processor. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of a negative electrode for a lithium secondary battery according to some embodiments of the present invention.

[0042] Figure 2 Examples of lithium salts and organic solvents used as impregnating liquid electrolytes in the manufacture of a protective layer for the negative electrode of a lithium secondary battery according to some embodiments of the present invention are shown in chemical formula form.

[0043] Figure 3 A graph showing the lithium-ion binding affinity of FSI anion, FSA organic solvent, FEC organic solvent and DMF organic solvent according to Experimental Example 1.

[0044] Figure 4 This is a graph showing the recovery of electrochemical properties (discharge capacity) after cycling in Experimental Example 2, based on the additional injected electrolyte.

[0045] Figure 5 This is a graph showing the recovery of electrochemical properties (battery voltage) after cycling, based on the additional electrolyte injected, in Experimental Example 2.

[0046] Figure 6 A graph showing the results of evaluating the electrolyte residual rate after cycling according to Experimental Example 2.

[0047] Figure 7 This is a graph showing the results of evaluating the reversible capacity of lithium after cycling, based on Experimental Example 2.

[0048] Figure 8 The figure shows the Raman spectroscopy analysis results based on Experimental Example 3.

[0049] Figure 9This is a snapshot of the SICC / gel polymer electrolyte interface, showing Li according to Experimental Example 4. + Space charge formation.

[0050] Figure 10 To display Li + The graph shows the distribution of concentrations of major electrolyte species as a function of distance from the SICC surface.

[0051] Figure 11 To illustrate the Li at the SICC / electrolyte interface according to Experimental Example 4 + A schematic diagram of accumulated potential.

[0052] Figure 12 A graph showing the coordination number of lithium ions based on the MD simulation results of Experimental Example 4.

[0053] Figure 13 A graph showing the simulation results of the evaluation of the average lithium-ion decomposition voltage according to Experimental Example 5.

[0054] Figure 14 This is a graph showing the results of evaluating the electrolyte decomposition current using linear sweep voltammetry in a Li / Cu half-cell according to Experimental Example 6.

[0055] Figure 15 This is a graph showing the time-dependent impedance evaluation results of the symmetrical cell based on Experimental Example 7.

[0056] Figure 16 This is a graph showing the results of evaluating the increase in the initial interface resistance of a symmetrical cell over time according to Experimental Example 8.

[0057] Figure 17 and Figure 18 This is a graph showing the evaluation results of the lifespan characteristics of the full cell based on Experimental Example 9.

[0058] Figure 19 A graph showing the 19F NMR analysis results of the residual electrolyte after 10 cycles of the full cell manufactured according to Experimental Example 10.

[0059] Figure 20 This is a graph showing the results of elemental ratio analysis within the SEI (solid electrolyte interface) of the full cell manufactured according to Experimental Example 10 after 10 cycles, analyzed by X-ray photoelectron spectroscopy (XPS).

[0060] Figure 21 This is a graph showing the results of evaluating the residual LiFSI fraction based on the cycling process after manufacturing a full cell, according to Experimental Example 10.

[0061] Figure 22The image shows a cross-sectional SEM image of a cycled lithium electrode according to Experimental Example 11, revealing a porous surface layer of approximately 3 micrometers exposed by FIB milling.

[0062] Figure 23 The image shows a cross-sectional SEM image of a cycled lithium electrode coated with SICC-GPE composite material according to Experimental Example 11, which shows a dense protective layer of approximately 8 micrometers.

[0063] Figure 24 This is a graph showing the results of evaluating the battery swelling characteristics based on the cycling process after manufacturing a full cell, according to Experimental Example 12. Detailed Implementation

[0064] The terms first, second, and third are used to describe (but are not limited to) various parts, components, regions, layers, and / or portions. These terms are used only to distinguish one part, component, region, layer, or portion from another. Therefore, a first part, component, region, layer, or portion described herein may be referred to as a second part, component, region, layer, or portion without departing from the scope of the invention.

[0065] The technical terminology used herein is intended only to indicate certain exemplary embodiments and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein include the plural forms. As used in the specification, “comprising / including / containing / having” means to specify the presence of a particular feature, area, value, step, behavior, element, and / or component, but does not exclude the presence or addition of any other feature, area, value, step, behavior, element, and / or component.

[0066] When a component is "on" or "above" another component, it can be directly on or above the other component, or it can include another component in between. Conversely, when it is indicated that an object is "directly on" another object, no object is inserted between them.

[0067] The term "gel polymer electrolyte" in this article refers to a polymer matrix swollen with a liquid electrolyte solvent, which traps solvent components and enables lithium-ion transport through the polymer network while maintaining mechanical self-support.

[0068] The term "lithium-ion binding energy" in this article refers to the calculated energy difference between the total energy of the lithium-ion / ligand complex and the sum of the individual energies of the lithium ion and ligand.

[0069] The term "interface region" in this article refers to a nanoscale region that forms and exhibits a compositional and concentration gradient different from that of the adjacent bulk phase when the gel polymer electrolyte and lithium-ion conductive nanoparticles (or other solid phases) come into contact.

[0070] The term "space charge layer" in this article refers to the region of charge imbalance that forms at the interface between two materials with different lithium chemical potentials.

[0071] This article applies Li to electrolytes + The term "coordination number" refers to the number of ligand atoms directly bonded within the first solvation shell of a lithium ion.

[0072] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms commonly defined in dictionaries are further interpreted as having meanings consistent with relevant technical literature and this invention, and should not be interpreted in an idealized or highly formalized sense unless defined.

[0073] Furthermore, unless otherwise noted, “%” means “weight %”, where 1 ppm is 0.0001 wt%.

[0074] In this specification, the term "combination thereof" as described in the Markush formal representation means one or more mixtures or combinations of components selected from the components described in the Markush formal representation, and means containing one or more components selected from the components.

[0075] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” are intended to include the plural forms as well. These terms are intended only to distinguish one component from another, and the terms do not limit the characteristics, order, or sequence of the constituent components. As used herein, the term “and / or” includes any and all combinations of one or more of the associated enumerated items. Furthermore, the terms “unit,” “device,” “component,” and “module” described in the specification mean a unit for performing at least one function and operation, and can be implemented by hardware components or software components and combinations thereof.

[0076] Although the exemplary embodiments are described as using multiple units to perform the exemplary process, it should be understood that the exemplary process can also be performed by one or more modules. Furthermore, it should be understood that the term controller / control unit refers to a hardware device that includes a memory and a processor and is specifically programmed to perform the processes described herein. The memory is configured to store the modules, and the processor is specifically configured to execute the modules, thereby performing one or more processes further described below.

[0077] Furthermore, the control logic of this invention can be embodied in a non-transitory computer-readable medium, including executable program instructions that can be executed by a processor, controller, etc. Examples of computer-readable media include, but are not limited to, ROM, RAM, optical disc (CD)-ROM, magnetic tape, floppy disk, flash drive, smart card, and optical data storage device. The computer-readable medium can also be distributed across a network-connected computer system, allowing it to be stored and executed in a distributed manner, for example, via a telematics server or a controller area network (CAN).

[0078] Unless otherwise stated or obvious from the context, as used herein, the term “about” is understood to mean within the normal tolerance range in the field, for example, within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the specified value. All numerical values ​​provided herein are modified by the term “about” unless obvious from the context.

[0079] The embodiments are described in detail below to enable those skilled in the art to readily practice the invention. Those skilled in the art will recognize that the described embodiments can be modified in various ways without departing from the spirit or scope of the invention.

[0080] 1. Anode used in lithium secondary batteries

[0081] Electrolytes containing solvents with low lithium coordination capacity or high concentrations of lithium salts can control lithium deposition density by increasing the coordination of anions around lithium ions and inducing anion decomposition to form a thin and stable passivation layer (SEI; solid electrolyte interface) on the lithium metal surface.

[0082] However, if there are excessive anions in the lithium-ion solvation structure, these anions are continuously consumed at both the positive and negative electrodes during battery cycling, and the degree to which lithium ions coordinate with anions gradually decreases. Consequently, the oxidative stability of the electrolyte also decreases, leading to a deterioration in battery performance. Therefore, suppressing the decomposition of anions in a low-electrolyte environment is a key factor in achieving the excellent lifespan characteristics of high-energy-density lithium metal batteries.

[0083] Therefore, through repeated research, the inventors discovered that by further placing the protective layer according to the present invention on the lithium-based negative electrode active material layer, the electrolyte decomposition in the battery can be reduced, thereby improving the battery's lifespan characteristics, and thus the present invention was completed.

[0084] Specifically, according to one embodiment of the present invention, the negative electrode for a lithium secondary battery includes a current collector; a lithium-based negative electrode active material layer located on the current collector; and a protective layer located on the lithium-based negative electrode active material layer.

[0085] The protective layer comprises a gel polymer electrolyte and lithium-ion conductive nanoparticles, wherein the gel polymer electrolyte comprises lithium ions, anions, organic solvents and polymers derived from lithium salts.

[0086] At this point, the lithium-ion binding energy of the anion is greater than that of the lithium-ion binding energy of the organic solvent.

[0087] More specifically, the negative electrode used in lithium secondary batteries can satisfy the following equation 1.

[0088] [Formula 1]

[0089] BE Li (Anion)-BE Li (Organic solvent) ≥0.25 (eV)

[0090] In Equation 1, BE Li (Anion) is the lithium-ion binding energy of the anion, BE Li (Organic solvent) refers to the lithium-ion binding energy of the organic solvent.

[0091] In this way, when the lithium-ion binding energy of the anions in the protective layer is greater than that of the lithium-ion binding energy of the organic solvent, or preferably when Equation 1 is satisfied, the oxygen in the polymer on the surface of the lithium-ion conductive nanoparticles and in the gel polymer electrolyte can actively participate in the lithium-ion coordination of the electrolyte. Therefore, the existing solvation structure with a large number of anions coordinated to lithium ions can be disrupted, thereby improving the battery's lifespan characteristics. Over-coordinated lithium ions from anions rapidly consume the anions through the reaction between lithium metal and the negative electrode. This consumption of anions reduces the oxidative stability of the electrolyte and accelerates the degradation of the positive electrode, leading to a deterioration in the battery's lifespan characteristics.

[0092] Furthermore, the average lithium-ion concentration of the lithium-ion conductive nanoparticles in the negative electrode according to the present invention can be greater than the average lithium-ion concentration of the gel polymer electrolyte. Therefore, an interface region is formed between the gel polymer electrolyte and the lithium-ion conductive nanoparticles, and a lithium-ion concentration gradient may exist in the interface region.

[0093] When a lithium ion concentration gradient exists in such an interface region, a space charge consisting solely of lithium ions (free Li) can form due to the chemical potential difference of the lithium ions. +This space charge is primarily coordinated with the polymer or lithium-ion conductive nanoparticles, resulting in less electrolyte coordination compared to conventional electrolytes or gel polymer electrolytes. In this way, the reduced lithium-ion-electrolyte coordination at the interface region can significantly reduce electrolyte decomposition during lithium deposition and preferably improve the lifetime characteristics of the resulting battery.

[0094] Regarding this point, Figure 1 This is a conceptual diagram of a negative electrode for a lithium secondary battery according to some embodiments of the present invention, showing the formation process of space charge consisting only of lithium ions. However, Figure 1 Examples of LiFSI (lithium bis(fluorosulfonyl)imide) as a lithium salt and FSA (N,N-dimethylaminosulfonyl fluoride) as an organic solvent are shown, but these are merely examples, and the lithium salts and organic solvents according to the present invention are not necessarily limited thereto. Furthermore, Figure 2 Examples of lithium salts and organic solvents used as impregnating liquid electrolytes in the manufacture of a protective layer for the negative electrode of a lithium secondary battery according to some embodiments of the present invention are shown, which are represented by the chemical formulas LiFSI and FSA, respectively.

[0095] Specifically, the average lithium-ion concentration of the lithium-ion conductive nanoparticles can be greater than or equal to 30M, more specifically greater than or equal to 35M. Furthermore, the average lithium-ion concentration of the gel polymer electrolyte can be less than 3M, more specifically less than 2M. When the average lithium-ion concentrations of the lithium-ion conductive nanoparticles and the gel polymer electrolyte meet the above ranges, space charge is formed more effectively in the interface region, and lithium-ion-electrolyte coordination is reduced, thus enabling a more effective improvement in battery life characteristics.

[0096] Furthermore, the coordination number between lithium ions and anions in the interface region can be 1 or less, more specifically 0.8 or 0.5 or less. Additionally, the coordination number between lithium ions and the organic solvent in the interface region can be 0.5 or less, more specifically 0.45 or less. When the coordination number between lithium ions and anions and the coordination number between lithium ions and the organic solvent in the interface region are sufficiently low (e.g., within the ranges described above), it is more preferable to achieve an improved battery life characteristics.

[0097] Furthermore, the coordination number between lithium ions and lithium-ion conductive nanoparticles in the interface region can be 50% or greater of the total coordination number of lithium ions, more specifically 55% or greater. In this way, because the proportion of coordination number between lithium ions and lithium-ion conductive nanoparticles is sufficiently large, the coordination number between lithium ions and anions and between lithium ions and organic solvents is relatively reduced, making it more preferable to achieve the effect of improving battery life characteristics.

[0098] The lithium salt can be LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiBF4 (lithium tetrafluoroborate), LiPF6 (lithium hexafluorophosphate), LiBOB (lithium bis(oxalate)borate) or a combination thereof.

[0099] The organic solvent can be FSA (N,N-dimethylaminosulfonyl fluoride), DME (1,2-dimethoxyethane), FEC (fluoroethylene carbonate), or a combination thereof.

[0100] At this point, lithium salts and organic solvents can be appropriately selected and combined such that the anionic binding energy of the organic solvents in the listed compounds and the lithium ion binding energy are within the range of the present invention, i.e. preferably satisfying Formula 1.

[0101] Preferably, as an example, the lithium salt can be LiFSI, and the organic solvent can be FSA. When the lithium salt and organic solvent are selected as compounds, their lithium-ion binding capacity meets the scope of the invention, thereby preferably achieving the effect of improving the battery's lifespan characteristics.

[0102] Simultaneously, the polymer is formed through cross-linking of polymeric compounds, and the polymeric compounds can be PEGDA (poly(ethylene glycol) diacrylate), PEGDMA (polyethylene glycol dimethacrylate), PEG (poly(ethylene glycol)), EGDMA (ethylene glycol dimethacrylate), PEGDE (poly(ethylene glycol) diglycidyl ether), or combinations thereof. When the polymeric compound is in this manner, by coordinating the functional groups of the compound with lithium ions, there is an advantage in reducing the coordination of the electrolyte with lithium ions.

[0103] The molecular weight of the polymeric compound can range from 500 g / mol to 5000 g / mol, more specifically from 500 g / mol to 2000 g / mol or from 500 g / mol to 1000 g / mol. If the molecular weight of the polymeric compound is too small, insufficient swelling of the electrolyte after polymerization may result in low ionic conductivity. If the molecular weight of the polymeric compound is too large, excessive swelling of the electrolyte after polymerization may weaken the durability of the protective layer.

[0104] The molecular weight of the polymer can range from 10,000 to 1,000,000. If the molecular weight of the polymer is too small, the durability of the protective layer may deteriorate as the effectiveness of the adhesive decreases. If the molecular weight of the polymer is too large, there may be a problem of low ionic conductivity due to the reduced mobility of the polymer chains coordinated with lithium ions.

[0105] Lithium-ion conductive nanoparticles can be oxide nanoparticles. In this case, the lithium-ion conductive nanoparticles can be LLZO-based oxides, LSTP-based oxides, LATP-based oxides, LAGP-based oxides, LLTO-based oxides, LGPO-based oxides, or combinations thereof.

[0106] More specifically, the lithium-ion conductive nanoparticles can be LLZO-based oxides represented by the following chemical formula 1. When lithium-ion conductive nanoparticles are in this manner, the high internal lithium-ion concentration offers the advantage of maximizing the chemical potential with the gel polymer electrolyte.

[0107] [Chemical Formula 1]

[0108] Li a M1 b La c Zr d M2 e O f

[0109] In Equation 1 above, M1 is Al, M2 is Ta, Nb, W or a combination thereof, 5≤a≤7, 0≤b≤3, 2≤c≤4, 1≤d≤3, 0≤e≤2 and 10≤f≤14.

[0110] At this point, the average particle diameter D50 of the lithium-ion conductive nanoparticles can range from 100 nm to 5 μm. If the average particle diameter D50 of the lithium-ion conductive nanoparticles is too small, the durability of the protective layer may be problematic. If the average particle diameter D50 of the lithium-ion conductive nanoparticles is too large, there may be a problem with reduced conductivity of lithium ions across the interface with the gel polymer electrolyte. In this specification, the average particle diameter D50 can be defined as the particle diameter corresponding to 50% of the volumetric accumulation on the particle diameter distribution curve. The average particle diameter D50 can be measured, for example, using laser diffraction.

[0111] The weight ratio of lithium-ion conductive nanoparticles to the total weight of lithium salt and polymer (lithium-ion conductive nanoparticles: lithium salt + polymer) can range from 5:5 to 9:1. If the content of lithium-ion conductive nanoparticles is too low compared to the total weight of lithium salt and polymer, there may be a problem of reduced conductivity of lithium ions across the interface between the lithium-ion conductive nanoparticles and the gel polymer electrolyte. If the content of lithium-ion conductive nanoparticles is too high compared to the total weight of lithium salt and polymer, there may also be a problem of reduced conductivity of lithium ions across the interface between the lithium-ion conductive nanoparticles and the gel polymer electrolyte.

[0112] The weight ratio of lithium salt to polymer (lithium salt:polymer) can be from 2:8 to 9:1. If the lithium salt content is too low compared to the polymer, the conductivity of dissociated lithium ions may be reduced due to the swelling of the polymer. If the lithium salt content is too high compared to the polymer, the binding effect of the protective layer may be reduced due to the polymer.

[0113] The thickness of the protective layer can range from 1 μm to 20 μm, more specifically from 5 μm to 15 μm. If the thickness of the protective layer is too small, the effect of improving the lifetime characteristics due to the introduction of the protective layer may be negligible. If the thickness of the protective layer is too large, there may be problems with excessive increase in battery resistance and decrease in energy density.

[0114] Meanwhile, the lithium-based anode active material layer can be a conventional lithium-based anode active material layer containing lithium metal or lithium alloy (e.g., an alloy of lithium with metals such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium), and therefore its detailed description will be omitted.

[0115] 2. Manufacturing method for the negative electrode of a lithium secondary battery

[0116] Another embodiment of the present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, the method comprising the steps of: preparing a lithium-based negative electrode active material layer; applying and drying a solution for forming a protective layer on the lithium-based negative electrode active material layer to form a pre-protective layer, the solution comprising lithium-ion conductive nanoparticles, a first lithium salt and a polymerizable compound; and impregnating the pre-protective layer with a liquid electrolyte comprising a second lithium salt and an organic solvent to form a protective layer having a gel polymer electrolyte.

[0117] The following describes in detail a method for manufacturing a negative electrode for a lithium secondary battery according to another embodiment of the present invention.

[0118] First, a lithium-based anode active material layer is prepared.

[0119] The lithium-based anode active material layer can be a conventional lithium-based anode active material layer containing lithium metal or lithium alloy (e.g., an alloy of lithium with metals such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium), and can be prepared by methods commonly used in the art.

[0120] Then, a solution for forming a protective layer is applied to and dried on the lithium-based anode active material layer to form a pre-protective layer, the solution comprising lithium-ion conductive nanoparticles, a first lithium salt, and a polymerizable compound.

[0121] During the coating and drying process, the polymeric compounds crosslink with each other to form a crosslinked polymer, and thus a pre-protective layer can be formed comprising lithium-ion conductive nanoparticles and a polymer (the polymer being in a state prior to being impregnated, swollen, and gelled by a liquid electrolyte used for impregnation in the steps described below).

[0122] Lithium-ion conductive nanoparticles can be oxide nanoparticles. In this case, the lithium-ion conductive nanoparticles can be LLZO-based oxides, LSTP-based oxides, LATP-based oxides, LAGP-based oxides, LLTO-based oxides, LGPO-based oxides, or combinations thereof.

[0123] More specifically, lithium-ion conductive nanoparticles can be LLZO-based oxides represented by the following chemical formula 1. Their benefits are as described above and will therefore be omitted.

[0124] [Chemical Formula 1]

[0125] Li a M1 b La c Zr d M2 e O f

[0126] In the above chemical formula 1, M1 is Al, M2 is Ta, Nb, W or a combination thereof, 5≤a≤7, 0≤b≤3, 2≤c≤4, 1≤d≤3, 0≤e≤2 and 10≤f≤14.

[0127] The polymeric compound is PEGDA (poly(ethylene glycol) diacrylate), PEGDMA (poly(ethylene glycol) dimethacrylate), PEG (poly(ethylene glycol)), EGDMA (ethylene glycol dimethacrylate), PEGDE (poly(ethylene glycol) diglycidyl ether), or a combination thereof. Its benefits are as described above and will therefore be omitted.

[0128] The first lithium salt is LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiBF4 (lithium tetrafluoroborate), LiPF6 (lithium hexafluorophosphate), LiBOB (lithium bis(oxalate)borate), or a combination thereof.

[0129] The solvent used in the solution for forming the protective layer can be, for example, EC (ethylene carbonate), DEC (diethyl carbonate), or a mixture thereof.

[0130] Drying can be carried out at a temperature range of approximately 40°C to 80°C for approximately 5 to 15 hours.

[0131] Then, a liquid electrolyte containing a second lithium salt and an organic solvent is impregnated into the pre-protective layer to form a protective layer with a gel polymer electrolyte.

[0132] A gel polymer electrolyte can be formed by impregnating and swelling the polymer within the pre-protective layer using a liquid electrolyte for impregnation and gelation.

[0133] The organic solvent can be FSA (N,N-dimethylaminosulfonyl fluoride), DME (1,2-dimethoxyethane), FEC (fluoroethylene carbonate), or a combination thereof.

[0134] The second lithium salt can be LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiBF4 (lithium tetrafluoroborate), LiPF6 (lithium hexafluorophosphate), LiBOB (lithium bis(oxalate)borate), or a combination thereof.

[0135] The first lithium salt and the second lithium salt may be the same or different, but preferably they may be the same. The role of the first lithium salt is to mitigate battery degradation due to the consumption of the second lithium salt by maintaining a constant lithium salt concentration within the battery during cycling.

[0136] Therefore, a negative electrode for a lithium secondary battery according to an embodiment of the present invention can be manufactured, the negative electrode having a structure in which a protective layer of gel polymer electrolyte and lithium-ion conductive nanoparticles is located on a lithium-based negative electrode active material layer.

[0137] 3. Lithium secondary batteries

[0138] Another embodiment of the present invention provides a lithium secondary battery comprising the above-described negative electrode for a lithium secondary battery.

[0139] A lithium secondary battery may more specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, a separator inserted between the positive and negative electrodes, and an electrolyte.

[0140] The negative electrode is as described above.

[0141] In addition, lithium secondary batteries may optionally include a battery container and a sealing element for sealing the battery container, the battery container housing an electrode assembly of a positive electrode, a negative electrode, and a separator.

[0142] The 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 contain positive active material.

[0143] There are no particular restrictions on the positive electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. For example, it can be made of stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with surface treatments using carbon, nickel, titanium, silver, etc. Furthermore, the thickness of the positive electrode current collector can typically range from 3 μm to 500 μm, and fine protrusions and depressions can be formed on its surface to improve the adhesion strength of the positive electrode active material. It can be used in various forms (e.g., films, sheets, foils, meshes, porous materials, foams, nonwoven fabrics, etc.).

[0144] Compounds capable of reversibly inserting and deintercalating lithium (lithiation intercalation compounds) can be used as positive electrode active materials. Specifically, at least one composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used, and specific examples can be compounds represented by one of the following chemical formulas:

[0145] Li a A 1-b R b D2 (where 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5), Li a E 1-b R b O 2-c D c (where 0.90≤a≤1.8, 0≤b≤0.5 and 0≤c≤0.05), LiE 2-b R b O 4-c D c (where 0 ≤ b ≤ 0.5 and 0 ≤ c ≤ 0.05), Li a Ni 1-b-c Co b R c D α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α≤2), Li a Ni 1-b- c Co b R c O 2-α Z α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2), Li a Ni 1-b-c Co b R c O 2-α Z2 (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2), Li a Ni 1-b-c Mn b Rc D α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α≤2), Li a Ni 1-b-c Mn b R c O 2-α Z α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2), Li a Ni 1-b-c Mn b R c O 2-α Z2 (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2), Li a Ni b E c G d O2 (where 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5 and 0.001≤d≤0.1), Li a Ni b Co c Mn d GeO2 (where 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5 and 0.001≤e≤0.1), Li a NiG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1), Li a CoG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1), Li a MnG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1), Li a Mn2G b O4 (where 0.90≤a≤1.8 and 0.001≤b≤0.1), QO2, QS2, LiQS2, V2O5, LiV2O5, LiTO2, LiNiVO4, Li (3-f) J2PO 43 (0≤f≤2), Li (3-f) Fe2PO 43 (0≤f≤2) and LiFePO4.

[0146] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z 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; T is Cr, V, Fe, Sc, Y or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0147] Of course, compounds with a coating on their surface or mixtures of compounds and coatings can also be used.

[0148] The coating may contain at least one coating element compound selected from oxides, hydroxides, hydroxyoxides, oxycarbonates, and hydroxycarbonates of the coating element. The compounds forming these coatings may be amorphous or crystalline. The coating elements included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating can be formed by any coating method (e.g., spraying, immersion, etc.) as long as the use of these elements in the compound does not adversely affect the properties of the positive electrode active material. Since this is well known to those skilled in the art, a detailed explanation thereof will be omitted.

[0149] The positive electrode active material layer may also include an adhesive and / or conductive material together with the aforementioned positive electrode active material.

[0150] Adhesives are used to improve the adhesion between positive electrode active material particles and the adhesion strength between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, 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 substances may be used alone or as a mixture of two or more, but is not limited thereto. The adhesive may be included in an amount from 1% to 30% by weight of the total weight of the positive electrode active material layer.

[0151] Conductive materials are used to provide conductivity to electrodes and can be used in batteries without particular limitations, as long as they do not cause chemical changes and are electronically conductive. Specific examples include graphite (e.g., natural or synthetic graphite), carbon-based materials (e.g., carbon black, acetylene black, Ketjen black, channel black, furnace black, lampblack, summer black, and carbon fiber), metal powders or fibers (e.g., copper, nickel, aluminum, and silver), conductive whiskers (e.g., zinc oxide, potassium titanate, etc.), conductive metal oxides (e.g., titanium oxide), or conductive polymers (e.g., polyphenylene derivatives). One of these substances can be used alone or as a mixture of two or more of these substances, but is not limited thereto. Conductive materials can typically be included in an amount from 1% to 30% by weight of the total weight of the positive electrode active material layer.

[0152] The positive electrode can be manufactured using conventional positive electrode manufacturing methods.

[0153] Specifically, the positive electrode can be manufactured by applying a composition for forming a layer of positive electrode active material onto a positive electrode current collector, followed by drying and rolling. The composition comprises a positive electrode active material and optionally a binder, conductive material, or solvent. In this case, the type and amount of the positive electrode active material, binder, and conductive material are as described above.

[0154] The solvent can be a commonly used solvent in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water. One of these substances can be used alone, or a mixture of two or more can be used. Considering the coating thickness and manufacturing yield of the slurry, the amount of solvent used is sufficient to dissolve or distribute the positive electrode active material, conductive material, and binder, and its viscosity allows for excellent thickness uniformity in subsequent coating processes during positive electrode fabrication.

[0155] Alternatively, the positive electrode can be manufactured by casting a composition for forming the positive electrode active material layer onto a separate support, peeling the resulting film off the support, and then laminating the resulting film onto the positive electrode current collector.

[0156] The separator separates the positive and negative electrodes and provides a channel for lithium-ion movement. If it is a separator commonly used in lithium secondary batteries, it can be used without any particular restrictions. Preferred separators exhibit low resistance to ion movement of the electrolyte and excellent electrolyte retention. Specifically, porous polymer membranes (e.g., porous polymer membranes made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers) or stacked structures of two or more layers thereof can be used. Alternatively, conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc., can also be used. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength and can be selectively used as single-layer or multi-layer structures.

[0157] The electrolyte can be an impregnation electrolyte used to form the above-mentioned gel polymer electrolyte.

[0158] In addition to the electrolyte components mentioned above, the electrolyte may also contain one or more additives, such as halogenated hydrocarbon carbonate compounds (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, ammonium hexametaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride, to improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity. In this case, the additives may be included in an amount from 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0159] The embodiments of the present invention are described in more detail below through examples. However, the following embodiments are merely preferred embodiments, and the present invention is not limited to the following embodiments.

[0160] Example 1 (negative electrode with the formed protective layer)

[0161] (1) Preparation of negative electrode

[0162] A current collector-lithium metal layer laminate is manufactured by stacking a lithium metal layer on the current collector as a lithium-based negative electrode active material layer using conventional methods.

[0163] (Preparation of the solution for forming the protective layer) Then, Li with an average particle diameter D50 of 500 nm was... 6.4 La3Zr 1.4 Ta 0.6 O 12Oxide nanoparticles (hereinafter referred to as "SICC"), lithium bis(fluorosulfonyl)imide (LiFSI) lithium salt, and a polymerizable compound of PEGDA (poly(ethylene glycol) diacrylate) with a molecular weight of 575 g / mol were added to a mixed solvent of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1 to form a solution for forming a protective layer. At this time, the injected Li... 6.4 La3Zr 1.4 Ta 0.6 O 12 The weight ratio of oxide nanoparticles: LiFSI (lithium bis(fluorosulfonyl)imide) lithium salt: PEGDA (poly(ethylene glycol) diacrylate) polymer compound is 80:10:10.

[0164] (Formation of the pre-protective layer) Then, the solution for forming the protective layer is applied to the lithium metal layer by a doctor blade casting method and dried at 60°C for 10 hours to form a cross-linked polymer containing PEGDA (poly(ethylene glycol) diacrylate) polymer compound and Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Pre-protective layer for oxide nanoparticles.

[0165] (Formation of the protective layer) Then, the pre-protective layer was impregnated using an electrolyte (hereinafter “F-2 electrolyte”) of 3.34M LiFSI dissolved in FSA (N,N-dimethylaminosulfonyl fluoride) solvent as the liquid electrolyte for impregnation, and a protective layer was formed in which a gel polymer electrolyte (hereinafter also “GPE”) was formed as a crosslinked polymer that swelled by the liquid electrolyte for impregnation.

[0166] In this way, a negative electrode with a current collector-lithium metal layer-protective layer sequentially stacked structure was manufactured.

[0167] (2) Preparation of full cells

[0168] Using the manufactured negative electrode, with LiNi applied 0.5 Co 0.2 Mn 0.3 A full cell is manufactured using an O2 positive electrode active material and the same electrolyte as the liquid electrolyte used for impregnation described above.

[0169] Example 2 (negative electrode with the formed protective layer)

[0170] In the protective layer formation step, the negative electrode and the full cell are manufactured in the same manner as in Example 1, except that an electrolyte containing 3.34 M of LiFSI dissolved in FSA solvent and 1% FEC (fluoroethylene carbonate) electrolyte additive is used as the liquid electrolyte for impregnation (hereinafter referred to as "F-3 electrolyte").

[0171] Comparative Example 1 (Negative electrode without protective layer)

[0172] A negative electrode with a current collector-lithium metal layer laminate was manufactured by laminating a lithium metal layer on the current collector using conventional methods as the active material layer of the lithium-based negative electrode (i.e., a negative electrode without the formed protective layer compared to Example 1). Furthermore, by configuring the negative electrode and applying LiNi... 0.5 Co 0.2 Mn 0.3 A full cell is made by using O2 as the positive electrode active material and F-2 as the electrolyte.

[0173] Comparative Example 2 (negative electrode without protective layer)

[0174] The negative electrode and the full cell were manufactured in the same manner as in Comparative Example 1, except that F-3 electrolyte was used as the electrolyte.

[0175] Experimental Example 1: Evaluation of Lithium-ion Binding Force and Satisfaction of Equation 1

[0176] The lithium-ion binding capacity of the FSI anion, FSA organic solvent, commonly used FEC (fluoroethylene carbonate) organic solvent, and DME (1,2-dimethoxyethane) organic solvent used in Examples 1 and 2 was evaluated and is shown in the figure. Figure 3 And in Table 1 below.

[0177] (Table 1)

[0178] Lithium-ion binding force (eV) <![CDATA[FSI - ]]> 0.49 FSA 0.15 FEC 0.34 DME 0.89

[0179] (Table 2)

[0180] <![CDATA[BE Li (Anion)-BE Li (organic solvents) Example 1 0.34 Example 2 0.34

[0181] refer to Figure 3 Table 1 confirms that the FSA organic solvent used in Examples 1 and 2 has extremely low lithium-ion binding capacity. Therefore, it is confirmed that the negative electrodes manufactured according to Examples 1 and 2 satisfy the following formula 1.

[0182] [Formula 1]

[0183] BE Li (Anion)-BE Li (Organic solvent) ≥0.25 (eV)

[0184] In Equation 1, BE Li (Anion) represents the lithium-ion binding energy of the anion in the protective layer, BE Li (Organic solvent) refers to the lithium-ion binding energy of the organic solvent in the protective layer.

[0185] Experimental Example 2: Analysis of the reasons for the deterioration of battery life characteristics when no protective layer is applied

[0186] When a 20μm Li-NCM811 pouch cell with a small amount (5 g / Ah) of F-2 electrolyte was injected, the initial capacity based on the cycling progress and the initial capacity after the additional addition of F-2 electrolyte were evaluated. The results are shown in [Table data would be inserted here]. Figure 4 and Figure 5 middle.

[0187] refer to Figure 4 and Figure 5 It was found that the consumption of F-2 electrolyte was the cause of the deterioration in lifetime characteristics.

[0188] In addition, a 20 μm Li-NCM811 pouch cell with a small amount (5 g / Ah) of F-2 electrolyte was run and cyclically injected to evaluate the electrolyte residual rate of the degraded cell, as shown in the figure. Figure 6 The lithium reversible capacity of the degraded battery is evaluated, as shown in the figure. Figure 7 middle.

[0189] refer to Figure 6 and Figure 7 It was found that the decomposition of FSI anions (especially FSI anions in F-2 electrolyte) is the direct cause of the deterioration in lifetime characteristics.

[0190] Experimental Example 3: Raman Spectroscopy Analysis

[0191] Raman spectroscopy analysis was performed on the protective layer, F-2 electrolyte, 1M LiFSI electrolyte dissolved in FSA, and FSA solvent in the negative electrode manufactured according to Example 1, and the results are shown below. Figure 8 middle.

[0192] refer to Figure 8 This confirmed the observation of very low coordination between lithium ions and FSI anions within the protective layer.

[0193] Experimental Example 4: MD Simulation Analysis

[0194] To illustrate the experimental results of Example 3, MD simulation analysis was performed, and the obtained lithium ion concentration results are illustrated in the figure below. Figures 9 to 11 And as shown in Table 3 below. Furthermore, the resulting coordination number of lithium ions is illustrated in the figure below. Figure 12 And in Table 4 below.

[0195] (Table 3)

[0196] Average lithium-ion concentration (M) Lithium-ion conductive nanoparticles 39 Gel polymer electrolyte 1.6

[0197] (Table 4)

[0198]

[0199] refer to Figures 9 to 12 Tables 3 and 4 confirm a significant difference in average lithium-ion concentration between the lithium-ion conductive nanoparticles and the gel polymer electrolyte, and the existence of a lithium-ion concentration gradient in their interfacial region. Furthermore, it was confirmed that due to the chemical potential difference of these lithium ions, a space charge consisting solely of lithium ions is formed in the interfacial region. Additionally, it was confirmed that, compared to the electrolyte or gel polymer electrolyte region, the Li-O(FSA) and Li-O(FSI) regions in the interfacial region exhibit higher concentrations. - The coordination number between ) and Li-O (PEGDA) was significantly reduced.

[0200] Experimental Example 5: Evaluation of the Average Decomposition Voltage of Lithium Ions

[0201] The average lithium-ion decomposition voltage in the interface region of lithium-ion conductive nanoparticles-gel polymer electrolyte was evaluated by simulation calculation and is shown in the figure. Figure 13 middle.

[0202] refer to Figure 13 It was confirmed that reducing lithium-ion-electrolyte coordination in the lithium-ion conductive nanoparticle-gel polymer electrolyte interface region can not only reduce electrolyte decomposition, but also lower the average decomposition voltage of lithium ions during lithium electrodeposition.

[0203] Experimental Example 6: Evaluation of Electrolyte Decomposition Current

[0204] The electrolyte decomposition current was evaluated by applying a Li / Cu half-cell to the negative electrode fabricated according to Example 1 and Comparative Example 1 and using linear sweep voltammetry. The results are shown in... Figure 14 middle.

[0205] refer to Figure 14 In Comparative Example 1, where the protective layer was not applied, it was confirmed that a significant amount of electrolyte decomposition current could be observed even at voltages of 2V or higher. That is, in the case of this example, it was confirmed that electrolyte decomposition was reduced due to the application of the protective layer.

[0206] Experimental Example 7: Evaluation of Time-Related Impedance of Symmetrical Cells

[0207] A symmetrical cell was applied to the negative electrode manufactured according to Example 1 and Comparative Example 1, and time-related impedance measurements of the cell were performed, as shown in... Figure 15 middle. Figure 15The left figure is a comparative example 1, and the right figure is the corresponding figure of example 1.

[0208] refer to Figure 14 In the comparative embodiment, the interface resistance continuously increases due to the continuous side reactions during the impedance measurement process. However, in the embodiment, it was confirmed that the change in interface resistance obtained with the application of the protective layer is significantly reduced. Therefore, it was confirmed that structural / chemical stability is improved when the protective layer is applied to the lithium metal layer.

[0209] Experimental Example 8: Evaluation of the increase in interfacial resistance over time in a symmetrical cell

[0210] The increase in initial interface resistance over time was evaluated by applying symmetrical cells to negative electrodes manufactured according to Example 1 and Comparative Example 1, and the results are shown in... Figure 16 middle.

[0211] refer to Figure 16 In the embodiments, it was confirmed that the initial interface resistance remained almost constant over time when the protective layer was applied, while in the comparative embodiments, the initial interface resistance increased significantly over time. Therefore, it was confirmed that structural / chemical stability is improved when the protective layer is applied to the lithium metal layer.

[0212] Experimental Example 9: Evaluation of Full Battery Life Characteristics

[0213] The lifetime characteristics of the full cells manufactured according to Examples 1 to 2 and Comparative Examples 1 to 2 were evaluated and shown in the figure. Figure 17 (Example 1 and Comparative Example 1) and Figure 18 (In Example 2 and Comparative Example 2), and Table 5 below shows the number of cycles when the initial discharge capacity becomes 80%. In addition, Table 4 below shows the evaluation results of the life characteristics of the full cells manufactured according to Comparative Examples 3 to 4.

[0214] (Table 5)

[0215] Number of cycles (when 80% of the initial discharge capacity is reached) Example 1 200 Example 2 250 Comparative Example 1 120 Comparative Example 2 160

[0216] refer to Figure 17 and Figure 18 Table 5 confirms that, compared to comparative examples with different conditions, the negative electrode for lithium secondary batteries according to the examples (where the lithium-ion binding energy of the anion and the organic solvent is appropriately adjusted to the range according to the invention) has significantly improved lifetime characteristics.

[0217] Experimental Example 10: Evaluation of Component Analysis During Cycling

[0218] After 10 cycles of the full cells manufactured according to Example 2 and Comparative Example 2, 19F NMR analysis of the residual electrolyte was performed, and the results are shown below. Figure 19 Furthermore, the elemental composition within the SEI (solid electrolyte interface) film was evaluated by X-ray photoelectron spectroscopy (XPS), and the results are shown in [Figure / Reference]. Figure 20 Furthermore, the LiFSI maintenance rate based on the cyclic process was evaluated and shown in the figure. Figure 21 middle.

[0219] refer to Figure 19 and Figure 20 In Example 2, unlike Comparative Example 2, it was confirmed that the low electrolyte decomposition voltage induced the decomposition of free FECs; therefore, all FECs were consumed as cycling progressed. Consequently, the proportion of carbon in the SEI film increased, and the proportion of Li decreased.

[0220] refer to Figure 21 In Example 2, it was confirmed that electrolyte decomposition was reduced throughout the cycle compared to Comparative Example 2, resulting in a higher LiFSI retention rate.

[0221] Experimental Example 11: Evaluation of the cross-sectional shape of the negative electrode

[0222] After 10 cycles, the negative electrode in the full cell manufactured according to Example 2 and Comparative Example 2 was subjected to FIB milling, and the cross-sectional SEM images were analyzed and shown. Figure 22 (Comparative Example 2) and Figure 23 In (Example 2).

[0223] exist Figure 22 In the case of and refer to Figure 23 In the embodiments, unlike the comparative embodiments, it was confirmed that as electrolyte decomposition decreased, porous layer deposition was suppressed, and the porous layer maintained a uniform thickness. On the other hand, in the case of the comparative embodiments, it was confirmed that porous layer deposition increased compared to the embodiments, and an uneven porous layer was found.

[0224] Meanwhile, it was confirmed that the thickness of the protective layer in the embodiment was approximately 8 μm.

[0225] Experimental Example 12: Evaluation of Battery Swelling Characteristics

[0226] The degree of swelling of the full cells manufactured according to Example 2 and Comparative Example 2 was evaluated based on the cycling process and is shown in the figure. Figure 24 middle.

[0227] refer to Figure 24 In Example 2, it was confirmed that, compared with Comparative Example 2, the degree of battery swelling was worse as the deposition of the porous layer was suppressed, depending on the progress of cycling.

[0228] Although the invention has been described above with respect to preferred embodiments, the invention is not limited thereto, but can be explored in various ways within the scope of the claims, detailed descriptions, and drawings.

[0229] Modifications can be made to implement this invention, and these modifications naturally fall within the scope of this invention.

[0230] Therefore, the actual scope of the present invention can be considered to be defined by the appended claims and their equivalents.

Claims

1. A negative electrode for a lithium secondary battery, the negative electrode comprising: Current collector; A lithium-based negative electrode active material layer is located on the current collector; as well as A protective layer is located on the lithium-based anode active material layer. The protective layer comprises a gel polymer electrolyte and lithium-ion conductive nanoparticles. The gel polymer electrolyte comprises lithium ions, anions, an organic solvent, and a polymer derived from lithium salts, and The lithium-ion binding energy of the anion is greater than that of the organic solvent.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein, The negative electrode satisfies: BE Li Anion-BE Li Organic solvents ≥0.25 eV BE Li The anion is the lithium-ion binding energy of the anion, BE. Li The organic solvent is the lithium-ion binding energy of the organic solvent.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein, The average lithium-ion concentration of the lithium-ion conductive nanoparticles is greater than the average lithium-ion concentration of the gel polymer electrolyte.

4. The negative electrode for a lithium secondary battery according to claim 1, wherein, An interface region is formed between the gel polymer electrolyte and the lithium-ion conductive nanoparticles, and the interface region has a lithium-ion concentration gradient.

5. The negative electrode for a lithium secondary battery according to claim 1, wherein, The average lithium-ion concentration of the lithium-ion conductive nanoparticles is greater than or equal to 30M, and the average lithium-ion concentration of the gel polymer electrolyte is less than or equal to 3M.

6. The negative electrode for a lithium secondary battery according to claim 4, wherein, The interface region forms a space charge composed of lithium ions.

7. The negative electrode for a lithium secondary battery according to claim 4, wherein, The coordination number between lithium ions and anions in the interface region is 1 or less.

8. The negative electrode for a lithium secondary battery according to claim 4, wherein, The coordination number between lithium ions and organic solvent in the interface region is 0.5 or less.

9. The negative electrode for a lithium secondary battery according to claim 4, wherein, The coordination number between lithium ions and lithium-ion conductive nanoparticles in the interface region is greater than or equal to 50% of the total coordination number of lithium ions.

10. The negative electrode for a lithium secondary battery according to claim 1, wherein, The lithium salt is lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis(oxalate)borate, or a combination thereof.

11. The negative electrode for a lithium secondary battery according to claim 1, wherein, The organic solvent is N,N-dimethylaminosulfonyl fluoride, 1,2-dimethoxyethane, fluoroethylene carbonate, or a combination thereof.

12. The negative electrode for a lithium secondary battery according to claim 1, wherein, The polymer is formed by cross-linking a polymer compound, and the polymer compound is poly(ethylene glycol) diacrylate, polyethylene glycol dimethacrylate, poly(ethylene glycol), ethylene glycol dimethacrylate, poly(ethylene glycol) diglycidyl ether, or a combination thereof.

13. The negative electrode for a lithium secondary battery according to claim 12, wherein, The molecular weight of the polymeric compound is from 500 g / mol to 5000 g / mol, and the molecular weight of the polymer is from 10000 to 1000000.

14. The negative electrode for a lithium secondary battery according to claim 1, wherein, The lithium-ion conductive nanoparticles are oxide nanoparticles.

15. The negative electrode for a lithium secondary battery according to claim 1, wherein, The lithium-ion conductive nanoparticles are LLZO type oxides, LSTP type oxides, LATP type oxides, LAGP type oxides, LLTO type oxides, LGPO type oxides, or combinations thereof.

16. The negative electrode for a lithium secondary battery according to claim 1, wherein, The lithium-ion conductive nanoparticles are LLZO type oxides represented by the following chemical formula: Li a M1 b La c Zr d M2 e O f Where M1 is Al, M2 is Ta, Nb, W or a combination thereof, 5≤a≤7, 0≤b≤3, 2≤c≤4, 1≤d≤3, 0≤e≤2 and 10≤f≤14.

17. The negative electrode for a lithium secondary battery according to claim 1, wherein, The average particle diameter D50 of the lithium-ion conductive nanoparticles is 100 nm to 5 μm.

18. The negative electrode for a lithium secondary battery according to claim 1, wherein, The weight ratio of the lithium-ion conductive nanoparticles to the total weight of the lithium salt and polymer is 5:5 to 9:1, and the weight ratio of the lithium salt to the polymer is 2:8 to 9:

1.

19. The negative electrode for a lithium secondary battery according to claim 1, wherein, The thickness of the protective layer is 1 μm to 20 μm.

20. A lithium secondary battery, the lithium secondary battery comprising the negative electrode for a lithium secondary battery according to claim 1.

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