Anode for lithium secondary battery and the manufacturing method of the same

Abstract

A negative electrode for a lithium secondary battery according to one embodiment of the present invention comprises: a current collector; a negative electrode active material layer disposed on the current collector; and a surface layer disposed on the negative electrode active material layer, wherein when XRD analysis is performed on the negative electrode for the lithium secondary battery, the ratio (I2 / I1) of the peak intensity (I1) of the first peak observed at a position where 2θ is 24±0.2° to the peak intensity (I2) of the second peak observed at a position where 2θ is 23.5±0.2° is 0.21 or higher, and when XPS analysis is performed on the negative electrode for the lithium secondary battery, the ratio (I4 / I3) of the peak intensity (I4) of the fourth peak observed at a range of 684.0 eV to 685.5 eV to the peak intensity (I3) of the third peak observed at a range of 686.0 eV to 688.0 eV may be 1.5 or lower.

Description

Technology Field

[0001] The present invention relates to a negative electrode for a lithium secondary battery and a method for manufacturing the same, and specifically to a pre-lithiated negative electrode and a method for manufacturing the same. Background Technology

[0002] Recently, as the use of fossil fuels is being avoided to address environmental problems caused by carbon dioxide (CO2), the automotive industry, a means of transportation, is showing great interest in electric vehicles that use secondary batteries. Currently, lithium-ion batteries allow for a driving range of approximately 400 km on a single charge, but issues such as instability at high temperatures and fire still exist. To solve these problems, many companies are competitively developing next-generation secondary batteries.

[0003] All-solid-state batteries, which are attracting attention as next-generation lithium secondary batteries, have the advantage of having high mechanical strength and a lower risk of fire and explosion compared to the aforementioned lithium-ion batteries that use flammable organic solvents as electrolytes, as all their components are made of solids. The all-solid-state battery generally comprises a positive electrode including a positive active material layer bonded to a positive current collector, a negative electrode including a negative active material layer bonded to a negative current collector, and a solid electrolyte layer located between the positive active material layer and the negative active material layer.

[0004] Generally, the negative electrode active material layer included in the aforementioned all-solid-state battery consists of a negative electrode active material containing graphite-based materials; however, conventional negative electrodes containing graphite-based materials have theoretical limitations in realizing all-solid-state batteries with high energy density. Therefore, metallic materials capable of alloying with lithium, including silicon, are attracting attention as negative electrode materials. However, these new materials also exhibit lower-than-expected energy density due to low initial efficiency compared to their high theoretical capacity.

[0005] In addition, during the initial charging of an all-solid-state battery, some lithium ions react with the negative electrode material (e.g., graphite-based material, silicon-based material, etc.) to form a layer called the Solid Electrolyte Interphase (SEI). This SEI layer plays an important role in stabilizing the battery's performance and preventing adverse reactions between the electrolyte and the negative electrode material. However, there was a problem of irreversible capacity loss, where lithium ions are consumed during the process of forming the SEI layer and cannot be reused in subsequent charge-discharge cycles, resulting in a decrease in the battery's total capacity after the initial charge.

[0006] Accordingly, methods are being developed to prevent capacity degradation by pre-lithiating through methods such as inserting lithium into the above-mentioned cathode. In particular, when using silicon-based active materials such as Si and SiO, which have high theoretical capacity as cathode active materials, a pre-lithiation process is required to increase the initial Coulomb efficiency. However, there was a problem in that the lifespan characteristics were degraded by a byproduct layer formed on the cathode due to pre-lithiation. Prior art literature

[0007] Korean Registered Patent No. 10-0291067 The problem to be solved

[0008] The objective of the present invention is to provide a negative electrode for a lithium secondary battery that has excellent initial capacity and initial efficiency and operates stably even during long-term operation.

[0009] Another problem to be solved by the present invention is to provide a method for manufacturing a negative electrode for a lithium secondary battery that has excellent initial capacity and initial efficiency and operates stably even during long-term operation. means of solving the problem

[0010] (1) The present invention provides a negative electrode for a lithium secondary battery comprising: a current collector; a negative electrode active material layer disposed on the current collector; and a surface layer disposed on the negative electrode active material layer, wherein when XRD analysis is performed on the negative electrode for the lithium secondary battery, the ratio (I2 / I1) of the peak intensity (I1) of the first peak observed at a position where 2θ is 24±0.2° to the peak intensity (I2) of the second peak observed at a position where 2θ is 23.5±0.2° is 0.21 or higher, and when XPS analysis is performed on the negative electrode for the lithium secondary battery, the ratio (I4 / I3) of the peak intensity (I4) of the fourth peak observed at a range of 684.0 eV to 685.5 eV to the peak intensity (I3) of the third peak observed at a range of 686.0 eV to 688.0 eV is 1.5 or lower.

[0011] (2) The present invention provides a negative electrode for a lithium secondary battery according to (1), wherein the I1 value is 4,000 au or more and 6,000 au or less.

[0012] (3) The present invention provides a negative electrode for a lithium secondary battery in which, in (1) or (2), the I2 value is 1,000 au or more and 1,500 au or less.

[0013] (4) The present invention provides a negative electrode for a lithium secondary battery in any one of (1) to (3), wherein the I3 value is 10,000 au or more and 13,000 au or less.

[0014] (5) The present invention provides a negative electrode for a lithium secondary battery in any one of (1) to (4), wherein the I4 value is 14,000 au or more and 19,000 au or less.

[0015] (6) The present invention provides a negative electrode for a lithium secondary battery having a color in which, in any one of (1) to (5), the red color value (R) on the RCB color chart is 115 or higher and 125 or lower, the green color value (G) is 115 or higher and 125 or lower, and the blue color value (B) is 90 or higher and 100 or lower.

[0016] (7) The present invention provides a negative electrode for a lithium secondary battery in any one of (1) to (6), wherein the thickness of the surface layer is 10 nm or more and 100 nm or less.

[0017] (8) The present invention provides a lithium secondary battery comprising a negative electrode for a lithium secondary battery according to any one of (1) to (7) above.

[0018] (9) The present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, comprising the steps of: forming a negative electrode active material layer comprising a carbon-based compound and a silicon-based compound on a current collector (S1); applying an electrolyte containing a phosphorus fluoride-based lithium salt to one surface of the negative electrode active material layer (S2); and contacting a lithium metal on the negative electrode active material layer coated with the electrolyte for a period of time of 75 minutes or more and 150 minutes or less (S3).

[0019] (10) In the present invention, in (9), the contact of step (S3) is 0.2 kg / cm 2 Above, 1 kg / cm² 2 A method for manufacturing a negative electrode for a lithium secondary battery is provided, which is carried out under the following pressure conditions.

[0020] (11) The present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, wherein in any one of (9) and (10), the contact in step (S3) is performed for a time of 90 minutes or more and 120 minutes or less.

[0021] (12) The present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, wherein, in any one of (9) to (11), after step (S3), the step (S4) further comprises removing the lithium metal and the electrolyte. Effects of the invention

[0022] A lithium secondary battery negative electrode is manufactured according to a method for manufacturing a lithium secondary battery negative electrode according to one embodiment of the present invention, having excellent initial capacity and initial efficiency, and operating stably even during long-term operation. Brief explanation of the drawing

[0023] FIG. 1 schematically illustrates a method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention. FIG. 2 is an XRD analysis graph of a negative electrode for a lithium secondary battery according to Examples 1 and 2 and Comparative Examples 1 to 6 of the present invention. Figure 3 is an XRD analysis graph of a negative electrode for a lithium secondary battery according to Comparative Example 7 of the present invention. Figure 4 is an XRD analysis graph of a negative electrode for a lithium secondary battery according to Comparative Example 8 of the present invention. Figures 5 and 6 are XPS analysis graphs for negative electrodes for lithium secondary batteries according to Examples 1 and 2 and Comparative Examples 1 to 7 of the present invention. FIG. 7 is an image of Example 1 and Comparative Example 1 of the present invention. FIG. 8 is a CS-SEM image showing a cross-section according to the charging and discharging process of Example 1 and Comparative Example 1 of the present invention. FIGS. 9 and 10 illustrate a negative electrode for a lithium secondary battery according to Examples 1 and 2 and Comparative Examples 1 to 6 of the present invention. st Cycle, 5 th Cycles and / or 10 th This is a cycle charge / discharge graph. Specific details for implementing the invention

[0024] Hereinafter, the present invention will be described in more detail to aid in understanding the invention. In this case, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0025] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0026] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0028] <Cathode for Lithium Secondary Battery>

[0029] The present invention provides a negative electrode for a lithium secondary battery.

[0030] Generally, during the initial charging of an all-solid-state battery, some lithium ions react with the negative electrode material (e.g., graphite-based material, silicon-based material, etc.) to form a layer called the Solid Electrolyte Interphase (SEI). However, during the process of forming the SEI layer, lithium ions are consumed and cannot be reused in subsequent charge-discharge cycles, resulting in an irreversible capacity loss where the total capacity of the battery decreases after the initial charge.

[0031] To reduce such initial irreversible capacity loss, a method has been proposed to supply additional necessary lithium ions by applying a pre-lithiation technology that adds lithium to the cathode in advance. However, the aforementioned pre-lithiation method had a problem in that, depending on the method and conditions of application, an excessive byproduct layer was generated, which affected the lifespan characteristics of the cathode for lithium secondary batteries.

[0032] Accordingly, the inventors discovered that by appropriately controlling the composition of the byproduct layer formed on the cathode from the pre-lithiation method, the initial irreversible capacity loss is reduced while the lifespan characteristics become excellent, and thus they have completed the present invention.

[0034] A negative electrode for a lithium secondary battery according to one embodiment of the present invention comprises at least a current collector; a negative electrode active material layer disposed on the current collector; and a surface layer disposed on the negative electrode active material layer, wherein when XRD analysis is performed on the negative electrode for the lithium secondary battery, the ratio (I2 / I1) of the peak intensity (I1) of the first peak observed at a position where 2θ is 24±0.2° to the peak intensity (I2) of the second peak observed at a position where 2θ is 23.5±0.2° is 0.21 or higher, and when XPS analysis is performed on the negative electrode for the lithium secondary battery, the ratio (I4 / I3) of the peak intensity (I4) of the fourth peak observed at a range of 684.0 eV to 685.5 eV to the peak intensity (I3) of the third peak observed at a range of 686.0 eV to 688.0 eV is 1.5 or lower.

[0036] A negative electrode for a lithium secondary battery according to one embodiment of the present invention may have a color in which the red color value (R) on the RCB color chart is 115 or higher and 125 or lower, the green color value (G) is 115 or higher and 125 or lower, and the blue color value (B) is 90 or higher and 100 or lower. This is expected to be due to various compounds formed during the process of manufacturing a negative electrode for a lithium secondary battery, which will be described later.

[0038] Hereinafter, each component forming the negative electrode for a lithium secondary battery according to one embodiment of the present invention will be described in detail.

[0040] The whole house

[0041] According to one embodiment of the present invention, the current collector may be a negative current collector and may be a plate-shaped substrate having electrical conductivity. Specifically, the current collector may have the form of a sheet, a thin film, or a foil.

[0042] According to one embodiment of the present invention, the current collector may include a material that does not react with lithium. Specifically, the negative current collector may include at least one selected from the group consisting of Ni, Cu, SUS (Stainless Steel), and combinations thereof.

[0044] cathode active material layer

[0045] According to one embodiment of the present invention, a negative active material layer may be disposed on the current collector.

[0046] A negative electrode active material layer according to one embodiment of the present invention may include a negative electrode active material, a solid electrolyte, a binder, etc.

[0047] According to one embodiment of the present invention, the negative electrode active material may include a carbon-based compound and a silicon-based compound.

[0048] According to one embodiment of the present invention, the carbon-based compound may be amorphous carbon such as graphite, hard carbon, and soft carbon, such as mesocarbon microbeads (MCMB) and highly oriented graphite (HOPG), and the silicon-based compound may be SiO x It may be a compound represented by (0≤x<2).

[0049] A negative electrode active material according to one embodiment of the present invention may have a structure in which the silicon-based compound is disposed on a core comprising the carbon-based compound. In this case, the core comprising the carbon-based compound may have a porous interior, and the silicon-based compound may be disposed on the outer surface of the core and on the surface of the porous structure inside to form a coating layer covering them. The average particle size (D) of the core 50 The thickness of the coating layer may be 5㎛ or more and 20㎛ or less, preferably 8㎛ or more and 15㎛ or less. The thickness of the coating layer may be 10nm or more and 50nm or less, preferably 20nm or more and 40nm or less.

[0050] In the case where the negative electrode active material according to one embodiment of the present invention has the core and coating layer structure described above, the negative electrode active material may be produced by depositing a gaseous silicon-based compound onto a graphite-based compound by chemical vapor deposition.

[0052] According to one embodiment of the present invention, the carbon-based compound and the silicon-based compound can each be lithiated by a pre-lithiation step (i.e., step (S3)) of the method for manufacturing a negative electrode for a lithium secondary battery described below. A detailed description of the specific process conditions of the pre-lithiation step described above will be provided later.

[0053] The above carbon-based compound is Stage 2 (LiC) by the aforementioned pre-lithiation step. 12 It can be lithiated to the Stage 1 (LiC6) phase via the ) phase, and the silicon-based compound can be Li by the pre-lithiation step. 15 It can be lithiated into Si4 phase.

[0054] In this regard, since silicon-based compounds have slower electronic conductivity than carbon-based compounds, the rate of lithium formation of carbon-based compounds may be faster than that of silicon-based compounds, and accordingly, the Li of silicon-based compounds15 The phase transition to the Si4 phase can occur after the phase transition to the Stage 1 phase of the carbon-based compound has taken place. Therefore, regarding the Li of the silicon-based compound with respect to the content of the Stage 1 phase of the carbon-based compound 15 Content ratio of Si4 phase (Li 15 By calculating Si4 / LiC6), it is possible to determine whether pre-lithiation within the negative electrode active material layer according to one embodiment of the present invention has been properly performed.

[0055] When performing XRD analysis on a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the peak intensity (I1) of the first peak observed at a position where 2θ is 24±0.2° is the peak intensity associated with the Stage 1 phase (LiC6), and is proportional to the content of the Stage 1 phase (LiC6) present in the negative electrode, and the peak intensity (I2) of the second peak observed at a position where 2θ is 23.5±0.2° is the phase Li 15 As the intensity of the peak associated with the Si4 phase, the Li present in the cathode 15 It can be proportional to the content of the Si4 phase.

[0056] According to one embodiment of the present invention, I1 may be 4,000 au or more and 6,000 au or less, and as a specific example, may be 4,100 au or more, 4,200 au or more, 4,300 au or more, 4,400 au or more, or 4,500 au or more, and may also be 5,900 au or less, 5,800 au or less, 5,700 au or less, 5,600 au or less, or 5,500 au or less. If the above-described range is satisfied, the lithiation of the carbon-based compound may be sufficiently achieved.

[0057] According to one embodiment of the present invention, the I2 may be 1,000 au or more and 1,500 au or less, and as a specific example, may be 1,050 au or more, 1,100 au or more, 1,150 au or more, 1,200 au or more, or 1,250 au or more, and may also be 1,450 au or less, 1,400 au or less, 1,350 au or less, or 1,300 au or less. If the above-described range is satisfied, the lithiumization of the silicon-based compound may be sufficiently achieved.

[0058] According to one embodiment of the present invention, the I2 / I1 ratio may be 0.21 or higher, and specifically, it may be 0.212 or higher, 0.214 or higher, 0.216 or higher, 0.218 or higher, 0.220 or higher, 0.222 or higher, 0.224 or higher, 0.226 or higher, 0.228 or higher, or 0.230 or higher. If the above-described range is satisfied, both the carbon-based compound and the silicon-based compound included in the negative electrode active material may be sufficiently lithiated. If the I2 / I1 ratio is less than the above-described range, Li 15 Since the content of the Si4 phase is low, the lithiumization of the silicon-based compound is not sufficiently achieved, which may result in a decrease in the initial charge capacity and / or initial efficiency of the lithium secondary battery.

[0060] According to one embodiment of the present invention, the solid electrolyte may be an oxide-based solid electrolyte or a sulfide-based solid electrolyte. It may be preferable to use a sulfide-based solid electrolyte with high lithium ion conductivity.

[0061] According to one embodiment of the present invention, the sulfide-based solid electrolyte is Li6PS5X (X = one or more selected from the group consisting of Cl, Br, and I), Li 10 GeP2S 12 , Li3PS4, Li7P3S 11, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2SSiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, In) and may include one or more selected from the group consisting of combinations thereof.

[0063] According to one embodiment of the present invention, the conductive material is configured to form an electron conduction path within the electrode. The conductive material may be an sp2 carbon material such as carbon black, conducting graphite, ethylene black, carbon nanotube, etc., or graphene.

[0065] According to one embodiment of the present invention, the binder may be BR (butadiene rubber), NBR (nitrile butadiene rubber), HNBR (hydrogenated nitrile butadiene rubber), PVDF (polyvinylidene difluoride), PTFE (polytetrafluoroethylene), CMC (carboxymethylcellulose), etc.

[0067] surface layer

[0068] According to one embodiment of the present invention, a surface layer may be disposed on the negative electrode active material layer. The surface layer is formed by a pre-lithiation step (i.e., step (S3)) of the method for manufacturing a negative electrode for a lithium secondary battery described below, and may be a layer formed by a compound formed by the pre-lithiation step.

[0069] A surface layer according to one embodiment of the present invention may include a lithium fluoride-based compound and a lithium fluoride phosphate-based compound. The lithium fluoride-based compound and the lithium fluoride phosphate-based compound are compounds formed by the pre-lithiation step (i.e., step (S3)) of the method for manufacturing a negative electrode for a lithium secondary battery described below, and can serve to impart excellent mechanical properties and high ionic conductivity to the surface layer. The lithium fluoride-based compound is Li x F y It is a compound represented by, and the lithium fluoride phosphate-based compound is Li x PO y F z It may be a compound represented by .

[0070] Specifically, according to one embodiment of the present invention, the lithium fluoride-based compound can improve the ionic conductivity of the surface layer, and the lithium fluoride phosphate-based compound can improve the mechanical properties of the surface layer. However, if the content of the lithium fluoride-based compound is excessive, the electronic conductivity of the surface layer becomes very low, and consequently, charge transfer of the surface layer is limited, which may result in an increase in the internal resistance of the battery. Accordingly, it is necessary to appropriately adjust the content ratio of the lithium fluoride-based compound and the lithium fluoride phosphate-based compound within the surface layer.

[0071] When XPS analysis is performed on a negative electrode for a lithium secondary battery according to one embodiment of the present invention, the peak intensity (I3) of the third peak observed in the range of 686.0 eV to 688.0 eV is the peak intensity associated with the lithium fluoride phosphate-based compound and may be proportional to the content of the lithium fluoride phosphate-based compound present in the negative electrode, and the peak intensity (I4) of the fourth peak observed in the range of 684.0 eV to 685.5 eV is the peak intensity associated with the lithium fluoride-based compound and may be proportional to the content of the lithium fluoride-based compound present in the negative electrode.

[0072] According to one embodiment of the present invention, the I3 may be 10,000 au or more and 13,000 au or less, and as a specific example, may be 10,100 au or more, 10,200 au or more, 10,300 au or more, 10,400 au or more, or 10,500 au or more, and may also be 12,900 au or less, 12,800 au or less, 12,700 au or less, 12,600 au or less, or 12,500 au or less. If the above range is satisfied, the lithium fluoride phosphate-based compound may be present in an appropriate amount.

[0073] According to one embodiment of the present invention, the I4 may be 14,000 au or more and 19,000 au or less, and as a specific example, may be 14,100 au or more, 14,200 au or more, 14,300 au or more, 14,400 au or more, or 14,500 au or more, and may also be 18,500 au or less, 18,000 au or less, 17,500 au or less, 17,000 au or less, or 16,000 au or less. If the above range is satisfied, the lithium fluoride-based compound may be present in an appropriate amount.

[0074] According to one embodiment of the present invention, the I4 / I3 ratio may be 1.5 or less, and as specific examples, may be 1.0 or more, 1.02 or more, 1.04 or more, 1.06 or more, 1.08 or more, or 1.1 or more, and may also be 1.48 or less, 1.46 or less, 1.44 or less, 1.42 or less, or 1.4 or less. When the I4 / I3 ratio satisfies the above-described range, the ratio of the lithium fluoride-based compound and the lithium fluoride phosphate-based compound is appropriately present, thereby improving the mechanical properties of the surface layer while exhibiting appropriate electronic conductivity and ionic conductivity, which can improve the lifespan characteristics of the battery. If the above I4 / I3 is less than the range described above, the content of the lithium fluoride-based compound may decrease more than necessary, and the ionic conductivity of the surface layer may decrease; if the above I4 / I3 exceeds the range described above, the content of the lithium fluoride-based compound may increase more than necessary, and the electrical conductivity of the surface layer may decrease, and accordingly, the lifespan characteristics of the battery may decrease.

[0076] According to one embodiment of the present invention, the thickness of the surface layer may be 10 nm or more and 100 nm or less, and as a specific example, may be 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, or 35 nm or more, and may also be 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, or 50 nm or less. When the above-described ranges are satisfied, the mechanical properties of the negative electrode for a lithium secondary battery may be improved.

[0078] Method for manufacturing a negative electrode for a lithium secondary battery

[0079] The present invention provides a method for manufacturing a negative electrode for a lithium secondary battery.

[0080] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention comprises at least the steps of: forming a negative electrode active material layer comprising a carbon-based compound and a silicon-based compound on a current collector (S1); applying an electrolyte containing a phosphorus fluoride-based lithium salt to one surface of the negative electrode active material layer (S2); and contacting a lithium metal on the negative electrode active material layer coated with the electrolyte for a time of 75 minutes or more and 150 minutes or less (S3).

[0082] FIG. 1 schematically illustrates a method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention. Hereinafter, with reference to FIG. 1, a method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention will be described in detail step by step.

[0084] (S1) Step

[0085] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention may include the step (S1) of forming a negative electrode active material layer comprising a carbon-based compound and a silicon-based compound on a current collector.

[0086] According to one embodiment of the present invention, the step (S1) can be performed by introducing carbon-based compound powder and silicon-based compound raw material gas into a reactor and carrying out a chemical vapor deposition method to produce a powder having a structure in which a core made of a carbon-based compound and a silicon-based compound coated on the core are produced, and then introducing the produced powder into an NMP (N-methyl-2-pyrrolidone) solvent to produce a slurry, and then applying it onto a prepared current collector.

[0088] (S2) Step

[0089] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention may include a step (S2) of applying an electrolyte containing a phosphorus-fluoride-based lithium salt to one surface of the negative electrode active material layer.

[0090] According to one embodiment of the present invention, the electrolyte may include a material having high lithium ion conductivity and may include a lithium salt and an organic solvent. The phosphorus fluoride-based lithium salt may be LiPF6.

[0091] According to one embodiment of the present invention, the concentration of the lithium salt may be in 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 lithium ions can move effectively.

[0092] According to one embodiment of the present invention, the organic solvent may be used without special limitations as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. For example, the organic solvent may include any one selected from the group consisting of ester-based solvents, ether-based solvents, ketone-based solvents, aromatic hydrocarbon-based solvents, carbonate-based solvents, alcohol-based solvents, nitrile-based solvents, amide-based solvents, dioxalan-based solvents, sulfolane-based solvents, and combinations thereof.

[0093] Specifically, the above organic solvents 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; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); and 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 2 to 20 carbon atoms and may include a double bond-directing ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used.

[0094] The organic solvent according to one embodiment of the present invention may, more specifically, be a carbonate-based solvent, and a mixture of a cyclic carbonate having high ionic conductivity and high dielectric constant capable of improving the charge / discharge performance of a battery (e.g., ethylene carbonate or propylene carbonate, etc.) and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferable. In this case, using a mixture of the cyclic carbonate and the chain carbonate in a volume ratio of about 1:1 to about 1:9 may result in excellent performance of the electrolyte.

[0096] (S3) Step

[0097] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention may include a step (S3) of contacting a lithium metal on a negative electrode active material layer coated with the electrolyte for a time of 75 minutes or more and 150 minutes or less.

[0099] According to one embodiment of the present invention, a pressurized structure can be formed by applying the electrolyte onto a negative electrode active material layer and then stacking lithium metal as a lithium source. The lithium metal provides lithium ions to the negative electrode active material layer during the pre-lithiation step described later, and may include, for example, a lithium foil (Li foil). In this case, the area of ​​the lithium metal may be greater than or equal to the area of ​​the negative electrode active material layer.

[0100] Subsequently, pressure can be applied to the above-mentioned pressurized structure in the stacking direction to form a surface layer on the above-mentioned cathode active material layer. According to one embodiment of the present invention, the pressure applied to the above-mentioned pressurized structure is 0.2 kg / cm² 2 More than 1 kg / cm² 2 Below, that is, the contact in step (S3) above is 0.2 kg / cm 2 More than 1 kg / cm² 2 It may be carried out under the following pressure conditions, specifically as an example, 0.25 kg / cm² 2Above, 0.3 kg / cm² 2 Above, 0.35 kg / cm² 2 Above, 0.4 kg / cm² 2 Above or 0.45 kg / cm² 2 It may be more than, and also, 0.9 kg / cm² 2 Below, 0.8 kg / cm² 2 Below, 0.7 kg / cm² 2 Below, 0.6 kg / cm² 2 Less than or equal to 0.5 kg / cm² 2 It may be less than or equal to the above range. If the above range is satisfied, pre-lithiation can be performed smoothly.

[0101] According to one embodiment of the present invention, the contact in step (S3) may be performed for a time of 75 minutes or more and 150 minutes or less. Specifically, it may be 80 minutes or more, 82 minutes or more, 84 minutes or more, 86 minutes or more, 88 minutes or more, or 90 minutes or more, and may also be 145 minutes or less, 140 minutes or less, 135 minutes or less, 130 minutes or less, 125 minutes or less, or 120 minutes or less. If the above range is satisfied, the XRD peak intensity ratio and XPS peak intensity ratio as described above can be satisfied. If the contact time in step (S3) is less than the above-described range, the lithiation of the carbon-based compound or silicon-based compound in the negative electrode active material is not sufficiently achieved, and the content of the lithium fluoride-based compound in the surface layer is reduced, which may lower the initial charge capacity and / or initial efficiency of the lithium secondary battery. In addition, if the contact time of step (S3) above exceeds the range described above, the content of the lithium fluoride-based compound in the surface layer becomes excessively high, the electrical conductivity of the surface layer decreases, and consequently, the lifespan characteristics of the battery may decrease.

[0103] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention may further include a step (S4) of removing the lithium metal and electrolyte after step (S3).

[0105] All-solid-state battery

[0106] The present invention provides an all-solid-state battery comprising the negative electrode for the lithium secondary battery.

[0107] According to one embodiment of the present invention, the all-solid-state battery may comprise a negative electrode, a solid electrolyte layer, a positive active material layer, and a positive current collector stacked thereon. Since the description of the negative electrode is identical to the description of the negative electrode for a lithium secondary battery described above, a detailed description of the negative electrode will be omitted below.

[0108] According to one embodiment of the present invention, the solid electrolyte layer is configured to transfer lithium ions between the anode and the cathode and may include a solid electrolyte having lithium ion conductivity. The solid electrolyte may include at least one selected from the group consisting of oxide-based solid electrolytes, sulfide-based solid electrolytes, polymer electrolytes, and combinations thereof, and preferably may include a sulfide-based solid electrolyte.

[0109] According to one embodiment of the present invention, the sulfide-based solid electrolyte is Li6PS5X (X = one or more selected from the group consisting of Cl, Br, and I), Li 10 GeP2S 12 , Li3PS4, Li7P3S 11 , Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2SSiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Lix MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, In) and may include one or more selected from the group consisting of combinations thereof.

[0110] According to one embodiment of the present invention, the positive active material layer may include a positive active material, a solid electrolyte, a conductive material, a binder, etc.

[0111] According to one embodiment of the present invention, the positive electrode active material is not particularly limited but may be, for example, an oxide active material or a sulfide active material.

[0112] According to one embodiment of the present invention, the oxide active material is LiCoO2, LiMnO2, LiNiO2, LiVO2, Li 1+x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 Rock salt layer type active materials such as O2, LiMn2O4, Li(Ni 0.5 Mn 1.5 Spinel-type active materials such as )O4, inverse spinel-type active materials such as LiNiVO4 and LiCoVO4, olivine-type active materials such as LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4, silicon-containing active materials such as Li2FeSiO4 and Li2MnSiO4, LiNi 0.8 Co (0.2-x) Al x Salt layer type active material in which some of the transition metals are replaced with heterogeneous metals, such as O2 (0<x<0.2), Li 1+x Mn 2-x-y M y Spinel-type active material in which a portion of the transition metal is replaced with a heterogeneous metal, such as O4 (M is at least one of Al, Mg, Co, Fe, Ni, Zn and 0 < x+y < 2), Li4Ti5O 12 It may be lithium titanate.

[0113] According to one embodiment of the present invention, the sulfide active material may be copper chevrell, iron sulfide, cobalt sulfide, nickel sulfide, etc.

[0114] According to one embodiment of the present invention, the solid electrolyte may be an oxide-based solid electrolyte or a sulfide-based solid electrolyte. It may be preferable to use a sulfide-based solid electrolyte with high lithium ion conductivity.

[0115] According to one embodiment of the present invention, the conductive material and binder are as described above, so a detailed description thereof is omitted.

[0116] According to one embodiment of the present invention, the positive current collector may be a plate-shaped substrate having electrical conductivity. Specifically, the positive current collector may have the form of a sheet or a thin film.

[0117] According to one embodiment of the present invention, the positive current collector may include at least one selected from the group consisting of indium, copper, magnesium, aluminum, stainless steel, iron, and combinations thereof.

[0118] According to one embodiment of the present invention, the solid electrolyte self-supporting film is located between the negative electrode active material layer and the positive electrode active material layer and is configured to facilitate the movement of lithium ions.

[0120] 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.

[0122] 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.

[0124] Example 1

[0125] <Manufacturing of Cathode Active Material Layer>

[0126] Graphite powder and SiH4 gas were introduced into a reactor to carry out the Chemical Vapor Deposition (CVD) method, and Si-G powder was obtained.

[0127] A slurry was prepared by adding the Si-G powder obtained above and polyacrylic acid to NMP (N-methyl-2-pyrrolidone) solvent at a weight ratio of 95:5 (Si-G:PAA). The slurry was applied to a Ni-coated Cu thin film serving as a cathode current collector, vacuum dried for 24 hours (in a 50°C oven), and the mass of the electrode punched to 12.9Φ was weighed using a precision weigher (loading per area = 2.2 mg / cm²). 2 A cathode with a cathode active material layer formed thereon was fabricated.

[0129] Pre-lithiation process

[0130] 200 μl of an electrolyte having a concentration of 1.15 M and a composition of LiPF6 in EC / EMC (v:v=3:7) 5 wt% FEC was applied onto the negative electrode active material layer prepared above. A lithium foil (Li foil; 3 cm x 4 cm, thickness 500 μm) larger than the diameter of the negative electrode was placed on the electrolyte applied onto the positive electrode active material layer to completely cover the negative electrode active material layer.

[0131] Next, a pressurized structure including the cathode, electrolyte, and lithium source was placed on a glass plate (lower glass plate), and then another glass plate (upper glass plate) was laminated on the upper surface of the pressurized structure as a pressurized plate. Subsequently, the lower glass plate and the upper glass plate were 0.2 kg / cm² 2 ~ 1 kg / cm 2 A surface layer was formed on the negative electrode active material layer by performing pre-lithiation by applying pressure for 120 minutes.

[0132] Subsequently, the pressure applied to the above-mentioned pressurized structure was removed and the negative electrode was collected, and the solvent was removed by washing the collected negative electrode with dimethyl carbonate solvent and drying it under vacuum at room temperature for 1 hour to manufacture a negative electrode for a lithium secondary battery.

[0134] Example 2

[0135] A negative electrode for a lithium secondary battery was prepared in the same manner as in Example 1, except that the lower glass plate and the upper glass plate were pressed for 90 minutes during the pre-lithiation process.

[0137] Comparative Example 1

[0138] Graphite powder and SiH4 gas were introduced into a reactor to carry out the Chemical Vapor Deposition (CVD) method, and Si-G powder was obtained.

[0139] A slurry was prepared by adding the Si-G powder obtained above and polyacrylic acid to NMP (N-methyl-2-pyrrolidone) solvent at a weight ratio of 95:5 (Si-G:PAA). The slurry was applied to a Ni-coated Cu thin film serving as a cathode current collector, vacuum dried for 24 hours (in a 50°C oven), and the mass of the electrode punched to 12.9Φ was weighed using a precision weigher (loading per area = 2.2 mg / cm²). 2 A negative electrode for a lithium secondary battery was fabricated by forming a negative electrode active material layer.

[0141] Comparative Example 2

[0142] A negative electrode for a lithium secondary battery was prepared in the same manner as in Example 1, except that the lower glass plate and the upper glass plate were pressed for 30 minutes during the pre-lithiation process.

[0144] Comparative Example 3

[0145] A negative electrode for a lithium secondary battery was prepared in the same manner as in Example 1, except that the lower glass plate and the upper glass plate were pressed for 60 minutes during the pre-lithiation process.

[0147] Comparative Example 4

[0148] A negative electrode for a lithium secondary battery was prepared in the same manner as in Example 1, except that the lower glass plate and the upper glass plate were pressed for 180 minutes during the pre-lithiation process.

[0150] Comparative Example 5

[0151] A negative electrode for a lithium secondary battery was prepared in the same manner as in Example 1, except that the lower glass plate and the upper glass plate were pressed for 300 minutes during the pre-lithiation process.

[0153] Comparative Example 6

[0154] <Manufacturing of Cathode Active Material Layer>

[0155] Graphite powder and SiH4 gas were introduced into a reactor to carry out the Chemical Vapor Deposition (CVD) method, and Si-G powder was obtained.

[0156] A slurry was prepared by adding the Si-G powder obtained above and polyacrylic acid to NMP (N-methyl-2-pyrrolidone) solvent at a weight ratio of 95:5 (Si-G:PAA). The slurry was applied to a Ni-coated Cu thin film serving as a cathode current collector, vacuum dried for 24 hours (in a 50°C oven), and the mass of the electrode punched to 12.9Φ was weighed using a precision weigher (loading per area = 2.2 mg / cm²). 2 A cathode with a cathode active material layer formed thereon was fabricated.

[0158] Pre-lithiation process

[0159] A lithium foil (Li foil; 3 cm x 4 cm, thickness 500 μm) larger than the diameter of the cathode was placed directly on top of the cathode active material layer prepared above as a lithium source to completely cover the cathode active material layer.

[0160] Next, a pressure structure including the cathode and lithium source was placed on a glass plate (lower glass plate), and then another glass plate (upper glass plate) was laminated on the upper surface of the pressure structure as a pressure plate. Subsequently, the lower glass plate and the upper glass plate were 0.2 kg / cm² 2 ~ 1 kg / cm 2 A surface layer was formed on the negative electrode active material layer by performing pre-lithiation by applying pressure for 300 minutes.

[0161] Subsequently, the pressure applied to the above-mentioned pressurized structure was removed and the negative electrode was collected, and the solvent was removed by washing the collected negative electrode with dimethyl carbonate solvent and drying it under vacuum at room temperature for 1 hour to manufacture a negative electrode for a lithium secondary battery.

[0163] Comparative Example 7

[0164] <Manufacturing of Cathode Active Material Layer>

[0165] Graphite powder and SiH4 gas were introduced into a reactor to carry out the Chemical Vapor Deposition (CVD) method, and Si-G powder was obtained.

[0166] A slurry was prepared by adding the Si-G powder obtained above and polyacrylic acid to NMP (N-methyl-2-pyrrolidone) solvent at a weight ratio of 95:5 (Si-G:PAA). The slurry was applied to a Ni-coated Cu thin film serving as a cathode current collector, vacuum dried for 24 hours (in a 50°C oven), and the mass of the electrode punched to 12.9Φ was weighed using a precision weigher (loading per area = 2.2 mg / cm²). 2 A cathode with a cathode active material layer formed thereon was fabricated.

[0168] Pre-lithiation process

[0169] A coin cell half-cell was constructed using 1.15M LiPF6 in EC / EMC with 5wt% FEC electrolyte, a 12.9Φ punched Si-G electrode, and lithium metal, and lithiation was performed down to 0.01 V at a current density of 150 mA / g in the system.

[0170] Comparative Example 8

[0171] <Manufacturing of Cathode Active Material Layer>

[0172] Graphite powder and SiH4 gas were introduced into a reactor to carry out the Chemical Vapor Deposition (CVD) method, and Si-G powder was obtained.

[0173] A slurry was prepared by adding the Si-G powder obtained above and polyacrylic acid to NMP (N-methyl-2-pyrrolidone) solvent at a weight ratio of 95:5 (Si-G:PAA). The slurry was applied to a Cu-coated Ni thin film serving as a cathode current collector, vacuum dried for 24 hours (in a 50°C oven), and the mass of the electrode punched to 12.9Φ was weighed using a precision weigher (loading per area = 2.2 mg / cm²). 2 A cathode with a cathode active material layer formed thereon was fabricated.

[0175] Pre-lithiation process

[0176] A coin cell half-cell was constructed using 1.15M LiPF6 in EC / EMC with 5wt% FEC electrolyte, a 12.9Φ punched Si-G electrode, and lithium metal, and lithiation was performed by maintaining a constant voltage of 0 V in the system for 210 minutes.

[0178] Experimental Example 1 - XRD Analysis

[0179] Figure 2 shows the results of X-ray diffraction analysis performed on the cathodes prepared in Examples 1 and 2 and Comparative Examples 1 to 6 using Xpert-Pro (PANalytical) at a voltage of 40 kV, a current of 30 mA CuKα, 2θ (Bragg angle) = 22° to 28°, and a scan speed of 0.01° / 100 sec, and the intensity of each observed peak is shown in Table 1 below.

[0181] That 15 Si4(220) Stage 1; LiC6(001) Stage 2; LiC 12 (002) That 15 Si4(310) graphite(002) I2 / I1 Example 1 1149.0 4855.3 - 408.7 - 0.237 Example 2 1257.4 5741.2 - 496.6 - 0.219 Comparative Example 1 - - - - 9033.9 - Comparative Example 2 - - 3954.8 - - - Comparative Example 3 763.2 3696.3 160.4 252.2 - 0.206 Comparative Example 4 1278.9 5518.8 - 496.8 - 0.232 Comparative Example 5 1355.2 5544.7 - 473.1 - 0.244 Comparative Example 6 - - - - 7476.9 -

[0182] Referring to Fig. 2, the peak observed at a position where 2θ is 23.5±0.2° is Li 15 The peak associated with the (220) plane of Si4 (first peak) and the peak observed at a position where 2θ is 24±0.2° is the peak associated with the (001) plane of Stage 1 (LiC6) (second peak), and the peak observed at a position where 2θ is 23.5±0.2° is Stage 2 (LiC 12 It is a peak associated with the (002) plane of ), and the peak observed at position 26.1±0.2° is Li 15 The peak is associated with the (310) plane of Si4, and the peak observed at the position 26.5±0.2° is associated with the (002) plane of graphite.

[0183] In this regard, the cathode active material layer used in the cathodes of Examples 1 and 2 and Comparative Examples 1 to 6 may include carbon-based compounds and silicon-based compounds. The carbon-based compound becomes lithiated through pre-lithiation, and Stage 2 (LiC 12 It is lithiated to the Stage 1 (LiC6) phase via the ) phase, and silicon-based compounds are lithiated through pre-lithiation, and Li 15 Lithiogenesis occurs into the Si4 phase. Therefore, it was confirmed that in the cathode of Comparative Example 1, where pre-lithiation was not performed, no peaks other than the peak related to the (002) plane of graphite were observed, and referring to Examples 1 and 2 and Comparative Examples 2 to 5, as the pre-lithiation time increases, Li15 It was possible to confirm that the intensity (I1) of the peak (first peak) associated with the (220) plane of Si4 was increasing.

[0184] Furthermore, during pre-lithiation, since silicon-based compounds generally have slower electronic conductivity than carbon-based compounds, the lithiation rate of carbon-based compounds may be faster than that of silicon-based compounds, and accordingly, the Li of silicon-based compounds 15 The phase transition to the Si4 state can occur after the phase transition to the Stage 1 state of carbon-based compounds has been completed to some extent. Based on this, Li 15 By calculating the ratio (I2 / I1) of the intensity of the peak (I2) of the (001) plane of Stage 1 (LiC6) (2nd peak) to the intensity (I1) of the peak (1st peak) of the (220) plane of Si4, it is possible to verify whether the lithiation of carbon-based compounds and the lithiation of silicon-based compounds through prior lithiation have been properly carried out.

[0185] Through this, the Li of Comparative Examples 2 and 3, which have relatively short pre-lithiation times among Examples 1 and 2 and Comparative Examples 2 to 5, 15 Since the ratio of the peak (2nd peak) related to the (001) plane of Stage 1 (LiC6) to the intensity of the peak (1st peak) related to the (220) plane of Si4 does not exceed 0.21, it can be confirmed that the lithiation of carbon-based compounds and the lithiation of silicon-based compounds present in the negative electrode active material were not properly carried out. In particular, in the case of Comparative Examples 2 and 3, it was confirmed that the phases were mixed (Stage 1 and Stage 2 were mixed) because the lithiation of carbon-based compounds was not completely carried out.

[0186] Meanwhile, in the case of Comparative Example 6, in which a lithium source is brought into contact with the negative electrode active material layer without an electrolyte to pre-lithiate, no peaks other than the peak related to the (002) plane of the graphite were observed, so it was confirmed that pre-lithiation was not properly performed.

[0188] Experimental Example 2 - XRD Analysis

[0189] During pre-lithiation according to each of Comparative Examples 7 and 8, X-ray diffraction analysis was performed on the cathode undergoing pre-lithiation at different times using Xpert-Pro (PANalytical) at a voltage of 40 kV, a current of 30 mA CuKα, 2θ (Bragg angle) = 12° to 18°, and a scan speed of 0.01° / 100 sec. The results are shown in Figures 3 and 4, respectively.

[0191] Referring to Fig. 3, the silicon-based compound Li-lithized only after a pre-lithiation time of 8 hours 15 It was confirmed that the Si4 phase was observed, and this confirms that the rate of the pre-lithiation reaction according to electrochemical lithiation (Comparative Example 7) is very slow compared to the pre-lithiation method of the example.

[0192] In addition, referring to Fig. 4, in the pre-lithiation reaction according to the electrochemical short (Comparative Example 8), although the lithiumization of the silicon-based compound occurs, it was confirmed that the lithiumization of the graphite-based compound did not proceed uniformly even after the pre-lithiation time of 210 minutes, resulting in a mixture of phases (Stage 1 and Stage 2 being mixed).

[0194] Experimental Example 3 - XPS Analysis

[0195] XPS analysis was performed on the cathodes prepared in Examples 1 and 2 and Comparative Examples 1 to 7 to obtain F1s spectra, which are shown in Figures 5 and 6, and the intensity of each peak observed in the spectrum is shown in Table 2 below.

[0196] The above XPS analysis was performed using a spectrometer (Thermo Scientific, NEXSA, AlKα, acceleration voltage: 1486.6 eV, maximum resolution: 0.50 eV).

[0198] Li x PO y F z (I4) LiF(I3) I3 / I4 Example 1 11840.15 14642.94 1.24 Example 2 11247.6 14769.3 1.31 Comparative Example 1 - - - Comparative Example 2 14127.9 18769.9 1.33 Comparative Example 3 9694.77 13283.6 1.37 Comparative Example 4 15659.38 24489.24 1.56 Comparative Example 5 15786 29792 1.89 Comparative Example 7 9922.9 6063.6 0.61

[0199] Referring to FIGS. 5 and 6, the peak observed in the range from 684.0 eV to 686.0 eV (third peak) is a peak for the LiF compound observed at the cathode of Examples 1 and 2 and Comparative Examples 1 to 5 and 7, and the peak observed in the range from 686.1 eV to 688.0 eV (fourth peak) is the Li observed at the cathode of Examples 1 and 2 and Comparative Examples 1 to 5 and 7. x PO y F z This is the peak for the compound.

[0200] Referring to Table 2 above, in the case of Comparative Example 1, where no prior lithiation was performed, the LiF compound and Li x PO y F z It was confirmed that no compound was observed.

[0201] In addition, in Comparative Examples 4 and 5, where the pre-lithiation time exceeded 150 minutes, it was confirmed that the LiF compound was excessively produced and the I3 / I4 value exceeded 1.5.

[0202] Meanwhile, in the case of the pre-lithiation reaction by electrochemical lithiation, it was confirmed that the I3 / I4 value was less than 1.0 because the LiF compound was not sufficiently formed.

[0204] Experimental Example 4 - Color Analysis

[0205] The cathodes prepared in Example 1 and Comparative Example 1 above were photographed and are shown in FIG. 7, and the RGB colors of the photographed images were measured using Illustrator software.

[0206] Referring to FIG. 7, the RGB color of Comparative Example 1 was measured to be R: 93, G: 92, B: 97, indicating a dark gray color, while the RGC color of Example 1 was measured to be R: 121, G: 119, B: 96, indicating a blackish-yellow color. The reason the color of Example 1 appears yellower compared to that of Comparative Example 1 is due to the compounds formed by the prior lithiation reaction, namely LiC6, Li 15 Si4, Li x PO y F z It is expected to be due to the presence of compounds and LiF compounds.

[0208] Experimental Example 5 - CS-SEM Analysis

[0209] For each of the half cells according to Example 1 and Comparative Example 1 prepared in Experimental Example 4 above, cross-sections of i) the initial state, ii) the state in which an operating voltage of 0.01V to 1.5V and a current density of 100 mA / mg were applied under driving pressure conditions of 60℃ and 65MPa, and iii) the discharged state were each captured using CS-SEM, and the images are shown in FIG. 8.

[0211] Referring to Fig. 8, in the case of Example 1, which underwent pre-lithiation, it was confirmed that the thickness changed from 35.0 μm to 25.0 μm to 32.3 μm during the Pristine → delithiation → lithiation process, and in the case of Comparative Example 1, which did not undergo pre-lithiation, it was confirmed that the thickness changed from 17.4 μm to 26.1 μm to 17.8 μm during the Pristine → lithiation → delithiation process. Through this, it was confirmed that the negative electrode for a lithium secondary battery in Example 1 showed less thickness change compared to the negative electrode for a lithium secondary battery in Comparative Example 1, thereby suppressing operating pressure loss even when the battery is operated for a long time and improving lifespan characteristics.

[0213] Experimental Example 6 - Battery Characteristics Analysis

[0214] For the negative electrodes for lithium secondary batteries prepared in each of Examples 1 and 2 and Comparative Examples 1 to 6, a sulfide-based solid electrolyte (Li6PS5Cl 0.5 Br 0.5 ) 150~200 mg of powder was filled and a solid electrolyte layer was placed by applying pressure of 500 MPa, and then a lithium metal foil (Honjo chemical corp.) with a thickness of 150 μm and punched with a diameter of 11 Ф was inserted on the opposite side of the solid electrolyte layer, and then T-shaped members acting as lids were inserted in the upper and lower directions of the annular mold to seal it. Afterwards, the annular mold was fastened using a pressure jig with a tightening pressure of 3 Nm torque to produce a half cell.

[0215] For each half-cell according to Examples 1 and 2 and Comparative Examples 1 to 6, a cycle was defined as applying an operating voltage of 0.01V to 1.5V and a current density of 100 mA / mg under driving pressure conditions of 60℃ and 65MPa, and discharging, and the first, fifth, and tenth cycles were plotted in FIGS. 9 and 10. Additionally, the initial charge capacity and initial efficiency measured in the first cycle of Examples 1 and 2 and Comparative Examples 1 to 5 are shown in Table 3 below.

[0217] Initial charge capacity (mAh / g) Initial efficiency (%) Example 1 1028.3 87.3 Example 2 1105.5 93.1 Comparative Example 1 1118.2 79.6 Comparative Example 2 828.9 70.7 Comparative Example 3 955.1 111.6 Comparative Example 4 1105.1 90.6 Comparative Example 5 1115.5 948.2 Comparative Example 6 16.5 1.25

[0218] Referring to Table 3 above, it can be seen that the initial charging capacity and initial efficiency of Examples 1 and 2 are both excellent, and that Comparative Example 1, in which no pre-lithiation was performed, and Comparative Example 2, in which the pre-lithiation time was relatively short, show lower initial efficiency compared to the Examples. In addition, in the case of Comparative Example 6, in which pre-lithiation was performed without an electrolyte, it was confirmed that the initial charging capacity was significantly lower.

[0219] Referring to FIGS. 9 and FIGS. 10, it was confirmed that in the 10th cycle, the half-cells according to Examples 1 and 2 operated stably without lifespan degradation, whereas Comparative Examples 2 and 3 had a short circuit and were difficult to operate stably.

[0220] In the case of Comparative Example 4, it was confirmed that lifespan degradation occurred due to the over-formed LiF compound during the pre-lithiation process as the cycle progressed, and in the case of Comparative Example 5, it was confirmed that it did not operate in all cycles.

Claims

Claim 1 A negative electrode for a lithium secondary battery comprising: a current collector; a negative electrode active material layer disposed on the current collector; and a surface layer disposed on the negative electrode active material layer, wherein, when XRD analysis is performed on the negative electrode for the lithium secondary battery, the ratio (I2 / I1) of the peak intensity (I1) of a first peak observed at a position where 2θ is 24±0.2° to the peak intensity (I2) of a second peak observed at a position where 2θ is 23.5±0.2° is 0.21 or higher, and when XPS analysis is performed on the negative electrode for the lithium secondary battery, the ratio (I4 / I3) of the peak intensity (I4) of a fourth peak observed at a range of 684.0 eV to 685.5 eV to the peak intensity (I3) of a third peak observed at a range of 686.0 eV to 688.0 eV is 1.5 or lower. Claim 2 A negative electrode for a lithium secondary battery according to claim 1, wherein the I1 value is 4,000 au or more and 6,000 au or less. Claim 3 A negative electrode for a lithium secondary battery according to claim 1, wherein the I2 value is 1,000 au or more and 1,500 au or less. Claim 4 A negative electrode for a lithium secondary battery according to claim 1, wherein the I3 value is 10,000 au or more and 13,000 au or less. Claim 5 A negative electrode for a lithium secondary battery according to claim 1, wherein the I4 value is 14,000 au or more and 19,000 au or less. Claim 6 A negative electrode for a lithium secondary battery according to claim 1, having a color in which the red color value (R) on the RCB color chart is 115 or higher and 125 or lower, the green color value (G) is 115 or higher and 125 or lower, and the blue color value (B) is 90 or higher and 100 or lower. Claim 7 A negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the surface layer is 10 nm or more and 100 nm or less. Claim 8 A lithium secondary battery comprising a negative electrode for a lithium secondary battery according to any one of claims 1 to 7. Claim 9 A method for manufacturing a negative electrode for a lithium secondary battery, comprising: a step (S1) of forming a negative electrode active material layer comprising a carbon-based compound and a silicon-based compound on a current collector; a step (S2) of applying an electrolyte comprising a phosphorus fluoride-based lithium salt to one surface of the negative electrode active material layer; and a step (S3) of contacting a lithium metal on the negative electrode active material layer coated with the electrolyte for a time of 75 minutes or more and 150 minutes or less. Claim 10 In claim 9, the contact in step (S3) is 0.2 kg / cm 2 Above, 1 kg / cm² 2 A method for manufacturing a negative electrode for a lithium secondary battery, carried out under the following pressure conditions. Claim 11 A method for manufacturing a negative electrode for a lithium secondary battery according to claim 9, wherein the contact in step (S3) is performed for a time of 90 minutes or more and 120 minutes or less. Claim 12 A method for manufacturing a negative electrode for a lithium secondary battery according to claim 9, further comprising a step (S4) of removing the lithium metal and electrolyte after the step (S3) above.

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