Method for manufacturing pre-lithiated negative electrode, negative electrode manufactured thereby, and lithium secondary battery comprising negative electrode

Abstract

The present invention relates to a method for manufacturing a pre-lithiated negative electrode, a negative electrode having improved air stability prepared thereby, and a lithium secondary battery comprising the negative electrode, the method comprising the steps of: wetting a negative electrode active material layer including a silicon-based negative electrode active material with a pre-lithiation electrolyte; and bringing a lithium metal layer into contact with at least one surface of the negative electrode active material layer wetted with the pre-lithiation electrolyte, wherein the pre-lithiation electrolyte includes a lithium salt having a concentration of greater than 3M and a non-aqueous solvent.

Description

Method for manufacturing a lithium-ion cathode, a cathode manufactured thereby, and a lithium secondary battery including the cathode

[0001] This invention claims the benefit of Korean Patent Application No. 10-2023-0189412, filed with the Korean Intellectual Property Office on December 22, 2023, and Korean Patent Application No. 10-2024-0189739, filed with the Korean Intellectual Property Office on December 18, 2024, the entire contents of which are incorporated herein by reference.

[0002] Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy is increasing, and as part of this, the most actively researched field is power generation and storage using electrochemical reactions.

[0003] A representative example of an electrochemical device that currently utilizes this electrochemical energy is the secondary battery, and its application area is gradually expanding.

[0004] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used. Furthermore, active research is being conducted on methods for manufacturing high-density electrodes with even higher energy density per unit volume as electrodes for these high-capacity lithium secondary batteries.

[0005] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and deintercalates lithium ions from the positive electrode. Silicon particles with a high discharge capacity can be used as the negative electrode active material.

[0006] Meanwhile, lithium secondary batteries begin to lose lithium from the first charge after manufacturing. This loss, however small, continues during subsequent charge-discharge cycles and high-temperature storage, leading to battery degradation. To compensate for this loss, the process of adding lithium to the battery before operation is called prelithiation. The expected benefits of prelithiation include increased battery capacity (energy density) or improved cycle life.

[0007] Among the prelithiation methods, one involves injecting compounds containing excessive amounts of lithium as additives during battery manufacturing, typically as positive or negative electrode additives. Lithium alloy compounds exhibit low redox potential and high capacity, making them suitable as negative electrode prelithiation additives. However, lithium alloy compounds are typically highly reactive and unstable in air, making them difficult to apply in the battery manufacturing process.

[0008] In addition to the aforementioned method of adding high-capacity lithium compounds to the electrode, there is also a method of directly injecting lithium into the electrode. Representative methods of injecting lithium into the electrode include electrochemical prelithiation and direct lithium contact. Direct lithium contact prelithiation methods include dry prelithiation, which does not use an electrolyte, and wet prelithiation, which uses an electrolyte.

[0009] Meanwhile, in the case of silicon-based negative electrode active materials, despite the high capacity of 3579 mAh / g, the large volume change of up to 300% during charge and discharge resulted in poor cycle life characteristics, making commercialization difficult. To overcome this problem, active research has been conducted on lithiation of silicon-based negative electrodes. When silicon-based negative electrodes are lithiated, a Li-Si alloy is formed, and as with the aforementioned lithiation additive, ensuring the air stability of the Li-Si alloy is of utmost importance.

[0010] [Prior Art Literature]

[0011] [Patent Document]

[0012] Korean Patent Publication No. 10-2019-0083304

[0013] The present invention relates to a method for manufacturing a lithium-ion cathode capable of improving air stability, a cathode manufactured thereby, and a lithium secondary battery including the cathode.

[0014] One embodiment of the present specification comprises a step of wetting a negative electrode active material layer including a silicon-based negative electrode active material in an electrolyte for prelithiation; and

[0015] A step of contacting a lithium metal layer with at least one surface of a negative electrode active material layer wetted in the above-described lithium-ion electrolyte,

[0016] The above-mentioned electrolyte for lithium ion provides a method for manufacturing a lithium ion negative electrode, which comprises a lithium salt having a concentration exceeding 3 M and a non-aqueous solvent.

[0017] One embodiment of the present specification provides a lithium-ion cathode manufactured by the above-described manufacturing method.

[0018] One embodiment of the present specification is a bipolar;

[0019] The aforementioned prelithiated negative electrode;

[0020] a separator provided between the positive electrode and the lithium-ion cathode; and

[0021] A lithium secondary battery including an electrolyte is provided.

[0022] One embodiment of the present specification provides a battery module including the aforementioned lithium secondary battery.

[0023] Another embodiment of the present disclosure provides a battery pack comprising the battery module described above.

[0024] Finally, one embodiment of the present specification provides a battery pack including the aforementioned lithium secondary battery.

[0025] The present invention provides a method for manufacturing a lithium-ion negative electrode, which can be lithium-ionized using a high-concentration lithium-ion electrolyte that maintains high ionic conductivity of a CIP (Contact Ion Pair) structure, by a wet lithium-ion method, and at the same time, form an artificial solid electrolyte interphase layer (SEI) having a high LiF content and a uniformity, thereby improving air stability, and a lithium secondary battery including the negative electrode and a lithium-ion battery manufactured thereby.

[0026] Figure 1 is a diagram showing the laminated structure of a lithium-ion negative electrode manufactured according to one embodiment of the present invention.

[0027] Figure 2 is a diagram showing a laminated structure of a lithium secondary battery manufactured according to one embodiment of the present invention.

[0028] Figure 3 is a flow chart showing a method for manufacturing a lithium-ion cathode according to one embodiment of the present specification.

[0029] Figure 4 is a diagram showing the Raman spectrum of the electrolyte for lithium ionization of each example and comparative example according to Manufacturing Example 1 measured by Raman spectroscopy.

[0030] Figure 5 is a diagram showing discharge curves in the first charge / discharge cycle for each of the coin-full cells exposed to dry air for 7 days and non-exposed to dry air for each of the examples and comparative examples according to Manufacturing Example 1.

[0031] Figure 6 is a diagram showing the discharge curves at the 50th charge / discharge cycle for each of the coin-full cells exposed to dry air for 7 days and unexposed to dry air for each of the examples and comparative examples according to Manufacturing Example 1.

[0032] Figure 7 is a diagram showing the ionic conductivity measured according to the lithium salt concentration of the electrolyte for lithium ionization used in each of the examples, reference examples, and comparative examples according to Manufacturing Example 2.

[0033] Figure 8 is a diagram showing the C-rate characteristics according to the lithium salt concentration of the electrolyte for lithium ionization of each comparative example according to Manufacturing Example 2.

[0034] Figure 9 is a diagram showing the C-rate characteristics according to the lithium salt concentration of the electrolyte for lithium ionization of each example and reference example according to Manufacturing Example 2.

[0035] Figure 10 is a diagram comparing the C-rate characteristics of Example 2-1 and Comparative Example 2-4 according to Manufacturing Example 2.

[0036] Before explaining the present invention, some terms are first defined.

[0037] When a part of this specification is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0038] In this specification, ‘p to q’ means a range of ‘p or more and q or less.’

[0039] In this specification, "specific surface area" is measured by the BET method, and specifically, is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan. That is, in this specification, the BET specific surface area may mean the specific surface area measured by the above measurement method.

[0040] In this specification, "Dn" means particle size distribution, and means the particle size at the n% point of the cumulative distribution of particle numbers according to particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative distribution of particle numbers according to particle size, D90 is the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of particle numbers according to particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction pattern according to particle size is measured when the particles pass through a laser beam, thereby calculating the particle size distribution.

[0041] In one embodiment of the present specification, particle size or particle diameter may mean the average diameter or representative diameter of each grain forming the metal powder.

[0042] In this specification, the structure of the electrolyte can be observed through Raman spectroscopy. The Raman spectroscopy was performed using a Raman spectrometer (DXR2xi, Thermo Fisher, USA). In order to measure the Raman spectrum of various electrolytes, each electrolyte was filled into a 2 mL vial without air bubbles, and then 700 cm -1 760cm in height -1 Raman analysis was performed in the range.

[0043] In this specification, the ionic conductivity of the electrolyte for lithium ionization was measured using a METTLER TOLEDO SevenDirect SD30 ionic conductivity measuring device.

[0044] The terms and words used in this specification should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0045] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0046] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0047] A method for manufacturing a prelithiated negative electrode according to one embodiment of the present specification includes the steps of wetting a negative electrode active material layer including a silicon-based negative electrode active material in an electrolyte for prelithiation; and the step of contacting a lithium metal layer on at least one surface of the negative electrode active material layer wetted in the electrolyte for prelithiation, wherein the electrolyte for prelithiation includes a lithium salt having a concentration exceeding 3 M and a non-aqueous solvent.

[0048] Lithium secondary batteries begin to lose lithium from the first charge after battery manufacturing, and as a small amount of lithium continues to be lost during subsequent charge / discharge cycles and high-temperature storage periods, the battery deteriorates. In order to compensate for this lithium loss, the present invention performs a pre-lithiation process to additionally inject lithium into the battery before operating the battery, and among these, an ex situ wet pre-lithiation process is performed, which is economical and does not cause heat generation problems, thereby increasing the capacity (energy density) of the battery or improving the cycle performance of the battery.

[0049] Meanwhile, the present invention uses a silicon-based negative electrode to obtain a high-capacity battery, but there may be a problem in that the SEI (Solid Electrolyte Interphase) layer is damaged due to a volume change of up to 300% during charging and discharging.

[0050] At this time, the SEI layer is a thin solid film that is formed on the surface of the negative electrode due to a chemical reaction that occurs when the substances in the electrolyte are first electrolyzed during the process of lithium ions moving to the negative electrode during the first charge after the battery is manufactured. The SEI layer prevents further decomposition reactions of the electrolyte in the battery and allows only lithium ions to move through the electrolyte. In particular, LiF is the main component of this SEI layer, and because it is the most electrochemically stable, it can maintain the SEI layer more stably.

[0051] When exposed to air during the storage process prior to battery assembly after wet pre-lithiation, if the oxidation durability of the SEI layer is insufficient, the SEI layer may be damaged, which may cause rapid lithium loss and battery degradation of the pre-lithiated negative electrode. To solve this problem, the present invention provides a method for manufacturing a pre-lithiated negative electrode capable of forming a high LiF content and uniform artificial SEI layer by using a high-concentration lithium salt and a non-aqueous solvent, such as an ether solvent, as the pre-lithiation electrolyte used in wet pre-lithiation.

[0052] That is, the present invention aims to improve the capacity and cycle performance of a silicon-based negative electrode through lithiation, while improving the air safety of the lithiated negative electrode before assembling the battery by performing wet lithiation in an ex situ manner. To this end, the present invention is characterized in that an electrolyte containing a high concentration of lithium salt in a non-aqueous solvent, such as an ether solvent, is used as the electrolyte for lithiation, so as to form an artificial SEI layer containing abundant and uniform LiF due to the CIP structure of the electrolyte.

[0053] In addition, generally, when using an electrolyte containing a high concentration of lithium salt, problems such as increased viscosity and decreased ion conductivity (or ion diffusion rate) may occur, but the electrolyte for prelithiation of the present invention can maintain high ion conductivity despite its high concentration by using a combination of an ether solvent and a specific lithium salt.

[0054] A method for manufacturing a lithium-ion negative electrode according to one embodiment of the present specification may include a step of wetting a negative electrode active material layer including a silicon-based negative electrode active material in an electrolyte for lithium-ion.

[0055] In one embodiment of the present specification, the step of wetting the negative electrode active material layer in the electrolyte for lithium ion can be performed by soaking the negative electrode active material layer in the electrolyte for lithium ion.

[0056] The electrolyte for prelithiation according to one embodiment of the present specification serves as a passage for moving lithium ions in the process of prelithiation by contacting a lithium metal layer with a negative electrode active material layer, and may include a lithium salt having a concentration exceeding 3 M.

[0057] In one embodiment of the present specification, the electrolyte for lithium ionization may contain a lithium salt having a concentration exceeding 3 M, and specifically, may contain 4 M or more.

[0058] In one embodiment of the present specification, the electrolyte for lithium ionization may include a lithium salt having a concentration of more than 3 M and less than or equal to 10 M, specifically, may include a concentration of more than 4 M and less than or equal to 8 M, and the concentration of the lithium salt is based on room temperature and normal pressure.

[0059] Depending on the interaction between the lithium salt and solvent that make up the electrolyte, the solvation structure of the electrolyte changes, which also affects the characteristics of the SEI. In the case of a low-concentration electrolyte solution (Dilute Electrolyte Solution) where the lithium salt concentration is less than 1 M, the lithium ions are coordinated by about 3-4 solvent molecules, so that the lithium ions and anions of the lithium salt are separated to form a SSIP (Solvent Separated Ion Pair) structure. In addition, the free solvent that does not interact with the lithium ions becomes abundant, and as this free solvent is mainly distributed on the electrode surface, an SEI layer whose main component is the solvent component is formed.

[0060] However, in one embodiment of the present specification, when the concentration of the lithium salt is high, exceeding 3M, the solvent becomes thin, the number of solvents coordinating lithium ions decreases to 1-2, and the lithium ions and anions of the lithium salt come into contact with each other to form a Contact Ion Pair (CIP) or Cation-Anion Aggregate (AGG) structure. In addition, since there is almost no free solvent that does not interact with the lithium ions, the anions of the lithium salt are mainly distributed on the electrode surface, so that a thin and dense artificial SEI layer rich in LiF components can be formed.

[0061] That is, when an electrolyte for prelithiation is used in which the concentration of a lithium salt according to one embodiment of the present specification satisfies the above range, a thin and dense artificial SEI layer rich in LiF components can be formed.

[0062] In addition, in one embodiment of the present specification, the lithium salt is BF4 as an anion. - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2- , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - and may include at least one selected from the group consisting of combinations thereof.

[0063] Specifically, in one embodiment of the present specification, the anion of the lithium salt is BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - and may include at least one selected from the group consisting of combinations thereof, and more specifically, the anion of the lithium salt is (FSO2)2N - It could be.

[0064] In one embodiment of the present specification, when the lithium salt contains the anion, it has a solubility suitable for use in an ether solvent, and in particular, (FSO2)2N as the anion. -The lithium salt containing is a hydrophilic salt that forms a white powder form expressed as LiFSI (lithium bis(trifluoromethanesulfonyl)imide), which has a high decomposition temperature and can affect the thermal stability of the SEI layer, and is stable to moisture, so it is more suitable than LiPF6, which is used as a lithium salt in electrolytes for general lithium secondary batteries. The amount of HF generated by reacting with moisture inside the battery is significantly small, resulting in a stable effect.

[0065] The electrolyte for prelithiation according to one embodiment of the present specification may include a non-aqueous solvent. The non-aqueous solvent serves to help lithium ions dissolve in the salt, and allows the lithium metal layer to contact the negative electrode active material layer to allow the lithium ions to move smoothly during prelithiation.

[0066] In addition, when a high concentration of lithium salt is used together with a carbonate solvent, the viscosity of the electrolyte may increase and the ionic conductivity may decrease, which may cause problems. However, a non-aqueous solvent, particularly an ether solvent according to an embodiment of the present specification, can reduce the decrease in ionic conductivity even at a high concentration by being used together with a specific lithium salt.

[0067] The non-aqueous solvent included in the electrolyte for lithium ion according to one embodiment of the present specification may include at least one selected from the group consisting of diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, dioxolane, methyldioxolane, oxane, dioxane, trioxane, tetrahydrofuran, dihydropyran, tetrahydropyran, methyltetrahydrofuran, furan, methylfuran, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, and combinations thereof.

[0068] The non-aqueous solvent included in the electrolyte for lithium ion according to one embodiment of the present specification may include at least one selected from the group consisting of diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, dioxolane, methyldioxolane, oxane, dioxane, trioxane, tetrahydrofuran, dihydropyran, tetrahydropyran, methyltetrahydrofuran, furan, methylfuran, and combinations thereof.

[0069] The non-aqueous solvent included in the electrolyte for lithium ion according to one embodiment of the present specification may include at least one selected from the group consisting of diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, tetrahydrofuran, dihydropyran, tetrahydropyran, methyltetrahydrofuran, furan, methylfuran, and combinations thereof.

[0070] The non-aqueous solvent included in the electrolyte for lithium ion according to one embodiment of the present specification may include at least one selected from the group consisting of diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, and combinations thereof.

[0071] The non-aqueous solvent included in the electrolyte for lithium ion according to one embodiment of the present specification may be dimethoxyethane (DME).

[0072] The electrolyte for prelithiation according to one embodiment of the present specification has a different purpose from the electrolyte used in assembling a secondary battery described later. The electrolyte for prelithiation is used to prelithiate a silicon-based negative electrode to improve capacity and cycle performance, but the electrolyte used in assembling a secondary battery described later is used to enable lithium ions to move between the positive electrode and the negative electrode during charging and discharging of the battery.

[0073] The solvation structure of the electrolyte is affected not only by the concentration of the lithium salt but also by the solvation ability of the solvent. The electrolyte for prelithiation according to one embodiment of the present specification uses the non-aqueous solvent, particularly an ether solvent, and thus has a lower solvation ability than a carbonate solvent used as a solvent for a general lithium secondary battery electrolyte, which allows the lithium salt to form a CIP structure. In addition, it has the advantage of high chemical stability for the high-concentration lithium salt, and in particular, since the dimethoxyethane has a small molecular weight, it can satisfy an appropriate viscosity for use as an electrolyte when used in a high-concentration electrolyte.

[0074] In one embodiment of the present specification, the step of wetting the negative electrode active material layer in the electrolyte for lithium ion may be wetting the negative electrode active material layer for 11 hours or longer, and specifically, may be wetting the negative electrode active material layer for 12 hours or longer.

[0075] The wetting step according to one embodiment of the present specification has the effect of enabling more uniform prelithiation in the electrode thickness direction during prelithiation by wetting the negative active material layer in the electrolyte for prelithiation for the above range of time.

[0076] In one embodiment of the present specification, the step of wetting the negative electrode active material layer in the electrolyte for lithium ion conversion may be performed under a temperature condition of 0°C or more and 100°C or less, specifically, may be performed under a temperature condition of 10°C or more and 80°C or less, and more specifically, may be performed at room temperature, but there is no limitation thereto.

[0077] A method for manufacturing a prelithiated negative electrode according to one embodiment of the present specification may include a step of contacting a lithium metal layer on at least one surface of a negative electrode active material layer wetted with the electrolyte for prelithiation, which is a step for performing wet prelithiation by direct lithium contact on the negative electrode active material layer of the present invention.

[0078] The method for manufacturing a lithium-ion cathode according to the present specification is characterized by performing wet lithium-ion, which does not cause a serious heat generation problem compared to dry lithium-ion, and has the advantage of a simpler lithium-ion process compared to a case where lithium-ion is performed by an electrochemical method using the same electrolyte as the lithium-ion electrolyte according to one embodiment of the present specification.

[0079] Specifically, prelithiation by an electrochemical method involves constructing a battery using lithium metal as an anode and then electrochemically discharging the battery to perform prelithiation of the anode. Compared to the method for manufacturing a prelithiated anode according to one embodiment of the present disclosure, in which prelithiation is performed by simply contacting lithium metal with an electrode, the electrochemical method has the complexity of requiring the additional construction of a separate battery for prelithiation.

[0080] In one embodiment of the present specification, the method may further include a step of preparing a lithium metal layer-containing laminate for lithium ion conversion and a substrate layer before the step of contacting a lithium metal layer with at least one surface of the negative electrode active material layer wetted with the lithium metal layer-containing electrolyte; and a step of positioning the lithium metal layer-containing laminate so that the lithium metal layer faces at least one surface of the negative electrode active material layer.

[0081] A method for manufacturing a prelithiated negative electrode according to one embodiment of the present specification may include a step of preparing a prelithiation laminate including a lithium metal layer and a substrate layer. That is, the prelithiation laminate for prelithiating an anode active material layer may include a lithium metal layer and a substrate layer.

[0082] In one embodiment of the present specification, the laminate for lithiation includes a lithium metal layer, wherein the lithium metal layer is a layer including lithium metal for lithiation of at least one surface of the negative electrode active material layer, and a commonly used Li metal foil may be used, but is not limited thereto.

[0083] In one embodiment of the present specification, the thickness of the lithium metal layer may be 0.5 μm, specifically 1 μm or more, and more specifically 2 μm or more.

[0084] In one embodiment of the present specification, the thickness of the lithium metal layer may be 15 μm or less, specifically 10 μm or less, and more specifically 7 μm or less.

[0085] In one embodiment of the present specification, the thickness of the lithium metal layer may be 0.5 μm or more and 15 μm or less, specifically 1 μm or more and 10 μm or less, and more specifically 2 μm or more and 7 μm or less.

[0086] In one embodiment of the present specification, when the thickness of the lithium metal layer satisfies the above range, prelithiation can be achieved to a degree that can sufficiently compensate for the irreversible capacity, thereby having the effect of improving the energy density of the battery.

[0087] In one embodiment of the present specification, the laminate for prelithiation may include a substrate layer, and the substrate layer may be used without limitation as long as it has the characteristics of being able to withstand process conditions such as high temperature in the step of depositing the lithium metal layer and preventing the problem of the lithium metal layer being delaminated onto the substrate layer during the process of prelithiating the deposited lithium metal layer.

[0088] Specifically, in one embodiment of the present specification, the substrate layer may be at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), polymethylmethacrylate (PMMA), polypropylene, polyethylene, and polycarbonate, and preferably polyethylene terephthalate (PET).

[0089] In one embodiment of the present specification, the thickness of the substrate layer may be 1 μm or more.

[0090] In one embodiment of the present specification, the thickness of the substrate layer may be 300 μm or less, specifically 100 μm or less, and more specifically 50 μm or less.

[0091] In one embodiment of the present specification, the thickness of the substrate layer may be 1 μm or more and 300 μm or less, and specifically, may satisfy a range of 1 μm or more and 100 μm or less, and more specifically, 1 μm or more and 50 μm or less.

[0092] As the thickness of the above-mentioned substrate layer satisfies the above range, the transfer of lithium metal toward the electrode active material layer can occur efficiently, and it has the characteristic of being able to prevent reverse transfer.

[0093] In one embodiment of the present specification, a deposition method for depositing the lithium metal layer on the substrate layer may be selected from among evaporation deposition, chemical vapor deposition, and physical vapor deposition, but is not limited thereto, and various deposition methods used in the art may be used.

[0094] In one embodiment of the present specification, the lithium metal layer may be deposited on the substrate layer by evaporation deposition, and specifically, may be deposited by vacuum thermal evaporation deposition.

[0095] In one embodiment of the present specification, the lithium-ion layered body may further include a heterostructure layer between the substrate layer and the lithium metal layer.

[0096] In one embodiment of the present specification, the release layer may be at least one selected from the group consisting of polycarbonate (PC), polydimethylsiloxane (PDMS), polymethylhydrosiloxane (PMHS), polyimide (PI), and polymethylmethacrylate (PMMA), and preferably polymethylmethacrylate (PMMA).

[0097] In one embodiment of the present specification, the thickness of the heterogeneous layer may be 0.2 μm or more, and specifically, 0.5 μm or more.

[0098] In one embodiment of the present specification, the thickness of the heterogeneous layer may be 3 μm or less, and specifically, 1 μm or less.

[0099] In one embodiment of the present specification, the thickness of the heterogeneous layer may be 0.2 μm or more and 3 μm or less, and specifically, 0.5 μm or more and 1 μm or less.

[0100] In one embodiment of the present specification, when the thickness of the release layer satisfies the above range, sufficient release force of the lithium metal layer can be secured, and the release layer located on the surface after the prelithiation does not play a role in blocking heat release, so that formation of by-products may not be accelerated.

[0101] In one embodiment of the present specification, the release layer can be formed by a coating method, and for example, the coating method can be a method selected from the group consisting of dip coating, spray coating, spin coating, die coating, gravure coating, micro-gravure coating, comma coating, and roll coating, but is not limited thereto, and various coating methods that can be used to form a coating layer in the art can be used.

[0102] In one embodiment of the present specification, the step of positioning the lithium metal layer facing the negative electrode active material layer on at least one surface of the negative electrode active material layer is a step for lithium metallizing the negative electrode active material layer.

[0103] In one embodiment of the present specification, after the step of bringing the negative electrode active material layer into contact with the lithium metal layer, the step of pressurizing and prelithiating the negative electrode active material layer in contact with the lithium metal layer may be further included.

[0104] In the pressurizing step according to one embodiment of the present specification, the pressurizing condition may be 5 MPa or more and 50 MPa or less, and specifically, 10 MPa or more and 40 MPa or less.

[0105] In one embodiment of the present specification, the pressurizing step has the effect of enabling more active lithiumization on at least one surface of the negative electrode active material layer, and forming the negative electrode thin despite having a high energy density.

[0106] Specifically, after positioning the lithium metal layer on one or both sides of the negative electrode active material layer so that the lithium metal layer faces it, a pressure of 5 MPa to 50 MPa is applied, and a wet lithium direct contact method process can be performed.

[0107] As the pressure conditions increase in the above pressurizing step, the lithiation reaction can proceed more quickly, and in particular, when the above range is satisfied, there is an effect of suppressing the volume expansion of the active material during lithiation, thereby stably maintaining the conductive structure of the electrode.

[0108] A manufacturing method according to one embodiment of the present specification may include a step of removing the substrate layer or the release layer and the substrate layer.

[0109] In one embodiment of the present specification, the step of removing the substrate layer or the release layer and substrate layer may be performed after contacting the lithium metal layer with the negative electrode active material layer and applying pressure to prelithiate the lithium metal layer.

[0110] A method for manufacturing a prelithiated negative electrode according to one embodiment of the present specification may be such that prelithiation occurs from the time point at which the lithium metal layer contacts at least one surface of the negative electrode active material layer, and prelithiation may occur by pressurizing the negative electrode active material layer to which the lithium metal layer has contacted.

[0111] In a method for manufacturing a lithium-ion negative electrode according to one embodiment of the present specification, the negative electrode active material layer includes a silicon-based negative electrode active material, and the silicon-based negative electrode active material may include at least one selected from the group consisting of Si, silicon oxide, Si / C, and Si alloy.

[0112] In one embodiment of the present specification, the silicon-based negative electrode active material may include at least one selected from the group consisting of Si and silicon oxide.

[0113] In one embodiment of the present specification, the silicon-based negative electrode active material includes Si, and the Si may be included in an amount of 60 parts by weight or more based on 100 parts by weight of the silicon-based negative electrode active material.

[0114] In one embodiment of the present specification, the negative electrode active material layer may use pure silicon (Si) as the negative electrode active material. Using pure silicon (Si) as the negative electrode active material may mean that, based on 100 parts by weight of the total negative electrode active material as described above, the negative electrode active material layer may include pure Si particles that are not combined with other particles or elements in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may include 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less.

[0115] Specifically, in one embodiment of the present specification, the silicon-based negative electrode active material may contain Si in an amount of 60 parts by weight or more and 95 parts by weight or less, specifically 65 parts by weight or more and 90 parts by weight or less, and even more specifically 70 parts by weight or more and 85 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer. When the silicon-based negative electrode active material contains Si in the above range, a high-capacity battery can be obtained.

[0116] In a manufacturing method according to one embodiment of the present specification, the silicon-based negative electrode active material may further include at least one selected from the group consisting of silicon oxide, Si / C, and Si alloy.

[0117] In one embodiment of the present specification, the silicon-based negative electrode active material may further include silicon oxide, and the silicon oxide corresponds to an amorphous matrix in the silicon-based negative electrode active material. The silicon oxide may be in a form partially including Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si included in the silicon oxide.

[0118] In one embodiment of the present specification, the negative electrode active material layer may contain 40 parts by weight or more, preferably 50 parts by weight or more, and more preferably 60 parts by weight or more of the silicon oxide based on 100 parts by weight of the negative electrode active material layer, and may contain 100 parts by weight or less, preferably 90 parts by weight or less, and more preferably 80 parts by weight or less. When the negative electrode active material layer contains silicon oxide within the above range, the discharge capacity of the lithium secondary battery may be improved.

[0119] In one embodiment of the present specification, the silicon-based negative electrode active material may include metal impurities.

[0120] The above metal impurities are impurities that can be included in silicon, and their content can satisfy a range of 0.1 parts by weight or less based on 100 parts by weight of the silicon-based negative electrode active material.

[0121] Meanwhile, the silicon-based negative electrode active material of the present specification includes Si, and the average particle diameter (D50) of the Si may be 5 nm to 10 μm, specifically 5.5 nm to 8 μm, and more specifically 10 nm to 7 μm.

[0122] When the average particle diameter is within the above range, the specific surface area of ​​the particles is within an appropriate range, so that the viscosity of the negative electrode slurry is formed within an appropriate range. Accordingly, the particles constituting the negative electrode slurry are smoothly dispersed. In addition, when the size of the silicon-based active material is greater than the range of the lower limit, the contact area between the silicon particles and the conductive material is excellent due to the composite composed of the conductive material and the binder in the negative electrode slurry, so that the possibility of the conductive network continuing increases, thereby increasing the capacity retention rate. Meanwhile, when the average particle diameter satisfies the above range, excessively large silicon particles are excluded, so that the surface of the negative electrode is formed smoothly, and thus the phenomenon of uneven current density during charge and discharge can be prevented.

[0123] In one embodiment of the present specification, the silicon-based negative electrode active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 m 2 / g to 150.0 m 2 / g, more preferably 0.1 m 2 / g to 100.0 m 2 / g, especially preferably 0.2 m 2 / g to 80.0 m 2 / g, most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET surface area is measured according to DIN 66131 (using nitrogen).

[0124] In one embodiment of the present disclosure, the silicon-based negative electrode active material may exist in, for example, a crystalline or amorphous form, and is preferably non-porous. The silicon particles are preferably spherical or fragment-shaped particles. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or be present in the form of a silicon-containing film or coating.

[0125] In one embodiment of the present specification, the silicon-based negative electrode active material may be at least 40 parts by weight based on 100 parts by weight of the total negative electrode active material layer.

[0126] In one embodiment of the present specification, the silicon-based negative electrode active material may be 40 parts by weight or more and 95 parts by weight or less, specifically 50 parts by weight or more and 90 parts by weight or less, and more specifically 60 parts by weight or more and 80 parts by weight or less, based on 100 parts by weight of the total negative electrode active material layer.

[0127] In the charge / discharge reaction of a lithium secondary battery, lithium released from the positive electrode is inserted into the negative electrode during charging, and desorbed from the negative electrode and returned to the positive electrode during discharge. However, in the case of silicon-based active materials, the volume change and surface side reactions are severe, so a large amount of lithium inserted into the negative electrode during the initial charge does not return to the positive electrode, resulting in a problem of high initial irreversible capacity. If the initial irreversible capacity increases, the battery capacity and cycles decrease rapidly.

[0128] In the case of the present invention, in order to solve the above-mentioned problem, the initial irreversible capacity problem is solved by prelithiating the negative electrode active material layer before manufacturing a lithium secondary battery, and specifically, the present invention relates to a prelithiation method that can improve the capacity (energy density) or cycle performance of a battery through a wet prelithiation process using a lithium direct contact method, while forming an artificial SEI layer with a high LiF content and uniformity, thereby improving the air stability of the negative electrode and the battery, i.e., oxidation durability.

[0129] In a manufacturing method according to one embodiment of the present specification, the negative electrode active material layer may further include a negative electrode conductive material and a negative electrode binder.

[0130] Previously, graphite compounds were typically used solely as anode active materials. However, with the increasing demand for high-capacity batteries, attempts to mix silicon-based compounds to increase capacity have been increasing. However, silicon-based compounds have limitations in that their volume rapidly expands during the charge / discharge process, damaging the conductive path formed within the anode active material layer and lowering battery performance. Therefore, the type of anode conductive material used together with the silicon-based active material is important.

[0131] Accordingly, in one embodiment of the present specification, the negative electrode conductive material may include at least one selected from the group consisting of a planar conductive material, a linear conductive material, and a dot-shaped conductive material, and specifically, may include at least one selected from the group consisting of a planar conductive material and a dot-shaped conductive material.

[0132] In one embodiment of the present specification, the negative electrode conductive material may be 1 part by weight or more and 40 parts by weight or less based on 100 parts by weight of the total negative electrode active material layer.

[0133] Specifically, in the above embodiment, the negative electrode conductive material may be included in an amount of 1 part by weight or more and 40 parts by weight or less, specifically 5 parts by weight or more and 30 parts by weight or less, and more specifically 10 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the total negative electrode active material layer.

[0134] When the content of the negative electrode conductive material satisfies the above range, there is an effect in which charge and discharge capacity is stably expressed while maintaining the conductive network structure of the electrode without damaging the conductive path formed within the negative electrode active material layer.

[0135] In one embodiment of the present specification, the planar conductive material used as the aforementioned negative electrode conductive material has a structure and function different from those of carbon-based active materials generally used as negative electrode active materials. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material processed into a spherical or dot-shaped form to facilitate the storage and release of lithium ions.

[0136] On the other hand, the planar conductive material used as the negative electrode conductive material is a material in the form of a plane or plate, and can be expressed as plate-shaped graphite. In other words, it refers to a material included to maintain a conductive path within the negative electrode active material layer, and is not a material that plays a role in storing and releasing lithium, but rather a material that secures a conductive path in the form of a plane within the negative electrode active material layer.

[0137] That is, in one embodiment of the present specification, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-shaped form and used as a material that secures a conductive path rather than a role of storing or releasing lithium. In this case, the included negative electrode active material has high capacity characteristics for lithium storage and release, and plays a role of storing and releasing all lithium ions transferred from the positive electrode.

[0138] On the other hand, in one embodiment of the present specification, the use of a carbon-based active material as an active material means that it is processed into a dot or spherical shape and used as a material that plays a role in storing or releasing lithium.

[0139] In one embodiment of the present specification, the negative conductive material may include a planar conductive material.

[0140] In the present specification, the "planar conductive material" refers to a conductive material having a two-dimensional (2D) structure in which atoms form a crystal structure on a plane with a thickness of a single atomic layer or two or more atomic layers, and can play a role in improving conductivity by increasing surface contact between silicon particles within a cathode and simultaneously suppressing disconnection of a conductive path due to volume expansion, and can be expressed as a plate-shaped conductive material or a bulk-shaped conductive material.

[0141] In one embodiment of the present specification, the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-shaped graphite.

[0142] In one embodiment of the present specification, the average particle diameter (D50) of the planar conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the above range is satisfied, dispersion is easy without causing excessive viscosity increase of the negative electrode slurry due to sufficient particle size. Therefore, the dispersion effect is excellent when dispersion is performed using the same equipment and time.

[0143] In one embodiment of the present specification, the surface-shaped conductive material may have a D10 of 0.5 μm or more and 1.7 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.8 μm or more and 15.0 μm or less.

[0144] In one embodiment of the present specification, the planar conductive material may be a high-specific surface area planar conductive material having a high BET specific surface area; or a low-specific surface area planar conductive material.

[0145] In one embodiment of the present specification, a high surface area surface conductive material or a low surface area surface conductive material may be used without limitation as the surface conductive material, but in particular, since the surface conductive material according to the present specification may be affected to some extent by dispersion effects on electrode performance, it may be particularly preferable to use a low surface area surface conductive material that does not cause dispersion problems.

[0146] In one embodiment of the present specification, the surface-shaped conductive material has a BET specific surface area of ​​5 m 2 / g can be more than that.

[0147] In another embodiment, the surface-shaped conductive material has a BET surface area of ​​5 m 2 / g or more than 500m 2 / g or less, preferably 5m 2 / g or more than 300m 2 / g or less, more preferably 5m 2 / g or more than 250m 2 / g can be less.

[0148] In another embodiment, the surface-shaped conductive material is a high surface area surface-shaped conductive material, and has a BET surface area of ​​50 m 2 / g or more than 500m 2 / g or less, preferably 80m 2 / g or more than 300m 2 / g or less, more preferably 100m 2 / g or more than 300m 2 / g can satisfy the range below.

[0149] In another embodiment, the surface-shaped conductive material is a low surface area surface-shaped conductive material, and has a BET surface area of ​​5 m 2 / g or more than 40m 2 / g or less, preferably 5m 2 / g or more than 30m 2 / g or less, more preferably 5m 2 / g or more than 25m 2 / g can satisfy the range below.

[0150] In one embodiment of the present specification, the cathode conductive material may include a dot-shaped conductive material.

[0151] The dot-shaped conductive material may be used to improve conductivity of the cathode, and refers to a conductive material having conductivity without causing chemical changes. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in terms of implementing high conductivity and excellent dispersibility.

[0152] In one embodiment of the present specification, the dot-shaped conductive material has a BET specific surface area of ​​40 m 2 / g or more than 70m 2 / g or less, preferably 45m 2 / g or more than 65m 2 / g or less, more preferably 50m 2 / g or more than 60m 2 / g can be less.

[0153] In one embodiment of the present specification, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0154] The negative electrode conductive material according to this specification has a completely separate composition from the conductive material applied to the positive electrode. That is, the negative electrode conductive material according to this specification serves to secure the contact between silicon-based active materials, which undergo a significant volume expansion of the electrode due to charging and discharging, and is completely different in composition and role from the positive electrode conductive material, which acts as a buffer when rolled and provides some conductivity.

[0155] In addition, the negative electrode conductive material according to the present specification is applied to a silicon-based negative electrode active material and has a completely different composition from the conductive material applied to a graphite-based active material. That is, the conductive material used in an electrode having a graphite-based active material simply has smaller particles than the active material, and thus has the characteristics of improving output characteristics and imparting some conductivity, and is completely different in composition and role from the negative electrode conductive material applied together with a silicon-based negative electrode active material as in the present invention.

[0156] In this specification, a “linear conductive material” refers to a conductive material having a one-dimensional (1D) structure with a diameter in the nanometer order and a high aspect ratio, or a conductive material having a fibrous structure such as a cylindrical type or tube type.

[0157] In one embodiment of the present specification, a carbon nanotube (CNT) may be used as the linear conductive material, and the carbon nanotube may be a bundle-type carbon nanotube. The bundle-type carbon nanotube may include a plurality of carbon nanotube units. Specifically, the term "bundle type" herein refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in a substantially identical orientation in a longitudinal direction of the carbon nanotube units or are entangled. The carbon nanotube unit has a graphite sheet having a cylindrical shape with a nano-sized diameter, and is sp 2It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or semiconductor. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be uniformly dispersed during the manufacture of the cathode, and can smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0158] In one embodiment of the present specification, the linear conductive material has a BET specific surface area of ​​100 m 2 / g or more than 10,000m 2 / g or less, preferably 500m 2 / g or more than 5,000m 2 / g or less, more preferably 1,000m 2 / g or more than 1,500m 2 / g can be less.

[0159] In addition, in one embodiment of the present specification, the aspect ratio of the linear conductive material may be 500 or more, preferably 1,000 or more, more preferably 10,000 or more, and may be 1,000,000 or less, preferably 100,000 or less.

[0160] In one embodiment of the present specification, when the linear conductive material satisfies the BET specific surface area and aspect ratio range, the conductive network structure of the electrode is stably maintained, thereby providing an effect of stably expressing charge / discharge capacity.

[0161] In one embodiment of the present specification, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyacrylamide, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and a material in which hydrogens thereof are substituted with Li, Na, Ca, or the like, and may also include various copolymers thereof.

[0162] The negative electrode binder according to one embodiment of the present specification serves to hold the active material and the conductive material in order to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon-based active material expands and relaxes. If the above-mentioned role is satisfied, all general binders can be applied, and specifically, it can include one or more binders selected from the group consisting of polyacrylamide (PAM) and styrene butadiene rubber.

[0163] In one embodiment of the present specification, the negative electrode binder may be 1 part by weight or more and 30 parts by weight or less, specifically 1 part by weight or more and 20 parts by weight or less, and more specifically 3 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the total negative electrode active material layer.

[0164] In one embodiment of the present invention, the weight average molecular weight of the negative electrode binder may be 100,000 g / mol or more and 1,500,000 g / mol or less.

[0165] When the weight-average molecular weight of the negative electrode binder satisfies the above range, the binder exhibits excellent mechanical strength and high intermolecular interaction, resulting in excellent electrode bonding properties. Furthermore, when the above range is satisfied, the binder's viscosity can be appropriately selected, thereby further improving the coating properties of the electrode when used to manufacture a negative electrode.

[0166] A prelithiated negative electrode according to one embodiment of the present specification comprises a negative electrode current collector layer; and a negative electrode active material layer provided on at least one surface of the negative electrode current collector layer, and may be manufactured using the manufacturing method described above. The negative electrode active material layer may include the negative electrode active material. Furthermore, the negative electrode active material layer may further include a thickener.

[0167] FIG. 1 is a diagram showing a laminated structure of a pre-lithiated negative electrode according to one embodiment of the present specification. Specifically, a pre-lithiated negative electrode (100) including a negative electrode active material layer (20) on one surface of a negative electrode current collector layer (10) can be confirmed. FIG. 1 shows that the negative electrode active material layer (20) is formed on one surface of the negative electrode current collector layer (10), but it may be formed on both surfaces of the negative electrode current collector layer (10). In addition, although not shown in FIG. 1, the negative electrode active material layer (20) is pre-lithiated.

[0168] In one embodiment of the present specification, the negative electrode current collector layer may generally have a thickness of 1 μm to 100 μm. The negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. In addition, the bonding strength of the negative electrode active material may be strengthened by forming fine unevenness on the surface, and may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0169] In one embodiment of the present specification, the thickness of the negative electrode current collector layer is 1 μm to 100 μm, and the thickness of the negative electrode may be 20 μm or more and 500 μm or less. However, the thickness may be modified in various ways depending on the type and purpose of the negative electrode active material, conductive material, binder, etc. used, and is not limited thereto.

[0170] The above negative electrode active material layer can be formed by coating a negative electrode slurry containing the above-described negative electrode active material, negative electrode binder, negative electrode conductive material and / or thickener on at least one surface of the negative electrode current collector layer, which means that the negative electrode slurry can be formed by applying the negative electrode slurry to at least one surface of the negative electrode current collector layer and drying and rolling.

[0171] In one embodiment of the present specification, the negative electrode slurry may include a negative electrode active material layer composition including the negative electrode active material, a negative electrode binder, a negative electrode conductive material, and / or a thickener; and a slurry solvent.

[0172] In one embodiment of the present specification, the solid content of the cathode slurry can satisfy 5% or more and 40% or less.

[0173] In another embodiment, the solid content of the cathode slurry can satisfy a range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0174] The solid content of the above negative electrode slurry may refer to the content of the negative electrode active material layer composition included in the negative electrode slurry, and may refer to the content of the negative electrode active material composition based on 100 parts by weight of the negative electrode slurry.

[0175] When the solid content of the above-mentioned negative electrode slurry satisfies the above range, the viscosity is appropriate when forming the negative electrode active material layer, thereby minimizing particle agglomeration of the negative electrode active material layer composition, thereby enabling the formation of the negative electrode active material layer efficiently.

[0176] In one embodiment of the present specification, the solvent may include those known in the art. For example, the solvent may be water (e.g., distilled water) or NMP (N-methyl-2-pyrrolidone).

[0177] According to one embodiment of the present specification, a negative electrode can be formed by coating and drying the negative electrode slurry on one or both sides of a negative electrode current collector layer, and the slurry solvent in the negative electrode slurry can be dried through the drying step.

[0178] A lithium secondary battery according to one embodiment of the present specification may include a positive electrode; the aforementioned pre-lithiated negative electrode; a separator provided between the positive electrode and the pre-lithiated negative electrode; and an electrolyte.

[0179] In addition, in one embodiment of the present specification, the lithium secondary battery may have a discharge capacity ratio of 1:0.99 to 1:1 after 50 charge / discharge cycles of the lithium secondary battery using the pre-lithiated negative electrode immediately after completion of pre-lithiation as the negative electrode and the lithium secondary battery using the pre-lithiated negative electrode exposed to air having a moisture content of less than 1.0 ppm for 7 days after completion of pre-lithiation as the negative electrode, and at this time, the C-rate during the charge / discharge cycle may be 0.5C, and the charging may be performed at an upper limit voltage of 4.2V, a constant current / constant voltage mode (CC / CV mode), and a cut-off current of 0.05C, and the discharging may be performed at a lower limit voltage of 3.0V, a constant current mode (CC mode).

[0180] That is, a lithium secondary battery according to one embodiment of the present specification has improved air stability, and is characterized by almost no change in capacity during the course of a charge / discharge cycle even when a silicon-based negative electrode is used that has been exposed to dry air for a certain period of time after completion of prelithiation.

[0181] Since the above-mentioned lithium-ion cathode has been described above, a detailed description thereof will be omitted.

[0182] FIG. 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present specification. Specifically, a pre-lithiated negative electrode (100) including a negative electrode active material layer (20) on one surface of a negative electrode current collector layer (10) can be confirmed, and a positive electrode (200) including a positive electrode active material layer (40) on one surface of a positive electrode current collector layer (50) can be confirmed, and the pre-lithiated negative electrode (100) and the positive electrode (200) are shown to be formed in a laminated structure with a separator (30) interposed therebetween. At this time, the pre-lithiated negative electrode may be manufactured according to a manufacturing method according to one embodiment of the present specification.

[0183] FIG. 3 is a flow chart illustrating a method for manufacturing a prelithiated negative electrode according to one embodiment of the present disclosure. Specifically, FIG. 3(a) illustrates a method for manufacturing a prelithiated negative electrode, including a step (S1) of wetting a negative electrode active material layer including a silicon-based negative electrode active material in an electrolyte for prelithiation; and a step (S2) of contacting the negative electrode active material layer wetted in the electrolyte for prelithiation with a lithium metal layer.

[0184] FIG. 3(b) shows a method for manufacturing a prelithiated negative electrode, including a step (S1) of wetting a negative electrode active material layer including a silicon-based negative electrode active material in an electrolyte for prelithiation; a step (S2) of contacting the negative electrode active material layer wetted in the electrolyte for prelithiation with a lithium metal layer; and a step (S3) of pressurizing and prelithiating the negative electrode active material layer in contact with the lithium metal layer.

[0185] At this time, the method for manufacturing a prelithiated negative electrode according to one embodiment of the present specification may further include a step (not shown) of providing a negative electrode active material layer on at least one surface of the negative electrode current collector layer, and this may be performed before step S1, but there is no limitation thereon.

[0186] The above positive electrode may include a positive electrode current collector layer and a positive electrode active material layer formed on at least one surface of the positive electrode current collector layer, and including the positive electrode active material.

[0187] In the above positive electrode, the positive electrode current collector layer is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector layer may typically have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector layer to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, or a non-woven fabric.

[0188] According to one embodiment of the present specification, the positive electrode active material may include at least one selected from the group consisting of lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, lithium aluminum oxide, or a lithium composite oxide comprising these.

[0189] Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4(0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by O2 (wherein, M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.5); chemical formula LiMn 2-c3 M c3Lithium manganese composite oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or LiMn2O4 in which a portion of Li in the chemical formula is replaced with an alkaline earth metal ion; but is not limited thereto. The positive electrode may be Li-metal.

[0190] The above-described positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

[0191] At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, it can be used without special restrictions as long as it does not cause a chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used.

[0192] In addition, the positive electrode binder plays a role of improving the adhesion between positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0193] The solvent used in the positive electrode composition slurry may be a solvent generally used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or as a mixture of two or more. The amount of the solvent used is sufficient to dissolve or disperse the active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive and negative electrodes. In addition, as another method, the positive and negative electrodes may be manufactured by casting the composition for forming the active material layer on a separate support, and then laminating the film obtained by peeling it from the support on a current collector.

[0194] The separator is used to separate the negative electrode and the positive electrode and to provide a passage for lithium ions. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0195] Examples of the above electrolyte include, but are not limited to, organic liquid electrolyte, inorganic liquid electrolyte, solid polymer electrolyte, gel-type polymer electrolyte, solid inorganic electrolyte, and molten inorganic electrolyte that can be used in the manufacture of lithium secondary batteries.

[0196] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0197] As the above non-aqueous organic solvent, for example, aprotic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate Organic solvents may be used.

[0198] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte having high electrical conductivity can be produced, so that they can be used even more preferably.

[0199] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3- , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0200] In one embodiment of the present specification, the above-mentioned ether solvent and lithium salt are used as components of an electrolyte for prelithiating a negative electrode active material layer, and have a different role from the generally used carbonate organic solvent and lithium salt.

[0201] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0202] A battery module according to one embodiment of the present specification may include the lithium secondary battery described above.

[0203] Another embodiment of the present disclosure may include a battery pack comprising the aforementioned lithium secondary battery or a battery module including the aforementioned lithium secondary battery.

[0204] The lithium secondary battery according to the embodiments of the present specification stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and therefore can be used as a power source for portable devices such as mobile phones, laptop computers, and digital cameras, as well as medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. For example, the battery module or battery pack can be used as a power source for any one or more medium- to large-sized devices selected from the group consisting of power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0205] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0206] Manufacturing Example 1

[0207] Example 1-1

[0208] <Manufacturing of the cathode>

[0209] A negative electrode active material layer composition was prepared using Si (average particle diameter (D50): 5 μm) as a negative electrode active material, plate-shaped graphite as a conductive material, and polyacrylamide binder in a weight ratio of 80:10:10. A negative electrode slurry was prepared by adding distilled water as a solvent for forming a negative electrode slurry.

[0210] As a mixing method, the above-mentioned conductive material, binder, and water were dispersed using a homogenous mixer at 2500 rpm for 30 min, and then the active material was added and dispersed at 2500 rpm for 30 min to produce a negative electrode slurry.

[0211] The above negative electrode slurry was applied to both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector at 11.5 mAh / cm 2 The coating was performed with a capacity of , roll-pressed, and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode (diameter: 12 mm) for manufacturing a coin cell.

[0212] <All-lithiation>

[0213] The above-mentioned negative electrode (diameter: 12 mm) was wetted in a solution for pre-lithiation having a composition (4 M lithium salt LiFSI and solvent dimethoxyethane (DME)) according to Example 1-1 of Table 1 below for 12 hours, and then a lithium metal layer (thickness: 6.2 μm) and a PET substrate layer-containing pre-lithiation laminate (diameter: 12 mm) were placed in contact with each other and placed into a coin cell component. At this time, a spring component was not placed to transmit pressure through a hot press, and three 1 mm thick spacers and a solution for pre-lithiation having a composition according to Table 1 below were placed together, and the coin cell was compressed using a hot press method to obtain a current density of 1.24 mAh / cm 2 A lithium-ion cathode was manufactured with a capacity of .

[0214] <Coin-full cell manufacturing>

[0215] Li[Ni as a cathode active material 0.8 Co 0.1 Mn 0.1 ]O2 (diameter: 10 mm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a cathode slurry at a weight ratio of 96:2:2 to prepare a cathode slurry.

[0216] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12㎛) as a positive electrode collector at a density of 4.0 mAh / cm. 2 A positive electrode for manufacturing a coin cell was manufactured by coating with a capacity of 10 mm, rolling, and drying in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (diameter: 10 mm).

[0217] A PP2400 separator (diameter: 18 mm) from Celgard was interposed between the positive electrode and the lithium-ion negative electrode, and an electrolyte was injected to manufacture a coin-full cell of Example 1-1 in a glove box under an argon (Ar) atmosphere.

[0218] The above electrolyte is an organic solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a volume ratio of 50:50, to which LiPF6 as a lithium salt is added at a concentration of 1 M.

[0219] Comparative Example 1-1

[0220] Lithium metal (thickness: 6.2 μm) was transferred (dry prelithiation) to the Si negative electrode of the above Example 1-1 to obtain 1.24 mAh / cm 2 Coin-full cells were manufactured using the same manufacturing method as in Example 1-1, except that lithiumation was performed with a capacity of .

[0221] Comparative Example 1-2

[0222] A coin-full cell was manufactured using the same manufacturing method as in Example 1-1, except that the lithium-ion battery was manufactured using an electrolyte having a composition according to Comparative Example 1-2 in Table 1 below.

[0223] Electrolyte composition for lithium ionization Solvent Lithium salt Comparative example 1-1 Unused (dry) Comparative example 1-2 Dimethoxyethane (DME) 1M LiFSI Example 1-1 Dimethoxyethane (DME) 4M LiFSI

[0224] Experimental Example 1-1: Raman Spectroscopy of Electrolyte for Lithium Ionization

[0225] In order to confirm the solvation structure according to the concentration of the electrolyte for lithium ion, the electrolyte for lithium ion used in Comparative Example 1-2 and Example 1-1 was observed using Raman spectroscopy, and the results are shown in Figure 4.

[0226] At this time, Raman spectroscopy was measured using a Raman spectrometer (DXR2xi, Thermo Fisher, USA). To measure the Raman spectra of various electrolytes, each electrolyte was filled into a 2 mL vial without air bubbles, and then measured at 700 cm -1 760cm in height -1 Raman analysis was performed in the range.

[0227] Referring to Fig. 4, it can be confirmed that the electrolyte for lithium ion of Comparative Example 1-2 has the highest SSIP structure, and that the electrolyte for lithium ion of Example 1-1 has the highest AGG structure and CIP structure, and in particular, it can be confirmed that the CIP structure has the highest development.

[0228] As described above, the negative electrode of Example 1-1 using a high-concentration CIP structured prelithiation electrolyte forms an artificial SEI layer rich in LiF components, thereby enabling the manufacture of a lithium secondary battery with improved air stability in dry air. Whether the air stability of a lithium secondary battery in dry air is improved can be confirmed through Experimental Example 1-2 below.

[0229] Experimental Example 1-2: Stability Evaluation in Dry Air

[0230] In order to evaluate the air stability according to the composition of the pre-lithiation electrolyte, charge and discharge cycles were performed on the coin-full cells of Example 1-1, Comparative Examples 1-1 and 1-2, which were assembled into coin-full cells without air exposure immediately after the pre-lithiation of the negative electrode (hereinafter referred to as non-exposed coin-full cells and indicated as “Fresh” in FIGS. 5 and 6), and on the coin-full cells of Example 1-1, Comparative Examples 1-1 and 1-2, which were assembled into coin-full cells after exposure to dry air for 7 days before the pre-lithiation and before the cell assembly (hereinafter referred to as 7-day exposed coin-full cells and indicated as “7 Days” in FIGS. 5 and 6).

[0231] At this time, the cathode exposed to dry air for 7 days after lithiumation was recovered in a glove box with an argon (Ar) atmosphere, placed in a vial, and stored for 7 days in an environment simulating a dry room (moisture content less than 1.0 ppm) by injecting dry air from the outside and removing argon (Ar).

[0232] In addition, the first cycle charge / discharge conditions were charge CC / CV mode, 0.1C, 2.5V - 4.2V, 0.05C cut-off, discharge CC mode, 0.1C, 2.5V - 4.2V, and the charge / discharge conditions during the 50th cycle charge / discharge were charge CC / CV mode, 0.5C, 3.0V - 4.2V, 0.05C cut-off, discharge CC mode, 0.5C, 3.0V - 4.2V.

[0233] For each case, the discharge curve in the first charge / discharge cycle is shown in Fig. 5, and the discharge capacity in the first charge / discharge cycle is measured and shown in Table 2 below.

[0234] In addition, in each case, the capacity ratio between the unexposed coin-full cell and the 7-day exposed coin-full cell was calculated according to the following calculation formula and shown in Table 2 below.

[0235] Similarly, for each case, the discharge curve after the 50th charge / discharge cycle is shown in Fig. 6, and the capacity ratio between the unexposed coin-full cell and the 7-day exposed coin-full cell, calculated according to the following formula from the measured discharge capacity and the discharge capacity of each case, is shown in Table 3 below.

[0236]

[0237] Comparative Example 1-1 Comparative Example 1-2 Example 1-1 Capacity@1 st Cycle(mAh / cm 2 )(Unexposed)3.944.073.85Capacity@1 st Cycle(mAh / cm 2 )(7 days exposure)3.743.973.83Capacity Ratio@1 st Cycle (-)(7 days exposure / non-exposure)0.9500.9760.994

[0238] Comparative Example 1-1 Comparative Example 1-2 Example 1-1 Capacity@50 th Cycle (mAh / cm 2 )(Unexposed)3.193.222.94Capacity@50 th Cycle (mAh / cm 2 )(7 days exposure)3.083.132.93Capacity Ratio@50 th Cycle (-)(7 days exposure / non-exposure)0.9640.9690.997

[0239] Referring to Table 2 and FIG. 5 above, it was confirmed that the capacity ratio of the coin-full cell of Example 1-1 using the negative electrode prelithiated in 4 M LiFSI DME electrolyte was closest to 1, compared to the coin-full cell of Comparative Example 1-1 using the dry-type prelithiated negative electrode without using the electrolyte for prelithiation and the coin-full cell of Comparative Example 1-2 using the negative electrode prelithiated in 1 M LiFSI DME electrolyte. In other words, it was found that the coin-full cell of Example 1-1 of the present invention had the best air stability, showing almost the same discharge capacity as when not exposed to dry air even when stored in dry air for 7 days.

[0240] Likewise, referring to Table 3 and FIG. 6 above, even when 50 charge / discharge cycles were performed, it was confirmed that the coin-full cell of Example 1-1 using a cathode prelithiated in a 4M LiFSI DME electrolyte showed almost the same discharge capacity as when not exposed to dry air even when stored in dry air for 7 days, compared to the coin-full cells of Comparative Examples 1-1 and 1-2.

[0241] Manufacturing Example 2

[0242] Example 2-1

[0243] An electrolyte for lithium ion conversion having the same composition as the electrolyte for lithium ion conversion (lithium salt LiFSI with a concentration of 4 M and solvent dimethoxyethane (DME)) used in the lithium ion conversion of Example 1-1 of Table 1 above was prepared.

[0244] Reference Example 2-1

[0245] An electrolyte for prelithiation was prepared in the same manner as in Example 2-1, except that a lithium salt LiFSI with a concentration of 3 M and a solvent dimethoxyethane (DME) were used.

[0246] Reference Example 2-2

[0247] An electrolyte for prelithiation was prepared in the same manner as in Example 2-1, except that a lithium salt LiFSI having a concentration of 2 M and a solvent dimethoxyethane (DME) were used.

[0248] Reference Example 2-3

[0249] An electrolyte for prelithiation was prepared in the same manner as in Example 2-1, except that a lithium salt LiFSI with a concentration of 1 M and a solvent dimethoxyethane (DME) were used.

[0250] Comparative Example 2-1

[0251] An electrolyte for prelithiation was prepared in the same manner as in Example 2-1, except that 10 wt% of fluoroethylene carbonate (FEC) as an additive and 4 M concentration of LiPF6 as a lithium salt were added to an organic solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a volume ratio of 50:50.

[0252] Comparative Example 2-2

[0253] An electrolyte for prelithiation was prepared in the same manner as the preparation method of Comparative Example 2-1, except that LiPF6 was added as a lithium salt at a concentration of 3 M.

[0254] Comparative Example 2-3

[0255] An electrolyte for prelithiation was prepared in the same manner as the preparation method of Comparative Example 2-1, except that LiPF6 was added as a lithium salt at a concentration of 2 M.

[0256] Comparative Example 2-4

[0257] An electrolyte for prelithiation was prepared in the same manner as the preparation method of Comparative Example 2-1, except that LiPF6 was added as a lithium salt at a concentration of 1 M.

[0258] Experimental Example 2-1: Evaluation of the ionic conductivity of the electrolyte for lithium ion battery

[0259] In order to confirm the change in ionic conductivity according to the concentration of the electrolyte for prelithiation when using a carbonate solvent and lithium salt LiPF6 and when using the ether solvent and lithium salt LiFSI of the present invention, the ionic conductivity of the electrolyte for prelithiation of Example 2-1, Reference Examples 2-1 to 2-3, and Comparative Examples 2-1 to 2-4 was measured, and the results are shown in Table 4 and Fig. 7 below.

[0260] Specifically, the ionic conductivity of the electrolyte for lithium ionization was measured using a METTLER TOLEDO SevenDirect SD30 ionic conductivity measuring instrument.

[0261] Lithium salt concentration (M) Ionic conductivity (mS / cm) EC / DEC (1 / 1 v / v) + FEC 10 wt% Lithium salt LiPF6DME Lithium salt LiFSI4 Comparative example 2-10.9 Example 2-16.63 Comparative example 2-22.2 Reference example 2-18.22 Comparative example 2-34.7 Reference example 2-214.01 Comparative example 2-47.3 Reference example 2-315.4

[0262] Referring to Table 4 and FIG. 7, the electrolyte for pre-lithiation of Comparative Example 2-4 with a concentration of 1 M showed an ionic conductivity of 7.3 mS / cm, and as the concentration increased, the ionic conductivity gradually decreased, and it was confirmed that it greatly decreased to 0.9 mS / cm in the electrolyte for pre-lithiation of Comparative Example 2-1 with a concentration of 4 M. However, it was confirmed that the electrolyte for pre-lithiation of Example 2-1 showed a relatively high ionic conductivity of 6.6 mS / cm even when the lithium salt concentration increased to 4 M, and it was confirmed that this was approximately 90.4% of the ionic conductivity of Comparative Example 2-4 with a concentration of 1 M, which showed the highest ionic conductivity.

[0263] Through this, it can be confirmed that, in general, as the concentration of the lithium salt increases, the viscosity of the electrolyte for pre-lithiation also increases, which may decrease the diffusion speed of lithium ions, but it can be seen that this tendency is more prominent when a carbonate-based solvent is used as the solvent of the electrolyte for pre-lithiation. However, it can be seen that the electrolyte for pre-lithiation according to one embodiment of the present specification can secure high ionic conductivity even at a high concentration by using a non-aqueous solvent, particularly an ether-based solvent, together with a specific lithium salt, specifically LiFSI.

[0264] Experimental Example 2-2: Evaluation of C-rate Characteristics of Electrolyte for Lithium Ionization

[0265] In order to evaluate the C-rate characteristics according to the solvent and lithium salt combination of the electrolyte for prelithiation, coin-half cells were manufactured using the electrolyte for prelithiation of Example 2-1, Reference Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-4 and a micron silicon negative electrode, and the capacity change according to the C-rate was measured, and is shown in FIGS. 8 and 9.

[0266] At this time, the micron silicon negative electrode was prepared by preparing a negative electrode active material layer composition with Si (average particle diameter (D50): 5 μm) as a negative electrode active material, SWCNT as a conductive material, and SBR (Styrene-Butadiene Rubber) and CMC (Carboxymethyl Cellulose) binder in a weight ratio of 80:0.5:12.5:7. The negative electrode slurry was prepared by adding distilled water as a solvent for forming a negative electrode slurry.

[0267] As a mixing method, the above active material, conductive material, CMC binder, and water were dispersed using a paste mixer at 1600 rpm for 40 min, and then SBR was added and dispersed at 1600 rpm for 3 min to produce a negative electrode slurry.

[0268] The above negative electrode slurry was applied to both sides of a copper current collector (thickness: 19 μm) as a negative electrode current collector at 3.9 mAh / cm 2The coating was performed with a capacity of , roll-pressed, and dried in a vacuum oven at 120°C for 7 hours to form a negative electrode (diameter: 13 mm) for manufacturing a coin cell.

[0269] The coin-half cell uses the micron silicon cathode manufactured above as the working electrode and a 1.7671 cm 2 A 1 mm thick lithium metal foil cut into a circle was used, a polyethylene separator was interposed between the working electrode and the counter electrode, and the case was built into a coin type case, and 50 μL of an electrolyte was injected to manufacture the same. At this time, the electrolyte used was the electrolyte for lithium ion of Example 2-1, Reference Examples 2-1 to 2-3, and Comparative Examples 2-1 to 2-4.

[0270] For the above half-cell, CC / CV charging and CC discharging were performed several times using an electrochemical charger / discharger, and the C-rate and cut-off conditions for charging / discharging for each cycle are as shown in Table 5 below.

[0271] Cycle No.LithiationDelithiationCC C-rateCut-off V(CC mode)Cut-off I(CV mode)CC C-rateCut-off V10.03C0.01V0.01C0.1C1.5V20.1C0.01V0.01C0.1C1.5V3-70.5C0.06V0.05C0.5C1V8-121C0.06V 0.05C0.5C1V13-172C0.06V0.05C0.5C1V18-223C0.06V0.05C0.5C1V23-270.5C0.06V0.05C0.5C1V

[0272] Referring to Fig. 8, in the case of Comparative Examples 2-1 to 2-4 using a carbonate solvent and lithium salt LiPF6, it was confirmed that as the C-rate increased, the capacity decrease due to the increase in lithium salt concentration increased.

[0273] In contrast, in the case of Example 2-1 and Reference Examples 2-1 to 2-3 using the ether solvent and lithium salt LiFSI, the C-rate characteristics were similar even when the lithium salt concentration increased, and in particular, at a high C-rate of 3C, it was confirmed that the high-concentration Example 2-1 and Reference Example 2-1 showed a higher capacity than the low-concentration Reference Examples 2-2 and 2-3.

[0274] Meanwhile, the C-rate characteristics of the half-cell of Comparative Example 2-4, which showed the highest ionic conductivity among the comparative examples of Experimental Example 2-1 described above, and Example 2-1, which showed similar ionic conductivity, were directly compared and shown in Fig. 10. Referring to Fig. 10, it was confirmed that the half-cell of Example 2-1 showed C-rate characteristics equivalent to or higher, even though the ionic conductivity of the electrolyte for prelithiation of Comparative Example 2-4 was slightly higher.

[0275] Through this, it can be seen that when using the electrolyte for lithium ionization according to one embodiment of the present specification, the C-rate characteristics are also excellent due to the characteristic of maintaining high ionic conductivity even when the concentration of lithium salt increases.

[0276] In conclusion, by prelithiating a silicon-based negative electrode in a wet manner using a high-concentration electrolyte solution that maintains high ionic conductivity as an electrolyte for prelithiation using a combination of a lithium salt and a non-aqueous solvent having a concentration exceeding 3 M according to one embodiment of the present specification, an artificial SEI layer rich in LiF components can be formed on the surface of the prelithiated silicon-based negative electrode, thereby improving air stability and maintaining excellent capacity characteristics even when stored in dry air before cell assembly.

[0277]

[0278] [Explanation of symbols]

[0279] 10: Negative current collector layer

[0280] 20: Negative active material layer

[0281] 30: Membrane

[0282] 40: Positive active material layer

[0283] 50: Positive current collector layer

[0284] 100: Lithium-ion cathode

[0285] 200: Bipolar

Claims

1. A step of wetting a negative electrode active material layer including a silicon-based negative electrode active material in an electrolyte for lithium ionization; and A step of contacting a lithium metal layer with at least one surface of a negative electrode active material layer wetted with the above-mentioned lithium-ion electrolyte, A method for manufacturing a lithium-ion negative electrode, wherein the electrolyte for lithium-ion conversion comprises a lithium salt having a concentration exceeding 3 M and a non-aqueous solvent.

2. In claim 1, The above lithium salt has an anion of BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - A method for producing a prelithiated negative electrode, comprising at least one selected from the group consisting of: and combinations thereof.

3. In claim 1, The anion of the above lithium salt is (FSO2)2N - A method for manufacturing a lithium-ion cathode.

4. In claim 1, A method for manufacturing a prelithiated negative electrode, wherein the non-aqueous solvent includes an ether solvent.

5. In claim 1, A method for producing a prelithiated negative electrode, wherein the non-aqueous solvent comprises at least one selected from the group consisting of diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, dioxolane, methyldioxolane, oxane, dioxane, trioxane, tetrahydrofuran, dihydropyran, tetrahydropyran, methyltetrahydrofuran, furan, methylfuran, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, and combinations thereof.

6. In claim 1, A method for manufacturing a lithium negative electrode, wherein the electrolyte for lithium conversion comprises a lithium salt having a concentration of 4 M or more and a non-aqueous solvent.

7. In claim 1, After the step of bringing the negative active material layer into contact with the lithium metal layer, A method for manufacturing a prelithiated negative electrode, further comprising the step of pressurizing and prelithiating the negative electrode active material layer in contact with the lithium metal layer.

8. In claim 1, A method for manufacturing a prelithiated negative electrode, wherein the silicon-based negative electrode active material comprises at least one selected from the group consisting of Si, silicon oxide, Si / C, and Si alloy.

9. In claim 1, A method for manufacturing a prelithiated negative electrode, wherein the silicon-based negative electrode active material contains Si, and the Si is contained in an amount of 60 parts by weight or more based on 100 parts by weight of the silicon-based negative electrode active material.

10. In claim 1, A method for manufacturing a prelithiated negative electrode, wherein the thickness of the lithium metal layer is 1 μm or more and 10 μm or less.

11. Contains a negative electrode current collector layer, A lithium-ion negative electrode manufactured by a manufacturing method according to any one of claims 1 to 10.

12. Bipolar; The lithium-ion cathode of claim 11; A separator provided between the positive electrode and the lithium-ion cathode; and A lithium secondary battery containing an electrolyte.

13. In claim 12, The lithium secondary battery using the pre-lithiated negative electrode immediately after completion of pre-lithiation as the negative electrode and the lithium secondary battery using the pre-lithiated negative electrode exposed to air having a moisture content of less than 1.0 ppm for 7 days after completion of pre-lithiation as the negative electrode have a discharge capacity ratio of 1:0.99 to 1:1 after 50 charge and discharge cycles. A lithium secondary battery in which the C-rate was set to 0.5C during the above charge / discharge cycle, charging was performed with an upper limit voltage of 4.2 V, constant current / constant voltage mode (CC / CV mode), and cut-off current of 0.05C, and discharging was performed with a lower limit voltage of 3.0 V, constant current mode (CC mode).

14. A battery module comprising a lithium secondary battery according to claim 12.

15. A battery pack comprising a lithium secondary battery according to claim 12.

16. A battery pack comprising a battery module according to claim 14.

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