Method for manufacturing anode having inorganic coating layer

Abstract

The present invention relates to a method for manufacturing a negative electrode, which includes the steps of: coating at least one surface of a current collector with a negative electrode slurry containing a negative electrode active material to form a negative electrode active material layer; pre-lithiating the negative electrode; and aging the pre-lithiated negative electrode in a CO atmosphere to form an inorganic coating layer on the surface of the negative electrode active material layer.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0134992 dated October 19, 2020, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing a negative electrode and a negative electrode manufactured by the method for manufacturing a negative electrode, and more particularly, to a method for manufacturing a negative electrode having an inorganic coating layer formed thereon and a negative electrode manufactured by the method. [Background technology]

[0003] Recently, rechargeable secondary batteries have been widely used as energy sources for wireless mobile devices. Secondary batteries are also attracting attention as energy sources for electric vehicles and hybrid electric vehicles, which have been proposed as a solution to address air pollution caused by existing gasoline and diesel vehicles that use fossil fuels. As such, the application fields using secondary batteries are becoming increasingly diverse due to the advantages of secondary batteries, and it is expected that secondary batteries will be applied to more fields and products in the future.

[0004] Such secondary batteries may be classified into lithium ion batteries, lithium ion polymer batteries, lithium polymer batteries, etc. according to the configuration of the electrodes and electrolyte, and among them, the use of lithium ion polymer batteries, which are less likely to leak electrolyte and are easy to manufacture, is increasing. In general, secondary batteries are classified into cylindrical batteries and prismatic batteries in which an electrode assembly is housed in a cylindrical or prismatic metal can, and pouch-type batteries in which an electrode assembly is housed in a pouch-type case of an aluminum laminate sheet, according to the shape of the battery case. The electrode assembly housed in the battery case is a power generating element that is capable of charging and discharging and has a structure of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and is classified into a jelly roll type in which a separator is interposed between a long sheet-like positive electrode and a negative electrode coated with an active material and wound up, and a stack type in which a number of positive electrodes and negative electrodes of a predetermined size are stacked in sequence with a separator interposed between them.

[0005] The positive electrode and the negative electrode are formed by applying a positive electrode slurry containing a positive electrode active material and a negative electrode slurry containing a negative electrode active material to a positive electrode current collector and a negative electrode current collector, respectively, to form a positive electrode active material layer and a negative electrode active material layer, and then drying and rolling the layers.

[0006] In the case of such a negative electrode, a passivation film such as a solid electrolyte interface layer (SEI layer) is formed on the surface of the negative electrode during initial charging. The passivation film prevents an organic solvent from being inserted into the negative electrode and inhibits the decomposition reaction of the organic solvent, thereby stabilizing the structure of the negative electrode and improving the reversibility of the negative electrode, enabling its use as a negative electrode. However, the reaction of forming the passivation film is an irreversible reaction. This causes a problem of reducing the capacity of the battery by consuming lithium ions. In addition, as the battery cycle is repeated, the lithium ions are consumed, causing a problem of reducing the capacity and shortening the cycle life.

[0007] Therefore, a method has been developed to prevent the capacity from decreasing and improve the cycle life by forming a passivation film on the surface of the negative electrode in advance by pre-lithiation using a method such as inserting lithium into the negative electrode. Such pre-lithiation methods include a physical method in which lithium metal is directly brought into contact with the surface of the negative electrode, and a method in which lithium metal is connected to the negative electrode and then electrochemically charged.

[0008] However, because the prelithiated anode is in a reduced state, lithium ions react with the air or moisture in the air to generate by-products, which causes a loss of lithium introduced during the prelithiated process, resulting in a reduction in the targeted lithium dosage. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing an anode that can minimize the loss of lithium due to an oxidation-reduction reaction of the anode with air and moisture in the air after prelithiation, and an anode manufactured by the same. [Means for solving the problem]

[0010] The method for producing a negative electrode according to the present invention includes the steps of: coating at least one surface of a current collector with a negative electrode slurry containing a negative electrode active material to form a negative electrode active material layer; pre-lithiating the negative electrode; and subjecting the pre-lithiated negative electrode to CO 2 and aging the negative electrode active material layer in an atmosphere to form an inorganic coating layer on the surface of the negative electrode active material layer.

[0011] At this time, the inorganic coating layer is Li 2 O, LiOH and Li 2 CO 3 The compound includes one or more compounds selected from the group consisting of:

[0012] In a specific example, the inorganic coating layer is Li 2 O, LiOH and Li 2 CO 3 may include all of the above.

[0013] The negative electrode active material may be at least one selected from the group consisting of graphite-based active materials and silicon-based active materials.

[0014] In one example, the step of prelithiating the negative electrode can be carried out by directly contacting lithium metal on the negative electrode active material layer.

[0015] Here, the step of prelithiating the negative electrode includes a process of bonding a lithium metal film onto the negative electrode active material layer and then laminating the same.

[0016] In another example, the step of prelithiating the negative electrode can be performed by coupling the negative electrode with lithium metal followed by electrochemical charging.

[0017] On the other hand, in a specific example, CO 2 The pressure may be 0.1 to 10 mTorr.

[0018] In a specific example, the aging temperature may be 20 to 60°C.

[0019] In a specific example, the aging time may be 10 to 60 hours.

[0020] The present invention also provides a negative electrode. The negative electrode has a structure in which a negative electrode active material layer is formed by coating a negative electrode slurry containing a negative electrode active material. The negative electrode active material layer is pre-lithiated, and Li is formed on the surface of the negative electrode active material layer. 2 O, LiOH and Li 2 CO 3 An inorganic coating layer may be formed that includes one or more compounds selected from the group consisting of:

[0021] The present invention also provides a secondary battery including the negative electrode described above. Effect of the Invention

[0022] The present invention uses a prelithiated anode with CO 2 Aging in the atmosphere can form an inorganic coating layer on the surface of the negative electrode that can block redox reactions, which can minimize the loss of lithium due to the redox reaction of the negative electrode with air and moisture in the air, and can prevent a decrease in the capacity and cycle characteristics of the battery. [Brief description of the drawings]

[0023] [Figure 1] 2 is a flowchart showing the steps of a method for producing a negative electrode according to the present invention. [Diagram 2] FIG. 1 is a schematic diagram illustrating a prelithiation process according to one embodiment of the present invention. [Diagram 3] FIG. 2 is a schematic diagram illustrating a pre-lithiation process according to another embodiment of the present invention. [Figure 4] 1 is a graph showing changes in lithium dosage depending on storage time for negative electrodes according to Example 1 of the present invention and Comparative Example 1. [Diagram 5] 1 is a graph showing the capacity retention rates of secondary batteries according to Example 2 of the present invention and Comparative Examples 3 and 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will be described in detail below. Before that, the terms and words used in the specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor himself can appropriately define the concept of the term in order to best describe the invention.

[0025] In this application, the terms "comprise" and "have" are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, and are to be understood as not precluding the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof. In addition, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only the case where it is "directly under" the other part, but also the case where there is another part in between. In addition, in this application, being "on" may include not only the case where it is located on the top, but also the case where it is located on the bottom.

[0026] The present invention will be described in detail below.

[0027] FIG. 1 is a flow chart showing the steps of a method for producing a negative electrode according to the present invention.

[0028] Referring to FIG. 1, the method for producing a negative electrode according to the present invention includes the steps of: coating a negative electrode slurry containing a negative electrode active material on a current collector to produce a negative electrode having a negative electrode active material layer (S10); pre-lithiating the negative electrode (S20); and discharging the pre-lithiated negative electrode by CO 2 and forming an inorganic coating layer on the surface of the negative electrode active material layer by aging in an atmosphere (S30).

[0029] As described above, since the prelithiated negative electrode is in a reduced state, lithium ions react with the air or moisture in the air to generate by-products. The generation of such by-products results in a loss of lithium introduced during the prelithiated process, resulting in a reduction in the targeted lithium dosage.

[0030] The present invention uses a prelithiated anode with CO 2Aging in the atmosphere can form an inorganic coating layer on the surface of the negative electrode that can block redox reactions, which can minimize the loss of lithium due to the redox reaction of the negative electrode with air and moisture in the air, and can prevent the capacity and cycle characteristics of the battery from decreasing.

[0031] Each step of the method for producing a negative electrode according to the present invention will now be described in detail.

[0032] <Production of negative electrodes> First, in order to carry out prelithiation, a negative electrode to be subjected to prelithiation is produced.

[0033] The negative electrode may be manufactured by coating at least one surface of a negative electrode current collector with a negative electrode slurry including a negative electrode active material to form a negative electrode active material layer. The negative electrode slurry may further include a conductive material and a binder.

[0034] In the case of the negative electrode current collector, it is generally made to a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the positive electrode current collector, the surface can be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0035] The negative electrode active material may include at least one selected from the group consisting of a carbon-based active material and a silicon-based active material.

[0036] The silicon-based active material can impart excellent capacity characteristics to the negative electrode or secondary battery of the present invention, and SiO x (0≦x<2) 2In the case of , it does not react with lithium ions, so lithium cannot be stored. Therefore, x is preferably within the above range, and more preferably, the silicon-based oxide may be SiO. The average particle diameter (D 50 The average particle size (D) may be 1 to 30 μm, preferably 3 to 15 μm, in order to reduce side reactions with the electrolyte while ensuring structural stability during charging and discharging. 50 ) can be measured, for example, using the laser diffraction method.

[0037] The carbon-based active material can impart excellent cycle characteristics or battery life performance to the negative electrode for secondary battery or secondary battery of the present invention. Specifically, the carbon-based active material can include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon. Preferably, the carbon-based active material can include at least one selected from the group consisting of artificial graphite and natural graphite. The average particle diameter (D 50 ) may be 10 to 30 μm, preferably 15 to 25 μm, in order to reduce side reactions with the electrolyte while ensuring structural stability during charging and discharging.

[0038] Specifically, the negative electrode active material may be either the silicon-based active material or the carbon-based active material in terms of simultaneously improving capacity characteristics and cycle characteristics. Specifically, the negative electrode active material may contain the carbon-based active material and the silicon-based active material in a weight ratio of 50:50 to 95:5, preferably 60:40 to 80:20.

[0039] The conductive material is usually added in an amount of 1 to 30% by weight based on the weight of the entire mixture including the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite, carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives can be used.

[0040] The binder is a component that assists in binding the active material and conductive material and binding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the weight of the entire mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butylene rubber, fluororubber, and various copolymers.

[0041] <Pre-lithiation> After the negative electrode is fabricated, it is prelithiated.

[0042] In the present invention, there is no particular limitation on the pre-lithiation method of the negative electrode. For example, either a physicochemical method or an electrochemical method may be used.

[0043] In one example, the step of prelithiating the negative electrode is performed by directly contacting lithium metal on the negative electrode active material layer.

[0044] FIG. 2 is a schematic diagram illustrating a prelithiation process according to one embodiment of the present invention.

[0045] Referring to FIG. 2, the step of prelithiating the negative electrode 10 includes bonding a lithium metal film 20 onto the negative electrode active material layer 12 followed by lamination.

[0046] Specifically, after the negative electrode 10 is prepared, the lithium metal film 20 is laminated. This process can be performed, for example, by a roll-to-roll process. In this case, the negative electrode is wound by an unwinding roller (not shown), but is unwound from there when lamination begins. The lithium metal film 20 is also wound on a separate roll (not shown), but is unwound from there when lamination begins. Here, the lithium metal film 20 itself can be used, but a separate polymer film (not shown) to which the lithium metal film is bonded on one side can also be used. The thickness of the lithium metal film 20 may be 1 to 10 μm, and more specifically, 3 to 8 μm. When the thickness of the lithium metal film 20 is within the above range, the negative electrode can be doped with an appropriate amount of lithium ions.

[0047] Thereafter, the lithium metal film 20 is bonded to the negative electrode active material layer 12 formed on the negative electrode current collector 11. Next, the lithium metal film 20 and the negative electrode 10 are pressed using a pressure member 30. There is no particular limitation on the shape of the pressure member 30, but a pair of pressure rollers may be used as shown in FIG. 2, or a rectangular pressure jig may be used to apply surface pressure to the lithium metal film 20 and the negative electrode 10. However, when a pair of pressure rollers is used, a nip pressure is applied to the negative electrode 10 and the lithium metal film 20, so that a uniform pressure can be applied, and a pressure slightly lower than that when surface pressure is applied can be applied.

[0048] The negative electrode 10 laminated with the lithium metal film 20 can be stored for a predetermined period of time to allow the lithium ions inserted by prelithiation to be more uniformly diffused on the surface and inside of the negative electrode active material layer 12.

[0049] FIG. 3 is a schematic diagram illustrating a prelithiation process according to another embodiment of the present invention.

[0050] Referring to FIG. 3, the step of prelithiating the negative electrode is carried out by connecting the negative electrode 10 to lithium metal 50 and then electrochemically charging the same.

[0051] In this case, the pre-lithiation is performed in a pre-lithiation reaction tank 40 containing a pre-lithiation solution 41. Specifically, the negative electrode 10 is accommodated in the pre-lithiation reaction tank 40 containing the pre-lithiation solution 41 in a state separated from the lithium metal 50, and the negative electrode 10 and the lithium metal 50 are connected to a charger / discharger 60, respectively, and then electrochemical charging can be performed. The lithium metal 50 may be in the form of a sheet arranged to face the negative electrode 10. The lithium metal 50 is separated from the negative electrode 10, so that a short circuit phenomenon that may occur due to direct contact between the negative electrode 10 and the lithium metal 50 during electrochemical charging can be prevented. In addition, a step of immersing the negative electrode 10 in the pre-lithiation solution 41 for a predetermined time before electrochemical charging can be performed.

[0052] The pre-lithiation solution 41 may include a lithium salt and an organic solvent.

[0053] Specifically, the lithium salt is LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , C.H. 3 SO 3 Li, C.F. 3 SO 3 Li, (CF 3 SO 2 ) 2 NLi, (FSO 2 ) 2The lithium borane may comprise NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, or one or more of these.

[0054] For example, the organic solvent may include a carbonate-based solvent, an ester-based solvent, or two or more of these. Examples of the non-aqueous solvent include, but are not limited to, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (g-butyrolactone), ethyl propionate, methyl propionate, etc., which may be used alone or in combination of two or more.

[0055] Similarly, the electrochemically charged negative electrode 10 may be stored for a predetermined time after washing and drying to allow the lithium ions inserted by prelithiation to be more uniformly diffused on the surface and within the negative electrode active material layer.

[0056] <Aging> After prelithiation was complete, the prelithiated anode was charged with CO 2 The negative electrode is aged in a CO atmosphere to form an inorganic coating layer on the surface of the negative electrode. 2 During the aging process in the atmosphere, the lithium ions in the negative electrode active material layer and CO 2 react to form an inorganic coating layer.

[0057] Here, the inorganic coating layer is Li 2 O, LiOH and Li 2 CO 3 In particular, the inorganic coating layer may contain one or more compounds selected from the group consisting of Li 2 O, LiOH and Li 2 CO 3The above compounds have excellent electron transfer blocking ability. Therefore, when an inorganic coating layer containing such compounds is formed, it can effectively block the oxidation-reduction reaction between the lithium ions introduced into the negative electrode active material layer and the air or moisture in the air.

[0058] That is, by minimizing the loss of lithium ions introduced in advance through pre-lithiation, the amount of lithium ions that can be utilized as a lithium reservoir can be increased even if the same amount of lithium ions is introduced, thereby preventing the capacity and cycle characteristics of the battery from decreasing.

[0059] Specifically, the aging can be carried out in a vacuum-based environment. For example, the prelithiated negative electrode can be stored in a sealed chamber and then aged in CO 2 This can be done in a CO 2 Aging is performed in a CO atmosphere. 2 The aging process may be performed under a pressure as low as a vacuum. 2 The pressure may be 0.1 to 10 mTorr. In particular, during aging, 2 The pressure may be 1 to 5 mTorr. Within the above pressure range, it is possible to form an inorganic coating layer of a suitable thickness. 2 If the pressure is below the above range, the lithium ions and CO 2 The reaction may not proceed smoothly. 2 If the pressure of CO exceeds the above range, 2 The amount of lithium ions reacting with the

[0060] In the aging process, the aging temperature may be 20 to 60° C., more specifically, 30 to 50° C. Within the above temperature range, the lithium ions introduced into the negative electrode are converted to CO 2 at a suitable rate.

[0061] In the aging process, the aging time may be 10 to 60 hours. In particular, it may be 20 to 50 hours. When the aging time is within the above range, a suitable amount of lithium ions is introduced into the CO 2 When the aging time is less than the above range, the lithium ions and CO 2 If the reaction does not proceed smoothly and the aging time exceeds the above range, 2 The amount of lithium ions reacting with the

[0062] Thus, the present invention uses a prelithiated anode with CO 2 By aging in this atmosphere, an inorganic coating layer capable of blocking redox reactions can be formed on the surface of the negative electrode, which can minimize the loss of lithium due to the redox reaction of the negative electrode with air and moisture in the air, and can prevent the capacity and cycle characteristics of the battery from decreasing.

[0063] <Negative electrode> The present invention further provides a negative electrode.

[0064] The negative electrode has a structure in which a negative electrode active material layer is formed by coating a negative electrode slurry containing a negative electrode active material, and the negative electrode active material layer is pre-lithiated, and Li is applied to the surface of the negative electrode active material layer. 2 O, LiOH and Li 2 CO 3 The negative electrode contains one or more compounds selected from the group consisting of: Here, the negative electrode can be produced by the method for producing a negative electrode as described above.

[0065] The negative electrode according to the present invention has an inorganic coating layer formed on the surface thereof, which can block an oxidation-reduction reaction, and thus can minimize the loss of lithium caused by the oxidation-reduction reaction of the negative electrode with air and moisture in the air, thereby preventing a decrease in the capacity and cycle characteristics of the battery.

[0066] <Secondary battery> The present invention also provides a method for producing a secondary battery including the above-mentioned negative electrode.

[0067] The secondary battery has an electrode assembly in which a separator is interposed between a positive electrode and a negative electrode, the electrode assembly being housed in a battery case. The positive electrode has a structure in which a positive electrode active material layer is formed by coating a positive electrode current collector with a positive electrode slurry containing a positive electrode active material, and the negative electrode may be one described above, and may be manufactured by the method for manufacturing a negative electrode according to the present invention.

[0068] In the present invention, the positive electrode current collector is generally made to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may have fine irregularities on its surface to increase the adhesive force of the positive electrode active material, and may be in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0069] In the present invention, the positive electrode active material is a material capable of undergoing an electrochemical reaction, that is, a lithium transition metal oxide, which contains two or more transition metals. For example, lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganates substituted with one or more transition metals, with the formula LiNi 1-y M y O 2 (wherein M is Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga, and contains one or more of the above elements, and 0.01≦y≦0.7), Li 1+z Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , Li 1+z Ni 0.4 Mn0.4 Co 0.2 O 2 Li 1+z Ni b Mn c Co 1-(b+c+d) M d O (2-e) A e (wherein, -0.5≦z≦0.5, 0.1≦b≦0.8, 0.1≦c≦0.8, 0≦d≦0.2, 0≦e≦0.2, b+c+d<1, M is Al, Mg, Cr, Ti, Si or Y, and A is F, P or Cl), lithium nickel cobalt manganese composite oxide represented by the chemical formula Li 1+x M 1-y M' y PO 4-z X z (wherein M is a transition metal, preferably Fe, Mn, Co or Ni, M′ is Al, Mg or Ti, X is F, S or N, −0.5≦x≦+0.5, 0≦y≦0.5, 0≦z≦0.1), and the like.

[0070] The positive electrode slurry further contains a conductive material and a binder in addition to the positive electrode active material, as described above.

[0071] The separator is interposed between the positive and negative electrodes, and is an insulating thin film having high ion permeability and mechanical strength. The pore diameter of the separator is generally 0.01 to 10 μm, and the thickness is generally 5 to 300 μm. As such a separator, for example, a sheet or nonwoven fabric made of an olefin polymer such as polypropylene, which is chemically resistant and hydrophobic, glass fiber, or polyethylene, etc. is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator.

[0072] Meanwhile, the battery case is not particularly limited as long as it is used as an exterior material for packaging a battery, and may be cylindrical, rectangular, or pouch-shaped. In particular, a pouch-shaped battery case may be used. The pouch-shaped battery case is generally made of an aluminum laminate sheet, and may be composed of an inner sealant layer for sealing, a metal layer for preventing the penetration of substances, and an outer resin layer forming the outermost part of the case. Hereinafter, detailed description of the battery case will be omitted since it is well known to ordinary skilled artisans.

[0073] When the electrode assembly is accommodated in the battery case, the battery case is sealed after injecting an electrolyte, and then the battery is activated to manufacture a final secondary battery. The electrolyte may use the lithium salt and organic solvent used in the pre-lithiation solution described above. Details regarding the electrolyte are also well known to those skilled in the art, so a detailed description will be omitted.

[0074] The present invention will be described in detail below with reference to examples to aid in understanding the present invention. However, the examples of the present invention can be modified in various different forms, and the scope of the present invention should not be construed as being limited to the following examples. The examples of the present invention are provided to more completely explain the present invention to those having average knowledge in the art.

[0075] Example 1 <Production of negative electrodes> A mixture of 85% by weight of graphite and 15% by weight of SiO was prepared as the negative electrode active material. A negative electrode slurry was produced by adding 94.5% by weight of the above negative electrode active material, 1.3% by weight of Denka Black as a conductive material, 3.0% by weight of SBR as a binder, and 1.2% by weight of CMC as a thickener to water.

[0076] The negative electrode slurry was loaded onto both sides of a copper current collector (thickness: 8 μm) at a rate of 6.48 mAh / cm 2 The copper negative electrode current collector was coated with the negative electrode active material so that the negative electrode active material layer was formed on both sides of the copper negative electrode current collector, followed by drying in a vacuum oven at 130° C. and rolling again, thereby producing a negative electrode.

[0077] <Pre-lithiation> A lithium metal film having a thickness of 6 μm was bonded and laminated onto the negative electrode active material layer of the negative electrode, and then the negative electrode was stored for a predetermined period of time to be prelithiated.

[0078] <Aging> The prelithiated anode was subjected to 1 mTorr pressure of CO 2 The sample was aged for 20 hours in the chamber with the atmosphere to form an inorganic coating layer on the surface. At this time, the temperature inside the chamber was maintained at 50°C.

[0079] Comparative Example 1 A pre-lithiated negative electrode was prepared in the same manner as in Example 1, except that the aging process was not performed.

[0080] Comparative Example 2 A negative electrode was prepared in the same manner as in Example 1, except that the pre-lithiation and aging processes were not performed.

[0081] Experimental Example 1 <Half-cell manufacturing> The negative electrodes produced in Example 1 and Comparative Example 1 above and a lithium metal having a thickness of 150 μm as a counter electrode were prepared.

[0082] A polypropylene separator was interposed between the negative electrode according to Example 1 and Comparative Example 1 and the lithium metal counter electrode, and an electrolyte was injected to prepare a lithium secondary battery. The electrolyte was an organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70, and LiPF 6 was added at a concentration of 1 M, and fluoroethylene carbonate (FEC) was added as an additive at 2 wt % based on the total weight of the pre-lithiation solution.

[0083] <Measurement of lithium dosage in negative electrode> Each of the half cells was fully charged at a constant current (CC) of 0.1 C, left for 20 minutes, and then discharged at a constant current (CC) of 0.1 C to 3.0 V. A discharge profile was obtained from the half cells, and the discharge capacity (Capacity 1) was calculated.

[0084] In addition, for the negative electrodes according to Example 1 and Comparative Example 1, the negative electrodes in the step before pre-lithiation were prepared as half cells (reference cells) in the same manner as above, and the reference cells were charged and discharged in the same manner as above to calculate the discharge capacity (capacity 2). The lithium dosage was calculated as follows from the difference between the above capacity 1 and capacity 2.

[0085] Lithiation dosage (%) = (Dose 1 - Dose 2) * 100 / Dose 2

[0086] The negative electrodes according to Example 1 and Comparative Example 1 were stored in a dry room at room temperature, and the lithium dosage was measured immediately after storage, on the first day, the fifth day, and the twelfth day after storage, using the method described above. The results are shown in FIG.

[0087] Referring to FIG. 4, immediately after storage of the negative electrode, the lithium dosage was the same for both the negative electrode according to Example 1 and the negative electrode according to Comparative Example 1, but as the storage period became longer, the lithium dosage of the negative electrode according to Comparative Example 1 decreased compared to that of the negative electrode according to Example 1. This is because, in the case of the negative electrode according to Comparative Example 1, an inorganic coating layer was not formed, and the lithium ions introduced into the negative electrode reacted with the air and moisture in the air. In contrast, in the case of the negative electrode according to Example 1, Li 2 O, LiOH and Li 2 CO 3 It can be seen that the formation of an inorganic coating layer containing ruthenium oxide minimizes the reaction of the lithium ions introduced into the negative electrode with the air and moisture in the air.

[0088] Example 2 LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1O 2 The positive electrode slurry was made by mixing super C as a conductive material and PVdF as a binder in a weight ratio of 97:1.5:1.5, and was coated on an aluminum current collector, rolled, and dried at 130°C to prepare a positive electrode.

[0089] A polypropylene separator was interposed between the negative electrode and the positive electrode according to Example 1, and an electrolyte was injected to prepare a lithium secondary battery. The electrolyte was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 in an organic solvent, and then dissolving LiPF 6 was added at a concentration of 1 M, and fluoroethylene carbonate (FEC) was added as an additive at 2 wt % based on the total weight of the pre-lithiation solution.

[0090] Comparative Example 3 A lithium secondary battery was produced in the same manner as in Example 2 using the negative electrode of Comparative Example 1.

[0091] Comparative Example 4 A lithium secondary battery was produced in the same manner as in Example 2 using the negative electrode of Comparative Example 2.

[0092] Experimental Example 2 <Evaluation of capacity retention rate> The capacity retention rate of the lithium secondary batteries according to the examples and comparative examples was evaluated using an electrochemical charger / discharger. During charging, the batteries were charged at a current density of 0.1 C-rate up to a voltage of 4.2 V, and during discharging, the batteries were discharged at the same current density up to a voltage of 2.5 V. Under these conditions, charging and discharging were performed up to the 200th cycle.

[0093] During this process, the capacity retention rate was evaluated according to the following formula 2, and the results are shown in FIG.

[0094] [Formula 2] Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at 1st cycle)} x 100 (In the above formula 2, N is an integer from 1 to 200)

[0095] 5, it can be seen that the lithium secondary battery according to Example 2 has a better capacity retention rate than Comparative Examples 3 and 4. This is because, as described above, the secondary battery according to Example 2 uses Li 2 O, LiOH and Li 2 CO 3 This is because the inorganic coating layer containing , minimizes the reaction of the lithium ions introduced into the negative electrode with the air and moisture in the air, which maximizes the amount of lithium ions stored in the negative electrode and maximizes the capacity of the positive electrode.

[0096] The above description is merely illustrative of the technical idea of ​​the present invention, and it can be said that various modifications and variations are possible within the scope of the essential characteristics of the present invention if one having ordinary knowledge in the technical field to which the present invention belongs. Therefore, the drawings disclosed in the present invention are for the purpose of explaining, not limiting, the technical idea of ​​the present invention, and the scope of the technical idea of ​​the present invention is not limited by such drawings. The scope of protection of the present invention should be interpreted by the claims, and all technical ideas within the scope equivalent thereto should be interpreted as being included in the scope of the rights of the present invention.

[0097] Meanwhile, although terms indicating directions such as up, down, left, right, front, and back are used in this specification, it is obvious that such terms are used for convenience of explanation and may change depending on the position of the object of interest, the position of the observer, etc. [Explanation of symbols]

[0098] 10:Negative electrode 11: Current collector 12: Negative electrode active material layer 20: Lithium metal film 30: Pressure member 40: Prelithiation Reactor 41: Prelithiated solution 50: Lithium metal 60: Charger

Claims

1. a step of coating at least one surface of a current collector with a negative electrode slurry containing a negative electrode active material to manufacture a negative electrode having a negative electrode active material layer formed thereon; prelithiating the negative electrode; The prelithiated negative electrode was treated with CO ２ and forming an inorganic coating layer on the surface of the negative electrode active material layer by aging the negative electrode active material layer under an atmosphere. CO during aging ２ The pressure in the step is 0.1 to 10 mTorr.

2. The inorganic coating layer is ２ O, LiOH and Li ２ CO ３ The method for producing a negative electrode according to claim 1 , further comprising one or more compounds selected from the group consisting of:

3. The inorganic coating layer is ２ O, LiOH and Li ２ CO ３ The method for producing a negative electrode according to claim 1 or 2, comprising:

4. The method for producing a negative electrode according to claim 1 , wherein the negative electrode active material is at least one selected from the group consisting of a graphite-based active material and a silicon-based active material.

5. The method for producing a negative electrode according to claim 1 , wherein the step of prelithiating the negative electrode is carried out by directly contacting lithium metal on the negative electrode active material layer.

6. The step of prelithiating the negative electrode comprises:

6. The method of claim 5, further comprising bonding a lithium metal film onto the negative electrode active material layer.

7. The step of prelithiating the negative electrode comprises: The method for producing a negative electrode according to claim 1 , wherein the negative electrode is connected to lithium metal and then electrochemically charged.

8. The method for producing a negative electrode according to any one of claims 1 to 7, wherein the aging temperature is 20 to 60°C.

9. The method for producing a negative electrode according to any one of claims 1 to 8, wherein the aging time is 10 to 60 hours.

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