Pre-lithiation negative electrode and secondary battery including the pre-lithiation negative electrode

Abstract

A pre-lithiated negative electrode is disclosed, comprising: a negative electrode collector; and a negative electrode active material layer formed on at least one surface of the negative electrode collector, wherein the negative electrode active material layer comprises high-capacity artificial graphite without a carbon coating, the negative electrode active material layer is pre-lithiated, and based on the content of lithium embedded when the pre-lithiated negative electrode is charged to 100%, the content of lithium embedded in the pre-lithiated negative electrode active material layer is 3% to 5%.

Description

Technical Field

[0001] The present disclosure relates to a pre-lithiated negative electrode and a secondary battery including the pre-lithiated negative electrode. Specifically, the present disclosure relates to a pre-lithiated negative electrode having high capacity and energy density and showing improved cycle characteristics, and a secondary battery including the pre-lithiated negative electrode.

[0002] This application claims the priority of Korean Patent Application No. 10-2019-0144564 filed in Korea on November 12, 2019, the disclosure of which is incorporated herein by reference. Background Art

[0003] Energy storage technology has received increasing attention recently. As the application of energy storage technology has expanded to energy sources for mobile phones, cameras and laptops, and even electric vehicles, research and development work on electrochemical devices has been increasingly put into practice. In this context, electrochemical devices have received the most attention. Among these electrochemical devices, the development of rechargeable secondary batteries has become the focus. Recently, research and design of a new type of electrode and battery to improve the capacity density and specific energy of such batteries has been actively studied.

[0004] Among commercially available secondary batteries, lithium secondary batteries developed in the early 1990s have attracted much attention because they have higher operating voltage, significantly higher energy density, longer cycle life and lower self-discharge rate compared to conventional batteries using liquid electrolytes such as nickel-metal hydride, nickel-cadmium and lead sulfate batteries.

[0005] Since conventional lithium secondary batteries use LiCoO 2 or LiMn 2 O 4 Since the lithium intercalation compound is used as the positive electrode, such batteries are manufactured by using a carbon electrode that is not intercalated with lithium as the negative electrode. In the case of a carbon electrode, a passivation coating film is formed on its surface at the time of initial charge, and this coating film prevents the organic solvent from being inserted into the gap between the carbon lattice layers and inhibits the decomposition of the organic solvent. In this way, the stability of the carbon structure and the reversibility of the carbon electrode can be improved to allow the carbon electrode to be used as the negative electrode of a lithium secondary battery.

[0006] However, since the formation of this coating is an irreversible reaction, lithium ions are consumed, resulting in an undesirable decrease in battery capacity. In addition, since the charge / discharge efficiency of the carbon electrode and the positive electrode is not completely 100%, lithium ions are consumed as the number of cycles increases, resulting in a decrease in electrode capacity and a decrease in cycle life. Summary of the invention

[0007] Technical issues

[0008] The present disclosure is designed to solve the problems of the prior art, and thus the present disclosure aims to provide a pre-lithiation negative electrode capable of providing a secondary battery having increased capacity and energy density and capable of improving cycle characteristics.

[0009] The present disclosure also aims to provide a secondary battery comprising the pre-lithiation negative electrode.

[0010] In addition, the present disclosure aims to provide a method for manufacturing the pre-lithiation negative electrode.

[0011] Technical Solution

[0012] In one aspect of the present disclosure, a pre-lithiated negative electrode according to any one of the following embodiments is provided.

[0013] According to a first embodiment, a pre-lithiation negative electrode is provided, comprising:

[0014] A negative electrode current collector; and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises high-capacity artificial graphite without a carbon coating,

[0015] The negative electrode active material layer is pre-lithiated,

[0016] And the content of lithium embedded in the pre-lithiated negative electrode active material layer is 3% to 5% based on the content of lithium embedded when the pre-lithiated negative electrode is charged to 100%.

[0017] According to a second embodiment of the present disclosure, there is provided a pre-lithiated negative electrode as defined in the first embodiment,

[0018] The capacity of the high-capacity artificial graphite is 360 mAh / g or more.

[0019] According to a third embodiment of the present disclosure, there is provided a pre-lithiated negative electrode as defined in the first embodiment or the second embodiment,

[0020] The average particle size (D 50 ) is 18μm or more.

[0021] According to a fourth embodiment of the present disclosure, a pre-lithiated negative electrode as defined in any one of the first to third embodiments is provided,

[0022] Pre-lithiation is carried out by using a lithium ion supply metal sheet via direct electric contact.

[0023] According to a fifth embodiment of the present disclosure, there is provided a secondary battery including the pre-lithiated negative electrode as defined in any one of the first to fourth embodiments, a positive electrode, and a separator interposed between the pre-lithiated negative electrode and the positive electrode.

[0024] According to a sixth embodiment of the present disclosure, there is provided a secondary battery as defined in the fifth embodiment,

[0025] The capacity retention rate (%) of the secondary battery at the 500th cycle is 10% higher than the capacity retention rate (%) of the secondary battery including the non-pre-lithiation artificial graphite negative electrode at the 500th cycle, and in the fourth week of the test for determining the high-temperature storage performance, the high-temperature storage performance retention rate (%) of the secondary battery is 5% higher than the high-temperature storage performance retention rate (%) of the secondary battery including the non-pre-lithiation artificial graphite negative electrode.

[0026] According to a seventh embodiment of the present disclosure, there is provided a secondary battery as defined in the fifth embodiment or the sixth embodiment,

[0027] The positive electrode comprises lithium cobalt oxide.

[0028] According to an eighth embodiment of the present disclosure, there is provided a secondary battery as defined in any one of the fifth to seventh embodiments,

[0029] The secondary battery is a pouch-type secondary battery.

[0030] According to a ninth embodiment of the present disclosure, there is provided a method for manufacturing a pre-lithiation negative electrode, comprising the following steps:

[0031] preparing an initial negative electrode having a negative electrode active material layer, the negative electrode active material layer comprising high-capacity artificial graphite without a carbon coating; and

[0032] An initial negative electrode and a lithium ion supplying metal sheet as a counter electrode are immersed in an electrolyte, and a current is applied thereto to perform pre-lithiation by inserting lithium ions into the negative electrode active material layer, wherein the content of lithium inserted into the pre-lithiated negative electrode active material layer is 3% to 5% based on the content of lithium inserted when the pre-lithiated negative electrode is charged to 100%.

[0033] According to a tenth embodiment of the present disclosure, there is provided a method for manufacturing a pre-lithiated negative electrode as defined in the ninth embodiment,

[0034] The high-capacity artificial graphite is obtained by the following process, which comprises:

[0035] thermally treating the carbon precursor to obtain primary particles; and

[0036] The step of mixing primary particles with an asphalt binder and heat-treating them to obtain secondary particles does not include the step of forming a carbon coating on the secondary particles.

[0037] According to an eleventh embodiment of the present disclosure, there is provided a method for manufacturing a pre-lithiated negative electrode as defined in the ninth embodiment or the tenth embodiment, wherein the electrolyte includes a lithium salt and a non-aqueous solvent.

[0038] Beneficial Effects

[0039] According to an embodiment of the present disclosure, a negative electrode active material layer including a high-capacity artificial graphite without a carbon coating is preliminarily pre-lithiated to 3% to 5% of the content of lithium embedded when the negative electrode is charged to 100% by an electrochemical charging process. As a result, a pre-lithiated negative electrode having improved cycle characteristics, showing high capacity and high energy characteristics and having improved high temperature storage stability and a secondary battery including the pre-lithiated negative electrode can be provided. DETAILED DESCRIPTION

[0040] Hereinafter, the preferred embodiments of the present disclosure will be described in detail. Before the description, it should be understood that the terms used in the specification and the appended claims should not be interpreted as being limited to the common meaning and dictionary meaning, but rather interpreted based on the meaning and concept of the technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to appropriately define the terms for the best interpretation.

[0041] In one aspect of the present disclosure, a pre-lithiation negative electrode is provided, comprising:

[0042] a negative electrode current collector; and a negative electrode active material layer formed on at least one surface of the negative electrode current collector,

[0043] wherein the negative electrode active material layer comprises high-capacity artificial graphite without a carbon coating,

[0044] The negative electrode active material layer is pre-lithiated,

[0045] And the content of lithium inserted into the pre-lithiated negative electrode active material layer is 3% to 5% based on the content of lithium inserted when the pre-lithiated negative electrode is charged to 100%.

[0046] There is no particular limitation on the negative electrode current collector, as long as it has conductivity and does not cause any chemical changes in the corresponding battery. Specific examples of negative electrode current collectors include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel, aluminum-cadmium alloy, or the like that has been surface-treated with carbon, nickel, titanium, silver, etc. In addition, similar to the positive electrode current collector, fine surface irregularities can be formed on the surface of the negative electrode current collector to enhance the binding force with the negative electrode active material. The negative electrode current collector can be used in various shapes including films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, or similar shapes.

[0047] The negative electrode current collector generally has a thickness of 3 μm to 500 μm.

[0048] The negative electrode active material layer may include a negative electrode active material, a conductive material, a binder, or the like. The negative electrode active material layer may further include a filler as needed.

[0049] According to an embodiment of the present disclosure, the negative active material includes high-capacity artificial graphite without a carbon coating layer, ie, 100% artificial graphite.

[0050] Here, the capacity of the high-capacity artificial graphite may be 360 ​​mAh / g or more, or 361 mAh / g to 365 mAh / g.

[0051] Relatively speaking, low-capacity artificial graphite refers to artificial graphite with a capacity of less than 355 mAh / g.

[0052] When conventional artificial graphite has a carbon coating formed thereon, the disadvantage of the soft carbon forming the carbon coating is that it consumes capacity. Therefore, since the high-capacity artificial graphite according to the present disclosure has no carbon coating, it can be used as a negative electrode active material to provide a secondary battery with increased capacity and energy density.

[0053] According to an embodiment of the present disclosure, the average particle size (D 50 ) may be 18 μm or more, 12 μm to 22 μm, or 15 μm to 20 μm. When the average particle size of the high-capacity artificial graphite is within the above range, a capacity of 360 mAh / g or more may be achieved with such a sufficiently large particle size.

[0054] Here, D 50 is the particle size at the 50% point in the cumulative distribution of particle number as a function of particle size. 50It can be determined by using the laser diffraction method. Specifically, the powder to be analyzed is dispersed in a dispersion medium and introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500) to measure the difference in the diffraction pattern depending on the particle size when the particles pass through the laser beam, and then the particle size distribution can be calculated. Then, D can be determined by calculating the particle size at the 50% point in the cumulative distribution of the number of particles depending on the particle diameter in the analyzer system. 50 .

[0055] According to an embodiment of the present disclosure, in addition to the above high-capacity artificial graphite, the negative electrode may include a carbonaceous material, a silicon-based material (e.g., silicon oxide of SiO x (0 < x < 2)), Si, or the like as the negative electrode active material.

[0056] The carbonaceous material may be at least one selected from the group consisting of crystalline natural graphite, amorphous hard carbon, low-crystalline soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon.

[0057] According to an embodiment of the present disclosure, in addition to the above high-capacity artificial graphite, specific examples of the negative electrode active material include metal composite oxides such as Li x Fe 2 O 3 (0 ≤ x ≤ 1), Li x WO 2 (0 ≤ x ≤ 1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, an element of Group 1, Group 2, or Group 3 in the periodic table, or a halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8), or the like; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO 2 , PbO, PbO 2 , Pb 2 O 3 , Pb 3 O 4 , Sb 2 O 3 , Sb 2 O 4 , Sb 2 O 5 , GeO, GeO 2 , Bi 2 O 3 , Bi 2 O4 、Bi 2 O 5 , or the like; conductive polymers such as polyacetylene; Li-Co-Ni type materials; titanium oxide; lithium titanium oxide; or the like. Specifically, the negative electrode active material may include a carbonaceous material and / or Si.

[0058] The conductive material is usually added in an amount of 1 wt % to 50 wt % based on the total weight of the mixture including the negative electrode active material. Such a conductive material is not particularly limited as long as it has conductivity and does not cause any chemical changes in the corresponding battery. Specific examples of conductive materials include: graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers, such as carbon fibers or metal fibers; metal powders, such as carbon fluoride powders, aluminum powders or nickel powders; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials such as polyphenylene derivatives; or the like.

[0059] Meanwhile, a graphite material having elasticity may be used as the conductive material optionally in combination with the above-mentioned materials.

[0060] The binder is a component that helps the active material to be bonded to the conductive material and to the current collector, and is generally added in an amount of 1% to 50% by weight based on the total weight of the mixture including the negative electrode active material. Specific examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, or the like.

[0061] The dispersion medium may include water, alcohols (such as ethanol), acetone, or the like.

[0062] The filler is a component that suppresses the expansion of the negative electrode and is optionally used. This filler is not particularly limited as long as it is a fiber material and does not cause any chemical changes in the corresponding battery. Specific examples of the filler include: olefin polymers such as polyethylene or polypropylene; and fiber materials such as glass fiber or carbon fiber.

[0063] According to an embodiment of the present disclosure, based on 100 parts by weight of the high-capacity artificial graphite as the negative electrode active material, the negative electrode active material layer may include a binder in an amount of 1.5 parts by weight to 3.0 parts by weight or 2 parts by weight to 2.5 parts by weight, and a conductive material in an amount of 0.2 parts by weight to 1.0 parts by weight or 0.5 parts by weight to 0.7 parts by weight.

[0064] According to an embodiment of the present disclosure, pre-lithiation may be performed by using a lithium ion supply metal sheet via direct electric contact.

[0065] Here, the expression "pre-lithiation via direct electrical contact" refers to a process comprising the following steps: immersing the negative electrode before pre-lithiation (initial negative electrode) and the lithium ion supplying metal sheet in an electrolyte, and charging by applying an electric current, etc., so that the lithium ions separated from the lithium ion supplying metal sheet can be embedded in the negative electrode active material layer of the initial negative electrode.

[0066] The lithium ion supply metal sheet is used as a source of lithium ions to be doped into the negative electrode active material layer, and may include a lithium ion-containing material selected from lithium, a lithium alloy, and a mixture thereof. The lithium alloy may include Li-Al, Li-Cu, Li-Si, or the like, but is not limited thereto.

[0067] The metal sheet may include a metal selected from lithium, lithium alloys and mixtures thereof alone, or may further include a substrate attached to one surface of the metal to support the metal. The substrate may include stainless steel (SUS), aluminum, nickel, titanium, calcined carbon, copper, or the like.

[0068] The metal sheet may have a thickness of 15 μm to 300 μm or 20 μm to 100 μm.

[0069] The content of lithium embedded in the pre-lithiated negative electrode active material layer is 3% to 5% based on the content of lithium embedded when the pre-lithiated negative electrode is charged to 100%. According to an embodiment of the present disclosure, the content of lithium may be 3.5% to 4.5%, 3% to 4.5%, or 4.5% to 5%.

[0070] The expression "the content of lithium embedded in the pre-lithiated negative electrode active material layer" refers to the content of lithium ions embedded in the negative electrode active material layer before the battery formed using the pre-lithiated negative electrode according to the present disclosure is operated, and can also be referred to as the lithiation dosage (%) of the negative electrode active material layer.

[0071] When the content of lithium embedded in the pre-lithiated negative electrode active material layer is less than 3%, there is a problem of limited improvement in cycle characteristics due to insufficient reversible lithium source. When the content of lithium is greater than 5%, there is a problem that the negative electrode shows a reduced potential due to excessive lithium source, so lithium metal may be deposited on the negative electrode surface, and the deposited lithium metal may increase the electrode resistance and battery resistance as a resistor, thereby reducing the capacity and energy density of the secondary battery.

[0072] The amount of lithium inserted into the pre-lithiated negative active material layer can be determined by using a device that allows current to flow through the connection between the working electrode and the counter electrode under low-rate charging conditions.

[0073] In another aspect of the present disclosure, there is provided a method for manufacturing a pre-lithiation negative electrode, comprising the following steps:

[0074] preparing an initial negative electrode having a negative electrode active material layer, the negative electrode active material layer comprising high-capacity artificial graphite without a carbon coating; and

[0075] An initial negative electrode and a lithium ion supplying metal sheet as a counter electrode are immersed in an electrolyte, and a current is applied thereto to perform pre-lithiation by inserting lithium ions into the negative electrode active material layer, wherein the content of lithium inserted into the pre-lithiated negative electrode active material layer is 3% to 5% based on the content of lithium inserted when the pre-lithiated negative electrode is charged to 100%.

[0076] In the following, each step will be explained in more detail.

[0077] An initial negative electrode having a negative electrode active material layer including high-capacity artificial graphite without a carbon coating layer is prepared.

[0078] A negative electrode slurry is prepared by dispersing a negative electrode active material, a conductive material, and a binder in a dispersion medium, and an initial negative electrode is obtained by applying the negative electrode slurry to a negative electrode collector, followed by drying. The negative electrode slurry may further include a filler as needed.

[0079] High-capacity artificial graphite without carbon coating was used as the negative electrode active material.

[0080] According to an embodiment of the present disclosure, high-capacity artificial graphite is obtained by the following process, which includes the step of heat-treating a carbon precursor to obtain primary particles; and mixing the primary particles with a bitumen binder and heat-treating them to obtain secondary particles, and does not include the step of forming a carbon coating on the secondary particles.

[0081] Any material can be used as a carbon precursor as long as it can be graphitized by heat treatment. Specific examples of carbon precursors may include coke, needle coke, mosaic coke, or a mixture of two or more thereof. The heat treatment temperature for obtaining primary particles may be 1,200°C to 1,800°C, or 1,500°C to 1,700°C.

[0082] Next, the obtained primary particles are mixed with an asphalt binder and heat-treated to obtain secondary particles, wherein the heat-treatment temperature may be 2,200° C. to 2,800° C., or 2,400° C. to 2,600° C. The asphalt binder may include coal tar pitch, petroleum pitch, or the like.

[0083] According to an embodiment of the present disclosure, the asphalt binder may be mixed with the primary particles in an amount of 3 parts by weight to 5 parts by weight based on 100 parts by weight of the primary particles.

[0084] In addition, reference may be made to the above description regarding the negative electrode current collector, the high-capacity artificial graphite, the conductive material, the binder, and the filler.

[0085] The dispersion medium may include water, alcohols (such as ethanol), acetone, or the like.

[0086] Next, the initial negative electrode and the lithium ion supplying metal sheet as the counter electrode are immersed in an electrolyte, and a current is applied thereto so that lithium ions can be intercalated into the negative electrode active material layer. In this way, pre-lithiation is performed.

[0087] Here, the content of lithium inserted into the pre-lithiated negative electrode active material layer is 3% to 5% based on the content of lithium inserted when the pre-lithiated negative electrode is charged to 100%.

[0088] The lithium ion supply metal sheet is used as a source for supplying lithium ions doped to the negative electrode, and may include a lithium ion-containing material selected from lithium, lithium alloys, and mixtures thereof. The lithium alloy may include Li-Al, Li-Cu, Li-Si, or the like, but is not limited thereto. The metal sheet may include a metal selected from lithium, lithium alloys, and mixtures thereof alone, or may further include a substrate attached to one surface of the metal to support the metal. The substrate may include stainless steel (SUS), aluminum, nickel, titanium, calcined carbon, copper, or the like. The metal sheet may have a thickness of 15 μm to 300 μm, or 20 μm to -100 μm.

[0089] The electrolyte used for pre-lithiation may include a lithium salt and a non-aqueous solvent.

[0090] Lithium salts may include LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 、LiPF 6 、LiCF 3 SO 3 、LiAsF 6 、LiSbF 6 、LiAlCl 4 , CH3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2 ) 2 NLi, lithium chloroborate, lithium lower aliphatic carboxylate, lithium 4-phenylborate, or two or more thereof.

[0091] The non-aqueous solvent may be any organic solvent conventionally used in the art without particular limitation. Preferably, a high boiling point organic solvent may be used to minimize consumption of the electrolyte used for pre-lithiation due to evaporation during the pre-lithiation process.

[0092] The non-aqueous solvent may include a carbonate solvent, an ester solvent, or two or more thereof. Specific 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, ethyl propionate, and methyl propionate, but are not limited thereto, and these solvents may be used alone or in combination.

[0093] The electrolyte used for pre-lithiation may further include additives.

[0094] The additives may include vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, salicylic acid, LiBF 4 , lithium bis(trifluoromethanesulfonyl)imide (LITFSI), lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalate)borate (LiODFB), or two or more thereof.

[0095] According to an embodiment of the present disclosure, the initial negative electrode and the lithium ion supply metal sheet can be immersed in the electrolyte for pre-lithiation for 5 to 10 hours, so that the initial negative electrode can be fully wetted by the electrolyte used for pre-lithiation. When the immersion time meets the range defined above, the negative electrode active material can be fully wetted by the electrolyte used for pre-lithiation, thereby promoting the subsequent process-pre-lithiation. In addition, problems caused by too long an immersion time, including reduced electrode durability and easy detachment of active materials from the current collector during processing, can be prevented. When the electrolyte used for pre-lithiation is uniformly infiltrated into the negative electrode by wetting, the lithium ions separated from the lithium ion supply metal sheet can be uniformly diffused to the negative electrode, thereby pre-lithiation can be performed with a uniform lithium ion concentration over the entire negative electrode.

[0096] In order to facilitate immersing the initial negative electrode in the electrolyte for pre-lithiation / wetting the initial negative electrode with the electrolyte for pre-lithiation, the reactor used for wetting may be converted to a vacuum state of less than 760 mmHg. Here, the electrolyte for pre-lithiation used to wet the initial negative electrode may have a temperature of 30°C to 60°C.

[0097] Then, electrochemical charging is performed by applying current to the initial negative electrode immersed in the electrolyte for pre-lithiation and the lithium ion supplying metal sheet as the counter electrode. In this way, the initial negative electrode can be pre-lithiated.

[0098] According to an embodiment of the present disclosure, electrochemical charging can be performed by using a charger, after immersing the initial negative electrode and the lithium ion supplying metal sheet as the counter electrode in the electrolyte for pre-lithiation, even the inside of the negative electrode active material layer of the initial negative electrode is sufficiently wetted with the electrolyte for pre-lithiation.

[0099] Here, the current during charging can be 0.1 mA / cm 2 Up to 10mA / cm 2 , 0.5mA / cm 2 Up to 3mA / cm 2 , or 0.5mA / cm 2 Up to 2mA / cm 2 When the current during charging satisfies the above-defined range, lithium ions can react with the negative electrode stably and uniformly.

[0100] The electrochemical charging is performed in such a manner that the content of lithium embedded in the pre-lithiated negative electrode active material layer may be 3% to 5% based on the content of lithium embedded when the pre-lithiated negative electrode is charged to 100%. According to an embodiment of the present disclosure, the content of lithium embedded in the pre-lithiated negative electrode active material layer may be 3.5% to 4.5%.

[0101] When the content of lithium embedded in the pre-lithiated negative electrode active material layer satisfies the range of 3% to 5%, the capacity, initial efficiency and cycle characteristics of the battery can be improved, thereby increasing the energy density and reducing cycle swelling.

[0102] When the content of lithium embedded in the pre-lithiated negative electrode active material layer is less than 3%, the effect of improving the cycle characteristics cannot be fully obtained due to the small amount of lithium. When the content of lithium embedded in the pre-lithiated negative electrode active material layer is greater than 5%, lithium electrodeposition may occur, resulting in decreased stability, and the resistance of the battery may increase due to the excessive amount of lithium.

[0103] The amount of lithium inserted into the pre-lithiated negative active material layer can be determined by using a device that allows current to flow through the connection between the working electrode and the counter electrode under low-rate charging conditions.

[0104] The pre-lithiated initial negative electrode can then be removed from the electrolyte used for pre-lithiation, washed with an organic solvent, and then dried. The organic solvent used for washing may include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or the like. In this way, the lithium salt can be fully dissolved and the negative electrode can be washed without causing damage to the negative electrode.

[0105] The drying may be performed by methods known to those skilled in the art. For example, the negative electrode may be dried in a drying chamber at 20° C. to 40° C. for 10 minutes to 5 hours.

[0106] In another aspect of the present disclosure, a lithium secondary battery including the above-mentioned pre-lithiated negative electrode is provided. In other words, an electrode assembly can be formed by using a positive electrode including a positive electrode active material, a separator and the pre-lithiated negative electrode, and the electrode assembly and the electrolyte can be introduced into a battery case to provide a lithium secondary battery.

[0107] According to an embodiment of the present disclosure, there is provided a secondary battery including the pre-lithiated negative electrode, a positive electrode, and a separator interposed between the pre-lithiated negative electrode and the positive electrode.

[0108] According to an embodiment of the present disclosure, the capacity retention rate (%) of a secondary battery including a pre-lithiated negative electrode at the 500th cycle may be 10% higher, or 10% to 14% higher, than the capacity retention rate (%) of a secondary battery including a non-pre-lithiated artificial graphite negative electrode at the 500th cycle.

[0109] In the secondary battery according to the embodiment of the present disclosure, the reversible lithium pre-lithiated on the negative electrode prevents degradation and improves the cycle characteristics as the charge / discharge cycle proceeds. As a result, the secondary battery can have a higher capacity retention rate (%) than a non-pre-lithiated secondary battery.

[0110] In addition, in the fourth week of the test for determining high-temperature storage performance, the high-temperature storage performance retention rate (%) of the secondary battery including the pre-lithiated negative electrode can be 5% higher, or 5% to 8% higher, than the high-temperature storage performance retention rate (%) of the secondary battery including the non-pre-lithiated artificial graphite negative electrode.

[0111] Based on the capacity achieved when fully charged after charging / discharging at 0.33C and room temperature, the high temperature storage performance retention rate was calculated as the capacity retention rate (%) by measuring the remaining capacity of the secondary battery after self-discharging of lithium in the fourth week and discharging the battery at 0.33C in constant current (CC) mode. The secondary battery according to an embodiment of the present disclosure has a higher high temperature storage performance retention rate (%) because the reversible lithium source additionally supplied by pre-lithiation of the negative electrode reduces the loss of the lithium source during self-discharge, thereby increasing the remaining capacity retention rate (%).

[0112] Compared to a secondary battery including artificial graphite that is not pre-lithiated, a secondary battery including a pre-lithiated negative electrode according to an embodiment of the present disclosure may have an increased energy density, for example, an increase in energy density of 4% to 7%. In other words, according to an embodiment of the present disclosure, the energy density of a secondary battery including the negative electrode can be calculated by applying the battery capacity and nominal voltage of the negative electrode reflecting the content of lithium in the pre-lithiated negative electrode.

[0113] Specific examples of positive electrode active materials include, but are not limited to, lithium cobalt oxide (LiCoO 2 ) and lithium nickel oxide (LiNiO 2 ) or those compounds substituted with one or more transition metals; such as those having the chemical formula Li 1+y Mn 2-y O 4 (where y = 0-0.33), LiMnO 3 、LiMn 2 O 3 , and LiMnO 2 Lithium manganese oxide; lithium copper oxide (Li 2 CuO 2 ); such as LiV 3 O 8 , LiV 3 O 4 、V 2 O5 , or Cu 2 V 2 O 7 vanadium oxides such as these; lithium nickel oxides represented by the chemical formula LiNi 1- y M y O 2 (where M is Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and y = 0.01 - 0.3); lithium nickel oxides represented by the chemical formula LiMn 2-y M y O 2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and y = 0.01 - 0.1) or Li 2 Mn 3 MO 8 (where M = Fe, Co, Ni, Cu, or Zn); ternary lithium manganese composite oxides; LiMn 2 O 4 in which the Li part is substituted by alkaline earth metal ions; disulfide compounds; and Fe 2 (MoO 4 ) 3 ; ternary lithium transition metal composite oxides such as Li(Ni a Co b Mn c )O 2 (0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1); or the like.

[0114] According to an embodiment of the present disclosure, the positive electrode active material may include lithium cobalt oxide, such as LiCoO 2 or the like. When lithium cobalt oxide is used as the positive electrode active material, other metals such as nickel and manganese do not dissolve in the negative electrode.

[0115] The positive electrode active material may be dispersed in a solvent together with a binder polymer, a conductive material, and other additives to form a positive electrode mixture slurry. Then, the positive electrode mixture slurry may be coated on at least one surface of the positive electrode current collector, followed by drying and pressing to form a positive electrode.

[0116] Non-limiting examples of the positive electrode current collector include foils made of aluminum, nickel, or a combination thereof, or the like, while non-limiting examples of the negative electrode current collector include foils made of copper, gold, nickel, copper alloy, or a combination thereof, or the like.

[0117] The binder polymer, conductive material, and other additives for the positive electrode may be the same as or different from those for the negative electrode. For the binder polymer and conductive material, reference may be made to the above description.

[0118] The separator is interposed between the positive electrode and the negative electrode, and an insulating film having high ion permeability and mechanical strength is used as a separator. The separator generally has a pore size of 0.01 μm to 10 μm and a thickness of 5 μm to 300 μm. The separator may include a porous polymer substrate alone, such as a porous polymer film substrate or a porous polymer nonwoven web substrate, or may further include a porous coating layer disposed on at least one surface of the porous polymer substrate and comprising inorganic particles and a binder polymer. The porous polymer film substrate may be a porous polymer film made of a polyolefin such as polyethylene or polypropylene. In addition to polyolefins, the porous polymer film substrate can be made of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalene, or the like, alone or in combination.

[0119] Non-limiting examples of binder polymers include, but are not limited to, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polybutylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxymethyl cellulose, or the like.

[0120] According to the embodiment of the present disclosure, the binder polymer can be divided into a dispersant binder polymer and a non-dispersant binder polymer that is also used as a dispersant. The dispersant binder polymer is a polymer having at least one functional group that contributes to dispersion in the main chain or side chain of the polymer, and the functional group that contributes to dispersion includes an OH group, a CN group or the like. Specific examples of dispersant binder polymers include cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, or the like. In addition to the examples of dispersant binder polymers, specific examples of non-dispersant binder polymers include the binder polymers listed above.

[0121] For example, the weight ratio of the inorganic particles to the total weight of the binder polymer and the cross-linked polymer may be 50:50 to 99:1, particularly 70:30 to 95:5. When the weight ratio of the inorganic particles to the total weight of the binder polymer and the cross-linked polymer satisfies the above range, the problem of reduced pore size and porosity of the resulting coating caused by increased content of the binder polymer and the cross-linked polymer can be prevented. The problem of decreased peeling resistance of the resulting coating caused by reduced content of the binder polymer and the cross-linked polymer can also be solved.

[0122] Nonlimiting examples of the inorganic particles include inorganic particles having a dielectric constant of 5 or more, particularly 10 or more, inorganic particles having a lithium ion transporting capability, or a mixture thereof.

[0123] Non-limiting examples of inorganic particles having a dielectric constant of 5 or more may include BaTiO 3 、Pb(Zr,Ti)O 3 (PZT), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT), Pb(Mg 1 / 3 Nb 2 / 3 ) 3 PbTiO 3 (PMN-PT), hafnia, HfO2 ) SrTiO 3 SnO 2 CeO 2 MgO, NiO, CaO, ZnO, ZrO 2 Y 2 O 3 Al 2 O 3 SiC, AlO(OH), Al 2 O 3 . H 2 O, or a mixture thereof.

[0124] As used herein, the term "inorganic particles having lithium ion transport ability" refers to inorganic particles that contain lithium element and do not store lithium but transport lithium ions. Non-limiting examples of inorganic particles having lithium ion transport ability include lithium phosphate (Li 3 PO 4 ); lithium titanium phosphate (Li x Ti y (PO 4 ) 3 , 0 < x < 2, 0 < y < 3); lithium aluminum titanium phosphate (Li x Al y Ti z (PO 4 ) 3 , 0 < x < 2, 0 < y < 1, 0 < z < 3); (LiAlTiP) x O y -based glass (1 < x < 4, 0 < y < 13), such as 14Li 2 O - 9Al 2 O 3 - 38TiO 2 - 39P 2 O 5 ; lithium lanthanum titanate (Li x La y TiO 3 , 0 < x < 2, 0 < y < 3); lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), such as Li 3.25 Ge 0.25 P 0.75 S 4 ; lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), such as Li 3 N; SiS2 Base glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), such as Li 3 PO 4 -Li 2 S-SiS 2 ; and P 2 S 5 Base glass (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), such as LiI-Li 2 S-P 2 S 5 ; or a mixture thereof.

[0125] Although there is no particular limitation on the thickness of the porous coating, the thickness can be 1 μm to 10 μm, or 1.5 μm to 6 μm. In addition, the porosity of the porous coating is not particularly limited, but can preferably be 35% to 65%.

[0126] The electrolyte includes conventional electrolyte components, such as organic solvents and electrolyte salts. The electrolyte salts that can be used are salts having an A + B - structure, where A + includes alkali metal cations such as Li + , Na + , K + , or a combination thereof, and B - includes such as PF 6 - , BF 4 - , Cl - , Br - , I - , ClO 4 - , AsF 6 - , CH 3 CO 2 - , CF 3 SO 3 - , N(CF 3 SO 2 ) 2 - , C(CF 2 SO 2 ) 3 -, or a combination thereof. In particular, lithium salts are preferred. For example, LiClO 4 、LiCF 3 SO 3 、LiPF 6 、LiAsF 6 、LiN(CF 3 SO 2 ) 2 , or a mixture thereof.

[0127] The organic solvent for the electrolyte may include solvents generally known to those skilled in the art, such as cyclic carbonate solvents, linear carbonate solvents, ester solvents, nitrile solvents, phosphate solvents, or mixtures thereof, which may or may not contain halogen substituents. Specific examples of usable solvents include 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 (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, amyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, or mixtures thereof.

[0128] According to the manufacturing process of the final product and the performance required by the final product, the injection of the electrolyte can be performed at an appropriate step during the process of manufacturing the battery. In other words, the injection of the electrolyte can be performed before the battery assembly or in the last step of the battery assembly.

[0129] The appearance or housing of the secondary battery according to the embodiment of the present disclosure is not particularly limited. For example, the secondary battery may have a cylindrical shape, a prismatic shape, a pouch shape, or a coin shape using a can. The secondary battery according to the embodiment of the present disclosure may be in a pouch shape.

[0130] In addition, the secondary battery according to an embodiment of the present disclosure may be a lithium secondary battery. The lithium secondary battery may include any conventional lithium secondary battery, such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0131] Embodiments will be described more fully hereinafter so that the present disclosure can be easily understood. However, the following examples can be embodied in a variety of different forms and should not be interpreted as being limited to the exemplary embodiments set forth herein. On the contrary, these exemplary embodiments are provided so that the present disclosure will be thorough and complete, and the scope of the present disclosure will be fully conveyed to those skilled in the art.

[0132] In the following examples and comparative examples, “average particle size, D 50 " is the particle diameter at the 50% point in the cumulative distribution of the number of particles as a function of the particle size, and is determined by using a laser diffraction method. Specifically, the powder to be analyzed is dispersed in a dispersion medium and introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500) to measure the difference in diffraction patterns depending on the particle size when the particles pass through a laser beam, and then the particle size distribution can be calculated. Then, the average particle size, D, can be determined by calculating the particle diameter at the 50% point in the cumulative distribution of the number of particles depending on the particle size in the analyzer system. 50 .

[0133] Example 1

[0134] <Manufacturing of negative electrode>

[0135] First, needle coke was heat-treated and graphitized at 1,500°C for 12 hours to obtain primary particles. Next, the primary particles were mixed with a pitch binder and heat-treated at 2,900°C for 12 hours to increase the crystallinity of the active material and form secondary particles, thereby providing artificial graphite.

[0136] The obtained artificial graphite was not coated with carbon and was a high-capacity artificial graphite having a capacity of 360 mAh / g and an average particle size of 18 μm.

[0137] Then, the artificial graphite, Super C65 as a conductive material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed at a weight ratio of 96:1:2:1, and water was added to the resulting mixture to obtain a negative electrode slurry.

[0138] The negative electrode slurry was heated to 3.6 mAh / cm 2 The current collector coated with the slurry was then pressed and vacuum dried at about 130° C. for 8 hours to obtain an initial negative electrode including a negative electrode active material layer formed on the current collector.

[0139] Afterwards, 1M LiPF 6 The nonaqueous electrolyte was prepared by adding a nonaqueous electrolyte solvent including ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0140] The initial negative electrode and the lithium ion supply metal sheet (lithium metal / SUS formed by depositing lithium metal on a stainless steel (SUS) substrate) as the counter electrode are introduced into the electrolyte for pre-lithiation, and a current is applied thereto at 0.1C for 8 hours to insert lithium into the negative electrode active material layer. Pre-lithiation is performed in this way. Here, based on the content of lithium inserted when the pre-lithiation negative electrode is charged to 100%, the content of lithium inserted into the pre-lithiation negative electrode active material layer is 4.5%. In this way, the pre-lithiation initial negative electrode is completed.

[0141] <Manufacturing of positive electrode>

[0142] First, lithium cobalt oxide LiCoO as the positive electrode active material 2 , carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methylpyrrolidone (NMP) as a solvent in a weight ratio of 96:2:2 to prepare a positive electrode active material slurry. The slurry was coated on one surface of an aluminum current collector having a thickness of 15 μm, and then dried and pressed under the same conditions as the negative electrode to obtain a positive electrode. Here, the positive electrode active material layer was 20 mg / cm based on dry weight. 2 The amount of load.

[0143] <Manufacturing of Pouch-Type Secondary Battery>

[0144] First, 1M LiPF 6 The nonaqueous electrolyte was prepared by adding a nonaqueous electrolyte solvent including ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0145] Next, a polyolefin separator was interposed between the positive electrode and the negative electrode obtained as described above, the resultant structure was introduced into a pouch type case, and then an electrolyte was injected therein to obtain a secondary battery.

[0146] <Manufacturing of coin-type half-cell secondary battery>

[0147] The negative electrode obtained as described above and lithium metal as a counter electrode were used. In addition, a polyolefin separator was interposed between the negative electrode and the lithium metal to form an electrode assembly.

[0148] Then, 1M LiPF 6 An electrolyte prepared by adding to a nonaqueous electrolyte solvent including ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a volume ratio of 3:7 was injected into an electrode assembly to obtain a coin-type half-cell secondary battery.

[0149] Comparative Example 1

[0150] <Manufacturing of negative electrode>

[0151] First, needle coke was heat-treated and graphitized at 1,500°C for 12 hours to obtain primary particles. Next, the primary particles were mixed with a pitch binder and heat-treated at 2,900°C for 12 hours to increase the crystallinity of the active material and form secondary particles, thereby providing artificial graphite.

[0152] The obtained artificial graphite was not coated with carbon and was a high-capacity artificial graphite having a capacity of 360 mAh / g and an average particle size of 18 μm.

[0153] Then, the artificial graphite, Super C65 as a conductive material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed at a weight ratio of 96:1:2:1, and water was added to the resulting mixture to obtain a negative electrode slurry.

[0154] The negative electrode slurry was heated to 3.6 mAh / cm 2 The loading amount of the slurry was coated on one surface of the copper foil (current collector). Then, the current collector coated with the slurry was pressed and vacuum dried at about 130° C. for 8 hours to obtain an initial negative electrode that was not pre-lithiated and included a negative electrode active material layer formed on the current collector. In other words, the initial negative electrode obtained in the same manner as described in Example 1 was used as the negative electrode.

[0155] A pouch-type secondary battery and a coin-type secondary battery were obtained in the same manner as in Example 1, except that the negative electrode was used.

[0156] Comparative Example 2

[0157] In the same manner as in Example 1, an initial negative electrode was obtained.

[0158] The initial negative electrode and the lithium ion supply metal sheet (lithium metal / SUS formed by depositing lithium metal on a stainless steel (SUS) substrate) as the counter electrode are introduced into the electrolyte for pre-lithiation, and a current is applied thereto at 0.1C for 4 hours to insert lithium into the negative electrode active material layer. Pre-lithiation is performed in this way. Here, based on the content of lithium inserted when the pre-lithiation negative electrode is charged to 100%, the content of lithium inserted into the pre-lithiation negative electrode active material layer is 2%. In this way, the pre-lithiation initial negative electrode is completed.

[0159] A pouch-type secondary battery and a coin-type secondary battery were obtained in the same manner as in Example 1, except that the negative electrode was used.

[0160] Comparative Example 3

[0161] In the same manner as in Example 1, an initial negative electrode was obtained.

[0162] The initial negative electrode and the lithium ion supply metal sheet (lithium metal / SUS formed by depositing lithium metal on a stainless steel (SUS) substrate) as the counter electrode are introduced into the electrolyte for pre-lithiation, and a current is applied thereto at 0.1C for 15 hours to insert lithium into the negative electrode active material layer. Pre-lithiation is performed in this way. Here, based on the content of lithium inserted when the pre-lithiation negative electrode is charged to 100%, the content of lithium inserted into the pre-lithiation negative electrode active material layer is 8%. In this way, the pre-lithiation initial negative electrode is completed.

[0163] A pouch-type secondary battery and a coin-type secondary battery were obtained in the same manner as in Example 1, except that the negative electrode was used.

[0164] Comparative Example 4

[0165] In the same manner as in Example 1, an initial negative electrode was obtained.

[0166] The initial negative electrode and the lithium ion supply metal sheet (lithium metal / SUS formed by depositing lithium metal on a stainless steel (SUS) substrate) as the counter electrode are introduced into the electrolyte for pre-lithiation, and a current is applied thereto at 0.1C for 30 hours to insert lithium into the negative electrode active material layer. Pre-lithiation is performed in this way. Here, based on the content of lithium inserted when the pre-lithiation negative electrode is charged to 100%, the content of lithium inserted into the pre-lithiation negative electrode active material layer is 15%. In this way, the pre-lithiation initial negative electrode is completed.

[0167] A pouch-type secondary battery and a coin-type secondary battery were obtained in the same manner as in Example 1, except that the negative electrode was used.

[0168] Comparative Example 5

[0169] In the same manner as in Example 1, an initial negative electrode was obtained.

[0170] The initial negative electrode and the lithium ion supply metal sheet (lithium metal / SUS formed by depositing lithium metal on a stainless steel (SUS) substrate) as the counter electrode are introduced into the electrolyte for pre-lithiation, and a current is applied thereto at 0.1C for 40 hours to insert lithium into the negative electrode active material layer. Pre-lithiation is performed in this way. Here, based on the content of lithium inserted when the pre-lithiation negative electrode is charged to 100%, the content of lithium inserted into the pre-lithiation negative electrode active material layer is 20%. In this way, the pre-lithiation initial negative electrode is completed.

[0171] A pouch-type secondary battery and a coin-type secondary battery were obtained in the same manner as in Example 1, except that the negative electrode was used.

[0172] <Discharge capacity test>

[0173] Each of the pouch-type secondary batteries according to Example 1 and Comparative Examples 1 to 5 was charged / discharged at a rate of 0.5C, a charge cutoff voltage of 4.4V, and at a rate of 0.5C, a discharge cutoff voltage of 3.3V to determine the charge capacity and discharge capacity during the charge / discharge process. The results are shown in Table 1 below.

[0174] <High temperature cycle characteristics test>

[0175] Each of the pouch-type secondary batteries according to Example 1 and Comparative Examples 1 to 5 was subjected to 500 charge / discharge cycles at a temperature of 45°C at a rate of 0.5C, a charge cutoff voltage of 4.4V, and a discharge cutoff voltage of 3.3V at a rate of 0.5C. The ratio of the discharge capacity of the last cycle to the discharge capacity of the first cycle was calculated as the high temperature cycle characteristics (%). The results are shown in Table 1 below.

[0176] <Room temperature cycle characteristics test>

[0177] Each of the pouch-type secondary batteries according to Example 1 and Comparative Examples 1 to 5 was subjected to 500 charge / discharge cycles at a temperature of 25° C. at a rate of 0.5 C, a charge cutoff voltage of 4.4 V, and a discharge cutoff voltage of 3.3 V at a rate of 0.5 C. The ratio of the discharge capacity of the last cycle to the discharge capacity of the first cycle was calculated as the room temperature cycle characteristics (%). The results are shown in Table 1 below.

[0178] <High temperature storage test>

[0179] Each coin-type half-cell according to Example 1 and Comparative Examples 1 to 5 was charged at 25° C. in a constant current (CC) / constant voltage (CV) mode of 0.1C and 5 mV, with a cut-off current of 0.005C, and then discharged to 1.5V in a CC mode of 0.1C. The above charge / discharge cycle was repeated twice. Then, in the third cycle, each battery was discharged at 0.05C to a state of charge (SOC) of 5% and the state of charge was set to 95% SOC.

[0180] The coin-type half-cell with the SOC set to 95% was stored in a high-temperature chamber at 60° C. for 4 weeks and discharged at 0.1 C to determine the remaining capacity retention rate (%). The results are shown in Table 1 below.

[0181] <Energy Density>

[0182] Each of the pouch-type secondary batteries according to Example 1 and Comparative Examples 1 to 5 was subjected to 500 charge / discharge cycles at a temperature of 25°C at a rate of 0.5C, a charge cutoff voltage of 4.4V, and a discharge cutoff voltage of 3.3V at a rate of 0.5C. Then, the discharge capacity of the last cycle was determined. The energy density was calculated in Wh / L, representing the battery capacity per liter of negative electrode, with the discharge capacity of the last cycle as the battery capacity. The results are shown in Table 1 below.

[0183] [Table 1]

[0184] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Discharge capacity(mAh) 2340 2200 2150 2170 2120 2110 High temperature cycle characteristics (%) 80 70 65 68 63 66 Room temperature cycle characteristics (%) 91 81 76 79 74 71 High temperature capacity retention rate (%) 91 87 86 85 80 77 Energy density (Wh / L) 706 700 698 697 678 669

[0185] Referring to Table 1, the secondary battery according to Example 1 uses a negative electrode that has been pre-lithiated in advance, so that the content of lithium embedded in the negative electrode active material layer of the high-capacity artificial graphite including the carbon-free coating layer is 4.5% (in the range of 3-5%) based on the content of lithium embedded when the pre-lithiated negative electrode is charged to 100%, thereby showing improved cycle characteristics, high capacity and high energy density, and improved high-temperature storage stability. In contrast, compared with the secondary battery according to Example 1, each secondary battery including a negative electrode that is not pre-lithiated according to Comparative Example 1, and each negative electrode that has been pre-lithiated to 2% (less than the range of 3% to 5%) according to Comparative Example 2 and each negative electrode that has been pre-lithiated to 8%, 15%, and 20% (greater than the range of 3% to 5%) according to Comparative Examples 3 to 5 shows degraded results in terms of high temperature and room temperature cycle characteristics, high temperature storage characteristics, and energy density.

[0186] The present disclosure has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present disclosure, are given by way of illustration only, since various changes and modifications within the scope of the present disclosure will be apparent to those skilled in the art from this detailed description.

Claims

1. A pre-lithiation negative electrode, include: Anode current collector; and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, The negative electrode active material layer comprises high-capacity artificial graphite and pre-lithiated intercalated lithium, The high-capacity artificial graphite is obtained by the following process, which includes a step of heat-treating a carbon precursor to obtain primary particles; and a step of mixing the primary particles with a pitch binder and heat-treating them to obtain secondary particles, and does not include a step of forming a carbon coating on the secondary particles; the capacity of the high-capacity artificial graphite is 360 mAh / g or more and has no carbon coating, and The pre-lithiation is performed by direct electrical contact using a lithium ion supplying metal sheet until the content of lithium inserted into the pre-lithiated negative electrode active material layer is 3.5% to 4.5% based on the content of lithium inserted when the pre-lithiated negative electrode is charged to 100%.

2. The pre-lithiation negative electrode according to claim 1, wherein the average particle size D of the high-capacity artificial graphite is 50 18μm or more.

3. The pre-lithiation negative electrode according to claim 1, wherein the pre-lithiation is carried out via direct electrical contact. include: The initial negative electrode and the lithium ion supplying metal sheet are immersed in an electrolyte and charged by applying an electric current so that the lithium ions separated from the lithium ion supplying metal sheet are inserted into the negative electrode active material layer of the initial negative electrode. 4 . A secondary battery, comprising the pre-lithiated negative electrode as defined in any one of claims 1 to 3 , a positive electrode, and a separator interposed between the pre-lithiated negative electrode and the positive electrode.

5. The secondary battery according to claim 4, wherein the capacity retention rate (%) of the secondary battery at the 500th cycle is 10% higher than the capacity retention rate (%) of the secondary battery including the non-pre-lithiation artificial graphite negative electrode at the 500th cycle, and in the fourth week of the test for determining the high temperature storage performance, the high temperature storage performance retention rate (%) of the secondary battery is 5% higher than the high temperature storage performance retention rate (%) of the secondary battery including the non-pre-lithiation artificial graphite negative electrode. The secondary battery according to claim 4 , wherein the positive electrode comprises lithium cobalt oxide. 7 . The secondary battery according to claim 4 , which is a pouch type secondary battery.

8. A method for manufacturing a pre-lithiated negative electrode, The following steps are involved: Preparation of high-capacity artificial graphite: heat-treating a carbon precursor to obtain primary particles, mixing the primary particles with a pitch binder and heat-treating the primary particles to obtain secondary particles, and not including forming a carbon coating on the secondary particles, to obtain the high-capacity artificial graphite having a capacity of 360 mAh / g or more and without a carbon coating; Using the high-capacity artificial graphite as a negative electrode active material to prepare an initial negative electrode having a negative electrode active material layer; and The initial negative electrode and a lithium ion supplying metal sheet as a counter electrode are immersed in an electrolyte, and a current is applied thereto to pre-lithiate by inserting lithium ions into the negative electrode active material layer until the content of lithium inserted into the pre-lithiated negative electrode active material layer is 3.5% to 4.5% based on the content of lithium inserted when the pre-lithiated negative electrode is charged to 100%, so as to manufacture the pre-lithiated negative electrode. 9 . The method for manufacturing a pre-lithiation negative electrode according to claim 8 , wherein the electrolyte comprises a lithium salt and a non-aqueous solvent.