Lithium secondary battery containing positive electrode additive

Abstract

The present invention relates to a lithium secondary battery. The positive electrode of the lithium secondary battery is manufactured by including a positive electrode additive represented by Chemical Formula 1 in a positive electrode mixture layer as an irreversible additive, and since the ratio of carbon monoxide and carbon dioxide generated according to whether the positive electrode additive is used is adjusted during the activation process to meet a specific range, the content ratio of hydrogen and hydrocarbon relative to the total amount of gas generated during the activation process is reduced. Therefore, the advantages are that the safety of the lithium secondary battery is improved and the discharge efficiency of the lithium secondary battery is improved.

Description

Technical Field

[0001] The present invention relates to a lithium secondary battery including a positive electrode additive, and more particularly to a lithium secondary battery including the positive electrode additive in a positive electrode mixture layer.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0070875 filed on June 1, 2021, and incorporates the entire contents of the Korean Patent Application by reference. Background Art

[0003] Recently, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries with high energy density and voltage, long cycle life and low self-discharge rate have been commercialized and widely used.

[0004] Graphite is mainly used as the negative electrode material of lithium secondary battery, but because graphite has a small unit mass capacity of 372mAh / g, it is difficult to increase the capacity of lithium secondary battery. Therefore, in order to increase the capacity of lithium secondary battery, negative electrode materials that form intermetallic compounds with lithium, such as silicon, tin and oxides thereof, are being developed and used as non-carbon-based negative electrode materials with higher energy density than graphite. However, in the case of such non-carbon-based negative electrode materials, the problem is that, although the capacity is large, the initial efficiency is low, the lithium consumption during the initial charge and discharge is large, and the irreversible capacity loss is large.

[0005] In this regard, a method of providing a lithium ion source or storage for a positive electrode material and overcoming the irreversible negative electrode capacity loss has been proposed, which uses a material that is electrochemically active after the first cycle so as not to deteriorate the overall performance of the battery. Specifically, a method of applying an oxide containing excess lithium (e.g., Li6CoO4) as a sacrificial positive electrode material or an irreversible additive (or overdischarge inhibitor) to the positive electrode is known.

[0006] Meanwhile, conventional positive electrode additives such as Li6CoO4 are usually prepared by reacting cobalt oxides and the like with excess lithium oxides. The irreversible additives prepared in this way are structurally unstable, so that a large amount of oxygen (O2) gas may be generated as the charging proceeds, and when the secondary battery is initially charged, that is, when all irreversible additives remain unreacted after the battery is activated, a reaction may occur during the subsequent charge / discharge process to generate side reactions or a large amount of oxygen inside the battery. The oxygen generated in this way may cause the volume expansion of the electrode assembly and become one of the main factors leading to the deterioration of battery performance.

[0007]

[0008] Furthermore, the conventionally used irreversible additives show a 10 -11 The extremely low powder conductivity is less than 1000 S / cm, which is close to the conductivity of an insulator. The low powder conductivity increases the resistance of the positive electrode, and in this case, a high capacity of more than 200 mAh / g is shown at a low C rate, but when the C rate increases, the high resistance accompanying the charge and discharge causes the performance to drop rapidly, so there are limitations in that the charge / discharge capacity of the battery drops and it is difficult to charge / discharge quickly.

[0009] Therefore, there is a need to develop a lithium secondary battery having improved battery safety and excellent electrical performance.

[0010] [Related technical literature]

[0011] [Patent Document]

[0012] Korean Patent Application Publication No. 10-2019-0064423 Summary of the invention

[0013] [Technical issues]

[0014] An object of the present invention is to provide a lithium secondary battery having excellent electrical properties and improved safety.

[0015] [Technical solution]

[0016] The present invention aims to solve the above problems and provides a lithium secondary battery, the lithium secondary battery comprising an electrolyte and an electrode assembly, the electrode assembly comprising a positive electrode, a negative electrode and a separator between the positive electrode and the negative electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode mixture layer located on the positive electrode current collector, wherein the positive electrode mixture layer comprises a positive electrode active material, a positive electrode additive represented by the following chemical formula 1, a conductive material and a binder, and the lithium secondary battery satisfies the following expression 1 after being charged to a state of charge (SoC) of 100% during an activation process under the conditions of a voltage of 3.5V to 4.5V and a current of 0.1C to 0.5C, being 2.0 or more and 20.0 or less:

[0017] [Chemical formula 1]

[0018] Li p Co (1-q) M 1 q O4

[0019] In the above chemical formula 1, M 1represents one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and p and q are 5≤p≤7 and 0≤q≤0.5, respectively; and

[0020] [Expression 1]

[0021] A LCO / A0

[0022] In expression 1, A LCO A represents the gas generation amount (ml / Ah) of carbon monoxide (CO) and carbon dioxide (CO2) when the positive electrode includes the positive electrode additive represented by Chemical Formula 1, and A0 represents the gas generation amount (ml / Ah) of carbon monoxide (CO) and carbon dioxide (CO2) when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1.

[0023] The lithium secondary battery may satisfy Expression 1 to be 3.0 or more.

[0024] The present invention provides a lithium secondary battery, which satisfies the following expression 2 to be less than 0.8:

[0025] [Expression 2]

[0026] B LCO / B0

[0027] In expression 2, B LCO represents the gas generation amount (ml / Ah) of propylene (C3H6) and propane (C3H8) when the positive electrode includes the positive electrode additive represented by Chemical Formula 1, and B0 represents the gas generation amount (ml / Ah) of propylene (C3H6) and propane (C3H8) when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1.

[0028] In the present invention, the positive electrode additive may have a tetragonal structure with a space group of P42 / nmc.

[0029] The positive electrode additive may be included in an amount of 0.1 to 5 parts by weight relative to 100 parts by weight of the positive electrode mixture layer.

[0030] The positive electrode active material is a lithium metal composite oxide represented by the following chemical formula 2:

[0031] [Chemical formula 2]

[0032] Li x [Ni y Co z Mn w M 2 v ]Ou

[0033] In the above chemical formula 2, M 2 represents one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and x, y, z, w, v and u are 1.0≤x≤1.30, 0.1≤y<0.95, 0.01 <z≤0.5,0.01<w≤0.5,0≤v≤0.2,1.5≤u≤4.5。

[0034] The conductive material may include one or more materials selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, super-P, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

[0035] The conductive material may be contained in an amount of 0.1 to 5 parts by weight relative to 100 parts by weight of the positive electrode mixture layer.

[0036] In the lithium secondary battery of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode mixture layer located on the negative electrode current collector and containing a negative electrode active material. In addition, the negative electrode active material may contain a carbon material and a silicon material.

[0037] Silicon materials may include silicon (Si) particles and silicon oxide (SiO X , 1≤X≤2) particles, and the content of the silicon material may be 1 to 20 parts by weight relative to 100 parts by weight of the negative electrode mixture layer.

[0038] In one embodiment, the present invention provides a method for activating a lithium secondary battery, the method comprising charging the lithium secondary battery to a state of charge (SoC) of 10% to 100% under the conditions of a voltage of 3.5V to 4.5V and a current of 0.1C to 0.5C.

[0039] [Beneficial Effects]

[0040] In the lithium secondary battery of the present invention, the positive electrode can be manufactured by including the positive electrode additive represented by Chemical Formula 1 in the positive electrode mixture layer as an irreversible additive, and since the ratio of carbon monoxide and carbon dioxide generated during the activation process can be adjusted to meet a specific range depending on whether the positive electrode additive is used, the content ratio of hydrogen and hydrocarbon relative to the total amount of gas generated during the activation process can be reduced. Therefore, the present invention has the advantages of improving the safety of the lithium secondary battery and improving the charging and discharging efficiency of the lithium secondary battery. DETAILED DESCRIPTION

[0041] The present invention is susceptible to various modifications and alternative forms, and specific embodiments thereof will be described in detail.

[0042] It should be understood, however, that the invention is not to be limited to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

[0043] It should also be understood that when used herein, the terms "comprise / include" indicate the presence of stated features, integers, steps, operations, components, parts or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts or combinations thereof.

[0044] In addition, when a layer, film, region or plate is referred to as being "formed on" another layer, film, region or plate, it includes the case where the layer, film, region or plate is directly formed on the other layer, film, region or plate, and the case where another layer, film, region or plate is inserted between the layer, film, region or plate and the other layer, film, region or plate. In contrast, when a layer, film, region or plate is referred to as being "formed under" another layer, film, region or plate, it includes the case where the layer, film, region or plate is directly formed under the other layer, film, region or plate, and the case where another layer, film, region or plate is inserted between the layer, film, region or plate and the other layer, film, region or plate. In addition, in this specification, when a component is referred to as being disposed "on" another component, it includes the case where the component is disposed above the other component and the case where the component is disposed below the other component.

[0045] In addition, in the present invention, the term "main ingredient" may refer to a component whose amount is 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 97.5% by weight or more relative to the total amount of the composition or a specific component, and in some cases, may refer to a component constituting the entire composition or a specific component, that is, a component whose amount is 100% by weight.

[0046] In addition, in the present invention, "Ah" is a unit of lithium secondary battery capacity, called "ampere-hour", and is the amount of current per hour. For example, when the battery capacity is "3000mAh", it means that the battery can be discharged at a current of 3000mA for 1 hour.

[0047] Hereinafter, the present invention will be described in more detail.

[0048] Lithium secondary battery

[0049] In one embodiment, the present invention provides a lithium secondary battery including an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode.

[0050] In this case, the positive electrode includes a positive electrode collector and a positive electrode mixture layer formed by coating, drying and pressing a positive electrode slurry on the positive electrode collector, wherein the positive electrode mixture layer has a configuration including a positive electrode active material, a positive electrode additive, a conductive material and a binder.

[0051] In a specific example, the positive electrode additive may be lithium cobalt oxide represented by the following Chemical Formula 1:

[0052] [Chemical formula 1]

[0053] Li p Co (1-q) M 1 q O4

[0054] In the above chemical formula 1, M 1 It represents one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and p and q are 5≤p≤7 and 0≤q≤0.5 respectively.

[0055] The positive electrode additive may contain an excess of lithium to provide lithium for lithium consumption caused by irreversible chemical and physical reactions at the negative electrode during initial charging, and thereby can increase the charge capacity of the battery and reduce the irreversible capacity of the battery, thereby improving the life characteristics of the battery.

[0056] Among the positive electrode additives, the positive electrode additive represented by the above chemical formula 1 has a higher lithium ion content than the nickel-containing oxide commonly used in the art, so it can supplement the lithium ion loss caused by the irreversible reaction during the initial activation of the battery, thereby significantly improving the charge / discharge capacity of the battery. In addition, compared with the iron and / or manganese-containing oxides commonly used in the art, there is no side reaction caused by the dissolution of transition metals during the charge and discharge of the battery, so the battery has excellent stability. The lithium metal oxide represented by chemical formula 1 may include Li6CoO4, Li6Co 0.5 Zn 0.5 O4、Li6Co 0.7 Zn 0.3 O4, etc.

[0057] In addition, the cathode additive represented by Chemical Formula 1 may have a tetragonal crystal structure, and may be included in a P42 / nmc space group having a twisted tetrahedral structure formed of a cobalt element and an oxygen element in the tetragonal crystal structure.

[0058] In addition, the content of the positive electrode additive can be 0.1 to 10 parts by weight relative to 100 parts by weight of the positive electrode mixture layer, specifically, the content can be 0.1 to 5 parts by weight, 0.1 to 4.5 parts by weight, 0.3 to 4 parts by weight, 0.3 to 3.5 parts by weight, 0.5 to 3 parts by weight, 0.5 to 2.5 parts by weight, 0.7 to 2 parts by weight, or 0.7 to 1.8 parts by weight relative to 100 parts by weight of the positive electrode mixture layer. In the present invention, by adjusting the amount of the positive electrode additive within the above range, the charge / discharge capacity can be prevented from being reduced due to insufficient replenishment of lithium ions lost by irreversible reactions due to the low amount of the positive electrode additive, and a large amount of oxygen can be generated during the battery charging and discharging process due to excessive positive electrode additives.

[0059] In addition, the lithium secondary battery may include the positive electrode additive represented by Chemical Formula 1, and the ratio of carbon monoxide and carbon dioxide generated during activation may be adjusted to meet a specific range, and thereby the safety of the battery may be improved and excellent performance may be achieved during charging and discharging.

[0060] Specifically, the conventionally used irreversible additives have a problem of structural instability, thereby generating a large amount of gas as charging proceeds. However, in the lithium secondary battery of the present invention, although the positive electrode contains the positive electrode additive represented by Chemical Formula 1 in the positive electrode mixture layer, the content ratio of hydrogen and hydrocarbon relative to the total amount of gas generated during activation can be reduced. Therefore, the safety of the battery can be improved, and excellent performance can be achieved during charging and discharging.

[0061] In one example, the lithium secondary battery of the present invention can be charged to a 100% state of charge (SoC) during activation under the conditions of a voltage of 3.5 V to 4.5 V and a current of 0.1 C to 0.5 C, and then the following expression 1 can be satisfied to be 2.0 or more and 20.0 or less, where the expression 1 represents the ratio (A) of the amount of carbon monoxide (CO) and carbon dioxide (CO2) generated by the lithium secondary battery containing the positive electrode additive represented by Chemical Formula 1 to the amount of carbon monoxide (CO) and carbon dioxide (CO2) generated by the lithium secondary battery without the positive electrode additive. LCO / A0). Specifically, the lithium secondary battery may satisfy the following Expression 1 of 2.5 or more, 3.0 or more, 3.2 or more, 3.5 or more, 2.5 to 20, 3.0 to 18, 3.2 to 16, or 3.5 to 15.

[0062] [Expression 1]

[0063] A LCO / A0

[0064] In expression 1, A LCO represents the gas generation amount (ml / Ah) of carbon monoxide and carbon dioxide when the positive electrode includes the positive electrode additive represented by Chemical Formula 1, and A0 represents the gas generation amount (ml / Ah) of carbon monoxide and carbon dioxide when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1.

[0065] In another example, the lithium secondary battery of the present invention can be charged to SoC 100% during the activation process, and then can satisfy the following expression 2 of 0.8 or less, which represents the ratio of the gas generation amount of propylene (C3H6) and propane (C3H8) of the lithium secondary battery containing the positive electrode additive represented by Chemical Formula 1 to the gas generation amount of propylene (C3H6) and propane (C3H8) of the lithium secondary battery without the positive electrode additive represented by Chemical Formula 1 (B LCO / B0). Specifically, the lithium secondary battery may satisfy the following Expression 2 of 0.75 or less, 0.70 or less, 0.68 or less, 0.20 to 0.75, 0.30 to 0.70, or 0.40 to 0.68.

[0066] [Expression 2]

[0067] B LCO / B0

[0068] In expression 2, B LCO represents the gas generation amount (ml / Ah) of propylene (C3H6) and propane (C3H8) when the positive electrode includes the positive electrode additive represented by Chemical Formula 1, and B0 represents the gas generation amount (ml / Ah) of propylene (C3H6) and propane (C3H8) when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1.

[0069] That is, when the lithium secondary battery of the present invention including the positive electrode additive represented by Chemical Formula 1 is charged to SoC 100% during activation, the total gas generation amount may increase, but the ratio of carbon monoxide and carbon dioxide can be adjusted as described above, and thus the content ratio of hydrogen and hydrocarbons relative to the total gas generation amount can be reduced.

[0070] Meanwhile, in the present invention, the gas generation amount is the gas generation amount (ml) relative to the capacity (Ah) of each battery cell.

[0071] The positive electrode active material is a positive electrode active material capable of reversibly intercalating and deintercalating, and may include a lithium metal composite oxide represented by the following Chemical Formula 2 as a main component:

[0072] [Chemical formula 2]

[0073] Li x [Ni y Co z Mn w M 2 v ]O u

[0074] In the above chemical formula 2, M 2 represents one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and x, y, z, w, v and u are 1.0≤x≤1.30, 0.1≤y<0.95, 0.01 <z≤0.5,0.01<w≤0.5,0≤v≤0.2,1.5≤u≤4.5。

[0075] The lithium metal composite oxide represented by Chemical Formula 2 is a composite metal oxide containing lithium and nickel, and may include a metal selected from the group consisting of LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.9 Co 0.05 Mn 0.05 O2、LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2、LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2 and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 One or more compounds of the group consisting of O2.

[0076] In addition, the content of the positive electrode active material may be 85 to 95 parts by weight, specifically 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight, relative to 100 parts by weight of the positive electrode mixture layer.

[0077] In addition, the conductive material is a material used to improve the electrical properties of the positive electrode, and materials commonly used in the art can be applied thereto. Specifically, the conductive material can include one or more materials selected from the following group: natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, super-P, channel black, furnace black, lamp black, thermal black, graphene and carbon nanotubes.

[0078] For example, carbon black or Denka black may be used as the conductive material alone or in combination.

[0079] In addition, the content of the conductive material can be 0.1 to 5 parts by weight, specifically, 0.1 to 4 parts by weight, 2 to 4 parts by weight, 1.5 to 5 parts by weight, 1 to 3 parts by weight, 0.1 to 2 parts by weight or 0.1 to 1 part by weight relative to 100 parts by weight of the positive electrode mixture layer.

[0080] In addition, the binder plays the role of bonding the positive active material, the positive electrode additive and the conductive material to each other, and any binder having this function can be used without particular limitation. Specifically, the binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate and copolymers thereof. For example, the binder may include polyvinylidene fluoride.

[0081] In addition, the content of the binder may be 1 to 10 parts by weight, specifically, 2 to 8 parts by weight or 1 to 5 parts by weight, relative to 100 parts by weight of the total amount of the positive electrode mixture layer.

[0082] In addition, the average thickness of the positive electrode mixture layer is not particularly limited, and specifically, the average thickness may be 50 to 300 μm, more specifically, 100 to 200 μm, 80 to 150 μm, 120 to 170 μm, 150 to 300 μm, 200 to 300 μm, or 150 to 190 μm.

[0083] In addition, as the positive electrode current collector of the positive electrode, a material with high conductivity that does not cause chemical changes in the battery can be used. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used. In the case of using aluminum or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector can form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and can be formed into various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc. In addition, considering the conductivity and total thickness of the positive electrode to be manufactured, the average thickness of the positive electrode current collector can be appropriately applied to be 3μm to 500μm.

[0084] In addition, the negative electrode of the lithium secondary battery of the present invention can be manufactured by coating, drying and pressing the negative electrode active material on the negative electrode collector, and can optionally further include the same conductive material, organic binder polymer, additives, etc. as in the positive electrode as needed.

[0085] In addition, the negative electrode active material may include, for example, carbon material and silicon material. Carbon material is a carbon material with carbon element as the main component, and examples of carbon material may include: graphite with complete layered crystal structure such as natural graphite, layered crystal structure with low crystallinity (graphene structure; structure of carbon layered arrangement of hexagonal honeycomb plane) soft carbon, hard carbon, artificial graphite, expanded graphite, carbon fiber, difficult graphitization carbon, carbon black, acetylene black, Ketjen black, carbon nanotubes, fullerene, activated carbon, graphene, carbon nanotubes, etc., mixed with these structures and amorphous parts, and preferably may include one or more materials selected from natural graphite, artificial graphite, graphene and carbon nanotubes. More preferably, the carbon material may include natural graphite and / or artificial graphite, and may include any one or more of graphene and carbon nanotubes and natural graphite and / or artificial graphite. In this case, the carbon material may include 0.1 to 10 parts by weight of graphene and / or carbon nanotubes relative to a total amount of 100 parts by weight of the carbon material, and more specifically, may include 0.1 to 5 parts by weight or 0.1 to 2 parts by weight of graphene and / or carbon nanotubes relative to a total amount of 100 parts by weight of the carbon material.

[0086] In addition, the silicon material has particles containing silicon (Si) as a metal component as a main component, and may include silicon (Si) particles and silicon oxide (SiO X , 1≤X≤2) particles. As an example, the silicon material may include silicon (Si) particles, silicon monoxide (SiO) particles, silicon dioxide (SiO2) particles, or a mixture thereof.

[0087] In addition, the silicon material may have a form in which crystalline particles and amorphous particles are mixed, and the ratio of the amorphous particles may be 50 to 100 parts by weight, specifically, 50 to 90 parts by weight, 60 to 80 parts by weight, or 85 to 100 parts by weight relative to 100 parts by weight of the total amount of the silicon material. In the present invention, by controlling the ratio of the amorphous particles contained in the silicon material within the above range, the thermal stability and flexibility can be improved within the range of not reducing the electrical properties of the electrode.

[0088] In addition, the negative electrode active material may include a carbon material and a silicon material, wherein the content of the silicon material may be 1 to 20 parts by weight relative to 100 parts by weight of the negative electrode mixture layer, specifically, the content may be 5 to 20 parts by weight, 3 to 10 parts by weight, 8 to 15 parts by weight, 13 to 18 parts by weight, or 2 to 7 parts by weight relative to 100 parts by weight of the negative electrode mixture layer.

[0089] In the present invention, by adjusting the amounts of carbon material and silicon material contained in the negative electrode active material within the above range, the charge capacity per unit mass can be increased while reducing lithium consumption and irreversible capacity loss during initial charge and discharge of the battery.

[0090] As an example, with respect to 100 parts by weight of the negative electrode mixture layer, the negative electrode active material may include 95±2 parts by weight of graphite, and 5±2 parts by weight of a mixture in which silicon monoxide (SiO) particles and silicon dioxide (SiO2) particles are uniformly mixed. In the present invention, by adjusting the amount of carbon material and silicon material contained in the negative electrode active material within the above range, the charging capacity per unit mass can be increased while reducing lithium consumption and irreversible capacity loss during initial charging and discharging of the battery.

[0091] In addition, the negative electrode mixture layer may have an average thickness of 100 to 200 μm, specifically, the average thickness may be 100 to 180 μm, 100 to 150 μm, 120 to 200 μm, 140 to 200 μm, or 140 to 160 μm.

[0092] In addition, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, calcined carbon, etc. can be used in the negative electrode current collector, and when copper or stainless steel is used, a material surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, like the positive electrode current collector, the negative electrode current collector may be formed with fine irregularities on its surface to enhance the binding force with the negative electrode active material, and may be formed in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc. In addition, considering the conductivity and total thickness of the negative electrode to be manufactured, the average thickness of the negative electrode current collector may be appropriately applied as 3 μm to 500 μm.

[0093] In addition, the diaphragm is arranged between the positive electrode and the negative electrode, and an insulating film with high ion permeability and mechanical strength is used as a diaphragm. The diaphragm is not particularly limited as long as it is commonly used in the art, and specifically a sheet or non-woven fabric made of chemically resistant and hydrophobic polypropylene, glass fiber, polyethylene, etc. can be used, and in some cases, a composite diaphragm in which a porous polymer material such as a sheet or a non-woven fabric is coated with inorganic particles / organic particles by an organic binder polymer can be used. In the case of using a solid electrolyte such as a polymer as an electrolyte, the solid electrolyte can also serve as a diaphragm. In addition, the diaphragm can have a hole with an average diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0094] Meanwhile, the positive electrode and the negative electrode may be wound in a jelly roll form and may be accommodated in a cylindrical battery, a prismatic battery, or a pouch type battery, or accommodated in a pouch type battery in a folded or stack-folded form, but the present invention is not limited thereto.

[0095] In addition, the lithium salt-containing electrolyte of the present invention may be composed of an electrolyte and a lithium salt, and examples of the lithium salt-containing electrolyte may include a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like.

[0096] Examples of the non-aqueous organic solvent may include aprotic organic solvents such as N-methyl-2-pyrrolidone, ethylene carbonate (EC), propylene carbonate, butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfranc, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, and the like.

[0097] Examples of the organic solid electrolyte may include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, poly-agitated lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymer materials containing ion dissociative groups, and the like.

[0098] Examples of inorganic solid electrolytes may include Li nitrides, halides, sulfates, and the like, such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, and the like.

[0099] Lithium salts are materials that are easily soluble in non-aqueous electrolytes. Examples of lithium salts may include LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, imide, etc.

[0100] In addition, in order to improve the charge and discharge characteristics, flame retardancy, etc., pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum chloride, etc. may be added to the electrolyte. In some cases, in order to impart non-flammability, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene may be further included, and in order to improve high-temperature storage characteristics, carbon dioxide gas and fluoroethylene carbonate (FEC), propylene sultone (PRS), etc. may be further included.

[0101] Activation method of lithium secondary battery

[0102] In one embodiment, the present invention provides a method for activating a lithium secondary battery, the method comprising charging the lithium secondary battery to 10% to 100% SoC under the conditions of a voltage of 3.5V to 4.5V and a current of 0.1C to 0.5C.

[0103] In a lithium secondary battery, when the initial charge is performed, lithium ions originating from lithium transition metal oxides such as positive electrode active materials and positive electrode additives contained in the positive electrode move to the carbon electrode as the negative electrode. Since lithium ions are highly reactive, lithium ions react with the carbon negative electrode to generate compounds such as Li2CO3, LiO, LiOH, etc., and a solid electrolyte interface (SEI) film is formed on the surface of the negative electrode by such compounds. The SEI film is an insulator formed when the amount of ion movement in the battery increases, and when the SEI film is formed, the SEI film prevents lithium ions from reacting with other materials at the negative electrode during subsequent secondary battery charging, and the SEI film acts as a type of ion tunnel, allowing only lithium ions to pass through it. After the SEI film is formed, lithium ions do not react with the negative electrode or other materials, so that the amount of lithium ions can be reversibly maintained, and the charging and discharging of the secondary battery can be reversibly maintained, resulting in an improved life of the secondary battery, and the SEI film is not easy to collapse even when placed at high temperatures or repeatedly charged and discharged, and the thickness of the battery changes less.

[0104] Therefore, in the activation method of the present invention, lithium ions originating from the positive electrode active material and / or the positive electrode additive of the positive electrode form a SEI film on the surface of the negative electrode, and current is applied to the lithium secondary battery to cause delithiation and decomposition of the positive electrode additive, thereby forming a gas from the positive electrode additive inside the battery while the battery is charged.

[0105] In addition, in order to reduce the resistance of the electrode, the activation operation can be performed at a temperature higher than room temperature. Specifically, each activation operation can be performed at a temperature of 40°C to 70°C, more specifically, at a temperature of 40°C to 60°C, 45°C to 60°C, 50°C to 65°C, 50°C to 60°C, or 52°C to 58°C. In the present invention, by performing each activation operation under a temperature condition satisfying the above range, the secondary battery can be charged under a condition of lower positive electrode resistance, thereby improving the efficiency of the activation method and improving the uniformity of the SEI film formed in the first activation operation.

[0106] Furthermore, each activation operation may be performed for 1 to 100 minutes, specifically, 1 to 100 minutes, 1 to 60 minutes, 1 to 40 minutes, 10 to 40 minutes, 20 to 40 minutes, 10 to 30 minutes, or 1 to 10 minutes.

[0107] In addition, a process of degassing the gas formed inside the lithium secondary battery that has been activated may be performed. In the lithium secondary battery that has been activated, a large amount of gas is generated due to the delithiation and / or decomposition of the positive electrode additive contained in the mixture layer of the positive electrode, and when the generated gas is not removed, it may cause the battery to swell with the gas. However, in the present invention, the expansion phenomenon can be prevented by additionally degassing the lithium secondary battery after the activation operation.

[0108] Here, degassing can be performed by pressurizing the outer surface of the lithium secondary battery using a pressurizing device such as a jig, and the pressurization can be performed at 10 kgf / cm 2 Up to 900kgf / cm 2 The process is performed for 4 to 6 seconds, but the present invention is not limited thereto.

[0109] In this case, the gas removed when the lithium secondary battery is degassed may satisfy Expression 1 of 2.0 or more and 20.0 or less.

[0110] [Expression 1]

[0111] A LCO / A0

[0112] In expression 1, A LCO A represents the gas generation amount (ml / Ah) of carbon monoxide (CO) and carbon dioxide (CO2) when the positive electrode includes the positive electrode additive represented by Chemical Formula 1, and A0 represents the gas generation amount (ml / Ah) of carbon monoxide (CO) and carbon dioxide (CO2) when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1.

[0113] In addition, the method for activating a lithium secondary battery of the present invention may further include an aging operation for aging the activated lithium secondary battery after performing the third activation operation. The aging operation may stabilize and reform the SEI film to have a uniform thickness through thermal energy and electrochemical energy. To this end, the aging operation may be performed at 20 to 40° C., more specifically at 20 to 30° C. or 20 to 25° C. for 0.5 to 30 hours.

[0114] [Example]

[0115] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

[0116] However, the following Examples and Comparative Examples are only for illustrating the present invention, and the contents of the present invention are not limited to the Examples and Comparative Examples described below.

[0117] Example 1

[0118] 1) Manufacturing of lithium secondary batteries

[0119] Weigh 96 parts by weight of LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, 1 part by weight of Li6CoO4 as a positive electrode additive, 2 parts by weight of PVdF as a binder and 3 parts by weight of carbon black as a conductive material (positive electrode active material: positive electrode additive = 99.15:0.85) were mixed in an N-methylpyrrolidone (NMP) solvent to prepare a positive electrode mixture layer slurry. The positive electrode mixture layer slurry was coated on an aluminum foil, dried and then rolled to form a positive electrode containing a positive electrode mixture layer (average thickness: 130 μm).

[0120] Natural graphite as a negative electrode active material, carbon black conductive material and PVdF binder were mixed in an N-methylpyrrolidone solvent at a weight ratio of 85:10:5 to prepare a negative electrode mixture layer slurry. The negative electrode mixture layer slurry was coated on a copper foil to manufacture a negative electrode including a negative electrode mixture layer (average thickness: 180 μm).

[0121] A separator (thickness: about 16 μm) made of a porous polyethylene (PE) film is laminated to be inserted between the manufactured positive electrode and the manufactured negative electrode to manufacture an electrode assembly. After the electrode assembly is placed in the battery case, the electrolyte is injected into the case, and then the electrode assembly is placed at room temperature for 3 days to fully impregnate the electrolyte, thereby manufacturing a lithium secondary battery. In this case, the electrolyte is prepared by dissolving lithium hexafluorophosphate (LiPF6) at a concentration of 1.0 M in an organic solvent composed of EC / DMC / ethyl methyl carbonate (EMC) (the mixed volume of EC / DMC / EMC is 3 / 4 / 3).

[0122] 2) Activation of lithium secondary batteries

[0123] The manufactured lithium secondary battery was activated. Specifically, the activation operation was performed at a temperature of 55°C by charging the secondary battery under the conditions of a 0.2C constant current and a 4.3V voltage so that the capacity (SoC) became 100%. After charging, the gas in the battery was degassed using a jig.

[0124] Examples 2 and 3 and Comparative Examples 1 to 3. Fabrication and Activation of Lithium Secondary Batteries

[0125] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the amounts of the positive electrode active material and the positive electrode additive were changed when manufacturing the lithium secondary battery. An activation operation was performed on the manufactured lithium secondary battery.

[0126] In this case, the compositions of the respective positive electrodes manufactured in Examples and Comparative Examples are shown in Table 1 below.

[0127] [Table 1]

[0128]

[0129] Experimental example

[0130] In order to evaluate the performance of the positive electrode for a lithium secondary battery of the present invention, an experiment was conducted as follows.

[0131] A. Analysis of the composition and amount of gases generated during activation

[0132] The components and amounts of various gases generated inside the lithium secondary batteries during the activation process (formation) of the lithium secondary batteries of Examples and Comparative Examples were analyzed, and the results of the analysis are shown in Table 2 below.

[0133] [Table 2]

[0134]

[0135] As shown in Table 2 above, the gas generation amount of the lithium secondary battery containing the positive electrode additive is higher than that of the lithium secondary battery without the positive electrode additive. In particular, it can be seen that the gas generation amount (ml / Ah) relative to the battery capacity increases as the amount of the positive electrode additive increases.

[0136] The amounts of carbon monoxide and carbon dioxide generated inside the lithium secondary batteries during the activation (formation) of the lithium secondary batteries of the examples and comparative examples were evaluated. The evaluation results are shown in Table 3 below.

[0137] [Table 3]

[0138]

[0139] Referring to Table 3 above, the gas generation of carbon monoxide and carbon dioxide of the lithium secondary battery containing the positive electrode additive is higher than that of the lithium secondary battery without the positive electrode additive. In particular, it can be seen that as the amount of the positive electrode additive increases, the gas generation of carbon monoxide and carbon dioxide increases. The amount of hydrogen and hydrocarbons other than carbon monoxide and carbon dioxide in the gas generated during the activation process is shown in Table 4 below.

[0140] [Table 4]

[0141]

[0142] Referring to Table 4 above, it was confirmed that when the positive electrode additive was used, the total amount of gas generated during the activation process increased, but by adjusting the ratio of carbon monoxide and carbon dioxide to meet the specific range, the content ratio of hydrogen and hydrocarbons relative to the total amount of gas generated during the activation process decreased. In particular, in the case of Example 2, it was confirmed that the gas generation amount of hydrogen and hydrocarbons relative to the total amount of gas generated was 0.49. It was confirmed by gas composition and content analysis that the lithium secondary battery activated under the conditions of the embodiment and the comparative example met A LCO / A0 value is 3.0 or more.

[0143] On the other hand, for the activated lithium secondary battery of Comparative Example 3, the total amount of gas generation was too high at 169.2 ml, resulting in volume expansion of the electrode assembly, etc., which led to deterioration of battery performance.

[0144] In addition, the amounts of propylene and propane generated inside the lithium secondary batteries during the activation process (formation) of the lithium secondary batteries of Examples and Comparative Examples were evaluated. The evaluation results are shown in Table 5 below.

[0145] [Table 5]

[0146]

[0147] It was confirmed through gas composition and content analysis that the lithium secondary batteries activated under the conditions of the examples and comparative examples satisfied the following Expression 2 to be 0.8 or less.

[0148] Cycle life performance evaluation

[0149] The lithium secondary batteries activated in the examples and comparative examples were discharged to 2 V (C rate = 0.1 C), and then the capacity retention rate [%] was measured while charging and discharging 100 times (n = 100) at 25° C. under the conditions of a charge termination voltage of 4.25 V, a discharge termination voltage of 2.5 V, and 0.5 C / 0.5 C. In this case, the capacity retention rate was calculated using the following equation 1, and the calculation results are shown in Table 6 below:

[0150] [Equation 1]

[0151] Capacity retention rate (%) = (discharge capacity of n charge / discharge times / discharge capacity of 1 charge / discharge time) × 100

[0152] [Table 6]

[0153] Initial charge capacity [mAh / g] Capacity retention after 100 charge / discharge cycles [%] Example 1 712 98％ Example 2 721 97％ Comparative Example 1 709 89％ Comparative Example 2 706 92％ Comparative Example 3 692 94％

[0154] Referring to Table 6 above, it is confirmed that the initial charge capacity of the lithium secondary battery activated in the embodiment is 710 mAh / g or more, and the capacity retention rate after 100 cycles of charge and discharge is 97% or more, while the lithium secondary battery activated in the comparative example has lower initial charge capacity and capacity retention rate after 100 cycles of charge and discharge than the lithium secondary battery in the embodiment.

[0155] The above results confirm that in the lithium secondary battery of the present invention, the gas generation amount of carbon monoxide and carbon dioxide increases with the increase in the amount of the positive electrode additive represented by Chemical Formula 1 as an irreversible additive contained in the positive electrode mixture layer, but by adjusting the ratio of carbon monoxide and carbon dioxide within a specific range, the content ratio of hydrogen and hydrocarbon relative to the total amount of gas generated during activation is reduced. Therefore, the lithium secondary battery of the present invention not only has the advantage of improving safety, but also can easily improve the charging and discharging efficiency of the lithium secondary battery.

[0156] Although exemplary embodiments of the present invention and their advantages have been described above in detail, those skilled in the art should understand that various changes, substitutions and alterations may be made herein without departing from the scope of the invention as defined by the appended claims.

[0157] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the appended claims.

Claims

1. A lithium secondary battery comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode, a negative electrode and a separator between the positive electrode and the negative electrode, in, The positive electrode includes a positive electrode current collector and a positive electrode mixture layer, the positive electrode mixture layer is located on the positive electrode current collector and contains a positive electrode active material, a positive electrode additive represented by the following Chemical Formula 1, a conductive material and a binder, wherein the content of the positive electrode additive is 0.5 to 5 parts by weight relative to 100 parts by weight of the positive electrode mixture layer, and The lithium secondary battery satisfies the following Expression 1 of 2.0 or more and 20.0 or less after being charged to a state of charge (SoC) of 100% during activation under conditions of a voltage of 3.5 V to 4.5 V and a current of 0.1 C to 0.5 C: [Chemical formula 1] Li p Co (1-q) M 1 q O4 In the above chemical formula 1, M 1 represents one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and p and q are 5≤p≤7 and 0≤q≤0.5, respectively; and [Expression 1] TO LCO / A0 In Expression 1, A LCO represents the gas generation amount of carbon monoxide (CO) and carbon dioxide (CO2) when the positive electrode contains the positive electrode additive represented by Chemical Formula 1, in ml / Ah, and A0 represents the gas generation amount of carbon monoxide (CO) and carbon dioxide (CO 2 ) when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1, and the unit is ml / Ah.

2. The lithium secondary battery according to claim 1, wherein The lithium secondary battery satisfies Expression 1 of 3.0 or more.

3. The lithium secondary battery according to claim 1, wherein The lithium secondary battery satisfies the following expression 2 which is less than 0.8: [Expression 2] B LCO / B0 In expression 2, B LCO represents the gas generation amount of propylene (C3H6) and propane (C3H8) when the positive electrode contains the positive electrode additive represented by Chemical Formula 1, in ml / Ah, and B0 represents the gas generation amount of propylene (C3H6) and propane (C3H8) when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1, and the unit is ml / Ah.

4. The lithium secondary battery according to claim 1, wherein The positive electrode additive has a tetragonal structure with a space group of P42 / nmc.

5. The lithium secondary battery according to claim 1, wherein The content of the positive electrode additive is 0.5 to 4 parts by weight relative to 100 parts by weight of the positive electrode mixture layer.

6. The lithium secondary battery according to claim 1, wherein The positive electrode active material is a lithium metal composite oxide represented by the following chemical formula 2: [Chemical formula 2] Li x [Ni y Co z Mr w M 2 v ]O u In the above chemical formula 2, M 2 represents one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, v, and u are 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 0.95, 0.01 < z ≤ 0.5, 0.01 < w ≤ 0.5, 0 ≤ v ≤ 0.2, and 1.5 ≤ u ≤ 4.5, respectively.

7. The lithium secondary battery according to claim 1, wherein: The conductive material includes one or more materials selected from the group consisting of natural graphite, artificial graphite, carbon black, graphene, and carbon nanotubes.

8. The lithium secondary battery according to claim 7, wherein: The carbon black is selected from the group consisting of acetylene black, ketjen black, super-P, channel black, furnace black, lamp black and thermal black.

9. The lithium secondary battery according to claim 7, wherein: The carbon black is Denka black.

10. The lithium secondary battery according to claim 1, wherein The conductive material may be contained in an amount of 0.1 to 5 parts by weight relative to 100 parts by weight of the positive electrode mixture layer.

11. The lithium secondary battery according to claim 1, wherein The negative electrode includes a negative electrode current collector and a negative electrode mixture layer located on the negative electrode current collector and containing a negative electrode active material. Wherein, the negative electrode active material contains carbon material and silicon material.

12. The lithium secondary battery according to claim 11, wherein The silicon material includes one or more of silicon (Si) particles and silicon oxide particles, wherein the silicon oxide is represented by SiO X , 1≤X≤2.

13. The lithium secondary battery according to claim 11, wherein The silicon material may be contained in an amount of 1 to 20 parts by weight relative to 100 parts by weight of the negative electrode mixture layer. 14 . A method of activating the lithium secondary battery of claim 1 , comprising charging the lithium secondary battery to a state of charge (SoC) of 10% to 100% under the conditions of a voltage of 3.5V to 4.5V and a current of 0.1C to 0.5C.

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