Lithium secondary battery containing positive electrode additive

Abstract

The present invention relates to a lithium secondary battery, and the positive electrode of the lithium secondary battery is manufactured by incorporating a positive electrode additive represented by Chemical Formula 1 as an irreversible additive into a positive electrode composite layer. Depending on whether or not the positive electrode additive is used, the ratio of carbon monoxide and carbon dioxide generated during an activation process can be adjusted to satisfy a specific range, thereby reducing the content of hydrogen and hydrocarbons relative to the total amount of gas generated during the activation process. This has the advantages of improving the safety of the lithium secondary battery as well as improving the charge / discharge efficiency of the lithium secondary battery.

Description

[Technical field]

[0001] The present invention relates to a lithium secondary battery containing a positive electrode additive, and more particularly to a lithium secondary battery containing a 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 dated June 1, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference. [Background technology]

[0003] Recently, the demand for secondary batteries as an energy source has been increasing rapidly. Among such secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Graphite is mainly used as the negative electrode material for lithium secondary batteries, but since graphite has a small capacity per unit mass of 372 mAh / g, it is difficult to increase the capacity of lithium secondary batteries. As a result, in order to increase the capacity of lithium secondary batteries, negative electrode materials that form intermetallic compounds with lithium, such as silicon, tin, and their oxides, have been developed and used as non-carbon-based negative electrode materials that have a higher energy density than graphite. However, such non-carbon-based negative electrode materials have a problem that although they have a large capacity, they have a low initial efficiency, resulting in a large amount of lithium consumption during initial charging and discharging, and a large irreversible capacity loss.

[0005] In this regard, a method has been proposed to overcome the irreversible capacity loss of the negative electrode by using a material that can provide a lithium ion source or reservoir for the positive electrode material and is electrochemically active after the first cycle so as not to degrade the performance of the entire battery. Specifically, a method is known in which an oxide containing an excess amount of lithium, such as Li6CoO4, is applied to the positive electrode as a sacrificial positive electrode material or an irreversible additive (or overdischarge inhibitor).

[0006] Meanwhile, conventional irreversible additives such as Li6CoO4 are generally prepared by reacting cobalt oxide with an excess amount of lithium oxide. The thus-prepared irreversible additive is structurally unstable and generates a large amount of oxygen gas (O2) as charging proceeds, as described below. If the irreversible additive does not completely react during initial charging of the secondary battery, i.e., during activation of the battery, it may react during subsequent charging and discharging processes to generate side reactions and a large amount of oxygen gas inside the battery. The oxygen gas thus generated may induce volume expansion of the electrode assembly, and act as one of the main factors that cause deterioration of battery performance.

[0007] [ka]

[0008] In addition, the non-reversible additives that are commonly used in the past are almost non-conductive due to their 2D percolating network, with a resistance of ~10 -11 It exhibits very low powder electrical conductivity of 1.5 S / cm. Such low powder electrical conductivity increases the electrical resistance of the positive electrode, and in this case, it shows a large capacity of over 200mAh / g at a low C-rate, but as the C-rate increases, the performance rapidly decreases as charging and discharging proceeds due to the large resistance, so there is a limit in that high-speed charging and discharging is difficult.

[0009] Therefore, there is a demand for the development of lithium secondary batteries that not only have excellent electrical performance but also have improved battery safety. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Korean Patent Publication No. 10-2019-0064423 Summary of the Invention [Problem to be solved by the invention]

[0011] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a lithium secondary battery having excellent electrical performance and improved safety. [Means for solving the problem]

[0012] To solve the above problems, In one embodiment, the present invention comprises: an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; An electrolyte solution, The positive electrode includes a positive electrode current collector and a positive electrode mixture layer located on the positive electrode current collector and including a positive electrode active material, a positive electrode additive represented by the following chemical formula 1, a conductive material, and a binder; The lithium secondary battery satisfies the following formula 1 of 2.0 or more and 20.0 or less after charging to SOC 100% in an activation step under conditions of a voltage of 3.5 to 4.5 V and a current of 0.1 to 0.5 C:

[0013] [Chemical formula 1] Li p Co (1-q) M 1 q O4

[0014] In the above chemical formula 1, M 1 is 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; p and q are 5≦p≦7 and 0≦q≦0.5, respectively;

[0015] [Formula 1] A LCO / A0

[0016] In formula 1, ALCO indicates the amount (ml) of carbon monoxide (CO) and carbon dioxide (CO2) gas generated when the positive electrode contains the positive electrode additive represented by chemical formula 1, A0 indicates the amount (ml) of carbon monoxide (CO) and carbon dioxide (CO2) gas generated when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1.

[0017] Specifically, the lithium secondary battery can satisfy Formula 1 of 3.0 or more.

[0018] The present invention also provides a lithium secondary battery, in which the following formula 2 satisfies 0.8 or less:

[0019] [Formula 2] B LCO / B0

[0020] In formula 2, B LCO indicates the amount (ml) of propene (C3H6) and propane (C3H8) gas generated when the positive electrode contains the positive electrode additive represented by chemical formula 1, B0 indicates the amount (ml) of gas generated from propene (C3H6) and propane (C3H8) when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1.

[0021] On the other hand, in the present invention, the positive electrode additive may have a tetragonal structure whose space group is P42 / nmc.

[0022] The content of the positive electrode additive may be 0.1 to 5 parts by weight with respect to 100 parts by weight of the positive electrode mixture layer.

[0023] The positive electrode active material may be a lithium metal composite oxide represented by the following Chemical Formula 2:

[0024] [Chemical formula 2] Li x [Ni y Co z Mn w M 2v ]O u

[0025] In the above chemical formula 2, M 2 is 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; x, y, z, w, v, and u are within the range of 1.0≦x≦1.30, 0.1≦y<0.95, and 0.01, respectively. <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0026] In addition, the conductive material may include at least one 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.

[0027] 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.

[0028] In the lithium secondary battery according to the present invention, the negative electrode comprises 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. The negative electrode active material may contain a carbon material and a silicon material.

[0029] The silicon material may be silicon (Si) particles and silicon oxide (SiO X , 1≦X≦2) particles, and the silicon material may be included in an amount of 1 to 20 parts by weight based on 100 parts by weight of the negative electrode mixture layer.

[0030] In one embodiment, the present invention provides a method for producing a composition comprising: The present invention provides a method for activating a lithium secondary battery, which includes a process of charging the lithium secondary battery to SOC 10% to 100% under conditions of a voltage of 3.5 to 4.5 V and a current of 0.1 to 0.5 C. Effect of the Invention

[0031] In the lithium secondary battery according to the present invention, the positive electrode is manufactured by incorporating a positive electrode additive represented by Chemical Formula 1 in the positive electrode composite layer as a non-reversible additive, and the ratio of carbon monoxide and carbon dioxide generated during the activation process can be adjusted to satisfy a specific range depending on whether or not the positive electrode additive is used, thereby reducing the content of hydrogen and hydrocarbons relative to the total amount of gas generated during the activation process. As a result, the present invention has the advantage of improving not only the safety of the lithium secondary battery, but also the charge and discharge efficiency of the lithium secondary battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] While the present invention may be modified in many ways and may have a variety of embodiments, a particular embodiment will be described in detail.

[0033] It should be understood, however, that this is not intended to limit the invention to the particular embodiment, but rather to include all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0034] In the present invention, the terms "comprise" or "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0035] In addition, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion in between. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion in between. In addition, in the present application, being "located on" may include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0036] In addition, in the present invention, a "major component" means 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 of the total weight of the composition or specific component, and in some cases, it can also mean 100% by weight when it constitutes the entire composition or specific component.

[0037] In the present invention, "Ah" is a unit of capacity of a lithium secondary battery, and is called "ampere-hour" and means the amount of current per hour. For example, if a battery capacity is "3000mAh", it means that it can be discharged at a current of 3000mA for one hour.

[0038] The present invention will now be described in more detail.

[0039] <Lithium secondary battery> In one embodiment, the present invention comprises: A positive electrode and A negative electrode; an electrode assembly including a separator disposed between a positive electrode and a negative electrode; and an electrolyte.

[0040] In this case, the positive electrode includes a positive electrode current collector and a positive electrode mixture layer produced by applying a positive electrode slurry onto the positive electrode current collector, drying and pressing the positive electrode mixture layer, and the positive electrode mixture layer has a configuration containing a positive electrode active material, a positive electrode additive, a conductive material, and a binder.

[0041] In a specific example, the positive electrode additive may be lithium cobalt oxide represented by the following Chemical Formula 1:

[0042] [Chemical formula 1] Li p Co (1-q) M 1 q O4

[0043] In the above chemical formula 1, M 1 is 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; p and q are 5≦p≦7 and 0≦q≦0.5, respectively.

[0044] The positive electrode additive contains an excess of lithium and can provide lithium to replace lithium consumption that occurs due to irreversible chemical and physical reactions at the negative electrode during initial charging, thereby increasing the charging capacity of the battery and reducing the irreversible capacity, thereby improving the life characteristics.

[0045] Among them, the positive electrode additive represented by the above formula 1 has a higher lithium ion content than nickel-containing oxides commonly used in the industry, and therefore can replenish lithium ions lost in irreversible reactions during initial activation of the battery, thereby significantly improving the charge / discharge capacity of the battery. Also, compared to iron- and / or manganese-containing oxides commonly used in the industry, there is no side reaction caused by the elution of transition metals during charging and discharging of the battery, and therefore the battery has excellent stability. Examples of lithium metal oxides represented by the formula 1 include Li6CoO4, Li6Co 0.5 Zinc 0.5 O4, Li6Co 0.7 Zinc 0.3 It may also include O4.

[0046] In addition, the positive electrode additive represented by the above formula 1 may have a tetragonal crystal structure, and among them, it may be included in the space group P42 / nmc having a distorted tetrahedral structure formed by cobalt and oxygen elements.

[0047] The positive electrode additive may be included in an amount of 0.1 to 10 parts by weight relative to 100 parts by weight of the positive electrode mixture layer, specifically, 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. By adjusting the content of the positive electrode additive within the above range, the present invention can prevent a decrease in charge / discharge capacity due to a low content of the positive electrode additive that is not sufficient to replenish lithium ions lost due to an irreversible reaction, and can prevent a large amount of oxygen gas from being generated during charging and discharging of the battery due to an excessive amount of the positive electrode additive.

[0048] Furthermore, the lithium secondary battery contains the positive electrode additive represented by Chemical Formula 1, and adjusts the ratio of carbon monoxide and carbon dioxide generated during an activation process to satisfy a specific range, thereby improving the safety of the battery and achieving excellent performance during charging and discharging.

[0049] Specifically, the irreversible additives commonly used in the past have a problem of being structurally unstable and generating a large amount of gas as charging proceeds, as described below. However, in the lithium secondary battery of the present invention, the positive electrode contains the positive electrode additive represented by Chemical Formula 1 in the positive electrode mixture layer, and yet the proportion of hydrogen and hydrocarbon content in the total amount of gas generated during the activation process can be reduced. This improves the safety of the battery and realizes excellent performance during charging and discharging.

[0050] As an example, the lithium secondary battery according to the present invention is charged to 100% SOC in an activation process under conditions of a voltage of 3.5 to 4.5 V and a current of 0.1 to 0.5 C, and the ratio A of the amount of carbon monoxide (CO) and carbon dioxide (CO2) generated in a lithium secondary battery containing a positive electrode additive represented by Chemical Formula 1 to the amount of carbon monoxide (CO) and carbon dioxide (CO2) generated in a lithium secondary battery not containing a positive electrode additive is LCO The following formula 1 representing / A0 can satisfy 2.0 or more and 20.0 or less. Specifically, it can satisfy 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:

[0051] [Formula 1] A LCO / A0

[0052] In formula 1, A LCO indicates the amount of carbon monoxide and carbon dioxide gas generated (ml / Ah) when the positive electrode contains the positive electrode additive represented by chemical formula 1, A0 indicates the amount of carbon monoxide and carbon dioxide gas generated (ml / Ah) when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1.

[0053] As another example, the lithium secondary battery according to the present invention, after charging to 100% SOC in the activation process, has a ratio B of the amount of gas generated of propene (C3H6) and propane (C3H8) in the lithium secondary battery containing the positive electrode additive represented by Chemical Formula 1 to the amount of gas generated of propene (C3H6) and propane (C3H8) in the lithium secondary battery not containing the positive electrode additive represented by Chemical Formula 1. LCO The following formula 2 representing / B0 can satisfy 0.8 or less. Specifically, it can satisfy 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.

[0054] [Formula 2] B LCO / B0

[0055] In formula 2, BLCO indicates the amount of gas generated (ml / Ah) of propene (C3H6) and propane (C3H8) when the positive electrode contains the positive electrode additive represented by chemical formula 1, B0 indicates the amount of gas generated (ml / Ah) of propene (C3H6) and propane (C3H8) when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1.

[0056] That is, in the lithium secondary battery according to the present invention, when the positive electrode additive represented by Chemical Formula 1 is contained after charging to SOC 100% in the activation process, the total gas generation amount can be increased, but the content of hydrogen and hydrocarbon relative to the total gas generation amount can be reduced by adjusting the ratio of carbon monoxide and carbon dioxide as described above.

[0057] On the other hand, in the present invention, the amount of gas generated means the amount of gas generated (ml) relative to the capacity (Ah) of each battery cell.

[0058] The positive electrode active material is a positive electrode active material capable of reversible intercalation and deintercalation, and may contain a lithium metal composite oxide represented by the following chemical formula 2 as a main component:

[0059] [Chemical formula 2] Li x [Ni y Co z Mn w M 2 v ]O u

[0060] In the above chemical formula 2, M 2 is 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; x, y, z, w, v, and u are within the range of 1.0≦x≦1.30, 0.1≦y<0.95, and 0.01, respectively. <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0061] The lithium metal composite oxide represented by the above chemical formula 2 is a composite metal oxide containing lithium and nickel, 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 The gas may contain one or more compounds selected from the group consisting of O2.

[0062] 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.

[0063] In addition, the conductive material is used to improve the electrical performance of the positive electrode, and may be any conductive material commonly used in the art. Specifically, the conductive material may include at least one 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.

[0064] As an example, the conductive material may be carbon black or denka black, which may be used alone or in combination.

[0065] The conductive material may be contained in an amount of 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.

[0066] In addition, the binder functions to bind the positive electrode active material, the positive electrode additive, and the conductive material to each other, and may be used without any particular limitation as long as it has such a function. 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, polymethylmethacrylate, and copolymers thereof. As an example, the binder may include polyvinylidene fluoride.

[0067] The binder may be contained in an amount of 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 entire mixture layer.

[0068] Additionally, the average thickness of the composite layer is not particularly limited, but may be specifically 50 μm to 300 μm, and more specifically 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0069] In addition, the positive electrode can be a positive electrode current collector having high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used, and in the case of aluminum or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector can be formed with fine irregularities on the surface to increase the adhesive force of the positive electrode active material, and can be in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc. In addition, the average thickness of the current collector can be appropriately applied to 3 to 500 μm in consideration of the conductivity and total thickness of the positive electrode to be manufactured.

[0070] In addition, the negative electrode of the lithium secondary battery according to the present invention is manufactured by applying a negative electrode active material onto a negative electrode current collector, drying and pressing the negative electrode active material, and may further selectively include the same conductive material, organic binder polymer, additives, etc. as those of the positive electrode, as necessary.

[0071] The negative electrode active material may include, for example, a carbon material and a silicon material. The carbon material means a carbon material mainly composed of carbon atoms, and examples of such carbon materials include graphite having a perfect layered crystal structure like natural graphite, soft carbon having a low crystalline layered crystal structure (graphene structure; a structure in which hexagonal honeycomb-shaped carbon planes are arranged in layers), and hard carbon in which such a structure is mixed with a non-crystalline portion, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, acetylene black, ketjen black, carbon nanotubes, fullerene, activated carbon, graphene, carbon nanotubes, etc., and preferably, may include one or more selected from the group consisting of natural graphite, artificial graphite, graphene, and carbon nanotubes. More preferably, the carbon material may include natural graphite and / or artificial graphite, and may include at least one of graphene and carbon nanotubes together with the natural graphite and / or artificial graphite. In this case, the carbon substance may contain 0.1 to 10 parts by weight of graphene and / or carbon nanotubes relative to 100 parts by weight of the total carbon substance, and more specifically, may contain 0.1 to 5 parts by weight, or 0.1 to 2 parts by weight of graphene and / or carbon nanotubes relative to 100 parts by weight of the total carbon substance.

[0072] The silicon substance is a particle containing silicon (Si) as a metal component as a main component, and is a silicon (Si) particle and a 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 of these particles.

[0073] In addition, the silicon material may have a mixed form of crystalline particles and amorphous particles, 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, based on 100 parts by weight of the total silicon material. By controlling the ratio of the amorphous particles contained in the silicon material within the above range, the present invention can improve thermal stability and flexibility without deteriorating the electrical properties of the electrode.

[0074] In addition, the silicon material may include a carbon material and a silicon material, and may be included in an amount of 1 to 20 parts by weight relative to 100 parts by weight of the negative electrode composite layer. Specifically, the silicon material may be included in an amount of 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 composite layer.

[0075] By adjusting the contents of the carbon material and silicon material contained in the negative active material within the above ranges, the present invention can reduce the lithium consumption and irreversible capacity loss during the initial charge and discharge of the battery, and improve the charge capacity per unit mass.

[0076] For example, the negative electrode active material may include 95±2 parts by weight of graphite and 5±2 parts by weight of a mixture of silicon monoxide (SiO) particles and silicon dioxide (SiO2) particles uniformly mixed, relative to 100 parts by weight of the negative electrode composite layer. By adjusting the contents of the carbon material and silicon material contained in the negative electrode active material within the above ranges, the present invention can reduce lithium consumption and irreversible capacity loss during initial charging and discharging of the battery, and improve the charging capacity per unit mass.

[0077] The negative electrode mixture layer may have an average thickness of 100 μm to 200 μm, specifically, 100 μm to 180 μm, 100 μm to 150 μm, 120 μm to 200 μm, 140 μm to 200 μm, or 140 μm to 160 μm.

[0078] In addition, the negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. can be used. In the case of copper or stainless steel, it is also possible to use a material that has been surface-treated with carbon, nickel, titanium, silver, etc. In addition, the negative electrode current collector can be formed with fine irregularities on the surface in the same manner as the positive electrode current collector to strengthen the binding force with the negative electrode active material, and can be in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc. In addition, the average thickness of the negative electrode current collector can be appropriately applied to 3 to 500 μm in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0079] The separator is a thin insulating membrane having high ion permeability and mechanical strength, which is interposed between the positive and negative electrodes. The separator is not particularly limited as long as it is one commonly used in the industry. Specifically, a sheet or nonwoven fabric made of chemically resistant and hydrophobic polypropylene, glass fiber, or polyethylene may be used. In some cases, a composite separator made of a porous polymer substrate such as the sheet or nonwoven fabric and inorganic particles / organic particles coated with an organic binder polymer may be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator. The pore diameter of the separator may be an average of 0.01 to 10 μm, and the thickness may be an average of 5 to 300 μm.

[0080] Meanwhile, the positive and negative electrodes may be wound in a jelly roll form and housed in a cylindrical battery, a prismatic battery, or a pouch battery, or may be housed in a pouch battery in a folded or stack-and-folded form, but is not limited thereto.

[0081] The lithium salt-containing electrolyte according to the present invention may be composed of an electrolyte and a lithium salt. The electrolyte may be a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte.

[0082] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0083] Examples of the organic solid electrolyte that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymerizing agents containing an ionic dissociation group.

[0084] Examples of the inorganic solid electrolyte that can be used include nitrides, halides, and sulfates of Li, such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2.

[0085] The lithium salt is a substance that is easily dissolved in a non-aqueous electrolyte, and examples of the lithium salt include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylates, lithium tetraphenylboronate, imides, etc. can be used.

[0086] In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the electrolyte may contain, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be further contained, and in order to improve high-temperature storage characteristics, carbon dioxide gas may be further contained, and fluoroethylene carbonate (FEC), propene sultone (PRS), etc. may be further contained.

[0087] <How to activate lithium secondary batteries> In one embodiment, the present invention comprises: The present invention provides a method for activating a lithium secondary battery, which includes a process of charging the lithium secondary battery to SOC 10% to 100% under conditions of a voltage of 3.5 to 4.5 V and a current of 0.1 to 0.5 C.

[0088] When a lithium secondary battery is initially charged, lithium ions originating from the positive electrode active material and lithium transition metal oxides such as positive electrode additives contained in the positive electrode move to the carbon electrode of the negative electrode. The lithium ions are highly reactive and react with the carbon negative electrode to form compounds such as Li2CO3, LiO, and LiOH, which form an SEI film on the surface of the negative electrode. The SEI film is a non-conductor formed when the amount of ion movement in the battery increases. When the SEI film is formed, it prevents the lithium ions from reacting with other materials at the negative electrode during subsequent charging of the secondary battery, and acts as a kind of ion tunnel to allow only lithium ions to pass through. When such an SEI film is formed, the lithium ions do not react with the negative electrode or other materials, so the amount of lithium ions is reversibly maintained, and the charge and discharge of the secondary battery is reversibly maintained, thereby improving the life of the secondary battery. It does not easily break down even when left at high temperatures or when repeatedly charged and discharged, so there is little change in the thickness of the battery.

[0089] As a result, in the activation method according to the present invention, lithium ions derived from the positive electrode active material of the positive electrode and / or the positive electrode additive form an SEI film (solid electrolyte interphase) on the surface of the negative electrode, and a current is applied to the lithium secondary battery to induce delithiation and decomposition of the lithium ions of the positive electrode additive, thereby forming gas derived from the positive electrode additive inside the battery while charging the battery.

[0090] In addition, the activation step may be performed at a temperature higher than room temperature in order to reduce the resistance of the electrode. Specifically, the activation steps may be performed at a temperature of 40° C. to 70° C., and 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, the activation steps are performed at temperatures that satisfy the above ranges, so that the secondary battery can be charged under lower resistance conditions of the positive electrode, thereby increasing the efficiency of the activation steps and improving the uniformity of the SEI coating film formed in one activation step.

[0091] In addition, the activation steps may be performed for 1 to 100 minutes, specifically, for 1 to 100 minutes, 1 to 60 minutes, 1 to 40 minutes, 10 to 40 minutes, 20 to 40 minutes, 10 to 30 minutes, and 1 to 10 minutes, respectively.

[0092] In addition, a process of degassing the gas formed inside the lithium secondary battery after the activation step may be performed. In the lithium secondary battery after the activation step, a large amount of gas is generated inside due to delithiation and / or decomposition of the positive electrode additive contained in the positive electrode composite layer, and if this gas is not removed, it may cause a swelling phenomenon of the battery together with the gas. However, the present invention can prevent this by further degassing the lithium secondary battery after the activation step.

[0093] Here, the degassing may be performed by applying pressure to the outer surface of the lithium secondary battery using a pressure device such as a jig, and the pressure may be 10 to 900 kgf / cm. 2 The time required for the image acquisition may be 4 to 6 seconds, but is not limited to this.

[0094] At this time, the gas removed during degassing of the lithium secondary battery can satisfy Formula 1 of 2.0 or more and 20.0 or less:

[0095] [Formula 1] A LCO / A0

[0096] In formula 1, A LCO indicates the amount of carbon monoxide (CO) and carbon dioxide (CO2) gas generated (ml / Ah) when the positive electrode contains the positive electrode additive represented by chemical formula 1, A0 indicates the amount of carbon monoxide (CO) and carbon dioxide (CO2) gas generated (ml / Ah) when the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1.

[0097] Furthermore, the activation method of the lithium secondary battery according to the present invention may further include an aging step of aging the activated lithium secondary battery after the activation step. The aging step may further stabilize the SEI film by thermal energy and electrochemical energy and re-form it with a uniform thickness. To this end, the aging step may be performed at 20 to 40°C, specifically, 20 to 30°C or 20 to 25°C, for 0.5 to 30 hours.

[0098] The present invention will now be described in more detail with reference to examples and experimental examples.

[0099] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0100] <Example 1> 1) Manufacture of lithium secondary batteries LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.1 Al 0.1 96 parts by weight of 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 were weighed and mixed in N-methylpyrrolidone (NMP) solvent to prepare a slurry for a positive electrode composite layer (positive electrode active material: positive electrode additive = 99.15:0.85). The slurry for the positive electrode composite layer was applied to aluminum foil, dried, and then rolled to form a positive electrode having a positive electrode composite layer (average thickness: 130 μm).

[0101] As the negative electrode active material, natural graphite, carbon black conductive material, and PVDF binder were mixed in a weight ratio of 85:10:5 in N-methylpyrrolidone solvent to prepare a slurry for the negative electrode composite layer, which was then applied to copper foil to prepare a negative electrode having a negative electrode composite layer (average thickness: 180 μm).

[0102] The prepared positive and negative electrodes were laminated with a separator (thickness: about 16 μm) made of a porous polyethylene (PE) film between them to prepare an electrode assembly. The electrode assembly was placed inside a battery case, and an electrolyte was injected into the case. The case was then left at room temperature for 3 days to allow the electrolyte to be fully impregnated, to prepare a lithium secondary battery. The electrolyte was prepared by dissolving 1.0M lithium hexafluorophosphate (LiPF6) in an organic solvent made of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (EC / DMC / EMC mixed in a volume ratio of 3 / 4 / 3).

[0103] 2) Activation of lithium secondary batteries The activation step was carried out on the manufactured lithium secondary battery. Specifically, the activation step was carried out at a temperature of 55°C, and the secondary battery was charged at a constant current of 0.2C and 4.3V until the capacity (SOC) of the secondary battery reached 100%, thereby carrying out the activation step of the lithium secondary battery. After charging, the gas in the battery was degassed using a jig.

[0104] <Examples 2 to 3 and Comparative Examples 1 to 3. Production and activation of lithium secondary batteries> Except for changing the contents of the positive electrode active material and the positive electrode additive during the preparation of the lithium secondary battery, the lithium secondary battery was prepared in the same manner as in Example 1. The prepared lithium secondary battery was subjected to an activation step.

[0105] The compositions of the positive electrodes produced in the examples and comparative examples are shown in Table 1 below.

[0106] [Table 1]

[0107] <Experimental Example> In order to evaluate the performance of the positive electrode for a lithium secondary battery according to the present invention, the following experiment was carried out.

[0108] A. Analysis of the components and content of gas generated during the activation process The components and contents of each gas generated inside the lithium secondary batteries according to the examples and comparative examples during the activation process were analyzed, and the results are shown in Table 2 below.

[0109] [Table 2]

[0110] As shown in Table 2, the lithium secondary battery containing the positive electrode additive had a higher gas generation rate than the lithium secondary battery not containing the positive electrode additive. In particular, the gas generation rate (ml / Ah) relative to the cell capacity was higher as the content of the positive electrode additive was higher.

[0111] The amounts of carbon monoxide and carbon dioxide generated inside the lithium secondary batteries during the formation process according to the examples and comparative examples were evaluated, and the results are shown in Table 3 below.

[0112] [Table 3]

[0113] Referring to Table 3, the lithium secondary battery containing the positive electrode additive generated higher amounts of carbon monoxide and carbon dioxide gases than the lithium secondary battery not containing the positive electrode additive. In particular, the amount of carbon monoxide and carbon dioxide gases generated increases as the content of the positive electrode additive increases. The contents of hydrogen and hydrocarbons, excluding carbon monoxide and carbon dioxide, in the gas generated during the activation process are shown in Table 4 below.

[0114] [Table 4]

[0115] Referring to Table 4 above, it was confirmed that the total amount of gas generated during the activation process increased depending on whether or not the positive electrode additive was used, but the ratio of hydrogen and hydrocarbon content to the total amount of gas generated during the activation process was reduced by adjusting the ratio of carbon monoxide and carbon dioxide to satisfy a specific range. In particular, it was confirmed that the amount of hydrogen and hydrocarbon gas generated relative to the total amount of gas generated in Example 2 was 0.49. The lithium secondary batteries activated under the conditions of the Examples and Comparative Examples were found to have a gas content of A through analysis of the gas components and contents. LCO It was confirmed that the / A0 value was 3.0 or more.

[0116] On the other hand, the activated lithium secondary battery of Comparative Example 3 had a very high total gas generation amount of 169.2 (ml), which was determined to induce volume expansion of the electrode assembly, resulting in a decrease in battery performance.

[0117] In addition, the contents of propene and propane generated inside the lithium secondary batteries during the formation process according to the examples and comparative examples were evaluated, and the results are shown in Table 5 below.

[0118] [Table 5]

[0119] It was confirmed through the analysis of gas components and contents of the lithium secondary batteries activated under the conditions of the Examples and Comparative Examples that the following formula 3 satisfies 0.8 or less.

[0120] B. Evaluation of cycle life performance The activated lithium secondary batteries in the examples and comparative examples were discharged at 2V (C-rate=0.1C), and then charged and discharged 100 times (n=100) at 25°C under the conditions of a charge cut-off voltage of 4.25V, a discharge cut-off voltage of 2.5V, and 0.5C / 0.5C, to measure the capacity retention (Capacity Retention [%]). The capacity retention was calculated using the following formula 1, and the results are shown in Table 6 below:

[0121] [Formula 1] Capacity retention rate (%) = (discharge capacity after n charge / discharge cycles / discharge capacity after 1 charge / discharge cycle) x 100

[0122] [Table 6]

[0123] Referring to Table 6 above, it was confirmed that the lithium secondary battery activated according to the embodiment has an initial charge capacity of 710 mAh / g or more and a capacity retention rate after 100 charge / discharge cycles of 97% or more, whereas the lithium secondary battery activated according to the comparative example has an initial charge capacity and a capacity retention rate after 100 charge / discharge cycles lower than those of the lithium secondary battery of the embodiment.

[0124] From these results, it was confirmed that the amount of carbon monoxide and carbon dioxide gas generated in the lithium secondary battery according to the present invention increases as the content of the positive electrode additive represented by Chemical Formula 1 in the positive electrode mixture layer as a non-reversible additive increases, but by adjusting the ratio of carbon monoxide and carbon dioxide to satisfy a specific range, the content of hydrogen and hydrocarbon relative to the total amount of gas generated during the activation process is reduced. As a result, the lithium secondary battery according to the present invention has the advantage of being able to improve safety as well as easily improve the charge and discharge efficiency of the lithium secondary battery.

[0125] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood that a person skilled in the art or having ordinary knowledge in the art can make various modifications and variations to the present invention without departing from the spirit and technical scope of the present invention as described in the claims below.

[0126] 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 claims.

Claims

1. an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and an electrolyte solution, The positive electrode comprises a positive electrode current collector and a positive electrode mixture layer located on the positive electrode current collector and including a positive electrode active material, a positive electrode additive represented by the following Chemical Formula 1, a conductive material, and a binder, The method for producing the lithium secondary battery includes the steps of: The method includes an activation step of charging the battery to 100% SOC under conditions of a temperature of 40° C. to 70° C., a voltage of 3.5 V to 4.5 V, and a current of 0.1 C to 0.5 C, and after the activation step, the following formula 1 satisfies 2.0 or more and 20.0 or less: A method for producing a lithium secondary battery, comprising forming an SEI film containing lithium ions derived from a positive electrode additive on a surface of a negative electrode during the activation step: [Chemical formula 1] Li ｐ Co （１－ｑ） M １ ｑ O ４ In the above Chemical Formula 1, M １ is 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; p and q are 5≦p≦7 and 0≦q≦0.5, respectively; [Formula 1] A ＬＣＯ / A ０ In formula 1, A ＬＣＯ is a graph showing the relationship between the amount of carbon monoxide (CO) and carbon dioxide (CO) in the case where the positive electrode contains a positive electrode additive represented by Chemical Formula 1. ２ ) gas generation amount (ml / Ah), A ０ is the amount of carbon monoxide (CO) and carbon dioxide (CO) in the case where the positive electrode does not contain the positive electrode additive represented by Chemical Formula 1. ２ ) gas generation amount (ml / Ah) is shown.

2. The method for producing a lithium secondary battery according to claim 1 , wherein Formula 1 satisfies 3.0 or more.

3. 2. The method for producing a lithium secondary battery according to claim 1, wherein the lithium secondary battery satisfies the following formula 2 of 0.8 or less after the activation step: [Formula 2] B ＬＣＯ / B ０ In formula 2, B ＬＣＯ is a graph showing the effect of propene (C ３ H ６ ) and propane (C ３ H ８ ) gas generation amount (ml / Ah), B ０ is the amount of propene (C ３ H ６ ) and propane (C ３ H ８ ) gas generation amount (ml / Ah) is shown.

4. The positive electrode additive has a space group of P4 ２ 2. The method for producing a lithium secondary battery according to claim 1, wherein the lithium secondary battery has a tetragonal structure in which the lattice constant is 0.1 / nmc.

5. 2. The method for producing a lithium secondary battery according to claim 1, wherein the content of the positive electrode additive is 0.7 to 1.8 parts by weight per 100 parts by weight of the positive electrode mixture layer.

6. The method for producing a 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 Mn ｗ M ２ ｖ ]O ｕ In the above Chemical Formula 2, M ２ is 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; x, y, z, w, v, and u are within the ranges of 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. 2. The method for producing a lithium secondary battery according to claim 1, wherein the conductive material comprises at least one material selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

8. 2. The method for producing a lithium secondary battery according to claim 1, wherein the conductive material is contained in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the positive electrode mixture layer.

9. 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, The method for producing a lithium secondary battery according to claim 1 , wherein the negative electrode active material contains a carbon material and a silicon material.

10. The silicon material is composed of silicon (Si) particles and silicon oxide (SiO Ｘ 10. The method for producing a lithium secondary battery according to claim 9, wherein the lithium secondary battery comprises at least one of the following particles:

11. 10. The method for manufacturing a lithium secondary battery according to claim 9, wherein the silicon material is contained in an amount of 1 to 20 parts by weight based on 100 parts by weight of the negative electrode mixture layer.

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