Fomation method of lithium secondary battery

Abstract

The activation method of the present invention comprises: (a) a primary charging process for charging a lithium secondary battery; (b) a degassing process for discharging an internal gas containing oxygen to the outside of the secondary battery or moving it to a gas pocket; (c) an aging process for aging the secondary battery; and (d) a degassing process for removing gas from the aged secondary battery, wherein the degassing process (b) is performed between the primary charging process (a) and the aging process (c). By releasing internal gases containing oxygen gas early, the oxygen gas is prevented from reacting with the electrolyte or film, thereby improving the capacity and lifespan characteristics of the battery.

Description

Technology Field

[0001] The present invention relates to a method for activating a lithium secondary battery in which a large amount of oxygen is generated during the activation process due to the characteristics of the positive electrode active material or the positive electrode additive. Background Technology

[0003] With the increasing technological development and demand for mobile devices, the demand for rechargeable batteries as an energy source is rapidly rising. Among these rechargeable batteries, lithium-ion batteries, which possess high energy density and operating potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Recently, as lithium-ion batteries are being utilized as power sources for medium-to-large devices such as electric vehicles, there is an increasing demand for higher capacity, higher energy density, and lower costs. Consequently, irreversible additives used in electrodes are also required to possess higher irreversible capacity. However, it is true that there have been limitations in the development of cathode additives with such high irreversible capacity.

[0005] Meanwhile, conventional irreversible additives such as the above Li6CoO4 are generally manufactured by reacting cobalt oxide, etc., with an excess amount of lithium oxide. Irreversible additives manufactured in this way are structurally unstable and generate a large amount of oxygen gas (O2). In addition, lithium or manganese-rich cathode active materials with high capacity are also known to generate a large amount of oxygen gas. This oxygen gas chemically reacts with the electrolyte or film to further increase gas generation, hinder the normal formation of the film, and degrade the performance of the film.

[0006] Conventionally, in order to activate a secondary battery, a primary charging process was performed to charge the secondary battery impregnated with an electrolyte until it reached a predetermined range of SOC, and an aging process was performed to age the secondary battery that had been charged in the primary process, followed by a degassing process to discharge gas from inside the secondary battery.

[0007] However, when such conventional activation methods are applied to a secondary battery equipped with a cathode containing the aforementioned cathode active material or cathode additive that causes a large amount of oxygen to be generated during primary charging, the large amount of oxygen gas generated during the primary charging process reacts with the electrolyte or SEI film, further increasing gas generation, hindering the formation of the film, and degrading the performance of the film.

[0008] Therefore, in a lithium secondary battery equipped with a cathode containing a cathode active material or a cathode additive, there is a need to develop technology for an activation method to remove a large amount of oxygen generated. Prior art literature

[0010] Republic of Korea Published Patent No. 10-2021-0032205 The problem to be solved

[0011] The present invention aims to solve the problems of the prior art described above and provides a method for activating a lithium secondary battery that can improve the electrical performance and safety of the lithium secondary battery. means of solving the problem

[0013] The method for activating a lithium secondary battery according to the present invention comprises: (a) a primary charging process for charging the lithium secondary battery; (b) a degassing process for discharging an internal gas containing oxygen to the outside of the secondary battery or moving it to a gas pocket; (c) an aging process for aging the secondary battery; and (d) a degassing process for removing gas from the aged secondary battery, wherein the degassing process (b) is performed between the primary charging process (a) and the aging process (c).

[0014] In one embodiment of the present invention, the (b) degassing process is initiated when the charge depth of the secondary battery is 20% to 80% SOC.

[0015] In one embodiment of the present invention, the (b) degassing process is initiated when the charge depth of the secondary battery is 40% to 70%.

[0016] In one embodiment of the present invention, the (d) degassing process is performed after the (c) aging process.

[0017] In one embodiment of the present invention, (e) further includes a secondary charging process for additionally charging a secondary battery, and the (e) secondary charging process is performed between the (b) degassing process and the (c) aging process.

[0018] In one embodiment of the present invention, the (e) secondary charging process is to charge to an SOC of 20% to 100%.

[0019] In one embodiment of the present invention, the lithium secondary battery comprises a positive electrode including a positive electrode additive represented by the following chemical formula 1.

[0020] [Chemical Formula 1]

[0021] Li p Co (1-q) M 1 q O4

[0022] In the above chemical formula 1,

[0023] M 1 It 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, and

[0024] p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0025] In one embodiment of the present invention, in Formula 1, M 1 is a Zn element, and q is 0.2≤q≤0.4.

[0026] In one embodiment of the present invention, the anode additive is included in an amount of 0.1 to 5 weight percent based on the total weight of the anode mixture.

[0027] In one embodiment of the present invention, the lithium secondary battery comprises a positive electrode comprising one or more types selected from positive electrode active materials represented by the following chemical formulas 2 to 5.

[0028] [Chemical Formula 2]

[0029] Li x [Ni a Co b Mn c ]O2(0.95≤x≤1.05, 0≤ a, b, c ≤1, a+b+c = 1, provided that a and c cannot be 0 at the same time)

[0030] [Chemical Formula 3]

[0031] Li[Li x Ni a Co b Mn c ]O2(0.05≤x≤0.6, x+a+b+c = 1)

[0032] [Chemical Formula 4]

[0033] Li x [Ni a Co b Mn c ]O2(0.95≤x≤1.05, 0 < a, b, c ≤1, a+b+c =1, 0.4 <c<1)

[0034] [Chemical Formula 5]

[0035] LiMn 2-x M x O4(M=one or more elements selected from the group consisting of Ni, Co, Fe and Al, and 0≤x≤2)

[0036] In one embodiment of the present invention, the (b) degassing process is to discharge an internal gas containing oxygen gas to the outside of the secondary battery.

[0037] In one embodiment of the present invention, the (b) degassing process may include: (b-1) cutting a part of the gas pocket or forming a through hole; (b-2) discharging gas inside the secondary battery to the outside of the secondary battery; and (b-3) re-sealing the gas pocket.

[0038] In another embodiment of the present invention, the (b) degassing process is to move the internal gas from the electrode assembly to the gas pocket portion.

[0039] In one embodiment of the present invention, the (b) degassing process may involve pressurizing the secondary battery by roll pressing or jig pressing to move the internal gas remaining in the electrode assembly to the gas pocket portion.

[0040] In one embodiment of the present invention, the (a) primary charging process may include a process of charging the secondary battery while the secondary battery is under pressure. Effects of the invention

[0042] The activation method of the present invention, in the activation process of a lithium secondary battery in which a large amount of oxygen is generated due to the characteristics of the positive electrode active material or positive electrode additive, performs a degassing process during or immediately after the initial charging process to immediately remove internal gases containing oxygen, thereby minimizing the reaction of oxygen gas with the electrolyte or film, so that the SEI film is stably formed and the battery capacity and lifespan characteristics are excellent. Brief explanation of the drawing

[0044] FIGS. 1 and FIGS. 2 are flowcharts of an activation method according to an embodiment of the present invention. FIGS. 3 and FIGS. 4 are schematic diagrams of a degassing process according to another embodiment of the present invention. Specific details for implementing the invention

[0045] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0046] Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention; thus, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0048] The present invention will be described in more detail below.

[0050] <Activation method according to the first embodiment>

[0051] FIG. 1 is a flowchart of a method for activating a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the activation method according to the present invention comprises: (a) a primary charging process for charging a lithium secondary battery; (b) a degassing process for discharging an internal gas containing oxygen to the outside of the secondary battery or moving it to a gas pocket; (c) an aging process for aging the secondary battery; and (d) a degassing process for removing gas from the aged secondary battery. The degassing process (b) is performed between the primary charging process (a) and the aging process (c).

[0052] The above (a) primary charging process is a step of charging a secondary battery to form a SEI (Solid electrolyte interface, hereinafter referred to as "SEI") film layer of the negative electrode, and is a process of charging the assembled secondary battery to a predetermined range of SOC level of full charge capacity (SOC 100, SOC; State Of Charge), and the (c) aging process stabilizes or accelerates the formation of the SEI film formed during the primary charging process.

[0053] When the primary charging process of a lithium secondary battery is performed, lithium ions originating from lithium transition metal oxides, such as the cathode active material and cathode additive contained in the cathode, move to the carbon electrode of the anode. Since these lithium ions are highly reactive, they react with the carbon anode to produce compounds such as Li2CO3, LiO, and LiOH, and an SEI film is formed on the surface of the anode by these compounds. The SEI film is an insulator that forms when the amount of ion movement in the battery increases. Once the SEI film is formed, it prevents lithium ions from reacting with other materials at the anode during subsequent secondary battery charging, and functions as a kind of ion tunnel to allow only lithium ions to pass through. Since lithium ions do not react with the anode or other materials once this SEI film is formed, the amount of lithium ions is reversibly maintained, and the charging and discharging of the secondary battery are maintained reversibly, thereby improving the lifespan of the secondary battery. Furthermore, because it does not easily collapse even when left at high temperatures or subjected to repeated charging and discharging, changes in the battery thickness occur less.

[0054] However, due to the material characteristics of the cathode active material or cathode additive, a large amount of oxygen gas may be generated during the activation process. In particular, the oxygen gas generated during the primary charging process, where the SEI film is first formed, can hinder the formation of such an SEI film, degrade the performance of the formed SEI film, and generate more internal gas through reaction with the electrolyte.

[0055] Accordingly, the activation method of the present invention performs (a) a degassing process in which internal gas containing oxygen generated during the first charging process is immediately discharged, and then performs (c) an aging process. As a result, the oxygen gas generated during the first charging process is discharged as much as possible before reacting with the electrolyte or the initial film, thereby minimizing side reactions caused by the oxygen gas and inducing more stable film formation on the cathode.

[0056] The first charging process of (a) above is a process of charging a lithium secondary battery to a predetermined range of State of Charge (SOC; State Of Charge, hereinafter referred to as "SOC") based on the full charge capacity (SOC 100%). Here, the predetermined range may be from 20% to 100% SOC, and an appropriate level of SOC is set considering the capacity of the secondary battery and the material characteristics of the cathode material, anode material, and electrolyte. For example, if a large amount of gas is generated during the first charging process due to material characteristics, the first charging process may be performed by setting the SOC to a relatively lower level.

[0057] In the first charging process of (a) above, the charging conditions may be performed according to conditions known in the art. Specifically, the charging method may be performed in a constant current manner until the charging termination voltage is reached. At this time, the charging rate (c-rate) may be 0.01C to 2C, 0.1C to 1.5C, or 0.2C to 1C, but is not necessarily limited thereto and can be appropriately changed according to the characteristics of the positive and negative electrode materials.

[0058] In one specific example, the activation method of the present invention may pressurize the secondary battery during the (a) primary charging process. That is, the secondary battery may be charged while in a pressurized state. Pressurizing the secondary battery simultaneously with the charging process in this way has the effect of preventing the gas generated during the charging process from being trapped inside the electrode assembly.

[0059] Pressurization of such a secondary battery can be performed by jig pressurization capable of applying surface pressurization to both sides of the secondary battery, but is not limited thereto.

[0060] The degassing process of (b) above is a process of discharging or pushing out internal gases containing oxygen generated during primary charging due to the material characteristics of the cathode active material or cathode additive to the outside of the electrode assembly.

[0061] This (b) degassing process may be initiated in one specific example when the charge depth of the secondary battery is 20% to 80% SOC, preferably 40% to 70% SOC. Since the (b) degassing process is intended to remove internal gases containing oxygen from the electrode assembly before oxygen gas reacts with the electrolyte or the initial film, it is efficient to initiate the degassing process at the SOC level within the above range.

[0062] In the activation method according to the first embodiment of the present invention, the (b) degassing process is to discharge internal gas containing oxygen gas to the outside of the secondary battery. The (a) primary charging process is performed on a secondary battery in which an electrode assembly is housed in a battery case, an electrolyte is injected, and then sealed, and after the (a) primary charging process, an opening is formed in the sealed battery to discharge internal gas of the secondary battery to the outside through the opening.

[0063] This (b) degassing process can be performed without limitation using methods commonly used in the battery field.

[0064] In one specific example, the above (b) degassing process comprises: (b-1) a step of cutting a part of the gas pocket portion to form an opening or a through hole; (b-2) a step of discharging gas inside the secondary battery to the outside of the secondary battery through the opening or through hole; and (b-3) a step of re-sealing the gas pocket portion.

[0065] The step of forming the opening or through hole (b-1) above is to form an opening or through hole in a part of the gas pocket portion through which gas can be exhausted in order to discharge gas inside the sealed secondary battery to the outside. A part of the pouch may be cut to form the opening, and a piercing means capable of forming a hole in the pouch may be used to form the through hole, and it is preferable that the location where the opening and through hole are formed is the upper part of the gas pocket portion.

[0066] The step of (b-2) of exhausting internal gas to the outside is a step of exhausting gas containing oxygen present inside the battery case to the outside through an opening or through hole formed in the gas pocket. At this time, the chamber containing the lithium secondary battery can be created into a vacuum state to exhaust and remove the internal gas of the lithium secondary battery to the outside. In addition, a pressurization process of the lithium secondary battery may be performed during the exhaust process.

[0067] (b-3) The step of re-sealing the gas pocket portion is a step of re-sealing the lithium secondary battery for an aging process or an additional charging process after a degassing process. In one specific example, the gas pocket portion may be sealed by cutting out the gas pocket portion area including the opening or through hole, removing the opening or through hole from the gas pocket portion, and sealing the cut surface.

[0068] The aging process of (c) above is a process of aging the secondary battery under various conditions to accelerate the stabilization of the SEI film formed through the primary charging process of (a).

[0069] The above aging process may undergo a room temperature aging process in which the secondary battery is aged for a predetermined period of time under room temperature / atmospheric pressure conditions, and depending on the purpose, high temperature aging may be performed instead of room temperature aging, or both room temperature aging and high temperature aging may be performed. The above high temperature aging is a process of aging the battery in a high temperature environment, which can accelerate the stabilization of the SEI film, and the high temperature aging and room temperature aging processes may be performed sequentially on the primary charged battery.

[0070] In one specific example, the high-temperature aging may be carried out at a temperature of 50°C to 100°C, preferably 50°C to 80°C. The high-temperature aging may be carried out for 1 hour to 30 hours, preferably 2 hours to 24 hours.

[0071] In one specific example, the room temperature aging may be carried out at a temperature of 18°C ​​to 28°C, more specifically 19°C to 27°C, more specifically 20°C to 26°C, and even more specifically 21°C to 25°C. The room temperature aging may be carried out for 12 to 120 hours, or 18 to 72 hours.

[0072] The above (d) degassing process is a process of discharging oxygen gas generated during the aging process after performing the above (c) aging process. The specific method of the above (d) degassing process may be the same as the above-described degassing process (b).

[0073] FIG. 2 is a flowchart of an activation method according to an embodiment of the present invention. Referring to FIG. 2, the activation method of the present invention may further include (e) a secondary charging process for additionally charging a secondary battery between (b) a degassing process and (c) an aging process. Accordingly, the activation method is performed sequentially as follows: (a) a primary charging process - (b) a degassing process - (e) a secondary charging process - (c) an aging process - (d) a degassing process.

[0074] The above (e) secondary charging process may be charging to an SOC of 20% to 100%. By performing a step-by-step charging process that includes a secondary charging process after the primary charging, the battery can be stably activated. Additionally, due to the material characteristics of the battery, if a large amount of oxygen is generated when performing a primary charging to a normally set SOC level, a method of charging may be adopted in which the primary charging is performed to a lower SOC level than the normally set SOC level, oxygen gas is removed through the degassing process of (b), and then the remaining charge depth is filled through the (e) secondary charging. For example, the (a) primary charging process may be charging the secondary battery to an SOC of 10% to 20%, and the (e) secondary charging process may be charging the secondary battery to an SOC of 30% to 60%.

[0075] In one specific example, after the degassing process of (d), a full discharge and full charge process may be further performed in which the secondary battery is fully discharged to near 0% SOC, and then charged to 95% (95% SOC) or more of the discharged secondary battery's design capacity. The full discharge and full charge process may be performed once or repeated two or more times.

[0076] In one specific example, the method for activating a secondary battery according to the present invention may further perform an additional aging process after the full discharge and full charge processes. The additional aging process is a process for stabilizing the secondary battery and can be performed at room temperature or high temperature, specifically for 1 to 21 days. The additional aging process may include a monitoring (OCV tracking) process that includes measuring the open circuit voltage (OCV) of the battery at regular time intervals to identify low-voltage defective batteries in which a voltage drop occurs to a range exceeding the battery's self-discharge.

[0077] In addition, the activation method of the present invention includes (a) a primary charging process, (b) a degassing process, (c) an aging process, and (d) a degassing process, and may further include a pre-aging process before performing the primary charging process (a).

[0078] The above pre-aging process is a process of aging the battery after assembly so that the electrolyte is sufficiently impregnated into the electrode assembly. Once the assembly of the secondary battery is complete, a pre-aging process may be performed to stabilize the secondary battery by leaving it at room temperature for a certain period of time so that the electrolyte injected into the secondary battery is sufficiently wetted inside the electrode assembly.

[0079] More specifically, when a secondary battery is charged, electrons travel along the wire to the negative electrode and become charged; subsequently, lithium ions are absorbed into the negative electrode to achieve charge neutrality. At this time, lithium ions can be absorbed in the electrolyte-impregnated area—that is, the area where the ion movement path is maintained (wetting area)—but absorption becomes relatively difficult in the electrolyte-non-impregnated area (non-wetting area). Therefore, through a pre-aging process, the battery can be aged in an environment with specific humidity and temperature conditions to allow the electrolyte to permeate well into the positive and negative electrodes.

[0080] In one specific example, the time required for the pre-aging process may be, specifically, 3 to 72 hours, 6 to 60 hours, or 12 to 48 hours, and this can be appropriately adjusted depending on the materials of the anode, cathode, and electrolyte, the design capacity of the secondary battery, etc.

[0081] In addition, the temperature during pre-aging can be performed at room temperature conditions of 18°C ​​to 28°C, specifically at 19°C to 27°C, more specifically at 20°C to 26°C, and even more specifically at 21°C to 25°C, but is not necessarily limited thereto and can be appropriately changed according to the characteristics of the battery to be designed.

[0083] Hereinafter, a lithium secondary battery manufactured according to the activation method of the present invention will be described in detail.

[0084] The lithium secondary battery of the present invention is manufactured by housing an electrode assembly having a positive electrode / separator / negative electrode structure in a battery case, injecting an electrolyte, and sealing it.

[0085] Specifically, an electrode mixture containing an electrode active material and a binder is applied to an electrode current collector to manufacture an anode and a cathode, respectively, and then a separator is interposed between the anode and the cathode to prepare an electrode assembly.

[0086] After placing the prepared electrode assembly into the battery case, the electrolyte is injected, and the battery case is sealed to assemble the battery.

[0087] The steps for assembling such batteries are not particularly limited and can be performed according to known methods.

[0088] In addition, the electrode assembly is not particularly limited as long as it has a structure including an anode, a cathode, and a separator interposed between the anode and the cathode, and may be, for example, a jelly-roll type, a stack type, or a stack / folding type.

[0089] The above battery case is not particularly limited as long as it is used as an outer material for packaging batteries, and cylindrical, prismatic, or pouch-type cases may be used.

[0090] In the case where the battery case is of the pouch type, an aluminum laminated pouch including an aluminum layer may be used. After injecting the electrolyte, the opened portion of the aluminum laminated pouch can be sealed by heat welding or heat fusion.

[0091] The lithium secondary battery of 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, and an electrolyte.

[0092] The above-mentioned anode comprises an anode current collector and an anode active material layer prepared by applying, drying, and pressing an anode composite slurry onto the anode current collector. The anode composite comprises an anode active material and a binder, and may further comprise an anode additive, a conductive material, and a filler as needed.

[0093] The lithium secondary battery of the present invention is a lithium secondary battery having a positive electrode comprising a positive electrode additive represented by the following chemical formula 1, wherein such a positive electrode additive contains an excess amount of lithium and can provide lithium to compensate for the lithium consumption caused by irreversible chemical / physical reactions at the negative electrode during primary charging, thereby increasing the charging capacity of the battery and decreasing the irreversible capacity, so that the lifespan characteristics can be improved.

[0094] However, since such anode additives are structurally unstable and generate a large amount of oxygen gas as charging proceeds, it is desirable to apply the activation method of the present invention.

[0095] [Chemical Formula 1]

[0096] Li p Co (1-q) M 1 q O4

[0097] In the above chemical formula 1,

[0098] M 1 It 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, and

[0099] p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0100] As such an anode additive, the present invention may include a lithium cobalt oxide represented by Formula 1, wherein the lithium cobalt oxide represented by Formula 1 is Li6CoO4, Li6Co 0.5 Zn 0.5 O4, Li6Co 0.7 Zn 0.3O4, etc. can be used alone or in combination. Compared to nickel-containing oxides commonly used in the industry, the lithium cobalt oxide represented by Chemical Formula 1 has a high lithium ion content and a low voltage range required for delithiation, which has the advantage of being able to delithiate lithium ions without affecting the reaction of the cathode active material during battery activation.

[0101] In addition, the lithium cobalt metal oxide represented by Chemical Formula 1 above may have a tetragonal crystal structure, and among these, may have a space group of P42 / nmc. Generally, lithium metal oxides having a tetragonal crystal structure have a structurally unstable structure due to the distortion of the tetrahedral structure formed by cobalt and oxygen elements, and due to this structural instability, gas containing oxygen is generated even during the primary charging of the battery. In the present invention, by immediately removing the generated oxygen gas, the reaction of oxygen gas is blocked, thereby improving the decomposition and / or delithiation efficiency of the cathode additive during primary charging and the charge / discharge capacity of the lithium secondary battery, as well as inhibiting film formation by oxygen gas and suppressing reaction with the electrolyte.

[0102] In addition, the content of the anode additive may be 0.1 to 5 parts by weight per 100 parts by weight of the total anode mixture, specifically 0.1 to 3 parts by weight; or 1 to 3 parts by weight.

[0103] The cathode composite containing the above cathode additive may include a lithium nickel composite oxide represented by the following chemical formula 6 as a cathode active material capable of reversible intercalation and deintercalation:

[0104] [Chemical Formula 6]

[0105] Li x [Ni y Co z Mn w M 2 v]O u

[0106] In the above chemical formula 6,

[0107] 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, and

[0108] x, y, z, w, v, and u are 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≤4.5이다.

[0109] The lithium nickel composite oxide represented by the above chemical formula 6 is a composite metal oxide comprising lithium, nickel, cobalt, and manganese, and in some cases, other transition metals (M 2 It can have a form doped with ). For example, the cathode active material is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 O2 and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 It may include one or more compounds selected from the group consisting of O2. As one example, the cathode active material is a lithium nickel composite metal oxide represented by Chemical Formula 2, such as LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.8 Co 0.1Mn 0.1 O2 can be used individually or in combination.

[0110] In addition, the content of the above-mentioned positive active material may be 85 to 99 parts by weight per 100 parts by weight of the positive composite, and specifically, may be 88 to 98 parts by weight, 90 to 97 parts by weight, or 92 to 95 parts by weight.

[0111] In addition, the lithium secondary battery of the present invention may be a secondary battery having a cathode comprising one or more types selected from the cathode active materials represented by the following chemical formulas 2 to 5. Such cathode active materials are rich in lithium or manganese and are used in high-capacity batteries, but due to their characteristics, a large amount of oxygen gas is generated, so it is desirable to apply the activation method of the present invention.

[0112] [Chemical Formula 2]

[0113] Li x [Ni a Co b Mn c ]O2(0.95≤x≤1.05, 0≤ a, b, c ≤1, a+b+c = 1, provided that a and c cannot be 0 at the same time)

[0114] [Chemical Formula 3]

[0115] Li[Li x Ni a Co b Mn c ]O2(0.05≤x≤0.6, x+a+b+c = 1)

[0116] [Chemical Formula 4]

[0117] Li x [Ni a Co b Mn c ]O2(0.95≤x≤1.05, 0 < a, b, c ≤1, a+b+c =1, 0.4 <c<1)

[0118] [Chemical Formula 5]

[0119] LiMn 2-x Mx O4(M=one or more elements selected from the group consisting of Ni, Co, Fe and Al, and 0≤x≤2)

[0121] The anode composite of the present invention may additionally include a binder and a conductive material in addition to the anode active material, and the content of the anode active material may be 85 to 99 parts by weight with respect to 100 parts by weight of the anode composite, and specifically may be 88 to 98 parts by weight, 90 to 97 parts by weight, or 92 to 95 parts by weight.

[0122] The above conductive material may be used to improve performance such as the electrical conductivity of the anode, and one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber may be used. For example, the above conductive material may include acetylene black.

[0123] In addition, the conductive material may be included in an amount of 1 to 10 parts by weight per 100 parts by weight of the composite layer, specifically 2 to 8 parts by weight; or 2 to 6 parts by weight of the conductive material.

[0124] In addition, the binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As one example, the binder may include polyvinylidene fluoride.

[0125] In addition, the binder may be included in an amount of 1 to 10 parts by weight with respect to 100 parts by weight of the total composite layer, specifically 1 to 8 parts by weight; or 1 to 6 parts by weight.

[0126] In addition, the average thickness of the above composite layer is not particularly limited, but specifically may be 50㎛ to 300㎛, and more specifically may be 100㎛ to 200㎛; 80㎛ to 150㎛; 120㎛ to 170㎛; 150㎛ to 300㎛; 200㎛ to 300㎛; or 150㎛ to 190㎛.

[0127] In addition, the above-mentioned positive electrode may be used as a current collector that has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used, and in the case of aluminum or stainless steel, surface-treated materials such as carbon, nickel, titanium, silver, etc. may be used. Furthermore, the above-mentioned current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible. Moreover, the average thickness of the above-mentioned current collector may be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured positive electrode.

[0128] In addition, the negative electrode of the lithium secondary battery used in the present invention is manufactured by coating, drying, and pressing a negative electrode active material onto a negative electrode current collector, and, if necessary, a conductive material, an organic binder polymer, an additive, etc., as in the positive electrode may be optionally further included.

[0129] In addition, the above-mentioned cathode active material is, for example, carbon and graphite materials such as graphite having a completely formed layered crystal structure like natural graphite, soft carbon having a low-crystallinity layered crystal structure (graphene structure; a structure in which hexagonal honeycomb-shaped planes of carbon are arranged in layers), hard carbon in which such structures are mixed with amorphous parts, artificial graphite, expanded graphite, carbon fiber, non-graphitized carbon, carbon black, carbon nanotubes, fullerene, activated carbon, etc.; or LixFe2O3(0≤x≤1), LixWO2(0≤x≤1), SnxMe1-xMe'yOz (Me: Mn, Fe, Pb, Ge; Me', Al, B, P, Si, elements of Group 1, Group 2, and Group 3 of the periodic table, halogen; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni계 재료; 티타늄 산화물; 리튬 티타늄 산화물 등을 사용할 수 있다.

[0130] As an example, the cathode active material may include graphite and silicon (Si) containing particles together, and the graphite may include one or more of natural graphite having a layered crystal structure and artificial graphite having an isotropic structure, and the silicon (Si) containing particles may include silicon (Si) particles, SiO particles, SiO2 particles, or a mixture of one or more of these particles, as particles containing silicon (Si) as a main component as a metal component.

[0131] In this case, the negative electrode active material may comprise 80 to 95 parts by weight of graphite and 1 to 20 parts by weight of silicon (Si) containing particles, based on 100 parts by weight of the total. By controlling the content of graphite and silicon (Si) containing particles included in the negative electrode active material to the above range, the present invention can improve the charge capacity per unit mass while reducing lithium consumption and irreversible capacity loss during the initial charge and discharge of the battery.

[0132] In addition, the cathode composite layer may have an average thickness of 100㎛ to 200㎛, and specifically, may have an average thickness of 100㎛ to 180㎛, 100㎛ to 150㎛, 120㎛ to 200㎛, 140㎛ to 200㎛, or 140㎛ to 160㎛.

[0133] In addition, the above-mentioned negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. may be used, and in the case of copper or stainless steel, surface-treated carbon, nickel, titanium, silver, etc. may be used. Furthermore, similar to the positive electrode current collector, the above-mentioned negative electrode current collector may form fine irregularities on its surface to strengthen the bonding force with the negative electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible. In addition, the average thickness of the above-mentioned negative electrode current collector may be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured negative electrode.

[0134] In addition, the separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The separator is not particularly limited as long as it is commonly used in the industry, but specifically, a sheet or nonwoven fabric made of chemically resistant and hydrophobic polypropylene; glass fiber; or polyethylene may be used, and in some cases, a composite separator in which inorganic particles / organic particles are coated by an organic binder polymer on a porous polymer substrate such as the sheet or nonwoven fabric 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. Furthermore, 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.

[0135] The above electrolyte may include an organic solvent, a lithium salt, and an additive.

[0136] The above organic solvent is not limited as long as it minimizes decomposition due to oxidation reactions, etc. during the charging and discharging process of the battery, and may be, for example, cyclic carbonates, linear carbonates, esters, ethers, or ketones. These may be used alone or two or more may be used in combination.

[0137] Among the above organic solvents, carbonate-based organic solvents may be particularly preferred. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), while examples of linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), and ethylpropyl carbonate (EPC).

[0138] The above lithium salts may be used without limitation as lithium salts commonly used in the electrolytes of lithium secondary batteries, such as LiPF6, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiFSI, LiBF4, LiBF6, LiSbF6, LiN(C2F5SO2)2, LiAlO4, LiAlCl4, LiSO3CF3, and LiClO4, and may be used individually or in combination of two or more types.

[0139] In addition, the electrolyte may further include additives, for example, to stably form an SEI film, any one selected from the group consisting of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sulfone, unsaturated sulfone, acyclic sulfone, lithium oxalyl difluoroborate (LiODFB), and derivatives thereof, or a mixture of two or more of these may be used as the additive, but is not limited thereto.

[0140] Examples of the above-mentioned cyclic sulfites include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethyl propylene sulfite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, 1,3-butylene glycol sulfite, etc. Examples of saturated sulfones include 1,3-propane sulfone, 1,4-butane sulfone, etc. Examples of unsaturated sulfones include ethene sulfone, 1,3-propene sulfone, 1,4-butene sulfone, 1-methyl-1,3-propene sulfone, etc. Examples of acyclic sulfones include divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, methyl vinyl sulfone, etc. there is.

[0141] These additives are added to the electrolyte to improve low-temperature output characteristics by forming a robust SEI film on the cathode, as well as to suppress the decomposition of the anode surface that may occur during high-temperature cycle operation and to prevent oxidation reactions of the electrolyte.

[0143] <Activation method according to the second embodiment>

[0144] In the activation method according to the second embodiment of the present invention, the (b) degassing process is to move the internal gas containing oxygen from the electrode assembly to the gas pocket portion. While the (b) degassing process according to the first embodiment described above was to remove the internal gas containing oxygen by discharging it to the outside of the secondary battery, the (b) degassing process according to the second embodiment is not to discharge the internal gas to the outside of the battery, but to move it as much as possible to the gas pocket portion.

[0145] The gas pocket is a space for capturing internal gas and is typically located in an area within the battery case where the electrode assembly and electrolyte are not situated. Therefore, by moving internal gas containing oxygen as much as possible into the gas pocket, the reaction of oxygen gas with the electrolyte or the initial film can be prevented to some extent.

[0146] In one specific example, the above (b) degassing process can move internal gas remaining in the electrode assembly to the gas pocket portion by pressurizing the secondary battery by roll pressing or jig pressing.

[0147] The degassing process (b) of this embodiment has the advantage of being relatively simple compared to a method of removing gas by forming an opening in the gas pocket, exhausting the gas, and then resealing, because the internal gas can be moved to the gas pocket by pressurizing the battery.

[0148] FIG. 3 is a schematic diagram of the roll-pressing pressure and FIG. 4 is a schematic diagram of the jig pressure.

[0149] Referring to FIG. 3, the pressurization by the roll pressing can be achieved by driving the lithium secondary battery (10) between a pair of lower pressurizing rollers (21) and upper pressurizing rollers (22). At this time, it is preferable to perform roll pressing sequentially from the electrode assembly (11) toward the gas pocket (12) so that the internal gas containing oxygen moves from the electrode assembly (11) toward the gas pocket (12). Since the part of the area pressurized by the rollers changes sequentially from the electrode assembly toward the gas pocket and has directionality, this pressurization by roll pressing can be more effective than the jig pressurization described later in terms of preventing internal gas trapping.

[0150] At this time, the line pressure applied to the lithium secondary battery is 0.1 kgf / cm to 20 kgf / cm, or 0.5 kgf / cm to 15 kgf / cm, or 1 kgf / cm to 10 kgf / cm, and preferably 2 kgf / cm to 5 kgf / cm.

[0151] Referring to FIG. 4, the jig pressing method is a method of pressing a lithium secondary battery (10) by interposing it between a pair of flat plate-shaped first plate (31) and a second plate (32).

[0152] At this time, the numerical range of pressure applied to the lithium secondary battery is specifically 0.1 kgf / ㎠ to 20 kgf / ㎠, or 0.5 kgf / ㎠ to 15 kgf / ㎠, or 1 kgf / ㎠ to 10 kgf / ㎠, but is not limited thereto.

[0154] The present invention will be described in more detail below through examples and the like. However, since the configurations described in the examples described in this specification are merely one embodiment of the present invention and do not represent all of the technical ideas of the present invention, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0156] Preparation Example 1: Preparation of a secondary battery having a cathode containing a cathode additive

[0157] LiNi as a positive electrode active material 0.8 Co 0.1 Mn 0.1 O295 parts by weight, Li6Co as anode additive 0.7 Zn 0.3 0.9 parts by weight of O4, 1.6 parts by weight of PVdF as a binder, and 2.5 parts by weight of carbon black as a conductive material were weighed and mixed in an N-methylpyrrolidone (NMP) solvent to prepare a slurry for an anode composite layer. The slurry for the composite layer was applied to an aluminum foil, dried, and then rolled to form an anode having an anode composite layer (average thickness: 130 μm).

[0158] A slurry for a cathode composite layer was prepared by mixing 85 parts by weight of natural graphite as a carbon-based active material, 5 parts by weight of SiO (silicon oxide) as a silicon-based active material, 6 parts by weight of carbon black as a conductive material, and 4 parts by weight of PVDF as a binder in an N-methylpyrrolidone solvent, and the slurry was coated onto a copper foil to produce a cathode having a cathode composite layer (average thickness: 180 μm).

[0159] An electrode assembly was manufactured by laminating a separator (thickness: about 16 μm) made of porous polyethylene (PE) film between each manufactured positive electrode and negative electrode. After placing the electrode assembly inside a battery case, an electrolyte was injected into the case to manufacture a lithium secondary battery. The electrolyte is an electrolyte in which 1M LiPF6 is dissolved in an organic solvent in which ethyl methyl carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a composition of 3:7 (volume ratio).

[0161] Preparation Example 2: Preparation of a secondary battery having a cathode comprising a cathode active material containing a large amount of lithium

[0162] In the above Preparation Example 1, the composition of the anode is Li[Li 0.29 Ni 0.14 Co 0.11 Mn 0.46A secondary battery was manufactured using the same method as in Example 1, except that the composition was changed to 5.9 parts by weight of O29, 1.6 parts by weight of PVdF as a binder, and 2.5 parts by weight of carbon black as a conductive material.

[0164] Example 1

[0165] The secondary battery of Manufacturing Example 1 above was pre-aged by leaving it at room temperature (23°C) for 36 hours. The pre-aged battery was first charged to an SOC of 30%. A through hole was formed at the top of the gas pocket portion of the first-charged battery using a piercing member, and the gas inside the battery was exhausted to the outside through the through hole using a depressurization means. Subsequently, a first degassing process was performed by cutting the area containing the through hole and resealing the cut surface. Afterward, the battery was secondarily charged to an SOC of 100%, aged by leaving it at room temperature (23°C) for 48 hours, and a second degassing process was performed again. The second degassing process was performed in the same manner as the first degassing process.

[0167] Example 2

[0168] For the secondary battery of Manufacturing Example 2 above, an activation process was performed in the same manner as in Example 1 above.

[0170] Example 3

[0171] The secondary battery of Manufacturing Example 1 above was pre-aged by leaving it at room temperature (23°C) for 36 hours. The pre-aged battery was first charged to an SOC of 30%. A first degassing process was performed by roll-pressing the battery using a pair of pressure rollers as shown in Fig. 3. At this time, roll-pressing was performed from the electrode assembly housing towards the gas pocket, and the applied line pressure was 3 kgf / cm. Afterward, the battery was secondarily charged to an SOC of 100%, aged by leaving it at room temperature (23°C) for 48 hours, and a second degassing process was performed. The second degassing process was performed by forming a through hole at the top of the gas pocket of the battery using a piercing member, and then exhausting the gas inside the battery to the outside through the through hole using a pressure reduction means. Afterward, the area including the through hole was cut, and the cut surface was re-sealed.

[0173] Example 4

[0174] For the secondary battery of Manufacturing Example 2 above, an activation process was performed in the same manner as in Example 3 above.

[0176] Comparative Example 1

[0177] For the battery of Manufacturing Example 1 above, the activation process was performed in the same manner as Example 1, except that the first degassing process of Example 1 above was omitted.

[0179] Comparative Example 2

[0180] For the battery of Manufacturing Example 2 above, the activation process was performed in the same manner as Example 1, except that the first degassing process of Example 1 above was omitted.

[0182] Experimental Example 1: Discharge-to-Charge Efficiency

[0183] For the batteries manufactured by the activation methods of the above examples and comparative examples, in order to verify the charge-to-discharge efficiency, each was charged to a voltage of 4.3V at 0.1C and then discharged to 2.5V at 0.1C. The charge capacity and discharge capacity measured during the above charging and discharging process were substituted into the following formula to show the charge-to-discharge efficiency in Table 1.

[0184] Charge / Discharge Efficiency (%) = Discharge Capacity × 100 / Charge Capacity

[0186] Experimental Example 2: Reversible Capacity

[0187] For the batteries manufactured by the activation methods of the above examples and comparative examples, to verify the reversible capacity, charging and discharging were performed at 0.1 C and 0.5 C, respectively, at a voltage of 2.5 V to 4.3 V, and the capacity was verified. The results are shown in Table 1 as the capacity ratio compared to Example 1.

[0189] Experimental Example 3: Dose Retention Rate

[0190] For the batteries manufactured by the activation methods of the above examples and comparative examples, charging under constant current / constant voltage conditions up to 4.3V at a rate of 0.8C and cutting off charging at 0.05C were performed, and then discharging at 3.0V at 0.5C. Subsequently, charging under constant current / constant voltage conditions up to 4.3V at a rate of 0.8C and cutting off charging at 0.05C were performed, and discharging at 3.0V at 0.5C at room temperature was performed as one cycle. The cycle capacity retention rate after 100 cycles was expressed as a percentage relative to the capacity per cycle and is listed in Table 1 below.

[0191] Capacity retention rate (%) = × 100

[0193] Experimental Example 4: High-temperature storage thickness increase rate

[0194] For the batteries manufactured by the activation methods of the above examples and comparative examples, charging under constant current / constant voltage conditions up to 4.3V at a rate of 0.8C and cutting off charging at 0.05C were performed, and the increase in thickness after one month while storing at 60℃ was expressed as a percentage relative to the initial thickness and is listed in Table 1 below.

[0195] Discharge efficiency relative to charge Reversible capacity (discharge capacity %, 0.1C / 0.5C) Capacity retention rate High-temperature storage thickness increase rate (%) Example 1 99.7 100 / 100 96.7 4.5 Example 2 99.5 100 / 100 95.1 5.5 Example 3 99.6 100 / 100 96.1 4.7 Example 4 99.4 100 / 100 94.9 5.8 Comparative Example 1 96.4 96.3 / 94.0 90.1 8.3 Comparative Example 2 93.1 94.5 / 92.2 88.2 11.2

[0196] As shown in Table 1 above, the battery according to the activation method of the example showed superior charge / discharge efficiency, reversible capacity, capacity retention rate, and thickness increase rate compared to the battery according to the activation method of the comparative example. Through this, it can be confirmed that, depending on the material characteristics of the cathode material, it is desirable to remove oxygen that can react with the electrolyte or the initial film early during the activation of the battery.

Claims

Claim 1 (a) a primary charging process for charging a lithium secondary battery; (b) a degassing process for discharging an internal gas containing oxygen to the outside of the secondary battery or moving it to a gas pocket; (e) a secondary charging process for further charging the secondary battery; (c) an aging process for aging the secondary battery; and (d) a degassing process for removing gas from the aged secondary battery, wherein the (a) primary charging process, the (b) degassing process, the (e) secondary charging process, the (c) aging process, and the (d) degassing process are performed sequentially, and the (b) degassing process is initiated when the charge depth of the secondary battery is 20% to 80% SOC, and the lithium secondary battery comprises a cathode comprising a cathode additive represented by the following chemical formula 1, a method for activating a lithium secondary battery: [Chemical Formula 1]Li p Co (1-q) M 1 q In the above chemical formula 1, O4, 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, and p and q are 5≤p≤7 and 0, respectively. <q≤0.5이다. Claim 2 delete Claim 3 In claim 1, the above (b) degassing process is a method for activating a lithium secondary battery that is initiated when the charge depth of the secondary battery is 40% to 70%. Claim 4 In claim 1, the (d) degassing process is a method for activating a lithium secondary battery performed after the (c) aging process. Claim 5 delete Claim 6 In claim 1, the (e) secondary charging process is a method for activating a lithium secondary battery by charging to an SOC of 20% to 100%. Claim 7 delete Claim 8 In claim 1, in the above chemical formula 1, M 1 A method for activating a lithium secondary battery in which is a Zn element and q is 0.2≤q≤0.

4. Claim 9 A method for activating a lithium secondary battery according to claim 1, wherein the anode additive is included in an amount of 0.1 to 5 weight% based on the total weight of the anode mixture. Claim 10 The method of activating a lithium secondary battery according to claim 1, wherein the lithium secondary battery comprises a positive electrode including one or more selected from the positive electrode active materials represented by the following chemical formulas 2 to 5. [Chemical Formula 2]Li x [Ni a Co b Mn c ]O2(0.95≤x≤1.05, 0≤ a, b, c ≤1, a+b+c = 1, provided that a and c cannot be 0 simultaneously)[Chemical Formula 3]Li[Li x Ni a Co b Mn c ]O2(0.05≤x≤0.6, x+a+b+c = 1)[Chemical Formula 4]Li x [Ni a Co b Mn c ]O2(0.95≤x≤1.05, 0 < a, b, c ≤1, a+b+c =1, 0.4 <c<1)[화학식 5]LiMn 2-x M x O4(M=one or more elements selected from the group consisting of Ni, Co, Fe and Al, and 0≤x≤2) Claim 11 A method for activating a lithium secondary battery according to claim 1, wherein the (b) degassing process is to discharge an internal gas containing oxygen gas to the outside of the secondary battery. Claim 12 In claim 11, the above (b) degassing process comprises: (b-1) cutting a part of the gas pocket or forming a through hole; (b-2) discharging gas inside the secondary battery to the outside of the secondary battery; and (b-3) re-sealing the gas pocket. A method for activating a lithium secondary battery. Claim 13 A method for activating a lithium secondary battery according to claim 1, wherein the (b) degassing process is to move the internal gas from the electrode assembly to the gas pocket portion. Claim 14 In claim 13, the above (b) degassing process is a method for activating a lithium secondary battery in which the secondary battery is pressurized by roll pressing or jig pressing to move the internal gas remaining in the electrode assembly to the gas pocket portion. Claim 15 In claim 1, the above (a) primary charging process comprises a process of charging the secondary battery while the secondary battery is under pressure, a method for activating a lithium secondary battery.

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