Activation method for lithium secondary batteries

Abstract

The activation method of the present invention includes (a) a primary charging process for charging a lithium secondary battery, (b) a degassing process for discharging 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, and the above (b) degassing process is performed between (a) the primary charging process and (c) the aging process. This has the effect of quickly discharging internal gases, including oxygen gas, and preventing the oxygen gas from reacting with the electrolyte or the coating, thereby improving the capacity and life characteristics of the battery.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0163390 dated November 24, 2021 and Korean Patent Application No. 10-2022-0156297 dated November 21, 2022.

[0002] 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 a positive electrode active material or a positive electrode additive. [Background technology]

[0003] As technological development and demand for mobile devices increases, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density, working potential, long cycle life, and low self-discharge rate, have become commercially available and are widely used.

[0004] In recent years, the use of lithium secondary batteries as power sources for medium- to large-sized devices such as electric vehicles has led to a demand for higher capacity, higher energy density, and lower cost for lithium secondary batteries, and the irreversible additives used in electrodes are also required to have higher irreversible capacities. However, the development of positive electrode additives with such high irreversible capacities has been limited.

[0005] Meanwhile, existing irreversible additives such as Li6CoO4 are generally prepared by reacting cobalt oxide with an excess amount of lithium oxide. The resulting irreversible additives are structurally unstable and generate large amounts of oxygen gas (O2). High-capacity cathode active materials rich in lithium or manganese are also known to generate large amounts of oxygen gas. This oxygen gas chemically reacts with the electrolyte or coating, further increasing gas generation, preventing normal coating formation and degrading coating performance.

[0006] Conventionally, to activate a secondary battery, a primary charging process is performed in which a secondary battery impregnated with an electrolyte is charged until it reaches a predetermined range of SOC, and an aging process is performed in which the primary charged secondary battery is aged, followed by a degassing process in which gas inside the secondary battery is discharged.

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

[0008] Therefore, in a lithium secondary battery having a positive electrode containing a positive electrode active material or a positive electrode additive, there is a need to develop a technology for activating the battery to remove oxygen generated in large amounts. Summary of the Invention [Problem to be solved by the invention]

[0009] SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and aims to provide a method for activating a lithium secondary battery that can improve the electrical performance and safety of the lithium secondary battery. [Means for solving the problem]

[0010] The activation method for a lithium secondary battery according to the present invention includes (a) a primary charging process for charging the lithium secondary battery, (b) a degassing process for discharging 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, and the above (b) degassing process is carried out between the (a) primary charging process and the (c) aging process.

[0011] In one embodiment of the present invention, the above (b) degassing process is initiated when the state of charge of the secondary battery is between 20% and 80% SOC.

[0012] In one embodiment of the present invention, the above (b) degassing process is initiated when the state of charge of the secondary battery is between 40% and 70% SOC.

[0013] In one embodiment of the present invention, the degassing step (d) is carried out after the aging step (c).

[0014] In one embodiment of the present invention, the method further includes (e) a secondary charging process of additionally charging the secondary battery, and the (e) secondary charging process is performed between the (b) degassing process and the (c) aging process.

[0015] In one embodiment of the present invention, the (e) secondary charging step is performed at an SOC of 20% to 100%.

[0016] In one embodiment of the present invention, the lithium secondary battery includes a positive electrode containing a positive electrode additive represented by the following Chemical Formula 1:

[0017] [Chemical formula 1] Li p Co (1-q) M 1 q O4

[0018] 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, and p and q are 5≦p≦7 and 0≦q≦0.5, respectively.

[0019] In one embodiment of the present invention, in the above formula 1, M 1 is the element Zn, and q is 0.2≦q≦0.4.

[0020] In one embodiment of the present invention, the positive electrode additive is contained in an amount of 0.1 to 5% by weight based on the total weight of the positive electrode mixture.

[0021] In one embodiment of the present invention, the lithium secondary battery includes a positive electrode containing one or more positive electrode active materials selected from the group consisting of those represented by the following Chemical Formulas 2 to 5.

[0022] [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, except that a and c cannot be 0 at the same time)

[0023] [Chemical formula 3] Li x Ni a Co b Mn c ]O2 (0.05≦x≦0.6, x+a+b+c=1)

[0024] [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)

[0025] [Chemical formula 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)

[0026] In one embodiment of the present invention, the (b) degassing step is to discharge internal gases containing oxygen gas to the outside of the secondary battery.

[0027] In one embodiment of the present invention, the (b) degassing process may include: (b-1) cutting a portion of the gas pocket or forming a through-hole; (b-2) discharging gas from the inside of the secondary battery to the outside of the secondary battery; and (b-3) re-sealing the gas pocket.

[0028] In another embodiment of the present invention, the degassing step (b) is to move the internal gas from the electrode assembly to the gas pocket.

[0029] In one embodiment of the present invention, the degassing step (b) may be performed by pressing the secondary battery by roll pressing or jig pressure to move the internal gas remaining in the electrode assembly to the gas pocket.

[0030] In one embodiment of the present invention, the (a) primary charging process may include charging the secondary battery in a pressurized state. [Effects of the Invention]

[0031] In the activation method of the present invention, a degassing process is performed during or immediately after the first charging process in the activation process of a lithium secondary battery in which a large amount of oxygen is generated due to the characteristics of a positive electrode active material or a positive electrode additive. This immediately removes internal gas containing oxygen, thereby minimizing the reaction of oxygen gas with the electrolyte or the coating, thereby stably forming an SEI coating and improving the capacity and life characteristics of the battery. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a flowchart of an activation method according to one embodiment of the present invention. [Figure 2] 1 is a flowchart of an activation method according to one embodiment of the present invention. [Figure 3] FIG. 4 is a schematic diagram of a degassing process according to another embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram of a degassing process according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Before that, the terms and words used in the specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concepts of the terms to best describe his own invention.

[0034] Therefore, it should be understood that 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 the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can replace them at the time of this application.

[0035] The present invention will now be described in more detail.

[0036] (Activation method according to the first embodiment) FIG. 1 is a flowchart of an activation method for a lithium secondary battery according to one embodiment of the present invention. Referring to FIG. 1, the activation method according to the present invention includes (a) a primary charging process for charging a lithium secondary battery, (b) a degassing process for discharging 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 (a) primary charging process and the (c) aging process.

[0037] The (a) primary charging process is a step of charging a secondary battery to form an SEI (Solid electrolyte interface, hereinafter referred to as "SEI") film layer on the negative electrode, and is a process of charging the assembled secondary battery at a SOC level within a predetermined range of the full charge capacity (SOC100, State of Charge; SOC). The (c) aging process stabilizes or accelerates the formation of the SEI film formed during the primary charging process.

[0038] During the primary charge process of a lithium secondary battery, lithium ions derived from the positive electrode active material and lithium transition metal oxides, such as positive electrode additives, migrate to the carbon negative electrode. These highly reactive lithium ions react with the carbon negative electrode to form compounds such as Li2CO3, LiO, and LiOH, which then form an SEI film on the negative electrode surface. The SEI film is a non-conductor that forms when the amount of ion movement in the battery increases. The formation of the SEI film prevents 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, allowing only lithium ions to pass through. The formation of this SEI film prevents lithium ions from reacting with the negative electrode or other materials, thereby maintaining the amount of lithium ions reversibly and enabling the secondary battery to be charged and discharged reversibly, thereby extending the life of the secondary battery. Furthermore, because it is not easily degraded even when exposed to high temperatures or subjected to repeated charging and discharging, it also reduces changes in battery thickness.

[0039] However, depending on the material properties of the positive electrode active material or positive electrode additive, a large amount of oxygen gas may be generated during the activation process. In particular, oxygen gas generated during the primary charging process, in which the SEI film is first formed, may hinder the formation of such an SEI film, reduce the performance of the formed SEI film, and generate more internal gas due to reaction with the electrolyte.

[0040] Therefore, the activation method of the present invention (a) immediately discharges the internal gas, including oxygen, generated during the primary charging process (b) performs a degassing process, and then (c) performs an aging process. This allows the oxygen gas generated during the primary charging process to be discharged as much as possible before it reacts with the electrolyte or the initial film, thereby minimizing side reactions caused by the oxygen gas and inducing more stable film formation on the anode.

[0041] The primary charging process (a) is a process of charging a lithium secondary battery at a predetermined state of charge (SOC) range based on the full charge capacity (SOC 100%). Here, the predetermined range may be SOC 20% to SOC 100%, and an appropriate level of SOC is set in consideration of 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 primary charging due to material characteristics, the SOC may be set relatively low to perform the primary charging process.

[0042] In the primary charging step (a), charging may be performed under conditions known in the art. Specifically, charging may be performed at a constant current until the end-of-charge voltage is reached. The charging rate (c-rate) may be 0.01 C to 2 C, 0.1 C to 1.5 C, or 0.2 C to 1 C, but is not limited thereto and may be suitably changed depending on the material properties of the positive and negative electrodes.

[0043] In one embodiment, 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 being pressurized. Pressurizing the secondary battery simultaneously with the charging process in this manner has the effect of preventing gas generated during the charging process from being trapped inside the electrode assembly.

[0044] Such pressure application to the secondary battery can be performed by a jig pressurizing device capable of applying pressure to both surfaces of the secondary battery, but is not limited to this.

[0045] The degassing process (b) is a process of discharging or pushing out internal gases, including oxygen, generated during primary charging due to the material properties of the positive electrode active material or positive electrode additive to the outside of the electrode assembly.

[0046] In one embodiment, the (b) degassing process can be initiated when the state of charge of the secondary battery is between 20% and 80% SOC, preferably between 40% and 70% SOC. Since the purpose of the (b) degassing process is to remove internal gas containing oxygen from the electrode assembly before the oxygen gas reacts with the electrolyte or the initial film, it is efficient to initiate the degassing process at an SOC level within the above range.

[0047] In the activation method according to the first embodiment of the present invention, the (b) degassing process is to discharge internal gases including oxygen gas to the outside of the secondary battery. The (a) primary charging process is performed on a secondary battery that is sealed after housing an electrode assembly in a battery case and injecting an electrolyte solution, and after the (a) primary charging process, an opening is formed in the sealed battery and the internal gases of the secondary battery are discharged to the outside through the opening.

[0048] Such a degassing step (b) can be carried out by any method commonly used in the battery field without any restrictions.

[0049] In one specific example, the (b) degassing process includes: (b-1) cutting a portion of the gas pocket to form an opening or a through-hole; (b-2) discharging gas inside the secondary battery to the outside of the secondary battery through the opening or the through-hole; and (b-3) resealing the gas pocket.

[0050] The step (b-1) of forming an opening or a through-hole is a step of forming an opening or a through-hole in a part of the gas pocket portion through which gas can be vented in order to discharge gas inside the sealed secondary battery to the outside. To form the opening, a part of the pouch can be cut open, and to form the through-hole, a piercing means can be used to form a hole in the pouch. The opening and the through-hole are preferably formed at the upper end of the gas pocket portion.

[0051] The step (b-2) of discharging the internal gas to the outside is a step of discharging the oxygen-containing gas present inside the battery case to the outside through an opening or through-hole formed in the gas pocket. At this time, the chamber housing the lithium secondary battery may be evacuated to a vacuum state, and the internal gas of the lithium secondary battery may be discharged to the outside and removed. Furthermore, the lithium secondary battery may be pressurized during the discharging process.

[0052] (b-3) Resealing the gas pocket is a step of resealing the lithium secondary battery after the degassing process for an aging process or an additional charging process. In one embodiment, the gas pocket can be sealed by cutting out the gas pocket area including the opening or through-hole, removing the opening or through-hole from the gas pocket, and sealing the cut surface.

[0053] The aging process (c) is a process of aging the secondary battery under various conditions to accelerate the stabilization of the SEI film formed during the first charging process (a).

[0054] The aging process can be a room temperature aging process in which the secondary battery is aged for a predetermined time under room temperature / normal pressure conditions, or high temperature aging can be performed instead of room temperature aging depending on the purpose, or both room temperature aging and high temperature aging can be performed. The high temperature aging is a process in which the battery is aged in a high temperature environment, which can accelerate the stabilization of the SEI film, and the high temperature aging and room temperature aging processes can be performed sequentially on a primarily charged battery.

[0055] In one specific example, the high-temperature aging can be carried out at a temperature of 50° C. to 100° C., preferably 50° C. to 80° C. The high-temperature aging can be carried out for 1 hour to 30 hours, preferably 2 hours to 24 hours.

[0056] In one specific example, the room temperature aging can be carried out at a temperature of 18° C. to 28° C., 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 can be carried out for 12 hours to 120 hours, or 18 hours to 72 hours.

[0057] The degassing step (d) is a step of discharging oxygen gas generated during the aging step (c) after the aging step (c). The specific method of the degassing step (d) may be the same as the degassing step (b) described above.

[0058] 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 of additionally charging the secondary battery between (b) a degassing process and (c) an aging process. In this activation method, (a) a primary charging process - (b) a degassing process - (e) a secondary charging process - (c) an aging process - (d) a degassing process are sequentially performed.

[0059] The (e) secondary charging process may involve charging at an SOC of 20% to 100%. Stable activation of the battery can be achieved through stepwise charging, which involves a primary charge followed by a secondary charge. Furthermore, if a large amount of oxygen is generated during primary charging at a normally set SOC level due to the characteristics of the battery's materials, a method may be employed in which the primary charge is performed at an SOC level lower than the normally set SOC level, oxygen gas is removed through the (b) degassing process, and then the remaining depth of charge is filled through the (e) secondary charge. For example, the (a) primary charging process may involve charging the secondary battery to an SOC of 10% to 20%, and the (e) secondary charging process may involve charging the secondary battery to an SOC of 30% to 60%.

[0060] In one embodiment, after the degassing step (d), a full discharge and full charge step may be further performed in which the secondary battery is fully discharged to approximately 0% SOC and then charged to 95% or more of the discharged secondary battery's design capacity (SOC 95%). The full discharge and full charge step may be performed once or repeated two or more times.

[0061] In one embodiment, the method for activating a secondary battery according to the present invention may further include 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 may be performed at room temperature or at a high temperature, specifically for 1 to 21 days. The additional aging process may include a monitoring (OCV tracking) process, which includes measuring the open circuit voltage (OCV) of the battery at regular time intervals, in order to screen for low-voltage defective batteries in which the voltage drops beyond the self-discharge of the battery.

[0062] 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 (a) primary charging process.

[0063] The pre-aging process is a process of aging a battery after assembly so that the electrolyte is sufficiently impregnated into the electrode assembly. After the assembly of a secondary battery is completed, the secondary battery into which the electrolyte has been injected may undergo a pre-aging process in which the secondary battery is left at room temperature for a certain period of time to stabilize so that the electrolyte injected into the secondary battery is sufficiently wetted into the electrode assembly.

[0064] More specifically, when a secondary battery is charged, electrons travel along a conductor to the negative electrode, and lithium ions are absorbed into the negative electrode to achieve charge neutrality. Lithium ions can be absorbed in areas impregnated with electrolyte, i.e., wetting areas where ion migration paths are maintained, but absorption is relatively difficult in non-wetting areas. Therefore, through the pre-aging process, the battery can be aged in an environment with consistent humidity and temperature conditions to ensure that the electrolyte penetrates the positive and negative electrodes.

[0065] In one specific example, the time required for the pre-aging process may be 3 to 72 hours, 6 to 60 hours, or 12 to 48 hours, and this time may be suitably adjusted depending on the materials of the positive electrode, negative electrode, and electrolyte, the design capacity of the secondary battery, etc.

[0066] Furthermore, the temperature during pre-aging may be under normal temperature conditions of 18°C ​​to 28°C, specifically 19°C to 27°C, more specifically 20°C to 26°C, and even more specifically 21°C to 25°C, but is not necessarily limited to these and may be suitably changed depending on the characteristics of the battery to be designed.

[0067] The lithium secondary battery produced according to the activation method of the present invention will now be described in detail.

[0068] The lithium secondary battery of the present invention is manufactured by placing an electrode assembly having a structure of a positive electrode / separator / negative electrode in a battery case, injecting an electrolyte solution into the battery case, and sealing the battery case.

[0069] Specifically, an electrode mixture containing an electrode active material and a binder is applied to an electrode current collector to prepare a positive electrode and a negative electrode, respectively, and then a separator is interposed between the positive electrode and the negative electrode to prepare an electrode assembly.

[0070] The electrode assembly thus prepared is housed in a battery case, and then an electrolyte is injected and the battery case is sealed to assemble the battery.

[0071] The steps for assembling such a battery are not particularly limited and can be carried out according to known methods.

[0072] In addition, the electrode assembly is not particularly limited as long as it has a structure including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and may be, for example, a jelly roll type, a stack type, or a stack / folding type.

[0073] The battery case is not particularly limited as long as it can be used as an exterior packaging material for packaging a battery, and cylindrical, square, or pouch-shaped cases can be used.

[0074] When the battery case is a pouch type, an aluminum laminated pouch including an aluminum layer can be used. After the electrolyte is injected, the opened portion of the aluminum laminated pouch can be sealed by heat welding or heat sealing.

[0075] The lithium secondary battery of the present invention includes 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.

[0076] The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed by applying a positive electrode mixture slurry onto the positive electrode current collector, drying, and pressing. The positive electrode mixture includes a positive electrode active material and a binder, and may further include a positive electrode additive, a conductive material, and a filler, as needed.

[0077] The lithium secondary battery of the present invention is a lithium secondary battery having a positive electrode containing a positive electrode additive represented by the following Chemical Formula 1. Since the positive electrode additive contains an excess amount of lithium, it can provide lithium to replace the lithium generated by an irreversible chemical / physical reaction in the negative electrode during primary charging. As a result, the charge capacity of the battery can be increased, the irreversible capacity can be reduced, and the life characteristics can be improved.

[0078] However, such positive electrode additives are structurally unstable and generate a large amount of oxygen gas when charged, so it is preferable to apply the activation method of the present invention.

[0079] [Chemical formula 1] Li p Co (1-q) M 1 q O4

[0080] In the above chemical formula 1, M 1is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and p and q are 5≦p≦7 and 0≦q≦0.5, respectively.

[0081] As such a positive electrode additive, the present invention may include lithium cobalt oxide represented by Chemical Formula 1, where the lithium cobalt oxide represented by Chemical Formula 1 is Li6CoO4, Li6Co 0.5 Zn 0.5 O4, Li6Co 0.7 Zn 0.3 O4, etc. may be used alone or in combination. The lithium cobalt oxide represented by Chemical Formula 1 has a higher lithium ion content and a lower voltage range required for delithiation compared to nickel-containing oxides commonly used in the industry, and therefore has the advantage of being able to desorb lithium ions without affecting the reaction of the positive electrode active material during battery activation.

[0082] Furthermore, the lithium cobalt metal oxide represented by Chemical Formula 1 may have a tetragonal crystal structure, particularly a P42 / nmc space group. Generally, lithium metal oxides with a tetragonal crystal structure have a structurally unstable structure due to the twist of the tetrahedral structure formed by the cobalt and oxygen elements. This structural instability can lead to the generation of gases, including oxygen, during the primary charge of the battery. The present invention immediately removes the generated oxygen gas, thereby blocking the reaction of the oxygen gas. This not only improves the decomposition and / or delithiation efficiency of the positive electrode additive during the primary charge and the charge / discharge capacity of the lithium secondary battery, but also suppresses the interference of oxygen gas with film formation and the reaction with the electrolyte.

[0083] The content of the positive electrode additive may be 0.1 to 5 parts by weight, specifically 0.1 to 3 parts by weight, or 1 to 3 parts by weight, relative to 100 parts by weight of the total positive electrode mixture.

[0084] The positive electrode mixture containing the positive electrode additive may contain a lithium nickel composite oxide represented by the following chemical formula 6 as a positive electrode active material capable of reversible intercalation and deintercalation.

[0085] [Chemical formula 6] Li x [Ni y Co z Mn w M 2 v ]O u

[0086] In the above chemical formula 6, 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 x, y, z, w, v, and u are in the ranges 1.0≦x≦1.30, 0.1≦y<0.95, 0.01 <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0087] The lithium nickel composite oxide represented by the above chemical formula 6 is a composite metal oxide containing lithium, nickel, cobalt, and manganese, and may contain other transition metals (M 2 ) may be doped. For example, the positive electrode active material may be 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 0.1O2. As an example, the positive electrode active material may contain one or more compounds selected from the group consisting of LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.8 Co 0.1 Mn 0.1 O2 may be used alone or in combination.

[0088] The content of the positive electrode active material may be 85 to 99 parts by weight, specifically 88 to 98 parts by weight, 90 to 97 parts by weight, or 92 to 95 parts by weight, relative to 100 parts by weight of the positive electrode mixture.

[0089] Furthermore, the lithium secondary battery of the present invention may be a secondary battery having a positive electrode containing one or more positive electrode active materials selected from the positive electrode active materials represented by the following Chemical Formulas 2 to 5. Such positive electrode active materials are rich in lithium or manganese and are therefore used in high-capacity batteries. However, due to their characteristics, they generate large amounts of oxygen gas, so it is preferable to apply the activation method of the present invention.

[0090] [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, except that a and c cannot be 0 at the same time)

[0091] [Chemical formula 3] Li x Ni a Co b Mn c ]O2 (0.05≦x≦0.6, x+a+b+c=1)

[0092] [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)

[0093] [Chemical formula 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)

[0094] The positive electrode mixture for the positive electrode of the present invention may further contain a binder and a conductive material in addition to the positive electrode active material, and the content of the positive electrode active material may be 85 to 99 parts by weight, specifically 88 to 98 parts by weight, 90 to 97 parts by weight, or 92 to 95 parts by weight, relative to 100 parts by weight of the positive electrode mixture.

[0095] The conductive material may be used to improve the performance of the positive electrode, such as electrical conductivity, and may be one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber. For example, the conductive material may include acetylene black.

[0096] The conductive material may be contained in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or 2 to 6 parts by weight of conductive material, per 100 parts by weight of the mixture layer.

[0097] 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. For example, the binder may include polyvinylidene fluoride.

[0098] The binder may be contained in an amount of 1 to 10 parts by weight, specifically 1 to 8 parts by weight, or 1 to 6 parts by weight, relative to 100 parts by weight of the entire mixture layer.

[0099] Furthermore, the average thickness of the mixture layer is not particularly limited, but may specifically be 50 μm to 300 μm, 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.

[0100] The positive electrode current collector may be made of a material that has high conductivity and does not induce chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used. In the case of aluminum or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, etc. The current collector may also be formed with fine irregularities on its surface to enhance adhesion of the positive electrode active material, and may be in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric. The average thickness of the current collector may be preferably 3 to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0101] The negative electrode of the lithium secondary battery used in the present invention is prepared by applying a negative electrode active material to a negative electrode current collector, followed by drying and pressing, and may optionally further contain a conductive material, an organic binder polymer, an additive, and the like, similar to those of the positive electrode, as needed.

[0102] In addition, the negative electrode active material may be, for example, graphite having a completely layered crystalline structure such as natural graphite, soft carbon having a low-crystalline layered crystalline structure (graphene structure; a structure in which planes of hexagonal honeycomb patterns of carbon are arranged in layers), hard carbon in which these structures are mixed with amorphous parts, carbon and graphite materials such as artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerene, activated carbon, etc.; Li x Fe2O3(0≦x≦1), Lix WO₂ (0 ≤ x ≤ 1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO₂, PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄, and Bi₂O₅; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxides; lithium titanium oxides, etc. can be used.

[0103] As an example, the negative electrode active material may contain both graphite and silicon (Si)-containing particles. The graphite may include any one or more of natural graphite having a layered crystal structure and artificial graphite having an isometric structure. The silicon (Si)-containing particles are particles containing silicon (Si) as a main component as a metal component, and may include silicon (Si) particles, SiO particles, SiO₂ particles, or a mixture of one or more of these particles.

[0104] In this case, the negative electrode active material may contain 80 to 95 parts by weight of graphite and 1 to 20 parts by weight of silicon (Si)-containing particles with respect to 100 parts by weight in total. By adjusting the contents of graphite and silicon (Si)-containing particles contained in the negative electrode active material within the above ranges, the present invention can improve the charge capacity per unit mass while reducing the lithium consumption amount and the loss of irreversible capacity during the initial charge and discharge of the battery.

[0105] Also, the negative electrode binder layer may have an average thickness of 100 μm to 200 μm. Specifically, it may have an average thickness of 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.

[0106] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, calcined carbon, etc. can be used. In the case of copper or stainless steel, it can also be surface-treated with carbon, nickel, titanium, silver, etc. Furthermore, like the positive electrode current collector, the negative electrode current collector can have fine irregularities on its surface to strengthen its bonding with the negative electrode active material, and can be in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric. The average thickness of the negative electrode current collector is preferably 3 to 500 μm, taking into account the conductivity and total thickness of the negative electrode to be manufactured.

[0107] The separator is a thin insulating membrane interposed between the positive and negative electrodes, exhibiting high ion permeability and mechanical strength. The separator may be any commonly used material in the art, including sheets or nonwoven fabrics made of chemically resistant and hydrophobic materials such as polypropylene, glass fiber, or polyethylene. In some cases, composite separators may be used, in which inorganic particles or organic particles are coated with an organic binder polymer on a porous polymer substrate such as a sheet or nonwoven fabric. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also function as the separator. The separator may have an average pore diameter of 0.01 to 10 μm and an average thickness of 5 to 300 μm.

[0108] The electrolyte may include an organic solvent, a lithium salt, and an additive.

[0109] The organic solvent is not limited as long as it can minimize decomposition due to oxidation during the charge and discharge process of the battery, and may be, for example, a cyclic carbonate, a linear carbonate, an ester, an ether, a ketone, etc. These may be used alone or in combination of two or more.

[0110] Of the above organic solvents, carbonate organic solvents are particularly preferred. Cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), and linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0111] The lithium salt may be any lithium salt commonly used in electrolytes for 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 alone or in combination of two or more thereof.

[0112] The electrolyte solution may further contain an additive. For example, the additive may be any one or a mixture of two or more selected from the group consisting of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sultone, unsaturated sultone, acyclic sulfone, lithium oxalyl difluoroborate (LiODFB), and derivatives thereof, but is not limited thereto, in order to stably form an SEI film.

[0113] Examples of the cyclic sulfite include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethylethylene sulfite, 4,5-diethylethylene sulfite, propylene sulfite, 4,5-dimethylpropylene sulfite, 4,5-diethylpropylene sulfite, 4,6-dimethylpropylene sulfite, 4,6-diethylpropylene sulfite, and 1,3-butylene glycol sulfite. Examples of saturated sultones include 1,3-propane sultone and 1,4-butane sultone. Examples of unsaturated sultones include ethene sultone, 1,3-propene sultone, 1,4-butene sultone, and 1-methyl-1,3-propene sultone. Examples of acyclic sulfones include divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone.

[0114] These additives are added to the electrolyte to improve low-temperature output characteristics by forming a strong SEI film on the negative electrode, as well as to suppress decomposition of the positive electrode surface that may occur during high-temperature cycle operation and prevent oxidation of the electrolyte.

[0115] (Activation method according to the second embodiment) In the activation method according to the second embodiment of the present invention, the degassing process (b) is to move the internal gas containing oxygen from the electrode assembly to the gas pocket. While the degassing process (b) according to the first embodiment is to remove the internal gas containing oxygen by discharging it to the outside of the secondary battery, the degassing process (b) according to the second embodiment is to move the internal gas to the gas pocket as much as possible instead of discharging it to the outside of the battery.

[0116] The gas pocket is a space for collecting internal gas and is typically located in an area where the electrode assembly and electrolyte are not located inside the battery case. Therefore, by maximizing the movement of internal gas, including oxygen, to the gas pocket, it is possible to prevent the oxygen gas from reacting with the electrolyte or the initial coating to some extent.

[0117] In one embodiment, the degassing step (b) may involve pressurizing the secondary battery by roll pressing or jig pressure to move internal gas remaining in the electrode assembly to the gas pocket.

[0118] The (b) degassing process of this embodiment has the advantage that the process is relatively simple compared to a method of removing gas by forming an opening in the gas pocket, evacuating the gas, and then resealing the opening, since the internal gas can be moved to the gas pocket by pressurizing the battery.

[0119] FIG. 3 is a schematic diagram of the roll pressing, and FIG. 4 is a schematic diagram of the jig pressing.

[0120] 3, the pressurization by roll pressing may be performed by running the lithium secondary battery 10 between a pair of lower and upper pressure rollers 21 and 22. At this time, it is preferable to perform the roll pressing sequentially from the electrode assembly 11 toward the gas pocket 12 so that the internal gas, including oxygen, moves from the electrode assembly 11 toward the gas pocket 12. Pressurization by roll pressing has a direction in which the area pressed by the rollers changes sequentially from the electrode assembly toward the gas pocket, and therefore may be more effective in preventing the trapping of internal gas than jig pressing, which will be described later.

[0121] At this time, the linear 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.

[0122] Referring to FIG. 4, the jig pressing is a method of pressing the lithium secondary battery 10 between a pair of flat first and second plates 31 and 32.

[0123] At this time, the numerical range of pressure applied to the lithium secondary battery is specifically 0.1 kgf / cm 2 ~20kgf / cm 2 , or 0.5 kgf / cm 2 ~15kgf / cm 2 , or 1 kgf / cm 2 ~10kgf / cm 2 However, it is not limited to this.

[0124] The present invention will be described in more detail below through examples, etc. However, the configurations described in the examples described in this specification are merely examples of the present invention and do not represent all of the technical ideas of the present invention, so it should be understood that there may be various equivalents and modifications that can replace them at the time of filing this application.

[0125] <Production Example 1: Production of a secondary battery having a positive electrode containing a positive electrode additive> LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 95 parts by weight of O2, Li6Co as a positive electrode additive 0.7 Zn 0.3 A positive electrode mixture layer slurry was prepared by weighing 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 in an N-methylpyrrolidone (NMP) solvent. The mixture layer slurry was applied to an aluminum foil, dried, and then rolled to form a positive electrode having a positive electrode mixture layer (average thickness: 130 μm).

[0126] A negative electrode mixture layer slurry 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. The slurry was then applied to copper foil to prepare a negative electrode having a negative electrode mixture layer (average thickness: 180 μm).

[0127] A separator (thickness: approximately 16 μm) made of porous polyethylene (PE) film was interposed between each of the fabricated positive and negative electrodes to fabricate an electrode assembly. The electrode assembly was placed inside a battery case, and an electrolyte was injected into the case to fabricate a lithium secondary battery. The electrolyte was 1M LiPF6 dissolved in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a 3:7 (volume ratio) mixture.

[0128] <Production Example 2: Production of a secondary battery having a positive electrode including a positive electrode active material containing a large amount of lithium> In the above Production Example 1, the composition of the positive electrode was changed to Li[Li 0.29 Ni 0.14 Co 0.11 Mn 0.46 A secondary battery was manufactured in the same manner as in Preparation Example 1, except that the amount of the cellulose acylate was changed to 95.9 parts by weight of cellulose acetate, 1.6 parts by weight of PVDF as a binder, and 2.5 parts by weight of carbon black as a conductive material.

[0129] Example 1 The secondary battery of Preparation Example 1 was left at room temperature (23°C) for 36 hours to undergo pre-aging. The pre-aged battery was then subjected to a primary charge to an SOC of 30%. A through hole was formed at the top of the gas pocket of the primarily charged battery using a piercing member, and the gas inside the battery was vented to the outside through the through hole using a pressure reducing means. The area including the through hole was then cut and the cut surface was resealed to perform a primary degassing process. The secondary charge was then performed to an SOC of 100%, and the battery was then left at room temperature (23°C) for 48 hours to undergo aging, after which a secondary degassing process was performed again. The secondary degassing process was performed in the same manner as the primary degassing process.

[0130] <Example 2> The secondary battery of Preparation Example 2 was subjected to an activation process in the same manner as in Example 1.

[0131] Example 3 The secondary battery of Preparation Example 1 was left at room temperature (23°C) for 36 hours for pre-aging. 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. Roll-pressing was performed from the electrode assembly housing toward the gas pocket, and a linear pressure of 3 kgf / cm was applied. After a second charge to an SOC of 100%, the battery was left at room temperature (23°C) for 48 hours for aging 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 venting the gas inside the battery to the outside through the through-hole using a pressure reducing means. The area including the through-hole was then cut, and the cut surface was resealed.

[0132] Example 4 The secondary battery of Preparation Example 2 was subjected to an activation process in the same manner as in Example 3.

[0133] <Comparative Example 1> The battery of Preparation Example 1 was activated in the same manner as in Example 1, except that the first degassing process was omitted.

[0134] <Comparative Example 2> The battery of Preparation Example 2 was activated in the same manner as in Example 1, except that the first degassing process was omitted.

[0135] <Experimental Example 1: Discharge efficiency compared to charging> To check the discharge efficiency compared to the charge efficiency of the batteries prepared by the activation methods of the above Examples and Comparative Examples, they were charged to a voltage of 4.3 V at 0.1 C and then discharged to 2.5 V at 0.1 C. The charge capacity and discharge capacity measured during the above charge and discharge processes were substituted into the following equation, and the discharge efficiency compared to the charge efficiency was shown in Table 1.

[0136] Charge / discharge efficiency (%) = discharge capacity x 100 / charge capacity

[0137] <Experimental Example 2: Reversible Capacity> To confirm the reversible capacity of the batteries manufactured by the activation methods of the above Examples and Comparative Examples, they were charged and discharged at 0.1 C and 0.5 C, respectively, at a voltage of 2.5 V to 4.3 V. The results are shown in Table 1 as a capacity ratio compared to Example 1.

[0138] <Experimental Example 3: Capacity Retention Rate> The batteries prepared by the activation methods of the above Examples and Comparative Examples were charged at a constant current / constant voltage at a 0.8 C rate to 4.3 V, charged with a 0.05 C cutoff, and then discharged to 0.5 C and 3.0 V. Subsequently, one cycle was defined as charging at a constant current / constant voltage at a 0.8 C rate to 4.3 V, charged with a 0.05 C cutoff, and then discharged to 0.5 C and 3.0 V at room temperature. After 100 cycles, the cycle capacity retention was expressed as a percentage of the single-cycle capacity and is shown in Table 1 below.

[0139] Capacity retention rate (%) = 100 cycles discharge capacity x 100 / 1 cycles discharge capacity

[0140] <Experimental Example 4: Thickness increase rate during high temperature storage> The batteries prepared by the activation methods of the above Examples and Comparative Examples were charged at a constant current / constant voltage condition of 0.8C rate up to 4.3V and charged with a 0.05C cut-off, and then stored at 60°C for one month. The thickness increase after one month was expressed as a percentage compared to the initial thickness and is shown in Table 1 below.

[0141] [Table 1]

[0142] As can be seen from Table 1 above, the batteries according to the activation methods of the Examples were superior in charge / discharge efficiency, reversible capacity, capacity retention rate, and thickness increase rate compared to the batteries according to the activation methods of the Comparative Examples. This confirms that, depending on the material properties of the cathode material, it is preferable to remove oxygen early during battery activation, which may react with the electrolyte or initial film.

Claims

1. (a) a primary charging process for charging a lithium secondary battery; (b) a degassing step of discharging internal gas containing oxygen to the outside of the lithium secondary battery or moving it to a gas pocket; (c) an aging process for aging the lithium secondary battery; and (d) a degassing step for removing gas from the aged secondary battery; The (b) degassing step is performed between the (a) primary charging step and the (c) aging step; (e) further comprising a secondary charging step of additionally charging the lithium secondary battery; The (e) secondary charging process is performed between the (b) degassing process and the (c) aging process, and the (a) primary charging process - the (b) degassing process - the (e) secondary charging process - the (c) aging process - the (d) degassing process are performed sequentially; The (a) primary charging process charges the secondary battery from SOC 10% to SOC 20%; The (b) degassing step is The method for activating a lithium secondary battery comprises moving the internal gas from the electrode assembly to the gas pocket without discharging the gas from the electrode assembly to the outside of the battery.

2. 2. The method of claim 1, wherein the (e) secondary charging step is performed at an SOC of 20% to 100%.

3. 2. The method of claim 1, wherein the lithium secondary battery comprises a positive electrode containing a positive electrode additive represented by the following Chemical Formula 1: [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.

4. In the above formula 1, M １ 4. The method for activating a lithium secondary battery according to claim 3, wherein q is Zn and q satisfies the condition 0.2≦q≦0.

4.

5. 4. The method for activating a lithium secondary battery according to claim 3, wherein the positive electrode additive is contained in an amount of 0.1 to 5% by weight based on the total weight of the positive electrode mixture.

6. The method for activating a lithium secondary battery according to claim 1, wherein the lithium secondary battery is provided with a positive electrode containing one or more positive electrode active materials selected from the group consisting of positive electrode active materials represented by the following chemical formulas 2 to 5: [Chemical formula 2] Li ｘ [Ni ａ Co ｂ Mn ｃ ]O ２ (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) [Chemical formula 3] Li [Li ｘ Ni ａ Co ｂ Mn ｃ ]O ２ (0.05≦x≦0.6, x+a+b+c=1) [Chemical formula 4] Li ｘ [Ni ａ Co ｂ Mn ｃ ]O ２ (0.95≦x≦1.05、0<a、b、c≦1、a+b+c=1、0.4<c<1) [Chemical formula 5] LiMn ２－ｘ M ｘ O ４ (M=one or more elements selected from the group consisting of Ni, Co, Fe and Al, and 0≦x≦2).

7. 2. The method of claim 1, wherein the degassing step (b) comprises pressurizing the lithium secondary battery by roll pressing or jig pressure to move internal gas remaining in the electrode assembly to the gas pocket.

8. 2. The method of claim 1, wherein the (a) primary charging step includes charging the lithium secondary battery in a pressurized state.

9. a process for producing a positive electrode and a negative electrode; a step of preparing an electrode assembly by interposing a separator between the positive electrode and the negative electrode; a step of assembling a battery by placing the electrode assembly in a battery case, injecting an electrolyte, and sealing the battery case; an activation step of activating the battery, The method for manufacturing a lithium secondary battery, wherein the activation process is carried out by the method for activating a lithium secondary battery according to claim 1 .

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