Activation method of lithium secondary battery

Abstract

Disclosed herein is a method of activating a lithium secondary battery of the present invention, the method including: a pressurizing process of pressurizing the lithium secondary battery while changing the pressure for one or more than two periods selected from the group consisting of before the activation process, after the activation process, and between the activation steps. Accordingly, as the gas bubbles in the electrolyte or the gas generated in the activation process move to the gas pocket portion, internal gas is prevented from being trapped within the electrode assembly, thereby improving battery performance.

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application No. 10-2021-0150214, filed on November 4, 2021, the entire contents of which are incorporated herein by reference.

[0002] This invention relates to an activation method for lithium secondary batteries, the method preventing the retention of internal gases generated during the activation process. Background Technology

[0003] Generally, rechargeable batteries can be classified into cylindrical, prismatic, and pouch-shaped types based on their shape. Among them, pouch-shaped rechargeable batteries are made of an outer material consisting of a metal layer (foil) and a multi-layered synthetic resin coating on the upper and lower surfaces of the metal layer. Compared with cylindrical or prismatic batteries that use metal cans, pouch-shaped batteries achieve significant weight reduction, and they are also attracting attention due to their ability to be shaped into various forms.

[0004] In this type of pouch-type secondary battery, electrode assemblies are stored in a stacked configuration, with electrode tabs and electrode leads connected to the assembly, and the electrode leads protruding from the outer material of the pouch. These electrode leads are electrically connected to an external device via contacts, supplying power from the external device.

[0005] Pouch-type secondary batteries are manufactured through a battery assembly process and a battery activation process. In the battery activation process, the individual secondary battery cells are loaded into a charging and discharging device and charged and discharged under the conditions required for activation. Thus, the process of using a charging and discharging device to perform predetermined charging and discharging to activate the battery is called the formation process.

[0006] Figure 1 and Figure 2 The apparatus used in the formation process is shown. (Reference) Figure 1 The formation apparatus includes a frame (1), a pressure plate (2), and a drive unit (3: 3a, 3b). The drive unit includes a drive shaft (3a) and a drive motor (3b).

[0007] Multiple pressure plates (2) are placed inside the frame (1), and secondary batteries (B) undergoing formation are inserted between the pressure plates (2).

[0008] like Figure 1As shown, when the drive shaft (3a) rotates due to the rotation of the drive motor (3b), causing the multiple pressure plates (2) meshing with it to move in one direction, the pressure plates (2) apply pressure to both sides of the secondary battery (B), as shown in Figure 2. Compared with non-pressurized formation, the advantage of pressurized formation is that it can allow the electrode interface to adhere and control the expansion of the negative electrode, thereby inducing a uniform activation reaction.

[0009] However, even during this pressurized formation process, gases present in the form of bubbles from the injection step onwards, or gases generated during the formation process, are often not completely removed. In particular, gas in the form of bubbles can hinder the movement of lithium ions, leading to uneven local charging and even lithium deposition. Therefore, a technology that can more effectively remove gases is needed in the activation process. Summary of the Invention

[0010] [Technical Issues]

[0011] The present invention aims to solve the problems of the prior art, and the purpose of the present invention is to provide an activation method for a secondary battery, which enables the effective removal of air bubbles in the electrolyte or gas between the electrode layers.

[0012] [Technical Solution]

[0013] An activation method for a lithium secondary battery according to an exemplary embodiment of the present invention includes: an activation step of pressurizing and charging the lithium secondary battery; and a pressurizing step of pressurizing the lithium secondary battery while changing the pressure, wherein the activation step consists of n (n is an integer of 3 or more) activation steps, and the activation steps are configured with different activation conditions according to each step, the activation conditions including one or more selected from: state of charge termination (SOC), charging rate (C-rate), and pressure applied to the battery. The pressurizing step can be performed during one or more selected periods: before the activation step, after the activation step, and between the activation steps.

[0014] In an exemplary embodiment of the present invention, the pressurization process may include a pressure of 0.1 to 1.0 kgf / cm². 2 The first pressurization step of pressurizing the battery under pressure and at 2.5 kgf / cm 2 Up to 7.5 kgf / cm 2 The second pressurization step involves pressurizing the battery under pressure, and the first and second pressurization steps can be performed sequentially.

[0015] In an exemplary embodiment of the present invention, the first pressurization step and the second pressurization step can be performed for 0.1 to 10 minutes, and can be performed in 1 to 5 groups, wherein one group consists of the first pressurization step and the second pressurization step.

[0016] In an exemplary embodiment of the present invention, the pressurization process may be performed before the activation process, after the activation process, and between each of the n activation steps.

[0017] In an exemplary embodiment of the present invention, the activation process and the pressurization process can be carried out at a temperature of 40°C to 70°C.

[0018] In an exemplary embodiment of the present invention, the activation process may include: (a) pressurizing the battery during charging at a pressure of 0.1 kgf / cm². 2 Up to 1.0 kgf / cm 2 (a) the activation step; and (b) the pressure applied to the battery during charging at 2.5 kgf / cm². 2 Up to 7.5 kgf / cm 2 The activation step (a) may precede the activation step (b) in time.

[0019] In an exemplary embodiment of the present invention, the activation process may include: a slow charging activation step with a charging rate of 0.01C to 0.5C; and a fast charging activation step with a charging rate of 0.6C to 1.5C. The slow charging activation step may precede the fast charging activation step in time.

[0020] The activation method according to an exemplary embodiment of the present invention may further include a degassing step, wherein the degassing step removes gas by venting the gas inside the secondary battery to the outside.

[0021] The activation process in an exemplary embodiment of the present invention may include: a first activation step of charging the lithium secondary battery to a SOC of less than 10%; a second activation step of charging the lithium secondary battery that has undergone the first activation step to a SOC in the range of 10% to 30%; a third activation step of charging the lithium secondary battery that has undergone the second activation step to a SOC in the range of 35% to 50%; and a fourth activation step of charging the lithium secondary battery that has undergone the third activation step to a SOC in the range of greater than 50% and less than or equal to 70%.

[0022] In an exemplary embodiment of the present invention, in the first activation step and the second activation step, the pressure applied to the battery during charging can be 0.1 kgf / cm². 2 Up to 1.0 kgf / cm 2 Furthermore, in the third and fourth activation steps, the pressure applied to the battery during charging can be 2.5 kgf / cm². 2 ~7.5 kgf / cm 2 .

[0023] In an exemplary embodiment of the present invention, in the first activation step, the charging rate can be from 0.01C to 0.5C, and in the second to fourth activation steps, the charging rate can be from 0.6C to 1.5C, respectively.

[0024] In an exemplary embodiment of the present invention, the pressurization process can be performed in the following five periods.

[0025] (i) Before the first activation step

[0026] (ii) Between the first and second activation steps

[0027] (iii) Between the second and third activation steps

[0028] (iv) Between the third and fourth activation steps

[0029] (v) After the fourth activation step

[0030] In an exemplary embodiment of the present invention, the activation process and the pressurization process can be performed by a formation apparatus that pressurizes the outer surface of the lithium secondary battery.

[0031] The activation method according to embodiments of the present invention may further include a pre-aging process for aging the assembled secondary battery before the activation process.

[0032] The activation method according to an embodiment of the present invention may further include an aging process for aging the secondary battery after the activation process and the pressurization process.

[0033] In an exemplary embodiment of the present invention, the secondary battery may not be charged during the pressurization process.

[0034] Beneficial effects

[0035] The activation method according to the invention includes a pressurization step, wherein the lithium secondary battery is pressurized while changing pressure during one or more of the following periods: before the activation step, after the activation step, and between the activation steps, by moving gas in the form of bubbles in the electrolyte and gas generated in the activation step to a gas bag portion to prevent internal gas from being trapped inside the electrode assembly, thereby improving battery performance. Attached Figure Description

[0036] Figure 1 and Figure 2 This is a schematic diagram of the formation device.

[0037] Figure 3This is a flowchart of an activation method according to an exemplary embodiment of the present invention.

[0038] Figure 4 This is a conceptual diagram illustrating the effect of the activation method of the present invention.

[0039] Figure 5 This is a flowchart of an activation method according to an exemplary embodiment of the present invention.

[0040] Figure 6 This is a flowchart of an activation method according to an exemplary embodiment of the present invention.

[0041] Figure 7 This is a flowchart of an activation method according to an exemplary embodiment of the present invention.

[0042] Figure 8 This is a flowchart of an activation method according to another exemplary embodiment of the present invention. Detailed Implementation

[0043] The preferred embodiments of the invention will be described in detail below with reference to the accompanying drawings. Prior to this, the terms or words used in this specification and claims should not be construed as having their ordinary or dictionary meaning, but rather should be interpreted as meanings and concepts consistent with the technical concept of the invention, based on the principle that the inventor is able to appropriately define the concepts of the terms in order to best describe and explain his or her invention.

[0044] Therefore, since the embodiments described in the specification and the structures described in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical concepts of the present invention, it should be understood that there are many equivalents and variations that can replace them when this application is filed.

[0045] Activation method according to the first embodiment

[0046] An activation method according to an exemplary embodiment of the present invention includes: an activation step of pressurizing and charging the lithium secondary battery; and a pressurizing step of pressurizing the lithium secondary battery while changing the pressure. The activation step comprises n (n is an integer of 3 or more) activation steps, and each activation step is configured with different activation conditions, including one or more selected from: state of charge termination (SOC), charging rate (C-rate), and pressure applied to the battery. Furthermore, the pressurizing step can be performed during one or more of the following periods: before the activation step, after the activation step, and between the activation steps.

[0047] In the activation method of the present invention, in order to prevent internal gas present in the form of bubbles from the injection step or gas generated in the activation process from remaining inside the electrode assembly, the pressurization step is performed during one or more of the following periods: before the activation process, after the activation process, and between the activation steps.

[0048] Figure 4 This is a conceptual diagram illustrating the effect of the activation method of the present invention. (Reference) Figure 4 As a pair of pressure plates (10, 20) pressurize both sides of the secondary battery (B) placed therebetween, the electrode layer and the gap between the electrode layer and the separator narrow. Therefore, gases in the form of bubbles present in the electrode assembly and gases generated during the activation process are propelled from the electrode assembly to the gas bag section (P). This minimizes gas retention and allows for more efficient removal of these gases during the degassing process, which occurs in the latter part of the activation process.

[0049] The activation process is a step of charging the secondary battery to form an SEI (solid electrolyte interface, hereinafter referred to as "SEI") film layer on the negative electrode, and it is a process of charging the assembled secondary battery within a predetermined range relative to its full charge capacity (SOC 100%, SOC: state of charge). Here, the predetermined range of SOC can be from 20% to 80%, more preferably from 40% to 70%.

[0050] During the activation process of a lithium-ion secondary battery, lithium ions from lithium transition metal oxides such as positive electrode active materials and positive electrode additives contained in the positive electrode migrate to the carbon electrode of the negative electrode. These lithium ions are highly reactive and react with the carbon negative electrode to generate compounds such as Li₂CO₃, LiO, and LiOH, which form an SEI film on the surface of the negative electrode. The SEI film is a non-conductive material formed as the amount of ion movement in the battery increases. After the SEI film forms, during subsequent charging of the secondary battery, it prevents lithium ions from reacting with other substances in the negative electrode, acting as an ion channel that only allows lithium ions to pass through. With such an SEI film formed, lithium ions do not react with the negative electrode or other substances, thus reversibly maintaining the amount of lithium ions and reversibly maintaining the charging and discharging of the secondary battery, thereby improving the battery's lifespan. Furthermore, because it is not easily destroyed even when placed at high temperatures or subjected to repeated charging and discharging, the battery thickness is less prone to change.

[0051] In the activation method of the present invention, the activation process consists of n (n is an integer of 3 or more) activation steps, and each activation step is set with different activation conditions, the activation conditions including one or more of the following: charge termination state of charge (SOC), charging speed (C rate) and pressure applied to the battery.

[0052] That is, the activation process of the present invention consists of three or more activation steps, and each activation step is set with one or more activation conditions selected from the group consisting of: charge termination state of charge (SOC), charging speed, and pressure. When the activation process is performed while changing the activation conditions of each step, the battery can be charged under appropriate charging conditions according to the battery's depth of charge, thereby achieving more uniform and effective activation. Furthermore, the pressurization process can be performed between activation steps, and when the pressurization process is performed after each activation step, the gas generated in each activation step can immediately move to the gas bag section. Therefore, this prevents gas from stagnating inside the electrode assembly and is more effective for gas venting.

[0053] To reduce electrode resistance, each activation step in the activation process of this invention can be performed at a temperature above room temperature. Specifically, each activation step can be performed at a temperature between 40°C and 70°C, specifically between 40°C and 60°C, 45°C and 60°C, 50°C and 65°C, 50°C and 60°C, or 52°C and 58°C. The temperature can be adjusted by a pressure device that pressurizes the battery. For example, the temperature conditions can be adjusted by heating a pressure plate that presses against the outer surface of the battery to a temperature within the above-mentioned range.

[0054] In this invention, by performing each activation step under temperature conditions that meet the above range, the secondary battery can be charged under lower resistance conditions than the positive electrode, thereby improving the efficiency of each activation step and improving the uniformity of the SEI film formed in the initial activation step.

[0055] Furthermore, the activation steps can be performed for 1 minute to 100 minutes. Specifically, they can be performed for 1 minute to 100 minutes, 1 minute to 60 minutes, 1 minute to 40 minutes, 10 to 40 minutes, 20 to 40 minutes, 10 to 30 minutes, 1 to 10 minutes, and 2 to 9 minutes, respectively.

[0056] In the activation process of the present invention, in order to pressurize the lithium secondary battery even during charging, a pressurizing device capable of pressurizing the outer surface of the lithium secondary battery can be used. Figure 1 and Figure 2The diagram shows a formation apparatus that pressurizes the secondary battery while charging it during the activation process. Referring to these figures, the formation apparatus used in the activation process includes: a frame (1), a pressure plate (2), a drive unit (3: 3a and 3b), and a charging / discharging unit (not shown). The drive unit (3) includes a drive shaft (3a) and a drive motor (3b).

[0057] Multiple pressure plates (2) are placed inside the frame 1, and the secondary battery (B) undergoing the formation process is inserted between the pressure plates. Figure 1 As shown, when the rotation of the drive motor (3b) drives the drive shaft (3a) to rotate, causing the multiple pressure plates (2) meshing with it to move in one direction, the pressure plates (2) press against both sides of the secondary battery (B), as shown. Figure 2 As shown. The formation apparatus is configured to pressurize the lithium secondary battery while it is inserted between a pair of pressure plates.

[0058] Because the formation apparatus includes pressing components such as pressure plates, it is used not only in the activation process but also in the pressurization process.

[0059] Furthermore, the activation process of the present invention may include: (a) pressurizing the battery during charging at a pressure of 0.1 to 1.0 kgf / cm². 2 (a) the activation step; and (b) the pressure applied to the battery during charging at 2.5–7.5 kgf / cm². 2 The activation step, wherein the activation step (a) may precede the activation step (b) in time. That is, in the initial activation step, the battery can be activated at a rate of 0.1 to 1.0 kgf / cm². 2 Under pressure, and in the subsequent activation step, the battery can be subjected to pressures ranging from 2.5 to 7.5 kgf / cm². 2 Apply pressure.

[0060] To ensure that the lithium secondary battery contains an appropriate amount of electrolyte to exhibit excellent performance, the pressure applied to the battery is increased as the activation step proceeds. That is, in the initial state, a low pressure is applied to the lithium secondary battery to allow the electrolyte to fully impregnate the electrodes, and a high pressure is applied as gas is generated.

[0061] The pressure applied to the battery in the initial activation step (a) can be from 0.1 to 1.0 kgf / cm². 2 Preferably, it is 0.2 to 0.8 kgf / cm³. 2 More preferably 0.3 to 0.7 kgf / cm 2 The pressure applied to the battery in activation step (b) can be from 2.5 to 7.5 kgf / cm². 2Preferably, it is 3.0 to 7.0 kgf / cm³. 2 More preferably 3.5 to 6.5 kgf / cm³ 2 .

[0062] Furthermore, the activation process of the present invention includes: a slow-charge activation step at a rate of 0.01 to 0.5C; and a fast-charge activation step at a rate of 0.6 to 1.5C. The slow-charge activation step may precede the fast-charge activation step in time. In other words, when the electrolyte has not sufficiently impregnated the electrodes of the lithium secondary battery, the electrodes in the lithium secondary battery are charged at a relatively low charging rate in the initial activation step, and the charging rate is increased in subsequent activation steps, thereby inducing gas generation as the activation steps proceed.

[0063] The charging rate in the slow charging activation step can be from 0.01C to 0.5C, preferably from 0.05C to 0.35C, and more preferably from 0.1C to 0.3C. Furthermore, the charging rate in the fast charging activation step can be from 0.6C to 1.5C, preferably from 0.7C to 1.3C, and more preferably from 0.75C to 1.25C.

[0064] The pressurization step according to the invention is a step performed separately from the activation step, and in the invention, it differs from the pressurization performed during the activation step. The pressurization step of the invention is based on the idea that it is difficult to completely prevent gas from stagnating within the electrode assembly by pressurizing solely during the activation step, thus it is a step independent of the activation step.

[0065] The pressurization process is a process of pressurizing both sides of the battery, and the bubbles present in the electrolyte and the gas generated during the activation process can be moved from the electrode assembly to the gas bag section through the pressurization process.

[0066] In an exemplary embodiment of the present invention, the secondary battery may not be charged during the pressurization process. Since the pressurization process involves pressurizing the battery to move gas or bubbles from the electrode assembly to the gas bag portion, charging during the pressurization process could generate new gas due to the reaction between the electrodes and the electrolyte. Therefore, it is preferable that charging is not performed artificially during the pressurization process.

[0067] The pressurization step of the present invention is performed during one or more of the following periods: before the activation step, after the activation step, and between the activation steps. For example, the activation method of the present invention can be performed in the order of <pressurization step → activation step>, or as follows: Figure 3As shown, it is carried out in the order of <pressurization process → activation process → pressurization process>, and it can also be carried out in the order of <pressurization process → first activation step → pressurization process → second activation step → pressurization process → third activation step>, and it can also be carried out in the order of <pressurization process → first activation step → pressurization process → second activation step → pressurization process → third activation step → pressurization process>.

[0068] In a preferred embodiment of the present invention, the pressurization process can be performed before and after the activation process, and can also be performed between each of the n activation steps. That is, the pressurization process of the present invention can be performed before and after the activation process, and can also be performed between the activation steps.

[0069] The pressurization process can be performed at temperatures above room temperature to reduce electrode resistance. Specifically, the pressurization process can be performed at temperatures between 40°C and 70°C, more specifically, between 40°C and 60°C, 45°C and 60°C, 50°C and 65°C, 50°C and 60°C, or 52°C and 58°C, respectively. The temperature can be regulated by a pressurizing device used to pressurize the battery. For example, the temperature can be regulated by heating a pressure plate that presses against the outer surface of the battery within the aforementioned ranges.

[0070] The pressurization process includes pressures ranging from 0.1 to 1.0 kgf / cm². 2 The first pressurization step of pressurizing the battery under pressure and at 2.5 kgf / cm 2 Up to 7.5 kgf / cm 2 The first pressurization step involves pressurizing the battery under pressure, and the second pressurization step can be performed sequentially. Therefore, by performing the first pressurization step and the second pressurization step sequentially in one pressurization process, the battery can be pressurized while changing the pressure.

[0071] At this point, the first pressurization step and the second pressurization step can be performed for 0.1 to 10 minutes or 0.5 to 5 minutes, respectively.

[0072] Furthermore, the pressurization process of the present invention can be performed in 1 to 5 sets, where each set consists of a first pressurization step and a second pressurization step. That is, the pressurization process consisting of the first pressurization step and the second pressurization step is repeated 1 to 5 times. By repeatedly performing low-pressure pressurization and high-pressure pressurization, the removal efficiency of the activated gas can be maximized.

[0073] The pressurization pressure in the first pressurization step can be from 0.1 to 1.0 kgf / cm³. 2 Preferably, it is 0.2 to 0.8 kgf / cm³. 2 More preferably 0.3 to 0.7 kgf / cm 2The pressurization pressure in the second pressurization step can be 2.5 to 7.5 kgf / cm³. 2 Preferably, it is 3.0 to 7.0 kgf / cm³. 2 More preferably 3.5 to 6.5 kgf / cm³ 2 .

[0074] Figure 8 An activation method according to an exemplary embodiment of the present invention is shown. (Reference) Figure 8 The activation process in an exemplary embodiment of the present invention may include: a first activation step of charging the lithium secondary battery to a SOC of less than 10%; a second activation step of charging the lithium secondary battery that has undergone the first activation step to a SOC in the range of 10% to 30%; a third activation step of charging the lithium secondary battery that has undergone the second activation step to a SOC in the range of 35% to 50%; and a fourth activation step of charging the lithium secondary battery that has undergone the third activation step to a SOC in the range of greater than 50% and less than or equal to 70%.

[0075] The first activation step is to charge to a state of charge (SOC) of less than 10%, and the SOC at the end of charging can be less than 10%, preferably 1% to 8%, and more preferably 2% to 6%.

[0076] The second activation step is to charge the battery until the SOC reaches a range of 10% to 30%, and the SOC at the end of charging can be 10% to 30%, preferably 12% to 28%, and more preferably 15% to 25%.

[0077] The third activation step is to charge the battery until the SOC reaches a range of 35% to 50%, and the SOC at the end of charging can be 35% to 50%, preferably 38% to 48%, and more preferably 42% to 46%.

[0078] The fourth activation step is to charge the battery until the SOC reaches a range of greater than 50% and less than or equal to 70%. The SOC at the end of charging can be greater than 50% and less than or equal to 70%, 53% to 67%, or 55% to 65%.

[0079] Furthermore, the pressurization process can be performed separately at (i) before the first activation step, (ii) between the first and second activation steps, (iii) between the second and third activation steps, (iv) between the third and fourth activation steps, and (v) after the fourth activation step. By performing the pressurization process between each of these activation steps, the gas discharge effect can be further maximized.

[0080] In a specific example, when the activation process includes four steps, the pressure applied to the battery during charging in the first and second activation steps can be from 0.1 to 1.0 kgf / cm², respectively. 2 In the third and fourth activation steps, the pressure applied to the battery during charging can be from 2.5 to 7.5 kgf / cm², respectively. 2 .

[0081] Furthermore, in the first activation step, the charging rate can be from 0.01C to 0.5C, and in the second to fourth activation steps, the charging rate can be from 0.6C to 1.5C.

[0082] The lithium secondary battery manufactured according to the activation method of the present invention will be described in detail below.

[0083] 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 electrolyte and sealing it.

[0084] Specifically, an electrode mixture containing electrode active materials and binders is applied to an electrode current collector to manufacture positive and negative electrodes respectively, and then an electrode assembly is prepared by inserting a diaphragm between the positive and negative electrodes.

[0085] After the prepared electrode assembly is housed in the battery case, electrolyte is injected and the battery case is sealed to assemble the battery.

[0086] There are no particular restrictions on the steps involved in assembling the battery; they can be performed using known methods.

[0087] Furthermore, the electrode assembly is not particularly limited, as long as it has a structure that includes a positive electrode, a negative electrode, and a diaphragm inserted between the positive and negative electrodes. For example, it can be a jelly roll type, a stacked type, or a stacked / folded type.

[0088] There are no particular restrictions on the battery casing, as long as it is used as the outer material for packaging the battery, and it can be cylindrical, prismatic, or pouch-shaped.

[0089] When the battery casing is pouch-shaped, an aluminum laminated bag containing an aluminum layer can be used. After the electrolyte is injected, the opening of the aluminum laminated bag can be sealed by heat welding or heat fusion.

[0090] The lithium secondary battery of the present invention includes an electrode assembly having a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0091] The positive electrode includes a positive electrode active material layer, and the positive electrode active material layer is manufactured by applying a positive electrode mixture slurry onto a positive electrode current collector, followed by drying and pressing. The positive electrode mixture includes a positive electrode active material and a binder, and may further optionally contain positive electrode additives, a conductive material and a filler.

[0092] The positive electrode is a compound capable of reversibly intercalating and deintercalating lithium, and specifically, it may contain a lithium composite metal oxide comprising lithium and one or more metals such as cobalt, manganese, nickel or aluminum. More specifically, the lithium composite metal oxide may include one or two or more compounds selected from the group consisting of: lithium-manganese based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt based oxides (e.g., LiCoO2, etc.), lithium-nickel based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese oxides (e.g., LiNi 1-Y Mn Y O2 (here, 0<Y<1), LiMn 2-z Ni z O4 (here, 0<Z<2), etc.), lithium-nickel-cobalt based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0<Y1<1), etc.), lithium-manganese-cobalt based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (here, 0<Y2<1), LiMn 2-z1 Co z1 O4 (here, 0<Z1<2), etc.), lithium-nickel-manganese-cobalt based oxides (e.g., Li(Ni p Co q Mn r1 )O2 (here, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2 )O4 (here, 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.) or lithium-nickel-manganese-cobalt composite oxides such as Li(Ni p2 Co q2 Mn r3 M S2 )O2 (here, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo; p2, q2, r3 and s2 are each the atomic fraction of the independent element, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1), etc.). In terms of improving battery capacity and stability, the lithium composite metal oxide may be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxides (e.g., Li(Ni 0.6Mn 0.2 Co 0.2 O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 O2 or Li(Ni) 0.8 Mn 0.1 Co 0.1 O2), lithium nickel cobalt aluminum oxides (such as Li(Ni) 0.8 Co 0.15 Al 0.05 (O2, etc.). Considering the significant improvement obtained by controlling the types and proportions of constituent elements in the formation of lithium composite metal oxides, the lithium composite metal oxide can be Li(Ni) 0.7 Mn 0.15 Co 0.15 O2 or Li(Ni) 0.8 Mn 0.1 Co 0.1 O2, etc., or a mixture of one or more thereof.

[0093] Furthermore, relative to 100 parts by weight of the positive electrode mixture, the content of the positive electrode active material may be 85 to 99 parts by weight, or 88 to 98 parts by weight, 90 to 97 parts by weight, or 92 to 95 parts by weight.

[0094] The conductive material can be used to improve the properties of the positive electrode, such as conductivity, and can 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.

[0095] Furthermore, relative to 100 parts by weight of the mixture layer, the content of the conductive material may be 1 to 10 parts by weight, specifically 2 to 8 parts by weight; or the content of the conductive material may be 2 to 6 parts by weight.

[0096] Furthermore, the adhesive may comprise one or more resins selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. As an example, the adhesive may comprise polyvinylidene fluoride.

[0097] Furthermore, the content of the adhesive may be 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 total mixture.

[0098] In addition, the average thickness of the mixture layer is not particularly limited, but specifically, it may 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.

[0099] In addition, as the current collector in the positive electrode, a current collector having high conductivity without causing chemical changes in the battery can be used. For example, stainless steel, aluminum, nickel, titanium, calcined carbon and the like can be used, and in the case of aluminum or stainless steel, aluminum or stainless steel with a surface coated with carbon, nickel, titanium, silver or the like can be used. In addition, the current collector may be formed with micro / nano-scale irregularities on the surface to increase the adhesion strength of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a mesh, a porous material, a foam, and a non-woven fabric. Furthermore, in consideration of the conductivity and total thickness of the manufactured positive electrode, the average thickness of the current collector may be 3 to 500 μm.

[0100] In addition, the negative electrode of the lithium secondary battery used in the present invention is manufactured by coating a negative electrode active material on a negative electrode current collector, drying and pressing, and if necessary, it may optionally further contain the same conductive material, organic binder polymer, additives and the like as those for the positive electrode.

[0101] In addition, the negative electrode active material may include, for example: carbon and graphite materials such as graphite having a complete layered crystal structure, soft carbon having a graphene structure (a structure in which hexagonal honeycomb planes of carbon are arranged in layers), hard carbon having the above structure combined with an amorphous portion, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene, activated carbon and the like; metal composite oxides such as Li x Fe₂O₃ (0≤x≤1), Li x WO₂ (0≤x≤1), Sn x Me 1-x Me' y O z (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); 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 and the like; conductive polymers such as polyacetylene; Li-Co-Ni based materials; titanium oxide; lithium titanium oxide and the like.

[0102] As an example, the negative electrode active material may comprise both graphite and silicon (Si) particles. As graphite, it may include one or more of the following: natural graphite with a layered crystal structure and artificial graphite with a perovskite structure. The silicon (Si) particles are particles with silicon (Si) as the main metallic component, and may include silicon (Si) particles, SiO particles, SiO2 particles, or a mixture of one or more thereof.

[0103] 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) particles relative to 100 parts by weight. By adjusting the content of graphite and silicon particles contained in the negative electrode active material within the above range, the present invention can improve the charging capacity per unit mass while reducing lithium consumption and irreversible capacity loss during the initial charging / discharging of the battery.

[0104] Furthermore, the average thickness of the negative electrode mixture layer can be 100 μm to 200 μm, specifically 100 μm to 180 μm, 100 μm to 150 μm, 120 μm to 200 μm, 140 μm to 200 μm, or 140 μm to 160 μm.

[0105] Furthermore, there are no particular limitations on the negative electrode current collector, as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, nickel, titanium, sintered carbon, etc., can be used. In the case of copper or stainless steel, copper or stainless steel with a surface coated with carbon, nickel, titanium, silver, etc., can be used. In the same manner as the positive electrode current collector, the negative electrode current collector can have micron / nanoscale irregularities formed on its surface to enhance the bonding force with the negative electrode active material, and can be varied in form such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric. Moreover, considering the conductivity and total thickness of the manufactured negative electrode, the average thickness of the negative electrode current collector can be in the range of 3 to 500 μm.

[0106] Furthermore, the separator is inserted between the positive and negative electrodes and uses an insulating film with high ion permeability and mechanical strength. The separator is not particularly limited, as long as it is commonly used in the art; specifically, it can be a sheet or nonwoven fabric made of chemically resistant and hydrophobic polypropylene, glass fiber, or polyethylene. In some cases, a composite separator in which inorganic / organic particles are coated onto a porous polymer substrate such as a sheet or nonwoven fabric using an organic binder polymer can be used. When a solid electrolyte, such as a polymer, is used as the electrolyte, the solid electrolyte can also serve as the separator. Furthermore, the average pore size of the separator can be from 0.01 to 10 μm, and the average thickness can be from 5 to 300 μm.

[0107] The electrolyte may contain organic solvents, lithium salts, and additives.

[0108] There are no limitations on the organic solvent used, as long as it minimizes decomposition due to oxidation or other reactions during the charging / discharging process of the battery. For example, it can be a cyclic carbonate, linear carbonate, ester, ether, or ketone. It can be used alone or in combination of two or more of them.

[0109] Among the aforementioned organic solvents, carbonate organic solvents are preferred. Representative examples of cyclic carbonates are ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC), while representative examples of linear carbonates are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0110] Lithium salts commonly used in electrolytes for lithium secondary batteries, such as LiPF6, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiBF4, LiBF6, LiSbF6, LiN(C2F5SO2)2, LiAlO4, LiAlCl4, LiSO3CF3, and LiClO4, can be used as the lithium salts without limitation, and they can be used alone or in combination of two or more.

[0111] In addition, the electrolyte also contains additives. For example, any one or more mixtures selected from the group consisting of, but not limited to, the following can be used as additives to stably form an SEI film: vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sulfonyl lactone, unsaturated sulfonyl lactone, acyclic sulfone, lithium oxaloyl difluoroborate (LiODFB) and its derivatives.

[0112] Activation method according to the second embodiment

[0113] Figure 5 An activation method according to a second embodiment of the present invention is shown. (Reference) Figure 5 In the activation method of the present invention, a pre-aging process for aging the assembled secondary battery may be included before the pressurization process and the activation process. Regarding the activation method according to the second embodiment, as described above, the activation process may consist of three or more activation steps, and since the starting point of the pressurization process is the same as described above, further detailed description will be omitted.

[0114] The pre-aging process is a process of aging the battery to ensure that the electrolyte is fully immersed in the electrode assembly. When the secondary battery is assembled, a pre-aging process can be performed. This process stabilizes the secondary battery by placing it at room temperature for a certain period of time after electrolyte injection, ensuring that the electrolyte injected into the secondary battery is fully wetted within the electrode assembly.

[0115] More specifically, when the secondary battery is charged, if electrons are introduced into the negative electrode after moving along the wire, lithium ions are inserted into the negative electrode to achieve charge neutrality. At this time, lithium ions can be inserted into the portion impregnated by the electrolyte, i.e., the portion where the ion migration path is maintained (the wetting region), but insertion into the non-wetting region of the electrolyte is relatively difficult. Therefore, through the pre-aging process, the battery can be aged in a constant temperature and humidity environment, thereby allowing the electrolyte to effectively impregnate both the positive and negative electrodes.

[0116] In one specific example, the time required for the pre-aging process can be 3 to 72 hours, 6 to 60 hours, or 12 to 48 hours. This can be appropriately adjusted based on the materials of the positive electrode, negative electrode, and electrolyte, as well as the design capacity of the secondary battery.

[0117] Furthermore, the pre-aging temperature can be carried out at room 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, but is not necessarily limited thereto, and can be changed according to the characteristics of the battery to be designed.

[0118] Figure 6 An activation method according to an exemplary embodiment of the present invention is shown. (Reference) Figure 6 According to an exemplary embodiment of the present invention, the activation process may further include an aging process for the secondary battery after the activation process and the pressurization process.

[0119] The aging process is a process of aging the secondary battery under various conditions to accelerate the stabilization of the SEI film formed through the activation process.

[0120] In the aging process, a room temperature aging process can be performed to age the secondary battery for a predetermined time at room temperature. Depending on the purpose, high temperature aging can be performed instead of room temperature aging, or both room temperature aging and high temperature aging can be performed. The high temperature aging process is a process of aging the battery in a high temperature environment, and it can accelerate the stabilization of the SEI film. The high temperature aging and room temperature aging processes can be performed sequentially on the initially charged battery.

[0121] 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.

[0122] 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.

[0123] Figure 7 An activation method according to an embodiment of the present invention is shown. (Reference) Figure 7 The activation method of the present invention may further include a degassing step in addition to the activation step and the pressurization step. The degassing step is a step of removing gas by venting the gas inside the secondary battery to the outside. Specifically, it is a step of removing gas by venting the internal gas retained in the gas bag to the outside of the battery.

[0124] The pressurization process is a process of pressurizing the battery to move air bubbles or gas in the electrode assembly to the gas bag section. The pressurization process does not have the effect of venting internal gas to the outside, but because the degassing process vents the internal gas to the outside of the battery, there is a difference between the pressurization process and the degassing process.

[0125] The degassing process can be performed after the activation and pressurization processes. Figure 7 An embodiment is shown in which the degassing process is performed after the pressurization process and the aging process. Alternatively, the degassing process may be performed between the final pressurization process and the aging process.

[0126] The degassing process can employ various degassing techniques known at the time of this invention. For example, the degassing process can be performed by cutting open a portion of the gas bag to release the internal gas to the outside through the cut, and then sealing the cut portion. However, since such degassing techniques are known to those skilled in the art, further detailed descriptions will be omitted.

[0127] In the activation method of the present invention, a full charge and discharge process can be performed, in which the secondary battery is completely discharged to near SOC 0%, and then the discharged battery is charged to 95% or more of its design capacity (SOC 95%). The full charge and discharge process can be performed once or repeated more than twice.

[0128] In one specific example, in the activation method of the secondary battery according to the invention, an additional aging process can be performed after the full discharge and charge processes. This additional aging process is a process to stabilize the secondary battery, and it can be performed at room temperature or high temperature, specifically for 1 to 21 days. To screen out low-voltage defective batteries whose voltage drops beyond the battery's self-discharge range, the additional aging process may include a monitoring (OCV tracking) process, which includes periodically measuring the battery's open-circuit voltage (OCV).

[0129] The present invention will be described in detail below with reference to embodiments. However, various other modifications can be made to the embodiments according to the present invention, and the scope of the invention should not be construed as limited to the embodiments described below. Embodiments of the invention are provided to provide a more complete description of the invention to those skilled in the art.

[0130] Preparation example: Preparation of lithium secondary batteries

[0131] By using 95 parts by weight of LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, 0.9 parts by weight of Li6Co as a positive electrode additive 0.7 Zn 0.3 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 mixed in N-methylpyrrolidone (NMP) solvent to prepare a slurry for a positive electrode mixture layer. The slurry for the mixture layer was coated onto aluminum foil, dried, and then rolled to form a positive electrode with a positive electrode mixture layer (average thickness: 130 μm).

[0132] A slurry for a negative electrode mixture layer was prepared by mixing 85 parts by weight of natural graphite as a carbon active material, 5 parts by weight of SiO (silicon oxide) as a silicon active material, 6 parts by weight of carbon black as a conductive material, and 4 parts by weight of PVDF as a binder into an N-methylpyrrolidone solvent. The slurry was then coated onto a copper foil to form a negative electrode with a negative electrode mixture layer (average thickness: 180 μm).

[0133] Electrode assemblies were fabricated by arranging and laminating porous polyethylene (PE) membranes (approximately 16 μm thick) between the prepared positive and negative electrodes. After arranging the electrode assemblies within a battery case and injecting electrolyte into the case, the secondary battery was placed at room temperature for three days to allow the electrolyte to fully impregnate the electrode assemblies, thereby fabricating the lithium secondary battery. The battery was fabricated by injecting an electrolyte obtained in which 1 M LiPF6 was dissolved in an organic solvent containing a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a 3:7 (volume ratio).

[0134] Example 1

[0135] An assembled lithium secondary battery for the preparation example was prepared and pre-aged by aging at room temperature (25°C) for 24 hours. Furthermore, the pressurization and activation steps were performed according to... Figure 8 The pre-aged secondary battery is subjected to five cycles in the sequence shown. After the final pressurization process, degassing is performed by forming a through-hole in the air bag to release the gas inside the battery to the outside, and the area around the through-hole is cut open and the battery is resealed.

[0136] At this time, the conditions for the pressurization process, as well as the charging speed, charging termination SOC, and pressing conditions for each step of the activation process, are as follows.

[0137] [Table 1]

[0138]

[0139] Comparative example

[0140] The battery was activated in the same manner as in Example 1, except that the five pressurization processes were not performed.

[0141] Experimental example: Observe lithium deposition after 100 cycles.

[0142] The secondary batteries manufactured in the examples and comparative examples were charged at a rate of 0.8C up to 4.35V under constant current / constant voltage conditions and then discharged at 0.5C to 3.0V. Subsequently, 100 cycles were performed, with one cycle consisting of charging at a rate of 0.8C up to 4.3V under constant current / constant voltage conditions and then discharging at 0.5C to 3.0V at room temperature. The batteries were then disassembled to observe for lithium deposition. As a result, no lithium was deposited in the batteries of the examples, but lithium was deposited in the batteries of the comparative examples.

Claims

1. A method for activating a lithium secondary battery, comprising: An activation process that involves pressurizing and charging a lithium secondary battery; The pressurization process involves changing the pressure while simultaneously pressurizing the lithium secondary battery. The activation process includes n activation steps, where n is an integer greater than or equal to 3; The activation step is configured with different activation conditions depending on each step. The activation conditions include one or more of the following: state of charge termination (SOC), charge rate (C), and pressure applied to the battery. The pressurization process is performed during one or more of the following periods: before the activation process, after the activation process, and between the activation steps. The pressurization process includes: At 0.1 kgf / cm 2 Up to 1.0 kgf / cm 2 The first pressurization step involves pressurizing the battery under pressure. At 2.5 kgf / cm 2 Up to 7.5 kgf / cm 2 The second pressurization step involves pressurizing the battery under pressure. And the first and second pressurization steps are performed sequentially, and The pressurization process is performed in 1 to 5 groups, one of which consists of the first pressurization step and the second pressurization step.

2. The activation method for a lithium secondary battery according to claim 1, wherein the first pressurization step and the second pressurization step are performed for 0.5 minutes to 5 minutes respectively.

3. The activation method for a lithium secondary battery according to claim 1, wherein the pressurization step is performed before the activation step, after the activation step, and between the n activation steps.

4. The activation method for a lithium secondary battery according to claim 1, wherein the activation step and the pressurization step are performed at a temperature of 40°C to 70°C.

5. The activation method for a lithium secondary battery according to claim 1, wherein the activation step comprises: (a) The pressure applied to the battery during charging is 0.1 kgf / cm². 2 Up to 1.0 kgf / cm 2 The activation step; (b) The pressure applied to the battery during charging is 2.5 kgf / cm². 2 Up to 7.5 kgf / cm 2 The activation step, Furthermore, the activation step (a) precedes the activation step (b) in time.

6. The activation method for a lithium secondary battery according to claim 1, wherein the activation step includes: Slow charging activation steps with a charging rate of 0.01C to 0.5C; and Fast charging activation steps with charging speeds ranging from 0.6C to 1.5C. Furthermore, the slow charging activation step precedes the fast charging activation step in time.

7. The activation method for a lithium secondary battery according to claim 1 further includes a degassing step, wherein the degassing step removes gas by venting the gas inside the secondary battery to the outside.

8. The activation method for a lithium secondary battery according to claim 1, wherein the activation step includes: The first activation step involves charging the lithium secondary battery to a state of charge (SOC) of less than 10%. The lithium secondary battery that has undergone the first activation step is charged to a second activation step with a state of charge (SOC) of 10% to 30%. The lithium secondary battery, having undergone the second activation step, is then charged to a third activation step with a state of charge (SOC) of 35% to 50%; and The lithium secondary battery, which has undergone the third activation step, is then charged to a fourth activation step with a state of charge (SOC) greater than 50% and less than or equal to 70%.

9. The activation method for a lithium secondary battery according to claim 8, wherein in the first activation step and the second activation step, the pressure applied to the battery during charging is 0.1 kgf / cm², respectively. 2 Up to 1.0 kgf / cm 2 , Furthermore, in the third and fourth activation steps, the pressure applied to the battery during charging is 2.5 kgf / cm². 2 ~7.5 kgf / cm 2 .

10. The activation method for a lithium secondary battery according to claim 8, wherein in the first activation step, the charging rate is 0.01C to 0.5C, and in the second to fourth activation steps, the charging rate is 0.6C to 1.5C.

11. The activation method for a lithium secondary battery according to claim 8, wherein the pressurization step is performed in the following five stages: (i) Before the first activation step (ii) Between the first and second activation steps (iii) Between the second and third activation steps (iv) Between the third and fourth activation steps (v) After the fourth activation step.

12. The activation method for a lithium secondary battery according to claim 1, wherein the activation step and the pressurization step are performed by a formation apparatus that pressurizes the outer surface of the lithium secondary battery.

13. The activation method for a lithium secondary battery according to claim 1, Prior to the activation process, a pre-aging process is also included to age the assembled secondary batteries.

14. The activation method for a lithium secondary battery according to claim 1, After the activation and pressurization processes, an aging process is also included to age the secondary battery.

15. The activation method for a lithium secondary battery according to claim 1, wherein... The secondary battery is not charged during the pressurization process.

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