Method for activating lithium secondary batteries

Abstract

The activation method of the lithium secondary battery according to the present invention includes a pressurizing process of pressurizing the lithium secondary battery by changing the pressure at one or more selected from before the activation process, after the activation process, and during the activation step. This allows air bubbles in the electrolyte or gas generated during activation to move to the gas pocket, preventing internal gas from being trapped within the electrode assembly and improving battery performance.

Description

[Technical field]

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0150214, filed November 4, 2021.

[0002] The present invention relates to a method for activating a lithium secondary battery, which prevents internal gas generated during the activation process from being trapped. [Background technology]

[0003] Generally, secondary batteries can be classified into cylindrical, square, pouch, etc., depending on their shape. Among them, pouch-type secondary batteries are garnering much attention because they have the advantage of being able to significantly reduce the weight of the battery compared to cylindrical or square types that use metal cans, as their exterior is constructed using a pouch exterior material made of a multi-layered film of a metal layer (foil) and a synthetic resin layer coated on the upper and lower surfaces of the metal layer, making it possible to reduce the weight of the battery and change it into various shapes.

[0004] In such a pouch-type secondary battery, electrode assemblies are housed in a stacked form, and electrode tabs and electrode leads are connected to the electrode assemblies, and the electrode leads protrude from the pouch exterior material. The electrode leads are electrically connected to an external device through contact with the external device, and are supplied with power from the external device.

[0005] A pouch-type secondary battery is manufactured through a process of assembling cells and a process of activating the battery. In the battery activation stage, the secondary battery cell is mounted in a charge / discharge device and charged and discharged under conditions required for activation. This process of performing a predetermined charge and discharge using a charge / discharge device to activate the battery is called the activation process or formation process.

[0006] 1 and 2 show an apparatus for the formation process. Referring to Fig. 1, the formation apparatus includes a frame 1, a pressure plate 2, and a driving unit 3: 3a, 3b. The driving unit 3 includes a driving shaft 3a and a driving motor 3b.

[0007] A plurality of pressure plates 2 are arranged inside the frame 1, and between the pressure plates 2, secondary batteries B that undergo a formation process are arranged.

[0008] As shown in Fig. 1, when the driving shaft 3a rotates due to the rotation of the driving motor 3b and the multiple pressurizing plates 2 meshing with it move in one direction, the pressurizing plates 2 pressurize both sides of the secondary battery B as shown in Fig. 2. This pressurized formation has the advantage that it can bring the electrode interface into close contact and control the expansion of the negative electrode, thereby inducing a uniform activation reaction, as compared with the non-pressurized formation.

[0009] However, even if such a pressurized formation process is applied, there are often cases where gas bubbles that have been present since the injection stage and gas generated during the formation process cannot be completely removed. In particular, gas bubbles hinder the movement of lithium ions, causing localized charging non-uniformity and even causing lithium precipitation. Therefore, the reality is that technology development is required to more effectively remove gas in the activation process. Summary of the Invention [Problem to be solved by the invention]

[0010] 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 effectively exhaust air bubbles in the electrolyte and gas between electrode layers. [Means for solving the problem]

[0011] An activation method for a lithium secondary battery according to one embodiment of the present invention includes an activation process of pressurizing and charging a lithium secondary battery, and a pressurizing process of pressurizing the lithium secondary battery by changing the pressure, the activation process consisting of n (n is an integer of 3 or more) activation steps, the activation steps being set such that one or more activation conditions selected from an end-of-charge SOC, a charging rate (c-rate), and a pressure applied to the battery are different for each step, and the pressurizing process may be performed at one or more selected from before the activation process, after the activation process, and between the activation steps.

[0012] In one embodiment of the present invention, the pressurization step is performed by pressing the battery with a pressure of 0.1 kgf / cm 2 ~1.0kgf / cm 2 One stage pressurizes the battery at 2.5kgf / cm 2 ~7.5kgf / cm 2 The first and second pressurizing stages may be carried out sequentially.

[0013] In one embodiment of the present invention, the first and second pressurizing stages may each be performed for 0.1 to 10 minutes, and the first and second pressurizing stages, which form one set, may be performed 1 to 5 times.

[0014] In one embodiment of the present invention, the pressurizing process may be performed before the activation process, after the activation process, and between each of the n activation stages.

[0015] In one embodiment of the present invention, the activation process and the pressurization process may be carried out at a temperature of 40°C to 70°C.

[0016] In one embodiment of the present invention, the activation process includes the steps of: (a) applying pressure to the battery during charging to a pressure of 0.1 kgf / cm 2 ~1.0kgf / cm 2 and (b) the pressure applied to the battery during charging is 2.5 kgf / cm 2 ~7.5kgf / cm 2and the activation step (a) may precede the activation step (b) in time.

[0017] In one embodiment of the present invention, the activation process may include a low-rate charge activation stage having a charge rate of 0.01 C-rate to 0.5 C-rate and a high-rate charge activation stage having a charge rate of 0.6 C-rate to 1.5 C-rate, and the low-rate charge activation stage may precede the high-rate charge activation stage.

[0018] The activation method according to an embodiment of the present invention may further include a degassing process for removing gas from inside the secondary battery by discharging it to the outside.

[0019] In one embodiment of the present invention, the activation process may include an activation 1 stage in which the lithium secondary battery is charged to an SOC of less than 10%, an activation 2 stage in which the lithium secondary battery that has undergone the activation 1 stage is charged to an SOC of 10% to 30%, an activation 3 stage in which the lithium secondary battery that has undergone the activation 2 stage is charged to an SOC of 35% to 50%, and an activation 4 stage in which the lithium secondary battery that has undergone the activation 3 stage is charged to an SOC of more than 50% to 70% or less.

[0020] In one embodiment of the present invention, the pressure applied to the battery during charging in the first and second activation stages is 0.1 kgf / cm 2 ~1.0kgf / cm 2 and the pressure applied to the battery during charging in the third and fourth activation stages may be 2.5 kgf / cm 2 ~7.5kgf / cm 2 It could be.

[0021] In one embodiment of the present invention, the first activation stage can be charged at a charging rate of 0.01 C-rate to 0.5 C-rate, and the second activation stage to the fourth activation stage can be charged at a charging rate of 0.6 C-rate to 1.5 C-rate, respectively.

[0022] In one embodiment of the present invention, the pressurization process can be carried out at the following five points: (i) Before activation step 1 (ii) Between activation stage 1 and activation stage 2 (iii) Between activation stage 2 and activation stage 3 (iv) Between activation stage 3 and activation stage 4 (v) After four activation steps

[0023] In one embodiment of the present invention, the activation process and the pressurizing process may be performed by a formation device that pressurizes the outer surface of the lithium secondary battery.

[0024] The activation method according to an embodiment of the present invention may further include a pre-aging process of aging the assembled secondary battery prior to the activation process.

[0025] 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 pressurizing process.

[0026] In one embodiment of the present invention, the secondary battery may not be charged during the pressurization process. Effect of the Invention

[0027] The activation method according to the present invention includes a pressurizing process of pressurizing a lithium secondary battery by changing the pressure at one or more selected from before, after, and during the activation process, thereby moving gas bubbles in the electrolyte and gas generated during the activation process to gas pockets, preventing internal gas from being trapped within the electrode assembly, and improving battery performance. [Brief description of the drawings]

[0028] [Figure 1] FIG. 2 is a schematic diagram showing a formation device. [Diagram 2] FIG. 2 is a schematic diagram showing a formation device. [Diagram 3]2 is a flow chart of an activation method according to one embodiment of the present invention. [Figure 4] FIG. 2 is a conceptual diagram illustrating the effect of the activation method of the present invention. [Diagram 5] 2 is a flow chart of an activation method according to one embodiment of the present invention. [Figure 6] 2 is a flow chart of an activation method according to one embodiment of the present invention. [Figure 7] 2 is a flow chart of an activation method according to one embodiment of the present invention. [Figure 8] 4 is a flowchart of an activation method according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, the preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Before that, the terms and words used in the specification and claims should not be interpreted limitedly 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 concept of the term in order to best describe his own invention.

[0030] Therefore, it should be understood that the embodiment described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiment 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.

[0031] (Activation method according to the first embodiment) An activation method according to one embodiment of the present invention includes an activation process of pressurizing and charging a lithium secondary battery, and a pressurizing process of pressurizing the lithium secondary battery by changing the pressure, the activation process consisting of n (n is an integer of 3 or more) activation steps, the activation steps being set such that one or more activation conditions selected from an end-of-charge SOC, a charging rate (c-rate), and a pressure applied to the battery are different for each step, and the pressurizing process is performed at one or more selected from before the activation process, after the activation process, and during the activation steps.

[0032] In the activation method of the present invention, a pressurization process is performed at one or more selected points among before, after, and during the activation process in order to prevent gas bubbles present from the liquid injection step and gas generated during the activation process from being trapped inside the electrode assembly.

[0033] FIG. 4 is a conceptual diagram illustrating the effect of the activation method of the present invention. Referring to FIG. 4, a pair of pressure plates 10, 20 pressurize both sides of a secondary battery B interposed between the pressure plates to bring the electrode layer and the electrode layer and the separator into close contact with each other. As a result, gas bubbles present in the electrode assembly and gas generated during the activation process are pushed and moved from the electrode assembly to the gas pocket portion P, thereby minimizing the gas trapping phenomenon and being more effective in removing these gases in the degassing process performed in the latter half of the activation process.

[0034] The activation process is a step of forming a SEI (Solid electrolyte interface, hereinafter referred to as "SEI") coating layer of the negative electrode by charging the secondary battery, and is a process of charging the assembled secondary battery to a predetermined SOC level of the full charge capacity (SOC 100%, SOC; State Of Charge). Here, the predetermined SOC range may be SOC 20% to 80%, and more preferably SOC 40% to 70%.

[0035] When a lithium secondary battery is activated, lithium ions derived from the lithium transition metal oxides, such as the positive electrode active material and the positive electrode additive, move to the carbon electrode, which is the negative electrode. The lithium ions are highly reactive and react with the carbon negative electrode to produce compounds such as Li2CO3, LiO, and LiOH, which form an SEI film on the surface of the negative electrode. The SEI film is a non-conductor formed when the amount of ion movement in the battery increases. When the SEI film is formed, it prevents the lithium ions from reacting with other materials at the negative electrode during subsequent charging of the secondary battery, and acts as a kind of ion tunnel to allow only lithium ions to pass through. When such an SEI film is formed, the lithium ions do not react with the negative electrode or other materials, so the amount of lithium ions is reversibly maintained, and the charge and discharge of the secondary battery is reversibly maintained, which can improve the life of the secondary battery. In addition, it is not easily destroyed even when left at high temperatures or when repeatedly charged and discharged, so there is little change in the thickness of the battery.

[0036] In the activation method of the present invention, the activation process comprises n (n is an integer of 3 or more) activation steps, and each of the activation steps is set so that one or more activation conditions selected from the end-of-charge SOC, the charging rate (c-rate), and the applied pressure to the battery are different for each step.

[0037] That is, the activation process of the present invention comprises three or more activation steps, and each activation step activates the secondary battery by setting one or more different activation conditions selected from the group consisting of the end-of-charge SOC, the charge rate, and the pressure. By performing the activation process by changing the activation conditions for each step in this manner, the secondary battery can be activated more uniformly and effectively since the secondary battery can be charged under suitable charging conditions according to the charge depth of the battery. In addition, a pressure process can be performed between activation steps, and a pressure process can be performed after each activation step, which prevents the gas from being trapped inside the electrode assembly and is more effective in discharging the gas since the gas generated in each activation step can move immediately to the gas pocket.

[0038] Each of the activation steps constituting the activation process of the present invention may be performed at a temperature higher than room temperature in order to reduce the resistance of the electrodes. Specifically, each activation step may be performed at a temperature of 40°C to 70°C, more specifically, at a temperature of 40°C to 60°C, 45°C to 60°C, 50°C to 65°C, 50°C to 60°C, or 52°C to 58°C. The above temperature may be adjusted via a pressurizing means for pressurizing the battery. For example, the above temperature condition may be adjusted by heating a pressurizing plate for pressurizing the outer surface of the battery to a temperature in the above range.

[0039] In the present invention, by performing each activation step under a temperature condition that satisfies the above range, the secondary battery can be charged under a lower resistance condition of the positive electrode, thereby increasing the efficiency of each activation step and improving the uniformity of the SEI film formed in the initial activation step.

[0040] Furthermore, each activation step may be performed for 1 to 100 minutes, specifically 1 to 100 minutes, 1 to 60 minutes, 1 to 40 minutes, 10 to 40 minutes, 20 to 40 minutes, 10 to 30 minutes, 1 to 10 minutes, and 2 to 9 minutes, respectively.

[0041] In the activation process of the present invention, a pressurizing means capable of pressing the outer surface of the lithium secondary battery can be used to pressurize the lithium secondary battery even during charging. FIGS. 1 and 2 show a formation device that pressurizes the secondary battery simultaneously with charging during the activation process. Referring to these drawings, the formation device used in the activation process includes a frame 1, a pressurizing plate 2, a driving unit 3: 3a, 3b, and a charge / discharge unit (not shown). The driving unit 3 includes a driving shaft 3a and a driving motor 3b. A plurality of pressurizing plates 2 are arranged inside the frame 1, and a secondary battery B to undergo the formation process is arranged between the pressurizing plates 2. As shown in FIG. 1, when the driving shaft 3a rotates due to the rotation of the driving motor 3b and the plurality of pressurizing plates 2 meshed with it move in one direction, the pressurizing plates 2 pressurize both sides of the secondary battery B as shown in FIG. 2. In this way, the formation device is configured to pressurize the battery with the lithium secondary battery interposed between a pair of pressurizing plates.

[0042] Since the formation device includes a pressure member such as a pressure plate, it can be used not only in the activation process but also in the pressure application process.

[0043] The activation process of the present invention is as follows: (a) the pressure applied to the battery during charging is 0.1 to 1.0 kgf / cm 2 (b) the pressure applied to the battery during charging is 2.5 to 7.5 kgf / cm 2 In the initial activation stage, the battery is pressurized with a pressure of 0.1 to 1.0 kgf / cm. 2 In the subsequent activation stage, the battery is pressurized to 2.5 to 7.5 kgf / cm 2In this manner, the pressure applied to the battery is increased as the activation stage proceeds by initially applying a low pressure to the lithium secondary battery so that the electrodes in the lithium secondary battery can be sufficiently impregnated with the electrolyte, and then applying a high pressure as gas is generated, so that the lithium secondary battery contains a suitable amount of electrolyte and exhibits excellent performance.

[0044] The pressure applied to the battery in the initial activation stage of (a) is 0.1 to 1.0 kgf / cm 2 and preferably 0.2 to 0.8 kgf / cm 2 , and more preferably 0.3 to 0.7 kgf / cm 2 The pressure applied to the battery in the activation step (b) is 2.5 to 7.5 kgf / cm. 2 and preferably 3.0 to 7.0 kgf / cm 2 , and more preferably 3.5 to 6.5 kgf / cm 2 It could be.

[0045] In addition, the activation process of the present invention includes a low-rate charge activation stage at a charge rate of 0.01 to 0.5 C-rate and a high-rate charge activation stage at a charge rate of 0.6 to 1.5 C-rate, and the low-rate charge activation stage precedes the high-rate charge activation stage in time. That is, in the initial activation stage where the electrolyte is not sufficiently impregnated into the electrodes in the lithium secondary battery, charging is performed at a relatively low charge rate, and as the activation stage progresses, the charging rate may be increased in the activation stage after the initial activation stage in order to induce gas generation.

[0046] The charging rate in the low-rate charging activation stage may be 0.01 C-rate to 0.5 C-rate, preferably 0.05 C-rate to 0.35 C-rate, and more preferably 0.1 C-rate to 0.3 C-rate, and the charging rate in the high-rate charging activation stage may be 0.6 C-rate to 1.5 C-rate, preferably 0.7 C-rate to 1.3 C-rate, and more preferably 0.75 C-rate to 1.25 C-rate.

[0047] The pressurization process according to the present invention is a process carried out separately from the activation process, and is distinguished from the pressurization carried out during the activation process in the present invention. The pressurization process according to the present invention was devised in view of the fact that it is difficult to completely prevent gas from being trapped inside the electrode assembly only by the pressurization carried out during the activation process, and is a separate process independent of the activation process.

[0048] The pressurization process is a process of applying pressure to both sides of the battery, and the air bubbles present in the electrolyte and the gas generated during the activation process can move from the electrode assembly to the gas pockets by the pressurization process.

[0049] In one embodiment of the present invention, the pressurization process may not be performed during charging the secondary battery. The pressurization process is a process of pressurizing the battery in order to move gas or bubbles in the electrode assembly to a gas pocket portion. If charging is performed during the pressurization process, new gas may be generated due to a reaction between the electrodes and the electrolyte. Therefore, it is preferable not to perform charging artificially during the pressurization process.

[0050] The pressurization process of the present invention is carried out at one or more selected points among before the activation process, after the activation process, and during the activation steps. For example, the activation method of the present invention may be carried out in the order of pressurization process → activation process, and may be carried out in the order of pressurization process → activation process → pressurization process as shown in Fig. 3, or in the order of pressurization process → activation step 1 → pressurization process → activation step 2 → pressurization process → activation step 3, or in the order of pressurization process → activation step 1 → pressurization process → activation step 2 → pressurization process → activation step 3 → pressurization process.

[0051] In a preferred embodiment of the present invention, the pressurization process is performed before and after the activation process. It may also be performed between the n activation steps. That is, the pressurization process of the present invention may be performed before and after the activation process, and between the activation steps.

[0052] The pressurizing process may be performed at a temperature higher than room temperature in order to reduce the resistance of the electrodes. Specifically, the pressurizing process may be performed at a temperature of 40°C to 70°C, more specifically, at a temperature of 40°C to 60°C, 45°C to 60°C, 50°C to 65°C, 50°C to 60°C, or 52°C to 58°C. The temperature may be adjusted via a pressurizing means for pressurizing the battery. For example, the temperature condition may be adjusted by heating a pressurizing plate for pressurizing the outer surface of the battery to a temperature in the above range.

[0053] The above pressurization process is performed by applying pressure of 0.1 to 1.0 kgf / cm 2 One stage pressurizes the battery at a pressure of 2.5 to 7.5 kgf / cm 2 In other words, by sequentially performing the first and second pressurizing stages in one pressurizing process, the battery can be pressurized with different pressurizing forces.

[0054] In this case, the first pressurizing step and the second pressurizing step may be carried out for 0.1 to 10 minutes or 0.5 to 5 minutes, respectively.

[0055] In addition, the pressurization process of the present invention may be performed 1 to 5 times, with the pressurization stage 1 and the pressurization stage 2 being one set. That is, the pressurization process consisting of the pressurization stage 1 and the pressurization stage 2 is repeated 1 to 5 times. In this way, by repeatedly performing low pressure pressurization and high pressure pressurization in the pressurization process, the efficiency of gas removal during the activation process can be maximized.

[0056] The pressure in the first step is 0.1 to 1.0 kgf / cm 2and preferably 0.2 to 0.8 kgf / cm 2 , and more preferably 0.3 to 0.7 kgf / cm 2 The pressure in the two pressurizing stages may be 2.5 to 7.5 kgf / cm. 2 and preferably 3.0 to 7.0 kgf / cm 2 , and more preferably 3.5 to 6.5 kgf / cm 2 It could be.

[0057] Fig. 8 illustrates an activation method according to an embodiment of the present invention. Referring to Fig. 8, the activation process according to an embodiment of the present invention may include an activation stage 1 in which a lithium secondary battery is charged to an SOC of less than 10%, an activation stage 2 in which the lithium secondary battery that has undergone the activation stage 1 is charged to an SOC of 10% to 30%, an activation stage 3 in which the lithium secondary battery that has undergone the activation stage 2 is charged to an SOC of 35% to 50%, and an activation stage 4 in which the lithium secondary battery that has undergone the activation stage 3 is charged to an SOC of more than 50% to 70% or less.

[0058] The first activation step is a step of charging to a level of less than 10% SOC, and the end-of-charge SOC may be less than 10%, preferably SOC 1% to SOC 8%, and more preferably SOC 2% to SOC 6%.

[0059] The above two activation stages are stages in which the battery is charged until it reaches an SOC range of 10% to 30%, and the end-of-charge SOC may be 10% to 30%, preferably SOC 12% to SOC 28%, and more preferably SOC 15% to SOC 25%.

[0060] The three activation stages are stages in which the battery is charged until it reaches an SOC range of 35% to 50%, and the end-of-charge SOC may be 35% to 50%, preferably SOC 38% to SOC 48%, and more preferably SOC 42% to SOC 46%.

[0061] The four activation stages are stages in which the battery is charged until it reaches an SOC in the range of more than 50% and not more than 70%, and the end-of-charge SOC can be more than 50% and not more than 70%, 53% to 67%, or 55 to 65%.

[0062] The pressurization process may be carried out (i) before activation step 1, (ii) between activation steps 1 and 2, (iii) between activation steps 2 and 3, (iv) between activation steps 3 and 4, and (v) after activation step 4. By carrying out the pressurization process between each activation step, the gas discharge effect can be further maximized.

[0063] In one specific example, when the activation process is composed of four stages, the pressure applied to the battery during charging in the first and second activation stages is 0.1 to 1.0 kgf / cm. 2 The pressure applied to the battery during charging in the third and fourth activation stages may be 2.5 to 7.5 kgf / cm. 2 It could be.

[0064] In addition, the first activation stage may be charged at a charging rate of 0.01 C-rate to 0.5 C-rate, and the second activation stage to the fourth activation stage may be charged at a charging rate of 0.6 C-rate to 1.5 C-rate, respectively.

[0065] The lithium secondary battery produced according to the activation method of the present invention will now be described in detail.

[0066] 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, and sealing the battery case.

[0067] 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 an electrode assembly is prepared by interposing a separator between the positive electrode and the negative electrode.

[0068] The electrode assembly thus prepared is housed in a battery case, an electrolyte is injected, and the battery case is sealed to assemble the battery.

[0069] The step of assembling such a battery is not particularly limited and can be carried out according to a known method.

[0070] 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.

[0071] The battery case is not particularly limited as long as it is used as an exterior material for packaging a battery, and a cylindrical, rectangular or pouch type battery case may be used.

[0072] 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.

[0073] 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.

[0074] The positive electrode includes a positive electrode current collector and a positive electrode active material layer produced by applying a positive electrode mixture slurry onto the positive electrode current collector, drying and pressing the positive electrode mixture. 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 necessary.

[0075] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite metal oxide may be a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y MnY O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2) (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), etc. may be mentioned, and any one or two or more of these compounds may be included. Among them, in terms of enhancing the capacity characteristics and stability of the battery, the above lithium composite metal oxides are LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 0.6 Mn 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), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 Considering the remarkable improvement effect by controlling the types and content ratio of the constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide may be Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, and the like, and any one or mixtures of two or more of these may be used.

[0076] 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.

[0077] The conductive material may be used to improve the performance of the positive electrode, such as the 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.

[0078] 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, per 100 parts by weight of the mixture layer.

[0079] The binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As an example, the binder may include polyvinylidene fluoride.

[0080] 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 total mixture.

[0081] Furthermore, the average thickness of the mixture layer is not particularly limited, but may be specifically 50 μm to 300 μm, and more specifically 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0082] In addition, the positive electrode may use a current collector having high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used, and in the case of aluminum or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the current collector may have fine irregularities on its surface to increase the adhesive strength of the positive electrode active material, and may be in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc. In addition, the average thickness of the current collector may be preferably 3 to 500 μm, taking into consideration the conductivity and total thickness of the positive electrode to be manufactured.

[0083] In addition, the negative electrode of the lithium secondary battery used in the present invention is manufactured by applying a negative electrode active material onto a negative electrode current collector, drying and pressing the negative electrode active material, and may further selectively contain a conductive material, an organic binder polymer, an additive, etc., similar to those of the positive electrode, as necessary.

[0084] In addition, the negative electrode active material may be, for example, graphite with a completely formed layered crystal structure such as natural graphite, soft carbon having a low-crystalline layered crystal structure (graphene structure; a structure in which planes of a hexagonal honeycomb pattern of carbon are arranged in layers), and hard carbon in which these structures are mixed with an amorphous portion, artificial graphite, expanded graphite, carbon fiber, graphitization-resistant carbon, carbon black, carbon nanotube, fullerene, activated carbon, and other carbon and graphite materials, 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, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 < x ≦ 1, 1 ≦ y ≦ 3, 1 ≦ z ≦ 8), etc. metal composite oxides, lithium metal, lithium alloy, silicon-based alloy, tin-based alloy, SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5, etc. metal oxides, conductive polymers such as polyacetylene, Li-Co-Ni-based materials, titanium oxide, lithium titanate, etc. can be used.

[0085] 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.

[0086] 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, based on a total of 100 parts by weight. 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 charging capacity per unit mass while reducing the lithium consumption and irreversible capacity loss during initial charging and discharging of the battery.

[0087] The negative electrode mixture layer may have an average thickness of 100 μm to 200 μm, specifically, 100 μm to 180 μm, 100 μm to 150 μm, 120 μm to 200 μm, 140 μm to 200 μm, or 140 μm to 160 μm.

[0088] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and may be, for example, copper, stainless steel, nickel, titanium, calcined carbon, etc., and in the case of copper or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, etc. The negative electrode current collector may be formed with fine irregularities on the surface to strengthen the binding force with the negative electrode active material, as with the positive electrode current collector, and may be in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc. The average thickness of the negative electrode current collector may be suitably applied to be 3 to 500 μm in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0089] The separator is interposed between the positive and negative electrodes, and is a thin insulating membrane having high ion permeability and mechanical strength. The separator is not particularly limited as long as it is a membrane commonly used in the art. Specifically, a sheet or nonwoven fabric made of chemically resistant and hydrophobic polypropylene, glass fiber, or polyethylene may be used. In some cases, a composite separator in which inorganic particles / organic particles are coated with an organic binder polymer on a porous polymer substrate such as the sheet or nonwoven fabric may be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator. The pore diameter of the separator may be an average of 0.01 to 10 μm, and the thickness may be an average of 5 to 300 μm.

[0090] The electrolyte may include an organic solvent, a lithium salt, and an additive.

[0091] The organic solvent is not limited as long as it can minimize decomposition due to oxidation reaction during charging and discharging 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.

[0092] Of the above organic solvents, carbonate-based organic solvents are particularly preferably used. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Representative examples of 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).

[0093] The lithium salt may be any lithium salt 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, without any restrictions, and may be used alone or in combination of two or more.

[0094] The electrolyte solution further includes an additive. For example, the additive may be any one selected from the group consisting of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, cyclic sulfurous acid, saturated sultone, unsaturated sultone, acyclic sulfone, lithium oxalyl difluoroborate (LiODFB), and derivatives thereof, or a mixture of two or more of these, but is not limited thereto, in order to stably form an SEI film.

[0095] (Activation method according to the second embodiment) 5 illustrates an activation method according to a second embodiment of the present invention, and referring to FIG. 5, the activation method according to the present invention may further include a pre-aging process for aging the assembled secondary battery before the pressurizing process and the activation process. In the activation method according to the second embodiment, the activation process may include three or more activation steps as described above, and the timing of the pressurizing process is as described above, so further detailed description will be omitted.

[0096] The pre-aging process is a process of aging a battery so that the electrolyte is sufficiently impregnated into the electrode assembly after the battery is assembled. When the secondary battery is assembled, the secondary battery into which the electrolyte is injected may undergo a pre-aging process of being left at room temperature for a certain period of time to be stabilized so that the electrolyte injected into the secondary battery is sufficiently wetted into the electrode assembly.

[0097] More specifically, when a secondary battery is charged, electrons travel on a conductor to the negative electrode and are charged, and lithium ions are absorbed into the negative electrode to achieve charge neutrality. At this time, lithium ions can be absorbed in areas impregnated with electrolyte, i.e., areas where the ion migration path is maintained (wetting areas), but it is relatively difficult to absorb them in non-wetting areas where the electrolyte is not impregnated. Therefore, through the pre-aging process, the battery can be aged in an environment with certain humidity and temperature conditions so that the electrolyte can be well absorbed into the positive and negative electrodes.

[0098] In one embodiment, the time required for the pre-aging process may be specifically 3 hours to 72 hours, 6 hours to 60 hours, or 12 hours to 48 hours, which may be suitably adjusted depending on the materials of the positive electrode, negative electrode, and electrolyte, the design capacity of the secondary battery, etc.

[0099] In addition, 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 thereto and may be suitably changed depending on the characteristics of the battery to be designed.

[0100] FIG. 6 illustrates an activation method according to one embodiment of the present invention. Referring to FIG. 6, the activation method according to one embodiment of the present invention may further include an aging process for aging the secondary battery after the activation process and the pressurization process.

[0101] The aging process is a process of aging the secondary battery under various conditions in order to accelerate the stabilization of the SEI film formed during the activation process.

[0102] The aging process may include a room temperature aging process in which the secondary battery is aged for a predetermined time under room temperature / pressure conditions, or high temperature aging may be performed instead of room temperature aging depending on the purpose, or both room temperature aging and high temperature aging may be performed. The high temperature aging is a process in which the battery is aged in a high temperature environment, which may accelerate the stabilization of the SEI film, and the high temperature aging and room temperature aging processes may be performed sequentially on an initially charged battery.

[0103] In one specific example, the high-temperature aging may be carried out at a temperature of 50° C. to 100° C., preferably 50° C. to 80° C. The high-temperature aging may be carried out for 1 hour to 30 hours, preferably 2 hours to 24 hours.

[0104] In one specific example, the room temperature aging may be performed 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 may be performed for 12 hours to 120 hours, or 18 hours to 72 hours.

[0105] 7 illustrates an activation method according to an embodiment of the present invention, and referring to FIG 7, the activation method of the present invention may further include a degassing process in addition to the activation process and the pressurization process. The degassing process is a process of discharging and removing gas inside the secondary battery to the outside, specifically, a process of discharging and removing internal gas trapped in a gas pocket through the pressurization process to the outside of the battery.

[0106] The pressurization process is a process of pressurizing the battery in order to move bubbles and gas in the electrode assembly to the gas pocket portion. The pressurization process does not have the effect of discharging internal gas to the outside, whereas the degassing process discharging internal gas to the outside of the battery, which is a difference between the two.

[0107] The degassing process may be carried out after the activation process and the pressurizing process. Although FIG. 7 illustrates an example in which the degassing process is carried out after the pressurizing process and the aging process, the degassing process may alternatively be carried out between the final pressurizing process and the aging process.

[0108] Such a degassing process may employ various degassing techniques known at the time of filing of the present invention. For example, the degassing process may be performed by cutting a part of the gas pocket, discharging and removing the internal gas to the outside through the cut part, and then sealing the cut part. However, such degassing techniques are widely known to those skilled in the art, and therefore a detailed description thereof will be omitted.

[0109] The activation method of the present invention may further include a full discharge and full charge process in which the secondary battery is fully discharged to about SOC 0% and then charged to 95% or more of the design capacity (SOC 95%) of the discharged secondary battery. The full discharge and full charge process may be performed once or repeated two or more times.

[0110] 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 including a process of measuring the open circuit voltage (OCV) of the battery at regular time intervals in order to select a low-voltage defective battery in which a voltage drop occurs beyond the self-discharge of the battery.

[0111] The present invention will be described in more detail below with reference to examples, etc. However, the configurations described in the examples described in this specification are merely examples of the present invention and do not fully represent 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.

[0112] <Manufacturing example: manufacturing of lithium secondary batteries> 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 Zinc 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).

[0113] 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, and the slurry was applied to a copper foil to prepare a negative electrode having a negative electrode mixture layer (average thickness: 180 μm).

[0114] A separator (thickness: about 16 μm) made of a porous polyethylene (PE) film was interposed between each of the manufactured positive and negative electrodes, and the electrodes were laminated to manufacture an electrode assembly. The electrode assembly was placed inside a battery case, and an electrolyte was injected into the case, and the case was left at room temperature for 3 days so that the electrolyte was sufficiently impregnated, thereby manufacturing a lithium secondary battery. The electrolyte was prepared by injecting 1MLiPF6 dissolved in an organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a ratio of 3:7 (volume ratio) to manufacture the battery.

[0115] <Example> The assembled lithium secondary battery of the above manufacturing example was prepared and pre-aged at room temperature of 25° C. for 24 hours, and the pre-aged secondary battery was subjected to five pressurization and activation steps according to the procedure shown in Fig. 8. After the final pressurization step, a through hole was formed in the gas pocket, and a degassing step was performed to exhaust the gas inside the battery to the outside. The periphery of the through hole was cut and the battery was resealed.

[0116] At this time, the conditions of the pressurizing process, the charging rate of each activation step, the charge end SOC, and the pressurizing force conditions are as follows:

[0117] [Table 1]

[0118] <Comparative Example> The battery was activated in the same manner as in the above example, except that the five pressurization processes were omitted.

[0119] <Experimental example: Observation of lithium deposition after 100 cycles> Each secondary battery manufactured in the above examples and comparative examples was charged at 0.8C-rate to 4.35V under constant current / constant voltage conditions and 0.05C cut-off charge, and discharged to 0.5C3.0V. Subsequently, 100 cycles were performed, with one cycle being charged at 0.8C-rate to 4.35V under constant current / constant voltage conditions and 0.05 cut-off charge, and discharged to 0.5C3.0V at room temperature, and then the battery was disassembled to observe whether lithium was precipitated. As a result, lithium was not precipitated in the battery of the example, but lithium was precipitated in the battery of the comparative example.

Claims

1. An activation process in which the lithium secondary battery is pressurized and charged; A pressurizing step of pressurizing the lithium secondary battery by changing the pressure is included, The activation process comprises n (n is an integer of 3 or more) activation steps, The activation step is set such that one or more activation conditions selected from a charging end SOC, a charging rate, and a pressure applied to the battery are different for each step, The pressurizing step is performed at one or more selected from the group consisting of before the activation step, after the activation step, and during the activation step; The pressurizing process includes: The lithium secondary battery was subjected to a load of 0.1 kgf / cm ２ ~1.0kgf / cm ２ One pressure stage is pressurized with a pressure of The lithium secondary battery is subjected to 2.5 kgf / cm ２ ~7.5kgf / cm ２ It includes two stages of pressurization, The first pressurization step and the second pressurization step are carried out sequentially, During the pressurization process, the lithium secondary battery is not charged. A method for activating a lithium secondary battery.

2. The first and second pressurizing steps are each performed for 0.5 to 5 minutes, 2. The method for activating a lithium secondary battery according to claim 1, wherein the first pressurizing step and the second pressurizing step form one set and are carried out 1 to 5 sets.

3. An activation process in which the lithium secondary battery is pressurized and charged; A pressurizing step of pressurizing the lithium secondary battery by changing the pressure is included, The activation process comprises n (n is an integer of 3 or more) activation steps, The activation step is set such that one or more activation conditions selected from a charging end SOC, a charging rate, and a pressure applied to the battery are different for each step, The pressurizing step is performed at one or more selected from the group consisting of before the activation step, after the activation step, and during the activation step; The pressurizing process includes: are performed before the activation process, after the activation process, and between each of the n activation steps, During the pressurization process, the lithium secondary battery is not charged. A method for activating a lithium secondary battery.

4. 2. The method for activating a lithium secondary battery according to claim 1, wherein the activation process and the pressurization process are carried out at a temperature of 40° C. to 70° C.

5. An activation process in which the lithium secondary battery is pressurized and charged; A pressurizing step of pressurizing the lithium secondary battery by changing the pressure is included, The activation process comprises n (n is an integer of 3 or more) activation steps, The activation step is set such that one or more activation conditions selected from a charging end SOC, a charging rate, and a pressure applied to the battery are different for each step, The pressurizing step is performed at one or more selected from the group consisting of before the activation step, after the activation step, and during the activation step; The activation process includes: (a) The pressure applied to the lithium secondary battery during charging is 0.1 kgf / cm ２ ~1.0kgf / cm ２ and an activation step, (b) The pressure applied to the lithium secondary battery during charging is 2.5 kgf / cm ２ ~7.5kgf / cm ２ and an activation step in which the activation step (a) precedes the activation step (b) in time; During the pressurization process, the lithium secondary battery is not charged. A method for activating a lithium secondary battery.

6. The activation process includes: a slow charge activation stage in which the charge rate is between 0.01 C-rate and 0.5 C-rate; a fast charge activation stage in which the charge rate is between 0.6 C-rate and 1.5 C-rate; 2. The method for activating a lithium secondary battery according to claim 1, wherein the slow-charge activation step precedes the fast-charge activation step in time.

7. 2. The method of claim 1, further comprising a degassing process for removing gas from inside the lithium secondary battery by discharging it to the outside.

8. An activation process in which the lithium secondary battery is pressurized and charged; A pressurizing step of pressurizing the lithium secondary battery by changing the pressure is included, The activation process comprises n (n is an integer of 3 or more) activation steps, The activation step is set such that one or more activation conditions selected from a charging end SOC, a charging rate, and a pressure applied to the battery are different for each step, The pressurizing step is performed at one or more selected from the group consisting of before the activation step, after the activation step, and during the activation step; The activation process includes: an activation step of charging the lithium secondary battery to an SOC of less than 10%; a second activation step of charging the lithium secondary battery after the first activation step to an SOC of 10% to 30% or less; a third activation step in which the lithium secondary battery that has undergone the second activation step is charged to an SOC of 35% to 50%; The activation step includes a fourth activation step of charging the lithium secondary battery that has been subjected to the third activation step to an SOC of more than 50% to 70%, During the pressurization process, the lithium secondary battery is not charged. A method for activating a lithium secondary battery.

9. In the first activation stage and the second activation stage, the pressure applied to the lithium secondary battery during charging is 0.1 kgf / cm ２ ~1.0kgf / cm ２ and In the third activation stage and the fourth activation stage, the pressure applied to the lithium secondary battery during charging is 2.5 kgf / cm ２ ~7.5kgf / cm ２ The method for activating a lithium secondary battery according to claim 8,

10. The first activation step is performed at a charging rate of 0.01C-rate to 0.5C-rate, 9. The method of activating a lithium secondary battery according to claim 8, wherein the second activation stage to the fourth activation stage are charged at a charging rate of 0.6 C-rate to 1.5 C-rate.

11. 9. The method of claim 8, wherein the pressurizing process is performed at the following five points: (i) Before activation step 1 (ii) Between activation stage 1 and activation stage 2 (iii) Between activation stage 2 and activation stage 3 (iv) Between activation stage 3 and activation stage 4 (v) After four activation steps.

12. 2. The method of claim 1, wherein the activation process and the pressurization process are performed by a formation device that pressurizes the outer surface of the lithium secondary battery.

13. 2. The method for activating a lithium secondary battery according to claim 1, further comprising a pre-aging process for aging the assembled lithium secondary battery prior to the activation process.

14. 2. The method for activating a lithium secondary battery according to claim 1, further comprising an aging process for aging the lithium secondary battery after the activation process and the pressurizing process.

15. Assembling the cells and activating the battery, A method for producing a pouch-type secondary battery, wherein the step of activating the battery is performed by the method for activating a lithium secondary battery according to any one of claims 1 to 14.

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