Method for manufacturing lithium secondary battery

Abstract

The present invention relates to a method for manufacturing a lithium secondary battery, the method comprising: a step (S1) of manufacturing a preliminary battery comprising a positive electrode containing a positive electrode active material, a negative electrode, a separator, and an electrolyte; and a step (S2) of charging the preliminary battery to a charge cut-off voltage and discharging the preliminary battery to a discharge cut-off voltage to activate the preliminary battery, in which the positive electrode active material contains a lithium-rich manganese-based oxide containing 50 mol% or more of manganese (Mn) among all metals other than lithium, and the molar ratio of lithium to all metals other than lithium (Li / Me) exceeds 1, and wherein the charge cut-off voltage is greater than 4.3 V and the discharge cut-off voltage is 2.6 V or more.

Description

TECHNICAL FIELD

[0001] Cross Reference to Related Applications

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0124358, filed on September 18, 2023, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

[0003] The present application relates to a method of manufacturing a lithium secondary battery, and more particularly, to a method of manufacturing a lithium secondary battery capable of reducing the amount of gas generated in an activation process of a battery including a lithium-rich manganese-based oxide and achieving excellent capacity characteristics and resistance characteristics. BACKGROUND

[0004] A lithium secondary battery is an energy storage medium that has been applied to various fields since it was commercially used in 1991. As the market for products equipped with a lithium secondary battery expands, research into improving the energy density of a lithium secondary battery has been actively conducted. One of the most focused methods is to develop a positive active material having a composition that can utilize a larger amount of lithium than before.

[0005] As a positive active material that can utilize a larger amount of lithium, a lithium-rich transition metal oxide having a layered structure and a molar ratio of lithium to transition metal greater than 1 has been developed. Because such a lithium-rich transition metal oxide achieves capacity by not only utilizing a cation redox reaction of a transition metal but also utilizing an anion redox reaction of oxygen used in a positive electrode structure, it can exhibit higher capacity characteristics.

[0006] A lithium secondary battery applying such a lithium-rich transition metal oxide generally achieves high capacity by performing an activation process at a high voltage of 4.3 V or more. However, in such a high-voltage activation process, oxygen desorption can occur, which can cause excessive gas to be generated. Such gas can make it difficult for the activation process to proceed, and can cause the battery quality to decrease. In addition, there is a problem in that oxygen desorption and cation mixing are induced in the crystal structure of the lithium-rich transition metal oxide, resulting in a significant increase in the resistance of the positive electrode. In addition, in the high-voltage activation process, elution of transition metals such as manganese occurs, and the transition metals can be deposited on the negative electrode to cause the negative electrode to deteriorate, thereby decreasing the life characteristics of the secondary battery.

[0007] When the activation voltage is lowered, the amount of gas generated during the activation process can be reduced, but in this case, abnormal behavior in which the capacity is abnormally increased during the operation of the battery can occur, and problems such as generation of additional gas can occur. SUMMARY

[0008] TECHNICAL PROBLEM

[0009] An object of the present invention is to provide a method for manufacturing a lithium secondary battery, which can reduce the amount of gas generated in the activation process of a lithium secondary battery containing a lithium-rich manganese-based oxide and achieve excellent resistance characteristics and capacity characteristics.

[0010] Technical solution

[0011] According to an embodiment of the present invention, there is provided a method for manufacturing a lithium secondary battery, the method comprising: Step (S1): manufacturing a preliminary battery, the preliminary battery including a positive electrode containing a positive electrode active material, a negative electrode, a separator, and an electrolyte; and Step (S2): charging the preliminary battery to a charging cut-off voltage and discharging the preliminary battery to a discharging cut-off voltage to activate the preliminary battery, where the positive electrode active material includes a lithium-rich manganese-based oxide, the lithium-rich manganese-based oxide contains 50 mol% or more of manganese (Mn) among all metals other than lithium, and the molar ratio of lithium to all metals other than lithium (Li / Me) exceeds 1, and

[0012] The average particle size (D ) of the positive electrode active material may be 1.5 μm to 13 μm.

[0013] The positive electrode active material includes a first positive electrode active material and a second positive electrode active material having different average particle sizes (D 50 ), and the average particle size of the first positive electrode active material may be greater than the average particle size of the second positive electrode active material. <{

[0014] The average particle size (D 50 ) of the first positive electrode active material may be 6 μm to 15 μm.

[0015] The average particle size (D 50 ) of the second positive electrode active material may be 0.5 μm to 6 μm.

[0016] The lithium-rich manganese-based oxide may be represented by Chemical Formula 1 below.

[0017] [Chemical Formula 1]

[0018] Li x1 Mn y1 M 1 1-y1 O2

[0019] where in Chemical Formula 1, 1 < x1 ≤ 1.5 and 0.5 ≤ y1 ≤ 1, and M 1 It is at least one element selected from Ni, Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr.

[0020] In the activation step, charging may include a first charge at a C rate of 0.04C to 0.5C and a second charge at a C rate of 0.3C to 1.2C.

[0021] The first charge can be performed until the SOC of the pre-charged battery is between 1 and 10, and a second charge can be performed after the first charge until the SOC of the pre-charged battery is between 80 and 100.

[0022] The second charge may include a 2-1 charge at a C rate of 0.8C to 1.2C and a 2-2 charge at a C rate of 0.3C to 0.6C.

[0023] 2-1 charging can be performed after the first charging until the SOC of the pre-charged battery becomes between 40 and 80%, and 2-2 charging can be performed after 2-1 charging until the SOC of the pre-charged battery becomes between 80 and 100%.

[0024] The first charge can be performed in constant current mode (CC mode).

[0025] The second charge can be performed in constant current-constant voltage mode, and the second charge can be performed up to a charging cutoff current of 0.02C to 0.25C.

[0026] The discharge cutoff voltage can be above 2.7 V and below 3.5 V.

[0027] During the activation step, the discharge can be carried out at a C-rate of 0.4C to 1.5C.

[0028] Beneficial effects

[0029] According to the present invention, when a lithium secondary battery containing lithium-rich manganese oxides is activated, the charging cut-off voltage and the discharging cut-off voltage are adjusted to a specific range to minimize cation mixing and oxygen desorption.

[0030] As a result, the resistance characteristics of the positive electrode and the battery are improved, the amount of gas generated and manganese dissolution during the high-voltage activation process is minimized, and the activation time is shortened, thereby improving productivity. Furthermore, the lithium secondary battery manufactured by the method of this invention exhibits excellent capacity characteristics and suppresses the increase in positive electrode resistance during charging and discharging, thus resulting in excellent resistance and lifespan characteristics. Detailed Implementation

[0031] The embodiments of the present invention will be described in more detail below.

[0032] The terms or words used in this specification and claims should not be construed as limited to ordinary or dictionary terms, and the invention should be interpreted as having meanings and concepts consistent with the technical concept of the invention, based on the principle that inventors can appropriately define the concepts of terms to best describe their own invention.

[0033] The terminology used herein is for describing exemplary embodiments but does not limit the concept of the invention. Unless the context clearly indicates otherwise, the singular form includes the plural form.

[0034] It should be understood that the terms “comprising,” “including,” “having,” etc., are used herein to explicitly state the presence of the stated feature, integer, step, element, or combination thereof, but do not exclude the presence or addition of more than one other feature, integer, step, element, or combination thereof.

[0035] In this invention, "particle size D" 50 The average particle size refers to the particle size corresponding to 50% of the cumulative volume in the particle size distribution of the cathode material powder, and can be measured by laser diffraction. For example, the average particle size can be measured by dispersing the cathode material powder in a dispersion medium, introducing the resulting material into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiating it with ultrasound at a frequency of approximately 28 kHz and an output of 60 W, obtaining a volumetric particle size distribution map, and then determining the particle size corresponding to 50% of the cumulative volume.

[0036] As used in this article, "specific surface area" is measured by the BET (Brunauer-Emmett-Teller) method, and in particular, it can be calculated by the amount of nitrogen adsorbed at liquid nitrogen temperature (77 K) using the BELSORP-miniII, which is available from BEL Japan Inc.

[0037] As used herein, “SOC (State of Charge) X” refers to the percentage (%) of the capacity charged in a battery cell relative to the discharge capacity when the battery cell is discharged to the discharge cutoff voltage, for example, from 4.6 V to, for example, 2.0 V.

[0038] Because lithium-rich manganese oxides achieve high capacity by utilizing both the cation redox reaction of transition metals and the anion redox reaction of oxygen in the cathode structure, they can achieve high capacity. Specifically, lithium-rich manganese oxides have a structure in which LiMO2 (where M is a transition metal) with a layered structure and Li2MnO3 with a rock salt structure are mixed. The activation process is carried out at a high voltage of 4.3 V or higher, thereby activating Li2MnO3 to achieve high capacity. However, the problem is that oxygen desorption occurs during the high-voltage activation process, resulting in excess gas, a significant increase in the resistance of the cathode, and the dissolution of transition metals such as manganese. If the activation voltage is reduced, the amount of gas generated during the activation process can be reduced, but in this case, an abnormal increase in capacity may occur when the residual Li2MnO3 phase in the crystal structure is activated during battery operation, and the problem of generating additional gas may arise.

[0039] The inventors conducted repeated research to improve the resistance and capacity characteristics of lithium secondary batteries using lithium-rich manganese oxides. As a result, they discovered that by performing an activation process under specific charge and discharge conditions during the manufacture of lithium secondary batteries, cation mixing and oxygen desorption are minimized, thereby improving the resistance and capacity characteristics of the cathode and the battery, reducing gas generation and manganese dissolution, and thus improving the battery's lifespan. This led to the completion of this invention.

[0040] Methods for manufacturing lithium secondary batteries

[0041] A method for manufacturing a lithium secondary battery according to one embodiment includes: Step (S1): Manufacturing a pre-battery, said pre-battery comprising a positive electrode containing a positive electrode active material, a negative electrode, a separator, and an electrolyte; and Step (S2): Charge the pre-battery to the charging cutoff voltage and discharge the pre-battery to the discharging cutoff voltage to activate the pre-battery. The positive electrode active material comprises a lithium-rich manganese oxide, wherein the lithium-rich manganese oxide contains more than 50 mol% manganese (Mn) in all metals other than lithium, and the molar ratio of lithium to all metals other than lithium (Li / Me) exceeds 1. The charging cutoff voltage is greater than 4.3 V, and the discharging cutoff voltage is greater than 2.6 V.

[0042] The steps of a method for manufacturing a lithium secondary battery according to one embodiment will now be described in detail.

[0043] (1) Step S1: Manufacturing a preparatory battery

[0044] First, step (S1) is performed: a pre-battery is manufactured, which includes a positive electrode containing a positive active material, a negative electrode, a separator, and an electrolyte.

[0045] In this case, the steps for manufacturing a pre-built battery may include: The steps of sequentially stacking the positive electrode, separator, and negative electrode to assemble the electrode assembly; and The steps involve housing the electrode assembly in a battery case, injecting electrolyte, and then sealing the battery case.

[0046] Sealing can be achieved by heat welding or heat fusion of the openings in the battery casing.

[0047] In this context, a "prepared battery" can refer to a lithium secondary battery prior to the activation step. Specifically, it can refer to a lithium secondary battery that has not yet undergone an activation process through charging or charge / discharge.

[0048] The positive electrode contains a positive electrode active material. Specifically, the positive electrode may include: a positive electrode current collector; and a layer of positive electrode active material located on the positive electrode current collector, and the positive electrode active material layer may contain positive electrode active material.

[0049] There are no particular restrictions on the positive electrode current collector, as long as it has high conductivity and will not cause chemical changes in the battery. Materials used include, for example, stainless steel, aluminum, nickel, titanium, sintered carbon; or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness of 3 to 500 μm. Additionally, the positive electrode current collector can have fine irregularities formed on its surface to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabric structures.

[0050] The positive electrode active material layer can be located on the positive electrode current collector; specifically, it can be located on one or both surfaces of the positive electrode current collector. The positive electrode active material layer can have a single layer or a multilayer structure with two or more layers.

[0051] The positive electrode active material comprises a lithium-rich manganese oxide, wherein the lithium-rich manganese oxide contains more than 50 mol% manganese (Mn) in all metals other than lithium, and the molar ratio of lithium to all metals other than lithium (Li / Me) exceeds 1.

[0052] In the case of lithium-rich manganese oxides containing excessive lithium, it has a structure in which a layered phase (LiM'O2) and a rock salt phase (Li2MnO3) are mixed. When the rock salt phase is activated during the initial activation process, excessive lithium ions are generated, thereby enabling high capacity.

[0053] For example, the lithium-rich manganese-based oxide can be represented by the following [Chemical Formula 1].

[0054] [Chemical Formula 1]

[0055] Li x1 Mn y1 M 1 1-y1 O2

[0056] Among them, in Chemical Formula 1, M 1 is at least one element selected from Ni, Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0057] x1 is the molar ratio of Li in the lithium-rich manganese-based oxide, which can be 1 < x1 ≤ 1.5, preferably 1.1 ≤ x1 ≤ 1.5. When x1 satisfies the above range, the irreversible capacity of the negative electrode active material can be fully compensated, and high-capacity characteristics can be achieved.

[0058] y1 is the molar ratio of Mn in the lithium-rich manganese-based oxide, which can be 0.5 ≤ y1 ≤ 1, preferably 0.5 ≤ y1 < 1 or 0.55 ≤ y1 ≤ 0.85. When y1 is less than 0.5, the proportion of the rock salt phase is too small, so the compensation of the negative electrode irreversibility and the capacity improvement effect are slight.

[0059] On the other hand, in the lithium-rich manganese-based oxide represented by [Chemical Formula 1], the molar ratio of Li to the total number of moles of all metal elements other than Li (Li / Me) can be 1.1 to 1.5, 1.13 to 1.5, or 1.2 to 1.4. When the Li / Me ratio satisfies the above range, the rate performance and capacity characteristics are excellent. If the Li / Me ratio is too high, the conductivity decreases and the rock salt phase (Li2MnO3) increases, which may accelerate the deterioration rate, and if the Li / Me ratio is too low, the energy density improvement effect is slight.

[0060] Preferably, the lithium-rich manganese-based oxide can be represented by the following [Chemical Formula 1-1].

[0061] [Chemical Formula 1-1]

[0062] Li x2 Ni y2 Co z2 Mn w2 M 2 v2 O2

[0063] Among them, in Chemical Formula 1-1, M 2 can be at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0064] On the other hand, x2 can be the molar ratio of Li in the lithium-rich manganese-based oxide, and can be 1 < x2, 1.1 ≤ x2 ≤ 1.5 or 1.2 ≤ x2 ≤ 1.4. When a satisfies the above range, the irreversible capacity of the negative electrode can be sufficiently compensated, and high-capacity characteristics can be achieved.

[0065] y2 can be the molar ratio of Ni in the lithium-rich manganese-based oxide, and can be 0 ≤ y2 ≤ 0.5, 0.1 ≤ y2 ≤ 0.4 or 0.2 ≤ y2 ≤ 0.4.

[0066] z2 is the molar ratio of Co in the lithium-rich manganese-based oxide, and can be 0 ≤ z2 ≤ 0.1, 0 ≤ z2 ≤ 0.08 or 0 ≤ z2 ≤ 0.05. If z2 is greater than 0.1, it is difficult to ensure high capacity, and the generation of gas and the deterioration of the positive electrode active material may become aggravated, which may reduce the life characteristics.

[0067] w2 is the molar ratio of Mn in the lithium-rich manganese-based oxide, and can be 0.5 ≤ w2 < 1.0, 0.50 ≤ w2 ≤ 0.80 or 0.50 ≤ w2 ≤ 0.70. If w2 is less than 0.5, the proportion of the rock salt phase is too small, and the negative electrode irreversible compensation and capacity improvement effects are slight.

[0068] v2 is the molar ratio of the doping element M in the lithium-rich manganese-based oxide, and can be 0 ≤ v2 ≤ 0.2, 0 ≤ v2 ≤ 0.1 or 0 ≤ v2 ≤ 0.05. If the content of the doping element is too high, it may have an adverse effect on the capacity of the active material.

[0069] On the other hand, the composition of the lithium-rich manganese-based oxide can be represented by the following [Chemical Formula 2].

[0070] [Chemical Formula 2]

[0071] a2 Li2MnO3·(1 - a2)Li[Ni 1-b2-c2-d2 Mn b2 Co c2 M 4 d2 O2

[0072] Wherein in [Chemical Formula 2], M 4 can be at least one selected from metal ions Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr.

[0073] a2 refers to the proportion of the Li2MnO3 phase in lithium-rich manganese oxides, which can be 0.2≤a2≤0.5, 0.25≤a2≤0.5, or 0.25≤a2≤0.4. When the proportion of the Li2MnO3 phase in the lithium-rich manganese oxide meets the above range, the irreversible capacity of the negative electrode can be fully compensated, and high capacity characteristics can be achieved.

[0074] b2 refers to the molar ratio of Mn in the layered phase LiM'O2, which can be 0.4≤b2<1, 0.4≤b2≤0.8, or 0.4≤b2≤0.7.

[0075] c2 refers to the molar ratio of Co in the layered phase LiM'O2, which can be 0 ≤ c2 ≤ 0.1, 0 ≤ c2 ≤ 0.08, or 0 ≤ c2 ≤ 0.05. When c2 is greater than 0.1, gas generation and degradation of the positive electrode active material may become more pronounced, which may lead to a decrease in lifetime characteristics.

[0076] d2 is the dopant element M in the LiM'O2 layer. 4 The molar ratio can be 0≤d2≤0.2, 0≤d2≤0.1, or 0≤d2≤0.05.

[0077] On the other hand, if desired, the positive electrode active material can also include a coating on the surface of a lithium-rich manganese oxide. When the positive electrode active material includes a coating, the contact between the lithium-rich manganese oxide and the electrolyte is suppressed by the coating, and side reactions of the electrolyte are reduced, thereby achieving the effect of improved lifespan characteristics.

[0078] The coating may include coating element M 5 And coated element M 5 It can be at least one selected from, for example, Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, preferably Al, Co, Nb, W, and combinations thereof, more preferably Al, Co, and combinations thereof. Coating element M 5 It can contain more than two types, such as Al and Co.

[0079] The coating can be formed using methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). Among these, atomic layer deposition is preferred because the coating can be formed with a wider area.

[0080] Based on the total surface area of ​​lithium-rich manganese oxide particles, the coating formation area can be 10% to 100%, preferably 30% to 100%, and more preferably 50% to 100%. When the coating formation area meets the above range, the effect of improving lifespan characteristics is excellent.

[0081] On the other hand, the positive electrode active material according to the present invention can be in the form of primary particles or secondary particles in which multiple primary particles are aggregated.

[0082] Average particle size D of positive electrode active material 50 The particle size can range from 1.5 μm to 13 μm. The average particle size (D) of the positive electrode active material... 50 The electrode thickness can be 1.5 μm or larger, 2 μm or larger, or 2.3 μm or larger, and can be 13 μm or smaller, 12 μm or smaller, 11 μm or smaller, 10 μm or smaller, or 9 μm or smaller. When the above ranges are met, excellent electrode density can be achieved, and the reduction in capacity and rate characteristics can be minimized.

[0083] Specifically, the positive electrode active material can contain materials with different average particle sizes (D). 50 The first positive electrode active material and the second positive electrode active material are selected, and the average particle size of the first positive electrode active material can be larger than the average particle size of the second positive electrode active material. In this case, when rolling the electrode, the smaller particle size of the second positive electrode active material can be filled into the voids of the larger particle size of the first positive electrode active material, thereby increasing the electrode density and achieving a high energy density per unit volume.

[0084] The average particle size (D) of the first positive electrode active material 50 The particle size can range from 6 μm to 15 μm. Specifically, the average particle size (D) of the first positive electrode active material... 50 The size can be 6 μm or larger, 6.5 μm or larger, 7 μm or larger, 7.5 μm or larger, 8 μm or larger, 8.5 μm or larger, or 9 μm or larger, and can be 15 μm or smaller, 14 μm or smaller, 13 μm or smaller, 12 μm or smaller, or 11 μm or smaller.

[0085] The average particle size (D) of the second positive electrode active material 50 The particle size can range from 0.5 μm to 6 μm. Specifically, the average particle size (D) of the second positive electrode active material... 50 The size can be 0.5 μm or larger, 1.0 μm or larger, 1.5 μm or larger, 2 μm or larger, or 2.5 μm or larger, and can be 6 μm or smaller, 5.5 μm or smaller, 5 μm or smaller, 4.5 μm or smaller, or 4 μm or smaller.

[0086] When the average particle size of the first and second positive electrode active materials meets the aforementioned range, the particles of the second positive electrode active material fill the spaces between the particles of the first positive electrode active material, thereby improving the tap density of the positive electrode active material containing it. A higher tap density results in a higher electrode packing density. Therefore, when using it to manufacture electrodes, a slurry containing positive electrode active material with the aforementioned tap density can be thinly coated onto the surface of the positive electrode current collector, thereby improving the thickness of the coated electrode to be thin. During the calendering process, lower pressure is required to achieve an electrode thickness matching the calendering density, thereby reducing cracking of the positive electrode active material caused by calendering. Furthermore, with the improvement in energy density per unit volume, capacity characteristics can also be further improved.

[0087] Furthermore, the BET specific surface area of ​​the positive electrode active material can be 0.9 m². 2 / g to 5.0 m 2 / g. Specifically, the BET surface area of ​​the positive electrode active material can be 0.9 m². 2 / g or more, 0.95 m 2 / g or more, 1.0 m 2 / g or more, 1.05 m 2 / g or more, 1.1m 2 / g or more, 1.15 m 2 / g or more or 1.2 m 2 / g or more, and 5.0 m 2 / g or less, 4.5 m 2 / g or less, 4.0 m 2 / g or less, 3.5 m 2 / g or less, 3.0 m 2 / g or less or 2.5 m 2 / g or less. When the BET surface area of ​​the positive electrode active material meets the above range, it can ensure that the migration rate (kinetics) of lithium ions at the interface between the positive electrode active material and the electrolyte is above a certain level, thereby achieving sufficient capacity. At the same time, it can prevent side reactions with moisture or electrolyte to reduce gas generation, thereby improving lifetime characteristics.

[0088] On the other hand, lithium-rich manganese oxides can be produced by mixing transition metal precursors with lithium feedstocks and then calcining the mixture.

[0089] As lithium raw materials, lithium-containing carbonates (such as lithium carbonate), hydrates (such as lithium hydroxide hydrate (LiOH·H2O)), hydroxides (such as lithium hydroxide), nitrates (such as lithium nitrate (LiNO3)), chlorides (such as lithium chloride (LiCl)) can be used, and one or a mixture of two or more of them can be used.

[0090] On the other hand, the transition metal precursor can be in the form of hydroxides, oxides, or carbonates. Using a carbonate precursor is preferred because it allows for the creation of a positive electrode active material with a relatively high specific surface area.

[0091] Transition metal precursors can be prepared via coprecipitation. For example, transition metal precursors can be prepared by dissolving various transition metal-containing raw materials in a solvent to prepare a metal solution, then mixing the metal solution, an ammonium cation complexing agent, and a basic compound, and carrying out a coprecipitation reaction. Furthermore, if desired, an oxidizing agent or oxygen can be added during the coprecipitation reaction.

[0092] At this point, the raw materials containing transition metals can be various transition metal acetates, carbonates, nitrates, sulfates, halides, sulfides, etc. Specifically, the raw materials containing transition metals can be NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halides, etc.

[0093] The ammonium cation complex forming agent can be at least one selected from NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4 and (NH4)2CO3.

[0094] The basic compound can be at least one selected from NaOH, Na₂CO₃, KOH, and Ca(OH)₂. The form of the precursor can vary depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a precursor in the form of a hydroxide can be obtained, and when Na₂CO₃ is used as the basic compound, a precursor in the form of a carbonate can be obtained. Furthermore, when the basic compound is used in conjunction with an oxidizing agent, a precursor in the form of an oxide can be obtained.

[0095] On the other hand, the transition metal precursor can be mixed with the lithium raw material in an amount such that the molar ratio of all transition metals (Ni+Co+Mn):Li is 1:1.05 to 1:2, preferably 1:1.1 to 1:1.8, and more preferably 1:1.25 to 1:1.8.

[0096] On the other hand, firing can be carried out at temperatures of 600°C to 1000°C or 700°C to 950°C, and the firing time can be 5 hours to 30 hours or 5 hours to 20 hours. In addition, the firing atmosphere can be an air atmosphere or an oxygen atmosphere, such as an atmosphere containing 20 to 100% by volume oxygen.

[0097] On the other hand, in addition to the positive electrode active material, the positive electrode active material layer may also include the positive electrode conductive material and the positive electrode binder.

[0098] Examples of positive electrode conductive materials include: spherical or sheet-like graphite; carbonaceous materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, carbon fibers, single-walled carbon nanotubes, and multi-walled carbon nanotubes; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One or more of these materials may be used alone, or in mixtures thereof. Based on the total weight of the positive electrode active material layer, the content of the positive electrode conductive material can range from 0.1% by weight to 20% by weight.

[0099] Furthermore, the positive electrode binder may include, for example, polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and may use any one of them alone or a mixture of two or more thereof. Based on the total weight of the positive electrode active material layer, the content of the positive electrode binder may be from 1 to 20% by weight.

[0100] The positive electrode can be manufactured according to conventional positive electrode manufacturing methods. For example, the positive electrode can be manufactured by mixing positive electrode active material, positive electrode binder and / or positive electrode conductive material in a positive electrode solvent to prepare a positive electrode slurry, coating the positive electrode slurry onto a positive electrode current collector, and then drying and calendering it.

[0101] The cathode solvent can be any solvent commonly used in the art. Solvents can be dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, water, etc., and can be used alone or in mixtures of two or more of them. As long as the solvent can dissolve or disperse the cathode active material, conductive material, and binder, and thus has a viscosity that exhibits excellent thickness uniformity when used for coating the cathode, the amount of solvent used will be sufficient, taking into account the thickness of the slurry to be coated and the manufacturing yield.

[0102] Alternatively, the positive electrode can be manufactured by casting the positive electrode slurry onto a separate carrier and then stacking the film obtained by peeling it off from the carrier onto the positive electrode current collector.

[0103] On the other hand, the negative electrode may contain a negative electrode active material. Specifically, the negative electrode may contain a negative electrode current collector and a layer of negative electrode active material located on the negative electrode current collector, and the negative electrode active material layer may contain negative electrode active material.

[0104] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes to the electrode. Examples of negative electrode current collectors can include: copper, stainless steel, aluminum, nickel, titanium, calcined carbon; copper or stainless steel surface-treated with carbon, nickel, silver, etc.; aluminum-cadmium alloys, etc. Furthermore, the thickness of the negative electrode current collector can typically range from 3 to 500 μm. Similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the negative electrode active material. For example, negative electrode current collectors can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabric structures.

[0105] The negative electrode active material layer can be located on the negative electrode current collector, specifically, it can be located on one or both surfaces of the negative electrode current collector.

[0106] As anode active materials, compounds capable of reversibly inserting and de-intercalating lithium can be used. Specific examples of anode active materials can include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, or amorphous carbon; (semi-metallic) materials capable of forming alloys with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and (semi-metallic) oxides capable of doping and de-doping lithium, such as SiO2. β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or composites containing (semi)metallic materials and carbonaceous materials such as Si-C composites or Sn-C composites, and any one or a mixture of two or more thereof may be used.

[0107] Furthermore, lithium metal films can be used as negative electrode active materials. Additionally, carbonaceous materials can be either low-crystallinity carbon or high-crystallinity carbon. Soft carbon and hard carbon are typical examples of low-crystallinity carbon. Typical examples of high-crystallinity carbon include irregular, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, high-temperature calcined carbons such as mesophase pitch, and coke derived from petroleum or coal tar pitch.

[0108] On the other hand, in addition to the negative electrode active material, the negative electrode active material layer may optionally further include a negative electrode conductive material and a negative electrode binder.

[0109] Furthermore, the negative electrode conductive material is used to impart conductivity to the electrode, and there are no restrictions on the use of conductive materials, as long as they are electronically conductive and do not cause chemical changes in the battery to be constructed. Specific examples include: graphite such as natural graphite and artificial graphite; carbonaceous materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, carbon fiber, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, etc. One or a mixture of two or more of these can be used. Based on the total weight of the negative electrode active material layer, the content of the negative electrode conductive material can be 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0110] The adhesive plays a role in ensuring good adhesion between the particles of the negative electrode active material and further improving the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof may be used. Based on the total weight of the negative electrode active material layer, the content of the negative electrode adhesive may be 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0111] The negative electrode can be manufactured according to conventional negative electrode manufacturing methods. For example, the negative electrode can be manufactured by mixing negative electrode active material, negative electrode binder and / or negative electrode conductive material in a negative electrode solvent to prepare a negative electrode slurry, coating the negative electrode slurry onto a negative electrode current collector, and then drying and calendering it.

[0112] In terms of promoting the dispersibility of the negative electrode slurry components, the negative electrode solvent can be at least one selected from distilled water, ethanol, methanol and isopropanol, preferably distilled water.

[0113] Alternatively, the negative electrode can be manufactured by casting the negative electrode slurry onto a separate carrier and then stacking the film obtained by peeling it off from the carrier onto the negative electrode current collector.

[0114] Next, the separator is used to separate the negative and positive electrodes and provide a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion movement are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers; or laminated structures having two or more layers. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. In addition, separators coated with ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0115] On the other hand, the electrode assembly can be any form of electrode assembly well known in the art, such as jelly-roll type, stacked type, stacked and layered type, or stacked and folded type electrode assembly, and there are no particular limitations on its form.

[0116] Roll-type electrode assemblies can be manufactured by inserting a sheet-like diaphragm between a sheet-like positive electrode and a sheet-like negative electrode, and then winding it in one direction.

[0117] Stacked electrode assemblies can be manufactured by cutting the positive electrode, separator, and negative electrode into the desired shape and then stacking the cut positive electrode / separator / negative electrode in sequence.

[0118] Stacked and layered electrode assemblies can be manufactured by stacking positive electrodes, separators and negative electrodes to produce multiple cell units, stacking multiple cell units with separators in between, and then layering them by methods such as heating.

[0119] Stacked and folded electrode assemblies can be manufactured by stacking positive electrodes, separators, and negative electrodes to create multiple cell units, arranging multiple cell units on one or two surfaces of a long folded separator, and then winding the folded separator.

[0120] On the other hand, the electrolytes used in this article may include a variety of electrolytes that can be used in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes or combinations thereof, and there are no particular limitations on their types.

[0121] For example, electrolytes can contain organic solvents and lithium salts.

[0122] Organic solvents can be used without any particular restrictions, as long as they serve as a medium through which ions participating in the electrochemical reactions of the battery can migrate. Specific examples of organic solvents can include: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene or fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); alcohol solvents such as ethanol or isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolane such as 1,3-dioxolane; sulfolane, etc.

[0123] Lithium salts can be used without any particular restrictions, as long as they are compounds capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be at least one selected from the following: F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - Furthermore, the lithium salts that can be used in this paper include: LiPF6, LiN(FSO2)2, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used in the range of 0.1 to 5.0 M.

[0124] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the electrolyte components mentioned above, the electrolyte may also contain additives. For example, additives may include at least one selected from: halogen-substituted carbonate compounds, sulfate compounds, sulfonyl lactone compounds, borate ester compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds. For example, as additives, they may be used alone or in combination: alkyl halides of carbonate such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted sulfadiazine ketones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc., but are not limited thereto. Based on the total weight of the electrolyte, the content of additives may be 0.1 to 10% by weight, preferably 0.1 to 5% by weight.

[0125] On the other hand, various battery cases known in the art can be used as battery cases, such as cylindrical battery cases, prismatic battery cases, or pouch-shaped battery cases, and there are no particular restrictions on their type.

[0126] (2) Step S2: Activate the prepared battery

[0127] After manufacturing the pre-battery in step S1, the pre-battery is activated by charging it to the charging cut-off voltage and discharging it to the discharging cut-off voltage (step S2).

[0128] The activation step refers to the process of charging and discharging the battery to impart electrical properties and forming an SEI (solid electrolyte interface) film on the electrodes to stabilize the battery, thereby bringing it to a practically usable state. Furthermore, the charging cut-off voltage refers to the voltage at the end of the charging process. The discharging cut-off voltage refers to the voltage at the end of the discharging process.

[0129] In one embodiment, the activation step involves charging and discharging to satisfy the range of charging and discharging cutoff voltages, thereby enabling the lithium secondary battery containing lithium-rich manganese oxides to achieve high capacity and suppressing oxygen desorption and cation mixing during the activation process. As a result, the amount of gas generated by the battery can be reduced, resistance characteristics improved, and the increase in positive electrode resistance during charging and discharging suppressed, thereby improving resistance and lifespan characteristics. Furthermore, because the activation time is shortened, manufacturing time can be reduced when producing lithium secondary batteries, thereby improving processability and productivity.

[0130] First, the pre-charged battery is charged to the charging cutoff voltage.

[0131] In this case, the charging cutoff voltage is greater than 4.3 V. Specifically, the charging cutoff voltage can be greater than 4.3 V, above 4.35 V, above 4.4 V, above 4.45 V, above 4.5 V and below 4.7 V, below 4.68 V, below 4.65 V, below 4.64 V, below 4.62 V, or below 4.6 V. When lithium-rich manganese oxides are activated at low voltages, an abnormal behavior occurs in which the capacity increases abnormally while activating the residual Li2MnO3 phase in the crystal structure during battery operation, and additional gas is generated. Therefore, one embodiment of the method solves the above-mentioned problem by charging the lithium secondary battery to a charging cutoff voltage greater than 4.3 V during charging. On the other hand, if the charging cutoff voltage is greater than 4.7 V, excessive oxygen desorption may occur in the lithium-rich manganese oxides, generating excessive gas, which may reduce the processability, stability, and lifespan characteristics of the battery. Therefore, if the charging cutoff voltage meets the above range, the lithium-rich manganese oxides can be activated, thereby improving lifespan characteristics while achieving high capacity characteristics.

[0132] On the other hand, charging may include a first charge at a C-rate of 0.04C to 0.5C and a second charge at a C-rate of 0.3C to 1.2C. In the activation step, charging is performed in two or more steps with different C-rates, thereby forming a robust SEI film on the electrode while maximally suppressing oxygen desorption and cation mixing during the activation step.

[0133] The first charge can be performed at a C rate of 0.04C to 0.5C. Specifically, the first charge can be performed at a C rate of 0.04C or higher, 0.06C or higher, 0.08C or higher, 0.1C or higher, 0.12C or higher, 0.14C or higher, 0.16C or higher, or 0.18C or higher, and at a C rate of 0.5C or lower, 0.48C or lower, 0.46C or lower, 0.44C or lower, 0.42C or lower, 0.4C or lower, 0.38C or lower, 0.36C or lower, 0.34C or lower, 0.32C or lower, 0.3C or lower, 0.28C or lower, 0.26C or lower, 0.24C or lower, or 0.22C or lower.

[0134] If the charge rate (C) in the first charge is greater than 0.5C, the SEI film may form unstablely on the electrode surface. Furthermore, if the SEI film forms unstablely on the electrode surface, it may easily decompose during battery operation, leading to rapid electrode degradation and potentially a significant reduction in lifetime characteristics. Additionally, if the charge rate in the first charge is less than 0.04C, a significant amount of time is required for activation, which may reduce the mass production rate of lithium-ion batteries. In other words, if the first charge is performed at the stated C rate, the SEI film can be firmly formed on the electrode surface during the activation step while simultaneously ensuring the mass production rate of lithium-ion batteries.

[0135] The first charge can be performed until the SOC of the pre-charge battery becomes 1 to 10. This means that the first charge can start from the SOC of the pre-charge battery being 0 and continue until the SOC becomes 1 to 10. Specifically, the first charge can be performed until the SOC of the pre-charge battery becomes 1 or higher, 2 or higher, 2.5 or higher and 10 or lower, 9 or lower, 8 or lower, 7 or lower, 6 or lower, 5 or lower, 4 or lower, or 3 or lower. In this case, in the lithium secondary battery manufactured by activating the pre-charge battery, a strong and dense SEI film is formed on the electrode surface, thereby achieving excellent lifetime characteristics.

[0136] The first charge can be performed in constant current mode (CC mode).

[0137] The second charge can be performed at a C rate of 0.3C to 1.2C. Specifically, the second charge can be performed at C rates of 0.3C or higher, 0.32C or higher, 0.34C or higher, 0.36C or higher, 0.38C or higher, and 0.4C or higher, and at C rates of 1.2C or lower, 1.18C or lower, 1.16C or lower, 1.14C or lower, 1.12C or lower, 1.1C or lower, 1.08C or lower, 1.06C or lower, 1.04C or lower, 1.02C or lower, and 1.0C or lower.

[0138] When the second charge is performed at a C-rate within the aforementioned range, the activation of the Li₂MnO₃ (monoclinic) phase in the crystal structure of the positive electrode active material containing lithium-rich manganese oxides is reduced, thereby suppressing oxygen desorption and cation mixing during the activation process. As a result, the amount of gas generated in the activation step can be reduced. Furthermore, the second charge is performed at a C-rate that is relatively faster than the first charge, thereby reducing the time required for activating the pre-charged battery, shortening the manufacturing time of the lithium secondary battery, and improving mass production efficiency.

[0139] A second charge can be performed after the first charge until the SOC of the pre-charged battery becomes between 80 and 100. This could mean performing a first charge until the SOC of the pre-charged battery becomes between 1 and 10, and then performing a second charge until the SOC becomes between 80 and 100. Specifically, a second charge can be performed after the first charge until the SOC of the pre-charged battery becomes 80 or higher, 82 or higher, 84 or higher, 86 or higher, 88 or higher, 90 or higher, 92 or higher, 94 or higher, 96 or higher, or 98 or higher but below 100. When the SOC meets the above range, incomplete SEI film formation can be prevented, and oxygen desorption and cation mixing can be reduced during the pre-charged battery activation step, thereby minimizing the increase in positive electrode resistance.

[0140] On the other hand, if necessary, the second charging can be performed in two or more steps with different C rates. For example, the second charging may include a 2-1 charging at a C rate of 0.8C to 1.2C and a 2-2 charging at a C rate of 0.3C to 0.6C. Specifically, the 2-1 charging may be performed at C rates of 0.8C or higher, 0.85C or higher, 0.9C or higher, or 0.95C or higher, and at C rates of 1.2C or lower, 1.15C or lower, 1.1C or lower, or 1.05C or lower. Furthermore, the 2-2 charging may be performed at C rates of 0.3C or higher, 0.32C or higher, 0.34C or higher, 0.36C or higher, or 0.38C or higher, and at C rates of 0.6C or lower, 0.55C or lower, 0.5C or lower, or 0.45C or lower.

[0141] At this point, a 2-1 charge can be performed after the first charge until the SOC of the pre-charged battery becomes 40 to 80%. Specifically, the 2-1 charge can be performed after the first charge until the SOC of the pre-charged battery becomes 40 or higher, 45 or higher, 50 or higher, 55 or higher, or 60 or higher, and can be performed until it becomes 80 or lower, 75 or lower, 70 or lower, or 65 or lower. Furthermore, a 2-2 charge can be performed after the 2-1 charge until the SOC of the pre-charged battery becomes 80 to 100%. Specifically, the 2-2 charge can be performed after the 2-1 charge until the SOC of the pre-charged battery becomes 80 or higher, 85 or higher, 90 or higher, or 95 or higher, and can be performed until it becomes 100 or lower. By performing the second charge step in two steps as described above, even in the high SOC region, lithium ions can be smoothly inserted into the negative electrode, thereby preventing lithium plating on the negative electrode surface and ensuring battery performance and stability.

[0142] The second charge can be performed in constant current mode (CC mode) or constant current-constant voltage mode (CC-CV mode). Specifically, charge 2-1 can be performed in constant current mode, and charge 2-2 can be performed in constant current-constant voltage mode.

[0143] Specifically, when the second charge or 2-2 charge is performed in constant current-constant voltage mode, the second charge or 2-2 charge can be performed until the charging cutoff current. The charging cutoff current can be from 0.02C to 0.25C. Specifically, the charging cutoff current can be a C-rate of 0.02C or higher, 0.04C or higher, 0.06C or higher, or 0.08C or higher, and can be a C-rate of 0.25C or lower, 0.23C or lower, 0.21C or lower, 0.2C or lower, 0.18C or lower, 0.16C or lower, 0.14C or lower, 0.12C or lower, or 0.1C or lower. When constant voltage charging is performed, the current value decreases while maintaining the full charge voltage, and the current value at which charging stops is called the charging cutoff current. When the above-mentioned charging cutoff current range is met, Li2MnO3 can be fully activated in the activation preparation battery step, and the activation time can be shortened, thereby improving the large-scale production rate.

[0144] Next, the process involves discharging the battery to its discharge cutoff voltage.

[0145] In this case, the discharge cutoff voltage is 2.6 V or higher. Specifically, the discharge cutoff voltage can be 2.6 V or higher, 2.65 V or higher, 2.7 V or higher, 2.75 V or higher, 2.8 V or higher, 2.85 V or higher, 2.9 V or higher, 2.95 V or higher, 3.0 V or higher, 3.05 V or higher, 3.1 V or higher, 3.15 V or higher, 3.2 V or higher, or 3.25 V or higher, and can be below 3.7 V, below 3.65 V, below 3.6 V, below 3.55 V, below 3.5 V, below 3.45 V, below 3.4 V, below 3.35 V, or below 3.3 V. When the discharge cutoff voltage is adjusted to 2.6 V or higher, side reactions occurring on the positive electrode surface during charging and discharging can be reduced, thereby reducing surface oxides. Furthermore, when the discharge cutoff voltage is too high, reverse voltage can occur. Therefore, when the discharge cutoff voltage meets the above range, the resistance characteristics of the positive electrode and the battery are improved, the initial resistance can be reduced, the time required for battery activation can be shortened, thereby enhancing mass production efficiency and improving the life characteristics of lithium secondary batteries.

[0146] On the other hand, during the activation step, discharge can be performed at a C-rate ranging from 0.4C to 1.5C. Specifically, discharge can be performed at C-rates above 0.4C, 0.45C, 0.5C, 0.55C, and 0.6C, and at C-rates below 1.5C, 1.45C, 1.4C, 1.35C, 1.3C, 1.25C, 1.2C, 1.15C, 1.1C, 1.05C, or 1.0C. Meeting these ranges shortens the activation time, thereby ensuring high-volume production efficiency while fully activating the battery.

[0147] An activation step can be performed to make the ratio (B / A) of the charge capacity (B) in the range from 4.3 V to the charge cutoff voltage to the total charge capacity (A) when the battery is charged to the charge cutoff voltage less than or equal to 0.60. Specifically, the activation step can be performed to make B / A less than or equal to 0.60, 0.59, or 0.58. When the above range is met, gas generation and transition metal dissolution during battery operation can be suppressed, thereby improving the battery's lifespan characteristics.

[0148] Furthermore, if necessary, the activation process can be performed under pressure. Pressure can be applied by mounting the battery cells on a fixture and then using the fixture to apply pressure to the battery cells. If the activation process is performed under pressure, it has the advantage that gases generated during the activation process can be easily released.

[0149] On the other hand, although not mandatory, the activation step may include an aging step if needed. The aging step is designed to allow the electrolyte to permeate uniformly into the electrode assembly and to stabilize the battery. It can be performed before charging, during charging, and / or after discharging, and may be performed more than once.

[0150] The aging process can be carried out at temperatures, for example, 20°C to 60°C, preferably 20°C to 50°C, and more preferably 30°C to 50°C. When aging is carried out at the above temperatures, electrolyte impregnation and lithium mobility are improved, thereby allowing for smoother activation.

[0151] The following section will describe the method for manufacturing lithium secondary batteries in more detail through specific examples.

[0152] Example 1

[0153] <Preparation for Battery Manufacturing>

[0154] Li, as the positive electrode active material 1.14 [Ni 0.45 Mn 0.55 ] 0.86O2, carbon nanotubes (CNTs) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in N-methylpyrrolidone at a weight ratio of 97:1:2 to prepare a positive electrode forming composition. The positive electrode forming composition was coated onto a 12 μm thick aluminum (Al) metal film, dried, and then calendered to prepare the positive electrode. At this point, the BET specific surface area of ​​the positive electrode active material was measured; for small-particle-size positive electrode active materials, it was 1.34 m². 2 / g and for large-particle-size positive electrode active materials, it is 1.37 m 2 / g, and measured the average particle size (D 50 The particle size is 3.96 μm for small-particle-size positive electrode active materials and 9.56 μm for large-particle-size positive electrode active materials.

[0155] A negative electrode forming composition was prepared by mixing graphite as the negative electrode active material, carbon nanotubes (CNTs) as the conductive material, and styrene-butadiene rubber (SBR) / carboxymethyl cellulose (CMC) as the binder in distilled water at a weight ratio of 96:1:3. The negative electrode forming composition was coated onto a copper (Cu) metal film with a thickness of 8 μm, dried, and then calendered to prepare the negative electrode.

[0156] The separator is inserted between the positive and negative electrodes prepared as described above to prepare an electrode assembly. The electrode assembly is then inserted into the battery case, and electrolyte is injected to manufacture a pre-battery.

[0157] <Manufacturing of Lithium Secondary Batteries>

[0158] The pre-existing battery was charged at 45°C under CC and 0.2C conditions until SOC 3 (first charge), and then charged under CC and 1.0C conditions until SOC 60 (2-1 charge). It was then constant-current charged to a charging cutoff voltage of 4.6 V under CC-CV (constant current-constant voltage) and 0.4C conditions, followed by constant-voltage charging to a charging cutoff current of 0.05C (2-2 charge). Subsequently, the pre-existing battery was discharged at 1.0C to a discharge cutoff voltage of 3.0 V to activate it, thereby manufacturing a lithium secondary battery.

[0159] Example 2

[0160] Except that after charging the pre-battery, the pre-battery is discharged at 1.0C to a discharge cutoff voltage of 3.5 V to activate the pre-battery, the lithium secondary battery is manufactured in the same manner as in Example 1.

[0161] Example 3

[0162] <Preparation for Battery Manufacturing>

[0163] Li, as the positive electrode active material 1.15 Ni0.29 Mn 0.56 O2, carbon nanotubes (CNTs) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in N-methylpyrrolidone at a weight ratio of 94:1:2 to prepare a positive electrode forming composition. The positive electrode forming composition was coated onto a 12 μm thick aluminum (Al) metal film, dried, and then calendered to prepare the positive electrode. At this point, the BET specific surface area of ​​the positive electrode active material was measured, which was 4.49 m² for small-particle-size positive electrode active materials. 2 / g and for large-particle-size positive electrode active materials, it is 4.07 m 2 / g, and measured the average particle size (D 50 The particle size is 2.9 μm for small-particle-size positive electrode active materials and 10.5 μm for large-particle-size positive electrode active materials.

[0164] A negative electrode forming composition was prepared by mixing graphite as the negative electrode active material, carbon nanotubes (CNTs) as the conductive material, and styrene-butadiene rubber (SBR) / carboxymethyl cellulose (CMC) as the binder in distilled water at a weight ratio of 96:1:3. The negative electrode forming composition was coated onto a copper (Cu) metal film with a thickness of 8 μm, dried, and then calendered to prepare the negative electrode.

[0165] The separator is inserted between the positive and negative electrodes prepared as described above to prepare an electrode assembly. The electrode assembly is then inserted into the battery case, and electrolyte is injected to manufacture a pre-battery.

[0166] <Manufacturing of Lithium Secondary Batteries>

[0167] The pre-existing battery was charged at 45°C under CC and 0.2C conditions until SOC 3 (first charge), and then charged under CC and 1.0C conditions until SOC 60 (2-1 charge). It was then constant-current charged to a charging cutoff voltage of 4.6 V under CC-CV (constant current-constant voltage) and 0.4C conditions, followed by constant-voltage charging to a charging cutoff current of 0.05C (2-2 charge). Subsequently, the pre-existing battery was discharged at 0.6C to a discharge cutoff voltage of 3.0 V to activate it, thereby manufacturing a lithium secondary battery.

[0168] Example 4

[0169] Except that after charging the pre-battery, the pre-battery is discharged at 0.6C to a discharge cutoff voltage of 3.5 V to activate the pre-battery, the lithium secondary battery is manufactured in the same manner as in Example 3.

[0170] Comparative Example 1

[0171] Except that after charging the pre-battery, the pre-battery is discharged at 1.0C to a discharge cutoff voltage of 2.0V to activate the pre-battery, the lithium secondary battery is manufactured in the same manner as in Example 1.

[0172] Comparative Example 2

[0173] Except that after charging the pre-battery, the pre-battery is discharged at 0.6C to a discharge cutoff voltage of 2.0 V to activate the pre-battery, the lithium secondary battery is manufactured in the same manner as in Example 3.

[0174] For Examples 1-4 and Comparative Examples 1-2, the ratio (B / A) of the charging capacity (B) in the range of 4.3 V to the charging cutoff voltage to the total charging capacity (A) when the pre-charged battery is charged to the charging cutoff voltage is shown in Table 1 below.

[0175] [Table 1]

[0176] Experimental Example 1: Measurement of Initial Discharge Capacity

[0177] The lithium secondary batteries manufactured by performing the activation process of Examples 1-2 and Comparative Example 1 were charged and discharged at 0.33C in a voltage range of 2.0 V to 4.35 V, and the discharge capacity of the second cycle was measured. As a result of the measurement, the relative initial discharge capacity of Examples 1-2 relative to the initial discharge capacity of Comparative Example 1 shown in A is shown in Table 2 below, and the relative initial discharge capacity of Examples 3-4 relative to the initial discharge capacity of Comparative Example 2 shown in B is shown in Table 2 below.

[0178] [Table 2]

[0179] Referring to Table 2, it can be confirmed that Examples 1-2 and 3-4 have improved initial discharge capacity compared to Comparative Examples 1 and 2.

[0180] Experiment Example 2: Measurement of Initial Discharge Resistance

[0181] The discharge resistance values ​​of the lithium secondary batteries manufactured in Examples 1-2 and Comparative Example 1 were measured.

[0182] Specifically, for the lithium secondary batteries manufactured in Examples 1-2 and Comparative Example 1, the battery resistance (SOC50 discharge resistance) was measured by dividing the voltage drop under conditions where a discharge pulse was applied at 2.5C for 0.1 seconds and 10 seconds at SOC 50% by the current value. The relative discharge resistance values ​​compared to Comparative Example 1 are shown in Table 3 below, where the discharge resistance of Comparative Example 1 at 0.1 seconds and 10 seconds is represented by C and D, respectively.

[0183] [Table 3]

[0184] Referring to Table 3, it can be confirmed that the discharge resistance of the lithium secondary batteries in Examples 1 and 2 is reduced compared to that of Comparative Example 1.

[0185] Experiment Example 3: Measurement of Activation Time

[0186] During the manufacture of lithium secondary batteries of Examples 1-4 and Comparative Examples 1-2, the time required to activate the pre-batteries of Examples 1-4 and Comparative Examples 1-2 was measured. The results are shown in Table 4 below.

[0187] [Table 4]

[0188] Referring to Table 4, it can be confirmed that the activation time of the lithium secondary batteries in Examples 1 and 2 is shortened compared to that of Comparative Example 1. Similarly, the activation time of the lithium secondary batteries in Examples 3 and 4 is shortened compared to that of Comparative Example 2. Therefore, it can be understood that the lithium secondary batteries of Examples 1-2 and 3-4 can respectively improve the processability of the lithium secondary battery manufacturing process compared to those of Comparative Examples 1 and 2.

Claims

1. A method of manufacturing a lithium secondary battery, the method comprising: a step (S1) of manufacturing a preliminary battery including a positive electrode containing a positive electrode active material, a negative electrode, a separator, and an electrolyte; and a step (S2) of charging the preliminary battery to a charge cut-off voltage and discharging the preliminary battery to a discharge cut-off voltage to activate the preliminary battery, wherein the positive electrode active material contains a lithium-rich manganese-based oxide containing 50 mol% or more of manganese (Mn) among all metals other than lithium, and a molar ratio of lithium to all metals other than lithium (Li / Me) exceeds 1, and wherein the charge cut-off voltage is greater than 4.3 V, and the discharge cut-off voltage is 2.6 V or more.

2. The method of manufacturing a lithium secondary battery according to claim 1, wherein the discharge cut-off voltage is 2.7 V or more and 3.5 V or less.

3. The method of manufacturing a lithium secondary battery according to claim 1, wherein in the activation step, the discharging is performed at a C rate of 0.4 C to 1.5 C.

4. The method of manufacturing a lithium secondary battery according to claim 1, wherein the charge cut-off voltage is greater than 4.3 V and 4.65 V or less.

5. The method of manufacturing a lithium secondary battery according to claim 1, wherein in the activation step, the charging includes a first charging performed at a C rate of 0.04 C to 0.5 C and a second charging performed at a C rate of 0.3 C to 1.2 C.

6. The method of manufacturing a lithium secondary battery according to claim 5, wherein the second charging includes a 2-1 charging performed at a C rate of 0.8 C to 1.2 C and a 2-2 charging performed at a C rate of 0.3 C to 0.6 C.

7. The method of manufacturing a lithium secondary battery according to claim 6, wherein the 2-1 charging is performed after the first charging until the SOC of the preliminary battery becomes between 40 and 80, and the 2-2 charging is performed after the 2-1 charging until the SOC of the preliminary battery becomes between 80 and 100.

8. The method of manufacturing a lithium secondary battery according to claim 5, wherein the first charging is performed in a constant current mode (CC mode).

9. The method of manufacturing a lithium secondary battery according to claim 5, wherein the second charging is performed in a constant current-constant voltage mode (CC-CV mode), and the second charging is performed until a charge cut-off current is 0.02 C to 0.25 C.

10. The method of manufacturing a lithium secondary battery according to claim 1, wherein the lithium-rich manganese-based oxide is represented by the following Chemical Formula 1: [Chemical Formula 1] wherein in Chemical Formula 1, Li x1 Mn y1 M 1 1-y1 O2 1 < x1≤ 1.5, 0.5≤ y1≤ 1, and the average particle size of the first positive electrode active material has a value greater than that of the second positive electrode active material. M 1 is at least one element selected from the group consisting of Ni, Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

11. The method of manufacturing a lithium secondary battery according to claim 1, wherein the average particle size (D 50 ) of the positive electrode active material is 1.5 μm to 13 μm. 12.The method of manufacturing a lithium secondary battery according to claim 1, wherein the positive active material comprises a first positive active material and a second positive active material having different average particle sizes (D 50 ). ​ 13. The method of manufacturing a lithium secondary battery according to claim 12, wherein the average particle size (D 50 ) of the first positive electrode active material is 6 μm to 15 μm, and the average particle size (D 50 ) of the second positive electrode active material is 15 μm to 30 μm. The average particle size (D50) of the second positive electrode active material is 0.5 μm to 6 μm. 50 ) is 0.5 μm to 6 μm.

14. The method of manufacturing a lithium secondary battery according to claim 1, wherein the BET specific surface area of the positive electrode active material is 0.9 m 2 / g to 5.0 m 2 / g.

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