Manufacturing method of lithium secondary batteries

Abstract

A step of preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte, the positive electrode including a hyperlithium manganese-based oxide in which the content of manganese exceeds 50 mol% of the total metal excluding lithium and the ratio (Li / Me) of the number of moles of lithium to the number of moles of the total metal excluding lithium exceeds 1; and a step of charging and discharging the battery cell one or more times for activation, wherein the battery cell has a discharge capacity ratio per unit area of the negative electrode to the discharge capacity per unit area of the positive electrode (N / P ratio) of 1.05 to 1.15 when charged to 2.0 V to 4.3 V, and in the step of activation, the charging is performed up to SOC60 to SOC65. The present invention relates to a method for manufacturing a lithium secondary battery.

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority rights based on Korean Patent Application No. 10-2022-0183739 dated December 23, 2022, and Korean Patent Application No. 10-2023-0187697 dated December 20, 2023, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein as part of this specification.

[0002] The present invention relates to a method for manufacturing a lithium secondary battery, and more specifically, to a method for manufacturing a lithium secondary battery containing an overlithium manganese oxide that can appropriately control the activation voltage conditions and improve the negative electrode over-design. [Background technology]

[0003] Lithium-ion batteries, since their commercialization in 1991, are energy storage media that have been applied in a wide range of fields. As the market for products incorporating lithium-ion batteries expands, research into increasing the energy density of lithium-ion batteries is actively being conducted, and one of the most noteworthy methods is the development of cathode active materials with compositions that can utilize more lithium than existing ones.

[0004] As a positive electrode active material that can utilize more lithium, perlithium-based transition metal oxides have been developed that have a layered structure and a molar ratio of lithium to transition metal greater than 1. Lithium secondary batteries using such perlithium-based transition metal oxides can generally achieve high capacity by performing the activation process at a high voltage of 4.4V or higher.

[0005] On the other hand, because the aforementioned perlithium-based transition metal oxides have high initial irreversibility, a negative electrode design higher than the actual drive capacity is required to accommodate a high positive electrode capacity during the high-voltage activation process and prevent lithium deposition. However, over-designing the negative electrode in this way leads to the problem of increased volume and weight of the secondary battery.

[0006] Therefore, in order to achieve miniaturization and weight reduction of lithium secondary batteries used as power supply devices for electric vehicles, portable electronic devices, etc., there is a high need for new technological development that can solve the problem of increased volume and weight of lithium secondary batteries.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention is for solving such problems, and an object thereof is to provide a method for manufacturing a lithium secondary battery including a lithium-rich manganese-based oxide that can appropriately control activation conditions and improve excessive negative electrode design.

Means for Solving the Problems

[0009] On one aspect, the present invention includes the steps of preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte including a lithium-rich manganese-based oxide in which the content of manganese among all metals excluding lithium exceeds 50 mol%, and the ratio (Li / Me) of the number of moles of lithium to the number of moles of all metals excluding lithium exceeds 1; and activating the battery cell by charging and discharging it one or more times, wherein the battery cell has a discharge capacity ratio per unit area of the negative electrode to the discharge capacity per unit area of the positive electrode (N / P ratio) of 1.05 to 1.15 when charged to 2.0 V to 4.3 V, and in the step of activating, the charging is performed up to SOC60 to SOC65, and provides a method for manufacturing a lithium secondary battery.

[0010] The lithium-rich manganese-based oxide may be represented by the following Chemical Formula 1.

[0011] [Chemical Formula 1] Li aNi b Co c Mn d M e O2 In Chemical Formula 1, 1 < a, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, 0.5 ≤ d < 1.0, 0 ≤ e ≤ 0.2, and M is one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0012] The charging step can be performed at a rate of 0.3C to 1.0C until the SOC reaches 60% to 65%.

[0013] The charging step can include a first charging step of charging at a rate of 0.1C to 0.3C in the SOC range of 0% to 5%, and a second charging step of charging at a rate of 0.3C to 1.0C until the SOC reaches 60% to 65% after the first charging step.

[0014] The charging step can be performed in a constant current mode (CC mode) or a constant current constant voltage mode (CCCV mode).

[0015] The activation step can include a step of discharging at a rate of 0.3C to 0.7C until reaching 2.0V.

Best Mode for Carrying Out the Invention

[0016] The terms or words used in this specification and the claims are not to be construed as being limited to their ordinary or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way, they are to be construed in a meaning and concept consistent with the technical idea of the present invention.

[0017] In this invention, "primary particle" refers to a particle unit in which no grain boundaries are visible when observed using a scanning electron microscope at a field of view of 5,000 to 20,000 times magnification. "Average particle size of primary particles" refers to the arithmetic mean calculated after measuring the particle sizes of primary particles observed in scanning electron microscope images.

[0018] In this invention, "secondary particles" refer to particles formed by the aggregation of multiple primary particles.

[0019] In this invention, "average particle size D50" refers to the particle size at 50% of the volume-cumulative particle size distribution of the particle powder to be measured (e.g., positive electrode active material powder, negative electrode active material powder, etc.). The average particle size D50 can be measured using the laser diffraction method. For example, after dispersing the powder of the particles to be measured in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiated with ultrasound at approximately 28 kHz with an output of 60 W, and then measured by obtaining a volume-cumulative particle size distribution graph and determining the particle size corresponding to 50% of the volume-cumulative amount.

[0020] Furthermore, in this invention, "SOC X" refers to a state in which the percentage of the capacity charged in the battery cell is X, based on the discharge capacity that appears when the battery cell is discharged from 4.6V to 2.0V.

[0021] The inventors of the present invention conducted extensive research to improve the volume and weight increase problems of lithium secondary batteries using perlithium manganese oxides. As a result, they discovered that by performing an activation step under specific charging conditions during the manufacturing of lithium secondary batteries, the negative electrode loading amount can be set to the amount required for the actual drive voltage, thereby solving the volume and weight increase problems of lithium secondary batteries, and thus completed the present invention.

[0022] The method for manufacturing a lithium secondary battery according to the present invention will be described below.

[0023] The present invention provides a method for manufacturing a lithium secondary battery, comprising the steps of: preparing a battery cell containing a positive electrode, a negative electrode, and an electrolyte, wherein the manganese content in the total metals excluding lithium exceeds 50 mol%, and the ratio of the number of moles of lithium to the total number of moles of metals excluding lithium (Li / Me) exceeds 1; and activating the battery cell by charging and discharging it once or more, wherein when the battery cell is charged to 2.0V to 4.3V, the ratio of the discharge capacity per unit area of ​​the negative electrode to the discharge capacity per unit area of ​​the positive electrode (N / P ratio) is 1.05 to 1.15, and in the activation step, the charging is performed to SOC60 to SOC65.

[0024] (1) Steps to prepare the battery cells First, prepare a battery cell containing a positive electrode, a negative electrode, and an electrolyte.

[0025] The battery cell can be manufactured, for example, by forming an electrode assembly including a positive electrode and a negative electrode, then housing the electrode assembly in a battery case, and finally injecting an electrolyte to seal the battery case. In this case, the electrode assembly may include a separator membrane between the positive electrode and the negative electrode.

[0026] The components of the battery cell of the present invention will be described in more detail below.

[0027] positive electrode The positive electrode according to the present invention contains a perlithium manganese oxide in the positive electrode active material in which the manganese content exceeds 50 mol% of the total metal excluding lithium, and the ratio of the number of moles of lithium to the total number of moles of metal excluding lithium (Li / Me) exceeds 1. Specifically, the positive electrode according to the present invention includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector, and the positive electrode active material layer contains a perlithium manganese oxide in which the ratio of the number of moles of lithium to the total number of moles of metal excluding lithium (Li / Me) exceeds 1.

[0028] In the case of a lithium manganese oxide containing an excess of lithium, it has a structure in which a layered structure phase (LiM’O2) and a rock salt type structure phase (Li2MnO3) coexist. In the initial activation process, the rock salt type structure phase is activated, generating excess lithium ions, and a high capacity can be achieved.

[0029] Preferably, the over-lithium manganese oxide can be represented by Chemical Formula 1.

[0030] [Chemical Formula 1] Li a Ni b Co c Mn d M e O2 In Chemical Formula 1, M may be one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0031] On the other hand, a is the molar ratio of Li in the over-lithium manganese oxide, and 1 < a, 1.1 ≤ a ≤ 1.5, or 1.1 ≤ a ≤ 1.3 may be satisfied.

[0032] b is the molar ratio of Ni in the over-lithium manganese oxide, and 0 ≤ b ≤ 0.5, 0.1 ≤ b ≤ 0.4, or 0.2 ≤ b ≤ 0.4 may be satisfied.

[0033] c is the molar ratio of Co in the over-lithium manganese oxide, and 0 ≤ c ≤ 0.1, 0 ≤ c ≤ 0.08, or 0 ≤ c ≤ 0.05 may be satisfied. When c exceeds 0.1, it is difficult to ensure a high capacity, gas generation and degradation of the positive electrode active material become severe, and the life characteristics may deteriorate.

[0034] d is the molar ratio of Mn in the over-lithium manganese oxide, and 0.5 ≤ d < 1.0, 0.50 ≤ d ≤ 0.80, or 0.50 ≤ d ≤ 0.70 may be satisfied. When d is less than 0.5, the ratio of the rock salt type structure phase is too small, and the negative electrode irreversible compensation and capacity improvement effects are negligible.

[0035] The aforementioned e is the molar ratio of the doping element M in the perlithium manganese oxide, and may be 0 ≤ e ≤ 0.2, 0 ≤ e ≤ 0.1, or 0 ≤ e ≤ 0.05. Too high a doping element content may adversely affect the active material capacity.

[0036] On the other hand, in the perlithium manganese oxide represented by chemical formula 1, the molar ratio of Li to the total number of moles of metal elements excluding Li (Li / Me) may be 1.2 to 1.5, 1.25 to 1.5, or 1.25 to 1.4. When the Li / Me ratio satisfies the above range, the rate characteristics and capacity characteristics appear to be excellent. If the Li / Me ratio is too high, the electrical conductivity decreases, the rock salt type structural phase (Li2MnO3) increases, and the degeneration rate may accelerate. If it is too low, the effect of improving energy density is minimal.

[0037] On the other hand, the composition of the perlithium manganese oxide may be that shown in the following chemical formula 2.

[0038] [Chemical formula 2] XLi2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M w ]O2 In the above chemical formula 2, M may be one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0039] The aforementioned X represents the ratio of the Li2MnO3 phase in the perlithium manganese oxide, and may be 0.2 ≤ X ≤ 0.5, 0.25 ≤ X ≤ 0.5, or 0.25 ≤ X ≤ 0.4. When the ratio of the Li2MnO3 phase in the perlithium manganese oxide satisfies the above range, high capacity characteristics can be achieved.

[0040] The aforementioned y is the molar ratio of Mn in the LiM'O2 layered structure phase, and may be 0.4 ≤ y < 1, 0.4 ≤ y ≤ 0.8, or 0.4 ≤ y ≤ 0.7.

[0041] The value of z is the molar ratio of Co in the LiM'O2 layered structure phase, and may be 0 ≤ z ≤ 0.1, 0 ≤ z ≤ 0.08, or 0 ≤ z ≤ 0.05. If z exceeds 0.1, gas generation and degradation of the positive electrode active material become more severe, which may reduce the lifetime characteristics.

[0042] The aforementioned w is the molar ratio of the doping element M in the LiM'O2 layered structure phase, and may be 0 ≤ w ≤ 0.2, 0 ≤ w ≤ 0.1, or 0 ≤ w ≤ 0.05.

[0043] On the other hand, the positive electrode active material according to the present invention may further include a coating layer on the surface of the perlithium manganese oxide, if necessary. When the positive electrode active material includes a coating layer, the coating layer suppresses contact between the perlithium manganese oxide and the electrolyte, reducing side reactions of the electrolyte, thereby improving the lifespan characteristics.

[0044] The aforementioned coating layer contains coating element M 1 It may include the coating element M 1 The coating element M can be, for example, one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, preferably Al, Co, Nb, W, and combinations thereof, and more preferably Al, Co, and combinations thereof. 1 It can contain two or more types, for example, Al and Co.

[0045] The aforementioned coating element exists in the coating layer in the form of an oxide, i.e., M 1 It can exist within Oz (1 ≤ z ≤ 4).

[0046] The aforementioned coating layer can be formed by 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 it allows for the formation of a large coating layer area.

[0047] The area of ​​the coating layer can be 10 to 100%, preferably 30 to 100%, and more preferably 50 to 100%, based on the total surface area of ​​the perlithium manganese oxide particles. When the area of ​​the coating layer satisfies the above range, the effect of improving life characteristics is excellent.

[0048] On the other hand, the positive electrode active material according to the present invention may be in the form of secondary particles formed by the aggregation of a plurality of primary particles, and the average particle size D50 of the secondary particles may be 2 μm to 10 μm, preferably 2 μm to 8 μm, and more preferably 4 μm to 8 μm. When the D50 of the positive electrode active material satisfies the above range, excellent electrode density can be achieved, and the decrease in capacity and rate characteristics can be minimized.

[0049] Furthermore, the positive electrode active material has a BET specific surface area of ​​1 m². 2 / g~10m 2 / g, 3-8m 2 / g or 4-6m 2 It may also be / g. If the specific surface area of ​​the positive electrode active material BET is too low, the reaction area with the electrolyte will be insufficient, making it difficult to achieve sufficient capacity. If the specific surface area is too high, moisture absorption will be rapid, accelerating side reactions with the electrolyte and making it difficult to ensure lifespan characteristics.

[0050] On the other hand, the perlithium manganese oxide can be produced by mixing a transition metal precursor with a lithium raw material and then calcining it.

[0051] Examples of the lithium raw material include lithium-containing carbonates (e.g., lithium carbonate), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide), nitrates (e.g., lithium nitrate (LiNO3)), chlorides (e.g., lithium chloride (LiCl)), and others. One of these alone or a mixture of two or more can be used.

[0052] On the other hand, the transition metal precursor may be in the form of a hydroxide, oxide, or carbonate. Using a carbonate precursor is more preferable because it allows for the production of a positive electrode active material with a relatively high specific surface area.

[0053] The transition metal precursor can be produced through a coprecipitation process. For example, the transition metal precursor can be produced by dissolving each transition metal-containing raw material in a solvent to produce a metal solution, then mixing the metal solution, an ammonium positive ion complex-forming agent, and a basic compound, and finally carrying out a coprecipitation reaction. Furthermore, an oxidizing agent or oxygen gas may be added during the coprecipitation reaction as needed.

[0054] In this case, the transition metal-containing raw material may be an acetate, carbonate, nitrate, sulfate, halogen compound, sulfide, etc. of each transition metal. Specifically, the transition metal-containing raw material may be NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, Mn2O3, MnO2, Mn3O4MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, etc.

[0055] The ammonium positive ion complex-forming agent may be one or more selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3.

[0056] The basic compound may be one or more selected from the group consisting of NaOH, Na2CO3, KOH, and Ca(OH)2. The form of the precursor may differ depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a hydroxide-form precursor can be obtained, and when Na2CO3 is used as the basic compound, a carbonate-form precursor can be obtained. Furthermore, when used together with an oxidizing agent, an oxide-form precursor can be obtained.

[0057] On the other hand, the transition metal precursor and the lithium raw material can be mixed in such an amount that the molar ratio of the entire transition metal (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.

[0058] On the other hand, the firing can be carried out at a temperature of 600°C to 1000°C or 700°C to 950°C, and the firing time may be 5 to 30 hours or 5 to 20 hours. The firing atmosphere may be an air atmosphere or an oxygen atmosphere, for example, an atmosphere containing 20 to 100% by volume of oxygen.

[0059] On the other hand, the positive electrode active material layer may further include a conductive material and a binder in addition to the positive electrode active material.

[0060] Examples of the conductive material include spherical or flake graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, single-walled carbon nanotubes, and multi-walled 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. One of these can be used alone or in mixtures of two or more. The conductive material may be present in an amount of 0.1 to 20% by weight, 1 to 20% by weight, or 1 to 10% by weight, based on the total weight of the positive electrode active material layer.

[0061] Furthermore, the binder may include, for example, a fluororesin-based binder containing polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); a rubber-based binder containing styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; a cellulose-based binder containing carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, or regenerated cellulose; a polyalcohol-based binder containing polyvinyl alcohol; a polyolefin-based binder containing polyethylene or polypropylene; a polyimide-based binder; a polyester-based binder; and a silane-based binder. The binder may be present in an amount of 1-20% by weight, 2-20% by weight, or 2-10% by weight based on the total weight of the positive electrode active material layer.

[0062] negative electrode The negative electrode may include, for example, a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector. The negative electrode active material layer may selectively include a binder and a conductive material together with the negative electrode active material.

[0063] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity, but for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The negative electrode current collector can usually have a thickness of 3 to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0064] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include (0<β<2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides that can be doped and dedoped with lithium; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these mixtures can be used.

[0065] Furthermore, a metallic lithium thin film can be used as the negative electrode active material. In addition, low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0066] The conductive material is used to impart conductivity to the electrodes and can be used without special limitations in the battery it is configured in, as long as it does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal 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. One of these can be used alone or in mixtures of two or more. The conductive material can usually be present in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0067] The binder plays a role in improving the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include fluororesin binders containing polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders containing styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose binders containing carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; polyalcohol binders containing polyvinyl alcohol; polyolefin binders containing polyethylene and polypropylene; polyimide binders; polyester binders; and silane binders, of which one or more can be used. The binder may be present in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0068] The negative electrode active material layer can be manufactured, for example, by applying a negative electrode slurry containing a negative electrode active material and selectively a binder and conductive material onto a negative electrode current collector and drying it, or by casting the negative electrode slurry onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0069] On the other hand, when the battery cell of the present invention is charged at 2.0V to 4.3V, the ratio of the discharge capacity per unit area of ​​the negative electrode to the discharge capacity per unit area of ​​the positive electrode (N / P ratio) can be 1.05 to 1.15. When the ratio of the discharge capacity per unit area of ​​the negative electrode to the discharge capacity per unit area of ​​the positive electrode (N / P ratio) is within the above range, it is possible to secure a negative electrode capacity that can accommodate the high positive electrode capacity that is expressed in the activation step, thereby ensuring the stability of the secondary battery.

[0070] Separation membrane The lithium secondary battery according to the present invention may further include a separation membrane interposed between the positive electrode and the negative electrode. The separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separation membrane commonly used in lithium secondary batteries can be used without special limitations, and those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can be used. Furthermore, a coated separation membrane containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure.

[0071] electrolyte The electrolyte can be any of the various electrolytes usable in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, or combinations thereof, and the type is not particularly limited.

[0072] For example, the electrolyte may include an organic solvent and a lithium salt.

[0073] The aforementioned organic solvent can be used without special limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; tolyls such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used.

[0074] The lithium salt can be used without any special restrictions, as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, as the negative ion of the lithium salt, 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 - The lithium salt can be one or more selected from the group consisting of the following, and the lithium salt can be LiPF6, LiN(FSO2)2, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0 M.

[0075] Furthermore, the electrolyte may contain additives in addition to the above-mentioned components for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. For example, the additives may be, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, either alone or in combination. The additives may be present in an amount of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, relative to the total weight of the electrolyte.

[0076] On the other hand, the electrode assembly may be any form of electrode assembly well known in the art, such as a jelly roll type, a stack type, a stack and lamination type, or a stack and folding type electrode assembly, and its form is not particularly limited.

[0077] A jelly roll type electrode assembly can be manufactured by interposing a sheet-shaped separator membrane between a sheet-shaped positive electrode and a sheet-shaped negative electrode, and then winding the assembly in one direction.

[0078] Stacked electrode assemblies can be manufactured by cutting the positive electrode, separator membrane, and negative electrode into the desired shapes, and then sequentially stacking the cut positive electrode / separator membrane / negative electrode.

[0079] A stack-and-lamination electrode assembly can be manufactured by stacking a positive electrode, a separator membrane, and a negative electrode to produce multiple unit cells, stacking the multiple unit cells with the separator membrane in between, and then laminating them by methods such as heating.

[0080] A stack-and-fold electrode assembly can be manufactured by stacking a positive electrode, a separator membrane, and a negative electrode to produce multiple unit cells, arranging the multiple unit cells on one or both sides of a long folding separator membrane, and then winding up the folding separator membrane.

[0081] On the other hand, the electrical case can be a variety of battery cases known in the art, such as cylindrical battery cases, rectangular battery cases, or pouch-type battery cases, and the type is not particularly limited.

[0082] (2) Activation step Next, an activation step is performed in which the battery cell is charged and discharged once or more to electrically activate the battery. This activation step is a process of stabilizing the battery by charging and discharging the battery cell to impart electrical characteristics and forming an SEI (Solid Electrolyte Interphase) film on the electrodes.

[0083] In this invention, in the step of preparing the battery cell, the ratio of the discharge capacity per unit area of ​​the negative electrode to the discharge capacity per unit area of ​​the positive electrode (N / P ratio) is controlled to 1.05 to 1.15, and an activation step is performed in which the battery is charged to SOC60 to SOC65. This makes it possible to set the amount of negative electrode loading required for actual operation, thereby solving the problem of increased volume and weight of the secondary battery due to the use of unnecessary negative electrodes.

[0084] More specifically, it is preferable to control the ratio of the discharge capacity per unit area of ​​the negative electrode to the discharge capacity per unit area of ​​the positive electrode (N / P ratio) to 1.05 to 1.10. Within this range, it is possible to maximize the capacity of the positive electrode while preventing over-design of the negative electrode.

[0085] First, the charging step can be performed at a rate of 0.3C to 1.0C from SOC60 to SOC65. More specifically, the charging step may include a first charging step of charging to SOC5 or below, and a second charging step of charging from SOC60 to SOC65 at a rate of 0.3C to 1.0C after the first charging step.

[0086] Specifically, the first charging step can be performed at a rate (C-rate) of 0.3C or less, preferably 0.1C to 0.3C, for SOC0 to SOC5.

[0087] When the charging capacity in the first charging step satisfies the range, a hard and dense SEI film is formed on the electrode surface, enabling excellent lifespan characteristics.

[0088] Furthermore, in the first charging step, if the current rate is fast at 0.3C or higher, the SEI film may be unstablely formed on the electrode surface. If the SEI film is unstablely formed on the electrode surface, the SEI film may easily decompose during battery operation, causing rapid deterioration of the electrode, which may significantly reduce the lifespan characteristics.

[0089] On the other hand, the first charging step can be performed in constant current mode (CC mode).

[0090] Next, the activation step may include a second charging step that charges from the completion of the first charging step to SOC60 to SOC65.

[0091] Specifically, the charging step can be performed at a rate of 0.3C to 1.0C from SOC60 to SOC65.

[0092] If the charging capacity in the second charging step meets the range, it is possible to suppress the emergence of an activation capacity that is excessively high relative to the driving capacity, and to obtain an actual driving charge / discharge capacity at the same level as the activation charge / discharge capacity, thus eliminating the need for the oversized negative electrode design that was required to perform the activation process.

[0093] On the other hand, if the second charging step is performed to a state of charge (SOC) of less than 60, Li2MnO3 is not activated at all, and therefore the characteristics of batteries using perlithium manganese oxides that aim to achieve high capacity through the Li2MnO3 activation reaction cannot be realized. Furthermore, if the second charging step is performed to a range exceeding SOC 65, an excessively high positive electrode capacity is obtained compared to the design standard positive electrode drive capacity, and the difference between the design standard discharge capacity ratio (N / P ratio) and the drive voltage standard discharge capacity ratio (N / P ratio) becomes large, resulting in the problem of requiring a negative electrode design that is thicker than the actual required negative electrode.

[0094] On the other hand, the second charging step can be performed in constant current mode (CC mode) or constant current constant voltage mode (CCCV mode).

[0095] When the second charging step is performed in constant current constant voltage (CCCV) mode, CC charging is performed with a C rate of 0.3C to 1.0C supplied from SOC60 to SOC65, and once SOC60 to SOC65 is reached, CV charging can be performed in which the charging C rate is sequentially reduced to approximately 0.05C.

[0096] Next, the activation step discharges the battery cells that have been charged through the first and second charging steps. At this time, the discharge can be performed at a C rate of 0.3C to 0.7C. When the discharge rate satisfies this range, the activation time can be appropriately controlled, and a desired range of discharge capacity characteristics can be achieved.

[0097] On the other hand, the discharge can be performed in constant current mode (CC mode).

[0098] On the other hand, the discharge termination voltage can be 2.0V to 3.0V, specifically 2.0V.

[0099] On the other hand, the activation step is preferably carried out at a temperature of 25°C to 70°C, more preferably 40°C to 50°C. When the activation step is carried out within this temperature range, the effect of achieving high capacity through appropriate activation of Li2MnO3 can be obtained.

[0100] Furthermore, the activation process can be carried out under pressurized conditions as needed. This pressurization can be performed by mounting the battery cells in a jig and then applying pressure to the battery cells through the jig. Performing the activation process under pressurized conditions has the advantages of improved electrolyte impregnation and easier gas discharge during the activation process.

[0101] On the other hand, although not essential, the activation step may further include an aging step, which is intended to allow the electrolyte to be uniformly impregnated into the electrode assembly and stabilize the battery, and can be performed before charging, during charging, and / or after discharging, and may be performed one or more times.

[0102] The aging step can be carried out at a temperature of, for example, 20°C to 60°C, 20°C to 50°C, preferably 30°C to 50°C. When aging is performed at the above temperature, electrolyte impregnation and lithium mobility are improved, and activation can be carried out more smoothly.

[0103] The present invention will be described in more detail below through specific examples.

[0104] Example 1. (Battery cell manufacturing) A positive electrode slurry was prepared by mixing positive electrode active material, conductive material, and PVDF binder in a weight ratio of 97:1:2 in N-methylpyrrolidone. At this time, the positive electrode active material contained Li 1.16 Ni 0.31 Mn 0.53 O2 was used, and carbon nanotubes (CNTs) were used as the conductive material. The positive electrode slurry was applied to an aluminum current collector sheet, dried, and then rolled to produce the positive electrode.

[0105] A negative electrode slurry was prepared by mixing negative electrode active material, conductive material, and binder in water in a weight ratio of 96:1:3. Graphite was used as the negative electrode active material, carbon black as the conductive material, and SBR and CMC as the binder in a weight ratio of 2:1. The negative electrode slurry was applied to a copper current collector sheet, dried, and then rolled to produce the negative electrode (loading amount: 7.5 mg / cm²). 2 They manufactured it.

[0106] At this time, the ratio of the discharge capacity per unit area of ​​the negative electrode to the discharge capacity per unit area of ​​the positive electrode (N / P ratio) was set to 1.10.

[0107] An electrode assembly was manufactured by interposing a separator membrane between the positive and negative electrodes produced as described above. After inserting the electrode assembly into a battery case, an electrolyte solution was injected to manufacture a battery cell.

[0108] (Activation step) After pre-aging the aforementioned battery cells for two days, they were charged to SOC3 in a constant current mode of 0.2C at 45°C (first charging step), then charged to SOC60 in a constant current mode of 0.3C, then charged to 0.05C at a constant voltage (second charging step), and finally discharged to 2.0V at a constant current of 0.5C to produce a lithium secondary battery.

[0109] Example 2. A lithium secondary battery was manufactured by pre-aging a battery cell produced in the same manner as in Example 1 for two days, then charging it to SOC60 in a constant current mode of 0.3C at 45°C, then charging it to 0.05C at a constant voltage (second charging step), and finally performing an activation process in which it was discharged to 2.0V at a constant current of 0.5C.

[0110] Comparative Example 1. (Battery cell manufacturing) A positive electrode slurry was prepared by mixing positive electrode active material, conductive material, and PVDF binder in a weight ratio of 97:1:2 in N-methylpyrrolidone. At this time, Li was used as the positive electrode active material. 1.16Ni 0.31 Mn 0.53 O2 was used, and carbon nanotubes (CNTs) were used as the conductive material. The positive electrode slurry was applied to an aluminum current collector sheet, dried, and then rolled to produce the positive electrode.

[0111] A negative electrode slurry was prepared by mixing negative electrode active material, conductive material, and binder in water in a weight ratio of 96:1:3. Graphite was used as the negative electrode active material, carbon black as the conductive material, and SBR and CMC as the binder in a weight ratio of 2:1. The negative electrode slurry was applied to a copper current collector sheet, dried, and then rolled to produce the negative electrode (loading amount: 13.0 mg / cm²). 2 They manufactured ).

[0112] At this time, the ratio of the discharge capacity per unit area of ​​the negative electrode to the discharge capacity per unit area of ​​the positive electrode (N / P ratio) was set to 1.49.

[0113] An electrode assembly was manufactured by interposing a separator membrane between the positive electrode and negative electrode manufactured as described above. After inserting the electrode assembly into a battery case, an electrolyte solution was injected to manufacture a battery cell.

[0114] (Activation step) After pre-aging the aforementioned battery cells for two days, they were charged to SOC3 in a constant current mode of 0.2C at 45°C (first charging step), then charged to SOC60 in a constant current mode of 0.3C, then charged to 0.05C at a constant voltage (second charging step), and finally discharged to 2.0V at a constant current of 0.5C to produce a lithium secondary battery.

[0115] Experimental Example 1. The battery cells manufactured in Example 1, Example 2, and Comparative Example 1 were each charged to 4.3V at room temperature (25°C) in a constant current / constant voltage mode of 0.33C (0.05C cutoff), and then discharged to 2.0V at a constant current of 0.33C. A single charge / discharge cycle was performed, and the initial charge / discharge capacity was measured and is shown in Table 1 below.

[0116] [Table 1]

[0117] As can be seen from Table 1 above, the lithium secondary batteries of Example 1 and Example 2 manufactured according to the present invention achieve an initial charge / discharge capacity equivalent to that of the lithium secondary battery of Comparative Example 1, even though the negative electrode is not over-designed.

[0118] Experimental Example 2. (Request for provision of storage characteristics or cycle characteristics) The battery cells manufactured in Example 1, Example 2, and Comparative Example 1 were each charged to 4.3V at 45°C in a constant current / constant voltage mode of 0.33C (0.05C cutoff), and discharged to 2.0V at a constant current of 0.33C. 200 charge-discharge cycles were performed, and the ratio of the discharge capacity after 200 cycles to the initial discharge capacity is shown in Table 2 below as the cycle capacity retention rate.

[0119] Furthermore, the battery cells of Example 1, Example 2, and Comparative Example 1 were each charged to 4.3V at 25°C in a constant current / constant voltage mode of 0.33C (0.05C cutoff), then discharged to 2.0V at a constant current of 0.33C to measure the initial discharge capacity. They were then charged again at 25°C to 4.3V in a constant current / constant voltage mode of 0.33C (0.05C cutoff), stored in a 60°C chamber for 8 weeks, and then discharged to 2.0V at a constant current of 0.33C. The ratio of the discharge capacity after storage to the discharge capacity before storage was measured, and the results are shown in Table 2 below as the storage capacity retention rate.

[0120] [Table 2]

[0121] As can be seen in Table 2 above, the lithium secondary batteries of Example 1 and Example 2 manufactured according to the present invention exhibit capacity retention rates and high-temperature storage characteristics equivalent to, or even superior to, the lithium secondary battery of Comparative Example 1, despite not over-designing the negative electrode. This is understood to be because the lithium secondary battery of Comparative Example 1 experienced increased side reactions due to the over-design of the negative electrode. [Industrial applicability]

[0122] The lithium secondary battery manufacturing method according to the present invention can improve the negative electrode over-design and solve the problem of increased volume and weight of the lithium secondary battery by completing charging at SOC60 to SOC65 in the activation step.

Claims

1. A step of preparing a battery cell comprising a positive electrode, a negative electrode, and an electrolyte containing a perlithium manganese oxide in which the manganese content of the total metals excluding lithium exceeds 50 mol%, and the ratio of the number of moles of lithium to the total number of moles of metals excluding lithium (Li / Me) exceeds 1, and The step includes activating the battery cell by charging and discharging it once or more times, The aforementioned battery cell has a discharge capacity ratio (N / P ratio) of 1.05 to 1.15 for the negative electrode to the positive electrode when charged to 2.0V to 4.3V. In the activation step, the charging is performed from SOC60 to SOC65, where SOC X represents the state where the percentage of the capacity charged to the battery cell is X, based on the discharge capacity that appears when the battery cell is discharged from 4.6V to 2.0V. The aforementioned perlithium manganese oxide is represented by the following chemical formula 1, [Chemical formula 1] Li a Ni b Co c M n d M e O 2 A method for manufacturing a lithium secondary battery, wherein in the chemical formula 1, 1 < a, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, 0.5 ≤ d < 1.0, and 0 ≤ e ≤ 0.2, and M is one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

2. A method for manufacturing a lithium secondary battery according to claim 1, wherein in the chemical formula 1, 1.1 ≤ a ≤ 1.5, 0.1 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.05, 0.5 ≤ d ≤ 0.80, and 0 ≤ e ≤ 0.

1.

3. The method for manufacturing a lithium secondary battery according to claim 1, wherein the charging is performed in constant current mode (CC mode) or constant current constant voltage mode (CCCV mode).

4. The method for manufacturing a lithium secondary battery according to claim 1, wherein the charging is performed at a rate of 0.3C to 1.0C from SOC60 to SOC65.

5. The method for manufacturing a lithium secondary battery according to claim 1, wherein the charging includes a first charging step of charging in the section SOC0 to SOC5 at a rate of 0.1C to 0.3C, and a second charging step of charging from SOC60 to SOC65 at a rate of 0.3C to 1.0C after the first charging step.

6. The method for manufacturing a lithium secondary battery according to claim 5, wherein the first charging step and / or the second charging step are performed in constant current mode (CC mode).

7. The method for manufacturing a lithium secondary battery according to claim 1, wherein the activation step includes a step of discharging at a rate of 0.3C to 0.7C until the voltage reaches 2.0V.

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