Activation method of rechargeable lithium battery and rechargeable lithium battery

Abstract

The invention relates to an activation method of a rechargeable lithium battery and the rechargeable lithium battery. The activation method includes performing a first charge and discharge process on the rechargeable lithium battery, and performing a second charge and discharge process on the rechargeable lithium battery. The rechargeable lithium battery includes: a positive electrode including a positive electrode active material including a layered lithium nickel manganese-based composite oxide; a negative electrode; a separator between the positive electrode and the negative electrode; and an electrolyte solution. The upper limit voltage of the second charging and discharging process is higher than the upper limit voltage of the first charging and discharging process.

Description

Technical Field

[0001] A method for activating a rechargeable lithium battery and a rechargeable lithium battery are disclosed. Background Art

[0002] Portable information devices (such as cellular phones, laptop computers, smart phones, etc.) and electric vehicles use rechargeable lithium batteries with high energy density and easy to carry as drive power sources. Also, research has been conducted on using rechargeable lithium batteries with high energy density as drive power sources or power storage power sources for hybrid vehicles or electric vehicles.

[0003] Various positive electrode active materials have been studied to realize rechargeable lithium batteries for different uses. Among them, lithium nickel-based oxides, lithium nickel manganese cobalt-based composite oxides, lithium nickel cobalt aluminum-based composite oxides, and lithium cobalt-based oxides are most commonly used as positive electrode active materials. However, although the demand for large-sized, high-capacity, or high-energy-density rechargeable lithium batteries has recently increased, the supply of positive electrode active materials containing rare metal cobalt is expected to be severely short. And because cobalt is expensive and the remaining reserves are not much, it is necessary to develop positive electrode active materials that exclude cobalt or reduce the cobalt content. Summary of the Invention

[0004] In a rechargeable lithium battery using a positive electrode active material including a layered lithium nickel manganese-based composite oxide (hereinafter, may be abbreviated as "lithium nickel manganese-based composite oxide"), high-voltage activation is applied to increase the capacity, while synchronously preventing lithium precipitation caused by the reversal of the negative electrode capacity / positive electrode capacity (N / P) ratio and improving the reversible capacity and cycle life characteristics.

[0005] In some embodiments, a method for activating a rechargeable lithium battery includes: performing a first charge and discharge process on the rechargeable lithium battery, and performing a second charge and discharge process on the rechargeable lithium battery cell after the first charge and discharge process, wherein the rechargeable lithium battery includes: a positive electrode including a positive electrode active material, the positive electrode active material including a lithium nickel manganese-based composite oxide; a negative electrode; a separator between the positive electrode and the negative electrode; and an electrolyte, wherein the upper limit voltage of the second charge and discharge process is higher than the upper limit voltage of the first charge and discharge process.

[0006] In some embodiments, a rechargeable lithium battery includes: a positive electrode including a positive electrode active material, the positive electrode active material including a layered lithium nickel manganese-based composite oxide; a negative electrode; a separator between the positive electrode and the negative electrode; and an electrolyte, wherein the initial N / P ratio of the rechargeable lithium battery is about 1.13 to about 1.15, and the N / P ratio when the rechargeable lithium battery is charged at a voltage of about 4.6 V or higher is greater than or equal to about 1.

[0007] When applying the method for activating a rechargeable lithium battery according to some embodiments, lithium precipitation due to the reversal of the N / P ratio is prevented while maximizing the capacity, and the reversible capacity and cycle life characteristics can also be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figures 1 to 4 FIG. is a schematic cross-sectional view of a rechargeable lithium battery according to some embodiments.

[0009] Figure 5 FIG. is a graph for evaluating the high-temperature cycle life characteristics of rechargeable lithium battery cells of Comparative Examples 1 to 3 and Example 2.

[0010] Figure 6 FIG. is a graph showing the evaluation of the high-temperature cycle life characteristics of rechargeable lithium battery cells of Examples 1 to 4.

[0011] Figure 7 FIG. is a graph showing the evaluation of the high-temperature cycle life characteristics of rechargeable lithium battery cells of Comparative Examples 2 to 4 and Example 4.

[0012] Figure 8 FIG. is a graph of the peaks corresponding to the (020) crystal plane in the X-ray diffraction analysis (XRD) of the positive electrode plates after activation of Comparative Example 1 and Example 2.

[0013] Figures 9 to 11 FIG. shows the dQ / dV curves of the third cycle after activation of Comparative Example 1, Comparative Example 3, and Example 2.

[0014] <DESCRIPTION OF REFERENCE NUMERALS>

[0015] 100: Rechargeable lithium battery 10: Positive electrode

[0016] 11: Positive electrode lead tab 12: Positive electrode terminal

[0017] 20: Negative electrode 21: Negative electrode lead tab

[0018] 22: Negative electrode terminal 30: Separator

[0019] 40: Electrode assembly 50: Housing

[0020] 60: Sealing member 70: Electrode tab

[0021] 71: Positive electrode tab 72: Negative electrode tab DETAILED DESCRIPTION

[0022] Hereinafter, specific embodiments will be described in detail so that those of ordinary skill in the art can easily implement them. However, the present disclosure can be implemented in many different forms and is not limited to the example embodiments set forth herein.

[0023] The terms are used herein only to describe the embodiments and do not necessarily limit the present disclosure. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0024] As used herein, "a combination thereof" means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

[0025] In this document, terms such as "comprises", "includes", or "has" are intended to indicate the presence of specific features, quantities, steps, elements, or combinations thereof, but they do not exclude the possibility of the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0026] In the drawings, for clarity, the thicknesses of layers, films, panels, regions, etc. are exaggerated, and throughout the specification, the same reference numerals denote the same elements. It will be understood that when an element (such as a layer, film, region, or substrate) is referred to as being "on" another element (such as a layer, film, region, or substrate), it can be directly on the other element (such as a layer, film, region, or substrate), or intervening elements may also be present. In contrast, when an element (such as a layer, film, region, or substrate) is referred to as being "directly on" another element (such as a layer, film, region, or substrate), no intervening elements are present.

[0027] In addition, a "layer" in this document includes not only a shape formed on the entire surface when viewed in a plan view but also a shape formed on a partial surface.

[0028] The average particle size can be measured by methods well known to those skilled in the art, for example, by a particle size analyzer, by a transmission electron microscope image, or by a scanning electron microscope image. Optionally, the average particle size value can be obtained by: using the dynamic light scattering method, performing data analysis, counting the number of particles in each particle size range, and calculating therefrom. Unless otherwise defined, the average particle size (D 50 ) means the diameter of the particle at which the cumulative volume in the particle size distribution is 50% by volume. As used herein, when no other limitation is provided, the average particle size (D 50 ) means the diameter of the particle at which the cumulative volume in the particle size distribution is 50% by volume, obtained by randomly measuring the sizes (diameter or major axis length) of about 20 particles in a scanning electron microscope image.

[0029] In this text, "or" is not construed in an exclusive sense. For example, "A or B" is construed to include A, B, A + B, etc.

[0030] "Metal" is construed to include the concepts of common metals, transition metals, and metalloids (semi-metals).

[0031] In some embodiments, a method of activating a rechargeable lithium battery includes sequentially performing a first charge and discharge process and a second charge and discharge process. The rechargeable lithium battery includes: a positive electrode including a positive electrode active material, the positive electrode active material including a layered lithium nickel manganese composite oxide; a negative electrode; a separator between the positive electrode and the negative electrode; and an electrolyte, wherein the upper limit voltage of the second charge process is higher than the upper limit voltage of the first charge process.

[0032] Due to the recent sharp increase in the price of the rare metal cobalt, it is necessary to develop positive electrode active materials that exclude cobalt or reduce the cobalt content. Among these positive electrode active materials, those having an olivine crystal structure (such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), lithium manganese iron phosphate (LMFP), etc.) and those having a spinel crystal structure (such as lithium manganese oxide (LMO), etc.) have limitations in achieving high capacity due to the small amount of lithium available within the structure. The layered lithium nickel manganese composite oxide positive electrode active material has excellent capacity and efficiency characteristics due to the high available lithium capacity in the structure, making it suitable as a material for high-capacity batteries. However, as cobalt, which plays a key role in the layered structure, is removed, the structural stability decreases, the resistance increases, and it becomes difficult to ensure long cycle life characteristics. In particular, as the cycling progresses, the cation mixing of Ni 2+ and Li + becomes more severe, resulting in a structural change of the layered lithium nickel manganese composite oxide positive electrode active material, thereby increasing the resistance, generating more cracks due to swelling, and there is a problem of a significant reduction in the reversible capacity compared to conventional layered nickel cobalt composite oxide positive electrode active materials. The deterioration of long-term cycle life characteristics is also a problem.

[0033] In a battery using a layered lithium nickel manganese composite oxide positive electrode active material, the capacity can be improved by activating the battery at a high voltage higher than the normal voltage, but there is a problem that the N / P ratio is reversed due to the rapid increase in the first charge capacity. This problem can cause lithium metal to precipitate on the negative electrode, and greatly reduce the cycle life of the battery or cause micro-short circuits and lead to a reduction in safety. If the designed N / P ratio is increased, the capacity can be increased by increasing the negative electrode potential, but there is another problem, namely, accompanied by the deterioration of cycle life characteristics and a reduction in energy density.

[0034] Accordingly, some embodiments propose a method of applying stepped high voltage activation to prevent lithium precipitation on the negative electrode due to N / P reversal, and also to improve the reversible capacity and cycle life characteristics. In the activation process of a rechargeable lithium battery, the first charge and discharge (i.e., the first cycle) are performed within the normal voltage range, and then, the second charge and discharge (i.e., the second cycle) are performed within a high voltage range higher than the normal voltage range to prevent N / P reversal and improve the capacity and cycle life characteristics without increasing the designed N / P ratio.

[0035] In the activation method of a rechargeable lithium battery according to some embodiments, the upper limit voltage of the first charge may be less than or equal to about 4.5V, and the upper limit voltage of the second charge may be greater than about 4.5V. In more specific embodiments, the upper limit voltage of the first charge may be less than or equal to about 4.4V, may be about 4.0V to about 4.4V or about 4.2V to about 4.4V, and the upper limit voltage of the second charge may be greater than or equal to about 4.6V, may be about 4.6V to about 4.8V or about 4.6V to about 4.7V.

[0036] After activation, the third charge and discharge may be performed within the same voltage range as the first charge and discharge. That is, the upper limit voltage of the third charge and discharge may be the same as or similar to the upper limit voltage of the first charge.

[0037] The first charge and discharge and the second charge and discharge may be performed at the same or different rates, and the rate may be less than or equal to about 0.2C.

[0038] The designed N / P ratio of a rechargeable lithium battery according to some embodiments may be about 1.13 to about 1.15. The designed N / P ratio of a rechargeable lithium battery means the initial N / P ratio of the rechargeable lithium battery before its first charge. If the N / P ratio is designed within this range, N / P ratio reversal or lithium metal precipitation may not occur at the negative electrode, but the reversible capacity and cycle life characteristics may be improved. Herein, the designed N / P ratio refers to the ratio of the negative electrode capacity to the positive electrode capacity, and the theoretical capacity of each electrode can be calculated as {(specific capacity of the active material) × (amount of the active material) × (loading level)}. The specific capacity of the active material may refer to the first discharge specific capacity measured after manufacturing a half-cell monomer using lithium metal as the counter electrode.

[0039] A rechargeable lithium battery activated according to some embodiments may have a charging N / P ratio of about 1 or greater during the second charge and discharge; more specifically, may have a charging N / P ratio of about 1 to about 1.1, about 1 to about 1.05, or about 1.01 to about 1.03. In other words, even when applying the high voltage formation method, N / P ratio reversal can be prevented.

[0040] In the X-ray diffraction analysis of the positive electrode after the second charge and discharge, the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane can be greater than or equal to about 3.5 and less than or equal to about 4.5; more specifically, the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane can be greater than or equal to about 3.5 and less than or equal to about 4.2, greater than or equal to about 3.7 and less than or equal to about 4.1, or greater than or equal to about 3.8 and less than or equal to about 4.0. Additionally, the full width at half maximum (FWHM) of the (003) plane can be greater than or equal to about 0.090 and less than or equal to about 0.12, and the full width at half maximum (FWHM) of the (104) plane can be greater than or equal to about 0.175 and less than or equal to about 0.190. After applying the activation method, the positive electrode active material maintains a layered structure.

[0041] Hereinafter, each component of the battery will be described in detail.

[0042] Rechargeable lithium battery

[0043] Rechargeable lithium batteries can be classified according to shape into cylindrical, prismatic, pouch, coin-shaped, and so on. Figures 1 to 4 For showing a schematic diagram of a rechargeable lithium battery according to some embodiments, wherein Figure 1 is a cylindrical battery, Figure 2 is a prismatic battery, and Figure 3 and Figure 4 are pouch batteries. Referring to Figures 1 to 4 , the rechargeable lithium battery 100 includes: an electrode assembly 40 having a separator 30 inserted between a positive electrode 10 and a negative electrode 20; and a housing 50 that houses the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). As shown in Figure 1 , the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50. Additionally, as shown in Figure 2 , the rechargeable lithium battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in Figure 3 and Figure 4 , the rechargeable lithium battery 100 includes electrode tabs 70, that is, a positive electrode tab 71 and a negative electrode tab 72, which serve as a circuit path for leading out the current formed in the electrode assembly 40 to the outside of the battery.

[0044] Positive electrode

[0045] The positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and may optionally further include a binder, a conductive material, or a combination thereof. In some embodiments, the positive electrode active material layer includes a positive electrode active material including a layered lithium nickel manganese composite oxide.

[0046] Positive electrode active material

[0047] In the layered lithium nickel manganese composite oxide, based on the total metals other than lithium in 100 mol% of the lithium nickel manganese composite oxide, the nickel content can be greater than or equal to about 60 mol%, for example, about 60 mol% to about 80 mol%, about 65 mol% to about 80 mol%, about 70 mol% to about 80 mol%, about 60 mol% to about 79 mol%, about 60 mol% to about 78 mol%, or about 60 mol% to about 75 mol%. If the nickel content meets these ranges, high capacity can be achieved and structural stability can be increased even when the cobalt content is reduced.

[0048] Based on the total metals other than lithium in 100 mol% of the lithium nickel manganese composite oxide, the manganese content can be greater than or equal to about 10 mol%, for example, about 15 mol% to about 40 mol%, about 15 mol% to about 35 mol%, about 15 mol% to about 30 mol%, or about 20 mol% to about 30%. If the manganese content meets these ranges, the positive electrode active material can improve structural stability while having high capacity.

[0049] The layered lithium nickel manganese composite oxide can be a lithium nickel manganese aluminum composite oxide that further includes aluminum in addition to nickel and manganese. If the layered lithium nickel manganese composite oxide contains aluminum, it is beneficial to maintain a stable layered structure even when the cobalt element is excluded from the structure. Based on 100 mol% of the layered lithium nickel manganese composite oxide, the aluminum content can be greater than or equal to about 0.1 mol%, greater than or equal to about 0.5 mol%, or greater than or equal to about 1 mol%, for example, about 1 mol% to about 3 mol%, about 1 mol% to about 2.5 mol%, about 1 mol% to about 2 mol%, or about 1.5 mol% to about 2.5 mol%. If the aluminum content meets these ranges, a stable layered structure can be maintained even when cobalt is reduced or removed, the problem of structural collapse due to charge and discharge can be suppressed, and long cycle life characteristics of the positive electrode active material can be achieved.

[0050] According to some embodiments, the concentration of aluminum in the layered lithium nickel manganese composite oxide is uniform. In various embodiments, there may be no concentration gradient of aluminum from the center to the surface within the layered lithium nickel manganese composite oxide, or the aluminum concentration inside the particles including the layered lithium nickel manganese composite oxide is neither higher nor lower than the aluminum concentration outside the particles, and the aluminum within the particles including the layered lithium nickel manganese composite oxide is uniformly distributed. This structure can be obtained during the production of the precursor by using an aluminum raw material without additional doping of aluminum during the synthesis of the layered lithium nickel manganese composite oxide, thereby synthesizing the composite oxide using a nickel manganese aluminum hydroxide as the precursor. For this reason, even if cobalt is absent or present in a very small amount, a stable layered structure can be maintained, and no aluminum by-products or aluminum aggregates are formed. Therefore, the capacity, efficiency, and cycle life characteristics of the positive electrode active material can all be improved.

[0051] The layered lithium nickel manganese composite oxide can be specifically represented by Chemical Formula 1.

[0052] [Chemical Formula 1]

[0053] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1

[0054] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.8, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.4, 0 ≤ z1 ≤ 0.03, 0 ≤ w1 ≤ 0.3, 0.9 ≤ x1 + y1 + z1 + w1 ≤ 1.1, and 0 ≤ b1 ≤ 0.1, M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0055] In a further embodiment, in Chemical Formula 1, 0.9 ≤ a1 ≤ 1.5, or 0.9 ≤ a1 ≤ 1.2. Additionally, Chemical Formula 1 may contain aluminum, in which case, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.39, 0.01 ≤ z1 ≤ 0.03, and 0 ≤ w1 ≤ 0.29 may be satisfied, or for example, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.39, 0.01 < z1 ≤ 0.03, and 0 ≤ w1 ≤ 0.29 may be satisfied.

[0056] In other embodiments, in Chemical Formula 1, 0.6 ≤ x1 ≤ 0.79, 0.6 ≤ x1 ≤ 0.78, 0.6 ≤ x1 ≤ 0.75, 0.65 ≤ x1 ≤ 0.8, or 0.7 ≤ x1 ≤ 0.79, 0.1 ≤ y1 ≤ 0.35, 0.1 ≤ y1 ≤ 0.30, 0.1 ≤ y1 ≤ 0.29, 0.15 ≤ y1 ≤ 0.39, or 0.2 ≤ y1 ≤ 0.3, 0.01 ≤ z1 ≤ 0.025, 0.01 < z1 ≤ 0.02, or 0.01 < z1 ≤ 0.019, and 0 ≤ w1 ≤ 0.28, 0 ≤ w1 ≤ 0.27, 0 ≤ w1 ≤ 0.26, 0 ≤ w1 ≤ 0.25, 0 ≤ w1 ≤ 0.24, 0 ≤ w1 ≤ 0.23, 0 ≤ w1 ≤ 0.22, 0 ≤ w1 ≤ 0.21, 0 ≤ w1 ≤ 0.2, 0 ≤ w1 ≤ 0.15, 0 ≤ w1 ≤ 0.1, or 0 ≤ w1 ≤ 0.09.

[0057] The layered lithium nickel manganese composite oxide may contain no cobalt or may contain a small amount of cobalt, and based on 100 mol% of the total metals other than lithium, the cobalt content is about 0 mol% to about 0.01 mol%.

[0058] The positive electrode active material may include large particles having an average particle diameter (D 50 ) of about 10 μm to about 25 μm and small particles having an average particle diameter (D 50 ) of about 0.5 μm to about 8 μm. By mixing the large particles and the small particles, the capacity and energy density of the lithium nickel manganese positive electrode can be maximized and its cycle life characteristics and durability can be improved.

[0059] The large particles may be in the form of secondary particles formed by aggregating a plurality of primary particles. The small particles may be in the form of secondary particles, single particles, or a combination thereof. In one example, the positive electrode active material may include large particles in the form of secondary particles and small particles in the form of single particles. By mixing the large particles in the form of secondary particles and the small particles in the form of single particles, the capacity and energy density of the lithium nickel manganese positive electrode can be maximized and the cycle life characteristics and durability can be improved.

[0060] The average particle diameter (D 50 ) of the large particles may be about 10 μm to about 25 μm, such as about 10 μm to about 20 μm, about 10 μm to about 18 μm, or about 12 μm to about 16 μm. The average particle diameter (D 50 ) of the second positive electrode active material may be, for example, about 0.5 μm to about 8 μm, about 1 μm to about 7 μm, about 1.5 μm to about 6 μm, or about 2 μm to about 5 μm. If the average particle diameter of each positive electrode active material satisfies these ranges, high capacity and high energy density can be achieved.

[0061] Based on 100 wt% of the total large particles and small particles, the content of the large particles can be about 60 wt% to about 95 wt%, for example, about 70 wt% to about 90 wt%. Based on 100 wt% of the total large particles and small particles, the content of the small particles can be about 5 wt% to about 40 wt%, for example, about 10 wt% to about 30 wt%. If the mixing ratio satisfies these ranges, the energy density can be increased while maximizing the capacity.

[0062] The positive electrode active material includes: core particles including a layered lithium nickel manganese composite oxide and a coating on the surface of the core particles, wherein the coating includes at least one element selected from Al, B, Co, Mg, Y, and Zr.

[0063] Binder

[0064] The binder improves the bonding characteristics between the positive electrode active material particles and the bonding characteristics between the positive electrode active material particles and the positive electrode current collector. Examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate esterified styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon. However, the present disclosure is not limited to such examples.

[0065] Conductive material

[0066] A conductive material is included to provide electrode conductivity, and any conductive material can be used as the conductive material as long as the conductive material does not cause a chemical change. Examples of the conductive material include carbon materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.); metal materials including metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); and mixtures thereof.

[0067] Based on 100 wt% of the positive electrode active material layer, the respective contents of the binder and the conductive material can be about 0.5 wt% to about 5 wt%.

[0068] The positive electrode current collector may include Al foil, but the present disclosure is not limited thereto.

[0069] According to some embodiments, the loading level of the positive electrode active material layer can be about 10 mg / cm 2 ~ about 40 mg / cm 2 For example, about 10 mg / cm 2 ~ about 30 mg / cm 2, or about 10 mg / cm 2 ~ about 20 mg / cm 2 . Additionally, the density (mixture density) of the positive electrode active material layer in the finally pressed positive electrode can be about 3.3 g / cc to about 3.7 g / cc, such as about 3.3 g / cc to about 3.6 g / cc or about 3.4 g / cc to about 3.58 g / cc.

[0070] Negative electrode

[0071] The negative electrode may include a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, and may further include a negative electrode active material, a binder, a conductive material, or a combination thereof.

[0072] Negative electrode active material

[0073] The negative electrode active material may include: a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, or a transition metal oxide.

[0074] The material that reversibly intercalates / deintercalates lithium ions may include, for example, crystalline carbon, amorphous carbon, or a combination thereof as a carbon-based negative electrode active material. The crystalline carbon may be amorphous, flake, sheet, spherical, or fibrous natural graphite or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonized product, calcined coke, etc.

[0075] The lithium metal alloy includes an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0076] The material capable of doping / dedoping lithium may be a Si-based negative electrode active material (also referred to as "silicon-based negative electrode active material") or a Sn-based negative electrode active material. The Si-based negative electrode active material may include silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2), a Si-Q alloy. In this case, Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof. For example, Q may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof. The Sn-based negative electrode active material may be Sn, SnO x(0 < x ≤ 2) (e.g., SnO 2 ), Sn alloy, or a combination thereof.

[0077] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D 50 ) of the silicon-carbon composite particles may be, for example, about 0.5 μm to about 20 μm. According to some embodiments, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. The silicon-carbon composite may include secondary particles (cores) in which silicon primary particles are aggregated and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon may also be present between the silicon primary particles. For example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0078] The silicon-carbon composite may further include crystalline carbon. The silicon-carbon composite may include: a core including crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon may include soft carbon or hard carbon, mesophase pitch carbonized products, and calcined coke.

[0079] When the silicon-carbon composite includes silicon and amorphous carbon, based on 100 wt% of the silicon-carbon composite, the content of silicon may be about 10 wt% to about 50 wt% and the content of amorphous carbon may be about 50 wt% to about 90 wt%. Additionally, when the silicon-carbon composite includes silicon, amorphous carbon, and crystalline carbon, based on 100 wt% of the silicon-carbon composite, the content of silicon may be about 10 wt% to about 50 wt%, the content of crystalline carbon may be about 10 wt% to about 70 wt%, and the content of amorphous carbon may be about 20 wt% to about 40 wt%.

[0080] The thickness of the amorphous carbon coating may be about 5 nm to about 100 nm. The average particle size (D 50 ) of the silicon particles (primary particles) may be about 10 nm to about 1 μm or about 10 nm to about 200 nm. The silicon particles may exist in the form of elemental silicon, a silicon alloy, or an oxidized form of silicon. The oxidized form of silicon may be represented by SiO x (0 < x ≤ 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may be about 99:1 to about 33:67.

[0081] The Si-based negative electrode active material or the Sn-based negative electrode active material may be mixed with the carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material is mixed with the carbon-based negative electrode active material, the mixing ratio of the Sn-based negative electrode active material to the carbon-based negative electrode active material may be a weight ratio of about 1:99 to about 90:10.

[0082] Binder

[0083] The binder is used to bond the negative electrode active material particles to each other and also bond the negative electrode active material to the negative electrode current collector. The binder can be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0084] The non-aqueous binder can include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0085] The aqueous binder can include styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, epichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0086] When the aqueous binder is used as the binder in the negative electrode active material layer, it can include a cellulose compound capable of imparting viscosity. As the cellulose compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts can be mixed and used. The alkali metal can be Na, K, or Li.

[0087] The dry binder can be a polymer material capable of becoming fibers and can be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0088] Conductive material

[0089] A conductive material is included to provide electrode conductivity, and any conductive material can be used as long as the conductive material does not cause a chemical change. Examples of the conductive material include carbon materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.); metal materials including metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); or a mixture thereof.

[0090] Based on 100 wt% of the negative electrode active material layer, the content of the negative electrode active material can be about 95 wt% to about 99.5 wt%, and based on 100 wt% of the negative electrode active material layer, the content of the binder can be about 0.5 wt% to about 5 wt%. For example, the negative electrode active material layer can include about 90 wt% to about 99 wt% of the negative electrode active material, about 0.5 wt% to about 5 wt% of the binder, and about 0.5 wt% to about 5 wt% of the conductive material.

[0091] Current collector

[0092] The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and may be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, about 1 μm to about 20 μm, about 5 μm to about 15 μm, or about 7 μm to about 10 μm.

[0093] Electrolyte

[0094] The electrolyte for a rechargeable lithium battery may include a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery. The non-aqueous organic solvent may include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or a combination thereof.

[0095] The carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. The ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. The ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. The ketone solvents may include cyclohexanone, etc. The alcohol solvents may include ethanol, isopropanol, etc., and the aprotic solvents may include nitriles such as R-CN (where R is a C2-C20 straight-chain, branched-chain, or cyclic hydrocarbon group and may include double bonds, aromatic rings, or ether groups, etc.); amides (such as dimethylformamide); dioxolanes (such as 1,3-dioxolane, 1,4-dioxolane, etc.); sulfolane, etc.

[0096] The non-aqueous organic solvents may be used alone or as a mixture of two or more of their types. When used as a mixture of two or more of their types, the mixing ratio may be adjusted according to the desired battery performance, which is well known to those skilled in the art.

[0097] When using carbonate solvents, cyclic carbonates and chain carbonates may be mixed and used. The cyclic carbonate and the chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9.

[0098] The non-aqueous organic solvent may include an aromatic hydrocarbon organic solvent. For example, a carbonate solvent and an aromatic hydrocarbon organic solvent may be mixed and used at a volume ratio of about 1:1 to about 30:1.

[0099] The electrolyte may further include vinylene carbonate, vinylene carbonate or ethylene carbonate compounds to improve the battery cycle life. Examples of ethylene carbonate compounds may include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate and cyanoethylene carbonate.

[0100] The lithium salt dissolved in the non-aqueous organic solvent supplies lithium ions in the battery, ensuring the basic operation of the rechargeable lithium battery and improving the transport of lithium ions between the positive and negative electrodes. Examples of lithium salts include those selected from LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiPO 2 F 2 , LiCl, LiI, LiN(SO 3 C 2 F 5 ), 2 , Li(FSO 2 ), 2 N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC 4 F 9 SO 3 , LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 )(where x and y are each integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro bis(oxalate) phosphate (LiDFBOP) and lithium bis(oxalate) borate (LiBOB), and at least one of them.

[0101] The concentration of the lithium salt may be in the range of about 0.1 M to about 2.0 M. When the concentration of the lithium salt is within this range, the electrolyte has appropriate ionic conductivity and viscosity. Therefore, excellent performance can be achieved and lithium ions can move effectively.

[0102] Separator

[0103] Depending on the type of rechargeable lithium battery, a separator may be present between the positive electrode and the negative electrode. The separator may include a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, or a multilayer film of two or more of its layers (such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.).

[0104] The separator may include a porous substrate and a coating on one or both surfaces of the porous substrate, the coating including an organic material, an inorganic material, or a combination thereof.

[0105] The porous substrate may be a polymer film formed from any one polymer selected from the following or a copolymer or mixture of two or more thereof: polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyarylether ketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene ethers, cycloolefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene

[0106] The porous substrate may have a thickness of about 1 μm to about 40 μm (for example, about 1 μm to about 30 μm, about 1 μm to about 20 μm, about 5 μm to about 15 μm, or about 10 μm to about 15 μm).

[0107] The organic material may include a (meth)acrylamide copolymer, the (meth)acrylamide copolymer including a first structural unit derived from (meth)acrylamide, and a second structural unit including at least one of a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or its salt.

[0108] The inorganic material may include selected from Al 2 O 3 、SiO 2 、TiO 2 、SnO 2 、CeO 2 、MgO、NiO、CaO、GaO、ZnO、ZrO 2 、Y 2 O 3 、SrTiO 3 、BaTiO 3 、Mg(OH) 2 、boehmite, and inorganic particles of combinations thereof, but the present disclosure is not limited thereto. The average particle size (D 50 ) of the inorganic particles may be about 1 nm to about 2000 nm, for example, about 100 nm to about 1000 nm or about 100 nm to about 700 nm.

[0109] An organic material and an inorganic material can be mixed in a coating, or a coating including an organic material and a coating including an inorganic material can be stacked.

[0110] The thickness of the coating can be about 0.5 μm to about 20 μm, for example, about 1 μm to about 10 μm or about 1 μm to about 5 μm.

[0111] Design of a rechargeable lithium battery

[0112] In some embodiments, a rechargeable lithium battery includes: a positive electrode including a positive electrode active material, the positive electrode active material including a layered lithium nickel manganese composite oxide; a negative electrode; a separator between the positive electrode and the negative electrode; and an electrolyte, wherein the N / P ratio is about 1.13 to about 1.15, and when the battery is charged at about 4.6 V or higher, the N / P ratio is greater than or equal to about 1. If the N / P ratio is set within the range of about 1.13 to about 1.15 and the above activation method is applied, when charging at about 4.6 V or higher (for example, during the second charge and discharge process in the above activation method), the N / P ratio can be about 1 or greater. In other words, a high voltage formation method can be applied to improve the capacity and also prevent the reversal of the N / P ratio, thereby preventing lithium precipitation at the negative electrode and improving the cycle life characteristics.

[0113] If a rechargeable lithium battery is charged at about 4.6 V or higher, the N / P ratio can be, for example, about 1 to about 1.1, about 1 to about 1.05, or about 1.01 to about 1.03.

[0114] The rechargeable lithium battery can have a driving range of less than about 4.6 V, less than about 4.5 V, less than or equal to about 4.4 V, or about 4.0 V to about 4.4 V. During the activation process, the first cycle charge and discharge process can be performed within this driving voltage range, and the second cycle charge and discharge process can be performed up to an upper limit voltage of greater than or equal to about 4.6 V to significantly improve the reversible capacity. Additionally, if the charge and discharge process is performed at greater than or equal to about 4.5 V, the N / P ratio may not reverse but be about 1 or greater.

[0115] The positive electrode, negative electrode, separator, and electrolyte are the same as those described above and will not be repeated here.

[0116] Examples and comparative examples of the present disclosure are described below. However, the following examples are only examples of the present disclosure, and the present disclosure is not limited to the following examples.

[0117] Example 1

[0118] 1. Preparation of positive electrode active material

[0119] Ni0.75 Mn 0.23 Al 0.02 (OH) 2 and LiOH are mixed at a molar ratio of 1:1.05, and then heat-treated in an oxygen atmosphere at 855 °C for 15 hours to prepare a lithium nickel manganese-based active material (i.e., a preliminary positive electrode active material).

[0120] The preliminary positive electrode active material is secondarily heat-treated at 825 °C for 20 hours to prepare large particles having a composition of Li 1.05 Ni 0.75 Mn 0.23 Al 0.02 O 2 and having a form of secondary particles with an average particle size (D 50 ) of about 14 μm.

[0121] Furthermore, Ni 0.75 Mn 0.25 (OH) 2 and LiOH are mixed at a molar ratio of 1:1.05, and then heat-treated twice in an oxygen atmosphere at 850 °C to prepare small particles having a composition of LiNi 0.75 Mn 0.25 O 2 and having a form of single particles with an average particle size (D 50 ) of about 4 μm. In the secondary heat treatment, the single small particles are surface-coated.

[0122] The large particles and the small particles are mixed at a weight ratio of 7:3 to prepare a final positive electrode active material.

[0123] 2. Manufacture of a rechargeable lithium battery cell

[0124] 97.7 wt% of the prepared positive electrode active material, 1.3 wt% of a polyvinylidene fluoride binder, and 1.0 wt% of a carbon-based conductive material are mixed to prepare a positive electrode active material layer slurry, and the positive electrode active material layer slurry is coated on a 13.5-μm-thick aluminum foil current collector to about 30 mg / cm 2 , and then dried and pressed at 110 °C for 1 hour to manufacture a positive electrode having a mixture density of about 3.5 g / cm 3 .

[0125] A negative electrode active material slurry is prepared by mixing SBR (styrene-butadiene rubber) and CMC (carboxymethyl cellulose) at a weight ratio of 1:1 to obtain a mixture, and then mixing graphite powder as a negative electrode active material with the mixture at a weight ratio of 97:3.

[0126] On an 8-μm thick copper foil current collector, the prepared negative electrode active material slurry was coated to about 17 mg / cm 2 or so. The coated electrode plate was dried at 100 °C for 1 hour or longer, and then pressed to fabricate a negative electrode with a mixture density of 1.5 g / cm 3 .

[0127] The positive electrode and the negative electrode were used together with a polyethylene separator (STAR 20, Asahi) and an electrolyte (the electrolyte was prepared by dissolving 1.15 M of LiPF 6 ) in a mixed solvent of EC (ethylene carbonate): EMC (ethyl methyl carbonate): DMC (dimethyl carbonate) (volume ratio 2:4:4) to fabricate a rechargeable lithium battery cell with a capacity of 30 mAh.

[0128] Example 1 was designed to have an N / P ratio of 1.12.

[0129] 3. Activation of the rechargeable lithium battery cell

[0130] At 25 °C, the first charge and discharge process was carried out by charging the rechargeable lithium battery cell at a constant current of 0.2C to an upper limit voltage of 4.4V and discharging it at 0.2C to a cut-off voltage of 2.8V. Subsequently, the second charge and discharge process was carried out by charging the battery cell at a constant current of 0.2C to an upper limit voltage of 4.6V and discharging it at 0.2C to a cut-off voltage of 2.8V.

[0131] Examples 2 to 4 and Comparative Examples 1 to 4

[0132] Rechargeable lithium battery cells were fabricated in substantially the same manner as in Example 1, except that, as shown in Table 1, the upper limit voltage of the first charge and discharge process, the upper limit voltage of the second charge and discharge process, and the designed N / P ratio were changed.

[0133] (Table 1)

[0134]

[0135] Evaluation Example 1: Evaluation of the N / P ratio, lithium precipitation, BOL capacity, and high-temperature cycle life characteristics for charging at 4.6V

[0136] The rechargeable lithium battery cells of Examples 1 to 4 and Comparative Examples 1 to 4 were charged and discharged at 4.6 V, and the N / P ratio was calculated at each cycle, and the results are shown in Table 2. Since Comparative Example 1 did not have a charge and discharge cycle at 4.6 V, the N / P ratio at the first charge was changed to be shown in Table 2. In addition, after full charge at 4.6 V, the battery cells were disassembled for visual inspection to confirm whether lithium was deposited at each of the negative electrodes, and the results are shown in Table 2.

[0137] In addition, the rechargeable lithium battery cells of Examples 1 to 4 and Comparative Examples 1 to 4 were charged and discharged at 0.33 C in the range of 2.8 V to 4.4 V as the third cycle after the second charge and discharge to measure the discharge capacity, that is, the specific capacity (mAh / g) during BOL (beginning of life), which is shown in Table 2.

[0138] After the third cycle, the battery cells were cycled 200 times or more by repeatedly charging and discharging at 0.5 C in the range of 2.8 V to 4.4 V at 45 °C. The discharge specific capacity according to the number of cycles is shown in Figures 5 to 7 and the discharge specific capacity at 200 cycles is shown in Table 2.

[0139] (Table 2)

[0140]

[0141]

[0142] Referring to Table 2 and comparing with the comparative examples, the examples that were initially charged and discharged at 4.4 V and secondarily charged and discharged at 4.6 V showed an increased BOL capacity and capacity at 200 cycles.

[0143] Referring to Figure 5 Tables 1 and 2, Comparative Examples 2 and 3 that were first charged and discharged at 4.6 V showed a sharp decline in cycle life due to lithium deposition even though the N / P ratio of Comparative Example 3 was 1.13; Example 2 that was secondarily charged and discharged at 4.6 V and had an N / P ratio designed to be 1.13 showed improved capacity and cycle life characteristics without significantly reducing the cycle life.

[0144] Referring to Figure 6, Tables 1 and 2, where Examples 1 to 4 with the N / P ratio designed in the range of 1.13 to 1.15 showed excellent cycle life characteristics without lithium precipitation; in addition, as the N / P ratio increased, there was a tendency for the capacity to increase first and then converge, resulting in a slight deterioration of the cycle life characteristics; correspondingly, Example 2 with the N / P ratio designed to be 1.13 showed the best capacity and high-temperature cycle life characteristics.

[0145] Reference Figure 7 , Tables 1 and 2, where Comparative Example 4, which was charged and discharged for the first time at 4.6V and had an N / P ratio of 1.15, showed no lithium precipitation but showed deteriorated BOL capacity and cycle life characteristics compared to Example 4, which was charged and discharged for the second time at 4.6V.

[0146] Evaluation Example 2: XRD analysis of the positive electrode plate after activation

[0147] After activating the battery cells of Comparative Example 1 and Example 2, XRD analysis was performed on each positive electrode plate. Table 3 shows the lattice constant of the a-axis (L a ), the lattice constant of the c-axis (L c ), the ratio of the peak intensity of the (003) crystal plane to the peak intensity of the (104) crystal plane (I (003) / I (104) ), the full width at half maximum (FWHM) of the (003) crystal plane (i.e., FWHM (003) ) and the full width at half maximum (FWHM) of the (104) crystal plane (i.e., FWHM (104) ). In addition, the peak corresponding to the (020) crystal plane was magnified and shown in Figure 8 .

[0148] (Table 3)

[0149] Comparative Example 1 Example 2 <![CDATA[L a > 2.871 2.876 <![CDATA[L c > 14.260 14.249 <![CDATA[I (003) / I (104) > 4.220 3.972 <![CDATA[FWHM (003) > 0.088 0.095 <![CDATA[FWHM (104) > 0.173 0.184

[0150] Referring to Table 3, when using the activation method according to some embodiments, the positive electrode active material maintains a layered structure. In addition, referring to Figure 8 , compared with Comparative Example 1, Example 2 showed a significantly reduced peak intensity of the (020) crystal plane after activation, and correspondingly, it is understood that a part of Li 2 MnO 3 was activated at high voltage and contributed to the increase in capacity.

[0151] Evaluation Example 3: dQ / dV analysis

[0152] After activation as in Evaluation Example 1, the battery cells of Comparative Examples 1 and 3 and Example 2 were charged and discharged in the third cycle at a rate of 0.33C in the voltage range of 2.8V to 4.4V. The dQ / dV curves of the battery cells were analyzed and Figure 9 In Figure 9 In the figure of , the 3.4V~3.6V area is enlarged and in Figure 10 is shown in the figure, and the region 4.15V to 4.3V is enlarged and is shown in the figure. Figure 11 In addition, in Figure 9 , marked as peak The peak intensity of the region Mark as Peak The peak intensity of the region and as the peak intensity ratio The ratio of the former to the latter is shown in Table 4.

[0153] (Table 4)

[0154]

[0155] References Figures 9 to 11 and Table 4, Example 2 shows a greatly increased peak corresponding to 3.5V The peak intensity of , and accordingly, the activation method according to the embodiment also increases the capacity.

[0156] Although the present disclosure has been described in conjunction with exemplary embodiments currently considered to be practical, it should be understood that the present disclosure is not limited to the disclosed embodiments. Instead, the present disclosure includes various modifications and equivalent arrangements.​​​​​​​​​​​

Claims

1. A method for activating a rechargeable lithium battery, the method comprising: Performing a first charging and discharging process on the rechargeable lithium battery; After the first charging and discharging process, the rechargeable lithium battery is subjected to a second charging and discharging process, The rechargeable lithium battery comprises: A positive electrode comprising a positive electrode active material, wherein the positive electrode active material comprises a layered lithium nickel manganese composite oxide, Negative electrode, a separator between the positive electrode and the negative electrode, and electrolyte, and The upper limit voltage of the second charging and discharging process is higher than the upper limit voltage of the first charging and discharging process.

2. The activation method according to claim 1, wherein an upper limit voltage of a third charging and discharging process performed after the second charging and discharging process is the same as an upper limit voltage of the first charging and discharging process.

3. The activation method of claim 1, wherein the upper limit voltage of the first charge and discharge process is less than or equal to 4.5V, and the upper limit voltage of the second charge and discharge process is greater than 4.5V.

4. The activation method of claim 1, wherein the upper limit voltage of the first charge and discharge process is less than or equal to 4.4V, and the upper limit voltage of the second charge and discharge process is greater than or equal to 4.6V. 5 . The activation method according to claim 1 , wherein the upper limit voltage of the first charge and discharge process is 4.0V to 4.4V, and the upper limit voltage of the second charge and discharge process is 4.6V to 4.8V. 6 . The activation method according to claim 1 , wherein a rate of the first charge and discharge process and a rate of the second charge and discharge process are the same as or different from each other and are each 0.2 C or less. 7 . The activation method of claim 1 , wherein the initial N / P ratio of the rechargeable lithium battery is 1.13 to 1.

15.

8. The activation method of claim 1, wherein a charge N / P ratio of the rechargeable lithium battery during the second charge and discharge process is greater than or equal to 1.

9. The activation method according to claim 1, wherein The layered lithium nickel manganese-based composite oxide has a nickel content of greater than or equal to 60 mol % based on 100 mol % of the total metal content excluding lithium.

10. The activation method according to claim 1, wherein The layered lithium nickel manganese-based composite oxide has a nickel content of 60 mol % to 80 mol % and a manganese content of greater than or equal to 10 mol % based on 100 mol % of the total metal content excluding lithium; and The layered lithium nickel manganese-based composite oxide further includes aluminum, and the aluminum content is 1 mol% to 3 mol% based on 100 mol% of the total metal content except lithium; and In the layered lithium nickel manganese composite oxide, the cobalt content is 0 mol% to 0.01 mol% based on 100 mol% of the total metals except lithium.

11. The activation method according to claim 1, wherein the layered lithium nickel manganese composite oxide is represented by the following formula: Li a1 Ni x1 Mr y1 Al z1 M 1 w1 O 2-b1 X b1 Where 0.9≤a1≤1.8, 0.6≤x1≤0.8, 0.1≤y1≤0.4, 0≤z1≤0.03, 0≤w1≤0.3, 0.9≤x1+y1+z1+w1≤1.1, and 0≤b1≤0.1, M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y and Zr, and X is one or more elements selected from F, P and S.

12. The activation method according to claim 1, wherein the positive electrode active material comprises an average particle size D 50 Large particles with an average particle size of 10 μm to 25 μm 50 The particles are small in size of 0.5 μm to 8 μm.

13. The activation method of claim 12, wherein the large particles are in the form of secondary particles made by aggregating a plurality of primary particles, and wherein the small particles are in the form of secondary particles, single particles or a combination thereof; and The content of the large particles is 60 wt % to 95 wt %, and the content of the small particles is 5 wt % to 40 wt %, based on 100 wt % in total of the large particles and the small particles.

14. A rechargeable lithium battery comprising: A positive electrode, comprising a positive electrode active material, wherein the positive electrode active material comprises a layered lithium nickel manganese composite oxide; Negative electrode; a separator between the positive electrode and the negative electrode; and Electrolyte, wherein the initial N / P ratio of the rechargeable lithium battery is 1.13 to 1.15, and The rechargeable lithium battery has an N / P ratio greater than or equal to 1 when charged at a voltage of 4.6 V or greater.

15. The rechargeable lithium battery of claim 14, wherein: In the layered lithium nickel manganese-based composite oxide, the nickel content is 60 mol% to 80 mol% and the manganese content is greater than or equal to 10 mol% based on 100 mol% of the total metal content except lithium. 16 . The rechargeable lithium battery of claim 14 , wherein the layered lithium nickel manganese based composite oxide further comprises aluminum, and the aluminum content is 1 mol % to 3 mol % based on 100 mol % of the total metal content except lithium.

17. The rechargeable lithium battery of claim 14, wherein the layered lithium nickel manganese-based composite oxide is represented by the following formula: Li a1 Ni x1 Mr y1 Al z1 M 1 w1 O 2-b1 X b1 Where 0.9≤a1≤1.8, 0.6≤x1≤0.8, 0.1≤y1≤0.4, 0≤z1≤0.03, 0≤w1≤0.3, 0.9≤x1+y1+z1+w1≤1.1, and 0≤b1≤0.1, M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y and Zr, and X is one or more elements selected from F, P and S.

18. The rechargeable lithium battery of claim 14, wherein The positive electrode active material includes an average particle size D 50 Large particles with an average particle size of 10 μm to 25 μm 50 The particles are small in size of 0.5 μm to 8 μm.

19. The rechargeable lithium battery of claim 18, wherein the large particles are in the form of secondary particles made by aggregating a plurality of primary particles, and wherein the small particles are in the form of secondary particles, single particles or a combination thereof; and The content of the large particles is 60 wt % to 95 wt % and the content of the small particles is 5 wt % to 40 wt %, based on 100 wt % in total of the large particles and the small particles.

20. The rechargeable lithium battery of claim 14, wherein the negative electrode comprises lithium metal, a carbon-based negative electrode active material, a silicon-based negative electrode active material, or a combination thereof.

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