Positive electrode active material for secondary battery, positive electrode for secondary battery, and lithium secondary battery including the same

Abstract

The positive electrode active material for a secondary battery according to one embodiment of the present application contains a lithium metal oxide, and a C-axis lattice retention rate (R CL ) of the positive electrode active material for a secondary battery defined by the following Formula 1 is 95% to 97%.[Formula 1] R CL = (C 最小 / C 最大 ) 100 (in Formula 1, R CL is the C-axis lattice retention rate, C 最小 and C 最大 are the minimum and maximum values, respectively, in the C-axis lattice constant of the positive electrode active material observed by X-ray diffraction analysis (XRD) when the charging voltage is raised to the terminal voltage).

Description

Technical Field

[0001] This invention provides a positive electrode active material for secondary batteries, a positive electrode for secondary batteries, and a lithium secondary battery including the same. Background Technology

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged. With the development of the information communication and display industries, rechargeable batteries are widely used as power sources for portable electronic communication devices such as portable cameras, mobile phones, and laptops. In addition, in recent years, battery packs including rechargeable batteries have been developed for use as power sources in environmentally friendly vehicles such as hybrid electric vehicles.

[0003] Secondary batteries can be categorized into, for example, lithium secondary batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous for charging speed and lightweight design, so they are being actively developed and applied.

[0004] For example, a lithium secondary battery may include: an electrode assembly comprising a positive electrode, a negative electrode, and a separator; and an electrolyte impregnating the electrode assembly. The lithium secondary battery may also include an outer packaging material housing the electrode assembly and the electrolyte, such as a pouch-type outer packaging material.

[0005] Lithium-ion rechargeable batteries ideally possess both high capacity and operational and storage stability under extreme high or low temperature conditions. Therefore, there is a need to develop a cathode material for lithium-ion rechargeable batteries that can achieve both high capacity and high stability. Summary of the Invention

[0006] (a) Technical problems to be solved One technical problem of the present invention is to provide a positive electrode active material for secondary batteries with improved electrochemical and physical properties.

[0007] One technical problem of the present invention is to provide a positive electrode for a secondary battery comprising the aforementioned positive electrode active material for a secondary battery.

[0008] One technical problem of the present invention is to provide a lithium secondary battery including the positive electrode for the secondary battery.

[0009] (II) Technical Solution According to one embodiment of the present invention, the positive electrode active material for a secondary battery comprises lithium metal oxide, and the C-axis lattice retention rate (Rc) of the positive electrode active material for the secondary battery is defined by the following formula 1. CL The percentage is 95% to 97%.

[0010] [Formula 1] R CL =C 最小(min) / C 最大(max) 100 In Equation 1, R CL C is the lattice retention ratio along the C-axis. 最小 and C 最大 These are the minimum and maximum values ​​of the C-axis lattice constant of the positive electrode active material, as observed by X-ray diffraction (XRD) analysis after the charging voltage is increased to the termination voltage.

[0011] According to one embodiment, in Formula 1, the termination voltage can be 4V to 5V.

[0012] According to one embodiment, in Formula 1, the charging voltage can be increased from above 3V to less than 4V.

[0013] According to one implementation scheme, in Equation 1, C 最小(min) It can be between 13.78 and 14.5.

[0014] According to one implementation scheme, in Equation 1, C 最大(max) It can be 14 to 15.

[0015] According to one implementation, the C-axis lattice constant can be measured by in-situ X-ray diffraction analysis (In-situ XRD).

[0016] According to one embodiment, the nickel content in the total molar number of elements other than lithium and oxygen in the lithium metal oxide can be from 50 mol% to 90 mol%.

[0017] According to one embodiment, the lithium metal oxide may further comprise cobalt. In the total molar number of elements other than lithium and oxygen in the lithium metal oxide, the molar ratio of nickel to cobalt may be greater than 1 and less than 7.

[0018] According to one embodiment, the lithium metal oxide may further comprise manganese. In the total molar number of elements other than lithium and oxygen in the lithium metal oxide, the molar ratio of nickel to manganese may be from 1.2 to 5.

[0019] According to one embodiment, the positive electrode active material for the secondary battery can satisfy the following formula 2.

[0020] [Equation 2] 572-115 X <Y<310–50.91 X In Equation 2, X is the termination voltage value in Equation 1 in V, and Y is the nickel content in the total number of moles of elements other than lithium and oxygen in the lithium metal oxide, in mol%.

[0021] According to one embodiment, the lithium metal oxide may include a crystal structure represented by Chemical Formula 1 below.

[0022] [Chemical Formula 1] Li a Ni b M1 1-b O c In Chemical Formula 1, 0 < a ≤ 1.2, 0.5 ≤ b ≤ 0.9, 2 ≤ c ≤ 2.02, and M1 may include at least one selected from Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, and B.

[0023] The positive electrode for a secondary battery according to an embodiment of the present invention includes: a positive electrode current collector; and a positive electrode active material layer provided on one surface of the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material for a secondary battery, the positive electrode active material for a secondary battery contains a lithium metal oxide, and the c-axis lattice retention rate (R CL ) of the positive electrode active material for a secondary battery is 95% to 97%.

[0024] [Formula 1] R CL =(C 最小 / C 最大 ) × 100 In Formula 1, R CL is the c-axis lattice retention rate, and C 最小 and C 最大 are the minimum value and the maximum value of the c-axis lattice constants of the positive electrode active material observed by X-ray diffraction analysis (XRD) when the charging voltage is increased to the termination voltage, respectively.

[0025] According to one embodiment, in Formula 1, the termination voltage may be 4 V to 5 V.

[0026] According to one embodiment, in Formula 1, the charging voltage may be increased starting from above 3 V and less than 4 V.

[0027] According to one embodiment, when the content of nickel in the total molar number of elements other than lithium and oxygen in the lithium metal oxide is 50 mol% to 65 mol%, the termination voltage may be about 4.4 V to 5 V.

[0028] According to one embodiment, when the nickel content in the total moles of elements other than lithium and oxygen in the lithium metal oxide is greater than 65 mol% and less than 80 mol%, the termination voltage can be approximately 4.35 V to 4.5 V.

[0029] According to one embodiment, when the nickel content in the total moles of elements other than lithium and oxygen in the lithium metal oxide is greater than 80 mol% and less than 90 mol%, the termination voltage can be approximately 4.22 V to 4.4 V.

[0030] The lithium secondary battery according to the present invention includes: a positive electrode; and a negative electrode, the negative electrode being disposed opposite to the positive electrode. The positive electrode includes: a positive electrode current collector; and a positive electrode active material layer disposed on at least one side of the positive electrode current collector. The positive electrode active material layer comprises a positive electrode active material containing lithium metal oxide, and the C-axis lattice retention rate (Rc) of the positive electrode active material layer is defined by the following formula 1. CL The percentage is 95% to 97%.

[0031] [Formula 1] R CL =(C 最小 / C 最大 ) 100 In Equation 1, R CL C is the lattice retention ratio along the C-axis. 最小 and C 最大 These are the minimum and maximum values ​​of the C-axis lattice constant of the positive electrode active material, as observed by X-ray diffraction (XRD) analysis after the charging voltage is increased to the termination voltage.

[0032] According to one embodiment, the negative electrode may include: a negative electrode current collector; and a negative electrode active material layer disposed on at least one side of the negative electrode current collector and comprising artificial graphite and silicon-based active material.

[0033] According to one embodiment, the content of the silicon-based active material in the total weight of the negative electrode active material layer can be from 2% to 10% by weight.

[0034] According to one embodiment, the content of the artificial graphite in the total weight of the negative electrode active material layer can be from 65% to 95% by weight.

[0035] (III) Beneficial Effects According to one embodiment of the present invention, the positive electrode active material for secondary batteries can ensure the stability of the crystal structure even at high voltage, so that even during repeated charge and discharge, a battery with high capacity can be achieved while preventing the degradation of life characteristics.

[0036] A lithium secondary battery according to one embodiment of the present invention includes the positive electrode, which ensures the stability of the crystal structure even at high voltages. Therefore, during repeated charge and discharge cycles, the capacity can be maintained at a value close to the initial capacity, and the battery life characteristics can be improved.

[0037] The positive electrode active material, positive electrode, and battery of this invention can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-based solar power generation and wind power generation. Furthermore, the positive electrode active material, positive electrode, and battery of this invention can be used in eco-friendly electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and greenhouse gas emissions. Attached Figure Description

[0038] Figure 1 and Figure 2 These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to one implementation scheme.

[0039] Figure 3 This is a graph showing the capacity retention rate of a half-cell according to the number of cycles in an embodiment.

[0040] Figure 4 This is a graph showing the capacity retention rate of the half-cells of Example 3 and Comparative Examples 1, 3, and 5 according to the number of cycles.

[0041] Figure 5 This is a graph showing the capacity retention rate of the secondary batteries of Examples 8 to 12 and Comparative Example 8 at 45°C according to the number of cycles.

[0042] Figure 6 This is a graph showing the rapid charge-discharge capacity retention rate of the secondary batteries of Examples 8 to 12 and Comparative Example 8 based on the number of cycles.

[0043] [Explanation of reference numerals in the attached figures] 100: Positive electrode; 105: Positive electrode current collector 110: Positive electrode active material layer; 120: Negative electrode active material layer 125: Negative electrode current collector; 130: Negative electrode 140: Diaphragm; 150: Electrode assembly 160: Casing Detailed Implementation

[0044] According to one embodiment of the present invention, a positive electrode for a secondary battery with improved crystal structure stability is provided. Furthermore, according to one embodiment of the present invention, a lithium secondary battery including the aforementioned positive electrode for a secondary battery is provided.

[0045] The present invention will now be described in detail with reference to the accompanying drawings. However, this is merely exemplary, and the present invention is not limited to the specific embodiments described herein.

[0046] The positive electrode active material for secondary batteries according to the present invention comprises lithium metal oxide. Lithium metal oxide can increase the capacity of the battery, but the stability of lithium metal oxide may be lower than that of lithium manganese iron phosphate.

[0047] According to one embodiment, the lithium metal oxide may comprise lithium, nickel, oxygen, and an element different from nickel. In the lithium metal oxide, nickel may have the highest content among the total molar amounts of elements other than lithium and oxygen.

[0048] The nickel content in the total molar number of elements other than lithium and oxygen in the lithium metal oxide can be from 50 mol% to 90 mol%. For example, the nickel content in the total molar number of elements other than lithium and oxygen in the lithium metal oxide can be from 55 mol% to 90 mol% or from 60 mol% to 88 mol%.

[0049] According to one embodiment, the lithium metal oxide may contain nickel, cobalt, and manganese.

[0050] For example, nickel can be provided as a metal relevant to the power and / or capacity of lithium secondary batteries. Higher nickel content improves the capacity characteristics of lithium metal oxides, but may reduce stability.

[0051] For example, manganese (Mn) can be provided as a metal related to the mechanical and electrical stability of lithium secondary batteries. For example, cobalt (Co) can be a metal related to the conductivity or resistance of lithium secondary batteries.

[0052] According to one embodiment, the cobalt content in the total molar number of elements other than lithium and oxygen in the lithium metal oxide can be greater than 0 mol% and less than 20 mol%. According to some embodiments, the cobalt content in the total molar number of elements other than lithium and oxygen in the lithium metal oxide can be from 5 mol% to 15 mol%.

[0053] According to one embodiment, in the total molar number of elements other than lithium and oxygen in the lithium metal oxide, the molar ratio of nickel to cobalt can be greater than 1 and less than 7. According to some embodiments, in the total molar number of elements other than lithium and oxygen in the lithium metal oxide, the molar ratio of nickel to cobalt can be from 4 to 6.5.

[0054] According to one embodiment, among the total molar amounts of elements other than lithium and oxygen in the lithium metal oxide, the content of manganese can be greater than 0 mol% and 40 mol% or less. According to some embodiments, among the total molar amounts of elements other than lithium and oxygen in the lithium metal oxide, the content of manganese can be 25 mol% to 35 mol%.

[0055] According to one embodiment, among the total molar amounts of elements other than lithium and oxygen in the lithium metal oxide, the molar ratio of nickel to manganese can be 1.2 to 5. According to some embodiments, among the total molar amounts of elements other than lithium and oxygen in the lithium metal oxide, the molar ratio of nickel to manganese can be 1.5 to 2.5.

[0056] Within the above ranges, the stability and conductivity of the crystal structure can be improved without reducing the capacity of the lithium metal oxide.

[0057] According to one embodiment, the lithium metal oxide particles can include a crystal structure represented by Chemical Formula 1 below.

[0058] [Chemical Formula 1] Li a Ni b M1 1-b O c In Chemical Formula 1, 0 < a ≤ 1.2, 0.5 ≤ b ≤ 0.9, 2 ≤ c ≤ 2.02, and M1 can include at least one selected from Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, and B.

[0059] In some embodiments, in Chemical Formula 1, 0.6 ≤ b ≤ 0.88.

[0060] According to one embodiment, the lithium metal oxide particles can include a crystal structure represented by Chemical Formula 1-1 below.

[0061] [Chemical Formula 1-1] Li a Ni b Co c Mn d M2 1-b-c-d O f In Chemical Formula 1-1, it can be 0 < a ≤ 1.2, 0.5 ≤ b ≤ 0.9, 0 < c ≤ 0.2, 0 < d ≤ 0.4, 0.5 < b + c + d ≤ 1, 2 ≤ f ≤ 2.02, and M2 can include at least one selected from Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, and B.

[0062] In Chemical Formula 1-1, it can be 0.6 ≤ b ≤ 0.88.

[0063] In Chemical Formula 1-1, it can be 0.01 ≤ c ≤ 0.15.

[0064] In Chemical Formula 1-1, it can be 0.03 ≤ d ≤ 0.35.

[0065] In some embodiments, the concentration ratio (or molar ratio) of nickel: cobalt: manganese in the lithium metal oxide particles can be adjusted to about 6:1:3.

[0066] According to one embodiment, the lithium metal oxide may further include a coating on its surface. For example, the coating may include Al, Ti, Ba, Zr, Si, B, Mg, P, W, or their alloys or their oxides. These can be used alone or in combination of two or more. Through the coating, the active material particles are passivated, thereby further improving the penetration stability and lifespan of the battery.

[0067] In one embodiment, the elements, alloys, or oxides of the above coating can also be embedded inside the lithium metal oxide particles as dopants.

[0068] In the positive electrode active material for the secondary battery, the c-axis lattice retention rate (R CL ) defined by the following Formula 1 is 95% to 97%.

[0069] [Formula 1] R CL =(C 最小 / C 最大 ) × 100 In Formula 1, R CL is the c-axis lattice retention rate, C 最小 and C 最大 are respectively the minimum value and the maximum value of the c-axis lattice constants of the positive electrode active material observed by X-ray diffraction analysis (XRD) when the charging voltage is raised to the end voltage.

[0070] The increase in the charging voltage may refer to the operation of a battery including a positive electrode containing the positive electrode active material.

[0071] In one implementation, in Formula 1, C 最小 It can be from 13.78 to 14.5. In some embodiments, in Formula 1, C 最小 It can range from 13.78 to 14.15.

[0072] In one implementation, in Formula 1, C 最大 It can be 14 to 15. In one embodiment, in Formula 1, C 最大 It can be between 14 and 14.6.

[0073] Within the aforementioned range, even during repeated charging and discharging of the battery, a high-capacity battery can be achieved while preventing degradation of its lifespan characteristics.

[0074] The C-axis lattice retention rate can be measured, for example, by the following method: 最小 and C 最大 Perform the calculation.

[0075] For example, multiple batteries can be constructed, each including a positive electrode and a negative electrode containing the positive electrode active material. By charging each of the multiple batteries with the charging voltage increased to different termination voltages and then charging them, XRD analysis can be performed on the positive electrode separated from each battery. Through this XRD analysis, the C-axis lattice constant can be measured, and the minimum and maximum values ​​of the measured C-axis lattice constant can be represented by C in Equation 1. 最小 and C 最大 .

[0076] The C-axis lattice constant can be calculated by performing Rietveld refinement on data obtained from X-ray diffraction analysis (XRD).

[0077] When the C-axis lattice retention rate, as defined by Equation 1, is less than 95%, the crystal structure of the positive electrode active material may undergo drastic changes during lithium-ion insertion / extraction. This can lead to an increase in gas generation inside the battery due to side reactions with the electrolyte. Furthermore, the battery capacity decreases sharply, potentially reducing the battery's lifespan.

[0078] When the C-axis lattice retention rate defined by Equation 1 is greater than 97%, the battery cannot operate at a sufficiently high voltage, and therefore the capacity and energy achieved from the positive electrode with the same load will be reduced.

[0079] In one embodiment, the termination voltage in Formula 1 can be from 4V to 5V. In some embodiments, the termination voltage in Formula 1 can be from 4.2V to 4.9V.

[0080] In one embodiment, in Formula 1, the charging voltage can be increased starting from above 3V and below 4V. In some embodiments, in Formula 1, the charging voltage can be increased starting from 3V to 3.8V.

[0081] For example, when the nickel content in the total moles of elements other than lithium and oxygen in the lithium metal oxide is 50 mol% to 65 mol%, the termination voltage can be approximately 4.4 V to 5 V.

[0082] For example, when the nickel content in the total moles of elements other than lithium and oxygen in the lithium metal oxide is greater than 65 mol% and less than 80 mol%, the termination voltage can be approximately 4.35 V to 4.5 V.

[0083] For example, when the nickel content in the total moles of elements other than lithium and oxygen in the lithium metal oxide is greater than 80 mol% and less than 90 mol%, the termination voltage can be approximately 4.22 V to 4.4 V.

[0084] According to one embodiment, the positive electrode active material for a secondary battery can satisfy the following formula 2.

[0085] [Equation 2] 572-115 X <Y<310-50.91 X In Equation 2, X can be the termination voltage value in Equation 1, expressed in V. Y can be the nickel content in the total moles of elements other than lithium and oxygen in the lithium metal oxide, expressed in mol%.

[0086] When Equation 2 is satisfied, a certain level of lifespan can be ensured in the positive electrode material, while high-capacity batteries can be achieved.

[0087] The positive electrode for a secondary battery according to the present invention comprises: a positive electrode current collector; and a positive electrode active material layer disposed on one side of the positive electrode current collector. The positive electrode active material layer may be formed on one or both sides of the positive electrode current collector.

[0088] The positive electrode active material layer contains the positive electrode active material. The positive electrode active material contains lithium metal oxide. The details regarding the lithium metal oxide are the same as described above.

[0089] The positive electrode active material has a C-axis lattice retention rate (R) of 95% to 97%, as defined by Formula 1 below. CL ).

[0090] [Formula 1] R CL =(C 最小 / C 最大 ) 100 In Equation 1, R CL C is the lattice retention ratio along the C-axis. 最小 and C 最大 These are the minimum and maximum values ​​of the C-axis lattice constant of the positive electrode active material, as observed by X-ray diffraction (XRD) analysis after the charging voltage is increased to the termination voltage.

[0091] The increase in charging voltage may refer to the operation of a battery including a positive electrode containing the positive electrode active material.

[0092] In one implementation, in Formula 1, C 最小 It can be from 13.78 to 14.5. In some embodiments, in Formula 1, C 最小 It can range from 13.78 to 14.15.

[0093] In one implementation, in Formula 1, C 最大 It can be 14 to 15. According to one embodiment, in equation 1, C... 最大 It can be between 14 and 14.6.

[0094] Within the aforementioned range, even during repeated charging and discharging of the battery, changes in the crystal structure can be mitigated, thereby improving the battery's lifespan characteristics.

[0095] The C-axis lattice retention rate can be measured, for example, by the following method: 最小 and C 最大 Perform the calculation.

[0096] For example, multiple batteries can be constructed, each including a positive electrode and a negative electrode containing the positive electrode active material. By charging each of the multiple batteries with the charging voltage increased to different termination voltages and then charging them, XRD analysis can be performed on the positive electrode separated from each battery. Through this XRD analysis, the C-axis lattice constant can be measured, and the minimum and maximum values ​​of the measured C-axis lattice constant can be represented by C in Equation 1. 最小 and C 最大 .

[0097] When the C-axis lattice retention rate, as defined by Equation 1, is less than 95%, the crystal structure of the positive electrode active material may change drastically during lithium-ion insertion / extraction. This can lead to an increase in gas generation inside the battery due to side reactions with the electrolyte. Furthermore, the battery capacity decreases sharply, potentially reducing battery life characteristics.

[0098] When the C-axis lattice retention rate defined by Equation 1 is greater than 97%, the battery cannot operate at a sufficiently high voltage, and therefore the capacity and energy achieved from the positive electrode with the same load will be reduced.

[0099] In one embodiment, the termination voltage in Formula 1 can be from 4V to 5V. In some embodiments, the termination voltage in Formula 1 can be from 4.2V to 4.9V.

[0100] In one embodiment, in Formula 1, the charging voltage can be increased starting from above 3V and below 4V. In some embodiments, in Formula 1, the charging voltage can be increased starting from 3V to 3.8V.

[0101] The positive current collector may include, for example, stainless steel, nickel, aluminum, titanium, copper or alloys thereof, preferably aluminum or aluminum alloys.

[0102] In one embodiment, the positive electrode active material layer may contain a positive electrode active material containing lithium metal oxide.

[0103] It may include conductive materials to facilitate electron migration between active material particles. For example, the conductive materials may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes; metal-based conductive materials such as tin, tin oxide, and titanium oxide; and perovskite materials such as LaSrCoO3 and LaSrMnO3. These can be used alone or in combination of two or more.

[0104] According to one embodiment, the content of conductive material in the total weight of the positive electrode active material layer can be from 0.1% to 5% by weight. According to some embodiments, the content of conductive material in the total weight of the positive electrode active material layer can be from 0.3% to 2% by weight.

[0105] The adhesive can be an organic adhesive such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or a water-based adhesive such as styrene-butadiene rubber (SBR), and can be used with a thickener such as carboxymethyl cellulose (CMC).

[0106] For example, a PVDF-based binder can be used to form the positive electrode. In this case, the amount of binder used to form the positive electrode active material layer can be reduced, and the amount of the first positive electrode active material particles can be relatively increased, thus improving the power and capacity of the secondary battery.

[0107] According to one embodiment, the binder content in the total weight of the positive electrode active material layer can be from 0.5% to 10% by weight. According to some embodiments, the binder content in the total weight of the positive electrode active material layer can be from 1% to 5% by weight.

[0108] According to one embodiment, the thickness of the positive electrode active material layer can be from 10 μm to 100 μm. According to some embodiments, the thickness of the positive electrode active material layer can be from 20 μm to 60 μm.

[0109] In one embodiment, the loading of the positive electrode active material layer can be 15 g / cm³. 2 Up to 30g / cm 2 In some embodiments, the loading of the positive electrode active material layer can be 18 g / cm³. 2 Up to 25g / cm 2 Within the aforementioned range, the energy density of the positive electrode can be increased.

[0110] The secondary battery according to the present invention includes: a positive electrode; and a negative electrode, the negative electrode being disposed opposite to the positive electrode. The positive electrode includes: a positive electrode current collector; and a positive electrode active material layer, the positive electrode active material layer being disposed on at least one side of the positive electrode current collector.

[0111] The positive electrode active material layer comprises a positive electrode active material containing lithium metal oxide, and the C-axis lattice retention rate (R) of the positive electrode active material layer is defined by the following formula 1. CL The percentage is 95% to 97%.

[0112] [Formula 1] R CL =(C 最小 / C 最大 ) 100 In Equation 1, R CL C is the lattice retention ratio along the C-axis. 最小 and C 最大 These are the minimum and maximum values ​​of the C-axis lattice constant of the positive electrode active material, as observed by X-ray diffraction (XRD) analysis after the charging voltage is increased to the termination voltage.

[0113] The increase in charging voltage may refer to the operation of a battery including a positive electrode containing the positive electrode active material.

[0114] In one implementation, in Formula 1, C 最小 It can be from 13.78 to 14.5. In some embodiments, in Formula 1, C 最小 It can range from 13.78 to 14.15.

[0115] In one implementation, in Formula 1, C 最大 It can be 14 to 15. In one embodiment, in Formula 1, C 最大 It can be between 14 and 14.6.

[0116] Within the aforementioned range, even during repeated charging and discharging of the battery, changes in the crystal structure can be mitigated, thereby improving the battery's lifespan characteristics.

[0117] The C-axis lattice retention rate can be measured, for example, by the following method: 最小 and C 最大 Perform the calculation.

[0118] For example, multiple batteries can be constructed, each including a positive electrode and a negative electrode containing the positive electrode active material. By charging each of the multiple batteries with the charging voltage increased to different termination voltages and then charging them, XRD analysis can be performed on the positive electrode separated from each battery. Through this XRD analysis, the C-axis lattice constant can be measured, and the minimum and maximum values ​​of the measured C-axis lattice constant can be represented by C in Equation 1. 最小 and C 最大 .

[0119] When the C-axis lattice retention rate, as defined by Equation 1, is less than 95%, the crystal structure of the positive electrode active material may change drastically during lithium-ion insertion / extraction. This can lead to an increase in gas generation inside the battery due to side reactions with the electrolyte. Furthermore, the battery capacity decreases sharply, potentially reducing battery life characteristics.

[0120] When the C-axis lattice retention rate defined by Equation 1 is greater than 97%, the battery cannot operate at a sufficiently high voltage, and therefore the capacity and energy achieved from the positive electrode with the same load will be reduced.

[0121] In one embodiment, the termination voltage in Formula 1 can be from 4V to 5V. In some embodiments, the termination voltage in Formula 1 can be from 4.2V to 4.9V.

[0122] In one embodiment, in Formula 1, the charging voltage can be increased starting from above 3V and below 4V. In some embodiments, in Formula 1, the charging voltage can be increased starting from 3V to 3.8V.

[0123] Figure 1 and Figure 2 These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to one implementation scheme. Specifically, Figure 2 It is along Figure 1A cross-sectional view of the I-I' line taken along the thickness direction of the lithium secondary battery.

[0124] Reference Figure 1 and Figure 2 A lithium secondary battery may include an electrode assembly 150 housed within a casing 160. For example... Figure 2 As shown, the electrode assembly 150 may include a positive electrode 100, a negative electrode 130, and a separator 140 that are repeatedly stacked.

[0125] The positive electrode 100 may include a positive electrode active material layer 110 coated on the positive electrode current collector 105. The positive electrode 100 may be the same as described above.

[0126] The negative electrode 130 may include: a negative electrode current collector 125; and a negative electrode active material layer 120, the negative electrode active material layer 120 being disposed on at least one side of the negative electrode current collector 125.

[0127] The negative electrode active material layer 120 may, without particular limitation, contain materials known in the art that enable lithium ion insertion and extraction. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium alloys; silicon or tin, etc., may be used. Examples of amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) calcined below 1500°C, and mesophase pitch-based carbon fiber (MPCF). Examples of crystalline carbon include graphite-based carbon such as natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Elements included in the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0128] For example, the negative electrode active material layer 120 may comprise artificial graphite and silicon-based active material. The artificial graphite may have high stability, and the silicon-based active material may increase the capacity of the negative electrode.

[0129] For example, the content of the silicon-based active material in the total weight of the negative electrode active material layer 120 can be from 2% to 10% by weight. According to some embodiments, the content of the silicon-based active material in the total weight of the negative electrode active material layer 120 can be from 3% to 8% by weight or from 3% to 5% by weight.

[0130] Within the aforementioned range, battery life characteristics can be further improved.

[0131] For example, the content of the artificial graphite in the total weight of the negative electrode active material layer 120 can be from 50% to 97% by weight. According to some embodiments, the content of the artificial graphite in the total weight of the negative electrode active material layer 120 can be from 65% to 95% by weight.

[0132] Within the aforementioned range, the volume stability of the negative electrode can be further improved, and high capacity and high energy density can be achieved.

[0133] The negative electrode current collector 125 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, preferably copper or copper alloys.

[0134] In some embodiments, the negative electrode active material can be mixed and stirred in a solvent with a binder, conductive material, and / or dispersant to prepare a slurry. The slurry can be coated onto at least one side of the negative electrode current collector 125 and then dried and calendered to manufacture the negative electrode 130.

[0135] The adhesive and the conductive material may be substantially the same as or similar to the substances used in the positive electrode active material layer 110. In some embodiments, for example, for compatibility with carbon-based active materials, the adhesive used to form the negative electrode may include a water-based adhesive such as styrene-butadiene rubber (SBR) and may be used with a thickener such as carboxymethyl cellulose (CMC).

[0136] A separator 140 can be disposed between the positive electrode 100 and the negative electrode 130. The separator 140 may comprise a porous polymer membrane prepared from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer. The separator 140 may also comprise a nonwoven fabric formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0137] In some embodiments, the area (e.g., the area in contact with the separator 140) and / or volume of the negative electrode 130 can be larger than that of the positive electrode 100. Therefore, lithium ions generated from the positive electrode 100 can migrate smoothly to the negative electrode 130 without precipitation in between. Thus, it is easier to achieve the effect of simultaneously improving power and stability through the combination of the first and second positive electrode active material layers.

[0138] According to one embodiment, the battery cell can be defined by a positive electrode 100, a negative electrode 130, and a separator 140, and an electrode assembly 150 can be formed, for example, in the form of a jelly roll, by stacking multiple battery cells. For example, the electrode assembly 150 can be formed by winding, lamination, folding, etc., of the separator 140.

[0139] The electrode assembly 150 can be housed together with the electrolyte in the housing 160, thereby defining a lithium secondary battery. According to one embodiment, the electrolyte can be a non-aqueous electrolyte.

[0140] Non-aqueous electrolytes may contain a lithium salt as the electrolyte and an organic solvent, wherein the lithium salt may be, for example, Li... + X - This indicates that the anion (X) of the lithium salt is... - ), can be exemplified by F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - wait.

[0141] The organic solvents may include, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0142] like Figure 1 As shown, the tabs (positive tab and negative tab) can protrude from the positive current collector 105 and negative current collector 125 belonging to each cell and extend to one end of the housing 160. The tabs can be fused to said end of the housing 160 to form electrode leads (positive lead 107 and negative lead 127) extending to or exposed outside the housing 160.

[0143] exist Figure 1 Although the diagram shows the positive electrode lead 107 and the negative electrode lead 127 protruding from the upper edge of the housing 160 in the planar direction, the position of the electrode leads is not limited to this. For example, the electrode leads may also protrude from at least one of the two sides of the housing 160, or they may protrude from the lower edge of the housing 160. Alternatively, the positive electrode lead 107 and the negative electrode lead 127 may be formed to protrude from different edges of the housing 160, respectively.

[0144] The lithium secondary battery can be manufactured in shapes such as cylindrical, prismatic, pouch, or coin, for example, using a can.

[0145] The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating the present invention and are not intended to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and its technical concept, which is obvious to those skilled in the art, and such variations and modifications naturally fall within the scope of the claims.

[0146] Example 1 Manufacturing of the positive electrode Will have LiNi 0.6 Co 0.1 Mn 0.3A positive electrode slurry is prepared by mixing lithium metal oxide (O2), polyvinylidene fluoride (PVDF) as a binder, multi-walled carbon nanotubes (MWCNTs) as a conductive material, and carbon nanotube dispersion material in a weight ratio of 98.26:0.9:0.7:0.14 and dispersing them in N-methylpyrrolidone as a solvent.

[0147] The positive electrode slurry was coated onto one side of an aluminum foil (12 μm thick), and then dried and calendered to form a 20 g / cm³ electrode. 3 The loading capacity and 3.6 g / cm 3 The density of the positive electrode.

[0148] Manufacturing of half-cells A lithium metal foil (1 mm thick) opposite to the positive electrode is used as the counter electrode, thereby forming multiple half-cells.

[0149] The charging voltage of the multiple half-cells was increased from 3.7V to 4.65V at CC 0.1C, and the cells were disassembled at voltage intervals of 0.01V. The C value was calculated by XRD analysis of the separated positive electrodes. 最小 and C 最大 .

[0150] X-ray diffraction analysis was performed under the following conditions.

[0151] -X-ray source anode: Cu - Generator Voltage: 45kV, Tube Current: 40mA - Scan 2θ range: 10-80° - Step Size: 0.00656° - Time per scan: 100 seconds Example 2 The C-axis lattice constant (C) was calculated using the same method as in Example 1. 最小 C 最大 The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 4.80V.

[0152] Example 3 The C-axis lattice constant (C) was calculated using the same method as in Example 1. 最小 C 最大 The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 4.90V.

[0153] Example 4 The positive electrode was fabricated using the same method as in Example 1, except that a LiNi alloy was used. 0.88 Co 0.07 Mn 0.05 The composition of O2 in lithium metal oxide formation has a concentration of 19.6 g / cm³. 3 The loading capacity and 3.63 g / cm³ 3 A layer of positive electrode active material with a certain density.

[0154] Furthermore, the C-axis lattice constant (C) was calculated using the same method as in Example 1. 最小 C 最大 The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 4.22V.

[0155] Example 5 The C-axis lattice constant (C) was calculated using the same method as in Example 4. 最小 C 最大 The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 4.35V.

[0156] Example 6 The positive electrode was fabricated using the same method as in Example 1, except that a LiNi alloy was used. 0.765 Co 0.015 Mn 0.22 The composition of O2 is used to form lithium metal oxides with a concentration of 21.6 g / cm³. 3 The loading capacity and 3.6 g / cm 3 A layer of positive electrode active material with a certain density.

[0157] Furthermore, the C-axis lattice constant (C) was calculated using the same method as in Example 1. 最小 C 最大 The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 4.35V.

[0158] Example 7 The C-axis lattice constant (C) was calculated using the same method as in Example 6. 最小 C 最大 The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 4.40V.

[0159] Comparative Example 1 The C-axis lattice constant (C) was calculated using the same method as in Example 1. 最小 C 最大The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 5.20V.

[0160] Comparative Example 2 The C-axis lattice constant (C) was calculated using the same method as in Example 1. 最小 C 最大 The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 4.35V.

[0161] Comparative Example 3 The C-axis lattice constant (C) was calculated using the same method as in Example 4. 最小 C 最大 The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 4.45V.

[0162] Comparative Example 4 The C-axis lattice constant (C) was calculated using the same method as in Example 4. 最小 C 最大 The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 4.20V.

[0163] Comparative Example 5 The C-axis lattice constant (C) was calculated using the same method as in Example 6. 最小 C 最大 The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 4.60V.

[0164] Comparative Example 6 The C-axis lattice constant (C) was calculated using the same method as in Example 6. 最小 C 最大 The difference is that the analysis is performed by increasing the charging voltage of the half-cell from 3.7V to 4.30V.

[0165] The composition of Ni, Co and Mn, C-axis lattice constant, C-axis lattice retention rate and whether Equation 2 above is satisfied in the positive electrode active materials of the examples and comparative examples are shown in Table 1 below.

[0166] [Table 1] Experimental Example 1: Evaluation of Room Temperature Lifetime Characteristics For the half-cells of the examples and comparative examples, at 25 °C, charging was carried out under CC-CV (0.1C, corresponding voltage, 0.05C cut-off) conditions and discharging was carried out under CC (0.1C, 3.0V cut-off) conditions for 1 cycle, and this cycle was repeated 200 times. In this case, the discharge capacity after repeating 1 cycle and the capacity retention rates at 50, 100, 150, and 200 cycles are shown in Table 2.

[0167] In addition, Figure 3 is a graph showing the capacity retention rate of the half-cell of the example according to the number of cycles, Figure 4 is a graph showing the capacity retention rate of the half-cells of Example 3 and Comparative Examples 1, 3, and 5 according to the number of cycles.

[0168] [Table 2] Referring to Table 2 above and Figure 3 , the half-cell including the positive electrode of the example has improved room-temperature life characteristics, and even after repeating charge and discharge 200 times, a capacity retention rate of more than 55% can be provided.

[0169] Referring to Figure 4 , compared with Figure 3 Example 3 with the least significant effect among the above, the life characteristics of the battery including the positive electrode active material of the comparative example are further deteriorated. In addition, in the half-cell including the positive electrode of the comparative example, the comparative example with a C-axis lattice retention rate less than 95% had a sharp drop in capacity before repeating 200 cycles, and the capacity retention rate could not be measured. In addition, in the half-cell including the positive electrode of the comparative example, the comparative example with a C-axis lattice retention rate greater than 97% had a reduced capacity and energy achieved from the positive electrode with the same loading amount because the battery could not be operated at a sufficiently high voltage.

[0170] Example 8 Manufacture of full cell Artificial graphite, silicon-based active material (SiOx, 0 < x < 2), single-walled carbon nanotubes as a conductive material, carbon nanotube dispersion material, carboxymethyl cellulose as a thickener, and styrene-butadiene rubber as an adhesive were mixed at a weight ratio of 92.05:5:0.1:0.15:1.2:1.5 and dispersed in water as a solvent to prepare a negative electrode slurry.

[0171] The negative electrode slurry was coated on both sides of a copper foil, dried and calendered to form a negative electrode active material layer with a loading amount of 11.4 g / cm 2 and a density of 1.55 g / cm 3 to manufacture a negative electrode.

[0172] A separator is inserted between the positive electrode, which is manufactured according to the same method as in Example 1, and the negative electrode to create a laminate. The separator is a 11 μm thick porous polyethylene membrane coated with 1 μm of inorganic material on both sides, with a total thickness of 13 μm.

[0173] The laminated body is placed in a soft package, three sides are sealed, electrolyte is injected, and the remaining side is sealed.

[0174] The electrolyte is a solution of 1 M LiPF6 dissolved in a solvent containing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 20:80.

[0175] The dimensions of the positive electrode, negative electrode, and separator used are as follows: Positive electrode: 262mm wide, 102mm long; Negative electrode: 267mm wide, 105mm long; Separator: 274mm wide, 106.5mm long The laminate is stacked in the order of separator, negative electrode, separator, positive electrode, and then stacked in the order of separator, negative electrode, separator, separator. The number of positive electrode, negative electrode, and polyethylene film layers used in the laminate is as follows: Positive electrode: 37, Negative electrode: 38, Separator: 78 Multiple full cells were constructed, and the charging voltage was increased from 3.7V to 4.65V at CC 0.1C. The cells were then disassembled at voltage intervals of 0.01V, and the Cg was calculated by XRD analysis of the separated positive electrodes. 最小 and C 最大 .

[0176] X-ray diffraction analysis was performed under the following conditions.

[0177] -X-ray source anode: Cu Generator voltage: 45kV, tube current: 40mA - Scan 2θ range: 10-80° -Step size: 0.00656° - Scan time per scan: 100 seconds Example 9 The full cell was manufactured using the same method as in Example 8, except that a positive electrode manufactured using the same method as in Example 5 was used. Multiple full cells were constructed, and the charging voltage was increased from 3.7V to 4.35V at CC 0.1C. The cells were then disassembled at voltage intervals of 0.01V, and the Cg was calculated by XRD analysis of the separated positive electrodes. 最小 and C 最大 .

[0178] Example 10 The full cell was fabricated by the same method as in Example 9, except that artificial graphite, silicon-based active material (SiOx, 0 < x < 2), single-walled carbon nanotubes as a conductive material, carbon nanotube dispersion material, carboxymethyl cellulose as a thickening agent, and styrene-butadiene rubber as a binder were mixed at a weight ratio of 94.05:3:0.1:0.15:1.2:1.5, and the negative electrode was fabricated in the form of a negative electrode active material layer with a loading of 12.4 g / cm 2 of. Multiple full cells were constructed, the charging voltage was increased from 3.7 V to 4.35 V at CC 0.1C, the cells were disassembled at a voltage interval of 0.01 V, and C 最小 and C 最大 were calculated by performing XRD analysis on the separated positive electrode.

[0179] Example 11 The full cell was fabricated by the same method as in Example 9, except that artificial graphite, natural graphite, silicon-based active material (SiOx, 0 < x < 2), single-walled carbon nanotubes as a conductive material, carbon nanotube dispersion material, carboxymethyl cellulose as a thickening agent, and styrene-butadiene rubber as a binder were mixed at a weight ratio of 64.435:27.615:5:0.1:0.15:1.2:1.5 to fabricate the negative electrode. Multiple full cells were constructed, the charging voltage was increased from 3.7 V to 4.35 V at CC 0.1C, the cells were disassembled at a voltage interval of 0.01 V, and C 最小 and C 最大 were calculated by performing XRD analysis on the separated positive electrode.

[0180] Example 12 The full cell was fabricated by the same method as in Example 8, except that the positive electrode fabricated by the same method as in Example 6 was used. Multiple full cells were constructed, the charging voltage was increased from 3.7 V to 4.35 V at CC 0.1C, the cells were disassembled at a voltage interval of 0.01 V, and C 最小 and C 最大 were calculated by performing XRD analysis on the separated positive electrode.

[0181] Comparative Example 7 The full cell was fabricated by the same method as in Example 9, except that the positive electrode fabricated by the same method as in Comparative Example 4 was used. Multiple full cells were constructed, the charging voltage was increased from 3.7 V to 4.20 V at CC 0.1C, the cells were disassembled at a voltage interval of 0.01 V, and C 最小 and C 最大 were calculated by performing XRD analysis on the separated positive electrode.

[0182] Comparative Example 8 The full cell was manufactured using the same method as in Example 8, except that a positive electrode manufactured using the same method as in Comparative Example 3 was used. The c-axis lattice constant (C) was calculated using the same method as in Example 4. 最小 C 最大 The difference is that multiple full cells are constructed, the charging voltage is increased from 3.7V to 4.45V at CC 0.1C, the cells are disassembled at voltage intervals of 0.01V, and the separated positive electrodes are subjected to XRD analysis.

[0183] The composition of Ni, Co and Mn, C-axis lattice constant, C-axis lattice retention rate and whether Equation 2 above is satisfied in the positive electrode active materials of the examples and comparative examples are shown in Table 3 below.

[0184] [Table 3] Experimental Example 3: Evaluation of High-Temperature Lifetime Characteristics For the secondary batteries of Examples 8 to 12 and Comparative Examples 7 to 8, charge and discharge cycles were performed at 45°C, with one cycle consisting of charging at 4% SOC (CC-CV 1 / 3C SOC 98%, 0.05C cutoff) and discharging (CC, 1 / 3C SOC 4% cutoff). A 20-minute rest time was set between charge and discharge cycles, and the lifetime capacity retention rate at 45°C was measured while repeating the cycle. The capacity retention rates after 200 cycles, 400 cycles, 600 cycles, and 800 cycles are shown in Table 4.

[0185] Figure 5 This is a graph showing the capacity retention rate of the secondary batteries of Examples 8 to 12 and Comparative Example 8 at 45°C based on the number of cycles.

[0186] Experiment Example 4: Evaluation of rapid life characteristics For the secondary batteries of Examples 8 to 12 and Comparative Examples 7 to 8, a rapid charge-discharge cycle was performed at 2.5C / 2.25C / 2.0C / 1.75C / 1.5C / 1.25C / 1.0C rates (C-rate) followed by a 1 / 3C rate discharge. The batteries were charged in stages within a DOD range of 70% (SOC 10-80%) at 25°C. A 20-minute rest period was set between charge-discharge cycles, and the cycles were repeated. The capacity retention rate after rapid charging was measured. The capacity retention rates after 100, 200, 300, and 400 cycles are shown in Table 4.

[0187] Figure 6 This is a graph showing the rapid charge-discharge capacity retention rate of the secondary batteries of Examples 8 to 12 and Comparative Example 8 based on the number of cycles.

[0188] Experimental Example 5: Evaluation of Battery Discharge Capacity and Energy Density The secondary batteries of Examples 8 to 12 and Comparative Examples 7 to 8 were charged at 0.3C and discharged at 0.3C to measure the discharge capacity. Furthermore, the battery thickness at 30% SOC was measured, and the discharge capacity was divided by the battery thickness at 30% SOC to evaluate the relative energy density. The evaluation results are shown in Table 5 below.

[0189] [Table 4] [Table 5] See Tables 4 and 5 above. Figure 5 and Figure 6 The battery in this embodiment retains a capacity of over 78% even when repeatedly charged and discharged at high temperatures, and retains a capacity of over 78.5% after 400 cycles even when repeatedly charged and discharged at high speeds.

[0190] On the other hand, the battery of Comparative Example 8 exhibits significantly worse lifespan characteristics. In particular, when repeatedly charged and discharged at 45°C, the capacity retention rate of the battery of Comparative Example 8 drops sharply after only 400 cycles. The battery of Comparative Example 7, due to its lattice retention rate being greater than 97%, has a lower proportion of discharge capacity per unit thickness, resulting in a lower energy density.

[0191] The above description is merely an example of applying the principles of this invention, and other configurations may be further included without departing from the scope of this invention.

Claims

1. A positive electrode active material for a secondary battery, comprising lithium metal oxide, wherein the C-axis lattice retention ratio R of the positive electrode active material for the secondary battery is defined by the following formula 1. CL 95% to 97% [Formula 1] R CL =(C 最小 / C 最大 ) 100 In Equation 1, R CL C is the lattice retention ratio along the C-axis. 最小 and C 最大 These are the minimum and maximum values ​​of the C-axis lattice constant of the positive electrode active material, as observed by X-ray diffraction (XRD) analysis after the charging voltage is increased to the termination voltage.

2. The positive electrode active material for secondary batteries according to claim 1, wherein, In Formula 1, the cut-off voltage is 4V to 5V.

3. The positive electrode active material for secondary batteries according to claim 1, wherein, In Formula 1, the charging voltage starts to increase from above 3V and less than 4V.

4. The positive electrode active material for secondary batteries according to claim 1, wherein, In Equation 1, C 最小 The range is 13.78 to 14.

5.

5. The positive electrode active material for secondary batteries according to claim 1, wherein, In Equation 1, C 最大 It is between 14 and 15.

6. The positive electrode active material for secondary batteries according to claim 1, wherein, Among the total molar amounts of elements other than lithium and oxygen in the lithium metal oxide, the content of nickel is 50 mol% to 90 mol%.

7. The positive electrode active material for secondary batteries according to claim 6, wherein, The lithium metal oxide further contains cobalt. Among the total molar amounts of elements other than lithium and oxygen in the lithium metal oxide, the molar ratio of nickel to cobalt is greater than 1 and 7 or less.

8. The positive electrode active material for secondary batteries according to claim 6, wherein, The lithium metal oxide further contains manganese. Among the total molar amounts of elements other than lithium and oxygen in the lithium metal oxide, the molar ratio of nickel to manganese is 1.2 to 5.

9. The positive electrode active material for secondary batteries according to claim 6, wherein, The positive electrode active material for a secondary battery satisfies the following Formula 2: [Formula 2] 572-115 X<Y<310-50.91 X In Formula 2, X is the value of the cut-off voltage in Formula 1 in units of V, Y is the content of nickel in units of mol% among the total molar amounts of elements other than lithium and oxygen in the lithium metal oxide.

10. The positive electrode active material for secondary batteries according to claim 1, wherein, The lithium metal oxide contains a crystal structure represented by the following Chemical Formula 1: [Chemical Formula 1] Li a Ni b M1 1-b O c In Chemical Formula 1, 0 < a ≤ 1.2, 0.5 ≤ b ≤ 0.9, 2 ≤ c ≤ 2.02, and M1 includes at least one selected from Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, and B.

11. A positive electrode for a secondary battery, comprising: A positive electrode current collector; And A positive electrode active material layer provided on at least one surface of the positive electrode current collector, The positive electrode active material layer comprises a positive electrode active material containing lithium metal oxide, and the C-axis lattice retention ratio R of the positive electrode active material layer is defined by the following formula 1. CL 95% to 97% [Formula 1] R CL =(C 最小 / C 最大 ) 100 In Equation 1, R CL C is the lattice retention ratio along the C-axis. 最小 and C 最大 These are the minimum and maximum values ​​of the C-axis lattice constant of the positive electrode active material, as observed by X-ray diffraction (XRD) analysis after the charging voltage is increased to the termination voltage.

12. The positive electrode for a secondary battery according to claim 11, wherein, In the Formula 1, the cut-off voltage is 4V to 5V.

13. The positive electrode for a secondary battery according to claim 11, wherein, In the Formula 1, the charging voltage starts to increase from above 3V and less than 4V.

14. The positive electrode for a secondary battery according to claim 11, wherein, When the content of nickel among the total molar amounts of elements other than lithium and oxygen in the lithium metal oxide is 50 mol% to 65 mol%, the cut-off voltage is 4.4V to 5V.

15. The positive electrode for a secondary battery according to claim 11, wherein, When the content of nickel among the total molar amounts of elements other than lithium and oxygen in the lithium metal oxide is greater than 65 mol% and 80 mol% or less, the cut-off voltage is 4.35V to 4.5V.

16. The positive electrode for a secondary battery according to claim 11, wherein, When the content of nickel among the total molar amounts of elements other than lithium and oxygen in the lithium metal oxide is greater than 80 mol% and 90 mol% or less, the cut-off voltage is 4.22V to 4.4V.

17. A lithium secondary battery, comprising: A positive electrode; And A negative electrode, the negative electrode being disposed opposite to the positive electrode, Wherein, the positive electrode includes: A positive electrode current collector; and A positive electrode active material layer provided on at least one surface of the positive electrode current collector, The positive electrode active material layer comprises a positive electrode active material containing lithium metal oxide, and the C-axis lattice retention ratio R of the positive electrode active material layer is defined by the following formula 1. CL 95% to 97% [Formula 1] R CL =(C 最小 / C 最大 ) 100 In Equation 1, R CL C is the lattice retention ratio along the C-axis. 最小 and C 最大 These are the minimum and maximum values ​​of the C-axis lattice constant of the positive electrode active material, as observed by X-ray diffraction (XRD) analysis after the charging voltage is increased to the termination voltage.

18. The lithium secondary battery according to claim 17, wherein, The negative electrode includes: a negative electrode current collector; and a negative electrode active material layer provided on at least one surface of the negative electrode current collector and containing artificial graphite and a silicon-based active material.

19. The lithium secondary battery according to claim 18, wherein, Among the total weight of the negative electrode active material layer, the content of the silicon-based active material is 2 wt% to 10 wt%.

20. The lithium secondary battery according to claim 18, wherein, Among the total weight of the negative electrode active material layer, the content of the artificial graphite is 65 wt% to 95 wt%.

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