Positive electrode, lithium secondary battery comprising positive electrode, and method for manufacturing positive electrode

Abstract

The present invention relates to a positive electrode containing a positive electrode active material, wherein the resistance component ratio defined by the following relational expression 1 is 2 or more. [Relation Formula 1] Rct / Rs. In the equation, Rct is a charge transfer resistance of the positive electrode measured in a first frequency domain of the secondary battery including the positive electrode, and Rs is a surface or interface resistance of the positive electrode measured in a second frequency domain of the secondary battery including the positive electrode, the first frequency domain being 1 Hz to 1 kHz, and the second frequency domain being greater than 1 kHz to 1,000 kHz.

Description

Technical Field

[0001] This invention relates to a positive electrode, a lithium secondary battery containing a positive electrode, and a method for preparing a positive electrode. Background Technology

[0002] The rapid proliferation of battery-powered electronic devices, such as mobile phones, laptops, computers, and electric vehicles, has led to a surge in demand for small, lightweight, and relatively high-capacity rechargeable batteries. In particular, lithium-ion batteries have gained attention as a power source for portable devices due to their lightweight nature and high energy density. Therefore, research and development efforts are actively underway to improve the performance of lithium-ion batteries.

[0003] Carbon-based materials such as graphite are primarily used as anode materials in lithium-ion batteries. However, carbon-based materials have low capacity per unit mass, making it difficult to achieve high capacity in lithium-ion batteries. Therefore, silicon-based compounds, which exhibit higher capacity compared to carbon-based materials, have been developed and used as anode materials. However, excessive use of silicon-based compounds can lead to sudden degradation, or lithium-ion batteries using these compounds may experience unexpected problems such as shortened lifespan at temperatures below room temperature.

[0004] As one method for measuring the performance or state of lithium-ion batteries, the previous approach primarily used methods that employed hybrid pulse power characterization (HPPC) to measure resistance or battery capacity. However, while these methods enable the evaluation of lithium-ion battery performance, they have limitations in performing specific diagnostics by individually identifying the state of the positive and / or negative electrodes, which are components of the lithium-ion battery.

[0005] Therefore, there is a need for a method to improve the performance and lifespan of lithium secondary batteries by identifying and controlling the performance factors of the positive and / or negative electrodes, which are components of the battery (as factors affecting the performance and lifespan of lithium secondary batteries). Summary of the Invention

[0006] Technical goals

[0007] The present invention is designed to solve the above-mentioned problems and thus indirectly control the reaction amount of the negative electrode by adjusting the reaction resistance of the positive electrode (a component of a lithium secondary battery), thereby providing a positive electrode in a lithium secondary battery with improved life and / or performance.

[0008] In addition, the present invention relates to providing lithium secondary batteries with improved lifespan and / or performance by using electrochemical impedance spectroscopy (EIS) (a non-destructive measurement method) to extract and analyze resistivity components directly related to the degradation of lithium secondary batteries.

[0009] Technical solution

[0010] The present invention provides a positive electrode comprising a positive electrode active material and having a resistivity ratio greater than or equal to 2 as defined by the following relationship 1.

[0011] [Relation 1]

[0012] R ct / R s

[0013] In relation 1 above, R ct This refers to the charge transfer resistance of the positive electrode, measured in the first frequency domain of a secondary battery including the positive electrode, and R... s It refers to the surface or interface resistance of the positive electrode measured in a second frequency domain of a secondary battery including the positive electrode, wherein the first frequency domain is greater than or equal to 1 Hz and less than or equal to 1 kHz, and the second frequency domain is greater than 1 kHz and less than or equal to 1,000 kHz.

[0014] In an example implementation, impedance information can be obtained by performing electrochemical impedance spectroscopy (EIS) on the secondary battery, relaxation time distribution (DRT) analysis can be performed on the impedance information to generate a frequency-based impedance map, and R can be determined based on the value obtained by integrating the impedance map into a first domain corresponding to a first frequency domain. ct Furthermore, impedance information can be obtained by performing EIS on the secondary battery, DRT analysis can be performed on the impedance information to generate a frequency-based impedance map, and R is determined based on the value obtained by integrating the impedance map into a second domain corresponding to the second frequency domain. s .

[0015] In an example implementation, the positive electrode active material may include particles with different average particle sizes (D0, D ...). 50 The first positive electrode active material and the second positive electrode active material.

[0016] In an example implementation, the positive electrode active material may include a first positive electrode active material represented by Formula 1 and a second positive electrode active material represented by Formula 2:

[0017] [Formula 1]

[0018] Li 1+a1 Ni x1 Co y1 Mn z1 Al w1 M 1 v1 O2

[0019] In Equation 1 above,

[0020] 0 ≤ a1 ≤ 0.3, 0.6 ≤ x1 ≤ 1.0, 0 ≤ y1 ≤ 0.2, 0 ≤ z1 ≤ 0.2, 0 ≤ w1 ≤ 0.2, 0 ≤ v1 ≤ 0.1, and

[0021] M 1 It is a doping element that includes at least one selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, Ba and Mo.

[0022] [Equation 2]

[0023] Li 1+a2 Ni x2 Co y2 Mn z2 Al w2 M 2 v2 O2

[0024] In equation 2 above,

[0025] 0 ≤ a² ≤ 0.3, 0.6 ≤ x² ≤ 1.0, 0 ≤ y² ≤ 0.2, 0 ≤ z² ≤ 0.2, 0 ≤ w² ≤ 0.2, 0 ≤ v² ≤ 0.1, and

[0026] M 2 It is a doping element that includes at least one selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, Ba and Mo.

[0027] In the example embodiment, the average particle size (D) of the first positive electrode active material 50 The diameter can range from 6 μm to 12 μm.

[0028] In the example embodiment, the average particle size (D) of the second positive electrode active material 50 The diameter can range from 1.5 μm to 5 μm.

[0029] In an example implementation, the weight ratio of the first positive electrode active material to the second positive electrode active material may be from 80:20 to 40:60.

[0030] In an example implementation, the positive electrode active material can be obtained by mixing the positive electrode active material in distilled water, washing it with water, and then drying it.

[0031] In addition, the present invention provides a lithium secondary battery comprising a positive electrode active material and having a resistivity ratio greater than or equal to 2 as defined by the following relationship 1.

[0032] [Relation 1]

[0033] R ct / R s

[0034] In relation 1 above, R ct This refers to the charge transfer resistance of the positive electrode of a lithium secondary battery, measured in the first frequency domain, and R... s This refers to the surface or interface resistance of the positive electrode of a lithium secondary battery measured in the second frequency domain. The first frequency domain is greater than or equal to 1 Hz and less than or equal to 1 kHz, and the second frequency domain is greater than 1 kHz and less than or equal to 1,000 kHz.

[0035] In an example implementation, impedance information can be obtained by performing EIS on the lithium secondary battery, DRT analysis can be performed on the impedance information to generate a frequency-based impedance map, and R can be determined based on the value obtained by integrating the impedance map into a second domain corresponding to the second frequency domain. s Furthermore, impedance information can be obtained by performing EIS on the lithium secondary battery, DRT analysis can be performed on the impedance information to generate a frequency-based impedance map, and R is determined based on the value obtained by integrating the impedance map into a second domain corresponding to the second frequency domain. s .

[0036] In an example embodiment, the negative electrode may include a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material may include at least one of silicon-based negative electrode active material and carbon-based negative electrode active material.

[0037] In an example implementation, the content of silicon-based anode active material can be from 1% to 30% by weight relative to the total weight of the anode active material layer.

[0038] In an example embodiment, the negative electrode may comprise a silicon-based negative electrode active material and a carbon-based negative electrode active material, and the weight ratio of the silicon-based negative electrode active material to the carbon-based negative electrode active material may be from 1:99 to 30:70.

[0039] In addition, the present invention provides a method for preparing a positive electrode, the method comprising: (A) mixing a positive electrode active material in distilled water and washing the positive electrode active material with water; (B) drying the washed positive electrode active material; and (C) applying a positive electrode slurry containing the dried positive electrode active material onto a positive electrode current collector.

[0040] In an example implementation, step (A) may include (a1) mixing a first positive electrode active material in distilled water and performing a first water wash and (a2) mixing a second positive electrode active material in distilled water and performing a second water wash, wherein the first positive electrode active material and the second positive electrode active material may have different average particle sizes (D) from each other. 50 ).

[0041] In the example implementation, the first water wash can be performed at a higher temperature than the second water wash.

[0042] In an example implementation, the first water wash can be performed at a temperature of 20°C to 40°C.

[0043] In the example implementation, the second water wash can be performed at 3°C ​​to 18°C.

[0044] In an example implementation, the first water wash can be performed by mixing the first positive electrode active material in an amount of 50% to 70% by weight relative to the total weight of distilled water.

[0045] In an example implementation, the second water washing can be performed by mixing the second positive electrode active material in an amount of 65% to 85% by weight relative to the total weight of distilled water.

[0046] Beneficial effects

[0047] According to the example implementation, a lithium secondary battery with improved lifespan and / or performance can be provided by identifying and extracting the performance factors of the lithium secondary battery and analyzing and adjusting the performance factors of the lithium secondary battery.

[0048] According to an example implementation, the resistance characteristics of the positive and / or negative electrodes associated with the degradation of a lithium secondary battery can be extracted and analyzed by using electrochemical impedance spectroscopy (EIS) (a non-destructive measurement method) and performing relaxation time distribution (DRT) analysis, and the results are used as frequency-based impedance maps. Therefore, the performance and / or lifetime characteristics of a lithium secondary battery can be improved without affecting the components and performance of the lithium secondary battery.

[0049] In particular, among the performance factors of lithium secondary batteries, the state of the positive and / or negative electrodes can be analyzed and diagnosed separately. Therefore, by adjusting the resistance characteristics of the positive electrode to indirectly control the reaction amount of the negative electrode, the performance and lifespan characteristics of lithium secondary batteries prepared including the aforementioned positive electrode can be improved. Attached Figure Description

[0050] Figure 1 A frequency-based impedance diagram of the positive electrode of Example 1 of Experimental Example 1 according to the present invention is shown.

[0051] Figure 2A frequency-based impedance diagram of the positive electrode of Comparative Example 1 of Experimental Example 1 according to the present invention is shown.

[0052] Figure 3 A frequency-based impedance diagram of the positive electrode of Comparative Example 2 of Experimental Example 1 according to the present invention is shown.

[0053] Figure 4 The results of evaluating the room temperature lifetime characteristics of the lithium secondary batteries of Example 1, Comparative Example 1, and Comparative Example 2 according to Experimental Example 2 of the present invention are shown. Detailed Implementation

[0054] The terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical idea of ​​the invention, based on the inventor's ability to appropriately define the concepts of the terms in order to best interpret the principles of his or her invention.

[0055] Therefore, it should be understood that the configurations of the embodiments described in this specification are one of the most desirable embodiments of the present invention and do not represent the entire technical concept of the present invention. Thus, various equivalents and improved embodiments that can replace the embodiments at the time of filing this application are possible. In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0056] In this specification, if a section “comprises” an element, it means that the section may also include other elements rather than exclude other elements, unless specifically stated otherwise. Thus, for example, a composition comprising compound A may contain other compounds besides A. However, in some embodiments, the term “comprises” also covers the more restrictive meanings of “substantially / inherently constitutes” and “consisting of”, and for example, a “composition comprising compound A” may also (substantially / inherently) consist of compound A.

[0057] In this regard, as described in this specification, it should be understood that terms such as “set up” or “have” are intended to specify the presence of the implemented features, quantities, steps, components or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, quantities, steps, components or combinations thereof.

[0058] In this specification, if any layer is located "on" or "between" any other layer, it includes not only the case where this layer is in contact with the other layer, but also the case where there is another layer or another substance between the two layers.

[0059] If quantities, concentrations, or other values ​​or parameters are given in this specification as a list of ranges, desired ranges, desired upper limits, and desired lower limits, it should be understood that all ranges that can be formed by any pair of any upper or desired range value and any lower or desired range value are specifically disclosed, regardless of whether the range is disclosed individually. If a numerical range is mentioned in this specification, the range is intended to include endpoint values ​​as well as all integers and fractions within that range, unless otherwise stated, such as with limiting terms like greater than and less than. The scope of this invention is not intended to be limited to the specific values ​​mentioned when defining the range.

[0060] In this specification, the physical properties mentioned, where the measurement temperature affects the relevant physical properties, are measured at room temperature unless otherwise stated. The term room temperature is the natural temperature without heating or cooling, and may mean, for example, any temperature between about 10°C and 30°C, about 23°C, or about 25°C. Furthermore, unless otherwise stated, the unit of temperature in this specification is °C.

[0061] In addition, regarding the physical properties mentioned in this specification, unless otherwise stated, the physical properties are measured at normal pressure (i.e., atmospheric pressure (approximately 1 atm) where the measurement pressure affects the relevant physical properties.

[0062] In this specification, "single-particle type particle" refers to a particle composed of 30 or fewer nodules, and includes the concepts of single particles and pseudo-single particles. "Single particle" refers to a particle composed of a single nodule, and "pseudo-single particle" refers to a particle of a complex formed by more than one nodule and less than or equal to 30 nodules.

[0063] In this specification, "nodule" refers to the particle unit that constitutes a single particle or pseudo-single particle, and when observed using a scanning electron microscope (SEM) at a field of view of 5,000 to 20,000x, a nodule can be a single crystal without grain boundaries or a polycrystalline material without distinct grain boundaries.

[0064] As used herein, the term "particle" may include at least one, two or more, or all of the following: a single particle, a pseudo-single particle, a primary particle, a tuberculous particle, and a secondary particle.

[0065] In this specification, "average particle size D" 50"50%" refers to the particle size based on the 50% (%) of the volumetric cumulative particle size distribution of the positive electrode active material powder, and can be measured using laser diffraction. For example, when the positive electrode active material powder is dispersed in a dispersion medium, a commercially available laser diffraction particle size measurement device (e.g., Microtrac MT 3000) is introduced, and ultrasonic waves with an output of approximately 28 kHz at 60 W are used to obtain a volumetric cumulative particle size distribution map. The particle size corresponding to 50% volumetric cumulative particle size is then determined, and the average particle size D can be measured. 50 .

[0066] This invention relates to a positive electrode.

[0067] The positive electrode may include a positive electrode active material and has a resistivity ratio greater than or equal to 2 as defined by the following relationship 1.

[0068] [Relation 1]

[0069] R ct / R s

[0070] R ct It can refer to the charge transfer resistance of the positive electrode of a secondary battery, including the positive electrode, measured in the first frequency domain.

[0071] R s It can refer to the surface or interface resistance of the positive electrode of a secondary battery, including the positive electrode, measured in the second frequency domain.

[0072] The first frequency domain can be a frequency domain greater than or equal to 1 Hz and less than or equal to 1 kHz.

[0073] The second frequency domain can be a frequency domain greater than 1 kHz and less than or equal to 1,000 kHz.

[0074] Impedance information can be obtained by performing electrochemical impedance spectroscopy (EIS) on the secondary battery. Relaxation time distribution (DRT) analysis is then performed on the impedance information to generate a frequency-based impedance map. R is determined based on the value obtained by integrating the impedance map into a first domain corresponding to a first frequency domain. ct .

[0075] Impedance information can be obtained by performing EIS on the secondary battery, and DRT analysis can be performed on the impedance information to generate a frequency-based impedance map. R is then determined based on the value obtained by integrating the impedance map into a second domain corresponding to the second frequency domain. s .

[0076] Previously, hybrid pulse power characterization (HPPC) was used to evaluate the state of lithium secondary batteries, thus it could only assess battery performance but was difficult to analyze each specific component. However, according to the present invention, by using analytical methods performed through electrochemical impedance spectroscopy (EIS) and relaxation time distribution (DRT) analysis, the resistance factors of individual components of the battery (components that have a major impact on performance, such as the positive and / or negative electrodes) are analyzed, and the state of each component (e.g., the positive and / or negative electrodes) is evaluated, thereby ultimately improving the performance of lithium secondary batteries.

[0077] The resistivity ratio R expressed by Equation 1 above ct / R s The value of can be greater than or equal to 2, specifically greater than or equal to 2 and less than or equal to 8, and more specifically greater than or equal to 2 and less than or equal to 6. As mentioned above, when the resistive component is greater than R ct / R s A value greater than or equal to 2 can improve the lifespan characteristics of lithium secondary batteries. Specifically, when the resistivity component is greater than R... ct / R s When the value is greater than or equal to 2, room temperature lifetime characteristics can be improved in lithium secondary batteries with a silicon-based and graphite hybrid negative electrode.

[0078] When the resistivity ratio is R ct / R s When the value of R is less than 2, due to the rapid degradation of the SiO / graphite anode during cycling, a sharp decrease in charge / discharge capacity may occur; while when R... ct / R s When the value is greater than 8, the capacity may be reduced due to decreased fast charging performance and / or increased resistance.

[0079] R ct and / or R s The value of the resistivity component increases with the number of cycles of the lithium secondary battery, but regardless of the number of cycles, the resistivity component remains constant compared to R. ct / R s All values ​​can satisfy this range.

[0080] For example, R measured after 200 cycles of a lithium secondary battery. ct / R s The value can be greater than or equal to 2, and can be, for example, a range of 2 to 8 or a range of 2 to 6.

[0081] In an exemplary embodiment of the present invention, specifically, by adjusting the ratio of the charge transfer resistance value of the positive electrode to the resistance value at the surface or interface of the positive electrode, the reaction amount at the negative electrode can be indirectly adjusted, and thus battery degradation can be prevented, and performance, including the life characteristics of lithium secondary batteries, can be improved.

[0082] The resistivity ratio R can be adjusted based on the type of materials included in the positive electrode, the content ratio of the materials, and / or the preparation conditions. ct / R s Specifically, the resistivity ratio can be adjusted based on the transition metal composition of the positive electrode active material, the type of dopant, the average particle size of the positive electrode active material, and the calcination or washing conditions during preparation. Furthermore, when the positive electrode contains different types of positive electrode active materials, the resistivity ratio can vary depending on their mixing ratio. Additionally, the resistivity ratio can be adjusted based on the type of conductive material and the type of binder contained in the positive electrode, and can also be adjusted based on the mixing ratio of the positive electrode active material, conductive material, and binder, the thickness of the positive electrode active material layer, and the preparation conditions of the positive electrode. By referring to the embodiments and comparative examples of the present invention, the resistivity ratio can be easily adjusted to the desired ratio, rather than uniformly limiting the conditions for adjusting the resistivity ratio to a predetermined level.

[0083] Positive electrode active materials can include those with different average particle sizes (D0). 50 The first positive electrode active material and the second positive electrode active material.

[0084] The average particle size (D) of the first positive electrode active material 50 The particle size can be larger than the average particle size (D) of the second positive electrode active material. 50 ).

[0085] The positive electrode active material may include a first positive electrode active material represented by the following formula 1 and a second positive electrode active material represented by the following formula 2.

[0086] [Formula 1]

[0087] Li 1+a1 Ni x1 Co y1 Mn z1 Al w1 M 1 v1 O2

[0088] In Equation 1 above,

[0089] 0 ≤ a1 ≤ 0.3, 0.6 ≤ x1 ≤ 1.0, 0 ≤ y1 ≤ 0.2, 0 ≤ z1 ≤ 0.2, 0 ≤ w1 ≤ 0.2, 0 ≤ v1 ≤ 0.1, and

[0090] M 1 It is a doping element that includes at least one selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, Ba and Mo.

[0091] [Equation 2]

[0092] Li 1+a2 Ni x2 Co y2 Mn z2 Al w2 M 2 v2 O2

[0093] In equation 2 above,

[0094] 0 ≤ a² ≤ 0.3, 0.6 ≤ x² ≤ 1.0, 0 ≤ y² ≤ 0.2, 0 ≤ z² ≤ 0.2, 0 ≤ w² ≤ 0.2, 0 ≤ v² ≤ 0.1, and

[0095] M 2 It is a doping element that includes at least one selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, Ba and Mo.

[0096] The first positive electrode active material may include a ternary lithium transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn). In addition to nickel, cobalt, and manganese, the first positive electrode active material may also include elements such as aluminum (Al), and may include quaternary lithium transition metal oxides. Furthermore, the first positive electrode active material may include M... 1 As a doping element other than aluminum (Al), or may include M as a doping element 1 And aluminum (Al).

[0097] The first positive electrode active material, which includes ternary lithium transition metal oxides, also includes materials such as aluminum (Al) and / or M. 1 With equal doping elements, the first positive electrode active material can have structural or electrochemical stability, and thus can improve stability and / or capacity characteristics at high potentials by suppressing cation mixing during charging and discharging.

[0098] In Equation 1 above, M 1 It can be one or more types of doping elements selected from, for example, the group consisting of W, Y, Ba, Ca, Ti, Mg, Ta and Nb.

[0099] 1 + a1 may refer to the molar ratio of lithium (Li) in the first positive electrode active material of the above formula (1), and may be 0 ≤ a1 ≤ 0.3, preferably 0 ≤ a1 ≤ 0.2, more preferably 0 ≤ a1 ≤ 0.15, even more preferably 0 ≤ a1 ≤ 0.1. When a1 is less than 0, there is a risk that the capacity may decrease, while when a1 is greater than 0.3, the particles may sinter during the calcination process, making it difficult to prepare the first positive electrode active material. Therefore, when this range is satisfied, a balance can be achieved between the significant effect of improving the capacity characteristics of the first positive electrode active material by controlling the Li content and / or the sinterability during the preparation of the first positive electrode active material.

[0100] x1 may refer to the molar ratio of nickel among all metals other than lithium in the first positive electrode active material, and may be 0.6 ≤ x1 ≤ 1.0, preferably 0.7 ≤ x1 ≤ 1.0, more preferably 0.8 ≤ x1 ≤ 1.0, or 0.9 ≤ x1 ≤ 1.0. Additionally, x1 may specifically be 0.6 ≤ x1 < 1.0, more specifically 0.7 ≤ x1 < 1.0, 0.8 ≤ x1 < 1.0, 0.85 ≤ x1 < 1.0, or 0.9 ≤ x1 < 1.0. When this range is satisfied, a sufficient nickel content that contributes to charging and discharging can be ensured in the first positive electrode active material, and thus a high capacity can be achieved.

[0101] y1 may refer to the molar ratio of cobalt (Co) among all metals other than lithium in the first positive electrode active material, and may be 0 ≤ y1 ≤ 0.2, preferably 0 ≤ y1 ≤ 0.18, more preferably 0.01 ≤ y1 ≤ 0.15, even more preferably 0.03 ≤ y1 ≤ 0.12, even more preferably 0.05 ≤ y1 ≤ 0.10. As an option, the molar ratio may be 0 < y1 ≤ 0.2, specifically 0 < y1 ≤ 0.18, or 0 < y1 ≤ 0.15. When y1 satisfies this range, good resistance characteristics and output characteristics can be achieved while having a cost advantage by containing a small amount of cobalt.

[0102] z1 may refer to the molar ratio of manganese (Mn) among all metals other than lithium in the first positive electrode active material, and may be 0 ≤ z1 ≤ 0.2, preferably 0 ≤ z1 ≤ 0.18, more preferably 0.01 ≤ z1 ≤ 0.15, even more preferably 0.03 ≤ z1 ≤ 0.10. As an option, the molar ratio may be 0 < z1 ≤ 0.2, specifically 0 < z1 ≤ 0.18, or 0 < z1 ≤ 0.15. When z1 satisfies this range, the structural stability of the first positive electrode active material can be improved.

[0103] w1 may refer to the molar ratio of aluminum (Al) among all metals other than lithium in the first positive electrode active material, and may be 0 ≤ w1 ≤ 0.2, preferably 0 ≤ w1 ≤ 0.18, more preferably 0.01 ≤ w1 ≤ 0.15, still more preferably 0.03 ≤ w1 ≤ 0.10. As an option, the molar ratio may be 0 < w1 ≤ 0.2, specifically 0 < w1 ≤ 0.18, or 0 < w1 ≤ 0.15. When this range is satisfied, the thermal stability of the first positive electrode active material can be improved due to the high binding force with oxygen.

[0104] v1 may refer to M 1 in the molar ratio of all metals other than lithium in the first positive electrode active material, and may be 0 ≤ v1 ≤ 0.1, preferably 0 ≤ v1 ≤ 0.08, more preferably 0 ≤ v1 ≤ 0.05.

[0105] In Formula 2 above, M 2 may be, for example, one or more types of doping elements selected from the group consisting of W, Y, Ba, Ca, Ti, Mg, Ta, and Nb.

[0106] 1 + a2 may refer to the molar ratio of lithium (Li) in the second positive electrode active material of Formula 2 above, and may be 0 ≤ a2 ≤ 0.3, preferably 0 ≤ a2 ≤ 0.2, more preferably 0 ≤ a2 ≤ 0.15, even more preferably 0 ≤ a2 ≤ 0.1. When a2 is less than 0, there is a risk that the capacity may decrease, and when a2 is greater than 0.3, the particles may sinter during the calcination process, making it difficult to prepare the second positive electrode active material. Therefore, when this range is satisfied, a balance can be achieved between the significant effect of improving the capacity characteristics of the second positive electrode active material by controlling the Li content and / or the sinterability during the preparation of the second positive electrode active material.

[0107] x2 may refer to the molar ratio of nickel among all metals other than lithium in the second positive electrode active material, and may be 0.6 ≤ x2 ≤ 1.0, preferably 0.7 ≤ x2 ≤ 1.0, more preferably 0.8 ≤ x2 ≤ 1.0, or 0.9 ≤ x2 ≤ 1.0. Additionally, x2 may specifically be 0.6 ≤ x2 < 1.0, more specifically 0.7 ≤ x2 < 1.0, 0.8 ≤ x2 < 1.0, 0.85 ≤ x2 < 1.0, or 0.9 ≤ x2 < 1.0. When this range is satisfied, a sufficient nickel content that contributes to charging and discharging can be ensured in the second positive electrode active material, and thus high capacity can be achieved.

[0108] y2 may refer to the molar ratio of cobalt (Co) among all metals other than lithium in the second positive electrode active material, and may be 0 ≤ y2 ≤ 0.2, preferably 0 ≤ y2 ≤ 0.18, more preferably 0.01 ≤ y2 ≤ 0.15, even more preferably 0.03 ≤ y2 ≤ 0.12, and even more preferably 0.05 ≤ y2 ≤ 0.10. As an option, the molar ratio may be 0 < y2 ≤ 0.2, specifically 0 < y2 ≤ 0.18, or 0 < y2 ≤ 0.15. When y2 satisfies this range, good resistance characteristics and output characteristics can be achieved, while having a cost advantage by including a small amount of cobalt.

[0109] z2 may refer to the molar ratio of manganese (Mn) among all metals other than lithium in the second positive electrode active material, and may be 0 ≤ z2 ≤ 0.2, preferably 0 ≤ z2 ≤ 0.18, more preferably 0.01 ≤ z2 ≤ 0.15, even more preferably 0.03 ≤ z2 ≤ 0.10. As an option, the molar ratio may be 0 < z2 ≤ 0.2, specifically 0 < z2 ≤ 0.18, or 0 < z2 ≤ 0.15. When z2 satisfies this range, the structural stability of the second positive electrode active material can be improved.

[0110] w2 may refer to the molar ratio of aluminum (Al) among all metals other than lithium in the second positive electrode active material, and may be 0 ≤ w2 ≤ 0.2, preferably 0 ≤ w2 ≤ 0.18, more preferably 0.01 ≤ w2 ≤ 0.15, more preferably 0.03 ≤ w2 ≤ 0.10. As an option, the molar ratio may be 0 < w2 ≤ 0.2, specifically 0 < w2 ≤ 0.18, or 0 < w2 ≤ 0.15. When this range is satisfied, the thermal stability of the second positive electrode active material can be improved due to the high binding force with oxygen. [[ID=�]]

[0111] v2 may refer to the molar ratio of M 2 among all metals other than lithium in the second positive electrode active material, and may be 0 ≤ v2 ≤ 0.1, preferably 0 ≤ v2 ≤ 0.08, more preferably 0 ≤ v2 ≤ 0.05.

[0112] The first positive electrode active material may be selected to have an average particle size (D 50 ) larger than that of the second positive electrode active material. Therefore, during electrode rolling, the second positive electrode active material with a small particle size is filled into the pores of the first positive electrode active material with a large particle size, so that the electrode density can be increased and a high energy density can be achieved, and thus high capacity characteristics can be realized. In addition, in the case of using two types of positive electrode active materials with different average particle sizes as described above, the value of R ct / R s can be satisfied, and therefore the performance and / or life of the lithium secondary battery can be improved.

[0113] For example, the average particle size (D50 The particle size can be from 6 μm to 12 μm, and the average particle size (D) of the second positive electrode active material is... 50 The diameter can be from 1.5 μm to 5 μm.

[0114] Specifically, the average particle size of the first positive electrode active material can be greater than 6 μm, greater than 6.2 μm, greater than 6.4 μm, greater than 6.6 μm, greater than 6.8 μm, greater than 7 μm, greater than 7.2 μm, greater than 7.4 μm, greater than 7.6 μm, greater than 7.8 μm, greater than 8 μm, greater than 8.2 μm, or greater than 8.4 μm, or less than 12 μm, less than 11.8 μm, less than 11.6 μm, less than 11.4 μm, less than 11.2 μm, less than 11 μm, less than 10.8 μm, less than 10.6 μm, less than 10.4 μm, less than 10.2 μm, less than 10 μm, less than 9.8 μm, less than 9.6 μm, less than 9.4 μm, less than 9.2 μm, less than 9 μm, less than 8.8 μm, or less than 8.6 μm. For example, the average particle size of the first positive electrode active material can be 6 μm to 12 μm, preferably 7.4 μm to 11 μm, more preferably 8 μm to 9.6 μm, and even more preferably 8.2 μm to 9 μm. When this range is met, the rolling density of the positive electrode active material can be increased, and thus the electrode density can be improved during electrode fabrication, and therefore excellent energy density can be achieved.

[0115] Specifically, the average particle size of the second positive electrode active material can be 1.5 μm or more, 1.7 μm or more, 1.9 μm or more, 2 μm or more, 2.2 μm or more, 2.4 μm or more, 2.6 μm or more, 2.8 μm or more, or 3 μm or more, and can be less than 5 μm, less than 4.8 μm, less than 4.6 μm, less than 4.4 μm, less than 4.2 μm, less than 4 μm, less than 3.8 μm, less than 3.6 μm, less than 3.4 μm, or less than 3.2 μm. For example, the average particle size of the second positive electrode active material can be from 1.5 μm to 5 μm, preferably from 2 μm to 4.5 μm, more preferably from 2.6 μm to 4.2 μm, more preferably from 3 μm to 4 μm, and even more preferably from 3 μm to 3.4 μm. When this range is met, the rolling density of the positive electrode active material can be increased, and thus the electrode density can be improved during electrode fabrication, and therefore excellent energy density can be achieved.

[0116] The content of the first positive electrode active material relative to the total weight of the positive electrode active material can be from 20% to 80% by weight, preferably from 30% to 70% by weight, and more preferably from 40% to 60% by weight. When this range is met, a high energy density can be achieved by increasing the rolling density.

[0117] The content of the second positive electrode active material relative to the total weight of the positive electrode active material can be from 20% to 80% by weight, preferably from 30% to 70% by weight, and more preferably from 40% to 60% by weight. When this range is met, a high energy density can be achieved by increasing the rolling density.

[0118] The weight ratio of the first positive electrode active material to the second positive electrode active material can be from 80:20 to 40:60. Specifically, the weight ratio can be from 75:25 to 45:55, more specifically from 70:30 to 50:50, and even more specifically from 65:45 to 55:45. When the aforementioned weight ratio is met, the improvement in high-temperature and room-temperature lifetime characteristics and / or resistivity characteristics can be maximized, while energy density can also be improved.

[0119] In the positive electrode, the weight of the first positive electrode active material can be greater than the weight of the second positive electrode active material.

[0120] The first positive electrode active material may include single-particle type particles. When the first positive electrode active material includes single-particle type particles, the large size of these particles and the long diffusion distance of lithium lead to increased diffusion resistance, potentially resulting in low efficiency of the positive electrode. Therefore, by including a silicon-based negative electrode active material in the negative electrode, the efficiency can be balanced with that of the negative electrode. This solves the problem of lithium-ion loss due to irreversible capacity in existing silicon-based negative electrode active material applications and prevents lithium deposition on the surface of the negative electrode, thus improving the lifespan characteristics of lithium secondary batteries using the positive electrode of this invention. Furthermore, unlike existing methods using sacrificial positive electrode materials, including single-particle type particles in the first positive electrode active material prevents the generation of lithium byproducts from the sacrificial positive electrode material during charging and discharging, resulting in excellent high-temperature storage characteristics and / or high-temperature lifespan characteristics.

[0121] The second positive electrode active material may include single-particle type particles. When the second positive electrode active material includes single-particle type particles, the large size of these particles results in a long diffusion distance for lithium, leading to increased diffusion resistance and potentially low efficiency of the positive electrode. Therefore, by including a silicon-based negative electrode active material, efficiency can be balanced with that of the negative electrode. This solves the problem of lithium-ion loss due to irreversible capacity in existing silicon-based negative electrode active materials and prevents lithium deposition on the surface of the negative electrode, thus improving the lifespan characteristics of lithium secondary batteries using the positive electrode of the present invention. Furthermore, by including single-particle type particles in the second positive electrode active material, unlike existing methods using sacrificial positive electrode materials, the generation of lithium byproducts from the sacrificial positive electrode material during charging and discharging can be prevented, resulting in superior high-temperature storage characteristics and / or high-temperature lifespan characteristics.

[0122] The positive electrode active material can be obtained by mixing the positive electrode active material in distilled water, washing it with water, and then drying it. When subjected to the above water washing treatment, the positive electrode of the present invention can satisfy the value R. ct / R s This has the effect of preventing negative electrode degradation or improving the lifespan of lithium secondary batteries.

[0123] The positive electrode active material can be prepared as a transition metal precursor, and the lithium precursor can be mixed by methods such as co-precipitation, and then the positive electrode active material is washed with distilled water and dried.

[0124] When the positive electrode active material may include a first positive electrode active material and a second positive electrode active material, the first positive electrode active material and the second positive electrode active material may undergo the above-described water washing treatment. In this case, the water washing treatment of the first positive electrode active material and the second positive electrode active material may be carried out under the same conditions and by the same method, or may be carried out under different conditions and by different methods, but is not limited thereto.

[0125] The positive electrode may include a positive electrode current collector and a positive electrode active material layer comprising the aforementioned positive electrode active material. In addition to the aforementioned positive electrode active material, the positive electrode active material layer may optionally include at least one selected from positive electrode conductive material, positive electrode binder, and additives. When the positive electrode active material comprises a first positive electrode active material and a second positive electrode active material, the positive electrode active material layer may optionally include at least one selected from positive electrode conductive material, positive electrode binder, and additives, in addition to the first and second positive electrode active materials.

[0126] There are no particular restrictions on the positive electrode current collector, as long as it is conductive and does not cause chemical changes in the battery, and it can be composed of, for example, copper (Cu), nickel (Ni), aluminum (Al), vanadium (V), gold (Au), platinum (Pt), chromium (Cr), iron (Fe), zinc (Zn), indium (In), germanium (Ge), lithium (Li), magnesium (Mg), stainless steel (e.g., SUS), titanium (Ti), cobalt (Co), or alloys thereof.

[0127] The positive electrode current collector can have a thickness ranging from 3 μm to 500 μm and can have fine irregularities formed on its surface, thus increasing the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms, such as membranes, sheets, foils, meshes, porous materials, foams, and nonwoven materials. In some cases, the positive electrode current collector can be omitted.

[0128] The positive electrode active material layer can be located on the positive electrode current collector, and specifically on one or both surfaces of the positive electrode current collector. The positive electrode active material layer can have a single-layer structure or a multilayer structure with two or more layers. In addition, the bonding force of the positive electrode active material can be enhanced by forming fine irregularities on the surface of the positive electrode current collector.

[0129] Positive electrode conductive materials are used to provide conductivity to the electrode and can be used without particular restrictions, provided they do not cause chemical changes and are electronically conductive. Specific examples can be graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, and carbon nanotubes; metal powders or fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, which may be used individually or in mixtures of two or more types. The content of the positive electrode conductive material relative to the total weight of the positive electrode active material layer is typically from 1% to 30% by weight, specifically from 1% to 20% by weight, and more specifically from 1% to 10% by weight.

[0130] The positive electrode binder is used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material layer and the positive electrode current collector. Specific examples can be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol (PVA), polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone (PVP), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one type or a mixture of two or more types can be used. The content of the positive electrode binder relative to the total weight of the positive electrode active material layer can be from 1% to 30% by weight, specifically from 1% to 20% by weight, and more specifically from 1% to 10% by weight.

[0131] Additives may also include, for example, fillers, coating agents, dispersants, thickeners and ionic conductive agents, and any known materials commonly used in electrodes can be used without limitation.

[0132] The positive electrode can be prepared according to general methods for preparing positive electrodes, the difference being the use of the positive electrode active material. The positive electrode can be prepared by applying a positive electrode active material layer forming composition containing the positive electrode active material to one or both surfaces of a positive electrode current collector, removing the solvent through a drying process, and then rolling the positive electrode current collector while the positive electrode active material layer is applied. Alternatively, when applying the positive electrode active material layer forming composition, a positive electrode including an uncoated area can be prepared by not applying the positive electrode active material layer forming composition to a portion of the positive electrode current collector (e.g., one end of the positive electrode current collector).

[0133] In this case, the composition for forming the positive electrode active material layer may also include a solvent, and the solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water, and may be a single type or a mixture of two or more types. Considering the applied thickness of the slurry and the production yield, the amount of solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, etc., and has a viscosity that indicates excellent thickness uniformity when applied for subsequent preparation of the positive electrode.

[0134] The positive electrode can also be prepared by casting the composition for forming the positive electrode active material layer onto a separate carrier, and then pressing the film layer obtained by peeling it off from the carrier onto the positive electrode current collector.

[0135] This invention provides a lithium secondary battery.

[0136] The lithium secondary battery may include a positive electrode active material and may include: a positive electrode having a resistivity ratio greater than or equal to 2 as defined by the following relationship 1; a negative electrode; and an electrolyte.

[0137] [Relation 1]

[0138] R ct / R s

[0139] In relation 1 above, R ct This refers to the charge transfer resistance of the positive electrode measured in the first frequency domain of a lithium secondary battery, and R... s This refers to the surface or interface resistance of the positive electrode measured in the second frequency domain of a lithium secondary battery. The first frequency domain is greater than or equal to 1 Hz and less than or equal to 1 kHz, and the second frequency domain is greater than 1 kHz and less than or equal to 1,000 kHz.

[0140] Impedance information can be obtained by performing electrochemical impedance spectroscopy (EIS) on the secondary battery. Relaxation time distribution (DRT) analysis is then performed on the impedance information to generate a frequency-based impedance map. R is determined based on the value obtained by integrating the impedance map into a first domain corresponding to a first frequency domain. ct Furthermore, impedance information can be obtained by performing EIS on the secondary battery, DRT analysis can be performed on the impedance information to generate a frequency-based impedance map, and R is determined based on the value obtained by integrating the impedance map into a second domain corresponding to the second frequency domain. s .

[0141] For positive electrode, positive electrode active material, R ct and R s The above content can be applied in the same way.

[0142] The negative electrode may include a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material. The negative electrode active material may include at least one of silicon-based negative electrode active materials and carbon-based negative electrode active materials.

[0143] In addition to the aforementioned negative electrode active material, the negative electrode active material layer may optionally include at least one selected from negative electrode conductive material, negative electrode binder, and additives.

[0144] The negative electrode active material layer can be located on the negative electrode current collector, and specifically on one or both surfaces of the negative electrode current collector. The negative electrode active material layer can have a single-layer structure or a multilayer structure with two or more layers.

[0145] In another example, the negative electrode can be a negative electrode for an anode-free battery, wherein the negative electrode active material layer is not included immediately after the battery is fabricated, but is formed during charging, such as a lithium metal layer.

[0146] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity without causing chemical changes in the battery, and it can be made of, for example, copper, stainless steel (e.g., SUS), aluminum, nickel, titanium, sintered carbon, copper or stainless steel with surface treatment or coating of carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0147] Negative electrode current collectors can typically have a thickness ranging from 3 μm to 500 μm, and the bonding force of the negative electrode active material can be enhanced by forming fine irregularities on the surface of the negative electrode current collector. For example, negative electrode current collectors can be used in various forms, such as membranes, sheets, foils, meshes, porous materials, foams, and nonwoven materials.

[0148] Silicon-based anode active materials may include silicon (Si), and for example, silicon-based anode active materials may include particles containing silicon (Si).

[0149] Specifically, the silicon-based anode active material can be SiO2. x (0≤x≤2), Si / C composites, Si (pure Si), or combinations thereof. SiO x (0≤x≤2) can be in the form of including both Si and SiO2. In other words, x corresponds to SiO2. x The ratio of O to Si contained in the material is (0 ≤ x ≤ 2). Preferably, the silicon-based anode active material can be SiO₂. x (0≤x≤2), the optimal choice is SiO.

[0150] When the negative electrode includes a silicon-based negative electrode active material, compared to the existing method using only carbon-based negative electrode active materials, the advantage of the negative electrode lies in its very high charge and discharge capacity. However, a problem with silicon-based negative electrode active materials is that the life characteristics of lithium secondary batteries deteriorate due to the large irreversible capacity. The lithium secondary battery of the present invention solves this problem by adjusting the resistivity ratio of the positive electrode to a predetermined range.

[0151] Negative electrode active materials can include silicon-based negative electrode active materials. Negative electrode active materials can also include carbon-based negative electrode active materials.

[0152] The content of silicon-based anode active material relative to the total weight of the anode active material layer can be from 1 wt% to 30 wt%, specifically from 1 wt% to 25 wt%, and more specifically from 2 wt% to 20 wt%. Alternatively, the content of silicon-based anode active material relative to the total weight of the anode active material layer can be from 1 wt% to 10 wt%, or from 5 wt% to 10 wt%. When the content of silicon-based anode active material meets this range, sufficient capacity characteristics can be achieved.

[0153] Carbon-based anode active materials can be one or more types selected from the group consisting of: graphite, such as natural or artificial graphite; and carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, and carbon nanotubes. Including carbon-based anode active materials can suppress the degradation of lifetime characteristics caused by volume changes in silicon-based anode active materials during charging and discharging.

[0154] When the negative electrode comprises both silicon-based and carbon-based anode active materials, the weight ratio of the silicon-based to carbon-based anode active materials can be from 1:99 to 30:70. Specifically, the weight ratio can be from 1.5:98.5 to 20:80, more specifically from 2:98 to 15:85, and even more specifically from 2.5:97.5 to 10:90. When the weight ratio of silicon-based to carbon-based anode active materials meets this range, both capacity and lifetime characteristics can be excellent.

[0155] The content of carbon-based anode active material relative to the total weight of the anode active material layer can be from 70% to 99% by weight, specifically from 75% to 99% by weight, and more specifically from 80% to 98% by weight. When the content of carbon-based anode active material meets this range, the battery's lifespan characteristics can be improved, while sufficient capacity characteristics can be achieved.

[0156] The negative electrode conductive material is used to provide conductivity to the electrode and can be used without particular restrictions, provided that it does not cause a chemical change and has electronic conductivity. Specific examples can be graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotubes; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, which may be used alone or in mixtures of two or more types. The content of the negative electrode conductive material relative to the total weight of the negative electrode active material layer can be from 1% to 30% by weight, specifically from 1% to 20% by weight, and more specifically from 1% to 10% by weight.

[0157] The negative electrode binder is used to improve the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples can be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol (PVA), polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone (PVP), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one type or a mixture of two or more types can be used. The content of the negative electrode binder relative to the total weight of the negative electrode active material layer can be from 1% to 30% by weight, preferably from 1% to 20% by weight, and more preferably from 1% to 10% by weight.

[0158] Additives may also include, for example, fillers, coating agents, dispersants, thickeners and ionic conductive agents, and any known materials commonly used in electrodes can be used without limitation.

[0159] The negative electrode can be prepared according to general methods for preparing negative electrodes, the difference being the use of the negative electrode active material. The negative electrode can be prepared by applying a negative electrode active material layer forming composition containing the negative electrode active material to one or both surfaces of a negative electrode current collector and drying it, or by casting the negative electrode active material layer forming composition onto a separate carrier, and then pressing the film layer obtained by peeling it from the carrier onto the negative electrode current collector. The negative electrode active material layer forming composition may also include a solvent, and the solvent may be selected from examples of solvents contained in the above-described positive electrode active material layer forming composition.

[0160] In lithium secondary batteries, the electrolyte can be, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used in the preparation of lithium secondary batteries.

[0161] Electrolytes may include, for example, organic solvents and / or lithium salts.

[0162] Organic solvents can be used without particular restrictions, as long as they can serve as a medium through which ions involved in the electrochemical reactions of the battery can move. Specifically, as organic solvents, the following can be used: straight-chain ester solvents, such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, or butyl propionate; cyclic ester solvents, such as γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, or ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic solvents, such as benzene or fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); alcohol solvents, such as ethanol or isopropanol; nitriles, such as R-CN (R is a straight-chain, branched, or cyclic C2-C20 hydrocarbon group, and may include double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant (which can improve the charge / discharge performance of the battery) with low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are even more preferred. In this case, cyclic carbonates and linear carbonates can be mixed in a volume ratio of about 1:1 to about 1:9 to simultaneously satisfy the characteristics of high dielectric constant and low viscosity and achieve excellent ionic conductivity, thereby achieving excellent electrolyte performance.

[0163] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the electrolyte components, the electrolyte may also include one or more types of additives, such as alkylene carbonate halide compounds, such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the content of the additives may be from 0.1% by weight to 5% by weight relative to the total weight of the electrolyte.

[0164] Lithium salts can be used, albeit with special restrictions, as long as they are compounds that can provide lithium ions for use in lithium-ion secondary batteries. For example, lithium salts may include Li as a cation. + and as an anion selected from F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - AlO4 - AlCl4 - PF6 - BF6 - SF6 - B 10 Cl 10 - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - F3SO3 - C4F9SO3 - CF3CF2SO3 - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - CH3SO3 - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - At least one of them.

[0165] Specifically, the lithium salt can be selected from LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, and LiB. 10 Cl 10The lithium salt may include at least one material selected from the group consisting of LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI (LiN(SO2CF2CF3)2). Specifically, the lithium salt may include a single material or a mixture of two or more materials selected from the group consisting of LiBF4, LiClO4, LiPF6, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), and LiBETI (LiN(SO2CF2CF3)2).

[0166] The concentration of lithium salt in the electrolyte can be from 0.1 M to 4 M, specifically from 0.1 M to 2 M, and more specifically from 0.8 M to 1.6 M. Within this range of lithium salt concentration, the electrolyte can possess suitable conductivity and viscosity, thus enabling excellent electrolyte performance, efficient lithium ion movement, and consequently improved output characteristics of the lithium secondary battery.

[0167] Electrolytes may include solid electrolytes, and in cases where solid electrolytes are included, the solid electrolyte can replace the diaphragm, and therefore the diaphragm may not be required.

[0168] Solid electrolytes may include, for example, oxide solid electrolytes, sulfide solid electrolytes, phosphoric acid solid electrolytes, polymer solid electrolytes, or halide solid electrolytes, but are not limited thereto.

[0169] Sulfide-based solid electrolytes may include sulfur atoms (S), have ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table, and possess electronic insulating properties. Sulfide-based solid electrolytes may preferably include at least Li, S, and P as elements and have lithium-ion conductivity, but may include elements other than Li, S, and P, depending on the purpose or circumstances.

[0170] Specifically, as sulfide-based solid electrolytes, Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-H2S, Li2S-P2S5-H2S-LiCl, Li2S-LiI-P2S5, Li2S-LiI-Li2OP2S5, Li2S-LiBr-P2S5, Li2-SLi2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SiS2-LiCl, Li2S-P2S5-SnS, and Li2S-P2 S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, Li2SGa2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S-GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS 2. Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-LiI, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li 10 GeP2S 12 wait.

[0171] Oxide solid electrolytes can be, for example, Li xa La ya TiO3 (xa=0.3 to 0.7, ya=0.3 to 0.7) (LLTO), Li xb La yb Zr zb Mbb mb O nb (Mbb is an element of at least one or more types selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, xb satisfies 5 ≤ ​​xb ≤ 10, yb satisfies 1 ≤ yb ≤ 4, zb satisfies 1 ≤ zb ≤ 4, mb satisfies 0 ≤ mb ≤ 2, and nb satisfies 5 ≤ ​​nb ≤ 20), Li xc B yc Mcc zc O nc (Mcc is an element of at least one or more types from C, S, Al, Si, Ga, Ge, In, and Sn, where xc satisfies 0 ≤ xc ≤ 5, yc satisfies 0 ≤ yc ≤ 1, zc satisfies 0 ≤ zc ≤ 1, and nc satisfies 0 ≤ nc ≤ 6), Li xd (Al, Ga) yd (Ti, Ge) zd Si ad Pmd O nd (However, 1≤xd≤3, 0≤yd≤1, 0≤zd≤2, 0≤ad≤1, 1≤md≤7, 3≤nd≤13), Li (3-2xe) Mee xe DeeO (xe represents a divalent metal atom greater than 0 and less than or equal to 0.1, Dee represents a halogen atom or a combination of two or more types of halogen atoms), Li xf Si yf O zf (1≤xf≤5, 0 <yf≤3, 1≤zf≤10)、Li xg S yg O zg (1≤xg≤3, 0 <yg≤2, 1≤zg≤10)、Li3BO3-Li2SO4、Li2O-B2O3-P2O5、Li2O-SiO2、Li6BaLa2Ta2O 12 Li3PO (4-3 / 2w) N w Li (where w is w<1) has a lithium super ion conductor (LISICON) type crystal structure 3.5 Zn 0.25 GeO4, La with a perovskite-type crystal structure 0.55 Li 0.35 TiO3, LiTi2P3O with a sodium (Na) super ionic conductor (NASICON) type crystal structure 12 Li 1+xh+yh (Al, Ga) xh (Ti, Ge) 2-xh Si yh P3- yh O 12 (However, 0≤xh≤1, 0≤yh≤1) and Li7La3Zr2O with garnet crystal structure 12 (LLZO). Alternatively, phosphorus compounds containing Li, P, and O can also be used. Examples include lithium phosphate (Li3PO4) and LiPON in which some of the oxygen in lithium phosphate is replaced by nitrogen and LiPOD1 (D1 is at least one type selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc.). Alternatively, LiAlON (Al is at least one type selected from Si, B, Ge, Al, C, Ga, etc.) can also be used.

[0172] Polymer-based solid electrolytes are ion-conducting materials and include, but are not particularly limited to, polymeric materials commonly used as solid electrolyte materials in all-solid-state batteries. Polymer-based solid electrolytes may, for example, include polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxane polymers, phosphazene polymers, polyethylene oxide (PEO), polyethylene derivatives, epoxy alkane derivatives, phosphate ester polymers, polylysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, or polymers including ion-dissociating groups. Alternatively, polymer-based solid electrolytes may include branched copolymers, comb-like polymeric resins, and cross-linked polymeric resins copolymerized as comonomers of amorphous polymers such as polymethyl methacrylate (PMMA), polycarbonate, polysiloxane, and / or phosphazene on the main chain of polyethylene oxide (PEO) as the polymeric resin.

[0173] Solid electrolytes can include gel-type polymeric electrolytes. Gel-type polymeric electrolytes include organic electrolytes comprising lithium salts and polymeric resins, wherein the organic electrolyte comprises 60 to 400 parts by weight relative to 100 parts by weight of polymeric resin. The polymeric resin applied to the gel-type polymeric electrolyte is not limited to a specific component, but can include, for example, polyvinyl chloride (PVC), poly(methyl methacrylate) (PMMA), polyacrylonitrile (PAN), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), etc.

[0174] Lithium secondary batteries may optionally also include a separator.

[0175] Meanwhile, when the electrolyte includes the aforementioned solid electrolyte, since the solid electrolyte is used as a separator, the lithium secondary battery may not include a separate separator, but is not limited to this.

[0176] There are no particular limitations on the use of a separator that separates the negative and positive electrodes and provides a migration channel for lithium ions, as long as it can generally be used as a separator in lithium secondary batteries, and particularly preferably it has low resistance to ion movement of the electrolyte and excellent electrolyte impregnation characteristics. Specifically, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof. Alternatively, general porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, separators including ceramic components or polymer coatings can be used to ensure heat resistance or mechanical strength, and can optionally be used in single-layer or multi-layer structures. In some cases, the separator can also be omitted.

[0177] This invention provides a method for preparing a positive electrode.

[0178] The method for preparing the positive electrode may include: (A) mixing the positive electrode active material in distilled water and washing the positive electrode active material with water; (B) drying the washed positive electrode active material; and (C) applying a positive electrode slurry containing the dried positive electrode active material onto a positive electrode current collector.

[0179] In step (A), water washing can be performed at a temperature between 3°C and 40°C. Step (A) may include (a1) mixing the first positive electrode active material in distilled water and performing a first water wash; and (a2) mixing the second positive electrode active material in distilled water and performing a second water wash. Therefore, the resistivity composition of the positive electrode can be adjusted to a specific range, and the positive electrode of the present invention can satisfy R ct / R s The value of this can improve the performance of lithium secondary batteries.

[0180] The first and second positive electrode active materials can have different average particle sizes (D) from each other. 50 ).

[0181] In step (a1), the washing intensity of the first positive electrode active material can be higher than that of the second positive electrode active material in step (a2). In other words, the first water wash can be performed at a higher temperature than the second water wash. Therefore, the resistivity of the positive electrode can be adjusted to a specific range.

[0182] The first water wash can be performed at temperatures ranging from 20°C to 40°C. Specifically, it can be performed at temperatures ranging from 25°C to 35°C, and more specifically, from 27°C to 38°C. When the first water wash is performed within the aforementioned temperature range, the interface resistance of the positive electrode can be adjusted to the desired range.

[0183] In step (a1), a first water wash can be performed by mixing the first positive electrode active material in an amount of 50% to 70% by weight relative to the total weight of distilled water. Specifically, the first water wash can be performed by mixing the first positive electrode active material in an amount of 55% to 65% by weight, more specifically 57% to 63% by weight. In this case, high-temperature durability degradation can be prevented by reducing the amount of residual lithium on the surface of the positive electrode active material.

[0184] In step (a2), the second positive electrode active material has a smaller particle size and a larger specific surface area than the first positive electrode active material. By washing the second positive electrode active material with water at a low intensity, the high-temperature durability degradation of the second positive electrode active material can be prevented, and the resistivity composition of the positive electrode can be adjusted to a specific range.

[0185] The second water wash can be performed at temperatures ranging from 3°C to 18°C. Specifically, the second water wash can be performed at temperatures ranging from 5°C to 15°C, and more specifically at temperatures ranging from 7°C to 13°C. Performing the second water wash within the aforementioned temperature range can prevent high-temperature durability degradation and simultaneously adjust the resistivity of the positive electrode to the desired range.

[0186] In step (a2), a second water wash can be performed by mixing the second positive electrode active material in an amount of 65% to 85% by weight relative to the total weight of distilled water. Specifically, the second water wash can be performed by mixing the second positive electrode active material in an amount of 70% to 80% by weight, more specifically 72% to 78% by weight. In this case, high-temperature durability degradation can be prevented by reducing the amount of residual lithium on the surface of the positive electrode active material.

[0187] The drying in step (B) can be carried out in a temperature range selected from 60°C to 200°C. The drying can be carried out in a temperature range selected from 70°C to 180°C, more specifically 80°C to 160°C.

[0188] In other words, step (B) may include drying the washed positive electrode active material at a temperature range selected from 60°C to 200°C. The drying method may be a general method for drying positive electrode active materials and is not particularly limited.

[0189] Step (B) may include (b1) drying the first positive electrode active material that was first washed in step (a1) and (b2) drying the second positive electrode active material that was second washed in step (a2).

[0190] The drying in steps (b1) and (b2) can be carried out in a temperature range selected from 60°C to 200°C.

[0191] Drying can be carried out in a temperature range selected from 70°C to 180°C, more specifically from 80°C to 160°C.

[0192] The drying in steps (b1) and (b2) can be carried out at the same temperature within the range, or at different temperatures.

[0193] Step (C) is the step of applying a positive electrode slurry containing dried positive electrode active material to a positive electrode current collector, and includes the preparation of the positive electrode slurry by mixing the positive electrode active material in a solvent and then applying it to the positive electrode current collector.

[0194] In this case, the positive electrode active material may include a first positive electrode active material and a second positive electrode active material, and the above description may be applied in the same manner to both the first and second positive electrode active materials.

[0195] The positive electrode slurry may also contain a positive electrode binder, a positive electrode conductive material and / or additives, and the above description may apply in the same manner to the positive electrode binder, the positive electrode conductive material and the additives.

[0196] The description of the solvents contained in the above-described composition for forming the positive electrode active material layer can be applied in the same manner to the solvents used in the positive electrode slurry.

[0197] In step (C), the positive electrode can be prepared by applying a positive electrode slurry onto the positive electrode current collector to form a positive electrode active material layer. Specifically, the positive electrode can be prepared as follows: the positive electrode slurry is applied to one or both surfaces of the positive electrode current collector, then dried and rolled to form a positive electrode active material layer. The positive electrode slurry can be the same as the composition for forming the positive electrode active material layer described above.

[0198] Application can be performed continuously or discontinuously using various application methods known in the art, such as slit coating, sliding coating, and curtain coating, but is not limited thereto.

[0199] Following step (C), step (D) may further include applying the positive electrode slurry onto the positive electrode current collector and then drying the positive electrode slurry. The drying in step (D) may be performed at temperatures ranging from 40°C to 180°C, specifically from 60°C to 160°C, and more specifically from 70°C to 150°C. The drying method can be applied without limitation, as long as it is a method for drying the electrode.

[0200] Following step (D), step (E) may also include rolling the dried positive electrode slurry and positive electrode current collector. Rolling can be performed according to, but is not limited to, rolling methods in which the thickness of the positive electrode is adjusted by controlling the upper / lower roller gap.

[0201] This invention provides a method for preparing a negative electrode.

[0202] Methods for preparing a negative electrode may include forming a negative electrode active material layer by applying a negative electrode slurry containing a negative electrode active material onto a negative electrode current collector, drying the negative electrode current collector and the negative electrode active material layer, and rolling the dried negative electrode current collector and the negative electrode active material layer.

[0203] The above description can be applied in the same way to both the negative electrode active material and the negative electrode current collector.

[0204] The negative electrode slurry may also include a negative electrode binder, a negative electrode conductive material and / or additives, and the above description may apply in the same manner to the negative electrode binder, negative electrode conductive material and additives.

[0205] The solvent used in the negative electrode slurry can be an aqueous solvent, an organic solvent, or a combination thereof.

[0206] Aqueous solvents may include, for example, water, and organic solvents may include one or more types selected from the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dihydro-L-glucosidone (Cyrene), γ-valerolactone, dimethyl isosorbide (DMI), and methyl-5-(dimethylamino)-2-methyl-5-oxovalerate, and may preferably include N-methylpyrrolidone.

[0207] Application can be performed continuously or discontinuously using various application methods known in the art, such as slit coating, sliding coating, and curtain coating, but is not limited thereto.

[0208] The negative electrode active material layer and the negative electrode current collector can be dried at temperatures ranging from 40°C to 180°C. Specifically, drying can be carried out at temperatures ranging from 60°C to 160°C, and more specifically, at temperatures ranging from 70°C to 150°C.

[0209] Roll forming can be performed according to various methods, including adjusting the thickness of the negative electrode by controlling the gap between the upper and lower rollers, but is not limited to this.

[0210] Lithium secondary batteries can be pouch-shaped, cubic, or cylindrical, and their shape and size can be used without restrictions, as long as they are commonly used secondary batteries.

[0211] Additionally, the lithium secondary battery may also include a housing for a sealed electrode assembly, such as a container, bag, pouch, or module, which houses the electrode assembly including a positive electrode, an electrolyte, and a negative electrode. The housing may optionally also include a sealing member.

[0212] The present invention will be explained in detail below with reference to embodiments in order to specifically explain the disclosure of the present invention as described above, as well as the intended actions and effects of the present invention. However, the embodiments can be modified into various other forms, and the scope of this specification should not be construed as limited to the described embodiments. It should be emphasized that the embodiments represent the present invention and are provided to explain the present invention in more detail to those skilled in the art.

[0213] Example

[0214] <Example 1> - Water washing treatment

[0215] <Preparation of the First Positive Electrode Active Material>

[0216] A transition metal aqueous solution was prepared by mixing NiSO4, CoSO4 and MnSO4 in distilled water at a nickel:cobalt:manganese molar ratio of 83:7:10.

[0217] Next, when deionized water is added to the reactor, nitrogen is purged into the reactor to remove dissolved oxygen and establish a non-oxidizing atmosphere. Then, a co-precipitation reaction is carried out while NaOH is added to prepare an average particle size (D). 50 The thickness is 8.6 μm and it is made of Ni. 0.8 Co 0.1 Mn 0.1 (OH)2 represents the precursor.

[0218] The precursor and LiOH were mixed in a 1:1.05 ratio, then mixed with Al as a dopant element, and calcined at 910°C for 16 hours to prepare Li[Ni] 0.81 Co 0.07 Mn 0.10 Al 0.02 ]O2 represents lithium transition metal oxide.

[0219] Then, the lithium transition metal oxide was mixed in distilled water at 30°C to a solid content of 60% by weight, washed with water, and dried to prepare the first positive electrode active material. The first positive electrode active material was confirmed to have an average particle size (D) of 8.6 μm. 50 And it is a single-particle type particle.

[0220] <Preparation of the Second Positive Electrode Active Material>

[0221] A transition metal aqueous solution was prepared by mixing NiSO4, CoSO4 and MnSO4 in distilled water at a nickel:cobalt:manganese molar ratio of 83:7:10.

[0222] Next, when deionized water is added to the reactor, nitrogen is purged into the reactor to remove dissolved oxygen and establish a non-oxidizing atmosphere. Then, a co-precipitation reaction is carried out while NaOH is added to prepare an average particle size (D). 50 The thickness is 3.1 μm and it is made of Ni. 0.8 Co 0.1 Mn 0.1 (OH)2 represents the precursor.

[0223] The precursor and LiOH were mixed in a 1:1.05 ratio, then mixed with Al as a dopant element, and calcined at 910°C for 16 hours to prepare Li[Ni] 0.81 Co 0.07 Mn 0.10 Al 0.02 ]O2 represents lithium transition metal oxide.

[0224] Then, the lithium transition metal oxide was mixed with distilled water at 10°C to a solid content of 75% by weight, washed with water, and dried to prepare the second positive electrode active material. The second positive electrode active material was confirmed to have an average particle size (D) of 3.1 μm. 50 And it is a single-particle type particle.

[0225] <Preparation of the positive electrode>

[0226] A positive electrode material is prepared by mixing the first and second positive electrode active materials prepared above at a weight ratio of 60:40. A positive electrode slurry is prepared by mixing the positive electrode material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone solvent at a weight ratio of 96:2:2. The positive electrode slurry is then applied to the surface of an aluminum current collector with a thickness of 20 μm, dried at 130°C, and then rolled to prepare a positive electrode with a thickness of 70 μm.

[0227] <Preparation of Lithium Secondary Batteries>

[0228] A negative electrode active material was obtained by mixing SiO and artificial graphite at a weight ratio of 5:95. The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were then mixed in distilled water at a weight ratio of 95.6:1.0:2.3:1.1 to prepare a negative electrode slurry. The negative electrode slurry was then applied to the surface of a 12 μm thick copper current collector, dried at 130°C, and then rolled to prepare the negative electrode (slurry solids content: 50% by weight relative to the total weight of the negative electrode slurry).

[0229] An electrode assembly was prepared by inserting a porous polyethylene separator between the positive and negative electrodes prepared above. The electrode assembly was then placed inside a battery casing, and an electrolyte was injected, thus preparing a lithium secondary battery. In this case, the following electrolyte was used: 1.0 M LiPF6 dissolved in an organic solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0230] <Comparative Example 1> - Boron Coating

[0231] <Preparation of the First Positive Electrode Active Material>

[0232] A transition metal aqueous solution was prepared by mixing NiSO4, CoSO4 and MnSO4 in distilled water at a nickel:cobalt:manganese molar ratio of 83:7:10.

[0233] Next, when deionized water is added to the reactor, nitrogen is purged into the reactor to remove dissolved oxygen and establish a non-oxidizing atmosphere. Then, a co-precipitation reaction is carried out while NaOH is added to prepare an average particle size (D). 50 The thickness is 8.6 μm and it is made of Ni. 0.8 Co 0.1 Mn 0.1 (OH)2 represents the precursor.

[0234] The precursor and LiOH were mixed in a 1:1.05 ratio, then mixed with Al as a dopant element, and calcined at 910°C for 16 hours to prepare Li[Ni] 0.81 Co 0.07 Mn 0.10 Al 0.02 ]O2 represents lithium transition metal oxide.

[0235] Then, a B-coated first positive electrode active material was prepared by mixing the lithium transition metal oxide with a boron precursor and subsequently heat-treating at 750°C for 5 hours. The first positive electrode active material was confirmed to have an average particle size (D0) of 6 μm to 12 μm. 50 And it is a single-particle type particle.

[0236] <Preparation of the Second Positive Electrode Active Material>

[0237] A transition metal aqueous solution was prepared by mixing NiSO4, CoSO4 and MnSO4 in distilled water at a nickel:cobalt:manganese molar ratio of 83:7:10.

[0238] Next, when deionized water is added to the reactor, nitrogen is purged into the reactor to remove dissolved oxygen and establish a non-oxidizing atmosphere. Then, a co-precipitation reaction is carried out while NaOH is added to prepare an average particle size (D). 50 The thickness is 3.1 μm and it is made of Ni. 0.8 Co 0.1 Mn 0.1 (OH)2 represents the precursor.

[0239] The precursor and LiOH were mixed in a 1:1.05 ratio, then mixed with Al as a dopant element, and calcined at 910°C for 16 hours to prepare Li[Ni] 0.81 Co 0.07 Mn 0.10 Al 0.02 ]O2 represents lithium transition metal oxide.

[0240] Then, a second positive electrode active material coated with B was prepared by mixing the lithium transition metal oxide with a boron precursor and subsequently heat-treating at 750°C for 5 hours. The second positive electrode active material was confirmed to have an average particle size (D) of 3.97 μm. 50 And it is a single-particle type particle.

[0241] <Preparation of the positive electrode>

[0242] A positive electrode material is prepared by mixing the first and second positive electrode active materials prepared above at a weight ratio of 60:40. A positive electrode slurry is prepared by mixing the positive electrode material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone solvent at a weight ratio of 96:2:2. The positive electrode slurry is then applied to the surface of an aluminum current collector with a thickness of 20 μm, dried at 130°C, and then rolled to prepare a positive electrode with a thickness of 70 μm.

[0243] <Preparation of Lithium Secondary Batteries>

[0244] A negative electrode active material was obtained by mixing SiO and artificial graphite at a weight ratio of 6:94. The negative electrode active material, carbon black as a conductive material, SBR as a binder, and CMC as a thickener were then mixed in distilled water at a weight ratio of 95.6:1.0:2.3:1.1 to prepare a negative electrode slurry. The negative electrode slurry was then applied to the surface of a 12 μm thick copper current collector, dried at 130°C, and then rolled to prepare the negative electrode (slurry solids content: 50% by weight relative to the total weight of the negative electrode slurry).

[0245] An electrode assembly was prepared by inserting a porous polyethylene separator between the positive and negative electrodes prepared above. The electrode assembly was then placed inside a battery casing, and an electrolyte was injected, thus preparing a lithium secondary battery. In this case, the following electrolyte was used: 1.0 M LiPF6 was dissolved in an organic solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0246] Comparative Example 2 > - Cobalt Coating

[0247] <Preparation of the First Positive Electrode Active Material>

[0248] A transition metal aqueous solution was prepared by mixing NiSO4, CoSO4 and MnSO4 in distilled water at a nickel:cobalt:manganese molar ratio of 83:7:10.

[0249] Next, when deionized water is added to the reactor, nitrogen is purged into the reactor to remove dissolved oxygen and establish a non-oxidizing atmosphere. Then, a co-precipitation reaction is carried out while NaOH is added to prepare an average particle size (D). 50 The thickness is 8.6 μm and it is made of Ni. 0.8 Co 0.1 Mn 0.1 (OH)2 represents the precursor.

[0250] The precursor and LiOH were mixed in a 1:1.05 ratio, then mixed with Al as a dopant element, and calcined at 910°C for 16 hours to prepare Li[Ni] 0.81 Co 0.07 Mn 0.10 Al 0.02 ]O2 represents lithium transition metal oxide.

[0251] Then, a Co-coated first positive electrode active material was prepared by mixing the lithium transition metal oxide with Co(OH)₂ and heat-treating at 750°C for 5 hours. The first positive electrode active material was confirmed to have an average particle size (D) of 6 μm to 12 μm. 50 And it is a single-particle type particle.

[0252] <Preparation of the Second Positive Electrode Active Material>

[0253] A transition metal aqueous solution was prepared by mixing NiSO4, CoSO4 and MnSO4 in distilled water at a nickel:cobalt:manganese molar ratio of 83:7:10.

[0254] Next, when deionized water is added to the reactor, nitrogen is purged into the reactor to remove dissolved oxygen and establish a non-oxidizing atmosphere. Then, a co-precipitation reaction is carried out while NaOH is added to prepare an average particle size (D). 50 The thickness is 3.1 μm and it is made of Ni. 0.8 Co 0.1 Mn 0.1 (OH)2 represents the precursor.

[0255] The precursor and LiOH were mixed in a 1:1.05 ratio, then mixed with Al as a dopant element, and calcined at 910°C for 16 hours to prepare Li[Ni] 0.81 Co 0.07 Mn 0.10 Al 0.02 ]O2 represents lithium transition metal oxide.

[0256] Then, a Co-coated second positive electrode active material was prepared by mixing the lithium transition metal oxide with Co(OH)₂ and heat-treating at 750°C for 5 hours. The second positive electrode active material was confirmed to have an average particle size (D) of 6.19 μm. 50 And it is a single-particle type particle.

[0257] <Preparation of the positive electrode>

[0258] A positive electrode material is prepared by mixing the first and second positive electrode active materials prepared above at a weight ratio of 60:40. A positive electrode slurry is prepared by mixing the positive electrode material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone solvent at a weight ratio of 96:2:2. The positive electrode slurry is then applied to the surface of an aluminum current collector with a thickness of 20 μm, dried at 130°C, and then rolled to prepare a positive electrode with a thickness of 70 μm.

[0259] <Preparation of Lithium Secondary Batteries>

[0260] A negative electrode active material was obtained by mixing SiO and artificial graphite at a weight ratio of 6:94. The negative electrode active material, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were then mixed in distilled water at a weight ratio of 95.6:1.0:2.3:1.1 to prepare a negative electrode slurry. The negative electrode slurry was then applied to the surface of a 12 μm thick copper current collector, dried at 130°C, and then rolled to prepare the negative electrode (slurry solids content: 50% by weight relative to the total weight of the negative electrode slurry).

[0261] An electrode assembly was prepared by inserting a porous polyethylene separator between the positive and negative electrodes prepared above. The electrode assembly was then placed inside a battery casing, and an electrolyte was injected, thus preparing a lithium secondary battery. In this case, the following electrolyte was used: 1.0 M LiPF6 dissolved in an organic solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0262] <Experimental Example 1> - Rct / Rs Evaluation

[0263] An electrode assembly was prepared by inserting a porous polyethylene separator between the positive and negative electrodes prepared in Example 1 and Comparative Examples 1 and 2. The electrode assembly was then placed inside a battery casing, and an electrolyte was injected to prepare a lithium secondary battery. In this case, the following electrolyte was used: 1.0 M LiPF6 was dissolved in an organic solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0264] Next, the prepared lithium secondary battery was charged to 4.2 V at 0.1 C at 25 °C under constant current-constant voltage (CC-CV) charging conditions, and then cut off at 0.05 C. It was then discharged to 3.0 V at 0.1 C under CC conditions, constituting one cycle. After 100 cycles, the prepared lithium secondary battery was charged to 50% SOC, and R was measured by relaxation time distribution (DRT) analysis of the impedance information. s and R ct The impedance information was obtained by performing electrochemical impedance spectroscopy (EIS) on the secondary cell using a Biologic VMP3 device (at 1,000 kHz to 10 mHz and 25 °C). The results are shown in Table 1 below.

[0265] Table 1

[0266]

[0267] Referring to Table 1, it can be confirmed that the positive electrode prepared in Example 1 has an R value greater than or equal to 2. ct / R s However, the positive electrodes prepared in Comparative Examples 1 and 2 have an R value less than 2. ct / R s value.

[0268] <Experimental Example 2> - Room Temperature Lifetime Characteristics Evaluation

[0269] The lithium secondary batteries prepared in Example 1 and Comparative Examples 1 and 2 were charged to 4.2 V at 0.5 C at 45 °C under constant current-constant voltage (CC-CV) conditions using an electrochemical charger and discharger, then discharged to 3.0 V at 0.1 C under CC conditions, constituting one cycle. Capacity retention was evaluated after 300 charge-discharge cycles. The results are shown in... Figure 4 middle.

Claims

1. A positive electrode comprising a positive electrode active material, and having a resistance component ratio defined by the following relation 1 of greater than or equal to 2: [Relation 1] R2 / R1 > 2 wherein the first frequency domain is a frequency domain of greater than or equal to 1 Hz and less than or equal to 1 kHz, and the second frequency domain is a frequency domain of greater than 1 kHz and less than or equal to 1,000 kHz. R ct / R s wherein In the above relational expression 1, R ct is a charge transfer resistance of the positive electrode measured in a first frequency domain with respect to a secondary battery including the positive electrode, and R s is a surface or interface resistance of the positive electrode measured in a second frequency domain with respect to the secondary battery including the positive electrode, and 2. The positive electrode according to claim 1, 3. The positive electrode according to claim 1, 4. The positive electrode according to claim 1, wherein Obtaining impedance information by electrochemical impedance spectroscopy (EIS) on the secondary battery, performing relaxation time distribution (DRT) analysis on the impedance information to generate a frequency-based impedance plot, and determining R based on a value obtained by integrating a first domain corresponding to a first frequency domain of the impedance plot ct and Obtaining impedance information by performing EIS on the secondary battery, performing DRT analysis on the impedance information to generate a frequency-based impedance plot, and determining R based on a value obtained by integrating a second domain of the impedance plot corresponding to a second frequency domain s . wherein the positive electrode active material comprises a first positive electrode active material represented by the following formula 1, and a second positive electrode active material represented by the following formula 2: wherein the positive electrode active material comprises a first positive electrode active material and a second positive electrode active material having average particle diameters D 50 different from each other. [Formula 1] Li a1M x1M' y1M" z1M" w1M" v1O2 wherein in the above formula 1, 0 < a1 < 0.3, 0.6 < x1 < 1.0, 0 < y1 < 0.2, 0 < z1 < 0.2, 0 < w1 < 0.2, 0 < v1 < 0.1, and [Formula 2] Li a2M x2M' y2M" z2M" w2M" v2O2 wherein in the above formula 2, Li 1+a1 Ni x1 Co y1 Mn z1 Al w1 M 1 v1 O2 wherein, 0 < a2 < 0.3, 0.6 < x2 < 1.0, 0 < y2 < 0.2, 0 < z2 < 0.2, 0 < w2 < 0.2, 0 < v2 < 0.1, and 5. The positive electrode according to claim 1, M 1 is a dopant element comprising at least one selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, Ba, and Mo, 6. The positive electrode according to claim 1, Li 1+a2 Ni x2 Co y2 Mn z2 Al w2 M 2 v2 O2 7. The positive electrode according to claim 1, wherein the weight ratio of the first positive electrode active material and the second positive electrode active material contained therein is 80:20 to 40:

60. M 2 is a dopant element including at least one selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, Ba, and Mo.

8. The positive electrode according to claim 1, wherein the average particle diameter D 50 is 6 μm to 12 μm. wherein the positive electrode active material is obtained when the positive electrode active material is mixed in distilled water, washed with water, and then dried. wherein the average particle diameter D50 of the second positive electrode active material is 1.5 μm to 5 μm. 50 1.5 μm to 5 μm.

9. A lithium secondary battery comprising: a positive electrode comprising a positive electrode active material, and having a resistance component ratio defined by the following relation 1 of greater than or equal to 2; a negative electrode; and an electrolyte, [Relation 1] R2 / R1 > 2 wherein the first frequency domain is a frequency domain of greater than or equal to 1 Hz and less than or equal to 1 kHz, and the second frequency domain is a frequency domain of greater than 1 kHz and less than or equal to 1,000 kHz.

10. The lithium secondary battery according to claim 9, 11. The lithium secondary battery according to claim 9, wherein the negative electrode comprises: a negative electrode current collector, and a negative electrode active material layer comprising a negative electrode active material, R ct / R s wherein, in the above relational expression 1, R ct is the charge transfer resistance of the positive electrode measured in a first frequency domain for the lithium secondary battery, and R s refers to the surface or interface resistance of the positive electrode measured in a second frequency domain for the lithium secondary battery, and wherein the negative electrode active material comprises at least one of a silicon-based negative electrode active material and a carbon-based negative electrode active material.

12. The lithium secondary battery according to claim 11, wherein the content of the silicon-based negative electrode active material is 1 to 30% by weight with respect to the total weight of the negative electrode active material layer. wherein, Obtaining impedance information by electrochemical impedance spectroscopy (EIS) on the secondary battery, performing relaxation time distribution (DRT) analysis on the impedance information to generate a frequency-based impedance plot, and determining R based on a value obtained by integrating a first domain corresponding to a first frequency domain of the impedance plot ct and Obtaining impedance information by performing EIS on the lithium secondary battery, performing DRT analysis on the impedance information to generate a frequency-based impedance plot, and determining R based on a value obtained by integrating a second domain of the impedance plot corresponding to a second frequency domain s .

13. The lithium secondary battery according to claim 11, wherein the negative electrode comprises the silicon-based negative electrode active material and the carbon-based negative electrode active material, wherein the weight ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material contained therein is 1:99 to 30:

70.

14. A method of producing a positive electrode, the method comprising: (A) mixing a positive electrode active material in distilled water and washing the positive electrode active material with water; (B) drying the washed positive electrode active material; and (C) applying a positive electrode slurry comprising the dried positive electrode active material to a positive electrode current collector.

15. The method according to claim 14, wherein step (A) comprises: ​ ​ ​ ​ ​ ​ ​ ​ (a1) mixing a first positive electrode active material in distilled water and performing a first water washing; and (a2) mixing a second positive electrode active material in distilled water and performing a second water washing, wherein the first positive electrode active material and the second positive electrode active material have different average particle diameters D from each other 50 .

16. The method of claim 15, wherein the first water washing is performed at a higher temperature than the second water washing.

17. The method of claim 15, wherein the first water washing is performed at 20 °C to 40 °C.

18. The method of claim 15, wherein the second water washing is performed at 3 °C to 18 °C.

19. The method of claim 15, wherein the first water washing is performed by mixing the first positive electrode active material in an amount of 50% to 70% by weight with respect to the total weight of the distilled water.

20. The method of claim 15, wherein the second water washing is performed by mixing the second positive electrode active material in an amount of 65% to 85% by weight with respect to the total weight of the distilled water.

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