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

Abstract

The present invention relates to a positive electrode comprising a positive electrode active material, wherein a resistance component ratio, as defined by equation 1 below, is 2 or more. [Equation 1] Rct / Rs. In the equation, Rct means a charge transfer resistance of the positive electrode, which is measured in a first frequency range for a secondary battery comprising the positive electrode, Rs means a surface or interface resistance of the positive electrode, which is measured in a second frequency range for the secondary battery comprising the positive electrode, the first frequency range is from 1 Hz to 1 kHz, and the second frequency range is from more than 1 kHz to 1,000 kHz.

Description

Anode, a lithium secondary battery including the same, and a method for manufacturing the anode

[0001] The present invention relates to a positive electrode, a lithium secondary battery including the same, and a method for manufacturing the positive electrode.

[0002] The recent rapid proliferation of battery-powered electronic devices such as mobile phones, laptops, computers, and electric vehicles has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity secondary batteries. In particular, lithium secondary batteries, with their lightweight yet high energy density, are attracting attention as power sources for portable devices. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0003] Carbon-based materials such as graphite have been primarily used as anode materials for lithium secondary batteries. However, carbon-based materials have a low capacity per unit mass, making it difficult to achieve high capacity in lithium secondary batteries. Consequently, silicon-based compounds are being developed and used as non-carbon-based anode materials that exhibit higher capacity than carbon-based materials. However, excessive use of silicon-based compounds can lead to sudden degradation, and lithium secondary batteries using these compounds can experience unexpected problems, such as reduced battery life at temperatures below room temperature.

[0004] One of the methods used to measure the performance or condition of lithium secondary batteries has been resistance measurement using Hybrid Pulse Power Characterization (HPPC) or battery capacity measurement. While these methods can assess lithium secondary battery performance, they have limitations in providing a specific diagnosis by individually identifying the condition of the positive and / or negative electrodes as components of the battery.

[0005] Therefore, there is a need for a method to improve the performance and lifespan of lithium secondary batteries by identifying the performance factors of the positive and / or negative electrode components that affect the performance and lifespan of lithium secondary batteries and controlling them.

[0006] The present invention is designed to solve the above problems, and aims to provide a positive electrode with improved lifespan and / or performance of a lithium secondary battery by indirectly controlling the reaction amount of the negative electrode by controlling the reaction resistance of the positive electrode, which is one of the components of the lithium secondary battery.

[0007] In addition, the present invention aims to provide a lithium secondary battery with improved lifespan and / or performance by extracting and analyzing a resistance component directly related to the deterioration of a lithium secondary battery using electrochemical impedance spectroscopy (EIS), which is a non-destructive measurement method.

[0008] The present invention relates to a positive electrode including a positive electrode active material and having a resistance component ratio of 2 or more as defined by the following equation 1.

[0009] [Formula 1]

[0010] R ct / R s

[0011] In the above formula, the R ct means the charge transfer resistance of the positive electrode measured in the first frequency range for a secondary battery including the positive electrode, and the R s refers to the surface or interface resistance of the positive electrode measured in a second frequency range for a secondary battery including the positive electrode, wherein the first frequency range is a frequency range of 1 Hz or more and 1 kHz or less, and the second frequency range is a frequency range of more than 1 kHz and 1,000 kHz or less.

[0012] In one embodiment, the R ctThe impedance information obtained by performing electrochemical impedance spectroscopy (EIS) on the secondary battery is analyzed by distribution of relaxation time (DRT) to generate an impedance graph according to frequency, and the R is determined based on a value obtained by integrating the first region corresponding to the first frequency region of the graph. s The impedance information obtained by performing an electrochemical impedance analysis method on the secondary battery is analyzed for relaxation time distribution to generate an impedance graph according to frequency, and the impedance can be determined based on a value obtained by integrating a second area corresponding to the second frequency area of ​​the graph.

[0013] In one embodiment, the positive electrode active material has an average particle diameter (D 50 ) may include different first positive electrode active materials and second positive electrode active materials.

[0014] In one embodiment, the positive electrode active material may include a first positive electrode active material represented by the following chemical formula 1 and a second positive electrode active material represented by the following chemical formula 2.

[0015] [Chemical Formula 1]

[0016] Li 1+a1 Ni x1 Co y1 Mn z1 Al w1 M 1 v1 O2

[0017] In the above chemical formula 1,

[0018] 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,

[0019] M 1is a doping 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,

[0020] [Chemical Formula 2]

[0021] Li 1+a2 Ni x2 Co y2 Mn z2 Al w2 M 2 v2 O2

[0022] In the above chemical formula 2,

[0023] 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,

[0024] M 2 is a doping 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.

[0025] In one embodiment, the average particle diameter (D) of the first positive electrode active material 50 ) may be 6 ㎛ to 12 ㎛.

[0026] In one embodiment, the average particle diameter (D) of the second positive electrode active material 50 ) may be 1.5 ㎛ to 5 ㎛.

[0027] In one embodiment, the first positive electrode active material and the second positive electrode active material may be included in a weight ratio of 80:20 to 40:60.

[0028] In one embodiment, the positive electrode active material may be obtained by mixing the positive electrode active material in distilled water, washing it, and then drying it.

[0029] The present invention also relates to a lithium secondary battery comprising a positive electrode active material, a negative electrode, and an electrolyte, wherein the resistance component ratio defined by the following formula 1 is 2 or more.

[0030] [Formula 1]

[0031] R ct / R s

[0032] In the above formula, the R ct means the charge transfer resistance of the positive electrode measured in the first frequency range for the lithium secondary battery, and the R s refers to the surface or interface resistance of the positive electrode measured in the second frequency range for the lithium secondary battery, wherein the first frequency range is a frequency range of 1 Hz or more and 1 kHz or less, and the second frequency range is a frequency range of more than 1 kHz and 1,000 kHz or less.

[0033] In one embodiment, the R ct The impedance information obtained by performing electrochemical impedance spectroscopy (EIS) on the lithium secondary battery is analyzed by distribution of relaxation time (DRT) to generate an impedance graph according to frequency, and the first region corresponding to the first frequency region of the graph is integrated to determine the value based on the obtained value, and the R s It may be determined based on a value obtained by performing an electrochemical impedance analysis on the secondary battery, performing a relaxation time distribution analysis on the impedance information, generating an impedance graph according to frequency, and integrating a second area corresponding to the second frequency area of ​​the graph.

[0034] In one embodiment, the negative electrode includes a negative current collector; and a negative electrode active material layer including a negative electrode active material; wherein the negative electrode active material may include at least one of a silicon-based negative electrode active material and a carbon-based negative electrode active material.

[0035] In one embodiment, the silicon-based negative electrode active material may be included in an amount of 1 wt% to 30 wt% based on the total weight of the negative electrode active material layer.

[0036] In one embodiment, the negative electrode may include the silicon-based negative electrode active material and the carbon-based negative electrode active material, and the silicon-based negative electrode active material and the carbon-based negative electrode active material may be included in a weight ratio of 1:99 to 30:70.

[0037] In addition, the present invention relates to a method for manufacturing a positive electrode, comprising the steps of: (A) mixing a positive electrode active material in distilled water and washing it; (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.

[0038] In one embodiment, the step (A) comprises: (a1) a step of mixing a first positive electrode active material in distilled water and performing a first washing; and (a2) a step of mixing a second positive electrode active material in distilled water and performing a second washing; wherein the first positive electrode active material and the second positive electrode active material have an average particle diameter (D 50 ) may be different from each other.

[0039] In one embodiment, the first washing step may be performed at a higher temperature than the second washing step.

[0040] In one embodiment, the first washing step may be performed at 20° C. to 40° C.

[0041] In one embodiment, the second washing step may be performed at 3° C. to 18° C.

[0042] In one embodiment, the first washing step may be performed by mixing the first positive electrode active material in an amount of 50 wt% to 70 wt% based on the total weight of the distilled water.

[0043] In one embodiment, the second washing step may be performed by mixing the second positive electrode active material in an amount of 65 wt% to 85 wt% based on the total weight of the distilled water.

[0044] The present invention can provide a lithium secondary battery with improved lifespan and / or performance by identifying and extracting performance factors of a lithium secondary battery and analyzing and controlling the same.

[0045] The present invention utilizes electrochemical impedance spectroscopy (EIS), which is a non-destructive measurement method, and performs a distribution of relaxation time (DRT) analysis to obtain a result as an impedance graph according to frequency, thereby extracting and analyzing the resistance characteristics of a positive electrode and / or negative electrode related to the deterioration of a lithium secondary battery, thereby improving the performance and / or life characteristics without affecting the components and performance of the lithium secondary battery.

[0046] In particular, since the state of the positive electrode and / or negative electrode among the performance factors of a lithium secondary battery can be individually analyzed and specifically diagnosed, the performance and life characteristics of a lithium secondary battery manufactured including the positive electrode can be improved by indirectly controlling the reaction amount of the negative electrode by controlling the resistance characteristic parameter of the positive electrode.

[0047] Figure 1 is a diagram showing an impedance graph according to the frequency of the anode of Example 1 according to Experimental Example 1 of the present invention.

[0048] Figure 2 is a diagram showing an impedance graph according to the frequency of the anode of Comparative Example 1 according to Experimental Example 1 of the present invention.

[0049] Figure 3 is a diagram showing an impedance graph according to the frequency of the anode of Comparative Example 2 according to Experimental Example 1 of the present invention.

[0050] Figure 4 is a diagram showing the results of evaluating the room temperature life characteristics of lithium secondary batteries of Example 1 and Comparative Examples 1 and 2 according to Experimental Example 2 of the present invention.

[0051] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0052] Therefore, the configuration of the embodiments described in this specification is only one of the most preferred embodiments of the present invention and does not represent all of the technical ideas of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist that can replace them at the time of filing this application. In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0053] When a part in this specification is said to “comprise” a certain component, this does not exclude other components unless specifically stated to the contrary, but rather means that other components may be included. Thus, for example, a composition comprising compound A may include compounds other than A. However, the term “comprise” also encompasses, as a specific embodiment thereof, the more restrictive meanings of “consisting essentially / essentially of” and “consisting of,” so that, for example, “a composition comprising compound A” may also consist (essentially / essentially) of compound A.

[0054] In this connection, it should be understood that terms such as “have” or “have” as used herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0055] When it is said in this specification that any layer is located “on” or “between” any other layer, this includes not only cases where any layer is in contact with any other layer, but also cases where another layer or material, etc., exists between the two layers.

[0056] Where an amount, concentration, or other value or parameter is given herein as a range, a preferred range, or an enumeration of an upper preferred value and a lower preferred value, this should be understood to specifically disclose any range that can be formed by any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether the range is separately disclosed. Where a range of numerical values ​​is recited herein, unless otherwise stated, e.g., there is no limiting term such as greater than, less than, etc., the range is intended to include the endpoint values ​​and all integers and fractions within the range. The scope of the present invention is not intended to be limited to the specific values ​​recited when defining a range.

[0057] Among the properties mentioned in this specification, if the measurement temperature affects the property, the property is measured at room temperature unless otherwise specified. The term "room temperature" refers to the natural temperature without heating or cooling, and may mean, for example, any temperature within the range of about 10°C to 30°C, or about 23°C or about 25°C. In addition, unless otherwise specified, the unit of temperature in this specification is ℃.

[0058] In addition, among the properties mentioned in this specification, if the measurement pressure affects the property, the property is measured at normal pressure, i.e., atmospheric pressure (approximately 1 atm), unless otherwise specified.

[0059] In this specification, “single particle” means a particle composed of 30 or fewer nodules, and is a concept that includes single particles and pseudo-single particles. “Single particle” means a particle composed of one single nodule, and “pseudo-single particle” means a particle that is a composite formed of 30 or fewer nodules.

[0060] In this specification, “nodule” means a particle unit body constituting a single particle and a pseudo-single particle, and the nodule may be a single crystal lacking a crystalline grain boundary, or a polycrystal without a grain boundary when observed under a scanning electron microscope (SEM) at a magnification of 5,000 to 20,000 times.

[0061] The term “particle” as used herein may include at least one of a single particle, a quasi-single particle, a primary particle, a nodule, and a secondary particle, or may include two or more of them, or may include all of them.

[0062] In this specification, “average particle diameter D 50" refers to the particle size at 50% of the volume cumulative particle size distribution of the positive electrode active material powder, and can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then calculating the particle size corresponding to 50% of the volume cumulative amount.

[0063] The present invention relates to a positive electrode.

[0064] The above positive electrode includes a positive electrode active material, and may have a resistance component ratio defined by the following equation 1 of 2 or more.

[0065] [Formula 1]

[0066] R ct / R s

[0067] The above R ct may refer to the charge transfer resistance of the positive electrode measured in the first frequency range for a secondary battery including the positive electrode.

[0068] The above R s may refer to the surface or interface resistance of the positive electrode measured in the second frequency range for a secondary battery including the positive electrode.

[0069] The above first frequency range may be a frequency range of 1 Hz or more and 1 kHz or less.

[0070] The above second frequency range may be a frequency range exceeding 1 kHz and less than or equal to 1,000 kHz.

[0071] The above R ctThe impedance information obtained by performing electrochemical impedance spectroscopy (EIS) on the secondary battery is analyzed by distribution of relaxation time (DRT) to generate an impedance graph according to frequency, and the impedance can be determined based on a value obtained by integrating a first region corresponding to the first frequency region of the graph.

[0072] The above R s It may be determined based on a value obtained by performing an electrochemical impedance analysis on the secondary battery, performing a relaxation time distribution analysis on the impedance information, generating an impedance graph according to frequency, and integrating a second area corresponding to the second frequency area of ​​the graph.

[0073] Previously, since HPPC was used to evaluate the state of lithium secondary batteries, only the evaluation of battery performance was possible, and analysis of each specific component was difficult. However, according to the present invention, through an analysis method completed using electrochemical impedance analysis (EIS) and distribution relaxation time (DRT) analysis, the resistance factors of individual components of the battery (e.g., positive electrode and / or negative electrode, etc.) that have a major influence on performance are analyzed, and the state of individual components (positive electrode and / or negative electrode, etc.) is evaluated from the analysis, ultimately improving the performance of the lithium secondary battery.

[0074] Resistance component ratio R expressed by the above formula 1 ct / R s The value can be 2 or greater, specifically 2 or greater and 8 or less, and more specifically 2 or greater and 6 or less. As above, the resistance component ratio R ct / R s When the value is 2 or more, there is an effect of improving the life characteristics of the lithium secondary battery. In particular, the resistance component ratio Rct / R s When the value is 2 or more, the room temperature cycle life characteristics can be improved in lithium secondary batteries using silicon-based and graphite mixed negative electrodes.

[0075] The above resistance component ratio R ct / R s When the value is less than 2, a steep decline in charge / discharge capacity may occur due to rapid degradation of the SiO / graphite cathode as the cycle progresses, and R ct / R s If the value exceeds 8, rapid charging performance may deteriorate and / or capacity may decrease due to increased resistance.

[0076] The above R ct and / or R s The resistance component of the lithium secondary battery increases in value according to the number of cycles, but the resistance component ratio R is constant regardless of the change in the number of cycles. ct / R s The value can satisfy the above range.

[0077] The above R ct / R s The value may satisfy a range of 2 or more, for example, a range of 2 to 8, or a range of 2 to 6, as measured after 200 cycles of a lithium secondary battery.

[0078] As one embodiment of the present invention, by specifically controlling the ratio of the charge transfer resistance value of the positive electrode and the resistance value at the surface or interface, the reaction amount of the negative electrode can be indirectly controlled to prevent battery degradation and improve the performance, including the life characteristics, of the lithium secondary battery.

[0079] The above resistance component ratio R ct / R sThe resistance component ratio can be adjusted depending on the type of material included in the positive electrode, the content ratio of the material, and / or the manufacturing conditions. Specifically, the resistance component ratio can be adjusted depending on the transition metal composition of the positive electrode active material included in the positive electrode, the type of doping element, the average particle size of the positive electrode active material, the sintering conditions or washing conditions during manufacturing, etc., and when different types of positive electrode active materials are included in the positive electrode, it can vary depending on the mixing ratio therebetween. In addition, the resistance component ratio can be adjusted depending on the type of conductive material included in the positive electrode, the type of binder, and can be adjusted depending on the mixing ratio of the positive electrode active material, conductive material, and binder, the thickness of the positive electrode active material layer, the manufacturing conditions of the positive electrode, etc. The conditions for adjusting the resistance component ratio to a certain level can be easily adjusted to a desired resistance component ratio by referring to the examples and comparative examples of the present invention rather than being uniformly defined.

[0080] The above positive electrode active material has an average particle diameter (D 50 ) may include different first positive electrode active materials and second positive electrode active materials.

[0081] The average particle diameter (D) of the first positive electrode active material 50 ) is the average particle diameter (D) of the second positive electrode active material. 50 ) may be larger.

[0082] The above positive electrode active material may include a first positive electrode active material represented by the following chemical formula 1 and a second positive electrode active material represented by the following chemical formula 2.

[0083] [Chemical Formula 1]

[0084] Li 1+a1 Ni x1 Co y1 Mn z1 Al w1 M 1 v1 O2

[0085] In the above chemical formula 1,

[0086] 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,

[0087] M 1 is a doping 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,

[0088] [Chemical Formula 2]

[0089] Li 1+a2 Ni x2 Co y2 Mn z2 Al w2 M 2 v2 O2

[0090] In the above chemical formula 2,

[0091] 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,

[0092] M 2 is a doping 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.

[0093] The first positive electrode active material may include a ternary lithium transition metal oxide including nickel (Ni), cobalt (Co), and manganese (Mn). In addition, the first positive electrode active material may include a quaternary lithium transition metal oxide including an element such as aluminum (Al) in addition to nickel, cobalt, and manganese. In addition, the first positive electrode active material may include M in addition to aluminum (Al). 1 It can contain M as a doping element, or together with aluminum (Al). 1 It can also be included as a doping element.

[0094] The first cathode active material including the above ternary lithium transition metal oxide is aluminum (Al) and / or M 1 When a doping element such as is further included, structural stability or electrochemical stability can be achieved, so that cation mixing can be suppressed during charge and discharge, thereby improving stability and / or capacity characteristics at high potentials.

[0095] In the above chemical formula 1, the M 1 may be one or more doping elements selected from the group consisting of, for example, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb.

[0096] The above 1+a1 may refer to the molar ratio of lithium (Li) in the first positive electrode active material of the above chemical formula 1, and may be 0≤a1≤0.3, preferably 0≤a1≤0.2, more preferably 0≤a1≤0.15, and even more preferably 0≤a1≤0.1. If the above a1 is less than 0, there is a concern that the capacity may be reduced, and if it exceeds 0.3, the particles may be sintered during the sintering process, making it difficult to manufacture the first positive electrode active material. Therefore, when the above range is satisfied, a balance between the remarkable effect of improving the capacity characteristics of the first positive electrode active material according to the Li content control and / or the sinterability during the manufacture of the first positive electrode active material can be achieved.

[0097] The above x1 may refer to the molar ratio of nickel among the total metal excluding 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. In addition, the above x1 may be specifically 0.6≤x1<1.0, and more specifically 0.7≤x1<1.0, or 0.8≤x1<1.0, 0.85≤x1<1.0, or 0.9≤x1<1.0. When the above range is satisfied, a nickel content sufficient to contribute to charge and discharge in the first positive electrode active material is secured, thereby promoting high capacity.

[0098] The above y1 may mean the molar ratio of cobalt (Co) among the total metals excluding 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, and even more preferably 0.05≤y1≤0.10. Or 0 <y1≤0.2, 구체적으로는 0<y1≤0.18, 또는 0<y1≤0.15 일 수 있다. 상기 y1이 상기 범위를 만족할 경우, 코발트를 적은 함량으로 포함하여 비용적인 이점을 가지면서도 양호한 저항 특성 및 출력 특성을 구현할 수 있다.

[0099] The above z1 may refer to the molar ratio of manganese (Mn) among the total metals excluding 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, and even more preferably 0.03≤z1≤0.10. Or 0 <z1≤0.2, 구체적으로는 0<z1≤0.18, 또는 0<z1≤0.15 일 수 있다. 상기 z1이 상기 범위를 만족할 경우, 제1 양극 활물질의 구조적 안정성을 향상시킬 수 있다.

[0100] The above w1 may mean the molar ratio of aluminum (Al) among the total metals excluding 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, and even more preferably 0.03≤w1≤0.10. Or 0 <w1≤0.2, 구체적으로는 0<w1≤0.18, 또는 0<w1≤0.15 일 수 있다. 상기 범위를 만족할 경우, 산소와의 높은 결합력으로 인하여 제1 양극 활물질의 열적 안정성을 향상시킬 수 있다.

[0101] The above v1 is M of the total metal excluding lithium in the first positive electrode active material. 1 It may mean the molar ratio of 0≤v1≤0.1, preferably 0≤v1≤0.08, more preferably 0≤v1≤0.05.

[0102] In the above chemical formula 2, the M 2 may be one or more doping elements selected from the group consisting of, for example, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb.

[0103] The above 1+a2 may refer to the molar ratio of lithium (Li) in the second positive electrode active material of the above chemical formula 2, and may be 0≤a2≤0.3, preferably 0≤a2≤0.2, more preferably 0≤a2≤0.15, and even more preferably 0≤a2≤0.1. If the above a2 is less than 0, there is a concern that the capacity may be reduced, and if it exceeds 0.3, the particles may be sintered during the sintering process, making it difficult to manufacture the second positive electrode active material. Therefore, when the above range is satisfied, a balance between the remarkable effect of improving the capacity characteristics of the second positive electrode active material according to the Li content control and / or the sinterability during the manufacture of the second positive electrode active material can be achieved.

[0104] The above x2 may refer to the molar ratio of nickel (Ni) among the total metals excluding 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. In addition, the above x2 may be specifically 0.6≤x2<1.0, and more specifically 0.7≤x2<1.0, or 0.8≤x2<1.0, 0.85≤x2<1.0, or 0.9≤x2<1.0. When the above range is satisfied, a nickel content sufficient to contribute to charge and discharge in the second positive electrode active material is secured, thereby promoting high capacity.

[0105] The above y2 may mean the molar ratio of cobalt (Co) among the total metals excluding 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. Or 0 <y2≤0.2, 구체적으로는 0<y2≤0.18, 또는 0<y2≤0.15 일 수 있다. 상기 y2가 상기 범위를 만족할 경우, 코발트를 적은 함량으로 포함하여 비용적인 이점을 가지면서도 양호한 저항 특성 및 출력 특성을 구현할 수 있다.

[0106] The above z2 may refer to the molar ratio of manganese (Mn) among the total metals excluding 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, and even more preferably 0.03≤z2≤0.10. Or 0 <z2≤0.2, 구체적으로는 0<z2≤0.18, 또는 0<z2≤0.15 일 수 있다. 상기 z2가 상기 범위를 만족할 경우, 제2 양극 활물질의 구조적 안정성을 향상시킬 수 있다.

[0107] The above w2 may refer to the molar ratio of aluminum (Al) among the total metals excluding 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, and even more preferably 0.03≤w1≤0.10. Or 0 <w2≤0.2, 구체적으로는 0<w2≤0.18, 또는 0<w2≤0.15 일 수 있다. 상기 범위를 만족할 경우, 산소와의 높은 결합력으로 인하여 제2 양극 활물질의 열적 안정성을 향상시킬 수 있다.

[0108] The above v2 is M among all metals excluding lithium in the second positive electrode active material. 2 It may mean the molar ratio of 0≤v2≤0.1, preferably 0≤v2≤0.08, more preferably 0≤v2≤0.05.

[0109] The above first positive electrode active material has an average particle diameter (D 50 ) can be selected in a larger range than the second positive electrode active material. Accordingly, when the electrode is rolled, the second positive electrode active material with a small particle size is filled in the pores of the first positive electrode active material with a large particle size, thereby increasing the electrode density and realizing a high energy density, thereby achieving high capacity characteristics. Furthermore, in the case of using two types of positive electrode active materials with different average particle sizes as described above, R ct / R s The performance and / or life of a lithium secondary battery can be improved by satisfying the values.

[0110] For example, the average particle diameter (D) of the first positive electrode active material 50 ) may be 6 ㎛ to 12 ㎛, and the average particle diameter (D) of the second positive electrode active material 50 ) may be 1.5 ㎛ to 5 ㎛.

[0111] Specifically, the average particle diameter of the first positive electrode active material may be 6 ㎛ or more, 6.2 ㎛ or more, 6.4 ㎛ or more, 6.6 ㎛ or more, 6.8 ㎛ or more, 7 ㎛ or more, 7.2 ㎛ or more, 7.4 ㎛ or more, 7.6 ㎛ or more, 7.8 ㎛ or more, 8 ㎛ or more, 8.2 ㎛ or more, 8.4 ㎛ or more, 12 ㎛ or less, 11.8 ㎛ or less, 11.6 ㎛ or less, 11.4 ㎛ or less, 11.2 ㎛ or less, 11 ㎛ or less, 10.8 ㎛ or less, 10.6 ㎛ or less, 10.4 ㎛ or less, 10.2 ㎛ or less, 10 ㎛ or less, 9.8 ㎛ or less, 9.6 ㎛ or less, 9.4 ㎛ or less, 9.2 ㎛ or less, 9 ㎛ Below, it may be 8.8 ㎛ or less, or 8.6 ㎛ or less. For example, the average particle diameter of the first positive electrode active material may be 6 ㎛ to 12 ㎛, preferably 7.4 ㎛ to 11 ㎛, more preferably 8 ㎛ to 9.6 ㎛, and even more preferably 8.2 ㎛ to 9 ㎛. When the above range is satisfied, the rolling density of the positive electrode active material can be increased, and thus the electrode density is improved during electrode manufacturing, so that excellent energy density can be realized.

[0112] Specifically, the average particle diameter of the second positive electrode active material may 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, 3 µm or more, and 5 µm or less, 4.8 µm or less, 4.6 µm or less, 4.4 µm or less, 4.2 µm or less, 4 µm or less, 3.8 µm or less, 3.6 µm or less, 3.4 µm or less, 3.2 µm or less. For example, the average particle diameter of the second positive electrode active material may be 1.5 μm to 5 μm, preferably 2 μm to 4.5 μm, more preferably 2.6 μm to 4.2 μm, even more preferably 3 μm to 4 μm, and even more preferably 3 μm to 3.4 μm. When the above range is satisfied, the rolling density of the positive electrode active material can be increased, and thus the electrode density is improved during electrode manufacturing, thereby realizing excellent energy density.

[0113] The above first positive electrode active material may be included in an amount of 20 wt% to 80 wt%, preferably 30 wt% to 70 wt%, and more preferably 40 wt% to 60 wt%, based on the total weight of the positive electrode active material. When the above range is satisfied, the rolling density can be improved, thereby realizing high energy density.

[0114] The second positive electrode active material may be included in an amount of 20 wt% to 80 wt%, preferably 30 wt% to 70 wt%, and more preferably 40 wt% to 60 wt%, based on the total weight of the positive electrode active material. When the above range is satisfied, the rolling density can be improved, thereby realizing high energy density.

[0115] The first positive electrode active material and the second positive electrode active material may be included in a weight ratio of 80:20 to 40:60. Specifically, the first positive electrode active material and the second positive electrode active material may be included in a weight ratio of 75:25 to 45:55, more specifically, 70:30 to 50:50, and even more specifically, 65:45 to 55:45. When the above weight ratio is satisfied, the effect of improving high temperature and room temperature life characteristics and / or resistance characteristics can be maximized while improving energy density.

[0116] The positive electrode may contain the first positive electrode active material in a greater weight than the second positive electrode active material.

[0117] The first positive electrode active material may include single-particle particles. When the first positive electrode active material includes single-particle particles, since the single-particle particle size is large, the diffusion distance of lithium is long, which increases the diffusion resistance, so that the positive electrode may have low efficiency. Therefore, when the negative electrode includes a silicon-based negative electrode active material, the efficiency can be balanced with the negative electrode. Accordingly, the problem of lithium ion loss due to irreversible capacity when applying a conventional silicon-based negative electrode active material can be solved, and the lithium precipitation phenomenon on the surface of the negative electrode can be prevented, so that the life characteristics of a lithium secondary battery applying the positive electrode according to the present invention can be improved. In addition, when the first positive electrode active material includes single-particle particles, unlike when using a conventional sacrificial positive electrode material, the generation of lithium byproducts due to the sacrificial positive electrode material during charge and discharge can be prevented, so that high-temperature storage characteristics and / or high-temperature life characteristics can be excellent.

[0118] The second positive electrode active material may include single-particle particles. When the second positive electrode active material includes single-particle particles, since the single-particle particle size is large, the diffusion distance of lithium is long, which increases the diffusion resistance, so that the positive electrode may have low efficiency. However, when a silicon-based negative electrode active material is included, the efficiency can be balanced with the negative electrode. Accordingly, the problem of lithium ion loss due to irreversible capacity when applying a conventional silicon-based negative electrode active material can be solved, and the lithium precipitation phenomenon on the surface of the negative electrode can be prevented, so that the life characteristics of a lithium secondary battery applying the positive electrode according to the present invention can be improved. In addition, when the second positive electrode active material includes single-particle particles, unlike when using a conventional sacrificial positive electrode material, the generation of lithium byproducts due to the sacrificial positive electrode material during charge and discharge can be prevented, so that high-temperature storage characteristics and / or high-temperature life characteristics can be excellent.

[0119] The above positive electrode active material may be obtained by mixing the positive electrode active material in distilled water, washing it, and then drying it. In the case of undergoing the above washing treatment, the positive electrode of the present invention is R ct / R s It has the effect of preventing deterioration of the negative electrode by satisfying the value, or can improve the life of a lithium secondary battery.

[0120] The above positive electrode active material may be obtained by mixing a transition metal precursor and a lithium precursor by a method such as co-precipitation when manufacturing the positive electrode active material, and then washing the positive electrode active material with distilled water before drying.

[0121] When the above-mentioned positive electrode active material includes the first positive electrode active material and the second positive electrode active material, the first positive electrode active material and the second positive electrode active material may have undergone the above-mentioned washing treatment. In this case, the washing treatment of the first positive electrode active material and the second positive electrode active material may be performed under the same conditions and in the same manner, or may be performed under different conditions and in different manners, but is not limited thereto.

[0122] The positive electrode may include a positive electrode current collector and a positive electrode active material layer including the positive electrode active material described above. In addition to the positive electrode active material described above, the positive electrode active material layer may optionally further include at least one selected from a positive electrode conductive material, a positive electrode binder, and an additive. When the positive electrode active material includes a first positive electrode active material and a second positive electrode active material, the positive electrode active material layer may optionally further include at least one selected from a positive electrode conductive material, a positive electrode binder, and an additive, in addition to the first positive electrode active material and the second positive electrode active material.

[0123] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and may be made 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 an alloy thereof.

[0124] The above-mentioned positive electrode current collector may have a thickness of 3 μm to 500 μm, and may form fine irregularities on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc. The above-mentioned positive electrode current collector may be omitted in some cases.

[0125] The positive electrode active material layer may be positioned on the positive electrode current collector, and specifically, may be positioned on one or both sides of the positive electrode current collector. The positive electrode active material layer may have a single layer or a multilayer structure of two or more layers. In addition, fine irregularities may be formed on the surface of the positive electrode current collector to strengthen the bonding strength of the positive electrode active material.

[0126] The above-mentioned positive electrode conductive material is used to provide conductivity to the electrode, and can be used without special restrictions as long as it does not cause chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotube; 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, and the like. One of these may be used alone or a mixture of two or more may be used. The positive electrode conductive material may typically be included in an amount of 1 wt% to 30 wt%, specifically 1 wt% to 20 wt%, and more specifically 1 wt% to 10 wt%, based on the total weight of the positive electrode active material layer.

[0127] The above-mentioned positive electrode binder serves 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 thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol (PVA), polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone (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 of these may be used alone or a mixture of two or more thereof. The positive electrode binder may be included in an amount of 1 wt% to 30 wt%, specifically 1 wt% to 20 wt%, and more specifically 1 wt% to 10 wt%, based on the total weight of the positive electrode active material layer.

[0128] The above additives may further include additives such as fillers, coating agents, dispersants, thickeners, and ion conductivity aids, and any known material generally used in electrodes may be used without limitation.

[0129] The positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material is used. The positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer including the positive electrode active material to one or both sides of a positive electrode current collector, removing the solvent through a drying process, and then rolling. Meanwhile, a positive electrode including a non-coated region can be manufactured by not applying the composition for forming a positive electrode active material layer to a part of the positive electrode current collector, for example, to one end of the positive electrode current collector, when applying the composition for forming a positive electrode active material layer.

[0130] At this time, the composition for forming the positive electrode active material layer may further include a solvent, and the solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these may be used alone or as a mixture of two or more. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, etc., taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0131] The above positive electrode can also be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the resulting film on a positive electrode current collector by peeling it off from the support.

[0132] The present invention provides a lithium secondary battery.

[0133] The above lithium secondary battery may include a positive electrode including a positive electrode active material and having a resistance component ratio of 2 or more defined by the following formula 1; a negative electrode; and an electrolyte.

[0134] [Formula 1]

[0135] Rct / R s

[0136] In the above formula, the R ct means the charge transfer resistance of the positive electrode measured in the first frequency range for the lithium secondary battery, and the R s refers to the surface or interface resistance of the positive electrode measured in the second frequency range for the lithium secondary battery, wherein the first frequency range is a frequency range of 1 Hz or more and 1 kHz or less, and the second frequency range is a frequency range of more than 1 kHz and 1,000 kHz or less.

[0137] The above R ct The impedance information obtained by performing electrochemical impedance spectroscopy (EIS) on the lithium secondary battery is analyzed by distribution of relaxation time (DRT) to generate an impedance graph according to frequency, and the R can be determined based on a value obtained by integrating a first region corresponding to the first frequency region of the graph. s It may be determined based on a value obtained by performing an electrochemical impedance analysis on the secondary battery, performing a relaxation time distribution analysis on the impedance information, generating an impedance graph according to frequency, and integrating a second area corresponding to the second frequency area of ​​the graph.

[0138] The above positive electrode, positive electrode active material, R ct and R s The same can be applied to the above.

[0139] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer including a negative electrode active material. The negative electrode active material may include at least one of a silicon-based negative electrode active material and a carbon-based negative electrode active material.

[0140] The above-described negative electrode active material layer may optionally further include at least one selected from a negative electrode conductive material, a negative electrode binder, and an additive in addition to the above-described negative electrode active material.

[0141] The negative electrode active material layer may be positioned on the negative electrode current collector, and specifically, may be positioned on one or both sides of the negative electrode current collector. The negative electrode active material layer may have a single layer or a multilayer structure of two or more layers.

[0142] In another example, the above negative electrode may be an anode for an anodeless battery, which does not include a negative electrode active material layer immediately after battery manufacturing, but in which a negative electrode active material layer, such as a lithium metal layer, is formed through charging.

[0143] The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel (e.g., SUS), aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated or coated with carbon, nickel, titanium, silver, etc., or an aluminum-cadmium alloy, etc. can be used.

[0144] The negative electrode current collector may typically have a thickness of 3 μm to 500 μm, and may have fine irregularities formed on the surface of the negative electrode current collector to enhance the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0145] The above silicon-based negative electrode active material may include silicon (Si), and for example, the above silicon-based negative electrode active material may include particles including silicon (Si).

[0146] Specifically, the silicon-based negative electrode active material is SiO x(0≤x≤2), Si / C composite, Si (pure Si) or a combination thereof. The SiO x (0≤x≤2) may be a form containing Si and SiO2. That is, the x above is the SiO x (0≤x≤2) corresponds to the number ratio of O to Si included in it. Preferably, the silicon-based negative electrode active material is SiO x (0≤x≤2), most preferably SiO.

[0147] When the above-mentioned negative electrode comprises a silicon-based negative electrode active material, it has the advantage of having a much higher charge / discharge capacity than when using only a conventional carbon-based negative electrode active material. However, the silicon-based negative electrode active material has a problem in that its large irreversible capacity reduces the lifespan characteristics of the lithium secondary battery. The lithium secondary battery according to the present invention solves the above-mentioned problem by controlling the resistance component ratio of the positive electrode within a specific range.

[0148] The above negative electrode active material may include a silicon-based negative electrode active material. The above negative electrode active material may further include a carbon-based negative electrode active material.

[0149] The silicon-based negative electrode active material may be included in an amount of 1 wt% to 30 wt%, specifically 1 wt% to 25 wt%, and more specifically 2 wt% to 20 wt%, based on the total weight of the negative electrode active material layer. Alternatively, the silicon-based negative electrode active material may be included in an amount of 1 wt% to 10 wt%, or 5 wt% to 10 wt%, based on the total weight of the negative electrode active material layer. When the content of the silicon-based negative electrode active material satisfies the above range, sufficient capacity characteristics can be realized.

[0150] The above carbon-based negative electrode active material may be at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; and carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotube. When the above carbon-based negative electrode active material is included, the deterioration of the life characteristics due to the volume change of the silicon-based negative electrode active material during charge and discharge can be suppressed.

[0151] When the negative electrode includes the silicon-based negative electrode active material and the carbon-based negative electrode active material, the silicon-based negative electrode active material and the carbon-based negative electrode active material may be included in a weight ratio of 1:99 to 30:70. Specifically, the negative electrode active material may be included in a weight ratio of 1.5:98.5 to 20:80, more specifically, 2:98 to 15:85, and even more specifically, 2.5:97.5 to 10:90. When the weight ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material satisfies the above range, the capacity characteristics may be excellent and the life characteristics may be excellent.

[0152] The carbon-based negative electrode active material may be included in an amount of 70 wt% to 99 wt%, specifically 75 wt% to 99 wt%, and more specifically 80 wt% to 98 wt%, based on the total weight of the negative electrode active material layer. When the amount of the carbon-based negative electrode active material satisfies the above range, the lifespan characteristics of the battery can be improved while implementing sufficient capacity characteristics.

[0153] The above-mentioned negative electrode conductive material is used to provide conductivity to the electrode, and can be used without special restrictions as long as it does not cause chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotube; 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, and the like. One of these may be used alone or a mixture of two or more may be used. The negative electrode conductive material may typically be included in an amount of 1 wt% to 30 wt%, specifically 1 wt% to 20 wt%, and more specifically 1 wt% to 10 wt%, based on the total weight of the negative electrode active material layer.

[0154] The above negative electrode binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol (PVA), polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone (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 of these may be used alone or a mixture of two or more thereof. The above negative electrode binder may be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of the negative electrode active material layer.

[0155] The above additives may further include additives such as fillers, coating agents, dispersants, thickeners, and ion conductivity aids, and any known material generally used in electrodes may be used without limitation.

[0156] The above negative electrode can be manufactured according to a conventional negative electrode manufacturing method, except that the negative electrode active material is used. The negative electrode can be manufactured by applying a composition for forming a negative electrode active material layer containing the negative electrode active material to one or both sides of a negative electrode current collector and drying it, or by casting the composition for forming a negative electrode active material layer on a separate support, and then laminating the resulting film on a negative electrode current collector by peeling it off from the support. The composition for forming a negative electrode active material layer can further include a solvent, and the solvent can be selected from examples of solvents included in the composition for forming a positive electrode active material layer described above.

[0157] In the lithium secondary battery, the electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used in manufacturing a lithium secondary battery.

[0158] The electrolyte may include, for example, an organic solvent and / or a lithium salt.

[0159] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include linear 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 hydrocarbon solvents such as benzene or fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); alcohol solvents such as ethyl alcohol or isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, which may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used.Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable. In this case, the cyclic carbonate and the linear carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9 to simultaneously satisfy the high dielectric constant and low viscosity characteristics and implement excellent ionic conductivity characteristics, so that the performance of the electrolyte can be excellent.

[0160] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0161] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. For example, the above lithium salt can be Li as a cation. + , and the anion is 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 - It may include at least one selected from the group consisting of .

[0162] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10, 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 substance or a mixture of two or more substances 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).

[0163] The concentration of the lithium salt may be included in the electrolyte in a range of 0.1 M to 4 M, specifically, in a range of 0.1 M to 2 M, and more specifically, in a range of 0.8 M to 1.6 M. When the concentration of the lithium salt is included in the above range, the electrolyte may have appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance, and lithium ions may move effectively, thereby improving the output characteristics of the lithium secondary battery.

[0164] The above electrolyte may include a solid electrolyte, and when the solid electrolyte is included, the solid electrolyte may replace the role of the separator, so the separator may not be included.

[0165] The above solid electrolyte may include, but is not limited to, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a phosphoric acid-based solid electrolyte, a polymer-based solid electrolyte, or a halide-based solid electrolyte.

[0166] The above sulfide-based solid electrolyte contains sulfur atoms (S), has ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and may have electronic insulation properties. The above sulfide-based solid electrolyte preferably contains at least Li, S, and P as elements and has lithium ion conductivity, but may contain other elements other than Li, S, and P depending on the purpose or case.

[0167] As specific sulfide-based solid electrolytes, for example, Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-H2S, Li2S-P2S5-H2S-LiCl, Li2S-LiI-P2S5, Li2S-LiI-Li2OP2S5, Li2S-LiBr-P2S5, Li2SLi2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SiS2-LiCl, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, Li2SGa2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S-GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2SSiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-LiI, Li2S-SiS2-Li4SiO4, Li2SSiS2-Li3PO4, or Li 10 GeP2S 12 etc. can be used.

[0168] As the above oxide-based solid electrolyte, for example, Li xa La ya TiO3 [xa=0.3~0.7, ya=0.3~0.7](LLTO), Li xb La yb Zr zb Mbb mb O nb(Mbb is at least one element among 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 at least one element among C, S, Al, Si, Ga, Ge, In, and Sn, 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 P md 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 number greater than or equal to 0 and less than or equal to 0.1, Mee represents a divalent metal atom, Dee represents a halogen atom or a combination of two or more 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 (w is w<1), Li with LISICON (Lithium super ionic conductor) type crystal structure 3.5 Zn 0.25 GeO4, La with perovskite crystal structure 0.55Li 0.35 LiTi2P3O with TiO3, NASICON (Sodium(Na) super ionic conductor) 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), Li7La3Zr2O having a garnet-type crystal structure 12 (LLZO), etc. Alternatively, phosphorus compounds containing Li, P, and O may also be used. Examples thereof include lithium phosphate (Li3PO4), LiPON, LiPOD1 (wherein D1 is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, and Au), etc., in which some of the oxygen of lithium phosphate is replaced with nitrogen. Alternatively, LiA1ON (wherein A1 is at least one selected from Si, B, Ge, Al, C, and Ga), etc., may also be used.

[0169] The above polymer-based solid electrolyte is an ion-conducting material, and includes, but is not particularly limited to, a polymer material typically used as a solid electrolyte material for an all-solid-state battery. The polymer-based solid electrolyte may include, for example, a polyether-based polymer, a polycarbonate-based polymer, an acrylate-based polymer, a polysiloxane-based polymer, a phosphazene-based polymer, polyethylene oxide (PEO), a polyethylene derivative, an alkylene oxide derivative, a phosphoric acid ester polymer, polyazation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, or a polymer containing an ionic dissociation group. Alternatively, the polymer-based solid electrolyte may include, as a polymer resin, a branched copolymer, a comb-like polymer, or a cross-linked polymer resin, in which an amorphous polymer such as polymethyl methacrylate (PMMA), polycarbonate, polysiloxane, and / or phosphazene is copolymerized as a comonomer into a polyethyleneoxide (PEO) main chain.

[0170] The above solid electrolyte may include a gel-type polymer electrolyte. The gel-type polymer electrolyte includes an organic electrolyte containing a lithium salt and a polymer resin, and the organic electrolyte is included in an amount of 60 to 400 parts by weight based on 100 parts by weight of the polymer resin. The polymer resin applied to the gel-type polymer electrolyte is not limited to a specific component, but may include, for example, polyvinylchloride (PVC), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), or polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0171] The above lithium secondary battery may optionally further include a separator.

[0172] Meanwhile, when the electrolyte includes the aforementioned solid electrolyte, the lithium secondary battery may not include a separate separator since the solid electrolyte serves as a separator, but is not limited thereto.

[0173] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, if it is used as a separator in a lithium secondary battery, it can be used without any special restrictions, and in particular, it is preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure. The separator may be omitted in some cases.

[0174] The present invention provides a method for manufacturing a positive electrode.

[0175] The method for manufacturing the positive electrode may include: (A) a step of mixing a positive electrode active material in distilled water and washing it; (B) a step of drying the washed positive electrode active material; and (C) a step of applying a positive electrode slurry containing the dried positive electrode active material onto a positive electrode current collector.

[0176] In the above step (A), the washing may be performed at a temperature of 3° C. to 40° C. The step (A) may include: (a1) a step of mixing the first positive electrode active material in distilled water and performing the first washing; and (a2) a step of mixing the second positive electrode active material in distilled water and performing the second washing. As a result, the resistance component of the positive electrode can be controlled within a specific range, and the positive electrode of the present invention has R ct / R s The performance of lithium secondary batteries can be improved by satisfying the values.

[0177] The above first positive electrode active material and the above second positive electrode active material have an average particle diameter (D 50 ) may be different from each other.

[0178] In the above step (a1), the washing intensity of the first positive electrode active material may be performed at a higher temperature than that of the second positive electrode active material in the above step (a2). That is, the first washing step may be performed at a higher temperature than the second washing step. This allows the resistance component of the positive electrode to be controlled within a specific range.

[0179] The above first washing step may be performed at a temperature of 20°C to 40°C. Specifically, it may be performed at a temperature of 25°C to 35°C, more specifically, at a temperature of 27°C to 38°C. When the first washing is performed in the above temperature range, the interface resistance of the anode can be controlled to a desired range.

[0180] In the above step (a1), the first washing step may be performed by mixing the first positive electrode active material in an amount of 50 wt% to 70 wt% based on the total weight of distilled water. Specifically, it may be performed by mixing in an amount of 55 wt% to 65 wt%, and more specifically, 57 wt% to 63 wt%. In this case, the amount of residual lithium on the surface of the positive electrode active material may be reduced, thereby preventing deterioration of high-temperature durability.

[0181] In the above 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 performing the washing intensity of the second positive electrode active material at a low level, the high-temperature durability deterioration of the second positive electrode active material can be prevented, and the resistance component of the positive electrode can be controlled within a specific range.

[0182] The above second washing step can be performed at a temperature of 3°C to 18°C. Specifically, it can be performed at a temperature of 5°C to 15°C, and more specifically, at a temperature of 7°C to 13°C. When the second washing is performed within the above temperature range, the resistance component of the anode can be controlled within the desired range while preventing deterioration of high-temperature durability.

[0183] In the above step (a2), the second washing step may be performed by mixing the second positive electrode active material in an amount of 65 wt% to 85 wt% based on the total weight of distilled water. Specifically, it may be performed by mixing in an amount of 70 wt% to 80 wt%, and more specifically, 72 wt% to 78 wt%. In this case, residual lithium on the surface of the positive electrode active material can be reduced, thereby preventing deterioration of high-temperature durability.

[0184] The drying step of the above step (B) may be performed at a temperature range selected from 60°C to 200°C. Specifically, the drying step may be performed at a temperature range selected from 70°C to 180°C, more specifically, 80°C to 160°C.

[0185] That is, the step (B) may include a step of drying the washed positive electrode active material at a temperature range selected from 60°C to 200°C. The drying method may be any method for drying a positive electrode active material, and is not particularly limited.

[0186] The above step (B) may include: (b1) a step of drying the first positive electrode active material washed in the first step (a1); and (b2) a step of drying the second positive electrode active material washed in the second step (a2).

[0187] The drying step in the above steps (b1) and (b2) may be performed at a temperature range selected from 60°C to 200°C.

[0188] The above drying step can be performed at a temperature range selected specifically from 70°C to 180°C, more specifically from 80°C to 160°C.

[0189] The drying steps in the above steps (b1) and (b2) may be performed at the same temperature within the above range, or may be performed at different temperatures.

[0190] The above step (C) is a step of applying a positive electrode slurry containing the above-described dry positive electrode active material onto a positive electrode current collector, and includes a step of preparing a positive electrode slurry by mixing the positive electrode active material into a solvent before applying the positive electrode slurry onto the positive electrode current collector.

[0191] At this time, the positive electrode active material may include the first positive electrode active material and the second positive electrode active material, and the above-described description may be equally applied to the first positive electrode active material and the second positive electrode active material.

[0192] The above positive electrode slurry may further include a positive electrode binder, a positive electrode conductive material and / or an additive, and the above-described description may be equally applied to the positive electrode binder, positive electrode conductive material and additive.

[0193] The solvent used in the above positive electrode slurry may be identically applied to the description of the solvent included in the composition for forming the positive electrode active material layer described above.

[0194] In the above step (C), the positive electrode slurry can be applied to a positive electrode current collector to form a positive electrode active material layer, thereby manufacturing the positive electrode. Specifically, the positive electrode slurry can be applied to one or both sides of the positive electrode current collector, and then dried and rolled to form a positive electrode active material layer, thereby manufacturing the positive electrode. The positive electrode slurry may be the same as the composition for forming the positive electrode active material layer described above.

[0195] The above application may be performed continuously or discontinuously using various application methods well known in the art, such as slot die coating, slide coating, curtain coating, etc., but is not limited thereto.

[0196] After the above step (C), a step (D) of drying the positive electrode slurry after applying it to the positive electrode current collector may be further included. The drying step in the above step (D) may be performed at a temperature of 40°C to 180°C, specifically 60°C to 160°C, and more specifically 70°C to 150°C. Any drying method can be applied without limitation as long as it is a method for drying an electrode.

[0197] After the above step (D), the step (E) of rolling the dried positive electrode slurry and positive electrode current collector may be further included. The rolling may be performed according to a roll press method in which the positive electrode thickness is adjusted by adjusting the upper / lower gap of the rolls, but is not limited thereto.

[0198] The present invention provides a method for manufacturing a cathode.

[0199] The method for manufacturing the negative electrode may include a step of forming a negative electrode active material layer by applying a negative electrode slurry containing the negative electrode active material to a negative electrode current collector; a step of drying the negative electrode current collector and the negative electrode active material layer; and a step of rolling the dried negative electrode current collector and the negative electrode active material layer.

[0200] The above description can be applied equally to the negative electrode active material and negative electrode current collector.

[0201] The above-described negative electrode slurry may further include a negative electrode binder, a negative electrode conductive material and / or an additive, and the above-described description may be equally applied to the negative electrode binder, negative electrode conductive material and additive.

[0202] The solvent used in the above cathode slurry may be an aqueous solvent, an organic solvent, or a combination thereof.

[0203] The aqueous solvent may include, for example, water, and the organic solvent may include at least one selected from the group consisting of N-methyl pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dihydrolevoglucosenone (Cyrene), γ-valerolactone, dimethyl isosorbide (DMI), and methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate, and preferably N-methyl pyrrolidone.

[0204] The above application may be performed continuously or discontinuously using various application methods well known in the art, such as slot die coating, slide coating, curtain coating, etc., but is not limited thereto.

[0205] The step of drying the negative electrode active material layer and the negative electrode current collector may be performed at a temperature of 40°C to 180°C. Specifically, it may be performed at a temperature of 60°C to 160°C, and more specifically, at a temperature of 70°C to 150°C.

[0206] The above rolling can be performed by a roll press method that adjusts the thickness of the cathode by adjusting the upper / lower gap of the roll, but is not limited thereto.

[0207] The above lithium secondary battery may be pouch-shaped, square-shaped, or cylindrical, and its shape and size may be applied without limitation as long as it is a commonly used secondary battery.

[0208] In addition, the lithium secondary battery may further include a case capable of sealing the electrode assembly, such as a container, pouch, pack, or module that houses the electrode assembly including the positive electrode, electrolyte, and negative electrode. The case may optionally further include a sealing member.

[0209] Hereinafter, the present invention will be described in detail by way of examples to specifically illustrate the disclosure and intended functions and effects of the present invention as described above. However, the examples may be modified in various ways, and the scope of this specification is not construed as being limited to these examples. It is emphasized that the examples are provided to represent the present invention and to provide a more concrete explanation to those skilled in the art.

[0210]

[0211] Example

[0212] <Example 1> - Water treatment

[0213] <Manufacture of the first cathode active material>

[0214] A transition metal aqueous solution was prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in an amount such that the molar ratio of nickel:cobalt:manganese was 83:7:10.

[0215] Next, deionized water is added to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor, and then NaOH is added to carry out a coprecipitation reaction, thereby obtaining an average particle size (D 50) is 8.6 ㎛, and Ni 0.8 Co 0.1 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0216] The above precursor and LiOH were mixed in a ratio of 1:1.05, and Al was mixed as a doping element and calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 ] Lithium transition metal oxide represented by O2 was prepared.

[0217] Then, the lithium transition metal oxide was mixed in distilled water at 30°C to a solid content of 60 wt%, washed, and dried to prepare a first cathode active material. The first cathode active material had an average particle diameter (D 50 ) was confirmed to be 8.6 ㎛ and a single particle.

[0218] <Manufacturing of the second cathode active material>

[0219] A transition metal aqueous solution was prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in an amount such that the molar ratio of nickel:cobalt:manganese was 83:7:10.

[0220] Next, deionized water is added to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor, and then NaOH is added to carry out a coprecipitation reaction, thereby obtaining an average particle size (D 50 ) is 3.1 ㎛, and Ni 0.8 Co 0.1 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0221] The above precursor and LiOH were mixed in a ratio of 1:1.05, and Al was mixed as a doping element and calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02] Lithium transition metal oxide represented by O2 was prepared.

[0222] Then, the lithium transition metal oxide was mixed in distilled water at 10°C with a solid content of 75 wt%, washed, and dried to prepare a second positive electrode active material. The second positive electrode active material had an average particle diameter (D 50 ) was confirmed to be 3.1 ㎛ and a single particle.

[0223] <Cathode manufacturing>

[0224] The first positive electrode active material and the second positive electrode active material manufactured above were mixed in a weight ratio of 60:40 to manufacture a positive electrode material, and the positive electrode material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a weight ratio of 96:2:2 in an N-methylpyrrolidone solvent to manufacture a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector having a thickness of 20 μm, dried at 130°C, and then rolled to manufacture a positive electrode having a thickness of 70 μm.

[0225] <Lithium secondary battery manufacturing>

[0226] A negative electrode slurry was prepared by mixing a negative electrode active material of SiO:artificial graphite in a weight ratio of 5:95, a conductive material of carbon black, a binder of SBR, and a thickener of CMC in a weight ratio of 95.6:1.0:2.3:1.1 in distilled water. The negative electrode slurry was applied to one surface of a 12 ㎛ thick copper current collector, dried at 130°C, and then rolled to prepare a negative electrode (slurry solid content: 50 wt% based on the total weight of the negative electrode slurry).

[0227] An electrode assembly was manufactured by interposing a porous polyethylene separator between each of the positive and negative electrodes manufactured above, and then positioning it inside a battery case, and then injecting an electrolyte to manufacture a lithium secondary battery. At this time, an electrolyte solution was used in which 1.0 M LiPF6 was dissolved in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0228]

[0229] <Comparative Example 1> - Boron coating

[0230] <Manufacture of the first cathode active material>

[0231] A transition metal aqueous solution was prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in an amount such that the molar ratio of nickel:cobalt:manganese was 83:7:10.

[0232] Next, deionized water is added to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor, and then NaOH is added to carry out a coprecipitation reaction, thereby obtaining an average particle size (D 50 ) is 8.6 ㎛, and Ni 0.8 Co 0.1 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0233] The above precursor and LiOH were mixed in a ratio of 1:1.05, and Al was mixed as a doping element and calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 ] Lithium transition metal oxide represented by O2 was prepared.

[0234] Then, a boron precursor was mixed into the lithium transition metal oxide and heat-treated at 750°C for 5 hours to prepare a B-coated first cathode active material. The first cathode active material had an average particle diameter (D 50) was confirmed to be 6 to 12 ㎛ in size and to be a single particle.

[0235] <Manufacturing of the second cathode active material>

[0236] A transition metal aqueous solution was prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in an amount such that the molar ratio of nickel:cobalt:manganese was 83:7:10.

[0237] Next, deionized water is added to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor, and then NaOH is added to carry out a coprecipitation reaction, thereby obtaining an average particle size (D 50 ) is 3.1 ㎛, and Ni 0.8 Co 0.1 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0238] The above precursor and LiOH were mixed in a ratio of 1:1.05, and Al was mixed as a doping element and calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 ] Lithium transition metal oxide represented by O2 was prepared.

[0239] Then, a boron precursor was mixed into the lithium transition metal oxide and heat-treated at 750°C for 5 hours to prepare a B-coated second cathode active material. The second cathode active material had an average particle diameter (D 50 ) was confirmed to be 3.97 ㎛ and a single particle.

[0240] <Cathode manufacturing>

[0241] The first positive electrode active material and the second positive electrode active material manufactured above were mixed in a weight ratio of 60:40 to manufacture a positive electrode material, and the positive electrode material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a weight ratio of 96:2:2 in an N-methylpyrrolidone solvent to manufacture a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector having a thickness of 20 μm, dried at 130°C, and then rolled to manufacture a positive electrode having a thickness of 70 μm.

[0242] <Lithium secondary battery manufacturing>

[0243] A negative electrode slurry was prepared by mixing a negative electrode active material of SiO:artificial graphite in a weight ratio of 6:94, a conductive material of carbon black, a binder of SBR, and a thickener of CMC in a weight ratio of 95.6:1.0:2.3:1.1 in distilled water. The negative electrode slurry was applied to one surface of a 12 μm thick copper current collector, dried at 130°C, and then rolled to prepare a negative electrode (slurry solid content: 50 wt% based on the total weight of the negative electrode slurry).

[0244] An electrode assembly was manufactured by interposing a porous polyethylene separator between each of the positive and negative electrodes manufactured above, and then positioning it inside a battery case, and then injecting an electrolyte to manufacture a lithium secondary battery. At this time, an electrolyte solution was used in which 1.0 M LiPF6 was dissolved in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0245]

[0246] <Comparative Example 2> - Cobalt coating

[0247] <Manufacture of the first cathode active material>

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

[0249] Next, deionized water is added to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor, and then NaOH is added to carry out a coprecipitation reaction, thereby obtaining an average particle size (D 50 ) is 8.6 ㎛, and Ni 0.8 Co 0.1 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0250] The above precursor and LiOH were mixed in a ratio of 1:1.05, and Al was mixed as a doping element and calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 ] Lithium transition metal oxide represented by O2 was prepared.

[0251] Then, Co(OH)2 was mixed with the lithium transition metal oxide and heat-treated at 750°C for 5 hours to prepare a Co-coated first cathode active material. The first cathode active material had an average particle diameter (D 50 ) was confirmed to be 6 to 12 ㎛ in size and to be a single particle.

[0252] <Manufacturing of the second cathode active material>

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

[0254] Next, deionized water is added to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor, and then NaOH is added to carry out a coprecipitation reaction, thereby obtaining an average particle size (D 50 ) is 3.1 ㎛, and Ni 0.8 Co 0.1 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0255] The above precursor and LiOH were mixed in a ratio of 1:1.05, and Al was mixed as a doping element and calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 ] Lithium transition metal oxide represented by O2 was prepared.

[0256] Then, Co(OH)2 was mixed with the lithium transition metal oxide and heat-treated at 750°C for 5 hours to prepare a Co-coated second cathode active material. The second cathode active material had an average particle diameter (D 50 ) was confirmed to be 6.19 ㎛ and a single particle.

[0257] <Cathode manufacturing>

[0258] The first positive electrode active material and the second positive electrode active material manufactured above were mixed in a weight ratio of 60:40 to manufacture a positive electrode material, and the positive electrode material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a weight ratio of 96:2:2 in an N-methylpyrrolidone solvent to manufacture a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector having a thickness of 20 μm, dried at 130°C, and then rolled to manufacture a positive electrode having a thickness of 70 μm.

[0259] <Lithium secondary battery manufacturing>

[0260] A negative electrode slurry was prepared by mixing a negative electrode active material of SiO:artificial graphite in a weight ratio of 6:94, a conductive material of carbon black, a binder of SBR, and a thickener of CMC in a weight ratio of 95.6:1.0:2.3:1.1 in distilled water. The negative electrode slurry was applied to one surface of a 12 μm thick copper current collector, dried at 130°C, and then rolled to prepare a negative electrode. (Slurry solid content: 50% by weight based on the total weight of the negative electrode slurry)

[0261] An electrode assembly was manufactured by interposing a porous polyethylene separator between each of the positive and negative electrodes manufactured above, and then positioning it inside a battery case, and then injecting an electrolyte to manufacture a lithium secondary battery. At this time, an electrolyte solution was used in which 1.0 M LiPF6 was dissolved in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0262]

[0263] <Experimental Example 1> - Rct / Rs Evaluation

[0264] An electrode assembly was manufactured by interposing a porous polyethylene separator between each of the positive and negative electrodes manufactured in Example 1 and Comparative Examples 1 and 2, and then positioning the electrode assembly inside a battery case, and then injecting an electrolyte to manufacture a lithium secondary battery. At this time, the electrolyte used was 1.0 M LiPF6 dissolved in a mixed organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0265] Next, the manufactured lithium secondary battery was charged under CC / CV, 0.1C, 4.2V, 0.05C cut conditions at 25℃, and discharged under CC, 0.1C, 3.0V conditions, which is considered as one cycle, for 100 cycles, and then charged to SOC 50%. Electrochemical impedance spectroscopy (EIS) was performed using a Biologic VMP3 device (1,000 kHz to 10 mHz range, 25℃ conditions), and the obtained impedance information was analyzed by Distribution of Relaxation Time (DRT) to obtain R s and R ct was measured. The results are shown in Table 1 below.

[0266]

[0267] 100 cycle anode interface, surface resistance (R)s ) [Ω]100 cycle anode charge transfer resistance (R ct ) [Ω]R ct / R s Example 1 (#4) 0.187 0.46 22.471 Comparative Example 1 (#3) 0.144 0.20 21.403 Comparative Example 2 (#5) 0.266 0.129 0.485

[0268]

[0269] Referring to Table 1 above, the positive electrode manufactured in Example 1 is R ct / R s The value is 2 or more, but the anodes manufactured in comparative examples 1 and 2 have R ct / R s You can see that the value is less than 2.

[0270]

[0271] <Experimental Example 2> - Evaluation of room temperature life characteristics

[0272] The lithium secondary batteries manufactured in Example 1 and Comparative Examples 1 and 2 were charged to 4.2 V, 0.05 C cut condition under CC / CV, 0.5 C condition at 45°C using an electrochemical charger / discharger, and then discharged to 3.0 V under CC, 1.0 C condition, which is considered one cycle, for a total of 300 charge / discharge cycles, and the capacity retention rate was evaluated. The results are shown in Fig. 4.

Claims

1. A cathode comprising a cathode active material and having a resistance component ratio of 2 or more as defined by the following formula 1: [Formula 1] R ct / R s In the above formula, R ct refers to the charge transfer resistance of the positive electrode measured in the first frequency range for a secondary battery including the positive electrode, Above R s refers to the surface or interface resistance of the positive electrode measured in the second frequency range for a secondary battery including the positive electrode, The above first frequency range is a frequency range of 1 Hz or more and 1 kHz or less, The above second frequency range is a frequency range exceeding 1 kHz and less than or equal to 1,000 kHz.

2. In paragraph 1, Above R ct is determined based on a value obtained by performing an electrochemical impedance analysis (EIS) on the secondary battery, performing a Distribution of Relaxation Time (DRT) analysis on the impedance information, generating an impedance graph according to frequency, and integrating a first area corresponding to the first frequency area of ​​the graph. Above R s A cathode, wherein the cathode is determined based on a value obtained by performing an electrochemical impedance analysis method on the secondary battery, performing a relaxation time distribution analysis on the impedance information, generating an impedance graph according to frequency, and integrating a second area corresponding to the second frequency area of ​​the graph.

3. In paragraph 1, The above positive electrode active material has an average particle diameter (D 50 ) A positive electrode comprising different first positive electrode active materials and second positive electrode active materials.

4. In paragraph 1, The above positive electrode active material is a first positive electrode active material represented by the following chemical formula 1, A positive electrode comprising a second positive electrode active material represented by the following chemical formula 2: [Chemical Formula 1] Li 1+a1 Ni x1 Co y1 Mr z1 Al w1 M 1 v1 O 2 In the above chemical 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, M 1 is a doping 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, [Chemical formula 2] Li 1+a2 Ni x2 Co y2 Mr z2 Al w2 M 2 v2 O 2 In the above chemical formula 2, 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, M 2 is a doping 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.

5. In paragraph 1, The average particle diameter (D) of the first positive electrode active material 50 ) is 6 ㎛ to 12 ㎛, anode.

6. In paragraph 1, The average particle diameter (D) of the second positive electrode active material 50 ) is 1.5 ㎛ to 5 ㎛, anode.

7. In paragraph 1, A positive electrode, wherein the first positive electrode active material and the second positive electrode active material are included in a weight ratio of 80:20 to 40:

60.

8. In paragraph 1, The positive electrode is obtained by mixing the positive electrode active material in distilled water, washing it, and then drying it.

9. A cathode comprising a cathode active material and having a resistance component ratio of 2 or more as defined by the following formula 1; cathode; and electrolyte; Lithium secondary battery including: [Formula 1] R ct / R s In the above formula, R ct means the charge transfer resistance of the positive electrode measured in the first frequency range for the lithium secondary battery, Above R s refers to the surface or interface resistance of the positive electrode measured in the second frequency range for the lithium secondary battery, The above first frequency range is a frequency range of 1 Hz or more and 1 kHz or less, The above second frequency range is a frequency range exceeding 1 kHz and less than or equal to 1,000 kHz.

10. In paragraph 9, Above R ct is determined based on a value obtained by performing an electrochemical impedance analysis (EIS) on the lithium secondary battery, performing a Distribution of Relaxation Time (DRT) analysis on the impedance information, generating an impedance graph according to frequency, and integrating a first area corresponding to the first frequency area of ​​the graph. Above R s A lithium secondary battery, wherein the impedance information obtained by performing an electrochemical impedance analysis method on the secondary battery is subjected to a relaxation time distribution analysis to generate an impedance graph according to frequency, and the impedance is determined based on a value obtained by integrating a second area corresponding to the second frequency area of ​​the graph.

11. In paragraph 9, The above negative electrode is a negative current collector; and A negative electrode active material layer including a negative electrode active material; A lithium secondary battery, 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. In paragraph 11, A lithium secondary battery, wherein the silicon-based negative electrode active material is included in an amount of 1 wt% to 30 wt% based on the total weight of the negative electrode active material layer.

13. In paragraph 11, The above negative electrode comprises the silicon-based negative electrode active material and the carbon-based negative electrode active material, A lithium secondary battery, wherein the silicon-based negative electrode active material and the carbon-based negative electrode active material are contained in a weight ratio of 1:99 to 30:

70. 14.(A) A step of mixing the positive electrode active material in distilled water and washing it; (B) a step of drying the washed positive electrode active material; and (C) a step of applying a cathode slurry containing the above-mentioned dry cathode active material onto a cathode current collector; A method for manufacturing a cathode comprising:

15. In paragraph 14, Step (A) above, (a1) a step of mixing the first cathode active material in distilled water and performing a first washing; and (a2) a second washing step by mixing the second positive electrode active material in distilled water; Including, The above first cathode active material and the above second cathode active material have an average particle diameter (D 50 ) are different from each other, and the method for manufacturing the positive electrode is different.

16. In paragraph 15, A method for manufacturing an anode, wherein the first washing step is performed at a higher temperature than the second washing step.

17. In paragraph 15, A method for manufacturing an anode, wherein the first washing step is performed at 20° C. to 40° C.

18. In paragraph 15, A method for manufacturing an anode, wherein the second washing step is performed at 3°C ​​to 18°C.

19. In Article 15, A method for manufacturing a positive electrode, wherein the first washing step is performed by mixing the first positive electrode active material in an amount of 50 wt% to 70 wt% based on the total weight of the distilled water.

20. In paragraph 15, A method for manufacturing a positive electrode, wherein the second washing step is performed by mixing the second positive electrode active material in an amount of 65 wt% to 85 wt% based on the total weight of the distilled water.

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