Cathode active materials, preparing method thereof, cathode and electrochemical devices

Abstract

A positive electrode active material that improves the performance of an electrochemical device is disclosed. According to one aspect, a positive electrode active material is provided that includes an overlithiated layered oxide (OLO) and has an R value of 27 or less calculated by Formula 1 below. [Equation 1] R=(PA / PB) Based on SAXS (Small-Angle X-ray Scattering): In the above Equation 1, PA is the volume (cm3 / g) of macropores contained in the cathode active material, and PB is the volume (cm3 / g) of micropores contained in the cathode active material, the macropores exhibit the highest volume fraction (cm3g-1 / Å) at a radius of 102.5Å to 103.5Å, and the micropores exhibit the highest volume fraction at a radius of 101Å to 102.5Å.

Description

Technology Field

[0001] The present disclosure relates to a positive electrode active material, and more specifically to a positive electrode active material, a method for manufacturing the same, a positive electrode, and an electrochemical device. Background Technology

[0002] With the increasing technological development and demand for mobile devices, the demand for rechargeable batteries as an energy source is rapidly rising. Among these rechargeable batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used.

[0003] Lithium transition metal composite oxides are used as cathode active materials for lithium-ion batteries. Among these, lithium cobalt composite metal oxides, such as LiCoO2, which exhibit high operating voltage and excellent capacity characteristics, are primarily used. However, LiCoO2 has limitations in mass use as a power source in fields such as electric vehicles because its thermal properties are very poor due to the instability of its crystal structure caused by lithium ion desorption, and it is also expensive.

[0004] To address this, overlithiated layered oxides (OLOs) were proposed, but the oxidation / reduction reaction of oxygen involves oxidized oxygen species (O) within the cathode structure n- There was a problem in that it generated ) and caused instability, leading to continuous structural degradation during the charging / discharging process. In addition, irreversibility caused by oxygen gas release, etc., had a fatal impact on battery performance. Prior art literature

[0005] Korean Published Patent Application 10-2023-0051828 A (Published April 19, 2023) The problem to be solved

[0006] According to one aspect of the present invention, a positive electrode active material is provided that improves the performance of an electrochemical device.

[0007] According to another aspect of the present invention, a positive electrode active material is provided that can improve irreversibility in the charging / discharging process due to the instability of oxidized oxygen.

[0008] According to another aspect of the present invention, a cathode active material is provided in which primary and secondary particles grow evenly, the uniformity of particle shape is excellent, and structural stability is improved.

[0009] According to another aspect of the present invention, a positive electrode active material is provided that can increase the mobility of lithium ions and increase the charge / discharge speed of an electrochemical device.

[0010] According to another aspect of the present invention, a positive electrode comprising the positive electrode active material is provided.

[0011] According to another aspect of the present invention, an electrochemical device having high charging capacity, discharge capacity, and Coulomb efficiency is provided.

[0012] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof described in the specification. means of solving the problem

[0013] According to one aspect of the present invention, a cathode active material is provided comprising an overlithiated layered oxide (OLO), wherein R calculated by Formula 1 below is 27 or less.

[0014] [Equation 1]

[0015] R=(P A / P B )

[0016] Based on SAXS (Small-Angle X-ray Scattering): In Equation 1 above, PA is the volume (cm²) of the macropores contained in the above-mentioned cathode active material 3 / g) and, P B is the volume (cm²) of micropores contained in the above-mentioned cathode active material 3 / g), and the above macropores are 10 2.5 Å~10 3.5 The highest volume fraction (cm²) at a radius of Å. 3 g -1 It represents / Å), and the micropores are 10 1 Å~10 2.5 It exhibits the highest volume fraction at a radius of Å.

[0017] Preferably, the positive electrode active material may include a compound represented by the following general formula 1.

[0018] [General Formula 1]

[0019] xLi2MnO3ㆍ(1-x)Li[Mn a M1 b M2 c ]O2

[0020] In the above general formula 1, 0 <x<1이고 a+b+c=1이고, 0<a<1, 0≤b<1 및 0≤c<1이고, M1 및 M2는 서로 상이한 전이금속으로서 Ni 또는 Co이다

[0021] Preferably, the positive electrode active material may include a compound represented by the following general formula 2.

[0022] [General Formula 2]

[0023] y[LiMn p Ni (1-p-q-r) Co q M3 r O2]·(1-y)[Li2Mn s M4 (1-s) O3]

[0024] In the above general formula 2: M3 and M4 are each independently selected from the group consisting of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na and Pt, and 0.500 <y<0.800, 0.450<p<0.650, 0≤q≤0.025, 0≤r≤0.100, 0.900≤s≤1.000이다.

[0025] Preferably, based on X-ray diffraction (XRD) analysis: (104) Diffraction X-ray intensity at the peak (I (104) Regarding ), diffracted X-ray intensity at the (003) peak (I (003) The ratio of )(I (003) / I (104) A positive electrode active material having a value of 1.31 or higher may be provided.

[0026] Preferably, based on SAXS (Small-Angle X-ray Scattering): the pore volume of the macropore is 0.35 cm 3 / g or more 0.45 cm 3 It may be less than / g.

[0027] Preferably, based on SAXS (Small-Angle X-ray Scattering): the volume of the micropores is 0.017 cm³ 3 / g or more 0.025 cm 3 It may be less than / g.

[0028] Preferably, based on SAXS (Small-Angle X-ray Scattering): the total pore volume contained in the cathode active material is 0.475 cm² 3 It may be less than / g.

[0029] According to another aspect of the present invention, a method for manufacturing a cathode active material is provided, comprising: (S1) a step of preparing a mixture comprising a lithium-rich layered oxide precursor and a lithium precursor; and (S2) a step of heat-treating the mixture to manufacture a cathode active material, wherein in the reaction for manufacturing the cathode active material, the molar content of the lithium precursor is lower than the stoichiometric molar content.

[0030] Preferably, the molar content of the lithium precursor may be lower than 0.5 mol% or more and 3 mol% or less compared to the stoichiometric molar content.

[0031] Preferably, the above step (S2) may include the step of heat-treating the mixture at an atmospheric temperature of 800°C or higher and 1100°C or lower for 0.5 hours or more and 15 hours or less.

[0032] According to another aspect of the present invention, a positive electrode active material produced by the method for producing a positive electrode active material is provided.

[0033] According to another aspect of the present invention, a positive electrode comprising a positive electrode active material of several embodiments is provided.

[0034] According to another aspect of the present invention, an electrochemical device is provided comprising an anode of some embodiment; a cathode; a separator interposed between the anode and the cathode; and an electrolyte.

[0035] The means for solving the above problem are not all of the features of the present invention and may be combined with some embodiments of this specification. Various features of the present invention and the advantages and effects derived therefrom may be understood in more detail by referring to the specific description below. Effects of the invention

[0036] According to one aspect of the present invention, by realizing a positive electrode active material in which primary and secondary particles grow evenly and the uniformity of particle shape is excellent, the irreversibility in the charging / discharging process caused by the instability of oxidized oxygen can be improved.

[0037] According to another aspect of the present invention, a positive electrode active material capable of increasing the mobility of lithium ions and increasing the charge / discharge speed of an electrochemical device can be realized.

[0038] According to another aspect of the present invention, an electrochemical device with high charging capacity, discharge capacity, and Coulomb efficiency can be realized.

[0039] In addition to the effects described above, specific effects of the present invention are described together with the following explanation of specific details for implementing the invention. Furthermore, the effects of the present invention are not limited to those mentioned above and can be easily realized by means and combinations thereof described in the specification. Brief explanation of the drawing

[0040] FIG. 1a shows Ni according to the preparation example. 0.25 Mn 0.75 This is the result of SEM-EDS (Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy) analysis of CO3. FIG. 1b shows the Ni of the preparation example. 0.25 Mn 0.75 This is the result of the XRD (X-ray diffraction) analysis of CO3. Figure 2 shows the XRD analysis results of the cathode active materials according to Comparative Examples 1 and 2 and the Examples. Figure 3a shows the XRD analysis results of the cathode active material according to Comparative Example 1. Figure 3b shows the XRD analysis results of the cathode active material according to Comparative Example 2. Figure 3c is the XRD analysis result of the cathode active material according to the example. Fig. 4a is a Scanning Electron Microscope (SEM) image of the cathode active material according to Comparative Example 1. Fig. 4b is an enlarged SEM image of Fig. 4a. Fig. 5a is an SEM image of the cathode active material according to Comparative Example 2. Fig. 5b is an enlarged SEM image of Fig. 5a. Fig. 6a is an SEM image of a cathode active material according to an example. Fig. 6b is an enlarged SEM image of Fig. 6a. FIG. 7a is a TEM (Transmission Electron Microscope) image of a cross-section of a cathode active material according to Comparative Examples 1 and 2 and an Example. FIG. 7b is a TEM image showing the atomic arrangement analysis of the cathode active material according to Comparative Examples 1 and 2 and the Example. Figure 8 shows the electron energy loss spectroscopy results for the cathode active materials according to Comparative Example 2 and the Example. Figure 9a shows the results of SAXS (Small-Angle X-ray Scattering) analysis of the cathode active materials according to Comparative Examples 1 and 2 and the Example. Figure 9b is a SAXS analysis result showing the volume fraction according to the radius of micropores and the volume fraction according to the radius of macropores in the cathode active materials according to Comparative Examples 1 and 2 and the Example. FIG. 10a is a charge / discharge profile of an electrochemical device according to Comparative Example 1. FIG. 10b is a charge / discharge profile of an electrochemical device according to Comparative Example 2. FIG. 10c is a charge / discharge profile of an electrochemical device according to an embodiment. FIG. 11 is a graph showing the capacity according to the number of cycles of an electrochemical device according to Comparative Examples 1 and 2 and the Example. Figure 12 is an X-ray absorption spectroscopy (XAS) result showing the change in the oxidation state of the transition metal of the positive electrode active material in the electrochemical device according to Comparative Examples 1 and 2 and the Example. Figure 13a is the result of X-ray absorption spectroscopy showing the oxidation states of Ni and Mn transition metals changing during the charging / discharging process of an electrochemical device according to Comparative Example 1. Figure 13b is the result of X-ray absorption spectroscopy showing the oxidation states of Ni and Mn transition metals changing during the charging / discharging process of an electrochemical device according to Comparative Example 2. FIG. 13c is an X-ray absorption spectroscopy result showing the oxidation states of Ni and Mn transition metals that change during the charging / discharging process of an electrochemical device according to an example. Specific details for implementing the invention

[0041] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0042] In this specification, expressions such as first, second, (S1), (S2), etc., may modify various components regardless of order and / or importance and do not limit such components. These expressions may be used to distinguish one component from another. For example, without departing from the scope of the present disclosure, the first component may be named the second component, and similarly, the second component may be renamed the first component.

[0043] In this specification, a range of numerical values ​​indicated by the term 'to' represents a range of numerical values ​​that includes the values ​​listed before and after the term as the lower and upper limits, respectively. For example, if 'a to b' is described in the specification, it may be understood that 'a to b' (a to b) is described.

[0044] In the present specification, if multiple numerical values ​​are disclosed for the upper and lower limits of any numerical range, the numerical range disclosed in the present specification may be understood as a range of any numerical values ​​in which any one of the multiple lower limit values ​​and any one of the multiple upper limit values ​​are respectively the lower limit value and the upper limit value. For example, if a or greater, or b or greater; and c or less, or d or less is described, it may be understood as a or greater and c or less, a or greater and d or less, b or greater and c or less, or b or greater and d or less.

[0045] In this specification, the SAXS (Small-Angle X-ray Scattering) analysis method can be used as an analysis method capable of determining the size, volume, shape, and distribution of pores by analyzing the scattering pattern generated when X-rays interact with the cathode active material.

[0046] According to one aspect of the present invention, a cathode active material is provided comprising an overlithiated layered oxide (OLO), wherein R calculated by Formula 1 below is 27 or less.

[0047] [Equation 1]

[0048] R=(P A / P B )

[0049] Based on SAXS (Small-Angle X-ray Scattering): In Equation 1 above, P A is the volume (cm²) of the macropores contained in the above-mentioned cathode active material 3 / g) and, P B is the volume (cm²) of micropores contained in the above-mentioned cathode active material 3 / g), and the above macropores are 10 2.5 Å~10 3.5 The highest volume fraction (cm²) at a radius of Å. 3 g -1It represents / Å), and the micropores are 10 1 Å~10 2.5 It exhibits the highest volume fraction at a radius of Å.

[0050] R, defined in Equation 1 above, is a parameter that varies depending on the content of the lithium source (lithium precursor). It is a parameter derived from experimental results showing that as the content of the lithium source decreases relative to the stoichiometric content, the volume of macropores (Pore volume) within the cathode active material decreases and the volume of micropores (Pore volume) increases. If R in Equation 1 above exceeds the above numerical range, the radius and volume of macropores increase, which may lead to problems such as reduced performance of the electrochemical device, including charge capacity, discharge capacity, and Coulomb efficiency. According to one aspect of the present invention, by satisfying the above numerical range of R in Equation 1 above, a cathode active material is realized in which primary and secondary particles grow evenly and the uniformity of particle shape is excellent, thereby improving irreversibility during the charge / discharge process caused by the instability of oxidized oxygen. According to another aspect of the present invention, by controlling R in Equation 1 above to the above numerical range, a cathode active material can be realized that increases the mobility of lithium ions and increases the charge / discharge speed of the electrochemical device.

[0052] The configuration of the present invention will be described in more detail below.

[0053] 1. Cathode active material

[0054] The cathode active material according to the present invention includes an overlithiated layered oxide (OLO).

[0055] In this specification, a lithium-overlayered oxide is defined as a compound in which the molar ratio of lithium to the total transition metal (Li / Metal molar ratio) is greater than 1. For example, the lithium-overlayered oxide may include one or more phases.

[0056] The positive electrode active material according to the present invention satisfies that R calculated in Formula 1 below is 27 or less.

[0057] [Equation 1]

[0058] R=(P A / P B )

[0059] Based on SAXS (Small-Angle X-ray Scattering): In Equation 1 above, P A is the volume (cm²) of the macropores contained in the above-mentioned cathode active material 3 / g) and, P B is the volume (cm²) of micropores contained in the above-mentioned cathode active material 3 / g), and the above macropores are 10 2.5 Å~10 3.5 The highest volume fraction (cm²) at a radius of Å. 3 g -1 It represents / Å), and the micropores are 10 1 Å~10 2.5 It exhibits the highest volume fraction at a radius of Å. Here, radius refers to the radius of each pore.

[0060] Small-Angle X-ray Scattering (SAXS) is a method for analyzing the structural characteristics of nanomaterials by analyzing the X-ray scattering intensity in the small-angle region. For example, when performing SAXS analysis on a cathode active material, the microstructure changes due to the pores distributed within the particles, resulting in different scattering degrees. By analyzing this, a graph plotting the radius of each pore (x-axis) versus the volume fraction of the pore (y-axis) can be generated to analyze the structure of porous materials.

[0061] In the present invention, a graph of the radius (x-axis) of each pore and the volume fraction (y-axis) of the pore was used to distinguish between the macropores and micropores within a general over-lithium layered oxide cathode active material, and by finely controlling them, a cathode active material with excellent electrochemical performance was manufactured.

[0062] In some embodiments of the present invention, R may be 27 or less, 26 or less, 25 or less, 24 or less, 23 or less, 22 or less, or 21 or less, and specifically, 19 or more and any one of the plurality of upper limits; or 20 or more and any one of the plurality of upper limits. In some embodiments of the present invention, by adjusting R to the above numerical range, a positive electrode active material can be realized in which primary and secondary particles grow evenly and the uniformity of particle shape is excellent, and accordingly, irreversibility in the charging / discharging process due to the instability of oxidized oxygen can be improved. In addition, by adjusting R of Equation 1 to the above numerical range, a positive electrode active material can be realized that increases the mobility of lithium ions and increases the charging / discharging speed of the electrochemical device.

[0063] In some embodiments of the present invention, the positive active material may include a compound represented by the following general formula 1.

[0064] [General Formula 1]

[0065] xLi2MnO3ㆍ(1-x)Li[Mn a M1 b M2 c ]O2

[0066] In the above general formula 1, 0 <x<1이고 a+b+c=1이고, 0<a<1, 0≤b<1 및 0≤c<1이고, M1 및 M2는 서로 상이한 전이금속으로서 Ni 또는 Co이다. 상기 일반식 1로 표시되는 화합물에서 x는 두 상(Phase)의 혼합비율을 결정할 수 있다. 상기 일반식 1로 표시되는 화합물은 도핑이 되지 않은 과리튬 층상계 산화물로서 리튬 과잉 상태를 나타내는 xLi2MnO3를 통해 전기화학소자의 용량을 높이는 효과와, (1-x)Li[Mn a M1 b M2 c Through O2, the effect of improving the structural stability and thermal stability of the cathode active material can be achieved simultaneously.

[0067] In some other embodiments of the present invention, the positive active material may include a compound represented by the following general formula 2.

[0068] [General Formula 2]

[0069] y[LiMn p Ni (1-p-q-r) Co q M3 r O2]·(1-y)[Li2Mn s M4 (1-s) O3]

[0070] In the above general formula 2, M3 and M4 are each independently selected from the group consisting of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0.500 <y<0.800, 0.450<p<0.650, 0≤q≤0.025, 0≤r≤0.100, 0.900≤s≤1.000이다. 구체적으로 상기 일반식 2로 표시되는 화합물에서 y는 두 상(Phase)의 혼합 비율을 결정할 수 있다. 상기 일반식 2로 표시되는 화합물은 상기 일반식 1의 화합물과 달리, M3 및 M4로 도핑된 과리튬 층상계 산화물일 수 있다. 구체적으로 상기 일반식 2로 표시되는 화합물은 M3 및 M4로 도핑되기 때문에 리튬 과량 구조의 안정성을 강화하고 장시간 사이클 성능을 향상시킬 수 있다.

[0071] In some embodiments of the present invention, based on X-ray diffraction (XRD) analysis: (104) Diffraction X-ray intensity at the peak (I (104) Regarding ), diffracted X-ray intensity at the (003) peak (I (003) The ratio of )(I (003) / I (104) ) can be greater than 1.31. Specifically, the diffracted X-ray intensity (I) at the (104) peak. (104) Regarding ), diffracted X-ray intensity at the (003) peak (I (003) The ratio of )(I (003) / I (104) ) may be 1.31 or higher, 1.32 or higher, 1.33 or higher, 1.34 or higher, or 1.35 or higher.

[0072] In some non-limiting examples (104) diffracted X-ray intensity at the peak (I (104) Regarding ), diffracted X-ray intensity at the (003) peak (I (003) The ratio of )(I (003) / I (104) ) is a parameter that varies depending on the content of the lithium source (lithium precursor), Li + / Ni 2+It may be a factor affecting cation mixing by site exchange.

[0073] In some embodiments of the present invention, the diffracted X-ray intensity (I) at the (104) peak is (104) Regarding ), diffracted X-ray intensity at the (003) peak (I (003) The ratio of )(I (003) / I (104) As ) is controlled to the above numerical range, cations (e.g., Li) + / Ni 2+ By reducing cation mixing caused by site exchange, the blockage of the lithium ion transport pathway can be effectively prevented.

[0074] In some embodiments of the present invention, based on SAXS (Small-Angle X-ray Scattering): the pore volume of the macropore is 0.35 cm 3 / g or more 0.45 cm 3 It may be less than / g. Specifically, the volume of the above macropores is 0.35 cm³ 3 / g or more, 0.36 cm 3 / g or more, 0.37 cm 3 / g or more, 0.38 cm 3 / g or more, 0.39 cm 3 / g or more, 0.40 cm 3 / g or more, or 0.41 cm 3 / g or more; and 0.42 cm 3 / g or less, 0.43 cm 3 / g or less, 0.44 cm 3 / g or less or 0.45 cm 3It may be less than / g. In some embodiments of the present invention, by controlling the volume of the macropores to the above numerical range, it is possible to realize an anode active material in which primary and secondary particles grow evenly and the uniformity of particle shape is excellent, and accordingly, irreversibility during the charge / discharge process due to the instability of oxidized oxygen can be improved.

[0075] In some embodiments of the present invention, based on SAXS (Small-Angle X-ray Scattering): the volume of the micropore is 0.017 cm³ 3 / g or more 0.025 cm 3 It may be less than / g. Specifically, the volume of the micropores is 0.017 cm³ 3 / g or more, 0.018 cm 3 / g or more, 0.019 cm 3 / g or more, or 0.020 cm 3 / g or more; and 0.021 cm 3 / g or less, 0.022 cm 3 / g or less, 0.023 cm 3 / g or less, 0.024 cm 3 / g or less or 0.025 cm 3 It may be less than / g. In some embodiments of the present invention, by controlling the volume of the micropores to the above numerical range, it is possible to realize an anode active material in which primary and secondary particles grow evenly and the uniformity of particle shape is excellent, and accordingly, irreversibility during the charge / discharge process due to the instability of oxidized oxygen can be improved.

[0076] In some embodiments of the present invention, based on Small-Angle X-ray Scattering (SAXS): the total pore volume contained in the cathode active material is 0.475 cm³ 3 It may be less than / g. Specifically, the total pore volume contained in the above-mentioned cathode active material is 0.470 cm³3 / g or less, 0.46 cm 3 / g or less, or 0.45 cm 3 It may be less than / g, specifically 0.40 cm 3 / g or greater, and may be less than or equal to any one of the above multiple upper limits. In some embodiments of the present invention, by controlling the total volume of pores contained in the cathode active material to the above numerical range, it is possible to realize a cathode active material in which primary and secondary particles grow evenly and the uniformity of particle shape is excellent, and accordingly, irreversibility during the charge / discharge process due to the instability of oxidized oxygen can be improved.

[0077] In this specification, the average particle size of a particle is the particle size (D) at which the cumulative percentage in the volume-based particle size distribution curve reaches 50% when measured by a laser diffraction particle size distribution measuring device. 50 It can be defined as ). For example, the average particle size of the above particles can be calculated by dispersing the particles to be measured in a dispersion medium, introducing them into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and measuring the difference in diffraction patterns according to particle size as the particles pass through a laser beam.

[0078] In some embodiments of the present invention, the cathode active material may be a secondary particle in which a primary particle is aggregated. In some non-limiting examples, the average particle size of the primary particle may be 50 to 100 nm, and the average particle size of the secondary particle may be 7 to 9 μm.

[0079] In some embodiments of the present invention, the grain size of the cathode active material may be 15 nm or more and 20 nm or less. For example, the grain size of the cathode active material may be calculated using X-ray diffraction (XRD) analysis and the Scherrer equation.

[0081] 2. Method for manufacturing cathode active material

[0082] In this specification, a precursor is defined as a compound that participates in a chemical reaction to produce another compound in chemistry.

[0083] According to another aspect of the present invention, a method for manufacturing a cathode active material is provided, comprising: (S1) a step of preparing a mixture comprising a lithium-rich layered oxide precursor and a lithium precursor; and (S2) a step of heat-treating the mixture to manufacture a cathode active material, wherein in the manufacturing reaction of the cathode active material, the molar content of the lithium precursor is lower than the stoichiometric molar content. Specifically, by controlling the molar content of the lithium precursor in the manufacturing reaction of the cathode active material to be lower than the stoichiometric molar content, a cathode active material is realized in which primary and secondary particles grow evenly and the uniformity of particle shape is excellent, and a cathode active material is realized that can increase the mobility of lithium ions and increase the charge / discharge speed of an electrochemical device.

[0084] The lithium-overlayered oxide precursor according to the present invention is a precursor of a lithium-overlayered oxide. In some non-limiting examples, the lithium-overlayered oxide precursor is Ni 0.25 Mn 0.75 It may contain CO3.

[0085] In some non-limiting examples, the lithium precursor may be a lithium salt in which lithium and an anion are combined, specifically lithium carbonate. Alternatively, the lithium precursor may be named a lithium source.

[0086] In some embodiments of the present invention, the molar content of the lithium precursor may be lower than 0.5 mol% or more and 3 mol% or less compared to the stoichiometric molar content. In some embodiments of the present invention, by controlling the molar content of the lithium precursor to the above numerical range compared to the stoichiometric molar content, a positive electrode active material can be realized in which primary and secondary particles grow evenly and the uniformity of particle shape is excellent, and accordingly, irreversibility in the charging / discharging process due to the instability of oxidized oxygen can be improved.

[0087] In some embodiments of the present invention, the step (S2) may include the step of heat-treating the mixture under an atmospheric atmosphere at a temperature of 800°C or higher and 1100°C or lower for 0.5 hours or more and 15 hours or less. Specifically, the heat-treatment temperature of the mixture may be 800°C or higher, 850°C or higher, or 900°C or higher; and 950°C or lower, 1000°C or lower, 1050°C or lower, or 1100°C or lower, and the heat-treatment time may be 0.5 hours or more, 0.7 hours or more, 0.9 hours or more, or 1 hour or more; and 1.2 hours or less, 1.4 hours or less, 1.6 hours or less, 1.8 hours or less, 2.0 hours or less, 5.0 hours or less, 10.0 hours or less, or 15.0 hours or less. In some embodiments of the present invention, the heat treatment temperature and heat treatment time of the mixture are controlled within the above numerical range, thereby enabling the realization of an anode active material in which primary and secondary particles grow evenly and the uniformity of particle shape is excellent, and accordingly, the irreversibility during the charge / discharge process caused by the instability of oxidized oxygen can be improved.

[0089] 3. Anode

[0090] According to another aspect of the present invention, a positive electrode comprising a positive electrode active material of several embodiments is provided.

[0091] The anode according to the present invention may include an anode current collector and an anode active material layer disposed on at least one surface of the anode current collector. The anode active material layer may include an anode active material, a conductive material, and an anode binder.

[0092] For example, the positive current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the positive current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy. The positive current collector may typically have a thickness of 6 to 20 μm.

[0093] The conductive material can improve conductivity between active material particles or with a metal current collector at the electrode and prevent the binder from acting as an insulator. The conductive material may be, for example, a mixture of one or more conductive materials selected from the group consisting of graphite, carbon black, carbon fiber, metal fiber, metal powder, conductive whiskers, conductive metal oxide, activated carbon, and polyphenylene derivatives; more specifically, it may be a mixture of one or more conductive materials selected from the group consisting of natural graphite, artificial graphite, Super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermo black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide.

[0094] For example, the anode binder is poly(vinylidene fluoride-hexafluoropropylene (poly(vinylidene fluoride) co -hexafluoropropylene)), polyvinylidene fluoride-trichloroethylene(poly(vinylidene fluoride- co-trichloroethylene)), poly(methylmethacrylate)), poly(ethylhexylacrylate)), poly(butylacrylate)), poly(acrylonitrile)), poly(vinylpyrrolidone)), poly(vinyl acetate)), poly(ethylene-co-vinyl acetate)), poly(ethylene oxide)), polyacrylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl poly(vinylalcohol)), cyanoethylcellulose, It may be one or more selected from the group consisting of cyano ethylsucrose, pullulan, and carboxyl methyl cellulose, but is not limited thereto.

[0096] 4. Electrochemical devices

[0097] In this specification, the term "electrochemical device" is defined as any device that performs an electrochemical reaction. For example, the electrochemical device may be a secondary battery or a supercapacitor, and specifically may be a lithium metal battery or a lithium-ion secondary battery.

[0098] cathode

[0099] The cathode according to the present invention may comprise a cathode current collector and a cathode active material layer disposed on at least one surface of the cathode current collector, or may be lithium metal (Li metal).

[0100] For example, the cathode active material layer may include the cathode active material, the conductive material, and the cathode binder.

[0101] The above-mentioned negative current collector can serve as a channel to transfer electrons from the outside to cause an electrochemical reaction to occur in the negative active material, or to receive electrons from the negative active material and send them to the outside. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., may be used as the negative current collector, and specifically, transition metals that adsorb carbon well, such as copper and nickel, may be used as the current collector. For example, the thickness of the above-mentioned negative current collector may be 6㎛ to 20㎛, but the thickness of the above-mentioned negative current collector is not limited thereto.

[0102] The conductive material included in the above cathode may be the same as or different from the conductive material included in the above anode.

[0103] If necessary, the cathode active material layer may further include an additive. The additive may be, for example, at least one selected from the group consisting of dispersants, plasticizers, antioxidants, lubricants, stabilizers, and antistatic agents.

[0104] Separator

[0105] The separator according to the present invention includes a porous substrate to electrically insulate the cathode and the anode to prevent a short circuit.

[0106] As long as the constituent material of the above porous substrate is an organic or inorganic material having electrical insulating properties, it may be used without particular limitation. The above porous substrate may include, for example, at least one selected from the group consisting of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene, and specifically may include polyolefin. Polyolefin not only has excellent coating properties but also allows for a thinner separator thickness, thereby increasing the proportion of the electrode active material layer within the battery and increasing the capacity per volume. Specifically, the weight-average molecular weight (M) of the above polyolefin w The weight-average molecular weight of the polyolefin may be 100,000 to 500,000 g / mol. If the weight-average molecular weight of the polyolefin is below the above numerical range, it may be difficult to secure sufficient mechanical properties, and if it exceeds the above numerical range, the shutdown function may not be implemented or molding may be difficult. The shutdown function refers to a function in which, when the temperature of the secondary battery rises, the thermoplastic resin melts to close the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery.

[0107] The thickness of the porous substrate may be, for example, 3 to 12 μm or 5 to 12 μm. If the thickness of the porous substrate is less than the numerical range, the function of the conductive barrier may not be sufficient, and if it exceeds the numerical range, the resistance of the separator may increase excessively.

[0108] The average diameter of the pores included in the porous substrate may be, for example, 10 to 100 nm. The pores included in the porous substrate have a structure in which they are interconnected, so that gas or liquid can pass from one side of the porous substrate to another side.

[0109] According to some embodiments of the present invention, a coating layer may be disposed on at least one surface of the porous substrate. Specifically, the coating layer can improve the mechanical strength and heat resistance of the separator and increase the ion conductivity in the secondary battery.

[0110] The coating layer according to the present invention may include a binder polymer and inorganic particles.

[0111] The binder polymer according to the present invention can connect inorganic particles and stably fix them. The above binder polymer is, for example, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, poly(ethylene-co-vinyl acetate), polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, One or more selected from the group consisting of cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxymethylcellulose, acrylonitrile-styrene butadiene copolymer, polyimide, and styrene-butadiene rubber may be used in combination.

[0112] According to another embodiment of the present invention, the weight ratio of the inorganic particles to the binder polymer (inorganic particles:binder polymer) may be 50:50 to 99:1, and specifically 70:30 to 95:5. If the content ratio of inorganic particles to the binder polymer is less than the above numerical range, the content of the binder polymer increases, which may reduce the performance of improving the thermal safety of the separator, and the pore size and porosity decrease due to the reduction of empty spaces formed between the inorganic particles, which may cause a decrease in the performance of the final battery, and if it exceeds the above numerical range, the content of the binder polymer is too low, which may weaken the peel resistance of the coating layer.

[0113] The inorganic particles according to the present invention can contribute to improving the mechanical strength and heat resistance of a separator for a secondary battery. Specifically, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are applicable within the operating voltage range of the secondary battery (e.g., Li / Li). + It is not specifically limited as long as oxidation and / or reduction reactions do not occur at a standard of 0~5V.

[0114] As an example, when using inorganic particles with a high dielectric constant, the ionic conductivity of the electrolyte can be improved by contributing to an increase in the degree of dissociation of electrolyte salts, such as lithium salts, within the liquid electrolyte. For the reasons mentioned above, the inorganic particles may be inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transport capability, or a mixture thereof.

[0115] The above inorganic particles having a dielectric constant of 5 or greater are Al2O3, SiO2, ZrO2, AlO(OH), Al(OH)3, Mg(OH)2, BaSO4, TiO2, BaTiO3, Pb(Zr x Ti 1-x )O3(PZT, where 0 <x<1), Pb 1-x La x Zr 1-y Tiy O3(PLZT, where, 0 < x < 1, 0 < y < 1), (1-x)Pb(Mg 1 / 3 Nb 2 / 3 )O 3-x It may be one or more selected from the group consisting of PbTiO3 (PMN-PT, where 0 < x < 1), HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO and SiC.

[0116] The inorganic particles having the above lithium ion transfer capability are lithium phosphate (Li3PO4) and lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y Series glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride(Li x N y , 0 < x < 4, 0 < y < 2), SiS2 series glass(Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4) and P2S5 series glass (Li x P y S z It may be one or more types selected from the group consisting of , 0 < x < 3, 0 < y < 3, 0 < z < 7).

[0117] For example, the average particle size (D) of the above inorganic particles 50 The particle size may be 1 nm to 10 µm for the formation of a coating layer of uniform thickness and appropriate porosity, specifically 10 nm to 2 µm, and more specifically 50 nm to 1 µm. The "average particle size (D50)" refers to the particle size at the 50% point of the cumulative distribution of the number of particles according to particle size. The average particle size can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, the particle size distribution can be calculated by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and measuring the difference in diffraction patterns according to particle size as the particles pass through the laser beam.

[0118] electrolytes

[0119] The electrolyte according to the present invention may include a solvent and a lithium salt.

[0120] The solvent according to the present invention is, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone, ethyl methyl carbonate (EMC), gamma-butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, It may be one or more mixtures selected from the group consisting of ethyl propionate and butyl propionate.

[0121] The lithium salt according to the present invention is, for example, NO3 - , F - , Cl - , Br - , I - , PF6 - It may include negative ions such as the back.

[0122] The secondary battery according to the present invention may be a cylindrical, prismatic, or pouch-type secondary battery, but is not particularly limited as long as it corresponds to a charge / discharge device.

[0123] According to another aspect of the present invention, a battery module comprising the electrochemical element as a unit cell and a battery pack comprising the same may be provided. The battery pack may be used as a power source for one or more medium-to-large devices selected from the group consisting of, for example, a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0124] Hereinafter, embodiments of the present invention are described in detail to enable those skilled in the art to easily implement the invention; however, this is merely an example, and the scope of the present invention is not limited by the following. In this specification, terms such as "about" or "substantially" refer to a reasonable amount of variation of a modified term so as not to significantly alter the final result. Such terms may be interpreted to include a deviation of at least ±5% or at least ±10% to the extent that the deviation does not alter or invalidate the meaning of the word.

[0126] [Preparation Example: Preparation of Co-precipitation Precursor]

[0127] Ni provided by the Korea Atomic Energy Research Institute (KAERI) 0.25 Mn 0.75 A CO3 co-precipitation precursor was prepared.

[0128] [Experimental Example 1: SEM-EDS Analysis Results of Co-precipitation Precursor]

[0129] FIG. 1a shows Ni according to the preparation example. 0.25 Mn 0.75 This is the result of SEM-EDS (Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy) analysis of CO3.

[0130] Referring to Figure 1a, it can be inferred that the particle size of the co-precipitated precursor is about 7 to 8 μm and that Ni and Mn are evenly distributed in a molar ratio of 1:3.

[0131] FIG. 1b shows the Ni of the preparation example. 0.25 Mn 0.75 This is the result of the XRD (X-ray diffraction) analysis of CO3. Specifically, the Mo Ka (λ= 0.71Å) wavelength of the Malvern PANalytical Empyrean model was used, and measurements were taken in an angular range of 2θ=5~35° with a step size of 0.016°.

[0132] Referring to Figure 1b, it was confirmed that the R-3c space group matched well with the existing Ref and no other impurities were observed.

[0134] [Preparation Example 1: Preparation of Cathode Active Material]

[0135] Preparation of the mixture by mixing precursors:

[0136] Ni 0.25 Mn 0.75 A mixture was prepared by weighing the CO3 precursor and Li2CO3 according to the composition listed in Table 1 below, and then mixing them for 30 minutes using an agate mortar and pestle.

[0137] Step of heat-treating the mixture:

[0138] The above mixture was introduced into an alumina boat and tapped, and the cathode active material was prepared by heat-treating it through an electric furnace at 900°C for 1 hour in an atmospheric environment.

[0139] division chemical formula Ni 0.25 Mn 0.75 CO3 and molar ratio of Li2CO3 molar percentage of Li2CO3 Comparative Example 1 Li 1.2 Ni 0.2 Mr 0.6 O2 Stoichiometric molar ratio 1:0.75 Approximately 42.8 mol% (standard) Comparative Example 2 Li 1.26 Ni 0.2 Mr 0.6 O2 Stoichiometric molar ratio 1:0.7875 Approximately 44.1 mol% (base +5 mol%; Excess) Examples Li 1.176 Ni 0.2 Mr 0.6 O2 Stoichiometric molar ratio 1:0.735 Approximately 42.4 mol% (baseline -2 mol%; Less)

[0141] [Experimental Example 2: XRD Analysis of Cathode Active Material]

[0142] Figure 2 shows the XRD analysis results of the cathode active materials according to Comparative Examples 1 and 2 and the Example. Specifically, the Mo Ka (λ = 0.71 Å) wavelength of the Malvern PANalytical Empyrean model was used, and measurements were taken with a step size of 0.016° in an angle range of 2θ = 5~35°.

[0143] Referring to FIG. 2, it was confirmed that the cathode active materials according to Comparative Examples 1 and 2 and the Example all exhibit a lithium-based layered structure composed of R-3m and C2 / m space groups.

[0145] [Experimental Example 3: XRD Analysis of Cathode Active Material]

[0146] Figure 3a shows the XRD analysis results of the cathode active material according to Comparative Example 1. Figure 3b shows the XRD analysis results of the cathode active material according to Comparative Example 2. Figure 3c shows the XRD analysis results of the cathode active material according to the Example.

[0147] Specifically, the Mo Ka (λ = 0.71 Å) wavelength of the Malvern PANalytical Empyrean model was used, and measurements were taken in an angular range of 2θ = 5–35° with a step size of 0.016°. The Full-Width-Half-Maximum (FWHM) for the (003) and (104) peaks of the cathode active materials prepared through Experimental Example 3, respectively, and the intensity (I at the (104) peak (104) Intensity at the (003) peak for ) (I (003) The ratio of )(I (003) / I (104) ) was produced.

[0148] Referring to Figures 3a to 3c, it was confirmed that the position and full width at half maximum of the XRD peaks did not change significantly as the lithium source content was controlled. On the other hand, as the lithium source content decreased, I (003) / I (104) We confirmed this increasing trend. Through this, by lowering the content of the lithium source (lithium precursor) relative to the stoichiometric molar ratio, Li + / Ni2+ It can be inferred that the blockage of the lithium ion transport pathway can be effectively prevented by reducing cation mixing caused by site exchange.

[0149] Specifically, the intensity (I) at the peak (104) of the positive electrode active material according to the embodiment. (104) Intensity at the (003) peak for ) (I (003) The ratio of )(I (003) / I (104) It was confirmed that ) is 1.35 or higher.

[0151] [Experimental Example 4: SEM Photographs and Morphological Analysis of Cathode Active Material]

[0152] Figure 4a is a Scanning Electron Microscope (SEM) image of the cathode active material according to Comparative Example 1, and Figure 4b is an enlarged SEM image of Figure 4a.

[0153] Referring to Figures 4a and 4b, it was confirmed that the primary and secondary particles grew evenly compared to Comparative Example 2, which will be described later, but some particles grew unevenly.

[0154] Fig. 5a is an SEM image of the cathode active material according to Comparative Example 2, and Fig. 5b is an enlarged SEM image of Fig. 5a.

[0155] Referring to Figures 5a and 5b, Ni 25 Mn 75 Primary particles that grew excessively compared to CO3 were observed, and secondary particles grew indiscriminately, resulting in reduced uniformity.

[0156] Fig. 6a is an SEM image of a positive electrode active material according to an example, and Fig. 6b is an enlarged SEM image of Fig. 6a.

[0157] Referring to FIGS. 6a and 6b, the cathode active material according to an embodiment of the present invention showed that the primary particles and secondary particles grew evenly and the uniformity of the particle shape was greatly improved.

[0159] [Experimental Example 5: TEM cross-sectional image of cathode active material]

[0160] FIG. 7a is a TEM (Transmission Electron Microscope) image of a cross-section of a cathode active material according to Comparative Examples 1 and 2 and an Example.

[0161] Referring to Fig. 7a, it was confirmed that in Comparative Example 2, large internal pores were formed due to the indiscriminate growth of primary particles. When comparing Comparative Example 2 with Comparative Example 1 and the Example, it was confirmed that as the lithium source content decreases, the size of the internal pores decreases as the primary particles align toward the center of the particles.

[0162] FIG. 7b is a TEM image showing the atomic arrangement analysis of the cathode active material according to Comparative Examples 1 and 2 and the Example.

[0163] Referring to Fig. 7b, in Comparative Example 2, a rock-salt layer was formed on the surface of the cathode active material, whereas in the example, a thin and uniformly formed spinel structure was confirmed on the surface of the cathode active material. Since the rock-salt structure is an electrochemically inactive phase, it has high resistance to the movement of lithium ions or charge transfer. This property lowers the mobility of lithium ions within the rock-salt structure and, having the same crystal orientation as the internal layered structure, fails to suppress the irregular growth of particles.

[0164] On the other hand, it can be inferred that the lithium ion mobility can be increased because the spinel structure formed on the surface of the cathode active material of the example suppresses the irregular growth of primary particles and arranges them directionally within the secondary particles. Through this, it can be inferred that the charge / discharge speed of the electrochemical device can also be improved.

[0166] [Experimental Example 6: Analysis of Particle Surface Electronic Structure via Electron Energy Loss Spectroscopy]

[0167] Figure 8 shows the electron energy loss spectroscopy results for the cathode active materials according to Comparative Example 2 and the Example.

[0168] Referring to Fig. 8, in Comparative Example 2, some Mn at the Mn L-edge 2+ It was detected, which is M formed on the surface 2+ O 2- It was confirmed that it is due to a rock salt layer. The cathode active material of the example contains Mn only near the surface. 3+ It was discovered, and LiMn 3.5+ It was confirmed that this is due to Mn present in the 2O4 spinel structure.

[0170] [Experimental Example 7: Pore Analysis of Anode Active Material via Small-Angle X-ray Scattering Analysis]

[0171] Figure 9a shows the results of SAXS (Small-Angle X-ray Scattering) analysis of the cathode active materials according to Comparative Examples 1 and 2 and the Example. Here, the SAXS graph is a graph showing the intensity of X-rays according to the scattering vector (Q).

[0172] Figure 9b is a SAXS analysis result showing the volume fraction according to the radius of micropores and the volume fraction according to the radius of macropores in the cathode active materials according to Comparative Examples 1 and 2 and the Example.

[0173] Specifically, the manufactured lithium-rich layered cathode material was evenly dispersed on a tape and sampled. Lab-SAXS instruments from NANOPIX and Rigaku were used with Cu Ka (wavelength: 1.54 Å) values, and Sample-to-detector distances (SDDs) of 1.3 m and 0.15 m were measured.

[0174] At this time, the measurement conditions were set to a Q range of 0.003 to 0.13 Å. Here, Q = [4π / λ]*sin(θ / 2), where Q is the magnitude of the scattering vector and theta is the scattering angle. Data calibration was performed using the standard material AgBe (silver behenate), and data analysis was conducted using the Igor program and the available HANARO SANS data reduction software (provided by KAERI).

[0175] Table 2 below summarizes the pore volumes for each pore based on SAXS (Small-Angle X-ray Scattering) analysis.

[0176] division Macropore volume (P A ) Micropore volume (P B ) Total pore volume R=P A / P B *) Comparative Example 2 (Li 5 mol%) 0.4744 cm 3 g -1 0.0167 cm 3 g -1 0.4911 cm 3 g -1 28.4072 Comparative Example 1 (Li 0 mol%) 0.4650 cm 3 g -1 0.0165 cm 3 g -1 0.4815 cm 3 g -1 28.1818 Example (Li -2 mol%) 0.4200 cm 3 g -1 0.0202 cm 3 g -1 0.4402 cm 3 g -1 20.7921 * Value rounded to the fourth decimal place

[0177] Referring to Table 2 and Figures 9a and 9b above, it was confirmed that the radius and pore volume of macropores increase as the lithium source content increases. In addition, it was also confirmed that the total pore volume decreases as the lithium source content decreases.

[0178] In the present invention, unlike the conventional notion of adding an excess amount of lithium source when manufacturing a lithium-rich layered oxide cathode active material, the amount of added lithium source was lowered, thereby allowing for precise control of macropores and micropores within the cathode active material, which enabled the growth of uniform cathode active material particles and excellent electrochemical performance.

[0180] [Manufacturing Example 2: Manufacture of Coin Cell]

[0181] Manufacturing of the anode:

[0182] A mixed powder comprising the cathode active material of Preparation Example 1, a conductive material (Super P), and a binder (polyvinylidene fluoride) mixed in a weight ratio of 80:10:10 was added to a solvent (N-methylpyrrolidone), and then mixed using a Pulverisette 23 Mini Mill at 20 rpm for 1 hour to prepare a cathode slurry having a total solid content of 50 wt%. The prepared cathode slurry was applied to one surface of an aluminum current collector (thickness: approximately 15 μm) at a concentration of approximately 3 mg / cm² 2 After coating, the anode was prepared by drying in a vacuum oven at 100°C for 12 hours.

[0183] Preparation of the counter electrode (negative electrode):

[0184] A lithium metal (thickness: about 1 mm) was prepared as the counter electrode.

[0185] Preparation of the separator:

[0186] Single-layer polypropylene separator (Celgard ® 2400 (thickness: approximately 25 μm) was prepared.

[0187] Electrolyte injection step:

[0188] An electrode assembly consisting of the anode, separator, and counter electrode and an electrolyte were injected into a glove box under an argon atmosphere to assemble a CR-2032 type coin cell. At this time, the electrolyte used was an electrolyte in which 1.2M LiPF6 was dissolved in a mixed solvent in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a volume ratio of 2:4:4.

[0190] [Experimental Example 8: Evaluation of Charge / Discharge Performance of Coin Cells]

[0191] FIG. 10a is the charge / discharge profile of a coin cell according to Comparative Example 1. FIG. 10b is the charge / discharge profile of a coin cell according to Comparative Example 2. FIG. 10c is the charge / discharge profile of a coin cell according to an embodiment. Specifically, at 30°C, the current density (1C = 250 mA / g) and the voltage are 2.0–4.7V (vs. Li / Li+ After setting it to ), the charge / discharge performance was evaluated using a battery charger / discharger.

[0192] division R=P A / P B *) 1 st Charging capacity (mAh / g) 1 st Discharge capacity (mAh / g) Initial Coulombic Efficiency (%) Comparative Example 2 (Li 5 mol%) 28.4072 295.2 200.8 68 Comparative Example 1 (Li 0 mol%) 28.1818 318.7 250.4 78.6 Example (Li -2 mol%) 20.7921 341.5 277.1 81.1 * Value rounded to the fourth decimal place Initial Coulomb efficiency = (1 st Discharge capacity / 1 st Charging capacity) X 100

[0193] Referring to Figures 10a to 10c and Table 3 above, the example confirmed that the initial charge capacity, initial discharge capacity, and initial Coulomb efficiency were all increased by satisfying the ratio of the volume of macropores to the volume of micropores to 27 or less compared to Comparative Examples 1 and 2.

[0195] [Experimental Example 9: Evaluation of Coin Cell Lifespan Performance]

[0196] FIG. 11 is a graph showing the capacity according to the number of cycles of coin cells according to Comparative Examples 1 and 2 and the Example. 2.0-4.7 V (vs. Li / Li + After proceeding with initial formation at ), the upper voltage limit is 4.5 V (vs. Li / Li + Except for setting it to ), the lifespan of the coin cell was evaluated in the same way as in Experimental Example 8 above.

[0197] Referring to Fig. 11, Comparative Example 2 (Li 5 mol%) showed a tendency for the capacity to gradually increase during continuous cycles due to the failure to achieve the initial capacity, but the reversible capacity itself was very low, and Comparative Example 1 (Li 0 mol%) was confirmed to maintain 80% of the initial capacity after 200 charge-discharge cycles, as the capacity of the electrochemical device decreased relatively rapidly.

[0198] On the other hand, the example (Li -2 mol%) showed the highest capacity and retention rate (90%), confirming that the difference in electrochemical performance is clearly pronounced depending on the particle shape of the manufactured lithium-based layered cathode active material.

[0200] [Experimental Example 10: Analysis of Changes in Transition Metal Oxidation Numbers]

[0201] FIG. 12 is an X-ray absorption spectroscopy (XAS) result showing the change in the oxidation state of the transition metal of the cathode active material in a coin cell according to Comparative Examples 1 and 2 and the Example. Specifically, FIG. 12 (a) is the result of measuring the Ni K-edge and FIG. 12 (b) is the result of measuring the Mn K-edge.

[0202] After disassembling the charged / discharged coin cell in an Ar atmosphere glove box, the separated electrodes were immersed in a dimethyl carbonate solution to remove foreign substances formed on the electrode surfaces. After sealing with a polyimide film to block contact with external air, the Ni K-edge / Mn K-edge region was measured using the 7D-XAFS beamline at Pohang Accelerator Laboratory.

[0203] Referring to Fig. 12, it was confirmed that Ni was partially more oxidized in Comparative Example 2 (Li 5 mol%), and Mn showed the same 4+ oxidation state in all samples of the Comparative Example and the Example.

[0204] Figure 13a is an X-ray absorption spectroscopy result showing the oxidation states of Ni and Mn transition metals changing during the charging / discharging process of a coin cell according to Comparative Example 1.

[0205] Comparing Pristine and Full Discharged in Figure 13a, it was confirmed that the oxidation state of Ni could be restored to its initial state even after charging and discharging, but Mn was partially reduced in Full Discharged. This is thought to be due to the deterioration of some of the material as Mn exhibited a large capacity.

[0206] Figure 13b is the result of X-ray absorption spectroscopy showing the oxidation states of Ni and Mn transition metals changing during the charging / discharging process of an electrochemical device according to Comparative Example 2.

[0207] Referring to Fig. 13b, Ni 2+ / Ni 4+ It was confirmed that Ni was oxidized without change in Mn during the reaction phase, the Pristine-Half charged phase, and subsequently, during the oxygen reaction phase at the flat potential, a change in the K-edge shape was observed due to changes in the adjacent local environment. In addition, it was confirmed that neither Ni nor Mn recovered to their initial state during the full discharge state.

[0208] FIG. 13c is an X-ray absorption spectroscopy result showing the oxidation states of Ni and Mn transition metals that change during the charging / discharging process of an electrochemical device according to an example.

[0209] Referring to Fig. 13c, it was confirmed that the example exhibited the same trend as the comparative example; however, seeing that the X-ray absorption spectrograph of the example's Mn in the full discharge state was closer to Pristine than the X-ray absorption spectrograph of the comparative example's Mn, it was confirmed that the oxidation state of the Mn in the example was reduced less than that of the comparative example. This suggests that the structural degradation of the example was suppressed compared to the comparative example.

[0210] The features described in the above-described embodiment may be combined with other embodiments unless explicitly stated otherwise. Furthermore, although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

Claims

Claim 1 A cathode active material comprising a lithium-rich layered oxide, wherein R calculated by Formula 1 below is 27 or less, wherein the cathode active material comprises a compound represented by the following general formula 1, and wherein the cathode active material particles are secondary particles formed by the aggregation of primary particles, the average particle size of the primary particles is 50 to 100 nm, and the average particle size of the secondary particles is 7 to 9 μm, [Formula 1] R=(P A / P B Based on ) SAXS: In Equation 1 above, P A is the volume (cm²) of the macropores contained in the above-mentioned cathode active material 3 / g) and,P B is the volume (cm²) of micropores contained in the above-mentioned cathode active material 3 / g) and the above macropores are 10 2.5 Å~10 3.5 Volume fraction (cm²) corresponding to a pore radius of Å 3 g -1 It is the sum of / Å), and the above micropores are 10 1 Å~10 2.5 It represents the sum of volume fractions corresponding to a pore radius of Å. [General Formula 1] In the above general formula 1:0 <x<1이고 a+b+c=1이고, 0<a<1, 0≤b<1 및 0≤c<1이고, M1 및 M2는 서로 상이한 전이금속으로서 Ni 또는 Co이다.

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