Positive electrode active material and lithium secondary battery including same

Abstract

The present invention relates to a positive electrode active material and a lithium secondary battery comprising the same, and more particularly, to a positive electrode active material and a lithium secondary battery comprising the same, and more particularly, to a lithium secondary battery comprising a positive electrode active material in which lithium impurities such as LiOH and Li2CO3 remaining on the surface of the positive electrode active material are removed by surface modification without reducing the content of lithium impurities remaining on the surface of the positive electrode active material through a water washing process. The positive electrode active material and the lithium secondary battery using the positive electrode including the positive electrode active material can prevent and / or alleviate degradation of electrochemical characteristics and service life of the positive electrode active material due to lithium impurities and / or a water washing process.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery comprising the same. More specifically, the present invention relates to a positive electrode active material that does not require a water washing process to reduce the content of lithium impurities such as LiOH and Li2CO3 remaining on the surface of the positive electrode active material, but removes lithium impurities through surface modification, thereby preventing and / or alleviating the reduction in electrochemical characteristics and life of the positive electrode active material caused by lithium impurities and / or a water washing process, and a lithium secondary battery using a positive electrode including the above-mentioned positive electrode active material. Background Art

[0002] Batteries use materials that can undergo electrochemical reactions at the positive and negative electrodes to store electrical energy. A typical example of such batteries is a lithium secondary battery that stores electrical energy through the chemical potential difference when lithium ions are inserted / released between the positive and negative electrodes.

[0003] The lithium secondary battery is prepared by using a substance capable of reversibly inserting and extracting lithium ions as a positive electrode active material and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

[0004] Lithium composite oxides are used as positive electrode active materials for lithium secondary batteries, and for example, composite oxides such as LiCoO2, LiMn2O4, LiNiO2, and LiMnO2 are currently under study.

[0005] Among the above-mentioned positive electrode active materials, LiCoO2 is the most widely used due to its excellent life performance and charge and discharge efficiency, but has the disadvantage of limited price competitiveness because cobalt used as a raw material is expensive.

[0006] Lithium manganese-based oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low price, but have the problems of small capacity and poor high temperature characteristics. In addition, LiNiO2-based positive electrode active materials have battery characteristics of high discharge capacity, but due to the active cation mixing between lithium and nickel, it is not only difficult to synthesize, but also has the problem that the rate performance and life performance of the synthesized positive electrode active materials are very low.

[0007] Accordingly, in order to improve the low rate performance and life performance while maintaining the high reversible capacity of LiNiO2, the so-called ternary type, the so-called NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) ternary type or NCMA (Ni-Co-Mn-Al) quaternary type lithium composite oxides such as ternary type in which a part of nickel is replaced by cobalt, manganese and / or aluminum have been developed. Since the lower the nickel content in the ternary or quaternary lithium composite oxide as described above, the lower the reversible capacity, therefore, recently, active research has been conducted to increase the nickel content in the lithium composite oxide.

[0008] However, as the nickel content in the lithium composite oxide increases, the cation mixing phenomenon in the crystal structure also increases, resulting in a decrease in stability or an increase in the content of unreacted lithium impurities such as LiOH and Li2CO3 on the surface.

[0009] As the content of lithium impurities remaining on the surface of the lithium composite oxide increases, gas generation and swelling in a lithium secondary battery using the lithium composite oxide as a positive electrode active material may be aggravated. As the content of lithium impurities remaining on the surface of the lithium composite oxide increases, when the paste for forming a positive electrode active material layer is prepared using the lithium composite oxide, there is a problem that the paste composition gels due to the lithium impurities.

[0010] Therefore, in the preparation process of the positive electrode active material, a water washing process must be performed to remove the lithium impurities remaining on the surface of the lithium composite oxide. However, since the surface of the lithium composite oxide is damaged by the water washing process, the electrochemical characteristics and stability of the lithium secondary battery using the lithium composite oxide as the positive electrode active material are reduced, and in particular, the problem of premature failure of the life may be caused.

[0011] In order to solve the lithium impurity problem, a method has been proposed in which a coating is formed after the lithium composite oxide is subjected to a water washing process to cover the surface defects of the lithium composite oxide with the coating. However, in this case, since the surface resistance characteristics of the lithium composite oxide change, it is difficult to fully exert the electrochemical characteristics. In addition, since the residual lithium content that can react with the coating raw material is insufficient after the water washing process, it is difficult to form a uniform coating, and there is a problem that it is difficult to fully alleviate the problem of reduced life caused by damage to the surface of the lithium composite oxide caused by the water washing process.

[0012] In addition, a method has been proposed, in which a coating is formed by reacting lithium impurities with a coating raw material containing a metal element instead of subjecting the lithium composite oxide to a water washing process. However, the above method also has the problem of changes in the surface resistance characteristics of the lithium composite oxide, resulting in a decrease in the charge and discharge capacity of a lithium secondary battery using the lithium composite oxide as a positive electrode active material, and other problems of reduced electrochemical characteristics. Summary of the invention

[0013] Technical issues

[0014] The object of the present invention is to provide a positive electrode active material, which can prevent and / or alleviate the reduction of electrochemical properties and stability of the positive electrode active material caused by lithium impurities by effectively controlling the lithium impurity content present on the surface of the positive electrode active material (lithium composite oxide) without the need for a water washing process.

[0015] In addition, another object of the present invention is to provide a positive electrode active material, which forms a fluorine-containing coating by reacting lithium impurities present on the surface of the positive electrode active material (lithium composite oxide) with a fluorine-containing raw material, and reduces the changes in the electrochemical properties of the lithium composite oxide caused by the fluorine-containing coating by controlling the content of other elements other than fluorine in the coating.

[0016] In addition, another object of the present invention is to provide a lithium secondary battery using the positive electrode active material defined herein.

[0017] The purpose of the present invention is not limited to the purpose mentioned above, and other purposes and advantages of the present invention not mentioned can be understood through the following description, and can be more clearly understood through the embodiments of the present invention. In addition, it can be easily understood that the purpose and advantages of the present invention can be achieved by the means and combinations thereof in the claims.

[0018] Solutions to the problem

[0019] According to one aspect of the present invention for solving the above-mentioned technical problems, there is provided a positive electrode active material including a core portion including a lithium composite oxide capable of reversibly inserting and extracting lithium ions and a shell portion existing on at least a part of the surface of the core portion and containing fluorine.

[0020] In one embodiment, the lithium composite oxide includes at least one transition metal selected from nickel, cobalt, manganese and aluminum. Preferably, the lithium composite oxide is a lithium nickel-based composite oxide containing nickel. Furthermore, the lithium nickel-based composite oxide may further include at least one selected from manganese and aluminum.

[0021] In one embodiment, the lithium composite oxide may be represented by the following Chemical Formula 1.

[0022] [Chemical formula 1]

[0023] Li a Ni 1-(b+c+d) Co b M1 c M2 d O 2-e X e

[0024] Wherein, M1 is at least one selected from Mn and Al, M2 is at least one selected from Na, K, Mg, Ca, Ba, Mn, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu, M1 and M2 are different from each other, X is at least one anion element selected from F, P, S, Cl and Br, 0.5≤a≤1.5, 0≤b≤0.20, 0≤c≤0.30, 0≤d≤0.10, 0≤e≤0.10.

[0025] In other embodiments, the lithium composite oxide may be represented by the following Chemical Formula 2.

[0026] [Chemical formula 2]

[0027] Li a' Ni 1-(b'+d') Mn b' M2 d' O 2-e' X e'

[0028] Wherein, M2 is at least one selected from Na, K, Mg, Ca, Ba, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu, X is at least one anion element selected from F, P, S, Cl and Br, 0.95≤a'≤1.05, 0 <b'≤0.5,0≤d'≤0.10,0≤e'≤0.10。

[0029] In one embodiment, the lithium composite oxide may exist in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the shell portion may exist on the surface of the primary particles and at least a portion of a grain boundary between adjacent primary particles.

[0030] Furthermore, according to another aspect of the present invention, a positive electrode including the positive electrode active material is provided.

[0031] According to still another aspect of the present invention, there is provided a lithium secondary battery using the positive electrode.

[0032] Effects of the Invention

[0033] According to the present invention, by reacting lithium impurities present on the surface of the positive electrode active material (lithium composite oxide) with a fluorine-containing raw material to form a fluorine-containing coating layer, the content of lithium impurities present on the surface of the positive electrode active material (lithium composite oxide) can be effectively controlled without going through a water washing process, thereby preventing and / or alleviating the reduction in the electrochemical properties and stability of the positive electrode active material caused by lithium impurities.

[0034] In addition, according to the present invention, by controlling the content of other heterogeneous elements (especially carbon) and functional groups derived from heterogeneous elements in the fluorine-containing coating present on the surface of the positive electrode active material (lithium composite oxide), the changes in the electrochemical properties of the above-mentioned lithium composite oxide caused by the above-mentioned fluorine-containing coating can be reduced.

[0035] In addition to the above-described effects, specific effects of the present invention will be described while explaining specific details for implementing the present invention. DETAILED DESCRIPTION

[0036] Specific terms are defined herein for ease of understanding. Unless specifically defined herein, scientific terms and technical terms used herein should have the meanings commonly understood by those skilled in the art. In addition, it should be understood that as used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form, and vice versa.

[0037] Positive active material

[0038] A positive electrode active material according to one aspect of the present invention includes: a core portion including a lithium composite oxide capable of reversibly inserting and extracting lithium ions; and a shell portion present on at least a portion of a surface of the core portion and containing fluorine.

[0039] The lithium composite oxide is a composite metal oxide capable of inserting and extracting lithium ions and has a layered crystal structure belonging to the R-3m space group. The lithium composite oxide having a layered crystal structure exhibits a characteristic peak in the 2θ=18.6±1° region in a diffraction pattern obtained by XRD analysis.

[0040] When the lithium composite oxide contained in the positive electrode active material defined herein exists as an aggregate formed by agglomerating a plurality of primary particles, the lithium composite oxide may be referred to as a secondary particle.

[0041] The primary particles constituting the above-mentioned lithium composite oxide may have a rod (rod) shape, an elliptical shape and / or an irregular shape. In addition, unless specially designed in the preparation process, primary particles of various shapes may exist in the same positive electrode active material. In addition, the above-mentioned primary particles refer to particle units that do not appear to have grain boundaries when observed with a scanning electron microscope at a magnification of 5000 to 20000 times.

[0042] The average particle size of the primary particles constituting the lithium composite oxide defined herein may be 0.06 μm to 2 μm, preferably 0.06 μm to 1.2 μm, more preferably 0.25 μm to 0.75 μm. At this time, as the average particle size of the primary particles, the average value of the length in the major axis direction and the length in the minor axis direction of the primary particles ([major axis length + minor axis length] / 2) may be used.

[0043] The primary particle may be composed of a single crystal grain or a plurality of crystal grains. In this case, the size of the crystal grain may be inferred from a diffraction pattern obtained by XRD analysis of the lithium composite oxide, or calculated by substituting the full width at half maximum of a representative crystal plane characteristic peak into the Scherrer equation.

[0044] The crystallite size in the lithium composite oxide is preferably 40 nm to 130 nm. Alternatively, the crystallite size in the lithium composite oxide may be 40 nm to 120 nm, 45 nm to 110 nm, or 48 nm to 100 nm.

[0045] When the above-mentioned grain size is less than 40nm, the grain size of the material constituting the above-mentioned primary particles is too small, so it is possible to reduce the particle strength of the above-mentioned lithium composite oxide. In addition, as the size of the above-mentioned primary particles is excessively reduced, the specific surface area may increase, thereby promoting the generation of gas due to side reactions with the electrolyte. On the other hand, when the above-mentioned grain size is greater than 130nm, as the above-mentioned primary particles grow excessively, the initial capacity and initial efficiency of the lithium secondary battery using it as the positive electrode active material may decrease. In addition, when a fluorine-containing coating is formed on the surface of the overgrown primary particles, the degradation of other electrochemical properties may be caused by changes in surface resistance.

[0046] The average particle size of the secondary particles may be 0.5 μm to 15 μm, preferably, 1.0 μm to 12 μm. The average particle size of the secondary particles may vary according to the number of the primary particles constituting the secondary particles. The average particle size (D50) of the secondary particles may be measured using a laser diffraction method. For example, after the secondary particles are dispersed in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiated with ultrasonic waves of about 28 kHz at a power of 60 W, and then the volume cumulative particle size distribution diagram is obtained, and the particle size equivalent to 50% of the volume cumulative amount is obtained to achieve measurement.

[0047] Unless otherwise defined, the term "surface of the primary particle" as used herein refers to the outer surface of the primary particle exposed to the outside. Similarly, the term "surface of the secondary particle" as used herein refers to the outer surface of the secondary particle exposed to the outside. In this case, the "surface of the secondary particle" formed by the agglomeration of multiple primary particles is equivalent to the exposed surface of the primary particle existing on the surface of the secondary particle.

[0048] In addition, unless otherwise defined, the term "surface portion of a particle" as used herein refers to a region relatively close to the "outermost surface" of a particle, and "center portion of a particle" refers to a region relatively close to the "exact center" of a particle compared to the above-mentioned "surface portion". Therefore, the "surface portion of a primary particle" refers to a region relatively close to the "outermost surface" of the above-mentioned primary particle, and the "center portion of a primary particle" refers to a region relatively close to the "exact center" of the above-mentioned primary particle compared to the above-mentioned "surface portion". Similarly, the "surface portion of a secondary particle" refers to a region relatively close to the "outermost surface" of the above-mentioned secondary particle, and the "center portion of a secondary particle" refers to a region relatively close to the "exact center" of the above-mentioned secondary particle compared to the above-mentioned "surface portion".

[0049] At this time, a region other than the “surface portion of the particle” within any particle can be defined as the “center portion of the particle”.

[0050] The lithium composite oxide includes lithium and at least one transition metal. The transition metal may be at least one selected from nickel, cobalt, manganese and aluminum.

[0051] In one embodiment, the lithium composite oxide may be represented by the following Chemical Formula 1.

[0052] [Chemical formula 1]

[0053] Li a Ni 1-(b+c+d) Co b M1 c M2d O 2-e X e

[0054] Wherein, M1 is at least one selected from Mn and Al, M2 is at least one selected from Na, K, Mg, Ca, Ba, Mn, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu, M1 and M2 are different from each other, X is at least one anion element selected from F, P, S, Cl and Br, 0.5≤a≤1.5, 0≤b≤0.20, 0≤c≤0.30, 0≤d≤0.10, 0≤e≤0.10.

[0055] a, which represents the ratio of lithium to all elements other than lithium in the lithium composite oxide, may be 0.5 to 1.5, 0.75 to 1.25, 0.90 to 1.1, or 0.95 to 1.05.

[0056] The molar fraction of nickel relative to the total elements other than lithium in the lithium composite oxide may be 60% or more. In this case, in Chemical Formula 1, b+c+d is 0.40 or less. In addition, the molar fraction of nickel relative to the total elements other than lithium in the lithium composite oxide may be 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more.

[0057] When the lithium composite oxide contains cobalt, the molar fraction of cobalt relative to the entire elements other than lithium in the lithium composite oxide may be 20% or less, 15% or less, 10% or less, or 5% or less. When the lithium composite oxide contains cobalt, b in the chemical formula 1 is greater than 0, and when the lithium composite oxide is a cobalt-free lithium composite oxide that does not contain cobalt, b in the chemical formula 1 is 0.

[0058] When the lithium composite oxide contains manganese and / or aluminum, the molar fraction of manganese and / or aluminum relative to the total elements other than lithium in the lithium composite oxide may be 30% or less, 20% or less, 15% or less, 10% or less, or 5% or less. When the lithium composite oxide contains manganese and / or aluminum, c in the chemical formula 1 is greater than 0.

[0059] In the above chemical formula 1, M2 refers to a dopant present in the above secondary particles. The above dopant may be present in the lattice of the above primary particles in a doped state. When the above lithium composite oxide contains a dopant, M2 in the above chemical formula 1 is greater than 0. In addition, the molar fraction of the dopant relative to the entire elements other than lithium in the above lithium composite oxide may be 10% or less, 5% or less, 2% or less, or less than 2%.

[0060] As represented by the above chemical formula 1, at least a portion of the oxygen in the above lithium composite oxide can be substituted by at least one anion element selected from F, P, S, Cl and Br, preferably F. In particular, F has an ionic radius similar to that of oxygen, so compared with other anion elements, F can be more stably present in the crystal structure of the above lithium composite oxide. In addition, F can form a strong M-F bond by partially replacing the oxygen that forms the M (metal)-O bond, thereby helping to strengthen the crystal structure of the above lithium composite oxide.

[0061] In other embodiments, the lithium composite oxide may be represented by the following Chemical Formula 2.

[0062] [Chemical formula 2]

[0063] Li a' Ni 1-(b'+d') Mn b' M2 d' O 2-e' X e'

[0064] Wherein, M2 is at least one selected from Na, K, Mg, Ca, Ba, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu, X is at least one anion element selected from F, P, S, Cl and Br, 0.95≤a'≤1.05, 0 <b'≤0.5,0≤d'≤0.10,0≤e'≤0.10。

[0065] The molar fraction of nickel in the metal elements other than lithium in the lithium composite oxide represented by the above chemical formula 2 may be 0.60 to 0.95, preferably 0.70 to 0.90, and the molar fraction of manganese in the metal elements other than lithium may be 0.05 to 0.40, preferably 0.10 to 0.40, and more preferably 0.10 to 0.30.

[0066] When the molar fraction of nickel in the lithium composite oxide is less than 0.60, the proportion of the spinel phase in the lithium composite oxide may increase. The higher the proportion of the spinel phase in the lithium composite oxide, the higher the required operating voltage. Therefore, the capacity characteristics of the lithium secondary battery using the lithium composite oxide with a higher proportion of the spinel phase as the positive electrode active material may decrease. In addition, as the nickel content in the lithium composite oxide decreases and the manganese increases, the cation mixing in the lithium composite oxide may increase overall.

[0067] The charge of all transition metals constituting the lithium composite oxide is preferably in a trivalent state so as to present a stable charge neutrality state. At this time, when synthesizing a lithium composite oxide with a low cobalt content and a high manganese content, Mn 4+ becomes excessive, so in order to present a charge neutral state, it replaces Ni 3+ And you 2+ The content will increase. The excess Ni in the synthesis reaction 2+ Similar to Li + The size of cations can therefore occupy the 3a position of Li in the crystal structure of the above-mentioned lithium composite oxide. This phenomenon is called cation mixing.

[0068] On the other hand, when nickel is present in excess in the lithium composite oxide, the lithium composite oxide exhibits the same characteristics as LiNiO2. LiNiO2 not only has low thermal stability, but also, when an internal short circuit occurs due to external pressure, etc. in a charged state, the lithium composite oxide decomposes itself, or a side reaction occurs at the interface and surface between the electrolyte and the lithium composite oxide, resulting in rupture and fire of the lithium secondary battery.

[0069] On the other hand, when the molar fraction of manganese in the lithium composite oxide is greater than 0.40, the same problem as when the molar fraction of nickel is less than 0.60 may occur.

[0070] The positive electrode active material according to the present invention includes a shell portion, which is present on at least a portion of the surface of the core portion of the lithium composite oxide defined above. The shell portion may contain fluorine, more specifically, may contain LiF as a fluorine-containing compound. LiF may be formed by the reaction of a fluorine-containing polymer with lithium impurities (e.g., LiOH and Li2CO3, etc.) present on the surface of the core portion.

[0071] The fluorine content determined by IC analysis of the positive electrode active material is preferably 0.1 wt % to 0.5 wt %. When the fluorine content is less than 0.1 wt %, it is difficult to fully remove the lithium impurities present on the surface of the core, and an additional water washing process must be performed to reduce the content of lithium impurities. On the other hand, when the fluorine content exceeds 0.5 wt %, the LiF present on the surface of the core increases excessively, so that the surface resistance or electrochemical characteristics of the positive electrode active material may deteriorate.

[0072] The lithium impurities present on the surface of the core react with the fluorinated polymer (e.g., PVDF, PTFE, etc.) to generate LiF, so the content of lithium impurities present on the surface of the core can be reduced without the need for a separate water washing process for reducing the content of lithium impurities. Therefore, there is an advantage that the electrochemical characteristics and life of the positive electrode active material caused by the lithium impurities and / or the water washing process can be prevented and / or alleviated in advance.

[0073] When a single particle comprising the core and the shell is defined as a core-shell particle, the volume occupied by the core and the shell in the core-shell particle can be calculated from the cross section of the core-shell particle. For example, after obtaining a cross-sectional SEM image of the core-shell particle, the radius of the core and the radius of the shell are measured respectively, and then the volume of the core and the volume of the shell can be calculated from the radius of the core and the radius of the shell, respectively. In addition, the thickness of the shell in the core-shell particle can be greater than 1 nm and less than 50 nm.

[0074] When the thickness of the shell is less than 1 nm, it is difficult to fully remove the lithium impurities present on the surface of the core, and an additional water washing process must be performed to reduce the content of lithium impurities. On the other hand, when the thickness of the shell exceeds 50 nm, the surface resistance or electrochemical characteristics of the positive electrode active material may be reduced due to excessive LiF present on the surface of the core.

[0075] The lithium composite oxide corresponding to the core portion exists in the form of secondary particles formed by agglomeration of a plurality of primary particles, and thus the shell portion may exist on the surface of the primary particle and at least part of the grain boundary between adjacent primary particles.

[0076] Therefore, the shell portion is defined as a region where LiF exists on the surface of the primary particle and / or the secondary particle, and the shell portion may be formed entirely or partially (in the form of islands) on the surface of the primary particle and / or the secondary particle.

[0077] When the shell portion is present at a grain boundary between adjacent primary particles, the weight ratio of fluorine to nickel (F / Ni) present at the grain boundary is preferably 0.02 to 0.05.

[0078] The fluorine may be present at a higher concentration on the surface of the secondary particle than in the interior of the secondary particle. In this case, the fluorine may form a concentration gradient that decreases from the surface of the secondary particle toward the interior of the secondary particle along the interface between the primary particles.

[0079] On the other hand, when the lithium impurities present on the surface of the core react with the fluorinated polymer to form LiF, the fluorinated polymer may remain in the positive electrode active material, or elements (e.g., carbon) from the fluorinated polymer may remain. When the fluorinated polymer or elements (especially functional groups from the above elements) from the fluorinated polymer remain in the positive electrode active material, the surface resistance or electrochemical characteristics of the positive electrode active material may change differently than expected.

[0080] Therefore, when the above-mentioned positive electrode active material is subjected to XPS analysis, preferably, no peak is observed in the region exceeding 686eV and below 689eV, and an F1s peak is observed in the region above 684eV and below 686eV. Here, the F1s peak observed in the region above 684eV and below 686eV is a peak due to the presence of LiF on the surface of the above-mentioned core. On the other hand, if a peak is observed in a region exceeding 686eV and below 689eV, the above-mentioned peak indicates the presence of PVDF on the surface of the above-mentioned core. When PVDF is present on the surface of the core comprising a lithium composite oxide having a crystal structure defined herein, the surface resistance or electrochemical characteristics of the above-mentioned positive electrode active material may be reduced.

[0081] Furthermore, I(F1s) / I(C1s) determined by XPS analysis of the positive electrode active material may be 1.0 to 2.5, 1.1 to 2.3, 1.2 to 2.0, or 1.22 to 1.96.

[0082] Here, I(F1s) represents the intensity of the F1s peak observed in the region of 684 eV to 686 eV, and I(C1s) represents the intensity of the C1s peak caused by the C=O bond observed in the region of 288 eV to 292 eV. The intensity of the C1s peak caused by the C=O bond increases not only with the increase of carbon from the fluorine-containing polymer and the functional group from carbon, i.e., C=O, on the surface of the core, but also with the increase of the content of lithium impurities (Li2CO3) present on the surface of the core.

[0083] Therefore, when I(F1s) / I(C1s) is less than 1.0, it means that the carbon derived from the fluorine-containing polymer on the surface of the core, C=O derived from the carbon, and lithium impurities (Li2CO3) present on the surface of the core are present in excess.

[0084] As described above, when the carbon from the fluorinated polymer on the surface of the core and the C=O from the carbon and the lithium impurities (Li2CO3) present on the surface of the core are excessively present, the surface resistance and electrochemical characteristics of the positive electrode active material may be reduced. When I(F1s) / I(C1s) is greater than 2.5, it means that LiF is excessively present on the surface of the core. In this case, the excess LiF may cause the surface resistance or electrochemical characteristics of the positive electrode active material to decrease.

[0085] Lithium secondary battery

[0086] According to another aspect of the present invention, a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector may be provided. The positive electrode active material layer may include a positive electrode active material according to various embodiments of the present invention. Therefore, the positive electrode active material is the same as that described previously, so for convenience, its specific description is omitted, and only the remaining components not described above are described below.

[0087] As long as the positive electrode current collector does not induce chemical changes in the battery and has conductivity, there is no particular restriction. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or the surface of aluminum or stainless steel may be treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector may generally have a thickness of 3 μm to 500 μm, and fine concavoconvexities may be formed on the surface of the current collector to improve the bonding force of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven body.

[0088] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition including the positive electrode active material, a conductive material, and optionally a binder as required, on the positive electrode current collector.

[0089] In this case, the content of the positive electrode active material can be 80 wt % to 99 wt %, more specifically 85 wt % to 98.5 wt % relative to the total weight of the positive electrode active material layer. When the positive electrode active material is included in the above content range, excellent capacity performance can be shown, but it is not limited thereto.

[0090] The above-mentioned conductive materials are used to impart conductivity to the electrode. In the battery formed, as long as they do not cause chemical changes and have electronic conductivity, they can be used without limitation. As specific examples, 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, and carbon fiber; 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, etc., and one of them or a mixture of two or more thereof can be used. The above-mentioned conductive material may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0091] The above-mentioned binder plays a role in improving the adhesion between multiple positive electrode active material particles and the bonding force between the positive electrode active material and the current collector. As a specific example, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber (EPDM), sulfonated ethylene propylene diene monomer rubber, styrene butadiene rubber (SBR), fluororubber or various copolymers thereof, etc., can be used. One or a mixture of two or more thereof. Relative to the total weight of the positive electrode active material layer, 0.1 wt % to 15 wt % of the above-mentioned binder may be included.

[0092] In addition to using the above-mentioned positive electrode active material, the above-mentioned positive electrode can be prepared according to a common positive electrode preparation method. Specifically, it can be prepared by coating a positive electrode slurry composition on a positive electrode current collector and then drying and rolling it. The above-mentioned positive electrode slurry composition is prepared by dissolving or dispersing the above-mentioned positive electrode active material in a solvent and selectively dissolving or dispersing a binder and a conductive material in a solvent.

[0093] The above-mentioned solvent may be a solvent commonly used in the art, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water, and a mixture of one or more thereof may be used. Considering the coating thickness and preparation yield of the slurry, the amount of the above-mentioned solvent used is sufficient to dissolve or disperse the above-mentioned positive electrode active material, conductive material and binder and have a viscosity that can show excellent thickness uniformity when applied to prepare the positive electrode.

[0094] Furthermore, in another embodiment, the positive electrode may be prepared by casting the positive electrode slurry composition on a separate support, and then laminating a thin film obtained by peeling the support on a positive electrode current collector.

[0095] In addition, according to another aspect of the present invention, an electrochemical device comprising the positive electrode described above can be provided. Specifically, the electrochemical device described above can be a battery, a capacitor, etc., and more specifically, can be a lithium secondary battery.

[0096] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separation membrane and an electrolyte disposed between the positive electrode and the negative electrode. The positive electrode is the same as the above description, so for convenience, the specific description is omitted, and only the remaining configuration not described above is described below.

[0097] The lithium secondary battery may further include: a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode and the separation membrane; and a sealing member for sealing the battery container.

[0098] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0099] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can usually have a thickness of 3μm to 500μm. Similar to the positive electrode current collector, the binding force of the negative electrode active material can be strengthened by forming fine concave and convex on the surface of the current collector. For example, it can be used in various forms such as thin film, sheet, foil, net, porous body, foam, non-woven body, etc.

[0100] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition including the negative electrode active material and a conductive material and optionally including a binder as required on the negative electrode current collector.

[0101] As the negative electrode active material, a compound capable of reversibly inserting and extracting lithium ions can be used. Specific examples include carbon materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO β(0<β<2), SnO2, vanadium oxide, lithium vanadium oxide, metal oxides capable of being doped and dedoped with lithium; or composites containing the above metal compounds and carbon materials such as Si-C composites or Sn-C composites, etc., and one or a mixture of two or more of them can be used. In addition, as the above-mentioned negative electrode active material, a metal lithium film can also be used. In addition, both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Representative low-crystalline carbons are soft carbon and hard carbon, and representative high-crystalline carbons are amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, mesophase carbon microbeads, mesophase pitches, and high-temperature calcined carbons such as petroleum or coal tar pitch derived cokes.

[0102] The negative electrode active material layer may contain 80 wt % to 99 wt % of the negative electrode active material, based on the total weight of the negative electrode active material layer.

[0103] The binder is a component that helps to bind the conductive material, the active material and the current collector. Usually, based on the total weight of the negative electrode active material layer, 0.1 wt % to 10 wt % of the binder can be added. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber, sulfonated ethylene propylene diene monomer rubber, styrene butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0104] The conductive material is a component used to further improve the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, the conductive material can be added in an amount of 10% by weight or less, preferably 5% by weight or less. There are no particular restrictions on such conductive materials as long as they do not induce chemical changes in the corresponding battery and have conductivity. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0105] In one embodiment, the negative electrode active material layer can be prepared by coating a negative electrode slurry composition on a negative electrode current collector and drying it, wherein the negative electrode slurry composition is prepared by dissolving or dispersing the negative electrode active material in a solvent and selectively dissolving or dispersing a binder and a conductive material in a solvent, or by casting the negative electrode slurry composition on a separate support and laminating a thin film obtained by peeling off the support on the negative electrode current collector.

[0106] On the other hand, in the above-mentioned lithium secondary battery, the separation membrane is used to separate the negative electrode and the positive electrode and provide a mobile channel for lithium ions. As long as the separation membrane commonly used in the lithium secondary battery, it can be used without restriction, especially, preferably, for the ion movement of the electrolyte, the impedance is low and there is excellent electrolyte moisture-containing capacity. Specifically, a porous polymer film can be used, for example, a porous polymer film prepared by polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers or their two or more layers of stacked structures. In addition, a common porous non-woven fabric can also be used, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. In addition, in order to ensure heat resistance or mechanical strength, a separation membrane coated with a ceramic component and a polymer substance can also be used, which can be selectively used with a single layer or multilayer structure.

[0107] Furthermore, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in preparing lithium secondary batteries.

[0108] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0109] As the above-mentioned organic solvent, any organic solvent that can act as a medium for the movement of ions involved in the electrochemical reaction of the battery can be used without limitation. Specifically, as the above-mentioned organic solvent, ester solvents such as methylacetate, ethylacetate, γ-butyrolactone, ε-caprolactone, etc.; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (EPC), etc. can be used. Carbonate solvents such as polycarbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (r is a straight-chain, branched or cyclic hydrocarbon group with 2 to 20 carbon atoms, which may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane. Among them, carbonate solvents are preferred, and more preferably, a mixture of cyclic carbonates (such as ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and low-viscosity linear carbonate compounds (such as ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate). In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, excellent electrolyte performance can be shown.

[0110] The above-mentioned lithium salt can be used without limitation as a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the above-mentioned lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI or LiB(C2O4)2, etc. Preferably, the concentration of the above-mentioned lithium salt is used in the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, and therefore, excellent electrolyte performance can be shown, and lithium ions can be effectively moved.

[0111] When the electrolyte used herein is a solid electrolyte, for example, a solid inorganic electrolyte such as a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, or a halide solid electrolyte can be used, and preferably a sulfide solid electrolyte can be used.

[0112] As the material of the sulfide solid electrolyte, a solid electrolyte containing Li, an X element (wherein X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga and In) and S can be used. Examples of the above-mentioned sulfide solid electrolyte materials include Li2S-P2S5, Li2S-P2S-LiX (wherein X is a halogen element such as I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are integers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (wherein p and q are integers, and M is P, Si, Ge, B, Al, Ga or In), etc.

[0113] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be in an amorphous state, a crystalline state, or a mixed state of the amorphous state and the crystalline state.

[0114] Examples of materials for oxide-based solid electrolytes include Li7La3Zr2O 12 , Li 7-x LqCy 1-x Nb x O 12 , Li 7- 3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3、Li 1+x Al x Ti 2-x (PO4)3、Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x GeO4(LISICON), etc.

[0115] The solid electrolyte may be arranged between the positive electrode and the negative electrode as a separate layer (solid electrolyte layer). In addition, the solid electrolyte may be partially contained in the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or the solid electrolyte may be partially contained in the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer.

[0116] In addition to the above electrolyte components, the electrolyte may further include one or more additives such as halogenated alkylene carbonate compounds such as bisfluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, 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 chloride, etc., for the purpose of improving the life characteristics of the battery, inhibiting the reduction of the battery capacity, and increasing the discharge capacity of the battery. In this case, the above additives may be included in an amount of 0.1 wt% to 5 wt% relative to the total weight of the electrolyte.

[0117] As described above, the lithium secondary battery containing the positive electrode active material of the present invention stably shows excellent discharge capacity, output characteristics and life characteristics, and can therefore be used in portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEV).

[0118] The external shape of the lithium secondary battery according to the present invention is not particularly limited, and may be a cylindrical shape using a can, a prismatic shape, a pouch shape, a coin shape, etc. Also, preferably, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but also as a unit battery of a medium or large battery module including a plurality of battery cells.

[0119] According to another aspect of the present invention, a battery module including the above-mentioned lithium secondary battery as a unit cell and / or a battery pack including the same may be provided.

[0120] The battery module or the battery pack can be used as a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle and a plug-in hybrid electric vehicle (PHEV); or a power source for one or more medium or large devices in a power storage system.

[0121] Hereinafter, the present invention will be described in more detail by way of examples. However, these examples are only for illustrating the present invention, and the scope of the present invention should not be construed as being limited by these examples.

[0122] Preparation Example 1. Preparation of positive electrode active material

[0123] Comparative Example 1

[0124] Ni was synthesized by a known co-precipitation method using an aqueous solution of metal salts of nickel sulfate and manganese sulfate mixed in a molar ratio of 75:25. 0.75 Mn 0.25 (OH)2 hydroxide precursor.

[0125] Then, the hydroxide precursor was mixed with LiOH (Li / (metal other than Li) molar ratio=1.01), and then heat treated in an O 2 atmosphere at 850° C. for 12 hours to obtain a positive electrode active material.

[0126] Comparative Example 2

[0127] Ni was synthesized by a known coprecipitation method using an aqueous solution of metal salts of nickel sulfate and manganese sulfate mixed in a molar ratio of 75:25. 0.75 Mn 0.25 (OH)2 hydroxide precursor.

[0128] Then, the hydroxide precursor was mixed with LiOH (Li / (metal other than Li) molar ratio = 1.01), and then heat treated at 850° C. for 12 hours in an O 2 atmosphere to obtain an intermediate product.

[0129] Then, the intermediate product was heat treated in an O 2 atmosphere at 150° C. for 8 hours to obtain a positive electrode active material.

[0130] Comparative Example 3

[0131] A positive electrode active material was prepared in the same manner as in Comparative Example 2 except that the heat treatment temperature of the intermediate product was changed to 300°C.

[0132] Comparative Example 4

[0133] A positive electrode active material was prepared in the same manner as in Comparative Example 2 except that the heat treatment temperature of the intermediate product was changed to 350°C.

[0134] Comparative Example 5

[0135] A positive electrode active material was prepared in the same manner as in Comparative Example 2 except that the heat treatment temperature of the intermediate product was changed to 400°C.

[0136] Comparative Example 6

[0137] A positive electrode active material was prepared in the same manner as in Comparative Example 2 except that the heat treatment temperature of the intermediate product was changed to 500°C.

[0138] Comparative Example 7

[0139] A positive electrode active material was prepared in the same manner as in Comparative Example 2 except that the heat treatment temperature of the intermediate product was changed to 600°C.

[0140] Comparative Example 8

[0141] Ni was synthesized by a known coprecipitation method using an aqueous solution of metal salts of nickel sulfate and manganese sulfate mixed in a molar ratio of 75:25. 0.75 Mn 0.25 (OH)2 hydroxide precursor.

[0142] Then, the hydroxide precursor was mixed with LiOH (Li / (metal other than Li) molar ratio = 1.01), and then heat treated at 850° C. for 12 hours in an O 2 atmosphere to obtain an intermediate product.

[0143] Then, the intermediate product was mixed with 0.1 wt % of PVDF and then heat-treated in an O 2 atmosphere at 350° C. for 8 hours to obtain a positive electrode active material.

[0144] Comparative Example 9

[0145] Ni was synthesized by a known coprecipitation method using an aqueous solution of metal salts of nickel sulfate and manganese sulfate mixed in a molar ratio of 75:25. 0.75 Mn 0.25 (OH)2 hydroxide precursor.

[0146] Then, the hydroxide precursor was mixed with LiOH (Li / (metal other than Li) molar ratio = 1.01), and then heat treated at 850° C. for 12 hours in an O 2 atmosphere to obtain an intermediate product.

[0147] Then, the intermediate product was mixed with 5.0 wt % of PVDF and then heat-treated in an O 2 atmosphere at 350° C. for 8 hours to obtain a positive electrode active material.

[0148] Comparative Example 10

[0149] Ni was synthesized by a known coprecipitation method using an aqueous solution of metal salts of nickel sulfate and manganese sulfate mixed in a molar ratio of 75:25. 0.75 Mn 0.25 (OH)2 hydroxide precursor.

[0150] Then, the hydroxide precursor was mixed with LiOH (Li / (metal other than Li) molar ratio = 1.01), and then heat treated at 850° C. for 12 hours in an O 2 atmosphere to obtain an intermediate product.

[0151] Then, the intermediate product was mixed with 0.35 wt % of PVDF and then heat-treated in an O 2 atmosphere at 150° C. for 8 hours to obtain a positive electrode active material.

[0152] Comparative Example 11

[0153] Ni was synthesized by a known coprecipitation method using an aqueous solution of metal salts of nickel sulfate and manganese sulfate mixed in a molar ratio of 75:25. 0.75 Mn 0.25 (OH)2 hydroxide precursor.

[0154] Then, the hydroxide precursor was mixed with LiOH (Li / (metal other than Li) molar ratio = 1.01), and then heat treated at 850° C. for 12 hours in an O 2 atmosphere to obtain an intermediate product.

[0155] Then, the intermediate product was mixed with 0.35 wt % of PVDF and then heat-treated in an O 2 atmosphere at 300° C. for 8 hours to obtain a positive electrode active material.

[0156] Comparative Example 12

[0157] Ni was synthesized by a known coprecipitation method using an aqueous solution of metal salts of nickel sulfate and manganese sulfate mixed in a molar ratio of 75:25. 0.75 Mn 0.25 (OH)2 hydroxide precursor.

[0158] Then, the hydroxide precursor was mixed with LiOH (Li / (metal other than Li) molar ratio = 1.01), and then heat treated in an O2 atmosphere at 750°C for 12 hours to obtain an intermediate product.

[0159] Then, the intermediate product was mixed with 0.35 wt % of PVDF and then heat-treated in an O 2 atmosphere at 400° C. for 8 hours to obtain a positive electrode active material.

[0160] Comparative Example 13

[0161] Ni was synthesized by a known coprecipitation method using an aqueous solution of metal salts of nickel sulfate and manganese sulfate mixed in a molar ratio of 75:25. 0.75 Mn 0.25 (OH)2 hydroxide precursor.

[0162] Then, the hydroxide precursor was mixed with LiOH (Li / (metal other than Li) molar ratio = 1.01), and then heat treated at 950° C. for 12 hours in an O 2 atmosphere to obtain an intermediate product.

[0163] Then, the intermediate product was mixed with 0.35 wt % of PVDF and then heat-treated in an O 2 atmosphere at 400° C. for 8 hours to obtain a positive electrode active material.

[0164] Example 1

[0165] Ni was synthesized by a known coprecipitation method using an aqueous solution of metal salts of nickel sulfate and manganese sulfate mixed in a molar ratio of 75:25. 0.75 Mn 0.25 (OH)2 hydroxide precursor.

[0166] Then, the hydroxide precursor was mixed with LiOH (Li / (metal other than Li) molar ratio = 1.01), and then heat treated at 850° C. for 12 hours in an O 2 atmosphere to obtain an intermediate product.

[0167] Then, the intermediate product was mixed with 0.35 wt % of PVDF and then heat-treated in an O 2 atmosphere at 350° C. for 8 hours to obtain a positive electrode active material.

[0168] Example 2

[0169] A positive electrode active material was prepared in the same manner as in Example 1 except that the heat treatment temperature of the intermediate product was changed to 400°C.

[0170] Example 3

[0171] A positive electrode active material was prepared in the same manner as in Example 1 except that the heat treatment temperature of the intermediate product was changed to 500°C.

[0172] Example 4

[0173] A positive electrode active material was prepared in the same manner as in Example 1 except that the heat treatment temperature of the intermediate product was changed to 600°C.

[0174] Example 5

[0175] Ni was synthesized by a known coprecipitation method using an aqueous solution of metal salts of nickel sulfate and manganese sulfate mixed in a molar ratio of 75:25. 0.75 Mn 0.25 (OH)2 hydroxide precursor.

[0176] Then, the hydroxide precursor was mixed with LiOH (Li / (metal other than Li) molar ratio = 1.01), and then heat treated at 850° C. for 12 hours in an O 2 atmosphere to obtain an intermediate product.

[0177] Then, the intermediate product was mixed with 0.5 wt % of PVDF and then heat-treated in an O 2 atmosphere at 400° C. for 8 hours to obtain a positive electrode active material.

[0178] Example 6

[0179] Ni was synthesized by a known coprecipitation method using an aqueous solution of metal salts of nickel sulfate and manganese sulfate mixed in a molar ratio of 75:25. 0.75 Mn 0.25 (OH)2 hydroxide precursor.

[0180] Then, the hydroxide precursor was mixed with LiOH (Li / (metal other than Li) molar ratio = 1.01), and then heat treated in an O2 atmosphere at 800°C for 12 hours to obtain an intermediate product.

[0181] Then, the intermediate product was mixed with 0.35 wt % of PVDF and then heat-treated in an O 2 atmosphere at 400° C. for 8 hours to obtain a positive electrode active material.

[0182] Preparation Example 2. Fabrication of a lithium secondary battery (half-cell)

[0183] 94 wt % of each positive electrode active material prepared according to Preparation Example 1, 3 wt % of carbon black and 3 wt % of PVDF binder were dispersed in 30 g of N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was evenly coated on an aluminum film having a thickness of 15 μm and vacuum dried at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0184] Relative to the above-mentioned positive electrode, lithium foil is used as a counter electrode, a porous polyethylene film (Celgard 2300, thickness: 25μm) is used as a separation membrane, and an electrolyte solution containing LiPF6 at a concentration of 1.15M in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7 is used to prepare a half-cell.

[0185] Experimental Example 1. IC and XRD analysis of positive electrode active material

[0186] The positive electrode active materials prepared according to Preparation Example 1 were subjected to ion chromatography (IC) analysis using an IC device (Thermo Dionex ICS-6000) to measure the F content in the positive electrode active materials.

[0187] In addition, each positive electrode active material prepared according to Preparation Example 1 was subjected to X-ray diffraction (XRD) analysis, and the obtained half-peak full width was substituted into the Scherrer equation to calculate the grain size of the lithium composite oxide contained in the above positive electrode active material. XRD analysis was performed using a Bruker D8 Advance diffractometer.

[0188] The above measurement results are shown in Table 1 below.

[0189] Table 1

[0190]

[0191]

[0192] For the positive electrode active material according to Comparative Example 10, it can be confirmed that the heat treatment temperature after mixing the intermediate product and PVDF is too low, resulting in most of the PVDF remaining as unreacted. Therefore, since F doping and / or conversion of lithium impurities to LiF hardly occurs in the above-mentioned positive electrode active material, F is not detected when the positive electrode active material according to Comparative Example 10 is subjected to IC analysis.

[0193] For the positive active material according to Comparative Example 12, due to the low heat treatment temperature (calcination temperature) of the hydroxide precursor, insufficient crystal growth was caused, and thus the grain size was confirmed to be about 28 nm. On the other hand, in the case of the positive active material according to Comparative Example 13, due to the high heat treatment temperature (calcination temperature) of the hydroxide precursor, excessive crystal growth was caused, and thus the grain size was confirmed to be about 200 nm.

[0194] Experimental Example 2. XPS Analysis of Positive Electrode Active Material

[0195] XPS analysis was performed on each positive electrode active material prepared according to Preparation Example 1 to confirm the composition of the surface (especially the shell) of the positive electrode active material. XPS analysis was performed using K-alpha TM The analysis was performed using a Thermo UK spectrometer (accelerating voltage: 100 eV to 3 keV, energy resolution: 0.50 eV).

[0196] Specifically, by the above XPS analysis, it is confirmed whether there is a PVDF characteristic peak in the region of more than 686eV and less than 689eV, and whether there is an F1s peak in the region of more than 684eV and less than 686eV. In addition, the ratio of the intensity of the F1s peak observed in the region of more than 684eV and less than 686eV to the intensity of the C1s peak caused by the C=O bond observed in the region of more than 288eV and less than 292eV is calculated, that is, I(F1s) / I(C1s).

[0197] The XPS analysis results are shown in Table 2 below.

[0198] Table 2

[0199]

[0200]

[0201] In the case of the positive electrode active material according to Comparative Example 8, since the PVDF content mixed with the intermediate product is too low, the XPS analysis results do not detect the peak corresponding to unreacted PVDF, but since the intensity of the F1s peak is extremely weak, I(F1s) / I(C1s) converges to 0.

[0202] In the case of the positive electrode active material according to Comparative Example 9, since the PVDF content mixed with the intermediate product is too high, most of it remains in the form of unreacted PVDF, so there is a PVDF characteristic peak in the region of more than 686eV and less than 689eV. In addition, not only is there an excessive amount of unreacted PVDF, but as shown in the residual lithium analysis results of Experimental Example 4, the residual lithium (Li2CO3) content is too high, resulting in I(C1s) being too large despite the presence of the F1s peak, so that I(F1s) / I(C1s) converges to 0.

[0203] In the case of the positive electrode active material according to Comparative Example 10, since the heat treatment temperature after mixing with PVDF was too low, the lithium impurities were hardly converted into LiF, and thus the XPS analysis results showed that no F1s peak was detected.

[0204] Similarly, in the case of the positive electrode active material according to Comparative Example 11, since the heat treatment temperature after PVDF mixing is low, the PVDF mixed with the intermediate product only partially reacts with the lithium impurities and is converted into LiF. Therefore, the XPS analysis results not only show the presence of a peak corresponding to unreacted PVDF, but also the intensity of the F1s peak is low, thereby confirming that I(F1s) / I(C1s) is less than 1.0.

[0205] Experimental Example 3. Evaluation of electrochemical characteristics of positive electrode active material

[0206] The lithium secondary battery (half cell) prepared according to Preparation Example 2 was subjected to a charge / discharge experiment using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0 V to 4.4 V, and a discharge rate of 0.1 C to measure the initial charge capacity, initial discharge capacity, and initial efficiency.

[0207] In addition, the same lithium secondary battery (half-cell) was charged / discharged 50 times at 25°C, a voltage range of 3.0 V to 4.4 V, and 1C to 1C / 1C using an electrochemical analyzer (Toyo, Toscat-3100), and then the ratio of the discharge capacity at the 50th cycle (cycle capacity retention) was measured.

[0208] The above measurement results are shown in Table 3 below.

[0209] Table 3

[0210]

[0211] Referring to the results in Table 3, it can be confirmed that the lithium secondary batteries using the positive electrode active materials according to Examples 1 to 6 have improved electrochemical characteristics such as capacity characteristics, rate characteristics, and capacity retention ratio.

[0212] Experimental Example 4. Analysis of Residual Lithium in Positive Electrode Active Material

[0213] The residual lithium (lithium impurity) content in the positive electrode active material prepared according to Preparation Example 1 was analyzed by pH titration. As a pH titration method, the residual lithium (lithium impurity) content was measured by pH titration of the above-mentioned positive electrode active material with 0.1M HCl used until the pH value reached 4. Specifically, 5g of each positive electrode active material prepared according to Preparation Example 1 was added to 100ml of deionized water (DIW), stirred for 15 minutes and filtered, 50ml of the filtered solution was taken, and 0.1M HCl was added thereto to measure the HCl consumption according to the pH change, and the content of LiOH and Li2CO3 was calculated.

[0214] The above measurement results are shown in Table 4 below.

[0215] Table 4

[0216] Classification LiOH(ppm) <![CDATA[LiCO3(ppm)]]> Total (ppm) Example 1 1786 1574 3361 Example 2 1986 1664 3650 Example 3 2341 1992 4333 Example 4 2583 2115 4698 Example 5 2622 1761 4383 Example 6 4049 1444 5493 Comparative Example 1 3250 4242 7492 Comparative Example 2 2391 3398 5790 Comparative Example 3 2214 3505 5720 Comparative Example 4 2046 3927 5973 Comparative Example 5 2203 3246 5449 Comparative Example 6 2277 3238 5516 Comparative Example 7 2060 2813 4873 Comparative Example 8 2017 3368 5385 Comparative Example 9 565 15201 15766 Comparative Example 10 2697 2857 5554 Comparative Example 11 2314 2863 5177 Comparative Example 12 4154 4530 8684 Comparative Example 13 1230 946 2176

[0217] Referring to the results of Table 4 above, it can be confirmed that the positive electrode active materials according to Examples 1 to 6 are reduced in lithium impurity content (5,500 ppm or less) by surface modification without a water washing process for reducing the content of lithium impurities such as LiOH and Li2CO3 remaining on the surface of the positive electrode active material, compared with Comparative Example 1. In particular, in the case of the positive electrode active materials according to Examples 1 to 6, the reduction in Li2CO3 among the lithium impurities is large.

[0218] In addition, although the residual lithium content of the positive electrode active materials according to Examples 1 to 6 is similar to that of Comparative Examples 2, 5, 6, 7, 8, 10, 11 and 13, it can be verified by Experimental Example 3 that they exhibit better electrochemical properties.

[0219] Although the embodiments of the present invention are described above, those skilled in the art will understand that various modifications and changes can be made to the present invention by adding, modifying, deleting, increasing, etc., without departing from the scope of the idea of ​​the present invention as described in the claims, and these also fall within the scope of the rights of the present invention.

Claims

1. A positive electrode active material comprising a core portion comprising a lithium composite oxide capable of reversibly inserting / extracting lithium ions and a shell portion present on at least a portion of the surface of the core portion and containing fluorine, wherein the positive electrode active material is characterized in that: The crystal size of the lithium composite oxide is not less than 40 nm and not more than 130 nm. When the positive electrode active material was subjected to XPS analysis, no peak was observed in the region exceeding 686 eV and below 689 eV, but an F1s peak was observed in the region from 684 eV to 686 eV.

2. The positive electrode active material according to claim 1, characterized in that The ratio of the intensity of the F1s peak observed in the region of 684 eV to 686 eV and the intensity of the C1s peak due to the C=O bond observed in the region of 288 eV to 292 eV determined by XPS analysis of the positive electrode active material, i.e., I(F1s) / I(C1s), is 1.0 to 2.

5.

3. The positive electrode active material according to claim 1, characterized in that The lithium composite oxide includes at least one transition metal selected from the group consisting of nickel, cobalt, manganese and aluminum.

4. The positive electrode active material according to claim 1, characterized in that The lithium composite oxide is represented by the following chemical formula 1: [Chemical formula 1] Li a Ni 1-(b+c+d) Co b M1 c M2 d O 2-e X e (in, M1 is at least one selected from Mn and Al, M2 is at least one selected from Na, K, Mg, Ca, Ba, Mn, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu, M1 and M2 are different from each other. X is at least one anion element selected from F, P, S, Cl and Br, 0.5≤a≤1.5, 0≤b≤0.20, 0≤c≤0.30, 0≤d≤0.10, 0≤e≤0.10).

5. The positive electrode active material according to claim 4, characterized in that In the lithium composite oxide, the molar fraction of nickel relative to all elements other than lithium is 60% or more.

6. The positive electrode active material according to claim 1, characterized in that The lithium composite oxide is represented by the following chemical formula 2: [Chemical formula 2] The a' Nor 1-(b'+d') Mn b' M2 d' O 2-e' X e' (in, M2 is at least one selected from Na, K, Mg, Ca, Ba, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu, X is at least one anion element selected from F, P, S, Cl and Br, 0.95≤a'≤1.05,0 <b'≤0.5,0≤d'≤0.10,0≤e'≤0.10)。 7. The positive electrode active material according to claim 6, characterized in that In the lithium composite oxide, the molar fraction of nickel relative to all elements other than lithium is 60% or more and 95% or less.

8. The positive electrode active material according to claim 1, characterized in that The shell portion includes LiF.

9. The positive electrode active material according to claim 1, characterized in that The lithium composite oxide exists in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the shell portion exists on the surface of the primary particles and at least a part of the grain boundary between adjacent primary particles.

10. The positive electrode active material according to claim 9, characterized in that The weight ratio of fluorine to nickel (F / Ni) present in the grain boundaries between adjacent primary particles is 0.02 to 0.

05.

11. The positive electrode active material according to claim 1, characterized in that The fluorine content determined by IC analysis of the positive electrode active material is 0.1 wt % to 0.5 wt %.

12. The positive electrode active material according to claim 1, characterized in that The shell portion has a thickness of not less than 1 nm and not more than 50 nm.

13. The positive electrode active material according to claim 1, characterized in that The total content of LiOH and Li2CO3 present in the above-mentioned positive electrode active material is 5,500 ppm or less.

14. A positive electrode, characterized in that: The positive electrode active material comprises the positive electrode active material according to any one of claims 1 to 13.

15. A lithium secondary battery, characterized in that: The positive electrode according to claim 14 is used.

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