Positive electrode active material and lithium secondary battery containing the same

Abstract

The present invention relates to a cathode active material and a lithium secondary battery including the same. More specifically, the present invention relates to a cathode active material that can remove lithium impurities, such as LiOH and Li2CO3, remaining on the surface of the cathode active material through surface modification without a water washing process for reducing the content of the lithium impurities, thereby preventing and / or mitigating deterioration in the electrochemical properties and lifespan of the cathode active material due to the lithium impurities and / or the water washing process, and a lithium secondary battery using a cathode including the cathode active material.

Description

[Technical Field]

[0001] The present invention relates to a cathode active material and a lithium secondary battery including the same. More specifically, the present invention relates to a cathode active material that can remove lithium impurities, such as LiOH and Li2CO3, remaining on the surface of the cathode active material through surface modification without a water washing process for reducing the content of the lithium impurities, thereby preventing and / or mitigating deterioration in the electrochemical properties and lifespan of the cathode active material due to the lithium impurities and / or the water washing process, and a lithium secondary battery using a cathode including the cathode active material. [Background technology]

[0002] Batteries store electricity by using materials capable of electrochemical reactions at the positive and negative electrodes. A typical example of such batteries is a lithium secondary battery, which stores electrical energy by utilizing the difference in chemical potential when lithium ions are intercalated / deintercalated at the positive and negative electrodes.

[0003] The lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte solution or a polymer electrolyte solution between the positive electrode and the negative electrode.

[0004] Lithium composite oxides are used as the positive electrode active material for lithium secondary batteries, and composite oxides such as LiCoO2, LiMn2O4, LiNiO2, and LiMnO2 are examples of the oxides that have been researched.

[0005] Among the positive electrode active materials, LiCoO2 is the most widely used due to its excellent lifespan characteristics and charge / discharge efficiency. However, it has a drawback in that it is expensive due to the limited availability of cobalt as a raw material, limiting its price competitiveness.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal safety and low cost, but have problems such as low capacity and poor high-temperature characteristics. Also, LiNiO2-based positive electrode active materials exhibit high discharge capacity battery characteristics, but are difficult to synthesize due to the problem of cation mixing between Li and transition metals, which results in significant problems with rate characteristics.

[0007] As a result, ternary-type lithium composite oxides such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), in which part of the nickel is replaced with cobalt, manganese, and / or aluminum, or quaternary-type lithium composite oxides such as NCMA (Ni-Co-Mn-Al) have been developed as a way to improve the low rate and cycle characteristics while maintaining the high reversible capacity of LiNiO2. The lower the nickel content in these ternary or quaternary lithium composite oxides, the lower the reversible capacity, so recently, active research has been conducted into increasing the nickel content in lithium composite oxides.

[0008] However, as the nickel content in the lithium composite oxide increases, cation mixing within the crystal structure increases, which leads to problems such as a decrease in stability and an increase in the content of unreacted lithium impurities such as LiOH and Li2CO3 on the surface.

[0009] The greater the content of lithium impurities remaining on the surface of the lithium composite oxide, the more likely it is that gas generation and swelling will occur in a lithium secondary battery using the lithium composite oxide as a positive electrode active material.Furthermore, the greater the content of lithium impurities remaining on the surface of the lithium composite oxide, the more likely it is that the lithium impurities will cause gelation of the paste composition when preparing a paste for forming a positive electrode active material layer using the lithium composite oxide.

[0010] Therefore, a water washing process is essential for removing lithium impurities remaining on the surface of the lithium composite oxide during the manufacturing process of the positive electrode active material. However, damage to the surface of the lithium composite oxide caused by the water washing process can result in deterioration of the electrochemical characteristics and stability of a lithium secondary battery using the lithium composite oxide as a positive electrode active material, particularly in premature deterioration of the battery's lifespan.

[0011] In order to solve the problem of lithium impurities, a method has been proposed in which the lithium composite oxide is washed with water, and then a coating layer is formed to cover surface defects of the lithium composite oxide with the coating layer. However, it has been pointed out that this method may change the surface resistance characteristics of the lithium composite oxide, making it difficult to exhibit sufficient electrochemical properties. Furthermore, since there is insufficient residual lithium that can react with the coating raw material after the water washing process, it is difficult to form a uniform coating layer, making it difficult to sufficiently alleviate the reduction in lifespan due to surface damage of the lithium composite oxide caused by the water washing process.

[0012] In addition, instead of washing the lithium composite oxide with water, a method of forming a coating layer by reacting a coating raw material containing lithium impurities and metal elements has been proposed. However, this method also has problems in that the surface resistance of the lithium composite oxide changes, resulting in a decrease in the electrochemical characteristics, such as a decrease in the charge / discharge capacity of a lithium secondary battery using the lithium composite oxide as a positive electrode active material. Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention aims to provide a positive electrode active material that can prevent and / or mitigate deterioration in the electrochemical properties and stability of the positive electrode active material due to lithium impurities by effectively controlling the content of lithium impurities present on the surface of the positive electrode active material (lithium composite oxide) without the need for a water washing process.

[0014] Another object of the present invention is to provide a cathode active material in which a fluorine-containing coating layer is formed by reacting lithium impurities present on the surface of the cathode active material (lithium composite oxide) with a fluorine-containing raw material, and the content of elements other than fluorine in the coating layer is controlled to reduce changes in the electrochemical properties of the lithium composite oxide caused by the fluorine-containing coating layer.

[0015] It is yet another object of the present invention to provide a lithium secondary battery using the positive electrode active material defined herein.

[0016] The objects of the present invention are not limited to the objects mentioned above, and other objects and advantages of the present invention not mentioned above can be understood from the following description and can be more clearly understood from the examples of the present invention. Furthermore, it can be easily seen that the objects and advantages of the present invention can be realized by the means and combinations thereof as claimed. [Means for solving the problem]

[0017] 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 containing a lithium composite oxide capable of reversible intercalation / deintercalation of lithium ions; and a shell portion containing fluorine and present on at least a portion of the surface of the core portion.

[0018] In one embodiment, the lithium composite oxide contains at least one transition metal selected from nickel, cobalt, manganese, and aluminum. Preferably, the lithium composite oxide is a lithium-nickel composite oxide containing nickel. The lithium-nickel composite oxide may further contain at least one selected from manganese and aluminum.

[0019] In one embodiment, the lithium composite oxide may be represented by the following Chemical Formula 1:

[0020] [Chemical formula 1] Li a Ni 1-(b+c+d) Co b M1 c M2 d O 2-e X e 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, and 0.5≦a≦1.5, 0≦b≦0.20, 0≦c≦0.30, 0≦d≦0.10, and 0≦e≦0.10.

[0021] In another embodiment, the lithium composite oxide may be represented by the following Chemical Formula 2:

[0022] [Chemical formula 2] Li a′ Ni 1-(b′+d′) Mn b′ M2 d′ O 2-e′ X e′ 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; and 0.95≦a′≦1.05, 0 <b′≦0.5、0≦d′≦0.10、0≦e′≦0.10である。

[0023] In one embodiment, the lithium composite oxide may exist as secondary particles formed by aggregation of a plurality of primary particles, and the shell portion may exist on the surface of the primary particles and at least a part of the grain boundaries between adjacent primary particles.

[0024] According to another aspect of the present invention, there is provided a positive electrode including the above-described positive electrode active material.

[0025] According to yet another aspect of the present invention, there is provided a lithium secondary battery using the above-described positive electrode. [Effects of the Invention]

[0026] According to the present invention, the lithium impurities present on the surface of a positive electrode active material (lithium composite oxide) are reacted with a fluorine-containing raw material to form a fluorine-containing coating layer, thereby effectively controlling the content of lithium impurities present on the surface of the positive electrode active material (lithium composite oxide) without the need for a water washing process, thereby preventing and / or mitigating the deterioration of the electrochemical properties and stability of the positive electrode active material due to the lithium impurities.

[0027] Furthermore, according to the present invention, by controlling the contents of heterogeneous elements (particularly carbon) other than fluorine and functional groups derived from heterogeneous elements in the fluorine-containing coating layer present on the surface of the positive electrode active material (lithium composite oxide), it is possible to reduce changes in the electrochemical properties of the lithium composite oxide caused by the fluorine-containing coating layer.

[0028] The above-mentioned effects and specific effects of the present invention will be described below together with specific matters for carrying out the invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] For convenience, certain terms are defined herein to make the present invention more readily understandable. Unless otherwise defined herein, scientific and technical terms used herein shall have the meanings that are commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise indicated by context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0030] positive electrode active material A positive electrode active material according to one embodiment of the present invention includes: a core portion containing a lithium composite oxide capable of reversible intercalation / deintercalation of lithium ions; and a shell portion containing fluorine and present on at least a portion of the surface of the core portion.

[0031] The lithium composite oxide is a composite metal oxide capable of intercalating / deintercalating 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 specific peak in the region of 2θ=18.6±1° in the diffraction pattern obtained by XRD analysis.

[0032] When the lithium composite oxide included in the positive electrode active material defined herein exists as an aggregate of a plurality of primary particles, the lithium composite oxide may be referred to as a secondary particle.

[0033] The primary particles constituting the lithium composite oxide may have a rod shape, an elliptical shape, and / or an irregular shape. Furthermore, unless otherwise intended in the manufacturing process, primary particles of various shapes may exist within the same positive electrode active material. Furthermore, the primary particles refer to particle units that do not appear to have grain boundaries when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope.

[0034] The primary particles constituting the lithium composite oxide defined in the present application may have an average particle size of 0.06 μm to 2 μm, preferably 0.06 μm to 1.2 μm, more preferably 0.25 μm to 0.75 μm. In this case, the average particle size of the primary particles can be calculated by 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).

[0035] The primary particle may consist of a single crystallite or multiple crystallites. In this case, the crystallite size can be estimated from a diffraction pattern obtained by XRD analysis of the lithium composite oxide, or calculated by substituting the half-width of a peak specific to a representative crystal plane into the Scherrer equation.

[0036] The crystallite size present in the lithium composite oxide is preferably 40 nm or more and 130 nm or less, and may be 40 nm or more and 120 nm or less, 45 nm or more and 110 nm or less, or 48 nm or more and 100 nm or less.

[0037] If the crystallite size is less than 40 nm, the crystallite size constituting the primary particles may be too small, resulting in reduced particle strength of the lithium composite oxide. Furthermore, if the primary particle size is too small, the specific surface area may increase, accelerating gas generation due to side reactions with the electrolyte. On the other hand, if the crystallite size is more than 130 nm, the primary particles may grow excessively, resulting in reduced initial capacity and initial efficiency of a lithium secondary battery using the primary particles as a positive electrode active material. Furthermore, when a fluorine-containing coating layer is formed on the surface of the overgrown primary particles, changes in surface resistance may occur, resulting in degradation of other electrochemical properties.

[0038] 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 depending on the number of primary particles constituting the secondary particles. The average particle size (D50) of the secondary particles can be measured using a laser diffraction method. For example, the secondary particles are dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W. After obtaining a volume cumulative particle size distribution graph, the particle size corresponding to 50% of the volume cumulative amount can be measured.

[0039] Unless otherwise defined, the term "surface of the primary particle" used herein refers to the outer surface of the primary particle exposed to the outside. Similarly, the term "surface of the secondary particle" 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 aggregation of a plurality of primary particles corresponds to the exposed surface of the primary particle present in the surface portion of the secondary particle.

[0040] Unless otherwise defined, the term "surface portion of a particle" used herein refers to a region relatively closer to the "outermost surface" of a particle, and "center portion of a particle" refers to a region relatively closer to the "middle" of a particle than the "surface portion." Accordingly, "surface portion of a primary particle" refers to a region relatively closer to the "outermost surface" of a primary particle, and "center portion of a primary particle" refers to a region relatively closer to the "middle" of a primary particle than the "surface portion." Similarly, "surface portion of a secondary particle" refers to a region relatively closer to the "outermost surface" of a secondary particle, and "center portion of a secondary particle" refers to a region relatively closer to the "middle" of a secondary particle than the "surface portion."

[0041] In this case, the region of any particle excluding the "surface portion of the particle" can be defined as the "center portion of the particle."

[0042] The lithium composite oxide contains lithium and at least one transition metal, which may be at least one selected from nickel, cobalt, manganese, and aluminum.

[0043] In one embodiment, the lithium composite oxide may be represented by the following Chemical Formula 1:

[0044] [Chemical formula 1] Li a Ni 1-(b+c+d) Co b M1 c M2 d O 2-e X e 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, and 0.5≦a≦1.5, 0≦b≦0.20, 0≦c≦0.30, 0≦d≦0.10, and 0≦e≦0.10.

[0045] In the lithium composite oxide, a, which indicates the ratio of lithium to all elements other than lithium, may be 0.5 to 1.5, 0.75 to 1.25, 0.90 to 1.1, or 0.95 to 1.05.

[0046] The mole fraction of nickel relative to all elements other than lithium in the lithium composite oxide may be 60% or more. In this case, b+c+d in Formula 1 is 0.40 or less. The mole fraction of nickel relative to all 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.

[0047] When the lithium composite oxide contains cobalt, the molar fraction of cobalt relative to all 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 Chemical Formula 1 is greater than 0, and when the lithium composite oxide is a cobalt-free lithium composite oxide, b in Chemical Formula 1 is 0.

[0048] When the lithium composite oxide contains manganese and / or aluminum, the molar fraction of manganese and / or aluminum relative to all 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 Formula 1 is greater than 0.

[0049] In Formula 1, M2 represents a dopant present in the secondary particles. The dopant may be present in a doped state within the crystal lattice of the primary particles. When the lithium composite oxide includes a dopant, M2 in Formula 1 is greater than 0. In addition, the molar fraction of the dopant relative to all elements other than lithium in the lithium composite oxide may be 10% or less, 5% or less, 2% or less, or less than 2%.

[0050] As shown in Chemical Formula 1, at least a portion of the oxygen in the lithium composite oxide may be substituted with 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 and may exist more stably in the crystal structure of the lithium composite oxide than other anion elements. In addition, F may partially replace oxygen forming an M(metal)-O bond to form a strong M-F bond, which may contribute to strengthening the crystal structure of the lithium composite oxide.

[0051] In another embodiment, the lithium composite oxide may be represented by the following Chemical Formula 2:

[0052] [Chemical formula 2] Li a′ Ni 1-(b′+d′) Mn b′ M2 d′ O 2-e′ X e′ 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; and 0.95≦a′≦1.05, 0 <b′≦0.5、0≦d′≦0.10、0≦e′≦0.10である。

[0053] In the lithium composite oxide represented by Chemical Formula 2, the molar fraction of nickel in the metal elements excluding lithium may be 0.60 to 0.95, preferably 0.70 to 0.90, and the molar fraction of manganese in the metal elements excluding lithium may be 0.05 to 0.40, preferably 0.10 to 0.40, more preferably 0.10 to 0.30.

[0054] When the mole 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 be high. As the proportion of the spinel phase in the lithium composite oxide increases, a higher operating voltage is required, and the capacity characteristics of a lithium secondary battery using the lithium composite oxide with a high proportion of the spinel phase as a positive electrode active material may be reduced. Furthermore, as the nickel content in the lithium composite oxide decreases, the increase in manganese may increase overall cation mixing within the lithium composite oxide.

[0055] The charge of the entire transition metal constituting the lithium composite oxide is preferably in a trivalent state to exhibit stable charge neutrality. In this case, when synthesizing a lithium composite oxide with a low cobalt content and a high manganese content, Mn 4+ Since there is an excess amount of Ni, 3+ Instead of Ni 2+ The content of Ni increases. 2+ (0.69Å) is Li + Since the cations have a similar size to the cations (0.76 Å), they can occupy the 3a site of Li in the crystal structure of the lithium composite oxide, and this occupancy phenomenon is called cation mixing.

[0056] On the other hand, when the lithium composite oxide contains excessive amounts of nickel, the lithium composite oxide exhibits properties similar to those of LiNiO2. LiNiO2 not only has low thermal stability, but also has the problem of decomposing itself or causing side reactions at the interface and surface of the electrolyte and the lithium composite oxide when an internal short circuit occurs due to external pressure during charging, which can lead to explosion and fire of the lithium secondary battery.

[0057] If the mole fraction of manganese in the lithium composite oxide exceeds 0.40, the same problems as those occurring when the mole fraction of nickel is less than 0.60 may occur.

[0058] The positive electrode active material according to the present invention includes a shell portion present on at least a portion of the surface of a core portion containing the lithium composite oxide defined above. The shell portion may contain fluorine, more specifically, LiF as a fluorine-containing compound. LiF may be formed by a reaction between a fluorine-containing polymer and lithium impurities (e.g., LiOH and Li2CO3) present on the surface of the core portion.

[0059] The fluorine content of the positive electrode active material determined by IC analysis is preferably 0.1 wt% to 0.5 wt%. If the fluorine content is less than 0.1 wt%, it is difficult to sufficiently remove lithium impurities present on the surface of the core part, and as a result, an additional water washing process must be performed to reduce the content of lithium impurities. On the other hand, if the fluorine content exceeds 0.5 wt%, the amount of LiF present on the surface of the core part becomes excessive, which may result in a decrease in the surface resistance or electrochemical properties of the positive electrode active material.

[0060] The lithium impurities present on the surface of the core part react with a fluorine-containing polymer (e.g., PVDF, PTFE, etc.) to form LiF, thereby reducing the amount of lithium impurities present on the surface of the core part without the need for a separate water washing process for reducing the amount of lithium impurities. This has the advantage of preventing and / or mitigating deterioration in the electrochemical properties and lifespan of the positive electrode active material due to lithium impurities and / or the water washing process.

[0061] When a particle including the core portion and the shell portion is defined as a core-shell particle, the volumes of the core portion and the shell portion of 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 semidiameter of the core portion and the semidiameter of the shell portion can be measured, and the volumes of the core portion and the shell portion can be calculated from the semidiameter of the core portion and the semidiameter of the shell portion, respectively. In addition, the thickness of the shell portion of the core-shell particle may be 1 nm or more and 50 nm or less.

[0062] If the thickness of the shell is less than 1 nm, it may be difficult to sufficiently remove lithium impurities present on the surface of the core, and an additional water washing process may be required to reduce the content of lithium impurities. On the other hand, if the thickness of the shell is more than 50 nm, the amount of LiF present on the surface of the core may be excessive, which may result in a decrease in the surface resistance or electrochemical properties of the positive electrode active material.

[0063] The lithium composite oxide corresponding to the core portion may exist as a secondary particle formed by aggregation of a plurality of primary particles, and the shell portion may exist on the surface of the primary particle and at least a part of the grain boundary between adjacent primary particles.

[0064] Thus, the shell portion is defined as a region where LiF is present 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.

[0065] When the shell portion is present at the 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.

[0066] Fluorine may be present at a higher concentration on the surface of the secondary particles than in the interior of the secondary particles, and in this case, the fluorine may form a concentration gradient that decreases from the surface of the secondary particles to the interior of the secondary particles along the interface between the primary particles.

[0067] In addition, when lithium impurities present on the surface of the core react with the fluorine-containing polymer to form LiF, the fluorine-containing polymer or elements derived from the fluorine-containing polymer (e.g., carbon) may remain in the positive electrode active material. If the fluorine-containing polymer or elements derived from the fluorine-containing polymer (e.g., functional groups derived from the elements) remain in the positive electrode active material, the surface resistance or electrochemical characteristics of the positive electrode active material may change unexpectedly.

[0068] Therefore, it is preferable that, in XPS analysis of the positive electrode active material, no peak is observed in the region exceeding 686 eV but less than 689 eV, and an F1s peak is observed in the region of 684 eV to 686 eV. Here, the F1s peak observed in the region of 684 eV to 686 eV is a peak that appears due to the presence of LiF on the surface of the core part. On the other hand, if a peak is present in the region exceeding 686 eV but less than 689 eV, this indicates the presence of PVDF on the surface of the core part. If PVDF is present on the surface of a core part containing a lithium composite oxide having the crystal structure defined herein, the surface resistance or electrochemical properties of the positive electrode active material may be reduced.

[0069] In addition, the I(F1s) / I(C1s) ratio 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.

[0070] Here, I(F1s) refers to the intensity of the F1s peak observed in the region of 684 eV to 686 eV, and I(C1s) refers to the intensity of the C1s peak due to the C=O bond observed in the region of 288 eV to 292 eV. The intensity of the C1s peak due to the C=O bond can be stronger as the content of not only the fluorine-containing polymer-derived carbon and the carbon-derived functional group C=O on the surface of the core part, but also the content of lithium impurities (Li2CO3) present on the surface of the core part increases.

[0071] Therefore, I(F1s) / I(C1s) smaller than 1.0 means that there is an excessive amount of carbon derived from the fluorine-containing polymer, the carbon-derived functional group C=O, and lithium impurities (Li2CO3) present on the surface of the core part.

[0072] As described above, if the fluorine-containing polymer-derived carbon, the carbon-derived functional group C=O, and the lithium impurity (Li2CO3) present on the surface of the core portion are present in excessive amounts, the surface resistance and electrochemical properties of the positive electrode active material may be reduced. An I(F1s) / I(C1s) ratio greater than 2.5 indicates that an excessive amount of LiF is present on the surface of the core portion. In this case, the excessive amount of LiF may reduce the surface resistance or electrochemical properties of the positive electrode active material.

[0073] Lithium secondary battery According to another aspect of the present invention, a positive electrode may be provided, including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Here, the positive electrode active material layer may include a positive electrode active material according to various embodiments of the present invention. Therefore, since the positive electrode active material is the same as that described above, detailed description thereof will be omitted for brevity, and only the remaining components not described above will be described below.

[0074] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0075] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition containing the positive electrode active material, a conductive material, and optionally a binder, on the positive electrode current collector.

[0076] In this case, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when the amount is within this range, but the amount is not necessarily limited thereto.

[0077] The conductive material is used to impart conductivity to the electrode and can be any material that provides electronic conductivity without causing chemical changes in the resulting battery. Specific examples include graphite (e.g., natural graphite or artificial graphite); carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon-based materials (e.g., carbon fiber); metal powder or metal fiber (e.g., copper, nickel, aluminum, or silver); conductive whiskers (e.g., zinc oxide or potassium titanate); conductive metal oxides (e.g., titanium oxide); and conductive polymers (e.g., polyphenylene derivatives). These materials may be used alone or in combination. The conductive material may be present in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0078] The binder serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be included in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

[0079] The positive electrode may be fabricated by a conventional method for fabricating a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be fabricated by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, which is then coated on a positive electrode current collector, followed by drying and rolling.

[0080] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0081] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on a positive electrode current collector.

[0082] According to yet another aspect of the present invention, there may be provided an electrochemical device including the above-described positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0083] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is as described above, detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below.

[0084] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0085] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0086] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0087] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition containing the negative electrode active material, a conductive material, and optionally a binder, on the negative electrode current collector.

[0088] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. One or a mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon may also be used as the carbon material. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0089] The negative electrode active material may be included in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0090] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and may typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0091] The conductive material may be added as a component for further improving the conductivity of the negative electrode active material in an amount of 10 wt % or less, preferably 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fiber and metal fiber, 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, and conductive materials such as polyphenylene derivatives.

[0092] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and then laminating the resulting film on the negative electrode current collector.

[0093] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. It is particularly preferable that the separator has low resistance to ion migration and excellent electrolyte humidification ability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can be used, and it can be selectively used in a single-layer or multi-layer structure.

[0094] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0095] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0096] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone, ether solvents such as dibutyl ether and tetrahydrofuran, ketone solvents such as cyclohexanone, aromatic hydrocarbon solvents such as benzene and fluorobenzene, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 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, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constants, which can enhance the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9 to produce excellent electrolyte performance.

[0097] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within a range of 0.1M to 2.0M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0098] When the electrolyte used in the present application is a solid electrolyte, for example, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a nitride-based solid electrolyte, or a halide-based solid electrolyte may be used, and preferably, a sulfide-based solid electrolyte may be used.

[0099] As the material for the sulfide-based 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 may be used. Examples of the sulfide-based solid electrolyte material 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-ZmSn (wherein m and n are integers and Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(where p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In).

[0100] The solid electrolyte, preferably the sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a mixed state of amorphous and crystalline.

[0101] The oxide-based solid electrolyte material is Li7La3Zr2O 12 , Li 7-x La3Zr 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, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x Examples include GeO4 (LISICON).

[0102] The solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Alternatively, the solid electrolyte may be included in a portion of the positive electrode active material layer of the positive electrode, independent of the solid electrolyte layer, or in a portion of the negative electrode active material layer of the negative electrode, independent of the solid electrolyte layer.

[0103] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity reduction, improving battery discharge capacity, etc. In this case, the additives may be contained in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0104] As described above, a lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0105] 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 square shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

[0106] According to yet another aspect of the present invention, there may be provided a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same.

[0107] The battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool, an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV), or a power storage system.

[0108] The present invention will be described in more detail below with reference to examples. However, these examples are for the purpose of illustrating the present invention and are not to be construed as limiting the scope of the present invention.

[0109] Production Example 1: Production of positive electrode active material Comparative Example 1 Ni was extracted using a metal salt aqueous solution in which nickel sulfate and manganese sulfate were mixed in a molar ratio of 75:25 by a known co-precipitation method. 0.75 Mn 0.25 (OH)2 hydroxide precursor was synthesized.

[0110] Next, the hydroxide precursor was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.01), and then heat-treated in an O2 atmosphere at 850°C for 12 hours to obtain a positive electrode active material.

[0111] Comparative Example 2 Ni was extracted using a metal salt aqueous solution in which nickel sulfate and manganese sulfate were mixed in a molar ratio of 75:25 by a known co-precipitation method. 0.75 Mn 0.25 (OH)2 hydroxide precursor was synthesized.

[0112] Next, the hydroxide precursor was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.01), and then heat-treated in an O2 atmosphere at 850°C for 12 hours to obtain an intermediate product.

[0113] Next, the intermediate product was heat-treated in an O2 atmosphere at 150°C for 8 hours to obtain a positive electrode active material.

[0114] Comparative Example 3 A positive electrode active material was prepared in the same manner as in Comparative Example 2, except that the intermediate product was heat-treated at 300°C.

[0115] Comparative Example 4 A positive electrode active material was prepared in the same manner as in Comparative Example 2, except that the intermediate product was heat-treated at 350°C.

[0116] Comparative Example 5 A positive electrode active material was prepared in the same manner as in Comparative Example 2, except that the intermediate product was heat-treated at 400°C.

[0117] Comparative Example 6 A positive electrode active material was prepared in the same manner as in Comparative Example 2, except that the intermediate product was heat-treated at 500°C.

[0118] Comparative Example 7 A positive electrode active material was prepared in the same manner as in Comparative Example 2, except that the intermediate product was heat-treated at 600°C.

[0119] Comparative Example 8 Ni was extracted using a metal salt aqueous solution in which nickel sulfate and manganese sulfate were mixed in a molar ratio of 75:25 by a known co-precipitation method. 0.75 Mn 0.25 (OH)2 hydroxide precursor was synthesized.

[0120] Next, the hydroxide precursor was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.01), and then heat-treated in an O2 atmosphere at 850°C for 12 hours to obtain an intermediate product.

[0121] Next, the intermediate product was mixed with 0.1 wt % of PVDF, and then heat-treated in an O2 atmosphere at 350°C for 8 hours to obtain a positive electrode active material.

[0122] Comparative Example 9 Ni was extracted using a metal salt aqueous solution in which nickel sulfate and manganese sulfate were mixed in a molar ratio of 75:25 by a known co-precipitation method. 0.75 Mn 0.25 (OH)2 hydroxide precursor was synthesized.

[0123] Next, the hydroxide precursor was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.01), and then heat-treated in an O2 atmosphere at 850°C for 12 hours to obtain an intermediate product.

[0124] Next, the intermediate product was mixed with 5.0 wt % of PVDF, and then heat-treated in an O2 atmosphere at 350°C for 8 hours to obtain a positive electrode active material.

[0125] Comparative Example 10 Ni was extracted using a metal salt aqueous solution in which nickel sulfate and manganese sulfate were mixed in a molar ratio of 75:25 by a known co-precipitation method. 0.75 Mn 0.25 (OH)2 hydroxide precursor was synthesized.

[0126] Next, the hydroxide precursor was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.01), and then heat-treated in an O2 atmosphere at 850°C for 12 hours to obtain an intermediate product.

[0127] Next, the intermediate product was mixed with 0.35 wt % of PVDF, and then heat-treated in an O2 atmosphere at 150°C for 8 hours to obtain a positive electrode active material.

[0128] Comparative Example 11 Ni was extracted using a metal salt aqueous solution in which nickel sulfate and manganese sulfate were mixed in a molar ratio of 75:25 by a known co-precipitation method. 0.75 Mn 0.25 (OH)2 hydroxide precursor was synthesized.

[0129] Next, the hydroxide precursor was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.01), and then heat-treated in an O2 atmosphere at 850°C for 12 hours to obtain an intermediate product.

[0130] Next, the intermediate product was mixed with 0.35 wt % of PVDF, and then heat-treated in an O2 atmosphere at 300°C for 8 hours to obtain a positive electrode active material.

[0131] Comparative Example 12 Ni was extracted using a metal salt aqueous solution in which nickel sulfate and manganese sulfate were mixed in a molar ratio of 75:25 by a known co-precipitation method. 0.75 Mn 0.25 (OH)2 hydroxide precursor was synthesized.

[0132] Next, the hydroxide precursor was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.01), and then heat-treated in an O2 atmosphere at 750°C for 12 hours to obtain an intermediate product.

[0133] Next, the intermediate product was mixed with 0.35 wt % of PVDF, and then heat-treated in an O2 atmosphere at 400°C for 8 hours to obtain a positive electrode active material.

[0134] Comparative Example 13 Ni was extracted using a metal salt aqueous solution in which nickel sulfate and manganese sulfate were mixed in a molar ratio of 75:25 by a known co-precipitation method. 0.75 Mn 0.25 (OH)2 hydroxide precursor was synthesized.

[0135] Next, the hydroxide precursor was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.01), and then heat-treated in an O2 atmosphere at 950°C for 12 hours to obtain an intermediate product.

[0136] Next, the intermediate product was mixed with 0.35 wt % of PVDF, and then heat-treated in an O2 atmosphere at 400°C for 8 hours to obtain a positive electrode active material.

[0137] Example 1 Ni was extracted using a metal salt aqueous solution in which nickel sulfate and manganese sulfate were mixed in a molar ratio of 75:25 by a known co-precipitation method. 0.75 Mn 0.25 (OH)2 hydroxide precursor was synthesized.

[0138] Next, the hydroxide precursor was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.01), and then heat-treated in an O2 atmosphere at 850°C for 12 hours to obtain an intermediate product.

[0139] Next, the intermediate product was mixed with 0.35 wt % of PVDF, and then heat-treated in an O2 atmosphere at 350°C for 8 hours to obtain a positive electrode active material.

[0140] Example 2 A positive electrode active material was prepared in the same manner as in Example 1, except that the intermediate product was heat-treated at 400°C.

[0141] Example 3 A positive electrode active material was prepared in the same manner as in Example 1, except that the intermediate product was heat-treated at 500°C.

[0142] Example 4 A positive electrode active material was prepared in the same manner as in Example 1, except that the intermediate product was heat-treated at 600°C.

[0143] Example 5 Ni was extracted using a metal salt aqueous solution in which nickel sulfate and manganese sulfate were mixed in a molar ratio of 75:25 by a known co-precipitation method. 0.75 Mn 0.25 (OH)2 hydroxide precursor was synthesized.

[0144] Next, the hydroxide precursor was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.01), and then heat-treated in an O2 atmosphere at 850°C for 12 hours to obtain an intermediate product.

[0145] Next, the intermediate product was mixed with 0.5 wt % of PVDF, and then heat-treated in an O2 atmosphere at 400°C for 8 hours to obtain a positive electrode active material.

[0146] Example 6 Ni was extracted using a metal salt aqueous solution in which nickel sulfate and manganese sulfate were mixed in a molar ratio of 75:25 by a known co-precipitation method. 0.75 Mn 0.25 (OH)2 hydroxide precursor was synthesized.

[0147] Next, the hydroxide precursor was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.01), and then heat-treated in an O2 atmosphere at 800°C for 12 hours to obtain an intermediate product.

[0148] Next, the intermediate product was mixed with 0.35 wt % of PVDF, and then heat-treated in an O2 atmosphere at 400°C for 8 hours to obtain a positive electrode active material.

[0149] Manufacturing example 2. Manufacturing of lithium secondary battery (half cell) A positive electrode slurry was prepared by dispersing 94 wt% of the positive electrode active material prepared in Preparation Example 1, 3 wt% of carbon black, and 3 wt% of PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on a 15 μm-thick aluminum foil and dried under vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0150] A half cell was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution of 1.15 M LiPF in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0151] Experimental Example 1: IC and XRD analysis of positive electrode active material The F content in each positive electrode active material prepared in Preparation Example 1 was measured through IC (ion chromatography) analysis using IC equipment (Thermo Dionex ICS-6000).

[0152] In addition, X-ray diffraction (XRD) analysis was performed on each positive electrode active material prepared in Preparation Example 1, and the peak half-width obtained was substituted into the Scherrer equation to calculate the crystallite size of the lithium composite oxide contained in the positive electrode active material. XRD analysis was performed using a Bruker D8 Advance diffractometer using Cu-Kα radiation (1.540598 Å).

[0153] The measurement results are shown in Table 1 below.

[0154] [Table 1]

[0155] In the case of the cathode active material of Comparative Example 10, it was confirmed that the heat treatment temperature after mixing the intermediate product with PVDF was too low, resulting in most of the PVDF remaining as unreacted. As a result, F doping and / or conversion of lithium impurities to LiF hardly occurred in the cathode active material, and thus F was not detected during IC analysis of the cathode active material of Comparative Example 10.

[0156] In the case of the cathode active material of Comparative Example 12, the heat treatment temperature (calcination temperature) of the hydroxide precursor was too low, resulting in insufficient crystal growth, and it was confirmed that this resulted in a crystallite size of approximately 28 nm. On the other hand, in the case of the cathode active material of Comparative Example 13, the heat treatment temperature (calcination temperature) of the hydroxide precursor was too high, resulting in excessive crystal growth, and it was confirmed that this resulted in a crystallite size of approximately 200 nm.

[0157] Experimental Example 2: XPS analysis of positive electrode active material XPS analysis was performed on each of the positive electrode active materials produced in Production Example 1 to confirm the composition of the surface (particularly the shell portion) of the positive electrode active material. TM This was performed using a Thermo UK spectrometer (accelerating voltage: 100 eV to 3 keV, energy resolution: 0.50 eV).

[0158] Specifically, the XPS analysis was used to determine whether a peak specific to PVDF was present in the region exceeding 686 eV but less than 689 eV, and whether an F1s peak was present in the region of 684 eV to 686 eV. In addition, I(F1s) / I(C1s), which is 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 C=O bonds observed in the region of 288 eV to 292 eV, was calculated.

[0159] The results of the XPS analysis are shown in Table 2 below.

[0160] [Table 2]

[0161] In the case of the positive electrode active material of Comparative Example 8, the content of PVDF mixed with the intermediate product was too small, so that the XPS analysis results showed no peak corresponding to unreacted PVDF, but the F1s peak was present with very weak intensity, and therefore I(F1s) / I(C1s) converged to 0.

[0162] In the case of the cathode active material of Comparative Example 9, the amount of PVDF mixed with the intermediate product was too high, so most of it remained as unreacted PVDF, resulting in the presence of a peak specific to PVDF in the region exceeding 686 eV and below 689 eV. In addition, as confirmed by the residual lithium analysis results of Experimental Example 4, not only was there an excessive amount of unreacted PVDF, but the amount of residual lithium (Li2CO3) was also too high, resulting in an excessively large I(C1s) and a convergence of I(F1s) / I(C1s) to 0, despite the presence of an F1s peak.

[0163] In the case of the cathode active material of Comparative Example 10, the heat treatment temperature after mixing with PVDF was too low, so that the conversion of lithium impurities to LiF hardly occurred, and therefore, it was confirmed that the F1s peak was not observed in the XPS analysis results.

[0164] Similarly, in the case of the cathode active material of Comparative Example 11, the heat treatment temperature after mixing with PVDF was low, and therefore only a portion of the PVDF mixed with the intermediate product reacted with lithium impurities and was converted to LiF. As a result, XPS analysis showed not only the presence of a peak corresponding to unreacted PVDF, but also a low F1s peak intensity, confirming that I(F1s) / I(C1s) was less than 1.0.

[0165] Experimental Example 3: Evaluation of the electrochemical properties of the positive electrode active material The lithium secondary battery (half cell) prepared in Preparation Example 2 was subjected to a charge-discharge experiment at 25°C, a voltage range of 3.0 V to 4.4 V, and a discharge rate of 0.1 C using an electrochemical analyzer (Toyo, Toscat-3100) to measure the initial charge capacity, initial discharge capacity, and initial efficiency.

[0166] In addition, the same lithium secondary battery (half cell) was charged and discharged 50 times using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0 V to 4.4 V, and 1 C / 1 C, and the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention) was measured.

[0167] The measurement results are shown in Table 3 below.

[0168] [Table 3]

[0169] Referring to the results in Table 3, it can be seen 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.

[0170] Experimental Example 4: Analysis of residual lithium in positive electrode active material The residual lithium (lithium impurity) content in the positive electrode active material prepared according to Preparation Example 1 was analyzed by pH titration. The pH titration method measured the residual lithium (lithium impurity) content by the amount of 0.1 M HCl used until the pH reached 4 through pH titration of the positive electrode active material. Specifically, 5 g of each positive electrode active material prepared according to Preparation Example 1 was placed in 100 ml of DIW, stirred for 15 minutes, and then filtered. 50 ml of the filtered solution was taken and 0.1 M HCl was added thereto. The amount of HCl consumed due to the change in pH was measured, and the contents of LiOH and Li2CO3 were calculated.

[0171] The measurement results are shown in Table 4 below.

[0172] [Table 4]

[0173] Referring to the results in Table 4, it can be seen that in the case of the positive electrode active materials according to Examples 1 to 6, the content of lithium impurities (5,500 ppm or less) was reduced by surface modification without undergoing 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, compared to Comparative Example 1. In particular, it can be seen that the reduction in the amount of Li2CO3, among the lithium impurities, was large in the case of the positive electrode active materials according to Examples 1 to 6.

[0174] Furthermore, although the positive electrode active materials according to Examples 1 to 6 have similar residual lithium contents to those of Comparative Examples 2, 5, 6, 7, 8, 10, 11, and 13, they exhibit improved electrochemical properties, as confirmed through Experimental Example 3.

[0175] Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art may modify and change the present invention in various ways by adding, changing, deleting or adding components within the scope of the concept of the present invention as set forth in the claims, and this also falls within the scope of the present invention.

Claims

1. a core portion including a lithium composite oxide capable of reversible intercalation / deintercalation of lithium ions; a shell portion that is present on at least a portion of a surface of the core portion and contains fluorine, The lithium composite oxide has a crystallite size of 40 nm or more and 130 nm or less, When the positive electrode active material is analyzed by XPS, no peak is observed in a region exceeding 686 eV and less than 689 eV, and an F1s peak is observed in a region of 684 eV or more and 686 eV or less.

2. 2. The positive electrode active material according to claim 1, wherein I(F1s) / I(C1s), which is a ratio of the intensity of an F1s peak observed in a region of 684 eV to 686 eV and the intensity of a C1s peak due to a C═O bond observed in a region of 288 eV to 292 eV, determined by XPS analysis of the positive electrode active material, is 1.0 or more and 2.5 or less.

3. 2. The positive electrode active material according to claim 1, wherein the lithium composite oxide contains at least one transition metal selected from nickel, cobalt, manganese, and aluminum.

4. The positive electrode active material of claim 1 , wherein 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 (where, 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 , wherein the mole fraction of nickel relative to all elements other than lithium in the lithium composite oxide is 60% or more.

6. The positive electrode active material of claim 1 , wherein the lithium composite oxide is represented by the following Chemical Formula 2: [Chemical formula 2] Li ａ′ ii １－（ｂ′＋ｄ′） 7N ｂ′ 72 ｄ′ 9 ２－ｅ′ 8 ｅ′ (where, 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. 7. The positive electrode active material according to claim 6, wherein the mole fraction of nickel relative to all elements other than lithium in the lithium composite oxide is 60% or more and 95% or less.

8. The positive electrode active material according to claim 1 , wherein the shell portion contains LiF.

9. The lithium composite oxide exists as secondary particles formed by aggregation of a plurality of primary particles, The positive electrode active material according to claim 1 , wherein the shell portion is present on the surface of the primary particle and at least part of the grain boundary between adjacent primary particles.

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

05.

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

12. The cathode active material according to claim 1 , wherein the shell portion has a thickness of 1 nm or more and 50 nm or less.

13. LiOH and Li present in the positive electrode active material ２ CO ３ The positive electrode active material according to claim 1 , wherein the total content of

14. A positive electrode comprising the positive electrode active material according to claim 1 .

15. A lithium secondary battery using the positive electrode according to claim 14.

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