Positive electrode active material and lithium secondary battery comprising same

Abstract

The present invention relates to a positive electrode active material and a lithium secondary battery comprising same and, more specifically, relates to a positive electrode active material and a lithium secondary battery comprising same, wherein the positive electrode active material is synthesized by using a precursor that is synthesized using a dopant and that has the dopant uniformly distributed therein, so as to control the growth of primary particles and crystallites, thereby improving high-temperature cycle life characteristics and storage stability.

Description

positive electrode active material and lithium secondary battery containing the same

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery including the same. More specifically, the present invention relates to a positive electrode active material and a lithium secondary battery including the same, wherein the growth of primary particles and crystallites is controlled by using a dopant during the synthesis of a precursor of the positive electrode active material and synthesizing the positive electrode active material using a precursor in which the dopant obtained therefrom is uniformly distributed, thereby improving the lifespan characteristics and storage stability at high temperatures.

[0002]

[0003] A battery stores electrical power by using materials capable of electrochemical reactions at the positive and negative electrodes. A representative example of such a battery is the lithium secondary battery, which stores electrical energy based on the difference in chemical potential when lithium ions intercalate or deintercalate at the positive and negative electrodes.

[0004] The above lithium secondary battery is manufactured by using materials capable of reversible intercalation / deintercalation of lithium ions as positive and negative active materials, and by filling an organic electrolyte or a polymer electrolyte between the positive and negative electrodes.

[0005] Lithium transition metal oxides are used as cathode active materials for lithium secondary batteries, and examples of such composite oxides are being studied include LiCoO2, LiMn2O4, LiNiO2, and LiMnO2.

[0006] Among the aforementioned cathode active materials, LiCoO2 is the most widely used due to its excellent lifespan characteristics and charge / discharge efficiency; however, it has the disadvantage of limited price competitiveness because it is expensive due to the resource limitations of cobalt used as a raw material.

[0007] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low cost, but they have the problem of low capacity and poor high-temperature characteristics. In addition, LiNiO2-based cathode active materials have the advantage of exhibiting high discharge capacity, but they are difficult to synthesize due to active cation mixing of Li and Ni, and the rate characteristics and lifespan characteristics of the synthesized cathode active materials are very low.

[0008] Accordingly, in order to improve low rate and lifetime characteristics while maintaining the high reversible capacity of LiNiO2, lithium transition metal oxides of the ternary type, such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or the quaternary type, such as NCMA (Ni-Co-Mn-Al), in which some of the nickel is substituted with cobalt, manganese, and / or aluminum, have been developed. Since the reversible capacity decreases as the nickel content in these ternary or quaternary type lithium transition metal oxides decreases, research to increase the nickel content in lithium transition metal oxides has been actively conducted recently.

[0009] However, as the nickel content in lithium transition metal oxides increases, there are problems such as reduced stability due to increased cation mixing within the crystal structure, or an increase in the content of unreacted lithium impurities on the surface, such as LiOH and Li2CO3.

[0010] As the content of lithium impurities remaining on the surface of the lithium transition metal oxide increases, gas generation and swelling phenomena may be promoted in a lithium secondary battery using the lithium transition metal oxide as a positive electrode active material. In addition, as the content of lithium impurities remaining on the surface of the lithium transition metal oxide increases, there is a problem that the paste composition becomes gelled due to the lithium impurities when manufacturing a paste for forming a positive electrode active material layer using the lithium transition metal oxide.

[0011] Nevertheless, high-Ni type cathode active materials with a high nickel content are attracting attention for the manufacture of higher-performance lithium secondary batteries. However, as mentioned above, high-Ni type cathode active materials exhibit low lifespan characteristics (especially at high temperatures) and storage stability due to issues such as reduced crystallinity and gas generation caused by cation mixing; therefore, there is a need to develop cathode active materials to improve these characteristics.

[0012]

[0013] With the recent growth of the electric vehicle industry, the lithium-ion battery market is expanding rapidly, and the demand and required performance of the cathode materials used in them are also continuously changing. For example, while LFP-based lithium-ion batteries, which emphasize safety, were traditionally used, there is a recent trend toward the increased use of nickel-based lithium transition metal oxides, which offer higher energy density per unit weight. Of course, relatively inexpensive LFP is still sometimes used to reduce the cost of lithium-ion batteries.

[0014] Nickel-based lithium transition metal oxides, which are mainly used as cathode active materials for high-capacity lithium secondary batteries, generally have a composition of a ternary type such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) or a quaternary type such as NCMA (Ni-Co-Mn-Al).

[0015] As mentioned above, increasing the nickel content in these ternary or quaternary type nickel-based lithium transition metal oxides may lead to problems such as reduced crystallinity and gas generation due to cation mixing, which ultimately acts as a factor that lowers the lifespan characteristics and storage stability of the lithium secondary battery.

[0016] Meanwhile, numerous techniques have been introduced to improve the electrochemical properties of cathode active materials when using dopants during the synthesis of cathode active materials for lithium secondary batteries. However, the inventors have confirmed that by using a dopant during the synthesis of a precursor of a cathode active material and synthesizing the cathode active material using a precursor in which the obtained dopant is uniformly distributed, the growth of primary particles and crystallites can be controlled, thereby improving lifespan characteristics at high temperatures and storage stability.

[0017] In addition, the inventors confirmed that the lifespan characteristics at high temperatures and storage stability can be improved only when the cathode active material obtained using a dopant during precursor synthesis satisfies certain crystallographic characteristics.

[0018] Under the background described above, the present invention aims to provide an anode active material comprising a lithium transition metal oxide having a layered crystal structure belonging to the R-3m space group and existing in a doped state within the crystal lattice.

[0019] In particular, the present invention aims to provide a positive electrode active material with improved lifespan characteristics at high temperatures and storage stability by having the average crystallite size obtained from Rietveld analysis of the diffraction spectrum obtained from X-ray diffraction analysis using Cu-Kα rays for the positive electrode active material and the average aspect ratio of the primary particles calculated from the cross-sectional SEM image of the lithium transition metal oxide exist within a predetermined range.

[0020] In addition, another objective of the present invention is to provide a lithium secondary battery using the positive active material defined herein.

[0021] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0022]

[0023] The present invention for solving the aforementioned technical problem includes the following invention.

[0024] [1] A positive electrode active material comprising a lithium transition metal oxide having a layered crystal structure belonging to the R-3m space group, wherein at least one dopant selected from Al, Zr, Na, S, Mg, Ti and B exists in a doped state within the crystal lattice of the lithium transition metal oxide, and the average crystallite size obtained from Rietveld analysis of the diffraction spectrum obtained from X-ray diffraction analysis using Cu-Kα rays for the positive electrode active material is greater than 57 nm and less than 95 nm, and the average aspect ratio of primary particles calculated from a cross-sectional SEM image of the lithium transition metal oxide is 1.9 or greater and less than 2.6.

[0025] [2] The positive electrode active material described in [1], wherein at least one dopant selected from Al, Zr, Na, S, Mg, Ti and B among the lithium transition metal oxides is present in an amount of 0.1 mol% or more and 1 mol% or less with respect to all elements excluding lithium.

[0026] [3] The above lithium transition metal oxide comprises at least one selected from nickel, cobalt, manganese and aluminum, the positive active material described in [1] or [2].

[0027] [4] The above lithium transition metal oxide is a positive active material described in any one of [1] to [3], comprising nickel, cobalt and manganese.

[0028] [5] The above lithium transition metal oxide is a positive active material described in any one of [1] to [4], containing at least 75 mol% of nickel with respect to all elements excluding lithium.

[0029] [6] The above lithium transition metal oxide is an anode active material described in any one of [1] to [5] having an average composition represented by the following chemical formula 1.

[0030] [Chemical Formula 1]

[0031] Li a Ni1-(b+c+d+e)Co b Mn c M1 d M2 e O2

[0032] In the above chemical formula 1,

[0033] M1 is at least one selected from Al, Zr, Na, S, Mg, Ti, and B, and

[0034] M2 is at least one selected from K, Ca, Sr, Ba, Rb, Ce, Hf, Ta, Cr, F, V, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd and Cu, and

[0035] 0.95≤a≤1.15, 0≤b≤0.20, 0≤c≤0.20, 0.001≤d≤0.01, 0≤e≤0.05, 0.75≤1-(b+c+d+e).

[0036] [7] A positive active material described in any one of [1] to [6], wherein the crystallite size calculated by Scherrer's formula from the diffraction peak corresponding to the (003) plane in the diffraction spectrum obtained from X-ray diffraction analysis using Cu-Kα rays for the positive active material is 40 nm or more and less than 80 nm.

[0037] [8] A positive active material described in any one of [1] to [7], wherein the ratio of the crystallite size calculated by Scherrer's formula from the diffraction peak corresponding to the (003) plane in the diffraction spectrum obtained from X-ray diffraction analysis using Cu-Kα rays for the positive active material is 0.55 or more and 0.80 or less.

[0038] [9] A positive electrode active material described in any one of [1] to [8], comprising a coating layer formed on at least a portion of the surface of the lithium transition metal oxide, wherein the coating layer comprises at least one selected from Ti, Al, Cr, Zr, B, Na and Ca.

[0039]

[0010] The lithium transition metal oxide is a secondary particle formed by the aggregation of a plurality of primary particles, and the coating layer has an island shape formed on at least one of the surface of the primary particles, the interface between the primary particles, and the surface of the secondary particles, or has a shape covering at least one of the surface of the primary particles, the interface between the primary particles, and the surface of the secondary particles, as described in [9].

[0040]

[0011] The anode active material described in [9] or

[0010] , wherein the coating layer comprises at least one metal oxide represented by the following chemical formula 2.

[0041] [Chemical Formula 2]

[0042] Li f M3 g O h

[0043] In the above chemical formula 2,

[0044] M3 is at least one selected from Ti, Al, Cr, Zr, B, Na, and Ca, and

[0045] 0≤f≤10, 0 <g≤8, 0<h≤15이다.

[0046]

[0012] The anode active material described in any one of [9] to

[0011] , wherein the coating layer further comprises at least one metal oxide represented by the following chemical formula 3.

[0047] [Chemical Formula 3]

[0048] Li i M4 j O k

[0049] In the above chemical formula 3,

[0050] M4 is at least one selected from Ni, Mn, Co, S, Mg, Ca, Sr, Ba, Rb, Ce, Hf, Ta, F, V, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd and Cu, and

[0051] 0≤i≤10, 0 <j≤8, 0<k≤15이다.

[0052] In addition, the present invention includes other embodiments as follows.

[0053]

[0013] A positive electrode comprising a positive electrode active material described in any one of [1] to

[0012] .

[0054]

[0014] A lithium secondary battery using the positive electrode described in

[0013] .

[0055]

[0056] According to the present invention, by using a dopant during the synthesis of a precursor of a positive electrode active material and using a precursor in which the obtained dopant is uniformly distributed, a difference in heat quantity is achieved during the reaction between the doped precursor and the lithium raw material, thereby enabling control of the growth of primary particles and crystallites constituting the lithium transition metal oxide during the calcination step.

[0057] In addition, according to the present invention, by controlling the aspect ratio of primary particles constituting the lithium transition metal oxide and the size of crystallites within a predetermined range through the method described above, the lifespan characteristics at high temperatures and storage stability can be improved without degrading the capacity characteristics.

[0058]

[0059] For convenience, specific terms are defined herein to facilitate a better understanding of the present invention. Unless otherwise defined herein, scientific and technical terms used in this invention shall have the meanings generally understood by those skilled in the art. Furthermore, unless specifically indicated in the context, terms in their singular form shall be understood to include their plural form, and terms in their plural form shall be understood to include their singular form.

[0060]

[0061] positive electrode active material

[0062] In the present invention, the positive electrode active material comprises a lithium transition metal oxide capable of reversible intercalation / deintercalation of lithium ions. Here, the term lithium transition metal oxide refers to an oxide in which lithium and at least one transition metal are combined.

[0063] The above lithium transition metal oxide is a complex metal oxide capable of lithium ion intercalation / deintercalation and has a layered crystal structure belonging to the R-3m space group.

[0064] The lithium transition metal oxide having a layered crystal structure belonging to the R-3m space group exhibits a specific diffraction peak corresponding to the (003) plane in the region where 2θ is 18° to 20° in the diffraction spectrum obtained from XRD analysis using Cu-Kα lines (λ=1.5406Å). Additionally, the lithium transition metal oxide having a layered crystal structure belonging to the R-3m space group exhibits a specific diffraction peak corresponding to the (003) plane in the region where 2θ is 44° to 46° in the diffraction spectrum obtained from XRD analysis using Cu-Kα lines (λ=1.5406Å).

[0065] The lithium transition metal oxide comprises at least lithium and a transition metal. The transition metal may comprise at least one, at least two, or all selected from nickel, cobalt, and manganese.

[0066] Preferably, the lithium transition metal oxide may be a lithium nickel-based composite oxide containing nickel. Additionally, the lithium transition metal oxide may be a lithium nickel-based composite oxide containing nickel and cobalt.

[0067] In addition, to improve low rate characteristics and lifetime characteristics while maintaining the high reversible capacity of LiNiO2, the lithium nickel-based composite oxide may be a lithium transition metal oxide of the ternary type, such as so-called NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or the quaternary type, such as NCMA (Ni-Co-Mn-Al), in which a portion of the nickel is substituted with cobalt, manganese, and / or aluminum. The ternary or quaternary type lithium transition metal oxide may further include dopants other than nickel, cobalt, manganese, and aluminum.

[0068] The above lithium transition metal oxide may be a high-Ni type lithium nickel-based composite oxide containing 75 mol% or more of nickel relative to the total elements excluding lithium. By using a high-Ni type lithium nickel-based composite oxide with a nickel content of 75 mol% or more, excellent electronic conductivity during the discharge process and high capacity characteristics are exhibited, thereby improving the initial capacity and energy density of the lithium secondary battery. In addition, by using a high-Ni type lithium nickel-based composite oxide with a nickel content of 75 mol% or more, a stable structure can be maintained even during charging and discharging under high voltage, thereby improving the output characteristics and high-rate charge / discharge performance of the lithium secondary battery.

[0069] Meanwhile, as mentioned above, high-Ni type lithium-nickel composite oxides may exhibit low lifespan characteristics (especially at high temperatures) and storage stability due to issues such as reduced crystallinity and gas generation resulting from cation mixing. Additionally, there is a concern that structural stability may deteriorate as the nickel content in the lithium transition metal oxide increases.

[0070] According to the present invention, by using a dopant during the synthesis of a precursor of a positive electrode active material and using a precursor in which the obtained dopant is uniformly distributed, a difference in heat quantity is achieved during the reaction between the doped precursor and the lithium raw material, thereby enabling control of the growth of primary particles and crystallites constituting the lithium transition metal oxide during the calcination step.

[0071] In addition, according to the present invention, the structural stability of a high-Ni type lithium nickel-based composite oxide can be improved by controlling the aspect ratio of primary particles constituting the lithium transition metal oxide and the size of crystallites within a predetermined range through the method described above. Accordingly, the lifespan characteristics and storage stability at high temperatures can be improved without degradation of capacity characteristics.

[0072] The above lithium transition metal oxide may be a cobalt-free type lithium transition metal oxide that does not contain cobalt within the bulk particles. The above cobalt-free type lithium transition metal oxide may further include dopants other than nickel, cobalt, and manganese.

[0073] The above lithium transition metal oxide may have an average composition represented by the following chemical formula 1. The average composition of the above lithium transition metal oxide can be measured according to a known ICP analysis method using an inductively coupled plasma spectrometer (ICP).

[0074] [Chemical Formula 1]

[0075] Li a Ni1-(b+c+d+e)Co b Mn c M1 d M2 e O2

[0076] In the above chemical formula 1,

[0077] M1 is at least one selected from Al, Zr, Na, S, Mg, Ti, and B, and

[0078] M2 is at least one selected from K, Ca, Sr, Ba, Rb, Ce, Hf, Ta, Cr, F, V, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd and Cu, and

[0079] 0.95≤a≤1.15, 0≤b≤0.20, 0≤c≤0.20, 0.001≤d≤0.01, 0≤e≤0.05, 0.75≤1-(b+c+d+e).

[0080] In the above chemical formula 1, a, representing the ratio of lithium to all elements other than lithium in the lithium transition metal oxide (Li / Ni+Co+Mn+M1+M2), may be 0.95 or more, 0.96 or more, 0.97 or more, 0.98 or more, 0.99 or more, 1.00 or more, 1.01 or more, 1.02 or more, 1.03 or more, 1.04 or more, or 1.05 or more. Additionally, a may be 1.15 or less, 1.14 or less, 1.13 or less, 1.12 or less, 1.11 or less, 1.10 or less, 1.09 or less, 1.08 or less, 1.07 or less, 1.06 or less, or 1.05 or less. The upper and lower limits of the mole fraction of lithium relative to all elements other than lithium in the above lithium transition metal oxide can be appropriately selected within a range that satisfies the definition described above. When the mole fraction of lithium in the above lithium transition metal oxide satisfies the above range, a stable crystal structure can be formed.

[0081] In the above chemical formula 1, 1-(b+c+d+e), representing the mole fraction of nickel (Ni / Ni+Co+Mn+M1+M2) relative to all elements other than lithium in the lithium transition metal oxide, may be 0.75 or more, 0.77 or more, 0.80 or more, 0.82 or more, 0.83 or more, 0.84 or more, 0.85 or more, 0.86 or more, 0.87 or more, 0.88 or more, 0.89 or more, 0.90 or more, 0.91 or more, 0.92 or more, 0.93 or more, 0.94 or more, or 0.95 or more. Additionally, 1-(b+c+d+e) may be less than 1.0, 0.99 or less, 0.98 or less, 0.97 or less, or 0.96 or less. The upper and lower limits of the mole fraction of nickel relative to all elements other than lithium in the above lithium transition metal oxide can be appropriately selected within a range that satisfies the definition described above. When the mole fraction of nickel in the above lithium transition metal oxide satisfies the above range, a stable crystal structure can be formed and high energy density can be exhibited.

[0082] In the above chemical formula 1, b, representing the mole fraction of cobalt (Co / Ni+Co+Mn+M1+M2) relative to all elements other than lithium in the lithium transition metal oxide, may be 0.20 or less, 0.19 or less, 0.18 or less, 0.17 or less, 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, 0.10 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, or 0.02 or less. If the lithium transition metal oxide is a cobalt-free type lithium transition metal oxide, b may be 0. When the lithium transition metal oxide contains cobalt, b may be greater than 0, greater than or equal to 0.01, or greater than or equal to 0.02. The upper and lower limits of the mole fraction of cobalt relative to all elements other than lithium in the lithium transition metal oxide may be appropriately selected within a range that satisfies the definition described above. When the mole fraction of cobalt in the lithium transition metal oxide satisfies the above range, a stable crystal structure can be formed and good output characteristics can be exhibited.

[0083] In the above chemical formula 1, c, representing the mole fraction of manganese (Mn / Ni+Co+Mn+M1+M2) relative to all elements other than lithium in the lithium transition metal oxide, may be 0.20 or less, 0.19 or less, 0.18 or less, 0.17 or less, 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, 0.10 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, or 0.02 or less. If the lithium transition metal oxide contains manganese, c may be greater than 0, 0.01 or more, or 0.02 or more. The upper and lower limits of the mole fraction of manganese relative to all elements other than lithium in the above lithium transition metal oxide can be appropriately selected within a range that satisfies the definition described above. When the mole fraction of manganese in the above lithium transition metal oxide satisfies the above range, a stable crystal structure can be formed.

[0084] In the above chemical formula 1, M1 and M2 represent dopants that may exist within the crystal lattice of the lithium transition metal oxide. The lithium transition metal oxide has a layered crystal structure in which a lithium layer containing lithium and a transition metal layer containing a transition metal are alternately arranged, and the dopant may be incorporated into at least one of the lithium layer and the transition metal layer.

[0085] At least one dopant M1 selected from Al, Zr, Na, S, Mg, Ti, and B exists in a doped state within the crystal lattice of the lithium transition metal oxide. The dopant M1 may include at least one selected from Al, Zr, Na, S, Mg, Ti, and B, preferably at least one selected from Al, Zr, Mg, Ti, and B, and more preferably at least one selected from Al, Zr, and Ti. Additionally, preferably, the dopant M1 may be Zr.

[0086] In the above chemical formula 1, d, representing the mole fraction of dopant M1 (M1 / Ni+Co+Mn+M1+M2) of all elements other than lithium among the lithium transition metal oxides, may be 0.001 or more and 0.01 or less. Additionally, d may preferably be 0.001 or more and 0.009 or less, 0.001 or more and 0.008 or less, 0.001 or more and 0.007 or less, 0.001 or more and 0.006 or less, 0.001 or more and 0.005 or less, or 0.001 or more and 0.004 or less, more preferably 0.001 or more and less than 0.004, and even more preferably 0.001 or more and 0.003 or less.

[0087] When the lithium transition metal oxide additionally includes a dopant M2 other than M1, e, which represents the mole fraction of dopant M2 (M2 / Ni+Co+Mn+M1+M2) relative to all elements other than lithium in the lithium transition metal oxide in Formula 1, may be 0.05 or less, 0.045 or less, 0.04 or less, 0.035 or less, 0.03 or less, 0.025 or less, 0.02 or less, 0.015 or less, 0.01 or less, 0.009 or less, 0.008 or less, 0.007 or less, 0.006 or less, 0.005 or less, 0.004 or less, 0.003 or less, 0.002 or less, and 0.001 or less.

[0088] When the lithium transition metal oxide optionally includes dopant M2, the dopant may include at least one selected from K, Ca, Sr, Ba, Rb, Ce, Hf, Ta, Cr, F, V, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd, and Cu, preferably at least one selected from K, Ca, Sr, Ba, Ce, Cr, F, V, Fe, Zn, Si, Y, Nb, Mo, W, and P, more preferably at least one selected from K, Ca, Sr, Ba, Ce, V, Si, Y, Nb, Mo, W, and P.

[0089] The type, combination, and content of the above-mentioned dopant M2 can be appropriately selected within a range that does not negatively affect the electrochemical properties and stability of the above-mentioned positive active material.

[0090] The above-mentioned dopant may be doped into the precursor of the lithium transition metal oxide during the synthesis step (co-precipitation step) of the precursor of the lithium transition metal oxide. Additionally, the above-mentioned dopant may be doped into the lithium transition metal oxide by mixing the precursor of the lithium transition metal oxide with a dopant-containing raw material and then performing heat treatment (calcination). The lithium transition metal oxide may be obtained by mixing the precursor of the lithium transition metal oxide, a lithium raw material (e.g., LiOH, Li2CO3, or a combination thereof), and the dopant-containing raw material, and then performing heat treatment (calcination). The dopant-containing material may be a fluoride, chloride, carbonate, sulfate, nitrate, phosphate, oxide, and / or hydroxide containing the aforementioned dopant.

[0091] In addition, when forming a coating layer on at least a portion of the surface of the lithium transition metal oxide by mixing the lithium transition metal oxide and the coating raw material and then heat-treating, the dopant among the coating raw material may be incorporated into the crystal lattice of the lithium transition metal oxide.

[0092] However, unlike the above dopant M2, in order to control the growth of primary particles and crystallites constituting the lithium transition metal oxide during the calcination step by implementing a difference in heat quantity during the reaction between the lithium transition metal oxide precursor and the lithium raw material, it is preferable that the raw material containing the above dopant M1 be used in the synthesis step (e.g., co-precipitation step) of the lithium transition metal oxide precursor (generally, a hydroxide precursor) so that the above dopant M1 is doped into the lithium transition metal oxide precursor.

[0093] In the present invention, the lithium transition metal oxide may be a secondary particle formed by the aggregation of a plurality of primary particles.

[0094] Unless otherwise defined herein, the primary particles may have a rod shape, an elliptical shape, and / or an irregular shape. Additionally, primary particles of various shapes may exist within the same cathode active material unless specifically intended during the manufacturing process. Furthermore, the primary particles refer to particle units that do not appear to have grain boundaries when observed using a scanning electron microscope at a magnification of 5,000 to 20,000 times.

[0095] The average particle size (D) of the above primary particles 50 ) may be 0.02μm to 0.5μm, 0.03μm to 0.5μm, 0.04μm to 0.5μm, 0.05μm to 0.5μm, 0.06μm to 0.5μm, 0.07μm to 0.8μm, 0.09μm to 0.5μm, or 0.1μm to 0.5μm.

[0096] The average particle size (D) of the above primary particles 50) can be calculated as the average value of the length in the major axis direction and the length in the minor axis direction of the unit particle ([major axis length + minor axis length] / 2). The average particle size of the primary particle can be calculated as the average value of the particle sizes of all unit particles observed from the surface SEM image and / or cross-sectional SEM image of the lithium transition metal oxide according to a known method.

[0097] The average aspect ratio of primary particles can be calculated from a cross-sectional SEM image of the lithium transition metal oxide according to a known method. For example, the ratio of the length in the major axis direction to the length in the minor axis direction of the primary particles observed from the cross-sectional SEM image of the lithium transition metal oxide can be defined as the aspect ratio, and the average value of the aspect ratio of the primary particles observed from the cross-sectional SEM image can be calculated. At this time, the average aspect ratio of the primary particles can be calculated as the average value of the aspect ratios measured from the entire primary particle, 10% of the entire primary particle, 20% of the entire primary particle, 30% of the entire primary particle, 40% of the entire primary particle, or 50% of the entire primary particle observed from the cross-sectional SEM image.

[0098] If there are no major and minor axes within any primary particle observed from the cross-sectional SEM image above, the aspect ratio of the primary particle will have a value of 1.

[0099] The average aspect ratio of the primary particles constituting the lithium transition metal oxide defined herein may be 1.9 or higher and less than 2.6. Specifically, the average aspect ratio of the primary particles calculated from the cross-sectional SEM image of the lithium transition metal oxide may be 1.9 or higher and less than 2.6. If the average aspect ratio of the primary particles calculated from the cross-sectional SEM image of the lithium transition metal oxide is less than 1.9 or 2.6 or higher, the high-temperature life is reduced and gas generation may increase during charging / discharging and / or storage.

[0100] In order to improve the lifespan characteristics and storage stability at high temperatures of the cathode active material defined herein, the average aspect ratio of the primary particles is one of the structural features that must be controlled. The average aspect ratio of the primary particles constituting the lithium transition metal oxide may have a value of 1.9 or more and less than 2.6, preferably 1.9 or more and less than 2.5, or 1.9 or more and less than 2.4, more preferably 1.97 or more and less than 2.5, 1.96 or more and less than 2.4, or 1.97 or more and less than 2.38.

[0101] The average particle size of the above secondary particles can be measured using the laser diffraction method. For example, after dispersing the secondary particles in a dispersion medium, they can be introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiated with ultrasound of approximately 28 kHz at an output of 60 W, and then a volume-cumulative particle size distribution graph is obtained. The average particle size of the above secondary particles (D 50 ) may be 2.0μm or more and 18.0μm or less.

[0102] The average crystallite size of the lithium transition metal oxide may be greater than 57 nm and less than 95 nm. Preferably, the average crystallite size of the lithium transition metal oxide may be greater than 57 nm, greater than 60 nm, greater than 65 nm, greater than 68 nm, greater than 68 nm, greater than 70 nm, greater than 71 nm, greater than 72 nm, or greater than 73 nm. Additionally, the average crystallite size of the lithium transition metal oxide may be less than 95 nm, less than 90 nm, less than 85 nm, less than 80 nm, less than 80 nm, less than 78 nm, less than 78 nm, or less than 76 nm.

[0103] If the average crystallite size of the lithium transition metal oxide is 57 nm or less, the crystallinity of the lithium transition metal oxide is excessively low, making it difficult to achieve an appropriate capacity and potentially leading to a decrease in high-temperature lifespan. On the other hand, if the average crystallite size of the lithium transition metal oxide exceeds 95 nm, the lithium ion diffusion path within the crystal becomes longer and the diffusion resistance increases, which not only degrades high-rate charge / discharge performance but also causes microcracks to occur during repeated electrode expansion / contraction, potentially degrading lifespan characteristics.

[0104] In order to improve the lifetime characteristics and storage stability at high temperatures of the cathode active material defined herein, the average crystallite size of the lithium transition metal oxide is one of the crystallographic characteristics that must be controlled. By controlling the average crystallite size of the lithium transition metal oxide to the above range together with the average aspect ratio of the primary particles, the lifetime characteristics and storage stability of the cathode active material at high temperatures can be improved.

[0105] The above average crystallite size can be quantitatively analyzed through X-ray diffraction analysis (XRD) by Cu-Kα X-rays on the lithium transition metal oxide. Specifically, the above average crystallite size can be calculated through Rietveld analysis of the X-ray diffraction spectrum in the 2θ=10°~120° region obtained through XRD analysis of the cathode active material containing the lithium transition metal oxide.

[0106] Apart from the average crystallite size calculated through the above Rietveld analysis, the crystallite size corresponding to a specific crystal plane can be calculated using Scherrer's equation. The crystallite size calculated using Scherrer's equation is calculated through the full width at half maximum of the diffraction peak corresponding to the specific crystal plane.

[0107] The crystallite size calculated by Scherrer's formula from the diffraction peak corresponding to the (003) plane in the diffraction spectrum obtained from X-ray diffraction analysis using Cu-Kα rays for the above positive active material may be 40 nm or more and less than 80 nm.

[0108] (003) If the crystallite size in the (003) plane is less than 40 nm, the crystallites become excessively fine and the surface area becomes excessively large, so side reactions occur due to the increased contact area with the electrolyte, which increases the initial irreversible capacity and may lead to gas generation at high temperatures and deterioration of storage characteristics. Conversely, if the crystallite size in the (003) plane is 80 nm or more, structural defects increase during the crystal growth process or internal stress of the particles increases, which increases the likelihood of cracks occurring during repeated charge and discharge cycles, and consequently, lifespan characteristics may deteriorate.

[0109] Accordingly, in the present invention, the crystallite size of the (003) plane is controlled to be 40 nm or more and less than 80 nm to ensure regularity of the layered crystal structure, thereby improving high-temperature life characteristics and storage stability. Preferably, the crystallite size corresponding to the (003) plane may be 40 nm or more and 75 nm or less, 45 nm or more and 70 nm or less, 50 nm or more and 65 nm or less, 55 nm or more and 65 nm or less, 58 nm or more and 65 nm or less, or 60 nm or more and 65 nm or less.

[0110] In addition, the crystallite size calculated by Scherrer's formula from the diffraction peak corresponding to the (104) plane in the diffraction spectrum obtained from X-ray diffraction analysis using Cu-Kα rays for the above positive active material may be 30 nm or more and 60 nm or less, 30 nm or more and 50 nm or less, 35 nm or more and 46 nm or less, or 38 nm or more and 46 nm or less.

[0111] It is preferable that C(104) / C(003), which is the ratio of the crystallite size (C(003)) calculated by Scherrer's formula from the diffraction peak corresponding to the (104) plane to the crystallite size (C(104)) calculated by Scherrer's formula from the diffraction peak corresponding to the (104) plane in the diffraction spectrum obtained from X-ray diffraction analysis using Cu-Kα rays for the above positive active material, is 0.55 or higher and 0.80 or lower.

[0112] The (003) plane is a crystal plane that reflects the interlayer direction (c-axis direction) growth of the layered crystal structure, and the (104) plane is a crystal plane that reflects the anisotropic growth state inside the crystal grain. If C(104) / C(003) is less than 0.55, the growth of the (003) plane is excessively dominant compared to the growth of the (104) plane, causing the crystal grain to become excessively flattened, which may lead to cracking and deterioration of life characteristics due to structural stress concentration during repeated charge-discharge cycles. On the other hand, if the (003) / (104) ratio is greater than 0.80, the growth of the (104) plane becomes relatively larger, which reduces the regularity of the layered crystal structure and intensifies cation mixing between the lithium layer and the transition metal layer, causing the lithium ion diffusion path to become unbalanced, and as a result, there is a concern that the residual capacity retention rate and storage stability at high temperatures may be reduced. Therefore, by controlling the ratio of the crystallite size of the (104) plane to the crystallite size of the (003) plane, i.e., C(104) / C(003), to be between 0.55 and 0.80, the growth balance of the (003) plane and (104) plane crystallites can be secured, and the stability of the layered crystal structure can be improved, thereby enhancing high-temperature life characteristics and storage stability.

[0113] In addition, the ratio of the crystallite size of the (104) plane to the crystallite size of the (003) plane, i.e., C(104) / C(003), may preferably be 0.60 or more and 0.75 or less, 0.60 or more and 0.71 or less, 0.60 or more and less than 0.71, 0.65 or more and 0.70 or less, 0.67 or more and 0.69 or less, or 0.672 or more and 0.683 or less.

[0114] It is preferable that the FWHM (104) / FWHM (003), which is the ratio of the diffraction peak corresponding to the (003) plane (FWHM (003)) and the diffraction peak corresponding to the (104) plane (FWHM (104)) in the diffraction spectrum obtained from X-ray diffraction analysis using Cu-Kα rays for the above positive active material, be greater than 1.522 and less than 1.622.

[0115] It may include a coating layer formed on at least a portion of the surface of the lithium transition metal oxide. Additionally, the coating layer may have an island shape formed on at least one portion of the surface of the primary particle, the interface between the primary particles, and the surface of the secondary particle, or may have a shape that covers at least one of the surface of the primary particle, the interface between the primary particles, and the surface of the secondary particle.

[0116] The coating layer may include at least one selected from Ti, Al, Cr, Zr, B, Na, and Ca.

[0117] At this time, the coating layer may include at least one metal oxide represented by the following chemical formula 2. The metal oxide represented by chemical formula 2 is an oxide different from the lithium transition metal oxide represented by chemical formula 1.

[0118] [Chemical Formula 2]

[0119] Li f M3 g O h

[0120] In the above chemical formula 2, M3 is at least one selected from Ti, Al, Cr, Zr, B, Na, and Ca, and 0≤f≤10, 0 <g≤8, 0<h≤15이다. 상기 화학식 2로 표시되는 상기 금속 산화물의 비제한적인 예로는 Li f Ti g O h , Li f Al g O h , Li f Zr g O h , Li f B g O h , Ti g O h , Al g O h , Zr g O h , B g O h There are others. Preferably, M3 is at least one selected from Ti, Al, and Zr, or may include Ti, Al, and Zr.

[0121] As the metal oxide diffuses from the surface of the secondary particle toward the center of the secondary particle along the grain boundaries between the primary particles, a gradient in which the concentration of M3 decreases from the surface of the secondary particle toward the center of the secondary particle may be formed. The concentration gradient of M3 can be confirmed by SEM / EDS analysis of the lithium transition metal oxide, etc.

[0122] In addition, the coating layer may further include at least one metal oxide represented by the following chemical formula 3. In this case, the metal oxide represented by chemical formula 3 is an oxide different from the metal oxide represented by chemical formula 2. Also, the metal oxide represented by chemical formula 3 is an oxide different from the lithium transition metal oxide represented by chemical formula 1.

[0123] [Chemical Formula 3]

[0124] Li i M4j O k

[0125] In the above chemical formula 3, M4 is at least one selected from Ni, Mn, Co, S, Mg, Ca, Sr, Ba, Rb, Ce, Hf, Ta, F, V, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd, and Cu, and 0≤i≤10, 0 <j≤8, 0<k≤15이다.

[0126] In the above chemical formula 3, M4 may be one or two elements selected from Ni, Mn, Co, S, Mg, Ca, Sr, Ba, Rb, Ce, Hf, Ta, F, V, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd, and Cu.

[0127]

[0128] lithium secondary battery

[0129] According to another aspect of the present invention, an anode may be provided comprising an anode current collector and an anode active material layer formed on the anode current collector. Herein, the anode active material layer may include an anode active material according to various embodiments of the present invention. Accordingly, since the anode active material is the same as previously described, a specific description is omitted for convenience, and only the remaining unmentioned components will be described below.

[0130] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive 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 increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0131] The above positive active material layer can be manufactured by applying a positive slurry composition, which includes a conductive material and optionally a binder together with the positive active material, to the positive current collector.

[0132] At this time, the anode 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 anode slurry for forming the anode active material layer. Excellent capacity characteristics may be exhibited when included within the above-mentioned content range, but it is not necessarily limited thereto.

[0133] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.1 wt% to 15 wt% relative to the total weight of the anode slurry for forming the anode active material layer.

[0134] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive slurry for forming the positive active material layer.

[0135] The above-described anode can be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, it can be manufactured by applying an anode slurry composition, prepared by dissolving or dispersing the above-described anode active material and optionally a binder and a conductive material in a solvent, onto an anode current collector, and then drying and rolling.

[0136] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0137] In addition, in another embodiment, the anode may be manufactured by casting the anode slurry composition onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0138] In addition, according to another aspect of the present invention, an electrochemical device comprising the anode described above may be provided. Specifically, the electrochemical device may be a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0139] Specifically, the above lithium secondary battery may include a positive electrode, a negative electrode positioned opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is the same as previously described, a detailed description is omitted for convenience, and only the remaining components not previously mentioned are described in detail below.

[0140] The above lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0141] The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

[0142] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0143] The above-mentioned cathode active material layer can be manufactured by applying a cathode slurry composition, which includes a conductive material and optionally a binder together with the above-mentioned cathode active material, to the above-mentioned cathode current collector.

[0144] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. 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, or Al alloys; and SiO₂ βExamples include metal oxides capable of doping and dedoping lithium, such as (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, the carbon material may include low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0145] The above-mentioned cathode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the cathode slurry for forming the cathode active material layer.

[0146] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the cathode slurry for forming the cathode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0147] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode slurry for forming the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and 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 fiber or metal fiber; metal powder such as carbon fluoride, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used.

[0148] In one embodiment, the negative active material layer may be manufactured by applying a negative slurry composition, prepared by dissolving or dispersing a negative active material and optionally a binder and a conductive material in a solvent, onto a negative current collector and drying it, or by casting the negative slurry composition onto a separate support and then laminating the film obtained by peeling it off from the support onto a negative current collector.

[0149] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0150] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0151] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0152] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0153] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the above lithium salt is 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., may be used. It is preferable to use the lithium salt within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0154] When the electrolyte used in the present invention is a solid electrolyte, for example, solid inorganic electrolytes such as sulfide-based solid electrolytes, oxide-based solid electrolytes, nitride-based solid electrolytes, halide-based solid electrolytes, etc. may be used, and preferably, sulfide-based solid electrolytes may be used.

[0155] As a material for a sulfide-based solid electrolyte, a solid electrolyte containing Li, an element X (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 above-mentioned sulfide-based 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, and Li2S-P2S5-Z m S n (Here, m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (Here, p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In) etc.

[0156] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a mixed state of amorphous and crystalline.

[0157] Li7La3Zr2O is used as a material for oxide-based solid electrolytes. 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 PO4-x N x (LiPON), Li 2+2x Zn 1-x There are GeO4 (LISICON), etc.

[0158] The aforementioned solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the anode and the cathode. Additionally, the solid electrolyte may be partially included within the anode active material layer of the anode independently of the solid electrolyte layer, or the solid electrolyte may be partially included within the cathode active material layer of the cathode independently of the solid electrolyte layer.

[0159] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0160] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0161] The external shape of the lithium secondary battery according to the present invention is not subject to any particular limitations, but may be cylindrical, prismatic, pouch, or coin-shaped using a can. In addition, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but can also preferably be used as a unit cell in a medium-to-large battery module containing a plurality of battery cells.

[0162] According to another aspect of the present invention, a battery module comprising the lithium secondary battery as a unit cell and / or a battery pack comprising the same may be provided.

[0163] The battery module or the battery pack may be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0164]

[0165] The present invention will be described in more detail below through examples. However, these examples are intended solely to illustrate the present invention and should not be interpreted as limiting the scope of the present invention.

[0166]

[0167] Preparation Example 1. Preparation of positive electrode active material

[0168] Example 1

[0169] (a) A NiCoMnZr(OH)2 hydroxide precursor was synthesized using nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium oxide (ZrO2) by a known co-precipitation method. In the hydroxide precursor, the molar ratio of Ni:Co:Mn:Zr was designed to be 89.85:8.35:1.55:0.25.

[0170] (b) A first mixture was prepared by mixing the hydroxide precursor obtained in step (a) with LiOH (Li / (Ni+Co+Mn+Zr) molar ratio = 1.05). Subsequently, the first mixture was subjected to a first heat treatment (first calcination) at 685°C for 12.5 hours under an O2 atmosphere to obtain an intermediate.

[0171] (c) A second mixture was prepared by adding the intermediate obtained in step (b), 0.1 mol% ZrO2, 0.6 mol% Al2O3, and 0.6 mol% TiO2. Subsequently, the second mixture was subjected to a second heat treatment (second calcination) at 700°C for 12.5 hours under an O2 atmosphere to obtain a lithium transition metal oxide. The lithium transition metal oxide was washed and dehydrated, and then heat-treated at 320°C for 8 hours under an O2 atmosphere to dry it, thereby obtaining a final product.

[0172]

[0173] Example 2

[0174] A positive electrode active material was prepared in the same manner as in Example 1, except that in step (a) above, the molar ratio of the hydroxide precursors was designed as Ni:Co:Mn:Zr=89.9:8.4:1.6:0.1.

[0175]

[0176] Example 3

[0177] A positive electrode active material was prepared in the same manner as in Example 1, except that in step (a) above, the molar ratio of the hydroxide precursors was designed as Ni:Co:Mn:Zr=89.85:8.35:1.5:0.3.

[0178]

[0179] Comparative Example 1

[0180] (a) A NiCoMn(OH)2 hydroxide precursor was synthesized using nickel sulfate, cobalt sulfate, and manganese sulfate by a known co-precipitation method. In the hydroxide precursor, the molar ratio of Ni:Co:Mn was designed to be 89.9:8.4:1.7.

[0181] (b) A first mixture was prepared by mixing the hydroxide precursor obtained in step (a) with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.05). Subsequently, the first mixture was subjected to a first heat treatment (first calcination) at 685°C for 12.5 hours under an O2 atmosphere to obtain an intermediate.

[0182] (c) A second mixture was prepared by adding the intermediate obtained in step (b), 0.1 mol% ZrO2, 0.6 mol% Al2O3, and 0.6 mol% TiO2. Subsequently, the second mixture was subjected to a second heat treatment (second calcination) at 700°C for 12.5 hours under an O2 atmosphere to obtain a lithium transition metal oxide. The lithium transition metal oxide was washed and dehydrated, and then heat-treated at 320°C for 8 hours under an O2 atmosphere to dry it, thereby obtaining a final product.

[0183]

[0184] Comparative Example 2

[0185] A positive electrode active material was prepared in the same manner as in Example 1, except that in step (a) above, the molar ratio of the hydroxide precursors was designed as Ni:Co:Mn:Zr=89.5:8.4:1.7:0.4.

[0186]

[0187] Comparative Example 3

[0188] A positive electrode active material was prepared in the same manner as in Example 1, except that the first heat treatment temperature in step (b) above was set to 700℃.

[0189]

[0190] Comparative Example 4

[0191] A positive electrode active material was prepared in the same manner as in Example 1, except that the first heat treatment temperature in step (b) above was set to 660℃.

[0192]

[0193] Comparative Example 5

[0194] (a) A NiCoMn(OH)2 hydroxide precursor was synthesized using nickel sulfate, cobalt sulfate, and manganese sulfate by a known co-precipitation method. In the hydroxide precursor, the molar ratio of Ni:Co:Mn was designed to be 89.9:8.4:1.7.

[0195] (b) A first mixture was prepared by mixing the hydroxide precursor obtained in step (a), zirconium oxide (ZrO2), and LiOH (Li / (Ni+Co+Mn+Zr) molar ratio = 1.05). Zirconium oxide (ZrO2) was mixed to be 0.3 mol% relative to the total metal elements excluding lithium in the first mixture. Subsequently, the first mixture was subjected to a first heat treatment (first calcination) at 700°C for 12.5 hours under an O2 atmosphere to obtain an intermediate.

[0196] (c) A second mixture was prepared by adding the intermediate obtained in step (b), 0.1 mol% ZrO2, 0.6 mol% Al2O3, and 0.6 mol% TiO2. Subsequently, the second mixture was subjected to a second heat treatment (second calcination) at 700°C for 12.5 hours under an O2 atmosphere to obtain a lithium transition metal oxide. The lithium transition metal oxide was washed and dehydrated, and then heat-treated at 320°C for 8 hours under an O2 atmosphere to dry it, thereby obtaining a final product.

[0197]

[0198] Preparation Example 2. Preparation of a lithium secondary battery (half-cell)

[0199] A positive electrode slurry was prepared by dispersing 94 wt% of the positive electrode active material prepared according to 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 onto an aluminum thin film with a thickness of 15 μm and vacuum dried at 135°C to produce a positive electrode for a lithium secondary battery.

[0200] A half-cell was prepared using a lithium foil as the counter electrode for the above anode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separator, and an electrolyte in which LiPF6 is present at a concentration of 1.15 M in a solvent mixed with ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

[0201]

[0202] Preparation Example 3. Preparation of a lithium secondary battery (full-cell)

[0203] A cathode slurry was prepared by dispersing 90 wt% of the cathode active material prepared according to Preparation Example 1, 4.5 wt% of carbon black, and 5.5 wt% of PVDF binder in N-methyl-2-pyrrolidone (NMP).

[0204] The above anode slurry was uniformly applied to an aluminum thin film with a thickness of 15 μm and vacuum dried at 135°C to produce an anode for a lithium secondary battery in which an anode active material layer was formed.

[0205] A full cell was prepared using a graphite electrode as the counter electrode for the anode, a porous polyethylene membrane (Celgard 2300, thickness: 20 μm) as the separator, and an electrolyte in which LiPF6 is present at a concentration of 1.15 M in a solvent mixed with ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4.

[0206]

[0207] Experimental Example 1. SEM analysis of the cathode active material

[0208] The lithium transition metal oxide contained in each cathode active material prepared in Preparation Example 1 was cross-sectionally treated with a Focused Ion Beam (FIB) and then photographed with a Scanning Electron Microscope to obtain a cross-sectional SEM image. Subsequently, the aspect ratio was defined as the ratio of the length in the major axis direction to the length in the minor axis direction of the primary particles observed in the cross-sectional SEM image (length in the major axis direction / length in the minor axis direction), and 10% of the total primary particles were randomly selected from the cross-sectional SEM image to calculate the average aspect ratio.

[0209] The above measurement results are shown in Table 1 below.

[0210] Aspect Ratio (Major Axis Length / Minor Axis Length) Example 12.05 Example 21.97 Example 32.38 Comparative Example 13.69 Comparative Example 22.75 Comparative Example 32.60 Comparative Example 42.35 Comparative Example 51.85

[0211]

[0212] Referring to the results in Table 1, it can be confirmed that the average aspect ratio of the primary particles included in the cathode active materials according to Examples 1 to 3 is 1.9 or higher and less than 2.6. In the case of Comparative Example 1, it can be confirmed that the average aspect ratio of the primary particles is excessively large compared to Examples 1 to 3 because a Zr dopant is not used in the synthesis step (co-precipitation step) of the hydroxide precursor. In the case of Comparative Example 2, it can be confirmed that the average aspect ratio of the primary particles has a value of 2.6 or higher because the content of the Zr dopant used in the synthesis step (co-precipitation step) of the hydroxide precursor becomes excessively high. In the case of Comparative Example 5, it can be confirmed that the growth of the primary particles in the long axis direction is excessively suppressed compared to Comparative Example 1 because a Zr dopant is not used in the synthesis step (co-precipitation step) of the hydroxide precursor, but a Zr dopant is used in the calcination step of the hydroxide precursor.

[0213]

[0214] Experimental Example 2. XRD Analysis of Anode Active Material

[0215] X-ray diffraction (XRD) analysis was performed on each positive electrode active material prepared according to Preparation Example 1 to measure the average crystallite size, (003) plane half-width, (104) plane half-width, a-axis length, and c-axis length of the lithium transition metal oxide contained in the positive electrode active material. The XRD analysis was performed using a Bruker D8 Endeavor diffractometer with Cu-Kα radiation (1.5406 Å).

[0216] The average crystallite size (C.Size) of the above lithium transition metal oxide was calculated as an Lvol-IB value through Rietveld refinement using TOPAS software from the diffraction spectrum obtained from XRD analysis of each cathode active material prepared according to Preparation Example 1.

[0217] In addition, the crystallite size of the (003) plane (C(003)) was calculated by substituting the full width at half maximum of the diffraction peak corresponding to the (003) plane in the diffraction spectrum obtained from the XRD analysis into Scherrer's equation, and the crystallite size of the (104) plane (C(104)) was calculated by substituting the full width at half maximum of the diffraction peak corresponding to the (003) plane calculated by Scherrer's equation.

[0218] The above measurement results are shown in Tables 2 and 3 below.

[0219] Classification C. Size (nm) FWHM (003) (°) FWHM (104) (°) FWHM (104) / FWHM (003) C (003) (nm) C (104) (nm) C (104) / C (003) Example 1 760.1270.2011.58363430.683 Example 2 760.1240.1961.58165440.677 Example 3 730.1320.2081.57661410.672 Comparative Example 1 780.1250.1951.56064440.688 Comparative Example 2 740.1270.2061.62263420.667 Comparative Example 3950.1170.1861.59069460.667 Comparative Example 4570.1410.2221.57457390.684 Comparative Example 5760.1290.1941.52262440.710

[0220] Classification a-axis length (Å) c-axis length (Å) c-axis length / a-axis length Example 1 2.870 814.18 874.942 Example 2 2.870 814.18 764.942 Example 3 2.870 814.18 754.942 Comparative Example 1 2.871 714.18 634.940 Comparative Example 2 2.872 314.18 84.940 Comparative Example 3 2.872 114.18 744.940 Comparative Example 4 2.28 1714.18 636.217 Comparative Example 5 2.871 114.18 634.941

[0221]

[0222] Referring to the results in Tables 2 and 3, it can be confirmed that the average crystallite size obtained from Rietveld analysis of the cathode active materials according to Examples 1 to 3 is greater than 57 nm and less than 95 nm. In addition, it can be confirmed that the crystallite size calculated by Scherrer's equation from the diffraction peak corresponding to the (003) plane of the cathode active materials according to Examples 1 to 3 is 40 nm or greater and less than 80 nm, and the ratio of the crystallite size calculated by Scherrer's equation from the diffraction peak corresponding to the (003) plane to the crystallite size calculated by Scherrer's equation from the diffraction peak corresponding to the (104) plane is 0.55 or greater and 0.80 or less.

[0223] As described above, in the case of Comparative Example 2, as the content of the Zr dopant used in the synthesis step (co-precipitation step) of the hydroxide precursor becomes excessively high, the average aspect ratio of the primary particles has a value of 2.6 or higher, and it can be confirmed that C(104) / C(003) is lower than that of Examples 1 to 3. In addition, it can be confirmed that FWHM(104) / FWHM(003) is excessively large compared to Examples 1 to 3.

[0224] In the case of Comparative Example 3, as the calcination temperature (700°C) of the Zr-doped hydroxide precursor is higher than that of Examples 1 to 3 (685°C), it can be seen that the average crystallite size of the lithium transition metal oxide has become excessively large. In the case of Comparative Example 4, as the calcination temperature (660°C) of the Zr-doped hydroxide precursor is lower than that of Examples 1 to 3 (685°C), it can be seen that the average crystallite size of the lithium transition metal oxide has become excessively small.

[0225] In the case of Comparative Example 5, since a Zr dopant is used in the calcination step of the hydroxide precursor instead of the synthesis step (co-precipitation step) of the hydroxide precursor, it can be seen that the average crystallite size is smaller compared to Examples 1 to 3, and the C (104) / C (003) ratio is excessively larger than in other examples and comparative examples. Additionally, it can be seen that the FWHM (104) / FWHM (003) is excessively smaller compared to Examples 1 to 3.

[0226]

[0227] Experimental Example 3. Evaluation of High-Temperature Life Characteristics of a Lithium Secondary Battery (Half-Cell)

[0228] For the lithium secondary battery (half-cell) prepared in Preparation Example 2, 50 charge / discharge cycles were performed under 1C / 1C conditions within a driving voltage range of 3.0V to 4.4V at 45℃ using an electrochemical analyzer (Toyo, Toscat-3100), and the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention rate) was measured.

[0229] Classification Cycle Capacity Retention Rate (%) Example 190.9 Example 290.5 Example 388.8 Comparative Example 182.7 Comparative Example 280.8 Comparative Example 385.4 Comparative Example 484.2 Comparative Example 583.2

[0230]

[0231] Referring to the results in Table 4, it can be confirmed that the high-temperature life characteristics of Examples 1 to 3, in which the dopant exists in a doped state within the crystal lattice of the lithium transition metal oxide, the average aspect ratio of the primary particles is 1.9 or higher and less than 2.6, and the average crystallite size obtained from Rietveld analysis is greater than 57 nm and less than 95 nm, are improved compared to Comparative Examples 1 to 5.

[0232]

[0233] Experimental Example 4. Evaluation of Gas Generation in a Lithium Secondary Battery (Full-Cell)

[0234] For the lithium secondary battery (full-cell) prepared in Preparation Example 3, a 3-cycle formation process was completed using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a formation voltage range of 2.75V to 4.3V, and conditions of 0.2C / 0.2C. After formation, charge / discharge cycles of 1 to 500 were performed, and the rate of change in cell volume was measured every 100 cycles using a digital density hydrometer. Table 5 shows the rate of volume increase after 500 cycles relative to the initial volume.

[0235] Meanwhile, the amount of stored gas generated was determined by charging a lithium secondary battery (full-cell) formed in the same manner as described above to 4.3V, and then storing the full-cell in an oven with an internal temperature set to 70℃. Table 5 shows the volume increase rate after 28 days relative to the initial volume.

[0236] Classification Volume Increase Rate (%) After 500 Cycles After 28 Days of Storage Example 15.15.6 Example 25.35.8 Example 34.35.3 Comparative Example 110.812.5 Comparative Example 27.17.8 Comparative Example 36.78.2 Comparative Example 47.410.5 Comparative Example 512.510.2

[0237]

[0238] Referring to the results in Table 5, it can be confirmed that the amount of gas generated after long-term cycling and long-term storage of Examples 1 to 3, in which the dopant in the crystal lattice of the lithium transition metal oxide exists in a doped state, the average aspect ratio of the primary particles is 1.9 or greater and less than 2.6, and the average crystallite size obtained from Rietveld analysis is greater than 57 nm and less than 95 nm, is reduced compared to Comparative Examples 1 to 5.

[0239]

[0240] Although embodiments of the present invention have been described above, those skilled in the art may modify and change the present invention in various ways by adding, changing, deleting, or adding components, etc., without departing from the spirit of the present invention as described in the claims, and such modifications and changes are also to be included within the scope of the rights of the present invention.

Claims

A positive electrode active material comprising a lithium transition metal oxide having a layered crystal structure belonging to the R-3m space group, At least one dopant selected from Al, Zr, Na, S, Mg, Ti, and B exists in a doped state within the crystal lattice of the lithium transition metal oxide, and The average crystallite size obtained from Rietveld analysis of the diffraction spectrum obtained from X-ray diffraction analysis using Cu-Kα rays for the above-mentioned positive electrode active material is greater than 57 nm and less than 95 nm, and The average aspect ratio of the primary particles calculated from the cross-sectional SEM image of the above lithium transition metal oxide is 1.9 or higher and less than 2.6, Positive active material. In paragraph 1, Among the lithium transition metal oxides, at least one dopant selected from Al, Zr, Na, S, Mg, Ti, and B is present in an amount of 0.1 mol% or more and 1 mol% or less with respect to all elements excluding lithium. Positive active material. In paragraph 1 or 2, The above lithium transition metal oxide comprises at least one selected from nickel, cobalt, manganese, and aluminum, Positive active material. In any one of paragraphs 1 through 3, The above lithium transition metal oxide includes nickel, cobalt, and manganese, Positive active material. In any one of paragraphs 1 through 4, The above lithium transition metal oxide contains 75 mol% or more of nickel with respect to all elements excluding lithium, Positive active material. In any one of paragraphs 1 through 5, The above lithium transition metal oxide is a positive electrode active material having an average composition represented by the following chemical formula 1: [Chemical Formula 1] Li a Ni1-(b+c+d+e)Co b Mr c M1 d M2 e O2 In the above chemical formula 1, M1 is at least one selected from Al, Zr, Na, S, Mg, Ti, and B, and M2 is at least one selected from K, Ca, Sr, Ba, Rb, Ce, Hf, Ta, Cr, F, V, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd and Cu, and 0.95≤a≤1.15, 0≤b≤0.20, 0≤c≤0.20, 0.001≤d≤0.01, 0≤e≤0.05, 0.75≤1-(b+c+d+e). In any one of paragraphs 1 through 6, A crystallite size calculated by Scherrer's equation from the diffraction peak corresponding to the (003) plane in the diffraction spectrum obtained from X-ray diffraction analysis using Cu-Kα rays for the above positive active material, which is 40 nm or more and less than 80 nm Positive active material. In any one of paragraphs 1 through 7, A ratio of the crystallite size calculated by Scherrer's formula from the diffraction peak corresponding to the (104) plane to the crystallite size calculated by Scherrer's formula from the diffraction peak corresponding to the (003) plane in the diffraction spectrum obtained from X-ray diffraction analysis using Cu-Kα rays for the above positive active material is 0.55 or greater and 0.80 or less, Positive active material. In any one of paragraphs 1 through 8, It includes a coating layer formed on at least a portion of the surface of the lithium transition metal oxide, and The coating layer comprises at least one selected from Ti, Al, Cr, Zr, B, Na, and Ca, Positive active material. In Paragraph 9, The above lithium transition metal oxide is a secondary particle formed by the aggregation of a plurality of primary particles, and The coating layer has an island shape formed on a part of at least one of the surface of the primary particle, the interface between the primary particles, and the surface of the secondary particle, or has a shape that surrounds at least one of the surface of the primary particle, the interface between the primary particles, and the surface of the secondary particle. Positive active material. In Article 9 or Article 10, The above coating layer comprises at least one metal oxide represented by the following chemical formula 2, Positive active material: [Chemical Formula 2] Read f M3 g Oh h In the above chemical formula 2, M3 is at least one selected from Ti, Al, Cr, Zr, B, Na, and Ca, and 0≤f≤10, 0 <g≤8, 0<h≤15이다. In any one of paragraphs 9 through 11, The coating layer further comprises at least one metal oxide represented by the following chemical formula 3, Positive active material: [Chemical Formula 3] Li i M4 j About k In the above chemical formula 3, M4 is at least one selected from Ni, Mn, Co, S, Mg, Ca, Sr, Ba, Rb, Ce, Hf, Ta, F, V, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd and Cu, and 0≤i≤10, 0 <j≤8, 0<k≤15이다. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 12. A lithium secondary battery using a positive electrode according to Paragraph 13.