Positive electrode active material and lithium secondary battery containing the same

Abstract

The present invention relates to a positive electrode active material and a lithium secondary battery containing the same, and more specifically, to a positive electrode active material and a lithium secondary battery containing the same, which comprises a lithium composite oxide containing at least nickel and titanium, wherein the titanium is doped in the lithium composite oxide and exists in the form of an oxide on at least a portion of the surface of the lithium composite oxide, wherein the output efficiency and high-temperature life characteristics (high-temperature cycle capacity retention rate) of the lithium secondary battery using the positive electrode active material can be simultaneously improved.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery containing the same, and more specifically, to a positive electrode active material and a lithium secondary battery containing the same, which comprises a lithium composite oxide containing at least nickel and titanium, wherein the titanium is doped in the lithium composite oxide and exists in the form of an oxide on at least a portion of the surface of the lithium composite oxide, wherein the output efficiency and high-temperature life characteristics (high-temperature cycle capacity retention rate) of the lithium secondary battery using the positive electrode active material can be simultaneously improved. Background Art

[0002] Batteries use materials capable of electrochemical reactions at their positive and negative electrodes to store electrical energy. A typical example of this type of battery is a lithium secondary battery, which stores electrical energy through the difference in chemical potential when lithium ions are inserted and released between the positive and negative electrodes.

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

[0004] Lithium composite oxides are used as positive electrode active materials for lithium secondary batteries. For example, composite oxides such as LiCoO 2 , LiMn 2 O 4 , LiNiO 2 , and LiMnO 2 are being studied.

[0005] Among the above-mentioned positive electrode active materials, LiCoO2 is widely used due to its excellent life characteristics and charge and discharge efficiency. However, the resources of cobalt used as a raw material are limited and expensive, so it has the disadvantage of limited price competitiveness.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low price, but they have the problems of low capacity and poor high-temperature performance. In addition, LiNiO2 positive electrode active materials show battery characteristics of high discharge capacity, but due to the problem of cation mixing between Li and transition metals, it is difficult to synthesize, and thus has major problems in rate performance.

[0007] Furthermore, depending on the severity of this cation mixing, a large amount of Li by-products is produced. Most of these Li by-products are composed of LiOH and Li2CO3 compounds. When preparing the positive electrode slurry, they cause gelation problems and cause gas generation during charge and discharge after electrode preparation. Residual Li2CO3 reduces cycling by increasing monomer swelling and also causes battery expansion.

[0008] In addition, in order to prepare higher-specification lithium secondary batteries, high-Ni (high-Ni) positive electrode active materials with high Ni content in the positive electrode active material have attracted much attention. However, as with the aforementioned LiNiO2 positive electrode active material, such high-Ni positive electrode active materials are accompanied by problems caused by cation mixing. Therefore, for high-Ni positive electrode active materials, attempts are being made to improve the stability of the positive electrode active material by doping or coating with other metal elements that are not the main transition metal elements. Summary of the Invention

[0009] Technical issues

[0010] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles dominates the market. At the same time, the demand for positive electrode materials used in lithium secondary batteries is also changing.

[0011] For example, lithium secondary batteries using LFP have been mainly used in the past from the perspective of ensuring safety, but recently, the use of nickel-based lithium composite oxides, which have a higher energy capacity per unit weight than LFP, has been increasing.

[0012] Therefore, positive electrode active materials used in higher-specification lithium secondary batteries should meet the expected stability and reliability even under more severe operating conditions.

[0013] Taking into account such various environments, the object of the present invention is to provide a positive electrode active material comprising a lithium composite oxide containing at least nickel and titanium, wherein the above-mentioned titanium is doped in the above-mentioned lithium composite oxide and exists in the form of an oxide in at least a portion of the surface of the above-mentioned lithium composite oxide, wherein the output efficiency and high-temperature life characteristics (high-temperature cycle capacity retention rate) of a lithium secondary battery using the above-mentioned positive electrode active material can be improved at the same time.

[0014] Furthermore, another object of the present invention is to provide a positive electrode comprising the positive electrode active material defined in the present application.

[0015] Meanwhile, another object of the present invention is to provide a lithium secondary battery using the positive electrode defined in this application.

[0016] Solutions to the Problem

[0017] According to one aspect of the present invention, a positive electrode active material is provided, which comprises a lithium composite oxide containing at least nickel and titanium, wherein the titanium is doped in the lithium composite oxide and exists in the form of an oxide in at least a portion of the surface of the lithium composite oxide, wherein the output efficiency and high-temperature life characteristics (high-temperature cycle capacity retention rate) of a lithium secondary battery using the positive electrode active material can be improved simultaneously.

[0018] Specifically, the above-mentioned lithium composite oxide is a secondary particle formed by the aggregation of multiple primary particles, and the titanium content (molar percentage) calculated by using the line sum spectrum of titanium obtained by performing EDX line scanning (line scanning) in the short axis direction of the primary particles selected from the cross-sectional transmission electron microscope (TEM) image of the above-mentioned lithium composite oxide can satisfy the following formula 1.

[0019] Formula 1: 1.4≤[(a1+a2) / 2] / b1≤3.25

[0020] (Wherein, when the minor axis diameter of the primary particles selected from the above cross-sectional transmission electron microscopic image is set to r, a1 is the average content (molar percentage) of titanium measured based on all metal elements except lithium in the region from 0 to 0.05r from the starting point of the above line and spectrum, a2 is the average content (molar percentage) of titanium measured based on all metal elements except lithium in the region from 0.95r to r from the starting point of the above line and spectrum, and b1 is the average content (molar percentage) of titanium measured based on all metal elements except lithium in the region from 0.05r to 0.95r from the starting point of the above line and spectrum.)

[0021] In one embodiment, the titanium in the lithium composite oxide may be present in an amount greater than 0.2 mol % and less than 3.3 mol % based on all metal elements except lithium.

[0022] Based on all metal elements except lithium, the titanium in the above-mentioned lithium composite oxide is present in an amount greater than 0.2 mole percent, thereby improving the comprehensive indicators showing the electrochemical characteristics of the lithium secondary battery using the above-mentioned positive electrode active material (for example, charging capacity, discharge capacity, charge and discharge efficiency, cycle capacity retention rate, impedance characteristics, output efficiency, etc.), especially, improving the high-temperature life characteristics.

[0023] In one embodiment, at least a portion of the titanium in the lithium composite oxide may be doped in the primary particles.

[0024] At this time, preferably, the average content (molar percentage) of titanium measured based on all metal elements except lithium in the region of 0.05r to 0.95r from the starting point of the above line and spectrum is greater than 0.083 molar percent and less than 0.832 molar percent.

[0025] The titanium present in the region of 0.05r to 0.95r from the starting point of the above-mentioned line and spectrum may correspond to the titanium present in a state of being doped in the above-mentioned initial particles, and based on all metal elements except lithium in the region of 0.05r to 0.95r from the starting point of the above-mentioned line and spectrum, the average content (molar percentage) of titanium is present in an amount greater than 0.083 molar percent, thereby improving the output efficiency of the lithium secondary battery using the above-mentioned positive electrode active material.

[0026] The lithium composite oxide may further include at least one metal element selected from the group consisting of cobalt, manganese, and aluminum.

[0027] Specifically, the primary particles may be represented by the following Chemical Formula 1.

[0028] Chemical formula 1: Li w Ni 1-(x+y+z) Ti x M1 y M2 z O2

[0029] (Wherein, M1 is at least one selected from Co, Mn, and Al; M2 is at least one selected from P, Sr, Ba, Zr, Co, Mn, Al, W, Ce, Hf, Ta, F, Mg, V, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, B, Nb, Gd, and Cu; M1 and M2 are different from each other, 0.5≤w≤1.5, 0≤x≤0.50, 0≤y≤0.40, and 0≤z≤0.20.)

[0030] In one embodiment, the primary particles are core-shell particles including a core and a shell present on at least a portion of the surface of the core. The shell may contain a metal oxide represented by the following Chemical Formula 2.

[0031] Chemical formula 2: Li a Ti b M3 c O d

[0032] (Wherein, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd and Nd, 0≤a≤10, 0 <b≤8,0≤c≤8,2≤d≤13。)

[0033] The metal oxide may include at least one selected from titanium oxide and lithium titanium oxide.

[0034] The metal oxide represented by Chemical Formula 2 is present on at least a portion of the surface of the core, thereby increasing the titanium content on the surface of the primary particles to a predetermined amount or more. This improves the impedance characteristics and high-temperature cycle capacity retention of a lithium secondary battery using this positive electrode active material.

[0035] Furthermore, according to another aspect of the present invention, there is provided a positive electrode comprising the positive electrode active material defined in the present application.

[0036] Meanwhile, according to another aspect of the present invention, a lithium secondary battery using the positive electrode defined in this application is provided.

[0037] Effects of the Invention

[0038] According to the present invention, the titanium exists in the state of being doped in the lithium composite oxide and exists in the form of an oxide in at least a portion of the surface of the above-mentioned lithium composite oxide, thereby simultaneously improving the output efficiency and high-temperature life characteristics (high-temperature cycle capacity retention rate) of the lithium secondary battery.

[0039] At this time, when the content of titanium doped in the lithium composite oxide is greater than a predetermined ratio relative to the content of titanium present in at least a portion of the surface of the lithium composite oxide in the form of an oxide, the surface resistance of the lithium composite oxide increases, thereby reducing the impedance characteristics and the cycle capacity retention rate.

[0040] Furthermore, when the content of titanium present in at least a portion of the surface of the lithium composite oxide in the form of oxide is greater than a predetermined ratio relative to the content of titanium doped in the lithium composite oxide, the output efficiency of a lithium secondary battery using the lithium composite oxide as a positive electrode active material may be reduced.

[0041] According to the present invention, comprehensive indicators related to the electrochemical characteristics of lithium secondary batteries, including output efficiency, impedance characteristics and high-temperature life characteristics (high-temperature cycle capacity retention rate), can be improved by controlling the content of titanium doped in the above-mentioned lithium composite oxide and the content of at least a portion of titanium present in the form of oxide on the surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a transmission electron microscope image of a cross section of the lithium composite oxide contained in the positive electrode active material of Example 1. Figure 1 The arrow direction in shows the line scanning direction along the minor axis direction of the primary particle, and the dotted line shows the line and spectrum interval.

[0043] Figure 2 Show the basis Figure 1 The lines and spectrum of titanium in the line scan direction are shown in .

[0044] Figure 3 Shown with Figure 1 Transmission electron microscope images of a cross section of the lithium composite oxide contained in the positive electrode active material of Example 1, taken at different angles, and EDX mapping results for titanium.

[0045] Figure 4 This is a transmission electron microscope image of a cross section of the lithium composite oxide contained in the positive electrode active material of Comparative Example 1. Figure 4 The arrow direction in shows the line scanning direction along the minor axis direction of the primary particle.

[0046] Figure 5 Show the basis Figure 4 The lines and spectrum of titanium in the line scanning direction are shown in FIG, and the dotted lines show the line and spectrum intervals.

[0047] Figure 6 Shown with Figure 4 Transmission electron microscope images of a cross section of the lithium composite oxide contained in the positive electrode active material of Comparative Example 1, taken at different angles, and EDX mapping results for titanium.

[0048] Figure 7 This is a transmission electron microscope image of a cross section of the lithium composite oxide contained in the positive electrode active material of Comparative Example 4. Figure 7 The arrow direction in shows the line scanning direction along the minor axis direction of the primary particle, and the dotted line shows the line and spectrum interval.

[0049] Figure 8 Show the basis Figure 7 The lines and spectrum of titanium in the line scan direction are shown in .

[0050] Figure 9 Shown with Figure 7 Transmission electron microscope images of a cross section of the lithium composite oxide contained in the positive electrode active material of Comparative Example 4, taken at different angles, and EDX mapping results for titanium. DETAILED DESCRIPTION

[0051] Hereinafter, the positive electrode active material of the present invention and the lithium secondary battery including the positive electrode active material will be described in more detail.

[0052] positive electrode active material

[0053] According to one aspect of the present invention, a positive electrode active material is provided, comprising a lithium composite oxide containing at least nickel and titanium. Furthermore, the lithium composite oxide contains lithium in addition to the nickel and titanium, and is a composite metal oxide having a layered crystalline structure capable of intercalating and deintercalating lithium ions.

[0054] The lithium composite oxide contained in the positive electrode active material defined in the present application may be a secondary particle containing at least one primary particle. In this case, the primary particle may be expressed as crystallite.

[0055] Here, "secondary particles comprising at least one type of primary particles" should be interpreted as including both "particles formed by aggregation of a plurality of primary particles" and "non-aggregated single particles consisting of a single crystallite".

[0056] The primary particles and the secondary particles may each independently have a rod-like, oval, and / or irregular shape.

[0057] When the average major axis length is used as an indicator of the size of the primary particles and the secondary particles, the average major axis length of the primary particles constituting the lithium composite oxide may be 0.1 μm to 5 μm, and the average major axis length of the secondary particles may be 1 μm to 30 μm. The average major axis length of the secondary particles may vary depending on the number of the primary particles constituting the secondary particles, and the positive electrode active material may include particles having various average major axis lengths.

[0058] In the case where the above-mentioned lithium composite oxide is a "non-aggregated single particle composed of a single microcrystal" or a "particle formed by the aggregation of a smaller number of primary particles", the size (average particle size) of the primary particles contained in the "non-aggregated single particle composed of a single microcrystal" or the "particle formed by the aggregation of a smaller number of primary particles" may be larger than the size (average particle size) of the primary particles contained in the "secondary particles formed by the aggregation of tens to hundreds or more primary particles".

[0059] As described above, compared to the conventional preparation of "secondary particles formed by aggregation of tens to hundreds or more primary particles," lithium composite oxides that are "non-aggregated single particles composed of single crystallites" or "particles formed by aggregation of a smaller number of primary particles" require strong heat treatment conditions (high heat treatment temperature / long heat treatment). It is well known that heat treatment at a relatively high temperature (e.g., 800°C or above) for a long time promotes particle growth (crystallization growth), thereby increasing the size of single particles while reducing the degree of particle aggregation to obtain a positive electrode active material.

[0060] For example, when the lithium composite oxide is a "non-aggregated single particle composed of a single crystallite" or a "particle formed by aggregation of a relatively small number of primary particles," the average major axis length of the primary particles may be in the range of 0.5 μm to 20 μm. Conversely, when the lithium composite oxide is a "particle formed by aggregation of a plurality (tens to hundreds or more) of primary particles," the average major axis length of the primary particles may be in the range of 0.1 μm to 5 μm.

[0061] In one embodiment, at least a portion of the titanium in the lithium composite oxide may be doped in the primary particles.

[0062] The content of titanium doped in the primary particles can be calculated from the content of the titanium raw material mixed with the hydroxide precursor of the lithium composite oxide, or can be measured by transmission electron microscopy (TEM)-EDX or EP-EDX analysis of the primary particles.

[0063] Furthermore, according to the present invention, the titanium exists in a doped state in the above-mentioned lithium composite oxide, and at the same time, exists in the form of an oxide in at least a portion of the surface of the above-mentioned lithium composite oxide, thereby simultaneously improving the output efficiency and high-temperature life characteristics (cycle capacity retention rate) of the lithium secondary battery using the above-mentioned lithium composite oxide as the positive electrode active material.

[0064] To achieve the above-mentioned effects, preferably, the titanium in the lithium composite oxide is present in an amount greater than 0.2 mol% based on all metal elements except lithium. In this case, the titanium content in the lithium composite oxide can be confirmed by measuring the bulk composition of the lithium composite oxide through ICP analysis.

[0065] Based on all metal elements except lithium, the titanium in the above-mentioned lithium composite oxide is present in an amount greater than 0.2 mole percent, thereby improving the comprehensive indicators showing the electrochemical characteristics of the lithium secondary battery using the above-mentioned positive electrode active material (for example, charging capacity, discharge capacity, charge and discharge efficiency, cycle capacity retention rate, impedance characteristics, output efficiency, etc.).

[0066] On the other hand, preferably, the titanium in the lithium composite oxide is present in an amount of less than 3.3 mol% based on all metal elements excluding lithium. If the titanium content in the lithium composite oxide is too high, the charge capacity, discharge capacity, and charge-discharge efficiency of a lithium secondary battery using the lithium composite oxide as a positive electrode active material may be reduced.

[0067] The lithium composite oxide may further contain at least one metal element selected from the group consisting of cobalt, manganese, and aluminum. Furthermore, the primary particles constituting the lithium composite oxide may also contain at least one metal element selected from the group consisting of cobalt, manganese, and aluminum.

[0068] Specifically, the primary particles may be represented by the following Chemical Formula 1. Furthermore, the overall composition of the secondary particles formed by aggregation of a plurality of primary particles may also be represented by the following Chemical Formula 1.

[0069] Chemical formula 1: Li w Ni 1-(x+y+z) Ti x M1 y M2 z O2

[0070] (Wherein, M1 is at least one selected from Co, Mn, and Al; M2 is at least one selected from P, Sr, Ba, Zr, Co, Mn, Al, W, Ce, Hf, Ta, F, Mg, V, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, B, Nb, Gd, and Cu; M1 and M2 are different from each other, 0.5≤w≤1.5, 0≤x≤0.50, 0≤y≤0.40, and 0≤z≤0.20.)

[0071] The lithium composite oxide may be a high-Ni type lithium composite oxide in which the concentrations (molar percentages) of Ni, M1, M2, and Ti in the chemical formula 1 satisfy the following relational formula 1.

[0072] Relationship 1: Ni / (Ni+M1+M2+Ti)≥80.0

[0073] Furthermore, when the above-mentioned lithium composite oxide contains cobalt, the high-Ni / low-Co type lithium composite oxide is less than 10 mol percent, preferably less than 5 mol percent, and more preferably less than 3 mol percent based on all metal elements in the above-mentioned lithium composite oxide except lithium.

[0074] Generally, it is known that increasing the nickel content in lithium composite oxides leads to structural instability due to the mixing of Li / Ni cations. Furthermore, decreasing the cobalt content in lithium composite oxides leads to an increase in initial overvoltage (resistance), inevitably reducing efficiency characteristics.

[0075] However, in the lithium composite oxide contained in the positive electrode active material defined in the present application, the titanium exists in the state of being doped in the above-mentioned lithium composite oxide, and at the same time, exists in the form of an oxide in at least a part of the surface of the above-mentioned lithium composite oxide. Thus, the output efficiency and high-temperature life characteristics (high-temperature cycle capacity retention rate) of the lithium secondary battery using the high-Ni type lithium composite oxide or the high-Ni / low-Co type lithium composite oxide as the positive electrode active material can be improved at the same time.

[0076] In addition, when the content of titanium doped in the lithium composite oxide is greater than a predetermined ratio relative to the content of titanium present in at least a portion of the surface of the lithium composite oxide in the form of an oxide, the surface resistance of the lithium composite oxide increases, thereby reducing the impedance characteristics and the cycle capacity retention rate.

[0077] Furthermore, when the content of titanium present in at least a portion of the surface of the lithium composite oxide in the form of oxide is greater than a predetermined ratio relative to the content of titanium doped in the lithium composite oxide, the output efficiency of a lithium secondary battery using the lithium composite oxide as a positive electrode active material can be reduced.

[0078] Therefore, as described later, in the above-mentioned lithium composite oxide defined in the present application, the comprehensive indicators related to the electrochemical characteristics of lithium secondary batteries, including output efficiency, impedance characteristics and high-temperature life characteristics (high-temperature cycle capacity retention rate), can be improved by controlling the content of titanium doped in the above-mentioned lithium composite oxide and the content of at least a portion of titanium present in the form of oxide on the surface.

[0079] Specifically, in the above-mentioned lithium composite oxide defined in the present application, the titanium content (molar percentage) calculated using the titanium line and spectrum obtained by EDX line scanning in the short axis direction of the primary particles selected from the cross-sectional transmission electron microscope image of the above-mentioned lithium composite oxide can satisfy the following formula 1.

[0080] Formula 1: 1.4≤[(a1+a2) / 2] / b1≤3.25

[0081] (Wherein, when the minor axis diameter of the primary particles selected from the above cross-sectional transmission electron microscopic image is set to r, a1 is the average content (molar percentage) of titanium measured based on all metal elements except lithium in the region from 0 to 0.05r from the starting point of the above line and spectrum, a2 is the average content (molar percentage) of titanium measured based on all metal elements except lithium in the region from 0.95r to r from the starting point of the above line and spectrum, and b1 is the average content (molar percentage) of titanium measured based on all metal elements except lithium in the region from 0.05r to 0.95r from the starting point of the above line and spectrum.)

[0082] That is, a1 and a2 respectively show the average titanium content (molar percentage) in the surface part of the above-mentioned primary particles (equivalent to a length of 5% of the minor axis diameter of the primary particles) based on the above-mentioned lines and spectrum, and b1 shows the average titanium content (molar percentage) in the center part of the above-mentioned primary particles (equivalent to a length of 90% of the minor axis diameter of the primary particles) based on the above-mentioned lines and spectrum.

[0083] Based on all metal elements except lithium in the region of 0.05r to 0.95r from the starting point of the above-mentioned line and spectrum, the average content (molar percentage) of titanium is greater than 0.083 molar percent and less than 0.832 molar percent, preferably greater than 0.3 molar percent and less than 0.7 molar percent.

[0084] The titanium existing in the region of 0.05r to 0.95r from the above-mentioned line and the starting point of the spectrum may correspond to the titanium existing in a state of being doped in the above-mentioned primary particles.

[0085] At this time, the content of titanium doped in the primary particles does not match the content of the titanium-containing raw material after mixing with the lithium composite oxide hydroxide precursor and then heat-treating (corresponding to the first heat treatment in Preparation Example 1).

[0086] That is, part of the titanium in the titanium-containing raw material mixed with the lithium composite oxide hydroxide precursor and then heat-treated may also exist in the regions of 0 to 0.05r and 0.95r to r from the starting point of the line and spectrum.

[0087] Based on all metal elements except lithium in the region of 0.05r to 0.95r from the starting point of the above-mentioned line and spectrum, the average content (molar percentage) of titanium is present in an amount greater than 0.083 molar percent, thereby improving the output efficiency of the indicators related to the electrochemical characteristics of the lithium secondary battery using the above-mentioned positive electrode active material.

[0088] On the other hand, preferably, the average titanium content (molar percentage) is less than 0.832 molar percent based on all metal elements other than lithium in the region from 0.05r to 0.95r from the starting point of the above line and spectrum. If the average titanium content in the above region is higher, the output efficiency of the lithium secondary battery using the above positive electrode active material can be further improved. On the contrary, the effect of reducing the surface resistance of the above lithium composite oxide is negligible, making it difficult to improve the impedance characteristics and cycle capacity retention rate of the lithium secondary battery using the above positive electrode active material.

[0089] Furthermore, the average of the average titanium content (molar percentage) measured based on all metal elements except lithium in the region from 0 to 0.05r from the starting point of the above-mentioned line and spectrum and the average titanium content (molar percentage) measured based on all metal elements except lithium in the region from 0.95r to r is greater than 0.227 molar percentage and less than 2.699 molar percentage, preferably greater than 0.8 molar percentage and less than 1.2 molar percentage.

[0090] The titanium existing in the regions of 0 to 0.05r and 0.95r to r from the starting point of the above-mentioned line and spectrum may be coated on the surface of the above-mentioned primary particles, or may correspond to titanium existing in a state of being doped in a region adjacent to the outermost periphery of the primary particles.

[0091] At this time, the content of titanium coated on the surface of the above-mentioned primary particles or doped in the area adjacent to the outermost periphery of the primary particles is not consistent with the content of the titanium-containing raw material material mixed with the above-mentioned lithium composite oxide and then heat-treated (equivalent to the second heat treatment in Preparation Example 1).

[0092] That is, at least a portion of the titanium in the titanium-containing raw material mixed with the lithium composite oxide and then heat-treated may also exist in the region of 0.05r to 0.95r from the starting point of the line and spectrum.

[0093] When the average value of the average titanium content (molar percentage) measured based on all metal elements except lithium in the region from 0 to 0.05r from the starting point of the above-mentioned line and spectrum and the average titanium content (molar percentage) measured based on all metal elements except lithium in the region from 0.95r to r is less than 0.227 molar percent, it is difficult to improve the impedance characteristics and cycle capacity retention rate of the lithium secondary battery using the above-mentioned positive electrode active material.

[0094] On the other hand, if the average of the titanium content (molar percentage) measured based on all metal elements other than lithium in the region of 0 to 0.05r from the starting point of the line and spectrum and the average titanium content (molar percentage) measured based on all metal elements other than lithium in the region of 0.95r to r is greater than 2.669 mole percent, the output efficiency of the lithium secondary battery using the positive electrode active material, an indicator related to electrochemical characteristics, is reduced. As mentioned above, the content of titanium doped in the primary particles is not necessarily the same as the content of the titanium-containing raw material after heat treatment (equivalent to the first heat treatment in Preparation Example 1) after mixing with the hydroxide precursor of the lithium composite oxide and the content of the titanium-containing raw material after heat treatment (equivalent to the second heat treatment in Preparation Example 1) and the average titanium content (molar percentage) measured based on all metal elements other than lithium in the region of 0 to 0.05r, the region of 0.05r to 0.95r, and the region of 0.95r to r from the starting point of the line and spectrum in the minor axis direction of the primary particles.

[0095] Therefore, in the present invention, instead of considering the amount of titanium-containing raw material used, the titanium content in each region on the above-mentioned line and spectrum is measured, and a significant correlation is derived between the titanium content in each region and the electrochemical characteristics (especially, high-temperature life characteristics) of the lithium secondary battery using the above-mentioned lithium composite oxide as the positive electrode active material.

[0096] The results are summarized as follows: on the premise that [(a1+a2) / 2] / b1 defined above satisfies the range of Formula 1, based on all metal elements other than lithium, the titanium content in the above-mentioned lithium composite oxide is greater than 0.2 mol percent and less than 3.3 mol percent, and the average titanium content (molar percentage) measured based on all metal elements other than lithium in the region of 0 to 0.05r, the region of 0.05r to 0.95r, and the region of 0.95r to r in the short axis direction of the above-mentioned initial particles is within the specified range, thereby simultaneously improving comprehensive indicators related to the electrochemical characteristics of lithium secondary batteries, including output efficiency, impedance characteristics, and high-temperature life characteristics (high-temperature cycle capacity retention rate).

[0097] Even if the titanium content in the above-mentioned lithium composite oxide and the above-mentioned primary particles meets the above-mentioned range, when [(a1+a2) / 2] / b1 is less than 1.4, the output efficiency such as c-rate of the lithium secondary battery using the above-mentioned lithium composite oxide as the positive electrode active material can be improved, but the improvement effect on other indicators (for example, charging capacity, discharge capacity, charging and discharging efficiency, impedance characteristics and life characteristics, etc.) is negligible.

[0098] On the contrary, even if the titanium content in the above-mentioned lithium composite oxide and the above-mentioned primary particles meets the above-mentioned range, when [(a1+a2) / 2] / b1 is greater than 3.25, the EIS and cycle capacity retention rate of the lithium secondary battery using the above-mentioned lithium composite oxide as the positive electrode active material can be improved, but the improvement effect on the charging capacity, discharge capacity, charge and discharge efficiency and output characteristics (c-rate) is negligible.

[0099] The primary particles may be defined as core-shell particles including a core and a shell present on at least a portion of the surface of the core. In this case, a metal oxide represented by the following Chemical Formula 2 may be present in the shell.

[0100] Chemical formula 2: Li a Ti b M3 c O d

[0101] (Wherein, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd and Nd, 0≤a≤10, 0 <b≤8,0≤c≤8,2≤d≤13。)

[0102] That is, the shell may be defined as a region where the metal oxide represented by the above Chemical Formula 2 exists.

[0103] As mentioned above, when the above-mentioned initial particles are defined as core-shell particles, a1 and a2 in the above-mentioned formula 1 are the average titanium content (molar percentage) measured based on all metal elements except lithium in the region from 0 to 0.05r from the outermost periphery of the above-mentioned core-shell particles (in this case, a1 and a2 refer to the titanium content in the region located at the starting point and end point of the line scan based on the line and spectrum, respectively), and b1 is the average titanium content (molar percentage) measured based on all metal elements except lithium in the region from 0.05r to 0.95r from the outermost periphery of the above-mentioned core-shell particles.

[0104] At least one selected from titanium oxide and lithium titanium oxide may be present in the shell. Furthermore, the titanium oxide and / or the lithium titanium oxide may be a metal oxide complexed with M3.

[0105] The metal oxide may be physically and / or chemically bonded to the primary particles, or may exist in a solid solution with the primary particles.

[0106] When the secondary particles are used as a reference, the metal oxide may be partially or completely present at the interface between the primary particles located inside the secondary particles and / or on the surface of the secondary particles. In the case where the metal oxide is partially present on the surface of the primary particles and / or the secondary particles, the shell may exist in the form of an island.

[0107] lithium secondary batteries

[0108] According to another embodiment of the present invention, the present invention can provide a positive electrode comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode active material layer may comprise the positive electrode active material of various embodiments of the present invention. Therefore, the positive electrode active material is the same as previously described, and for convenience, its detailed description is omitted. The following description only includes the remaining components not previously described.

[0109] 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, or calcined carbon can be used, or aluminum or stainless steel can be surface-treated with carbon, nickel, titanium, silver, or the like. Furthermore, the positive electrode current collector typically has a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the binding force of the positive electrode active material. For example, it can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0110] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition comprising the positive electrode active material, a conductive material, and optionally a binder as needed, on the positive electrode current collector.

[0111] In this case, the content of the positive electrode active material relative to the total weight of the positive electrode active material layer may be 80 weight percent to 99 weight percent, more specifically 85 weight percent to 98.5 weight percent. When the positive electrode active material is included in the above content range, excellent capacity characteristics can be shown, but it is not limited thereto.

[0112] The conductive materials mentioned above are used to impart conductivity to the electrodes. Any material can be used without limitation as long as it does not cause chemical changes and exhibits electronic conductivity in the resulting battery. 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 powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. One or a mixture of two or more of these can be used. The conductive materials mentioned above can be included in an amount of 0.1 to 15 weight percent relative to the total weight of the positive electrode active material layer.

[0113] The binder serves to improve the adhesion between the plurality of positive electrode active material particles and the bonding force between the positive electrode active material and the collector. As a specific example, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber (EPDM), sulfonated ethylene propylene diene monomer rubber, styrene butadiene rubber (SBR), fluororubber or various copolymers thereof, etc., can be used. One or a mixture of two or more thereof can be used. Relative to the total weight of the positive electrode active material layer, the binder can be included in an amount of 0.1 weight percent to 15 weight percent.

[0114] In addition to utilizing the aforementioned positive electrode active material, the aforementioned positive electrode can be prepared according to conventional positive electrode preparation methods. Specifically, the positive electrode slurry composition can be prepared by coating the positive electrode current collector, followed by drying and rolling. The positive electrode slurry composition is prepared by dissolving or dispersing the aforementioned positive electrode active material in a solvent and optionally dissolving or dispersing a binder and a conductive material in the solvent.

[0115] The solvent may be a commonly used solvent in the art, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or a mixture of two or more thereof may be used. Considering the coating thickness and production yield of the slurry, the amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder and to have a viscosity sufficient to exhibit excellent thickness uniformity when applied to prepare the positive electrode.

[0116] Furthermore, in another embodiment, the positive electrode may be prepared by casting the positive electrode slurry composition onto a separate support, and then laminating a thin film obtained by peeling the thin film from the support onto a positive electrode current collector.

[0117] Meanwhile, according to another embodiment of the present invention, an electrochemical device comprising the positive electrode can be provided, wherein the electrochemical device is specifically a battery, a capacitor, etc., and more specifically a lithium secondary battery.

[0118] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode disposed opposite the positive electrode, and a separator and electrolyte disposed between the positive and negative electrodes. The positive electrode is the same as described above, and therefore, for convenience, a detailed description thereof is omitted. The following description only includes the remaining components not described above.

[0119] The lithium secondary battery may optionally further include: a battery container for housing the electrode assembly of the positive electrode, the negative electrode, and the separator; and a sealing member for sealing the battery container.

[0120] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0121] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys can be used. Furthermore, the negative electrode current collector typically has a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to enhance the binding force of the negative electrode active material. For example, it can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0122] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition comprising the negative electrode active material, a conductive material, and optionally a binder as needed, on the negative electrode current collector.

[0123] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbon materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO β(0<β<2), metal oxides capable of doping and dedoping lithium such as SnO2, vanadium oxide, lithium vanadium oxide; or composites containing the above metal compounds and carbon materials such as Si-C composites or Sn-C composites, etc., and a mixture of one or more of them can be used. In addition, as the above-mentioned negative electrode active material, a metal lithium film can also be used. In addition, both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Representative low-crystalline carbons are soft carbon and hard carbon, and representative high-crystalline carbons are amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, kishgraphite, pyrolytic carbon, mesophase pitch based carbon fiber, mesophase carbon microbeads, mesophase pitch, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0124] Based on the total weight of the negative electrode active material layer, the negative electrode active material may be included in an amount of 80 weight percent to 99 weight percent.

[0125] The binder is a component that facilitates bonding between the conductive material, the active material, and the current collector. Typically, 0.1 to 10 weight percent of the binder can be added based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, EPDM rubber, sulfonated EPDM rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0126] The conductive material is used to further enhance the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, the conductive material may be added in an amount of up to 10 weight percent, preferably up to 5 weight percent. There are no particular limitations on the conductive material, as long as it does not induce chemical changes in the battery and exhibits conductivity. Examples include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0127] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition on a negative electrode current collector and drying the negative electrode slurry composition, wherein the negative electrode active material is dissolved or dispersed in a solvent and a binder and a conductive material are selectively dissolved or dispersed in a solvent. Alternatively, the negative electrode slurry composition may be cast on a separate support and then a thin film obtained by peeling the support off is laminated on the negative electrode current collector.

[0128] Furthermore, in another embodiment, the negative electrode active material layer can also be prepared by coating a negative electrode slurry composition on a negative electrode collector and drying it. The negative electrode slurry composition is prepared by dissolving or dispersing the negative electrode active material in a solvent and selectively dissolving or dispersing a binder and a conductive material in a solvent. Alternatively, the negative electrode slurry composition is cast on a separate support and then a thin film obtained by peeling off the support is laminated on the negative electrode collector.

[0129] In addition, in the above-mentioned lithium secondary battery, the separator is used to separate the negative electrode and the positive electrode and provide a mobile channel for lithium ions. As long as the separator commonly used in the lithium secondary battery, it can be used without restriction. In particular, preferably, for the ion movement of the electrolyte, the impedance is low and there is excellent electrolyte moisture-containing ability. Specifically, a porous polymer film can be used, for example, a porous polymer film prepared by polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or their two or more layers of stacked structures. In addition, a common porous non-woven fabric can also be used, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. In addition, in order to ensure heat resistance or mechanical strength, a separation membrane comprising a coating of ceramic component and polymeric substance can also be used, selectively capable of being used with a single layer or multilayer structure.

[0130] Furthermore, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in preparing lithium secondary batteries.

[0131] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0132] As the above-mentioned organic solvent, any organic solvent that can act as a medium for the movement of ions participating in the electrochemical reaction of the battery can be used without limitation. Specifically, as the above-mentioned organic solvent, ester solvents such as methylacetate, 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; dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (EPC), and the like can be used. Carbonate solvents such as carbonate (PC); alcohol solvents such as ethanol and isopropyl alcohol; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, which may contain double-bonded aromatic rings or ether bonds); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane. Among these, carbonate solvents are preferred, and more preferred are mixtures of cyclic carbonates (such as ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can improve battery charge and discharge performance, and low-viscosity linear carbonate compounds (such as ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate). In this case, when the cyclic carbonate and linear carbonate are mixed in a volume ratio of approximately 1:1 to approximately 1:9, excellent electrolyte performance can be achieved.

[0133] The above-mentioned lithium salt can use compounds that can provide lithium ions used in lithium secondary batteries without limitation. Specifically, the above-mentioned lithium salt can use LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, Li N(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI or LiB(C2O4)2, etc. Preferably, the concentration of the above-mentioned lithium salt needs to be used in the range of 0.1M to 2.0M. If the concentration of the lithium salt is included in the above range, the electrolyte has appropriate conductivity and viscosity, and therefore, can show excellent electrolyte performance and can effectively move lithium ions.

[0134] In addition to the above electrolyte components, the electrolyte may further include one or more additives such as halogenated alkylene carbonate compounds such as bis(fluoroethylene 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 chloride for the purposes of improving battery life characteristics, suppressing battery capacity reduction, and increasing battery discharge capacity. In this case, the electrolyte may contain 0.1 to 5 weight percent of the above additives relative to the total weight of the electrolyte.

[0135] As described above, the lithium secondary battery containing the positive electrode active material of the present invention stably shows excellent discharge capacity, output efficiency and life characteristics, and therefore can be used in portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEV).

[0136] The external shape of the lithium secondary battery of the present invention is not particularly limited and may be cylindrical, prismatic, pouch, or coin-shaped using a can. Furthermore, the lithium secondary battery can preferably be used not only as a battery cell used as a power source for small devices but also as a unit cell of a medium or large battery module including a plurality of battery cells.

[0137] According to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same may be provided.

[0138] The battery module or battery pack can be used as a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power source for one or more medium or large devices in a power storage system.

[0139] The present invention will be described in more detail below by way of examples. However, these examples are merely for illustrating the present invention and should not be construed as limiting the scope of the present invention to these examples.

[0140] Preparation Example 1. Preparation of positive electrode active material

[0141] (a) Ni was prepared by mixing nickel sulfate, cobalt sulfate and manganese sulfate in a molar ratio of 80:10:10 using a known co-precipitation method. 0.80 Co 0.10 Mn 0.10 Hydroxide precursor of (OH)2.

[0142] (b) After mixing the above-mentioned hydroxide precursor, LiOH (Li / (Ni+Co+Mn) molar ratio (mol ratio) = 1.03) and TiO2, maintaining an O2 atmosphere in a sintering furnace, heating to 720°C at a heating rate of 2°C per minute, and performing a first heat treatment at 720°C for 12 hours to obtain a lithium composite oxide.

[0143] (c) After mixing the above-mentioned lithium composite oxide and TiO2, an O2 atmosphere is maintained in a sintering furnace, and the temperature is increased to 700°C at a heating rate of 2°C per minute. A second heat treatment is then performed at 700°C for 8 hours to obtain a lithium composite oxide with Ti coated on the surface.

[0144] The overall composition confirmed by ICP analysis of the TiO2 content used in the above step (b) (the molar percentage calculated based on the metal element in the above hydroxide precursor), the TiO2 content used in the above step (c) (the molar percentage calculated based on the metal element other than lithium in the above lithium composite oxide), and the positive electrode active material finally obtained by the above step (c) is shown in the following Table 1.

[0145] Table 1

[0146]

[0147]

[0148] Preparation Example 2. Preparation of lithium secondary battery

[0149] A positive electrode slurry was prepared by dispersing 92 weight percent of the positive electrode active material prepared according to Preparation Example 1, 4 weight percent of artificial graphite, and 4 weight percent of a polyvinylidene fluoride binder in 30 g of N-methylpyrrolidone. The positive electrode slurry was evenly coated on a 15 μm thick aluminum film and vacuum-dried at 135°C to prepare a positive electrode for a lithium secondary battery.

[0150] Relative to the above-mentioned positive electrode, lithium foil was used as the counter electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) was used as the separation membrane, and a button battery was prepared using an electrolyte solution containing LiPF6 at a concentration of 1.15 M in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0151] Experimental Example 1. Composition Analysis of Positive Electrode Active Material

[0152] In order to confirm the concentration of cobalt in the lithium composite oxide contained in the positive electrode active material prepared according to Preparation Example 1, transmission electron microscopy (TEM) / EDX analysis was performed.

[0153] First, the lithium composite oxides contained in the positive electrode active material prepared according to Preparation Example 1 were screened, and then cross-sections of the lithium composite oxides were processed using FIB (Ga-ion source), and transmission electron microscope images of the cross sections were taken using a scanning electron microscope.

[0154] Next, after screening 10 primary particles from the multiple primary particles confirmed by the above-mentioned cross-sectional transmission electron microscope images, titanium, which is the target transition metal, was mapped by EDX analysis of the screened primary particles, and the concentration change of titanium was confirmed by line scanning in the short axis direction of the primary particles and along the short axis direction of the above-mentioned primary particles.

[0155] Figure 1 This is a transmission electron microscope image of a cross section of the lithium composite oxide contained in the positive electrode active material of Example 1. Figure 1 The arrow direction in shows the line scanning direction along the minor axis direction of the primary particle, and the dotted line shows the line and spectrum interval. Figure 2 To show the basis Figure 1 The lines and spectrum of titanium in the line scan direction are shown in . Figure 3 To show that Figure 1 Transmission electron microscope images of a cross section of the lithium composite oxide contained in the positive electrode active material of Example 1, taken at different angles, and EDX mapping results for titanium.

[0156] Reference Figures 1 to 3 Titanium was confirmed to be present in the region corresponding to the core of the primary particle, indicating the titanium doping state of the primary particle. Furthermore, titanium was present in the region corresponding to the shell of the primary particle, and when compared to the region corresponding to the core of the primary particle, a relatively high amount of titanium was confirmed. These results indicate that the surface of the primary particle is coated with titanium.

[0157] Figure 4 This is a transmission electron microscope image of a cross section of the lithium composite oxide contained in the positive electrode active material of Comparative Example 1. Figure 4 The arrow direction in shows the line scanning direction along the minor axis direction of the primary particle. Figure 5 Show the basis Figure 4 The lines and spectrum of titanium in the line scanning direction are shown in FIG, and the dotted lines show the line and spectrum intervals. Figure 6 Shown with Figure 4 Transmission electron microscope images of a cross section of the lithium composite oxide contained in the positive electrode active material of Comparative Example 1, taken at different angles, and EDX mapping results for titanium.

[0158] Reference Figures 4 to 6 , titanium exists in the region corresponding to the core of the primary particle. However, when compared with the positive electrode active material of Example 1, it can be confirmed that the titanium doped in the primary particle is extremely small. Moreover, when compared with the region corresponding to the core of the primary particle, it can be confirmed that most of the titanium exists on the surface of the primary particle.

[0159] Figure 7 This is a transmission electron microscope image of a cross section of the lithium composite oxide contained in the positive electrode active material of Comparative Example 4. Figure 7 The arrow direction in shows the line scanning direction along the minor axis direction of the primary particle, and the dotted line shows the line and spectrum interval. Figure 8 Show the basis Figure 7 The lines and spectrum of titanium in the line scan direction are shown in . Figure 9 Shown with Figure 7 Transmission electron microscope images of a cross section of the lithium composite oxide contained in the positive electrode active material of Comparative Example 4, taken at different angles, and EDX mapping results for titanium.

[0160] Reference Figures 7 to 9 It can be confirmed that titanium exists almost uniformly in the region corresponding to the core of the primary particle and the region corresponding to the shell of the primary particle.

[0161] The average values of the titanium concentrations in the core and shell regions of the lithium composite oxide (primary particles) contained in the positive electrode active material prepared in Preparation Example 1 were calculated according to the aforementioned method. The calculation results are shown in Table 2 below.

[0162] Table 2

[0163] Classification (a1+a2) / 2 b1 [(a1+a2) / 2] / b1 Example 1 1.062 0.504 2.106 Example 2 0.924 0.623 1.484 Example 3 1.156 0.466 2.481 Example 4 1.043 0.529 1.973 Example 5 0.903 0.617 1.464 Example 6 1.137 0.454 2.502 Comparative Example 1 1.378 0.330 4.178 Comparative Example 2 1.206 0.357 3.375 Comparative Example 3 0.546 0.468 1.168 Comparative Example 4 0.528 0.476 1.109 Comparative Example 5 0.227 0.083 2.735 Comparative Example 6 2.699 0.832 3.244 Comparative Example 7 1.233 0.336 3.673 Comparative Example 8 1.202 0.368 3.268 Comparative Example 9 0.528 0.477 1.107 Comparative Example 10 0.511 0.489 1.045

[0164] Wherein, when the minor axis diameter of the initial particles selected from the above-mentioned cross-sectional transmission electron microscopy image is set to r, a1 is the average titanium content (molar percentage) measured based on all metal elements except lithium in the region from 0 to 0.05r from the starting point of the above-mentioned line and spectrum, a2 is the average titanium content (molar percentage) measured based on all metal elements except lithium in the region from 0.95r to r from the starting point of the above-mentioned line and spectrum, and b1 is the average titanium content (molar percentage) measured based on all metal elements except lithium in the region from 0.05r to 0.95r from the starting point of the above-mentioned line and spectrum.

[0165] Experimental Example 2. Evaluation of electrochemical characteristics of lithium secondary batteries

[0166] Charge capacity, discharge capacity and charge and discharge efficiency

[0167] For the lithium secondary battery (button battery) prepared in Preparation Example 2, a charge and discharge experiment was carried out using an electrochemical analyzer (Toyo, Toscat-3100) at a temperature of 25°C, a voltage range of 3.0V to 4.25V, and a discharge rate of 0.2C to measure the charge capacity, discharge capacity, and charge and discharge efficiency.

[0168] High temperature life characteristics (cycle capacity retention)

[0169] For the same lithium secondary battery, two charge / discharge cycles were performed at a temperature of 25°C, a voltage range of 3.0V to 4.4V, and a condition of 0.1C / 0.1C. After one charge / discharge cycle was performed at a temperature of 45°C, a voltage range of 3.0V to 4.4V, and a condition of 0.1C / 0.1C, and after 50 charge / discharge cycles were performed at a temperature of 45°C, a voltage range of 3.0V to 4.4V, and a condition of 1.0C / 1.0C, the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention) was measured.

[0170] Impedance (Electrochemical Impedance Spectroscopy (EIS)) characteristics

[0171] For the same lithium secondary battery, after charging at 1C, the resistance is measured by electrochemical impedance spectroscopy within the frequency range (10kHz to 0.01Hz, 10mV), and R is calculated. ct (Charge transfer resistance).

[0172] Output efficiency

[0173] The same lithium secondary battery was subjected to a charge-discharge test using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0V to 4.3V, and a discharge rate of 0.1C to 5.0C to measure the output efficiency (C-rate) at 5.0C / 0.1C.

[0174] The measurement results are shown in Table 3 below.

[0175] Table 3

[0176]

[0177]

[0178] Referring to the results of Examples 1 to 3 and Comparative Examples 1 to 4 in Table 3 above, it can be confirmed that in the case of Comparative Examples 1 and 2, where the [(a1+a2) / 2] / b1 value is greater than 3.25, the EIS and cycle capacity retention rates are superior to those of Examples 1 to 3, and the improvement effects on the charge capacity, discharge capacity, charge and discharge efficiency, and output efficiency (c-rate) are negligible.

[0179] Furthermore, in the case of Comparative Examples 3 and 4 where the value of [(a1+a2) / 2] / b1 is less than 1.4, it can be confirmed that the improvement effects of all indicators except the output efficiency (c-rate) are negligible compared to Examples 1 to 3.

[0180] That is, it was confirmed that the lithium secondary batteries using the positive electrode active materials according to Examples 1 to 3 showed overall improvement effects in various indicators related to electrochemical characteristics compared to Comparative Examples 1 to 4.

[0181] Referring to the results of Examples 4 to 6 and Comparative Examples 7 to 10 in Table 3 above, it can be confirmed that in the case of Comparative Examples 7 and 8, where the [(a1+a2) / 2] / b1 value is greater than 3.25, the EIS and cycle capacity retention rates are better than those of Examples 4 to 6, but the improvement effects on the charge capacity, discharge capacity, charge and discharge efficiency, and output efficiency (c-rate) are negligible.

[0182] Furthermore, in the case of Comparative Examples 9 and 10 where the value of [(a1+a2) / 2] / b1 is less than 1.4, it was confirmed that all indicators except the output efficiency (c-rate) were lower than those of Examples 1 to 3.

[0183] That is, it was confirmed that the lithium secondary batteries using the positive electrode active materials of Examples 1 to 3 showed overall improvement effects in various indicators related to electrochemical characteristics compared to the lithium secondary batteries using the positive electrode active materials of Comparative Examples 1 to 4.

[0184] In addition, referring to the results in Table 2, it can be confirmed that the titanium content in the core and shell of the primary particles constituting the positive electrode active materials of Comparative Examples 5 and 6 is too small or too large.

[0185] The [(a1+a2) / 2] / b1 value of the positive electrode active material of Comparative Example 5 is less than 3.25, but referring to the results in Table 3, it can be confirmed that in the lithium secondary battery using the positive electrode active material of Comparative Example 5 in which the titanium content in the core and shell of the above-mentioned initial particles is too low, the overall improvement effect on various indicators related to electrochemical characteristics is negligible.

[0186] Moreover, the [(a1+a2) / 2] / b1 value of the positive electrode active material of Comparative Example 6 is less than 3.25. Referring to the results in Table 3, it can be confirmed that in the lithium secondary battery using the positive electrode active material of Comparative Example 6 in which the titanium content in the core and shell of the above-mentioned initial particles is too high, the improvement effect on the charging capacity, discharge capacity and charge-discharge efficiency is negligible.

Claims

1. A positive electrode active material comprising a lithium composite oxide containing at least nickel and titanium, characterized in that: The lithium composite oxide is a secondary particle formed by the aggregation of multiple primary particles. The titanium content calculated using the titanium line sum spectrum obtained by performing EDX line scanning in the short axis direction of the primary particles selected from the cross-sectional transmission electron microscopy image of the lithium composite oxide satisfies the following equations 1 and 2, wherein the unit of the titanium content is molar percentage, Formula 1: 1.4≤[(a1+a2) / 2] / b1≤3.25 Formula 2: 0.227 < (a1 + a2) / 2 < 2.699 Wherein, when the minor axis diameter of the primary particles selected from the above cross-sectional transmission electron microscope image is set to r, a1 is the average content of titanium measured based on all metal elements except lithium in the region from 0 to 0.05r from the starting point of the above line and spectrum, the unit of the above average content of titanium is molar percentage, a2 is the average content of titanium measured based on all metal elements except lithium in the region from 0.95r to r from the starting point of the above line and spectrum, the unit of the above average content of titanium is molar percentage, b1 is the average content of titanium measured based on all metal elements except lithium in the region from 0.05r to 0.95r from the starting point of the above line and spectrum, the unit of the above average content of titanium is molar percentage, Based on all metal elements except lithium, titanium in the lithium composite oxide is present in an amount greater than 0.2 mol % and less than 3.3 mol %. At least a portion of the titanium in the lithium composite oxide is present in a state of being doped in the primary particles. The average content of titanium measured based on all metal elements except lithium in the region of 0.05r to 0.95r from the starting point of the above line and spectrum is greater than 0.083 mol% and less than 0.832 mol%, Titanium exists in the form of an oxide on at least a portion of the surface of the lithium composite oxide.

2. The positive electrode active material according to claim 1, characterized in that The lithium composite oxide further contains at least one metal element selected from the group consisting of cobalt, manganese, and aluminum.

3. The positive electrode active material according to claim 1, characterized in that The above-mentioned primary particles are represented by the following chemical formula 1: Chemical formula 1: Li w Ni 1-(x+y+z) Ti x M1 y M2 z O2 in, M1 is at least one selected from Co, Mn and Al, M2 is at least one selected from P, Sr, Ba, Zr, Co, Mn, Al, W, Ce, Hf, Ta, F, Mg, V, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, B, Nb, Gd and Cu, M1 and M2 are different from each other. 0.5≤w≤1.5,0 <x≤0.50,0≤y≤0.40,0≤z≤0.20。 4. The positive electrode active material according to claim 1, characterized in that The primary particles are core-shell particles comprising a core and a shell present on at least a portion of the surface of the core. In the shell there exists a metal oxide represented by the following chemical formula 2, Chemical formula 2: Li a Ti b M3 c O d in, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd and Nd, 0≤a≤10,0 <b≤8,0≤c≤8,2≤d≤13。 5. The positive electrode active material according to claim 4, characterized in that At least one selected from titanium oxide and lithium titanium oxide exists in the shell.

6. A positive electrode, characterized in that The positive electrode active material according to any one of claims 1 to 5 is included.

7. A lithium secondary battery, characterized in that: The positive electrode according to claim 6 is used.

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