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, to: a positive electrode active material including a mid-Ni type lithium transition metal oxide having a relatively low nickel content, wherein regions having different interplanar distances in unit particles constituting a lithium transition metal oxide having a polycrystalline structure can be locally formed to improve the efficiency of reversible intercalation / deintercalation of lithium ions and thereby improve the electrochemical properties of the mid-Ni type lithium transition metal oxide having electrochemical properties inferior to those of a high-Ni type lithium transition metal oxide having a relatively high nickel content; and a lithium secondary battery comprising same.

Description

Cathode 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, and more specifically, to a positive electrode active material including a Mid-Ni type lithium transition metal oxide having a relatively low nickel content, which locally forms regions having different interplanar distances within unit particles constituting a lithium transition metal oxide having a polycrystalline structure, thereby improving the efficiency of reversible intercalation / deintercalation of lithium ions, and thereby improving the electrochemical characteristics of a low Mid-Ni type lithium transition metal oxide having a relatively high nickel content, which are inferior to those of a high-Ni type lithium transition metal oxide, and to a lithium secondary battery including the same.

[0002]

[0003] Batteries store electricity by utilizing materials capable of electrochemical reactions in their anode and cathode. A representative example of such batteries is the lithium secondary battery, which stores electrical energy through the difference in chemical potential resulting from the intercalation / deintercalation of lithium ions between the anode and cathode.

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

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

[0006] Among the above positive electrode active materials, LiCoO2 is the most widely used due to its excellent life characteristics and charge / discharge efficiency, but it has the disadvantage of limited price competitiveness because cobalt used as a raw material is expensive.

[0007] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low price, but they have the problems of small capacity and poor high-temperature characteristics. In addition, LiNiO2-based cathode active materials have the advantage of showing high discharge capacity, but not only is their synthesis difficult due to the active cation mixing of Li and Ni, but the rate characteristics and cycle life characteristics of the synthesized cathode active materials are very low.

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

[0009] However, as the content of nickel in the lithium transition metal oxide increases, there is a problem that the mixing of cations within the crystal structure increases, resulting in a decrease in stability, or an increase in the content of unreacted lithium impurities such as LiOH and Li2CO3 on the surface.

[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 accelerated 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 in that when preparing a paste for forming a positive electrode active material layer using the lithium transition metal oxide, the paste composition becomes gel-like due to the lithium impurities.

[0011] Accordingly, a washing process must be included during the manufacturing process of the positive electrode active material to remove lithium impurities remaining on the surface of the lithium transition metal oxide. However, this washing process may cause damage to the surface of the lithium transition metal oxide, thereby deteriorating the electrochemical characteristics and stability of a lithium secondary battery using the lithium transition metal oxide as a positive electrode active material, and in particular, may cause problems such as premature deterioration of the lifespan.

[0012] Furthermore, with the recent rapid growth in demand for lithium secondary batteries and the increasing cost of raw materials, the lithium secondary battery market is facing strong demands for cost reduction. In particular, cathode active materials account for the largest portion of the cost in lithium secondary batteries. In particular, as the content of nickel, an essential element in ternary or quaternary lithium transition metal oxides, increases, the cost of cathode active materials inevitably increases.

[0013] That is, when the content of nickel in the positive electrode active material increases, the reversible capacity improves, but this causes problems in a trade-off relationship, such as an increase in lithium impurities in the positive electrode active material and an increase in the cost of the positive electrode active material.

[0014] Therefore, it is necessary to develop a Mid-Ni type cathode active material that can achieve the goal of improving the stability and reducing the cost of the cathode active material by reducing the nickel content in the cathode active material, while solving problems such as deterioration of electrochemical characteristics due to a decrease in the nickel content in the cathode active material.

[0015]

[0016] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is driving the market, and accordingly, demand for cathode active materials used in lithium secondary batteries is also continuously increasing.

[0017] For example, in the past, lithium secondary batteries using lithium iron phosphate (LFP) were mainly used from the perspective of ensuring safety, but recently, the use of nickel-based lithium transition metal oxides, which have a larger energy capacity per weight than LFP, is expanding (of course, relatively inexpensive LFP is still used to reduce costs).

[0018] In addition, nickel-based lithium transition metal oxides, which are mainly used as positive electrode active materials for recent 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) with a nickel content of about 70 to 80 mol% or more.

[0019] However, as previously mentioned, increasing the nickel content in lithium transition metal oxides improves reversible capacity, but this can also lead to increased lithium impurities in the cathode active material or decreased stability of the cathode active material. Furthermore, trade-off issues, such as increased cost of the cathode active material, inevitably arise.

[0020] Conversely, if the nickel content in the lithium transition metal oxide is reduced to achieve the goal of cost-down of the positive electrode active material, this may entail problems such as a deterioration in electrochemical characteristics such as capacity or rate characteristics (discharge capacity ratio).

[0021] Accordingly, the present invention provides a positive electrode active material comprising a Mid-Ni type lithium transition metal oxide having a relatively low nickel content (e.g., about 70 mol% or less or about 65 mol% or less), which locally forms regions in which the interplanar distances are different within unit particles constituting the lithium transition metal oxide having a polycrystalline structure, thereby improving the efficiency of lithium ion intercalation / deintercalation of the Mid-Ni type lithium transition metal oxide, thereby improving the electrochemical characteristics that are insufficient compared to the High-Ni type lithium transition metal oxide having a relatively high nickel content.

[0022] In addition, the present invention aims to provide a positive electrode active material comprising a Mid-Ni type lithium transition metal oxide having a relatively low nickel content (e.g., about 70 mol% or less or about 65 mol% or less), which is capable of improving the structural stability of the Mid-Ni type lithium transition metal oxide during charge / discharge by locally forming regions in which the interplanar distances are different within unit particles constituting the lithium transition metal oxide having a polycrystalline structure.

[0023] In addition, another object of the present invention is to provide a positive electrode and a lithium secondary battery using the positive electrode active material defined herein.

[0024] The purposes of the present invention are not limited to those mentioned above, and other unmentioned purposes and advantages of the present invention can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the purposes and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0025]

[0026] The present invention, which aims to solve the above-described technical problems, includes the following inventions.

[0027] [1] A cathode active material comprising a lithium transition metal oxide capable of reversible intercalation / deintercalation of lithium ions, wherein the lithium transition metal oxide has a secondary particle form in which a plurality of unit particles are aggregated, and at least one of the unit particles includes a first region and a second region in which the average values ​​of the interplanar distance (d-spacing) with respect to the (003) crystal plane are different, wherein the second region is a cathode active material that exists locally within the unit particle.

[0028] [2] The positive electrode active material described in [1], which includes secondary particles having a hollow structure.

[0029] [3] The secondary particle having the hollow structure is divided into a low-density region in which a gap exists between adjacent unit particles and a high-density region in which the aggregation density of the unit particles is higher than that of the low-density region, and the average value of the ratio of the outer diameter of the low-density region to the particle diameter of the secondary particle is 5% to 90%, according to any one of [1] and [2].

[0030] [4] The positive electrode active material according to any one of [1] to [3], wherein the second region exists as an isolated region within the unit particle.

[0031] [5] The positive electrode active material according to any one of [1] to [3], wherein the second region exists as a plurality of independent islands within the unit particle.

[0032] [6] A positive electrode active material according to any one of [1] to [3], wherein at least a portion of the second region is present so as to be in contact with the surface of the unit particle.

[0033] [7] The positive electrode active material according to any one of [1] to [6], wherein the lithium transition metal oxide partially comprises unit particles in which the second region is locally present.

[0034] [8] The positive electrode active material according to any one of [1] to [6], wherein the average value of the interplanar distance (d-spacing) for the (003) crystal plane in the first region is greater than the average value of the interplanar distance (d-spacing) for the (003) crystal plane in the second region.

[0035] [9] The positive electrode active material according to any one of [1] to [8], wherein the average value of the interplanar distance (d-spacing) for the (003) crystal plane in the first region is smaller than the average value of the interplanar distance (d-spacing) for the (003) crystal plane in the second region.

[0036]

[0010] The positive electrode active material according to any one of [1] to [9], wherein the average content of manganese in the second region is greater than the average content of manganese in the first region.

[0037]

[0011] A positive electrode active material according to any one of [1] to

[0010] , wherein the ratio (c2 / c1) of the average content of manganese (c2) in the second region and the average content of manganese (c1) in the first region is greater than 1 and less than or equal to 2.

[0038]

[0012] The lithium transition metal oxide is a positive electrode active material according to any one of [1] to

[0011] , having an average composition represented by the following chemical formula 1.

[0039] [Chemical Formula 1]

[0040] Li a Ni 1-(b+c+d) Co b Mn c M1 d O2

[0041] In the above chemical formula 1,

[0042] M1 is at least one selected from Na, K, Mg, Ba, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, W, Mo, P, Sr, Ge, Nd, Gd and Cu,

[0043] 0.95≤a≤1.15, 0.02≤b≤0.20, 0.15≤c≤0.35, 0≤d≤0.2, 0.3≤1-(b+c+d)<0.7.

[0044]

[0013] The average particle diameter (D) of the above unit particles 50 ) is a positive electrode active material described in any one of [1] to

[0012] , having a diameter of 0.02 μm or more and 0.5 μm or less.

[0045]

[0014] The average particle diameter (D) of the above secondary particles 50 ) is a positive electrode active material described in any one of [1] to

[0013] , having a diameter of 2.0 μm or more and 18.0 μm or less.

[0046] In addition, the present invention includes other aspects as follows.

[0047]

[0015] A positive electrode comprising a positive electrode active material as described in any one of [1] to

[0014] .

[0048]

[0016] A lithium secondary battery using the positive electrode described in

[0015] .

[0049]

[0050] According to the present invention, by locally forming regions with different interplanar distances within unit particles constituting a lithium transition metal oxide having a polycrystalline structure, the efficiency of reversible intercalation / deintercalation of lithium ions is improved, and thereby the electrochemical characteristics, particularly the capacity or rate characteristics (discharge capacity ratio), of a mid-Ni type lithium transition metal oxide having a relatively high nickel content can be improved compared to a high-Ni type lithium transition metal oxide having a relatively low nickel content.

[0051] In addition, according to the present invention, as a positive electrode active material including a Mid-Ni type lithium transition metal oxide having a relatively low nickel content (e.g., about 70 mol% or less or about 65 mol% or less), by locally forming regions in which the interplanar distances are different within unit particles constituting the lithium transition metal oxide having a polycrystalline structure, the structural stability of the Mid-Ni type lithium transition metal oxide during charge / discharge can be improved.

[0052] In addition to the effects described above, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

[0053]

[0054] Figure 1 shows a cross-sectional SEM image of a lithium transition metal oxide included in a positive electrode active material according to PAM1 manufactured according to Manufacturing Example 1.

[0055] Figure 2 shows a cross-sectional SEM image of a lithium transition metal oxide included in a positive electrode active material according to PAM2 manufactured according to Manufacturing Example 1.

[0056] Figure 3 shows a cross-sectional SEM image of a lithium transition metal oxide included in a positive electrode active material according to PAM3 manufactured according to Manufacturing Example 1.

[0057] Figure 4 shows a cross-sectional SEM image of a lithium transition metal oxide included in a positive electrode active material according to PAM4 manufactured according to Manufacturing Example 1.

[0058] Figure 5 shows the SEM-EDS mapping results for PAM1.

[0059] Figure 6 shows the SEM-EDS mapping results for PAM2.

[0060] Figure 7 shows the SEM-EDS mapping results for PAM3.

[0061] Figure 8 shows the SEM-EDS mapping results for PAM4.

[0062] Figure 9 schematically shows the TEM-FFT analysis results for PAM1.

[0063]

[0064] To facilitate a better understanding of the present invention, certain terms are defined herein for convenience. Unless otherwise defined herein, scientific and technical terms used herein shall have the meanings commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise specified by context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0065]

[0066] Hereinafter, a lithium secondary battery using a positive electrode active material according to the present invention and a positive electrode including the positive electrode active material will be described in more detail.

[0067]

[0068] positive electrode active material

[0069] In the present invention, the cathode active material includes a lithium transition metal oxide capable of reversible intercalation / deintercalation of lithium ions. Here, the lithium transition metal oxide refers to an oxide in which lithium and a metal element are combined.

[0070] The above lithium transition metal oxide is a composite metal oxide capable of lithium ion intercalation / deintercalation and has a layered crystal structure belonging to the R-3m space group. The above lithium transition metal oxide having a layered crystal structure exhibits a specific peak in the region where 2θ is 18° to 20° among the rotation patterns obtained from XRD analysis.

[0071] The above 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.

[0072] Preferably, the lithium transition metal oxide may be a lithium nickel-based composite oxide containing nickel. In addition, the lithium transition metal oxide may be a lithium nickel-based composite oxide containing nickel and cobalt.

[0073] In order to improve the low rate characteristics and cycle life characteristics while maintaining the high reversible capacity of LiNiO2, the lithium nickel-based composite oxide may be a ternary type lithium transition metal oxide such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), in which some of the nickel is replaced by cobalt, manganese, and / or aluminum, or a quaternary type lithium transition metal oxide such as NCMA (Ni-Co-Mn-Al). The ternary or quaternary type lithium transition metal oxide may further include a dopant other than nickel, cobalt, manganese, and aluminum.

[0074] The above lithium transition metal oxide may be a cobalt-free type lithium transition metal oxide that does not contain cobalt within bulk particles. The cobalt-free type lithium transition metal oxide may further contain a dopant other than nickel, cobalt, and manganese.

[0075] The lithium transition metal oxide defined herein is a Mid-Ni type lithium transition metal oxide having a relatively low nickel content. In the present invention, a lithium transition metal oxide having a nickel content of less than 70 mol% among the transition metals is referred to as a Mid-Ni type lithium transition metal oxide, and a lithium transition metal oxide having a nickel content of 70 mol% or more among the transition metals is defined as a High-Ni type lithium transition metal oxide.

[0076] In the case of conventional Mid-Ni type lithium transition metal oxides, as the content of manganese increases more than the content of cobalt, the kinetic characteristics such as the conductivity of lithium ions decrease, which may lead to a tendency for the rate characteristics to deteriorate. However, the lithium transition metal oxide according to the present invention can prevent the above-mentioned problem by forming multiple regions having distinct crystallographic characteristics (e.g., interplanar distance, etc.) within a unit particle.

[0077] The above lithium transition metal oxide may have an average composition represented by the following chemical formula 1. The average composition of the lithium transition metal oxide may be measured according to a known inductively coupled plasma spectrometer (ICP) analysis method using an inductively coupled plasma spectrometer (ICP).

[0078] [Chemical Formula 1]

[0079] Li a Ni 1-(b+c+d) Co b Mn c M1 d O2

[0080] In the above chemical formula 1,

[0081] M1 is at least one selected from Na, K, Mg, Ba, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, W, Mo, P, Sr, Ge, Nd, Gd and Cu,

[0082] 0.95≤a≤1.15, 0.02≤b≤0.20, 0.15≤c≤0.35, 0≤d≤0.2, 0.3≤1-(b+c+d)<0.7.

[0083] The a representing the ratio of lithium to all elements other than lithium among the lithium transition metal oxides (Li / Ni+Co+Mn+M1) 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. In addition, the 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 molar fraction of lithium to all elements other than lithium among the lithium transition metal oxides may be appropriately selected within a range satisfying the above-described definition. When the molar fraction of lithium in the lithium transition metal oxide satisfies the above range, a stable crystal structure can be formed. For example, when a in the chemical formula 1 is less than 0.95, the capacity of the positive electrode active material including the lithium transition metal oxide represented by the chemical formula 1 may decrease. On the other hand, when a in the chemical formula 1 is greater than 1.15, phase separation may occur due to lithium and manganese existing in excess in the lithium transition metal oxide, and an impurity phase belonging to a space group other than the R-3m space group may be generated.

[0084] In the above chemical formula 1, 1-(b+c+d), which represents the ratio of nickel to the total elements other than lithium among the lithium transition metal oxides (Ni / Ni+Co+Mn+M1), may be 0.30 or more, 0.35 or more, 0.40 or more, 0.45 or more, 0.50 or more, 0.51 or more, 0.52 or more, 0.53 or more, 0.54 or more, 0.55 or more, 0.56 or more, 0.57 or more, 0.58 or more, 0.59 or more, or 0.60 or more. In addition, the above 1-(b+c+d) may be less than 0.70, 0.69 or less, 0.68 or less, 0.67 or less, 0.66 or less, or 0.65 or less. The upper and lower limits of the mole fraction of nickel relative to all elements other than lithium in the lithium transition metal oxide may be appropriately selected within a range satisfying the above-described definition. When the mole fraction of nickel in the lithium transition metal oxide satisfies the above-described range, a stable Mid-Ni type crystal structure can be formed.

[0085] For example, when the content of nickel in the lithium transition metal oxide is 70 mol% or more, the mixing of cations within the crystal structure may increase, resulting in a decrease in stability, or the content of unreacted lithium impurities such as LiOH and Li2CO3 on the surface may increase. In addition, as described below, when there are multiple distinct regions as a crystal structure within a unit particle constituting the lithium transition metal oxide, the stability of the crystal structure may be lowered due to an excessive amount of nickel.

[0086] On the other hand, when the content of nickel in the lithium transition metal oxide is less than 30 mol%, phase separation may be caused by other transition metals (e.g., manganese, etc.) present in excess other than nickel, resulting in the generation of an impurity phase belonging to a space group other than the R-3m space group. The impurity phase may directly affect the deterioration of the electrochemical characteristics of the positive electrode active material.

[0087] In the above chemical formula 1, b, which represents the ratio of cobalt to the total elements other than lithium in the lithium transition metal oxide (Co / Ni+Co+Mn+M1), 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, or 0.05 or less. When the lithium transition metal oxide includes cobalt, b may be 0.02 or more, 0.03 or more, 0.04 or more, or 0.05 or more. 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 satisfying the above-described definition. When the mole fraction of cobalt in the lithium transition metal oxide satisfies the above-described range, a stable crystal structure can be formed and good output characteristics can be exhibited.

[0088] For example, if the content of cobalt in the lithium transition metal oxide exceeds 20 mol%, the goal of cost-down of the positive electrode active material cannot be achieved. In addition, if the content of cobalt in the lithium transition metal oxide is excessively high, the operating voltage of a lithium secondary battery using the positive electrode active material may decrease, making it difficult to exhibit high output characteristics at relatively high voltages. In addition, as described below, if there are multiple distinct regions as a crystal structure within a unit particle constituting the lithium transition metal oxide, the stability of the crystal structure may be lowered due to an excessive amount of cobalt.

[0089] In the above chemical formula 1, c, which represents the ratio of manganese to the total elements other than lithium among the lithium transition metal oxides (Mn / Ni+Co+Mn+M1), may be 0.15 or more, 0.16 or more, 0.17 or more, 0.18 or more, 0.19 or more, 0.20 or more, 0.21 or more, 0.22 or more, 0.23 or more, 0.24 or more, 0.25 or more, 0.26 or more, 0.27 or more, 0.28 or more, 0.29 or more, or 0.30 or more. In addition, the above c may be 0.35 or less, 0.34 or less, 0.33 or less, 0.32 or less, 0.31 or less, 0.30 or less, 0.29 or less, 0.28 or less, 0.27 or less, 0.26 or less, 0.25 or less, 0.24 or less, 0.23 or less, 0.22 or less, 0.21 or less, or 0.20 or less. When the mole fraction of manganese in the lithium transition metal oxide satisfies the above range, a stable crystal structure can be formed.

[0090] When the content of manganese in the lithium transition metal oxide exceeds 35 mol%, phase separation is promoted by the manganese present in excess in the lithium transition metal oxide, and an impurity phase belonging to a space group other than the R-3m space group may be formed throughout the particle.

[0091] On the other hand, when the manganese content in the lithium transition metal oxide is less than 15 mol%, the operating voltage of a lithium secondary battery using the positive electrode active material may be low, making it difficult to exhibit high output characteristics at relatively high voltages. In addition, it may be difficult to stably form multiple regions having distinct crystallographic characteristics (e.g., interplanar distance, etc.) within a unit particle constituting the lithium transition metal oxide.

[0092] The above lithium transition metal oxide further includes cobalt and manganese as transition metals, and the content of manganese in the lithium transition metal oxide may be greater than the content of cobalt.

[0093] In the above chemical formula 1, M1 refers to a dopant that can be incorporated into the crystal structure 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 can be incorporated into at least one crystal layer among the lithium layer and the transition metal layer.

[0094] When the lithium transition metal oxide contains a dopant, d, which represents the mole fraction (M1 / Ni+Co+Mn+M1) of the dopant to the total elements other than lithium in the lithium transition metal oxide in the chemical formula 1, is 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, 0.045 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 Below, 0.007 or less, 0.006 or less, 0.005 or less, 0.004 or less, 0.003 or less, 0.002 or less, 0.001 or less.

[0095] When the lithium transition metal oxide optionally includes a dopant, the dopant may include at least one selected from Na, K, Mg, Ba, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, P, Sr, Ge, Nd, Gd and Cu, preferably at least one selected from Mg, Ca, Ba, B, V, Ti, Fe, Zr, Zn, Si, Nb, Mo, W and Cu, more preferably at least one selected from Mg, Ca, Ba, B, Ti, Zr, Si, Nb, Mo and W. The type, combination and content of the dopant may be appropriately selected within a range that does not negatively affect the electrochemical characteristics and stability of the positive electrode active material.

[0096] The above lithium transition metal oxide may have the form of a secondary particle in which a plurality of unit particles are aggregated. The unit particles may be interpreted in the same sense as primary particles.

[0097] The above unit particles may have a rod shape, an oval shape, and / or an irregular shape. In addition, unit particles of various shapes may exist within the same positive electrode active material unless specifically intended during the manufacturing process. In addition, the above unit particles refer to particle units that do not have grain boundaries when observed using a scanning electron microscope at a magnification of 5,000 to 20,000 times.

[0098] The average particle diameter of the above unit particles (D 50 ) may be 0.02 μm to 0.5 μm, 0.03 μm to 0.5 μm, 0.04 μm to 0.5 μm, 0.05 μm to 0.5 μm, 0.06 μm to 0.5 μm, 0.07 μm to 0.8 μm, 0.09 μm to 0.5 μm, or 0.1 μm to 0.5 μm.

[0099] The average particle diameter of the above unit particles (D50 ) 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 diameter of the unit particle can be calculated as the average value of the particle diameters 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.

[0100] When the average particle diameter of the above unit particles is smaller than 0.02 μm, the specific surface area of ​​the positive electrode active material including a lithium transition metal oxide with a polycrystalline structure may become excessively large, which may cause a decrease in stability due to a side reaction with the electrolyte.

[0101] On the other hand, if the average particle diameter of the unit particles is greater than 0.5 μm, it may be difficult to form a lithium transition metal oxide having a polycrystalline structure.

[0102] The average particle size of the above secondary particles can be measured using a laser diffraction method. For example, after dispersing the secondary particles in a dispersion medium, the secondary particles can be introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating the secondary particles with an ultrasonic wave of approximately 28 kHz at an output of 60 W, obtaining a volume-cumulative particle size distribution graph, and then determining the particle size corresponding to 50% of the volume-cumulative amount.

[0103] The average particle diameter (D) of the above lithium transition metal oxide 50 ) may be 2.0 μm or more and 18.0 μm or less.

[0104] For example, the cathode active material defined herein can be used as a cathode active material exhibiting a bimodal type or trimodal type particle size distribution to improve energy density per unit volume. Accordingly, the lithium transition metal oxide defined herein can be used as a small particle and / or a large particle of a cathode active material exhibiting a bimodal type particle size distribution, or can be used as a small particle, a medium particle (particles having an intermediate average particle size), and / or a large particle of a cathode active material exhibiting a trimodal type particle size distribution.

[0105] When the lithium transition metal oxide defined herein is used as a cathode active material exhibiting a bimodal type particle size distribution or a cathode active material exhibiting a trimodal type particle size distribution, the average particle diameter (D) of the secondary particles 50 ) may be 2.0 μm to 8.0 μm, or 2.0 μm to 6.0 μm, or 2.0 μm to 5.0 μm.

[0106] When the lithium manganese oxide defined herein is used as a positive electrode active material exhibiting a bimodal type particle size distribution or as a counterpart of a positive electrode active material exhibiting a trimodal type particle size distribution, the average particle diameter (D) of the secondary particles 50 ) may be 6.0 μm to 18.0 μm, 6.0 μm to 16.0 μm, or 6.0 μm to 15.0 μm.

[0107] When the lithium manganese oxide defined herein is used as a neutralizer of a positive electrode active material exhibiting a trimodal type particle size distribution, the average particle diameter (D) of the secondary particles 50 ) may be 5.0 μm to 15.0 μm, 5.0 μm to 10.0 μm, or 5.0 μm to 8.0 μm.

[0108] In this application, “particle size” is used interchangeably with “particle diameter” or “particle size”, and unless otherwise defined, all “average particle size” means the median volume-based particle size determined by laser diffraction.

[0109] The above-described positive electrode active material may include secondary particles having a hollow structure. Accordingly, the positive electrode active material may be composed of secondary particles having a hollow structure, or may include secondary particles having a hollow structure and secondary particles not having a hollow structure. The secondary particle having a hollow structure means that there are pores in the center having a size of tens to hundreds of nm or more. The pores present in the center of the secondary particle refer to gaps formed between adjacent unit particles.

[0110] The secondary particle having the above hollow structure can be divided into a low-density region where a gap exists between adjacent unit particles and a high-density region where the aggregation density of the unit particles is higher than that of the low-density region.

[0111] The low-density region has a lower agglomeration density of the unit particles than the high-density region, and a void is formed in the center of the secondary particle as a gap exists between the unit particles. The agglomeration density of the unit particles may refer to the number of the unit particles existing within a reference area. For example, the agglomeration density of the unit particles may be calculated as the number of the unit particles within a reference area within the low-density region and the number of the unit particles within a reference area within the high-density region based on a cross-sectional SEM image of the secondary particle (the reference area within the low-density region and the reference area within the high-density region are the same area).

[0112] The low-density region may be formed entirely within the secondary particle, or may be partially formed. Furthermore, multiple low-density regions may exist within the secondary particle. The presence of multiple low-density regions within the secondary particle may indicate the presence of multiple cavities within the secondary particle.

[0113] In addition, for convenience, the low-density region and the high-density region can be divided by the ratio of the outer diameter to the particle diameter of the secondary particles. The average value of the ratio of the outer diameter of the low-density region to the particle diameter of the secondary particles can be 5% to 90%, 5% to 80%, 5% to 70%, 5% to 60%, or 5% to 50%. When the average value of the ratio of the outer diameter of the low-density region to the particle diameter of the secondary particles exceeds 90%, there is a concern that the physical strength of the secondary particles may be reduced.

[0114] Since the secondary particles have the aforementioned hollow structure, even if regions with different inter-face distances within the unit particles are locally formed, the structural stability during charging / discharging can be prevented and / or alleviated in advance.

[0115] In order to improve the efficiency of reversible intercalation / deintercalation of lithium ions by the lithium transition metal oxide, and thereby to improve the electrochemical properties which are inferior to those of the high-Ni type lithium transition metal oxide having a relatively high nickel content, the present invention is characterized by locally forming regions in which the inter-planar distances are different within the unit particles constituting the lithium transition metal oxide having a polycrystalline structure.

[0116] Specifically, at least one of the unit particles constituting the lithium transition metal oxide may include a first region and a second region having distinct crystallographic characteristics (e.g., interplanar spacing, etc.). The first region and the second region may be distinguished by the interplanar spacing (d-spacing) for the (003) crystal plane. The average value of the interplanar spacing (d-spacing) for the (003) crystal plane in the first region and the second region may be measured through cross-sectional TEM analysis of the unit particle according to a known method. For example, the interplanar spacing for the (003) crystal plane in the unit particle may be measured through high-resolution imaging analysis (HR-TEM) at the atomic level for a cross-sectional TEM image of the lithium transition metal oxide. That is, the interplanar spacing for the (003) crystal plane in the unit particle refers to the distance between adjacent (003) crystal planes from an electron diffraction pattern obtained through HR-TEM analysis.

[0117] The average values ​​of the interplanar spacing (d-spacing) for the (003) crystal planes in the first region and the second region may be different, and the second region may exist locally within the unit particle. That the second region exists locally within the unit particle means that a distorted region having a different interplanar spacing exists within the unit particle having a uniform interplanar spacing for the (003) crystal plane. That is, a region having an average interplanar spacing of the lithium transition metal oxide including the unit particle is the first region, and a region having an interplanar spacing that is significantly different from the first region can be defined as the second region.

[0118] Conversely, the absence of the second region within the unit particle means that there is no region in which the interplanar distance (d-spacing) of the (003) crystal planes within the unit particle constituting the lithium transition metal oxide is significantly different. When the second region within the unit particle does not exist, the difference between the maximum and minimum values ​​of the interplanar distance (d-spacing) of the (003) crystal planes within the unit particle may be less than 0.01 Å.

[0119] The average value of the interplanar distance (d-spacing) for the (003) crystal plane within the first region may be greater than or less than the average value of the interplanar distance (d-spacing) for the (003) crystal plane within the second region, and preferably, the average value of the interplanar distance (d-spacing) for the (003) crystal plane within the first region may be less than the average value of the interplanar distance (d-spacing) for the (003) crystal plane within the second region. In this case, the absolute value (|d1-d2|) of the difference between the average value (d1) of the interplanar distance (d-spacing) for the (003) crystal plane within the first region and the average value (d2) of the interplanar distance (d-spacing) for the (003) crystal plane within the second region may be 0.01 Å or more, 0.02 Å or more, or 0.03 Å or more.

[0120] That is, the fact that the second region exists locally within the unit particle means that a distorted region having an average value (d2) of the interplanar spacing (d-spacing) for the (003) crystal plane within the first region, the absolute value of the difference from the average value (d1) of the interplanar spacing (d-spacing) for the (003) crystal plane within the first region, is 0.01 Å or more, 0.02 Å or more, or 0.03 Å or more, exists locally within the unit particle.

[0121] In the present invention, the first region and the second region having distinct crystallographic characteristics means that the interplanar distances for any crystal plane within the first region and the second region are different.

[0122] In addition, both the first region and the second region may have phases belonging to the R-3m space group, but are not necessarily limited thereto. For example, both the first region and the second region may be composed only of phases belonging to the R-3m space group, but the interplanar distances for the (003) crystal planes within the first region and the second region may be different. In other cases, the first region may be composed only of phases belonging to the R-3m space group, but the second region may be composed only of phases belonging to a space group other than the R-3m space group (for example, phases belonging to the c2 / m space group), or may be a region in which phases belonging to the R-3m space group and phases belonging to a space group other than the R-3m space group coexist.

[0123] The second region may exist as an isolated region within the unit particle, or may exist as a plurality of independent islands within the unit particle. In addition, at least a portion of the second region may be in contact with the surface of the unit particle.

[0124] Additionally, at least some of the unit particles constituting the lithium transition metal oxide may include the first region and the second region, or all of the unit particles constituting the lithium transition metal oxide may include the first region and the second region.

[0125] The average content of manganese in the second region may be greater than the average content of manganese in the first region. At this time, the ratio (c2 / c1) of the average content of manganese (c2) in the second region and the average content of manganese (c1) in the first region may be greater than 1 and less than or equal to 2, greater than or equal to 1.05 and less than or equal to 2, or greater than or equal to 1.1 and less than or equal to 2. Alternatively, the difference between the average content of manganese in the second region and the average content of manganese in the first region may be 5 mol% to 20 mol%.

[0126] When the difference between the average content of manganese in the second region and the average content of manganese in the first region is less than 5 mol%, it may be difficult for the first region and the second region to have crystallographic characteristics that distinguish them from each other. That is, it may be difficult to make the absolute value (|d1-d2|) of the difference between the average value (d1) of the interplanar distance (d-spacing) for the (003) crystal plane in the first region and the average value (d2) of the interplanar distance (d-spacing) for the (003) crystal plane in the second region be 0.01 Å or more. In this case, it may be difficult to improve the electrochemical characteristics, particularly the capacity or rate characteristics (discharge capacity ratio), of the Mid-Ni type lithium transition metal oxide, which is inferior to the High-Ni type lithium transition metal oxide in which the nickel content is relatively high.

[0127] On the other hand, if the difference between the average content of manganese in the second region and the average content of manganese in the first region exceeds 20 mol%, the difference between the content of manganese in the first region and the content of manganese in the second region may be excessively large, and the instability of the crystal structure within the particle may rapidly increase.

[0128] Additionally, since the average content of manganese in the second region is greater than the average content of manganese in the first region, the average content of nickel in the second region may be less than the average content of nickel in the first region.

[0129] On the other hand, the difference between the average content of cobalt in the first region and the average content of cobalt in the second region may not be significant. That the difference between the average content of cobalt in the first region and the average content of cobalt in the second region is not significant may mean that the average content of cobalt in the first region and the average content of cobalt in the second region are the same, or that the difference between the average content of cobalt in the first region and the average content of cobalt in the second region is 5 mol% or less.

[0130]

[0131] lithium secondary battery

[0132] According to another aspect of the present invention, a positive electrode may be provided, comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Here, the positive electrode active material layer may include a positive electrode active material according to various embodiments of the present invention. Therefore, since the positive electrode active material is the same as described above, a detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described below.

[0133] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change 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 positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0134] The above positive electrode active material layer can be manufactured by applying a positive electrode slurry composition including the positive electrode active material, a conductive material, and optionally a binder as needed, to the positive electrode current collector.

[0135] At this time, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer. When included in the above-mentioned content range, excellent capacity characteristics may be exhibited, but the present invention is not necessarily limited thereto.

[0136] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0137] The above binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0138] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material described above and optionally a binder and a conductive agent in a solvent, is applied onto a positive electrode current collector, followed by drying and rolling.

[0139] The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0140] Additionally, in another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, and then laminating the resulting film onto a positive electrode current collector by peeling it off from the support.

[0141] In addition, according to another aspect of the present invention, an electrochemical device including the above-described positive electrode may be provided. The electrochemical device may be, specifically, a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0142] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive electrode and the negative electrode. Here, the positive electrode is the same as described above, so a detailed description thereof is omitted for convenience, and only the remaining components not described above will be described in detail below.

[0143] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0144] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0145] The negative electrode 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., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 μm to 500 μm, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0146] The above negative electrode active material layer can be manufactured by applying a negative electrode slurry composition including the negative electrode active material, a conductive material, and optionally a binder as needed, to the negative electrode current collector.

[0147] As the 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 alloy, Sn alloy, or Al alloy; SiO β(0 < β < 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, 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.

[0148] The above negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0149] The above binder is a component that assists in 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 negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0150] The conductive agent 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 active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0151] In one embodiment, the negative electrode active material layer may be manufactured by applying and drying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode slurry composition on a separate support and then laminating the resulting film on a negative electrode current collector by peeling it off from the support.

[0152] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0153] In addition, 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-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0154] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0155] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc., can be used. Among these, a carbonate solvent is preferable, 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 linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0156] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the above lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. It is preferable to use the concentration of the lithium salt within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0157] When the electrolyte used herein is a solid electrolyte, for example, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a nitride-based solid electrolyte, a halide-based solid electrolyte, etc. can be used, and preferably, a sulfide-based solid electrolyte can be used.

[0158] As a material of the sulfide-based solid electrolyte, a solid electrolyte containing Li, X element (wherein, X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S can be used. Examples of the sulfide-based solid electrolyte material include Li2S-P2S5, Li2S-P2S-LiX (wherein, X is a halogen element such as I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where, m, n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (where p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In).

[0159] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous, crystalline, or a mixture of amorphous and crystalline.

[0160] 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.

[0161] The aforementioned solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. In addition, the solid electrolyte may be partially included in the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or the solid electrolyte may be partially included in the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer.

[0162] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0163] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0164] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. 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 be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0165] According to another aspect of the present invention, a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same can be provided.

[0166] The above battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, including power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0167]

[0168] Hereinafter, the present invention will be described in more detail through examples. However, these examples are intended solely to illustrate the present invention, and the scope of the present invention is not to be construed as being limited by these examples.

[0169]

[0170] Manufacturing Example 1. Manufacturing of positive electrode active material

[0171] PAM1

[0172] (a) Ni using nickel sulfate, cobalt sulfate and manganese sulfate through a known co-precipitation method. 0.60 Co 0.10 Mn 0.30 (OH)2 hydroxide precursor (Ni:Co:Mn = 60:10:30 (mol%)) was synthesized.

[0173] (b) A mixture was prepared by mixing the hydroxide precursor obtained in the above step (a), LiOH, and ZrO2. LiOH was mixed so that the molar ratio of Li / (Ni+Co+Mn+Zr) based on the intermediate product was 0.70. ZrO2 was mixed so that it was 0.2 mol% based on the total metal elements excluding lithium in the mixture. Subsequently, the mixture was calcined at 800°C for 6 hours in an O2 atmosphere to obtain an intermediate product.

[0174] (c) The intermediate product obtained in the above step (b) was mixed with LiOH, and then calcined at 600°C for 10 hours in an O2 atmosphere to obtain a final product (a cathode active material including a lithium transition metal oxide in the form of a single particle and a pseudo-single particle). The LiOH mixed with the intermediate product was used so that the molar ratio of Li / (Ni+Co+Mn+Zr) based on the final product was 1.05.

[0175] Referring to the cross-sectional SEM image of Fig. 1, it can be confirmed that the positive electrode active material according to PAM1 includes a lithium transition metal oxide having a polycrystalline structure. In addition, it can be confirmed that the positive electrode active material according to PAM1 includes a lithium transition metal oxide having a hollow structure.

[0176]

[0177] PAM2

[0178] A positive electrode active material was manufactured in the same manner as PAM1, except that the heat treatment temperature in step (c) above was set to 800°C.

[0179] Referring to the cross-sectional SEM image of Fig. 2, it can be confirmed that the positive electrode active material according to PAM2 includes a lithium transition metal oxide having a polycrystalline structure. In addition, it can be confirmed that the positive electrode active material according to PAM2 includes a lithium transition metal oxide having a hollow structure.

[0180]

[0181] PAM3

[0182] A positive electrode active material was manufactured in the same manner as PAM1, except that the heat treatment temperature in step (c) above was set to 900°C.

[0183] Referring to the cross-sectional SEM image of Fig. 3, it can be confirmed that the positive electrode active material according to PAM3 includes a lithium transition metal oxide having a polycrystalline structure. In addition, it can be confirmed that the positive electrode active material according to PAM3 includes a lithium transition metal oxide having a hollow structure.

[0184]

[0185] PAM4

[0186] (a) Ni using nickel sulfate, cobalt sulfate and manganese sulfate through a known co-precipitation method. 0.60 Co 0.10 Mn 0.30 (OH)2 hydroxide precursor (Ni:Co:Mn = 60:10:30 (mol%)) was synthesized.

[0187] (b) A mixture was prepared by mixing the hydroxide precursor obtained in the above step (a), LiOH, and ZrO2. LiOH was mixed so that the molar ratio of Li / (Ni+Co+Mn+Zr) based on the intermediate product was 1.05. ZrO2 was mixed so that it was 0.2 mol% based on the total metal elements excluding lithium in the mixture. Subsequently, the mixture was calcined at 900°C for 10 hours in an O2 atmosphere to obtain the final product.

[0188] Referring to the cross-sectional TEM image of Fig. 4, it can be confirmed that the positive electrode active material according to PAM4 includes a lithium transition metal oxide with a polycrystalline structure. However, unlike PAM1 to PAM3, it can be confirmed that the positive electrode active material according to PAM4 does not have a hollow structure.

[0189]

[0190] Manufacturing Example 2. Manufacturing of a lithium secondary battery (half-cell)

[0191] A positive electrode slurry was prepared by dispersing 94 wt% of each of the positive electrode active materials manufactured according to Manufacturing 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 applied to a 15 μm thick aluminum thin film and vacuum-dried at 135°C to prepare a positive electrode for a lithium secondary battery.

[0192] A half-cell was manufactured using a lithium foil as a counter electrode for the above anode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte containing LiPF6 at a concentration of 1.15 M in a solvent containing ethylene carbonate and ethyl methyl carbonate mixed at a volume ratio of 3:7.

[0193]

[0194] Experimental Example 1. SEM-EDS Analysis of Positive Active Material

[0195] Each positive electrode active material manufactured in Manufacturing Example 1 was cross-sectionally processed using a cross-section polisher (acceleration voltage 5.0 kV, 4-hour milling) and then photographed using a FE-SEM (scanning electron microscope) to obtain a cross-sectional FE-SEM image. Subsequently, target elements Ni, Co, and Mn were subjected to EDS mapping for the cross-sectional FE-SEM image.

[0196] Referring to FIGS. 5 to 8 showing the SEM-EDS Mapping results of PAM1 to PAM4, it can be confirmed that there is a region where manganese is locally concentrated in at least one unit particle constituting the lithium transition metal oxide observed from PAM 1 to PAM3 (when the SEM-EDS Mapping image is converted to black and white, the degree of manganese distribution may appear somewhat unclear. However, in the SEM-EDS Mapping image converted to black and white, the pixels are expressed relatively darker in the region where the manganese signal is stronger, and accordingly, the region where the density of dark pixels is relatively high can be interpreted as the region where manganese is locally concentrated). On the other hand, it can be confirmed that nickel and manganese are uniformly distributed in the unit particles constituting the lithium transition metal oxide observed from PAM4 (unlike the SEM-EDS Mapping images for PAM1 to PAM3, there is no area with a relatively high density of dark pixels in the SEM-EDS Mapping image for PAM4, and the bright and dark pixels are uniformly distributed overall).

[0197]

[0198] Experimental Example 2. TEM Analysis of Positive Active Material

[0199] Each positive electrode active material manufactured in Manufacturing Example 1 was cross-sectionally processed using a FIB (Focused ion beam) and then photographed using a transmission electron microscope to obtain a cross-sectional TEM image. Subsequently, target elements such as Ni, Co, and Mn were subjected to EDS mapping on the cross-sectional TEM image.

[0200] The region where manganese is locally concentrated is the region where the relative concentration of manganese significantly increases compared to the background. When line scanning is performed, the manganese concentration shows a gradient increasing from the background to the region where manganese is locally concentrated, and in the region where manganese is locally concentrated, the relative concentration of manganese is maintained in a form of increased compared to the background for a certain period. Accordingly, in this experimental example, the region where the manganese concentration measured through line scanning after TEM-EDS mapping is maintained in a form of increased relative concentration compared to the background is defined as the second region where manganese is locally concentrated, and the other regions are defined as the first region.

[0201] The results of measuring the average manganese content in the first and second regions through line scanning are shown in Table 1 below.

[0202] Average manganese content in area 1 (c1) Average manganese content in area 2 (c2) c2 / c1 Unit at% at% - PAM 1 30 39 1.3 PAM 2 29 37 1.28 PAM 3 25 31 1.24

[0203] As confirmed in Experimental Example 1, at least one unit particle constituting the lithium transition metal oxide observed from PAM 1 to PAM3 has a region where manganese is locally concentrated, whereas nickel and manganese are uniformly distributed in the unit particle constituting the lithium transition metal oxide observed from PAM4. Similar to the results of Experimental Example 1, referring to the results of PAM1 to PAM3 described in Table 1, it can be confirmed that the average content of manganese in the second region is greater than the average content of manganese in the first region. On the other hand, in the case of PAM5, there was no region in which the average content of manganese in the unit particle was different.

[0204] Additionally, the diffraction pattern obtained by FFT (fast Fourier transform) for the cross-sectional HR-TEM image of each positive electrode active material manufactured in Manufacturing Example 1 was indexed to confirm the crystal structure within the unit particle constituting the lithium transition metal oxide observed from PAM1 to PAM4.

[0205] Figure 9 schematically illustrates the results of TEM-FFT analysis for PAM1. The region including the part marked ② in Figure 11 is the region where the concentration of manganese measured through line scanning after TEM-EDS mapping is maintained in a form in which the relative concentration is increased compared to the background, and corresponds to the second region, which is the region where manganese is locally concentrated, and the region including the part marked ① corresponds to the first region, which is the region outside the second region.

[0206] The interplanar distance (d-spacing) of the (003) crystal planes within the first region and the second region segmented through the aforementioned line scanning was measured, and the interplanar distances of 10 or more consecutive crystal planes were measured, and the average values ​​thereof are shown in Table 2 below.

[0207] Unlike PAM1 to PAM3, the average value of the interplanar distance (d-spacing) of the (003) crystal planes within the unit particle constituting the lithium transition metal oxide in PAM4 was measured to be approximately 4.941 Å, and no region was observed where the interplanar distance (d-spacing) of the (003) crystal planes within the unit particle constituting the lithium transition metal oxide was significantly different.

[0208] Mean distance between the inner surfaces of the first area (d1) Mean distance between the inner surfaces of the second area (d2) |d1-d2| Unit ÅÅÅPAM14.9175.0180.101PAM24.8365.1200.284PAM34.8024.9510.149

[0209] Referring to the results in Table 2, it can be confirmed that a distorted region (second region) having an average value (d2) of interplanar spacing (d-spacing) whose absolute value of difference from the average value (d1) of interplanar spacing (d-spacing) for the (003) crystal plane within the first region is 0.01 Å or more exists locally within the first region.

[0210]

[0211] Experimental Example 3. Evaluation of the Electrochemical Characteristics of a Lithium Secondary Battery (Half-Cell)

[0212] For the lithium secondary battery (half-cell) manufactured in Manufacturing Example 2, the charge / discharge efficiency and rate capability (discharge capacity ratio; rate capability (C-rate)) were measured through a charge / discharge experiment using an electrochemical analysis device (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0 V to 4.6 V, and a discharge rate of 0.1 C to 2.0 C.

[0213] In addition, for the same lithium secondary battery, 50 charge / discharge cycles were performed under the conditions of 1C / 1C within the operating voltage range of 3.0 V to 4.4 V at 45°C, and the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention) was measured.

[0214] The above measurement results are shown in Table 3 below.

[0215] Classification Charge / Discharge Efficiency (%) Discharge Capacity Ratio (2.0C / 0.1C) (%) Life Maintenance Rate @50cy (%) PAM188.086.489.3 PAM291.687.592.2 PAM391.186.992.5 PAM487.684.087.8

[0216] Referring to the results in Table 3, it can be confirmed that the charge / discharge efficiency, discharge capacity ratio (rate characteristic), and life maintenance rate of PAM1 to PAM3, which are locally present in the first region, are improved compared to PAM4 in the distorted region (second region) having an average value (d2) of interplanar spacing (d-spacing) in which the absolute value of the difference from the average value (d1) of interplanar spacing (d-spacing) for the (003) crystal plane in the first region is 0.01 Å or more.

[0217]

[0218] Above, the embodiments of the present invention have been described, but those of ordinary skill in the art will be able to modify and change the present invention in various ways by adding, changing, deleting or adding components, etc., within the scope that does not depart from the spirit of the present invention described in the claims, and this will also be considered to be included within the scope of the rights of the present invention.

Claims

1. Contains a lithium transition metal oxide capable of reversible intercalation / deintercalation of lithium ions, The above lithium transition metal oxide has a secondary particle form in which multiple unit particles are aggregated, At least one of the above unit particles, (003) Includes a first region and a second region having different average values ​​of the interplanar distance (d-spacing) for the crystal plane, wherein the second region exists locally within the unit particle. Positive active material.

2. In paragraph 1, The above positive electrode active material includes secondary particles having a hollow structure. Positive active material.

3. In paragraph 2, The secondary particles having the above hollow structure are divided into a low-density region where a gap exists between adjacent unit particles and a high-density region where the aggregation density of the unit particles is higher than that of the low-density region. The average value of the ratio of the outer diameter of the low-density region to the particle diameter of the secondary particles is 5% to 90%. Positive active material.

4. In paragraph 1, The above second region exists as an isolated region within the unit particle, Positive active material.

5. In paragraph 1, The above second region exists as a plurality of independent islands within the unit particle, Positive active material.

6. In paragraph 1, At least a portion of the second region exists so as to be in contact with the surface of the unit particle, Positive active material.

7. In paragraph 1, The lithium transition metal oxide partially comprises unit particles in which the second region is locally present, Positive active material.

8. In paragraph 1, The average value of the interplanar distance (d-spacing) for the (003) crystal plane within the first region is smaller than the average value of the interplanar distance (d-spacing) for the (003) crystal plane within the second region. Positive active material.

9. In paragraph 1, The average content of manganese in the second region is greater than the average content of manganese in the first region. Positive active material.

10. In paragraph 9, The ratio (c2 / c1) of the average content of manganese (c2) in the second region and the average content of manganese (c1) in the first region is greater than 1 and less than or equal to 2. Positive active material.

11. In paragraph 1, The above lithium transition metal oxide has an average composition represented by the following chemical formula 1: Cathode active material: [Chemical Formula 1] Li a Ni 1-(b+c+d) Co b Mr c M1 d O2 In the above chemical formula 1, M1 is at least one selected from Na, K, Mg, Ba, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, W, Mo, P, Sr, Ge, Nd, Gd and Cu, 0.95≤a≤1.15, 0.02≤b≤0.20, 0.15≤c≤0.35, 0≤d≤0.2, 0.3≤1-(b+c+d)<0.

7.

12. In paragraph 1, The average particle diameter of the above unit particles (D 50 ) is 0.02 μm or more and 0.5 μm or less, Positive active material.

13. In paragraph 1, The average particle diameter of the above secondary particles (D 50 ) is 2.0 μm or more and 18.0 μm or less, Positive active material.

14. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 13.

15. A lithium secondary battery using a positive electrode according to Article 14.

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