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 and a lithium secondary battery comprising same, the positive electrode active material comprising a lithium transition metal oxide composed of one grain and a lithium transition metal oxide composed of a plurality of aggregated grains, wherein the proportion of the lithium transition metal oxide composed of one grain and the lithium transition metal oxide composed of a plurality of aggregated grains, which are present in the positive electrode active material, and the proportion of isolated grains in the lithium transition metal oxide composed of a plurality of aggregated grains are reduced such that the energy density of the positive electrode active material is improved and capacity loss due to the isolated grains is prevented and reduced.

Description

positive electrode active material and lithium secondary battery containing the same

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery including the same. More specifically, the present invention relates to a positive electrode active material comprising a lithium transition metal oxide composed of a single grain and a lithium transition metal oxide aggregated with a plurality of grains, wherein the energy density of the positive electrode active material is improved by reducing the ratio of the lithium transition metal oxide composed of a single grain and the lithium transition metal oxide aggregated with a plurality of grains present in the positive electrode active material, and the ratio of isolated grains within the lithium transition metal oxide aggregated with a plurality of grains, and furthermore, the capacity loss caused by isolated grains is prevented and mitigated in advance. The invention also relates to a positive electrode active material and a lithium secondary battery including the same.

[0002]

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

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

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

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

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

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

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

[0010] In addition, most lithium transition metal oxides have a secondary particle form in which multiple primary particles are aggregated, and the more primary particles constituting the secondary particles, the larger the specific surface area. As the specific surface area of ​​the lithium transition metal oxide increases, the likelihood of cracks occurring within the secondary particles increases when strain caused by random volume contraction / expansion of the primary particles due to repeated charging / discharging accumulates, and stability may rapidly decrease due to side reactions with the electrolyte on the surface of the primary particles.

[0011] Therefore, recently, in order to solve the aforementioned problem, there have been attempts to reduce the specific surface area of ​​lithium transition metal oxides by inducing the growth of grains constituting the lithium transition metal oxides. However, since it is difficult to grow the grains uniformly, there is a problem of non-uniformity in the size and distribution of the grains and lithium transition metal oxides. In addition, when grain growth is induced, there is a problem of degraded kinetic properties as the overall particle size of the lithium transition metal oxide increases.

[0012] In particular, within a particle in which multiple grains are aggregated, there are inevitably isolated grains that are not exposed to the outside. When the grain size is small, even if isolated grains exist inside, the diffusion of lithium ions between adjacent grains is easy during charging and discharging, so the capacity loss due to the presence of isolated grains inside is minimal.

[0013] On the other hand, when the lithium transition metal oxide exists in an aggregated form with a relatively small number of grains (e.g., 10 or fewer or 20 or fewer) as grains are grown through so-called single crystallization, the loss of lithium ion diffusion pathways due to the presence of isolated grains within the kinetic degradation and the resulting capacity loss can be maximized.

[0014] In addition, if cracks occur within the particles due to random volume shrinkage / expansion of the grains during repeated charging / discharging, and the surface of the internally isolated grains is newly exposed, it may lead to a surge in side reactions or an increase in the resistance of the cathode active material.

[0015]

[0016] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is acting as a driving force, and accordingly, the 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 for the sake of ensuring safety, but recently, there has been a growing trend of using nickel-based lithium transition metal oxides, which have a higher energy capacity per unit weight compared to LFP (of course, relatively cheaper LFP is still used to reduce costs).

[0018] In addition, nickel-based lithium transition metal oxides, which are mainly used as cathode active materials for high-capacity lithium secondary batteries, generally have compositions of ternary types such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) or quaternary types such as NCMA (Ni-Co-Mn-Al).

[0019] As mentioned above, in order to improve the energy density of such ternary or quaternary type nickel-based lithium transition metal oxides while preventing a decrease in lifespan and stability, it may be advantageous to induce the growth of grains constituting the lithium transition metal oxide. However, if grain growth is induced through so-called single crystallization, the kinetics are reduced, and due to the reduction in kinetics, the loss of lithium ion diffusion pathways caused by the presence of isolated grains inside and the resulting capacity loss may be maximized.

[0020] Therefore, it is expected that capacity loss can be reduced by inducing the growth of grains constituting the lithium transition metal oxide in a way that reduces the proportion of internally isolated grains.

[0021] Under the background described above, the present invention aims to provide a positive electrode active material comprising a lithium transition metal oxide composed of a single grain and a lithium transition metal oxide aggregated from a plurality of grains, wherein the ratio of the lithium transition metal oxide composed of a single grain and the lithium transition metal oxide aggregated from a plurality of grains present in the positive electrode active material is controlled to mitigate kinetic degradation and improve energy density.

[0022] In addition, the present invention aims to provide a positive electrode active material comprising a lithium transition metal oxide composed of a single grain and a lithium transition metal oxide aggregated with multiple grains, wherein the positive electrode active material is capable of preventing and mitigating capacity loss caused by isolated grains by reducing the proportion of isolated grains within the lithium transition metal oxide aggregated with multiple grains.

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

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

[0025]

[0026] The present invention for solving the aforementioned technical problem includes the following invention.

[0027] [1] A positive electrode active material comprising a lithium transition metal oxide consisting of a single grain and a lithium transition metal oxide in which a plurality of grains are aggregated, wherein, based on a cross-sectional SEM image of the positive electrode active material, the ratio of a grain isolated by being surrounded by a plurality of grains among all grains constituting the positive electrode active material is 10% or less.

[0028] [2] Based on a cross-sectional SEM image of the positive active material, the ratio of grains isolated by being surrounded by a plurality of grains among all grains constituting the positive active material is 1.5% or more, as described in [1].

[0029] [3] Based on a cross-sectional SEM image of the positive electrode active material, the proportion of lithium transition metal oxide consisting of one grain of the total lithium transition metal oxide constituting the positive electrode active material is greater than 8% and less than or equal to 70%, as described in [1] or [2].

[0030] [4] A positive electrode active material described in any one of [1] to [3], wherein, based on a cross-sectional SEM image of the positive electrode active material, the ratio of lithium transition metal oxides in which a plurality of grains are aggregated among the total lithium transition metal oxides constituting the positive electrode active material is 30% or more and less than 92%.

[0031] [5] Average particle size of lithium transition metal oxide consisting of a single grain (D 50 ) is a positive active material described in any one of [1] to [4], having a thickness of 0.2 μm or more and 5.0 μm or less.

[0032] [6] Average particle size of lithium transition metal oxide aggregated with multiple grains (D 50 ) is a positive active material described in any one of [1] to [5], having a thickness of 1.0 μm or more and 10.0 μm or less.

[0033] [7] The positive active material described in any one of [1] to [6], wherein the positive active material satisfies the following formula 1.

[0034] [Equation 1]

[0035] (D 90 -D 10 ) / D 50 < 0.65

[0036] (In the above Equation 1, based on the cross-sectional SEM image of the cathode active material, the size of the grain that is 10% of the volume accumulation amount from the volume accumulation particle size distribution graph for the grains constituting the cathode active material is D 10 and the grain size that is 50% of the volume accumulation is D 50 and the grain size that accounts for 90% of the volume accumulation is D 90 am)

[0037] [8] Based on the cross-sectional SEM image of the anode active material, the size D of the grain that is 50% of the volume accumulation from the volume accumulation particle size distribution graph of the grain constituting the anode active material 50 A positive active material described in any one of [1] to [7] having a thickness of 2.0 μm or more and 5.0 μm or less.

[0038] [9] Based on the cross-sectional SEM image of the anode active material, the size D of the grain that is 10% of the volume accumulation from the volume accumulation particle size distribution graph of the grain constituting the anode active material 10 A positive active material described in any one of [1] to [8] having a thickness greater than 1.75 μm and less than or equal to 3.0 μm.

[0039]

[0010] Based on the cross-sectional SEM image of the anode active material, the size D of the grain that is 90% of the volume cumulative amount from the volume cumulative particle size distribution graph of the grain constituting the anode active material 90A positive active material described in any one of [1] to [9], having a thickness of 3.0 μm or more and 4.9 μm or less.

[0040]

[0011] The lithium transition metal oxide comprises at least lithium and a transition metal, wherein the content of nickel among the transition metals is 70 mol% or more, and the positive electrode active material described in any one of [1] to

[0010] .

[0041]

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

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

[0042] [Chemical Formula 1]

[0043] Li a Ni 1-(b+c+d) Co b Mn c M1 d O2

[0044] In the above chemical formula 1,

[0045] 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, Mo, P, Sr, Ge, Nd, Gd and Cu, and

[0046] 0.95≤a≤1.15, 0≤b≤0.20, 0≤c≤0.20, 0≤d≤0.10, 0.7≤1-(b+c+d).

[0047] In addition, the present invention includes other embodiments as follows.

[0048]

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

[0012] .

[0049]

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

[0013] .

[0050]

[0051] According to the present invention, it is possible to mitigate kinetic degradation and improve energy density by controlling the ratio of a lithium transition metal oxide consisting of a single grain and a lithium transition metal oxide composed of a plurality of aggregated grains present in the positive electrode active material.

[0052] In addition, according to the present invention, it is possible to prevent and / or mitigate capacity loss caused by isolated grains by reducing the proportion of isolated grains within a lithium transition metal oxide in which a plurality of grains are aggregated.

[0053] In addition, according to the present invention, by reducing the proportion of isolated grains within a lithium transition metal oxide in which a plurality of grains are aggregated, it is possible to prevent and / or mitigate side reactions and / or an increase in resistance of the cathode active material that occur as the surface of the isolated grains is newly exposed due to random volume contraction / expansion of the grains during repeated charging / discharging.

[0054] In addition, according to the present invention, by controlling the particle size distribution of a lithium transition metal oxide consisting of a single grain and a lithium transition metal oxide in which a plurality of grains are aggregated within the positive electrode active material, it is possible to prevent and / or mitigate the overvoltage phenomenon that occurs when using a positive electrode active material that exhibits non-uniform particle size and / or distribution as the growth of grains is induced irregularly through so-called single crystallization.

[0055]

[0056] Figures 1 to 4 are cross-sectional SEM images of PAM1 to PAM4 prepared according to Preparation Example 1, respectively.

[0057]

[0058] For convenience, specific terms are defined herein to facilitate a better understanding of the present invention. Unless otherwise defined herein, scientific and technical terms used in this invention shall have the meanings generally understood by those skilled in the art. Furthermore, unless specifically indicated in the context, terms in their singular form shall be understood to include their plural form, and terms in their plural form shall be understood to include their singular form.

[0059]

[0060] positive electrode active material

[0061] In the present invention, the positive electrode active material comprises a lithium transition metal oxide capable of reversible intercalation / deintercalation of lithium ions. Here, the term lithium transition metal oxide refers to an oxide in which lithium and at least one transition metal are combined.

[0062] The above lithium transition metal oxide is a complex metal oxide capable of lithium ion intercalation / deintercalation and has a layered crystal structure belonging to the R-3m space group. The above lithium transition metal oxide having a layered crystal structure exhibits a specific peak in the region where 2θ is 18° to 20° (e.g., the region where 2θ = 18.6 ± 1°) among the rotation patterns obtained from XRD analysis.

[0063] The lithium transition metal oxide comprises at least lithium and a transition metal. The transition metal may comprise at least one, at least two, or all selected from nickel, cobalt, and manganese.

[0064] Preferably, the lithium transition metal oxide may be a lithium nickel-based composite oxide containing nickel. Additionally, the lithium transition metal oxide may be a lithium nickel-based composite oxide containing nickel and cobalt.

[0065] In addition, to improve low rate characteristics and lifetime characteristics while maintaining the high reversible capacity of LiNiO2, the lithium nickel-based composite oxide may be a lithium transition metal oxide of the ternary type, such as so-called NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or the quaternary type, such as NCMA (Ni-Co-Mn-Al), in which a portion of the nickel is substituted with cobalt, manganese, and / or aluminum. The ternary or quaternary type lithium transition metal oxide may further include dopants other than nickel, cobalt, manganese, and aluminum.

[0066] The above lithium transition metal oxide may be a cobalt-free type lithium transition metal oxide that does not contain cobalt within the bulk particles. The above cobalt-free type lithium transition metal oxide may further include dopants other than nickel, cobalt, and manganese.

[0067] The above lithium transition metal oxide may have an average composition represented by the following chemical formula 1. The average composition of the above lithium transition metal oxide can be measured according to a known ICP analysis method using an inductively coupled plasma spectrometer (ICP).

[0068] [Chemical Formula 1]

[0069] Li a Ni 1-(b+c+d) Co b Mn c M1 d O2

[0070] 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, Mo, P, Sr, Ge, Nd, Gd and Cu, and 0.95≤a≤1.15, 0≤b≤0.20, 0≤c≤0.20, 0≤d≤0.10, 0.7≤1-(b+c+d).

[0071] In the above chemical formula 1, a, representing the ratio of lithium to all elements other than lithium in the lithium transition metal oxide (Li / Ni+Co+Mn+M1), may be 0.95 or more, 0.96 or more, 0.97 or more, 0.98 or more, 0.99 or more, 1.00 or more, 1.01 or more, 1.02 or more, 1.03 or more, 1.04 or more, or 1.05 or more. Additionally, a may be 1.15 or less, 1.14 or less, 1.13 or less, 1.12 or less, 1.11 or less, 1.10 or less, 1.09 or less, 1.08 or less, 1.07 or less, 1.06 or less, or 1.05 or less. The upper and lower limits of the mole fraction of lithium to all elements other than lithium in the lithium transition metal oxide may be appropriately selected within a range that satisfies the definition described above. When the mole fraction of lithium among the above lithium transition metal oxides satisfies the above range, a stable crystal structure can be formed.

[0072] In the above chemical formula 1, 1-(b+c+d), which represents the mole fraction of nickel (Ni / Ni+Co+Mn+M1) relative to all elements other than lithium in the lithium transition metal oxide, may be 0.70 or more, 0.72 or more, 0.75 or more, 0.77 or more, 0.80 or more, 0.82 or more, 0.83 or more, 0.84 or more, 0.85 or more, 0.86 or more, 0.87 or more, 0.88 or more, 0.89 or more, 0.90 or more, 0.91 or more, 0.92 or more, 0.93 or more, 0.94 or more, or 0.95 or more. Additionally, 1-(b+c+d) may be less than 1.0, 0.99 or less, 0.98 or less, 0.97 or less, or 0.96 or less. The upper and lower limits of the mole fraction of nickel relative to all elements other than lithium in the above lithium transition metal oxide can be appropriately selected within a range that satisfies the definition described above. When the mole fraction of nickel in the above lithium transition metal oxide satisfies the above range, a stable crystal structure can be formed and high energy density can be exhibited.

[0073] In the above chemical formula 1, b, which represents the mole fraction of cobalt (Co / Ni+Co+Mn+M1) relative to all elements other than lithium in the lithium transition metal oxide, may be 0.20 or less, 0.19 or less, 0.18 or less, 0.17 or less, 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, 0.10 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, or 0.02 or less. If the lithium transition metal oxide is a cobalt-free type lithium transition metal oxide, b may be 0. When the lithium transition metal oxide contains cobalt, b may be greater than 0, greater than or equal to 0.01, or greater than or equal to 0.02. The upper and lower limits of the mole fraction of cobalt relative to all elements other than lithium in the lithium transition metal oxide may be appropriately selected within a range that satisfies the definition described above. When the mole fraction of cobalt in the lithium transition metal oxide satisfies the above range, a stable crystal structure can be formed and good output characteristics can be exhibited.

[0074] In the above chemical formula 1, c, representing the mole fraction of manganese (Mn / Ni+Co+Mn+M1) relative to all elements other than lithium in the lithium transition metal oxide, may be 0.20 or less, 0.19 or less, 0.18 or less, 0.17 or less, 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, 0.10 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, or 0.02 or less. If the lithium transition metal oxide contains manganese, c may be greater than 0, 0.01 or more, or 0.02 or more. The upper and lower limits of the mole fraction of manganese relative to all elements other than lithium in the above lithium transition metal oxide can be appropriately selected within a range that satisfies the definition described above. When the mole fraction of manganese in the above lithium transition metal oxide satisfies the above range, a stable crystal structure can be formed.

[0075] In the above chemical formula 1, M1 represents a dopant that may exist within 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 may be incorporated into at least one of the lithium layer and the transition metal layer.

[0076] When the lithium transition metal oxide contains a dopant, d, which represents the mole fraction of the dopant (M1 / Ni+Co+Mn+M1) relative to the total elements other than lithium in the lithium transition metal oxide in Formula 1, may be 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 or less, 0.007 or less, 0.006 or less, 0.005 or less, 0.004 or less, 0.003 or less, 0.002 or less, and 0.001 or less.

[0077] 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, Al, V, Ti, Fe, Zr, Zn, Si, Nb, Mo, W, and Cu, more preferably at least one selected from Mg, Ca, Ba, B, Al, 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 properties and stability of the cathode active material.

[0078] The above dopant can be doped into the lithium transition metal oxide by mixing the precursor of the lithium transition metal oxide with a dopant-containing raw material and then heat-treating (calcining). The lithium transition metal oxide can be obtained by mixing the precursor of the lithium transition metal oxide, a lithium raw material (e.g., LiOH, Li2CO3, or a combination thereof), and the dopant-containing raw material, and then heat-treating (calcining). The dopant-containing material may be a fluoride, chloride, carbonate, sulfate, nitrate, phosphate, oxide, and / or hydroxide containing the aforementioned dopant.

[0079] In the present invention, the positive electrode active material comprises a lithium transition metal oxide composed of a single grain and a lithium transition metal oxide in which multiple grains are aggregated. For convenience, the lithium transition metal oxide composed of a single grain may be referred to as the first lithium transition metal oxide, and the lithium transition metal oxide in which multiple grains are aggregated may be referred to as the second lithium transition metal oxide. The positive electrode active material may comprise multiple lithium transition metal oxides composed of a single grain and multiple lithium transition metal oxides in which multiple grains are aggregated.

[0080] The above grains may have a rod shape, an elliptical shape, and / or an irregular shape. Additionally, grains of various shapes may exist within the same cathode active material unless specifically intended during the manufacturing process. Furthermore, the above grains refer to particle units that do not have visible grain boundaries when observed using a scanning electron microscope at a magnification of 5,000 to 20,000 times.

[0081] Generally, ternary or quaternary type lithium transition metal oxides have a secondary particle form in which hundreds or thousands of unit particles are aggregated. The second lithium transition metal oxide defined herein can also be said to have a secondary particle form in that it has a form in which multiple grains are aggregated. However, the second lithium transition metal oxide described herein is distinguished from conventional polycrystalline lithium transition metal oxides having a secondary particle form in which hundreds or thousands of unit particles are aggregated, in that it has an aggregate form in which 30 or fewer, 25 or fewer, 20 or fewer, 15 or fewer, and / or 10 or fewer grains are aggregated. Furthermore, the primary particles constituting the conventional polycrystalline lithium transition metal oxide have a particle size smaller than that of the grains defined herein (e.g., less than 0.2 μm).

[0082] The second lithium transition metal oxide may have a form in which 30 or fewer, 25 or fewer, 20 or fewer, 15 or fewer, and / or 10 or fewer grains are aggregated. The number of grains constituting the second lithium transition metal oxide may vary depending on the size of the grains. For example, as the average size of the grains constituting the second lithium transition metal oxide increases, the number of grains constituting the second lithium transition metal oxide may decrease.

[0083] The number of grains constituting the second lithium transition metal oxide can be measured from a cross-sectional SEM image of the second lithium transition metal oxide according to a known method. Additionally, the number of grains constituting the second lithium transition metal oxide in the present invention can be calculated as the average value of the number of grains constituting a plurality of second lithium transition metal oxides observed from a cross-sectional SEM image of the positive electrode active material.

[0084] As the first lithium transition metal oxide is composed of a single grain, the average particle size of the grain becomes the average particle size of the first lithium transition metal oxide. The average particle size (D) of the first lithium transition metal oxide. 50 ) may be 0.2μm or more and 5.0μm or less, 0.2μm to 4.5μm, 0.2μm to 4.0μm, 0.5μm to 5μm, 0.5μm to 4.5μm, 0.5μm to 4.0μm, 1.0μm to 5.0μm, 1.0μm to 4.5μm, 1.0μm to 4.0μm, 1.5μm to 5.0μm, 1.5μm to 4.5μm, 1.5μm to 4.0μm, 2.0μm to 5.0μm, 2.0μm to 4.5μm, or 2.5μm to 4.0μm or less.

[0085] If the average particle size of the first lithium transition metal oxide is smaller than 0.5 μm, the specific surface area of ​​the first lithium transition metal oxide and the cathode active material containing it increases, which may lead to a decrease in stability due to side reactions with the electrolyte. On the other hand, if the average particle size of the first lithium transition metal oxide is larger than 5.0 μm, the growth of the grains is excessively induced, which may instead lead to a decrease in the diffusivity or kinetic properties of lithium ions mediated by the first lithium transition metal oxide.

[0086] Average particle size (D of the second lithium transition metal oxide above) 50 ) may be 1.0 μm or more, 2.0 μm or more, 3.0 μm or more, or 3.1 μm or more. In addition, the average particle size (D) of the second lithium transition metal oxide is 50 ) may be 10.0 μm or less, 9.0 μm or less, 8.0 μm or less, 7.0 μm or less, 6.0 μm or less, 5.0 μm or less, 4.0 μm or less, 3.8 μm or less, or 3.7 μm or less. The average particle size (D) of the second lithium transition metal oxide above 50 The upper and lower limits of ) can be appropriately selected within a range that satisfies the definition described above.

[0087] The grains constituting the second lithium transition metal oxide may have an average particle size equivalent to the average particle size of the first lithium transition metal oxide. For example, the average particle size (D) of the grains constituting the second lithium transition metal oxide 50 ) may be 0.2μm or more and 5.0μm or less, 0.2μm to 4.5μm, 0.2μm to 4.0μm, 0.5μm to 5μm, 0.5μm to 4.5μm, 0.5μm to 4.0μm, 1.0μm to 5.0μm, 1.0μm to 4.5μm, 1.0μm to 4.0μm, 1.5μm to 5.0μm, 1.5μm to 4.5μm, 1.5μm to 4.0μm, 2.0μm to 5.0μm, 2.0μm to 4.5μm, or 2.5μm to 4.0μm or less.

[0088] Average particle size (D) of the above grain, the first lithium transition metal oxide, and the second lithium transition metal oxide 50 ) can be calculated as the average value of the length in the major axis direction and the length in the minor axis direction of the unit particle ([major axis length + minor axis length] / 2). The average particle size can be calculated as the average value of the particle sizes of all particles observed from surface SEM images and / or cross-sectional SEM images of the lithium transition metal oxide constituting the positive electrode active material according to a known method.

[0089] According to the present invention, by controlling the particle size distribution of grains constituting the first lithium transition metal oxide and the second lithium transition metal oxide, it is possible to prevent and / or mitigate the overvoltage phenomenon when using an anode active material that exhibits non-uniform particle size and / or distribution as the growth of grains is induced irregularly through so-called single crystallization.

[0090] The particle size distribution of the grains constituting the first lithium transition metal oxide and the second lithium transition metal oxide can be measured through cross-sectional SEM image analysis of the cathode active material comprising the first lithium transition metal oxide and the second transition metal oxide. After obtaining a volume-cumulative particle size distribution graph from the sizes of a plurality of grains constituting the first lithium transition metal oxide and the second transition metal oxide (e.g., 100 or more, 200 or more, 300 or more, 400 or more, 500 or more, 600 or more, 700 or more, 800 or more, 900 or more, or 1,000 or more) observed from the cross-sectional SEM image, the sizes of the grains corresponding to 10%, 50%, and 90% of the volume-cumulative amount can be determined.

[0091] Based on the cross-sectional SEM image of the above-mentioned positive electrode active material, the size of the grain that constitutes 10% of the volume accumulation amount from the volume accumulation particle size distribution graph for the grains constituting the positive electrode active material is D 10 and the grain size that is 50% of the volume accumulation is D 50 and the grain size that accounts for 90% of the volume accumulation is D 90 When said, the above positive active material can satisfy the following Equation 1.

[0092] [Equation 1]

[0093] (D 90 -D 10 ) / D 50 < 0.65

[0094] In addition, (D measured according to the aforementioned method 90 -D 10 ) / D 50 may be less than 0.65, 0.64 or less, 0.63 or less, 0.62 or less, or 0.61 or less. (D measured according to the above-described method 90 -D 10 ) / D 50Having a value of less than 0.65 means that the plurality of grains constituting the first lithium transition metal oxide and the second transition metal oxide have a uniform size.

[0095] Based on the cross-sectional SEM image of the above-mentioned positive electrode active material, the grain size D that is 50% of the volume accumulation from the volume accumulation particle size distribution graph for the grains constituting the positive electrode active material 50 may be 2.0 μm or more, 3.0 μm or more, or 3.1 μm or more. In addition, the above D 50 It may be 5.0 μm or less, 4.0 μm or less, 3.8 μm or less, or 3.7 μm or less. The above D 50 The upper and lower limits of can be appropriately selected within a range that satisfies the definition described above.

[0096] Based on the cross-sectional SEM image of the above-mentioned positive electrode active material, the grain size D that is 50% of the volume accumulation from the volume accumulation particle size distribution graph for the grains constituting the positive electrode active material 10 may be greater than 1.75 μm, 1.8 μm or more, 1.85 μm or more, 1.9 μm or more, 1.95 μm or more, or 1.96 μm or more. In addition, the above D 10 It may be 3.0 μm or less, 2.9 μm or less, 2.8 μm or less, 2.7 μm or less, 2.6 μm or less, 2.5 μm or less, 2.45 μm or less, or 2.43 μm or less. The above D 10 The upper and lower limits of can be appropriately selected within a range that satisfies the definition described above.

[0097] Based on the cross-sectional SEM image of the above-mentioned positive electrode active material, the grain size D that accounts for 90% of the volume accumulation from the volume accumulation particle size distribution graph for the grains constituting the positive electrode active material 90This may be 3.0 μm or more, 3.1 μm or more, 3.2 μm or more, 3.3 μm or more, 3.4 μm or more, 3.5 μm or more, 3.6 μm or more, 3.7 μm or more, 3.8 μm or more, or 3.85 μm or more. In addition, the above D 90 It may be 4.9 μm or less, 4.85 μm or less, 4.8 μm or less, 4.75 μm or less, 4.7 μm or less, 4.65 μm or less, or 4.63 μm or less. The above D 90 The upper and lower limits of can be appropriately selected within a range that satisfies the definition described above.

[0098] D calculated from the volume cumulative particle size distribution graph of the grains constituting the cathode active material based on the cross-sectional SEM image of the cathode active material 10 , D 50 , D 90 and (D 90 -D 10 ) / D 50 By satisfying the aforementioned definition, the overvoltage phenomenon when using a positive electrode active material that exhibits non-uniform particle size and / or distribution can be prevented and / or mitigated.

[0099] According to the present invention, it is possible to mitigate kinetic degradation and improve energy density by controlling the ratio of the first lithium transition metal oxide and the second lithium transition metal oxide present in the positive electrode active material.

[0100] Based on a cross-sectional SEM image of the above-mentioned positive electrode active material, the proportion of the first lithium transition metal oxide among the total lithium transition metal oxides constituting the above-mentioned positive electrode active material may be greater than 8%, 8.1% or more, 9% or more, 10% or more, 11% or more, 12% or more, 13% or more, 14% or more, 15% or more, 16% or more, 17% or more, 18% or more, 19% or more, or 20% or more. Additionally, based on a cross-sectional SEM image of the above-mentioned positive electrode active material, the proportion of the first lithium transition metal oxide among the total lithium transition metal oxides constituting the above-mentioned positive electrode active material may be 70% or less, 65% or less, 60% or less, 55% or less, 52% or less, 50% or less, 49% or less, 48% or less, 47% or less, 46% or less, or 45% or less. The upper and lower limits of the ratio of the first lithium transition metal oxide among the total lithium transition metal oxides constituting the above-mentioned positive electrode active material can be appropriately selected within a range that satisfies the definition described above.

[0101] By inducing the growth of the above grains to increase the proportion of the first lithium transition metal oxide among the total lithium transition metal oxides constituting the positive electrode active material, the proportion of isolated grains surrounded by multiple grains among the total grains constituting the positive electrode active material can be reduced.

[0102] However, if the growth of the grain is excessively induced to increase the proportion of the first lithium transition metal oxide among the total lithium transition metal oxides constituting the positive electrode active material, the size and distribution of the grain, the first lithium transition metal oxide, and / or the second lithium transition metal oxide become non-uniform, and the size of the grain constituting the first lithium transition metal oxide and / or the second transition metal oxide becomes excessively large, resulting in a problem of degraded kinetic properties.

[0103] If the proportion of the first lithium transition metal oxide among the total lithium transition metal oxides constituting the above positive active material exceeds 70%, a loss of capacity may occur due to a decrease in kinetic properties.

[0104] In addition, excessive single crystallization to increase the proportion of the first lithium transition metal oxide among the total lithium transition metal oxides constituting the positive electrode active material may induce irregular grain growth, and accordingly, the size and distribution of the grains constituting the positive electrode active material, the first lithium transition metal oxide, and / or the second lithium transition metal oxide may become non-uniform. When using a positive electrode active material that exhibits such non-uniform particle size and / or distribution, capacity loss may be caused by an overvoltage phenomenon.

[0105] On the other hand, if the proportion of the first lithium transition metal oxide among the total lithium transition metal oxides constituting the positive electrode active material is 8% or less, the proportion of isolated grains surrounded by multiple grains among the total grains constituting the positive electrode active material may increase.

[0106] Based on a cross-sectional SEM image of the above-described positive electrode active material, the proportion of the second lithium transition metal oxide among the total lithium transition metal oxides constituting the above-described positive electrode active material may be 30% or more, 35% or more, 40% or more, 45% or more, 46% or more, 47% or more, 48% or more, 49% or more, 50% or more, 51% or more, 52% or more, 53% or more, 54% or more, or 55% or more. Additionally, the proportion of the second lithium transition metal oxide among the total lithium transition metal oxides constituting the above-described positive electrode active material may be less than 92%, 91% or less, 90% or less, 89% or less, 88% or less, 87% or less, 86% or less, 85% or less, 84% or less, 83% or less, 82% or less, 81% or less, or 80% or less. The upper and lower limits of the ratio of the second lithium transition metal oxide among the total lithium transition metal oxides constituting the above-mentioned positive electrode active material can be appropriately selected within a range that satisfies the definition described above.

[0107] If the proportion of the second lithium transition metal oxide among the total lithium transition metal oxides constituting the positive electrode active material exceeds 92%, the proportion of the second lithium transition metal oxide containing isolated grains surrounded by multiple grains among the positive electrode active material may increase. Additionally, the proportion of isolated grains surrounded by multiple grains among the total grains constituting the positive electrode active material may increase.

[0108] In addition, if cracks occur within the second lithium transition metal oxide due to random volume contraction or expansion of the grains during repeated charging and discharging, the surface of the internally isolated grains may be newly exposed. This newly exposed grain surface may lead to increased adverse reactions with the electrolyte or an increase in the resistance of the cathode active material.

[0109] Based on a cross-sectional SEM image of the positive electrode active material, the ratio of grains isolated by being surrounded by a plurality of grains among the total grains constituting the positive electrode active material may be 10% or less, less than 10%, 9.5% or less, 9% or less, 8.5% or less, 8% or less, 7.5% or less, 7% or less, 6.5% or less, 6% or less, 5.5% or less, 5% or less, or 4.8% or less. Additionally, based on a cross-sectional SEM image of the positive electrode active material, the ratio of grains isolated by being surrounded by a plurality of grains among the total grains constituting the positive electrode active material may be 1.5% or more, 1.6% or more, 1.7% or more, 1.8% or more, 1.9% or more, or 2.0% or more.

[0110] By ensuring that the ratio of isolated grains in the above-mentioned positive active material is 10% or less, it is possible to prevent and / or mitigate capacity loss caused by isolated grains. Additionally, by ensuring that the ratio of isolated grains in the above-mentioned positive active material is 10% or less, it is possible to prevent and / or mitigate side reactions and / or an increase in the resistance of the positive active material that occur as the surface of the isolated grains inside is newly exposed due to random volume contraction / expansion of the grains during repeated charging / discharging.

[0111] Meanwhile, in order to ensure that the proportion of isolated grains in the above-mentioned positive electrode active material is less than 1.5%, it is inevitable to increase the proportion of the first lithium transition metal oxide among the total lithium transition metal oxides constituting the above-mentioned positive electrode active material. Furthermore, as previously mentioned, if the growth of the grains is excessively induced to increase the proportion of the first lithium transition metal oxide among the total lithium transition metal oxides constituting the above-mentioned positive electrode active material, the size and distribution of the grains, the first lithium transition metal oxide, and / or the second lithium transition metal oxide become non-uniform, and the size of the grains constituting the first lithium transition metal oxide and / or the second transition metal oxide may become excessively large, thereby degrading the kinetic properties.

[0112]

[0113] lithium secondary battery

[0114] According to another aspect of the present invention, an anode may be provided comprising an anode current collector and an anode active material layer formed on the anode current collector. Herein, the anode active material layer may include an anode active material according to various embodiments of the present invention. Accordingly, since the anode active material is the same as previously described, a specific description is omitted for convenience, and only the remaining unmentioned components will be described below.

[0115] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0116] The above positive active material layer can be manufactured by applying a positive slurry composition, which includes a conductive material and optionally a binder together with the positive active material, to the positive current collector.

[0117] At this time, the anode active material may be included in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 98.5 wt%, based on the total weight of the anode slurry for forming the anode active material layer. Excellent capacity characteristics may be exhibited when included within the above-mentioned content range, but it is not necessarily limited thereto.

[0118] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.1 wt% to 15 wt% relative to the total weight of the anode slurry for forming the anode active material layer.

[0119] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive slurry for forming the positive active material layer.

[0120] The above-described anode can be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, it can be manufactured by applying an anode slurry composition, prepared by dissolving or dispersing the above-described anode active material and optionally a binder and a conductive material in a solvent, onto an anode current collector, and then drying and rolling.

[0121] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0122] In addition, in another embodiment, the anode may be manufactured by casting the anode slurry composition onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0123] In addition, according to another aspect of the present invention, an electrochemical device comprising the anode described above may be provided. Specifically, the electrochemical device may be a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0124] Specifically, the above lithium secondary battery may include a positive electrode, a negative electrode positioned opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is the same as previously described, a detailed description is omitted for convenience, and only the remaining components not previously mentioned are described in detail below.

[0125] The above lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0126] The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

[0127] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0128] The above-mentioned cathode active material layer can be manufactured by applying a cathode slurry composition, which includes a conductive material and optionally a binder together with the above-mentioned cathode active material, to the above-mentioned cathode current collector.

[0129] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ βExamples include metal oxides capable of doping and dedoping lithium, such as (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, the carbon material may include low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0130] The above-mentioned cathode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the cathode slurry for forming the cathode active material layer.

[0131] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the cathode slurry for forming the cathode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0132] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode slurry for forming the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; metal powder such as carbon fluoride, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used.

[0133] In one embodiment, the negative active material layer may be manufactured by applying a negative slurry composition, prepared by dissolving or dispersing a negative active material and optionally a binder and a conductive material in a solvent, onto a negative current collector and drying it, or by casting the negative slurry composition onto a separate support and then laminating the film obtained by peeling it off from the support onto a negative current collector.

[0134] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0135] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0136] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0137] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0138] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the above lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2, etc., may be used. It is preferable to use the lithium salt within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0139] When the electrolyte used in the present invention is a solid electrolyte, for example, solid inorganic electrolytes such as sulfide-based solid electrolytes, oxide-based solid electrolytes, nitride-based solid electrolytes, halide-based solid electrolytes, etc. may be used, and preferably, sulfide-based solid electrolytes may be used.

[0140] As a material for a sulfide-based solid electrolyte, a solid electrolyte containing Li, an element X (wherein X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In) and S may be used. Examples of the above-mentioned sulfide-based solid electrolyte materials include Li2S-P2S5, Li2S-P2S-LiX (wherein X is a halogen element such as I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S n (Here, m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (Here, p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In) etc.

[0141] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a mixed state of amorphous and crystalline.

[0142] Li7La3Zr2O is 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.

[0143] The aforementioned solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the anode and the cathode. Additionally, the solid electrolyte may be partially included within the anode active material layer of the anode independently of the solid electrolyte layer, or the solid electrolyte may be partially included within the cathode active material layer of the cathode independently of the solid electrolyte layer.

[0144] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0145] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0146] The external shape of the lithium secondary battery according to the present invention is not subject to any particular limitations, but may be cylindrical, prismatic, pouch, or coin-shaped using a can. In addition, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but can also preferably be used as a unit cell in a medium-to-large battery module containing a plurality of battery cells.

[0147] According to another aspect of the present invention, a battery module comprising the lithium secondary battery as a unit cell and / or a battery pack comprising the same may be provided.

[0148] The battery module or the battery pack may be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0149]

[0150] The present invention will be described in more detail below through examples. However, these examples are intended solely to illustrate the present invention and should not be interpreted as limiting the scope of the present invention.

[0151]

[0152] Preparation Example 1. Preparation of positive electrode active material

[0153] 1. Manufacture of PAM1

[0154] NiCoMn(OH)2 hydroxide precursor (Ni:Co:Mn = 96:2:2 (at%)) was synthesized using nickel sulfate, cobalt sulfate, and manganese sulfate via the known co-precipitation method.

[0155] A mixture was prepared by mixing the above hydroxide precursor, LiOH (Li / (Ni+Co+Mn) mol ratio = 1.02), and Ba(OH)2·H2O. Ba(OH)2·H2O was mixed to be 0.5 mol% relative to the total metal elements excluding lithium in the mixture. Subsequently, the mixture was heat-treated (first calcination) at 830°C for 8 hours in an O2 atmosphere to obtain an intermediate product.

[0156] Subsequently, the above intermediate product was mixed with 2 mol% of Co(OH)2 and then heat-treated (secondary calcination) at 770°C for 8 hours in an O2 atmosphere to obtain a final product, a positive electrode active material containing a lithium transition metal oxide.

[0157]

[0158] 2. Manufacture of PAM2

[0159] PAM2 was manufactured in the same way as PAM1, except that the first firing temperature was set to 810℃.

[0160]

[0161] 3. Manufacture of PAM3

[0162] NiCoMn(OH)2 hydroxide precursor (Ni:Co:Mn = 96:2:2 (at%)) was synthesized using nickel sulfate, cobalt sulfate, and manganese sulfate via the known co-precipitation method.

[0163] A solution containing 30 wt% of the above hydroxide precursor as a solid content is prepared using a bead mill D 50 This was milled to 300 nm. Subsequently, the milled solution was spray-dried to obtain a NiCoMn(O) oxide precursor.

[0164] A mixture was prepared by mixing the above oxide precursor, LiOH (Li / (Ni+Co+Mn) mol ratio = 1.02), and Ba(OH)2·H2O. Ba(OH)2·H2O was mixed to be 0.5 mol% relative to the total metal elements excluding lithium in the mixture. Subsequently, the mixture was heat-treated (first calcination) at 830°C for 8 hours in an O2 atmosphere, and then ground once at 18,000 rpm using a jet mill to obtain an intermediate product.

[0165] Subsequently, the above intermediate product was mixed with 2 mol% of Co(OH)2 and then heat-treated (secondary calcination) at 770°C for 8 hours in an O2 atmosphere to obtain a final product, a positive electrode active material containing a lithium transition metal oxide.

[0166]

[0167] 4. Manufacture of PAM4

[0168] PAM4 was manufactured in the same way as PAM3, except that the first firing temperature was set to 810℃.

[0169]

[0170] Preparation Example 2. Preparation of a lithium secondary battery (half-cell)

[0171] A positive electrode slurry was prepared by dispersing 94 wt% of the positive electrode active material prepared according to Preparation Example 1, 3 wt% of carbon black, and 3 wt% of PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated onto an aluminum thin film with a thickness of 15 μm and vacuum dried at 135°C to produce a positive electrode for a lithium secondary battery.

[0172] A half-cell was prepared using a lithium foil as the counter electrode for the above anode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separator, and an electrolyte in which LiPF6 is present at a concentration of 1.15 M in a solvent mixed with ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

[0173]

[0174] Experimental Example 1. Cross-sectional SEM analysis of the cathode active material

[0175] After obtaining a cross-sectional SEM image of the lithium transition metal oxide contained in the cathode active material prepared according to Preparation Example 1 using FE-SEM (Bruker), the ratio of the lithium transition metal oxide consisting of a single grain (first lithium transition metal oxide) and the lithium transition metal oxide consisting of multiple aggregated grains (second lithium transition metal oxide) observed from the cross-sectional SEM image was calculated.

[0176] In addition, based on the cross-sectional SEM image of the anode active material, the size and number of all grains constituting the anode active material and the ratio of grains isolated by being surrounded by multiple grains among the total grains are calculated, and from the volume cumulative particle size distribution graph for the grains constituting the anode active material, the size of the grain (D) that is 10% of the volume cumulative amount 10 ), grain size that is 50% of the volume accumulation (D 50 ), the grain size that is 90% of the volume accumulation (D 90 ) was produced.

[0177] Figure 1 is a cross-sectional SEM image of PAM1, Figure 2 is a cross-sectional SEM image of PAM2, Figure 3 is a cross-sectional SEM image of PAM3, and Figure 4 is a cross-sectional SEM image of PAM4.

[0178] The results of the above analysis are shown in Table 1 below.

[0179] Classification ABCDEFGHI Unit %%eaea%μmμmμm-PAM18.092.01131412.392.23.74.60.65PAM27.392.71642515.241.753.14.951.03PAM345.055.04012.502.433.74.630.59PAM420.879.210654.721.963.13.850.61

[0180]

[0181] A: The ratio of lithium transition metal oxide (first lithium transition metal oxide) consisting of a single grain among the total lithium transition metal oxides constituting the positive electrode active material.

[0182] B: Proportion of lithium transition metal oxide (secondary lithium transition metal oxide) in which multiple grains are aggregated, among the total lithium transition metal oxide constituting the positive electrode active material

[0183] C: Total number of grains constituting the above positive active material

[0184] D: Number of grains isolated by being surrounded by multiple grains out of the total grains

[0185] E: Ratio of grains isolated by being surrounded by multiple grains to the total grains

[0186] F: Grain size that is 10% of the volume accumulation (D 10 )

[0187] G: Grain size that is 50% of the volume accumulation (D 50 )

[0188] H: Grain size that is 90% of the volume accumulation (D 90 )

[0189] I : (Grain size at 90% of volume accumulation - Grain size at 10% of volume accumulation) / Grain size at 50% of volume accumulation

[0190]

[0191] Experimental Example 2. Evaluation of Electrochemical Characteristics of a Lithium Secondary Battery (Half-Cell)

[0192] For the lithium secondary battery (half-cell) prepared in Preparation Example 2, the initial charge capacity, initial discharge capacity, and initial efficiency were measured through charge / discharge experiments using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0V to 4.3V, and a discharge rate of 1.0C / 0.1C.

[0193] The above measurement results are shown in Tables 2 and 3 below.

[0194] Classification D 50 Charge Capacity Discharge Capacity Initial Efficiency Unit μm mAh / g mAh / g% PAM 1 3.7 239.4 201.08 4.0 PAM 3 3.7 239.8 202.98 4.6

[0195] Classification D 50 Charge Capacity Discharge Capacity Initial Efficiency Unit μm mAh / g mAh / g% PAM 2 3.12 4 3.12 0 8.18 5.6 PAM 4 3.12 4 3.5 2 11.38 6.8

[0196]

[0197] Since capacity characteristics can vary depending on the average particle size of the lithium transition metal oxide constituting the cathode active material, the capacity characteristics of cathode active materials in which the lithium transition metal oxide constituting the cathode active material has the same average particle size were compared to determine whether the ratio of grains isolated by being surrounded by multiple grains affects the capacity characteristics of the cathode active material.

[0198] D 50 When comparing PAM1 and PAM3, which are 3.7μm, it can be confirmed that the charge capacity, discharge capacity, and initial efficiency of PAM3 are improved compared to PAM1, as PAM3 has a lower proportion of isolated grains surrounded by multiple grains. Likewise, D 50 When comparing PAM2 and PAM4 with a particle size of 3.1 μm, the charge capacity of PAM2 and PAM4 is almost identical, but it can be seen that the discharge capacity and the resulting initial efficiency of PAM4 are improved compared to PAM2, as PAM4 has a lower ratio of isolated grains surrounded by multiple grains. In other words, even if the particle size of the lithium transition metal oxide is the same, reducing the ratio of isolated grains among the lithium transition metal oxides can contribute to the improvement of capacity characteristics.

[0199]

[0200] Although embodiments of the present invention have been described above, those skilled in the art may modify and change the present invention in various ways by adding, changing, deleting, or adding components, etc., without departing from the spirit of the present invention as described in the claims, and such modifications and changes are also to be included within the scope of the rights of the present invention.

Claims

1. A positive electrode active material comprising a lithium transition metal oxide consisting of a single grain and a lithium transition metal oxide in which a plurality of grains are aggregated, Based on a cross-sectional SEM image of the above-mentioned positive electrode active material, the ratio of grains isolated and surrounded by a plurality of grains among the total grains constituting the above-mentioned positive electrode active material is 10% or less, Positive active material.

2. In Paragraph 1, Based on a cross-sectional SEM image of the above-mentioned positive electrode active material, the ratio of grains isolated and surrounded by multiple grains among the total grains constituting the above-mentioned positive electrode active material is 1.5% or more, Positive active material.

3. In Paragraph 1, Based on a cross-sectional SEM image of the above-mentioned positive electrode active material, the ratio of lithium transition metal oxide consisting of one grain among the total lithium transition metal oxides constituting the above-mentioned positive electrode active material is greater than 8% and less than or equal to 70%, Positive active material.

4. In Paragraph 1, Based on a cross-sectional SEM image of the above-mentioned positive electrode active material, the ratio of lithium transition metal oxides in which a plurality of grains are aggregated among the total lithium transition metal oxides constituting the above-mentioned positive electrode active material is 30% or more and less than 92%, Positive active material.

5. In Paragraph 1, Average particle size (D) of lithium transition metal oxide consisting of a single grain 50 ) is 0.2μm or more and 5.0μm or less, Positive active material.

6. In Paragraph 1, Average particle size (D) of lithium transition metal oxide in which multiple grains are aggregated 50 ) is 1.0μm or more and 10.0μm or less, Positive active material.

7. In Paragraph 1, The above positive active material satisfies the following Equation 1, [Equation 1] (D 90 -D 10 ) / D 50 < 0.65 (In the above Equation 1, Based on the cross-sectional SEM image of the above-mentioned positive electrode active material, the size of the grain that constitutes 10% of the volume accumulation amount from the volume accumulation particle size distribution graph for the grains constituting the positive electrode active material is D 10 and the grain size that is 50% of the volume accumulation is D 50 and the grain size that accounts for 90% of the volume accumulation is D 90 am) Positive active material.

8. In Paragraph 7, Based on the cross-sectional SEM image of the above-mentioned positive electrode active material, the grain size D that is 50% of the volume accumulation from the volume accumulation particle size distribution graph for the grains constituting the positive electrode active material 50 This is 2.0μm or more and 5.0μm or less, Positive active material.

9. In Paragraph 7, Based on the cross-sectional SEM image of the above-mentioned positive electrode active material, the size D of the grain that is 10% of the volume accumulation from the volume accumulation particle size distribution graph for the grains constituting the positive electrode active material 10 This is greater than 1.75μm and less than or equal to 3.0μm, Positive active material.

10. In Paragraph 7, Based on the cross-sectional SEM image of the above-mentioned positive electrode active material, the grain size D that accounts for 90% of the volume accumulation from the volume accumulation particle size distribution graph for the grains constituting the positive electrode active material 90 This is 3.0μm or more and 4.9μm or less, Positive active material.

11. In Paragraph 1, The above lithium transition metal oxide comprises at least lithium and a transition metal, and Among the above transition metals, the nickel content is 70 mol% or more, Positive active material.

12. In Paragraph 1, The above lithium transition metal oxide has an average composition represented by the following chemical formula 1, Positive 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, Mo, P, Sr, Ge, Nd, Gd and Cu, and 0.95≤a≤1.15, 0≤b≤0.20, 0≤c≤0.20, 0≤d≤0.10, 0.7≤1-(b+c+d).

13. A positive electrode comprising a positive electrode active material according to any one of paragraphs 1 to 12.

14. A lithium secondary battery using a positive electrode according to Paragraph 13.

Images