Positive electrode active material and lithium secondary battery using the same

Abstract

The present invention relates to a cobalt-free positive electrode active material having improved thermal stability and electrochemical characteristics, and a lithium secondary battery using the same.

Description

Technical Field

[0001] This invention relates to a cobalt-free cathode active material with improved thermal stability and electrochemical properties, and a lithium secondary battery using the cathode active material. Background Technology

[0002] Batteries use materials capable of electrochemical reactions at the positive and negative electrodes to store electrical energy. As a representative example of such batteries, there are lithium-ion secondary batteries that store electrical energy through the difference in chemical potential during the insertion / extraction of lithium ions at the positive and negative electrodes.

[0003] The aforementioned lithium secondary battery is prepared by using materials capable of reversible lithium-ion insertion / extraction as positive and negative electrode active materials, and filling the space between the positive and negative electrodes with organic or polymer electrolytes.

[0004] Representative materials used as positive electrode active materials in lithium secondary batteries include lithium composite oxides. Examples of such lithium composite oxides include LiCoO2, LiMn2O4, LiNiO2, LiMnO2, or oxides of Ni, Co, Mn, or Al complexes as disclosed in Korean Patent Publication No. 10-2015-0069334 (publication date: June 23, 2015).

[0005] Commercial lithium composite oxides such as nickel-cobalt-manganese (NCM) include cobalt as an essential element in order to balance electrochemical properties and stability.

[0006] However, recently, with the rapid growth of the lithium-ion battery market, the cost of raw materials has also increased, leading to another issue in cost reduction. In particular, the positive electrode active material accounts for the largest share of the cost of lithium-ion batteries. Among them, cobalt, an essential element in lithium composite oxides such as nickel-cobalt-manganese (NCM), is not only the most expensive metal, but also has relatively high supply and demand instability. Therefore, the market demand for positive electrode active materials that reduce costs by adopting cobalt-free compositions is increasing.

[0007] On the other hand, even a slight reduction in the cobalt content from commercially available lithium composite oxides such as nickel-cobalt-manganese (NCM) increases the resistance of the positive electrode active material, inevitably leading to a decrease in the rate performance and other electrochemical characteristics of lithium-ion batteries using such positive electrode active materials. Furthermore, as the cobalt content in these lithium composite oxides decreases, particle stability rapidly declines, resulting in premature degradation of the lifespan of lithium-ion batteries using these lithium composite oxides as the positive electrode active material. Summary of the Invention

[0008] Technical issues

[0009] In the lithium secondary battery market, while the growth of lithium secondary batteries for electric vehicles plays a dominant role, the demand for positive electrode active materials used in lithium secondary batteries is also constantly changing.

[0010] For example, in the prior art, from the point of view of ensuring safety, lithium secondary batteries using lithium iron phosphate (LFP) are mainly used. However, recently, the use of nickel-based lithium composite oxides with a larger energy capacity per unit weight compared to LFP is expanding.

[0011] Furthermore, in recent years, nickel-based lithium composite oxides, which are mainly used as positive electrode active materials in high-capacity lithium secondary batteries, must use ternary metal elements such as nickel, cobalt, and manganese, or nickel, cobalt, and aluminum. However, due to the unstable supply and demand of cobalt and its excessively high price compared to other raw materials, there is a need for a new type of positive electrode active material with a cobalt-free composition that can reduce the cobalt content.

[0012] Taking all these factors into account, cobalt-free lithium composite oxides that do not use cobalt in commercially available ternary lithium composite oxides composed of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) are attracting attention.

[0013] While the aforementioned cobalt-free lithium composite oxides meet the expectations of the market, they have limitations in terms of lacking electrochemical properties or stability as positive electrode active materials to replace commercially available ternary lithium composite oxides composed of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA).

[0014] For example, the lower the cobalt content in commercially available ternary lithium composite oxides composed of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA), the higher the resistance of the positive electrode active material. Therefore, as mentioned above, the electrochemical characteristics of lithium secondary batteries using the above-mentioned positive electrode active materials inevitably decrease, such as the rate characteristics.

[0015] In addition, as the cobalt content in the aforementioned lithium composite oxide decreases, the stability of the particles (crystal stability, thermal stability, or particle strength, etc.) rapidly decreases, leading to premature degradation of the lifespan of lithium secondary batteries using the aforementioned lithium composite oxide as the positive electrode active material.

[0016] However, compared with commercially available ternary lithium composite oxides composed of nickel cobalt manganese (NCM) or nickel cobalt aluminum (NCA), the electrochemical properties and stability of existing cobalt-free lithium composite oxides are indeed slightly lower. But the inventors have demonstrated that by redesigning the main structure and main composition of the above-mentioned cobalt-free lithium composite oxides, the above-mentioned cobalt-free lithium composite oxides can exhibit commercially viable levels of electrochemical properties and stability.

[0017] Therefore, the object of the present invention is to provide a cobalt-free positive electrode active material with improved thermal stability and electrochemical properties by controlling the main structure and main composition, and a lithium secondary battery using the positive electrode active material.

[0018] Solution to the problem

[0019] To address the aforementioned technical problems, according to one aspect of the present invention, a positive electrode active material comprising a lithium composite oxide containing at least nickel and manganese is provided. In this case, the lithium composite oxide is divided into an inner bulk and an outer bulk, the outer bulk surrounding the surface of the inner bulk.

[0020] In one embodiment, the Ni / Mn molar ratio of the external body is preferably lower than that of the internal body. Specifically, the Ni / Mn molar ratio of the internal body can be greater than 4.26 and less than 9.00, and the Ni / Mn molar ratio of the external body can be greater than 1.0 and less than 2.33.

[0021] In one embodiment, the volume fraction of the external body in the total volume of the lithium composite oxide is preferably less than the volume fraction of the internal body. More specifically, the volume fraction of the external body in the total volume of the lithium composite oxide can be 7.4% or more and less than 27.1%.

[0022] As described above, by controlling the main structure and composition of the aforementioned lithium composite oxide, the cobalt-free lithium composite oxide can exhibit commercially viable electrochemical properties and stability.

[0023] In one embodiment, by controlling the main structure and composition of the lithium composite oxide, a cation mixing layer can exist on at least a portion of the surface of the outer main body. In this case, by designing the cation mixing ratio of the outer main body to be greater than that of the inner main body, the crystal stability of the lithium composite oxide surface is improved while the cation mixing ratio of the inner main body is reduced, thereby preventing the deterioration of the overall electrochemical properties of the lithium composite oxide.

[0024] In one embodiment, the lithium composite oxide described above can be represented by the following chemical formula 1.

[0025] [Chemical Formula 1]

[0026] Li a Ni 1-(b+c+d) Mn b M1 c M2 d O 2-e X e

[0027] (Where M1 and M2 are each independently selected from at least one of Ti, Zr, Nb, Al, B, V, W, Ca, K, S, P, Sr, Ba, Mn, Ce, Hf, Ta, Cr, Mg, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, Gd, and Cu, M1 and M2 are mutually exclusive, X is a halogen element existing in a state of substitution with oxygen present in the above lithium composite oxide, 0.95≤a≤1.05, 0 <b≤0.5,0≤c≤0.05,0≤d≤0.05,0≤e≤0.10)。

[0028] In another embodiment, a coating comprising a metal oxide represented by the following chemical formula 2 may be formed on at least a portion of the surface of the lithium composite oxide.

[0029] [Chemical Formula 2]

[0030] Li f M3 g O h

[0031] (Where M3 is selected from at least one of Ni, Mn, Co, Ti, Zr, Nb, Al, B, V, W, Ca, K, S, P, Sr, Ba, Mn, Ce, Hf, Ta, Cr, Mg, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, Gd and Cu, 0≤f≤10, 0≤g≤8, 2≤h≤13, but f and g are not both 0).

[0032] The coating formed on at least a portion of the surface of the aforementioned lithium composite oxide can help improve the conductivity of the aforementioned outer body, which is relatively lower than that of the aforementioned inner body.

[0033] Furthermore, according to another aspect of the present invention, a positive electrode comprising the above-described positive electrode active material is provided.

[0034] Furthermore, according to another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided. Detailed Implementation

[0035] Specific terms are defined herein for ease of understanding. Unless specifically defined herein, scientific and technical terms used herein should have the meanings commonly understood by those skilled in the art. Furthermore, it should be understood that, as used herein, the singular form is intended to include the plural form, and vice versa, unless the context clearly indicates otherwise.

[0036] Positive electrode active material

[0037] According to one aspect of the present invention, a positive electrode active material comprising a lithium composite oxide containing at least nickel and manganese is provided.

[0038] In addition to nickel and manganese, the aforementioned lithium composite oxide also includes lithium. In this case, the aforementioned lithium composite oxide is a composite metal oxide having a layered crystal structure capable of intercalating / deintercalating lithium ions.

[0039] Compared to commercially available ternary lithium composite oxides, the lithium composite oxides defined in this paper have a relatively high proportion of manganese in the total metal element (e.g., more than 50 mol%), and are therefore different from overlithiated layered oxides (OLO) which exist in a state of solid solution of phases belonging to the C2 / m space group and phases belonging to the R3-m space group.

[0040] The lithium composite oxides described above, as defined herein, can be particles that include at least one primary particle.

[0041] When the aforementioned lithium composite oxide exists as a single initial particle, it can be referred to as a single particle. On the other hand, when the aforementioned lithium composite oxide exists as an aggregate of multiple initial particles, it can be referred to as a secondary particle.

[0042] The aforementioned positive electrode active material may include at least one selected from lithium composite oxides existing as single particles and lithium composite oxides existing as secondary particles formed by the aggregation of multiple initial particles.

[0043] The initial particles constituting the aforementioned lithium composite oxide can have rod-like, elliptical, and / or irregular shapes. Furthermore, unless specifically designed during manufacturing, initial particles of various shapes exist within the same positive electrode active material.

[0044] The average particle size of the initial particles constituting the lithium composite oxide as defined herein can be from 0.1 μm to 5 μm, preferably from 0.1 μm to 1.0 μm, and more preferably from 0.25 μm to 0.75 μm. The average particle size of the initial particles can be calculated as the average of the major axis length and minor axis length of the initial particles.

[0045] When the average particle size of the initial particles is less than 0.1 μm, the specific surface area of ​​the lithium composite oxide (secondary particles) composed of these initial particles is relatively large. In this case, the possibility of side reactions between the lithium composite oxide and the electrolyte during the storage or operation of the lithium secondary battery increases.

[0046] On the other hand, when the average particle size of the initial particles is greater than 5 μm, the growth of the initial particles is over-induced, thus lengthening the diffusion path of lithium ions within the initial particles. When the diffusion path of lithium ions within the initial particles is too long, the mobility of lithium ions within the initial particles and the diffusivity of lithium ions through the initial particles decrease, which increases the resistance of the lithium composite oxide (secondary particles) composed of the initial particles.

[0047] Therefore, in order to reduce the specific surface area of ​​the lithium composite oxide while preventing a decrease in the mobility of lithium ions in the initial particles and a decrease in the diffusion of lithium ions between adjacent initial particles, the average particle size of the initial particles is preferably 0.1 μm to 5 μm, more preferably 0.1 μm to 1.0 μm, and even more preferably 0.25 μm to 0.75 μm.

[0048] When the aforementioned lithium composite oxide exists as a secondary particle formed by the aggregation of multiple initial particles, the secondary particle can have an average particle size of 1 μm to 30 μm. The average particle size of the secondary particle can vary depending on the number of initial particles constituting the secondary particle.

[0049] The nickel content (mol%) in the above-mentioned lithium composite oxide, calculated based on all elements other than lithium, can be 50 mol% or more and less than 95 mol%, preferably 60 mol% or more and less than 90 mol%, and more preferably 75 mol% or more and less than 85 mol%.

[0050] When the nickel content in the aforementioned lithium composite oxide is less than 50 mol%, the proportion of lithium composite oxides with a spinel crystal structure in the aforementioned positive electrode active material may increase. As the proportion of lithium composite oxides with a spinel crystal structure in the aforementioned positive electrode active material increases, a higher operating voltage is required; therefore, the capacity characteristics of lithium-ion batteries using the aforementioned lithium composite oxide as the positive electrode active material may deteriorate. Furthermore, due to the increase in manganese in the aforementioned lithium composite oxide, the overall cation mixing in the aforementioned lithium composite oxide may increase.

[0051] Specifically, the charge of all transition metals constituting the aforementioned lithium composite oxide is preferably in a trivalent state to achieve a stable charge neutrality. In this case, during the synthesis of lithium composite oxides with low cobalt and high manganese content, Mn... 4+ It becomes excessive, therefore, in order to achieve a charge-neutral state, Ni is replaced. 3+ And Ni 2+ The content will increase. Excess Ni present during the synthesis reaction... 2+ Having similarity to Li + The size of the lithium composite oxide allows it to occupy the 3a site of Li in the crystal structure described above, a phenomenon known as cation mixing.

[0052] On the other hand, when nickel is present in excess in the aforementioned lithium composite oxide, the lithium composite oxide exhibits the same characteristics as LiNiO2. LiNiO2 not only has low thermal stability, but also, when an internal short circuit occurs due to external pressure or other factors during charging, the positive electrode active material decomposes on its own, or side reactions occur at the interface and surface between the electrolyte and the positive electrode active material, leading to the rupture and fire of the lithium secondary battery.

[0053] On the other hand, the manganese content (mol%) in the lithium composite oxide, calculated based on all elements other than lithium, can be greater than 5 mol% and less than 50 mol%, preferably more than 10 mol% and less than 40 mol%, and more preferably more than 10 mol% and less than 30 mol%.

[0054] In order to design the main composition of the above-mentioned lithium composite oxide to be cobalt-free, the manganese content in the above-mentioned lithium composite oxide is preferably greater than at least 5 moles.

[0055] Conversely, when the manganese content in the aforementioned lithium composite oxide is greater than 50 mol%, the proportion of lithium composite oxides with a spinel crystal structure in the aforementioned positive electrode active material may increase. As described above, with the increase in the proportion of lithium composite oxides with a spinel crystal structure in the aforementioned positive electrode active material, a higher operating voltage is required; therefore, the capacity characteristics of lithium secondary batteries using the aforementioned lithium composite oxide as the positive electrode active material may deteriorate. Furthermore, with the increase in the manganese content in the aforementioned lithium composite oxide, the overall cation mixing in the aforementioned lithium composite oxide may increase.

[0056] The lithium composite oxides defined herein are divided into an inner bulk and an outer bulk, wherein the outer bulk surrounds the surface of the inner bulk.

[0057] At this point, the internal and external components can be distinguished by the Ni / Mn molar ratio. For example, in the process of synthesizing the hydroxide precursor of the lithium composite oxide using the co-precipitation method, by continuously changing the concentrations of nickel and manganese present in the aqueous metal salt solution to synthesize the hydroxide precursor, a hydroxide precursor in which the concentrations of nickel and manganese continuously change from the center to the surface can be obtained.

[0058] However, as mentioned above, when the concentrations of nickel and manganese change continuously from the center to the surface of the aforementioned hydroxide precursor, the Ni / Mn molar ratio also changes continuously from the center to the surface of the hydroxide precursor. Therefore, it is impossible to distinguish the internal and external main components based on the Ni / Mn molar ratio.

[0059] Conversely, for example, when an inner matrix is ​​synthesized using a first metal salt aqueous solution with a nickel to manganese molar ratio of 85:15, and an outer matrix is ​​synthesized using a second metal salt aqueous solution with a nickel to manganese molar ratio of 50:50, the Ni / Mn molar ratios of both the inner and outer matrixes are subordinate to the Ni / Mn molar ratios of the first and second metal salt aqueous solutions, respectively. Therefore, the inner and outer matrices can be distinguished based on the Ni / Mn molar ratio.

[0060] The concentration of the transition metal in the aforementioned lithium composite oxide can be determined using various known methods. For example, after cross-sectional processing of the lithium composite oxide, EDS mapping can be performed, and then the concentration change of the target transition metal can be determined by linescanning.

[0061] Additionally, there are irradiations applied to the surface of the aforementioned lithium composite oxide based on the accelerating voltage (V). acc Energy-dispersive X-ray spectroscopy (EP-EDS) is an energy analysis method used to determine the concentration of a target transition metal at a depth penetrated by an electron beam of high intensity.

[0062] In one embodiment, the Ni / Mn molar ratio of the external body is less than that of the internal body. When the Ni / Mn molar ratio of the external body is designed to be less than that of the internal body, the Mn content in the external body is greater than that in the internal body.

[0063] By reducing the Mn content and increasing the Ni content in the aforementioned internal matrix, the cation mixing in the aforementioned internal matrix can be reduced, thereby improving the expected capacity and rate performance of the aforementioned internal matrix.

[0064] Furthermore, by increasing the Mn content in the aforementioned external host, the cation mixture present in the aforementioned lithium composite oxide can be locally present in the aforementioned external host, and thus locally present on the surface of the aforementioned lithium composite oxide.

[0065] That is, when the above-mentioned cation mixing ratio and manganese content of the lithium composite oxide as defined herein are proportional, the cation mixing ratio of the above-mentioned external host can be greater than the cation mixing ratio of the above-mentioned internal host.

[0066] When the aforementioned cation mixture is locally present on the surface of the aforementioned lithium composite oxide, the cation mixture layer may exist on at least a portion of the surface of the aforementioned lithium composite oxide.

[0067] Unlike the cation mixture present in the aforementioned internal matrix, the cation mixture present in the aforementioned external matrix enhances the surface stability of the aforementioned lithium composite oxide, thereby contributing to the improvement of the stability (crystal stability, thermal stability, or particle strength, etc.) of the aforementioned lithium composite oxide.

[0068] The aforementioned cation-mixed layer may contain at least one phase selected from layered structures, rock salt structures, and spinel structures. In this case, the layered structure present in the aforementioned cation-mixed layer may be at least different from the layered structures present in the aforementioned inner matrix and the aforementioned outer matrix.

[0069] Specifically, in order to reduce cation mixing in the aforementioned internal body and improve capacity and rate performance from the aforementioned internal body, the molar ratio of Ni in the aforementioned internal body relative to all metal elements except lithium is 0.7 or more and less than 1.0, and the Ni / Mn molar ratio of the aforementioned internal body can be designed to be greater than 4.26 and less than 9.00, preferably 4.56 or more and less than 7.33.

[0070] When the Ni / Mn molar ratio of the aforementioned internal matrix is ​​4.26 or less, the Mn content in the aforementioned internal matrix may become too high, thereby increasing cation mixing in the aforementioned internal matrix. Conversely, when the Ni / Mn molar ratio of the aforementioned internal matrix is ​​9.00 or more, the Ni content in the aforementioned internal matrix becomes too high, and therefore the thermal stability of the aforementioned internal matrix may deteriorate.

[0071] Furthermore, in order to improve the surface stability and overall electrochemical properties of the lithium composite oxide by concentrating the cations present in the lithium composite oxide on the surface of the lithium composite oxide, the molar ratio of Ni in the external host relative to all metal elements except lithium is 0.5 or more and less than 0.8, and the Ni / Mn molar ratio of the external host can be designed to be 1.0 or more and less than 2.33, preferably 1.0 or more and less than 1.5.

[0072] When the Ni / Mn molar ratio of the external host is less than 1.0, the Mn content in the external host may become too high, leading to an unexpected phase transition in the external host. On the other hand, when the Ni / Mn molar ratio of the external host is 2.33 or higher, the cation mixture present in the lithium composite oxide can be uniformly dispersed in both the internal host and the external host, rather than being locally present in the external host.

[0073] Furthermore, as described above, in order to ensure that the cation mixture present in the above-mentioned lithium composite oxide is partially present in the above-mentioned outer body, the ratio of the Ni content (mol%) of the above-mentioned outer body to the Ni content (mol%) of the above-mentioned inner body is greater than 0.556 and less than 0.740, preferably 0.588 or more and 0.732 or less, and the ratio of the Mn content (mol%) of the above-mentioned outer body to the Mn content (mol%) of the above-mentioned inner body can be designed to be 2.2 or more and less than 5.0, preferably 2.2 or more and 3.75 or less.

[0074] On the other hand, in order for the above-mentioned cobalt-free lithium composite oxide to exhibit commercially viable electrochemical properties and stability, it is necessary to design the Ni / Mn molar ratio of the above-defined internal and external substrates to be within the range defined above, while also controlling the volume fraction of the above-defined internal and external substrates.

[0075] In one embodiment, the volume fraction of the external body in the total volume of the lithium composite oxide is preferably smaller than the volume fraction of the internal body.

[0076] By designing the volume fraction of the external substrate to be smaller than that of the internal substrate, the ratio of regions containing cation mixtures in the total volume of the lithium composite oxide is reduced. This allows the external substrate containing cation mixtures to be locally present on the surface of the lithium composite oxide, thereby simultaneously improving the surface stability and electrochemical properties of the lithium composite oxide.

[0077] More specifically, the volume fraction of the external matrix in the total volume of the lithium composite oxide can be designed to be 7.4% or more and less than 27.1%, preferably 8.7% or more and less than 24.7%.

[0078] When the volume fraction of the external host is less than 7.4%, the volume occupied by the external host in the total volume of the lithium composite oxide is small, making it difficult for the cation mixture present in the lithium composite oxide to be effectively concentrated in the external host. Conversely, when the volume fraction of the external host is 27.1% or more, the volume occupied by the external host containing the cation mixture in the lithium composite oxide is too large, which may lead to a deterioration in the electrochemical properties of the lithium composite oxide, including capacity characteristics and rate performance.

[0079] The volume fraction of the internal body in the total volume of the aforementioned lithium composite oxide can be calculated using the ratio of the radius of the internal body to the radius of the lithium composite oxide. Specifically, the volume fraction of the internal body in the total volume of the aforementioned lithium composite oxide can be expressed as the ratio of the volume of the internal body to the total volume of the lithium composite oxide calculated using the radius of the lithium composite oxide ([volume of the internal body / total volume of the lithium composite oxide] × 100).

[0080] Furthermore, the volume fraction of the outer body in the total volume of the aforementioned lithium composite oxide can be calculated using the ratio of the thickness of the outer body to the radius of the aforementioned lithium composite oxide. Specifically, the volume fraction of the outer body in the total volume of the aforementioned lithium composite oxide can be expressed as the ratio of the difference between the total volume of the aforementioned lithium composite oxide calculated using the radius of the aforementioned lithium composite oxide and the volume calculated using the radius of the aforementioned inner body ([total volume of the aforementioned lithium composite oxide - volume of the aforementioned inner body / total volume of the aforementioned lithium composite oxide] × 100).

[0081] In order for the volume fraction of the external body in the total volume of the lithium composite oxide to satisfy the above definition, the ratio of the thickness of the external body to the radius of the lithium composite oxide can be designed to be greater than 0.025 and less than 0.10, preferably, it can be designed to be greater than 0.030 and less than 0.090.

[0082] When the ratio of the thickness of the outer body relative to the radius of the lithium composite oxide is 0.025 or less, the volume occupied by the outer body in the total volume of the lithium composite oxide may be too small. Conversely, when the ratio of the thickness of the outer body relative to the radius of the lithium composite oxide is 0.10 or more, the volume occupied by the outer body containing cation mixtures in the lithium composite oxide is too large, which may deteriorate the electrochemical properties of the lithium composite oxide, including capacity characteristics and rate performance.

[0083] In one embodiment, the lithium composite oxide described above may be a cobalt-free lithium composite oxide represented by the following chemical formula 1. The composition represented by the following chemical formula 1 represents the average composition of the internal matrix and the external matrix.

[0084] [Chemical Formula 1]

[0085] Li a Ni 1-(b+c+d) Mn b M1 c M2 d O 2-e X e

[0086] (Where M1 and M2 are each independently selected from at least one of Ti, Zr, Nb, Al, B, V, W, Ca, K, S, P, Sr, Ba, Mn, Ce, Hf, Ta, Cr, Mg, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, Gd, and Cu, M1 and M2 are mutually exclusive, X is a halogen element existing in a state of substitution with oxygen present in the above lithium composite oxide, 0.95≤a≤1.05, 0 <b≤0.5,0≤c≤0.05,0≤d≤0.05,0≤e≤0.10)。

[0087] In the above chemical formula 1, "1-(b+c+d)" representing the nickel content (molar ratio) in the above lithium composite oxide can be 0.5 or more and less than 0.95, preferably 0.6 or more and less than 0.9, and more preferably 0.75 or more and less than 0.85.

[0088] In addition, in the above chemical formula 1, the "b" representing the manganese content (molar ratio) in the above lithium composite oxide can be greater than 0 and less than 0.50, preferably greater than 0.05 and less than 0.5, more preferably more than 0.10 and less than 0.40, and even more preferably more than 0.10 and less than 0.30.

[0089] On the other hand, by making the Ni / Mn molar ratio of the external host lower than that of the internal host, the electrochemical properties expected of the internal host, including capacity and rate performance, are improved, and the cation mixing is concentrated in the external host, thereby improving the surface stability of the lithium composite oxide. However, when the cation mixing is concentrated in the external host, the conductivity of the lithium composite oxide surface decreases, thereby reducing the charge-transfer and / or diffusion of lithium ions on the lithium composite oxide surface (i.e., surface kinetics).

[0090] Therefore, when a coating comprising a metal oxide represented by the following chemical formula 2 is formed on at least a portion of the surface of the lithium composite oxide (i.e., at least a portion of the surface of the outer body), the conductivity of the outer body, which is relatively lower than that of the inner body, can be improved, thereby helping to improve the surface kinetics of the lithium composite oxide.

[0091] [Chemical Formula 2]

[0092] Li f M3 g O h

[0093] (Where M3 is selected from at least one of Ni, Mn, Co, Ti, Zr, Nb, Al, B, V, W, Ca, K, S, P, Sr, Ba, Mn, Ce, Hf, Ta, Cr, Mg, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, Gd and Cu, 0≤f≤10, 0≤g≤8, 2≤h≤13, but f and g are not both 0).

[0094] Non-limiting examples of the metal oxides represented by the above chemical formula 2 include Li g Zr h O i Li g Ti h O i Li g Ni h O i Li g Nb h O i Li g Co h O i Li g Si h O i Li g Al h O i Co h O i Mn h O i Al h O i Si h O i Zr h O i Ti h O i Furthermore, at least a portion of the surface of the aforementioned lithium composite oxide may independently contain a metal oxide represented by the aforementioned chemical formula 2.

[0095] The surface where adjacent initial particles meet within the aforementioned secondary particles can be referred to as the interface between the initial particles, and this interface can be defined as the grain boundary between the initial particles. Furthermore, the initial particles can be spaced apart from adjacent initial particles within the aforementioned secondary particles to form internal voids.

[0096] The surface of the secondary particles, which are formed by the aggregation of multiple initial particles, is equivalent to the exposed surface of the initial particles that exist on the surface of the secondary particles.

[0097] The coating is defined as the metal oxide present in the region of the initial particles and / or the secondary particles, and the coating may be formed wholly or partially on the surface of the initial particles and / or the secondary particles. When the coating is partially formed on the surface of the initial particles and / or the secondary particles, the shape of the coating may be referred to as island-shaped.

[0098] Furthermore, the aforementioned metal oxides may exist on the surface of the aforementioned initial particles and / or the aforementioned secondary particles in a physically and / or chemically bonded state, or may exist in a partially dissolved state.

[0099] As the metal oxide diffuses along the grain boundaries between the initial particles from the surface of the secondary particles to the center of the secondary particles, the coating existing inside the secondary particles can be formed. As the metal oxide diffuses from the surface of the secondary particles to the center of the secondary particles, at least one element contained in the metal oxide (e.g., M3) can exhibit a decreasing concentration gradient from the surface of the secondary particles to the center of the secondary particles.

[0100] The gradient of the aforementioned metal oxide can be determined by cross-sectional processing of the aforementioned lithium composite oxide, followed by EDS mapping and line scanning to measure the concentration changes of elements specific to the aforementioned metal oxide, or by energy-dispersive X-ray spectroscopy to measure the energy distribution of the concentration of elements specific to the aforementioned metal oxide based on the penetration depth of the electron beam irradiating the surface of the aforementioned lithium composite oxide.

[0101] Lithium secondary batteries

[0102] According to another aspect of the present invention, the present invention can provide a positive electrode comprising a positive current collector and a positive active material layer formed on the positive current collector. The positive active material layer may contain the positive active material of various embodiments of the present invention. Therefore, the positive active material is the same as described above, and for convenience, its specific description will be omitted hereafter; only the remaining undescribed components will be described.

[0103] There are no particular limitations on the aforementioned positive electrode current collector, as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., can be used. Furthermore, the aforementioned positive electrode current collector typically has a thickness of 3μm to 500μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, it can be used in various forms such as thin films, sheets, foils, meshes, porous bodies, foams, and nonwovens.

[0104] The aforementioned positive electrode active material layer can be prepared by coating the aforementioned positive electrode current collector with a positive electrode slurry composition comprising the aforementioned positive electrode active material, a conductive material, and, if desired, a binder.

[0105] In this case, the content of the positive electrode active material relative to the total weight of the positive electrode active material layer can be from 80% to 99% by weight, more specifically from 85% to 98.5% by weight. When the positive electrode active material is included in the above content range, excellent capacity characteristics can be exhibited, but it is not limited thereto.

[0106] The aforementioned conductive materials are used to impart conductivity to the electrodes. In the constructed battery, they can be used without restriction as long as they do not cause chemical changes and possess electronic conductivity. Specific examples include graphite such as natural or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One or more mixtures of these materials may be used. The total weight of the positive electrode active material layer may range from 0.1% to 15% by weight of the aforementioned conductive materials.

[0107] The aforementioned binder enhances the adhesion between multiple positive electrode active material particles and the bonding force between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof; one or more mixtures thereof may be used. The binder may comprise 0.1% to 15% by weight of the aforementioned binder relative to the total weight of the positive electrode active material layer.

[0108] In addition to utilizing the aforementioned positive electrode active material, the positive electrode can be prepared according to conventional positive electrode preparation methods. Specifically, it can be prepared by coating a positive electrode slurry composition onto a positive electrode current collector and then drying and calendering it. The positive electrode slurry composition is prepared by dissolving or dispersing the aforementioned positive electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material in the solvent.

[0109] The solvents mentioned above can be solvents commonly used in this technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or a mixture of two or more of them can be used. Considering the coating thickness and preparation yield of the slurry, the amount of the solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to have a viscosity that exhibits excellent thickness uniformity when coated for the preparation of the positive electrode.

[0110] Furthermore, in another embodiment, the positive electrode can also be prepared by casting the positive electrode slurry composition onto a separate support, and then laminating the thin film obtained by peeling off the support onto the positive electrode current collector.

[0111] Furthermore, according to another aspect of the present invention, an electrochemical device including the aforementioned positive electrode can be provided. Specifically, the aforementioned electrochemical device is a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0112] Specifically, the aforementioned lithium secondary battery may include a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separator and electrolyte disposed between the positive electrode and the negative electrode. The positive electrode is the same as described above; therefore, for convenience, a detailed description is omitted. The remaining components not previously described will be explained below.

[0113] The aforementioned lithium secondary battery may optionally include: a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separation membrane; and a sealing component for sealing the battery container.

[0114] The aforementioned negative electrode may include a negative current collector and a layer of negative active material located on the aforementioned negative current collector.

[0115] There are no particular limitations on the aforementioned negative electrode current collector, as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the aforementioned negative electrode current collector can typically have a thickness of 3μm to 500μm. Similar to the positive electrode current collector, the bonding force of the negative electrode active material can be enhanced by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as thin films, sheets, foils, meshes, porous bodies, foams, and nonwovens.

[0116] The aforementioned negative electrode active material layer can be prepared by coating the aforementioned negative electrode current collector with a negative electrode slurry composition comprising the aforementioned negative electrode active material and conductive material, and selectively including a binder as needed.

[0117] As the aforementioned negative electrode active material, compounds capable of reversible lithium insertion and extraction can be used. Specific examples include carbon materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; and metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; such as SiO₂. β Metal oxides capable of being doped and dedoped with lithium, such as (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above-mentioned metal compounds and carbon materials, such as Si-C composites or Sn-C composites, may be used, and one or more mixtures thereof may be used. Furthermore, lithium metal films may also be used as the above-mentioned negative electrode active material. Moreover, both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Representative low-crystalline carbons are soft carbon and hard carbon, while representative high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitch, and high-temperature calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0118] Based on the total weight of the negative electrode active material layer, it may contain 80% to 99% of the aforementioned negative electrode active material.

[0119] The aforementioned binder is a component that facilitates the bonding between the conductive material, the active material, and the current collector. Typically, based on the total weight of the negative electrode active material layer, 0.1% to 10% of the aforementioned binder can be added. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0120] The aforementioned conductive material is a component used to further improve the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, up to 10% by weight of the aforementioned conductive material can be added, preferably up to 5% by weight. There are no particular limitations on this conductive material as long as it does not induce chemical changes in the corresponding battery and has conductivity. For example, graphite such as natural graphite or artificial graphite can be used; 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 fluorinated carbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0121] In one embodiment, the aforementioned negative electrode active material layer can be prepared by coating a negative electrode slurry composition onto a negative electrode current collector and drying it. The negative electrode slurry composition is prepared by dissolving or dispersing the negative electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material in the solvent. Alternatively, the negative electrode slurry composition can be cast onto a separate support, and then a thin film layer obtained by peeling off the support can be pressed onto the negative electrode current collector.

[0122] Furthermore, in another embodiment, the aforementioned negative electrode active material layer can also be prepared by coating a negative electrode slurry composition onto a negative electrode current collector and drying it. The aforementioned negative electrode slurry composition is prepared by dissolving or dispersing the negative electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material in the solvent. Alternatively, the aforementioned negative electrode slurry composition can be cast onto a separate support, and then a thin film layer obtained by peeling off the support can be pressed onto the negative electrode current collector.

[0123] Furthermore, in the aforementioned lithium secondary battery, the separator membrane is used to separate the negative and positive electrodes and provide a channel for lithium ion movement. Any separator membrane commonly used in lithium secondary batteries can be used without limitation. In particular, it is preferable to have low impedance and excellent electrolyte moisture-holding capacity for electrolyte ion movement. Specifically, porous polymer films can be used, for example, porous polymer films prepared from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or their two- or more-layered stacked structures. Furthermore, conventional porous nonwoven fabrics can also be used, for example, nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Moreover, to ensure heat resistance or mechanical strength, separator membranes coated with ceramic components and polymeric substances can also be used, selectively in single-layer or multi-layer structures.

[0124] Furthermore, examples of electrolytes used in this invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, but they are not limited to these.

[0125] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0126] As the aforementioned organic solvents, organic solvents that can act as a medium for the movement of ions participating in the electrochemical reaction of the battery can be used without limitation. Specifically, as the aforementioned organic solvents, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorinated benzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (EPC) can be used. Carbonate solvents such as ate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where r is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, which may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxanes such as 1,3-dioxane; or sulfolane, etc. Among these, carbonate solvents are preferred, and more preferably, mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate, etc.) with high ionic conductivity and high dielectric constant, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) that can improve the charge-discharge performance of the battery are preferred. In this case, when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, excellent electrolyte performance can be observed.

[0127] The lithium salts described above can be any compound capable of providing lithium ions for use in lithium secondary batteries. Specifically, the lithium salts can be 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. Preferably, the concentration of the lithium salts is in the range of 0.1M to 2.0M. If the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, thus exhibiting excellent electrolyte performance and enabling efficient movement of lithium ions.

[0128] When the electrolyte used herein is a solid electrolyte, such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, etc., solid inorganic electrolytes can be used. Preferably, sulfide solid electrolytes can be used.

[0129] As materials for sulfide-based solid electrolytes, solid electrolytes containing Li, X (where 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 aforementioned sulfide-based solid electrolyte materials include Li₂S-P₂S₅, Li₂S-P₂S-LiX (where 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 (Where m and n are integers, and Z is Ge, Zn, or Gam), 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, etc.)

[0130] The solid electrolyte, preferably, is a sulfide-based solid electrolyte, which can be amorphous, crystalline, or a mixture of amorphous and crystalline states.

[0131] Examples of oxide-based solid electrolytes include Li7La3Zr2O. 12 Li 7-x La3Zr1-x Nb x O 12 Li 7- 3x La3Zr2Al x O 12 Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x GeO4 (LISICON), etc.

[0132] The aforementioned solid electrolyte can be arranged as a separate layer (solid electrolyte layer) between the positive and negative electrodes. Furthermore, the aforementioned solid electrolyte can be partially contained independently of the aforementioned solid electrolyte layer within the positive electrode active material layer of the positive electrode, or the aforementioned solid electrolyte can be partially contained independently of the aforementioned solid electrolyte layer within the negative electrode active material layer of the negative electrode.

[0133] In addition to the electrolyte components described above, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and increasing battery discharge capacity, the electrolyte may also contain, for example, one or more additives such as halogenated alkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the electrolyte may contain 0.1 to 5% by weight of the aforementioned additives relative to its total weight.

[0134] As described above, lithium secondary batteries containing the positive electrode active material according to the present invention stably exhibit excellent discharge capacity, output characteristics and lifespan characteristics, and therefore can be used in portable devices such as mobile phones, laptops, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0135] The lithium secondary battery of the present invention is not particularly limited in shape and can be cylindrical, prismatic, pouch-shaped, or coin-shaped, etc. Furthermore, preferably, the lithium secondary battery can be used not only as a single battery cell for powering small devices, but also as a unit battery in medium or large battery modules comprising multiple battery cells.

[0136] According to another aspect of the present invention, a battery module comprising the aforementioned lithium secondary battery as a single unit and / or a battery pack comprising the same can be provided.

[0137] The aforementioned battery module or battery pack can be used as a power tool; an electric vehicle, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or a power source for one or more medium or large-sized devices in an energy storage system.

[0138] The present invention will now be described in more detail through embodiments. However, these embodiments are merely illustrative and should not be construed as limiting the scope of the invention to these embodiments.

[0139] Preparation Example 1. Preparation of Positive Electrode Active Material

[0140] Example 1

[0141] Step (a): A hydroxide precursor was synthesized by a co-precipitation method, which was divided into an inner matrix and an outer matrix surrounding the surface of the inner matrix.

[0142] First, an aqueous solution of a first metal salt, consisting of nickel sulfate and manganese sulfate weighed in a manner that creates a Ni:Mn molar ratio of 83:17, is added to the reactor. The mixture is then stirred at 450 rpm for 1,437 minutes to form a Ni-containing... 0.83 Mn 0.17 The internal bulk consists of an (OH)₂ average composition and a radius of 4.850 μm. The volume of the internal bulk, calculated using the radius of the aforementioned internal bulk, is 477.6 μm. 3 .

[0143] Step (b): After the synthesis of the above-mentioned internal matrix is ​​completed, an aqueous solution of a second metal salt, consisting of nickel sulfate and manganese sulfate weighed in a Ni:Mn molar ratio of 50:50, is added to the reactor. The mixture is stirred at 450 rpm for 153 minutes to form a Ni-containing surface on the internal matrix. 0.50 Mn0.50 An outer body with an average composition of (OH)₂ and a thickness of 0.150 μm. The volume of the outer body, calculated using the thickness of the aforementioned outer body, is 45.7 μm. 3 .

[0144] At this point, the average composition of the final synthesized hydroxide precursor, comprising the aforementioned internal matrix and the aforementioned external matrix, is Ni. 0.80 Mn 0.20 (OH)2, with a radius of 5.0 μm.

[0145] Step (c): The hydroxide precursor obtained in step (b) is mixed with LiOH (weighed so that the molar ratio of Li to the total metal element content is 1.02 based on the final product), and then heated to 820°C at a rate of 2°C per minute in a sintering furnace while maintaining an O2 atmosphere. The mixture is then heat-treated at 820°C for 8 hours to obtain a lithium composite oxide with a radius of 5.0 μm.

[0146] Examples 2 to 8

[0147] Except for the conditions described in Tables 1 and 2 below, the positive electrode active materials of Examples 2 to 8 were prepared in the same manner as in Example 1.

[0148] Table 1

[0149]

[0150] Table 2

[0151]

[0152]

[0153] Example 9

[0154] After mixing the lithium composite oxide, TiO2, and ZrO2 obtained in step (c) of Example 1, the mixture was heated to 720°C at a rate of 2°C per minute in a sintering furnace while maintaining an O2 atmosphere, and then heat-treated at 720°C for 8 hours. TiO2 and ZrO2 were weighed such that the content of Ti and Zr in the lithium composite oxide, based on the metal elements other than lithium, was 0.1 mol%, and then mixed with the lithium composite oxide.

[0155] Through the above heat treatment, the residual lithium present on the surface of the above lithium composite oxide reacts with Ti and Zr to obtain the final product with an oxide containing Ti and Zr coated on the surface.

[0156] Comparative Example 1

[0157] Step (a): An aqueous solution of nickel sulfate and manganese sulfate, weighed in such a way that the molar ratio of Ni:Mn is 80:20, is added to the reactor and stirred at 450 rpm for 1,493 minutes to form a Ni-containing... 0.80 Mn 0.20 The hydroxide precursor has an average composition of (OH)₂ and a radius of 5.0 μm. The volume of the aforementioned hydroxide precursor, calculated using its radius, is 523.3 μm. 3 .

[0158] Step (b): The hydroxide precursor obtained in step (a) is mixed with LiOH (weighed so that the molar ratio of Li to the total metal element content is 1.02 based on the final product), and the mixture is heated to 820°C at a rate of 2°C per minute while maintaining an O2 atmosphere in a sintering furnace. The mixture is then heat-treated at 820°C for 8 hours to obtain a lithium composite oxide with a radius of 5.0 μm.

[0159] Comparative Examples 2 to 8

[0160] Except for the conditions described in Tables 3 and 4 below, the positive electrode active materials according to Comparative Examples 2 to 8 were prepared in the same manner as in Example 1.

[0161] Table 3

[0162]

[0163]

[0164] Table 4

[0165]

[0166] Comparative Example 9

[0167] After mixing the lithium composite oxide, TiO2, and ZrO2 obtained in step (b) of Comparative Example 1, the mixture was heated to 720°C at a rate of 2°C per minute while maintaining an O2 atmosphere in a sintering furnace, and then heat-treated at 720°C for 8 hours. TiO2 and ZrO2 were weighed such that the content of Ti and Zr in the above-mentioned lithium composite oxide, based on the metal elements other than lithium, was 0.1 mol%, and then mixed with the above-mentioned lithium composite oxide.

[0168] Through the above heat treatment, the residual lithium present on the surface of the above lithium composite oxide reacts with Ti and Zr to obtain the final product with an oxide containing Ti and Zr coated on the surface.

[0169] The Ni / Mn molar ratio of the inner body (A), the Ni / Mn molar ratio of the outer body (B), the ratio of the Ni content (mol%) of the outer body to the Ni content (mol%) of the inner body (C), the ratio of the Mn content (mol%) of the outer body to the Mn content (mol%) of the inner body (D), the ratio of the thickness of the outer body to the radius of the lithium composite oxide (E), and the volume fraction (F) of the outer body in the total volume of the lithium composite oxide are shown in Table 5 below.

[0170] Table 5

[0171] Classification A B C D E F Example 1 4.88 1.00 0.602 2.941 0.030 8.73％ Example 2 5.67 1.00 0.588 3.333 0.050 14.26％ Example 3 4.56 1.22 0.671 2.500 0.030 8.73％ Example 4 5.25 1.22 0.655 2.813 0.050 14.26％ Example 5 7.33 1.22 0.625 3.750 0.090 24.64％ Example 6 4.56 1.50 0.732 2.222 0.030 8.73％ Example 7 4.88 1.50 0.723 2.353 0.050 14.26％ Example 8 6.69 1.50 0.690 3.077 0.090 24.64％ Example 9 4.88 1.00 0.602 2.941 0.030 8.73％ Comparative Example 1 - - - - - - Comparative Example 2 4.56 1.00 0.610 2.778 0.025 7.31％ Comparative Example 3 9.00 1.00 0.556 5.000 0.100 27.10％ Comparative Example 4 4.26 1.50 0.741 2.105 0.025 7.31％ Comparative Example 5 7.33 1.50 0.682 3.333 0.100 27.10％ Comparative Example 6 4.26 2.33 0.864 1.579 0.025 7.31％ Comparative Example 7 4.56 2.33 0.854 1.667 0.050 14.26％ Comparative Example 8 5.25 2.33 0.833 1.875 0.100 27.10％ Comparative Example 9 - - - - - -

[0172] Preparation Example 2. Preparation of Lithium Secondary Batteries

[0173] A positive electrode slurry was prepared by dispersing 92% by weight of each of the positive electrode active materials prepared according to Preparation Example 1, 4% by weight of artificial graphite, and 4% by weight of PVDF binder in 30g of N-methyl-2-pyrrolidone (NMP). The above positive electrode slurry was uniformly coated on an aluminum film with a thickness of 15μm and vacuum dried at 135°C to prepare a positive electrode for lithium secondary batteries.

[0174] In contrast to the above positive electrode, a lithium foil was used as the counter electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) was used as the separation membrane, and a half-cell was prepared using an electrolyte containing 1.15 M of LiPF6 in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0175] Experimental Example 1: Thermogravimetric Analysis of Positive Electrode Active Material

[0176] The lithium secondary battery (half-cell) prepared according to Preparation Example 2 was charged to 4.3V at a temperature of 25°C and a constant current of 0.1C / 0.1C, and then disassembled to recover the positive electrode active material.

[0177] The thermal stability of the recovered positive electrode active material was evaluated by thermogravimetric analysis (TGA).

[0178] TGA was performed under the following conditions, and Table 6 below shows the on-set temperature at which the weight reduction of the aforementioned positive electrode active material began to occur via TGA.

[0179] Sample: 65 mg of lithium composite oxide

[0180] Measurement atmosphere: Ar gas (gas flow rate: 60 ml / min)

[0181] Measurement conditions: Heating from 30℃ to 350℃ at a rate of 10℃ / min.

[0182] Table 6

[0183] Classification Starting temperature (°C) Example 1 224.2 Example 2 229.7 Example 3 223.9 Example 4 227.9 Example 5 225.4 Example 6 223.8 Example 7 227.1 Example 8 224.6 Example 9 224.2 Comparative Example 1 196.6 Comparative Example 2 212.0 Comparative Example 3 218.7 Comparative Example 4 208.9 Comparative Example 5 218.6 Comparative Example 6 206.9 Comparative Example 7 219.8 Comparative Example 8 215.9 Comparative Example 9 197.2

[0184] Referring to Table 6 above, it can be confirmed that the thermal stability of the positive electrode active materials according to Examples 1 to 9 is higher than that of the positive electrode active materials according to Comparative Examples 1 to 9. In particular, it can be seen that the thermal stability of the positive electrode active materials according to Comparative Examples 1 and 9 is lower than that of the positive electrode active materials according to the other comparative examples. When a positive electrode active material with low thermal stability is used, the positive electrode active material deteriorates prematurely during the charging / discharging process of the lithium secondary battery, thereby potentially reducing the lifespan of the lithium secondary battery.

[0185] Experimental Example 2. Evaluation of the Electrochemical Characteristics of Lithium Secondary Batteries

[0186] Each lithium secondary battery (half-cell) prepared in Preparation Example 2 was charged to 4.3V at 25°C and under constant current conditions of 0.1C / 0.1C, and then discharged to 3.0V. The initial charge capacity, initial discharge capacity, and rate capability (discharge capacity ratio; rate capability (C-rate)) were measured.

[0187] Furthermore, the same lithium secondary battery was subjected to 50 charge / discharge cycles at 1C / 1C conditions within a driving voltage range of 3.0V to 4.3V at 45°C. The ratio of the discharge capacity at the 50th cycle to the initial capacity was then measured (capacity retention). The results of these measurements are shown in Table 7 below.

[0188] Table 7

[0189]

[0190] Referring to Table 7 above, the lithium secondary batteries using the positive electrode active materials of Examples 1 to 9 in the operating voltage range of 3.0V to 4.3V have generally improved initial charge capacity, initial discharge capacity, rate characteristics and cycle capacity retention compared with the lithium secondary batteries using the positive electrode active materials of Comparative Examples 1 to 9.

[0191] Furthermore, when comparing the results of lithium secondary batteries using the positive electrode active materials according to Examples 1 and 9, it can be confirmed that the rate performance is improved by forming a conductive coating on the surface of the aforementioned lithium composite oxide.

[0192] In addition, in order to evaluate the electrochemical characteristics of the above-mentioned lithium secondary batteries within a relatively high operating voltage range, the initial charge capacity, initial discharge capacity, rate capability, and cycle capacity retention were measured in the same manner as described above, except that the operating voltage range of 3.0V to 4.5V was used.

[0193] The results of the above measurements are shown in Table 8 below.

[0194] Table 8

[0195]

[0196] Referring to Table 8 above, even within the operating voltage range with a relatively high upper limit voltage (4.5V), the lithium secondary battery using the positive electrode active material according to Examples 1 to 9 has an overall improved initial charge capacity, initial discharge capacity, rate characteristics, and cycle capacity retention compared to the lithium secondary battery using the positive electrode active material according to Comparative Examples 1 to 9.

[0197] Furthermore, when comparing the results of lithium secondary batteries using the positive electrode active materials according to Examples 1 and 9, it can be confirmed that the rate performance is improved by forming a conductive coating on the surface of the aforementioned lithium composite oxide.

Claims

1. A positive electrode active material, comprising a lithium composite oxide containing at least nickel and manganese, characterized in that, The above-mentioned lithium composite oxide is a cobalt-free lithium composite oxide. The aforementioned lithium composite oxide is divided into an inner matrix and an outer matrix, wherein the outer matrix surrounds the surface of the inner matrix, and the Ni / Mn molar ratio of the outer matrix is ​​1.0 or more and less than 2.

33. The Ni / Mn molar ratio of the external body is less than that of the internal body. The volume fraction of the aforementioned external matrix in the total volume of the lithium composite oxide is 7.4% or more and less than 27.1%.

2. The positive electrode active material according to claim 1, characterized in that, The Ni / Mn molar ratio of the aforementioned external body is above 1.0 and below 1.

5.

3. The positive electrode active material according to claim 1, characterized in that, The Ni / Mn molar ratio of the aforementioned internal matrix is ​​greater than 4.26 and less than 9.

00.

4. The positive electrode active material according to claim 1, characterized in that, In the aforementioned internal matrix, the molar ratio of Ni relative to all metal elements except lithium is greater than 0.7 and less than 1.

0.

5. The positive electrode active material according to claim 1, characterized in that, In the aforementioned external body, the molar ratio of Ni relative to all metal elements except lithium is greater than 0.5 and less than 0.

8.

6. The positive electrode active material according to claim 1, characterized in that, The ratio of the thickness of the outer body to the radius of the aforementioned lithium composite oxide is greater than 0.025 and less than 0.

10.

7. The positive electrode active material according to claim 1, characterized in that, The ratio of the Ni content of the external body to the Ni content of the internal body is greater than 0.556 and less than 0.740, where the Ni content is in moles.

8. The positive electrode active material according to claim 1, characterized in that, The ratio of the Mn content of the external body to the Mn content of the internal body is 2.2 or more and less than 5.0, where the unit of the Mn content is moles.

9. The positive electrode active material according to claim 1, characterized in that, The cationic mixed layer is present on at least a portion of the surface of the aforementioned outer body.

10. The positive electrode active material according to claim 1, characterized in that, The cation mixing rate of the aforementioned external host is greater than that of the aforementioned internal host.

11. The positive electrode active material according to claim 1, characterized in that, The above-mentioned lithium composite oxide is represented by the following chemical formula 1: [Chemical Formula 1] The a Nor 1-(b+c+d) Mn b M1 c M2 d O 2-e X e (in, M1 and M2 are each independently selected from at least one of Ti, Zr, Nb, Al, B, V, W, Ca, K, S, P, Sr, Ba, Mn, Ce, Hf, Ta, Cr, Mg, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, Gd, and Cu. M1 and M2 are mutually exclusive. X is a halogen element existing in a state where it is substituted with oxygen present in the above-mentioned lithium composite oxide. 0.95≤a≤1.05, 0 <b≤0.5,0≤c≤0.05,0≤d≤0.05,0≤e≤0.10)。 12. The positive electrode active material according to claim 1, characterized in that, A coating comprising a metal oxide represented by the following chemical formula 2 is formed on at least a portion of the surface of the aforementioned lithium composite oxide: [Chemical Formula 2] Read f M3 g Oh h (Where M3 is selected from at least one of Ni, Mn, Co, Ti, Zr, Nb, Al, B, V, W, Ca, K, S, P, Sr, Ba, Ce, Hf, Ta, Cr, Mg, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, Gd, and Cu.) 0≤f≤10, 0≤g≤8, 2≤h≤13 (but f and g are not both 0).

13. The positive electrode active material according to claim 12, characterized in that, The M3 mentioned above includes at least one selected from Ti and Zr.

14. A positive electrode, characterized in that, Includes the positive electrode active material according to any one of claims 1 to 13.

15. A lithium secondary battery, characterized in that, Use the positive electrode as described in claim 14.

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