Positive electrode active material, positive electrode, and lithium secondary battery

Abstract

Provided are a positive electrode active material, a positive electrode, and a lithium secondary battery that suppress a side reaction between a positive electrode active material and a sulfide-based solid electrolyte, improve compatibility, and improve the life and rate-determining performance of an all-solid-state lithium secondary battery. 【Solution means】Provided is a positive electrode active material including lithium transition metal composite oxide particles and a surface modification part present on at least a part of the surface of the particles, wherein the surface modification part includes a compound represented by the following chemical formula 1. [Chemical formula 1]M 1 a M 2 b (SO3) c In Chemical formula 1, M 1 includes one or more selected from the group consisting of Li, B, P, Nb, Zr, Al, Ti, and Ta, M 2 includes one or more selected from the group consisting of Ni, Co, Mn, and Fe, 0 ≦ a ≦ 2, 0 ≦ b ≦ 4, 1 ≦ c ≦ 4, and at least one of a and b is not 0.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for all-solid-state batteries, a positive electrode containing the same, and an all-solid-state lithium secondary battery. [Background technology]

[0002] Lithium-ion batteries, particularly those using a liquid electrolyte, are the most commonly used type of secondary battery. In these batteries, the negative and positive electrodes are typically separated by a polymer separator, and a liquid electrolyte is used. However, because the electrolyte exists in a liquid state within the battery, these lithium-ion batteries face various safety challenges.

[0003] Therefore, development of all-solid-state batteries, which use a solid electrolyte instead of a liquid electrolyte as the electrolyte for lithium secondary batteries, is continuing. All-solid-state batteries include a negative electrode, a positive electrode, and a solid electrolyte, and all components of the battery are solid, thus preventing the safety problems associated with liquid electrolytes compared to lithium secondary batteries that use liquid electrolytes.

[0004] Among all-solid-state lithium-ion batteries using inorganic solid electrolytes, sulfide-based solid electrolytes, in particular, are highly regarded for their excellent ionic conductivity and bonding properties with electrode active materials, and are considered very close to commercialization. However, sulfide-based solid electrolytes cause side reactions with the oxide-based positive electrode active material, forming side reaction products at the interface. This forms a resistive layer at the interface between the positive electrode and the sulfide-based solid electrolyte, which is the main cause of degradation of the electrochemical properties of the all-solid-state lithium-ion battery. To prevent this, methods have been proposed to coat the surface of the positive electrode active material with a coating material such as a stable oxide like Li2ZrO3, LiNbO3, or LiTaO3, or a phosphorus oxide like Li3PO4. Furthermore, to solve the contact problem between the positive electrode and the solid electrolyte, a method has been proposed in which the positive electrode active material is coated with an oxide or phosphorus oxide, and then further coated with a sulfide-based solid electrolyte. Thus, when further coating a positive electrode active material coated with an oxide or phosphoroxide with a sulfide-based solid electrolyte, the coating method used involves forming the sulfide-based solid electrolyte in a liquid phase with an organic solvent on the oxide or phosphoroxide coating layer. However, as mentioned above, when coating with a sulfide-based solid electrolyte, the ionic conductivity of the sulfide-based solid electrolyte decreases rapidly during the process of dispersing it in the organic solvent, and the formed coating layer acts as a new resistance layer. Furthermore, when coating with a sulfide-based solid electrolyte as described above, the difficulty of the liquid phase process of the coating solution makes it difficult to coat the surface of the positive electrode active material with a thin and uniform sulfide-based solid electrolyte layer.

[0005] On the other hand, currently used coating materials such as oxides or phosphoroxides can significantly reduce side reactions between the positive electrode active material and the sulfide-based solid electrolyte. However, since the above-mentioned oxides or phosphoroxides are similar oxides or phosphoroxides to the positive electrode active material, the positive electrode active material coated with these materials inevitably has low compatibility with the sulfide-based solid electrolyte. Therefore, during long-term battery operation, the stability of the coating layer made of oxides or phosphoroxides cannot be guaranteed, and there is a problem in that stable contact with the sulfide-based solid electrolyte cannot be maintained for a long period of time. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Korean Patent Application No. 10-2021-0136594A [Overview of the project] [Problems that the invention aims to solve]

[0007] The problem that this invention aims to solve is to suppress side reactions between the positive electrode active material and the sulfide-based solid electrolyte, and to improve compatibility, when used as a positive electrode active material for an all-solid-state lithium secondary battery containing a sulfide-based solid electrolyte.

[0008] In other words, the present invention aims to provide a positive electrode active material that can improve the lifespan and rate-limiting performance of an all-solid-state lithium secondary battery by suppressing side reactions between the positive electrode active material and the sulfide-based solid electrolyte, and improving compatibility, by including a surface-modified portion in which interfacial reaction products are artificially formed on the surface of the particles with sulfur (S).

[0009] Furthermore, the present invention aims to provide a positive electrode containing the positive electrode active material.

[0010] Furthermore, the present invention aims to provide a lithium secondary battery including the positive electrode. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides a positive electrode active material, a positive electrode, and a lithium secondary battery.

[0012] (1) The present invention provides a positive electrode active material including lithium transition metal composite oxide particles and a surface modification part present on at least a part of the surface of the particles, wherein the surface modification part contains a compound represented by the following chemical formula 1. [Chemical formula 1] M 1 a M 2 b (SO3) c In the chemical formula 1, M 1 includes one or more selected from the group consisting of Li, B, P, Nb, Zr, Al, Ti, and Ta, M 2 includes one or more selected from the group consisting of Ni, Co, Mn, and Fe, 0 ≦ a ≦ 2, 0 ≦ b ≦ 4, 1 ≦ c ≦ 4, and at least one of a and b is not 0.

[0013] (2) The present invention provides, in the above (1), a positive electrode active material in which the surface modification part contains a compound represented by the following chemical formula 2. [Chemical formula 2] M 1 a’ M 2 b’ (SO x ) c’ In the chemical formula 2, M 1 includes one or more selected from the group consisting of Li, B, P, Nb, Zr, Al, Ti, and Ta, M 2 includes one or more selected from the group consisting of Ni, Co, Mn, and Fe, 0 ≦ a' ≦ 2, 0 ≦ b' ≦ 4, 1 ≦ c' ≦ 4, and at least one of a' and b' is not 0, and 1 ≦ x < 3 or 3 < x ≦ 10.

[0014] (3) The present invention provides, in the above (1) or (2), a positive electrode active material in which the surface modification part is M 1 with respect to M 2The present invention provides a positive electrode active material whose molar ratio satisfies the following equation 1. [Formula 1] 0<[M 2 ] / [M 1 ]≦0.5 In the above formula 1, M 1 It includes one or more elements selected from the group consisting of Li, B, P, Nb, Zr, Al, Ti, and Ta, and M 2 It includes one or more elements selected from the group consisting of Ni, Co, and Mn.

[0015] (4) In any one of (1) to (3) above, the present invention provides a positive electrode active material in which the surface modified portion contains a metal sulfide.

[0016] (5) In any one of (1) to (4) above, the present invention provides a positive electrode active material in which the surface modified portion contains the compound represented by chemical formula 1 in the highest content among the components containing element S.

[0017] (6) The present invention provides a positive electrode active material in which, in any one of (1) to (5) above, the content of element S, as confirmed by ICP-OES analysis, is 200 ppm or more and 20,000 ppm or less.

[0018] (7) In any one of (1) to (6) above, when the distance between the outermost surface (OSM) of the positive electrode active material including the surface modification portion and the interface (ICP) between the surface modification portion and the surface of the particles is A, the point (A) is 50% of the distance A. 50 Based on ), the point (A) is 50% of the distance A from the outermost surface (OSC) of the positive electrode active material including the surface modification portion confirmed by XPS analysis. 50 The region between (OSM-A) 50 The concentration of element S at the point where it becomes 50% of the concentration at distance A (A 50 ) and the region between the interface (ICP) between the surface modified portion and the surface of the particle (A 50 This provides a positive electrode active material with a higher concentration of S element than that of -ICP.

[0019] (8) In the present invention, in (7) above, the point (A) is 50% of the distance A. 50 ) and the region between the interface (ICP) between the surface modified portion and the surface of the particle (A 50 The concentration of element S at -ICP) is at the point (A) where it is 50% of the distance A. 50 The present invention provides a positive electrode active material having a concentration gradient that gradually decreases from the surface of the particles in the direction of the interface (ICP).

[0020] (9) The present invention provides a positive electrode active material in any one of (1) to (8) above, wherein the positive electrode active material includes a coating portion present on at least a part of the surface of the particles.

[0021] (10) The present invention provides a positive electrode active material in which the coating portion comprises one or more selected from the group consisting of Li2CO3, LiOH, and a compound represented by the following chemical formula 3, as described in (9). [Chemical formula 3] Li m M 3 n O (m+o) / 2 In the above chemical formula 3, M 3 o is one or more elements selected from the group consisting of Nb, B, P, W, Ti, Ta, Sn, Zr, and Al, where 1 ≤ m ≤ 10 and 1 ≤ n ≤ 10, and o is M 3 This is the oxidation number of [the substance].

[0022] (11) In the present invention, the surface modification portion provides a positive electrode active material present on at least a portion of the surface of the coating portion, in accordance with (9) or (10) above.

[0023] (12) The present invention provides a positive electrode active material in any one of (1) to (11) above, in which the positive electrode active material does not contain a bond (SP) between S element and P element.

[0024] (13) In any one of the above (1) to (12), the present invention provides a positive electrode active material in which the lithium transition metal composite oxide particles are one or more selected from the group consisting of single crystal single particles, polycrystalline single particles, and secondary particles formed by aggregation of a plurality of primary particles.

[0025] (14) In any one of the above (1) to (13), the present invention provides a positive electrode active material in which the lithium transition metal composite oxide particles have an average composition represented by the following Chemical Formula 4. [Chemical Formula 4] Li p Ni q Co r M 4 s M 5 t O2 In the Chemical Formula 4, M 4 is Mn, Al, or a combination thereof, and M 5 includes one or more selected from the group consisting of Nb, Ta, B, Zr, Cr, and W, 0.8 ≦ p ≦ 1.3, 0 < q < 1, 0 < r < 1, 0 < s < 1, 0 ≦ t ≦ 0.2, and q + r + s + t = 1.

[0026] (15) In the above (14), the present invention provides a positive electrode active material in which 0.8 ≦ q < 1, 0 < r ≦ 0.2, 0 < s ≦ 0.2, and 0 ≦ t ≦ 0.1.

[0027] (16) The present invention provides a positive electrode including the positive electrode active material according to any one of the above (1) to (15).

[0028] (17) The present invention provides a lithium secondary battery including the positive electrode according to the above (16).

[0029] (18) In the above (17), the present invention provides a lithium secondary battery including the positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode.

[0030] (19) In the above (18), the present invention provides a lithium secondary battery in which the solid electrolyte layer includes a sulfide-based solid electrolyte.

[0031] (20) The present invention provides a lithium secondary battery in which the sulfide-based solid electrolyte comprises an argyrodite-type sulfide-based solid electrolyte as described in (19). [Effects of the Invention]

[0032] The positive electrode active material of the present invention includes a surface-modified portion in which interfacial reaction products are artificially formed with sulfur (S) on the surface of lithium transition metal composite oxide particles. This suppresses side reactions between the positive electrode active material and the sulfide-based solid electrolyte, improves compatibility, and enhances the lifespan and rate-limiting performance of the all-solid-state lithium secondary battery. [Brief explanation of the drawing]

[0033] [Figure 1] This is a cross-sectional view showing the stacked structure of an all-solid-state lithium secondary battery. [Figure 2] This is a cross-sectional view showing the formation position of the surface modification portion of the positive electrode active material according to one embodiment of the present invention. [Figure 3] This is a cross-sectional view showing the formation positions of the coating portion and the surface modification portion of the positive electrode active material according to one embodiment of the present invention. [Figure 4] This graph shows the intensity of SO-, PO-, LiS-, and PS- ions as the material surface is sputtered during TOF-SIMS analysis of Reference Example 1 of the present invention, with respect to sputtering time. [Figure 5] This graph shows the intensity of SO-, PO-, LiS-, and PS- ions against sputtering time as the material is sputtered from the surface of the material during TOF-SIMS analysis of Reference Example 2 of the present invention. [Figure 6] This graph shows the intensity of SO-, PO-, LiS-, and PS- ions as the material surface is sputtered during TOF-SIMS analysis of Reference Example 3 of the present invention, with respect to sputtering time. [Figure 7]This is a TOF-SIMS analysis result for Reference Example 4 of the present invention, showing the intensity of SO-, PO-, LiS-, and PS- ions as the material is sputtered from the surface of the material, with respect to sputtering time. [Figure 8] This graph shows the XPS analysis results for Reference Examples 1-4 of the present invention, specifically the results for S 2p. [Figure 9] This graph shows the XPS analysis results for the positive electrode active material produced in Example 3 of the present invention. [Figure 10] This graph shows the XPS analysis results for the positive electrode active material produced in Example 9 of the present invention. [Figure 11] This graph shows the XPS analysis results for the positive electrode active material produced in Comparative Example 1 of the present invention. [Figure 12] This graph shows the XPS analysis results for the positive electrode active material produced in Comparative Example 2 of the present invention. [Figure 13] This graph shows the intensity of NiO-, SO-, PO-, LiS-, and PS- ions against the sputtering time while sputtering from the surface of the positive electrode active material during TOF-SIMS analysis of Example 3 of the present invention. [Figure 14] This graph shows the intensity of NiO-, SO-, PO-, LiS-, and PS- ions as the sputtering time is varied while sputtering from the surface of the positive electrode active material during TOF-SIMS analysis of Example 9 of the present invention. [Figure 15] This graph shows the intensity of NiO-, SO-, PO-, LiS-, and PS- ions as the sputtering time is applied to the surface of the positive electrode active material during TOF-SIMS analysis of Comparative Example 1 of the present invention. [Figure 16] This graph shows the intensity of NiO-, SO-, PO-, LiS-, and PS- ions against the sputtering time while sputtering from the surface of the positive electrode active material during TOF-SIMS analysis of Comparative Example 2 of the present invention. [Figure 17]This graph shows the mass-to-charge ratio (Peak M / Z, ±0.03) at which the SO3- and SO4- peaks are observed during TOF-SIMS analysis of Example 3 of the present invention. [Figure 18] This graph shows the mass-to-charge ratio (Peak M / Z, ±0.03) at which the SO3- and SO4- peaks are observed during TOF-SIMS analysis of Example 9 of the present invention. [Figure 19] This graph shows the mass-to-charge ratio (Peak M / Z, ±0.03) at which the SO3- and SO4- peaks are observed during TOF-SIMS analysis of Comparative Example 1 of the present invention. [Figure 20] This graph shows the mass-to-charge ratio (Peak M / Z, ±0.03) at which the SO3- and SO4- peaks are observed during TOF-SIMS analysis of Comparative Example 2 of the present invention. [Figure 21] This graph shows the XPS depth analysis results for Example 3 of the present invention. [Figure 22] This graph shows the XPS depth analysis results for Example 8 of the present invention. [Figure 23] This graph shows the XPS depth analysis results for Example 9 of the present invention. [Figure 24] This graph shows the XPS depth analysis results for Comparative Example 1 of the present invention. [Figure 25] This graph shows the XPS depth analysis results for Comparative Example 2 of the present invention. [Figure 26] This graph compares the initial discharge capacities of all-solid-state lithium secondary batteries manufactured using the positive electrode active materials produced in Examples 1-8 and Comparative Example 1 of the present invention. [Figure 27] This graph compares the DC resistance of all-solid-state lithium secondary batteries manufactured using the positive electrode active materials produced in Examples 1-8 and Comparative Example 1 of the present invention. [Figure 28] This graph shows the specific capacity of all-solid-state lithium secondary batteries produced using the positive electrode active materials manufactured in Examples 3 and 9 of the present invention, and Comparative Examples 1 and 2, for each charge-discharge cycle. [Figure 29] This graph shows the initial charge-discharge capacity of all-solid-state lithium secondary batteries manufactured using the positive electrode active materials produced in Examples 3 and 9 of the present invention and Comparative Examples 1 and 2. [Figure 30] This graph shows the GITT analysis results measured after 300 charge-discharge cycles of all-solid-state lithium secondary batteries manufactured containing the positive electrode active materials produced in Examples 3 and 9 of the present invention and Comparative Examples 1 and 2. [Figure 31] This graph shows the specific capacities of all-solid-state lithium secondary batteries manufactured using the positive electrode active materials produced in Examples 3 and 9 of the present invention, and Comparative Examples 1 and 2, at different charge-discharge cycles over 300 cycles. [Figure 32] This is a TEM image of the separated positive electrode active material after 300 charge-discharge cycles of an all-solid-state lithium secondary battery manufactured containing the positive electrode active material produced in Example 3 of the present invention. [Figure 33] This is a TEM image of the separated positive electrode active material after 300 charge-discharge cycles of an all-solid-state lithium secondary battery manufactured containing the positive electrode active material produced in Example 9 of the present invention. [Figure 34] This is a TEM image of the separated positive electrode active material after 300 charge-discharge cycles of an all-solid-state lithium secondary battery manufactured containing the positive electrode active material produced in Comparative Example 1 of the present invention. [Figure 35] This is a TEM image of the separated positive electrode active material after 300 charge-discharge cycles of an all-solid-state lithium secondary battery manufactured containing the positive electrode active material produced in Comparative Example 2 of the present invention. [Modes for carrying out the invention]

[0034] The present invention will be described in more detail below to facilitate understanding of it.

[0035] The terms and words used in the description and claims of this invention should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​this invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0036] The positive electrode active material, positive electrode, and / or lithium secondary battery according to the present invention comprises at least one of the configurations disclosed below, and may include any combination of technically possible configurations.

[0037] positive electrode active material The present invention provides a positive electrode active material.

[0038] According to one embodiment of the present invention, the positive electrode active material includes a surface-modified portion in which an interfacial reaction product is artificially formed on the surface of lithium transition metal composite oxide particles using sulfur (S). This suppresses side reactions between the positive electrode active material and the sulfide-based solid electrolyte and improves compatibility. Therefore, the positive electrode active material may be particularly useful in an all-solid-state lithium secondary battery containing a sulfide-based solid electrolyte.

[0039] According to one embodiment of the present invention, the positive electrode active material 100, 100' may include lithium transition metal composite oxide particles 110, 110' and surface modified portions 120, 122 present on at least a portion of the surface of the particles, and the surface modified portion may include a compound represented by the following chemical formula 1.

[0040] [Chemical formula 1] M 1 a M 2 b (SO3) c

[0041] In the above chemical formula 1, M 1 It includes one or more elements selected from the group consisting of Li, B, P, Nb, Zr, Al, Ti, and Ta, and M 2It contains one or more elements selected from the group consisting of Ni, Co, Mn, and Fe, where 0 ≤ a ≤ 2, 0 ≤ b ≤ 4, 1 ≤ c ≤ 4, and at least one of a and b is not 0.

[0042] According to one embodiment of the present invention, the compound represented by chemical formula 1 may be a compound formed by the reaction of the surface of lithium transition metal composite oxide particles with sulfur (S). As a specific example, the compound represented by chemical formula 1 may be a compound formed by artificially reacting lithium transition metal composite oxide with sulfur (S). Here, the M 1 The M may be a metallic element derived from one or more elements selected from the group consisting of residual lithium, doping elements, and coating elements present on the surface of lithium transition metal composite oxide particles. 2 This may be a metallic element derived from a transition metal element present on the surface of lithium transition metal composite oxide particles.

[0043] According to one embodiment of the present invention, the compound represented by chemical formula 1 is M 1 and / or M 2 SO3 2- It may be one or more compounds selected from the group of compounds containing ions, and a specific example is one or more compounds selected from the group consisting of CoSO3, MnSO3, NiSO3, Li2SO3, Li2Co(SO3)2, Li2Mn(SO3)2, Li2Ni(SO3)2, LiB(SO3)2, and PO2SO3.

[0044] According to one embodiment of the present invention, the surface modification portion may include a compound represented by the following chemical formula 2.

[0045] [Chemical formula 2] M 1 a’ M 2 b’ (SO x ) c’

[0046] In the above chemical formula 2, M 1It includes one or more elements selected from the group consisting of Li, B, P, Nb, Zr, Al, Ti, and Ta, and M 2 x includes one or more elements selected from the group consisting of Ni, Co, Mn, and Fe, where 0 ≤ a' ≤ 2, 0 ≤ b' ≤ 4, 1 ≤ c' ≤ 4, and at least one of a' and b' is not 0, and 1 ≤ x < 3 or 3 <x≦10である。

[0047] According to one embodiment of the present invention, the compound represented by chemical formula 2 may be a compound formed by the reaction of the surface of lithium transition metal composite oxide particles with sulfur (S). As a specific example, the compound represented by chemical formula 2 may be a compound formed by artificially reacting lithium transition metal composite oxide with sulfur (S).

[0048] According to one embodiment of the present invention, the compound represented by chemical formula 2 is M 1 and / or M 2 Furthermore, it may be one or more compounds selected from the group containing sulfide ions, and specific examples include P4(SO2)3, CoSO4, MnSO4, NiSO4, Li2SO4, Li2Co(SO4)2, Li2Mn(SO4)2, Li2Ni(SO4)2, LiB(SO4)2, CoSO5, CoSO 10 , Co3(SO6)2, MnSO5, MnSO6, Ni(SO6)2, NiSO5, NiSO9, NiSO 10 , P2S2O3, P4SO6, P4SO7, Nb2S3O 14 ,Nb8S8O 45 It may also be one or more selected from the group consisting of, and B2S2O9, etc.

[0049] According to one embodiment of the present invention, the surface modification portion is M 1 M for 2 The molar ratio can satisfy the following equation 1.

[0050] [Formula 1] 0<[M 2 ] / [M 1 ]≦0.5

[0051] In the above formula 1, M 1 It includes one or more elements selected from the group consisting of Li, B, P, Nb, Zr, Al, Ti, and Ta, and M 2 It includes one or more elements selected from the group consisting of Ni, Co, Mn, and Fe. According to computational science, the nearest neighbor hopping activation energy (NNH Ea) of Li2SO4 is 286 meV, and the 1d diffusion energy is 737 meV. On the other hand, the NNH Ea of Li2Ni(SO4)2 is 987 meV, and the 1d diffusion energy is 1,609 meV. The NNH Ea of Li2Co(SO4)2 and Li2Mn(SO4)2 are 1,128 meV and 1,841 meV, respectively. The Li-Li distance of Li2Co(SO4)2 is 4.84 Å, and the Li-Li distance of Li2Mn(SO4)2 is 4.92 Å, making it difficult to generate a diffusion pathway. That is, this is M 1 The molar ratio is M 2 When the molar ratio is greater than that, specifically when equation 1 is satisfied, the activation energy of lithium ion conduction is lower, further improving lithium ion conductivity and further reducing interfacial resistance.

[0052] According to one embodiment of the present invention, the surface modification portion may include a metal sulfide. The metal sulfide may be one or more selected from the group consisting of metal sulfides in which lithium and / or a transition metal is bonded to sulfur (S), such as Li2S, NiS, CoS, and MnS.

[0053] According to one embodiment of the present invention, among the components containing element S, the compound represented by chemical formula 1 can be included in the highest content. As a specific example, the surface modification portion can contain the compound represented by chemical formula 1 and, selectively, the compound represented by chemical formula 2 and / or a metal sulfide simultaneously, in which case the compound represented by chemical formula 1 can be included as the dominant species, i.e., in the highest content. When the compound represented by chemical formula 1 is included in the highest content in this way, further side reactions between the positive electrode active material and the sulfide-based solid electrolyte can be further suppressed.

[0054] According to one embodiment of the present invention, the positive electrode active material may have a sulfur content of 200 ppm or more and 20,000 ppm or less, as confirmed by ICP-OES analysis. As a specific example, the positive electrode active material may have a sulfur content of 200 ppm or more, 225 ppm or more, 250 ppm or more, 275 ppm or more, 300 ppm or more, 325 ppm or more, 350 ppm or more, 375 ppm or more, 400 ppm or more, 425 ppm or more, 450 ppm or more, 475 ppm or more, 500 ppm or more, 525 ppm or more, 550 ppm or more, 575 ppm or more, 600 ppm or more ppm or higher, 625 ppm or higher, 650 ppm or higher, 675 ppm or higher, 700 ppm or higher, 725 ppm or higher, 750 ppm or higher, 775 ppm or higher, 800 ppm or higher, 825 ppm or higher, 850 ppm or higher, 875 ppm or higher, 900 ppm or higher, 925 ppm or higher, 950 ppm or higher, or 975 ppm or higher, and also 20,000 ppm or less, 19,500 ppm or less, 19,000 ppm or less, 18,500ppm or less, 18,000ppm or less, 17,500ppm or less, 17,000ppm or less, 16,500ppm or less, 16,000ppm or less, 15,500ppm or less, 15,000ppm or less , 14,500ppm or less, 14,000ppm or less, 13,500ppm or less, 13,000ppm or less, 12,500ppm or less, 12,000ppm or less, 11,500ppm or less, 11,000ppm or less The content may be 10,500 ppm or less, 10,000 ppm or less, 9,500 ppm or less, 9,000 ppm or less, 8,500 ppm or less, 8,000 ppm or less, 7,500 ppm or less, 7,000 ppm or less, 6,500 ppm or less, 6,000 ppm or less, 5,500 ppm or less, 5,000 ppm or less, 4,500 ppm or less, 4,000 ppm or less, 3,500 ppm or less, or 3,000 ppm or less. When the positive electrode active material contains S element in the above-mentioned amounts, it is possible to prevent the surface modification portion from becoming unnecessarily thick, thereby preventing a decrease in lithium ion mobility due to the surface modification portion and preventing a decrease in electrochemical properties.

[0055] According to one embodiment of the present invention, when the distance between the outermost surface (OSM) of the positive electrode active material including the surface modification portion and the interface (ICP) between the surface modification portion and the surface of the particles is A, the point (A) is 50% of the distance A. 50 Based on ), the point (A) is 50% of the distance A from the outermost surface (OSC) of the positive electrode active material including the surface modification portion confirmed by XPS analysis. 50 The region between (OSM-A) 50 The concentration of element S at the point where it becomes 50% of the concentration at distance A (A 50 ) and the region between the interface (ICP) between the surface modified portion and the surface of the particle (A 50 The concentration of element S may be higher than that of -ICP. As a specific example, at a point that is 50% of the distance A (A 50 ) and the region between the interface (ICP) between the surface modified portion and the surface of the particle (A 50 The concentration of element S at -ICP) is at the point (A) where it is 50% of the distance A. 50 The concentration gradient may be such that it gradually decreases from the surface of the particles toward the interface (ICP). By adjusting the concentration of element S in the surface modification portion as described above, the degree of sulfidation at the contact point with the sulfide-based solid electrolyte is increased, and the control of side reactions can be maximized.

[0056] According to one embodiment of the present invention, the positive electrode active material 100' may include a coating portion 121 present on at least a part of the surface of the particles. The coating portion may include a residual lithium compound present on the surface of the lithium transition metal composite oxide particles. Furthermore, the coating portion may originate from a coating portion previously formed on the lithium transition metal composite oxide particles before the formation of a surface modification portion on the surface of the lithium transition metal composite oxide particles. As a specific example, the coating portion may include one or more selected from the group consisting of Li2CO3, LiOH, and a compound represented by the following chemical formula 3. The Li2CO3 and LiOH may originate from a residual lithium compound, and the compound represented by the following chemical formula 3 may be a component included in the coating portion previously formed on the surface of the lithium transition metal composite oxide particles.

[0057] [Chemical Formula 3] Li m M 3 n O (m+o) / 2

[0058] In Chemical Formula 3 above, M 3 is one or more selected from the group consisting of Nb, B, P, W, Ti, Ta, Sn, Zr, and Al, 1 ≦ m ≦ 10, 1 ≦ n ≦ 10, and o is the oxidation number of M 3 .

[0059] According to an embodiment of the present invention, the surface modification part may be formed in the presence of the coating part, whereby the surface modification part 122 can exist on at least a part of the surface of the coating part 121. As a specific example, when the coating part is formed on a part of the surface of the lithium transition metal compound particles, the surface modification part can exist on the surface of the lithium transition metal compound particles where the coating part is not formed and / or on at least a part or all of the surface of the coating part. Further, the surface modification part may exist only on the surface of the lithium transition metal compound particles where the coating part is not formed, or may exist only on at least a part or all of the surface of the coating part. Also, when the coating part is formed on the entire surface of the lithium transition metal compound particles, the surface modification part can exist on at least a part or all of the coating part. The formation position of the surface modification part as described above can be adjusted by adjusting the reaction conditions during the formation of the surface modification part.

[0060] According to an embodiment of the present invention, the positive electrode active material may not contain a bond (S-P) between S element and P element. Here, not containing a bond (S-P) between S element and P element may mean not containing an S-P bond formed by an artificial reaction. For example, when applying Li3PO4 as the coating part, it means that the P atom of the coating part does not bond with the S atom of the surface modification part.

[0061] According to an embodiment of the present invention, the lithium transition metal composite oxide particles may be one or more selected from the group consisting of single crystal single particles, polycrystalline single particles, and secondary particles formed by aggregation of a plurality of primary particles. Thus, the positive electrode active material can also include single particles and / or secondary particles formed by aggregation of a plurality of primary particles. The single crystal single particles and polycrystalline single particles mean that the lithium transition metal composite oxide particles are in the form of single particles (single particle), and single crystal and polycrystalline can be classified into crystals classified by grain boundaries (grain boundary) in the single particle. Single crystal single particles may mean that there are no grain boundaries in the single particle, and polycrystalline single particles may mean that there are grain boundaries in the single particle and a plurality of crystals form one particle. Also, the secondary particles formed by aggregation of the plurality of primary particles can include all forms of secondary particles formed by aggregation of two or more primary particles.

[0062] According to an embodiment of the present invention, the lithium transition metal composite oxide particles may have an average composition represented by the following Chemical Formula 4. That is, the lithium transition metal composite oxide may be a high-nickel lithium transition metal composite oxide.

[0063] [Chemical Formula 4] Li p Ni q Co r M 4 s M 5 t O2

[0064] In Chemical Formula 4, M 4is Mn, Al, or a combination thereof, and M 5 includes one or more selected from the group consisting of Nb, Ta, B, Zr, Cr, and W, where 0.8 ≦ p ≦ 1.3, 0 < q < 1, 0 < r < 1, 0 < s < 1, 0 ≦ t ≦ 0.2, and q + r + s + t = 1.

[0065] According to one embodiment of the present invention, in the chemical formula 4, M 5 may be a doping element that can be included in the lithium transition metal composite oxide and can be appropriately selected as needed.

[0066] According to one embodiment of the present invention, in the chemical formula 4, p is the molar ratio of lithium to the transition metal in the lithium transition metal composite oxide and may be 0.8 or more, 0.85 or more, 0.90 or more, 0.95 or more, or 1.0 or more, and may also be 1.3 or less, 1.25 or less, 1.2 or less, 1.15 or less, 1.1 or less, 1.05 or less, or 1.03 or less.

[0067] According to one embodiment of the present invention, in the chemical formula 1, q, r, s, and t are each the molar fraction with respect to nickel (Ni), cobalt (Co), M 4 and M 5 [[ID=二十]]may be the molar fraction of the transition metal. As a specific example, q may be 0.8 or more as the molar fraction with respect to nickel (Ni) among the transition metals, and may also be less than 1.0, 0.99 or less, 0.98 or less, 0.97 or less, 0.96 or less, 0.95 or less, 0.94 or less, 0.93 or less, 0.92 or less, 0.91 or less, 0.90 or less, 0.89 or less, 0.88 or less, 0.87 or less, 0.86 or less, 0.85 or less, 0.84 or less, or 0.83 or less. Also, r may be more than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more as the molar fraction with respect to cobalt (Co) among the transition metals, and may also be less than 0.40, 0.30 or less, 0.20 or less, or 0.10 or less. s is the molar fraction of M among the transition metals 4The mole fraction of may be greater than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more, and may also be less than 0.40, 0.30 or less, 0.20 or less, or 0.10 or less. The above t is M among the transition metals. 5 The mole fraction relative to 0 can be 0, 0.01 or higher, 0.02 or higher, 0.03 or higher, 0.04 or higher, 0.05 or higher, 0.06 or higher, 0.07 or higher, 0.08 or higher, 0.09 or higher, 0.10 or higher, 0.11 or higher, 0.12 or higher, 0.13 or higher, 0.14 or higher, 0.15 or higher, 0.16 or higher, 0.17 or higher, 0.18 or higher, or 0.19 or higher. Furthermore, it may also be less than 0.20, 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, 0.02 or less, or 0.01 or less.

[0068] According to one embodiment of the present invention, the positive electrode active material is D 50 The particle size may be 1 μm or more and 20 μm or less. As a specific example, the positive electrode active material is D 50 The size may be 1.0 μm or more, 1.5 μm or more, 2.0 μm or more, 2.5 μm or more, or 3.0 μm or more, and may also be 20.0 μm or less, 19.0 or less, 18.0 or less, 17.0 or less, 16.0 or less, 15.0 or less, 14.0 or less, 13.0 or less, 12.0 or less, 11.0 or less, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, or 6.0 μm or less. 50 This can mean the particle size at the 50% point of the volume cumulative distribution based on particle size measured by a laser diffraction particle size analyzer.

[0069] According to one embodiment of the present invention, the positive electrode active material may have an average particle size of 1 μm or more and 20 μm or less. Specifically, the positive electrode active material may have an average particle size of 1.0 μm or more, 1.5 μm or more, 2.0 μm or more, 2.5 μm or more, or 3.0 μm or more, and may also have an average particle size of 20.0 μm or less, 19.0 or less, 18.0 or less, 17.0 or less, 16.0 or less, 15.0 or less, 14.0 or less, 13.0 or less, 12.0 or less, 11.0 or less, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, or 6.0 μm or less. The average particle size may mean the average particle size calculated by the arithmetic mean of particle diameters measured based on the major axis of particles confirmed from images using a scanning electron microscope.

[0070] The methods for satisfying each of the components of the positive electrode active material described above are not limited, but according to one embodiment of the present invention, the positive electrode active material can be manufactured by heat-treating lithium transition metal composite oxide particles in the presence of sulfur (S) powder. In this case, since the surface modification is carried out by depositing sulfur (S) derived from the sulfur (S) powder onto the surface of the lithium transition metal composite oxide particles in a gaseous state, a very uniform and thin surface modification can be formed.

[0071] According to one embodiment of the present invention, the heat treatment can be carried out using a furnace after mixing lithium transition metal composite oxide particles and sulfur powder in a crucible. Here, the sulfur powder can react with the surface of the lithium transition metal composite oxide particles while changing state to sulfur gas. If the lithium transition metal composite oxide includes a coating, the sulfur gas can react with the surface of the lithium transition metal composite oxide particles or the coating. The surface modified portion thus formed does not form a large concentration gradient because the chemical potential of the sulfide-based solid electrolyte and lithium ions are similar, and excellent compatibility can be imparted to the interface between the positive electrode active material and the sulfide-based solid electrolyte. Furthermore, the surface modified portion not only protects the positive electrode active material itself, but can also control side reactions.

[0072] According to one embodiment of the present invention, the sulfur powder used during the heat treatment may have a purity of 99.50% or higher, 99.60% or higher, 99.70% or higher, 99.80% or higher, 99.90% or higher, 99.95% or higher, or 99.99% or higher. In this case, the high purity minimizes side reactions during the heat treatment.

[0073] According to one embodiment of the present invention, the heat treatment can be carried out at a temperature of 150°C or higher and 450°C or lower. Specifically, the heat treatment can be carried out at a temperature of 150°C or higher, 160°C or higher, 170°C or higher, 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, 250°C or higher, 260°C or higher, 270°C or higher, 280°C or higher, or 290°C or higher, and can also be carried out at a temperature of 450°C or lower, 440°C or lower, 430°C or lower, 420°C or lower, 410°C or lower, 400°C or lower, 390°C or lower, 380°C or lower, 370°C or lower, 360°C or lower, 350°C or lower, 340°C or lower, 330°C or lower, 320°C or lower, or 310°C or lower. When the heat treatment temperature is adjusted within the aforementioned range, unintended side reactions can be minimized when sulfur (S) is introduced to the surface of the lithium transition metal composite oxide to form a surface modification layer.

[0074] According to one embodiment of the present invention, the heat treatment can be carried out for a time of 1 hour or more, 1 hour 30 minutes or more, 2 hours or more, 2 hours 30 minutes or more, 3 hours or more, or 3 hours 30 minutes or more, and can also be carried out for a time of 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, or 5 hours or less. When the heat treatment time is adjusted within the above range, unintended side reactions can be minimized when sulfur (S) is introduced to the surface of the lithium transition metal composite oxide to form a surface modification.

[0075] The positive electrode active material of the present invention can improve the performance of the positive electrode active material in all-solid-state lithium secondary batteries containing a sulfide-based solid electrolyte by surface modification using sulfur (S). Needless to say, this reduces costs compared to using expensive coating materials, and the coating process can be eliminated or minimized, thereby improving productivity. In particular, in lithium secondary batteries using a liquid electrolyte, the interface of the positive electrode active material can be controlled by adjusting the surface modification, similar to controlling the interfacial SEI with electrolyte additives.

[0076] positive electrode The present invention provides a positive electrode containing the above-described positive electrode active material.

[0077] According to one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material.

[0078] According to one embodiment of the present invention, the positive electrode current collector can contain a highly conductive metal, is not particularly limited as long as the positive electrode active material layer adheres easily to it, and is unreactive within the battery voltage range. As a specific example, the positive electrode current collector can be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment using carbon, nickel, titanium, silver, etc. The positive electrode current collector can also have a thickness of about 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector, or the adhesion strength of the positive electrode active material can be increased by surface treatment. Furthermore, the positive electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric, etc.

[0079] According to one embodiment of the present invention, the positive electrode active material layer may selectively include a solid electrolyte, a binder, and a conductive material together with the positive electrode active material. Here, the positive electrode active material may be included in an amount of 80% to 99% by weight relative to the total weight of the positive electrode active material layer, and within this range, excellent capacity characteristics and improved energy density can be observed.

[0080] According to one embodiment of the present invention, if the positive electrode active material layer includes a solid electrolyte, the solid electrolyte may be the same as or different from the solid electrolyte included in the solid electrolyte layer of an all-solid-state battery. As a specific example, the solid electrolyte included in the positive electrode active material layer may be an argyrodite-type sulfide-based solid electrolyte.

[0081] According to one embodiment of the present invention, if the positive electrode active material layer includes a binder, the binder is a component that helps to bond the components of the positive electrode active material layer, such as the positive electrode active material, solid electrolyte, and conductive material, and may be one or more selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butylene rubber (SBR), and fluororubber.

[0082] According to one embodiment of the present invention, if the positive electrode active material layer includes a conductive material, the conductive material may be one or more selected from the group consisting of: graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as 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.

[0083] Lithium-ion battery The present invention provides a lithium secondary battery including the above-described positive electrode.

[0084] According to one embodiment of the present invention, the lithium secondary battery may be an all-solid-state lithium secondary battery. As a specific example, the lithium secondary battery may include the positive electrode 10, the negative electrode 20, and a solid electrolyte layer 30 interposed between the positive electrode 10 and the negative electrode 20.

[0085] According to one embodiment of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector.

[0086] According to one embodiment of the present invention, the negative electrode current collector can contain a highly conductive metal, and the negative electrode active material layer can adhere to it easily, but it is not particularly limited as long as it is not reactive within the battery voltage range. As a specific example, the negative electrode current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment using carbon, nickel, titanium, silver, etc. Furthermore, the negative electrode current collector can have a thickness of 3 μm to 500 μm, and the bonding strength of the negative electrode active material can be increased by forming fine irregularities on the surface of the current collector or by surface treatment. In addition, the negative electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric, etc.

[0087] According to one embodiment of the present invention, the negative electrode active material layer may selectively include a solid electrolyte, a binder, and a conductive material together with the negative electrode active material.

[0088] According to one embodiment of the present invention, the negative electrode active material can be a compound capable of reversible intercalation and deintercalation of lithium. Specifically, the negative electrode active material layer may include one or more negative electrode active materials selected from the group consisting of carbon-based negative electrode active materials, silicon-based negative electrode active materials, and lithium metal negative electrode active materials. More specifically, the negative electrode active material may be a carbon-based negative electrode active material such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon; Si, Si alloys, and SiO xSilicone-based negative electrode active materials such as (0 < x < 2); metallic compounds capable of alloying with lithium such as Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; metal oxides such as SnO2, vanadium oxides, lithium vanadium oxides that can dope and undope lithium; or composites containing the above metallic compounds and carbonaceous materials such as Si-C composites or Sn-C composites, etc. may be mentioned, and any one or a mixture of two or more of these can be used. Further, as the negative electrode active material, a lithium metal thin film which is a lithium negative electrode active material may be used. Also, as the carbon-based negative electrode active material, both low-crystalline carbon and high-crystalline carbon can be used. Examples of low-crystalline carbon include soft carbon and hard carbon, and examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural graphite 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. The negative electrode active material can be contained in a content of 80% to 99% by weight based on the total weight of the negative electrode active material layer, and within this range, excellent capacity characteristics and improved energy density can be exhibited.

[0089] According to one embodiment of the present invention, when the negative electrode active material layer contains a solid electrolyte, the solid electrolyte may be the same as or different from the solid electrolyte contained in the solid electrolyte layer of the all-solid-state battery. As a specific example, the solid electrolyte contained in the negative electrode active material layer may be an argyrodite-type sulfide-based solid electrolyte.

[0090] According to one embodiment of the present invention, if the negative electrode active material layer includes a binder, the binder is a component that helps to bond the components of the negative electrode active material layer, such as the positive electrode active material, solid electrolyte, and conductive material, and may be one or more selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butylene rubber (SBR), and fluororubber.

[0091] According to one embodiment of the present invention, if the negative electrode active material layer includes a conductive material, the conductive material only needs to be conductive and not cause a chemical change in the all-solid-state lithium secondary battery. Specific examples include one or more conductive materials selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as 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.

[0092] According to one embodiment of the present invention, the solid electrolyte layer may contain a sulfide-based solid electrolyte and may selectively contain a binder together with the solid electrolyte.

[0093] According to one embodiment of the present invention, the solid electrolyte of the solid electrolyte layer may be the same as, or different from, the solid electrolyte that may be included in the negative electrode active material layer and / or positive electrode active material layer. As a specific example, the solid electrolyte included in the solid electrolyte layer may be one or more selected from the group consisting of sulfide-based solid electrolytes, oxide-based solid electrolytes, chloride-based solid electrolytes and polymer solid electrolytes, and as a more specific example, it may be an argyrodite-type sulfide-based solid electrolyte.

[0094] According to one embodiment of the present invention, if the solid electrolyte layer includes a binder, the binder is a component that helps to bond the solid electrolytes together and may be one or more selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butylene rubber (SBR), and fluororubber.

[0095] Lithium secondary batteries containing the positive electrode active material according to the present invention exhibit excellent capacity characteristics, power characteristics, and life characteristics in a stable manner, making them particularly useful in the field of electric vehicles, such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0096] The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, rectangular, pouch-type, or coin-type using a can. Furthermore, the lithium secondary battery can be used as a unit battery in a medium-to-large battery module containing a large number of battery cells. Accordingly, the present invention provides a battery module that includes the lithium secondary battery as a unit cell and a battery pack that includes the same.

[0097] According to one embodiment of the present invention, the battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0098] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0099] Examples and Comparative Examples Example 1 Solid-phase sulfur (99.998% purity) was pulverized to prepare fine sulfur powder. The prepared sulfur powder and LiNi 0.8 Co 0.1 Mn 0.1 It has the composition of O2, D 50 The particles were 3 μm in size, and the lithium transition metal composite oxide in secondary particle form was mixed using a mixer mill (Retsch MM400) at approximately 30 Hz for approximately 3 minutes to obtain a mixture. Here, 0.05 parts by weight of sulfur powder was mixed with 100 parts by weight of the lithium transition metal composite oxide.

[0100] The mixture was placed in a sealed tube under an argon atmosphere and heat-treated at approximately 300°C for approximately 4 hours to produce a positive electrode active material in which surface-modified portions were formed on the surface of the particles.

[0101] Example 2 In the same manner as in Example 1, a positive electrode active material having a surface-modified portion formed on the surface of the particles was produced, except that, during the production of the mixture, 0.07 parts by weight of sulfur powder was mixed with 100 parts by weight of lithium transition metal composite oxide instead of 0.05 parts by weight.

[0102] Example 3 In the same manner as in Example 1, a positive electrode active material having a surface-modified portion formed on the surface of the particles was produced, except that, during the production of the mixture, 0.10 parts by weight of sulfur powder was mixed with 100 parts by weight of lithium transition metal composite oxide instead of 0.05 parts by weight.

[0103] Example 4 In the same manner as in Example 1, a positive electrode active material having a surface-modified portion formed on the surface of the particles was produced, except that, during the production of the mixture, 0.30 parts by weight of sulfur powder was mixed with 100 parts by weight of lithium transition metal composite oxide instead of 0.05 parts by weight.

[0104] Example 5 In the same manner as in Example 1, a positive electrode active material having a surface-modified portion formed on the surface of the particles was produced, except that, during the production of the mixture, 0.50 parts by weight of sulfur powder was mixed with 100 parts by weight of lithium transition metal composite oxide instead of 0.05 parts by weight.

[0105] Example 6 In the same manner as in Example 1, a positive electrode active material having a surface-modified portion formed on the surface of the particles was produced, except that, during the production of the mixture, 0.70 parts by weight of sulfur powder was mixed with 100 parts by weight of lithium transition metal composite oxide instead of 0.05 parts by weight.

[0106] Example 7 In the same manner as in Example 1, a positive electrode active material having a surface-modified portion formed on the surface of the particles was produced, except that, during the production of the mixture, 1.00 part by weight of sulfur powder was mixed with 100 parts by weight of lithium transition metal composite oxide instead of 0.05 parts by weight of sulfur powder.

[0107] Example 8 In the same manner as in Example 1, a positive electrode active material having a surface-modified portion formed on the surface of the particles was produced, except that, during the production of the mixture, 1.50 parts by weight of sulfur powder was mixed with 100 parts by weight of lithium transition metal composite oxide instead of 0.05 parts by weight.

[0108] Example 9 A coating solution was prepared by dissolving 0.12 parts by weight of lithium ethoxide (Kojundo, CH3CH2OLi 99.9%) and 0.125 parts by weight of polyphosphoric acid (Aldrich, H3PO4 115%) in approximately 30 ml of reagent alcohol (CH3CH2OH) solvent, so that Li3PO4 was present in a ratio of 0.15 parts by weight per 100 parts by weight of lithium transition metal composite oxide. LiNi 0.8 Co 0.1 Mn 0.1 It has the composition of O2, D 50 The particle size was 3 μm, and approximately 3 g of lithium transition metal composite oxide in secondary particle form was added. Next, the solvent was evaporated by stirring at approximately 70°C. Then, the residual solvent was completely evaporated in a vacuum oven, and the mixture was heat-treated at approximately 400°C for approximately 1 hour to obtain an intermediate in which the surface of the lithium transition metal composite oxide particles was coated with Li3PO4.

[0109] Next, solid-phase sulfur (99.998% purity) was pulverized to prepare fine sulfur powder. The prepared sulfur powder and the intermediate were mixed using a mixer mill (Retsch MM400) at approximately 30 Hz for approximately 3 minutes to obtain a mixture. Here, 0.10 parts by weight of the sulfur powder was mixed with 100 parts by weight of the lithium transition metal composite oxide.

[0110] The mixture was placed in a sealed tube under an argon atmosphere and heat-treated at approximately 300°C for approximately 4 hours to produce a positive electrode active material in which a coating portion and a surface modification portion were formed on the surface of the particles.

[0111] Example 10 In Example 9, a positive electrode active material having a surface-modified portion formed on the surface of the particles was produced in the same manner as in Example 1, except that when producing the mixture, 1.50 parts by weight of sulfur powder was mixed with 100 parts by weight of lithium transition metal composite oxide instead of 0.10 parts by weight of sulfur powder.

[0112] Comparative Example 1 LiRing 0.8 Co 0.1 Mn 0.1 It has the composition of O2, D 50 The particle size was 3 μm, and the lithium transition metal composite oxide in secondary particle form was used directly as the cathode active material.

[0113] Comparative Example 2 The intermediate produced in Example 2 was used directly as the positive electrode active material.

[0114] Experimental Example 1: ICP-OES Analysis ICP-OES analysis was performed on the positive electrode active materials produced in Examples 3 and 8-10 and Comparative Example 1, in accordance with the KS M 2005 general rules for mass spectrometry, under conditions of 18°C ​​and 38% humidity. The content of each element, the increase in sulfur (S) content compared to Comparative Example 1, and the amount of sulfur (S) remaining in the positive electrode active material relative to the amount of sulfur (S) added are shown in Table 1 below.

[0115] [Table 1]

[0116] As shown in Table 1 above, when a surface modification layer is formed using sulfur powder, it was confirmed that a sulfur (S) component can be detected. However, assuming that the surface of the lithium transition metal composite oxide particles is coated with a single substance of sulfur (S), the sulfur (S) content should increase in proportion to the amount of sulfur (S) added. However, it was confirmed that there is a considerable difference between the sulfur (S) content added and the sulfur (S) content remaining in the positive electrode active material. This is presumed to be because, during the formation of the surface modification layer, sulfur (S) does not form a coating layer as a single substance, but rather forms the surface modification layer through a reaction on the surface of the lithium transition metal composite oxide particles, and because no solvent is used, the sulfur (S) does not completely react with the lithium transition metal composite oxide during the heat treatment process, but partially sublimes and disappears.

[0117] These results confirm that even with an increased sulfur (S) content, there is a limit to the reaction on the surface of lithium transition metal composite oxide particles, the rate of sulfur (S) disappearance increases, and the sulfur (S) content that substantially forms the surface modification zone reaches a saturated state at a predetermined level.

[0118] Furthermore, the results from Examples 3 and 8-10 confirmed that the presence or absence of a coating on the surface of lithium transition metal composite oxide particles does not affect the formation of the surface modification.

[0119] Reference Experiment Example 1: TOF-SIMS Analysis To clarify that the presence or absence of a coating on the surface of lithium transition metal composite oxide particles, as confirmed in Experimental Example 1, does not affect the formation of the surface-modified area, surface modification was directly performed on Li3PO4 (Reference Example 1) instead of lithium transition metal composite oxide.

[0120] Specifically, solid-phase sulfur (99.998% purity) was pulverized to prepare fine sulfur powder. The prepared sulfur powder and Li3PO4 were mixed using a mixer mill (Retsch MM400) at approximately 30 Hz for approximately 3 minutes to obtain a mixture. Here, the sulfur powder was mixed with 100 parts by weight of Li3PO4 in amounts of 0.10 parts by weight (Reference Example 2), 1.00 parts by weight (Reference Example 3), and 2.00 parts by weight (Reference Example 4), respectively.

[0121] The mixture was placed in a sealed tube under an argon atmosphere and heat-treated at approximately 300°C for approximately 4 hours to form a sulfur (S) coating layer on the surface of Li3PO4.

[0122] TOF-SIMS analysis was performed on the Li3PO4 and Li3PO4 containing a sulfur (S) coating layer produced in Reference Examples 1-4 using TOFSIMS.5 from ION-TOF (Germany) under analytical conditions of Bi1+, 30 keV, and 1 pA, while sputtering each substance from the surface of the material, and the SO2 content was determined by the sputtering time. - , PO - LiS - and PS - The intensity against ions was measured and is shown in Figures 4 (Reference Example 1), 5 (Reference Example 2), 6 (Reference Example 3), and 7 (Reference Example 4).

[0123] As can be seen from Figures 4 to 7, Reference Examples 2 to 4, which have a sulfur (S) coating layer, are compared to Reference Example 1, with SO - , PO - LiS - and PS - We were able to confirm that there was not much difference in terms of ionic strength. From these results, we were able to confirm that even when a sulfur (S) coating layer is formed on Li3PO4, the sulfur (S) does not react with Li3PO4. This is presumably because the heat treatment using sulfur (S) powder is performed at a relatively low temperature, preventing the sulfur (S) from cleaving the PO bonds of Li3PO4 and forming PS bonds.

[0124] Reference Experiment Example 2: XRD Analysis In addition to Reference Experiment Example 1, XRD analysis was performed on Reference Examples 1-4 using Empyrean from Malvern Panalytical, and the results are shown in Figure 8.

[0125] As can be seen in Figure 8, no peak was observed for sulfur (S), which is the same result as the analysis results in Reference Experiment Example 1.

[0126] Experimental Example 2: XPS Analysis 1 XPS analysis was performed on the positive electrode active materials produced in Examples 3 and 9 and Comparative Examples 1 and 2 using a Thermo Scientific K-Alpha+ under the conditions of Al ka (1486.6 eV), 12KeV / 6 mA, and beam size: 400 μm. The results are shown in Figures 9 (Example 3), 10 (Example 9), 11 (Comparative Example 1), and 12 (Comparative Example 2), and SO3 2- and SO4 2- The intensity and the ratio between them (SO3 2- / SO4 2- The results are shown in Table 2 below.

[0127] [Table 2]

[0128] As shown in Table 2 above, the positive electrode active materials produced in Examples 3 and 9 of the present invention, compared to the positive electrode active materials produced in Comparative Examples 1 and 2, show a difference in SO3 due to surface modification. 2- and SO4 2- We were able to confirm that the intensity of the compound increased. From these results, we were able to confirm that the positive electrode active material produced in the examples of the present invention contains compounds represented by chemical formulas 1 and 2.

[0129] Experimental Example 3: TOF-SIMS Analysis 1 TOF-SIMS analysis was performed on the positive electrode active materials produced in Examples 3 and 9 and Comparative Examples 1 and 2 using the same method as in Reference Experiment Example 1, and NiO was analyzed by sputtering from the surface of each positive electrode active material while considering the sputtering time. - , SO - , PO - LiS - and PS - The intensity against ions was measured and is shown in Figure 13 (Example 3), Figure 14 (Example 9), Figure 15 (Comparative Example 1), and Figure 16 (Comparative Example 2). Also, S - HS - , SO - SO2 - and SO3 - For each ion, the intensity of each ion was calculated using the following method, and this was indexed relative to Comparative Example 1 for Example 3, and relative to Comparative Example 2 for Example 9, and SO3 - and SO2 - The ratio (SO3 - / SO2 - ), and SO - and SO3 - The ratio (SO - / SO3 - The results are shown in Table 3 below.

[0130] [Table 3]

[0131] As can be seen from Figures 13 to 16, in Examples 3 and 9, where a surface modification was formed using sulfur (S), SO was used on the surface. - and LiS - Ions were detected with high intensity, and in Example 9 and Comparative Example 2, which included the Li3PO4 coating, PO - Ions were detected with high intensity. However, as confirmed from Reference Experiment Example 1 above, in Example 9, PS - No ions were detected.

[0132] Furthermore, as shown in Table 3, in Examples 3 and 9, where a surface modification was formed using sulfur (S),- HS - , SO - SO2 - and SO3 - We were able to confirm that the ion intensity increased significantly compared to Comparative Examples 1 and 2, respectively.

[0133] Experimental Example 4: TOF-SIMS Analysis 2 TOF-SIMS analysis was performed on the positive electrode active materials produced in Examples 3 and 9 and Comparative Examples 1 and 2 using TOFSIMS.5 from ION-TOF (Germany) under analytical conditions of Bi1+, 30 keV, and 1 pA. The results are shown in Figures 17 (Example 3), 18 (Example 9), 19 (Comparative Example 1), and 20 (Comparative Example 2), and SO3 - and SO4 - The mass-to-charge ratio (Peak M / Z, ±0.03) for each peak, the intensity of the peak area, and SO3 - SO4 for peak area - The ratio of peak areas is shown in Table 4 below.

[0134] [Table 4]

[0135] As shown in Table 4 above, the positive electrode active materials produced in Examples 3 and 9 of the present invention differ from those produced in Comparative Examples 1 and 2 in terms of SO3 - SO4 - We were able to confirm that the peak area decreased significantly. Therefore, when forming a surface modification using sulfur (S), SO4 - SO3 - We were able to confirm that it was formed in a well-balanced ratio.

[0136] Experimental Example 5: XPS Depth Analysis XPS depth analysis was performed on the positive electrode active materials produced in Examples 3, 8, and 9, and Comparative Examples 1 and 2, using a Thermo Scientific K-Alpha+ with the following conditions: Sputter ion gun (Ar+): 1 keV, analytical conditions Al ka (1486.6 eV) 12 KeV / 6 mA, and beam size: 400 μm. The results are shown in Figures 21 (Example 3), 22 (Example 8), 23 (Example 9), 24 (Comparative Example 1), and 25 (Comparative Example 2).

[0137] As can be seen from Figures 21 to 25, in Examples 3, 8, and 9, in which sulfur (S) was used to form the surface modification, it was confirmed that the reaction product of sulfur (S) was formed at a shallow depth from the surface. In particular, from Figures 22 and 23, when the distance A is the outermost surface (OSM) of the positive electrode active material including the surface modification and the interface (ICP) between the surface modification and the surface of the particles, the point (A) that is 50% of distance A 50 Based on ), the point (A) is 50% of the distance A from the outermost surface (OSC) of the positive electrode active material including the surface modification portion confirmed by XPS analysis. 50 The region between (OSM-A) 50 The concentration of element S at the point where it becomes 50% of the concentration at distance A (A 50 ) and the region between the interface (ICP) between the surface modified portion and the surface of the particle (A 50 It was confirmed that the concentration of element S was higher than that of -ICP. Furthermore, at the point (A) which is 50% of the aforementioned distance A 50 ) and the region between the interface (ICP) between the surface modified portion and the surface of the particle (A 50 The concentration of element S at -ICP) is at the point (A) where it is 50% of the distance A. 50 It was confirmed that the concentration gradient gradually decreases from the surface of the particle in the direction of the intercellular interface (ICP).

[0138] Experimental Example 6: Evaluation of Cell Characteristics 1 Using the positive electrode active materials produced in Examples 3 and 9 and Comparative Example 1, a solid electrolyte and conductive material with a Li6PS5Cl composition were prepared in a ratio of 62:37:1, and a positive electrode was fabricated using an Al foil current collector. A lithium metal foil was used as the negative electrode, and a cell was fabricated using a solid electrolyte with a Li6PS5Cl composition as the solid electrolyte layer.

[0139] Using the manufactured cells, they were charged to 4.3V with a constant current of 0.1C in CC / CV mode at 25°C, then discharged to 2.5V at 0.1C. The initial charge capacity and initial discharge capacity were measured, and the efficiency was calculated. Next, charge-discharge cycles were performed at 0.1C for the first 3 cycles, 0.2C for the 4th to 6th cycles, 0.33C for the 7th to 9th cycles, 0.5C for the 10th to 12th cycles, 1.0C for the 13th to 15th cycles, 2.0C for the 16th to 19th cycles, and then at 0.5C for 100 cycles from the 20th cycle onward. The DC resistance at 2 charge-discharge cycles, the rate-limiting characteristics at each rate-limiting cycle, and the rate-limiting characteristics and maintenance rate at 100 cycles were calculated and are shown in Table 5 below.

[0140] [Table 5]

[0141] As shown in Table 5 above, it was confirmed that the all-solid-state lithium secondary batteries containing the positive electrode active material manufactured in Examples 3 and 9 of the present invention showed significant improvements in discharge capacity, efficiency, DC resistance, rate-limiting characteristics, and capacity retention rate.

[0142] Experimental Example 7: Evaluation of Cell Characteristics 2 Using the positive electrode active materials produced in Examples 1, 2 and 4-8, a cell was manufactured in the same manner as in Experimental Example 6.

[0143] Next, the cell characteristics were measured using the same method as in Experimental Example 6, and the results, along with those for Example 3 and Comparative Example 1, are shown in Tables 6 and 7 below. The discharge capacity is shown in Figure 26, and the DC resistance in Figure 27.

[0144] [Table 6]

[0145] [Table 7]

[0146] As shown in Tables 6 and 7 above, it was confirmed that the all-solid-state lithium secondary batteries containing the positive electrode active material manufactured in Examples 1 to 8 of the present invention all showed significant improvements in discharge capacity, efficiency, DC resistance, rate-limiting characteristics, and capacity retention rate. In particular, it was confirmed that the all-solid-state lithium secondary batteries containing the positive electrode active material manufactured in Examples 1 to 3 had excellent discharge capacity and DC resistance.

[0147] Experimental Example 8: Evaluation of Rate-Determining Characteristics Using the positive electrode active material produced in Comparative Example 2, a cell was manufactured in the same manner as in Experimental Example 6.

[0148] Next, using the cells containing the positive electrode active material produced in Examples 3 and 9 manufactured in Experimental Example 6, the cells containing the positive electrode active material produced in Comparative Example 1, and the cells containing the positive electrode active material produced in Comparative Example 2, charging and discharging were performed at 25°C in CC / CV mode at 10 mA / g for the first 3 charge-discharge cycles, 20 mA / g for the 4th to 6th charge-discharge cycles, 60 mA / g for the 7th to 11th charge-discharge cycles, 100 mA / g for the 12th to 16th charge-discharge cycles, 200 mA / g for the 17th to 21st charge-discharge cycles, and 10 mA / g for the 22nd to 24th charge-discharge cycles. The specific capacity (mAh / g) for each charge-discharge cycle is shown in Figure 28. The initial charge-discharge capacity during the above charging and discharging is shown in Figure 29.

[0149] As can be seen from Figures 28 and 29, the positive electrode active material produced in Example 3 showed improved initial capacity and rate-limiting characteristics compared to the positive electrode active material produced in Comparative Example 1, and also showed improved rate-limiting characteristics compared to Comparative Example 2, which included a Li3PO4 coating. In particular, the positive electrode active material produced in Example 9, which included a Li3PO4 coating and also included a surface modification portion, showed improved initial capacity and rate-limiting characteristics compared to the positive electrode active material produced in Comparative Example 2.

[0150] Experimental Example 9: GITT (Galvanostatic Intermittent Titration Technique) Analysis Using the cells containing the positive electrode active material from Examples 3 and 9 produced in Experimental Example 6, the cells containing the positive electrode active material from Comparative Example 1, and the cells containing the positive electrode active material from Comparative Example 2 produced in Experimental Example 8, a charge-discharge cycle was performed for 300 cycles at 25°C in CC / CV mode, where each cycle consisted of charging to 4.32V with a constant current of 3C and then discharging to 2.52V with 3C.

[0151] GITT analysis was performed under the conditions of 0.1C, 10 minutes of pulse, and 60 minutes of rest, and the results are shown in Figure 30.

[0152] As can be seen from Figure 30, the positive electrode active materials produced in Examples 3 and 9 of the present invention showed higher lithium-ion diffusion compared to Comparative Examples 1 and 2 throughout the entire period in which the charging pulse was applied. In particular, this difference in lithium-ion diffusion was maximized in the high-voltage region (4.1V to 4.3V).

[0153] Experimental Example 10: Evaluation of Lifetime Characteristics 1 Using the cells containing the positive electrode active material from Examples 3 and 9 produced in Experimental Example 6, the cells containing the positive electrode active material from Comparative Example 1, and the cells containing the positive electrode active material from Comparative Example 2 produced in Experimental Example 8, a charge-discharge cycle was performed for 300 cycles at 25°C in CC / CV mode, where each cycle consisted of charging to 4.32V with a constant current of 3C and then discharging to 2.52V with 3C. The specific capacity (mAh / g) for each charge-discharge cycle is shown in Figure 31.

[0154] As can be seen from Figure 31, the all-solid-state lithium secondary batteries containing the positive electrode active material produced in Examples 3 and 9 showed higher specific capacities throughout the entire range compared to Comparative Examples 1 and 2. In particular, it was confirmed that the all-solid-state lithium secondary battery containing the positive electrode active material produced in Example 9 showed a significant improvement in specific capacity.

[0155] Experimental Example 11: Evaluation of Lifetime Characteristics 2 Using the cells containing the positive electrode active material from Examples 3 and 9 produced in Experimental Example 6, the cells containing the positive electrode active material from Comparative Example 1, and the cells containing the positive electrode active material from Comparative Example 2 produced in Experimental Example 8, a charge-discharge cycle was performed for 300 cycles at 25°C in CC / CV mode, where each cycle consisted of charging to 4.32V with a constant current of 3C and then discharging to 2.52V with 3C.

[0156] After 300 charge-discharge cycles were completed, the cell was disassembled and the positive electrode active material was separated. For each positive electrode active material obtained from the cell in Examples 3 and 9, and Comparative Examples 1 and 2, the positive electrode was cut using a Focused Ion Beam (FIB), and then imaged using a Transmission Electron Microscope (TEM). The TEM images of each positive electrode active material are shown in Figure 32 (Example 3), Figure 33 (Example 9), Figure 34 (Comparative Example 1), and Figure 35 (Comparative Example 2).

[0157] As can be seen from Figures 32 to 35, the positive electrode active materials produced in Examples 3 and 9, by including the surface modification portion, showed reduced surface degradation compared to the positive electrode active materials produced in Comparative Examples 1 and 2, respectively.

[0158] These results confirm that the positive electrode active material of the present invention, by including a surface-modified portion in which interfacial reaction products are artificially formed with sulfur (S) on the surface of lithium transition metal composite oxide particles, can suppress side reactions between the positive electrode active material and the sulfide-based solid electrolyte, improve compatibility, and thereby improve the lifespan and rate-limiting performance of all-solid-state lithium secondary batteries. [Explanation of Symbols]

[0159] 10 positive electrode 20 negative electrode 30 Solid electrolyte layer 100, 100' positive electrode active material 110, 110' Lithium transition metal composite oxide particles 120, 122 Surface modification section 121 Coating section

Claims

1. Lithium transition metal composite oxide particles, The particle includes a surface modification portion present on at least a portion of the surface of the particle, The surface-modified portion comprises a positive electrode active material containing a compound represented by the following chemical formula 1. [Chemical formula 1] M １ ａ M ２ ｂ (SO ３ ) ｃ In the aforementioned chemical formula 1, M １ It includes one or more elements selected from the group consisting of Li, B, P, Nb, Zr, Al, Ti, and Ta. M ２ It includes one or more elements selected from the group consisting of Ni, Co, Mn, and Fe. 0 ≤ a ≤ 2, 0 ≤ b ≤ 4, 1 ≤ c ≤ 4, and at least one of a and b is not 0.

2. The positive electrode active material according to claim 1, wherein the surface modified portion contains a compound represented by the following chemical formula 2. [Chemical formula 2] M １ ａ’ M ２ ｂ’ (SO ｘ ) ｃ’ In the aforementioned chemical formula 2, M １ It includes one or more elements selected from the group consisting of Li, B, P, Nb, Zr, Al, Ti, and Ta. M ２ It includes one or more elements selected from the group consisting of Ni, Co, Mn, and Fe. 0 ≤ a' ≤ 2, 0 ≤ b' ≤ 4, 1 ≤ c' ≤ 4, and at least one of a' and b' is not 0, and 1 ≤ x < 3 or 3 < x ≤ 10.

3. The surface modification portion is M １ M for ２ The positive electrode active material according to claim 1, wherein the molar ratio satisfies the following formula 1. [Formula 1] 0<[M ２ ] / [M １ ]≦0.5 In the above formula 1, M １ It includes one or more elements selected from the group consisting of Li, B, P, Nb, Zr, Al, Ti, and Ta. M ２ This includes one or more elements selected from the group consisting of Ni, Co, and Mn.

4. The positive electrode active material according to claim 1, wherein the surface modified portion contains a metal sulfide.

5. The positive electrode active material according to claim 1, wherein the surface modified portion contains the compound represented by chemical formula 1 in the highest content among the components containing element S.

6. The positive electrode active material according to claim 1, wherein the sulfur content, as confirmed by ICP-OES analysis, is 200 ppm or more and 20,000 ppm or less.

7. When the distance between the outermost surface (OSM) of the positive electrode active material including the surface modification portion and the interface (ICP) between the surface modification portion and the surface of the particles is A, the point at which the distance A is 50% (A ５０ Based on this, the point (A) is 50% of the distance A from the outermost surface (OSC) of the positive electrode active material including the surface modification portion confirmed by XPS analysis. ５０ The region between (OSM-A) ５０ The concentration of element S at the point where it becomes 50% of the concentration at distance A (A ５０ ) and the region between the interface (ICP) between the surface modified portion and the surface of the particle (A ５０ The positive electrode active material according to claim 1, wherein the concentration of S element is higher than that of ICP.

8. The point that is 50% of the aforementioned distance A (A ５０ ) and the region between the interface (ICP) between the surface modified portion and the surface of the particle (A ５０ -ICP) The concentration of element S is at the point (A) where it is 50% of the distance A. ５０ The positive electrode active material according to claim 7, having a concentration gradient that gradually decreases from the surface of the particles in the direction of the interface (ICP).

9. The positive electrode active material according to claim 1, wherein the positive electrode active material includes a coating portion present on at least a portion of the surface of the particles.

10. The coating portion is Li ２ CO ３ The positive electrode active material according to claim 9, comprising one or more selected from the group consisting of LiOH and a compound represented by the following chemical formula 3. [Chemical formula 3] Li ｍ M ３ ｎ O （ｍ＋ｏ）／２ In the aforementioned chemical formula 3, M ３ is one or more selected from the group consisting of Nb, B, P, W, Ti, Ta, Sn, Zr, and Al. 1 ≤ m ≤ 10, 1 ≤ n ≤ 10, and o is M ３ This is the oxidation number of [the substance].

11. The positive electrode active material according to claim 9, wherein the surface modification portion is present in at least a part of the surface of the coating portion.

12. The positive electrode active material according to claim 1, wherein the positive electrode active material does not contain a bond between an S element and a P element (S-P).

13. The positive electrode active material according to claim 1, wherein the lithium transition metal composite oxide particles are one or more selected from the group consisting of single crystal single particles, polycrystalline single particles, and secondary particles formed by the aggregation of multiple primary particles.

14. The positive electrode active material according to claim 1, wherein the lithium transition metal composite oxide particles have an average composition represented by the following chemical formula 4. [Chemical formula 4] Li ｐ Ni ｑ Co ｒ M ４ ｓ M ５ ｔ O ２ In the aforementioned chemical formula 4, M ４ These are Mn, Al, or a combination thereof. M ５ It includes one or more elements selected from the group consisting of Nb, Ta, B, Zr, Cr, and W. 0.8 ≤ p ≤ 1.3, 0 < q < 1, 0 < r < 1, 0 < s < 1, 0 ≤ t ≤ 0.2, and q + r + s + t = 1.

15. The positive electrode active material according to claim 14, wherein 0.8 ≤ q < 1, 0 < r ≤ 0.2, 0 < s ≤ 0.2, and 0 ≤ t ≤ 0.

1.

16. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 15.

17. A lithium secondary battery comprising the positive electrode described in claim 16.

18. The lithium secondary battery according to claim 17, comprising the positive electrode, the negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode.

19. The lithium secondary battery according to claim 18, wherein the solid electrolyte layer comprises a sulfide-based solid electrolyte.

20. The lithium secondary battery according to claim 19, wherein the sulfide-based solid electrolyte includes an argyrodite-type sulfide-based solid electrolyte.

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