Positive electrode active materials for secondary batteries

Abstract

The present invention relates to a positive electrode active material for a secondary battery, and the positive electrode active material has a structure in which a shell composed of niobium oxide containing a portion of an alkaline earth metal is adsorbed on the surface of a core containing lithium metal oxide, thereby reducing a void phenomenon that may occur between the positive electrode active material and a solid electrolyte and a side reaction between them, and suppressing an increase in electrode resistance due to charging and discharging, thereby improving the life of a secondary battery including the same.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0149123 dated November 2, 2021 and Korean Patent Application No. 10-2022-0143856 dated November 1, 2022, and all contents disclosed in the documents of the relevant Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material for a secondary battery. [Background technology]

[0003] All-solid-state lithium batteries use sulfide-based or oxide-based solid electrolytes and can directly convert chemical energy into electrical energy by oxidizing or reducing lithium ions through the all-solid-state material. Demand for these batteries is growing as they are environmentally friendly, safe, and offer high energy density and capacity storage, which overcomes the limitations of currently used lithium secondary batteries, such as low energy density, high cost, and toxicity.

[0004] However, all-solid-state batteries are facing problems such as irreversibility due to side reactions at the interface between the sulfide-based or oxide-based solid electrolyte and the positive electrode during charge and discharge reactions, and a decrease in battery capacity due to interface resistance and uneven distribution of electrode charge due to space-charge layer formation.In addition, the low ionic conductivity of all-solid-state materials themselves is hindering the commercialization of next-generation lithium all-solid-state batteries.

[0005] To address these issues, cathode active materials using metal oxides as a medium have been developed. However, while the cathode active materials developed to date have significantly improved charge / discharge performance compared to oxide-based cathode active materials, they also suffer from increased resistance as charge / discharge cycles progress, significantly reducing capacity retention compared to existing cathode active materials or anode active materials.

[0006] In addition, a technology has been developed in which the surface of the positive electrode active material is treated with metal oxides or the like and applied to all-solid-state batteries, but this also has a negligible effect on improving charge / discharge performance, and the high unit price of the raw materials used makes it unsuitable for commercialization. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Korean Patent Publication No. 10-1582394 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an object of the present invention is to provide a positive electrode active material for a secondary battery that can prevent the occurrence of a void phenomenon that may occur between a positive electrode active material and a solid electrolyte or the induction of a side reaction between them, and that can suppress an increase in electrode resistance during charge and discharge, thereby improving the lifespan of the battery. [Means for solving the problem]

[0009] To solve the above-mentioned problems, In one embodiment, the present invention comprises: The present invention provides a positive electrode active material for a secondary battery, comprising: a core containing a lithium metal oxide; and a shell adsorbed on the surface of the core and containing a niobium oxide, the niobium oxide containing an alkaline earth metal.

[0010] In addition, the lithium metal oxide provides a positive electrode active material for a secondary battery represented by the following Chemical Formula 1: [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O u In the above Chemical Formula 1, M1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are 1.0≦x≦1.30, 0.1≦y<0.95, and 0.01 <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0011] At this time, niobium oxides containing alkaline earth metals are SrNbO, SrNbO 2、 SrNbO3, Sr(NbO3)2, BaNbO, BaNbO 2、 BaNbO3, Ba(NbO3)2, RaNbO, RaNbO 2、 It can be selected from the group consisting of RaNbO3 and Ra(NbO3)2.

[0012] The alkaline earth metal may be contained in an amount of 0.01 to 10 wt % based on the total weight of the niobium oxide.

[0013] The niobium oxide may be contained in an amount of 0.1 to 10 wt % based on the total weight of the positive electrode active material.

[0014] At the same time, the average particle size of the positive electrode active material for a secondary battery may be 0.5 μm to 10 μm.

[0015] In addition, the shell containing niobium oxide may be adsorbed on an area of ​​60% or more of the total area of ​​the core.

[0016] The present invention also provides a positive electrode active material for a secondary battery, further comprising a coating layer containing carbon on the shell.

[0017] At this time, the content of carbon contained in the coating layer may be 0.1 to 2.0 wt % based on the total weight of the active material.

[0018] In one embodiment, the present invention provides a method for preparing a positive electrode active material for a secondary battery, the method comprising: preparing a mixture containing lithium metal oxide, niobium oxide, and an alkaline earth metal; and heat-treating the mixture.

[0019] In this case, the lithium metal oxide may be represented by the following Chemical Formula 1: [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O u In the above Chemical Formula 1, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are 1.0≦x≦1.30, 0.1≦y<0.95, and 0.01 <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0020] At this time, in the step of preparing the mixture, the mixture may contain 0.1 to 10 wt % of niobium oxide based on the total weight of lithium metal oxide.

[0021] Also, the heat treatment may be performed at a temperature of 300 to 900°C.

[0022] Also, the heat treatment may be performed in the range of 0.1 atm to 10.0 atm.

[0023] The heat treatment may be performed for a period of 1 hour to 10 hours.

[0024] The method for manufacturing a positive electrode active material for a secondary battery further includes the step of forming a coating layer containing carbon on at least a portion of the shell surface after the heat treatment step.

[0025] The present invention provides a method for manufacturing a positive electrode active material for a secondary battery, wherein the carbon content in the coating layer is 0.1 to 2.0 wt % based on the total weight of the positive electrode active material.

[0026] Furthermore, in one embodiment, the present invention provides an all-solid-state lithium secondary battery including: a positive electrode including the above-described positive electrode active material according to the present invention; a negative electrode; and a sulfide-based solid electrolyte disposed between the positive electrode and the negative electrode.

[0027] In this case, the sulfide-based solid electrolyte may include one or more selected from the group consisting of Li2S—SiS2, LiI—Li2S—SiS2, LiI—Li2S—P2S5, LiI—Li2S—B2S3, Li3PO4—Li2S—Si2S, Li3PO4—Li2S—SiS2, LiPO4—Li2S—SiS, LiI—Li2S—P2O5, LiI—Li3PO4—P2S5, and Li2S—P2S5.

[0028] Furthermore, in one embodiment, the present invention provides a device including the above-described all-solid-state lithium secondary battery according to the present invention.

[0029] The device may be an electric vehicle.

[0030] Furthermore, in one embodiment, the present invention provides a catalyst comprising a core comprising a lithium metal oxide; and a shell adsorbed on the surface of the core and comprising a niobium oxide, the niobium oxide comprising an alkaline earth metal; The lithium metal oxide is represented by the following formula 1: [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O u In the above Chemical Formula 1, M 1is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are 1.0≦x≦1.30, 0.1≦y<0.95, and 0.01 <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5で、 Niobium oxides containing alkaline earth metals include SrNbO, SrNbO 2、 SrNbO3, Sr(NbO3)2, BaNbO, BaNbO 2、 BaNbO3, Ba(NbO3)2, RaNbO, RaNbO 2、 selected from the group consisting of RaNbO3 and Ra(NbO3)2; The content of the alkaline earth metal is 0.01 to 10 wt % based on the total weight of the niobium oxide, The content of the niobium oxide is 0.1 to 10 wt % based on the total weight of the positive electrode active material, The average particle size of the positive electrode active material is 0.5 μm to 10 μm, The average particle size of the niobium oxide is 0.1 nm to 40 nm, The shell containing the niobium oxide provides a positive electrode active material for a secondary battery, adsorbed to an area of ​​60% or more of the total area of ​​the core. [Effects of the Invention]

[0031] The cathode active material for a secondary battery according to the present invention has a structure in which a shell composed of niobium oxide partially containing alkaline earth metal is adsorbed on the surface of a core containing lithium metal oxide. This reduces the void phenomenon that may occur between the cathode active material and the solid electrolyte and side reactions between them, and also suppresses an increase in electrode resistance during charge and discharge, thereby improving the lifespan of the secondary battery including the cathode active material. [Brief explanation of the drawings]

[0032] [Figure 1]1A is a diagram showing the results of SEM photography of the positive electrode composite layer of Example 1, and FIG. 1B is a diagram showing the results of observation by energy dispersive X-ray spectroscopy (EDX). [Figure 2] 1 is a diagram showing the results of SEM photography of a positive electrode mixture layer of Comparative Example 1. [Figure 3] 1 is a diagram showing the results of photographing the positive electrode active material of Example 8 with a transmission electron microscope (TEM). [Figure 4] 1 is a diagram showing the results of photographing the positive electrode active material of Example 8 with a transmission electron microscope (TEM). DETAILED DESCRIPTION OF THE INVENTION

[0033] Because the present invention is susceptible to various modifications and embodiments, specific embodiments are described in detail in the detailed description.

[0034] However, this is not intended to limit the invention to any particular embodiment, but should be understood to include all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

[0035] In the present invention, the terms "comprise" or "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0036] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion in between. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion in between. Furthermore, in this application, being "located on" may include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0037] At the same time, in the present invention, "contained as a main component" may mean 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 97.5% by weight or more of the total weight of the composition such as a slurry or a specific component, and in some cases may mean 100% by weight when it constitutes the entire composition or specific component.

[0038] The present invention will now be described in more detail.

[0039] Cathode active material for secondary batteries In one embodiment, the present invention comprises: The present invention provides a positive electrode active material for a secondary battery, comprising: a core containing a lithium metal oxide; and a shell adsorbed on the surface of the core and containing a niobium oxide, the niobium oxide containing an alkaline earth metal.

[0040] The cathode active material according to the present invention is used in a secondary battery and has a structure including a lithium metal oxide core that exhibits electrical activity during charging and discharging of the battery, and particles including niobium oxide adsorbed on the surface of the core to form a shell.

[0041] In one embodiment of the present invention, the secondary battery may be an all-solid-state battery.

[0042] In one embodiment of the present invention, the all-solid-state battery may be a sulfide-based all-solid-state battery.

[0043] Here, the lithium metal oxide may be any lithium metal oxide that provides lithium ions by reversibly reacting during charging and discharging of the battery, and specifically may include a lithium metal oxide represented by the following Chemical Formula 1: [Chemical formula 1] Li x [Ni y Co z Mn w M 1v ]O u In the above Chemical Formula 1, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are 1.0≦x≦1.30, 0.1≦y<0.95, and 0.01 <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0044] The lithium metal oxide represented by Formula 1 may be an oxide containing lithium and a transition metal, and may contain a high content of nickel among the transition metals. For example, the lithium metal oxide may be LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 and LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 O2. The lithium metal oxide contains a high content of nickel, and is therefore effective in improving the charge and discharge capacity of the battery.

[0045] In addition, the core has a structure in which a shell containing niobium oxide is adsorbed on the surface thereof, thereby reducing the interfacial resistance between the positive electrode active material and the solid electrolyte, improving the ability to resist side reactions between the positive electrode active material and the solid electrolyte, and suppressing the loss of lithium ions, thereby improving the electrical performance of the battery.

[0046] The niobium oxide may have the form of NbO, NbO2, Nb2O5, Nb2O6, etc. For example, the niobium oxide may contain a uniform mixture of Nb2O5 and Nb2O6, with Nb2O6 being the main component. In this case, Nb2O5 may be contained in an amount of 10 wt% or less based on the total weight of the niobium oxide. In some cases, Nb2O5 may be absent, resulting in a content of 0 wt% based on the total weight of the niobium oxide. The niobium oxide has excellent electrical properties and high thermodynamic state stability, which allows it to effectively suppress side reactions between the positive electrode active material and the sulfide-based solid electrolyte during battery charge and discharge, as well as offering excellent workability.

[0047] The niobium oxide may further contain an alkaline earth metal. The alkaline earth metal may be partially contained in the niobium oxide constituting the shell. For example, the niobium oxide containing an alkaline earth metal may be SrNbO, SrNbO 2、 SrNbO3, Sr(NbO3)2, BaNbO, BaNbO 2、 BaNbO3, Ba(NbO3)2, RaNbO, RaNbO 2、 It can have forms such as RaNbO3 and Ra(NbO3)2.

[0048] This prevents the shell from being detached from the core surface due to the contraction and expansion of the core during charging and discharging of the battery, thereby preventing cracks from occurring between the core and the shell, and also prevents the occurrence of voids at the interface between the active material and the electrolyte.

[0049] Specifically, the lithium metal oxide represented by Chemical Formula 1 has a layered structure and exhibits significant contraction and expansion during charge and discharge of a secondary battery. Therefore, when the lithium metal oxide is incorporated into the core as a cathode active material, repeated contraction and expansion of the core during charge and discharge of the battery causes detachment of the shell on the core surface, resulting in increased electrode resistance and contact breakdown at the interface between the active material and the electrolyte, limiting battery life. However, the alkaline earth metal-containing niobium oxide of the present invention has excellent structural fluidity. When the lithium metal oxide represented by Chemical Formula 1 is adsorbed onto the core, detachment of the shell due to contraction and expansion of the core during charge and discharge of the battery does not occur, and contact breakdown at the interface between the active material and the electrolyte is significantly improved.

[0050] The alkaline earth metal may include one or more of strontium (Sr), barium (Ba), and radium (Ra), which have atomic radii equal to or larger than those of niobium (Nb). Specifically, strontium (Sr) and barium (Ba) may be included individually or together.

[0051] At the same time, the alkaline earth metal may be contained in an amount of 0.01 to 10 wt % based on the total weight of the niobium oxide contained in the shell, specifically, 0.01 to 8 wt %, 0.01 to 6 wt %, 0.01 to 5 wt %, 0.01 to 3 wt %, 0.01 to 2 wt %, 0.01 to 1 wt %, or 0.01 to 0.5 wt % based on the total weight of the niobium oxide.

[0052] By controlling the content of alkaline earth metal contained in the niobium oxide within the above range, the present invention can provide excellent electrical conductivity to the surface of the positive electrode active material during charge and discharge of the battery, and can provide insulation to the shell when the electrochemical function of the battery is not performed (e.g., when charge and discharge are not performed), thereby preventing the battery from self-discharge.

[0053] In addition, the niobium oxide particles may be included in an amount of 0.1 to 10 wt % based on the total weight of the positive electrode active material, and specifically, may be included in an amount of 0.1 to 8 wt %, 0.1 to 6 wt %, 0.1 to 5 wt %, 0.1 to 3 wt %, 1 to 4 wt %, 1 to 3 wt %, 2 to 6 wt %, 4 to 8 wt %, 0.1 to 2 wt %, 0.1 to 1.5 wt %, 0.3 to 1.5 wt %, 0.5 to 1.5 wt %, 0.9 to 1.5 wt %, 0.3 to 0.9 wt %, or 0.1 to 1.2 wt % based on the total weight of the positive electrode active material.

[0054] By controlling the content of niobium oxide contained in the positive electrode active material within the above range, the present invention can prevent contact breakdown at the interface between the positive electrode active material and the electrolyte, and can prevent a situation in which the content of niobium oxide particles is too low to adequately surround the surface of the lithium metal oxide, or an excessive amount of niobium oxide particles agglomerating together and failing to coat the surface of the lithium metal oxide.

[0055] At the same time, the positive electrode active material may have an average particle size of 0.5 μm to 10 μm, and the niobium oxide located on the surface of the positive electrode active material may have a particle shape with an average particle size of 0.1 nm to 40 nm.

[0056] More specifically, the positive electrode active material may have an average particle size of 0.5 μm to 8 μm, 0.5 μm to 6 μm, 0.5 μm to 5 μm, 0.5 μm to 4 μm, 5 μm to 9 μm, 1 μm to 4 μm, 2 μm to 4 μm, 4 μm to 7 μm, 0.5 μm to 3 μm, 1 μm to 3 μm, or 3 μm to 8 μm, and the average particle size of the niobium oxide particles located on the surface of the positive electrode active material may be 0.1 nm to 30 nm, 0.1 nm to 20 nm, 0.1 nm to 10 nm, 5 nm to 30 nm, 5 nm to 20 nm, 8 nm to 15 nm, or 4 nm to 15 nm.

[0057] In the present invention, by controlling the average particle size of the positive electrode active material within the above range, the electrode activity of the positive electrode can be further improved, and by controlling the average particle size of the niobium oxide contained in the shell within the above range, the decrease in the electrical activity of the lithium metal oxide in the core can be minimized, side reactions at the interface with the solid electrolyte can be effectively suppressed, and cracks that may occur on the surface of the positive electrode active material can be prevented.

[0058] Furthermore, the shell containing niobium oxide may surround at least 60% of the entire surface of the core containing lithium metal oxide. Specifically, the niobium oxide particles may be uniformly adsorbed physically, rather than chemically, on the surface of the core containing lithium metal oxide. Here, the area where the niobium oxide particles are adsorbed may be at least 60% of the surface area of ​​the core, more specifically, at least 70%, at least 80%, at least 90%, at least 95%, or at least 98%. By controlling the area where the shell containing lithium metal oxide is adsorbed on the surface of the core at the above ratio, the present invention can avoid the use of excessive niobium oxide and effectively suppress side reactions between the positive electrode active material and the solid electrolyte.

[0059] In addition, the cathode active material according to the present invention may further include a coating layer containing carbon on the shell. By including such a carbon coating layer, the electrical conductivity of the secondary battery may be improved. In addition, the content of the conductive material may be reduced, thereby preventing the conductive material from clumping together, and the content of the active material may be increased, thereby improving the electrical performance of the battery.

[0060] The carbon contained in the coating layer may be at least one carbon material selected from the group consisting of carbon (C) alone and Li—C compounds.

[0061] The carbon content of the coating layer may be 0.1 to 2.0 wt % based on the total weight of the positive electrode active material, specifically, 0.3 to 1.0 wt % based on the total weight of the positive electrode active material.

[0062] The carbon coating on the shell may be applied using RAM (Resodyn Acoustic Mixers) mixing, but is not limited to this example and may be applied by any method that can form a carbon-containing coating layer on the shell.

[0063] The positive electrode active material for a secondary battery according to the present invention has a structure in which a shell including niobium oxide particles having a specific size is adsorbed on the surface of a core including lithium metal oxide, thereby reducing cracks that may occur between the positive electrode active material and the solid electrolyte and the reactivity between them, thereby improving the mobility of lithium ions and achieving high charge / discharge capacity.

[0064] Method for producing positive electrode active material for secondary battery In one embodiment, the present invention further comprises: A method for producing a positive electrode active material for a secondary battery is provided, comprising the steps of: preparing a mixture containing lithium metal oxide, niobium oxide, and an alkaline earth metal; and heat-treating the mixture.

[0065] Here, the lithium metal oxide may be represented by the following chemical formula 1: [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O u In the above Chemical Formula 1, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are 1.0≦x≦1.30, 0.1≦y<0.95, and 0.01 <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0066] The method for preparing a positive electrode active material for a secondary battery according to the present invention may be performed by preparing a mixture containing a lithium metal oxide represented by Formula 1 forming a core and a niobium oxide forming a shell, and then heat-treating the mixture.

[0067] At this time, the step of mixing the lithium metal oxide and the niobium oxide to prepare a mixture may be performed using a dry mixer, a stirrer, a shaker such as an orbital shaker, a mortar mixer, a milling machine such as an oil-type ball mill, or the like, which are used in the art to mix powders of metal compounds, but is not limited thereto.

[0068] For example, the step of preparing the mixture may be carried out using an oil-based ball mill at a speed of 50 to 500 rpm for 0.1 to 10 hours and at a power of 1 to 100 kWH / 1 kg per 1 kg of mixture.

[0069] As another example, the step of preparing the mixture may be performed by mixing for 1 to 10 hours, specifically 2 to 8 hours, using a shaker.

[0070] In addition, in the mixture, the lithium metal oxide represented by Chemical Formula 1 may be an oxide containing lithium and a transition metal, and in particular, may contain a high content of nickel among the transition metals. For example, the lithium metal oxide may be LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al0.1 O2 and LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 O2.

[0071] In addition, the niobium oxide may further include an alkaline earth metal. When the alkaline earth metal is partially contained in the niobium oxide constituting the shell, the shell may be detached from the surface of the core due to the contraction and expansion of the core containing the lithium metal oxide during charge and discharge of the battery, which may prevent cracks from occurring between the core and the shell, and may also prevent voids from occurring at the interface between the active material and the electrolyte.

[0072] The alkaline earth metal may include one or more of strontium (Sr), barium (Ba), and radium (Ra), which have atomic radii equal to or larger than those of niobium (Nb). Specifically, strontium (Sr) and barium (Ba) may be included individually or together.

[0073] At the same time, the alkaline earth metal may be contained in an amount of 0.01 to 5 wt % based on the total weight of the niobium oxide contained in the shell, specifically, 0.01 to 3 wt %, 0.01 to 2 wt %, 0.01 to 1 wt %, or 0.01 to 0.5 wt % based on the total weight of the niobium oxide.

[0074] The niobium oxide may also be used in the form of particles, and the average particle size of the particles may be 0.1 nm to 40 nm; 0.1 nm to 30 nm; 0.1 nm to 20 nm; 0.1 nm to 10 nm; 5 nm to 30 nm; 5 nm to 20 nm; 8 nm to 15 nm; or 4 nm to 15 nm.

[0075] In addition, the mixture may contain 0.1 to 10 wt% of niobium oxide based on the total weight of the lithium metal oxide, specifically, 0.1 to 8 wt%, 0.1 to 6 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 1 to 4 wt%, 1 to 3 wt%, 2 to 6 wt%, 4 to 8 wt%, 0.1 to 2 wt%, 0.1 to 1.5 wt%, 0.3 to 1.5 wt%, 0.5 to 1.5 wt%, 0.9 to 1.5 wt%, 0.3 to 0.9 wt%, or 0.1 to 1.2 wt% of niobium oxide based on the total weight of the lithium metal oxide.

[0076] By controlling the content of niobium oxide mixed with lithium metal oxide within the above range, the present invention can prevent a situation in which the content of niobium oxide particles is too low to sufficiently surround the surface of the lithium metal oxide, or an excessive amount of niobium oxide particles aggregates together and fails to coat the surface of the lithium metal oxide.

[0077] In addition, the step of heat-treating the mixture containing lithium metal oxide and niobium oxide can be said to be a step of fixing the niobium oxide physically adsorbed on the surface of the lithium metal oxide core.

[0078] In this case, the heat treatment temperature may be 300°C or higher, and preferably 300°C to 900°C, 400°C to 900°C, 500°C to 900°C, 600°C to 900°C, or 600°C to 800°C. In the present invention, by adjusting the heat treatment temperature of the mixture containing lithium metal oxide and niobium oxide within the above range, niobium oxide can be easily fixed to the surface of the lithium metal oxide core without side reactions occurring on the surface of the lithium metal oxide.

[0079] At this time, the heat treatment step may be carried out in the range of 0.1 atm to 10.0 atm, and preferably 0.3 atm to 9.5 atm; 0.5 atm to 9.0 atm; 0.7 atm to 8.5 atm; or 1.0 atm to 8.0 atm.

[0080] The heat treatment may be performed for a period of 1 to 10 hours, preferably 1.5 to 9.5 hours, 2 to 9 hours, 2.5 to 8.5 hours, or 3 to 8 hours.

[0081] In addition, the cathode active material according to the present invention may further include a coating layer containing carbon on the shell, and the coating layer may be formed using RAM (Resodyn Acoustic Mixers) mixing. However, the present invention is not limited to this example, and any method may be used as long as it can form a coating layer containing carbon on the shell.

[0082] The present invention provides a method for manufacturing a positive electrode active material for a secondary battery, wherein the carbon content in the coating layer is 0.1 to 2.0 wt % based on the total weight of the positive electrode active material.

[0083] The method for manufacturing a positive electrode active material for a secondary battery according to the present invention has an advantage in that it is possible to form a shell in which niobium oxide is uniformly coated on the surface of a core containing lithium metal oxide, thereby providing excellent manufacturing efficiency for a positive electrode active material having a core-shell structure.

[0084] All-solid-state lithium secondary battery Furthermore, in one embodiment, the present invention provides There is provided an all-solid-state lithium secondary battery including a positive electrode including the above-described positive electrode active material according to the present invention; a negative electrode; and a sulfide-based solid electrolyte disposed between the positive electrode and the negative electrode.

[0085] The all-solid-state lithium secondary battery according to the present invention includes a cathode containing the cathode active material of the present invention, and exhibits excellent lithium ion mobility in the electrode because the void phenomenon occurring at the interface between the cathode active material and the solid electrolyte is significantly reduced and side reactions are suppressed.

[0086] In this case, the positive electrode may have a structure in which a positive electrode mixture layer containing the positive electrode active material of the present invention is formed on a positive electrode current collector.

[0087] The positive electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, it may include stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, or the like.

[0088] The positive electrode mixture layer contains a positive electrode active material, a conductive material, a binder, and a solid electrolyte, and may further contain an additive, if necessary.

[0089] Here, the positive electrode active material may have a structure including a core including a lithium metal oxide represented by the following Chemical Formula 1; and a shell including a niobium oxide adsorbed on the surface of the core.

[0090] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O u In the above Chemical Formula 1, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are 1.0≦x≦1.30, 0.1≦y<0.95, and 0.01 <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0091] The lithium metal oxide may be any compound represented by Chemical Formula 1 without any particular limitation. Specifically, the lithium metal oxide may be LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.7 Co 0.15 Mn0.15 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 and LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 O2.

[0092] In addition, the niobium oxide may further include an alkaline earth metal. When the alkaline earth metal is partially contained in the niobium oxide constituting the shell, the shell may be detached from the surface of the core due to the contraction and expansion of the core containing the lithium metal oxide during charge and discharge of the battery, which may prevent cracks from occurring between the core and the shell, and may also prevent voids from occurring at the interface between the active material and the electrolyte.

[0093] The alkaline earth metal may include one or more of strontium (Sr), barium (Ba), and radium (Ra), which have atomic radii equal to or larger than those of niobium (Nb). Specifically, strontium (Sr) and barium (Ba) may be included individually or together.

[0094] At the same time, the alkaline earth metal may be contained in an amount of 0.01 to 5 wt % based on the total weight of the niobium oxide contained in the shell, specifically, 0.01 to 3 wt %, 0.01 to 2 wt %, 0.01 to 1 wt %, or 0.01 to 0.5 wt % based on the total weight of the niobium oxide.

[0095] The niobium oxide may have a particulate form, and the average particle size of the particles may be 0.1 nm to 40 nm, 0.1 nm to 30 nm, 0.1 nm to 20 nm, 0.1 nm to 10 nm, 5 nm to 30 nm, 5 nm to 20 nm, 8 nm to 15 nm, or 4 nm to 15 nm.

[0096] In addition, the average particle size of the positive electrode active material may be 0.5 μm to 10 μm; 0.5 μm to 8 μm; 0.5 μm to 6 μm; 0.5 μm to 5 μm; 0.5 μm to 4 μm; 5 μm to 9 μm; 1 μm to 4 μm; 2 μm to 4 μm; 4 μm to 7 μm; 0.5 μm to 3 μm; 1 μm to 3 μm; or 0.5 μm to 2 μm.

[0097] The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. Specifically, graphite, carbonaceous materials, metal powder or metal fiber, needle-like or branch-like conductive whiskers, conductive metal oxides, conductive polymers, and any one or a mixture of these may be used. More specifically, examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; needle-shaped or branch-shaped conductive whiskers such as zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicone carbide whiskers, and aluminum whiskers; conductive metal oxides such as titanium oxide, and conductive polymers such as polyphenylene derivatives. Any one of these or a mixture of two or more thereof may be used.

[0098] In addition, the binder for the positive electrode may be any one selected from the group consisting of N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), conjugated diene rubber latex such as acrylonitrile-styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), and butadiene rubber (BR), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers, or a mixture of two or more thereof.

[0099] At the same time, the negative electrode may have a structure in which a negative electrode mixture layer containing a negative electrode active material is formed on a negative electrode current collector.

[0100] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, it may include stainless steel, copper, nickel, titanium, calcined carbon, or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0101] The negative electrode mixture layer includes a negative electrode active material, a conductive material, a binder, and a solid electrolyte, and may further include an additive, if necessary.

[0102] At this time, the negative electrode active material can be one selected from the group consisting of lithium metal, lithium alloy, lithium metal composite oxide, lithium-containing titanium composite oxide (LTO), and combinations thereof. Here, as the lithium alloy, an alloy composed of lithium and at least one metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn can be used. Further, the lithium metal composite oxide is an oxide (MeOx) of any one metal (Me) selected from the group consisting of lithium and Si, Sn, Zn, Mg, Cd, Ce, Ni, and Fe. As an example, Li x Fe2O3 (0 < x ≦ 1) or Li x WO2 (0 < x ≦ 1) may be used.

[0103] At the same time, as the negative electrode active material, Sn x Me 1‐x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), etc. metal composite oxides; oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5 can be used, and carbon-based negative electrode active materials such as crystalline carbon, amorphous carbon, or carbon composites can be used alone or in combination of two or more.

[0104] At the same time, examples of the conductive material include nickel powder, cobalt oxide, titanium oxide, carbon, etc. As carbon, any one selected from the group consisting of ketjen black, acetylene black, furnace black, graphite, carbon fiber, and fullerene or one or more of these can be mentioned.

[0105] In addition, the binder for the negative electrode may be any one selected from the group consisting of N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), conjugated diene rubber latex such as styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), and butadiene rubber (BR), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers, or a mixture of two or more thereof.

[0106] Furthermore, the solid electrolyte includes sulfide-based particles, and the sulfide-based particles may be those commonly used in the art as electrolytes for sulfide-based all-solid-state batteries. Specifically, one or more amorphous solid electrolytes selected from the group consisting of Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, and Li2S-P2S5 may be used.

[0107] The sulfide-based particles may have an average particle size of 0.1 μm to 50 μm, specifically 0.1 μm to 10 μm. By controlling the average particle size of the sulfide-based particles constituting the solid electrolyte within this range, the present invention can alleviate the problem of reduced battery capacity due to high porosity of the solid electrolyte.

[0108] The present invention will be explained in more detail below with reference to examples and experimental examples.

[0109] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0110] Examples 1 to 8 and Comparative Examples 1 to 3. Production of cathode active materials for sulfide-based all-solid-state batteries LiNi with an average particle size of 5±0.1μm 0.8 Co 0.1 Mn 0.1 Niobium oxide (Ni2O5) was weighed based on the total weight of O2 as shown in Table 1 below and placed in a ball mill jar. Ball milling was carried out at a speed of 200±50 rpm and a force of 10 kWh / 1 kg for 1 hour to obtain LiNi 0.8 Co 0.1 Mn 0.1 A homogeneous mixture of O2 and niobium oxide was obtained. At this time, the niobium oxide contained 0.3 wt% of the alkaline earth metals shown in Table 1 based on the total weight of the niobium oxide, and the amounts used were as shown in Table 1.

[0111] The mixture was transferred to an oven and then heat-treated at atmospheric pressure (1 atm) and 700±10°C for 2 hours to form the core LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode active material (average particle size: 5±0.1 μm) was obtained in which the surface of O2 was uniformly coated with SrNbO3.

[0112] At this time, as shown in Table 1 below, when the content of niobium oxide is less than 0.1 wt % based on the total weight of lithium metal oxide, the core LiNi 0.8 Co 0.1 Mn 0.1 It was confirmed that the surface of LiNiO2 could not be sufficiently coated; when the niobium oxide content exceeds 10 wt%, the niobium oxide particles aggregated together in the mixture, forming LiNiO2. 0.8 Co 0.1 Mn 0.1 It was confirmed that O2 was not uniformly adsorbed on the surface.

[0113] [Table 1]

[0114] In addition, the LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode active material of Example 8 was prepared by further coating carbon (C) on a positive electrode active material in which niobium oxide was uniformly coated on the surface of an O2 core. Specifically, the primary coated active material and carbon black were mixed quantitatively in Resodyn Acoustic Mixers (RAM) (gravitational acceleration strength: 100G, time: 2 minutes) and then gently heated at a temperature below 100°C. The coating amount in Example 8 was 0.5 wt% by weight of carbon black relative to the active material, and the carbon (C) coated positive electrode active material was prepared.

[0115] Examples 9 to 16 and Comparative Examples 4 to 6. Production of sulfide-based all-solid-state batteries Using each of the positive electrode active materials prepared in Examples 1 to 8 and Comparative Examples 1 to 3, sulfide-based all-solid-state batteries were fabricated.

[0116] Specifically, the positive electrode active material prepared in each of the examples and comparative examples, sulfide-based solid electrolyte (LiS-P2S5), conductive material (carbon black), and binder (PVDF) were mixed in a weight ratio of 80:15:3:2, coated on an aluminum sheet (thickness: 40 μm), and rolled at room temperature to prepare a positive electrode.

[0117] Separately, a lithium metal (Li) thin plate (thickness: 40 μm) was prepared as the negative electrode. A solid electrolyte membrane (70 μm, 2.8 × 10 ‐3 S / cm, Li 10 SnP2S 12 ) was used to fabricate a sulfide-based all-solid-state battery.

[0118] [Table 2]

[0119] Experimental Example In order to evaluate the performance of the sulfide-based cathode active material for an all-solid-state battery according to the present invention, the following experiment was carried out.

[0120] a) Cross-sectional structure analysis of the positive electrode composite layer The sulfide-based all-solid-state batteries manufactured in the Examples and Comparative Examples were prepared in a non-atmospheric environment and allowed to run for a certain period of time under conditions of room temperature (25±1°C), 3.0 to 4.25 V, and 0.1 C. After that, each battery was disassembled and a scanning electron microscope (SEM) analysis was performed on the cathode composite layer.

[0121] First, the results of SEM photographs of the positive electrode composite layer of Example 1 are shown in FIG. 1. In FIG. 1, (a) shows the SEM cross section of the positive electrode composite layer of Example 1, and (b) shows the results of observation by energy dispersive X-ray spectroscopy (EDX). As a result, it was found that the lithium metal oxide (LiNi 0.8 Co 0.1 Mn 0.1 It was confirmed that niobium oxide was uniformly adsorbed on the surface of the lithium metal oxide core. This means that the void phenomenon that occurs at the interface between the lithium metal oxide contained in the core and the sulfide-based solid electrolyte is prevented, and side reactions are suppressed.

[0122] On the other hand, the SEM photograph of the positive electrode mixture layer of Comparative Example 1 is shown in FIG. 2. As a result, the lithium metal oxide (LiNi 0.8 Co 0.1 Mn 0.1 It was confirmed that cracks had occurred between the oxide (O2) and the sulfide-based solid electrolyte.

[0123] The positive electrode active material of Example 8 was photographed with a transmission electron microscope (TEM) and shown in Figure 3, which confirmed that a carbon coating layer was formed on the niobium oxide coating layer. In addition, the positive electrode active material of Example 8 was photographed with a transmission electron microscope (TEM) and shown in Figure 4, which confirmed that a carbon layer was uniformly coated on the primary coating layer.

[0124] From these results, it can be seen that the cathode active material of the sulfide-based all-solid-state battery according to the present invention has a structure in which niobium oxide containing alkaline earth metal is adsorbed on the surface of a core containing lithium metal oxide to form a shell, thereby preventing the occurrence of a void phenomenon and side reactions between the core lithium metal oxide and the solid electrolyte.

[0125] a) Battery life evaluation The sulfide-based all-solid-state batteries prepared in Examples 9 to 16 and Comparative Examples 4 to 6 were fixed in a jig in a chamber at 60°C, and initial charge / discharge was performed under the condition of 0.1 C to measure the initial charge capacity. At this time, the charge was performed in a constant current charge (CCC) mode, and c / o was controlled at 0.05 C.

[0126] After repeating charge and discharge 300 times under the same conditions, the charge capacity was measured after the 300th charge, and the percentage of the maintained charge capacity was calculated based on the initial charge capacity. The results are shown in Table 3 below.

[0127] [Table 3]

[0128] As shown in Table 3, the cathode active material for a sulfide-based all-solid-state battery of the example has a structure in which a shell including niobium oxide containing alkaline earth metal is adsorbed on the surface of a core including lithium metal oxide, and it was confirmed that the cathode active material has a high charge capacity retention rate of 90% or more even after repeated charge and discharge.

[0129] In addition, in the case of Example 16, in which a carbon coating layer was added on top of the niobium oxide coating layer, it was confirmed that the life characteristics could be maintained even when the content of the active material was increased, and the energy density per volume could be increased.

[0130] This means that the cathode active material of the present invention does not cause shell detachment due to core contraction / expansion even when repeatedly charged and discharged, and the void phenomenon between the cathode active material and the electrolyte is improved, preventing an increase in electrode resistance.

[0131] From these results, it can be seen that the cathode active material for a sulfide-based all-solid-state battery according to the present invention reduces the occurrence of voids and side reactions at the interface between the cathode active material and the solid electrolyte, thereby preventing an increase in electrode resistance during charge and discharge, thereby improving the battery life.

[0132] In addition, the results of Example 16 show that the energy density can be secured by increasing the content of the active material.

[0133] Although the present invention has been described above with reference to preferred embodiments, it will be understood that a person skilled in the art or with ordinary knowledge in the art can modify and change the present invention in various ways without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0134] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

1. a core comprising a lithium metal oxide; and a shell comprising a niobium oxide adsorbed on a surface of the core, the niobium oxide comprising an alkaline earth metal; The content of the alkaline earth metal is 0.01 wt % to 10 wt % based on the total weight of the niobium oxide. The content of niobium oxide is 0.1 wt % to 10 wt % based on the total weight of the positive electrode active material. The positive electrode active material for a secondary battery, wherein the alkaline earth metal is at least one selected from the group consisting of strontium and barium.

2. 2. The positive electrode active material for a secondary battery according to claim 1, wherein the lithium metal oxide is represented by the following chemical formula 1: [Chemical formula 1] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ｕ In the above Chemical Formula 1, M １ is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are in the ranges of 1.0≦x≦1.30, 0.1≦y<0.95, 0.01<z≦0.5, 0.01<w≦0.5, 0≦v≦0.2, and 1.5≦u≦4.5, respectively.

3. 10. The positive electrode active material for a secondary battery according to claim 1, wherein the content of the alkaline earth metal is 0.01 to 1 wt % based on the total weight of the niobium oxide.

4. 10. The positive electrode active material for a secondary battery according to claim 1, wherein the content of the niobium oxide is 2 to 10 wt % based on the total weight of the positive electrode active material.

5. The positive electrode active material for a secondary battery according to claim 1 , wherein the shell containing niobium oxide is adsorbed to an area of ​​60% or more of the total area of ​​the core.

6. The positive electrode active material for a secondary battery according to claim 1 , further comprising a coating layer containing carbon on the shell.

7. 7. The positive electrode active material for a secondary battery according to claim 6, wherein the carbon content of the coating layer is 0.1 wt % to 2.0 wt % based on the total weight of the positive electrode active material.

8. The positive electrode active material for a secondary battery according to claim 1 , wherein the secondary battery is an all-solid-state battery.

9. The positive electrode active material for a secondary battery according to claim 8 , wherein the all-solid-state battery is a sulfide-based all-solid-state battery.

10. preparing a mixture comprising lithium metal oxide, niobium oxide, and an alkaline earth metal; and heat treating the mixture; The content of the alkaline earth metal is 0.01 wt % to 10 wt % based on the total weight of the niobium oxide. The content of niobium oxide is 0.1 wt % to 10 wt % based on the total weight of the mixture, The alkaline earth metal is at least one selected from strontium and barium. A method for producing a positive electrode active material for a secondary battery.

11. The method for producing a positive electrode active material for a secondary battery according to claim 10, wherein the lithium metal oxide is represented by the following chemical formula 1: [Chemical formula 1] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ｕ In the above Chemical Formula 1, M １ is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are in the ranges of 1.0≦x≦1.30, 0.1≦y<0.95, 0.01<z≦0.5, 0.01<w≦0.5, 0≦v≦0.2, and 1.5≦u≦4.5, respectively.

12. The method for producing a positive electrode active material for a secondary battery according to claim 10, wherein the mixture contains 2 wt % to 10 wt % of niobium oxide based on the total weight of the mixture.

13. 11. The method of claim 10, wherein the heat treatment is performed at a temperature of 300 to 900°C.

14. 11. The method of claim 10, wherein the heat treatment is performed in a range of 0.1 atm to 10.0 atm.

15. 11. The method of claim 10, wherein the heat treatment is performed for a period of 1 hour to 10 hours.

16. The method of claim 10, further comprising: forming a coating layer containing carbon on at least a portion of the shell surface after the heat treatment.

17. 17. The method of claim 16, wherein the carbon content of the coating layer is 0.1 wt % to 2.0 wt % based on the total weight of the positive electrode active material.

18. A positive electrode comprising the positive electrode active material according to claim 1; a negative electrode; and An all-solid-state lithium secondary battery comprising a sulfide-based solid electrolyte disposed between the positive electrode and the negative electrode.

19. The sulfide-based solid electrolyte is Li ２ S-SiS ２ , LiI-Li ２ S-SiS ２ , LiI-Li ２ S-P ２ S ５ , LiI-Li ２ S-B ２ S ３ , Li ３ P.O. ４ -Li ２ S-Si ２ S., Li. ３ P.O. ４ -Li ２ S-SiS ２ , LiPO ４ -Li ２ S-SiS, LiI-Li ２ S-P ２ O ５ , LiI-Li ３ P.O. ４ -P ２ S ５ , and Li ２ S-P ２ S ５ 19. The all-solid-state lithium secondary battery according to claim 18, comprising one or more selected from the group consisting of:

20. 20. A device comprising the all-solid-state lithium secondary battery of claim 18.

21. 21. The device of claim 20, wherein the device is an electric vehicle.

22. a core comprising a lithium metal oxide; and a shell comprising a niobium oxide adsorbed on a surface of the core, the niobium oxide comprising an alkaline earth metal; The lithium metal oxide is represented by the following formula 1: [Chemical formula 1] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ｕ In the above Chemical Formula 1, M １ is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are each 1.0≦x≦1.30, 0.1≦y<0.95, 0.01<z≦0.5, 0.01<w≦0.5, 0≦v≦0.2, and 1.5≦u≦4.5, The content of the alkaline earth metal is 0.01 to 10 wt % based on the total weight of the niobium oxide, The content of the niobium oxide is 0.1 wt % to 10 wt % based on the total weight of the positive electrode active material, the alkaline earth metal is at least one selected from strontium and barium; The shell containing the niobium oxide is adsorbed to an area of ​​60% or more of the total area of ​​the core.

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