Cathode active material, method for preparing same, cathode comprising same, and all-solid state battery

Abstract

A cathode active material, according to one embodiment of the present invention, comprises: a core including a lithium-transition metal composite oxide; a first coating layer formed on the surface of the core; and a second coating layer formed on the surface of the first coating layer, wherein the first coating layer includes a lithium-transition metal composite oxide having a structure that is different from the lithium-transition metal composite oxide included in the core, and the second coating layer includes a sulfur compound.

Description

Positive electrode active material, method for producing same, positive electrode and all-solid-state battery containing same

[0001] The present disclosure relates to a positive electrode active material, a method for producing the same, a positive electrode including the same, and an all-solid-state battery.

[0002] Recently, due to environmental issues such as global warming, interest in eco-friendly electric vehicles (EVs) that can replace fossil fuel-based vehicles has grown. Lithium secondary batteries are one of the primary energy sources driving the current EV market due to their high energy density and advanced industrial technology. However, existing lithium secondary batteries, which utilize liquid electrolytes such as organic solvents, pose risks such as the risk of fire due to electrolyte leakage upon impact, and the risk of battery expansion and explosion due to chemical decomposition and gas generation of the electrolyte. Therefore, to address the aforementioned issues, all-solid-state batteries using solid-state electrolytes are attracting attention as next-generation energy sources, and active research and development are underway.

[0003] One aspect of the present disclosure is to provide a cathode active material capable of improving the life characteristics of a battery.

[0004] Another aspect of the present disclosure is to provide a high-capacity cathode active material.

[0005] Another aspect of the present disclosure is to provide a positive electrode active material having excellent resistance performance.

[0006] Another aspect of the present disclosure is to provide an all-solid-state battery having excellent electrochemical performance.

[0007] Another aspect of the present disclosure is to provide an all-solid-state battery having excellent safety.

[0008] According to one embodiment, a cathode active material comprises a core including a lithium-transition metal composite oxide; a first coating layer formed on a surface of the core; and a second coating layer formed on a surface of the first coating layer, wherein the first coating layer includes a lithium-transition metal composite oxide having a different structure from the lithium-transition metal composite oxide included in the core, and the second coating layer includes a sulfur compound.

[0009] The above core may include a lithium-transition metal composite oxide having a layered structure.

[0010] The above core may include a lithium-transition metal composite oxide according to the following chemical formula 1.

[0011] [Chemical Formula 1]

[0012] Li a Ni b M c O2

[0013] In the above chemical formula 1,

[0014] M is one or more elements selected from Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, and 0.90 <a<1.5, 0.33≤b≤1, 0≤c≤0.7이다.

[0015] The first coating layer may include a lithium-transition metal composite oxide having a spinel structure.

[0016] The first coating layer may further include at least one of a lithium-transition metal composite oxide having a rock salt structure and a lithium-transition metal composite oxide having a layered structure.

[0017] The first coating layer may include a lithium-transition metal composite oxide according to the following chemical formula 2.

[0018] [Chemical Formula 2]

[0019] Li x M y O z

[0020] In the above chemical formula 2,

[0021] M is one or more elements selected from Ni, Co, Mn, Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, and 0≤x≤4, 0≤y≤4, 0≤z≤8.

[0022] The thickness of the first coating layer may be 0.1 to 500 nm.

[0023] The above positive electrode active material may have a cation mixing ratio of 7% or less.

[0024] The above sulfur compound may include one or more compounds according to the following chemical formula 3.

[0025] [Chemical Formula 3]

[0026] Li x M y S z O f

[0027] In the above chemical formula 3,

[0028] M is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups, and combinations thereof, and 0≤x≤10, 0≤y≤10, 0 <z≤10, 0≤f≤24이다.

[0029] The above sulfur compound may include sulfur oxide.

[0030] The above sulfur oxide may be included in an amount of 200 to 8,000 ppm based on the total weight of the second coating layer.

[0031] The second coating layer may further include one or more elements selected from P, B, Si, Al, and W.

[0032] A method for manufacturing a positive electrode active material according to one embodiment manufactures a positive electrode active material according to any one of the above-described embodiments.

[0033] The method for manufacturing the above positive electrode active material may include a step of preparing a base material to form a core by a dry heat treatment process for a mixture of a precursor containing a transition metal raw material and a lithium raw material; and a step of pretreatment of the base material to form a precursor coating layer on the surface of the core.

[0034] The method for manufacturing the above positive electrode active material may further include a coating layer forming step of forming a first coating layer and a second coating layer.

[0035] In the above coating layer forming step, the first coating layer can be formed through a heat treatment process on the core.

[0036] In the above coating layer forming step, the second coating layer can be formed of a complex sulfate compound according to the following chemical formula 4.

[0037] [Chemical Formula 4]

[0038]

[0039] In the above chemical formula 4,

[0040] X is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, Group 16 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups, and combinations thereof, and 1≤a≤5 and 1≤b≤5.

[0041] In the above coating layer forming step, the heat treatment process can be carried out in air at a temperature of 300°C or less and for a time of 20 hours or less.

[0042] A positive electrode according to one embodiment comprises a positive electrode active material according to any one of the above-described embodiments.

[0043] An all-solid-state battery according to one embodiment comprises a positive electrode according to any one of the embodiments described above.

[0044] The above all-solid-state battery may further include a sulfide-based solid electrolyte.

[0045] The above sulfide-based solid electrolyte may be an argyrodite-based solid electrolyte.

[0046] According to one embodiment of the present disclosure, direct contact between the solid electrolyte and the positive electrode active material can be suppressed.

[0047] According to another embodiment of the present disclosure, the life performance of a battery can be improved.

[0048] According to another embodiment of the present disclosure, smooth movement of lithium ions inside a battery can be induced.

[0049] According to another embodiment of the present disclosure, leakage current occurring inside a battery can be reduced.

[0050] According to another embodiment of the present disclosure, a high-capacity positive electrode active material having excellent resistance performance can be provided.

[0051] According to another embodiment of the present disclosure, an all-solid-state battery having excellent electrochemical performance can be provided.

[0052] According to another embodiment of the present disclosure, an all-solid-state battery with excellent safety can be provided.

[0053] Figure 1 is a conceptual drawing showing the shape of a positive electrode active material according to one embodiment.

[0054] FIG. 2a and FIG. 2b are conceptual drawings sequentially illustrating a method for manufacturing a positive electrode active material according to one embodiment.

[0055] Figure 3a is a diagram showing the results of evaluating the charge-discharge capacity of a battery including a positive electrode active material according to an example and a comparative example.

[0056] Figure 3b is a diagram showing the results of evaluating discharge capacity values ​​according to the number of cycles of batteries including positive electrode active materials according to examples and comparative examples.

[0057] Figure 3c is a diagram showing the results of evaluating the discharge capacity retention rate according to the number of cycles of batteries including positive electrode active materials according to examples and comparative examples.

[0058] Figure 4 is a diagram showing the results of evaluating the resistance characteristics of batteries including positive electrode active materials according to examples and comparative examples.

[0059] Hereinafter, preferred embodiments will be described with reference to various examples. However, the embodiments are not limited to the implementation examples described below and may be modified into various other forms.

[0060] In this specification, the 'mother material' refers to a lithium-transition metal composite oxide corresponding to the core (100), which means a material obtained by mixing a precursor containing a transition metal raw material and a lithium raw material and then performing sintering, and may have substantially the same composition as the core (100).

[0061] For the commercialization of next-generation all-solid-state batteries, interfacial stability between the active material and the solid electrolyte may be required. When the cathode active material comes into direct contact with the solid electrolyte, a resistive layer may form due to interfacial diffusion of the constituent elements. Furthermore, as the battery cycles, the cathode active material undergoes repeated contraction and expansion. These volumetric changes can lead to cracks that restrict the movement of lithium ions, leading to contact and desorption with the electrolyte and the partial generation of inactivated cathode active material. This, in turn, can lead to a decline in battery performance due to overvoltage. Therefore, to practically overcome these issues, it may be necessary to secure interfacial stability by applying a suitable surface film to the cathode active material.

[0062] According to one implementation example, to address the aforementioned issues, a separate coating layer containing a spinel-structured active material can be formed on the surface of the positive electrode active material. However, such a single coating layer alone may have limitations in controlling interfacial diffusion between the positive electrode active material and the solid electrolyte.

[0063] According to one embodiment, the multi-coating layer structure can improve the life performance of a battery by suppressing direct contact between a solid electrolyte and an active material, interfacial diffusion of constituent elements, and side reactions, and can also provide a high-capacity cathode active material with excellent resistance performance by facilitating the movement of lithium ions and reducing leakage current generation. Specific details are disclosed below with reference to FIGS. 1 to 4.

[0064] Figure 1 is a conceptual drawing showing the shape of a positive electrode active material according to one embodiment.

[0065] FIG. 2a and FIG. 2b are conceptual drawings sequentially illustrating a method for manufacturing a positive electrode active material according to one embodiment.

[0066] Figure 3a is a diagram showing the results of evaluating the charge-discharge capacity of a battery including a positive electrode active material according to an example and a comparative example.

[0067] Figure 3b is a diagram showing the results of evaluating discharge capacity values ​​according to the number of cycles of batteries including positive electrode active materials according to examples and comparative examples.

[0068] Figure 3c is a diagram showing the results of evaluating the discharge capacity retention rate according to the number of cycles of batteries including positive electrode active materials according to examples and comparative examples.

[0069] Figure 4 is a diagram showing the results of evaluating the resistance characteristics of batteries including positive electrode active materials according to examples and comparative examples.

[0070] positive electrode active material

[0071] According to one embodiment, a cathode active material (1000) includes a core (100) including a lithium-transition metal composite oxide; a first coating layer (110) formed on a surface of the core; and a second coating layer (120) formed on a surface of the first coating layer, wherein the first coating layer includes a lithium-transition metal composite oxide having a different structure from the lithium-transition metal composite oxide included in the core, and the second coating layer includes a sulfur compound.

[0072] The above-described positive electrode active material (1000) has a multilayer structure, specifically, a bilayer structure, formed on its surface, thereby providing excellent structural stability, thereby improving electrochemical performance, such as life characteristics. Hereinafter, the core (100), first coating layer (110), and second coating layer (120) of the positive electrode active material will be described in more detail.

[0073] Core

[0074] The core (100) above corresponds to a base material of a positive electrode active material including a lithium-transition metal composite oxide, and refers to a portion on the surface of which a coating layer, which will be specifically described below, is formed. Specifically, the core (100) may be substantially composed of a lithium-transition metal composite oxide in particle form. That is, the core itself may be a lithium-transition metal composite oxide particle.

[0075] The lithium-transition metal composite oxide included in the core (100) may have a layered structure. That is, the core may include a lithium-transition metal composite oxide having a layered structure. The layered structure of the lithium-transition metal composite oxide is a structure in which lithium and the transition metal are arranged in different layers, and the lithium-transition metal composite oxide having a layered structure has a lithium diffusion coefficient that is 10,000 times higher and an electrical conductivity that is 1,000 times higher than that of lithium iron phosphate (LFP) having an olivine structure, and thus has the advantage of having a high energy density.

[0076] The lithium-transition metal composite oxide included in the core (100) may be represented by the following chemical formula 1. That is, the core (100) may include a lithium-transition metal composite oxide according to the following chemical formula 1.

[0077] [Chemical Formula 1]

[0078] Li a Ni b M c O2

[0079] In the above chemical formula 1,

[0080] M is one or more elements selected from Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, and 0.90 <a<1.5, 0.33≤b≤1, 0≤c≤0.7이다. 상기 코어(100)가 화학식 1에 따른 리튬-전이금속 복합 산화물을 포함할 경우, 양극 활물질의 용량을 개선하면서 코어를 통해 이하에서 서술할 제1코팅층(110)을 더욱 용이하게 형성할 수 있다.

[0081] The lithium-transition metal oxide may be a secondary particle formed by agglomeration of a plurality of primary particles into a substantially single particle, or may be in the form of a single particle. The single particle form may mean that the primary particles exist in an individual or partially aggregated form, or may mean that they exist in the form of a single crystal (SC). In embodiments, the positive electrode active material may include all of a single particle, a secondary particle, or a mixture thereof.

[0082] <First coating layer>

[0083] The first coating layer (110) is a coating layer formed on the surface of the core (100) and includes a lithium-transition metal composite oxide having a different structure from the lithium-transition metal composite oxide included in the core. The first coating layer (110) can improve the ion conductivity characteristics and capacity of the positive electrode active material by allowing relatively smooth movement of lithium ions, and can contribute to maintaining a high capacity retention rate even when the battery undergoes multiple charge / discharge cycles.

[0084] The lithium-transition metal composite oxide included in the first coating layer (110) may have a spinel structure. That is, the first coating layer (110) may include a lithium-transition metal composite oxide having a spinel structure. In this case, the lithium-transition metal composite oxide included in the core may have a layered structure. When the lithium-transition metal composite oxide has a spinel structure, which is a stable three-dimensional channel structure, the lithium diffusion barrier is relatively low compared to the layered structure, so that the conductivity of lithium ions is excellent, and the capacity of the positive electrode active material can be further improved.

[0085] The first coating layer (110) may further include at least one of a lithium-transition metal composite oxide having a rock salt structure and a lithium-transition metal composite oxide having a layered structure. Specifically, the first coating layer (110) may further include at least one of a lithium-transition metal composite oxide having a rock salt structure and a lithium-transition metal composite oxide having a layered structure, in addition to a lithium-transition metal composite oxide having a spinel structure.

[0086] The first coating layer (110) may be formed on the surface of the core (100) through a heat treatment process, and the structure of the lithium-transition metal composite oxide included in the first coating layer (110) may change depending on the heat treatment temperature. Therefore, in the process of forming the first coating layer (110), a lithium-transition metal composite oxide having a structure other than a spinel structure may be formed in the first coating layer, and the lithium-transition metal composite oxide having such a structure may remain in the first coating layer of the cathode active material that is ultimately manufactured. The process of forming the first coating layer, etc. will be described in more detail below.

[0087] The lithium-transition metal composite oxide included in the first coating layer (110) may be represented by the following chemical formula 2. That is, the first coating layer (110) may include a lithium-transition metal composite oxide according to the following chemical formula 2.

[0088] [Chemical Formula 2]

[0089] Li x M y O z

[0090] In the above chemical formula 2,

[0091] M is at least one element selected from Ni, Co, Mn, Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, and 0≤x≤4, 0≤y≤4, 0≤z≤8. When the first coating layer (110) includes a lithium-transition metal composite oxide according to Chemical Formula 2, the movement of lithium ions through the first coating layer is easy, so that the electrochemical performance of the positive electrode active material can be improved to an excellent level, and the structural stability of the first coating layer can also be secured.

[0092] The thickness of the first coating layer (110) may be 0.1 to 500 nm. Specifically, the thickness of the first coating layer may be 5 nm or more and 100 nm or less. The method for measuring the thickness of the first coating layer (110) is not particularly limited, and for example, the thickness may be calculated through measurement using a transmission electron microscope (TEM) and fast Fourier transform (FFT) analysis.

[0093] The above positive electrode active material (1000) may have a cation mixing ratio of 7% or less. Specifically, the positive electrode active material (1000) may have a cation mixing ratio of 5% or less and 2.2% or more.

[0094] The cation mixing ratio is an indicator that can be used to determine the degree of hybrid rearrangement of cations such as lithium and transition metals when analyzing positive electrode active materials through X-ray diffraction (XRD). The cation mixing ratio may appear differently depending on the structure and composition of the positive electrode active material.

[0095] For example, in a layered cathode active material containing lithium (Li) and nickel (Ni), Li and Ni are arranged in different layers, but as the Ni content increases or the number of charge / discharge cycles increases, the positions of Li and Ni may be exchanged. When the cations contained in the layered cathode active material undergo a hybrid rearrangement in this way, the layered structure may change into a spinel structure or a rock salt structure.

[0096] Accordingly, since the first coating layer includes a lithium-transition metal composite oxide having a different structure from the core, when measuring the cation mixing ratio for the positive electrode active material including the core (100) and the first coating layer (110), the degree to which the first coating layer is formed in the positive electrode active material can be confirmed. For example, as the cation mixing ratio measured for the positive electrode active material increases, it can be determined that the first coating layer (110) is formed thicker.

[0097] When the cation mixing ratio of the above-described positive electrode active material (1000) is within the above-described range, a positive electrode active material having excellent performance can be manufactured by forming the first coating layer to an appropriate degree without inhibiting the effect of the core.

[0098] <Second coating layer>

[0099] The second coating layer (120) is a coating layer containing a sulfur compound, and is formed on the surface of the first coating layer (110) to further improve the interface stability and electrochemical performance of the positive electrode active material. Specifically, the sulfur compound can combine with lithium remaining on the surface of the positive electrode active material to reduce leakage current generation and improve resistance characteristics.

[0100] The above sulfur compound may include one or more compounds according to the following chemical formula 3.

[0101] [Chemical Formula 3]

[0102] Li x M y S z O f

[0103] In the above chemical formula 3,

[0104] M is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, ammonium ions, substituted or unsubstituted aliphatic hydrocarbon groups, and combinations thereof, and 0≤x≤10, 0≤y≤10, 0 <z≤10, 0≤f≤24이다. 상기 제2코팅층(120)에 포함되는 황 화합물이 상술한 종류의 화합물을 포함할 경우, 고체전해질과 양극 활물질 간의 구성 원소 확산 및 부반응을 효과적으로 억제할 수 있으며, 계면 저항층의 형성 및 전지의 사이클 성능 저하를 방지하고 전기화학적 성능을 개선할 수 있다.

[0105] The above sulfur compound may include sulfur oxide, and the sulfur oxide may be included in an amount of 200 to 8,000 ppm based on the total weight of the second coating layer (120). The sulfur oxide may be included in the second coating layer (120) in the form of sulfur monoxide (SO), sulfur dioxide (SO2), sulfur trioxide (SO3), etc., and the content of sulfur oxide included in the second coating layer (120) may be measured by mass spectrometry using inductively coupled plasma (ICP), etc. When the second coating layer (120) includes sulfur oxide within the above-described range, capacity retention, etc. may be further improved.

[0106] The second coating layer (120) may further include one or more elements selected from P, B, Si, Al, and W.

[0107] The above positive electrode active material (1000) can be manufactured by any one of the manufacturing methods described below.

[0108] Method for manufacturing positive electrode active material

[0109] A method for manufacturing a positive electrode active material according to one embodiment manufactures a positive electrode active material (1000) according to any one of the above-described embodiments. Hereinafter, the method for manufacturing the positive electrode active material will be described in detail with reference to FIGS. 2A and 2B.

[0110] <Material preparation stage (S0) and material pretreatment stage (S1)>

[0111] The method for manufacturing the above-mentioned positive electrode active material may include a base material preparation step (S0) as a process / step for synthesizing a base material. Specifically, the base material preparation step (S0) may form a core through a dry heat treatment process for a mixture of a precursor including a transition metal raw material and a lithium raw material. The lithium raw material may be, for example, lithium hydroxide (LiOH), lithium carbonate (Li2CO3), or a combination thereof. The base material manufactured in the base material preparation step (S0) may have substantially the same composition as the core (100).

[0112] The above dry heat treatment process can be performed by heat treating at 700°C or higher for 6 hours or longer.

[0113] The method for manufacturing the above-described positive electrode active material may further include a base material pretreatment step (S1) for the core (100), which is a base material manufactured as described above. Specifically, the base material pretreatment step (S1) is a step of forming a precursor coating layer (105) on the surface of the core, and may include a water washing and then a dry heat treatment process. More specifically, the base material pretreatment step (S1) may include a water washing process (S1-1) and a dry heat treatment process (S1-2) for the core (100) (see FIG. 2a).

[0114] The above washing process (S1-1) can be carried out by preparing an aqueous solution containing a coating precursor in an appropriate stoichiometric ratio of a material to be coated on a positive electrode active material, adding the positive electrode active material to the aqueous solution, and then drying the positive electrode active material to remove moisture.

[0115] The above aqueous solution may contain a complex sulfate compound according to the following chemical formula 4.

[0116] [Chemical Formula 4]

[0117]

[0118] In the above chemical formula 4,

[0119] X is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, Group 16 elements, rare earth elements, ammonium ions, substituted or unsubstituted aliphatic hydrocarbon groups, and combinations thereof, and 1≤a≤5 and 1≤b≤5.

[0120] The above dry heat treatment process (S1-2) can be performed by heat treatment at 80°C or higher for 6 hours or longer.

[0121] The coating of the precursor coating layer (105) formed in the drying process after the above washing does not only mean complete film-type adhesion, and may also include a case where some components of the precursor coating layer are adhered on the surface of the core (100).

[0122] <Coating layer formation step (S2)>

[0123] The method for manufacturing the above-mentioned positive electrode active material may include a coating layer forming step (S2) of forming a first coating layer (110) and a second coating layer (120), and in the coating layer forming step (S2), the first coating layer (110) may be formed by a heat treatment process for the core (100). According to one embodiment, the coating layer forming step (S2) may be performed by a heat treatment process for the core (100), and the first coating layer (110) may be a coating layer formed to include a spinel structure by causing a phase transition on the outer surface of the core (100) by the heat treatment process in the coating layer forming step (S2).

[0124] According to another embodiment, the coating layer forming step (S2) may be performed as a heat treatment process for a core (100) having a bulb coating layer (105) formed on a surface, and the bulb coating layer (105) may be a multilayer structure including a first bulb coating layer having a layered structure in which a phase transition has partially occurred on the outer surface of the core (100); and a second bulb coating layer formed on the surface of the first bulb coating layer. In this case, the first coating layer (110) may be a coating layer formed by transforming the first bulb coating layer by the heat treatment process in the coating layer forming step (S2) to include a spinel structure.

[0125] The heat treatment process may be carried out at a temperature of 300°C or less. Specifically, the temperature of the heat treatment process may be 280°C or less or 200°C or less, or 80°C or more, 100°C or more, or 150°C or more. In addition, the heat treatment process may be carried out for 20 hours or less. Specifically, the time of the heat treatment process may be 15 hours or less or 10 hours or less, or 1 hour or more or 3 hours or more.

[0126] As described above, the structure of the lithium-transition metal composite oxide may change depending on the conditions of the heat treatment process for the core (100). Specifically, as the temperature increases due to the heat treatment, the structure of the lithium-transition metal composite oxide may change in the order of a layered structure, a spinel structure, and a rock salt structure. For example, the lithium-transition metal composite oxide may have a layered structure below 80°C, the layered structure may change to a spinel structure between 80°C and 280°C, the spinel structure may change to a rock salt structure at a temperature exceeding 280°C, and may have a complete rock salt structure at 600°C.

[0127] Therefore, when the conditions such as temperature and time of the heat treatment process for the core (100) are adjusted within the above-described range, the first coating layer (110) can be effectively formed to include a lithium-transition metal composite oxide having a structure different from the structure of the lithium-transition metal composite oxide included in the core (100).

[0128] In the above coating layer forming step (S2), the second coating layer (120) can be formed of a complex sulfate compound according to the following chemical formula 4.

[0129] [Chemical Formula 4]

[0130]

[0131] In the above chemical formula 4,

[0132] X is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, Group 16 elements, rare earth elements, ammonium ions, substituted or unsubstituted aliphatic hydrocarbon groups, and combinations thereof, and 1≤a≤5 and 1≤b≤5. When the above-described type of compound is applied as the complex sulfate compound, improved capacity and relatively superior capacity retention can be expected.

[0133] According to one embodiment, the second coating layer (120) may be formed by a heat treatment process on a mixture of the core (100) on which the first coating layer (110) is formed on the surface and the complex sulfate compound.

[0134] The method for manufacturing the mixture of the core (100) and the complex sulfate compound described above for the first coating layer (11) and the second coating layer (120) is not particularly limited, and dry mixing or wet mixing can be applied.

[0135] The above dry mixing method can be applied alone or in combination with a dry mixer such as a mortar and pestle or a vortex mixer. In addition, the above wet mixing method can be applied by dissolving the components using a solvent such as water or ethanol.

[0136] According to another embodiment, the second coating layer (120) may be formed by a heat treatment process on a core (100) having a bulb coating layer (105) formed on the surface. At this time, the bulb coating layer (105) may be a multilayer structure including a first bulb coating layer having a layered structure in which a phase transition has partially occurred on the outer surface of the core (100); and a second bulb coating layer formed on the surface of the first bulb coating layer, and the second coating layer (120) may be a coating layer formed by deforming the second bulb coating layer by a heat treatment process in the coating layer forming step (S2).

[0137] In addition, the second bulb coating layer may be a coating layer formed in the process of forming a bulb coating layer (105) on the surface of the core (100) by a drying heat treatment process after washing the core (100) in the above-described parent material pretreatment step (S1), and at this time, the washing treatment may be performed using an aqueous solution in which a complex sulfate compound according to the chemical formula 4 is dissolved in water.

[0138] In the above coating layer forming step (S2), the heat treatment process for the core (100) having the first coating layer (110) formed on the surface and the mixture of the complex sulfate compound; or the core (100) having the precursor coating layer (105) formed on the surface may be performed at a temperature of 300°C or lower. Specifically, the temperature of the heat treatment process may be 280°C or lower or 200°C or lower, or 80°C or higher, 100°C or higher, or 150°C or higher. In addition, the heat treatment process may be performed for 20 hours or lower. Specifically, the time of the heat treatment process may be 15 hours or lower or 10 hours or lower, or 1 hour or higher or 3 hours or higher.

[0139] The content of the composite sulfate compound introduced based on the weight of the positive electrode active material on which the first coating layer (110) is formed on the surface of the core (100) may be 200 to 5,000 ppm.

[0140] The above mixture or aqueous solution may further include an additional compound comprising one or more elements selected from P, B, Si, Al, and W. When the above mixture or aqueous solution further includes such an additional compound, the second coating layer (120) may further include one or more elements selected from P, B, Si, Al, and W.

[0141] Bipolar and all-solid-state batteries

[0142] A positive electrode according to one embodiment comprises a positive electrode active material according to any one of the above-described embodiments. For example, the positive electrode may comprise a positive electrode current collector; and a positive electrode mixture layer formed on at least one surface of the positive electrode current collector, wherein the positive electrode mixture layer may comprise a positive electrode active material according to any one of the above-described embodiments.

[0143] The components of the above-mentioned positive electrode collector are not particularly limited, and a plate or foil made of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof may be used.

[0144] The above-mentioned positive electrode mixture layer may further include a binder. The binder may include, for example, one or two or more kinds of polyvinylidene fluoride, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate.

[0145] The above-described positive electrode mixture layer may further include a conductive material. Examples of the conductive material include one or more types of graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotubes (CNT); metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives.

[0146] An all-solid-state battery according to one embodiment includes a positive electrode according to any one of the above-described embodiments. For example, the all-solid-state battery may include a positive electrode according to any one of the above-described embodiments; and a negative electrode.

[0147] The above negative electrode may include a negative electrode current collector; and a negative electrode composite layer formed on at least one surface of the negative electrode current collector.

[0148] The components of the above negative electrode collector are not particularly limited, and a plate or foil made of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof may be used.

[0149] The above negative electrode composite layer is a negative electrode active material, including carbon-based active materials such as artificial graphite and natural graphite, and silicon oxide (SiOx; 0 <x<2), Si-C 복합체 등의 규소계 활물질, 리튬 메탈 등의 금속을 포함할 수 있다.

[0150] The above-mentioned negative electrode composite layer may further include a binder. The binder may include, for example, one or two or more types of styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc.

[0151] The above-described negative electrode composite layer may further include a conductive material. Examples of the conductive material include one or more types of graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotubes (CNT); metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives.

[0152] The above-described all-solid-state battery may further include a solid electrolyte. The solid electrolyte may be an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a polymer-based solid electrolyte, and specifically, may be a sulfide-based solid electrolyte. That is, the all-solid-state battery according to one embodiment may further include a sulfide-based solid electrolyte. For example, the all-solid-state battery may include a positive electrode according to any one of the above-described embodiments; a negative electrode, and a sulfide-based solid electrolyte disposed between the positive electrode and the negative electrode.

[0153] The above sulfide-based solid electrolyte is Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m, n are positive numbers, Z is one of Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In), Li 7-x PS 6-x Clx (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2) and Li 7-x PS 6-x I x There can be one or more selected from (0≤x≤2).

[0154] The above sulfide-based solid electrolyte may be an argyrodite-based solid electrolyte. The above argyrodite-based solid electrolyte may be a compound represented by the following chemical formula 5.

[0155] [Chemical Formula 5]

[0156] Li a + A + b Q c X -d

[0157] In the above chemical formula 5, 1≤a≤12, 0≤b≤5, 0≤c≤10, 0≤d≤2, A is at least one of P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta, Q is at least one of S, Se, or Te, and X is at least one of Cl, Br, I, F, CN, OCN, SCN, or N3.

[0158] Specifically, the above argyrodite-based solid electrolyte is Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), Li 7-x PS 6-x I x (0≤x≤2), Li6PS5Cl, Li6PS5Br, , Li6PS5I, Li 6.5 Sb 0.5 Ge 0.5 S5I, Li 5.7 PS 4.7 Cl 1.3 , Li 6.6 Sb 0.5 Si0.6 It may be a compound represented by a chemical formula such as S5I.

[0159] Example

[0160] 1. Manufacturing of positive electrode active materials and composite positive electrodes

[0161] 1) Example

[0162] (1) Preparation of parent material

[0163] A positive electrode active material matrix was manufactured by calcining a metal hydroxide and a lithium salt. Specifically, the mixture manufactured by continuously adding an aqueous solution containing a metal-containing salt in a co-precipitation environment was washed, filtered, and dried, and then dry-heat-treated in an oven at 700°C or higher for 6 hours or longer, thereby manufacturing a core including a lithium-transition metal composite oxide according to the following chemical formula 1 as an NCM-based positive electrode active material having a layered structure.

[0164] [Chemical Formula 1]

[0165] Li a Ni b M c O2

[0166] In the above chemical formula 1,

[0167] M is one or more elements selected from Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn and Ba, and 0.90 <a<1.5, 0.33≤b≤1, 0≤c≤0.7이다.

[0168] (2) Pretreatment of base material and formation of coating layer

[0169] The NCM-based positive electrode active material core having a layered structure manufactured as described above was washed in deionized water (DW) (see Fig. 2a). Specifically, when washing the base material, an aqueous solution in which a complex sulfate compound represented by the following chemical formula 4 was dissolved in deionized water (DW) was used to form a precursor coating layer for forming a wet coating layer on the surface of the positive electrode active material core.

[0170] [Chemical Formula 4]

[0171]

[0172] In the above chemical formula 4,

[0173] X is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, Group 16 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups, and combinations thereof, and 1≤a≤5 and 1≤b≤5.

[0174] At this time, the content of the introduced complex sulfate compound was adjusted to 200 to 5,000 ppm based on the weight of the positive electrode active material on which the first coating layer was formed on the core surface. Thereafter, the washed positive electrode active material was dried by dry heat treatment at 80°C or higher for 6 hours or more, and fired in a kiln, and then dry heat treatment was performed in air at 180°C for 3 hours or more to form a first coating layer by phase transition of the core surface layer, and a second coating layer was formed by heat treatment and firing of the precursor coating layer, which is a coating layer precursor attached to the surface of the existing positive electrode base material through a wet coating layer process (see Fig. 2b).

[0175] 2) Comparative examples 1 and 2

[0176] An active material having a layered structure, which is a lithium-transition metal composite oxide, did not undergo the first coating layer / second coating layer forming process and thus did not have a first coating layer or a second coating layer formed was used as the positive electrode active material of Comparative Example 1. In addition, an active material manufactured in the same manner as the examples but did not undergo the second coating layer forming process and thus did not include a second coating layer was used as the positive electrode active material of Comparative Example 2.

[0177] 2. Manufacturing of composite anodes

[0178] A composite positive electrode was manufactured by mixing the positive electrode active material, argyrodite-based sulfide-based solid electrolyte, and conductive material (material including carbon black, etc.) according to the examples and comparative examples. At this time, the content of the positive electrode active material was 60 wt% or more, the content of the conductive material was 6 wt% or less, and the remaining proportions were composed of the content of the sulfide-based solid electrolyte based on the total weight of the composite positive electrode.

[0179] 3. Manufacturing of pressurized cells

[0180] A sulfide-based solid electrolyte, the manufactured positive electrode, and the Li-In negative electrode were sequentially poured into a 1 cm diameter pressurized cell mold, and then pressurized to manufacture a dry pressurized cell. At this time, the pressurized cell mold was placed on the lower body, the upper body was closed, and the first compression was performed using a (wing) screw, and then a torque wrench was tightened. In addition, in order to prevent the sulfide-based solid electrolyte from coming into contact with moisture in the air, which may cause hydrogen sulfide generation and conductivity reduction, the space between the pressurized cells was blocked with an O-ring, and the space between the cap and body was sealed with Parafilm.

[0181] 4. Performance Evaluation

[0182] 1) Mars charge / discharge capacity

[0183] The pressurized cell manufactured as described above was charged at a constant current of 0.1 C at 30°C until the voltage reached 3.65 V, and then the mode was changed to a constant voltage state of 3.65 V, and the remaining section was charged to measure the charge capacity. Subsequently, the cell was discharged at a constant current of 0.1 C until the voltage reached 1.88 V, and the discharge capacity was measured. The measured charge capacity and discharge capacity values ​​for each example and comparative example are shown in Fig. 3a and Table 1.

[0184] 2) Life performance (capacity retention rate)

[0185] For the pressurized cell at 30℃, the same as above, constant current charging was performed at 0.1C rate until the voltage reached 3.65 V at 30℃, and the mode was changed to a constant voltage state of 3.65 V, and the remaining section was charged to measure the charge capacity. Next, the discharge capacity was measured by discharging at a constant current of 0.1C rate until the voltage reached 1.88 V. After repeating the cycle more than 30 times under the following conditions, some of the discharge capacity values ​​measured according to the number of cycles are shown in Fig. 3b. In addition, the discharge capacity retention rate compared to the initial cycle discharge capacity was measured as a %, and the results are shown in Fig. 3c and Table 1.

[0186] Here, Comparative Examples 1 and 2 and the Examples refer to three types of positive electrode active materials that have undergone different processing. More specifically, Comparative Example 1 refers to a positive electrode active material in a base material state without a coating layer formed, Comparative Example 2 refers to a positive electrode active material including a first coating layer containing a component having a spinel structure, and the Examples refer to a final positive electrode active material having a double coating layer formed.

[0187] 3) Cell resistance characteristics

[0188] After recharging the pressurized cells that had been cycled more than 30 times at 30°C to a SOC range of 100%, the pressurized cells of Comparative Example 1 and Example 1 were subjected to a step of measuring the impedance resistance change within the immersed pressurized cells by electrochemical impedance spectroscopy (EIS) using a potentiostat at 25°C. The results of representing the corresponding behavior as a Nyquist plot are shown in Fig. 4. At this time, the measurement scan range was 7 MHz to 100 mHz, the resistance was measured at 10-point intervals, and the sinus amplitude was 50 mV.

[0189] Capacity (mAh / g) Capacity retention rate (%) (@ 10 Cycle) Charge capacity Discharge capacity Comparative example 1210.3124.371.7 Comparative example 2199.7132.165.0 (@ 9 Cycle) Example 237.7140.176.5

[0190] Referring to Table 1 and FIGS. 3a to 4, when the active material of Example 1 having both the first coating layer and the second coating layer formed was applied, the capacity value and capacity retention rate of the pressurized cell were found to be relatively superior compared to the cases of Comparative Example 1 having no separate coating layer formed and Comparative Example 2 having only the first coating layer formed. This is believed to be due to the increase in the capacity of the active material as the conductivity of lithium ions is improved due to the second coating layer including a sulfur compound, and when the second coating layer including a sulfur compound is included, the intermediate layers between the base material and the solid electrolyte are relatively stably maintained over the cycle, and the life characteristics are also believed to be improved.

[0191] In addition, when the coating layer of Example 1 was applied, the cell resistance value was found to be relatively lower than that of Comparative Example 1. Specifically, referring to FIG. 4, the Example showed a resistance that was about 950 ohm lower than that of Comparative Example 1 in the Nyquist plot, indicating a resistance performance that was improved by about 23.1%. Considering that the difference between Comparative Example 1 and the Example is based only on the positive electrode active material, the semi-circle in the EIS data according to FIG. 4 can be predicted to be related to the resistance of the positive electrode active material. Specifically, the resistance of the positive electrode active material can be classified into the interfacial resistance between the positive electrode active material and the solid electrolyte and the resistance due to Li ion diffusion within the positive electrode active material, and considering the frequency range, the resistance performance measured by the EIS data according to FIG. 4 can be predicted to be the interfacial resistance between the positive electrode active material and the solid electrolyte.

[0192] Therefore, when a second coating layer containing a sulfur compound according to the following chemical formula 3 is formed on the first coating layer, it is judged that a resistance reduction effect due to the high Li ion conductivity of the second coating layer can be expected.

[0193] [Chemical Formula 3]

[0194] Li x M y S z O f

[0195] In the above chemical formula 3,

[0196] M is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups, and combinations thereof, and 0≤x≤10, 0≤y≤10, 0 <z≤10, 0≤f≤24이다.

[0197] In addition, in the case of the active material of Example 1 having a solid double coating layer formed, it is expected that the inter-diffusion phenomenon between elements will be suppressed and the formation of a resistance layer will be reduced during the charge / discharge cycle. Therefore, when an optimal double coating layer is formed on the positive electrode active material including a lithium-transition metal composite oxide as in Example 1, the electrochemical performance including capacity characteristics, life characteristics, and resistance characteristics will be excellent, and an advanced positive electrode active material applicable to an all-solid-state battery can be provided.

[0198] Although the embodiments of the present disclosure have been described in detail above, the scope is not limited thereto, and it will be apparent to those skilled in the art that various modifications and variations are possible within a scope that does not depart from the technical spirit of the present disclosure described in the claims.

[0199] [Explanation of symbols]

[0200] 100: Positive active material core

[0201] 105: Bulb coating layer

[0202] 110: First coating layer

[0203] 120: Second coating layer

[0204] 1000: Positive electrode active material

[0205] As described above, the features of the present invention can be applied in whole or in part to a positive electrode active material, a method for producing the same, a positive electrode including the same, and an all-solid-state battery.

Claims

1. A core comprising a lithium-transition metal composite oxide; and A first coating layer formed on the surface of the core; and a second coating layer formed on the surface of the first coating layer, The first coating layer includes a lithium-transition metal composite oxide having a different structure from the lithium-transition metal composite oxide included in the core, The second coating layer comprises a sulfur compound, Positive active material.

2. In paragraph 1, The above core comprises a lithium-transition metal composite oxide having a layered structure. Positive active material.

3. In paragraph 1, The above core comprises a lithium-transition metal composite oxide according to the following chemical formula 1. Positive active material. [Chemical Formula 1] Li a Ni b M c O2 In the above chemical formula 1, M is one or more elements selected from Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, and 0.90 <a<1.5, 0.33≤b≤1, 0≤c≤0.7이다.

4. In paragraph 1, The first coating layer comprises a lithium-transition metal composite oxide having a spinel structure. Positive active material.

5. In paragraph 4, The first coating layer further comprises at least one of a lithium-transition metal composite oxide having a rock salt structure and a lithium-transition metal composite oxide having a layered structure. Positive active material.

6. In paragraph 1, The first coating layer comprises a lithium-transition metal composite oxide according to the following chemical formula 2. Positive active material. [Chemical Formula 2] Li x M y O z In the above chemical formula 2, M is one or more elements selected from Ni, Co, Mn, Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, and 0≤x≤4, 0≤y≤4, 0≤z≤8.

7. In paragraph 1, The thickness of the first coating layer is 0.1 to 500 nm, Positive active material.

8. In paragraph 1, Cation mixing ratio is less than 7%, Positive active material.

9. In paragraph 1, The above sulfur compound comprises at least one compound according to the following chemical formula 3: Positive active material. [Chemical Formula 3] Li x M y S z O f In the above chemical formula 3, M is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups, and combinations thereof, and 0≤x≤10, 0≤y≤10, 0 <z≤10, 0≤f≤24이다.

10. In paragraph 1, The above sulfur compound includes sulfur oxide, The above sulfur oxide is included in an amount of 200 to 8,000 ppm based on the total weight of the second coating layer. Positive active material.

11. In paragraph 1, The second coating layer further includes at least one element selected from P, B, Si, Al, and W. Positive active material.

12. Manufacturing a positive electrode active material according to any one of clauses 1 to 11, Method for manufacturing positive electrode active material.

13. In paragraph 12, A step of preparing a core by a dry heat treatment process for a mixture of a precursor containing a transition metal raw material and a lithium raw material; and Comprising a pretreatment step of the base material to form a precursor coating layer on the surface of the core, Method for manufacturing positive electrode active material.

14. In paragraph 13, Further comprising a coating layer forming step of forming a first coating layer and a second coating layer, In the above coating layer forming step, the first coating layer is formed through a heat treatment process for the core. Method for manufacturing positive electrode active material.

15. In paragraph 14, In the above coating layer forming step, the second coating layer is formed of a complex sulfate compound according to the following chemical formula 4. Method for manufacturing positive electrode active material. [Chemical Formula 4] In the above chemical formula 4, X is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, Group 16 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups, and combinations thereof, and 1≤a≤5 and 1≤b≤5.

16. In paragraph 14, In the above coating layer forming step, the heat treatment process is carried out in the air at a temperature of 300°C or less and for a time of 20 hours or less. Method for manufacturing positive electrode active material.

17. Containing a positive electrode active material according to any one of claims 1 to 11; anode.

18. Containing the positive electrode according to Article 17, All-solid-state battery.

19. In paragraph 18, Further comprising a sulfide-based solid electrolyte, All-solid-state battery.

20. In paragraph 19, The above sulfide-based solid electrolyte is an argyrodite-based solid electrolyte. All-solid-state battery.

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