Positive electrode active material composite, positive electrode comprising same, and lithium ion secondary battery comprising same

Abstract

The invention provides a positive electrode active material composite, a positive electrode comprising the positive electrode active material composite, and a lithium ion secondary battery comprising the positive electrode. The positive electrode active material composite comprises a positive electrode active material base material and a compound coating layer comprising elements Li, P and F. The compound coating layer is coated on the positive electrode active material base material.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2023-0111722, filed on August 25, 2023, and Korean Patent Application No. 10-2024-0113050, filed on August 22, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a positive electrode active material composite, a positive electrode comprising the composite, and a lithium-ion secondary battery comprising the positive electrode. Background Technology

[0003] Compared to nickel-manganese or nickel-cadmium batteries, lithium-ion rechargeable batteries have the advantages of higher energy density, lower self-discharge rate and longer life, but their disadvantages include stability relative to overheating and low power output.

[0004] To overcome the problems of lithium-ion rechargeable batteries, all-solid-state batteries have been proposed as an alternative. An all-solid-state battery includes an electrolyte layer containing a solid electrolyte, a positive electrode layer and a negative electrode layer containing solid electrolyte formed on both sides of the electrolyte layer, and each electrode has a structure with a bonding current collector.

[0005] All-solid-state batteries can be classified into oxide, polymer, and sulfide batteries based on the materials used in their solid electrolytes. Sulfide all-solid-state batteries exhibit superior lithium-ion conductivity compared to other types of batteries. However, compared to traditional liquid electrolyte batteries, they suffer from lower ionic conductivity and higher resistance between the positive / negative electrode and the solid electrolyte, resulting in reduced lifespan and power output.

[0006] In other words, it is known that the positive electrode active material and the sulfide-based solid electrolyte react at the interface to form a resistive material that interferes with the operation of all-solid-state batteries. This resistive material reduces the initial capacity and efficiency of the all-solid-state battery.

[0007] To address these issues, techniques for forming various coatings on the surface of positive electrode active materials are known. For example, there are known techniques for coating Li-MO (where M is B, Al, Zr, P, Ti, Nb, W, etc.) lithium oxide onto the surface of positive electrode active materials.

[0008] However, this coated positive electrode active material does not seem to be able to sufficiently and effectively reduce the interfacial resistance between the positive electrode active material and the sulfide-based solid electrolyte and improve lithium-ion conductivity.

[0009] [Existing technical documents]

[0010] [Patent Literature]

[0011] Korean Patent Application Publication No. 10-2018-0123369 Summary of the Invention

[0012] Technical issues

[0013] The present invention is designed to solve the above-mentioned problems of the prior art. One object is to provide a positive electrode active material composite that can improve the driving characteristics and lifespan characteristics of a battery by reducing the interfacial resistance between the positive electrode active material and the solid electrolyte and improving the lithium-ion conductivity, a positive electrode containing the positive electrode active material composite, and a lithium-ion secondary battery containing the positive electrode.

[0014] Technical solution

[0015] To achieve the above objectives, the present invention provides a positive electrode active material composite, comprising a positive electrode active material substrate and a coating layer coated on the positive electrode active material substrate.

[0016] The coating layer comprises at least one selected from the group consisting of LiPF6, LiDFBOP (lithium difluorodioxanol phosphate), and LiTFOP (lithium tetrafluorooxanol phosphate).

[0017] The present invention also provides a positive electrode comprising the positive electrode active material composite of the present invention.

[0018] The present invention also provides a lithium-ion secondary battery comprising the positive electrode, the negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode.

[0019] Beneficial effects

[0020] The positive electrode active material composite of the present invention provides the effect of reducing the interfacial resistance between the positive electrode active material and the solid electrolyte and improving the lithium-ion conductivity by forming a coating layer on the surface of the positive electrode active material.

[0021] In addition, the above effects provide improvements in the battery's driving characteristics and lifespan.

[0022] By incorporating the aforementioned positive electrode active material, the lithium-ion secondary battery of the present invention can provide excellent driving characteristics and lifespan characteristics. Detailed Implementation

[0023] The invention will be described in more detail below to provide a better understanding of it.

[0024] The terms and words used in this specification and claims should not be construed as having their conventional or dictionary meanings, but rather as meanings and concepts consistent with the technical spirit of the invention, based on the principle that the inventors may define the concepts of the terms in a manner they deem appropriate in order to best illustrate their invention. Furthermore, the terminology used herein is for describing exemplary instances only and is not intended to limit the invention. Unless the context clearly indicates otherwise, singular expressions include plural forms.

[0025] When it is said that a component is “connected to, contained in, laminated on, or mounted on” another component, it should be understood that it can be directly connected to or mounted on the other component, but other components may be present in between. On the other hand, when it is said that a component is “directly connected to or mounted on” another component, it should be understood that there are no other components between them. Other expressions describing the relationship between components, such as “on top of” and “directly on top of”, or “between” and “directly between”, or “adjacent” and “directly adjacent”, should be interpreted similarly.

[0026] Unless otherwise specified, the term "combination" as used herein includes mixtures, alloys, reaction products, etc.

[0027] The positive electrode active material composite of the present invention is characterized in that it comprises a positive electrode active material substrate and a coating layer coated on the positive electrode active material substrate.

[0028] The coating layer comprises at least one selected from the group consisting of LiPF6, LiDFBOP (lithium difluorodioxanol phosphate), and LiTFOP (lithium tetrafluorooxanol phosphate).

[0029] The positive electrode active material composite of the present invention is characterized by reducing the interfacial resistance between the positive electrode active material and the solid electrolyte by including a coating layer, and improving lithium-ion conductivity by the structure of the coated particles constituting the coating layer.

[0030] In addition to at least one selected from the group consisting of LiPF6, LiDFBOP (lithium difluorodioxophosphate) and LiTFOP (lithium tetrafluorooxophosphate), the coating may also comprise other coating substrates known in the art.

[0031] The positive electrode active material substrate can be a compound represented by the following chemical formula 1:

[0032] [Chemical Formula 1]

[0033] Li a (Ni 1-x-y-z Co x M1 y M2 z O2

[0034] Wherein, M1 is manganese (Mn), aluminum (Al), or a combination thereof;

[0035] M2 is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), aluminum (Al), or any combination of two or more of these; and

[0036] 0.95≤a≤1.3, 0 <x<1,0≤y<1,0≤z<1。

[0037] However, the positive electrode active material substrate is not limited to the above-mentioned compounds, and any positive electrode active material known in the art can be used or further comprised. Specifically, at least one selected from the group consisting of NCM, NCMA, LFP, LCA, LCO, LMO, etc., can be used as the positive electrode active material substrate. More specifically, LiNi can be used. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.75 Co 0.1 Mn 0.1 Al 0.05 O2, LiFePO4, etc.

[0038] Based on the total weight of the positive electrode active material composite, the coating content can be from 0.1 to 4.5 wt%, preferably from 0.1 to 4.5 wt%, more preferably from 0.1 to 3 wt%. If the coating content is less than 0.1 wt%, the effect of reducing the interfacial resistance between the positive electrode active material and the solid electrolyte and improving lithium-ion conductivity may be negligible, while if it exceeds 4.5 wt%, the interfacial resistance increases due to the increased lithium-ion migration distance between the active material and the solid electrolyte, which is therefore undesirable.

[0039] In addition, the thickness of the coating can range from 10 nm to 200 nm.

[0040] The coating can be formed by wet or dry mixing of the positive electrode active material substrate and the coating substrate. Dry mixing can be high-shear mixing.

[0041] The particle size (D50) of the positive electrode active material substrate can be from 10 nm to 10 μm, and the particle size (D50) of the coated substrate can be from 10 nm to 200 nm.

[0042] In this invention, particle size can be measured using a particle size analyzer. For example, a Mastersizer 3000 (Malvem panalytical) instrument can be used for measurement.

[0043] In one embodiment of the invention, the positive electrode active material composite may further comprise a solid electrolyte. In this case, the solid electrolyte may be the same as the solid electrolyte described later in the positive electrode active material layer.

[0044] The present invention also relates to a positive electrode comprising the positive electrode active material composite.

[0045] The positive electrode is characterized in that it comprises the positive electrode active material composite of the present invention. Since this positive electrode active material composite is consistent with the foregoing description, its description is omitted.

[0046] The positive electrode of the present invention can be a self-standing positive electrode made of positive electrode active material layer components, or it can be in the form of a positive electrode active material layer stacked on the positive electrode current collector.

[0047] In addition to the positive electrode active material composite, the positive electrode active material layer may also contain positive electrode active materials known in the art.

[0048] Specific examples of known positive electrode active materials in this art include, but are not limited to, lithium salts such as lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (hereinafter referred to as NCA), lithium nickel cobalt manganese oxide (hereinafter referred to as NCM), lithium manganese oxide, and lithium iron phosphate, as well as lithium sulfide.

[0049] The positive electrode active material layer may also include a solid electrolyte. As the solid electrolyte, any solid electrolyte known in the art can be used without limitation; for example, oxide-based solid electrolytes, polymer-based solid electrolytes, or sulfide-based solid electrolytes can be used, with sulfide-based solid electrolytes being particularly preferred. Alternatively, the positive electrode active material layer may be in a form that does not include a polymer-based solid electrolyte.

[0050] Sulfide solid electrolytes can include Li₂S-P₂S₅, Li₂S-P₂S₅-LiX (where 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, and Li₂S-P₂S₅-Z. m S n (Where m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (Where p and q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, or In) or any combination thereof. The solid electrolyte may contain one material selected from these sulfide-based solid electrolyte materials, or may contain two or more materials selected from them.

[0051] Sulfide solid electrolytes may include solid electrolytes represented by the following chemical formula 2.

[0052] [Chemical Formula 2]

[0053] Li x M' y PS z A w

[0054] Where x, y, z, and w are independently 0 to 6;

[0055] M' is at least one of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; and

[0056] A is at least one of F, Cl, Br or I.

[0057] As a solid electrolyte, sulfide-based solid electrolyte materials containing sulfur (S), phosphorus (P), and lithium (Li) can be used as components. For example, materials containing Li₂S-P₂S₅ can be used. When using materials containing Li₂S-P₂S₅ as sulfide-based solid electrolyte materials, the mixing molar ratio of Li₂S and P₂S₅ can be selected, for example, in the range of 50:50 to 90:10.

[0058] Based on the total weight of the positive electrode active material layer, the content of solid electrolyte can be 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 10 to 20% by weight.

[0059] The positive electrode current collector can be in the form of a plate or a foil. The positive electrode current collector can be, for example, one metal or an alloy of two or more metals selected from indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium and lithium.

[0060] In addition, the positive electrode active material layer may also contain conductive agents and binders, as well as additives such as fillers, dispersants or ionic conductive agents.

[0061] The conductive materials used to impart conductivity to the electrodes can be used in the battery to be manufactured without special restrictions, as long as they are electronically conductive and do not cause chemical changes. Specific examples include: graphite, such as natural or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fiber, carbon nanotubes, etc.; metal powders or metal fibers, such as copper, nickel, aluminum, silver, etc.; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and mixtures of one or more of these can be used.

[0062] Based on the total weight of the positive electrode active material layer, the content of conductive material can be from 0.01 to 10% by weight, preferably from 0.1 to 5% by weight, and more preferably from 0.1 to 2% by weight.

[0063] Adhesives are used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include: polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), PVDF-co-HFP copolymer, polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and mixtures selected from one or more of them may be used.

[0064] Based on the total weight of the positive electrode active material layer, the content of the binder can be 0.5 to 20% by weight, preferably 1 to 10% by weight, and more preferably 1 to 5% by weight.

[0065] As a filler, dispersant, or ion-conducting agent, any known material commonly used in electrodes for lithium-ion secondary batteries can be used.

[0066] The positive electrode active material layer of the present invention may comprise 50 to 90 wt% of a positive electrode active material composite, 1 to 30 wt% of a solid electrolyte, 0.1 to 5 wt% of a conductive material and 0.5 to 20 wt% of a binder; preferably, it may comprise 75 to 85 wt% of a positive electrode active material composite, 10 to 20 wt% of a solid electrolyte, 0.1 to 2 wt% of a conductive material and 0.5 to 3 wt% of a binder.

[0067] The present invention also relates to a lithium-ion secondary battery comprising the positive electrode, the negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode.

[0068] Lithium-ion secondary batteries can be all-solid-state batteries. All-solid-state batteries are defined as batteries that not only consist of a solid electrolyte, but also include electrolytes in which some liquid electrolyte is added.

[0069] The following examples illustrate lithium-ion secondary batteries.

[0070] A lithium secondary battery includes a positive electrode, a negative electrode disposed opposite to the positive electrode, and a solid electrolyte layer inserted between the positive and negative electrodes, and may optionally include a separator.

[0071] (1) Positive electrode

[0072] The lithium-ion secondary battery of the present invention is characterized by comprising the positive electrode described above. Therefore, the description of the positive electrode is omitted.

[0073] (2) Negative electrode

[0074] The negative electrode includes a self-standing negative electrode and a negative electrode with a layer of negative electrode active material stacked on a negative electrode current collector. There are no particular limitations on the negative electrode in a lithium-ion secondary battery; any negative electrode known in the art can be used without restriction.

[0075] There are no particular limitations on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, it can be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel with a surface treated with carbon, nickel, titanium, or silver, or an aluminum-cadmium alloy. The thickness of the negative electrode current collector is typically 3 to 500 μm, and like the positive electrode current collector, fine irregularities can be formed on its surface to improve the adhesion of the negative electrode active material. Various forms can be used as negative electrode current collectors, such as films, sheets, foils, meshes, porous materials, foams, and non-woven materials.

[0076] The negative electrode active material layer includes a negative electrode active material, and may optionally also include a binder and a conductive material. It may also include a solid electrolyte.

[0077] As anode active materials, compounds capable of reversibly inserting and de-intercalating lithium can be used. Specific examples include: carbon materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and metal oxides capable of doping and de-doping lithium, such as SiO₂. β (where 0 < β < 2), SnO2, vanadium oxide, lithium vanadium oxide, etc.; or complexes containing metal compounds and carbon materials, such as Ag-C complexes, Si-C complexes or Sn-C complexes, and a mixture of one or more of these may be used.

[0078] In addition, lithium metal thin film can be used as the negative electrode active material, and the negative electrode-free battery does not need to contain any other negative electrode active material.

[0079] The conductive materials used to impart conductivity to the electrodes can be used in the battery to be manufactured without special restrictions, as long as they are electronically conductive and do not cause chemical changes. Specific examples include: graphite, such as natural or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fiber, carbon nanotubes, etc.; metal powders or metal fibers, such as copper, nickel, aluminum, silver, etc.; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and mixtures of one or more of these can be used.

[0080] Based on the total weight of the negative electrode active material layer, the content of conductive material can typically be 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight.

[0081] Adhesives are used to enhance the adhesion between particles of the negative electrode active material and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include: polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), PVDF-co-HFP copolymer, polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and mixtures selected from one or more of them may be used.

[0082] Based on the total weight of the negative electrode active material layer, the content of the binder can be 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight.

[0083] As a solid electrolyte, any solid electrolyte known in the art can be used without limitation, such as oxide solid electrolytes, polymer solid electrolytes, or sulfide solid electrolytes, with sulfide solid electrolytes being particularly preferred. As a sulfide solid electrolyte, any sulfide solid electrolyte previously described can be used.

[0084] Based on the total weight of the negative electrode active material layer, the content of solid electrolyte can be 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 10 to 20% by weight.

[0085] The negative electrode active material layer can be prepared by coating a negative electrode slurry and drying it, or by casting the negative electrode slurry onto a separate support and then stacking the film layer peeled off from the support onto the negative electrode current collector.

[0086] (3) Solid electrolyte layer

[0087] The solid electrolyte layer contains a solid electrolyte capable of migrating ions. As the solid electrolyte, any solid electrolyte known in the art can be used without limitation; for example, oxide-based solid electrolytes, polymer-based solid electrolytes, or sulfide-based solid electrolytes can be used, with sulfide-based solid electrolytes being particularly preferred. As a sulfide-based solid electrolyte, any sulfide-based solid electrolyte previously described can be used.

[0088] Solid electrolytes can be amorphous or crystalline. They can also be a mixture of amorphous and crystalline states.

[0089] The solid electrolyte layer may also contain an adhesive. Adhesive materials may include, for example, resins such as styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, and polyacrylic acid. The adhesive may contain the same or different materials as the adhesives in the positive and negative electrode active material layers.

[0090] In the lithium-ion secondary battery of the present invention, for other components besides the above-described positive electrode active material composite, known structures in the art can be used without limitation. Therefore, more specific descriptions are omitted.

[0091] Example

[0092] The present invention will be described in detail below with reference to embodiments. However, the embodiments of the present invention can be modified in many other ways, and the scope of the present invention should not be construed as limited to the embodiments described below. Embodiments of the present invention are provided to more fully illustrate the invention to those skilled in the art.

[0093] Example 1: Manufacturing of Positive Electrode Active Material Composite

[0094] (1) Manufacturing of positive electrode active material substrate

[0095] Use a mixer to mix Li2CO3 and Ni 0.8 Co 0.1 Mn 0.1 (OH)₂ was mixed in a weight ratio of 1.1:1 to form a reaction mixture. The reaction mixture was then placed in a stainless steel crucible and subjected to a first heat treatment at 600°C in an atmospheric atmosphere for 5 hours to form a plasticized mixture, which was then cooled. Next, the mixture was crushed and sieved. The crushed plasticized mixture was placed in an aluminum crucible and subjected to a second heat treatment at 800°C in an atmospheric atmosphere for 10 hours to prepare LiNi with a particle size (D50) of 5 μm. 0.8 Co 0.1 Mn 0.1 O2.

[0096] (2) Manufacturing of the coated substrate

[0097] LiPF6 powder (98%, Sigma-Aldrich) was dissolved in ethanol to prepare a LiPF6 solution (containing 0.2 g of LiPF6).

[0098] (3) Manufacturing of positive electrode active material composite

[0099] 99.8 g of LiNi with a particle size (D50) of 5 μm was used as the substrate for the positive electrode active material prepared in (1). 0.8 Co 0.1 Mn 0.1O2 powder was added to the LiPF6 solution (containing 0.2 g of LiPF6) prepared in (2) to prepare a mixed solution. The mixed solution was mixed for 24 hours using a Lab Blender (Waring), and the solvent ethanol was removed by vacuum drying to prepare the LiNi... 0.8 Co 0.1 Mn 0.1 A positive electrode active material composite with a LiPF6 coating layer formed on an O2 substrate.

[0100] Example 2: Manufacturing of Positive Electrode Active Material Composite

[0101] Except that a LiPF6 solution (containing 0.7 g of LiPF6) was used instead of the LiPF6 solution (containing 0.2 g of LiPF6) in Example 1, the LiNi was prepared by the same method as in Example 1. 0.8 Co 0.1 Mn 0.1 A positive electrode active material composite with a LiPF6 coating layer formed on an O2 substrate.

[0102] Example 3: Fabrication of Positive Electrode Active Material Composite

[0103] Except that a LiPF6 solution (containing 3 g of LiPF6) was used instead of the LiPF6 solution (containing 0.2 g of LiPF6) in Example 1, the LiNi was prepared by the same method as in Example 1. 0.8 Co 0.1 Mn 0.1 A positive electrode active material composite with a LiPF6 coating layer formed on an O2 substrate.

[0104] Example 4: Fabrication of Positive Electrode Active Material Composite

[0105] Except that a LiPO₂F₂ solution (containing 0.7 g of LiPO₂F₂) was used instead of the LiPF₆ solution (containing 0.2 g of LiPF₆) in Example 1, the LiNi₂ solution was prepared by the same method as in Example 1. 0.8 Co 0.1 Mn 0.1 A positive electrode active material composite with a LiPO2F2 coating layer formed on an O2 substrate.

[0106] Example 5: Fabrication of Positive Electrode Active Material Composite

[0107] Except that a LiDFBOP solution (containing 0.7 g of LiDFBOP) was used instead of the LiPF6 solution (containing 0.2 g of LiPF6) in Example 1, the LiNi alloy was prepared by the same method as in Example 1. 0.8 Co0.1 Mn 0.1 A positive electrode active material composite with a LiDFBOP coating layer formed on an O2 substrate.

[0108] Comparative Example 1: Manufacturing of Positive Electrode Active Materials

[0109] Without a coating layer, the LiNi prepared in Example 1 was used. 0.8 Co 0.1 Mn 0.1 O2 is used as the positive electrode active material.

[0110] Comparative Example 2: Fabrication of Positive Electrode Active Material Composite

[0111] Except that a LiPF6 solution (containing 5 g of LiPF6) was used instead of the LiPF6 solution (containing 0.2 g of LiPF6) in Example 1, the LiNi was prepared by the same method as in Example 1. 0.8 Co 0.1 Mn 0.1 A positive electrode active material composite with a LiPF6 coating layer formed on an O2 substrate.

[0112] Examples 6 to 10 and Comparative Examples 3 and 4: Fabrication of all-solid-state lithium-ion secondary batteries

[0113] (1) Manufacturing of the positive electrode

[0114] 81.9% by weight of the positive electrode active material composites prepared in Examples 1 to 5 and Comparative Examples 1 and 2 (in the case of Comparative Example 1, the positive electrode active material), 15.6% by weight of solid electrolyte LPS (Li6PS5Cl), 1.5% by weight of carbon black powder, and 1% by weight of PTFE as a binder were mixed at 5000 rpm for 1 minute without solvent using a Lab Blender (Waring) (first mixing). Next, a dough was prepared by high-shear mixing (using PBV-0.1L, Irie Shokai) with a shear force of 100 N to the mixture (second mixing). The dough was then used to manufacture an electrode layer with a self-supporting structure using a two-roll mill MR-3 (Inoue).

[0115] The positive electrode is formed by placing the electrode layer on one side of an aluminum current collector with a thickness of 15 μm and applying pressure.

[0116] (2) Manufacturing of all-solid-state lithium-ion secondary batteries

[0117] Using lithium metal with a thickness of 40 μm as the negative electrode, a Li6PS5Cl solid electrolyte membrane with a thickness of 50 μm is inserted between each of the positive and negative electrodes prepared above. Then, pressure is applied at 500 MPa to prepare a clamp cell with a driving pressure of 3 MPa and a capacity of 5 mAh.

[0118] Experimental Example 1: Battery Characteristic Evaluation

[0119] (1) Evaluation of the initial discharge capacity and efficiency of all-solid-state batteries

[0120] The clamp cells prepared in Examples 6 to 10, and Comparative Examples 3 and 4, were charged at a rate of 0.1C (C-rate) until the voltage reached 4.25V (vs. Li), and then cut off at a rate of 0.05C while maintaining 4.25V (vs. Li). They were then discharged at a rate of 0.1C (C-rate) until the voltage at discharge reached 3.0V (vs. Li) (first cycle). The initial efficiency was calculated as discharge capacity / charge capacity × 100 (%). The experimental results are shown in Table 1 below.

[0121] (2) Evaluation of lifespan characteristics of all-solid-state batteries

[0122] The clamp cells prepared in Examples 6 to 10 and Comparative Examples 3 and 4 were charged at a rate of 0.33C (C-rate) until the voltage reached 4.25V (vs. Li), and then cut off at a rate of 0.1C while maintaining 4.25V (vs. Li). They were then discharged at a rate of 0.33C (C-rate) until the voltage at discharge reached 3.0V (vs. Li) (first cycle). This charge-discharge test was repeated 50 cycles to measure the capacity retention during discharge. The experimental results are shown in Table 1 below.

[0123] [Table 1]

[0124]

Claims

1. A positive electrode active material composite, comprising a positive electrode active material substrate and a coating layer coated on the positive electrode active material substrate, in, The coating layer comprises at least one selected from the group consisting of LiPF6, LiDFBOP (lithium difluorodioxanol phosphate), and LiTFOP (lithium tetrafluorooxanol phosphate).

2. The positive electrode active material composite as described in claim 1, in, The positive electrode active material substrate is a compound represented by chemical formula 1. [Chemical Formula 1] The a (Nor 1-x-y-z Co x M1 y M2 z )O2 Wherein, M1 is manganese (Mn), aluminum (Al), or a combination thereof; M2 is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), aluminum (Al), or any combination of two or more of these elements; and 0.95≤a≤1.3, 0 <x<1,0≤y<1,0≤z<1。 3. The positive electrode active material composite as described in claim 1, in, The content of the coating layer is 0.1 to 4.5% by weight, based on the total weight of the positive electrode active material composite.

4. The positive electrode active material composite as described in claim 1, in, The thickness of the coating layer is from 10 nm to 200 nm.

5. The positive electrode active material composite as described in claim 1, in, The coating layer is formed by wet or dry mixing of the positive electrode active material substrate and the coating substrate.

6. A positive electrode comprising the positive electrode active material composite of claim 1.

7. The positive electrode as described in claim 6, It also contains sulfide solid electrolytes.

8. The positive electrode as described in claim 7, in, The sulfide-based solid electrolyte is a compound represented by chemical formula 2. [Chemical Formula 2] Li x M' y P.S. z A w Where x, y, z, and w are independently 0 to 6; M' is at least one of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; and A is at least one of F, Cl, Br or I.

9. A lithium-ion secondary battery comprising: a positive electrode, a negative electrode as described in claim 6, and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

10. The lithium-ion secondary battery as described in claim 9, in, The lithium-ion secondary battery is a sulfide-based all-solid-state battery.

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