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

Abstract

The present invention provides a cathode active material composite including a cathode active material substrate and a coating layer coated on the cathode active material substrate, the coating layer including a compound represented by Chemical Formula 1 below; a cathode including the same; and a lithium ion secondary battery including the cathode: [Chemical formula 1] Li a Ti b O c-d X d

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0106837, filed August 16, 2023, and Korean Patent Application No. 10-2024-0109422, filed August 14, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material composite, a positive electrode including the same, and a lithium ion secondary battery including the positive electrode. [Background technology]

[0003] Compared to nickel-manganese batteries and nickel-cadmium batteries, lithium-ion secondary batteries have the advantages of higher energy density, lower self-discharge rate, and longer lifespan, but drawbacks include stability issues against overheating and low output.

[0004] To overcome the problems of lithium-ion secondary batteries, all-solid-state batteries have been proposed as an alternative. The all-solid-state battery has a structure in which an electrolyte layer containing a solid electrolyte, a positive electrode layer and a negative electrode layer each containing a solid electrolyte are formed on both sides of the electrolyte layer, and a current collector is attached to each electrode.

[0005] All-solid-state batteries can be divided into oxide-based, polymer-based, and sulfide-based batteries depending on the raw material of the solid electrolyte. The sulfide-based all-solid-state battery has superior lithium ion conductivity compared to other types of batteries. However, compared to batteries using conventional liquid electrolytes, it has the disadvantage of lower ion conductivity and higher electrical resistance between the positive electrode, negative electrode, and solid electrolyte, resulting in reduced lifespan and output.

[0006] That is, it is known that the cathode active material and the sulfide-based solid electrolyte react with each other at the interface to form a resistive material that hinders the operation of the all-solid-state battery, resulting in problems such as a decrease in the initial capacity and efficiency of the all-solid-state battery.

[0007] To solve these problems, various coating layers are known to be formed on the surface of the positive electrode active material, such as a Li-MO (M: B, Al, Zr, P, Ti, Nb, W, etc.) lithium oxide coating.

[0008] However, in the case of such a coated positive electrode active material, it is believed that the effects of reducing the interfacial resistance between the positive electrode active material and the sulfide-based solid electrolyte and improving the lithium ion conductivity are insufficient. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 2018-0123369 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been devised to solve the above-mentioned problems of the prior art. The present invention provides a cathode active material composite that can improve the driving characteristics and life characteristics of a battery by reducing the interfacial resistance between a cathode active material and a solid electrolyte and improving lithium ion conductivity, a cathode including the cathode, and a lithium ion secondary battery including the cathode. [Means for solving the problem]

[0011] In order to achieve the above object, the present invention provides Provided is a positive electrode active material composite including a positive electrode active material substrate and a coating layer coated on the positive electrode active material substrate, the coating layer including a compound represented by the following Formula 1:

[0012] [Chemical formula 1] Li a Ti b O c-d X d In the above formula, X is N, P, or S; 1≦a≦6, 1≦b≦6, 3≦c≦15, and 0 <d≦1.5である。

[0013] The present invention also provides A positive electrode comprising the positive electrode active material composite of the present invention is provided.

[0014] The present invention also provides There is also provided a lithium ion secondary battery comprising the positive electrode of the present invention, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode. [Effects of the Invention]

[0015] The cathode active material composite of the present invention provides the effect of reducing the interfacial resistance between the cathode active material and the solid electrolyte and improving lithium ion conductivity due to the coating layer formed on the surface of the cathode active material.

[0016] Furthermore, the above-mentioned effects provide the effect of improving the driving characteristics and life characteristics of the battery.

[0017] The lithium ion secondary battery of the present invention contains the positive electrode active material, and thus provides excellent driving characteristics and life characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will now be described in more detail to aid in understanding the invention.

[0019] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that correspond to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concepts of terms in order to best describe his or her invention. Furthermore, the terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expression includes the plural expression unless a clearly different meaning is present in the context.

[0020] When a component is described as being "connected to, provided with, stacked on, or mounted on" another component, it should be understood that the component may be directly connected to or mounted on the other component, but there may also be other components in between. On the other hand, when a component is described as being "directly connected to or mounted on" another component, it should be understood that there are no other components in between. Meanwhile, other expressions describing the relationship between components, such as "on top of" and "directly on top of," or "between" and "immediately between," or "adjacent to" and "directly adjacent to," should be interpreted similarly.

[0021] As used herein, the term "combination" is inclusive of mixtures, alloys, reaction products, and the like, unless specifically stated to the contrary.

[0022] The positive electrode active material composite of the present invention is The positive electrode active material substrate includes a coating layer containing a compound represented by the following Formula 1, coated on the positive electrode active material substrate:

[0023] [Chemical formula 1] Li a Ti b O c-d X d In the above formula, X is N, P, or S; 1 ≤ a ≤ 6, 1 ≤ b ≤ 6, 3 ≤ c ≤ 15, and 0 < d ≤ 1.5.

[0024] By including the coating layer, the cathode active material composite of the present invention reduces the interfacial resistance between the cathode active material and the solid electrolyte, and has the characteristic that the lithium ion conductivity is improved by the structure of the coating particles constituting the coating layer. That is, the coating particles forming the coating layer have a form in which oxygen contained in LTO is substituted by a non-metallic element X. Therefore, compared with conventional LTO coating particles, the crystal distance between the coating particles increases, providing better lithium ion conductivity.

[0025] In addition to the compound of Chemical Formula 1, the coating layer may further contain other known coating substrates in this field.

[0026] Chemical Formula 1 preferably has a range of 3 ≤ a ≤ 5, 4 ≤ b ≤ 6, 10 ≤ c ≤ 14, and 0 < d ≤ 1. More preferably, a is 4, b is 5, c is 12, and d may be 0.1 to 0.3.

[0027] The cathode active material substrate may be a compound represented by the following Chemical Formula 2.

[0028] [Chemical Formula 2] Li a (Ni 1-x-y-z Co x M1 y M2 z )O2 In the above formula, 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 a combination of two or more of these, 0.95≦a≦1.3, 0 <x<1、0≦y<1、0≦z<1である。

[0029] However, the positive electrode active material base is not limited to the above compounds, and may use or further include any positive electrode active material known in the art.

[0030] Specifically, the positive electrode active material substrate may be one or more selected from the group consisting of NCM, NCMA, LFP, LCA, LCO, LMO, and the like.

[0031] More specifically, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.75 Co 0.1 Mn 0.1 Al 0.05 O2, LiFePO4, etc. may also be used.

[0032] The coating layer may be included in an amount of 0.1 to 5 wt %, more preferably 0.5 to 2 wt %, and even more preferably 0.7 to 1.3 wt %, based on the total weight of the cathode active material composite. If the coating layer is included in an amount of less than 0.1 wt %, the effect of reducing the interfacial resistance between the cathode active material and the solid electrolyte and improving lithium ion conductivity may be negligible. If the coating layer is included in an amount of more than 5 wt %, the distance of lithium ion migration between the active material and the solid electrolyte increases, which may actually increase the interfacial resistance, which is undesirable.

[0033] The coating layer may have a thickness of 10 nm to 200 nm.

[0034] In the coating layer, the molar ratio of Ti to X may be 1:0.01-0.2, preferably 1:0.01-0.1, and more preferably 1:0.02-0.06. If the molar ratio of X is less than 0.01, the oxygen content increases and the distance between crystals decreases, making it difficult to expect an improvement in lithium ion conductivity. If the molar ratio of X exceeds 0.2, the non-metallic element content increases, destroying the crystalline structure of conventional lithium titanium oxides and preventing the formation of a homogeneous structure, which is undesirable.

[0035] The coating layer may be formed by dry mixing of the positive electrode active material substrate and the coating substrate, but is not limited thereto, and may also be formed by a wet process. The dry mixing may be high shear mixing.

[0036] The particle size (D50) of the positive electrode active material substrate may be 10 nm to 10 μm, and the particle size (D50) of the coating substrate may be 10 nm to 200 nm.

[0037] In the present invention, the particle size can be measured using a particle size analyzer, for example, a Mastersizer 3000 (Malvem Panalytical) instrument.

[0038] In one embodiment of the present invention, the cathode active material composite may further include a solid electrolyte. In this case, the solid electrolyte may include the same solid electrolyte as that described in the cathode active material layer below.

[0039] The present invention also relates to a positive electrode comprising the positive electrode active material composite.

[0040] The positive electrode is characterized by including the positive electrode active material composite of the present invention. The positive electrode active material composite follows the above description, and therefore, further explanation will be omitted.

[0041] The positive electrode of the present invention may be a free-standing type produced from the constituent components of the positive electrode active material layer, or may be in a form in which the positive electrode active material layer is laminated on a positive electrode current collector.

[0042] The positive electrode active material layer may further include a positive electrode active material known in the art in addition to the positive electrode active material composite.

[0043] Specific examples of the known positive electrode active material include, but are not limited to, 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 salts such as lithium manganese oxide and lithium iron phosphate, and lithium sulfide.

[0044] The positive electrode active material layer may further include a solid electrolyte. The solid electrolyte may be any solid electrolyte known in the art, such as an oxide-based solid electrolyte, a polymer-based solid electrolyte, or a sulfide-based solid electrolyte, and is particularly preferably a sulfide-based solid electrolyte.

[0045] The sulfide-based solid electrolytes include 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, and Li2S-P2S5-Z m S n (m and n are positive numbers, Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(p and q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In), or a combination thereof. The solid electrolyte may be made of one material selected from these sulfide-based solid electrolyte materials, or may be made of two or more materials.

[0046] The sulfide-based solid electrolyte may include a solid electrolyte represented by the following Chemical Formula 3: [Chemical formula 3] Li x M' y PS z A w In the above formula, x, y, z, and w are, independently of one another, between 0 and 6; M' is one or more of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; A is one or more of F, Cl, Br, or I.

[0047] The solid electrolyte may be any of the sulfide-based solid electrolyte materials containing sulfur (S), phosphorus (P), and lithium (Li) as constituent elements. For example, a material containing Li2S-P2S5 may be used. When a sulfide-based solid electrolyte material containing Li2S-P2S5 is used, the molar ratio of Li2S to P2S5 may be selected from the range of Li2S:P2S5=50:50 to 90:10.

[0048] The solid electrolyte may be contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 10 to 20% by weight, based on the total weight of the positive electrode active material layer.

[0049] The positive electrode current collector may be in the form of a plate or foil, and may be made of one metal or an alloy of two or more metals selected from the group consisting of indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, and lithium.

[0050] The positive electrode active material layer may further include a conductive material and a binder, and may further include additives such as a filler, a dispersant, or an ion-conductive auxiliary.

[0051] The conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause chemical changes in the battery that is constructed and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube, and other carbon-based materials; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0052] The conductive material may be contained in an amount of usually 0.01 to 10% by weight, preferably 0.1 to 5% by weight, and more preferably 0.1 to 2% by weight, relative to the total weight of the positive electrode active material layer.

[0053] The binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the positive electrode current collector. Specific examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0054] The binder may be contained in an amount of 0.5 to 20% by weight, preferably 1 to 10% by weight, and more preferably 1 to 5% by weight, based on the total weight of the positive electrode active material layer.

[0055] As the filler, dispersant, ion-conducting aid, or the like, known materials that are generally used in electrodes of lithium ion secondary batteries can be used.

[0056] The positive electrode active material layer of the present invention may contain 50 to 90% by weight of the positive electrode active material composite, 1 to 30% by weight of a solid electrolyte, 0.1 to 5% by weight of a conductive material, and 0.5 to 20% by weight of a binder; preferably, it may contain 75 to 85% by weight of the positive electrode active material composite, 10 to 20% by weight of a solid electrolyte, 0.1 to 2% by weight of a conductive material, and 0.5 to 3% by weight of a binder.

[0057] The present invention also relates to a lithium ion secondary battery comprising the positive electrode of the present invention, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode.

[0058] The lithium ion secondary battery may be an all-solid-state battery, which is defined as including not only a battery consisting of a solid electrolyte but also a battery in which a liquid electrolyte is partially added to a solid electrolyte.

[0059] Hereinafter, an embodiment of the lithium ion secondary battery will be described as an example.

[0060] The lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, a solid electrolyte layer interposed between the positive electrode and the negative electrode, and may optionally include a separator.

[0061] (1) Positive electrode The lithium ion secondary battery of the present invention is characterized by including the above-described positive electrode of the present invention, and therefore, a description of the positive electrode will be omitted.

[0062] (2) Negative electrode The negative electrode includes a free-standing type negative electrode and a type in which a negative electrode active material layer is laminated on a negative electrode current collector. In the lithium ion secondary battery, the negative electrode is not particularly limited, and any negative electrode known in this field can be used without limitation.

[0063] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc. may be used. The negative electrode current collector typically has a thickness of 3 to 500 μm, and, like the positive electrode current collector, the current collector surface may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector may be in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0064] The negative electrode active material layer includes a negative electrode active material, and may optionally further include a binder and a conductive material, and may further include a solid electrolyte.

[0065] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbon materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO β (0<β<2), metal oxides that can be doped and dedoped with lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above metallic compounds and carbonaceous materials, such as Ag-C composites, Si-C composites, and Sn-C composites, and any one or a mixture of two or more of these may be used.

[0066] In addition, a metallic lithium thin film may be used as the negative electrode active material, and an anodeless battery may not include a separate negative electrode active material.

[0067] The conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause chemical changes in the battery that is constructed and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube, and other carbon-based materials; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0068] The conductive material may be contained in an amount of usually 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0069] The binder serves to improve adhesion between particles of the negative electrode active material and between the negative electrode active material and the negative electrode current collector. Specific examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0070] The binder may be contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, based on the total weight of the negative electrode active material layer.

[0071] The solid electrolyte may be any known solid electrolyte in this field without limitation, for example, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or a sulfide-based solid electrolyte, and is particularly preferably a sulfide-based solid electrolyte. The sulfide-based solid electrolyte may be any of the sulfide-based solid electrolytes described above.

[0072] The solid electrolyte may be contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 10 to 20% by weight, based on the total weight of the negative electrode active material layer.

[0073] The negative electrode active material layer may be prepared by coating and drying the negative electrode slurry, or by casting the negative electrode slurry on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0074] (3) Solid electrolyte layer The solid electrolyte layer includes a solid electrolyte capable of transferring ions. The solid electrolyte may be any solid electrolyte known in the art, including, for example, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or a sulfide-based solid electrolyte. The sulfide-based solid electrolyte may be the sulfide-based solid electrolyte described above.

[0075] The solid electrolyte may be in an amorphous state, a crystalline state, or a mixture of amorphous and crystalline states.

[0076] The solid electrolyte layer may further include a binder. Examples of the binder material include resins such as styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and polyacrylic acid. The binder may be the same as or different from the binders in the positive electrode active material layer and the negative electrode active material layer.

[0077] In the lithium ion secondary battery of the present invention, the components other than the cathode active material composite may be any known components in this field without any restrictions, and therefore, a more detailed description thereof will be omitted.

[0078] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0079] Example 1: Preparation of positive electrode active material composite (1) Manufacturing of the positive electrode active material substrate Li2CO3 and Ni 0.8 Co 0.1 Mn 0.1 The mixture was mixed with (OH)2 in a mixer at a weight ratio of 1.1:1 to form a reaction mixture, which was then placed in a stainless steel crucible and subjected to a primary heat treatment at 600°C in an air atmosphere for 5 hours to form a sintered mixture, which was then cooled. After crushing and sieving, the crushed sintered mixture was placed in an aluminum crucible and subjected to a secondary heat treatment at 800°C in an air atmosphere for 10 hours to obtain LiNi particles with a particle size (D50) of 5 μm. 0.8 Co 0.1 Mn 0.1 O2 was produced.

[0080] (2) Manufacturing of coating substrates Li2CO3, TiO2, and Melamine (C3N3(NH2)3) were mixed in a mortar in a stoichiometric ratio for 4 hours, then the mixture was placed in a tube furnace with an inner diameter of 50 mm and a length of 1,000 mm and heat-treated at 700°C for 12 hours to produce Li4Ti5O 11.8 N 0.2 was manufactured.

[0081] (3) Manufacturing of the positive electrode active material composite The positive electrode active material substrate manufactured in (1) was LiNi 0.8 Co 0.1 Mn 0.1 99 g of O2 powder and the Li4Ti5O produced in (2) above 11.8 N 0.2 1 g of powder was placed in a container and mixed for 1 minute at 5,000 rpm using a Lab Blender (Waring) without the use of a separate solvent. The mixture was then subjected to high-shear mixing (NOB-130, Hosokawa Micron) at 3,000 rpm for 10 minutes to obtain LiNi 0.8 Co 0.1 Mn 0.1 Li4Ti5O on O2 substrate 11.8 N 0.2 A positive electrode active material composite having a coating layer formed thereon was manufactured.

[0082] Example 2: Preparation of positive electrode active material composite Li2CO3, TiO2, and NH4H2PO4 were mixed in a mortar in a stoichiometric ratio for 4 hours, then the mixture was placed in a tube furnace with an inner diameter of 50 mm and a length of 1,000 mm and heat-treated at 800°C for 6 hours to produce Li4Ti5O 11.8 P 0.2 was manufactured.

[0083] In Example 1, Li4Ti5O 11.8 N 0.2 Instead of Li4Ti5O produced above 11.8 P 0.2 The same procedure as in Example 1 was carried out except that LiNi 0.8 Co0.1 Mn 0.1 Li4Ti5O on O2 substrate 11.8 P 0.2 A cathode active material composite coated with the cellulose acylate was prepared.

[0084] Example 3: Preparation of positive electrode active material composite Titanium (IV) isopropoxide (Ti(OC3H7)4), lithium hydroxide (LiOH), and thioacetamide (C2H5NS) were dissolved in a stoichiometric ratio in a mixed solvent of ethanol and distilled water (3:1 by weight), and then mixed for about 2 hours to prepare a solution.

[0085] LiNi prepared in the same manner as in Example 1 0.8 Co 0.1 Mn 0.1 O2 was added to the solution prepared above, and then dried under vacuum at 80°C.

[0086] Finally, the mixture was placed in a tube furnace with an inner diameter of 50 mm and a length of 1,000 mm, and then heat-treated at 600°C for 10 hours to obtain LiNi 0.8 Co 0.1 Mn 0.1 Li4Ti5O on O2 substrate 11.8 S 0.2 A cathode active material composite coated with the cellulose acylate was prepared.

[0087] Comparative Example 1: Production of Positive Electrode Active Material Composite Li2CO3 and TiO2 were mixed in a mortar in a weight ratio of 1:2.5 for 4 hours, then the mixture was placed in a tube furnace with an inner diameter of 50 mm and a length of 1,000 mm, and heat-treated at 800°C for 12 hours to obtain Li4Ti5O 12 was manufactured.

[0088] In Example 1, Li4Ti5O 11.8 N 0.2 Instead of Li4Ti5O produced above 12 The same procedure as in Example 1 was carried out except that LiNi 0.8 Co 0.1 Mn 0.1Li4Ti5O on O2 substrate 12 A cathode active material composite coated with the cellulose acylate was prepared.

[0089] Examples 4 to 6 and Comparative Example 2: Production of all-solid-state lithium-ion secondary batteries (1) Manufacturing of the positive electrode 81.9 wt% of each of the cathode active material composites prepared in Examples 1 to 3 and Comparative Example 1, 15.6 wt% of solid electrolyte LPS (Li6PS5Cl), 1.5 wt% of carbon black powder, and 1 wt% of PTFE binder were mixed without solvent using a Lab Blender (Waring) at 5000 rpm for 1 minute (primary mixing). Next, the mixture was subjected to high shear mixing (using PBV-0.1L, Irie Shokai) at a shear force of 100 N (secondary mixing) to produce a dough. Next, the dough was used in a Two Roll Mill MR-3 (Inoue) to produce a free-standing electrode layer.

[0090] The electrode layer was placed on one side of an aluminum current collector having a thickness of 15 μm and pressed to prepare each positive electrode.

[0091] (2) Manufacturing of all-solid-state lithium-ion secondary batteries A 40 μm thick lithium metal was used as the negative electrode, and a 50 μm thick Li6PS5Cl solid electrolyte membrane was interposed between each of the positive and negative electrodes. Then, the resulting mixture was pressurized at 500 MPa to prepare jig cells of Examples 4 to 6 and Comparative Example 2 having a driving pressure of 3 MPa and a capacity of 5 mAh.

[0092] Experimental example 1: Battery characteristic evaluation (1) Evaluation of initial discharge capacity and efficiency of all-solid-state batteries The ZIG cells prepared in Examples 4 to 6 and Comparative Example 2 were charged at a 0.1 C rate until the voltage reached 4.25 V (vs. Li), and then cut off at a 0.05 C rate while maintaining 4.25 V (vs. Li). Subsequently, they were discharged at a 0.1 C rate until the discharge voltage reached 3.0 V (vs. Li) (first cycle). The initial efficiency was calculated as discharge capacity / charge capacity x 100 (%). The experimental results are shown in Table 1 below.

[0093] (2) Evaluation of life characteristics of all-solid-state batteries The ZIG cells prepared in Examples 4 to 6 and Comparative Example 2 were charged at a 0.33 C rate until the voltage reached 4.25 V (vs. Li), and then cut off at a 0.1 C rate while maintaining 4.25 V (vs. Li). Subsequently, they were discharged at a 0.33 C rate until the discharge voltage reached 3.0 V (vs. Li) (first cycle). This charge-discharge test was repeated 50 times, and the capacity retention rate of the discharge capacity was measured. The experimental results are shown in Table 1 below.

[0094] [Table 1] [Table 1]

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, the coating layer including a compound represented by the following Chemical Formula 1: [Chemical formula 1] Li ａ Ti ｂ O ｃ－ｄ X ｄ In the above formula, X is N, P, or S; 1≦a≦6, 1≦b≦6, 3≦c≦15, and 0<d≦1.

5.

2. 2. The cathode active material composite according to claim 1, wherein a is 4, b is 5, c is 12, and d is 0.1 to 0.

3.

3. 2. The cathode active material composite according to claim 1, wherein the cathode active material substrate is a compound represented by the following Chemical Formula 2: [Chemical formula 2] Li ａ (N １－ｘ－ｙ－ｚ Co ｘ M1 ｙ M2 ｚ )O ２ In the above formula, 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 a combination of two or more thereof; 0.95≦a≦1.3, 0<x<1, 0≦y<1, 0≦z<1.

4. 10. The cathode active material composite of claim 1, wherein the coating layer is present in an amount of 0.1 to 5 wt % based on the total weight of the cathode active material composite.

5. The cathode active material composite of claim 1, wherein the coating layer has a thickness of 10 nm to 200 nm.

6. 6. The cathode active material composite according to claim 1, wherein the molar ratio of Ti to X in the coating layer is 1:0.01 to 0.

2.

7. The positive electrode active material composite of claim 1 , wherein the coating layer is formed by dry mixing a positive electrode active material substrate and a coating substrate.

8. A positive electrode comprising the positive electrode active material composite according to claim 1 .

9. 9. The positive electrode of claim 8, further comprising a sulfide-based solid electrolyte.

10. The positive electrode according to claim 9, wherein the sulfide-based solid electrolyte is a compound represented by the following Chemical Formula 3: [Chemical formula 3] Li ｘ M' ｙ PS ｚ A ｗ In the above formula, x, y, z, and w are each independently 0 to 6; M' is one or more of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; A is one or more of F, Cl, Br, or I.

11. A lithium ion secondary battery comprising the positive electrode according to claim 8, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode.

12. The lithium ion secondary battery according to claim 11, wherein the lithium ion secondary battery is a sulfide-based all-solid-state battery.

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