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

Abstract

The present invention provides: a positive electrode active material composite comprising a positive electrode active material substrate and a compound coating layer applied onto the positive electrode active material substrate and comprising Li, P, and F elements; a positive electrode comprising the positive electrode active material composite; and a lithium ion secondary battery comprising the positive electrode.

Description

A cathode active material composite, a cathode comprising the same, and a lithium ion secondary battery comprising the cathode

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0111722, filed August 25, 2023, and Korean Patent Application No. 10-2024-0113050, filed August 22, 2024, the entire contents of which are incorporated herein by reference.

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

[0003] Lithium-ion secondary batteries have the advantages of high energy density, low self-discharge rate, and long lifespan compared to nickel-manganese or nickel-cadmium batteries, but their disadvantages include stability issues due to overheating and low output.

[0004] To overcome the problems of lithium-ion secondary batteries, all-solid-state batteries are being 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 containing a solid electrolyte, and a negative electrode layer containing a solid electrolyte are formed on both sides of the electrolyte layer, and a current collector is bonded to each electrode.

[0005] The above-mentioned all-solid-state batteries can be categorized into oxide-based, polymer-based, and sulfide-based types, depending on the raw material of the solid electrolyte. The sulfide-based all-solid-state batteries exhibit superior lithium ion conductivity compared to other types of batteries. Nevertheless, compared to batteries using conventional liquid electrolytes, they have lower ion conductivity and higher electrical resistance between the anode, cathode, and solid electrolyte, resulting in reduced lifespan and output.

[0006] That is, the positive active material and the sulfide-based solid electrolyte are known to react with each other at the interface to form a resistive material that impedes the operation of the all-solid-state battery. This resistive material lowers the initial capacity of the all-solid-state battery and reduces its efficiency.

[0007] To address these issues, technologies for forming various coating layers on the surface of positive electrode active materials are known. For example, technologies for coating lithium oxides such as Li-MO (M: B, Al, Zr, P, Ti, Nb, W, etc.) on the surface of positive electrode active materials are known.

[0008] However, in the case of this type of coated cathode active material, the effect of reducing the interfacial resistance between the cathode active material and the sulfide-based solid electrolyte and improving the lithium ion conductivity appears to be insufficient.

[0009] [Prior art literature

[0010] [Patent Document]

[0011] Republic of Korea Publication Patent No. 10-2018-0123369

[0012]

[0013] The present invention has been devised to solve the above problems of the prior art.

[0014] The purpose of the present invention is to provide a cathode active material composite capable of improving the operating characteristics and life characteristics of a battery by lowering the interfacial resistance between the cathode active material and the solid electrolyte and improving lithium ion conductivity, a cathode including the composite, and a lithium ion secondary battery including the cathode.

[0015] In order to achieve the above purpose, the present invention

[0016] It includes a positive electrode active material substrate and a coating layer coated on the positive electrode active material substrate,

[0017] The above coating layer provides a composite of positive electrode active materials including at least one selected from the group consisting of LiPF6, LiDFBOP (lithium difluorobis(oxalato)phosphate), and LiTFOP (lithium tetrafluoro(oxalato)phosphate).

[0018]

[0019] In addition, the present invention

[0020] A positive electrode comprising the positive electrode active material composite of the present invention is provided.

[0021]

[0022] In addition, the present invention

[0023] The present invention provides a lithium ion secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0024] The positive electrode active material composite of the present invention provides the effect of lowering the interfacial resistance between the positive electrode active material and the solid electrolyte and improving lithium ion conductivity by a coating layer formed on the surface of the positive electrode active material.

[0025] In addition, it provides the effect of improving the driving characteristics and life characteristics of the battery by the above effects.

[0026] The lithium ion secondary battery of the present invention provides excellent driving characteristics and life characteristics by including the positive electrode active material.

[0027]

[0028] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0029] The terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Rather, they should be construed with meanings and concepts consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of a term to best describe his or her invention. Furthermore, the terminology used in this specification is used merely to describe exemplary embodiments and is not intended to limit the present invention. The singular expression "a" includes plural expressions unless the context clearly indicates otherwise.

[0030] When a component is referred to as being "connected, provided, laminated, or installed" to another component, it should be understood that it may be directly connected or installed to that other component, but there may also be other components present in between. Conversely, when a component is referred to as being "directly connected or installed" to another component, it should be understood that there are no other components present in between. Similarly, other expressions describing the relationship between components, such as "on top of" and "directly on top of," "between" and "directly between," or "adjacent to" and "directly adjacent to," should be interpreted similarly.

[0031] The term "combination" in this specification includes mixtures, alloys, reaction products, etc., unless specifically stated otherwise.

[0032]

[0033] The positive electrode active material composite of the present invention

[0034] It includes a positive electrode active material substrate and a coating layer coated on the positive electrode active material substrate,

[0035] The above coating layer is characterized in that it includes at least one selected from the group consisting of LiPF6, LiDFBOP (lithium difluorobis(oxalato)phosphate), and LiTFOP (lithium tetrafluoro(oxalato)phosphate).

[0036] The positive electrode active material composite of the present invention has the characteristics of lowering the interfacial resistance between the positive electrode active material and the solid electrolyte by including the coating layer, and improving lithium ion conductivity by the structure of the coating particles constituting the coating layer.

[0037] The above coating layer may further include other coating materials known in the art in addition to one or more selected from the group consisting of LiPF6, LiDFBOP (lithium difluorobis(oxalato)phosphate), and LiTFOP (lithium tetrafluoro(oxalato)phosphate).

[0038]

[0039] The above positive electrode active material substrate may be a compound represented by the following chemical formula 1.

[0040] [Chemical Formula 1]

[0041] Li a (Ni 1-x-y-z Co x M1 y M2 z )O2

[0042] In the above formula

[0043] M1 is manganese (Mn), aluminum (Al), or a combination thereof;

[0044] 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,

[0045] 0.95≤a≤1.3, 0 <x<1, 0≤y<1, 0≤z<1이다.

[0046] However, the above-mentioned positive electrode active material substrate is not limited to the above-mentioned compound, and it is also possible to use or include a positive electrode active material known in this field. Specifically, at least one selected from the group consisting of NCM, NCMA, LFP, LCA, LCO, LMO, etc. may be used as the positive electrode active material substrate. More specifically, LiNi 0.8 Co 0.1 Mn 0.1 O 2, LiNi 0.75 Co 0.1 Mn 0. 1Al 0.05 O 2, LiFePO4, etc. can be used.

[0047]

[0048] The coating layer may be included in an amount of 0.1 to 4.5 wt%, preferably 0.1 to 4.5 wt%, and more preferably 0.1 to 3 wt%, based on the total weight of the positive electrode active material composite. When the coating layer is included in an amount of less than 0.1 wt%, the effect of lowering the interfacial resistance between the positive electrode active material and the solid electrolyte and improving lithium ion conductivity may be minimal, and when it exceeds 4.5 wt%, the interfacial resistance increases because the lithium ion movement distance between the active material and the solid electrolyte increases, which is not preferable.

[0049] Additionally, the thickness of the coating layer may be 10 nm to 200 nm.

[0050] The above coating layer can be formed by wet or dry mixing of the positive electrode active material substrate and the coating substrate. The dry mixing may be high-shear mixing.

[0051] The particle size (D50) of the above positive electrode active material substrate may be 10 nm to 10 ㎛, and the particle size (D50) of the above coating substrate may be 10 nm to 200 nm.

[0052] In the present invention, the particle size can be measured using a particle size analyzer. For example, it can be measured using a Mastersizer 3000 (Malvem panalytical) device.

[0053] In one embodiment of the present invention, the positive electrode active material composite may further include a solid electrolyte. In this case, the solid electrolyte may include the same solid electrolyte as the solid electrolyte described in the positive electrode active material layer below.

[0054]

[0055] In addition, the present invention relates to a positive electrode comprising the above positive electrode active material composite.

[0056] The above positive electrode is characterized by including the positive electrode active material composite of the present invention. Since the above positive electrode active material composite follows the description above, a description thereof is omitted.

[0057] The positive electrode of the present invention may be a freestanding type manufactured from a positive electrode active material layer component, and may also be in a form in which the positive electrode active material layer is laminated on a positive electrode current collector.

[0058] The above-mentioned positive electrode active material layer may further include a positive electrode active material known in the art in addition to the above-mentioned positive electrode active material composite.

[0059] Specific examples of the above-mentioned known positive electrode active material include, but are not limited to, lithium cobaltate (hereinafter referred to as LCO), lithium nickelate, lithium nickel cobaltate, lithium nickel cobalt aluminumate (hereinafter referred to as NCA), lithium nickel cobalt manganeseate (hereinafter referred to as NCM), lithium manganese acid, and lithium salts such as lithium iron phosphate, and lithium sulfide.

[0060] The above-described positive electrode active material layer may further include a solid electrolyte. As the solid electrolyte, any solid electrolyte known in the art may be used without limitation, and for example, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or a sulfide-based solid electrolyte may be used, and in particular, a sulfide-based solid electrolyte may be preferably used. In addition, the above-described positive electrode active material layer may be in a form that does not include a polymer-based solid electrolyte.

[0061] 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 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, M is one of P, Si, Ge, B, Al, Ga or In), or a combination thereof. The solid electrolyte may be composed of one material selected from the sulfide-based solid electrolyte materials, or may be composed of two or more materials.

[0062] The above sulfide-based solid electrolyte may include a solid electrolyte represented by the following chemical formula 2:

[0063] [Chemical Formula 2]

[0064] Li x M' y PS z A w

[0065] In the above chemical formula 1,

[0066] x, y, z, w are independently 0 to 6;

[0067] M' is one or more of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta;

[0068] A is one or more of F, Cl, Br, or I.

[0069] As the above solid electrolyte, a sulfide-based solid electrolyte material containing sulfur (S), phosphorus (P), and lithium (Li) as constituent elements can be used. For example, one containing Li2S-P2S5 can be used. When using a sulfide-based solid electrolyte material containing Li2S-P2S5, the mixing molar ratio of Li2S and P2S5 can be selected in the range of, for example, Li2S:P2S5 = 50:50 to 90:10.

[0070] The above solid electrolyte may be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 10 to 20 wt%, based on the total weight of the positive electrode active material layer.

[0071] The positive electrode collector may be in the form of a plate or foil. The positive electrode collector may be, for example, one type of metal selected from indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, and lithium, or an alloy of two or more types of metals.

[0072] Additionally, the positive electrode active material layer may further include a conductive agent and a binder, and may further include additives such as a filler, a dispersant, or an ion conductive auxiliary agent.

[0073] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include 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, thermal black, carbon fiber, and carbon nanotube; 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; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used.

[0074] The above-mentioned conductive material may be included in an amount of 0.01 to 10 wt%, preferably 0.1 to 5 wt%, and more preferably 0.1 to 2 wt%, based on the total weight of the positive electrode active material layer.

[0075] The above binder serves 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 thereof include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0076] The above binder may be included in an amount of 0.5 to 20 wt%, preferably 1 to 10 wt%, and more preferably 1 to 5 wt%, based on the total weight of the positive electrode active material layer.

[0077] As the above filler, dispersant, or ion conductive auxiliary agent, any known material commonly used in electrodes of lithium ion secondary batteries can be used.

[0078] The positive electrode active material layer of the present invention may include 50 to 90 wt% of the positive electrode active material composite, 1 to 30 wt% of the solid electrolyte, 0.1 to 5 wt% of the conductive material, and 0.5 to 20 wt% of the binder; preferably, it may include 75 to 85 wt% of the positive electrode active material composite, 10 to 20 wt% of the solid electrolyte, 0.1 to 2 wt% of the conductive material, and 0.5 to 3 wt% of the binder.

[0079]

[0080] In addition, the present invention relates to a lithium ion secondary battery including the positive electrode, the negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode of the present invention.

[0081] The above lithium-ion secondary battery may be an all-solid-state battery. An all-solid-state battery is defined as one that is composed solely of a solid electrolyte, as well as one that includes an electrolyte in which a portion of a liquid electrolyte is added to the solid electrolyte.

[0082] Hereinafter, embodiments of the lithium ion secondary battery will be described as examples.

[0083] The above lithium secondary battery includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and may optionally include a separator.

[0084] (1) Bipolar

[0085] The lithium ion secondary battery of the present invention is characterized by including the positive electrode of the present invention described above. Therefore, a description of the positive electrode is omitted.

[0086] (2) Cathode

[0087] The above negative electrode includes a free-standing type negative electrode and a type of negative electrode in which a negative electrode active material layer is laminated on a negative electrode current collector. The negative electrode in the lithium ion secondary battery is not particularly limited, and any negative electrode known in the art can be used without limitation.

[0088] The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. The negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. Various forms can be used as the negative electrode current collector, for example, a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0089] The above negative electrode active material layer includes a negative electrode active material, and may optionally further include a binder and a conductive material. In addition, the negative electrode active material layer may further include a solid electrolyte.

[0090] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples 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 alloy, Sn alloy, or Al alloy; SiO β(0 <β< 2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above metal compounds and carbonaceous materials, such as Ag-C composites, Si-C composites, or Sn-C composites, and any one or a mixture of two or more of these may be used.

[0091] Additionally, 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.

[0092] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include 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, thermal black, carbon fiber, and carbon nanotube; 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; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used.

[0093] The above-mentioned conductive material may be typically included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

[0094] The above binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0095] The above binder may be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

[0096] As the above solid electrolyte, any solid electrolyte known in the art can be used without limitation, and for example, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or a sulfide-based solid electrolyte can be used, and in particular, a sulfide-based solid electrolyte can be preferably used. The sulfide-based solid electrolyte described above can be used as the above sulfide-based solid electrolyte.

[0097] The above solid electrolyte may be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 10 to 20 wt%, based on the total weight of the negative electrode active material layer.

[0098] The above negative electrode active material layer may be manufactured by applying and drying the negative electrode slurry, or by casting the negative electrode slurry on a separate support, and then laminating the resulting film on a negative electrode current collector by peeling it off from the support.

[0099]

[0100] (3) Solid electrolyte layer

[0101] The above solid electrolyte layer includes a solid electrolyte capable of moving ions. Any solid electrolyte known in the art can be used as the solid electrolyte without limitation. For example, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or a sulfide-based solid electrolyte can be used. In particular, a sulfide-based solid electrolyte can be preferably used. The sulfide-based solid electrolyte described above can be used as the sulfide-based solid electrolyte.

[0102] The above solid electrolyte may be in an amorphous or crystalline state. Additionally, it may be in a mixed amorphous and crystalline state.

[0103] The above 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 materials constituting the binders in the positive electrode active material layer and the negative electrode active material layer.

[0104]

[0105] In the lithium ion secondary battery of the present invention, other components, excluding the positive electrode active material composite, can be applied without limitation to any component known in the art. Therefore, a more detailed description is omitted.

[0106] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the present invention. However, the examples according to the present invention may be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those of average skill in the art.

[0107]

[0108] Example 1: Preparation of a positive electrode active material composite

[0109] (1) Manufacturing of positive electrode active material substrate

[0110] Li2CO3 and Ni 0.8 Co 0.1 Mn 0.1 (OH)2 was mixed in a mixer at a weight ratio of 1.1:1 to form a reaction mixture, and the reaction mixture was 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 plastic mixture, and then cooled. After being crushed and sieved, the crushed plastic 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 form LiNi having a particle size (D50) of 5 μm. 0.8 Co 0.1 Mn 0.1 O2 was manufactured.

[0111] (2) Manufacturing of coating substrate

[0112] LiPF6 powder (98%, Sigma-Aldrich) was dissolved in ethanol to prepare a LiPF6 solution (containing 0.2 g of LiPF6).

[0113] (3) Manufacturing of a composite of positive electrode active materials

[0114] LiNi having a particle size (D50) of 5㎛ as a positive electrode active material substrate manufactured in the above (1) 0.8 Co 0.1 Mn 0.1 A mixed solution was prepared by adding 99.8 g of O2 powder to the LiPF6 solution (containing 0.2 g of LiPF6) prepared in the above (2). The mixed solution was mixed for 24 hours using a Lab Blender (Waring), and vacuum-dried to remove the solvent ethanol, thereby obtaining LiNi 0.8 Co 0.1 Mn 0.1 A composite of positive electrode active materials was manufactured in which a LiPF6 coating layer was formed on an O2 substrate.

[0115]

[0116] Example 2: Preparation of a positive electrode active material composite

[0117] LiNi was prepared in the same manner as in Example 1, except that LiPF6 solution (containing 0.7 g of LiPF6) was used instead of LiPF6 solution (containing 0.2 g of LiPF6) in Example 1. 0.8 Co 0.1 Mn 0.1 A composite of positive electrode active materials was manufactured in which a LiPF6 coating layer was formed on an O2 substrate.

[0118]

[0119] Example 3: Preparation of a positive electrode active material composite

[0120] LiNi was prepared in the same manner as in Example 1, except that LiPF6 solution (containing 3 g of LiPF6) was used instead of LiPF6 solution (containing 0.2 g of LiPF6) in Example 1. 0.8 Co 0.1 Mn 0.1 A composite of positive electrode active materials was manufactured in which a LiPF6 coating layer was formed on an O2 substrate.

[0121]

[0122] Example 4: Preparation of a positive electrode active material composite

[0123] LiNi was prepared in the same manner as in Example 1, except that LiPO2F2 solution (containing 0.7 g of LiPO2F) was used instead of LiPF6 solution (containing 0.2 g of LiPF) in Example 1. 0.8 Co 0.1 Mn 0.1 A composite of positive electrode active materials was manufactured in which a LiPO2F2 coating layer was formed on an O2 substrate.

[0124]

[0125] Example 5: Preparation of a positive electrode active material composite

[0126] In Example 1, LiDFBOP solution (containing 0.2 g of LiPF6) was used instead of LiPF6 solution (containing 0.2 g of LiPF6). LiNi was prepared in the same manner as in Example 1, except that 0.7 g was used. 0.8 Co 0.1Mn 0.1 LiDFBOP on O2 substrate A composite of positive electrode active materials with a coating layer was manufactured.

[0127]

[0128] Comparative Example 1: Preparation of positive electrode active material

[0129] LiNi prepared in Example 1 0.8 Co 0.1 Mn 0.1 O2 was used as the positive electrode active material without coating.

[0130]

[0131] Comparative Example 2: Preparation of a positive electrode active material composite

[0132] LiNi was prepared in the same manner as in Example 1, except that LiPF6 solution (containing 5 g of LiPF6) was used instead of LiPF6 solution (containing 0.2 g of LiPF6) in Example 1. 0.8 Co 0.1 Mn 0.1 A composite of positive electrode active materials was manufactured in which a LiPF6 coating layer was formed on an O2 substrate.

[0133]

[0134] Examples 6 to 10 and Comparative Examples 3 to 4: Manufacturing of all-solid-state lithium-ion secondary batteries

[0135] (1) Positive electrode manufacturing

[0136] 81.9 wt% of each of the positive electrode active material composites manufactured in Examples 1 to 5 and Comparative Examples 1 to 2 (the positive electrode active material in Comparative Example 1), 15.6 wt% of the solid electrolyte LPS (Li6PS5Cl), 1.5 wt% of the carbon black powder, and 1 wt% of the PTFE as a binder were mixed at 5000 rpm for 1 minute without a solvent using a Lab Blender (Waring Co., Ltd.) (first mixing). Next, a shear force of 100 N was applied to the mixture to perform high-shear mixing (using PBV-0.1L, Irie Shokai Co., Ltd.) (second mixing) to manufacture a dough. Next, the dough was used to manufacture a free-standing electrode layer using a Two roll mill MR-3 (Inoue Co., Ltd.).

[0137] The above electrode layer was positioned on one side of an aluminum current collector having a thickness of 15 μm and pressed to manufacture a positive electrode.

[0138] (2) Manufacturing of all-solid-state lithium-ion secondary batteries

[0139] A lithium metal having a thickness of 40 μm was used as the negative electrode, and a Li6PS5Cl solid electrolyte membrane having a thickness of 50 μm was interposed between each of the positive electrodes manufactured above and the negative electrode, and then pressurized at a pressure of 500 MPa to manufacture a jig cell having a driving pressure of 3 MPa and a capacity of 5 mAh.

[0140]

[0141] Experimental Example 1: Battery Characteristic Evaluation

[0142] (1) Evaluation of initial discharge capacity and efficiency of all-solid-state batteries

[0143] The jig cells manufactured in Examples 6 to 10 and Comparative Examples 3 to 4 were charged at a rate (C-rate) of 0.1 C until the voltage reached 4.25 V (vs. Li), and then cut-off was achieved at a rate of 0.05 C while maintaining 4.25 V (vs. Li). Subsequently, they were discharged at a rate (C-rate) of 0.1 C until the voltage reached 3.0 V (vs. Li) (1st cycle). The initial efficiency was calculated as discharge capacity / charge capacity × 100 (%). The experimental results are shown in Table 1 below.

[0144] (2) Evaluation of the life characteristics of all-solid-state batteries

[0145] The jig cells manufactured in Examples 6 to 10 and Comparative Examples 3 to 4 were charged at a rate (C-rate) of 0.33 C until the voltage reached 4.25 V (vs. Li), and then cut-off was achieved at a rate of 0.1 C while maintaining 4.25 V (vs. Li). Subsequently, the cells were discharged at a rate (C-rate) of 0.33 C until the voltage reached 3.0 V (vs. Li) (1st cycle). The above charge-discharge test was repeated 50 cycles, and the capacity retention rate of the discharge capacity was measured. The experimental results are shown in Table 1 below.

[0146] Test cellCoating materialCoating content (wt%)0.1C initial capacity (mAh)0.1C initial efficiency (%)Life characteristics0.33C 50 cycle capacity retention (%)Example 6LiPF60.25.094.494.1Example 7LiPF60.75.094.395.0Example 8LiPF63.05.094.494.2Example 9LiPO2F20.75.094.693.9Example 10LiDFBOP0.75.094.492.8Comparative example 3LiPF60.4.588.353.1Comparative example 4LiPF65.04.086.524.1

Claims

1. Includes a positive electrode active material substrate and a coating layer coated on the positive electrode active material substrate, The above coating layer is a composite of a cathode active material including at least one selected from the group consisting of LiPF6, LiDFBOP (lithium difluorobis(oxalato)phosphate), and LiTFOP (lithium tetrafluoro(oxalato)phosphate).

2. In paragraph 1, A positive electrode active material composite characterized in that the positive electrode active material substrate is a compound represented by the following chemical formula 1. [Chemical Formula 1] The a (Nor 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<1이다.

3. In paragraph 1, A cathode active material composite, characterized in that the coating layer is included in an amount of 0.1 to 4.5 wt% based on the total weight of the cathode active material composite.

4. In paragraph 1, A composite of positive electrode active materials, characterized in that the thickness of the coating layer is 10 nm to 200 nm.

5. In paragraph 1, A positive electrode active material composite characterized in that the coating layer is formed by wet mixing or dry mixing of a positive electrode active material substrate and a coating substrate.

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

7. In paragraph 6, A cathode further comprising a sulfide-based solid electrolyte.

8. In paragraph 7, A cathode characterized in that the above sulfide-based solid electrolyte is a compound represented by the following chemical formula 2. [Chemical Formula 2] Li x M' y P.S. z A w In the above chemical formula 1, x, y, z, w are independently greater than or equal to 0 and less than or equal 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.

9. A lithium ion secondary battery comprising the positive electrode, the negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode of clause 6.

10. In paragraph 9, A lithium ion secondary battery characterized in that the above lithium ion secondary battery is a sulfide-based all-solid-state battery.