Composite positive electrode active material, method for manufacturing the same, and lithium secondary battery containing the same

Abstract

The present invention relates to a composite positive electrode active material that can improve the conductivity, capacity, and output characteristics of a lithium secondary battery by allowing an oxide-based solid electrolyte to adhere to it without degrading the physical properties of the positive electrode active material itself, a method for producing the same, and a lithium secondary battery containing the same. The composite positive electrode active material comprises positive electrode active material particles, oxide-based solid electrolyte particles formed on the positive electrode active material particles, and a crosslinked polymer binder, wherein the oxide-based solid electrolyte particles can adhere to the surface of the positive electrode active material particles via the crosslinked polymer binder.

Description

Technical Field

[0001] [Cross - reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2023 - 0075012 filed on June 12, 2023 and Korean Patent Application No. 10 - 2024 - 0031896 filed on March 6, 2024, and all the contents disclosed in the documents of the Korean patent applications are incorporated herein by reference in their entirety.

[0002] The present invention relates to a composite cathode active material capable of improving the conductivity, capacity, and output characteristics of a lithium secondary battery by attaching an oxide - based solid electrolyte without degrading the physical properties of the cathode active material itself, a method for manufacturing the same, and a lithium secondary battery including the same.

Background Art

[0003] Recently, as the application fields of lithium secondary batteries have rapidly expanded not only to power supply for electronic devices such as electric, electronic, communication, and computers but also to power storage supply for large - scale devices such as automobiles and power storage devices, the demand for high - capacity, high - output, long - life, and high - stability lithium secondary batteries has been increasing.

[0004] Therefore, in order to improve the capacity, output, and conductivity within the electrode of a lithium secondary battery and enhance its stability, methods such as including inorganic solid electrolyte particles together within the active material layer of the cathode, or coating such inorganic solid electrolyte particles on the cathode active material particles to manufacture and use a coated or composite cathode active material have been proposed.

[0005] Conventionally, in order to manufacture the composite cathode active material, a method of mixing cathode active material particles and inorganic solid electrolyte particles wet or dry, selectively milling, and then firing has been considered. However, recently, since cathode active materials containing a high content of nickel are mainly used to increase the capacity and energy density of lithium secondary batteries, such high - content nickel - containing cathode active materials exhibit low moisture stability, so the wet method has not been easily applicable.

[0006] Furthermore, conventional methods have the disadvantage of requiring firing and re-firing at very high temperatures in order to attach inorganic solid electrolyte particles to the positive electrode active material particles. Moreover, during such high-temperature firing processes, the crystal structure of the surface of the positive electrode active material particles may change, leading to a decrease in their electrochemical properties and stability. Additionally, aggregation during high-temperature firing can generate large particles, necessitating re-pulverization.

[0007] Furthermore, when the firing temperature is reduced, a large number of the inorganic solid electrolyte particles detach from the positive electrode active material particles, which has the disadvantage of making it difficult to fully achieve the capacity, output, or conductivity improvement effects achieved by coating the inorganic solid electrolyte.

[0008] Therefore, there is a continuing demand for the development of technologies related to composite cathode active materials that can improve the capacity and output characteristics of lithium secondary batteries by allowing oxide-based solid electrolytes to adhere well without degrading the properties and stability of the cathode active material itself due to high-temperature firing or other processes. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Therefore, the present invention provides a composite positive electrode active material that allows oxide-based solid electrolytes to adhere well without reducing the physical properties and stability of the positive electrode active material itself, thereby improving the conductivity, capacity, and output characteristics of a lithium secondary battery.

[0010] Furthermore, the present invention provides a method for producing a composite cathode active material that can be manufactured by a simplified process and a heat treatment process at a relatively low temperature.

[0011] The present invention further provides a positive electrode and a lithium secondary battery that exhibit excellent capacity and output characteristics by including the composite positive electrode active material. [Means for solving the problem]

[0012] This invention comprises positive electrode active material particles, The positive electrode active material particles comprise oxide-based solid electrolyte particles and a crosslinked polymer binder, The present invention provides a composite cathode active material in which the oxide-based solid electrolyte particles are attached to the surface of the cathode active material particles via the cross-linked polymer binder.

[0013] The present invention also provides a method for producing a composite positive electrode active material, comprising the steps of mixing positive electrode active material particles, oxide-based solid electrolyte particles, and a polymer binder, and thermally curing the mixture.

[0014] Furthermore, the present invention provides a positive electrode for a lithium secondary battery, comprising a metal current collector and a positive electrode active material layer formed on the metal current collector and containing the composite positive electrode active material and a conductive material.

[0015] The present invention also provides a lithium secondary battery comprising the positive electrode, the negative electrode, and the electrolyte. [Effects of the Invention]

[0016] The composite cathode active material of the present invention has oxide-based solid electrolyte particles attached to cathode active material particles via a cured and crosslinked polymer binder, and can be manufactured in a simplified process at a relatively low curing temperature.

[0017] Therefore, it is possible to suppress the deterioration of the properties and stability of the positive electrode active material due to high-temperature heat treatment processes, as well as the generation of large particles. At the same time, the oxide-based solid electrolyte particles are stably attached to and maintained on the positive electrode active material particles, thereby improving the capacity, output, and conductivity of the lithium secondary battery.

[0018] Therefore, the present invention can greatly contribute to the development of next-generation lithium-ion batteries exhibiting improved capacity and output characteristics. [Brief explanation of the drawing]

[0019] [Figure 1] The results of analyzing the particle size distribution of the composite cathode active material particles of Example 1 and the cathode active material particles of Comparative Example 1 are shown. [Figure 2] The results of evaluating the resistance of lithium secondary batteries in Example 1, Comparative Examples 1 and 2 at different charge states are shown. [Modes for carrying out the invention]

[0020] Terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner and concept consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors can appropriately define the concepts of terms in order to best describe their invention.

[0021] In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the presence of implemented features, figures, stages, components, or combinations thereof, and should be understood not to preemptively exclude the possibility of the presence or addition of one or more other features, figures, stages, components, or combinations thereof.

[0022] According to one embodiment of the invention, positive electrode active material particles and The positive electrode active material particles comprise oxide-based solid electrolyte particles and a crosslinked polymer binder, A composite cathode active material is provided, in which the oxide-based solid electrolyte particles are attached to the surface of the cathode active material particles via the cross-linked polymer binder.

[0023] In the composite cathode active material of the above embodiment, oxide-based solid electrolyte particles are attached to the cathode active material particles via a cured and crosslinked polymer binder. Furthermore, as will be explained in more detail below, such a composite cathode active material of the above embodiment can be manufactured at a relatively low temperature corresponding to the curing temperature of the polymer binder. As a result, the deterioration of the properties and stability of the cathode active material due to conventional high-temperature heat treatment processes such as multiple firing processes at high temperatures, as well as the generation of large particles during the manufacturing process, can be suppressed, and it can be manufactured in a simplified process without the need for additional heat treatment or additional grinding.

[0024] In particular, with the composite positive electrode active material, there is almost no change in the crystal structure of the positive electrode active material surface (for example, a change from a rock salt structure to a layered structure on the surface), so the risk of battery ignition or explosion due to such changes in crystal structure is reduced, and the safety of lithium secondary batteries can be greatly improved.

[0025] Consequently, the oxide-based solid electrolyte particles can be firmly attached to the cured and crosslinked polymer binder and stably maintained on the positive electrode active material particles. As a result, the capacity, output, and conductivity of the lithium secondary battery can be further improved by coating with the oxide-based solid electrolyte particles.

[0026] The following describes in more detail the composite positive electrode active material, its manufacturing method, the positive electrode, and the lithium secondary battery according to the embodiments.

[0027] In the composite positive electrode active material of the above embodiment, the positive electrode active material particles are compounds capable of reversible intercalation and deintercalation of lithium, and specifically may include lithium metal oxides comprising one or more metals such as iron, cobalt, manganese, nickel, or aluminum, and lithium.

[0028] Specifically, the lithium metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), a lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of the respective independent elements, and 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s < 1, p2 + q2 + r2 + s2 = 1), etc.), or a lithium iron oxide (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b(Here, M is one or more selected from Al, Mg, and Ti, and X is one or more selected from F, S, and N, with -0.5 ≤ a ≤ +0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1) and so on, and one or more of these compounds may be included.

[0029] In particular, the positive electrode active material includes a lithium metal oxide containing two or more transition metals, including lithium and nickel, and the lithium metal oxide may contain 80 mol% or more, or 80-99 mol%, or 85-95 mol% of nickel relative to the total transition metal content excluding lithium. Such a lithium metal oxide may be represented, for example, by the following chemical formula 1: [Chemical formula 1] Li x Ni a Co b M 1 c M 2 d O2 In the above chemical formula 1, the above M 1 M may be one or more selected from Mn and Al, or a combination thereof. 2 x may be one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and may be 0.90≦x≦1.1, or 0.95≦x≦1.08, or 1.0≦x≦1.08, or 0.80≦a<1.0, or 0.80≦a≦0.99, or 0.85≦a≦0.95, and b, c, and d may each be independently 0 or greater and less than 0.2 (except when b, c, and d are all 0).

[0030] By using a lithium metal oxide containing such a high nickel content as the positive electrode active material, the capacity and energy density of the lithium secondary battery can be further improved. Furthermore, in one embodiment of the composite positive electrode active material, even when using such high nickel-containing positive electrode active material particles, the oxide-based solid electrolyte particles can be attached without changing the crystal structure of the positive electrode active material particles due to high-temperature firing or other processes. Therefore, while maintaining the high capacity and energy density, the capacity and output characteristics of the lithium secondary battery can be further improved by adding the oxide-based solid electrolyte particles.

[0031] Furthermore, as oxide-based solid electrolyte particles adhering to the positive electrode active material particles, any solid electrolyte having a lithium ion supply source by containing lithium in its structure and having the form of lithium metal oxide or lithium metal phosphorus oxide can be used.

[0032] Specific examples include one or more lithium metal oxides or lithium metal phosphoroxides selected from Nasicon-type solid electrolytes, Lisicon-type solid electrolytes, Garnet-type solid electrolytes, Perovskite-type solid electrolytes, and LiPON-type solid electrolytes. More specific examples include one or more compounds selected from the group consisting of LAGP (lithium aluminum germanium phosphate) compounds, LLZO (lithium lanthanum zirconium oxide) compounds, LATP (lithium aluminum titanium phosphate) compounds, LLZTO (lithium lanthanum zirconium tantalum oxide) compounds, LLTO (lithium lanthanum titanium oxide) compounds, LSTP (lithium silicon titanium phosphate) compounds, and LGPO (lithium germanium phosphate) compounds.

[0033] In particular, NASCICON-type solid electrolytes such as the LAGP-based or LATP-based compounds can be appropriately used because they adhere well to the positive electrode active material particles by cross-linked polymer binders, thereby improving the conductivity and output of lithium secondary batteries.

[0034] The oxide-based solid electrolyte particles may be included in an amount of 0.1 to 5 parts by weight, 0.5 to 4 parts by weight, or 1 to 3.5 parts by weight based on 100 parts by weight of the positive electrode active material particles. This allows the oxide-based solid electrolyte particles to adhere well to the surface of the positive electrode active material particles, effectively improving the electrochemical properties of the lithium secondary battery without hindering the properties of the positive electrode active material particles.

[0035] Furthermore, in the composite positive electrode active material of the embodiment described above, the positive electrode active material particles can have an average particle size (D50) of 3 to 15 μm, 5 to 13 μm, or 7 to 12 μm, and the oxide-based solid electrolyte particles can have an average particle size (D50) of 100 nm to 1.3 μm, 150 nm to 1.0 μm, or 200 nm to 800 nm. As a result, multiple oxide-based solid electrolyte particles can be well attached to or bonded to the surface of the positive electrode active material particles, and the composite positive electrode active material of the embodiment can exhibit excellent electrochemical properties.

[0036] At this time, the average particle size (D50) of each particle can be calculated, for example, by measuring the particle size distribution of the positive electrode active material particles or the oxide-based solid electrolyte particles using laser diffraction and a laser diffraction particle size analyzer, using the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve.

[0037] On the other hand, the composite positive electrode active material of the above embodiment includes a crosslinked polymer binder that binds to or adheres to the positive electrode active material particles, thereby allowing the oxide-based solid electrolyte particles to adhere well to their surface. Such a crosslinked polymer binder is formed by curing and crosslinking the polymer binder in or out of the presence of a crosslinking agent, and such a polymer binder before curing and crosslinking may be the same type of polymer as the polymer binder separately contained in the positive electrode active material described later.

[0038] Furthermore, the crosslinked polymer binder may be formed in a form that adheres to or binds to the surface of the positive electrode active material particles, while covering at least a portion of the oxide-based solid electrolyte particles on the positive electrode active material particles.

[0039] Through such a cross-linked polymer binder, the oxide-based solid electrolyte particles can bond or adhere well to the surface of the positive electrode active material particles without a high-temperature firing process, thereby enabling the composite positive electrode active material of one embodiment to exhibit improved stability and electrochemical properties.

[0040] The crosslinked polymer binder is any polymer known to be usable as a binder in the active material layer of a lithium secondary battery, and which can be cured by methods such as thermosetting or photocuring. More specifically, it may be a polymer that has been cured and crosslinked at a temperature of 100°C or higher, or 100-200°C. Specific examples include one or more polymers selected from the group consisting of polyvinylidene fluoride polymers, polyvinyl alcohol polymers, cellulose polymers, polyvinylpyrrolidone polymers, polytetrafluoroethylene polymers, and polyolefin polymers, or a polymer obtained by curing a copolymer or mixture of two or more polymers. However, considering the characteristics of the positive electrode and the good adhesion of the oxide-based solid electrolyte particles, a polyvinylidene fluoride polymer crosslinked by thermosetting can be appropriately used.

[0041] The crosslinked polymer binder may be present in an amount of 0.03 to 2 parts by weight, 0.05 to 1.5 parts by weight, or 0.1 to 1.0 parts by weight based on 100 parts by weight of the positive electrode active material particles. This allows the oxide-based solid electrolyte particles to adhere well to the positive electrode active material particles and reduces the increase in resistance caused by the crosslinked polymer binder.

[0042] The composite cathode active material of the above-described embodiment can exhibit a uniform particle size distribution by reducing particle aggregation due to high-temperature firing or other processes during the manufacturing process. Specifically, the composite cathode active material can exhibit a small deviation in particle size, for example, a SPAN derived from the results of the particle size distribution analysis of 0.3 to 5 μm, 0.5 to 3 μm, or 0.5 to 1.5 μm.

[0043] On the other hand, the composite positive electrode active material of the above-described embodiment can be manufactured by a method comprising the steps of mixing positive electrode active material particles, oxide-based solid electrolyte particles, and a polymer binder, and thermally curing the mixture.

[0044] In such a manufacturing method, the thermosetting step may be carried out in the presence or absence of a crosslinking agent or curing initiator, depending on the type of polymer binder, and may be carried out in a temperature range of 20°C above the minimum curing temperature of the polymer binder. Specifically, the thermosetting step may be carried out at a temperature of 100-200°C, 105-180°C, or 110-150°C.

[0045] Through such thermosetting, the polymer binder hardens and crosslinks, forming a crosslinked polymer binder. The oxide-based solid electrolyte particles adhere to the surface of the positive electrode active material particles using this crosslinked polymer binder, thereby producing a composite positive electrode active material according to one embodiment.

[0046] This manufacturing method eliminates the need for high-temperature re-calcination steps to adhere the oxide-based solid electrolyte particles, and consequently reduces aggregation between positive electrode active material particles during the manufacturing process, thereby reducing the need for additional grinding steps. As a result, the manufacturing process is simplified, while the deterioration of the properties and stability of the positive electrode active material due to high-temperature re-calcination steps and other processes can be suppressed, enabling the production of a composite positive electrode active material with a uniform particle size distribution.

[0047] On the other hand, in some cases, hardening and adhesion may occur between the cross-linked polymer binders, and if necessary, the process may further include a step of pulverizing the composite cathode active material after the thermosetting step.

[0048] On the other hand, according to another embodiment of the invention, a positive electrode for a lithium secondary battery is provided, comprising the composite positive electrode active material of the above-described embodiment. Such a positive electrode may include a metal current collector and a positive electrode active material layer formed on the metal current collector, comprising the composite positive electrode active material of the above-described embodiment and a conductive material.

[0049] In the positive electrode of such other embodiments, the metal current collector is not particularly limited as long as it is conductive without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., can be used.

[0050] Furthermore, the positive electrode active material layer may contain the above-mentioned composite positive electrode active material and conductive material, and may further selectively contain a polymer binder.

[0051] In this case, the composite positive electrode active material of the above embodiment may be present in an amount of 60-99% by weight, 70-99% by weight, or 80-98% by weight, based on the total weight of the positive electrode active material layer.

[0052] Furthermore, the conductive material contained in the positive electrode active material layer is a component for further improving the conductivity of the composite positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystalline structure; conductive nanomaterials such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used. In particular, by including conductive nanomaterials such as carbon nanotubes or carbon nanofibers in the conductive material, the resistance of the lithium secondary battery containing the positive electrode can be further reduced, and the output characteristics can be further improved.

[0053] Typically, the conductive material may be present in an amount of 1 to 20% by weight, 1 to 15% by weight, or 1 to 10% by weight, based on the total weight of the positive electrode active material layer.

[0054] The polymer binder selectively contained in the positive electrode active material layer is a component that assists in the bonding of the composite positive electrode active material to conductive materials and to the current collector. Examples of such polymer binders include polyvinylidene fluoride polymers; polyvinyl alcohol polymers; cellulose polymers such as carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, or regenerated cellulose; polyvinylpyrrolidone polymers; polytetrafluoroethylene polymers; polyolefin polymers such as polyethylene (PE), polypropylene, ethylene-propylene-diene, or sulfonated ethylene-propylene-diene; or rubber polymers such as nitrile rubber, styrene-butadiene rubber, or fluororubber. A mixture or copolymer of two or more selected from these may be used.

[0055] In the positive electrode according to other embodiments, not only the polymer binder contained in the positive electrode active material layer, but also the crosslinked polymer binder contained in the composite positive electrode active material of one embodiment can act as a type of polymer binder. Therefore, the polymer binder contained in the positive electrode active material layer becomes the same type of polymer as the crosslinked polymer binder of the composite positive electrode active material, and may, for example, become the same polymer as before the crosslinked polymer binder was cured and crosslinked. This makes it possible to reduce the content of the polymer binder contained in the positive electrode active material layer by the amount of the crosslinked polymer binder, while maintaining the excellent electrical properties of the positive electrode.

[0056] The polymer binder may be present in an amount of 1 to 20% by weight, 1 to 15% by weight, or 1 to 10% by weight relative to the total weight of the positive electrode active material layer, based on the total content of the polymer binder and the crosslinked polymer binder contained in the composite positive electrode active material.

[0057] Furthermore, a filler may be selectively added to the positive electrode as a component to suppress its expansion. Such a filler is not particularly limited as long as it can suppress the expansion of the electrode without inducing a chemical change in the battery, and for example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers; etc. can be used.

[0058] The positive electrode of the above-described embodiment can be manufactured, for example, by dispersing and mixing the composite positive electrode active material, polymer binder, and conductive material in a dispersion medium (solvent) to create a slurry, coating this slurry onto a metal current collector, and then drying and rolling it. In this case, the dispersion medium can be NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof, but is not necessarily limited to these.

[0059] On the other hand, according to another embodiment of the invention, a lithium secondary battery is provided that includes the positive electrode, negative electrode, and electrolyte described above. By including the composite positive electrode active material and positive electrode of the above embodiment, the lithium secondary battery of this other embodiment can exhibit excellent stability, capacity, and output characteristics.

[0060] In lithium secondary batteries of such other embodiments, the negative electrode may have a conventional configuration known in the art. For example, the negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on such a negative electrode current collector, the negative electrode active material layer of which may include, for example, a negative electrode active material and optionally additives such as conductive materials, binders, and fillers. Alternatively, such a negative electrode may be formed by a common method of dispersing and mixing the components of the negative electrode active material layer in a dispersion medium (solvent) to create a slurry, coating the slurry onto the negative electrode current collector, and then drying and rolling it.

[0061] In this case, the negative electrode current collector can be made of platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), copper (Cu), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO2), FTO (F doped SnO2), and alloys thereof, as well as copper (Cu) or stainless steel with a surface treatment of carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but is not necessarily limited to these. The negative electrode current collector may take the form of foil, film, sheet, punched material, porous material, foam, etc.

[0062] Furthermore, as the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous 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, Sb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metallic oxides capable of doping and dedoping with lithium, such as SiOβ (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. One or more of these mixtures can be used. In addition, a metallic lithium thin film may be used as the negative electrode active material.

[0063] Additionally, all types of carbonaceous materials can be used, including low-crystalline carbon and high-crystalline carbon. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0064] The negative electrode active material described above may be present in an amount of 60-99% by weight, 70-99% by weight, or 80-98% by weight, based on the total weight of the negative electrode active material layer.

[0065] In other embodiments, the negative electrode may not include a negative electrode active material layer, but only a negative electrode current collector. In such a negative electrode, lithium ions that have moved from the positive electrode during the charge-discharge process can be electrodeposited onto the negative electrode current collector to form a lithium metal layer, and this lithium metal layer can act as a negative electrode active material.

[0066] On the other hand, the binder and conductive material contained in the negative electrode active material layer can be the same as those described for the positive electrode, so no further explanation regarding this is necessary.

[0067] The lithium secondary batteries of the other embodiments described above further include an electrolyte. In one embodiment, the electrolyte may be a liquid electrolyte comprising a lithium salt and a non-aqueous organic solvent. Such an electrolyte acts as a transfer medium for lithium ions between the positive and negative electrodes.

[0068] The lithium salt contained in the electrolyte is used as a medium for transferring ions in a lithium secondary battery. The lithium salt is, for example, Li as a cation. + Includes F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - ClO4 - B 10 Cl 10 - AlCl4 - AlO2 - PF6 - CF3SO3 - CH3CO2 - CF3CO2 - AsF6 - SbF6 - CH3SO3 - , (CF3CF2SO2)2N - (CF3SO2)2N - , (FSO2)2N - BF2C2O4 - BC4O8 - PF4C2O4- PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - , C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2) 2CH - CF3(CF2)7SO3 - and SCN - It can also contain anions selected from the group consisting of the following.

[0069] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 It may contain one or more selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (Lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl)imide, LiN(SO2CF2CF3)2, and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, LiN(SO2CF3)2).

[0070] The concentration of the lithium salt can be appropriately changed within a range that is normally usable, and may be included in the electrolyte at a concentration of 0.5 M to 6 M, or 1 M to 5 M.

[0071] On the other hand, the type of non-aqueous organic solvent included in the electrolyte is not particularly limited, and any organic solvent that has been known to be applicable to lithium-ion battery electrolytes can be used. Examples of such organic solvents include one or more selected from the group consisting of carbonate-based solvents, ether-based solvents, nitrile-based solvents, phosphate-based solvents, and sulfone-based solvents.

[0072] More specifically, as the carbonate-based solvent, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, or methyl (2,2,2-trifluoroethyl) carbonate can be used, and as the phosphate-based solvent, trimethyl phosphate, triethyl phosphate, or 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphorane 2-oxide can be used.

[0073] Furthermore, as the ether-based solvent, dibutyl ether, tetraglyceride, diglyme, dimethoxyethane, or tetrahydrofuran derivatives such as 2-methyltetrahydrofuran can be used, and as the nitrile-based solvent, succinonitrile, adiponitrile, sebaconitrile, acetonitrile, or propionitrile can be used. As the sulfone-based solvent, dimethyl sulfone, ethyl methyl sulfone, or sulforane can be used.

[0074] On the other hand, the lithium secondary battery of the other embodiment described above may further include a porous separator membrane interposed between the positive electrode and the negative electrode.

[0075] Such porous separation membranes can be used in the form of sheets, multilayer membranes, fine porous films, woven fabrics, and nonwoven fabrics, but are not necessarily limited to these forms. However, it is preferable to use porous polyethylene or porous glass fiber nonwoven fabric (glass filter) as the separation membrane, and it is even more preferable to use a porous glass filter (glass fiber nonwoven fabric) as the separation membrane. The separation membrane may be a thin insulating film with high ion permeability and mechanical strength, and the pore size of the separation membrane may generally be in the range of 0.01 to 10 μm, and the thickness may generally be in the range of 5 to 300 μm, but is not limited to these.

[0076] Furthermore, in other embodiments of the lithium secondary battery, the separation membrane may not be present, and the electrolyte described above may be interposed between the positive and negative electrodes in the form of an electrolyte membrane or electrolyte film. In this case, the electrolyte membrane or electrolyte film may be in the form of a polymer matrix containing the lithium salt, non-aqueous organic solvent and / or solid electrolyte described above, or it may be in the form of a solid electrolyte membrane or solid electrolyte film containing a solid electrolyte such as a polymer-based solid electrolyte, oxide-based solid electrolyte, sulfide-based solid electrolyte, or halide-based solid electrolyte. In a more specific example, the electrolyte membrane or electrolyte film may contain the same type of oxide-based solid electrolyte as the oxide-based solid electrolyte contained in the composite positive electrode active material of one embodiment. As the polymer matrix, well-known polymer-based solid electrolytes can be used. On the other hand, the type of solid electrolyte and the configuration of the electrolyte membrane or electrolyte film may follow the general configuration of a semi-solid-state battery or an all-solid-state battery, so further explanation regarding this is omitted.

[0077] As described above, a battery in which an electrolyte membrane containing a solid electrolyte is interposed between the positive and negative electrodes, either as a substitute for or in addition to the separator membrane interposed between the positive and negative electrodes, may be a semi-solid battery using both a liquid and a solid electrolyte, or an all-solid battery containing only a solid electrolyte.

[0078] On the other hand, lithium secondary batteries of the other embodiments described above can be manufactured by conventional methods in the art. For example, an electrode assembly including a positive electrode, a negative electrode, and a separator membrane (or electrolyte membrane) can be housed in a case and manufactured by injecting and impregnating the electrolyte described above.

[0079] Such lithium secondary batteries are not only suitable for use as battery cells in power supplies for small devices, but are also particularly suitable for use as unit batteries in battery modules that power medium to large devices.

[0080] The invention will be described in more detail below through specific examples. However, the following examples are merely illustrative for understanding the invention and do not limit the scope of the invention.

[0081] Example 1: Manufacturing of composite cathode active material, cathode, and lithium secondary battery As the positive electrode active material, lithium nickel cobalt manganese composite oxide (NCM811; D50: 10 μm) containing 80 mol% nickel in the total transition metal is used, and as the oxide-based solid electrolyte, LiAl with D50: 300 nm is used. 0.3 Ti 1.7 (PO4)3 (LATP-based) compound particles were used. Polyvinylidene fluoride (PVdF) was used as the binder.

[0082] To produce the composite cathode active material of Example 1, 100 parts by weight of the cathode active material particles was mixed with 3 parts by weight of oxide-based solid electrolyte particles and 0.1 parts by weight of a binder. The mixture was then further mixed and heat-cured at a temperature of 150-180°C for 2 hours, and then dried in a vacuum oven at 100°C for 24 hours to coat the oxide-based solid electrolyte particles with the cured (crosslinked) binder.

[0083] The composite cathode active material, conductive material (carbon nanotubes), and binder (PVdF) were mixed in a weight ratio of 97:1:2 and dispersed in NMP solvent at 3000 rpm to produce a slurry. This slurry was then coated onto 25 μm thick aluminum foil using a blade-type coating machine, a Mathis coater (Labdryer / coater type LTE, Werner Mathis AG), to a uniform thickness. The mixture was dried in a vacuum oven at 130°C for 24 hours and then rolled using a roll press machine to produce a cathode for lithium secondary batteries.

[0084] Using SiO as the negative electrode active material, the negative electrode was manufactured by mixing the negative electrode active material, conductive material, and binder in a weight ratio of 96.5:1.5:2, and then proceeding with the same process as for the positive electrode.

[0085] After punching out the positive and negative electrodes, an electrode assembly was manufactured by laminating them with a separation membrane made of porous polyethylene (PE) film interposed between them.

[0086] The manufactured electrode assemblies were placed in pouches and sealed, then dried in a 60°C vacuum oven for 24 hours, and the electrolyte was injected to produce pouch-type lithium secondary batteries. The electrolyte was prepared by dissolving 1.0 M LiPF6 in an organic solvent consisting of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixed volume ratio of 3 / 7).

[0087] Comparative Example 1: Manufacturing of Cathode and Lithium Secondary Battery Instead of the composite cathode active material in Example 1, an uncoated lithium nickel cobalt manganese composite oxide (NCM811; D50: 10 μm) was used as the cathode active material.

[0088] The positive electrode active material, conductive material (carbon nanotubes), and binder (PVdF) were mixed in a weight ratio of 97:1:2 and dispersed in NMP solvent at 3000 rpm to produce a slurry. This slurry was then coated onto 25 μm thick aluminum foil using a blade-type coating machine, a Mathis coater (Labdryer / coater type LTE, Werner Mathis AG), to a uniform thickness. The mixture was dried in a vacuum oven at 130°C for 24 hours and then rolled using a roll press machine to produce a positive electrode for a lithium secondary battery.

[0089] A lithium secondary battery was manufactured using such a positive electrode in the same manner as in Example 1.

[0090] Comparative Example 2: Production of a positive electrode (mixture of positive electrode active material and oxide-based solid electrolyte) and a lithium secondary battery A non-aqueous organic solvent composition was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70. To this composition, 5% by weight of trimethylolpropane triacrylate (TMPTA) and 0.02% by weight of the polymerization initiator AIBN were added and mixed to produce a gel polymer electrolyte composition.

[0091] In such a gel polymer electrolyte composition, the positive electrode active material is lithium nickel cobalt manganese composite oxide (NCM811; D50: 10 μm) containing 80 mol% nickel in the total transition metal, and LiAl with D50: 300 nm. 0.3 Ti 1.7 An oxide-based solid electrolyte of a (PO4)3 (LATP) compound was added and mixed in the same amount as in Example 1. Next, this mixture was placed in a heating chamber and heated at 70°C for 5 hours to produce a positive electrode active material.

[0092] In such a positive electrode active material, the positive electrode active material particles and oxide-based solid electrolyte particles were present in a mixed and dispersed state on a gel polymer on which the TMPTA had been cured and crosslinked.

[0093] The aforementioned mixed cathode active material, conductive material (carbon nanotubes), and binder (PVdF) were mixed in a weight ratio of 97:1:2 and dispersed in NMP solvent at 3000 rpm to produce a slurry. This slurry was then uniformly coated onto 25 μm thick aluminum foil using a blade-type coating machine, a Mathis coater (Labdryer / coater type LTE, Werner Mathis AG), dried in a vacuum oven at 130°C for 24 hours, and rolled using a roll press machine to produce a cathode for lithium secondary batteries.

[0094] A lithium secondary battery was manufactured using such a positive electrode in the same manner as in Example 1.

[0095] Experimental Example 1: Fabrication of composite cathode active material, cathode, and lithium secondary battery The particle size distribution of the composite cathode active material of Example 1 and the cathode active material of Comparative Example 1 was analyzed using a Malvern Mastersizer, and the analysis results are shown in Figure 1. Referring to Figure 1, the composite cathode active material of Example 1 showed a single peak at 9.0 μm corresponding to D50, similar to the cathode active material of Comparative Example 1, and the SPAN value was confirmed to be 0.5 to 0.8 μm.

[0096] From this, it was confirmed that in the composite positive electrode active material of Example 1, the oxide-based solid electrolyte particles coated on the positive electrode active material particles did not detach, and were uniformly coated on the positive electrode active material particles by the crosslinked binder.

[0097] Experimental Example 2: Resistance evaluation by charge state (SOC) For the lithium secondary batteries of Example 1, Comparative Examples 1 and 2, the resistance was measured for each state of charge (SOC) while repeatedly performing charge-discharge tests at room temperature (approximately 25°C) under the conditions of 1) 0.2C-0.33C charging (cut-off: 4.2V, 0.05C) and 2) 0.2C-0.33C discharging (cut-off: 2.5V).

[0098] Specifically, under a SOC of 10% to 90%, the above charge-discharge test was repeatedly performed, and after each charge-discharge, the DC resistance (2.5C discharge (cut-off: 10s or 2V)) was measured.

[0099] The resistance measurement results for each charge state are shown in Figure 2, and the resistance evaluation results at SOC 10% and 50% are also shown in Table 1 below:

[0100] [Table 1]

[0101] Referring to Table 1 and Figure 2 above, the lithium secondary battery using the composite positive electrode active material of Example 1 showed lower resistance and higher ionic conductivity at different charge states compared to Comparative Example 1 (using a general positive electrode active material) and Comparative Example 2 (a mixture of positive electrode active material and an oxide-based solid electrolyte), and was confirmed to show particularly superior performance in the SOC 50-70% range.

[0102] Experimental Example 3: Rate-Determining Evaluation Charge and discharge tests were conducted on the lithium secondary batteries of Example 1, Comparative Examples 1 and 2 at a temperature of 25°C.

[0103] Specifically, charging was carried out under the conditions of 0.2C (cut-off: 4.2V, 0.05C), and discharge was carried out by changing the discharge rate to 0.2C, 0.33C, 0.5C, 1C, 2C, and 3C (cut-off: 2.5V). After conducting 3 to 30 charge-discharge tests under each discharge-limiting condition, the capacity retention rate was evaluated, and the comparative evaluation results of the capacity retention rate under a discharge-limiting 3C condition (@16 to 18 cycles) are shown in Table 2 below:

[0104] [Table 2]

[0105] Referring to Table 2, it was confirmed that the lithium secondary battery of Example 1 had a higher discharge capacity retention rate and superior output characteristics compared to Comparative Examples 1 and 2, even under the high discharge rate limiting condition of 3C.

Claims

1. Positive electrode active material particles, The positive electrode active material particles comprise oxide-based solid electrolyte particles and a crosslinked polymer binder, A composite cathode active material in which the oxide-based solid electrolyte particles are attached to the surface of the cathode active material particles via the cross-linked polymer binder.

2. The positive electrode active material particles include lithium and a lithium metal oxide containing two or more transition metals, including nickel. The composite cathode active material according to claim 1, wherein the lithium metal oxide contains 80 mol% or more nickel with respect to the total transition metal content excluding lithium.

3. The composite cathode active material according to claim 1, wherein the oxide-based solid electrolyte particles include one or more lithium metal oxides or lithium metal phosphorides selected from Nasicon-type solid electrolytes, Lisicon-type solid electrolytes, Garnet-type solid electrolytes, Perovskite-type solid electrolytes, and LiPON-type solid electrolytes.

4. The composite cathode active material according to claim 1, wherein the oxide-based solid electrolyte particles include one or more selected from the group consisting of LAGP (lithium aluminum germanium phosphate) compounds, LLZO (lithium lanthanum zirconium oxide) compounds, LATP (lithium aluminum titanium phosphate) compounds, LLZTO (lithium lanthanum zirconium tantalum oxide) compounds, LLTO (lithium lanthanum titanium oxide) compounds, LSTP (lithium silicon titanium phosphate) compounds, and LGPO (lithium germanium phosphate) compounds.

5. The composite cathode active material according to claim 1, wherein the crosslinked polymer binder comprises a crosslinked polymer obtained by curing one or more polymers, copolymers, or mixtures selected from the group consisting of polyvinylidene fluoride polymers, polyvinyl alcohol polymers, cellulose polymers, polyvinylpyrrolidone polymers, polytetrafluoroethylene polymers, and polyolefin polymers.

6. The positive electrode active material particles have an average particle size (D50) of 3 to 15 μm. The composite cathode active material according to any one of claims 1 to 5, wherein the oxide-based solid electrolyte particles have an average particle size (D50) of 100 nm to 1.3 μm.

7. The composite cathode active material according to claim 6, wherein the composite cathode active material has a particle size distribution SPAN of 0.3 to 5 μm.

8. The composite positive electrode active material according to any one of claims 1 to 5, wherein the oxide-based solid electrolyte particles are contained in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the positive electrode active material particles.

9. The composite positive electrode active material according to any one of claims 1 to 5, wherein the crosslinked polymer binder is contained in an amount of 0.03 to 2 parts by weight based on 100 parts by weight of the positive electrode active material particles.

10. The process involves mixing positive electrode active material particles, oxide-based solid electrolyte particles, and polymer binder. A method for producing a composite positive electrode active material according to claim 1, comprising the step of thermally curing the mixture.

11. The method for producing a composite cathode active material according to claim 10, wherein the thermosetting step is carried out at a temperature of 100 to 200°C.

12. The method for producing a composite cathode active material according to claim 10, wherein the thermosetting step is carried out in the presence of a crosslinking agent or a curing initiator.

13. A method for producing a composite cathode active material according to claim 10, further comprising the step of pulverizing the resulting material after the thermosetting step.

14. Metal current collector and A positive electrode for a lithium secondary battery comprising a positive electrode active material layer formed on the metal current collector and containing the composite positive electrode active material and conductive material described in claim 1.

15. The positive electrode for a lithium secondary battery according to claim 14, wherein the positive electrode active material layer further comprises a polymer binder of the same type as the crosslinked polymer binder of the composite positive electrode active material.

16. The positive electrode for a lithium secondary battery according to claim 15, wherein the polymer binder comprises one or more selected from the group consisting of polyvinylidene fluoride polymers, polyvinyl alcohol polymers, cellulose polymers, polyvinylpyrrolidone polymers, polytetrafluoroethylene polymers, and polyolefin polymers.

17. A lithium secondary battery comprising the positive electrode, the negative electrode, and the electrolyte as described in claim 14.

18. The separation membrane interposed between the positive electrode and the negative electrode may further include The lithium secondary battery according to claim 17, wherein the electrolyte has the form of an electrolyte membrane or electrolyte film containing a solid electrolyte and is interposed between the positive electrode and the negative electrode.

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