Positive electrode active material, method of preparation and positive electrode, battery

Abstract

The application discloses a positive electrode active material and a preparation method thereof, a positive electrode and a battery, and relates to a first positive electrode active material and a second positive electrode active material; the first positive electrode active material comprises a single-crystal-like lithium manganate and a coating layer coated on the surface of the single-crystal-like lithium manganate; the second positive electrode active material comprises secondary spherical lithium manganate and a coating layer coated on the surface of the secondary spherical lithium manganate; the coating layer comprises a MXene material and a metal oxide; by forming a composite coating layer on the surface of the single-crystal-like lithium manganate and the secondary spherical lithium manganate respectively, the particle breakage of the lithium manganate material in the processes of rolling and charging and discharging can be effectively prevented; the compaction density of the positive electrode is improved, and the cycle performance and the rate performance of the battery are effectively improved.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, specifically to a positive electrode active material, a preparation method, a positive electrode, and a battery. Background Technology

[0002] Lithium manganese oxide (LiMn2O4) has advantages such as low price, high potential, environmental friendliness, and high safety performance as a positive electrode active material. advantage, Commonly used lithium manganese oxide can be classified according to its structure into secondary spherical lithium manganese oxide, near-monocrystalline lithium manganese oxide, and monocrystalline lithium manganese oxide. Monocrystalline lithium manganese oxide has lower capacity and larger particle size, resulting in slower lithium-ion transport. Secondary spherical lithium manganese oxide particles have higher capacity but lower compaction density. Near-monocrystalline lithium manganese oxide has a compact structure, smaller exposed area, smaller particle size, and faster lithium-ion transport rate. However, both secondary spherical lithium manganese oxide particles and near-monocrystalline lithium manganese oxide particles will break down during rolling and long-term battery cycling, increasing the contact area between the particles and the electrolyte, leading to manganese ion dissolution and deterioration of battery cycle performance.

[0003] Therefore, developing a lithium manganese oxide composite material that combines high solid density and structural stability to obtain a high-performance lithium-ion battery is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a positive electrode active material and its preparation method, including a positive electrode and a battery, comprising a near-monocrystalline lithium manganese oxide and a secondary spherical lithium manganese oxide with coating layers formed on their respective surfaces. On the one hand, the combination of near-monocrystalline lithium manganese oxide and secondary spherical lithium manganese oxide can increase the compaction density of the electrode and the lithium ion migration rate. On the other hand, by forming an HF-resistant coating layer on the surface of the near-monocrystalline lithium manganese oxide and the secondary spherical lithium manganese oxide, the coating can effectively prevent the near-monocrystalline lithium manganese oxide and the secondary spherical lithium manganese oxide from breaking or even being structurally damaged during the rolling process and subsequent charge-discharge cycles. It can also prevent HF in the electrolyte from corroding the coating layer and causing coating failure.

[0005] The technical solution of this invention is implemented as follows:

[0006] In a first aspect, this application provides a positive electrode active material, including a first positive electrode active material and a second positive electrode active material;

[0007] The first positive electrode active material includes a single-crystal lithium manganese oxide and a coating layer covering the surface of the single-crystal lithium manganese oxide;

[0008] The second positive electrode active material includes secondary spherical lithium manganese oxide and a coating layer covering the surface of the secondary spherical lithium manganese oxide;

[0009] The coating layer comprises MXene material and metal oxide.

[0010] In one embodiment, the MXene material includes any one or a combination of at least two of Ti3C2Tx, Nb2CTx, Ta4C3Tx, or V4C3Tx.

[0011] In one embodiment, the sum of the masses of the quasi-monocrystalline lithium manganese oxide and the secondary spherical lithium manganese oxide is m0, and the mass of the MXene material is m1. Then m0 and m1 satisfy m1 / m0 = 0.1% to 1%.

[0012] In one embodiment, the metal oxide includes at least one of MgO, Al2O3, Nb2O5, ZrO2, and WO3.

[0013] In one embodiment, the sum of the masses of the quasi-monocrystalline lithium manganese oxide and the secondary spherical lithium manganese oxide is m0, and the mass of the metal oxide is m2. Then m0 and m2 satisfy m2 / m0 = 0.1% to 1%.

[0014] In one embodiment, the thickness of the coating layer is 10–100 nm.

[0015] In one embodiment, the particle size D50 of the secondary spherical lithium manganese oxide is greater than the particle size D50 of the quasi-monocrystalline lithium manganese oxide.

[0016] In one embodiment, the particle size D50 of the secondary spherical lithium manganese oxide is 7–10 μm.

[0017] In one embodiment, the particle size D50 of the quasi-monocrystalline lithium manganese oxide is 1–3 μm.

[0018] In one embodiment, the general formula of the quasi-monocrystalline lithium manganese oxide is Li. 1+a Mn 2-a-b-c Al b B c O4; where 0.001≤a≤0.30, 0.001≤b≤0.2, 0.001≤c≤0.1.

[0019] In one embodiment, the secondary spherical lithium manganese oxide has the general formula Li. 1+x Mn 2-x-y M y O4; wherein 0.001≤x≤0.20, 0.001≤y≤0.3, and M includes at least two of Mg, Al, Nb, and Co.

[0020] In a preferred embodiment, M includes two of Al, Nb, and Co.

[0021] In one embodiment, the mass ratio of the quasi-monocrystalline lithium manganese oxide to the secondary spherical lithium manganese oxide is (1-4):(9-6).

[0022] Secondly, this application provides a method for preparing the positive electrode active material as described in the first aspect, comprising the following steps:

[0023] 1) Mix the near-monocrystalline lithium manganese oxide and the secondary spherical lithium manganese oxide evenly to form the first mixture;

[0024] 2) Mix the first mixture, MXene material, metal oxide, and solvent to obtain a mixed solution;

[0025] 3) Spray dry the mixed solution to obtain the positive electrode active material.

[0026] In one embodiment, step 1) includes uniformly mixing quasi-monocrystalline lithium manganese oxide and secondary spherical lithium manganese oxide at a mass ratio of (1-4):(9-6).

[0027] In one embodiment, in step 2), the mass ratio of MXene material to the first mixture is 0.1 to 1:100.

[0028] In one embodiment, in step 2), the mass ratio of the metal oxide to the first mixture is 0.1 to 1:100.

[0029] In one embodiment, in step 2), the solvent includes one of an ethanol solution, NMP, or a propanol solution.

[0030] In one embodiment, step 2) includes stirring and mixing the first mixture, MXene material, metal oxide and solvent to obtain a mixed solution, wherein the stirring time is 2 to 8 hours.

[0031] In one embodiment, in step 3), the inlet temperature of the spray dryer is 200-400°C and the outlet temperature is 50-100°C.

[0032] Thirdly, this application provides a positive electrode, comprising the positive electrode active material as described in the first aspect.

[0033] Fourthly, this application provides a battery comprising a positive electrode active material as described in the first aspect or a positive electrode as described in the third aspect.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: By forming a coating layer on the surface of the near-monocrystalline lithium manganese oxide and the secondary spherical lithium manganese oxide, the present application can effectively prevent the near-monocrystalline lithium manganese oxide and the secondary spherical lithium manganese oxide from being broken into particles during rolling and during battery cycling, thus ensuring the cycle stability of the lithium manganese oxide material and ensuring the good ion transport performance of the near-monocrystalline lithium manganese oxide material.

[0035] The coating layer is a composite coating of MXene and metal oxide. Both materials have good pressure resistance, preventing damage to the near-monocrystalline lithium manganese oxide and secondary spherical lithium manganese oxide caused by rolling. On the other hand, both materials are resistant to HF corrosion, ensuring the stability of the positive electrode interface. This allows the modified interface to form a more stable CEI film during charge and discharge, achieving better isolation between the electrolyte and the lithium manganese oxide material. Thirdly, the synergistic effect of MXene and metal oxide helps to improve the ionic conductivity of the coating layer.

[0036] The coated near-monocrystalline lithium manganese oxide and secondary spherical lithium manganese oxide are mixed. Due to the certain particle size difference between the two, the small near-monocrystalline lithium manganese oxide particles can be uniformly filled into the gaps between the large secondary spherical lithium manganese oxide particles. Therefore, the combination of the two can effectively improve the compaction density of the positive electrode active material. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used in the detailed description is for the purpose of describing particular embodiments only and is not intended to limit the invention; the specification and claims of this invention are intended to cover non-exclusive inclusion.

[0039] In the description of specific embodiments of the present invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, "multiple" means two or more, unless otherwise explicitly defined.

[0040] In this invention, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0041] In the description of the embodiments of this invention, the term "and / or" is merely a description of the relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this invention, the character " / " generally indicates that the preceding and following associated objects have an "or" relationship.

[0042] Throughout this invention, numerical values ​​represent approximate measurements or limits of a range to cover minute deviations from a given value, as well as embodiments with approximately the mentioned value and embodiments with the exact mentioned value. Except for the working examples provided at the end of the detailed description, all numerical values ​​of parameters (e.g., quantities or conditions) in this specification (including the appended claims) should be understood to be modified in all cases by the term “about,” regardless of whether “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows for some minor inaccuracy (approaching the exact value in some way; approximately or reasonably approaching the value; almost). If the inaccuracy provided by “about” is not otherwise understood in this general sense in the art, then “about” as used in this invention at least indicates a variation that can be produced by common methods of measuring and using such a parameter. For example, “about” may include a variation less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in some respects, optionally less than or equal to 0.1%.

[0043] Additionally, the disclosure of the range includes the disclosure of all values ​​across the entire range and the disclosure of further subdivided ranges, including the endpoints and subranges given for these ranges.

[0044] Because lithium manganese oxide materials and electrolytes are prone to side reactions, trivalent manganese ions in lithium manganese oxide materials undergo disproportionation reactions, and the resulting divalent manganese ions easily move to the negative electrode side, where they undergo reduction reactions and deposit on the negative electrode side, continuously damaging the SEI film. This causes the SEI film to be constantly damaged and regenerated, consuming lithium ions and resulting in deterioration of the battery's cycle performance.

[0045] On the other hand, commonly used lithium manganese oxide materials all have different problems. Based on the requirements for capacity and rate performance, this application uses a combination of near-monocrystalline lithium manganese oxide and secondary spherical lithium manganese oxide. At the same time, the coating not only effectively avoids structural damage and particle breakage that may occur in near-monocrystalline lithium manganese oxide and secondary spherical lithium manganese oxide during the rolling process and subsequent charge and discharge cycles, but also effectively isolates the electrolyte from contact with lithium manganese oxide. In addition, by selecting the coating material, the stability of the positive electrode interface is ensured, so that the modified interface can form a more stable CEI film during charge and discharge.

[0046] The technical solution of this invention is implemented as follows:

[0047] In a first aspect, this application provides a positive electrode active material, including a first positive electrode active material and a second positive electrode active material;

[0048] The first positive electrode active material includes a single-crystal lithium manganese oxide and a coating layer on the surface of the single-crystal lithium manganese oxide;

[0049] The second positive electrode active material includes secondary spherical lithium manganese oxide and a coating layer covering the surface of the secondary spherical lithium manganese oxide;

[0050] In one embodiment, the coating layer comprises an MXene material and a metal oxide.

[0051] This application effectively prevents the particle breakage of lithium manganese oxide and secondary spherical lithium manganese oxide during rolling and battery cycling by forming a coating layer on their surfaces, thus ensuring the cycle stability of the lithium manganese oxide material and the good ion transport performance of the lithium manganese oxide material.

[0052] The coating layer is a composite coating of MXene and metal oxide. Both materials have good pressure resistance, preventing damage to the near-monocrystalline lithium manganese oxide and secondary spherical lithium manganese oxide caused by rolling. On the other hand, both materials are resistant to HF corrosion, ensuring the stability of the positive electrode interface and enabling the modified interface to form a more stable CEI film during charge and discharge. Thirdly, the synergistic effect of MXene and metal oxide helps to improve the ionic conductivity of the coating layer.

[0053] In one embodiment, the MXene material includes any one or a combination of at least two of Ti3C2Tx, Nb2CTx, Ta4C3Tx, or V4C3Tx.

[0054] In one embodiment, the sum of the masses of the quasi-monocrystalline lithium manganese oxide and the secondary spherical lithium manganese oxide is m0, and the mass of the MXene material is m1. Then, m0 and m1 satisfy m1 / m0 = 0.1% to 1%. Specifically, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%. Of course, it can also be any value within this range, and the present invention does not impose any limitations on it.

[0055] In one embodiment, the metal oxide includes at least one of MgO, Al2O3, Nb2O5, ZrO2, and WO3.

[0056] In one embodiment, the sum of the masses of the quasi-monocrystalline lithium manganese oxide and the secondary spherical lithium manganese oxide is m0, and the mass of the metal oxide is m2. Then, m0 and m2 satisfy m2 / m0 = 0.1% to 1%. Specifically, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%. Of course, it can also be any value within this range, and the present invention does not impose any limitations on it.

[0057] In one embodiment, the thickness of the coating layer is 10–100 nm. Specifically, it can be 10 nm, 25 nm, 40 nm, 55 nm, 70 nm, 85 nm, or 100 nm. Of course, it can also be any value within this range, and the present invention does not impose any limitation on it.

[0058] In one embodiment, the particle size D50 of the secondary spherical lithium manganese oxide is greater than the particle size D50 of the quasi-monocrystalline lithium manganese oxide.

[0059] In one embodiment, the particle size D50 of the secondary spherical lithium manganese oxide is 7–10 μm. Specifically, it can be 7 μm, 7.6 μm, 8 μm, 8.3 μm, 9 μm, 9.5 μm, or 10 μm. Of course, it can also be any value within this range, and the present invention does not impose any limitation on it.

[0060] In one embodiment, the particle size D50 of the quasi-monocrystalline lithium manganese oxide is 1–3 μm. Specifically, it can be 1 μm, 1.2 μm, 1.8 μm, 2 μm, 2.5 μm, 2.7 μm, or 3 μm. Of course, it can also be any value within this range, and the present invention does not impose any limitations on it.

[0061] In one embodiment, the general formula of the lithium manganese oxide-like monocrystalline oxide is Li 1+a Mn 2-a-b-c Al b B c O4; where 0.001≤a≤0.30, 0.001≤b≤0.2, 0.001≤c≤0.1.

[0062] It is understandable that simultaneously doping lithium manganese oxide with Al and B can improve the lattice stability and cycle stability of the material. Furthermore, B doping can lower the melting point of lithium manganese oxide and facilitate the formation of a near-single-crystal material.

[0063] In one embodiment, the general formula of secondary spherical lithium manganese oxide is Li 1+x Mn 2-x-y M y O4; wherein 0.001≤x≤0.20, 0.001≤y≤0.3, and M includes at least two of Mg, Al, Nb, and Co.

[0064] In a preferred embodiment, M includes two of Al, Nb, and Co.

[0065] Doping with multiple elements can further improve the structural stability of lithium manganese oxide materials.

[0066] In one embodiment, the mass ratio of quasi-monocrystalline lithium manganese oxide to secondary spherical lithium manganese oxide is (1-4):(9-6). Specifically, it can be 1:9, 2:8, 2:7, 3:7, or 4:6. Of course, it can also be any value within this range, and the present invention does not impose any limitations on it.

[0067] Understandably, the mass of near-monocrystalline lithium manganese oxide is less than that of secondary spherical lithium manganese oxide, which is beneficial for the cathode active material to provide higher capacity.

[0068] Secondly, this application provides a method for preparing a positive electrode active material as described in the first aspect, comprising the following steps:

[0069] 1) Mix the near-monocrystalline lithium manganese oxide and the secondary spherical lithium manganese oxide evenly to form the first mixture;

[0070] 2) Mix the first mixture, MXene material, metal oxide, and solvent to obtain a mixed solution;

[0071] 3) Spray dry the mixed solution to obtain the positive electrode active material.

[0072] In one embodiment, step 1) includes uniformly mixing quasi-monocrystalline lithium manganese oxide and secondary spherical lithium manganese oxide at a mass ratio of (1-4):(9-6).

[0073] In one embodiment, in step 2), the mass ratio of MXene material to the first mixture is 0.1 to 1:100.

[0074] In one embodiment, in step 2), the mass ratio of the metal oxide to the first mixture is 0.1 to 1:100.

[0075] In one embodiment, in step 2), the solvent includes one of an ethanol solution, NMP, or a propanol solution.

[0076] In one embodiment, step 2) includes stirring and mixing the first mixture, MXene material, metal oxide and solvent to obtain a mixed solution, wherein the stirring time is 2 to 8 hours.

[0077] In one embodiment, in step 3), the inlet temperature of the spray dryer is 200-400°C and the outlet temperature is 50-100°C.

[0078] In one embodiment, step 1) is preceded by the preparation of a quasi-monocrystalline lithium manganese oxide, comprising the following steps:

[0079] Mix spherical or near-spherical metal oxides or sulfates containing Mn precursors, lithium sources, Al sources, and B sources evenly according to stoichiometric ratios;

[0080] After calcination in air, a quasi-monocrystalline lithium manganese oxide powder was obtained.

[0081] In a preferred embodiment, the Mn-containing precursor includes one or a mixture of two of manganese tetroxide, manganese trioxide, or manganese carbonate.

[0082] In a preferred embodiment, the lithium source is one or a mixture of lithium carbonate and lithium hydroxide.

[0083] In a preferred embodiment, the Al source is Al2O3 or Al(OH)3.

[0084] In a preferred embodiment, the source B is H3BO3.

[0085] In a preferred embodiment, the calcination temperature in the step of obtaining quasi-monocrystalline lithium manganese oxide powder by calcination in air is 600-900℃, and the calcination time is 8-20h.

[0086] In one embodiment, the preparation of secondary spherical lithium manganese oxide is included before step 1), comprising the following steps:

[0087] Mix spherical or near-spherical metal oxides or sulfates containing Mn precursors, lithium sources, and metal M sources uniformly according to stoichiometric ratios;

[0088] After calcination in air, secondary spherical lithium manganese oxide powder was obtained.

[0089] In one embodiment, the calcination temperature is 400-800℃ and the calcination time is 8-20h.

[0090] In one embodiment, the metal M includes at least two of Mg, Al, Nb, and Co.

[0091] In a preferred embodiment, the metal M includes at least two of Al, Nb, and Co.

[0092] Thirdly, this application provides a positive electrode, including the positive electrode active material as described in the first aspect.

[0093] In one embodiment, the positive electrode includes a positive electrode layer.

[0094] In some embodiments, the positive electrode layer further includes a binder. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode material layer and the positive electrode current collector.

[0095] In some embodiments, non-limiting examples of adhesives include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0096] In some embodiments, the positive electrode layer includes a conductive agent, thereby imparting conductivity to the electrode. The conductive agent may include any conductive material, as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powders, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0097] In some embodiments, the mass percentage of the positive electrode active material in the positive electrode layer is 80%-99% based on the total mass of the positive electrode layer.

[0098] In some embodiments, the mass of the conductive agent accounts for 1%-20% of the mass of the positive electrode layer.

[0099] In some embodiments, the binder accounts for 1%-20% of the mass of the positive electrode layer.

[0100] In some embodiments, the positive electrode layer provided by the present invention further includes solid electrolyte powder to improve the ionic conductivity of the positive electrode layer. The present invention does not limit the type of solid electrolyte powder, and it can be oxide solid electrolyte powder, sulfide solid electrolyte powder, or halide solid electrolyte powder. Optionally, the mass of the solid electrolyte powder accounts for 1%-20% of the mass of the positive electrode layer; preferably 5%-20%.

[0101] In some embodiments, the thickness of the positive electrode layer in the positive electrode provided by the present invention is 30-400 μm, such as 30 μm, 40 μm, 50 μm, 80 μm, 110 μm, 200 μm, 300 μm, 400 μm, preferably 50-110 μm.

[0102] In some embodiments, the positive electrode includes a positive current collector, which, for example, may be aluminum (Al), but is not limited thereto.

[0103] Fourthly, this application provides a battery, including a positive electrode active material as in the first aspect or a positive electrode as in the third aspect.

[0104] In one embodiment, the battery further includes a negative electrode, a separator, and an electrolyte.

[0105] Negative electrode plate:

[0106] In some embodiments, the negative electrode includes a current collector and a layer of negative electrode active material disposed on the current collector.

[0107] In this invention, the specific type of negative electrode active material is not specifically limited and can be selected according to requirements. Specifically, the negative electrode active material is selected from natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 One or more of Li-Al alloys. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon, and mixtures thereof. Crystalline carbon can be amorphous or flake-shaped, small flake-shaped, spherical, or fibrous natural or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbides, calcined coke, etc.

[0108] In some embodiments, elemental metals and metal compounds may also be selected as negative electrode active materials, such as compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0109] In some embodiments, the mass percentage of the negative electrode active material contained in the negative electrode active material layer can be 80%-99%, for example, 80%, 85%, 90%, 95%, 97%, 99%, etc., preferably 95%-97%.

[0110] In some embodiments, the negative electrode material layer may include a binder; the binder enhances the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector.

[0111] In some embodiments, non-limiting examples of adhesives include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0112] In some embodiments, the negative electrode active material layer can be obtained by coating a negative electrode slurry onto a negative electrode current collector and then performing operations such as drying. The negative electrode slurry includes at least a negative electrode active material and a negative electrode binder. When an aqueous solvent is used as the liquid medium for forming the negative electrode slurry, it is preferable to use a thickener for slurry formation. The thickener is typically used to adjust the viscosity of the slurry.

[0113] In some embodiments, the aforementioned thickener may be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and their salts, etc.

[0114] In some embodiments, the mass percentage of the thickener in the negative electrode slurry can be 0.1%-5%, for example, 0.1%, 0.2%, 0.5%, 0.6%, 1%, 2%, 3%, 4%, 5%, etc., preferably 0.5%-3%, and more preferably 0.6%-2%.

[0115] In some embodiments, the negative electrode active material layer includes a conductive material, thereby making the electrode conductive. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powders, metal fibers, such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0116] In some embodiments, the negative current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0117] Diaphragm:

[0118] In some embodiments, the lithium battery and electrochemical device of the present invention have a separator between the positive and negative electrodes to prevent short circuits. The material and shape of the separator used in the electrochemical device of the present invention are not particularly limited and can be any technology disclosed in the prior art.

[0119] In some embodiments, the diaphragm comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0120] In some embodiments, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide.

[0121] Electrolyte:

[0122] The lithium battery and electrochemical device involved in this invention also include an electrolyte.

[0123] In some embodiments, the electrolyte includes a lithium salt and a solvent.

[0124] In some embodiments, the lithium salt includes at least one of organic lithium salts or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0125] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0126] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.

[0127] In some embodiments, the aforementioned additives include at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, vinyl sulfate, 4-methylvinyl sulfate, propylene sulfate, saturated phosphate compounds and unsaturated phosphate compounds, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, tris(triethylsilane) borate, succinic anionyl, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptacyanide, octanoic anionyl, azelonitrile, sebacate, and compounds comprising the following chemical formulas:

[0128]

[0129] Among them, R 41 R 42 R 43 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H2m+1 )3, m is a natural number from 1 to 3, and R 41 R 42 R 43 At least one of them is an unsaturated hydrocarbon group.

[0130] In some embodiments, the secondary battery of the present invention is made by stacking the above-mentioned positive and negative electrode sheets.

[0131] In some embodiments, the secondary battery of the present invention may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft pack, such as a pouch-type soft pack. The material of the soft pack may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0132] In some embodiments, the present invention also provides a battery module. The battery module includes the aforementioned secondary battery. The battery module of the present invention may contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0133] In some embodiments, the present invention also provides a battery pack comprising the aforementioned battery modules. The number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0134] The embodiments of the present invention are described below based on the technical content of the present invention, but should not be limited to the following embodiment 1.

[0135] I. Preparation of positive electrode active materials:

[0136] 1) Preparation of single-crystal lithium manganese oxide:

[0137] The manganese-containing precursor Mn3O4, lithium source Li2CO3, H3BO3 and metal oxide Al2O3 were mixed evenly according to the stoichiometric ratio.

[0138] Lithium manganese oxide (Li1) was obtained by calcination at 750℃ in air for 20 hours. 1.1 Mn 1.75 Al 0.1 B 0.05 O4;

[0139] The particle size D50 of the single-crystal lithium manganese oxide is 2 μm.

[0140] 2) Preparation of secondary spherical lithium manganese oxide:

[0141] The manganese-containing precursor Mn3O4, the lithium source Li2CO3, and the metal oxides Al2O3 and Nb2O5 were mixed evenly according to the stoichiometric ratio.

[0142] Secondary spherical lithium manganese oxide (Li) was obtained by calcination at 650℃ in air for 16 hours. 1.05 Mn 1.84 Al 0.1 Nb 0.01 O4;

[0143] The particle size D50 of the secondary spherical lithium manganese oxide is 9 μm.

[0144] 3) Preparation of positive electrode active material: Lithium manganese oxide quasi-monocrystalline and secondary spherical lithium manganese oxide are mixed evenly at a mass ratio of 2:8 to form the first mixture;

[0145] The first mixture, Ti3C2T x WO3 and solvent NMP were stirred and mixed for 6 hours to obtain a mixed solution; wherein, Ti3C2T x The mass ratio of WO3 to the first mixture is 0.5:100; the mass ratio of WO3 to the first mixture is 0.5:100.

[0146] The mixed solution is spray-dried to obtain a positive electrode active material, which includes a first positive electrode active material and a second positive electrode active material.

[0147] II. Preparation of the positive electrode:

[0148] The above-mentioned positive electrode active material, conductive agent Super-P, and binder PVDF are weighed and mixed evenly in a mass ratio of 95:2:3. The mixture is then mixed with solvent NMP to obtain a positive electrode slurry, which is evenly coated on aluminum foil, dried, and rolled to form a positive electrode.

[0149] Preparation of negative electrode: The negative electrode active material graphite, conductive agent Super-P, binder CMC and SBR are weighed and mixed evenly in a mass ratio of 95:3:1:1, and mixed with deionized water solvent to obtain negative electrode slurry. The slurry is evenly coated on copper foil, dried and rolled to form negative electrode.

[0150] Electrolyte composition: solvent propylene carbonate and lithium salt LiPF6, with an electrolyte salt concentration of 1 mol / L.

[0151] Battery fabrication: The positive electrode, negative electrode, and separator are assembled, and an electrolyte is injected to form a battery.

[0152] Example 2

[0153] The difference between Example 2 and Example 1 is that the mass ratio of near-monocrystalline lithium manganese oxide to secondary spherical lithium manganese oxide is 3:7.

[0154] The MXene material is Ta4C3Tx;

[0155] The metal oxide is Nb2O5, and all other technical characteristics are the same.

[0156] Example 3

[0157] The difference between Example 3 and Example 1 is that the mass ratio of near-monocrystalline lithium manganese oxide to secondary spherical lithium manganese oxide is 1:9. All other technical features are the same.

[0158] Example 4

[0159] The difference between Example 4 and Example 1 is that the mass ratio of near-monocrystalline lithium manganese oxide to secondary spherical lithium manganese oxide is 4:6. All other technical features are the same.

[0160] Example 5

[0161] The difference between Example 4 and Example 1 is that the mass ratio of near-monocrystalline lithium manganese oxide to secondary spherical lithium manganese oxide is 5:5. All other technical features are the same.

[0162] Example 6

[0163] The difference between Example 6 and Example 1 is:

[0164] Ti3C2T x The mass ratio of the first mixture to the first mixture is 1:100;

[0165] The mass ratio of WO3 to the first mixture is 1:100. All other technical features are the same.

[0166] Example 7

[0167] The difference between Example 7 and Example 1 is as follows:

[0168] Ti3C2T x The mass ratio of the first mixture to the first mixture is 0.1:100;

[0169] The mass ratio of WO3 to the first mixture is 0.1:100. All other technical features are the same.

[0170] Comparative Example 1

[0171] The difference between Comparative Example 1 and Example 1 is that neither the single-crystal lithium manganese oxide nor the secondary spherical lithium manganese oxide has a coating layer on its surface.

[0172] Comparative Example 2

[0173] The difference between Comparative Example 2 and Example 1 is that the positive electrode material contains only the second positive electrode active material.

[0174] Comparative Example 3

[0175] The difference between Comparative Example 3 and Example 1 is that the positive electrode material contains only the first positive electrode active material.

[0176] Comparative Example 4

[0177] The difference between Comparative Example 4 and Example 1 is that the coating layer only includes WO3.

[0178] Comparative Example 5

[0179] The difference between Comparative Example 5 and Example 1 is that the coating layer only includes Ti3C2T. x .

[0180] Comparative experiment:

[0181] The following tests were conducted on the batteries from Examples 1-7 and Comparative Examples 1-3.

[0182] 1. Battery capacity retention after 200 cycles:

[0183] At a temperature of 45℃, the battery is charged at a current of 0.2C to the charging cutoff voltage of 4.2V, then switched to constant voltage charging to the cutoff current of 0.05C, and left to stand for 0.5 hours. Then, it is discharged at a current of 0.2C to the cutoff voltage of 3.0V, left to stand for 0.5 hours, and then enters the next charge-discharge cycle. This process is repeated for a total of 200 charge-discharge cycles. The cycle retention rate after 200 cycles is equal to the discharge capacity of the battery on the 200th cycle divided by the initial discharge capacity.

[0184] 2. Ratio performance:

[0185] At a temperature of 45℃, a fully charged battery is discharged at a current of 0.1C to a cutoff voltage of 3.0V, and the capacity obtained by the test is C0.

[0186] At a temperature of 45℃, a fully charged battery is discharged at a current of 3C to a cutoff voltage of 3.0V. The capacity obtained by the test is C1, and C1 / C0 is the 3C discharge capacity retention rate mentioned below.

[0187] 3. Protective layer thickness test

[0188] Using a TEM electron microscope, the thickness was measured at ten different locations, and the average value was taken.

[0189] 4. Compacted density test

[0190] Take the positive electrode sheet, roll it, and measure the thickness of the electrode sheet at five different positions. The compaction density is obtained according to the formula: compaction density (g / cm3) = surface density (mg / cm2) / thickness (μm).

[0191] 5. Discharge capacity test

[0192] At 25°C, the prepared battery was discharged at a constant current of 0.2C to the cutoff voltage of 3.0V, and the initial discharge capacity of the battery was recorded.

[0193]

[0194]

[0195] Compared with the comparative examples, this application can effectively prevent the particle breakage of lithium manganese oxide and secondary spherical lithium manganese oxide during rolling and battery cycling by forming a coating layer on the surface of the lithium manganese oxide-like monocrystalline and secondary spherical lithium manganese oxide, thus ensuring the cycle stability of the lithium manganese oxide material and the good ion transport performance of the lithium manganese oxide-like monocrystalline material.

[0196] Forming a composite coating of MXene material and metal oxide on the surface of quasi-monocrystalline lithium manganese oxide and secondary spherical lithium manganese oxide can further improve the cycle performance and rate performance of the battery. A possible reason is that both MXene material and metal oxide have resistance to HF corrosion, ensuring the stability of the cathode interface. This allows the modified interface to form a more stable CEI film during charge and discharge, achieving better isolation between the electrolyte and the lithium manganese oxide material. Thirdly, the synergistic effect of MXene material and metal oxide helps to improve the ionic conductivity of the coating layer. The above are merely possible speculations about the mechanism and do not constitute a limitation on the scope of protection of this application.

[0197] Compared to Example 1, Comparative Examples 2 and 3, the coated monocrystalline lithium manganese oxide and secondary spherical lithium manganese oxide mixture has a certain particle size difference. The small monocrystalline lithium manganese oxide particles can be uniformly filled into the gaps between the large secondary spherical lithium manganese oxide particles. Therefore, the combination of the two can effectively improve the compaction density of the positive electrode active material.

[0198] It should be particularly noted that, for lithium-ion battery manufacturers and those skilled in the art, if inspired by the above technical solutions and embodiments, they select or modify technical features to obtain technical solutions that are substantially the same as those of the present invention, and the lithium batteries manufactured thereby should fall within the protection scope of the present invention.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes a first positive electrode active material and a second positive electrode active material; The first positive electrode active material includes a single-crystal lithium manganese oxide and a coating layer covering the surface of the single-crystal lithium manganese oxide; The second positive electrode active material includes secondary spherical lithium manganese oxide and a coating layer covering the surface of the secondary spherical lithium manganese oxide; The coating layer comprises MXene material and metal oxide; The general formula of the lithium manganese oxide-like monocrystalline oxide is Li 1+a Mn 2-a-b-c Al b B c O4; where 0.001≤a≤0.30, 0.001≤b≤0.2, 0.001≤c≤0.1; The general formula of the secondary spherical lithium manganese oxide is Li 1+x Mn 2-x-y M y O4; wherein 0.001≤x≤0.20, 0.001≤y≤0.3, and M includes at least two of Mg, Al, Nb, and Co.

2. The positive electrode active material according to claim 1, characterized in that, The MXene material includes any one or a combination of at least two of Ti3C2Tx, Nb2CTx, Ta4C3Tx, or V4C3Tx.

3. The positive electrode active material according to claim 1, characterized in that, The metal oxide includes at least one of MgO, Al2O3, Nb2O5, ZrO2, and WO3.

4. The positive electrode active material according to claim 1, characterized in that, The thickness of the coating layer is 10–100 nm.

5. The method for preparing the positive electrode active material according to claim 1, characterized in that, The method includes the following steps: 1) Mix the near-monocrystalline lithium manganese oxide and the secondary spherical lithium manganese oxide evenly to form the first mixture; 2) Mix the first mixture, MXene material, metal oxide, and solvent to obtain a mixed solution; 3) Spray dry the mixed solution to obtain the positive electrode active material.

6. The preparation method according to claim 5, characterized in that, Step 1) includes uniformly mixing quasi-monocrystalline lithium manganese oxide and secondary spherical lithium manganese oxide at a mass ratio of (1-4):(9-6).

7. Positive electrode, characterized in that, The positive electrode includes the positive electrode active material as described in claim 1.

8. A battery, characterized in that, The battery includes the positive electrode active material as described in claim 1 or the positive electrode as described in claim 7.

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