Positive electrode active material, electrochemical device and electrical device

Abstract

This application discloses a positive electrode active material, an electrochemical device, and an electrical device. The positive electrode active material of this application comprises lithium manganese oxide, and the X-ray diffraction pattern of the positive electrode active material has a first diffraction peak in the range of 14.3° to 16.3° and a second diffraction peak in the range of 17.3° to 19.3°. The positive electrode active material of this application has high charge specific capacity and good structural stability, which can improve the energy density and service life of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a positive electrode active material, an electrochemical device, and an electrical device. Background Art

[0002] To address the severe global energy crisis, environmental pollution, climate change, and the development of a low-carbon economy, the research and application of electric vehicles, large-scale power supplies, and energy storage technologies have become essential. Spinel LiMn₂O₄ and olivine-type LiFePO₄ are widely used as positive electrode active materials due to their low cost, high initial efficiency, and good safety and reliability. However, because spinel LiMn₂O₄ and olivine-type LiFePO₄ have low charging capacity, and the negative electrode requires the consumption of active Li to form a solid electrolyte interphase (SEI) film, and to ensure safety, the active material at the negative electrode is usually in excess, resulting in a lower capacity utilization of LiMn₂O₄ or LiFePO₄ in the battery. Furthermore, during cycling, the SEI film is damaged and regenerated, further consuming active Li, leading to reduced structural stability of spinel LiMn₂O₄ and olivine-type LiFePO₄ under charging conditions, thus deteriorating battery lifespan. Summary of the Invention

[0003] In view of the above-mentioned problems existing in the prior art, this application provides a positive electrode active material, an electrochemical device, and an electrical device to solve the problems existing in the prior art to some extent.

[0004] In a first aspect, this application provides a positive electrode active material comprising lithium manganese oxide. The X-ray diffraction pattern of the positive electrode active material exhibits a first diffraction peak in the range of 14.3° to 16.3° and a second diffraction peak in the range of 17.3° to 19.3°. The first diffraction peak is a (010) characteristic peak of the o-phase (cubic phase) in the lithium manganese oxide, and the second diffraction peak is a (001) characteristic peak of the m-phase (monoclinic phase) in the lithium manganese oxide. The coexistence of the o-phase and m-phase in the lithium manganese oxide forms a solid solution, improving the structural stability of the lithium manganese oxide under the charging state of the electrochemical device. The solid solution formed by the coexistence of the two phases contains oxygen vacancies, which can promote the extraction of lithium ions, thereby improving the charging specific capacity of the lithium manganese oxide. Simultaneously, through the synergistic effect of the solid solution, the stability of the Mn-O bond can be increased, thereby inhibiting the dissolution of Mn in the lithium manganese oxide, and thus improving the service life of the electrochemical device.

[0005] In some embodiments, the X-ray diffraction pattern of the positive electrode active material has a third diffraction peak in the range of 45.7° to 47.7°. The third diffraction peak corresponds to the (111) crystal plane of the m-phase in lithium manganese oxide. The presence of this crystal plane can stabilize the crystal structure of the m-phase, thereby improving the first coulombic efficiency of lithium manganese oxide.

[0006] In some embodiments, the peak intensity of the first diffraction peak is I. A The peak intensity of the second diffraction peak is I. B Satisfying: 0.05≤I A / I B ≤20.

[0007] In some embodiments, 0.05 ≤ I A / I B ≤0.9, or 6≤I A / I B ≤20. At this point, there is a significant difference in the content of the m-phase and o-phase in lithium manganese oxide, which can work synergistically to form a solid solution, promoting the extraction of Li ions from lithium manganese oxide, thereby further improving the specific charging capacity of lithium manganese oxide.

[0008] In some embodiments, the full width at half maximum (FWHM) of the first diffraction peak is W. A The full width at half maximum (FWHM) of the second diffraction peak is W. B Satisfying: 0.3≤W A / W B ≤3.

[0009] In some embodiments, 0.75 ≤ W A / W B ≤1.65. At this value, the full width at half maximum (FWHM) of both the o-phase and m-phase in lithium manganese oxide are narrower, indicating higher structural stability. This further suppresses the dissolution of Mn from lithium manganese oxide and improves the service life of the electrochemical device.

[0010] In some embodiments, the peak intensity of the second diffraction peak is I. B The peak intensity of the third diffraction peak is I. C I B and I C Satisfy: 0.08≤I C / I B ≤0.35. At this value, the peak intensity of the third diffraction peak is relatively strong, and there are fewer crystal defects in the m-phase, which can improve the first coulombic efficiency of the positive electrode active material.

[0011] In some embodiments, the lithium manganese oxide contains an element M, which includes at least one selected from Cr, Al, Mg, Ti, Y, Nb, W, Ga, Zr, V, Sr, Mo, Ru, Ag, Sn, Au, La, Ce, Pr, Nd, Sm, Gd, Cu, Na, Zn, Fe, Co, Ni, or Ca. The molar ratio of element M to element Mn in the lithium manganese oxide is from 0.001:1 to 0.1:1. The presence of element M in the lithium manganese oxide promotes the formation of a monoclinic phase, thereby improving the structural stability of the lithium manganese oxide, inhibiting the dissolution of Mn, and thus improving the service life of the electrochemical device.

[0012] In some embodiments, the average particle size Dv50 of the positive electrode active material is 2 μm to 35 μm.

[0013] In some embodiments, the lithium manganese oxide has a layered structure. The layered structure facilitates the extraction of Li ions from the lithium manganese oxide, thereby improving the specific charge capacity of the lithium manganese oxide.

[0014] In some embodiments, the molar ratio of Li to Mn in the positive electrode active material is 0.9 to 1.15.

[0015] In some embodiments, the lithium manganese oxide includes Li x Mn y M z O2, wherein 0.9 ≤ x ≤ 1.15, 0.9 ≤ y ≤ 1, 0 ≤ z ≤ 0.1, and M includes at least one of Cr, Al, Mg, Ti, Y, Nb, W, Ga, Zr, V, Sr, Mo, Ru, Ag, Sn, Au, La, Ce, Pr, Nd, Sm, Gd, Cu, Na, Zn, Fe, Co, Ni, or Ca. In some embodiments, 0.9 ≤ x ≤ 1.2, 0.9 ≤ y ≤ 1, and 0.001 ≤ z ≤ 0.1.

[0016] In some embodiments, the positive electrode active material is assembled with lithium metal to form a coin cell. The voltage-capacity differential dQ / dV curve of the coin cell during its first charge cycle has characteristic peaks in the ranges of 3.5V-3.7V and 3.85V-4.05V, and the voltage-capacity differential dQ / dV curve of the coin cell during its first discharge cycle has characteristic peaks in the range of 3.8V-4.0V. Here, 3.5V-3.7V corresponds to the charging capacity of the o-phase, and 3.85V-4.05V corresponds to the charging capacity of the m-phase. The characteristic peaks in the voltage-capacity differential dQ / dV curves of the coin cell during its first charge cycle in the ranges of 3.5V-3.7V and 3.85V-4.05V indicate that there are two phases in the lithium manganese oxide, and their synergistic effect improves the specific charging capacity of the lithium manganese oxide. The voltage-capacity differential dQ / dV curve of the first discharge of the coin cell has a characteristic peak in the range of 3.8V-4.0V, indicating that a uniform phase is formed when Li ions are reinserted into the lithium manganese oxide, thereby improving the stability of the material.

[0017] In a second aspect, this application provides a method for preparing a positive electrode active material, comprising: mixing a manganese oxide, a lithium source, and an optional M element source to obtain a mixture; calcining the mixture under a first atmosphere and a first temperature to obtain the positive electrode active material; wherein the manganese oxide and the lithium source are mixed in a lithium-manganese molar ratio (Li / Mn) ranging from 0.90 to 1.15; and the first atmosphere is an inert atmosphere.

[0018] In some embodiments, the inert atmosphere includes at least one of nitrogen, argon, or helium.

[0019] In some embodiments, the first temperature is 880°C-1100°C.

[0020] In some embodiments, the calcination time is 5 to 20 hours.

[0021] In some embodiments, the manganese oxide includes Mn3O4.

[0022] In some embodiments, the M element includes at least one selected from Cr, Al, Mg, Ti, Y, Nb, W, Ga, Zr, V, Sr, Mo, Ru, Ag, Sn, Au, La, Ce, Pr, Nd, Sm, Gd, Cu, Na, Zn, Fe, Co, Ni, or Ca.

[0023] In some embodiments, the source of element M includes at least one of CrO2, Al2O3, MgO, TiO2, or Y2O3.

[0024] In some embodiments, the manganese oxide and the M element source are mixed in a molar ratio of M to Mn ranging from 0.001:1 to 0.1:1.

[0025] In some embodiments, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate, or lithium sulfate.

[0026] In a third aspect, this application provides an electrochemical device comprising a positive electrode active material as described in the first aspect of this application or a positive electrode active material prepared in accordance with the second aspect of this application.

[0027] In a fourth aspect, this application provides an electrical device that includes the electrochemical device described in the third aspect of this application.

[0028] This application provides a positive electrode active material comprising lithium manganese oxide. By having both o-phase (cubic phase) and m-phase (monoclinic phase) coexist in the lithium manganese oxide, the positive electrode active material has both high charge specific capacity and good structural stability, which can reduce the amount of Mn dissolved in the electrochemical device under charging conditions, thereby improving the service life of the electrochemical device.

[0029] Additional aspects and advantages of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0030] Figure 1 The XRD pattern of the positive electrode active material in Example 1 is shown.

[0031] Figure 2 The first charge-discharge curve of the coin cell in Example 1 is shown.

[0032] Figure 3 The voltage-capacity differential dQ / dV curves for the first charge-discharge cycle of the coin cell in Example 1 are shown. Detailed Implementation

[0033] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0034] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0035] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0036] I. Electrochemical Device

[0037] In some embodiments, this application provides an electrochemical device, which includes a positive electrode, a negative electrode, and an electrolyte.

[0038] 1. Positive electrode

[0039] In some embodiments, the positive electrode comprises a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector, the positive electrode material layer comprising a positive electrode active material comprising lithium manganese oxide, and the X-ray diffraction pattern of the positive electrode active material having a first diffraction peak in the range of 14.3° to 16.3°. In some embodiments, the X-ray diffraction pattern of the positive electrode active material has a first diffraction peak in the range of 14.5° to 16°. In some embodiments, the X-ray diffraction pattern of the positive electrode active material has a first diffraction peak in the range of 14.8° to 15.8°. In some embodiments, the X-ray diffraction pattern of the positive electrode active material has a first diffraction peak in the range of 15° to 15.6°.

[0040] In some embodiments, the X-ray diffraction pattern of the positive electrode active material has a second diffraction peak in the range of 17.3° to 19.3°. In some embodiments, the X-ray diffraction pattern of the positive electrode active material has a second diffraction peak in the range of 17.5° to 19°. In some embodiments, the X-ray diffraction pattern of the positive electrode active material has a second diffraction peak in the range of 17.8° to 18.8°. In some embodiments, the X-ray diffraction pattern of the positive electrode active material has a second diffraction peak in the range of 18° to 18.5°.

[0041] Among them, the first diffraction peak is the (010) characteristic peak of the o-phase (cubic phase) in lithium manganese oxide, and the second diffraction peak is the (001) characteristic peak of the m-phase (monoclinic phase) in lithium manganese oxide. The coexistence of the o-phase and m-phase in lithium manganese oxide forms a solid solution, which improves the structural stability of lithium manganese oxide under the charging state of the electrochemical device. The solid solution formed by the coexistence of the two phases has oxygen vacancies, which can promote the desorption of lithium ions, thereby improving the charging specific capacity of lithium manganese oxide. At the same time, through the synergistic effect of the solid solution, the stability of Mn-O bond can be increased, thereby inhibiting the dissolution of Mn in lithium manganese oxide, and thus improving the service life of the electrochemical device.

[0042] In some embodiments, the X-ray diffraction pattern of the positive electrode active material has a third diffraction peak in the range of 45.7° to 47.7°. In some embodiments, the X-ray diffraction pattern of the positive electrode active material has a third diffraction peak in the range of 46° to 47.5°. In some embodiments, the X-ray diffraction pattern of the positive electrode active material has a third diffraction peak in the range of 46.4° to 47°. The third diffraction peak corresponds to the (111) crystal plane of the m-phase in lithium manganese oxide. The presence of this crystal plane can stabilize the crystal structure of the m-phase, thereby improving the first coulombic efficiency of lithium manganese oxide.

[0043] In some embodiments, the peak intensity of the first diffraction peak is I. A The peak intensity of the second diffraction peak is I. B Satisfying: 0.05≤I A / I B ≤20. In some embodiments, I A / I B The value is 0.05, 0.08, 0.09, 0.15, 0.05, 0.06, 0.08, 0.09, 0.1, 0.15, 0.5, 0.8, 13, 1.5, 2, 3, 5, 8, 9, 10, 12, 14, 16, 18, 20, or a range of any two of these values.

[0044] In some embodiments, 0.05 ≤ I A / I B ≤0.9, or 6≤I A / I B ≤20. At this point, there is a significant difference in the content of the m-phase and o-phase in lithium manganese oxide, which can work synergistically to form a solid solution, promoting the extraction of Li ions from lithium manganese oxide, thereby further improving the specific charging capacity of lithium manganese oxide.

[0045] In some embodiments, the full width at half maximum (FWHM) of the first diffraction peak is W. A The full width at half maximum (FWHM) of the second diffraction peak is W. B Satisfying: 0.3≤WA / W B ≤3. In some embodiments, W A / W B The value is 0.3, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 2.8, 3, or a range of any two of these values.

[0046] In some embodiments, 0.75 ≤ W A / W B ≤1.65. At this value, the full width at half maximum (FWHM) of both the o-phase and m-phase in lithium manganese oxide are narrower, indicating higher structural stability. This further suppresses the dissolution of Mn from lithium manganese oxide and improves the service life of the electrochemical device.

[0047] In some embodiments, the peak intensity of the second diffraction peak is I. B The peak intensity of the third diffraction peak is I. C Satisfying: 0.08≤I C / I B ≤0.35. In some embodiments, I C / I B The values ​​are 0.08, 0.1, 0.13, 0.15, 0.18, 0.2, 0.25, 0.28, 0.3, 0.32, 0.35, or any combination of these values. A stronger third diffraction peak and fewer crystal defects in the m-phase can improve the first coulombic efficiency of the positive electrode active material.

[0048] In some embodiments, the lithium manganese oxide contains element M, which includes at least one selected from Cr, Al, Mg, Ti, Y, Nb, W, Ga, Zr, V, Sr, Mo, Ru, Ag, Sn, Au, La, Ce, Pr, Nd, Sm, Gd, Cu, Na, Zn, Fe, Co, Ni, or Ca. The molar ratio of element M to element Mn in the lithium manganese oxide is from 0.001:1 to 0.1:1. In some embodiments, the molar ratio of element M to element Mn is 0.001:1, 0.005:1, 0.012:1, 0.015:1, 0.02:1, 0.03:1, 0.06:1, 0.1:1, or any combination of these values. The presence of element M in the lithium manganese oxide promotes the formation of a monoclinic phase, thereby improving the structural stability of the lithium manganese oxide, inhibiting the dissolution of Mn, and thus improving the service life of the electrochemical device.

[0049] In some embodiments, the average particle size Dv50 of the positive electrode active material is from 2 μm to 35 μm. In some embodiments, the average particle size Dv50 of the positive electrode active material is 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 24 μm, 26 μm, 28 μm, 30 μm, 32 μm, 35 μm, or a range of any two of these values.

[0050] In some embodiments, the lithium manganese oxide has a layered structure. The layered structure facilitates the extraction of Li ions from the lithium manganese oxide, thereby improving the specific charge capacity of the electrochemical device.

[0051] In some embodiments, the molar ratio of Li to Mn in the positive electrode active material is 0.9 to 1.15.

[0052] In some embodiments, the lithium manganese oxide includes Li x Mn y M z O2, wherein 0.9 ≤ x ≤ 1.15, 0.9 ≤ y ≤ 1, 0 ≤ z ≤ 0.1, and M includes at least one of Cr, Al, Mg, Ti, Y, Nb, W, Ga, Zr, V, Sr, Mo, Ru, Ag, Sn, Au, La, Ce, Pr, Nd, Sm, Gd, Cu, Na, Zn, Fe, Co, Ni, or Ca. In some embodiments, 0.9 ≤ x ≤ 1.2, 0.9 ≤ y ≤ 1, and 0.001 ≤ z ≤ 0.1.

[0053] In some embodiments, the positive electrode active material is assembled with lithium metal to form a coin cell. The voltage-capacity differential dQ / dV curve of the coin cell during its first charge cycle exhibits characteristic peaks in the ranges of 3.5V-3.7V and 3.85V-4.05V. The 3.5V-3.7V range corresponds to the charging capacity of the o-phase, and the 3.85V-4.05V range corresponds to the charging capacity of the m-phase. The characteristic peaks in the voltage-capacity differential dQ / dV curve of the coin cell during its first charge cycle indicate the presence of two phases in the lithium manganese oxide, which work synergistically to improve the specific charging capacity of the lithium manganese oxide.

[0054] In some embodiments, the voltage-capacity differential dQ / dV curve of the coin cell during its first discharge cycle exhibits a characteristic peak in the range of 3.8V-4.0V. This characteristic peak in the 3.8V-4.0V range indicates that a uniform phase is formed during the re-intercalation of Li ions in the lithium manganese oxide, thereby improving the material's stability.

[0055] In one embodiment, this application provides a method for preparing a positive electrode active material, the method comprising:

[0056] A mixture is prepared by mixing manganese oxide, a lithium source, and an optional M element source; the mixture is then calcined under a first atmosphere and a first temperature to obtain the positive electrode active material.

[0057] In some embodiments, the first atmosphere is an inert atmosphere. In some embodiments, the inert atmosphere includes at least one of nitrogen, argon, or helium.

[0058] In some embodiments, the first temperature is 880°C-1100°C.

[0059] In some embodiments, the first temperature is a range of 880°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, or any combination of these values.

[0060] In some embodiments, the calcination time is from 5 hours to 20 hours. In some embodiments, the first heat treatment time is a range of 5 hours, 7 hours, 9 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, or any combination of these values.

[0061] In some embodiments, the manganese oxide and the lithium source are mixed in a lithium-manganese molar ratio ranging from 0.90 to 1.15. In some embodiments, the lithium-manganese molar ratio is 0.90, 0.92, 0.95, 0.98, 1, 1.05, 1.1, 1.15, or any combination of these values.

[0062] In some embodiments, the manganese oxide includes Mn3O4.

[0063] In some embodiments, element M includes at least one selected from Cr, Al, Mg, Ti, Y, Nb, W, Ga, Zr, V, Sr, Mo, Ru, Ag, Sn, Au, La, Ce, Pr, Nd, Sm, Gd, Cu, Na, Zn, Fe, Co, Ni, or Ca. In some embodiments, the source of element M includes at least one selected from CrO2, Al2O3, MgO, TiO2, or Y2O3.

[0064] In some embodiments, the manganese oxide and the M element source are mixed in a molar ratio of M to Mn ranging from 0.001:1 to 0.1:1. In some embodiments, the molar ratio of M to Mn, M:Mn, is 0.001:1, 0.005:1, 0.012:1, 0.015:1, 0.02:1, 0.03:1, 0.06:1, 0.1:1, or any combination of these values.

[0065] In some embodiments, the lithium source is selected from at least one of the following: lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate, or lithium sulfate.

[0066] In some embodiments, the positive electrode material layer includes a conductive agent. In some embodiments, the conductive agent includes at least one of graphite, conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0067] In some embodiments, the content of the conductive agent is from 0.5% to 20% based on the total mass of the positive electrode material layer. In some embodiments, the content of the conductive agent is 0.5%, 1%, 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or any combination of these values, based on the total mass of the positive electrode material layer.

[0068] In some embodiments, the positive electrode material layer includes an adhesive. In some embodiments, the adhesive includes at least one of styrene-butadiene rubber (SBR), aqueous acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), or polyvinyl alcohol (PVA).

[0069] In some embodiments, the binder content is 0.1% to 5% based on the total mass of the positive electrode material layer. In some embodiments, the binder content is 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range of any two of these values, based on the total mass of the positive electrode material layer.

[0070] In some embodiments, the positive current collector comprises a metal foil or a porous metal plate. In some embodiments, the positive current collector comprises a foil or porous plate of a metal such as aluminum, copper, nickel, titanium, or silver, or alloys thereof. In some embodiments, the positive current collector is aluminum foil.

[0071] In some embodiments, the thickness of the positive current collector is from 5 μm to 20 μm. In some embodiments, the thickness of the positive current collector is 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or a range of any two of these values.

[0072] In some embodiments, the positive electrode can be obtained by mixing a positive electrode active material, a conductive agent, and a binder in a solvent to prepare a positive electrode slurry, coating the positive electrode slurry onto a positive electrode current collector, drying, and then cold-pressing to obtain the positive electrode. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone, etc.

[0073] 2. Electrolyte

[0074] The electrolyte that can be used in the embodiments of this application can be an electrolyte known in the prior art.

[0075] In some embodiments, the electrolyte comprises an organic solvent, a lithium salt, and additives. The organic solvent of the electrolyte according to this application may be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the lithium salt used in the electrolyte according to this application; it may be any lithium salt known in the prior art. The additives of the electrolyte according to this application may be any additives known in the prior art that can be used as electrolyte additives.

[0076] In some embodiments, the organic solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0077] In some embodiments, the organic solvent includes at least one 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), butenyl 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), or diethyl sulfone (ESE).

[0078] In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0079] 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).

[0080] In some embodiments, the concentration of lithium salt in the electrolyte is 0.5 mol / L to 3 mol / L. In some embodiments, the concentration of lithium salt in the electrolyte is 0.8 mol / L to 1.5 mol / L.

[0081] 3. Negative electrode

[0082] In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode material layer located on one or both surfaces of the negative electrode current collector. The negative electrode material layer contains a negative electrode active material. The negative electrode material layer can be one or more layers, and each layer in a multilayer negative electrode material layer can contain the same or different negative electrode active materials. The negative electrode active material is any substance capable of reversibly inserting and deintercalating lithium ions.

[0083] In some embodiments, examples of the negative electrode current collector include, but are not limited to, foils or perforated plates made of metallic materials such as copper, aluminum, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper foil.

[0084] In some embodiments, the thickness of the negative electrode current collector is from 1 μm to 50 μm.

[0085] There are no particular restrictions on the negative electrode active material, as long as it can reversibly absorb and release lithium ions. Examples of negative electrode active materials include, but are not limited to, carbon materials such as graphite and hard carbon; and silicon materials such as silicon (Si), silicon-oxygen materials, and silicon-carbon materials. Negative electrode active materials can be used alone or in combination.

[0086] In some embodiments, the negative electrode material layer may further include a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When using an aqueous solvent to prepare the negative electrode slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.

[0087] In some embodiments, the negative electrode can be prepared by coating a negative electrode slurry containing a negative electrode active material, a negative electrode binder, etc. onto a negative electrode current collector, drying it, and then cold pressing it to obtain the negative electrode.

[0088] 4. Separating membrane

[0089] In some embodiments, a separator is typically provided between the positive and negative electrodes to prevent short circuits. There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator material may be a resin, glass fiber, inorganic material, etc., that is stable to the electrolyte of this application. In some embodiments, the separator comprises a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of resin materials may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0090] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0091] Examples of inorganic materials may include, but are not limited to, alumina, silica, boehmite, aluminum nitride, silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). The form of inorganic materials may include, but is not limited to, granular, plate-like, or fibrous forms.

[0092] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the separator is within the range of any two of the above values. When the thickness of the separator is within the above range, insulation and mechanical strength can be ensured, and the rate capability and energy density of the electrochemical device can be ensured.

[0093] The porosity of the separator is arbitrary. In some embodiments, the porosity of the separator is greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the porosity of the separator is less than 60%, less than 50%, or less than 45%. In some embodiments, the porosity of the separator is within the range of any two of the above values. When the porosity of the separator is within the above range, insulation and mechanical strength can be ensured, and membrane resistance can be suppressed, giving the electrochemical device good rate performance.

[0094] 5. Electrochemical device

[0095] The electrochemical device of this application includes any device in which an electrochemical reaction occurs, and specific examples include all kinds of primary or secondary batteries. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries or lithium-ion secondary batteries.

[0096] This application also provides an electrical device that includes the electrochemical device described in this application.

[0097] The application of the electrochemical device described in this application is not particularly limited, and it can be used in any electrical device known in the prior art. In some embodiments, the electrochemical device described in this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, portable cleaners, portable CD players, transceivers, electronic notebooks, calculators, portable recorders, radios, backup power supplies, electric vehicles, electric motorcycles, electric bicycles, lighting fixtures, toys, game consoles, clocks, power tools, cameras, large household batteries, and lithium-ion capacitors, etc.

[0098] The following uses a lithium-ion button battery as an example and specific embodiments to illustrate the positive electrode active material of this application. Those skilled in the art will understand that the embodiments described in this application are merely examples and not limitations on the scope of protection of this application.

[0099] Example 1

[0100] 1. Preparation of positive electrode active materials

[0101] (1) Place Mn(OOH) in a crucible and heat it to 500℃ at a heating rate of 5℃ / min under an air atmosphere and keep it at a constant temperature for 4h to obtain anhydrous Mn3O4.

[0102] (2) The anhydrous Mn3O4 obtained in step (1) is mixed with LiOH at a molar ratio of Li:Mn of 1.05:1, and then an M element source is added at a molar ratio of M element:Mn of 0.03:1. The mixture is mixed for 8 hours to obtain a mixture in which the M element is Al and the M element source is nano-Al2O3; and

[0103] (3) Place the above mixture in a corundum crucible, at a depth of 2m 3 Nitrogen gas is introduced at a rate of 1 h, and the temperature is increased to 940℃ at a rate of 5℃ / min. The material is then sintered at 940℃ for 10 h and naturally cooled to room temperature to obtain a layered LiMnO2 positive electrode active material.

[0104] 2. Preparation of the positive electrode

[0105] The positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive carbon black were mixed in a mass ratio of 90:5:5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was uniformly coated on one surface of a 13 μm thick aluminum foil current collector, dried at 90 °C, cold-pressed, and then cut into 1.4 cm diameter discs to obtain the positive electrode.

[0106] 3. Preparation of electrolyte

[0107] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly in a volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 was dissolved in the above organic solvent to obtain an electrolyte, wherein the concentration of LiPF6 in the electrolyte was 1 mol / L.

[0108] 4. Preparation of lithium-ion button batteries

[0109] The obtained positive electrode, polypropylene separator and lithium metal sheet are placed in sequence in the steel shell of the coin cell, an appropriate amount of electrolyte is added, and after sealing, a lithium-ion coin cell is obtained.

[0110] The Dv50 of the LiMnO2 cathode active material obtained in Example 1 is 17 μm; its X-ray diffraction pattern (XRD) is as follows. Figure 1 As shown, the first charge-discharge curve of the lithium-ion coin cell is as follows: Figure 2 As shown, the voltage-capacity differential dQ / dV curves for the first charge-discharge cycle are as follows: Figure 3 As shown.

[0111] The difference between the preparation methods of the positive electrode active materials in Examples 2-22 and Example 1 lies in the parameters in Table 1. The Cr element source is CrO2, the Ti element source is TiO2, the Mg element source is MgO, and the Y element source is Y2O3. Examples 17-22 contain two or more M elements. Taking Example 17 as an example, the M element type in Example 17 is Al+Cr, and the M / Mn ratio is 0.02:1+0.01:1, representing that the M elements in this example are Al and Cr, and the molar ratios of Al and Cr to Mn are 0.02:1 and 0.01:1, respectively. Examples 18-22 follow the same pattern.

[0112] Comparative Example 1

[0113] The traditional method involves mixing Mn₂O₃ and Na₂CO₃ at a Na:Mn molar ratio of 1.05:1, then heating the mixture to 800℃ at a rate of 5℃ / min under a N₂ atmosphere and maintaining the temperature for 24 hours to obtain NaMnO₂. A 5 mol / L LiBr ethanol solution is then added at a LiBr:NaMnO₂ molar ratio of 10:1, and the mixture is exchanged at 180℃ for 8 hours under an air atmosphere. After this process, the powder is washed with ethanol and then dried in a 120℃ oven for 5 hours to obtain lithium manganese oxide produced by the traditional method.

[0114] Comparative Example 2

[0115] Li₂CO₃ and MnO₂ were weighed according to a Li:Mn molar ratio of 0.56:1, and Al₂O₃ was added according to an Al:Mn molar ratio of 0.03. The mixture was mixed in a high-speed mixer at a speed of 300 r / min for 20 min to obtain a mixture. The mixture was placed in an air furnace and heated to 790℃ at a speed of 5℃ / min and held for 24 h. After natural cooling, it was taken out and passed through a 300-mesh sieve to obtain spinel-type lithium manganese oxide.

[0116] Test methods

[0117] 1. XRD test

[0118] The positive electrode active material powder was placed in the sample stage of an XRD instrument (model Bruker, D8). An X-ray diffraction pattern was obtained using a scan rate of 2° / min and a scan angle range of 10° to 90°. The position, intensity, and full width at half maximum (FWHM) of each peak were then recorded.

[0119] 2. Morphological testing

[0120] The positive electrode active material powder was tested using a scanning electron microscope (SEM); an SEM image with a magnification of 10,000 was selected.

[0121] 3. Average particle size test

[0122] The average particle size Dv50 of the positive electrode active material was measured using a particle size analyzer.

[0123] Dv50 refers to the particle size that reaches 50% of the total volumetric size in a volumetric particle size distribution, starting from the smallest particle size.

[0124] 4. Element content testing methods

[0125] The positive electrode active material is dissolved in a mixed solvent (for example, 0.4g of positive electrode active material is dissolved in a mixed solvent of 10ml aqua regia (nitric acid and hydrochloric acid mixed in a 1:1 ratio) and 2ml HF), and the volume is adjusted to 100mL. Then, the content of elements such as M, Mn and Li in the positive electrode active material is obtained by using an ICP analyzer.

[0126] 5. Lithium-ion button battery charge and discharge test

[0127] The LAND series battery testing system was used to conduct charge and discharge tests on lithium-ion coin cells to assess their charge and discharge performance. The cells were charged at a constant current rate of 0.1C at 45°C until the voltage reached 4.3V. They were then further charged at a constant voltage of 4.3V until the current decreased to 0.05C, bringing them to a fully charged state at 4.3V. The resulting charge specific capacity was recorded as the first charge specific capacity. Subsequently, the cells were discharged at a constant current rate of 0.1C until the voltage reached 3V. The resulting discharge specific capacity was recorded as the first discharge specific capacity. The ratio of the first discharge specific capacity to the first charge specific capacity was recorded as the initial efficiency at 45°C.

[0128] 6. dQ / dV test

[0129] By performing differential integration on the first charge and discharge data of the lithium-ion coin cell, the voltage-capacity differential dQ / dV curve is obtained.

[0130] 7. Test of Mn dissolution amount

[0131] The lithium-ion coin cell battery was charged to 4V at a constant current of 0.1C. After disassembly, the positive electrode was immersed in an electrolyte at 60℃ for 7 days. The Mn content in the electrolyte was tested using ICP. Mn dissolution amount = Mn content in electrolyte / mass of positive electrode active material.

[0132] Test Results

[0133] Tables 1 and 2 show the preparation parameters and related properties of the positive electrode active materials in Examples 1 to 22 and Comparative Examples 1 and 2. Among them, I... A The peak intensity of the first diffraction peak; I B The peak intensity of the second diffraction peak; W A W is the full width at half maximum (FWHM) of the first diffraction peak. B The full width at half maximum (FWHM) of the second diffraction peak; I C The peak intensity of the third diffraction peak.

[0134] Table 1

[0135]

[0136] The " / " indicates that the substance or performance parameter does not exist.

[0137] Table 2

[0138]

[0139]

[0140] The " / " indicates that the substance or performance parameter does not exist.

[0141] As can be seen from the comparison of Examples 1-22 with Comparative Examples 1 and 2, when the X-ray diffraction pattern of the positive electrode active material has a first diffraction peak in the range of 14.3° to 16.3° and a second diffraction peak in the range of 17.3° to 19.3°, the lithium-ion coin cell has a higher specific capacity and a lower amount of Mn dissolved. The possible reason is that the first diffraction peak is the (010) characteristic peak of the o-phase (cubic phase) in lithium manganese oxide, and the second diffraction peak is the (001) characteristic peak of the m-phase (monoclinic phase) in lithium manganese oxide. The coexistence of the o-phase and m-phase in lithium manganese oxide forms a solid solution, which improves the structural stability of lithium manganese oxide in the battery charging state. The solid solution formed by the coexistence of the two phases has oxygen vacancies, which can promote the desorption of lithium ions, thereby improving the charging specific capacity of lithium manganese oxide. At the same time, through the synergistic effect of the solid solution, the stability of Mn-O bond can be increased, thereby inhibiting the dissolution of Mn in lithium manganese oxide, and thus improving the battery life.

[0142] A comparison of Examples 1-5, 7-10, and 12-22 with other examples shows that when 0.05 ≤ I A / I B ≤0.9, or 6≤I A / I B When W ≤ 20, lithium-ion coin cells can exhibit a higher specific charge capacity. This may be because the significant difference in the content of the m-phase and o-phase in lithium manganese oxide allows them to synergistically form a solid solution, promoting the extraction of Li ions from the lithium manganese oxide and thus further enhancing its specific charge capacity. A comparison of Examples 1-2, 5-10, and 13-22 with other examples shows that when 0.75 ≤ W... A / W B When the concentration is ≤1.65, the amount of Mn leaching decreases further. This may be because, at this concentration, the half-widths of the o-phase and m-phase in lithium manganese oxide are both narrower, and the structural stability is higher, which further inhibits the leaching of Mn from lithium manganese oxide.

[0143] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A positive electrode active material comprising lithium manganese oxide, wherein the X-ray diffraction pattern of the positive electrode active material has a first diffraction peak in the range of 14.3° to 16.3° and a second diffraction peak in the range of 17.3° to 19.3°; in, The full width at half maximum (FWHM) of the first diffraction peak is W A The full width at half maximum (FWHM) of the second diffraction peak is W. B , 0.75≤W A / IN B ≤1.65。 2. The positive electrode active material according to claim 1, wherein, The positive electrode active material satisfies at least one of the following conditions: (1) The X-ray diffraction pattern of the positive electrode active material has a third diffraction peak in the range of 45.7° to 47.7°; (2) The peak intensity of the first diffraction peak is I A The peak intensity of the second diffraction peak is I. B ,satisfy: 0.05≤I A / I B ≤20。 3. The positive electrode active material according to claim 2, wherein, 0.05 ≤ I A / I B ≤0.9, or 6≤I A / I B ≤20.

4. The positive electrode active material according to claim 2, wherein, The peak intensity of the second diffraction peak is I B The peak intensity of the third diffraction peak is I. C Satisfying: 0.08≤I C / I B ≤0.

35.

5. The positive electrode active material according to claim 1, wherein, The positive electrode active material satisfies at least one of the following conditions: (1) The lithium manganese oxide contains element M, which includes at least one of Cr, Al, Mg, Ti, Y, Nb, W, Ga, Zr, V, Sr, Mo, Ru, Ag, Sn, Au, La, Ce, Pr, Nd, Sm, Gd, Cu, Na, Zn, Fe, Co, Ni or Ca, and the molar ratio of element M to element Mn in the lithium manganese oxide is from 0.001:1 to 0.1:1; (2) The average particle size Dv50 of the positive electrode active material is 2 μm to 35 μm; (3) The lithium manganese oxide has a layered structure; (4) The molar ratio of Li to Mn in the lithium manganese oxide is 0.9 to 1.15; (5) The lithium manganese oxide includes Li x Mn y M z O2, wherein 0.9≤x≤1.15, 0.9≤y≤1, 0≤z≤0.1, and M includes at least one of Cr, Al, Mg, Ti, Y, Nb, W, Ga, Zr, V, Sr, Mo, Ru, Ag, Sn, Au, La, Ce, Pr, Nd, Sm, Gd, Cu, Na, Zn, Fe, Co, Ni, or Ca.

6. The positive electrode active material according to claim 1, wherein, The positive electrode active material is assembled with lithium metal to form a coin cell. The voltage-capacity differential dQ / dV curve of the coin cell during the first charge cycle has characteristic peaks in the ranges of 3.5V-3.7V and 3.85V-4.05V, and the voltage-capacity differential dQ / dV curve of the coin cell during the first discharge cycle has characteristic peaks in the range of 3.8V-4.0V.

7. A method for preparing a positive electrode active material, the method comprising: A mixture is obtained by mixing manganese oxide, a lithium source, and an optional M element source; The mixture is calcined under a first atmosphere and a first temperature to obtain the positive electrode active material. The manganese oxide and the lithium source are mixed in a lithium-manganese molar ratio of 0.90-1.

15. The first atmospheric condition is an inert atmosphere, wherein the X-ray diffraction pattern of the positive electrode active material has a first diffraction peak in the range of 14.3° to 16.3° and a second diffraction peak in the range of 17.3° to 19.3°; the full width at half maximum (FWHM) of the first diffraction peak is W. A The full width at half maximum (FWHM) of the second diffraction peak is W. B , 0.75≤W A / W B ≤1.

65.

8. The method for preparing the positive electrode active material according to claim 7, wherein, The preparation method satisfies at least one of the following conditions: (1) The inert atmosphere includes at least one of nitrogen, argon or helium; (2) The first temperature is 880℃-1100℃; (3) The calcination time is 5 to 20 hours; (4) The manganese oxides include Mn3O4; (5) The M element includes at least one of Cr, Al, Mg, Ti, Y, Nb, W, Ga, Zr, V, Sr, Mo, Ru, Ag, Sn, Au, La, Ce, Pr, Nd, Sm, Gd, Cu, Na, Zn, Fe, Co, Ni or Ca; (6) The source of element M includes at least one of CrO2, Al2O3, MgO, TiO2 or Y2O3; (7) The manganese oxide and the M element source are mixed in a molar ratio of M element to Mn element ranging from 0.001:1 to 0.1:1; (8) The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate or lithium sulfate.

9. An electrochemical device, wherein, The electrochemical device comprises a positive electrode active material according to any one of claims 1-6 or a positive electrode active material prepared by a method according to any one of claims 7-8.

10. An electrical device comprising the electrochemical device according to claim 9.

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