A lithium iron manganese phosphate-based composite cathode material, a preparation method thereof, a cathode sheet, and a secondary battery

Abstract

The application belongs to the technical field of battery active materials, and specifically discloses a lithium manganese iron phosphate composite positive electrode material, a preparation method thereof, a positive electrode sheet and a secondary battery. 0.6(1‑x‑y) Fe 0.4(1‑x‑y) Ni x Ti y PO4, wherein 0≤x≤0.05 and 0≤y≤0.05; and the component B comprises amorphous carbon. The Ni+Ti co-doping strategy adopted in the application effectively slows down the energy density and capacity attenuation of the lithium manganese iron phosphate positive electrode material, so that the lithium manganese iron phosphate can better exert its obvious advantages of high energy density, good safety and low cost, and is beneficial to improving the capacity and cycle stability of the lithium manganese iron phosphate battery.

Description

Technical Field

[0001] This invention relates to the field of battery active materials technology, and in particular to a lithium manganese iron phosphate composite cathode material and its preparation method, cathode sheet, and secondary battery. Background Technology

[0002] With increasing demands for higher energy density, safety, and cost control in lithium-ion batteries, the development of cathode materials, a key component of lithium-ion batteries, has attracted significant attention. While lithium iron phosphate (LFP) offers advantages such as good safety, low cost, and environmental friendliness, its low plateau voltage (~3.4V) and low energy density (580Wh / kg) are drawbacks. Nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary cathode materials offer high energy density, but their high cost and poor safety also constrain their development. In contrast, lithium manganese iron phosphate (LFP) provides a higher energy density at a 4.1V voltage plateau, and its stable phosphate groups offer superior safety performance compared to NCM or NCM ternary cathode materials, while also being less expensive than ternary cathode materials using nickel-cobalt. Therefore, LFP cathode materials, with their high energy density, high safety, and low cost, hold promise as a competitive cathode material for lithium-ion batteries.

[0003] However, while the stable phosphate group in lithium manganese iron phosphate cathode materials ensures thermodynamic stability, it also hinders metal ion transport, resulting in a lower intrinsic conductivity of the material. The Mn3+ in lithium manganese iron phosphate cathode materials... + The Ginger-Taylor effect exists, and Mn dissolution during cycling causes capacity decay. Furthermore, the decay of the Mn plateau voltage in lithium manganese iron phosphate cathode materials leads to energy density decay, which is also one of the problems that urgently needs to be solved in lithium manganese iron phosphate cathode materials. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a lithium manganese iron phosphate composite cathode material, electrode sheet and preparation method thereof, so as to enhance the structural stability and conductivity of lithium manganese iron phosphate cathode material and improve the capacity and cycle stability of lithium manganese iron phosphate battery.

[0005] To achieve the above and other related objectives, this invention provides a lithium manganese iron phosphate composite cathode material, comprising component A and component B; wherein component A is a Ni / Ti co-doped lithium manganese iron phosphate material, and the chemical formula of the Ni / Ti co-doped lithium manganese iron phosphate material is LiMn. 0.6(1 - x - y) Fe 0.4(1 - x-y) Ni x Ti yPO4, wherein 0 ≤ x ≤ 0.05, 0 ≤ y ≤ 0.05; component B includes amorphous carbon.

[0006] Furthermore, in the Ni / Ti co-doped lithium manganese iron phosphate material, the ratio of the sum of the molar contents of Ni and Ti to the sum of the molar contents of Mn and Fe is 0.06–0.08: 0.92–0.94.

[0007] Furthermore, in the Ni / Ti co-doped lithium manganese iron phosphate material, the molar ratio of Ni to Ti is 1:1 to 1.6.

[0008] Furthermore, component B is a network-like thin film that coats component A.

[0009] Furthermore, the mass percentage of component B in the lithium manganese iron phosphate composite cathode material is 1% to 2.5%.

[0010] This invention also provides a method for preparing a lithium iron phosphate composite cathode material, comprising the following steps:

[0011] A slurry is prepared by mixing lithium, manganese, iron, nickel, titanium, phosphorus, and carbon sources. The molar ratio of Li, Mn, Fe, Ni, Ti, and P elements in the slurry is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6(1-xy):0.4(1-x-y):x:y:1.

[0012] The slurry was dried and then sintered to obtain the lithium iron phosphate composite cathode material.

[0013] Furthermore, in the slurry, the mass of the carbon source is 8% to 12% of the total mass of the lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source.

[0014] Furthermore, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, or lithium dihydrogen phosphate.

[0015] Furthermore, the manganese source is selected from at least one of manganese oxalate, manganese carbonate, manganese tetroxide, manganese phosphate, manganese oxide, or manganese ammonium phosphate.

[0016] Furthermore, the iron source is selected from at least one of ferrous oxalate, ferrous pyrophosphate, ferric phosphate, ferric oxide, or metallic iron.

[0017] Furthermore, the nickel source is selected from at least one of nickel oxide, nickel hydroxide, or nickel tetroxide.

[0018] Furthermore, the titanium source is selected from at least one of titanium dioxide, tetrabutyl titanate, or metatitanic acid.

[0019] Furthermore, the phosphorus source is selected from at least one of iron phosphate, ammonium dihydrogen phosphate, lithium phosphate, or lithium dihydrogen phosphate.

[0020] Furthermore, the carbon source is selected from at least one of glucose, polyethylene glycol, sucrose, citric acid, or graphite.

[0021] Furthermore, sintering is carried out under a protective gas atmosphere at a temperature of 650℃ to 850℃ for a duration of 6 hours to 12 hours.

[0022] The present invention also provides a positive electrode sheet, comprising a positive current collector and a positive active material layer at least on one side of the positive current collector, wherein the positive active material layer comprises a positive active material, wherein the positive active material comprises a lithium manganese iron phosphate composite positive electrode material as described above, and / or a lithium manganese iron phosphate composite positive electrode material prepared by the method described above.

[0023] The present invention also provides a secondary battery, including the positive electrode sheet as described above.

[0024] As described above, the lithium manganese iron phosphate composite cathode material, electrode sheet, and preparation method of the present invention have the following beneficial effects:

[0025] The present invention provides a lithium iron phosphate composite cathode material LiMn 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y PO4 / C is doped with the metallic elements Ni and Ti. Ni+Ti co-doping accelerates the ion diffusion rate of the material and suppresses phase separation during the cycling process of lithium manganese iron phosphate, thereby effectively reducing the decay rate of the Mn plateau. Simultaneously, the presence of Ni further increases the crystal structure stability of lithium manganese iron phosphate because Ni… 2+ -O-Mn 2+ There is a super-exchange interaction that inhibits Mn 3+ The variable valence of the crystal structure mitigates the Jameer-Taylor effect, effectively stabilizing the crystal structure. This stable crystal structure helps reduce capacity decay during lithium-ion battery cycling, thus maintaining a high capacity retention rate. Ti doping reduces particle size because the atomic radius of Ti is smaller than that of Mn and Fe, which helps reduce the cell volume and control particle size. This is beneficial for interparticle ion transport and increases the uniformity of Mn and Fe in the material, thereby improving the material's conductivity. In contrast, single Ni doping does not significantly control particle size, and single Ti doping is insufficient to stabilize the crystal structure. Therefore, the Ni+Ti co-doping strategy adopted in this invention effectively mitigates the energy density and capacity decay problems of lithium manganese iron phosphate cathode materials, allowing lithium manganese iron phosphate to better leverage its advantages of high energy density, good safety, and low cost, thereby improving the capacity and cycle stability of lithium manganese iron phosphate batteries.

[0026] The LiMn provided by this invention 0.6(1-x-y) Fe 0.4(1 - x-y) Ni x Ti y In PO4 / C, carbon coating can form a conductive network between particles, thereby improving electronic conductivity.

[0027] The LiMn provided by this invention 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y PO4 / C is synthesized in a one-step process, which is simple and suitable for large-scale industrial production. Attached Figure Description

[0028] Figure 1 The image shows the lithium manganese iron phosphate composite cathode material LiMn prepared in Example 2 of this invention. 0.6 Fe 0.4 Ni 0.03 Ti 0.05 SEM image of PO4 / C.

[0029] Figure 2 The graph shows the 1C charge-discharge curves of batteries made from lithium manganese iron phosphate composite cathode materials prepared in Example 2 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0030] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0031] In this invention, unless otherwise stated, the term "multiple" means two or more.

[0032] The character "+" indicates that the objects before and after it are in a "plus" relationship. For example, A+B means: A and B.

[0033] The character " / " indicates that the objects before and after it are in a "and" or "or" relationship. For example, A / B means either A and B, or A or B.

[0034] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0035] One embodiment of the present invention provides a lithium manganese iron phosphate composite cathode material, comprising component A and component B; wherein component A is a Ni / Ti co-doped lithium manganese iron phosphate material, and the chemical formula of the Ni / Ti co-doped lithium manganese iron phosphate material is LiMn. 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y PO4, wherein 0 ≤ x ≤ 0.05, 0 ≤ y ≤ 0.05; component B includes amorphous carbon.

[0036] The present invention provides a lithium iron phosphate composite cathode material LiMn 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y PO4 / C is doped with the metallic elements Ni and Ti, which are uniformly distributed within the lithium manganese iron phosphate particles. Ni+Ti co-doping accelerates the ion diffusion rate and suppresses phase separation during the cycling process of lithium manganese iron phosphate, thereby effectively reducing the Mn plateau decay rate. Specifically, the presence of Ni further increases the crystal structure stability of lithium manganese iron phosphate because Ni… 2+ -O-Mn 2+ There is a super-exchange interaction that inhibits Mn 3+ The variable valence of the crystal structure mitigates the Jameer-Taylor effect, effectively stabilizing the crystal structure. This stable crystal structure helps reduce capacity decay during lithium-ion battery cycling, thus maintaining a high capacity retention rate. Ti doping reduces particle size because the atomic radius of Ti is smaller than that of Mn and Fe, which helps reduce the cell volume and control particle size. This is beneficial for interparticle ion transport and increases the uniformity of Mn and Fe in the material, thereby improving the material's conductivity. In contrast, single Ni doping does not significantly control particle size, and single Ti doping is insufficient to stabilize the crystal structure. Therefore, the Ni+Ti co-doping strategy adopted in this invention effectively mitigates the energy density and capacity decay problems of lithium manganese iron phosphate cathode materials, allowing lithium manganese iron phosphate to better leverage its advantages of high energy density, good safety, and low cost, thereby improving the capacity and cycle stability of lithium manganese iron phosphate batteries.

[0037] In addition, the LiMn provided by this invention 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y In PO4 / C, carbon coating can form a conductive network between particles, thereby improving electronic conductivity.

[0038] In some embodiments, in the Ni / Ti co-doped lithium manganese iron phosphate material, the ratio of the sum of the molar contents of Ni and Ti to the sum of the molar contents of Mn and Fe is 0.06–0.08:0.92–0.94. A certain amount of Ni+Ti doping is required in the lithium manganese iron phosphate material to achieve a balanced improvement in discharge capacity, capacity retention, and other aspects.

[0039] In some embodiments, the molar ratio of Ni to Ti in the Ni / Ti co-doped lithium manganese iron phosphate material is 1:1 to 1.6. Under the same Ni+Ti doping conditions, a higher Ti doping amount will have a greater advantage in terms of capacity.

[0040] In some embodiments, component B is uniformly coated with component A in a network-like thin film, and the uniform coating of component B on the outer layer of component A can further increase the conductivity of the material.

[0041] In some embodiments, the mass percentage of component B in the lithium manganese iron phosphate composite cathode material is 1% to 2.5%. X-ray diffraction (XRD) results show that no graphite characteristic peaks appear in the lithium manganese iron phosphate composite cathode material prepared by the method of the present invention, indicating that its coated carbon layer exists in the form of amorphous carbon. Therefore, the mass percentage of amorphous carbon in the lithium manganese iron phosphate composite cathode material of the present invention is 1% to 2.5%.

[0042] Another embodiment of the present invention provides a method for preparing the lithium iron phosphate composite cathode material as described above, comprising the following steps:

[0043] A slurry is prepared by mixing lithium, manganese, iron, nickel, titanium, phosphorus, and carbon sources. The molar ratio of Li, Mn, Fe, Ni, Ti, and P elements in the slurry is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6(1-xy):0.4(1-x-y):x:y:1.

[0044] The slurry was dried and then sintered to obtain the lithium iron phosphate composite cathode material.

[0045] The LiMn of the present invention 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti yPO4 / C is synthesized in a one-step process, which is simple and suitable for large-scale industrial production. The content of each element in the finished material can be controlled by adjusting the feed ratio. The content and proportion of each metal element in the finished material can be obtained by detecting the content of each metal element using inductively coupled plasma (ICP) testing. Notably, the Li content in the finished material was found to be slightly lower than the feed ratio, which may be due to the light weight of Li causing a certain amount of lithium loss during the calcination process.

[0046] In some embodiments, the mass of the carbon source in the slurry is 8% to 12% of the total mass of the lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source, so that the mass percentage of component B in the prepared lithium manganese iron phosphate composite cathode material is 1% to 2.5%.

[0047] In some embodiments, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, or lithium dihydrogen phosphate, but is not limited thereto; the manganese source is selected from at least one of manganese oxalate, manganese carbonate, manganese tetroxide, manganese phosphate, manganese sulfide, or manganese ammonium phosphate, but is not limited thereto; the iron source is selected from at least one of ferrous oxalate, ferrous pyrophosphate, ferric phosphate, ferric oxide, or metallic iron, but is not limited thereto; the nickel source is selected from at least one of nickel oxide, nickel hydroxide, or nickel tetroxide, but is not limited thereto; the titanium source is selected from at least one of titanium dioxide, tetrabutyl titanate, or metatitanic acid, but is not limited thereto; the phosphorus source is selected from at least one of ferric phosphate, ammonium dihydrogen phosphate, lithium phosphate, or lithium dihydrogen phosphate, but is not limited thereto; and the carbon source is selected from at least one of glucose, polyethylene glycol (PEG), sucrose, citric acid, or graphite, but is not limited thereto.

[0048] In some embodiments, water is used as the dispersion medium to prepare the slurry, and the water includes, but is not limited to, deionized water, pure water, ultrapure water, purified water, etc.

[0049] In some embodiments, the slurry drying method is selected from spray drying, but is not limited thereto.

[0050] In some embodiments, sintering is carried out under a protective gas atmosphere at a temperature of 650°C to 850°C for a duration of 6 hours to 12 hours. The protective gas includes, but is not limited to, nitrogen, helium, and argon.

[0051] Another embodiment of the present invention provides a positive electrode sheet, comprising a positive current collector and a positive active material layer at least on one side of the positive current collector. The positive active material layer comprises a positive active material, which includes the lithium manganese iron phosphate composite positive electrode material as described above, and / or a lithium manganese iron phosphate composite positive electrode material prepared by the method described above. Compared with traditional lithium manganese iron phosphate materials, the lithium manganese iron phosphate composite positive electrode material provided by the present invention has better structural stability and conductivity. Using it as a positive active material can improve the capacity and cycle stability of secondary batteries such as lithium-ion batteries. The positive current collector is, for example, a foil formed by surface treatment of nickel, titanium, aluminum, silver, stainless steel, or carbon. In addition to foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. The thickness of the positive current collector is, for example, 8 μm to 15 μm, and the single-sided coating thickness of the positive active material layer is, for example, 20 μm to 100 μm. Furthermore, in one specific embodiment, the positive current collector is, for example, an aluminum foil, and the thickness of the aluminum foil is, for example, 13 μm, and the single-sided coating thickness of the positive active material layer is 50 μm.

[0052] In some embodiments, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent, etc., and the mass ratio of the positive electrode active material, the conductive agent, and the binder can be, for example, 90-98:1-5:1-5. The positive electrode active material can be only the lithium manganese iron phosphate composite positive electrode material as described above, or other materials commonly used as positive electrode active materials can be added, such as those with the chemical formula Li. x [Ni y Co z Mn t M (1-y-z-t) O 2-δThe material, wherein M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, or Zn, 0.9 < x < 1.1, 0.65 ≤ y < 1.0, 0 ≤ z < 0.5, 0 ≤ t < 0.5, 0 ≤ δ ≤ 0.1, including but not limited to lithium nickel manganese oxide, lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide. The binder is selected, for example, from any one or more of polyvinylidene fluoride (PVDF), poly(ethylene oxide) (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate (polyacrylate), polyvinyl ether (polyvinyl ether), polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), or polyhexafluoropropylene (polyhexafluoropropylene). The conductive agent is selected from any one or more of conductive carbon black (Super P), acetylene black, carbon nanotubes, and graphene.

[0053] In one specific embodiment, the positive electrode active material is, for example, the lithium manganese iron phosphate composite material as described above, the binder is, for example, selected from polyvinylidene fluoride, and the conductive agent is, for example, selected from conductive carbon black. The positive electrode active material, conductive agent, and binder are mixed, for example, in a mass ratio of 90:5:5, and an organic solvent is added. The mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The organic solvent is, for example, selected from N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated onto aluminum foil, dried in an oven, and then subjected to cold pressing and slitting processes to obtain the positive electrode sheet. In other embodiments, the positive electrode sheet can also be obtained by any other method of forming the positive electrode sheet.

[0054] Another embodiment of the present invention provides a secondary battery, including the positive electrode sheet as described above.

[0055] In some embodiments, the secondary battery may be, for example, a lithium-ion battery, a sodium-ion battery, a potassium-ion battery, etc., but is not limited thereto.

[0056] In some embodiments, the secondary battery is a lithium-ion battery, including an electrolyte, a casing, and a bare cell disposed within the casing. The bare cell includes a positive electrode as described above, as well as a negative electrode and a separator.

[0057] In one specific embodiment, the method for preparing the lithium-ion battery includes the following steps: stacking a positive electrode, a separator, and a negative electrode sequentially, ensuring that a separator is present between any positive and negative electrode; obtaining a multi-layered stack by winding; and inserting this stack as a bare cell into a battery casing. Finally, injecting electrolyte into the casing once or in multiple stages, so that the bare cell is completely immersed in the electrolyte. In other words, the electrolyte is injected and fills the entire internal space of the battery, and the positive electrode, separator, and negative electrode are completely immersed in the electrolyte.

[0058] In some embodiments, the negative electrode sheet in the above-described implementations and / or examples includes a negative current collector and a negative active material layer coated at least on one surface of the negative current collector. The negative current collector is selected from, for example, any one of copper foil current collectors, composite copper foil current collectors, carbon current collectors, foamed copper current collectors, or stainless steel current collectors. The thickness of the negative current collector is, for example, 8 μm to 15 μm, and the single-sided coating thickness of the negative active material layer is, for example, 10 μm to 80 μm. In a specific embodiment, the negative current collector is, for example, copper foil, and the thickness of the copper foil is, for example, 13 μm, and the single-sided coating thickness of the negative active material layer is 50 μm.

[0059] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a thickener, etc., and the mass ratio of the negative electrode active material, conductive agent, binder, and thickener can be, for example, 90-96:1-2:1-3:2-5. The negative electrode active material is a compound capable of intercalating and deintercalating lithium ions, such as graphite, soft carbon, hard carbon, artificial graphite, natural graphite, silicon, and silicon oxides (SiO₂). x The conductive agent is selected from at least one of the following: 0 < x < 2, silicon carbide compounds, or lithium titanate. The conductive agent is selected from any one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene. The binder is selected from any one or more of polyvinylidene fluoride, polyethylene oxide, polyamide, polypropylene, polyacrylate, polyethylene ether, polymethyl methacrylate, polyhexamethylene propylene, or polymerized styrene-butadiene rubber (SBR). The thickener is selected from, for example, sodium carboxymethyl cellulose (CMC-Na).

[0060] In one specific embodiment, the negative electrode active material is selected from graphite, the conductive agent is selected from acetylene black, the binder is selected from styrene-butadiene rubber, and the thickener is selected from sodium carboxymethyl cellulose. The negative electrode active material, conductive agent, binder, and thickener are mixed in a mass ratio of 97:1:1:1, deionized water is added, and the mixture is stirred evenly under vacuum to obtain a negative electrode slurry. The negative electrode slurry is coated onto copper foil, dried in an oven, and then subjected to cold pressing and slitting processes to obtain the negative electrode sheet. In other embodiments, the negative electrode sheet can also be obtained by any other method of forming a negative electrode sheet.

[0061] In some embodiments, the electrolyte includes an electrolyte lithium salt, a solvent, and additives. In secondary batteries, the electrolyte plays a role in ion transport and maintaining chemical stability. The various components in the electrolyte can be categorized according to their function and dosage as electrolyte lithium salt, solvent, and additives. Lithium salt is primarily used to provide lithium ions to form ion channels. In the entire electrochemical system of the battery, the directional movement of lithium ions and electrons generates electricity. Lithium salt has a significant impact on the energy density, power density, wide electrochemical window, cycle life, and safety performance of lithium batteries. The solvent is used to dissolve the lithium salt and additives. Additives, added in small amounts to the electrolyte, are numerous and each plays a different role, for example, improving the battery's high and low temperature performance, cycle performance, and film-forming properties.

[0062] In some embodiments, the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methanesulfonate, or lithium trifluoromethylsulfonate, and the mass percentage of the electrolyte lithium salt is 12% to 16% based on the total mass of the electrolyte. This invention does not limit the type of lithium salt; a single lithium salt or a mixture of lithium salts can be used.

[0063] In some embodiments, the solvent is selected from at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, or nitrile solvents, and the solvent accounts for 70% to 80% of the total mass of the electrolyte. Examples of carbonate solvents include ethylene carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, and polycarbonate; examples of carboxylic acid ester solvents include ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, and propyl propionate; examples of ether solvents include ethylene glycol dimethyl ether and diethanol diethyl ether; and examples of nitrile solvents include acetonitrile, propionitrile, butyronitrile, and valerate. This invention does not limit the type of solvent; a single solvent or a mixture of solvents can be used.

[0064] In some embodiments, the additive is selected from at least one of vinylene carbonate (VC), methylene methanedisulfonate (MMDS), propylene sulfite (PS), ethylene sulfate (1,3,2-dioxathiolane 2,2-dioxide (DTD)), and ethylenesulfite (ES), and the mass percentage of the additive is 0.1% to 5% based on the total mass of the electrolyte. This invention does not limit the type of additive; a single additive or a mixture of additives may be used.

[0065] In some embodiments, the diaphragm is, for example, a polyethylene (PE) membrane, a polypropylene (PP) membrane, a glass fiber membrane, or a composite membrane, and the thickness of the diaphragm is, for example, 9 μm to 15 μm, the air permeability is, for example, 150 s / 100 mL to 350 s / 100 mL, and the porosity is, for example, 30% to 50%.

[0066] The following specific examples illustrate the present invention in detail. It should also be understood that the following examples are only for specific illustrative purposes and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0067] Example 1

[0068] This embodiment prepares a lithium manganese iron phosphate composite cathode material LiMn. 0.6 Fe 0.4 Ni 0.03 Ti 0.03 PO4 / C (abbreviated as Ni3Ti3-LMFP), designated as 1, has the following specific preparation steps:

[0069] S1. Using deionized water as the dispersion medium, a sand mill is used to uniformly mix lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source to prepare a slurry. In the slurry, the molar ratio of Li, Mn, Fe, Ni, Ti and P elements is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6:0.4:0.03:0.03:1, and the mass of carbon source is 10% of the total mass of lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source.

[0070] S2. After spray drying the slurry obtained in step S1, sinter it at 750°C for 9 hours under a nitrogen atmosphere; grind and crush the sintered product to obtain the target material.

[0071] Example 2

[0072] This embodiment prepares a lithium manganese iron phosphate composite cathode material LiMn. 0.6 Fe 04 Ni 0.03 Ti 0.05 PO4 / C (abbreviated as Ni3Ti5-LMFP), designated as No. 2, has the following specific preparation steps:

[0073] S1. Using deionized water as the dispersion medium, a sand mill is used to uniformly mix lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source to prepare a slurry. In the slurry, the molar ratio of Li, Mn, Fe, Ni, Ti and P elements is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6:0.4:0.03:0.05:1, and the mass of carbon source is 10% of the total mass of lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source.

[0074] S2. After spray drying the slurry obtained in step S1, sinter it at 750°C for 9 hours under a nitrogen atmosphere; grind and crush the sintered product to obtain the target material.

[0075] Example 3

[0076] This embodiment prepares a lithium manganese iron phosphate composite cathode material LiMn. 0.6 Fe 04 Ni 0.04 Ti 0.04 PO4 / C (abbreviated as Ni4Ti4-LMFP), numbered 3, has the following specific preparation steps:

[0077] S1. Using deionized water as the dispersion medium, a sand mill is used to uniformly mix lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source to prepare a slurry. In the slurry, the molar ratio of Li, Mn, Fe, Ni, Ti and P elements is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6:0.4:0.04:0.04:1, and the mass of carbon source is 10% of the total mass of lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source.

[0078] S2. After spray drying the slurry obtained in step S1, sinter it at 750°C for 9 hours under a nitrogen atmosphere; grind and crush the sintered product to obtain the target material.

[0079] Example 4

[0080] This embodiment prepares a lithium manganese iron phosphate composite cathode material LiMn. 0.6 Fe 0.4 Ni 0.05 Ti 0.03 PO4 / C (abbreviated as Ni5Ti3-LMFP), numbered 4, has the following specific preparation steps:

[0081] S1. Using deionized water as the dispersion medium, a sand mill is used to uniformly mix lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source to prepare a slurry. In the slurry, the molar ratio of Li, Mn, Fe, Ni, Ti and P elements is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6:0.4:0.05:0.03:1, and the mass of carbon source is 10% of the total mass of lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source.

[0082] S2. After spray drying the slurry obtained in step S1, sinter it at 750°C for 9 hours under a nitrogen atmosphere; grind and crush the sintered product to obtain the target material.

[0083] Comparative Example 1

[0084] This comparative example prepared a lithium manganese iron phosphate composite cathode material LiMn 0.6 Fe 0.4 PO4 / C (LMFP), designated as No. 5, has the following specific preparation steps:

[0085] S1. Using deionized water as the dispersion medium, a sand mill is used to uniformly mix lithium source, manganese source, iron source, phosphorus source and carbon source to prepare a slurry. In the slurry, the molar ratio of Li, Mn, Fe and P elements is Li:Mn:Fe:P = 1.05:0.6:0.4:1, and the mass of carbon source is 10% of the total mass of lithium source, manganese source, iron source, phosphorus source and carbon source.

[0086] S2. After spray drying the slurry obtained in step S1, sinter it at 750°C for 9 hours under a nitrogen atmosphere; grind and crush the sintered product to obtain the target material.

[0087] Comparative Example 2

[0088] This comparative example prepared a lithium manganese iron phosphate composite cathode material LiMn 0.6 Fe 0.4 Ni 0.08 PO4 / C (Ni-LMFP), designated as No. 6, has the following specific preparation steps:

[0089] S1. Using deionized water as the dispersion medium, a sand mill is used to uniformly mix lithium source, manganese source, iron source, nickel source, phosphorus source and carbon source to prepare a slurry. In the slurry, the molar ratio of Li, Mn, Fe, Ni and P elements is Li:Mn:Fe:Ni:P = 1.05:0.6:0.4:0.08:1, and the mass of carbon source is 10% of the total mass of lithium source, manganese source, iron source, nickel source, phosphorus source and carbon source.

[0090] S2. After spray drying the slurry obtained in step S1, sinter it at 750°C for 9 hours under a nitrogen atmosphere; grind and crush the sintered product to obtain the target material.

[0091] Comparative Example 3

[0092] This comparative example prepared a lithium manganese iron phosphate composite cathode material LiMn 0.6 Fe 0.4 Ti 0.08 PO4 / C (Ti-LMFP), designated as No. 7, has the following specific preparation steps:

[0093] S1. Using deionized water as the dispersion medium, a sand mill is used to uniformly mix lithium source, manganese source, iron source, titanium source, phosphorus source and carbon source to prepare a slurry. In the slurry, the molar ratio of Li, Mn, Fe, Ti and P elements is Li:Mn:Fe:Ti:P = 1.05:0.6:0.4:0.08:1, and the mass of carbon source is 10% of the total mass of lithium source, manganese source, iron source, titanium source, phosphorus source and carbon source.

[0094] S2. After spray drying the slurry obtained in step S1, sinter it at 750°C for 9 hours under a nitrogen atmosphere; grind and crush the sintered product to obtain the target material.

[0095] Physicochemical characterization was performed on the lithium iron phosphate composite cathode material No. 1N7 prepared in Example 1N4 and Comparative Example 1N3.

[0096] Figure 1 The image shows LiMn prepared in Example 2. 0.6 Fe 0.4 Ni 0.03 Ti 0.05 SEM image of PO4 / C. As can be seen from the electron microscope image, the Ni / Ti co-doped lithium manganese iron phosphate material is granular, and the outer layer of the particles is coated with a network-like thin film of carbon.

[0097] The content of each metal element was determined by ICP testing to obtain the proportion of metal elements in the finished material. It was found that the proportion of Li was slightly lower than the initial feed ratio, which may be due to the light weight of Li causing some lithium loss during the calcination process. XRD characterization showed that when x < 0.05, the prepared material was entirely pure lithium manganese iron phosphate, without the characteristic diffraction peaks of Ni or Ti impurities, indicating that Ni and Ti were successfully doped into the bulk phase of the material. Furthermore, the XRD results did not show graphite characteristic peaks, indicating that the coated carbon layer exists in an amorphous carbon form.

[0098] Using lithium manganese iron phosphate composite cathode materials (numbered 1N7) prepared in Example 1N4 and Comparative Example 1N3 respectively as cathode active materials, lithium-ion batteries were prepared according to the following method, and performance tests were performed. The test results are shown in Table 1 and 2. Figure 2 As shown.

[0099] 1. Preparation of the positive electrode sheet:

[0100] A composite cathode material of lithium manganese iron phosphate, polyvinylidene fluoride, and conductive carbon black were mixed at a mass ratio of 90:5:5. N-methylpyrrolidone was then added, and the mixture was stirred under vacuum until homogeneous to obtain a cathode slurry. The cathode slurry was uniformly coated onto a 13 μm thick aluminum foil, then air-dried at room temperature before being transferred to an oven for further drying. Following cold pressing and slitting, the cathode sheet was obtained.

[0101] 2. Preparation of the negative electrode sheet:

[0102] The negative electrode active materials graphite, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a mass ratio of 97:1:1:1. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain a negative electrode slurry. The negative electrode slurry was coated onto a copper foil with a thickness of 13 μm, and then dried at room temperature before being transferred to an oven for drying. After cold pressing and slitting, the negative electrode sheet was obtained.

[0103] 3. Preparation of electrolyte:

[0104] In an argon-filled glove box with a moisture content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed uniformly at a mass ratio of 3:5:2 to obtain a mixed solvent. Then, dried lithium hexafluorophosphate and the additive ethylene carbonate were added to the mixed solvent and mixed thoroughly to obtain the electrolyte. In the obtained electrolyte, based on a total electrolyte mass percentage of 100%, the mass percentage of lithium hexafluorophosphate was 12.5%, the mass percentage of the mixed solvent was 84.5%, and the mass percentage of the additive was 3%.

[0105] 4. Battery manufacturing:

[0106] The positive electrode, separator (8μm polyethylene film), and negative electrode are sequentially wound together, with the separator positioned between the positive and negative electrodes to act as a separator, resulting in a cylindrical bare cell. This cell is then placed in a circular casing, dried in a vacuum oven, injected with the electrolyte prepared above, and sealed to allow electrolyte formation, thus obtaining a lithium-ion battery.

[0107] 5. Battery performance test:

[0108] Under normal temperature conditions, the battery cycle performance and rate performance were tested using the following method.

[0109] Battery rate test: After activation at 0.1C for 3 cycles in an oven at 25℃, the battery was cycled at 1C, 2C, 3C, 5C, 7C, and 10C rates, and finally a 0.1C charge-discharge test was performed to test the battery stability.

[0110] Battery cycle performance test: In an oven at 25°C, perform 50 charge-discharge cycles at a current of 1C within a specified potential range, and record the discharge capacity of each cycle.

[0111] Table 1. Test results of material and battery electrochemical performance.

[0112]

[0113] Note: In Table 1, the 10C capacity retention rate is the discharge specific capacity retention rate at 10C rate relative to 1C rate, and the 1C cycle retention rate is the percentage of discharge specific capacity of the battery after 100 cycles at 25℃ relative to the first cycle.

[0114] From Table 1 and Figure 2 From this analysis, the following conclusions can be drawn:

[0115] Compared to LMFP, Ni-LMFP, and Ti-LMFP, lithium-ion batteries using materials numbered 1-4 as cathode active materials exhibit higher 1C discharge capacity, 10C capacity retention, and 1C cycle retention. Among these, lithium-ion batteries using material number 2 (Ni3Ti5-LMFP) as the cathode active material show the highest 1C discharge capacity, 10C capacity retention, and 1C cycle retention, along with the best battery capacity and cycle stability. This indicates that the Ni+Ti co-doping strategy is more beneficial for improving the capacity and cycle stability of lithium manganese iron phosphate (LFP) batteries compared to single Ni doping or single Ti doping. The main reason is that the Ni+Ti co-doping strategy can more effectively mitigate the energy density and capacity decay issues of LFP cathode materials, allowing LFP to better leverage its significant advantages of high energy density, good safety, and low cost, thereby improving the capacity and cycle stability of LFP batteries.

[0116] Comparing the electrochemical performance of lithium-ion batteries fabricated using materials numbered 2 to 4 as positive electrode active materials, it was found that the 1C discharge capacity, 10C capacity retention, and 1C cycle retention all increased with increasing Ti doping concentration. This indicates that, under the same Ni+Ti doping concentration, a higher Ti doping concentration is more advantageous in terms of capacity utilization and is more conducive to improving the capacity and cycle stability of lithium manganese iron phosphate batteries.

[0117] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A composite cathode material based on lithium iron phosphate manganese phosphate, characterized in that, Includes component A and component B; Component A is a Ni / Ti co-doped lithium manganese iron phosphate material, and the chemical formula of the Ni / Ti co-doped lithium manganese iron phosphate material is LiMn. 0.6(1-x-y) Fe 0.4(1-x-y) Ni x Ti y PO4, where 0 ≤ x ≤ 0.05, 0 ≤ y ≤ 0.05; Component B includes amorphous carbon.

2. The lithium iron phosphate composite cathode material according to claim 1, characterized in that: In the Ni / Ti co-doped lithium manganese iron phosphate material, the ratio of the sum of the molar contents of Ni and Ti to the sum of the molar contents of Mn and Fe is 0.06–0.08: 0.92–0.

94.

3. The lithium iron phosphate composite cathode material according to claim 1 or 2, characterized in that: In the Ni / Ti co-doped lithium manganese iron phosphate material, the molar ratio of Ni to Ti is 1:1 to 1.

6.

4. The lithium iron phosphate composite cathode material according to claim 1, characterized in that: Component B is a network-like thin film that coats component A; And / or, the mass percentage of component B in the lithium manganese iron phosphate composite cathode material is 1% to 2.5%.

5. A method for preparing a lithium iron phosphate composite cathode material, characterized in that, Includes the following steps: A slurry is prepared by mixing lithium, manganese, iron, nickel, titanium, phosphorus and carbon sources. The molar ratio of Li, Mn, Fe, Ni, Ti and P elements in the slurry is Li:Mn:Fe:Ni:Ti:P = 1.05:0.6(1-xy):0.4(1-xy):x:y:

1. The slurry was dried and then sintered to obtain the lithium iron phosphate composite cathode material.

6. The method for preparing the lithium iron phosphate composite cathode material according to claim 5, characterized in that: In the slurry, the carbon source mass is 8%N12% of the total mass of lithium source, manganese source, iron source, nickel source, titanium source, phosphorus source and carbon source.

7. The method for preparing the lithium iron phosphate composite cathode material according to claim 5 or 6, characterized in that: The lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, or lithium dihydrogen phosphate. And / or, the manganese source is selected from at least one of manganese oxalate, manganese carbonate, manganese tetroxide, manganese phosphate, manganese oxide, or manganese ammonium phosphate; And / or, the iron source is selected from at least one of ferrous oxalate, ferrous pyrophosphate, ferric phosphate, ferric oxide, or metallic iron; And / or, the nickel source is selected from at least one of nickel oxide, nickel hydroxide, or nickel tetroxide; And / or, the titanium source is selected from at least one of titanium dioxide, tetrabutyl titanate, or metatitanic acid; And / or, the phosphorus source is selected from at least one of iron phosphate, ammonium dihydrogen phosphate, lithium phosphate, or lithium dihydrogen phosphate; And / or, the carbon source is selected from at least one of glucose, polyethylene glycol, sucrose, citric acid, or graphite.

8. The method for preparing the lithium iron phosphate composite cathode material according to claim 5, characterized in that, Sintering is carried out under a protective gas atmosphere at a temperature of 650℃ to 850℃ for 6 hours to 12 hours.

9. A positive electrode sheet, characterized in that: It includes a positive electrode current collector and a positive electrode active material layer at least on one side of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, the positive electrode active material including the lithium manganese iron phosphate composite positive electrode material according to any one of claims 1 to 4, and / or the lithium manganese iron phosphate composite positive electrode material prepared by the method according to any one of claims 5 to 8.

10. A secondary battery, characterized in that: Includes the positive electrode sheet as described in claim 9.

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