Carbon-coated lithium iron manganese phosphate positive electrode material, preparation method thereof, positive electrode sheet and battery

Abstract

The application discloses a carbon-coated lithium manganese iron phosphate positive electrode material, a preparation method thereof, a positive electrode sheet and a battery. The preparation method of the carbon-coated lithium manganese iron phosphate positive electrode material comprises the following steps: obtaining a lithium manganese iron phosphate material containing vacancies; mixing a carbon source containing a lone pair of electrons with the lithium manganese iron phosphate material containing vacancies, and performing heat treatment under a non-active atmosphere to obtain the carbon-coated positive electrode material. According to the embodiment of the application, the preparation method is simple in process, can improve the uniformity of carbon coating, and can improve the electronic conductivity, discharge capacity and cycle performance of the positive electrode material.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, and particularly relates to a carbon-coated lithium manganese iron phosphate cathode material, its preparation method, cathode sheet, and battery. Background Technology

[0002] Because phosphate-based lithium-ion battery materials have low intrinsic conductivity, they are modified using methods such as carbon coating, particle refinement, and metal doping. Among these methods, surface carbon coating is the most common modification in the field of new energy materials. The principle is that during high-temperature sintering, carbon source materials undergo a carbonization reaction, resulting in structural changes and a certain degree of graphitization. This improves the conductivity of the material and provides a stable chemical and electrochemical reaction interface.

[0003] However, current carbon coating methods suffer from problems such as poor coating uniformity, inconsistent carbon layer thickness, and poor electronic conductivity. Therefore, achieving effective carbon coating is of particular importance. Summary of the Invention

[0004] This application provides a carbon-coated lithium manganese iron phosphate cathode material, its preparation method, cathode sheet, and battery. The preparation method is simple and can improve the uniformity of carbon coating, as well as the electronic conductivity, discharge capacity, and cycle performance of the cathode material.

[0005] In a first aspect, embodiments of this application provide a method for preparing a carbon-coated lithium manganese iron phosphate cathode material, comprising:

[0006] Lithium iron manganese phosphate material containing vacant sites was obtained;

[0007] A carbon source containing lone pairs of electrons is mixed with lithium iron phosphate material containing vacancies, and then heat-treated in an inactive atmosphere to obtain a carbon-coated cathode material.

[0008] In any embodiment of this application, it includes:

[0009] Materials containing iron, phosphorus, manganese, lithium and solvent are dispersed according to a preset molar ratio to obtain a mixture. The mixture is then evaporated to dryness and heat-treated in an atmosphere containing at least an inactive gas to obtain lithium manganese iron phosphate material containing vacancies.

[0010] A carbon source containing lone pairs of electrons is mixed with lithium iron phosphate material containing vacancies, and then heat-treated in an inactive atmosphere to obtain a carbon-coated cathode material.

[0011] In any embodiment of this application, in the step of obtaining lithium manganese iron phosphate material containing vacant sites,

[0012] The amount of lithium source added is calculated according to the number of moles of lithium element, denoted as x; the amount of iron source added is calculated according to the number of moles of iron element, denoted as y; and the amount of manganese source added is calculated according to the number of moles of manganese element, denoted as z. The preset molar ratio is x:(y+z)=1:(0.95-1).

[0013] In any embodiment of this application, the atmosphere is an inactive gas, which includes at least one of nitrogen, helium, argon and neon.

[0014] In any embodiment of this application, the heat treatment temperature is 400-600℃ and the holding time is 6-12h.

[0015] In any embodiment of this application, the heating rate of the heat treatment is 5-20°C / min.

[0016] In any embodiment of this application, in the step of obtaining lithium manganese iron phosphate material containing vacant sites,

[0017] The amount of lithium source added is calculated based on the number of moles of lithium, denoted as x; the amount of iron source added is calculated based on the number of moles of iron, denoted as y; and the amount of manganese source added is calculated based on the number of moles of manganese, denoted as z. The preset molar ratio is x:(y+z)=1:1.

[0018] In any embodiment of this application, the atmosphere is a mixture of inactive gas and reducing gas, wherein the volume of inactive gas is 50%-90% and the volume of reducing gas is 10%-50%.

[0019] In any embodiment of this application, the inactive gas includes at least one of nitrogen, helium, argon and neon, and the reducing gas includes at least one of hydrogen, carbon monoxide, methane and hydrogen sulfide.

[0020] In any embodiment of this application, the heat treatment temperature is 400-600℃ and the holding time is 6-12h.

[0021] In any embodiment of this application, the heating rate of the heat treatment is 5-20°C / min.

[0022] In any embodiment of this application, in the step of mixing a carbon source containing lone pairs of electrons with a lithium manganese iron phosphate material containing vacancies and performing heat treatment under an inactive atmosphere,

[0023] Carbon sources containing lone pairs of electrons include at least one of thiols, thiophenols, thioethers, amines, nitrogen heterocycles, nitriles, sulfoxides, and nitro compounds.

[0024] In any embodiment of this application, the carbon source containing lone pairs of electrons accounts for 0.5%-5% of the lithium manganese iron phosphate material containing vacancies.

[0025] In any embodiment of this application, the carbon source containing lone pairs of electrons accounts for 2%-3% of the lithium manganese iron phosphate material containing vacancies.

[0026] In any embodiment of this application, the inactive atmosphere is independently selected from at least one of nitrogen, helium, argon and neon.

[0027] In any embodiment of this application, the heat treatment temperature is 600-800℃ and the holding time is 4-8h.

[0028] In any embodiment of this application, the solvent is independently selected from at least one of water, ethanol, and acetone.

[0029] In any embodiment of this application, the lithium source includes at least one of Li2O, Li2CO3, LiH2PO4, LiOH·H2O, CH3COOLi, and LiNO3.

[0030] In any embodiment of this application, the iron source includes at least one of FeCl3, Fe(NO3)3, Fe2O3 and FeSO4·7H2O.

[0031] In any embodiment of this application, the phosphorus source includes at least one of (NH4)3PO4, LiH2PO4, and H3PO4.

[0032] In any embodiment of this application, the manganese source includes at least one of MnO2, Mn(NO3)2, MnSO4 and Mn3(PO4)2·3H2O.

[0033] In any embodiment of this application, the lithium manganese iron phosphate material containing vacant sites also includes doping elements.

[0034] In any embodiment of this application, the doping element includes at least one of Mg, Al, Cu, Ni, Ti, Zr, V, Co and Mo.

[0035] Secondly, embodiments of this application provide a carbon-coated lithium manganese iron phosphate cathode material, obtained using the above-described preparation method.

[0036] Thirdly, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer includes a carbon-coated lithium manganese iron phosphate positive electrode material prepared by the above-described preparation method or the above-described carbon-coated lithium manganese iron phosphate positive electrode material.

[0037] Fourthly, embodiments of this application provide a battery including the aforementioned positive electrode sheet.

[0038] This application discloses a carbon-coated lithium manganese iron phosphate cathode material, its preparation method, cathode electrode, and battery. The vacancies in the lithium manganese iron phosphate material have a strong specific adsorption effect on carbon sources containing lone pairs of electrons, which can improve the uniformity of carbon coating. Moreover, this special connection can enhance the contact density between LFMP (lithium manganese iron phosphate) and the carbon layer, thereby improving electronic conductivity. Attached Figure Description

[0039] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram illustrating the specific adsorption of vacancies with carbon sources containing lone pairs of electrons in this application.

[0041] Figure 2 The images show the electrochemical impedance spectroscopy (EIS) spectra of the cathode materials in Example 1 and Comparative Example 1.

[0042] Figure 3 This is a scanning electron microscope image of the carbon-coated lithium manganese iron phosphate cathode material in Example 1.

[0043] Figure 4 This is a scanning electron microscope image of the carbon-coated lithium manganese iron phosphate cathode material in Comparative Example 1. Detailed Implementation

[0044] To better understand the above-mentioned objectives, features, and advantages of this application, the solution of this application will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0045] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this application may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of this application, and not all embodiments.

[0046] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the carbon-coated lithium manganese iron phosphate cathode material, its preparation method, cathode sheet, and battery. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0047] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0049] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0050] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0051] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0052] Unless otherwise specified, this application uses conventional testing methods or testing methods recommended by the instrument.

[0053] It should be noted that, in this document, the terms "coating layer" or "coating" refer to a material layer coating a material such as lithium manganese iron phosphate. This material layer may completely or partially coat the material. The use of "coating layer" is for ease of description only and is not intended to limit this application. Furthermore, each coating layer may be a complete or partial coating.

[0054] Contact density refers to the degree of contact or adhesion between the carbon layer and the outer surface of pure lithium manganese iron phosphate. The higher the contact density, the better the adhesion of the carbon layer and the faster the electron transport.

[0055] The uniformity of carbon coating is influenced by various factors, including the nature of the carbon source, reaction conditions, the type and concentration of surfactants, and metal catalysts. Furthermore, the nucleation and growth mechanisms during the carbon coating process can also lead to non-uniform carbon coating. Nucleation refers to the focusing process of carbon atoms on the substrate surface, while growth refers to the outward expansion of carbon atoms from the nucleation point to form a carbon coating layer. These two processes can be affected by factors such as substrate surface energy, the carbon source supply rate, and temperature, thus potentially leading to non-uniform carbon coating. In addition, the reaction kinetics during the carbon coating process can also affect the uniformity of carbon coating. For example, local concentration differences or mass transfer limitations during the reaction may lead to uneven carbon coating.

[0056] To address this issue, this application addresses the problem by controlling the molar ratio of lithium, iron, and manganese to create an imbalance in the main composition, thereby generating vacancies on the lithium manganese iron phosphate material. Alternatively, during the heat treatment of the precursor mixture, the atmosphere is controlled to be a mixture of specific reducing and inactive gases, also creating vacancies on the lithium manganese iron phosphate material. Furthermore, by selecting a carbon source containing specific functional groups, i.e., a carbon source containing lone pairs of electrons, the vacant lithium manganese iron phosphate material is carbon-coated. Through the specific adsorption of lone pairs of electrons by the vacancies, the uniformity of the carbon coating is improved. This special connection enhances the contact density between LFMP and the carbon layer, thereby increasing electronic conductivity.

[0057] Preparation method of carbon-coated lithium manganese iron phosphate cathode material

[0058] This application provides a method for preparing a carbon-coated lithium manganese iron phosphate cathode material, including:

[0059] Lithium iron manganese phosphate material containing vacant sites was obtained;

[0060] A carbon source containing lone pairs of electrons is mixed with lithium iron phosphate material containing vacancies, and then heat-treated in an inactive atmosphere to obtain a carbon-coated cathode material.

[0061] Because of energy fluctuations, some atoms will always have enough energy to overcome the binding force of surrounding atoms, and may migrate to other places. This will create nodes at the original equilibrium positions, called vacancies.

[0062] Lithium manganese iron phosphate (LiFePO4) materials containing vacancies refer to materials containing at least one of the following: Li, Mn, Fe, P, and O. The concentration of vacancies can be adjusted from 0.05% to 2.50% by methods such as reducing atmosphere, main stoichiometric imbalance, and dopant element dosage. Vacancies can be formed by controlling the molar ratios of manganese, iron, and lithium in the raw materials to create a main stoichiometric imbalance; or by controlling the atmosphere during the heat treatment of LiFePO4 materials to a mixture of specific reducing and inactive gases. Vacancies formed by controlling the main stoichiometric imbalance are mainly surface vacancies and bulk vacancies. Compared to the former, vacancies formed by controlling a mixture of specific reducing and inactive gases are more likely to form, and these are surface vacancies. Among different vacancies, surface vacancies are more likely to pair with lone pairs of electrons, thereby forming a dense coating layer.

[0063] Lone pairs of electrons refer to the non-bonded electrons that exist in the outermost electron shell of atoms in a molecule, besides the bonding electrons used to form covalent bonds. These unbonded valence electron pairs are called lone pairs. They are called "lone" because they are not bonded, and "pair" because two electrons with opposite spins will pair up. Lone pairs of electrons are electron pairs in molecules or ions that do not share a valence shell. The presence and distribution of lone pairs of electrons in molecules affect the molecular shape, dipole moment, bond length, bond energy, etc., with a particularly significant impact on molecules composed of light atoms.

[0064] Because vacancies have a strong adsorption effect on lone pair electrons, they can improve the uniformity of carbon coating, and this special connection can enhance the contact density between LFMP and the carbon layer and improve electronic conductivity.

[0065] In some embodiments, including:

[0066] Materials containing iron, phosphorus, manganese, lithium and solvent are dispersed according to a preset molar ratio to obtain a mixture. The mixture is then evaporated to dryness and heat-treated in an atmosphere containing at least an inactive gas to obtain lithium manganese iron phosphate material containing vacancies.

[0067] A carbon source containing lone pairs of electrons is mixed with lithium iron phosphate material containing vacancies, and then heat-treated in an inactive atmosphere to obtain a carbon-coated cathode material.

[0068] The preset molar ratio is the molar ratio between manganese, iron and lithium. The preset molar ratio can be 1:(0.95-1), which is the case of imbalance of the main components, or it can be 1:1, which is the case of no imbalance of the main components.

[0069] An atmosphere containing at least an inert gas can be an atmosphere containing only an inert gas or a mixture of an inert gas and a reducing gas.

[0070] Different preset molar ratios can be combined with different atmospheres containing at least an inert gas to form new solutions. For example, in some embodiments, the preset molar ratio is 1:(0.95-1), and the atmosphere containing at least an inert gas is a mixed atmosphere containing both an inert gas and a reducing gas. In some embodiments, the preset molar ratio is 1:(0.95-1), and the atmosphere containing at least an inert gas is an atmosphere containing only an inert gas. In some embodiments, the preset molar ratio is 1:1, and the atmosphere containing at least an inert gas is an atmosphere containing only an inert gas. In some embodiments, the preset molar ratio is 1:1, and the atmosphere containing at least an inert gas is a mixed atmosphere containing both an inert gas and a reducing gas.

[0071] In some embodiments, in the step of obtaining lithium manganese iron phosphate material containing vacant sites,

[0072] The amount of lithium source added is calculated based on the molar number of lithium elements, denoted as x; the amount of iron source added is calculated based on the molar number of iron elements, denoted as y; and the amount of manganese source added is calculated based on the molar number of manganese elements, denoted as z. The preset molar ratio is x:(y+z)=1:(0.95-1). This can cause an imbalance in the main proportions, thereby creating vacancies in the lithium manganese iron phosphate material. If (y+z) is less than 0.95, it will lead to an imbalance in the proportions, affecting performance, and in severe cases, impurity phases will appear.

[0073] In some embodiments, in the step of obtaining lithium manganese iron phosphate material containing vacancies, the heat treatment temperature is 400-600°C and the holding time is 6-12 hours.

[0074] In some embodiments, the heating rate of the heat treatment is 5-20°C / min.

[0075] In some embodiments, in the step of obtaining lithium manganese iron phosphate material containing vacant sites,

[0076] The amount of lithium source added is calculated based on the number of moles of lithium, denoted as x; the amount of iron source added is calculated based on the number of moles of iron, denoted as y; and the amount of manganese source added is calculated based on the number of moles of manganese, denoted as z. The preset molar ratio is x:(y+z)=1:1.

[0077] In some embodiments, the atmosphere is a mixture of an inactive gas and a reducing gas, with the inactive gas comprising 50%-90% of the volume and the reducing gas comprising 10%-50%. In a mixed atmosphere containing a reducing gas, such as a mixed atmosphere containing hydrogen, H2 reacts with oxygen or lithium atoms on the surface of lithium manganese iron phosphate (approximately 1-3 nm) to generate H2O. This, in turn, consumes oxygen or lithium atoms in the lithium manganese iron phosphate, creating vacancies in the lithium manganese iron phosphate material.

[0078] The volume of reducing gas is 10%-50%. Within this range, vacancies can be formed without forming impurity phases; if it is below this range, vacancies cannot be formed; if it is above this range, it is too dangerous and too much manganese, iron, and oxygen are easily reduced, forming impurity phases.

[0079] In some embodiments, the heat treatment temperature is 400-600℃, and the holding time is 6-12h.

[0080] In some embodiments, the heating rate of the heat treatment is 5-20°C / min.

[0081] In some embodiments, in the step of mixing a carbon source containing lone pairs of electrons with a lithium manganese iron phosphate material containing vacancies and performing heat treatment under an inactive atmosphere,

[0082] Carbon sources containing lone pairs of electrons include at least one of thiols, thiophenols, thioethers, amines, nitrogen heterocycles, nitriles, sulfoxides, and nitro compounds. Carbon sources containing lone pairs of electrons contain functional groups such as -C=O, -C=N, -C=S, -C=S, and -S=O.

[0083] In some embodiments, the carbon source containing lone pairs of electrons accounts for 0.5%-5% of the vacant lithium manganese iron phosphate material. Preferably, the proportion is 2%-3%.

[0084] In some embodiments, in the step of mixing a carbon source containing lone pairs of electrons with a lithium manganese iron phosphate material containing vacancies and performing heat treatment under an inactive atmosphere,

[0085] The heat treatment temperature is 600-800℃, and the holding time is 4-8h.

[0086] In some embodiments, the solvent is independently selected from at least one of water, ethanol, and acetone.

[0087] In some embodiments, the lithium manganese iron phosphate material containing vacancies further includes doping elements. The lithium manganese iron phosphate material can be single-doped, double-doped, or multi-doped to create vacancies. The amount of doping element added (by weight) is 0.2%-0.4% of the carbon-coated lithium manganese iron phosphate cathode material. This can reduce the amount of lithium added when the main coordination of manganese, iron, and lithium is imbalanced, thereby saving production costs.

[0088] Carbon-coated lithium manganese iron phosphate cathode material

[0089] Lithium manganese iron phosphate (LFP) is formed by iron doping on modified lithium manganese phosphate. Like lithium iron phosphate, it has an olivine structure, exhibiting structural stability and a high voltage plateau, making it a promising new cathode material. However, LFP suffers from low conductivity. Structurally, LFP lacks a continuous FeO6 (MnO6) octahedral network; instead, it is connected by PO4 tetrahedra. This prevents the formation of a continuous Co-O-Co structure like lithium cobalt oxide, restricting lithium movement within one-dimensional channels and resulting in poor conductivity, consequently leading to poor high-rate charge / discharge performance.

[0090] This application improves the carbon coating method to make the carbon coating layer uniform, thereby improving the electronic conductivity, discharge capacity and cycle performance of lithium manganese iron phosphate cathode material.

[0091]

Positive Electrode

[0092] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer includes the carbon-coated lithium manganese iron phosphate positive electrode material described above or the carbon-coated lithium manganese iron phosphate positive electrode material prepared by the above preparation method. For example, the positive current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0093] In some embodiments, the positive electrode film layer includes the carbon-coated lithium manganese iron phosphate positive electrode material obtained by the preparation method of the first aspect of this application and / or the carbon-coated lithium manganese iron phosphate positive electrode material of the second aspect of this application. However, the positive electrode film layer used in the positive electrode sheet of this application does not exclude other positive electrode active materials besides the carbon-coated lithium manganese iron phosphate positive electrode material obtained by the above preparation method and / or the above-mentioned carbon-coated lithium manganese iron phosphate positive electrode material. For example, other positive electrode active materials can be positive electrode active materials known in the art for lithium-ion batteries, including but not limited to LiCoO2, lithium manganese oxide, ternary positive electrode materials, etc. These other positive electrode film layers can be used alone or in combination of two or more.

[0094] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0095] In some embodiments, this application does not impose any particular limitation on the type of positive electrode binder. For example, the positive electrode binder may include at least one of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0096] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of a metal material may be at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. An example of a polymer substrate may be polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0097] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0098] The positive electrode sheet does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of this application further includes a conductive undercoating layer (e.g., composed of a conductive agent and a binder) sandwiched between the positive current collector and the positive electrode film layer and disposed on the surface of the positive current collector. In other embodiments, the positive electrode sheet of this application further includes a protective layer covering the surface of the positive electrode film layer.

[0099]

Battery

[0100] This application provides a battery including the above-described positive electrode.

[0101] In some embodiments, the battery is a lithium-ion battery, including a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process, lithium ions repeatedly insert and extract between the positive and negative electrodes, while the electrolyte acts as a conductor between them. The battery of this application can be applied to energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in various fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0102] Comparative Example 1

[0103] (1) Weigh 1 mol LiNO3, 0.5 mol Fe(NO3)3, 1 mol NH4H2PO4, 0.5 mol Mn(NO3)2 and 500 mL of water, mix them evenly to form a mixture, heat and stir the mixture until the water evaporates to dryness, and obtain a solid precursor material.

[0104] (2) The solid precursor material obtained in step (1) is pounded into powder, spray-dried, and then placed in a tube furnace. Under a nitrogen atmosphere of 100% purity, the temperature is increased to 600℃ at 5℃ / min and then kept at a constant temperature for 10h.

[0105] (3) Add LiMn in step (2) 0.5 Fe 0.5 PO4 (product LMFP) was mixed with 5% by weight of PVP (polyvinylpyrrolidone) powder, and then heated to 700℃ at 5℃ / min under a nitrogen atmosphere of 100% purity, followed by constant temperature treatment for 5h to obtain LiMn. 0.5 Fe 0.5 PO4.

[0106] Example 1

[0107] The experimental procedure was the same as in Comparative Example 1, except that the nitrogen atmosphere in step (3) was changed to a hydrogen / nitrogen mixed atmosphere, in which the volume percentage of hydrogen was 10% and the volume percentage of nitrogen was 90%, to obtain LiMn. 0.5 Fe 0.5 PO3.95, Li 0.95 Mn 0.5 Fe 0.5 PO4.

[0108] Example 2

[0109] The experimental procedure was the same as in Comparative Example 1, except that the molar ratio of LiNO3, Fe(NO3)3, and Mn(NO3)2 in step (1) was changed to LiNO3:(Fe(NO3)3+Mn(NO3)2)=1:0.95, resulting in LiMn 0.475 Fe 0.475 PO4.

[0110] Example 3

[0111] The experimental procedure was the same as in Comparative Example 1, except that magnesium nitrate was added in step (1) in an additional amount of 0.03 mol of magnesium ions (i.e., a doping amount of 0.3%), resulting in LiMn. 0.5 Fe 0.5 Mg 0.003 PO4.

[0112] Example 4

[0113] The experimental procedure was the same as in Example 3, except that magnesium nitrate in step (1) was replaced with aluminum nitrate, resulting in LiMn. 0.5 Fe 0.5 Al 0.003 PO4.

[0114] Example 5

[0115] The experimental procedure was the same as in Example 3, except that magnesium nitrate in step (1) was replaced with nickel acetate, resulting in LiMn. 0.5 Fe 0.5 Ni 0.003 PO4.

[0116] Example 6

[0117] The experimental procedure was the same as in Example 3, except that magnesium nitrate in step (1) was replaced with vanadium trioxide, resulting in LiMn. 0.5 Fe 0.5 V 0.003 PO4.

[0118] Example 7

[0119] The experimental procedure was the same as in Example 3, except that magnesium nitrate in step (1) was replaced with vanadium pentoxide, resulting in LiMn. 0.5 Fe 0.5 V 0.003 PO4.

[0120] Example 8

[0121] The experimental procedure was the same as in Example 3, except that magnesium nitrate in step (1) was replaced with molybdenum trioxide, resulting in LiMn. 0.5 Fe 0.5 Mo 0.003 PO4.

[0122] Example 9

[0123] The experimental procedure was the same as in Example 3, except that magnesium nitrate in step (1) was replaced with molybdenum trioxide to obtain LiMn. 0.5 Fe 0.5 Mo 0.003 PO4.

[0124] Example 10

[0125] The experimental procedure was the same as in Example 3, except that magnesium nitrate in step (1) was replaced with titanium dioxide (0.15% doping) and vanadium trioxide (0.15% doping) to obtain LiMn. 0.5 Fe 0.5 Ti 0.0015 V 0.0015 PO4.

[0126] Example 11

[0127] The experimental procedure was the same as in Example 3, except that magnesium nitrate in step (1) was replaced with titanium dioxide (0.15% doping) and cobalt nitrate (0.15% doping), to obtain LiMn. 0.5 Fe 0.5 Ti 0.0015 Co 0.0015 PO4.

[0128] Example 12

[0129] The experimental procedure was the same as in Example 3, except that magnesium nitrate in step (1) was replaced with titanium dioxide (0.15% doping) and zirconium nitrate (0.15% doping) to obtain LiMn. 0.5 Fe 0.5 Ti 0.0015 Zr 0.0015 PO4.

[0130] Example 13

[0131] The experimental procedure was the same as in Example 3, except that magnesium nitrate in step (1) was replaced with zirconium nitrate (0.15% doping) and molybdenum trioxide (0.15% doping), to obtain LiMn. 0.5 Fe 0.5 Mo 0.0015 Zr 0.0015 PO4.

[0132] Example 14

[0133] The experimental procedure was the same as in Example 3, except that magnesium nitrate in step (1) was replaced with cobalt nitrate (0.15% doping) and vanadium pentoxide (0.15% doping), to obtain LiMn. 0.5 Fe 0.5 V 0.0015 Co 0.0015 PO4.

[0134] Comparative Example 2

[0135] The experimental procedure was the same as in Example 1, except that PVP in step (3) was replaced with hexadecane to obtain LiMn. 0.5 Fe 0.5 PO3.95、 Li 0.95 Mn 0.5 Fe 0.5 PO4.

[0136]

[0137]

[0138] The electronic conductivity of carbon-coated lithium iron manganese phosphate obtained in Example 1 and Comparative Example 1 was measured using electrochemical impedance spectroscopy.

[0139] like Figure 2 As shown, the charge transfer resistance of Comparative Example 1 is significantly greater than that of Example 1. This indicates that the coating method of the adsorption groups that selectively capture lone pair electrons of the carbon source, as described in this application, can greatly increase the coating density between the carbon layer and the lithium manganese iron phosphate bulk, thereby enhancing the electron conductivity.

[0140] The morphology of carbon-coated lithium iron manganese phosphate obtained in Example 1 and Comparative Example 1 was characterized using transmission electron scanning microscopy (TEM), and the results are as follows: Figure 3 , 4 As shown.

[0141] Depend on Figure 3 , 4 It can be seen that the coating uniformity of Comparative Example 1 is significantly worse than that of Example 1. This is mainly due to the selective coating of carbon source and bulk vacancy.

[0142] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A method for preparing a carbon-coated lithium manganese iron phosphate cathode material, characterized in that, include: A lithium manganese iron phosphate material containing vacancies was obtained, wherein the vacancies include at least one of Li, Mn, Fe, P, and O vacancies, and the concentration of vacancies in the lithium manganese iron phosphate material containing vacancies is 0.05%-2.50%; A carbon source containing lone pairs of electrons is mixed with the lithium manganese iron phosphate material containing vacancies, and then heat-treated under an inactive atmosphere to obtain the carbon-coated cathode material. The carbon source containing lone pairs of electrons accounts for 0.5%-5% of the mass of the lithium manganese iron phosphate material containing vacancies.

2. The preparation method according to claim 1, characterized in that, include: Materials containing iron, phosphorus, manganese, lithium and solvent are dispersed according to a preset molar ratio to obtain a mixture. The mixture is then evaporated to dryness and heat-treated in an atmosphere containing at least an inactive gas to obtain the lithium manganese iron phosphate material containing vacancies. A carbon source containing lone pairs of electrons is mixed with the lithium manganese iron phosphate material containing vacancies, and then heat-treated under an inactive atmosphere to obtain the carbon-coated cathode material.

3. The preparation method according to claim 2, characterized in that, In the step of obtaining lithium manganese iron phosphate material containing vacant sites, The amount of lithium source added is calculated according to the number of moles of lithium, denoted as x; the amount of iron source added is calculated according to the number of moles of iron, denoted as y; and the amount of manganese source added is calculated according to the number of moles of manganese, denoted as z. The preset molar ratio x:(y+z)=1:(0.95-1). And / or, the atmosphere is an inactive gas, which includes at least one of nitrogen, helium, argon and neon; And / or, the heat treatment temperature is 400-600 ℃, and the holding time is 6-12 h; And / or, the heating rate of the heat treatment is 5-20 °C / min.

4. The preparation method according to claim 2, characterized in that, In the step of obtaining lithium manganese iron phosphate material containing vacant sites, The amount of lithium source added is calculated according to the number of moles of lithium element, denoted as x; the amount of iron source added is calculated according to the number of moles of iron element, denoted as y; the amount of manganese source added is calculated according to the number of moles of manganese element, denoted as z; and the preset molar ratio x:(y+z)=1:

1. And / or, the atmosphere is a mixture of inactive gas and reducing gas, wherein the volume of inactive gas is 50%-90% and the volume of reducing gas is 10%-50%; And / or, the heat treatment temperature is 400-600 ℃, and the holding time is 6-12 h; And / or, the heating rate of the heat treatment is 5-20 °C / min.

5. The preparation method according to claim 4, characterized in that, In the step of obtaining lithium manganese iron phosphate material containing vacant sites, The inactive gas includes at least one of nitrogen, helium, argon and neon, and the reducing gas includes at least one of hydrogen, carbon monoxide, methane and hydrogen sulfide.

6. The preparation method according to claim 1 or 2, characterized in that, In the step of mixing a carbon source containing lone pairs of electrons with the lithium manganese iron phosphate material containing vacancies and performing heat treatment under an inactive atmosphere, The carbon source containing lone pairs of electrons includes at least one of thiols, thiophenols, thioethers, amines, nitrogen heterocycles, nitriles, sulfoxides, and nitro compounds. And / or, the inactive atmosphere is independently selected from at least one of nitrogen, helium, argon and neon; And / or, the heat treatment temperature is 600-800 ℃, and the holding time is 4-8 h.

7. The preparation method according to claim 6, characterized in that, The carbon source containing lone pairs of electrons accounts for 2%-3% of the vacant lithium manganese iron phosphate material.

8. The preparation method according to claim 2, characterized in that, The solvent is independently selected from at least one of water, ethanol, and acetone; And / or, the lithium source includes at least one of Li2O, Li2CO3, LiH2PO4, LiOH·H2O, CH3COOLi and LiNO3; And / or, the iron source includes at least one of FeCl3, Fe(NO3)3, Fe2O3 and FeSO4·7H2O; And / or, the phosphorus source includes at least one of (NH4)3PO4, LiH2PO4 and H3PO4; And / or, the manganese source includes at least one of MnO2, Mn(NO3)2, MnSO4 and Mn3(PO4)2·3H2O.

9. The preparation method according to claim 1 or 2, characterized in that, The lithium manganese iron phosphate material containing vacancies also includes doping elements.

10. The preparation method according to claim 9, characterized in that, The doping element includes at least one of Mg, Al, Cu, Ni, Ti, Zr, V, Co and Mo.

11. A carbon-coated lithium manganese iron phosphate cathode material, characterized in that, It is obtained by the preparation method according to any one of claims 1-10.

12. A positive electrode sheet, comprising a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector, characterized in that, The positive electrode film layer includes a carbon-coated lithium manganese iron phosphate positive electrode material prepared by any one of the preparation methods of claims 1-10 or the carbon-coated lithium manganese iron phosphate positive electrode material of claim 11.

13. A battery, characterized in that, Includes the positive electrode sheet as described in claim 12.

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