Modified lithium iron phosphate cathode material and preparation method and application thereof

Abstract

The present application discloses a modified lithium iron phosphate cathode material and its preparation method and application. A modified lithium iron phosphate cathode material, the chemical expression of the modified lithium iron phosphate cathode material is Li 1‑x Na x Fe 1‑y Ti y PO 4‑z Cl z / C, wherein Na is doped at the Li position, Ti is doped at the Fe position, Cl is doped at the O position, and 0.002≤x≤0.004, 0.002≤y≤0.004, 0.002≤z≤0.004, and the carbon content is 1.0wt%-2.0wt%. According to the embodiments of the present application, the electrochemical performance of the modified lithium iron phosphate positive electrode material can be improved, so that it has high energy density and high power density.

Description

Technical Field

[0001] The present invention relates to lithium-ion battery technology, and more particularly to a modified lithium iron phosphate cathode material, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium iron phosphate (LFP) cathode material has rapidly developed into a very important lithium-ion battery cathode material due to its many advantages, including high safety, long cycle life, low cost, abundant resources, environmental friendliness, and stable operating voltage. It has been widely used in communication base stations, energy storage, and power vehicles. In recent years, with the rapid development of the new energy vehicle industry, the demand for lithium-ion power batteries has continued to increase. Among them, the proportion of power battery installed capacity using LFP as the cathode material has also been increasing, resulting in a rapid growth momentum in the LFP cathode material market.

[0003] However, compared with ternary positive electrode materials, the energy density and compaction density of LFP positive electrode materials are relatively low. At the same time, the lower lithium ion diffusion and electronic conductivity make the rate performance of LFP positive electrode materials poor, which greatly limits its commercial application extension in the field of high-rate lithium-ion batteries. Summary of the Invention

[0004] The embodiments of the present application provide a modified lithium iron phosphate positive electrode material and a preparation method and application thereof, which can improve the electrochemical performance of the modified lithium iron phosphate positive electrode material so that it has high energy density and high power density.

[0005] In a first aspect, an embodiment of the present application provides a modified lithium iron phosphate positive electrode material.

[0006] A modified lithium iron phosphate cathode material, the chemical expression of the modified lithium iron phosphate cathode material is Li 1- x Na x Fe 1-y Ti y PO 4-z Cl z / C, wherein Na is doped into the Li position, Ti is doped into the Fe position, Cl is doped into the O position, C is a coating layer, and 0.002≤x≤0.004, 0.002≤y≤0.004, 0.002≤z≤0.004, and the carbon content is 1.0wt%-2.0wt%.

[0007] In any embodiment of the present application, the average particle size of the modified lithium iron phosphate positive electrode material is 0.3-0.4 μm.

[0008] In a second aspect, an embodiment of the present application provides a method for preparing a modified lithium iron phosphate positive electrode material.

[0009] The preparation method of the modified lithium iron phosphate positive electrode material comprises:

[0010] Mixing materials containing phosphate, iron source, lithium source, sodium source, titanium source, chlorine source, carbon source and solvent to obtain a slurry;

[0011] The slurry is spray-dried to obtain a powder spray material;

[0012] The powder spray material is heat-treated under preset conditions to obtain a modified lithium iron phosphate positive electrode material;

[0013] The lithium source, sodium source, iron source, titanium source, phosphate and chlorine source are mixed according to the element molar ratio of Li:Na:Fe:Ti:O:Cl=1-x:x:1-y:y:4-z:z, wherein 0.002≤x≤0.004, 0.002≤y≤0.004, and 0.002≤z≤0.004.

[0014] In any embodiment of the present application, in the step of mixing materials containing phosphate, iron source, lithium source, sodium source, titanium source, chlorine source, carbon source and solvent, the carbon source includes at least one of glucose, sucrose, citric acid and polyethylene glycol.

[0015] In any embodiment of the present application, in the step of mixing the materials containing phosphate, iron source, lithium source, sodium source, titanium source, chlorine source, carbon source and solvent, the mixing includes ball milling and / or sand milling.

[0016] In any embodiment of the present application, the phosphate includes at least one of ferric phosphate, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate.

[0017] In any embodiment of the present application, the iron source includes at least one of ferric phosphate, ferric nitrate, ferric chloride, and ferrous sulfate.

[0018] In any embodiment of the present application, the lithium source includes at least one of lithium carbonate, lithium dihydrogen phosphate, and lithium hydroxide.

[0019] In any embodiment of the present application, the sodium source includes at least one of sodium chloride, sodium carbonate, sodium bicarbonate, sodium sulfate, and sodium dihydrogen phosphate.

[0020] In any embodiment of the present application, the titanium source includes at least one of titanium dioxide, titanyl sulfate, titanium tetrachloride, and tetrabutyl titanate.

[0021] In any embodiment of the present application, the chlorine source includes at least one of sodium chloride and ammonium chloride.

[0022] In any embodiment of the present application, the solvent includes at least one of water, ethanol, and acetone.

[0023] In any embodiment of the present application, in the step of spray-drying the slurry, the atomization frequency during the spray-drying process is 40-100 Hz.

[0024] In any embodiment of the present application, the heated air inlet temperature during the spray drying process is 120-320°C.

[0025] In any embodiment of the present application, the outlet temperature of the heated air during the spray drying process is 80-240°C.

[0026] In any embodiment of the present application, in the step of subjecting the powder spray material to heat treatment under preset conditions, the heat treatment is performed in an inert gas, and the inert gas includes at least one of nitrogen, argon, neon, and helium.

[0027] In any embodiment of the present application, the heat treatment includes pre-sintering and sintering.

[0028] In any embodiment of the present application, the pre-sintering temperature is 300-600° C., and the pre-sintering time is 2-4 hours.

[0029] In any embodiment of the present application, the sintering temperature is 600-800° C., and the sintering time is 6-16 hours.

[0030] In a third aspect, an embodiment of the present application provides a positive electrode plate.

[0031] A positive electrode plate comprises a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the modified lithium iron phosphate positive electrode material or the modified lithium iron phosphate positive electrode material obtained by the above-mentioned preparation method.

[0032] In a fourth aspect, an embodiment of the present application provides a battery.

[0033] A battery comprises the above-mentioned positive electrode plate.

[0034] In the modified lithium iron phosphate cathode material, preparation method, and application thereof, a sodium source, a titanium source, and a chlorine source are simultaneously added to the reaction system to achieve sodium ion doping of the Li site, titanium ion doping of the Fe site, and chlorine ion doping of the O site in the modified lithium iron phosphate cathode material. The co-doping of sodium ions, titanium ions, and chloride ions at three different sites produces a synergistic effect, enhancing the lithium ion and electron transport capabilities of the modified lithium iron phosphate cathode material while maintaining its compaction density, thereby achieving high energy density and high power density. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0036] Figure 1 XRD patterns of the modified lithium iron phosphate positive electrode materials in Examples 1-3 and Comparative Examples 1 and 6 of the present application;

[0037] Figure 2 The scanning electron microscope images of Example 1 and Comparative Example 1 of the present application are shown, with a scale of 10.0 μm.

[0038] Figure 3 The electrochemical performance diagrams of Examples 1-3 and Comparative Examples 1, 5 and 6 are shown. DETAILED DESCRIPTION

[0039] In order to more clearly understand the above-mentioned objectives, features and advantages of the present application, the scheme of the present application will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0040] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present application may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present application, rather than all of the embodiments.

[0041] Below, the modified lithium iron phosphate positive electrode material of the present application, its preparation method and application implementation methods are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0042] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0044] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0045] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0046] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0047] Unless otherwise specified, this application adopts conventional test methods or test methods recommended by the instrument.

[0048] It should be noted that, in this document, the terms "coating layer" and "coating" refer to a material layer coated on a core material such as lithium iron phosphate. The material layer may completely or partially cover the core. The use of "coating layer" is for ease of description only and is not intended to limit this application. In addition, each coating layer may completely or partially cover the core.

[0049] In order to improve the electrochemical performance and compaction density of LFP positive electrode materials in the existing technology, technicians often use methods such as morphology and size control, carbon coating and ion doping to overcome the inherent defects of the material. Compared with other modification methods such as morphology control and surface coating, the advantage of ion doping is that it has little effect on the tap density of LFP positive electrode materials while being able to increase the volume energy density, which is beneficial to enhancing the high-rate performance of LFP batteries. On the one hand, the doped ions unequally replace the Li, Fe or O atoms in the LFP positive electrode material, which can promote the generation of favorable defects in the material's lattice; on the other hand, the doping elements with different electronic structures match the LFP lattice, which can widen the Li + diffusion channels, increasing Li + The diffusion dynamics in the lattice can improve the high-rate performance of the material. According to the position occupied by the doping ions, the doping modification of LFP cathode materials can be divided into Li-site doping, Fe-site doping, O-site doping, etc.

[0050] However, most of the disclosed doping methods only consider Li sites and / or Fe sites. It is impossible to predict which vacancies form co-doping, which doping elements are selected for different vacancies, and what impact the doping amounts of different doping elements have on the overall performance of the modified lithium iron phosphate positive electrode material.

[0051] Therefore, the present application proposes a method of modification by co-doping lithium, iron and oxygen sites, using specific elements to dope specific doping sites with specific doping amounts, using the doping of non-metallic ions to alleviate the reduction in compaction density caused by transition metal ion doping, and then using the synergistic effect produced by the simultaneous doping of different elements at multiple sites to improve the overall performance of the modified lithium iron phosphate positive electrode material, so that the material has high energy density and high power density.

[0052]

Modified lithium iron phosphate cathode material

[0053] A modified lithium iron phosphate cathode material, the chemical expression of the modified lithium iron phosphate cathode material is Li 1- x Na x Fe 1-y Ti y PO 4-z Cl z / C, wherein Na is doped to the Li position, Ti is doped to the Fe position, Cl is doped to the O position, C is a coating layer, and 0.002≤x≤0.004, 0.002≤y≤0.004, 0.002≤z≤0.004, and the carbon content is 1.0wt%-2.0wt%. The doping of Na element at the Li position can expand the interlayer spacing of lithium in the one-dimensional channel, thereby improving the Li + After the Ti element is substituted by an equivalent or a different valent metal ion at the Fe position, the bond length and bond angle of the crystal are changed, and the lattice defects of the modified lithium iron phosphate cathode material are increased. At the same time, ion vacancies are generated, which reduces the bond energy of the Li-O bond and improves the Li + The diffusion capacity of the modified lithium iron phosphate positive electrode material is improved, thereby improving the thermal stability and structural stability of the modified lithium iron phosphate positive electrode material, reducing resistance and improving conductivity. Doping of the Cl element at the O position can change the electronic structure of the material and improve the electrochemical stability of the crystal. The doping amount of the Na element at the Li position is 0.002≤x≤0.004, the doping amount of the Ti element at the Fe position is 0.002≤y≤0.004, and the doping amount of the Cl element at the O position is 0.002≤z≤0.004, which can produce a synergistic effect and improve the electrochemical performance of the modified lithium iron phosphate positive electrode material, so that it has high energy density and high power density. The carbon content is 1.0wt%-2.0wt%. Optionally, the carbon content is 1.5wt%. Carbon coating modification can improve the electronic conductivity of the lithium iron phosphate positive electrode material.

[0054] In some embodiments, the modified lithium iron phosphate cathode material has an average particle size of 0.3-0.4 μm. Average particle size: For an actual particle population composed of particles of varying sizes and shapes, compared to a hypothetical particle population composed of uniform spherical particles, if both have the same overall length, the diameter of the spherical particles is the average particle size of the actual particle population. Alternatively, the average particle size of the modified lithium iron phosphate cathode material is 0.32 μm.

[0055] In some embodiments, the compaction density of the modified lithium iron phosphate cathode material reaches 2.40-2.60 g / cm 3 The compaction density is measured under a pressure of 1 ton. This is beneficial for further improving the capacity and energy density of lithium-ion batteries. The powder compaction density of the modified lithium iron phosphate positive electrode material can be measured using instruments and methods known in the art. For example, it can be measured using an electronic pressure testing machine, such as the UTM7305 electronic pressure testing machine, with reference to the GB / T24533-2009 powder compaction density determination method.

[0056]

Preparation method

[0057] The preparation method of the modified lithium iron phosphate positive electrode material comprises:

[0058] Mixing materials containing phosphate, iron source, lithium source, sodium source, titanium source, chlorine source, carbon source and solvent to obtain a slurry;

[0059] The slurry is spray-dried to obtain a powder spray material;

[0060] The powder spray material is heat-treated under preset conditions to obtain a modified lithium iron phosphate positive electrode material;

[0061] A lithium source, a sodium source, an iron source, a titanium source, a phosphate, and a chlorine source are mixed in a molar ratio of Li:Na:Fe:Ti:O:Cl = 1-x:x:1-y:y:4-z:z, where 0.002≤x≤0.004, 0.002≤y≤0.004, and 0.002≤z≤0.004. The preparation method utilizes inexpensive and widely available raw materials, is simple to manufacture, and can be industrialized for mass production.

[0062] In some embodiments, in the step of mixing the materials comprising a phosphate, an iron source, a lithium source, a sodium source, a titanium source, a chlorine source, a carbon source, and a solvent, the carbon source comprises at least one of glucose, sucrose, citric acid, and polyethylene glycol. Alternatively, the carbon source comprises glucose and polyethylene glycol. The amount of carbon source added is such that the carbon content of the final modified lithium iron phosphate cathode material is 1.0 wt% to 2.0 wt%.

[0063] In some embodiments, in the step of mixing the materials comprising phosphate, iron source, lithium source, sodium source, titanium source, chlorine source, carbon source, and solvent, the mixing comprises ball milling and / or sand milling. The ball milling and / or sand milling can control the average particle size of the slurry to 0.3-0.4 μm.

[0064] In some embodiments, the phosphate comprises at least one of ferric phosphate, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate. Optionally, the phosphate is ferric phosphate.

[0065] In some embodiments, the iron source comprises at least one of ferric phosphate, ferric nitrate, ferric chloride and ferrous sulfate. Alternatively, the iron source is ferric phosphate.

[0066] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium dihydrogen phosphate, and lithium hydroxide.

[0067] In some embodiments, the sodium source comprises at least one of sodium chloride, sodium carbonate, sodium bicarbonate, sodium sulfate, and sodium dihydrogen phosphate. Alternatively, the sodium source is sodium bicarbonate.

[0068] In some embodiments, the titanium source includes at least one of titanium dioxide, titanyl sulfate, titanium tetrachloride, and tetrabutyl titanate. Alternatively, the titanium source is titanium dioxide.

[0069] In some embodiments, the chlorine source comprises at least one of sodium chloride and ammonium chloride. Alternatively, the chlorine source is ammonium chloride.

[0070] In some embodiments, the solvent comprises at least one of water, ethanol and acetone. Alternatively, the solvent is ethanol.

[0071] Spray drying is a systematic method for drying materials. The thin material is first atomized in a drying chamber. Then, upon contact with hot air, the water rapidly vaporizes, resulting in a dry product. This method can directly dry solutions and emulsions into powdered or granular products, eliminating evaporation and pulverization steps.

[0072] In some embodiments, in the step of spray drying the slurry, the atomization frequency during the spray drying is 40-100 Hz.

[0073] In some embodiments, the heated air inlet temperature during the spray drying process is 120-320°C.

[0074] In some embodiments, the outlet temperature of the heated air during the spray drying process is 80-240°C.

[0075] In some embodiments, in the step of subjecting the powder spray material to heat treatment under predetermined conditions, the heat treatment is performed in an inert gas, and the inert gas includes at least one of nitrogen, argon, neon, and helium.

[0076] In some embodiments, the heat treatment includes pre-sintering and sintering. The pre-sintering temperature is 300-600°C, the pre-sintering time is 2-4h, the sintering temperature is 600-800°C, and the sintering time is 6-16h. Pre-sintering can remove moisture and decompose some easily decomposable salts into corresponding oxides, which is beneficial to the subsequent solid-phase reaction. In addition, the raw material particles will also grow to a certain extent. Sintering can cause the raw materials to undergo a solid-phase reaction within a preset temperature range to generate the target product, accompanied by crystallization and crystal growth.

[0077]

Positive electrode

[0078] A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the modified lithium iron phosphate positive electrode material described above or the modified lithium iron phosphate positive electrode material obtained by the above-described preparation method. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0079] In some embodiments, the positive electrode film layer includes the modified lithium iron phosphate positive electrode material of the first aspect of the embodiment of the present application and / or the modified lithium iron phosphate positive electrode material obtained by the preparation method of the second aspect of the embodiment of the present application, but the positive electrode film layer used in the positive electrode sheet of the present application does not exclude other positive electrode active materials other than the above-mentioned modified lithium iron phosphate positive electrode material and / or the modified lithium iron phosphate positive electrode material obtained by the preparation method. For example, other positive electrode active materials can adopt positive electrode active materials for lithium-ion batteries known in the art, 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.

[0080] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. For example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0081] In some embodiments, the present application has no particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorine-containing acrylic resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and at least one of carboxymethyl chitosan (CMCS).

[0082] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0083] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0084] The positive electrode sheet does not exclude other additional functional layers in addition to the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of the present application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the positive electrode current collector and sandwiched between the positive electrode current collector and the positive electrode film layer. In other embodiments, the positive electrode sheet described in the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0085]

Battery

[0086] A battery comprises the above-mentioned positive electrode plate.

[0087] In some embodiments, the battery is a lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte. During the battery's charge and discharge process, lithium ions are intercalated and released between the positive and negative electrode sheets, and the electrolyte conducts lithium ions between the positive and negative electrode sheets. The battery of the present application can be applied to energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields.

[0088] In some embodiments, the battery has a discharge capacity greater than 164 mAh g at 0.1 C. –1 , the discharge capacity of 1C is greater than 150mAh g –1 .

[0089] In some embodiments, the battery has a first coulombic efficiency greater than 99%.

[0090] Example 1

[0091] Preparation of modified lithium iron phosphate positive electrode material:

[0092] Lithium carbonate, sodium bicarbonate, ferric phosphate, titanium dioxide, and ammonium chloride were weighed at an element molar ratio of Li:Na:Fe:Ti:O:Cl = 0.998:0.002:0.998:0.002:3.998:0.002 and mixed in anhydrous ethanol; 10 wt% (based on the total mass of the mixture) of glucose was then added to the mixture, and the mixture was ball-milled and sand-milled to obtain a slurry, with a particle size of the slurry controlled to be 0.32 μm;

[0093] The slurry was spray-dried at an atomization frequency of 50 Hz, a heated air inlet temperature of 200°C, and an air outlet temperature of 100°C to obtain a powder spray material;

[0094] Finally, the powder spray material was placed in a nitrogen atmosphere furnace, pre-sintered at 550 ° C for 4 hours, and then sintered at 760 ° C for 10 hours. After calcination, it was crushed to obtain a black powder modified lithium iron phosphate positive electrode material, the chemical expression of which is Li0.998 Na 0.002 Fe 0.998 Ti 0.002 PO 3.998 Cl 0.002 / C, carbon content is 1.62wt%.

[0095] Example 2

[0096] Preparation of modified lithium iron phosphate positive electrode material:

[0097] Lithium carbonate, sodium bicarbonate, ferric phosphate, titanium dioxide, and ammonium chloride were weighed at an element molar ratio of Li:Na:Fe:Ti:O:Cl = 0.997:0.003:0.997:0.003:3.997:0.003 and mixed in anhydrous ethanol; 10 wt% (based on the total mass of the mixture) of glucose was then added to the mixture, followed by ball milling and sand milling to obtain a slurry, wherein the slurry particle size was controlled to be 0.32 μm;

[0098] The slurry was spray-dried at an atomization frequency of 50 Hz, a heated air inlet temperature of 200°C, and an air outlet temperature of 100°C to obtain a powder spray material;

[0099] Finally, the powder spray material was placed in a nitrogen atmosphere furnace, pre-sintered at 550 ° C for 4 hours, and then sintered at 760 ° C for 10 hours. After calcination, it was crushed to obtain a black powder modified lithium iron phosphate positive electrode material, the chemical expression of which is Li 0.997 Na 0.003 Fe 0.997 Ti 0.003 PO 3.997 Cl 0.003 / C, carbon content is 1.50wt%.

[0100] Example 3

[0101] Preparation of modified lithium iron phosphate positive electrode material:

[0102] Lithium carbonate, sodium bicarbonate, ferric phosphate, titanium dioxide, and ammonium chloride were weighed at an element molar ratio of Li:Na:Fe:Ti:O:Cl = 0.996:0.004:0.996:0.004:3.996:0.004 and mixed in anhydrous ethanol; 10 wt% (based on the total mass of the mixture) of glucose was then added to the mixture, followed by ball milling and sand milling to obtain a slurry, wherein the slurry particle size was controlled to be 0.32 μm;

[0103] The slurry was spray-dried at an atomization frequency of 50 Hz, a heated air inlet temperature of 200°C, and an air outlet temperature of 100°C to obtain a powder spray material;

[0104] Finally, the powder spray material was placed in a nitrogen atmosphere furnace, pre-sintered at 550 ° C for 4 hours, and then sintered at 760 ° C for 10 hours. After calcination, it was crushed to obtain a black powder modified lithium iron phosphate positive electrode material, the chemical expression of which is Li 0.996 Na 0.004 Fe 0.996 Ti 0.004 PO 3.996 Cl 0.004 / C, carbon content is 1.46wt%.

[0105] Comparative Example 1

[0106] The experimental steps were the same as those in Example 1, except that “lithium carbonate, sodium bicarbonate, iron phosphate, titanium dioxide and ammonium chloride were weighed at an element molar ratio of Li: Na: Fe: Ti: O: Cl = 0.998:0.002: 0.998:0.002: 3.998:0.002 and mixed in anhydrous ethanol” was changed to “lithium carbonate and iron phosphate were weighed at an element molar ratio of Li: Fe: P = 1:1:1 and mixed in anhydrous ethanol” to obtain a modified lithium iron phosphate positive electrode material having a chemical expression of LiFePO4 / C and a carbon content of 1.96 wt%.

[0107] Comparative Example 2

[0108] The experimental steps were the same as those in Example 1, except that “lithium carbonate, sodium bicarbonate, iron phosphate, titanium dioxide and ammonium chloride were weighed and mixed in anhydrous ethanol at an element molar ratio of Li: Na: Fe: Ti: O: Cl = 0.998: 0.002: 0.998: 0.002: 3.998: 0.002” was changed to “lithium carbonate, potassium carbonate, iron phosphate, titanium dioxide and ammonium chloride were weighed and mixed in anhydrous ethanol at an element molar ratio of Li: K: Fe: Ti: O: Cl = 0.998: 0.002: 0.998: 0.002: 3.998: 0.002” to obtain a modified lithium iron phosphate positive electrode material having a chemical expression of Li 0.998 K 0.002 Fe 0.998 Ti 0.002 PO 3.998 Cl 0.002 / C, carbon content is 1.60wt%.

[0109] Comparative Example 3

[0110] The experimental steps were the same as those in Example 1, except that “lithium carbonate, sodium bicarbonate, iron phosphate, titanium dioxide and ammonium chloride were weighed and mixed in anhydrous ethanol at an element molar ratio of Li: Na: Fe: Ti: O: Cl = 0.998: 0.002: 0.998: 0.002: 3.998: 0.002” was changed to “lithium carbonate, sodium bicarbonate, iron phosphate, vanadium oxide and ammonium chloride were weighed and mixed in anhydrous ethanol at an element molar ratio of Li: Na: Fe: V: O: Cl = 0.998: 0.002: 0.998: 0.002: 3.998: 0.002” to obtain a modified lithium iron phosphate positive electrode material having a chemical expression of Li 0.998 Na 0.002 Fe 0.998 V 0.002 PO 3.998 Cl 0.002 / C, carbon content is 1.59wt%.

[0111] Comparative Example 4

[0112] The experimental steps were the same as those in Example 1, except that “lithium carbonate, sodium bicarbonate, iron phosphate, titanium dioxide and ammonium chloride were weighed and mixed in anhydrous ethanol at an element molar ratio of Li: Na: Fe: Ti: O: Cl = 0.998: 0.002: 0.998: 0.002: 3.998: 0.002” was changed to “lithium carbonate, sodium bicarbonate, iron phosphate, titanium dioxide and ammonium fluoride were weighed and mixed in anhydrous ethanol at an element molar ratio of Li: Na: Fe: Ti: O: F = 0.998: 0.002: 0.998: 0.002: 3.998: 0.002” to obtain a modified lithium iron phosphate positive electrode material having a chemical expression of Li 0.998 Na 0.002 Fe 0.998 Ti 0.002 PO 3.998 F 0.002 / C, carbon content is 1.61wt%.

[0113] Comparative Example 5

[0114] The experimental steps were the same as those in Example 1, except that “lithium carbonate, sodium bicarbonate, iron phosphate, titanium dioxide and ammonium chloride were weighed and mixed in anhydrous ethanol at an element molar ratio of Li: Na: Fe: Ti: O: Cl = 0.998: 0.002: 0.998: 0.002: 3.998: 0.002” was changed to “lithium carbonate, sodium bicarbonate, iron phosphate and titanium dioxide were weighed and mixed in anhydrous ethanol at an element molar ratio of Li: Na: Fe: O: Cl = 0.998: 0.002: 1.00: 3.998: 0.002” to obtain a modified lithium iron phosphate positive electrode material having a chemical expression of Li0.998 Na 0.002 FePO 3.998 Cl 0.002 / C, carbon content is 1.68wt%.

[0115] Comparative Example 6

[0116] Preparation of modified lithium iron phosphate positive electrode material:

[0117] Lithium carbonate, sodium bicarbonate, ferric phosphate, titanium dioxide, and ammonium chloride were weighed at an element molar ratio of Li:Na:Fe:Ti:O:Cl = 0.995:0.005:0.995:0.005:3.995:0.005 and mixed in anhydrous ethanol; 10 wt% (based on the total mass of the mixture) of glucose was then added to the mixture, and the mixture was ball-milled and sand-milled to obtain a slurry, with a particle size of the slurry controlled to be 0.32 μm;

[0118] The slurry was spray-dried at an atomization frequency of 50 Hz, a heated air inlet temperature of 200°C, and an air outlet temperature of 100°C to obtain a powder spray material;

[0119] Finally, the powder spray material was placed in a nitrogen atmosphere furnace, pre-sintered at 550 ° C for 4 hours, and then sintered at 760 ° C for 10 hours. After calcination, it was crushed to obtain a black powder modified lithium iron phosphate positive electrode material, the chemical expression of which is Li 0.995 Na 0.005 Fe 0.995 Ti 0.005 PO 3.995 Cl 0.005 / C, carbon content is 1.41wt%.

[0120] Data Analysis:

[0121] X-ray diffraction and morphology analysis were performed on the modified lithium iron phosphate cathode materials in Examples 1-3 and Comparative Examples 1 and 6. Figure 1 and Figure 2 shown.

[0122] Depend on Figure 1 It can be seen that doping does not change the crystal structure type of the sample.

[0123] Depend on Figure 2 It can be seen that doping can appropriately inhibit the growth of powder particles.

[0124] The modified lithium iron phosphate cathode materials in Examples 1-3 and Comparative Examples 1-6 were tested for carbon content and compaction density. The compaction density was measured under a pressure of 1 ton. The test method can be performed using instruments and methods known in the art, such as an electronic pressure tester, such as the UTM7305, in accordance with GB / T 24533-2009, for determining the compaction density of powders. The results are shown in the following table:

[0125] Table 1

[0126]

[0127]

[0128] The modified lithium iron phosphate cathode materials in Examples 1-3 and Comparative Examples 1-6 were assembled into lithium secondary batteries. The assembly method was as follows:

[0129] In the glove box, the negative electrode shell, spring, steel sheet, lithium sheet, diaphragm, positive electrode sheet and positive electrode shell were assembled in sequence. 80 μL of electrolyte was injected during the process, and then the button battery was sealed with a sealing machine. The electrochemical performance of these 9 sets of button batteries was tested. The assembled lithium secondary battery was subjected to electrochemical performance testing. The test conditions were determined according to the industry standard test method, such as Figure 3 The results are shown in the following table:

[0130] Table 2

[0131]

[0132]

[0133] As shown in Table 2, the electrochemical performance of the appropriate amount of Na, Ti, and Cl doping (Examples 1-3) is significantly better than that of the undoped (Comparative Example 1) and the double doping (Comparative Example 5). In Examples 1-3, as the doping concentrations of Na, Ti, and Cl increase, the corresponding electrochemical performance first improves and then deteriorates. This may be because excessive doping concentrations can cause unfavorable distortion of the unit cell (such as Comparative Example 6). In addition, the doping combination effect of Na, Ti, and Cl (Example 1) is also better than the doping combination effect of K, Ti, and Cl (Comparative Example 2), Na, V, and Cl (Comparative Example 3), and Na, Ti, and F (Comparative Example 4).

[0134] The above description is only a specific embodiment of the present application. Those skilled in the art will clearly understand that for the convenience and brevity of description, the specific working processes of the systems, modules and units described above can refer to the corresponding processes in the aforementioned method embodiments, and will not be repeated here. It should be understood that the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the scope of protection of the present application.

Claims

1. A modified lithium iron phosphate positive electrode material, characterized in that: The chemical expression of the modified lithium iron phosphate cathode material is Li 1-x Na x Fe 1-y Ti y PO 4-z Cl z / C, wherein Na is doped into the Li position, Ti is doped into the Fe position, Cl is doped into the O position, C is a coating layer, and 0.002≤x≤0.004, 0.002≤y≤0.004, 0.002≤z≤0.004, and the carbon content is 1.0wt%-2.0wt%.

2. The modified lithium iron phosphate cathode material according to claim 1, characterized in that The average particle size of the modified lithium iron phosphate positive electrode material is 0.3-0.4 μm.

3. The method for preparing the modified lithium iron phosphate cathode material according to any one of claims 1 to 2, characterized in that: include: Mixing materials containing phosphate, iron source, lithium source, sodium source, titanium source, chlorine source, carbon source and solvent to obtain a slurry; The slurry is spray-dried to obtain a powder spray material; heat-treating the powder spray material under preset conditions to obtain the modified lithium iron phosphate positive electrode material; The lithium source, the sodium source, the iron source, the titanium source, the phosphate and the chlorine source are mixed according to the element molar ratio of Li:Na:Fe:Ti:O:Cl=1-x:x:1-y:y:4-z:z, wherein 0.002≤x≤0.004, 0.002≤y≤0.004, and 0.002≤z≤0.

004.

4. The preparation method according to claim 3, characterized in that In the step of mixing materials containing phosphate, an iron source, a lithium source, a sodium source, a titanium source, a chlorine source, a carbon source, and a solvent, the phosphate comprises at least one of iron phosphate, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate; and / or, the iron source comprises at least one of ferric phosphate, ferric nitrate, ferric chloride and ferrous sulfate; And / or, the lithium source includes at least one of lithium carbonate, lithium dihydrogen phosphate and lithium hydroxide; and / or, the sodium source comprises at least one of sodium chloride, sodium carbonate, sodium bicarbonate, sodium sulfate and sodium dihydrogen phosphate; And / or, the titanium source includes at least one of titanium dioxide, titanyl sulfate, titanium tetrachloride and tetrabutyl titanate; And / or, the chlorine source includes at least one of sodium chloride and ammonium chloride.

5. The preparation method according to claim 3, characterized in that In the step of mixing the materials containing phosphate, iron source, lithium source, sodium source, titanium source, chlorine source, carbon source and solvent, the carbon source comprises at least one of glucose, sucrose, citric acid and polyethylene glycol; And / or, the solvent includes at least one of water, ethanol and acetone.

6. The preparation method according to claim 3, characterized in that In the step of mixing the materials containing phosphate, iron source, lithium source, sodium source, titanium source, chlorine source, carbon source and solvent, the mixing includes ball milling and / or sand milling.

7. The preparation method according to claim 3, characterized in that In the step of spray drying the slurry, the atomization frequency during the spray drying is 40-100 Hz; and / or, the heated air inlet temperature during the spray drying process is 120-320° C.; And / or, the outlet temperature of the heated air during the spray drying process is 80-240°C.

8. The preparation method according to claim 3, characterized in that In the step of heat-treating the powder spray material under preset conditions, the heat treatment is performed in an inert gas, wherein the inert gas includes at least one of nitrogen, argon, neon and helium; and / or, the heat treatment includes pre-sintering and sintering, The pre-sintering temperature is 300-600 ℃ and the pre-sintering time is 2-4 h. The sintering temperature is 600-800 °C, and the sintering time is 6-16 h.

9. A positive electrode plate, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, and the positive electrode film layer includes the modified lithium iron phosphate positive electrode material according to any one of claims 1-2 or the modified lithium iron phosphate positive electrode material obtained by the preparation method according to any one of claims 3-8.

10. A battery, characterized in that: Including the positive electrode sheet according to claim 9.

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