A phosphate material, a modified phosphate material, and a method for preparing the same

Abstract

The application discloses a phosphate material, a modified phosphate material and a preparation method thereof, and the phosphate material has a chemical formula of LiM 1‑x N x PO4, wherein M is at least one of Ni, Co, Mn and Fe, N is at least one of Mg, Ti, Al, Zr, Ba, V, Ni, Co and Mn, and 0<=x<=0.1; D90, D50 and D10 of the phosphate material satisfy a relationship formula of (D90-D10) / D50<=2. The relationship formula indicates that the phosphate material has good particle dispersity and uniform particle size. The uniform particle size can make the material particles keep synchronous de-lithiation and lithium intercalation during the charging and discharging process of a battery, thereby inhibiting excessive charging or discharging of some particles, prolonging the service life of the battery. In addition, the uniform particle size can also reduce mechanical stress, improve the cycle stability and safety of the battery, and significantly improve the electrochemical performance of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a phosphate material, a modified phosphate material and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have been widely used in many fields such as new energy vehicles, 3C electronic products, electric tools and the like due to their high energy density, portability, environmental protection characteristics and safety. In recent years, the positive electrode material field of lithium ion batteries has experienced rapid development, mainly forming three categories: layered positive electrode materials (including lithium cobaltate and ternary materials), spinel structure lithium manganate materials and phosphate positive electrode materials. Among them, lithium iron phosphate material is widely used because of its excellent safety performance, long cycle life, high temperature stability and cost effectiveness. With the increasing demand of the market for battery energy density, lithium manganese iron phosphate and other transition metal phosphate materials have also been closely watched by the research community.

[0003] However, a key challenge faced by phosphate positive electrode materials is their extremely low conductivity, which greatly limits the performance potential of the materials. In order to overcome this difficulty, researchers have explored various optimization and modification strategies, mainly including doping modification technology, surface coating treatment and fine design of micro-morphology, etc.

[0004] Phosphate materials synthesized by solvothermal method are characterized by good particle uniformity, usually exhibiting excellent rate performance and low temperature performance. Further improving the performance of such materials depends on optimizing the morphology control and enhancing the effect of carbon coating, which are two important directions of current research. However, the existing technology for these two directions is still limited at this stage.

[0005] In view of the above-mentioned defects of the existing phosphate materials, it is necessary to provide a technical solution to solve the above-mentioned problems. SUMMARY

[0006] The present application aims to provide a phosphate material with small particle size, good dispersibility and good particle size uniformity, and its surface has active dangling bonds, which helps to obtain a more uniform carbon coating layer in the subsequent process.

[0007] In order to achieve this purpose, the present application provides the following solutions:

[0008] A phosphate material, whose chemical formula is LiM 1-x N xPO4, wherein M is at least one of Ni, Co, Mn and Fe, N is at least one of Mg, Ti, Al, Zr, Ba, V, Ni, Co and Mn, and 0≤x≤0.1; the D90, D50 and D10 of the phosphate material satisfy the relationship: (D90-D10) / D50≤2.

[0009] Preferably, the phosphate material has active dangling bonds on the surface thereof.

[0010] Preferably, the D50 of the phosphate material is b, and b satisfies the relationship: 0.3um≤b≤0.6um.

[0011] Preferably, the phosphate material has a flake-like or flake-like structure.

[0012] Preferably, the phosphate material has an average diameter d and an average thickness h, and the d and the h satisfy the relationship: d / h≥2.

[0013] Preferably, the phosphate material has a crystal preferred orientation of (010).

[0014] A modified phosphate material, comprising the phosphate material described above and a carbon coating layer coated on the surface of the phosphate material.

[0015] A preparation method of a modified phosphate material, comprising the following steps:

[0016] Step one: a lithium source, an M source, an N source, a phosphorus source and a solvent are weighed and configured into a mixture A, and an aromatic amine additive is configured into an additive solution;

[0017] Step two: the mixture A and the additive solution are transferred into a high-pressure reaction kettle, mixed well, sealed and heated under an inert atmosphere, and a solvothermal reaction is performed;

[0018] Step three: after the reaction kettle is cooled, the reacted solid is separated and washed to obtain a phosphate material;

[0019] Step four: the phosphate material, a carbon source and a dispersant are mixed uniformly to obtain a mixed slurry, and the mixed slurry is dried to obtain a mixture B;

[0020] Step five: the mixture B is sintered to obtain a modified phosphate material.

[0021] Preferably, in the step one, the lithium source, the M source, the N source and the phosphorus source are weighed according to the molar ratio Li:(M+N):P of (3-4):1:(1-1.2).

[0022] Preferably, in the step one, the aromatic amine additive includes at least one of aniline, p-phenylenediamine, methoxyaniline, N-methylaniline and o-toluidine.

[0023] Preferably, in the step one, the concentration of the additive solution is 0.1-0.6 mol / L.

[0024] Preferably, in the step one, the solvent in the mixture A includes at least one of ethanol, ethylene glycol, methanol, polyethylene glycol, isopropyl alcohol, glycerol and water.

[0025] Preferably, in the step one, when configuring the additive solution, an alcohol solution is selected as the solvent, and the alcohol solution includes at least one of ethanol, ethylene glycol, methanol, polyethylene glycol, isopropyl alcohol and glycerol.

[0026] Preferably, in the step one, the M source is at least one of divalent sulfate, nitrate, acetate and chloride of the corresponding transition metal.

[0027] Preferably, in the step one, the N source is at least one of oxide, phosphide, phosphate, sulfate, nitrate, acetate and chloride of the corresponding metal element.

[0028] Preferably, in the step one, when the M element is iron, inert gas is introduced into the solvent to discharge oxygen and an antioxidant is pre-added when configuring the M source solution; the antioxidant includes at least one of ascorbic acid, citric acid and oxalic acid.

[0029] Preferably, in the step one, the lithium source is at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate, lithium oxalate, lithium phosphate, lithium dihydrogen phosphate and lithium hydrogen phosphate.

[0030] Preferably, in the step one, the phosphorus source is one or more of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, sodium phosphate, potassium phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, lithium phosphate, lithium dihydrogen phosphate and lithium hydrogen phosphate.

[0031] Preferably, in the step one, the temperature of the solvothermal reaction is 130-280℃, and the reaction time is 1-12h; more preferably, the temperature of the solvothermal reaction is 150-200℃, and the reaction time is 4-6h.

[0032] Preferably, in the step four, the carbon source includes at least one of glucose, sucrose, citric acid, oleic acid, ascorbic acid, dopamine, starch, PEG and PVP, and the proportion of the sugar is not less than 50% of the total weight of the carbon source.

[0033] Preferably, in the step four, the mixing mode is mechanical stirring dispersion, wet grinding dispersion or liquid phase ultrasonic dispersion; more preferably, the liquid phase ultrasonic dispersion, the ultrasonic frequency of the liquid phase ultrasonic dispersion is > 80 kHz, and the dispersion time is 0.5-12 h.

[0034] Preferably, in the step four, the mass ratio of the carbon source to the phosphate material is 0.05-0.2:1, and more preferably, 0.06-0.12:1.

[0035] Preferably, in the step four, the drying mode is a drum drying oven drying, a vacuum oven drying or a spray drying; and more preferably, the spray drying.

[0036] Preferably, in the step five, the sintering atmosphere is one or more of argon, nitrogen, hydrogen / argon mixed gas, and more preferably, the nitrogen.

[0037] Preferably, in the step five, the sintering temperature is 450-800℃, and the sintering time is 2-12 h, and more preferably, the sintering temperature is 600-700℃, and the sintering time is 5-8 h.

[0038] The application further provides a positive electrode sheet comprising a positive electrode material, a conductive agent and a binder, wherein the positive electrode material is the modified phosphate material described above.

[0039] The application further provides a secondary battery comprising a diaphragm, a negative electrode sheet, an electrolyte, a battery shell and the positive electrode sheet described above.

[0040] Compared with the prior art, the application has the beneficial effects that the application provides a phosphate material with the chemical formula of LiM 1-x N x PO4, wherein M is at least one of Ni, Co, Mn and Fe, N is at least one of Mg, Ti, Al, Zr, Ba, V, Ni, Co and Mn, and 0≤x≤0.1; the D90, D50 and D10 of the phosphate material satisfy the relationship (D90-D10) / D50≤2. The relationship shows that the phosphate material of the application has good particle dispersity and uniform particle size. The uniform particle size can make the material particles keep synchronous de-lithiation and lithium intercalation during the charging and discharging process of the battery, thereby inhibiting the overcharging or discharging of some particles and prolonging the service life of the battery. In addition, the uniform particle size can also reduce mechanical stress, improve the cycle stability and safety of the battery, and significantly improve the electrochemical performance of the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The scanning electron microscope image of the phosphate material prepared in Example 1. DETAILED DESCRIPTION

[0042] In order to make the technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in conjunction with specific embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0043] In the first aspect according to the present application, a phosphate material is provided, which has a chemical formula of LiM 1-x N x PO4, wherein M is at least one of Ni, Co, Mn and Fe, N is at least one of Mg, Ti, Al, Zr, Ba, V, Ni, Co and Mn, and 0≤x≤0.1; the D90, D50 and D10 of the phosphate material satisfy the relationship (D90-D10) / D50≤2. The relationship shows that the phosphate material of the present application has good particle dispersion and uniform particle size. The uniform particle size can make the material particles keep synchronous de-lithiation and lithium intercalation during the charging and discharging process of the battery, thereby inhibiting the overcharging or discharging of some particles and prolonging the service life of the battery. In addition, the uniform particle size can also reduce mechanical stress, improve the cycle stability and safety of the battery, and significantly improve the electrochemical performance of the secondary battery.

[0044] In an embodiment according to the present application, the phosphate material has active dangling bonds on the surface. The phosphate material has active dangling bonds on the surface, which can act as active sites to promote the progress of chemical reactions and help the combination with the carbon source in the subsequent carbon coating process, so as to obtain a more uniform carbon coating layer and further improve the overall electrochemical performance of the phosphate material.

[0045] In an embodiment according to the present application, the D50 of the phosphate material is b, and b satisfies the relationship 0.3um≤b≤0.6um.

[0046] The small particle size of the phosphate material can bring many benefits. The small particle size helps to shorten the diffusion path of lithium ions, reduce polarization, and thus improve the large-rate charging and discharging performance of the battery. At the same time, small particles can make more effective use of active materials, increase the capacity and energy density of the battery.

[0047] In an embodiment according to the present application, the structure of the phosphate material is a sheet or sheet-like structure, the average diameter of the phosphate material is d, and the average thickness is h, d and h satisfy the relationship d / h≥2, and the crystallographic preferred orientation of the material is (010). The phosphate material, represented by lithium iron phosphate, has one-dimensional lithium ion diffusion channels, Li +The charge transfer mainly occurs on the (010) crystal face. Therefore, the material with (010) preferred orientation is more conducive to lithium ion transmission during charging and discharging, and the material has better rate performance.

[0048] In the second aspect of the present application, a modified phosphate material is also provided, comprising the above phosphate material and a carbon coating layer coated on the surface of the phosphate material. The material has the characteristics of small particle size, good dispersibility, and high particle size uniformity, and has excellent Li + The diffusion path is short, the difference between particles is small, and the material has excellent rate performance, low temperature performance and long cycle performance.

[0049] In the third aspect of the present application, a preparation method of a modified phosphate material is also provided, comprising the following steps:

[0050] Step one: the lithium source, M source, N source, phosphorus source and solvent are weighed and configured into mixture A, and the aromatic amine additive is configured into a solution;

[0051] Step two: mixture A and the solution are transferred to a high-pressure reaction kettle for thorough mixing, and are sealed and heated under inert atmosphere for solvothermal reaction;

[0052] Step three: the solid after reaction is filtered and washed to obtain the phosphate material;

[0053] Step four: the phosphate material, carbon source and dispersant are mixed uniformly to obtain a mixed slurry, and the mixed slurry is dried to obtain mixture B;

[0054] Step five: mixture B is sintered to obtain the modified phosphate material.

[0055] In an embodiment according to the present application, in step one, the lithium source, M source, N source and phosphorus source are weighed according to the molar ratio Li:(M+N):P as (3-4):1:(1-1.2).

[0056] In an embodiment according to the present application, in step one, the aromatic amine additive includes at least one of aniline, p-phenylenediamine, methoxyaniline, N-methylaniline and o-toluidine. The aromatic amine additive is introduced in step one of the synthesis, and the aromatic amine group in the additive forms N-H-O-P bond on the surface of the particles, which can limit the agglomeration and continuous growth of the particles, so that the phosphate material with small particles and uniform particle size is obtained. In addition, the additive will form an active dangling bond on the surface of the generated phosphate material particles after the solvothermal reaction, so that a more uniform carbon coating layer with less free carbon can be obtained in the subsequent carbon coating process.

[0057] In one embodiment of the present invention, in step one, the concentration of the additive when preparing the solution is 0.1 to 0.6 mol / L.

[0058] In one embodiment of the present invention, in step one, when preparing the solution of the additive, an alcohol solution is selected, which includes at least one of ethanol, ethylene glycol, methanol, polyethylene glycol, isopropanol, and glycerol.

[0059] In one embodiment of the present invention, in step one, the M source is at least one of a divalent sulfate, nitrate, acetate, and chloride of the corresponding transition metal;

[0060] In one embodiment of the present invention, in step one, the N source is at least one selected from oxides, phosphides, phosphates, sulfates, nitrates, acetates, and chlorides of the corresponding metal element.

[0061] In one embodiment of the present invention, in step one, when element M is iron, when preparing the source solution of M, it is necessary to first introduce an inert gas into the solvent to remove oxygen and pre-add an antioxidant; the antioxidant includes at least one of ascorbic acid, citric acid and oxalic acid.

[0062] In one embodiment of the present invention, in step one, the lithium source is at least one selected from lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate, lithium oxalate, lithium phosphate, lithium dihydrogen phosphate, and lithium hydrogen phosphate.

[0063] In one embodiment of the present invention, in step one, the phosphorus source is one or more of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, sodium phosphate, potassium phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, lithium phosphate, lithium dihydrogen phosphate, and lithium dihydrogen phosphate.

[0064] In one embodiment of the present invention, in step one, the solvent in mixture A is at least one of ethanol, ethylene glycol, methanol, polyethylene glycol, isopropanol, glycerol and water.

[0065] In one embodiment of the present invention, in step one, the temperature of the solvothermal reaction is 130–280°C, and the reaction time is 1–12 h; more preferably, the temperature of the solvothermal reaction is 150–200°C, for example, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C; and the reaction time is 4–6 h, for example, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h, 5.0 h, 5.1 h, 5.2 h, 5.3 h, 5.4 h, 5.5 h, 5.6 h, 5.7 h, 5.8 h, 5.9 h, or 6.0 h. The advantages of solvothermal preparation of phosphate materials are that the reaction conditions are relatively mild, and it can produce cathode materials with high crystallinity, easy morphology control, high purity and good powder quality. At the same time, it has fast reaction kinetics, few material defects and excellent electrochemical performance.

[0066] In one embodiment of the present invention, in step four, the carbon source includes at least one of glucose, sucrose, citric acid, oleic acid, ascorbic acid, dopamine, starch, PEG and PVP, wherein the proportion of sugars is not less than 50% of the total weight of the carbon source.

[0067] In one embodiment of the present invention, in step four, the mixing method is mechanical stirring dispersion, wet grinding dispersion, or liquid-phase ultrasonic dispersion; more preferably, liquid-phase ultrasonic dispersion is used, wherein the ultrasonic frequency of liquid-phase ultrasonic dispersion is >80kHz, and the dispersion time is 0.5 to 12 hours, for example, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours. Liquid-phase ultrasonic dispersion can form a stable dispersion with particle sizes as small as micrometers or even nanometers, and the droplet size distribution range is narrow; it has a wide range of applications and can adapt to various working environments; at the same time, ultrasonic dispersion can directly transfer a large amount of energy to the reaction medium, effectively converting electrical energy into mechanical energy, and the dispersion effect can be controlled by adjusting the ultrasonic energy. This process has low energy consumption, high production efficiency, and low cost; in addition, using high-frequency ultrasonic dispersion to mix phosphate materials and carbon sources can maintain the original excellent morphological characteristics of phosphate materials while ensuring thorough mixing.

[0068] In one embodiment of the present invention, in step four, the mass ratio of carbon source to phosphate material is 0.05 to 0.2:1, and more preferably 0.06 to 0.12:1.

[0069] In one embodiment of the present invention, in step four, the drying method is drying in a blower drying oven, drying in a vacuum oven, or spray drying; more preferably, spray drying.

[0070] In one embodiment of the present invention, in step five, the sintering atmosphere is one or more of argon, nitrogen, and hydrogen / argon mixture, more preferably, the sintering atmosphere is nitrogen.

[0071] In one embodiment of the present invention, in step five, the sintering temperature is 450℃~800℃, and the sintering time is 2~12h. More preferably, the sintering temperature is 600℃~700℃, for example, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, or 700℃; and the sintering time is 5~8h, for example, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, or 8h.

[0072] In a third aspect of the present invention, a positive electrode sheet is also provided, comprising a positive electrode material, a conductive agent and a binder, wherein the positive electrode material is the aforementioned composite positive electrode material.

[0073] In a fourth aspect of the invention, a secondary battery is also provided, comprising a separator, a negative electrode, an electrolyte, a battery casing, and the aforementioned positive electrode.

[0074] The negative electrode includes a negative current collector and a negative active material layer coated on at least one surface of the negative current collector. The negative active material layer may be one or more of the following, including but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium.

[0075] The graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is typically a structure or component that collects current. The negative electrode current collector can be any material suitable for use as a negative electrode current collector in a secondary battery, for example, it can be, but is not limited to, metal foil, and more specifically, it can be, but is not limited to, copper foil.

[0076] The secondary battery also includes an electrolyte, which comprises an organic solvent, an electrolyte lithium salt, and additives. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-resistant electrolytes; or it can be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DEC, DMC, or EMC; or it can be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include, but are not limited to, at least one of film-forming additives, conductive additives, flame-retardant additives, overcharge-resistant additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.

[0077] The present invention will be further described below through specific embodiments.

[0078] Example 1

[0079] Preparation of modified phosphates:

[0080] Step 1: Calculate the feed amounts of lithium acetate, manganese acetate, ferrous sulfate, nickel acetate, and ammonium dihydrogen phosphate according to the molar ratio of Li:Mn:Fe:Ni:P of 3.2:0.6:0.38:0.02:1. Prepare aqueous solutions with lithium concentration of 4.5 mol / L, phosphorus concentration of 3 mol / L, and iron, manganese, and nickel concentration of 1 mol / L respectively using water as the solvent. Prepare 50 ml of a solution containing 0.1 mol / L p-phenylenediamine using polyethylene glycol with a molecular weight of 500 as the solvent.

[0081] Step 2: Transfer the mixture A and the solution to a high-pressure reactor and mix thoroughly. Seal the reactor under an argon atmosphere and heat it to 200°C for 2 hours to carry out a solvothermal reaction.

[0082] Step 3: Filter out the solid after the reaction, wash and centrifuge to obtain phosphate material; wherein, the surface of the phosphate material has active dangling bonds, and (D90-D10) / D50=1.8; the preferred crystal orientation is (010);

[0083] Step 4: The phosphate material, carbon source, and dispersant are ultrasonically dispersed at 200 kHz for 2 hours to obtain a mixed slurry. The mixed slurry is then spray-dried to obtain mixture B. The carbon source is glucose and PVP in a mass ratio of 7:1, the dispersant is ethanol, and the mass ratio of carbon source to phosphate material is 0.8:1. The outlet temperature of the spray drying process is 85℃.

[0084] Step 5: Anneal mixture B at 580°C for 10 hours in a nitrogen atmosphere to obtain the modified phosphate material.

[0085] Preparation of secondary batteries:

[0086] Modified phosphate was used as the positive electrode material and mixed with conductive carbon black and PVDF at a mass ratio of 95:3:2. The mixture was then dispersed in NMP to form a slurry. After stirring, coating, drying, rolling and slitting, the positive electrode sheet was obtained.

[0087] Artificial graphite is used as the negative electrode active material. It is mixed with conductive carbon black and PVDF in a mass ratio of 94:3:3 and dispersed in NMP to form a slurry. After stirring, coating, drying, rolling and slitting, the negative electrode sheet is obtained.

[0088] The negative electrode, positive electrode, and separator are interleaved and wound together, then subjected to terminal welding, aluminum foil packaging, electrolyte injection, encapsulation formation, and degassing molding steps to finally produce a soft-pack lithium-ion battery with a designed capacity of 2500mAh. The electrolyte consists of 1mol / L LiPF6 as the solute and EC, DMC, and DEC as the solvent in a volume ratio of 1:1:1.

[0089] Example 2

[0090] Unlike Example 1, in the preparation of the modified phosphate:

[0091] Step 1: Calculate the feed amounts of lithium carbonate, ferrous sulfate, magnesium sulfate, and phosphoric acid according to the molar ratio of Li:Fe:Mg:P of 3.03:0.99:0.01:1. Prepare aqueous solutions with lithium concentration of 4.8 mol / L, phosphorus concentration of 3 mol / L, and iron and magnesium concentration of 1.5 mol / L using a mixture of ethylene glycol and water (volume ratio 1:4) as the solvent. Before preparing the iron and magnesium solutions, purge with nitrogen to remove oxygen and add 0.05 mol of citric acid. Prepare 50 ml of a solution containing 0.2 mol / L p-aniline using ethanol as the solvent.

[0092] Step 2: Transfer the mixture A and the solution to a high-pressure reactor and mix thoroughly. Seal the reactor under an argon atmosphere and heat it to 160°C for 8 hours to carry out a solvothermal reaction.

[0093] Step 3: Filter out the solid after the reaction, wash and centrifuge to obtain phosphate material; wherein, the surface of the phosphate material has active dangling bonds, and (D90-D10) / D50=1.5;

[0094] Step 4: The phosphate material, carbon source, and dispersant are ultrasonically dispersed at 120 kHz for 5 hours to obtain a mixed slurry. The mixed slurry is then spray-dried to obtain mixture B. The carbon source is sucrose and PEG in a mass ratio of 6:2, the dispersant is water, and the mass ratio of carbon source to phosphate material is 0.8:1. The outlet temperature of the spray drying process is 90℃.

[0095] Step 5: Anneal mixture B at 650°C for 12 hours in a nitrogen atmosphere to obtain the modified phosphate material.

[0096] The rest is the same as in Example 1, and will not be repeated here.

[0097] Example 3

[0098] Unlike Example 1, in the preparation of the modified phosphate:

[0099] Step 1: Calculate the feed amounts of lithium hydroxide, manganese sulfate, ferrous sulfate, and phosphoric acid according to the molar ratio of Li:Mn:Fe:P of 3:0.1:0.9:1. Prepare aqueous solutions with lithium concentration of 4.5 mol / L, phosphorus concentration of 4 mol / L, and iron and manganese concentration of 2 mol / L respectively using a mixture of ethylene glycol and water (volume ratio 1:4) as solvent. Before preparing the iron and manganese solution, purge with nitrogen to remove oxygen and add 0.01 mol of ascorbic acid. Prepare 50 ml of a solution containing 0.2 mol / L p-methoxyaniline using methanol as solvent.

[0100] Step 2: Transfer the mixture A and the solution to a high-pressure reactor and mix thoroughly. Seal the reactor under an argon atmosphere and heat it to 180°C for 6 hours to carry out a solvothermal reaction.

[0101] Step 3: Filter out the solid after the reaction, wash and centrifuge to obtain phosphate material; wherein, the surface of the phosphate material has active dangling bonds, and (D90-D10) / D50=1.8;

[0102] Step 4: The phosphate material, carbon source, and dispersant are ball-milled for 0.5 hours to obtain a mixed slurry. The mixed slurry is then spray-dried to obtain mixture B. The carbon source is glucose and PEG in a mass ratio of 8:2, the dispersant is water, and the mass ratio of carbon source to phosphate material is 0.1:1. The outlet temperature of the spray drying process is 90°C.

[0103] Step 5: Anneal mixture B at 600°C for 6 hours in a nitrogen atmosphere to obtain the modified phosphate material.

[0104] The rest is the same as in Example 1, and will not be repeated here.

[0105] Example 4

[0106] Unlike Example 1, in the preparation of the modified phosphate:

[0107] Step 1: Calculate the feed amounts of lithium phosphate, manganese sulfate, ferrous sulfate, and phosphoric acid according to the molar ratio of Li:Mn:Fe:P of 3.06:0.5:0.5:1.02. Prepare aqueous solutions with lithium concentration of 4.5 mol / L, phosphorus concentration of 4 mol / L, and iron and manganese concentration of 1.25 mol / L using a mixture of ethylene glycol and water (volume ratio 1:4) as solvent. Before preparing the iron and manganese solution, purge with nitrogen to remove oxygen and add 0.015 mol of ascorbic acid. Prepare 50 ml of a solution containing 0.2 mol / L N-methylaniline and o-toluidine using isopropanol as solvent.

[0108] Step 2: Transfer the mixture A and the solution to a high-pressure reactor and mix thoroughly. Seal the reactor under an argon atmosphere and heat it to 200°C for 2 hours to carry out a hydrothermal reaction.

[0109] Step 3: Filter out the solid after the reaction, wash and centrifuge to obtain phosphate material; wherein, the surface of the phosphate material has active dangling bonds, and (D90-D10) / D50=1.6;

[0110] Step 4: The phosphate material, carbon source, and dispersant are ball-milled for 0.5 hours to obtain a mixed slurry. The mixed slurry is then spray-dried to obtain mixture B. The carbon source is glucose, starch, and PEG in a mass ratio of 5:1:1, the dispersant is water, and the mass ratio of carbon source to phosphate material is 0.07:1. The outlet temperature of the spray drying process is 80°C.

[0111] Step 5: Anneal mixture B at 700°C for 5 hours in a nitrogen atmosphere to obtain the modified phosphate material.

[0112] The rest is the same as in Example 1, and will not be repeated here.

[0113] Example 5

[0114] Unlike Example 1, in the preparation of the modified phosphate:

[0115] Step 1: Calculate the amounts of lithium sulfate, ferrous sulfate, and sodium phosphate according to the molar ratio of Li:Fe:P of 3:1:1. Prepare solutions with lithium concentrations of 2 mol / L, phosphorus concentrations of 2 mol / L, and iron concentrations of 1 mol / L using a mixture of ethylene glycol and water (volume ratio 1:2) as the solvent. Before preparing the iron solution, purge with nitrogen to remove oxygen and add 0.03 mol of ascorbic acid. Prepare 50 ml of a solution containing 0.2 mol / L p-phenylenediamine using glycerol as the solvent.

[0116] Step 2: Transfer the mixture A and the solution to a high-pressure reactor and mix thoroughly. Adjust the pH value to neutral, seal and heat to 180°C for 4 hours under an argon atmosphere to carry out a hydrothermal reaction.

[0117] Step 3: Filter out the solid after the reaction, wash with ethanol, and centrifuge to obtain the phosphate material; wherein, the surface of the phosphate material has active dangling bonds, and (D90-D10) / D50=1.7;

[0118] Step 4: The phosphate material, carbon source, and dispersant are ball-milled for 0.5 hours to obtain a mixed slurry. The mixed slurry is then spray-dried to obtain mixture B. The carbon source is sucrose and PEG in a mass ratio of 6:3, the dispersant is water, and the mass ratio of carbon source to phosphate material is 0.09:1. The outlet temperature of the spray drying process is 80°C.

[0119] Step 5: Anneal mixture B at 700°C for 4 hours in a nitrogen atmosphere to obtain the modified phosphate material.

[0120] The rest is the same as in Example 1, and will not be repeated here.

[0121] Comparative Example 1:

[0122] Unlike Example 1, no p-phenylenediamine was added in step one of the preparation process, and the phosphate material obtained in step three had no active dangling bonds and (D90-D10) / D50 = 5.

[0123] The rest is exactly the same as in Example 1, and will not be repeated here.

[0124] Comparative Example 2:

[0125] Unlike Example 3, no methoxyaniline was added in step one of the preparation process, and the phosphate material obtained in step three had no active dangling bonds and (D90-D10) / D50 = 8.

[0126] The rest is exactly the same as in Example 3, and will not be repeated here.

[0127] Comparative Example 3:

[0128] Unlike Example 5, no p-phenylenediamine was added in step one of the preparation process, and the phosphate material obtained in step three had no active dangling bonds, and (D90-D10) / D50 = 4.

[0129] The rest is exactly the same as in Example 5, and will not be repeated here.

[0130] Comparative Example 4:

[0131] Unlike Example 1, this comparative example uses a solid-state method to synthesize carbon-coated lithium iron phosphate material. The specific steps are as follows:

[0132] Step 1: Iron phosphate and lithium carbonate are mixed in a Li:Fe:P molar ratio of 1:1:1, while glucose and PEG are added at 8% and 2% of the weight of lithium iron phosphate, respectively.

[0133] Step 2: Grind and mix the above raw materials in a high-speed ball mill using water as the dispersion medium, and then spray dry.

[0134] Step 3: Sinter the spray-dried material at 700℃ for 12 hours under a nitrogen atmosphere to obtain carbon-coated lithium iron phosphate material.

[0135] Performance testing:

[0136] The electrochemical performance of the secondary batteries in the above examples and comparative examples was tested, and the test results are shown in Table 1.

[0137] The specific performance testing steps and data processing methods are as follows.

[0138] Capacity and cycle performance testing: At 25℃, the electrode was charged at a constant current of 0.5C (1250mA) to the charging cutoff voltage, then charged at a constant voltage to 0.05C (125mA), and then discharged at 0.5C (1250mA) to 2.0V. This charge-discharge cycle was repeated 1000 times, and the discharge capacity at the first cycle and the discharge capacity at the 1000th cycle were measured. The cutoff voltage varies depending on the positive electrode active material; for example, when the positive electrode active material is lithium iron phosphate, the charging cutoff voltage is set to 3.7V; when the positive electrode active material is lithium manganese iron phosphate, the charging cutoff voltage is set to 4.5V; and when the positive electrode active material is a cobalt or nickel-containing phosphate material, the charging cutoff voltage is set to 5.0V.

[0139] First-cycle discharge specific capacity (mAh / g) = first-cycle discharge capacity (mAh) / mass of positive electrode active material (g);

[0140] 1000-cycle capacity retention = (1000th cycle discharge capacity / 1st cycle discharge capacity) × 100%.

[0141] Rate testing: At 25℃, charge at a constant current of 0.5C (1250mA) to the cutoff voltage, maintain the voltage at 0.05C (125mA), and then discharge at 0.5C (1250mA) to 2.0V. Repeat this cycle 10 times and calculate the average discharge energy, recorded as the 0.5C cycle discharge energy. Similarly, charge at a constant current of 0.5C (1250mA) to the cutoff voltage, maintain the voltage at 0.05C (125mA), and then discharge at 10C (25000mA) to 2.0V. Repeat this cycle 10 times and calculate the average discharge energy, recorded as the 10C cycle discharge energy. The cutoff voltage varies depending on the positive electrode active material; for example, when the positive electrode active material is lithium iron phosphate, the charging cutoff voltage is set to 3.7V; when the positive electrode active material is lithium manganese iron phosphate, the charging cutoff voltage is set to 4.5V; and when the positive electrode active material is a cobalt or nickel-containing phosphate material, the charging cutoff voltage is set to 5.0V.

[0142] Rate discharge energy retention rate = (10C cycle discharge energy / 0.5C cycle discharge energy) × 100%.

[0143] Low-temperature test: At 25℃, charge at a constant current of 0.5C (1250mA) to the cutoff voltage, then charge at a constant voltage to 0.05C (125mA), and then discharge at 0.5C (1250mA) to 2.0V under low-temperature conditions. The cutoff voltage varies depending on the positive electrode active material. For example, when the positive electrode active material is lithium iron phosphate, the charging cutoff voltage is set to 3.7V; when the positive electrode active material is lithium manganese iron phosphate, the charging cutoff voltage is set to 4.5V; and when the positive electrode active material is a cobalt or nickel-containing phosphate material, the charging cutoff voltage is set to 5.0V.

[0144] Low-temperature discharge capacity retention rate = Low-temperature discharge capacity / 25℃ discharge capacity × 100%.

[0145] Table 1

[0146]

[0147] As shown in Table 1, the test data indicate that the electrochemical performance of the secondary batteries in Examples 1-5 is superior to that in Comparative Examples 1-3. This demonstrates that the present invention introduces aromatic amine additives in the first preparation step. The aromatic ammonium groups in these additives form NHOP bonds on the particle surface. These bonds can limit particle agglomeration and continuous growth, resulting in phosphate materials with smaller and more uniform particle size. The uniform particle size enables the material particles to undergo synchronous delithiation and lithium insertion during charging and discharging, thereby suppressing overcharging or discharging of certain particles and extending the battery's lifespan.

[0148] Furthermore, this additive will form active dangling bonds on the surface of the resulting phosphate particles after the solvothermal reaction, resulting in a more uniform carbon coating layer with less free carbon during the subsequent carbon coating process. This coating layer can effectively improve the conductivity of the cathode material, promote lithium-ion migration and electron transfer, thereby reducing the internal resistance of the battery and enhancing its charge-discharge performance. In addition, less free carbon means fewer unnecessary side reactions, further improving the safety and stability of the battery. Therefore, a uniform carbon coating layer with less free carbon in the cathode material is one of the key technologies for improving the electrochemical performance of batteries.

[0149] As shown in Table 1, the electrochemical performance of the secondary batteries in Examples 1 to 5 is significantly better than that of Comparative Example 4, indicating that the modified phosphate material prepared by the preparation method of the present invention has better performance than the cathode material prepared by the conventional solid-state method.

[0150] like Figure 1 As shown in the scanning electron microscope image of Example 1, the phosphate material obtained in Example 1 of the present invention has small particles, good dispersibility and uniform particle size. The structure is lamellar and the (010) crystal plane is preferred. This indicates that the present invention introduces aromatic amine additives in the preparation step one. The aromatic ammonium groups in the additive form NHOP bonds on the particle surface. These bonds can limit particle agglomeration and continuous growth, resulting in phosphate material with small particles, good dispersibility and uniform particle size.

[0151] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A phosphate material, characterized in that, Its chemical formula is LiM 1-x N x PO4, wherein M is at least one of Ni, Co, Mn and Fe, and N is at least one of Mg, Ti, Al, Zr, Ba, V, Ni, Co and Mn, and 0 ≤ x ≤ 0.1; the D90, D50 and D10 of the phosphate material satisfy the relationship: (D90-D10) / D50 ≤ 2; the structure of the phosphate material is a plate-like or plate-like structure, and the preferred crystal orientation of the phosphate material is (010); active dangling bonds exist on the surface of the phosphate material; The preparation method of the phosphate material includes the following preparation steps: Step 1: Weigh the lithium source, M source, N source, phosphorus source and solvent separately and prepare them into mixture A. At the same time, prepare the aromatic amine additive into a solution. The aromatic amine additive includes at least one of aniline, p-phenylenediamine, methoxyaniline, N-methylaniline and o-toluidine. Step 2: Transfer the mixture A and the solution to a high-pressure reactor and mix thoroughly. Seal and heat under an inert atmosphere to carry out a solvothermal reaction. Step 3: Filter out the solid after the reaction and wash it to obtain the phosphate material.

2. The phosphate material according to claim 1, characterized in that, The average diameter of the phosphate material is d, and the average thickness is h. The relationship between d and h is: d / h≥2.

3. A modified phosphate material, characterized in that, It includes the phosphate material as described in any one of claims 1 to 2 and a carbon coating layer covering the surface of the phosphate material.

4. A method for preparing a modified phosphate material, characterized in that, Includes the following steps: Step 1: Weigh the lithium source, M source, N source, phosphorus source and solvent separately and prepare mixture A. At the same time, prepare the aromatic amine additive into a solution. Step 2: Transfer the mixture A and the solution to a high-pressure reactor and mix thoroughly. Seal and heat under an inert atmosphere to carry out a solvothermal reaction. Step 3: Filter out the solid after the reaction and wash it to obtain the phosphate material as described in claim 1 or 2; Step 4: Thoroughly mix the phosphate material, carbon source, and dispersant to obtain a mixed slurry. Dry the mixed slurry to obtain mixture B. Step 5: Sinter mixture B under an inert atmosphere to obtain the modified phosphate material.

5. The method for preparing the modified phosphate material according to claim 4, characterized in that, In step four, the carbon source includes at least one of glucose, sucrose, citric acid, oleic acid, ascorbic acid, dopamine, starch, PEG, and PVP.

6. The method for preparing the modified phosphate material according to claim 4, characterized in that, In step four, the mixing method is mechanical stirring and dispersion.

7. The method for preparing the modified phosphate material according to claim 4, characterized in that, In step four, the mixing method is wet grinding dispersion or liquid phase ultrasonic dispersion.

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