Phosphate material, modified phosphate material and preparation method thereof

Abstract

The invention discloses a phosphate material, a modified phosphate material and a preparation method thereof, the chemical formula of the phosphate material is LiM1-xNxPO4, 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 x is greater than or equal to 0 and less than or equal to 0.1; d90, D50 and D10 of the phosphate material meet the relational expression that (D90-D10) / D50 is smaller than or equal to 2. The relational expression shows that the phosphate material particles are good in dispersity and uniform in particle size. The uniform particle size can enable material particles to keep synchronous lithium removal and lithium intercalation in the charging and discharging process of the battery, so that overcharging or discharging of some particles is inhibited, and the service life of the battery is prolonged. In addition, the mechanical stress can be reduced due to the uniform particle size, the cycling stability and safety of the battery are improved, and the electrochemical performance of the secondary battery is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and particularly to a phosphate material, a modified phosphate material, and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have been widely used in many fields such as new energy vehicles, 3C electronic products, and power tools due to their high energy density, portability, environmental protection characteristics, and safety. In recent years, the field of lithium-ion battery cathode materials has experienced rapid development, mainly forming three categories: layered cathode materials (covering lithium cobaltate and ternary materials), spinel-structured lithium manganate materials, and phosphate cathode materials. Among them, lithium iron phosphate materials are widely used due to their excellent safety performance, long cycle life, high-temperature stability, and cost-effectiveness. With the continuous increase in the market demand for battery energy density, lithium manganese iron phosphate and other transition metal phosphate materials have also received increasing attention from the research community.

[0003] However, a key challenge faced by phosphate cathode materials is their extremely low conductivity, which greatly limits the exertion of their performance potential. To overcome this problem, researchers have explored various optimization and modification strategies, mainly including doping modification technology, surface coating treatment, and fine design of microtopography, etc.

[0004] Phosphate materials synthesized by the solvothermal method are characterized by good particle uniformity and usually exhibit excellent rate performance and low-temperature performance. The key to further improving the performance of such materials lies in optimizing their morphology control and enhancing the effect of carbon coating, which are two important research directions at present, but the existing technology at the present stage has limited research on these two directions.

[0005] In view of the above defects existing in current phosphate materials, it is indeed necessary to provide a technical solution to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to provide a phosphate material, which has the characteristics of small particles, good dispersibility, and good particle size uniformity, and at the same time has active dangling bonds on its surface, which helps to obtain a more uniform carbon coating layer subsequently.

[0007] To achieve this purpose, the present invention provides the following solutions:

[0008] A phosphate material, the chemical formula of which is LiM 1-x N xPO4, where 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, there are active dangling bonds on the surface of the phosphate material.

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

[0011] Preferably, the structure of the phosphate material is a flaky or quasi-flaky structure.

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

[0013] Preferably, the crystallization preferred orientation of the phosphate material is (010).

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

[0015] A method for preparing a modified phosphate material, comprising the following steps:

[0016] Step 1: Weigh the lithium source, M source, N source, phosphorus source, and solvent respectively and prepare them into a mixture A, and at the same time prepare an additive solution of aromatic amine additives;

[0017] Step 2: Transfer the mixture A and the additive solution to an autoclave, mix them thoroughly, seal and heat in an inert atmosphere, and carry out a solvothermal reaction;

[0018] Step 3: After the autoclave is cooled, filter and separate the reacted solid and wash it to obtain a phosphate material;

[0019] Step 4: Mix the phosphate material, carbon source, and dispersant evenly to obtain a mixed slurry, and perform a drying treatment on the mixed slurry to obtain a mixture B;

[0020] Step 5: Sinter the mixture B to obtain a modified phosphate material.

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

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

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

[0024] Preferably, in the first step, the solvent included in the mixture A is at least one of ethanol, ethylene glycol, methanol, polyethylene glycol, isopropanol, glycerol, and water.

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

[0026] Preferably, in the first step, the M source is at least one of divalent sulfates, nitrates, acetates, and chlorides of the corresponding transition metals;

[0027] Preferably, in the first step, the N source is at least one of oxides, phosphides, phosphates, sulfates, nitrates, acetates, and chlorides of the corresponding metal elements.

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

[0029] Preferably, in the first step, 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 first step, 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 first step, 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; the reaction time is 4 - 6 h.

[0032] Preferably, in the fourth step, 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.

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

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

[0035] Preferably, in the fourth step, the drying method is drying in a blast drying oven, vacuum drying oven or spray drying; more preferably, it is spray drying.

[0036] Preferably, in the fifth step, the sintering atmosphere is one or more of argon, nitrogen, hydrogen / argon mixture, and more preferably, it is nitrogen.

[0037] Preferably, in the fifth step, the sintering temperature is 450°C - 800°C, and the sintering time is 2 - 12 h. Further preferably, the sintering temperature is 600°C - 700°C, and the sintering time is 5 - 8 h.

[0038] The present invention also provides a positive electrode sheet, which includes a positive electrode material, a conductive agent and a binder, and the positive electrode material is the above-mentioned modified phosphate material.

[0039] The present invention also provides a secondary battery, which includes a separator, a negative electrode sheet, an electrolyte, a battery case and the above-mentioned positive electrode sheet.

[0040] Compared with the prior art, the beneficial effect of the present invention is that: the present invention provides a phosphate material, whose chemical formula is LiM 1-x N x PO4, where 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. This relationship shows that the phosphate material of the present invention has good particle dispersion and uniform particle size. The uniform particle size can enable the material particles to maintain synchronous de-lithiation and intercalation during the charge and discharge process of the battery, thereby inhibiting the overcharge or over-discharge 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 THE DRAWINGS

[0041] Figure 1 It is a scanning electron microscope image of the phosphate material prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0042] To make the technical solutions and advantages of the present invention clearer, the following will, in conjunction with specific embodiments, clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0043] In a first aspect according to the present invention, a phosphate material is provided, and its chemical formula is LiM 1-x N x PO4, where 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. This relationship indicates that the phosphate material particles of the present invention have good dispersibility and uniform particle size. The uniform particle size enables the material particles to maintain synchronous de-lithiation and intercalation during the charge and discharge process of the battery, thereby inhibiting overcharging or over-discharging of some particles and extending 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 invention, there are active dangling bonds on the surface of the phosphate material. By providing active dangling bonds on the surface of the phosphate material, it can serve as an active site to promote the progress of chemical reactions, contribute to the combination with the carbon source during the subsequent carbon coating process, thereby obtaining a more uniform carbon coating layer, and further improving the overall electrochemical performance of the phosphate material.

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

[0046] Small phosphate material particles can bring many benefits. The smaller particle size helps to shorten the diffusion path of lithium ions, reduce the polarization phenomenon, and thus improve the high-rate charge and discharge performance of the battery. At the same time, small particles can more effectively utilize the active material, increasing the capacity and energy density of the battery.

[0047] In an embodiment according to the present invention, the structure of the phosphate material is a flake or quasi-flake 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 crystal preferred orientation of the material is (010). For phosphate materials, represented by lithium iron phosphate, its lithium ion diffusion channel is one-dimensional, Li +Diffusing along the

[010] direction, the charge transfer mainly occurs on the (010) crystal plane. Therefore, materials with (010) preferred sampling are more conducive to the lithium ion transport during the charge and discharge process, and the materials will have better rate performance.

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

[0049] In the third aspect of the present invention, a preparation method of a modified phosphate material is further provided, including the following steps:

[0050] Step 1: Weigh the lithium source, M source, N source, phosphorus source and solvent respectively and configure them into mixture A, and at the same time configure the aromatic amine additive into a solution;

[0051] Step 2: Transfer mixture A and the solution to an autoclave, mix them thoroughly, seal and heat them in an inert atmosphere for solvothermal reaction;

[0052] Step 3: Filter out the solid after the reaction and wash it to obtain the phosphate material;

[0053] Step 4: Mix the phosphate material, carbon source and dispersant evenly to obtain a mixed slurry, and perform a drying treatment on the mixed slurry to obtain mixture B;

[0054] Step 5: Sinter mixture B to obtain the modified phosphate material.

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

[0056] In an embodiment according to the present invention, in step 1, the aromatic amine additive includes at least one of aniline, p-phenylenediamine, methoxyaniline, N-methylaniline and o-toluidine. The present invention introduces an aromatic amine additive in the synthesis step 1. The aromatic ammonium group in this additive forms an N-H-O-P bond on the particle surface, which can play a role in restricting particle agglomeration and continuous growth, and obtain a phosphate material with smaller particles and uniform particle size. In addition, this additive will also form active dangling bonds 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 during 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 - 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, and the alcohol solution 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 divalent sulfates, nitrates, acetates, and chlorides of the corresponding transition metals;

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

[0061] In one embodiment of the present invention, in step one, when the M element is iron, an inert gas needs to be introduced into the solvent to expel oxygen and an antioxidant needs to be pre-added when preparing the M source solution; 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 of 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 hydrogen 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 according to 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, it can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C; the reaction time is 4 - 6 h, for example, it can be 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, 6.0 h. The advantages of preparing phosphate materials by the solvothermal method are that its reaction conditions are relatively mild, and it can prepare cathode materials with high crystallinity, easy-to-control morphology, 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 according to 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 according to the present invention, in step four, the mixing method is mechanical stirring dispersion, wet grinding dispersion or liquid-phase ultrasonic dispersion; more preferably, it is liquid-phase ultrasonic dispersion. The ultrasonic frequency of the liquid-phase ultrasonic dispersion > 80 kHz, and the dispersion time is 0.5 - 12 h, for example, it can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h. Liquid-phase ultrasonic dispersion can form a stable dispersion liquid with particle sizes as small as micrometers or even nanometers, and the droplet size distribution range is narrow; it has a wide application range and can adapt to various working environments; at the same time, ultrasonic dispersion can directly deliver a large amount of energy to the reaction medium, effectively convert electrical energy into mechanical energy, and can control the dispersion effect by regulating the ultrasonic energy size. This process has low energy consumption, high production efficiency and low cost; in addition, by using high-frequency ultrasonic dispersion to mix the phosphate material and the carbon source, the excellent original morphology characteristics of the phosphate material can be better maintained while being fully mixed.

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

[0069] In one embodiment according to the present invention, in step four, the drying method is drying in a forced-air drying oven, vacuum drying oven or spray drying; further preferably, it is 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°C to 800°C, and the sintering time is 2 to 12 h. Further preferably, the sintering temperature is 600°C to 700°C, for example, it can be 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700; the sintering time is 5 to 8 h. For example, it can be 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h.

[0072] In the third aspect of the present invention, a positive electrode sheet is further provided, which includes a positive electrode material, a conductive agent, and a binder, and the positive electrode material is the above-mentioned composite positive electrode material.

[0073] In the fourth aspect of the present invention, a secondary battery is further provided, which includes a separator, a negative electrode sheet, an electrolyte, a battery case, and the above-mentioned positive electrode sheet.

[0074] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material layer can be one or several of, 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, etc.

[0075] Among them, the graphite can be selected from one or several of artificial graphite, natural graphite, and modified graphite; the silicon-based materials can be selected from one or several of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys; the tin-based materials can be selected from one or several of elemental tin, tin oxides, and tin alloys. The negative electrode current collector is usually a structure or part that collects current, and the negative electrode current collector can be various materials in the art suitable for use as the negative electrode current collector of a secondary battery. For example, the negative electrode current collector can be, but not limited to, metal foils, etc., and more specifically can be, but not limited to, copper foils, etc.

[0076] The secondary battery further includes an electrolyte, which includes an organic solvent, an electrolyte lithium salt, and an additive. Among them, 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-proof electrolytes; it can also 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; it can also be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additive includes at least one of, but not limited to, a film-forming additive, a conductive additive, a flame retardant additive, an overcharge prevention additive, an additive for controlling the content of H2O and HF in the electrolyte, an additive for improving low-temperature performance, and a multifunctional additive.

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

[0078] Example 1

[0079] Preparation of modified phosphate:

[0080] Step 1: Calculate the feeding 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, and prepare aqueous solutions with a lithium concentration of 4.5 mol / L, a phosphorus concentration of 3 mol / L, and a total concentration of iron, manganese, and nickel of 1 mol / L using water as a solvent; use polyethylene glycol with a molecular weight of 500 as a solvent to prepare a 50 ml solution containing 0.1 mol / L of p-phenylenediamine;

[0081] Step 2: Transfer the mixture A and the solution to a high-pressure reaction kettle, mix them thoroughly, seal them under an argon atmosphere, heat them to 200 °C, and keep them warm for 2 h to carry out a solvothermal reaction;

[0082] Step 3: Filter out the solid after the reaction, wash it, and perform centrifugal separation to obtain a phosphate material; among them, the surface of the phosphate material has active dangling bonds, and (D90 - D10) / D50 = 1.8; the crystallization preferred orientation is (010);

[0083] Step 4: Ultrasonically disperse the phosphate material, carbon source, and dispersant using ultrasonic waves at 200 kHz for 2 h to obtain a mixed slurry, and perform spray drying on the mixed slurry to obtain a mixture B; among them, the carbon source is glucose and PVP with a mass ratio of 7:1, the dispersant is ethanol, and the mass ratio of the carbon source to the phosphate material is 0.8:1; the outlet temperature of the spray drying process is 85 °C;

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

[0085] Preparation of secondary battery:

[0086] Using the modified phosphate as the cathode material, mix it with conductive carbon black and PVDF in a mass ratio of 95:3:2, and disperse the mixture in NMP to form a slurry. After stirring, coating, drying, rolling, and slitting, a cathode sheet is obtained.

[0087] Using artificial graphite as the anode active material, mix it with conductive agent conductive carbon black and PVDF in a mass ratio of 94:3:3, and disperse the mixture in NMP to form a slurry. After stirring, coating, drying, rolling, and slitting, an anode sheet is obtained.

[0088] Interleave and wind the anode sheet, cathode sheet, and separator, and then go through the steps of terminal welding, packaging with aluminum foil encapsulation, injecting electrolyte, encapsulating and forming, and evacuating and forming. Finally, a soft-packaged lithium-ion battery is prepared, and the designed capacity of the battery is 2500 mAh. Among them, the solute of the electrolyte is 1 mol / L LiPF6, and the solvents are EC, DMC, and DEC with a volume ratio of 1:1:1.

[0089] Example 2

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

[0091] Step 1: Calculate the feeding 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 a lithium concentration of 4.8 mol / L, a phosphorus concentration of 3 mol / L, and a combined 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-magnesium solution, pre-pass nitrogen to remove oxygen and add 0.05 mol of citric acid; Using ethanol as the solvent, prepare a 50 ml solution containing 0.2 mol / L of p-phenylenediamine.

[0092] Step 2: Transfer the mixture A and the solution to a high-pressure reaction kettle, mix them thoroughly, seal them under an argon atmosphere, heat to 160 °C, and hold for 8 h to carry out a solvothermal reaction.

[0093] Step 3: Filter out the reacted solid, wash it, and perform centrifugal separation to obtain the phosphate material; Among them, the surface of the phosphate material has active dangling bonds, and (D90 - D10) / D50 = 1.5.

[0094] Step 4: Ultrasonically disperse the phosphate material, carbon source, and dispersant using ultrasonic waves at 120 kHz for 5 h to obtain a mixed slurry, and perform spray drying on the mixed slurry to obtain mixture B; wherein, the carbon source is sucrose and PEG with a mass ratio of 6:2, the dispersant is water, and the mass ratio of the carbon source to the phosphate material is 0.8:1; the outlet temperature of the spray drying process is 90 °C;

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

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

[0097] Example 3

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

[0099] Step 1: Calculate the feeding 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, and prepare aqueous solutions with a lithium concentration of 4.5 mol / L, a phosphorus concentration of 4 mol / L, and a combined iron and manganese concentration of 2 mol / L respectively using a mixture of ethylene glycol and water (volume ratio 1:4) as the solvent; prior to preparing the iron-manganese solution, nitrogen is introduced to remove oxygen and 0.01 mol of ascorbic acid is added; using methanol as the solvent, prepare a 50 ml solution containing 0.2 mol / L of p-methoxyaniline;

[0100] Step 2: Transfer the mixture A and the solution to a high-pressure reactor, mix them thoroughly, seal them under an argon atmosphere, heat to 180 °C, and keep warm for 6 h to carry out a solvothermal reaction;

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

[0102] Step 4: Ball-mill and mix the phosphate material, carbon source, and dispersant for 0.5 h to obtain a mixed slurry, and perform spray drying on the mixed slurry to obtain mixture B; wherein, the carbon source is glucose and PEG with a mass ratio of 8:2, the dispersant is water, and the mass ratio of the carbon source to the phosphate material is 0.1:1; the outlet temperature of the spray drying process is 90 °C;

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

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

[0105] Example 4

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

[0107] Step 1: Calculate the feeding 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 a lithium concentration of 4.5 mol / L, a phosphorus concentration of 4 mol / L, and a combined iron and manganese concentration of 1.25 mol / L using a mixture of ethylene glycol and water (volume ratio 1:4) as the solvent; Prior to preparing the iron-manganese solution, nitrogen is introduced to remove oxygen and 0.015 mol of ascorbic acid is added; Using isopropanol as the solvent, prepare a 50 ml solution containing 0.2 mol / L of N-methylaniline and o-toluidine;

[0108] Step 2: Transfer the mixture A and the solution to an autoclave, mix well, seal it under an argon atmosphere, heat it to 200 °C, and hold for 2 h for hydrothermal reaction;

[0109] Step 3: Filter out the reacted solid, wash it, and perform centrifugal separation to obtain the phosphate material; Among them, the surface of the phosphate material has active dangling bonds, and (D90 - D10) / D50 = 1.6;

[0110] Step 4: Ball-mill the phosphate material, carbon source, and dispersant for 0.5 h to obtain a mixed slurry, and perform spray drying on the mixed slurry to obtain mixture B; Among them, the carbon source is glucose, starch, and PEG with a mass ratio of 5:1:1, the dispersant is water, and the mass ratio of the carbon source to the phosphate material is 0.07:1; The outlet temperature of the spray drying process is 80 °C;

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

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

[0113] Example 5

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

[0115] Step 1: Calculate the feeding 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 a lithium concentration of 2 mol / L, a phosphorus concentration of 2 mol / L, and an iron concentration of 1 mol / L using a mixture of ethylene glycol and water (volume ratio 1:2) as the solvent; Prior to preparing the iron solution, nitrogen is introduced to remove oxygen and 0.03 mol of ascorbic acid is added; Using glycerol as the solvent, prepare a 50 ml solution containing 0.2 mol / L of p-phenylenediamine;

[0116] Step 2: Transfer the mixture A and the solution to an autoclave, mix them thoroughly, adjust the pH value to neutral, seal them under an argon atmosphere, heat them to 180 °C and keep them at this temperature for 4 h to carry out a hydrothermal reaction;

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

[0118] Step 4: Mix the phosphate material, a carbon source and a dispersant by ball milling for 0.5 h to obtain a mixed slurry, and perform spray drying on the mixed slurry to obtain a mixture B; wherein, the carbon source is sucrose and PEG with a mass ratio of 6:3, the dispersant is water, and the mass ratio of the carbon source to the phosphate material is 0.09:1; the outlet temperature of the spray drying process is 80 °C;

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

[0120] The rest is the same as that of Example 1 and will not be elaborated here.

[0121] Comparative Example 1:

[0122] Different from Example 1, p-phenylenediamine is not added in Preparation Step 1, the obtained phosphate material in Step 3 has no active dangling bonds, and (D90 - D10) / D50 = 5.

[0123] The rest is exactly the same as that of Example 1 and will not be elaborated here.

[0124] Comparative Example 2:

[0125] Different from Example 3, methoxyaniline is not added in Preparation Step 1, the obtained phosphate material in Step 3 has no active dangling bonds, and (D90 - D10) / D50 = 8.

[0126] The rest is exactly the same as that of Example 3 and will not be elaborated here.

[0127] Comparative Example 3:

[0128] Different from Example 5, p-phenylenediamine is not added in Preparation Step 1, the obtained phosphate material in Step 3 has no active dangling bonds, and (D90 - D10) / D50 = 4.

[0129] The rest is exactly the same as that of Example 5 and will not be elaborated here.

[0130] Comparative Example 4:

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

[0132] Step 1: iron phosphate and lithium carbonate are prepared according to a molar ratio of Li:Fe:P of 1:1:1, and glucose and PEG are added at the same time, and the addition amounts are 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 with water as the dispersion medium, and then spray dry;

[0134] Step 3: Sinter the spray-dried material at 700° C. for 12 h in a nitrogen atmosphere to obtain a carbon-coated lithium iron phosphate material.

[0135] Performance Test:

[0136] The secondary batteries of the above embodiments and comparative examples were subjected to electrochemical performance tests, and the test results are shown in Table 1.

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

[0138] Capacity and cycle performance test: At 25°C, charge at a constant current of 0.5C (1250mA) to the charge cut-off voltage, then charge at a constant voltage to 0.05C (125mA), and then discharge at 0.5C (1250mA) to 2.0V, repeat this charge and discharge cycle 1000 times, and measure the discharge capacity at the first cycle and the discharge capacity at the 1000th cycle. Among them, the cut-off voltage varies according to the different positive electrode active materials; for example, when the positive electrode active material is lithium iron phosphate, the charge cut-off voltage is set to 3.7V; when the positive electrode active material is lithium manganese iron phosphate, the charge cut-off voltage is set to 4.5V; when the positive electrode active material is a phosphate material containing cobalt or nickel, the charge cut-off voltage is set to 5.0V.

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

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

[0141] Rate test: At 25°C, charge at a constant current of 0.5C (1250 mA) until the cut-off voltage, then charge at a constant voltage until 0.05C (125 mA), and then discharge at 0.5C (1250 mA) to 2.0V. Repeat this cycle 10 times and calculate the average discharge energy, which is denoted as the 0.5C cyclic discharge energy; charge at a constant current of 0.5C (1250 mA) until the cut-off voltage, then charge at a constant voltage until 0.05C (125 mA), and then discharge at 10C (25000 mA) to 2.0V. Repeat this cycle 10 times and calculate the average discharge energy, which is denoted as the 10C cyclic discharge energy. Among them, the cut-off voltage varies according to the different cathode active materials; for example, when the cathode active material is lithium iron phosphate, the charging cut-off voltage is set to 3.7V; when the cathode active material is lithium iron manganese phosphate, the charging cut-off voltage is set to 4.5V; when the cathode active material is a phosphate material containing cobalt or nickel, the charging cut-off voltage is set to 5.0V.

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

[0143] Low-temperature test: At 25°C, charge at a constant current of 0.5C (1250 mA) until the cut-off voltage, then charge at a constant voltage until 0.05C (125 mA), and then discharge at 0.5C (1250 mA) to 2.0V under low-temperature conditions; among them, the cut-off voltage varies according to the different cathode active materials; for example, when the cathode active material is lithium iron phosphate, the charging cut-off voltage is set to 3.7V; when the cathode active material is lithium iron manganese phosphate, the charging cut-off voltage is set to 4.5V; when the cathode active material is a phosphate material containing cobalt or nickel, the charging cut-off voltage is set to 5.0V.

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

[0145] Table 1

[0146]

[0147] As can be seen from the test data shown in Table 1, the electrochemical performance of the secondary batteries in Examples 1 to 5 is better than that of Comparative Examples 1 to 3, indicating that in the preparation step 1 of the present invention, an aromatic amine additive is introduced. The aromatic ammonium group in this additive forms an N-H-O-P bond on the particle surface, which can play a role in restricting particle agglomeration and continuous growth, resulting in a phosphate material with smaller particles and a uniform particle size; the uniform particle size enables the material particles in the battery to maintain synchronous de-lithiation and lithium intercalation during charge and discharge, thereby inhibiting overcharging or over-discharging of some particles and extending the service life of the battery.

[0148] In addition, the additive will also form active dangling bonds on the surface of the generated phosphate material particles after the solvothermal reaction, enabling a more uniform carbon coating layer with less free carbon to be obtained during the subsequent carbon coating process. This coating layer can effectively improve the conductivity of the cathode material, promote the migration of lithium ions and the transfer of electrons, thereby reducing the internal resistance of the battery and enhancing the charge-discharge performance of the battery. Additionally, 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 on the cathode material is one of the key technologies for enhancing the electrochemical performance of the battery.

[0149] As can be seen from the test data 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 performance of the modified phosphate material prepared by the preparation method of the present invention is superior to that of the cathode material prepared by the conventional solid-phase method.

[0150] As Figure 1 can be seen from the scanning electron micrograph of Example 1 shown, the phosphate material obtained in Example 1 of the present invention has small particles, good dispersion, and uniform particle size. The structure is sheet-like and preferentially oriented on the (010) crystal plane, indicating that an aromatic amine additive is introduced in the first preparation step of the present invention. The aromatic ammonium group in this additive forms an N-H-O-P bond on the particle surface, and this bond can play a role in restricting particle agglomeration and continuous growth, resulting in a phosphate material with small particles, good dispersion, and uniform particle size.

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

Claims

1. A phosphate material, characterized in that, Its chemical formula is LiM 1-x N x PO4, where 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.

2. The phosphate material according to claim 1, wherein Active dangling bonds exist on the surface of the phosphate material.

3. The phosphate material according to claim 1, wherein The structure of the phosphate material is a flake or flake-like structure.

4. The phosphate material according to claim 3, characterized in that, The average diameter of the flaky phosphate material is d, and the average thickness is h, and d and h satisfy the relationship: d / h≥2.

5. The phosphate material according to claim 1, wherein The preferred crystal orientation of the phosphate material is (010).

6. A modified phosphate material, characterized in that, The invention comprises the phosphate material according to any one of claims 1 to 5 and a carbon coating layer coated on the surface of the phosphate material.

7. A method for preparing a modified phosphate material, characterized in that, The following steps are involved: Step 1: The lithium source, M source, N source, phosphorus source and solvent are weighed respectively and prepared into a mixture A, and the aromatic amine additive is prepared into a solution; Step 2: transferring the mixture A and the solution into a high-pressure reactor, mixing them thoroughly, sealing and heating them under an inert atmosphere to perform a solvothermal reaction; Step 3: filtering out the solid after the reaction, and washing it to obtain a phosphate material; Step 4: fully and uniformly mix the phosphate material, the carbon source and the dispersant to obtain a mixed slurry, and dry the mixed slurry to obtain a mixture B; Step 5: Sintering the mixture B under an inert atmosphere to obtain a modified phosphate material.

8. The preparation method of the modified phosphate material according to claim 7, characterized in that, In the step 1, the aromatic amine additive includes at least one of aniline, p-phenylenediamine, methoxyaniline, N-methylaniline and o-toluidine.

9. The preparation method of the modified phosphate material according to claim 7, wherein In step 4, the carbon source includes at least one of glucose, sucrose, citric acid, oleic acid, ascorbic acid, dopamine, starch, PEG and PVP.

10. The preparation method of the modified phosphate material according to claim 7, wherein, In the step 4, the mixing method is mechanical stirring dispersion, wet grinding dispersion or liquid phase ultrasonic dispersion.

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