A rate type lithium iron phosphate cathode material, a preparation method and a battery thereof

Abstract

The application discloses a kind of rate type lithium iron phosphate positive electrode material, preparation method and battery thereof, first using hydrochloric acid dopamine to modify treatment to iron phosphate, improve the surface activity of iron phosphate, it is beneficial to subsequent cobalt, magnesium doping, can limit grain excessive growth in high-temperature sintering, and introduce nitrogen carbon in lithium iron phosphate inside, form carbon nitrogen coating layer, improve electronic conductivity;Then, using isopropyl tri (dioctyl pyrophosphoric acid acyl oxygen) titanate, cobalt oxide and magnesium oxide to prepare dopant, make cobalt, magnesium evenly doped into lithium iron phosphate crystal lattice to form phase doping, cobalt magnesium co-doped synergistically improve the electronic conductivity and structural stability of lithium iron phosphate material;Finally, using biomass carbon source β-cyclodextrin carries out carbon coating, forms uniform carbon layer on the surface of lithium iron phosphate, further improves the electrochemical performance of lithium iron phosphate;Lithium iron phosphate material prepared by the application also has good electrochemical performance under high rate.

Description

Technical Field

[0001] This invention relates to the field of lithium iron phosphate preparation technology, and more specifically, to a rate-capable lithium iron phosphate cathode material, its preparation method, and its battery. Background Technology

[0002] In the field of new energy vehicles, high-rate lithium batteries significantly shorten the charging time of electric vehicles, helping to alleviate users' anxiety about range and charging time, and improving the convenience of vehicle use. In energy storage systems, they can be applied to grid peak shaving, large-scale emergency power supplies, and distributed energy storage facilities to meet the needs of rapid charging and discharging, addressing power supply and demand imbalances. In industrial equipment and drones, high-rate lithium batteries can significantly improve work efficiency for portable devices requiring frequent high-power output or rapid power replenishment, such as power tools and drones. As the core component of a battery, the cathode material directly affects the battery's energy density, rate performance, and overall performance and cost. Therefore, developing high-performance cathode materials for lithium-ion batteries is crucial for promoting the continued high-quality development of the electric vehicle industry and other energy storage power sectors.

[0003] Cathode materials, due to their advantages such as low cost, environmental friendliness, long cycle life, and high safety, have been widely researched and entered the mass application stage, occupying more than half of the market share. Rate performance is a key consideration for phosphate cathode materials, significantly impacting the battery's rapid charge and discharge performance over a short period. However, the poor electronic conductivity and lithium-ion mobility of lithium iron phosphate materials limit their rate performance, making it difficult to meet the power performance requirements of power lithium-ion batteries, thus restricting the application of lithium iron phosphate electrode materials.

[0004] Therefore, improving the rate performance of lithium iron phosphate materials has become one of the key research directions for lithium iron phosphate cathode materials. Currently, methods such as bulk doping, morphology control, crystal-surface conductive layer coating, and constructing three-dimensional conductive structures are used to accelerate lithium-ion migration and shorten its diffusion path, and improve electronic conductivity. For example, Chinese patent CN119674025A discloses a carbon-coated titanium-doped lithium iron phosphate cathode material and its preparation method. The method involves mixing a ferrous iron solution and a phosphorus source solution in a specific ratio, adding dopamine hydrochloride, adjusting the pH, adding a titanium source solution, stirring until homogeneous, and then further adjusting the pH to obtain pre-embedded titanium-coated polydopamine-coated ferrous phosphate octahydrate. This pre-embedded titanium-coated polydopamine-coated ferrous phosphate octahydrate is then calcined in an inert gas atmosphere to obtain carbon-coated titanium-doped anhydrous ferrous phosphate. Finally, the carbon-coated titanium-doped anhydrous ferrous phosphate is mixed with lithium phosphate and a carbon source through ball milling, spray drying, and calcination to obtain the carbon-coated titanium-doped lithium iron phosphate cathode material. This invention increases the stability of the precursor through dopamine hydrochloride and its polymer polydopamine, providing a more uniform titanium source distribution for titanium doping of lithium iron phosphate. The titanium doping and carbon coating provide richer channels for electron transport, improving the electronic conductivity of the material.

[0005] For example, Chinese patent CN116895748A discloses an LFMP@LFMCP composite material, which includes an LFMP core and an LFMCP shell coated on its surface in situ; wherein, LFMP is magnesium-doped lithium iron phosphate; LFMCP is magnesium-cobalt co-doped lithium iron phosphate; by combining magnesium and cobalt doping, a core-shell structure is formed to improve the electrochemical performance of lithium iron phosphate materials. For example, Chinese patent CN102227024A discloses a cathode material, lithium iron phosphate, suitable for power lithium-ion batteries, and its preparation method. The method involves mixing a lithium source compound, an iron source compound, and a phosphate source compound to obtain a lithium iron phosphate precursor mixture. Then, one or more dopant elements, such as manganese, cobalt, vanadium, nickel, aluminum, magnesium, calcium, and zinc, are added to the lithium iron phosphate precursor mixture to obtain a doped lithium iron phosphate precursor. Subsequently, an organic carbon source and / or an inorganic carbon source are added to obtain the precursor of the lithium iron phosphate cathode material for power lithium-ion batteries. Finally, a protective gas or reducing gas is introduced for high-temperature sintering to obtain lithium iron phosphate suitable for power lithium-ion battery cathode materials. This method improves the electronic conductivity of the material and enhances its electrochemical performance through metal compound doping and carbon coating.

[0006] The combined application of these methods in the existing technology can improve the rate performance of lithium iron phosphate materials to a certain extent, but there are problems in terms of the uniformity of doping and the stability of the material after doping modification. Based on this, it is of great significance to further study how to better improve the rate performance of lithium iron phosphate cathode materials. Summary of the Invention

[0007] In view of the above, the present invention provides a rate-adjustable lithium iron phosphate cathode material, a preparation method and a battery thereof. First, the surface activity of the lithium iron phosphate is improved to facilitate subsequent doping. Then, Co and Mg are uniformly doped to make the lithium iron phosphate crystal structure more stable. Finally, a uniform carbon layer is formed on the surface of the lithium iron phosphate, which significantly improves the electrochemical performance of the lithium iron phosphate.

[0008] This invention provides a method for preparing a rate-adjustable lithium iron phosphate cathode material, characterized by comprising the following steps:

[0009] (1) Add dopamine hydrochloride to Tris-HCl buffer, stir evenly, then add ferric phosphate, sonicate to disperse, let stand at room temperature, filter, wash, and vacuum dry to obtain modified ferric phosphate.

[0010] (2) Isopropyl tris(dioctyl pyrophosphoryloxy) titanate was added to an ethanol solution and stirred until homogeneous. Then cobalt oxide and magnesium oxide were added, heated and stirred, and then filtered, washed and vacuum dried to obtain the dopant.

[0011] (3) The modified iron phosphate, lithium carbonate, β-cyclodextrin and dopants were mixed and ball-milled, and then vacuum-dried to obtain dried particles;

[0012] (4) The dry particles are sintered under a nitrogen atmosphere and naturally cooled to room temperature to obtain a rate-type lithium iron phosphate cathode material.

[0013] This invention first modifies ferric phosphate with dopamine hydrochloride, wherein the dopamine hydrochloride contains catechol groups and amino groups. The catechol groups can coordinate with Fe on the surface of ferric phosphate. 3+ Combined, forming dopamine-Fe 3+ The complex is adsorbed onto the surface of iron phosphate particles. The amino group -NH2 interacts with the functional groups such as -OH on the surface of iron phosphate through electrostatic interaction or hydrogen bonding, which enhances the adsorption stability. In a weakly alkaline environment, dopamine undergoes an oxidative self-polymerization reaction to form polydopamine. The polydopamine formed by self-polymerization forms an organic coating layer on the surface of iron phosphate particles, which contains a large number of phenolic hydroxyl groups, amino groups and other functional groups. These functional groups can serve as active sites to enhance the interfacial reactivity of iron phosphate and provide a favorable environment for subsequent element doping.

[0014] Meanwhile, the polydopamine layer formed on the surface of iron phosphate will carbonize after high-temperature sintering, transforming into a nitrogen-doped carbon layer, introducing nitrogen and carbon into the lithium iron phosphate to form a CN bond layer. Among them, the carbon layer acts as a conductive network, directly improving the electronic conductivity of iron phosphate. Nitrogen doping can significantly reduce the interfacial resistance of iron phosphate particles by introducing defect sites or changing the electronic structure of the carbon layer, further enhancing the electrochemical activity of the material. In addition, the polydopamine layer formed on the surface of iron phosphate will have a steric hindrance effect, which can limit excessive grain growth during subsequent high-temperature sintering.

[0015] Then, dopants were prepared using isopropyltris(dioctylpyrophosphoryloxy)titanate, cobalt oxide, and magnesium oxide. Isopropyltris(dioctylpyrophosphoryloxy)titanate is a long-chain molecule that can form a barrier on the surface of cobalt oxide and magnesium oxide, preventing agglomeration. At the same time, it can reduce the surface energy of the particles and reduce the tendency of spontaneous agglomeration, making the distribution of cobalt oxide and magnesium oxide in the dopants more uniform and having good dispersibility and stability. This allows cobalt and magnesium to be uniformly doped into the lattice of lithium iron phosphate to form bulk doping, making the crystal structure of lithium iron phosphate more stable.

[0016] Finally, β-cyclodextrin, a biomass carbon source, was used for carbon coating to form a uniform carbon layer on the surface of lithium iron phosphate, which further improved the electrochemical performance of lithium iron phosphate. In the end, a cobalt-, magnesium-, and nitrogen-doped surface carbon-coated lithium iron phosphate cathode material was formed, which has excellent electrochemical performance.

[0017] In step (1), the concentration of the Tris-HCl buffer is 5-15 mmol / L, the pH is 8.5, and the volume is 300-800 mL.

[0018] Tris-HCl buffer affects the quality of the coating layer; a suitable pH allows dopamine hydrochloride to be uniformly coated on the surface of ferric phosphate particles.

[0019] In step (1), the mass ratio of dopamine hydrochloride to ferric phosphate is 0.5 to 2:10.

[0020] The dosage of dopamine hydrochloride and iron phosphate needs to be appropriate to obtain modified iron phosphate with good dispersibility, stability, and surface activity, resulting in lithium iron phosphate material with a balance between conductivity and active material ratio. Excessive dopamine hydrochloride will increase the viscosity of the reaction system, reduce the dispersibility of iron phosphate, leading to poor doping effect of dopants, and an excessively thick carbon-nitrogen coating layer after carbonization, which hinders electron migration and reduces the rate performance and other electrochemical properties of lithium iron phosphate. Insufficient dopamine hydrochloride will result in insufficient surface modification of iron phosphate particles, leading to inadequate dispersibility, stability, and surface activity, which is detrimental to doping. Furthermore, an excessively thin carbon-nitrogen coating layer after carbonization results in low electronic conductivity, which is also detrimental to the electrochemical performance of lithium iron phosphate.

[0021] In step (1), the ultrasonic dispersion power is 200-500W, the frequency is 50-70kHz, and the time is 1-2h; the room temperature standing time is 8-16h.

[0022] In step (2), the mass ratio of isopropyltris(dioctylpyrophosphoryloxy)titanate, cobalt oxide, magnesium oxide and ethanol solution is 0.05-0.2:1-2:1-2:10-50.

[0023] The dopant of this invention is prepared separately and combined with the good dispersibility and surface activity of modified iron phosphate to uniformly dope cobalt and magnesium. At the same time, cobalt oxide and magnesium oxide, as active components, modify the stability, conductivity and other properties of lithium iron phosphate. The synergistic effect of cobalt and magnesium, together with the internal carbon-nitrogen coating layer and the surface carbon coating layer, forms a uniform and continuous conductive network, which together improves the electrochemical performance of lithium iron phosphate, such as electronic conductivity, specific capacity, and rate performance. Insufficient use of isopropyltris(dioctylpyrophosphoryloxy)titanate may lead to poor interfacial bonding of various substances, easy agglomeration, and is not conducive to uniform doping and the formation of a uniform and continuous conductive network. Excessive use of isopropyltris(dioctylpyrophosphoryloxy)titanate may form an excessive organic layer, which is not conducive to subsequent synthesis reactions, affects the performance of lithium iron phosphate, and may even introduce impurities. The amount of cobalt and magnesium also needs to be appropriate. Too little will not achieve good results, while too much will be detrimental to the stability of lithium iron phosphate and may even block electron transport channels, reducing the electrochemical performance of lithium iron phosphate. Therefore, appropriate amounts of isopropyltris(dioctylpyrophosphoryloxy)titanate, cobalt oxide, and magnesium oxide can better form a uniformly dispersed dopant, which is more conducive to uniformly doping cobalt and magnesium into lithium iron phosphate, forming a uniform and continuous conductive network, and improving the stability, electronic conductivity, specific capacity, rate performance, and other electrochemical performance of lithium iron phosphate.

[0024] In step (2), the ethanol solution is an aqueous ethanol solution with a concentration of 70-95 wt%.

[0025] In step (2), the heating and stirring temperature is 70-90℃ and the time is 0.5-2h.

[0026] In step (3), the total mass ratio of the modified iron phosphate and lithium carbonate to the mass ratio of β-cyclodextrin and dopant is 1:0.02 to 0.1:0.005 to 0.02, wherein the molar ratio of iron to lithium is 1:1.0 to 1.1.

[0027] The cobalt and magnesium doping, carbon and nitrogen coating, and surface carbon coating form a uniform and continuous conductive network, which together improves the electrochemical performance of lithium iron phosphate. It is necessary to control the amount of each substance to maximize their synergistic effect and avoid problems such as insufficient stability, coating defects, and obstructed and lengthened electron transport channels caused by an imbalance in the content of a certain element.

[0028] In step (3), the specific conditions for ball milling are as follows: rotation speed is 200-500 rpm, the ball milling medium is anhydrous ethanol, the material-to-liquid ratio is 1:1-2, the grinding balls are zirconia balls, the ball-to-material ratio is 5-15:1, and the ball milling time is 3-6 hours.

[0029] In step (4), the sintering temperature is 600-800℃ and the sintering time is 8-12h.

[0030] The present invention provides a rate-type lithium iron phosphate cathode material, which is prepared by a method for preparing rate-type lithium iron phosphate cathode materials.

[0031] The present invention relates to a battery in which the positive electrode material is a high-rate lithium iron phosphate positive electrode material.

[0032] The present invention has at least the following beneficial effects:

[0033] (1) First, dopamine hydrochloride is used to modify iron phosphate to improve the surface activity of iron phosphate, which is beneficial to the subsequent doping of cobalt and magnesium. At the same time, it can limit the excessive growth of grains during high-temperature sintering and introduce nitrogen and carbon into the lithium iron phosphate to form a carbon-nitrogen coating layer, improve electronic conductivity, and improve the electrochemical performance of lithium iron phosphate.

[0034] (2) Then, dopants were prepared using isopropyltris(dioctylpyrophosphoryloxy)titanate, cobalt oxide and magnesium oxide. The cobalt oxide and magnesium oxide of this dopant are uniformly dispersed, allowing cobalt and magnesium to be uniformly doped into the lithium iron phosphate lattice to form bulk doping, making the lithium iron phosphate crystal structure more stable. Cobalt and magnesium co-doping synergistically improves the electronic conductivity and structural stability of lithium iron phosphate materials, and improves the electrochemical performance of lithium iron phosphate materials.

[0035] (3) Finally, β-cyclodextrin, a biomass carbon source, was used for carbon coating to form a uniform carbon layer on the surface of lithium iron phosphate, which further improved the electrochemical performance of lithium iron phosphate.

[0036] (4) The present invention prepares a rate-type lithium iron phosphate cathode material with uniform co-doping of cobalt and magnesium, as well as a carbon-nitrogen coating layer inside the lithium iron phosphate and a uniform carbon coating layer on the surface of the lithium iron phosphate. The synergistic effect of cobalt and magnesium forms a uniform and continuous conductive network with the internal carbon-nitrogen coating layer and the surface carbon coating layer, which significantly improves the electrochemical performance of lithium iron phosphate. Its discharge specific capacity at 25℃ and 0.1C is ≥173mAh / g, and its discharge specific capacity at 25℃ and 20C is ≥140mAh / g, which has good discharge specific capacity and rate performance. Detailed Implementation

[0037] The embodiments of this application will now be described in more detail. This application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to provide a more thorough and complete understanding of the application. It should be understood that the embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0038] Example 1:

[0039] The embodiments of the present invention are implemented according to the following technical solution, including the following steps:

[0040] (1) Add dopamine hydrochloride to 500 mL of Tris-HCl buffer solution with a concentration of 10 mmol / L and a pH of 8.5, stir well, then add ferric phosphate, wherein the mass ratio of dopamine hydrochloride to ferric phosphate is 1:10, and then sonicate for 1 h at a power of 300 W and a frequency of 55 kHz, let stand at room temperature for 12 h, filter, wash three times with anhydrous ethanol and deionized water, and vacuum dry at 80 °C to obtain modified ferric phosphate;

[0041] (2) Isopropyl tris(dioctylpyrophosphoryloxy) titanate was added to a 95wt% aqueous ethanol solution and stirred until homogeneous. Then cobalt oxide and magnesium oxide were added. The mass ratio of isopropyl tris(dioctylpyrophosphoryloxy) titanate, cobalt oxide, magnesium oxide and ethanol solution was 0.1:1:2:30. The mixture was stirred at 80℃ for 1 h, then filtered, washed three times with anhydrous ethanol, and dried under vacuum at 80℃ to obtain the dopant.

[0042] (3) Modified iron phosphate, lithium carbonate, β-cyclodextrin and dopant are mixed and ball-milled, wherein the total mass ratio of modified iron phosphate and lithium carbonate to β-cyclodextrin and dopant is 1:0.05:0.01, the molar ratio of iron to lithium is 1:1.05, and the mixture is vacuum dried to obtain dry particles; wherein the specific ball milling conditions are: rotation speed of 300 rpm, ball milling medium is anhydrous ethanol, material-to-liquid ratio is 1:1.5, grinding balls are zirconium oxide balls, ball-to-material ratio is 10:1, and ball milling time is 4 h;

[0043] (4) The dry particles are sintered under a nitrogen atmosphere at a temperature of 700°C for 10 hours and then naturally cooled to room temperature to obtain a rate-type lithium iron phosphate cathode material.

[0044] Example 2:

[0045] The embodiments of the present invention are implemented according to the following technical solution, including the following steps:

[0046] (1) Add dopamine hydrochloride to 500 mL of Tris-HCl buffer solution with a concentration of 10 mmol / L and a pH of 8.5, stir well, then add ferric phosphate, wherein the mass ratio of dopamine hydrochloride to ferric phosphate is 1:10, and then sonicate for 1 h at a power of 300 W and a frequency of 55 kHz, let stand at room temperature for 12 h, filter, wash three times with anhydrous ethanol and deionized water, and vacuum dry at 80 °C to obtain modified ferric phosphate;

[0047] (2) Isopropyl tris(dioctylpyrophosphoryloxy) titanate was added to a 90wt% aqueous ethanol solution and stirred until homogeneous. Then cobalt oxide and magnesium oxide were added. The mass ratio of isopropyl tris(dioctylpyrophosphoryloxy) titanate, cobalt oxide, magnesium oxide and ethanol solution was 0.1:1.5:1.5:30. The mixture was stirred at 80℃ for 1 h, then filtered, washed three times with anhydrous ethanol, and dried under vacuum at 80℃ to obtain the dopant.

[0048] (3) Modified iron phosphate, lithium carbonate, β-cyclodextrin and dopant are mixed and ball-milled, wherein the total mass ratio of modified iron phosphate and lithium carbonate to β-cyclodextrin and dopant is 1:0.05:0.01, the molar ratio of iron to lithium is 1:1.05, and the mixture is vacuum dried to obtain dry particles; wherein the specific ball milling conditions are: rotation speed of 300 rpm, ball milling medium is anhydrous ethanol, material-to-liquid ratio is 1:1.5, grinding balls are zirconium oxide balls, ball-to-material ratio is 10:1, and ball milling time is 4 h;

[0049] (4) The dry particles are sintered under a nitrogen atmosphere at a temperature of 700°C for 10 hours and then naturally cooled to room temperature to obtain a rate-type lithium iron phosphate cathode material.

[0050] Example 3:

[0051] The embodiments of the present invention are implemented according to the following technical solution, including the following steps:

[0052] (1) Add dopamine hydrochloride to 500 mL of Tris-HCl buffer solution with a concentration of 10 mmol / L and a pH of 8.5, stir well, then add ferric phosphate, wherein the mass ratio of dopamine hydrochloride to ferric phosphate is 1:10, and then sonicate for 1 h at a power of 300 W and a frequency of 55 kHz, let stand at room temperature for 12 h, filter, wash three times with anhydrous ethanol and deionized water, and vacuum dry at 80 °C to obtain modified ferric phosphate;

[0053] (2) Isopropyl tris(dioctylpyrophosphoryloxy) titanate was added to a 90wt% aqueous ethanol solution and stirred until homogeneous. Then cobalt oxide and magnesium oxide were added. The mass ratio of isopropyl tris(dioctylpyrophosphoryloxy) titanate, cobalt oxide, magnesium oxide and ethanol solution was 0.1:2:1:30. The mixture was stirred at 80℃ for 1 h, then filtered, washed three times with anhydrous ethanol, and dried under vacuum at 80℃ to obtain the dopant.

[0054] (3) Modified iron phosphate, lithium carbonate, β-cyclodextrin and dopant are mixed and ball-milled, wherein the total mass ratio of modified iron phosphate and lithium carbonate to β-cyclodextrin and dopant is 1:0.05:0.01, the molar ratio of iron to lithium is 1:1.05, and the mixture is vacuum dried to obtain dry particles; wherein the specific ball milling conditions are: rotation speed of 300 rpm, ball milling medium is anhydrous ethanol, material-to-liquid ratio is 1:1.5, grinding balls are zirconium oxide balls, ball-to-material ratio is 10:1, and ball milling time is 4 h;

[0055] (4) The dry particles are sintered under a nitrogen atmosphere at a temperature of 700°C for 10 hours and then naturally cooled to room temperature to obtain a rate-type lithium iron phosphate cathode material.

[0056] Example 4

[0057] The embodiments of the present invention are implemented according to the following technical solution, including the following steps:

[0058] (1) Add dopamine hydrochloride to 800 mL of Tris-HCl buffer solution with a concentration of 5 mmol / L and pH of 8.5, stir well, and then add ferric phosphate. The mass ratio of dopamine hydrochloride to ferric phosphate is 0.5:10. Then, it is ultrasonically dispersed for 1 h at a power of 300 W and a frequency of 55 kHz, and then allowed to stand at room temperature for 12 h. After filtration, it is washed three times with anhydrous ethanol and deionized water, and then vacuum dried at 80 °C to obtain modified ferric phosphate.

[0059] (2) Isopropyl tris(dioctyl pyrophosphoryloxy) titanate was added to an 80 wt% aqueous ethanol solution and stirred until homogeneous. Then cobalt oxide and magnesium oxide were added. The mass ratio of isopropyl tris(dioctyl pyrophosphoryloxy) titanate, cobalt oxide, magnesium oxide and ethanol solution was 0.2:1.5:2:50. The mixture was stirred at 70 °C for 2 h, then filtered, washed three times with anhydrous ethanol, and dried under vacuum at 80 °C to obtain the dopant.

[0060] (3) Modified iron phosphate, lithium carbonate, β-cyclodextrin and dopant are mixed and ball-milled, wherein the total mass ratio of modified iron phosphate and lithium carbonate to β-cyclodextrin and dopant is 1:0.1:0.005, the molar ratio of iron to lithium is 1:1.05, and the mixture is vacuum dried to obtain dry particles; wherein the specific ball milling conditions are: rotation speed is 300 rpm, the ball milling medium is anhydrous ethanol, the material-to-liquid ratio is 1:1.5, the grinding balls are zirconium oxide balls, the ball-to-material ratio is 10:1, and the ball milling time is 4 h.

[0061] (4) The dry particles are sintered under a nitrogen atmosphere at a temperature of 700°C for 10 hours and then naturally cooled to room temperature to obtain a rate-type lithium iron phosphate cathode material.

[0062] Example 5

[0063] The embodiments of the present invention are implemented according to the following technical solution, including the following steps:

[0064] (1) Add dopamine hydrochloride to 300 mL of Tris-HCl buffer solution with a concentration of 15 mmol / L and a pH of 8.5, stir well, then add ferric phosphate, wherein the mass ratio of dopamine hydrochloride to ferric phosphate is 2:10, and then sonicate for 1 h at a power of 300 W and a frequency of 55 kHz, let stand at room temperature for 12 h, filter, wash three times with anhydrous ethanol and deionized water, and dry under vacuum at 80 °C to obtain modified ferric phosphate.

[0065] (2) Isopropyl tris(dioctyl pyrophosphoryloxy) titanate was added to a 70 wt% aqueous ethanol solution and stirred until homogeneous. Then cobalt oxide and magnesium oxide were added. The mass ratio of isopropyl tris(dioctyl pyrophosphoryloxy) titanate, cobalt oxide, magnesium oxide and ethanol solution was 0.05:1:1:10. The mixture was stirred at 90 °C for 0.5 h, then filtered, washed three times with anhydrous ethanol, and dried under vacuum at 80 °C to obtain the dopant.

[0066] (3) Modified iron phosphate, lithium carbonate, β-cyclodextrin and dopant were mixed and ball-milled, wherein the total mass ratio of modified iron phosphate and lithium carbonate to β-cyclodextrin and dopant was 1:0.02:0.02, the molar ratio of iron to lithium was 1:1.05, and the mixture was vacuum dried to obtain dry particles; wherein the specific ball milling conditions were: rotation speed of 300 rpm, ball milling medium of anhydrous ethanol, material-to-liquid ratio of 1:1.5, grinding balls of zirconium oxide, ball-to-material ratio of 10:1, and ball milling time of 4 h;

[0067] (4) The dry particles are sintered under a nitrogen atmosphere at a temperature of 700°C for 10 hours and then naturally cooled to room temperature to obtain a rate-type lithium iron phosphate cathode material.

[0068] Comparative Example 1: Unmodified iron phosphate:

[0069] The embodiments of the present invention are implemented according to the following technical solution, including the following steps:

[0070] (1) Isopropyl tris(dioctyl pyrophosphoryloxy) titanate was added to a 90 wt% aqueous ethanol solution and stirred until homogeneous. Then cobalt oxide and magnesium oxide were added. The mass ratio of isopropyl tris(dioctyl pyrophosphoryloxy) titanate, cobalt oxide, magnesium oxide and ethanol solution was 0.1:1:2:30. The mixture was stirred at 80 °C for 1 h, then filtered, washed three times with anhydrous ethanol, and dried under vacuum at 80 °C to obtain the dopant.

[0071] (2) Iron phosphate, lithium carbonate, β-cyclodextrin and dopant were mixed and ball-milled, wherein the total mass ratio of iron phosphate and lithium carbonate to the mass ratio of β-cyclodextrin and dopant was 1:0.05:0.01, the molar ratio of iron to lithium was 1:1.05, and the mixture was vacuum dried to obtain dry particles; the specific conditions for ball milling were: rotation speed of 300 rpm, ball milling medium of anhydrous ethanol, material-to-liquid ratio of 1:1.5, grinding balls of zirconium oxide, ball-to-material ratio of 10:1, and ball milling time of 4 h.

[0072] (4) The dry particles are sintered under a nitrogen atmosphere at a temperature of 700°C for 10 hours and then naturally cooled to room temperature to obtain a rate-type lithium iron phosphate cathode material.

[0073] Comparative Example 2: Dopants were cobalt oxide and magnesium oxide, which were directly mixed with modified iron phosphate, lithium carbonate, and β-cyclodextrin and ball-milled.

[0074] The embodiments of the present invention are implemented according to the following technical solution, including the following steps:

[0075] (1) Add dopamine hydrochloride to 500 mL of Tris-HCl buffer solution with a concentration of 10 mmol / L and a pH of 8.5, stir well, then add ferric phosphate, wherein the mass ratio of dopamine hydrochloride to ferric phosphate is 1:10, and then sonicate for 1 h at a power of 300 W and a frequency of 55 kHz, let stand at room temperature for 12 h, filter, wash three times with anhydrous ethanol and deionized water, and vacuum dry at 80 °C to obtain modified ferric phosphate;

[0076] (2) Modified iron phosphate, lithium carbonate, β-cyclodextrin and dopant were mixed and ball-milled. The total mass ratio of modified iron phosphate and lithium carbonate to β-cyclodextrin and dopant was 1:0.05:0.01, the molar ratio of iron to lithium was 1:1.05, and the dopant was obtained by mixing cobalt oxide and magnesium oxide in a mass ratio of 2:1. The mixture was then vacuum-dried to obtain dry particles. The specific ball-milling conditions were as follows: rotation speed was 300 rpm, the ball-milling medium was anhydrous ethanol, the material-to-liquid ratio was 1:1.5, the grinding balls were zirconium oxide balls, the ball-to-material ratio was 10:1, and the ball-milling time was 4 h.

[0077] (4) The dry particles are sintered under a nitrogen atmosphere at a temperature of 700°C for 10 hours and then naturally cooled to room temperature to obtain a rate-type lithium iron phosphate cathode material.

[0078] Comparative Example 3: The dopant was cobalt oxide, which was directly mixed with modified iron phosphate, lithium carbonate, and β-cyclodextrin and ball-milled.

[0079] The embodiments of the present invention are implemented according to the following technical solution, including the following steps:

[0080] (1) Add dopamine hydrochloride to 500 mL of Tris-HCl buffer solution with a concentration of 10 mmol / L and a pH of 8.5, stir well, then add ferric phosphate, wherein the mass ratio of dopamine hydrochloride to ferric phosphate is 1:10, and then sonicate for 1 h at a power of 300 W and a frequency of 55 kHz, let stand at room temperature for 12 h, filter, wash three times with anhydrous ethanol and deionized water, and vacuum dry at 80 °C to obtain modified ferric phosphate;

[0081] (2) Isopropyl tris(dioctyl pyrophosphoryloxy) titanate was added to a 90 wt% aqueous ethanol solution and stirred until homogeneous. Then cobalt oxide was added. The mass ratio of isopropyl tris(dioctyl pyrophosphoryloxy) titanate, cobalt oxide and ethanol solution was 0.1:3:30. The mixture was stirred at 80 °C for 1 h, then filtered, washed three times with anhydrous ethanol, and dried under vacuum at 80 °C to obtain the dopant.

[0082] (3) Modified iron phosphate, lithium carbonate, β-cyclodextrin and dopant are mixed and ball-milled, wherein the total mass ratio of modified iron phosphate and lithium carbonate to β-cyclodextrin and dopant is 1:0.05:0.01, the molar ratio of iron to lithium is 1:1.05, and the mixture is vacuum dried to obtain dry particles; wherein the specific ball milling conditions are: rotation speed of 300 rpm, ball milling medium is anhydrous ethanol, material-to-liquid ratio is 1:1.5, grinding balls are zirconium oxide balls, ball-to-material ratio is 10:1, and ball milling time is 4 h;

[0083] (4) The dry particles are sintered under a nitrogen atmosphere at a temperature of 700°C for 10 hours and then naturally cooled to room temperature to obtain a rate-type lithium iron phosphate cathode material.

[0084] Comparative Example 4: The dopant was magnesium oxide, which was directly mixed with modified iron phosphate, lithium carbonate, and β-cyclodextrin and ball-milled.

[0085] The embodiments of the present invention are implemented according to the following technical solution, including the following steps:

[0086] (1) Add dopamine hydrochloride to 500 mL of Tris-HCl buffer solution with a concentration of 10 mmol / L and a pH of 8.5, stir well, then add ferric phosphate, wherein the mass ratio of dopamine hydrochloride to ferric phosphate is 1:10, and then sonicate for 1 h at a power of 300 W and a frequency of 55 kHz, let stand at room temperature for 12 h, filter, wash three times with anhydrous ethanol and deionized water, and vacuum dry at 80 °C to obtain modified ferric phosphate;

[0087] (2) Isopropyl tris(dioctyl pyrophosphoryloxy) titanate was added to a 90 wt% aqueous ethanol solution and stirred until homogeneous. Then magnesium oxide was added. The mass ratio of isopropyl tris(dioctyl pyrophosphoryloxy) titanate, magnesium oxide and ethanol solution was 0.1:3:30. The mixture was stirred at 80 °C for 1 h, then filtered, washed three times with anhydrous ethanol, and dried under vacuum at 80 °C to obtain the dopant.

[0088] (3) Modified iron phosphate, lithium carbonate, β-cyclodextrin and dopant are mixed and ball-milled, wherein the total mass ratio of modified iron phosphate and lithium carbonate to β-cyclodextrin and dopant is 1:0.05:0.01, the molar ratio of iron to lithium is 1:1.05, and the mixture is vacuum dried to obtain dry particles; wherein the specific ball milling conditions are: rotation speed of 300 rpm, ball milling medium is anhydrous ethanol, material-to-liquid ratio is 1:1.5, grinding balls are zirconium oxide balls, ball-to-material ratio is 10:1, and ball milling time is 4 h;

[0089] (4) The dry particles are sintered under a nitrogen atmosphere at a temperature of 700°C for 10 hours and then naturally cooled to room temperature to obtain a rate-type lithium iron phosphate cathode material.

[0090] The lithium iron phosphate cathode materials obtained in the above examples and comparative examples were subjected to button cell tests: the obtained lithium iron phosphate cathode materials, acetylene black, and polyvinylidene fluoride were dissolved in an appropriate amount of N-methylpyrrolidone solvent at a mass ratio of 8:1:1, mixed in a homogenate, coated on aluminum foil, vacuum dried, and then cut into electrode sheets with a diameter of 14 mm and an areal density of 8 mg / cm³. 2 The positive electrode was fabricated using a lithium metal sheet as the negative electrode; the separator was an imported polypropylene microporous membrane (Celgard 2400); the electrolyte was a 1 mol / L LiPF6 solution, with a volume ratio of ethylene carbonate (EC) to dimethyl carbonate (DMC) of 1:1 as the solvent. The cells were assembled into button batteries (CR2032) in an argon-filled glove box, and then the assembled batteries were tested for charge and discharge using a Blue Electric testing system. The discharge specific capacity at 0.1C and 20C rates at 25°C for the examples and comparative examples is shown in Table 1.

[0091] As shown in Table 1, the rate-adjustable lithium iron phosphate cathode material prepared by this invention has excellent electrochemical performance. Compared with comparative examples 1-4, examples 1-5 have higher discharge specific capacity and capacity retention at both 0.1C and 20C rates. Their discharge specific capacity at 25℃ and 0.1C is ≥173mAh / g, and their discharge specific capacity at 25℃ and 20C is ≥140mAh / g, which fully demonstrates that this invention can significantly improve the discharge performance and rate performance of lithium iron phosphate.

[0092] In Comparative Example 1, the unmodified iron phosphate significantly reduced the electrochemical performance of the resulting lithium iron phosphate cathode material, demonstrating that iron phosphate modification plays a crucial role in improving the electrochemical performance of lithium iron phosphate cathode materials. In Comparative Example 2, the unmodified cobalt oxide and magnesium oxide, without mixing with isopropyltris(dioctylpyrophosphoryloxy)titanate, also resulted in a significant reduction in the electrochemical performance of the resulting lithium iron phosphate cathode material, proving that the dopant prepared in this invention has better dispersibility and doping performance, playing a vital role in improving the electrochemical performance of lithium iron phosphate cathode materials. The low electrochemical performance of Comparative Examples 3 and 4 fully demonstrates that the synergistic effect of cobalt and magnesium is far better than the doping effect of cobalt or magnesium alone. In summary, the uniform co-doping of cobalt and magnesium in this invention, along with the combined effect of the carbon-nitrogen coating layer inside the lithium iron phosphate and the uniform carbon coating layer on the surface of the lithium iron phosphate, significantly improves the specific capacity, rate performance, and other electrochemical properties of the lithium iron phosphate material.

[0093] Table 1. Performance test results of the products in the examples and comparative examples.

[0094]

[0095] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. A method for preparing a rate-dependent lithium iron phosphate cathode material, characterized in that, Includes the following steps: (1) Add dopamine hydrochloride to Tris-HCl buffer, stir evenly, then add ferric phosphate, sonicate to disperse, let stand at room temperature, filter, wash, and vacuum dry to obtain modified ferric phosphate. (2) Isopropyl tris(dioctyl pyrophosphoryloxy) titanate was added to an ethanol solution and stirred until homogeneous. Then cobalt oxide and magnesium oxide were added, heated and stirred, and then filtered, washed and vacuum dried to obtain the dopant. (3) The modified iron phosphate, lithium carbonate, β-cyclodextrin and dopants were mixed and ball-milled, and then vacuum-dried to obtain dried particles; (4) The dry particles are sintered under a nitrogen atmosphere and naturally cooled to room temperature to obtain a rate-type lithium iron phosphate cathode material.

2. The method for preparing a rate-multiplying lithium iron phosphate cathode material according to claim 1, characterized in that, In step (1), the concentration of the Tris-HCl buffer is 5-15 mmol / L, the pH is 8.5, and the volume is 300-800 mL.

3. The method for preparing a rate-multiplying lithium iron phosphate cathode material according to claim 1, characterized in that, In step (1), the mass ratio of dopamine hydrochloride to ferric phosphate is 0.5 to 2:

10.

4. The method for preparing a rate-multiplying lithium iron phosphate cathode material according to claim 1, characterized in that, In step (1), the ultrasonic dispersion power is 200-500W, the frequency is 50-70kHz, and the time is 1-2h; the room temperature standing time is 8-16h.

5. The method for preparing a rate-multiplying lithium iron phosphate cathode material according to claim 1, characterized in that, In step (2), the mass ratio of isopropyltris(dioctylpyrophosphoryloxy)titanate, cobalt oxide, magnesium oxide and ethanol solution is 0.05-0.2:1-2:1-2:10-50.

6. A method for preparing a rate-multiplying lithium iron phosphate cathode material according to any one of claims 1 or 5, characterized in that, In step (2), the ethanol solution is an aqueous ethanol solution with a concentration of 70-95 wt%.

7. The method for preparing a rate-multiply lithium iron phosphate cathode material according to claim 1, characterized in that, In step (2), the heating and stirring temperature is 70-90℃ and the time is 0.5-2h.

8. The method for preparing a rate-multiplying lithium iron phosphate cathode material according to claim 1, characterized in that, In step (3), the total mass ratio of the modified iron phosphate and lithium carbonate to the mass ratio of β-cyclodextrin and dopant is 1:0.02 to 0.1:0.005 to 0.02, wherein the molar ratio of iron to lithium is 1:1.0 to 1.

1.

9. The method for preparing a rate-multiplying lithium iron phosphate cathode material according to claim 1, characterized in that, In step (3), the specific conditions for ball milling are as follows: rotation speed is 200-500 rpm, the ball milling medium is anhydrous ethanol, the material-to-liquid ratio is 1:1-2, the grinding balls are zirconia balls, the ball-to-material ratio is 5-15:1, and the ball milling time is 3-6 hours.

10. The method for preparing a rate-multiplying lithium iron phosphate cathode material according to claim 1, characterized in that, In step (4), the sintering temperature is 600-800℃ and the sintering time is 8-12h.

11. A rate-capable lithium iron phosphate cathode material, characterized in that, It is prepared by the method for preparing rate-type lithium iron phosphate cathode material according to any one of claims 1 to 10.

12. A battery, characterized in that, The positive electrode material of the battery is the high-rate lithium iron phosphate positive electrode material as described in claim 11.

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