A low-temperature phosphate material and its preparation method

Abstract

This disclosure provides a low-temperature phosphate material and its preparation method, relating to the field of lithium battery technology. The preparation method includes mixing a lithium source, a metal source, phosphoric acid, and water to obtain a slurry; subjecting the slurry to a hydrothermal reaction to obtain a reactant; mixing the reactant with a carbon source to obtain a large-particle-size precursor with a particle size of 0.6–1.5 μm and a small-particle-size precursor with a particle size of 50–500 nm. After mixing the large-particle-size and small-particle-size precursors, sintering is performed to obtain a low-temperature phosphate material. The phosphate material has a composition of LiMPO4 / C, where M is selected from one or more of iron, manganese, nickel, cobalt, and vanadium. By optimizing the liquid-phase preparation process, precursors of different particle sizes can be prepared. By doping liquid-phase precursor particles of different particle sizes and then sintering, a low-temperature phosphate material is obtained, simplifying the process and achieving better low-temperature rate performance.

Description

Technical Field

[0001] This disclosure relates to the field of lithium battery technology, and in particular to a low-temperature phosphate material and its preparation method. Background Technology

[0002] With the increasing prominence of energy and environmental issues, lithium-ion batteries, due to their excellent comprehensive performance and environmentally friendly characteristics, are widely used in smartphones, digital cameras, electric vehicles, and other fields. Among lithium-ion batteries, lithium iron phosphate (LFP) materials have advantages such as low price, good safety performance, and long lifespan, making them the main power material for lithium batteries. The true density of LFP is 3.6 g / mL, but because it contains carbon and voids, its compacted density is generally much lower than 3.6 g / mL. Currently, the highest compacted density of LFP on the market is generally 2.5 g / mL. Current technology employs a multi-stage sintering process to obtain LFP cathode materials, which include a mixture of large and small LFP particles, from the LFP precursor. This multi-stage heating sintering method controls the orientation and growth of LFP particles. However, this method has high energy consumption, and while the sintered product can improve the capacity retention rate at room temperature to some extent, its low-temperature rate performance is poor.

[0003] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] To address the aforementioned technical problems, this disclosure provides a low-temperature phosphate material and its preparation method.

[0005] The first aspect of this disclosure provides a method for preparing a low-temperature phosphate material, comprising: S1, mixing a lithium source, a metal source, phosphoric acid, and water to obtain a slurry; subjecting the slurry to a hydrothermal reaction to obtain a reactant; mixing the reactant with a carbon source to obtain a large-particle-size precursor, wherein the metal source is one or more of an iron source, a manganese source, a nickel source, a cobalt source, and a vanadium source; and the particle size of the large-particle-size precursor is 0.6~1.5 μm;

[0006] S2, a lithium source, a metal source, phosphoric acid and water are mixed to obtain a slurry, and the slurry is subjected to a hydrothermal reaction to obtain a reactant; the reactant is mixed with a carbon source to obtain a small-particle-size precursor, wherein the metal source is one or more of iron, manganese, nickel, cobalt and vanadium; the particle size of the small-particle-size precursor is 50~500nm.

[0007] S3, after mixing the large-particle-size precursor and the small-particle-size precursor, sintering is performed to obtain a low-temperature phosphate material. The composition of the phosphate material is LiMPO4 / C, wherein M is selected from one or more of iron, manganese, nickel, cobalt and vanadium.

[0008] In one exemplary embodiment of this disclosure, the particle size of the large-particle precursor is 1.2~1.5 μm.

[0009] In one exemplary embodiment of this disclosure, the particle size of the small-diameter precursor is 100~300nm.

[0010] In an exemplary embodiment of this disclosure, step S1, the hydrothermal reaction step includes: reacting the slurry under high pressure at 200~250°C for 5~10 hours, and then separating the reactant to obtain the reactant.

[0011] In an exemplary embodiment of this disclosure, step S1, the hydrothermal reaction step includes: reacting the slurry under high pressure at 230°C for 5-10 hours, and then separating the reactant to obtain the reactant.

[0012] In an exemplary embodiment of this disclosure, step S2, the hydrothermal reaction step includes: reacting the slurry under high pressure at 170~220°C for 2~5 hours, and then separating the reactant to obtain the reactant.

[0013] In an exemplary embodiment of this disclosure, step S2, the hydrothermal reaction step includes: reacting the slurry under high pressure at 180°C for 2-5 hours, and then separating the reactant to obtain the reactant.

[0014] In an exemplary embodiment of this disclosure, in step S3, the large-particle-size precursor and the small-particle-size precursor are mixed in a mass ratio of 7:3 to 1:1.

[0015] In an exemplary embodiment of this disclosure, in step S3, the sintering temperature is 700~850℃, the sintering time is 2~10h, and after sintering, the material is obtained by airflow crushing.

[0016] In an exemplary embodiment of this disclosure, in steps S1 and S2, an antioxidant is further added to the slurry, wherein the antioxidant is 0.1% to 0.5% of the mass of the metal source.

[0017] In an exemplary embodiment of this disclosure, in steps S1 and S2, the reactants and carbon source are mixed and then spray-dried to obtain the precursor.

[0018] In one exemplary embodiment of this disclosure, the solid content of the material is controlled to be 25-50% before spray drying.

[0019] The second aspect of this disclosure provides a low-temperature phosphate material prepared according to any one of the above methods.

[0020] The beneficial effects of the low-temperature phosphate material and its preparation method disclosed in this embodiment are:

[0021] This disclosure discloses a low-temperature phosphate material prepared by controlling the time and temperature of a high-pressure hydrothermal reaction to obtain precursor particles of different sizes. After mixing the precursor particles of different sizes in a certain proportion, sintering is performed to obtain a high-compacted low-temperature phosphate material. The preparation process requires only one sintering step, simplifying the process and reducing energy consumption. The large-diameter precursor particles range from 0.6 to 1.5 μm, while the small-diameter precursor particles range from 50 to 500 nm. After sintering, a mixed structure of large and small particles is formed, improving the overall compaction effect and exhibiting excellent low-temperature rate performance.

[0022] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating a method for preparing a low-temperature phosphate material according to an embodiment of this disclosure.

[0025] Figure 2 This is a SEM image of the lithium iron phosphate material provided in Embodiment 1 of this disclosure. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] The following is a detailed description of the low-temperature phosphate material and its preparation method according to the embodiments of this disclosure.

[0028] This disclosure provides a method for preparing a low-temperature phosphate material, including:

[0029] S1, a lithium source, a metal source, phosphoric acid, and water are mixed to obtain a slurry. The slurry is subjected to a hydrothermal reaction to obtain a reactant. The reactant is then mixed with a carbon source to obtain a large-particle-size precursor. The metal source is one or more of iron, manganese, nickel, cobalt, and vanadium sources. The particle size of the large-particle-size precursor is 0.6~1.5μm.

[0030] S2, a lithium source, a metal source, phosphoric acid and water are mixed to obtain a slurry, and the slurry is subjected to a hydrothermal reaction to obtain a reactant; the reactant is mixed with a carbon source to obtain a small-particle-size precursor, wherein the metal source is one or more of iron, manganese, nickel, cobalt and vanadium; the particle size of the small-particle-size precursor is 50~500nm.

[0031] S3, after mixing the large-particle-size precursor and the small-particle-size precursor, sintering is performed to obtain a low-temperature phosphate material. The composition of the phosphate material is LiMPO4 / C, wherein M is selected from one or more of iron, manganese, nickel, cobalt and vanadium.

[0032] In one embodiment, in steps S1 and S2, the lithium source includes, but is not limited to, one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate. The phosphorus source includes, but is not limited to, phosphoric acid and ammonium dihydrogen phosphate. The iron source includes, but is not limited to, one or more of ferric phosphate, ferrous oxalate, ferric oxide, and ferrous sulfate. The manganese source includes, but is not limited to, one or more of manganese carbonate, manganese acetate, and manganese oxide. The nickel source includes, but is not limited to, nickel oxide, nickel sulfate, and nickel chloride. The cobalt source includes, but is not limited to, one or more of cobalt oxide, cobalt hydroxide, cobalt sulfate, and cobalt carbonate. The vanadium source includes, but is not limited to, one or more of vanadium chloride and ammonium metavanadate.

[0033] It is understandable that different types of phosphate materials are generated when the metal source has different compositions. For example, when the metal source is iron, the liquid-phase large particles are composed of lithium iron phosphate. When the metal source is manganese, the liquid-phase large particles are composed of lithium manganese phosphate. When the metal source is both iron and manganese, the liquid-phase large particles are composed of lithium iron manganese phosphate.

[0034] In one embodiment, in steps S1 and S2, an antioxidant is further added to the slurry, the antioxidant being 0.1% to 0.5% of the mass of the metal source. More preferably, the antioxidant is selected from ascorbic acid. By adding the antioxidant, oxidation of the metal source is prevented.

[0035] In one embodiment, in steps S1 and S2, the reactants and carbon source are mixed and then spray-dried to obtain the precursor. Before spray drying, the solid content of the material is controlled to be 25-50%. Controlling the solid content of the material is beneficial for forming a product with uniform particle size.

[0036] In one embodiment, in steps S1 and S2, the inlet air temperature of the spray dryer is 200~250℃, and the outlet air temperature is 70~100℃. Controlling the inlet and outlet air temperatures of the spray dryer is beneficial for the subsequent sintering process of the product.

[0037] Furthermore, in one embodiment, a dopant is added to the reactant after the addition of the carbon source. The reactant, carbon source, and dopant are mixed and then spray-dried to obtain the precursor. Specifically, the dopant contains one or more metallic elements selected from V, Cr, Nb, Ti, La, W, Y, Zr, and Mg. The dopant can be, for example, high-valence metal oxides such as titanium dioxide, vanadium pentoxide, manganese oxide, zirconium oxide, and niobium oxide.

[0038] In one embodiment, in step S1, the mass fraction of the lithium source in the slurry is 2% to 6%. By controlling the mass concentration of the slurry, it is helpful to form a precursor with a larger particle size.

[0039] In one embodiment, step S1, the hydrothermal reaction step includes: reacting the slurry under high pressure at 200-250°C for 5-10 hours, and then separating the reactant. More preferably, the slurry is reacted under high pressure at 230°C for 5-10 hours, and then separated to obtain the reactant. After the high-pressure reaction, the liquid is removed by centrifugation or pressure filtration to obtain filter residue, which is then washed with pure water to obtain the reactant. The washing water can be, for example, 10-30 times the mass of the filter residue. The washing can be performed once or multiple times.

[0040] In one embodiment, in step S2, the lithium source has a mass fraction of 7% to 10% in the slurry. By controlling the mass concentration of the slurry, it is helpful to form precursors with smaller particle sizes.

[0041] In one embodiment, step S2, the hydrothermal reaction step includes: reacting the slurry under high pressure at 170~220℃ for 2~5 hours, and then separating the reactant. More preferably, in this step, the hydrothermal reaction step includes: reacting the slurry under high pressure at 180℃ for 2~5 hours, and then separating the reactant. After the high-pressure reaction, the liquid is removed by centrifugation or pressure filtration to obtain filter residue, which is then washed with pure water to obtain the reactant. The washing water can be, for example, 10~30 times the mass of the filter residue. The washing can be done once or multiple times. During the high-pressure reaction, the time and temperature of the high-pressure hydrothermal reaction are controlled to obtain a precursor with the desired particle size.

[0042] In one embodiment, the particle size of the large-particle-size precursor is preferably 1.2~1.5μm; the particle size of the small-particle-size precursor is preferably 100~300nm. By controlling the particle size of the precursor, a mixed product with different particle sizes is formed, thereby improving the overall compaction of the product.

[0043] In one embodiment, in step S3, the large-particle-size precursor and the small-particle-size precursor are mixed at a mass ratio of 7:3 to 1:1. By adjusting the ratio of the large-particle-size precursor to the small-particle-size precursor, better low-temperature cycling performance can be obtained.

[0044] In one embodiment, in step S3, the sintering temperature is 700~850℃, the sintering time is 2~10h, and after sintering, the material is obtained by airflow crushing.

[0045] This disclosure also provides a low-temperature phosphate material, which is obtained according to the preparation method described above.

[0046] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0047] Example 1

[0048] This embodiment provides a lithium iron phosphate material, which is prepared according to the following steps:

[0049] (1) 7.8 kg of lithium hydroxide monohydrate, 7.3 kg of phosphoric acid, 17.6 kg of ferrous sulfate heptahydrate, 50 g of ascorbic acid, and 150 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 230°C, and kept at that temperature for 8 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form powder a. The primary particle size of powder a was 1.2 μm.

[0050] (2) 8.3 kg of lithium hydroxide monohydrate, 7.3 kg of phosphoric acid, 17.6 kg of ferrous sulfate heptahydrate, 50 g of ascorbic acid, and 70 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 180°C, and kept at that temperature for 3 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form powder b. The primary particle size of powder b was 200 nm.

[0051] (3) Powder a and powder b are mixed at a mass ratio of 7:3 and then sintered at 750°C for 5 hours. The sintered material is then pulverized by airflow to obtain lithium iron phosphate product.

[0052] Example 2

[0053] The lithium iron phosphate material provided in this embodiment differs from that in Embodiment 1 in that:

[0054] Powder a and powder b were mixed at a mass ratio of 6:4, and then sintered at 750°C for 5 hours. The sintered material was then subjected to air jet milling to obtain lithium iron phosphate product.

[0055] Example 3

[0056] The lithium iron phosphate material provided in this embodiment differs from that in Embodiment 1 in that:

[0057] Powder a and powder b were mixed at a mass ratio of 5:5, and then sintered at 750°C for 5 hours. The sintered material was then subjected to air jet milling to obtain lithium iron phosphate product.

[0058] Example 4

[0059] The lithium iron phosphate material provided in this embodiment differs from that in Embodiment 1 in that:

[0060] (1) 7.6 kg of lithium hydroxide monohydrate, 7.3 kg of phosphoric acid, 17.6 kg of ferrous sulfate heptahydrate, 50 g of ascorbic acid, and 150 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 230°C, and kept at that temperature for 9 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form powder a. The primary particle size of powder a was 1.5 μm.

[0061] (2) 8.3 kg of lithium hydroxide monohydrate, 7.3 kg of phosphoric acid, 17.6 kg of ferrous sulfate heptahydrate, 50 g of ascorbic acid, and 70 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 180°C, and kept at that temperature for 3 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form powder b. The primary particle size of powder b was 200 nm.

[0062] (3) Powder a and powder b are mixed at a mass ratio of 7:3 and then sintered at 750°C for 5 hours. The sintered material is then pulverized by airflow to obtain lithium iron phosphate product.

[0063] Example 5

[0064] This embodiment provides a lithium iron phosphate material, which is prepared according to the following steps:

[0065] (1) 7.8 kg of lithium hydroxide monohydrate, 7.3 kg of phosphoric acid, 17.6 kg of ferrous sulfate heptahydrate, 50 g of ascorbic acid, and 150 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 230°C, and kept at that temperature for 8 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form powder a. The primary particle size of powder a was 1.2 μm.

[0066] (2) 8.5 kg of lithium hydroxide monohydrate, 7.3 kg of phosphoric acid, 17.6 kg of ferrous sulfate heptahydrate, 50 g of ascorbic acid, and 70 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 180°C, and kept at that temperature for 3 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form powder b. The primary particle size of powder b was 200 nm.

[0067] (3) Powder a and powder b are mixed at a mass ratio of 7:3 and then sintered at 750°C for 5 hours. The sintered material is then pulverized by airflow to obtain lithium iron phosphate product.

[0068] Comparative Example 1

[0069] The lithium iron phosphate material provided in this comparative example is prepared according to the following steps:

[0070] 8.0 kg of lithium hydroxide monohydrate, 7.3 kg of phosphoric acid, 17.6 kg of ferrous sulfate heptahydrate, 50 g of ascorbic acid, and 90 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 200°C, and held at that temperature for 3 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form a powder. The powder was sintered at 650°C for 3 hours. The sintered material was then subjected to air jet milling to obtain lithium iron phosphate product with a particle size of 200 nm.

[0071] Comparative Example 2

[0072] The lithium iron phosphate material provided in this comparative example is prepared according to the following steps:

[0073] 8.0 kg of lithium hydroxide monohydrate, 7.3 kg of phosphoric acid, 17.6 kg of ferrous sulfate heptahydrate, 50 g of ascorbic acid, and 90 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 220°C, and held at that temperature for 8 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form a powder. The powder was sintered at 790°C for 8 hours. The sintered material was then subjected to air jet milling to obtain lithium iron phosphate product with a particle size of 1.2 μm.

[0074] Comparative Example 3

[0075] The lithium iron phosphate material provided in this comparative example is prepared according to the following steps:

[0076] 8.0 kg of lithium hydroxide monohydrate, 7.3 kg of phosphoric acid, 17.6 kg of ferrous sulfate heptahydrate, 50 g of ascorbic acid, and 90 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 220°C, and held at that temperature for 8 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form a powder. The powder was ground and sieved to obtain powder a with a particle size of 1.2 μm and powder b with a particle size of 200 nm.

[0077] Powder a and powder b were mixed at a mass ratio of 7:3, and then sintered at 750°C for 5 hours. The sintered material was then subjected to air jet milling to obtain lithium iron phosphate product.

[0078] Comparative Example 4

[0079] The lithium iron phosphate material provided in this comparative example is prepared according to the following steps:

[0080] 100g of ferric phosphate, 24.87g of lithium carbonate, 12g of glucose, and 200g of pure water were added to a mixing tank and mixed evenly. The mixture was then ground in a sand mill to a particle size of 1.2μm and 200nm respectively, yielding abrasives of different particle sizes. After spray drying, the abrasives of different particle sizes were transferred to a sintering furnace and sintered at 780℃ for 12 hours under a nitrogen atmosphere. After cooling, a second sintering was performed at 820℃ for 5 hours. After sintering, the abrasives were further crushed by airflow to obtain large solid particles and small solid particles respectively.

[0081] Lithium iron phosphate material is obtained by mixing large solid particles and small solid particles at a mass ratio of 7:3.

[0082] The performance of the lithium iron phosphate products obtained in Examples 1-5 and Comparative Examples 1-3 was measured:

[0083] (1) The compaction density was determined using a powder internal resistance meter with a test area of ​​φ16mm. The test parameters are shown in Table 1.

[0084] Table 1

[0085]

[0086] (2) Electrical performance measurement:

[0087] A positive electrode material was prepared by mixing lithium iron phosphate, acetylene black, and PVDF binder in a mass ratio of 90:4:6. A coin cell was assembled using mesophase carbon microspheres (MCMB) as the negative electrode material and 1.0M LiPF6, EC (ethylene carbonate), and EMC (ethyl methyl carbonate) as the electrolyte. The discharge capacity and cycle performance were then tested.

[0088] Test method: After the battery is placed at -20℃ for 12 hours, it is charged and discharged at 0.1C, with a charge / discharge cutoff voltage of 2.5~3.8V. The battery is then discharged at 0.1C to 2.5V, and the discharge capacity is recorded as A1.

[0089] After the battery was placed at -20℃ for 12 hours, it was charged and discharged at 5C, with a charge / discharge cutoff voltage of 2.5~3.8V. The battery was then discharged at 5C to 2.5V, and the discharge capacity A2 was recorded. The value obtained by dividing A2 / A1 and multiplying it by 100% gives 5C / 0.1C / %, which characterizes the rate discharge performance of the cathode material.

[0090] At -20℃, after the battery is placed for 12 hours, it is discharged at a constant current of 1C to 2.0V and cycled for 500 times. The ratio of the 1C discharge capacity at -20℃ to the 1C discharge capacity at room temperature is recorded, which is the capacity retention rate after 500 cycles at -20℃.

[0091] The results of compaction density and electrical property tests are shown in Table 2. Table 2

[0092] As shown in Table 2, compared to obtaining materials of different particle sizes through grinding and then mixing, this embodiment directly sintered precursor particles of different sizes. Large precursor particles (powder a) were maintained in the range of 1.2–1.5 μm, and small precursor particles (powder b) were maintained in the range of 100–300 nm. The cathode material obtained after sintering the mixture at a ratio of (7–5):(3–5) had a high compaction density of 2.66 g / cm³. 3 The above demonstrates excellent low-temperature performance and rate capability.

[0093] Example 5

[0094] This embodiment provides a lithium manganese phosphate material, which is prepared according to the following steps:

[0095] (1) 7.8 kg of lithium hydroxide monohydrate, 7.30 kg of phosphoric acid, 10.6 kg of manganese sulfate, 50 g of ascorbic acid, and 90 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 230°C, and kept at that temperature for 8 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form powder a. The primary particle size of powder a was 1.2 μm.

[0096] (2) 8.3 kg of lithium hydroxide monohydrate, 7.30 kg of phosphoric acid, 10.6 kg of manganese sulfate, 50 g of ascorbic acid, and 70 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 180°C, and kept at that temperature for 3 hours. After cooling, the mother liquor was removed by plate and frame filtration. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form powder b. The primary particle size of powder b was 200 nm.

[0097] (3) Powder a and powder b were mixed at a mass ratio of 7:3, and then sintered at 750°C for 5 hours. The sintered material was then subjected to air jet milling to obtain lithium manganese iron phosphate product.

[0098] According to the above test method, the capacity retention rate of the lithium manganese phosphate product in this embodiment after 500 cycles at -20℃ is 82.3%.

[0099] Example 6

[0100] This embodiment provides a lithium iron manganese phosphate material, which is prepared according to the following steps:

[0101] (1) 7.8 kg of lithium hydroxide monohydrate, 7.30 kg of phosphoric acid, 8.8 kg of ferrous sulfate heptahydrate, 5.3 kg of manganese sulfate, 50 g of ascorbic acid, and 90 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 230°C, and kept at that temperature for 8 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form powder a. The primary particle size of powder a was 1.2 μm.

[0102] (2) 8.3 kg of lithium hydroxide monohydrate, 7.30 kg of phosphoric acid, 8.8 kg of ferrous sulfate heptahydrate, 5.3 kg of manganese sulfate, 50 g of ascorbic acid, and 70 kg of water were added to a mixing tank and stirred until homogeneous to obtain a slurry. The slurry was transferred to a high-pressure reactor, heated to 180°C, and kept at that temperature for 3 hours. After cooling, the slurry was filtered through a plate and frame filter to remove the mother liquor. 200 kg of pure water was then introduced for washing. 1 kg of glucose was added to the washed slurry and stirred until homogeneous to obtain a mixture. Pure water was added to control the solid content of the mixture to 30%. The mixture was then spray-dried to form powder b. The primary particle size of powder b was 200 nm.

[0103] (3) Powder a and powder b are mixed at a mass ratio of 7:3 and then sintered at 750°C for 5 hours. The sintered material is then pulverized by airflow to obtain lithium manganese iron manganese phosphate product.

[0104] According to the above test method, the capacity retention rate of the lithium iron manganese phosphate product in this embodiment after 500 cycles at -20℃ is 86.5%.

[0105] In summary, the low-temperature phosphate material disclosed herein, through a specific hydrothermal process and optimized hydrothermal and sintering conditions, yields both large-particle-size and small-particle-size precursors. The large-particle-size and small-particle-size precursors are mixed and sintered to obtain the low-temperature phosphate material. The preparation process requires only one sintering step, resulting in low energy consumption. During sintering, precursors of different particle sizes achieve a high-pressure compaction effect. The product exhibits a complete crystal structure, and at an ultra-low temperature of -20℃, it retains over 80% of its capacity after 500 cycles of 1C discharge.

[0106] The embodiments described above are some, but not all, of the embodiments of this disclosure. The detailed description of the embodiments of this disclosure is not intended to limit the scope of the claimed disclosure, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

Claims

1. A method for preparing a low-temperature phosphate material, characterized in that, include: S1, a lithium source, a metal source, phosphoric acid and water are mixed to obtain a slurry, and the slurry is subjected to a hydrothermal reaction to obtain a reaction material; The reactants and carbon source are mixed to obtain a large-particle-size precursor, wherein the metal source is one or more of iron, manganese, nickel, cobalt, and vanadium; the particle size of the large-particle-size precursor is 0.6~1.5μm. S2, a lithium source, a metal source, phosphoric acid and water are mixed to obtain a slurry, and the slurry is subjected to a hydrothermal reaction to obtain a reactant; the reactant is mixed with a carbon source to obtain a small-particle-size precursor, wherein the metal source is one or more of iron, manganese, nickel, cobalt and vanadium; the particle size of the small-particle-size precursor is 50~500nm. S3, the large-particle-size precursor and the small-particle-size precursor are mixed and then sintered to obtain a low-temperature phosphate material. The composition of the phosphate material is LiMPO4 / C, wherein M is selected from one or more of iron, manganese, nickel, cobalt, and vanadium. In step S1, the hydrothermal reaction step includes: reacting the slurry under high pressure at 200~250℃ for 5~10 hours, and then separating the reactant to obtain the reactant. In step S2, the hydrothermal reaction step includes: reacting the slurry under high pressure at 170~220℃ for 2~5 hours, and then separating the reactant to obtain the reactant.

2. The method for preparing the low-temperature phosphate material according to claim 1, characterized in that, The particle size of the large-particle precursor is 1.2~1.5μm.

3. The method for preparing low-temperature phosphate materials according to claim 1, characterized in that, The particle size of the small-diameter precursor is 100~300nm.

4. The method for preparing low-temperature phosphate materials according to claim 1, characterized in that, In step S1, the hydrothermal reaction step includes: reacting the slurry under high pressure at 230°C for 5-10 hours, and then separating the reactant.

5. The method for preparing the low-temperature phosphate material according to claim 1, characterized in that, In step S2, the hydrothermal reaction step includes: reacting the slurry under high pressure at 180°C for 2-5 hours, and then separating the reactant.

6. The method for preparing the low-temperature phosphate material according to claim 1, characterized in that, In step S3, the large-particle-size precursor and the small-particle-size precursor are mixed at a mass ratio of 7:3 to 1:

1.

7. The method for preparing the low-temperature phosphate material according to claim 1, characterized in that, In step S3, the sintering temperature is 700~850℃, the sintering time is 2~10h, and after sintering, the material is obtained by airflow crushing.

8. The method for preparing the low-temperature phosphate material according to claim 1, characterized in that, In steps S1 and S2, an antioxidant is also added to the slurry, and the antioxidant is 0.1% to 0.5% of the mass of the metal source.

9. The method for preparing the low-temperature phosphate material according to claim 1, characterized in that, In steps S1 and S2, the reactants and carbon source are mixed and then spray-dried to obtain the precursor.

10. The method for preparing the low-temperature phosphate material according to claim 9, characterized in that, Before spray drying, the solid content of the material should be controlled to be 25-50%.

11. A low-temperature phosphate material, characterized in that, Prepared by the method according to any one of claims 1 to 10.

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