A high-pressure lithium iron phosphate, its preparation method and application

Abstract

This invention provides a high-compact lithium iron phosphate, its preparation method, and its application, relating to the technical field of lithium-ion batteries. The preparation method includes: mixing battery-grade iron oxide red, phosphoric acid solution, and water, and performing a first milling to obtain slurry A; adding lithium dihydrogen phosphate to slurry A to obtain slurry B; adding a lithium source to slurry B to obtain slurry C; adding ferrous oxalate and water to slurry C to obtain slurry D; adding a carbon source to slurry D and performing a second milling to obtain slurry E; atomizing and drying slurry E to obtain a lithium iron phosphate precursor; calcining the lithium iron phosphate precursor to obtain a calcined product; and pulverizing, sieving, and demagnetizing the calcined product to obtain high-compact lithium iron phosphate. The lithium iron phosphate prepared by the method of this invention has high compaction density, complete and uniform carbon coating, low internal resistance of the powder, high charge-discharge efficiency, and excellent high-temperature cycling stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a high-pressure lithium iron phosphate, its preparation method, and its application. Background Technology

[0002] Current high-compact lithium iron phosphate (LFP) production mainly relies on a single process route, but all have significant drawbacks. The iron oxide red process uses ferric oxide as the iron source, offering low cost and significant environmental advantages, but the raw material particles are large (micron-sized), resulting in uneven particle size distribution after sintering and making it difficult to exceed 2.6 g / cm³ in compaction density. 3 Furthermore, its electrochemical performance is limited. While the ferrous oxalate method can achieve a relatively high compaction density (approximately 2.7 g / cm³), it also has limitations. 3 However, the process is complex and energy-intensive, requiring multiple sintering steps and fine particle size control. Furthermore, the raw material ferrous oxalate is prone to introducing impurities, affecting the purity of the material. Lithium dihydrogen phosphate, as an emerging bifunctional lithium-phosphorus source, has a low decomposition temperature (approximately 200°C) and high reactivity, which can reduce energy consumption and improve purity. However, in traditional processes, uneven coating can easily sacrifice compaction density.

[0003] The industry has attempted to alleviate the problem by improving processes, but with limited success. For example, CN119349536A uses a dry mixing process to simplify the procedure, but it cannot solve the problem of iron oxide particle breakage. While the two-step sintering method from Liyuan Company combines composite iron salts to improve conductivity, it relies on expensive precursors, resulting in poor economics for mass production. Furthermore, a single raw material route struggles to achieve a balance in performance: the iron oxide process is low-cost but has insufficient compaction density; the ferrous oxalate method has high density but weakens rate performance; and lithium dihydrogen phosphate has excellent activity but requires complex coating. These contradictions are particularly pronounced in fast-charging battery scenarios, such as CATL's Shenxing Plus product, which requires a compaction density ≥2.6 g / cm³. 3 It also supports high-rate charging and discharging, which is difficult to meet with existing technologies.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a high-pressure lithium iron phosphate, its preparation method and application, aiming to improve the shortcomings of the current high-pressure lithium iron phosphate preparation, which mainly relies on a single process route and has the disadvantages of the traditional iron red route, such as difficult raw material processing, high temperature difference of finished product, and high magnetic foreign matter content.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a method for preparing high-pressure lithium iron phosphate, the method comprising: Battery-grade iron oxide red, phosphoric acid solution and water are mixed and subjected to a first sand milling to obtain slurry A; Lithium dihydrogen phosphate was added to slurry A to obtain slurry B; A lithium source is added to slurry B to obtain slurry C; Ferrous oxalate and water were added to slurry C to obtain slurry D. A carbon source is added to the slurry D, and a second milling is performed to obtain slurry E; The slurry E was atomized and dried to obtain a lithium iron phosphate precursor. The lithium iron phosphate precursor was calcined to obtain the calcined product; The calcined product is pulverized, sieved, and demagnetized to obtain high-pressure lithium iron phosphate.

[0007] Furthermore, in the process of preparing the slurry A, the battery-grade iron oxide red and phosphoric acid solution are added at a molar ratio of iron to phosphorus of (0.6~0.8):1.

[0008] Furthermore, the phosphoric acid solution has a mass percentage content of 70-85%.

[0009] Furthermore, in the slurry A, the mass percentage of the battery-grade iron oxide is 30-50%.

[0010] Furthermore, the first grinding mill adopts a closed-loop circulation method.

[0011] Furthermore, the first grinding time is 30-40 minutes.

[0012] Furthermore, the rotational speed of the first mill is 1600~1800 r / min.

[0013] Furthermore, the grinding media of the first grinding mill is zirconia ceramic balls with a diameter of 0.2~0.3 mm.

[0014] Furthermore, the lithium dihydrogen phosphate is fed in a molar ratio of lithium dihydrogen phosphate to phosphoric acid of (0.3~0.5):1.

[0015] Furthermore, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium oxalate.

[0016] Furthermore, the lithium source is fed in slurry E with a molar ratio of lithium to iron of (1.01~1.03):1.

[0017] Furthermore, the ferrous oxalate is added according to the molar ratio of iron to phosphorus in the slurry D of (0.96~0.97):1.

[0018] Furthermore, in the process of preparing the slurry D, the water is added according to the solid content of slurry D being 40~45 wt%.

[0019] Furthermore, the carbon source includes glucose and / or sucrose.

[0020] Furthermore, the carbon source is fed in at a carbon coating content of 1.2~1.3 wt% in the finished high-pressure lithium iron phosphate.

[0021] Furthermore, the second grinding mill adopts a closed-loop circulation method.

[0022] Furthermore, the grinding media of the second grinding mill is zirconia ceramic balls with a diameter of 0.1~0.2 mm.

[0023] Furthermore, the particle size D50 of the slurry E is 0.3~0.4 μm.

[0024] Furthermore, the particle size D50 of the dried material obtained by atomization drying is 18~30 μm; the water content of the dried material is 1~3 wt%.

[0025] Furthermore, the calcination temperature is 750~800℃, and the calcination time is 10~14 h.

[0026] Furthermore, the pulverization method is airflow pulverization.

[0027] Furthermore, the mesh size of the sieve is 150 mesh or 200 mesh.

[0028] In a second aspect, the present invention provides a high-pressure lithium iron phosphate, wherein the high-pressure lithium iron phosphate is prepared by the high-pressure lithium iron phosphate preparation method as described in the first aspect.

[0029] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising high-pressure lithium iron phosphate as described in the first aspect.

[0030] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode as described in the third aspect.

[0031] Fifthly, the present invention provides a battery pack comprising a lithium-ion battery as described in the fourth aspect.

[0032] In a sixth aspect, the present invention provides an electrical device comprising a lithium-ion battery as described in the fourth aspect or a battery pack as described in the fifth aspect.

[0033] Compared with the prior art, the present invention has the following beneficial effects: (1) The preparation method described in this invention adopts a dual iron source compound structure of iron red and ferrous oxalate. By relying on the natural gradation of the two iron source particles to fill the gaps, the density of powder packing is effectively improved and the high compaction level is stably achieved. It solves the inherent defects of coarse and uneven particle size of single iron red raw material. The particle morphology is round and dispersed without serious agglomeration. The particles are not easy to break during roll pressing, which is suitable for the high volumetric energy density requirements of power batteries. At the same time, it maintains the raw material cost advantage by relying on the main iron red raw material.

[0034] (2) The preparation method of the present invention combines multiple types of lithium phosphorus raw materials to construct a composite reaction system. The liquid phase stepwise feeding combined with gradient sand milling achieves uniform fusion of various elements and improves the purity of the crystal phase. The carbon source uniformly adheres to the particle surface to form a continuous conductive coating layer, which greatly reduces the internal resistance of the powder and the lithium ion conduction resistance is smaller. The material has excellent initial charge and discharge efficiency and better high-rate charge and discharge performance, breaking the industry contradiction that traditional processes cannot balance compaction performance and electrochemical kinetics.

[0035] (3) The preparation method of the present invention has a simple process flow, requiring only one high-temperature calcination, which consumes less energy compared to the multi-step sintering process; it uses low-cost iron red as the main iron source, with a small amount of auxiliary iron source added, so the overall raw material cost is controllable and the environmental pressure of production is small. The finished product has a stable crystal structure, and the crystal lattice is not easily damaged during high-temperature cycling, with fewer side reactions and significantly improved cycle durability. Attached Figure Description

[0036] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 This is a SEM image of the high-pressure lithium iron phosphate prepared in Example 1 of the present invention.

[0038] Figure 2 This is a schematic diagram of the battery structure provided by the present invention.

[0039] Figure 3 This is a schematic diagram of the battery pack provided by the present invention.

[0040] Figure 4 This is a schematic diagram of the electrical device provided by the present invention. Detailed Implementation

[0041] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0042] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] In a first aspect, the present invention provides a method for preparing high-pressure lithium iron phosphate, the method comprising: Battery-grade iron oxide red, phosphoric acid solution and water are mixed and subjected to a first sand milling to obtain slurry A; Lithium dihydrogen phosphate was added to slurry A to obtain slurry B; A lithium source is added to slurry B to obtain slurry C; Ferrous oxalate and water were added to slurry C to obtain slurry D. A carbon source is added to the slurry D, and a second milling is performed to obtain slurry E; The slurry E was atomized and dried to obtain a lithium iron phosphate precursor. The lithium iron phosphate precursor was calcined to obtain the calcined product; The calcined product is pulverized, sieved, and demagnetized to obtain high-pressure lithium iron phosphate.

[0044] It should be noted that the preparation method described in this invention employs a step-by-step feeding process combined with two stages of differentiated sand milling. First, iron oxide red and phosphoric acid are mixed and sand-milled initially to break up coarse iron oxide red particles and mitigate the accumulation defects caused by the large initial particle size. Then, lithium dihydrogen phosphate, a lithium source, and ferrous oxalate are added sequentially, gradually adjusting the lithium-phosphorus-iron ratio of the system. Lithium dihydrogen phosphate, with its high activity, can pre-build a uniform lithium-phosphorus reaction substrate. Ferrous oxalate serves as an auxiliary iron source, filling the gaps between particles to achieve graded stacking and simultaneously mitigating the uneven particle size problem of single iron oxide red. Finally, a carbon source is added for a second stage of fine sand milling, allowing the carbonaceous components to uniformly coat the particle surface, forming a complete conductive network and reducing the material's internal resistance. Step-by-step liquid-phase mixing ensures uniform microscopic mixing of all elements and reduces sintering impurities. A single calcination simplifies the process and reduces energy consumption, while the dual iron source synergistically balances low cost and high compaction. The precursor is spray-dried to form particles with regular and rounded morphology. After calcination, the crystal structure is stable, and the demagnetization process improves the cleanliness of the material. The overall process not only solves the pain point of the traditional single raw material route's difficulty in balancing compaction and electrochemical performance, but also adapts to mass production lines, taking into account processability, cycle stability, and production economy.

[0045] As an optional implementation, in the process of preparing the slurry A, the battery-grade iron oxide red and phosphoric acid solution are added at a molar ratio of iron to phosphorus of (0.6~0.8):1, for example, 0.60:1, 0.62:1, 0.64:1, 0.66:1, 0.68:1, 0.70:1, 0.72:1, 0.74:1, 0.76:1, 0.78:1, 0.80:1, etc.

[0046] As an optional implementation, the phosphoric acid solution has a mass percentage of 70-85%, for example, it can be 70%, 72%, 74%, 76%, 78%, 80%, 81%, 82%, 83%, 84%, 85%, etc.

[0047] As an optional implementation, the total mass percentage of water in the slurry A is 30-50%, for example, it can be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, etc.

[0048] As an optional implementation, the first grinding process adopts a closed-loop circulation method.

[0049] As an optional implementation, the first grinding time is 30 to 40 minutes, for example, it can be 30 minutes, 31 minutes, 32 minutes, 33 minutes, 34 minutes, 35 minutes, 36 minutes, 37 minutes, 38 minutes, 39 minutes, 40 minutes, etc.

[0050] As an optional implementation, the rotational speed of the first mill is 1600~1800 r / min, for example, it can be 1600 r / min, 1620 r / min, 1640 r / min, 1660 r / min, 1680 r / min, 1700 r / min, 1720 r / min, 1740 r / min, 1760 r / min, 1780 r / min, 1800 r / min, etc.

[0051] As an optional implementation, the grinding media of the first sand mill is a zirconia ceramic ball with a diameter of 0.2~0.3 mm, such as 0.2 mm, 0.21 mm, 0.22 mm, 0.23 mm, 0.24 mm, 0.25 mm, 0.26 mm, 0.27 mm, 0.28 mm, 0.29 mm, 0.3 mm, etc.

[0052] As an optional implementation, the lithium dihydrogen phosphate is fed in a molar ratio of lithium dihydrogen phosphate to phosphoric acid of (0.3~0.5):1, for example, 0.30:1, 0.32:1, 0.34:1, 0.36:1, 0.38:1, 0.40:1, 0.42:1, 0.44:1, 0.46:1, 0.48:1, 0.50:1, etc.

[0053] As an optional implementation, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium oxalate.

[0054] As an optional implementation, the lithium source is fed in slurry E with a molar ratio of lithium to iron of (1.01~1.03):1, for example, 1.01:1, 1.012:1, 1.014:1, 1.016:1, 1.018:1, 1.02:1, 1.022:1, 1.024:1, 1.026:1, 1.028:1, 1.03:1, etc.

[0055] As an optional implementation, the ferrous oxalate is added according to a molar ratio of iron to phosphorus in the slurry D of (0.96~0.97):1, for example, it can be 0.96:1, 0.961:1, 0.962:1, 0.963:1, 0.964:1, 0.965:1, 0.966:1, 0.967:1, 0.968:1, 0.969:1, 0.97:1, etc.

[0056] As an optional implementation, in the process of preparing the slurry D, the water is added at a solid content of 40~45 wt%, for example, it can be 40 wt%, 40.5 wt%, 41 wt%, 41.5 wt%, 42 wt%, 42.5 wt%, 43 wt%, 43.5 wt%, 44 wt%, 44.5 wt%, 45 wt%, etc.

[0057] As an optional implementation, the carbon source includes glucose and / or sucrose.

[0058] As an optional implementation, the carbon source is fed in at a carbon coating content of 1.2~1.3 wt% in the finished high-pressure lithium iron phosphate, for example, it can be 1.2 wt%, 1.21 wt%, 1.22 wt%, 1.23 wt%, 1.24 wt%, 1.25 wt%, 1.26 wt%, 1.27 wt%, 1.28 wt%, 1.29 wt%, 1.3 wt%, etc.

[0059] As an optional implementation, the second grinding process adopts a closed-loop circulation method.

[0060] As an optional implementation, the rotational speed of the second mill is 1800~2200 r / min, for example, it can be 1800 r / min, 1820 r / min, 1840 r / min, 1860 r / min, 1880 r / min, 1900 r / min, 1920 r / min, 1940 r / min, 1960 r / min, 1980 r / min, 2000 r / min, 2020 r / min, 2040 r / min, 2060 r / min, 2080 r / min, 2100 r / min, 2120 r / min, 2140 r / min, 2160 r / min, 2180 r / min, 2200 r / min, etc.

[0061] As an optional implementation, the grinding media of the second mill is a zirconia ceramic ball with a diameter of 0.1~0.2 mm, such as 0.1 mm, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, 0.15 mm, 0.16 mm, 0.17 mm, 0.18 mm, 0.19 mm, 0.2 mm, etc.

[0062] As an optional implementation, the particle size D50 of the slurry E is 0.3~0.4 μm, for example, it can be 0.3 μm, 0.31 μm, 0.32 μm, 0.33 μm, 0.34 μm, 0.35 μm, 0.36 μm, 0.37 μm, 0.38 μm, 0.39 μm, 0.4 μm, etc.

[0063] As an optional implementation, the particle size D50 of the dried material obtained by atomization drying is 18~30 μm, for example, it can be 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, etc.; the water content of the dried material is 1~3 wt%, for example, it can be 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, etc.

[0064] As an optional implementation, the calcination temperature is 750~800℃, for example, it can be 750℃, 755℃, 760℃, 765℃, 770℃, 775℃, 780℃, 785℃, 790℃, 795℃, 800℃, etc., and the calcination time is 10~14h, for example, it can be 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, 14h, etc.

[0065] As an optional implementation, the pulverization method is air jet pulverization.

[0066] As an optional implementation, the process parameters of the airflow pulverization include: nitrogen gas, pressure of 0.3~0.6 MPa, for example, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, etc.; feeding rate of 300~400 kg / h, for example, 300 kg / h, 320 kg / h, 340 kg / h, 360 kg / h, 380 kg / h, 400 kg / h, etc.; and classification frequency of 40~50 Hz, for example, 40 Hz, 42 Hz, 44 Hz, 46 Hz, 48 Hz, 50 Hz, etc.

[0067] As an optional implementation, the sieve mesh size is 150 mesh or 200 mesh.

[0068] In a second aspect, the present invention provides a high-pressure lithium iron phosphate, wherein the high-pressure lithium iron phosphate is prepared by the high-pressure lithium iron phosphate preparation method as described in the first aspect.

[0069] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising high-pressure lithium iron phosphate as described in the first aspect.

[0070] Fourthly, the present invention provides a lithium-ion battery, such as... Figure 2 As shown, the lithium-ion battery includes a positive electrode as described in the third aspect.

[0071] This invention does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is a square-structured battery as an example. It is understood that the arrangement of the terminals (or electrode terminals) is not limited to the same-side positive and negative terminals shown in the figure, and they can also be arranged at two opposite ends of the battery. This invention does not limit this arrangement.

[0072] In some embodiments, the battery includes a casing, within which electrode assemblies are encapsulated. The battery may contain one or more electrode assemblies, which can be selected by those skilled in the art according to specific practical needs.

[0073] Fifthly, the present invention provides a battery pack, such as... Figure 3 As shown, the battery pack includes a lithium-ion battery as described in the fourth aspect.

[0074] In some implementations, batteries can be assembled into battery modules, and battery modules can be assembled into battery packs. The number of battery modules contained in a battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0075] Figure 3 An exemplary structure of a battery pack is shown. Figure 3 As shown, the battery pack includes a housing and multiple battery modules housed within the housing. The housing comprises a lower housing and an upper housing, with the upper housing covering the lower housing and together forming a closed space to accommodate the battery modules. The multiple battery modules can be arranged in any manner within the housing.

[0076] Sixthly, the present invention provides an electrical device, such as... Figure 4 As shown, the electrical device includes a lithium-ion battery as described in the fourth aspect or a battery pack as described in the fifth aspect.

[0077] According to another aspect of the present invention, an electrical device is provided, comprising at least one of the above-described solid-state battery, battery module, or battery pack. The solid-state battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include mobile devices (typically mobile phones, laptops, etc.), electric vehicles (typically pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, or energy storage systems, etc.

[0078] Figure 4 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0079] The present invention will be further illustrated below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0080] Example 1 This embodiment provides a high-pressure lithium iron phosphate, which is prepared by the following steps: (1) Weigh out battery-grade iron oxide red, phosphoric acid solution (concentration of 85%), and pure water respectively. Slowly pour the battery-grade iron oxide red and phosphoric acid solution into a stirring device and stir for 10 min. Then pour in pure water and continue stirring to mix evenly to obtain a slurry. The molar ratio of iron to phosphorus is 0.7:1. In the slurry A, the mass percentage of battery-grade iron oxide red is 40%. (2) Using a closed-loop circulation method, the slurry from step (1) is milled for 35 min to obtain slurry A, wherein the milling speed is 1800 r / min and the milling media diameter is 0.2~0.3 mm zirconia ceramic balls; (3) Weigh lithium dihydrogen phosphate, pour it into slurry A from step (2), and stir it thoroughly to obtain slurry B; wherein, the amount of lithium dihydrogen phosphate is weighed according to the molar ratio of lithium dihydrogen phosphate to phosphoric acid of 0.4:1. (4) Weigh the lithium source (lithium carbonate), slowly pour it into the slurry B in step (3), and stir it thoroughly for 10 min to obtain slurry C; wherein, the weight of the lithium source is weighed according to the ratio of the molar amount of lithium element to the molar amount of iron element in slurry E of 1.03:1. (5) Weigh ferrous oxalate and pure water separately, slowly pour them into slurry C in step (4), and stir thoroughly to obtain slurry D; wherein, the amount of ferrous oxalate is weighed according to the ratio of the molar amount of iron to the molar amount of phosphorus in slurry D is 0.96:1; pure water is added according to the solid content of slurry D being 40 wt%; (6) Weigh the carbon source (a mixture of glucose and PEG, with a PEG mass fraction of 15%), slowly pour it into the slurry D from step (5), and stir thoroughly. Use a closed-loop circulation method to grind the slurry to obtain slurry E (slurry particle size D50 = 0.3~0.4 μm). The grinding mill speed is 2000 r / min, the grinding media diameter is 0.1~0.2 mm zirconia ceramic balls, and the carbon source is weighed according to the carbon coating amount of the finished lithium iron phosphate of 1.2 wt%. (7) The slurry E from step (6) is atomized and dried by spray drying to obtain lithium iron phosphate precursor A; wherein the particle size D50 of the dried material obtained by atomization drying is 18~30 μm; and the water content of the dried material is 2 wt%; (8) Calcine the precursor A from step (7) in a nitrogen atmosphere at a temperature of 780°C for 12 h. (9) The material after calcination in step (8) is subjected to air jet pulverization, sieving, and demagnetization to obtain the final product, high-pressure lithium iron phosphate; wherein the process parameters of the air jet pulverization include: nitrogen, 0.45 MPa, feeding rate 350 kg / h, and grading frequency 45 Hz; the mesh size of the sieve is 200 mesh.

[0081] Figure 1 The images show scanning electron microscope (SEM) images of the high-pressure lithium iron phosphate cathode material at different magnifications. As can be seen from the images, the particles are well dispersed with almost no agglomerates. The particle size distribution is uniform, and the particle morphology is relatively round. The carbon coating on the particle surface is relatively uniform, and there is no obvious free carbon present.

[0082] Example 2 This embodiment provides a high-pressure lithium iron phosphate, which is prepared by the following steps: (1) Weigh out battery-grade iron oxide red, phosphoric acid solution (concentration of 85%), and pure water respectively. Slowly pour the battery-grade iron oxide red and phosphoric acid solution into a stirring device and stir for 10 min. Then pour in pure water and continue stirring to mix evenly to obtain a slurry. The molar ratio of iron to phosphorus is 0.6:1. In the slurry A, the mass percentage of battery-grade iron oxide red is 40%. (2) Using a closed-loop circulation method, the slurry from step (1) is milled for 30 min to obtain slurry A, wherein the milling speed is 1800 r / min and the milling media diameter is 0.2~0.3 mm zirconia ceramic balls; (3) Weigh lithium dihydrogen phosphate, pour it into slurry A from step (2), and stir it thoroughly to obtain slurry B; wherein, the amount of lithium dihydrogen phosphate is weighed according to the ratio of the molar amount of lithium dihydrogen phosphate to the molar amount of phosphoric acid of 0.3:1. (4) Weigh the lithium source (lithium carbonate), slowly pour it into the slurry B in step (3), and stir it thoroughly for 10 min to obtain slurry C; wherein, the weight of the lithium source is weighed according to the ratio of the molar amount of lithium element to the molar amount of iron element in slurry E of 1.02:1. (5) Weigh ferrous oxalate and pure water separately, slowly pour them into slurry C in step (4), and stir thoroughly to obtain slurry D; wherein, the amount of ferrous oxalate is weighed according to the ratio of the molar amount of iron to the molar amount of phosphorus in slurry D is 0.965:1; pure water is added according to the solid content of slurry D being 42 wt%; (6) Weigh the carbon source (a mixture of glucose and PEG, with a PEG mass fraction of 10%), slowly pour it into the slurry D from step (5), and stir thoroughly. Use a closed-loop circulation method to grind the slurry to obtain slurry E (slurry particle size D50 = 0.3~0.4 μm). The grinding mill speed is 2000 r / min, the grinding media diameter is 0.1~0.2 mm zirconia ceramic balls, and the carbon source is weighed according to the carbon coating amount of the finished lithium iron phosphate of 1.25 wt%. (7) The slurry E from step (6) is atomized and dried by spray drying to obtain lithium iron phosphate precursor A; wherein the particle size D50 of the dried material obtained by atomization drying is 18~30 μm; and the water content of the dried material is 2 wt%; (8) Calcine the precursor A from step (7) in a nitrogen atmosphere at a temperature of 750°C for 14 h. (9) The material after calcination in step (8) is subjected to airflow pulverization, sieving, and demagnetization to obtain the final product, high-pressure lithium iron phosphate; wherein, nitrogen, 0.3 MPa, feeding rate 300 kg / h, grading frequency 40 Hz; the sieve mesh number is 150 mesh.

[0083] Example 3 This embodiment provides a high-pressure lithium iron phosphate, which is prepared by the following steps: (1) Weigh out battery-grade iron oxide red, phosphoric acid solution (concentration of 85%), and pure water respectively. Slowly pour the battery-grade iron oxide red and phosphoric acid solution into a stirring device and stir for 10 min. Then pour in pure water and continue stirring to mix evenly to obtain a slurry. The molar ratio of iron to phosphorus is 0.8:1. In the slurry A, the mass percentage of battery-grade iron oxide red is 40%. (2) Using a closed-loop circulation method, the slurry from step (1) is milled for 40 min to obtain slurry A, wherein the milling speed is 1800 r / min and the milling media diameter is 0.2~0.3 mm zirconia ceramic balls; (3) Weigh lithium dihydrogen phosphate, pour it into slurry A from step (2), and stir it thoroughly to obtain slurry B; wherein, the amount of lithium dihydrogen phosphate is weighed according to the ratio of the molar amount of lithium dihydrogen phosphate to the molar amount of phosphoric acid of 0.5:1. (4) Weigh the lithium source (specific name: lithium carbonate), slowly pour it into the slurry B in step (3), and stir it thoroughly for 10 minutes to obtain slurry C; wherein, the weight of the lithium source is weighed according to the ratio of the molar amount of lithium element to the molar amount of iron element in slurry E of 1.01:1. (5) Weigh ferrous oxalate and pure water separately, slowly pour them into slurry C in step (4), and stir thoroughly to obtain slurry D; wherein, the amount of ferrous oxalate is weighed according to the ratio of the molar amount of iron to the molar amount of phosphorus in slurry D is 0.97:1; pure water is added according to the solid content of slurry D being 45 wt%; (6) Weigh the carbon source (a mixture of glucose and PEG, with a PEG mass fraction of 20%), slowly pour it into the slurry D from step (5), and stir thoroughly. Use a closed-loop circulation method to grind the slurry to obtain slurry E (slurry particle size D50 = 0.3~0.4 μm). The grinding mill speed is 2000 r / min, the grinding media diameter is 0.1~0.2 mm zirconia ceramic balls, and the carbon source is weighed according to the carbon coating amount of the finished lithium iron phosphate of 1.3 wt%. (7) The slurry E from step (6) is atomized and dried by spray drying to obtain lithium iron phosphate precursor A; wherein the particle size D50 of the dried material obtained by atomization drying is 18~30 μm; and the water content of the dried material is 2 wt%; (8) Calcine the precursor A from step (7) in a nitrogen atmosphere at a temperature of 800°C for 10 h. (9) The material after calcination in step (8) is subjected to air jet pulverization, sieving, and demagnetization to obtain the final product, high-pressure lithium iron phosphate; wherein the process parameters of the air jet pulverization include: nitrogen, 0.6 MPa, feeding rate 400 kg / h, and grading frequency 50 Hz; the mesh size of the sieve is 200 mesh.

[0084] Example 4 This embodiment provides a high-pressure lithium iron phosphate, which differs from Embodiment 1 only in that the lithium source is replaced with an equal mass of lithium hydroxide, while the other steps are the same as in Embodiment 1.

[0085] Example 5 This embodiment provides a high-pressure lithium iron phosphate, which differs from Embodiment 1 only in that the lithium source is replaced with an equal mass of lithium nitrate, while the other steps are the same as in Embodiment 1.

[0086] Example 6 This embodiment provides a high-density lithium iron phosphate, which differs from Embodiment 1 only in that the lithium source is replaced with an equal mass of lithium oxalate, while the other steps are the same as in Embodiment 1.

[0087] Example 7 This embodiment provides a high-pressure lithium iron phosphate, which differs from Embodiment 1 only in that the carbon source is replaced with an equal mass of sucrose, while the other steps are the same as in Embodiment 1.

[0088] Comparative Example 1 This comparative example provides a lithium iron phosphate, which is prepared by the following steps: (1) Prepare a phosphorus source according to the ratio of phosphoric acid to lithium dihydrogen phosphate in step (3) of Example 1; (2) Weigh out iron red and phosphorus source according to the iron-phosphorus ratio in step (5) of Example 1; (3) Weigh the lithium source according to the lithium-iron ratio in step (4) of Example 1; (4) Prepare materials according to the slurry concentration of step (5) in Example 1; (5) Weigh the carbon source, grind the material according to step (6) of Example 1, and control the grinding process and particle size standard; (6) Following steps (7), (8), and (9) of Example 1, the material obtained in step (5) of Comparative Example 1 is further processed.

[0089] Note: The only difference between this comparative example and Example 1 is that the dual phosphorus sources of phosphoric acid and lithium dihydrogen phosphate are retained, but iron oxide red and ferrous oxalate are no longer added sequentially. All iron source materials are directly mixed at once, thus losing the stepwise liquid phase wetting and particle classification and forming effect, and there is no ordered gradation and stacking effect.

[0090] Comparative Example 2 This comparative example provides a lithium iron phosphate, which is prepared by the following steps: (1) Weigh iron oxide and lithium dihydrogen phosphate according to the lithium-iron ratio in step (4) of Example 1; (2) Weigh phosphoric acid according to the iron-phosphorus ratio in step (5) of Example 1; (3) Prepare materials according to the slurry concentration of step (5) in Example 1; (4) Weigh the carbon source, grind the material according to the carbon coating amount, grinding regime and material particle size standard control grinding according to step (6) of Example 1; (5) Following steps (7), (8), and (9) of Example 1, the material obtained in step (4) of Comparative Example 2 is further processed.

[0091] Note: The only difference between this comparative example and Example 1 is that only lithium dihydrogen phosphate is used as a single phosphorus source, and the phosphoric acid combination is omitted. The phosphorus source system is singular and lacks the effect of refining iron oxide particles through early liquid-phase acidification, resulting in a decrease in the uniformity of element mixing.

[0092] Comparative Example 3 This comparative example provides a lithium iron phosphate, which is prepared by the following steps: (1) Weigh iron oxide and phosphoric acid according to the iron-phosphorus ratio in step (5) of Example 1; (2) Weigh the lithium source according to the lithium-iron ratio in step (4) of Example 1; (3) Prepare materials according to the slurry concentration of step (5) in Example 1; (4) Weigh the carbon source, grind the material according to the carbon coating amount, grinding regime and material particle size standard control grinding according to step (6) of Example 1; (5) Following steps (7), (8), and (9) of Example 1, the material obtained in step (4) of Comparative Example 3 is further processed.

[0093] Note: The only difference between this comparative example and Example 1 is that it uses only iron red as the sole iron source and phosphoric acid as the sole phosphorus source, completely abandoning the two functional excipients, ferrous oxalate and lithium dihydrogen phosphate, and returning to the traditional pure iron red single route, which is the most basic control benchmark.

[0094] Comparative Example 4 This comparative example provides a lithium iron phosphate, which is prepared by the following steps: (1) is completely consistent with step (1) of Example 1.

[0095] (2) is completely consistent with step (2) of Example 1.

[0096] (3) Weigh lithium dihydrogen phosphate, lithium source, ferrous oxalate, carbon source and pure water, pour them into slurry A in step (2) and stir them thoroughly to obtain slurry B; wherein, the amount of lithium dihydrogen phosphate, ferrous oxalate, carbon source and pure water added is consistent with steps (3) to (6) of the example; (4) The sanding step is the same as step (6) in Example 1.

[0097] (5) Following steps (7), (8), and (9) of Example 1, the material obtained in step (4) of Comparative Example 4 is further processed.

[0098] Test case Test methods Button Battery Preparation: The positive electrode materials obtained in Examples 1-7 and Comparative Examples 1-4 were assembled into button batteries, as follows: Positive electrode material, conductive agent (acetylene black), and binder (PVDF) were weighed according to a mass ratio of 90%:5%:5%. The weighed positive electrode material and acetylene black were mixed and ground in an agate mortar. After grinding evenly, the mixture was added to N-methylpyrrolidone (NMP), which had fully reacted with PVDF, and ground continuously until the slurry became a viscous liquid with a certain degree of fluidity. The ground slurry was evenly transferred onto aluminum foil, and the sample was evenly coated using a 300 μm thick coater. It was then pre-baked in air at 60°C for 5 hours, followed by vacuum drying at 90°C for 12 hours to remove water and organic matter from the coated sample. Electrode sheets were then cut to size for later use, yielding the positive electrode sheet.

[0099] Using lithium foil as the negative electrode and a prepared electrode sheet as the positive electrode, with an electrolyte ratio of EC:DMC=1:1, a coin cell was assembled and tested using a BTV charge-discharge tester. At 60℃, the lithium-ion battery assembled with the above positive electrode sheet underwent 100 charge-discharge cycles at a working voltage of 2.0-3.65V using a 1C / 1C charge-discharge method.

[0100] The test results are shown in Table 1: Table 1

[0101] As shown in Table 1, the high-compaction lithium iron phosphate cathode materials prepared in the three sets of embodiments of the present invention exhibit comprehensive performance superior to the three control samples. Compared with Comparative Examples 1, 2, and 3, the embodiments show higher overall powder compaction values, significantly lower powder resistivity, and clear advantages in charge specific capacity, initial discharge efficiency, and capacity retention rate at 60°C for 100 cycles. The difference in powder resistivity is particularly striking; the higher resistivity values ​​of the comparative examples indicate greater lithium-ion conduction resistance and weaker electrochemical kinetics performance, while the embodiments demonstrate excellent conductivity and less polarization during charge and discharge. Furthermore, the embodiments show higher initial charge and discharge efficiency, fewer ineffective side reactions within the material, stronger structural stability under high-temperature long-cycle conditions, and a much slower capacity decay rate than the comparative examples.

[0102] In terms of product generation indicators, the powder compaction performance of the embodiment has reached or is close to the industry standard level of fourth-generation lithium iron phosphate, which can meet the needs of high energy density fast-charging power batteries; the compaction level of the three comparative proportions only stays at the level of 3.5-generation conventional lithium iron phosphate, with insufficient packing density, which makes it difficult to meet the stringent requirements of high-end cells for simultaneous improvement in compaction density, cycle life and rate performance, fully demonstrating the significant performance improvement effect brought about by the stepwise preparation process of dual iron source and dual phosphorus source of this invention.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing high-pressure lithium iron phosphate, characterized in that, The preparation method includes: Battery-grade iron oxide red, phosphoric acid solution and water are mixed and subjected to a first sand milling to obtain slurry A; Lithium dihydrogen phosphate was added to slurry A to obtain slurry B; A lithium source is added to slurry B to obtain slurry C; Ferrous oxalate and water were added to slurry C to obtain slurry D. A carbon source is added to the slurry D, and a second milling is performed to obtain slurry E; The slurry E was atomized and dried to obtain a lithium iron phosphate precursor. The lithium iron phosphate precursor was calcined to obtain the calcined product; The calcined product is pulverized, sieved, and demagnetized to obtain high-pressure lithium iron phosphate.

2. The method for preparing high-pressure lithium iron phosphate according to claim 1, characterized in that, In the process of preparing the slurry A, the battery-grade iron oxide red and phosphoric acid solution are added at a molar ratio of iron to phosphorus of (0.6~0.8):

1. Preferably, the phosphoric acid solution has a mass percentage content of 70-85%; Preferably, in the slurry A, the mass percentage of battery-grade iron oxide is 30-50%.

3. The method for preparing high-pressure lithium iron phosphate according to claim 1, characterized in that, The first grinding mill adopts a closed-loop circulation method; Preferably, the first grinding time is 30-40 minutes; Preferably, the rotational speed of the first mill is 1600~1800 r / min; Preferably, the grinding media of the first sand mill is a zirconia ceramic ball with a diameter of 0.2~0.3 mm.

4. The method for preparing high-pressure lithium iron phosphate according to claim 1, characterized in that, The lithium dihydrogen phosphate is fed in a molar ratio of lithium dihydrogen phosphate to phosphoric acid of (0.3~0.5):

1. Preferably, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium oxalate; Preferably, the lithium source is fed in slurry E at a molar ratio of lithium to iron of (1.01~1.03):

1. Preferably, the ferrous oxalate is added according to a molar ratio of iron to phosphorus in the slurry D of (0.96~0.97):1; Preferably, in the process of preparing the slurry D, the water is added according to the solid content of slurry D being 40~45 wt%; Preferably, the carbon source includes glucose and / or sucrose; Preferably, the carbon source is fed in at a carbon coating content of 1.2~1.3 wt% in the finished high-pressure lithium iron phosphate.

5. The method for preparing high-pressure lithium iron phosphate according to claim 1, characterized in that, The second grinding mill adopts a closed-loop circulation method; Preferably, the grinding media of the second sand mill is zirconia ceramic balls with a diameter of 0.1~0.2 mm; Preferably, the particle size D50 of the slurry E is 0.3~0.4 μm; Preferably, the particle size D50 of the dried material obtained by atomization drying is 18~30 μm; the water content of the dried material is 1~3wt%; Preferably, the calcination temperature is 750~800℃, and the calcination time is 10~14 h; Preferably, the pulverization method is air jet milling; Preferably, the mesh size of the sieve is 150 mesh or 200 mesh.

6. A high-pressure lithium iron phosphate, characterized in that, The high-pressure lithium iron phosphate is prepared by the method for preparing high-pressure lithium iron phosphate as described in any one of claims 1 to 5.

7. A positive electrode sheet, characterized in that, The positive electrode includes the high-pressure lithium iron phosphate as described in claim 6.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 7.

9. A battery pack, characterized in that, The battery pack includes the lithium-ion battery as described in claim 8.

10. An electrical device, characterized in that, The electrical device includes the lithium-ion battery as described in claim 8 or the battery pack as described in claim 9.

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