Lithium iron phosphate and preparation method thereof, battery, battery pack and electric equipment

Abstract

The invention relates to the technical field of batteries, in particular to lithium iron phosphate and a preparation method thereof, a battery, a battery pack and electric equipment, the lithium iron phosphate comprises first particles, the Dv50 of the first particles is 0.75-2.0 [mu] m, the first particles are obtained by crushing secondary particles, and the mechanical strength of the secondary particles is larger than 6 mN; and a second particle, wherein the Dv50 of the second particle is 0.55 [mu] m to 1.3 [mu] m. The lithium iron phosphate can realize relatively high compaction density, so that the battery adopting the lithium iron phosphate can realize relatively high energy density.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to lithium iron phosphate and a preparation method thereof, a battery, a battery pack and electrical equipment. Background Art

[0002] Lithium iron phosphate materials are widely used in the field of new energy because of their advantages such as stable structure, high safety performance, long cycle life, and no memory effect. In actual use, the main disadvantage of lithium iron phosphate materials is their low energy density. Increasing the compaction density of lithium iron phosphate materials is one of the main ways to increase energy density and thus increase the vehicle's range. The high-density materials currently in mass production or research and development are mainly achieved by adjusting the particle size and proportion and optimizing the particle combination to achieve the optimal stacking density, but this involves many technical difficulties. Therefore, the current high-density lithium iron phosphate related technologies still need to be improved. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, the present invention provides a lithium iron phosphate with a high compaction density and a preparation method thereof, a battery, a battery pack and an electric device.

[0004] In a first aspect of the present application, a lithium iron phosphate is provided. According to an embodiment of the present application, the lithium iron phosphate includes a first particle and a second particle, wherein the Dv50 particle size of the first particle is 0.75 μm to 2.0 μm, the first particle is obtained by crushing a secondary particle, and the mechanical strength of the secondary particle is 6 to 15 mN; the Dv50 particle size of the second particle is 0.55 μm to 1.3 μm.

[0005] Specifically, the secondary particles have high mechanical strength, that is, high density. The first particles obtained by crushing them inherit the high mechanical strength, high density and low porosity of the secondary particles, which is more conducive to the close stacking of the first particles, so that the first particles themselves have a higher compaction density. At the same time, when used in combination with the second particles, a higher compaction density can be achieved, thereby improving the energy density of the battery using the lithium iron phosphate.

[0006] According to an embodiment of the present application, the aspect ratio of the first particles may be 1.26 to 1.83. With the above aspect ratio, the first particles have a rounder shape, which is more conducive to dense packing, thereby increasing the compaction density of lithium iron phosphate.

[0007] According to an embodiment of the present application, the particle size distribution width K is defined as (Dv90-Dv10) / Dv50, and the particle size distribution width K of the first particle can be 2.5 to 4.0. With the above particle size distribution, the particle size distribution range of the first particle is relatively wide, and it can cooperate with the second particle to achieve a tighter stacking, thereby achieving a higher compaction density.

[0008] According to an embodiment of the present application, based on the total mass of the first particles, the carbon content in the first particles is 1 wt % to 1.5 wt %.

[0009] According to an embodiment of the present application, the secondary particles include a plurality of primary particles, and a phosphate binder is distributed between adjacent primary particles in the secondary particles. The primary particles are bonded by the phosphate binder, which can effectively improve the mechanical strength and density of the secondary particles, and is also conducive to obtaining the first particles after air flow crushing.

[0010] According to an embodiment of the present application, the phosphate binder includes at least one of aryl phosphate and alkyl phosphate, thereby facilitating the formation of first particles with high density, high mechanical strength and high compaction density.

[0011] According to an embodiment of the present application, the second particles are rod-shaped, so that the second particles can be well filled into the gaps formed between the first particles, thereby achieving a high packing density between large and small particles and improving the compaction density of lithium iron phosphate.

[0012] According to an embodiment of the present application, the aspect ratio of the second particles is 1.3 to 3.7. Thus, the second particles can better cooperate with the first particles, thereby achieving a higher compaction density.

[0013] According to an embodiment of the present application, based on the total mass of the second particles, the carbon content in the second particles is 1 wt % to 2.5 wt %.

[0014] According to an embodiment of the present application, based on the total mass of the lithium iron phosphate, the mass percentage of the first particles is 50% to 90%. Within this ratio range, the lithium iron phosphate can be more densely stacked, thereby achieving a higher compaction density, and can achieve a compaction density higher than other ratios.

[0015] According to the embodiment of the present application, the compaction density of lithium iron phosphate is 2.7 g / cc to 2.8 g / cc. Therefore, the battery using the lithium iron phosphate has a higher energy density, which is beneficial to improve the performance of the battery.

[0016] In the second aspect of the present application, a method for preparing the lithium iron phosphate described above is provided. According to an embodiment of the present application, the method comprises: mixing iron phosphate, a carbon source, and a lithium source in a stoichiometric ratio to obtain a raw material mixture; mixing the raw material mixture with a phosphate binder, and spraying and granulating the obtained spray mixture to obtain secondary particles; sintering the secondary particles to obtain a sintered material; crushing the sintered material to obtain a first particle; providing a second particle; mixing the first particle and the second particle to obtain the lithium iron phosphate. The present application, by adding a binder, bonds the formed primary particles together to form secondary particles with high mechanical strength, high density, and low porosity, which can reduce the pores between the primary particles and ensure that the material has a high density during the preparation process. After crushing, the obtained first particles have high mechanical strength, as well as optimized morphology and a wide particle size distribution, and are further used in combination with second particles of suitable particle size to effectively achieve the goal of high compaction density.

[0017] According to an embodiment of the present application, based on the total mass of the spray mixture, the amount of the phosphate binder added is 1 wt% to 5 wt%. Within this amount range, the mechanical strength and density of the first particles can be effectively improved, the morphology of the first particles can be optimized, and the compaction density of the first particles can be increased, while the gram capacity of the lithium iron phosphate is basically not affected.

[0018] According to an embodiment of the present application, before being mixed with the phosphate binder, the raw material mixture is sand-ground until the Dv50 particle size of the sand-ground slurry is 300nm to 600nm. Within the above particle size range, it is conducive to better interaction with the phosphate binder, thereby improving the density and mechanical strength of the first particles and improving the compaction density of the first particles.

[0019] According to an embodiment of the present application, the inlet temperature of the spray granulation is 220° C. to 250° C., and the outlet temperature is 90° C. to 100° C. This facilitates obtaining first particles with suitable morphology and particle size, thereby increasing the compaction density of lithium iron phosphate.

[0020] According to an embodiment of the present application, the Dv50 particle size of the secondary particles is 20 μm to 30 μm. Within this particle size range, the secondary particles have high density and mechanical strength, which is conducive to the subsequent acquisition of first particles with high compaction density.

[0021] According to an embodiment of the present application, the sintering includes sintering for 15h to 20h under a protective atmosphere at 750° C. to 820° C. Under the sintering conditions, lithium iron phosphate material can be effectively obtained, and the phosphate binder can be converted into phosphate, which basically does not affect the electrochemical properties of the lithium iron phosphate material.

[0022] According to an embodiment of the present application, after the sand grinding process and before the spray granulation, the process further includes: removing iron from the sand grinding slurry. As a result, the iron-containing substance content in the lithium iron phosphate is low, which can effectively improve the negative impact of the iron-containing substance when the lithium iron phosphate is used in batteries, thereby improving the electrochemical performance of the battery using the lithium iron phosphate.

[0023] According to an embodiment of the present application, the second particles are prepared by a hydrothermal method, so that the particle size and morphology of the obtained second particles can better match those of the first particles, which is beneficial to improving the compaction density of lithium iron phosphate.

[0024] In a third aspect of the present application, a battery is provided. According to an embodiment of the present application, the battery comprises the lithium iron phosphate described above or the lithium iron phosphate prepared by the method described above. The battery can achieve a higher energy density and a longer cycle life, thereby expanding its application range.

[0025] In a fourth aspect of the present application, a battery pack is provided. According to an embodiment of the present application, the battery pack includes the battery described above. The battery pack has a high energy density and a long service life.

[0026] In a fifth aspect of the present application, an electric device is provided. According to an embodiment of the present application, the electric device comprises the battery or the battery pack described above. The electric device has better endurance and longer service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the first particle spray granulation process of one embodiment of the present application.

[0028] Figure 2 This is a SEM photograph of the cross section of the sintered product during the preparation of the first particle in Example 5 of the present application.

[0029] Figure 3 This is a SEM photograph of the powder of the first particles obtained after airflow pulverization in Example 5 of the present application.

[0030] Figure 4 This is a SEM photograph of a cross section of the second particle in Example 5 of the present application.

[0031] Figure 5 This is a SEM photograph of the cross section of the sintered product during the preparation of the first particle in Comparative Example 2 of the present application.

[0032] Figure 6 This is a SEM photograph of the powder of the first particles obtained after airflow pulverization in Comparative Example 2 of the present application.

[0033] Figure 7It is a schematic diagram of the principle of mechanical strength test of secondary particles in an embodiment of the present application.

[0034] Reference numerals:

[0035] 10: primary particles 20: phosphate binder 30: secondary particles DETAILED DESCRIPTION

[0036] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0037] In a first aspect of the present application, a lithium iron phosphate is provided. According to an embodiment of the present application, the lithium iron phosphate includes a first particle and a second particle, wherein the Dv50 particle size of the first particle is 0.75 μm to 2.0 μm, the first particle is obtained by crushing a secondary particle, and the mechanical strength of the secondary particle is 6 to 15 mN; the Dv50 particle size of the second particle is 0.55 μm to 1.3 μm.

[0038] In some embodiments, the Dv50 particle size of the first particles can be 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2.0 μm, etc. In some embodiments, the Dv50 particle size of the second particles can be 0.55 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, etc. In some embodiments, the mechanical strength of the secondary particles can be 6 mN, 7 mN, 8 mN, 9 mN, 10 mN, 11 mN, 12 mN, 13 mN, 14 mN, 15 mN, etc.

[0039] In this article, Dv50 particle size is also called median diameter or median particle size, which refers to the particle size corresponding to when the volume cumulative particle size distribution percentage of a sample reaches 50%; its physical meaning is that particles with a particle size larger than it account for 50% of the volume, and particles with a particle size smaller than it also account for 50% of the volume.

[0040] Specifically, the secondary particles have high mechanical strength, that is, high density. The first particles obtained by crushing them inherit the high mechanical strength, high density and low porosity of the secondary particles, which is more conducive to the close stacking of the first particles, so that the first particles themselves have a higher compaction density. At the same time, when used in combination with the second particles, a higher compaction density can be achieved, thereby improving the energy density of the battery using the lithium iron phosphate.

[0041] According to the embodiments of the present application, the specific method of crushing the secondary particles is not particularly limited, and can be specifically air flow crushing. Thus, the first particles obtained have high mechanical strength, suitable particle size range, and wide particle size distribution width, which is conducive to improving the compaction density of lithium iron phosphate.

[0042] According to an embodiment of the present application, the aspect ratio of the first particles may be 1.26 to 1.83, specifically 1.26, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.83, etc. With the above aspect ratio, the first particles have a rounder morphology, which is more conducive to dense stacking, thereby increasing the compaction density of lithium iron phosphate.

[0043] Herein, the aspect ratio of the first particle refers to the ratio of the distance between the long side and the short side of the first particle, which can be specifically characterized by counting the sizes of the first particles in the SEM image of the first particles, wherein the long side of the first particle is the distance between the two points with the largest distance on the contour line of the first particle in the SEM image, and the short side of the first particle is the distance between the two points with the smallest distance on the contour line of the first particle in the SEM image.

[0044] According to an embodiment of the present application, the particle size distribution width K is defined as (Dv90-Dv10) / Dv50, and the particle size distribution width K of the first particle can be 2.5-4.0, specifically 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, etc. With the above particle size distribution, the particle size distribution range of the first particle is wider, and it can cooperate with the second particle to achieve a tighter stacking, thereby achieving a higher compaction density.

[0045] In this article, Dv90 and Dv10 have similar meanings to Dv50. Dv90 refers to the particle size corresponding to 90% of the volume cumulative particle size distribution of a sample; its physical meaning is that particles with a particle size larger than it account for 10% of the volume, and particles with a particle size smaller than it account for 10% of the volume; Dv10 refers to the particle size corresponding to 10% of the volume cumulative particle size distribution of a sample; its physical meaning is that particles with a particle size larger than it account for 90% of the volume, and particles with a particle size smaller than it account for 90% of the volume. The test method for Dv90 and Dv10 can be the same as the test method for Dv50.

[0046] According to an embodiment of the present application, based on the total mass of the first particles, the carbon content in the first particles is 1wt% to 1.5wt%, such as 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt% and the like.

[0047] According to an embodiment of the present application, the second particles are rod-shaped, so that the second particles can be well filled into the gaps formed between the first particles, thereby achieving a high packing density between large and small particles and improving the compaction density of lithium iron phosphate.

[0048] According to an embodiment of the present application, the aspect ratio of the second particles is 1.3 to 3.7, specifically 1.3, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.7, etc. Thus, the second particles can better cooperate with the first particles to achieve a higher compaction density.

[0049] According to an embodiment of the present application, based on the total mass of the second particles, the carbon content in the second particles is 1wt% to 2.5wt%, specifically 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.9wt%, 2.2wt%, 2.5wt% and the like.

[0050] According to an embodiment of the present application, the secondary particles include a plurality of primary particles, and a phosphate binder is distributed between adjacent primary particles in the secondary particles. The primary particles are bonded by the phosphate binder, which can effectively improve the mechanical strength and density of the secondary particles, and is also conducive to obtaining the first particles after crushing.

[0051] According to an embodiment of the present application, the phosphate binder includes at least one of aryl phosphate and alkyl phosphate, thereby facilitating the formation of first particles with high density, high mechanical strength and high compaction density.

[0052] According to some embodiments of the present application, during the preparation process of the first particles, by introducing phosphate esters with a low carbon content as a binder, the primary particles are more likely to be bonded together during the spray granulation stage to maintain a high density between the particles, rather than forming a carbon coating to disperse the primary particles. Further, through sintering, the overall particle density is increased, thereby improving the compaction density of the particles themselves.

[0053] According to an embodiment of the present application, based on the total mass of the lithium iron phosphate, the mass percentage of the first particles is 50% to 90%, specifically 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc. Within this ratio range, the lithium iron phosphate can be more densely stacked, thereby achieving a higher compaction density, and can achieve a compaction density higher than other ratios.

[0054] According to the embodiments of the present application, the compaction density of lithium iron phosphate is 2.7 g / cc to 2.8 g / cc, specifically 2.7 g / cc, 2.71 g / cc, 2.72 g / cc, 2.73 g / cc, 2.74 g / cc, 2.75 g / cc, 2.76 g / cc, 2.77 g / cc, 2.78 g / cc, 2.79 g / cc, 2.8 g / cc, etc. Therefore, the battery using the lithium iron phosphate has a higher energy density, which is beneficial to improve the performance of the battery.

[0055] In the second aspect of the present application, a method for preparing the lithium iron phosphate described above is provided. According to an embodiment of the present application, the method comprises: mixing the raw material mixture with a phosphate binder, and spray granulating the obtained spray mixture to obtain secondary particles; sintering the secondary particles to obtain a sintered material; crushing the sintered material to obtain a first particle; providing a second particle; mixing the first particle and the second particle to obtain the lithium iron phosphate. The present application bonds the formed primary particles together by adding a phosphate binder, thereby reducing the pores between the primary particles and ensuring that the material has a high density during the synthesis process. The density of the particles can be further improved after sintering. After crushing, the first particles obtained have a high mechanical strength, as well as an optimized morphology and a wide particle size distribution. They are further used in combination with second particles of suitable particle size to effectively achieve the goal of high compaction density. Figure 1 A schematic diagram showing the formation of secondary particles by bonding primary particles through a phosphate binder during the spray granulation process is shown. The obtained secondary particles have fewer pores, higher density and mechanical strength. After crushing, the obtained first particles also have fewer pores, higher density and mechanical strength, thereby achieving a higher compaction density.

[0056] According to an embodiment of the present application, the second particles are prepared by a hydrothermal method. Specifically, the second particles synthesized by the hydrothermal method have a smaller particle size and can be well filled into the gaps formed between the first particles, thereby achieving a high packing density between large and small particles and improving the compaction density of lithium iron phosphate. Furthermore, by controlling the pressure and temperature in the reactor during the hydrothermal reaction and adjusting the nucleation rate and growth rate, second particles with special morphology can be obtained, and after airflow crushing, rod-shaped and round second particles can be obtained.

[0057] It can be understood that by selecting two lithium iron phosphate materials with different processes and different particle sizes and optimizing the process, lithium iron phosphate particles with special morphology and particle size distribution can be obtained, and then by mixing the two types of lithium iron phosphate particles, a high compaction density of lithium iron phosphate can be achieved; thereby, the development cycle of lithium iron phosphate materials can be greatly shortened, the development cost of lithium iron phosphate materials can be reduced, and mass production can be quickly introduced.

[0058] According to the embodiments of the present application, a carbon-free or low-carbon binder can be selected, whereby the binder can mainly play an adhesive role, so that the primary particles are firmly bonded, thereby obtaining first particles with higher density, rather than forming a carbon coating, which makes the primary particles tend to disperse. In some specific embodiments, the phosphate binder can specifically include at least one of an aryl phosphate and an alkyl phosphate. Thus, it is conducive to forming a first particle with high mechanical strength and high density, thereby achieving a higher compaction density.

[0059] According to an embodiment of the present application, based on the total mass of the spray mixture, the amount of the binder added is 1wt% to 5wt%, specifically 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, etc. Within this amount range, the mechanical strength and density of the first particles can be effectively improved, the morphology of the first particles can be optimized, and the compaction density of the first particles can be increased, while the gram capacity of the lithium iron phosphate is basically not affected.

[0060] According to an embodiment of the present application, before being mixed with the phosphate binder, the raw material mixture is sand-ground until the Dv50 particle size of the sand-ground slurry is 300nm to 600nm, specifically 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, etc. Within the above particle size range, it is conducive to better interaction with the binder, thereby improving the density and mechanical strength of the first particles, and improving the compaction density of the first particles.

[0061] According to the embodiments of the present application, the inlet temperature of the spray granulation is 220°C to 250°C (specifically 220°C, 225°C, 230°C, 235°C, 240°C, 245°C, 250°C, etc.), and the outlet temperature is 90°C to 100°C (specifically 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C, 100°C, etc.). Thus, it is beneficial to obtain the first particles with suitable morphology and particle size, thereby increasing the compaction density of lithium iron phosphate.

[0062] According to an embodiment of the present application, the Dv50 particle size of the secondary particles is 20 μm to 30 μm, specifically 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, etc. Within this particle size range, the density and mechanical strength of the secondary particles are relatively high, which is conducive to the subsequent acquisition of first particles with high compaction density.

[0063] According to an embodiment of the present application, the sintering includes sintering for 15h to 20h (specifically 15h, 16h, 17h, 18h, 19h, 20h, etc.) under a protective atmosphere and 750°C to 820°C (specifically 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, etc.). Under the sintering conditions, lithium iron phosphate material can be effectively obtained, and the binder can be converted into phosphate, which basically does not affect the electrochemical properties of the lithium iron phosphate material.

[0064] According to an embodiment of the present application, after sintering, the sintered material is further crushed to obtain first particles with a more suitable particle size. The specific crushing method can be air flow crushing. As a result, the morphology, particle size and particle size distribution, mechanical strength, etc. of the obtained first particles are more conducive to improving the compaction density of the lithium iron phosphate material.

[0065] According to an embodiment of the present application, after the sand milling treatment and before the spray granulation, it also includes: removing iron from the sand milled slurry. Specifically, the iron removal may include electromagnetic iron removal and permanent magnetic iron removal, wherein the electromagnetic iron removal intensity is greater than 12000Gs, and the permanent magnetic iron removal intensity is greater than 8000Gs. As a result, the iron-containing substance content in lithium iron phosphate is low, which can effectively improve the negative impact of iron-containing substances when lithium iron phosphate is used in batteries, thereby helping to improve the electrochemical performance of batteries using the lithium iron phosphate.

[0066] In a third aspect of the present application, a battery is provided. According to an embodiment of the present application, the battery comprises the lithium iron phosphate described above or the lithium iron phosphate prepared by the method described above. The battery can achieve a higher energy density and a longer cycle life, thereby expanding its application range.

[0067] It is understood that the battery can be a lithium battery, for example, including but not limited to lithium-ion batteries, lithium metal batteries, etc. The specific shape of the above-mentioned battery can be square, cylindrical, and other regular or irregular shapes; the outer packaging of the battery can be a hard shell (such as a steel shell, a hard plastic shell, etc.), or a soft shell (such as an aluminum-plastic film, a bag-type soft shell, etc.). The above-mentioned battery can be a battery cell, or a secondary battery assembled from multiple battery cells, or a battery module, a battery pack, etc. that is further assembled.

[0068] It can be understood that the above-mentioned battery may include a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte (including an electrolyte, a semi-solid electrolyte, a solid electrolyte, etc.) and an outer package. In the battery, the positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence, and an electrode assembly is made by winding or lamination process, and the electrode assembly and the electrolyte can be contained in the outer package. The positive electrode sheet may include a positive electrode collector and a positive electrode film layer arranged on at least one side of the positive electrode collector. The positive electrode film layer may include a positive electrode active material, a binder and a conductive agent, and the positive electrode active material is the lithium iron phosphate described above.

[0069] In a fourth aspect of the present application, a battery pack is provided. According to an embodiment of the present application, the battery pack includes the battery described above. The battery pack has a high energy density and a long service life.

[0070] Specifically, the battery pack may include a plurality of the aforementioned batteries, and the plurality of batteries are electrically connected in parallel, in series, etc. to form a battery pack. As an example, the battery pack may be in the form of a battery module, a battery pack, etc., and the present application has no particular limitation.

[0071] In a fifth aspect of the present application, an electric device is provided. According to an embodiment of the present application, the electric device comprises the battery or the battery pack described above. The electric device has better endurance and longer service life.

[0072] According to an embodiment of the present application, the power-consuming device may include a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. The battery may be used as a power source for the power-consuming device, or may be used as an energy storage unit for the power-consuming device.

[0073] It can be understood that in addition to the batteries or battery packs mentioned above, the electrical equipment may also include necessary structures and components of conventional electrical equipment. Taking electric vehicles as an example, they may include necessary structures and components such as body, windows, chassis, engine, seats, tires, etc., which will not be elaborated here one by one.

[0074] The embodiments of the present application are described in detail below.

[0075] Example 1

[0076] (1) The first particle is synthesized as follows:

[0077] 500 kg of iron phosphate, 125.9 kg of lithium carbonate and 55 kg of glucose were mixed; the mixture was mixed with ultrapure water and then sand-milled; the coarse grinding time was 200 min; the fine grinding particle size was controlled at Dv50 of 500 nm;

[0078] The sand-grinding slurry undergoes electromagnetic iron removal and permanent magnetic iron removal, wherein the electromagnetic iron removal strength is greater than 12000Gs, and the permanent magnetic iron removal strength is greater than 8000Gs;

[0079] The demagnetized sand-ground slurry is transferred to a mixing tank, 1%wt of dimethyl methyl phosphate is added as a binder, and the mixture is fully mixed;

[0080] The mixed slurry was transferred to a spray drying device for spray granulation, and the inlet temperature was set to 230°C ± 2°C and the outlet temperature was set to 95°C ± 2°C; the Dv50 particle size of the spray product was 25 μm;

[0081] The above-mentioned sprayed product was sintered in an atmosphere furnace, the sintering atmosphere was nitrogen, the sintering temperature was 775°C, and the sintering time was 15.5h to obtain a sintered product, the cross-sectional SEM photo of which is shown in Figure 2 , it can be clearly found that the density inside the first particle is higher and there are fewer pores between the primary particles;

[0082] The sintered product was subjected to air flow pulverization and classification to obtain first particles with a Dv50 particle size of 1.08 μm. The cross-sectional SEM photograph of the particles is shown in FIG. Figure 3 .

[0083] (2) The second particle is synthesized as follows:

[0084] Excess lithium hydroxide, ferrous sulfate, and phosphoric acid are added to a CTAB organic solvent at a molar ratio of Li:Fe:P of 1.05:1:1 for dissolution and emulsification; the reaction solution is placed in a high-pressure reactor, the heating temperature is set to 300°C, and the insulation time is 4.5 hours to allow it to react fully; the solution after the reaction is filtered and washed 5 times to obtain a purified lithium iron phosphate wet material;

[0085] The wet lithium iron phosphate material is dried and mixed with the organic carbon source glucose; the mixed material is sintered at high temperature in a nitrogen atmosphere, the sintering temperature is set between 685°C, and the sintering time is 13h;

[0086] The sintered product was air flow crushed to obtain a second particle with a Dv50 particle size of 1.21 μm. The cross-sectional SEM photograph is shown in FIG. Figure 4 The particle morphology is rod-shaped and round.

[0087] The prepared first particles and the second particles are mixed in a mass ratio of 9:1 to obtain a lithium iron phosphate positive electrode material.

[0088] Example 2

[0089] (1) The first particle is synthesized as follows:

[0090] 500 kg of iron phosphate, 125.9 kg of lithium carbonate and 55 kg of glucose were mixed; the mixture was mixed with ultrapure water and then sand-milled; the coarse grinding time was 200 min; the fine grinding particle size was controlled at Dv50 of 500 nm;

[0091] The sand-grinding slurry undergoes electromagnetic iron removal and permanent magnetic iron removal, wherein the electromagnetic iron removal strength is greater than 12000Gs, and the permanent magnetic iron removal strength is greater than 8000Gs;

[0092] The demagnetized sand-ground slurry is transferred to a mixing tank, and 1.5%wt of tri-xylene phosphate is added to mix the mixture thoroughly.

[0093] The mixed slurry was transferred to a spray drying device for spray granulation, and the inlet temperature was set to 225°C ± 2°C and the outlet temperature was set to 97°C ± 2°C; the Dv50 particle size of the spray product was 25 μm;

[0094] The sprayed product is sintered in an atmosphere furnace, the sintering atmosphere is nitrogen, the sintering temperature is 780°C, and the sintering time is 15 hours to obtain a sintered product;

[0095] The sintered product was subjected to air flow crushing and classification to obtain first particles with a Dv50 particle size of 1.12 μm.

[0096] (2) The second particle is synthesized as follows:

[0097] Same as the second particles in Example 1.

[0098] The prepared large particles and small particles are mixed in a mass ratio of 9:1 to obtain a lithium iron phosphate positive electrode material.

[0099] Example 3

[0100] (1) The first particle is synthesized as follows:

[0101] 500 kg of iron phosphate, 125.9 kg of lithium carbonate and 55 kg of glucose were mixed; the mixture was mixed with ultrapure water and then sand-milled; the coarse grinding time was 200 min; the fine grinding particle size was controlled at Dv50 of 500 nm;

[0102] The sand-grinding slurry undergoes electromagnetic iron removal and permanent magnetic iron removal, wherein the electromagnetic iron removal strength is greater than 12000Gs, and the permanent magnetic iron removal strength is greater than 8000Gs;

[0103] The demagnetized sand-ground slurry is transferred to a mixing tank, and 2.0%wt of tri-xylene phosphate is added to mix the mixture thoroughly.

[0104] The mixed slurry was transferred to a spray drying device for spray granulation, and the inlet temperature was set to 235°C ± 2°C and the outlet temperature was set to 94°C ± 5°C; the Dv50 particle size of the spray product was 27 μm;

[0105] The sprayed product is sintered in an atmosphere furnace, the sintering atmosphere is nitrogen, the sintering temperature is 788°C, and the sintering time is 15.5h to obtain a sintered product;

[0106] The sintered product was subjected to air flow crushing and classification to obtain first particles with a Dv50 particle size of 1.18 μm.

[0107] (2) The second particle is synthesized as follows:

[0108] Excess lithium hydroxide, ferrous sulfate, and phosphoric acid are added into an organic solvent CTAB solution according to a molecular ratio of Li:Fe:P of 1.05:1:1 for dissolution and emulsification; the reaction solution is placed in a high-pressure reactor, the heating temperature is set to 310°C, and the insulation time is 4 hours to allow it to react fully; the solution after the reaction is filtered and washed 5 times to obtain a purified lithium iron phosphate wet material;

[0109] The wet lithium iron phosphate material is dried and mixed with the organic carbon source glucose; the mixed material is sintered at high temperature in a nitrogen atmosphere, the sintering temperature is set between 685°C, and the sintering time is 14h;

[0110] The sintered product was subjected to air flow milling to obtain second particles with a Dv50 particle size of 1.08 μm.

[0111] The prepared first particles and the second particles are mixed in a mass ratio of 9:1 to obtain a lithium iron phosphate positive electrode material.

[0112] Example 4

[0113] (1) The first particle is synthesized as follows:

[0114] 500 kg of iron phosphate, 125.9 kg of lithium carbonate and 55 kg of glucose were mixed; the mixture was mixed with ultrapure water and then sand-milled; the coarse grinding time was 200 min; the fine grinding particle size was controlled at Dv50 of 500 nm;

[0115] The sand-grinding slurry undergoes electromagnetic iron removal and permanent magnetic iron removal, wherein the electromagnetic iron removal strength is greater than 12000Gs, and the permanent magnetic iron removal strength is greater than 8000Gs;

[0116] The demagnetized sand-ground slurry is transferred to a mixing tank, and 2.5%wt of tri-isopropylphenyl phosphate is added to mix the mixture thoroughly.

[0117] The mixed slurry was transferred to a spray drying device for spray granulation, and the inlet temperature was set to 240°C ± 2°C and the outlet temperature was set to 92°C ± 2°C; the Dv50 particle size of the spray product was 28 μm;

[0118] The sprayed product is sintered in an atmosphere furnace, the sintering atmosphere is nitrogen, the sintering temperature is 788°C, and the sintering time is 16 hours to obtain a sintered product;

[0119] The sintered product was subjected to air flow crushing and classification to obtain first particles with a Dv50 particle size of 1.32 μm.

[0120] (2) The second particle is synthesized as follows:

[0121] Excess lithium hydroxide, ferrous sulfate, and phosphoric acid are added into an organic solvent CTAB solution according to a molecular ratio of Li:Fe:P of 1.05:1:1 for dissolution and emulsification; the reaction solution is placed in a high-pressure reactor, the heating temperature is set to 315°C, and the insulation time is 5 hours to allow it to react fully; the solution after the reaction is filtered and washed 5 times to obtain a purified lithium iron phosphate wet material;

[0122] The wet lithium iron phosphate material is dried and mixed with the organic carbon source glucose; the mixed material is sintered at high temperature in a nitrogen atmosphere, the sintering temperature is set between 685°C, and the sintering time is 14h;

[0123] The sintered product was subjected to air flow milling to obtain second particles with a Dv50 particle size of 0.98 μm.

[0124] The prepared first particles and the second particles are mixed in a mass ratio of 9:1 to obtain a lithium iron phosphate positive electrode material.

[0125] Example 5

[0126] (1) The first particle is synthesized as follows:

[0127] 500 kg of iron phosphate, 125.9 kg of lithium carbonate and 55 kg of glucose were mixed; the mixture was mixed with ultrapure water and then sand-milled; the coarse grinding time was 200 min; the fine grinding particle size was controlled at Dv50 of 500 nm;

[0128] The sand-grinding slurry undergoes electromagnetic iron removal and permanent magnetic iron removal, wherein the electromagnetic iron removal strength is greater than 12000Gs, and the permanent magnetic iron removal strength is greater than 8000Gs;

[0129] The demagnetized sand-ground slurry was transferred to a mixing tank, and 3.0%wt of tri-tert-butylphenyl phosphate was added to mix the mixture thoroughly.

[0130] The mixed slurry was transferred to a spray drying device for spray granulation, and the inlet temperature was set to 245°C ± 2°C and the outlet temperature was set to 90°C ± 2°C; the Dv50 particle size of the spray product was 30 μm;

[0131] The above-mentioned sprayed product was sintered in an atmosphere furnace, the sintering atmosphere was nitrogen, the sintering temperature was 795°C, the sintering time was 16.5h, and a sintered product was obtained; the cross-sectional SEM photo of the product is shown in Figure 2 , it can be clearly found that the density inside the first particle is higher and there are fewer pores between the primary particles;

[0132] The sintered product was subjected to air flow crushing and classification to obtain the first particles with a Dv50 particle size of 1.28 μm; the surface SEM photo of the particles is shown in Figure 3 .

[0133] (2) The second particle is synthesized as follows:

[0134] Excess lithium hydroxide, ferrous sulfate, and phosphoric acid are added into an organic solvent CTAB solution according to a molecular ratio of Li:Fe:P of 1.05:1:1 for dissolution and emulsification; the reaction solution is placed in a high-pressure reactor, the heating temperature is set to 320°C, and the insulation time is 5 hours to allow it to react fully; the solution after the reaction is filtered and washed 5 times to obtain a purified lithium iron phosphate wet material;

[0135] The wet lithium iron phosphate material is dried and mixed with the organic carbon source glucose; the mixed material is sintered at high temperature in a nitrogen atmosphere, the sintering temperature is set between 685°C, and the sintering time is 14h;

[0136] The sintered product was air flow crushed to obtain the second particle with a Dv50 particle size of 0.81 μm; the surface SEM photo is shown in Figure 4 The particle morphology is rod-shaped and round.

[0137] The prepared first particles and the second particles are mixed in a mass ratio of 9:1 to obtain a lithium iron phosphate positive electrode material.

[0138] Example 6

[0139] (1) The first particle is synthesized as follows:

[0140] 500 kg of iron phosphate, 125.9 kg of lithium carbonate and 55 kg of glucose were mixed; the mixture was mixed with ultrapure water and then sand-milled; the coarse grinding time was 200 min; the fine grinding particle size was controlled at Dv50 of 500 nm;

[0141] The sand-grinding slurry undergoes electromagnetic iron removal and permanent magnetic iron removal, wherein the electromagnetic iron removal strength is greater than 12000Gs, and the permanent magnetic iron removal strength is greater than 8000Gs;

[0142] The demagnetized sand-ground slurry is transferred to a mixing tank, and 3.5%wt of tri-xylene phosphate is added to mix the mixture thoroughly.

[0143] The mixed slurry was transferred to a spray drying device for spray granulation, and the inlet temperature was set to 230°C ± 2°C and the outlet temperature was set to 95°C ± 2°C; the Dv50 particle size of the spray product was 26 μm;

[0144] The sprayed product is sintered in an atmosphere furnace, the sintering atmosphere is nitrogen, the sintering temperature is 800°C, and the sintering time is 16 hours to obtain a sintered product;

[0145] The sintered product was subjected to air flow crushing and classification to obtain first particles with a Dv50 particle size of 1.24 μm.

[0146] (2) The second particle is synthesized as follows:

[0147] Excess lithium hydroxide, ferrous sulfate, and phosphoric acid are added into an organic solvent CTAB solution according to a molecular ratio of Li:Fe:P of 1.05:1:1 for dissolution and emulsification; the reaction solution is placed in a high-pressure reactor, the heating temperature is set to 330°C, and the insulation time is 5.5h to allow it to react fully; the solution after the reaction is filtered and washed 5 times to obtain a purified lithium iron phosphate wet material;

[0148] The wet lithium iron phosphate material is dried and mixed with the organic carbon source glucose; the mixed material is sintered at high temperature in a nitrogen atmosphere, the sintering temperature is set between 685°C, and the sintering time is 14h;

[0149] The sintered product was subjected to air flow milling to obtain second particles with a Dv50 particle size of 0.65 μm.

[0150] The prepared first particles and the second particles are mixed in a mass ratio of 9:1 to obtain a lithium iron phosphate positive electrode material.

[0151] Example 7

[0152] (1) The first particle is synthesized as follows:

[0153] 500 kg of iron phosphate, 125.9 kg of lithium carbonate and 55 kg of glucose were mixed; the mixture was mixed with ultrapure water and then sand-milled; the coarse grinding time was 200 min; the fine grinding particle size was controlled at Dv50 of 500 nm;

[0154] The sand-grinding slurry undergoes electromagnetic iron removal and permanent magnetic iron removal, wherein the electromagnetic iron removal strength is greater than 12000Gs, and the permanent magnetic iron removal strength is greater than 8000Gs;

[0155] The demagnetized sand-ground slurry was transferred to a mixing tank, and 4.0%wt of methyl phosphate was added to mix the mixture thoroughly.

[0156] The mixed slurry was transferred to a spray drying device for spray granulation, and the inlet temperature was set to 235°C ± 2°C and the outlet temperature was set to 97°C ± 2°C; the Dv50 particle size of the spray product was 26 μm;

[0157] The sprayed product is sintered in an atmosphere furnace, the sintering atmosphere is nitrogen, the sintering temperature is 805°C, and the sintering time is 17 hours to obtain a sintered product;

[0158] The sintered product was subjected to air flow crushing and classification to obtain first particles with a Dv50 particle size of 1.61 μm.

[0159] (2) The second particle is synthesized as follows:

[0160] Same as the second particles in Example 5.

[0161] The prepared first particles and the second particles are mixed in a mass ratio of 9:1 to obtain a lithium iron phosphate positive electrode material.

[0162] Example 8

[0163] (1) The first particle is synthesized as follows:

[0164] 500 kg of iron phosphate, 125.9 kg of lithium carbonate and 55 kg of glucose were mixed; the mixture was mixed with ultrapure water and then sand-milled; the coarse grinding time was 200 min; the fine grinding particle size was controlled at Dv50 of 500 nm;

[0165] The sand-grinding slurry undergoes electromagnetic iron removal and permanent magnetic iron removal, wherein the electromagnetic iron removal strength is greater than 12000Gs, and the permanent magnetic iron removal strength is greater than 8000Gs;

[0166] The demagnetized sand-ground slurry is transferred to a mixing tank, and 5.0%wt of methacrylic acid phosphate is added to mix the mixture thoroughly.

[0167] The mixed slurry was transferred to a spray drying device for spray granulation, and the inlet temperature was set to 230°C ± 2°C and the outlet temperature was set to 95°C ± 2°C; the Dv50 particle size of the spray product was 25 μm;

[0168] The sprayed product is sintered in an atmosphere furnace, the sintering atmosphere is nitrogen, the sintering temperature is 815° C., and the sintering time is 18.5 h to obtain a sintered product;

[0169] The sintered product was subjected to air flow crushing and classification to obtain first particles with a Dv50 particle size of 1.83 μm.

[0170] (2) The second particle is synthesized as follows:

[0171] Excess lithium hydroxide, ferrous sulfate, and phosphoric acid are added into an organic solvent CTAB solution according to a molecular ratio of Li:Fe:P of 1.05:1:1 for dissolution and emulsification; the reaction solution is placed in a high-pressure reactor, the heating temperature is set to 295°C, and the insulation time is 4 hours to allow it to react fully; the solution after the reaction is filtered and washed 5 times to obtain a purified lithium iron phosphate wet material;

[0172] The wet lithium iron phosphate material is dried and mixed with the organic carbon source glucose; the mixed material is sintered at high temperature in a nitrogen atmosphere, the sintering temperature is set between 685°C, and the sintering time is 14h;

[0173] The sintered product was subjected to air flow milling to obtain second particles with a Dv50 particle size of 1.28 μm.

[0174] The prepared first particles and the second particles are mixed in a mass ratio of 9:1 to obtain a lithium iron phosphate positive electrode material.

[0175] Example 9

[0176] (1) The first particle is synthesized as follows:

[0177] Same as the first particle in Example 5.

[0178] (2) The second particle is synthesized as follows:

[0179] Same as the second particles in Example 5.

[0180] The prepared first particles and second particles are mixed in a mass ratio of 8:2 to obtain a lithium iron phosphate positive electrode material.

[0181] Example 10

[0182] (1) The first particle is synthesized as follows:

[0183] Same as the first particle in Example 5.

[0184] (2) The second particle is synthesized as follows:

[0185] Same as the second particles in Example 5.

[0186] The prepared first particles and second particles are mixed in a mass ratio of 7:3 to obtain a lithium iron phosphate positive electrode material.

[0187] Comparative Example 1

[0188] Large particle synthesis:

[0189] Same as Example 5, except that no binder was added, the Dv50 particle size of the obtained large particles was 0.85 μm, and the cross-sectional SEM photograph of the sintered product was shown in Figure 5 ,and Figure 2 Compared with the conventional powder, it is obvious that its density is lower and the pores are more. The SEM photo of the powder of large particles after air flow crushing is shown in Figure 6 , it can be seen that the particles have low roundness and are irregularly distributed.

[0190] Synthesis of small particles:

[0191] Same as the second particles in Example 1.

[0192] The prepared large particles and small particles are mixed in a mass ratio of 9:1 to obtain a lithium iron phosphate positive electrode material.

[0193] Performance Testing:

[0194] 1. Aspect ratio test:

[0195] Take 10 SEM photos of the powder (5K) (Note: if field emission electron microscopy, hydrothermal method and solid phase method are used for small particles, select 10 SEM photos of 10K size);

[0196] Open ImageJ software, File-open, import the above selected photos. Click on the image to magnify it and indicate the minimum cell size;

[0197] Select a single particle in the photo and calibrate the size along the longest side of the particle; for the same particle, calibrate the size of the shortest side of the particle along the perpendicular direction of the longest side. In this way, count all the particles in the photo; (Note: The selection of particles must ensure a complete and clear boundary outline)

[0198] The aspect ratio is calculated as the ratio of the longest side to the shortest side.

[0199] 2. Dv50 particle size and particle size distribution width test:

[0200] The particle size test of this patent is obtained by SEM particle statistics of finished powder;

[0201] Take 10 SEM photos of the powder (5K) (Note: if field emission electron microscopy, hydrothermal method and solid phase method are used for small particles, select 10 SEM photos of 10K size);

[0202] Open ImageJ software, File-open, import the above selected photos. Click on the image to magnify it and indicate the minimum cell size;

[0203] Select a single particle in the photo and calibrate the size along the longest side of the particle. In this way, count all particles in the photo and output them; (Note: The selection of particles must ensure a complete and clear boundary outline)

[0204] Convert the above statistical particle size into volume distribution and output D10, D50, and D90;

[0205] Particle size distribution width K = (D90-D10) / D50.

[0206] 3. Carbon content test:

[0207] Use carbon and sulfur analyzers to test. First, turn on the equipment (need to preheat for half an hour) and turn on the oxygen switch;

[0208] First, calibrate the standard sample. Take 0.2g of the standard sample and place it in a special dry pot, add 2 flat spoons of solvent, and then test. Repeat the above steps 5-6 times until the deviation of the two consecutive test results is within 0.01%;

[0209] Take 0.2g of the sample to be tested and place it in a special dry pot, add 2 level spoons of solvent, and start the test;

[0210] The test results are directly output to the computer.

[0211] 4. Compaction density test:

[0212] A certain amount of positive electrode binder PVDF and solvent NMP are dispersed for 5 hours to obtain a glue solution with a solid content of 6%, wherein the mass percentage of the binder PVDF is 3% based on the total mass of the solid matter;

[0213] Adding a conductive agent carbon nanotube (CNT) with a solid content of 5% to the above-mentioned uniformly dispersed glue, and dispersing at high speed for 1 hour to obtain a conductive slurry, wherein the mass ratio of the conductive agent is 1% based on the total mass of the solid matter;

[0214] The lithium iron phosphate positive electrode material in each embodiment and comparative example is added to the above-mentioned uniformly dispersed conductive slurry, and high-speed dispersion mixing is performed for 2 hours to obtain a positive electrode slurry, wherein the mass ratio of the lithium iron phosphate positive electrode material is 96% based on the total mass of the solid matter;

[0215] Use a 200-mesh screen to sieve the positive electrode slurry and sieve it according to the surface density of 400g / m 2Double-sided coating on the surface of carbon-coated aluminum foil; cut the coated electrode into fixed-size electrode pieces of 4cm×10cm, and place them in the middle of the roller axis of the roller press, set the roller gap to 0.12mm, set the roller pressure to 35 tons, and roll the front and back sides of the electrode piece once respectively to obtain the positive electrode piece;

[0216] Use diameter A fixed-size circular sampler was used to take 5 positive electrode sheets after rolling, and the mass and thickness data of the positive electrode active material layer on each positive electrode sheet were tested respectively (Note: 5 sets of thickness values ​​were tested for each positive electrode sheet and the average value was taken), and the compaction density of the positive electrode sheet was calculated.

[0217] Table 1: Performance test results

[0218]

[0219] 5. Secondary particle mechanical strength test

[0220] Test method: disperse the secondary particle powder into the liquid, drip it onto the glass slide, locate the single particle under an optical microscope, use Yuanneng Technology's single particle mechanical properties test system SPFT1000 to test the mechanical strength of the single particle, control the pressure head to press down at a constant speed, collect the force and displacement curve during the particle crushing process, and the pressure corresponding to the single particle crushing point is the mechanical strength. Figure 7 The test results are shown in Table 2 below.

[0221] Table 2

[0222] Example 3 Example 5 Example 7 Example 9 Example 10 Comparative Example 1 Mechanical strength / mN 6.213 8.81 11.662 10.103 9.809 1.832

[0223] The above test results show that a higher compaction density can be achieved by mixing the first particles obtained by crushing the secondary particles with the addition of a binder and the second particles.

[0224] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0225] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A lithium iron phosphate, characterized in that: include: first particles, wherein Dv50 of the first particles is 0.75 μm to 2.0 μm, the first particles are obtained by crushing secondary particles, and the mechanical strength of the secondary particles is 6 to 15 mN; The second particles have a Dv50 of 0.55 μm to 1.3 μm.

2. The lithium iron phosphate according to claim 1, characterized in that: The aspect ratio of the first particles is 1.26 to 1.

83.

3. The lithium iron phosphate according to claim 1, characterized in that: The particle size distribution width K is defined as (Dv90-Dv10) / Dv50, and the particle size distribution width K of the first particles is 2.5-4.

0.

4. The lithium iron phosphate according to claim 1, characterized in that: The carbon content in the first particles is 1 wt % to 1.5 wt % based on the total mass of the first particles.

5. The lithium iron phosphate according to claim 1, characterized in that: The secondary particles include a plurality of primary particles, and in the secondary particles, a phosphate binder is distributed between adjacent primary particles.

6. The lithium iron phosphate according to claim 5, characterized in that: The phosphate ester binder includes at least one of aryl phosphate ester and alkyl phosphate ester.

7. The lithium iron phosphate according to claim 1, characterized in that: The second particles are rod-shaped.

8. The lithium iron phosphate according to claim 1, characterized in that: The aspect ratio of the second particles is 1.3 to 3.

7.

9. The lithium iron phosphate according to claim 1, characterized in that: The carbon content in the second particles is 1 wt % to 2.5 wt % based on the total mass of the second particles.

10. The lithium iron phosphate according to claim 1, characterized in that: Based on the total mass of the lithium iron phosphate, the mass percentage of the first particles is 50% to 90%.

11. The lithium iron phosphate according to claim 1, characterized in that: The compacted density is 2.7g / cc to 2.8g / cc.

12. A method for preparing the lithium iron phosphate according to any one of claims 1 to 11, characterized in that: include: The iron phosphate, the carbon source and the lithium source are mixed according to a stoichiometric ratio to obtain a raw material mixture; The raw material mixture is mixed with a phosphate binder, and the obtained spray mixture is spray-granulated to obtain secondary particles; sintering the secondary particles to obtain a sintered material; crushing the sintered material to obtain first particles; providing a second particle; The first particles and the second particles are mixed to obtain the lithium iron phosphate.

13. The method according to claim 12, characterized in that Based on the total mass of the spray mixture, the added amount of the phosphate binder is 1 wt% to 5 wt%.

14. The method according to claim 12, characterized in that Satisfy at least one of the following conditions: Before mixing with the phosphate binder, the raw material mixture is sand-milled until the Dv50 particle size of the sand-milled slurry is 300nm to 600nm; The inlet temperature of the spray granulation is 220°C to 250°C, and the outlet temperature is 90°C to 100°C; The Dv50 particle size of the secondary particles is 20 μm to 30 μm; The sintering includes sintering for 15h to 20h under the conditions of protective atmosphere and 750°C to 820°C.

15. The method according to claim 14, characterized in that After the sand milling process and before the spray granulation process, the method further includes: removing iron from the sand mill slurry.

16. The method according to claim 12, characterized in that The second particles are prepared by a hydrothermal method.

17. A battery, characterized in that: The invention comprises the lithium iron phosphate according to any one of claims 1 to 11 or the lithium iron phosphate prepared by the method according to any one of claims 12 to 16.

18. A battery pack, characterized in that: Comprising the battery of claim 17.

19. An electrical equipment, characterized in that: Comprising the battery according to claim 17 or the battery pack according to claim 18.

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