Positive electrode active material and preparation method thereof, positive electrode plate, battery and electric equipment

Abstract

The invention provides a positive active material and a preparation method thereof, a positive pole piece, a battery and electric equipment, the positive active material comprises secondary particles formed by primary particles, the positive active material comprises Li1 + aFebMc (PO4) d,-0.1 < = a < = 0.1, 0 < b < = 1, 0 < = c < = 0.5, 0 < d < = 1, and M comprises at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Sb, Co, Ni, V, Mg, Na, B and Al; the porosity of the positive electrode active material is 6.5%-15%, and the average pore size of the positive electrode active material is 145 nm-290 nm. The battery containing the positive electrode active material provided by the invention has excellent capacity, rate capability and cycle performance.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to positive electrode active materials and their preparation methods, positive electrode sheets, batteries, and electrical devices. Background Technology

[0002] As the positive electrode active material for lithium-ion batteries, lithium iron phosphate materials have a low tap density, resulting in a low specific capacity. Due to the structural characteristics of lithium iron phosphate materials, their electronic conductivity and ion diffusion coefficient are low, leading to higher internal resistance in batteries containing them. Internal resistance is an important parameter for measuring battery performance and is closely related to battery life, capacity, rate capability, and other performance characteristics. Summary of the Invention

[0003] This application aims to at least partially solve one of the technical problems in the related art. This application proposes a positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device. The positive electrode active material proposed in this application can enable lithium-ion batteries to have excellent capacity, rate performance, and cycle performance.

[0004] A first aspect of this application provides a positive electrode active material, the positive electrode active material comprising single crystal particles, the positive electrode active material comprising: Li 1+a Fe b M c (PO4) d Wherein, -0.1≤a≤0.1, 0<b≤1, 0≤c≤0.5, 0<d≤1, and M includes at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Sb, Co, Ni, V, Mg, Na, B, and Al; the porosity of the positive electrode active material is 6.5%-15%, and the average pore size of the positive electrode active material is 145nm-290nm.

[0005] The positive electrode active material proposed in this application, by controlling the porosity of lithium iron phosphate positive electrode active materials to 6.5%-15%, achieves high density due to fewer pores within the particles. This results in a more compact structure, leading to higher particle strength, higher rate performance, and better low-temperature performance. Increased particle strength helps maintain structural stability during charge and discharge, improving battery cycle performance. Furthermore, controlling the average pore size of the positive electrode active material to 145nm-290nm ensures more uniform primary particles and pore sizes, eliminating excessively large particles and pores. This allows for more thorough wetting of the positive electrode active material by the electrolyte, further enhancing the battery's rate performance. In summary, using the positive electrode active material of this application can improve the capacity, rate performance, and cycle performance of batteries containing it.

[0006] According to some embodiments of this application, M includes at least one of Sb, Al, W, Co, V and Ti; the porosity of the positive electrode active material is 7.5%-13.5%, optionally 7.5%-11%; the average pore size of the positive electrode active material is 150nm-250nm, optionally 160nm-190nm.

[0007] According to some embodiments of this application, the positive electrode active material satisfies at least one of the following conditions: the total pore volume of the positive electrode active material is 0.02 cm³. 3 / g-0.04cm 3 / g; the oil absorption capacity of the positive electrode active material is 25mL / 100g-35mL / 100g; the BET specific surface area of ​​the positive electrode active material is 6.0m². 2 / g-10.0m 2 / g.

[0008] According to some embodiments of this application, the primary particle size of the positive electrode active material is 120nm-150nm.

[0009] According to some embodiments of this application, the positive electrode active material satisfies at least one of the following conditions: the particle strength of the positive electrode active material is 80MPa-160MPa; the volume average particle size D of the positive electrode active material is... 50 The diameter is 5μm-15μm, D 100 The particle size is 35μm-60μm.

[0010] The second aspect of this application provides a method for preparing the positive electrode active material provided in the first aspect of this application, the method comprising: mixing an iron phosphate precursor, a lithium source, a carbon source, an optional dopant and water to obtain a mixed solution; and grinding, spray drying and sintering the mixed solution to obtain the positive electrode active material.

[0011] The positive electrode active material prepared in this application has low porosity and uniform pores with an average pore size of 150nm-250nm, which can improve the specific capacity, rate performance and cycle performance of batteries containing it.

[0012] According to some embodiments of this application, the method satisfies at least one of the following conditions: the volume average particle size D of the iron phosphate precursor. 50 The surface area is 5μm-12μm; the specific surface area of ​​the iron phosphate precursor is 4m³. 2 / g-13m 2 / g; the average particle size of the primary particles of the iron phosphate precursor is 80nm-200nm; the molar ratio of iron to phosphorus in the iron phosphate precursor is 0.960-0.980; the molar ratio of lithium in the lithium source to iron in the iron phosphate precursor is 1.01-1.07; the carbon source includes two or more of glucose, sucrose, starch, polyethylene glycol, and citric acid; the added carbon source accounts for 1.1%-1.6% of the mass of the positive electrode active material; the solid content of the mixture is 30%-60%.

[0013] According to some embodiments of this application, the method satisfies at least one of the following conditions: after grinding, the volume average particle size D of the material is... 50 The thickness is 0.15μm-0.35μm; the sintering temperature is 750℃-840℃, and the time is 5h-12h.

[0014] The third aspect of this application provides a positive electrode sheet, including the positive active material provided in the first aspect of this application or the positive active material prepared by the method provided in the second aspect of this application.

[0015] The fourth aspect of this application provides a battery including the positive electrode provided in the third aspect of this application.

[0016] The fifth aspect of this application provides an electrical device, including the battery provided in the fourth aspect of this application. Attached Figure Description

[0017] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 The image shows a SEM image of the positive electrode active material prepared in Example 1 of this application.

[0018] Figure 2 A cross-sectional view of the positive electrode active material prepared in Example 1 of this application is shown.

[0019] Figure 3 The image shows a SEM image of the positive electrode active material prepared in Comparative Example 1 of this application.

[0020] Figure 4 The diagram shows a cross-sectional view of the positive electrode active material prepared in Comparative Example 1 of this application. Detailed Implementation

[0021] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0022] A first aspect of this application provides a positive electrode active material, the positive electrode active material comprising single crystal particles, the positive electrode active material comprising: Li 1+a Fe b M c (PO4) d Wherein, -0.1≤a≤0.1, 0<b≤1, 0≤c≤0.5, 0<d≤1, and M includes at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Sb, Co, Ni, V, Mg, Na, B, and Al; wherein, the porosity of the positive electrode active material is 6.5%-15%, and the average pore size of the positive electrode active material is 145nm-290nm.

[0023] For example, 'a' can be a range of -0.1, -0.05, 0, 0.02, 0.04, 0.05, 0.07, 0.09, 0.1, or any of the above values; 'b' can be a range of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any two of the above values; 'c' can be a range of 0, 0.1, 0.2, 0.3, 0.4, 0.5, or any of the above values; 'd' can be a range of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any two of the above values.

[0024] The positive electrode active material proposed in this application, by controlling the porosity of lithium iron phosphate positive electrode active materials to 6.5%-15%, achieves high density due to fewer pores within the particles. This results in a more compact structure, leading to higher particle strength, higher rate performance, and better low-temperature performance. Increased particle strength helps maintain structural stability during charge and discharge, improving battery cycle performance. Furthermore, controlling the average pore size of the positive electrode active material to 145nm-290nm results in more uniform primary particles and pore sizes, and denser secondary particles with uniform pore distribution. The absence of excessively large primary particles and pore sizes allows for more thorough wetting of the positive electrode active material by the electrolyte, further enhancing battery rate performance. In summary, using the positive electrode active material of this application can improve the capacity, rate performance, and cycle performance of batteries containing it.

[0025] It is understandable that the chemical formula of the positive electrode active material can be determined by the ICP method (inductively coupled plasma technology): the instrument used is PE Optima 7000DV, and the test conditions are that 0.1g of sample is completely dissolved in a mixed acid solution of 3mL HNO3 + 9mL HCl, and then diluted to 250mL for testing.

[0026] According to some embodiments of this application, M includes at least one of Sb, Al, W, Co, V, and Ti. Using these elements as dopant elements can further improve the capacity, rate performance, and cycle performance of the cathode active material.

[0027] According to some embodiments of this application, the porosity of the positive electrode active material is 6.5%-15%, for example, it can be 6.5%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 15%, or any two of the above values. According to other embodiments of this application, the porosity of the positive electrode active material is 7.5%-13.5%, for example, 7.5%-11%. By controlling the porosity of the positive electrode active material within the above range, the internal pores of the positive electrode active material particles are reduced, resulting in high density. The structure of the positive electrode active material is more compact, which can give the positive electrode active material high particle strength, high rate performance, and better low-temperature performance. The enhanced particle strength helps maintain the structural stability of the particles during charge and discharge, and improves the cycle performance of the battery.

[0028] In addition, within the aforementioned porosity range, the small gaps between primary particles can provide a larger expansion and contraction space for charge-discharge cycles, improving the cycle performance of the positive electrode active material. At the same time, it can also avoid excessive loss of the good conductivity and mass transfer properties between the positive electrode active materials, which is conducive to the positive electrode active material achieving good rate performance.

[0029] The porosity of a positive electrode active material refers to the proportion of the pore area to the total cross-sectional area of ​​the secondary particles in the positive electrode active material. The porosity of a positive electrode active material can be determined by the following method: taking a 10.0K magnification scanning electron microscope image of the secondary particles of the positive electrode active material, and the porosity can be obtained using the LIBMAS intelligent image analysis system. The porosity is calculated as the ratio of the pore area to the total cross-sectional area.

[0030] According to some embodiments of this application, the average pore size of the positive electrode active material is 145nm-290nm. For example, it can be 145nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, 280nm, 290nm, or any combination of two of these values. According to other embodiments of this application, the average pore size of the positive electrode active material is 150nm-250nm, for example, 160nm-190nm. Controlling the average pore size of the positive electrode active material within the above range makes the primary particles of the positive electrode active material more uniform, and the pore size more uniform, without excessively large primary particles or excessively large pore sizes. This allows for more thorough wetting of the positive electrode active material by the electrolyte, further contributing to improved battery rate performance.

[0031] It can be understood that the average pore size of the positive electrode active material refers to the size of the gap between adjacent primary particles in the secondary particles, and can be measured using the following methods: The conductive agent in the sample was embedded and cured. The sample was then cut using a CP ion abrasive section polisher. The cut sample was then photographed using SEM. The images were then analyzed using porosity analysis software to calculate the average pore size.

[0032] According to some embodiments of this application, the total pore volume of the positive electrode active material is 0.02 cm³. 3 / g-0.04cm 3 / g. For example, it could be 0.02cm. 3 / g, 0.025cm 3 / g, 0.03cm 3 / g, 0.035cm 3 / g, 0.04cm 3 / g or any two of the above values ​​can be used to understand that the total pore volume of the positive electrode active material refers to the volume of the pores inside each gram of secondary particles of the positive electrode active material. Controlling the total pore volume of the positive electrode active material within the above range results in a denser structure, which can give the positive electrode active material high particle strength, high rate performance, and better low-temperature performance. Increased particle strength helps maintain the structural stability of the particles during charge and discharge, thus improving the cycle performance of the battery.

[0033] It is understood that the total pore volume of the positive electrode active material can be determined by the following method: using a surface analyzer based on the N2 adsorption-desorption isotherm, which can be obtained using a Micromeritics Tristar 3030 surface analyzer. The N2 adsorption-desorption isotherm analysis is the total pore volume calculated from the amount of N2 adsorbed when the relative pressure (p / p0) of the N2 adsorption isotherm is 0.995. According to some embodiments of this application, the oil absorption capacity of the positive electrode active material is 25mL / 100g-35mL / 100g. For example, the oil absorption capacity of the positive electrode active material can be 25mL / 100g, 26mL / 100g, 27mL / 100g, 28mL / 100g, 29mL / 100g, 30mL / 100g, 31mL / 100g, 32mL / 100g, 33mL / 100g, 34mL / 100g, 35mL / 100g, or any two of the above values. Controlling the oil absorption capacity of the positive electrode active material within the above range results in a smaller oil absorption capacity, leading to fewer pores in the secondary particles. This makes the secondary particles denser and the pores more uniformly distributed. This not only improves the strength and tap density of the secondary particles, helping to maintain the structural stability of the particles during charge and discharge, and improving the cycle performance and specific capacity of the battery, but also allows for better wetting performance of the electrolyte on the positive electrode active material, thus improving the rate performance of the battery.

[0034] It is understood that the oil absorption of positive electrode active material can be determined by the following method: Weigh a sample of positive electrode active material and place it on a glass plate. Use a burette to add NMP (N-methylpyrrolidone) drop by drop while stirring the sample until the mixture becomes a paste and the last drop can be made into a spiral shape with a spatula. The oil absorption is characterized by the volume of NMP required per 100g of sample.

[0035] According to some embodiments of this application, the BET specific surface area of ​​the positive electrode active material is 6.0 m². 2 / g-10.0m 2 / g. For example, the specific surface area of ​​BET can be 6.0m². 2 / g, 6.5m 2 / g, 7m 2 / g, 7.5m 2 / g, 8m 2 / g, 8.5m 2 / g, 9m 2 / g, 9.5m 2 / g, 10m 2 / g or any two of the above values ​​are used to control the BET specific surface area of ​​the positive electrode active material within the above range. This results in a shorter lithium ion transport path, improving rate performance, while the BET specific surface area is not too large, which would lead to more side reactions between the positive electrode active material and the electrolyte, thus giving the battery excellent cycle performance.

[0036] It is understandable that the BET specific surface area of ​​the positive electrode active material can be determined by the following method: it is obtained by testing with a specific surface area analyzer of the Tristar 3030 model from Micromeritics.

[0037] According to some embodiments of this application, the primary particle size of the positive electrode active material is 120nm-150nm. For example, the primary particle size of the positive electrode active material can be 120nm, 125nm, 130nm, 135nm, 140nm, 145nm, 150nm, or any two of the above values. By controlling the primary particle size of the positive electrode active material within the above range, the primary particle size distribution is narrow, and there are no excessively large or small primary particles. This makes the primary particles of the positive electrode active material more uniform, and the pore size is also more uniform. The secondary particles are dense and the pore distribution is uniform, without excessively large primary particles or excessively large pore sizes. This allows the electrolyte to more fully wet the positive electrode active material, which is beneficial to improving the rate performance of the battery.

[0038] It is understandable that the primary particle size of the positive electrode active material can be determined by the following method: taking a 30.0K magnification scanning electron microscope image of the prepared lithium iron phosphate positive electrode active material, and using LIBMAS and Nano Measurer software to calculate its average primary particle size.

[0039] According to some embodiments of this application, the particle strength of the positive electrode active material is 80 MPa-160 MPa. As an example, the particle strength of the positive electrode active material can be 80 MPa, 90 MPa, 100 MPa, 110 MPa, 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, or any combination of two of these values. Controlling the particle strength of the positive electrode active material within this range allows the material to possess high particle strength, high rate performance, and superior low-temperature performance. Increased particle strength helps maintain the structural stability of the particles during charge and discharge, thus improving the battery's cycle performance. It is understandable that the particle strength of the positive electrode active material can be determined by the following method: using a particle strength analyzer, the positive electrode active material sample is placed on the sample stage, and by setting parameters such as particle type, applied pressure value and compression speed, the maximum pressure is applied and held for 5 seconds before the system is analyzed to obtain the final particle strength data.

[0040] According to some embodiments of this application, the D of the positive electrode active material 50 Particle size is 5μm-15μm, D 100 Particle size of 35μm-60μm, for example, D 50 The particle size can be 5μm, 7μm, 9μm, 10μm, 12μm, 14μm, 15μm, or any range of two of these values; D 100 The particle size can be 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, or any combination of two of these values. This further facilitates obtaining uniform pores with low porosity and an average pore size of 150nm-250nm, which can improve the specific capacity, rate performance, and cycle performance of batteries containing this material.

[0041] According to an embodiment of this application, the volume average particle size D 50 As is well-known in the art, also called median particle size or median particle size, it is used to represent the average particle size of powder. Physically, it means that particles smaller than this size account for 50% of the total particle volume, and particles larger than this size also account for 50% of the total particle volume. 100 The physical meaning of particle size is that particles smaller than a certain size account for 100% of the total particle volume; the volume average particle size D is... 50 and D 100 Particle size can be conveniently determined using a laser particle size analyzer, for example, according to the standard GB / T 19077-2016 "Particle Size Distribution by Laser Diffraction", using the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0042] In summary, the positive electrode active material proposed in this application is a spherical lithium iron phosphate positive electrode active material with high tap strength, high particle strength, high rate capability, and excellent low-temperature performance. The spherical shape provides high particle strength, which helps maintain the structural stability of the particles during charge and discharge. During high-current charge and discharge, it can better withstand the stress changes caused by the rapid insertion and extraction of lithium ions, reducing particle breakage and pulverization, and making the diffusion path of lithium ions inside and on the surface of the particles more stable, thus improving rate performance. The high strength of the spherical particles also results in tighter and more stable contact between particles, which is conducive to forming good electron and ion transport channels and reducing the battery's internal resistance. Lower internal resistance means less energy loss during charge and discharge, enabling more efficient conversion of chemical energy into electrical energy and improving battery efficiency.

[0043] High-strength spherical positive electrode active material particles possess unique advantages in processing performance. When formed into slurry, the interaction forces between particles are stronger, making them less prone to agglomeration and sedimentation. This results in better stability and uniformity of the slurry, which is beneficial for coating, rolling, and other processes during battery manufacturing, thus improving the quality of electrode preparation. Spherical positive electrode active material particles also better maintain their shape and size during coating, are less prone to deformation or breakage, and can improve coating precision and uniformity, resulting in more uniform electrode thickness and density, which is beneficial for improving battery performance and consistency.

[0044] In a second aspect, this application provides a method for preparing the above-mentioned positive electrode active material. According to an embodiment of this application, the method includes: S1: Mix the iron phosphate precursor, lithium source, carbon source, optional dopant and water to obtain a mixture.

[0045] According to some embodiments of this application, the volume average particle size D of the iron phosphate precursor 50 The particle size is 5μm-12μm, for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, or any combination of two of the above values. The volume average particle size D of the iron phosphate precursor is... 50 By controlling the particle size within the above range, it is easier to obtain a high-density positive electrode active material with uniform primary particle size and no excessively large primary particles or excessively large pore size through subsequent grinding.

[0046] It's understandable, D 50 Particle size has already been explained above and will not be repeated here.

[0047] According to some embodiments of this application, the specific surface area of ​​the iron phosphate precursor is 4 m². 2 / g-13m 2 / g. For example, it could be 4m. 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g or any two of the above values, which facilitates the subsequent preparation of a high-density, uniformly sized primary particle, positive electrode active material without excessively large primary particles or excessively large pores through grinding.

[0048] According to some embodiments of this application, the average particle size of the primary particles of the iron phosphate precursor is 80nm-200nm. For example, the average particle size of the primary particles can be 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, or any combination of two of the above values. Controlling the average particle size of the primary particles of the iron phosphate precursor within the above range is beneficial for obtaining a positive electrode active material with a primary particle size of 120nm-150nm and a porosity of 7.5%-13.5%.

[0049] According to some embodiments of this application, in the iron phosphate precursor, the molar ratio of iron to phosphorus is 0.960-0.980, for example, it can be 0.960, 0.965, 0.970, 0.975, 0.980 or any two of the above values. Controlling the molar ratio of iron to phosphorus within the above range facilitates the obtaining of a chemically stable positive electrode active material.

[0050] According to some embodiments of this application, the molar ratio of lithium in the lithium source to iron in the iron phosphate precursor is 1.01-1.07. As an example, the ratio can be 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, or any combination of two of these values. Controlling the molar ratio of lithium to iron within this range yields a structurally stable and high-capacity positive electrode active material.

[0051] According to some embodiments of this application, the lithium source includes lithium carbonate, and the purity of the lithium carbonate is ≥99.6%, for example, it can be 99.6%, 99.7%, 99.8%, 99.9% or any two of the above values. This can improve the purity of the obtained positive electrode active material and improve the battery capacity and cycle stability.

[0052] According to some embodiments of this application, the carbon source includes two or more of glucose, sucrose, starch, polyethylene glycol, and citric acid. Using two or more of the above carbon sources can significantly improve the conductivity of the obtained positive electrode active material.

[0053] According to some embodiments of this application, the added carbon source accounts for 1.1%-1.6% of the mass of the positive electrode active material. For example, it can be 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, or any two of the above values. Controlling the amount of carbon source added within the above range is sufficient to improve the conductivity of the positive electrode active material without causing the content to be too high and affecting the capacity of the battery containing it.

[0054] According to some embodiments of this application, the solid content of the mixture is 30%-60%. For example, it can be 30%, 40%, 50%, 60%, or any two of the above values. Controlling the solid content of the mixture within the above range facilitates obtaining a positive electrode active material with high density, uniform primary particle size, and no excessively large primary particles or excessively large pore size.

[0055] It can be understood that the solid content of a mixture refers to the mass percentage of the components other than water in the mixture.

[0056] According to some embodiments of this application, the dopant includes one or more of aluminum oxide, titanium dioxide, ammonium metavanadate, tungsten trioxide, magnesium oxide, cobalt hydroxyl oxide, antimony trioxide, yttrium oxide, and niobium pentoxide; the above dopant can improve the capacity and cycle stability of the positive electrode active material.

[0057] According to some embodiments of this application, based on the total mass of the positive electrode active material, the doping amount of titanium is 2000ppm-6000ppm, for example, it can be 2000ppm, 3000ppm, 4000ppm, 5000ppm, 6000ppm or any two of the above values; the doping amount of vanadium is 0ppm-3000ppm, for example, it can be 0ppm, 1000ppm, 2000ppm, 3000ppm or any two of the above values; thereby, the capacity and cycle stability of the prepared positive electrode active material can be further improved.

[0058] S2: Grind, spray dry, and sinter the mixture to obtain the positive electrode active material.

[0059] Therefore, by wet milling and spray drying, it is easy to obtain uniform pores with low porosity and an average pore size of 150nm-250nm in the embodiments of this application, which can improve the specific capacity, rate performance and cycle performance of batteries containing them.

[0060] According to some embodiments of this application, after grinding, the volume average particle size D of the material is... 50 The particle size is 0.15μm-0.35μm. For example, it can be 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, or any combination of two of these values. The volume average particle size D of the ground mixture is... 50 Controlling the particle size within the above range further facilitates obtaining uniform pores with a primary particle size of 120nm-150nm, low porosity, and an average pore size of 150nm-250nm through spray drying, which can improve the specific capacity, rate performance, and cycle performance of batteries containing it.

[0061] According to some embodiments of this application, the grinding is carried out using wet sand milling, and the particle size of the wet grinding slurry is determined according to the gradation method.

[0062] According to some embodiments of this application, the inlet air temperature of the spray dryer is between 200°C and 280°C, and the outlet air temperature is between 80°C and 120°C. As an example, the inlet air temperature of the spray dryer can be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, or any combination of two of these values, and the outlet air temperature can be 80°C, 90°C, 100°C, 110°C, 120°C, or any combination of two of these values. This further facilitates obtaining uniform pores with low porosity and an average pore size of 150nm-250nm, which can improve the specific capacity, rate performance, and cycle performance of batteries containing this material.

[0063] According to some embodiments of this application, the mass percentage of water in the spray-dried particles is ≤3.0%, for example, it can be 0.01%, 0.1%, 1%, 2%, 3% or any two of the above values. Controlling the water content of the spray-dried particles within the above range can reduce the water content of the obtained positive electrode active material and improve the cycle performance of the battery.

[0064] According to some embodiments of this application, the sintering temperature is 750℃-840℃, and the time is 5h-12h. As an example, the sintering temperature can be 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, or any combination of two of these values, and the time can be 5h, 7h, 9h, 10h, 12h, 15h, or any combination of two of these values. This further facilitates obtaining uniform pores with low porosity and an average pore size of 150nm-250nm, which can improve the specific capacity, rate performance, and cycle performance of batteries containing these pores.

[0065] In summary, the method for preparing the positive electrode active material proposed in this application produces a positive electrode active material with low porosity and uniform pores with an average pore size of 150nm-250nm, which can improve the specific capacity, rate performance, and cycle performance of batteries containing it. Furthermore, the process is simple and suitable for large-scale industrial production.

[0066] In a third aspect, this application proposes a positive electrode sheet. According to embodiments of this application, the positive electrode sheet comprises the positive active material described in the first aspect of this application or a positive active material obtained using the method described in the second aspect of this application.

[0067] According to an embodiment of this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes the aforementioned positive active material. The positive current collector can be a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector). For example, the positive current collector can be an aluminum foil.

[0068] According to some embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorinated acrylate resin.

[0069] According to some embodiments of this application, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0070] According to some embodiments of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0071] It should be noted that the features and advantages described above for the positive electrode active material and its preparation method also apply to this positive electrode sheet, and will not be repeated here.

[0072] In a fourth aspect, this application discloses a battery. According to an embodiment of this application, the battery includes the positive electrode sheet described above.

[0073] As an example, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, with the separator located between the positive and negative electrodes. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0074] According to an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode current collector can be a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector). For example, the positive electrode current collector can be a copper foil.

[0075] According to some embodiments of the present invention, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc.

[0076] According to some embodiments of the present invention, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0077] According to some embodiments of the present invention, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0078] According to some embodiments of the present invention, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, and binder, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes.

[0079] According to further embodiments of the present invention, the type of separator is not particularly limited, and any known porous separator with good chemical and mechanical stability can be selected. As an example, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0080] According to further embodiments of the present invention, there is no specific limitation on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be in a gel state or a completely solid state. According to some specific embodiments of the present invention, the electrolyte is an electrolyte solution comprising a lithium salt and a solvent.

[0081] According to some specific embodiments of the present invention, the lithium salt may include at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, or lithium bis(trifluoromethanesulfonyl)imide.

[0082] According to some specific embodiments of the present invention, the solvent may include at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone, or diethyl sulfone.

[0083] In some embodiments of this application, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0084] It should be noted that the features and advantages described above for the positive electrode also apply to this battery, and will not be repeated here.

[0085] In a fifth aspect, the present invention provides an electrical device. According to an embodiment of the invention, the electrical device includes the battery described above. According to an embodiment of the invention, the electrical device may include, but is not limited to, mobile phones, laptops, electric vehicles, etc.

[0086] It should be noted that the features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0087] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0088] Example 1 Anhydrous ferric phosphate, lithium carbonate, titanium dioxide, ammonium metavanadate, sucrose, and citric acid were sequentially added to pure water and mixed in a stirred mill to form a dispersion, yielding a slurry with a solid content of 42%. The volume average particle size D of the ferric phosphate was [not specified]. 50 The thickness is 8.75 μm, and the specific surface area of ​​iron phosphate is 5.83 m². 2 / g, the primary particle size of iron phosphate is 140nm, the molar ratio of iron to phosphorus is 0.970, the molar ratio of lithium to iron is 1.04, and the added carbon source accounts for 1.5% of the mass of the positive electrode active material; then the slurry is fed into a sand mill and ground at below 45℃ to control the grinding particle size D. 50The particle size was 0.26 μm, resulting in the first slurry. The first slurry was then spray-dried, with the inlet temperature controlled at 245℃ and the outlet temperature at 100℃, to obtain a particle size D. 50 A 10μm sprayable feed precursor with a moisture content ≤3.0% was prepared. The sprayable feed precursor was calcined at high temperature under a nitrogen atmosphere, with the sintering temperature controlled at 800℃ and the sintering time controlled at 11h. The final particle size D was controlled. 50 It is 10.0 μm, D 100 A spherical lithium iron phosphate cathode active material with a diameter of 50.0 μm was prepared.

[0089] The mass ratio of anhydrous ferric phosphate, lithium carbonate, titanium dioxide, and ammonium metavanadate is 1:0.2535:0.0018:0.0024, the mass ratio of sucrose to anhydrous ferric phosphate is 1:0.090, and the mass ratio of citric acid to anhydrous ferric phosphate is 1:0.028.

[0090] The differences between the remaining embodiments, comparative examples and Embodiment 1 are shown in the table below.

[0091] Performance testing 1. Morphological testing The positive electrode active material prepared in Example 1 was subjected to SEM scanning electron microscopy testing, and the results were obtained. Figure 1 ,Depend on Figure 1 It can be seen that the positive electrode active material prepared in Example 1 has relatively uniform primary particle size, with no particularly large or small primary particles, and the pore size formed by the primary particles is also relatively uniform.

[0092] A CP cross-sectional image was obtained from the positive electrode active material prepared in Example 1. Figure 2 ,from Figure 2 As can be seen from the above, the pore distribution between different primary particles in the positive electrode active material of Example 1 is uniform.

[0093] The positive electrode active material prepared in Comparative Example 1 was analyzed by scanning electron microscopy (SEM) to obtain... Figure 3 ,Depend on Figure 3 It can be seen that the primary active material prepared in Comparative Example 1 has uneven primary particle size, with some primary particles being particularly large or small, and the pore size formed by the primary particles is also uneven.

[0094] A CP profile was plotted on the positive electrode active material prepared in Comparative Example 1 to obtain... Figure 4 ,from Figure 4 As can be seen from the data, in the positive electrode active material of Comparative Example 1, the pore distribution between different primary particles is very uneven, and the size of the primary particles is also very uneven.

[0095] 2. Parameter Testing Porosity testing of positive electrode active materials: The secondary particles of the positive electrode active material are photographed with a scanning electron microscope at 10.0K magnification. The porosity can be obtained using the LIBMAS intelligent image analysis system. The porosity is calculated as the ratio of the pore area to the total cross-sectional area.

[0096] Average pore size test of positive electrode active material: The conductive agent of the sample is embedded and cured. The sample is cut by CP ion polishing section polisher. The cut sample is photographed by SEM. The porosity analysis software is used to calculate the average pore size.

[0097] Single-particle strength test of positive electrode active material: Using a particle strength analyzer, the positive electrode active material sample is placed on the sample stage. By setting parameters such as particle type, applied pressure value and compression speed, the maximum pressure is applied and held for 5 seconds before system analysis to obtain the final particle strength data.

[0098] Oil absorption test of positive electrode active material: Weigh the positive electrode active material sample and place it on a glass plate. Use a burette to add NMP drop by drop while stirring the sample until the mixture becomes a paste and the last drop can be made into a spiral shape with a spatula. The oil absorption is characterized by the volume of NMP required per 100g of sample.

[0099] BET specific surface area test of the positive electrode active material: obtained by using a Tristar 3030 specific surface area analyzer from Micromeritics.

[0100] Total pore volume of the positive electrode active material was measured using a surface analyzer based on the N2 adsorption-desorption isotherm. This analysis was conducted using a Micromeritics Tristar 3030 surface analyzer. The N2 adsorption-desorption isotherm analysis was performed by calculating the total pore volume from the amount of N2 adsorbed when the relative pressure (p / p0) of the N2 adsorption isotherm was 0.995.

[0101] Primary particle size test of positive electrode active material: Scanning electron microscope (SEM) images of the prepared lithium iron phosphate positive electrode active material were taken at 30.0K magnification, and the average primary particle size was calculated using LIBMAS and Nano Measurer software.

[0102] Test of tap density change rate of positive electrode active material: Weigh 50.0g of the spherical lithium iron phosphate positive electrode active material prepared in the examples and comparative examples and put it into the tapping cylinder. Put the cylinder into the tapping device to start the test and vibrate 3000 times. Calculate the tap density change rate based on the change in powder volume: (volume before vibration - volume after vibration) / volume before vibration × 100%.

[0103] The parameters and test results of the positive electrode active materials of each embodiment and comparative example are shown in Table 1.

[0104] Table 1

[0105] The battery manufacturing process is as follows: Preparation of positive electrode sheet: The positive active material prepared above, 50% Compressed Denka Black, and PVDF (polyvinylidene fluoride) are dispersed in NMP (N-methylpyrrolidone) at a mass ratio of 96.5:1.5:2. After ball milling and uniform dispersion, the mixture is coated on aluminum foil and vacuum dried to obtain the positive electrode sheet.

[0106] Battery assembly: The electrolyte is 1.1 mol / L LiPF6, with a solvent volume ratio of EC:EMC:DMC = 1:1:1 (volume ratio). The separator is Celgard polypropylene membrane, and the lithium metal sheet is the negative electrode. Together, they are assembled into a coin cell.

[0107] Electrochemical performance testing: The test voltage range is 2.5V-4.2V. Charge to 4.2V using constant current and constant voltage charging, and discharge to 2.5V using constant current discharging. The charge / discharge current is 0.1C for 2 cycles, then 0.2C for 1 cycle, then 0.33C for 1 cycle, then 0.5C for 1 cycle, then 1C for 1 cycle, and then 2C for 1 cycle. The cutoff voltage condition is the same as for 0.1C. Record the discharge capacity at 0.5C and 2C respectively.

[0108] Low-temperature capacity retention test method: At room temperature (25℃), the test voltage range is 2.5V-3.65V. Charge to 3.65V using constant current and constant voltage charging, then discharge to 2.5V using constant current discharging, with a charge / discharge current of 0.1C for 2 cycles; then charge / discharge at 0.3C for 2 cycles; then charge at 0.3C for 1 cycle; then transfer the coin cell half-cell to a -10℃ low-temperature constant temperature chamber for discharge testing, and discharge at 0.3C for 1 cycle. The low-temperature capacity retention rate is calculated as: Low-temperature capacity retention rate = (0.3C discharge capacity at -10℃ ÷ 0.3C discharge capacity at 25℃) × 100%.

[0109] The test results of the batteries in the examples and comparative examples are shown in Table 2.

[0110] Table 2

[0111] As shown in Tables 1 and 2, in Examples 1-12 of this application, by controlling the porosity and average pore size of the lithium iron phosphate cathode active material, the cathode active material has higher tap density, higher particle strength, lower oil absorption, better rate discharge capacity, and better low-temperature performance, resulting in batteries containing cathode active materials having excellent capacity, rate performance, and cycle performance.

[0112] In Comparative Example 1, the positive electrode active material has excessively high porosity and average pore size, resulting in significantly reduced particle strength, increased oil absorption and BET specific surface area, as well as increased total pore volume and primary particle size. Consequently, the cycle stability of the positive electrode active material is reduced, and its capacity and rate performance are also significantly decreased. In Comparative Examples 2 and 3, the positive electrode active materials have excessively low porosity and average pore size. Although the particle strength is somewhat increased, the total pore volume is too small, leading to poor wetting of the positive electrode active material by the electrolyte. This affects the capacity of the positive electrode active material and the transport of lithium ions. Therefore, the battery's capacity, rate performance, and cycle performance are all relatively low.

[0113] Compared to Example 1, the primary particle size of the positive electrode active material in Example 8 is smaller, which reduces the pore size and porosity of the positive electrode active material. Although the particle strength is increased, the wetting performance of the electrolyte on the positive electrode active material is reduced, affecting the capacity of the positive electrode active material and the transport of lithium ions. Therefore, the battery capacity, rate performance and cycle performance are all lower.

[0114] Compared to Example 1, the primary particle size of the positive electrode active material in Example 9 is higher, which increases the pore size and porosity of the positive electrode active material. However, the particle strength of the positive electrode active material is reduced, which affects the stability of the positive electrode active material during cycling. In addition, the increased gap between the primary particles causes the lithium ion transport distance to increase, which also affects the rate performance. Therefore, the battery capacity, rate performance and cycle performance are all low.

[0115] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0116] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material comprises secondary particles formed from primary particles, and the positive electrode active material includes: Li 1+a Fe b M c (PO4) d , Wherein, -0.1≤a≤0.1, 0<b≤1, 0≤c≤0.5, 0<d≤1, and M includes at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Sb, Co, Ni, V, Mg, Na, B, and Al; The porosity of the positive electrode active material is 6.5%-15%, and the average pore size of the positive electrode active material is 145nm-290nm.

2. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material satisfies at least one of the following conditions: M includes at least one of Sb, Al, W, Co, V, and Ti; The porosity of the positive electrode active material is 7.5%-13.5%, and can be selected as 7.5%-11%; The average pore size of the positive electrode active material is 150nm-250nm, and can be selected as 160nm-190nm.

3. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material satisfies at least one of the following conditions: The total pore volume of the positive electrode active material is 0.02 cm³. 3 / g-0.04cm 3 / g; The oil absorption capacity of the positive electrode active material is 25mL / 100g-35mL / 100g; The BET specific surface area of ​​the positive electrode active material is 6.0 m². 2 / g-10.0m 2 / g.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, The primary particle size of the positive electrode active material is 120nm-150nm.

5. The positive electrode active material according to any one of claims 1-3, characterized in that, The positive electrode active material satisfies at least one of the following conditions: The particle strength of the positive electrode active material is 80MPa-160MPa; The volume average particle size D of the positive electrode active material 50 The diameter is 5μm-15μm, D 100 The particle size is 35μm-60μm.

6. A method for preparing the positive electrode active material according to any one of claims 1-5, characterized in that, include: The iron phosphate precursor, lithium source, carbon source, optional dopant and water are mixed to obtain a mixture; The mixture is ground, spray-dried, and sintered to obtain a positive electrode active material.

7. The method according to claim 6, characterized in that, The method satisfies at least one of the following conditions: The volume average particle size D of the iron phosphate precursor 50 The thickness ranges from 5μm to 12μm. The specific surface area of ​​the iron phosphate precursor is 4m². 2 / g-13m 2 / g; The average particle size of the primary particles of the iron phosphate precursor is 80nm-200nm. In the iron phosphate precursor, the molar ratio of iron to phosphorus is 0.960-0.

980. The molar ratio of lithium in the lithium source to iron in the iron phosphate precursor is 1.01-1.

07. The carbon source includes two or more of glucose, sucrose, starch, polyethylene glycol, and citric acid. The carbon source is added at a mass ratio of 1.1%-1.6% of the positive electrode active material. The solid content of the mixture is 30%-60%.

8. The method according to claim 6, characterized in that, The method satisfies at least one of the following conditions: After grinding, the volume average particle size D of the material 50 The thickness ranges from 0.15μm to 0.35μm. The sintering temperature is 750℃-840℃, and the time is 5h-12h.

9. A positive electrode sheet, characterized in that, The positive electrode active material includes any one of claims 1-5 or any one of claims 6-8 prepared by the method thereof.

10. A battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

11. An electrical appliance, characterized in that, Includes the battery as described in claim 10.

Images