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 Li1 + aFebMc (PO4) d, a is greater than or equal to-0.1 and less than or equal to 0.1, b is greater than 0 and less than or equal to 1.2, c is greater than or equal to 0 and less than or equal to 0.1, d is greater than 0 and less than or equal to 1.2, 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; based on the total mass of the positive electrode active material, the mass ratio of the ferrous phosphide is 10 ppm to 80 ppm. The positive electrode active material provided by the invention has excellent gram volume.

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] Lithium iron phosphate batteries are favored by many due to their extremely high safety performance, ultra-long cycle life, significant cost advantages, and wide range of applications. They have become one of the mainstream lithium-ion battery technologies and are widely used in new energy vehicles and energy storage power stations.

[0003] With the widespread application of lithium iron phosphate (LFP) in many fields, it has experienced rapid development, and correspondingly, the requirements for compaction of LFP have become increasingly stringent. High-compaction LFP typically refers to LFP with a compaction density ≥ 2.60 g / cm³. 3 Lithium iron phosphate (LFP) cathode active materials have a higher compaction density, meaning more active material can be packed into the same volume, thus significantly improving battery range or energy storage capacity. In existing production technologies, high-compaction LFP production is divided into single-firing and double-firing processes. Comparatively, the single-firing process is simpler, consumes less energy, and requires less equipment investment, which not only facilitates stable production but also offers significant cost advantages. However, it also brings the negative impact of ferrous phosphide.

[0004] In the preparation process of lithium iron phosphate cathode active materials under high pressure, ferrous phosphide (Fe2P) is a common byproduct. Excessive Fe2P content can have a significant negative impact on the electrochemical performance of lithium iron phosphate cathode active materials. Summary of the Invention

[0005] 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 achieves excellent electrochemical performance by controlling the ferrous phosphide content.

[0006] A first aspect of this application provides a positive electrode active material, the positive electrode active material comprising: Li 1+a Fe b M c (PO4) d Wherein, -0.1≤a≤0.1, 0<b≤1.2, 0≤c≤0.1, 0<d≤1.2, 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; based on the total mass of the positive electrode active material, the mass percentage of ferrous phosphide is 10ppm-80ppm.

[0007] The cathode active material proposed in this application controls the ferrous phosphide content in lithium iron phosphate cathode active materials, while keeping other parameters of the cathode active material relatively stable (e.g., unit cell parameters). This avoids the reduction in electrochemical performance caused by excessively high or low ferrous phosphide content in the cathode active material. When the ferrous phosphide content in the cathode active material is too high, Fe2P is an inactive phase (does not participate in Li...). + The insertion / extraction reaction (IoP) can cause a decrease in the specific capacity of the positive electrode active material, and excessive ferrous phosphide can also block lithium-ion transport, causing cracking and pulverization of the positive electrode active material particles. Furthermore, excessive ferrous phosphide may also lead to dendrite formation in the negative electrode, affecting battery safety performance. Because lithium iron phosphate positive electrode active materials themselves have poor electronic conductivity and slow ion diffusion rates, while ferrous phosphide is a metallic conductor, too low a ferrous phosphide content in the positive electrode active material will result in poor rate performance (weak high-current charge / discharge capability) and incomplete capacity utilization. In summary, the positive electrode active material proposed in this application, by controlling the ferrous phosphide content in lithium iron phosphate positive electrode active materials, maintains relatively stable other parameters, resulting in excellent specific capacity and first-time efficiency.

[0008] According to some embodiments of this application, based on the total mass of the positive electrode active material, the mass percentage of ferrous phosphide is 15ppm-50ppm; and / or, 0≤c≤0.015; preferably, 0.003≤c≤0.009.

[0009] According to some embodiments of this application, the positive electrode active material satisfies at least one of the following conditions: the cell parameter a of the positive electrode active material is 6.00 Å - 6.02 Å, preferably 6.003 Å - 6.010 Å; the cell parameter c of the positive electrode active material is 4.68 Å - 4.70 Å, preferably 4.690 Å - 4.693 Å; the cell parameter c / a of the positive electrode active material is 0.777 - 0.783, preferably 0.780 - 0.782.

[0010] According to some embodiments of this application, the compaction density of the positive electrode active material at 3 tons is 2.55 g / cm³. 3 -2.62g / cm 3 .

[0011] According to some embodiments of this application, the positive electrode active material satisfies at least one of the following conditions: the median particle size D50 of the positive electrode active material is 0.8 μm-1 μm; and the mass percentage of carbon element based on the total mass of the positive electrode active material is 1.20%-1.40%.

[0012] 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 includes: dispersing a lithium source, a phosphorus source, an iron source, optionally a carbon source, optionally an M source, and additives in a solvent, grinding, and spray drying to obtain a spray material; sintering the spray material at 780℃-820℃, cooling to 600℃-650℃, and then heating to 680℃-720℃ to sinter again to obtain the positive electrode active material.

[0013] The positive electrode active material prepared in this application can control the content of ferrous phosphide in the positive electrode active material from 10ppm to 80ppm by controlling different sintering temperatures in a single sintering process, thereby improving the specific capacity of the positive electrode active material.

[0014] According to some embodiments of this application, the method satisfies at least one of the following conditions: the sintering time at 780℃-820℃ is 120min-360min; the sintering time at 680℃-720℃ is 240min-480min.

[0015] 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.

[0016] The fourth aspect of this application provides a battery including the positive electrode provided in the third aspect of this application.

[0017] The fifth aspect of this application provides an electrical device, including the battery provided in the fourth aspect of this application. Attached Figure Description

[0018] 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 These are XRD patterns of the positive electrode active materials prepared in Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0019] 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.

[0020] A first aspect of this application provides a positive electrode active material, the positive electrode active material comprising: Li 1+a Fe b M c (PO4) dWherein, -0.1≤a≤0.1, 0<b≤1.2, 0≤c≤0.1, 0<d≤1.2, 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; based on the total mass of the positive electrode active material, the mass percentage of ferrous phosphide is 10ppm-80ppm.

[0021] As an example, a can be a range of -0.1, -0.05, 0, 0.05, 0.1, or any two of the above values; b can be a range of 0.1, 0.3, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 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 two of the above values. According to some embodiments of this application, 0 ≤ c ≤ 0.015; preferably, 0.003 ≤ c ≤ 0.009; d can be a range of 0.1, 0.3, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, or any two of the above values.

[0022] The cathode active material proposed in this application controls the ferrous phosphide content in lithium iron phosphate cathode active materials, while keeping other parameters of the cathode active material relatively stable (e.g., unit cell parameters). This avoids the reduction in electrochemical performance caused by excessively high or low ferrous phosphide content in the cathode active material. When the ferrous phosphide content in the cathode active material is too high, Fe2P is an inactive phase (does not participate in Li...). + The insertion / extraction reaction (IoP) can cause a decrease in the specific capacity of the positive electrode active material, and excessive ferrous phosphide can also block lithium-ion transport, causing cracking and pulverization of the positive electrode active material particles. Furthermore, excessive ferrous phosphide may also lead to dendrite formation in the negative electrode, affecting battery safety performance. Because lithium iron phosphate positive electrode active materials themselves have poor electronic conductivity and slow ion diffusion rates, while ferrous phosphide is a metallic conductor, too low a ferrous phosphide content in the positive electrode active material will result in poor rate performance (weak high-current charge / discharge capability) and incomplete capacity utilization. In summary, the positive electrode active material proposed in this application, by controlling the ferrous phosphide content in lithium iron phosphate positive electrode active materials, maintains relatively stable other parameters, resulting in excellent specific capacity and first-time efficiency.

[0023] It is understandable that the chemical formula and subscripts of each element of the positive electrode active material can be determined by ICP (inductively coupled plasma) method: the instrument used is PE Optima 7000DV, the test conditions are 0.1g sample completely dissolved in 3mL HNO3 + 9mL HCl mixed acid solution, diluted to 250mL for testing.

[0024] The mass percentage of ferrous phosphide in the positive electrode active material can be determined by the following methods: 1. Prepare hydrochloric acid: 18% HCl dilute solution (volume fraction); 2. Magnetic rod cleaning: Demagnetize a 6000Gs magnetic rod by rolling it in 5L of ultrapure water for 10 minutes; 3. Material weighing and adsorption: 1000g of positive electrode active material + 5L of water + 6000Gs magnetic rod are rolled in a mixer at 40Hz for 15 minutes; 4. Circulation and rolling: After 15 minutes of adsorption, transfer the magnetic rod to another drum containing 5L of pure water, roll for 15 minutes, and repeat once more. 5. Magnetic rod cleaning: Use ceramic scissors to scrape all the black material adsorbed by the magnetic rod into a 500mL beaker. Then use a small magnetic rod to adsorb the black material at the bottom of the beaker and wash the black material with pure water 3-5 times. 6. Acid washing: Sonicate with 20mL of 18% HCl for 2 minutes, then use a small magnetic rod to hold the bottom of the beaker and rinse with pure water 2-3 times; 7. Weighing Test: Filter the liquid in the beaker onto the filter membrane, dry it, and weigh it. The mass percentage of ferrous phosphide in the positive electrode active material is then calculated as (Mm) / 1000×100%, where M is the weight of the membrane with ferrous phosphide after drying, and m is the weight of the blank membrane.

[0025] According to some embodiments of this application, the mass percentage of ferrous phosphide, based on the total mass of the positive electrode active material, is 10ppm-80ppm. For example, it can be 10ppm, 15ppm, 20ppm, 25ppm, 30ppm, 35ppm, 40ppm, 45ppm, 50ppm, 60ppm, 70ppm, 80ppm, or any combination of two of the above values. According to other embodiments of this application, the mass percentage of ferrous phosphide, based on the total mass of the positive electrode active material, is 15ppm-50ppm. Therefore, when the mass percentage of ferrous phosphide in the positive electrode active material is greater than 50ppm, excessive Fe2P will occupy some active sites, resulting in a decrease in the amount of Fe that can participate in the reaction per unit mass of positive electrode active material. 2+ The reduced quantity of ferrous phosphide leads to a decrease in the specific capacity of the positive electrode active material. Furthermore, due to the significant difference in crystal structure between Fe2P and lithium iron phosphate (Fe2P has a hexagonal structure, while lithium iron phosphate has an orthorhombic structure), excessive ferrous phosphide not only blocks lithium-ion migration channels during battery charge-discharge cycles, affecting cycle life, but also increases the interfacial stress between Fe2P and lithium iron phosphate as Li₂P decreases. +The repeated intercalation and deintercalation of ferrous phosphide leads to cumulative changes, causing particle cracking and pulverization, which greatly impairs the cycle life of the battery. Furthermore, due to its excellent electronic conductivity, ferrous phosphide particles may form tiny conductive bridges within the positive electrode. During battery charging and discharging, ferrous phosphide may precipitate and form metallic iron dendrites at the negative electrode. These dendrites can grow and pierce the separator, directly causing internal short circuits, leading to thermal runaway, fire, or even explosion. When the mass percentage of ferrous phosphide in the positive electrode active material is less than 15 ppm, the intrinsic electronic conductivity of lithium iron phosphate positive electrode active materials is extremely low (~10 ppm). -10 ~10 -8 (S / cm), electrons are difficult to pass through Fe. 3+ / Fe 2+ The transfer between redox centers leads to poor battery rate performance (weak high-current charge / discharge capability) and incomplete capacity utilization. Ferrous phosphide, on the other hand, boasts an electronic conductivity as high as 10⁻⁶. 2 ~10 3 With a concentration of S / cm, a certain amount of ferrous phosphide, dispersed in nanoparticle form on or within the cathode active material particles, can not only form continuous "electron channels" and reduce electron transport resistance, but also shorten the electron transport path between lithium iron phosphate cathode active material particles, reducing the charge transfer impedance (Rct) at the electrode / electrolyte interface, thus making the electrochemical reaction smoother and improving electrochemical performance. In summary, controlling the ferrous phosphide content in the cathode active material within the above range can ensure the optimal capacity utilization of the cathode active material.

[0026] According to some embodiments of this application, the cell parameter a of the positive electrode active material is 6.00 Å to 6.02 Å. As an example, the cell parameter a can be 6.00 Å, 6.003 Å, 6.005 Å, 6.0062 Å, 6.0061 Å, 6.0062 Å, 6.010 Å, 6.015 Å, 6.02 Å, or any range of two of the above values. According to other embodiments of this application, the cell parameter a of the positive electrode active material is 6.003 Å to 6.010 Å. Therefore, the cell parameter a can be used to characterize the structural regularity and crystallinity of the positive electrode active material. Controlling the cell parameter a within the above range indicates that, under the condition of controlling the ferrous phosphide content in the positive electrode active material, the smaller the deviation of the a value from the standard (6.0080), the more regular the structure, the better the crystallinity, which is beneficial to lithium-ion diffusion and can improve the specific capacity and rate performance of the positive electrode active material.

[0027] According to some embodiments of this application, the cell parameter c of the positive electrode active material is 4.68 Å to 4.70 Å. For example, c can be 4.68 Å, 4.685 Å, 4.6904 Å, 4.6905 Å, 4.6906 Å, 4.6907 Å, 4.6908 Å, 4.6909 Å, 4.6910 Å, 4.6911 Å, 4.6912 Å, 4.695 Å, 4.70 Å, or any range of two of the above values. According to other embodiments of this application, c is 4.690 Å to 4.693 Å. Therefore, the cell parameter c value can be used to characterize the interlayer spacing of the crystal structure of the positive electrode active material. The larger the cell parameter c value, the larger the interlayer spacing, the larger the lithium-ion diffusion channel, and the more favorable the lithium-ion diffusion. By controlling the cell parameter c of the positive electrode active material within the above range, it is shown that the cell parameter c value does not change much when controlling the ferrous phosphide content in the positive electrode active material, which can improve the specific capacity and rate performance of the positive electrode active material.

[0028] According to some embodiments of this application, the cell parameter c / a of the positive electrode active material is 0.777-0.783. For example, the cell parameter c / a can be 0.777, 0.78, 0.7809, 0.7810, 0.7811, 0.782, 0.783, or any range of two of the above values. The value of the cell parameter c / a can be used to characterize the interlayer spacing of the crystal structure of the positive electrode active material. The larger the value of the cell parameter c / a, the larger the interlayer spacing, the larger the lithium-ion diffusion channel, and the more favorable it is for lithium-ion diffusion. Controlling the cell parameter c / a of the positive electrode active material within the above range indicates that, under the condition of controlling the ferrous phosphide content in the positive electrode active material, the value of the cell parameter c / a does not change much, which can improve the specific capacity and rate performance of the positive electrode active material.

[0029] It is understandable that the cell parameters a and c of the positive electrode active material can be measured by XRD. By testing the XRD pattern of the positive electrode active material and further refining the full spectrum, the cell parameters a and c can be obtained.

[0030] According to some embodiments of this application, the compaction density of the positive electrode active material at 3 tons is 2.55 g / cm³. 3 -2.62g / cm 3 For example, the compaction density of the positive electrode active material under 3 tons can be 2.55 g / cm³. 3 2.56 g / cm 3 2.57 g / cm 3 2.58 g / cm 3 2.59 g / cm 3 2.60 g / cm 3 2.61 g / cm 32.62 g / cm 3 Or it can be a range consisting of any two of the above values. Therefore, the positive electrode active material has a higher compaction density, allowing more positive electrode active material to be filled within the same volume, thus increasing the energy density of batteries containing it.

[0031] It is understandable that the compaction density of the positive electrode active material at 3 tons can be determined by the following method: direct testing using a Sansi Zongheng (UTM7305) compaction density meter.

[0032] According to some embodiments of this application, the median particle size D50 of the positive electrode active material is 0.8μm-1μm, for example, it can be 0.8μm, 0.85μm, 0.9μm, 0.95μm, 1μm or any two of the above values. This can shorten the transport path of lithium ions in the positive electrode, and the contact area between the positive electrode active material and the electrolyte will not be too large, thus avoiding excessive side reactions. This can improve the cycle performance and rate performance of the battery containing the positive electrode active material.

[0033] According to embodiments of this application, the median particle size is a well-known concept in the art, also known as the median particle size or average particle size Dv50, 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. The median particle size can be conveniently determined using a laser particle size analyzer, such as GB / T 19077-2016 "Particle Size Distribution - Laser Diffraction Method", using a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0034] According to some embodiments of this application, the mass percentage of carbon element in the positive electrode active material is 1.20%-1.40% based on the total mass of the positive electrode active material. For example, it can be 1.20%, 1.25%, 1.30%, 1.35%, 1.40%, or any two of the above values. By controlling the carbon element content in the positive electrode active material within the above range, the carbon content is neither too high, which would affect the transport of lithium ions and occupy too much mass of the positive electrode active material, nor too low, which would result in insufficient improvement in conductivity. This can further improve the capacity and cycle performance of the positive electrode active material.

[0035] 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: Disperse lithium source, phosphorus source, iron source, optional carbon source, optional M source, and additives in a solvent, grind, and spray dry to obtain spray material; According to some embodiments of this application, the phosphorus source and iron source are selected from commercially available common raw materials. This application does not impose specific limitations; they can be independent raw materials for phosphorus and iron, or a combination of phosphorus and iron. Those skilled in the art can select according to their needs. For example, the iron source can be selected from ferric phosphate, ferric nitrate, ferric sulfate, ferrous oxalate, ferrous carbonate, ferric oxide, etc., and the phosphorus source can be selected from phosphoric acid, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, lithium phosphate, etc. Combinations of phosphorus + iron and manganese + iron can be selected from ferric phosphate.

[0036] According to some embodiments of this application, the lithium source, M source, and carbon source are not specifically limited in this application. The lithium source can be lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, etc. The M source can be M oxide, M hydroxide, M carbonate, etc. The carbon source can be at least one of glucose, sucrose, organic polymers, etc.

[0037] According to some embodiments of this application, the solvent may include water, ethanol, etc.

[0038] According to some embodiments of this application, the median particle size D50 of the material finally obtained by grinding is 0.35μm-0.45μm.

[0039] In principle, the present invention does not limit the parameters of grinding and spray drying processes. Those skilled in the art can set the parameters according to the equipment.

[0040] S2: The spray material is sintered at 780℃-820℃, cooled to 600℃-650℃, and then heated to 680℃-720℃ for sintering to obtain the positive electrode active material.

[0041] As an example, in S2, the three sintering temperatures are: the first temperature can be 780℃, 790℃, 800℃, 810℃, 820℃, or any combination of two of the above values; the second temperature can be 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, or any combination of two of the above values; and the third temperature can be 680℃, 690℃, 700℃, 710℃, 720℃, or any combination of two of the above values.

[0042] Therefore, this application utilizes the difference in the formation conditions of lithium iron phosphate cathode active material and ferrous phosphide. By optimizing the sintering process during the preparation process, the sintering temperature is lowered when ferrous phosphide side reaction occurs, thereby disrupting the high-temperature environment required for ferrous phosphide formation and reducing ferrous phosphide formation. However, this does not affect the growth of the primary particles of the already formed lithium iron phosphate cathode active material, nor does it damage other properties of the cathode active material, thus improving the specific capacity of the cathode active material.

[0043] According to some embodiments of this application, the sintering time at 780℃-820℃ is 120min-360min. For example, the sintering time can be 120min, 150min, 180min, 200min, 240min, 250min, 300min, 360min, or any combination of two of the above values. Thus, by controlling the sintering time at 780℃-820℃ within the above range, this application can generate lithium iron phosphate cathode active materials. It can also reduce the increased decomposition and reduction capacity of organic carbon sources caused by excessively long sintering times, providing more sufficient thermodynamic driving force for the formation of ferrous phosphide. This promotes the reduction of some divalent iron to elemental iron, which reacts with phosphorus to generate ferrous phosphide, thereby controlling the ferrous phosphide content in the cathode active material within the required range.

[0044] As an example, when no side reactions occur, i.e. at the lower sintering temperature of this application, the formation equation for lithium iron phosphate cathode active materials is: 2FePO4+Li2CO3+C→2LiFePO4+CO2↑+CO↑.

[0045] When the sintering temperature increases, the following side reactions occur: 4LiFePO4+7C (or 14C)→2Fe2P+2Li2O+2P+7CO2↑(14CO↑); 4LiFePO4+C (or 2C)→2Fe2P+2Li4P2O7+2P+CO2↑(2CO↑).

[0046] According to some embodiments of this application, the sintering time at 680℃-720℃ is 240min-480min. For example, it can be 240min, 300min, 360min, 400min, 420min, 450min, 480min, or any combination of two of the above values. This allows for a higher compaction density of the positive electrode active material and reduces the excessive formation of ferrous phosphide caused by insufficient sintering time, thus controlling the ferrous phosphide content in the positive electrode active material within the desired range.

[0047] According to some embodiments of this application, sintering is carried out under an inert atmosphere, such as a nitrogen atmosphere or an argon atmosphere.

[0048] In summary, the method for preparing the positive electrode active material proposed in this application, through a single sintering process and optimized sintering curve, involves a sudden temperature drop during the formation of ferrous phosphide, which disrupts the formation conditions of ferrous phosphide. The subsequent optimized sintering curve also features a lower temperature sintering plateau, promoting the conversion of already formed ferrous phosphide. This not only effectively inhibits the formation of ferrous phosphide as a byproduct during the reaction of lithium iron phosphate positive electrode active material, but also reduces the content of already formed ferrous phosphide in lithium iron phosphate, without compromising other properties. This method achieves the preparation of high-pressure compaction lithium iron phosphate positive electrode active material, resulting in better safety and facilitating large-scale production. Furthermore, the elimination of secondary sintering significantly reduces production costs.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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)).

[0061] 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.

[0062] According to some embodiments of the present invention, the negative electrode sheet may also be a lithium metal sheet.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] Example 1 Step 1: Weigh and mix lithium carbonate, iron phosphate, carbon source (glucose), and additive (titanium dioxide) according to their molar ratio, add them to deionized water as solvent, and the solid content is 40%. Grind the mixture using a ball mill. First, coarsely grind (1200 rpm) to obtain a median particle size of 0.60 μm, then finely grind (1200 rpm) to obtain a median particle size D50 of 0.35 μm. Then, use a centrifugal atomizing dryer (inlet temperature set to 245℃, outlet temperature set to 100℃) to feed the ground material into the inlet for spray drying to obtain sprayable material. Step 2: The spray material obtained in Step 1 is heated to 800℃ at a heating rate of 2.5℃ / min under a nitrogen atmosphere, held at this temperature for 4 hours, cooled to 650℃, then heated to 700℃ and held for 8 hours, cooled to room temperature, and ground to obtain the positive electrode active material.

[0073] The differences between the remaining embodiments and comparative examples and Example 1 are shown in the table below. The data of the positive electrode active materials of each embodiment and comparative example are also shown in the table below. Among them, the difference between Comparative Example 1 and Example 1 is that in step 2, the sintering method is to directly heat to 820°C at a heating rate of 2.5°C / min and hold at that temperature for 8 hours.

[0074] Table 1

[0075] Performance testing In the above embodiments and comparative examples, the relevant parameters were obtained through testing using the following methods: (1) XRD test: The positive electrode active materials prepared in the examples and comparative examples, as well as the positive electrode plates prepared in each example and comparative example, were prepared according to the method below and XRD test was performed. The equipment was a SmartLab 9KW model. The test target was Cu and the analysis was performed under Cu Kα radiation. The tube voltage of the equipment was set to 40 kV, the tube current was set to 200mA, the test angle range of the sample was 5° to 120°, the scan rate was 2° / min, and the scan step size was 0.02°.

[0076] The XRD patterns of the positive electrode active materials prepared in Example 1 and Comparative Example 1 are shown below. Figure 1As shown, the diffraction peaks of the positive electrode active materials in Example 1 and Comparative Example 1 correspond one-to-one, with no impurity peaks appearing in the positive electrode active material of Comparative Example 1. Furthermore, the diffraction peaks of the positive electrode active material in Example 1 are stronger and sharper than those in Comparative Example 1. This indicates that the positive electrode active material in Example 1 has better crystallinity, fewer lattice defects, and a more orderly internal crystal arrangement. This not only helps reduce energy loss and improve migration efficiency during lithium-ion transport but also enhances structural stability, making the positive electrode active material less prone to lattice distortion during charge-discharge cycles and enabling it to maintain an effective lithium-ion transport channel for a long time.

[0077] Unit cell parameters a and c were determined by XRD. By testing the XRD pattern of the positive electrode active material and further refining the full spectrum, the unit cell parameters a and c, as well as c / a, can be obtained.

[0078] The mass percentage of ferrous phosphide was determined based on the total mass of the positive electrode active material: 1. Preparation of hydrochloric acid: 18% HCl dilute solution (volume fraction); 2. Magnetic rod cleaning: a 6000Gs magnetic rod was rolled in 5L of ultrapure water for 10 minutes to remove magnetism; 3. Material weighing and adsorption: 1000g of positive electrode active material + 5L of water + a 6000Gs magnetic rod were rolled in a mixer at 40Hz for 15 minutes; 4. Circulating rolling: after 15 minutes of adsorption, the magnetic rod was transferred to another container containing 5... 5. Magnetic rod cleaning: Scrape all the black material adsorbed by the magnetic rod into a 500mL beaker with ceramic scissors. Then, use a small magnetic rod to adhere to the bottom of the beaker and wash the black material with pure water 3-5 times. 6. Acid washing: Sonicate with 20mL of 18% HCl for 2 minutes, then use a small magnetic rod to adhere to the bottom of the beaker and wash with pure water 2-3 times. 7. Weighing test: Filter the liquid in the beaker onto the filter membrane, dry it, and weigh it. Then, the mass percentage of ferrous phosphide in the positive electrode active material = (Mm) / 1000×100%, where M is the weight of the membrane with ferrous phosphide after drying, and m is the weight of the blank membrane.

[0079] The compaction density of the positive electrode active material at 3 tons was determined by direct testing using a Sansi Zongheng (UTM7305) compaction density meter.

[0080] Determination of median particle size D50 of positive electrode active material: Refer to standard GB / T 19077-2016 "Particle size distribution by laser diffraction" and use a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0081] The mass percentage of carbon element was determined based on the total mass of the positive electrode active material: the carbon-sulfur analyzer was used with a self-contained balance in accordance with standard GB / T 20123.

[0082] The electrochemical performance of the positive electrode active material was tested using an R2025 coin cell lithium-ion battery. The specific preparation process of the R2025 coin cell lithium-ion battery for testing is as follows: Electrode preparation: The above-prepared positive electrode active material, conductive agent SuperP and polyvinylidene fluoride (PVDF) are thoroughly mixed with an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1.5:2 to form a uniform slurry. The slurry is coated on aluminum foil and dried at 120°C for 12 h. Then, it is stamped and formed using a pressure of 100 MPa to produce a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm.

[0083] Battery Assembly: In an argon-filled glove box with both water and oxygen content less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into an R2025 coin cell and then left to stand for 6 hours. The negative electrode used a 15.6 mm diameter, 0.45 mm thick lithium metal sheet; the separator used a 25 μm polypropylene microporous membrane (Celgard 2325); and the electrolyte used was a 1 mol / L mixture of equal parts LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0084] Electrochemical performance testing: In the following examples and comparative examples, the Shenzhen Xinwei Battery Testing System was used to test the electrochemical performance of R2025 coin cells. The initial charge and discharge capacity test conditions were: 25℃, 0.1C and 0.5C charge and discharge, voltage range of 2.5-4.2V, and constant voltage cutoff current of 0.05C. The 0.1C charge capacity and discharge capacity, 0.1C first effect, 0.5C charge capacity and discharge capacity, and 0.5C first effect were measured respectively.

[0085] The test results of the batteries in the examples and comparative examples are shown in Table 2.

[0086] Table 2

[0087] As shown in Tables 1 and 2, compared with Comparative Example 1, the positive electrode active material of Example 1 after sintering optimization has a larger c value and c / a value. This means that the crystal size in the c-axis direction is relatively large and the interlayer spacing is relatively wide, which is beneficial to improving the diffusion rate of lithium ions.

[0088] Similarly, the a-value of the positive electrode active material in Example 1 deviates less from the standard lattice parameter (6.008), indicating that the crystal structure of the positive electrode active material is more regular, with high crystallinity and fewer defects, which is conducive to the diffusion and transport of lithium ions in the lattice. Furthermore, Example 1 also demonstrates higher compaction density, extremely low ferrous phosphide content, and superior electrical performance compared to Comparative Example 1. In Comparative Example 1, the ferrous phosphide mass ratio is too high, and the 0.5C first-time efficiency of the positive electrode active material is significantly reduced.

[0089] Comparative studies of Examples 1, 2, 3, and 4 show that when the ferrous phosphide content fluctuates within a low range, the physicochemical and electrical properties of the corresponding positive electrode active material do not change significantly. Comparing Example 4 with Comparative Example 1, Example 4, under the optimized sintering process, exhibits lower ferrous phosphide content, higher compaction, and relatively better electrical properties.

[0090] Compared with Examples 1 and 5, Example 5 introduces an appropriate M source and ensures that its amount is within a certain range. With other conditions unchanged, under the optimized sintering process, the corresponding positive electrode active material can still maintain high compaction and low ferrous phosphide while possessing excellent electrochemical performance.

[0091] Comparing Examples 1, 6, 7, and 8, when more dopants were introduced and the amount of dopants was further increased, the cell parameters a and c of the positive electrode active material changed significantly while other conditions remained constant. This means that the introduction of dopants led to a significant change in the crystal structure of the positive electrode active material. The compaction density of the positive electrode active material in Example 6 was 2.09 g / cm³. 3 It is evident that changes in the type and amount of dopant will require higher sintering temperatures; furthermore, the introduction of appropriate dopant elements is beneficial for improving the electrical properties of the material.

[0092] Comparing Examples 1 and 9, when the dopant elements are completely removed, ferrous phosphide will be generated in large quantities at the same sintering temperature, which will impair the electrical performance.

[0093] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are 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.

[0094] 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 includes: Li 1+a Fe b M c (PO4) d , Wherein, -0.1≤a≤0.1, 0<b≤1.2, 0≤c≤0.1, 0<d≤1.2, 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; Based on the total mass of the positive electrode active material, the mass percentage of ferrous phosphide is 10ppm-80ppm.

2. The positive electrode active material according to claim 1, characterized in that, Based on the total mass of the positive electrode active material, the mass percentage of ferrous phosphide is 15ppm-50ppm; and / or, 0 ≤ c ≤ 0.015; preferably, 0.003 ≤ c ≤ 0.

009.

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 cell parameter of the positive electrode active material is a = 6.00 Å - 6.02 Å, preferably 6.003 Å - 6.010 Å; The cell parameters of the positive electrode active material are c = 4.68 Å - 4.70 Å, preferably 4.690 Å - 4.693 Å; The cell parameter c / a of the positive electrode active material is 0.777-0.783, preferably 0.780-0.

782.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, The compaction density of the positive electrode active material at 3 tons is 2.55 g / cm³. 3 -2.62g / cm 3 .

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 median particle size D50 of the positive electrode active material is 0.8 μm-1 μm; Based on the total mass of the positive electrode active material, the mass percentage of carbon is 1.20%-1.40%.

6. A method for preparing the positive electrode active material according to any one of claims 1-5, characterized in that, include: A lithium source, a phosphorus source, an iron source, and optionally a carbon source and an M source are dispersed in a solvent, ground, and spray-dried to obtain a spray material; The spray material is sintered at 780℃-820℃, cooled to 600℃-650℃, and then heated to 680℃-720℃ for sintering to obtain the 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 sintering time at 780℃-820℃ is 120min-360min; The sintering time at 680℃-720℃ is 240min-480min.

8. A positive electrode sheet, characterized in that, The positive electrode active material includes any one of claims 1-5 or any one of claims 6-7 prepared by the method thereof.

9. A battery, characterized in that, Includes the positive electrode sheet as described in claim 8.

10. An electrical appliance, characterized in that, Includes the battery as described in claim 9.

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