Positive electrode material, and preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of lithium-ion batteries, and provides a positive electrode material, and a preparation method therefor and a use thereof. The positive electrode material of the present invention has a volume-based particle size distribution curve exhibiting a bimodal distribution. A lithium-rich positive electrode material is composed of large-particle-size secondary spherical particles and small-particle-size secondary spherical particles; the large-particle-size secondary spherical particles are composed of small-particle-size primary spherical particles, and the small-particle-size secondary spherical particles are composed of large-particle-size primary spherical particles; and the volume-based average particle size of the large-particle-size secondary spherical particles is 8.0-12.0 μm, and the volume-based average particle size of the small-particle-size secondary spherical particles is 2.0-4.0 μm. In a scanning electron microscopy image of the positive electrode material, the maximum diameter of an individual small-particle-size secondary spherical particle is not more than 5 μm, and the minimum diameter of an individual large-particle-size secondary spherical particle is not less than 5 μm. Compared with the prior art, the present invention provides a positive electrode material comprising two types of secondary spherical particles having different primary spherical particle sizes, thereby improving the compaction density and cycle stability of the positive electrode material.

Description

A cathode material, its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 202510018772.6, filed on January 7, 2025, entitled "A cathode material and its preparation method and application", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of lithium-ion battery technology, and more specifically, to a cathode material, its preparation method, and its application. Background Technology

[0003] Lithium-ion rechargeable batteries have become the mainstream choice for electric vehicle power batteries. The cathode material largely determines the main performance of lithium-ion rechargeable batteries. One of the most important performance indicators is energy density, which determines one of the most critical parameters of electric vehicles: driving range. Currently, the mainstream cathode materials for power batteries exhibit a two-way competition: lithium iron phosphate (LFP) and medium-high nickel ternary materials. These two types of cathode materials have distinct characteristics. LFP cathodes offer excellent safety and cycle stability, but have relatively low energy density. Medium-high nickel ternary materials have higher energy density and good cycle stability, but their safety performance is inferior to LFP. Therefore, manganese-based cathode materials, with their more balanced overall performance, are the next-generation cathode solution that the industry is constantly pursuing. Lithium-rich manganese-based cathodes are a typical example, possessing high energy density, safety performance, and cycle stability, and are less expensive than ternary cathodes. However, the industrialization of lithium-rich cathodes still faces some challenges, such as low compaction density.

[0004] Currently, the commercially viable voltage for lithium-rich manganese-based lithium-ion batteries is 4.5V vs Graphite and below. Within this voltage range, their specific capacity can reach 230mAh g. -1 Higher nickel cathodes still have advantages, exhibiting higher specific capacity performance than medium-nickel high-voltage ternary cathodes. Correspondingly, the average discharge voltage of lithium-rich manganese-based cathodes within this specific capacity range is 3.6–3.65V vs Graphite, slightly lower than medium-high nickel ternary cathodes by 0.05–0.1V. In summary, the specific energy density of lithium-rich cathodes is essentially equivalent to that of ultra-high nickel ternary cathodes.

[0005] In fact, the energy density of power batteries must consider not only specific gravimetric energy density but also specific volumetric energy density. This is because sedans and SUVs are the mainstream passenger vehicles, and volumetric energy density determines the energy capacity of the battery pack that can be installed in the same vehicle class. Higher volumetric energy density allows passenger vehicles to carry higher-energy battery packs, increasing driving range, while also making the interior space more spacious and comfortable. Lithium-rich manganese-based cathodes have a higher proportion of Li atoms in their unit cells, and manganese has a slightly lower relative atomic mass than nickel and cobalt. This results in a lower true density of the unit cell compared to medium-high nickel ternary materials. Typically, the true density of the unit cell of lithium-rich manganese-based cathodes ranges from 4.3 to 4.4 g / cm³. 3 The true density of the high-nickel cathode cell reaches 4.8 g / cm³. 3 Common high-nickel cathode powders have a high compaction density, reaching up to 3.5 g / cm³. 3 The usable compaction density of lithium-rich cathode powder is currently typically only 2.8–2.9 g / cm³. 3 Therefore, it is necessary to further increase the compaction density of lithium-rich cathodes to make their volumetric energy density similar to that of ultra-high nickel ternary cathodes.

[0006] Lithium-rich cathodes, due to their inferior kinetic performance compared to ternary cathodes, are currently mostly produced in the form of secondary pellets in industrial applications. Single-crystal and near-single-crystal products are rarely used due to their low capacity. For secondary pellet products, improving their compaction density typically involves developing products with a dual-size distribution. In ternary cathodes, due to their excellent material kinetics, the porosity and primary particle size of the secondary pellets in dual-size or wide-size distribution products are usually similar, resulting in a denser system and significantly improved compaction density while maintaining excellent capacity. In lithium-rich cathode systems, due to the poorer kinetic performance of lithium-rich materials, it is necessary to specifically design the primary particle size, porosity, and modification schemes for large and small particles in dual-size or wide-size distribution systems to ensure a balance between high capacity, high compaction density, and high stability. Summary of the Invention

[0007] Based on the above, this invention proposes a cathode material with a bimodal particle size distribution, in which the large and small secondary spherical particles that make up the material have different sizes of primary spherical particles. Compared with single-distribution lithium-rich cathode products, this system has higher compaction density, excellent cycle stability and capacity performance, which can meet the performance requirements of power batteries for lithium-rich cathode products and help accelerate the industrialization of lithium-rich cathodes.

[0008] This invention provides a cathode material. The volume-based particle size distribution curve of the cathode material is a bimodal distribution. The cathode material is composed of large-diameter secondary spherical particles and small-diameter secondary spherical particles. The large-diameter secondary spherical particles are composed of small-diameter primary spherical particles, and the small-diameter secondary spherical particles are composed of large-diameter primary spherical particles. The volume-based average particle size of the large-diameter secondary spherical particles is 8.0-12.0 μm, and the volume-based average particle size of the small-diameter secondary spherical particles is 2.0-4.0 μm. The maximum diameter of a single small-diameter secondary sphere does not exceed 5 μm, and the minimum diameter of a single large-diameter secondary sphere is not less than 5 μm.

[0009] The average particle size of both small and large primary spherical particles satisfies the following condition: 0.5 ≤ l / m ≤ 0.75.

[0010] Where l is the average particle size of small-diameter primary spherical particles, and m is the average particle size of large-diameter primary spherical particles.

[0011] Compared with existing technologies, this invention proposes a cathode material incorporating two types of secondary spherical particles with different primary particle sizes to improve the compaction density and cycle stability of the cathode material. Specifically, the smaller-sized secondary spherical particles are composed of larger-sized primary spherical particles, while the larger-sized secondary spherical particles are composed of smaller-sized primary spherical particles. Firstly, this maximizes the capacity utilization of the two different particle sizes within the mixed-size secondary spherical particles with a bimodal distribution, ultimately resulting in excellent capacity performance of the mixed system. Lithium-rich cathode kinetics are less favorable than ternary cathodes; therefore, in the case of larger-sized secondary spherical particles, their capacity utilization is more significantly affected by the size and packing density of the primary spherical particles, leading to more pronounced capacity fluctuations.

[0012] Secondly, the compaction density was maximized. The size of the primary spherical particles constituting the small-diameter secondary spherical particles was appropriately increased to improve their packing density and structural strength, preventing breakage during electrode pressing and exposure of fresh interfaces that could affect system stability. Simultaneously, the average size of the primary spherical particles was controlled to not exceed twice the average size of the primary spherical particles constituting the large-diameter secondary spherical particles, ensuring excellent capacity utilization of the small-diameter secondary spherical particles and balancing the capacity utilization and cycling stability of the dual-size distribution system.

[0013] Appropriately increasing the size of the primary spherical particles that make up the small-diameter secondary spherical particles can reduce their specific surface area. In medium-to-high voltage (4.5V vs graphite) systems, interfacial side reactions are highly correlated with the material's specific surface area. Reducing the material's specific surface area effectively suppresses interfacial side reactions, thereby improving the long-term stability of the system. This avoids various problems caused by interfacial side reactions, such as transition metal dissolution, electrolyte oxidation and decomposition, battery drain failure, and gas expansion.

[0014] This lithium-rich cathode system with a dual-size distribution of secondary spherical particles of varying primary particle sizes exhibits better pressure resistance than lithium-rich cathodes with single-size secondary spherical particles. This is because the smaller-diameter secondary spherical particles are composed of larger-diameter primary spherical particles, thus enhancing the system's structural strength. Larger-diameter secondary spherical particles, due to their smaller primary particle size, are prone to breakage if used alone due to their lower structural strength, affecting long-term cycle stability. In the lithium-rich cathode with a dual-size distribution of secondary spherical particles of this invention, the smaller-diameter, high-strength secondary spherical particles enter the voids formed by the larger-diameter secondary spherical particles. The higher structural strength of the smaller-diameter secondary spherical particles provides stable support, improving the material's pressure resistance. This allows for the use of higher pressures to fabricate the electrode sheets, resulting in higher compaction density and effectively increasing the volumetric energy density of the lithium-ion battery.

[0015] In one possible implementation, the positive electrode material has the chemical formula Li. 1+x Ni t Mn u M 1-x-t-u O 2-z S z , where 0.1≤x≤0.2, 0.1≤t≤0.4, 0.5≤u≤0.7, 0.002≤z≤0.02, 0.95≤x+t+u<1.0, and M is selected from one or more of Nb, Cr, Ta, P, Mg, Ti, Mo, W, Sn, Sr, Al, Y, La, Ti, Zr, Ce, Si, Ba, and B.

[0016] Compared with existing technologies, this invention can significantly improve the theoretical capacity of materials by adjusting parameters such as x, t, u, z in the formula and selecting appropriate M elements, thereby increasing the energy density of batteries. At the same time, by doping different types of M elements and controlling their content ratio, changes in crystal structure during charging and discharging can be effectively suppressed, thereby improving the cycle performance and service life of materials.

[0017] In one possible implementation, the cathode material includes a coating layer, and the material of the coating layer is selected from one or more of Al2O3, LiAlO2, Li3PO4, and AlPO4, and the mass percentage of the coating layer in the lithium-rich cathode material is 0.2-2.0 wt%.

[0018] Compared with existing technologies, this invention also incorporates a coating layer. This coating layer effectively inhibits direct contact between the electrolyte and the positive electrode material, reducing the occurrence of side reactions. This helps prevent damage to the material structure, thereby extending the battery's lifespan. Appropriate coating treatment can mitigate the negative impact of material volume changes during charging and discharging, maintaining good particle integrity and thus alleviating the problem of capacity decline over time. The coating layer can also improve the interfacial properties between the positive electrode and the electrolyte, promoting lithium-ion transport while preventing electrons from passing through, thereby improving the overall efficiency of the battery.

[0019] In one possible implementation, the average particle size of the cathode material, based on volume, is 5.0-8.0 μm.

[0020] In one possible implementation, the average grain size of the cathode material is 80-130 nm. It is worth noting that the present invention uses the Rietveld method to refine the XRD pattern of the cathode material, and the refined XRD results show that the average grain size of the cathode material is 80-130 nm. This size is the optimal average grain size range suitable for medium-to-high voltage lithium-rich cathode materials. Within this range, the material capacity can be fully utilized, and the lattice stress will not increase significantly due to excessively large grain size. Simultaneously, an average grain size of not less than 80 nm ensures that the primary particle size of the material is not too small, preventing serious side reactions caused by electrolyte infiltration due to excessive grain boundaries, resulting in high structural strength.

[0021] In one possible implementation, the Span value of the positive electrode material is 1.2-1.6, where Span = (D 90 -D 10 ) / D 50 .

[0022] In one possible implementation, the specific surface area of ​​the cathode material is 0.7-3.0 m². 2 / g.

[0023] In one possible implementation, the cathode material has a powder compaction density ≥3.05 g / cm³ under a pressure of 3.5 T. 3 .

[0024] In one possible implementation, in the particle size distribution curve of the cathode material, the relative height of the left peak and the relative height of the right peak satisfy: 0.3 ≤ I A :I B ≤0.6, where I A The relative height of the left wing, I B The relative height of the right winger.

[0025] Compared with the prior art, in the bimodal distribution lithium-rich cathode system of large-diameter secondary spherical particles and small-diameter secondary spherical particles of the present invention, and with the left peak intensity limited to 0.3 to 0.6 times the right peak intensity, the compaction density of the system is significantly higher than that of products with a single particle size distribution.

[0026] In one possible implementation, the average cross-sectional porosity of the large-diameter secondary spherical particles and the average cross-sectional porosity of the small-diameter secondary spherical particles satisfy: 1.2≤α / β≤1.8, where α is the average cross-sectional porosity of the large-diameter secondary spherical particles and β is the average cross-sectional porosity of the small-diameter secondary spherical particles.

[0027] Compared with existing technologies, this invention further limits the porosity of the secondary spherical cross-section to ensure that the large-diameter secondary spherical particles have a appropriately higher porosity than the small-diameter secondary spherical particles. Its effects are: 1. Enhanced ion transport efficiency: Within this ratio range, the large-diameter particles provide larger channels, facilitating electrolyte penetration and rapid ion transport; while the small-diameter particles increase the total surface area, providing more active sites. This combination can significantly improve the ion conductivity of the electrode material; 2. Increased reaction interface: Due to their higher specific surface area, the small-diameter particles can provide more reaction interfaces, promoting chemical reactions. Simultaneously, the presence of large-diameter particles ensures the structural stability of the material, avoiding structural collapse or agglomeration caused by excessive refinement, thereby improving the overall utilization rate of the active material.

[0028] The second objective of this invention is to provide a method for preparing a cathode material, the method specifically comprising the following steps:

[0029] S1. Hydroxide precursors of small-diameter secondary spherical particles and large-diameter secondary spherical particles were synthesized respectively.

[0030] S2. The hydroxide precursor of small-diameter secondary spherical particles and hydroxide precursor of large-diameter secondary spherical particles obtained in step S1, lithium source and additives are mixed, sintered once and then cooled to room temperature naturally. After crushing and sieving, the cathode material is obtained.

[0031] Since the cathode material has a bimodal particle size distribution (large-diameter secondary spherical particles of 8.0-12.0 μm and small-diameter secondary spherical particles of 2.0-4.0 μm), the preparation method of this invention adopts the method of separately synthesizing hydroxide precursors of small-diameter secondary spherical particles and hydroxide precursors of large-diameter secondary spherical particles, and independently optimizing the two precursors of different sizes to ensure that the required bimodal particle size distribution can be formed in the subsequent sintering process.

[0032] In one possible implementation, the specific steps for synthesizing the hydroxide precursor of small-diameter secondary spherical particles in step S1 are as follows:

[0033] A1. Set the stirring speed to 600-1000 rpm and the temperature to 50-60℃. After purging with protective gas for 2-3 hours, add the metal salt solution, precipitant, and complexing agent, and maintain the pH of the reaction system at 9.5-11.0.

[0034] A2. Wait for the particle size to grow to D. 50 Within the range of 2.0-4.0 μm, stop feeding and collect the slurry;

[0035] A3. After the slurry collected in step A2 is subjected to aging, washing, centrifugation and drying, hydroxide precursors of small-diameter secondary spherical particles are obtained.

[0036] The specific steps for synthesizing the hydroxide precursor of large-diameter secondary spherical particles are as follows:

[0037] B1. Set the stirring speed to 600-1000 rpm and the temperature to 50-60℃. After purging with protective gas for 2-3 hours, add the metal salt solution, precipitant, and complexing agent, and maintain the pH of the reaction system at 9.5-11.0.

[0038] B2. Wait for the particle size to grow to D. 50 Within the range of 8.0-12.0 μm, stop feeding and collect the slurry;

[0039] B3. The slurry collected in step B2 is subjected to aging, washing, centrifugation and drying processes in sequence to obtain hydroxide precursors of large-diameter secondary spherical particles.

[0040] It is worth mentioning that, unlike the steps required for preparing precursors for small-diameter secondary spherical particles, this invention introduces an appropriate amount of oxygen during the preparation of precursors for large-diameter secondary spherical particles, thereby controlling the primary particle size of the precursors for large-diameter secondary spherical particles.

[0041] In some embodiments, in steps A1 and B1, the total molar concentration of the metal salt solution is 2-3 mol / L, and the solutes are nickel sulfate and manganese sulfate, wherein the molar ratio of nickel to manganese is the same as the ratio of small-diameter secondary spherical particles, the precipitant is a sodium hydroxide solution with a concentration of 8-12 mol / L, and the complexing agent is an 8-12 wt% ammonia solution.

[0042] In some embodiments, the protective gas in step A1 is nitrogen, and the protective gas in step B1 is nitrogen containing 0.5-5.0 vol% oxygen.

[0043] In one possible implementation, the process further includes step S4: mixing the positive electrode material and the coating agent evenly, performing secondary sintering, and then sequentially cooling, crushing, and sieving to obtain a positive electrode material containing a coating layer. The coating agent is selected from one or more of Al2O3, LiAlO2, Li3PO4, and AlPO4.

[0044] In one possible implementation, the parameters for a single sintering are as follows: heating rate of 1-3℃ / min, sintering temperature of 900-950℃, and holding time of 8-15h.

[0045] In one possible implementation, the parameters for the secondary sintering are as follows: heating rate of 1-3℃ / min, sintering temperature of 500-700℃, and holding time of 8-12h.

[0046] Compared with existing technologies, by setting the primary sintering parameters as a heating rate of 1-3℃ / min, a sintering temperature of 900-950℃, and a holding time of 8-15 hours, and the secondary sintering parameters as a heating rate of 1-3℃ / min, a sintering temperature of 500-700℃, and a holding time of 8-12 hours, this invention ensures uniform heating, sufficient crystal phase transformation, and structural optimization of the cathode material, thereby improving the structural stability, purity, and electrochemical performance of the material, while reducing internal stress and defects, ultimately achieving the preparation of high-quality, high-performance cathode materials.

[0047] The present invention also provides a positive electrode sheet, which includes any of the above-described positive electrode materials or positive electrode materials prepared by any of the above-described preparation methods.

[0048] The third objective of this invention is to provide an application of a cathode material in lithium-ion batteries.

[0049] In summary, the dual-distribution cathode material of the present invention combines excellent capacity performance, high compaction density, and excellent cycle stability, making it a novel high-performance cathode material suitable for industrialization. Attached Figure Description

[0050] Figure 1 is a SEM image of the cathode material in Example 1;

[0051] Figure 2 shows the particle size distribution curves of the cathode materials of Example 1, Comparative Example 1, and Comparative Example 2.

[0052] Figure 3 shows the powder compaction density of the cathode materials of Example 1, Comparative Example 1, and Comparative Example 2 measured under different pressures;

[0053] Figure 4 shows the cycle performance curves of liquid coin cells assembled from the cathode materials of Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0054] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0055] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as any other stated value or each smaller range between intermediate values ​​within a range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0056] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This application specification and embodiments are merely exemplary.

[0057] The technical effects of the present invention will be described below with reference to specific embodiments.

[0058] It is worth mentioning that in the detection method used in the embodiments of the present invention:

[0059] Primary particle size, specific surface area, and particle size determination: The morphology of the cathode materials obtained in all examples and comparative examples was observed using SEM, and the average thickness and length of at least 100 random primary particles in a selected area of ​​the SEM were determined using Nano Measure software; the specific surface area was determined using the nitrogen adsorption BET method, referring to the test method specified in national standard GB / T19587-2017; the particle size was determined using a laser particle size analyzer. 10 This represents the particle size at which the cathode material particles reach 10% of the total volume in the volumetric particle size distribution; D 50 This represents the particle size at which the cathode material particles reach 50% of the total volume, starting from the smallest particle size side, in the volumetric particle size distribution; D 90 This represents the particle size at which the cathode material particles reach 90% of the total volume in the volumetric particle size distribution.

[0060] Cross-sectional porosity determination: SEM images were taken of the cathode materials obtained in all embodiments and comparative examples. Then, ImageJ software was used to quantitatively analyze the grayscale of a single secondary spherical cross-section of the material. Specifically, the RGB threshold was first set to 90, and the area ratio of the region with RGB range 0 to 90 in the selected area image of a single secondary spherical cross-section was obtained, denoted as X1. Similarly, the area ratio of the region with RGB range 0 to 252 in the same selected area image of the same single secondary spherical cross-section was denoted as X2. The porosity of the material cross-section was then obtained as X1 / X2*100%. Ten sets of data were tested, and the average value was taken to obtain the porosity of the material cross-section.

[0061] Chemical composition determination: The actual chemical composition of the cathode material was determined by ICP-AES. The results showed that the actual chemical composition of each finished product was basically consistent with the design ratio of each sample in the table.

[0062] Average grain size: calculated according to the Scherrer formula, i.e., D=Kλ / (βcosθ). Where K is a constant, λ is the X-ray wavelength, and the (003) or (104) peak is selected. β and θ are the full width at half maximum (FWHM) and diffraction angle of the diffraction peak obtained by full spectrum fitting in Topas software. K is taken as 0.89.

[0063] Tap density: determined according to the method specified in national standard GB / T 5162-2006;

[0064] Powder compaction: A particle density analyzer (CARVER4350) was used. 2-3g samples were taken and pressurized using different pressure molds with a radius r = 0.65cm. The pressure was maintained for 1 minute, and the height of the sample after compaction was measured to obtain the powder compaction density. The formula for calculating powder compaction density is ρ = m / (πr^2{(h1+h2+h3+h4+h5+h6) / 6-d}). Note: г is the radius of the mold cylinder, d is the height from the upper mold cover to the top of the filling barrel when empty, and h is the height from the upper mold cover to the top of the filling barrel after powder compaction.

[0065] Example 1:

[0066] This embodiment provides a cathode material with the chemical formula: Li 1.15 Ni 0.29 Mn 0.53 W 0.02 La 0.01 O 1.995 S 0.005 It is prepared by the following method:

[0067] S1, Hydroxide precursor for synthesizing small-diameter secondary spherical particles (D) 50 =3.0μm):

[0068] S11. Prepare a nickel and manganese salt solution with a total molar ratio of 2.5 mol / L, where the nickel and manganese sources are nickel sulfate and manganese sulfate, respectively, and the molar ratio of nickel to manganese is 35:65; prepare a 10 mol / L sodium hydroxide solution and a 10 wt% ammonia complexing agent solution.

[0069] S12. Fill the 50L reactor with clean water and set the stirring speed of the reactor to 800rpm and the temperature to 55℃. Introduce nitrogen gas and exhaust it for 2 hours. Then, introduce metal salt solution, precipitant, and complexing agent into the reactor to maintain the pH of the reaction system at 10.0.

[0070] S13, Wait for the particle size to grow to D 50 =Once the target particle size reaches 3.0 μm, stop feeding and collect the slurry in the reactor;

[0071] S14. The slurry collected in S13 is subjected to aging, washing, centrifugation, and drying to obtain hydroxide precursors of small-diameter secondary spherical particles.

[0072] S2, Hydroxide precursor for synthesizing large-diameter secondary spherical particles (D 50 =10μm):

[0073] S21. Prepare a nickel and manganese salt solution with a total molar ratio of 2.5 mol / L, where the nickel and manganese sources are nickel sulfate and manganese sulfate, respectively, and the molar ratio of nickel to manganese is 35:65; prepare a 10 mol / L sodium hydroxide solution and a 10 wt% ammonia complexing agent solution.

[0074] S22. Fill a 50L reactor with clean water and set the stirring speed of the reactor to 800rpm and the temperature to 55℃. Add nitrogen gas containing 1.0 vol% oxygen and exhaust the gas for 2 hours. Then, introduce metal salt solution, precipitant, and complexing agent into the reactor to maintain the pH of the reaction system at 10.0.

[0075] S23, Wait for the particle size to grow to D 50 =After the target particle size reaches 10.0μm, stop feeding and collect the slurry in the reactor;

[0076] S24. The slurry collected in S23 is subjected to aging, washing, centrifugation, and drying to obtain hydroxide precursors of large-diameter secondary spherical particles.

[0077] S3. Then, the hydroxide precursors of the small-diameter secondary spherical particles and the hydroxide precursors of the large-diameter secondary spherical particles are mixed with lithium carbonate and additive WO3 in stoichiometric ratio, and sintered once in a box furnace or roller kiln. The heating rate is 2℃ / min, the sintering temperature is 920℃, the holding time is 10h, and then the mixture is naturally cooled to room temperature, crushed, and sieved to obtain high-pressure long-cycle cathode material.

[0078] S4. Mix it further with the coating agent Al2O3 until uniform, and control the mass percentage of the coating layer to be 0.5%. Then, perform secondary sintering in a box furnace or roller kiln with a heating rate of 2℃ / min, a sintering temperature of 600℃, and a holding time of 10h. After that, let it cool naturally to room temperature, crush it, and sieve it to obtain the coated high-pressure long-cycle cathode material.

[0079] It is worth noting that in this embodiment, steps S1 and S2 are not sequential in other embodiments and can be performed simultaneously.

[0080] Example 2:

[0081] This embodiment provides a cathode material, which differs from Embodiment 1 only in that the chemical formula of the lithium-rich cathode material in this embodiment is: Li 1.2 Ni 0.19 Mn 0.58 W 0.02 La 0.01 O 1.995 S 0.005 During its preparation, the components are proportioned according to the stoichiometric ratio of the chemical formula, l / m=0.62, α / β=1.4, D 50 =7.3μm, Span=1.35, average grain size is 110nm, and in S12 and S22, the stirring speed is set to 600rpm, the temperature is 50℃, and after purging with protective gas for 2.5h, the pH of the reaction system is maintained at 9.5. Other preparation steps are the same as in Example 1, and will not be repeated here.

[0082] Example 3

[0083] This embodiment provides a cathode material, which differs from Embodiment 1 only in that the chemical formula of the lithium-rich cathode material in this embodiment is: Li 1.12 Ni 0.34 Mn 0.51 W 0.02 La 0.01 O 1.995 S 0.005 During its preparation, it is proportioned according to the stoichiometric ratio of the chemical formula, l / m=0.6, α / β=1.5, D 50 =7.4μm, Span=1.38, average grain size is 112nm, stirring speed is set to 1000rpm, temperature is 60℃, after purging with protective gas for 3h, metal salt solution, precipitant and complexing agent are added, the pH of the reaction system is kept at 11.0, other preparation steps are the same as in Example 1, and will not be repeated here.

[0084] Example 4

[0085] This embodiment provides a cathode material, which differs from Embodiment 1 only in that the chemical formula of the lithium-rich cathode material in this embodiment is: Li 1.15 Ni 0.28 Mn 0.52 Mg 0.02 Al 0.03 O 1.995 S 0.005 During its preparation, the components are proportioned according to the stoichiometric ratio of the chemical formula, l / m=0.63, α / β=1.61, D 50 =7.5μm, Span=1.42, average grain size is 118nm. The parameters for the first sintering process are as follows: heating rate is 1℃ / min, sintering temperature is 900℃, holding time is 8h. Other preparation steps are the same as in Example 1, and will not be repeated here.

[0086] Example 5

[0087] This embodiment provides a cathode material, which differs from Embodiment 1 only in that the chemical formula of the lithium-rich cathode material in this embodiment is: Li 1.15 Ni 0.28 Mn 0.52 Cr 0.04 Mo 0.01 O 1.995 S 0.005 During its preparation, the components are proportioned according to the stoichiometric ratio of the chemical formula, l / m = 0.58, α / β = 1.55, D 50 =7.4μm, Span=1.44, average grain size is 103nm. The parameters for the first sintering process are as follows: heating rate is 3℃ / min, sintering temperature is 950℃, holding time is 15h. Other preparation steps are the same as in Example 1, and will not be repeated here.

[0088] Example 6

[0089] This embodiment provides a cathode material, differing from Embodiment 1 only in that the mass percentage content of the coating layer in this embodiment is 2.0%, l / m = 0.6, α / β = 1.56, and D... 50 =7.5μm, Span=1.34, average grain size is 108nm. The parameters of the secondary sintering treatment are as follows: heating rate is 1℃ / min, sintering temperature is 500℃, holding time is 8h. Other preparation steps are the same as in Example 1, and will not be repeated here.

[0090] Example 7

[0091] This embodiment provides a positive electrode material, differing from Embodiment 1 only in that the coating layer in this embodiment is composed of Al2O3 and AlPO4, with mass percentages of 1.0% and 1.0%, respectively, l / m = 0.63, α / β = 1.48, and D... 50 =7.4μm, Span=1.41, average grain size is 108nm. The parameters of the secondary sintering treatment are as follows: heating rate is 3℃ / min, sintering temperature is 700℃, holding time is 12h. Other preparation steps are the same as in Example 1, and will not be repeated here.

[0092] Example 8

[0093] This embodiment provides a positive electrode material, differing from Embodiment 1 only in that the coating layer in this embodiment is composed of LiAlO2 with a mass percentage of 0.5%, l / m = 0.61, α / β = 1.52, and D... 50 =7.43μm, Span=1.4, average grain size is 116nm, the protective gas in step S22 is nitrogen containing 0.5 vol% oxygen, and the other preparation steps are the same as in Example 1, and will not be repeated here.

[0094] Comparative Example 1

[0095] This comparative example provides a cathode material with a single particle size, and its chemical formula is:

[0096] Li 1.15 Ni 0.29 Mn 0.53 W 0.02 La 0.01 O 1.995 S 0.005 Its preparation process is as follows:

[0097] S1, Hydroxide precursor for synthesizing small-diameter secondary spherical particles (D) 50 =3.0μm):

[0098] S11. Prepare a nickel and manganese salt solution with a total molar ratio of 2.5 mol / L, where the nickel and manganese sources are nickel sulfate and manganese sulfate, respectively, and the molar ratio of nickel to manganese is 35:65; prepare a 10 mol / L sodium hydroxide solution and a 10 wt% ammonia complexing agent solution.

[0099] S12. Fill the 50L reactor with clean water and set the stirring speed of the reactor to 800rpm and the temperature to 55℃. Introduce nitrogen gas and exhaust it for 2 hours. Then, introduce metal salt solution, precipitant, and complexing agent into the reactor to maintain the pH of the reaction system at 10.0.

[0100] S13, Wait for the particle size to grow to D 50=Once the target particle size reaches 3.0 μm, stop feeding and collect the slurry in the reactor;

[0101] S14. The slurry collected in S13 is subjected to aging, washing, centrifugation, and drying to obtain hydroxide precursors of small-diameter secondary spherical particles.

[0102] S2. Then, the hydroxide precursor of the above small-diameter secondary spherical particles is mixed with lithium carbonate and additive WO3 in stoichiometric ratio, and sintered once in a box furnace or roller kiln. The heating rate is 2℃ / min, the sintering temperature is 920℃, the holding time is 10h, and then the mixture is naturally cooled to room temperature, crushed, and sieved to obtain the cathode material.

[0103] S3. Mix it further with the coating agent Al2O3 until uniform, and control the mass percentage of the coating layer to be 0.5%. Then, perform secondary sintering in a box furnace or roller kiln with a heating rate of 2℃ / min, a sintering temperature of 600℃, and a holding time of 10h. After that, let it cool naturally to room temperature, crush it, and sieve it to obtain the positive electrode material.

[0104] Comparative Example 2

[0105] This comparative example provides a cathode material with a single particle size, and its chemical formula is:

[0106] Li 1.15 Ni 0.29 Mn 0.53 W 0.02 La 0.01 O 1.995 S 0.005 Its preparation process is as follows:

[0107] S1, Hydroxide precursor for synthesizing large-diameter secondary spherical particles (D) 50 =10μm):

[0108] S11. Prepare a nickel and manganese salt solution with a total molar ratio of 2.5 mol / L, where the nickel and manganese sources are nickel sulfate and manganese sulfate, respectively, and the molar ratio of nickel to manganese is 35:65; prepare a 10 mol / L sodium hydroxide solution and a 10 wt% ammonia complexing agent solution.

[0109] S12. Fill the 50L reactor with clean water and set the stirring speed of the reactor to 800rpm and the temperature to 55℃. Add nitrogen gas containing 1.0 vol% oxygen and exhaust the gas for 2 hours. Then, introduce metal salt solution, precipitant, and complexing agent into the reactor to maintain the pH of the reaction system at 10.0.

[0110] S13, Wait for the particle size to grow to D 50 =After the target particle size reaches 10.0μm, stop feeding and collect the slurry in the reactor;

[0111] S14. The slurry collected in S23 is subjected to aging, washing, centrifugation, and drying to obtain hydroxide precursors of large-diameter secondary spherical particles.

[0112] S2. Then, the hydroxide precursor of the above large-diameter secondary spherical particles is mixed with lithium carbonate and additive WO3 in stoichiometric ratio, and sintered once in a box furnace or roller kiln. The heating rate is 2℃ / min, the sintering temperature is 920℃, the holding time is 10h, and then it is naturally cooled to room temperature, crushed, and sieved to obtain the cathode material.

[0113] S3. Mix it further with the coating agent Al2O3 until uniform, and control the mass percentage of the coating layer to be 0.5%. Then, perform secondary sintering in a box furnace or roller kiln with a heating rate of 2℃ / min, a sintering temperature of 600℃, and a holding time of 10h. After that, let it cool naturally to room temperature, crush it, and sieve it to obtain the coated cathode material.

[0114] Comparative Example 3

[0115] This comparative example provides a cathode material, differing from Example 1 only in that, in this comparative example, l / m = 1.1, α / β = 0.85, and D... 50 =7.5μm, Span=1.4, average grain size is 145nm, other preparation steps are the same as in Example 1, and will not be repeated here.

[0116] Comparative Example 4

[0117] This comparative example provides a cathode material, differing from Example 1 only in that, in this comparative example, l / m = 0.7, α / β = 1.4, and D... 50 =8.7μm, Span=1.55, average grain size is 122nm, other preparation steps are the same as in Example 1, and will not be repeated here.

[0118] Comparative Example 5

[0119] This comparative example provides a cathode material, differing from Example 1 only in that, in this comparative example, l / m = 0.66, α / β = 1.43, and D... 50 =4.6μm, Span=1.32, average grain size is 108nm, other preparation steps are the same as in Example 1, and will not be repeated here.

[0120] Comparative Example 6

[0121] This comparative example provides a cathode material, differing from Example 1 only in that, in this comparative example, l / m = 0.63, α / β = 1.38, and D... 50 =6.5μm, Span=1.62, average grain size is 116nm, other preparation steps are the same as in Example 1, and will not be repeated here.

[0122] Comparative Example 7

[0123] This comparative example provides a cathode material, differing from Example 1 only in that, in this comparative example, l / m = 0.60, α / β = 1.43, and D... 50 =8.3μm, Span=1.13, average grain size is 109nm, other preparation steps are the same as in Example 1, and will not be repeated here.

[0124] Comparative Example 8

[0125] This comparative example provides a cathode material, differing from Example 1 only in that, in this comparative example, l / m = 0.4, α / β = 2.3, and D... 50 =7.5μm, Span=1.43, average grain size is 76nm, other preparation steps are the same as in Example 1, and will not be repeated here.

[0126] The inventors summarized the synthesis parameters and physicochemical parameters of Examples 1-8 and Comparative Examples 1-8, and the results are shown in Table 1:

[0127] Table 1 Synthesis parameters and physicochemical parameters of Examples 1-8 and Comparative Examples 1-8

[0128] Furthermore, the inventors conducted performance tests on the cathode materials obtained in Examples 1-8 and Comparative Examples 1-8, and the test results are shown in Table 2:

[0129] Table 2: Electrical performance results of the cathode materials obtained in Examples 1-8 and Comparative Examples 1-8

[0130] In Table 2, M represents small-diameter secondary spherical particles, and L represents large-diameter secondary spherical particles.

[0131] In addition, the inventors further observed the cathode material of Example 1, and the results are shown in Figure 1. As can be seen from Figure 1, in the cathode material prepared in Example 1, the size of the primary spherical particles that make up the large-diameter secondary spherical particles is significantly smaller than the size of the primary spherical particles that make up the small-diameter secondary spherical particles.

[0132] Furthermore, the inventors summarized the particle size distribution of the cathode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2. The results are shown in Figure 2. As can be seen from Figure 2, the cathode material prepared using the comparative example has a single particle size distribution, while the cathode material prepared using Example 1 has a dual particle size distribution. Moreover, the positions of the two peaks basically coincide with the positions of the single peaks in the comparative example. This indicates that the cathode material prepared by the method of the present invention is indeed composed of two particle sizes with a single particle size distribution. This distribution can thus provide a higher compaction density.

[0133] Furthermore, the inventors statistically analyzed the powder compaction density of the cathode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2 under different pressures. The results are shown in Figure 3. As can be seen from Figure 3, the compaction density of the small particle single size distribution sample is relatively low, while the compaction density of the large particle single size distribution sample is improved. However, the sample with a bimodal double size distribution can achieve the highest compaction density.

[0134] The inventors conducted further performance testing by assembling liquid coin cells: The positive electrode materials obtained in Examples 1-8 and Comparative Examples 1-8 were assembled into liquid coin cells. The assembly method was as follows: The obtained positive electrode material, conductive agent Super-P, and binder PVDF were added to NMP solvent in a ratio of 94:3:3 and mixed evenly to obtain a slurry. The obtained slurry was then coated, dried, punched, and rolled to obtain a positive electrode sheet. The stainless steel shell, positive electrode sheet, PP separator, and lithium sheet of the coin cell were stacked in sequence, a certain amount of electrolyte was added, and the cells were sealed and allowed to stand to obtain a liquid coin cell.

[0135] The liquid coin cell was subjected to the following tests:

[0136] 1. 0.2C discharge capacity

[0137] Test method: After the assembled battery has been left to stand for 5 hours, it is charged at a constant current of 0.2C to 4.55V, then charged at a constant voltage of 4.55V until the cutoff current is equal to 0.05C. After standing for 5 minutes, it is discharged at a constant current of 0.2C to 2.5V. The resulting discharge capacity is the 0.2C discharge capacity.

[0138] 2. First Coulomb Efficiency

[0139] Test method: After the assembled battery has been left to stand for 5 hours, it is charged at a constant current of 0.2C to 4.55V, then charged at a constant voltage of 4.55V until the cutoff current is equal to 0.05C. After standing for 5 minutes, it is discharged at a constant current of 0.2C to 2.5V. The resulting discharge capacity / charge capacity is the initial coulombic efficiency.

[0140] 3. Capacity retention rate after 150 cycles at 1.0C

[0141] Test method: After the battery completes the first discharge capacity test, it is charged at a constant current of 1.0C to 4.55V, then charged at a constant voltage of 4.55V until the cutoff current is equal to 0.05C. After resting for 5 minutes, it is discharged at a constant current of 1.0C to 2.5V. This process is repeated 150 times, that is, 150 charge-discharge cycles at a 1.0C rate. The discharge capacity of the 150th cycle / the discharge capacity of the 1st cycle is the capacity retention rate of the battery after 150 cycles at 1.0C.

[0142] Application Examples

[0143] The prepared positive electrode was subjected to battery testing to verify the capacity, specific energy and cycle performance of the positive electrode imparted by the substrate. The lithium button battery was tested at 2.5-4.55V with a nominal capacity of 250mAhg-1. The first cycle was performed at 0.1C for 1 cycle, followed by 2.0C for 1 cycle, and then 150 cycles at 1.0 / 1.0C.

[0144] The test results are shown in Table 3:

[0145] Table 3: Performance test results of liquid coin half-cells assembled from the cathode materials prepared in Examples 1-8 and Comparative Examples 1-8

[0146] Furthermore, the inventors tested the cycle performance of liquid coin cells assembled from the cathode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2. The test results are shown in Figure 4. As can be seen from Figure 4, the sample with bimodal particle size distribution has better performance than the sample with single particle size distribution due to the better gradation between particles. The battery made with its cathode material has higher cycle stability.

[0147] The data from Comparative Examples 1 and 2 show that both single-particle-size small-diameter secondary sphere lithium-rich cathodes and single-particle-size large-diameter secondary sphere lithium-rich cathodes that meet the L and M requirements have acceptable capacity performance, but their compaction density is too low, and their cycle stability is worse than that of the dual-size lithium-rich cathode of this invention. Therefore, the energy density and stability provided by single-particle-size cathode materials are too low and cannot meet the requirements for industrialization. The data from Comparative Example 3 shows that when the size of the primary particles constituting L is too large, the porosity decreases significantly when the conditions of this invention are not met, the capacity performance of the system decreases significantly, the power performance is insufficient, and the volumetric energy density is lower than that of single-particle-size products. In addition, due to the excessively large size of the primary particles constituting L, its kinetic performance is poor, and the 1C / 1C cycle performance is also significantly deteriorated. The data from Comparative Examples 4 and 5 show that when the L particle size is too large, the capacity performance of the system will be limited because the lithium ion transport distance in L is too long. When the L particle size is too small, the compaction density of the system cannot meet the requirements and cannot provide the ideal volumetric energy density. The results from Comparative Examples 4 and 5 show that when the particle size of M is too small, the cycle stability decreases because M can undergo deep delithiation, accelerating the structural decay rate. When the particle size of M is too large, the system compaction density decreases because M cannot completely fill the voids left by L, preventing L from achieving close packing. Comparative Example 8 shows that when the size of the primary particles constituting L is too small, the average grain size decreases due to the increased porosity of L, significantly reducing the system compaction density, increasing the system specific surface area, intensifying interfacial side reactions, and significantly decreasing cycle stability.

[0148] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A positive electrode material, characterized in that, The volumetric particle size distribution curve of the cathode material exhibits a bimodal distribution. The cathode material is composed of large-diameter secondary spherical particles and small-diameter secondary spherical particles. The large-diameter secondary spherical particles are composed of small-diameter primary spherical particles, and vice versa. The average volumetric particle size of the large-diameter secondary spherical particles is 8.0-12.0 μm, and the average volumetric particle size of the small-diameter secondary spherical particles is 2.0-4.0 μm. The maximum diameter of a single small-diameter secondary sphere does not exceed 5 μm, and the minimum diameter of a single large-diameter secondary sphere is not less than 5 μm. The average particle size of the small-diameter and large-diameter primary spherical particles satisfies the following conditions: 0.5≤l / m≤0.75， Where l is the average particle size of small-diameter primary spherical particles, and m is the average particle size of large-diameter primary spherical particles.

2. The cathode material as described in claim 1, characterized in that, The chemical formula of the positive electrode material is Li 1+x Ni t Mn u M 1-x-t-u O 2-z S z , where 0.1≤x≤0.2, 0.1≤t≤0.4, 0.5≤u≤0.7, 0.002≤z≤0.02, 0.95≤x+t+u<1.0, and M is selected from one or more of Nb, Cr, Ta, P, Mg, Ti, Mo, W, Sn, Sr, Al, Y, La, Ti, Zr, Ce, Si, Ba, and B.

3. The cathode material as described in claim 1 or 2, characterized in that, The cathode material includes a coating layer, and the material of the coating layer is selected from one or more of Al2O3, LiAlO2, Li3PO4, and AlPO4. The mass percentage of the coating layer in the cathode material is 0.2-2.0 wt%.

4. The cathode material according to any one of claims 1-3, characterized in that, The average particle size of the positive electrode material, based on volume, is 5.0-8.0 μm; And / or, the average grain size of the cathode material is 80-130 nm; And / or, the Span value of the positive electrode material is 1.2-1.6, where Span = (D 90 -D 10 ) / D 50 ; And / or, the specific surface area of ​​the positive electrode material is 0.7-3.0 m². 2 / g; And / or, the positive electrode material has a powder compaction density ≥3.05 g / cm³ under a pressure of 3.5 T. 3 .

5. The cathode material according to any one of claims 1-3, characterized in that, In the particle size distribution curve of the cathode material, the relative height of the left peak and the relative height of the right peak satisfy: 0.3 ≤ I A :I B ≤0.6, where I A The relative height of the left wing, I B The relative height of the right winger.

6. The cathode material according to any one of claims 1-3, characterized in that, The average cross-sectional porosity of the large-diameter secondary spherical particles and the average cross-sectional porosity of the small-diameter secondary spherical particles satisfy the following condition: 1.2≤α / β≤1.8, where α is the average cross-sectional porosity of the large-diameter secondary spherical particles and β is the average cross-sectional porosity of the small-diameter secondary spherical particles.

7. A method for preparing a positive electrode material as described in any one of claims 1-6, characterized in that, The preparation method specifically includes the following steps: S1. Hydroxide precursors of small-diameter secondary spherical particles and large-diameter secondary spherical particles were synthesized respectively. S2. The hydroxide precursor of small-diameter secondary spherical particles and the hydroxide precursor of large-diameter secondary spherical particles obtained in step S1, lithium source and additives are mixed, sintered once and then cooled, and then crushed and sieved to obtain the cathode material.

8. The preparation method according to claim 7, characterized in that, In step S1, the specific steps for synthesizing the hydroxide precursor of small-diameter secondary spherical particles are as follows: A1. Set the stirring speed to 600-1000 rpm and the temperature to 50-60℃. After purging with protective gas for 2-3 hours, add the metal salt solution, precipitant, and complexing agent, and maintain the pH of the reaction system at 9.5-11.

0. A2. Wait for the particle size to grow to D. 50 Within the range of 2.0-4.0 μm, stop feeding and collect the slurry; A3. After the slurry collected in step A2 is subjected to aging, washing, centrifugation and drying, hydroxide precursors of small-diameter secondary spherical particles are obtained. The specific steps for synthesizing the hydroxide precursor of large-diameter secondary spherical particles are as follows: B1. Set the stirring speed to 600-1000 rpm and the temperature to 50-60℃. After purging with protective gas for 2-3 hours, add the metal salt solution, precipitant, and complexing agent, and maintain the pH of the reaction system at 9.5-11.

0. B2. Wait for the particle size to grow to D. 50 Within the range of 8.0-12.0 μm, stop feeding and collect the slurry; B3. The slurry collected in step B2 is subjected to aging, washing, centrifugation and drying processes in sequence to obtain hydroxide precursors of large-diameter secondary spherical particles.

9. The preparation method according to claim 8, wherein In steps A1 and B1, the total molar concentration of the metal salt solution is 2-3 mol / L, and the solutes are nickel sulfate and manganese sulfate, wherein the molar ratio of nickel to manganese is the same as the ratio of small-diameter secondary spherical particles. The precipitant is a sodium hydroxide solution with a concentration of 8-12 mol / L, and the complexing agent is an 8-12 wt% ammonia solution. And / or, the protective gas in step A1 is nitrogen, and the protective gas in step B1 is nitrogen containing 0.5-5.0 vol% oxygen.

10. The preparation method according to claim 8, characterized in that, The process also includes step S4, where the positive electrode material and the coating agent are mixed evenly, and after secondary sintering, the mixture is cooled, crushed, and sieved to obtain a positive electrode material with a coating layer. The coating agent is selected from one or more of Al2O3, LiAlO2, Li3PO4, and AlPO4.

11. The preparation method according to claim 10, characterized in that, The parameters for a single sintering are as follows: heating rate is 1-3℃ / min, sintering temperature is 900-950℃, and holding time is 8-15h; And / or, the parameters for secondary sintering are as follows: heating rate of 1-3℃ / min, sintering temperature of 500-700℃, and holding time of 8-12h.

12. A positive electrode plate, characterized in that, The positive electrode sheet comprises the positive electrode material according to any one of claims 1-6 or the positive electrode material prepared by the preparation method according to any one of claims 7-11.

13. An application of the cathode material as described in any one of claims 1-6 in a lithium-ion battery.

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