Positive electrode material and preparation method thereof, positive electrode plate and secondary battery

Abstract

The invention provides a positive electrode material and a preparation method thereof, a positive electrode plate and a secondary battery. In the positive electrode material, the number ratio R of particles with the particle size of less than 1 [mu] m is more than or equal to 8% and less than or equal to 20%; and under the condition of 25 MPa, the conductivity T of a pole piece of the positive electrode material is greater than 0.025 S / cm. The positive electrode material disclosed by the invention has relatively high pole piece conductivity, the resistance and power consumption of the prepared battery are effectively reduced, the energy transmission efficiency is improved, and in addition, the positive electrode material has the advantages of high compaction density and high material activity by limiting the quantity ratio R of the microparticles in the positive electrode material to be 8-20%; and the problems of surface side reaction increase, gas production increase and the like caused by uncontrollable number of microparticles faced by the positive electrode material are solved, and the safety and cycle performance are improved.

Description

[0001] This application is a divisional application of patent application No. 202411940456.6, filed on December 26, 2024, entitled "Positive Electrode Material and Preparation Method Thereof, Positive Electrode Sheet and Secondary Battery". Technical Field

[0002] This application relates to the field of battery cathode material technology, specifically to a cathode material and its preparation method, a cathode sheet, and a secondary battery. Background Technology

[0003] With the rapid development of the global new energy materials field, the demand for lithium-ion batteries is also increasing. Cathode materials, as a key component of battery materials, are undergoing rapid iteration and updates. Among various cathode materials, ternary cathode materials occupy a certain market share due to their relatively high energy density. Currently, commercially available ternary cathode materials are prone to structural collapse and intergranular cracks during charge and discharge processes, affecting the cycle life of the cathode material and urgently requiring improvement. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above defects, it is necessary to provide a cathode material.

[0005] In addition, it is necessary to provide a method for preparing the aforementioned positive electrode material, as well as a positive electrode sheet and a secondary battery using the aforementioned positive electrode material.

[0006] In a first aspect, embodiments of this application provide a positive electrode material in which, in an image under a scanning electron microscope at 3k magnification, the proportion R of particles smaller than 1μm in the positive electrode material satisfies: 8% ≤ R ≤ 20%; and under 25MPa conditions, the electrode conductivity T of the positive electrode material satisfies: T > 0.025S / cm.

[0007] In some possible embodiments, at a scanning electron microscope magnification of 3k, the cathode material has a first region and a second region, wherein the first region has a particle size distribution of less than 1μm ...

[0008] In some possible embodiments, the peak of the particle size distribution curve of the cathode material is asymmetrical, with the area to the left of the peak being larger than the area to the right of the peak.

[0009] In some possible embodiments, the cathode material is a single-crystal cathode material, and the average particle size of a single particle in the cathode material is 1 μm to 4 μm.

[0010] In some possible embodiments, the general formula of the positive electrode material is as follows: Li a Ni b Co c Q d M (1-a-b-c-d) N e O2, wherein the element Q is selected from at least one of Mn and Al, the element M is selected from at least one of Zr, Ti, Al, Mg and Y, the element N is selected from at least one of Zr, Ti, Al, Co, Mg, W, Ce, Y, K and Na, and 0.95≤a≤1.2, 0<b≤1, 0≤c≤1, 0<d≤1, b+c+d+e≤1, 0≤e<1.

[0011] In some possible embodiments, the median particle size D50 of the cathode material is 2.5 μm to 5 μm, D10 is 1 μm to 2.5 μm, D90 is 6 μm to 10 μm, and 1.0 ≤ (D90-D10) / D50 ≤ 1.5.

[0012] In some possible embodiments, the specific surface area of ​​the positive electrode material is 0.5 m². 2 / g~1.4m 2 / g.

[0013] In some possible embodiments, the compaction density of the cathode material is >3.0 g / cm³. 3 .

[0014] In some possible embodiments, the tap density of the cathode material is >1.5 g / cc.

[0015] In some possible embodiments, the loose packing density of the positive electrode material is >0.5 g / cm³. 3 .

[0016] In some possible embodiments, the positive electrode material has a discharge specific capacity of 2.8V to 4.35V at 0.1C >

[0017] 175mAh / g.

[0018] Secondly, embodiments of this application also provide a method for preparing a cathode material, comprising the following steps: mixing an oxide precursor with a lithium source and a dopant and sintering the mixture to obtain a cathode material matrix; and pulverizing the cathode material matrix and coating it with a coating agent to obtain the cathode material, wherein, in an image under a scanning electron microscope at 3k magnification, the percentage R of particles smaller than 1μm in the cathode material satisfies: 8% ≤ R ≤ 20%; and under 25MPa conditions, the electrode conductivity T of the cathode material satisfies: T > 0.025S / cm.

[0019] In some possible embodiments, in the step of atomizing and pyrolyzing the metal mixture solution to obtain the oxide precursor, the total metal concentration in the solution is controlled to be in the range of 2 mol / L to 8 mol / L.

[0020] In some possible embodiments, in the step of atomizing and pyrolyzing the metal mixture solution to obtain the oxide precursor, the feed flow rate is controlled to be 0.5 m³ / s. 3 / h~5m 3 / h.

[0021] In some possible embodiments, in the step of atomizing and pyrolyzing the metal mixture solution to obtain the oxide precursor, the atomizing airflow rate is controlled to be 50 m³ / h. 3 / h~300m 3 / h, atomization pressure is 100kPa~700kPa.

[0022] In some possible embodiments, in the step of atomizing and pyrolyzing the metal mixture solution to obtain the oxide precursor, the pyrolysis temperature is controlled to be 400°C to 1200°C.

[0023] In some possible embodiments, the sintering includes a first sintering stage, a second sintering stage, a third sintering stage, and a fourth sintering stage performed sequentially. The sintering temperature of the first sintering stage is 300℃ to 600℃, and the time is 3h to 5h; the sintering temperature of the second sintering stage is 700℃ to 1000℃, and the time is 4h to 12h; the sintering temperature of the third sintering stage is 500℃ to 700℃, and the time is 2h to 6h; and the sintering temperature of the fourth sintering stage is 700℃ to 1000℃, and the time is 1h to 3h.

[0024] In some possible embodiments, the dopant element M in the dopant is selected from at least one of Zr, Ti, Al, Mg and Y.

[0025] In some possible embodiments, the coating element N in the coating agent is selected from at least one of Zr, Ti, Al, Co, Mg, W, Ce, Y, K, and Na.

[0026] Thirdly, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes the positive electrode material as described above or a positive electrode material prepared by the method for preparing the positive electrode material as described above.

[0027] Fourthly, embodiments of this application provide a secondary battery, including the positive electrode material as described above or a positive electrode material prepared by the method described above.

[0028] The cathode material provided in this application has an electrode conductivity T of T > 0.025 S / cm at 25 MPa. This high electrode conductivity gives the cathode material excellent electrical conductivity, effectively reducing battery resistance and power consumption, and improving energy transfer efficiency. Furthermore, by controlling the proportion of microparticles in the cathode material to 8%–20%, the presence of an appropriate amount of microparticles allows the cathode material to simultaneously possess the advantages of high compaction density and high material activity. It also addresses the issue of an uncontrollable number of microparticles leading to a large number of active sites, reducing surface side reactions, decreasing gas production, and improving battery safety and cycle performance. In addition, by controlling the proportion of microparticles smaller than 1 μm in the cathode material within the aforementioned range, these microparticles can also act as a buffer in the cathode material, dispersing stress and suppressing material volume changes caused by high conductivity during charge and discharge, thereby increasing the structural stability and cycle performance of the cathode material. Attached Figure Description

[0029] Figure 1 A cross-sectional schematic diagram of a lithium-ion battery using the cathode material of this application embodiment during charging.

[0030] Figure 2 This is a cross-sectional schematic diagram of a lithium-ion battery using the cathode material of this application during discharge.

[0031] Figure 3 This is a scanning electron microscope (SEM) image of the oxide precursor of Example 1 of this application.

[0032] Figure 4 This is a scanning electron microscope (SEM) image of the cathode material of Example 1 of this application.

[0033] Figure 5 This is a particle size distribution curve for Example 1 of this application. Detailed Implementation

[0034] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.

[0035] This application provides a positive electrode material in which, in an image under a scanning electron microscope at 3k magnification, the proportion R of particles smaller than 1μm in the positive electrode material satisfies: 8% ≤ R ≤ 20%; and under 25MPa conditions, the electrode conductivity T of the positive electrode material satisfies: T > 0.025S / cm.

[0036] By controlling the electrode conductivity T of the cathode material at 25 MPa to satisfy T > 0.025 S / cm, the cathode material exhibits excellent conductivity, effectively reducing the resistance and power consumption of the prepared battery and improving energy transfer efficiency. However, a higher electrode conductivity in a cathode material means a greater number of active sites within the material, which can lead to numerous side reactions. Therefore, this application's embodiments limit the proportion R of microparticles in the cathode material to 8%-20%, enabling the cathode material to simultaneously possess the advantages of high compaction density and high material activity. This also solves the problems of uncontrollable microparticle numbers leading to increased surface side reactions and gas production in existing cathode materials, thus improving safety and cycle performance. Furthermore, through extensive experimental research, the inventors discovered that by controlling the proportion of microparticles smaller than 1 μm in the cathode material within the aforementioned range, these microparticles can also act as buffers in the cathode material, dispersing stress and suppressing material volume changes caused by high conductivity during charging and discharging, thereby increasing the structural stability and cycle performance of the cathode material.

[0037] For example, the percentage of microparticles smaller than 1 μm in the cathode material can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any value within the range of any two of the above values. Further, the percentage of microparticles smaller than 1 μm in the cathode material is 12% to 20%. Appropriately increasing the microparticle content in the cathode material can promote microparticle dispersion stress and reduce localized stress concentration experienced by large particles during volume changes.

[0038] In some embodiments, under a scanning electron microscope (SEM) at 3k magnification, the cathode material has a first region and a second region. The first region has a microparticle quantity ratio of R1, and the second region has a microparticle quantity ratio of R2, wherein |R1-R2|≤9% and / or 0.5≤R1 / R2≤2. The similar microparticle quantity ratios in the first and second regions indicate that the microparticles are more uniformly dispersed in the cathode material, which is beneficial to further promote microparticle dispersion stress, reduce local stress concentration of large particles during volume changes, thereby increasing the structural stability of the cathode material and improving its cycle performance.

[0039] In some embodiments, the particle size distribution curve of the cathode material exhibits an asymmetry on both sides of the peak, with the area to the left of the peak being larger than the area to the right. This indicates that the number of particles to the left of the peak is greater than the number of particles to the right. Specifically, particles with a diameter less than 2 μm are defined as small particles, including the aforementioned microparticles, while particles with a diameter greater than 2 μm are defined as large particles. The wider distribution of small and large particles further promotes the dispersion of microparticle stress and reduces local stress concentration experienced by large particles during volume changes, thereby increasing the structural stability of the cathode material and improving its cycle performance.

[0040] In some embodiments, the average particle size of a single particle in the cathode material is 1 μm to 4 μm. The particle is a primary particle. The presence of a certain proportion of microparticles in the cathode material can reduce the average particle size, ensuring that the average particle size of a single particle is within the above range. This is beneficial for the transport of lithium ions during charging and discharging, improving ionic conductivity and thus reducing impedance. At the same time, particles within the above particle size range can control the specific surface area within a suitable range, improving material activity while reducing side reactions between the material and the electrolyte.

[0041] In some embodiments, the median particle size D50 of the cathode material is 2.5 μm to 5 μm, where D50 represents the particle size of the material when the cumulative particle size distribution percentage reaches 50% by volume. This application controls the median particle size of the cathode material within the above-mentioned appropriate range, resulting in moderate particle size. This facilitates controlling the specific surface area of ​​the particles within a suitable range, improving material activity while reducing side reactions between the particles and the electrolyte, thereby improving the cycle life of the battery. Furthermore, particles within the above-mentioned size range also help reduce internal stress within the particles, lowering the risk of electrochemical polarization of lithium ions inside and outside the particles, thereby increasing the capacity of the cathode material. Exemplarily, the median particle size D50 of the cathode material can be 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or any value within the range of any two of the above values.

[0042] In some embodiments, the particle size D10 of the cathode material is 1 μm to 2.5 μm, and the particle size D90 is 6 μm to 10 μm, and 1.0 ≤ (D90 - D10) / D50 ≤ 1.5. D10 represents the particle size corresponding to a cumulative particle size distribution reaching 10%, meaning that 10% of the particles in the particle group are smaller than this size. Typically, D10 is used to describe the finer particles in the particle group. D90 represents the particle size corresponding to a cumulative particle size distribution reaching 90%, meaning that 90% of the particles in the particle group are smaller than this size. D90 is typically used to describe the coarser particles in the particle group. (D90-D10) / D50 represents the width of the particle size distribution in the cathode material. This application controls the particle size distribution to be 1.0 ≤ (D90-D10) / D50 ≤ 1.5, resulting in a wider particle size distribution in the cathode material. This improves the compaction density and activity of the material while reducing side reactions between the material and the electrolyte, thus ensuring that the cathode material possesses high compaction density, high activity, low impedance, and excellent cycle performance. For example, (D90-D10) / D50 can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or any value within the range of any two of the above values. D10 can be 1.0, 1.3, 1.5, 1.6, 1.8, 1.9, 2.0, 2.2, 2.3, 2.5, or any value within the range of any two of the above values. D90 can be 6.0, 6.3, 6.5, 6.8, 6.9, 7.0, 7.2, 7.5, 8.1, 8.5, 9.2, 10µm or any value within the range of any two of the above values.

[0043] In some embodiments, the cathode material is a single-crystal cathode material, and the average particle size of a single particle in the cathode material is 1 μm to 4 μm. Exemplarily, the average particle size of a single particle can be 1 μm, 2 μm, 3 μm, 4 μm, or any value within the range of any two of the above values.

[0044] In some embodiments, the specific surface area of ​​the cathode material is 0.5 m². 2 / g~1.4m 2 / g, the interparticle spaces in the cathode material contain a certain number of microparticles, which can control the specific surface area within the aforementioned suitable range. This is beneficial for improving the activity of the cathode material, while reducing side reactions between the cathode material and the electrolyte, thus improving the long-term cycle performance of the cathode material. For example, the specific surface area of ​​the cathode material can be 0.5m². 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g or any value within the range of any two of the above values.

[0045] In some embodiments, the compaction density of the cathode material is >3.0 g / cm³. 3 By controlling the proportion of microparticles in the cathode material to be 8% to 20%, it can be ensured that when external force is applied to the cathode material during the electrode rolling process, the microparticles fill the gaps between large particles, thereby improving the uniform distribution of microparticles in the cathode material, promoting the dispersion of microparticle stress, reducing the local stress concentration of large particles during volume changes, thus increasing the structural stability of the cathode material and improving its cycle performance.

[0046] In some embodiments, the tap density of the cathode material is >1.5 g / cm³. 3 By controlling the proportion of microparticles in the cathode material to 8% to 20%, the tap density of the cathode material can be effectively improved, which is beneficial to improving the battery capacity and cycle performance.

[0047] In some embodiments, the loose packing density of the positive electrode material is >0.5 g / cm³. 3 By controlling the proportion of microparticles in the cathode material to 8%–20%, the loose packing density of the material can be controlled to be >0.5 g / cm³. 3 A suitable packing density can effectively increase the battery's capacity density while reducing the possibility of active material stripping during charging and discharging, which is beneficial for improving battery capacity and cycle life.

[0048] In some embodiments, the general formula of the positive electrode material is as follows: Li a Ni b Co c Q d M (1-b-c-d) N e O2, wherein the element Q is selected from at least one of Mn and Al, the element M is selected from at least one of Zr, Ti, Al, Mg and Y, the element N is selected from at least one of Zr, Ti, Al, Co, Mg, W, Ce, Y, K and Na, and 0.95≤a≤1.2, 0<b≤1, 0≤c≤1, 0<d≤1, b+c+d+e≤1, 0≤e<1.

[0049] The cathode material provided in this application has an electrode conductivity T of T > 0.025 S / cm at 25 MPa. This high electrode conductivity gives the cathode material excellent electrical conductivity, effectively reducing the resistance and power consumption of the prepared battery and improving energy transfer efficiency. However, a higher electrode conductivity means a greater number of active sites within the material, which can lead to numerous side reactions. Therefore, this application limits the proportion R of microparticles in the cathode material to 8%-20%, enabling the cathode material to simultaneously possess the advantages of high compaction density and high material activity. This also solves the problems of uncontrollable microparticle numbers leading to increased surface side reactions and gas production, thus improving safety and cycle performance. Furthermore, by controlling the proportion of microparticles smaller than 1 μm within the above range, these microparticles can also act as buffers in the cathode material, dispersing stress and suppressing material volume changes caused by high conductivity during charging and discharging, thereby increasing the structural stability and cycle performance of the cathode material.

[0050] It is important to note that the difference between single-crystal cathode materials and polycrystalline cathode materials (i.e., polycrystalline secondary particles) lies in the fact that the smallest particles in polycrystalline secondary particles are formed by the agglomeration of nanoscale primary particles. In contrast, the smallest particles in single-crystal cathode materials are typically micrometer-sized single primary particles. Generally, in addition to EBSD testing, scanning electron microscopy (SEM) and other characterization methods can be used to determine whether the obtained cathode product is a single-crystal material. For example, for single-crystal cathode materials, SEM can characterize the morphology of single-crystal particles, showing that they are generally regular or irregular spherical in shape, with no significant particle agglomeration. EBSD can also characterize the orientation of single-crystal cathode materials. EBSD observation shows that at least one grain has the same color, indicating that at least one grain has the same orientation; grains with the same orientation are single crystals. It is important to clarify that the "single-crystal cathode material" known to those skilled in the art is not a "single crystal" in the strict crystallographic sense. In crystallography, an ideal single crystal refers to a crystal with completely identical arrangement and orientation. However, due to limitations such as impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in the laboratory. Therefore, the single-crystal cathode materials known in the art are actually more "single-crystal-like" cathode materials, which only differ from polycrystalline materials composed of numerous small primary particles in size, exhibiting a large particle size similar to single crystals.

[0051] Understandably, a single grain in this application can be a single particle composed of a primary particle. The aforementioned single-crystal cathode material may also contain a small number of "quasi-secondary particles" formed by the adhesion of several single particles. "Primary particle" refers to the smallest particle unit identified when observing cathode active materials using a scanning electron microscope. "Secondary particle" refers to a secondary structure formed by the aggregation of multiple primary particles, exhibiting a relatively rounded spherical morphology. "Quasi-secondary particles" are formed by the adhesion of several single particles. Typically, the particle size of a single particle in these quasi-secondary particles is between 1 μm and 5 μm, and generally, the roundness of "quasi-secondary particles" is lower than that of conventional "secondary particles."

[0052] It should be further clarified that the "single crystal" in "single crystal cathode material" as known to those skilled in the art is not a "single crystal" in the strict sense. In crystallography, an ideal single crystal refers to a crystal with completely identical arrangement and orientation. However, due to limitations caused by impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in a laboratory. Therefore, the single crystal cathode materials known in the art are actually more accurately described as "single crystal-like morphology" cathode materials, which differ from polycrystalline materials composed of numerous small primary particles only in size due to their large particle size resembling single crystals.

[0053] This application also provides a method for preparing the aforementioned cathode material, specifically including the following steps:

[0054] Step S1: The metal mixed solution is atomized and pyrolyzed to obtain the oxide precursor.

[0055] Specifically, solutions of nickel, cobalt, and manganese or aluminum sources are mixed, and the mixture is thermally decomposed after atomization to obtain an oxide precursor.

[0056] In some embodiments, the nickel source, cobalt source, and manganese source or aluminum source can be sulfate, hydrochloride, nitrate, acetate solution, etc. of the corresponding metal element.

[0057] In some embodiments, the total metal concentration in the aforementioned mixed solution is controlled to be between 2 mol / L and 8 mol / L. By controlling the total metal concentration within this range, the particle size of the primary particles of the oxide precursor can be controlled, resulting in a wider particle size distribution of the primary precursor particles, which is beneficial for the formation of microparticles in the cathode material. Exemplarily, the total metal concentration in the solution can be 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, or any value within a range of any two of the above values.

[0058] In some embodiments, the feed flow rate is 0.5 m³ / s. 3 / h~5m 3By controlling the feed flow rate within the aforementioned range, the growth rate of the precursor particles can be effectively controlled, resulting in primary particles of suitable size. This reduces the activity of the precursor particles and promotes the formation of microparticles in the cathode material. For example, the feed flow rate can be 0.5 m³ / h. 3 / h、1m 3 / h, 15m 3 / h、2m 3 / h, 2.5m 3 / h、3m 3 / h, 35m 3 / h、4m 3 / h, 4.5m 3 / h、5m 3 / h or any value within the range of any two of the above values.

[0059] In some embodiments, during spray pyrolysis, the atomizing airflow rate is controlled to be 50 m³ / h. 3 / h~300m 3 The atomization pressure can range from 100 kPa to 700 kPa. Since the size of the precursor particles directly affects the subsequent reaction activity with the lithium source—larger particles result in weaker activity—controlling the atomization flow rate and pressure allows for the control of atomization intensity. This enables the various components in the mixture to fully decompose and react, controlling the primary particle formation rate of the precursor and ensuring the primary particle size remains within a suitable range. This reduces the subsequent reaction activity between the particles and the lithium source, promoting the formation of microparticles in the cathode material. Furthermore, the atomization flow rate can be 100 m³ / h. 3 / h~200m 3 / h, for example, the atomizing airflow rate can be 50m³ / h. 3 / h、80m 3 / h, 100m 3 / h, 120m 3 / h, 150m 3 / h, 180m 3 / h、200m 3 / h、230m 3 / h、270m 3 / h, 300m 3 / h or any value within the range of any two of the above values. Further, the atomizing pressure can be 100kPa to 400kPa. For example, the atomizing pressure can be 100kPa, 200kPa, 300kPa, 400kPa, 500kPa, 600kPa, 700kPa or any value within the range of any two of the above values.

[0060] In some embodiments, the nozzle diameter can be from 0.1 mm to 20 mm. By controlling the nozzle diameter, the formation rate of the precursor and the particle size of the primary particles can also be adjusted. For example, the nozzle diameter can be 0.1 mm, 1 mm, 3 mm, 5 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, or any value within the range of any two of the above values.

[0061] In some embodiments, the pyrolysis temperature is controlled to be between 400°C and 1200°C. Since the uncontrollable presence of microparticles in the cathode material leads to an increase in surface side reactions, this application, by controlling the pyrolysis temperature within the above range, can appropriately suppress the increase in the particle size of the precursor primary particles, thereby enhancing the activity of the primary particles. When reacting with lithium salts, larger particles are formed, thus inhibiting the formation of microparticles to a certain extent. This achieves the goal of controlling the proportion of microparticles in the cathode material, realizing controllable microparticle numbers, improving the activity of the cathode material while reducing side reactions.

[0062] In some embodiments, during the pulverization process of the oxide precursor, by controlling the frequency of the classifier in the airflow pulverization process to 30Hz to 50Hz and the air pressure to 300kPa to 500kPa, the size of the primary particles of the precursor can be further appropriately reduced to increase the activity of the primary particles. When reacting with lithium salt, the formation of microparticles can be further suppressed, and the proportion of microparticles can be controlled within a suitable range.

[0063] Step S2: The oxide precursor is mixed with the lithium source and dopant and sintered (defined here as a single sintering) to obtain the cathode material matrix.

[0064] The first sintering process includes a first sintering stage, a second sintering stage, a third sintering stage, and a fourth sintering stage performed sequentially.

[0065] In some embodiments, the temperature T1 of the first sintering stage is 300°C to 600°C, and the time is 3 hours to 5 hours. Heating the material to a lower temperature first allows the lithium salt to melt fully and the dopant to diffuse uniformly in the mixture. Exemplarily, the temperature of the first sintering stage can be any value within the range of 300°C, 400°C, 500°C, 600°C, or any two of these values; the sintering time can be any value within the range of 3 hours, 4 hours, 5 hours, or any two of these values.

[0066] In some embodiments, the temperature T2 of the second sintering stage is 700℃~1000℃, and the time is 4h~12h. This stage is the main stage of crystal formation and crystal growth. By controlling the sintering temperature and sintering time within the above range, lithium ion intercalation can be achieved, crystal growth can be promoted, and the growth rate and size of the particles can be controlled. Exemplarily, the temperature of the second sintering stage can be any value within the range of any two values ​​of 700℃, 800℃, 900℃, 1000℃, or above; the sintering time can be any value within the range of any two values ​​of 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, or above.

[0067] In some embodiments, the sintering temperature T3 of the third sintering stage is 500℃~700℃, and the time is 2h~6h. After high-temperature sintering, by controlling the temperature and time of low-temperature sintering within the above range, lithium ions can be further intercalated, while particle size growth is suppressed, and particle size is controlled to form microparticles with the required proportion. In addition, low-temperature sintering also has an annealing effect, effectively eliminating lattice stress, repairing micrograin boundaries, and reducing particle defects. Exemplarily, the temperature of the third sintering stage can be any value within the range of any two values ​​of 500℃, 600℃, 700℃, or above; the sintering time can be any value within the range of any two values ​​of 2h, 3h, 4h, 5h, 6h, or above.

[0068] In some embodiments, the sintering temperature T4 of the fourth sintering stage is 700℃~1000℃, and the time is 1h~3h. If the low-temperature sintering results in an excessively thick layer, a short-term high-temperature re-sintering can further increase lithium-ion intercalation and improve the crystal structure. Exemplarily, the temperature of the fourth sintering stage can be any value within the range of 700℃, 800℃, 900℃, 1000℃, or any two of these values; the sintering time can be any value within the range of 1h, 2h, 3h, or any two of these values.

[0069] In some embodiments, the total sintering time can be 12 to 26 hours. By controlling the total sintering time, the particle size can be controlled, thereby controlling the proportion of microparticles formed to be 8% to 20%. Exemplarily, the total sintering time can be any value within the range of 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, or any two of the above values.

[0070] In some embodiments, the temperature is increased from room temperature to the first sintering stage at a heating rate of 20°C / min, then increased from the first sintering stage to the second sintering stage at a heating rate of 0.5–3°C / min, then decreased to the third sintering stage at a cooling rate of 0.5–3°C / min, then increased to the fourth sintering stage at a heating rate of 0.5–3°C / min, and finally decreased from the fourth sintering stage to room temperature at a cooling rate of 0.5–3°C / min to obtain the cathode material matrix.

[0071] In some embodiments, the sintering atmosphere may be an oxygen atmosphere or an air atmosphere.

[0072] In some embodiments, the dopant element M in the dopant is selected from at least one of Zr, Ti, Al, Mg, and Y. The dopant can be an oxide of the aforementioned dopant element or a lithium-ion conductor.

[0073] In some embodiments, the dopant content is 200 ppm to 10000 ppm. Exemplarily, the dopant content is any value within the range of 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, or any two of the above values.

[0074] In some embodiments, the lithium source may be LiOH·H2O, Li2CO3, or a mixture of LiOH·H2O and Li2CO3.

[0075] In some embodiments, the molar ratio of lithium content in the lithium salt to nickel, cobalt, and manganese content in the precursor is 0.98 to 1.10.

[0076] In some embodiments, the particle size D50 of the lithium salt can be 5 μm to 30 μm.

[0077] This process begins with low-temperature sintering to achieve full melting of the lithium salt and uniform diffusion of the dopant; followed by high-temperature sintering to achieve lithium ion intercalation and initial particle growth; then low-temperature sintering to further intercalate lithium ions, control particle size, promote microparticle formation, and anneal to repair micrograin boundaries; finally, short-time high-temperature sintering to further promote lithium ion intercalation and further regulate the proportion of microparticles.

[0078] Step S3: The positive electrode material matrix is ​​pulverized and coated with a coating agent to obtain the positive electrode material. In the image under a scanning electron microscope at 3k magnification, the proportion R of microparticles smaller than 1μm in the positive electrode material satisfies: 8 ≤ %R ≤ 20%; and under 25MPa conditions, the conductivity T of the electrode sheet prepared by the positive electrode material satisfies: T > 0.025S / cm.

[0079] Specifically, the cathode material matrix obtained from the previous sintering step is pulverized. By controlling the classifier frequency in the airflow pulverizer at 40Hz-60Hz and the air pressure at 400kPa-600kPa, the particle size distribution of the matrix is ​​adjusted. The pulverized cathode material matrix undergoes a first coating and a second sintering to obtain a primary coated material. After the primary coated material undergoes a second coating and a third sintering, it is sieved and ground to finally obtain the cathode material. Through two coating and sintering processes, the coating agent can be uniformly coated on the surface of the cathode material matrix for surface modification, thereby further improving the structural stability and electrochemical performance of the cathode material.

[0080] The coating element N in each coating agent can be selected from at least one of Zr, Ti, Al, Co, Mg, W, Ce, Y, K, Na, etc., wherein the coating agent can be an oxide of the coating element N or a lithium-ion conductor.

[0081] In some embodiments, the temperature of the secondary sintering can be 400–600°C, and the sintering time can be 6–12 h. The temperature of the tertiary sintering can be 400°C–600°C, and the sintering time can be 6 h–10 h. By controlling the temperature and time of the secondary and tertiary sintering, the coating agent can be uniformly coated on the surface of the substrate in stages, further optimizing the surface structure of the cathode material, thereby further improving the structural stability and conductivity of the cathode material. Exemplarily, the temperature of the secondary sintering can be any value within the range of any two of 400°C, 500°C, 600°C, or higher, and the sintering time can be any value within the range of any two of 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, or higher; the temperature of the tertiary sintering can be any value within the range of any two of 400°C, 500°C, 600°C, or higher, and the sintering time can be any value within the range of any two of 6 h, 7 h, 8 h, 9 h, 10 h, or higher.

[0082] In some embodiments, the content of the coating element can be from 200 ppm to 5000 ppm. Exemplarily, the content of the coating element can be any value within the range of 200 ppm, 500 ppm, 800 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, or any two of the above values.

[0083] Hydroxide precursors prepared by traditional co-precipitation methods suffer from low crystallinity, poor tolerance to large-radius element doping, and a tendency for high-valence elements to adhere to the material surface, thus inhibiting crystal growth into well-dispersed single-crystal particles. Therefore, the cathode material preparation method provided in this application employs spray pyrolysis technology to prepare an oxide precursor, while appropriately reducing the reactivity of the oxide precursor. Then, multi-temperature sintering is used to react the oxide precursor with lithium salt to prepare a cathode material containing an appropriate amount of microparticles.

[0084] First, unlike hydroxide precursors, oxide precursors possess a crystalline structure, belonging to a two-phase mixture of spinel and rock salt. Oxide precursors exhibit a wider diffusion width during sintering with lithium salts. This relatively wider particle size distribution facilitates the formation of a suitable proportion of microparticles. In other words, the wider particle size distribution of the prepared oxide precursor results in lower reactivity with lithium salts, leading to insufficient diffusion of crystal particles during single crystal growth. Insufficient single crystallization of some particles results in the formation of smaller microparticles. By controlling the width of the aforementioned oxide precursor particle size distribution, the proportion of microparticles formed during sintering can be controlled within a suitable range of 8% to 20%, thereby improving the material's compaction density and energy density. Furthermore, the particle size distribution of this cathode material exhibits good inheritance; the cathode material can effectively inherit the particle size distribution of the matrix, and the matrix can, to some extent, inherit the particle size distribution of the oxide precursor.

[0085] Secondly, an appropriate proportion of microparticles is conducive to a more complete combination of the material and the conductive agent, reducing the proportion of micropores in the material. At the same time, coating the matrix material with nitrogen can also effectively improve the conductivity of the active material, thereby enabling the cathode material to have a high electrode conductivity.

[0086] In addition, the preparation method of this application embodiment has the advantages of short reaction time, high efficiency, low processing cost, low raw material cost, less pollution, no wastewater generation, and high recycling rate, making it suitable for large-scale industrial production.

[0087] This application also provides a positive electrode sheet using the aforementioned positive electrode material, including a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes the aforementioned positive electrode material.

[0088] The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, the current collector formed by combining the aforementioned conductive foil and polymer substrate.

[0089] This application also provides a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, an electrode assembly, and an electrolyte / electrolyte. Both the electrode assembly and the electrolyte / electrolyte are located within the casing. The electrode assembly includes a separator, a negative electrode, and the aforementioned positive electrode, with the separator disposed between the positive and negative electrode.

[0090] In some embodiments, the outer casing can be a packaging bag sealed with an encapsulating film (such as an aluminum-plastic film), for example, the secondary battery is a pouch battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0091] In some embodiments, the electrode assembly may be a stacked structure, which is formed by alternating layers of a positive electrode, a separator, and a negative electrode. In other embodiments, the electrode assembly may also be a wound structure, which is formed by winding a positive electrode, a separator, and a negative electrode after they are stacked in sequence.

[0092] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a layer of negative electrode active material disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material can 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. Silicon-based materials can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more. The battery provided in this application embodiment has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., and there is no limitation here.

[0093] like Figure 1 and Figure 2 The figures shown are schematic diagrams illustrating the lithium-ion battery prepared using the cathode material provided in the embodiments of this application during the charging and discharging processes, specifically the lithium delithiation and lithium insertion. Figure 1 As shown, when a lithium-ion battery is charged, lithium ions are released from the positive electrode and embedded in the negative electrode; as... Figure 2 As shown, when a lithium-ion battery discharges, lithium ions are released from the negative electrode and inserted back into the positive electrode.

[0094] This application embodiment uses the aforementioned cathode material to prepare a secondary battery. By controlling the proportion of microparticles R in the cathode material to be 8%–20%, and ensuring that the electrode conductivity T at 25 MPa is greater than 0.025 S / cm, the cathode material simultaneously possesses high compaction density and high material activity, thus improving the capacity and activity of the secondary battery. Furthermore, by limiting the proportion of microparticles R in the cathode material to 8%–20%, the cathode material simultaneously possesses the advantages of high compaction density and high material activity, while also solving the problems of increased surface side reactions and gas production caused by uncontrollable microparticle numbers in existing cathode materials, thereby improving safety and cycle performance. In addition, by controlling the proportion of microparticles smaller than 1 μm in the cathode material within the aforementioned range, the microparticles can also act as a buffer in the cathode material, dispersing stress and suppressing material volume changes caused by high conductivity during charge and discharge, thereby increasing the structural stability and cycle performance of the cathode material. The secondary battery using the aforementioned cathode material has a discharge specific capacity of >175mAh / g at 0.1C (2.8V to 4.35V) and a cycle retention rate of >95% after 50 cycles of 0.5C charge-1C discharge.

[0095] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the present application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically mentioned are all conventional commercially available products or open-source materials.

[0096] Example 1:

[0097] Step 1: Prepare a mixed metal salt solution with a Ni:Co:Mn molar ratio of 50:20:30, controlling the total metal concentration in the solution to 2 mol / L and the feed flow rate to 1.2 m³ / L. 3 / h, control the atomizing airflow to 150m³ / h. 3 The atomizing air pressure was controlled at 300 kPa / h, a nozzle with a diameter of 10 mm was selected, and the pyrolysis temperature was controlled at 550℃. The precursor was calcined in an air atmosphere. The precursor was then subjected to air jet milling, with the classifier frequency controlled at 40 Hz and the air pressure controlled at 400 kPa during the milling process, yielding an oxide precursor with a particle size D50 = 4.1 μm. Its main elemental chemical composition can be represented as Ni. 0.50 Co 0.20 Mn 0.30 O 1.2 (The content of each element is within ±1%).

[0098] Step 2: Mix the oxide precursor prepared in Step 1 with LiOH·H2O at a molar ratio of 1:1.03 until homogeneous. The average particle size of LiOH·H2O is 13 μm. Based on the mass of the oxide precursor, add 1200 ppm of nano-sized ZrO2.

[0099] Step 3: Place the mixture from Step 2 in an atmosphere furnace. Under an oxygen atmosphere, ① raise the temperature from room temperature to the first sintering stage temperature (300℃) at a heating rate of 20℃ / min, and hold for 3 hours; ② raise the temperature from the first sintering stage to the second sintering stage temperature (800℃) at a heating rate of 3℃ / min, and hold for 5 hours; ③ lower the temperature from the second sintering stage to the third sintering stage temperature (600℃) at a cooling rate of 2℃ / min, and hold for 4 hours; ④ raise the temperature again from the third sintering stage to the fourth sintering stage temperature (960℃) at a heating rate of 3℃ / min, and hold for 3 hours; ⑤ lower the temperature from the fourth sintering stage to room temperature at a cooling rate of 3℃ / min. The oxygen flow rate is controlled at 0.14 m³ / min during the sintering process. 3 / min, furnace pressure 7Pa, to obtain positive electrode material matrix (LiNi 0.50 Co 0.20 Mn 0.30 O2).

[0100] Step 4: The positive electrode material matrix from Step 3 is coarsely crushed using a roller mill to obtain coarse particle samples with an average particle size of 10μm to 20μm. The coarse particle samples are then pulverized using an air jet mill to obtain a sample with a D50 of 4.3μm. The grinding air pressure during the air jet milling process is 600kPa, and the classifier frequency is 52Hz.

[0101] Step 5: Mix the sample from Step 4 with 1000 ppm of nano-sized Al2O3, and heat it to 450℃ at a rate of 4℃ / min under an oxygen atmosphere and hold for 6 hours to obtain the first coating material.

[0102] Step 6: Mix the primary coating material from Step 5 with 800 ppm NaOH and KOH until homogeneous, then heat to 400℃ at a rate of 4℃ / min and hold for 6 hours in an oxygen atmosphere to obtain the secondary coating material.

[0103] Step 7: The secondary coating material from step 6 is sieved and ground for 30 minutes to obtain the cathode material.

[0104] Example 2

[0105] The difference from Example 1 is that in step 1, the atomizing airflow rate is adjusted to 120m³ / h. 3 / h, the atomizing air pressure is adjusted to 250kPa. Other steps are basically the same as in Example 1, please refer to Example 1.

[0106] Example 3

[0107] The difference from Example 1 is that the pyrolysis temperature in step 1 is 500°C. The other steps are basically the same as in Example 1; please refer to Example 1.

[0108] Example 4

[0109] The difference from Example 1 is that in step 1, the frequency of the classifier during the pulverization process of the large-particle oxide precursor is adjusted to 45 Hz, resulting in a precursor with a particle size D50 = 3.5 μm. The other steps are basically the same as in Example 1; please refer to Example 1.

[0110] Example 5

[0111] The difference from Example 1 is as follows: In step 3, ① the temperature is increased from room temperature to the first sintering stage temperature of 300℃ at a heating rate of 20℃ / min, and held for 3 hours; ② the temperature is increased from the first sintering stage to the second sintering stage temperature of 800℃ at a heating rate of 3℃ / min, and held for 5 hours; ③ the temperature is decreased from the second sintering stage to the third sintering stage temperature of 600℃ at a cooling rate of 2℃ / min, and held for 4 hours; ④ the temperature is increased again from the third sintering stage to the fourth sintering stage temperature of 990℃ at a heating rate of 3℃ / min, and held for 3 hours; ⑤ the temperature is decreased from the fourth sintering stage to room temperature at a cooling rate of 3℃ / min.

[0112] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0113] Example 6

[0114] The difference from Example 1 is as follows: In step 3, ① the temperature is increased from room temperature to the first sintering stage temperature of 300℃ at a heating rate of 20℃ / min, and held for 3 hours; ② the temperature is increased from the first sintering stage to the second sintering stage temperature of 800℃ at a heating rate of 3℃ / min, and held for 5 hours; ③ the temperature is decreased from the second sintering stage to the third sintering stage temperature of 600℃ at a cooling rate of 2℃ / min, and held for 4 hours; ④ the temperature is increased again from the third sintering stage to the fourth sintering stage temperature of 930℃ at a heating rate of 3℃ / min, and held for 3 hours; ⑤ the temperature is decreased from the fourth sintering stage to room temperature at a cooling rate of 3℃ / min.

[0115] In step 7, the grinding time is 10 minutes.

[0116] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0117] Example 7

[0118] The difference from Example 1 is that in step 5, the coating agent is 1000 ppm WO3.

[0119] In step 6, the total coating amount of NaOH and KOH is increased to 1000 ppm.

[0120] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0121] Example 8

[0122] The difference from Example 1 is that in step 3, the lithium source is Li2CO3 and the sintering atmosphere is air.

[0123] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0124] Example 9

[0125] The difference from Example 1 is that in step S3, the lithium source is a mixture of Li2CO3:LiOH·H2O = 1:1, and the sintering atmosphere is air.

[0126] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0127] Example 10

[0128] The difference from Example 1 is that in step 3, the gas flow rate is increased to 0.18 m³ / s. 3 / min, furnace pressure is 10Pa.

[0129] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0130] Example 11

[0131] The difference from Example 8 is that in step 1, the molar ratio of Ni:Co:Mn is controlled to be 60:10:30, and the oxide precursor Ni is obtained by pyrolysis. 0.60 Co 0.10 Mn 0.30 O 1.2 In step 3, ④ the temperature is increased again to the fourth sintering stage temperature of 920℃ at a heating rate of 3℃ / min, and held for 3 hours. The resulting cathode material has an elemental composition of LiNi. 0.60 Co 0.10 Mn 0.30 O2.

[0132] The other steps are basically the same as in Example 8; please refer to Example 8.

[0133] Example 12

[0134] The difference from Example 8 is that the molar ratio of Ni:Co:Mn is controlled to be 80:10:10, and the oxide precursor Ni is obtained by pyrolysis. 0.80Co 0.10 Mn 0.10 O 1.2 In step 3, ④ the temperature is increased again to the fourth sintering stage temperature of 880℃ at a heating rate of 3℃ / min, and held for 3 hours. The resulting cathode material has an elemental composition of LiNi. 0.80 Co 0.10 Mn 0.10 O2.

[0135] The other steps are basically the same as in Example 8; please refer to Example 8.

[0136] Example 13

[0137] The difference from Example 8 is that the molar ratio of Ni:Co:Mn was controlled to be 82.5:6.5:11, and the oxide precursor Ni was obtained by pyrolysis. 0.825 Co 0.065 Mn 0.11 O 1.2 In step 3, step ④ involves raising the temperature again at a rate of 3℃ / min during the third sintering stage to the fourth sintering stage temperature of 870℃, and holding at this temperature for 3 hours. The resulting cathode material has the chemical formula LiNi. 0.825 Co 0.065 Mn 0.11 O2.

[0138] The other steps are basically the same as in Example 8; please refer to Example 8.

[0139] Example 14

[0140] The difference from Example 1 is that in step 2, the precursor used is the oxide precursor Ni prepared in step 1 of Example 1. 0.50 Co 0.20 Mn 0.30 O 1.2 With the hydroxide precursor Ni 0.50 Co 0.20 Mn 0.30 A mixture of (OH)₂ is prepared with an oxide precursor to hydroxide precursor in a molar ratio of 1:1. This hydroxide precursor is prepared using a traditional co-precipitation method, as follows: A salt solution (such as NiSO₄, CoSO₄, MnSO₄, etc.) and an alkaline solution (such as NaOH, NH₃, etc.) of a certain concentration are continuously added to a reactor at a specific flow rate. The reaction is carried out at an appropriate reaction temperature (40–60℃), stirring rate, and pH value (10–13) to generate a hydroxide precipitate. The generated precipitate is then washed, filtered, and dried to finally obtain the hydroxide precursor material.

[0141] Step 2 also includes the following steps: mixing the precursor mixture with LiOH·H2O at a molar ratio of 1:1.05, and adding ZrO2 at a mass of 1200 ppm relative to the precursor.

[0142] Step 3 further includes the following steps: Under an oxygen atmosphere, ① the temperature is increased from room temperature to the first sintering stage temperature (300℃) at a heating rate of 20℃ / min, and held for 3 hours; ② the temperature is increased from the first sintering stage to the second sintering stage temperature (800℃) at a heating rate of 3℃ / min, and held for 7 hours; ③ the temperature is decreased from the second sintering stage to the third sintering stage temperature (600℃) at a cooling rate of 2℃ / min, and held for 4 hours; ④ the temperature is increased again from the third sintering stage to the fourth sintering stage temperature (960℃) at a heating rate of 3℃ / min, and held for 3 hours; ⑤ the temperature is decreased from the fourth sintering stage to room temperature at a cooling rate of 3℃ / min. The oxygen flow rate is controlled at 0.20 m³ / min during the sintering process. 3 / min, furnace pressure of 10 Pa, to obtain the positive electrode material matrix (LiNi 0.50 Co 0.20 Mn 0.30 O2).

[0143] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0144] Example 15

[0145] The difference between this embodiment and Embodiment 12 is that a metal salt mixed solution is prepared with a Ni:Co:Al molar ratio of 80:10:10, resulting in a cathode material with an elemental composition of LiNi. 0.80 Co 0.10 Al 0.10 O2.

[0146] The other steps are basically the same as in Example 12. Please refer to Example 12.

[0147] Comparative Example 1

[0148] The difference from Example 4 is that in step 4, during the crushing process of the positive electrode material matrix, the grinding air pressure is 600 kPa and the classifying wheel frequency is 60 Hz.

[0149] The other steps are basically the same as in Example 4; please refer to Example 4.

[0150] Comparative Example 2

[0151] The difference from Example 1 is as follows: In step 3, ① the temperature is increased from room temperature to the first sintering stage temperature of 300℃ at a heating rate of 20℃ / min, and held for 3 hours; ② the temperature is increased from the first sintering stage to the second sintering stage temperature of 700℃ at a heating rate of 3℃ / min, and held for 5 hours; ③ the temperature is decreased from the second sintering stage to the third sintering stage temperature of 500℃ at a cooling rate of 2℃ / min, and held for 4 hours; ④ the temperature is increased again from the third sintering stage to the fourth sintering stage temperature of 820℃ at a heating rate of 3℃ / min, and held for 3 hours; ⑤ the temperature is decreased from the fourth sintering stage to room temperature at a cooling rate of 3℃ / min. The resulting cathode material, LiNi, is then formed. 0.5 Co 0.2 Mn 0.3 O2 exhibits a polycrystalline morphology.

[0152] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0153] Comparative Example 3

[0154] The difference from Example 1 is that in step 2, the coprecipitated hydroxide precursor from Example 14 is selected as the raw material, and its chemical formula is Ni. 0.50 Co 0.2 Mn 0.3 The cathode material formed by (OH)2 exhibits a single-crystal morphology.

[0155] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0156] The following methods were used to test the performance of the cathode materials obtained in Examples 1-15 and Comparative Examples 1-3.

[0157] 1. Characterization of the proportion of micro powder:

[0158] Sample preparation: The powder sample was picked up with tweezers or other tools, spread evenly on conductive adhesive, and flattened. It was then tested under an electron beam of 5kV / 10mA. When testing the cross-section sample, the material was coated onto aluminum foil using a conventional electrode preparation process, then cut using a focused ion beam (FIB), and subsequently tested under the same conditions as the powder sample using SEM.

[0159] Characterization: The size of single-crystal particles can be characterized by software identification of the particle size in scanning electron microscope (SEM) images. One image is taken at 3K magnification for each particle. The longest diameter of all particles in the image is measured, and the size of each individual particle is counted. The total number of individual particles is denoted as N, and the number of particles with a diameter less than 1 μm is denoted as n. R represents the percentage of microparticles, where R = n / N * 100%.

[0160] 2. Specific surface area characterization:

[0161] Equipment: Specific surface area and pore structure analyzer.

[0162] Method: Weigh the empty sample tube (m1); add 3g of sample into the sample tube through a long-necked funnel; degas under vacuum at 300℃ for 1h, cool, and weigh the sample tube (m2); the sample mass is m = m2 - m1. Place the sample tube in liquid nitrogen and measure the nitrogen adsorption capacity V of the sample under a series of relative pressures P / P0 to obtain adsorption isotherms. P / P0 is set to 0.05 / 0.1 / 0.15 / 0.20 / 0.25 / 0.30. Fit the isothermal adsorption curve, calculate the monolayer saturated adsorption capacity Vm based on the slope and intercept, and then calculate the specific surface area based on Vm.

[0163] 3. Characterization of compacted density:

[0164] Using a Carver 4350 tester from the United States, a 1g sample was placed in a mold and pressed with a pressure of 3T for 30s. After pressing, the height was measured and the compaction density was calculated.

[0165] 4. Loose packing density characterization:

[0166] Equipment: Loose packing density meter

[0167] Method: Take an appropriate amount of sample and let it flow naturally into the cloth box, passing alternately through four glass plates with an inclination angle of 25° and a square funnel in the cloth box, and then into a cylindrical cup with a known volume (25ml). Finally, weigh the mass of the powder in the cylindrical cup.

[0168] 5. Tap density test:

[0169] The American CANTA DAT-4-220 tap density meter was used.

[0170] The testing procedure includes: cleaning the graduated cylinder and weighing it to m1; adding the sample into the graduated cylinder, ensuring the sample surface is as horizontal as possible, and wiping the surrounding area with a paper towel; weighing the total mass of the sample and graduated cylinder to m2; placing the graduated cylinder on the vibration stage and securing it with three symmetrical fixed feet; turning on the instrument and activating the vibration switch; the instrument will automatically stop after vibrating a specified number of times; removing the graduated cylinder and reading the sample volume. If the sample surface is horizontal after vibration, read the volume directly; if it is oblique, take the average of the readings at the highest and lowest points, V.

[0171] Calculation formula: Tap density = (m2-m1) / V.

[0172] 6. SEM and EDS characterization:

[0173] Equipment: Scanning electron microscope, energy scattering spectroscopy instrument.

[0174] SEM Testing Method: When testing powder samples, use tweezers or similar tools to pick up the powder sample, spread it evenly on conductive adhesive, and flatten it to create the test sample. Testing is then performed under an electron beam of 5kV / 10mA. In the particle count percentage test, a region of the test sample is randomly selected as the first region, and an image of this first region is acquired under a 3K magnification electron microscope. The percentage of particles smaller than 1μm in the SEM image of the first region is calculated as R1. Then, another region of the test sample is randomly selected as the second region, and an image of this second region is acquired under a 3K magnification electron microscope. The percentage of particles smaller than 1μm in the SEM image of the second region is calculated as R2. It is understood that there can be multiple first and second regions. The percentage of particles smaller than 1μm, R, is the average percentage of particles smaller than 1μm in n randomly selected regions of the sample, where n≥10.

[0175] EDS testing method: Adjust the electron beam voltage of the SEM to above 15kV, and then use EDS for selected area testing. The selected area is the center of each single crystal particle. When calculating the average Ni / Mn ratio, select 10 particles with a longest diameter less than 1.5μm and 10 particles with a longest diameter greater than 2.5μm, and perform EDS testing on each. From the obtained 10 Ni / Mn ratio values, remove the maximum and minimum values, and then calculate the average of the remaining 8 values.

[0176] 7. Particle size characterization:

[0177] Equipment: Wet particle size analyzer.

[0178] Method: Before testing, observe the laser intensity. If it is below 70%, notify the testing department to clean the lens and inlet / outlet water hoses. After starting the background measurement, perform external ultrasonication on the sample (using the instrument's automatic light and background measurement time for external ultrasonication can reduce the probability of sample contamination from prolonged storage). Perform external ultrasonication for 30 seconds while stirring back and forth. Before adding the sample, add 3 drops of sodium hexametaphosphate to the sample cell, stir, and pour the entire sample into the sample cell at once. After all the sample has been poured in, wait 10 seconds and then click "Start" to begin the sample test. The laser shading should be maintained between 7% and 12%.

[0179] 8. Battery electrode fabrication and conductivity characterization:

[0180] a. Battery electrode fabrication

[0181] The obtained positive electrode material was mixed with conductive carbon black and binder PVDF (polyvinylidene fluoride) in a mass ratio of 80:10:10. NMP (N-methylpyrrolidone) was added to form a uniform slurry, which was then coated onto copper foil, dried in an oven, and rolled under a pressure of 5 MPa to form a circular electrode sheet with a diameter of 14 mm.

[0182] b. Conductivity characterization:

[0183] Equipment: Electrode resistivity meter.

[0184] Method: The Kelvin four-line method was used for testing.

[0185] ① Set the test parameters as follows: experimental area = 153.94 mm 2 The pressure before the electrode roll is 5MPa, the pressure after the electrode roll is 25MPa, and the holding time is 15s.

[0186] ② Data recording: The resistivity data COV% collected in parallel should be less than 5%. Otherwise, the electrode needs to be prepared again for retesting until the requirements are met.

[0187] ③ The measured resistivity is denoted as ρ, and the conductivity σ is the reciprocal of the resistivity, σ = 1 / ρ.

[0188] 9. Battery manufacturing and performance testing

[0189] a. Sample preparation for electrochemical performance testing:

[0190] Button battery making:

[0191] ① Ingredients: NCM:SP:5% PVDF adhesive = 93:5:2 = 9.3g:0.5g:4.0g, NMP = 9g, stir at high speed to disperse evenly.

[0192] ② Coating and drying: Coat the slurry evenly on a 20μm thick aluminum foil using a 210µm coater, setting the coating length to the maximum length of the coater. Cut off the second half of the electrode and place it in a 100℃ forced-air drying oven to dry for more than 1.5 hours.

[0193] ③ Rolling, punching and drying:

[0194] During the rolling process, the roller press is adjusted to a single roll gap and rolled 3 times. After punching holes with a 14mm punching machine and weighing, the product is placed in a vacuum drying oven and vacuum dried at 85℃ for more than 8 hours.

[0195] ④ Button cell (LIR2016) assembly:

[0196] Positive electrode shell - 2 drops of electrolyte - Positive electrode plate (14mm) - 3 drops of electrolyte - 20μm separator - 2 drops of electrolyte - Lithium foil - 150μm nickel foam - negative electrode shell (dried at 50℃), the battery is assembled and sealed, and then taken out of the glove box for testing.

[0197] b. Button test:

[0198] After standing for 12 hours, perform battery testing according to the following procedure:

[0199] 0.1C charge and 0.1C discharge for 2 weeks (first effect), constant voltage cutoff current 0.005C;

[0200] Charge at 0.5C and discharge at 0.5C for one cycle (rate), constant voltage cutoff current 0.05C;

[0201] Charge at 0.5C, discharge at 1C for 1 cycle (rate), constant voltage cutoff current 0.05C;

[0202] Charge at 0.5C, discharge at 2C for 1 cycle (rate), constant voltage cutoff current 0.05C;

[0203] 0.5C charge 1C discharge 50 cycles, constant voltage cutoff current 0.05C.

[0204] The test results of the cathode materials of Examples 1-15 and Comparative Examples 1-3 are shown in Tables 1 and 2 below.

[0205] Table 1

[0206]

[0207] Table 2

[0208] index R R1 R2 |R1-R2| R1 / R2 unit ％ ％ ％ ％ / Example 1 17.39 18.21 15.36 2.85 1.19 Example 2 19.36 16.87 19.24 2.37 0.88 Example 3 13.19 11.81 15.32 3.51 0.77 Example 4 14.88 14.11 14.23 0.12 0.99 Example 5 19.58 19.44 16.23 3.21 1.20 Example 6 11.17 8.12 13.54 5.42 0.60 Example 7 16.47 11.16 17.91 6.75 0.62 Example 8 8.95 10.43 8.61 1.82 1.21 Example 9 10.22 13.44 9.72 3.72 1.38 Example 10 9.43 8.43 10.76 2.33 0.78 Example 11 16.57 18.24 15.97 2.27 1.14 Example 12 14.28 17.21 8.38 8.93 2.07 Example 13 10.57 16.61 9.59 7.02 1.73 Example 14 18.25 10 19.32 9.32 0.52 Example 15 12.41 15.36 12.01 3.35 1.28 Comparative Example 1 23.48 27.21 20.1 7.11 1.35 Comparative Example 2 5.20 4.99 7.83 2.84 0.64 Comparative Example 3 6.61 5.12 10.63 5.51 0.48

[0209] like Figure 3 The image shown is a SEM image of the oxide precursor prepared in Example 1. Figure 3 It can be seen that the oxide precursor particles have a certain crystal structure, and the particle size is relatively large and the dispersion is uniform.

[0210] like Figure 4 The image shown is a SEM image of the cathode material prepared in Example 1. Figure 4 It can be seen that Example 1 can form well-dispersed single crystal particles, and the gaps between the large particles are uniformly dispersed with small microparticles. Moreover, microparticles are present in different regions of the SEM image, and the proportion of microparticles in different regions is similar. In addition, the proportion of small particles with a diameter of less than 2 micrometers is relatively large.

[0211] Further integration Figure 5 As shown, this is the particle size distribution curve of the cathode material in Example 1. Figure 5 It can be seen that the peak (approximately 2 μm) of the particle size distribution curve of the cathode material in Example 1 is asymmetrical, with the area to the left of the peak being larger than the area to the right of the peak. This indicates that there are more particles to the left of the peak than to the right. Specifically, the proportion of small particles (including microparticles with a diameter of less than 1 μm) is greater than that of large particles with a diameter of more than 2 μm. The wider distribution of large and small particles is beneficial for further improving the compaction density and conductivity of the cathode material, while reducing impedance.

[0212] As can be seen from Tables 1 and 2, the proportion of microparticles with a particle size of less than 1 μm in the cathode materials prepared in Examples 1-15 is in the range of 8% to 20%. An appropriate amount of microparticles is beneficial to improving the compaction density of the cathode materials. The compaction density is greater than 3 g / cm3, which enables the prepared batteries to obtain higher energy density. The discharge specific capacity at 0.1C is greater than 175 mAh / g at 2.8V to 4.35V. The discharge specific capacity of the battery prepared from the cathode material of Example 13 is as high as 206.6 mAh / g. Secondly, the presence of microparticles reduces the average particle size, which helps shorten the lithium-ion transport path during charging and discharging, improves charge transfer efficiency, and increases electrode conductivity. The electrode conductivity T at 25 MPa is greater than 0.025 S / cm, with the cathode material in Example 5 exhibiting a high electrode conductivity of 0.0796 S / cm. This high conductivity results in excellent electrical conductivity, effectively reducing the resistance and power consumption of the prepared battery and improving energy transfer efficiency. Simultaneously, higher conductivity in cathode materials means a greater number of active sites within the material. Excessive active sites can lead to numerous side reactions. Therefore, Examples 1-15 limit the proportion of microparticles R to 8%-20%, enabling the cathode material to simultaneously possess the advantages of high compaction density and high material activity. This also solves the problems of uncontrollable microparticle numbers leading to increased surface side reactions and gas production in existing cathode materials, thus improving safety and cycle performance. Furthermore, the appropriate amount of microparticles dispersed in the gaps between large particles provides good support, reducing the risk of particle breakage during electrode rolling and thus improving battery cycle performance. On the other hand, microparticles can also act as a buffer in the cathode material, dispersing stress and suppressing volume changes caused by high conductivity during charge and discharge, thereby increasing the structural stability and cycle performance of the cathode material. Batteries prepared from the cathode materials in Examples 1-15 all exhibit good cycle performance, with a 50-cycle retention rate greater than 95%. In Examples 1-15, by changing different process parameters, the proportion of microparticles in the cathode material can be controlled, thereby optimizing the electrode conductivity and the capacity and cycle performance of the prepared batteries.

[0213] Compared to Example 1, Example 2 reduced the atomization intensity, which increased the particle size of the primary particles of the oxide precursor, weakened the reactivity, and widened the distribution of single crystal particles. This increased the proportion of microparticles in the cathode material, improved the compaction density of the powder, increased the discharge specific capacity of the battery to 177.4 mAh / g, improved the initial coulombic efficiency to 87.43%, and increased the electrode conductivity to 0.0621 S / cm.

[0214] Compared to Example 1, Example 3 lowers the pyrolysis temperature, which can reduce the primary particle size of the generated oxide precursor, increase the reactivity, and facilitate the growth of single crystal particles. This reduces the proportion of microparticles, lowers the compaction density of the powder, and also decreases the electrode conductivity.

[0215] Compared to Example 1, Example 4 increased the air crushing intensity during the precursor crushing process, which reduced the D50 of the oxide precursor and enhanced its reactivity. This was beneficial for the growth of single-crystal particles in the cathode material, and the proportion of microparticles decreased. Consequently, the compaction density of the powder and the conductivity of the electrode decreased accordingly.

[0216] Compared to Example 1, Example 5 increased the sintering temperature of the fourth sintering stage (high-temperature sintering stage), increased the primary particle size of the cathode material, and increased the microparticle content after matrix breakage, which can significantly improve the electrode conductivity and battery capacity and efficiency.

[0217] Compared to Example 1, in Example 6, the sintering temperature of the fourth sintering stage (high-temperature sintering stage) is reduced, the primary particle size of the cathode material is reduced, and the content of microparticles after crushing is reduced; in addition, the grinding time is reduced, the proportion of large particles increases, the proportion of microparticles decreases, and the conductivity decreases.

[0218] Compared to Example 1, in Example 7, Al2O3 is replaced with 1000ppm WO3, and the coating amounts of NaOH and KOH are increased to 1000ppm. The coating material is more active and has a higher mass of active material, which is beneficial to improving the conductivity of the electrode.

[0219] Compared to Example 1, Examples 8 and 9 changed the lithium source and sintering atmosphere in the first sintering process, using air atmosphere and lithium carbonate, which is conducive to the growth of single crystal particles of cathode material, reducing the proportion of microparticles. The more lithium carbonate, the lower the microparticle content.

[0220] Compared to Example 1, Example 10 increased the gas flow rate and furnace pressure during the first sintering process, which increased the contact between the material and oxygen during the thermal reaction, which helped to grow large single crystal materials and reduced the proportion of microparticles.

[0221] Compared to Example 8, Examples 11, 12, 13, and 15 adjusted the proportion of each metal element in the oxide precursor, and also obtained cathode materials with a microparticle content in the range of 8% to 20%. The electrode conductivity T at 25 MPa is greater than 0.033 S / cm. At the same time, with the increase of nickel ions, the discharge specific capacity of the battery increases, and is significantly higher than that of 5-series ternary cathode materials.

[0222] Compared to Example 1, Example 14 uses a mixture of oxide precursor and hydroxide precursor, which results in a wider diffusion width during the lithium salt sintering reaction and a significant increase in the proportion of microparticles. At the same time, by extending the holding time in the first sintering process and increasing the oxygen flow rate and furnace pressure, the proportion of microparticles can be controlled within the range of 8% to 20%, thereby optimizing the electrode conductivity and first-time efficiency of the cathode material.

[0223] Compared to Example 1, the value of R1 / R2 in Example 12 is larger, indicating that the uniformity of particle distribution below 1 μm in Example 12 is weaker than that in Example 1, resulting in a decrease in the first-efficiency and cycle performance of the cathode material.

[0224] Compared to Example 1, the value of |R1-R2| is larger in Example 14, indicating that the uniformity of particle distribution below 1μm in Example 14 is weaker than that in Example 1, resulting in a decrease in the cycle performance of the cathode material.

[0225] In Comparative Examples 1-3, the proportion of microparticles in the cathode materials did not fall within the range of 8% to 20%. The low number of microparticles resulted in a longer lithium-ion transport path during charging and discharging, reducing charge transfer efficiency and leading to lower electrode conductivity. Specifically, in Comparative Example 1, the grinding pressure and classifier wheel frequency were increased during the cathode material matrix crushing process, exacerbating particle crushing and increasing the microparticle proportion to over 20%. This increased microparticle count resulted in an electrode conductivity of only 0.0212 S / cm, and the large number of microparticles also intensified side reactions, reducing the cycle performance of the prepared battery. Comparative Example 2, with its lower sintering temperature, formed polycrystalline particles instead of a single-crystal cathode material. The polycrystalline material had fewer microparticles, lower compaction, and insufficient cathode particle growth, impacting electrochemical performance. Comparative Example 3 used a hydroxide precursor prepared by co-precipitation. Due to its low crystallinity, it exhibited a narrow diffusion width during the reaction with lithium salt, reducing the proportion of microparticles during the formation of the single-crystal cathode material, resulting in lower compaction and tap density, and consequently, lower electrical conductivity.

[0226] Therefore, the cathode materials prepared by the methods in Examples 1-15 of this application have an electrode conductivity T of T > 0.025 S / cm at 25 MPa. This high electrode conductivity results in excellent electrical conductivity, effectively reducing the resistance and power consumption of the prepared battery and improving energy transfer efficiency. Furthermore, the cathode materials in Examples 1-15 have a microparticle content in the range of 8%-20%, giving them the advantages of both high compaction density and high material activity. This also solves the problems faced by cathode materials, such as increased surface side reactions and gas production due to uncontrollable microparticle numbers, thus improving safety and cycle performance.

[0227] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A positive electrode material, characterized in that, In the image under a scanning electron microscope at 3k magnification, the proportion R of particles smaller than 1μm in the positive electrode material satisfies: 8% ≤ R ≤ 20%; and under 25MPa conditions, the electrode conductivity T of the positive electrode material satisfies: T > 0.025S / cm.

2. The cathode material according to claim 1, characterized in that, Under a scanning electron microscope at 3k magnification, the cathode material has a first region and a second region. The first region has a particle size of less than 1μm with a particle size of less than 1μm as the percentage of particles, and the second region has a particle size of less than 1μm with a particle size of less than 1μm as the percentage of particles, wherein |R1-R2|≤9% and / or 0.5≤R1 / R2≤2.

3. The cathode material according to claim 1, characterized in that, The particle size distribution curve of the cathode material is asymmetrical on both sides of the peak, with the area to the left of the peak being larger than the area to the right of the peak.

4. The cathode material according to claim 1, characterized in that, The cathode material is a single-crystal cathode material, and the average particle size of a single particle in the cathode material is 1μm to 4μm.

5. The positive electrode material according to claim 1, characterized in that, The general formula of the cathode material is as follows: Li a Ni b Co c Q d M (1-b-c-d) N e O2, wherein the element Q is selected from at least one of Mn and Al, the element M is selected from at least one of Zr, Ti, Al, Mg and Y, the element N is selected from at least one of Zr, Ti, Al, Co, Mg, W, Ce, Y, K and Na, and 0.95≤a≤1.2, 0<b≤1, 0≤c≤1, 0<d≤1, b+c+d+e≤1, 0≤e<1.

6. The cathode material according to claim 1, characterized in that, The median particle size of the cathode material is D50 of 2.5 μm to 5 μm, D10 of 1 μm to 2.5 μm, D90 of 6 μm to 10 μm, and 1.0 ≤ (D90-D10) / D50 ≤ 1.

5.

7. The positive electrode material according to claim 1, characterized in that, The cathode material also satisfies at least one of the following characteristics: (1) The specific surface area of ​​the positive electrode material is 0.5 m². 2 / g~1.4m 2 / g; (2) The compaction density of the positive electrode material is >3.0 g / cm³. 3 ; (3) The tap density of the positive electrode material is >1.5 g / cc; (4) The loose packing density of the positive electrode material is > 0.5 g / cm³. 3 .

8. The positive electrode material according to claim 1, characterized in that, The cathode material has a discharge specific capacity of >175mAh / g at 0.1C and 2.8V to 4.35V.

9. A positive electrode sheet, comprising a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, characterized in that, The positive electrode active material layer comprises the positive electrode material as described in any one of claims 1 to 8.

10. A secondary battery, characterized in that, Includes the cathode material as described in any one of claims 1 to 8.

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