Positive electrode material, positive electrode sheet and secondary battery
By unevenly distributing element M and appropriately doping sulfur in the cathode material, the cracking problem during cycling was solved, improving its stability and capacity, and achieving better cycle performance and rate performance.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- BTR (JIANGSU) NEW MATERIAL TECHNOLOGY CO LTD
- Filing Date
- 2025-12-18
- Publication Date
- 2026-07-02
Smart Images
Figure CN2025143647_02072026_PF_FP_ABST
Abstract
Description
Positive electrode material, positive electrode sheet and secondary battery
[0001] This application claims priority to Chinese patent application 202411981549.3, filed on December 26, 2024. The entire contents of the aforementioned Chinese patent application are incorporated herein by reference. Technical Field
[0002] This application relates to the field of battery cathode material technology, specifically to a cathode material, a cathode sheet, and a secondary battery. Background Technology
[0003] Cathode materials are one of the core materials for lithium batteries. However, the development of cathode materials has been slower compared to the development of high-capacity anode materials (approximately 800–1000 mAh / g). Improving the capacity of cathode materials is currently the main research direction. However, as the capacity of cathode materials increases, cracks will appear in the cathode materials during long-term charge-discharge cycles, affecting the cycle stability of the cathode materials. Summary of the Invention
[0004] In view of this, in order to solve at least one of the above defects, this application provides a cathode material that improves the cycle stability of the cathode material.
[0005] In addition, this application also provides a positive electrode sheet using positive electrode materials and a secondary battery.
[0006] This application provides a cathode material comprising element M, selected from at least one of Na, K, Mg, Ca, Sr, and Ba. The cathode material comprises multiple particles, each particle having a cross-section including a central region and a surface region. Energy dispersive spectroscopy (EDS) analysis of the particle cross-section reveals that the average concentration of element M in the central region is X1, and the average concentration of element M in the surface region is X2. X1 and X2 satisfy the condition: 1.2 ≤ X2 / X1 ≤ 20. The mass content of sulfur in the cathode material is A1, and the mass content of sulfur in the cathode material is A2. A1 and A2 satisfy the condition: (A2 / A1)% ≤ 70%.
[0007] This application also provides a positive electrode sheet, comprising the positive electrode material as described above.
[0008] This application also provides a secondary battery, including the positive electrode sheet or the positive electrode material as described above.
[0009] In this application, the cathode material contains element M, and element M is unevenly distributed in the particles. The average content of element M in the surface region and the central region of the particles satisfies 1.2≤X2 / X1≤20, which results in a higher content of element M in the surface region of the particles. Element M increases the unit cell volume in the surface region of the particles, while the content of element M in the central region of the particles is lower, resulting in a relatively smaller unit cell volume in the central region of the particles. This causes compressive stress to form in the particles from the surface region towards the central region. The compressive stress helps to suppress lattice expansion during the charging and discharging process, improves the stability of the particles, and thus improves the gas generation performance and long-term cycle performance of the cathode material. Meanwhile, in this application, the total mass content of sulfur in the cathode material is A1, and the mass content of sulfur in the free sulfate ions in the cathode material is A2. The ratio of A2 to A1 is ≤70%. A1 and A2 can characterize the enrichment degree of sulfur on the surface or surface layer of the cathode material. When the ratio of A2 to A1 in the cathode material is ≤70%, it indicates that at least 30% of sulfur atoms have entered the lattice of the cathode material. Appropriate sulfur atom doping can improve the migration rate of lithium ions, suppress heterogeneous reactions, reduce lattice rotation of the cathode material, improve the rate performance and structural stability of the cathode material, thereby improving the cycle stability of the cathode material. Attached Figure Description
[0010] Figure 1 is a cross-sectional schematic diagram of a lithium-ion battery using the cathode material of this application during charging.
[0011] Figure 2 is a cross-sectional schematic diagram of a lithium-ion battery using the cathode material of this application during discharge.
[0012] Figure 3 is a schematic diagram of the concentration distribution of element M in this application.
[0013] Figure 4 is a schematic diagram of the surface and central regions of the elongated particles in this application.
[0014] Explanation of main component symbols
[0015] Electrode assembly 100, positive electrode 101, negative electrode 102 and separator 103. Detailed Implementation
[0016] 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.
[0017] This application provides a secondary battery, including a casing, an electrode assembly, and an electrolyte (or liquid electrolyte solution). Both the electrode assembly and the electrolyte solution are located within the casing.
[0018] The outer casing can be a packaging bag encapsulated with a sealing film (such as aluminum-plastic film), for example, a pouch battery. In other embodiments, it can also be a steel-cased battery, an aluminum-cased battery, etc.
[0019] Referring to Figures 1 and 2, the electrode assembly 100 includes a positive electrode 101, a negative electrode 102, and a separator 103, with the separator 103 disposed between the positive electrode 101 and the negative electrode 102. Referring to Figure 1, during discharge, active ions (such as lithium ions) are deintercalated from the crystal lattice of the negative electrode material in the negative electrode 102, pass through the separator 103 via the electrolyte, reach the positive electrode 101, and embed into the crystal lattice of the positive electrode material (such as a lithium-ion intercalated compound). Electrons are generated and travel from the negative electrode 102 to the positive electrode 101 via an external circuit. The reverse movement of electrons forms a current, which can be used by electrical appliances. During charging, referring to Figure 2, active ions (such as lithium ions) are deintercalated from the crystal lattice of the positive electrode material (such as a lithium-ion intercalated compound) in the positive electrode 101, pass through the separator 103 via the electrolyte, reach the negative electrode 102, and embed into the crystal lattice of the negative electrode material.
[0020] In some embodiments, the electrode assembly 100 may be a stacked structure, which is formed by alternatingly stacking a positive electrode 101, a separator 103, and a negative electrode 102. In other embodiments, the electrode assembly 100 may also be a wound structure, which is formed by sequentially stacking and then winding a positive electrode 101, a separator 103, and a negative electrode 102.
[0021] This application also provides a cathode material, which includes element M, selected from at least one of Na, K, Mg, Ca, Sr, and Ba; the cathode material includes multiple particles, the cross-section of which includes a central region and a surface region. Energy dispersive spectroscopy (EDS) is used to test the cross-section of the particles. The average concentration of element M in the central region is X1, and the average concentration of element M in the surface region is X2. X1 and X2 satisfy: 1.2 ≤ X2 / X1 ≤ 20; the mass content of sulfur in the cathode material is A1, and the mass content of sulfur in the free sulfate ions in the cathode material is A2. A1 and A2 satisfy: (A2 / A1)% ≤ 70%.
[0022] The cathode material of this application includes a matrix material, which may be a lithium transition metal oxide. In this application, the cathode material contains element M, which is selected from at least one of Na, K, Mg, Ca, Sr, and Ba. The ionic radius of element M is larger than that of the transition metal in the cathode material.
[0023] Energy dispersive X-ray spectroscopy (EDS) is a method for qualitative and quantitative elemental analysis based on the energy differences of characteristic X-rays emitted by different elements. By using an energy dispersive X-ray spectrometer (such as an energy-dispersive X-ray spectrometer, EDS) to perform line or spot scans on a particle cross-section at 5K magnification, the mass content (i.e., number of atoms) of element M in the surface and central regions can be obtained, thus yielding the average concentration (i.e., average number of atoms) of element M in the surface and central regions. For example, in one embodiment, spot scanning can be used to measure the content of element M at 10 locations in the central region of the particle cross-section, and the average of these content values can be obtained to obtain the average number of atoms of element M in the central region of the particle; similarly, the content of element M at 10 locations in the surface region of the particle cross-section can be measured, and the average of these mass content values can be obtained to obtain the average number of atoms of element M in the surface region of the particle. Ten particles were randomly selected, and the number of atoms in the central region and the number of atoms in the surface region of each particle were characterized using the method described above. The average content of element M in the central region of each of the ten particles was summed and averaged to obtain the average content X1 (dimensionless) of element M in the central region. The average content X2 (dimensionless) of element M in the surface region of each of the ten particles was summed and averaged to obtain the average content X2 (dimensionless) of element M in the surface region. It should be further noted that, in this application, as shown in Figure 3, in the cross-sectional view of the particle, the center of the circumcircle of the particle is the center of the particle, the radius of the circumcircle is the radius L of the particle, the region from the center of the particle to a distance L / 2 from the center of the particle is the central region, and the region from the position L / 2 of the particle to the surface of the particle is the surface region.
[0024] It should be noted that when the cathode material contains two or more M elements, X1 and X2 are measured separately for each element, and the X2 / X1 value is calculated. That is, in this application, any M element satisfies 1.2≤X2 / X1≤20.
[0025] It should be further explained that, in this application, in the cross-sectional view of the cathode material, the diameter L of the particle is defined as the diameter of the intersection of the circumscribed circle and the particle's edge. The area covered by the central region of the circumscribed circle is the central region of the particle (i.e., the area from the center of the particle to a distance L / 2 from the center of the particle), and the area covered by the surface region of the circumscribed circle is the surface region of the particle (the area from the position L / 2 of the particle to the particle's surface is the surface region). For irregularly shaped particles, such as elongated particles, as shown in Figure 4, the center of the circumscribed circle is defined as the center of the particle, the diameter L of the particle is defined as the diameter of the particle, the portion of the particle covered by the surface region of the circumscribed circle is the surface region of the particle, and the area covered by the central region of the circumscribed circle is the central region of the particle.
[0026] This invention uses energy dispersive spectroscopy (EDS) to test the cross-section of particles. The average concentration of element M in the surface region of the particle is higher than that in the central region, and satisfies 1.2≤X2 / X1≤20. This results in a higher content of element M in the surface region of the particle, which increases the unit cell volume in the surface region. In contrast, the content of element M in the central region of the particle is lower, resulting in a relatively smaller unit cell volume in the central region. This creates compressive stress inside the particle, moving from the surface region toward the central region. This compressive stress helps to suppress lattice expansion during charging and discharging, reduce crack formation, improve particle stability, and thus improve the long-term cycle performance of the cathode material.
[0027] Furthermore, considering that the ratio of A1 to A2 in the cathode material of this application satisfies (A2 / A1)% ≤ 70%, A1 and A2 can characterize the proportion of sulfur in the free sulfate ions in the total sulfur content of the cathode material. Since the sulfur in the cathode material that is not incorporated into the lattice mainly exists in a free state, it is easily washed away by ultrasonic water washing. Therefore, the ratio of A2 to A1 in the cathode material is ≤ 70%, indicating that at least 30% of sulfur atoms have been doped into the lattice of the cathode material. After sulfur atoms are doped into the lattice of the cathode material, they can replace oxygen atoms in the layered structure of the cathode material, which can improve the migration rate of lithium ions, suppress heterogeneous reactions, reduce lattice rotation of the cathode material, improve the structural stability of the cathode material, maintain the compressive stress in the particles, and further suppress lattice expansion during charging and discharging, thereby improving the cycle stability of the cathode material.
[0028] When X2 / X1 < 1.2, the concentration difference of element M between the surface and central regions of the particles is small, and the unit cell volume of the surface and central regions is uniformly distributed, making it difficult to form compressive stress from the surface to the central region. When X2 / X1 > 20, excessive element M will accumulate in the surface region of the particles, occupying lithium ion positions in the crystal lattice, affecting the transport and diffusion of lithium ions at the interface, and reducing the rate performance of the secondary battery. When the value of (A2 / A1)% is greater than 70%, it indicates that most of the sulfur element in the cathode material is in the form of free SO42-. 2- The presence of sulfur in the bulk phase is relatively low, which hinders lithium ion migration and leads to a decrease in the capacity and rate performance of the cathode material.
[0029] In some embodiments, the ratio of X2 / X1 can be 1.2, 1.5, 2, 5, 7, 9, 10, 12, 14, 16, 18, 20, or any value within the range of any two of the above values. The value of element (A2 / A1)% can be 20%, 30%, 40%, 50%, 60%, 70%, or any value within the range of any two of the above values.
[0030] In some embodiments, 30% ≤ (A2 / A1)% ≤ 50% is within this range. This is beneficial for further reducing the lattice rotation of the cathode material, improving the rate performance and structural stability of the cathode material, thereby improving the cycle performance of the cathode material and further reducing the DC resistance.
[0031] In some embodiments, the mass content of element M is 50 ppm to 1000 ppm based on the total mass of the cathode material. A concentration of element M within this suitable range is beneficial for ensuring that the cathode material particles contain an appropriate amount of element M, which helps optimize the overall unit cell volume of the cathode material, thereby improving the cycle stability of the cathode material. If the mass content of element M is below 50 ppm, the effect of doping element M is not significant, making it difficult to form effective compressive stress; when the molar concentration of doped element M is too high, such as greater than 1000 ppm, it is not conducive to lithium-ion diffusion, resulting in increased impedance of the cathode material. In some embodiments, the mass content of element M can be 50 ppm, 80 ppm, 100 ppm, 150 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, or any value within the range of any two of the above values. Preferably, the mass content of element M is 200 ppm to 600 ppm based on the cathode material.
[0032] In some embodiments, the mass content of element S, based on the cathode material, is from 100 ppm to 3000 ppm. A suitable concentration of element S is beneficial for further improving the cathode material's tolerance to lattice deformation and enhancing its stability. In some embodiments, the mass content of element S can be 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, or any value within the range of any two of the above values. Preferably, based on the mass of the cathode material, the total content of element S is from 500 ppm to 2000 ppm.
[0033] In some embodiments, the cathode material is a single-crystal material comprising a plurality of primary particles, the average particle size of which is 1 μm to 5 μm. A particle size within this range is beneficial for maintaining good specific capacity and low DC resistance (DCR) of the cathode material, and also helps reduce side reactions between the primary particles and the electrolyte, thereby ensuring good cycle stability of the cathode material. In some embodiments, the average particle size of the primary particles can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any value within the range of any two of the above values. When the average particle size is less than 1 μm, the side reactions between the material and the electrolyte are severe, and the risk of gas generation during high-temperature storage is high; when the average particle size is greater than 5 μm, the diffusion path of Li ions is long, resulting in poor rate performance.
[0034] In this application, 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 secondary particles 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, characterization methods such as scanning electron microscopy (SEM) 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, without significant particle agglomeration. EBSD can also characterize the orientation of single-crystal cathode materials; EBSD can observe that the color within the grain is the same, indicating that the grains have the same orientation, and grains with the same orientation are single crystals. It should be specifically noted 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.
[0035] 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. "Quasi-secondary particles" refer to particles formed by the adhesion of several single particles. Typically, the particle size of a single particle in the aforementioned quasi-secondary particles is between 1 μm and 5 μm. Generally, the particle size and roundness of "quasi-secondary particles" are significantly different from those of conventional polycrystalline materials.
[0036] In some embodiments, the positive electrode material is fabricated into a mold battery, and the mold battery is characterized by in-situ XRD. During the first charge-discharge cycle of the positive electrode material, the structural recovery degree δ of the positive electrode material satisfies: 99.70% ≤ δ ≤ 100.00%, where δ = θ1 / θ2 × 100%, θ1 is the diffraction angle of the (003) peak of the X-ray diffraction at the beginning of the first charge cycle, and θ2 is the diffraction angle of the (003) peak of the X-ray diffraction at the end of the first discharge cycle. When the structural recovery degree δ of the positive electrode material is within the above-mentioned suitable range, the positive electrode material has good structural stability and capacity, and it is also beneficial to reduce the DC resistance of the positive electrode material. The structural recovery degree δ of the positive electrode material can be 99.7%, 99.8%, 99.9%, 100.0%, or any value within the range of any two of the above values.
[0037] In some embodiments, the general formula of the positive electrode material is: Li x Ni a Co b Q c M d O2, where 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.35, a+b+c=1, 0.00005<d≤0.001, and element Q includes at least one of Mn and Al, while element M is selected from at least one of Na, K, Mg, Ca, Sr, and Ba. The cathode material contains nickel, cobalt, and manganese. Element M has a relatively large ionic radius. After entering the transition metal layer and occupying the sites of Ni / Co / Mn elements, the large ionic radius of element M will increase the interlayer spacing of the transition metal layer, thereby increasing the unit cell volume in that region. Combined with the different amounts of element M in the central and surface regions, this forms compressive stress from the surface region towards the central region, improving the stability of the particles. Meanwhile, when some sulfur elements are doped into the crystal lattice, they can form O-TM-S chemical bonds. TM is a transition metal in the crystal lattice. This chemical bond has a stronger bond energy, which can enhance the cathode material's tolerance to lattice deformation, alleviate the generation of internal cracks and irreversible phase transitions in cathode material particles, and improve the cycle stability of the cathode material.
[0038] In some embodiments, the cathode material contains element N, which is selected from one or more of Zr, Ti, Al, W, Ce, and Y. Doping the cathode material with element N is beneficial for further reducing the DC internal resistance (DCR), stabilizing the structure of the cathode material, and improving the ionic conductivity and cycle stability of the cathode material. Based on the total molar amount of the cathode material, the molar content of element N is e, where 0 < e ≤ 0.05. The content of element N within the above-mentioned suitable range is beneficial for further stabilizing the structure of the cathode material and improving its cycle stability.
[0039] In some embodiments, the particle size D50 of the cathode material is 2.5 μm to 5.0 μm. A particle size distribution within this range is beneficial for maintaining good discharge capacity and rate performance, and improving the electrochemical performance of the cathode material. The particle size D50 of the cathode material can be 2.5 μm, 3 μm, 4 μm, 5 μm, or any value within the range of any two of the above values.
[0040] In some embodiments, the specific surface area of the cathode material is 0.5 m². 2 / g to 1.2m 2 / g. By controlling the specific surface area of the cathode material within the above range, it is beneficial to reduce the contact between the cathode material and the electrolyte, reduce the occurrence of side reactions, and enable the cathode material to have good discharge capacity and cycle performance. In some embodiments, 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、1m 2 / g, 1.1m 2 / g, 1.2m 2 / g or any value within the range of any two of the above values.
[0041] In some embodiments, the volume percentage of particles with a diameter of less than 1 μm in the cathode material is less than 4% under a pressure of 6t. The volume percentage of particles with a diameter of less than 1 μm in the cathode material under a pressure of 6t can be 3.9%, 3.8%, 3.6%, 3.5%, 3.2%, 2.9%, 2.5%, 2%, or 1.5%. A lower number of particles smaller than 1 μm under a pressure of 6t indicates higher pressure resistance of the cathode material, meaning the cathode material particles are less likely to be crushed during electrode fabrication, thus exhibiting better structural stability.
[0042] This application also provides a method for preparing a cathode material, including the following steps:
[0043] S1. According to the Ni:Co:Mn / Al:M molar ratio (0.5~0.95):(0~0.2):(0~0.35):(0.0005~0.001), add nickel salt, cobalt salt, manganese salt and M salt to water, mix evenly, and add an appropriate amount of H2SO4 to make the molar content of S element 100ppm~3000ppm; then stir and sonicate for more than 1 hour to obtain a mixed solution, wherein the element M is selected from at least one of Na, K, Mg, Ca, Sr and Ba.
[0044] The Ni salt, Co salt, Mn salt, Al salt, and M salt can be independently selected from at least one of chloride salts, nitrates, oxalates, and acetates, with nitrates being preferred.
[0045] In some embodiments, with the total molar content of metals Ni, Co, and Mn / Al being 100%, the amount of H2SO4 added is 0.015% to 0.3%. Specifically, the amount of H2SO4 added can be 0.015%, 0.03%, 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.2%, 0.25%, 0.3%, etc., and of course, other values within the above range are also possible, which are not limited here.
[0046] S2. The mixed solution is atomized using ultrasonic atomization to form microparticles ranging from 2 μm to 200 μm in size, which are then thermally decomposed in a calcination furnace to obtain the Ni / Co / Mn oxide precursor. In this step S2, the atomized droplets after ultrasonic atomization sequentially pass through three temperature zones of the calcination furnace.
[0047] The temperature in the first temperature zone is 300℃ to 500℃. Specifically, the temperature of the first temperature zone is 300℃, 350℃, 380℃, 400℃, 430℃, 450℃, or 500℃, etc., or other values within the above range. The residence time in the first temperature zone is 30s to 60s, specifically 30s, 35s, 40s, 45s, 50s, 55s, or 60s, etc., or other values within the above range. In the first temperature zone, the droplets rapidly dehydrate, causing them to form dry material.
[0048] The temperature of the second temperature zone is 1000℃~1200℃, and the specific temperature can be 1000℃, 1050℃, 1100℃, 1150℃, or 1200℃, or other values within the above range. The residence time in the second temperature zone is 2s~10s, and can be 2s, 3s, 5s, or 10s, or other values within the above range. The material (particles after dehydration in the first temperature zone) resides in the second temperature zone for 2s~10s. Within this time range, it prevents the precursor particles from growing too large, affecting the precursor's reactivity. Simultaneously, the brief high temperature promotes the incorporation of element S into the precursor.
[0049] The pyrolysis temperature in the third temperature zone is 500℃~800℃. Specifically, the temperature in this zone can be 510℃, 520℃, 530℃, 550℃, 600℃, 650℃, 680℃, 700℃, 750℃, or 800℃, or other values within this range. The material residence time in the third temperature zone is 2min~5min, specifically 2min, 2.3min, 2.5min, 2.8min, 3min, 3.5min, 4min, 4.5min, or 5min, or other values within this range. Within this third temperature zone, the Ni / Co / Mn / M metal salts further decompose to form oxide precursors.
[0050] By controlling the content of element M in step S1 and the temperature and time of each temperature zone in this step S2, the ratio of element M content X2 / X1 in the cathode material is made to satisfy 1.2≤X2 / X1≤20. Furthermore, by controlling the amount of sulfuric acid added in step S1 and the calcination temperature and atmosphere in this step S2, the ratio of A2 to A1 is made to be ≤70%.
[0051] Specifically, in step S2, the oxygen volume concentration in the calcining furnace is below 21%. When the oxygen volume concentration is ≤21%, a non-oxygen-rich environment is easily formed in the calcining furnace. The oxygen volume concentration in the calcining furnace can be 21%, 20%, 19%, 18%, 17%, 16%, 15%, 13%, 11%, 9%, or 5%. Under these conditions, some SO42- 2- Medium energy decomposes to form S 2- The presence of low-valence ions makes it easier for element S to enter the lattice inside the cathode material precursor, which is beneficial for the subsequent preparation of cathode materials with element S doped inside the grains, thereby improving the migration rate of Li.
[0052] In step S2, the general formula of the precursor is Ni a Co b Q c M d O y Wherein, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.35, 0.00005<d≤0.001, a+b+c=1, 1≤y≤1.4, and element Q includes at least one of Mn and Al. Element M is selected from at least one of Na, K, Mg, Ca, Sr, and Ba.
[0053] In step S2, the precursor particle size D50 can be controlled to be 2.5 μm to 4.5 μm and Dmax < 20 μm by airflow milling. The cathode material prepared from the precursor with this particle size has a dispersed morphology and a small number of micro powders. D50 can specifically be 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.2 μm, or 4.5 μm, etc., or other values within the above range.
[0054] S3. Weigh a mixture of oxide precursor and lithium source in a certain molar ratio and sinter it to obtain the cathode material.
[0055] In step S3, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium sulfate, and lithium oxalate. Preferably, the lithium salt is lithium carbonate.
[0056] In step S3, the amount of lithium source and oxide precursor added satisfies the following: the ratio of the molar amount of Li to the total molar amount of all metals in the oxide precursor is (0.98 to 1.1):1, specifically it can be 0.98:1, 1.02:1, 1.05:1, 1.1:1, etc., and of course it can also be other values within the above range, which are not limited here.
[0057] In step S3, the mixing conditions of the mixture are: solid-phase mixing at 10℃~50℃ for 0.3h~3h.
[0058] In step S3, the solid-phase mixing temperature can be 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃ or 50℃, and the solid-phase mixing time can be 0.3h, 0.4h, 0.5h, 0.6h, 0.8h, 1h, 1.5h, 1.8h, 2.5h or 3h, etc., or other values within the above range, which are not limited here.
[0059] In step S3, the mixing equipment can be at least one of a ball mill, a three-dimensional mixer, a high-speed mixer, and a VC mixer.
[0060] In step S3, an oxide (dopant) containing element N can be added and mixed evenly with lithium carbonate and oxide precursor, and then sintered at high temperature for 20 hours in an oxygen atmosphere to obtain the cathode material.
[0061] In step S3, the sintering temperature is 750℃~980℃. Specifically, the sintering temperature can be 750℃, 780℃, 800℃, 830℃, 850℃, 870℃, 900℃, 950℃ or 980℃, or other values within the above range, which are not limited here.
[0062] In step S3, the sintering time is 4h to 16h. Specifically, the sintering time can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, or 16h. Of course, other values within the above range are also possible and are not limited here.
[0063] In step S3, the oxide containing element N can be at least one of ZrO2, Y2O3, WO3, Al2O3, CeO2, and TiO2.
[0064] In step S3, the molar ratio of the oxide precursor, the N-containing oxide (dopant), and the lithium source is 1:(0-0.05):(0.98-1.1). Specifically, it can be 1:0.01:0.98, 1:0.02:0.99, 1:0.03:0.99, or 1:0.05:1.1. Of course, other values within the above range are also possible and are not limited here.
[0065] Negative electrode sheet
[0066] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector.
[0067] Negative current collectors include copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metal, or any combination thereof.
[0068] In some embodiments, the negative electrode active material layer includes a negative electrode active material. The specific type of negative electrode active material is not limited and can be selected according to requirements. In some embodiments, the negative electrode active material includes, but is not limited to: lithium metal, structured lithium metal, natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Li-Al alloys or any combination thereof. The silicon-carbon composite refers to a silicon-carbon anode active material containing at least about 5 wt% silicon by weight.
[0069] In some embodiments, the negative electrode active material comprises at least one of artificial graphite, natural graphite, hard carbon, soft carbon, silicon alloy, or silicon oxide.
[0070] When the negative electrode includes silicon-carbon compounds, based on the total weight of the negative electrode active material, the silicon:carbon ratio is approximately 1:10 to 10:1, and the median particle size Dv of the silicon-carbon compounds is... 50The micrometer size ranges from approximately 0.1 micrometers to 20 micrometers. When the negative electrode comprises an alloy material, the negative electrode active material layer can be formed using methods such as vapor deposition, sputtering, or plating. When the negative electrode comprises lithium metal, the negative electrode active material layer is formed, for example, using a conductive framework with a spherical twisted structure and metal particles dispersed within the conductive framework. In some embodiments, the spherical twisted conductive framework may have a porosity of approximately 5% to approximately 85%. In some embodiments, a protective layer may also be provided on the lithium metal negative electrode active material layer.
[0071] In some embodiments, the negative electrode active material layer may include an adhesive and optionally a conductive material. The adhesive enhances the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.
[0072] In some embodiments, the conductive material includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, and silver. In some embodiments, the conductive polymer is a polyphenylene derivative, such as polyphenylene ether, polyaniline, polyphenylene ether, polyphenylene sulfoxide, etc.
[0073] In some embodiments, the current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with a conductive metal, and any combination thereof.
[0074] The negative electrode can be prepared by methods known in the art. For example, the negative electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and then coating the active material composition onto a current collector. In some embodiments, the solvent may include, but is not limited to, water.
[0075] Separating membrane
[0076] The material and shape of the separator used in the secondary battery of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.
[0077] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.
[0078] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic materials. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.
[0079] The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, the polymer material of which is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).
[0080] electrolyte
[0081] According to some embodiments of this application, the electrolyte includes an organic solvent, a lithium salt, and optional additives.
[0082] The organic solvent in the electrolyte of this application can be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no restrictions on the electrolyte used in the electrolyte according to this application; it can be any electrolyte known in the prior art. The additives in the electrolyte according to this application can be any additives known in the prior art that can be used as electrolyte additives.
[0083] In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or ethyl propionate (EP).
[0084] In some embodiments, the organic solvent includes ether solvents, such as at least one selected from 1,3-dioxapentane (DOL) and dimethyl glycol ether (DME). In some embodiments, the lithium salt includes at least one selected from organic lithium salts or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(fluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one selected from fluoroethylene carbonate and adiponitrile.
[0085] According to some embodiments of this application, the secondary battery of this application includes, but is not limited to, a lithium-ion battery. In some embodiments, the secondary battery includes a lithium-ion battery.
[0086] This application also utilizes secondary batteries in electronic devices to power loads within those devices. The electronic devices described in this application are not particularly limited. In some embodiments, the electronic devices include, but are not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.
[0087] 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.
[0088] Example 1
[0089] In this embodiment, the cathode material is prepared according to the following method:
[0090] (1) Mass ratio (n) Ni :n Co :n Mn=0.60:0.1:0.3) Weigh nickel nitrate, cobalt nitrate, and manganese nitrate and add them to water to prepare a metal salt solution. In the metal salt solution, the sum of the moles of Ni, Co, and Mn is n mol. Then, add 0.0004 nmol of potassium nitrate and 0.012 nmol of H2SO4 to the mixed solution and stir ultrasonically for 2 hours to ensure thorough mixing and obtain a mixed solution.
[0091] (2) The above mixed solution was ultrasonically atomized to form droplets of 18μm to 20μm, and then the droplets were added to a calcining furnace for thermal decomposition to prepare the oxide precursor. The temperature in the first temperature zone was 400℃, and the material residence time was 30s; the temperature in the second temperature zone was 1100℃, and the material residence time was 5s; the temperature in the third temperature zone was 700℃, and the material residence time was 3min. The oxygen volume concentration in the calcining furnace was controlled at 15%. The chemical formula of the cathode material oxide precursor is Ni. 0.60 Co 0.1 Mn 0.3 K 0.0004 O1. The oxidized precursor is pulverized by air jet milling to a suitable particle size of D50 of 3.0 μm and Dmax of 15 μm.
[0092] (3) After mixing 1000g of cathode material oxide precursor, 460g of lithium carbonate, and 4g of zirconium oxide evenly, the mixture was heated to 930℃ under an oxygen atmosphere and sintered for 20h to obtain cathode material LiNi. 0.60 Co 0.1 Mn 0.3 K 0.0004 Zr 0.0025 O2.
[0093] Example 2
[0094] The difference between Example 2 and Example 1 is that the amount of H2SO4 added to the solution in step (1) is reduced to 0.0002 nmol. The remaining steps are the same as in Example 1.
[0095] Example 3
[0096] The difference between Example 3 and Example 1 is that the amount of H2SO4 added to the solution in step (1) is increased to 0.0027 nmol. The remaining steps are the same as in Example 1.
[0097] Example 4
[0098] The difference between Example 4 and Example 1 is that in step (2), the volume concentration of oxygen is controlled at 21%. The remaining steps are the same as in Example 1.
[0099] Example 5
[0100] The difference between Example 5 and Example 1 is that, in step (1), 0.0002 nmol of calcium nitrate is added to the mixed solution. The remaining steps are the same as in Example 1.
[0101] Example 6
[0102] The difference between Example 6 and Example 1 is that in step (1), 0.0002 nmol of barium nitrate is added to the mixed solution. The remaining steps are the same as in Example 1.
[0103] Example 7
[0104] The difference between Example 7 and Example 1 is that, in step (1), 0.0002 nmol of strontium nitrate is added to the mixed solution. The remaining steps are the same as in Example 1.
[0105] Example 8
[0106] The difference between Example 8 and Example 1 is that, in step (1), a potassium nitrate solution with a ratio of 0.001 nmol is added to the mixed solution. The remaining steps are the same as in Example 1.
[0107] Example 9
[0108] The difference between Example 9 and Example 1 is that, in step (1), a potassium nitrate solution with a ratio of 0.00005 nmol is added to the mixed solution. The remaining steps are the same as in Example 1.
[0109] Example 10
[0110] The difference between Example 10 and Example 1 is that in step (2), the volume concentration of oxygen is controlled at 12%. The remaining steps are the same as in Example 1.
[0111] Example 11
[0112] The difference between Example 11 and Example 1 is that in step (2), the temperature of the third temperature zone is 700°C and the dwell time is 2 minutes. The remaining steps are the same as in Example 1.
[0113] Example 12
[0114] Unlike Example 1, the amount of H2SO4 added to the solution in step (1) is 0.036 nmol. The remaining steps are the same as in Example 1.
[0115] Example 13
[0116] The difference between Example 13 and Example 1 is that, in step (1), 0.0002 nmol of potassium nitrate and 0.0002 nmol of calcium nitrate are added to the mixed solution. The remaining steps are the same as in Example 1.
[0117] Example 14
[0118] The difference between Example 14 and Example 1 is that, in step (1), 0.0004 nmol of strontium nitrate and 0.0005 nmol of barium nitrate are added to the mixed solution. The remaining steps are the same as in Example 1.
[0119] Example 15
[0120] Example 15 differs from Example 1 in that 1000g of cathode material oxide precursor, 460g of lithium carbonate, 4g of zirconium oxide, and 2g of yttrium oxide were mixed evenly and then sintered at 930°C for 20 hours under an oxygen atmosphere to obtain the cathode material LiNi. 0.60 Co 0.1 Mn 0.3 K 0.0004 Zr 0.0025 Y 0.0015 O2.
[0121] Example 16
[0122] Example 16 differs from Example 1 in that 1000g of cathode material oxide precursor, 460g of lithium carbonate, and 2.5g of titanium oxide are mixed evenly and then sintered at 930°C for 20 hours under an oxygen atmosphere to obtain cathode material LiNi. 0.60 Co 0.1 Mn 0.3 K 0.0004 Ti 0.0015 O2.
[0123] Example 17
[0124] (1) Weigh out nickel nitrate, cobalt nitrate, and aluminum nitrate in a molar ratio (nNi:nCo:nAl = 0.8:0.1:0.1) and add them to water to prepare a mixed metal salt solution. In the metal salt solution, the sum of the moles of Ni, Co, and Al is nmol. Then, add 0.0004 nmol of potassium nitrate and 0.012 nmol of H2SO4 to the mixed solution and stir ultrasonically for 2 hours to ensure thorough mixing and obtain the mixed solution.
[0125] (2) The above mixed solution was atomized by ultrasonication to form droplets of 18 μm to 20 μm. These droplets were then added to a calcining furnace for thermal decomposition to prepare the oxide precursor. The first temperature zone was 400℃ with a residence time of 30 s; the second temperature zone was 1100℃ with a residence time of 5 s; and the third temperature zone was 700℃ with a residence time of 3 min. The oxygen volume concentration in the calcining furnace was controlled at 15%. The chemical formula of the cathode material oxide precursor is Ni. 0.80 Co0.1 Al 0.1 K 0.0004 O1, the precursor is pulverized by airflow to a suitable particle size of D50 of 2.5 μm and Dmax of 15 μm.
[0126] (3) After mixing 1000g of cathode material oxide precursor, 460g of lithium carbonate, and 2.4g of zirconium oxide evenly, the mixture was heated to 830℃ under an oxygen atmosphere and sintered for 18h to obtain cathode material LiNi. 0.80 Co 0.1 Al 0.1 K 0.0004 Zr 0.0015 O2.
[0127] Example 18
[0128] The difference between Example 18 and Example 1 is that:
[0129] In step (1), nickel chloride, cobalt chloride, and manganese chloride are weighed out in molar ratio (nNi:nCo:nMn = 0.5:0.2:0.3) and added to water to prepare a mixed solution of metal salts.
[0130] Example 19
[0131] The difference between Example 19 and Example 1 is that:
[0132] In step (1), nickel chloride, cobalt chloride, and manganese chloride are weighed out in a molar ratio (nNi:nCo:nMn = 0.7:0.1:0.2) and added to water to prepare a mixed metal salt solution. In the metal salt solution, the sum of the moles of Ni, Co, and Mn is n mol. Then, 0.0006 nmol of strontium nitrate and 0.018 nmol of H2SO4 are added to the mixed solution, and the mixture is ultrasonically stirred for 2 hours to ensure thorough mixing and obtain the mixed solution.
[0133] (2) The above mixed solution was ultrasonically atomized to form droplets of 18 μm to 20 μm. These droplets were then added to a calcining furnace for thermal decomposition to prepare the oxide precursor. The first temperature zone was 400℃ with a residence time of 30 s; the second temperature zone was 1100℃ with a residence time of 5 s; and the third temperature zone was 700℃ with a residence time of 3 min. The oxygen volume concentration in the calcining furnace was controlled at 12%. The chemical formula of the cathode material oxide precursor is Ni. 0.70 Co 0.1 Mn 0.2 Sr 0.0006 O1, the precursor is pulverized by airflow to a suitable particle size of D50 of 3.2 μm and Dmax of 15 μm.
[0134] (3) After mixing 1000g of cathode material oxide precursor, 460g of lithium carbonate, and 3.8g of tungsten oxide evenly, the mixture was heated to 900℃ under an oxygen atmosphere and sintered for 16h to obtain cathode material LiNi. 0.70 Co 0.1 Mn 0.2 Sr 0.0006 W 0.002 O2.
[0135] Comparative Example 1
[0136] Unlike Example 1, in step (2), the calcining furnace has only two temperature zones, with the material moving directly from the first temperature zone to the third. The first temperature zone has a temperature of 400°C and a material residence time of 30 seconds; the third temperature zone has a temperature of 700°C and a material residence time of 3 minutes. The remaining steps are the same as in Example 1.
[0137] Comparative Example 2
[0138] Unlike Example 1, in step (2), the volume concentration of oxygen in the roasting furnace is controlled at 30%. The remaining steps are the same as in Example 1.
[0139] Comparative Example 3
[0140] Unlike Example 1, in step (1), a 0% potassium nitrate solution is added to the mixed solution. The remaining steps are the same as in Example 1.
[0141] Comparative Example 4
[0142] (1) Mass ratio (n) Ni :n Co :n Mn =0.60:0.1:0.3) Weigh nickel nitrate, cobalt nitrate, and manganese nitrate and add them to water to prepare a metal salt solution. In the metal salt solution, the sum of the moles of Ni, Co, and Mn is n mol. Then, add 0.0012n mol of H2SO4 to the mixed solution and stir ultrasonically for 2 hours to mix thoroughly and evenly to obtain a mixed solution.
[0143] (2) The above mixed solution was ultrasonically atomized to form droplets of 18 μm to 20 μm, and then thermally decomposed in a calcination furnace to prepare the oxide precursor. The first temperature zone was 400℃ with a material residence time of 30 s; the second temperature zone was 1100℃ with a material residence time of 3 s; and the third temperature zone was 700℃ with a material residence time of 3 min. The oxygen volume concentration in the calcination furnace was controlled at 15%. The chemical formula of the cathode material precursor is Ni. 0.60 Co 0.1 Mn 0.3O1, the precursor is pulverized by airflow to a suitable particle size of D50 of 3.0 μm and Dmax of 15.
[0144] (3) Mix 1000g of cathode material precursor, 460g of lithium carbonate, 4g of zirconium oxide, and 0.13g of potassium nitrate evenly, then heat to 930℃ under an oxygen atmosphere and sinter for 20h to obtain cathode material LiNi. 0.60 Co 0.1 Mn 0.3 K 0.0004 Zr 0.0025 O2.
[0145] Comparative Example 5
[0146] Unlike Example 1, in step 2, the pyrolysis temperature in the third temperature zone is 600°C and the residence time is 1 minute.
[0147] Test methods
[0148] Free SO4 2- Test: Weigh 0.5 g of sample and disperse it in 50 mL of pure water. After sonication for 5 min, filter the solution and measure the free SO4 in the filtrate using ion chromatography (instrument: Thermo Fisher ICS6000 HPIC). 2- The mass content of the ions is a2.
[0149] Since the molar mass percentage of sulfur in sulfate is 1 / 3, the mass content of sulfur in the free sulfate of the cathode material is A2 = a2 / 3.
[0150] Test of total molar content of M and S elements: Take 0.3g of sample, add aqua regia to digest, cool and make up to 100mL, and test the total mass content of M and S elements by Agilent 5110 ICP-OES, where the total mass content of S element is A1 (unit ppm).
[0151] The proportion of sulfur in the total sulfur content of the cathode material in free sulfate ions is α = A2 / A1. Since the sulfur elements not incorporated into the crystal lattice in the cathode material mainly exist in a free state, they are easily washed away by ultrasonic water washing. Therefore, the larger the ratio of A1 to A2, the more sulfur elements in the cathode material are in a free state and the less sulfur elements enter the bulk phase; the smaller the ratio of A1 to A2, the less sulfur elements in the cathode material are in a free state and the more sulfur elements enter the bulk phase.
[0152] The test method for the content distribution of element M is as follows:
[0153] The test method for the average concentration X1 of element M in the central region and the average concentration X2 of element M in the surface region of the cathode material particles is as follows: A cross-section sample is prepared using a Hitachi ion cutter (IM5000), a suitable field of view is selected using a Hitachi S4800 scanning electron microscope, and then an EDS (Bruker 30mm) is used. 2 A type of energy dispersive spectrometer (EDS) performs line or spot scans on the particle cross-section within a 5k field of view. For example, spot scanning can be used to measure the content of element M at 10 locations (generally at least 5 points) in the central region of the particle cross-section. The content of element M is then summed and averaged to obtain the number of atoms in the central region of the particle (dimensionless). The content of element M at 10 locations in the surface region of the particle cross-section is also measured, and the content of element M is summed and averaged to obtain the number of atoms in the surface region of the particle (dimensionless). Ten particles are then randomly selected, and the number of atoms in the central region and surface region of each particle is characterized using the above method. The number of atoms in the central region of each of the 10 particles is summed and averaged to obtain the average concentration X1 (dimensionless) of element M in the central region. The number of atoms in the surface region of each of the 10 particles is summed and averaged to obtain the average concentration X2 (dimensionless) of element M in the surface region.
[0154] As shown in Figure 3, in the cross-sectional view of the particle, within the circumcircle of the particle, with the center of the circumcircle as the center and the radius of the circumcircle as the radius L of the particle, the region from the center of the particle to a distance L / 2 from the center of the particle is the central region, and the region from the L / 2 position of the particle to the particle surface is the surface region. When the cathode material contains two or more elements M, the X1 and X2 of each element M are measured separately, and the corresponding X2 / X1 values are calculated. It should be further noted that, in this application, in the cross-sectional view of the cathode material, the diameter L of the particle is the intersection of the circumcircle and the particle edge, the region covered by the central region of the circumcircle is the central region of the particle (i.e., the region from the center of the particle to a distance L / 2 from the center of the particle), and the region covered by the surface region of the circumcircle is the surface region of the particle (the region from the L / 2 position of the particle to the particle surface is the surface region). For irregularly shaped particles, such as elongated particles, as shown in Figure 4, the center of the circumscribed circle is the center of the particle, the diameter L of the particle is the intersection of the circumscribed circle and the edge of the particle, the part of the particle covered by the surface area of the circumscribed circle is the surface area of the particle, and the area covered by the central area of the circumscribed circle is the central area of the particle.
[0155] For point scanning and line scanning, please refer to Figure 3 for the following explanation:
[0156] Point scan: Select 5-10 points in the central region (inside the dashed circle in Figure 3) for EDS measurement, and take the average value to obtain the average number of atoms in the central region X1; select 5-10 points in the surface region (outside the dashed circle in Figure 3) for EDS measurement, and take the average value to obtain the average number of atoms in the central region X2.
[0157] Line scan: At least three line positions are randomly selected in the central region (i.e., inside the dashed circle in Figure 3) for line scanning. The average value of the measurements is taken to obtain the average number of atoms in the central region X1. At least three line positions are randomly selected in the surface region (i.e., outside the dashed circle in Figure 3) for line scanning. The average value of the measurements is taken to obtain the average number of atoms in the central region X2. In actual testing, spot scanning and line scanning can also be used in combination. For example, spot scanning 5 times and line scanning 5 times are performed in the surface region, and spot scanning 5 times and line scanning 5 times are performed in the central region.
[0158] The test method for the structural resilience δ is as follows:
[0159] The structural changes during the charge and discharge process were tested using an electrochemical in-situ XRD (Bruker D8 Advance (Cu target)) device with a blue electric (5mA, 5V) device. The charge and discharge voltage range was 2.8V to 4.35V. The XRD spectrum was then fitted using Jade software to obtain the diffraction angles corresponding to the (003) peak at the beginning and end of the charge and discharge.
[0160] Specifically, the cathode materials prepared in the above embodiments and comparative examples are assembled to form mold batteries. The outer casing of the mold battery is provided by the Bruker in-situ XRD equipment, and the outer casing has a window that allows X-rays from the XRD equipment to pass through. The specific procedure is as follows: Cathode material, conductive carbon black, and PVDF are weighed in a mass ratio of 93:5:2. N-methyl-2-pyrrolidone (NMP) is added at a solid content of 50%, and dispersed into a viscous slurry using a high-speed disperser. The slurry is then uniformly coated onto aluminum foil using a 200-micron scraper. After baking in an oven at 80°C for 30 minutes, the slurry is rolled and punched into a cathode sheet with a diameter of 14 mm. The slurry is then placed back into the oven and baked at 80°C for 8 hours. Using a prepared positive electrode, a 16mm lithium sheet as the negative electrode, a Celgard polypropylene membrane as the separator, and a 1mol / L LiPF6 carbonate solution as the electrolyte, the mold battery was assembled in an argon-filled glove box using the casing of the XRD equipment. The mold battery was then subjected to charge-discharge tests at 25°C and 2.5V-4.35V, and the changes in the (003) and (104) peaks of the positive electrode material within one cycle were characterized by in-situ electrochemical XRD.
[0161] The particle size was determined using a Malvern 3000 laser particle size analyzer to obtain the average particle size of the volume or quantity distribution of the cathode material precursor or ternary cathode material. Specifically, an appropriate amount of sample was taken, poured into pure water, and ultrasonically dispersed evenly. Then, an appropriate amount of sodium hexametaphosphate (powder: surfactant = 1g: 1 drop) was added to the dispersed sample, stirred evenly, and poured into the sample cell of the testing equipment. After waiting for 10 seconds, the sample was started by clicking "Start Sample Testing".
[0162] The specific surface area of the cathode material was tested using a Tristar 3020 analyzer, as follows: The mass of the empty sample tube was weighed (m1); 3g of sample was added to the sample tube through a long-necked funnel; the sample was degassed under vacuum at 300℃ for 1 hour, and after cooling, the mass of the sample tube was weighed (m2); the sample mass m = m2 - m1. The sample tube was placed in liquid nitrogen, and the nitrogen adsorption capacity V was measured under a series of relative pressures P / P0 to obtain adsorption isotherms. P / P0 was set to 0.05 / 0.1 / 0.15 / 0.20 / 0.25 / 0.30. The isothermal adsorption curves were fitted, and the monolayer saturated adsorption capacity Vm was calculated based on the slope and intercept; then, the specific surface area was calculated based on Vm.
[0163] Test method for the volume percentage of cathode material particles with a diameter of less than 1μm: Test the volume percentage of cathode material particles with a diameter of less than 1μm: Weigh 1g of sample and put it into the mold of the compaction density meter (Carver 4350, USA) and press it with a pressure of 6T for 30s. Then take out the sample and use Malvern 3000 laser particle size analyzer to test the volume percentage of particles with a diameter of 1 micrometer.
[0164] Method for testing the average particle size of primary particles:
[0165] Cross-sectional samples of the cathode material were prepared using an ion cutter (IM5000), and the morphology of the cross-sections was tested using a Hitachi S4800 scanning electron microscope. Ten images were taken at 5K magnification. All images were imported into Nano Measure software, and the maximum diameter of the single-crystal particles that appeared completely within the field of view of the electron microscope image was measured. The average diameter of the particles was calculated as the average particle size. A single-crystal particle that appears completely within the field of view of the electron microscope image means that the outline of the single-crystal particle is fully displayed in the electron microscope image, and the outline of the single-crystal particle is not covered by other single-crystal particles in the field of view or divided by the boundaries of the electron microscope image. The maximum diameter of the single-crystal particle refers to the diameter of the circumcircle of the single-crystal particle in the electron microscope image.
[0166] Electrochemical performance testing:
[0167] The electrochemical performance of the materials was evaluated using coin cell half-cells. The positive electrode materials prepared in the above examples and comparative examples were assembled into coin cells. The specific procedure was as follows: Positive electrode material, conductive carbon black, and PVDF were weighed in a mass ratio of 93:5:2. N-methyl-2-pyrrolidone (NMP) was added at a solid content of 50%, and the mixture was stirred into a viscous slurry using a high-speed disperser. This slurry was then uniformly coated onto aluminum foil using a scraper, dried in an oven at 80°C, rolled, and cut into positive electrode sheets with a diameter of 14 mm. A 16 mm lithium sheet was used as the negative electrode, a Celgard polypropylene membrane as the separator, and a 1 mol / L LiPF6 carbonate solution as the electrolyte. The cells were assembled in an argon-filled glove box to obtain the coin cell half-cell.
[0168] After the assembled button cells were left to stand for 12 hours, capacity and cycle performance tests were conducted using the LAND battery testing system at 25°C and 3.0–4.45V. The nominal capacity at 1C was set to 200 mAh / g. The cells were cycled 50 times at a 0.5C charge-1C discharge rate. The ratio of the discharge capacity at the 50th cycle to the discharge capacity at the 1st cycle was taken as the 50-cycle retention rate.
[0169] Discharge specific capacity test method:
[0170] The assembled button cells were tested using a CT3002A battery testing system. Charge and discharge tests were conducted at 0.3C / 0.3C rates in the 3.0V-4.3V discharge range at 25℃ to obtain the 0.1C discharge specific capacity (discharge capacity / mass), 1C discharge specific capacity, and 2C discharge specific capacity.
[0171] Test method for DC internal resistance of positive electrode material:
[0172] The LAND battery testing system was used to conduct capacity and cycle performance tests at 25℃ and 3.0V–4.4V, with the nominal capacity set at 200mAh / g for 1C. Additionally, the voltage U at the initial moment of each weekly discharge cycle was recorded. A And the voltage data U at 60s B Discharge current I Dis The formula for calculating DC internal resistance is DCR = (U A -U B ) / I Dis .
[0173] Table 1
[0174] Table 2
[0175] As can be seen from Tables 1 and 2 above, compared with Comparative Examples 1 to 5, in the cathode materials of Examples 1 to 19, the average concentration X1 of element M in the surface region and the average concentration X2 of element M in the central region, X1 and X2 satisfy 1.2≤X2 / X1≤20. The total mass content A1 of sulfur in the cathode material and the mass content A2 of sulfur in the free sulfate ions in the cathode material, A1 and A2 satisfy (A2 / A1)%≤70%. Although the cathode materials of Comparative Examples 1 to 2 satisfy 1.2≤X2 / X1≤20, they do not satisfy (A2 / A1)%≤70%. Although the cathode materials of Comparative Examples 3 to 5 satisfy (A2 / A1)%≤70%, they do not satisfy 1.2≤X2 / X1≤20. The test results show that by controlling the elements M and sulfur in the cathode materials to satisfy the above relationship, Examples 1 to 19 achieve good specific capacity, good cycle performance, and lower DC internal resistance. After extensive experimentation, the applicant hypothesizes that the higher content of element M near the particle surface increases the unit cell volume in this region, while the lower content of M near the particle center results in a smaller unit cell volume. This creates compressive stress from the surface towards the center, which suppresses lattice expansion during charging and discharging, improves particle stability, and consequently enhances gas generation and long-term cycle performance. Furthermore, a ratio of A2 to A1 ≤ 70% indicates that some sulfur atoms have entered the cathode material's lattice. Appropriate sulfur doping can increase lithium-ion migration rate, suppress heterogeneous reactions, reduce lattice rotation in the cathode material, and improve its rate performance and structural stability.
[0176] Compared with Example 1, the second temperature zone was removed in Comparative Example 1. Characterization showed that the (A2 / A1)% of the cathode material was 90%, indicating that the S element in the cathode material was enriched. This indicates that the amount of S element doping in the bulk phase of the cathode material was relatively small, making it difficult to suppress lattice deformation during charging and discharging. As a result, the cycle stability of the cathode material in Comparative Example 1 decreased and the DC internal resistance increased.
[0177] Compared to Example 1, Comparative Example 2 controlled the oxygen volume concentration in the roasting furnace at 30%, which is a higher oxygen concentration and SO4 content. 2- It is difficult to decompose into S 2- The presence of low-valence ions resulted in a (A2 / A1)% ratio of 73% for the characterized cathode material, indicating that the S element in the cathode material was enriched. This suggests that the amount of S element doped in the bulk phase of the cathode material was relatively small, making it difficult to suppress lattice deformation during charging and discharging. Consequently, the cycle stability of the cathode material in Comparative Example 2 decreased, and the DC internal resistance increased.
[0178] Compared with Example 1, no K element was added in step (1) of Comparative Example 3. The obtained cathode material did not have the distribution difference of M element in the surface and inner regions. The crystal structure could not form compressive stress, which led to a decrease in the cycle stability of the cathode material in Comparative Example 3 and an increase in DC internal resistance.
[0179] Compared with Example 1, in Comparative Example 4, no K element was added in step (1), but K element was added in step (3) for solid-phase doping. Characterization showed that the distribution difference of K element in the surface region and inner region of the cathode material was small, and the crystal structure could not form compressive stress, resulting in a decrease in the cycle stability of the cathode material in Comparative Example 3 and an increase in DC internal resistance.
[0180] Compared with Example 1, in Comparative Example 5, the temperature and material residence time in the third temperature zone in step (2) were reduced. The concentration ratio of K element in the surface region and the central region of the obtained cathode material was 23. Excessive element M was enriched in the surface region of the particles, which would occupy the lattice lithium sites, resulting in a decrease in the cycle stability of the cathode material in Comparative Example 5 and an increase in DC internal resistance.
[0181] 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, The cathode material includes element M, which is selected from at least one of Na, K, Mg, Ca, Sr, and Ba. The cathode material comprises multiple particles, each particle having a cross-section including a central region and a surface region. The cross-section of the particles is measured using an energy dispersive spectroscopy (EDS) instrument. The average concentration of element M in the central region is X1, and the average concentration of element M in the surface region is X2. X1 and X2 satisfy the following condition: 1.2 ≤ X2 / X1 ≤ 20. The mass content of sulfur in the cathode material is A1, and the mass content of sulfur in the free sulfate ions of the cathode material is A2, where (A2 / A1)% ≤ 70%.
2. The cathode material as described in claim 1, characterized in that, The cathode material satisfies any one of the following conditions: (1) The ratio of X2 / X1 is within the range of 1.2, 1.5, 2, 5, 7, 9, 10, 12, 14, 16, 18, 20 or any two of these values; (2) 2.8 ≤ X2 / X1 ≤ 16; (3) 4.5 ≤ X2 / X1 ≤ 11.
3. The positive electrode material as described in claim 1, characterized in that, The cathode material satisfies at least one of the following conditions: (1) The value of (A2 / A1)% is 20%, 30%, 40%, 50%, 60%, 70%, or any value within the range of any two of these values; (2)30%≤(A2 / A1)%≤50%.
4. The positive electrode material as described in claim 1, characterized in that, Based on the cathode material, the mass content of element M is from 50 ppm to 1000 ppm.
5. The positive electrode material as described in claim 1, characterized in that, Based on the total mass of the cathode material, the mass content of element S is between 100 ppm and 3000 ppm.
6. The positive electrode material as described in claim 1, characterized in that, The cathode material is a single-crystal material, and the particles include primary particles with an average particle size of 1 μm to 5 μm.
7. The positive electrode material as described in claim 1, characterized in that, The positive electrode material is made into a mold battery, and the mold battery is characterized by in-situ XRD. During the first charge and discharge cycle of the mold battery, the structural recovery degree δ of the positive electrode material satisfies: 99.70% ≤ δ ≤ 100.00%, where δ = θ1 / θ2 × 100%, θ1 is the diffraction angle of the X-ray diffraction (003) peak of the positive electrode material at the beginning of the first charge cycle, and θ2 is the diffraction angle of the X-ray diffraction (003) peak of the positive electrode material at the end of the first discharge cycle.
8. The cathode material as described in claim 1, characterized in that, The general formula of the cathode material is: Li x Ni a Co b Q c M d O2, where 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.35, a+b+c=1, 0.00005<d≤0.001, and the Q element includes at least one of Mn and Al.
9. The positive electrode material as described in claim 1, characterized in that, The cathode material also contains element N, which is selected from one or more of Zr, Ti, Al, W, Ce, and Y.
10. The cathode material according to claim 9, characterized in that, Based on the total molar amount of the cathode material, the molar content of element N is e, where 0 < e ≤ 0.
05.
11. The cathode material as described in claim 1, characterized in that, The volumetric particle size D50 of the cathode material is 2.5 μm to 5.0 μm.
12. The cathode material as described in claim 1, characterized in that, The specific surface area of the positive electrode material is 0.5 m². 2 / g to 1.2m 2 / g.
13. The cathode material as described in claim 1, characterized in that, The volume percentage of particles with a diameter of less than 1 μm in the cathode material is less than 4% under a pressure of 6t.
14. 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 13.
15. A secondary battery, comprising a casing, an electrode assembly, and an electrolyte or electrolyte solution, wherein the electrode assembly and the electrolyte or electrolyte solution are both located within the casing, and the electrode assembly includes a separator and a negative electrode plate, characterized in that, The electrode assembly further includes the positive electrode as described in claim 14, wherein the separator is disposed between the positive electrode and the negative electrode.