Composite positive electrode material and preparation method therefor, positive electrode sheet, and secondary battery

Abstract

The present invention provides a composite positive electrode material and a preparation method therefor, a positive electrode sheet, and a secondary battery. The composite positive electrode material comprises a first positive electrode active material and a second positive electrode active material. The first positive electrode active material consists of monocrystalline particles in a P63mc crystal form, and the second positive electrode active material consists of polycrystalline particles in a Fd3m crystal form. The first positive electrode active material has an average particle size of D1, and the second positive electrode active material has an average particle size of D2, wherein 0.16≤D2 / D1≤0.414. A unique spatial structure enables the first positive electrode active material to avoid cycle fade caused by irreversible capacity loss; and the second positive electrode active material has a three-dimensional lithium ion diffusion channel, enabling rapid deintercalation of lithium ions under high voltages, thereby improving the low-temperature discharge performance of the composite positive electrode material. The combination of the first positive electrode active material and the second positive electrode active material enables the composite positive electrode material to take into account both the cycle performance and the low-temperature performance under high voltages.

Description

A composite cathode material and its preparation method, cathode sheet and secondary battery Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a composite cathode material and its preparation method, a cathode sheet, and a secondary battery. Background Technology

[0002] Since their commercialization in the 1990s, lithium-ion batteries have been widely used due to their advantages such as high energy density, high charge / discharge efficiency, low self-discharge, long lifespan, and environmental friendliness. They are currently applied in consumer electronics, aerospace, military, power tools, and electric vehicles. With technological advancements, both in the consumer and power battery sectors, the demand for longer driving ranges from lithium-ion batteries is increasing, making the development of high-energy-density lithium-ion batteries crucial. Developing high-energy-density lithium-ion batteries can be approached from two aspects: first, developing new high-specific-capacity positive and negative electrode materials; and second, increasing the charge / discharge voltage of lithium-ion batteries. Increasing the charge / discharge voltage of lithium-ion batteries can simultaneously improve both their mass energy density and volumetric energy density, while also reducing their cost, making it a hot research topic.

[0003] For cathode materials, the high delithiation caused by high voltage poses a significant challenge to their structural stability. Currently, the commonly used modification methods for lithium cobalt oxide are mainly to delay the phase transition voltage through bulk doping and surface coating. However, for voltages of 4.55V and above, the degree of irreversible phase transition is aggravated, and the effect of delaying the phase transition through doping and coating is not good. Moreover, the doping and coating materials are mostly inert metal oxides, which deteriorate the material kinetics and lead to the deterioration of low-temperature performance.

[0004] In view of this, it is indeed necessary to provide a technical solution to the above problems.

[0005] Summary of the Invention

[0006] One of the objectives of this invention is to provide a composite cathode material to address the shortcomings of existing technologies, thereby improving the poor cycle performance and low-temperature performance of current lithium-ion batteries under high voltage.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A composite cathode material includes a first cathode active material and a second cathode active material, wherein the first cathode active material is a single crystal particle of P63mc crystal form, and the second cathode active material is... The composite positive electrode material consists of polycrystalline particles of the same crystalline form; the average particle size of the first positive electrode active material is D1, and the average particle size of the second positive electrode active material is D2, with 0.16 ≤ D2 / D1 ≤ 0.414; in the composite positive electrode material, the mass of the first positive electrode active material is m1, and the mass of the second positive electrode active material is m2, with 0 < m2 / m1 < 1.

[0009] Preferably, the average particle size D1 of the first positive electrode active material satisfies: 10μm≤D1≤25μm; and the average particle size D2 of the second positive electrode active material satisfies: 0.2μm≤D2≤8μm.

[0010] Preferably, the composite cathode material has the general chemical formula: LiNi a Mn 2-a-b N b O4@Li x Na y Co 1-z M z O2, wherein M and N each include at least one of the elements Al, Mg, Ti, La, Y, Zn, Ni, Mn, Co, V, and Si; wherein 0 ≤ a < 0.6, 0 ≤ b < 0.02; 0.7 ≤ x < 1, 0.01 < y < 0.1, and 0 ≤ z < 0.02.

[0011] Preferably, the first positive electrode active material is Li. x Na y Co 1-z M z O2, the second positive electrode active material is LiNi a Mn 2-a-b N b O4; where 0≤a<0.6, 0≤b<0.02; 0.7≤x<1, 0.01<y<0.1, 0≤z<0.02.

[0012] Preferably, the mass m1 of the first positive electrode active material and the mass m2 of the second positive electrode active material satisfy the relationship: 0 < m2 / m1 ≤ 0.25.

[0013] Preferably, the XRD diffraction pattern of the composite cathode material contains at least three diffraction peaks in the range of 17.8° to 19°; it has a first diffraction peak in the range of 17.8° to 18.3° with a peak intensity of I1; and it has a second diffraction peak and a third diffraction peak in the range of 18.3° to 19.0° with peak intensities of I2 and I3, respectively; I2 corresponds to the (002) crystal plane of the first cathode active material, and I3 corresponds to the (111) crystal plane of the second cathode active material; the peak intensities of the diffraction peaks satisfy the following relationships: I2 / I1≥2, I3 / I1≥2, 0.5≤I3 / I2≤2.

[0014] The second objective of this invention is to provide a method for preparing a composite cathode material, comprising the following steps:

[0015] S1: Mix the cobalt salt solution and the salt solution of doped element M uniformly according to the molar ratio of Co to M of (1-z):z, add excess precipitant solution, stir and filter to obtain precipitate; sinter the precipitate at 400℃~600℃ for 6~12h to obtain (Co 1-z M z )3O4 powder, where 0≤z<0.02;

[0016] S2: (Co) 1-z M z Na₂O₄ and sodium salt were mixed uniformly at a molar ratio of Na to Co of (0.5–0.7):(1–1.2); and sintered at 800–1100 °C for 45–52 h to obtain Na₂O₄ with a P₆₃mc crystal phase structure. n Co 1-z M z O2, where 0.5 ≤ n ≤ 0.7;

[0017] S3: Put Na n Co 1-z M z O2 was dispersed in a lithium salt solution and mixed evenly with a Li to Na molar ratio ≥ 5. The mixture was reacted in a reactor at 140–160 °C for 22–26 h. After pressure filtration, the mixture was washed with deionized water, dried, and then mechanically crushed to obtain Li. x Na y Co 1-z M z O2 single crystal particles;

[0018] S4: Nickel salt solution, manganese salt solution, and N-doped salt solution are mixed uniformly at a Mn:Fe:N molar ratio of a:(2-ab):b to form a mixed solution. This mixed solution is then mixed with a carbonate solution at a (Ni+N+Mn) to carbonate ion molar ratio of (0.8–1.2):(1.6–2.2). The addition rates of the nickel salt solution, manganese salt solution, and N-doped salt solution are controlled to obtain a series of Ni particles with different particle sizes. a Mn 2-a-b N b CO3 precipitation; then Ni a Mn 2-a-b N b CO3 precipitate and lithium salt were mixed uniformly at a Li:(Ni+Mn+N) molar ratio of (1.0–1.5):(1.8–2.4), and sintered at 750–1000℃ for 8–12 h to prepare LiNi with different particle sizes. a Mn 2-a-b Nb O4 polycrystalline particles;

[0019] S5: Mix the materials prepared in steps S3 and S4 in a certain proportion, and sinter at 700-800℃ for 5-8 hours to obtain the composite cathode material.

[0020] Preferably, in step S4, the addition rate is 0.3 to 5.2 L / min.

[0021] A third objective of this invention is to provide a positive electrode sheet comprising the positive electrode material described in any of the preceding paragraphs.

[0022] The fourth objective of this invention is to provide a secondary battery, comprising a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode described above.

[0023] Compared to existing technologies, the advantages of this invention are as follows: The composite cathode material provided by this invention comprises P63mc crystalline phase cathode material and Composite materials of crystalline phase cathode materials; Under high voltage, P63mc crystalline phase cathode materials, due to the unique coplanar connection of LiO6 octahedra and CoO6 octahedra, only exhibit CoO2 layer slippage and Li vacancy arrangement, avoiding cycle decay caused by irreversible capacity loss. The crystalline cathode material possesses three-dimensional lithium-ion diffusion channels, enabling rapid lithium-ion extraction under high voltage and improving the low-temperature discharge performance of the composite material. The P63mc crystalline cathode material features a large-particle single-crystal design, reducing specific surface area, minimizing side reactions with the electrolyte, and improving cycle life. The secondary polycrystalline design of the cathode material with a crystalline phase structure increases the reactive sites, which is conducive to the rapid extraction of lithium ions and improves low-temperature performance. The low-temperature cycle performance of the electrode is balanced by designing a reasonable ratio of the two cathode materials. Detailed Implementation

[0024] To make the technical solution and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto.

[0025] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0026] 1. Cathode material

[0027] In a first aspect, the present invention provides a composite positive electrode material comprising a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material is a single crystal particle of the P63mc crystal form, and the second positive electrode active material is... The composite positive electrode material consists of polycrystalline particles of the same crystalline form; the average particle size of the first positive electrode active material is D1, and the average particle size of the second positive electrode active material is D2, with 0.16 ≤ D2 / D1 ≤ 0.414; in the composite positive electrode material, the mass of the first positive electrode active material is m1, and the mass of the second positive electrode active material is m2, with 0 < m2 / m1 < 1.

[0028] In some embodiments, the average particle size D1 of the first positive electrode active material satisfies: 10μm≤D1≤25μm; and the average particle size D2 of the second positive electrode active material satisfies: 0.2μm≤D2≤8μm.

[0029] In some embodiments, the composite cathode material has the general chemical formula: LiNi a Mn 2-a-b N b O4@Li x Na y Co 1-z M z O2, wherein M and N include at least one of the elements Al, Mg, Ti, La, Y, Zn, Ni, Mn, Co, V, and Si; wherein 0 ≤ a < 0.6, 0 ≤ b < 0.02; 0.7 ≤ x < 1, 0.01 < y < 0.1, and 0 ≤ z < 0.02.

[0030] In some embodiments, the LiNi a Mn 2-a-b NbO4 is the second positive electrode active material, wherein 0 ≤ a < 0.6, 0 ≤ b < 0.02; the Li x Na y Co 1-z M z O2 is the first positive electrode active material, where 0.7≤x<1, 0.01<y<0.1, and 0≤z<0.02.

[0031] In some embodiments, the mass m1 of the first positive electrode active material and the mass m2 of the second positive electrode active material satisfy the relationship: 0 < m2 / m1 ≤ 0.25.

[0032] In some embodiments, the XRD diffraction pattern of the active material contains at least three diffraction peaks in the range of 17.8° to 19°; a first diffraction peak with an intensity of I1 exists in the range of 17.8° to 18.3°; two relatively strong diffraction peaks with intensities of I2 and I3 exist in the range of 18.3° to 19.0°; I2 corresponds to the (002) crystal plane of the first positive electrode active material, and I3 corresponds to the (111) crystal plane of the second positive electrode active material; the peak intensities of the diffraction peaks satisfy I2 / I1≥2, I3 / I1≥2, and 0.5≤I3 / I2≤2.

[0033] A second aspect of the present invention provides a method for preparing the above-mentioned composite cathode material, comprising the following steps:

[0034] S1: Mix the cobalt salt solution and the salt solution of doped element M uniformly according to the molar ratio of Co to M of (1-z):z, add excess precipitant solution, stir and filter to obtain precipitate; sinter the precipitate at 400℃~600℃ for 6~12h to obtain (Co 1-z M z )3O4 powder, where 0≤z<0.02;

[0035] S2: (Co) 1-z M z Na₂O₄ and sodium salt were mixed uniformly at a molar ratio of Na to Co of (0.5–0.7):(1–1.2); and sintered at 800–1100 °C for 45–52 h to obtain Na₂O₄ with a P₆₃mc crystal phase structure. n Co 1-z M z O2, where 0.5 ≤ n ≤ 0.7;

[0036] S3: Put Na n Co 1-z M z O2 was dispersed in a lithium salt solution and mixed evenly with a Li to Na molar ratio ≥ 5. The mixture was reacted in a reactor at 140–160 °C for 22–26 h. After pressure filtration, the mixture was washed with deionized water, dried, and then mechanically crushed to obtain Li. x Na y Co 1-z M z O2 single crystal particles;

[0037] S4: Nickel salt solution, manganese salt solution, and N-doped salt solution are mixed uniformly at a Mn:Fe:N molar ratio of a:(2-ab):b to form a mixed solution. This mixed solution is then mixed with a carbonate solution at a (Ni+N+Mn) to carbonate ion molar ratio of (0.8–1.2):(1.6–2.2). The addition rates of the nickel salt solution, manganese salt solution, and N-doped salt solution are controlled to obtain a series of Ni particles with different particle sizes. a Mn 2-a-b N b CO3 precipitation; then Ni a Mn 2-a-b N b CO3 precipitate and lithium salt were mixed uniformly at a Li:(Ni+Mn+N) molar ratio of (1.0–1.5):(1.8–2.4), and sintered at 750–1000℃ for 8–12 h to prepare LiNi with different particle sizes. a Mn 2-a-b N b O4 polycrystalline particles;

[0038] S5: Mix the materials prepared in steps S3 and S4 in a certain proportion, and sinter at 700-800℃ for 5-8 hours to obtain the composite cathode material.

[0039] In steps S1 and S2, a high-temperature solid-state method was used to prepare (Co). 1-z M z )3O4 precursor and Na n Co 1-z M z O2, step S3 employs an ion exchange method to prepare Li with a P63mc crystal structure. x Na y Co 1-z M z O2 single-crystal particles, prepared in step S4 using a high-temperature solid-state method, have... LiNi structure a Mn 2-a-b N b O4 polycrystalline spherical particles. Among them, the powder particles prepared by the high-temperature solid-state method exhibit no agglomeration, good filling properties, and the high-temperature solid-state method has advantages such as low cost, high yield, and simple preparation process; Li with a P63mc structure was prepared using the ion exchange method. x Na y Co 1-z M z O2 large single-crystal particles allow for control over the particle size of the prepared materials, facilitating the formation of large single-crystal active materials. Simultaneously, in the preparation... LiNi structure a Mn2-a-b N b By controlling the rate of reaction of O4 polycrystalline spherical particles, Ni particles of different sizes can be obtained. a Mn 2-a-b N b CO3 precipitation lays the foundation for subsequent polycrystalline spherical particles.

[0040] In some embodiments, the addition rate of the (Ni+Al+Mn) salt solution is 0.3 to 5.2 L / min, specifically 0.3 L / min, 0.5 L / min, 1.0 L / min, 1.5 L / min, 2.0 L / min, 2.5 L / min, 3.0 L / min, 3.5 L / min, 4.0 L / min, 4.5 L / min, 5.0 L / min, and 5.2 L / min; it may include, but is not limited to, the addition rates listed above, and is preferably 2.0 L / min.

[0041] In some embodiments, the sintering temperature of step S1 is 400-600℃, specifically 400℃, 450℃, 500℃, 550℃, 600℃, and may include, but is not limited to, the temperature values ​​exemplified above; the sintering time is 6-12h, specifically 6h, 7h, 8h, 9h, 10h, 11h, 12h, and may include, but is not limited to, the sintering times listed above, preferably 10h.

[0042] In some embodiments, the sintering temperature of step S2 is 800℃~1100℃, specifically 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, and may include, but is not limited to, the sintering temperatures listed above. The sintering time is 45~52h, specifically 45h, 46h, 47h, 48h, 49h, 50h, 51h, 52h, and may include, but is not limited to, the sintering times listed above, preferably 48h.

[0043] In some embodiments, the temperature of the reactor in step S3 is 140-160°C, specifically 140°C, 145°C, 150°C, 155°C, or 160°C, and may include, but is not limited to, the reactor temperatures listed above, preferably 150°C; the reaction time in the reactor is 22-26 hours, specifically 22 hours, 23 hours, 24 hours, 25 hours, or 26 hours, and may include, but is not limited to, the reaction times listed above, preferably 24 hours.

[0044] In some embodiments, step S4 involves sintering at 750–1000°C in an oxygen atmosphere for 8–12 hours. The sintering temperature can specifically be 750°C, 800°C, 850°C, 900°C, 950°C, or 1000°C, and may include, but is not limited to, the sintering temperatures listed above. The sintering time is 8–12 hours, specifically 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours, and may include, but is not limited to, the sintering times listed above, preferably 10 hours.

[0045] In some embodiments, step S5 involves sintering at 700–800°C for 5–8 hours. The sintering temperature can specifically be 700°C, 750°C, or 800°C, and may include, but is not limited to, the sintering temperatures listed above, with 750°C being preferred. The sintering time is 5–8 hours, and can specifically be 5 hours, 6 hours, 7 hours, or 8 hours, and may include, but is not limited to, the sintering times listed above, with 6 hours being preferred.

[0046] In step S1, the cobalt salt solution can be one of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate, preferably cobalt sulfate; the M salt solution of the dopant element can be one of aluminum sulfate and magnesium sulfate, preferably aluminum sulfate; the precipitant solution can be one of sodium carbonate and sodium hydroxide, preferably sodium carbonate. Additionally, the (Co) prepared in step S1... 1-z M z For 3O4 powder, the value of z is in the range of 0≤z<0.02. Excessive doping is not conducive to particle growth.

[0047] In step S2, the molar ratio of Na to Co is (0.5–0.7):(1–1.2), specifically 0.5:1, 0.5:1.1, 0.5:1.2, 0.6:1, 0.6:1.1, 0.6:1.2, 0.7:1, 0.7:1.1, 0.7:1.2, which may include but are not limited to the values ​​exemplified above, but preferably 0.7:1. The generated Na with the P63mc structure... n Co 1-z M z O2, where 0.5 ≤ n ≤ 0.7. In step S3, the lithium salt solution can specifically be lithium nitrate, lithium chloride, lithium carbonate, or lithium acetate, preferably lithium nitrate; in addition, the molar ratio of Li to Na in step S3 is ≥ 5, specifically 5, 6, 7, 8, 9, 10, or 11; it can include, but is not limited to, the values ​​exemplified above. Preferably, the Li / Na molar ratio is 10. If the Li / Na ratio is too low, it will result in low ion exchange efficiency and affect the performance of the battery.

[0048] In step S4, the nickel salt solution includes one of nickel chloride, nickel sulfate, and nickel nitrate, preferably lithium nitrate; the manganese salt solution includes one of manganese chloride, manganese sulfate, and manganese nitrate, preferably manganese chloride; and the salt solution containing the dopant element N includes one of aluminum sulfate and magnesium sulfate, preferably aluminum sulfate.

[0049] In step S4, the molar ratio of (Ni+N+Mn) to carbonate ions is (0.8–1.2):(1.6–2.2), specifically 0.8:1.6, 0.8:1.7, 0.8:1.8, 0.8:1.9, 0.8:2.0, 0.8:2.1, 0.8:2.2, 0.9:1.6, 0.9:1.7, 0.9:1.8, 0.9:1.9, 0.9:2.0, 0.9:2.1, 0.9:2.2, 1.0:1.6, 1.0:1.7, or 1.0:1.8. The ratios can be 1.0:1.9, 1.0:2.0, 1.0:2.1, 1.0:2.2, 1.1:1.6, 1.1:1.7, 1.1:1.8, 1.1:1.9, 1.1:2.0, 1.1:2.1, 1.1:2.2, 1.2:1.6, 1.2:1.7, 1.2:1.8, 1.2:1.9, 1.2:2.0, 1.2:2.1, 1.2:2.2; and can include, but are not limited to, the ratios exemplified above, with 1:2 being preferred. Excess carbonate ions are beneficial for the full precipitation of metal ions.

[0050] In step 4, the Li:(Ni+Mn+N) molar ratio is (1.0~1.5):(1.8~2.4), specifically 1.0:1.8, 1.0:1.9, 1.0:2.0, 1.0:2.1, 1.0:2.2, 1.0:2.3, 1.0:2.4, 1.1:1.8, 1.1:1.9, 1.1:2.0, 1.1:2.1, 1.1:2.2, 1.1:2.3, 1.1:2.4, 1.2:1.8, 1.2:1.9, 1.2:2.0, 1.2:2.1, 1.2:2.2, 1.2:2.3, 1.2:2 4, 1.3:1.8, 1.3:1.9, 1.3:2.0, 1.3:2.1, 1.3:2.2, 1.3:2.3, 1.3:2.4, 1.4:1.8, 1.4:1.9, 1.4:2.0, 1.4:2.1, 1.4:2.2, 1.4:2.3, 1.4:2.4, 1.5:1.8, 1.5:1.9, 1.5:2.0, 1.5:2.1, 1.5:2.2, 1.5:2.3, 1.5:2.4; these ratios can include, but are not limited to, those exemplified above. Excessive lithium salts can prevent the volatilization of Li during high-temperature calcination, which can lead to "lithium depletion".

[0051] Compared to traditional single-phase cathode active materials, the composite cathode material in this application comprises two components: one containing P63mc crystalline cathode material and the other containing P63mc crystalline cathode material. The crystalline phase cathode materials are used to control high-temperature cycling and low-temperature discharge respectively. Simultaneously, the two components are combined using a special monocrystalline / polycrystalline configuration. Specifically, the P63mc crystalline phase cathode material features a large-particle single-crystal design to reduce specific surface area, minimize side reactions with the electrolyte, and improve cycle life. The secondary particle polycrystalline design of the cathode material with a crystalline phase structure increases the reactive sites, which is conducive to the rapid extraction of lithium ions and improves low-temperature performance. By designing a reasonable ratio of the two cathode materials, the low-temperature cycle performance of the electrode can be balanced.

[0052] 2. Positive electrode plate

[0053] A third aspect of the present invention provides a positive electrode sheet comprising the composite positive electrode material described above, specifically comprising a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector, wherein the positive electrode active material is the positive electrode material described in the present invention.

[0054] The positive electrode current collector can be any material suitable for use as a positive electrode current collector in the field. For example, the positive electrode current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil.

[0055] 3. Secondary battery

[0056] A fourth aspect of the present invention aims to provide a secondary battery, comprising a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode described above.

[0057] The negative electrode includes a negative current collector and a negative active material layer coated on at least one surface of the negative current collector. The negative active material layer can be one or more of the following, including but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Specifically, the graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative current collector is typically a structure or component that collects current. The negative current collector can be any material suitable for use as a negative current collector in lithium-ion batteries, for example, it can be, but is not limited to, metal foil, and more specifically, copper foil.

[0058] The separator can be any material suitable for lithium-ion battery separators in the art, for example, it can be one or more of the following: polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.

[0059] The secondary battery also includes an electrolyte, which comprises an organic solvent, an electrolyte lithium salt, and additives. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-resistant electrolytes; or it can be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DFC, DMC, or EMC; or it can be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include, but are not limited to, at least one of film-forming additives, conductive additives, flame-retardant additives, overcharge-resistant additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.

[0060] To make the technical solution and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto.

[0061] Example 1

[0062] The preparation method of the composite cathode material in this embodiment is as follows:

[0063] Step 1: Mix cobalt sulfate solution and aluminum sulfate at a Co to Al molar ratio of 0.99:0.01 until homogeneous. Add excess sodium carbonate solution, stir, and filter to obtain a precipitate. Sinter the precipitate at 550℃ for 10 hours to obtain (Co... 0.99 Al 0.01 )3O4 powder.

[0064] Step 2: Preparation of Na by high-temperature solid-state reaction 0.7 Co 0.99 Al 0.01 O2

[0065] (Co) 0.99 Al 0.01 Na₃O₄ and Na₂CO₃ were mixed uniformly at a Na to Co molar ratio of 0.7:1; and sintered at 950℃ for 48 h to obtain Na with a P63mc structure. 0.7 Co0.99 Al 0.01 O2.

[0066] Step 3: Preparation of P63mc structured Li by ion exchange method x Na y Co 1-z M z O2 large single crystal particles

[0067] Will Na 0.7 Co 0.99 Al 0.01 O2 and lithium nitrate were mixed uniformly at a Li:Na molar ratio of 10:1 and reacted at 200℃ for 24 h. The mixture was then washed with deionized water, dried, and mechanically crushed (feed frequency 35 Hz) to obtain Li with a Dv50 of 15 μm. 0.87 Na 0.13 Co 0.99 Al 0.01 O2 single crystal particles.

[0068] Step 4: High-temperature solid-state reaction preparation LiNi structure 0.5 Mn 1.49 Al 0.01 O4 polycrystalline spherical particles

[0069] Nickel sulfate solution, manganese sulfate solution, and aluminum sulfate solution were mixed thoroughly at a Ni:Mn:Al molar ratio of 0.5:1.49:0.01. The (Ni+Al+Mn) salt solution was added at a rate of 2 L / min. The solution was then mixed with sodium carbonate solution at a (Ni+Al+Mn) to carbonate molar ratio of 1:2. After thorough precipitation and filtration, Ni was obtained. 0.5 Mn 1.49 Al 0.01 CO3 precipitation was then performed; the precipitate was mixed with lithium hydroxide at a Li:(Ni+Mn+N) molar ratio of 1.2:2, and sintered at 750–1000 °C for 10 h to obtain LiNi with a Dv50 of 4 μm. 0.5 Mn 1.49 Al 0.01 O4 polycrystalline spherical particles.

[0070] Step 5: Preparation of composite cathode material

[0071] The Li prepared in step 3 0.87 Na 0.13 Co 0.99 Al 0.01 O2 cathode material and LiNi prepared in step 4 0.5 Mn 1.49 Al 0.01O4 cathode material was mixed at a mass ratio of 95:5 and sintered at 750℃ for 6 hours to obtain composite cathode material LNMO@LCO-1.

[0072] Example 2

[0073] The difference between this embodiment and Embodiment 1 is that, in step (3), the feeding frequency of the mechanical crusher is adjusted from 35Hz to 32Hz, resulting in the preparation of Li with a Dv50 of 10μm. 0.87 Na 0.13 Co 0.99 Al 0.01 O2 cathode material.

[0074] The rest is the same as in Example 1, and will not be repeated here.

[0075] Example 3

[0076] The difference between this embodiment and Embodiment 1 is that, in step (3), the feeding frequency of the mechanical crusher is adjusted from 35Hz to 41Hz, resulting in the preparation of Li with a Dv50 of 25μm. 0.87 Na 0.13 Co 0.99 Al 0.01 O2 cathode material.

[0077] The rest is the same as in Example 1, and will not be repeated here.

[0078] Example 4

[0079] The difference between this embodiment and Embodiment 1 is that, in step (4), the addition rate of the (Ni+Al+Mn) salt solution is controlled at 3.6 L / min to prepare LiNi. 0.5 Mn 1.49 Al 0.01 The Dv50 of the O4 cathode material is 6.2 μm.

[0080] The rest is the same as in Example 1, and will not be repeated here.

[0081] Example 5

[0082] The difference between this embodiment and Embodiment 1 is that, in step (4), the addition rate of the (Ni+Al+Mn) salt solution is controlled at 1.7 L / min to prepare LiNi. 0.5 Mn 1.49 Al 0.01 The Dv50 of the O4 cathode material is 3.4 μm.

[0083] The rest is the same as in Example 1, and will not be repeated here.

[0084] Example 6

[0085] The difference between this embodiment and embodiment 1 is that in step (5), Li 0.87 Na 0.13 Co 0.99 Al 0.01 O2 cathode material and LiNi 0.5 Mn 1.49 Al 0.01 The mass ratio of O4 cathode material is 80:20.

[0086] The rest is the same as in Example 1, and will not be repeated here.

[0087] Example 7

[0088] The difference between this embodiment and embodiment 1 is that in step (5), Li 0.87 Na 0.13 Co 0.99 Al 0.01 O2 cathode material and LiNi 0.5 Mn 1.49 Al 0.01 The mass ratio of O4 cathode material is 99:1.

[0089] The rest is the same as in Example 1, and will not be repeated here.

[0090] Comparative Example 1

[0091] Step 1: High-temperature solid-state reaction to prepare (Co) 0.99 Al 0.01 )3O4 precursor

[0092] Cobalt sulfate solution and aluminum sulfate were mixed evenly at a Co:Al molar ratio of 0.99:0.01. Excess sodium carbonate solution was added, and the mixture was stirred and filtered to obtain a precipitate. The precipitate was sintered at 550℃ for 10 hours to obtain (Co... 0.99 Al 0.01 )3O4 powder.

[0093] Step 2: Preparation of Na by high-temperature solid-state reaction 0.7 Co 0.99 Al 0.01 O2

[0094] (Co) 0.99 Al 0.01 Na₃O₄ and Na₂CO₃ were mixed uniformly at a Na to Co molar ratio of 0.7:1; and sintered at 950℃ for 48 h to obtain Na with a P63mc structure. 0.7 Co 0.99 Al 0.01 O2.

[0095] Step 3: Preparation of P63mc structured Li by ion exchange method x Nay Co 1-z M z O2 single crystal large particles

[0096] Will Na 0.7 Co 0.99 Al 0.01 O2 and lithium nitrate were mixed uniformly at a Li:Na molar ratio of 10:1 and reacted at 200℃ for 24 h. The mixture was then washed with deionized water, dried, and mechanically crushed to obtain Li with a Dv50 of 15 μm. 0.87 Na 0.13 Co 0.99 Al 0.01 O2 large-particle single crystal.

[0097] Step 4: The Li prepared in step 3... 0.87 Na 0.13 Co 0.99 Al 0.01 The O2 cathode material was sintered at 750℃ for 6 hours to obtain the comparative example LCO-1.

[0098] The rest is the same as in Example 1, and will not be repeated here.

[0099] Comparative Example 2

[0100] Step 1: High-temperature solid-state reaction preparation LiNi structure 0.5 Mn 1.49 Al 0.01 O4 polycrystalline spherical particles

[0101] Nickel sulfate solution, manganese sulfate solution, and aluminum sulfate solution were mixed thoroughly at a Ni:Mn:Al molar ratio of 0.5:1.49:0.01. The (Ni+Al+Mn) salt solution was added at a rate of 2 L / min. Then, it was mixed with sodium carbonate solution at a (Ni+Al+Mn) to carbonate molar ratio of 1:2. After thorough precipitation and filtration, Ni was obtained. 0.5 Mn 1.49 Al 0.01 CO3 precipitation was then performed; the precipitate was mixed with lithium hydroxide at a Li:(Ni+Mn+N) molar ratio of 1.2:2, and sintered at 900℃ for 10 h to obtain LiNi with a Dv50 of 4 μm. 0.5 Mn 1.49 Al 0.01 O4 polycrystalline spherical particles.

[0102] Step 2: The LiNi prepared in Step 1... 0.5 Mn 1.49 Al 0.01 The O4 cathode material was sintered at 750℃ for 6 hours to obtain the comparative LNMO-2.

[0103] Comparative Example 3

[0104] The difference between this comparative example and Example 1 is that in step (4), the addition rate of the (Ni+Al+Mn) salt solution is controlled at 0.5 L / min, resulting in the prepared LiNi 0.5 Mn 1.49 Al 0.01 The Dv50 of the O4 cathode material is 0.2 μm.

[0105] The rest is the same as in Example 1, and will not be repeated here.

[0106] Comparative Example 4

[0107] The difference between this comparative example and Example 1 is that in step (4), the addition rate of the (Ni+Al+Mn) salt solution is controlled at 5 L / min to prepare LiNi. 0.5 Mn 1.49 Al 0.01 The Dv50 of the O4 cathode material is 8 μm.

[0108] The rest is the same as in Example 1, and will not be repeated here.

[0109] Comparative Example 5

[0110] The difference between this comparative example and Example 1 is that, in step (5), Li 0.87 Na 0.13 Co 0.99 Al 0.01 O2 cathode material and LiNi 0.5 Mn 1.49 Al 0.01 The mass ratio of O4 cathode material is 50:50.

[0111] The rest is the same as in Example 1, and will not be repeated here.

[0112] The cathode materials obtained in Examples 1-7 and Comparative Examples 1-5 were used in lithium-ion coin cells. Specific capacity tests were conducted at 25°C with a charge / discharge rate of 0.1C and a range of 3.0V-4.60V. Cyclic tests were performed at 45°C for 100 cls with a charge / discharge rate of 1.0C and a range of 3.0V-4.60V. Low-temperature discharge tests were conducted at -10°C with a charge / discharge rate of 0.1C and a range of 3.0V-4.60V. The specific parameters and test results of the above examples and comparative examples are summarized in Tables 1 and 2.

[0113] Table 1

[0114] Table 2

[0115] As can be seen from the comparison of the results in Table 2 above, the composite cathode material in this invention utilizes the large single crystal of P63mc crystal cathode material and The polycrystalline design of the crystalline cathode material, along with particle size matching and ratio design, improves the structural stability and low-temperature kinetics of the composite material, enabling it to simultaneously achieve high-voltage cycle performance and low-temperature performance.

[0116] Based on the test results of Examples 1-7 and Comparative Examples 1-5, the P63mc crystal form of Li 0.87 Na 0.13 Co 0.99 Al 0.01 O2 large single crystal particles have high specific capacity, good cycle stability, but weak low-temperature performance. LiNi, a crystalline cathode material 0.5 Mn 1.49 Al 0.01 O4 polycrystalline particles exhibit good low-temperature performance but have relatively low specific capacity. When Li... 0.87 Na 0.13 Co 0.99 Al 0.01 When the O2 single crystal grain size increases, the specific capacity of the composite material decreases slightly, the cycle performance improves, and the low-temperature performance decreases; when LiNi 0.5 Mn 1.49 Al 0.01 When the particle size of O4 polycrystalline particles increases, the composite material's specific capacity, cycle performance, and low-temperature discharge performance do not change significantly due to their smaller proportion. The cathode material with P63mc crystal structure, Li... 0.87 Na 0.13 Co 0.99 Al 0.01 O2 and LiNi, a crystalline cathode material 0.5 Mn 1.49 Al 0.01 When the O4 mass ratio decreases, the specific capacity of the composite material decreases significantly.

[0117] In summary, this invention designs a cathode material comprising large single-crystal particles of P63mc crystalline phase and... Composite materials of polycrystalline particles for crystalline cathode materials; Under high voltage, the P63mc crystalline cathode material, due to the unique coplanar connection of LiO6 octahedra and CoO6 octahedra, only exhibits CoO2 layer slip and Li vacancy arrangement, avoiding cycle decay caused by irreversible capacity loss. Simultaneously, the single-crystal design effectively reduces interfacial side reactions and improves high-temperature cycling; in composite materials... The crystalline cathode material possesses a three-dimensional lithium-ion diffusion channel, enabling rapid lithium-ion extraction under high voltage. Simultaneously, its polycrystalline design with secondary particles increases reactive sites and improves the low-temperature discharge performance of the composite material. Optimization of P63mc crystalline cathode material and... The particle size design and ratio optimization of crystalline cathode materials can enable composite materials to achieve both high-voltage cycle performance and low-temperature performance.

[0118] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A composite cathode material, characterized in that, It includes a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material is a single crystal particle of P63mc crystal form, and the second positive electrode active material is... The composite positive electrode material consists of polycrystalline particles of the same crystalline form; the average particle size of the first positive electrode active material is D1, and the average particle size of the second positive electrode active material is D2, with 0.16 ≤ D2 / D1 ≤ 0.414; in the composite positive electrode material, the mass of the first positive electrode active material is m1, and the mass of the second positive electrode active material is m2, with 0 < m2 / m1 < 1.

2. The composite cathode material according to claim 1, characterized in that, The average particle size D1 of the first positive electrode active material satisfies: 10μm≤D1≤25μm, and the average particle size D2 of the second positive electrode active material satisfies: 0.2μm≤D2≤8μm.

3. The composite cathode material according to claim 1, characterized in that, The composite cathode material has the general chemical formula: LiNi a Mn 2-a-b N b O4@Li x Na y Co 1-z M z O2, wherein M and N each include at least one of the elements Al, Mg, Ti, La, Y, Zn, Ni, Mn, Co, V, and Si; wherein 0 ≤ a < 0.6, 0 ≤ b < 0.02; 0.7 ≤ x < 1, 0.01 < y < 0.1, and 0 ≤ z < 0.

02.

4. The composite cathode material according to claim 3, characterized in that, The first positive electrode active material is Li x Na y Co 1-z M z O2, the second positive electrode active material is LiNi a Mn 2-a-b N b O4; where 0≤a<0.6, 0≤b<0.02; 0.7≤x<1, 0.01<y<0.1, 0≤z<0.

02.

5. The composite cathode material according to claim 1, characterized in that, The mass m1 of the first positive electrode active material and the mass m2 of the second positive electrode active material satisfy the relationship: 0 < m2 / m1 ≤ 0.

25.

6. The composite cathode material according to claim 1, characterized in that, The XRD diffraction pattern of the composite cathode material contains at least three diffraction peaks in the range of 17.8° to 19°; it has a first diffraction peak in the range of 17.8° to 18.3° with a peak intensity of I1; and a second and a third diffraction peak in the range of 18.3° to 19.0° with peak intensities of I2 and I3, respectively; I2 corresponds to the (002) crystal plane of the first cathode active material, and I3 corresponds to the (111) crystal plane of the second cathode active material; the peak intensities of the diffraction peaks satisfy the following relationships: I2 / I1≥2, I3 / I1≥2, 0.5≤I3 / I2≤2.

7. A method for preparing a composite cathode material according to any one of claims 1-6, characterized in that, Includes the following steps: S1: Mix the cobalt salt solution and the salt solution of doped element M uniformly according to the molar ratio of Co to M of (1-z):z, add excess precipitant solution, stir and filter to obtain precipitate; sinter the precipitate at 400℃~600℃ for 6~12h to obtain (Co 1-z M z )3O4 powder, where 0≤z<0.02; S2: (Co) 1-z M z Na₂O₄ and sodium salt were mixed uniformly at a molar ratio of Na to Co of (0.5–0.7):(1–1.2); and sintered at 800–1100 °C for 45–52 h to obtain Na₂O₄ with a P₆₃mc crystal phase structure. n Co 1-z M z O2, where 0.5 ≤ n ≤ 0.7; S3: Put Na n Co 1-z M z O2 was dispersed in a lithium salt solution and mixed evenly with a Li to Na molar ratio ≥ 5. The mixture was reacted in a reactor at 140–160 °C for 22–26 h. After pressure filtration, the mixture was washed with deionized water, dried, and then mechanically crushed to obtain Li. x Na y Co 1-z M z O2 single crystal particles; S4: Nickel salt solution, manganese salt solution, and N-doped salt solution are mixed uniformly at a molar ratio of Mn, Fe, and N of a:(2-ab):b to form a mixed solution. This mixed solution is then mixed with a carbonate solution at a molar ratio of (Ni+N+Mn) to carbonate ions of (0.8–1.2):(1.6–2.2). The addition rates of the nickel salt solution, manganese salt solution, and N-doped salt solution are controlled to obtain Ni particles of different sizes. a Mn 2-a-b N b CO3 precipitation; then Ni a Mn 2-a-b N b CO3 precipitate and lithium salt were mixed uniformly at a Li:(Ni+Mn+N) molar ratio of (1.0–1.5):(1.8–2.4), and sintered at 750–1000℃ for 8–12 h to prepare LiNi with different particle sizes. a Mn 2-a-b N b O4 polycrystalline particles; S5: Mix the materials prepared in steps S3 and S4 in a certain proportion, and sinter at 700-800℃ for 5-8 hours to obtain the composite cathode material.

8. The method for preparing a composite cathode material according to claim 7, characterized in that, In step S4, the addition rate is 0.3 to 5.2 L / min.

9. A positive electrode plate, characterized in that, Includes the composite cathode material as described in any one of claims 1 to 6.

10. A secondary battery, comprising a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, characterized in that, The positive electrode is the positive electrode as described in claim 9.

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