A positive electrode material, a secondary battery, and an electric device

Abstract

The application discloses a positive electrode material, a secondary battery and an electric device, and belongs to the technical field of batteries. The application ensures the formation of a dense coating layer on the surface of the positive electrode active material, and simultaneously has suitable electron and ion transmission channels, effectively improves the electron conductivity and ion transmission of the positive electrode material of the secondary battery, by coating the positive electrode active material with a coating material containing an electron conductor and an ion conductor on at least part of the surface of the positive electrode active material, and controlling the ratio of the particle size Dv50 of the positive electrode active material and the electron conductor to be within the range of 1:(0.01-0.25), and the ratio of the particle size Dv50 of the positive electrode active material and the ion conductor to be within the range of 1:(0.08-0.5).

Description

Technical Field

[0001] This invention relates to the field of new energy technology, specifically to a cathode material, a secondary battery, and an electrical device. Background Technology

[0002] Secondary batteries, especially sodium-ion batteries, are an ideal alternative to lithium-ion batteries due to the abundance and low cost of sodium resources, and are receiving increasing attention in large-scale energy storage applications. Currently, the main cathode materials used in sodium-ion batteries include layered oxides and polyanionic cathode active materials. Layered oxides, used as cathode materials for sodium-ion batteries, offer advantages such as high capacity, high voltage, and high energy density, but they also have inherent limitations, such as low electronic conductivity and poor interfacial ion transport characteristics, leading to poor structural stability and rate performance. Polyanionic cathode active materials offer structural stability, high safety, and high operating voltage, but their low electronic conductivity limits their capacity.

[0003] Improving the electronic and ionic conductivity of cathode materials for sodium-ion batteries has become a pressing technical challenge. Summary of the Invention

[0004] Based on the deficiencies of existing technologies, the purpose of this invention is to provide a cathode material, a secondary battery, and an electrical device to effectively improve the electronic conductivity and ionic conductivity of the cathode material.

[0005] In a first aspect, the present invention provides a positive electrode material, comprising a positive electrode active material and a coating material, wherein the coating material is at least distributed on a portion of the surface of the positive electrode active material;

[0006] The coating material comprises electronic conductors and ionic conductors;

[0007] The ratio of the particle size Dv50 of the positive electrode active material and the electronic conductor is 1:(0.01~0.25);

[0008] The ratio of the particle size Dv50 of the positive electrode active material and the ion conductor is 1:(0.08~0.5).

[0009] Preferably, the particle size Dv50 of the ion conductor is 0.5–5 μm.

[0010] Preferably, the ionic conductor includes at least one of a first ionic conductor and a second ionic conductor, wherein the first ionic conductor has a Nasicon structure and the second ionic conductor has a layered structure.

[0011] Preferably, the first ionic conductor comprises Na 3+Ax Zr 2-0.5Ax Mx Si2PO 12 M is selected from at least one of Li, Ca, Mg, Sr, Ba, In, Ga, Nb, La, Cr, Mn, Zn, Al, Ge, and Bi, and A is the valence state of element M, 0 ≤ x ≤ 0.5; the second ionic conductor includes β”-Na y Al2O3, where 0 <y<1。

[0012] Preferably, the mass ratio of the first ionic conductor to the second ionic conductor is 1:(0.16-6).

[0013] Preferably, the coating material further includes a polymer, wherein the polymer includes at least one of polyacrylonitrile, polyvinylpyrrolidone, and polyethylene oxide.

[0014] Preferably, the mass of the polymer is 0.5% to 3% of the total mass of the coating material.

[0015] Preferably, the mass of the ionic conductor is 10% to 90% of the total mass of the electronic conductor and the ionic conductor.

[0016] Preferably, the thickness of the coating material on the surface of the positive electrode active material is 0.6–8 μm;

[0017] Secondly, the present invention provides a secondary battery comprising the aforementioned positive electrode material.

[0018] Thirdly, the present invention provides an electrical device including the aforementioned secondary battery, wherein the secondary battery serves as the power supply for the electrical device.

[0019] Compared with the prior art, the beneficial effects of this application are as follows:

[0020] (1) This application coats at least part of the surface of the positive electrode active material with a coating material containing electronic conductors and ionic conductors. The electronic conductor coating improves the conductivity of the positive electrode active material, the ionic conductor coating promotes the interfacial ion transport effect, and the coating layer formed by the electronic conductors and ionic conductors inhibits the phase transition of the positive electrode active material during the electrochemical process, thereby improving its stability. In addition, the ionic conductors on the surface can even effectively remove HF in the electrolyte, reduce the corrosion of the positive electrode active material by acid during the electrochemical process, reduce the dissolution of transition metal ions, and further improve the stability of the positive electrode active material.

[0021] (2) This application ensures that a dense coating layer is formed on the surface of the positive electrode active material by controlling the ratio of particle size Dv50 of the positive electrode active material and the electronic conductor to be in the range of 1:(0.01 to 0.25) and the ratio of particle size Dv50 of the positive electrode active material and the ion conductor to be in the range of 1:(0.08 to 0.5). This allows the ion conductor to not only be in close contact with the positive electrode active material to facilitate ion transport, but also to be in close contact with the electronic conductor to facilitate electron transport.

[0022] (3) This application effectively improves the electronic conductivity and ionic conductivity of the positive electrode material of secondary battery, and the method is simple and easy to industrialize and promote. Attached Figure Description

[0023] Figure 1 These are schematic diagrams of the cathode materials in each embodiment and comparative example;

[0024] Among them, 1-positive active material, 2-coating material. Detailed Implementation

[0025] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and comparative examples. The purpose of this description is to provide a detailed understanding of the invention, not to limit its scope. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this invention are commonly used reagents and instruments.

[0026] In this application, particle size Dv50 refers to the particle size when the volumetric cumulative distribution in the particle size distribution of the sample is 50%.

[0027] (1) Positive electrode material

[0028] According to a first aspect of this application, a method is provided that includes a positive electrode active material and a coating material, wherein the coating material is at least distributed on a portion of the surface of the positive electrode active material;

[0029] The coating material includes electronic conductors and ionic conductors;

[0030] The ratio of particle size Dv50 of the positive electrode active material and the electronic conductor is 1:(0.01~0.25);

[0031] The ratio of particle size Dv50 of the positive electrode active material and the ion conductor is 1:(0.08~0.5).

[0032] In this application, by coating at least a portion of the surface of the positive electrode active material with a coating material containing both electronic and ionic conductors, the conductivity of the positive electrode active material is improved by the electronic conductor coating, the interfacial ion transport effect is promoted by the ionic conductor coating, and the coating layer formed by the electronic and ionic conductors inhibits the phase transition of the positive electrode active material during electrochemical processes, thereby improving its stability. In addition, the ionic conductors on the surface can even effectively remove HF from the electrolyte, because the metal elements contained in the ionic conductors can combine with the fluorine element, reducing the generation of HF, thereby mitigating the corrosion of the positive electrode active material by acid during electrochemical processes, reducing the dissolution of transition metal ions, and further improving the stability of the positive electrode active material.

[0033] In practical applications, XPS argon ion etching can be used to remove the coating material of the positive electrode active material layer, followed by laser particle size analysis to measure the Dv50 of the main positive electrode active material. Alternatively, the main positive electrode active material can be dissolved with hydrochloric acid, retaining both ionic and electronic conductors. The electronic conductor can be removed by calcination, allowing the Dv50 of the ionic conductor to be measured using a laser particle size analyzer. Another option is to use aqua regia to remove the ionic conductor, retaining the electronic conductor, and then measure the Dv50 of the electronic conductor using a laser particle size analyzer.

[0034] In this application, by controlling the ratio of particle size Dv50 of the positive electrode active material and the electronic conductor to be within the range of 1:(0.01 to 0.25) and the ratio of particle size Dv50 of the positive electrode active material and the ion conductor to be within the range of 1:(0.08 to 0.5), a dense coating layer is formed on the surface of the positive electrode active material. This ensures that the ion conductor is not only in close contact with the positive electrode active material to facilitate ion transport, but also in close contact with the electronic conductor to facilitate electron transport. At the same time, the coating layer has suitable pore channels, further improving the transport efficiency of electrons and ions, thereby giving the battery better electrochemical performance, such as higher rate capability and better cycle stability.

[0035] In some embodiments, the particle size Dv50 of the positive electrode active material is 5–80 μm, the particle size Dv50 of the electronic conductor is 0.05–7.5 μm, and the particle size Dv50 of the ionic conductor is 0.075–15 μm. The positive electrode material of this application exhibits high electronic and ionic conductivity, effectively solving the technical problem of low electronic and ionic conductivity in existing secondary battery positive electrode materials. Furthermore, the production method is simple, facilitating industrial production and widespread application.

[0036] In some embodiments, the particle size Dv50 of the ion conductor is 0.5–5 μm. When the particle size distribution of the ion conductor is within the above range, it is beneficial to improve the compactness of the coating layer, thereby facilitating the transport of ions and electrons.

[0037] In some embodiments, the ionic conductor includes at least one of a first ionic conductor and a second ionic conductor. The first ionic conductor has a Nasicon structure, and the second ionic conductor has a layered structure. Both the first ionic conductor and the second ionic conductor have good ionic conduction properties, and both can effectively remove HF in the electrolyte, reduce the corrosion of the cathode active material by acid during the electrochemical process, reduce the dissolution of transition metal ions, and further improve the stability of the cathode active material.

[0038] In some specific embodiments, the ionic conductor includes a first ionic conductor and a second ionic conductor to optimize the ion transport efficiency and reduce the impedance by taking advantage of the differences in the particle shape structure and ionic conduction characteristics of the two. In some embodiments, the ionic conductivity of the ionic conductor is 1×10 -4 ~9×10 -3 S / cm.

[0039] In some embodiments, the first ionic conductor includes Na 3+Ax Zr 2-0.5Ax M x Si2PO 12 , where M is selected from at least one of Li, Ca, Mg, Sr, Ba, In, Ga, Nb, La, Cr, Mn, Zn, Al, Ge, Bi, A is the valence state of the M element, and 0≤x≤0.5; the second ionic conductor includes β”-Na y Al2O3, where 0<y<1. In some specific embodiments, the mass ratio of the first ionic conductor to the second ionic conductor is 1:(0.16~6). The above-mentioned first ionic conductor and second ionic conductor have excellent ionic conduction properties, which are beneficial to reducing the material impedance value and improving the battery rate performance. In practical applications, the proportions of the first ionic conductor and the second ionic conductor can be accurately calculated by measuring the content of characteristic elements by ICP. For example, by quantitatively testing the Zr element in the first ionic conductor and the Al element in the second ionic conductor, the specific contents and proportional relationships of the above two ionic conductors can be obtained.

[0040] In some embodiments, the coating material further includes a polymer, and the polymer includes at least one of polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), etc., but the types of polymers are not limited thereto. In some specific embodiments, the mass of the polymer is 0.5%~3% of the total mass of the coating material. By adding a polymer to the coating material, the components in the coating material are bonded together to make the coating layer denser.

[0041] In some embodiments, the cathode active material includes at least one of a layered oxide and a polyanionic cathode active material.

[0042] In some embodiments, the crystal structure of the layered oxide includes at least one of an O3 phase and a P2 phase. The O3 phase has open Na+ ions. + The channel has high capacity, but its stability is relatively poor. The P2 phase has a more stable structure.

[0043] In some specific embodiments, the layered oxide includes Na x MO2, where x ≤ 1, and M is at least one transition metal. M can be selected from at least one of Fe, Co, Ni, Mn, Ti, Cr, etc., but is not limited to these. When x is in the range of 0.8 to 1, Na... x The crystal structure of MO2 is the O3 phase; when x is in the range of 0.6 to 0.7, Na x The crystal structure of MO2 is a P2 phase.

[0044] In some specific embodiments, the polyanionic positive electrode active material includes Na3V2(PO4)3, but is not limited to this.

[0045] In some embodiments, the mass of the ionic conductor is 10% to 90% of the total mass of the electronic and ionic conductors. Preferably, the mass of the ionic conductor is 30% to 50% of the total mass of the electronic and ionic conductors to further improve the electronic conductivity and ionic conductivity of the cathode material.

[0046] In some embodiments, the mass ratio of the ion conductor to the positive electrode active material is 1:(10-500). Preferably, the mass ratio of the ion conductor to the positive electrode active material is 1:(100-300), and the molar ratio of the ion conductor to the positive electrode active material is 1:300 to 1:10. A mass ratio within the above range ensures that the positive electrode material has better ion conductivity, which is beneficial for ensuring that the positive electrode material has lower impedance.

[0047] In some embodiments, the thickness of the coating material on the surface of the positive electrode active material is 0.6–8 μm. If the thickness of the coating material on the surface of the positive electrode active material is too large, the battery efficiency will be low and the capacity decay will be rapid in the early stages of cycling; if the thickness of the coating material on the surface of the positive electrode active material is too small, it will be detrimental to the battery capacity and cycle performance. Therefore, the thickness of the coating material on the surface of the positive electrode active material is controlled within the range of 0.6–8 μm.

[0048] In some embodiments, the electronic conductor comprises a carbon material. The carbon material may be selected from at least one of hard carbon, soft carbon, graphene, carbon nanotubes, and graphene oxide, but is not limited thereto.

[0049] In some specific embodiments, the preparation method of the positive electrode material includes the following steps:

[0050] Sodium source, zirconium source, silicon source, phosphorus source, carbon source and positive electrode active material are added to a solvent and dispersed to obtain a precursor slurry;

[0051] After removing the solvent from the obtained precursor slurry, it was calcined under a protective atmosphere to obtain a surface-coated Na3Zr2Si2PO4. 12 The positive electrode active material is obtained by combining carbon materials. The sodium source includes, but is not limited to, sodium acetate, sodium citrate, sodium carbonate, and sodium bicarbonate; the zirconium source includes, but is not limited to, zirconium acetate, zirconium oxide, zirconium nitrate, and zirconium oxynitrate; the silicon source includes, but is not limited to, silicon dioxide, ethyl silicate, and sodium silicate; the phosphorus source includes, but is not limited to, phosphoric acid, ammonium hydrogen phosphate, sodium phosphate, and sodium hydrogen phosphate; the carbon source includes, but is not limited to, glucose, sucrose, starch, polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone, and polymethyl methacrylate; the solvent includes, but is not limited to, ethanol, acetone, methanol, isopropanol, N-methylpyrrolidone, N,N-dimethylformamide, and triethylene glycol; before preparation... When preparing the precursor slurry, the order in which the raw materials are added is not limited, as long as they are evenly dispersed. However, in some specific embodiments, when preparing the precursor slurry, the sodium source, zirconium source, silicon source, and phosphorus source are first added to the solvent and completely dissolved. Then, the carbon source is added and dispersed. Finally, the positive electrode active material is added and dispersed to obtain the precursor slurry. This method is more conducive to the even dispersion of the raw materials. After removing the solvent, the obtained precursor slurry can be directly calcined or pre-calcined before calcination. The pre-calcination temperature is 200-300℃ and the pre-calcination time is 1-5 hours. The calcination temperature is not lower than 800℃ and the calcination time is greater than 1 hour.

[0052] In some specific embodiments, the preparation method of the positive electrode material includes the following steps:

[0053] Aluminum source, sodium source and carbon source are added to solvent, completely dissolved and then the solvent is removed. The mixture is calcined to obtain Na-β”-Al2O3 block, which is then ground and sieved to obtain Na-β”-Al2O3 powder.

[0054] The obtained Na-β”-Al2O3 powder and carbon source were added to a solvent, dispersed, and then the positive electrode active material was added and dispersed to obtain a precursor slurry.

[0055] The obtained precursor slurry is calcined under a protective atmosphere after removing the solvent to obtain a positive electrode active material coated with Na-β”-Al2O3 and carbon material, i.e., the positive electrode material. The aluminum source includes, but is not limited to, aluminum chloride, aluminum nitrate, and aluminum sulfate; the sodium source includes, but is not limited to, sodium chloride, sodium nitrate, and sodium sulfate; the carbon sources used in preparing the Na-β”-Al2O3 block and the precursor slurry include, but are not limited to, glucose, sucrose, starch, polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone, and polymethyl methacrylate; the solvents used in preparing the Na-β”-Al2O3 block and the precursor slurry include, but are not limited to, water, ethanol, acetone, methanol, isopropanol, N-methylpyrrolidone, N,N-dimethylformamide, and triethylene glycol; the calcination temperature for preparing the Na-β”-Al2O3 block is not lower than 800℃, and the calcination time is greater than 1 hour; the calcination temperature for the precursor slurry is not lower than 600℃, and the calcination time is greater than 1 hour. The carbon source used to prepare Na-β”-Al2O3 blocks accounts for 0.5-2% of the total mass of all carbon sources. It should be noted that these examples only consider the mass of Al2O3 and the hard carbon contained therein when calculating the mass of Na-β”-Al2O3 powder, and the same applies below.

[0056] In some specific embodiments, the preparation method of the positive electrode material includes the following steps:

[0057] Aluminum source, sodium source and carbon source are added to solvent, completely dissolved and then the solvent is removed. The mixture is calcined to obtain Na-β”-Al2O3 block, which is then ground and sieved to obtain Na-β”-Al2O3 powder.

[0058] The obtained Na-β”-Al2O3 powder, sodium source, zirconium source, silicon source, phosphorus source, and carbon source were added to a solvent, dispersed, and then the positive electrode active material was added and dispersed to obtain a precursor slurry.

[0059] After removing the solvent, the obtained precursor slurry was calcined under a protective atmosphere to obtain a surface-coated Na-β”-Al2O3 and Na3Zr2Si2PO4. 12The positive electrode active material, along with carbon materials, yields the positive electrode material. The aluminum source includes, but is not limited to, aluminum chloride, aluminum nitrate, and aluminum sulfate; the sodium source used to prepare Na-β”-Al2O3 blocks includes, but is not limited to, sodium chloride, sodium nitrate, and sodium sulfate; the sodium source used to prepare the precursor slurry includes, but is not limited to, sodium acetate, sodium citrate, sodium carbonate, and sodium bicarbonate; the zirconium source includes, but is not limited to, zirconium acetate, zirconium oxide, zirconium nitrate, and zirconium oxynitrate; the silicon source includes, but is not limited to, silicon dioxide, ethyl silicate, and sodium silicate; the phosphorus source includes, but is not limited to, phosphoric acid, ammonium hydrogen phosphate, sodium phosphate, and sodium hydrogen phosphate; the materials used to prepare Na-β”-Al2O3 blocks and the precursor slurry... The carbon sources include, but are not limited to, glucose, sucrose, starch, polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone, and polymethyl methacrylate; the solvents used to prepare Na-β”-Al2O3 blocks and the solvents used to prepare the precursor slurry include, but are not limited to, water, ethanol, acetone, methanol, isopropanol, N-methylpyrrolidone, N,N-dimethylformamide, and triethylene glycol; the calcination temperature for preparing Na-β”-Al2O3 blocks is not lower than 800℃ and the calcination time is greater than 1 hour; the calcination temperature for the precursor slurry is not lower than 800℃ and the calcination time is greater than 1 hour.

[0060] (2) Secondary batteries / electrical equipment

[0061] According to a second aspect of this application, a secondary battery or electrical device is provided, including a positive electrode sheet, the positive electrode sheet including a positive current collector and the aforementioned positive electrode material, the aforementioned positive electrode material being distributed on at least one surface of the positive current collector.

[0062] This application does not impose specific restrictions on the selection of the positive electrode current collector; any positive electrode current collector of any secondary battery in this technical field can be selected.

[0063] In this application, the secondary battery also includes a negative electrode. This application does not impose specific restrictions on the selection of the negative electrode; any negative electrode from any secondary battery in this technical field can be used.

[0064] In this application, the secondary battery also includes a separator. This application does not impose specific limitations on the selection of the separator; any separator from the secondary battery field within this technical field can be used.

[0065] In this application, the secondary battery also includes an electrolyte. This application does not impose specific limitations on the selection of the electrolyte; any electrolyte from secondary batteries within the scope of this technical field can be used.

[0066] This application does not impose specific restrictions on electrical equipment, such as electric vehicles.

[0067] The present application will be further illustrated below through specific embodiments.

[0068] Example 1

[0069] This embodiment provides a positive electrode material, including a positive electrode active material and a coating material. The coating material is distributed at least on a portion of the surface of the positive electrode active material, and the coating material includes electronic conductors and ionic conductors. The positive electrode active material is O3-phase NaN. i0.33 Fe 0.33 Mn 0.33 O2, with hard carbon as the electronic conductor and Na3Zr2Si2PO as the ionic conductor. 12 The particle size ratio (Dv50) of the positive electrode active material and the electronic conductor is 1:0.01, and the particle size ratio (Dv50) of the positive electrode active material and the ion conductor is 1:0.08. The particle sizes (Dv10, Dv50, Dv90, Dv100) of the ion conductor are 0.9 μm, 2 μm, 10 μm, and 30 μm, respectively. The mass of the ion conductor is 10% of the total mass of the electronic conductor and the ion conductor. The mass ratio of the ion conductor to the positive electrode active material is 1:500. The thickness of the coating material on the surface of the positive electrode active material is 0.1 μm.

[0070] The preparation method of the positive electrode material in this embodiment includes the following steps: preparing 0.07g of ionic conductor Na3Zr2Si2PO 12 The required precursors Na₂CO₃, ZrO(NO₃)₂, SiO₂, and (NH₄)₂HPO₄ were added to 50 mL of ethanol (with 2% excess Na₂CO₃ to compensate for sodium volatilization during high-temperature sintering). The mixture was stirred evenly in a 60 °C water bath, and then 0.98 g of polyvinylpyrrolidone was added. The mixture was stirred for another 2 hours, and then 35.30 g of layered O₃ oxide NaN with a Dv₅₀ of 25 μm was added. i0.33 Fe 0.33 Mn 0.33 O2 was stirred into a viscous slurry and then dried in an oven at 80°C to obtain a positive electrode precursor. The obtained positive electrode precursor was pre-calcined in a muffle furnace at 230°C for 3 hours, then cooled to room temperature, ground into a uniform powder, and then transferred to a tube furnace with high-purity argon gas continuously introduced. The temperature was increased to 950°C at 5°C / min and sintered for 2 hours. After the temperature was reduced to room temperature, the O3 layered oxide positive electrode material with ion and electron double coating was obtained.

[0071] Examples 2 to 3

[0072] A positive electrode material was provided, and its preparation method was the same as in Example 1, except that the NaN was adjusted. i0.33 Fe 0.33 Mn 0.33 The particle size Dv50 of O2 is adjusted to control the ratio of Dv50 between the positive electrode active material and the electronic and ionic conductors.

[0073] Examples 4 to 5

[0074] The preparation process of the positive electrode material is the same as in Example 1, except that the heating rate is controlled to adjust the particle size of the generated ionic conductor.

[0075] Examples 6 to 9

[0076] The preparation process of the positive electrode material is the same as in Example 1, except that the amount of Na2CO3, ZrO(NO3)2, SiO2 and (NH4)2HPO4 added is adjusted to adjust the content of ionic conductors in the coating material.

[0077] Examples 10 to 15

[0078] The preparation process of the cathode material is the same as in Example 1, except that Na3Zr2Si2PO4 is used instead of Na3Zr2Si2PO4. 12 Replace with other different ionic conductors (see Table 1 for details).

[0079] Examples 16-18

[0080] The preparation process of the cathode material is the same as in the previous example. The difference is that after sintering at 950°C for 2 hours at a rate of 5°C / min and then cooling to room temperature, the powder is uniformly dispersed in a PAN (polyacrylonitrile) solution and dried to obtain the cathode material. By adjusting the concentration of the PAN solution, cathode materials with different PAN mass contents are obtained.

[0081] Examples 19-20

[0082] The preparation process of the positive electrode material is the same as in Example 1, except that NaNi is used. 0.33 Fe 0.33 Mn 0.33 O2 was replaced with other positive electrode active materials.

[0083] Comparative Examples 1 to 2

[0084] The preparation process of the cathode material is the same as in the previous example. The difference is that the heating rate and sintering temperature are adjusted to regulate the Dv50 of the ionic conductor and the electronic conductor.

[0085] Table 1

[0086]

[0087]

[0088] In Table 1, the first positive electrode active material represents O3 phase NaN. i0.33 Fe 0.33 Mn 0.33 O2, the second positive electrode active material represents the P2-O3 mixed phase Na 0.72 Ni 0.33 Fe0.058 Mn 0.532 Ti 0.08 O2, the third positive electrode active material is represented by Na3V2(PO4)3.

[0089] The cathode materials of each embodiment and comparative example were used to fabricate batteries, and the specific methods are as follows:

[0090] The positive electrode material, conductive agent carbon black, and binder PVDF were mixed evenly at a mass ratio of 90:5:5. Then, an appropriate amount of NMP was added and stirred to form a slurry. The slurry was coated onto one surface of an aluminum foil with a thickness of 16 μm to obtain the positive electrode sheet. Then, it was assembled into a button cell with the negative electrode sheet, a glass fiber separator, and an electrolyte (prepared by dissolving NaPF6 in a mixture of EC and PC, with a NaPF6 concentration of 1 mol / L and a volume ratio of EC to PC of 1:1).

[0091] The prepared battery was tested, and the test items are as follows:

[0092] 1) Rate performance test at room temperature and low temperature: Rate performance tests were conducted at room temperature (25℃) and low temperature (-20℃), respectively. The rate performance was tested at 0.5, 2C and 5C, and the reversible capacity of the battery at different rates was recorded.

[0093] 2) Cycle Performance Test: At 25℃, the battery is left to rest for 5 minutes, then charged at a constant current rate of 1C to 4.0V, followed by constant voltage charging until the current is less than or equal to 0.05C. After resting for 5 minutes, it is discharged at a constant current rate of 1C to 2.0V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is recorded as the discharge capacity of the lithium-ion secondary battery in the first cycle. The lithium-ion secondary battery is subjected to 200 charge-discharge cycles using the above method, and the discharge capacity of each and the last cycle is recorded. The capacity retention rate (%) after 200 cycles = discharge capacity of the 200th cycle / discharge capacity of the 1st cycle × 100%.

[0094] The test results are shown in Table 2.

[0095] Table 2

[0096]

[0097] As can be seen from the above data, when the ratio of particle size Dv50 of the positive electrode active material and the electronic conductor is 1:(0.01~0.25), and the ratio of particle size Dv50 of the positive electrode active material and the ion conductor is 1:(0.08~0.5), the rate performance and cycle performance of the battery can be significantly improved.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A positive electrode material, characterized in that, It includes a positive electrode active material and a coating material, wherein the coating material is at least distributed on a portion of the surface of the positive electrode active material; The coating material comprises electronic conductors and ionic conductors; The ratio of the particle size Dv50 of the positive electrode active material and the electronic conductor is 1: (0.01~0.25); The ratio of the particle size Dv50 of the positive electrode active material and the ion conductor is 1: (0.08~0.5); The particle size Dv50 of the positive electrode active material is 5~80μm, the particle size Dv50 of the electronic conductor is 0.05~7.5μm, and the particle size Dv50 of the ion conductor is 0.075~15μm. The ion conductor includes a first ion conductor and a second ion conductor. The first ion conductor has a Nasicon structure, and the second ion conductor has a layered structure. The mass ratio of the first ion conductor to the second ion conductor is 1:(0.16~6). The first ionic conductor includes Na 3+Ax Zr 2-0.5Ax M x Si2PO 12 M is selected from at least one of Li, Ca, Mg, Sr, Ba, In, Ga, Nb, La, Cr, Mn, Zn, Al, Ge, and Bi, and A is the valence state of element M, 0 ≤ x ≤ 0.5; The second ionic conductor includes β''-Na y Al2O3, where 0 <y<1; The mass of the ionic conductor is 10% to 90% of the total mass of the electronic conductor and the ionic conductor.

2. The cathode material as described in claim 1, characterized in that, The particle size Dv50 of the ionic conductor is 0.5~5μm.

3. The positive electrode material as described in claim 1, characterized in that, The coating material also includes a polymer, which includes at least one of polyacrylonitrile, polyvinylpyrrolidone, and polyethylene oxide.

4. The cathode material as described in claim 3, characterized in that, The polymer accounts for 0.5% to 3% of the total mass of the coating material.

5. The positive electrode material as described in claim 1, characterized in that, The coating material has a thickness of 0.6~8μm on the surface of the positive electrode active material.

6. A secondary battery, characterized in that, Includes the cathode material as described in any one of claims 1 to 5.

7. An electrical appliance, characterized in that, The device includes the secondary battery as described in claim 6, wherein the secondary battery serves as the power supply for the electrical equipment.

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