Positive electrode active material and preparation method thereof, positive electrode plate, battery and electric equipment

Abstract

The invention provides a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery and electric equipment, the positive electrode active material comprises: a matrix, the matrix comprises a compound represented by formula I: NaxMnyMzTi2-y-z (PO4) 3, where 2 < = xlt; y is greater than or equal to 1 and less than or equal to 1.5, z is greater than or equal to 0.005 and less than or equal to 0.1, and M comprises at least one of V, La, Al and Cr; the carbon material is coated on at least part of the surface of the matrix; the cell parameters a and c of the positive electrode active material respectively satisfy # imgabs 0 # imgabs 1 #, so that the gram capacity of the positive electrode active material is improved, the ionic conductivity and the electronic conductivity of the positive electrode active material are improved, the dissolution of Mn ions is inhibited, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular, to a positive electrode active material, a preparation method thereof, a positive electrode sheet, a battery, and an electrical device. Background Art

[0002] With the rapid development of the new energy vehicle power battery and energy storage battery markets, the market's demand for excellent electrochemical systems is becoming increasingly urgent. In existing electrochemical systems, lithium-ion batteries have developed the fastest and are the most widely used. However, the reserves of lithium resources in nature are limited and unevenly distributed, which to a certain extent restricts the large-scale application of lithium-ion batteries in the fields of energy storage and power. As an element in the same main group as lithium, sodium resources are very rich, widely distributed, and easy to extract. Developing sodium-ion batteries has important strategic significance.

[0003] The positive electrode material of the polyanionic sodium-ion battery has the advantages of low cost, long cycle life, high safety, etc., and has received extensive attention from scientific researchers. Na 3 MnTi(PO 4 ) 3 has a theoretical specific capacity of 117 mAh / g at 2.5V - 4.2V and a theoretical specific capacity of up to 170 mAh / g at a voltage of 1.5V - 4.2V. The theoretical capacity is close to that of lithium iron phosphate batteries, and the raw material cost is relatively low, making it very valuable for commercial research. However, due to low ion and conductivity, there is still a large gap between the actual capacity and the theoretical capacity, and there are problems such as manganese dissolution and cycle attenuation. Summary of the Invention

[0004] The present application aims to at least partly solve one of the technical problems in the related art.

[0005] In a first aspect of the present application, a positive electrode active material is provided. The positive electrode active material includes: a matrix, the matrix includes a compound represented by Formula Ι: Na x Mn y M z Ti 2-y-z (PO 4 ) 3 Formula Ι, where 2 ≤ x < 4, 1 ≤ y ≤ 1.5, 0.005 ≤ z ≤ 0.1, M includes at least one of V, La, Al, and Cr; a carbon material, the carbon material is coated on at least part of the surface of the matrix; the unit cell parameters a and c of the positive electrode active material respectively satisfy

[0006] The positive electrode active material proposed in this application has the following advantages: (1) By increasing the content of Mn element, the ionic conductivity and capacity of the positive electrode active material can be improved; (2) By doping a trivalent element with a larger ionic radius, the unit cell parameter of the positive electrode active material can be increased, promoting the growth of the dominant crystal plane; (3) By coating the carbon material on at least part of the surface of the matrix, the ionic conductivity and electronic conductivity of the positive electrode active material can be further improved, improving the rate performance of the positive electrode active material. The surface carbon coating can also inhibit the dissolution of manganese ions in the positive electrode active material, improving the cycle performance of the battery.

[0007] According to some embodiments of the present application, 1 < y / (2 - y - z) ≤ 1.5; preferably, 1.1 < y / (2 - y - z) ≤ 1.5. Thus, the ratio of the content of Mn element and Ti element is increased, improving the capacity of the positive electrode active material.

[0008] According to some embodiments of the present application, and / or

[0009] According to some embodiments of the present application, in the X-ray diffraction pattern of the positive electrode active material, the diffraction peak intensities of the (113) crystal plane, (116) crystal plane, and (110) crystal plane satisfy at least one of the following conditions: the diffraction peak intensity I (113) of the (113) crystal plane and the diffraction peak intensity I (116) of the (116) crystal plane satisfy: 0.925 ≤ I (113) / I (116) ≤ 0.955; the diffraction peak intensity I (110) of the (110) crystal plane and the diffraction peak intensity I (116) of the (116) crystal plane satisfy: 0.49 ≤ I (110) / I (116) ≤ 0.53. Thus, the dominant crystal plane (110) for ion transport has a relatively high proportion on the surface of the material (I (110) / I (116) = 30% in the standard pattern), and the non-dominant crystal plane (113) has a relatively low proportion on the surface of the material (I (113) / I (116) = 97.5% in the standard pattern), which is beneficial to improving the material kinetics, thereby improving the material capacity, efficiency, and rate performance.

[0010] According to some embodiments of the present application, the full width at half maximum (FWHM) of the (113) crystal plane and the (300) crystal plane in the X-ray diffraction pattern of the positive electrode active material satisfies at least one of the following conditions: the FWHM of the diffraction peak of the (113) crystal plane is 0.25 - 0.32; the FWHM of the diffraction peak of the (300) crystal plane is 0.35 - 0.41. Thus, the crystallinity of the material is better, the proportion of the crystalline phase in the bulk phase of the material is higher, the proportion of the amorphous phase is lower, the transmission channels of lithium ions in the structure with better crystallinity are more stable, and the cycling performance of the material is better.

[0011] According to some embodiments of the present application, based on the total mass of the positive electrode active material, the mass proportion of the carbon material is 12% - 14%. Thus, the ionic conductivity and electronic conductivity of the positive electrode active material are improved.

[0012] According to some embodiments of the present application, the specific surface area of the positive electrode active material is 5 m 2 / g - 7.5 m 2 / g. Thus, the primary particles have appropriate particle sizes, the lithium ion transmission path is shortened, and at the same time, the side reactions between the positive electrode active material and the electrolyte are reduced.

[0013] According to some embodiments of the present application, the average particle size D 50 of the positive electrode active material is 16 μm - 18 μm. Thus, the transmission rate of lithium ions is increased.

[0014] According to some embodiments of the present application, the volume impedance of the positive electrode active material is 10 Ω / cm - 240 Ω / cm, and the positive electrode active material has high ionic conductivity and electronic conductivity.

[0015] According to some embodiments of the present application, the tap density of the positive electrode active material is 2 g / cm 3 - 3 g / cm 3 . Thus, the energy density of the battery is increased.

[0016] According to some embodiments of the present application, the residual sodium content on the surface of the positive electrode active material is 800 ppm - 8000 ppm. Thus, the thickness of the inert layer on the surface of the positive electrode active material is reduced, and the influence on lithium ion transmission is reduced.

[0017] The second aspect of the present application provides a method for preparing the cathode active material provided in the first aspect of the present application. The method includes: mixing a Na source, a Ti source, a Mn source, a P source, an M source, a carbon source, a dispersant, and a solvent, dispersing and drying to obtain a precursor; sintering the precursor in a non-oxidizing atmosphere at a sintering temperature of 500°C - 700°C to obtain the cathode active material, and the sintering temperature is preferably 530°C - 680°C. The cathode active material prepared by the method proposed in the present application has all the characteristics and advantages of the cathode active material provided in the first aspect of the present application, which will not be elaborated here. In addition, this method also has the advantages of simple process and easy industrial scale-up.

[0018] According to some embodiments of the present application, the sintering time is 8h - 20h. Thereby, the purity of the cathode active material is improved, and the sodium content remaining on the surface of the cathode active material is controlled.

[0019] According to some embodiments of the present application, the carbon source includes an organic carbon source and an inorganic carbon source. The organic carbon source includes at least one of citric acid, polypyrrole, and polyvinylpyrrolidone, and the inorganic carbon source includes at least one of graphite, acetylene black, graphene, and carbon nanotubes. Thereby, the ionic conductivity and electronic conductivity of the cathode active material are improved, its discharge voltage is increased, and Mn dissolution is reduced.

[0020] According to some embodiments of the present application, the method satisfies at least one of the following conditions: the Na source includes at least one of sodium carbonate, sodium hydroxide, and sodium nitrate; the M source includes at least one of an oxide containing M, a phosphate containing M, a sulfate containing M, a chloride containing M, a nitrate containing M, and a carbonate containing M; the manganese source includes at least one of an oxide containing manganese, a phosphate containing manganese, a sulfate containing manganese, a chloride containing manganese, a nitrate containing manganese, and a carbonate containing manganese; the Ti source includes at least one of a phosphate containing Ti, an acetate containing Ti, a sulfate containing Ti, a chloride containing Ti, a nitrate containing Ti, and a carbonate containing Ti; the P source includes H 3 PO 4 、NH 4 H 2 PO 4 、(NH 4 ) 2 HPO 4 、(NH 4 ) 3 PO 4 、P 2 O 5 at least one of them.

[0021] The third aspect of the present application provides a positive electrode plate, including the positive electrode active material provided in the first aspect of the present application or the positive electrode active material prepared by the method provided in the second aspect of the present application.

[0022] The fourth aspect of the present application provides a battery, including the positive electrode plate provided in the third aspect of the present application.

[0023] The fifth aspect of the present application provides an electrical device, including the battery provided in the fourth aspect of the present application. Description of the Drawings

[0024] The above and / or additional aspects and advantages of the present application will become apparent and easy to understand from the description of the embodiments in conjunction with the following drawings, in which:

[0025] Figure 1 The SEM diagram of the positive electrode active material of an embodiment of the present application is shown.

[0026] Figure 2 The process schematic diagram of the method for preparing the positive electrode active material of an embodiment of the present application is shown. Detailed Embodiments

[0027] The embodiments of the present application are described in detail below. The following described embodiments are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those techniques or conditions not specified in the embodiments, they shall be carried out according to the techniques or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0028] The first aspect of the present application provides a positive electrode active material, referring to Figure 1 , the positive electrode active material includes:

[0029] A matrix, the matrix includes a compound shown in Formula Ι:

[0030] Na x Mn y M z Ti 2-y-z (PO 4 ) 3 Formula Ι,

[0031] wherein, 2≤x<4, 1≤y≤1.5, 0.005≤z≤0.1, and M includes at least one of V, La, Al, and Cr;

[0032] A carbon material, the carbon material is coated on at least a part of the surface of the matrix;

[0033] The unit cell parameters a and c of the positive electrode active material respectively satisfy

[0034] The positive electrode active material proposed in this application has the following advantages simultaneously: (1) By increasing the content of Mn element, more capacity can be released from the Mn element with a higher discharge voltage. At the same time, the ionic radius of Mn is larger than that of Ti. After the Mn content increases, the unit cell volume of the material increases, providing a larger space for lithium ion transport, less hindrance, and faster speed, which can improve the ionic conductivity of the material. (2) By doping the M element of the above type in the positive electrode active material, the M element has a larger volume and binds more firmly with O, which can play a role in pillar support, improving the structural stability and lithium ion transport rate of the positive electrode active material. (3) By coating the carbon material on the surface of the matrix, on the one hand, it can improve the ionic conductivity and electronic conductivity of the positive electrode active material; on the other hand, the coating can effectively prevent the dissolution of Mn ions in the matrix, reduce the side reactions of the battery, and improve the safety of the battery.

[0035] In summary, by increasing the content of Mn element, doping the M element in the positive electrode active material, and coating the carbon material on at least part of the surface of the matrix, the above characteristics work together synergistically to obtain a positive electrode active material with high capacity, relatively high ionic conductivity and electronic conductivity, more stable structure, fewer side reactions, and higher safety.

[0036] As an example, x can be 2, 2.5, 3, 3.5, 3.9, etc., or can be a range composed of any of the above values.

[0037] As an example, y can be 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, etc., or can be a range composed of any of the above values.

[0038] As an example, z can be 0.005, 0.01, 0.05, 0.1, etc., or can be a range composed of any of the above values.

[0039] In this application, the carbon material can form a continuous coating on the surface of the matrix; it can also form a discontinuous coating on the surface of the matrix. For example, it can be an island-like coating.

[0040] As an example, the unit cell parameter a can be etc., or can be a range composed of any of the above values. According to some specific embodiments of this application,

[0041] As an example, the unit cell parameter c can be etc., or can be a range composed of any of the above values. According to some specific embodiments of this application,

[0042] According to some embodiments of the present application, the unit cell volume V of the positive electrode active material can be etc., or can be a range composed of any of the above values.

[0043] According to some embodiments of the present application, 1 < y / (2 - y - z) ≤ 1.5. For example, it can be 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, etc., or can be a range composed of any of the above values. Thus, on the basis of increasing the content of Mn element, by further increasing the ratio of the content of Mn element to the content of Ti element, the discharge voltage of the positive electrode active material is increased, the specific capacity of the positive electrode active material is increased, and the capacity of the positive electrode active material is increased; at the same time, since the ionic radius of Mn ions is greater than the ionic radius of Ti ions, after increasing the ratio of the content of Mn element to the content of Ti element, the unit cell volume of the positive electrode active material can be increased, making the space for lithium ion transmission larger, the hindrance less, and the speed faster.

[0044] According to some embodiments of the present application, in the X-ray diffraction pattern of the positive electrode active material, the diffraction peak intensity I of the (113) crystal plane (113) and the diffraction peak intensity I of the (116) crystal plane (116) satisfy: 0.925 ≤ I (113) / I (116) ≤ 0.955. For example, it can be 0.925, 0.035, 0.945, 0.955, etc., or can be a range composed of any of the above values. Thus, the non-dominant crystal plane (113) for ion transmission accounts for a relatively low proportion on the surface of the material (I (113) / I (116) = 97.5% in the standard pattern), which is beneficial to the improvement of material kinetics, and thus improves the material capacity, efficiency and rate performance.

[0045] According to some embodiments of the present application, in the X-ray diffraction pattern of the positive electrode active material, the diffraction peak intensity I of the (110) crystal plane (110) and the diffraction peak intensity I of the (116) crystal plane (116) satisfy: 0.49 ≤ I (110) / I (116) ≤ 0.53. For example, it can be 0.49, 0.5, 0.51, 0.52, 0.53, etc., or can be a range composed of any of the above values. The dominant crystal plane (110) for ion transmission accounts for a relatively high proportion on the surface of the material (I (110) / I (116) = 30% in the standard pattern), which is beneficial to the improvement of material kinetics, and thus improves the material capacity, efficiency and rate performance.

[0046] According to some embodiments of the present application, in the X-ray diffraction pattern of the positive electrode active material, the full width at half maximum (FWHM) of the diffraction peak of the (113) crystal plane can be 0.25 - 0.32. For example, it can be 0.25, 0.27, 0.29, 0.31, 0.32, etc., or it can be a range composed of any of the above values.

[0047] According to some embodiments of the present application, in the X-ray diffraction pattern of the positive electrode active material, the full width at half maximum (FWHM) of the diffraction peak of the (300) crystal plane can be 0.35 - 0.41. For example, it can be 0.35, 0.36, 0.38, 0.4, 0.41, etc., or it can be a range composed of any of the above values. Thus, the crystallinity of the material is better, the proportion of the crystalline phase in the material bulk phase is higher, the proportion of the amorphous phase is lower, the transmission channels of lithium ions in the better crystalline structure are more stable, and the cycling performance of the material is better.

[0048] In the present application, the unit cell parameters, diffraction peak intensities and full widths at half maximum of different crystal planes of the positive electrode active material can be tested by an X-ray diffractometer. Specifically, the working voltage is 40 kV, the working current is 250 mA, continuous scanning is adopted, the scanning speed is 4° / min, the step size is 0.02°, and the scanning angle is 10° - 80°. The unit cell volume V = a 2 × c × sin120 o .

[0049] According to some embodiments of the present application, based on the total mass of the positive electrode active material, the mass ratio of the carbon material can be 12% - 14%. For example, it can be 12%, 13%, 14%, etc., or it can be a range composed of any of the above values.

[0050] In the present application, by forming a carbon material on at least part of the surface of the substrate and making the content of the carbon material within the above range, on the one hand, the ionic conductivity and electronic conductivity of the positive electrode active material can be improved; on the other hand, the coating of the carbon material can effectively hinder the dissolution of Mn ions inside the positive electrode active material, reduce the content of Mn ions diffused to the negative electrode side in the battery, reduce the occurrence of side reactions, and improve the safety of the battery.

[0051] According to some embodiments of the present application, the specific surface area of the positive electrode active material can be 5 m 2 / g - 7.5 m 2 / g. For example, it can be 5 m 2 / g, 5.5 m 2 / g, 6 m 2 / g, 6.5 m 2 / g, 7 m 2 / g, 7.5 m 2 / g, etc., or can be a range composed of any of the above values. When the specific surface area of the positive electrode active material is within the above range, the primary particles have appropriate particle size and tap density, which can shorten the transmission path of lithium ions, reduce the number of interfaces, and reduce the side reactions between the positive electrode active material and the electrolyte.

[0052] In this application, a Tristar3030 specific surface area analyzer can be used to test the specific surface area of the positive electrode active material.

[0053] According to some embodiments of the present application, the average particle size D of the positive electrode active material 50 is 16μm - 18μm. For example, it can be 16μm, 17μm, 18μm, etc., or can be a range composed of any of the above values. Thus, by making the average particle size of the positive electrode active material within the above range, the lithium ion transmission path can be shortened, the lithium ion transmission rate can be increased, and the capacity and rate performance of the battery can be improved.

[0054] In this application, the particle size distribution of the material can be tested by using a Mastersizer2000 laser particle size analyzer of Malvern Company.

[0055] According to some embodiments of the present application, the volume impedance of the positive electrode active material can be 10Ω / cm - 240Ω / cm. For example, it can be 10Ω / cm, 50Ω / cm, 100Ω / cm, 150Ω / cm, 200Ω / cm, 240Ω / cm. By making the volume impedance of the positive electrode active material within the above range, the positive electrode active material has high ionic conductivity and electronic conductivity, and the temperature rise during battery cycling can be reduced.

[0056] In this application, a Mitsubishi Chemical powder resistivity tester MCP-PD51 can be used to test the volume impedance of the material.

[0057] According to some embodiments of the present application, the tap density of the positive electrode active material is 2g / cm 3 - 3g / cm 3 . For example, it can be 2g / cm 3 、2.2g / cm 3 、2.4g / cm 3 、2.6g / cm 3 、2.8g / cm 3 、3g / cm 3 etc., or can be a range composed of any of the above values. Thus, the energy density of the battery is improved.

[0058] According to some embodiments of the present application, the residual sodium content on the surface of the positive electrode active material can be 800 ppm - 8000 ppm. For example, it can be 800 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, etc., or can be a range composed of any of the above values. When the residual sodium content is low, the active sodium content in the bulk and on the surface of the material is also correspondingly low, which is not conducive to improving the energy density of the battery; if the residual sodium content is too high, the inert layer on the surface of the positive electrode active material is relatively thick, which will affect the lithium ion transmission rate, and the residual sodium will react with the electrolyte to generate gas, affecting the safety of the battery.

[0059] In the present application, the residual sodium content can be tested by the following method: Mix the positive electrode active material and pure water in a mass ratio of 5:95 for 5 minutes, filter the mixed sample through a Buchner funnel to obtain a filtrate, and test the Na content of the filtrate using an inductively coupled plasma mass spectrometer (ICP).

[0060] The second aspect of the present application provides a method for preparing the positive electrode active material provided in the first aspect of the present application. The method includes: mixing a Na source, a Ti source, a Mn source, a P source, an M source, a carbon source, a dispersant, and a solvent, and obtaining a precursor after dispersion and drying; sintering the precursor under a non-oxidizing atmosphere, and the sintering temperature is 500 °C - 700 °C to obtain the positive electrode active material. The positive electrode active material prepared by the method proposed in the present application has all the characteristics and advantages of the positive electrode active material provided in the first aspect of the present application, which will not be elaborated here. In addition, this method also has the advantages of simple process and easy industrial scale-up.

[0061] The method proposed in the present application will be described in detail below. Refer to Figure 2 , the method includes:

[0062] S10: Mix a Na source, a Ti source, a Mn source, a P source, an M source, a carbon source, a dispersant, and a solvent, and obtain a precursor after dispersion and drying

[0063] In this step, a Na source, a Ti source, a Mn source, a P source, an M source, a carbon source, a dispersant, and a solvent are mixed, and a precursor is obtained after sanding, dispersion, and spray drying.

[0064] According to some embodiments of the present application, the Na source includes at least one of sodium carbonate, sodium hydroxide, and sodium nitrate.

[0065] According to some embodiments of the present application, the M source includes at least one of an oxide containing M, a phosphate containing M, a sulfate containing M, a chloride containing M, a nitrate containing M, and a carbonate containing M.

[0066] According to some embodiments of the present application, the manganese source includes at least one of manganese-containing oxides, manganese-containing phosphates, manganese-containing sulfates, manganese-containing chlorides, manganese-containing nitrates, and manganese-containing carbonates.

[0067] According to some embodiments of the present application, the Ti source includes at least one of Ti-containing phosphates, Ti-containing acetates, Ti-containing sulfates, Ti-containing chlorides, Ti-containing nitrates, and Ti-containing carbonates.

[0068] According to some embodiments of the present application, the P source includes H 3 PO 4 、NH 4 H 2 PO 4 、(NH 4 ) 2 HPO 4 、(NH 4 ) 3 PO 4 、P 2 O 5 or at least one of them.

[0069] According to some embodiments of the present application, the carbon source includes an organic carbon source and an inorganic carbon source. The organic carbon source includes at least one of citric acid, polypyrrole, and polyvinylpyrrolidone, and the inorganic carbon source includes at least one of graphite, acetylene black, graphene, and carbon nanotubes. Thereby, the ionic conductivity and electronic conductivity of the cathode active material are improved, its discharge voltage is increased, and Mn dissolution is reduced.

[0070] In the present application, by using an organic carbon source and an inorganic carbon source, on the one hand, the complexing effect of the organic carbon source in the sample preparation process is fully exerted to form a three-dimensional electron transport channel from the material bulk phase to the surface, improving the transport speed of electrons from the bulk phase to the outside and solving the problem of low bulk phase conductivity; on the other hand, the high ionic conductivity characteristics of the inorganic carbon source are utilized to form an electron transport network between the cathode active material particles, improving the electron transport efficiency of the cathode active material in the battery and improving the rate performance; at the same time, the surface-coated inorganic carbon layer can also effectively hinder the dissolution of manganese ions inside the cathode active material and their diffusion to the negative electrode side, improving the battery safety.

[0071] S20: Sinter the precursor under a non-oxidizing atmosphere at a temperature of 500°C - 700°C to obtain the cathode active material.

[0072] In this step, the non-oxygen atmosphere includes nitrogen or argon.

[0073] By sintering the precursor in a non-oxygen atmosphere, the controllable carbonization of the organic carbon source can be ensured; on the other hand, the Mn element and the M element can be maintained in a low chemical valence state, enabling the battery to have high capacity and rate performance.

[0074] As an example, the temperature of the sintering can be 500 °C, 600 °C, 700 °C, etc., or can be a range composed of any of the above values.

[0075] As an example, the time of the sintering can be 8 h, 14 h, 20 h, 24 h, etc., or can be a range composed of any of the above values.

[0076] By making the temperature of the sintering within the above range, the phase purity of the cathode active material can be improved, the content of residual sodium can be controlled, and the capacity and rate performance of the battery can be improved.

[0077] In summary, the cathode active material proposed in this application has the following advantages:

[0078] (1) By increasing the content of the Mn element, the discharge voltage and the unit cell volume of the cathode active material can be increased, thereby increasing the specific capacity and ionic conductivity of the cathode active material.

[0079] (2) On the basis of increasing the content of the Mn element, by further increasing the ratio of the content of the Mn element to the content of the Ti element, the specific capacity and ionic conductivity of the cathode active material can be further increased.

[0080] (3) By doping the M element in the cathode active material, the M element has a larger volume and is more firmly combined with O, which can play a role in pillar support, improving the structural stability and lithium ion transmission rate of the cathode active material.

[0081] (4) By coating the carbon material on the surface of the matrix, the ionic conductivity and electronic conductivity of the cathode active material can be improved, effectively preventing the dissolution of Mn ions in the matrix, reducing the side reactions of the battery, and improving the safety of the battery.

[0082] (5) By using both the organic carbon source and the inorganic carbon source, the ionic conductivity and electronic conductivity of the cathode active material can be further improved.

[0083] (6) By controlling the average particle size D 50 of the cathode active material, the specific surface area, and the content of residual sodium on the surface, while increasing the lithium ion transmission rate, the side reactions between the cathode active material and the electrolyte can be reduced, and the safety performance of the battery can be improved.

[0084] The third aspect of this application provides a cathode electrode sheet, including the cathode active material provided in the first aspect of this application or the cathode active material prepared by the method provided in the second aspect of this application.

[0085] The fourth aspect of the present application provides a battery, including the positive electrode sheet provided by the third aspect of the present application.

[0086] The fifth aspect of the present application provides an electrical device, including the battery provided by the fourth aspect of the present application.

[0087] The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0088] The embodiments of the present application will be described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those not specified in the embodiments, the techniques or conditions described in the literature in the field or according to the product specifications are followed. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial procurement.

[0089] Example 1

[0090] 1. Preparation of positive electrode active material

[0091] (1) Sodium acetate, manganese carbonate, titanium dioxide, ammonium dihydrogen phosphate, and graphene were mixed evenly in pure water according to the molar ratio of Na:Mn:Ti:V:C = 2.65:1.15:0.8:0.05:0.5, and then transferred to a sand mill for sanding treatment to obtain a nano-slurry with a D 50 of 100 nm. After spray drying, a precursor with a D 50 of 18 microns was obtained.

[0092] (2) The solution obtained in step (1) was placed in a tubular furnace for calcination. The heating rate was 1.5 °C / min, the calcination temperature was 550 °C, and the holding time was 10 h. The calcination atmosphere was nitrogen, and Na 2.65 Mn 1.15 Ti 0.80 V 0.05 (PO 4 ) 3 / 0.5C sample was obtained.

[0093] 2. Preparation of positive electrode sheet

[0094] The positive electrode active material Na 2.65 Mn 1.15 Ti 0.80 V 0.05 (PO 4 ) 3 / 0.5C, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 80:10:10, coated on an aluminum foil, and dried. The positive electrode plate was formed by stamping under a pressure of 100 MPa into a disk with a diameter of 12 mm and a thickness of 120 μm, and then the positive electrode plate was placed in a vacuum drying oven and dried at 120 °C for 12 h.

[0095] 3. Negative electrode plate

[0096] A Na metal sheet with a diameter of 17 mm and a thickness of 1 mm was used.

[0097] 4. Separator

[0098] A Celgard 2400 porous membrane with a thickness of 25 μm was used.

[0099] 5. Electrolyte

[0100] A mixed solution of 1 mol / L NaPF 6 , ethylene carbonate (EC), and diethyl carbonate (DEC) in equal amounts was used.

[0101] 6. Battery assembly

[0102] The positive electrode plate, separator, negative electrode plate, and 4 μL of electrolyte were assembled into a 2025-type coin cell in an Ar gas glove box with a water content and an oxygen content both less than 5 ppm.

[0103] The preparation methods of the batteries in Examples 2 - 12 and Comparative Examples 1 - 7 were the same as those in Example 1, and the differences are shown in Table 1 in detail.

[0104]

[0105]

[0106] Performance test

[0107] 1. Initial efficiency

[0108] The assembled battery was tested in a battery test cabinet. First, it was charged at a constant current and constant voltage to 4.3 V at a 0.1C rate, left to stand for ten minutes, and then discharged at a constant current to 2.5 V at a 0.1C rate. The specific capacity obtained during the discharge process was divided by the specific capacity obtained during the charging process, and the ratio was the initial efficiency.

[0109] 2. 1C discharge specific capacity

[0110] The assembled battery was tested in a battery test cabinet. It was charged at a constant current and constant voltage to 4.3 V at a 1C rate, left to stand for ten minutes, and then discharged at a constant current to 2.5 V at a 1C rate. The specific capacity obtained during the discharge process was the 1C discharge specific capacity.

[0111] 3. Cycle capacity retention rate

[0112] The assembled battery is tested in a battery test cabinet. It is charged at a constant current and constant voltage to 4.3V at a 1C rate, left to stand for ten minutes, and then discharged at a constant current to 2.5V at a 1C rate. The above process is repeated 100 times. The ratio of the specific capacity obtained in the 100th discharge process to the specific capacity obtained in the first discharge process is the cycle capacity retention rate.

[0113] 4. Mn ion dissolution amount

[0114] After the coin cell has been charged and discharged 100 cycles, it is disassembled. After all three batteries are disassembled, except for the positive electrode plate, the negative electrode plates, battery cases, separators, nickel foam, and absorbent paper of the three batteries are washed repeatedly with pure water. The washing solution is placed in a polytetrafluoroethylene beaker and boiled at 220°C for 10 minutes. 15 mL of nitric acid is added, and the sample is dissolved and then filtered after cooling. (Only the separator and absorbent paper are not dissolved in this process). The solution is made up to 50 mL and then tested on a machine to obtain the value of the Mn content, which is the Mn dissolution amount.

[0115] 5. XRD test

[0116] The working voltage is 40 kV, the working current is 250 mA, continuous scanning is adopted, the scanning speed is 4° / min, the step size is 0.02°, and the scanning angle is 10° - 80°. The unit cell volume V = a 2 × c × sin120 o .

[0117] 6. Specific surface area test

[0118] The specific surface area of the positive electrode active material is tested using a Tristar3030 specific surface area analyzer.

[0119] 7. Average particle size test

[0120] The particle size distribution of the material is tested using a Mastersizer2000 laser particle size analyzer from Malvern Corporation.

[0121] 8. Volume impedance

[0122] The volume impedance of the material is tested using a Mitsubishi Chemical powder resistivity tester MCP-PD51.

[0123] 9. Compaction density

[0124] The compaction density of the material is tested using a Shandong Yuntang YT-101F compaction density tester.

[0125] 10. Surface residual sodium content

[0126] Mix the positive electrode active material and pure water in a mass ratio of 5:95 for 5 minutes. Filter the mixed sample through a Buchner funnel to obtain the filtrate, and then test the Na content of the filtrate using an inductively coupled plasma mass spectrometer (ICP).

[0127] The test results of the batteries in Examples 1 - 12 and Comparative Examples 1 - 7 are shown in Tables 2 and 3.

[0128]

[0129]

[0130]

[0131] It can be seen from the comparison between Examples 1 - 12 and Comparative Examples 1 - 7 that the batteries made of the positive electrode active material proposed in this application have a higher initial efficiency, better cycling performance, and less Mn ion dissolution. This shows that by increasing the content of Mn element in the positive electrode active material, doping M element in the positive electrode active material, and coating with carbon material, the specific capacity per gram and ionic conductivity of the positive electrode active material layer can be synergistically improved, the structural stability of the positive electrode active material can be enhanced, Mn dissolution can be reduced, and side reactions of the battery can be decreased.

[0132] It can be seen from the comparison between Examples 1 - 6 and Comparative Examples 1 and 2 that during the preparation of the positive electrode active material, by controlling the feeding amount, the content of different elements in the positive electrode active material can be adjusted, and by controlling the sintering atmosphere and temperature, the unit cell parameters of the positive electrode active material can be adjusted. On the basis of increasing the content of Mn element, by controlling y / 2 - y - z, the ionic conductivity and specific capacity of the positive electrode active material can be further improved, thereby improving the initial efficiency and cycling performance of the battery.

[0133] It can be seen from the comparison between Example 1 and Comparative Examples 3 and 4 that if the content of the doped M element is too high and the unit cell parameter c of the positive electrode active material is too large, the ionic conductivity of the positive electrode active material will decrease; not doping with M element will also reduce the structural stability and ionic conductivity of the material, and decrease the initial efficiency and cycling performance of the battery.

[0134] It can be seen from the comparison between Example 1, Examples 10, 11, and Comparative Example 5 that when there is a coating layer formed by carbon material on the surface of the positive electrode active material, the ionic conductivity and electronic conductivity of the positive electrode active material can be improved, and at the same time, the dissolution of Mn ions can be reduced.

[0135] It can be seen from the comparison between Example 1 and Comparative Example 6 that when the sintering temperature is too high, the unit cell parameter a of the positive electrode active material will increase, affecting the transport of lithium ions and reducing the cycling performance and initial efficiency of the battery.

[0136] It can be seen from Examples 7 - 9 and Comparative Example 7 that by doping a specific type of M element, the unit cell volume of the cathode active material can be increased, the lithium ion transmission rate can be improved, and the initial efficiency and cycling performance of the battery can be enhanced.

[0137] It can be seen from the comparison between Example 1 and Example 12 that when both an organic carbon source and an inorganic carbon source are used, the initial efficiency of the battery can be further improved compared to using only the inorganic carbon source.

[0138] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0139] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present application.

Claims

1. A positive electrode active material, characterized in that: include: A matrix, wherein the matrix comprises a compound represented by formula I: Na x Mn y M z Ti 2-y-z (PO4)3 formula Ι, Wherein, 2≤x<4, 1≤y≤1.5, 0.005≤z≤0.1, and M includes at least one of V, La, Al, and Cr; A carbon material, wherein the carbon material is coated on at least a portion of the surface of the substrate; The unit cell parameters a and c of the positive electrode active material respectively satisfy 2. The positive electrode active material according to claim 1, characterized in that 1<y / (2-yz)≤1.5; preferably, 1.1<y / (2-yz)≤1.

5.

3. The positive electrode active material according to claim 1, characterized in that and / or 4. The positive electrode active material according to any one of claims 1 to 3, characterized in that: The diffraction peak intensities of the (113) crystal plane, (116) crystal plane, and (110) crystal plane in the X-ray diffraction spectrum of the positive electrode active material meet at least one of the following conditions: The diffraction peak intensity I of the (113) crystal plane (113) and the diffraction peak intensity I of the (116) crystal plane (116) Satisfy: 0.925≤I (113) / I (116) ≤0.955; The diffraction peak intensity I of the (110) crystal plane (110) and the diffraction peak intensity I of the (116) crystal plane (116) Satisfy: 0.49≤I (110) / I (116) ≤0.

53.

5. The positive electrode active material according to any one of claims 1 to 3, characterized in that: The half-peak widths of the (113) crystal plane and the (300) crystal plane in the X-ray diffraction spectrum of the positive electrode active material meet at least one of the following conditions: The half-peak width of the (113) crystal plane diffraction peak is 0.25-0.32; The half-peak width of the (300) crystal plane diffraction peak is 0.35-0.

41.

6. The positive electrode active material according to any one of claims 1 to 3, characterized in that: Based on the total mass of the positive electrode active material, the mass proportion of the carbon material is 12%-14%.

7. The positive electrode active material according to any one of claims 1 to 3, characterized in that: The specific surface area of ​​the positive electrode active material is 5 m 2 / g-7.5m 2 / g.

8. The positive electrode active material according to any one of claims 1 to 3, characterized in that: The average particle size D of the positive electrode active material 50 It is 16μm-18μm.

9. The positive electrode active material according to any one of claims 1 to 3, characterized in that: The volume impedance of the positive electrode active material is 10Ω / cm-240Ω / cm.

10. The positive electrode active material according to any one of claims 1 to 3, characterized in that: The compaction density of the positive electrode active material is 2 g / cm 3 -3g / cm 3 .

11. The positive electrode active material according to any one of claims 1 to 3, characterized in that: The residual sodium content on the surface of the positive electrode active material is 800ppm-8000ppm.

12. A method for preparing the positive electrode active material according to any one of claims 1 to 11, characterized in that: include: A Na source, a Ti source, a Mn source, a P source, an M source, a carbon source, a dispersant, and a solvent are mixed, dispersed, and dried to obtain a precursor; Sintering the precursor in a non-oxidizing atmosphere at a temperature of 500° C. to 700° C. to obtain the positive electrode active material; The sintering temperature is preferably 530°C-680°C.

13. The method according to claim 12, characterized in that The sintering time is 8h-20h.

14. The method according to claim 12 or 13, characterized in that The carbon source includes an organic carbon source and an inorganic carbon source. The organic carbon source includes at least one of citric acid, polypyrrole, and polyvinyl pyrrolidone. The inorganic carbon source includes at least one of graphite, acetylene black, graphene, and carbon nanotubes.

15. The method according to claim 12 or 13, characterized in that Satisfy at least one of the following conditions: The Na source includes at least one of sodium carbonate, sodium hydroxide and sodium nitrate; The M source includes at least one of an oxide containing M, a phosphate containing M, a sulfate containing M, a chloride containing M, a nitrate containing M, and a carbonate containing M; The manganese source includes at least one of an oxide containing manganese, a phosphate containing manganese, a sulfate containing manganese, a chloride containing manganese, a nitrate containing manganese, and a carbonate containing manganese; The Ti source includes at least one of a phosphate containing Ti, an acetate containing Ti, a sulfate containing Ti, a chloride containing Ti, a nitrate containing Ti, and a carbonate containing Ti; The P source includes at least one of H3PO4, NH4H2PO4, (NH4)2HPO4, (NH4)3PO4, and P2O5.

16. A positive electrode plate, characterized in that: The invention comprises the positive electrode active material according to any one of claims 1 to 11 or the positive electrode active material prepared by the method according to any one of claims 12 to 15.

17. A battery, characterized in that: Including the positive electrode sheet as described in claim 16.

18. An electrical equipment, characterized in that: Comprising the battery of claim 17.

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