Positive electrode plate, method for preparing the same, and sodium ion battery

Abstract

The present application belongs to the technical field of batteries, and specifically relates to a positive electrode plate, a preparation method thereof, and a sodium ion battery. The positive electrode plate includes a current collector and a positive electrode material layer formed on at least one surface of the current collector, the positive electrode material layer includes a layered transition metal oxide and a polyanion compound, and the mass ratio of the layered transition metal oxide to the polyanion compound is: [0010] TIFF2025501034000013.tif17170, ρ1 is the true density of the layered transition metal oxide, ρ2 is the true density of the polyanion compound, ρ1 / ρ2 satisfies 1.25≦ρ1 / ρ2≦1.86, and the particle size distribution of the layered transition metal oxide is [0025] TIFF2025501034000014.tif17170, and the particle size D' of the polyanion compound is 50 teeth, [0030] Meets TIFF2025501034000015.tif21170. The positive electrode plate of the present application has effectively improved air stability, higher press density, and excellent electrochemical performance.

Description

Technical Field

[0001] This application belongs to the technical field of batteries, and specifically relates to a positive electrode plate, a method for preparing the same, and a sodium ion battery.

[0002] Cross-reference to Related Applications This application claims priority based on a Chinese application filed with the Chinese Patent Office on November 29, 2022, with an application number of 202211514774.7 and a title of "Positive Electrode Plate, Method for Preparing the Same, and Sodium Ion Battery", and all of its content is incorporated herein by reference.

Background Art

[0003] With the wide application of lithium ion batteries in the field of electric vehicles, the demand for lithium resources has increased significantly. However, the lithium element content in the earth's crust is only 0.0017%, and there was no technology capable of effectively recovering lithium resources. It cannot meet the demand in the fields of large-scale energy storage and the like, such as electric vehicles. Therefore, from the perspective of the sustainable development and utilization of energy sources, it is important to find a new secondary battery system with low cost, high safety, and long cycle life. The sodium element content in the earth's crust accounts for about 2.36% (mass fraction), which is much higher than the lithium element content, the sodium element is widely distributed, and the cost is low. And sodium and lithium are homologous elements, and in either case, during the operation of the battery, it will be a "rocking chair type" electrochemical charge and discharge. Therefore, the development of high-performance and low-cost sodium ion battery technology is important for the sustainable development of fields such as large-scale energy storage and electric vehicles.

[0004] Currently, the most promising cathode materials for sodium-ion batteries mainly include layered transition metal oxides and polyanion compounds. Layered transition metal oxides have a higher specific capacity, which allows them to better meet the demand for high energy density. However, they have poor air stability and are prone to ion exchange reactions with hydrogen ions from water molecules in the air. This leads to the formation of alkaline oxides such as Na2CO3, NaHCO3, and NaOH on the material's surface, which directly absorb water molecules and form interlayer crystalline water. This changes the crystalline structure of the material, reducing its crystallinity. The relatively strong alkaline environment formed on the material's surface can defluorinate and render the binder ineffective. Furthermore, the alkali can corrode the aluminum foil current collector, which has amphoteric metal properties, significantly impairing battery performance. The industry's traditional solution involves converting layered transition metal oxides into micron-sized polycrystalline or single-crystalline particles, which can then be improved by doping or coating. However, this does not effectively improve the material's air stability. Polyanion compounds have attracted attention due to their stable framework structure, excellent cycle performance, and excellent air stability, but their poor intrinsic electronic conductivity limits their large-scale use. Currently, the main methods for improving polyanion compounds are nanosizing and carbon composites, but these methods result in a decrease in the volumetric energy density of the material.

[0005] It is with this in mind that the present application has been devised. Summary of the Invention

[0006] One of the objectives of the present application is to provide a positive electrode plate that solves the technical problems of poor air stability and low volumetric energy density of the positive electrode plates in the prior art.

[0007] Another object of the present application is to provide a method for preparing said positive electrode plate.

[0008] Another object of the present application is to provide a sodium-ion battery.

[0009] To achieve the above objectives of this application, the following technical solutions are adopted. The positive electrode plate includes a current collector and a positive electrode material layer formed on at least one surface of the current collector, and the positive electrode material layer includes a layered transition metal oxide and a polyanion compound. The chemical formula of the layered transition metal oxide is Na x MO2, where 0.6 ≤ x ≤ 1.0, and M includes at least one of Fe, Mn, Cr, Ni, Co, Cu, Mg, Zr, and Ti. The chemical formula of the polyanion compound is at least one of NaAPO4, Na y E2(XO) and Na2QP2O7, where A includes at least one of Fe and Mn, 1 ≤ y ≤ 4, E includes at least one of V, Fe, Ni, Mn, and Ti, X includes at least one of P, S, and Si, Q includes at least one of Fe, Mn, and Co. The mass ratio of the layered transition metal oxide to the polyanion compound is

Number

Number

Number

[0010] In one embodiment, the range of ρ1 is 4.4 - 4.65 g / cm 3 , and the range of ρ2 is 2.5 - 3.5 g / cm 3 .

[0011] In one embodiment, the D50 of the particle size of the layered transition metal oxide is 4 - 12 μm.

[0012] In one embodiment, the particle size D10 of the layered transition metal oxide is 1.27 to 3.82 μm.

[0013] In one embodiment, the particle size D' of the polyanion compound 50 is 0.41 to 1.24 μm.

[0014] In one embodiment, the positive electrode material layer further contains a conductive agent and a binder.

[0015] In one embodiment, the conductive agent includes at least one of carbon nanotubes, conductive carbon black, conductive graphite, graphene, and carbon fibers.

[0016] In one embodiment, the binder includes polyvinylidene fluoride.

[0017] In one embodiment, the total mass of the conductive agent and the binder is 5% or less of the mass of the positive electrode material layer.

[0018] In one embodiment, in the positive electrode material layer, the mass ratio of the conductive agent to the binder is (1.5 to 3.5):(1.5 to 3.5).

[0019] In one embodiment, the press density of the positive electrode plate is 3.0 to 3.6 g / cm 3 .

[0020] The method for preparing the positive electrode plate includes a step of preparing a positive electrode slurry containing a layered transition metal oxide and a polyanion compound, and a step of applying the positive electrode slurry to at least one surface of the current collector, followed by drying and pressing.

[0021] In one embodiment, the positive electrode slurry further contains a conductive agent, a binder, and a solvent.

[0022] In one embodiment, the method for preparing the positive electrode slurry includes the steps of dissolving the binder in the solvent, adding a conductive agent and uniformly mixing to obtain a conductive slurry, and uniformly mixing the conductive slurry, the layered transition metal oxide, and the polyanion compound to obtain a positive electrode slurry.

[0023] In one embodiment, the drying temperature is 75 to 120 °C.

[0024] In one embodiment, the pressure used for the pressing is 20 to 100 MPa.

[0025] The sodium ion battery includes the positive electrode plate.

[0026] Compared with the prior art, the present application has the following beneficial effects.

[0027] (1) By controlling the particle size relationship, particle size distribution, and mass ratio relationship between the transition metal oxide and the polyanion compound, the obtained positive electrode plate has effectively improved air stability, higher pressing density, and excellent electrochemical performance.

[0028] (2) The method for preparing the positive electrode plate according to the present application is simple and easy to implement. A positive electrode slurry containing a layered transition metal oxide and a polyanion compound may be applied to the surface of at least one side of the current collector, followed by drying and pressing.

[0029] (3) The sodium ion battery according to the present application has excellent electrochemical performance.

Brief Description of the Drawings

[0030] To more clearly explain the specific embodiments of the present application or the technical solutions in the prior art, the drawings used in the specific embodiments or the prior art are briefly described below. It should be noted that the drawings to be described only show some embodiments of the present application. Those skilled in the art can obtain other drawings based on these drawings without using inventive capabilities.

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0031] Hereinafter, embodiments of the present application will be described in detail with reference to examples. As will be understood by those skilled in the art, the following examples are merely for explaining the present application and do not limit the scope of the present application. In the examples, for conditions not specified specifically, it is possible to carry out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, it is possible to use commercially available conventional products.

[0032] The positive electrode plate includes a current collector and a positive electrode material layer formed on at least one surface of the current collector, and the positive electrode material layer includes a layered transition metal oxide and a polyanion compound.

[0033] The chemical formula of the layered transition metal oxide includes Na x MO2, where x satisfies 0.6 ≤ x ≤ 1.0, and M includes at least one of Fe, Mn, Cr, Ni, Co, Cu, Mg, Zr, and Ti.

[0034] The chemical formula of the polyanion compound includes at least one of NaAPO4, Na y E2(XO4)3, and Na2QP2O7, where A includes at least one of Fe and Mn, y satisfies 1 ≤ y ≤ 4, E includes at least one of V, Fe, Ni, Mn, and Ti, X includes at least one of P, S, and Si, and Q includes at least one of Fe, Mn, and Co. The mass ratio of the layered transition metal oxide to the polyanion compound (the layered transition metal oxide / the polyanion compound) is

Number

[0035] By controlling the particle size relationship, particle size distribution, and mass ratio relationship between the transition metal oxide and the polyanion compound in this application, the obtained positive electrode plate has effectively improved air stability, a higher press density, and excellent electrochemical performance.

[0036] True Density refers to the actual mass of the solid substance per unit volume of the material in a completely sealed state, that is, the density excluding internal voids or gaps between particles. For the measurement method, refer to GB / T 24586-2009.

[0037] When multiple types of layered transition metal oxides are selected, ρ1 is the average value of the true densities of the multiple types of layered transition metal oxides, and when multiple types of polyanion compounds are selected, ρ2 is the average value of the true densities of the multiple types of polyanion compounds.

[0038] The mechanism of this application includes the following. Assuming that all particles are spherical particles, when classifying the particles in order of size as primary particles, secondary particles, tertiary particles, quaternary particles, etc., the spherical particles are most densely packed, the secondary particles are filled between the primary particles, the tertiary particles are filled between the primary particles and the secondary particles, and other particles are filled in the same way. The porosity of the primary particles is about 38%, the porosity of the secondary particles is about 15%, the porosity of the tertiary particles is about 5%, and the porosity of the quaternary particles is about 2.0%. After particles of different sizes have three levels, even if smaller particles are further filled, the porosity cannot be significantly reduced and the bulk density of the particles cannot be increased. Therefore, this application is based on the deposition of three levels of particles. The D50 of the transition metal oxide is used as the particle size of the primary particles, the D10 of the transition metal oxide is used as the particle size of the secondary particles, and the D50 of the polyanion compound is used as the particle size of the tertiary particles. Three levels of particles are filled and deposited, and the sizes of the secondary particles and the tertiary particles can be calculated based on the size of the primary particles. According to the combination of the three levels of particles (D50 of the transition metal oxide, D10 of the transition metal oxide, and D50 of the polyanion compound), the deposition density (corresponding to the press density / volume density of the electrode plate) can be effectively increased.

[0039] After obtaining the sizes of the particles at each level, in order to improve the sensitivity of the layered transition metal oxide to air, it is necessary to uniformly distribute the polyanion compound at least in the outer layer of the layered oxide so as to block the contact between the layered transition metal oxide and air. Assuming that all particles are spheres, the D50 of the transition metal oxide and the D50 of the polyanion compound are used as the average particle sizes respectively, and thereby the surface areas of the corresponding spherical metal oxide particles can be calculated. In order to obtain the desired effect (the transition metal oxide is coated in the center by the polyanion compound), the polyanion compound is further assumed to be a sphere. The sum of the surface areas of all spheres is not less than the surface area of the layered oxide. Therefore, the relationship between the number of particles of the two can be obtained based on the areas of the two, and based on the particle sizes, the number of particles, and the true density of the two, the mass relationship between the two materials can be obtained.

[0040] Therefore, by controlling parameters such as particle size distribution and mass ratio, the press density can be increased, the sensitivity of the material to air can be reduced, the press density can be increased, and the voids can be reduced to a certain extent, thus suppressing the contact between the metal oxide and air. The metal oxide has a high capacity but poor cycle performance, while the polyanion compound has a low capacity but good cycle performance. By combining a metal oxide as the main component with some polyanion compounds, a relatively high capacity can be guaranteed and the cycle performance can be improved. In one embodiment, the particle size D' of the polyanion compound 50 is

Number

[0041] In one embodiment, x includes, but is not limited to, 0.6, 0.7, 0.8, 0.9, or 1.0. The chemical formula of the layered transition metal oxide is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, NaNi 1 / 3 Fe 1 / 3 Mg 1 / 3 O2, NaNi 1 / 5 Fe 2 / 5 Mn 2 / 5 O2, NaNi 1 / 3 Fe 1 / 3 Ti 1 / 3 O2, NaNi 3 / 9 Fe 3 / 9 Mn 2 / 9 Zr 1 / 9 O2, Na 0.9 Cu 0.25 Fe 0.3 Mn 0.45 O2, Na 2 / 3 Ni 1 / 3 Mn 5 / 6 Ti 1 / 6 O2, Na 0.75 MnO2, Na 2 / 3 Mn 2 / 3 Ni 1 / 3 O2, Na 2 / 3 Mn 5 / 9 Ni 3 / 9 Cr 1 / 9O2 or NaNi 1 / 5 Fe 1 / 5 Cu 1 / 5 Mn 2 / 5 including O2 and the like.

[0042] In one embodiment, the polyanion compound NaAPO4 is NaFePO4 or NaMnPO4 。 In one embodiment, Na y In E2(XO4)3, y includes 1, 2, 3, 4, but is not limited thereto. Na y E2(XO4)3 can be NaV2(PO4)3, NaFe2(PO4)3, NaNi2(PO4)3, NaTi2(PO4)3, NaV2(SO4)3, NaV2(SiO4)3, etc. In one embodiment, Na2QP2O7 is Na2FeP2O7, Na2MnP2O7, Na2CoP2O7.

[0043] In one embodiment, the range of ρ1 is 4.4 - 4.65 g / cm 3 for example, 4.5 g / cm 3 4.52 g / cm 3 or 4.6 g / cm 3 etc., and the range of ρ2 is 2.5 - 3.5 g / cm 3 for example, 2.64 g / cm 3 2.72 g / cm 3 2.8 g / cm 3 3 g / cm 3 or 3.2 g / cm 3 etc.

[0044] In one embodiment, ρ1 / ρ2 includes 1.3, 1.4, 1.46, 1.5, 1.52, 1.6 or 1.8, etc., but is not limited thereto.

[0045] In one embodiment, the particle size D50 of the layered transition metal oxide is 4 - 12 μm, for example, 5.03 μm, 6.87 μm, 7.4 μm, 8 μm, 9 μm or 10 μm, etc.

[0046] In one embodiment, the particle size D10 of the layered transition metal oxide is 1.27 to 3.82 μm, for example, 1.3 μm, 1.52 μm, 1.83 μm, 2.44 μm, 2.5 μm, 2.8 μm, 3 μm, 3.15 μm, 3.5 μm, or 3.76 μm, etc.

[0047] In one embodiment, the particle size D' of the polyanion compound 50 is 0.41 to 1.24 μm, for example, 0.44 μm, 0.51 μm, 0.62 μm, 0.7 μm, 0.9 μm, 1 μm, or 1.2 μm, etc.

[0048] In one embodiment, the positive electrode material layer further contains a conductive agent and a binder.

[0049] In one embodiment, the conductive agent includes at least one of carbon nanotubes (CNT), conductive carbon black (SP), conductive graphite, graphene, and carbon fibers. In one embodiment, the conductive agent is conductive carbon black and carbon nanotubes, and the mass ratio of conductive carbon black to carbon nanotubes is (1 to 3):0.5, for example, 1:0.5, 1.5:0.5, 2:0.5, 2.5:0.5, 2.8:0.5, etc.

[0050] In one embodiment, the binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyacrylic acid, polyacrylonitrile, styrene-butadiene rubber, and polyimide.

[0051] In one embodiment, the total mass of the conductive agent and the binder is 5% or less of the mass of the positive electrode material layer, for example, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 4.8%, etc. In one embodiment, the total mass of the conductive agent and the binder is 1% to 4.8% of the mass of the positive electrode material layer.

[0052] In one embodiment, in the positive electrode material layer, the mass ratio of the conductive agent to the binder is (1.5 to 3.5):(1.5 to 3.5), for example, 1.5:3.5, 2:3, 3.5:1.5, etc.

[0053] In one embodiment, the pressing density of the positive electrode plate is 3.0 to 3.6 g / cm 3 and, for example, 3.1 g / cm 3 , 3.2 g / cm 3 , 3.3 g / cm 3 , 3.4 g / cm 3 , 3.5 g / cm 3 etc.

[0054] As another aspect of the present application, the present application further provides a method for preparing the positive electrode plate. The preparation method includes a step of preparing a positive electrode slurry containing a layered transition metal oxide and a polyanion compound, and a step of applying the positive electrode slurry to at least one side surface of the current collector, followed by drying and pressing.

[0055] The method for preparing the positive electrode plate according to the present application is simple and easy to execute. It is only necessary to apply a positive electrode slurry containing a layered transition metal oxide and a polyanion compound to at least one side surface of the current collector, followed by drying and pressing.

[0056] In one embodiment, the current collector according to the present application is an aluminum foil or a composite aluminum foil.

[0057] In one embodiment, the positive electrode slurry further contains a conductive agent, a binder, and a solvent. In one embodiment, the solvent includes N-methylpyrrolidone (NMP).

[0058] The method for preparing the positive electrode slurry specifically includes a step of dissolving the binder in the solvent, adding the conductive agent and uniformly dispersing it to obtain a uniform conductive slurry, and a step of adding the layered transition metal oxide and the polyanion compound to the conductive slurry and uniformly dispersing it to obtain the positive electrode slurry.

[0059] In one embodiment, the drying temperature is 75 to 120 °C. In one embodiment, the drying temperature is 80 °C, 90 °C, 95 °C, 100 °C, 110 °C, 115 °C, or the like.

[0060] In one embodiment, the pressure used for the pressing is 20 to 100 MPa. In one embodiment, the pressure used for the pressing is 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, 95 MPa, or the like.

[0061] As another aspect of the present application, the present application further provides a sodium-ion battery. The sodium-ion battery includes the positive electrode plate. The sodium-ion battery according to the present application has excellent electrochemical performance.

[0062] Hereinafter, further interpretation and explanation will be made with reference to specific examples and comparative examples.

[0063] The discharge curve diagram of the battery cell according to Example 1 of the present application is shown in FIG. 1.

[0064] The cycle retention rate curve diagram of the battery cell according to Example 3 of the present application is shown in FIG. 2.

Examples

[0065] The method for preparing the positive electrode plate includes the following steps.

[0066] (a) 2.0 parts by mass of PVDF was put into an NMP solvent and dissolved, 2.0 parts by mass of SP and 0.5 part of CNT were added as conductive agents, and uniformly dispersed to obtain a conductive slurry S1.

[0067] (b) Layered transition metal oxide NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 75.5 parts by mass and polyanion compound Na3V2(PO4)3 20.0 parts by mass as the positive electrode material were put into the first conductive slurry in step (a) and uniformly dispersed to obtain a slurry S2, and NaNi as the positive electrode material1 / 3 Fe 1 / 3 Mn 1 / 3 O2 has a D 10 = 2.44 μm, and a D 50 = 6.87 μm, and a true density of 4.50 g / cm 3 As the positive electrode material, Na3V2(PO4)3 has a D 50 = 0.51 μm, and a true density of 3.24 g / cm 3 was obtained.

[0068] (c) The above slurry S2 was uniformly coated on an aluminum foil, and a positive electrode plate was obtained through heat drying and rolling.

[0069] A battery was assembled using the positive electrode plate, negative electrode, separator, electrolyte, etc. according to this example, and a measurement target battery cell was obtained through processes such as aging, formation, and aging.

Example

[0070] The method for preparing the positive electrode plate differed from Example 1 only in that the layered transition metal oxide was 88 parts by mass and the polyanion compound was 7.5 parts by mass, and other conditions were the same as in Example 1.

Example

[0071] Regarding the method for preparing the positive electrode plate, the layered transition metal oxide is Na 0.9 Cu 0.25 Fe 0.3 Mn 0.45 O2, and the particle size D 10 = 1.83 μm, and the particle size D 50 = 5.03 μm, and a true density of 4.55 g / cm 3 differed from Example 1 only in this regard, and other conditions were the same as in Example 1.

Example

[0072] Regarding the method for preparing the positive electrode plate, the polyanion compound is NaFePO4, and the particle size D 50 = 0.44 μm, and a true density of 3.14 g / cm 3It differed from Example 1 only in the points noted, and the other conditions were the same as those in Example 1.

Example

[0073] Regarding the method for preparing the positive electrode plate, the layered transition metal oxide contains NaNi with a mass ratio of 1:1 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 and Na 0.9 Cu 0.25 Fe 0.3 Mn 0.45 O2, and the polyanion compound contains NaFePO4, Na3V2(PO4)3, and Na2MnP2O7 with a mass ratio of 1:1:1. The true density of Na2MnP2O7 was 3.26 g / cm 3 It differed from Example 1 only in the points noted, and the other conditions were the same as those in Example 1.

[0074] [Comparative Example 1] The method for preparing the positive electrode plate includes the following steps.

[0075] (a) 2.0 parts of PVDF was put into an NMP solvent and dissolved, 2.0 parts of SP and 0.5 part of CNT were added as conductive agents, and they were uniformly dispersed to obtain a conductive slurry S1.

[0076] (b) 95.5 parts of the layered transition metal oxide NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was put into S1 and uniformly dispersed to obtain a slurry S2. The NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 had D 10 = 2.44 μm and D 50 = 6.87 μm.

[0077] (c) The above slurry S2 was uniformly coated on an aluminum foil, and a positive electrode plate was obtained through heat drying and rolling.

[0078] A battery was assembled using the positive electrode plate, negative electrode, separator, electrolyte, etc. according to this comparative example, and a battery cell to be measured was obtained through processes such as aging, formation, and storage.

[0079] [Comparative Example 2] The method for preparing the positive electrode plate included the following steps.

[0080] (a) 2.0 parts of PVDF was put into an NMP solvent and dissolved, 2.0 parts of SP and 0.5 part of CNT were added as conductive agents, and they were uniformly dispersed to obtain a conductive slurry S1.

[0081] (b) 95.5 parts of the polyanion compound Na3V2(PO4)3 as the positive electrode material was put into S1 and uniformly dispersed to obtain a slurry S2. The D of Na3V2(PO4)3 as the positive electrode material 50 = 0.51 μm.

[0082] (c) The above slurry S2 was uniformly coated on an aluminum foil, and a positive electrode plate was obtained through heat drying and rolling.

[0083] A battery was assembled using the positive electrode plate, negative electrode, separator, electrolyte, etc. according to this comparative example, and a battery cell to be measured was obtained through processes such as aging, formation, and storage.

[0084] [Comparative Example 3] Regarding the method for preparing the positive electrode plate, the layered transition metal oxide had a particle size D 10 = 2.8 μm, and the particle size D 50 = 15 μm, and the true density was 4.49 g / cm 3 It was different from Example 1 only in that the polyanion compound had a particle size D 50 = 1.65 μm and the true density was 3.25 g / cm 3 The other conditions were the same as those in Example 1.

[0085] [Experimental Example] Electrochemical performance tests were conducted on the positive electrode plates and sodium-ion batteries according to the examples and comparative examples by the following method.

[0086] I. Residual Alkali Measurement The positive electrode plate was stored for 12 h in an environment with a humidity of 26 ± 3%. Then, the powder material on the electrode plate was separated from the aluminum foil and transferred to a beaker. Deionized water was added and stirred for 60 s, followed by filtration. The filtrate was transferred to the sample stage of a potentiometric titration apparatus, and potentiometric titration was performed using hydrochloric acid. The carbonate ions and bicarbonate ions obtained by measurement were converted to the content of sodium ions. The content calculation standard is the mass of the layered transition metal oxide in the positive electrode powder material after separation from the aluminum foil.

[0087] II. Capacity Measurement Charge at a constant current and constant voltage up to 4.0 V at a rate of 0.5 C, with a cut-off current of 0.05 C, and let it stand for 30 min. Then, perform constant current discharge up to 2.0 V at a rate of 0.5 C, record the battery capacity, and convert it to the capacity per gram based on the mass of the active material in the positive electrode plate and record it as the reversible capacity.

[0088] III. Cycle Performance Measurement At 45 ± 2 °C, charge at a constant current and constant voltage up to 4.0 V at a rate of 0.5 C, with a cut-off current of 0.05 C, and let it stand for 30 min. Then, perform constant current discharge up to 2.0 V at a rate of 0.5 C, let it stand for 30 min, and cycle 500 times in this way. Record the ratio of the capacity at the 500th cycle to the initial capacity and record it as the capacity retention rate.

[0089] The measurement results are shown in Table 1.

[0090]

Table 1

[0091] As can be seen from Table 1, in each example of the present application, a layered transition metal oxide with a large particle size and a polyanion compound with a small particle size were filled with each other, with the polyanion compound as the main component, and a conductive agent and a binder were uniformly dispersed on the surface of the layered transition metal oxide as auxiliary components. In this way, on the one hand, the press density of the positive electrode plate is higher, and the energy density of the battery can be effectively increased. On the other hand, the positive electrode plate obtained by the composite has better air stability and cycle performance.

[0092] For Comparative Example 1 compared with Example 1, only a layered transition metal oxide was used as the active material. The obtained positive electrode plate had a low press density and a low retention rate after 500 cycles.

[0093] For Comparative Example 2 compared with Example 1, only a polyanion compound was used as the active material. The obtained positive electrode plate had a low press density and a low reversible capacity.

[0094] For Comparative Example 3 compared with Example 1, the particle size distribution of the active material did not fall within the protection scope of the present application. The obtained positive electrode plate had a low press density and a low cycle retention rate.

[0095] The above examples are only for explaining the technical solutions of the present application and do not limit them. Although the present application has been described in detail with reference to the above examples, those skilled in the art may modify the technical solutions described in the above examples, or perform equivalent substitutions for some or all of the technical features. These modifications or substitutions do not deviate from the essence of the corresponding technical solutions from the scope of the technical solutions of each example of the present application.

Claims

1. comprising a current collector and a positive electrode material layer formed on at least one surface of the current collector, the positive electrode material layer comprising a layered transition metal oxide and a polyanion compound, The chemical formula of the layered transition metal oxide is Na ｘ MO ２ and includes where x satisfies 0.6 ≦ x ≦ 1.0, M comprises at least one of Fe, Mn, Cr, Ni, Co, Cu, Mg, Zr and Ti, The chemical formula of the polyanion compound is NaAPO ４ , Na ｙ E ２ (XO ４ ) ３ and Na ２ QP ２ O ７ and includes at least one of them, A comprises at least one of Fe and Mn, where y satisfies 1 ≦ y ≦ 4, E comprises at least one of V, Fe, Ni, Mn and Ti, X comprises at least one of P, S and Si, Q comprises at least one of Fe, Mn and Co, the mass ratio of the layered transition metal oxide to the polyanion compound is, 【Number 1】 and, ρ １ is the true density of the layered transition metal oxide, ρ ２ is the true density of the polyanion compound, ρ １ / ρ ２ is 1.25 ≤ ρ １ / ρ ２ ≤ 1.86 is satisfied, the particle size distribution of the layered transition metal oxide is, 【Number 2】 satisfying, The particle size D' of the polyanion compound ５０ is [Number 3] satisfying a positive electrode plate characterized by the above.

2. Said ρ １ is in the range of 4.4 to 4.65 g / cm ３ and Said ρ ２ is in the range of 2.5 to 3.5 g / cm ３ 3 A positive electrode plate according to claim 1, characterized by the above.

3. (1) The D50 of the particle size of the layered transition metal oxide is 4 to 12 μm, (2) The D10 of the particle size of the layered transition metal oxide is 1.27 to 3.82 μm, (3) The particle size D' of the polyanion compound ５０ is 0.41 to 1.24 μm, including at least one of features (1) to (3) above A positive electrode plate according to claim 1, characterized by the above.

4. (1) The positive electrode material layer further includes a conductive agent and a binder, (2) When the positive electrode material layer further includes a conductive agent and a binder, the conductive agent includes at least one of carbon nanotubes, conductive carbon black, conductive graphite, graphene and carbon fibers, (3) When the positive electrode material layer further includes a conductive agent and a binder, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polyacrylonitrile, styrene-butadiene rubber and polyimide, (4) When the positive electrode material layer further includes a conductive agent and a binder, the total mass of the conductive agent and the binder is 5% or less of the mass of the positive electrode material layer, (5) When the positive electrode material layer further includes a conductive agent and a binder, in the positive electrode material layer, the mass ratio of the conductive agent to the binder is (1.5 to 3.5):(1.5 to 3.5), including at least one of features (1) to (5) above A positive electrode plate according to claim 1, characterized by the above.

5. The press density of the positive electrode plate is 3.0 to 3.6 g / cm ３ is A positive electrode plate according to claim 1, characterized by the above.

6. preparing a positive electrode slurry comprising a layered transition metal oxide and a polyanion compound, A step of applying the positive electrode slurry to the surface of at least one side of the current collector, drying, and pressing is included. A method for preparing a positive electrode plate according to any one of claims 1 to 5, characterized in that.

7. The positive electrode slurry further contains a conductive agent, a binder, and a solvent. A method for preparing a positive electrode plate according to claim 6, characterized in that.

8. A step of dissolving the binder in the solvent, adding a conductive agent, and uniformly mixing to obtain a conductive slurry; A step of uniformly mixing the conductive slurry, the layered transition metal oxide, and the polyanion compound to obtain a positive electrode slurry is included. A method for preparing a positive electrode plate according to claim 7, characterized in that.

9. (1) The temperature of the drying is 75 to 120 °C; (2) The pressure used for the pressing is 20 to 100 MPa. At least one of the features (1) to (2) is included. A method for preparing a positive electrode plate according to claim 6, characterized in that.

10. Including a positive electrode plate according to any one of claims 1 to 5. A sodium ion battery, characterized in that.

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