Positive electrode plate, its preparation method 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] 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.

[0002] Cross-reference to related applications This application claims priority based on a Chinese application filed with the China Patent Office on November 29, 2022, bearing application number 202211514774.7 and entitled "Positive electrode plate, its preparation method and sodium ion battery," the entire contents of which are incorporated herein by reference. [Background technology]

[0003] The widespread application of lithium-ion batteries in the electric vehicle field has significantly increased the demand for lithium resources. However, the reserves of elemental lithium in the Earth's crust are only 0.0017%, and there is no technology to effectively recover lithium resources. This makes it impossible to meet the demands of large-scale energy storage and electric vehicles. Therefore, in order to ensure the sustainable development and utilization of energy resources, it is important to find new secondary battery systems that are low-cost, highly safe, and have long cycle lives. The reserves of elemental sodium in the Earth's crust account for approximately 2.36% (mass fraction), far exceeding the reserves of elemental lithium. Elemental sodium is widely distributed and inexpensive. Furthermore, because sodium and lithium are homologous elements, whether used in conjunction with each other, batteries undergo a "rocking-chair" electrochemical charge and discharge cycle during operation. Therefore, the development of high-performance, low-cost sodium-ion battery technology is crucial for the sustainable development of 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. 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 The polyanion compound contains MO2, where x satisfies 0.6≦x≦1.0, and M contains at least one of Fe, Mn, Cr, Ni, Co, Cu, Mg, Zr, and Ti, and the chemical formula of the polyanion compound is NaAPO4, Na y A contains at least one of E2(XO4)3 and Na2QP2O7, A contains at least one of Fe and Mn, y satisfies 1≦y≦4, E contains at least one of V, Fe, Ni, Mn and Ti, X contains at least one of P, S and Si, and Q contains at least one of Fe, Mn and Co, and 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 to 4.65 g / cm 3 and the range of ρ2 is 2.5 to 3.5 g / cm 3 is.

[0011] In one embodiment, the particle size D50 of the layered transition metal oxide is 4 to 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 polyanionic compound 50 is 0.41 to 1.24 μm.

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

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

[0016] In one embodiment, the binder comprises 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 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 is.

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

[0021] In one embodiment, the positive electrode slurry further includes 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 the resulting mixture 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 in the press is 20 to 100 MPa.

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

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

[0027] (1) In this application, 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 effectively improves air stability, has a higher press density, and exhibits excellent electrochemical performance.

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

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

[0030] In order to more clearly describe 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 will be briefly described below. It should be noted that the drawings described only illustrate some embodiments of the present application. Those skilled in the art can obtain other drawings based on these drawings without using inventive ability. [Figure 1] FIG. 2 is a discharge curve diagram of a battery cell according to Example 1 of the present application. [Figure 2] FIG. 10 is a cycle retention curve diagram of a battery cell according to Example 3 of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present application will be described in detail below with reference to examples. As will be appreciated by those skilled in the art, the following examples are merely illustrative of the present application and are not intended to limit the scope of the present application. In the examples, specific conditions are not specified, and the experiments can be carried out under conventional conditions or under conditions recommended by the manufacturer. For reagents or equipment whose manufacturers are not specified, conventional commercially available products can be used.

[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, the positive electrode material layer including a layered transition metal oxide and a polyanion compound.

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

[0034] The chemical formula of the polyanion compound is NaAPO4, Na y The composition contains at least one of E2(XO4)3 and Na2QP2O7, A contains at least one of Fe and Mn, y satisfies 1≦y≦4, E contains at least one of V, Fe, Ni, Mn and Ti, X contains at least one of P, S and Si, and Q contains 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

number

number

[0035] In the present application, 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 effectively improves air stability, has a higher press density, and has excellent electrochemical performance.

[0036] True density refers to the actual mass of a solid substance per unit volume of a material in a completely sealed state, i.e., the density excluding internal voids or gaps between particles. For measurement methods, 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 the present application includes the following: If all particles are assumed to be spherical and the particles are classified in descending order of size into primary, secondary, tertiary, quaternary, etc., the spherical particles will be stacked closest, the secondary particles will be packed between the primary particles, the tertiary particles will be packed between the primary and secondary particles, and other particles will be packed in this manner. 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%. Even if smaller particles are added after three levels of different sizes have been created, it is not possible to significantly reduce the porosity and increase the particle volume density. Therefore, this application is based on the accumulation of three levels of particles, and three levels of particles are accumulated, with D50 of the transition metal oxide as the particle size of the primary particles, D10 of the transition metal oxide as the particle size of the secondary particles, and D50 of the polyanion compound as the particle size of the tertiary particles. The sizes of the secondary and tertiary particles can be calculated based on the size of the primary particles. The combination of three levels of particles (D50 of the transition metal oxide, D10 of the transition metal oxide, and D50 of the polyanion compound) can effectively increase the accumulation density (corresponding to the press density / volume density of the electrode plate).

[0039] After determining the particle size at each level, to improve the layered transition metal oxide's sensitivity to air, it is necessary to uniformly distribute the polyanion compound at least in the outer layer of the layered oxide in the electrode plate to block contact between the layered transition metal oxide and air. Assuming all particles are spherical, the D50 of the transition metal oxide and the D50 of the polyanion compound are used as the average particle diameters, which can then be used to calculate the surface area of ​​the corresponding spherical metal oxide particles. To achieve the desired effect (the polyanion compound covering the center of the transition metal oxide), the polyanion compound is further assumed to be spherical, and the sum of the surface areas of all spheres is equal to or greater than the surface area of ​​the layered oxide. Therefore, the particle number relationship between the two can be determined based on their areas, and the mass relationship between the two materials can be determined based on their particle sizes, particle numbers, and true densities.

[0040] Therefore, by controlling parameters such as particle size distribution and mass ratio, it is possible to increase the pressing density and reduce the material's sensitivity to air. This increases the pressing density while also reducing voids to a certain extent, thereby minimizing contact between the metal oxide and air. Metal oxides have high capacity but poor cycle performance, while polyanion compounds have low capacity but good cycle performance. By combining metal oxides with some polyanion compounds, it is possible to ensure a relatively high capacity and improve cycle performance. In one embodiment, the particle size D' of the polyanionic compound 50 teeth,

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 Includes O2 etc.

[0042] In one embodiment, the polyanionic compound NaAPO4 is NaFePO4 or NaMnPO4 。 In one embodiment, Na y In E2(XO4)3, y includes, but is not limited to, 1, 2, 3, and 4. 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 to 4.65 g / cm 3 For example, 4.5 g / cm 3 , 4.52g / cm 3 or 4.6 g / cm 3 The range of ρ2 is 2.5 to 3.5 g / cm 3 For example, 2.64 g / cm 3 , 2.72 g / cm 3 , 2.8g / cm 3 , 3g / cm 3 or 3.2 g / cm 3 And so on.

[0044] In one embodiment, ρ1 / ρ2 may be, but is not limited to, 1.3, 1.4, 1.46, 1.5, 1.52, 1.6, or 1.8.

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

[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.

[0047] In one embodiment, the particle size D' of the polyanionic 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.

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

[0049] In one embodiment, the conductive agent includes at least one of carbon nanotubes (CNTs), 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 the conductive carbon black to the carbon nanotubes is (1 to 3):0.5, such as 1:0.5, 1.5:0.5, 2:0.5, 2.5:0.5, or 2.8:0.5.

[0050] In one embodiment, the binder comprises at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polypropylene 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, the mass ratio of the conductive agent to the binder in the positive electrode layer is (1.5 to 3.5):(1.5 to 3.5), for example, 1.5:3.5, 2:3, or 3.5:1.5.

[0053] In one embodiment, the press density of the positive electrode plate is 3.0 to 3.6 g / cm 3 For example, 3.1 g / cm 3 , 3.2g / cm 3 , 3.3g / cm 3 , 3.4g / cm 3 , 3.5g / cm 3 And so on.

[0054] In another aspect, the present application also provides a method for preparing the positive electrode plate, the method including the steps of preparing a positive electrode slurry containing a layered transition metal oxide and a polyanion compound, and applying the positive electrode slurry to at least one surface of the current collector, drying, and pressing.

[0055] The method for preparing the positive electrode plate according to the present application is simple and easy to carry out, and involves applying a positive electrode slurry containing a layered transition metal oxide and a polyanion compound to at least one surface of a 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 includes 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 the steps of dissolving a binder in a solvent, adding and uniformly dispersing a conductive agent to obtain a uniform conductive slurry, and adding and uniformly dispersing a layered transition metal oxide and a polyanion compound to the conductive slurry to obtain a positive electrode slurry.

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

[0060] In one embodiment, the pressure used in the press is 20 to 100 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, 95 MPa, etc.

[0061] In another aspect, the present application further provides a sodium ion battery, which includes the positive electrode plate, and has excellent electrochemical performance.

[0062] The present invention will be further explained and explained below 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.

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

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

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

[0067] (b) Layered transition metal oxide NaNi as a positive electrode material 1 / 3 Fe 1 / 3 Mn 1 / 3 75.5 parts by mass of O2 and 20.0 parts by mass of a polyanion compound Na3V2(PO4)3 as a positive electrode material are added to the first conductive slurry of step (a) and uniformly dispersed to obtain a slurry S2, and NaNi1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is D 10 = 2.44 μm, D 50 = 6.87 μm and true density is 4.50 g / cm 3 The positive electrode material Na3V2(PO4)3 is D 50 =0.51 μm and true density is 3.24 g / cm 3 It was.

[0068] (c) The above slurry S2 was uniformly applied to an aluminum foil, which was then heated, dried, and rolled to obtain a positive electrode plate.

[0069] A battery was assembled using the positive electrode plate according to this example, a negative electrode, a separator, an electrolyte, etc., and then subjected to processes such as aging, chemical conversion, and aging to obtain a battery cell to be measured. [Example]

[0070] The preparation method of the positive electrode plate differed from that of 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 the other conditions were the same as those of Example 1. [Example]

[0071] Regarding the preparation method of the positive electrode plate, the layered transition metal oxide is Na 0.9 Cu 0.25 Fe 0.3 Mn 0.45 O2 and particle size D 10 = 1.83 μm, and particle size D 50 = 5.03 μm and true density is 4.55 g / cm 3 The only difference from Example 1 was that the temperature was 100°C, and the other conditions were the same as those of Example 1. [Example]

[0072] Regarding the preparation method of the positive electrode plate, the polyanion compound is NaFePO4, and the particle size is D 50 =0.44μm and true density is 3.14g / cm 3The only difference from Example 1 was that the temperature was 100°C, and the other conditions were the same as those of Example 1. [Example]

[0073] Regarding the preparation method of the positive electrode plate, the layered transition metal oxide is 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 The polyanion compound contains NaFePO, NaV(PO), and NaMnP0 in a mass ratio of 1:1:1, and the true density of NaMnP0 is 3.26 g / cm. 3 The only difference from Example 1 was that the temperature was 100°C, and the other conditions were the same as those of 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 dissolved in NMP solvent, and 2.0 parts of SP and 0.5 parts of CNT were added as conductive agents and dispersed uniformly to obtain a conductive slurry S1.

[0076] (b) Layered transition metal oxide NaNi as a positive electrode material 1 / 3 Fe 1 / 3 Mn 1 / 3 95.5 parts of O2 was added to S1 and dispersed uniformly to obtain slurry S2. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is D 10 = 2.44 μm, D 50 =6.87 μm.

[0077] (c) The above slurry S2 was uniformly applied to an aluminum foil, which was then heated, dried, and rolled to obtain a positive electrode plate.

[0078] A battery was assembled using the positive electrode plate according to this comparative example, a negative electrode, a separator, an electrolyte, etc., and then subjected to processes such as aging, chemical conversion, and aging to obtain a battery cell to be measured.

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

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

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

[0082] (c) The above slurry S2 was uniformly applied to an aluminum foil, which was then heated, dried, and rolled to obtain a positive electrode plate.

[0083] A battery was assembled using the positive electrode plate according to this comparative example, a negative electrode, a separator, an electrolyte, etc., and then subjected to processes such as aging, chemical conversion, and aging to obtain a battery cell to be measured.

[0084] Comparative Example 3 Regarding the preparation method of the positive electrode plate, the layered transition metal oxide is 10 = 2.8 μm, particle size D 50 = 15 μm and true density is 4.49 g / cm 3 and the polyanionic compound has a particle size D 50 = 1.65 μm and true density is 3.25 g / cm 3 The only difference from Example 1 was that the temperature was 100°C, and the other conditions were the same as those of Example 1.

[0085] [Experimental Example] The electrochemical performance tests were carried out on the positive electrode plates and sodium ion batteries of the examples and comparative examples by the following method.

[0086] 1. Residual alkali measurement The positive electrode plate was stored in a humidity environment of 26±3% for 12 hours, after which the powder material in the electrode plate was separated from the aluminum foil and transferred to a beaker, added with deionized water, stirred for 60 seconds, and filtered. The filtrate was transferred to the sample stage of a potentiometric titrator and titrated potentiometrically with hydrochloric acid. The carbonate ion and bicarbonate ion contents obtained were converted to sodium ion contents. The content calculation basis was the mass of layered transition metal oxide in the positive electrode powder material after separation from the aluminum foil.

[0087] 2. Capacity measurement The battery was charged at a constant current and constant voltage up to 4.0 V at a rate of 0.5 C, with a final current of 0.05 C. The battery was left to stand for 30 minutes, and then discharged at a constant current of 0.5 C down to 2.0 V. The battery capacity was recorded and converted to a capacity per gram based on the mass of the active material in the positive electrode plate, which was recorded as the reversible capacity.

[0088] 3. Cycle performance measurement The battery was charged at a constant current and constant voltage of 0.5 C to 4.0 V at 45±2°C, with a final current of 0.05 C, and allowed to stand for 30 minutes. It was then discharged at a constant current of 0.5 C to 2.0 V and allowed to stand for 30 minutes. This cycle was repeated 500 times, and the ratio of the 500th capacity to the initial capacity was recorded and recorded 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 this application, a layered transition metal oxide with a large particle size and a polyanion compound with a small particle size were packed together, with the polyanion compound as the main component and the conductive agent and binder as secondary components, uniformly dispersed on the surface of the layered transition metal oxide. This, on the one hand, increases the press density of the positive electrode plate, effectively increasing the energy density of the battery, and, on the other hand, the positive electrode plate obtained by this composite has better air stability and cycle performance.

[0092] In contrast to Example 1, the positive electrode plate obtained in Comparative Example 1, which employed only a layered transition metal oxide as the active material, had a low press density and a low retention rate after 500 cycles.

[0093] In contrast to Example 1, the positive electrode plate obtained in Comparative Example 2, in which only a polyanion compound was used as the active material, had a low press density and a low reversible capacity.

[0094] Compared to Example 1, the particle size distribution of the active material in Comparative Example 3 was not within the scope of protection of the present application, and the obtained positive electrode plate had a low press density and a low cycle retention rate.

[0095] The above embodiments are merely for illustrating the technical solutions of the present application, and are not intended to limit the same. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art may modify the technical solutions described in the above embodiments, and may make equivalent substitutions for some or all of the technical features therein. These modifications or substitutions do not deviate from the essence of the corresponding technical solutions and the scope of the technical solutions of the embodiments of the present application.

Claims

1. a current collector and a positive electrode material layer formed on at least one surface of the current collector, the positive electrode layer contains a layered transition metal oxide and a polyanion compound, The chemical formula of the layered transition metal oxide is Na ｘ MO ２ Including, x satisfies 0.6≦x≦1.0, M includes 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 A contains at least one of Fe and Mn, y satisfies 1≦y≦4, E contains at least one of V, Fe, Ni, Mn, and Ti; X contains at least one of P, S and Si; Q contains at least one of Fe, Mn, and Co; The mass ratio of the layered transition metal oxide to the polyanion compound is [Equation 1] and ρ １ is the true density of the layered transition metal oxide, ρ ２ is the true density of the polyanionic compound, ρ １ / ρ ２ is 1.25≦ρ １ / ρ ２ ≦1.86, The particle size distribution of the layered transition metal oxide is [Equation 2] Fulfilling The particle size D' of the polyanion compound ５０ teeth, [Equation 3] fulfill A positive electrode plate characterized by:

2. Said ρ １ The range is 4.4 to 4.65 g / cm ３ and Said ρ ２ The range is 2.5 to 3.5 g / cm ３ is The positive electrode plate according to claim 1 .

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

4. (1) the positive electrode layer further contains a conductive agent and a binder; (2) When the positive electrode material layer further contains a conductive agent and a binder, the conductive agent contains at least one of carbon nanotubes, conductive carbon black, conductive graphite, graphene, and carbon fibers; (3) When the positive electrode material layer further contains a conductive agent and a binder, the binder contains at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene acid, polyacrylonitrile, styrene-butadiene rubber, and polyimide; (4) When the positive electrode material layer further contains 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 contains a conductive agent and a binder, the mass ratio of the conductive agent to the binder in the positive electrode material layer is (1.5 to 3.5):(1.5 to 3.5); It includes at least one of the features (1) to (5). The positive electrode plate according to claim 1 .

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

6. preparing a positive electrode slurry containing a layered transition metal oxide and a polyanion compound; and applying the positive electrode slurry to at least one surface of the current collector, drying the positive electrode slurry, and pressing the positive electrode slurry. The method for preparing a positive electrode plate according to any one of claims 1 to 5.

7. The positive electrode slurry further includes a conductive agent, a binder, and a solvent. The method for preparing a positive electrode plate according to claim 6.

8. dissolving the binder in the solvent, adding a conductive agent and mixing them uniformly 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. The method for preparing a positive electrode plate according to claim 7.

9. (1) The drying temperature is 75 to 120°C; (2) The pressure used in the press is 20 to 100 MPa; It includes at least one of the features (1) to (2). The method for preparing a positive electrode plate according to claim 6.

10. The positive electrode plate according to any one of claims 1 to 5 is included. A sodium-ion battery characterized by:

Images