Positive electrode active material, method for manufacturing the same, positive electrode sheet, secondary battery, battery module, battery pack, and power tool

Abstract

The application provides a positive electrode active material, a preparation method thereof, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and a power utilization device. The positive electrode active material comprises: a polyanion compound, the polyanion compound has the following general formula: Na x R y (PO4) z (P2O7) k wherein R comprises at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4; and a first carbon material and a second carbon material which are compounded with the polyanion compound, the crystallinity of the first carbon material is higher than that of the second carbon material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a positive electrode active material, a preparation method thereof, a positive electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device. BACKGROUND

[0002] Sodium batteries have great application potential in large-scale energy storage due to their abundant reserves, low prices and wide working temperature.

[0003] Polyanion compounds are considered to be the most promising electrode materials due to their excellent structural stability, safety and suitable voltage platform. However, the application of polyanion compounds in sodium secondary batteries still has problems such as low electronic conductivity, low discharge capacity and poor cycle performance, which cannot meet the application needs of new generation electrochemical systems. SUMMARY

[0004] The present application is made in view of the above-mentioned problems, and aims to provide a positive electrode active material including a polyanion compound and two carbon materials on the surface of the polyanion compound, which are beneficial to form a synergistic effect on the surface of the polyanion, improve the conductivity of the positive electrode active carbon material and improve the processability of the polyanion material.

[0005] In a first aspect, the present application provides a positive electrode active material, which includes: a polyanion compound, the polyanion compound having the following general formula:

[0006] Na x R y (PO4) z (P2O7) k

[0007] wherein R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4; and a first carbon material and a second carbon material compounded with the polyanion compound, the crystallinity of the first carbon material being higher than that of the second carbon material.

[0008] The positive electrode active material comprises a first carbon material and a second carbon material composited with a polyanionic compound. The first carbon material has a higher degree of crystallinity than the second carbon material. On the one hand, the two carbon materials with different degrees of crystallinity can reduce agglomeration and achieve uniform distribution among the polyanionic compounds. On the other hand, the second carbon material with higher crystallinity can improve the conductivity of the positive electrode active material, thereby enhancing its coulombic efficiency and cycle performance. Furthermore, the composite of two carbon materials with different degrees of crystallinity helps optimize the particle size of the positive electrode active material, reducing the difficulty of grinding and processing, and also facilitates the crystal growth of the polyanionic compound, making its lattice regular, further improving the cycle stability of the positive electrode active material.

[0009] In any embodiment, the first carbon material I D / I G The value is less than 0.8, and the I of the second carbon material D / I G The value is greater than 0.8 and less than 1.2, the I D / I G The value was determined by Raman spectrophotometry and is located at 1300 cm⁻¹. -1 ~1400cm -1 Peak intensity I within the range D Located at 1580cm -1 ~1620cm -1 Peak intensity I within the range G The strength ratio.

[0010] First carbon material and second carbon material I D / I G The values ​​in different ranges indicate that the crystallinity of the two carbon materials is different. Combining the two carbon materials with different crystallinity with polyanionic compounds can improve the conductivity of the positive electrode active material and enhance the cycle performance of the battery.

[0011] In any embodiment, the first carbon material is distributed in particulate form between the primary particles of the polyanionic compound.

[0012] The first carbon material is distributed in particulate form among the primary particles of the polyanionic compound, which can effectively prevent the aggregation of polyanionic compounds and improve the processability of the positive electrode active material.

[0013] In any embodiment, the second carbon material is coated on the surface of the primary particles of the polyanionic compound in the form of a carbon film.

[0014] The second carbon material is coated on the surface of the primary particles of the polyanionic compound in the form of a carbon film, which can increase the contact area between the carbon material and the polyanionic compound, facilitate electron transport, and help improve the conductivity of the polyanionic compound.

[0015] In any embodiment, the primary particles of the polyanionic compound have a median particle size D50 of 0.1 μm to 2.0 μm. v 50 is 0.1 μm to 2.0 μm.

[0016] The median particle size D50 of the primary particles of the polyanionic compound is controlled v 50 is 0.1 μm to 2.0 μm, which is conducive to the uniform distribution of the first carbon material and the second carbon material on the surface of the polyanionic compound, avoids the agglomeration between the polyanionic compounds, and improves the crystallinity and conductivity of the positive electrode active material.

[0017] In any embodiment, the mass content of the first carbon material is 0.1% to 5%, which can be optionally 0.5% to 2%, based on the total mass of the positive electrode active material, and the mass content of the second carbon material is 0.1% to 10%, which can be optionally 0.5% to 2%.

[0018] Controlling the mass content of the first carbon material and the second carbon material within a suitable range can avoid the decrease of the specific capacity of the positive electrode active material caused by too high carbon content, and can also avoid the poor conductivity of the positive electrode active material caused by too low carbon content. A suitable mass content range of the first carbon material and the second carbon material can take into account the production cost, processability and electrical performance, so as to make the battery have excellent electrical performance and application prospect. Further controlling the mass content of the first carbon material and the second carbon material to be 0.5% to 2% is conducive to further improving the coulomb efficiency and cycle performance of the battery.

[0019] In any embodiment, the positive electrode active material has a median particle size D50 of 1.0 μm to 10 μm. v 50 is 1.0 μm to 10 μm, which can be optionally 1.5 μm to 5.0 μm.

[0020] Controlling the positive electrode active material within a suitable particle size range can avoid the physical gelation of the subsequent slurry caused by too small particle size, which increases the difficulty of coating. It can also avoid the decrease of the tap density caused by too large particle size, thereby reducing the kinetic performance of the positive electrode active material in the charge and discharge process, and taking into account the processability and electrical performance. Further controlling the median particle size D50 of the positive electrode active material to be 1.5 μm to 5.0 μm is conducive to further improving the coulomb efficiency and cycle performance of the battery. v 50 is 1.5 μm to 5.0 μm, which is conducive to further improving the coulomb efficiency and cycle performance of the battery.

[0021] In any embodiment, the tap density of the positive electrode active material is 1.5 g / cm3 to 3 g / cm3 under a pressure of 400 MPa. 3 3 .

[0022] ​The positive electrode active material provided in this application has a high powder compaction density, which can further improve the electrode compaction density. This is beneficial for further optimizing the specific capacity of the positive electrode active material and the energy density of the battery, so that the sodium secondary battery can also have excellent cycle life and safety during long-term fast charging.

[0023] In any embodiment, the powder resistivity of the positive electrode active material at 25°C is 1 kΩ·cm to 375 kΩ·cm.

[0024] The positive electrode active material powder provided in this application has low resistance, which enables the positive electrode sheet to have high conductivity, and enables the sodium secondary battery to have excellent cycle life and safety during long-term fast charging.

[0025] A second aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps:

[0026] The positive electrode active material is prepared by mixing and calcining a sodium source, an R source, a phosphorus source, a first carbon source, and a second carbon source, wherein the positive electrode active material comprises:

[0027] Polyanionic compounds, wherein the polyanionic compounds have the following general formula:

[0028] Na x R y (PO4) z (P2O7) k

[0029] Wherein, R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb, 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4; and

[0030] The first carbon material and the second carbon material are composited with the polyanionic compound, wherein the crystallinity of the first carbon material is higher than that of the second carbon material;

[0031] The first carbon material comes from the first carbon source, and the second carbon material comes from the second carbon source.

[0032] The preparation method of the above-mentioned positive electrode active material is simple and has low production cost. The co-sintering of at least two different carbon sources with other raw materials enables the carbon material to be uniformly distributed among the primary particles of the polyanionic compound, which can more effectively improve the conductivity of the positive electrode active material, resulting in excellent coulombic efficiency and cycle performance of the battery.

[0033] In any embodiment, the first carbon source is an inorganic carbon source, which includes one or more of natural graphite, artificial graphite, carbon black, carbon nanotubes, and graphene.

[0034] The aforementioned inorganic carbon source has high crystallinity and can be distributed in the form of particles among the primary particles of polyanionic compounds. This reduces the agglomeration and clumping of polyanionic compounds, improves the processability of positive electrode active materials, reduces the particle size of positive electrode active materials, and effectively enhances the conductivity of positive electrode active materials.

[0035] In any embodiment, the second carbon source is an organic carbon source, which includes one or more of sucrose, glucose, citric acid, starch, cyclodextrin, pitch, polyethylene glycol, and polyvinyl alcohol.

[0036] After calcination, the aforementioned organic carbon source coats the primary particle surface of the polyanionic compound in the form of a carbon film, which increases the contact area between the carbon material and the polyanionic compound, facilitates electron transport, and helps improve the conductivity of the polyanionic compound.

[0037] In any embodiment, the step of mixing and calcining the sodium source, R source, phosphorus source, first carbon source, and second carbon source to prepare the positive electrode active material specifically includes:

[0038] Sodium source, R source and phosphorus source are dissolved in solvent and ground to obtain the first mixed slurry;

[0039] The first carbon source and the second carbon source are dispersed in a solvent to obtain a carbon dispersion.

[0040] The first mixed slurry and the carbon dispersion are mixed, dried, and calcined to prepare the positive electrode active material.

[0041] Grinding other raw materials first, and then adding carbon source, helps to quickly grind the particles in the first mixed slurry to the ideal particle size, avoids thickening caused by the addition of nanomaterials in carbon dispersion, and greatly improves production efficiency.

[0042] In any embodiment, the D of the particles in the first mixed slurry v 50 is 0.05μm to 1.5μm, preferably 0.1μm to 0.8μm.

[0043] Controlling the particle size of the first mixed slurry to a suitable median range is beneficial for mixing the carbon dispersion with the first mixed slurry, so that the first carbon material / second carbon material can be uniformly combined with the polyanionic compound, thereby improving the processability of the positive electrode active material, as well as the battery capacity, coulombic efficiency and cycle performance.

[0044] In any embodiment, the R source includes one or more of the following: magnesium source, aluminum source, scandium source, titanium source, vanadium source, chromium source, manganese source, iron source, cobalt source, nickel source, copper source, zinc source, zirconium source, niobium source, molybdenum source, tin source, hafnium source, tantalum source, tungsten source, and lead source.

[0045] In any embodiment, the iron source includes one or more of ferrous oxalate, ferrous nitrate, ferrous sulfate, ferrous chloride, ferrous oxalate, ferric acetate, ferric oxide, ferrous oxide, and metallic iron.

[0046] A third aspect of this application provides a positive electrode sheet, including a positive electrode film layer, wherein the positive electrode film layer comprises the positive electrode active material described in the first aspect or the positive electrode active material prepared by the preparation method of the positive electrode active material described in the second aspect.

[0047] In any embodiment, the positive electrode film layer further includes a one-dimensional conductive material and a zero-dimensional conductive material.

[0048] The addition of one-dimensional and zero-dimensional conductive materials is beneficial to increasing the conductivity of the positive electrode.

[0049] In any embodiment, the one-dimensional conductive material includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes. Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material is 0.2% to 1%, optionally 0.5% to 1%.

[0050] Controlling the mass content of one-dimensional conductive material within a suitable range is beneficial for reducing the resistance of the electrode and improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the mass content of the one-dimensional conductive material to 0.5%–1% is beneficial for further improving the battery's coulombic efficiency.

[0051] In any embodiment, the zero-dimensional conductive material includes one or more of Super P, Ketjen Black, and acetylene black. Based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material is 1% to 3%, optionally 2% to 2.8%.

[0052] Controlling the mass content of zero-dimensional conductive material within a suitable range is beneficial for reducing the resistance of the electrode and improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the mass content of zero-dimensional conductive material to 2%–2.8% is beneficial for further improving the battery's coulombic efficiency.

[0053] In any embodiment, based on the total mass of the positive electrode film, the mass content of the binder is 1.5% to 3%, optionally 2.0% to 2.5%.

[0054] Controlling the binder content within a suitable range provides sufficient bonding strength without causing excessive electrode resistance, which helps reduce electrode resistance and improve battery capacity, coulombic efficiency, and cycle performance. Further controlling the binder content to 2.0%–2.5% further enhances battery cycle performance.

[0055] In any embodiment, the compaction density of the positive electrode film is 1.7 g / cm³. 3 ~2.3g / cm 3 .

[0056] The compacted density is 1.7 g / cm³. 3 ~2.3g / cm 3 The positive electrode film layer gives the battery higher capacity and energy density.

[0057] In any embodiment, the electrode resistance of the positive electrode is 0.1 Ω·cm to 10 Ω·cm.

[0058] Positive electrode plates with a resistance of 0.1Ω·cm to 10Ω·cm have good electron transport efficiency, which is beneficial to the performance of the battery.

[0059] A fourth aspect of this application provides a secondary battery, including a negative electrode and a positive electrode as described in the third aspect.

[0060] In any embodiment, the secondary battery is a sodium-free secondary battery without a negative electrode.

[0061] In any embodiment, the secondary battery further includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a base coating disposed on at least one surface of the negative current collector, the base coating including one or more of carbon nanotubes, graphite, graphene, carbon black, alumina, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0062] The aforementioned base coating not only has excellent conductivity, but also facilitates the uniform deposition of metal ions on the current collector surface, thereby improving the coulombic efficiency and cycle performance of the battery.

[0063] In any embodiment, the areal density of the base coating is 5 g / m³. 2 ~50g / m 2 .

[0064] The surface density is 5 g / m³ 2 ~50g / m 2 The base coating is beneficial to the uniform distribution of nucleation sites in the negative electrode-free secondary battery, promotes the uniform deposition of metal, and does not affect the electron transport behavior.

[0065] In any embodiment, the thickness of the base coating is 2 μm to 100 μm.

[0066] Controlling the thickness of the undercoat layer to 2μm to 100μm can provide enough nucleation sites for the negative electrode-free secondary battery, which is conducive to the uniform deposition of metal ions and suppresses dendrites.

[0067] The fifth aspect of this application provides an electrical device including a secondary battery as described in the fourth aspect of this application. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of a secondary battery cell according to one embodiment of this application;

[0069] Figure 2 yes Figure 1 An exploded view of a secondary battery cell according to an embodiment of this application is shown.

[0070] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0071] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0072] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0073] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0074] Explanation of reference numerals in the attached figures:

[0075] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0076] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its manufacturing method, secondary battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0077] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0078] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0079] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0080] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0081] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0082] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0083] In the existing technology, the positive electrode active material is generally carbon coated after sintering to improve its conductivity. However, this method has limited effect on improving the conductivity of polyanionic compounds and cannot further improve battery performance.

[0084] [Positive electrode active material]

[0085] Based on this, this application proposes a positive electrode active material, comprising: a polyanionic compound having the following general formula:

[0086] Na x R y (PO4) z (P2O7) k

[0087] Wherein, R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb, 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4; and

[0088] The first carbon material and the second carbon material are composites with polyanionic compounds, and the crystallinity of the first carbon material is higher than that of the second carbon material.

[0089] In this article, composite refers to the mixing of two phase materials in any form, including but not limited to coating, particle mixing, etc.

[0090] In some embodiments, R includes Fe. In some embodiments, R includes Al. In some embodiments, R includes V. In some embodiments, R includes Mn.

[0091] In some implementations, x can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, 0.4, 4.5, 5, 5.5, 6, 6.5, 7, or a value within the range formed by any two of the above points; y can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, or a value within the range formed by any two of the above points; z can be selected as 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a value within the range formed by any two of the above points; and k can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, or a value within the range formed by any two of the above points.

[0092] The crystallinity of carbon materials can be measured by any known method, including but not limited to Raman spectroscopy and X-ray diffraction. As an example, Raman spectroscopy is used to characterize the crystallinity of carbon materials. The Raman spectrum of carbon includes spectra at 1300 cm⁻¹. -1 ~1400cm -1 (approximately 1340cm) -1 ) range and 1580cm -1 ~1620cm -1 The main "resonance" bands of the range are denoted as "D" and "G" bands, respectively. The D band is generally considered to be attributed to disordered carbon defects, while the G band is attributed to the graphite's or "ordered" spp. 2 Carbon. Therefore, Raman spectroscopy is commonly performed at 1300 cm⁻¹. -1 ~1400cm -1 Peak intensity I within the range D Located at 1580cm -1 ~1620cm -1 Peak intensity I within the range G The strength ratio characterizes the disorder / crystallinity of carbon materials. Therefore, the first carbon material's I... D / I G The value is less than the I of the second carbon material. D / I G value.

[0093] It is understandable that the first carbon material and the second carbon material can be combined with polyanionic compounds in any way, such as by coating or mixing.

[0094] The positive electrode active material comprises a first carbon material and a second carbon material composited with a polyanionic compound. The first carbon material has a higher degree of crystallinity than the second carbon material. On the one hand, the two carbon materials with different degrees of crystallinity can reduce agglomeration and achieve uniform distribution among the polyanionic compounds. On the other hand, the second carbon material with higher crystallinity can improve the conductivity of the positive electrode active material, thereby enhancing its coulombic efficiency and cycle performance. Furthermore, the composite of two carbon materials with different degrees of crystallinity helps promote the crystal growth of the polyanionic compound, making its crystal lattice more regular, further improving the cycle stability of the positive electrode active material.

[0095] In some embodiments, the first carbon material I D / I G The value is less than 0.8, and the I of the second carbon material D / I G The value is greater than 0.8 and less than 1.2, the I D / I G The value was determined by Raman spectrophotometry and is located at 1300 cm⁻¹. -1 ~1400cm -1 Peak intensity I within the range D Located at 1580cm -1 ~1620cm -1 Peak intensity I within the range G The strength ratio.

[0096] When I D / I G When the value is less than 0.8, carbon materials exhibit a certain degree of graphitization. And I... D / I G When the value is greater than 0.8, it is mainly composed of amorphous carbon. In some embodiments, the first carbon material includes one or more of natural graphite powder, artificial graphite powder, carbon black, carbon nanotubes, and graphene; the second carbon material includes amorphous carbon.

[0097] In some embodiments, the first carbon material I D / I G The value can be selected from 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.75, or a value within the range formed by any two of the above points. The second carbon material I D / I G The value can be selected as 0.82, 0.85, 0.87, 0.9, 0.93, 0.95, 0.98, 1.0, 1.05, 1.1, 1.15, or a value within the range formed by any two of the above points.

[0098] First carbon material and second carbon material I D / I GThe values ​​in different ranges indicate that the crystallinity of the two carbon materials is different. Combining the two carbon materials with different crystallinity with polyanionic compounds can improve the conductivity of the positive electrode active material and enhance the cycle performance of the battery.

[0099] In some embodiments, the first carbon material is distributed in particulate form between the primary particles of the polyanionic compound.

[0100] In this paper, the term "primary particle" refers to particles of polyanionic compounds before they agglomerate.

[0101] In some embodiments, the median particle size D of the primary particles of the polyanionic compound v 50 is 0.1 μm to 2.0 μm. In some embodiments, the median particle size of the primary particles of the polyanionic compound can be selected as 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2.0 μm, or a value within the range formed by any two of the above points.

[0102] The median particle size of the primary particles of the polyanionic compound is 0.1 μm to 2.0 μm. The distribution of the first carbon material in this range makes it more effective in improving the conductivity of the positive electrode active material than a simple physical mixture of the first carbon material and the secondary particles of the polyanionic compound.

[0103] In this paper, the term "secondary particle" refers to particles formed by the aggregation of primary particles of polyanionic compounds.

[0104] In some embodiments, the second carbon material is coated on the surface of the primary particles of the polyanionic compound in the form of a carbon film.

[0105] The second carbon material is coated on the surface of the primary particles of the polyanionic compound in the form of a carbon film, which can increase the contact area between the carbon material and the polyanionic compound, facilitate electron transport, and help improve the conductivity of the polyanionic compound.

[0106] In some embodiments, the second carbon material is coated on the surface of the primary particles of the polyanionic compound in the form of a carbon film, and the first carbon material is distributed in particulate form between the primary particles of the polyanionic compound coated with the second carbon material.

[0107] The second carbon material and the first carbon material are composited with the polyanionic compound in different forms, and the conductivity of the positive electrode active material is improved through the interaction of point and surface. In addition, the second carbon material is mainly amorphous carbon, and its coating on the surface of the polyanionic compound can easily lead to the aggregation of the polyanionic compound, making it difficult to effectively reduce the particle size. The first carbon material has higher crystallinity, and its distribution among the primary particles of the polyanionic compound coating the second carbon material can effectively reduce the mutual adhesion between the second carbon materials and reduce the median particle size of the positive electrode active material.

[0108] In some embodiments, based on the total mass of the positive electrode active material, the mass content of the first carbon material is 0.1% to 5%, optionally 0.5% to 2%, and the mass content of the second carbon material is 0.1% to 10%, optionally 0.5% to 2%.

[0109] In some embodiments, based on the total mass of the positive electrode active material, the mass content of the first carbon material can be selected as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a value within the range formed by any two of the above points. The mass content of the second carbon material can be selected as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or a value within the range formed by any two of the above points.

[0110] Controlling the mass content of the first and second carbon materials within a suitable range can prevent both excessively high carbon content, which leads to a decrease in the specific capacity of the positive electrode active material, and excessively low carbon content, which leads to poor conductivity. A suitable mass content range for the first and second carbon materials balances production costs, processability, and electrical performance, resulting in batteries with excellent electrical performance and promising application prospects. Further controlling the mass content of the first and second carbon materials to 0.5%–2% is beneficial for further reducing electrode resistance and improving battery capacity, coulombic efficiency, and cycle performance.

[0111] In some embodiments, the median particle size D of the positive electrode active material v 50 is 1.0μm to 10μm, and can be selected from 1.5μm to 5.0μm.

[0112] In some embodiments, the median particle size D of the positive electrode active material v50 can be selected as 1.0μm, 1.5μm, 2.0μm, 2.5μm, 3.0μm, 3.5μm, 4.0μm, 4.5μm, 5.0μm, 5.5μm, 6.0μm, 6.5μm, 7.0μm, 7.5μm, 8.0μm, 8.5μm, 9.0μm, 9.5μm, 10μm, or a value within the range formed by any two of the above points.

[0113] Median particle size D of positive electrode active material v 50. Testing can be performed using any method known in the art. As an example, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, weigh 0.1g–0.13g of the positive electrode active material sample to be tested into a 50mL beaker, add 5g of anhydrous ethanol, place a stir bar of approximately 2.5mm in the beaker, and seal with plastic wrap. After ultrasonic treatment for 5 minutes, transfer the sample to a magnetic stirrer and stir at 500 rpm for at least 20 minutes. Two samples are taken from each batch for testing. Testing is performed using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0114] Controlling the particle size of the positive electrode active material within a suitable range can prevent physical gelation of the slurry due to excessively small particle size, which increases the difficulty of coating. It also avoids reduced compaction density due to excessively large particle size, which would decrease the kinetic performance of the positive electrode active material during charge and discharge, thus balancing processability and electrical performance. Further control of the median particle size D of the positive electrode active material is also crucial. v The electrode thickness ranges from 1.5μm to 5.0μm, which helps to further reduce the electrode resistance and improve the battery's capacity, coulombic efficiency, and cycle performance.

[0115] In some embodiments, the compacted density of the positive electrode active material powder at a pressure of 400 MPa is 1.5 g / cm³. 3 ~3g / cm 3 In some embodiments, the compaction density of the positive electrode active material powder at a pressure of 400 MPa can be selected as 1.5 g / cm³. 3 1.7g / cm 3 2.0g / cm 3 2.2g / cm 3 2.4g / cm 3 2.5g / cm 3 2.6g / cm 3 2.8g / cm 3 3g / cm 3 The value within the range formed by any two of the above points.

[0116] The compaction density of positive electrode active materials under 400 MPa pressure can be tested using any method known in the art. As an example, according to GB / T 24533-2009 Powder Compaction Density Method: During external force compression, as the powder moves and deforms, voids are filled, the contact area between particles increases, generating attractive forces between atoms and enhancing the mechanical cohesion between particles, thus forming a compact with a certain density: pC=m / V=m / (S×H) Where: pC---compaction density of the powder, unit: g / cm³ 3 m --- Sample mass, unit: g; S --- Mold bottom area, unit: 1.327 cm² 2 H---Compacted thickness, unit: cm. Specifically, it can be: take a certain amount of the powder sample to be tested and place it in a special compaction mold, then place the mold on a compaction density instrument, set different pressures, and the thickness of the powder under 400MPa pressure (thickness after depressurization) can be read on the instrument. The compaction density can be calculated by ρ=m / v.

[0117] The positive electrode active material provided in this application has a high compaction density, which is beneficial to further improve the specific capacity of the positive electrode active material and the energy density of its battery.

[0118] In some embodiments, the powder resistivity of the positive electrode active material at 25°C is 1 kΩ·cm to 375 kΩ·cm. In some embodiments, the powder resistivity of the positive electrode active material at 25°C can be selected from 1 kΩ·cm, 5 kΩ·cm, 10 kΩ·cm, 50 kΩ·cm, 100 kΩ·cm, 150 kΩ·cm, 200 kΩ·cm, 250 kΩ·cm, 300 kΩ·cm, 350 kΩ·cm, 370 kΩ·cm, 375 kΩ·cm, or a value within the range formed by any two of the above points.

[0119] The powder resistivity of the positive electrode active material at 25°C can be tested using any method known in the art. As an example, the powder resistivity testing instrument is a Yuaneng Technology PRCD1100, with a pressure range of 10MPa to 400MPa and an indenter size of 78.54mm. 2 A certain amount of powder is placed in a special compaction mold, and then the mold is placed on a compaction density instrument. Different pressures are set, and the resistivity of the powder under different pressures can be read on the equipment.

[0120] The positive electrode active material powder provided in this application has low resistivity, which is beneficial to the performance of the battery.

[0121] This application also provides a method for preparing a positive electrode active material, comprising the following steps:

[0122] A positive electrode active material is prepared by mixing and calcining a sodium source, an R source, a phosphorus source, a first carbon source, and a second carbon source. The positive electrode active material includes:

[0123] Polyanionic compounds, which have the following general formula:

[0124] Na x R y (PO4) z (P2O7) k

[0125] Wherein, R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb, 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4; and

[0126] The first carbon material and the second carbon material are composites with polyanionic compounds, and the crystallinity of the first carbon material is higher than that of the second carbon material.

[0127] The first carbon material comes from the first carbon source, and the second carbon material comes from the second carbon source.

[0128] In some embodiments, R includes Fe. In some embodiments, R includes Al. In some embodiments, R includes V. In some embodiments, R includes Mn.

[0129] In some implementations, x can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, 0.4, 4.5, 5, 5.5, 6, 6.5, 7, or a value within the range formed by any two of the above points. y can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, or a value within the range formed by any two of the above points. z can be selected as 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a value within the range formed by any two of the above points. k can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, or a value within the range formed by any two of the above points.

[0130] In some embodiments, calcination includes two stages: low-temperature calcination and high-temperature calcination. The temperature is increased to the calcination temperature at a rate of 0.1°C / min to 10°C / min. Low-temperature calcination is performed at 300°C to 350°C for 2 hours to 8 hours. High-temperature calcination is performed at 450°C to 700°C for 2 hours to 15 hours.

[0131] In some embodiments, the rate of heating to the calcination temperature can be selected as 0.1℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, or a value within the range formed by any two of the above points. The low-temperature calcination temperature can be selected as 300℃, 305℃, 310℃, 315℃, 320℃, 325℃, 330℃, 335℃, 340℃, 345℃, 350℃, or a value within the range formed by any two of the above points, and the time is 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, or a value within the range formed by any two of the above points. The high-temperature calcination temperature is 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, or any value within the range formed by any two of the above points, and the time is 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, or any value within the range formed by any two of the above points.

[0132] The positive electrode active material provided in this application has a low sintering temperature and the second carbon material cannot be completely carbonized. By combining the first carbon material, the conductivity, processing performance and particle size are simultaneously optimized, so that the sodium secondary battery can maintain excellent cycle life and safety even when used for long-term fast charging.

[0133] The preparation method of the above-mentioned positive electrode active material is simple and has low production cost. The co-sintering of at least two different carbon sources with other raw materials enables the carbon material to be uniformly distributed among the primary particles of the polyanionic compound, which can more effectively improve the conductivity of the positive electrode active material, resulting in excellent coulombic efficiency and cycle performance of the battery.

[0134] In some embodiments, the first carbon source is an inorganic carbon source, including one or more of natural graphite, artificial graphite, carbon black, carbon nanotubes, and graphene.

[0135] The aforementioned inorganic carbon source has high crystallinity and can be distributed in the form of particles among the primary particles of polyanionic compounds. This reduces the agglomeration and clumping of polyanionic compounds, improves the processability of positive electrode active materials, reduces the particle size of positive electrode active materials, and effectively enhances the conductivity of positive electrode active materials.

[0136] In some embodiments, the organic carbon source includes one or more of sucrose, glucose, citric acid, starch, cyclodextrin, pitch, polyethylene glycol, and polyvinyl alcohol.

[0137] After calcination, the aforementioned organic carbon source coats the primary particle surface of the polyanionic compound in the form of a carbon film, which increases the contact area between the carbon material and the polyanionic compound, facilitates electron transport, and helps improve the conductivity of the polyanionic compound.

[0138] In some embodiments, the preparation of the positive electrode active material by mixing and calcining a sodium source, an R source, a phosphorus source, a first carbon source, and a second carbon source specifically includes:

[0139] Sodium source, R source and phosphorus source are dissolved in solvent and ground to obtain the first mixed slurry;

[0140] The first carbon source and the second carbon source are dispersed in a solvent to obtain a carbon dispersion.

[0141] The first mixed slurry and carbon dispersion were mixed, dried, and calcined to prepare the positive electrode active material.

[0142] In some embodiments, the carbon dispersion includes at least one first carbon source. In some embodiments, the carbon dispersion includes at least one second carbon source. In some embodiments, the second carbon source can disperse the first carbon source, further improving the dispersibility of the dispersion and thus improving the dispersion of the carbon material among the polyanionic compounds. In some embodiments, the second carbon source includes at least one of polyethylene glycol and polyvinyl alcohol.

[0143] Grinding other raw materials first, and then adding carbon source, helps to quickly grind the particles in the first mixed slurry to the ideal particle size, avoids thickening caused by the addition of nanomaterials in carbon dispersion, and greatly improves production efficiency.

[0144] In some embodiments, the D of the particles in the first mixed slurry v 50 is 0.05μm to 1.5μm, preferably 0.1μm to 0.8μm.

[0145] In some embodiments, the D of the particles in the first mixed slurry v 50 can be selected as 0.05μm, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, or a value within the range formed by any two of the above points.

[0146] D of particles in the first mixed slurry v50 can be tested using any method known in the art. As an example, centrifugal sedimentation and laser particle size analyzer testing are used. First, the sample is centrifuged, deposited, and filtered to obtain a particle sample from the initial mixed slurry. Then, 0.1g–0.13g of the particle sample to be tested is weighed into a 50mL beaker, 5g of acetone is added, a stir bar of approximately 2.5mm is placed inside, and the beaker is sealed with plastic wrap. After ultrasonic treatment for 5 minutes, the sample is transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples are taken from each batch of product for testing. A Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, is used for testing.

[0147] Controlling the particle size of the first mixed slurry to a suitable median range is beneficial for mixing the carbon dispersion with the first mixed slurry, so that the first carbon material / second carbon material can be uniformly combined with the polyanionic compound, thereby improving the processability of the positive electrode active material, as well as the battery capacity, coulombic efficiency and cycle performance.

[0148] In some embodiments, the R source includes one or more of the following: magnesium source, aluminum source, scandium source, titanium source, vanadium source, chromium source, manganese source, iron source, cobalt source, nickel source, copper source, zinc source, zirconium source, niobium source, molybdenum source, tin source, hafnium source, tantalum source, tungsten source, and lead source.

[0149] In some embodiments, the iron source includes one or more of ferrous oxalate, ferrous nitrate, ferrous nitrate, ferrous sulfate, ferrous chloride, ferrous oxalate, ferric acetate, ferric oxide, ferrous oxide, and metallic iron.

[0150] In some embodiments, the calcination of the first mixed slurry and carbon dispersion includes two stages: low-temperature calcination and high-temperature calcination. The temperature is increased to the calcination temperature at a rate of 0.1°C / min to 10°C / min. The low-temperature calcination temperature is 300°C to 350°C, and the time is 2 hours to 8 hours. The high-temperature calcination temperature is 450°C to 700°C, and the time is 2 hours to 15 hours.

[0151] In some embodiments, the rate of heating to the calcination temperature can be selected as 0.1℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, or a value within the range formed by any two of the above points. The low-temperature calcination temperature can be selected as 300℃, 305℃, 310℃, 315℃, 320℃, 325℃, 330℃, 335℃, 340℃, 345℃, 350℃, or a value within the range formed by any two of the above points, and the time is 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, or a value within the range formed by any two of the above points. The high-temperature calcination temperature is 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, or any value within the range formed by any two of the above points, and the time is 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, or any value within the range formed by any two of the above points.

[0152] [Positive electrode plate]

[0153] A third aspect of this application provides a positive electrode sheet, including a positive electrode film layer, wherein the positive electrode film layer includes a positive electrode active material in some embodiments or a positive electrode active material prepared by a method for preparing a positive electrode active material in some embodiments.

[0154] In some embodiments, the positive electrode film layer further includes at least one of a one-dimensional conductive material and a zero-dimensional conductive material.

[0155] In some embodiments, the positive electrode film layer contains both one-dimensional and zero-dimensional conductive materials. The simultaneous addition of two types of conductive materials is beneficial for further increasing the conductivity of the positive electrode.

[0156] In some embodiments, the one-dimensional conductive material includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes. Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material is 0.2% to 1%, optionally 0.5% to 1%.

[0157] In this paper, the term "oligowalled carbon nanotubes" refers to a mixture comprising single-walled carbon nanotubes, double-walled carbon nanotubes, and triple-walled carbon nanotubes.

[0158] In some embodiments, the one-dimensional conductive material includes single-walled carbon nanotubes. In some embodiments, the one-dimensional conductive material includes multi-walled carbon nanotubes. In some embodiments, the one-dimensional conductive material includes both single-walled and multi-walled carbon nanotubes. In some embodiments, the one-dimensional conductive material includes single-walled carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes.

[0159] In some embodiments, based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material can be selected as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a value within a range consisting of any two of the above points.

[0160] Controlling the mass content of one-dimensional conductive material within a suitable range is beneficial for reducing the resistance of the electrode and improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the mass content of the one-dimensional conductive material to 0.5%–1% is beneficial for further improving the battery's coulombic efficiency.

[0161] In some embodiments, the zero-dimensional conductive material includes one or more of Super P, Ketjen Black, and acetylene black, and the mass content of the zero-dimensional conductive material is 1% to 3% based on the total mass of the positive electrode film, optionally 2% to 2.8%.

[0162] In some embodiments, the zero-dimensional conductive material includes Super P. In some embodiments, the zero-dimensional conductive material includes Ketjen Black. In some embodiments, the zero-dimensional conductive material includes both Super P and Ketjen Black.

[0163] In some embodiments, based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material can be selected as 1%, 1.2%, 1.5%, 1.7%, 2%, 2.2%, 2.5%, 2.7%, 3%, or a value within a range consisting of any two of the above points.

[0164] Controlling the mass content of zero-dimensional conductive material within a suitable range is beneficial for reducing the resistance of the electrode and improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the mass content of zero-dimensional conductive material to 2%–2.8% is beneficial for further improving the battery's coulombic efficiency.

[0165] In some embodiments, the binder content is 1.5% to 3% by mass based on the total mass of the positive electrode film, and can be optionally 2.0% to 2.5%.

[0166] In some embodiments, based on the total mass of the positive electrode film, the mass content of the binder can be selected as 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, or a value within a range consisting of any two of the above points.

[0167] Controlling the binder content within a suitable range provides sufficient bonding strength without causing excessive electrode resistance, which helps reduce electrode resistance and improve battery capacity, coulombic efficiency, and cycle performance. Further controlling the binder content to 2.0%–2.5% further enhances battery cycle performance.

[0168] In some embodiments, the compaction density of the positive electrode film is 1.7 g / cm³. 3 ~2.3g / cm 3 .

[0169] In some embodiments, the compaction density of the positive electrode film can be selected as 1.7 g / cm³. 3 1.8g / cm 3 1.9g / cm 3 2.0g / cm 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 The value within the range formed by any two of the above points.

[0170] The compaction density of the positive electrode film layer can be tested using any method known in the art. As an example, according to an embodiment of this application, the compaction density PD of the positive electrode film layer is determined by measuring the mass (g / cm³) of the positive electrode active material layer per unit area. 2 The density of the positive electrode sheet (PD) is determined by the thickness (cm) of the positive electrode active material layer (number of sampling points > 14). The compaction density PD of the positive electrode sheet is calculated as: (PD = mass of the positive electrode sheet per unit area, g / cm³) 2 ) / Negative electrode thickness (cm).

[0171] The compacted density is 1.7 g / cm³. 3 ~2.3g / cm 3 The positive electrode film layer gives the battery higher capacity and energy density.

[0172] In some implementations, the electrode resistance of the positive electrode is 0.1 Ω·cm to 10 Ω·cm.

[0173] In some embodiments, the resistance of the positive electrode can be selected as 0.1Ω·cm, 0.5Ω·cm, 1.0Ω·cm, 1.5Ω·cm, 2Ω·cm, 2.5Ω·cm, 3Ω·cm, 3.5Ω·cm, 4Ω·cm, 4.5Ω·cm, 5Ω·cm, 5.5Ω·cm, 6Ω·cm, 6.5Ω·cm, 7Ω·cm, 7.5Ω·cm, 8Ω·cm, 8.5Ω·cm, 9Ω·cm, 9.5Ω·cm, 10Ω·cm, or a value within the range formed by any two of the above points.

[0174] In this paper, the electrode resistance is mainly used to characterize the resistance of the positive electrode, which can reflect the electronic conductivity of the positive electrode and can be tested by any known method.

[0175] The resistance of the positive electrode can be tested using any method known in the art. As an example, after drying, the positive electrode film is cut into small circular pieces with a diameter of 3mm from the left, center, and right sides of the positive electrode. The Yuaneng Technology electrode resistance meter is powered on, placed at the appropriate position of the probe, and the "Start" button is clicked. Once the reading stabilizes, it is read. Two positions are tested for each small circular piece, and the average of the six measurements is calculated; this is the electrode resistance of the electrode.

[0176] Positive electrode plates with a resistance of 0.1Ω·cm to 10Ω·cm have good electron transport efficiency, which is beneficial to the performance of the battery.

[0177] In some embodiments, the positive electrode sheet further includes a positive current collector, which can be a conductive carbon sheet, a metal foil, a carbon-coated metal foil, a porous metal plate, or a composite current collector. The conductive carbon material of the conductive carbon sheet can be selected from one or more of SuperP, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metal materials of the metal foil, carbon-coated metal foil, and porous metal plate are each independently selected from at least one of copper, aluminum, nickel, and stainless steel. The composite current collector can be a composite current collector formed by combining a metal foil with a polymer base film.

[0178] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0179] [Negative electrode plate]

[0180] The negative electrode may consist only of the negative current collector and not contain the negative active material. Alternatively, a metallic phase may be pre-deposited on the negative current collector.

[0181] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil or copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0182] In some embodiments, the negative electrode sheet includes a negative current collector and a base coating disposed on at least one surface of the negative current collector. The base coating includes one or more of carbon nanotubes, graphite, graphene, carbon black, alumina, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0183] The aforementioned base coating not only has excellent conductivity, but also facilitates the uniform deposition of metal ions on the current collector surface, thereby improving the battery's cycle performance and safety.

[0184] In some embodiments, the areal density of the base coating is 5 g / m³. 2 ~50g / m 2 .

[0185] In some embodiments, the areal density of the base coating may be selected as 5 g / m³. 2 10g / m 2 15g / m 2 20g / m 2 25g / m 2 30g / m 2 35g / m 2 40g / m 2 45g / m 2 50g / m 2 The value within the range formed by any two of the above points.

[0186] The surface density is 5 g / m³ 2 ~50g / m 2 The base coating facilitates the uniform distribution of nucleation sites, promotes uniform metal deposition, and does not affect electron transport behavior.

[0187] In some embodiments, the thickness of the base coating is 2 μm to 100 μm.

[0188] In some embodiments, the thickness of the base coating can be selected as 2μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, or a value within the range formed by any two of the above points.

[0189] Controlling the thickness of the base coating to 2μm to 100μm can provide enough nucleation sites to facilitate the uniform deposition of metal ions and suppress dendrites.

[0190] [Isolation membrane]

[0191] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0192] In some embodiments, the material of the separator can be selected from at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0193] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0194] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0195] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0196] [Rechargeable Battery]

[0197] Secondary batteries can come in various forms, including, but not limited to, individual battery cells, battery modules, and battery packs.

[0198] A battery cell includes a positive electrode sheet, which includes a positive electrode active material in some embodiments or a positive electrode active material prepared by a preparation method in some embodiments.

[0199] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 Here is an example of a square-structured battery cell, 5. Figure 2 This is an exploded view of battery cell 5.

[0200] In some embodiments, the secondary battery cell also includes a negative electrode, a separator, and an electrolyte.

[0201] In some implementations, the secondary battery cell is a sodium-free secondary battery without a negative electrode.

[0202] In a negative electrode-less sodium secondary battery, no negative electrode active material is pre-deposited; it only contains a negative electrode current collector. During the first charge, sodium ions gain electrons on the cathode side and deposit metallic sodium on the surface of the current collector to form a sodium metal phase. During discharge, the metallic sodium can be converted back into sodium ions and return to the positive electrode, achieving cyclic charging and discharging. Compared to other sodium secondary batteries, a negative electrode-less sodium secondary battery can achieve higher energy density because it is not limited by negative electrode materials. Moreover, while maintaining high electrochemical performance, it can shorten the battery production cycle, reduce manufacturing costs, and greatly improve production efficiency.

[0203] In some implementations, the CB value of the sodium-free secondary battery is less than or equal to 0.1.

[0204] The CB value is the capacity per unit area of ​​the negative electrode in a secondary battery divided by the capacity per unit area of ​​the positive electrode. Since batteries without a negative electrode do not contain negative electrode active material, the capacity per unit area of ​​the negative electrode is relatively small, and the CB value of the secondary battery is less than or equal to 0.1.

[0205] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0206] [Battery Module]

[0207] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0208] Figure 3 This is battery module 4, used as an example. (See reference...)Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0209] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0210] [Battery Pack]

[0211] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0212] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0213] [Electrical appliances]

[0214] In one embodiment of this application, an electrical device is provided, including at least one of a secondary battery, a battery module, or a battery pack according to any embodiment.

[0215] Electrical devices include at least one of the secondary batteries, battery modules, or battery packs provided in this application. The secondary batteries, battery modules, or battery packs can be the power source of the electrical device or the energy storage unit of the electrical device. Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0216] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0217] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0218] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0219] Example

[0220] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0221] I. Preparation Method

[0222] Example 1

[0223] 1) Preparation of positive electrode active materials

[0224] Sodium pyrophosphate, ferrous oxalate, and ammonium dihydrogen phosphate were dissolved in deionized water at a molar ratio of 1:2.9:2 and stirred continuously at room temperature for 30 min to obtain an initial mixed slurry. Super P and glucose were dissolved in deionized water and mixed to obtain a carbon solution. The carbon solution was mixed with the initial mixed solution and stirred to obtain a mixed solution. The above mixed solution was spray-dried at an inlet air temperature of 220℃ and an outlet air temperature of 109℃ to obtain a powdered precursor. Finally, in a N2 atmosphere, the temperature was increased to 320℃ at a heating rate of 2℃ and held for 4 h, and then increased to 550℃ at a heating rate of 2℃ and held for 10 h. The sintered product was crushed and sieved to obtain Na4Fe 2.9 (PO4)2P2O7 / C positive electrode active material. Based on the total mass of the positive electrode active material, the mass content of the first carbon material formed by Super P is 1%, the mass content of the second carbon material formed by glucose is 1%, and the median particle size D of the positive electrode active material is... v The thickness of 50 is 3.0 μm, and the compaction density of the positive electrode active material is 1.93 g / cm³. 3 The resistance of the positive electrode active material is 268 kΩ·cm.

[0225] 2) Preparation of positive electrode sheet

[0226] 2.5 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone (NMP), then 2.0 wt% Super P, 1.0 wt% carbon nanotubes, and 94.5 wt% of the above-mentioned positive electrode active material were added and mixed evenly to obtain a positive electrode slurry. The slurry was evenly coated onto the surface of the current collector aluminum foil and then transferred to a vacuum drying oven for complete drying. The dried electrode sheet was rolled and punched to obtain the positive electrode sheet. The compaction density of the positive electrode sheet was 1.8 g / cm³. 3 The electrode resistance is 1 Ω·cm.

[0227] 3) Preparation of negative electrode sheet

[0228] Carbon nanotubes and carboxymethyl cellulose (CMC) were added to deionized water at a mass ratio of 1:0.4 and stirred to form a homogeneous slurry. This slurry was then coated onto the surface of a copper foil current collector for the negative electrode. After complete drying in a vacuum drying oven, the coating was die-cut to obtain a negative electrode sheet without a negative electrode structure. The thickness of the undercoating layer was 20 μm, and the areal density was 25 g / m³. 2 .

[0229] 4) Electrolyte

[0230] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium hexafluorophosphate (NaPF6) was dissolved in the organic solvent dimethyl ethylene glycol (DME) and stirred until homogeneous to obtain an electrolyte with a sodium salt concentration of 1.5 mol / L.

[0231] 5) Separating membrane

[0232] Polypropylene film is used as the separator.

[0233] 6) Battery manufacturing

[0234] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound, tabs are welded onto it, and the cell is placed in an aluminum casing. It is then baked at 80°C to remove moisture, followed by the injection of electrolyte and sealing to obtain a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the sodium-free secondary battery product of Example 1.

[0235] Examples 2-24

[0236] The batteries in Examples 2 to 24 are prepared in a similar manner to the battery in Example 1, but the materials and parameters of the positive electrode active material and the material of the negative electrode undercoat are adjusted. The specific parameters are shown in Table 1.

[0237] Comparative Examples 1-9

[0238] The battery preparation methods in Comparative Examples 1 to 9 are basically similar to those in Example 1, but the carbon coating layer only includes carbon materials derived from inorganic or organic carbon sources, or the negative electrode does not contain an undercoating layer. Specific parameters are shown in Table 1.

[0239] II. Performance Testing

[0240] 1. Mixed slurry

[0241] 1) Particle size test in the first mixed slurry

[0242] Centrifugal sedimentation and laser particle size analyzer were used for testing. First, the sample was centrifuged, sedimented, and filtered to obtain the initial particle sample from the mixed slurry. Then, 0.1g–0.13g of the sample to be tested was weighed into a 50mL beaker, 5g of acetone was added, a stir bar of approximately 2.5mm was placed inside, and the beaker was sealed with plastic wrap. After ultrasonic treatment for 5 minutes, the sample was transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples were taken from each batch for testing. A Mastersizer 2000E laser particle size analyzer (Malvin Instruments Ltd., UK) was used for testing.

[0243] 2. Performance testing of positive electrode active materials

[0244] 1) Median particle size D v 50 tests

[0245] Referring to GB / T 19077-2016, Laser Diffraction Method for Particle Size Distribution, 0.1g–0.13g of the positive electrode active material sample to be tested was weighed into a 50mL beaker, 5g of anhydrous ethanol was added, and a stir bar of approximately 2.5mm was placed inside before sealing with plastic wrap. The sample was sonicated for 5 minutes and then transferred to a magnetic stirrer, stirred at 500 rpm for at least 20 minutes. Two samples were randomly selected from each batch for testing. The particle size distribution was analyzed using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0246] 2) Compacted density

[0247] The test is based on GB / T 24533-2009 Powder Compacted Density Method: During the external force compression process, as the powder moves and deforms, the voids are filled, the contact area between particles increases, generating attractive forces between atoms and enhancing the mechanical cohesion between particles, thereby forming a compact with a certain density.

[0248] pC = m / V = m / (S*H)

[0249] Where: pC---compacted density of powder, g / cm³; m---sample mass, g; S---base area of ​​mold, 1.327 cm³ 2 H---Compacted thickness, cm.

[0250] A certain amount of powder is placed in a compaction mold, and then the mold is placed on a compaction density instrument. Different pressures are set, and the thickness of the powder under different pressures (the thickness after depressurization) can be read on the equipment. The compaction density is calculated by ρ = m / v.

[0251] 3) Resistance test

[0252] The powder resistivity tester was a Yuaneng Technology PRCD1100, with a pressure range of 10MPa to 400MPa and an indenter size of 78.54mm. 2 .

[0253] Test: Take a certain amount of powder and put it into a compaction mold. Then place the mold on a compaction density instrument and set a pressure of 400 MPa. The resistivity of the powder under a pressure of 400 MPa can be read on the instrument.

[0254] 4) Crystallinity test of carbon materials

[0255] The carbon material in the positive electrode active material was tested using Raman spectroscopy, and the carbon content at 1300 cm⁻¹ was determined by Raman spectroscopy. -1 ~1400cm -1 Peak intensity I within the range D Located at 1580cm -1 ~1620cm -1 Peak intensity I within the range G The strength ratio as I D / I G I D / I G The smaller the value, the higher the crystallinity of the carbon material.

[0256] 3. Electrode performance testing

[0257] 1) Compacted density

[0258] According to embodiments of this application, the compaction density PD of the positive electrode film is determined by measuring the mass (g / cm³) of the positive electrode film per unit area on one side. 2 The density of the positive electrode film (PD) is determined by the thickness of the positive electrode film on one side (cm) (number of sampling points > 14). Specifically, the compaction density of the positive electrode film (PD) is the mass of the positive electrode film per unit area on one side (g / cm³). 2 ) / Positive electrode film thickness (cm).

[0259] 2) Electrode resistor

[0260] Cut the dried positive electrode film into small round pieces with a diameter of 3cm from the left, center, and right sides of the positive electrode sheet. Turn on the Yuaneng Technology electrode resistance meter, place it at the appropriate position of the "probe" of the electrode resistance meter, click the "start" button, and wait for the reading to stabilize before taking the reading. Test two positions for each small round piece, and finally calculate the average of the six measurements, which is the electrode resistance of that electrode.

[0261] 4. Battery performance test

[0262] 1) Initial discharge capacity test

[0263] The first discharge capacity test process is as follows: At 25°C, the prepared battery is charged to 3.75V with a constant current of 1C, then charged at a constant voltage of 3.75V until the current drops to 0.05C, and then discharged to 1.5V with a constant current of 1C to obtain the first discharge capacity (Cd1).

[0264] 2) Coulomb efficiency test

[0265] The coulombic efficiency test procedure is as follows: At 25°C, the prepared battery is charged to 3.75V with a constant current of 1 / 5C, and then charged at a constant voltage of 3.75V until the current drops to 0.05C, obtaining the initial charge capacity (Cc1); then discharged to 1.5V with a constant current of 1 / 5C, obtaining the initial discharge capacity (Cd1), and the battery coulombic efficiency is calculated according to the following formula: Battery coulombic efficiency = Initial discharge capacity (Cd1) / Initial charge capacity (Cc1). The test procedures for the comparative example and other embodiments are the same as above.

[0266] 3) Battery cycle capacity retention test

[0267] The battery capacity retention rate test process is as follows: At 25°C, the prepared battery is charged to 3.75V with a constant current of 1C, then charged with a constant voltage of 3.75V until the current drops to 0.05C, and then discharged to 1.5V with a constant current of 1C. The resulting capacity is recorded as the initial capacity (C0). The above steps are repeated for the same battery, and the discharge capacity (Cn) of the battery after the nth cycle is recorded. The battery capacity retention rate after each cycle is Pn = Cn / C0 × 100%. A curve is obtained by plotting the 100 points P1, P2...100 as the vertical axis and the corresponding cycle number as the horizontal axis. In this test, the first cycle corresponds to n=1, the second cycle to n=2, ..., the 100th cycle to n=100. The battery capacity retention rate data corresponding to the examples or comparative examples in Table 2 are the data measured after 100 cycles under the above test conditions, i.e., the value of P100. The test process for the comparative examples and other examples is the same as above.

[0268] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0269] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Tables 1 and 2 below.

[0270] Table 1

[0271]

[0272]

[0273] Note: In Table 1, " / " indicates that this material is included.

[0274] Table 2

[0275]

[0276]

[0277] Based on the above results, it can be seen that Examples 1 to 24 all include positive electrode active materials, which include:

[0278] Polyanionic compounds, which have the following general formula:

[0279] Na x R y (PO4) z (P2O7) k

[0280] Wherein, R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb, 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4; and

[0281] A first carbon material and a second carbon material are located on at least a portion of the surface of the polyanionic compound, wherein the crystallinity of the first carbon material is higher than that of the second carbon material.

[0282] As can be seen from the comparison between Examples 1-6 and Comparative Examples 1-2, Examples 11-12 and Comparative Example 3, Examples 15-16 and Comparative Example 4, Examples 19-20 and Comparative Example 6, Examples 21-23 and Comparative Example 5, and Examples 24 and Comparative Example 7, compared with traditional cathode active materials that only include carbon materials derived from inorganic or organic carbon sources, the cathode active material in this application that includes carbon materials derived from both inorganic and organic carbon sources is beneficial to improving the initial coulombic efficiency and capacity retention rate after 100 cycles of the battery.

[0283] As can be seen from the comparison between Examples 1-9 and Comparative Examples 8-9, compared with the traditional positive electrode active material which only includes carbon material from inorganic or organic carbon sources and the negative electrode sheet which does not include a bottom coating, the positive electrode active material in this application includes carbon material from both inorganic and organic carbon sources, and the negative electrode sheet includes a bottom coating, which is beneficial to significantly improve the first coulombic efficiency and capacity retention rate after 100 cycles of the battery.

[0284] As can be seen from the comparison between Examples 1 and 7 and Examples 8-9, compared with the bottom coating of the negative electrode sheet including alumina or carbon black, the bottom coating of the negative electrode sheet including carbon nanotubes or graphite is beneficial to further improve the first coulombic efficiency and capacity retention rate after 100 cycles.

[0285] As can be seen from the comparison between Examples 10, 13-14, 17-18 and Comparative Example 4, compared with the Na4Fe3(PO4)2P2O7 positive electrode active material, Na4Fe 2.95 (PO4)2P2O7 positive electrode active material or Na4Fe 2.8 Due to the presence of iron defects, the (PO4)2P2O7 positive electrode active material is beneficial to increasing the compaction density of the positive electrode active material, reducing the resistance of the positive electrode active material and the electrode resistance of the positive electrode sheet, and improving the capacity retention rate of the battery after 100 cycles.

[0286] As can be seen from the comparison between Examples 11-12 and Comparative Example 3, Examples 15-16 and Comparative Example 4, and Examples 21-23 and Comparative Example 5, based on the total mass of the positive electrode active material, controlling the mass content of the second carbon material to be 0.5%-2% is beneficial to reducing the resistance of the positive electrode active material, improving the initial coulombic efficiency of the battery, and the capacity retention rate after 100 cycles.

[0287] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes: Polyanionic compounds, wherein the polyanionic compounds have the following general formula: Na x R y (PO4) z (P2O7) k Wherein, R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb, 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4; and The first carbon material and the second carbon material are composited with the polyanionic compound, wherein the crystallinity of the first carbon material is higher than that of the second carbon material; The first carbon material I D / I G The value is less than 0.8, and the I of the second carbon material D / I G The value is greater than 0.8 and less than 1.2, the I D / I G The value was determined by Raman spectrophotometry and is located at 1300 cm⁻¹. -1 ~1400 cm -1 Peak intensity I within the range D Located at 1580 cm -1 ~1620 cm -1 Peak intensity I within the range G The strength ratio.

2. The positive electrode active material according to claim 1, characterized in that, The first carbon material is distributed in particulate form between the primary particles of the polyanionic compound.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The second carbon material is coated on the surface of the primary particles of the polyanionic compound in the form of a carbon film.

4. The positive electrode active material according to claim 2 or 3, characterized in that, The median particle size D of the primary particles of the polyanionic compound v 50 ranges from 0.1 μm to 2.0 μm.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that, Based on the total mass of the positive electrode active material, the mass content of the first carbon material is 0.1% to 5%, and the mass content of the second carbon material is 0.1% to 10%.

6. The positive electrode active material according to claim 5, characterized in that, Based on the total mass of the positive electrode active material, the mass content of the first carbon material is 0.5% to 2%, and the mass content of the second carbon material is 0.5% to 2%.

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that, The median particle size D of the positive electrode active material v 50 is 1.0 µm to 10 µm.

8. The positive electrode active material according to claim 7, characterized in that, The median particle size D of the positive electrode active material v 50 is 1.5 µm to 5.0 µm.

9. The positive electrode active material according to any one of claims 1 to 8, characterized in that, The compacted density of the positive electrode active material at 400 MPa pressure is 1.5 g / cm³. 3 ~3 g / cm 3 .

10. The positive electrode active material according to any one of claims 1 to 9, characterized in that, The powder resistivity of the positive electrode active material at 25°C is 1 kΩ·cm to 375 kΩ·cm.

11. A method for preparing a positive electrode active material, characterized in that, Includes the following steps: The positive electrode active material is prepared by mixing and calcining a sodium source, an R source, a phosphorus source, a first carbon source, and a second carbon source, wherein the positive electrode active material comprises: Polyanionic compounds, wherein the polyanionic compounds have the following general formula: Na x R y (PO4) z (P2O7) k Wherein, R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb, 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4; and The first carbon material and the second carbon material are composited with the polyanionic compound, wherein the crystallinity of the first carbon material is higher than that of the second carbon material; The first carbon material is derived from the first carbon source, and the second carbon material is derived from the second carbon source; The first carbon material I D / I G The value is less than 0.8, and the I of the second carbon material D / I G The value is greater than 0.8 and less than 1.2, the I D / I G The value was determined by Raman spectrophotometry and is located at 1300 cm⁻¹. -1 ~1400 cm -1 Peak intensity I within the range D Located at 1580 cm -1 ~1620 cm -1 Peak intensity I within the range G The strength ratio.

12. The method for preparing the positive electrode active material according to claim 11, characterized in that, The first carbon source is an inorganic carbon source, which includes one or more of natural graphite, artificial graphite, carbon black, carbon nanotubes, and graphene.

13. The method for preparing the positive electrode active material according to claim 11 or 12, characterized in that, The second carbon source is an organic carbon source, which includes one or more of sucrose, glucose, citric acid, starch, cyclodextrin, asphalt, polyethylene glycol, and polyvinyl alcohol.

14. The method for preparing the positive electrode active material according to any one of claims 11 to 13, characterized in that, The preparation of the positive electrode active material by mixing and calcining the sodium source, R source, phosphorus source, first carbon source, and second carbon source specifically includes: Sodium source, R source and phosphorus source are dissolved in solvent and ground to obtain the first mixed slurry; The first carbon source and the second carbon source are dispersed in a solvent to obtain a carbon dispersion. The first mixed slurry and the carbon dispersion are mixed, dried, and calcined to prepare the positive electrode active material.

15. The method for preparing the positive electrode active material according to claim 14, characterized in that, D of particles in the first mixed slurry v 50 ranges from 0.05 μm to 1.5 μm.

16. The method for preparing the positive electrode active material according to claim 15, characterized in that, D of particles in the first mixed slurry v 50 is 0.1 μm to 0.8 μm.

17. The method for preparing the positive electrode active material according to any one of claims 11 to 16, characterized in that, The R source includes one or more of the following: magnesium source, aluminum source, scandium source, titanium source, vanadium source, chromium source, manganese source, iron source, cobalt source, nickel source, copper source, zinc source, zirconium source, niobium source, molybdenum source, tin source, hafnium source, tantalum source, tungsten source, and lead source.

18. The method for preparing the positive electrode active material according to claim 17, characterized in that, The iron source includes one or more of ferrous oxalate, ferric nitrate, ferrous sulfate, ferrous chloride, ferric oxalate, ferric acetate, ferric oxide, ferrous oxide, and metallic iron.

19. A positive electrode plate, characterized in that, It includes a positive electrode film layer, wherein the positive electrode film layer comprises the positive electrode active material according to any one of claims 1 to 10 or the positive electrode active material prepared by the preparation method of the positive electrode active material according to any one of claims 11 to 18.

20. The positive electrode sheet according to claim 19, characterized in that, The positive electrode film layer also includes at least one of a one-dimensional conductive material and a zero-dimensional conductive material.

21. The positive electrode sheet according to claim 20, characterized in that, The one-dimensional conductive material includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes, and / or Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material is 0.2% to 1%.

22. The positive electrode sheet according to claim 21, characterized in that, Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material is 0.5% to 1%.

23. The positive electrode sheet according to any one of claims 20 to 22, characterized in that, The zero-dimensional conductive material includes one or more of Super P, Ketjen Black, and acetylene black, and / or Based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material is 1% to 3%.

24. The positive electrode sheet according to claim 23, characterized in that, Based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material is 2% to 2.8%.

25. The positive electrode sheet according to any one of claims 19 to 24, characterized in that, The positive electrode film layer also includes a binder, and the mass content of the binder is 1.5% to 3% based on the total mass of the positive electrode film layer.

26. The positive electrode sheet according to claim 25, characterized in that, Based on the total mass of the positive electrode film, the mass content of the binder is 2.0% to 2.5%.

27. The positive electrode sheet according to any one of claims 19 to 26, characterized in that, The compaction density of the positive electrode film is 1.7 g / cm³. 3 ~2.3 g / cm 3 .

28. The positive electrode sheet according to any one of claims 19 to 27, characterized in that, The resistance of the positive electrode is 0.1 Ω·cm to 10 Ω·cm.

29. A secondary battery, characterized in that, It includes a negative electrode sheet and a positive electrode sheet as described in any one of claims 19 to 28.

30. The secondary battery according to claim 29, characterized in that, The secondary battery is a sodium-free secondary battery without a negative electrode.

31. The secondary battery according to claim 29 or 30, characterized in that, The negative electrode sheet includes a negative current collector and a base coating disposed on at least one surface of the negative current collector. The base coating includes one or more of carbon nanotubes, graphite, graphene, carbon black, alumina, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

32. The secondary battery according to claim 31, characterized in that, The areal density of the base coating is 5 g / m³. 2 ~50g / m 2 .

33. The secondary battery according to claim 31 or 32, characterized in that, The thickness of the base coating is 2 μm to 100 μm.

34. An electrical appliance, characterized in that, The secondary battery includes any one of claims 29 to 33.

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