Positive electrode active composite, method for producing the same, positive electrode sheet, secondary battery, and power-driven device

Abstract

The application provides a positive electrode active composite material, a preparation method thereof, a positive electrode sheet, a secondary battery and an electric device. The positive electrode active composite material comprises a carbon material, a transition metal M and a polyanion compound. The positive electrode active composite material has both graphitization degree and processability, improves the compaction density of the positive electrode active composite material and the compaction density of a positive electrode film layer, and improves the performance of the battery.

Description

TECHNICAL FIELD

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

[0002] In recent years, with the wide application of secondary batteries in energy storage power systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc., the market requirements for the performance of secondary batteries are also becoming higher and higher.

[0003] The performance of the positive electrode active material plays a key role in the performance of the battery. At present, the performance of the positive electrode active material cannot meet the application needs of the new generation of electrochemical systems. SUMMARY

[0004] The present application is made in view of the above-mentioned problems, and aims to provide a positive electrode active composite material having excellent conductivity and processability, which can improve the performance of the battery and reduce the manufacturing cost.

[0005] In a first aspect of the present application, a positive electrode active composite material is provided, which comprises a carbon material, a transition metal M and a polyanion compound.

[0006] The transition metal M can play a role in catalyzing the graphitization of the carbon material at low temperature, and can improve the graphitization degree of the carbon material during the compounding of the carbon material and the polyanion compound, thereby improving the conductivity of the positive electrode active composite material, reducing the amount of conductive agent and improving the power performance of the battery. At the same time, the distribution of the carbon material with high graphitization degree on the surface of the polyanion compound enables the polyanion compound to play a role in increasing flexibility by relative slipping, thereby improving the flexibility of the electrode sheet and improving the crack phenomenon of the inner ring of the bare battery cell. Furthermore, using the transition metal as a catalyst can improve the graphitization degree of the carbon material during the preparation of the positive electrode active composite material, which is more uniform than directly compounding the polyanion compound with the carbon material with high graphitization degree, so that the manufacturing cost of the positive electrode active composite material is lower, and the compaction density of the electrode sheet is higher. In addition, the transition metal M is also a highly conductive material, and its distribution in the composite material can further improve the conductivity of the positive electrode active composite material.

[0007] In any embodiment, the transition metal M comprises at least one of Pt, Pd, Fe, Co, Ni, Mn, Cu, Au, Ag, Ru, Rh.

[0008] The aforementioned metals are all catalytic materials with high catalytic activity, enabling low-temperature graphitization of carbon materials. They can improve the degree of graphitization of carbon materials under low-temperature calcination, thereby enhancing the conductivity of the positive electrode active composite material.

[0009] In any embodiment, the mass percentage of the transition metal M, based on the total mass of the carbon material, is 0.1% to 10%, optionally 1% to 10%.

[0010] Controlling the content of transition metal M within a suitable range can, on the one hand, provide enough transition metal M to improve the graphitization degree of carbon materials and enhance battery performance. On the other hand, it can also save production costs without negatively impacting battery performance due to excessive addition of transition metal elements, thus balancing battery performance and production costs.

[0011] In any embodiment, based on the total mass of the positive electrode active composite material, the mass content of the carbon material in the positive electrode active composite material is 0.1% to 10%, optionally 1% to 10%.

[0012] Controlling the carbon content within a suitable range can, on the one hand, effectively improve the conductivity of the positive electrode active composite material and reduce the agglomeration of the positive electrode active composite material particles to increase its compaction density; on the other hand, it can reduce the problem of reduced specific capacity of the positive electrode sheet caused by excessive carbon content.

[0013] In any embodiment, the carbon material is coated on the surface of the polyanionic compound in the form of a carbon film, and the transition metal M is distributed in the carbon film.

[0014] Carbon materials are coated onto the surface of the polyanionic compound in the form of a carbon film, which increases the contact area between the carbon materials and the polyanionic compound, facilitating electron transport and improving the conductivity of the polyanionic compound. Simultaneously, the transition metal M is distributed within the carbon film, which can effectively enhance the graphitization degree of the carbon materials through uniform dispersion. Furthermore, the synergy between the metal and carbon materials can further improve the conductivity of the positive electrode active composite material, thereby enhancing battery performance.

[0015] In any embodiment, the carbon material is coated on the surface of the primary particles of the polyanionic compound in the form of a carbon film, and the transition metal M is distributed in the carbon film.

[0016] The carbon material is coated on the surface of the primary particles of the polyanionic compound in the form of a carbon film, which can further improve the uniformity of carbon material distribution in the composite material and optimize the conductivity of the positive electrode active composite material.

[0017] In any embodiment, a chemical bond exists between the transition metal M and the carbon material.

[0018] During the preparation process, the transition metal M undergoes a chemical reaction with the carbon material, further enhancing the alloying effect. The chemical bonds effectively reduce the mutual agglomeration of the transition metal M and further improve the conductivity of the positive electrode active composite material.

[0019] In any embodiment, the polyanionic compound comprises a sodium-containing phosphate skeleton compound or a sodium-containing sulfate skeleton compound.

[0020] In any embodiment, the polyanionic compound comprises a sodium phosphate salt material and a sodium sulfate salt material; the sodium phosphate salt material comprises a compound as shown in any one of Formulas I-IV; the sodium phosphate salt material comprises a compound as shown in Formula V; Na x1 R y1 (PO4) z1 , Formula I

[0021] Wherein, 1≤x1≤3, 1≤y1≤2, 1≤z1≤3, and 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;

[0022] Na x2 R y2 (P2O7) z2 Formula II

[0023] Wherein, 1≤x2≤7, 1≤y2≤3, 1≤z2≤4, and 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;

[0024] Na x3 R y3 (PO4) z3 (P2O7) k3 Formula III

[0025] Wherein, 1≤x3≤7, 1≤y3≤4, 1≤z3≤2, 1≤k3≤4, and 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;

[0026] Na x4 R y4 (PO4) z4 M l1 Formula IV

[0027] Among them, 1 ≤ x4 ≤ 3, 1 ≤ y4 ≤ 2, 1 ≤ z4 ≤ 2, 1 ≤ l1 ≤ 3, 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, and M includes at least one of F, Cl, and Br;

[0028] Na x5 X y5 (SO4)3, formula V

[0029] Among them, 0 < x5 ≤ 2, 0 < y5 ≤ 2, and X includes at least one of Mn, Fe, Co, Ni, Cu, and Zn.

[0030] In any embodiment, the I D / I G value of the carbon material in the positive electrode active composite material is less than 0.8. The I D / I G value is the intensity ratio of the peak intensity I -1 ~1400 cm -1 in the range measured by Raman spectroscopy to the peak intensity I D at 1580 cm -1 ~1620 cm -1 in the range. G

[0031] The I D / I G value of the carbon material in the positive electrode active composite material being less than 0.8 indicates that the carbon material has a high degree of graphitization, which is beneficial to improving the conductivity of the positive electrode active composite material.

[0032] In any embodiment, the median particle size Dv50 of the positive electrode active composite material is 0.5 μm ≤ Dv50 ≤ 10 μm, and optionally 1.0 μm ≤ Dv50 ≤ 5.0 μm.

[0033] Controlling the median particle size Dv50 of the positive electrode active composite material within a suitable range can effectively reduce the physical gelation during the slurry coating process due to the too small particle size of the positive electrode active composite material; it can also effectively reduce the too low powder compaction density caused by the too large median particle size Dv50 of the positive electrode active composite material and the reduction of the kinetic performance of the battery during charge and discharge, taking into account the processability and electrochemical performance of the positive electrode active composite material.

[0034] In any embodiment, at 25 °C, the powder resistance of the positive electrode active composite material under a pressure of 200 MPa is 50 Ω·cm to 3500 Ω·cm.

[0035] The positive electrode active composite material powder provided in this application has low resistance, which gives the positive electrode sheet high electron transport capability, and enables the battery to have excellent cycle life and safety during long-term fast charging use.

[0036] A second aspect of this application provides a method for preparing a positive electrode active composite material, comprising the following steps:

[0037] Preparation of polyanionic compound precursors;

[0038] The precursor, carbon source and M source are mixed evenly and calcined at high temperature to prepare the positive electrode active composite material, wherein the M source contains a transition metal salt.

[0039] The positive electrode active composite material includes: carbon material, transition metal M, and polyanionic compound.

[0040] This preparation method effectively improves the graphitization degree of carbon materials while achieving uniform coating of carbon materials and polyanionic compounds. It solves the problems of carbon material agglomeration and uneven distribution caused by direct composite of high-graphitization carbon materials and positive electrode active materials, and also addresses the issue that high graphitization cannot be achieved with organic carbon coating at the sintering temperature of polyanionic compounds. Furthermore, the uniformly distributed high-graphitization carbon material in the positive electrode active composite material facilitates the slippage between particles, thus strengthening the electrode sheet.

[0041] In any embodiment, the polyanionic compound includes compounds as shown in any one of Formulas I-III;

[0042] Na x1 R y1 (PO4) z1 , Formula I

[0043] Wherein, 1≤x1≤3, 1≤y1≤2, 1≤z1≤3, and 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;

[0044] Na x2 R y2 (P2O7) z2 Formula II

[0045] Wherein, 1≤x2≤7, 1≤y2≤3, 1≤z2≤4, and 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;

[0046] Na x3 Ry3 (PO4) z3 (P2O7) k3 Formula III

[0047] Wherein, 1≤x3≤7, 1≤y3≤4, 1≤z3≤2, 1≤k3≤4, and 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;

[0048] The preparation of the polyanionic compound precursor includes the following steps:

[0049] Raw materials containing phosphorus source, sodium source and R source are mixed with solvent to obtain primary mixed slurry. The primary mixed slurry is dried and then calcined at low temperature to obtain polyanionic compound precursor.

[0050] Sodium pyrophosphate has a low decomposition temperature and a low high-temperature calcination temperature, making it difficult to achieve effective carbonization of the coating carbon material under existing process conditions. This method can significantly improve its conductivity and enhance battery performance.

[0051] In any embodiment, the primary mixed slurry also includes a carbon source.

[0052] The primary mixed slurry also includes a carbon source, which can help the carbon material to be evenly distributed among the primary particles of the polyanionic compound, effectively improving the conductivity of the material.

[0053] In any embodiment, the calcination temperature of the low-temperature calcination is 300℃~350℃, and the calcination time is 1h~6h.

[0054] Controlling the calcination temperature and time of low-temperature calcination within a suitable range is beneficial for controlling the particle size and crystallinity of the precursor within a suitable range, which is suitable for the preparation of positive electrode active composite materials.

[0055] In any embodiment, the calcination temperature is 450℃~700℃, and the calcination time is 5h~15h.

[0056] Controlling the calcination temperature and time during high-temperature calcination helps to control the particle size of the positive electrode active composite material within a suitable range, as well as to improve the graphitization degree of the carbon material, thus balancing the performance and production cost of the positive electrode active composite material.

[0057] In any embodiment, the carbon source includes one or more of sucrose, glucose, citric acid, starch, cyclodextrin, pitch, polypropylene, polyethylene, polyethylene glycol, and polystyrene.

[0058] All of the above-mentioned organic carbon sources can form a carbon film that coats the surface of the polyanionic compound, increasing the contact area between the carbon material and the polyanionic compound, facilitating electron transport, and thus improving the conductivity of the polyanionic compound.

[0059] 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.

[0060] In any embodiment, the M source includes one or more of the following: platinum source, palladium source, iron source, cobalt source, nickel source, and manganese source.

[0061] All of the aforementioned M sources can effectively catalyze the graphitization of carbon sources, thereby increasing the degree of graphitization of carbon materials. Furthermore, under high-temperature calcination conditions, the aforementioned M sources can be distributed in the carbon materials in the form of metal atoms, forming chemical bonds between the transition metal atoms and the carbon materials, further improving the stability between the transition metal M and the carbon materials, as well as the conductivity of the positive electrode active composite material.

[0062] A third aspect of this application provides a positive electrode sheet comprising a positive electrode film layer, the positive electrode film layer comprising a binder, a conductive agent, and a positive electrode active composite material as described in the first aspect or a positive electrode active composite material prepared by the preparation method described in the second aspect.

[0063] 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%.

[0064] Controlling the binder mass content within a suitable range provides sufficient bonding strength and is beneficial for improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the binder mass content to 2.0%–2.5% is beneficial for further improving the battery's cycle performance.

[0065] In any embodiment, the conductive agent includes at least one of a one-dimensional conductive material and a zero-dimensional conductive material.

[0066] The addition of one-dimensional and / or zero-dimensional conductive materials can help increase the conductivity of the positive electrode.

[0067] In any embodiment, the one-dimensional conductive material includes one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes, and / or

[0068] Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material is 0.2% to 1%, and can be selected as 0.5% to 1%.

[0069] Controlling the mass content of one-dimensional conductive material within a suitable range is beneficial for improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the mass content of one-dimensional conductive material to 0.5%–0.9% is beneficial for further improving the battery's coulombic efficiency.

[0070] In any embodiment, the zero-dimensional conductive material includes one or more of Super P, Ketjen Black, and acetylene black, and / or

[0071] Based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material is 1% to 3%, and can be selected as 2% to 2.8%.

[0072] Controlling the mass content of zero-dimensional conductive materials within a suitable range is beneficial for improving the battery's capacity, coulombic efficiency, and cycle performance. Further controlling the mass content of zero-dimensional conductive materials to 2%–2.8% is beneficial for further improving the battery's coulombic efficiency.

[0073] A fourth aspect of this application provides a secondary battery, including the positive electrode sheet described in the third aspect.

[0074] In any embodiment, the secondary battery is a sodium-free secondary battery without a negative electrode.

[0075] Compared to other sodium-ion batteries, the negative electrode-free sodium-ion battery does not require pre-coating or deposition of highly active sodium metal on the negative electrode side, thus improving battery energy density while optimizing the manufacturing feasibility and safety of the cell. In any embodiment, the secondary battery further includes a negative electrode sheet, which includes a negative electrode current collector and a base coating disposed on at least one surface of the negative electrode current collector. The base coating includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0076] 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.

[0077] In any embodiment, the areal density of the base coating is 5 g / m³. 2 ~50g / m 2 .

[0078] 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.

[0079] In any embodiment, the thickness of the base coating is 2 μm to 100 μm.

[0080] 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.

[0081] 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

[0082] Figure 1 This is a schematic diagram of a secondary battery cell according to one embodiment of this application;

[0083] Figure 2 yes Figure 1 An exploded view of a secondary battery cell according to an embodiment of this application is shown.

[0084] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0085] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0086] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0087] 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.

[0088] Explanation of reference numerals in the attached figures:

[0089] 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

[0090] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active composite material, its preparation method, the positive electrode sheet, the secondary battery, and the power application 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.

[0091] 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.

[0092] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0093] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0094] 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.

[0095] 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.

[0096] 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).

[0097] Polyanionic compounds (POCs) possess high chemical, thermal, and electrochemical stability, resulting in excellent cycle life and safety in batteries using them as cathode active materials. However, POCs suffer from poor conductivity, which directly affects their specific capacity and severely hinders their large-scale application. To address this issue, carbon coating is typically applied to the surface of POCs to improve conductivity. However, the low decomposition temperature of POCs prevents the carbon coating from carbonizing at high temperatures, hindering further improvements in conductivity and impeding the further development of their electrochemical performance. Directly coating POCs with highly graphitized carbon materials is also problematic, as the highly crystalline carbon material is difficult to disperse effectively and achieve uniform coating. Therefore, a cathode active material that balances graphitization degree and processability is needed to meet the requirements of next-generation batteries.

[0098] [Positive electrode active composite material]

[0099] Based on this, this application proposes a positive electrode active composite material, which includes carbon materials, transition metal M, and polyanionic compounds.

[0100] Transition metal M can catalyze the graphitization of carbon materials at low temperatures. During the composite process of carbon materials and polyanionic compounds, it can increase the degree of graphitization of the carbon materials, thereby improving the conductivity of the positive electrode active composite material. By reducing the amount of conductive agent used, the power performance of the battery can be improved. Simultaneously, the distribution of highly graphitized carbon materials on the surface of polyanionic compounds allows the polyanionic compounds to achieve a flexible effect through relative slippage, improving the flexibility of the electrode sheet and mitigating cracking in the inner ring of the bare cell. Furthermore, using a transition metal as a catalyst to increase the graphitization of carbon materials during the preparation of the positive electrode active composite material results in a more uniform composite of carbon materials and polyanionic compounds compared to directly compositing polyanionic compounds with highly graphitized carbon materials. This leads to lower manufacturing costs for the positive electrode active composite material and higher electrode compaction density. In addition, transition metal M is also a highly conductive material, and its distribution in the composite material can further improve the conductivity of the positive electrode active composite material.

[0101] In some embodiments, the transition metal M includes at least one of Pt, Pd, Fe, Co, Ni, Mn, Cu, Au, Ag, Ru, and Rh.

[0102] In some embodiments, M includes Pt. In some embodiments, M includes Pd. In some embodiments, M includes Fe. In some embodiments, M includes Co. In some embodiments, M includes Ni. In some embodiments, M includes Mn.

[0103] The aforementioned metals are all catalytic materials with high catalytic activity, enabling low-temperature graphitization of carbon materials. They can improve the degree of graphitization of carbon materials under low-temperature calcination, thereby enhancing the conductivity of the positive electrode active composite material.

[0104] In some embodiments, the mass percentage of transition metal M, based on the total mass of carbon materials, is 0.1% to 10%, and optionally 1% to 10%.

[0105] In some embodiments, based on the total mass of carbon materials, the mass percentage of transition metal M 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 a range consisting of any two of the above points.

[0106] Controlling the molar content of transition metal M within a suitable range can, on the one hand, provide enough transition metal M to improve the graphitization degree of carbon materials and enhance battery performance. On the other hand, it can also save production costs without negatively impacting battery performance due to excessive addition of transition metal elements, thus balancing battery performance and production costs.

[0107] In some embodiments, based on the total mass of the positive electrode active composite material, the mass content of carbon material in the positive electrode active composite material is 0.1% to 10%, optionally 1% to 10%.

[0108] In some embodiments, based on the total mass of the positive electrode active composite material, the mass content of carbon material in the positive electrode active composite material can be selected as 0.1%, 0.15%, 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 a range consisting of any two of the above points.

[0109] Controlling the carbon content within a suitable range can, on the one hand, effectively improve the conductivity of the positive electrode active composite material and reduce the agglomeration of the positive electrode active composite material particles to increase its compaction density; on the other hand, it can reduce the problem of reduced specific capacity of the positive electrode sheet caused by excessive carbon content.

[0110] In some embodiments, carbon material is coated on the surface of the polyanionic compound in the form of a carbon film, and the transition metal M is distributed in the carbon film.

[0111] Carbon materials are coated onto the surface of the polyanionic compound in the form of a carbon film, which increases the contact area between the carbon materials and the polyanionic compound, facilitating electron transport and improving the conductivity of the polyanionic compound. Simultaneously, the transition metal M is distributed within the carbon film, which can effectively enhance the graphitization degree of the carbon materials through uniform dispersion. Furthermore, the synergy between the metal and carbon materials can further improve the conductivity of the positive electrode active composite material, thereby enhancing battery performance.

[0112] In some embodiments, carbon material is coated on the surface of primary particles of the polyanionic compound in the form of a carbon film, and the transition metal M is distributed in the carbon film.

[0113] The carbon material is coated on the surface of the primary particles of the polyanionic compound in the form of a carbon film, which can further improve the uniformity of carbon material distribution in the composite material and optimize the conductivity of the positive electrode active composite material.

[0114] In some implementations, a chemical bond exists between the transition metal M and the carbon material.

[0115] During the preparation process, the transition metal M and carbon materials undergo a chemical reaction to form a chemical bond, which effectively reduces the mutual agglomeration of the transition metal M and further enhances the conductivity of the positive electrode active composite material through alloying.

[0116] The chemical bond between transition metal M and carbon can be characterized by transmission electron microscopy and fine absorption spectroscopy of synchrotron radiation.

[0117] In some embodiments, the polyanionic compound includes a sodium-containing phosphate backbone compound or a sodium-containing sulfate backbone compound.

[0118] In some embodiments, the polyanionic compound includes sodium phosphate material and sodium sulfate material; the sodium phosphate material includes compounds as shown in any one of Formulas I-IV; the sodium phosphate material comprises compounds as shown in Formula V;

[0119] Na x1 R y1 (PO4) z1 , Formula I

[0120] Among them, 1 ≤ x1 ≤ 3, 1 ≤ y1 ≤ 2, 1 ≤ z1 ≤ 3, and 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;

[0121] Na x2 R y2 (P2O7) z2 , formula II

[0122] Among them, 1 ≤ x2 ≤ 7, 1 ≤ y2 ≤ 3, 1 ≤ z2 ≤ 4, and 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;

[0123] Na x3 R y3 (PO4) z3 (P2O7) k3 , formula III

[0124] Among them, 1 ≤ x3 ≤ 7, 1 ≤ y3 ≤ 4, 1 ≤ z3 ≤ 2, 1 ≤ k3 ≤ 4, and 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;

[0125] Na x4 R y4 (PO4) z4 M l1 , formula IV

[0126] Among them, 1 ≤ x4 ≤ 3, 1 ≤ y4 ≤ 2, 1 ≤ z4 ≤ 2, 1 ≤ l1 ≤ 3, and 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, and M includes at least one of F, Cl, and Br;

[0127] Na x5 X y5 (SO4)3, formula V

[0128] Among them, 0 < x5 ≤ 2, 0 < y5 ≤ 2, and X includes at least one of Mn, Fe, Co, Ni, Cu, and Zn.

[0129] In some embodiments, R includes Fe. In some embodiments, R includes Al. In some embodiments, R includes V. In some embodiments, R includes Mn. In some embodiments, x1 can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, or a value within the range formed by any two of the above points; y1 can be selected as 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, or a value within the range formed by any two of the above points; z1 can be selected as 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, or a value within the range formed by any two of the above points.

[0130] In some embodiments, R includes Fe. In some embodiments, R includes Mg. In some embodiments, R includes Al. In some embodiments, R includes Ni. In some embodiments, R includes Mn. In some embodiments, x2 can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, or a value within the range formed by any two of the above points; y2 can be selected as 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, or a value within the range formed by any two of the above points; z2 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.

[0131] In some embodiments, R includes Fe. In some embodiments, R includes Co. In some embodiments, R includes V. In some embodiments, R includes Ni. In some embodiments, R includes Mn. In some embodiments, x3 can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, or a value within the range formed by any two of the above points; y3 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; z3 can be selected as 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, or a value within the range formed by any two of the above points; k3 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.

[0132] In some embodiments, R includes Fe. In some embodiments, R includes Co. In some embodiments, R includes V. In some embodiments, R includes Ni. In some embodiments, R includes Mn. In some embodiments, x4 can be selected as 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, or a value within the range formed by any two of the above points, and y4 can be selected as 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, or a range formed by any two of the above points. The values ​​in z4 can be 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, or any two of the above values. The values ​​in l1 can be 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, or any two of the above values.

[0133] In some embodiments, X includes Fe. In some embodiments, X includes Mn. In some embodiments, X includes Ni. In some embodiments, X includes Zn. In some embodiments, x5 can be selected as 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, or a value within the range formed by any two of the above points, and y5 can be selected as 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, or a value within the range formed by any two of the above points.

[0134] In some embodiments, the carbon material in the positive electrode active composite material is I D / I G Value less than 0.8, 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.

[0135] In some embodiments, the carbon material in the positive electrode active composite material is I D / I GThe value can be selected as 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.

[0136] I of carbon materials D / I G The value can be measured by any known means, including but not limited to Raman spectroscopy and X-ray diffraction. As an example, Raman spectroscopy is used to characterize the graphitization degree of carbon materials. The Raman spectrum of carbon includes values ​​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 degree of graphitization of carbon materials, I D / I G The smaller the value, the greater the degree of graphitization and the greater the crystallinity of the carbon material.

[0137] I of carbon materials in positive electrode active composite materials D / I G A value less than 0.8 indicates that the carbon material has a high degree of graphitization, which is beneficial to improving the conductivity of the positive electrode active composite material.

[0138] In some embodiments, the median particle size Dv50 of the positive electrode active composite material is 0.5 μm ≤ Dv50 ≤ 10 μm, and can be optionally 1.0 μm ≤ Dv50 ≤ 5.0 μm.

[0139] The Dv50 of the positive electrode active composite material can be measured by any known method, including but not limited to laser diffraction of particle size distribution. As an example, referring to GB / T 19077-2016 Laser Diffraction of Particle Size Distribution, weigh 0.1g–0.13g of the positive electrode active composite 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 randomly selected from each batch for testing. The test is performed using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0140] In some embodiments, the median particle size Dv50 of the positive electrode active composite material can be selected as 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10 μm, or a value within a range consisting of any two of the above points.

[0141] Controlling the median particle size Dv50 of the positive electrode active composite material within a suitable range can effectively reduce physical gelation during the slurry coating process caused by excessively small particle size of the positive electrode active composite material; it can also effectively reduce the low powder compaction density caused by excessively large median particle size Dv50 of the positive electrode active composite material, as well as the reduction in the kinetic performance of the battery during charge and discharge, thus balancing the processability and electrochemical performance of the positive electrode active composite material.

[0142] In some embodiments, at 25°C, the powder resistivity of the positive electrode active composite material at a pressure of 200 MPa is 50 Ω·cm to 3500 Ω·cm.

[0143] In some embodiments, at 25°C, the powder resistivity of the positive electrode active composite material under a pressure of 200 MPa can be selected as 50 Ω·cm, 100 Ω·cm, 200 Ω·cm, 300 Ω·cm, 400 Ω·cm, 500 Ω·cm, 600 Ω·cm, 700 Ω·cm, 800 Ω·cm, 900 Ω·cm, 1000 Ω·cm, 1500 Ω·cm, 2000 Ω·cm, 2500 Ω·cm, 3000 Ω·cm, or a value within a range consisting of any two of the above points.

[0144] The powder resistivity of the positive electrode active composite material can be measured by any known method, including but not limited to the powder resistivity method. As an example, the powder resistivity testing instrument is the Yuaneng Technology PRCD1100, with a pressure range of 10MPa to 400MPa and an indenter size of 78.54mm. 2 Test: A certain amount of positive electrode active composite material powder is placed in a compaction mold, and then the mold is placed on a powder resistivity testing instrument. A pressure of 200 MPa is set, and the powder resistivity under 200 MPa pressure can be read on the instrument.

[0145] The positive electrode active composite material powder provided in this application has low resistance, which gives the positive electrode sheet high electron transport capability, and enables the battery to have excellent cycle life and safety during long-term fast charging use.

[0146] This application also provides a method for preparing a positive electrode active composite material, comprising the following steps:

[0147] Preparation of polyanionic compound precursors;

[0148] The precursor, carbon source and M source are mixed evenly and calcined at high temperature to prepare a positive electrode active composite material, wherein the M source contains a transition metal salt.

[0149] Positive electrode active composite materials include carbon materials, transition metals M, and polyanionic compounds.

[0150] This preparation method effectively improves the graphitization degree of carbon materials while achieving uniform coating of carbon materials and polyanionic compounds. It solves the problems of carbon material agglomeration and uneven distribution caused by direct composite of high-graphitization carbon materials and positive electrode active materials, and also addresses the issue that high graphitization cannot be achieved with organic carbon coating at the sintering temperature of polyanionic compounds. Furthermore, the uniformly distributed high-graphitization carbon material in the positive electrode active composite material facilitates the slippage between particles, thus strengthening the electrode sheet.

[0151] In some embodiments, the polyanionic compound includes compounds as shown in any one of Formulas I-III;

[0152] Na x1 R y1 (PO4) z1 , Formula I

[0153] Wherein, 1≤x1≤3, 1≤y1≤2, 1≤z1≤3, and 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;

[0154] Na x2R y2 (P2O7) z2 Formula II

[0155] Wherein, 1≤x2≤7, 1≤y2≤3, 1≤z2≤4, and 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;

[0156] Na x3 R y3 (PO4) z3 (P2O7) k3 Formula III

[0157] Wherein, 1≤x3≤7, 1≤y3≤4, 1≤z3≤2, 1≤k3≤4, and 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;

[0158] The preparation of the polyanionic compound precursor includes the following steps:

[0159] Raw materials containing phosphorus source, sodium source and R source are mixed with solvent to obtain primary mixed slurry. The primary mixed slurry is dried and then calcined at low temperature to obtain polyanionic compound precursor.

[0160] Sodium pyrophosphate has a low decomposition temperature and a low high-temperature calcination temperature, making it difficult to achieve effective carbonization of the coating carbon material under existing process conditions. This method can significantly improve its conductivity and enhance battery performance.

[0161] In some embodiments, the primary mixed slurry also includes a carbon source.

[0162] The primary mixed slurry also includes a carbon source, which can help the carbon material to be evenly distributed among the primary particles of the polyanionic compound, effectively improving the conductivity of the material.

[0163] In some embodiments, the calcination temperature for low-temperature calcination is 300℃~350℃, and the calcination time is 1h~6h.

[0164] In some embodiments, the calcination temperature for low-temperature calcination can be selected as 300℃, 315℃, 320℃, 325℃, 330℃, 335℃, 340℃, 345℃, 350℃, or a value within the range formed by any two of the above points, and the calcination time can be selected as 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or a value within the range formed by any two of the above points.

[0165] Controlling the calcination temperature and time of low-temperature calcination within a suitable range is beneficial for controlling the particle size and crystallinity of the precursor within a suitable range, which is suitable for the preparation of positive electrode active composite materials.

[0166] In some embodiments, the calcination temperature is 450℃~700℃ and the calcination time is 5h~15h.

[0167] In some embodiments, the calcination temperature can be selected as 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, or a value within the range formed by any two of the above points, and the calcination time can be selected as 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, 14h, 14.5h, 15h, or a value within the range formed by any two of the above points.

[0168] Controlling the calcination temperature and time during high-temperature calcination helps to control the particle size of the positive electrode active composite material within a suitable range, as well as to improve the graphitization degree of the carbon material, thus balancing the performance and production cost of the positive electrode active composite material.

[0169] The technical solution provided in this application achieves the graphitization of carbon materials at low temperatures, and solves the technical problem of the difficulty in uniformly compounding highly graphitized carbon materials with polyanionic compounds at a low cost. In some embodiments, the carbon source includes one or more of sucrose, glucose, citric acid, starch, cyclodextrin, pitch, polypropylene, polyethylene, polyethylene glycol, and polystyrene.

[0170] In some embodiments, the carbon source includes sucrose. In some embodiments, the carbon source includes glucose. In some embodiments, the carbon source includes polypropylene. In some embodiments, the carbon source includes polyethylene glycol. In some embodiments, the carbon source includes sucrose and polystyrene.

[0171] All of the above-mentioned organic carbon sources can form a carbon film that coats the surface of the polyanionic compound, increasing the contact area between the carbon material and the polyanionic compound, facilitating electron transport, and thus improving the conductivity of the polyanionic compound.

[0172] 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.

[0173] In some implementations, the M source includes one or more of the following: platinum source, palladium source, iron source, cobalt source, nickel source, and manganese source.

[0174] In some embodiments, the M source includes a platinum source. In some embodiments, the M source includes an iron source. In some embodiments, the M source includes a cobalt source. In some embodiments, the M source includes both a platinum source and a cobalt source.

[0175] All of the aforementioned M sources can effectively catalyze the graphitization of carbon sources, thereby increasing the degree of graphitization of carbon materials. Furthermore, under high-temperature calcination conditions, the aforementioned M sources can decompose in situ to form metal atoms distributed in the carbon materials. The metal atoms form chemical bonds with the carbon materials, further improving the stability between the transition metal M and the carbon materials, as well as the conductivity of the positive electrode active composite material.

[0176] [Positive electrode plate]

[0177] This application also provides a positive electrode sheet, including a positive electrode film layer, which includes a binder, a conductive agent, and a positive electrode active composite material prepared by a method for preparing a positive electrode active composite material in some embodiments or in some embodiments.

[0178] 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%.

[0179] 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.

[0180] 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.

[0181] In some embodiments, the conductive agent includes at least one of a one-dimensional conductive material and a zero-dimensional conductive material.

[0182] In some embodiments, the conductive agent contains both one-dimensional and zero-dimensional conductive materials. The simultaneous addition of both forms of conductive material is beneficial for further increasing the conductivity of the positive electrode.

[0183] In some embodiments, the one-dimensional conductive material includes one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes, and / or

[0184] Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive material is 0.2% to 1%, and can be selected as 0.5% to 1%.

[0185] 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 both single-walled and multi-walled carbon nanotubes.

[0186] 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.

[0187] 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.

[0188] In some embodiments, the zero-dimensional conductive material includes one or more of Super P, Ketjen Black, and acetylene black, and / or

[0189] Based on the total mass of the positive electrode film, the mass content of the zero-dimensional conductive material is 1% to 3%, and can be selected as 2% to 2.8%.

[0190] 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.

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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 composite 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.

[0195] [Negative electrode plate]

[0196] 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.

[0197] 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.).

[0198] 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.

[0199] 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.

[0200] In some embodiments, the areal density of the base coating is 5 g / m³. 2 ~50g / m 2 .

[0201] 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.

[0202] 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.

[0203] In some embodiments, the thickness of the base coating is 2 μm to 100 μm.

[0204] 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.

[0205] 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.

[0206] [Isolation membrane]

[0207] 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.

[0208] 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.

[0209] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0210] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0211] 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.

[0212] [Rechargeable Battery]

[0213] Secondary batteries can come in various forms, including, but not limited to, individual battery cells, battery modules, and battery packs.

[0214] A battery cell includes a positive electrode sheet, which includes positive active composite materials in some embodiments or positive active composite materials prepared by some embodiments.

[0215] 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.

[0216] In some embodiments, the secondary battery cell also includes a negative electrode, a separator, and an electrolyte.

[0217] In some implementations, the secondary battery cell is a sodium-free secondary battery without a negative electrode.

[0218] A negative electrode-less sodium secondary battery refers to a battery in which no negative electrode active material layer is actively placed on the negative electrode side during the battery manufacturing process. For example, a sodium metal or carbonaceous active material layer is not formed at the negative electrode through coating or deposition processes. During the first charge, sodium ions gain electrons on the anode side and deposit metallic sodium on the current collector surface 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 a higher energy density due to the absence of a negative electrode active material layer.

[0219] In some implementations, in order to improve battery performance, the negative electrode side of the non-negative electrode sodium secondary battery can be provided with some conventional materials that can be used as negative electrode active materials, such as carbonaceous materials, metal oxides, alloys, etc. Although these materials have a certain capacity, since the amount of these materials is small, they are not used as the main negative electrode active materials in the battery, and therefore do not form a negative electrode active material layer. The sodium secondary battery constructed in this way can still be regarded as a non-negative electrode sodium secondary battery.

[0220] In some implementations, the CB value of the sodium-free secondary battery is less than or equal to 0.1.

[0221] 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 contain little or no 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.

[0222] 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.

[0223] [Battery Module]

[0224] 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.

[0225] 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.

[0226] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0227] [Battery Pack]

[0228] 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.

[0229] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5The 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.

[0230] [Electrical appliances]

[0231] 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.

[0232] 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.

[0233] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0234] 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.

[0235] 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.

[0236] Example

[0237] 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.

[0238] I. Preparation Method

[0239] Example 1

[0240] 1) Preparation of positive electrode active composite materials

[0241] 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 a mixed slurry. The mixed slurry was then milled to an average particle size of 0.2 μm. The slurry was spray-dried at an inlet air temperature of 220 °C and an outlet air temperature of 109 °C to obtain a powdered precursor. Subsequently, the sintered product was heated to 320 °C at a heating rate of 2 °C and held for 4 h in a N2 atmosphere. The product was then crushed and sieved to obtain Na4Fe. 2.9 (PO4)2P2O7 positive electrode active composite material precursor. Finally, Na4Fe 2.9 (PO4)2P2O7 positive electrode active composite material precursor, glucose, and ferric nitrate were mixed and ground for 30 min. The mixture was then heated to 520℃ at a rate of 2℃ and held for 10 h in a N2 atmosphere. The sintered product was then crushed and sieved to obtain a product containing Na4Fe. 2.9 (PO4)2P2O7, C and Fe positive electrode active composite material.

[0242] 2) Preparation of positive electrode sheet

[0243] 2.5 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone (NMP), and then 2.0 wt% Super P, 1.0 wt% carbon nanotubes, and 94.5 wt% of the above-mentioned positive electrode active composite material were added and stirred until homogeneous to obtain a positive electrode slurry. The slurry was uniformly coated on the surface of the current collector aluminum foil and then transferred to a vacuum drying oven for complete drying. The dried electrode sheet was then rolled and punched to obtain the positive electrode sheet.

[0244] 3) Preparation of negative electrode sheet

[0245] Single-walled 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 undercoat layer was 20 μm, and the areal density was 25 g / m³. 2 .

[0246] 4) Electrolyte

[0247] 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.

[0248] 5) Separating membrane

[0249] Polypropylene film is used as the separator.

[0250] 6) Battery manufacturing

[0251] 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.

[0252] Examples 2-24

[0253] The batteries in Examples 2-24 were prepared using a similar method to those in Example 1, but the contents of M, carbon, and polyanionic compounds in the positive electrode active composite material, as well as the types of polyanionic compounds, were adjusted. The specific parameters are shown in Table 1.

[0254] Comparative Example 1

[0255] The battery in Comparative Example 1 is prepared using a method similar to that in Example 1, but the preparation method of the positive electrode active composite material has been adjusted, and the preparation method is as follows:

[0256] 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 a mixed slurry. This mixed slurry was milled to an average particle size of 0.2 μm, and then a glucose aqueous solution was added and milled for 10 min to obtain the final slurry. The slurry was spray-dried at an inlet air temperature of 220℃ and an outlet air temperature of 109℃ to obtain a powdered precursor. Finally, under a N2 atmosphere, the temperature was increased to 320℃ at a heating rate of 2℃ and held for 4 h, 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 composite material.

[0257] 2) Preparation of positive electrode sheet

[0258] 2.5 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone (NMP), and then 2.0 wt% Super P, 1.0 wt% carbon nanotubes, and 94.5 wt% of the above-mentioned positive electrode active composite material were added and stirred until homogeneous to obtain a positive electrode slurry. The slurry was uniformly coated on the surface of the current collector aluminum foil and then transferred to a vacuum drying oven for complete drying. The dried electrode sheet was then rolled and punched to obtain the positive electrode sheet.

[0259] 3) Preparation of negative electrode sheet

[0260] 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 .

[0261] 4) Electrolyte

[0262] 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.

[0263] 5) Separating membrane

[0264] Polypropylene film is used as the separator.

[0265] 6) Battery manufacturing

[0266] 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 Comparative Example 1.

[0267] Comparative Examples 2-6

[0268] The batteries of Comparative Examples 2 to 6 were prepared using methods similar to those of Comparative Example 1, but the content of raw materials used in the preparation of the positive electrode active composite material was adjusted. The specific parameters are shown in Table 1.

[0269] II. Performance Testing

[0270] 1. Testing of positive electrode active composite materials

[0271] 1) Median particle size Dv50 test

[0272] Following the GB / T 19077-2016 standard for particle size distribution using laser diffraction, 0.1g–0.13g of the positive electrode active composite 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.

[0273] 2) Carbon materials I D / I G test

[0274] The carbon material in the positive electrode active composite material was tested using Raman spectroscopy. 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 graphitization degree of the carbon material.

[0275] 3) Resistance test

[0276] 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 .

[0277] Test: A certain amount of positive electrode active composite material powder is placed in a compaction mold, and then the mold is placed on the instrument. A pressure of 200 MPa is set, and the powder resistivity at 200 MPa pressure can be read on the equipment. 2. Positive electrode performance test

[0278] 1) Compacted density

[0279] 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).

[0280] 2) Electrode resistor

[0281] Cut the dried positive electrode film into small round pieces with a diameter of 10mm 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.

[0282] 3. Battery performance test

[0283] 1) Initial discharge capacity test

[0284] The initial 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 initial discharge capacity (Cd1). The test process for the comparative example and other embodiments is the same as above.

[0285] 2) First Coulomb efficiency test

[0286] The initial 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: Initial 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.

[0287] 3) Battery cycle capacity retention test

[0288] 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.

[0289] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0290] 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.

[0291] Table 1

[0292]

[0293]

[0294] Table 2

[0295]

[0296] Based on the above results, the positive electrode active composite materials of Examples 1 to 24 include: carbon material, transition metal M and polyanionic compound. The polyanionic compound has the following general formula: NaxRy(PO4)2P2O7, 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≤5, 1≤y≤4.

[0297] The comparison between Examples 1-5 and Comparative Example 1, Example 13 and Comparative Example 2, Example 14 and Comparative Example 3, Example 15 and Comparative Example 4, Examples 19-21 and Comparative Example 5, and Examples 22-23 and Comparative Example 6 shows that the positive electrode active composite material contains a transition metal M. The transition metal M can catalyze the graphitization of carbon materials, thereby increasing the graphitization degree of carbon materials, reducing the powder resistance of the positive electrode active composite material and the corresponding electrode resistance, increasing the compaction density of the electrode, and optimizing the electrochemical performance of the battery.

[0298] As can be seen from Examples 1-9, when the molar content of the transition metal M is 2% to 10% based on the total molar amount of the carbon material, the powder resistance of the positive electrode active composite material is further reduced, and the initial coulombic efficiency and cycle efficiency of the battery are further improved.

[0299] As can be seen from Examples 1-9, when the mass content of the carbon material in the positive electrode active composite material is 1% to 10%, the cycle performance of the battery is further improved, and when the mass content of the carbon material in the positive electrode active composite material is 1% to 3%, the cycle performance and capacity of the battery are comprehensively optimized.

[0300] A comparison of Examples 1-5, 19, and 22 with Examples 13-14 shows that sodium-rich or iron-poor polyanionic compounds help to further improve battery capacity.

[0301] 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 composite material, characterized in that, The positive electrode active composite material includes a carbon material, a transition metal M, and a polyanion compound; the carbon material is coated on the surface of the polyanion compound in the form of a carbon film, and the transition metal M is distributed in the carbon film.

2. The positive electrode active composite material according to claim 1, characterized in that, The transition metal M includes at least one of Pt, Pd, Fe, Co, Ni, Mn, Cu, Au, Ag, Ru, and Rh.

3. The positive electrode active composite material according to claim 1 or 2, characterized in that, Based on the total mass of the carbon material, the mass ratio of the transition metal M is 0.1% to 10%.

4. The positive electrode active composite material according to claim 3, characterized in that, Based on the total mass of the carbon material, the mass ratio of the transition metal M is 1% to 10%.

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

6. The positive electrode active composite material according to claim 5, characterized in that, Based on the total mass of the positive electrode active composite material, the mass content of the carbon material in the positive electrode active composite material is 1% to 10%.

7. The positive electrode active composite material according to any one of claims 1 to 6, characterized in that, The carbon material is coated on the surface of the primary particles of the polyanion compound in the form of a carbon film, and the transition metal M is distributed in the carbon film.

8. The positive electrode active composite material according to any one of claims 1 to 7, characterized in that, There is a chemical bond between the transition metal M and the carbon material.

9. The positive electrode active composite material according to any one of claims 1 to 8, characterized in that, The polyanion compound includes a sodium-containing phosphate backbone compound or a sodium-containing sulfate backbone compound.

10. The positive electrode active composite material according to any one of claims 1 to 9, characterized in that, The polyanion compound includes a sodium phosphate-based material and a sodium sulfate-based material, and the sodium phosphate-based material includes a compound shown in any one of Formula I - Formula IV; the sodium phosphate-based material contains a compound shown in Formula V; Na x1 R y1 (PO4) z1 , formula I where 1 ≤ x1 ≤ 3, 1 ≤ y1 ≤ 2, 1 ≤ z1 ≤ 3, and 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; Na x2 R y2 (P2O7) z2 , formula II where 1 ≤ x2 ≤ 7, 1 ≤ y2 ≤ 3, 1 ≤ z2 ≤ 4, and 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; Na x3 R y3 (PO4) z3 (P2O7) k3 , Formula III where 1 ≤ x3 ≤ 7, 1 ≤ y3 ≤ 4, 1 ≤ z3 ≤ 2, 1 ≤ k3 ≤ 4, and 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; Na x4 R y4 (PO4) z4 M l1 , formula IV where 1 ≤ x4 ≤ 3, 1 ≤ y4 ≤ 2, 1 ≤ z4 ≤ 2, 1 ≤ l1 ≤ 3, 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, and M includes at least one of F, Cl, and Br; Na x5 X y5 (SO4)3, formula V where 0 < x5 ≤ 2, 0 < y5 ≤ 2, and X includes at least one of Mn, Fe, Co, Ni, Cu, and Zn.

11. The positive electrode active composite material according to any one of claims 1 to 10, characterized in that, The carbon material in the positive electrode active composite material, I D / I G If the value is less than 0.8, then 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 positive electrode active composite material according to any one of claims 1 to 11, characterized in that, The median particle size D of the positive electrode active composite material v 50 is 0.5 µm≤D v 50 ≤10 µm.

13. The positive electrode active composite material according to any one of claims 1 to 12, characterized in that, The median particle size D of the positive electrode active composite material v 50 is 1.0 µm≤D v 50 ≤5.0 µm.

14. The positive electrode active composite material according to any one of claims 1 to 13, characterized in that, At 25°C, the powder resistance of the positive electrode active composite material under a pressure of 200 MPa is 50 Ω·cm to 3500 Ω·cm.

15. A method for preparing a positive electrode active composite material, characterized in that, Including the following steps: Prepare a polyanion compound precursor; The polyanionic compound precursor, carbon source and M source are mixed evenly and calcined at high temperature to prepare the positive electrode active composite material, wherein the M source contains a transition metal salt. The positive electrode active composite material includes a carbon material, a transition metal M, and a polyanionic compound; the carbon material is coated on the surface of the polyanionic compound in the form of a carbon film, and the transition metal M is distributed in the carbon film.

16. The preparation method according to claim 15, characterized in that, The polyanionic compound includes compounds as shown in any one of Formulas I-III; Na x1 R y1 (PO4) z1 , formula I Wherein, 1≤x1≤3, 1≤y1≤2, 1≤z1≤3, and 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; Na x2 R y2 (P2O7) z2 , Formula II Wherein, 1≤x2≤7, 1≤y2≤3, 1≤z2≤4, and 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; Na x3 R y3 (PO4) z3 (P2O7) k3 , Formula III Wherein, 1≤x3≤7, 1≤y3≤4, 1≤z3≤2, 1≤k3≤4, and 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; The preparation of the polyanionic compound precursor includes the following steps: Raw materials containing phosphorus source, sodium source and R source are mixed with solvent to obtain primary mixed slurry. The primary mixed slurry is dried and then calcined at low temperature to obtain polyanionic compound precursor.

17. The preparation method according to claim 16, wherein the primary mixed slurry further comprises a carbon source.

18. The preparation method according to claim 16, characterized in that, The calcination temperature of the low-temperature calcination is 300℃~350℃, and the calcination time is 1 h~6 h.

19. The preparation method according to any one of claims 15 to 18, characterized in that, The calcination temperature for the high-temperature calcination is 450℃~700℃, and the calcination time is 5 h~15 h.

20. The preparation method according to any one of claims 15 to 19, characterized in that, The carbon source includes one or more of sucrose, glucose, citric acid, starch, cyclodextrin, pitch, polypropylene, polyethylene, polyethylene glycol, and polystyrene.

21. The preparation method according to any one of claims 16 to 20, 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.

22. The preparation method according to any one of claims 15 to 21, characterized in that, The M source includes one or more of the following: platinum source, palladium source, iron source, cobalt source, nickel source, and manganese source.

23. A positive electrode plate, characterized in that, It comprises a positive electrode film layer, the positive electrode film layer including a binder, a conductive agent, and a positive electrode active composite material according to any one of claims 1 to 14 or a positive electrode active composite material prepared by any one of claims 15 to 22.

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 binder is 1.5% to 3%.

25. 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 binder is 2.0% to 2.5%.

26. The positive electrode sheet according to any one of claims 23 to 25, characterized in that, The conductive agent includes at least one of one-dimensional conductive materials and zero-dimensional conductive materials.

27. The positive electrode sheet according to claim 26, characterized in that, The one-dimensional conductive material includes one or more of single-walled carbon nanotubes and multi-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%.

28. The positive electrode sheet according to claim 27, 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%.

29. The positive electrode sheet according to any one of claims 26 to 28, 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%.

30. The positive electrode sheet according to claim 29, 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%.

31. A secondary battery, characterized in that, The positive electrode sheet includes any one of claims 23 to 30.

32. The secondary battery according to claim 31, characterized in that, The secondary battery is a sodium-free secondary battery without a negative electrode.

33. The secondary battery according to claim 31 or 32, characterized in that, The secondary battery further includes a negative electrode sheet, which 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, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

34. The secondary battery according to claim 33, characterized in that, The areal density of the base coating is 5 g / m³. 2 ~50g / m 2 .

35. The secondary battery according to claim 33 or 34, characterized in that, The thickness of the base coating is 2 μm to 100 μm.

36. An electrical appliance, characterized in that, Includes a secondary battery selected from any one of claims 31 to 35.

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