Sodium secondary battery positive electrode material and preparation method therefor, positive electrode sheet, sodium secondary battery, and electric device

Abstract

A sodium secondary battery positive electrode material and a preparation method therefor, a positive electrode sheet, a sodium secondary battery, and an electric device. The sodium secondary battery positive electrode material comprises a sodium-containing positive electrode material and a coating material located on at least part of the surface of the sodium-containing positive electrode material, wherein the coating material comprises a hydrophobic polymer.

Description

Sodium secondary battery positive electrode material and preparation method thereof, positive electrode sheet, sodium secondary battery and power-consuming device Technical Field

[0001] The present disclosure relates to the technical field of batteries, and provides a sodium secondary battery positive electrode material and a preparation method thereof, a positive electrode sheet, a sodium secondary battery, and an electrical device. Background Art

[0002] Secondary batteries, represented by sodium batteries, have been applied in energy storage power systems (such as hydropower, thermal power, wind power and solar power stations, etc.), as well as electric vehicles, aerospace and other fields. Compared with lithium batteries, sodium batteries have cost advantages in terms of raw materials, especially the sodium salts that are the main components of sodium battery positive electrode materials. The reserves are more abundant, and the price of sodium salts is much lower than the lithium salts used in lithium battery positive electrode materials, which makes the cost of sodium battery positive electrode materials lower than that of lithium batteries. However, the poor electrochemical performance of sodium batteries in terms of rate performance and stability has limited their practical applications.

[0003] Application Contents

[0004] In response to the above-mentioned problems, the purpose of this application is to provide a sodium secondary battery positive electrode material and its preparation method, a positive electrode plate, a sodium secondary battery, and an electrical device. The sodium secondary battery positive electrode material has high environmental stability and can improve the electrochemical performance of the battery.

[0005] A first aspect of the present application provides a sodium secondary battery positive electrode material, comprising a sodium-containing positive electrode material and a coating material located on at least a portion of the surface of the sodium-containing positive electrode material, wherein the sodium-containing positive electrode material comprises at least one of a layered oxide, a Prussian blue compound, or a polyanionic sodium-containing compound; and the coating material comprises a hydrophobic polymer.

[0006] In the sodium secondary battery positive electrode material of the present application, a coating material containing a hydrophobic polymer is introduced on the surface of the sodium-containing positive electrode material, which can effectively resist the reaction rate and ability of residual alkali (such as sodium bicarbonate, sodium carbonate, etc.) with air components (such as H2O, CO2), thereby improving the environmental stability of the material; in addition, the coating material containing the hydrophobic polymer can serve as a buffer layer to relieve the stress generated during the insertion / extraction of sodium ions. In this way, the sodium secondary battery positive electrode material can improve the conductivity and cycle stability of the battery.

[0007] In some embodiments of the present application, the hydrophobic polymer and the sodium-containing positive electrode material satisfy the following relationship: m <T a , where T m is the melting point of the hydrophobic polymer, T aThe hydrophobic polymer has high processability and can improve the coating efficiency on the surface of the sodium-containing positive electrode material.

[0008] In some embodiments of the present application, the phase transition temperature T a ≤600℃.

[0009] In some embodiments of the present application, the mass ratio of the hydrophobic polymer to the sodium-containing positive electrode material is (0.2-10):100.

[0010] In some embodiments of the present application, the hydrophobic polymer includes a first hydrophobic polymer material, and the first hydrophobic polymer material includes at least one of polyethylene, polypropylene, polystyrene, polydimethylsiloxane, polyethylene terephthalate, polytetrafluoroethylene, polyamide, polycarbonate or silicone wax.

[0011] In some embodiments of the present application, the hydrophobic polymer includes polydimethylsiloxane, thereby further improving the environmental stability of the positive electrode material.

[0012] In some embodiments of the present application, the hydrophobic polymer includes the first hydrophobic polymer material, and the mass ratio of the first hydrophobic polymer material to the sodium-containing positive electrode material is (0.3-3):100, and can further be (0.5-2):100.

[0013] In some embodiments of the present application, the hydrophobic polymer includes a second hydrophobic polymer material and / or a third hydrophobic polymer material; the second hydrophobic polymer material includes polyacrylonitrile; the third hydrophobic polymer material includes a conjugated polymer and is a thermal cracking product of polyacrylonitrile.

[0014] Optionally, the hydrophobic polymer includes the conjugated polymer. Thus, the conductivity of the positive electrode material can be further improved.

[0015] In some embodiments of the present application, the hydrophobic polymer includes the second hydrophobic polymer material and / or the third hydrophobic polymer material, and the mass ratio of the hydrophobic polymer to the sodium-containing positive electrode material is (0.5-10):100, and can further be (1-5):100.

[0016] In some embodiments of the present application, the thermal decomposition temperature T of the second hydrophobic polymer material satisfies the following relationship: T m1 <T<T a , where T m1 is the melting point of the second hydrophobic polymer material; T a is the phase transition temperature of the sodium-containing cathode material.

[0017] In some embodiments of the present application, the sodium-containing positive electrode material includes a polyanionic sodium-containing compound, and the chemical formula of the polyanionic sodium-containing compound is: Na x R y (PO4) Z (P2O7) k , wherein 1≤x≤7, 1≤y≤4, 1≤z≤2, and 1≤k≤4, and R is at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, or Pb. As a result, the sodium-containing positive electrode material has a low residual alkali content, further reducing the impact of residual alkali on battery performance.

[0018] In some embodiments of the present application, the sodium-containing positive electrode material includes the polyanionic sodium-containing compound and a carbon-based material modification layer located on at least a portion of its surface, thereby improving the conductivity of the sodium secondary battery positive electrode material.

[0019] In some embodiments of the present application, the carbon-based material includes a first carbon material and a second carbon material, wherein the first carbon material includes at least one of natural graphite powder, artificial graphite powder, carbon black, carbon nanotubes, or graphene, and the second carbon material includes a sintered product of an organic carbon source at 450°C to 550°C. Thus, the combination of the first and second carbon materials can limit the grain growth of the polyanionic sodium-containing compound during the sintering process, thereby improving the conductivity of the material.

[0020] Optionally, the organic carbon source includes at least one of sucrose, glucose, citric acid, starch, cyclodextrin, asphalt or the hydrophobic polymer.

[0021] In some embodiments of the present application, in the sodium-containing positive electrode material, the mass ratio of the first carbon material to the polyanionic sodium-containing compound is (0.5-2): 100. Thus, the conductivity is improved without affecting the capacity of the positive electrode sheet.

[0022] In some embodiments of the present application, in the sodium-containing positive electrode material, the mass ratio of the sintered product to the polyanionic sodium-containing compound is (0.5-2): 100. Thus, the conductivity is improved without affecting the capacity of the positive electrode sheet.

[0023] In some embodiments of the present application, the median particle size Dv of the sodium-containing positive electrode material is 50 2μm~8μm.

[0024] In some embodiments of the present application, the specific surface area BET of the sodium-containing positive electrode material is 3 m 2 / g~11m2 / g.

[0025] In some embodiments of the present application, the water content of the sodium secondary battery positive electrode material in a sealed environment is not higher than 2000 ppm.

[0026] Optionally, the water content of the sodium secondary battery positive electrode material in a sealed environment is 50 ppm to 1600 ppm.

[0027] A second aspect of the present application provides a method for preparing a positive electrode material for a sodium secondary battery, comprising: mixing a coating raw material with a sodium-containing positive electrode material, and performing a first sintering to form a coating material comprising a hydrophobic polymer on at least a portion of the surface of the sodium-containing positive electrode material, wherein the sodium-containing positive electrode material comprises at least one of a layered oxide, a Prussian blue compound, or a polyanionic sodium-containing compound.

[0028] In some embodiments of the present application, the first sintering temperature T1 satisfies the following relationship: m <T1<T a ; Among them, T m is the melting point of the coating material, T a The phase transition temperature of the sodium-containing positive electrode material is thereby increased, thereby improving the coating effect while minimizing the impact on the sodium-containing positive electrode material.

[0029] Optionally, the phase transition temperature T of the sodium-containing positive electrode material a ≤600℃.

[0030] In some embodiments of the present application, the coating raw material includes a first hydrophobic polymer material and / or a second hydrophobic polymer material; wherein, the first hydrophobic polymer material includes at least one of polyethylene, polypropylene, polystyrene, polydimethylsiloxane, polyethylene terephthalate, polytetrafluoroethylene, polyamide, polycarbonate or silicone wax; and the second hydrophobic polymer material includes polyacrylonitrile.

[0031] In some embodiments of the present application, the coating raw material includes the first hydrophobic polymer material, and the first sintering temperature T1 and the initial thermal cracking temperature T' of the first hydrophobic polymer material satisfy the relationship: T1 < T'. This minimizes decomposition of the coating raw material and ensures that the coating material has high hydrophobicity.

[0032] In some embodiments of the present application, the coating material includes polydimethylsiloxane.

[0033] Optionally, the first sintering temperature T1 is 180° C. to 260° C., and the sintering time is 2 hours to 8 hours.

[0034] Furthermore, the first sintering temperature T1 is 200°C to 250°C, and the sintering time is 4h to 7h. Thus, a positive electrode material uniformly coated with polydimethylsiloxane can be obtained by sintering, thereby improving the environmental stability of the material.

[0035] In some embodiments of the present application, the coating raw material includes the second hydrophobic polymer material (polyacrylonitrile), and the first sintering temperature T1 and the initial thermal cracking temperature T" of the second hydrophobic polymer material satisfy the following relationship: T1>T". Thus, the second hydrophobic polymer material is thermally cracked by sintering to form a hydrophobic polymer with a conjugated structure (i.e., a conjugated polymer), thereby improving conductivity.

[0036] Optionally, the first sintering temperature T1 is 350° C. to 550° C., and the sintering time is 4 hours to 12 hours.

[0037] Furthermore, the first sintering temperature T1 is 400°C to 500°C, and the sintering time is 5 hours to 12 hours. This can minimize the possibility that the carbonization degree of polyacrylonitrile due to excessively high temperature will be high, which will lead to a decrease in the hydrophobicity of the coating material, and can also minimize the possibility that the conjugation degree due to excessively low temperature will be too low, which will affect the electrical properties of the material.

[0038] In some embodiments of the present application, the sodium-containing positive electrode material comprises a polyanionic sodium-containing compound, and the chemical formula of the polyanionic sodium-containing compound is: Na x R y (PO4) Z (P2O7) k , wherein 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4, and R is at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W or Pb.

[0039] In some embodiments of the present application, the sodium-containing cathode material comprises the polyanionic sodium-containing compound and a carbon-based material modification layer located on at least a portion of its surface. The specific description of the sodium-containing cathode material is as shown in the first aspect of the present application.

[0040] The third aspect of the present application provides a positive electrode plate, comprising the sodium secondary battery positive electrode material described in the first aspect of the present application or the sodium secondary battery positive electrode material prepared by the method described in the second aspect of the present application.

[0041] The fourth aspect of the present application provides a sodium secondary battery, comprising the positive electrode sheet described in the third aspect of the present application.

[0042] In some embodiments of the present application, the sodium secondary battery includes a sodium ion secondary battery.

[0043] In some embodiments of the present application, the sodium secondary battery comprises a negative electrode-free sodium secondary battery. Since the negative electrode of the negative electrode-free sodium secondary battery does not pre-install sodium metal, it can effectively alleviate the problem of decreased coulombic efficiency and cycle performance caused by the vigorous reaction between sodium metal and electrolyte.

[0044] Optionally, the sodium secondary battery includes a negative electrode plate, and the negative electrode plate includes a negative electrode current collector and an optional conductive layer.

[0045] Optionally, the negative electrode plate includes the conductive layer, and the conductive layer is disposed on at least one side of the negative electrode current collector. The provision of the conductive layer is more conducive to sodium ions being reduced and deposited on the negative electrode current collector by electrons during charging to form a sodium metal negative electrode.

[0046] Optionally, the negative electrode current collector includes any one of bare copper, aluminum foil, aluminum alloy foil or aluminum-based composite current collector.

[0047] Optionally, the conductive layer includes a conductive agent and a binder.

[0048] Furthermore, the conductive agent includes at least one of graphite, graphene, carbon fiber, carbon black, carbon dots, soft carbon, hard carbon, multi-walled carbon nanotubes or single-walled carbon nanotubes.

[0049] A fifth aspect of the present application provides an electrical device comprising the sodium secondary battery.

[0050] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Various other advantages and benefits will become apparent to those skilled in the art by reading the detailed description of the preferred embodiment below. The accompanying drawings are only for the purpose of illustrating the preferred embodiment and are not to be considered as limiting the present application. In the accompanying drawings:

[0052] FIG1 is a scanning electron microscope image of the sodium-containing positive electrode material (NFPP@C) of Comparative Example 1;

[0053] FIG2 is a scanning electron microscope image of the sodium secondary battery positive electrode material (NFPP@C@PAN) of Example 1;

[0054] FIG3 is a transmission electron micrograph of the sodium secondary battery positive electrode material (NFPP@C@PAN) prepared in Example 2;

[0055] FIG4 is an EDS graph of the sodium secondary battery positive electrode material (NFPP@C@PDMS) prepared in Example 12;

[0056] FIG5 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0057] FIG6 is an exploded view of a battery cell according to an embodiment of the present application;

[0058] FIG7 is a schematic diagram of a battery module according to an embodiment of the present application;

[0059] FIG8 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0060] FIG9 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG8 ;

[0061] FIG10 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application.

[0062] Explanation of reference numerals: 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: battery cell; 51: housing; 52: electrode assembly; 53: top cover assembly. DETAILED DESCRIPTION

[0063] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0064] In this application, references to "embodiments" mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor do they represent independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0065] " Scope " disclosed in the present application is limited in the form of lower limit and / or upper limit, and given range is limited by selecting a lower limit and / or an upper limit, and the selected lower limit and / or the rear upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form the scope of not clearly recording, and any lower limit can be combined with other lower limits to form the scope of not clearly recording, and any upper limit can be combined with any other upper limit to form the scope of not clearly recording. In addition, each separately disclosed point or single numerical value itself can be used as lower limit or upper limit and any other point or single numerical value combination or with other lower limit or upper limit combination to form the scope of not clearly recording.

[0066] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0067] Unless otherwise specified, the terms "include," "comprising," "containing," "having," and "having" used in this application may be open-ended or closed-ended. For example, "include," "comprising," "containing," "having," and "having" may indicate that other components not listed may also be included or contained, or may indicate that only the listed components are included or contained. In addition, in this application, the terms "plurality," "multiple," and "at least one" refer to more than two. "Above" and "below" are inclusive of the number itself. For example, "two or more" includes two itself, such as two, three, four, or more.

[0068] Unless otherwise specified, the term "and / or" in this application simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Furthermore, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0069] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and any variations thereof are intended to cover non-exclusive inclusions. Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0070] Although the performance of sodium secondary battery positive electrode materials is similar to that of lithium secondary positive electrode materials, their interfaces are more sensitive to air and electrolyte during storage and use. Currently, in the field of sodium batteries, the positive electrode materials have residual alkali (such as sodium bicarbonate, sodium carbonate, etc.) on the surface of the materials due to reasons such as process and formula ratio. The residual alkali on the surface easily reacts with water and carbon dioxide in the air, resulting in poor environmental stability of the sodium battery materials, which is not conducive to the subsequent application of the materials. It is easy to cause bloating of the battery cells and reduced stability, which in turn leads to safety hazards and poor quality problems in the battery. Therefore, it is necessary to modify the sodium battery positive electrode materials.

[0071] Accordingly, in a first aspect, the present application provides a sodium secondary battery positive electrode material, comprising a sodium-containing positive electrode material and a coating material located on at least a portion of the surface of the sodium-containing positive electrode material, wherein the sodium-containing positive electrode material comprises at least one of a layered oxide, a Prussian blue compound, or a polyanionic sodium-containing compound, and the coating material comprises a hydrophobic polymer.

[0072] In this application, hydrophobic polymer refers to a polymer material that is not easy to absorb water and has waterproof and moisture-proof properties. The structure of the hydrophobic polymer usually does not contain hydrophilic groups such as hydroxyl groups, carboxyl groups, and sulfonic acid groups. In addition, the hydrophobicity of the polymer can also be judged according to its surface energy. The lower the surface energy, the greater the hydrophobicity, and the surface energy of the hydrophobic polymer is lower than the surface energy of water. Generally, the surface energy of the hydrophobic polymer measured by the contact angle method is less than 71mJ / m 2 .

[0073] In some embodiments, the hydrophobic polymer and the sodium-containing positive electrode material satisfy the following relationship:

[0074] T m <T a ,in,

[0075] T m is the melting point of the hydrophobic polymer,

[0076] T a The hydrophobic polymer has high processability and can improve the coating efficiency on the surface of the sodium-containing positive electrode material.

[0077] As an example, the phase transition temperature T of the sodium-containing positive electrode material is a ≤600℃.

[0078] As an example, the melting point of the hydrophobic polymer is T m ≤500℃.

[0079] In some embodiments, the hydrophobic polymer includes a first hydrophobic polymer material, and the first hydrophobic polymer material includes at least one of polyethylene, polypropylene, polystyrene, polydimethylsiloxane (PDMS), polyethylene terephthalate, polytetrafluoroethylene, polyamide, polycarbonate or silicone wax.

[0080] Furthermore, the hydrophobic polymer includes polydimethylsiloxane. Using polydimethylsiloxane as the coating material can further improve the environmental stability of the positive electrode material.

[0081] In other embodiments, the hydrophobic polymer includes a second hydrophobic polymer material and / or a third hydrophobic polymer material; the second hydrophobic polymer material includes polyacrylonitrile, and the third hydrophobic polymer material includes a conjugated polymer and is a thermal cracking product of polyacrylonitrile.

[0082] Optionally, the hydrophobic polymer includes the conjugated polymer. The conjugated polymer has semiconductor properties, thereby further improving the conductivity of the positive electrode material.

[0083] In some embodiments, the thermal cracking temperature T of the second hydrophobic polymer material (the temperature for forming the conjugated polymer) satisfies the following relationship: T m1 <T<T a , where T m1 is the melting point of the second hydrophobic polymer material; T a is the phase transition temperature of the sodium-containing cathode material.

[0084] Furthermore, the hydrophobic polymer is the thermal cracking product of the polyacrylonitrile. It can be understood that the polyacrylonitrile can be partially carbonized at the thermal cracking temperature to form double bonds (including carbon-carbon double bonds and carbon-nitrogen double bonds), and a conjugated structure is formed between the double bonds, thereby converting the polyacrylonitrile into a polymer with a conjugated structure and having conductivity.

[0085] In the present application, the sodium-containing cathode material includes one or more of layered oxides, Prussian blue compounds or polyanionic sodium-containing compounds.

[0086] As some examples, the chemical formula of the layered oxide can be Nax1MO2, 0 < x1 ≤ 1, and M includes at least one of transition metal elements. For example, M includes variable valence transition metals such as vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), etc. Examples of the layered oxide include, but are not limited to, NaCrO2, NaMnO2, NaMnO2, Na 0.61 Ti 0.48 Mn 0.52 O2, Na[Fe 0.5 Co 0.5 O2, etc.

[0087] In some embodiments, from the perspective of reducing the residual alkali content, the sodium-containing cathode material includes a polyanionic sodium-containing compound. The chemical formula of the polyanionic sodium-containing compound is: Na x R y (PO4) Z (P2O7) k , where 1 ≤ x ≤ 7, 1 ≤ y ≤ 4, 1 ≤ z ≤ 2, 1 ≤ k ≤ 4, and R is at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, or Pb.

[0088] As an example, the polyanionic sodium-containing compound is sodium phosphate-based salt Na4Fe3(PO4)2(P2O7) (abbreviated as NFPP).

[0089] In some embodiments, the sodium-containing positive electrode material includes the polyanionic sodium-containing compound and a carbon-based material modified layer located on at least a portion of its surface. The carbon-based material has high electrical conductivity, and the modified layer can compensate for the low electrical conductivity of the polyanionic sodium-containing compound.

[0090] In some embodiments, the carbon-based material includes a first carbon material and a second carbon material. The first and second carbon materials can be used together to limit grain growth of the polyanionic sodium-containing compound during sintering (grain growth decreases conductivity), thereby jointly improving the conductivity of the material. The first and second carbon materials are described separately below.

[0091] The first carbon material is a conductive carbon material, including at least one of natural graphite powder, artificial graphite powder, carbon black, carbon nanotubes or graphene.

[0092] Optionally, the mass ratio of the first carbon material to the polyanionic sodium-containing compound is (0.5-2):100, such as 0.5:100, 1:100, 1.5:100, 2:100, etc. This is conducive to obtaining a suitable surface carbon content, taking into account both cost and reducing membrane resistance.

[0093] The second carbon material comprises a sintered product of an organic carbon source at 450°C to 550°C. Optionally, the organic carbon source may include at least one of sucrose, glucose, citric acid, starch, cyclodextrin, asphalt, or the hydrophobic polymer. As an example, the second carbon material is a sintered product of glucose at 500°C. TGA testing shows that the residual carbon content of the glucose after sintering is approximately 20%.

[0094] Optionally, the mass ratio of the sintered product to the polyanionic sodium-containing compound is (0.5-2):100, such as 0.5:100, 1:100, 1.5:100, 2:100, etc. This is conducive to obtaining a suitable surface carbon content, taking into account both cost and reducing membrane resistance.

[0095] In some embodiments, in the sodium-containing positive electrode material, the thickness of the carbon-based material modification layer is 1 nm to 5 nm.

[0096] In some embodiments, the median particle size (Dv) of the sodium-containing positive electrode material 50 ) is 2 μm to 8 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, etc. In the present application, the median particle size Dv50 can be measured by particle size distribution-laser diffraction method with reference to GB / T19077-2016 standard.

[0097] In some embodiments, the specific surface area BET of the sodium-containing positive electrode material is 3 m2 / g~11m 2 / g, for example 3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、8m 2 / g、9m 2 / g、11m 2 In the present application, the specific surface area BET can be measured using a flow method gas adsorption type specific surface area measuring device with reference to GB / T 19587-2017 standard.

[0098] In some embodiments, the compaction density of the sodium-containing cathode material at a pressure of 100 MPa may be 1.3 g / cm 3 ~2.1g / cm 3 .

[0099] In some embodiments, the coating amount of the hydrophobic polymer can be determined according to the material type and coating thickness. Specifically, the coating amount of the hydrophobic polymer satisfies the following relationship:

[0100] M=A×(M0 / 100g)×(H / 10nm)×ρ

[0101] Wherein, M represents the coating thickness, in g;

[0102] A represents the specific surface area BET of the sodium-containing positive electrode material, in m 2 / g;

[0103] M0 represents the mass of the sodium-containing positive electrode material, in g;

[0104] H represents the thickness of the layer structure formed by the coating material, in nm;

[0105] ρ represents the density of the hydrophobic polymer in g / mL or g / cm 3 Thus, while ensuring the coating effect, the influence of the coating material on the battery capacity density is reduced. In addition, the coating thickness in this formula can refer to a preset coating thickness, that is, the coating amount of the hydrophobic polymer can be determined according to the desired coating thickness.

[0106] In some embodiments, the mass ratio of the hydrophobic polymer to the sodium-containing positive electrode material is (0.2-10):100, for example, 0.2:100, 0.3:100, 0.5:100, 0.8:100, 1:100, 2:100, 2.5:100, 3:100, 5:100, 8:100, etc.

[0107] Optionally, the hydrophobic polymer includes the first hydrophobic polymer material (such as PDMS), and the mass ratio of the first hydrophobic polymer material to the sodium-containing positive electrode material is (0.3-3):100, for example, 0.3:100, 0.5:100, 0.8:100, 1:100, 2:100, 3:100, etc. This can improve the environmental stability of the positive electrode material without affecting the electrochemical performance of the material. Further optionally, the mass ratio of the first hydrophobic polymer material to the sodium-containing positive electrode material is (0.5-2):100.

[0108] Optionally, the hydrophobic polymer includes the second hydrophobic polymer material and / or the third hydrophobic polymer material, and the mass ratio of the hydrophobic polymer to the sodium-containing positive electrode material is (0.5-10):100, for example, 0.5:100, 1:100, 2:100, 3:100, 4:100, 5:100, 8:100, 10:100, etc. Further, the mass ratio of the hydrophobic polymer to the sodium-containing positive electrode material is (1-5):100, thereby enabling the positive electrode material to have both high environmental stability and conductivity.

[0109] In some embodiments, in the sodium secondary battery positive electrode material, the thickness of the layer structure formed by the coating material and the total thickness of the carbon-based material modification layer ranges from 2 nm to 8 nm, and the thickness can be measured by transmission electron microscopy.

[0110] In some embodiments, the sodium secondary battery positive electrode material has a water content of no greater than 2000 ppm in a sealed environment, and may optionally be between 50 ppm and 1600 ppm. In this application, the water content of the material may be measured according to the method in GB / T 11133-2015. Optionally, the sealed environment has a temperature of 0°C to 10°C.

[0111] In a second aspect, the present application provides a method for preparing a positive electrode material for a sodium secondary battery, comprising: mixing a coating raw material with a sodium-containing positive electrode material, and performing a first sintering to form a coating material comprising a hydrophobic polymer on at least a portion of the surface of the sodium-containing positive electrode material, wherein the sodium-containing positive electrode material comprises at least one of a layered oxide, a Prussian blue compound, or a polyanionic sodium-containing compound.

[0112] In some embodiments, the coating material includes a first hydrophobic polymer material and / or a second hydrophobic polymer material. The first hydrophobic polymer material and the second hydrophobic polymer material are as described in the first aspect of the present application and will not be described in detail here.

[0113] In the present application, the temperature of the first sintering can be selected according to the type of sodium-containing positive electrode material and coating raw material. As some examples, the first sintering temperature T1 can be 180°C to 550°C.

[0114] In some embodiments, the mass ratio of the coating raw material to the sodium-containing positive electrode material is (0.2-10):100, for example, 0.2:100, 0.3:100, 0.5:100, 0.8:100, 1:100, 2:100, 2.5:100, 3:100, 5:100, 8:100, etc.

[0115] In some embodiments, the first sintering temperature T1 satisfies the relationship: m <T1<T a ; Among them, T m is the melting point of the coating material, T a The phase transition temperature of the sodium-containing positive electrode material is thereby increased, thereby improving the processing fluidity of the coating raw material to improve the coating effect, while minimizing the impact on the sodium-containing positive electrode material.

[0116] Optionally, the phase transition temperature T of the sodium-containing positive electrode material a ≤600℃.

[0117] In some embodiments, the coating raw material includes the first hydrophobic polymer material, and the mass ratio of the first hydrophobic polymer material to the sodium-containing positive electrode material is (0.3-3):100, for example, 0.3:100, 0.5:100, 0.8:100, 1:100, 2:100, 3:100, etc. As a result, the prepared positive electrode material has high environmental stability while not affecting the electrochemical performance of the material. Furthermore, the mass ratio of the coating raw material to the sodium-containing positive electrode material is (0.5-2):100.

[0118] In some embodiments, the coating raw material includes the first hydrophobic polymer material, and the first sintering temperature T1 is related to the initial thermal cracking temperature T' of the first hydrophobic polymer material by the equation: T1 < T'. This minimizes decomposition of the coating raw material, resulting in a highly hydrophobic coating material. It should be understood that the initial thermal cracking temperature refers to the temperature at which the polymer material begins to decompose. The initial thermal cracking temperature can be measured by thermogravimetric analysis (TGA).

[0119] In some specific embodiments, the coating material includes polydimethylsiloxane.

[0120] Optionally, the first sintering temperature T1 may be 180°C to 260°C, for example, 180°C, 200°C, 225°C, 230°C, 240°C, 250°C, 260°C, etc.

[0121] Optionally, the first sintering time is 2 hours to 8 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours.

[0122] Furthermore, the first sintering temperature T1 is 200°C to 250°C, and the sintering time is 4h to 7h. This sintering temperature is lower than the initial thermal decomposition temperature of PDMS (about 300°C), which can minimize the decomposition of polydimethylsiloxane, resulting in a uniformly polydimethylsiloxane-coated positive electrode material and improving the environmental stability of the material.

[0123] In some embodiments, the coating raw material includes the second hydrophobic polymer material, and the mass ratio of the coating raw material to the sodium-containing positive electrode material is (0.5-10):100, for example, 0.5:100, 1:100, 2:100, 3:100, 4:100, 5:100, 8:100, 10:100, etc. Furthermore, the mass ratio of the coating raw material to the sodium-containing positive electrode material is (1-5):100, thereby enabling the prepared positive electrode material to have both high environmental stability and conductivity.

[0124] In some embodiments, the coating raw material includes the second hydrophobic polymer material, and the first sintering temperature T1 and the starting thermal cracking temperature T" of the second hydrophobic polymer material are related by the formula: T1>T. Thus, the second hydrophobic polymer material (polyacrylonitrile) is thermally cracked by sintering to form a highly conjugated polymer. The resulting conjugated polymer is uniformly coated on the surface of the sodium-containing positive electrode material as a hydrophobic polymer, which can improve the conductivity of the material.

[0125] In some specific embodiments, the coating material includes polyacrylonitrile (PAN).

[0126] Optionally, the first sintering temperature T1 is 350°C to 550°C, such as 350°C, 400°C, 450°C, 500°C, 520°C, 550°C, etc. Optionally, the first sintering time is 4h to 12h, such as 4h, 5h, 6h, 8h, 10h, 12h, etc. In some examples, by infrared spectroscopy characterization and analysis of PAN and the sintering products at 400°C, 450°C, and 500°C, the polyacrylonitrile material has a spectral density of 2200cm -1 There is an obvious cyano (-C≡N) characteristic peak near the sintering products at three temperatures, but this characteristic peak disappears, and the peak at 1600cm -1 Obvious C=CC=N characteristic peaks appear nearby, indicating that PAN forms a conjugated structure after sintering.

[0127] Furthermore, the first sintering temperature T1 is 400°C to 500°C, and the sintering time is 5h to 12h. This can minimize the possibility that the carbonization degree of polyacrylonitrile due to excessively high temperature will be high, which will lead to a decrease in the hydrophobicity of the coating material, and can also minimize the possibility that the conjugation degree due to excessively low temperature will be too low, which will affect the electrical properties of the material.

[0128] In the present application, the coating raw material and the sodium-containing positive electrode material can be mixed in a dry mixing manner or in a wet manner, wherein the wet method can be carried out in the presence of a solvent, such as a polar organic solvent such as N,N-dimethylformamide (DMF), N-methylpyrrolidone, dimethyl sulfoxide, cyclopentane, ethyl nitrate, etc. When the wet method is adopted, the mixing further includes drying (such as spray drying) to remove the solvent. Alternatively, the coating raw material and the sodium-containing positive electrode material are mixed in a dry mixing manner, thereby simplifying the preparation process and reducing costs.

[0129] In the preparation method of the present application, the specific description of the sodium-containing positive electrode material is as described in the first aspect of the present application and will not be repeated here.

[0130] In some embodiments, the sodium-containing cathode material includes the polyanionic sodium-containing compound and a carbon-based material modification layer located on at least a portion of its surface. The method further includes preparing the sodium-containing cathode material, specifically comprising:

[0131] The sodium source, R source, phosphorus source and carbon source are mixed and subjected to a second sintering to obtain a sodium-containing positive electrode material; wherein,

[0132] The carbon source includes a first carbon material and an organic carbon source.

[0133] Optionally, the phase transition temperature of the polyanionic sodium-containing compound is less than 600° C. The second sintering temperature is 450° C. to 550° C., for example, 450° C., 500° C., 550° C., etc. A sintering temperature that is too low may result in a low degree of carbonization of the organic carbon source, affecting the conductivity of the material. A sintering temperature that is too high may cause rapid grain growth of the material, incomplete solid-phase reaction, and the generation of impurities.

[0134] Optionally, the second sintering time is 4 hours to 10 hours, for example, 4 hours, 5 hours, 7 hours, 8 hours, 10 hours, etc.

[0135] Optionally, the mixing in preparing the sodium-containing positive electrode material may be carried out in the presence of a solvent (eg, water).

[0136] As some examples, the sodium source may include sodium pyrophosphate (Na4P2O7).

[0137] As some examples, the R source may include an iron source, which may be selected from at least one of an inorganic iron salt, an organic iron salt (such as ferrous oxalate), metallic iron, or an iron oxide.

[0138] As some examples, the phosphorus source may include phosphoric acid, or phosphates (eg, ammonium dihydrogen phosphate).

[0139] In addition, the chemical formula Na x R y (PO4) Z(P2O7) k The specific explanations of the first carbon material and the organic carbon source are as described in the first aspect of this application and will not be repeated here.

[0140] In a third aspect, the present application provides a positive electrode sheet comprising the sodium secondary battery positive electrode material described in the first aspect of the present application or the sodium secondary battery positive electrode material prepared by the method described in the second aspect of the present application. In some embodiments, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises the sodium secondary battery positive electrode material.

[0141] In the present application, the positive electrode current collector may be, for example, a metal foil or a composite current collector. The metal foil may be, for example, aluminum foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one side of the polymer base layer. The metal layer may be made of, but is not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material of the polymer base layer may be, for example, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0142] In some embodiments, the sodium secondary battery positive electrode material is used as a positive electrode active material in a positive electrode film layer. In addition to the positive electrode material, the positive electrode film layer may optionally include a conductive agent and / or a binder. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers; the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorinated acrylate resin.

[0143] This application does not particularly limit the preparation method of the positive electrode sheet, and the preparation method can refer to existing methods. For example, the positive electrode slurry is coated on the positive electrode current collector, dried, and cold pressed to form the positive electrode sheet. The positive electrode slurry can be formed by dispersing the components such as the sodium secondary battery positive electrode material, an optional conductive agent, and an optional binder in a solvent (e.g., N-methylpyrrolidone) and stirring them uniformly.

[0144] In addition, the positive electrode sheet of the present application does not exclude other additional functional layers in addition to the positive electrode film layer. For example, the positive electrode sheet may also include a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed between the positive electrode current collector and the positive electrode film layer. For another example, the positive electrode sheet may also include a protective layer covering the surface of the positive electrode film layer.

[0145] A fourth aspect of the present application provides a sodium secondary battery comprising the positive electrode sheet described in the third aspect of the present application. The positive electrode sheet comprising the sodium battery positive electrode material serves as the positive electrode side, and the lower water content on the positive electrode side can slow the growth of sodium dendrites on the negative electrode side, thereby improving the quality and reliability of the battery.

[0146] As an example, a sodium secondary battery can be disassembled, the middle part of the positive electrode plate can be taken out and placed in a beaker, and an appropriate amount of NMP (N-methylpyrrolidone) is poured into it for soaking and cleaning. After continuous cleaning for multiple times, a cleaning liquid is obtained, and the cleaning liquid is centrifuged and dried to obtain a dry sodium secondary battery positive electrode material powder.

[0147] For sodium secondary battery positive electrode material powder, ICP (inductively coupled plasma emission spectroscopy) can be used to characterize the main element content of the particles; ion beam etching can also be used for etching, combined with XPS (X-ray photoelectron spectroscopy) to characterize the elements (such as oxygen, carbon) and element valence changes at different depths from the particle surface; TEM (transmission electron microscopy) can also be used to characterize the thickness of the layer structure formed by the coating material; infrared spectroscopy and / or Raman spectroscopy can also be used to characterize the characteristic functional groups of the hydrophobic polymer in the coating material to determine the corresponding hydrophobic polymer type.

[0148] In some embodiments, the sodium secondary battery comprises a sodium ion secondary battery.

[0149] In some embodiments, the sodium secondary battery further comprises a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0150] In some embodiments, the sodium secondary battery comprises a negative electrode-free sodium secondary battery. The negative electrode side of the negative electrode-free sodium secondary battery does not have sodium metal pre-set, thereby effectively alleviating the problem of decreased coulombic efficiency and cycle performance caused by the vigorous reaction between sodium metal and the electrolyte (especially the water therein).

[0151] [Negative electrode]

[0152] In some embodiments, the sodium secondary battery is a sodium ion secondary battery, and its negative electrode plate may include a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, and the negative electrode film layer may include a negative electrode active material.

[0153] In some embodiments, the negative electrode current collector may include a metal foil or a composite current collector. The metal foil is, for example, copper foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one side of the polymer base layer. The material of the metal layer includes, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, silver alloys, etc., and the polymer material of the polymer base layer includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0154] In some embodiments, the negative electrode active material may include negative electrode materials for secondary batteries known in the art. For example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxides, and tin alloys.

[0155] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder may include, for example, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl cellulose (CMC), or carboxymethyl chitosan (CMCS).

[0156] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0157] In some embodiments, the negative electrode film layer may further optionally contain other additives, such as a thickener. Specific examples of thickeners include, but are not limited to, sodium carboxymethyl cellulose (CMC-Na).

[0158] In other embodiments, the sodium secondary battery is a negative electrode-free sodium secondary battery, and its negative electrode includes a negative electrode current collector and an optional conductive layer.

[0159] Optionally, the negative electrode plate has a conductive layer, which is disposed on at least one side of the negative electrode current collector. The provision of the conductive layer is more conducive to sodium ions being reduced and deposited on the negative electrode current collector by electrons during charging to form a sodium metal negative electrode.

[0160] Optionally, the negative electrode current collector includes any one of bare copper, aluminum foil, aluminum alloy foil, and aluminum-based composite current collector.

[0161] Optionally, the conductive layer includes a conductive agent and a binder. The binder is as described above and will not be described in detail here.

[0162] Optionally, the conductive agent includes at least one of graphite, graphene, carbon fiber, carbon black, carbon dots, soft carbon, hard carbon, multi-walled carbon nanotubes or single-walled carbon nanotubes.

[0163] The present application does not particularly limit the preparation method of the negative electrode sheet, and the negative electrode sheet can be prepared by referring to existing methods. For example, the negative electrode components, such as the negative electrode material, conductive agent, and binder, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry; the negative electrode slurry is then coated on a negative electrode current collector, and the negative electrode sheet is obtained by drying and cold pressing.

[0164] [Electrolytes]

[0165] In the present application, the electrolyte can be selected with reference to existing secondary batteries.

[0166] In some embodiments, the electrolyte is an electrolyte solution.

[0167] In some embodiments, the electrolyte may include an organic solvent, a sodium salt, and an optional additive. The sodium salt includes, but is not limited to, at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, or Na(CH3)C6H4SO3. The organic solvent includes, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), diethyl sulfone (ESE), or an ether solvent. The ether solvent may include cyclic ethers and / or chain ethers. Specific examples of cyclic ethers include, but are not limited to, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), etc. Specific examples of chain ethers include, but are not limited to, ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), etc.

[0168] In some embodiments, the additives in the electrolyte may include negative electrode film-forming additives and positive electrode film-forming additives; they may also include additives that can improve certain performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high temperature or low temperature performance of the battery, etc. As an example, the additives may include, but are not limited to, at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propane sultone (PS), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl) phosphate (TMSP) or tris(trimethylsilyl) borate (TMSB).

[0169] [Isolation film]

[0170] In the present application, the isolation membrane is arranged between the positive electrode plate and the negative electrode plate, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The present application has no particular restrictions on the type of isolation membrane, and various porous structure isolation membranes well known in the art can be selected. In some embodiments, the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. In addition, the isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.

[0171] In some embodiments, a ceramic coating and / or a metal oxide coating is further provided on the isolation membrane.

[0172] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0173] In some embodiments, the battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0174] In this application, the outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery can also be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0175] The battery of the present application may include a battery cell form, a battery module form, and a battery pack form. The battery cell, battery module, and battery pack of the present application will be described below with reference to the accompanying drawings as appropriate.

[0176] The present application has no particular limitation on the shape of the battery, which can be cylindrical, square, or any other shape. For example, FIG5 shows a battery cell 5 with a square structure as an example.

[0177] In some embodiments, referring to Figure 6, the outer packaging may include a shell 51 and a top cover assembly 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell can be one or more, and those skilled in the art can select according to specific actual needs.

[0178] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0179] Figure 7 shows an example battery module 4. Referring to Figure 7 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple cells may be secured together using fasteners.

[0180] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0181] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0182] Figures 8 and 9 illustrate an example battery pack 1. Referring to Figures 8 and 9 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0183] The fifth aspect of the present application provides an electrical device, comprising the battery described in the fourth aspect of the present application. The battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device.

[0184] Electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0185] As an electrical device, a battery cell, battery module or battery pack can be selected according to its usage requirements.

[0186] Figure 10 shows an example of an electric device. This device can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the battery, a battery pack or battery module can be used.

[0187] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0188] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0189] The following examples are used to illustrate the sodium secondary battery positive electrode material and the preparation method thereof of the present application.

[0190] Example 1

[0191] (1) Preparation of NFPP@C cathode material

[0192] Sodium pyrophosphate, ammonium dihydrogen phosphate, and ferrous oxalate were prepared according to the stoichiometric ratio of Na4Fe3(PO4)2(P2O7) to obtain a composition, conductive carbon black and glucose (the mass ratio of conductive carbon black, glucose to the composition was 0.5:5:100) were added, and then added to deionized water and ground to obtain a positive electrode slurry. The positive electrode slurry was spray-dried, sintered at 500°C for 10h, and pulverized by air flow to obtain NFPP@C (Dv50 of 3μm, specific surface area BET of 7m 2 / g).

[0193] (2) Preparation of NFPP@C@PAN

[0194] NFPP@C and PAN were mixed uniformly in a mass ratio of 100:1 and sintered at 500°C for 10 h to obtain the sodium secondary battery positive electrode material NFPP@C@PAN.

[0195] Examples 2-5

[0196] The sodium secondary battery positive electrode material was prepared according to the method of Example 1, except that the relative amount of PAN was adjusted to obtain NFPP@C@PAN with different coating amounts.

[0197] Examples 6-11

[0198] The sodium secondary battery positive electrode material was prepared according to the method of Example 1, except that the sintering conditions after mixing NFPP@C and PAN were adjusted to obtain different NFPP@C@PAN.

[0199] Comparative Example 1

[0200] The NFPP@C prepared in Example 1 was used as a comparative sample.

[0201] Example 12

[0202] (1) Preparation of positive electrode material slurry

[0203] Same as Example 1.

[0204] (2) Preparation of NFPP@C

[0205] Same as Example 1.

[0206] (3) Preparation of NFPP@C@PDM

[0207] NFPP@C and PDMS were mixed evenly in a mass ratio of 100:0.5 and sintered at 230°C for 6 h to obtain the sodium secondary battery positive electrode material NFPP@C@PDMS.

[0208] Examples 13-16

[0209] The sodium secondary battery positive electrode material was prepared according to the method of Example 12, except that the relative amount of PDMS was adjusted to obtain NFPP@C@PDMS with different coating amounts.

[0210] Examples 17-20

[0211] The sodium secondary battery positive electrode material was prepared according to the method of Example 12, except that the sintering conditions after mixing NFPP@C and PDMS were adjusted to obtain different NFPP@C@PDMS.

[0212] Test section

[0213] 1. Cathode material characterization

[0214] (1) Median particle size (Dv 50 )test

[0215] The particle size test was performed using a Malvern laser particle size analyzer (Mastersizer-3000) with the reference standard being GB / T19077-2016.

[0216] Pretreatment: Add an appropriate amount of the sample to be tested and water into a beaker, and add a dispersant (sodium hexametaphosphate) and disperse by ultrasonication to ensure that the sample is completely dispersed in the dispersant.

[0217] (2) Specific surface area BET test

[0218] The specific surface area BET was tested using a specific surface area tester F-Sorb 1400CES in accordance with GB / T 19587-2017.

[0219] Pretreatment: Take a certain amount of powder and degas it in a nitrogen atmosphere at 80℃ for 12h.

[0220] (3) Environmental stability test

[0221] After heating the cathode material to 170°C and drying it, the material was stored in air at 50% relative humidity for 30 minutes. The water content before and after storage was measured according to the GB / T11133-2015 standard. Test steps: The solid sample was purged with dry gas into the titration cup of a Karl Fischer coulometer for titration, and the result was converted to the water content of the solid sample.

[0222] Calculation formula: Water content = (sample moisture value - blank moisture value) / sample mass.

[0223] 2. Performance Testing

[0224] The following is a performance test of the positive electrode materials prepared in the examples and comparative examples when applied to batteries.

[0225] Battery preparation

[0226] 1) Preparation of positive electrode sheet

[0227] The positive electrode materials of the embodiment and the comparative example were mixed with the conductive agent carbon black Super P and the binder PVDF in a mass ratio of 7:2:1 and an appropriate amount of solvent NMP and stirred to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on the surface of the aluminum foil, and then dried and punched to obtain a positive electrode sheet with a compaction density of 2g / cm 3 .

[0228] 2) Preparation of negative electrode sheet

[0229] The negative electrode material hard carbon, conductive agent carbon black Super P, and binder CMC were mixed with an appropriate amount of solvent water in a mass ratio of 8:1:1 and stirred evenly to obtain a negative electrode slurry; the negative electrode slurry was then evenly coated on the surface of the copper foil; after drying, cold pressing, and slitting, the negative electrode sheet was obtained with a compaction density of 1.8g / cm 3 .

[0230] 3) Preparation of electrolyte

[0231] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), sodium hexafluorophosphate (NaPF6) was dissolved in ethylene glycol dimethyl ether (DME) to obtain a NaPF6 electrolyte with a concentration of 0.5 mol / L.

[0232] 4) Preparation of sodium ion batteries

[0233] The positive electrode sheet, separator (polypropylene film), and negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and the separator is soaked in the above electrolyte to assemble into a laminated battery.

[0234] Battery performance test

[0235] 1) Coulomb efficiency test

[0236] The sodium ion battery was charged to 3.75V at a constant current of 1 / 3C at 25°C, and then charged at a constant voltage of 3.75V until the current dropped to 0.05C to obtain the first charge capacity (Cc1); then discharged to 1.5V at a constant current of 1 / 3C to obtain the first discharge capacity (Cd1), and the coulombic efficiency of the sodium ion battery was calculated according to the following formula.

[0237] Coulombic efficiency of sodium ion battery = first discharge capacity (Cd1) / first charge capacity (Cc1)

[0238] 2) Capacity retention test

[0239] The sodium ion battery was charged to 3.65V at a constant current of 1C at 25°C, then charged at a constant voltage of 3.65V until the current dropped to 0.05C, and then discharged to 1.5V at a constant current of 1C to obtain the first cycle discharge capacity (Cd1); this charge and discharge cycle was repeated until the nth cycle (n = 1000), and the discharge capacity of the sodium battery after n cycles (Cdn) was obtained. The capacity retention rate of the sodium battery was calculated according to the following formula:

[0240] Capacity retention rate = discharge capacity after n cycles (Cdn) / first cycle discharge capacity (Cd1).

[0241] The test results of battery performance are shown in Table 2.

[0242] Table 1

[0243] Note: The coating amount refers to the mass percentage of the coating raw material to the sodium-containing positive electrode material.

[0244] Table 2

[0245] As can be seen from Table 2, by comparing Examples 1-20 with Comparative Example 1, it can be seen that after the sodium-containing positive electrode material is coated and modified with PAN and PDMS, the stability of the material in a high humidity environment can be improved. The improvement of the environmental stability of the material is beneficial to the stability of the material performance in the subsequent use and processing process, and the prepared battery also has higher electrochemical performance.

[0246] Figure 1 shows a SEM image of the morphology of NFPP@C from Comparative Example 1, and Figure 2 shows a SEM image of the morphology of NFPP@C@PAN from Example 1. Comparing Figures 1 and 2, it can be seen that the surface of NFPP@C is rough before coating, but becomes smooth after coating.

[0247] FIG3 is a transmission electron microscope image of the positive electrode material prepared in Example 2. As can be seen from the image, the total thickness of the layer structure formed by the carbon modification layer and the coating material on the surface of NFPP is approximately between 2 nm and 6 nm.

[0248] FIG4 is an EDS image of the cathode material prepared in Example 12. As can be seen from the image, Si and O are distributed on the cathode material, indicating that PDMS is coated on NFPP@C.

[0249] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A positive electrode material for a sodium secondary battery, wherein, The positive electrode material of the sodium secondary battery includes a sodium-containing positive electrode material and a coating material located on at least a part of the surface of the sodium-containing positive electrode material; wherein, The sodium-containing positive electrode material includes at least one of a layered oxide, a Prussian blue compound, or a polyanion-type sodium-containing compound; The coating material contains a hydrophobic polymer.

2. The positive electrode material for a sodium secondary battery according to claim 1, wherein, Satisfy one or more of the following characteristics: (a) The hydrophobic polymer and the sodium-containing cathode material satisfy the relationship: T m < T a , where T m is the melting point of the hydrophobic polymer, and T a is the phase transition temperature of the sodium-containing cathode material; (b) The phase transition temperature T of the sodium-containing cathode material a ≤ 600 °C; (c) The mass ratio of the hydrophobic polymer to the sodium-containing positive electrode material is (0.2 to 10):

100.

3. The positive electrode material for a sodium secondary battery according to claim 1 or 2, wherein The hydrophobic polymer includes a first hydrophobic polymer material, and the first hydrophobic polymer material includes at least one of polyethylene, polypropylene, polystyrene, polydimethylsiloxane, polyethylene terephthalate, polytetrafluoroethylene, polyamide, polycarbonate, or silicone wax.

4. The positive electrode material for a sodium secondary battery according to claim 3, wherein Satisfy one of the following characteristics: (a) The mass ratio of the hydrophobic polymer to the sodium-containing positive electrode material is (0.3 to 3):100; or (b) The mass ratio of the hydrophobic polymer to the sodium-containing positive electrode material is (0.5 to 2):

100.

5. The positive electrode material for a sodium secondary battery according to any one of claims 1-4, wherein, The hydrophobic polymer includes a second hydrophobic polymer material and / or a third hydrophobic polymer material. Among them, the second hydrophobic polymer material includes polyacrylonitrile, the third hydrophobic polymer material includes a conjugated polymer, and the conjugated polymer is a thermal cracking product of polyacrylonitrile.

6. The positive electrode material for a sodium secondary battery according to claim 5, wherein, Satisfy one of the following characteristics: (a) The mass ratio of the hydrophobic polymer to the sodium-containing positive electrode material is (0.5 to 10):100; or (b) The mass ratio of the hydrophobic polymer to the sodium-containing positive electrode material is (1 to 5):

100.

7. The positive electrode material for a sodium secondary battery according to claim 5 or 6, wherein, The thermal cracking temperature T of the second hydrophobic polymer material satisfies the following relational expression: T m1 <T<T a , where T m1 is the melting point of the second hydrophobic polymer material; T a is the phase transition temperature of the sodium-containing cathode material.

8. The positive electrode material for a sodium secondary battery according to any one of claims 1 to 7, wherein, The sodium-containing cathode material contains a sodium-containing polyanionic compound, and the chemical formula of the sodium-containing polyanionic compound is: Na x R y (PO4) Z (P2O7) k , where 1 ≤ x ≤ 7, 1 ≤ y ≤ 4, 1 ≤ z ≤ 2, 1 ≤ k ≤ 4, and R is at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W or Pb.

9. The positive electrode material for a sodium secondary battery according to claim 8, wherein, The sodium-containing positive electrode material includes the polyanion-type sodium-containing compound and a carbon-based material modification layer located on at least a part of its surface; The carbon-based material modification layer includes a first carbon material and a second carbon material. The first carbon material includes at least one of natural graphite powder, artificial graphite powder, carbon black, carbon nanotubes, or graphene, and the second carbon material includes a sintering product of an organic carbon source at 450°C to 550°C.

10. The positive electrode material for a sodium secondary battery according to claim 9, wherein, Satisfy one or more of the following characteristics: (a) The organic carbon source includes at least one of sucrose, glucose, citric acid, starch, cyclodextrin, asphalt, or the hydrophobic polymer; (b) The mass ratio of the first carbon material to the polyanion-type sodium-containing compound is (0.5 to 2):100; (c) The mass ratio of the sintering product to the polyanion-type sodium-containing compound is (0.5 to 2):100; (d) The median particle size Dv of the sodium-containing cathode material 50 is 2 μm to 8 μm; (e) The specific surface area BET of the sodium-containing cathode material is 3 m 2 / g to 11 m 2 / g.

11. The positive electrode material for a sodium secondary battery according to any one of claims 1 to 10, wherein, Satisfy one of the following characteristics: (a) The water content in the sealed environment is not higher than 2000 ppm; or (b) The water content in the sealed environment is 50 ppm to 1600 ppm.

12. A method for preparing a positive electrode material for a sodium secondary battery, wherein, Include: Mix the coating raw materials and the sodium-containing positive electrode material and perform the first sintering to form a coating material containing a hydrophobic polymer on at least a part of the surface of the sodium-containing positive electrode material. The sodium-containing positive electrode material includes at least one of a layered oxide, a Prussian blue compound, or a polyanion-type sodium-containing compound.

13. The method according to claim 12, wherein, Satisfy one or more of the following characteristics: (a) The first sintering temperature T1 satisfies the relationship: T m <T1<T a , where T m is the melting point of the coating raw material, and T a is the phase transition temperature of the sodium-containing cathode material; (b) The phase transition temperature T of the sodium-containing cathode material a ≤600 °C; (c) The mass ratio of the coating raw material to the sodium-containing cathode material is (0.2 to 10):

100.

14. The method according to claim 12 or 13, wherein, Satisfies one of the following characteristics: (a) The coating raw material includes a first hydrophobic polymer material, and the first hydrophobic polymer material includes at least one of polyethylene, polypropylene, polystyrene, polydimethylsiloxane, polyethylene terephthalate, polytetrafluoroethylene, polyamide, polycarbonate, or silicone wax; or (b) The coating raw material includes polydimethylsiloxane.

15. The method according to claim 14, wherein Satisfies one of the following characteristics: (a) The mass ratio of the coating raw material to the sodium-containing cathode material is (0.3 to 3):100; or (b) The mass ratio of the coating raw material to the sodium-containing cathode material is (0.5 to 2):

100.

16. The method according to claim 14 or 15, wherein Satisfies one of the following characteristics: (a) The first sintering temperature T1 and the initial thermal cracking temperature T' of the first hydrophobic polymer material satisfy the following relationship: T1 < T'; or (b) The first sintering temperature T1 is 180°C to 260°C, and the sintering time is 2h to 8h; or (c) The first sintering temperature T1 is 200°C to 250°C, and the sintering time is 4h to 7h.

17. The method according to any one of claims 12 - 16, wherein, The coating raw material includes a second hydrophobic polymer material, and the second hydrophobic polymer material includes polyacrylonitrile.

18. The method according to claim 17, wherein Satisfies one of the following characteristics: (a) The mass ratio of the coating raw material to the sodium-containing cathode material is (0.5 to 10):100; or (b) The mass ratio of the coating raw material to the sodium-containing cathode material is (1 to 5):

100.

19. The method according to claim 17 or 18, wherein Satisfies one of the following characteristics: (a) The first sintering temperature T1 and the initial thermal cracking temperature T” of the second hydrophobic polymer material satisfy the following relationship: T1 > T”; or (b) The first sintering temperature T1 is 350°C to 550°C, and the sintering time is 4h to 12h; or (c) The first sintering temperature T1 is 400°C to 500°C, and the sintering time is 5h to 12h.

20. The method according to any one of claims 12-19, wherein, The sodium-containing cathode material contains a sodium-containing polyanionic compound, and the chemical formula of the sodium-containing polyanionic compound is: Na x R y (PO4) Z (P2O7) k , where 1 ≤ x ≤ 7, 1 ≤ y ≤ 4, 1 ≤ z ≤ 2, 1 ≤ k ≤ 4, and R is at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, or Pb.

21. The method according to claim 20, wherein, The sodium-containing cathode material includes the polyanion-type sodium-containing compound and a carbon-based material modification layer on at least part of its surface; The carbon-based material modification layer includes a first carbon material and a second carbon material; the first carbon material includes at least one of natural graphite powder, artificial graphite powder, carbon black, carbon nanotubes, or graphene, and the second carbon material includes a sintering product of an organic carbon source at 450°C to 550°C.

22. The method according to claim 21, wherein Satisfies one or more of the following characteristics: (a) The organic carbon source includes at least one of sucrose, glucose, citric acid, starch, cyclodextrin, asphalt, or the hydrophobic polymer; (b) The mass ratio of the first carbon material to the polyanion-type sodium-containing compound is (0.5 to 2):100; (c) The mass ratio of the sintering product to the polyanion-type sodium-containing compound is (0.5 to 2):100; (d) The median particle size Dv of the sodium-containing cathode material 50 is 2 μm to 8 μm; (e) The specific surface area BET of the sodium-containing cathode material is 3 m 2 / g to 11 m 2 / g.

23. A positive electrode plate, wherein, Includes the sodium secondary battery cathode material according to any one of claims 1-11 or the sodium secondary battery cathode material prepared by the method according to any one of claims 12-22.

24. A sodium secondary battery, wherein, Includes the positive electrode plate according to claim 23.

25. The sodium secondary battery according to claim 24, wherein, The sodium secondary battery includes a sodium ion secondary battery.

26. The sodium secondary battery according to claim 24, wherein The sodium secondary battery includes a sodium secondary battery without a negative electrode, and the sodium secondary battery without a negative electrode includes a negative electrode sheet, and the sodium secondary battery without a negative electrode satisfies one of the following characteristics: (a) The negative electrode sheet includes a negative electrode current collector; or (b) The negative electrode sheet includes a negative electrode current collector and a conductive layer.

27. The sodium secondary battery according to claim 26, wherein, The negative electrode sheet includes the conductive layer, and the conductive layer satisfies one or more of the following characteristics: (a) The conductive layer is disposed on at least one side of the negative electrode current collector; (b) The conductive layer includes a conductive agent and a binder; (c) The conductive agent includes at least one of graphite, graphene, carbon fiber, carbon black, carbon dots, soft carbon, hard carbon, multi-walled carbon nanotubes or single-walled carbon nanotubes.

28. An electrical device, wherein, Including the sodium secondary battery according to any one of claims 24-27.

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