Sodium secondary battery, positive electrode active material, preparation method of positive electrode active material and electric device

Abstract

The invention provides a sodium secondary battery, a preparation method of a positive electrode active material and a power utilization device. The sodium secondary battery comprises a positive pole piece, the positive pole piece comprises a positive active material, the positive active material comprises a sodium-containing layered oxide, the sodium-containing layered oxide is of an O3 type, a bulk phase of the sodium-containing layered oxide comprises NaxMyOz, M is a transition metal element, x is larger than 0.8 and smaller than or equal to 1, y is larger than or equal to 0.9 and smaller than or equal to 1.1, and z is larger than or equal to 1.8 and smaller than or equal to 2.2.

Description

TECHNICAL FIELD

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

[0002] In recent years, secondary batteries are widely used 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. With the popularization of secondary batteries, higher requirements are put forward for their cycle performance, service life, etc.

[0003] In terms of resources and costs, sodium secondary batteries have greater advantages than lithium secondary batteries, but how to further improve the capacity of sodium secondary batteries is a technical problem that needs to be solved in the art. SUMMARY

[0004] The present application is made in view of the above-mentioned problems, and aims to provide a sodium secondary battery with high capacity.

[0005] The first aspect of the present application provides a sodium secondary battery, which comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises a sodium-containing layered oxide, the sodium-containing layered oxide is of O3 type, and the bulk composition of the sodium-containing layered oxide comprises Na x M y O z , wherein M is a transition metal element, 0.8 < x < 1, 0.9 < y < 1.1, and 1.8 < z < 2.2.

[0006] The O3 type sodium-containing layered oxide bulk composition provided by the embodiments of the present application has a high sodium element ratio, indicating that the sodium-containing layered oxide has a high sodium content in the bulk phase, which is beneficial to the improvement of the capacity of the battery.

[0007] In any embodiment, M comprises one or more of Ni, Cu, Mn, Fe, Mg, Zn, Al, Cr, Ti, V.

[0008] The above-mentioned M element is easy to form a sodium-containing layered oxide, thereby improving the capacity of the sodium secondary battery.

[0009] In any embodiment, the bulk composition of the sodium-containing layered oxide comprises Na x Cu n Fe z Mn i R jO2, wherein n+z+i+j=1, 0

[0010] The copper iron sodium manganate has a moderate true density, and the above material with a high sodium content in the bulk phase can further balance the high energy density and high power density of the sodium secondary battery.

[0011] In any embodiment, the sodium-containing layered oxide has a diffraction angle 2theta of the (003) crystal face diffraction peak of 15.9-16.3° in an X-ray diffraction pattern with Cu as a target material.

[0012] The diffraction angle of the (003) crystal face diffraction peak of the sodium-containing layered oxide in the prior art is usually less than 15.9°, and the (003) crystal face diffraction peak of the sodium-containing layered oxide provided in the embodiments has a larger diffraction angle, indicating that the sodium-containing layered oxide has a relatively high content of bulk sodium, which is beneficial to the improvement of the capacity of the sodium secondary battery.

[0013] The second aspect of the present application also provides a preparation method of a positive electrode active material, including the following steps: obtaining a mixed raw material including a sodium source and an M source, sintering the mixed raw material under a first atmosphere to obtain a first precursor; adding a sodium source to the first precursor to obtain a second precursor, and sintering the second precursor in a second atmosphere to prepare the positive electrode active material, the second atmosphere including a reducing gas, the positive electrode active material including a sodium-containing layered oxide, the sodium-containing layered oxide being O3 type, and the composition of the bulk phase of the sodium-containing layered oxide including Na x M y O z , wherein M is a transition metal element, 0.8

[0014] Based on the phase diagram of the sodium source constructed according to the phase equilibrium theory, it can be known from the phase diagram that when the sintering gas atmosphere includes a reducing gas, the phase equilibrium of the sodium source can be adjusted from a low sodium vapor partial pressure phase region to a higher sodium vapor partial pressure phase region due to the reduction of the oxygen partial pressure in the gas atmosphere, thereby reducing the oxygen partial pressure of the sodium source and increasing the sodium vapor partial pressure of the sodium source, so that the sodium vapor partial pressure of the sodium source is greater than or close to the sodium vapor partial pressure of the product, which is beneficial to the improvement of the initial sodium content in the bulk phase of the sodium-containing layered oxide, thereby improving the capacity of the secondary battery.

[0015] In any embodiment, the first atmosphere includes at least one of air and oxygen.

[0016] The formation of oxide structures in a first atmosphere including air and / or oxygen facilitates the further insertion of sodium into the bulk phase in a reducing atmosphere later.

[0017] In any embodiment, the second atmosphere further includes an inert gas, the reducing gas including one or more of CO and H2, the inert gas including one or more of nitrogen, helium, and argon, and the partial pressure of the reducing gas in the second atmosphere is 2 kPa-10 kPa.

[0018] Controlling the partial pressure of the reducing gas in the second atmosphere is beneficial for sodium to enter the bulk phase during the second sintering process, and also allows the prepared sodium-containing layered oxide to retain the O3 phase.

[0019] In any embodiment, the M source includes one or more metal oxides, metal carbonates, metal acetates, and metal hydroxides containing the M element; the M element includes one or more of Ni, Cu, Mn, Fe, Mg, Zn, Al, Cr, Ti, and V.

[0020] In any embodiment, the sodium source includes one or more of sodium carbonate, sodium acetate, and sodium hydroxide.

[0021] In any embodiment, the molar ratio of sodium to M in the mixed raw materials is 0.6-0.8.

[0022] When the molar ratio of sodium to M in the mixed raw materials is within the above range, it helps sodium to further enter the bulk phase during sintering in the second atmosphere, thereby increasing the sodium content in the sodium-containing layered oxide.

[0023] In any embodiment, during the preparation of the positive electrode active material, the molar ratio of sodium element in the sodium source added to the first precursor to M element in the mixed raw materials is 0.25-0.45.

[0024] When the molar ratio of sodium in the sodium source added to the first precursor to M in the mixed raw materials is within the above-mentioned range, it is beneficial to increase the sodium partial pressure and generate O3-type sodium-containing layered oxides.

[0025] In any embodiment, the ratio of the total molar amount of sodium in the sodium source to the total molar amount of M in the M source is greater than 1.

[0026] A ratio greater than 1 between the total molar amount of sodium in the input sodium source and the total molar amount of M in the input M source can provide sufficient sodium supply, reduce the impact of sodium loss on the sodium content in the bulk phase, and increase the sodium content in the O3-type sodium-containing layered oxide bulk phase.

[0027] In any embodiment, the step of sintering the mixed raw materials under a first atmosphere to obtain the first precursor includes: sintering the mixed raw materials at a temperature of 800°C-865°C for 15-18 hours under a first atmosphere to obtain the first precursor.

[0028] In any embodiment, the step of adding a sodium source to the first precursor to obtain a second precursor, sintering the second precursor in a second atmosphere, and preparing the positive electrode active material includes: introducing an inert gas into the first atmosphere and then adding a carbon source, heating to obtain a second atmosphere containing a reducing gas and an inert gas.

[0029] In any embodiment, the molar ratio of carbon element in the carbon source to M element in the first precursor is 1%-5%, and can be selected as 1%-2%.

[0030] In any embodiment, the step of adding a sodium source to the first precursor to obtain a second precursor, sintering the second precursor in a second atmosphere, and preparing the positive electrode active material includes: continuously introducing a mixed gas comprising a reducing gas and an inert gas into a reaction vessel in which the second precursor is placed, and sintering the second precursor, wherein the inlet flow rate of the mixed gas is 200 mL / min to 500 mL / min.

[0031] A gas flow rate within the above-mentioned range is beneficial for reducing sodium loss in the gas phase, maintaining sodium partial pressure, and increasing sodium content in the bulk phase of the positive electrode active material.

[0032] The third aspect of this application provides an electrical device, including the secondary battery provided in the first aspect of this application. Attached Figure Description

[0033] Figure 1 This is a schematic phase diagram of sodium carbonate in the preparation of the positive electrode active material according to one embodiment of this application;

[0034] Figure 2 This is a schematic diagram of the X-ray diffraction pattern of the positive electrode active material in one embodiment and comparative example of this application;

[0035] Figure 3 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0036] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0037] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application;

[0038] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0039] Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown;

[0040] Figure 8 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.

[0041] Explanation of reference numerals in the attached figures:

[0042] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0043] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, positive electrode active material, preparation method thereof, and electrical 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.

[0044] 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.

[0045] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0046] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0047] 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.

[0048] 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.

[0049] 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).

[0050] Sodium-containing layered metal oxides typically include the O3 type and the P2 type. The O3 type refers to sodium-containing layered oxides containing sodium ions and O. 2- It is octahedral coordination, 3 represents the number of different positions occupied by transition metal ions, and P2 type refers to sodium ions and O in sodium-containing layered oxides. 2- The formation of triangular prism coordination is achieved. Compared to P2-type sodium-containing layered oxides, O3-type sodium-containing layered oxides often have a higher initial Na content, thus exhibiting higher capacity and promising application prospects in high-energy-density batteries. However, in existing technologies, some sodium elements in O3-type sodium-containing layered oxides remain on the surface during preparation, making it difficult to integrate into the bulk phase and hindering further capacity improvements in sodium secondary batteries.

[0051] Based on this, this application proposes a sodium secondary battery, which includes a positive electrode sheet, the positive electrode sheet including a positive electrode active material, the positive electrode active material including a sodium-containing layered oxide, the sodium-containing layered oxide being of the O3 type, and the bulk phase composition of the sodium-containing layered oxide including Na. x M y Oz , where M is a transition metal element, 0.8 < x ≤ 1, 0.9 ≤ y ≤ 1.1, 1.8 ≤ z ≤ 2.2.

[0052] In this article, "sodium secondary battery" refers to a secondary battery that uses sodium as the active ion, including sodium-ion batteries and sodium metal batteries. It should be understood that sodium metal batteries also include batteries without a negative electrode.

[0053] In this paper, the term "layered oxide" refers to an oxide material having a layered structure, consisting of parallel stacked layers composed of different ions or atoms.

[0054] Transition metals are a series of metallic elements in the d-block of the periodic table, also known as transition elements. These elements include those from Group 3 to Group 12. Transition metals have unfilled valence d orbitals, which makes their properties significantly different from those of other elements.

[0055] In some implementations, when the secondary battery is at 0% SOC, the sodium-containing layered oxide is of type O3.

[0056] In some implementations, x can be selected as 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, or any value range between two of these; y can be selected as 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.05, 1.1, or any value range between two of these; z can be selected as 1.8, 1.9, 2.0, 2.1, 2.2, or any value range between two of these.

[0057] The crystal structure of the sodium-containing layered oxide bulk phase can be tested using any method known in the art. As an example, the X-ray diffraction pattern of the sample is determined using an X-ray diffractometer, and its crystal structure is determined by comparison with a standard pattern. Specifically, a Bruker D8 X-ray diffractometer is used with Cu as the target material, a scanning rate of 5° / min, and a scanning range of 5°–90°.

[0058] The composition of the sodium-containing layered oxide bulk phase can be tested using any method known in the art. As an example, the crystal structure of the sample was determined using X-ray diffraction. The sodium-containing layered oxide was then surface-cleaned with 0.15 mol / L KOH solution to remove residual sodium, dried, and its composition was determined using a Thermo Fisher ICP-7400 inductively coupled plasma atomic emission spectrometer to identify the type of element M and the molar ratio between Na and M.

[0059] The O3-type sodium-containing layered oxide bulk composition provided in this application embodiment has a high sodium content, indicating that the sodium-containing layered oxide has a high sodium content in the bulk phase, which is beneficial to improving battery capacity.

[0060] In some embodiments, M includes one or more of Ni, Cu, Mn, Fe, Mg, Zn, Al, Cr, Ti, and V.

[0061] The aforementioned element M readily forms sodium-containing layered oxides, thereby improving the capacity and cycle stability of sodium secondary batteries.

[0062] In some embodiments, the composition of the sodium-containing layered oxide bulk phase includes Na. x Cu n Fe z Mn i R j O2, where n+z+i+j=1, 0<n<1, 0<z<1, 0<i<1, 0≤j<1, and R includes one or more of Li, Ni, Mg, Zn, Al, Cr, Ti, V, and Sb.

[0063] In some implementations, n can be selected as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any value between two of these; z can be selected as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any value between two of these; i can be selected as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any value between two of these; and j can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any value between two of these.

[0064] Sodium copper iron manganese oxide has a moderate true density, and the above-mentioned material with a high sodium content in the bulk phase can further balance the high energy density and high power density of sodium secondary batteries.

[0065] In some embodiments, the diffraction angle 2θ of the (003) crystal plane diffraction peak of the sodium-containing layered oxide in the X-ray diffraction pattern with Cu as the target material is 15.9°-16.3°, and can be optionally 16.0°-16.2°.

[0066] In X-ray diffraction patterns of sodium-containing layered oxides using Cu as the target, the diffraction angle 2θ of the (003) crystal plane diffraction peak can be obtained using X-ray diffraction (XRD). As an example, a Bruker D8 X-ray diffractometer was used with Cu as the target, a scan rate of 5° / min, and a scan range of 5°–90°. The diffraction angle 2θ of the (003) crystal plane diffraction peak in the X-ray diffraction pattern of sodium-containing layered oxides using Cu as the target reflects the interlayer spacing of the metal layers. According to the Scherrer equation, a larger diffraction angle indicates a smaller interlayer spacing between the metal layers. To maintain crystal structure stability, the interlayer spacing decreases with increasing bulk sodium content in the sodium-containing layered oxide. In other words, the diffraction angle 2θ of the (003) crystal plane diffraction peak can be used to characterize the sodium content of the bulk phase in sodium-containing layered oxides. The larger the diffraction angle 2θ of the (003) crystal plane diffraction peak, the higher the sodium content of the bulk phase in the sodium-containing layered oxides.

[0067] In some embodiments, the diffraction angle 2θ of the (003) crystal plane diffraction peak in the X-ray diffraction pattern of the sodium-containing layered oxide with Cu as the target material can be selected as 15.9°, 16.0°, 16.1°, 16.2°, 16.3° or any value range between the two.

[0068] In the prior art, the diffraction angle of the diffraction peak of the sodium-containing layered oxide (003) crystal plane is often less than 15.9°. The diffraction peak of the sodium-containing layered oxide (003) crystal plane provided in the embodiments of this application has a larger diffraction angle, indicating that the sodium-containing layered oxide has a relatively high content of bulk sodium, which is beneficial to improving the capacity of sodium secondary batteries.

[0069] The second aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps: Step S101, obtaining a mixed raw material including a sodium source and an M source, and sintering the mixed raw material under a first atmosphere to obtain a first precursor; Step S102, adding a sodium source to the first precursor to obtain a second precursor, and sintering the second precursor in a second atmosphere to prepare the positive electrode active material, wherein the second atmosphere includes a reducing gas; the positive electrode active material comprises a sodium-containing layered oxide, wherein the sodium-containing layered oxide is of the O3 type, and the bulk phase composition of the sodium-containing layered oxide includes Na. x M y O z , where M is a transition metal element, 0.8 < x ≤ 1, 0.9 ≤ y ≤ 1.1, 1.8 ≤ z ≤ 2.2.

[0070] In this paper, the term "reducing gas" refers to a gas that can lose electrons and be oxidized during combustion or a chemical reaction. It should be noted that reducing gases can be introduced during the preparation process or synthesized in situ.

[0071] A phase diagram of the sodium source was constructed based on phase equilibrium theory. The phase diagram shows that when the sintering gas atmosphere includes reducing gases, the decrease in oxygen partial pressure in the gas atmosphere can adjust the phase equilibrium of the sodium source from a low sodium vapor partial pressure phase region to a higher sodium vapor partial pressure phase region. This reduces the oxygen partial pressure of the sodium source and increases the sodium vapor partial pressure of the sodium source, making the sodium vapor partial pressure of the sodium source greater than or close to the sodium vapor partial pressure of the product. This is beneficial to increasing the initial sodium content in the sodium-containing layered oxide phase, thereby improving the capacity of the secondary battery.

[0072] In this paper, the term "phase diagram" refers to a method for studying multiphase equilibrium by graphically representing the relationship between temperature, pressure, and the composition of each phase in a multiphase equilibrium.

[0073] In this paper, the term "phase equilibrium" refers to the limiting state reached by the phase changes in a multiphase system. At this point, macroscopically, no matter is transferred between phases, but microscopically, matter in opposite directions is still transferred between phases at the same speed, so the net transfer rate is zero.

[0074] An example of phase diagrams using sodium carbonate as the sodium source is shown, such as... Figure 1 As shown, at a specific temperature, when the gas atmosphere does not include reducing gases, the equilibrium phase region of sodium carbonate falls in region F, which is a low sodium vapor partial pressure phase region; when the gas atmosphere includes reducing gases, the equilibrium phase region of sodium carbonate falls in region B, which is a high sodium vapor partial pressure phase region. In a gas atmosphere including reducing gases, the phase equilibrium of the sodium source shifts from a low sodium vapor partial pressure phase region to a higher sodium vapor partial pressure phase region, which is beneficial for increasing the sodium content entering the product.

[0075] The preparation method of this application does not require the introduction of other materials, has low cost, simple process and is easy to realize industrial production, providing a new method and new ideas for the preparation of high-capacity sodium-containing positive electrode active materials.

[0076] In some embodiments, the first atmosphere includes at least one of air and oxygen.

[0077] The formation of oxide structures in a first atmosphere including air and / or oxygen facilitates the further insertion of sodium into the bulk phase in a reducing atmosphere later.

[0078] In some embodiments, the second atmosphere further includes an inert gas, the reducing gas including one or more of CO and H2, the inert gas including one or more of nitrogen, helium, and argon, and the partial pressure of the reducing gas in the second atmosphere is 2 kPa-10 kPa.

[0079] In this paper, the term "partial pressure" refers to the pressure of a gas in a gas mixture if all other gases except a certain gas are removed from the mixture, while keeping the system volume and temperature constant.

[0080] In some embodiments, the partial pressure of the reducing gas in the gas atmosphere can be selected as 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa, 10 kPa or any value between the two.

[0081] Controlling the partial pressure of the reducing gas in the second atmosphere is beneficial for sodium to enter the bulk phase during the second sintering process, and also allows the prepared sodium-containing layered oxide to retain the O3 phase.

[0082] In some embodiments, the M source includes one or more metal oxides, metal carbonates, metal acetates, and metal hydroxides containing the M element; the M element includes one or more of Ni, Cu, Mn, Fe, Mg, Zn, Al, Cr, Ti, and V.

[0083] In some embodiments, the sodium source includes one or more of sodium carbonate, sodium acetate, and sodium hydroxide.

[0084] In some embodiments, the molar ratio of sodium to M in the mixed raw materials is 0.6-0.8.

[0085] In some embodiments, the molar ratio of sodium to M in the mixed raw materials can be selected as 0.6, 0.7, 0.8 or any value between the two.

[0086] When the molar ratio of sodium to M in the mixed raw materials is within the above range, it helps sodium to further enter the bulk phase during sintering in the second atmosphere, thereby increasing the sodium content in the sodium-containing layered oxide.

[0087] In some embodiments, during the preparation of the positive electrode active material, the molar ratio of sodium in the sodium source added to the first precursor to M in the mixed raw materials is 0.25-0.45.

[0088] In some embodiments, during the preparation of the positive electrode active material, the molar ratio of sodium element in the sodium source added to the first precursor to M element in the mixed raw materials can be selected as 0.25, 0.3, 0.35, 0.4, 0.45 or any value range between the two.

[0089] When the molar ratio of sodium in the sodium source added to the first precursor to M in the mixed raw materials is within the above-mentioned range, it is beneficial to increase the sodium partial pressure and generate O3-type sodium-containing layered oxides.

[0090] In some implementations, the ratio of the total molar amount of sodium in the sodium source to the total molar amount of M in the M source is greater than 1.

[0091] A ratio greater than 1 between the total molar amount of sodium in the input sodium source and the total molar amount of M in the input M source can provide sufficient sodium supply, reduce the impact of sodium loss on the sodium content in the bulk phase, and increase the sodium content in the O3-type sodium-containing layered oxide bulk phase.

[0092] In some embodiments, sintering the mixed raw materials under a first atmosphere to obtain a first precursor includes: sintering the mixed raw materials at a temperature of 800°C-865°C for 15-18 hours under a first atmosphere to obtain the first precursor.

[0093] In some embodiments, the insulation temperature under the first atmosphere can be selected as 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 865°C or any range between the two.

[0094] In some implementations, the holding time under the first atmosphere can be selected as 15 hours, 16 hours, 17 hours, 18 hours, or any value range between the two.

[0095] In some embodiments, adding a sodium source to the first precursor to obtain a second precursor, sintering the second precursor in a second atmosphere, and preparing the positive electrode active material includes: introducing an inert gas into the first atmosphere and then adding a carbon source, heating to obtain a second atmosphere containing a reducing gas and an inert gas.

[0096] Reducing gases can be produced by reacting a carbon source with the residual gas in the first atmosphere at high temperature.

[0097] In some embodiments, the molar ratio of carbon in the carbon source to M in the first precursor is 1%-5%, optionally 1%-2%.

[0098] In some embodiments, the molar ratio of carbon in the carbon source to M in the first precursor can be selected as 1%, 2%, 3%, 4%, 5%, or any value range between the two.

[0099] In some embodiments, the step of adding a sodium source to the first precursor to obtain a second precursor, sintering the second precursor in a second atmosphere, and preparing the positive electrode active material includes: continuously introducing a mixed gas comprising a reducing gas and an inert gas into a reaction vessel in which the second precursor is placed, and sintering the second precursor, wherein the inlet flow rate of the mixed gas is 200 mL / min to 500 mL / min.

[0100] In this paper, the term "flow rate" refers to the volume of fluid flowing per unit time.

[0101] In some embodiments, the inlet flow rate of the mixed gas can be selected as 200 mL / min, 300 mL / min, 400 mL / min, 500 mL / min or any value range between the two.

[0102] A gas flow rate within the above-mentioned range is beneficial for reducing sodium loss in the gas phase, maintaining sodium partial pressure, and increasing sodium content in the bulk phase of the positive electrode active material.

[0103] [Positive electrode plate]

[0104] A positive electrode typically includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive active material in some embodiments or a positive active material prepared by the preparation method in some embodiments.

[0105] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0106] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0107] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0108] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0110] [Negative electrode plate]

[0111] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0112] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0113] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil or aluminum 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, aluminum, aluminum 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.).

[0114] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an 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, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0115] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from 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), and carboxymethyl chitosan (CMCS).

[0116] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0117] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0118] In some implementations, the sodium secondary battery is a negative electrode-less battery.

[0119] A negative electrodeless battery is a battery in which a negative electrode active material layer is not actively placed on the negative electrode side during the battery manufacturing process. For example, a metal or carbonaceous active material layer is not formed at the negative electrode through coating or deposition processes to create a negative electrode film. During the first charge, active ions gain electrons on the anode side and deposit as a metallic phase on the surface of the current collector. During discharge, the metal can transform back into active ions and return to the positive electrode, achieving cyclic charging and discharging. Therefore, a negative electrodeless battery is also a type of metal battery. Compared to other rechargeable batteries, negative electrodeless batteries can achieve higher energy density because they do not have a pre-placed negative electrode film layer.

[0120] Although a negative electrodeless secondary battery does not require the formation of a negative electrode film layer by coating or deposition of a metal or carbonaceous active material layer, it often has an undercoat containing conductive material to induce deposition.

[0121] [Electrolytes]

[0122] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0123] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0124] In some embodiments, the electrolyte includes an electrolyte salt selected from at least one of NaPF6, NaBF4, NaN(SO2F)2 (NaFSI), NaClO4, NaAsF6, NaB(C2O4)2 (NaBOB), NaBF2(C2O4) (NaDFOB), NaN(SO2RF)2, and NaN(SO2F) (SO2RF), wherein RF represents C b F 2b+1b is an integer between 1 and 10, and can be an integer between 1 and 3.

[0125] In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaN(SO2F)2, NaN(CF3SO2)2, NaB(C2O4)2, and NaBF2(C2O4). In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaN(SO2RF)2, and NaBF2(C2O4). In some embodiments, RF is -CF3, -C2F5, or -CF2CF2CF3.

[0126] In some embodiments, the electrolyte includes a solvent, which includes at least one selected from chain carbonates, chain carboxylic esters, cyclic carbonates, ether solvents, sulfone solvents, and nitrile solvents. In some embodiments, the chain carbonate includes at least one selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, ethyl propyl carbonate, dipropyl carbonate, and dibutyl carbonate. In some embodiments, the chain carbonate includes at least one selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and methyl propyl carbonate (MPC). In some embodiments, the chain carboxylic ester includes at least one selected from methyl formate (MF), ethyl formate (EF), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), ethyl butyrate (EB), methyl acetate (MA), ethyl acetate (EA), and propyl acetate (PA). In some embodiments, the chain carboxylic ester includes at least one selected from methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl acetate (MA), ethyl acetate (EA), and propyl acetate (PA). In some embodiments, the ether solvent includes at least one selected from dioxolane (DOL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF), tetrahydropyran (THP), 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (DG), 1,2-diethoxyethane, and 1,2-dibutoxyethane.

[0127] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0128] [Isolation membrane]

[0129] 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.

[0130] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. 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.

[0131] [Rechargeable Battery]

[0132] In one embodiment of this application, a secondary battery is provided, including an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode, a separator, and a negative electrode in any embodiment.

[0133] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0134] 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.

[0135] 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.

[0136] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 The example shown is a square-structured secondary battery 5. Optionally, the secondary battery is a lithium-ion battery or a sodium-ion battery.

[0137] In some implementations, refer to Figure 4 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. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​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.

[0138] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module 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 module.

[0139] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple secondary batteries 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 secondary batteries 5 can be fixed in place using fasteners.

[0140] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0141] 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.

[0142] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0143] [Electrical appliances]

[0144] 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.

[0145] The electrical device includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is 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.

[0146] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0147] Figure 8 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.

[0148] 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.

[0149] Example

[0150] 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.

[0151] I. Preparation Method

[0152] Example 1

[0153] 100g of Na₂CO₃, Mn₂O₃, CuO, and Fe₂O₃ were mixed in a molar ratio of 0.7:0.55:0.3:0.3, and a precursor was synthesized using a solid-state method. The mixture was placed in a gas rotary furnace and heated to 850℃ at a heating rate of 5°C / min, and held at that temperature for 15 hours to synthesize the first precursor in an air atmosphere. Sodium source was then added to the first precursor, with a molar ratio of 0.35:0.7 to the initial sodium source. Simultaneously, a mixed gas consisting of reducing gases CO and nitrogen was introduced into the gas rotary furnace. The partial pressure of CO in the mixed gas was 0.05 Bar, and the gas flow rate was 500 mL / min. Sintering was carried out for 6 hours to prepare the positive electrode active material.

[0154] Comparative Example 1

[0155] 100g of Na₂CO₃, Mn₂O₃, CuO, and Fe₂O₃ were mixed in a ratio of 1.05:0.55:0.3:0.3, and a precursor was synthesized by solid-state sintering. The precursor was placed in a gas rotary furnace and heated to 850℃ at a heating rate of 5°C / min and held at that temperature for 21 hours. Air was then introduced into the gas rotary furnace at a flow rate of 500mL / min to prepare the positive electrode active material.

[0156] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0157] Test results show that the positive electrode active material prepared in Example 1 is Na0.95 Mn 0.55 Cu 0.15 Fe 0.3 The diffraction angle 2θ of the O2,(003) crystal plane diffraction peak is 16.05°, and the configuration is O3 type. The positive electrode active material prepared in Comparative Example 1 is Na. 0.73 Mn 0.55 Cu 0.15 Fe 0.3 The diffraction angle 2θ of the diffraction peak corresponding to the interlayer spacing of O2,(003) crystal planes is 15.83°.

[0158] 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 sodium secondary battery, characterized in that, The sodium secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, the positive electrode active material includes a sodium-containing layered oxide, the sodium-containing layered oxide is of the O3 type, and the bulk composition of the sodium-containing layered oxide includes Na. x M y O z , where M is a transition metal element, 0.8 < x ≤ 1, 0.9 ≤ y ≤ 1.1, 1.8 ≤ z ≤ 2.

2.

2. The sodium secondary battery according to claim 1, characterized in that, M includes one or more of Ni, Cu, Mn, Fe, Mg, Zn, Al, Cr, Ti, and V.

3. The sodium secondary battery according to claim 1 or 2, characterized in that, The composition of the sodium-containing layered oxide bulk phase includes Na x Cu n Fe z Mn i R j O2, Wherein, n+z+i+j=1, 0<n<1, 0<z<1, 0<i<1, 0≤j<1, and R includes one or more of Li, Ni, Mg, Zn, Al, Cr, Ti, V, and Sb.

4. The sodium secondary battery according to any one of claims 1 to 3, characterized in that, In the X-ray diffraction pattern of the sodium-containing layered oxide with Cu as the target material, the diffraction angle 2θ of the (003) crystal plane diffraction peak is 15.9°-16.3°.

5. A method for preparing a positive electrode active material, characterized in that, Includes the following steps: A mixed raw material comprising a sodium source and an M source is obtained, and the mixed raw material is sintered under a first atmosphere to obtain a first precursor; A second precursor is obtained by adding a sodium source to the first precursor, and the second precursor is sintered in a second atmosphere to prepare the positive electrode active material. The second atmosphere includes a reducing gas. The positive electrode active material includes a sodium-containing layered oxide, which is of the O3 type, and the bulk phase of the sodium-containing layered oxide includes Na. x M y O z , where M is a transition metal element, 0.8 < x ≤ 1, 0.9 ≤ y ≤ 1.1, 1.8 ≤ z ≤ 2.

2.

6. The preparation method according to claim 5, characterized in that, The first atmosphere includes at least one of air and oxygen.

7. The preparation method according to claim 5 or 6, characterized in that, The second atmosphere also includes an inert gas, wherein the reducing gas includes one or more of CO and H2, and the inert gas includes one or more of nitrogen, helium, and argon. The partial pressure of the reducing gas in the second atmosphere is 2 kPa-10 kPa.

8. The preparation method according to any one of claims 5 to 7, characterized in that, The M source includes one or more metal oxides, metal carbonates, metal acetates, and metal hydroxides containing the M element; the M element includes one or more of Ni, Cu, Mn, Fe, Mg, Zn, Al, Cr, Ti, and V.

9. The preparation method according to any one of claims 5 to 8, characterized in that, The sodium source includes one or more of sodium carbonate, sodium acetate, and sodium hydroxide.

10. The preparation method according to any one of claims 5 to 9, characterized in that, In the mixed raw materials, the molar ratio of sodium to M is 0.6-0.

8.

11. The preparation method according to any one of claims 5 to 10, characterized in that, In the preparation process of the positive electrode active material, the molar ratio of sodium element in the sodium source added to the first precursor to M element in the mixed raw materials is 0.25-0.

45.

12. The preparation method according to any one of claims 5 to 11, characterized in that, The ratio of the total molar amount of sodium in the input sodium source to the total molar amount of M in the input M source is greater than 1.

13. The preparation method according to any one of claims 5 to 12, characterized in that, The sintering of the mixed raw materials under a first atmosphere to obtain the first precursor includes: The mixed raw materials were sintered at 800℃-865℃ for 15-18 hours under a first atmosphere to obtain the first precursor.

14. The preparation method according to any one of claims 5 to 13, characterized in that, The step of adding a sodium source to the first precursor to obtain a second precursor, and sintering the second precursor in a second atmosphere to prepare the positive electrode active material includes: After introducing an inert gas into the first atmosphere, a carbon source is introduced and heated to obtain a second atmosphere containing reducing gas and inert gas.

15. The preparation method according to claim 14, characterized in that, The molar ratio of carbon element in the carbon source to M element in the first precursor is 1%-5%, and can be selected as 1%-2%.

16. The preparation method according to any one of claims 5 to 15, characterized in that, The step of adding a sodium source to the first precursor to obtain a second precursor, and sintering the second precursor in a second atmosphere to prepare the positive electrode active material includes: A mixture of reducing gas and inert gas is continuously introduced into a reaction vessel containing the second precursor, and the second precursor is sintered. The inlet flow rate of the mixed gas is 200 mL / min to 500 mL / min.

17. An electrical device, characterized in that, The electrical device includes the secondary battery as described in claims 1 to 4.

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