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

Abstract

The present application provides a sodium secondary battery, a positive electrode active material and a preparation method therefor, and an electric device. The sodium secondary battery 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 O3-type, and the composition of a sodium-containing layered oxide phase comprises NaxMyOz, wherein M is a transition metal element, 0.8<x≤1, 0.9≤y≤1.1, and 1.8≤z≤2.2.

Description

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

[0001] Cross-reference to related applications

[0002] This application is based on the Chinese Patent Application No. 202411087201.X, filed on August 8, 2024, and titled “Sodium secondary battery, positive electrode active material, preparation method thereof and electric device”, which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of secondary batteries, and in particular to a sodium secondary battery, a positive electrode active material, a preparation method thereof and an electric device. BACKGROUND

[0004] In recent years, secondary batteries are widely used in energy storage power systems such as hydroelectric, 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.

[0005] 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

[0006] The present application is made in view of the above-mentioned problems, and aims to provide a sodium secondary battery with high capacity.

[0007] The first aspect of the present application provides a sodium secondary battery, the sodium secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising a sodium-containing layered oxide, the sodium-containing layered oxide being of O3 type, and a bulk composition of the sodium-containing layered oxide comprising 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.

[0008] The O3 type sodium-containing layered oxide bulk composition provided by the embodiments of the present application has a high proportion of sodium element, 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.

[0009] In any embodiment, M comprises one or more of Ni, Cu, Mn, Fe, Mg, Zn, Al, Cr, Ti, V.

[0010] The above-mentioned M element is easy to form a sodium-containing layered oxide, thereby improving the capacity of the sodium secondary battery.

[0011] In any embodiment, 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

[0012] The copper iron sodium manganate 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 the sodium secondary battery.

[0013] In any embodiment, the sodium-containing layered oxide has a diffraction angle 2θ of the (003) crystal face diffraction peak of 15.9°-16.3° in the X-ray diffraction spectrum with Cu as the target material.

[0014] The diffraction angle of the (003) crystal face diffraction peak of the sodium-containing layered oxide in the prior art is often 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 phase sodium, which is beneficial to the improvement of the capacity of the sodium secondary battery.

[0015] The second aspect of the present application further provides a preparation method of a positive electrode active material, including the following steps: obtaining mixed raw materials including a sodium source and an M source, sintering the mixed raw materials 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, and the positive electrode active material including a sodium-containing layered oxide, the sodium-containing layered oxide being of 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

[0016] 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.

[0017] In any embodiment, the first atmosphere comprises at least one of air, oxygen.

[0018] The oxide structure is first formed in the first atmosphere comprising air and / or oxygen, which is beneficial for the further insertion of sodium element into the bulk phase in the later sintering under the reducing atmosphere.

[0019] In any embodiment, the second atmosphere further comprises an inert gas, the reducing gas comprises one or more of CO, H2, the inert gas comprises one or more of nitrogen, helium, argon, and the partial pressure of the reducing gas in the second atmosphere is 2-10 kPa.

[0020] Controlling the partial pressure of the reducing gas in the second atmosphere is beneficial for the insertion of sodium element into the bulk phase in the second sintering, and enables the prepared sodium-containing layered oxide to maintain O3 phase.

[0021] In any embodiment, the M source comprises one or more of metal oxide, metal carbonate, metal acetate, metal hydroxide containing M element; the M element comprises one or more of Ni, Cu, Mn, Fe, Mg, Zn, Al, Cr, Ti, V.

[0022] In any embodiment, the sodium source comprises one or more of sodium carbonate, sodium acetate, sodium hydroxide.

[0023] In any embodiment, in the mixed raw material, the molar ratio of sodium element to M element is 0.6-0.8.

[0024] The molar ratio of sodium element to M element in the mixed raw material within the above range is beneficial for the further insertion of sodium into the bulk phase in the sintering under the second atmosphere, and improves the sodium content in the sodium-containing layered oxide.

[0025] In any embodiment, in the preparation of the positive active material, the molar ratio of sodium element in the sodium source put into the first precursor to M element in the mixed raw material is 0.25-0.45.

[0026] The molar ratio of sodium element in the sodium source put into the first precursor to M element in the mixed raw material within the above range is beneficial for improving the sodium partial pressure and generating O3-type sodium-containing layered oxide.

[0027] In any embodiment, the ratio of the total molar amount of sodium element in the sodium source put into to the total molar amount of M element in the M source put into is greater than 1.

[0028] The ratio of the total molar amount of sodium element in the sodium source put into to the total molar amount of M element in the M source put into greater than 1 can provide sufficient sodium source supply, reduce the impact of sodium loss on the sodium content in the bulk phase, and improve the sodium content in the O3-type sodium-containing layered oxide bulk phase.

[0029] In any embodiment, the sintering of the mixed raw materials in the first atmosphere to obtain the first precursor includes: sintering the mixed raw materials at a temperature of 800-865°C for 15-18 hours in the first atmosphere to obtain the first precursor.

[0030] In any embodiment, the preparation of the positive electrode active material by adding a sodium source to the first precursor to obtain a second precursor and sintering the second precursor in a second atmosphere includes: after the inert gas is introduced in the first atmosphere, introducing a carbon source, and heating to obtain a second atmosphere containing a reducing gas and an inert gas.

[0031] In any embodiment, the molar ratio of carbon elements in the carbon source to M elements in the first precursor is 1%-5%, and optionally 1%-2%.

[0032] In any embodiment, the preparation of the positive electrode active material by adding a sodium source to the first precursor to obtain a second precursor and sintering the second precursor in a second atmosphere includes: continuously introducing a mixed gas containing a reducing gas and an inert gas into a reaction container in which the second precursor is placed, and sintering the second precursor, and the flow rate of the mixed gas is 200-500 mL / min.

[0033] The flow rate of the mixed gas in the above range is beneficial to reduce the loss of sodium in the gas phase, maintain the sodium partial pressure, and increase the sodium content in the bulk phase of the positive electrode active material.

[0034] The third aspect of the present application provides a power consumption device comprising the secondary battery of the first aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0035] FIG. 1 is a phase diagram of sodium carbonate in the preparation of the positive electrode active material according to an embodiment of the present application;

[0036] FIG. 2 is an X-ray diffraction pattern of the positive electrode active material in the example and the comparative example of the present application;

[0037] FIG. 3 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0038] FIG. 4 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG. 3;

[0039] FIG. 5 is a schematic diagram of a battery module according to an embodiment of the present application;

[0040] FIG. 6 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0041] FIG. 7 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 6;

[0042] FIG. 8 is a schematic diagram of a power consumption device using the secondary battery as a power source according to an embodiment of the present application.

[0043] Reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 top cap assembly. DETAILED DESCRIPTION

[0044] Hereinafter, specific embodiments of the secondary battery, the positive active material, the method of manufacturing the same, and the electric device according to the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed descriptions are omitted. For example, there will be cases where detailed descriptions of matters known well to those skilled in the art, repetitive descriptions of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided to allow those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0045] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., 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 particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing each and every numerical value that is contained within the range, wherein a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand manner of describing those numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0047] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0048] If not specified otherwise, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method further comprising step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0049] If not specified otherwise, the terms "comprising" and "including" mentioned in the present application mean open-ended, and can also mean closed-ended. For example, the terms "comprising" and "including" can mean that other components not listed can also be included, or can mean that only the listed components are included.

[0050] If not specified otherwise, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": 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).

[0051] The sodium-containing layered metal oxide generally includes O3 type and P2 type, the O3 type refers to sodium ions and O 2- is octahedral coordination, 3 is the number of different positions occupied by transition metal ions, and the P2 type refers to sodium ions and O 2- form a trigonal prism coordination. Compared with the P2 type sodium-containing layered oxide, the O3 type sodium-containing layered oxide often has a higher initial Na content, and thus has a higher capacity, and has a good application prospect in high energy density batteries. However, in the prior art, part of the sodium elements in the O3 type sodium-containing layered oxide remains on the surface during the preparation process, and it is difficult to enter the bulk phase, so that the capacity of the sodium secondary battery cannot be further improved.

[0052] Based on this, the present application provides a sodium secondary battery, the sodium secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising a sodium-containing layered oxide, the sodium-containing layered oxide being of O3 type, and the composition of the bulk phase of the sodium-containing layered oxide comprising 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.

[0053] In the present disclosure, the term "sodium secondary battery" refers to a secondary battery with sodium as the active ion, including sodium-ion batteries and sodium-metal batteries. It should be understood that sodium-metal batteries also include anode-free batteries.

[0054] In the present disclosure, the term "layered oxide" refers to an oxide material with a layered structure, composed of parallel stacked layers of different ions or atoms.

[0055] Transition metal elements are a series of metal elements in the d-block of the periodic table, also known as transition elements. These elements include elements from group 3 to group 12, and transition metal elements have an uncompleted valence d orbital, which makes their properties significantly different from other elements.

[0056] In some embodiments, the sodium-containing layered oxide is in the O3 type when the secondary battery is at 0% SOC.

[0057] In some embodiments, x can be selected from 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 numerical range between any two of them; y can be selected from 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 numerical range between any two of them; z can be selected from 1.8, 1.9, 2.0, 2.1, 2.2, or any numerical range between any two of them.

[0058] The crystal structure of the sodium-containing layered oxide phase can be tested by any method known in the art. As an example, the X-ray diffraction pattern of the sample is determined by an X-ray diffractometer, and the crystal structure is obtained by comparing with the standard pattern. Specifically, a Bruker D8 AX-ray diffractometer is used, with Cu as the target, a scanning rate of 5° / min, and a scanning range of 5°-90°.

[0059] The composition of the sodium-containing layered oxide phase can be tested by any method known in the art. As an example, the crystal structure of the sample is determined by an X-ray diffractometer, and the surface of the sodium-containing layered oxide is cleaned with a 0.15 mol / L KOH solution to remove residual sodium, then dried and treated, and an ICP-7400 inductively coupled plasma emission spectrometer is used to test the composition to determine the type of M element and the molar ratio between Na element and M element.

[0060] The O3-type sodium-containing layered oxide provided by the embodiments has a high sodium element proportion in the bulk phase composition, indicating that the sodium-containing layered oxide has a high sodium content in the bulk phase, which is beneficial to the capacity improvement of the battery.

[0061] In some embodiments, M includes one or more of Ni, Cu, Mn, Fe, Mg, Zn, Al, Cr, Ti, V.

[0062] The M element is easy to form the sodium-containing layered oxide, and improves the capacity and cycle stability of the sodium secondary battery.

[0063] In some embodiments, the composition of the bulk phase of the sodium-containing layered oxide includes Na x Cu n Fe z Mn i R j O2, wherein n+z+i+j=1, 0

[0064] In some embodiments, 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 numerical range between any two of them; 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 numerical range between any two of them; 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 numerical range between any two of them; 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 numerical range between any two of them.

[0065] The copper-iron-manganese sodium 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 the sodium secondary battery.

[0066] In some embodiments, in the X-ray diffraction spectrum of the sodium-containing layered oxide with Cu as the target material, the diffraction angle 2θ of the (003) crystal face diffraction peak is 15.9°-16.3°, which can be selected as 16.0°-16.2°.

[0067] The size of the diffraction angle 2theta of the (003) plane diffraction peak in the X-ray diffraction pattern of the sodium-containing layered oxide with Cu as the target material can be obtained by using an X-ray diffractometer (XRD). As an example, a Bruker D8 AX-ray diffractometer is used for testing with Cu as the target material, the scanning rate is 5° / min, and the scanning range is 5°-90°. The size of the diffraction angle 2theta of the (003) plane diffraction peak in the X-ray diffraction pattern of the sodium-containing layered oxide with Cu as the target material can reflect the size of the interlayer spacing of the metal layer of the sodium-containing layered oxide. According to the Bragg equation, the larger the diffraction angle, the smaller the interlayer spacing between the metal layers. In order to maintain the stability of the crystal structure, with the increase of the bulk sodium content in the sodium-containing layered oxide, the interlayer spacing of the metal layer decreases. In other words, the diffraction angle 2theta of the (003) plane diffraction peak can be used to characterize the bulk sodium content in the sodium-containing layered oxide, and the larger the diffraction angle 2theta of the (003) plane diffraction peak, the higher the bulk sodium content in the sodium-containing layered oxide.

[0068] In some embodiments, the diffraction angle 2theta of the (003) 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 numerical range between any two of them.

[0069] The diffraction angle of the (003) plane diffraction peak of the sodium-containing layered oxide in the prior art is often less than 15.9°, and the (003) plane diffraction peak of the sodium-containing layered oxide provided in the embodiments of the present 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 the improvement of the capacity of the sodium secondary battery.

[0070] The second aspect of the present application provides a preparation method of a positive electrode active material, comprising the following steps: step S101, obtaining a mixed raw material comprising a sodium source and an M source, 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 a positive electrode active material, the second atmosphere comprising a reducing gas; the positive electrode active material comprises a sodium-containing layered oxide, the sodium-containing layered oxide is of O3 type, and the composition of the bulk phase of the sodium-containing layered oxide comprises Na x M y O z , wherein M is a transition metal element, 0.8

[0071] In this paper, the term "reducing gas" refers to a gas that can lose electrons and be oxidized in combustion or chemical reaction. It should be pointed out that the reducing gas can be introduced during the preparation process, or it can be prepared in situ.

[0072] Based on the phase equilibrium theory, a phase diagram of the sodium source is constructed. 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. 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 improving the initial sodium content in the body phase of the sodium-containing layered oxide, thereby improving the capacity of the secondary battery.

[0073] In the present text, the term "phase diagram" refers to a method for studying the phase equilibrium by graphically representing the relationship between the temperature, pressure and composition of each phase in the phase equilibrium.

[0074] In the present text, the term "phase equilibrium" refers to the limit state reached by the change of each phase in a multi-phase system. At this time, there is no material transfer between phases in the macroscopic view, but in the microscopic view, there is still material transfer between phases in the opposite direction, and the speed is equal, so the net speed of transfer is zero.

[0075] In the present text, the term "phase diagram" refers to a method for studying the phase equilibrium by graphically representing the relationship between the temperature, pressure and composition of each phase in the phase equilibrium.

[0076] The preparation method of the present application does not need to introduce other materials, has low cost, simple process and is easy to realize industrial production, and provides a new method and new idea for the preparation of high-capacity sodium-containing positive electrode active materials.

[0077] In some embodiments, the first atmosphere includes at least one of air, oxygen.

[0078] In the first atmosphere including air and / or oxygen, the oxide structure is first generated, which is beneficial to the further insertion of sodium elements in the body phase under the reducing atmosphere in the later stage.

[0079] In some embodiments, the second atmosphere further includes an inert gas, the reducing gas includes one or more of CO, H2, the inert gas includes one or more of nitrogen, helium, argon, and the partial pressure of the reducing gas in the second atmosphere is 2-10 kPa.

[0080] In the present text, the term "partial pressure" refers to the pressure of a gas in a mixed gas system, assuming that all other gases except the gas are excluded from the system, and the volume and temperature of the system remain unchanged.

[0081] In some embodiments, the partial pressure of the reducing gas in the gas atmosphere can be selected from 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa, 10 kPa, or any value between any two of the above values.

[0082] Controlling the partial pressure of the reducing gas in the second atmosphere is conducive to the sodium element entering the bulk phase in the second sintering, and enables the prepared sodium-containing layered oxide to maintain the O3 phase.

[0083] In some embodiments, the M source comprises one or more of metal oxides, metal carbonates, metal acetates, and metal hydroxides containing the M element; the M element comprises one or more of Ni, Cu, Mn, Fe, Mg, Zn, Al, Cr, Ti, and V.

[0084] In some embodiments, the sodium source comprises one or more of sodium carbonate, sodium acetate, and sodium hydroxide.

[0085] In some embodiments, the molar ratio of the sodium element to the M element in the mixed raw materials is 0.6-0.8.

[0086] In some embodiments, the molar ratio of the sodium element to the M element in the mixed raw materials can be selected from 0.6, 0.7, 0.8, or any value between any two of the above values.

[0087] The molar ratio of the sodium element to the M element in the mixed raw materials within the above range is conducive to the sodium further entering the bulk phase in the sintering in the second atmosphere, and improves the sodium content in the sodium-containing layered oxide.

[0088] In some embodiments, the molar ratio of the sodium element in the sodium source added in the first precursor to the M element in the mixed raw materials in the preparation of the positive electrode active material is 0.25-0.45.

[0089] In some embodiments, the molar ratio of the sodium element in the sodium source added in the first precursor to the M element in the mixed raw materials in the preparation of the positive electrode active material can be selected from 0.25, 0.3, 0.35, 0.4, 0.45, or any value between any two of the above values.

[0090] The molar ratio of the sodium element in the sodium source added in the first precursor to the M element in the mixed raw materials within the above range is conducive to improving the sodium partial pressure and generating the O3-type sodium-containing layered oxide.

[0091] In some embodiments, the ratio of the total molar amount of the sodium element in the added sodium source to the total molar amount of the M element in the added M source is greater than 1.

[0092] The ratio of the total moles of sodium element in the sodium source to the total moles of M element in the M source is greater than 1, which can provide sufficient sodium source supply, reduce the influence 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.

[0093] In some embodiments, the sintering of the mixed raw materials in the first atmosphere to obtain the first precursor includes: sintering the mixed raw materials at a temperature of 800-865 DEG C for 15-18 hours in the first atmosphere to obtain the first precursor.

[0094] In some embodiments, the holding temperature in the first atmosphere can be selected from 800 DEG C, 810 DEG C, 820 DEG C, 830 DEG C, 840 DEG C, 850 DEG C, 860 DEG C, 865 DEG C, or a numerical range between any two of them.

[0095] In some embodiments, the holding time in the first atmosphere can be selected from 15 hours, 16 hours, 17 hours, 18 hours, or a numerical range between any two of them.

[0096] In some embodiments, the preparation of the positive electrode active material by adding a sodium source to the first precursor to obtain a second precursor and sintering the second precursor in a second atmosphere includes: after the inert gas is introduced into the first atmosphere, introducing a carbon source, and heating to obtain a second atmosphere containing a reducing gas and an inert gas.

[0097] The reducing gas can be obtained by the carbon source and the residual gas in the first atmosphere at high temperature.

[0098] In some embodiments, the molar ratio of carbon element in the carbon source to M element in the first precursor is 1%-5%, which can be selected from 1%-2%.

[0099] In some embodiments, the molar ratio of carbon element in the carbon source to M element in the first precursor can be selected from 1%, 2%, 3%, 4%, 5%, or a numerical range between any two of them.

[0100] In some embodiments, the preparation of the positive electrode active material by adding a sodium source to the first precursor to obtain a second precursor and sintering the second precursor in a second atmosphere includes: continuously introducing a mixed gas containing a reducing gas and an inert gas into the reaction container in which the second precursor is placed, and sintering the second precursor, and the flow rate of the mixed gas is 200-500 mL / min.

[0101] In this paper, the term "flow rate" refers to the volume of fluid flowing per unit time.

[0102] In some embodiments, the flow rate of the mixed gas can be selected from 200 mL / min, 300 mL / min, 400 mL / min, 500 mL / min, or a numerical range between any two of them.

[0103] The intake flow rate of the mixed gas within the above range is advantageous for reducing the loss of sodium in the gas phase, maintaining the sodium partial pressure, and increasing the sodium content in the positive electrode active material bulk phase.

[0104] [Positive electrode tab]

[0105] The positive electrode tab generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including the positive electrode active material in some embodiments or the positive electrode active material prepared by the preparation method in some embodiments.

[0106] As an example, the positive electrode current collector has two opposite surfaces in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0107] In some embodiments, the positive electrode current collector can adopt a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be adopted. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0108] In some embodiments, the positive electrode film layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0109] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0110] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode tab can be obtained.

[0111] [Negative electrode tab]

[0112] In some embodiments, the negative electrode tab includes a negative current collector and a negative film layer disposed on at least one surface of the negative current collector, the negative film layer including a negative active material.

[0113] As an example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative film layer is disposed on either one or both of the two surfaces of the negative current collector.

[0114] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0115] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone only one or in combination of two or more.

[0116] In some embodiments, the negative film layer can further optionally include a binder. The binder can 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).

[0117] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0118] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, etc., a negative electrode sheet can be obtained.

[0119] In some embodiments, the sodium secondary battery is a negative electrode-free battery.

[0120] A negative electrode-free battery refers to a battery that is not actively provided with a negative electrode active material layer on the negative electrode side during the manufacturing process of the battery, for example, a battery that is not provided with a metal or carbonaceous active material layer on the negative electrode by coating or deposition during the manufacturing process of the battery to form a negative electrode film layer. During the first charging, active ions obtain electrons on the anode side to deposit in the form of metal on the surface of the current collector to form a metal phase, and during discharging, the metal can be converted into active ions to return to the positive electrode, realizing cyclic charging and discharging. Therefore, the negative electrode-free battery is also a metal battery. Compared with other secondary batteries, the negative electrode-free battery can obtain higher energy density because it does not need to be provided with a negative electrode film layer in advance.

[0121] Although the negative electrode-free secondary battery does not need to be provided with a metal or carbonaceous active material layer to form a negative electrode film layer by coating or deposition, the negative electrode-free battery is often provided with a primer layer containing a conductive material to achieve the function of inducing deposition.

[0122] [Electrolyte]

[0123] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel or all-solid.

[0124] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0125] In some embodiments, the electrolyte solution includes an electrolyte salt, and the electrolyte salt is selected from at least one of NaPF6, NaBF4, NaN(SO2F)2(NaFSI), NaClO4, NaAsF6, NaB(C2O4)2(NaBOB), NaBF2(C2O4) (NaDFOB), NaN(SO2RF)2, NaN(SO2F)(SO2RF), wherein RF is represented as C b F 2b+1 b is an integer of 1-10, which can be optionally an integer of 1-3.

[0126] In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaN(SO2F)2, NaN(CF3SO2)2, NaB(C2O4)2, NaBF2(C2O4). In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaN(SO2RF)2, NaBF2(C2O4). In some embodiments, RF is -CF3, -C2F5, or -CF2CF2CF3.

[0127] In some embodiments, the electrolyte solution further includes a solvent. The solvent can include at least one of a chain carbonate, a chain carboxylate, a cyclic carbonate, an ether solvent, a sulfone solvent, a nitrile solvent. In some embodiments, the chain carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, ethyl propyl carbonate, dipropyl carbonate, dibutyl carbonate. In some embodiments, the chain carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC). In some embodiments, the chain carboxylate includes at least one of methyl formate (MF), ethyl formate (EF), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), ethyl butyrate (EB), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA). In some embodiments, the chain carboxylate includes at least one of methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA). In some embodiments, the ether solvent includes at least one of 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.

[0128] In some embodiments, the electrolyte solution further includes an additive. The additive can include, for example, a negative electrode film-forming additive, a positive electrode film-forming additive, and / or an additive that improves certain properties of the battery, such as an additive that improves overcharge performance of the battery, an additive that improves high-temperature or low-temperature performance of the battery, and / or the like.

[0129] [Separator]

[0130] In some embodiments, the secondary battery further includes a separator. The type of separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0131] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0132] [Secondary battery]

[0133] In one embodiment of the present application, a secondary battery is provided, which includes an electrode assembly and an electrolyte, the electrode assembly including the positive electrode tab of any of the embodiments, a separator film, and a negative electrode tab.

[0134] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator film can be formed into an electrode assembly by a winding process or a stacking process.

[0135] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0136] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0137] The shape of the secondary battery is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, FIG. 3 is a secondary battery 5 of a square structure as an example. Alternatively, the secondary battery can be a lithium-ion battery or a sodium-ion battery.

[0138] In some embodiments, referring to FIG. 4, the outer package can include a shell 51 and a cover plate 53. The shell 51 can 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 communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and a person skilled in the art can select according to the specific actual needs.

[0139] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0140] FIG. 5 is a battery module 4 as an example. Referring to FIG. 5, in the battery module 4, a plurality of secondary batteries 5 can be arranged in series along a length direction of the battery module 4. Of course, the plurality of secondary batteries 5 can be arranged in any other manner. The plurality of secondary batteries 5 can be further fixed by fasteners.

[0141] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of secondary batteries 5 can be accommodated in the accommodation space.

[0142] In some embodiments, the above-described battery module can be assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0143] FIGS. 6 and 7 are a battery pack 1 as an example. Referring to FIGS. 6 and 7, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0144] [Power-Consuming Device]

[0145] In one embodiment of the present application, a power-consuming device is provided, which includes at least one of the secondary battery of any embodiment, the battery module of any embodiment, or the battery pack of any embodiment.

[0146] The power-consuming device includes at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack can be used as a power source of the power-consuming device, or can be used as an energy storage unit of the power-consuming device. The power-consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0147] As the power-consuming device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0148] FIG. 8 is a power-consuming device as an example. The power-consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the power-consuming device, the battery pack or the battery module can be used.

[0149] As another example, the device can be a mobile phone, a tablet, a notebook computer, etc. The device generally requires thinning, and a secondary battery can be used as a power source.

[0150] Embodiments

[0151] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application and should not be understood as a limitation of the present application. In the embodiments, unless a specific technique or condition is specified, the technique or condition described in the literature in the art or according to the product manual is used. The reagents or instruments used, unless the manufacturer is specified, are all conventional products that can be obtained commercially.

[0152] I. Preparation method

[0153] Example 1

[0154] Na2CO3, Mn2O3, CuO, and Fe2O3 in a total amount of 100 g were mixed in a molar ratio of 0.7:0.55:0.3:0.3, and a precursor was synthesized by a solid phase method. The precursor was placed in a gas rotary furnace and heated to 850°C at a temperature increase rate of 5°C / min and held for 15 hours to synthesize a first precursor. The atmosphere was air. A sodium source was further added to the first precursor, and at this time, the molar ratio of the sodium source added to the sodium source added first was 0.35:0.7. A mixed gas including a reducing gas 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 of the mixed gas introduced was 500 mL / min. Sintering was performed for 6 hours to prepare a positive electrode active material.

[0155] Comparative Example 1

[0156] Na2CO3, Mn2O3, CuO, and Fe2O3 in a total amount of 100 g were mixed in a molar ratio of 1.05:0.55:0.3:0.3, and a precursor was synthesized by a solid phase sintering method. The precursor was placed in a gas rotary furnace and heated to 850°C at a temperature increase rate of 5°C / min and held for 21 hours. Air was introduced into the gas rotary furnace at a gas flow rate of 500 mL / min to prepare a positive electrode active material.

[0157] III. Analysis of test results of each embodiment and comparative example

[0158] The test results showed that the positive electrode active material prepared in Example 1 was Na 0.95 Mn 0.55 Cu 0.15 Fe 0.3 O2, the diffraction angle 2θ of the (003) crystal plane diffraction peak was 16.05°, and the configuration was O3 type. The positive electrode active material prepared in Comparative Example 1 was Na 0.73 Mn 0.55 Cu0.15 Fe 0.3 O2, (003) plane layer spacing corresponding to the diffraction angle 2 theta of the diffraction peak of the crystal face is 15.83°.

[0159] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. Furthermore, within the scope of the gist of the present application, various modifications that can be thought of by those skilled in the art are applied to the embodiments, and other modes constructed by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A sodium secondary battery characterized by comprising: The sodium secondary battery includes a 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 O3 type, and a bulk composition of the sodium-containing layered oxide including Na x M y O z wherein 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 comprises 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 comprises 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, the sodium-containing layered oxide has a diffraction angle 2θ of 15.9°-16.3° for a (003) crystal face diffraction peak in an X-ray diffraction pattern with Cu as a target material.

5. A method for producing a positive electrode active material, characterized by, comprising the following steps: obtaining a mixed raw material comprising 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 under a second atmosphere to prepare the positive electrode active material, wherein the second atmosphere comprises a reducing gas, The positive electrode active material includes a sodium-containing layered oxide, the sodium-containing layered oxide is of O3 type, and a composition of a bulk phase of the sodium-containing layered oxide includes Na x M y O z wherein 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 comprises at least one of air and oxygen. 7.The preparation method according to claim 5 or 6, characterized in that, the second atmosphere further comprises an inert gas, the reducing gas comprises one or more of CO and H 2, the inert gas comprises one or more of nitrogen, helium, and argon, and the partial pressure of the reducing gas in the second atmosphere is 2kPa-10kPa. 8.The preparation method according to any one of claims 5 to 7, characterized in that, the M source comprises one or more of metal oxides, metal carbonates, metal acetates, and metal hydroxides containing M elements, and the M elements comprise one or more of Ni, Cu, Mn, Fe, Mg, Zn, Al, Cr, Ti, and V.

9. The production method according to any one of claims 5 to 8, characterized by, the sodium source comprises one or more of sodium carbonate, sodium acetate, and sodium hydroxide.

10. The production method according to any one of claims 5 to 9, characterized by, In the mixed raw material, the molar ratio of sodium elements to M elements is 0.6-0.

8.

11. The production method according to any one of claims 5 to 10, characterized by, In the process of preparing the positive electrode active material, the molar ratio of sodium elements in the sodium source added to the first precursor to M elements in the mixed raw material 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 elements in the added sodium source to the total molar amount of M elements in the added M source is greater than 1.

13. The production method according to any one of claims 5 to 12, characterized by, the sintering of the mixed raw material under the first atmosphere to obtain the first precursor comprises: sintering the mixed raw material under the first atmosphere at a temperature of 800℃-865℃ for 15 hours-18 hours to obtain the first precursor.

14. The production method according to any one of claims 5 to 13, characterized by, the adding of the sodium source to the first precursor to obtain the second precursor and the sintering of the second precursor under the second atmosphere to prepare the positive electrode active material comprises: after the inert gas is introduced into the first atmosphere, a carbon source is added and heated to obtain the second atmosphere comprising the reducing gas and the inert gas.

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

16. The production method according to any one of claims 5 to 15, characterized by, The preparation of the positive active material includes: The mixed gas including the reducing gas and the inert gas is continuously introduced into the reaction container in which the second precursor is placed, and the second precursor is sintered, and the flow rate of the mixed gas is 200 mL / min-500 mL / min.

17. An electrical device, comprising: The electric device includes the sodium secondary battery in claims 1-4.

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