Cathode material for sodium-ion batteries, method for preparing the same, and its application.

Abstract

This invention relates to a positive electrode material for a sodium-ion battery, a method for preparing the same, and its applications. The general chemical formula of the positive electrode material for the sodium-ion battery is Na a Ni b Fe c Mn d M e A f The material is O2, with elements M and A acting as doping elements, the MO bond energy of element M being greater than 500 kJ / mol, the ionic radius of element A being 0.06 nm or greater, and the valence of element A being ≥ +3. In the XRD spectrum of the positive electrode material of the sodium-ion battery, there are no heterophase diffraction peaks in the range of 42.5° to 43.5°. Element M dops into the interstitial atomic sites, acting as a constraint on oxygen and limiting the release of oxygen in the desodium state, while element A preferentially replaces transition metals at transition metal sites, providing support and improving the gas generation problem in the cycle process of the positive electrode material of the sodium-ion battery.

Description

[Technical Field]

[0001] This application relates to the technical field of positive electrode materials for sodium-ion batteries, and more particularly to positive electrode materials for sodium-ion batteries, methods for preparing the same, and applications thereof.

[0002] In recent years, the new energy industry has been developing rapidly, and sodium-ion batteries have attracted attention due to their low cost, ease of preparation, and excellent performance. Among these, nickel-iron-manganese polycrystalline materials are being increasingly researched because they have advantages such as good processing performance, high capacity, and good cycle life. However, nickel-iron-manganese polycrystalline materials produce excessive gas during the cycle, which affects large-scale applications.

[0003] In sodium-ion batteries, the main reactions in layered oxide cathode materials are the insertion and removal of sodium ions. When sodium ions are inserted from the electrolyte into the layered oxide cathode material, the structure of the cathode material changes, and the layered oxide sheets expand outward, forming gaps. This process causes volume expansion and stress accumulation in the cathode material, affecting the battery's cycle life and safety.

[0004] When sodium ions are released from the layered oxide cathode material, the structure of the cathode material returns to its original state, and the layered oxide sheets are stacked again. However, the volume change of the cathode material increases the pressure inside the battery, which can cause not only gas to escape from the cathode material, but also cracks to form at the interface between the cathode material and the electrolyte, potentially causing gas to escape from the electrolyte.

[0005] Gas generation has a certain impact on both the performance and safety of sodium-ion batteries. First, gas generation increases the pressure inside the battery, potentially causing expansion, deformation, and even explosion. Second, gas generation occupies usable space inside the battery, reducing its energy density. Furthermore, gas generation hinders the insertion and removal of sodium ions, shortening the battery's lifespan. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Currently, methods to solve this problem include modifying the layered electrode structure or changing the electrolyte composition. The former allows for better accommodation of volume changes during the insertion and removal of sodium ions. The latter reduces gas generation by selecting an electrolyte with high solubility and low gas escape rate. It is also possible to improve the gas generation problem during cycling by using a water washing method or lowering the operating voltage. However, adding a water washing step complicates the manufacturing process and increases manufacturing costs, and lowering the operating voltage reduces capacity and affects the energy density of the cell. [Means for solving the problem]

[0007] In light of the above, we propose this application.

[0008] The first objective of this invention is to provide a cathode material for a sodium-ion battery that improves the gas generation problem that occurs during the cycle process of the cathode material by doping it with two doping elements having different properties. Here, the MO bond energy of element M is greater than 500 kJ / mol, the ionic radius of element A is 0.06 nm or greater, and the valence state of element A is +3 or greater. The action of element M is to dope the interstitial atomic sites, exert a binding effect on oxygen, and limit the release of oxygen in the desodium state. The doping of element A improves the gas generation problem that occurs during the cycle process of the sodium-ion cathode material by preferentially substituting transition metals at transition metal sites and performing a supporting effect that supports the internal structure of the layered material.

[0009] The second objective of the present application is to provide a method for preparing a cathode material for a sodium-ion battery, which method involves mixing a first additive containing element M and a second additive containing element A with a nickel-iron-manganese precursor material and a sodium source, followed by sintering to dope the two elements, improve the gas generation problem during the cycling process, and obtain a cathode material for a sodium-ion battery with better overall performance.

[0010] The third objective of the present application is to provide a cathode sheet for a sodium-ion battery containing the above-mentioned cathode material for a sodium-ion battery, and the cathode sheet can effectively improve the gas generation problem during the cycling process.

[0011] The fourth objective of the present application is to provide a sodium-ion battery containing the above-mentioned cathode sheet for a sodium-ion battery. By using the cathode sheet as described above, the sodium-ion battery can improve the gas generation problem during the cycling process and enhance the performance and safety of the sodium-ion battery.

[0012] The fifth objective of the present application is to provide an electrical equipment using the above-mentioned sodium-ion battery.

[0013] To achieve the above objectives of the present application, the following technical solutions are adopted.

[0014] The present application provides a cathode material for a sodium-ion battery with a chemical general formula of Na a Ni b Fe c Mn d M e A f O2, where 0.85 ≤ a ≤ 1.1, 0.1 ≤ b ≤ 0.5, 0.1 ≤ c ≤ 0.4, 0.1 ≤ d ≤ 0.4, 0.001 ≤ e ≤ 0.02, 0.001 ≤ f ≤ 0.02. Elements M and A are doping elements. The M-O bond energy of element M is greater than 500 kJ / mol, the ionic radius of element A is 0.06 nm or more, and the valence of element A is ≥ +3. There is no hetero-phase diffraction peak in the XRD spectrum in the range of 42.5° to 43.5°.

[0015] Preferably, the M - O bond energy of the element M is greater than 700 kJ / mol.

[0016] Preferably, the ionic radius of the element A is 0.06 nm to 0.11 nm.

[0017] Preferably, the hetero - diffraction peak is the diffraction peak of NiO and / or the diffraction peak of ZnO.

[0018] Preferably, the element M contains at least one of Al, Nb, Mg, Si, W, and Ti.

[0019] Preferably, the element M contains at least two of Al, Nb, Mg, Si, W, and Ti.

[0020] Preferably, the element A contains at least one of Y, Zr, Nb, Sb, Te, La, Ce, and Ta.

[0021] Preferably, in the cathode material of the sodium - ion battery, the Na - O interlayer distance is 3.30 Å to 3.50 Å.

[0022] Preferably, the cathode material of the sodium - ion battery has a chemical general formula of Na a Ni b Fe c Mn d M e A f and further includes a coating layer covering at least a part of the surface of the material of O2.

[0023] Preferably, the coating layer contains at least one of Al2O3, WO3, SrO, CeO2, and TiO2.

[0024] Preferably, the thickness of the coating layer is 50 nm or less.

[0025] Preferably, after roll - pressing at a pressure of 3 T The positive electrode material of the sodium-ion batteryD10 particle size, before roll pressing The positive electrode material of the sodium-ion battery The ratio to D10 particle size is 0.73 or higher.

[0026] The present invention provides a method for preparing a positive electrode material for a sodium-ion battery, comprising the steps of mixing a nickel-iron-manganese precursor, a sodium source, a first additive containing element M, and a second additive containing element A, and then sintering the mixture to obtain the positive electrode material for the sodium-ion battery, wherein the sintering step specifically includes performing a first heat-hold sintering at 600°C to 750°C, a second heat-hold sintering at 850°C to 920°C, and a third heat-hold sintering at 930°C to 980°C.

[0027] Preferably, the temperature of the first heat retention sintering is 600°C to 700°C, and the temperature of the second heat retention sintering is 850°C to 900°C.

[0028] Preferably, the duration of the first heat-holding sintering is 1 to 3 hours.

[0029] Preferably, the second heat retention sintering time is 1 to 3 hours.

[0030] Preferably, the third heat retention sintering time is 12 to 16 hours.

[0031] Preferably, the process further includes the step of crushing the sintered material after the third heat retention sintering, adding a coating layer material, and performing a fourth heat retention sintering.

[0032] Preferably, the temperature of the fourth heat retention sintering is 400°C to 450°C.

[0033] Preferably, the fourth heat retention sintering time is 12 to 16 hours.

[0034] This application provides a positive electrode sheet for a sodium-ion battery, which includes the positive electrode material for the sodium-ion battery.

[0035] This application provides a sodium-ion battery including a positive electrode sheet for the sodium-ion battery.

[0036] This application provides a power-using device that includes the aforementioned sodium-ion battery. [Effects of the Invention]

[0037] Compared to the prior art, the beneficial effects of this invention are as follows:

[0038] (1) The positive electrode material for a sodium-ion battery provided in this application improves the gas generation problem of the positive electrode material during the cycle process by doping it with two doping elements with different properties. Here, the MO bond energy of element M is greater than 500 kJ / mol, the ionic radius of element A is 0.06 nm or greater, and the valence state of element A is +3 or greater. Element M acts by doping the interstitial atomic sites, exerting a restrictive effect on oxygen and limiting the release of oxygen in the desodium state. Doping with element A preferentially replaces the transition metal at the transition metal sites, providing a supporting effect that supports the internal structure of the layered material, thereby improving the gas generation problem of the sodium-ion positive electrode material during the cycle process.

[0039] (2) The positive electrode material for sodium-ion batteries provided in this application has the characteristic of having a stable structure, good Na-O interlayer distance, and better cycle performance due to the positional action of element A and the absence of heterophase diffraction peaks in the 42.5° to 43.5° range of the XRD spectrum of the positive electrode material. cycle To improve the gas generation problem in the process.

[0040] (3) The positive electrode material of the sodium ion battery provided in this application is such that element A is a high number ion, and therefore Ni in the positive electrode material is Ni 2+ Ni can be biased and its valency can be changed. 2+ The capacity of the positive electrode material is improved by increasing its content.

[0041] (4) The positive electrode material of the sodium-ion battery provided in this invention further includes a dense coating layer, which can suppress corrosion of the positive electrode material by the electrolyte.

[0042] (5) The method for preparing a positive electrode material for a sodium-ion battery provided in this application involves mixing a first additive containing element M and a second additive containing element A with a nickel-iron-manganese precursor material and a sodium source, then sintering the mixture to dope it with the two elements, thereby improving the gas generation problem during the cycle process of the positive electrode material for a sodium-ion battery and obtaining a positive electrode material for a sodium-ion battery with superior overall performance.

[0043] (6) The method for preparing a positive electrode material for a sodium-ion battery provided in the present invention includes three heat retention sintering processes in the sintering step, the first heat retention sintering mainly removes heterogeneous phases of Fe2O3 and Mn3O4, the second heat retention sintering mainly removes heterogeneous peaks of NiO / ZnO, and the third heat retention sintering mainly performs a solid solution function. [Brief explanation of the drawing]

[0044] To more clearly illustrate the embodiments of this application or the technical concepts in the prior art, the drawings that may be used in describing the embodiments or the prior art are briefly described below. Clearly, the drawings in the following description are only a few embodiments of this application, and those skilled in the art can obtain other drawings based on these without any creative effort. [Figure 1] This is the XRD measurement spectrum from Example 1. [Figure 2] This is the XRD measurement spectrum from Example 2. [Figure 3] This is the XRD measurement spectrum of Comparative Example 1. [Figure 4] This is the XRD measurement spectrum of Comparative Example 2. [Figure 5] This is the XRD measurement spectrum of Comparative Example 9. [Modes for carrying out the invention]

[0045] The technical proposal of this application will be clearly and completely described below with reference to the drawings and specific embodiments. However, those skilled in the art should understand that the embodiments described below are only some embodiments of this application, not all embodiments, and are merely illustrative and not limiting the scope of this application. All other embodiments obtained by those skilled in the art without creative work based on the embodiments of this application are within the scope of protection of this application. Unless specific conditions are stated in the embodiments, the procedures were followed under normal conditions or conditions suggested by the manufacturer. The reagents or equipment used are not specified by manufacturer and are all common commercially available products.

[0046] Unless otherwise specified, the terms “includes” or “contains” as used in this application are open in meaning, but may also be closed in meaning. For example, “includes” and “contains” as described may include other components not listed, or may include only components not listed.

[0047] Unless otherwise specified, the term “or” is inclusive in this application, and for example, the expression “A or B” means any of “A,” “B,” or “both A and B.” More specifically, the condition “A or B” is satisfied in any of the following cases: 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).

[0048] Unless otherwise specified, in this application, "one or more types" or "at least one type" refers to any one, any two, or any two or more of the listed items. Here, "multiple types" means any two or more.

[0049] Unless otherwise specified, expressions such as "first aspect," "second aspect," "third aspect," and "fourth aspect" in this application are used solely for explanatory purposes and should not be understood as indicating or implying relative importance or quantity, nor should they be understood as implying the importance or quantity of the described technical features. Furthermore, it should be understood that terms such as "first," "second," "third," and "fourth" are not intended as an exhaustive list, and these terms do not imply quantitative limitations.

[0050] In a first embodiment, the present invention improves the selection of doping elements and the stability of the layered cathode material, taking into consideration the gas generation problem of sodium ion cathode materials, and wherein the general chemical formula is Na a Ni b Fe c Mn d M e A f The present invention provides a positive electrode material for a sodium-ion battery, which is O2, where 0.85≦a≦1.1, 0.1≦b≦0.5, 0.1≦c≦0.4, 0.1≦d≦0.4, 0.001≦e≦0.02, and 0.001≦f≦0.02, elements M and A are doping elements, the MO bond energy of element M is greater than 500 kJ / mol, the ionic radius of element A is 0.06 nm or greater, and the valence of element A is ≥ +3, and the XRD spectrum does not have any heterophase diffraction peaks in the range of 42.5°~43.5°.

[0051] Here, the doping element M functions as a gap atom in the layered material, exerting a binding effect on oxygen at the gap atom sites and suppressing oxygen release during the cycle process. For this effect to occur, the MO bond energy of element M must be greater than 500 kJ / mol. Doping with element A replaces the transition metal at the transition metal sites, providing support and supporting the internal structure of the layered material, thereby improving the gas generation problem that occurs during the cycle process of the sodium ion cathode material. The ionic radius of element A is 0.06 nm or greater, and the valence state of A is +3 or greater.

[0052] Furthermore, the XRD spectrum of the cathode material for the sodium-ion battery shows no heterophase diffraction peaks in the range of 42.5° to 43.5°. Combined with the positional effect of element A, this allows for the acquisition of a structurally stable cathode material, reducing structural changes during the desorption process of sodium ions and achieving excellent cycle stability.

[0053] To make it clear, the absence of heterophase diffraction peaks means that there are no clearly defined heterophase diffraction peaks. Specifically, "clear" refers to heterophase diffraction peaks with a peak intensity greater than 300.

[0054] Furthermore, the XRD spectrum of the cathode material of the sodium-ion battery does not show any clear NiO diffraction peaks and / or ZnO diffraction peaks in the range of 42.5° to 43.5°. In addition, the valence state of element A being +3 or higher indicates that Ni in the cathode material is more Ni 2+ Ni can be biased to change its valency. 2+ By increasing the content of this material, the capacity of the cathode material can also be improved.

[0055] Note that the above chemical formula is Na a Ni b Fe c Mn d M e A fIn O2, the value of a is any one point value among 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, or a range value between any two of the above values, but is not limited to these; the value of b is any one point value among 0.1, 0.2, 0.3, 0.4, 0.5, or a range value between any two of the above values, but is not limited to these; the value of c is any one point value among 0.1, 0.2, 0.3, 0.4, or a range value between any two of the above values, but is not limited to these; and the value of d is any one point among 0.1, 0.2, 0.3, 0.4 The value of e includes, but is not limited to, a single point value from among 0.001, 0.002, 0.005, 0.008, 0.01, 0.012, 0.014, 0.015, 0.018, 0.02, or a range

[0056] In some embodiments, a binding energy of MO greater than 500 kJ / mol includes, but is not limited to, any single point value among 500 kJ / mol, 700 kJ / mol, 700 kJ / mol, 800 kJ / mol, 900 kJ / mol, 1000 kJ / mol, 1100 kJ / mol, 1200 kJ / mol, 1300 kJ / mol, 1400 kJ / mol, 1500 kJ / mol, 1600 kJ / mol, 1700 kJ / mol, 1800 kJ / mol, 1900 kJ / mol, and 2000 kJ / mol, or a range between any two of the above values. Furthermore, the greater the binding energy of MO, the greater the binding effect on O, and it is preferable that the binding energy of MO is greater than 700 kJ / mol, and even more preferably between 700 kJ / mol and 2000 kJ / mol.

[0057] In some embodiments, the ionic radius of element A can also play a role in optimizing the layered material structure, and the ionic radius of element A is preferably 0.06 nm to 0.11 nm, and is 0.06 nm, 0.068 nm, 0.07 nm, 0.072 nm, 0.074 nm, 0.075 nm, 0.078 nm, 0.08 nm, 0.082 nm, 0.083 nm, 0.084 nm, 0.085 nm, 0.086 nm, 0.088 nm, 0.0 This includes, but is not limited to, any single point value from 9nm, 0.092nm, 0.093nm, 0.094nm, 0.095nm, 0.096nm, 0.097nm, 0.098nm, 0.099nm, 0.1nm, 0.102nm, 0.1032nm, 0.0104nm, 0.105nm, 0.106nm, 0.107nm, 0.108nm, 0.109nm, or 0.11nm, or a range value between any two of the above values.

[0058] The XRD spectra of conventional sodium-ion battery cathode materials show diffraction peaks for NiO and / or ZnO in the range of 42.5° to 43.5°, and it can be understood that the presence of NiO diffraction peaks reduces the capacity of the cathode material.

[0059] In some embodiments, the element M satisfying the above conditions includes, but is not limited to, at least one of Al, Nb, Mg, Si, W, and Ti. Furthermore, the doping of element M may be with one element, or two, three, or four elements may be doped simultaneously. Examples of possible combinations include, but are not limited to, Al / Si, Al / Mg, Mg / W, Si / Ti, Ti / Nb, and W / Mg / Al. Preferably, element M includes, at least By combining the two elements, the binding effect on oxygen is enhanced, further reducing the amount of gas generated during the cycle of the cathode material.

[0060] In some embodiments, element A satisfying the above conditions includes, but is not limited to, at least one of Y, Zr, Nb, Sb, Te, La, Ce, and Ta. Element A may be doped with a single element, or with two, three, or four elements simultaneously. Possible combinations include, but are not limited to, Y / Zr, Nb / Y, Sb / Te, Ta / Ce, and Y / Sb / Te.

[0061] In some embodiments, doping the positive electrode material of a sodium-ion battery with element A results in doping the transition metal layer with ions of a slightly larger radius, reducing the formation of heterogeneous phases in the material and making the structure of the resulting material more stable.

[0062] Furthermore, the interlayer distance of Na-O is 3.30 Å to 3.50 Å, and includes, but is not limited to, any single point value among 3.30 Å, 3.31 Å, 3.32 Å, 3.33 Å, 3.34 Å, 3.35 Å, 3.36 Å, 3.37 Å, 3.38 Å, 3.39 Å, 3.40 Å, 3.41 Å, 3.42 Å, 3.43 Å, 3.44 Å, 3.45 Å, 3.46 Å, 3.47 Å, 3.48 Å, 3.49 Å, and 3.50 Å, or a range value between any two of the above values.

[0063] In some embodiments, the positive electrode material of a sodium-ion battery further includes a coating layer. The dense coating layer can suppress erosion of the positive electrode material by the electrolyte, and as a result, a positive electrode material for a sodium-ion battery with superior overall performance can be obtained. Furthermore, the material of the coating layer includes, but is not limited to, at least one of Al2O3, WO3, SrO, CeO2, and TiO2.

[0064] In some embodiments, the thickness of the coating layer is 50 nm or less, preferably 20 nm to 50 nm, and includes, but is not limited to, any single point value among 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, and 50 nm, or a range value between any two of the above values. By adopting this thickness range, uniformity of the coating can be ensured while ensuring conductivity at the interface.

[0065] Furthermore, in some embodiments, the positive electrode material of the sodium-ion battery provided by this application has a ratio of 0.73 or higher between the D10 particle size after roll pressing at a pressure of 3T and the D10 particle size before roll pressing. Having a large ratio indicates that the change in D10 particle size before and after roll pressing is small, meaning that the material has high hardness, a stable structure, and high structural strength.

[0066] In a second embodiment, the present application provides a method for preparing a positive electrode material for a sodium-ion battery. The method includes the following steps:

[0067] A nickel-iron-manganese precursor, a sodium source, a first additive containing element M, and a second additive containing element A are mixed and then sintered to obtain a positive electrode material for a sodium-ion battery.

[0068] Here, the sintering step specifically includes performing a first heat-hold sintering at 600°C to 750°C, a second heat-hold sintering at 850°C to 920°C, and a third heat-hold sintering at 930°C to 980°C.

[0069] Furthermore, in some embodiments, the temperature of the first heat retention sintering is 600°C to 700°C, and the temperature of the second heat retention sintering is 850°C to 900°C. The above sintering temperatures make it possible to further reduce the amount of gas generated in a battery prepared with the positive electrode material provided by this application.

[0070] The method for preparing a positive electrode material for a sodium-ion battery provided in this application involves mixing a first additive containing element M and a second additive containing element A with a nickel-iron-manganese precursor material and a sodium source, then sintering the mixture to dope it with the two elements, thereby improving the problem of gas generation during the cycle process of the positive electrode material for a sodium-ion battery and obtaining a positive electrode material for a sodium-ion battery with superior overall performance.

[0071] In some embodiments, the sodium source includes, but is not limited to, at least one of sodium carbonate, sodium nitrate, and sodium bicarbonate.

[0072] In some embodiments, the additive containing element M includes an oxide, hydroxide, or salt containing element M.

[0073] In some embodiments, the additive containing element A includes an oxide, hydroxide, or salt containing element A.

[0074] In some embodiments, the sintering process is carried out in an oxygen-containing atmosphere.

[0075] In some embodiments, the present invention primarily improves the performance of layered cathode materials by doping elements, and the nickel-iron-manganese precursor material to which it is applied is Ni 0.33 Fe 0.33 Mn 0.33 (OH)2 precursor material, Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor material, Ni 0.2 Fe 0.4 Mn 0.4 (OH)2 precursor material, Ni 0.4 Fe 0.3 Mn 0.3 (OH)2 precursor material, Ni 0.25 Fe 0.40 Mn 0.35 This includes, but is not limited to, (OH)2 precursor materials.

[0076] Here, the first heat retention sintering mainly controls the formation of heterogeneous phases of Fe2O3 and Mn3O4, the second heat retention sintering removes the heterogeneous phase of NiO, and the third heat retention sintering mainly performs a solid solution function. By adding the first and second heat retention sintering, the formation of heterogeneous phases is reduced, which is advantageous in improving ion conductivity, contributes to improving the uniformity of the material before solid solution, enhances the integrity of the solid solution reaction, increases the interlayer distance of Na-O, reduces the difficulty of the sodium ion desorption process, contributes to improving the kinetic performance of the cathode material, and improves the capacity of the cathode material.

[0077] For the reasons stated above, the temperature for the first heat retention sintering is 600°C to 700°C, including, but not limited to, any single point value among 600°C, 630°C, 650°C, 680°C, and 700°C, or a range value between any two of the above values; the temperature for the second heat retention sintering is 850°C to 900°C, including, but not limited to, any single point value among 850°C, 860°C, 870°C, 880°C, 890°C, and 900°C, or a range value between any two of the above values; and the temperature for the third heat retention sintering is 930°C to 980°C, including, but not limited to, any single point value among 930°C, 935°C, 940°C, 945°C, 950°C, 955°C, 960°C, 965°C, 970°C, 975°C, and 980°C, or a range value between any two of the above values.

[0078] Furthermore, the duration of the first heat-hold sintering is 1h to 3h, and includes, but is not limited to, any single point value among 1h, 1.5h, 2h, 2.5h, and 3h, or a range value between any two of the above values.

[0079] Furthermore, the duration of the second heat-hold sintering is 1h to 3h, and includes, but is not limited to, any single point value among 1h, 1.5h, 2h, 2.5h, and 3h, or a range value between any two of the above values.

[0080] Furthermore, the third heat retention sintering time is 12h to 16h, and includes, but is not limited to, any single point value among 12h, 13h, 14h, 15h, and 16h, or a range value between any two of the above values.

[0081] In some embodiments, the heating rate of the first heat retention sintering is 2°C / min to 5°C / min, and includes, but is not limited to, any single point value among 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, and 5°C / min, or a range value between any two of the above values.

[0082] In some embodiments, the heating rate of the second heat retention sintering is 2°C / min to 5°C / min, and includes, but is not limited to, any single point value among 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, and 5°C / min, or a range value between any two of the above values.

[0083] In some embodiments, the heating rate of the third heat retention sintering is 1°C / min to 4°C / min, and includes, but is not limited to, any single point value among 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, and 4°C / min, or a range value between any two of the above values.

[0084] In some embodiments, as the temperature of the heat retention sintering gradually increases from the first heat retention sintering to the second heat retention sintering, and further to the third heat retention sintering, the heating rate gradually decreases, resulting in a cathode material with a more uniform crystalline phase.

[0085] In some embodiments, the present invention further includes a coating layer material. A mixed system may be obtained by directly mixing the sintered material and the coating layer material, and then the mixed system may be subjected to a firing treatment to coat at least a portion of the surface of the sintered material with the coating layer material to form the positive electrode material of the sodium-ion battery of the present invention. Alternatively, the sintered material may be dissolved in ethanol to obtain a first liquid phase, the coating layer material may be dissolved in the first liquid phase to obtain a mixed liquid phase, the mixed liquid phase may be subjected to a stirring, evaporation, and drying treatment to obtain a mixed system, and then the mixed system may be subjected to a firing treatment to coat at least a portion of the surface of the sintered material with the coating layer material to form the positive electrode material of the sodium-ion battery of the present invention. Alternatively, the sintered material may be dissolved in ethanol to obtain a first liquid phase, the coating layer material may be dissolved in ethanol to obtain a second liquid phase, the second liquid phase may be added to the first liquid phase to obtain a mixed liquid phase, the mixed liquid phase may be subjected to a stirring, evaporation, and drying treatment to obtain a mixed system, and then the mixed system may be subjected to a firing treatment to coat at least a portion of the surface of the sintered material with the coating layer material to form the positive electrode material of the sodium-ion battery of the present invention.

[0086] As an example, the process further includes crushing the sintered material after the third heat retention sintering, adding a coating layer material, and performing a fourth heat retention sintering.

[0087] In some embodiments, the temperature of the fourth heat retention sintering is 400°C to 450°C, and includes, but is not limited to, any single point value among 400°C, 410°C, 420°C, 430°C, 440°C, and 450°C, or a range value between any two of the above values. Furthermore, the duration of the fourth heat retention sintering is 12h to 16h, and includes, but is not limited to, any single point value among 12h, 13h, 14h, 15h, and 16h, or a range value between any two of the above values.

[0088] Furthermore, the process further includes a step of screening the sintered material to remove iron after the fourth heat retention sintering.

[0089] In a third embodiment, the positive electrode sheet for a sodium-ion battery provided by the present application includes a positive electrode material for a sodium-ion battery.

[0090] The positive electrode sheet may be understood to include a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode material of the first embodiment of the present application.

[0091] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer material substrate. Selectively, the metal material includes, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Selectively, the polymer material substrate includes, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0092] In some embodiments, the positive electrode film layer mainly consists of the positive electrode material of the sodium-ion battery, an adhesive, and a conductive agent.

[0093] As an example, the adhesive may contain at least one of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-fluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0094] As an example, the conductive agent may include at least one of carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and the carbon black may include superconducting carbon, acetylene black, or Ketjen black.

[0095] In some embodiments, a positive electrode sheet can be manufactured by dispersing components for manufacturing the positive electrode sheet, such as a positive electrode material for a sodium-ion battery, a conductive agent, an adhesive, and any other components, in a solvent to form a positive electrode slurry; applying the positive electrode slurry to a positive electrode current collector; and obtaining a positive electrode sheet through processes such as drying and cold pressing. The solvent may selectively include, but is not limited to, N-methylpyrrolidone.

[0096] In a fourth embodiment, the sodium-ion battery provided by the present application includes a positive electrode sheet for the sodium-ion battery.

[0097] In some embodiments, the sodium-ion battery mainly consists of a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. Here, any ordinary commercially available negative electrode sheet (or negative electrode material), separator, and electrolyte can be used.

[0098] In a fifth embodiment, the present application provides a power-using device that includes a sodium-ion battery.

[0099] The above-mentioned power-consuming equipment includes, but is not limited to, any equipment that uses the above-mentioned sodium-ion battery, such as electric vehicles, power tools, electronic products, energy storage systems, and office equipment.

[0100] Embodiments of the present application will be described in detail below with reference to examples, but those skilled in the art should understand that the following examples are merely illustrative and do not limit the scope of the present application. Unless otherwise specified in the examples, the procedures were carried out under normal conditions or conditions suggested by the manufacturer. Unless otherwise specified, the reagents or equipment used are all common products available commercially.

[0101] The main differences in the composition and preparation method parameters of the positive electrode material for sodium-ion batteries in Examples 1 to 15 and Comparative Examples 1 to 9 are shown in Tables 1 and 2 below.

[0102] [Table 1]

[0103] [Table 2]

[0104] The " / " indicates that the parameter does not exist and means that the element or step is omitted.

[0105] The method for preparing the positive electrode material of the sodium-ion battery in Examples 1 to 15 and Comparative Examples 1 to 9 includes the following steps.

[0106] A nickel-iron-manganese precursor with a sodium element in a molar ratio of 1:1 was added to a sodium source. Then, additives containing element M and element A were calculated and added according to the general formula in Table 1 or Table 2. Next, the first, second, and third heat-sintering processes were carried out in an air atmosphere. Here, the heating rate for the first heat-sintering was 3°C / min, the heating rate for the second heat-sintering was 2°C / min, and the heating rate for the third heat-sintering was 1°C / min. After heat-sintering, the material was subjected to mechanical grinding, screening, iron removal, and packaging in sequence to obtain the positive electrode material for a sodium-ion battery.

[0107] If the examples and comparative examples do not have the corresponding parameters in Tables 1 and 2, respectively, the corresponding step in the preparation method is omitted. Examples 16 to 30:

[0108] After mixing the sodium-ion battery positive electrode materials prepared in Examples 1 to 15 with Al2O3, the mixture was subjected to a fourth heat-sintering procedure at 400°C for 12 hours in an air atmosphere to obtain a sodium-ion battery positive electrode material having a coating layer.

[0109] Examples 16 to 30 have a one-to-one correspondence with Examples 1 to 15. That is, Example 16 is obtained after coating the material of Example 1, Example 17 is obtained after coating the material of Example 2, and so on, until Example 30 is obtained after coating the material of Example 15.

[0110] Experimental Example 1: XRD detection was performed on the positive electrode materials of the sodium-ion batteries prepared in Examples 1 to 15 and Comparative Examples 1 to 9, and the interlayer distances of Na-O in the positive electrode materials of each sodium-ion battery are shown in Table 3.

[0111] [Table 3]

[0112] As can be seen from Table 3, the positive electrode material for the sodium-ion battery provided in this application has a relatively good Na-O interlayer distance, facilitating ion insertion and deinsertion in the layered material. In the comparative examples, Comparative Example 3 is doped only with element A(Y), so it does not have a significant effect on the Na-O interlayer distance. However, as in Comparative Example 4, when only element (Al) is doped, the Na-O interlayer distance decreases. Furthermore, in Comparative Example 7, even when doped with element V, which has a small ionic radius, it fails to provide support to the layered material, reducing the Na-O interlayer distance. Comparative Examples 5 and 6 were also doped with element Y, but the doping amount was not as large as in Comparative Example 3, and the Na-O interlayer distance also decreased. This suggests that doping element M and element A act synergistically, reducing the amount of element A doped and allowing for the acquisition of a positive electrode material with a relatively large Na-O interlayer distance.

[0113] Furthermore, referring to Figures 1, 2, 3, and 4, Comparative Examples 1 and 2 removed the first and second heat retention sintering steps from Example 1, respectively. Compared to Example 1, heterogeneous NiO / ZnO peaks were generated, and the formation of heterogeneous phases affected the solid solution effect of the third heat retention sintering. Compared to Example 1, the interlayer distance of Na-O was also reduced. Specifically, Figures 1 and 2 show the XRD measurement spectra of the cathode materials prepared in Example 1 and Example 2, and there are no significant diffraction peaks in the 42.5° to 43.5° range, indicating that no heterogeneous phases were formed in the cathode. Figures 3 and 4 show the XRD spectra of the cathode materials prepared in Comparative Examples 1 and 2, and there are significant diffraction peaks in the 42.5° to 43.5° range, indicating that heterogeneous phases were formed.

[0114] Experimental Example 2 (Performance Test of Cathode Material): Sodium-ion batteries were manufactured using the positive electrode materials obtained in each of the above Examples 1 to 15 and Comparative Examples 1 to 9. Electrochemical tests were then performed on each sodium-ion battery to determine its battery capacity and cycle performance, and the results are shown in Table 4. Simultaneously, the amount of gas generated after leaving each battery at 45°C for 14 days was measured, and the results are also shown in Table 4.

[0115] Here, we adopt a technical method for manufacturing a lithium-ion battery using a cathode material well known to those skilled in the art. The layered materials obtained in the examples and comparative examples are assembled into a button-type battery. The specific method involves weighing the prepared sodium electrolytic layered cathode material, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 90:5:5, mixing them uniformly, and then applying NMP (Natural Microwave Processing). (N-methylpyrrolidone) The mixture was stirred for 2 hours to form a viscous slurry, which was uniformly coated onto aluminum foil, vacuum baked at 80°C, compressed into tablets, and cut into 14mm diameter positive electrode sheets. A 16mm diameter pure sodium sheet was used as the negative electrode sheet, ENA-18 (brand: Tenshi) was used as the electrolyte, and a PP / PE / PP composite separator was used to assemble a buckle-type battery in a glove box filled with argon gas.

[0116] The electrochemical tests include an initial discharge capacity test at 0.1C, an initial Coulomb efficiency (initial efficiency) test, and a capacity retention rate test after 100 cycles at 45°C.

[0117] For the initial discharge capacity at 0.1C, the assembled half-cell was left idle for 5 hours, and then charged and discharged at 0.1C / 0.1C using a battery test device manufactured by Wuhan Blue Electronics Co., Ltd., with a test temperature of 25±1℃, a test voltage of 2.0~4.0V, and a charge cutoff current of 0.05C. The charge and discharge capacities were obtained.

[0118] For the initial Coulomb efficiency, the assembled half-battery was left idle for 5 hours, and then charged and discharged at 0.1C / 0.1C in a battery test device manufactured by Wuhan Blue Electronics Co., Ltd. at a test temperature of 25±1℃, a test voltage of 2.0~4.0V, and a charge cutoff current of 0.05C. The charge and discharge capacities were obtained, and the initial Coulomb efficiency was calculated using the obtained discharge capacity / charge capacity ratio.

[0119] For the capacity retention rate after 100 cycles at 45°C, the Shin'i CT3008-5V3A-A1 was used, and 100 cycles were performed at 45°C with a cycle voltage of 2-4V and a constant voltage cutoff current of 20mA. 100th time The capacity was recorded and divided by the capacity of the first cycle to obtain the 100-cycle retention rate.

[0120] This section describes the test method for battery gas generation, specifically a gas generation performance test conducted at 45°C for 14 days. First, the battery is fully charged, and its volume V1 is tested. Then, the fully charged battery is stored at 45°C for 14 days, and its volume V2 is tested. The rate of increase is calculated using the formula: (V2 - V1) / V1 × 100%. The volume is measured using an electronic solid density meter, model TW-120E.

[0121] [Table 4]

[0122] As can be seen from Table 4, the positive electrode material of the sodium-ion battery prepared in the embodiment of the present invention has higher capacity and cycle stability performance. Comparative Example 3 has high SO because element M is not added. C In Comparative Example 1, oxygen ions became more easily released, resulting in a significant deterioration of cycle performance and gas generation performance, and an increase in gas generation. In Comparative Example 4, since element A was not added, the structural support effect was poor, resulting in low capacity and initial Coulomb efficiency, deterioration of both cycle performance and gas generation performance, and an increase in gas generation. In Comparative Example 5, Cu was introduced instead of M, and in Comparative Example 6, Co was introduced instead of M, resulting in less constraint on oxygen, deterioration of both cycle performance and gas generation performance, and an increase in gas generation. In Comparative Example 7, since V was introduced instead of doping element A, the ionic radius of V was small, resulting in poor support for the layered structure of the cathode material, loss of both capacity and initial Coulomb efficiency, deterioration of cycle performance and gas generation performance, and an increase in gas generation.

[0123] Furthermore, in Comparative Example 9, the sintering temperature for each step was lower than the lower temperature limit of the heat retention platform for each stage of the present invention, and there was a significant diffraction peak in the range of 42.5° to 43.5°, indicating the formation of a different phase, as shown in Figure 5.

[0124] Experimental Example 3 (D10 particle size test before and after roll pressing): The D10 particle size of the positive electrode material of the sodium-ion battery prepared in each of Examples 1 to 15 and Comparative Examples 1 to 9 was measured before and after roll pressing, and the results are shown in Table 5.

[0125] The specific roll press method involves using the TUM7105 equipment, with a die inner diameter of 13 mm. First, the equipment's deformation displacement is reset and calibrated with a force of 100 N. Next, 2 g of material is weighed and placed in the die, a pressure of 3 T (166 MPa) is applied, and after holding for 10 seconds, the material is removed.

[0126] [Table 5]

[0127] As can be seen from Table 5, the structure of the positive electrode material of the sodium-ion battery prepared in the embodiments of this application is stable, and the change in D10 particle size before and after roll pressing is small, which indicates that the structural strength of the positive electrode material of the sodium-ion battery prepared in each embodiment is high. The positive electrode material of the sodium-ion battery prepared in the comparative example showed a significant decrease in D10 particle size after roll pressing, indicating that the material hardness is low.

[0128] The thickness of the coating layer in the materials obtained in Examples 16-30 was measured using transmission electron microscopy, and the obtained data is shown in Table 6.

[0129] [Table 6]

[0130] As can be seen from Table 6, the thickness of the coating layer in Examples 16-30 is all less than 50 nm.

[0131] As described above, the positive electrode material for sodium-ion batteries provided in this application, by introducing elements M and A, effectively improves the problem of gas generation during the cycle process of the positive electrode sheet, and also improves the capacity and cycle life of the material.

[0132] Although this application has been described and explained using specific examples, it should be understood that these examples are merely illustrative of the technical means of this application and do not limit it. Those skilled in the art can make various modifications and equivalent substitutions of some or all technical features of the technical means described in the above examples without departing from the spirit and scope of this application. None of these modifications or substitutions deviate from the essence of the technical means provided by each example of this application. Therefore, it should be understood that the scope of this application includes all substitutions and modifications described in the appended claims.

[0133] This application claims priority to the Chinese patent application filed with the China National Patent Office on October 25, 2023, application number 202311390637.1, titled "Cathode material for sodium-ion batteries, method for preparing the same, and its applications," and incorporates its entire contents into this application by reference.

Claims

1. The general chemical formula is Na ａ Ni ｂ Fe ｃ Mn ｄ M ｅ A ｆ O ２ The sodium-ion battery cathode material is such that 0.85≦a≦1.1, 0.1≦b≦0.5, 0.1≦c≦0.4, 0.1≦d≦0.4, 0.001≦e≦0.02, and 0.001≦f≦0.02, and elements M and A are doping elements, the M-O bond energy of element M is greater than 500 kJ / mol, the ionic radius of element A is 0.06 nm or greater, the valence of element A is ≥+3, and in the XRD spectrum of the sodium-ion battery cathode material, there are no heterophase diffraction peaks in the range of 42.5° to 43.5°.

2. The positive electrode material for a sodium-ion battery according to claim 1, wherein the M-O bond energy of the element M is greater than 700 kJ / mol.

3. The positive electrode material for a sodium-ion battery according to claim 1, wherein the ionic radius of element A is 0.06 nm to 0.11 nm.

4. The cathode material for a sodium-ion battery according to claim 1, wherein in the XRD spectrum of the cathode material for the sodium-ion battery, there are no diffraction peaks of NiO and / or ZnO in the range of 42.5° to 43.5°.

5. The positive electrode material for a sodium-ion battery according to claim 1, wherein the element M comprises at least one of Al, Nb, Mg, Si, W, and Ti.

6. The positive electrode material for a sodium-ion battery according to claim 5, wherein the element M comprises at least two of Al, Nb, Mg, Si, W, and Ti.

7. The positive electrode material for a sodium-ion battery according to claim 1, wherein element A comprises at least one of Y, Zr, Nb, Sb, Te, La, Ce, and Ta.

8. The positive electrode material for a sodium-ion battery according to claim 1, wherein the interlayer distance of Na-O in the positive electrode material for the sodium-ion battery is 3.30 Å to 3.50 Å.

9. The positive electrode material of the sodium ion battery further includes a coating layer that coats at least a part of the surface of a material having a chemical general formula of Na ａ Ni ｂ Fe ｃ Mn ｄ M ｅ A ｆ O ２ and The aforementioned coating layer is Al ２ O ３ WO ３ SrO, CeO ２ and TiO ２ A positive electrode material for a sodium-ion battery according to any one of claims 1 to 8, comprising at least one of the following.

10. The positive electrode material for a sodium-ion battery according to claim 9, wherein the thickness of the coating layer is 50 nm or less.

11. A positive electrode material for a sodium-ion battery according to any one of claims 1 to 8, wherein the ratio of the D10 particle size after roll pressing with a pressure of 3T to the D10 particle size before roll pressing is 0.73 or more.

12. A method for preparing a positive electrode material for a sodium-ion battery according to any one of claims 1 to 11, The process includes the steps of mixing a nickel-iron-manganese precursor, a sodium source, a first additive containing element M, and a second additive containing element A, and then sintering the mixture to obtain the positive electrode material for the sodium-ion battery. A method for preparing a positive electrode material for a sodium-ion battery, wherein the sintering step specifically includes performing a first heat-hold sintering at 600°C to 750°C, a second heat-hold sintering at 850°C to 920°C, and a third heat-hold sintering at 930°C to 980°C.

13. The method for preparing a positive electrode material for a sodium-ion battery according to claim 12, wherein the temperature of the first heat retention sintering is 600°C to 700°C, and the temperature of the second heat retention sintering is 850°C to 900°C.

14. The duration of the first heat-holding sintering is 1 to 3 hours. and / or, the duration of the second heat-holding sintering is 1 to 3 hours. and / or the third heat retention sintering time is 12 to 16 hours, the method for preparing a positive electrode material for a sodium-ion battery according to claim 12 or 13.

15. A method for preparing a positive electrode material for a sodium-ion battery according to any one of claims 12 to 14, further comprising the step of crushing the sintered material after the third heat-sintering, adding a coating layer material, and performing a fourth heat-sintering.

16. The temperature for the fourth heat retention sintering is 400°C to 450°C. The method for preparing a positive electrode material for a sodium-ion battery according to claim 15, wherein the fourth heat retention sintering time is 12 to 16 hours.

17. A positive electrode sheet for a sodium-ion battery, comprising the positive electrode material for a sodium-ion battery described in any one of claims 1 to 11.

18. A sodium-ion battery comprising a positive electrode sheet for a sodium-ion battery as described in claim 17.

19. A power-using device comprising a sodium-ion battery as described in claim 18.

Images